Arctic foulers: foraging seabirds carry contaminants home.

When birds forage at sea, they pick up mercury and pesticide residues, which end up accumulating near nesting colonies, suggests a study in Arctic Canada.

Some 10,000 pairs of medium-size o seabirds called northern fulmars (Fulmarus glacialis) nest in a widespread colony on Devon Island 640 kilometers north of the Arctic Circle. Ponds on the island closer to the colony, where more of the fulmars' guano and debris falls, had higher concentrations of pollutants than did ponds situated farther from the colony, says Jules Blais of the University of Ottawa in Ontario. In the July 15 Science, he and his colleagues report that three of these ponds had so much mercury that they neared or passed Canada's limit for wildlife safety.

Scientists have documented winds bringing contaminants into the Arctic, where fish and their predators, including people, build up worrisome concentrations of the substances in their body tissues. Blais has been exploring what causes local variations in this pollution. In 2003, he and his collaborators reported that sockeye salmon pick up polychlorinated biphenyls (PCBs) at sea and transport the chemicals inland when the fish return to their birthplaces in Alaskan streams, spawn, and die. The researchers found that for remote locations, a big salmon run could bring in more than six times as much PCB contamination as wind does.

A study of two lakes in Norway found a similar effect for seabirds, attributing the more-intense contamination in one of the lakes to busier bird activity there. Blais and his colleagues undertook a more detailed study to check for bird transport of pollution in the Arctic.

On Devon Island, the northern fulmars breed on rocky cliffs and bring home most of their food from the seas between Ellesmere Island and Greenland, 400 km away. Below the nesting birds, dramatic green oases form as a rain of nitrogen-rich guano nourishes algae in ponds and mosses on rocks. These plants, in turn, provide food for other creatures.

In their pollution study, the researchers tested sediments in 11 ponds on the island at various distances from the fulmar colony. They used a nitrogen indicator to rank the ponds from the least to most altered by the birds' activities. Within this sequence, contamination in the sediment increased 10-fold for the pesticide hexachlorobenzene and 25-fold for mercury. Although DDT is banned in most of the world, concentrations of that pesticide and its breakdown products increased 60-fold across the ponds. Blais adds that unpublished data show a similar pattern for PCBs.

The fulmars are "acting as a funnel," inadvertently collecting contaminants by eating fish in the broad area where they forage and concentrating them at their breeding colony, says Blais.

"This is important from a subsistence standpoint," says Deborah Rocque of the U.S. Fish and Wildlife Service in Anchorage, Alaska. People living, hunting, and fishing in the vicinity of bird colonies might benefit from this finding about bird-transported pollution.

"It is a nicely designed study," comments Derek Muir of Environment Canada in Burlington, Ontario, who studies Arctic contamination. He says that the report suggests that scientists ought to study living organisms as pollution movers "not just for the Arctic but for any remote location."