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

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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.