World on alert over toxic mercury in food chain
Pastor Dale Morgan
World on alert over toxic mercury in food chain*
By Roger Highfield, Science Editor
Last Updated: 2:54am GMT 09/03/2007
A worldwide alert about rising levels of toxic mercury in the food chain
is issued today by scientists.
Fish: mercury levels warning
Fish concentrate harmful mercury in their bodies
The risks posed by mercury-contaminated fish are now big enough to
trigger a warning to the public to be careful about how much and which
fish they eat.
Children and women of childbearing age should take particular care, they
say.
Fish and shellfish have a natural tendency to concentrate mercury in
their bodies, often in the form of methylmercury, a toxic organic form.
Species high in the food chain, such as swordfish, king mackerel,
albacore tuna, shark and tilefish, contain higher concentrations of mercury.
There are concerns about the effects the mercury could have on humans,
particularly unborn children. Methylmercury exposure may also increase
the risk of cardiovascular disease.
Exposure to methylmercury now constitutes a public health problem in
most regions of the world and concentrations are now being found in a
number of fish-eating wildlife species in remote areas, according to the
Madison Declaration on Mercury Pollution published today in a special
issue of Ambio, the journal of the Royal Swedish Academy of Sciences.
Levels from developing countries over the past three decades have offset
a fall from developed nations, meriting a worldwide alert about the
dangers, say scientists.
Yet, they add, little is known about the behaviour of mercury in marine
ecosystems and methylmercury in marine fish
Developed at the Eighth International Conference on Mercury as a Global
Pollutant last August in Madison, Wisconsin, the declaration is a
synopsis of the latest scientific knowledge about the danger posed by
mercury pollution.
The declaration pulls together findings prepared by the world's leading
mercury scientists to summarise what is known about the sources and
movement of mercury in the atmosphere, the socioeconomic and health
effects of mercury pollution on human populations, and its effects on
fisheries and wildlife.
Methylmercury levels in fish-eating birds and mammals in some parts of
the world are reaching toxic levels, which may lead to population
declines in these species and possibly in fish populations as well.
A survey by Oregon State University and the US Environmental Protection
Agency of 2,700 fish in more than 600 rivers and streams in the western
United States published in January surprised researchers because, as one
put it, "mercury is everywhere."
However, the health effects are not clear cut. While mercury is known to
harm brain development, fish also contain omega-3 fatty acids and other
nutrients which are essential to brain development.
One study of 9,000 families taking part in the Children of the 90s
project at the University of Bristol concluded, in The Lancet, that the
risks of eating fish were outweighed by the benefits.
But the Food Standards Agency advises expectant mothers to avoid shark,
swordfish and marlin and to limit their consumption of tuna, because
these are the fish with the highest levels of mercury.
There are other sources of mercury than fish. On average, three times
more mercury is falling from the sky today than before the Industrial
Revolution as a result of the increasing use of mercury and industrial
emissions.