Mercury and selenium in biological pump under upwelling-downwelling influence in Cabo Frio shelf, South Atlantic Ocean, Brazil.

Abstract

The knowledge of metals concentration in upwelling areas are a concern due the higher productivity of these areas In Cabo Frio Upwelling-Downwelling System (CFUS) is high primary productivity area and has been identified as an Hg hotspot to biota in SE Brazil that has been susceptible to Hg inputs, due to growing industrialization in the region. To investigate the concentration of Hg and Se metals, as well as the trophic transfer of these metals, the present study investigated Hg and Se concentrations in 64 samples collected in net mesh of >20, >64, >150 and >300 μm, in 2012, in the region's water masses. Higher mean Hg concentrations were found in zooplankton, 0.15 ± 0.09 μg g^-1 (>300 μm) and 0.18 ± 0.1 μg g^-1 (>150 μm), compared to phytoplankton, 0.11 ± 0.11 μg g^-1 (>64 μm) and 0.06 ± 0.07 μg g^-1 (>20 μm), and the calculation of the biomagnification factor (BMF) indicated that there was a process of magnification and trophic transfer. An opposite trend was found for Se in phytoplankton: higher average Se concentrations were observed in phytoplankton, 93.0 ± 65.2 μg g^-1 (>64 μm), 93.8 ± 96.4 μg g^-1 (>20 μm), compared to zooplankton, 91.1 ± 67.3 μg g^-1 (>300 μm), 97.3 ± 71.3 μg g^-1 (>150 μm). A positive linear relationship for the Hg:Al vs P:Al ratios was identified and indicated intracellular incorporation of Hg according to plankton size. Anthropogenic Hg sources were identified in the plankton samples by comparison with the sediment background values for the CFUS. Upwelling waters probably increased the availability of Hg and Se, these elements tend to bioaccumulate 10 to 100 times more than in areas with the influence of upwelling, due to fertilization and the increase in primary production.