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<p>The Bienne river (Jura Mountain, France) drains a basin of medium altitude mountains characterized by extensive cattle breeding (mostly dairy cows). A monitoring of the contamination by veterinary pharmaceuticals was performed using passive sampling devices - POCIS (Polar Organic Chemical Integrative Samplers), between September 2019 and January 2020. Four hydrological conditions were analysed: a sever low-flow periods, two flood events and a winter situation close to the mean interannual flow. Each time, POCIS were exposed over 2 weeks at 2 stations located in the upper and downstream reaches of the river. 19 pharmaceuticals were selected from information given by local veterinarians and analysed by LC MS-MS: endo and ectoparasites treatments; antibiotics and non-steroidal anti-inflammatory drugs. The monitoring shows that most of these chemicals (12 substances) are quantified in all POCIS samples and the others show relatively high occurrences, between 25 and 88%. Average concentrations in water (calculated with the sampling rate i.e. considering the time of exposition of POCIS samplers in the river) are remarkably close between the 2 monitoring stations. Concentrations are high all over the studied period and reach a maximum during flood events. Thus, hazardous effects are expected on freshwater organisms, especially for macrocyclic lactones and pyrethroids and organophosphates pesticides. The antibiotics concentrations ranges can also disturb microbial communities existing in the river. Such results highlight an important impregnation by these pharmaceuticals at the catchment scale, involving diffuse sources as grasslands receiving contaminated cow dungs and manures. Veterinary compounds are strongly remobilized during rain episodes by run off and infiltration in soils. In the hydrogeological context of the Bienne basin, karstic flows emphasize the connectivity between grasslands and the river. Therefore, an important part of the contaminated leaching waters can rapidly reach the river via the soil drains and surface / subsurface flows. Rather than another part goes through less porosity pathways and delivers pollutants over a longer period. Wastewater discharges and sludges from rural and urban treatment plants can also contribute to this pollution for pharmaceuticals also used in human medications.</p>

The decrease in low-water flows and the increase in water temperature and other parameters as observed in the rivers over the last 50 years suggest that a concentration of compounds and pollutants is taking place, in connection with climate change and/or anthropisation (without discerning their respective contributions). These effects occur in a context where the rivers are already impacted by the presence of many pollutant cocktails (pesticides, drugs, and others). The authors now show that these pollutant cocktails – at the environmental concentrations currently found – constitute a threat to human health through their possible effects on the virulence of pathogenic bacteria. While certain genes of Salmonella Typhimurium may not experience an increased risk, the exposure to more concentrated cocktails (at a five-fold concentration) could potentially amplify certain virulent factors such as the motility of Pseudomonas aeruginosa H103. The findings indicate that pollution mixtures have an effect on the virulence potential of certain waterborne pathogenic bacteria, even at concentrations currently observed in rivers.