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.
Xylenes are resistant to hydrolysis, since there are no hydrolyzable functions.
Combining this ratio with oxygen reaeration rates for typical bodies of water, one estimates that the half-life for evaporation of xylenes from a typical river or pond is 29 and 144 hr, respectively. Xylenes are moderately mobile in soil and may leach into groundwater where they are known to persist for several years, despite some evidence that they biodegrade in both soil and groundwater. This evidence includes standard biodegradability tests using various inocula including sewage, activated sludge and sea water, where mixtures are completely degraded in 8 days in groundwater with an acclimation period of 3-4 days. Xylenes have been observed to pass through soil at a dune-infiltration site on the Rhine River and to leach into groundwater under a rapid infiltration site. Bioconcentration is not expected to be significant.