Indoor 222Rn survey in Zacatecas State, Mexico.

As part of a program for discovering whether afflicted areas exist, indoor (222)Rn concentrations in the State of Zacatecas were surveyed, (222)Rn concentration being measured by gamma-ray spectrometry of radon decay products adsorbed into charcoal canisters. A survey was implemented during Summer 2001: 228 dwellings in the state were tested by taking mean 254 measurements. Concentrations exhibited a left-skewed distribution of indoor (222)Rn, showing overall average, minimum, and maximum concentrations of 67, 26, and 511 Bqm(-3), respectively. Only seven of the measurements (2.7%) were found equal to or greater than the US EPA action limit (148 Bqm(-3)). Thus, we conclude that the indoor radon environment in Zacatecas State is under US EPA action limit. The few high concentration spots suggest that geological conditions rather than construction materials may be the determinant factor.