Occupational exposure of water-plant operators to high concentrations of radon-222 gas

Water-plant operators may be exposed to high airborne radon-222 (Rn-222) concentrations created when Rn-222 gas transfers from water to air during the water treatment processes. To evaluate this hazard, we placed yearlong alpha-track radon detectors in 31 water plants. The geometric mean of the annual average airborne Rn-222 concentrations was 3.4 pCi L(-1) (126 Bq m(-3)), with a maximum of 133 pCi L(-1) (4921 Bq m(-3)). We assessed the short-term temporal variability of Rn-222 by monitoring four water plants continuously for a 3- to 6-day period. Cumulative working level months were estimated for the time workers were in the water plants. Because airborne Rn-222 concentrations in water plants can reach levels considered unsafe for underground miners, it would be prudent to monitor airborne Rn-222 concentrations in water plants which aerate water as part of their treatment process.