Killer whales have the highest concentration of man-made toxins of all Arctic mammals tested in Europe because of the oceangoing predators' taste for fatty fish, according to a study released Monday.

Man-made toxins, such as PCBs, build up in animal fat and become more concentrated in moving up the food chain. Most toxins, often from household products, are carried to Arctic waters by ocean currents, winds, or in migratory fish and animals.

"Killer whales can be regarded as indicators of the health of our marine environment," Hans Wolkers, a researcher at the Norwegian Polar Institute in the Arctic city of Tromsoe, which carried out the study.

The high levels of contaminants "show that the Arctic seas are not as clean as they should be, which, in particular, affects animals at the top of the food chain," he added in a statement.

Killer whales, a type of dolphin also called orcas, migrate to western Norway's fjords to feed on herring during the winter. The herring have elevated toxin levels, which then build up in the orcas' blubber, according to the study, funded by the global conservation organization WWF.

The study was based on blubber samples taken from 10 male killer whales in 2002 and will continue with new samples taken in November.

Researchers say PCBs and other man-made toxins can cause hormonal imbalances in Arctic wildlife. One result was female bears with vestigial male sexual organs discovered in 1997 on Norway's Svalbard Archipelago high in the Arctic and the surrounding Barents Sea region.

The study said the levels found in Norwegian coastal killer whales exceed those of Svalbard polar bears, which are also at the top of the food chain and fond of fat.

PCBs — polychlorinated biphenyls — are chemical compounds, now largely banned in the West, that were widely used in plastics and electrical insulation and can take decades to break down.