Metallic mercury (Hg) is used in artisanal gold mining to recover fine gold particles through amalgamation. Most commonly, the gold is recovered by feeding sediments from river bottoms and adjacent areas through a number of Hg coated sieves, in this way, Hg amalgamates with the gold in the sediments separating the gold from the rest of the material. For each kilogram of gold an average of one kilogram of Hg is used. The characteristics of gold production processes and possibly the inadequate waste disposal practices contribute to the release of large quantities of Hg into the environment.

The release of Hg resulting from gold mining into the Amazon river and its tributaries has contaminated both the hydrosystem and the ecosystem along the river basins of Bolivia and Brazil. Artisanal gold mining also occurs in Colombia, Guyana, Nicaragua, Peru, Suriname, and Venezuela; suggesting that Hg pollution to the environment is a widespread problem in Latin America.

Consumption of contaminated fish is the major route of human exposure to the Hg released in the environment. Once in the water or soil, when hg comes in contact with organic matter, it is transformed into methylmercury (MeHg). In aquatic environments, MeHg accumulates in the tissue of fish through food intake and respired water. MeHg accumulates up aquatic food chains and organisms in the higher trophic levels have higher quantities of MeHg in their tissues.

Fish is an important source of protein for many riverside populations living downstream from gold mining areas and their high frequency of fish consumption, particularly of those species in the higher trophic levels, increases their exposure potential.

The target for MeHg toxicity is the nervous system. At high levels of exposure MeHg is a potent neurotoxin and its exposure has been associated with the development of severe disabilities. An outbreak of neurological disorders associated with the consumption of MeHg contaminated fish occurred in Japan, where industrial releases led to widespread Hg pollution in Minamata during the 1950s and 1960s. In Minamata, 23 children believed to be exposed prenatally when their mothers consumed contaminated fish were born with severe disabilities, including mental retardation and cerebral palsy.

In the winter of 1971-1972, a large outbreak of organic Hg poisoning occurred in Iraq as the result of eating bread prepared with wheat and other cereals treated with a MeHg fungicide. A study on 84 Iraqi infant-mother pairs reported a range of maternal hair Hg between 0.4 and 640 m g/g. At maternal hair concentrations above 70 m g/g children from the study group exhibited evidence of abnormal neurological signs, such as the inability to coordinate voluntary muscular movements.

The results of the Iraqi study led to the conclusion that children born to women with Hg hair concentrations above 70 m g/g had 30% risk of developing neurological signs and symptoms. The World Health Organization (WHO) used the data from the Iraqi study to extrapolate what would be the risk of developing neurologic disorders when children are exposed to lower Hg levels. The WHO calculated that Hg levels of 10-20 m g/g in maternal hair could be associated with 5% risk of developing neurologic disorders.

The next table shows data from several studies that were conducted in the period 1996-2001 to determine hair Hg concentrations in children and women of childbearing age living downstream from gold mining activities. Six studies from Brazil reported this information. The range of mean hair Hg concentrations reported in the studies was 0.8-94.7 m g/g among women and 0.4-94.5 m g/g among children.

Hair Mercury Concentrations from Riverside Populations in Brazil

In one of these studies, neuropsychological tests were administered to determine neurotoxicity from MeHg exposure. The results of this study found that the scores of the various neuropsychological tests administered decreased as the children’s hair Hg concentrations increased. These tests specifically measured manual motor ability, motor coordination and dexterity, short-term memory, information processing, and visual-constructional function. On the basis of these results the authors concluded that these children may not function as well intellectually as they would have in the absence of MeHg exposure.

Although the general population does not face a significant health risk from MeHg, the data from Brazil suggest that many children are at increased risk of exposure and development of adverse health effects related to this exposure. The number of children and women of childbearing age from the Latin American and Caribbean Region with hair Hg concentrations above 10 m g/g is not known with certainty, however, this number could be quite large. A clearer picture of the situation of the Region with respect to the number and characteristics of the children and mothers exposed to Hg through fish consumption and the body burden of these groups as well as related health impacts is needed. This is specially important for countries where no evidence that such evaluations are being conducted was found. Such assessment is important in that it would allow public health professionals to determine the extent of the problem and the types of interventions that would be necessary to address it.

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