Reconstruction of historical trends in potentially toxic elements from sediment cores collected in Bertioga channel, southeastern Brazil

Abstract

The study presents an evaluation of potentially toxic elements deposition in Bertioga Channel (Southeastern Brazilian coast) along the last 150 years, the main anthropogenic activity period in the area. Five sediment cores by means of ICP-OES to determine the levels of metals (Cd, Cr, Cu, Ni, Pb and Zn) and As. The pollution load index (PLI) and enrichment factor (EF) were calculated to identify the relative elements toxicity of the sediments and the anthropogenic contribution of the investigated elements. The indexes indicated the absence of contamination but a higher input of As in cores B2 and B5, which have been sampled in an area that presents higher sedimentation rates. Through an statistical analysis of time series decomposition, it was verified that the metals flux to the area follow the cycles of rainy (austral summer and autumn) and dry seasons (austral winter and spring). In conclusion, the enrichment corresponds to the end of the 19th Century, when Santos Harbor was inaugurated, and to the 1970s, when Santos Harbor activities expanded. In addition, the analysis of the indexes and the temporal decomposition indicate that these elements' input to Bertioga Channel is due to natural processes of weathering and sedimentation.