Biodegradation of organic micropollutants at the sediment-water interface of aquatic ecosystems

Organic micropollutants are a growing environmental concern, due to their ecotoxicological risks and impact on human health. Aquatic environments are particularly vulnerable, receiving inputs from multiple sources, with pesticides from agricultural run-off and pharmaceuticals from wastewater treatment plant effluents being among the most frequently detected contaminants. In these ecosystems micropollutants undergo non-transformative processes such as sorption and dilution, as well as transformative processes like bio- and photodegradation. However, transformative processes under different environmental conditions remain poorly constrained, even though they determine the persistence of micropollutants and can lead to transformation products that are more toxic or mobile than their parent compounds. To assess the effect of varying environmental conditions on the biodegradation of selected micropollutants, degradation experiments were conducted in single and co-occurrence of the antibiotic sulfamethoxazole and the herbicide S-metolachlor. River water and sediment microcosms from agricultural and urban sites enabled the evaluation of the effect of different matrices, organic matter and oxygen availability on biodegradation kinetics and transformation pathways. Within these conditions the half-lives varied between 4.2 ± 0.1 days and persistence after 90 days for sulfamethoxazole and 37 ± 7 days to persistence after 284 days for S-metolachlor. The results indicated that the presence and type of sediments are key factors of biodegradation. Furthermore, the detection of 4-aminobenzenesulfonamide, resulting from the ε-cleavage of sulfamethoxazole, as the main transformation product exhibits a novel biodegradation pathway. These findings provide environmentally relevant insights into micropollutant transformation and highlight key factors affecting their dissipation in aquatic environments.