Evaluation of direct and indirect photodegradation of mianserin with high-performance liquid chromatography and short-term bioassays

• Direct and indirect photodegradation of mianserin were investigated.
• Toxicity before and after irradiation with a battery of assays was assessed.
• Photoproducts had no impact to toxicity.

The widespread use of pharmaceuticals has lead to their detection in surface and ground waters. In the last year antidepressants in particular have shown very high growth dynamics of consumption and numerous research shows that these pharmaceuticals are detected in the environment and even in drinking water. Drugs and their metabolites can be subject to two types of photoreaction, direct and indirect photodegradation. These pharmaceuticals even at low concentration can have adverse effects on aquatic life, and the resulting photoproducts can be more toxic than parents compounds.The aim of this study was to evaluate the direct and indirect photodegradation of mianserin. The kinetics of the process and the identification of photoproducts were investigated by HPLC-PDA and HPLC–MS/MS, respectively. Ecotoxicity of mianserin before and after irradiation was assessed with a battery of assays with bacteria, protozoa and crustacea.The results show that mianserin was not toxic to Vibrio fischeri (Microtox), but its toxicity to protozoan Spirostomum ambiguum (Spirotox) and crustacean Thamnocephalus platyurus (Thamnotoxkit F™) was comparable to other antidepressants. On the basis of the results of the toxicity and HPLC before and after irradiation it can be seen that the decrease toxicity of mianserin was related only to a decrease of its concentration. The photoproducts had no impact to toxicity. The direct photodegradation of mianserin was more effective in UV/vis light than vis light. However the presence of humic acid in the indirect photodegradation increases the rate of degradation without regard to the kind of used light.