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Mercury in Fish
Mercury levels in fish are expressed
in terms of parts per million (ppm),
which is equivalent to 1 part
mercury per 1 million parts fish (1
mg mercury/kg fish). According to
the FDA (FDA Consumer, September
1994),
Fish absorb methyl mercury from
water as it passes over their gills
and as they feed on aquatic
organisms. Larger predator fish are
exposed to higher levels of methyl
mercury from their prey.
Methyl mercury binds tightly to the
proteins in fish tissue, including
muscle. Cooking does not appreciably
reduce the methyl mercury content of
the fish. Nearly all fish contain
trace amounts of methyl mercury,
some more than others. In areas
where there is industrial mercury
pollution, the levels in the fish
can be quite elevated. In general,
however, methyl mercury levels for
most fish range from less than 0.01
ppm to 0.5 ppm. It's only in a few
species of fish that methyl mercury
levels reach FDA limit for human
consumption of 1 ppm. This most
frequently occurs in some large
predator fish, such as shark and
swordfish. Certain species of very
large tuna, typically sold as fresh
steaks or sushi, can have levels
over 1 ppm. (Canned tuna, composed
of smaller species of tuna such as
skipjack and albacore, has much
lower levels of methyl mercury,
averaging only about 0.17 ppm.) The
average concentration of methyl
mercury for commercially important
species (mostly marine in origin) is
less than 0.3 ppm. Spot-caught
predator fresh-water species like
pike and walleye sometimes have
methyl mercury levels in the 1 ppm
range. Other fresh-water species
also have elevated levels,
particularly in areas where mercury
levels in the local environment are
elevated.
In a recent consumer advisory, The
FDA and EPA state (FDA 2004),
Fish and shellfish are an important
part of a healthy diet. Fish and
shellfish contain high-quality
protein and other essential
nutrients, are low in saturated fat,
and contain omega-3 fatty acids. A
well-balanced diet that includes a
variety of fish and shellfish can
contribute to heart health and
children's proper growth and
development. So, women and young
children in particular should
include fish or shellfish in their
diets due to the many nutritional
benefits.
However, nearly all fish and
shellfish contain traces of mercury.
For most people, the risk from
mercury by eating fish and shellfish
is not a health concern. Yet, some
fish and shellfish contain higher
levels of mercury that may harm an
unborn baby or young child's
developing nervous system. The risks
from mercury in fish and shellfish
depend on the amount of fish and
shellfish eaten and the levels of
mercury in the fish and shellfish.
Therefore, the Food and Drug
Administration (FDA) and the
Environmental Protection Agency
(EPA) are advising women who may
become pregnant, pregnant women,
nursing mothers, and young children
to avoid some types of fish and eat
fish and shellfish that are lower in
mercury.
To reduce exposure to mercury while
obtaining benefits of eating fish,
the FDA and EPA recommend that women
and children (FDA 2004):
1. Do not eat Shark, Swordfish, King
Mackerel, or Tilefish because they
contain high levels of mercury.
2. Eat up to 12 ounces (2 average
meals) a week of a variety of fish
and shellfish that are lower in
mercury.
· Five of the most commonly eaten
fish that are low in mercury are
shrimp, canned light tuna, salmon,
pollock, and catfish.
· Another commonly eaten fish,
albacore ("white") tuna has more
mercury than canned light tuna. So,
when choosing your two meals of fish
and shellfish, you may eat up to 6
ounces (one average meal) of
albacore tuna per week.
For fish caught by sports fishermen
(FDA 2004) FDA and EPA state, “Check
local advisories about the safety of
fish caught by family and friends in
your local lakes, rivers, and
coastal areas. If no advice is
available, eat up to 6 ounces (one
average meal) per week of fish you
catch from local waters, but don't
consume any other fish during that
week.”
The FDA has determined that mercury
levels in fish sold in the United
States must not exceed 1 ppm (FDA
Consumer, September 1994). To ensure
a safe fish supply (FDA Consumer,
September 1994), "FDA works with
state regulators when commercial
fish, caught and sold locally, are
found to contain methyl mercury
levels exceeding 1 ppm. The agency
also checks imported fish at ports
and refuses entry if methyl mercury
levels exceed the FDA limit."
Content Courtesy :
cerhr.niehs.nih.gov
Note : Information herein is
provided for informational purposes
only and is not a substitute for
professional medical advice. You
should not use this information for
diagnosing or treating a medical or
health condition. If you have or
suspect you have a medical problem,
promptly contact your professional
healthcare provider. Please consult
your healthcare provider before
beginning any course of
supplementation or treatment.
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