Evaluation of the Photocatalytic Degradation of Acetamiprid and its Ecotoxicological Impacts using ZnO

Abstract Acetamiprid (ACET), a neonicotinoid insecticide, is widely detected in aquatic and terrestrial ecosystems and has raised concern due to its environmental persistence, incomplete removal by conventional treatment processes, and the limited understanding of the ecotoxicological effects of its transformation products. In this study, the photocatalytic degradation of ACET was investigated using both a commercial formulation (Rescate 200SP, 20% ACET) and an analytical-grade reagent; additionally, the toxicity of the degradation products was assessed using Eisenia foetida as a biological model. Zinc oxide (ZnO) was synthesized by a low-cost precipitation–hydrothermal route at 120 °C using zinc acetate as precursor and cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. Characterization techniques such as XRD, Raman, UV–Vis spectroscopy, SEM, XRF, EDS, BET analysis, and TGA confirmed a hexagonal wurtzite phase with plate-like morphology, a reduced band gap of 2.76 eV, a maximum absorbance at 384 nm, and a high specific surface area (186.83 m 2 g⁻ 1 ). ZnO achieved 58% degradation of commercial acetamiprid (Rescate 200SP) and 86% of analytical-grade reagent ACET under the following photocatalytic conditions pH 10.0, 10 mg L⁻ 1 ACET, 0.2 g L⁻ 1 catalyst, 2 h irradiation. At the same time, mineralization remained limited (~ 22% COD removal), suggesting the formation of transformation products. The identified intermediates by GC–MS suggested a reduction in the toxicity of ACET and its byproducts, which correlated with acute toxicity assays using Eisenia foetida , showing a 50% reduction in mortality following treatment compared to untreated ACET. Therefore, this study shows that combining a simple CTAB-assisted ZnO synthesis with simultaneous evaluation of degradation efficiency, transformation pathways, and ecotoxicological assay demonstrates that unmodified ZnO can substantially reduce both ACET concentrations and associated toxicity, highlighting its potential as an accessible photocatalyst for pesticide-contaminated waters.