�Seabirds are very efficient concentrators of contaminants. If we can show that these chemicals flow in a predictable pattern, then we can alleviate the human problems just by altering food choices,� says Jules Blais at the University of Ottawa, lead author of the study.

For years, environmental chemists have been watching as toxic chemicals such as mercury, dioxins and polychlorinated biphenyls (PCBs) accumulate in Arctic air, soils, water, animals and people. Native populations of northern regions are amongst the most PCB-exposed in the world.

Pollutants have aggregated in the north through a process called �global distillation� � the tendency for pollutants to evaporate at warmer temperatures, travel northwards on atmospheric currents, and then condense out of the cooler air there.

But, says Blais, these long-range transport models could not explain why some communities have shown much higher exposure than others. �One thing the air and oceans can�t do is concentrate these chemicals into hotspots,� he says

Cliff-side colonies

Blais�s team posited that Arctic seabirds � which range up to 1000 kilometres on extended ocean feeding trips � might be responsible for magnifying contaminants.

Seabirds are among the dominant wildlife in these northern latitudes, nesting in dense cliff-side colonies of more than 20,000 individuals. Their guano (faeces) is the major source of nutrients for plants onshore, which are in turn eaten by a variety of animals.

So the team headed to Cape Vera in the high Arctic, a nesting ground of northern fulmars, to assess levels of the pesticide DDT, mercury, and several long-lived chlorinated pollutants such as hexachlorobenzene (HCB).

Guano runoff

Compared with soil and water far away from bird colonies, ponds in the direct path of guano runoff had up to 10 times the amount of HCB, 25 times the amount of mercury and 60 times the amount of DDT. The level of mercury exceeded the concentration deemed safe for wildlife preservation by Canadian authorities, states the study.

By mapping how the toxins move through the terrestrial food chain, Blais hopes that native populations in vulnerable areas will be able to safely stick to their traditional food sources, avoiding hotspots where wildlife may be more contaminated.

Previous food scares in the Arctic have led local communities to steer away from their traditional diets. This in turn resulted in increased levels of obesity and type II diabetes in the native Canadians, who are more susceptible to the conditions when on non-traditional diets.

Journal reference: Science (vol 309 p 445)

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