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Risk Assessment Strategies and Techniques for Combined Exposures
Citation:
Rider, C. AND J. Simmons. Risk Assessment Strategies and Techniques for Combined Exposures. Edition 1, Chapter 6, Jose A Torres and Sol Bobst (ed.), Toxicological Risk Assessment for Beginners. Springer International Publishing AG, Cham (ZG), Switzerland, 1(1):111-134, (2015).
Impact/Purpose:
This chapter provides a needed introductory level understanding of risk assessment methods and approaches for chemical mixtures. It illustrates risk assessment mixtures methods with water specific examples. More generally, it places research and work conducted by EPA scientists in a framework that demonstrates the values of the data, methods and models to risk assessment, risk reduction and risk remediation efforts for water-borne chemical mixtures.
Description:
Author: Cynthia V. Rider, Ph.D., and Jane Ellen Simmons, Ph.D.Abstract: Consideration of cumulative risk is necessary to evaluate properly the safety of, and the risks associated with, combined exposures. These combined exposures ("mixtures") commonly occur from exposure to: environmental contaminants in air, soil, and water; pharmaceuticals and dietary supplements; consumer and personal care products; food additives and residues; and nonchemical stressors (e.g., physical and psychosocial). Risk assessments of mixtures of chemicals are more complex than those of single chemicals for two major reasons: 1) in combining chemicals to estimate mixture risk, it is necessary to rely on multiple assumptions; and, 2) the potential for pharmacokinetic and/or pharmacodynamic interactions among mixture components. Additional difficulties exist for complex environmental mixtures due to the typical presence of a large fraction of total mixture mass of unknown identity and toxicity. The influence of data type, quality and quantity on the risk assessment approach is illustrated. Guidance is provided on when whole mixture risk assessment approaches are possible and when component-based approaches are needed. Advantages and disadvantages of whole mixture risk assessment approaches are discussed, including concerns due to unknown mixture mass and the current status of sufficient similarity methodology. Component-based methods based on dose-addition represent the majority of chemical mixture risk assessments that have been conducted to date; both hazard index-based (Hazard Index, Target Organ Toxicity Hazard Index, Interaction-Weighted Hazard Index) and index chemical (Relative Potency Factor and Toxic Equivalency Factor) approaches are reviewed. There is recognition of the need to consider the cumulative effects of both chemical and nonchemical stressors, but standard methods with a history of use are not available. Disclaimer: This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade name or commercial products does not constitute endorsement or recommendation for use. This article may be the work product of an employee or group of employees of the National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health (NIH), however, the statements, opinions or conclusions contained therein do not necessarily represent the statements, opinions or conclusions of NIEHS, NIH or the United States government.
