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Special delivery: How seabirds bring pollution to the Arctic

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The arctic landscape is beautifully pristine. You won't see many factories, highways or other signs of industrial civilization. So why do researchers keep finding high levels of pollution there?

It's the seabirds, scientists now say. The birds eat fish and other animals that contain large amounts of chemicals like mercury in their flesh. And, since what goes in must come out, the birds deliver these chemicals to the arctic lands through their droppings, which scientists call "guano."

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This isn't just a problem for the arctic plants and animals. Many of the native peoples in this region are also exposed to high levels of industrial chemicals from the environment. It's a complex problem to solve, though. Guano doesn't just have the harmful chemicals. It's also an important source of fertilizer for the arctic vegetation.

A good place to start could be cleaning up the oceans. Streams and rivers, for example, carry chemicals from pesticides, cars, factories, and other sources into the oceans. There, the chemicals get concentrated in small animals like shellfish. Larger animals eat the shellfish and so on, until the animals at the top of the ocean food chain contain relatively high levels of these chemicals.

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Seabirds travel long distances around the ocean, feeding off these larger ocean predators. Sometimes they catch their prey live; other times they find and eat dead animals. Many seabirds migrate to the arctic for the summer, where they leave behind lots of guano.

Until now, researchers have generally thought that wind currents carried most of the industrial pollutants up to the arctic, but Jules Blais of the University of Ottawa in Canada and his colleagues have discovered that seabirds concentrate the chemicals and funnel them into relatively small areas where the birds nest in large numbers.

The researchers studied a group of ponds below the cliffs at Cape Vera, on arctic Canada's Devon Island. Up on the cliffs lives large colony of northern fulmars, a medium-sized petrel found across the North Atlantic. The sediments of the ponds that receive the most bird droppings had higher levels of contaminants, such as mercury and chemicals used in some pesticides, than nearby ponds without many birds.

Their findings appear in the 15 June issue of the journal Science.