In the Wismut cohort the lung cancer risk increases proportionally with increasing radon exposure. The exposure to radon and its progeny is expressed in so-called "working level months" (WLM). The total exposure in WLM is calculated as the product of the energy emitted by the short lived radon daughters—or, in more simple terms—the radon concentration in one liter of air and the time a miner has spent in the respective environment.

Assigned radon exposures of the Wismut employees ranged from 0 (about 8,000 persons) to 3,224 WLM (mean = 280 WLM). Compared to non-exposed subjects, an exposure of 2,000 WLM resulted in a four-fold increase in lung cancer risk. However, this increase is also influenced by other factors like time since exposure, attained age and level of exposure. The increase in lung cancer risk per WLM is highest 5 to 14 years after exposure and among persons under 55 years of age. With increasing time since exposure lung cancer risk decreases by about a factor of 2 every ten years, but remains significant even after 35 years. Furthermore, the risk decreases with increasing attained age by 30 % every ten years. In addition a higher risk was observed when exposure was protracted over a longer period of time.

An analysis of the risk of death from lung cancer in uranium miners hired in 1960 or later, and thus exposed to rather low levels of radon, found a statistical significant association between lung cancer mortality and cumulative exposure to radon even in those low levels of radon exposure (Kreuzer et al. 2015). The mean radon exposure for those miners was 17 WLM which is only one tenth of the mean radon exposure in the whole cohort.

Additionally, the role of occupational quartz fine dust exposure as a risk factor for lung cancer mortality was analyzed (Sogl et al., 2012). The unit of exposure is dust-years (mg/m³-years). One dust-year is defined as an exposure to 1 mg/m³ quartz fine dust for 220 shifts of 8 hours. Cumulative quartz fine dust exposures range between 0 and 56 dust-years. Again, a significant increase in lung cancer risk with increasing dust exposure was observed. After adjustment for radon and arsenic, up to 10 dust-years no statistically significant increase of risk was observed. Above 10 dust-years, the risk increased linearly by 6.1 % per dust-year. The combined effect of radon and quartz fine dust is rather additive than multiplicative.

Leukaemia is a well-known long-term effect of radiation exposure. For a long time, the estimation of the risk for leukaemia has almost completely been based on studies on atomic bomb survivors of Hiroshima and Nagasaki. These persons were primarily exposed to a unique high dose of low-LET radiation. Recently published results of a study of nuclear workers (INWORKS study) showed an elevated risk for leukemia in subjects with a relatively low long-term radiation exposure (Leuraud et al. 2015). Exposure to low-LET radiation was also investigated in this study.

Wismut uranium miners were mainly exposed to radon and its progeny, leading to an internal radiation exposure due to inhalation. The corresponding dose can mainly be attributed to alpha radiation from radioactive decay products (high-LET radiation). In addition, the uranium miners were exposed to external radiation, particularly due to gamma radiation (low-LET radiation). In contrast to the exposure to radon and its progeny, this external radiation exposure with a mean of almost 50 millisievert is located in the low-dose range.

Therefore, the Wismut study offers the opportunity to examine the impact of the long-term radiation exposure on leukaemia risk both for low-LET radiation (as for the atomic bomb survivors and the nuclear workers) and for high-LET radiation, where so far findings are rare.

To examine the leukaemia risk in the Wismut cohort (Kreuzer et al., 2017), the doses for the red bone marrow were estimated from low-LET as well as from high-LET radiation. Since there is evidence from several epidemiological studies that the radiation-related risk for chronic lymphatic leukaemia (CLL) differs from other radiation-related risks for other types of leukaemia, the risk of CLL was analyzed separately.

There was a positive non-significant dose-response for mortality from non-CLL in relation to low-LET and high-LET radiation. Assessing subtypes of leukaemia, a statistically significant excess risk was found for the subgroup chronic myeloid leukaemia in relation to low-LET radiation and for the subgroup myeloid leukaemia (combining chronic and acute myeloid leukemia) in relation to high-LET radiation. Results indicate no association of death from CLL with either type of radiation. The leukaemia mortality risk was higher for high-LET radiation arising from radon and its progeny than for low-LET radiation.

Interestingly also in the INWORKS study the highest risk was found for mortality from chronic myeloid leukaemia in relation to low-LET radiation.

Radon is a radioactive noble-gas. The main radiation dose is received by the lung and to a minor degree by the nasopharyngeal region. Only a small fraction of radon enters the blood stream and thus reaches other organs. Therefore, it is plausible that the risk for tumours outside the respiratory tract is increased only very little if at all. Such low risks can only be detected in large observational studies with high radon exposures. Miner studies published up to now did not show any evidence for an increase in risk for tumours outside the lung due to radon. However, this may be due to the small size of these studies. The Wismut cohort might contribute substantially to answer this question.

Increases in risk with increasing radon exposure were found for several of the considered types of tumours. However, after adjustment for exposure to dust, external gamma radiation and long-lived radionuclides increases were no longer statistically significant (Kreuzer et al., 2008, Walsh et al. 2010). Only for tumours of the upper respiratory tract (mouth, nose, pharynx and larynx) a statistically significant increase in risk was found for the study period from 1946-2003 (177 cases) (Kreuzer et al., 2010). When follow-up was extended until the end of 2008 (234 cases), the increase in risk was no longer statistically significant (Kreuzer et al., 2014).

In general, neither mortality from stomach cancer (Kreuzer et al., 2012), nor mortality from liver cancer (Dufey et al., 2013) or from kidney cancer (n=174) (Drubay et al., 2014) was found to be associated statistically significantly with the respective organ dose from ionizing radiation (alpha and non-alpha radiation considered separately). The same is true for exposure to quartz fine dust or arsenic dust.

Until recently it was assumed that injuries due to ionizing radiation are mainly related to the risk of cancer. However, in the last years evidence for an increase in risk for cardiovascular diseases at low-dose exposures has been found for example, in the study on the atomic bomb survivors of Hiroshima and Nagasaki.

Evidence from miner studies is sparse and inconsistent. Therefore, the association between mortality due to cardiovascular diseases and external gamma radiation dose was investigated with data from the German uranium miner cohort including 9,039 cases of death due to cardiovascular diseases to the end of 2008 (Kreuzer et al., 2013). Among exposed miners the mean cumulative external gamma exposure is 47 millisieverts with a maximum of 909 millisieverts. In contrast to the lung, the relevant radiation dose here is mainly determined by gamma exposure.

Neither for the group of all cardiovascular diseases nor the subgroup of ischemic (caused by disturbed blood flow) or heart diseases (4,613 deaths) an increase in risk with gamma exposure has been observed. In the subgroup of cerebrovascular diseases the mortality risk is increased by 44 % per sievert. However, this increase is not statistically significant.

Within the Wismut cohort, 975 persons are known to have died from silicosis. Mortality from silicosis increases strongly with cumulative quartz fine dust exposure (Kreuzer et al, 2013). For exposures over 30 mg/m³-years a 90-fold increase is observed compared to exposures under 2 mg/m³-years. For other non-malignant respiratory diseases - including chronic obstructive pulmonary disease (COPD) – no significant association with quartz fine dust or radon exposure has been observed.