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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