revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 241
2. HEALTH EFFECTS
to the mean performance of U.S. children. The BSID Psychomotor Scale Indices at both measurement
intervals were two standard deviation units above U.S. norms, but were still consistent with previous
findings of motor precocity in children reared in African countries. The study found no effect that could be
attributed to mercury on the BSID scores obtained at either the 19- or 29-month measurement/testing
interval. The 29-month cohort represented 94% of the 779 mother-infant pairs initially enrolled in the
study, and approximately 50% of all live births in the Seychelles in 1989.
The only observation in the 29-month testing that might be attributable to prenatal mercury exposure was a
slight decrease in the activity level in boys (but not girls) as determined by the Bayley Infant Behavior
Record (subjective observation). Whereas this decrease was significant in males (p = 0.0004), it was not
statistically significant in females (p = 0.87). When the subjective activity scores for male and female
children were evaluated collectively, no statistically significant or remarkable decrease in activity was
apparent outside the >12 ppm maternal hair concentration group. The affect on activity level in boys is not
considered an adverse effect by the authors of the study.
Grandjean et al. (1997b, 1998) reported another epidemiological study of methylmercury exposure for a
population in the Faroe Islands. Although the Faroese are a fishing culture, the major source of
methylmercury exposure for this population is pilot whale meat, which is intermittently consumed as part
of the cultural tradition. The initial study cohort consisted of 1,022 singleton births occurring in a
21-month window during 1986-1987. At approximately 7 years of age, neurobehavioral testing was
conducted on 917 of the remaining cohort members. No abnormalities attributable to mercury were found
during clinical examinations or neurophysiological testing. A neuropsychological test battery was also
conducted, which included the following: Finger Tapping; Hand-Eye Coordination; reaction time on a
Continuous Performance Test; Wechsler Intelligence Scale for Children - Revised Digit Spans, Similarities,
and Block Designs; Bender Visual Motor Gestalt Test; Boston Naming Test; and California Verbal
Learning Test (Children). Neuropsychological tests emphasized motor coordination, perceptual-motor
performance, and visual acuity. Pattern reversal visual evoked potentials (VEP) with binocular full-field
stimulation, brain stem auditory evoked potentials (BAEP), postural sway, and the coefficient of variation
for R-R inter-peak intervals (CVRR) on the electrocardiogram were all measured. The neuropsychological
testing indicated mercury-related dysfunction in the domains of language, attention, memory, and
visuospatial and motor function (to a lesser extent), which the authors considered to remain after the
children of women with maternal hair mercury concentrations above 10 µg/g (10 ppm) were excluded.
While this study represents a significant contribution to the human database for methylmercury exposure