Degradation of the Neonicotinoid Thiamethoxam by the Solar-Fenton Process: Theoretical Insights and Ecotoxicological Evaluation

Abstract

Neonicotinoids are highly consumed pesticides, such as the insecticide Cruiser®/CRZ® (Thiamethoxam/TMX). They exhibit effects on non-target organisms and for these their slow degradation becomes a potential problem. Advanced oxidative processes (AOPs), such as photo-Fenton, chemically transform organic contaminants, forming byproducts with unknown toxicity. The effects were tested using the planarian Girardia tigrina exposed to the CRZ formulation, and the resulting byproducts after the process. Damage was assessed by acute (LC 50 /mortality) and chronic (locomotion, development, regeneration, and reproduction) effects. The degradation of CRZ by the AOPs process was also studied by theoretical studies. The degradation percentages were more than 70%. 48h LC 50 of CRZ and CRZ+photo-Fenton (pH 3 and 7), was 478.6, 15.91, and 2072 mg.L -1 of TMX, respectively. The sublethal effects showed significance only for regeneration. The treatment proved positive for degradation but needs to have the pH corrected to reduce the effects on G. tigrina.

Keywords: Neonicotinoid, Platyhelminthes, UV photo-Fenton process, Theoretical degradation