Mercury Biomagnification in a Tropical Black Water, Rio Negro, Brazil

Abstract

The population living along the riverbanks of the Amazon basin depends heavily on fish for nutritional support. Mono-methyl-mercury (MMHg) concentrates in fish, which can contaminate humans, the risk depending not only on fish MMHg concentration but also on the amount of fish consumed. We sampled nine locations of the Rio Negro basin, differing in water pH, Hg concentrations, and dissolved organic carbon (DOC), and determined total Hg from 951 fish samples of species representative of the food web: herbivorous, detritivorous, omnivorous, and piscivorous. Mercury concentrations varied widely in all species but showed a trend that depended on fish feeding strategies. The highest mean concentration was found in the piscivorous species (688.90 ng/g(-1)), followed by omnivorous (190.30 ng/g(-1)), detritivorous (136.04 ng/g(-1)), and herbivorous (70.39 ng/g(-1)). Fish Hg concentrations exceeding current safe limits (500 ng/g(-1)) for human consumption were found mainly in the piscivorous species (60%). Significant positive correlation between fish weight and Hg concentration was seen for the piscivorous Serrasalmus spp. (n = 326; r = 0.3977; p < 0.0001), Cichla spp. (n = 125; r = 0.4600; p < 0.0001), and Pimelodus spp. (n = 12; r = 0.8299; p = 0.0008), known locally as Piranha, Tucunaré, and Mandi, respectively. However, a negative correlation was seen for non-piscivorous Potamorhina latior (n = 30; r -0.3763; p = 0.0404) and Leporinus spp. (n = 44; r = -3987; p = 0.0073), known as Branquinha (detritivorous) and Aracu (omnivorous). Fish-Hg concentrations in the acidic waters (pH range, 4.09-6.31) of the Rio Negro habitat, with its wide gradient of Hg concentrations (3.4-11.9 microg/L(-1)) and DOC (1.85-15.3 mg/L(-1))--but no history of gold mining activity-are comparable to other Amazonian rivers. Opportunity fish catches in the Rio Negro habitat show high muscle-Hg derived from natural sources, but no systematic association with site-dependent geochemistry.

Mercury accumulation in bats near hydroelectric reservoirs in Peninsular Malaysia

“…Extensive deforestation and agricultural land use also release mercury from soils creating point sources of local, acute contamination (Barbosa et al 2003). Lake-sediment records suggest locations distant from point source contamination can also receive significant inputs of anthropogenically released mercury due to transcontinental and global distribution of highly volatile, atmospheric mercury (Fitzgerald et al 1998;Chan et al 2003).…”

“…forms of mercury are naturally present in the substrate, but can be transformed by sulphatereducing and iron-reducing bacteria to methylmercury (MeHg) (Chan et al 2003;Poulain and Barkay 2013). Significant amounts of mercury can be introduced into aquatic food webs during the flooding of forests (Barbosa et al 2003), such as during the construction of hydroelectric dams (Bodaly et al 1984;Stokes and Wren 1987;Ikingura and Akagi 2003). When a reservoir is created, submerged vegetation and organic material start to slowly decompose (Rodgers et al 1995), leading to a rise in the dissolution rate of organic carbon, increased release of mercury bound to organic material and higher net mercury methylation rates (Chan et al 2003).…”

“…Mercury biomagnifies as it moves up the food chain, with high trophic level species, such as top predators showing higher concentrations of mercury in their tissues than primary consumers, which absorb mercury (Barbosa et al 2003;Stewart et al 2008). Insects that have aquatic larval stages could act as biovectors, exporting methylmercury from aquatic systems upon emergence (Benoit et al 2013;Mogren et al 2013).…”

“…Baxter 1977;Tweedy et al 2013), have measured total mercury in fish (e.g. Barbosa et al 2003), aquatic insects (e.g. Hall et al 1998;Benoit et al 2013); or fish-eating birds and mammals (see Chan et al 2003 and references therein).…”

The influence of seasonalness on the structural characteristics of aquatic humic substances extracted from Negro River (Amazon State) waters: interactions with Hg(II)

“…19 Elevated levels of mercury have been detected in aquatic Amazonian soils and systems in localities geographically distant from anthropic emissions sources. [20][21][22][23][24][25] As a global pollutant derived from natural and anthropic processes, mercury has a permanence time in the atmosphere which is relatively long and is transported via dry and/or wet atmospheric depositing. Intensive intemperisms and lixiviation over the most part of the year have led to the diminishing of cations in the soil.…”