Neurophysiological Anomalies in Brainstem Responses of Mercury-Exposed Children of Andean Gold Miners

The health hazards of occupational exposure to Mercury (Hg) in adult gold miners are well known, but little attention has been given to the effects of Hg exposure in the children of gold miners. Children who assist their parents in gold mining operations or live in mining enclaves may be exposed to elemental Hg vapors or methylmercury-contaminated food, both of which may induce neurodevelopmental disabilities. Brainstem auditory-evoked responses (BAER) were measured as biomarkers of subtle mercury-induced neurological impairment in Andean children of gold miners living in the Ecuadorian gold mining settlement of Nambija, where Hg exposure is prevalent. Thirty-one children (19 boys and 12 girls, aged 4-14 years, mean age: 10 years) in the study group were found to have a mean blood mercury (HgB) level of 23.0 µg/L (SD: 19, range: 2.0-89.0 µg/L; median: 20 µg/L), which was significantly higher than the mean HgB level of a reference group of 21 Ecuadorian children (4.5 µg/L, SD: 2.3; t = 4.39, P = 0.0001), and in excess of the health-based biological limits for the U.S. (10 µg/L). The BAER measures indicated statistically significant differences in interpeak III-V (P = 0.03) and I-V (P = 0.008) neural conduction times for children with HgB levels above the median. BAERs at the conventional click stimulus rate of 10/second showed statistically significant positive correlations between HgB level and the absolute latency of wave V (P = 0.03), and the neural conduction times of the eighth nerve to midbrain I-V interval (P = 0.02). BAER at 50/second revealed statistically significant relationships between HgB and the latency of wave VI (P = 0.03), and the I-VI interpeak interval (P = 0.02). Brainstem neural conduction times suggested that some of the Hgintoxicated children in the study group have subtle neurophysiological anomalies that may be more manifest at higher BAER stimulus rates, and that the Hg-exposed children of gold miners are at risk for neurodevelopmental disabilities.