Science and Decisions Advancing Risk Assessment (2009) / Chapter Skim
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7 Implementing Cumulative Risk Assessment
7 Implementing Cumulative Risk Assessment
Pages 213-239
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From page 213... ...
that such a narrow focus does not accurately capture the risks associated with exposure, given simultaneous exposure to multiple chemical and nonchemical stressors and other factors that could influence vulnerability. More generally, a primary aim of risk assessment should be to inform decision-makers about the public-health implications of various strategies for reducing environmental exposure, and omission of the above factors may not provide the information needed to discriminate among competing options accurately.
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From page 214... ...
. The committee acknowledges the conceptual framework and broadened definitions of cumulative risk assessment as constituting a move toward making risk assessments more relevant to decision-making and to the concerns of affected communities.
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From page 215... ...
We conclude by providing some specific guidance about how the committee believes that cumulative risk assessment needs to be developed further, including the use of clear and consistent terminology; methods to incorporate interactions between chemical and nonchemical stressors; the use of biomonitoring, epidemiologic, and surveillance data; the need to develop simpler analytic tools to support more wide-ranging analyses; and the related need to engage stakeholders throughout the cumulative riskassessment process.
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From page 216... ...
. Although aggregate exposure assessments have been thoroughly constructed and the combination of dose addition for chemicals with similar MOAs and response addition for mixtures with different MOAs helped to expand the scope of the assessments, the scope of cumulative risk assessment did not consider nonchemical stressors, and insight about synergistic or antagonistic effects remained minimal.
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From page 217... ...
were considered to contribute to population health risks. Thus, in part because of the risk-management questions and regulatory issues historically facing EPA, cumulative risk assessments to date have largely focused on aggregate exposure assessment and have generally not considered nonchemical stressors.
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From page 218... ...
, but the approaches do not yet consider key dimensions of cumulative risk, such as nonchemical stressors, vulnerability, or multiple routes of exposure. A final setting outside EPA in which the general concepts of cumulative risk assessment have been applied is the assessment of the global burden of disease related to environmental and other risk factors.
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From page 219... ...
. However, cumulative risk assessments have generally not yet reached the potential implied by the stated definition; there has been less than optimal formal consideration of nonchemical stressors, aspects of vulnerability, background processes, and other factors that could be of interest to stakeholders concerned about effects of cumulative exposures.
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From page 220... ...
but want to take account of the full array of chemical and nonchemical stressors that have similar health effects. The framework proposed (Menzie et al.
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From page 221... ...
In principle, focusing on stressors relevant to risk-management strategies will help to ensure that analyses are aligned with EPA's mandated focus on chemical or biologic stressors while acknowledging the influence of nonchemical stressors. A modified version of the stressor-based paradigm from Menzie et al.
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From page 222... ...
. The model includes an MOA assessment, an assessment of background exposures to chemical and nonchemical stressors that may affect the same health outcome, and a vulnerability assessment that takes into account underlying disease processes in the population to which the chemicals in question may be adding.
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, that about 20,000 pesticide products are on the market and 80,000 existing chemicals are on the Toxic Substances Control Act inventory makes it impractical to try to account for all relevant synergisms and antagonisms. More broadly, cumulative risk assessment requires extensive information beyond chemical toxicity and MOAs, including aggregate exposure data and information on population characteristics and nonchemical stressors.
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From page 224... ...
For example, it will often be desirable to use CBPR approaches in cumulative risk assessments, although in principle a community-based risk assessment might not address cumulative risks, and a cumulative risk assessment (such as the pesticide analyses under the FQPA) may not always follow CBPR approaches.
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From page 225... ...
Moreover, as illustrated in the global analyses of burden of disease described above, data are available on the effects of a number of dietary, physical, and psychosocial risk factors, and extensive exposure data are available on many of these stressors. In addition, ecologic risk assessments commonly apply methods that simultaneously consider numerous chemical and nonchemical stressors in a single assessment in spite of the complexity of the system and the limitations of data availability.
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From page 226... ...
EPA should work to synthesize and develop datasets related to exposures to nonchemical stressors that influence similar health end points as key chemical stressors to allow these factors to be readily incorporated into cumulative risk assessments in settings where population-specific assessment is infeasible or impractical. Emphasis should be on characterization of distributions for key subpopulations and on evaluation of correlations between factors to allow more realistic assessments.
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Thus, a physiologically based conceptual model can readily incorporate nonchemical stressors into the cumulative risk assessment.
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The inclusion of nonchemical stressors as outlined above can lead to more informative assessments and correspondingly better decisions if used appropriately but can run the risk of contributing to less informative assessments if used in the wrong way. Information on the varied risk factors should not be used solely for risk comparisons that are uninformative from the perspective of the decisions faced by EPA.
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From page 229... ...
In summary, approaches to incorporate nonchemical stressors into cumulative risk assessment are feasible in the near term although there are many situations in which site-specific data needs may not be met. We recommend that EPA start to address nonchemical stressors in settings in which sufficient epidemiologic or pharmacokinetic and pharmacodynamic data are available to understand interactions with chemical stressors, following the tiered strategy articulated by Menzie et al.
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From page 230... ...
Thus, although it seems unlikely, because of both cost and limited interpretability, that biomarkers could be used directly to quantify the benefits of control strategies leading to marginal changes in exposures, biomarker studies can provide enhanced mechanistic understanding of the relationships among chemical and nonchemical stressors, and insight about highly-exposed populations or source category contributions that can allow for the development of targeted control strategies. Role of Epidemiology and Surveillance Data The cumulative risk-assessment paradigm, given its focus on communities or defined populations and consideration of such nonchemical stressors as SES and access to health care, lends itself to being informed by epidemiology.
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From page 231... ...
For example, an epidemiologic analysis done for its own sake will tend to focus on disentangling the contributions of individual risk factors in the presence of potential confounding, whereas an epidemiologic analysis done for cumulative risk assessment might characterize the risks of defined "bundles" of exposures without further decomposition. The interaction between epidemiology and cumulative risk assessment can be enhanced as risk assessments identify key uncertainties related to interactions among chemical and
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From page 232... ...
In general, as mentioned above, EPA and other agencies should pursue a long-term research agenda related to enhanced epidemiologic insight into interactions among chemical and nonchemical stressors and in the short term should work to develop internal capacity in a variety of epidemiologic disciplines to foster the development of new methods and knowledge. Although epidemiologic approaches may improve understanding of the effects of exposure to multiple stressors, for effects-based assessments, surveillance data may be needed both to identify the at-risk populations and to characterize patterns of disease and background exposures.
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From page 233... ...
Developing simpler tools seems to contradict the complexity of cumulative risks, but methods can be developed that capture the breadth of chemical and nonchemical stressors with less computational burden, at least for initial screening calculations. There will also need to be techniques to develop indicators or ranking approaches that could categorize the benefits of different strategies ordinally as has been done in ecologic risk assessment; for example, Thomas (2005)
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From page 234... ...
The concept of using a limited number of more extensive analyses to determine approximate relationships for an unstudied setting can be extended to exposures to nonchemical stressors or interactions among compounds. This can provide effective defaults in the absence of more detailed sitespecific data.
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From page 235... ...
, which provide extensive information about the locations of key emission sites for any given ZIP code, information about environmental-justice assessments, and links to related concentration data. However, none of the available resources provides the information or tools needed for stakeholders to understand their cumulative risks associated with chemical and nonchemical stressors or, more important, the potential benefits associated with specific control strategies.
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From page 236... ...
• In the near term, EPA should develop databases and default approaches to allow the incorporation of key nonchemical stressors in cumulative risk assessments in the absence of population-specific data, considering exposure patterns, contributions to relevant background processes, and interactions with chemical stressors. EPA should use existing nationally representative biomarker and surveillance databases and databases related to nonchemical stressors to help to construct the approaches, leveraging insight from social epidemiology and ecologic risk assessment.
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2005. Cal/EPA EJ Action Plan Pilot Projects Addressing Cumulative Impacts and Precautionary Approach.
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2003. Estimates of global and regional potential health gains from reducing multiple major risk factors.
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2005. Codorus Creek: Use of the relative risk model ecological risk assessment as a predictive model for decision-making.
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