Exposure to the insect repellent N,N-Diethyl-m-Toluamide (DEET) in the United States

Background: In 1946, the US Army developed N, N-Diethyl-m-toluamide (DEET). Since then, DEET has become the most effective and ubiquitous insect repellent in the United States. There are hundreds of insect repellent commercial formulations containing DEET at concentrations ranging from 4% to 100%, and human exposure to DEET is expected to occur. However, information on the extent of such exposure is rather limited. Aims: To evaluate human exposure to DEET by using the urinary concentrations of DEET and several of its metabolites. Methods: We determined the urinary concentrations of DEET and three DEET metabolites—N-ethyl-3-methylbenzamide (M1), N, N-diethyl-3-hydroxymethylbenzamide (M3), and 3-(diethylcarbamoyl)benzoic acid (M4)—by on-line solid-phase extraction–isotope dilution-high performance liquid chromatography–tandem mass spectrometry in convenience samples of U.S. residents with no known occupational exposure to DEET. Results: We detected M4, and to a lesser extent M1, most frequently and at the highest concentrations. By contrast, we detected DEET much less frequently and at concentrations orders of magnitude lower than those of M4. Conclusions: The significantly higher frequency of detection and urinary concentrations of certain DEET metabolites (e.g., M4, M1) than of DEET confirm the validity of these metabolites as biomarkers for DEET exposure assessment and suggests widespread exposure to DEET among the U.S. general population. More important, these data also suggest that the occurrence of exposure to DEET could be underestimated by using DEET as the sole urinary biomarker, particularly when evaluating background envi­ronmental exposures.