(Dec. 02, 2010) We may need to scrap the current regulatory regime governing low levels of radiation.
Prior to the Second World War, radiation was considered safe, even healthy, in small doses. After the war, and the horrors of Hiroshima and Nagasaki, scientific opinion swung to the theory that radiation posed a risk in any quantity, no matter how small.
That theory, now dominant, is called the linear no-threshold theory, or LNT for short. “Linear” because the risk is thought to be directly proportional to the dose — the lesser the dose, the lesser the risk. “No threshold” because there’s no size of dose at which radiation stops being harmful and is then deemed harmless. “Theory” because LNT is unproven and, in fact, cannot be proven to exist — at low doses, it would be a practical impossibility to get large enough population samples to statistically test the LNT theory.
Because of this LNT bedrock of scientific thinking, some industries are effectively outlawed and others — particularly those in the medical and nuclear energy fields — are dramatically curtailed. Now this bedrock has been cracked, thanks to a study that indicates we may have radiation-related regulations all wrong.
“Checking the Foundation: Recent Radiobiology and the Linear No-Threshold Theory,” a paper by Brant A. Ulsh published in the current issue of Health Physics, describes various independent studies of the effects of radiation on genes. In one large study of 23,040 genes (most of the estimated 25,000 genes in the human genome), 238 genes became more active after a small dose of radiation but not after a large one, while 89 genes became more active after a large dose but not after a small one. Meanwhile, a larger number of genes became less active after receiving a large dose.
The greater activity from the lower dose involved genes that produce proteins that protect the body (say, from heat shock), while the greater activity from the higher dose involved genes that produce tumour-killing proteins. Significantly in terms of the LNT theory, “the biological responses caused by low doses are qualitatively different than the biological responses caused by high doses,” explained Dr. Ulsh, a scientist at the National Institute for Occupational Safety and Health in Cincinnati.
“It is apples and oranges. The LNT theory predicts that high doses should cause the same response as low doses, just more of it — more apples, not apples and oranges. But that isn’t what we are seeing from the recent radiobiology studies reviewed in my paper.”
Dr. Ulsh’s paper showed that the behaviour of genes was not the only thing at odds with the LNT theory — the behaviour of cells and tissues, studies showed, also conflicted with the LNT theory.
The bottom line: The doctrine that radiation carries risk in direct proportion to the size of the dose delivered doesn’t square with the complex relationships seen in empirical scientific studies. The regulatory regime governing low levels of radiation may need to be scrapped, and replaced with one that reflects the real world.
Lawrence Solomon is executive director of Energy Probe and the author of The Deniers.
Dr. Ulsh’s paper has not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.