nuclear-news

For decades, studies have shown that even low doses of radiation are harmful to humans.

This week, the Associated Press reported that the Trump administration may be reconsidering that. The Environmental Protection Agency seemed to be looking at raising the levels of radiation considered dangerous to humans based on a controversial theory rejected by mainstream scientists. The theory suggests that a little radiation might actually be good for our bodies. In April, an EPA press release announced the proposal and included supporting comments from a vocal proponent of the hypothesis, known as hormesis. It prompted critical opinion pieces and sparked worry among radiation safety advocates.

EPA’s decision to move away from the radiation dose model widely accepted by the scientific mainstream. But by Friday, the EPA backed away from Calabrese’s stance in comments to Discover.

The debate cuts to the heart of the debate over the effects of low doses of radiation and reveals how difficult it is to craft clear guidelines in an area where scientific evidence is not clear cut.

Radiation Debate

When radiation damages our DNA, the body steps in to make repairs. Hormesis suggests that hitting the body with a little more radiation should kick our defensive mechanisms into overdrive. According to proponents of the theory, this results in the production of anti-oxidants and anti-inflammatory compounds that reduce our risk for cancer and heart disease, among other things. That’s why hormesis backers want the EPA to raise the level of acceptable radiation, pointing out that it would also save millions in safety costs.

It sounds convincing, and proponents have dozens of studies to point to that they say back up their claims. But, there’s never been a large-scale human study of hormesis. And while studies of low-dose radiation are very hard to do, so far, most suggest that radiation is indeed bad for us, at any dose.

“Large, epidemiological studies provide substantial scientific evidence that even low doses of radiation exposure increase cancer risk,” says Diana Miglioretti, a professor in biostatistics at the University of California, Davis in an email. “Risks associated with low-doses of radiation are small; however, if large populations are exposed, the evidence suggests it will lead to measurable numbers of radiation-induced cancers.”

Long-term studies of Hiroshima and Nagasaki bombing survivors show higher cancer risks. Marshall Islanders exposed to radiation from atomic bomb tests suffered a higher risk of thyroid disease. And patients who get CT scans, which deliver a dose of radiation equal to thousands of X-rays, saw cancer risks go up afterward. Researchers also found that radiation from childhood CT scans can triple the risk of leukemia and, at higher doses, triple the risk of brain cancers as well. Another found that low-dose radiation increased the risk of breast cancer among some some women.

And large-scale reviews of the evidence for hormesis find that it is decidedly lacking. Two studies, one in 2006 by the National Research Council, and another in 2018 by the National Council and Radiation Protection and Measurements looking at 29 studies of radiation exposure find no evidence for hormesis, and reiterate that the evidence points toward radiation being bad for us even at low doses.

Scientific Uncertainty

It’s difficult to study low doses of radiation, though, and that’s where much of the controversy comes from. At doses below a few hundred millisieverts (mSv), a radiation unit that accounts for its effects on the body, it becomes extraordinarily hard to separate out the effects of radiation from other things like lifestyle or genetics. Research on the effects of these small radiation doses often use data sets involving thousands of people to compensate for the minimal effect sizes, but even then it’s often not enough to be certain what’s happening.

“Data collected at low doses (defined by the scientific community [as] exposures less than 100 mSv) suffers from a ‘signal to noise’ problem which limits our ability to conclusively state effects one way or another,” says Kathryn Higley, head of the school of nuclear science and engineering at Oregon State University in an email.

A single CT scan delivers anywhere from 1 to 15 mSv, but some patients need many scans during the course of their treatment, increasing the total dose. Workers cleaning up after the Fukushima meltdown received radiation doses above 100 mSv in some cases. And current U.S. standards limit radiation workers to no more than 50 mSv of exposure per year.

Many studies indicate that there are dangers at that level, but it’s often an assumption. Those studies base their suppositions on what’s called the linear no-threshold model, which extrapolates more reliable data from studies of higher doses of radiation to lower doses. Though it may be an educated guess, for decades large-scale studies have indicated this is true.

……….. The EPA in recent days appeared to back away from the suggestion that it supported hormesis. The agency released a statement in response to the APstory affirming that it intends to continue using the linear no-threshold model when constructing radiation guidelines, something that contradicts Calabrese’s comments in the April press release.

“The proposed regulation doesn’t talk about radiation or any particular chemicals. EPA’s policy is to continue to use the linear-no-threshold model for population-level radiation protection purposes which would not – under the proposed regulation that has not been finalized – trigger any change in that policy,” said an EPA spokesman in response to a request for comment.

Radiologist Rebecca Smith-Bindman says the vast bulk of the evidence suggests even small amounts of radiation are harmful. We shouldn’t base our policies on an unproven theory, she adds.

“There is extensive evidence that ionizing radiation will cause cancer,” says Smith-Bindman, a professor of radiology at the University of California, San Francisco in an email exchange. “These data come from a range of different sources, including epidemiological data (such as studies of patients who have received diagnostic and therapeutic radiation and from environmental exposures and accidents), from animal studies and from basic science studies. While it is more difficult to precisely quantify the exposures — which will vary by many factors, such as age at exposure, and source of radiation, etc. — there is no uncertainty among the scientific community that radiation will cause cancer.”

She says that pointing to issues with the linear no-threshold model misses the point. Though it may not be totally accurate at very low doses, she says it’s unfair to use that uncertainty to cast doubt on data about radiation where there’s solid evidence.

…….. Miglioretti says “Based on the large body of evidence to date, I believe that revising the regulations to increase allowable radiation exposure limits will lead to an increase in the number of radiation-induced cancers in this country.”

That’s in line with what multiple experts Discover contacted believe — that radiation can harm even at low doses and raising limits would endanger the public, though the increase in risk would likely be small.

It’s not clear at the moment whether the EPA proposal to raise limits will pass, though it does follow in the footsteps of other Trump administration proposals to weaken safety standards. At the moment, it’s unclear what the effects on the public if the EPA raises radiation limits.

“Perhaps it might make nuclear power plants less expensive to build. It might lower the cost of cleanup of radioactively polluted sites,” says David Brenner, director of the Center for Radiological Research at Columbia University in an email. “But [it] begs the question of whether cleanup to a less rigorous standard is desirable.” http://blogs.discovermagazine.com/crux/2018/10/05/epa-trump-administation-radiation-guidelines/#.W99ZFtIzbGg