Geochemistry of the upper estuarine sediments of the Santos estuary, São Paulo, Brazil: provenance and anthropogenic pollution

Abstract

Major and trace element geochemistry of the upper estuarine sediments of the Santos estuary has been used to characterize sediment geochemistry, classification, distribution, and possible sources of industrial pollution. The vertical sediment cores were collected on the margin of the Cubatão, Perequê, Mogi, Piaçaguera and Jurubatuba rivers, the main effluents of the Santos estuarine system. Samples of selected basement rocks (n=12), industrial waste (n=2) and one weathering profile (organic soil, residual soil and saprolite rock) were also analyzed. The sedimentary deposits showed interbedding of medium, fine, and very fine sands in the upper portion of the estuary and subordinate silt-clay units derived from lower energy in swamp/mangroves deposits in the lower estuary. Marked geochemical differences occurred among these fluvial sediments. The calculated indices of chemical weathering, such as Chemical Index of Alteration (CIA) and A-CN-K ternary diagram indicate that the estuarine sediments display a wide range of weathering effects, from unweathered derived of Proterozoic gneiss and granitic rocks to intensely weathered site in the swamp deposits of the Piaçaguera River. Phosphogypsum waste stored in the catchment area of the Mogi River showed high concentrations of S, La, Ce, Ca, Sr, Nd, Nb, U, Ba, P, Y and F when compared with the regional rocks, soils and fluvial sediments samples analyzed in the study area, which make it a potential source of environmental contamination. The UCC-normalized patterns, geoaccumulation indexes (Igeo), robust linear regression (RA) and principal component analysis (PCA) were used to identify geochemical anomalies and discuss their probable sources. The principal component scores exhibited strong spatial association with anthropogenic sources. The principal component loading allowed to separate heavy metal elements (Cr, Cu, Ni, Pb and Zn) from the elements related to phosphogypsum waste (e.g., Ce, La, Nd and F). The geochemical anomalies of Ce, La, Nd and F in the fluvial sediments of the Mogi downstream River may be related to phosphogypsum waste in the catchment area, whereas the Cr, Cu and Ni anomalies may be related to fossil fuel, chemical industries and industrial waste deposits which occur near the Pereque and Cubatão rivers.