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Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br /> terms of the Cancer Slope Factor. The Cancer Slope Factor is the uppc 95 percent confidence <br /> limit on the probability of a carcinogenic response per daily intake of a chemical over a lifetime. <br />' Therefore, the Cancer Slope Factor is likely to overestimate the actt..-: potency of a chemical. <br /> 4.1.1 Benzene <br /> The Cancer Slope Factor for benzene is 0.029 (mg/kg-day)-` for the inhalation and oral exposure <br />' routes (EPA, 1991). The Cancer Slope Factor for benzene is based inhalation and oral <br /> exposures to benzene resulting from occupational activities (Ott et al., 1978; Rinsky et al., 1981; <br />' Wong et al., 1983: EPA, 1985e, 1987, 1989c). <br /> 4.2 NONCARCINOGENIC RESPONSE <br /> The safety factor approach is used to estimate effects that have a threshold. The safety factor <br /> approach is an appropriate method of estimating the effects in hu;fans if a dose-response <br /> relationship is unknown, cannot be accurately estimated, or models a threshold event. The <br /> concept of a threshold event is based on the assumption that there is a dose below which there <br /> is no effect. Health criteria levels are usually estimated from the no--observed adverse effect <br /> level (NOAEL) or the lowest observed adverse effect level (LOAEL,i determined in chronic <br /> ' animal studies. The NOAEL is defined as the highest dose at which ),,-, adverse effects occur. <br /> The LOAEL is defined as the lowest dose at which adverse effects be,in to appear. NOAEL <br /> and LOAEL derived from animal studies are used by the EPA to establish oral and inhalation <br /> Reference Doses and Reference Concentrations for human exposures. The Reference Dose is <br /> the dose to which an individual may be exposed daily for an entire lifetime without experiencing <br /> adverse health effects. The Reference Concentration is the concentration of a chemical in air <br /> to which an individual may be continually exposed for an entire lifeti,cc without experiencing <br /> ' adverse health effects. <br /> ' 4.2.1 Toluene <br /> ' The subchronic and chronic Reference Concentration for toluene is 2 mgim3 (EPA, 1991). The <br /> EPA derived subchronic and chronic oral Reference Doses for toluotte are 2 mg/kg-day and <br /> titin ♦ rr r 1- 7 -1_17-1- .L <br /> 0.2 mg/kg-day, respectively (EPA, 1771). The eilect U1 CU-11CL—TH C0.11SKIC1CU III GSLdMISHILIg L110 <br /> 1 r. <br /> 30-0136-11 4-3 <br /> 1 <br />