Do Microplastics Affect the Photodegradation of Duloxetine and Its Phototoxicity to Protozoan Spirostomum ambiguum (Müller, 1786) Ehrenberg, 1835?

As contaminants are often present in aquatic environments as mixtures, they may interact with each other and affect living organisms differently than when tested individually. Emerging pollutants such as pharmaceuticals and microplastics can be influenced by various environmental factors, with UV/Vis radiation being among the most significant. This study aimed to evaluate the photodegradation of the antidepressant duloxetine in the presence of four types of microplastics. Acute toxicity was tested using the Spirotox assay, duloxetine concentration was determined using HPLC-DAD analysis, and the resulting photodegradation products were tested using HPLC-MS/MS. Following 1 and 2 h of exposure in a sunlight simulator, the concentrations of duloxetine decreased by nine and thirteen times, respectively, while its toxicity to protozoa decreased by only two and three times. The presence of microplastics in the samples did not affect either the photodegradation process or the toxicity of duloxetine. HPLC-MS/MS analysis revealed the presence of 34 duloxetine photodegradation products. In silico toxicity analysis using the T.E.S.T. program for the protozoan Tetrahymena pyriformis indicated that one-third of the photoproducts were as toxic, and two products were found to be much more toxic than duloxetine. The high toxicity of one of these compounds was confirmed using the Spirotox test.