RISK ASSESSMENT OF CHEMICAL-MIXTURES FROM A PUBLIC-HEALTH PERSPECTIVE

Health risk assessment is the practice of evaluating the degree of dan ger associated with chemical exposure, whether the exposure is intenti onal (pharmacologic agents, pesticides) or unintentional (industrial/a utomobile by-products). Chemical exposure can either be to a single ch emical or to complex mixtures such as industrial effluents, municipal wastes, jet fuels, gasoline, or mixtures of drinking water contaminant s. The mixtures can be simple or complex; partially or completely char acterized; and stable or varying in composition. Three different appro aches are often used in health risk assessment of chemical mixtures (5 1 FR 33992-34054). These 3 approaches consist of (a) use of data on th e specific mixture of concern; (b) use of data on a similar mixture; a nd (c) use of data on each component of the mixture. The individual co mponent-based approach is by far the most often used because it allows the individual risks from each component to be combined, usually by d ose or response additivity, to calculate an overall risk for the mixtu re. In addition, several innovative methods, such as the toxicity equi valency factor, relative potency, and even the use of indicator chemic als, are also employed. More recently, a binary weight-of-evidence app roach has been proposed to evaluate potential interactions between the various components and to integrate them into the overall toxicity as sessment of the mixture. Because no single approach is suitable for as sessing the health risk associated with all the exposure scenarios ass ociated with the various types of mixtures, the use of professional ju dgment is still imperative in conducting health risk assessments.