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Risk assessment is defined by the National Academy of Sciences as the characterization of <br /> the probability of potentially adverse health effects from human exposures to environmental <br /> hazards (NAS, 1983). The risk assessment process is usually divided into four steps <br /> • Hazard identification <br /> • Dose-Response Assessment <br /> • Exposure Assessment <br /> • Risk Characterization (NAS, 1983; EPA, 1986) <br /> Hazard Identification is a qualitative assessment that contains a review of the relevant <br /> biological and chemical information to deternune whether or not exposure to an agent may <br /> pose a hazard or increase the incidence of a health condition or effect (e g, cancer, birth <br /> defects, etc ) (NAS, 1983, EPA, 1986) The available information is melded into a weight- <br /> of-evidence determination <br /> To evaluate the effects of chemicals in humans, epidemiological studies must be evaluated <br /> in terms of the study design, strengths and weaknesses of the study, and statistical power of <br /> the study. Epidemiological evidence can be used to define the "human experience" with <br /> • exposures to the chemical to determine whether effects in humans would be expected If <br /> no human studies on the endpoint exist, then the animal studies may be reviewed to <br /> determine the potential for human health effects In this circumstance, the design of the <br /> animal study must be considered For example, high doses produce multiple effects in <br /> animals and compromise the animal's ability to respond If normal defense mechanisms are <br /> saturated at these high exposure Ievels, then the ability of the animals to handle the <br /> chemical challenge is compromised. The usefulness of an extrapolation of this study to <br /> much lower human exposure levels where defense mechanisms would be expected to be <br /> intact is reduced. The Hazard Identification must evaluate the animal data to assist in <br /> understanding the potential for human health effects <br /> A Dose-Response Assessment is the process of characterizing the quantitative relationship <br /> between the dose of an agent and the incidence of adverse health effects in exposed <br /> populations (NAS, 1983) The end result of the dose-response assessment is a probability <br /> estimate of the incidence of the adverse effect as a function of human exposure to the <br /> chemical. Two endpoints are evaluated separately noncarcinogenic and carcinogenic <br /> effects. <br /> UM»AMFNLUm%W 2693 1-3 wk* IM <br />