A 100 mSv threshold for radiation effects?

In recent years, some scientists have promoted the view that there are no observable effects from radiation below 100 mSv, usually in their criticisms of the Linear No Threshold theory (I discuss the LNT here).

However, many studies show radiation effects well below 100 mSv. It is true that these effects are often numerically small, so that large studies are needed to yield findings which are statistically significant, but they do exist. These studies are conveniently set out in the table below: those with statistically significant findings are highlighted in green. The other studies are included because non-significant findings should also be shown, as they can indicate or support a trend. This is because the lack of statistical significance is often due simply to small numbers and not the absence of effect.

Study Effect Average dose or dose range Lowest estimated dose
Ukraine contaminated areas (Noschenko et al, 2001) leukemia 10 mSv 4.5 mGy
Chernobyl cleanup workers (Zablotska et al, 2012) leukemia 132 mGy bone marrow dose ~5 mGy bone marrow dose
Nevada test site (Steven et al, 1990) leukemia 6 to 30 mGy 6 mGy
Canadian radiation workers (Sont et al, 2001) solid cancers - 6.5 mSv
Nuclear industry workers (Cardis et al, 2005) leukemia 19 mSv “low”
In utero X-rays (Stewart et al,1956) leukemia 10 – 50 mSv ~10 mSv
Childhood thyroid exposures (Ron et al, 1996) thyroid cancer 50 mSv 10 mSv
US scoliosis from X-rays (Doody et al, 2000) breast cancer 100 mSv per 25 exposures 10 mSv
Childhood thyroid cancer (Jacob et al, 1999) thyroid cancer in Belarus + Russia 50 mGy thyroid dose 25 mGy thyroid dose
Japanese bomb survivors (Preston and Pierce, 2003) Solid cancers 200 mSv 34 mSv

Perhaps the most important of these studies (at least for risks from external exposures) is the Life Span Study of over 120,000 Japanese A-bomb survivors. The graph below reproduced from Preston et al (2003) shows the risks of solid cancers among the Japanese survivors. The data points are the mean of each dose category; the solid line is the weighted moving average of data points; the dotted line = ± 1 SE, and the dashed line is a linear fit to all data 0 – 2 Sv. This reveals 5 data points below 100 mSv.

Interestingly this graph appears to suggest that radiation rusks are supralinear between 250 and 350 mSv, ie even more hazardous than a linear model would suggest.

Conclusion

It can reasonably be concluded that very good evidence exists showing radiation effects well below 100 mSv.

References

Cardis E et al (2005) Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries. BMJ 2005;331:77.

Dale L. Preston, Yukiko Shimizu, Donald A. Pierce, Akihiko Suyama, and Kiyohiko Mabuchi (2003) Studies of Mortality of Atomic Bomb Survivors. Report 13: Solid Cancer and Noncancer Disease Mortality: 1950–1997. Radiation Research: October 2003, Vol. 160, No. 4, pp. 381-407.

Darby et al. Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ 2005;330:223.

Doody MM et al Land CE for the US Scoliosis Cohort Study Collaborators. Breast cancer mortality following diagnostic x rays: Findings from the US Scoliosis Cohort Study. Spine 25 (2000): 2052-2063.

Jacob P et al. Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia. British Journal of Cancer 80.9 (1999): 1461.

Noschenko et al. 2001. Patterns of Acute Leukemia Occurrence Among Children in the Chernnobyl Region.  Intl J of Epidemiology 30, 125-129.

Ron E and Schneider AB. Thyroid cancer. Cancer epidemiology and prevention 3 (1996): 975-994.

Sont WN, Zielinski JM, Ashmore JP, Jiang H, Krewski D, Fair ME, et al. 2001. First analysis of cancer incidence and occupational radiation exposure based on the National Dose Registry of Canada. Am J Epidemiol 153:309-318.

Stevens et al Leukemia in Utah and Radioactive Fallout From the Nevada Test Site: A Case-Control Study. JAMA. 1990;264(5):585-591. doi:10.1001/jama.1990.03450050043025.

Stewart A, Webb J, Giles D, and Hewitt D (1956) Malignant disease in childhood and diagnostic irradiation in utero. Lancet 271, 447.

Zablotska et al (2012) Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers. Environmental Health Perspectives. http://dx.doi.org/10.1289/ehp.1204996  Online 8 November 2012.

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