MIGRATING ducks and stray tumbleweeds have been contaminated with radioactivity after landing fleetingly in ponds of waste water at a nuclear facility in the US. The news raises questions about the practice of leaving such ponds open to the elements.

In the mid-1990s, staff at the Idaho National Engineering and Environmental Laboratory (INEEL) realised that tumbleweeds were able to "blow into waste-water ponds, and wash up on shore and blow out again", says Ronald Warren, an independent environmental monitoring expert who is contracted to scrutinise radioactivity at INEEL. "The tumbleweeds blew against the [2-metre high] fence where they built up, forming a ramp other weeds could climb over," he says.

In a two-year study, Warren and his colleagues measured how much radiation the tumbleweeds took with them from two waste ponds near a US Navy test reactor. The team found that the tumbleweeds, which were mostly Russian thistle (Salsola kali), carried out a total of 66 megabecquerels of radiation and spread it over a 32-hectare area.

"The activity from those tumbleweeds made a relatively small, around 15 per cent, increase to the activity due to global fallout in that area," he says. Risk to humans is slight since the nearest house is 42 kilometres away and the tumbleweeds travelled less than a kilometre.

Nonetheless, INEEL has taken action. "They've now made the fence higher and they go out and collect tumbleweeds and bury them," Warren says. Growing shrubs near the ponds has also hampered the tumbleweed.

But birdlife is not so easily thwarted. In research yet to be published, Warren says he has found 21 species of migratory duck that fly over INEEL-and some take a rest stop in the waste ponds. Warren says the duck's radiation levels wouldn't harm you, even if you ate a whole one. "The maximum radiation dose you'd get would be less than you'd get from a dental X-ray," he says.

This does not reassure everyone. "I haven't a clue why they don't cover the ponds with any kind of net," says Margaret Stewart of the Snake River Alliance, an anti-nuclear pressure group based in Idaho. "It seems like a sensible kind of thing to do if you're trying to keep birds out." But an INEEL spokesman maintains that radionuclide concentrations are so low in the ponds that birds would face more risk of death from entanglement in netting.

Britain had its own problem with birds in 1999, when researchers found that pigeons visiting contaminated buildings at the Sellafield nuclear complex were concentrating radioactivity in their droppings in the nearby village of Seascale.

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Author: Paul Marks

More at: Journal of Environmental Radioactivity (vol 54, p 361)
New Scientist issue: 31st March 2001
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