Anthropogenic pollutants in the Southwestern Atlantic Ocean slope: Is the Santos Bifurcation region a potential sink for organic contaminants?

The Santos Bifurcation, located off the southeastern coast of Brazil, represents a key mesoscale hydrodynamic system where the southward-flowing Brazil Current diverges, generating complex circulation patterns that influence sediment transport, biogeochemical cycling, and the accumulation of anthropogenic contaminants along the continental margin. The distribution, sources, and deposition dynamics of organic contaminants (including dichloro-diphenyl-trichloroethane (DDTs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs)) were assessed in surface sediments from the Santos Bifurcation (SBF) region, a distinctive oceanographic feature. PCBs, DDTs and PAHs concentrations varied from 0.04 to 0.92 ng g, 0.32 to 1.29 ng g dw, and 57.23 to 276.66 ng g dw, respectively. PCB sources were predominantly associated with long-range atmospheric transport. Historical widespread use of DDTs for agriculture and pest control in continental areas led to their accumulation in the SBF region, where they have undergone slow degradation. The primary sources of PAHs were fossil fuel combustion and petroleum inputs, with latitudinal variations attributed to continental contributions and increased river runoff in southern areas, which are advected northward by coastal currents. Both pyrogenic and petrogenic PAHs are transported by internal shelf currents directed towards the continental slope. All analyzed compounds were detected at higher concentrations in deeper stations (1000 m and 1500 m isobaths) within the SBF region, likely due to regional hydrodynamic processes that enhance the transfer and deposition of contaminants at greater depths.