Monday, April 25, 2011

Mercury Climbing in Food Chain, New Study Shows

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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