Mercury (Hg) is a global pollutant with a complex cycle, which alternates between different compartments such as air, water, sediments, soil and organisms. It has several chemical species, being considered the metal with the greatest toxic potential released into the environment, which undergoes biomagnification along the food chain. In the last century, mercury levels at the global level have increased as a result of the increasing pollution arising from the industrial, occupational and medicinal uses of this element. For the oceans, an increase of 150% in anthropogenic emissions in thermocline concentration has been reported since the pre-industrial period. This increase in Hg concentrations in the oceans has a direct relationship with the health of the marine and the human ecosystem due to the consumption of contaminated marine organisms. Thus, the objective of the present study was to determine the baseline of Hg concentrations in different water masses in the South Atlantic between 20º and 24ºS. Water sampling was carried out in two periods: November 6, 2016, on the oceanographic vessel OceanStalwart and December 4 to 20, 2016, on the NPqHO Vital de Oliveira (H39). During the November campaign, water was collected using a horizontal Niskin bottle, with surface water sampling at 20ºS. In the December campaign, water samples were collected in a Rossete system, sampled at different depths between 20º (Cabo Frio) and 24ºS (Vitória Trindade chain). In the laboratory of the Federal University of Rio Grande (FURG), the samples (unfiltered) were subjected to chemical treatment, and the HgT was analyzed in atomic fluorescence (TEKRAN® 2600 series). Thus, the total mercury obtained in Tropical Water was on average 6.3 ± 1.4 pM (n = 16). The Central Water of the South Atlantic presents an average of 5.9 ± 0.7 pM (n = 8). Antarctic Intermediate Water has a mean HgT of 5.3 ± 0.6 pM (n = 2). The Upper Circumpolar Water points to an HgT of 6.5 pM (n = 1). The North Atlantic Deep Waters exhibit an average HgT of 5.8 ± 0.9 pM (n = 12). The atmospheric deposition and the general circulation of the oceans were pointed out as responsible for the amount of Hg in the water masses of the study region. The results indicate that the presence of particles can play an important role in Hg concentration. The data agrees with the hypothesis that Hg accumulates slowly in the ocean’s deep waters, where in general, the highest concentrations were recorded. The tropical water samples closest to the coast showed the highest values, indicating the contribution of natural and human-made continental discharges. In this context, it is proposed that the shallower water bodies of the open ocean appear to have a lower average HgT, in proportions of the deep waters of the North Atlantic and Antarctic Bottom Water, which have HgT, in proportions above the most known sources, which reinforces our results.
|
