| A Revised Probabilistic Estimate of the Maternal Methyl Mercury Intake Dose Corresponding to a Measured Cord Blood Mercury Concentration Alan H. Stern Division of Science Research and Technology, New Jersey Department of Environmental Protection, Trenton, New Jersey, USA; and Division of Environmental and Occupational Health, University of Medicine and Dentistry of New Jersey-School of Public Health, Piscataway, New Jersey, USA Abstract
In 2001, the U.S. Environmental Protection Agency (EPA) adopted a revised reference dose (RfD) for methyl mercury (MeHg) of 0.1 µg/kg/day. The RfD is based on neurologic developmental effects measured in children associated with exposure in utero to MeHg from the maternal diet. The RfD derivation proceeded from a point of departure based on measured concentration of mercury in fetal cord blood (micrograms per liter) . The RfD, however, is a maternal dose (micrograms per kilogram per day) . Reconstruction of the maternal dose corresponding to this cord blood concentration, including the variability around this estimate, is a critical step in the RfD derivation. The dose reconstruction employed by the U.S. EPA using the one-compartment pharmacokinetic model contains two areas of significant uncertainty: It does not directly account for the influence of the ratio of cord blood: maternal blood Hg concentration, and it does not resolve uncertainty regarding the most appropriate central tendency estimates for pregnancy and third-trimester-specific model parameters. A probabilistic reassessment of this dose reconstruction was undertaken to address these areas of uncertainty and generally to reconsider the specification of model input parameters. On the basis of a thorough review of the literature and recalculation of the one-compartment model including sensitivity analyses, I estimated that the 95th and 99th percentiles (i.e., the lower 5th and 1st percentiles) of the maternal intake dose corresponding to a fetal cord blood Hg concentration of 58 µg/L are 0.3 and 0.2 µg/kg/day, respectively. For the 99th percentile, this is half the value previously estimated by the U.S. EPA. Key words: cord blood, maternal, mercury, methyl mercury, Monte Carlo, one-compartment, pharmacokinetic, probabilistic, reference dose, RfD. Environ Health Perspect 113:155-163 (2005) . doi:10.1289/ehp.7417 available via http://dx.doi.org/ [Online 4 November 2004]
Address correspondence to A.H. Stern, Division of Science Research and Technology, New Jersey Department of Environmental Protection, 401 E. State St., Trenton, NJ 08625 USA. Telephone: (609) 633-2374. Fax: (609) 777-2852. E-mail: Alan.Stern@dep.state.nj.us This work was supported, in part, under a contract with the U.S. Environmental Protection Agency (3W-1182-NAGX) . The author declares he has no competing financial interests. Received 14 July 2004 ; accepted 3 November 2004.
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