Environmental chemistry: What are we drinking?

Most ecosystems are exposed simultaneously to several stressors, in the so-called multiple-stress situation. Water scarcity is a key stressor with direct and indirect effects. The relevance of water scarcity as a stressor is most important in semi-arid regions such as the Mediterranean basin, characterized by highly variable river flows and the periodic occurrence of low flows and even no-flows. Climate change previsions forecast an increase in the frequency and magnitude of extreme events. Although extremes are part of the normal hydrologic behaviour in Mediterranean-type rivers, many already show a consistent trend towards decreased discharge. The first part of this presentation will show different examples on the risk of emerging contaminants, antibiotic resistance genes (ARG) nanomaterials and microplastics (MPs) in Mediterranean river catchments affected by water scarcity. Major conclusions of this reconnaissance study show that under extreme events pollutants effects on the biota are more relevant that under regular river flow conditions. Flash-flood events will mobilize pollutants from sediments with an increase of bioavailable chemicals in the surface river. Under water scarcity there are combined effects of stressors, chemicals and water flow, affecting biota. Lastly, wastewater treatment plants (WWTPs) discharges affect river macroinvertebrate river biodiversity and pollutants discharged are bioaccumulated in fishes. The second part of this lecture will discuss the increasing use of plastic litter and pharmaceuticals under Covid-19 outbreak. In this sense the excessive use and consumption of single-use plastics (including personal protective equipment such as masks and gloves) has negatively impacted the aquatic environment and agroecosystems among other compartments. Large amounts of antibiotics and paracetamol among other pharmaceuticals were positively correlated with levels of SARS-CoV-2 present in WWTPs and surface waters. Lastly, to overcome pollution problems in rivers under climate change effects, new solutions are required to improve river water quality and quantity like the use of advanced water treatment options. In short, by improving the water treatment the river water will be less toxic on the biota downstream. By doing this we are providing an additional source for different reuse options, like agriculture or groundwater recharge being one of the mitigation strategies against climate change and water scarcity.