Environmental Engineering Reference
In-Depth Information
(partly because they do not have the polar bear and bird option of moving mercury into hair
or feathers) and they showed high concentrations of mercury in brain tissue and associated
signs of neurochemical effects.
We should have a short digression here about the metal selenium. Since the 1970s, it
has been known that there is usually a strong positive correlation between selenium and
mercury concentrations in many species, especially marine mammals. It is believed that
these species are partly protected from mercury toxicity by selenium that is also taken in
with their diet. In a number of fish-eating birds and mammals, it has been found that when
methylmercury levels are low, most of the mercury in the liver is in this form. However,
as methylmercury levels rise, an increasing proportion in the liver is in an inorganic (non-
biologically available) form as a selenium-mercury complex. This suggests that perhaps
selenium is involved in a demethylation process. There is also evidence that selenium acts
as an antioxidant to protect against oxidative stress due to mercury exposure. Selenium is
present in very high concentrations in certain tissues of many Arctic marine species, such
as the livers of bearded and ringed seals and in muktuk (the fatty layer just below the skin
of whales) - all of which feature prominently in the traditional Inuit diet.
In this brief review of the POPs and heavy metal contamination, I have tried, more or
less, to match developments in knowledge with parallel “diplomatic” work to put in place
international controls on the offending substances. You will have noticed, however, that
this scheme has broken down with the mercury story, where, with the exception of human
exposure and impact, we have brought ourselves close to being up to date.
In 1994, when the CLRTAP heavy metals report was being written, we had evidence
that once again, some of the most exposed human populations to mercury were in the Arc-
tic or sub-Arctic, where fish and/or marine mammals form much of the diet. Canada uses a
blood-mercury guideline of 20 micrograms per litre of mercury that mothers and women of
childbearing age should not exceed. In the United States, the guideline is set at 5.8 micro-
grams per litre. In the 1990s, these values were being commonly exceeded in coastal Arctic
communities. For example, at this time, 52-76% of Inuit mothers and women of childbear-
ing age in Nunavik (Canada) and 68% of Inuit mothers in Nunavut (Canada) exceeded the
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