The amount of radiation that leaked in March at the nuclear fuel reprocessing plant in Tokai, Ibaraki Prefecture, is too small to pose a threat to human health, four members of the Japan Radiation Research Society claimed May 26 during a news briefing.

Representing a group of seven scientists who studied effects of the nation's worst nuclear accident, the four stressed that the small amount of radiation 37 workers at the facility were exposed to cannot cause cancer or hereditary problems. The scientists further challenged the general assumption that any amount of radiation affects health in a negative way, citing studies that showed the risks of cancer in areas with high natural radiation in China and India are not more than the average.

"Radiant rays are an environmental factor that can be measured to small precision," said Hiroshi Tanooka, a scientist at the National Cancer Center. "And if managed well, it is one of the safest environmental factors."

The seven scientists believe that a threshold -- the point at which negative effects start to be produced -- exists for radiation exposure as well, said Sohei Kondo, a professor emeritus of Osaka University, adding that "dose makes poison." After stating that their opinion does not reflect that of the society, Tanooka said the group hopes to trigger open debate over whether there is really no threshold in radiation exposure. "People seemed to be overly scared (of the radiation exposure). So we want people to judge under a correct understanding of the issue," Kondo said in explaining the reason for their study.