NRC Report: Recommendationa

EPA Response: Stated Policyb

EPA Response: Implementation Activityc



detailed procedures for chemical mixture assessment using data on the mixture of concern, data on a toxicologically similar mixture, and data on the mixture component chemicals. [It] is organized according to the type of data available to the risk assessor, ranging from data rich to data poor situations…. An evaluation of the data may lead the user to decide that only a qualitative analysis should be performed. This generally occurs in cases where data quality is poor, inadequate quantitative data are available, data on a similar mixture cannot be classified as “sufficiently similar” to the mixture of concern, exposures cannot be characterized with confidence, or method-specific assumptions about the toxicologic action of the mixture or of its components cannot be met. When this occurs, the risk assessor can still perform a qualitative assessment that characterizes the potential human health impacts from exposure to that mixture.”

pollutants; and (3) Provide the scientific basis to predict the interactive effects of pollutants in mixtures and the most appropriate approaches for combining effects and risks from pollutant mixtures.”



GAO 2006 at 50: “The extent to which program offices assess the effects of cumulative and aggregate exposures is related to the regulatory responsibilities of each office and by the availability of data. For example, the hazardous air pollutant office routinely analyzes a mix of chemicals from various emitting sources, such as petroleum refineries, to regulate hazardous air pollutants. Similarly, as mentioned above, the Office of Pesticide Programs is required to consider exposure to pesticides from various pathways, such as food, drinking water, and residential uses, and various routes, such as eating, breathing, and contact with skin.”



Note: The Toxic Substances Control Act does not require the Office of Pollution Prevention and Toxics to assess the risks of a new chemical that may occur through its interaction with other chemicals. The office also assesses the risks of existing chemicals but cannot conduct cumulative risk assessment for classes of chemical that share a common mode of action because no data exist.



EPA 2003b Framework for Cumulative Risk Assessment at xvii: “a simple, flexible structure for conducting and evaluating cumulative risk assessment within the EPA…. The framework describes three main phases to a cumulative risk assessment: (1) planning, scoping, and problem formulation, (2) analysis, and (3) risk characterization…Research and development needs are also discussed, including understanding the timing of exposure and its relationship to effects;



GAO 2006 at 49: “The branch of the Office of Air Quality Planning and Standards that regulates hazardous air pollutants employs the Multiple Pathways of Exposure model to

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