Long-term radon survey in Mexico City and other regions of the country

A long-term survey for indoor radon is ongoing in Mexico City, Guadalajara, Netzahualcoyotl, Pachuca, Puebla, Queretaro, Tecamachalco, Tehuacan, Tlaxcala, Toluca, Tula, and Zacatecas. The measurement program started six years ago for a national evaluation of indoor radon problems in the non-tropical regions of Mexico. Most of the houses being monitored have permanently open windows. We also gathered information on geology, topography, building materials, architecture, and ventilation systems. Each of these factors can significantly affect indoor radon concentrations. The passive radon detector is a chip of CR-39 polymer in a closed-end cup. This inexpensive device provides high detection efficiency, and does not require highly skilled training for persons engaged in the deployment and retrieval of the devices. The overall costs of a national survey of indoor radon can, therefore, be kept relatively low. A few of the radon levels (up to 260 Bq m(-3)) are of moderate concern for radon-related health effects. The average of the lower radon concentration levels was 50.6 Bq m(-3), which is most probably due to many houses having permanent openings to the outside.