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Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> E Tracy, California <br /> low levels of toluene produce depressant effects whereas higher cone-itrations have excitatory <br /> effects (EPA, 1984). <br />:1 <br /> 3.4 ETHYLBENZENE <br /> Ethylbenzene is an aromatic hydrocarbon (CsH,o) with a molecular weight of 106.17. Also <br /> known as phenylethane, this compound is a colorless, flammable liquid with a pungent odor <br /> r (Clayton and Clayton, 1981). It is insoluble in water and miscible with organic solvents <br /> (Merck, 1989). With its moderately high vapor pressure and high Henry's Law constant, <br /> ' ethylbenzene has a tendency to readily evaporate from water and soil (EPA, cm). <br /> Ethylbenzene is used as a solvent, as an intermediate in styrene' and synthetic polymer <br /> production, and as a component in automotive and aviation fuels (Clayton and Clayton, 1981). <br /> The chemical and physical properties of ethylbenzene are summarized =n Table 3-6. <br /> Concentrations of ethylbenzene in gasoline typically range from less than I percent to <br /> approximately 3 percent (CLUFTFM, 1989). Ethylbenzene is abs.Yrbed through inhalation, <br /> ingestion, and, to a lesser extent, dermal absorption (Clayton and Clayton, 1981). It is <br /> distributed throughout the body, and due to its lipophilic nature, cumulates primarily in <br /> adipose tissue (EPA, 1985c). In humans, 64 to 70 percent of the com,.ound is metabolized and <br /> ' the remainder is eliminated unchanged. <br /> 3.5 XYLENES <br /> 1 <br /> Commercial xylenes are a mixture of three isomers: ortho, meta, and ;,ara. The three isomers <br /> ' possess similar chemical and physical properties and comprise approximately 3 to 8 percent of <br /> total gasoline constituents (CLUFTFM, 1989). Xylenes are a colorless Iiquid with a mild, sweet <br /> ' odor and a molecular weight of 106.2. The substance is practically insoluble in water, but <br /> miscible with many organic solvents (EPA, 1985d). It is found in many petroleum products, <br /> coal naphthas, and as an impurity in petrochemicals such as benzene, toluene, and similar <br /> ' chemicals. The physical and chemical properties of xylenes are summarized in Table 3-7. <br /> 30-0136-11 <br /> 1. 3-11 <br />