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Mercury and Loons
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Mercury is released as a gas from a
variety of anthropogenic sources (coal burning plants, trash incinerators,
forest fires...), and is carried in the atmosphere on global currents, such
as the jet stream, from the
Midwest east across
North America to
New
England and eastern
Canada
. Mercury precipitates to earth attached to rain, snow, or dust particles,
and then runoff washes it into lakes and ponds. Contamination is highest in
acidic water bodies where elemental mercury is converted to methylmercury (a
more toxic form).
Water level fluctuations increase
methylmercury availability to biota. Other hydrological factors, as well as |
biogeochemical and physiognomy
factors, also contribute to elevated methylmercury levels.
Mercury concentrations in certain
freshwater and marine fish in
North America are at levels that pose significant
health risks to humans and wildlife that consume fish. In January, 2001, the
Environmental Protection Agency (EPA) issued a national advisory for women
of child-bearing age and young children to limit the consumption of
non-commercial freshwater fish to minimize the accumulation of mercury.
Recent research by the Northeast Loon Study Workgroup (NELSWG) has revealed
that mercury levels in loons generally increase from west to east across
North America , with the highest levels occurring in
birds breeding in
New England and eastern
Canada
.
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WHAT DOES MERCURY DO? |
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High levels of mercury are correlated
with behavioral changes in Common Loons that lead to decreased productivity,
decreased survival of juvenile loons, and may be related to increased
susceptibility to other diseases. Immature loons are more susceptible to the
toxic effects of mercury than are adult birds. Significant behavioral
differences occur in immature loons with high methylmercury levels,
including increased preening and decreased time spent riding on the parents’
backs. These behavioral changes result in increased exposure to predators
and increased energy expenditure, contributing to decreased survival of
young loons.
Blood and feather mercury levels in
loon chicks are indicative of
mercury levels obtained from prey items acquired solely on their natal
lakes. In contrast, adult blood mercury levels reflect recent dietary
uptake. Feather mercury levels in adult loons reflect mercury that has been
acquired over time while feeding at a variety of different |
water bodies on migration,
breeding, and wintering grounds. Adult birds with high methylmercury levels
exhibit behavioral changes that result in decreased normal activities, such
as foraging and defense from other loons and predators, as well as decreased
reproductive success, due to decreased incubation of eggs. Loons with
extremely elevated mercury levels fledge fewer young than pairs with lower
levels of mercury in their bodies.
Loons can rid their bodies of
mercury through deposition of mercury in feathers and eggs. Thus, with every
molt, and for females, with every egg laid, body burdens of mercury are
decreased. However, through continued ingestion of fish with a high mercury
content, loons accumulate mercury faster than they can rid their bodies of
it through depuration in feathers or sequestration in eggs. This is
particularly true for male loons, since they lay no eggs and, due to their
larger size, they eat larger fish than do females. |
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WHAT IS BEING DONE ABOUT MERCURY? |
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The Environmental
Protection Agency has recently issued a national fish consumption advisory
for women and children to reduce their exposure to fish containing mercury.
In addition, the NYS Department of Health (DOH) issues advisories
recommending limited human consumption of fish from specified water bodies
in
New York
. Behavioral and reproductive impacts from high mercury levels are likely in
the loons living on these lakes. The EPA has used the results of NELSWG’s
long-term loon contaminant research as one line of evidence in determining
the risk that atmospheric mercury poses to the environment.
BACK TO FACTORS |
When combined
with other ecological and human health studies, the data supported limiting
airborne mercury emissions from coal-fired power plants, and in December,
2000, the EPA announced that it will regulate these emissions. Regulations
will be proposed by 2003, and final regulations will be issued in 2004.
Research by
NELSWG members is expanding to look at mercury levels in loons on their
wintering water bodies, and to determine mercury and other contaminant
levels in other fish-eating animals, including mergansers, kingfishers,
cormorants, mink, and otters. The results of these research efforts will
provide for more defined management of water bodies and populations of
fish-eating animals, as well as to further promote more stringent regulation
of airborne contaminants. |
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