Rocky Benthic Communities response to sewage discharges and associated micropollutants in the southeastern Bay of Biscay

Resumen

The occurrence of micropollutants in the aquatic environment has become an environmental issue of major concern throughout the world because they may be potentially toxic, persistent and bioaccumulative in the environment even at low concentration levels. As wastewater treatment plants (WWTPs) are not specifically designed to eliminate this type of pollutants, a large range of micropollutants are found in wastewater effluents and then in the environment. This study, a dual-track approach between chemistry and biology, aims to provide a first insight of the occurrences and concentrations of priority and emerging substances in WWTP discharges and their potential impact on rocky benthic communities in the southeastern Bay of Biscay. These complementary approaches allow to study the benthic communities¿ response in both intertidal and subtidal zones and to quantify micropollutants in benthic organisms as well as in WWTP effluents. The results highlight that WWTP discharges constitute a source of micropollutants in coastal areas (especially metal, pharmaceutical and musk compounds) and that a number of substances are also found in benthic organisms but differences are identified between them. In general, Ulva spp. and Gelidium spp. are highlighted as the better bio-accumulator for this area. Results of the study of benthic communities¿ response suggest that benthic macroalgae constitute the best relevant biotic component to assess the effect of such a pressure in this area. Changes in the relative abundance of Ceramium spp., Corallina spp. and Halopteris scoparia (in the intertidal zone) and of Gelidium corneum and Metacallophyllis laciniata (in the subtidal zone) appear mainly responsible of the dissimilarities found between impacted and control locations. By contrast, no significant effect is detected using macrofauna assemblages and quality indices based on this biological element. The current `macroalgae¿ WDF index, contributing to assess the ecological quality status of the water body, appears to be sensitive to such a pressure because it highlights a clear effect of discharges in the intertidal and subtidal zones. Finally, those results provide a framework for future monitoring allowing an assessment of benthic communities¿ changes related to WWTP discharges and highlight the importance to reflect upon another method to integrate macrofauna in future monitoring for an efficient impact evaluation.