The impact of tailings dam spills and clean-up operations on sediment and water quality in river systems: the Rı´os Agrio–Guadiamar, Aznalco´llar, Spain

This study investigates the impact of the 1998 Aznalcollar tailings dam breach on the sediment and water quality of the Rı́os Agrio and Guadiamar river systems in Spain. The objective is to evaluate the effectiveness of clean-up operations conducted until January 1999 and their influence on contaminant concentrations. Methodology involves geomorphological and geochemical surveys, along with sediment and water sampling across six representative sites during January and May 1999. Results indicate that while clean-up efforts removed substantial amounts of spill-deposited sediment, achieving pre-spill concentrations of several metals in surface sediment, these levels remained above pre-mining values, highlighting ongoing mining-related contamination. Moreover, downstream dilution of sediments appeared to mitigate some metal concentrations, yet increases in metal and arsenic levels further downstream suggest the influence of other pollution sources, such as sewage and agriculture. In addition, river water analyses revealed higher dissolved metal and arsenic concentrations in May compared to January, likely due to increased sulfide oxidation from residual tailings as ambient temperatures rose. Overall, the findings underscore the persistent environmental challenges following industrial spills and the implications for future water quality management.