Sediment Ecotoxicological Stats for the Evaluation of Surface Water Quality: the Ebro River Basin

by Rebecca Herrera

Roig et al. (2014) assess various sites along the Ebro river basin and collect information on each site’s ecotoxicological status. The data are then used to complement traditional means of evaluating surface water quality. The researchers compare the effectiveness and viability of different ecotoxicicty tests, otherwise known as bioassays, performed with freshwater sediments, and evaluated the relationship between ecological status, pollutant concentrations and pore water and sediment ecotoxicity to make recommendations to the European Water Framework Directive (WFD). Their findings showed a high correspondence of the ecotoxicological measurements to prior measurements of ecological status, especially when ecosystem disruption due to numerous stressors was observed.

The Ebro River basin, located in North-East Spain, is characterized by the interannual variability associated with its Mediterranean climate. The researchers measured data at 12 sampling sites and one reference site. Sampling sites were chosen to create a representative picture of the river basin, while sampling adjacent to important agricultural, industrial, and urban areas. The reference point experiences relatively low environmental and anthropogenic stressors in comparison to the other sites.

Basic measurements of humidity, porosity, percentage fine and organic matter, organic carbon, ammonium, and pH were taken at all 13 sites. To determine if potentially toxic metals associated with sulfides were present in sediments, researchers analyzed acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM), and then checked to see which was greater. If SEM is greater than AVS, it is likely the sediment is nontoxic. Researchers also measured concentrations of potentially toxic elements, including arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc. The ecotoxicity of pore water was evaluated using the bacterium Vibrio fischeri, a freshwater green algae Pseudokirschneriella subcapitata, and the crustacean Daphnia magna. Whole sediment ecotoxicity was evaluated again with V. fischeri and D. magna, in addition to the benthic diatom Nitzschia paleax, and the midge Chironommus riparius.

All study sites showed poor chemical status according to the WFD’s strict guidelines, however, some sites were also considered of good or high quality when evaluated using a biological, physicochemical, and hydromorphological integrated approach. High coincidences were found when comparing the bioassays to prior methods, proving a high efficacy for the new ecotoxicological approach.

Measuring surface water toxicity through bioassays is an exciting prospect in that it is both cost-effective and rapid to complete for both pore water and whole sediments. While traditional, chemical monitoring provides a detailed picture, it fails to interpret the effect of toxins and varying levels of toxicity on biota. The ecotoxicity method provides a direct measure of significant toxicity of contaminated environments.

Roig, N., Sierra, J., Moreno-Garrido, I., Hampel, M., Gallego, E., Schuhmacher, M., Blasco, J. 2014. Assessment of sediment ecotoxicological status as a complementary tool for the evaluation of surface water quality: the Ebro river basin case study. Science of the Total Environment, 503-504, 269-278.



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