Sea birds drop radioactivity on land
04 January 03
Droppings from seabirds could be introducing radioactive isotopes into the food
chain. That is the conclusion of researchers who found high levels of
radioactivity in droppings and plants on an island close to the Arctic.
If tests confirm that the guano is bringing radioactivity ashore, it will need
to be factored into pollution assessments that gauge radiation risks to human
health and ecosystems. The risk is probably low at temperate latitudes, but
could be much greater in the fragile wastes of the Arctic. There, guano is a
major source of nutrients for plants, which are then eaten by animals.
Radioactive material gets into the oceans from natural geological processes on
the sea floor, but radioactive isotopes from human nuclear activity can add to
this. In the Arctic, radioactive material has been dumped in the Kara Sea to the
east of the Barents Sea.
And radioactive material from nuclear accidents such as the 1986 Chernobyl
disaster has reached the seas, along with particles from atmospheric tests of
The evidence that bird droppings are bringing radioactivity ashore comes from
Mark Dowdall and his team at the Norwegian Radiation Protection Authority in
Tromsø. They spent two years between 2000 and 2002 collecting soil, vegetation
and guano samples from a remote coastal inlet called Kongsfjord on the Arctic
archipelago of Svalbard, about halfway between the northern tip of Norway and
the North Pole.
The samples of bird droppings were from vast piles produced by two colonies of
seabirds supporting kittiwakes, puffins and fulmars. Tests showed the guano
contained 10 times the concentration of radioactive isotopes found at other
sites on the island.
The researchers found unusually high concentrations of the natural radioisotopes
uranium-238 and radium-226, which decay to form more hazardous isotopes. But
they also found high concentrations of the isotope caesium-137, which does not
occur naturally. Dowdall suspects this is from the fallout of atmospheric
nuclear tests carried out decades ago.
Tests on vegetation growing near the guano also revealed high concentrations of
radioactive material. "It means that low levels in the Arctic environment don't
stay low, they become concentrated," he says.
Fish and crustaceans
Dowdall believes the birds eat contaminated fish and crustaceans, and the
radioactive material is then concentrated in their faeces. The extra nutrients
the droppings provide encourage plants to grow, and the plants take up and
concentrate the radioactive material.
This poses a problem, because plants make up the bulk of the diet of many
animals, especially that of indigenous reindeer. "We're talking about a very
vulnerable environment, and when reindeer eat the [contaminated] vegetation,
it's in the food chain," says Dowdall.
Environmental researchers are intrigued by the finding. "I don't think people
have looked at this particular pathway before," says Scott Fowler at the
International Atomic Energy Authority's Marine Environmental Lab in Monaco.
However, in 1999, pigeons roosting in contaminated buildings on the site of
British Nuclear Fuels' Sellafield reprocessing complex in Cumbria were found to
contain 40 times the European Union's safe limit of caesium-137.
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