Assessment of Responses from Exposure to Hazardous Substances

2 Assessment of Responses from Exposure to Hazardous Substances 

For any hazardous substance, estimates of the relationship of dose to response in humans are based on either animal or human data. For example, only about 20 of the approximately 300 chemical carcinogens regulated by EPA have dose-response relationships based on human data from epidemiologic studies the remainder are based on animal bioassays. In contrast, the dose-response relationships for radiation are based primarily on the results of human epidemiologic studies. 

The doses of hazardous substances at which responses can be observed in humans or animals are higher (sometimes by large factors) than doses relevant to waste disposal and other routine exposure situations. Therefore, most dose-response relationships at the low doses of interest in protection of human health are calculated rather than measured they are based not only on scientific data but also on various assumptions and extrapolation models which, while scientifically plausible, cannot yet be subjected to empirical study 

8 In general, the relationship between dose and response can be represented by a variety of functional forms. At low doses of substances that cause stochastic effects, the dose-response relationship usually is assumed to be linear and, thus, can be expressed as a single probability coefficient. This coefficient is frequently referred to as a risk (or potency factor or unit risk factor or slope factor) in the literature. However, it is really the response (consequence) resulting from a dose of a hazardous substance, and it should not be confused with risk as defined and used in this Report. 

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