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I Ile SECTIONSIIX 11I3Kilhaea eflnuo® 6.9 INTRODUCTION Risk characterization is the final step of the risk assessment process In this step, the toxicity factors (RfDs and cancer SFs from Section S 0) for the chemicals of concern are applied in conjunction with estimated chenucal intakes to evaluate potential noncarcinogeruc and carcinogenic health risks to exposed individuals The potential for noncarcinogenic effects is characterized by comparing estimated daily chemical intakes with chemical-specific RfDs Potential carcinogenic effects are characterized in terms of the incremental or excess probability that an individual will develop cancer in lus or her lifetime due to the estimated exposure Excess cancer risk is estimated from the projected average daily intakes and the cancer slope factor, which represents an upper-bound estimate of the dose-response relationship Potential health risks associated with potential exposures are presented in Section 6 3 Uncertainties inherent in the risk assessment process are presented in Section 7 6.2 METHODOLOGY FOR QUANTITATIVE RISK ESTIMATION 6.2.1 Hazard Index for Moncarcinogenic Effects The potential for adverse noncarcinogenic effects resulting from exposure to a chemical of concern rs evaluated by comparing the average daily intake of the chemical (expressed as mg/kg-day) to a reference dose(expressed as mg/kg-day) The resulting ratio is called a hazard quotient (EPA 1989b) It is derived in the following manner Noncancer Hazard Quotient= Chemical Intake m -da RfD(mfg-day) Use of the Rfl) assumes a level of intake (the RfD) below which it is unlikely that even sensitive individuals will experience adverse health effects over a lifetime exposure If the average daily intake exceeds the RfD (that is, if the hazard quotient exceeds 10), there may be cause for concern for potential noncancer effects It should be noted, however, that the level of concern does not increase linearly as the RfD is approached or exceeded This is because all Ms. are not equally accurate and are not based on the same seventy of toxic effects Thus, the slopes of the dose-response curve in excess of the RfD can vary widely depending on the substance Furthermore, it must be emphasized that the hazard quotient does not represent a statistical probability of an effect occurring To assess the overall potential for adverse health effects posed by exposure to multiple chemicals, the hazard quotients for each chemical of concerti associated with a given exposure pathway are summed 711887\873000NA%STOCKTON%REPORT Si1OREM DOCO-FEMM73009NAMA 6-1