Radon as a potential health hazard for clients and workers of selected thermal spas in Poland.

The radiation exposure due to 222Rn and its progeny inhalation for clients and employees of selected thermal water spas was assessed. The radon risk was calculated using the measured 222Rn activity concentrations in the investigated thermal waters and radon transfer coefficient, defined as a fraction of radon released from the swimming pool water to the indoor air of swimming pool. The total radon in air concentration was not measured. The annual effective doses for workers and clients of the studied spa centers excluding Lądek-Zdrój ranged from 0.02 to 2.69 mSv and 0.40 to 48 μSv, respectively. For thermal water from Lądek-Zdrój (Lądek-Zdrój L-2), significantly elevated doses were observed both for workers (10.8 mSv) and clients (194 μSv).