Friday, July 17, 2009

An Update on Two Competing Models of Radiation: Linear No-Threshold vs Hormesis

The author of one of my favorite nuclear blogs, Rod Adams, found a new and compelling document explaining the beneficial health effects of low doses of radiation. The document has generated quite the number of comments at his site and I could see why. Here are some good quotes and background info from the paper (pdf):

In the early stages of nuclear development, more than 60 years ago, the world regulatory agencies (e.g. ICRP) had little understanding of the mechanisms by which nuclear radiation interacts with living things. They observed an excess incidence of cancer death following high dose exposures and measured a linear relationship between dose and cancer mortality in the high dose range. They were unable to observe excess cancers in the low dose range, so they assumed that excess cancer is proportional to dose in that range, all the way down to zero dose. That is, they made a linear extrapolation from evidence in the high range down through the low range, where there is no evidence of harmful effects. This is called the Linear No-Threshold (LNT) model. (p.4)

...

So what levels of radiation are harmful and what levels are not? Based upon human data, a single whole body dose of 150 mSv (15 rem) is safe. The high background of 700 mSv/year (70 rem/year) in the city of Ramsar, Iran, is also a safe dose limit for continuous chronic exposure. Both dose limits are also beneficial. However, our regulations limit exposure to human-made radiation to only 20 mSv/year (2 rem/year) for workers- and 1 mSv/year (0.1 rem/year) for the public. Why have these limits been set so low? (p. 6)

...

There is considerable evidence that exposure to a low dose or a low dose rate of radiation has a stimulatory effect on all living organisms. The immune system is stimulated by a short-term radiation dose. The body has built-in adaptive defences against higher levels of exposure after having been exposed to low-dose or low dose rates of radiation. This is called radiation hormesis. The extensive scientific evidence of the beneficial effects following low dose or low dose rate exposure (e.g. 192 studies in UNSCEAR 1994) and the scientific explanations for the effects appear to have been ignored by the government regulatory authorities (ICRP, NCRP). (p. 7)

...

The doses or dose rates of radiation received in the nuclear industry and by the public living near nuclear plants are within the range of natural background radiation levels and far below the levels where harmful effects have been observed. Radiobiological evidence supports the radiation hormesis model: beneficial health effects for low-dose or low dose rate radiation exposures and harmful effects for high-dose or high dose rate exposures. (p. 9) ...
It'll be interesting to watch how the regulators and public react as more and more evidence like this comes out explaining that radiation maybe isn't as bad as they think. Like I said before, radiation saves lives.

3 comments:

D. Kosloff said...

Actually, knowledge of radiation hormesis has been around for about fifty years. I still remember a photograph from a book I read about fifty years ago. It was a photo of rows of corn planted in concentric circles. At the center of the circles was a strong gamma source. The first two or three rows were dead. The next few rows were each a little higher as the distance from the source increased. The next rows were each shorter as the distance from the source continued to increase. Then at some point, the height leveled off.

Brian Mays said...

Early crop circles?!

Marje Hecht said...

There is a history of hormesis by Jim Muckerheide posted on the website of 21st Century Science & Technology,
http://www.21stcenturysciencetech.com/articles/nuclear.html

and several other articles on the subject.