Item

Abstract

The work described in this paper is part of an investigation of the natural radiation burden applied to the human body [although one wonders if activity induced by cigarette smoking can strictly be described as natural]. The radioactive content of polonium-210 in various cigarettes was measured, together with the activity appearing in the butt, ash and smoke, but details of the method of measurement are not given. From these measurements, it is calculated that the activity inhaled per cigarette is 0.1 pc. per day (1 pc. equals 10^-12 curie or 2.2 disintegrations per minute). Thus, a person who smokes 20 cigarettes per day inhales some 2 pc. of Po-210, compared with a calculated inhalation rate of 0.02 pc. per day from the open air. The polonium activity of various lung tissues was measured. For smokers, the values for the parenchyma ranged from 0.014 to 0.002 pc. per gm. compared with an average value of 0.0025 pc. for non-smokers. Similar activities were found in the bronchial tree and at the bifurcation. The activity of the epithelium is of particular interest, since it is stated that the basal cell layer of this tissue is especially important in carcinogenesis. The activity of the epithelium in smokers ranged from 0.15 to 0.01 pc. per gm. and 0.0018 to 0.0001 pc. per cm2. These values are considerably lower than those found by other authors quoted, but are in good agreement with a theoretical calculation based on a daily intake of 2 pc. and a half-life in the lung of 5 days. References are given to work showing that the area distribution of polonium-210 in the mucous layer of the epithelium is uniform. The thickness of this mucous layer is stated to be about 10h, and its distance from the basal cell layer between 60 and 90µ near the trachea, and 20-40µ in the subsegmental bronchi. If it is assumed that all the activity is in the mucous layer, the dose to the cells can readily be calculated. The dose rate to the basal cell layer for smokers is given as an average of 41 mrem. per year in the subsegmental bronchi and 79 mrem. per year in the terminal bronchi. The dose rate arising from polonium-210 in the atmosphere will be very much less than this. On the other hand, the dose rate due to the inhalation of radon and thoron from the open air has been calculated to be between 1 and 2 rem. per year, or about 10 times the maximum calculated as arising from Po-210 in smokers. The authors conclude that it seems to be unlikely that the radioactivity of Po-210 is the cause of carcinogenesis.
It is interesting to note that the calculated dose to the cell layer due to normal atmospheric activity is very much greater than the dose due to naturally occurring-β-radiation which is about 100 mrem. per year.