Gold-Mining Activities and Mercury Contamination of Native Amerindian Communities in French Guiana: Key Role of Fish in Dietary Uptake

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In 1994, the French National Public Health Network reported significant mercury exposure of native Amerindians in French Guiana. In 1997, a study was conducted in the Wayana community to quantify the dietary intake and to identify the fish species contributing the most to the contamination. The study was completed by an impregnation analysis based on Hg determination in hair samples. The methodology used was a detailed familial dietary study associated with Hg measurements in fish and some game. The study was conducted over 7 days in two different seasons in the four most populated Wayana villages on the upper part of the Maroni River (521 people; 70% of the Wayana population in French Guiana). Analysis was based on data on consumption obtained from 165 people in a 1-14 day period (i.e., 940 persons x days) and involved 270 fish samples from 48 species. Total Hg and monomethylmercury (MMHg) were also determined in hair samples (235 samples for total Hg). The results confirm mercury exposure of the Wayana population related to a diet rich in fish, which are relatively highly contaminated for certain species (up to 1.62 mg/kg fresh weight or 8.1 mg/kg dry weight in skeletal muscle). Results from hair samples showed that 57% of the Amerindians had Hg levels above the World Health Organization (WHO) safety limit (10 [micro] g/g); all those over 1 year of age had a Hg intake greater than the WHO safety limit (200 [micro] g MMHg/week for a 60-kg male). Hg concentrations in fish muscle were closely linked to the feeding regime and position of fish in the food webs. Overall, 14.5% of the fish collected exceeded the 0.5 mg/kg (fresh weight) safety limit. Four carnivorous species accounted for no less than 72% of the metal ingested by the Wayana families, although these represented only 28% of the consumed fish biomass. In conclusion, this study revealed excessive exposure to mercury in the Wayana population in French Guiana related to the consumption of contaminated fish. Key words. Amerindians, dietary uptake, fish, French Guiana, gold mining, hair, mercury. Environ Health Perspect 109:449-456 (2001). [Online 1 May 2001]

Gold-mining activities have been responsible for discharges of mercury into the environment as a consequence of using the mercury amalgamation method, where the gold obtained from river sediments, soils, or groundwater rocks is separated from elemental mercury (Hg [degrees]) by open circuit heating. In Brazil, for example, it is estimated that more than 130 tons of mercury are used per year, on the basis of 1.4 kg Hg for 1 kg of gold (1,2). More than 6 million people participated in gold prospecting in the Amazon region alone during the gold rush at the end of the 1880s (1). This volatile form of mercury is discharged into the atmosphere (55%) and aquatic biotopes (45%) (1). Within the biogeochemical cycle of the metal, Hg [degrees] can be oxidized in inorganic mercury (HgII) and then methylated by biotic (bacterial methylation) and/or abiotic (humic acids as methyl group donors for example) processes (3).

Studies in the Amazon Basin have shown numerous examples of contamination of hydrosystems by mercury. Concentrations measured in aquatic organisms were different according to their position within the food webs: predatory species, particularly the piscivorous species, have the highest levels of contamination due to the biomagnification of the methylated form of the metal. In a survey conducted between 1987 and 1990, approximately one-third of the carnivorous fish caught downstream from the Madeira River gold-mining area had mercury levels [is greater than] 0.5 [micro] g/g fresh weight (fw), which is the safety limit (4).

Riverside populations of the Amazon tend to present high Hg levels in hair because fish is their main protein source. For example, the average of hair Hg in family members of fishermen from the Duas Bocas Lake shores (Amapa State, Brazil), directly influenced by Hg releases from gold mining, was 28 [micro] g/g. …