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Wednesday, 29 May, 2002, 18:00 GMT 19:00 UK
Fears over nuclear pollutant cancer risk
Tritium is emitted by nuclear plants
Tritium is emitted by nuclear plants
People may be exposed to twice the level of a carcinogenic nuclear pollutant than previously thought, experts have admitted.

Tritium - a variation, or isotope, of hydrogen - is produced by hydrogen bomb tests and nuclear plants and factories.

Despite their revised estimates, experts say the health risks are still low because even the higher dose is well within international safety limits.

However, critics have warned people who eat fish from contaminated waters may have a have been exposed to much higher levels of radiation than supposed, and may therefore have an increased cancer risk.

For the most exposed people, we're talking about a dose which is about a tenth of the dose limit

Dr John Harrison, NRP
The National Radiological Protection Board decided to re-examine tritium exposure levels after it was discovered in the late 1990s that levels in fish near the Nycomed Amersham plant in Cardiff, which makes isotopes for the drugs industry, were hundreds of times higher than expected.

The NRPB then looked at how much radiation people are exposed to when they ate fish caught in the Severn Estuary.

It now says the dose was twice as high as previously assumed.

Weapons tests

New Scientist magazine reports animal studies showed tritium-carbon compounds could stay in the body for much longer than previously thought and that the biological effect of tritium in water could be more damaging.

The fear is that this means there is a higher chance that the radiation from tritium will trigger tumour growth.

Tritium was also released into the atmosphere in 1960s nuclear weapons tests .

And nuclear plants such as Savannah River in South Carolina, Sellafield in Cumbria and Chapelcross in southern Scotland still emit enormous amounts of tritium each year.

Dr John Harrison from the NRPB who wrote the original research, which was published in the journal Radiation Protection Dosimetry, told BBC News Online international standards assumed different types of radiation, from does of gamma ray, x-rays and beta radiation from tritium were the same.

After the Cardiff levels were discovered, this was reassessed by the NRPB.

Dr Harrison said: "Why the risk seems to be higher is because we're taking into account the fact that beta radiation produced from tritium can cause more damage per unit, per dose, than gamma rays.

"But even with this recalculation, for the most exposed people, we're talking about a dose which is about a tenth of the dose limit."

He added: "Tritium is a weakly carcinogenic. In terms of radio toxicity, it's a thousand times less than something like strontium and tens of thousands times less than plutonium 239."

Dose fears

"People should not be particularly concerned about this".

But Barrie Lambert, a radiation expert from St Bartholomew's Hospital in London, told New Scientist the NRPB's finding could have significant implications for people who eat a lot of fish from around the Cardiff plant.

He said their current radiation dose could double to 133 microsieverts a year and that the dose could have been twice as high when tritium discharges of tritium were at their highest.

International standards say the maximum dose should be no more than 300 microsieverts a year.

A spokeswoman for the Environment Agency, which checks tritium levels, said: "In 1998, when the bioaccumulation of tritium near Cardiff became known we asked Amersham to drastically reduce discharges.

"As a result of this pressure from the Agency, Amersham is currently developing a plant to recycle tritium instead of discharging it.

"In addition, over the past two years we have carried out an extensive study around England and Wales to check if major bioaccumulation of tritium was happening elsewhere including Sellafield. This study confirmed that major bioaccumulation is not occurring elsewhere."

See also:

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