Cumulative Risk: Screening Approach for Assessing Exposures and Effects. M. M. MacDonell, J. P. Butler, R. C. Hertzberg, and L. A. Haroun; Argonne National Laboratory, Tetra Tech EM Inc., US Environmental Protection Agency
Scientists have worked for decades to define safe levels of contaminants in the environment and the workplace. While these are essentially based on single chemicals, the importance of mixtures is receiving increased attention. This includes growing public interest in a more comprehensive process for addressing combined hazards that extend across and beyond the purviews of various regulatory programs. NIOSH and other federal agencies, together with industry, are developing national research agendas to better understand the effects of mixed exposures. EPA recently issued guidance for assessing mixtures risks that considers pair-wise interactions and indicator chemicals for similar classes, but it has not yet been applied for a broad mix of contaminants. Toxicity data to support quantitative assessments are limited, with studies of complex mixtures focusing on specialized subsets such as diesel particulates and jet fuel. Thus, risks at heterogeneously contaminated sites and facilities continue to be assessed on the basis of individual chemicals rather than as they actually exist, as mixtures. This practice can lead to program inefficiencies when resources are used to reduce risks of individual pollutants to levels that do not warrant further control while others go unmanaged. Because the scope of a cumulative assessment can be overwhelming, a tiered approach can be used to focus the analysis. A screening process is being developed that considers opportunities for cumulative effects, including the nature of contaminants and exposures (from acute to intermittent and chronic, by routes that may overlap); internal distribution and clearance; and effect severity, including persistence and reversibility. The approach also provides a means for grouping contaminants by target system/organ and incorporating secondary effects, as well as options for ranking effects. The paper presents this conceptual screening process for assessing cumulative risks and illustrates key features.
Work supported by U.S. Department of Energy: Environmental Management Program, Richland and Chicago Operations Offices; U.S. Environmental Protection Agency: Office of Research and Development, National Center for Environmental Assessment.
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