Article from Science-Week:

9. EFFECTS OF METHYLMERCURY EXPOSURE FROM FISH CONSUMPTION
Inorganic mercury discharged into lakes, rivers, and oceans is
converted to methylmercury by microorganisms and then bio-
accumulated up the aquatic food chain. Concern about the
potential public health threat from methylmercury arose in the US
in the early 1970s when elevated concentrations were found in
fish in the Great Lakes. At present, recreational fishing in the
US is restricted in many states, and US Food and Drug
Administration guidelines regulate interstate commerce of fish
because of their methylmercury content. A dose-response analysis
has suggested that fetal developmental effects of methylmercury
may occur at maternal hair concentrations as low as 10 ppm,
although there is considerable uncertainty in this estimate. The
average methylmercury hair concentration in the US is at present
1 ppm or less. ... ... Davidson et al (12 authors at 4 install-
ations, US SC SE) report a study of human neurodevelopmental
consequences of exposure to methylmercury from eating fish, the
study consisting of measurement of prenatal and postnatal
methylmercury exposure and 6 standard age-appropriate
neurodevelopmental tests in a total of 711 mother-child pairs in
the Republic of Seychelles, an archipelago in the Indian Ocean
where 85 percent of the population consumes ocean fish daily. The
authors report the mean maternal hair total mercury level was 6.8
ppm, and the mean child hair total mercury level at age 66 months
was 6.5 ppm. The authors report no adverse outcomes at 66 months
were associated with either prenatal or postnatal methylmercury
exposure. The authors suggest results from this study are
relevant for the US and other countries with similar dietary
intake of fish. The major source of methylmercury in Seychelles
is ocean fish, and the average fish methylmercury levels in the
Seychelles islands are similar to those on the US market. The
authors suggest the methylmercury levels of the Seychelles
population is 10 to 20 times higher than in the US because the
Seychelles population consumes more fish, not because they eat a
few fish with abnormally high levels of methylmercury. Thus, the
authors suggest, any potential adverse effects of methylmercury
in fish should be detected in the Seychelles long before such
effects would be seen in the US. The authors suggest their
results for children at 66 months of age strongly support their
previous findings at younger ages, and also support the
observations of other investigators that it would be inadvisable
to forgo the health benefits of fish consumption to protect
against a small risk of adverse effect at the levels of
methylmercury found in ocean fish on the US market.
... ... In a companion editorial comment in the same journal,
Kathryn R. Mahaffey (Environmental Protection Agency, US) points
out that defining the level of exposure for neurodevelopmental
toxic effects is influenced by the types of tests used as the end
points for neurological assessment. Traditional measurements of
child development were the basis of the conclusion by Davidson et
al that no effects were observed following in utero methylmercury
exposures. But use of additional tests designed to identify
subclinical neurocognitive function might provide an expanded
understanding of methylmercury effects. Mahaffey states: "Until
these data are available, current findings from the Seychelles
cohort must be regarded as interim." Mahaffey concludes:
"Advisories that recommend restrictions of fish consumption for
women of child-bearing age because of mercury contamination
should be followed carefully."
QY: Philip W. Davidson 
QY: Kathryn R. Mahaffey 
(J. Amer. Med. Assoc. 26 Aug 98 280:701,737)
(Science-Week 11 Sep 98)

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