Identification of the photoproducts of the antidiabetic drug metformin and the different impact of metformin compared to its photoproducts mixture on aquatic organisms

Photochemical degradation of the antidiabetic drug metformin in the presence of a quinone sensitiser was investigated under environmentally relevant UV light. Degradation products were identified using UHPLC-Q-TOF. The effects of the resulting photoproduct mixture and metformin itself (50-100 µg l⁻¹) were assessed on four aquatic species representing different trophic levels: Desmodesmus subspicatus, Lemna minor, Daphnia magna and Danio rerio embryos. The photoproduct mixture caused growth inhibition in photosynthesising organisms, reproductive disruption in Daphnia, developmental malformations in fish embryos, and significant changes in oxidative stress markers. This study provides the first evidence that photochemically generated transformation products of metformin are significantly more toxic than the parent compound, even at environmentally relevant concentrations. These findings highlight the importance of including not only parent pharmaceuticals but also their photoproducts in environmental risk assessments, as the latter may pose a greater ecological hazard in surface waters.