Evaluation of the occurrence and fate of pesticides in a typical Mediterranean delta ecosystem (EBRO RIVER delta) and risk assessment for aquatic organisms

Delta ecosystems are areas of high ecologic and economic values, where wildlife commonly shares the territory with intensive agricultural activities, particularly, rice cultivation and seafood production. This work aimed at evaluating the occurrence of a wide spectrum of pesticides and transformation products in the water of irrigation and drainage channels of the Ebro River Delta (NE Spain) during the main rice-growing season, when pesticide application is at its peak. Furthermore, the impact that these contaminants may have on local ecosystems and seafood production activities was assessed. A total of 35 pesticides, mainly associated with rice cultivation, out of the 66 analyzed were detected. Bentazone, propanil, MCPA, acetamiprid, and triallate were found at the μg/L level. Cybutryne was measured for the first time in the area and at concentrations above its environmental quality standard (11-49 ng/L), despite being banned in the European Union. Sixteen additional banned pesticides were also detected at trace levels, likely due to their desorption from soil and sediment particles. Bentazone, cybutryne, dicofol, imidacloprid, MCPA, and propanil posed a moderate to high risk for aquatic organisms at the normal concentration levels measured during the rice-growing season. The co-occurrence of pesticides may pose a high risk for aquatic organisms in all sampling locations. Despite its dilution when discharged into the bay, this study demonstrates that the agricultural use of pesticides may have important effects on water quality and may pose a serious hazard for aquatic non-target organisms, despite other factors such as temperature and salinity may play also a relevant role in pesticide toxicity. The finding of imidacloprid and acetamiprid, including in the Watch List, at concentrations above their maximum acceptable method detection limit, calls for control of their use and revision of their legal status.