A Summary of Publications on Methods and Tools for Assessing Cumulative Risk, Project Summary
NoticeEPA’s National Center for Environmental Assessment has recently published several papers that provide background information on cumulative risk assessment and approaches to characterize and quantify combined exposures and risks due to multiple agents or stressors, with an emphasis on chemical mixtures exposures, toxicity and risk.
Cumulative risk has been defined by the U.S. Environmental Protection Agency (EPA) as the combined risks from aggregate exposures (i.e., multiple route exposures) to multiple agents or stressors, where agents or stressors may include chemical and nonchemical stressors (U.S. EPA, 2003). Cumulative risk assessment (CRA) is an analysis, characterization and possible quantification of the combined risks to health or the environment from exposures to multiple agents or stressors. CRA differs from traditional chemical risk assessments as it has a population focus, and there is an emphasis on stakeholder involvement and population vulnerabilities. Further, CRA focuses on both human health and ecology, although an individual CRA may involve only a subset of these features.
This project summary and its related publications provide information and methods for evaluating combined exposures and cumulative risks in human health risk assessment, with an emphasis on chemical mixtures exposures, toxicity and risk. Lambert et al. (2011) present an overview of current thinking on CRA for chemical and nonchemical stressors (physical, biological, socio-economic) that includes a discussion of CRA initiating factors and population vulnerabilities. Rice et al. (2010) and Rice and MacDonell (2008) discuss an iterative approach for assessing multiple route exposures to environmental chemical mixtures and describe the utility of grouping the chemicals to be analyzed based on both physical-chemical properties and an understanding of environmental fate. Lipscomb et al. (2010) detail the state of the practice for estimating chemical mixtures toxicity and risk and discuss criteria for grouping chemicals by common toxic modes of action. Boobis et al. (2011) explore whether synergistic interactions can occur among chemicals at low, environmentally relevant exposure levels, finding only six studies out of 90 identified in the literature that could be used to quantify the magnitude of low dose synergy; for this small set of data, the magnitude of synergy at low doses did not exceed the levels predicted by additivity models by more than a factor of 4. Ragas et al. (2011) provide a comparison of chemical mixture risk assessment methods from human health and ecological risk assessment and propose approaches for integrating information from the two fields of study. Finally, Hertzberg et al. (2008) and Simmons and Teuschler (2010) discuss the risk assessment of complex mixtures of chemicals in drinking water, with an emphasis on multiple route exposures to drinking water disinfection byproducts.
This set of publications advances the science of analyzing the effects from chemical mixtures and the field of CRA and disseminates information to the scientific community and the general public to promote increased understanding of this area of research.
The research described here was conducted to advance the science of CRA and to be responsive to a number of environmental laws and publications by scientific expert panels. The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 first emphasized the need to address the dangers associated with the accumulation of hazardous chemical substances in the environment. Further, some of the earliest tenets of CRA were captured in the Superfund Amendments and Reauthorization Act of 1986, which included an increased focus on stakeholder (e.g., public, states) involvement. Under the Safe Drinking Water Act Amendments of 1996, EPA was specifically called upon to “develop new approaches to the study of complex mixtures, such as mixtures found in drinking water….” Also in 1996, the Food Quality Protection Act mandated the CRA of multiple-route exposures to pesticides acting by a common mechanism of toxicity. In 2008, the National Research Council’s National Academy of Sciences (NAS) published two expert panel reports related to CRA. One report advised EPA to conduct a CRA for mixtures of phthalates and other anti-androgens and discussed how this might be done (NAS, 2008a). The second described how environmental risk assessments can be improved, specifically recommending that CRA factors such as chemical mixtures and population vulnerabilities be addressed (NAS, 2008b).
- NAS (2008a) Science and decisions: advancing risk assessment. Washington, DC: National Academy of Sciences.
- NAS (2008b) Phthalates and cumulative risk assessment: the task ahead. Washington, DC: National Academy of Sciences.
- U.S. EPA (1986) Guidelines for health risk assessment of chemical mixtures. EPA/630/R-98/002. Federal Register 51:34014. September 24. Risk Assessment Forum. Washington, DC.
- U.S. EPA (2000) Supplementary guidance for conducting health risk assessment of chemical mixtures. EPA/630/R-00/002. Office of Research and Development, Washington, DC.
- U.S. EPA (2003) Framework for cumulative risk assessment. EPA/630/P-02/001F. Office of Research and Development, Washington, DC.
- U.S. EPA (2007) Concepts, Methods and Data Sources for Health Risk Assessment of Multiple Chemicals, Exposures and Effects. EPA/600/R-06/013A. ORD/NCEA. Cincinnati, Ohio.
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