Ecotoxicological status of sediments as a complementary tool for the surface water quality assessment under WFD

Trabajo presentado en la Final SCARCE International Conference (River Conservation Under Water Scarcity: Integration of water quantity and quality in Iberian Rivers under global change), celebrada en Tarragona el 20 y 21 de octubre de 2014.According to the European Water Framework Directive (WFD), assessment of surface water status is based on ecological and chemical status that not always are in coherence. In these situations, ecotoxicity tests could help to obtain a better characterization of the ecosystems. The general aim of this work was to design a cost-effective methodology to study the ecotoxicological status of freshwater systems that could be useful and complementary to ecological status defined by the WFD by applying a quality triad integrating chemical, physicochemical, biological and ecotoxicological data. The specific aims of this work have been: (1) to compare the effectiveness and viability of different ecotoxicity tests performed with freshwater sedimen ts (whole sediment and pore water) taking as target organisms different aquatic species, and (2) to evaluate the relationship between ecological status, pollutant concentrations (paying special attention to metals availability), and pore water and sediment ecotoxicity. For this purpose, sediments from thirteen sampling sites within the Ebro river watershed (NE Spain) were collected for ecotoxicity characterization. The ecotoxicity of pore water has been evaluated employing the test organisms Vibrio fischeri, Pseudokirschneriella subcapitata and Daphnia magna, while whole sediment ecotoxicity was evaluated using Vibrio fischeri, Daphnia magna, Nitzschia palea and Chironomus riparius. An analysis of acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) was performed to evaluate the sediment toxicity associated to bioavailable metals. Moreover, data about priority pollutants defined by the WFD in wate r, sediment and fish as well as data of surface water status of each sampling point were provided by the Monitoring and Control Program of the Ebro Waterbodies. In general terms, whole sediment bioassay s have shown more toxicity than pore water tests. Among the different organisms used, P.subcapitata and C. riparius were the most sensitive in pore water and whole sediment, respectively. Our evaluation of th e ecotoxicological status showed high coincidences with the ecological status, established according to the WFD, especially when ecosystem disruption due to numerous stressors (presence of metals and organi c pollution) was observed. These results allow us to confirm that, when chemical stressors affect the ec osystem functioning negatively, an ecotoxicological approach, provided by suitable bioassays in pore water and whole sediment, could be able to detect these changes with accurate sensitivity.Authors would like to thank the Spanish Ministry of Economy and Competitiveness for its financial support through the project SCARCE (Consolider-Ingenio 2010 CSD2009-00065).N