An overview of environmental and toxicological aspects of aromatic hydrocarbons. III. Xylene.

The commercial product "mixed xylenes" (a technical product generally containing approximately 40% m-xylene and 20% each of o-xylene, p-xylene and ethylbenzene, as well as small quantities of toluene) analogously to toluene is an agent of major chemical and occupational significance. It is produced in very large quantities and is extensively employed in a broad spectrum of applications, primarily as a solvent for which its use is increasing as a "safe" replacement for benzene, and in gasoline as part of the BTX component (benzene-toluene-xylene); xylenes are also frequently used in the rubber industry with other solvents such as toluene and benzene. As individual isomers they are extensively employed in the synthesis of synthetic agents, for example phthalic acid, isophthalic acid, terephthalic acid and dimethylterephthalate, which have very broad applications in the further preparation of phthalate ester plasticizers and components of polyester fiber, film and fabricated items. There is a broad potential for exposure both to industrial workers in the production and use of the xylenes and to the general public (via vehicle exhausts, consumer products, etc). Compared with benzene and toluene, very much less is known of the human health hazards, particularly the chronic effects of xylenes, either as mixed xylenes, as individual isomers or in admixture with other alkylbenzenes. It is of importance to note that coal-based solvents (e.g., xylene) have been suggested to be possible potent lymphocytic leukemogens, such as benzene, in a limited study of the relationship between lymphocytic leukemia and exposures to benzene and other solvents in the rubber industry. Available animal data on the carcinogenicity of xylene(s) are inadequate to permit an evaluation. Mixed xylenes are currently being investigated in a chronic bioassay by the National Toxicology Program. In limited studies thus far, the individual isomers have not been found genotoxic when tested in a number of short-term tests.