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Human Health Risk Assessment 0 Former Mobil Oil Bulk Plant 04-343 I 500 East Grant Line Road Tray, California r effects (API, 1986). The IARC (1982) reports that a relationship between benzene and acute myelogenous leukemia has been established in epidemiological stt dies performed among shoemakers and workers in the rubber, printing, and petroleum industries. These studies have been criticized, however, particularly regarding the association of the in ,deuce of leukemia with ' the low concentrations of benzene measured in these industries (API, 1986). Benzene has been placed into Group A, "known human carcinogen," under the EPA weight-of-evidence classification. I 3.3 TOLUENE Toluene is a monocyclic aromatic hydrocarbon (C6H5CH3) with a mol,•..;ular weight of 92.1. It is the lowest molecular weight member of the alkylbenzenes. Alkylbet�,%:nes, in general, possess properties similar to those described for benzene. Toluene is found in gasoline at concentrations ' ranging from approximately 3 to 22 percent (CLUFTFM, 1989). Alkti. - substitutions change the physical characteristic of toluene and, in turn, alter its absorption, partition, and metabolic properties. Toluene is a clear, colorless liquid with a pungent, benzene-like odor (EPA, 1985b). It is only slightly soluble in water, and is soluble in alcohol, ether, chloroform, acetone, glacial acetic acid, and carbon disulfide (Merck, 1989). Chemical processes and photochemical ' processes appear unlikely to compete significantly with volatilizatio;) and biodegradation as removal processes (EPA, 1985b). The physical and chemical pn iperties of toluene are summarized in Table 3--5. Toluene is readily absorbed in the lungs as a vapor and in the gastroin,estinal tract as a liquid. Once absorbed, the major excretory pathway is rapid oxidation of toluene to benzoic acid, which is conjugated with glycine and excreted as hippuric acid in urine. E:._cretion of hippuric acid ' may be proportional to exposure (Doull et al., 1980). Toluene ma ., be eliminated through respiration. Inspired toluene has an estimated biological half-life of 0.083 days ' (Cleland and Kingsbury, 1977). The odor threshold of toluene is 10.15 ppm, and at concentrations bef.,veen 300 and 400 ppm, ' eye irritation is experienced (OSHA, 1978). Perceptual speed is not significantly affected until exposure exceeds 700 ppm for a period of 20 minutes (EPA, 1985b). Evidence indicates that 30-0136-11 i 3-10 i