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

MERCURY 244
2. HEALTH EFFECTS
the human database for methylmercury exposure and effects, a number of factors that could have
contributed to the study results, but were not considered as possible statistical covariates, were discussed.
In the case of the Faroe study, the consumption of whale blubber, which is known to be contaminated with
PCBs, DDT, and possibly other organochlorines, introduces a potentially significant influence on the study
results. Weihe et al. (1996) reported that the PCB and DDT concentrations in blubber of pilot whales taken
in Faroese waters are about 30 ppm and 20 ppm, respectively. In contrast, the Seychellois population does
not eat marine mammals at all. In addition, the Faroe study did not address other possible statistical
covariates, such as the dietary and nutritional status of the study population and the use of tobacco during
pregnancy, further complicating the interpretation of the neuropsychological test results.
On November 18–20, 1998, a workshop on Scientific Issues Relevant to the Assessment of Health Effects
from Exposure to Methylmercury was conducted in Raleigh, North Carolina. The workshop was jointly
sponsored by the U.S. Department of Health and Human Services (DHHS), the National Institute of
Environmental Health Sciences (NIEHS), the Centers for Disease Control and Prevention (CDC), the Food
and Drug Administration (FDA), the U.S. Environmental Protection Agency (EPA), the National Oceanic
and Atmospheric Administration (NOAA), the Office of Science and Technology Policy (OSTP), the Office
of Management and Budget (OMB), and ATSDR. The purpose of this workshop was to discuss and
evaluate the major epidemiologic studies that associated methylmercury exposure and the results of an array
of developmental measures in children. These studies monitored and evaluated exposed populations in
Iraq, the Seychelles Islands, the Faroe Islands, and the Amazon River Basin. A number of animal studies
were also considered in support of a human health risk assessment. Presentation of each study by the
research team that conducted the study was followed by an expert panel evaluation that examined each
study, taking into consideration the exposure data, experimental design and statistical analysis, potential
confounders and variables, and neurobehavioral end points evaluated. A fifth panel evaluated the results of
relevant animal studies. Significant issues that were discussed included the use of umbilical cord blood
mercury levels versus hair mercury concentrations as an index of methylmercury exposure during
pregnancy, the patterns of exposure, the dietary/health status of study populations, other potentially relevant
exposures, other confounding influences, and the adjustments made for statistical covariates. All five
panels at this workshop commended the efforts of the investigators and respective staffs of the Seychelles
and Faroe studies for conducting highly sophisticated investigations under difficult conditions. However,
specific findings of several of the panels raise issues that, at present, preclude the Faroe data from
consideration as a starting point for MRL derivation.