Previous studies of the effects of 222 Rn in drinking water have centered on the long-term or chronic exposure to 222 Rn and its decay products. In this study, the possible effects that the transient increase caused by the release of 222 Rn from shower water can have on the 222 Rn concentration have been studied. In addition, the increment in the lung dose incurred by the occupants of a normally occupied home and the long-term increase in the 222 Rn concentration and the associated dose in the home has also been examined. Various parameters are of interest including the release of the 222 Rn from the shower water, the role of ventilation as a removal mechanism, and the behavior of the aerosol present in the home. Experimental work was performed in a shower stall constructed in the laboratory and in a bathroom in a normally occupied home. The home was supplied with water containing around 550 kBq m -3 of 222 Rn. A transfer coefficient around 0.70 and equilibrium factors up to 0.69 were measured in the laboratory. The ventilation rates measured in the home were in agreement with those found in the literature, 0.5-4.0 h -1 . The dose incurred was assessed using the lung dose model developed by the International Commission on Radiological Protection (ICRP). Calculations indicated that for homes with 222 Rn in the domestic water similar to the experimental home, the short-term exposure during showering could contribute a 17% increase in dose over the average daily dose. However, the increase in the long-term average concentration caused by the release of 222 Rn from water use in the home could more than double the average daily dose. Thus, the focus of concern regarding radon in domestic water should be primarily on its effects on the longterm airborne 222 Rn concentration.

In homes supplied by water with a high radon content, inhalation exposure from the radon in the water may occur on two different time scales: (a) long-term exposure that occurs due to an increase in the background radon concentration from radon released during water use and (b) short-term exposure that occurs during actual radon use such as in the bath, kitchen, and laundry room. While the former mode has been the subject of several studies, not much is known about the latter mode of exposure. During water use, the radon concentration can be considerably higher than the background and varies rapidly with time. Most of the exposure occurs well before a steady state can be reached. The goal of this work was to develop a dynamic, size-dependent model for the radon progeny activity during showering. The model includes radon and progeny decay, attachment of progeny to the existing aerosol, recoil, ventilation, and surface deposition. The model is used to evaluate radon exposure during and subsequent to showering as a function of environmental and other parameters (such as aerosol profile, bathroom dimensions, ventilation rate, and shower duration). These results are used in conjunction with a recent dosimetric model to obtain the integrated lung dose as a function of time.