Factors affecting use of CR-39 surface monitor technology to estimate past exposure to indoor radon

In an epidemiologic study investigating influences of life-style and environment on lung cancer risk, CR-39 alpha-particle detectors, identified here as surface monitors, were affixed to subjects' selected household glass, ceramic, or enameled objects to measure residual radioactivity from embedded radon (Rn) decay products. The purpose was to estimate past cumulative indoor Rn concentrations to which the object was exposed to infer past exposures of the subject. This approach was used to supplement exposure information obtained by methods traditionally used in Rn epidemiologic studies. In addition, surface monitors were affixed to objects of selected study subjects with complete exposure information to evaluate whether surface monitors provided estimates of cumulative past residential Rn exposure comparable to estimates obtained from year-long, ambient alpha track-etch measurements in each present and previous residence. These ambient measurements were time-weighted to estimate integrated exposure of objects and were adjusted for decay and ingrowth so as to be comparable to surface monitor measurements. A regression relationship was estimated between the two estimates of cumulative Rn exposure. Surface monitor measurements had a satisfactory correlation (0.63) with adjusted ambient Rn measurements for new, nonceramic objects. Although not included in the study design, factors that might affect use of the technology were also investigated. Regression relationships were compared in graduated smoking environments (as judged by the subjects) to investigate possible differential plate out of radon progeny. In addition, regression relationships for windows were compared with those for other objects to investigate whether there was a significant difference between windows and other objects. It has been suggested that windows may have a higher plate out rate because of locally increased air flow. Results suggested that surface monitor information was useful to fill time gaps in estimates of historical radon exposure data obtained by ambient measurements. Glass samples provided the best correlation. Ceramic materials sometimes provided excessively high radon estimates, probably due to glazes that contained significant uranium or thorium. Due to small sample sizes, investigations of other factors were inconclusive.