HIROSHIMA, Japan — The harmful effects of nuclear radiation have been grossly underestimated ever since the atomic bomb was first dropped on this Japanese city 42 years ago, scientists say.
A report from the Radiation Effects Research Foundation has shaken the foundations of radiation safety standards, including those for nuclear power plants, they say.
"There is no reason for mass hysteria or panic. But, on the average, we must double the (current) risk factor in relation to dosages," Dr. Itsuzo Shigematsu, chairman of the joint U.S.-Japan foundation, said in an interview.
He said nuclear safety standards are being overhauled as a result, a worldwide process to be completed in 1990.
Preliminary Report Issued
A preliminary report on the new risk factors for diseases such as leukemia and various forms of cancer was issued in August, and the full report will go to the International Commission on Radiological Protection this month, he said.
The report uses new calculations on the bombs dropped on Hiroshima and Nagasaki in August, 1945, at the end of World War II.
According to the new estimates, the bombs that killed 140,000 people in Hiroshima and 70,000 in Nagasaki released 20% to 30% less radiation than was previously thought.
Since the amount of radiation was less, the strength of the radiation--and thus its potential to harm people--must have been greater than had been believed, Shigematsu said.
Increases in the risk factor require a substantial lowering of radiation exposure ceilings.
Radiation risks, already an issue after accidents at Three Mile Island and Chernobyl nuclear energy plants, were highlighted again in Brazil two months ago when it was learned that up to 1,000 people were exposed to dangerous radioactivity levels from radioactive waste from a hospital.
World radiation standards for the past two decades have been based on surveys of Hiroshima and Nagasaki bomb victims and the detonation of a similar bomb in the Nevada desert in the early 1960s.
But scientists now believe the standards were wrong because they underestimated the effects of the radiation, partly because of faulty calculations and partly because of U.S. reluctance to release information on the atomic bombs.
Based on the foundation's preliminary findings, the International Commission on Radiological Protection has drastically lowered the recommended radioactivity safety ceilings in recent years, although few countries have accepted the new limits.
Soviet Scientists Visited
Several Soviet scientists have visited the radiation research center in Hiroshima to study how they could best continue to trace those exposed to fallout from the 1986 disaster at Chernobyl, Shigematsu said.
Around the world, doctors and physicists have heavily relied on surveys of the 360,000 Japanese surviving \o7 hibakushas\f7 --those exposed to radiation at Hiroshima or Nagasaki--for clues to radiation's aftereffects.
The foundation has been monitoring life span, cancer and leukemia rates and other problems among about 120,000 \o7 hibakushas \f7 in both cities since 1947.
Rates of cancer, and especially leukemia, are significantly higher among the people exposed to the radiation from the two bombs than the rest of Japan's population, foundation figures show.
"We must definitely continue our work until the last of the \o7 hibakusha \f7 has died, which would be another 40 years or so," Shigematsu said.
Offspring to Be Traced
"In addition, we must trace their offspring as well, although fortunately, we have not found any abnormalities among them."
A doctor in Nagasaki, who has been investigating the indirect effects of contaminated rainfall on people near the city, said they still have far more questions than answers about radiation.
"To put it modestly, our understanding of radiation is about the size of a small stone compared to the whole earth," Dr. Motomori Izumi said.
Shigematsu agreed, "Even after 40 years of detailed studies on radiation, it's like a thick fog. We can only make out the outline, we can't see the details."