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Mechanistic insight into the photoconversion of losartan potassium mediated by different types of microplastics
Summary
This study found that different types of microplastics — polystyrene, PET, and PLA — have distinct effects on how a common blood pressure drug (losartan) breaks down when exposed to sunlight in water, with aged and weathered microplastics generally accelerating the drug's transformation into unknown byproducts. This matters because microplastics and pharmaceutical pollutants commonly co-occur in water bodies, and their interactions could produce new contaminants with unpredictable health effects.
Nowadays the proliferation of microplastics (MPs) in aquatic environments and impacts on the fate of organic contaminants (OCs) has drawn sustained worldwide attention. In this study, we investigated the effects of different types and aging degrees of MPs, specifically polystyrene (PSMPs), polyethylene terephthalate (PETMPs), and polylactic acid (PLAMPs), on the photo-transformation of LSTPs. Our results revealed that the facilitation of LSTP photoconversion by PSMPs exhibited a positive linear relationship with aging degree. On the other hand, the effects of PETMPs with different oxidation levels on LSTP photoconversion were weak, while the contribution of PLAMPs decreased as aging increased. Characterizations, quenching and probing experiments showed the aging mechanisms and the generation of reactive oxygen species (ROS) converged among various MPs. Specifically, theoretical calculations, TOC and GC-MS were conducted to verify that in the PLA-mediated systems, it was the intermediates of PLA that prevailed in promoting the photoconversion of LSTP. The aged PLA own have a large propensity to consume ROS, which diminished their promotion of LSTP degradation. This differd from the reactions involving PSMPs and PETMPs, where the microplastic particles themselves were the main drivers of the photoconversion process rather than intermediates.