From the San Francisco Chronicle
April 20, 2011
Mercury climbing in food chain, new study shows
article by Kelly Zito
Levels of mercury have risen dramatically in some Pacific seabirds
in the past 120 years, suggesting that industrial emissions containing
the poisonous metal associated with fetal and brain damage may be
climbing the food chain and endangering sensitive species, according to
a new study.
While the study did not specifically address human-mercury exposure,
there is rising concern among scientists that more people are consuming
the heavy metal through tainted seafood, where the compound is known as
methylmercury.
"It's possible that any human populations that largely depend on the
same marine sources (of food) may be exposed to more methylmercury and
be at risk," said study co-author Anh-Thu Vo, a doctoral student in
integrative biology at UC Berkeley.
Vo's paper, published this week in the Proceedings of the National
Academy of Sciences, relied on 54 samples of breast feathers from the
black-footed albatross, an endangered, dusky-brown bird that feeds and
nests mainly in the northern Pacific. To measure the bird's mercury
concentrations historically, Vo gathered feathers dating from the 1880s
to 2002 from museums at Harvard University and the University of
Washington.
Through the food web
What Vo found indicates that mercury emissions from mineral mining
and burning coal may be invading the birds through the food web. That
is, microscopic organisms ingest mercury pollution in seawater. Those
organisms are eaten by small fish, which are eaten by bigger fish, and
so on, up to the seabirds. At each rung in the ladder, the mercury
becomes more concentrated.
The study found mercury levels jumped in the albatross at the same
time industrial production ramped up after World War II and again after
1990 when many Asian economies kicked into overdrive. Though the link
between pollution and mercury accumulation merits further examination,
researchers said, it suggests that modern human development is
reverberating throughout the natural world and could imperil rare and
dwindling species.
"We are starting to find high levels in endangered and sensitive
species across marine, freshwater and terrestrial ecosystems,
indicating that mercury pollution and its subsequent chemical reactions
in the environment may be important factors in species population
declines," said study co-author Michael Bank, a research associate at
Harvard's School of Public Health.
Limiting intake
Mercury, both a commercial byproduct and a naturally occurring
metal, is particularly damaging to the central nervous system and the
reproductive process. For that reason, the U.S. Food and Drug
Administration and the U.S. Environmental Protection Agency warn that
women of child-bearing age, nursing mothers and young children should
completely avoid swordfish, shark, king mackerel and tilefish and limit
their intake of tuna.
Earlier this year, a public health advocacy group found that tuna
and swordfish collected from California grocery stores and sushi
restaurants contained mercury levels as much as three times the
threshold that authorizes federal food regulators to pull seafood from
shelves.
Biologists and scientists have lobbied the federal government to
lower its warning level. But representatives for the seafood industry
say the current threshold has a large buffer built into it. They also
maintain that seafood is a critical part of a healthy diet and has rich
omega-3 fatty acids that boost brain development.
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