Exposure and toxic effects of elemental mercury in gold-mining activities in Ecuador

Traditional gold mining, using metallic mercury (Hg0) to form gold amalgam, followed by burning to remove the Hg0, is widely used in South America, Africa and Asia. The gold is sold to merchants who burn it again to eliminate remaining Hg0.In Ecuador, 200 gold miners, 37 gold merchants and 72 referents were studied. The median Hg concentrations in urine (U-Hg) were 3.3 (range 0.23–170), 37 (3.2–420), and 1.6 (0.2–13) μg/g creatinine, respectively, and in whole blood (B-Hg) were 5.2, 30, and 5.0 μg/L, respectively. Biomarker concentrations among merchants were statistically significantly higher than among miners and referents; also the miners differed from the referents. Burning of gold amalgam among miners was intermittent; U-Hg decreased in the burning-free period.In computerized neuromotor examinations, B-Hg and U-Hg concentrations were associated with increases in the centre frequency of the tremor, as well as in reaction time and postural stability.Retention of Hg (B-Hg), and the elimination rate (U-Hg) appears to be modified by polymorphism in a gene of an enzyme in the glutathione synthesis (GCLM), but there were no significant genetic modifications for the associations between exposure and neurotoxicity.Thus, the gold merchants have a much higher exposure and risk than the miners, in whom the exposure varies over time. The metabolism of Hg is modified by genetic traits. The present exposure to Hg had limited neurotoxic effects.

► In Ecuador, gold merchants have a statistically significant higher exposure to mercury (Hg) than the miners.
► Referents Hg median concentrations in urine and whole blood were lower than gold merchants and miners.
► Exposure to Hg was associated with neurotoxic effects: postural stability, centre frequency of tremor and reaction time.
► Metabolism of Hg was modified by polymorphism in a gene of an enzyme in the glutathione synthesis (GCLM).
► No significant genetic modifications of the relationships between exposure and neurotoxicity were found.