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MERCURY A-10
APPENDIX A
MINIMAL RISK LEVEL (MRL) WORKSHEET
Chemical Name: Methylmercury
CAS Number: 22967-92-6
Date: June 15, 2001
Profile Status: Final Draft
Route: [ ] Inhalation [ X ] Oral
Duration: [ ] Acute [ ] Intermediate [ X ] Chronic
Key to figure: 88
Species: Human
Minimal Risk Level: 0.0003 [ X ] mg/kg/day [ ] mg/m 3
Reference: Davidson et al. 1998. Effects of prenatal and postnatal methylmercury exposure from fish
consumption on neurodevelopment: Outcomes at 66 months of age in the Seychelles Child Development
Study. JAMA 280(8):701-707.
Experimental design. This MRL is based on the results of the Seychelles Child Development Study
(SCDS), a series of evaluations on a population in the Seychelles Islands. The chronic oral MRL for
methylmercury is based upon the Seychelles Child Development Study (SCDS), in which over 700
mother-infant pairs have, to date, been followed and tested from parturition through 66 months of age
(Davidson et al. 1998). The SCDS was conducted as a double-blind study and used maternal hair mercury
as the index of fetal exposure. Enrollees were recruited by the head nurse/hospital midwife by asking the
mothers if they wished to participate in the study when they arrived at the hospital for delivery. The first
779 who did not decline participation became the mothers in the study cohort. Of the initial 779 mothers
enrolled in the study at parturition, 740 remained at the predetermined child testing age of 6.5 months, 738
remained in the 19-month cohort, 736 remained at 29 months, and 711 remained for the 66-month
neurobehavioral and developmental examinations.
The Seychellois were chosen as a study population for a number of reasons. (1) All fish contain some level
of methylmercury (Davidson et al. 1998); and the Seychellois regularly consume a large quantity and
variety of ocean fish, with 12 fish meals per week representing a typical methylmercury exposure. (2) The
median total mercury concentration in 350 fish sampled from 25 species consumed by the Seychellois was