Levels of Dust and Radiation Exposure and Professional Risk Projection among Former Uranium Miners in Bulgaria

Zlatko G. Ivanov

National Center of Radiobiology and Radiation Protection, Sofia, Bulgaria
   
Corresponding author: Zlatko G. Ivanov, M.D.
    National Center of Radiobiology and Radiation Protection
    132 St. Clement Ohridsky Blvd, BG-1756 Sofia, Bulgaria

CEJOEM 1999, Vol.5. No.3-4.:280-285


Key words:
Uranium mining, radon and its daughters, potential alpha energy, occupational exposure, working levels, professional risk

Abbreviations:
CWLM = Cumulative Working Level Month
IARC = International Agency for Research and Cancer
ICRP = International Commission of Radiological Protection
NCRP = National Council on Radiation Protection and Measurements, USA
NCRRP = National Center of Radiobiology and Radiation Protection, Bulgaria
NIOSH = National Institute of Occupational Safety and Health, USA
NRC = National Research Council (USA) and BEIR-IV: Biological Effects of Ionizing Radiation
WL = Working Level = 1.3 × 105 MeV/l


Abstract:
Data on the history of uranium mining and potential alpha energy of 222Rn daughters decay in the basic sites of uranium industry in Bulgaria are dealt with. All these data, including the professional risk of the workers were treated as a secret until 1990. Personal records of the period 1986-1991 substantiate the validity of annual average values of the “potential hidden energy” of radon daughters the permissible levels of which were permanently exceeded. Taking into account these data and the main additional factor promoting fatal lung cancer, cigarette smoking, the predicted occupational risk is 20-80 times higher as compared to the spontaneous frequency of lung cancer in Bulgarian male population. For 46,350 former uranium miners, the expected frequency of lung cancer is 1934 cases among non-smokers and 3,320 for smokers (48% of the underground staff).
    Uranium mining history in Bulgaria is resumed with a retrospective study on the levels of “potential alpha energy” of 222Rn progeny and some other harmful factors (dust comprising silicon compounds) smoking habits, etc. that are important for the interpretation of excess lung cancer risk.
    We stated that acceptable levels are being permanently exceeded 5-10 times, in some cases up to 124 times. On the basis of the average values, we calculated the expected frequency of lung cancer for the concerned groups of miners as the main criterion for the professional risk in the underground mining. Purposeful retrospective epidemiological research amongst our uranium miners has not been carried out. An experiment to investigate 1200 former uranium miners was done from 1985 up to 1998. Twenty cases of lung cancer were found among underground miners and 7 among chemical enrichment factory workers. Their times of service were from 5 up to 27 years. The latency of lung cancer was between 15 and 47 years. An attempt to find a relationship between 210Pb blood levels and the cancer latency was done. However, the data were not reliable because of the small size of the miner population. In comparison with the spontaneous frequency (54 × 105 cases of lung cancer in men in 1990 and 68.2 × 105 in 1994) our predicted risk is 20-80 times higher.


Received:  26 August 1999
Accepted:  14 January 2000

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