An assessment of the potential toxicity of transformation products arising from the direct photolysis of psychotropic drugs: Decontamination vs. toxicity increase

Background: Psychotropic drugs are contaminants of emerging concern, and some of them are also very toxic to aquatic organisms. Photodegradation is a major removal pathway for these compounds in sunlit surface waters. Psychotropic drugs are known to generate transformation products (TPs) upon direct photolysis, and the environmental impact of these TPs should be assessed. Methods: The software ECOSAR was used to assess acute and chronic toxicity of the compounds towards fish, crustaceans, and algae. Results: The TPs were often less toxic than their parent molecules, and in silico evidence of a toxicity increase was obtained in around 10% of the cases. However, comparison with available experimental data for carbamazepine suggests that the formation of just one or few toxic TPs should trigger concern, because of the potential to increase the overall toxicity of the irradiated mixture. Conclusions: The direct photolysis appears to often produce decontamination, but there are several cases where formation of at least one more toxic TP should raise concern. For the drugs considered here, it is the case of alprazolam, carbamazepine and diazepam, and also of dezipramine because of the formation of mutagenic acridine.