Impact of Urbanization on Freshwater Sustainability: Microplastic Distribution in Sediments and Water and Occurrence in Amphibians (Genus Pelophylax) of Urban Lakes

Urban freshwater ecosystems are facing an increasing threat from microplastic (MP) pollution. However, standardized monitoring protocols and data on bioaccumulation in amphibians are still very scarce. This study investigated the distribution of MPs in the sediment and water of urban lakes, and their uptake and presence in various tissues of tadpoles of the green frog complex Pelophylax kl. esculentus. Sediment and water samples were collected from four urban lakes in Osijek, Croatia, representing various levels of anthropogenic pressure. In all studied lakes, the presence of MPs was confirmed, with synthetic fibers being the most common form. The highest concentration of MPs was recorded in the sediment of Bajer Jug 2 and in the water samples of Bajer Bosutsko naselje. In the second part of our research, tadpoles were collected from their natural habitat in one of the lakes, where they were exposed to MPs already present in the environment. Tadpoles and newly metamorphosed froglets were inspected for the presence of MPs, with different organs (liver, stomach, intestines, and brain) isolated for analysis. Particles that were visually classified as suspected microplastics were confirmed in most tadpoles/froglets, with the most important finding being the potential presence of these particles in the brains of individuals that had completed metamorphosis. Our results suggest the pervasive nature of plastic pollution in urban environments and underscore the need for sustainable management and conservation strategies for urban lakes in order to protect their biodiversity.