Blood mercury and auditory neuro-sensory responses in children and adults in the Nambija gold mining area of Ecuador.

This study investigated blood mercury (B-Hg) levels and the auditory neuro-sensory status of children and adults in the remote Andean settlement of Nambija, Ecuador where Hg is used in the extensive gold mining operations. The mean B-Hg level in 75 Nambija (Study Area) inhabitants (36 children and 39 adults) was 17.5 micrograms/L (SD = 11.0) vs 3.0 micrograms/L (SD = 1.6) in a second group of 34 subjects (15 children and 19 adults) in a non-gold mining area (Reference Area), the difference being statistically significant (p < 0.0001). Neuro-otological examinations revealed 34 subjects (45%) with complaints of headaches and/or memory loss, 3 cases of severe neurological impairment and 4 cases of middle ear pathology. Audiological tests on 40 persons in the Study Area (21 children and 19 adults) showed hearing thresholds ranging from normal to mildly abnormal at 2, 3, 4, 6 and 8 kHz for children, and normal to severely abnormal for adults. Correlation coefficients showed a significant relationship between B-Hg level and hearing level in children at 3 kHz in the right ear, and at no frequency for adults. Auditory brainstem evoked responses (ABR) on subjects in the Study Area showed a significant correlation between B-Hg and the I-III interpeak latency on the right side. The results indicated that the study population of the Nambija gold mining area had abnormally elevated B-Hg levels, and may be at neurological risk from exposure to methylmercury (MeHg) from the consumption of contaminated food and possibly from elemental Hg vapors inhaled during amalgam burning in the gold extraction process.