If Vancouver’s The Georgia Straight‘s Alex Roslin knows how to reliably estimate cancer risk from ultra-low radiation exposures which are, by his own report, below overall background, he knows something the world’s radiobiologists and cancer epidemiologists don’t, despite decades of intense study.
Roslin’s “Safe” radiation levels after Japan’s Fukushima nuclear disaster challenged by citizens, hits on two themes:
- Extremely low levels of iodine-131 radiation from Fukushima have been detected in North America. In this case, 1.1 Becquerels (1.1 disintegrations of atomic nuclei per second) of I-131 were found per litre of rainwater on Graham Island.
- Extreme suspicion toward any agency not alarmed by these levels, and a reliance on spokespersons who claim that real cancer risks are being ignored.
First, yes, extremely low levels of radiation have been detected. I have previously described just how hard it is to detect a level of radioactivity that low and pointed out the level of radioactivity in common foods right off the grocery shelf, such as 600-800 Bq in 1 litre concentrated OJ, or 1000 Bq in 1 kg of instant coffee. It is worth re-emphasizing: Fukushima radiation detected in North America is very, very low. Your own body radiates internally 100 times as intensely as the equivalent amount of Graham Island water (4400 Bq compared with 42 litres of 1.1 Bq Graham Island water, the average water content in a human adult body).
The “It’s above background” argument, which Roslin makes for I-131 is a misleading red herring and beside the point: The extra radiation from Fukushima, when compared with total radiation abundant in the environment, is totally overwhelmed by normal background radiation from our bodies, from soil, and from space.
Roslin insists there is, nonetheless, an important cancer risk, one which is being downplayed or maybe even covered up by Health Canada, to the detriment of Canadians. This is a serious charge. In support, Alex Roslin has leaned heavily on Gordon Edwards, president of the Canadian Coalition for Nuclear Responsibility.
Roslin claims the Health Canada limit is set at, “a level that causes 7.3 cancers per million people each year.” He cites Health Canada’s website. I’m unfortunately unable to find that link. I wish I could, because I am almost certain he has grossly misunderstood what is posted there. Why do I say that? Let’s have a look at the relationship between low dose radiation and cancer risk:
The legal limit for radiation exposure to the Canadian public, for exposure not originating from background or medical sources, is 1 mSv per year, at a rate no higher than 2.5 microSv per hour.
You have a roughly 44% lifetime risk of developing cancer as a male, and 38% as a female. (Yes, cancer is sexist.) The question then becomes the following: What is the excess risk added by radiation exposure? This is an area of ongoing, intense study. Most data come from Nagasaki and Hiroshima survivors, and survivors of other nuclear incidents, accidents, and other exposures.
We actually have no reliably demonstrated way of determining excess lifetime cancer risk until total exposure in an individual reaches 100 mSv, and the excess risk at that point is approximately 1%. This overall figure in any individual will vary with age at exposure, exposure rate, route of exposure, and gender, but as an overall figure, it is surprisingly robust as we follow the Nagasaki and Hiroshima cohort through time.
For exposures below 100 mSv, we essentially have to impose a model, the Linear No-Threshold (LNT) model, because the data don’t reliably demonstrate a statistically significant difference between exposed and unexposed populations. So, the model assumes that all exposure is bad and imposes a linear, dose-response relationship on radiation exposure and cancer risk. This relationship has never been demonstrated, and many radiobiologists contest its validity. Many animal species paradoxically show decreased cancer risk and longer lifespan when exposed to very low doses of radiation. The reasons are unknown.
For Alex Roslin to blithely assert that he can calculate the excess cancer risk from Fukushima radiation is beyond confident. Fortunately, it is also science fiction.