The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Toxicological Effects of Methylmercury
tion about the hair and blood Hg concentrations in the studies on which the following conclusions are based.
Several studies have detected significant MeHg-associated increases in the frequency of abnormal and questionable findings on standardized neurological examinations, although the functional importance of the apparent effects is uncertain.
Recent epidemiological studies provide little evidence that the ages at which children achieve major language and motor milestones are affected appreciably by low-dose prenatal MeHg exposure.
Two out of four studies using the Denver Developmental Screening Test reported an association of low-dose MeHg exposure on early childhood development.
Of the three major prospective long-term studies, the Faroes study reported associations between low-dose prenatal MeHg exposure and children's performance on standardized neurobehavioral tests, particularly in the domains of attention, fine-motor function, confrontational naming, visual-spatial abilities, and verbal memory, but the Seychelles study did not report such associations. The smaller New Zealand study also observed associations, as did a large pilot study conducted in the Seychelles.
Recent studies in adults suggest that hair Hg concentrations below 50 ppm are significantly associated with disturbances of the visual system (chromatic discrimination, contrast sensitivity, and peripheral fields) and with neuromotor deficits (tremor, dexterity, grip strength, complex-movement sequences, hand-eye coordination, and rapid alternating movement). Those findings suggest that the current reference dose for adults based on 50 ppm in hair might not be sufficiently protective.
Neurodevelopmental studies using animal models (nonhuman primates, rodents) exposed in utero and/or early postnatally to MeHg have reported a continuum of effects related to dose. Effects have been reported on sensory, sensorimotor, and cognitive development. Overall, sensory effects seem to be the most long-lasting.
Experimental studies of adult animal models exposed to MeHg have also reported a continuum of effects associated with dose. The