It has been over 20 years since Chernobyl exploded, scattering tons of radioactive debris and requiring a sarcophagus be built to forever entomb the remains of the accident site.
Chernobyl Offer New View of Radiation ExposureAfter the explosion, half a million workers were brought in to clean up and build the encapsulating structure that was required to control further damage from the nuclear meltdown. Such a huge number of workers were required due to constant turnover as clean-up crews reached their radiation dosage limit, sometimes after only a few hours of work. This population represents a lot of people who were exposed to radiation at moderate levels -- that is, more than you might want to be exposed to but far less than previous sample populations such as survivors of the atomic bombs at Hiroshima and Nagasaki.
Our current standards for "safe" limits of radiation exposure come from studies of such highly exposed people. Scientists must extrapolate backwards from the high exposure findings to guess the risks of low exposure. This results in a high degree of uncertainty and fails to account for differences in how the body reacts to low exposures, which may cause damage slowly enough that our bodies' own systems can make repairs to minimize the risks -- unlike high doses that overwhelm our reaction responses. Gamma and neutron rays from atomic bomb explosions also confound studies using bomb survivors.
A study led by Lydia Zablotska, MD, PhD, an associate professor of epidemiology and biostatistics of UCSF followed up with 111,000 Ukrainian workers from the Chernobyl clean-up crews. Zablotska hopes that the data from this study can be used to establish better estimates of the effects of low levels of radiation exposure -- the type of exposure relevant to miners, nuclear workers, and perhaps to people undergoing a large number of medical diagnostic tests. She emphasizes:
Low doses of radiation are important... We want to raise awareness of that.
Chronic Lymphocytic Leukemia Link SurpriseScientists have long known that radiation exposure increases leukemia risk by penetrating the body and damaging DNA in the bone marrow. They estimate 16% of the cases of leukemia diagnosed in the workers' study can be attributed to Chernobyl exposures (i.e. represent the increased risk compared to the general population).
But the team studying Chernobyl workers was surprised to find a significant increase in cases of chronic lymphocytic leukemia (CLL). An increased risk of chronic lymphocytic leukemia had not been found among survivors at Hiroshima and Nagasaki, and some scientists questioned whether there is any link between radiation and this type of leukemia. But Japanese people are inherently less susceptible to CLL, which accounts for only 3% of leukemia cases in Japan but causes a third of cases in the US and 40% of cases in the Ukraine.
Overall, it should be noted, there were only 137 cases of leukemia diagnosed over the 20-year span of the study, which is a tiny percentage compared to the number of workers involved, but still well above the 1 in a million excess cases of illness typically targeted when "safe" levels of exposure are determined.