Methylmercury Faroe studies

The concerns aroused by methylmercury in fish, arising from the susceptibility of the developing brain to this neurotoxicant, led to the design and execution of two large prospective studies. One was located in the Seychelle islands, which lie in the Indian Ocean. The other was located in the Faroe Islands, which lie in the North Sea. Both communities consume large quantities of seafood. In the Seychelles, it is almost exclusively in the form of fish. In the Faroes, virtually all the methylmercury comes from the consumption of pilot whales, which are also contaminated with polychlorinated biphenyls (PCBs). Both studies assayed maternal exposures to methylmercury. In the Seychelles, maternal hair was used as the index it reflects the history of blood levels. The Faroes study relied primarily on cord blood. 

Several recent epidemiological studies have involved examination of populations that consume unusually high levels of fish. One of these, conducted in the islands of the Seychelles, has not so far revealed behavioral and learning impairments in children whose mothers exhibited mercury levels (measured in hair) higher than those typically seen in the United States and European countries. But another study, conducted in the Faroe Islands, turned up evidence of cognitive and behavioral impairments in children. Scientists have struggled to understand why two well-done studies have produced such different outcomes, and some possible reasons have been suggested. The EPA and public health officials have acted on the basis of the Faroe data, out of both caution and also because they seem to be supported by other, more limited data, and by experimental studies. The debate is not so much about whether methylmercury is a developmental toxicant, but rather over the dose required. 

On the basis of maternal hair concentration, the third study (conducted in the Seychelles) did not find any association between prenatal methylmercury exposure and adverse neuro-psychologic effects (Myers et al. 2003). Reasons for the discrepancies are not known but have been suggested to include differences in the child s age at testing, genetic susceptibilities of the populations, patterns of exposure (episodic vs continuous), and coexposure to polychlorinated biphenyls in the Faroes but not Seychelles populations (Rice et al. 2003). 

The second prospective study of in utero exposure to methylmercury was initiated in the Republic of Seychelles and enrolled about 800 mother-infant pairs (Myers et al., 1995). In contrast to the Faroe Islands study, the investigation in the Seychelles did not find evidence of methylmercury-related adverse effects on the neuro-behavioural development of children through nine years of age (Myers et al., 2003). In some instances, prenatal mercury exposure was actually associated with precocious behaviour, and important developmental milestones were reached more quickly in the most highly exposed subjects. 

The diet in the two studies was also considerably different. The majority of the mercury exposure to the Faroe Island population came from whale meat (estimated at about 3 ppm in muscle tissue) with a relatively small portion coming from fish. Some of the mercury in whale meat is in the form of inorganic mercury. In the Seychelles study, all of the mercury came from fish as methylmercury with concentrations of around 0.3 ppm. Whale meat blubber is widely consumed in the Faroe Islands and also contains polychlorinated biphenyls (PCBs). Grandjean et al. (1995b) estimated a daily intake of 200 g of PCB. This value can be compared to the Tolerable Daily Intake of PCBs established by the FDA of 60-70 g/day for an adult. Further statistical analysis of the possible influence of PCBs on the observed study results needs to be conducted (see the discussion below on Peer Panel IReview of Kev Studies for additional comments). 

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. 

Prenatal exposure to methylmercury in the Faroe Islands and neurobehavioral performance at age seven years. Response to workgroup questions for presentation on 18-20 Nov. 1998. In Scientific Issues Relevant to Assessment of Health Effects from Exposure to Methylmercury. Appendix II-B. Faroe Islands Studies. National hrstitute for Environmental Health Sciences. Available "http //ntp-server.niehs.nih.gov/ Main Pages/ PUBS/MethMerc WkshpRpt.html"... 

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