Cumulative risk assessment is a science policy tool for organizing and analyzing information to examine, characterize, and possibly quantify combined threats from multiple environmental stressors. We briefly survey the state of the art regarding cumulative risk assessment, emphasizing challenges and complexities of moving beyond the current focus on chemical mixtures to incorporate nonchemical stressors, such as poverty and discrimination, into the assessment paradigm. Theoretical frameworks for integrating nonchemical stressors into cumulative risk assessments are discussed, the impact of geospatial issues on interpreting results of statistical analyses is described, and four assessment methods are used to illustrate the diversity of current approaches. Prospects for future progress depend on adequate research support as well as development and verification of appropriate analytic frameworks. EXPOSURE TO MULTIPLE environmental agents, including biologic, chemical, physical, radiologic, and psychosocial stressors, can, under the right circumstances, modify the toxic effects of these same agents acting alone so that combined outcomes are either antagonistic (less than additive) or synergistic (more than additive). 1 – 4 There is empirical evidence that interactive effects from exposure to a mixture of environmental stressors can contribute to three categories of adverse health effects: (1) those where exogenous agents interfere with normal development and distort physiologic function, such as neurobehavioral abnormalities and sex steroid hormonal disruption; (2) those where exogenous agents cause direct cellular damage, such as neurodegenerative diseases and cancer; and (3) those that contribute to illness through a combination of both physiologic disruption and cell damage, for example, in cardiovascular disease. 1 Because traditional risk assessment has not routinely taken account of the potential for combined effects from exposure to diverse environmental factors, like those found in the real world, there is growing urgency about the need to develop effective and practical tools for assessing cumulative health risks. 5 – 9 Cumulative risk assessment is a procedure for organizing and analyzing relevant information to examine, characterize, and possibly quantify the combined harmful effects from exposure to a mixture of environmental stressors. 7 , 8 The National Research Council 9 recently noted that although the need to evaluate combined risks from environmental stressors is becoming more acute, current practices do not adequately incorporate nonchemical stressors and important aspects of vulnerability into the assessment process. In the following, we provide a brief overview of the diversity of methods used to estimate cumulative health risks, distinguishing between traditional chemical-specific tools and the more recent approaches used to incorporate nonchemical stressors. Prominence is given to techniques that integrate psychological and social stressors, along with concepts of vulnerability, into the risk estimation procedure. The importance of spatial scale for analysis and interpretation of results is discussed, and practical applications of cumulative risk assessment are reviewed.
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