Dermal absorption of chemicals: Effect of application of chemicals as a solid, aqueous paste, suspension, or in volatile vehicle

Abstract

The purpose of this study was to investigate the dermal absorption of chemicals in different physical forms when applied to female F344 rats. Chemicals were applied either as a solid, aqueous paste, suspension, or dissolved in the volatile vehicle etha‐nol. The chemicals investigated were [¹⁴C]‐2‐sec‐butyl‐4,6‐dinitrophenol (DNBP, 4.2 μmol), 2,4,5,2’ ,4’ ,5’ ‐[¹⁴C]‐hexachlorobiphenyl (HCB, 2.3 μmol), and 3,4,3’,4'‐[¹⁴C]‐tetrachlorobiphenyl (TCB, 0.5 μmol). The chemicals were applied on the clipped mid‐dorsal region of the rat over a 2.54‐cm² treatment area, which was then occluded. Urine and feces were collected and assayed for radioactivity. Twenty‐four hours post‐application, the treated skin was washed with a mixture (1:1) of soap and water, dried, and reoccluded. The animals were sacrificed at 120 h by exsanguination under ether anesthesia. Radioactivity in the blood, skin (treated and untreated), and carcass was assayed. Dermal absorption of DNBP‐derived radioactivity was approximately 50% of the recovered dose after application in the four physical forms, and the major route of excretion was via the urine. Twelve percent of the absorbed dose of DNBP was retained in the body. Dermal penetration of HCB‐derived radioactivity was 5–8% of the recovered dose after application in the four forms, and the major route of excretion was via the feces. Greater than 90% of the absorbed dose of HCB‐derived radioactivity was retained in the body. Dermal penetration of TCB‐derived radioactivity was 6–8% of the recovered dose in the four forms, and the major route of excretion was via the feces. Approximately 21% of the absorbed dose was retained in the body at 120 h. Absorption of each chemical applied either as solid, aqueous paste, or suspension was compared to the absorption of the same chemical in ethanol. Absorption of HCB applied as a solid was significantly higher (p < .05) as compared to HCB applied in ethanol. There were no other significant differences in the comparisons of absorption. The data indicate that the chemicals examined in this study can penetrate the skin as readily when applied either as a solid, aqueous paste, or suspension, as when applied in the volatile vehicle ethanol.