Maximum dermal absorption of TCDD occurs in weanling rats

Structural and functional changes which occur in maturing and aging skin may alter the dermal absorption of xenobiotics, including halogenated aromatics. Among these persistent environmental contaminants, TCDD is by far the most toxic. In order to examine age-related changes in potential for systemic exposure to TCDD following dermal exposure, the absorption, distribution, and elimination of the compound were evaluated in male Fischer 344 rats during maturation (3,5, and 8 wks). 3H-TCDD was applied to the back at a dose of 0.2 nmol in 60 μl acetone and covered with a perforated cap. The treated animals were held in individual metabolism cages for 3 days, and radioactivity was determined in tissues and excreta. Dose distribution to tissues was aided by measurements of body composition of male F344 rats which yielded a linear relationship between body weight and adipose tissue content. Absorption in the weanling (3 wk) animals was 65% of the administered dose, while the 5-and 8-wk groups absorbed only 35-40%. Major tissues depots for TCDD were the liver, fat, skin, and muscle. Elimination was limited in all groups. Results degree through very young skin, and that a significant decrease in potential for systemic exposure via the skin may occur during maturation, preceding an additional decline during aging