Ecosystem Responses to Emerging Contaminants: Fate and Effects of Pharmaceuticals in a Mediterranean River

There is concern about the environmental effects of pharmaceuticals, since these substances have strong biological impacts and are found in an increasing number of sites, especially downstream from wastewater treatment plants (WWTP). Most information existing on the effects of pharmaceutical products is based on simple laboratory assays with single compounds, whereas pharmaceuticals in the environment typically appear in complex mixtures that include secondary metabolites as well as other pollutants. Therefore, real-world situations may contribute to the understanding of the fate and effects of pharmaceuticals in freshwaters. Here we report the effects of pharmaceuticals in the river Segre (Pyrenees, Iberian Peninsula) in a river segment affected by the effluent of a WWTP. The removal efficiencies of pharmaceuticals and their metabolites in both the WWTP and the river were analyzed by comparing the inflow and outflow concentrations at the WWTP and along the studied river segment, and their transformations and interactions were modeled. The WWTP had a higher removal efficiency (45%) than the river segment (20%), but the latter was also important. In general, the compounds most efficiently removed in the WWTP were also those more efficiently removed in the river. The removal efficiency in the river was higher during the day than during the night, suggesting that attenuation was driven by either photodegradation or biological transformation by primary producers. The effects of pharmaceuticals were analyzed across different scales, from those on biofilms to functional impairment of the river ecosystem. Laboratory toxicity tests showed that stream biofilms at the most polluted site developed community tolerance to anti-inflammatory drugs. Biofilms in the field also showed altered metabolic profiles and reduced algal diversity. WWTP effluents were able to alter the balance between autotrophic and heterotrophic processes: while ecosystem respiration was subsidized, gross primary production showed some stress effects.