Canadian scientists found that birds carry pollutants like DDT and mercury, and deposit them in sites where other animals feed.

They say this process may be contributing to the high levels of industrial chemicals found in some Arctic peoples.

The research is published in the journal Science.

It's been a rallying cry of environmental groups campaigning against industry's use of toxic chemicals; how can it be right to use them when they end up in the planet's most pristine regions?

Northern fulmer

According to a recent study, the levels of one important class of industrial chemicals, polychlorinated biphenyls (PCBs), are thirty times higher in Canadian Inuits living north of the Arctic circle than in residents of temperate Quebec.

PCBs are one example of a Persistent Organic Pollutant or POP - chemicals which are broken down very slowly by natural degradation, and which accumulate in living organisms, including humans; other examples are pesticides, including DDT, and multi-purpose substances such as hexachlorobenzene (HCB).

How these substances end up in the Arctic and inside Arctic organisms has not been entirely clear - the presumption has been that they are transported by several routes, as particles in the air, in the sea and perhaps in the bodies of migratory species.

Now a group led by Jules Blais from the University of Ottawa has confirmed the involvement of one migratory bird species, the northern fulmar.

"We were studying a population of northern fulmars on Devon Island in the Canadian Arctic, specifically at Cape Vera which is one of the most northern and isolated fulmar colonies in North America," he told the BBC News website.

"There's a large breeding colony, about 10,000 pairs at this location; and what we've been doing is looking at the distribution of some of these chemicals like PCBs and mercury and DDT in areas near the breeding colony."

Sites very close to breeding colonies are enriched in nitrogen, which comes from guano - bird excrement.

Blais found that sites high in nitrogen also contained elevated levels of DDT. Locations frequented by the fulmars showed levels of HCB 10 times higher, mercury 25 times higher and DDT 60 times higher than in the surrounding area - strongly suggesting that the chemicals were also deposited in guano.

These fulmars feed from the North Atlantic during the breeding season, scooping plankton, squid, fish and carrion from the sea; it appears that these foodstuffs are also the birds' source of DDT, mercury and HCB.

Seabird eggs

If the pollutants then stayed at the breeding sites, there might not be a significant problem; but Dr Blais believes that is not the case.