Finite dermal absorption after low dose TCDD exposure

Human dermal exposure to TCDD occurs through contact with soil and paper products. Relative dermal absorption of TCDD increases as the dose decreases. At doses approaching environmental levels, the absorption time course may have important implications for human dermal exposure. In order to examine the time course, the absorption, distribution and elimination were examined at 1, 4, 8, 12, 24, 48, 72, and 120 hr after dermal application of 0.2 nmol 3H-TCDD to 10 week male Fischer 344 rats. The compound was applied to the intrascapular region of the back at dose of 0.2 nmol in 60 μl acetone and covered with a perforated cap; animals were held individual metabolism cages. Within 120 hr after dosing, 82 pmol (26 ngram) of TCDD was absorbed. A constant amount of TCDD was absorbed per hour up to 48 hr after application; during this period the absorption rate was 1.5 pmol/hr (0.5 ngram/hr). For the next 72 hr little additional absorption occurred. At each time point, greater than 70% of the radioactivity 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 blood levels were never greater than 0.3% of the administered dose. Thus, absorption of TCDD through the skin from environmentally relevant concentrations is extremely slow and is essentially complete within 48 hours following exposure