Plutonium from Soviet underwater nuclear tests has contaminated life in an Arctic bay and spread in a plume to one of the world's most important fisheries.
In the first scientific investigation in the area, a team from Canada, Russia and the US has found high levels of two radioactive isotopes of the element in sediment from across Chernaya Bay.
Plutonium traces were found in molluscs and algae in the bay, four decades after it was used by the Soviet military for underwater nuclear testing in 1955 and 1957.
"This is one of the first sources of contamination of a body of water that has been positively identified," said John Smith, a marine environmental researcher with the Bedford Institute of Oceanography, Canada, whose research is published in the journal Continental Shelf Research.
His team was able to track the Chernaya Bay plutonium 100km into the Barents Sea, a major commercial fishing area, though the quantities fall within safety margins.
"It is possible that plutonium from Chernaya Bay has also caused some contamination of the central basins of the Arctic Ocean," Dr Smith said.
Radioactive material in the ocean also comes from dumped waste, fall-out from atmospheric weapons testing and outflows from the Sellafield reprocessing plant.
Bay of bombs: site still contaminated