Ecotoxicity of carbamazepine and its UV photolysis transformation products

► Carbamazepine is highly recalcitrant to standard wastewater treatment practices. ► This study investigated the ecotoxicity of carbamazepine UV-photolysis degradation products. ► Carbamazepine was less toxic to three standard test organisms than the tested degradation products. ► Recalcitrant mixture toxicity of the UV-treated solution was still observed at the end of treatment. ► UV-photolysis of carbamazepine may form toxicologically relevant transformation products.