Scientific Issues: Risk Assessment and Risk Management

Chapter 8

Scientific Issues: Risk Assessmentand Risk Management

Photo credit: Grant Heilman, Inc.

Contents

PageINTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ........225RISK ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .....225

Concerns and Postulated Environmental Risks of Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225Major Risk Assessment Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227Biotechnology Ecological Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231Applicability of Diverse Bodies of Knowledge to Assessments of Large-Scale

Commercial Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235Commercial Release Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

RISK MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .....247Design of Science-Based Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247Generic v. Case-by-Case Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...247Relative Risks Compared to Traditional Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Cost-Benefit Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Small-Scale v. Large-Scale Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

SCIENTIFIC METHODS OF MANAGING RISK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..........249Promoters Turned On or Off by Specific Stimuli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Suicide Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Prevention of Gene Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Combinations of Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ......250

AGRONOMIC METHODS OF MANAGING RISK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .......250Physical Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Spatial Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251Temporal Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

SUMMARY POINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ...251CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

BoxesBox Page8-A. Ecological Risk Assessment Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2338-B. Learning by Doing: Successive Field Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2388-C. Monitoring Microorganisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2458-D. Relevant Research Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

FiguresFigure Page8-1. Alternative Risk Analysis Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298-2. Risk Assessment Framework for Environmental Introductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

TableTable Page8-1. Comparison of Traditional and Developing Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

Chapter 8

Scientific Issues: Risk Assessment and Risk Management

INTRODUCTIONThe large-scale commercial use of agricultural bio-

technology gives rise to several questions. Does the re-lease of large numbers of genetically engineered organismsinto the environment pose special risks’? If so, what isthe order of magnitude of these risks compared to therisks of traditional agricultural practices’? What benefitsoffset such risks?

Generally, concerns about genetic engineering focus on:

possible ‘‘escape” of a genetically engineered or-ganism, such that it invades new ecological nichesor outcompetes naturally occurring organisms andbecomes a pest;possible disruption of a delicately balanced ecosystem;possible direct risks to humans or wildlife;possible problems of gene stability and of gene transferto unintended recipient organisms;possible impact on evolution; andthe sheer “newness” of the technique.

This chapter addresses these concerns and describesthe range of scientific views on biotechnology and risk.A consensus has developed that risk assessment is de-sirable and feasible. Risk assessment in general is foundedon principles and methodologies that can apply to bio-technology. We know what questions to ask in assessingecological risks of planned introductions. A knowledgebase already exists pertinent to these questions and riskassessment studies on this topic are proliferating. Sci-ence-based risk management builds on this technicalknowledge and on our capabilities for risk assessment.

Risk assessment methodologies and our technicalknowledge base make it possible to conduct effectiverisk assessments of specific introductions and to managerisks of acceptable introductions. Science-based regula-tions are central to effective management of risk. A va-riety of scientific and agricultural methods can be usedto manage risk in particular situations.

RISK ASSESSMENT

Concerns and Postulated EnvironmentalRisks of Biotechnology

General Concerns

Questions arise concerning the impact of introducedgenetically engineered organisms: What is the likelihood

that such organisms will persist in the environment”? Whatis the likelihood that they will spread, constituting aninvasion into the ecological community’? Will they be-come pests, with a deleterious effect on other species’?Will the expression of the gene itself lead to an unwantedeffect on the ecosystem’?

Other questions have to do with the recombinant geneitself (38): What avenues exist for gene transfer withinand between various species in nature’? How probableare such exchanges and at what rates would they occur.if at all? If introduced genes are transferred to genomesexisting in nature. how well— and how stably—will thefunctions for which they code be expressed?

Finally, broader, more fundamental questions can beposed: Are we in fact dealing with a phenomenon sonovel that we have no way of predicting outcomes, ofPerforming adequate risk assessment? Do we have a moralright to manipulate still further the species and the ecol-ogy of our planet’? Are we losing an intangible, aestheticquality to our lives by so doing’? Can we at-ford to sayno to the benefits that this technology can confer onagriculture

Concerns About Plants

Specific concerns relating to genetically engineeredplants include the possibility that transgenic plants willpersist and become serious agricultural weeds; that thetransgenic plants will invade natural habitats and disruptlocal ecological interactions; and that the pollen of trans-genic plants will act as a vector. bringing the introducedgenes to other species that may then themselves becomeproblem weeds. The likelihood of such possibilities oc-curring remains somewhat controversial, underscoringthe importance of information from field trials and re-search. It is noteworthy, however, that transfer of genesfrom conventionally bred crop plants to noncrop plantshas not created obvious problems in the past, and thattraditional crop plants rarely have invaded natural eco-systems ( I 4).

lnvasions of plants (by seeds. fruits. or vegetativelyreproducing units ) involves dispersal, persistence. andestablishment: all three stages must be ‘‘successful if’engineered plants are to become weeds. For transgenes(introduced genes) to move from crop plants and causeor contribute to a weed problem, hybridization with areproductively compatible species must occur. For tiny

given crop species, only a small number of the wildrelative species that are reproductively compatible areactually likely to present serious weed problems; how-ever, it is theoretically possible for a plant to become aweed in a novel environment (43).

One specific concern posed frequently by some en-vironmentalists, among others (32), is that genes for her-bicide tolerance might be transferred from crop plants toweeds. If this were to occur, natural selection could favorthe trait in weedy neighbors of crops treated with theherbicide. With any use of herbicides, furthermore, in-creased selection pressure is put on wild species for anyherbicide tolerance traits they might already possess. Suchdevelopments might lead eventually to increased use ofchemical herbicides. A fundamental debate has arisenbetween industry scientists who maintain that crops canbe genetically engineered to be tolerant of particularly‘‘environmentally friendly’ herbicides and some envi-ronmentalists who say. essentially, that no new tech-nology should be used to favor continued use of chemicalsin the environment.

Concerns About Microorganisms

In part because they are invisible and relatively “un-knowable, ” microorganisms tend to elicit more concernson the part of the public than do plants. Parameters ofconcern related to genetically engineered microorganismsinclude the possibility of gene transfer and recombination.the possibility of movement into new environments, andthe possibility of infection of nontarget organisms. Ques-tions asked include: Will genetically engineered microor-ganisms give rise to biological risks for humans or otherspecies? Will they give rise to environmental problems’?Do we have the technical understanding to evaluate andpredict any such problems’?

Whether bacteria, fungi. viruses, or baculoviruscs, mi-croorganisms suffer from a bad reputation at the broadestlevel of public perception: they are. after all often equatedwith“germs. ” One specific concern raised with regardto genetically engineered organisms is the possibility ofgenetic material from such organisms being transferredto human gut bacteria. The risk of infection of humans.or other deleterious effects, is clearly going to be ex-amined for planned introductions of microorganisms. Forexample. among the questions raised by Monterey Countystaff considering the Advanced Genetic Sciences (AGS)proposal to field test FrostbanR was whether or not thePseudomonas fluorescens could ‘ ‘sensitize or aggravateexisting health conditions among sensitive human pop-ulatitons living near the proposed test site’ (66).

To assess risk of problematic infection of humans bygenetically engineered organisms. information must beavailable on exposure level. This hinges on such factorsas bioavailability or likelihood of absorption into cellsor tissues, specificity, and level of interaction possibleof the microorganisms or their chemical products withnontarget (human) tissues; and potential of the micro-organisms for colonization or infectivity. The degree ofpathogenicity must be considered as well. Some relevantfactors include virulence. Possession of toxins, host range,and relative susceptibility. Generally. risk assessmentwill factor in predictability of the behavior of the recom-binant DNA identified microorganisms based on theirparent organisms, as well as knowledge of specific re-combinant techniques used (40).

Scientists’ concerns focus less on pathogenicity andmore on the possible impacts of genctically engineeredmicroorganisms on the environment. Suggested impactsinclude possible influences on: indigenous population size.diversity of species. the ecological community. naturalcycles, and evolution of the introduced organisms (76).Microbial environments are complex. By one estimatesome 109 microorganisms, representing a variety of tax-onomic groups, inhabit one gram ofsoil. Uncetantiesexist as to possible consequences of sudden introductionson balanced microbial ecosystems (46). Microbial di-versity in the soil is high (88). This limits the nichesavailable to introduced mirorganisms (86). While in-troduced microorganisms may thus compete poorly. theymay persist in low-density populations. A key issue iswhether or nor an unexpected later resurgent bloom orpopulation expansion from a low-density population canbe reasonably envisioned (84).

Since microorganisms can and do change location.questions of dispersal—and possible subsequent repro-duction in nontargeted ecological sites—also are raised.The ability of a particular strain to transfer genes to otherspecics will affect the likelihood of other microorganismsbeing affected in new. nontarget areas. All questionsbearing on survival, multiplicaton, and dispersal of ge-netically enginered microoganisms: on possible ex-change of genes between introduced and indigenousmicroorganisms: and ultimately on issues of environ-mental and public safety, are engaging attention of ac-ademic and industrial scientists, the public, andgovernmental regulators alike (22).

Views Held in the Scientific Community

Particularly in the early days. the issue of plannedintroductions of genetically engineered organisms sparked

a range of views on safety even among scientists (50).In the mid-eighties, microbiologist Winston Brill arguedthat. for centuries, traditional breeding has altered ani-mals and plants without negative consequence: and thatmicroorganisms, including pathogenic species, have beenadded to the soil in hopes 0ft beneficial impacts. alsowithout negative consequences (7). His conclusion thatthese observations alone formcd a basis for risk assess-ments of’ organsms that have had one or a few genesadded drew fire from a group of ecologists ( lo). Thesecritics pointed out that mutations that increase an organ-isms niche range can be ecologically significant. andthat some ramifications of an organism’s impact on theenvironment are not predictable from knowledge of itsintroduced genes alone. Casc-by-case quantitative riskassessment for deliberate release was recommended.

In 1987, Science published side-by-side articles byFrances Shw-pies (75) and Bernard Davis ( 15). Sharples.an ecologist. reaffirmed the need for casc-by-case as-sessments, given the complexity of any organism’s in-teractions with the environment. Molecular biologist Davissuggested that the experience of ecologists with intro-ductions of higher organisms is less pertinent to riskassessment of engineered microorganisms than are theinsights of fields mom concerned with the specific prop-erties of those microorganisms: population genetics. bac-terial physiology. epidemiology. and the study ofpathogenesis.

The range of possible views on safty runs from “zerorisk’ to catastrophic risk’; those who presume " small-risk, pending research occupy the middle of the spec-trum. In the mid-eighties, molecular biologists tended tostress the relavance of the safty record of laboratorybiotechnology and graviated toward the ‘‘zero-risk” endof the spectrum. Ecologists, who tended to stress thecomplexities of the natural environment. were less san-guine about potential risks. but stopped short of the catastrohic-risk position taken by certain envronmentalists.An important distinction exists between ecologists andevironmentaists. The former are:

●

The

●

scientists concerned with the fundamental proper-ties, proccsscs, and components of ecological sys-tems .

latter,

by definition, are concerned with various sociopol-itical aspects of environmental quality and manage-ment. They may or may not be experts inunderstanding ecological processes and the orga-nization of ecological systems (63).

Some environmentalists, keenly aware of problems posedby past technologies, argue that the proposed user of newtechnologies bears the burden of proving safety. Bio-technology proponents, in contrast, argue that any risksare to date hypothetical. so that the burden of proofshould rest with the doomsayer ( 5 I ).

In the late 1980s and early 1990s. discussion has in-creasingly centered around developing appropriate risk-assessment parameters and frameworks and designingregulator-y treatment according to risk. The current ‘‘op-erational’ approach is in agreement with analyses in keyreports that will be described in the next section (50).‘‘Presumed small risk. or risk in exceptional cases. withresearch or risk assessment required. is becoming moreof a common theme. Arguments are tending to becomemore refined. revolving about such issues as legitimacyof risk-assessment parameters; the degree to which les-sor-is from past field trials can be generalized: correctassessment procedures for casc-by-evaluations; de-velopment of predictive science related to these issues;science-btised regulations; and scientific mainagement ofrisk. Today the imminence of large-scale release is bring-ing all these discussions into sharp focus.

Major Risk Assessment Reports

Introduction to Risk Assessment

Why Risk Assessment Is Needed-Society today hasbeen ‘‘sensitized’ to technology the public, in all itsmany forms, looks at past technnologies—those of thechemical or nuclear industries for example-and seesnegative outcomes that were not thoroughly consideredprior to implementation of the technologies. Along withskepticism is a strong strain of environmentalism. a growinguneasiness that far too often, for our convenience. wecarelessly and permantly harm the environment. Fur-thermore, however unrealistic it may be, a desire for‘‘zero-risk seems to underliie many responses to tech-nology and to life in general today.

For these reasons as well as to achieve the fundamentalobjective of promoting safety it behooves regulatrs andother responsible parties to conduct reasonable risk as-sessments of new technologics. Biotechnology, in par-ticular planned introductions of recombinant DNA-modified orgainisms. is among the technologies for whichrisk assessment is now done. This is necessary for reg-ulators. important to the public’s sense of cconfidence,and useful to ‘‘users’ of biotechnology’. including re-searchers in academdia, industry. and government.

Principles of Risk Assessment—’ ’Risk” can be de-fined as the potential for negative or adverse consequentto arise from an activity or an event (23). Risk also canbe defined as the probability of an event occurring mul-tiplied by the cost of its occurrence (44). Risk assessmentcan be viewed as ‘‘the process of obtaining quantitativeor qualitative measures of risk levels. including estimatesof possible health effects and other consequences as wellas the degree of uncertainty in those estimates’ (23).

Risk assessment simply is an analytical tool that pullstogether a great deal of diverse data in order to estimatea potential risk from an event or a process (81). Often,historical data on possible adverse consequences are dif-ficult or impossible to obtain, making risk assessment‘‘an inexact process that attempts to characterize andquantify uncertainty, but never completely eliminates it. ”Nonetheless, despite the limitations and challenges, useof risk assessment principles makes it possible to orga-nize and interpret knowledge so as to improve the pre-diction of possible outcomes and ultimately to managerisk (23).

Risk assessment has been defined as a five-stage proc-ess:

1.

2.

3.

4.

5

Risk identification— defining the nature of the risk,source, mechanism of action, and possible adverseconsequences;Risk-source chracterization—characterizing thesource of potential risk;Exposureassessment— assesing the intensity. fre-quency and duration of human or environmentalexposures to risk agents;Dose-response assessment— assessing the relation-ship between dose of the risk agent and health orenvironmental consequences; andRisk estimation— intergrating a risk-source char-acterization with an assessment of exposure anddose-response, leading to overt measures of thelevel of the health, safety or environmental riskinvolved (59, 92).

Clearly these stages can be adapted to fit a variety ofkinds of risks, and the entire process can take severaldifferent forms. (See figure 8-1. )

The choice of an approach to risk assessment dependsin large part on the extent and quality of available knowl-edge, degree of expected precision, and importance at-tached to outcomes at a low probability. Where theknowledge base is large and little uncertainty exists, arisk or hazard may be described quite readily and a moreprecise “deterministic consequence analysis” might even

be performed. On the other hand, when less knowledgeis available and the level of uncertainty is high. a qual-itative risk screening may be all that is possible. perhapsleading to a more quantitative ‘probabilistic risk as-sessment.

A much-used framework to assess risk is that devel-oped for the evaluation of health effects associated withchemicals in the environment. This was endorsed by aNational Academy of Science report (67) and refined atthe Environmental Protection Agency (EPA). This chem-ical risk-assessment framework sometimes has beenadapted for evaluation of planned introductions of re-combinant DNA-modified organisms into the environ-ment (13. 16. 30).

The National Research Council (NRC) and the Eco-logical Society of America (ESA) (69, 85) developed in1989 risk assessment frameworks designed for recom-binant DNA-modified organisms. But they were quitedifferent from the chemical approach. The NRC proce-dure takes account of the degree of “familiarity”of aplanned introduction; the ESA uses a risk attributes cat-egorization; both lead towards the determintaion of anappropriate level of concern. While differing somewhatin perspective. the two approaches nonetheless resembleeach other in basic conclusions and therefore togetherprovide a solid framework for risk assessment of plannedintroductions. Clearly, choice of framework for risk as-sessment will influence the kinds of data required forevaluation and for permit applications (50). The two re-ports described below have had significant impact on therecent framing of discussions about planned introduc-tions. Even proponents of chemical risk-assessment pro-cedures point out that these procedures can be used todetermine whether or not a particular organism shouldbe evaluated intensively using an analogue of a chemicalrisk assessment (81).

National Research Council Report

Background—In late 1989, the National ResearchCouncil published Field Testing Genetically ModifiedOrganisms: Framework for Decisions. This was re-quested by the Biotechnology Science CoordinatingCommittee (BSCC) on behalf of its member regulatoryagencies. The report covered:

● plants and microorganisms,● field-test introductions (but not large-scale com-

mercial applications and related issues),● environmental (but not human health) effects,

Figure 8-l—Alternative Risk Analysis Approaches

Precisionof ananalysis

Probabilisticrisk assessment

Consequenceanalysis withconfidencebounds

Hazard Qualitativedescription risk screening

I > Level ofUncertainty

SOURCE: J. Fiksel and V.T. Covello, “The Suitability and Applicability of Risk Assessment Methods for Environmental Applications of Biotechnology” in Biotechnology Risk Assessment: Issues and Methods for Environmental Introductions (New York, NY: Pergamon Press, 1986), pp 1–34-

scientific issues principally (but not regulatory policy).field test conditions in the conterminous United States,andgeneral procedures for determining categories (notspecific case recommendations ).

fundamental principle underlying the study. and firstintroduced in an earlier National Academy of Sciencedocument (68), is that safety assessments of a recom-binant organism ”should be based on the nature of theorganism and the environment into which it will be in-troduced, not on the method by which it was modified.A related point is that ‘‘no conceptual distinction existsbetween genetic modification of plants and microorgan-isms by classical methods or by molecular methods thatmodify DNA and transfer genes.

Topics analyzed for the 1989 report include: relevantbiological characteristics of genetically modified plants;experience with genetic modification and introductionsof plants modified ‘ ‘traditionally” and by molecular ge-netic techniques; potential weediness: the features of thegenetic modification in microorganisms; phenotypiccharacteristics of the parent organism and of its geneti-cally modified derivatives: and relevant features of theenvironment into which the organism will be introduced.

Findings-The report recommends that the impactsof’ genetic modification on the phenotype of the organismand the mobility of the altered gene be assessed. In somecases. when persistence of’ the modified orgtanism is notwanted or when uncertainty exists as to effects on theimmediate environment. risk assessment should empha-size the phenotypic properties relating to the persistence

of the organism and its modification. Questions to beconsidered include: fitness of the genetically modifiedorganism; its tolerance to physicochemical stresses; itscompetitiveness range of available substrates; and. ifapplicable. pathogenicity, virulencc. and host range. Thereport describes the long historry of safety in the usefulemployment of’ plants and microorganisms. and under-scores the need for field tests to increase the capabilityto assess any risks of large-scale introductions.

Specific scientific conclusionss of the report pertainingto plants include:

1.

2.

3.

4.

5.

6.,

The current means for making evaluations of in-troductions of traditionally bred plants are appro-priate (on the basis of experience with field testsof hundreds of millions of genotypes over decades).Crops altered by molecular and cellular techniquesshould pose risks no different from those posed bycrops modified by traditional genetic methods forsimilar traits.The potential for enhanced weediness is the prin-cipal risk to the environment seen from introduc-tions of genetically moditied plants. although thelikelihood of this occurring is low.Confinement by biological. chemical spatial,physical. environmental and temporal means is theprincipal means of maintaining the safety of fieldintroductions of classically modified plants.Experimental plants grown in field confinement rarelyif ever escape to cause problems in the environment.Established confinement options are equally appli-cable to field introductions of plants modified with

——

230 . A New Technological Era for American Agriculture

molecular or cellular methods and to plants mod-ified with classical genetic methods.

Conclusions concerning microorganisms included:

1. Many molecular techniques make possible geneticchanges in microbial strains that can be fully char-acterized.

2. The molecular techniques are powerful in their ca-pability to isolate genes and transfer them acrossbiological barriers.

3. Field experience has given rise to a great deal ofinformation about some microorganisms; nonethe-less, less information exists on microbial ecologyand less experience with planned introductions ofgenetically modified microorganisms than there isfor plants. No adverse effects have been noted frommicrobial introductions to date; a field test shouldgO forward when sufficient information is availablefor its safety evaluation.

4. The probability of adverse effects can be minimizedor eliminated by appropriate means of confiningthe microorganism to the environment into whichit was introduced; one example would be the useof “ suicide genes.

The framework for evaluating risk developed in thereport is structured around the following questions:

1.

2.

3.

Are we familiar with the properties of the or-ganism and the environment into which it maybe introduced?Can we confine or control the organism effec-tively?What are the probable effects on the environ-ment should the introduced organism or a ge-netic trait persist longer than intended or spreadto nontarget environments? (69)

The familiarity criterion is key to this report and hasreappeared consistently in risk assessment discussionssince. Familiarity means having sufficient informationon which to base a reasonable assessment of safety orrisk. Thus, as our information base increases, so doesthe scope of “familiarity.” When the familiarity criterionis not met. the possibility of confining or controlling theorganism and the potential consequences of failing tocontrol it must be evaluated.

The report is intended to provide a basis for a “flex-ible, scientifically based. decisionrnaking process. Theclassification of an introduced organism into a particularrisk category is made possible by the framework forevaluating field tests (69).

The 1989 NRC report is often cited and has provideda conceptual framework for many approaches to riskassessment of planned introductions of genetically en-gineered organisms into the environment. Its level ofdetail made it more palatable to technical audiences thanthe 1987 pamphlet, which was at times criticized formaking assertions without documentation ( 11, 50).

The Ecological Society of America Report

Another seminal assessment was published in 1989,The Planned Introduction of Genetically Engineered Or-ganisms: Ecological Consideratons and Recommenda-tions (85). This report was prepared for the Public AffairsCommittee of the Ecological Society of America (ESA)and also has been broadly disseminated and cited. Dr.James Tiedje chaired a workshop committee in April1988, examining ecological aspects of planned environ-mental introductions of genetically engineered organ-isms. The Workshop Committee’s initial draft wasreviewed at great length by the ESA Public Affairs Com-mittee, the ESA Executive Committee, and other ecol-ogists. The report

supports the use of advanced biotechnology for the de-velopment of environmentally sound products. and statesthat the phenotype of a transgenic organism, not the proc-ess used to produce it, is the appropriate focus of regu-latory oversight. Ecological risk assessment of proposedintroductions must consider the characteristics of the en-gineered trait, the parent organism, and the environmentthat will receive the introduced organism (85).

Like the NRC report, the ESA report emphasizes prod-uct, rather than process, as the appropriate focus of eval-uation and regulation. Thus, ‘‘genetically engineeredorganisms should be evaluated and regulated accordingto their biological properties (phenotypes), rather thanaccording to the genetic techniques used to produce them”(85). Yet the report acknowledges the potential for nov-elty and consequent likelihood of evaluation inherent inthe new techniques. The report acknowledges, however,that ‘‘because many novel combinations of propertiescan be achieved only by molecular and cellular tech-niques, products of these techniques may often be sub-jected to greater scrutiny than the products of traditionaltechniques. Moreover, it recognizes that even precisegenetic characterization of transgenic organisms does notnecessarily allow scientists to predict all ecologically im-portant expressions of phenotype in the environment.

The ESA report emphasizes the importance of consid-ering a variety of ecological factors in ecological rami-fications of planned introductions. Among these are

survival, reproduction, interactions with other organ-isms, and effects on ecosystem function and dynamics.Potential undesirable impacts must he weighed in eval-uations. While explicitly calling attention to the com-plexities of ecological risk assessment, the report supportsthe position that “ecological oversight of planned intro-ductions should be directed at promoting effectivenesswhile guarding against potential problems. Thus, theauthors observe that most cases will present a minimalrisk to the environment and provide a set of specificscientific criteria for ‘‘sealing the level of oversight toindividual cases. The four categories of criteria included:

1. attributes of genetic alteration,2. attributes of the parent organism,3. phenotypic attributes of the engineered organism

in comparison with the parent organism. and4. attributes of the environment.

Specific attributes are grouped according to level of riskpresented and corresponding level of scientific risk as-sessment needed. Coming as it did from a group of ecol-ogists, the ESA report is often cited as a touchstone forthose wishing to balance the positive potential of bio-technology with a sensitivity to the environmental con-sequences of actions.

Biotechnology Ecological Risk Assessment

Introduction

A central goal of ecological risk assessment of plannedintroductions of recombinant DNA-modified organismsis to ‘‘make a reasonably accurate prerelease predictionof the behavior an organism is likely to exhibit in its newecological context and given its particular genetic mod-ification, and to be able to detect and avert potentialproblems before they occur” (76).

Most scientists seem to concur that the focus of riskassessment should be on a particular organism, with itscharacteristics (genetically modified or not) and the genesthat code for them, in a particular environment. Exper-imental protocols for ecological risk assessments need tobe refined to screen out potentially problematic intro-ductions before release (l4).

While scholars argue as to which risk assessment modelwould best apply to environmental introductions of re-combinant DNA-modified organisms, all agree that thecomplexity of ecological factors renders biotechnologyrisk assessment particularly challenging. Living organ-isms can change locution, reproduce, and perhaps ex-change genes. Once released into the environment. they

will interact in a dynamic fashion with other species.They are indeed different from chemicals.

Ecological risk assessment is a still young methodol-ogy, and not standardized. Some argue that directly rel-evant data are scarce enough, and ecological phenomenaare sufficiently complex that resasoned qualitative judg-ments are more feasible than more precise quantitativeassessments. In practice, expert review panels using goodscientific judgment and common sense. along with guide-lines of points to consider, achieve qualitative assess-ments of the riskiness of various combinations of factors.As experience is gained. codification of the principles ofreview should evolve for application to future cases.Augmentation of” human judgment with knowledge sys-tem technology has been suggested as a means of facil-itating the process (24, 66).

One way of conceptuall y applying risk assessment pro-cedures to planned introduction of recombinant DNA-modified organisms into the environment is to match thethree classic risk assessment stages (A. risk-source char-acterization: b. exposure assessment: and c. dose-re-sponse assessment) with the five stages involved in plannedintroductions. (See figure 8-2. ) Information about stageone. formation of a recombinant DNA-modifiedd organ-ism. and stage two, its deliberate release or accidentalescape into the environment contributes to risk-sourcecharacterization. Exposure assessment would take intoaccount data on stage three. proliferation of the organ-isms, including dispersal and possible exchange of ge-netic material, as well as stage tour. their establishmentin an ecosystem. Stage five, human and ecological ef-fects, relate quite directly to dose-response assessment(23).

Another way of looking at risk assessment of plannedintroductions is to consider the defination of ”risk” asthe product of’ ‘‘exposure’ and “hazard.” Exposure isrelated to the possibility of escape of the arganism, itssurvial. reproduction. and spretd. as well as to the genetransferred and the vector, if present. Assessment of thehazard, or potential environmental impact. depends onthe ultimate fate of the introduced organism-whetherit becomes extinct. establishes a balance with indigenousspecies. or overruns the recipient environment (53).

Specific objectives of ecological risk assessment forplants. for example. include:

1. determination of the potential for crops to persistand spread in a variety of habitats,

2. discovery of the range of species that can cross-pollinate with various transgenic crops.

232 ● A New Technological Era for American Agriculture

Figure 8-2—Risk Assessment Framework for Environmental Introductions

1 Release

3

5

f I 1

EstablishmentIn ecosystem

I I

SOURCE: Office of Technology Assessment, 1992.

3.

4.

Box

investigation of the ecological performance of hy-brid plants produced, anddevelopment of protocols making it possible forcrop breeders to carry out ecological risk assess-ments on new transgenic plants in the future.

8-A illustrates the sorts of specific questions thatcan be asked and answered about plant introductionsbased on field observations, field experiments, and con-tained experiments ( 14).

Risk assessment pertaining to genetically modified (ornonmodified) viruses used in weed biocontrol, as an ad-ditional example, would include:

1.

2.

3.

4.

In

information on virus attributes such as virulence,host range, vector specificity, survival, and dis-persal characteristics;information on desirable and undesirable virus at-tributes and on the stability of these attributes;information on the virus’ effect on the target weed’sgenetic stability; andinformation on the release site and how a varietyof ecological variables affect infection, dispersal,population dynamics, and safety (87).

summary, key features of ecological risk assess-ments of planned introductions include properties of the

Risk-sourcecharacterization

Exposure

Dose-responseEcological effects assessment

introduced organism (not the method by which it wasproduced) and of the recipient environment. includingthe demographic characteristics of the organism, the ge-netic stability and likelihood of gene transfer, and theinteractions between the species and the physical andbiological parameters of the environment. Scale and fre-quency of introductions should also be factored into riskassessments. Furthermore, since recapture or recall ofintroduced organisms usually will not be feasible, as-sessments should also consider possible means of con-tainment, monitoring, and possible mitigation if adverseconsequences occur (74).

Research Needs and Promise of RiskAssessment

The current interest in effective risk assessment of theproducts of biotechnology has stimulated workshops,conferences, discussions. and articles. More and morefrequently. insights from the fields of ecology. popula-tion biology, population genetics, and evolution are beingrecast into the language of risk assessment (31, 50, 52.62). Additional research needs to be undertaken on avariety of fronts to facilitate risk assessment. For ex-ample, a need exists to develop models and use data fromfield tests to predict the rate of spread of introducedorganisms in various situations (54).

Box 8-A—Ecological Risk Assessment Questions

Field observations Field experiments Contained experiments

PersistenceWhat is the survival of the What is the fate of seeds sown into How is pollen viability affected invegetative parts of the plant under a range of plant communities, transgenic plants?a range of climatic conditions, on including other arable crops, forage How is seed dormancy affected?soils of different kinds with different crops, permanent grasslands, andcategories of drainage? natural habitats? How do transgenic plants perform

How is perennation affected by the What is the fate of transplantedin competition experiments withcrop plants and with selected

introduced genes? seedlings in different habitats? native plants?What factors influence plant What is the fate of transplantedmortality outside arable fields and mature plants (or rootstock) inhow are these influenced by the different vegetation types?novel genes? How long does experimentallyWhat is the nature of seed planted seed remain dormant butdormancy under different viable in a range of soil types?environmental conditions, and howdoes the introduced geneticchange influence triggering,duration, and hardiness duringdormancy?

Spread of the vegetative plantWhat is the seed production of the What is the vegetative growth rate Is seed size or morphologyplant when grown in a crop and in on different substrates and with different in transgenic plants, andnatural vegetation? different competing species? how might this affect seed

Is seed production limited by the Is the thinning rule (i.e., density- dispersal?

rate of pollination? dependent plant mortality) similar Do transgenic plants present

What is the germination rate of for transgenic and nontransgenic greater risks of spread by

seeds in soil? plants? vegetative fragments?

What is the mortality of seeds and What kind of compensatory growth

seedlings in arable soils and is exhibited (e.g., gap-filling)?

beneath native vegetation?

What is the phenology of seedlingemergence and growth?

What are the natural enemies ofthe seedlings?

What is the role of vertebrate andinvertebrate herbivores in crop andnoncrop habitats?

What is the mechanism of seeddispersal?

How far are seeds dispersed andhow does this vary withenvironmental conditions?

Do the seeds produced by plantsgrown outside arable fields giverise to a second generation ofplants? (continued on next page)


t

Box 8-A—Ecological Risk Assessment Questions—Conthuecf

Field observations Field experiments Contained experiments

If the plant were to prove invasive,at what rate would it spread andwhich habitats would it occupy?

Which plant species (if any) aredisplaced when (and if) the plant isestablished in natural habitats?

Which plant species are responsi-ble for the competitive suppressionof the plant in different natural hab-itats?

Horizontal gene transfer throughpollenHow much pollen is produced? What is the fate of labeled pollen? Which plant species allow pollen

What is the phenology of pollen How much pollen reaches the stig- germination on their stigmas?production and what is the phenol- mas of other wild plants under dif- How is pollen dispersal affected inogy of stigma receptivity of other ferent conditions? transgenic plants?plant species growing in the neigh- Which insects carry the pollen? Which plant species form viable,borhood of crops (i.e., within 500-

How far away from the crop can an hybrid seed and at what rate is this1,000 m)?

individual, potted crop plant be pol- seed produced?Over what distance is pollen dis- Iinated and how does the rate of What is the germination rate of hy-persed under different meteorologi- pollination fall off with distance un- brid seed?cal conditions? der a range of habitat conditions? What phenotypes are exhibited byWhich is the pollen deposited, on What plants make the most effi- hybrid individuals?which species, and in what num-bers?

cient ‘pollen barriers’ for the con- What is the performance of hybridstruction of guard rows; is it

Where is the pollen deposited, onplants in competition experiments

nontransgenic members of the with crop plants and with selectedwhich species, and in what num- same species or plants that form native plants?bers? physical barriers to pollen flow or to

insect flight? What is the nature of perennationWhat is the geographic distribution and vegetative dormancy in hybridof closely related wild plants in the and transgenic plants?vicinity of centres of crop cultivationand what is their small-scale (100’sm) distribution as weeds within ara-ble fields and on land adjoiningfield foundaries?

What natural habitats are foundwithin 1,000 m of arable fields, inthose areas where the crops aregrown, and what flora is supportedby these habitats?

SOURCE: Michael J. Crawley, “The Ecology of Genetically Engineered Organisms: Assessing the Environmental Risks,” Intor-duction of Genetically Modified Organisms into the Environment, Harold A. Mooney and Giorgio Bernardi (eds.) (NewYork, NY: John Wiley and Sons, 1990).

Achieving predictive capabilities in extrapolating fromfield tests to large-scale introductions is an additionalgoal. Along with further research, data from field testsand research then can feed into the design of future fieldtests and large-scale introductions. our scientific under-standing pertinent to ecological risk assessment shouldincrease exponentially over the next few years.

This explosion of knowledge not only can improvesafety but also the effectiveness of introduced organismsin various habitats. There seems to be general agreement,even among ecologists and environmentalists, that mostbiotechnology products will not be harmful. However,because uncertainty does exist, for instance, as to whichapplications might be harmful. reasonable caution andwillingness to assess risk are appropriate (76).

Risk assessment prior to introductions is a reasonableand necessary step, consensus dictates. More researchcan sharpen our powers of prediction and build on an.already sol id foundation of information. Eventually, cri-teria can be developed to match individual cases withappropriate risk categories. In the meantime, as a broaderknowledge base is being built, the safety of each intro-duction needs to be judged, basically, on a case-by-casebasis (51). Understanding gained from case studies andother relevant research can be employed in the currenttransition to risk assessments of large-scale introductions.

Applicability of Diverse Bodies of Knowledgeto Assessments of Large-Scale Commercial

Release

Introduction

In all approaches to risk assessment, the key questionis predictability. Do we have sufficient information tomake a reasonable prediction as to what will occur fora particular release’? Can we in fact legitimately draw onknowledge gained from agricultural experience, labora-tory tests, past field tests of recombinant DNA-modifiedorganisms, and accumulated knowledge of genetics, mi-crobiology, molecular biologics, and ecology? Are thecharacteristics of any individual large-scale release fa-miliar enough that we can bring such knowledge to bearon the risk assessment’?

Species Introductions

Those interested in the evaluation of risks from bio-technology sometimes turn to the experience base withintroduced ‘‘exotics, species accidentally or deliber-ately released in a completely new environment. Dutchelm disease is often-cited as a consequence of the acci-

dental introduction of a fungus; kudzu vine. running ram-pant in the South after being brought in as a roadsideground cover, is pointed to as a deliberate introductiongone awry.

One viewpoint holds that species invasions may beuseful analogues of planned introductions of geneticallyengineered species, i.e., an invasion is an invasion. Thus.experience with analyses of key properties of ‘successfulinvaders, as well as of vulnerable environments. the-oretically can be brought to bear in evaluating plannedintroductions (63).

Most scientists agree, however, that invasions by ex-otics have limited applicability to planned introductionsof genetically modified species. For example, introducedexotic plants that have caused problems come with manytraits that enhance weediness; whereas genetically mod-ified plants, by contrast. are modified in only a fewcharacteristics (69). The distinction between the intro-duction of modified genotypes of crop organisms and theintroductions of totally new exotics-whether or not theyare genetically engineered—is, in fact, generally re-garded as an important one (14). Even so. lessons learnedas to the ecological parameters of ‘‘invading species’and recipient environments may be useful in categorizingdegrees of risk for a specific planned introduction of arecombinant DNA-modified organism. For example,comparisons can be made between the characteristics ofsuch an organism and the characteristics often found invery successful invading species. Habitat characteristicscan also be compared to help assess site for vulnerabilityor resistance to invasion (63).

Agriculture

Perhaps the oldest analogue to planned introductionsof genetically modified species is agriculture itself. Formuch of human history, new forms of crops and do-mesticated animals have been introduced to the environ-ment. Major crops have been bred by the millions forcenturies; all these field tests and commercial releasesprovide a substantial experience base. Throughout thisvast experience, no significant harm to human or animalhealth has occurred due to these introductions per se, norhave major crop plants become bad weeds. Normal se-lection procedures have eliminated plants with problems.Furthermore, “recalls” of crop varieties are commonunder the laws of supply and demand. In short, no ev-idence exists in the United States that plant breeding leadsto ecological problems (6).

The NRC report’s call for ● ’familiarity” as a criterionfor risk assessment makes drawing on the experience base


Photo credit: Monsanto

Genetically engineered tomato plants are shown beingplanted by researchers at a Monsanto-leased farm in

Jersey County, IL.

co.

of agriculture logical for most planned introductions ofgenetically modified agricultural organisms. A specificexample of how the agricultural experience can be ap-plied to biotechnology risk assessment is the 80 years ofusage of Bt (Bacillus thuringiensis with its toxin) as anatural insecticide; its history of safe use is often regardedas evidence that transferring the gene for a Bt toxin wouldbe environmentally safe (6). The 100-year experiencebase with vaccines, rhizobial bacteria, and other biolog-ical controls provides information applicable to large-scale microbial introductions (20, 29, 62, 90). As a finalexample, corn breeders have significantly changed thecorn genome and have conducted planned introductionsinto the environment of these modifications for the past70 years, without negative ecological experience. Breed-ers have gained experience in protecting the purity ofthese genomes, calculating the likelihood that the mod-ifications will spread to other plants, deploying the mod-ified genomes, and maximizing their strengths andminimizing their weaknesses ( 18).

Although there are limitations to the analogy betweenseed purity and gene transfer to weeds (notably, the risksassociated with weed genes contaminating seed for plant-ing crops are quite different from those associated withengineered genes getting into a weed population), thisanalogy does represent a useful starting point for riskassessment in controlled release.

Although some observers emphasize the novelty ofgene combinations that can be brought about throughbiotechnology, a key difference between traditional cropbreeding and the “new biotechnology” is that changesin genomes are more precise using biotechnology. With

genetic engineering, one gene is moved at a time; bycontrast, huge numbers of genes are recombined in crossesthat lead to new plant varieties. It is nonetheless true thatecological effects of a changed phenotype sometimesmay not be predictable even with precise changes ingenotype (85).

Certainly, risk assessments are needed of individualcases involving particular genes. For example, foragecrops such as alfalfa, which are not so dependent oncultivation practices, may have higher—and perhapsproblematic—survival capabilities outside of the farmthan others (6).

Two of the chief concerns about planned introductionof genetically modified species have no analogs in tra-ditional agriculture. With the exception of some intro-duced crops that become weeds in tropical countries, cropplants have not invaded natural habitats. Furthermore.no obvious problems have arisen due to transfer of genesfrom traditionally bred crops to wild plants ( 14).

Laboratory Testing

Results of laboratory tests have been drawn on by thoseinterested in risk assessment of genetically engineeredmicroorganisms in particular. Various studies of micro-bial genetics, as well as use of soil microcosms (or lab-oratory model ecosystems) that mimick the naturalenvironment, have provided useful information.

A great many reported laboratory tests involve inves-tigations of mechanisms and likelihoods of gene transfer.For example, transformation (the uptake of naked DNAinto a competent or receptive cell) is a form of genetransfer well understood in the laboratory, but not welldescribed in natural settings. Laboratory records on trans-duction (the transfer of genes between bacterial strainsby virus particles) have led to theoretical models pre-dicting the possibility and frequency of transduction froman introduced genetically modified microorganism to anatural species. Another mechanism of horizontal genetransfer studied in the laboratory is conjugation, the pro-cess of genetic exchange between bacterial cells. Finally,transposition, the process by which mobile genetic se-quences change positions within a genome can be as-sociated with gene transfer.

Soil microcosms, even with sterile soil, are a feasibleway of assessing what kind of gene transfer mechanismscan occur in nature; they are therefore a useful tool inrisk assessment (38, 70). Research has now been doneusing more realistic soil microcosms, with the objectiveof learning more about the impact of conjugation on

introduced genetically modified microorganisms. For ex-ample, some experiments have been done using non-sterile soils, in an attempt to produce a closer analogueto nature.

Another set of questions that laboratory tests can helpaddress is related to population biology. Relative fitnessof genetically modified microorganisms in the labora-tory, for example, pertains directly to establishment andpossible spread of introduced organisms in an environ-ment; some information toward quantitative risk assess-ments can be gained from contained laboratory testingin chemostats (44). Laboratory tests also can help illu-minate the role played by various soil environments insuccessful introductions (93).

Of course, constraints exist on the applicability of lab-oratory tests, having to do with feasibility and with theimpossibility of reproducing the full complexity of a nat-ural environment. Some important parameters relevantto introductions are, for example, the relative fitness ofthe introduced recombinant DNA-modified organism inthe new environment with its multiple dimensions ofbiological, chemical, and physical features, includingcompetition with other microorganisms; microbial pop-ulation density, which may vary over time and space;population dynamics; and availability of habitats (5). Thedynamic complexity of many such features makes it im-possible for a laboratory test to mimic reality completely.Work is beginning on testing for effects such as patho-genicity or toxicity in more realistic multispecies systemsor microcosms (26).

Perhaps the principal lessons learned from laboratoryresearch have to do with the potential to work creativelywith soil microcosms. The more realistic the soil micro-cosm used, the higher the predictive value of the labo-ratory tests is likely to be, particularly where extrapolationfrom the laboratory to the field is relatively well under-stood. It has been suggested that mesocosms (larger con-tained walk-in chambers, the environmental parametersof which can be controlled) could provide more realisticcomplexity than soil microcosms. This added realismmight improve risk assessment (93).

Small-Scale Field Tests

Field tests of conventionally produced crop varietiesrepresent part of a step-wise progression toward full-scalecommercialization; the same is true of field tests of re-combinant DNA-modified organisms. Initially. new va-rieties are assessed in a laboratory or greenhouse; thenthey are observed in small-scale field plots where theyare evaluated according to various protocols, statistical

Photo credit: Monsanto Co.

Researchers begin test of tomato plants carryingthe Bt toxin gene in test plant.

procedures, and analytical methods. Large-scale tests andcommercialization complete the process. Each stage pro-vides information for the next stage (53 ). For the mostpart. principles and procedures useful in small-scale fieldtests are also relevant at the large-scale test and com-mercialization stages as well (36). Field testing and mon-itoring constitute ‘‘real world empirical methods’ thatare important components of risk assessment (23).

Small-scale field tests can be used to elucidate char-acteristics that will be factored into risk assessments ofpossible large-scale planned introductions. For example,survival and spread of particular recombinant bacteria ina particular soil environment, as well as efficacy of func-tion and stability of an introduced gene. can be estimatedin field tests ( 1, 3, 47). Field tests also can be used toassess ‘‘invasiveness’ of transgenic crops (73). Datafrom field tests can be integrated into quantitative pre-dictive models of gene flow and gene spread (39).

Field tests also provide agronomically significant in-formation, including data on the expression or perfor-mance of the introduced gene and on the overall growthand vigor of the genetically modified plant (64). Forexample, 1990 field tests of insect-resistant cotton plantshave allowed such agronomic traits as yield, fiber length,fiber strength, fiber quality, seed composition, and qual-ity to be evaluated by Monsanto, which is planning forcommercial introduction in 1994 or 1995 ( 28).

Well-designed, well-monitored field tests of increas-ing scale and complexity also should allow undesirableimpacts to be observed while there is still an opportunityto correct them (43). A ‘‘stepwise progression in test

design” is seen as an approach to field trials that willreduce complexity and otherwise benefit later I urge-scaleefforts (47 ). (See box 8- B.) An important stage is ex-pansion from single-site into multisite field testing, whichallows sites to undergo different conditions, such asweather, and thus provides information on the variationpossible in performance and impact (73). Testing overmore than 1 year can provide information on the con-sistency of measured characteristics such as survival andefficacy. Such information will have significant impli-cations for commercial scale planned introductions. Good.statistically sound experimental design can be importantin facilitating effective transitions from the field test tocommercial-scale introduction (57). For agronomic andrisk assessment purposes. scale-up from field tests is auseful and informative process.

There are, however. a few constraints on the appli-cability of small-scale field tests to large-scale tests orcommercialization. An important one is the emphasisoften placed on containment in small-scale field testsinvolving recombinant DNA-modified organisms. Con-tainment is, of course, the antithesis of uncontained,large-scale introduction (36). Bagging plants, for ex-ample, prohibits pollination and, furthermore. would notbe feasible at a large-scale (53).

When a product is commercialized. it will be far morewidespread in the environment than it was in the daysof its field test; many more ‘‘nontarget species will beexposed to it (26). As people increasingly use transgenicplants. the chance for errors will increase because someusers may not follow safety procedures (43 ).

Despite these limitations, field tests are providing thedatai about agronomic qualities and risk assessment con-siderations needed for the design of’ large-scale tests andcommercialization. Detection and monitoring techniquesare improving. A step-by-step progression from individ-ual field tests through multisite field tests to large-scaletesting to commercialization is being followed for re-combinant DNA-modified organisms as it has been forconventionally produced organisms. without problems.Research still needs to be done to identify importantdistinctions between small-scale and large-scale tests; thisshould improve experimental design and efficiency (53).

Deliberations on Field Tests and onLarge-Scale Release

Over the past several years. field tests have made im-portant contributions to risk assessments for large-scalerelease of- DNA-modfied organisms. The data from fieldtests provide the most directly relevant basis for predic-

Box 8-B—Learning by Doing: Successive Field Releases

Crop Genetics International (CGI) is a company that has used a “stepwise progression in test design” as ithas moved from an initial field test to later tests. The focus was the delivery of biopesticidal gene products byendophytic bacteria inoculated into seeds. First tested was a bacterial endophyte (Clavibacter xyli subsp. cynodontis)genetically modified to produce low levels of the delta-endotoxin of Bacillus thuringiensis (Bt) subsp. kurstaki, andinoculated into corn seed. CGI developed a strategy for multiple risk assessment studies of field releases. Thefocus of the field release studies was twofold: performance of plants grown from endophyte-inoculated seed; andpersistence and spread of the genetically modified strain under different environmental conditions. The first tworeleases were used to develop a profile of the recombinant strain’s behavior in the environment. In 1989, the testdesign was extended to multiple sites in four States to examine its behavior overdiversified environmental conditions.This was the first release to take place in multiple States of a viable microorganism genetically modified to producea biopesticide. In 1990, a new recombinant strain selected for its activity against the target pest (European cornborer) was incorporated readily into the well-established testing procedures and program, with the objective ofdetermining efficiency. As the study progressed between 1988 and 1990, by agreement with regulators, levels ofcontainment were gradually lowered as data on safety were obtained. In fact, the early tests were specificallydesigned to address risk assessment issues such that future small-scale introductions could be made with lessrigid containment and such that containment requirements could be eliminated in large-scale field tests. Efficacystudies now can be done under reduced containment requirements. Multiple-site field testing of the improved strainsis the next logical step toward large-scale tests and commercialization. Stepwise progression of tests is a rationalstrategy from a company’s point of view, as well as from a regulator’s point of view.

SOURCE: Stanley J. Kostka, “The Design and Execution of Successive Field Releases of Genetically Engineered Microorgan-isms,” Biologicd Monitoring of Genetically Engineered Plants and Microbes, D.R. MacKenzie and Suzanne C. Henry(eds.) (International Symposium on the Biosafety Results of Field Tests of Genetically Modified Plants and Microor-ganisms, Kiawah Island, SC, Nov. 27-30, 1990) (Bethesda, MD: Agriculture Research Institute, 1991), pp. 167-176.

(ion as to the safety of large-scale release, particularlyin cases where a small-scale field test is itself scaled-upto a large-scale introduction. Equally important, scien-tists in many disciplines have been gaining practice throughfield testing in the process of risk assessment. Now thatapplications for large-scale release are imminent, re-searchers familiar with comparable evaluations at a small-scale can begin to integrate their experience and applyit to the new assessment task at hand.

Several recent conferences have helped to define ap-proaches to the risk assessment of large-scale introduc-tions. Commonalities arc emerging, suggesting that astate of readiness for large- scale introductions is in factbeing reached.

Several biological principles with implications for as-sessment of large-scale introductions emerged from theInternational Symposium on the Biosafety Results of FieldTests of Genetically Modified Plants and Microorgan-isms (November 27–30, 1990. Kiawah Island. SouthCarolina). For example:

●

●

●

●

●

The integration of genes into the chromosomes ofrecombinant DNA-modified organisms has provento be predictably stable.Gene transfer frequencies of recombinant DNA-modified organisms are consistent with patterns re-corded for natural populations.The frequencies of transposon relocations in recom-binant DNA-modified organisms are consistent withthose of natural populations.Some microorganism detection methods are ex-tremely sensitive. and this contributes to better un-derstanding of- the fate of a microorganism in theenvironment.Background microbial populations have been char-acterized as complex. and thus the release of ge-netically modified microbes may be insignificant bycomparison..

The symposium also highlighted the strong foundationof conventional knowledge in crop improvement, micro-bial testing. and food processing that is available to sup-port safe commercialization of biotechnology products.Research needs cited included: detection methods, sam-pling methodologies. monitoring protocols and modelingtechniques, and empirical data for improved design andevaluation of experiments (53).

A workshop on transgenic plants conducted by theMaryland Biotechnology Institute and the USEPA Officeof Pesticide Programs (June 18–20, 1990) evaluated thehuman and environmentall impacts that could result from

the ‘‘widespread. full scale”use of plants geneticallymodified to produce a pesticidal substance. Workgroupsdiscussed: 1) studies and information needed for assess-ment; 2) scientific rationale for determining the occa-sional need for specialized studies; and 3) availabilityand test protocols for developing risk assessment infor-mation.

The consensus of all groups was that such transgenicplants posed concerns and possible effects that are notunique, and risk assessment issues can be addressed throughreadily obtainable information on possible effects of theplant or of the pesticidal substance (89).

The USDA-sponsored ‘‘Workshop on Safeguards forPlanned Introductions of Transgenic oilsecd Crucifers’(October 9, 1990, Cornell University’) was held to iden-tify agricultural biosafety issues relevant to oilsecd rape(or canola) as soon as possible. Unlike most crops, oil-seed rape has weedy relations in North America. Thepotential for. and possible results of, gene transfer aretherefore of concern. The workshop group agreed thatwith mill ions of acres planted. gene transfer will occur.Therefore, an ‘‘ecological map’ of wild species wascalled for, so that the location of field trials could beplanned to deliberately minimize proximity and hencepossibility for gene transfer. Experimental trials and re-search were recommended to quantify risks. as were stud-ies of the factors influencing gene transfer potential-i .e.. travel of pollen. effective fertilization, the produc-tion of viable seed, and the plant reaching reproductiveage and passing on its new set of genes. The group agreedthat studies should emphasize the conditions under whichtransfer and expression of the transferred gene take place.and the consequenses-relative risk—of such events (61).A comparable meeting was held for maize and wheat(Keystone, Colorado, December 6–8, 1990); another isplanned for rice.

Summary

A long history of agriculture provides an immensebunk of data relevant to risk assessment: diverse scientificfields contribute principles and knowledge. Data fromsmall-scale field tests of recombinant DNA-modified o-ganisms not only provide specifics necessary for the eval-uation of large-scale counterparts. they also provide arisk assessment testing ground. Each risk assessment of-

a field test adds to the regulator's experience base inadopting risk assessment methodologies to planned in-troductions. This learning through experience is a naturalpart of the evolution of oversight as we move from small-scale to large-scalec introductions.


Commercial Release Issues

A variety of issues relevant to planned introductionsof recombinant DNA-modified organisms are receivingheightened attention as large-scale commercial releasesbecome imminent. Principal concerns focus on the fitnessof the engineered organism (defined as overall geneticcontribution to future generations, usually quantified asnumber of offspring produced) and its potential to be-come established as a weed or a pest, the stability of theengineered gene, the potential for gene transfer, and im-pact on other organisms and the environment. Basically,these concerns are the same ones raised with regard tosmall-scale field tests of genetically engineered organ-isms. Large-scale agricultural uses involve large numbersof organisms that are usually less contained than theirless numerous counterparts in field trials.

Fitness and Potential to Become Established

For a species to become established in a natural com-munity, its relative fitness must be such that it competessuccessfully with other species. The lack of weedinesson the part of most major crops illustrates a direct contrastbetween domestication and what is useful for survival inthe wild ( 14. 43). Many traits necessary for successfulweediness either have never existed in or have been de-liberately bred out of crop plants to maximize produc-tivity in a cultivated setting. One analysis showed thatserious weeds tend to have on average 10 to 11 ‘‘weedycharacteristics’; crop plants have on average only 5 ofthese characteristics (42). Thus, the chances of any cropplant simultaneously undergoing five to six relevant genechanges to become a weed are vanishingly small (37).

Features of organisms that ecologists identify withweediness include broad ecological tolerance, ability toexploit an under-utilized resource. or ‘‘readaptation’to a new habitat to which the organism is well-suited andin which controlling biological agents do not exist (76).Other characteristics that help to make a plant thrive asa weed include the following:

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●

●

●

●

●

●

●

●

rapid growth to a flowering stage,continuous seed production as long as growingconditions allow,high seed output.long-lived seed,pollination by wind or unspecialized insects,high competitive ability,broad environmental tolerance,seed dispersal over short and long distances, andvegetative persistence and propagation.

The probability of successful establishment of a re-combinant DNA-modified organism as compared to itsunmodified counterpart will naturally be dependent onthe nature and phenotypic expression of the specific gen-otypic modification made, along with the rest of theorganism’s phenotype, in relation to these ecological cri-teria. Different kinds of engineered genes will vary inthe degree and nature of their impact on the phenotypeof the engineered organism. Also, engineered genes mayvary in terms of the conditions under which they will beexpressed. For example, if a gene is only induced to beexpressed under specialized conditions, then its pheno-typic impact will be negligible the rest of the time.

It has been well established from studies of inducedmutations that most dramatic phenotypic changes in anorganism result in reduced fitness (2, 14). Engineeredgenes that affect the growth, resource allocation, or someother aspect of an organism may convey added economicvalue, but may also produce a maladapted plant that isunlikely to survive outside of cultivation. On the otherhand. genes that have relatively little effect on the overallphenotype, such as genes induced only on certain oc-casions for disease or pest resistance, might confer a realfitness advantage, even in natural populations. It is gen-erally assumed that genes for disease resistance presenta physiological cost that reduces fitness in the absenceof disease, although the importance of that cost has beenchallenged (7 I ). However, sometimes if the gene is notexpressed, such costs go down, contributing to its po-tential long-term persistence.

Assessments of the risks of introduced organisms be-coming pests must take these factors into account as wellas others. For example, introducing a character into anorganism whose ecological properties are otherwise well-known, or taking a particular property associated withterrestrial bacteria and introducing it into another terres-trial bacterium, enables some prediction of how that char-acter might respond in that target ecological setting. Thus,in assessing the potential risk associated with a particularphenotypic modification, the target environment shouldbe considered.

If a species became established as a pest, existingcommunities would be disrupted; fortunately, the like-lihood of either a genetically modified plant or a micro-organism becoming a pest is relatively low. Most cropvarieties produced through conventional means do notbecome pests (6). Experiments to date indicate that ge-netically modified microorganisms in some cases maynot persist at significant levels (3) and therefore may

often be unlikely to proliferate and disrupt existing communities composed of vast numbers and numerous spe-cies of microorganisms (19. 86). So for all organismsmodified in any way. emphases in risk assessment ofmicroorganisms should be placed on the specific product.Until more is known about consequences of large-scaleuse of genetically modified plants. a deliberate approachrather than complacency seems warranted.

Gene Stability

The stability of an engineered gene is important to riskassessments of planned introductions of recombinant DNA-modified organisms. A gene that has become a stablecomponent of the transgenic organism is more predictablein its function, expression. and possible mobility thanone that has not. one aspect of gene stability is persis-tence. An engineered gene construct usually consists ofseveral components, all of which must be present andintact for the gene to function. In addition to the structuralgene that codes for the desired gene product. a promotergene is needed for it to be expressed—to be turned ‘‘on’or ‘‘off. Such constructs maybe broken apart by naturalgenetic recombination. A promoter separated from its.structural gene is useless; the structural gene without thepromoter remains unexpressed.

The stability of a particular gene also may be directlyinfluenced by the vector used to introduce it into theengineered organism. Bacterial plasmids or DNA-car-rying bodies, are potentially the most mobile of the vec-tors used to insert genes. Plasmids function by insertingthemselves into the bacterial chromosome. carrying anengineered gene along with them. Insertion sites for suchplasm ids are nonrandom; they are specific sequences thatcould be recognized by other plasmids, which may pickup the inserted gene and carry it along to another organ-ism. on the other hand, it also is often true that insertionof a particular plasmid will immunize the cell againstinsertion of similar plasmids.

Genes directly inserted into chromosomes are morestable than genes carried by plasmids. However, chro-mosomes are complex structures, and the manner in whichparticular genes express or recombine is determined bytheir relative positions on chromosomes. An engineeredgene inserted in some parts of the chromosome may bemore exposed to recombination than genes on other partsof the chromosome. The relative stability of an engi-neered gene in a plant species can be increased by in-serting it into portions of chromosomes subject to lowerlevels of recombination.

To summarize. a gene’s stability depends on the natureof the gene itself and on the means of introducing it intothe recipient organism. Either of these can be manipu-lated deliberately to increase stability.

Gene Transfer

Another appropriate focus for risk asessments of plannedintroduction of recombinant DNA-modified organisms isthe possibility) that novel genes may become incorporatedinto related wild species. Such transfers, it is argued, mightlead to harmful bacteria or weeds with an " improved"characteristic such as resistance to pest attack: this mightmake them more difficult to control. Three key questionsto be considered are: What is the probability that a genewill move from an agricultural organism to wild species’?What can be done to lower the probability? What wouldbe the consequences of such gene transfer on agriculturaland natural communities<? (37 )

The probability of gene transfer from a recombinantDNA-modified organism to a wild relative depends onthe introduced organism and the nature of the originalgene transfer mechanism. For microorganisms such asbacteria the primary means of genetic transformation isby vectors that, as noted above. are readily incorporatedinto organisms and mobile between organisms. This opensup the prospect of horizontal transfer of modified genes.

In addition to vector-mediated gene transfers, or trans-duction, genetic transfer in bacteria can occur by trans-formation, in which DNA freely existing in the environmentis incorporated into living cells; and conjugation, in whichDNA is transferred by direct organism to organism con-tact (27). These mechanisms are well known from invitro studies of microorganisms under laboratory con-ditions; indeed, transduction has become a common toolin the introduction of engineered genes into bacteria (55).However, little is known of the properties of these trans-mission mechanisms in nature (80). Due to the com-plexity of the bacterial environment, the scope for bacteriato bacteria contact or for mobility of bacteriophages andbacteria are much more restricted in soil than in labo-ratory culture.

Risk assessment of gene transfer in natural bacteriapopulations is also problematic because species com-position and potential for gene transfer among species ispoorly understood. Only a small fraction of the bacterialspecies growing in soil occur in sufficient numbers to berecognized by standard isolation techniques (48). It hasbeen argued that slow-growing organisms occur in suf-ficiently low numbers that their potential interactions andany subsequent possible risks are negligible.

On the bright side, a number of recently developedtechniques exist that can greatly facilitate studies of bac-terial interactions in natural substrates (48), includingflow cytometry (a technique that involves the use of laser-activated fluorescence of stained particles) and poly-merase chain reaction (PCR) (65), involving the ampli-fication of a particular gene contained at low concentrationin soil to sufficiently high concentrations that it can bedetected by standard DNA analysis. PCR can be used tomonitor the movements of introduced genes in naturalsubstrates (79). This allows the population dynamics ofthe engineered organism to be more closely monitored,the transmission of the engineered gene to backgroundorganisms to be quantified, and potential risks to be eval-uated. Also, the introduced population can be “tagged’with a specific but nonfunctional DNA sequence suchthat the growth or decline of that population in the soilcan be monitored independently of the engineered gene(s).

Actual probabilities of gene transfer of various kindsamong microorganisms are still being researched. Al-though differing opinions certainly exist, one school ofthought is that the order of magnitude of microorganismspresent in the natural community, and the probable fre-quency with which they exchange genes, renders thepotential impact of most recombinant genes being trans-ferred relatively low.

For higher organisms. vector-mediated transfer of en-gineered genes is not a major concern. For example, awidely used vector for dicotyledormus plants, Agrobac-terium tumefaciens (crown gall virus) can be readilyscreened out of transformed organisms before they arereleased. Furthermore. for many important crop species,notably cereal crops, vectors for gene transfer are notused: rather ballistic incorporation of genetic materialinto tissue-cultured cells (using ‘“gene guns’ ) is the methodcurrently in development. Using this method there is nochance of vector-mediated gene transfer. This leaves genetransfer through hybridization of crops and reproduc-tively compatible (i. e., closely related) weeds as apossibility.

In higher plants, the main risk associated with genetransfer from transgenics into surrounding populationsis. in fact, that of hybridization. Modified genes poten-tially could be transferred from transgenic plants andincorporated into the genome of a weedy species throughintrogressive hybridization, whereby genes are transmit-ted through pollen in sexual reproduction. However,working against this possibility are limited viaility ofpollen, distance and physical barriers to pollination. ge-

netic dissimilarities (i. e., incompatible fertilization pro-cesses), and failure to produce viable, fertile offspring.

Most crops grown on a large scale in temperate re-gions, such as corn and wheat, are grown outside of theirgeographic region of origin; consequently there typicallyare no related weed species growing in association withthem. Therefore, for most crop species in the UnitedStates, pollen-mediated transfer of modified genesis onlyof theoretical concern. However, there are several im-portant crop species for which closely related weed spe-cies have become introduced. Specifically. many cropsin the family Brassicaceae. such as canola (oil-seed rape)and radishes, have co-occurring weedy relatives (21).Sunflowers had their center of origin in the United Statesand have related weedy species here as well.

Most major crop species originated in what arnowregarded as developing countries. For example, corn wasdeveloped in Central America, wheat was first cultivatedin the Middle East, rice in Southeast Asia. and potatoesin South America (77). Consequently, introduction ofgenetically engineered crops into such regions should behandled with particular attention to the probability ofgene transfer into background populations.

Additional concern focuses on the potential impact ofintroduced genes on the genetic structure of natural pop-ulations of plants related to important crop species. Thesepopulations represent the genetic heritage of the crop andare an irreplaceable reservoir of diverse genetic variationthat may be needed in future development of the crop (8).If, because of a novel gene effect, one strain or lineagebecame a super weed it might outcompete and thereforeeliminate other lineages; genetic variation potentially usefulfor crop development could be lost. More generally, bio-diversity is intrinsically valued by many ( 12).

Pollen-mediated transfer of novel genes from cropsinto related weeds might also result in weeds becomingsimilar to the crop species. A number of well-knowninstances exist where selection pressures exerted by tra-ditional agronomic practices have caused weedy speciesto evolve to resemble the crop species. Such weeds can-not be eliminated by standard control practices (4). Thus,weeds are capable of a wide range of genetic adaptationeven without the introduction of novel genes. Althoughthere could clearly be problems associated with potentialgene transfer from transgenic plants into weed popula-

tions. there is also a large experience base in agriculturaland natural populations on which to draw for predictionsin this area.

A great deal is known about pollen transfer in plants(35) and associated Likelihoods of gene transfer. In thepast few years, there has been a growing interest in track-ing pollen in natural populations through ‘‘paternity anal-ysis, ” a technique directly analogous to human paternityanalysis (58, 82). The development of such approachesprovides a useful means of evaluating the potential spreadof modified genes, as well as a means of testing theefficacy of various measures to prevent pollen spreadinto wild relatives.

Gene flow in many crop species has also been studiedextensively in order to determine necessary distances forgenetic isolation of different plots to reduce genetic con-tamination of seed crops in conventional agriculture. Forexample, genetic contamination of seed in plantations ofconifers can reach levels of 30 to 50 percent and is anextensively studied problem (78). A review of gene trans-fer from corn to related species concluded that the pros-pects for introgressive hybridization in corn were limited(17). However. it is unwise to dismiss completely con-sideration of gene transfer because genes transmitted atlow levels could be rapidly enhanced through naturalselection if they confer an advantage to their recipients.A study of hybridization among six different rice culti-vars developed through conventional agriculture and therelated weed red rice (Oryza sativa L.) found widelyvarying rates of hybridization with the different cultivars.The hybrids generally showed evidence of convergencetowards the crop, thus opening the possibility of gene-rating a particularly noxious weed that closely resemblesthe crop (49).

For specific applications of biotechnology, it is pos-sible to articulate potential risks of gene transfer andevaluate their probability. Furthermore, long-standingagricultural practices (e. g., isolation of crops for seedcertification) can be useful in managing this risk. For thefew U.S. crops with weedy relatives (i.e., canola), andfor other countries where crops have multiple relatedspecies, careful risk assessment should lead to reasonablerisk management. It is important to remember that suc-cessful cross hybridization is in fact a complex multistepprocess and does not usually lead to viable, fertile hy-brids. unless the species are closely related.

Evolutionary Pressures Placed on OtherOrganisms

Evolutionary pressures on indigenous organisms canarise in several ways. Novel organisms in a biotic com-munity may provide new levels of competitive interac-tions; they may impose direct selection pressures on the

native organisms; they may also enhance one species atthe expense of others. Thus the assessment of risks (andbenefits) associated with the planned introduction of re-combinant DNA-modified organisms must consider theengineered organisms’ probable interactions with the tar-get biotic community.

Many such interactions occur in convolution of a cul-tivated species and its associated pathogens. pests. andweeds. One interaction that should be beneficial in termsof controlling crop pathogens involves a pathogen’s re-sponse to “resistance factors.” Factors conferring resis-tance to pathogens can be conventionally bred or geneticallyengineered into plants. It is well established that theintroduction of pathogen resistance factors imposes se-lection pressures on pathogens to overcome these factorsby evolving greater virulence (34). Using conventionalbreeding methods, it can take longer to introduce a re-sistance factor into a crop species than it does for path-ogens to respond. Genetic engineering promises greatlyto reduce the time frame for introducing resistance fac-tors. This ‘‘buys” the crop some lead time before thepathogen evolves a response.

Strong selection pressures also are exerted on pestspecies to evolve counter measures to control technolo-gies. The use of Bacillus thurigiensis ( Bt. for example,is an effective means of controlling insect pests that couldbecome overutilized and thus rendered ineffective. Thebacterium itself often is used in broadcast spray appli-cations to control insect pests, and the gene for toxicagents in Bacillus thuringiensis has been cloned. Thegene now is being incorporated into crop species in fieldtests. This will exert even stronger selection pressure oninsect pests. Several approaches may help to diminishselection pressure and thus slow down the rate of evo-lution of resistance. (See ch. 6.) It may be possible, forexample, to introduce the Bt gene in such a way that itis only turned on during certain stages of development,only in certain parts of the plant. or only at times ofinsect attack, thus decreasing its impact. Scientists fromseveral agricultural companies have formed a Bt resis-

tance ‘‘club’ to discuss how to slow the evolution ofresistance to Bt.

Another concern is that use of genetically engineeredcrops for herbicide resistance may result in overuse ofspecific herbicides and thus impose strong selection onweeds to evolve resistance to those herbicides. For ex-ample. if even ‘‘environmenttally friendly" herbicides areoverused in conjunction with transgenic monoculture,weeds might evolve resistance fairly rapidly. This maylead to a “desperate” use of far more damaging herbi-


cides. Management strategies for slowing the develop-ment of resistance may be needed. (See ch. 6.)

The convolution of a cultivated species and its as-sociated pathogens and weeds is a quite predictableprocess if one genetic locus for one resistance factoris considered. The sequential introduction of resistancefactors in a crop species ultimately can lead to the so-called ‘‘gene for gene’ condition in which each genefor some resistance factor in the host is matched by agene for virulence in the pathogen. One way to breakthis cycle is simultaneously to introduce multiple re-sistance factors, thus impeding the pest’s evolutionaryresponse. Similarly, different resistance factors mightbe cycled from year to year so that the pest never fullyresponds to any one resistance factor (34). The use ofgenetic engineering techniques could greatly facilitatesuch strategies because it provides a tool for rapidgeneration of new lines containing different combi-nations of resistance factors.

Monitoring

Assessing the potential risks of environmental intro-ductions of recombinant DNA-modified organisms, andevaluating how best to manage these risks, entails spatialand temporal monitoring of the organisms and of theirintroduced genes. Monitoring contributes to risk assess-ment and management in two ways. First. in a specificsituation, it tracks indicators of gene transfer or spreadof introduced organisms so that action can be taken ifneeded. Beyond this, monitoring adds to our database,so that risk assessments of subsequent introductions areeven more accurate. Monitoring of field tests can provideinformation pertinent to subsequent field tests and tolarge-scale introductions. For example, presence or amountof gene transfer from transgenic crops to related or non-related weedy species could be estimated from monitor-ing species surrounding a test field containing a recom-binant DNA-modified crop. These data can be used infuture field tests or large-scale introductions involvingsimilar crop/weed complexes. Monitoring also can helpelucidate any spread of introduced microorganisms. Asthe ecology of their spread is understood more fully, riskassessments of new introductions can be improved. Thus,monitoring has an important role to play in the naturalevolution of science-based. risk-based regulatory over-sight. Highly sensitive monitoring techniques are devel-oping rapidly. (See box 8-C. )

The following is an example of the kind of data thatthe Animal and Plant Health Inspection Service (APHIS)can require from monitoring (in this case recombinant

entomocidal or insect-killing bacteria were field tested).Required monitoring provided data on:

1.

2.

3.

4.

5.

6.7.

8.

9.

plant colonization by the recombinant bacteria at 4weeks after inoculation;colonization of all plant parts by the recombinantbacteria monthly for 4 months;dispersal, natural and mechanical, in the field ofthe recombinant bacteria after 60 days;presence in run-off water of the recombinant bac-teria;presence in soil of recombinant bacteria popula-tions;effect on crop yield of the recombinant bacteria;effect on crop residue decomposition of the recom-binant bacteria;effect on vesicular-arbuscular mycorrhizae of therecombinant bacteria 3 and 6 weeks after planting;and .

effects of the recombinant bacteria on saprophyticgram-negative bacteria in the phylloplane.

Other points of interest needed to be addressed throughthe ability to track the recombinant bacteria, as well (22).

The monitoring data collected enabled APHIS to assesspatterns of the spread of the recombinant bacteria on thetargeted plant and its various parts, the dispersal of thebacteria in the field water and soil, effects of the bacteriaon crop yield and decomposition, and the effects of therecombinant bacteria on mycorrhizae and other plant bac-teria. In short, required monitoring of plants and soilcontributed directly to understanding of dispersal andeffects of the recombinant bacteria.

Plants generally are easier to monitor than microor-ganisms. As techniques for monitoring improve, fieldtest data and, soon, large-scale test data will improve ourknowledge of survival and spread of recombinant DNA-modified organisms and their genes. thus aiding us inreasoned risk assessment and management.

Research Needs

For the past two decades, basic research in molecularbiology has generated many novel scientific insights andproducts. As a result of strong government support forsuch research, we have reached a point where the plannedintroduction of recombinant DNA-modified organisms isa reality. However, the fields of ecology and evolutionarybiology, which can provide the kind of information andexpertise needed to predict the impacts of planned intro-ductions, have enjoyed less support. Fortunately, ecol-ogists are now taking a leading role in defining a research

Chapter 8—Scientific Issues: Risk Assessment and Risk Management ● 245

Box 8-C—Monitoring Microorganisms

Detection and tracking (monitoring) of recombinant DNA-modified organisms and their genes makes possiblequantification of persistence or spread. Highly sensitive new techniques, among them polymerase chain reaction(PCR) and antibodies, are being utilized to contribute to the efficacy of monitoring. Data resulting from monitoringin turn contribute to the knowledge base on which risk assessments of prospective small-scale and large-scaleintroductions can be based. In fact, regulatory agencies’ request that certain parameters be monitored in field testsallows them to fine tune upcoming assessments of large-scale applications, and to make plans for their management.

The first approved environmental introduction of a living genetically modified soil-borne bacterium in the UnitedStates, in fact, had as its goal monitoring of the bacterium’s population dynamics, persistence, and movementthrough the soil. The genes “lac Z“ and “lac Y“ were engineered into a root-colonizing fluorescent pseudomonas(P. aureofaciens), part of a bacterial group that often promotes plant growth and protects against some plantdiseases. The added genes allow the bacterium to use lactose as a source of carbon and energy and result inreadily discernible deep blue bacterial colonies on a petri dish, thus providing an excellent monitoring tool. Scientistsfrom Clemson University and Monsanto studied bacterial spread, population dynamics, and persistence over threecrop cycles (19 months) in a wheat field and found similar values for both the modified and the nonmodified strains.Both strains declined to below detectable limits 38 weeks after inoculation. Also monitored were the foliar tissueof the first winter wheat crop analyzed 3 weeks before harvest and found not to have either strain present; andnative soil bacteria, to which the Iac Z and Iac Y genes were not found to have transferred. The study’s multifacetedsampling design, use of new techniques such as chromosomal DNA fingerprint patterns, presence of a control inthe form of a nonengineered strain, and followup over three crop cycles set good examples for thorough monitoringstudies in other situations (45). This work also is noteworthy as the first study analyzing frequency of geneticexchange in the environment of genes inserted into bacterial chromosomes rather than plasmids. This “success”of the chromosomal approach has implications for scientific management of gene transfer in microorganisms.

In future monitoring studies, the transgenic organism or the inserted gene itself might be tracked by a nucleicacid probe for a specific DNA sequence; as well as by selective media for metabolic characteristics or by antibodiesto a characteristic antigen. Some tracking techniques require that bacteria be isolated and grown in the laboratory,but others are being developed that can analyze bacterial DNA as isolated from environmental samples, a capabilityuseful in estimating the population of the introduced organisms. Still other techniques, including pulsed field elec-trophoresis, can be used to analyze total DNA in a simple community and possibly to then quantify different membersfrom the sample. In communities that are more complex, higher resolution is needed and probes maybe necessary.In such cases, antibodies may give a great deal of information by tracking phenotype through detection of proteinspresent (19). Polymerase chain reaction methodology is an innovative technique that can be used essentially to“magnify” sensitivity of detection. Flow cytometry, a cell-sorting technique, may also have some application tomonitoring.

SOURCE: Philip C. Kearney and James M. Tiedje, ‘tMethods Used to Track Introduced Genetically Engineered Organisms,”Biiotechno/ogy for Crop Protection, Paul Hedin, Julius Menn, Robert Hollingworth (ads.) (Washington, DC: AmericanChemical Society, 1988).

agendna to respond to a variety of social needs, including tributions to these predictive capabilities. However. fundingthe planned introduction of’ recombinant DNA-modifiedorganisms (85 ). Since introduced species or their genesmay be incorporated into natural biota, over time. a sim-ilar agenda is needed for evolutionary biology to assessthe likelihood of propagation and persistence.

The likelihood of an introduced organism becomingestablished. competing with other organisms. spreading.exchanging genes with members of other species. indi-rectly affecting nontarget species, or changing over ev-

olutionary time all need to be predicted in risk assessment.A number of fields in biology are already making con-

for further research is needed. (See box 8-D. )

Development of mechanisms for effective coommuni-cation between fields is critical to meeting research needsassociated with the planned introduction of recombinantDNA-modified organisms. It has been noted that inter-disciplinary research is critical for the development ofrisk assessment and risk management pertinent to plannedintroductions (92). In particular. the gap between ecologyand molecular biology needs to be spanned. Scientists inboth areas need to be trained or encouraged to be moreaware of each other’s fields.

130x 8-D—Relevant Research Fields

Community EcologyCommunity ecology is the study of interactions of populations of different species in a given habitat. Interspecific

competition, predation, and other interactions are the province of this field. Modern community ecology is anexperimental field; however, most experimental studies are limited in scope to consideration of two, or at mostthree interacting species. Larger experiments focusing on more realistically complex interactions, and desirablepredictability of response to perturbation, will require more research. Ecological systems research on topics suchas nutrient cycling can provide relevant information as well.

Population EcologyPopulation ecology is the study of the dynamics and growth of populations. Such studies may emphasize

properties of the species itself, such as fecundity or mortality rates, or they may emphasize effects of environmentalor biotic interactions. There is a growing trend to incorporate population ecology into conservation biology. Analysisof life history can be used to determine which stages (e.g., seedling establishment versus adult survivorship) arelimiting to population growth. Such analyses of sensitivity in population dynamics (9) could be useful in risk as-sessment of ecological impacts of recombinant DNA-modified organisms.

Population GeneticsPopulation genetics is the analytical study of properties of genes and changes in gene frequency over time.

The mechanism by which genes are transmitted from one generation to the next and the relationship betweenparticular genes and fitness are key to this field. This field is distinctive among biological fields because of itssophisticated theoretical framework. The theory enables some level of prediction about the behavior of genes inpopulations, but more emphasis on empirical studies is needed to generate useful predictive models of gene change.

Evolutionary BiologyOne way to encourage empirical work in population genetics would be to place more emphasis on research

in evolutionary biology. Changes over time in genetic structure—and consequent phenotypes-of populations arefoci of evolutionary theory. Emphasis on dynamics of change predisposes the field towards questions of relativeSpread of genes and impact of phemotypes in an ecosystem over time; these are questions that are relevant to riskassessment of planned introductions.

SystematicThe field of systematic encompasses analysis of variation of different levels of taxonomic organization. Although

the ultimate goal of such analysis is taxonomic classification, this field is increasing in importance in analysis andmonitoring of biotic diversity. This field could contribute to risk assessment through analysis of species relationshipsand species ranges to evaluate the probabilities of hybridization.

Mathamatical ModelingMathematical modeling entails construction of a mathematical framework to describe a process and predict

outcomes from that process. Modeling has been an effective approach in risk assessment and strategic planningin agriculture, For example, models have demonstrated that allowing the existence of marginal populations of pestslets them serve as reservoirs for genes that confer susceptibility to pesticides and other means of control, suchpopulations therefore can beneficially slow the rate of evolution of resistance (34). This seemingly counterintuitiveresult contraindicates a straightforward program of eradication.

Risk Assessment MethodologiesRisk assessment involves the ranking of probable outcomes from possible events. As such, in order to rank

risks, one needs to first define the risks of a given practice. Development of risk assessment methodologies is anongoing practice, and practitioners must always be ready to adapt to new problems as they arise in differentsituations, such as commercialization of diverse crops in a variety of environments.

SOURCE: Office of Technology Assessment, 1992.

Chapter 8—Scientific Issues: Risk Assessment and Risk Management .247

More communication between scientists involved inbasic research and applied research is also needed. Justone example is the need for communication and inter-action between plant-resistance breeders and evolu-tionary biologists (33). Another example would becommunication between farm management systems re-search and ecology. Many people who work in basicresearch are in part motivated by applied concerns.However, it does little good to generate insights on anapplied problem unless there are lines of communi-cation whereby the results of those insights are incor-porated to solve the problem. Questions regardingapplied problems also need to be articulated to basicresearchers.

RISK MANAGEMENTGenetically modified organisms introduced into the

environment do not present us with radically novel prob-lems. Furthermore, we have a sufficient enough base oftechnical knowledge and risk assessment methodologiesthat we can make reasonable, science-based assessmentsof the likely impacts of individual proposed introduc-tions. The concerns raised do not need to paralyze ag-ricultural progress based on biotechnology. These concernscan be respected, weighed, and addressed as necessarythrough science-based regulations and scientific and ag-ronomic methods of managing risk.

Design of Science-Based Regulation

The 1986 Coordinated Framework (5 I FR 23302-23393,1986). the more recent scope document (55 FR 147,3118. 1990). and other reports attempt to create a tech-nically sound context for biotechnology oversight. (Seech. 7. ) Reviews of field trials to date have been basedon technical issues of risk reduction. Technically soundevaluations of safety can provide principles for regulationand oversight. Agencies receiving proposals can add spe-cific stipulations for risk management (66). A variety ofscientific fields ranging from molecular genetics to ecol-ogy need to be brought to bear on the design or perfor-mance of oversight. As research progresses. predictabilityabout risks and insights as to how they should be managedwill improve.

The imminence of large-scale introductions under-scores the need for clarification of how risk will be man-aged in various situations. Identification of issues.development of policy, and structure for large-scale testsand commericializations, along with modifications of the

approval process for small-scale field tests, are all beingrequested from regulatory agencies, who are themselvesgrappling with the issues involved (36).

Generic v. Case-by-Case Approach

Extrapolation of results of risk assessment from onesite to another still needs refining; this has ramifica-tions for multisite, large-scale introductions. Many be-lieve that ‘evaluation of risks must be specific to theparticular application. However, attempts have beenand doubtless will be made to associate individual caseswith appropriate categories of risk and to manage themaccordingly (51).

One key issue in the approach to risk management inplanned introductions of recombinant DNA-modified or-ganisms is whether to use a case-by-case analysis ap-proval process or a process built on generic categories.Some, looking at the large number of applications com-ing down the pipeline, advocate a shift from the currentcase-by-case review of experiments toward more of ageneric approach. Possible strategies under this approachinclude categorical exemptions, licensing certain cate-gories of tests. licensing individual scientists. or dele-gating authority to institutions (53). Others fully expectlarge-scale tests and commercialization. in particular, tobe reviewed on a case-by-case basis. but they do en-courage the rapid appearance of protocols or some otherform of guidance so that safe and effective products canbe developed (36).

Advocates of a case-by-case approach point to its flex-ibility. As different cases arise, each can be dealt within a manner appropriate to its nature; no one set of rulesand regulations, it is argued, will cover all of the manyand varied applications of biotechnologgy.

Nonetheless, over time, as our experience and researchbase grows it is likely that some generic approaches tocertain sorts of introductions in certain sorts of environ-ments will emerge. The criteria by which these genericapproaches are defined (some requiring more attentionthan others) will themselves change over time (74). Thesedevelopments were anticipated in the ESA report (85),which made a significant step toward scaling risks. Even-tually. generic categorizations of likely risk are probable,yet each case will need to be double-checked for anyidiosyncratic particularity that could trigger more focusedreview. It is important for the successful application ofbiotechnology to agriculture that sufficient long-termflexibility is built into the regulatory and oversight system

so that risk management can evolve based on improvedunderstanding.

Relative Risks Compared to TraditionalPractices

Risk management involves the weighing of costs andbenefits. To put planned introductions in context, their riskscould be compared to risks of traditional practices in ag-riculture and society. For example, risks today are asso-ciated with the widespread use of chemical pesticides;accumulation of nonbiodegradable materials; toxic wastes;agricultural practices giving rise to genetic uniformity infarm animals and crops, with loss of biological diversity;and ‘‘natural biological calamities, ’ such as the currentepidemic of AIDS. Not only are risks of planned intro-ductions put into perspective by these nonbiotechnology-related problems, but biotechnology itself may help to solvesome of them. For example, biotechnology can providealternatives to chemical pesticides, assist in the degradationof toxic wastes, provide alternatives to selective inbreeding,and contribute to development of diagnostics and vaccinesfor AIDs and other illnesses (74).

On a more specific level of cost/benefit comparisons,new biotechnology techniques can be compared to thoseassociated with traditional biotechnologies. (See table 8-1 for one view of such a comparison. ) Certainly contro-versy exists—for instance, over the relative predictabilityof the ecological behavior of the phenotypes of transgenicorganisms even when genotype changes are precise andwell-understood. On the other hand, conventional breed-ing changes many genes simultaneously, with consequentmultiple phenotypic changes. The newer, more precisetechniques may actually show up well in the comparison.

Cost-Benefit Analyses

Risk management includes the weighing of risks or ofactual costs on the one hand against benefits on the other,and then trying to achieve a reasonable balance (74).Agricultural biotechnology has potential to create posi-tive benefits for agriculture. horticulture, range manage-ment, and forestry in the 21st century (43) if it is notstalled in its developmental stages; on the other hand, itis to no one’s best interests to proceed without attentionto identifying and minimizing any likelihood of risks.An appropriate balance is necessary.

In a time when the expansion potential of land foragriculture is small, when labor is expensive, and whenadditional use of chemicals in agriculture generally isregarded as a negative, the possible exploitation of newcapabilities and new information through new technol-ogies cannot be ignored. Thus, regulations that are notscience-based could exact a very real ‘‘cost, that of notintroducing an innovative, promising product.

Small-Scale v. Large-Scale Issues

As agricultural biotechnology nears the commerciali-zation stage, risk management must take into account anumber of realities, as was mentioned in the previouschapter. For example, large plots at a number of locationsare needed to test a recombinant corn line. This testingneeds to be done within I to 2 years of the creation ofthe recombinant line for a company to stay competitivein the development of new varieties. Furthermore, manyhybrids will be undergoing evaluation at the same time;several of these may contain the same recombinant geneand several recombinant genes might be examined si-multaneously. In short, if the recombinant material goes

Table 8-l—Comparison of Traditional and Developing Biotechnology

Characteristics Organismal Cellular Molecular

Processes Breeding Culture - Cell rDNA- Anther- Embryo

Selection RegenerationMutation Fusion

Control over changes Random Semi-random Directed, precisePrimary changes Unknown Semi-known KnownNumber of variants needed Large Intermediate Small, in vitro selection methodsSpecies restriction Mainly within Within & across Within & acrossFamiliarity Very high Intermediate Low but expandingAbility to ask and answer risk questions Low Intermediate HighContainment Dependent on organism and independent of method;

established procedures for domesticated organisms.

SOURCE: R.W.F. Hardy, ‘(Large-Scale Field Testing and Commercialization: Thoughts on Issues,” Biological Monitoring of Genetically Engineered Plantsand Microbes, D.R. MacKenzie and S.C, Henry (ads. ) (Bethesda, MD: Agriculture Research Institute, 1991),

Chapter 8—Scientific Issues: Risk Assessment and Risk Management ● 249

successfully and quickly through testing, the breeder willsoon work to combine it with other useful traits, in dif-ferent genetic backgrounds, as part of genetic improve-ment. Large numbers of new lines will emerge from theintegration of recombinant genes into conventional breedingprograms so that new hybrids can be tested and com-mercialized.

Specific recommendations for risk management of thetransition to large-scale could include: I ) making geo-graphic maps of crop relatives and placing them in anaccessible database, and 2) modifying the process forapproving small-scale introductions based on experiencebase or familiarity (36). Marshaling evidence from ex-periences in agriculture, laboratory tests, introductions,field tests, and current, ongoing research will make pos-sible reasoned risk assessment and management.

SCIENTIFIC METHODS OFMANAGING RISK

The power and precision of biotechnology can be har-nessed for risk management itself. Controlling the spreadof introduced genes through the manner in which theyare introduced is one example. Risk management can begreatly aided by using supplementary transferred genesto ensure that the ensuing recombinant DNA-modifiedorganism only functions on certain occasions, under cer-tain environmental conditions, or for a finite period oftime. The genetic modification can be designed to: 1 )constrain the potential for gene transfer (increasing the“containment’ of the gene within the organism into whichit was inserted), and 2) maximize its key activity whileminimizing effects in the recipient environment (60).Mechanisms for fine-tuned technical control of this sortstill are being developed; a few approaches are describedbriefly here. In general. in addition to turning the geneon or off under certain conditions, several approaches tocontainment could be considered: ‘‘autodestruct’” mech-anisms (e. g., suicide genes), engineering genes such thatthe host has diminished survival (as through defectiveregulation of metabolism), and decreasing chances ofhorizontal gene transfer to other organisms (as throughreducing the stability or ease of inheritance of the intro-duced genes) ( 19).

Promoters Turned On or Offby Specific Stimuli

One way to limit the effect of the engineered geneitself is to attach it to a promoter that only allows expres-sion under certain conditions (83). When a gene is not

being expressed, the physiological expenditure associ-ated with expression of the gene can be allocated to otherpurposes. This maintains the “efficiency” of the organ-ism and keeps the impact of the gene’s phenotype to aminimum. For example, some genes are only expressedwhen triggered or induced (usually through a ‘‘pro-moter’ gene) by a certain chemical, such as a herbicide,or in the event of local disturbance of tissue, such as awound response resulting from chewing by insects. Agene for some form of pest resistance attached to suchan ‘‘inducible promoter’ gene would have little phen-otypic impact except in the presence of a pest. This is arealistic strategy with diverse applications, some of whichalready have been field tested. For example, a field testwas conducted by Iowa State University to assess whetheror not transgenic tobacco plants would respond to insectattack by turning on an inserted gene. Plants often canrespond to insect attack by activating genes coding fordefensive compounds. Such compounds may, for in-stance, block the digestive system of insects, reducingtheir leaf consumption. A marker gene—one used totrace the success of the recombination experiment—(chloramphenicol acetyl transferase, CAT). modified fromproteinase inhibitor II genes in the tomato family, wasput into tobacco to determine levels of its activation byinsects under actual field conditions. Upon insect attackon foliage, the transgenic plants showed induction of thetransferred proteinase inhibitor genes. This has positiveimplications for using the wound-inducible inhibitor pro-moter in biological control of insect-caused foliage dam-age. The potential exists for a well-managed. efficientsystem, in which the inserted genes function only on anas-needed basis (83).

Suicide Genes

When it is important that particular recombinant DNA-modified organisms not establish viable populations, amechanism that has been proposed for their containmentis to include, along with the desired gene, a "suicide"gene that will sufficiently cripple the organism that itwill not survive beyond its intended use. The suicidegene may, for example. prompt a metabolic pathwayresulting in death of the cell in the presence of a specificexternal cue (44, 70). Another approach to containmentis to introduce mutations that inactivate the transgenicorganism’s ability to synthesize necessary aromatic aminoacids or other key metabolic pathways of the cell ( 19).

Alternatively. a “kill” gene can be inserted to beexpressed constitutively — all the time-unless a ‘‘pro-tection” gene is turned on by the same promoter genethat causes expression of the key functional gene. That

297-937 0 - 92 - 9 QL 3


promoter can be geared to respond to some signal fromthe environment, such as temperature or presence of apollutant chemical. For instance, if a protection gene fora vaccine strain is only activated above temperatures of30 “C.. the vaccine organism will express the kill geneand die if it passes out of the host’s body ( 19).

The advantages of a “suicide” strategy are straight-forward. Existing experimental data indicate that genet-ically modified microorganisms introduced into theenvironment usually fail to establish viable populationsunless the numbers of introduced organisms are verylarge. To accomplish a useful effect, as in agriculturaltreatments or environmental clean-up, planned introduc-tions of microorganisms generally will require inoculaof large populations. Once the goal of the planned in-troduction has been met, a trigger factor to set off thesuicide gene can be introduced that will leave behindonly a small fraction of the introduced population, whichmay then be at too low a frequency to sustain itself.

Suicide genes are most frequently suggested for con-tainment of microorganisms; their feasibility in plantshas been questioned. With plants’ complicated physiol-ogy. difficulties could exist, for instance, in triggeringthe action of specific genes by any environmental cueother than some deliberate applied chemical, such as aherbicide (37). Overall, the potential effectiveness ofsuicide genes at this point is controversial (25). One keyproblem with the use of suicide genes is that naturalselection would encourage the evolution of geneticallybased mechanisms counteracting the suicide effect.

Prevention of Gene Transfer

In the case of transgenic plants, concerns exist aboutthe possible transfer of engineered genes to neighboringweedy populations of related species. One way to preventgene transfer through pollen would be to shut down pol-len production in the transgenic plant. This can be ac-complished by introducing a male-sterility factor into theplant along with the desired trait. The use of naturallyoccurring male-sterility mutants has been a significanttool in traditional plant breeding. Quite recently, genesfor male sterility have been cloned and reintroduced intoseveral plant species, including canola (56). These geneswere expressed in the transgenic plants and hence broughtabout male sterility. This strategy has a great deal ofpromise and currently is feasible. Its application to canolais especially pertinent because that species is among themost likel y to effect vector gene transfer to related speciesin North America.

For leafy crops (e.g., spinach) or root crops (e. g.,sugar beets), male sterility would not be problematic. Infact, it has been suggested that male sterility used intimber tree plantations would channel more of a tree’sresources to board feet production, in lieu of reproduc-tion. Some crops (e. g., cereals), however, require pol-lination, so that mixed varietal plantings of male steriletransgenic plants and male fertile. untransformed vari-eties could be needed (37).

Several strategies seem to have potential to decreasethe risks associated with gene transfer between micro-organisms. For example, a protection gene might be in-serted far away from a kill gene. which itself is close tothe desired gene being introduced to a host; then, if thefunctional gene happens to be transferred, the new re-cipient microorganism also would receive the kill gene,without the protection gene. Another approach might beto insert a gene for a particular active nuclease so thatwhen a cell dies, its DNA—including the introducedfragment-released after death will have been signifi-cantly reduced. A variety of ways of inserting defectsthat would disrupt the host’s mobilization and conjuga-tion systems could also cut down significantly on hori-zontal gene transfer (19). Engineering changes into achromosome rather than a plasmid may decrease the like-lihood of gene transfer between microorganisms; thisapproach also is being explored (45, 48).

Combinations of Genes

As the number of genes involved in a desired effectgoes up. so does the possibility that that effect will belost in the next and subsequent generations because ofnatural recombination. Thus, a possible strategy for de-creasing the long-term probability of establishment of anengineered genetic effect would be to have the desiredeffect depend on the interaction among several separategenes.

AGRONOMIC METHODS OFMANAGING RISK

Physical Barriers

Complete containment was the preferred method ofcontrolling risk when genetic engineering was introducedon a small scale. Examples of physical containment are“boundary strips” in the form of fences or hedgerowsthat can trap some large percentage of pollen. particularlythat dispersed by wind. This might, however, be un-feasible to install or cause unwanted shade (37). Overall.

Chapter 8—Scietific Issues: Risk Assessment and Risk Management ● 251

Photo credit: Grant Heilman, Inc.

A traditional approach to isolation of plants is to spatiallyseparate desired plants from other plants. Similar

guidelines for spatial segregation have been applied totransgenic plants as well.

a complete containment strategy has extremely limitedapplicability beyond small field tests. Once an organismhas been placed in the field in the numbers required byagricultural production, it is likely to be exposed to avariety of biotic interactions beyond the control of rea-sonable physical barriers.

Spatial Barriers

The traditional approach to isolation of plants genet-ically improved through conventional breeding, usuallyfor the purpose of generating a seed crop, is to isolatespatially the desired plants from other plants. Similarguidelines for spatial segregation have been applied totransgenic plants as well (64). Certainly this is feasibleat the small field trial stage, and could be effective in anexperimental setting to evaluate the properties of the or-ganism as a potential pest. Some spatial separation maybe feasible at the large-scale test stage, as well. Anotherapproach to separating plants in terms of gene flow is tosurround a field with flowers that will attract pollinatorsof the transgenic crop, so that these trap flowers ratherthan surrounding wild vegetation would be more likelyto receive any transgenic pollen. This approach mightconceivably diminish the pollinators’ activity in polli-nating the crop itself, however. Weed control practicesusing herbicides or cultivation could also decrease thechance of hybridization between the crop and wild spe-

cies. A straightforward mechanism is to decrease thelength of the boundary of the field and thus decrease thenumber of opportunities for neighbors along the bound-aries to exchange genes. Large, square fields minimizethese opportunities (37).

Temporal Barriers

Many problems associated with planned release couldbe addressed by the timing of the release. For example,if a given engineered line is released in an area with anuncultivated relative that could incorporate the engi-neered genes, one could manipulate the flowering (phen-ology) of the engineered organisms so that the crop didnot flower at the same time as the weed. For example,wild relatives need short days for flowering, bush typegreen beans do not (72). Similarly, one could release theintroduced plant at a time of year when the weed isdormant or even engineer the crops for cold tolerance,for example, to shift its flowering and production periodaway from that of its wild relatives. Agricultural expe-rience and ecological understanding will play a signifi-cant role in the development of such barriers. Someagronomic practices such as irrigation can allow cropproduction at a time of year unfavorable for related weeds,diminishing the possibility of cross hybridization.

Crop rotation could be used to force a weed rotation.This could decrease the number of weed individuals pres-ent in the field and, therefore, the likelihood of genetransfer; it might also eliminate hybrids produced in pre-ceding crop production periods. Crop rotation could pre-vent genes from being transferred to weeds outside thefield for a whole season or two at a time, diminishingthe chances that the gene would become established inthe weed community and making it more likely to belost due to genetic drift. The timing of harvesting couldalso build a barrier to cross hybridization. For some crops,such as cabbage, spinach, collards, lettuce, sugarbeets,carrots, turnips, radishes, celery, garlic, and onions, thecrop product is vegetative; careful harvesting would re-move the plants before their flowering, reproductive stage,thereby diminishing pollen transfer (37).

SUMMARY POINTSIssues and concerns raised by planned introductions

of recombinant DNA-modified organisms can be ad-dressed by the integration of risk assessment meth-odologies with the currently existing knowledge base,continuously augmented by ongoing research and byadditional data resulting from field tests. Risk man-agement is therefore possible, with its chief compo-


nents being science-based regulation, scientificmanagement methods, and agronomic managementmethods. A natural evolution of risk management andregulatory oversight is occurring as our experience basewith field tests and in performing ecological risk as-sessments grows. This step-by-step progression in theuse of recombinant DNA-modified organisms in theenvironment, emphasizing science-based risk assess-ment strikes a balance between a laissez-faire approachand a paralysis of the use of new technology. Bio-technology has the potential to contribute significantlyto agriculture; scientifically sound risk assessment andmanagement promote its acceptance as well as its safety.

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