Does Extremely Low Fukushima Radiation Increase Cancer Risk in North America?

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:

  1. 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.
  2. 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.

7 Responses to “Does Extremely Low Fukushima Radiation Increase Cancer Risk in North America?”

  1. Alex Roslin says:

    Hi Rob,

    Thanks for your report. A couple of notes:

    - The Health Canada information on cancer risks from radiation is available here:

    http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/radiological_para-radiologiques/index-eng.php

    - Canadian ceilings on radiation exposure for the public are based on a dose of 0.1 mSv, not 1 mSv.

    - You can read more detailed information on the Canadian government’s official cancer risk estimates at the Canadian Nuclear Safety Commission’s website (see section 2.1):

    http://nuclearsafety.gc.ca/eng/readingroom/healthstudies/tritium/

    - The concept that even low levels of radiation increase cancer risks is widely accepted in the scientific community and at radiological protection agencies. The most recent authoritative estimates for cancer risk – which are substantially higher than those used in Canada – were reported in the U.S. National Academy of Science’s landmark 2005 BEIR VII report:

    http://www.nap.edu/openbook.php?isbn=030909156X

    Regards,
    Alex

  2. Rob Tarzwell says:

    Hi Alex,

    Thanks for weighing in. I was hoping you’d drop by and comment.

    Thanks for that link. I was tearing my hair out trying to find it. I notice that under section 8.2 Health effects from radiation exposure, the formula, based on the LNT hypothesis (a statistical model, not an empirically demonstrated relationship – see the quotes from BEIR VII below) extrapolates from the demonstrated excess risk for an individual of 7.3% per per Sievert (5% risk of fatal cancers) to 0.0073% per 1 milliSv, or 0.00073% per 0.1 mSv. This is assuming that LNT is valid, which BEIR VII is quite open about it possibly not being valid.

    The regulatory limit of 1 mSv per year is exposure from all sources. The 0.1 mSv limit is exposure from drinking water only. The total absorbed dose from radiation exposure is based on the principles of MIRD (Medical Internal Radiation Dosimetry – here’s an overview: http://www.nucmedtutorials.com/dwraddosimetry/index.html).

    The thyroid is the organ that takes the highest dose from I-131 ingestion, because absorbed I-131 is trapped and organified. Assuming the thyroid traps 25% of I-131 it comes into contact with (a normal absorption for a healthy gland), the radiation dose is 351 milliSv per megaBq (one million Bq). This translates to 0.000351 mSv per litre of Graham Island water. So, the excess lifetime risk is:

    0.0073% per mSv x 0.000351 mSv per litre = 0.0000026% per litre of water consumed, over the lifetime of the individual.

    This figure is so small that it vanishes in the statistical noise.

    (Here’s a fact sheet on I-131. See Table 4 for dosimetry: http://www.nuclearonline.org/PI/mallinckrodt%20I-131%20Dx%20Caps.pdf)

    Now, what about that LNT hypothesis? Should we even accept it?

    Here’s an executive summary version of BEIR VII:
    http://dels-old.nas.edu/dels/rpt_briefs/beir_vii_final.pdf

    The key quotes regarding very low level radiation and cancer risk, in my view, are these:

    “The calculations in this report suggest
    approximately one cancer in 100 people could result
    from a single exposure 100 mSv of low-LET radiation.” (Caption to Figure 2.)

    “There are two competing hypotheses to the linear no-threshold model. One is that low doses of radiation are more harmful than a linear, no-threshold model of effects would suggest. BEIR VII finds that the radiation health effects research, taken as a whole, does not support this hypothesis. The other hypothesis suggests that risks are smaller than predicted by the linear no-threshold model are nonexistent, or that low doses of radiation may even be beneficial. The report concludes that the preponderance of information indicates that there will be some risk, even at low doses, although the risk is small.”
    (From the section “Risk Estimates at Very Low Doses”)

  3. Rob Tarzwell says:

    For anyone following the comment thread and curious, “BEIR” is an acronym for “Biological Effects of Ionizing Radiation.” It is the name of a standing international committee with numerous workgroups trying to understand and explain radiation health effects in a precise and quantifiable way.

  4. Alex Roslin says:

    Hi again Rob,

    Thanks for your comments. I think the band official on Graham Island was acting on the precautionary principle. He was concerned that he couldn’t know in advance how high the iodine-131 levels would spike.

    You may also be interested in reading the joint Health Canada-AECB report in 1998 on cancer risks from radiation:

    http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/98ehd-dhm216/index-eng.php

    It says: “In the case of non-carcinogenic chemicals, it is generally assumed that the dose-response relationship demonstrates a threshold below which no adverse health effects are observed. For carcinogenic chemicals, it is generally assumed that carcinogene-sis is a non-threshold phenomenon.”

    This report also found that ceilings for radiation are set at levels estimated to lead to numerous times more cancers than the guidelines generally used for carcinogenic chemicals. See for example Table 3.

    Regards,
    Alex

  5. Rob Tarzwell says:

    Hi Alex,

    I take the key quotation from the explanation to that table to be as follows:

    “Guidelines for radionuclides are set to protect public health at a given risk level; actual exposures are generally much lower.”

    But, even if we assume maximum exposure (0.1 mSv per year), and accept the LNT hypothesis (which BEIR VII directly states is not supported by the evidence at extremely low doses), the table *estimates* (a crucial term – this is not empirically demonstrated data) a “Risk per million people” of 400.

    The individual lifetime risk is therefore 400/1,000,000, or 1/2500, or 0.0004%.

    Again, the risk is super tiny and indistinguishable from noise, even granting lifetime maximum exposures and accepting the LNT hypothesis. Remember, as males, you and I have a lifetime cancer risk of 44%. Maximal allowable radiation in drinking water for a lifetime elevates this to 44.0004%.

    It’s riskier to take a highway day-trip in your car than to be exposed to a lifetime of maximum allowable radiation in water.

    The band official appears to have gone beyond the precautionary principle and advised a drinking ban even after being reassured by Health Canada, their advice very likely coming from similar risk calculations to what I’m showing here.

  6. Rob Tarzwell says:

    Correction! 1/2500 is 0.04%, not 0.0004%. My apologies. Lifetime cancer risk for males is therefore 44.04% instead of 44%, which still remains indistinguishable from noise. The relative risk in comparison with a highway day-trip is also unchanged.

    http://en.wikipedia.org/wiki/Traffic_collision

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  • Rob Tarzwell

    Rob is a Vancouver based physician with specialty training in psychiatry and nuclear medicine, and he is a Clinical Instructor on the Faculty of Medicine at UBC. He has publicly debated creationists and anti-WiFi activists, lectured on the importance of flu vaccines, and he writes articles in response to medical misinformation. He is convinced that, one day, one of those windmills he tilts at will actually fall over.