Low-Level Radioactivity Is Damaging: Study

First Posted: Nov 14, 2012 01:16 AM EST

Similarly we all are exposed to some kind of radiation that occurs naturally in soil and rocks. How dangerous even low level radioactivity can be is being studied by the researchers from the Universities of South Carolina and Paris-Sud. 

Exposure to any amount of radiation is harmful to human beings. There are enough examples in recent history chronicling the devastating effects of radiation. Most of the victims of the Nagasaki and Hiroshima bombings died not from the explosion but from the radiation released as a result of the explosion.  A year after the nuclear accident at Fukushima, Japan, the lives of hundreds of thousands continue to be affected by the disaster. All Japan's nuclear reactors were shut down in the months after the disaster at Fukushima, when an earthquake-sparked tsunami knocked out cooling systems and caused meltdowns that scattered radiation over a large area.

Similarly we all are exposed to some kind of radiation that occurs naturally in soil and rocks. How dangerous even low level radioactivity can be is being studied by the researchers from the Universities of South Carolina and Paris-Sud.

They conducted an analysis on 46 peer-reviewed studies published over the past 40 years. From their analysis they learnt that variation in low-level, natural background radiation was found to have small, but highly statistically significant, negative effect on DNA as well as several other measures of health.

This analysis was based on different locations around the world that had very high natural background radiation due to the minerals in the ground there. This included places like Ramsar in Iran, Mombasa, Kenya, Lodeve (France) and Yangjiang, China.

"When you're looking at such small effect sizes, the size of the population you need to study is huge," said co-author Timothy Mousseau, a biologist at the College of Arts and Sciences, University of South Carolina. "Pooling across multiple studies, in multiple areas, and in a rigorous statistical manner provides a tool to really get at these questions about low-level radiation."

For the study, Mousseau and co-author Anders Moller from the University of Paris-Sud examined more than 5,000 papers involving natural background radiation that were narrowed to 46 for quantitative comparison.

These selected groups examined both the control group and the highly irradiated population and quantified the size of the radiation levels for each. The paper also reported test statistics that allowed direct comparison between the studies.

The organisms studied included plants and animals, but had a large preponderance of human subjects. Each study examined one or more possible effects of radiation, such as DNA damage measured in the lab, prevalence of a disease such as Down's syndrome, or the sex ratio produced in offsprings. With the help of a statistical algorithm they generated a single value for each effect which could be compared across all the studies.

The negative effects as reported by the scientists were immunology, physiology, mutation and disease occurrence. The frequency of negative effects was beyond that of random chance.

"There's been a sentiment in the community that because we don't see obvious effects in some of these places, or that what we see tends to be small and localized, that maybe there aren't any negative effects from low levels of radiation," said Mousseau. "But when you do the meta-analysis, you do see significant negative effects."

"It also provides evidence that there is no threshold below which there are no effects of radiation," he added. "A theory that has been batted around a lot over the last couple of decades is the idea that there is a threshold of exposure below which there are no negative consequences. These data provide fairly strong evidence that there is no threshold, radiation effects are measurable as far down as you can go, given the statistical power you have at hand."

The scientists hope that their result, which is consistent with the "linear-no-threshold" model for radiation effects, will better inform the debate about exposure risks.

"With the levels of contamination that we have seen as a result of nuclear power plants, especially in the past, and even as a result of Chernobyl and Fukushima and related accidents, there's an attempt in the industry to downplay the doses that the populations are getting, because maybe it's only one or two times beyond what is thought to be the natural background level," he said. "But they're assuming the natural background levels are fine."

"And the truth is, if we see effects at these low levels, then we have to be thinking differently about how we develop regulations for exposures, and especially intentional exposures to populations, like the emissions from nuclear power plants, medical procedures, and even some x-ray machines at airports."

Scientists have concluded the study in the Cambridge Philosophical Society's journal Biological Reviews.

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