Qualitative assessment of visuospatial errors in mercury-exposed Amazonian children

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.