HIA - Environmental Medicine Ch63 - 2010

8/6/2019 HIA - Environmental Medicine Ch63 - 2010

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USING ENVIRONMENTAL HEALTH EVIDENCETO INFORM POLICY DEVELOPMENT

There are many ways of summarising and communicatingscientific evidence for use in policy development when theaim is to protect public health and the evidence concernsrisks from exposure to environmental pollutants. In thecontext of environmental medicine, one long-establishedapproach involves developing health-based guidelines forspecific pollutants. Typically, these guidelines are limitvalues, chosen so that if pollution is maintained at levelsbelow these limits, the consequent risks to the health of even the most vulnerable individuals in the populationare low.

Setting, implementing and maintaining health-basedguidelines has proved very important in protecting humanhealth. The approach has, however, some importantlimitations. First, it sometimes happens that, wherepollutant levels are lower than guideline values, it isconsidered acceptable to allow a drift upwards towardsthose guidelines; or, in an equivalent manner, that policiesor developments that imply an increase in pollution areconsidered acceptable as long as guideline levels are notexceeded. This ignores the possibility of effects atconcentrations below guidelines, a problem especially withpollutants that have no threshold at population level.

Second, health-based guidelines do not per se takeaccount of the difficulties and costs involved in achievingthem, and therefore they are not amenable for comparingthe costs and benefits of a new proposal. Third, measuresto reduce pollution to conform with limits may haveother unintended consequences, including health impacts

mediated through other environmental or socialdeterminants of health. Attempts to overcome theselimitations have contributed to the development andincreased use of other methods of using science to informthe development of policy. One such set of methods iscalled health impact assessment (HIA).

HEALTH IMPACT ASSESSMENT

Health impact assessment is the systematic prediction of the potential positive and negative health and well-beingimpacts of new policies, plans, programmes and projects(hereafter referred to as proposals), including how theseimpacts are distributed across the population. 1 It wasdefined by the Gothenburg Consensus as ‘A combinationof procedures, methods and tools by which a policy,program or project may be judged as to its potential effectson the health of a population, and the distribution of thoseeffects within the population’. 2

It works within an explicitly stated ethical frameworkthat promotes an impact assessment that is participatory,equitable, sustainable and ethical in its use of evidence andmaximizes health opportunities for the affected population.It also generally provides a set of recommendationsand/or a set of mitigation and enhancement measures sothat positive health impacts are maximized and negativehealth impacts minimized within a given population.HIA is therefore about both protecting health by reducingexposures to harmful agents, and improving health by capitalizing on opportunities to promote and enhancehealth and well-being. HIA is also concerned with the

Using environmental health evidenceto inform policy development 1

Health impact assessment 1Definition of health used in HIA 2The HIA process 2HIA in the context of other approaches 3

An overview of environmental HIA 4An example: environmental HIA of outdoor air pollution 8Current trends and future prospects 10Acknowledgements 10References 11

63Health impact assessment

FINTAN HURLEY, SALIM VOHRA AQ 1

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2 Health impact assessment

inequalities/inequities generated by the uneven distributionof health impacts within an affected population.

DEFINITION OF HEALTH USED IN HIA

HIA tends to use both a biomedical and a social definitionof health, recognizing that although illness and disease(mortality and morbidity) are useful ways of thinkingabout and measuring health, both health protection andhealth improvement need to be understood in ways thatare wider than the reduction of illness and disease. HIAtherefore generally uses the World Health Organization(WHO) definition that ‘Health is a state of completephysical, social and mental wellbeing and not simply theabsence of disease or infirmity’, 3 or the more recent WHOpsychosocial definition of health: ‘the extent to which anindividual or group is able to realize aspirations and satisfy needs, and to change or cope with the environment. Fromthis viewpoint health is therefore a resource for everyday life, not the objective of living; it is a positive concept,emphasizing social and personal resources, as well asphysical capacities.’4

THE HIA PROCESS

Key elements of the HIA process

There is a general consensus that the HIA process is madeup of nine partially overlapping stages:

1. screening;2. scoping;3. baseline data-gathering and community profiling;4. stakeholder involvement (this can be part of the other

stages as well as occurring separately; it tends to involvedifferent stakeholders at different points in time);

5. evidence-gathering and the identification of causalpathways;

6. an analysis of health impacts (identification,assessment of likelihood and magnitude);

7. making recommendations and/or developing a set of mitigation and enhancement measures, as well as howsuch recommendations/measures can be monitoredand evaluated once introduced;

8. writing the HIA report or statement and presenting thefindings to decision-makers;

9. follow-up of the HIA recommendations and of theHIA process (monitoring of the health impacts andevaluation of the HIA process).

Sources of evidence used in HIA

HIA uses a range of structured and evaluated sourcesof qualitative and quantitative evidence that includes

public health, epidemiological, toxicological and medicalknowledge, as well as public and other stakeholders’ viewsand experiences. This means it uses both quantitative andqualitative peer-reviewed scientific evidence as well ascommunity surveys and systematically collected andanalysed anecdotal evidence based on the experientialknowledge and judgement of stakeholders (communitiesand professionals).

Rapid and in-depth HIAs

HIAs can generally be characterized as rapid or in depthdepending on the level of detail of the analysis, thecomprehensiveness of the scientific literature review andthe breadth and depth of the community, and otherstakeholder, engagement. However, any particular analysiscan have both aspects because, although the nine stagesoutlined above are presented as linear, HIA tends to be aniterative process where findings and issues that emerge inlater steps can lead to earlier steps being revisited with thescope and analysis being revised. For example, causalpathways may be identified and a rapid analysis of theimportant pathways undertaken to provide a first estimateof the likely impacts. This estimate is then refined with amore in-depth analysis of the pathways shown to have animportant influence on the final answers, using better andmore detailed baseline information and cause-and-effectrelationship data.

Three practical considerations can and should have amajor influence on the degree of rigour of any particularanalysis:

1. Proportionality : It generally makes sense to put moreresources into HIA where the expected health impactsare large or controversial.

2. Timeliness : Because the point of HIA is to inform thedevelopment of a proposal or policy, a timely albeit lessin-depth analysis (but one whose strengths andweaknesses have been made explicit) will be moreuseful than a more comprehensive HIA that misses thedecision points of proposal development andimplementation. Meeting policy and decision-makingdeadlines can be a challenge even when a HIA isanticipated and planned well in advance.

3. Limitations of evidence and data : These can be to anextent overcome by making plausible assumptions andthen checking how robust or sensitive conclusions areto changes in these assumptions; HIA lends itself wellto sensitivity analyses along these lines.

Stakeholder involvement and communityengagement

Actively listening to and involving people who may beaffected by a proposal is an important part of HIA and its

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HIA in the context of other approaches 3

ethos of equity, participation, sustainability, accountability and transparency in the use of evidence and analysis.Involving the individuals and groups who are, or are likely to be, affected by a proposal is essential for obtaining arounded picture of the actual and potential impacts onhealth and well-being. It can also reduce actual andpotential concern, distrust and conflict, and so make anevidence-based decision more likely. Reasons why stakeholders should be, and generally are, actively involvedin a HIA, include the following:

1. Affected stakeholders will face the direct positive andnegative health consequences.

2. Stakeholders have valuable experiential knowledge thatcan inform the analysis of health impacts.

3. Not adequately and appropriately addressingstakeholder concerns can lead to them experiencingsocial and psychological distress.

4. Allowing residents and others to have a voice andinfluence in decision-making processes reduces thesense of social exclusion, democratic deficit andinequity.

A range of community consultation and involvementmethods can be used, from workshops and focus groups toone-to-one interviews and public meetings. The key issueis to be clear about the purpose of the activities and tocommunicate to stakeholders how the consultationfindings have been used to inform the HIA.

HIA IN THE CONTEXT OFOTHER APPROACHES

HIA and other forms of impact assessment

HIA has its roots firstly in the healthy public policy movement of the 1970s and 80s, which recognized thatnon-health policies, for example housing, transport andwelfare, are as important as, if not more important than,healthcare policy as determinants of public health. Ithas been rooted secondly in the environmental impactassessment movement from the 1950s onwards and itsperceived deficiencies in assessing the wider public healthimpacts of new projects, particularly infrastructureprojects in the developing world; 5 thirdly in the sociology of health; and finally in epidemiology and quantitativehealth risk assessment.

HIA is increasingly carried out either in conjunctionwith or by being integrated into other forms of impactassessment at both policy/plan and project/programmelevels; these include environmental impact assessment,strategic environmental assessment, sustainability appraisals, equalities impact assessment and policy appraisals.6 This is increasingly being badged as integratedimpact assessment or integrated policy appraisal.

HIA and evaluation studies

The purpose of HIA is to inform the development of newproposals in advance of their being put in place. Evaluationstudies are empirical investigations that aim to assess theactual impacts of proposals that have been implemented;

they are an elaboration of stage 9 of the HIA process. It isbest that evaluation studies are designed, and baselinemeasurements taken, in advance of a proposal being putinto place (cf. stage 7 of the HIA process).

HIA and evaluation studies are therefore different intone and focus, and they play a different role in policy development and review. Both HIA and evaluation should,however, be considered as part of the overall process of developing a proposal, and there is a close and mutually supportive relationship between the two. For example,some of the data used in the HIA may be relevant todeveloping the baseline for an evaluation study. In addition,evaluation studies (if properly conducted and sufficiently powerful) will help show to what extent the HIA predictions

have in fact been borne out by events (even thoughevaluation studies rarely aim to cover the full healthimpacts of a proposal).

HIA and health risk assessment

Health risk assessment is an established term formethodologies that aim to provide a quantitativeassessment of the adverse health impacts of populationexposure to single or multiple hazards, and in particularenvironmental and occupational exposure to chemicalpollutants released or transferred into the air, water andsoil and their direct physical health impacts. HIA includes

health risk assessment as one of its component parts(within stages 5 and 6, as listed above). However, HIA iswider than health risk assessment in several ways.

● It takes a wider view of health.● It considers health benefits as well as health hazards.● It aims to assess the full health impacts of policies, and

not only those which are mediated through changes inchemical and physical exposures.

● It examines the distribution of health impacts across apopulation.

Thus, HIA tends to be a broader and more holistic formof assessment that examines not only the effects of pollutants,

but also the direct and indirect impacts on the widerdeterminants of health, for example: employment andeconomy; housing and shelter; transport and connectivity;learning and education; crime and safety; public andcommercial services; social capital and community cohesion;culture, spirituality and faith; arts and leisure; lifestyle anddaily routines; governance and institutional structures;energy and waste; and land and spatial factors.

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AN OVERVIEW OF ENVIRONMENTAL HIA

Social HIA and environmental HIA

Given its historical roots, it is not surprising that HIAcan in practice be seen as the fusion of two broad traditions

of assessment – environmentally focused and socially focused HIA. ‘Social’ HIA has roots in the healthy publicpolicy movement, sociology and environmental impactassessment. It tends to take a wide view of what constituteshealth and, because of weaknesses in the evidence base, it hasa strong focus on qualitative analysis of the widerdeterminants of health and a strong focus also on community participation, and other stakeholder engagement, as a key part of the process.

In contrast, ‘Environmental’ HIA (EHIA) has a narrowerfocus, on those health effects which are mediated by theenvironment and by environmental pollutants in particular,and has closer roots in health risk assessment andepidemiology. Consequently, it tends to interpret ‘health’

in traditional biomedical terms of adverse consequences –death, disease, use of health services, illness and somehealth-related behaviours such as days off work or off school. The analysis stages tend to be expert driven,especially where there is strong evidence of causal andquantifiable exposure–response relationships, and thestages are often time-consuming. The relatively strongevidence base for some environment and health pathwaysbrings a danger of undue focus on what is quantifiable, atthe expense of downplaying other health effects that areimportant but unquantifiable. This danger can be reducedthrough community and other stakeholder consultation,which, for environmentally focused HIA, is undertakenlargely in the scoping phase where the question is framed,

and in consultation on the results and recommendations,rather than in the intermediate stage of analysis of impacts. 7

Environmental justice and health equity

Environmental burdens are often both geographically andsocially located, thereby affecting the poorest, mostvulnerable and already burdened members of a community or population. There is also some evidence that, over time,this becomes a systematic and institutionalized processthat is very difficult to shift. There is therefore a call forboth environmental justice and health equity in relation tonew proposals.

Socially focused HIAs have an explicit value framework,in line with the Gothenburg Consensus, while environ-mentally focused HIAs tend not to; hence, one of thedebates in the HIA community is whether it is the role of HIA to take a more overtly political and social stance,advocating health improvement and reductions in healthinequalities/inequities. This has led to two broad stereo-types of how HIA is practised that are often seen in

opposition to each other, with HIA being seen as either of the following:

1. a decision-support tool providing information andadvice to the policy and decision-making process(an objective, technical, informing tool);

2. a decision-influencing tool providing support tocommunities to have their voice, and their views onwhat decisions should be made, heard within thedecision-making process (a community advocacy andempowerment tool).

In reality, in most cases HIA is a mixture of the two. Itdoes give voice to the most vulnerable by providing astructured approach to including their views and wishesand focusing on health equity/inequality. However, it alsoprovides an evidence-based and systematic understandingof the potential positive and negative health impacts of thepolicy or measure under consideration – and this implies arole for subject matter experts. Part of the art of HIA is theability to combine these two aspects in a transparent,credible and robust way. Indeed, from one point of view,there is no need to identify environmental HIA for specialattention – all that applies to HIA and social HIA generally applies to EHIA also. In practice, however, EHIA hasdeveloped relatively independently from the wider socially focused HIA movement, and as noted it has some particularcharacteristics that give it a distinctive flavour within theHIA field. One such characteristic is a highly developedand often quantitative analysis stage, which will be thefocus of much of the rest of this chapter.

A framework for EHIA analysis: the impactpathway or full-chain approach

There have been several attempts to develop a usefulconceptual model for tackling the subject matter issuesthat are central to the analysis stage of EHIA and that formthe basis for much EHIA work. The impact pathway 8,9 or full-chain approach is one way of systematically describing the various linked stages of an analysis thattracks the fate of pollutants from emissions through tomonetary valuation. In terms of human health, thisinvolves tracking the fate of pollutant emissions through aset of stages, for example:

1. from (changes in) policies in various sectors, insofar asthey affect the environment; to consequent

2. (changes in) burdens, and emissions, to air, soil andwater; to

3. (changes in) pollutant concentrations inmicroenvironments; to

4. (changes in) the exposure of individuals and populations(by inhalational, dermal and/or ingestional routes); to

5. (changes in) internal dose at target organs in the body; to6. (changes in) the risks of health effects; to

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percentage change in (risk of) a specific health endpoint per unit exposure (concentration or dose);

● background rates of that health end point in the targetpopulation.

Issues of environmental justice/health equity/inequalitiesare relevant to all three components. That is, it is likely thatthere are differences between population subgroups interms of (1) environmental exposures; (2) risk functions,per unit exposure; and (3) background rates of morbidity and mortality, and that together these differences may imply important differences in health impacts by population subgroup. In principle, the size and nature of such differences should influence the extent to which thepopulation is disaggregated for any particular analysis, forexample by age, gender, social class/socioeconomic status,current health status/pre-existing disease, geographicalarea or other relevant factors. In practice, however, the levelof disaggregation is influenced strongly by limitations onresources needed for the analysis, such as data availability.

EXPOSURE ASSESSMENT

There are many definitions of environmental exposures,but they all include the key idea that exposure is a measureof the interaction (usually in a given time period) betweenpeople, or populations, and the environment(s) wherethey spend time. Exposure involves the interaction of two components – the state of the environment, and thetime–activity patterns of people in relation to thatenvironment. Note that a policy or measure may affectenvironmental exposures by affecting either (or both) thestate of the environment and how people interact with thatenvironment; and while pollution reduction might beconsidered the preferred option, there is a role also for theavoidance of exposure. Although the language of ‘exposure’and ‘risk function’ generally carries negative connotations,suggesting adverse health effects, the concept as describedhere (of an interaction between a population and itsenvironments) may also be life-enhancing. Therefore, forexample, ‘exposure’ may be a measure of proximity or easeof access to greenspace or open space, for recreation,physical activity or conviviality.

This very simple overview does not do justice to what inpractice may be a very detailed and time-consuming aspectof an analysis, i.e. identifying what microenvironmentsneed to be considered (e.g. at home, at work, outdoors inor near traffic, and outdoors elsewhere) and how theproposal may affect both pollutant concentrations and thetime–activity patterns of the target population and itsrelevant subpopulations. A fuller development of this areacan be found in Chapter 7.

CAUSALITY AND STRENGTH OF EVIDENCE

The various ‘pathways’ or ‘chains’ of an analysis carry theimplicit assumption that the environmental exposures

being analysed are causes of the health effects beingestimated, in the sense that changes in exposures will resultin changes in health impacts. The evaluation of causality can be difficult and is best done as a multidisciplinary exercise including as a minimum exposure assessment,toxicology, epidemiology and clinical expertise, eventhough an elaboration of a full-chain analysis followingthe acceptance of causality may draw on some of thesedisciplines much more than on others.

Effects should be included if, on the basis of the availableevidence, the chains leading to them are more likely thannot to express relationships that are causal (the balance of probabilities). This is a weaker criterion than that of ‘beyond reasonable doubt’, often applied in science. Somefavour it in HIA assessments because it is relevant to theaim of providing best estimates, and thus of giving a fairand unbiased assessment of the overall impacts: restrictingassessments to impacts and risk functions that arepractically certain gives an analysis that is biased towardsunderestimating overall health impacts, and so is in practice(although usually not intentionally) antiprecautionary. 11 The issue of evaluating strength of evidence in relation todifferent policy needs has been addressed moresystematically and more comprehensively elsewhere. 12

Causality is sometimes accepted for a pollution mixture,or for pollution from a source such as road traffic, but theparticular agents responsible, or more generally the role of the components of the mixture, may be unknown orcontested. This is not necessarily a barrier to HIA. It may be possible to quantify relationships based on proximity tosource (the presence or lack of a gas cooker, living or notliving with a smoker, or closeness of residence to roads).This gives a crude model in that it does not reflect theeffects of changes in intensity of exposure that wouldfollow from reduced emissions without elimination of thesource. It is nevertheless a model that may be useful.

Alternatively or in addition, one pollutant of a mixturemay be taken as a marker of or surrogate for the mixtureas a whole, with health effects being estimated for thatcomponent and taken as expressing the effects of the mixtureas a whole. For example, the health effects of outdoor airpollution as a whole are generally expressed via relationshipsin PM, represented as PM 2.5 and/or PM 10. Opinions vary onthe extent to which PM measured as PM 2.5 or PM 10 is thecausal agent of the mixture; it is widely accepted, however,that it is the single best marker. It is also possible to quantify in terms of other pollutants, for example nitrogen dioxide,where the associated risk functions are generally understoodas expressing the effects of traffic-related air pollution, ratherthan of whatever causal role nitrogen dioxide as a gas playswithin the mixture as a whole. This can work well as long aschanges in traffic-related nitrogen dioxide reflect changes inthe mixture as a whole. Such quantification would beseriously misleading, however, in estimating the healtheffects of proposals that reduce traffic-related nitrogendioxide without concomitant reductions in the othercomponents of the pollution mixture.

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An overview of environmental HIA 7

This emphasizes a more general point – that there arenot any universally best EHIA models. Rather, there aremodels of different complexity, with different assumptionsand different data needs, and different strengths andweaknesses in the context of different applications. Wesupport the concept of ‘fit for purpose’, not least because itpushes for early-stage clarification of what the purpose is,what degree of accuracy and precision is envisaged for theEHIA, and whether the resources (evidence, data, time andmoney) available are at all realistic in relation to theenvisaged purpose.

RISK FUNCTIONS

Estimates of risk functions vary between studies, and thisleads to interesting questions about which functions to usewhen ‘local’ estimates (i.e. those relating to the targetpopulation of the EHIA) are available, and about thetransferability of functions from elsewhere. The key issueis whether the variability between estimates from differenttimes and places arises from real known factors or from thecomplexity of issues we call ‘chance’. If the former, it may be possible to adjust for differences in these factors whentransferring relationships from one context to another. If the differences are best understood as chance effects, theuse of random effects methods in meta-analyses will givebetter estimates of effects and of the uncertainties withwhich they are estimated. In either case, we think that thewider international evidence should weigh strongly relativeto a particular, and possibly not large, local study, althoughstakeholder pressure to use local evidence may be strong.

For an informative discussion of these and many otherrelevant issues, see the reports of two WHO workshops, 13,14 the more recent focusing on outdoor air pollution butincluding many points of wider interest.

BACKGROUND RATES

For some health end points, relevant data may be collectedroutinely to a high standard across the target population,and be available for use. Often, background rates need tobe estimated, for example by extrapolating from a smallnumber of locations for which reliable data have beencollected as a result of special exercises is specific times andplaces as, for example, was done by the Air Pollution andHealth: A European Information System HIA team withrespect to hospital admissions in several European cities. 15 Alternatively, it may be possible to get good-quality dataon background rates from specific research studies carriedout by others. Because the focus here is on a health endpoint, these studies do not need to be limited to thoseinvestigating the environmental factors under considerationin the HIA.

In general, both analysts and stakeholders tend to bedrawn to paying much more attention to the choice of riskfunctions than to the estimation of background rates, andwhile there is some rationale to this in terms of the

influence on final estimates, more attention on estimatingbackground rates would be worthwhile.

AGGREGATION ACROSS HEALTH END POINTS

It is rare that the HIA of a proposal implies effects on only one health end point. In the more usual situation of multiple health end points, there is often an interest inaggregating results across health end points into a singlecomposite index. The two most commonly used approachesare disability-adjusted life–years, as used, for example, inthe WHO Global Burden of Disease analyses, and monetary valuation. 16,17 Insofar as any aggregation of this kind canbe done meaningfully, the results facilitate the comparisonbetween studies and between the effects of differentmeasures. Monetary valuation in addition allows a cost–benefit analysis of the proposal, which some decision-makers find particularly informative.

When aggregation is used, as it is widely, we recommendthat the underlying separate health effects estimates also bepresented. This not only increases the transparency of thefinal aggregated values, but also allows stakeholders toapply their own weighting factors. Indeed, the range anddiversity of health effects, and not just their aggregatedvalue, may be a spur to action to protect or improve health.

ISSUES OF SPACE AND TIME

Any full-chain analysis needs to consider issues of spaceand time in an integral way, from framing the question(e.g. what are the boundaries in space and time of theenvironmental exposures that are considered relevant, of the population at risk, and of the of the health effects?)through to the detailed linkage of information across thefull chain. Estimates of one component of the chain (e.g. adispersion-modelling of pollutants) may be carried out onquite a different spatial scale from estimates of othercomponents (e.g. background rates of morbidity ormortality). However, the full-chain analysis will requirelinkage of all the data spatially, and it is helpful to be awareof this from the outset. The detailed work of any componentmay need to be adapted so that the analysis as a wholebecomes workable. Similar issues apply to the timedimension, and this is greatly facilitated by going throughthe full chain more than once, first very approximately andthen in more detail.

An important issue is the extent to which results may besensitive to the spatial scale of the analysis; this is an areawhere sensitivity analyses may be helpful.

REPRESENTATION AND ASSESSMENT OF UNCERTAINTY

Any EHIA, indeed any full-chain analysis, impliesuncertainties at different stages and in the final estimatedhealth impacts, whether reported individually or inaggregated form. It is not practicable to pay close attentionto all of these. It is, however, both possible and necessary to

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be explicit about what these are, and to get some perspectiveon which of these matter in terms of their impact on thefinal answers. This also helps with identifying what aspectsof the full chain could most benefit from more attentionand improvement.

There are many more-or-less sophisticated approachesto the assessment and representation of uncertainty. Wesuggest that they should begin with identifying anddescribing the various sources, and with some qualitativeassessment of their size and importance to the finalanswers. This seems an essential precursor to moresophisticated methods, be these qualitative or quantitative,that attempt to assess and aggregate uncertainties acrossthe full chain, for example by assuming particulardistributional forms for the individual components, andusing Monte Carlo methods to explore how they combine.

AN EXAMPLE: ENVIRONMENTAL HIAOF OUTDOOR AIR POLLUTION

Policies affecting outdoor air pollution areamenable to HIA

Some of the history of the development of environmentally focused HIA and several of its interesting characteristicscan be illustrated with reference to the HIA of outdoorair pollution, the context within which EHIA is moststrongly established both methodologically and in termsof its use in policy development. There are severalreasons why the HIA of outdoor air pollution has gainedthis position:

● The impact pathway from emissions to health is relatively simple, with emissions to air and exposure by inhalation(although there are of course major complexities inmodelling the fate of relevant emissions to air).

● There is a very substantial body of research evidence –epidemiology, toxicology and human experimentalstudies – for the assessment of causality and forestimating relationships between exposure and the riskof adverse health effects (mortality and morbidity).

● The main epidemiological studies are based onconcentrations of outdoor air, as measured by fixed-point samplers located at background sites, rather thanon personal exposures. This in effect removes one of thesteps of the impact pathway and leads to a simplerschematic representation, as shown in Figure 63.2. 11

Early HIA analyses of outdoor air pollution:effects of daily variations in air pollution

Early examples of what were in effect this approach weredeveloped by Ostro and colleagues in the early 1990s, in aseries of analyses about the effects of air pollution fromelectricity generation and in burden of disease estimatesfor the World Bank. 18 The basic framework has changedlittle since then. The essentials of the methodology can befound elsewhere. 11,19

Those early analyses were based principally on studiesof daily variations in mortality and morbidity. In principle,it was necessary: (1) to construct the full annual pattern of daily concentrations of ambient pollutants, and how thesewould change with changes to policy; (2) to apply therelevant concentration–response functions andbackground rates in order to estimate daily impacts; andthen (3) to aggregate these impacts over days in the year toreach estimated annual impacts. In practice, however, theconcentration–response functions used were linear, withno threshold, and an equivalent answer could be providedby the simpler method of applying concentration–responsefunctions and background rates to annual average (changesin) ambient pollution, and then scaling appropriately.

Figure 63.2 Schematic diagram of the healthimpact assessment of outdoor air pollution.

Pollution sources:

VALUATIONS HEALTH IMPACTS

Benefits of improved air quality

Incrementalpollution

andbackground levels

Concentration–response functions:

risks as percentagechanges per unit of

pollutant

Population at risk: Backgroung data:emissions pathways overall and subgroups morbidity rates AQ

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An example: environmental HIA of outdoor air pollution 9

The simplification, which is substantial, is a consequenceof how the various component parts of the overall HIAprocess fit together; it is not a consequence of any one partof the process, viewed in isolation. This illustrates thebenefits of doing an HIA using the impact pathway approach, not as a once-and-for-all pass through thevarious stages, but rather as an iterative process, i.e. inoutline form initially, and then in more detail as the shapeof the component parts becomes evident. This has severalbenefits:

● It allows aspects of integration to be properly addressed.For example, with ozone, the modelling of ambientconcentrations may be in terms of 8 hour daily maximum ozone concentrations, whereas epidemiology uses other metrics, such as 1 hour daily maximum or24 hour average concentrations. An initial scopingexercise will identify the need to join these up, forexample by focusing on concentration–responsefunctions in the metric of the 8 hour daily maximum,by carrying out the ozone modelling in the metric of 1 hour daily maximum or 24 hour daily average, orby scaling the relevant concentration–response functionsaccording to the average relationships between 1 hourdaily maximum, 8 hour daily maximum and 24 hourdaily average.

● Initial scoping should help identify the most importantuncertainties and evidence gaps, i.e. those which mostaffect the final answers; this helps in prioritizing furtherwork.

● Viewing the process as a whole can lead to simplifications,as described earlier.

This period also saw an important debate about whowas at increased risk of mortality from higher daily valuesof outdoor air pollution, i.e. where the focus was on daily values within the ‘normal’ range of variation in Europe andNorth America, rather than during specific episodes of unusually high air pollution. The emerging consensus wasthat the associated ‘extra’ deaths attributable to air pollutionwere among people with already severe (albeit possibly undiagnosed) cardiorespiratory disease. The implicationwas that, on average, the life expectancy of those at risk wasless, and maybe very substantially less, than that of thegeneral population of similar age; air pollution was viewedas ‘bringing forward’ a death that might in any case haveoccurred before very long. 20

This was helpful in focusing attention on the fact thatdeath is unavoidable – air pollution does not lead to ‘extra’deaths, but rather it leads to earlier deaths. A complicationwas that the time series studies that quantified the risk of earlier deaths (attributable to daily variations in airpollution) were not directly informative about the degree of life-shortening. The debate, however, led to a questioning of the practice, until then current, of associating with theearlier (‘extra’) deaths attributable to air pollution a ‘valueof a statistical life’ that ignored the likelihood of pre-existing

serious cardiorespiratory disease among those effectively atrisk. This debate has not yet been fully resolved.

Some more recent developments:effects of long-term exposures

The emerging evidence in the mid-1990s, from two cohortstudies in the USA, 21,22 showed associations between long-term exposure to outdoor air pollution, specifically PM,and mortality. Earlier studies had suggested suchassociations; the cohort studies provided stronger evidencebecause they adjusted for confounding factors at theindividual level. Whether or not these studies expressed acausal relationship was disputed. It was clear, however, thatif they did – and it is now widely accepted that they do –they implied substantially greater public health effectsthan did the mortality studies of daily variations in airpollution. This was partly because the estimated relativerisks of mortality across the adult population weremuch higher than those implied by time series studies,and partly because the whole adult population – and not just those with pre-existing cardiorespiratory disease – wasconsidered to be at risk. Together, these implied muchgreater effects, especially when expressed in terms of accumulated life expectancy rather than ‘attributabledeaths’.

Despite the caveats about causality, the effects of long-term exposure, as expressed via these cohort studies,were included quite soon in some HIA assessments aspart of sensitivity analyses or as a central part of theassessment. 8,9 With growing epidemiological evidence 23 and a better understanding of possible mechanisms, aconsensus has emerged that the HIA of outdoor airpollution should include the mortality impacts of long-term exposure as not to do so implies a possibly seriousunderestimation of mortality impacts. The overallevidence has been reviewed by various expert groups,including the UK Expert Committee on the MedicalEffects of Air Pollutants. 24

Using the results of cohort studies for the HIA of outdoor air pollution has highlighted a number of methodological issues that have been resolved only inpart. 25 There are at least three.

First is how to express mortality impacts, in terms of life expectancy or as ‘attributable deaths’? A simple approach yielding estimates of ‘attributable deaths’ was used inExternE,8 and has continued to be used until recently. Theuse of life tables was proposed by Brunekreef 26 anddeveloped and recommended by others, for exampleExternE, Leksell and Rabl, and Miller and Hurley. 9,27,28 Both approaches were used in the HIA and associatedcost–benefit analysis of the Clean Air for Europe (CAFE)programme.

However, methodological work using life table methodshas shown that estimates of attributable deaths – which inHIA analyses are treated as reproducible year on year – do

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in fact change over time, as the different mortality patternsimply differences in the size of the underlying populationat risk.29,30 Specifically, if the same population is analysedunder two scenarios – lower and higher age-specific deathrates – there will initially be more deaths per year in thepopulation with higher death rates, but the situation willreverse in due course as the size of the surviving populationat risk (under higher death rates) decreases more rapidly than when death rates are lower. Currently and in general,HIA analyses of ‘attributable deaths’ do not take this effectinto account.

The second issue is the time lag between reductions in air pollution and the associated or consequent changes in risks of mortality – a concept sometimes known as cessation lag. Itis linked to, but is not identical with, the latency periodbetween exposure to ambient air pollution and theassociated risk of mortality. Studies in Dublin 31 and HongKong32 have shown that substantial reductions in airpollution can have clear and immediate benefits in termsof lower death rates. There may, however, also be delayedeffects, for example effects on birth weight or on lungfunction in childhood, which may affect mortality r isks inlater life. How cessation lag is treated within a HIA canhave substantial effects on the final results, especially if monetary values are linked with health impacts and if thediscount rate is large.

The final issue is the time frame for an analysis . When anHIA of outdoor air was focused on the effects of daily variations, the associated health effects were more or lessimmediate, and so there was a concordance between thetime frame of emissions and of effects – the two could beconsidered as concurrent, and effects ‘within a year’ was anunambiguous concept. With the effects of longer-termexposure, however, this identification was broken. It nowbecame necessary to distinguish between (1) the healthimpacts in a given year, arising from emissions, wheneverthey occurred, and (2) the health impacts whenever they occur, arising from emissions in a given year. The latter of these is more consistent with the HIA as a prospectiveexercise, and is what is generally used.

There are, however, other time frame issues to consider.While looking at the health effects of emissions in a given year may be helpful, for comparing with the costs of emission control in that same year, there is somethingartificial about an evaluation focused on one year’semissions given that policies to control air pollution areintended to be long-lasting, rather than reverting to thestatus quo after a single year. Consequently, how the HIAis framed in terms of time scale remains an issue that isvery relevant to the analysis and to the results, but whichthat not have an obvious solution.

HIA of the Clean Air for Europe programme

The HIA within the CAFE programme was carried out aspart of a wider cost–benefit analysis, commissioned by

Directorate-General for the environment. 33 This shows,inter alia, how the methods and results of the HIA andcost–benefit analysis were used by the Commission toinform its policy development on outdoor air pollution.Briefly, results showed that the estimated benefits of a 20per cent reduction in fine particulate air pollution (PMwith a diameter of 2.5 m or less [PM

2.5]) across the

European Union far outweighed the estimated costs. Thebenefits were largely attributable to the effects on mortality risks of long-term exposure to outdoor air pollution,expressed as PM 2.5.

CURRENT TRENDS AND FUTURE PROSPECTS

There is renewed and growing interest in both socially andenvironmentally focused HIA globally, as policies andmeasures are developed to tackle two major health issuesof the present period – the adverse effects of climatechange, and of poverty and income inequality. Successfully

tackling either of these issues requires policy-makers andothers to draw on the main strengths of both traditionsthat underlie HIA: the strengths of socially focused HIAsin analysing the wider, social determinants of health andgiving a voice in decision-making to all stakeholders,particularly those who are socially disadvantaged, and of environmentally focused HIA in providing precisenumerical estimates of health impact that can be linked tomonetary cost–benefit analyses which can support fine-grain decision-making between the costs and benefits of arange of proposal options.

All HIA, whether socially or environmentally focused,draws on both these traditions and, we see, method-ologically, moves towards a convergence, with an

increasing focus on quantifying health impacts in socially focused HIA and on including wider health impacts(including positive health impacts) and on community engagement in environmentally focused HIA. Socially focused HIA is reaching the limits of what can bedescribed and analysed qualitatively, and environmentally focused HIA is seeing the limits of focusing on tangible,chemical environmental exposures. This seems to show acoming together of the two approaches and an increasingintegration of the methodologies between the twotraditions of HIA, a direction that many strongly welcomeand support.

ACKNOWLEDGEMENTS

Work on this chapter was supported in part by HEIMTSA, an Integrated Project, funded under theEuropean Union Sixth Framework Programme – Priority 6.3 Global Change and Ecosystems, and draws ondiscussions with many HEIMTSA colleagues, whose helpwe acknowledge.

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References 11

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9. Holland MR, Forster D, for ExternE. : DGXII (JOULEProgramme).Externalities of Energy, ExternE Project . ReportNo. 7:Methodology . : Update 1998. 1999.

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22. Pope CA III, Thun MJ, Namboodiri MM et al. Particulate airpollution as predictor of mortality in a prospective study of US adults.Am J Resp Crit Care Med 1995; 151 : 669–74.

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25. Hurley F, Hunt A, Cowie H et al.Methodology for the Cost–Benefit Analysis for CAFÉ . Volume 2: Health Impact Assessment . Didcot: AEA Technology Environment, 2005.

26. Brunekreef B. Air pollution and life expectancy: is there arelation? Occup Environ Med 1997; 54 : 781–4.

27. Leksell L, Rabl A. Air pollution and mortality: quantificationand valuation of years of life lost.Risk Analysis 2001; 21 :843–57.

28. Miller BG, Hurley JF. Life table methods for quantitativeimpact assessments in chronic mortality. J Epidemiol Commun Health2003; 57 : 200–6.

29. Miller BG, Hurley JF.Comparing Estimated Risks for Air Pollutionwith Risks for Other Health Effects . IOM Report TM/06/01.Edinburgh: Institute of Occupational Medicine, 2006.

30. Brunekreef B, Miller BG, Hurley F. The brave new world of lives sacrificed and saved, and deaths, attributed to andavoided.Epidemiology 2007; 18 : 785–8.

31. Clancy L, Goodman P, Sinclair H, Dockery DW. Effect of air-pollution control on death rates in Dublin, Ireland: anintervention study. Lancet 2002; 360 : 1210–14.

32. Hedley AJ, Wong CM, Thach TQ, Ma SLS, Lam TH, AndersonHR. Cardiorespiratory and all-cause mortality afterrestrictions on sulphur content of fuel in Hong Kong: anintervention study. Lancet 2002; 360 : 1646–52.

33. Commission of the European Communities. CommissionStaff Working Paper. Annex to The Communication onThematic Strategy on Air Pollution, and The Directive on‘Ambient Air Quality and Cleaner Air for Europe’. ImpactAssessment. COM(2005)446 final. COM(2005)447 final.Available from: http://ec.europa.eu/environment/air/pdf/sec_2005_1133.pdf (accessed December 13, 2009).)

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Author queries

AQ1. Please confirm your affiliations, including position held, institutions and qualifications as you‘d like them to appearin the book, and please let me know any change of contact details.

AQ2. A framework for EHIA analysis, para 2 after list. ‘It helps if the analysis is best done more than once, e.g. rapidly‘ - isthis part of the sentence correct?

AQ3. Figure 1. Do you already have permission to reproduce this?AQ4. Figure 2. Does this come from reference 11 (in which case a credit line will need to be added to the caption) or is it

newly drawn for this chapter? If the former, has permission to reproduce it been obtained?AQ5. Refs 8, 9 and 18. Do you have a place of publication for these?AQ6. Ref 10. Please provide full details of the document that this appeared in.AQ7. Please could you indicate which (if any) of the references are to be annotated as seminal primary articles, or

alternatively as key review papers.

HIA - Environmental Medicine Ch63 - 2010

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