RESUMEN
In order to better define the effects of methylmercury (MeHg) exposure on neurodevelopment, qualitative error types observed in the responses of exposed children to the Stanford-Binet Copying Test were categorized and quantified using raw data from two studies of 395 Amazonian children aged 7-12 years (from Brazil and French Guiana). These outcomes were related to hair-mercury concentration as the biomarker of MeHg exposure (range=0.5-63.8 microg/g). The combined analysis of data from two separate countries had two major goals: (1) to gain clues concerning the underlying neuropathological mechanisms of observed effects based on convergent evidence of MeHg-related qualitative outcomes in the two studies and (2) to explore possible cultural determinants of test response based on divergent outcomes in the two countries. Multiple linear and logistic regression analyses were performed with adjustment for confounders. In the combined data set, mercury exposure was negatively associated with scores on the drawing task: a score reduction of 1.2 (s.e., 0.3) points was observed in the children with a hair-mercury concentration above 10 microg/g compared to those with a hair level below 1 microg/g; this effect appeared to be stronger in the younger children. Risk of committing one or more errors of rotation, simplification or perseveration in the drawings increased with hair-mercury concentration in both cultural settings, providing convergent evidence of specific types of MeHg-related neurocognitive outcomes. However, relationships between mercury exposure and scores on the Block organization component of the test varied according to the study site, indicating that other factors must be considered in evaluating responses to the demands of this cognitive task.
Asunto(s)
Cognición/efectos de los fármacos , Compuestos de Metilmercurio/toxicidad , Percepción Espacial/efectos de los fármacos , Visión Ocular/efectos de los fármacos , Factores de Edad , Brasil , Niño , Preescolar , Estudios Transversales , Exposición a Riesgos Ambientales , Etnicidad/psicología , Femenino , Guyana Francesa , Cabello/química , Humanos , Masculino , Compuestos de Metilmercurio/análisisRESUMEN
French Guiana, like its neighbors, suffers from environmental pollution with methylmercury from gold mining activities, and Amerindian communities are particularly affected. A neurological and a neurospsychological evaluation were carried out in children of three Amerindian communities with various levels of pollution: 156 children from the Upper Maroni (high exposure), 69 from Camopi on the Oyapock river (median exposure), and 153 from Awala on the Atlantic coast (low exposure). Exposure to methylmercury was measured by determination of total mercury in the hair of the children and their mothers (geometric mean, 12.7 microg/g in Upper Maroni). No major neurologic signs were observed in the children examined. After adjustment for potential confounders, we found a dose-dependent association between maternal hair mercury level and increased deep tendon reflexes, poorer coordination of the legs, and decreased performance in the Stanford-Binet Copying score, which measures visuospatial organization. In this last test, the frequency of rotation errors was high in the 5-6 years age group and increased with mercury exposure. These associations depended on the sex of child and were stronger among boys. The interpretation of these results is limited mainly by the cross-sectional design of the study. It identifies specific neurological and neuropsychological deficits, in some cases modulated by sex, which are consistent with known targets of mercury neurotoxicity.