The effect of DEET (N,N‐diethyl‐m‐toluamide) on dermal persistence and absorption of the insecticide fenitrothion in rats and monkeys

Abstract

The in vitro persistence of ¹⁴C‐ring‐labeled fenitrothion in acetone (F‐A) or N,N‐diethyl‐m‐toluamide (DEET) (F‐D) vehicles was determined, and in vivo studies were conducted to determine the persistence and absorption of [¹⁴C]fenitrothion in acetone or DEET applied to the skin of rats and rhesus monkeys. In vitro persistence of [¹⁴C]fenitrothion was significantly enhanced in DEET vehicle, and the percent residual ¹⁴C activity at 24 h was positively correlated with the amount (micrograms) of DEET employed (e.g., in vitro, 98.6 ± 7.7% ¹⁴C recovery after 24 h with [¹⁴C]fenitrothion in DEET versus 1.9 ± 0.3% without DEET).

Significantly greater (p < 0.05) fenitrothion ¹⁴C activity was detected in skin swabs taken after 24 h at the dose site with DEET vehicle from rats [acetone (F‐A): 15.0 ± 5.8%; DEET (F‐D): 31.5 ± 3.9%)] and monkeys (F‐A: 3.2 + 1.5%; F‐D: 9.7 ± 6.0%). A lag in the urinary excretion kinetics was observed for F‐D in comparison with F‐A for both rats and monkeys. The total percent urinary ¹⁴C recovery was significantly higher in rats dosed wth F‐A (73.0 ± 7.4%) than with F‐D (52.4 ± 8.8%) but not in monkeys (F‐A: 34.7 ± 7.1%; F‐D: 36.7 ± 2.9%). The observed species‐related differences are discussed in context with the use of animal models for predicting dermal penetration of pesticides in humans.