Neurocognitive screening of mercury-exposed children of Andean gold miners

Performance on Raven's Coloured Progressive Matrices (RCPM) test of visual-spatial reasoning was used to evaluate the effects of mercury (Hg) exposure on 73 Andean children aged 5 to 11 years (mean: 8.4) living in the Nambija and Portovelo gold mining areas of Ecuador, where Hg is widely used in amalgamation. Mean levels of Hg found in blood (Hg_B), urine (Hg _U), and hair (Hg_H) samples were 5.1 μg/L (SD: 2.4; range: 1-10 μg/L), 13.3 μg/L (SD: 25.9; range: 1-166 μg/L), and 8.5 μg/g (SD: 22.8; range: 1-135 μg/g), respectively. Of the children in the Nambija area 67-84.9% had abnormal RCPM standard scores (i.e., ≤ 25%tile), depending on the test norm used in the data analysis. Higher standard scores for Peruvian (t = 4.77; p = < 0.0001) and Puerto Rican (t = 4.51; p = < 0.0001) norms than for U.S. norms suggested a linguistic influence. No difference was found between Peruvian and Puerto Rican norms (t = 0.832; p = < 0.408), which showed a significant positive correlation (r = 0.915, p = < 0.0001). Children with abnormal Hg_B and Hg_H levels had significantly lower scores on the RCPM subtest B than did children with nontoxic Hg levels (t = -2.16; p = < 0.034). These results suggest that a substantial number of Hg-exposed children in the Nambija study area have neurocognitive deficits in visual-spatial reasoning.