Losartan potassium (LOS) is one of the most antihypertensives used in the world, and its presence in environmental matrices can cause impacts to biota. In this study, the ecotoxicity and genotoxicity of LOS was assessed before and after treatment by UVC/photolysis and UV/H 2 O 2 . The photodegradations were carried out at LOS solutions (2.5 mg L −1 ; 4.6 μM) for 30, 60, 90, 120, 240, and 480 min of treatment. For chromatographic analysis, the samples were submitted to solid-phase extraction (SPE) and analyzed by HPLC-DAD. Ecotoxicity bioassays were conducted using Daphnia magna (acute) and Desmodesmus subspicatus (chronic) for all the degradation times. To evaluate the genotoxicity, the comet assay was performed with a D. magna whole organism cell suspension applying the alkaline gel electrophoresis technique. For both process, the degradation rate was over 99% at 30 min, which reduced the acute toxicity of LOS to D. magna . In addition, only the sample treated at 240 min by UV/H 2 O 2 showed significant chronic and acute toxicity. However, the genotoxicity effect was observed for samples treated LOS before treatment and at 480 min by UV/H 2 O 2 . Therefore, even reaching high LOS degradation rates, for both processes, the bioassays demonstrated the importance of ecotoxicological analyses by AOPs treatment. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-020-11420-9.