The
news about mercury contamination in fish has been anything
but straightforward. Recently, the Consumer Reports organization
advised pregnant women not to eat any canned tuna, which
is generally considered a low-mercury seafood. At the same
time, a series of studies conducted by the Harvard Center
for Risk Analysis confirmed that the health benefits of
consuming seafood outweigh any risk due to trace amounts
of mercury in fish.
The Harvard studies, published in the November 2005 issue
of the American Journal of Preventive Medicine,
concluded that for women of childbearing age, health benefits
can be achieved with virtually no negative impact on the
developing child if she eats two servings of fish low in
mercury a week.
The
Harvard researchers stated that if everyone reduced their
fish consumption out of confusion about mercury, there will
be serious public health consequences – notably higher
death rates from heart disease and stroke. In short, they
found that not eating fish is more dangerous than eating
it.
For most people, the primary source of exposure to mercury
is through the consumption of contaminated fish. Effects
occur to the central nervous system, but are usually not
obvious. Symptoms in adults might include coordination loss,
tingling sensations, constriction of the visual field and
hearing impairment. These symptoms would be expected only
after prolonged intake of significant mercury sources. Some
studies have indicated that moderate-level exposure in the
womb or during the first years of life can cause subtle
learning problems in children. However, people should be
aware that the mercury caution levels now being used are
extremely vigilant. The FDA states that its Mercury Action
Level (one part-per-million in food) was established “to
limit consumers’ methyl mercury exposure to levels
10 times lower than the lowest levels associated with adverse
effects.”
In addition,
other researchers have found that simply measuring mercury
in food may not be a good indicator of possible toxicity.
Selenium, which is also present in seafood at varying amounts,
has protective properties against mercury. Selenium affects
all aspects of mercury uptake in humans, including its transport,
biogeochemical exposure, bioavailability, toxicological
consequences and remediation. The reaction between mercury
and selenium results in the sequestering (or isolation)
of mercury and reduces its biological availability.
In 1998,
Louisiana’s Department of Health and Hospitals conducted
a screening of blood mercury concentrations in 313 people
(http://www.dhh.louisiana.gov/offices/publications/pubs-205/Blood%20Mercury%20Levels.pdf).
The study looked at areas of the state with local mercury
advisories. Six people had elevated blood mercury levels
of 20 parts-per-billion or more; all were commercial fishermen
or family members of fishermen who resided in Morehouse
or Ouachita parishes. Ninety-eight percent of the people
who were screened had blood mercury levels in the normal
range, and none of those screened had levels in the toxic
range. This kind of information tends to indicate that people
should be aware of the problem but should not overreact.
More studies are underway or planned.
The
bottom line is that the jury isn’t in on the whole
mercury case. People should be aware of the local mercury
advisories, posted at http://www.deq.louisiana.gov/portal/tabid/1631/Default.aspx.
Additional information about the mercury issue in Louisiana
can be found at http://www.deq.louisiana.gov/portal/tabid/1637/Default.aspx.
Folks should definitely be careful about consumption of
fish that consistently carry significant amounts of mercury
(such as shark, swordfish, king mackerel and tile fish).
But most sources indicate that, in general, the benefits
of seafood consumption far outweigh the risks.
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