Long-term impacts on estuarine benthic assemblages (2015-2020) after a mine tailing spill in SE Brazil

The Rio Doce estuary was critically impacted in 2015 by the world's largest mining tailing spill, with still unclear long-term effects on the aquatic biota. Here we present a long-term (2015 to 2020) assessment of estuarine benthic assemblages, where we demonstrate that despite a decline in the absolute concentrations of potentially toxic elements; sediment contamination is still above pre-impact conditions. The presence of these contaminants is likely responsible for a continued low habitat quality for the benthic fauna, characterized by a reduction of 96 % of the macroinvertebrate density and persistent change in the benthic assemblage composition. Our study supports previous work indicating the long-term nature of pollution impacts in estuaries, and demonstrate that although water quality levels were quickly adequate under regulatory terms, they largely lack significance to the overall ecosystem health assessment, as they are not related to the recovery of bottom-dwelling assemblages in estuarine ecosystems.

Automated summary

This study presents a long-term assessment of benthic assemblages in the Rio Doce estuary, showing that sediment contamination is still above pre-impact levels despite a decline in toxic element concentrations. The presence of contaminants has led to a continued low habitat quality for benthic fauna, with a 96% reduction in macroinvertebrate density and persistent changes in benthic assemblage composition. The study highlights the long-term nature of pollution impacts in estuaries and emphasizes the lack of significance of water quality levels in assessing overall ecosystem health in estuarine ecosystems.