DROPPINGS from seabirds could be introducing radioactive isotopes into the food chain. That鈥檚 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 nuclear weapons.
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The evidence that bird droppings are bringing radioactivity ashore comes from Mark Dowdall and his team at the Norwegian Radiation Protection Authority in Troms酶. 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 doesn鈥檛 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. 鈥淚t means that low levels in the Arctic environment don鈥檛 stay low, they become concentrated,鈥� he says.
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. 鈥淲e鈥檙e talking about a very vulnerable environment, and when reindeer eat the [contaminated] vegetation, it鈥檚 in the food chain,鈥� says Dowdall.
Environmental researchers are intrigued by the finding. 鈥淚 don鈥檛 think people have looked at this particular pathway before,鈥� says Scott Fowler at the International Atomic Energy Authority鈥檚 Marine Environmental Lab in Monaco. However, in 1999, pigeons roosting in contaminated buildings on the site of British Nuclear Fuels鈥� Sellafield reprocessing complex in Cumbria were found to contain 40 times the European Union鈥檚 safe limit of caesium-137 (New 杏吧原创, 14 August 1999, p48).