Percutaneous absorption and dermal dose-cholinesterase response studies with parathion and carbaryl in the rat

Dermal dose-ChE response (toxicity) and percutaneous absorption of parathion and carbaryl were studied in the rat. Parathion was as toxic to young animals as it was to adults of the same sex and more toxic to adult females than to adult males. Carbaryl was nontoxic at administered dosages. In each percutaneous absorption study, [14C]parathion or [14C]carbaryl was applied to back skin (12.5-13.8 cm2) at 43.5 to 48 micrograms/cm2. Thirty-six rats were treated and three were killed at time intervals between 0.5 and 168 hr. The area of the skin which had been treated, plasma, heart, liver, kidneys, urine, feces, and the remaining carcass were analyzed for 14C. Recovery studies indicated that adult male and female rats, respectively, absorbed 59.2 and 57.0% of the applied parathion, while adult males absorbed 57.7% of the applied carbaryl. Parathion was lost from skin (t1/2, 28.6 hr) more rapidly than carbaryl (t1/2, 40.6 hr). Approximately 1.4 and 5.8%, respectively, of the applied parathion and carbaryl penetrated the skin within 1 hr and was available for absorption. Parathion was absorbed through skin of adult male and female rats, respectively, at rates of 0.33 and 0.49 micrograms hr-1 cm-2. Carbaryl was absorbed by male rats at the rate of 0.18 micrograms hr-1 cm-2. The half-lives for absorption of parathion by blood ranged between 0.38 and 2.1 hr, while elimination half-lives ranged between 28.6 and 39.5 hr. Carbaryl absorption and elimination half-lives were 1.26 and 67 hr, respectively.