Theoretical investigation on degradation of DEET by •OH in aqueous solution: Mechanism, kinetics, process optimization and toxicity evaluation

Abstract

N , N -diethyl-3-methylbenzamide (DEET), as a widely used insect repellent , is frequently detected in the environment. UV/H 2 O 2 is a valid technology to remove trace contaminants by generating hydroxyl groups. The density functional theory (DFT) calculation method was used to investigate the degradation mechanism and kinetics of DEET in water environment. •OH can attack DEET in two main modes, H-abstraction and •OH-addition, showing different reactivity. H-abstraction reaction is easier to occur compared with •OH-addition reaction. Especially the hydrogen on branch chain of DEET is more readily to be attacked by •OH. In the aqueous phase , the total rate constant is 2.04 × 10 9 M −1 s −1 at 298 K. Calculated results showed that R5, R6, R8, R9 and R12 paths preferentially occur. Under alkaline conditions, it can significantly inhibit the DEET degradation. The influence of natural organic matter (NOM) in water and oxidant dosage, DEET concentration was also considered. The response surface methodology (RSM) was used to optimize the process parameters. The maximum degradation efficiency of 95.64% can be achieved under optimal conditions. Since most of the products are homologues of the parent compound, their acute and chronic toxicity are not significantly reduced. The products are non-mutagenic and non-bioconcentrated, but they are developmentally toxic.