Percutaneous absorption of [formula omitted] from soil

Abstract

The objective was to determine percutaneous absorption of DDT and benzo[ a]pyrene in vitro and in vivo from soil into and through skin. Soil (Yolo County 65-California-57-8; 26% sand, 26% clay, 48% silt) was passed through 10-, 20-, and 48-mesh sieves. Soil then retained by 80-mesh was mixed with [ 14 C]-labeled chemical at 10 ppm. Acetone solutions at 10 ppm were prepared for comparative analysis. Human cadaver skin was dermatomed to 500 μm and used in glass diffusion cells with human plasma as the receptor fluid (3 ml/hr flow rate) for a 24-hr skin application time. With acetone vehicle, DDT (18.1 ± 13.4%) readily penetrated into human skin. Significantly less DDT (1.0 ± 0.7%) penetrated into human skin from soil. DDT would not partition from human skin into human plasma in the receptor phase (<0.1%). With acetone vehicle, benzo[ a]pyrene (23.7 ± 9.7%) readily penetrated into human skin. Significantly less benzo[ a]pyrene (1.4 ± 0.9%) penetrated into human skin from soil. Benzo[ a]pyrene would not partition from human skin into human plasma in the receptor phase (<0.1%). Substantivity (skin retention) was investigated by applying 14 C-labeled chemical to human skin in vitro for only 25 min. After soap and water wash, 16.7 ± 13.2% of DDT applied in acetone remained absorbed to skin. With soil only 0.25 ± 0.11% of DDT remained absorbed to skin. After soap and water wash 5.1 ± 2.1% of benzo[ a]pyrene applied in acetone remained absorbed to skin. With soil only 0.14 ± 0.13% of benzo[ a]pyrene remained absorbed to skin. In vivo percutaneous absorption of DDT in rhesus monkey was significantly less ( p < 0.02) from soil (3.3 ± 0.5%) than from acetone solution (18.9 ± 9.4%). DDT in vitro skin penetration values into human skin were similar to in vivo absorption values in the rhesus monkey. In vivo absorption in the rhesus was not statistically different from published in vivo absorption in man (10.4 ± 3.6%). In vivo percutaneous absorption of benzo[ a]pyrene in rhesus monkey was significantly less ( p < 0.015) from soil (13.2 ± 3.4%) than from acetone solution (51.0 ± 13.2%). Thus, with in vitro and animal in vivo systems relevant to man, skin absorption of DDT and benzo[ a]pyrene from soil was significantly less than when the chemicals were applied to skin in acetone solvent.