New Scientist (pg. 7)
June 14, 2003


Levels of mercury currently regarded as safe for adults could impair
brain function, according to a study in Brazil. The study has been
dismissed as too small to be conclusive, but if it is right, mercury
could be slightly reducing the mental performance of millions of
people worldwide.

Low levels of mercury are already thought to damage the nervous
systems of fetuses and babies. After a study in the Faroe Islands
showed that children exposed to mercury in the womb have memory,
attention and language problems at age seven, regulatory authorities
in the US and UK advised pregnant and nursing mothers not to eat large
predatory fish such as tuna, shark and king mackerel. Mercury and
methyl mercury (a more toxic form generated by bacteria) are most
concentrated in animals near the top of the food chain.

Now a study of villagers in Brazil suggests that adults may be at risk
too. "Adults may be just as sensitive to mercury as children," claims
Ellen Silbergeld at Johns Hopkins University in Baltimore, Maryland.
Her team studied 52 men and 77 women living in fishing villages
downstream of gold mines. Much of the mercury used to extract the gold
ends up in rivers and in fish. "They act almost literally as a
sponge," says Silbergeld.

The researchers tested the villagers' neurological abilities by asking
them, for instance, to remember a story and thread beads onto a piece
of string. The higher the levels of methyl mercury in the villagers'
hair - a measure of recent exposure - the greater the deficits in
memory and motor skills (Environmental Health: A Global Access Science
Source, vol 2, paper 8).

Most worryingly, exposure levels were not particularly high. Hair
concentrations in the villagers averaged 4 micrograms of mercury per
gram of hair. This is just a tenth of the level considered dangerous
for adults by the World Health Organization, and not much higher than
that found in many countries. In the US and Japan, for instance, the
average mercury concentration in hair is around 1 and 2 micrograms per
gram respectively.