快猫短视频

NUCLEAR regulators have miscalculated the health risks from one of the world鈥檚 most widespread nuclear pollutants. People are twice as likely as previously thought to develop cancer after being exposed to tritium spread in hydrogen bomb tests and discharged by nuclear plants and factories.

The risks remain low, as doses are still well within international safety limits, say British regulators. But radiation experts insist that the oversight is worrying, and that people who eat fish from contaminated waters may have received much higher levels of radiation than supposed.

Vast amounts of tritium, an isotope of hydrogen, were released into the atmosphere by nuclear weapons tests in the 1960s. Thousands of trillions of becquerels are still emitted each year by nuclear plants at Savannah River in South Carolina, Sellafield in Cumbria and Chapelcross in southern Scotland.

Yet it was discharges from a factory in Wales making isotopes for the drugs industry that alerted scientists to the potential problem. Levels of tritium in fish near the Nycomed Amersham plant in Cardiff were hundreds of times higher than expected (快猫短视频, 31 October 1998, p 10). This prompted Britain鈥檚 National Radiological Protection Board (NRPB) to look again at the amount of radiation people are exposed to when they eat fish from the Severn Estuary.

The NRPB has now concluded that they receive twice the dose of radiation from tritium as assumed in the past. Evidence from animal studies suggests that tritium-carbon compounds may persist in the body for longer than previously assumed, and that the biological effect of tritium in water may be more damaging. As a result, there is a higher chance that the beta radiation from tritium will trigger tumour growth.

John Harrison from the NRPB stresses that, even if the risk is doubled, it is still very small because even those with the highest doses would still be within international safety limits. 鈥淧eople should not be particularly concerned about this,鈥� he adds.

But Barrie Lambert, a radiation expert from St Bartholomew鈥檚 Hospital in London, disagrees. The finding could have significant implications for people who eat a lot of fish from around the Cardiff plant, he says. Their current radiation dose could double to reach 133 microsieverts a year and in the past, when discharges of tritium were at their maximum, that dose could have been twice as high again.

International regulatory agencies say that to minimise the risk to public safety, people should not be exposed to more than 300 microsieverts a year.