Assessment of the environmental fate and ecotoxicity of N,N-diethyl-m-toluamide (DEET).

N,N-diethyl-m-toluamide (DEET) is a key active ingredient in many insect repellents available commercially throughout the world. Owing to its popularity among consumers for nearly 30 years, considerable work conducted in the past has demonstrated-and continues to demonstrate-that human exposure to DEET poses no significant health risk to the general population. The results of several studies reported in this paper describe more recent work to understand the environmental fate of DEET, particularly in surface waters and soil, and the potential hazards to aquatic and terrestrial organisms. In summary, DEET enters the environment through several pathways: directly into air during spray application; to surface water from overspray and indirectly via wastewater treatment plant (WTTP) discharges (as a result of washing of skin and laundering of clothing); or to soil via overspray and application of treated sewage as an amendment. Multimedia environmental fate modeling predicts that DEET entering the environment is retained either in receiving waters (∼79%) or in soil (∼21%). Based on its physicochemical properties, DEET is expected to be moderately mobile in the soil column. In surface waters and soil, DEET degrades at a moderate to rapid rate (its half-life is measured in days to weeks). The small amounts of DEET retained in air are subject to rapid photo-oxidation via hydroxyl radical-mediated degradation or, if in droplet form, gravitational settling to soil or water. DEET does not interfere with ozone formation in the upper atmosphere. The bioaccumulation potential of DEET is low; it is neither a persistent, bioaccumulative toxicant nor a persistent organic pollutant. Among aquatic species, acute effect concentrations range between 4 and 388 mg/L. The chronic no-observed effect concentrations (NOEC) for daphnids and green algae range from approximately 0.5 to 24 mg/L. Measured concentrations of DEET in surface waters are several hundreds to thousands of times lower than the lowest NOEC measured, and thus the probability for adverse effects to environmental species is low. A separate paper by Aronson et al. (this issue) supports this conclusion by quantitatively exploring the risks to the aquatic environment using a combination of monitoring data and exposure modeling.