K.S.Parthasarathy
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Uranium munching fungi
Recently, Dundee University researchers found evidence that fungi can “lock” depleted uranium (DU) into a mineral form that may be less likely to find its way into plants, animals or water supply (Current Biology, May 6).
Depleted uranium
In a new report, they claimed that fungi may have an important role to play in the fate of potentially dangerous depleted uranium left in the environment during the war in Iraq (in 1991 and 2003) and in the Balkans (in 1995 and 1999).
DU is a by-product of uranium enrichment process. It is used to make ammunition because it is dense; also it resists deformation. When a DU round hits a target, it preserves its shape and “self- sharpens”, as it moves forward. Uranium dust generated at the time of impact can create a fierce fire, as uranium is pyrophoric.
British and US forces fired about 320 tonnes of depleted uranium munitions in the 1991 gulf war and may have used up to 2000 tonnes in the 2003 invasion of Iraq. (The British Medical Journal, November 11, 2006). DU is 40 per cent less radioactive than natural uranium. It is chemically toxic like cadmium or lead. The Royal Society studied the possible health impacts of DU.
Long term threat
“Our study … concluded that the soil around the impact site of depleted uranium penetrators may be heavily contaminated, and could be harmful if swallowed by children, for example. In addition, large numbers of corroding depleted uranium penetrators embedded in the ground might pose a long term threat if the uranium leaches into water supplies,” Professor Brian Spratt, who chaired the Royal Society Working Group, clarified.
Royal Society recommended that the fragments of depleted uranium penetrators should be removed and areas of contamination around depleted uranium penetrator impact site should be identified and, where necessary made safe.
The uranium munching fungi may be useful agents in remediation and re-vegetation techniques for soils polluted by uranium. These humble living things serve nature uniquely and incredibly. Some decompose organic matter.
Any material lying un-protected for some time in humid conditions will have hair like fungi growing on them. Some of these fungi have very useful biogeochemical properties.
All the species of fungi tested by UK researchers exhibited high DU tolerance. They could colonize uranium metal surfaces forming moisture-retaining bio-films. Fungi grew in the form of fine filaments.
Metal coupon
In the presence of air, the metal coupon corroded producing black and yellow decomposition products; they formed mixed oxides.
Fungal bio-films retained moisture on DU surfaces and facilitated corrosion. DU-colonizing fungi grew over the corrosion products.
After interacting with the DU metal, the fungi filaments developed a yellow hue in its growing part clearly demonstrating uranyl migration.
The metal coupons lost 5.5-8 per cent of weight over three months. Scientists studied the chemical species released in the micro-environment. DU- exposed fungi produced oxalic acid. Most such fungi showed greater accumulation of uranium with increasing amounts of excreted oxalate (Cell Biology, May 6, 2008)
DU-exposed fungi exhibited a notable ability to accumulate mobilized uranium in their biomass to the extent of 0.3 to 0.4 g per g of dry weight. The scientists clearly demonstrated extensive bio-mineralization by using sophisticated analytical tools.
Leaching out
Geoffrey Gadd, one of the researchers asserted that the fungal-produced minerals are capable of long term retention, so this may prevent uptake of uranium by plants, animals and microbes.
“It might also prevent the spent uranium from leaching out from the soil.” he claimed.
Cleaning up a vast uranium contaminated area is yet to be demonstrated.
K.S. PARTHASARATHY
Former Secretary, AERB (ksparth@yahoo.co.uk)
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