Long Term Exposure: Health Studies of Nuclear Pros
Large populations of people have been exposed to carefully measured quantities of radiation in their professional work with nuclear power plant systems. These long term exposures to low level radiation offer a unique opportunity to determine what risk, if any, this new industry has added to the general level of risk in people’s daily lives.
The Health of Nuclear Professionals Studied
Of course, scientists have not ignored the opportunity to study the health of nuclear professionals. One study involved 71,000 people who had worked in shipyards that built and serviced nuclear powered ships in the United States.
Three broad categories were recognized in the study. One group of 25,000 had accumulated a lifetime occupational exposure of greater than 5 mSv. One group of 10,000 incurred occupational exposure less than 5 mSv. The control group consisted of those workers that were not exposed to any radiation other than background levels.
The study showed that nuclear workers with more than 5 mSv of accumulated equivalent dose had a mortality rate that was 24 percent lower than expected, based on the control group. The workers with less than 5 mSv had a mortality rate that was 19 percent lower than the control group.
The death rates for both groups of exposed workers were equal to or lower than the expected death rates of the general population in all categories of disease studies except for mesothelioma. A total of 36 workers from the population of 71,000 died of mesothelioma. This disease of the lungs is closely associated with exposure to airborne asbestos fibers.
Why Were Study Results Delayed
The 1987 study was conducted at a cost of more than $10 million dollars by John Hopkins University under a Department of Energy contract, but was never published in scientific literature. Finally, in 1991, the 437-page study was made available to the public with a 2-page press release.
Some researchers have postulated that the release of the study was delayed nearly four year because of a fear of exposing the government to lawsuits for not adequately protecting workers from exposure to asbestos. With this decision, however, the good news about the lack of hazard from radiation never reached the public.
A similar study has been conducted in Great Britain of a population of workers with life-long employment in the nuclear industry. The vast majority of the workers, like those in the United States, had lifetime exposures that were within the variations in natural background levels. There were however, 542 people with exposures between 500 mSv and 2 Sv. These levels are between 200 and 800 times as high as the average annual background exposure.
This group had a measured mortality that was less than that of the general population. Their risk of lung cancer was significantly reduced, a fact attributed to their reduced smoking habits. It is difficult to smoke in anti-contamination clothing that is often worn in areas where workers can be exposed to relatively high radiation levels.
Unfortunately, many scientists review all the studies and still make the statement that they do not know the risk from low levels of radiation exposure. Because it is difficult to put an exact number on a risk that is vanishingly small, scientists can accurately claim that they do not know the exact risk. Their usual comment is that more study is needed.
In some ways, these researchers are engaging in job protection, their profession is to perform studies under contract to various organizations. In other ways, they are simply engaging in the old argument about how many angels can fit on the head of a pin.
The Bottom Line
Here are the facts: High levels of radiation are harmful, and the correlation between the dose and the danger at high levels is linear. At levels that are within the natural variation of background radiation, the risk is too small to measure. In fact, evidence indicates that a certain amount of radiation acutally has beneficial effects.
Whatever the exact relationship is between low levels of radiation and human illness, it is too small to worry about while ignoring far more serious risks to human health and safety.