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ii.yjJ'’ <br />¥ <br />t" <br />V: <br />v{\- <br />>■:— <br />•i-0.ir <br />:•■ r ' <br />ti?. <br />I""m <br />t <br />I? <br />ir-' <br />i:t" <br />f'% <br />I <br />f’ <br />I: <br />lp;t' <br />»■ <br />f> <br />:«. * » <br />92-47.03 <br />population, including sensitive subpopulations, that is likely to <br />be without an appreciable risk of deleterious effects". The RfD <br />is derived from human data, if available, or animal data and <br />represents "the highest level tested at which no adverse affects <br />. . . were demonstrated". It should be emphasized that the RfD <br />is a level at which no health effects have been shown, even to <br />more sensitive members of a population. <br />leve 1"The noncancer hazard quotient assumes that there is a <br />of exposure (i.e., RfD) below which it is unlikely for even <br />sensitive populations to experience adverse health effects" <br />(U.S. EPA, 1989). The hazard quotient is a measure used to <br />describe the potential for noncarcinogenic effects to occur in an <br />individual, but it does not express the probability of an effect <br />occurring. The following example explains the approach of <br />evaluating noncarcinogenic risks. <br />Assume that the U.S. EPA declares that the highest no­ <br />effect-level (RfD) for a certain compound is 5 milligrams per <br />day. Assume further that site data indicate that a person is <br />exposed to 2 milligrams of this compound per day. The ratio of <br />the site specific amount and the U.S. EPA's published value is <br />2/5 or 0.4, which is less than 1, where 1 is the level that <br />adverse effects mav begin to appear. <br />According to U.S. EPA guidelines (U.S. EPA, 1989), if the <br />Hazard Quotient is greater than unity (1), "there may be concern <br />for potential health effects". It is therefore desirable that: <br />Hazard Quotient < 1 <br />To assess the overall potential for noncarcinogenic effects <br />when there is more than one chemical of concern, individual <br />Hazard Quotients for a given exposure situation are summed to <br />provide a Hazard Index (U.S. EPA, 1989). <br />Hazard Index = ^ Hazard Quotients <br />As with the Hazard Quotient, when the Hazard Index is lower <br />than 1, there should be no impact and therefore it is desirable <br />that <br />Hazard Index < 1 <br />Carcinogenic risks are computed similarly to the <br />noncarcinogenic risks by multiplying the doses with the CSFs. <br />Therefore, <br />Carcinogenic Risk = Dose x CSF <br />12