9 Novembre 2012
November 9, 2012
WASHINGTON — Protracted exposure to low-level radiation is associated with a significant increase in the risk of leukemia, according to a long-term study published Thursday in a U.S. research journal.
The study released in the monthly Environmental Health Perspectives was based on a 20-year survey of around 110,000 workers who engaged in cleanup work related to the Chernobyl nuclear plant disaster in 1986.
Scientists from the University of California, San Francisco, the U.S. National Cancer Institute and the National Research Center for Radiation Medicine in Ukraine were among those who participated in the research.
The scientists conducted a followup health survey covering 110,645 cleanup workers through 2006. Of the workers, 137 contracted leukemia, including 79 chronic cases.
Of those surveyed, 87 percent had been exposed to cumulative radiation doses of below 200 millisieverts and 78 percent to below 100 millisieverts, indicating the impact on health of low-level exposure is not negligible.
After statistically excluding genetic and other factors that could cause leukemia, the study estimated that approximately 16 percent of all the leukemia cases confirmed during the 20-year followup study were attributable to radiation exposure from the Chernobyl disaster.
The finding was statistically consistent with estimates for Japanese atomic bomb survivors, the research team said.
The team said its finding is also useful in assessing the effects of exposure to radiation from medical equipment.
In the triple-meltdown disaster that started last year at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear complex, the maximum radiation exposure dose for workers was temporarily raised to 250 millisieverts a year from 100 millisieverts.
Keigo Endo, a radiologist and president of Kyoto College of Medical Science, pointed to previous data showing an increased risk of leukemia with cumulative radiation exposure of as low as 120 millisieverts.
"The latest finding underlines the importance of long-term followup surveys. Further details of the survey should be examined to confirm specific dose levels that could cause leukemia," Endo said.