Scientists warn full answers to nuclear radiation risk not available

THYROID cancer for sure.

Leukemia, probably. Too much radiation can raise the risk of developing cancer years down the road, scientists agree, and the young are most vulnerable. But just how much or how long an exposure is risky is not clear.

Those are among the unknowns scientists are contemplating as the crisis unfolds at Japan’s stricken nuclear power plant.

In Japan, the Science Ministry said radiation levels about 30km northwest of the Fukushima Dai-ichi plant rose at one point last Friday to 0.15 millisieverts per hour, about the amount absorbed in a chest X-ray. But levels have been fluctuating, and radiation at most sites that distance from the facility have been far below that.

Long term it is clear radiation can induce cancer. But researchers can’t just count cancer cases after a disaster and declare radiation responsible. Rates before and after must be compared to know if more cases occurred than would be expected.

That is why, 25 years after the Chernobyl accident, there is still controversy over its effects beyond the undisputed 6,000 cases of thyroid cancer. Of these cases, only 15 had proved fatal as of 2005, even though the Soviets were slow to treat victims of the catastrophe.

The records necessary to spot trends in other types of cancer as a result of Chernobyl are poor, said Dr Fred Mettler, a University of New Mexico scientist who led a United Nations-sponsored team investigating Chernobyl’s health effects.

The US Environmental Protection Agency says that no amount of radiation is absolutely safe above the 3 to 6 millisieverts a year that most of us get from normal living. In contrast, the Nuclear Regulatory Commission says that low doses — less than 100 millisieverts spread out over years — are not harmful. Researchers have not documented danger from such low levels, said Kelly Classic, a radiation physicist at the Mayo Clinic.

High doses — over 500 millisieverts — can raise the risk of leukemia, breast, bladder, colon, liver, lung, esophageal, ovarian and stomach cancers, and the blood cancer multiple myeloma, government scientists say.

Children are the ones at risk for radiation’s most obviously related cancer — thyroid. Potassium iodide pills can block its absorption and minimise harm, but they must be given within 12 hours.

When Chernobyl exploded, health workers “had millions of square kilometers to cover and it was all rural areas and they didn’t really have anything stockpiled,” Mettler said. Children also drank milk from cows that grazed on contaminated grass for weeks after the disaster, compounding their exposure and risk. More than 6,000 thyroid cancers have been documented in people who were children in the Ukraine, Belarus and Russia when the disaster occurred. But in Poland, where the antidote pills were given out, there were no higher rates.

The Chernobyl disaster provides the clearest information on cancer risk from a nuclear plant accident. It exposed 5 million people in Belarus, Russia and Ukraine to large amounts of radioactive material for 10 days, according to the 2008 report that Mettler helped write for the United Nations’ Scientific Committee on the effects of atomic radiation.

Exposure to cesium was a big concern because it affects the whole body, not just the thyroid gland.

And exposure among cleanup workers and emergency responders ranged as high as a few hundred millisieverts over the following few years.

Evidence suggests a higher rate of leukemia in these workers, “but it’s not certain,” Mettler said.

“Leukemia increases have not been seen in the children” who are now adults, he said. Nor have increases in breast, lung, stomach or other cancers been documented.

As bad as Chernobyl was, the average radiation dose over 20 years to people who live in contaminated areas was “relatively low” — 9 millisieverts, nearly the equivalent of a CT scan — once the short-term doses to the thyroid were subtracted, the UN report said.

The NRC has said that typical annual background exposure to radiation shaves 18 days off the expectedlifespan. Working in a nuclear plant under ordinary conditions — not in a crisis like the one unfolding in Japan — shortens life expectancy by 51 days. By comparison, being 15% overweight cuts two years; smoking a pack of cigarettes a day costs six years of life.