Methyl mercury exposure in northern Quebec. I. Neurologic findings in adults.

Cree Indians of northern Quebec were exposed to methyl mercury through contamination of local fish. The relationship between measures of exposure and neurologic abnormalities was studied in two communities in 1978 by comparing the exposure of 41 "cases" with selected neurologic abnormalities with that of 179 normal "controls." In the community of Mistassini, a significant positive association was found between neurologic abnormalities and methyl mercury exposure; in Great Whale, the association, although also positive, was not statistically significant. However, although allowance was made for confounding variables, it remains possible that the effects are not entirely attributable to methyl mercury. Further, the data do not permit estimation of a threshold level of exposure above which excess neurologic abnormalities might occur, because recent levels of exposure do not reflect those of the past. Whether the abnormalities observed in this study will remain stable, regress, or progress can only be determined by continued surveillance.