A study has been made of cause specific mortality among Italian miners, with special reference to respiratory malignancies. The contrast between observed and expected mortality rates for lung cancer in various cohorts of miners exposed to different levels of radiation provide figures for estimating the number of cases per working level month (WLM) and person years of exposure. Data was collected from the zinc lead silver mine located in Gorno (Lombardy).
A survey by the Energia Nucleare e delle Energie Alternative (ENEA) detected radon concentrations ranging between 27 and 130 pCi/l, corresponding to 0.20 to 1.03 working levels (WL), the median being 0.60 WL. A concurrent survey by Commissariat a l'Energie Atomique (CEA) estimated 0.10 to 0.90 WL, with a median value of 0.36.
The study included 1357 subject, 60 of whom were lost to follow up. The total number of deceased subjects was 527; for 30 of them it was not possible to ascertain the cause of death.
Overall mortality and mortality for all neoplasms were significantly increased with respect to expected figures. Oesophageal, gastric and lung cancer occurred at significantly increased rates.
Mortality for tubercolosis and for nonmalignant respiratory diseases showed a significant excess: 52 out 68 cases of death from respiratory disease were attributed to silicosis, which was also mentioned in 10 out 12 causes of death from respiratory tubercolosis. Mortality from violent causes was significantly increased, while diseases of the circulatory and digestive systems did not show significant departures from expected figures. Finally, a significant decrease in mortality for diabetes should be mentioned.
As far as surface workers were concerned, mortality for all causes and for all neoplasms did not significantly exceed expected values; a significant excess of liver cancer was detected. Silicosis accounted for 10 of 21 deaths for respiratory diseases and was mentioned in 2 of 4 death certificates referred to tubercolosis. Circulatory diseases showed a significant decrease and no case of diabetes was observed. Liver cirrhosis was increased, but not significantly.
The main finding of the study appears to be the elevated mortality for respiratory diseases observed in underground workers; among surface workers no excess of lung cancer was detected, while the occurrence of silicosis caused an increase in mortality for nonmalignant respiratory diseases.
If lung cancer mortality is considered taking into account duration of exposure and latency time, it can be seen that the extra cases among underground workers tend to occur after about 20 years from initial exposure.
The number of extra cases of lung cancer among underground miners was 16.4; since average duration of exposure was 17.93 years, and median level exposure to radon was 0.6 WL according to ENEA and 0.36 WL according to CEA, it was estimated that between 9.78 and 16.31 extra cases per 1E6 person years and WLM had occurred.