Effects of soil on the dermal bioavailability of m-xylene in male rats

Bioavailability of a chemical absorbed through the skin from contaminated soil may differ from that seen following exposure to the pure chemical. The objective of this research was to qualitatively and quantitatively assess the absorption, distribution, excretion, and metabolism of soil-adsorbed m-xylene versus pure m-xylene so that the potential for public health risk following dermal exposure could be evaluated. In this study a shallow glass cap covering a 13-cm2 area was fixed to the shaved skin of each male rat (6-10 rats per group) followed by the addition of 225 microliters of m-xylene containing 20 muCi of m-[14C]xylene alone or with one of two soils. Maximum plasma levels of radioactivity were highest for pure m-xylene while the values for the sandy and clay soil groups were approximately equal. Although clay soil statistically decreased the rate of absorption, the half-lives of elimination and the area under the plasma concentration time curve were not changed by either soil. The major route of excretion in the pure and sandy groups was via expired air followed by urine. However, in the presence of clay soil, the percentage of the initial dose in expired air was similar to that in urine. Forty-eight hours after treatment, skin application sites in both soil treatment groups contained amounts of radioactivity significantly higher than those of m-xylene treatment alone. In the presence of clay soil a statistical increase in m-xylene-derived radioactivity was also observed in fat beneath the treated skin area. Metabolite analysis by HPLC indicated that methylhippuric acid was the main urinary metabolite followed by xylenol and the parent compound in all groups.