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. There is inadequate evidence to state whether or not xylenes have the potential to cause cancer from lifetime exposures in drinking water. Most consumption of xylene mixtures is to produce the individual isomers, particularly p-xylene. As individual isomers they are extensively employed in the synthesis of synthetic agents. For example, phthalic acid, isophthalic acid, terephthalic acid, and diemthylterephthalate have very broad applications in the further preparation of phthalate ester plasticizers and components of polyester fiber, film and fabricated items.
Xylenes are a natural products of many plants, and are a component of petroleum and coal tar.
From 1987 to 1993, according to EPA's Toxic Chemical Release Inventory, xylene releases to land and water totalled nearly 4.8 billion lbs., of which about 81 percent was to land. These releases were primarily from petroleum industries which produce xylenes as by-products of gasoline refining. The largest releases occurred in Texas. The largest direct releases to water occurred in New Jersey and Georgia. The dominant removal process in water is volatilization.