Thursday, February 7, 2008

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.

2 comments:

Dale Dewar said...

I'm all for nuclear power - once it has discovered how to deal with the waste. This continued and perplexing problem makes it the outdoor "biffy" without a tank or a bail-out.

However, does it deal with global warming? Probably not since the construction of nuclear power plants requires so much energy and pay-back time is sufficiently long that we wouldn't start seeing results for almost twenty years after powering up.

So - fix the waste problem but in the meantime start investing in low-input technology. Nukes might be the way to keep us sustainable but not in the current pardon-the-pun climate.

Red Craig said...

Dale, thanks for taking the trouble to comment.

First, the technology for dealing with spent-fuel waste has been known for sixty years. Were it not for the opposition of anti-nuclear political groups we would already be recycling spent fuel.

Second, every study done by responsible analysts shows that nuclear energy is as effective at lowering greenhouse-gas emissions as any of the renewable energy sources.

For solid information from the most authoritative sources available, please look at The Case for Nuclear Energy: Greenhouse Gas Emissions.