Historical records of mercury deposition in dated sediment cores reveal the impacts of the legacy and present-day human activities in Todos os Santos Bay, Northeast Brazil.

We determined depth profiles of total mercury (T-Hg) in six ²¹⁰Pb-dated sediment cores from Todos os Santos Bay to reconstruct the history of anthropogenic Hg accumulation. We also assessed superficial sediments samples from five estuaries. T-Hg concentrations (5–3500 μg kg⁻¹) presented a large spatial and temporal variability. T-Hg concentrations in Ribeira Bay increased up to 200-fold along time, whereas the fluxes of T-Hg are substantially higher (up to 10,000 fold) than present-day wet deposition for industrialized areas. Sedimentary records indicate that a chlor-alkali plant has been the main source of Hg pollution until the present, although the T-Hg records suggest that harbor, shrimp farming, and oil refinery activities, besides Hg atmospheric depositions, are important across the bay. Sediments in the Ribeira Bay act as an important Hg sink. If sediments are eroded or disturbed, they may release Hg, thus posing a serious risk to wildlife and ecosystem health. Sedimentary cores provide data on preindustrial levels and also anthropogenic fluxes of Hg for the appraisal of the magnitude, processes and potential risks of the contamination. Unlabelled Image • Sediment cores provide a reliable archive of Hg contamination during the last century. • Hg levels increased up to 200-fold following the onset of a chlor-alkali plant. • Ribeira Bay acts as important sink for the legacy Hg. • Decline of the concentrations and fluxes of Hg during the last decades • Disturbance of bottom sediments may cause remobilization and reintroduction of Hg. [ABSTRACT FROM AUTHOR]