The Linear-No-Threshold Hypothesis

In a recent article we discussed the BEIR VII report's conclusion with respect to the linear-no-threshold (LNT) hypothesis concerning low-level radiation's possible health effects. It's worthwhile to compare it with other reports' findings, all from professional organizations in the US.

First, here's the pertinent statement in BEIR VII

"At doses of 100 mSv or less, statistical limitations make it difficult to evaluate cancer risk in humans. A comprehensive review of available biological and biophysical data led the committee to conclude that the risk would continue in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans." [A typical person in the US receives 3 milliSieverts per year.]

That's a tepid justification for retaining LNT, but compare that with the statement from the National Institutes of Health:

"It is very difficult to detect biologic effects in animals or people who are exposed to small doses of radiation. Based on studies in animals and in people exposed to large doses of radiation such as the atomic bomb survivors, scientists have made conservative estimates of what might be the largest doses that would be reasonably safe for a person over a lifetime. But these calculations are estimates only, based on mathematical models. Low-level exposures received by the general public have shown no link to cancer induction. Even so, the U.S. Government uses these estimates to set the limits on all potential exposures to radiation for workers in jobs that expose them to ionizing radiation. International experts and various scientific committees have, over the years, examined the massive body of knowledge about radiation effects in developing and refining radiation protection standards."

And with the statement from the Health Physics Society"

"There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 5–10 rem (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent."

"In view of the above, the Society has concluded that estimates of risk should be limited to individuals receiving a dose of 5 rem in one year or a lifetime dose of 10 rem in addition to natural background." [5 rems would be 50 milliSieverts.]

Professor Bernard Cohen goes on to estimate what would be the health effects of low-level exposures and compares them with other health risks, using the LNT model even though he shows in his analyses that it overstates the adverse effects and probably understates the beneficial (hormesis) effects of low-level radiation.

As an exercise we'll do something simple here. The BEIR report says ten million mSv would cause 1140 deaths. And it says that, on average, 304 million Americans receive 3 mSv per year, so the total would be 912 million mSv. So all of the radiation-induced deaths add up to 104,000 per year. Of that number, according to the report, 0.2% are due to nuclear energy, the rest mainly being due to natural radiation. If the LNT hypothesis is right, 208 deaths per year can be attributed to nuclear energy.

In comparison, every study done shows that tens of thousands of Americans die every year from the pollution generated by coal-fired power plants. The most comprehensive study done so far puts the range between 33,000 and 121,000 per year, just counting adults over 25. In 2006, according to DOE, coal generated 1930 billion KWH of electricity and nuclear generated 787 billion KWH, so if nuclear replaced coal an additional 510 deaths would take place, but at least 50,000 lives would be saved.

And all of the radiation-related deaths depend on a hypothesis that hasn't been proved and which specialized professionals don't believe.

Here's the kicker: Coal plants emit more than ten times as much radioactivity as nuclear power plants. If the LNT hypothesis were true, 5000 of the coal-related deaths would be avoided by converting to nuclear energy just because of reducing radioactive emissions.

If some form of renewable energy could provide full-time power, this might be a harder decision to make. As we saw in an earlier article, though, there aren't any that could.

So those are the two options. We can let over 50,000 Americans die every year from coal or we can switch to nuclear energy and start cleaning up the environment while minimizing the threat of global warming. What to do, what to do.

BEIR VII

Maybe the National Academy of Sciences has a perverse sense of humor. Otherwise, I can't explain its 2005 report, Biologic Effects of Ionizing Radiation (BEIR VII: HEALTH RISKS FROM EXPOSURE TO
LOW LEVELS OF IONIZING RADIATION).

In the very first paragraph of the summary brief, is this sentence:

"A comprehensive review of available biological and biophysical data supports a “linear-no-threshold” (LNT) risk model—--that the risk of cancer proceeds in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans."

This is a statement that could warm the heart of the most discouraged anti-nuke. NIRS jumped into this like a kid into a pond. Let's compare how NIRS represents the report with what the report says when you get past the first paragraph.

NIRS: "There is no safe level or threshold of ionizing radiation exposure."

BEIR: "At doses of 100 mSv or less, statistical limitations make it difficult to evaluate cancer risk in humans. A comprehensive review of available biological and biophysical data led the committee to conclude that the risk would continue in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans." [A typical person in the US receives 3 milliSieverts per year.]

This is quite a different statement. The report admits the data don't support the view that the risk continues all the way down to zero exposure, but concludes that it does anyway. This is the conundrum radiation safety analysts have struggled with for as long as there have been radiation safety analysts. The only way to be sure is to assume the worst case, so that's what we'll keep on doing.

The BEIR report gives anti-nukes what they want most, a solid-gold slogan, and then says something different in the explanation.

NIRS: "Radiation causes other health effects such as heart disease and stroke, and further study is needed to predict the doses that result in these non-cancer health effects."

BEIR: "Radiation exposure has been demonstrated to increase the risk of diseases other than cancer, particularly cardiovascular disease, in persons exposed to high therapeutic doses and also in A-bomb survivors exposed to more modest doses. However, there is no direct evidence of increased risk of non-cancer diseases at low doses, and data are inadequate to quantify this risk if it exists. Radiation exposure has also been shown to increase risks of some benign tumors, but data are inadequate to quantify this risk."

In this case NIRS turns the BEIR report upside down, attaching a conclusion for high-level radiation to low-level.

NIRS: "It is possible that children born to parents that have been exposed to radiation could be affected by those exposures."

BEIR: "Studies of 30,000 children of exposed A-bomb survivors show a lack of significant adverse genetic effects."

What does NIRS mean by "possible?" Is it possible in the sense that our atoms could all rearrange themselves and each of us could turn into linoleum flooring? The evidence says it hasn't happened, but it's still possible? That certainly isn't what BEIR says.

What is especially significant is what the anti-nukes don't say about the BEIR report. The report shows that of all the radiation a typical person receives, less than 0.2% comes from all of the nuclear fuel cycle. In comparison he gets sixteen times as much radiation from consumer products.

The report already has told us nothing can be concluded about doses under 100 mSv and at the end of it we learn what is needed:

Continued research is needed to further increase our understanding of the health risks of low levels of ionizing radiation. BEIR VII identifies the following top research needs:
• Determination of the level of various molecular markers of DNA damage as a function of low dose
ionizing radiation.
• Determination of DNA repair fidelity, especially double and multiple strand breaks at low doses, and whether repair capacity is independent of dose.
• Evaluation of the relevance of adaptation, low-dose hypersensitivity, bystander effect, hormesis, and genomic instability for radiation carcinogenesis.
• Identification of molecular mechanisms for postulated hormetic effects at low doses.
• Reduction of current uncertainties on the specific role of radiation in how tumors form.
• Studies on the genetic factors that influence radiation response and cancer risk.
• Studies on the heritable genetic effects of radiation.
• Continued medical radiation and occupational radiation studies.
• Continued follow-up health studies of the Japanese atomic-bomb survivors, 45% of whom were still alive in 2000.
• Epidemiologic studies to supplement studies of atomic-bomb survivors, for example studies of nuclear industry workers and persons exposed in countries of the former Soviet Union.

Setting out its own limitations makes the report more valuable. And it emphasizes the folly of drawing strong conclusions as NIRS has done.

The final irony is that anti-nukes have succeeded only in forcing the world to use more coal. And coal-fired power plants emit more than ten times as much radioactivity as nuclear power plants.