Effects of environmental contaminant exposure on visual brain development: a prospective electrophysiological study in school-aged children.

The Inuit from Nunavik (Northern Québec) are one of the most highly exposed populations to environmental contaminants in North America mainly due to the bioaccumulation of contaminants in fish and marine mammals that constitute an important part of their diet. This follow-up study aimed to assess the impact of exposure to contaminants on visual brain development in school-age Inuit children (mean age=10.9 years). Concentrations of polychlorinated biphenyls (PCBs), mercury (Hg), and lead (Pb) were measured in umbilical cord blood and again in blood samples at the time of testing, reflecting pre- and current exposure, respectively. Pattern-reversal visual evoked potentials (VEPs) were scalp-recorded at the occipital cortex. Visual stimulation consisted of achromatic gratings presented at four visual contrast levels: 95%, 30%, 12% and 4%. The relation between environmental contaminant body burdens and VEPs was examined by regression analysis controlling for confounding variables, including fish nutrients and other toxicants. No significant association was found for PCB exposure after statistical adjustments. Cord blood mercury level was associated with a reduction of the N75 amplitude at the highest contrast level and with a delay of the N75 latency at the 12% contrast level. Prenatal exposure to lead was associated with a delay of the N150 latency at most contrast levels. This study suggests that heavy metal exposure, in particular during the gestational period, can impair the development of visual processing.