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OCR for page 19
DEFINITIONS OF SELECTED TERMS Exposure: Contact with a substance by ingesting it, breathing it, or touching it with the skin or eyes. Exposure assessment: A determination of how people come into contact with a hazardous substance, how often and for how long they are in contact with it, and how much of it they are in contact with. Hazard: A source of potential harm from past, current, or future exposures. Minimal risk level: An Agency for Toxic Substances and Disease Registry estimate of daily human exposure to a hazardous substance at or below which the substance is unlikely to pose a measurable risk of harmful noncancerous effects. Reference dose: Defined by the Environmental Protection Agency as an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure of the human population (including sensitive groups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Generally used in noncancer health assessments. Risk: The probability of adverse effects of exposure to an environmental agent. Slope factor: Defined by the Environmental Protection Agency as an upper bound, approximating a 95% confidence limit, on the increased cancer risk posed by lifetime exposure to an agent. It is usually expressed in units of proportion (of a population) affected per mg/kg per day and is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks of less than 1 in 100. Standardized incidence ratio: The ratio of the number of observed cancer cases in a study population to the number expected in a standard population. If the ratio is greater than 1.0, it is said that there are excess cancers in the study population. 19