Chemical mixtures and autochthonous microbial community in an urbanized stretch of the River Danube

River pollution from different sources can affect ecosystems in different ways with consequences on water quality for both biota and human health. The River Danube was selected to perform chemical and biological analyses. The river was sampled at three different points, one inside Budapest and two just outside. Water samples were collected twice in the same year (April and November 2017) in order to determine metal concentrations, occurrence of ubiquitous contaminants such as Polycyclic Aromatic Hydrocarbons (PAHs) and some not-yet-regulated pharmaceuticals (17 beta-estradiol, 17 alpha-ethinylestradiol, estrone, fenoprofen, naproxen, ibuprofen, gemfibrozil, sulfamethoxazole and ciprofloxacin). Moreover, the structure of the natural microbial community was also analysed in terms of total microbial abundance and identification of the main bacterial groups by the Fluorescence In Situ method. Finally, the same water samples were tested to assess their possible estrogenic effects using the yeast estrogenic screen (YES). The results show diffuse residual concentrations of both PAHs and pharmaceuticals in the river stretch investigated, with the highest values in April (in line with a lower rainfall input) and at the sampling site inside the city of Budapest. At this latter point, the natural microbial community was less abundant than in the other sites, suggesting detrimental effects of the overall contaminants on its structure. Finally, an estrogenic activity was found in all water samples analysed with higher average values in line with higher amounts of contaminants in the April sampling.