Comparison between oral and dermal bioavailability of soil-adsorbed phenanthrene in female rats

Phenathrene is a major coal tar component found in hazardous waste disposal sites. The purpose of this study was to evaluate the extent to which phenanthrene adsorption to either of 2 different soils affects the manner in which phenanthrene is subsequently handled in orally and dermally exposed adult female rats. Absorption from the gastrointestinal tract was relatively rapid for all treatments with maximum plasma concentration of radioactivity occurring within 1 h following oral administration. After dermal application, the time to reach maximum plasma concentration (12 h) was the same in all 3 phenanthrene treatment groups although sandy soil lowered the area under the plasma concentration time curve (AUC) compared to the pure and clay soil groups. Dermal exposure increased absorption half-lives 8-fold compared to oral exposure in the pure group and 15-fold in each of the soil groups. After oral or dermal treatment with phenanthrene alone or adsorbed to soil, the urine represented the primary excretion route of 14C activity. Ileum contained the highest tissue concentration of radioactivity in all oral treatment groups. However, the skin application site contained the highest concentration of radioactivity followed by ileum after dermal exposure. Phenanthrenequinone and 9,10-phenanthrene dihydrodiol were the major urinary metabolites detected in the 0-12-h urine of all treatment groups in both routes of administration. The data suggest that the oral exposure route for phenanthrene is a greater health risk than the dermal route. However, the presence of sandy or clay soil tends to delay the elimination of phenanthrene from the plasma.