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

MERCURY 145
2. HEALTH EFFECTS
Temporary Weekly Intake of 0.3 mg recommended by WHO. In 1 of 8 consecutive births, the mercury
concentration in maternal hair exceeded a limit of 10 µg/g, a level where neurobehavioral dysfunction in the
child may occur. The maximum level was 39.1 µg/g. Mercury concentrations in umbilical cord blood
showed a similar distribution with a maximum of 351 µg/L. The large variation in mercury exposure is
associated with differences in the frequency of whale dinners. The average PCB concentration in pilot
whale blubber is very high (about 30 µg/g). With an estimated daily consumption of 7 g of blubber, the
average daily PCB intake could therefore exceed 200 µg (i.e., close to the Acceptable Daily Intake). In
Scandinavia, the average daily PCB intake is about 15–20 µg.
In the continuation of this work, Grandjean et al. (1997b, 1998) studied a cohort of 1,022 consecutive
singleton births generated during 1986–1987 in the Faroe Islands. Increased methylmercury exposure from
maternal consumption of pilot whale meat was estimated from mercury concentrations in cord blood and
maternal hair. At approximately 7 years of age, 917 of the children underwent detailed neurobehavioral
examination. Neuropsychological tests included 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). Neurophysiological 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 interpeak intervals (CVRR) on the electrocardiogram were measured. Mercury in cord blood,
maternal hair (at parturition), child hair at 12 months, and child hair at 7 years of age were measured. The
geometric average mercury concentrations were 22.9, 4.27, 1.12, and 2.99 µg/g, respectively. Mercury
concentrations in cord blood were most closely associated with the concentrations in maternal hair at
parturition and less so with children's hair at 12 months and 7 years. Clinical examination and
neurophysiological testing did not reveal any clear-cut mercury-related abnormalities. However,
mercury-related neuropsychological dysfunctions were most pronounced in the domains of language,
attention, and memory, and to a lesser extent in visuospatial and motor functions. The authors state that
these associations remain after adjustment for covariates and after exclusion of children with maternal hair
mercury concentrations above 10 µg/g (50 nmol/g). They further conclude that the effects on brain function
associated with prenatal methylmercury exposure appear diverse, with early dysfunction in the Faroe Island
population detectable at exposure levels currently considered to be safe.