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PPP-41

PESTICIDES AND ECOLOGICAL RISK ASSESSMENT

History, Science, and Process

Fred Whitford, Coordinator, Purdue Pesticide Programs

Douglas Urban, Senior Scientist, EPA Environmental Fate and Effects Division

Monte Mayes, Environmental Toxicologist, DowElanco

Jeff Wolt, Risk Assessment Leader, DowElanco

Edited by

Arlene Blessing, Purdue Pesticide Programs

TABLE OF CONTENTS PAGE

Introduction .................................................................................................................................... 3

The Evolution of Federal Pesticide Regulations ...................................................................................3

Early Federal Laws Focused Primarily on Benefits................................................................................ 5

Environmental Movement Changed Public Perception of Pesticides............................................................. 5

Government Policies Shift Toward Risk Reduction Strategies................................................................... 7

EPA Issued Scientific Testing Guidelines........................................................................................... 8

Pesticide Manufacturers to Follow Good Laboratory Practices................................................................... 8

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PPP-41 http://www.agcom.purdue.edu/AgCom/Pubs/BP/ppp-41/Index.html

EPA Moves Toward Risk Characterization......................................................................................... 9

EPA Policy Shifts to Reduced-Risk Pesticides.................................................................................... 10

The Food Quality Protection Act ....................................................................................................10

EPA Uses Risk Assessment to Set Safety Standards ...........................................................................11

Use of Risk Assessments: Registration, Reregistration, and Special Review................................................. 11

Benefits to EPA and the Public ......................................................................................................13

Risk Assessment as a Market-Oriented Process for Manufacturers....................................................... 14

The Science of Risk Assessment ...................................................................................................... 15

Risk Assessment as a Multistep Analysis.......................................................................................... 15

The Ecological Risk Assessment Process .......................................................................................... 18

Assessment Requires an Understanding of Toxicology, Ecology, and Processes........................................... 19

Toxicity Characterization ............................................................................................................20

Exposure Characterization ...........................................................................................................29

Risk Characterization ................................................................................................................. 39

Conclusions .................................................................................................................................. 45

Acknowledgments .......................................................................................................................... 46

PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE WEST LAFAYETTE, IN47907

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Introduction

Scientists and the public often are at oddswith respect to potential risk and theperception of risk. Are "risks" frompesticides in our environment real orperceived? What is their nature, and what is"reasonable risk"? These questions are at theheart of public debate concerning pesticideuse. The public wants absolute, clear,definitive answers; there is little tolerance forequivocal scientific terminology. Society hasbeen impatient with scientists and regulatorsover unresolved questions concerningpotential health and environmental risk; buttoday's risk assessment methodologiesfacilitate the process of addressing risk andrisk perception.

The risk assessment process is a criticalcomponent of pesticide productdevelopment and regulatory review. Theprinciples of risk assessment applied topesticides are fundamentally the same asthose applied to bridge and highway design,pharmaceuticals, and innumerable consumerproducts. The process is directed towardestablishing an objective basis on which toassess risk potential relative to the likelihoodof injury. This publication providesbackground information on the process ofrisk assessment and the role it plays inpesticide registration. It is intended to fostera better understanding of ecological riskassessment procedures, thus equipping thereader to make informed personal decisionson health and environmental risks associatedwith pesticide use.

The Evolution ofFederal PesticideRegulations

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The United States Congress legislatespesticide laws to manage health andenvironmental risk. Pesticides are currentlyregulated under two major federal laws: theFederal Insecticide, Fungicide, andRodenticide Act (FIFRA); and the FederalFood, Drug, and Cosmetic Act (FFDCA).FIFRA gives the U.S. EnvironmentalProtection Agency (EPA) the authority toregister pesticides; to require appropriatechemical, toxicological, and environmentalstudies; and to prescribe labeling userestrictions aimed to prevent unreasonableadverse effects on human health and theenvironment. Pesticides that come intocontact with food and animal feed areregulated under FFDCA, which gives EPAthe authority to establish tolerances(maximum pesticide residues allowed) infood and feed. The FQPA of 1996 modifiedFFDCA and FIFRA to broadly extend theauthority to conduct risk assessments.

Regulations for pesticide registration specifydata requirements, methods for conductingstudies, procedures for risk assessment, andlabeling content. EPA uses these as tools todetermine whether a pesticide can be usedwithout unreasonable effects on human andenvironmental health. EPA's assessment alsoaddresses specific risks to humans and theenvironment and appraises potentialeconomic, social, and environmental impactassociated with use of the pesticide. Ineffect, the decision-making process balancespotential risk to humans and the environmentagainst projected economic, social, andenvironmental benefits.

There have been many changes in pesticideproducts and registration requirements

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during the last decade. What was acceptablerisk, yesterday, may not be, today. Policiesand decisions on acceptable risk change,over time; and as public awareness andconcerns over pesticide risk increase, so doregistration requirements.

Early Federal LawsFocused Primarily onBenefits

The Insecticide Act (1910) prevented themanufacture, sale, or transport of impure orimproperly labeled insecticides andfungicides. Its primary focus was to ensurethat products were labeled adequately andthat container contents were stated precisely

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on the label. The Insecticide Act containedno registration requirements and did not setsafety standards.

The Insecticide Act was replaced in 1947 bya more comprehensive law: the FederalInsecticide, Fungicide, and Rodenticide Act(FIFRA). FIFRA was the first law to requirepesticide manufacturers to register theirproducts with the United States Departmentof Agriculture (USDA), which wasresponsible for registering all pesticides priorto sale or movement via interstate or foreigncommerce.

Pesticide regulations were expanded again in1954 with an amendment to the FederalFood, Drug, and Cosmetic Act. Theamendment required tolerance limits forpesticide residues on agriculturalcommodities; and it limited the amount ofresidue that could remain in or on a foodcrop after application, according to "goodagricultural practices." A 1958 amendment,the Delaney Clause, prohibited establishmentof tolerances for carcinogenic food additives.However, it applied only to pesticides forwhich residues were greater in the actualfood item than in the raw agriculturalcommodity. The registration process waschanged in 1964 when FIFRA was modifiedto give USDA the authority to deny orcancel product registration.

Environmental MovementChanged Public Perceptionof Pesticides

Increases in environmental awareness in the1960s, exemplified by Rachel Carson's SilentSpring, changed forever how pesticideswould be viewed by the American public.The most commonly used insecticides at thattime were part of a chemical class ofcompounds called chlorinated hydrocarbonswhich includes the well-known insecticide

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DDT. Emerging environmental groups andthe news media accurately portrayed thesepesticides as chemicals that bioaccumulate inthe environment, disrupt links in the foodchain, and poison wildlife. Silent Springcaptured the public's attention and rallied acry for greater public awareness ofenvironmental issues.

The environmental movement added balanceto discussion on the benefits of pesticide use,providing awareness of the risks posed topeople, wildlife, and ecosystems. FIFRA1964 established procedures for suspendingthe registration of pesticides determined tobe unsafe, and the growing environmentalmovement formed powerful lobbies thatsupported additional legislation. Politicallyastute individuals and organizations directedtheir attention to Congress, lobbying forlegislation that would help protect the

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economy, the environment, and publichealth. As a result, manufacturers and userswere held more accountable for reducingboth short- and long-term risks of pesticideuse. The public looked to Congress to passenforceable legislation requiring pesticides tobe scientifically evaluated prior to release foragricultural, commercial, or consumer use.While the debate has shifted over the yearsas issues have emerged and changed, itremains a primary obligation ofmanufacturers, through governmentoversight, to understand and minimize risksposed by pesticides.

Government Policies ShiftToward Risk ReductionStrategies

In 1970, Congress created the United StatesEnvironmental Protection Agency (EPA)and, in 1972, strengthened FIFRAdramatically to give EPA more regulatoryauthority.

Changes in FIFRA, since 1970, haveresulted in a major philosophical shift inpesticide regulation. Originally, FIFRArequired regulators to review and registerpesticide products. But in 1972, in theinterest of risk reduction and pollutionprevention, Congress changed FIFRA froma labeling law to a comprehensive statutedesigned to regulate the manufacture,distribution, and use of pesticides. Pesticidemanufacturers were then required to supportall registrations by providing prescribedscientific studies showing that use of theproduct would not cause "unreasonableadverse effects on human health or the

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environment."

In addition to requiring scientific data insupport of pesticide registration, FIFRA wasmodified to prohibit any use of a pesticideinconsistent with its labeling. In otherwords, the label became the law; andviolations for not following the label couldresult in label enforcement via licenserevocation and fines. Recognition that notall pesticides pose the same risk led to theFIFRA statute (1972) whereby pesticidesdeemed safe for application by the generalpublic are commonly referred to asgeneral-use pesticides, while those posinggreater risk are classified as restricted-usepesticides. The purchase and application ofrestricted-use pesticides are limited tocertified applicators or persons supervisedby certified individuals.

To ensure that adverse effects on humanhealth and the environment can beprevented, pesticide registration, productlabeling, government enforcement, andapplicator education form the foundation ofa comprehensive framework to regulate themanufacture, use, and disposal of pesticides.

Because Congress did not intend FIFRA tobe solely an environmental bill, an industrybill, or a farm bill, sincere efforts were madeto balance the needs of all stakeholders.Since benefits play an important role indecision-making under the act, Congressamended FIFRA to

allow USDA and interested parties to explain howcancellation of pesticides might impact the public adverselyby denying potential benefits along with potential risks.Regulatory decisions are based on the balance of risk versusbenefit (risk-benefit analysis).

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EPA Issued Scientific TestingGuidelines

As required under the revised FIFRA, EPA publishesscientific testing guidelines and regulations to ensure thatstudies in support of pesticide registration employ the bestscientific tests and methods. The regulations stipulate whattesting is required and how the studies are to be performed.Prior to the inclusion of testing guidelines, pesticidemanufacturers conducted many studies on the impact oftheir products on mammals, birds, fish, and the environment.EPA guidelines stipulated for the first time certaintoxicological, ecological, residual, and environmental fatestudies.

Risk assessments require data on toxicological end pointsand exposure. FIFRA guidelines and regulations place aformaland increasedresponsibility for testing requirementson pesticide manufacturers. The data developed as the resultof the guidelines, combined with the available tools toestimate exposure levels, formed the beginning of EPA's riskassessment process.

The generation of new data has allowed the registrationprocess to improve and mature. Advances in science, newexperimental tools, and new thinking (driven by desire onthe part of EPA and manufacturers to improve the scienceof risk assessment) yield more complex data for review;thus, EPA is obligated to review growing numbers ofmassive and intricate data sets supporting pesticideregistration and to upgrade its work force with scientistsschooled in such specific disciplines as environmentalchemistry and toxicology.

Pesticide Manufacturers toFollow Good LaboratoryPractices

Defensible scientific data from standardizedprocedures (protocols) are required ifregulators are to credibly assess productregistration. In the mid 1970s, fraudulentpractices surfaced in one large-contract

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toxicology laboratory, triggering questionswithin EPA as to the quality of data used asa basis for registration decisions. EPA'sconcern led to Good Laboratory

Practice Standards describing how studiesmust be conducted. These standards arecommonly called Good Laboratory Practices(GLPs).

The registration of a pesticide requireswell-designed studies conducted by trainedscientists and reported accurately, withdocumentation. GLPs ensure quality,integrity, credibility, and consistency of dataused in assessing risk. GLPs describe howlaboratory and field studies must be planned,performed, monitored, recorded, andreported. They require pesticidemanufacturers to comply with a set ofstandard quality assurance procedures forgenerating experimental data. Thisdocumentation provides an audit trail whichfacilitates verification that studies wereproperly performed and reported; and itaffords EPA reviewers confidence in theirconclusions.

EPA Moves Toward RiskCharacterization

In the early years of pesticide regulation,comprehensive risk assessments wereuncommon because the technology andscientific knowledge necessary to accuratelyinterpret the data were unavailable. But inthe late 1980s, risk assessors began todevelop a new philosophy. They recognizedthat the emphasis

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should shift from toxicity assessment, alone, to includeexposure studies, uncertainty, and professional judgment.The implementation of these additional considerations,coupled with improved scientific applications, has greatlyenhanced EPA's decision-making process.

EPA Policy Shifts to Reduced-RiskPesticides

In the late 1980s and 1990s, EPA developed a policyfocused on reduced-risk pesticides, offering manufacturersthe incentive of quicker registration decisions fordevelopment of "safer" products. The policy favorspesticides that have less potential to cause adverse healthand environmental effects than those currently registered.Registration applications documenting reduced, low-riskcharacteristics are granted priority consideration in thereview process, reducing the usual two- to four-yearregistration process to as little as six months. Expedientreviews allow "reduced-risk" pesticides to move morequickly to the marketplace; and the use of this incentive toencourage the development of "safer" pesticides places EPA

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in a better position to manage pesticide risk in themarketplace of tomorrow.

The Food Quality Protection Act

Congress passed the Food QualityProtection Act of 1996 (FQPA), amendingboth FIFRA and FFDCA to provide a morecomprehensive system for regulatingpesticides. Under previous pesticide laws,EPA was required to balance potential risksagainst potential benefits of a pesticideduring the registration review process; butFQPA established a single, health-basedsafety standard for all pesticide residues inall foods and greatly reduced considerationof pesticidal benefits. FQPA requires thattolerances must be determined to beexplicitly "safe"; that is, there must be"reasonable certainty" that tolerance levelswill result in "no harm." FQPA also requiresEPA to consider all nonoccupational sourcesof pesticide exposure, both dietary andnondietary, when establishing tolerances; andexposure to other chemicals that may have acommon mechanism of toxicity must beconsidered, as well.

FQPA further requires that EPA specificallyaddress potential risks to infants andchildren. It mandates that special attention

be paid to the possibility that chemicals may disruptthe endocrine system, and that periodic reevaluationof all pesticide registrations and tolerances isessential to ensure ongoing validity.

One of the consequences of FQPA is the need tofurther refine the risk assessment process,particularly in regard to assessing potential risks

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from multiple sources and routes of exposure. It isclear that risk assessment plays an increasinglycritical role in the process of pesticide registrationand reregistration.

EPA Uses RiskAssessment to Set SafetyStandards

In FIFRA, the United States Congress set thestandard for making pesticide registration decisions:"...any unreasonable risk to man or the environment,taking into account the economic, social, andenvironmental costs and benefits of the use of anypesticide." Thus, both human health and ecologicalrisk assessments are essential to the decision-makingprocess behind pesticide registration. Environment isdefined to include "water, air, land, and all plants andman and other animals living therein, and theinterrelationships which exist among these." Theenvironmental protection component weighs heavilyin risk assessment decisions.

Use of Risk Assessments:Registration, Reregistration, andSpecial Review

The primary decisions that EPA must makeconcerning pesticides are to

register a new product,

reregister an existing product,

cancel a current registration, and

determine if labeling protects human health andthe environment.

Risk assessments are performed by EPA duringregistration and reregistration processes. They are

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also conducted whenever new findings suggest thatadverse effects might result from use of a previouslyregistered product. There are four end points towhich assessments are directed: Experimental UsePermit; Registration; Reregistration; and SpecialReview.

Experimental Use Permit

Prior to completing all studies required for full registration, registrantsoften submit a smaller data package along with a request for anExperimental Use Permit (EUP); an EUP allows a registrant to applythe product to as many as 5,000 acres to evaluate performance. EPAreviews the abbreviated package and judges whether there is apotential for risk to humans or the environment under limited useconditions; if there is no such indication, an EUP is issued.

Registration

During the registration process, EPA evaluates all data in support ofactive ingredients not previously registered, as well as new uses (for aregistered product) that would require label changes. When requestingproduct registration, the pesticide manufacturer (registrant) mustsubmit to EPA all data required by FIFRA. When all individual studieshave been reviewed, the results are factored into human andecological risk assessments to evaluate whether requested uses for theproduct present unacceptable risk to human health or theenvironment. Review and assessment are conducted byrepresentatives of all disciplines within EPA: product, residue, andenvironmental chemistry; human health; and ecological effects.

Reregistration

From the very beginning, FIFRA intended that all registered pesticidesbe reregistered every five years; but economics nullified that intent.FIFRA Amended 1988 required additional feesreregistration feesto bepaid by manufacturers submitting a product for reregistration, thushelping to provide the necessary funding. All data used to supportpesticides registered before 1984 became subject to reevaluation andupgrading, if necessary, to comply with current guidelines andstandards. The refined data enhances the ability of EPA and theregistrant to judge whether risk conclusions and registration decisionsmade during the initial product registration process meet today's

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made during the initial product registration process meet today'sstandards.

Policy changes alter the emphasis ofregulatory actions in reregistrationprograms. Instead of moving riskierpesticides into the lengthy special reviewprocess, the focus is to reduce risk bynegotiation, e.g., by changing applicationrates, increasing application intervals, orusing alternative application methods. Thesemeasures often take the form of labelchanges designed to mitigate the amount andduration of exposure.

Special Review

FIFRA gives EPA the statutoryresponsibility not only to register pesticidesbut also to take regulatory actionsincludingcancellationunder certain unusual conditions:for instance, when new information on acurrently registered pesticide indicates thatnormal use of the product may result inunreasonable adverse effects. Specialreviews are initiated when concern isheightened by specific circumstances, suchas

when new evidence from laboratorystudies suggests that the pesticide may posehigher or different risks than were predicted;

when a pesticide is linked to fish or birdincidents; or

when workers become ill.

Benefits to EPA and thePublic

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The risk assessment process and theresources expended to conduct intensivespecial reviews provide benefits to EPA andthe public:

EPA's mission to protect public healthand the environment from unreasonableadverse effects can be more readily fulfilled.

The well-defined risk assessment processfor both human health and ecological effectshelps EPA make consistent, well-informedregistration decisions.

Effective communication of the processto pesticide manufacturers fosters timelyregistration decisions.

The risk assessment process encouragesin-depth review similar to peer review ofbasic research.

The process provides a forum where EPAscientists can reach consensus onconclusions drawn from risk assessment. Infact, scientists in academia and those fromthe private sector canand doshare theconsensus.

The process helps guide EPA's decisionon whether additional data are needed toclarify a potential risk.

Risk Assessment as aMarket-OrientedProcess forManufacturers

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Corporate decisions on whether or not todevelop potential pesticide products arebased on risk assessment, marketability, andprojected cost of production. Riskassessments must be conducted periodicallythroughout the development and commerciallife of a pesticide, oftentimes beginning withlimited, preliminary data acquired very earlyin the development process. As more databecome available, risk assessments arerefined by virtue of an enhancedunderstanding of the toxicological propertiesand chemical fate of the pesticide, as well asbetter exposure estimates. Scientists whodevelop data often serve as experts whopresent and interpret it for risk managers.The development team assesses data atvarious intervals to decide whether to cancelor continue research and plans forcommercialization of the product.

A thorough, well-organized risk assessmentprocess

defines guidelines for required tests andidentifies risk standards that will be used toquantify the data;

stipulates full reevaluation of studies thatsupported initial (or former) registration of aproduct to verify sufficiency according tocurrent standards and to identify any needfor additional testing prior to reregistration;

enables manufacturers to identify andeliminate high risk products early in thedevelopment process, thus minimizingexpenditures in support of a product thatmost likely would not be grantedregistration; and

requires sound, factual documentation ofthe registration process as a basis on whichcustomers, company management, andstockholders can calculate their commitmentto advancement of the product.

Registrants often use similar or morestringent criteria than those used by EPA and

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conduct a preliminary review of their owndata; this assists registrants in gauging theirproducts' prospects for registration.Preliminary reviews also may serve asindicators of the amount of time EPA mightspend evaluating the data, that is, howquickly products might be registered. Ifpotential adverse effects are identified duringany risk assessment, scientists must decide ifand how the potential risk can be reduced;for example, by changes in formulation,methods of application, use rates, andmarketing, or by use of personal protectiveequipment. Strategies for reducing riskinvolve what is known as risk refinement.

For example, suppose a pesticide applied ata rate of one pound of active ingredient peracre has the potential to cause unreasonablerisk to foraging bobwhite quail in treatedfields. A risk assessment may indicate thatrates at or below 0.75 pound per acre wouldnegate that potential. So, to mitigate risk,product development teams may be asked toreduce the proposed use rate.

Lowering the application rate of a productrequires reassessment of its efficacy. For thisexample, an application rate of 0.75 poundper acre would control most broadleafweeds in corn, but two resistant perennialweeds would not be controlled at that rate.Based on this information as well as dataindicating risk potential at higher rates, theproduct development team might concludethat the product would not competesuccessfully in the marketplace; if so,commercial development would cease.

The Science of Risk

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Assessment

As practiced by EPA, risk assessmentprovides the regulated pesticide industrywith straightforward methods and criteria toestimate risk. It is a well defined formaldecision-making process which, ideally,incorporates scientific knowledge about apesticide into the risk assessment along withinherent uncertainties. The result takes formas a set of science-based estimates thatdescribe the likelihood of the pesticide toadversely impact human health, wildlifesurvival and fitness, and environmentalquality, and which are sufficientlyconservative to account for uncertainties inthe process.

Risk Assessment as aMultistep Analysis

Human health and ecological riskassessments often are preliminary in natureand may be based on limited data and/orvery conservative assumptions. As moreresearch data are compiled and moreaccurate assumptions considered, the moreprecise and comprehensive the riskassessmentand the greater the confidence inconclusions drawn. However, if initial riskassessments indicate no cause for concern, amore refined risk assessment may not benecessary.

Quantitative risk assessment is a function oftoxicity and exposure. The risk assessmentprocess involves multiple steps, beginningwith an appraisal of toxicity and exposureand concluding with a characterization ofrisk.

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Toxicity Characterization

Toxicological characterization is commonlybased on laboratory studies; that is, itreflects adverse effects observed whenanimals are intentionally administered arange of concentrations of the pesticidebeing studied. Toxicity can be characterizedby mortality or by sublethal effects within therange of doses tested.

An important aspect of toxicologicalevaluation is determination of therelationship between magnitude of exposureand extent and severity of observedeffectscommonly referred to asdose-response. The dose-responserelationship identifies dose levels at whichadverse effects occur, as well as the noobserved effect concentration (NOEC). Forrisk assessment, the lowest NOEC, LD50,etc., is used to estimate risk.

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Exposure Characterization

Contact with a chemical in theenvironmentin the workplace, at home, or inair, food, water, or soilconstitutes exposure.Exposure concentrations may be eitherestimated or measured, based on theamounts and manner in which the chemical isused, the physical properties of the chemical,and data from laboratory and fieldexperiments. Exposure assessments ascertainthe exposure of people, wildlife, and plantsto pesticides in the environment. The extentof exposure depends on the type of use(crop, lawn, and garden treatment; mosquitocontrol; indoor pest control), applicationrate, method of application, and frequency of

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application, along with the breakdown,partitioning, and movement of the chemicalin the environment. An adverse effect ispredicted only if exposure approaches orexceeds dose levels that have resulted inadverse effects in toxicology studies.

Risk Characterization

Risk characterization defines the likelihoodthat humans or wildlife will be exposed tohazardous concentrations. Thus, riskcharacterization describes the relationshipbetween exposure and toxicity. Riskassessors identify species likely to beexposed, the probability of such exposureoccurring, and effects that might beexpected.

Suppose that a sampling for a givenpesticide in the environment yields anestimated exposure level of 3 ppb (parts perbillion) in water, and that a short-termlaboratory study shows that an exposurelevel of 100 ppb produces an adverse effectin bluegill sunfish. How could thisinformation be integrated to predict theoutcome of fish exposed to the chemical?

In this particular example, it is understoodthat fish may be exposed to 3 ppb without

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negative effects; but adverse effects dooccur in bluegill exposed, short-term, to 100ppb. A risk assessor might express noconcern for fish at an exposure level of 3ppb since it is significantly below the 100ppb threshold for injury. But riskcharacterization often is not that simple.

For example, the risk assessor may need toconsider whether prolonged exposure of thefish, at a level of 3 ppb, might triggeradverse effects; whether another life stage(e.g., embryo) might be more vulnerablethan the adult; and whether another fishspecies might be more sensitive than bluegill.Another consideration is that organisms(predators) higher in the food chain might beat risk if the pesticide accumulates in fish onwhich they prey.

The Ecological RiskAssessment Process

Ecological risk assessment is a process whereby toxicity(effects data) and exposure estimates (environmentalconcentrations) are evaluated for the likelihood that theintended use of a pesticide will adversely affect terrestrialand aquatic wildlife, plants, and other organisms. Datarequired to conduct an ecological risk assessment includethe following:

Toxicity to wildlife, aquatic organisms, plants, andnontarget insects

Environmental fate

Environmental transport

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Estimated environmental concentrations

Where and how the pesticide will be used

What animals and plants will be exposed

Climatologic, meterologic, and soilinformation

Assessment Requires anUnderstanding ofToxicology, Ecology, andProcesses

Assessing and characterizing risk toecological systems, including a myriad ofnontarget aquatic and terrestrial organismsas well as surface and ground water, is amuch younger and more complex sciencethan that of human health risk consideration.Ecological risk assessment considers agreater range of complex issues and coversmore species than does human health riskassessment: fish, aquatic invertebrates,aquatic and terrestrial plants, nontargetinsects, birds, wild mammals, reptiles, andamphibians.

Each species within an ecosystem fulfillsspecific ecological roles. Plants are theprimary producers of chemical energy in anyterrestrial or aquatic ecosystem. Theycapture sunlight and convert it to energizenew plant growth, forming the bottom of thefood chain. Energy flows through the foodchain when organisms consume plant tissuesand are, in turn, consumed. For instance,green algae are one-celled microscopicorganisms that are a staple food item forinvertebrates such as water fleas and mysidshrimp; these invertebrates, in turn, becomefood for young fish and small fish species.The fish are then consumed by predatorssuch as larger fish, amphibians, birds, andaquatic mammals. Because of the dynamics

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of the flow of energy, perturbations of themost seemingly minor species may lead toobservable (measurable) impact on the entireecosystem. However, because of the abilityof organisms and populations to adapt toperturbationsthat is, because they areresilienteffects on one or more componentsof an ecosystem may result in minimalecological change.

Adverse environmental effects at variouslevels may involve more than energy flow.For instance, adult mussels are nearlysedentary at the bottom of moderatelyflowing streams, but they filter algae andother small organisms from the water.Young mussels must attach to the gills orfins of certain fish, where they remain asharmless parasites (for weeks or months)until their internal organs develop; then theydrop from their host into the stream banksubstrate. Without the host species, somemussel populations cannot survive.

Toxicity Characterization

Toxicity testing identifies concentrationsthat, when administered to surrogateanimals, result in a measurable adversebiological response. These measuredconcentrations and associated toxicity endpoints basically describe what the chemicaldoes to the environmentin this case, a singleliving organism.

Testing for Adverse Effects onWildlife

Specific terrestrial and aquatic tests aremandated by federal law and described in the

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Code of Federal Regulations, 40 CFR Part158. Subpart E of Part 158, Terrestrial andAquatic Nontarget Organisms DataRequirements, clearly describes the testsrequired for registration of a pesticide. Sometests are not required for every pesticideproduct, but are listed in the regulations asconditionally required. Conditionallyrequired tests are not mandated unless theuse pattern or information generated fromrequired tests indicates a need for additionaltesting. For instance, early life stage fishtests or invertebrate life cycle tests areconditionally required for most pesticideproducts. These tests become mandatorywhen scientific data indicate that thepesticide is relatively stable in the aquaticenvironment and that concentrations at orbelow one part per million producesignificant acute mortality.

The technical grade of an active ingredientnormally is the substance used in pesticidescreening tests. Federal regulations specifythe conditions under which the end useproduct (the formulation) must be tested. Inall cases, effects observed and measurementsrecorded for animals and plants exposed topesticides must be compared to controlspecies (fish, invertebrates, birds, plants, oranimals) held under identical conditions butnot exposed to the chemical.

Testing surrogate species allows scientists toobserve adverse effects that may result fromshort-term (acute) and long-term (chronic)exposure. Exposure for short periods at highconcentrations is used to determineconcentration levels necessary to producemortalitylethal dosesas well as sublethaleffects on one stage of an organism (e.g.,juvenile or adult). These tests, for example,address immediate consequences to fish andwildlife exposed to concentrations of thepesticide.

The more complex chronic tests are used toexamine, in detail, how the pesticide willimpact various stages of an animal's life cycle

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(e.g., bird embryo development). As notedpreviously, chronic data are required whenacute tests indicate

that the toxicity of the pesticide exceeds atrigger limit and when the environmental fateor use of the pesticide indicates thatnontarget organisms may be impacted. Thedata from chronic tests are essential toaccurate prediction of long-term effects onfish and wildlife.

Potential Impacts Modeled byIndicator Species

Surrogate organisms used in toxicologicaltesting are selected to represent varioustrophic levels within an ecosystem. Forinstance, adverse effect data on bobwhitequail exposed to a pesticide are used togeneralize how that pesticide mightadversely affect all upland game birds.Daphnia (the water flea) models freshwatercrustaceans, and the Eastern oyster modelsfreshwater and marine mollusks. Anassumption key to ecological risk assessmentis that data on surrogate species adequatelydescribe how a pesticide will impact thebroader spectrum of plants and animals.

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A Tiered Approach to Testing

Toxic levels of a pesticide and descriptions of potentialadverse effects are developed using a tiered (sequential)approach. Tier 1 studies, the most fundamental, areprimarily acute laboratory studies that examineconcentrations necessary to cause mortality or acutesublethal effects. Tier 2 involves longer-term, reproductionand life-cycle studies that provide more complex data on thepesticide's impact on the entire life cycle of the test animal.Tier 3 studies examine the impact of a pesticide on animalsin simulated environmental or actual field conditions. Testing for Adverse Effects on Avian Species

There are three major laboratory tests for avian effects:

Acute oral LD50

Acute dietary LC50

Reproduction

In both acute oral and acute dietary studies, the primaryroute of exposure is through ingestion; either the pesticide isintroduced directly into the subjects' crops (acute oralexposure), or it is incorporated into their diet (acute dietaryexposure). Examples: Acute oral exposure occurs when abird ingests a large single dose. Acute dietary exposure mayresult from ingestion of pesticide residues on food items.

The acute avian oral LD50 test assesses the effect of asingle, oral dose of a pesticide administered to bobwhitequail or mallard ducks. Birds that survive a dose areobserved for two weeks for subsequent mortality andsublethal effects such as wing droop, disorientation,abnormal behavior, and reduced food consumption. The testyields the LD50 level and the NOEC. The LD50 levelrepresents the dose which can be expected to kill 50 percentof the test population; and the NOEC reflects the maximum

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dose that produces no observed effect on the testpopulation.

Deriving the acute avian dietary LC50 involves feedingbobwhite quail and mallard ducks a pesticide-treated diet forfive days. A three-day observation period follows, duringwhich the

Bobwhites from a one-generationreproduction study conducted toassess pesticidal effects onreproductive success.

birds are feda controldiet;abnormalbehavior andfoodconsumptionare recorded.In addition tothe LC50(lethalconcentrationof pesticidein the diet, inppb), theprocessyields theNOECvalues for thepesticidebeing tested.

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Avian reproduction testing involves feeding birds apesticide-treated diet for ten weeks prior to egg layingand throughout the laying season. Data generated fromthe reproduction study include the number of eggs laid,the number of normal hatchlings, the number of survivorsat 14 days after hatch, and eggshell thickness. The NOECfor any of these end points can be used in risk assessment.

In addition to the three major tests, simulated and actualfield tests are conditional, i.e., they may be required byEPA on a case-by-case basis.

Young bobwhite,approximately seven days old,from a reproduction studymonitored for effects onsurvival and growth.

A simulated field test might include placing mallards,bobwhite quail, or geese in outdoor cages, undercircumstances that mock exposure in the wild, andexposing them to the pesticide at a rate and frequencyprescribed by the pesticide label.

An actual field study might involve a pesticide applicationto an orchard, after which various data are recorded.Besides the

Canada geese on turf plot.Studies are conducted tomeasure avoidance of treatedturf. Birds are monitored todetermine amount of time spentin the treated and untreatedhalves of the test plot.

number of dead anddying birds observed,additional data mightbe gathered, includingsurvival of dependentyoung, residues onwildlife food sources,and residues in animaltissues (as evidencedby autopsy and tissuesampling).

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Testing for Adverse Effects onFreshwater and Estuarine/MarineFish

A single concentration of the test pesticide isadded to the water in an aquarium, and soonthereafter the fish are placed in the water.

Acute LC50 tests most often employrainbow trout and bluegill sunfish (testedseparately) that are actively feeding but haveyet to spawn. Fish are exposed to vari-ousconcentrations of the pesticide to determinethe dose-mortality response and, as well, thesublethal responses over 96 hours (4 days).

The results generated from acute LC50 testsinclude the 96-hour LC50 and the NOEC. Anumber of behavioral changes andpathological observations also are recorded,such as erratic movement and swimming atthe surface. Gross pathological observationscould include protrusion of the eyeball,sloughing of skin, and increased skinpigmentation.

The early life stage test examines how apesticide will impact the embryonic andlarval stages of fish. Data generated by earlylife stage tests include

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number of embryos hatched,

amount of time embryos require to hatch,

embryo mortality,

larval weight, and

larval length.

The NOEC for these parameters is determined bycomparing treatment groups with controls.

Fish life cycle studies use fathead minnows torepresent freshwater fish species and sheepsheadminnows as surrogates for estuarine fish species. Thetime needed to complete a fish life cycle study is 260 to300 days. Fish are exposed to a pesticide from one stage of theirlife cycle to the samestage in the subsequentgeneration (egg to egg).Fish embryos are placedinto water containing aknown pesticideconcentration, and

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observations are madefrom the egg stagethrough spawning. Theeggs laid by the firstgeneration and thelarvae that emerge arefollowed for anadditional 28 days.NOEC determination isbased on controlresponse and treatmentresponse.

Fish bioaccumulationstudies begin with fishexposed to a knownpesticide concentrationin water. During specifictime periods, fish aresacrificed to determinethe pesticide

concentration in their tissues. Fish are separated intofilet samples (edible portion) and samples with all otherparts combined [visceral (inedible) portion].Bioconcentration studies are conducted untilconcentrations identified in fish tissues remain fairlylevel for at least 28 days. The fish are then placed inclean water and the time required for residues to beremoved from their tissues determined. This providesinformation regarding potential food chain effects.

Testing for Adverse Effects on FreshwaterAquatic Invertebrates

Two primary tests are included in assessment of pesticidaleffects on invertebrate species: acute EC50, and aquaticinvertebrate life cycle. Daphnia (fresh-water crustaceansin which females can self-fertilize) are typically used inboth studies.

Invertebrate acute EC50 tests provide information on hownewly hatched daphnids respond to a pesticide over a 48-or 96-hour exposure period. The objective is to estimatethe concentration of pesticide that will immobilize thedaphnid. Immobilization is measured by gently shaking a

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vessel containing daphnids lying on thebottom. Those that swim for less than 15seconds are considered immobile. Theconcentration calculated to immobilize 50percent of the daphnids is considered theEC50.

Testing for Adverse Effects onEstuarine and Marine Organisms

The acute toxicity test is the primary studyused to address the toxicity of pesticides toestuarine organisms. A crustacean (mysidshrimp), an estuarine/marine fish(sheepshead minnow), and a marine mollusk(Eastern oyster) are used to evaluatepesticides. Sheepshead minnows and mysidshrimp are placed into separate aquariumscontaining specific concentrations of thepesticide for 96 hours. The mortality datagenerated is used to calculate the LC50and/or the EC50 .

Typically, one end pointthe pesticideconcentration that inhibits shell growth by50 percentis sought to estimate the impact ofa pesticide on mollusk species. The shellgrowth of young Eastern oysters is assessedby placing them in a series of pesticideconcentrations in water for 96 hours each.The concentration that inhibits shell growthby 50 percent is calculated. Such a study isregarded as an indirect measure of theimpact of the pesticide on the nutritionalstatus of the animal. A mollusk that closesits shell in the presence of a pesticide cannotfeed; thus, shell growth is severely limited.

Testing for Adverse Effects onMammals

Testing on wild mammals normally is notrequired. Data from testing for human health

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risks (using rats, mice, dogs, and rabbits)typically are used to predict toxicity to wildmammals. A situation where wild mammaltoxicity testing may be required is when ahighly toxic rodenticide or predacide is usedas a broadcast bait; minks often are used astest subjects to determine the potential forsecondary toxicity (toxic effects in predatorsthat have consumed poisoned animals).

The honeybee (Apis mellifera) is used as theprincipal insect pollinator. Tests used tomeasure effects of a pesticide on nontargetinsect pollinators are the honeybee acutecontact LD50 and the honeybee toxicity ofresidues on foliage.

Testing for Adverse Effects on NontargetInsect Pollinators

The acute contact LD50 testrequires that honeybees beanesthetized to facilitateplacement of the pesticidedirectly on the abdomen orthorax. Afterward, the bees aremonitored for 48 or 96 hours; theLD50 is calculated and expressedin micrograms (mg) of activeingredient per bee.

The honeybee toxicity of residueon foliage test determines howhoneybees can receive a toxicdose from dislodgeable residueson foliage. The pesticide isapplied to foliage which is thenharvested over a number of days.Harvested foliage is placed intocages containing worker bees,and the number of bees that diefrom contact with the foliage is

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recorded and compared withcontrols.

Testing for Adverse Effects on Plants Nontarget plants studies. Plants ofvarious species are monitored forseedling emergence and vegetativevigor.

Nontarget Terrestrial Plant Toxicity

Corn, soybeans, root crops, tomatoes,cucumbers, lettuce, cabbage, oats,ryegrass, and onions often are used to testeffects on nontarget plants. The soil istreated or the pesticide applied to thefoliage at the maximum rate allowed bythe label, or at a concentration three timesthe expected environmentalconcentration. Data collected in specifictests include

root length,

percent germination,

percent emergence,

time to emergence,

plant height,

dry plant weight, and

percent of plants exhibiting phytotoxic(morphologic) changes.

The NOEC is determined for each endpoint, such as growth and root length.The most sensitive NOEC may be used inrisk assessment.

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Nontarget Aquatic Plant Toxicity

Tier 1The two aquatic plant species mostcommonly tested for nontarget planttoxicity are Selenastrum capricornutum (afreshwater green alga) and Lemna gibba (amacrophyte duckweed). Water containingthe two species is treated with either

a single dose representing the maximumallowed rate, or

a concentration three times the expectedenvironmental concentration.

Tier 2

Five aquatic plant species are used for Tier2 testing: S. capricornutum, L. gibba;Anabaena flos-aquae (a blue-green alga);Skeletonema costatum (a marine diatom);and Navicula pelliculosa (a freshwaterdiatom). The focus is on growth rate datameasured either as increases in cells, or asfronds. Effects are expressed as EC50 (theconcentration of pesticide that reduces cellgrowth by 50 percent). Follow-up testsdetermine if the effects are temporary,permanent, or lethal.

ExposureCharacterization

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Environmental processes result intransformation, transfer, and transport ofpesticides. And the characterization ofenvironmental fate assesses what theenvironment does to the chemical so thatenvironmental exposurethat is,concentrations an

organism might actually encountercan beestimated. Knowledge of pesticideenvironmental fate and transportcharacteristics is essential to accurateestimation of the form and amount of thechemical that wildlife and aquatic organismsmight encounter in the environment.Laboratory and field studies make it possibleto predict how much of a molecule and itsmetabolites might reach nontargetorganisms.

Understanding how a pesticide can bemodified by the environment also is criticalin judging how it will affect its intendedtarget. For instance, a herbicide may offergreat promise, in the laboratory, insuppressing hard-to-control perennial weedsfound in cantaloupe and tomato fields. But ifenvironmental factors in the field breakdown the herbicide before the weeds canabsorb a sufficient dose, weed control isdiminished. Conversely, if the pesticide issomewhat resistant to environmentalbreakdown, concerns are raised about theproduct's residual action impacting waterquality, wildlife, soil, and rotational crops.

Complex Interactions Must BeStudied

The environment plays a major role indetermining

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how much pesticide residue remains;

how long it remains;

where it goes, ultimately;

what form it might assume; and

the toxicity of the molecule as it ismodified, over time.

How a pesticide reacts within a specificenvironment (the site of application) isdependent on its physical and chemicalcharacteristics as well as environmentalproperties such as soil type, landscapeposition, and weather. Soil properties suchas pH, temperature, moisture, and nutrientconcentrations influence how chemicals arechanged in the environment. Similarly,climatic factors such as temperature andrainfall impact pesticide persistence andmovement.

Site-specific differences such as how apesticide reacts, over time (when applied in aLouisiana sugarcane field versus an Indianacorn field, for example) are critical inestimating environmental exposure. Thecircumstances of use and the uniqueness ofeach chemical molecule make predictingenvironmental exposure across the UnitedStates very complex.

How will the pesticide be used?

Application rates andtechniques have directbearing on how a pesticideenters the environment.Thus, a pesticide applied at a

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rate of ounces or less peracre has a lower potentialfor exposing fish and wildlifethan the same chemicalapplied at a rate of poundsper acre.

A pesticide may be sosensitive to sunlight that itdecomposes soon afterapplication. If the sameproduct is protected fromsunlight by incorporationinto the soil, however, itspersistence in theenvironment may beextended.

An incorporated product isless likely to impact wildlifethan one which is leftexposed on the soil surface.For instance, a granularpesticide presents greaterexposure potential for birdsthan does the same chemicalapplied as a liquid. Thus,formulation is considered acritical factor in estimatingenvironmental exposure.

How will the pesticide betransformed by theenvironment? Research has shown that theenvironment often alterspesticide moleculesdramatically. The original(parent) molecule often ismodified as it enters andinteracts with theenvironment. Pesticidesoften are degraded in water(hydrolysis), by sunlight(photodegradation), and bysoil and aquaticmicroorganisms (microbialdegradation). Knowledge oftransformation rates and the

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products and toxicity oftransformation is key toassessing ecological risk.

Chemical properties ofpesticides, such as volatilityor water solubility, influencetheir transfer in theenvironment. For instance,the initial distribution of apesticide in soil and water,or between soil particles andthe air that surrounds them,might be 90 percent in soiland 10 percent in water. Thephysical characteristics of amolecule, in combinationwith chemical properties ofthe environment, influencewhether a pesticide moleculeresides mainly in soil, air, orwater.

How long will the pesticide persist in theenvironment?

A pesticide's continuedpresence in theenvironmentpersistenceis akey factor in predictingpotential exposure ofwildlife. Persistence isgenerally described as ahalf-life, that is, the length oftime it takes for thedisappearance of one half ofthe applied pesticide from anenvironmental compartment.Biological and chemicalprocesses that degrade ordissipate the pesticideinfluence its persistence.

How will the pesticide be transported from the

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original application site to off-site environments?

Pesticides and their metabolites (breakdownproducts) move in a number of ways. They can

leach downward into ground water,

attach to soil particles and be washed away insurface water runoff,

volatilize into the atmosphere, or

drift off-target.

Leaching, runoff, volatilization, and drift often aremodeled to show how pesticides move in theenvironment. Compounds that do not readily adsorbto soil particles often have a high potential forleaching to ground water or entering streams viasurface water runoff. Highly volatile pesticides mayescape the soil environment and dissipate into theatmosphere; when redeposited later, via rainfall, theymay interact with nontarget plants and animals. What is the range of pesticide concentrationsexpected to come in contact with biological systems?

Knowledge of the application rate and anunderstanding of how a pesticide can be transformed,transferred, and transported within the environmentfacilitate prediction of the range of concentrationsthat will actually interact with other organisms.

Development of expected environmentalconcentrations depends on information developedfrom a host of environmental fate and residuechemistry studies that describe transformation,transfer, and transport. The lists of studies on thefollowing page demonstrate the extensive laboratoryand field data required for estimation ofenvironmental concentrations.

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Gambrel's quail with radio transmitter. Studies with free-ranging buttrackable birds, conducted to monitor effects on survival and reproductiveperformance.

What organisms are expected to be exposed to apesticide?

Characterization of environmental exposure requiresconsideration of the inhabitantswildlife, aquaticorganisms, and nontarget plantsof sites where apesticide is likely to occur. An understanding of thenatural history (distribution, abundance, breedinghabits, and food sources) of nontarget speciesfacilitates identification of the predominant route ofexposure.

Laboratory and Field Data Required for Estimation ofEnvironmental Concentrations of Pesticides

Environmental Fate Data Requirements

Hydrolysis

Photodegradation in water

Photodegradation in air

Aerobic soil metabolism

Anaerobic soil metabolism

Anaerobic aquatic metabolism

Leaching and adsorption

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Laboratory volatility

Field volatility

Field dissipation, terrestrial uses

Field dissipation, aquatic uses

Forestry field dissipation

Confined rotational crop

Field rotational crop

Accumulation in irrigated crop

Accumulation in fish

Accumulation in aquatic nontarget organisms

Residue Chemistry Data Requirements

Chemical identification

Nature of residue in plants

Residue analytical methods, plants/animals

Magnitude of the residue in potable water

Magnitude of the residue in fish

Spray Drift Data Requirements

Droplet size spectrum

Drift field evaluation

Estimated EnvironmentalConcentration: A KeyEnvironmental End Point

Potentially, all pesticides pose some risk to

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nontarget organisms; and environmentalconcentration estimates are critical inestimating ecological risk. Data developedon the environmental fate of a pesticide,along with use information as stated in theproposed pesticide labeling, are used togenerate a value known as an EstimatedEnvironmental Concentration (EEC). TheEEC is an estimate of how much of apesticide might reach nontarget areas,potentially exposing wildlife, bees, worms,aquatic animals, and plants. EECs generallyare predicted for ground and surface water,soil, and nontarget food items.

The key word in Estimated EnvironmentalConcentration is estimated. Scientists cannotmeasure actual concentrations for everyconceivable environmental situation. Anactual concentration measured today mostlikely would not match measurements takensometime earlier or later. Therefore, EECsshould not be viewed as hard or fixedvalues, but as estimates based on dataavailability. Actual concentrations can anddo fluctuate according to numerousvariables: time of year, geographic location,weather patterns, soil conditions, croppingsystems, etc.

Mathematical models that simulate the fateof pesticides in the environment are used fordeveloping EECs. But initial models basedon preliminary data, very early in thepesticide development and testing processes,leave a window of uncertainty. This initiallack of specific pesticide informationtheunknownleads to this uncertainty indetermining accurate EECs. Therefore, thedegree of uncertainty is compensated by veryconservative assumptions.

As researchers gain a better understanding ofthe molecule through refined laboratory dataand in-depth analysisand as it becomesknown what influence factors such asweather conditions and soil characteristicsmight haveinput assumptions are modifiedand new EECs determined that are less

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uncertain, that is, refined.

The challenge in refining the EEC is toprovide greater scientific certainty andimproved interpretations of the availabledata. In this way, an improved understandingand approximation of the actualenvironmental concentration is achieved.The better the prediction, the better the riskestimate.

Developing EstimatedEnvironmental Concentrations forAquatic Organisms

There are four basic tiers used to estimateenvironmental exposure concentrations foraquatic systems. Each tier requiresadditional data or more refined data analysisthan lower tiers. The higher tiers employsophisticated models where principalparameters and site-specific scenarios havebeen developed. Aquatic EEC Tier 1: Single Event EECBased on a High-Exposure Scenario

The Generic Estimated EnvironmentalConcentration (GENEEC) model wasdeveloped by EPA to determine a genericEEC for aquatic environments. EECsderived from GENEEC models reflect thepesticide concentration expected underworst-case conditions: an application on ahighly erosive and very steep upland slope,with heavy rainfall occurring immediatelyafter. The watershed model is essentially tenacres of surface area. It is assumed that theentire area is treated, and that the treatedarea has uniformly high slopes so that runoffdrains directly into a six-foot-deep, one-acrepond.

The GENEEC model utilizes environmentalfate parameters identified by laboratory

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testing protocols, as well as informationobtained from the proposed pesticidelabeling. It also includes fixed soil andweather parameters. The model estimatespesticide runoff to the pond on the basis ofrate and method of application, watersolubility, soil binding (adsorption)characteristics, and persistence of thepesticide; spray drift is also a factor. Aquatic EEC Tier 2: Single Site, VariableWeather

Tier 2 assessments determine EECs basedon geographic areas nationwide and use sites(e.g., corn) in close proximity to ponds;many input variables are the same as thosefor GENEEC models, but additionalparameters more descriptive of use site maybe factored, as well. These data are used inmore comprehensive models(PRZM/EXAMS). Conditions typical ofproduct use sites, including specific soils andweather information (a distribution ofweather, including a one-in-ten-yearhigh-runoff incidence) are used. Singlemedian values for chemical characteristicsare selected from laboratory-derivedenvironmental half-lives in the upper tenpercent of the statistical distribution.Contributions from spray drift also arefactored into the estimate. The goal of Tier 2analysis is to better define the range ofEEC--as compared to the single, worst-caseTier 1 assessment--that

can be reasonably expected under variableweather conditions. Frequently, a case moretypical of the intended site is analyzed, aswell, for comparison against the worst casescenario. Aquatic EEC Tier 3: Multiple Sites,Multiple Weather Conditions

Tier 3 differs from tiers 1 and 2 in that bothuse-site and weather parameters are varied.Tier 3 assessments examine hypothetical

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circumstances representative of the regionsin and conditions under which the pesticideis likely to be used. Tier 3 modeling resultsin development of a distribution of EECsthat might be expected across use markets,recognizing that both soil properties andweather patterns will vary significantly bymarket region and years of use. Tier 3analysis is used by pesticide registrants toaddress environmental exposure concernsthat arise during product reregistrationprocesses.

Aquatic EEC Tier 4: Watershed SiteAssessment

Tier 4 assessments are complex analyses thatinvestigate how pesticides are likely tointeract with a landscape composed ofhundreds of thousands of acres. Thelandscape has diverse soils and climates,varied proximities of treated fields toreceiving waters, and randomly distributedbodies of water.

Geographic Information Systems (GISs) arecommonly used at Tier 4. GISs allowgraphical evaluation of concurrent riskfactors (within the regions of use) thatheighten concerns. In other words, GISsdistinguish high risk versus low risk areas ofuse on a regional basis.

Tier 4 procedures sometimes shift from riskcharacterization and modeling to actualenvironmental residue monitoring. Riskassessment equations and exposure estimatesfor EECs are validated by actualmeasurements in the environment, calledActual Environmental Concentrations(AECs). Although sampling provides actualresidue data, each set of data is valid onlyfor the point in time when the correspondingsamples are taken. And each sample yieldsonly a hint as to the scope of residueincidence. Modeling and monitoring oftenare combined within Tier 4 to provide afuller understanding of the distribution ofexposure occurring within treatedwatersheds.

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Predicting Environmental Concentrations forTerrestrial Organisms

Terrestrial (unlike aquatic) wildlife are exposed to pesticidesprimarily through the plant or animal material that they consumeas food. Other routes of exposure, such as dermal, inhalation, andocular, are considered less important and difficult to measure, andeffects are thought to at least resemble those associated with oraland dietary routes. For birds, the primary route of exposure isdietary exposure to residues on food items, although there is apotential to ingest granular pesticides. EECs are developed forthese routes of exposure.

Exposure estimates for wildlife vary according to the amount ofpesticide residue on food items and the actual consumption ofthose items. In determining EECs for terrestrial organisms, it isassumed that residue levels on food items increase as applicationrates per acre rise. Predicting Concentrations on Food Items

EPA and pesticide manufacturers, in performing Tier 1 riskassessments, use a series of tables that establish guidelines on howmuch pesticide residue might be expected on various types ofplants and insects. The original tables were developed by FredHoerger and Gene Kenega and refined by John Fletcher, JamesNellessen, and Thomas Pfleeger.

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Predicting the total amount of residueavailable on vegetation depends on twovariables: application rate and plant type.Plant types are assigned to a simple plantcharacterization scheme:

Short rangegrass

Long grass

Broadleaf plants/forage

Fruits

Seeds

A portion of the revised Kenega table (p.37), illustrates maximum expected residuesper plant species as a function of applicationrate. For instance, the table predicts amaximum EEC of 240 parts per million(ppb) on rangegrass immediately after apesticide application at one pound per acre.

EECs also are calculated for birds andmammals consuming pesticide-treatedinsects. It is important to note that theseEECs are based on application rates withoutregard to the characteristics of the pesticide.When actual residue data are not available,EECs of 58 and 135 (based on poundsapplied per acre) can be used as estimates ofresidues on large and small insects.

Models Can Account for Residue Declines

Residue levels from the Kenaga table can berefined. First, the most appropriateenvironmental fate half-life value is selected.Then degraded residue values are calculated,considering multiple applications and timeintervals between repeat applications. Thesevalues can be used as more realistic

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estimates of terrestrial residues. Furtherrefinements can factor in more specificfeeding habits, food sources, body weights,and ingestion rates for sensitive specieslikely to inhabit or infiltrate the treated area. Food Consumption Patterns Dictate theAmount of Exposure

Exposure of birds or mammals can berefined by incorporating weight of theanimal, percentage of food consumedrelative to body weight, and amount ofpesticide residue on the food item.

Example: A 100 gram (0.1 kilogam) bird isknown to consume seeds in an amountequivalent to 10 percent of its body weighteach day. The estimated EEC was predictedto be 23 ppm by using the Kenega table forfruits and seeds, with 1.5 pound of activeingredient applied per acre. We assume thatthis avian species feeds exclusively on theseeds. What is the EEC (total amount ofpesticide per kilogram of seeds consumeddaily)?

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Granular Product LD50 Per Square Foot

There is a potential for birds and mammals to ingest pesticide granules. Theinitial risk assessment of oral exposure of terrestrial vertebrates to a granularinsecticide considers an estimated number of unincorporated granules persquare foot in relation to the number per square foot that results in 50 percentmortality, that is, LD50. This procedure is based on

application rate,

concentration of the pesticide per granule,

a laboratory-derived LD50, and

body weight of the bird or mammal in question.

The procedure assumes that the bird or mammal will ingest all of the pesticideavailable within one square foot of treated area, and that all granules will beconsumed within a short period of time. The greater the LD50 per square foot,the greater the presumed risk. If a high level of risk is indicated, additionalresearch may be conducted to either confirm or refute the original findings.

Risk Characterization

Risk characterization is the summarizing step of a risk assessment. Once all available data on exposure(EEC) and toxicity are assembled, the overall ecological risk for a pesticide can be characterized. Theexposure and toxicity characterizations are integrated into a comprehensive, scientifically defensible

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description of the potential risk to the environment from use of the pesticide.

Key components of risk characterizationinclude

calculation of risk quotients,

level-of-concern analysis, and

weight-of-evidence analysis.

Risk characterization should yield clear,concise information on scientific rationaleapplied during the assessment process.

Risk Quotients: The Integration ofToxicity and Exposure

Integrating toxicity and exposure isaccomplished by developing an index calledthe risk quotient (RQ). This begins with aconservative Tier 1 assessment that utilizesthe highest EEC and the most sensitive endpoint to determine the quotient. An RQprovides general guidance on potential risksposed by a pesticide. It is derived by dividingthe EEC for a particular environmentalcompartment (such as water) by atoxicological end point (such as LC50) for anorganism (e.g., fish) subject to exposure inthat compartment.

In other words, an EEC for water may bedivided by an LC50 for fish to determine therisk quotient. An RQ of less than oneindicates an estimated exposureconcentration below the toxicity end point.Risk quotients greater than a level ofconcern indicate that exposure may exceedlevels shown in laboratory tests to produceadverse effects; it may lead to refined

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estimates of exposure and effects to gain abetter understanding of the risks which arelikely to occur in the environment.

Levels of Concern Establish Risk Parameters

Levels of Concern (LOCs) are trigger ratios used by regulatory authorities forcomparison against calculated RQs. LOCs incorporate (into risk assessment)uncertainties due to possible exposure of sensitive populations and estimatedenvironmental concentrations. It has long been recognized that the number oforganisms used to examine adverse effects is limited; thus, there remains thepossibility that untested organisms in the same environment may be moresensitive to a particular pesticide than those tested. EPA established LOC triggervalues to ensure adequate protection for more-sensitive, untested, and/orendangered species.

There are two general categories of LOCs (acute and chronic) for each of thenontarget fauna groups; and there is one category (acute) for each nontargetfloral group. To determine if an LOC has been exceeded, a risk quotient must bedetermined and compared to trigger values. The following table provides riskquotients and LOCs.

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LOCs are regulatory triggers used to categorize whether thepotential risk is of low, medium, or high concern. Forinstance, a risk quotient less than 0.5 developed for an avianacute response is of minimal concern to nonendangeredspecies, while a quotient of 0.5 or greater suggestspotentially higher acute risk.

LOCs differ among biological indicators and types of tests,as well as between nonendangered and endangered species.If the risk quotient is categorized as minimal for a chemicalwhere no LOC is triggered, the use of the pesticide ispredicted to cause no adverse effects when used inaccordance with the label; and registration or reregistrationgenerally is granted. A moderate risk quotient indicates thatapplicators should be educated on use of the pesticide tominimize the likelihood of adverse environmental effects;pesticides with moderate RQs usually are grantedrestricted-use registration.

Registrants of pesticides with risk quotients that generallyexceed the LOC supported by the weight of evidence faceextensive risk mitigation requirements prior to productregistration. Optimally, mitigation efforts lower potentialrisk concerns below the LOC, frequently through a refinedEEC. Reduced rates of application and number ofapplications, buffer strips, in-furrow application (vs.broadcast), and ground application (vs. aerial) are examplesof measures that can be taken to minimize fish and wildlifeexposure.

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The following is an example of the use of toxicological dataand EEC values to calculate a risk quotient; it is based on anapplication rate of one pound of active ingredient per acre.

The data and assessment show that the risk quotients forpesticide A do not exceed LOCs of acute and chronicexposures for fish and birds; thus, no additional testing ormitigation is required. For pesticide B, which is more toxic,the risk quotients are greater than the threshold forpresumption of risk for both acute and chronic exposure.Additional testing, or more extensive evaluation of the EEC,may be required to demonstrate a reduced risk; or, riskmitigation measures might be adopted. This exampleillustrates how two pesticides with different toxicologicalproperties but similar application rates can have differentpresumptions of risk, based on their toxicity.

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Application rates also influence risk assessment. The toxicological dataprovided (p. 43), assuming that Pesticide A has an application rate threetimes that of Pesticide B, illustrate that, although Pesticide B is more toxicto fish and birds, its presumption of risk is similar to less toxic Compound A.In the second illustration (p. 43) neither pesticide's RQ value exceeds thetriggers for presumption of risk, although pesticide B is acutely toxic to fishand birds. Weight of Evidence Analysis

Strengths, limitations, and uncertainties, as well as magnitude, frequency,and spatial and temporal patterns of previously identified adverse effects, arediscussed. Monitoring data and reported incidents of wildlife kills areincluded to help confirm risk potential. Dissipation and applicationcharacteristics of the pesticidedistance from application site, duration ofeffects, and time of year at which wildlife and aquatic organisms may bemost susceptibleare discussed in terms of likelihood of the pesticide to affectwildlife and aquatic organisms. Very often, discussions suggest a number ofpotential mitigation measures that may be used to reduce risk whilemaintaining benefits from continued registration of the pesticide.

Finally, potential risks of pesticide use are compared to potential risks frompesticides already used on the same site and, typically, for the same pests.This helps decision makers to view the overall picture of potential ecologicalrisk while making registration and reregistration decisions. The process endswith a summary statement on the likelihood of adverse effects based onevidence analysis and professional judgment.

Conclusions

Pesticides provide significant benefits to theAmerican public by controlling pests thatinvade agricultural crops, industrial sites,

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homes, schools, restaurants, and hospitals.Public health is enhanced when pesticidesare targeted against mosquitoes, ticks, androdents that carry disease; head lice; fleas;and allergy-producing cockroaches.Antimicrobial products disinfect drinkingwater supplies and reduce hazards fromorganisms that cause human diseases such ascholera. The motoring public andtransportation industries benefit whenherbicides eliminate plants that obscureroadway signs and encroach onrights-of-way. Pesticides are instrumental inprotecting native habitats and indigenousflora from non-native plant species. Otherpesticides protect and preserve homes,museums, and historic buildings fromwood-destroying insects such as termitesand carpenter ants.

But there are risks associated with pesticideuse, as well, and they draw public attention.Obviously, in order to be useful, mostpesticides are toxic to the target pest. It isvery difficult to develop a chemical that willaffect only the targeted pest and carry nopotential to harm nontarget wildlife species.No pesticide is risk-free, and certainly nopesticide is "safe" in all situations: All carrythe potential to cause adverse effects.

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Ecological risk assessment is a processwhere scientific information is used toaddress potential environmental risksassociated with pesticide use. Goodregulatory decisions depend on documentedscientific research, an understanding of thestrengths and weaknesses of the specific riskassessment, and sound professional judgmentin drawing conclusions from compiled data.Risk assessments should clearly identifypertinent facts and any assumptions deemednecessary to accurately evaluate thepesticide. If ecological risk assessments areclear, concise, and thorough, they add avitally important dimension to EPA'sdecision making process. Clarity andopenness in the risk assessment processpermit informed debate on pesticide use;ultimately, the registration of a pesticidemust withstand scientific inquiry, publicscrutiny, and legal review.

Acknowledgments

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Paula Adduci, i2i Interactive

Steve Adduci, i2i Interactive

Dan Barber, DowElanco

Val Beasley, University of Illinois

William Benson, The University of Mississippi

Chris Berry, Imagix, Inc.

John Carbone, Rohm and Haas Company

Charles Crawford, United States GeologicalSurvey

Gregory Dahl, North Dakota State University

Rob Dittmer, DuPont Agricultural Products

Sidney Draggan, United States EnvironmentalProtection Agency

David Fischer, Bayer

Joseph Gorsuch, Eastman Kodak Company

Ronald Hellenthal, University of Notre Dame

Paul Hendley, ZENECA Ag Products

Jeffrey Lucas, Purdue University

Jeffrey Martin, United States GeologicalSurvey

Ursula Petersen, Wisconsin Department ofAgriculture

Joseph Wisk, American Cyanamid

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New 12/97 The information given herein is supplied with the understanding that nodiscrimination is intended and no endorsement by the Purdue UniversityCooperative Extension Service is implied.

Cooperative Extension work in Agriculture and Home Economics, stateof Indiana, Purdue University and U.S. Department of Agriculturecooperating. H.A. Wadsworth, Director, West Lafayette, IN. Issued infurtherance of the acts of May 8 and June 30, 1914. The CooperativeExtension Service of Purdue University is an equal opportunity/equalaccess institution.

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