Resumo:
The mankind actions have lead us to the Anthropocene, a geological epoch when Nature
is not alone conducting the biogeochemical cycles of many trace elements. The objective
of this study was to use sediment cores to determine the chronological record of
anthropogenic impacts in five regions of Todos os Santos Bay, Bahia, Brazil. Trace metals
(Co, Cu, Mn, V, Pb, Zn, Fe, Al, Cr, Cd, Ni, and Ti) and Pb isotopes (208Pb, 206Pb, 207Pb, and 204Pb) were measured in five dated sediment cores (CI1QCI5). The sedimentation rates
raged from (0.38–2.60cm yrQ1). The grain size was homogeneous through time along all
cores, and was mainly composed by silt sediments. Trace elements concentrations
tended to increase especially after 1950, most of them showing low to moderate
enrichment. Increases in concentrations of trace metals were associated to different
anthropogenic activities: Pb smelting (CI2QCI3), burning of fossil fuels (all cores at some
extend), maritime traffic (CI4), petroleum related activities (CI5), and changes in land uses (CI1). All metals, except Cu at CI4, presented concentrations bellow TEL, indicating that contamination in the studied areas are not prone to cause adverse effects to biota.
Stable Pb isotopic ratios identify a decommissioned lead smelter and burning of fossil
fuels as the main sources of Pb to the bay.) The results of implementation of
environmental policies to improve the waters of the bay could not be noted by the evaluated cores.