Wismut Study: Increased risk of radon-related lung cancer also in the low-dose range

Age, time since exposure, and smoking influence the radon-related risk of lung cancer

With the German Uranium Miners Study (Wismut Study), the BfS conducts one of the largest studies on radiation risk world-wide. Results of new evaluations especially on the topic of low-dose range have now been published in "Radiation Research":

The uranium miners' radon-related lung cancer risk also increases in the low-dose range.
In the low-dose range, too, the radon-related lung cancer risk depends on the time since exposure, the age at exposure and the smoking behaviour.
These findings are relevant to the calculation of lifetime risks and causation probabilities. The latter play an important role in procedures for the recognition of occupational illnesses.

Current evaluations of the German Uranium Miners Study (Wismut Study) on the lung cancer risk due to radon were published in the scientific journal "Radiation Research" in December 2017. The focus of the current study was on the lung cancer risk in the low-dose range, for example at an accumulative radon exposure of below 50 or 100 Working Level Months (WLM), or in workers who started working at Wismut after the radon concentrations had been clearly reduced through various measures.

Glossary Entry Working Level Month (WLM)

The unit Working Level Month (WLM) is frequently used in the risk assessment of occupational radon exposure instead of a calculated dose in Millisievert. The advantage is, that the concentration can be measured directly. No further assumptions for the dose distribution in the body are necessary. To calculate the cumulative exposure to radon in WLM, the measured alpha energy concentration (unit: Working Level (WL)) in one litre air is multiplied by the time the miner has worked in this surrounding. 1 WLM equals an exposure of 1 WL (1.3 * 10⁵ Megaelectron-volt (MeV) potential alpha energy per litre air) over 170 working hours (monthly working time), or a half WL over 2 months (340 working hours), respectively.

The most important results are the following:

In purely mathematical terms, about 40 percent of the 3,942 fatalities as a result of lung cancer in the Wismut cohort can be attributed to occupational radon exposure. Most of these fatalities were persons who had been exposed to very high radon levels during the first years of uranium mining. During the years they were working at Wismut, the individual radon exposures of single workers in the cohort accumulated to levels of over 3,000 WLM.
A significant exposure-effect relation was also found for relatively low radon exposures below 50 WLM. The risk increases proportionally to the total exposure to radon. For comparison: Based on the standard assumptions of the International Commission on Radiological Protection (ICRP) for the duration of stay and the equilibrium factor, a total radon exposure of about 50 WLM also results for a duration of stay of under 40 years in an apartment with 300 Bq/m³.
The radon-related lung cancer risk decreases clearly with the length of time that has passed since the time of exposure, namely by 60 percent every ten years. Also the age at the time of exposure plays a role: For younger workers the radon exposure increases the lung cancer risk more strongly than for older workers.
Not only do the lung cancer risks of smokers and radon add up, but they nearly multiply. So, the presence of both risk factors means a particularly strong increase in the lung cancer risk.

What relevance do these results have?

That radon and its decay products cause lung cancer, has already been shown by studies on radon in dwellings and in former uranium ore miners. Not quite as clear is whether and to what extent further factors influence the radon-related lung cancer risk, in particular in the low-dose range, which is relevant today. The Wismut Study delivers important findings on this issue. This knowledge is necessary to calculate lifetime risks and causation probabilities. The latter play an important role in procedures for the recognition of occupational illnesses. With ProZES, a program for the calculation of these causation probabilities is currently being developed on behalf of the BfS.

Comparison with other miners studies

The radon-related lung cancer risks observed in the German Uranium Miners Study (Wismut Study) are about factor 2 lower than the results of other miners study – which are smaller in terms of extent and time of observation – which were used by the International Commission on Radiological Protection (ICRP) to convert radon exposure in WLM into an effective dose in Sievert. In view of the complex statistical models with their uncertainties, however, the results are statistically comparable.

Background

Two miners of Wismut work underground Wismut workers underground Source: Wismut GmbH

Since the 1990s, the BfS has been conducting the German Uranium Miners Study. In the context of the study, it is stated for nearly 60,000 former workers of the Wismut uranium mining company every five years whether they have died and, if so, what the cause of death was. During the observation period from 1946 to 2013, altogether 3,942 persons from the cohort died from lung cancer.

Wismut, which is established in Thuringia and Saxony, was among the largest uranium ore mining companies world-wide after World War II. Altogether several hundred thousand people were employed there. Especially in the early years the miners were exposed to very high radon concentrations underground. About from 1960, the concentrations were clearly reduced through various measures. Therefore, also risks in the low-dose range can be examined in the study.