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

MERCURY 238
2. HEALTH EFFECTS
• (4) The population is highly literate, cooperative, and has minimal immigration and emigration.
C (5) The Seychellois constitute a generally healthy population, with low maternal alcohol consumption
and tobacco use (700 mother-infant pairs).
C (7) Excellent retention of mother-infant pairs throughout the study (i.e., 711 of the initially enrolled
778 mother-infant pairs still participating at 66 months post-partum.
C (8) The use of standardized neurobehavioral tests.
The results of the 66-month testing in the SCDS revealed no evidence of adverse effects attributable to
chronic ingestion of low levels of methylmercury in fish (Davidson et al. 1998). In this study, developing
fetuses were exposed in utero through maternal fish ingestion before and during pregnancy (Davidson et al.
1998). Neonates continued to be exposed to maternal mercury during breastfeeding (i.e., some mercury is
secreted in breast milk), and methylmercury exposure from the solid diet began after the gradual
post-weaning shift to a fish diet. In the 66-month study cohort, the mean maternal hair level of total
mercury during pregnancy was 6.8 ppm (range, 0.5–26.7 ppm; n=711), and the mean child hair level at the
66-month testing interval was 6.5 ppm (range, 0.9–25.8 ppm; n=708). The mean maternal hair mercury
level in the highest exposed subgroup in the study was 15.3 ppm (range, 12–26.7; n=95). The 66-month
test battery, which was designed to test multiple developmental domains, included the following primary
measurements:
C (1) General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities (to estimate
cognitive ability);
C (2) the Preschool Language Scale (PLS) total score (to measure both expressive and receptive
language ability);
C (3) the Letter and Word Recognition and
C (4) Applied Problems subtests of the Woodcock-Johnson (W-J) Tests of Achievement (to measure
reading and arithmetic achievement);
C (5) the Bender-Gestalt test (to measure visual-spatial ability); and
C (6) the total T score from the Child Behavior Checklist (CBCL) (to measure the child's social and
adaptive behavior). Serum sampling revealed no detectable levels of PCBs (detection
limit=0.2 ng/mL).