Fenton and photo-Fenton strategies for sustainable pesticide decontamination. A review

Herbicides, insecticides, and fungicides are synthetic pesticides widely used to control or destroy pests in agriculture. Their toxic persistence as residues in waters and soils is hazardous for plants and animals, necessitating their removal. This article presents a critical and comprehensive review of recent trends of Fenton and photo-Fenton strategies to destroy such pollutants from 2021 to May 2025. In synthetic solutions, homogeneous Fenton with H₂O₂/Fe²⁺ yielding oxidant ^•OH was limited to pH = 3.0 and by Fe(OH)₃ sludge precipitation upon neutralization. Homogeneous Fenton-like processes with iron complexes solved this situation, allowing complete abatement of herbicides at higher pH values. Heterogeneous Fenton and Fenton-like processes with the generation of ^•OH, O₂^•-, and/or ¹O₂ oxidants also gave good degradation at pH > 3.0. Photo-Fenton upgraded Fenton by producing more ^•OH from photo-Fenton reaction and photolysis of final Fe(III)-carboxylate species. Fast degradation was achieved at pH = 3.0 by homogeneous photo-Fenton upon UVC light and at pH = 7.0 by solar heterogeneous photo-Fenton. Combined processes like photocatalysis/photo-Fenton were more effective in removing pesticides than the individual ones. Pesticides in real wastewater were more slowly remediated than in pure water by heterogeneous Fenton and photo-Fenton. Positive Fenton treatments were applied to soils contaminated with pesticides, using activators/oxidants added to soil or soil washing effluents. The toxicity analysis of treated pesticide solutions by predictive programs of primary by-products and experimental assessment with microalgae, bacteria, and plants is detailed. The scaling up for industrial pesticide wastewaters is discussed as the main challenge of these treatments.