Synergic Effect of Gold Mining and Damming on Mercury Contamination in Fish

Abstract

Since the late 1980s, several studies have shown that human populations in the Amazon basin are exposed to high mercury levels in their fish diet. Gold mining, which releases the metal during the amalgamation process and erodes soils naturally rich in mercury, is regarded as the main contamination source. Here, we present the results of a comparative study of mercury distribution in the water and fish of two adjacent rivers in French Guiana, with and without gold mining activities. As a consequence of a marked difference in suspended particulate matter between the two systems, total mercury concentrations in unfiltered water samples were higher in the mined river (25.4-34.9 ng L(-1)) as compared to the reference one (2.1-5.4 ng L(-1)). Surprisingly, no significant differences were observed in mercury concentrations between 13 common fish species at upstream sites. In sharp contrast, mercury concentration of fish caught downstream a hydroelectric reservoir, where the two rivers flow, was up to 8-fold higher than that upstream. Mercury speciation measurements allowed one to relate these differences in fish to the water distribution of monomethylmercury, the mercury chemical species that biomagnifies along aquatic foodwebs. Indeed, mean dissolved monomethylmercury concentrations were low and similar in both rivers (0.03-0.06 ng L(-1)), while they were 10 times higher (up to 0.56 ng L(-1)) in the water outflowing the hydroelectric dam. Dissolved monomethylmercury determinations along a water column profile suggest that methylation of inorganic mercury occurs in the deep anoxic part in reservoir. We conclude that mercury mobilization related to gold mining is not solely sufficient to account for high concentrations in fish and that environmental conditions that favor mercury methylation, such as anoxia, are needed.

Advances in the study of giant otter (Pteronura brasiliensis): ecology, behavior, and conservation: a review

“…Such unsafe concentrations of mercury present in the water, fish and sediments, pose serious threats to the giant otter, which depends on fish for its survival 4 Boudou et al, 2005;Durrieu et al, 2005).…”

“…Dias Fonseca et al (2005) analyzed different organs and tissues of two giant otters found dead in the Pantanal, in a region where no gold mining activity is reported, and found no evidence of contamination. However, especially in Brazil, where hydroelectric dams are an important component of development plans, a synergic effect of gold mining and damming on mercury contamination in fish should be considered as observed by Boudou et al (2005). They found that mercury mobilization related to gold mining account for even higher concentrations in fish when environmental conditions typical of a reservoir, such as anoxia, are present.…”

Interações Mercúrio-Selênio: Uma Abordagem Integrada De Avaliação De Exposição Ao Mercúrio Em Populações Ribeirinhas No Município De Porto Velho, Rondônia

“…Existem estudos que reportam, também, um incremento nas áreas à jusante de hidrelétricas, podendo atingir concentrações que representem um risco para a saúde das populações que dependem do consumo do peixe para sua subsistência (Verdon et al, 1991;Boudou et al, 2005;Hylander et al, 2006 (Veiga et al, 1994;Malm, 1998;Roulet et al, 1999;Wasserman et al, 2001;Lacerda e Malm, 2008).…”

Effects of Small-Scale Gold Mining Tailings on the Underwater Light Field in the Tapajós River Basin, Brazilian Amazon

“…In the Brazilian Amazon, for example, sediments from mining tailings in streams and rivers may vary between one and two tonnes per gram of gold produced [13]. One of the major impacts of water siltation is the increase in light attenuation by suspended particles, which can directly affect phytoplankton productivity by limiting the availability of Photosynthetic Active Radiation (PAR), and indirectly contribute to changes in biodiversity within rivers, including plankton [10], macroinvertebrates [14], and fish [15]. Specific to the Amazon Basin, a major reduction in phytoplankton density has been documented in Batata Lake due to a gain in suspended matter caused by mining activity [16].…”