If Cumulative Risk Assessment Is the Answer, What Is the Question?
Callahan, Michael A., Sexton, Ken, Environmental Health Perspectives
Cumulative risk refers to the combined threats from exposure via all relevant routes to multiple stressors including biological, chemical, physical, and psychosocial entities. Cumulative risk assessment is a tool for organizing and analyzing information to examine, characterize, and possibly quantify the combined adverse effects on human health or ecologic resources from multiple environmental stressors. The U.S. Environmental Protection Agency (EPA) has initiated a long-term effort to develop future guidelines for cumulative risk assessment, including publication in 2003 of a framework that describes important features of the process and discusses theoretical issues, technical matters, and key definitions. The framework divides the process of cumulative risk assessment into three interrelated phases: a) planning, scoping, and problem formulation; b) analysis; and c) interpretation and risk characterization. It also discusses the additional complexities introduced by attempts to analyze cumulative risks from multiple stressors and describes some of the theoretical approaches that can be used. The development of guidelines for cumulative risk assessment is an essential element in the transition of the U.S. EPA risk assessment methodology from a narrow focus on a single stressor, end point, source, pathway, and exposure route to a broader, more holistic approach involving analysis of combined effects of cumulative exposure to multiple stressors via all relevant sources, pathways, and routes. Key words: additivity assumption, combined risk, cumulative risk, mixtures, multiple stressors, risk assessment guidelines. Environ Health Perspect 115:799-806 (2006). doi:10.1289/ehp.9330 available via http://dx.doi.org/ [Online 24 January 2007]
Risk is a socially constructed and culturally mediated concept (Jasanoff 1991; Kasperson and Kasperson 1991; Linder 1997) that is used to give meaning to things, forces, or circumstances that pose danger to people or what they value [National Research Council (NRC) 1996]. Various forms of risk assessment have been around for centuries (Bernstein 1997) and each society has its own particular hazards that are of special concern (Kasperson and Kasperson 1991). During the latter half of the 20th century, risk from deleterious by-products of economic activity and technology came to be seen by industrialized societies as a noxious quality present in varying degrees in different environmental settings and geographic locations. Although risk is not necessarily an intrinsically quantifiable variable, virtually all of the formalized assessment methods that subsequently evolved, including those at the U.S. Environmental Protection Agency (EPA), implicitly assume that risk can be estimated, measured or expressed in numerical terms. Today, a quantitative, or at least semiquantitative, description of severity and likelihood of harm is the dominant paradigm for expressing risk from environmental hazards (NRC 1983, 1994, 1996).
Historical perspective. During the mid-1970s the U.S. Food and Drug Administration (U.S. FDA) and the U.S. EPA began to adopt systematic methods for assessing human health risks from exposure to environmental carcinogens. By the early 1980s, risk assessment played an important role in many regulatory decisions, and there were individuals in the public and private sectors who identified themselves as "risk assessors." The Supreme Court's 1980 decision in Industrial Union Department, AFL-CIO v. American Petroleum Institute, 448 U.S. 607 [cited in NRC (1994)], also known as the "Benzene Decision," provided a major push for development of risk assessment within regulatory agencies. The decision struck down the benezene standard developed by the Occupational Safety and Health Administration (OSHA), which was based on the policy of trying to reduce carcinogens in the workplace as far as technologically possible without consideration of whether actual concentrations posed a significant health risk. …