Effects of the drug carbamazepine on the structure and functioning of a freshwater aquatic ecosystem

Carbamazepine, a widely used psychotropic drug, has been frequently detected in surface waters due to its poor removal in conventional wastewater treatment and slow dissipation in aquatic systems. While carbamazepine's ecotoxicological effects have frequently been researched, most research focuses on high concentrations and single species, with only a few studies including more ecological complexity and environmentally relevant concentrations. With a mesocosm experiment, we investigated the long-term ecological effects of environmentally relevant concentrations of carbamazepine (0.001-100 µg/L, performed in triplicate) on 1200 L freshwater ecosystems to provide more ecologically relevant insights. The study intended to identify sensitive species and assess the overall impact on the structure and functioning of the aquatic ecosystem. The composition of macroinvertebrate, zooplankton and microbial communities, primary producers and several physicochemical variables were analysed over a 14-week exposure period to determine the effects of a range of carbamazepine concentrations. While sublethal effects on invertebrates may have gone undetected, any potential sublethal impacts did not translate into lasting population-level consequences. We found that exposure to environmentally realistic concentrations of carbamazepine in aquatic mesocosms did not impact water quality, primary producers, or invertebrate and bacterial communities. The findings suggest that carbamazepine, at current environmental levels, is unlikely to harm freshwater ecosystems that exclude larger predators like fish.