Degradation of imidacloprid by Phanerodontia chrysosporium on wood chips for stormwater treatment†

Abstract

Neonicotinoids, a widely used class of insecticides, enter surface waters through stormwater runoff and threaten the health of aquatic ecosystems. Imidacloprid is a commonly used neonicotinoid in the United States and is present in surface waters across North America. White-rot wood decay fungi can degrade neonicotinoid compounds, and their ability to grow on woody materials makes them well suited to passive fungal bioremediation applications. However, there is limited research on the viability of fungal bioremediation for stormwater treatment. In this study, we investigated the rate of imidacloprid degradation by the wood decay fungus Phanerodontia chrysosporium in suspended and attached growth systems. Cytochrome P450 enzyme inhibitor 1-aminobenzotriazole was used to investigate the degradation mechanism. Imidacloprid and fungal biomass were measured over four weeks in a synthetic stormwater fungal batch system and transformation products were identified. More than 90% of imidacloprid was degraded in four weeks in liquid and wood chip experiments, with more than 50% of degradation occurring in the first week. The cytochrome P450 enzyme inhibitor had no effect on imidacloprid degradation, suggesting that these enzymes were not responsible for the degradation under the imposed nutrient-limited conditions. Estimated first-order reaction rate constants for the liquid and wood chip culture treatments were 0.17 d⁻¹ and 0.11 d⁻¹ respectively. We tentatively identified three previously described transformation products, imidacloprid-nitrosoguanidine, imidacloprid-olefin, and 6-chloro-3-pyridylmethanol in fungal-amended samples. To our knowledge, this research represents the first study to examine and demonstrate fungal degradation of imidacloprid in synthetic stormwater, and the first to explore this degradation with wood chips as a fungal growth medium. Significant degradation (>50%) of imidacloprid after 7 days by P. chrysosporium suggests that fungal-based biodegradation may provide a valuable stormwater treatment option.