Metal concentrations, fluxes, inventories and chronologies in sediments from Sepetiba and Ribeira Bays: A comparative study

Abstract

Three sediment cores were sampled at Sepetiba bay and four cores at Ribeira bay, Rio de Janeiro State, Brazil. Sedimentation rates were determined applying 210Pb dating. In the Ribeira Bay, the sedimentation rate increases in the direction from sampling point RB1 (0.15 cm y−1), in the inner part of the bay, to 0.34 cm y−1 in the sampling point RB4, close to its entrance. For the Sepetiba Bay, two sedimentation rates were observed: a lower rate of 0.3 cm y−1, for the period before the 60’s, and a more recent rate of 0.75 cm y−1. These findings agree with the construction of the Santa Cecília impoundment (1955) that brings water from the Paraíba do Sul Basin into the Guandu River, increasing its flow from the original 20 m3 s−1 to 160 m3 s−1. In order to determine the elemental concentrations, aliquot from the SB1 and RB4 cores were taken, totally dissolved and analyzed by ICP-MS. The hypothesis that Ribeira Bay could constitute a reference database for metal concentrations in the neighboring Sepetiba Bay is valid for several elements as K, Ti, Mn, Zn, Ga, Rb, Sr among others, but it isn’t for other elements as V, Cr and Cd. Applying to the mean elemental concentration, of the upper contaminated 45 cm sediment layer, and to the elemental concentration of the deepest analyzed sediment layer a normalization to iron, a double ratio was calculated and it was concluded that the Sepetiba Bay sediments are, particularly, contaminated with Cr, may be, from a leather tanning plant existing in this region and Cd and Zn from the former Ingá Metais