Absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) after low dose dermal exposure

Human dermal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) occurs through contact with soil and paper products. In a previous study, relative percutaneous absorption of TCDD increased as the dose decreased (Brewster et al., 1989). To determine the rate of absorption of a low dose of TCDD, absorption, distribution, and elimination were examined at 1, 4, 8, 12, 24, 48, 72, and 120 hr after dermal application of 200 pmol (111 pmol/cm2) [3H]TCDD to 10-week-old male Fischer 344 rats. The compound was applied over a 1.8 cm2 area of the interscapular region of the back in 60 microliters acetone and covered with a perforated cap; animals were held in individual metabolism cages. Within 120 hr after dosing, 82 pmol (26 ng) of TCDD was absorbed. Absorption kinetics appeared to be first-order; the absorption rate constant was 0.005 hr-1. At each time point, greater than 70% of the radioactivity detected in the application site could be removed by swabbing with acetone. The time-related increase in the amount of TCDD in liver and fat closely paralleled the amount absorbed, while the percentage of the administered dose detected in the blood was never greater than 0.3%. Thus, absorption of a low dose of TCDD through the skin is extremely slow and appears to be a first-order process.