Photolytic degradation of N,N-diethyl-m-toluamide in ice and water: Implications in its environmental fate

• Photoinduced DEET degradation was investigated in water and ice.
• Different paths of transformation occur in temperate or cold environments.
• N-dealkylated TPs are marker of a photolysis process occurring in frozen phase.

The photochemical transformation of N,N-diethyl-m-toluamide (DEET), one of the most widespread and efficient mosquito repellents, has been investigated. Initially, photoinduced DEET degradation was investigated in liquid samples, at 20 °C and 0 °C, and in ice (−15 °C), aimed to simulate all possible photoinduced processes occurring in water and in cold environments. Under UV-illumination, DEET degradation was more efficient in ice than in water. The evaluation of transformation products (TPs) formed during the photolysis in solution and in ice evidences mostly the same degradation products, but with different concentration ratio and some peculiar differences. An hypothesis about what kind of processes may play a role is reported. In solution, the oxidative process mostly involved were (poly)hydroxylation or oxidation of the hydroxyl groups, while in ice N-dealkylation and monohydroxylation prevail. Finally, DEET and its TPs were searched out in snow and river water in wintertime.