Source and Distribution of Mercury in Sediments of the Brazilian Amazon Continental Shelf with Influence from Fluvial Discharges

Place and Aims: Total concentrations of Hg and geochemical analysis of sediments from the Amazon Continental Shelf (47º52'W-4º19'N, 51º04'W-2º16'S) were determined in 25 sampling sites, during the months of lowest flow of the Amazon River. The aim of this study was to determine the influence of fluvial discharge on mercury distribution and deposition in the environment.

Duration of Study: Between 1999 and 2011.

Analyzes: The marine sediments were used to identify heavy minerals, and determine grain size, organic content (organic matter and organic carbon), SiO2, Fe2O3, Al2O3 and MnO, and Hg levels using standard methods.

Results and Conclusion: The Hg concentrations varied from 14 to 160 ng g-1. The highest Hg concentrations occurred in the inner shelf. Both analysis of major oxides and identification of mineral composition in the sediments confirmed the influence of river discharge on Hg deposition in the inner shelf. The geochemical results suggested that the main Hg source in the study area was from natural origins due to erosion and subsequent leaching of tropical lateritic soils, although mining in the Madeira and Tapajos river basins is also a contributing factor.