Distribution of acid-volatile sulfides and simultaneously extracted metals in Guanabara Bay: combination of anthropogenic, sedimentological, and geochemical processes.

Coastal sedimentary systems are affected by continental and marine metal pollutant inputs associated with different hydrodynamic characteristics and geochemical processes. These include the formation of acid-volatile sulfides (AVS) within sediments, which affects metal bioavailability and associated aquatic biota toxicity risks. Physicochemical changes in these environments in the face of extreme natural or man-made environmental influences can dramatically alter metal bioavailability and toxicity through metal binding and immobilization as insoluble sulfides. Surface sediments from Guanabara Bay, river mouths, and two mangrove areas were collected, and AVS and simultaneously extracted metals Cd, Cu, Fe, Mn, Ni, Pb, and Zn and ΣSEM were determined to assess sediment quality. A severe eutrophication history favored AVS concentrations exceeding or close to the sum-SEM concentrations, demonstrating that AVS play an important role in making trace metals unavailable for assimilation by living organisms, mitigating the risks of contamination for the local biota. This eutrophication-driven sulfide accumulation may attenuate the sediment toxicity in sites heavily polluted by metals, while some fewer eutrophic sites became more exposed to metals in excess to AVS.

Combining geochemical and chemometric tools to assess the environmental impact of potentially toxic elements in surface sediment samples from an urban river.

This article investigates sediments collected from the banks of the Subaé River located in Todos os Santos Bay in the state of Bahia, Brazil, in 2018, twenty-five years after the closing of a former lead alloy processing plant. Ten sediment samples were collected at different points of the course of the river and its estuarine region. Chemometric tools were used to determine geochemical correlations between the organic matter content and concentration of sulfides and potentially toxic metals. The inorganic geochemical variables (enrichment factor [EF]) used in this evaluation were concentrations of the Pb, Cd, Cu, Zn, and Ni. Chemical element analyses were performed using ICP-OES. To assess the interaction between metals and sulfide or metals and organic matter, concentrations of Pb, Cd, Cu, Zn, Ni, sulfide, and the silt-clay fraction constituted the organic geochemical parameters selected to characterize the amount of organic matter present in Subaé River sediment samples, determining the carbon content (%TOC) to compose the matrix of the principal component analysis (PCA) and hierarchical cluster analysis. PCA showed that 88.3% of the samples were representative for assessing correlations between geochemical variables. A tendency toward binding was found among Cu, Cd, Ni, and sulfide, as well as the silt-clay fraction. The concentrations (mg kg-1) of lead, zinc, and copper were higher in both collection campaigns, ranging from 4.72 to 31.34, 12.76 to 54.24, and 5.34 to 31.37, respectively. Pb and Zn were presented in elemental form when assessed as a function of the pH and Eh of the environment. Except for Cd (EF: 0.51 to 5.49), the other elements exhibited little or no potential pollution in the aquatic environment of the Subaé River.

Ecological risk evaluation of sediment metals in a tropical Euthrophic Bay, Guanabara Bay, Southeast Atlantic.

Surface sediments were collected from Guanabara Bay, at 14 stations distributed in five sectors, over three sampling campaigns. Analyses of metals, grain size fractions and total organic carbon analyses were performed. The geo-accumulation index and the enrichment factor were estimated to assess contamination status based on background values. Additionally, the sediment quality guidelines were applied to evaluate the adverse biological effects. Results show that there was no seasonal variation in sediment quality based on any methodology, and all methods utilized showed that NW sector and HRJ sector were the worst affected and that the NE sector had the best conditions. The sediments of GB are polluted mainly by Cr, Pb and Zn. According to ΣSEM/AVS, these metals are not available to the biota, although toxicity tests dispute this. Among the various methods employed, those using background values for the area seem to best reflect the local historical contamination.