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

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 +/- 1.7% 14C recovery after 24 h with [14C]fenitrothion in DEET versus 1.9 +/- 0.3% without DEET). Significantly greater (p less than 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 with 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