RADIATION PROTECTION IN URANIUM MINING - 2 CHALLENGES

For uranium miners and mill workers, the main radiological risk is of developing a cancer of the lung due to the inhalation of radon progeny . This risk is generally expressed in terms of excess risk per unit ex posure of airborne radon decay products (Working Level Month, or WLM), assuming a non-threshold linear, or quadratic-linear, relationship be tween exposure and risk. However, there are wide differences in the ri sk factors derived from eleven major cohorts of miners exposed to rado n progeny and, in these cohorts, the risk seems to decrease as the fre quency of radon progeny sampling, and the reliability of exposure data , increase. Further, in two cohorts with relatively reliable exposure data, and in two other cohorts, the risk of lung cancer appears to be insensitive to increasing exposure, up to about 200 to 400 WLM of tota l exposure, a pattern which is indicative of the existence of a thresh old for the induction of lung cancer by radon progeny. This pattern is also consistent with other human epidemiological data and animal expe riments which also seem to support the notion of thresholds in the ind uction of cancer by internally deposited alpha emitters. The second pa rt of the paper examines the difficulties in the evaluation of exposur es and radiation doses from airborne radon progeny and long-lived radi oactive dust. It is shown, in particular, that the evalution of doses due to the inhalation of long-lived radioactive dust from dust samples collected on filters requires the development of new, appropriate tec hniques and procedures.