Trace metal bioavailability in sediments from a reference site, Ribeira Bay, Brazil

•Signs of generally low anthropogenic influences on metal levels were observed.•Cu and Pb were correlated with major geochemical carriers.•Zn and Ni were correlated with total P, suggesting an association with sewage inputs.•AVS and organic carbon levels were sufficient to control metal bioavailability.•Metal behavior contrasts imply in different sensitivities to environmental changes.

Surface sediments were collected near potential contamination sources impacting Ribeira Bay (Brazil), a system considered as a ‘reference site’ for trace metals. Physicochemical properties (pH and Eh), grain size and concentrations of total organic carbon (TOC), total phosphorus (TP), acid-volatile sulfides (AVS) and simultaneously-extracted metals (Fe, Mn, Cd, Cu, Ni, Pb and Zn) were analyzed. Although relatively low metal concentrations were found, correlations of Zn and Ni with high TP levels suggested an association with sewage inputs, while other metals presented associations with specific geochemical carriers (TOC, Fe and Mn compounds). AVS levels exceeding those of the sums of Cd, Cu, Ni, Pb and Zn (ΣSEM) by at least one order of magnitude and TOC-normalized differences between ΣSEM and AVS ((ΣSEM–AVS) / fOC) near to or below than − 200 μmol g OC− 1 indicated that there were sufficient AVS and TOC levels to control trace metal bioavailability in sediment pore water.