Deet is the main ingredient of insect repellent  and will be washed off from human skin and enter wastewater.  Deet are poorly adsorbed by soils and the metabolism of deet is slow, and thus they have the potential to reach groundwater under recharge conditions in semiarid climates. In Mezquital valley, it appears to be the highest detection frequencies in groundwater.

There is very little information about the microbial metabolism of DEET. Only partial degradation by the fungi Cunninghamella elegans and Mucor ramannianus R-56, via N oxidation and N deethylation, has been shown previously. Though DEET is not expected to bioaccumulate, it has been found to have a slight toxicity for freshwater fish such as rainbow trout and tilapia, and it also has been shown to be toxic for some species of freshwater zooplankton.