Exposure Due to Food Consumption
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| Organic mercury compounds like methyl mercury can enter
the body readily through three routes - lungs, skin and
stomach. The main human exposure to mercury is through
ingestion of fish that contain methyl mercury. Completely
cutting fish out of the diet is not advised however because
there are many benefits to eating fish. Fish are an excellent
source of protein and are low in saturated fat; therefore
a balanced diet is necessary. In order to protect Canadians,
Health Canada is advising a guideline of 0.5 parts per
million of total mercury per gram of fish tissue in commercial
fish. Commonly consumed marine species such as salmon,
cod, pollock, sole, shrimp, mussels, scallops and canned
tuna, have mercury levels that generally fall below this
limit and are therefore considered safe for consumption. |
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| Shark, swordfish and fresh or frozen tuna generally
have concentrations ranging from 0.5 to 1.5 ppm. This
occurs because methyl mercury accumulates in higher amounts
up the aquatic food web meaning that larger predator fish
have the highest content of methyl mercury. These fish
are considered to be the exceptions to the 0.5 ppm guideline
because they are considered "gourmet" fish and
are not typically eaten in high enough quantities to pose
a health hazard. A consumption limit of one meal per week
of these fish is recommended and women of child bearing
age, pregnant women, and children should not consume these
fish more than once per month. Fish containing over 1.5
ppm are not considered suitable for human consumption
at any time. |
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Freshwater fish species such as pike, bass and walleye have
also been know to attain elevated methyl mercury levels in various
lakes and river systems. If fish constitutes a staple part of
the diet, such as for indigenous peoples and recreational anglers,
consumption of these species may increase risk of mercury exposure.
In Canada, thousands of advisories on fish species from individual
water bodies are put in place in every year due to excessive
mercury contamination of fish tissues. The EPA’s 2001
National Listing of Fish & Wildlife Advisories consists
of more than 2,000 advisories in the United States to help the
public find sources where fish are low in toxic pollutants so
they can safely enjoy the benefits of eating fish. Each advisory
contains information about: |
- species and size of fish / wildlife covered in the advisory
- specific chemical contaminants of concern
- location of selected water-bodies
- special populations at risk
- names, phone numbers and web-sites of local contacts
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Exposure due to inhalation
| Mercury is extremely volatile in its elemental form
and can give off mercury vapor at room temperature. This
vapor can be inhaled into the lungs and passed into the
blood stream. Based on available science, normal air concentrations
of mercury vapor, averaging 1.6 nanograms per cubic meter
of air, do not appear to be a cause for concern. However,
inhalation can be a significant route of exposure when
mercury-silver amalgam is used in dental fillings. |
Exposure Due to Contact |
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Dermal contact is also a route of exposure to mercury with alkyl
mercury compounds being particularly notorious. Liquid mercury may
pass through the skin and into the blood stream causing it to be
lethal at some doses. In 1997, a researcher named Karen Wetterhahn,
from Dartmouth College in New Hampshire, died when a single drop
of dimethylmercury passed through her protective latex glove and
through her skin.
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For more information |
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