Total and methyl mercury distribution in water, sediment, plankton and fish along the Tapajós River basin in the Brazilian Amazon.

Mercury (Hg) is known as one of the major contaminants in the Amazon. The Tapajós River basin, in the Brazilian Amazon, has diverse anthropogenic activities which increase Hg concentrations in the aquatic ecosystem. Moreover, high concentrations of Hg are naturally found in this basin. Distribution of total (THg) and methyl (MeHg) mercury were assessed in unfiltered water (n = 47), suspended particulate matter (SPM, n = 30), superficial sediment (BS, n = 29), plankton (n = 28) and fishes (n = 129) from the Tapajós River basin. Suspended particles were the main carrier of Hg in the water column and sediment. Increased erosion, prompted by anthropic activities, led to higher Hg concentrations in water from the most impacted areas. Hg is transported mainly in particulate matter; thus, anthropic disturbances influence Hg concentrations downstream. Limnological parameters such as organic matter content influenced MeHg concentrations in water, plankton and sediment of the Tapajós basin. Hg methylation in total plankton was more efficient in lakes (13-66%) than in Tapajós River main channel (2-14%). Biotic and abiotic factors interact in a complex way in the aquatic ecosystem, making Hg concentrations to vary in food web. Gold mining and deforestation probably increase Hg levels in the Tapajós basin. Thus, in addition to Hg monitoring, prevention and remediation efforts should be focused on soil and sediment erosion control.

Mercury and selenium in fishes from the Tapajós River in the Brazilian Amazon: An evaluation of human exposure.

This work aimed to evaluate associated risks of fish consumption to human health, concerning mercury (Hg) and selenium (Se) concentrations in fish species largely consumed in the Tapajós River basin in the Brazilian Amazon. Total mercury (THg), methylmercury (MeHg) and Se concentrations were measured in 129 fish specimens from four sites of the Tapajós River basin. Estimated daily intake (EDI) of Hg and Se were reported regarding fish consumption. EDI were compared with the reference value of provisional tolerable daily intake proposed by the World Health Organization (WHO). Se:Hg ratios and selenium health benefit values (Se HBVs) seem to offer a more comprehensive fish safety model. THg concentrations in fishes ranged from 0.03 to 1.51 µg g-1 of wet weight (w.w.) and MeHg concentrations ranged from 0.02 to 1.44 µg g-1 (w.w.). 80% of the samples were below the value of Hg recommended by the WHO for human consumption (0.5 µg g-1 w.w.). However, Hg EDI exceeded the dose suggested by the United States Environmental Protection Agency (0.1 µg kg-1 day-1), due to the large level of fish consumption in that area. Se concentrations in fishes ranged from 0.02 to 0.44 µg g-1 w.w. An inverse pattern was observed between Hg and Se concentrations in the trophic chain (highest levels of Se in the lowest trophic levels). The molar ratio Se:Hg and Se HBVs were higher in iliophagous and herbivorous fishes, which is noteworthy to reduce toxic effects of Hg contamination. For planktivores, the content of Se and Hg was almost equimolar. Carnivorous fishes - with the exception of Hemisorubim platyrhynchos and Pseudoplatystoma fasciatum -, showed Se:Hg ratios <1. Thus, they do not act as a favorable source of Se in the diet. Therefore, reduced intake of carnivorous fishes with preferential consumption of iliophages, herbivores and, to some extent, even planktivores should be promoted as part of a healthier diet.

Metal bioaccumulation in consumed marine bivalves in Southeast Brazilian coast.

This work aimed to investigate metal bioaccumulation by mussels (Perna perna) and Lion's Scallop (Nodipecten nodosus) farmed in tropical bays, in order to estimate spatial and temporal variation in the exposure to these elements, as well as human health risk. The concentration of each measured element was considered for this evaluation, using maximum residue level (MRL) in foods established by the Brazilian (ANVISA), American (USFDA) and European Communities (EC) legislations. Values for estimated daily ingestion (EDI) were determined for metals intake through mussel and scallop consumption. These estimates were compared with the reference value of (PTDI) proposed by World Health Organization (WHO). Trace elements concentration was measured on ninety mussels P. perna (tissue) and ninety Lion's Scallop N. nodosus (muscle and gonad) reared in four different tropical areas of the Southeast Brazilian coast, between 2009 and 2010. Zinc (Zn), Iron (Fe), Copper (Cu), Manganese (Mn), Chrome (Cr), Nickel (Ni), Cadmium (Cd) and Lead (Pb) concentrations were measured by flame atomic absorption spectrometry after acid mineralization. Cd and Mn were more efficiently bioaccumulated by scallops than mussels and the opposite was found for Fe, Cu and Ni. Guanabara Bay and Sepetiba Bay were considered the most impacted between ecosystems studied. Higher Cd values in Arraial do Cabo in the other sites studied were associated with upwelling that occurs in the region. Consumption of both species cannot be considered safe, because the Cu and Cr concentrations, in accordance with the limits established by the Brazilian Agency (ANVISA). On the other hand, any EDI value exceeded the corresponding value of the PTDI, proposed by World Health Organization (WHO).