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, Guadala jara, Netzahualcoyotl, Pachuca, Puebla, Queretaro, Tecamachalco, Tehua can, Tlaxcala, Toluca, Tula, and Zacatecas. The measurement program st arted six years ago for a national evaluation of indoor radon problems in the non-tropical regions of Mexico. Most of the houses being monit ored have permanently open windows. We also gathered information on ge ology, topography, building materials, architecture, and ventilation s ystems. Each of these factors can significantly affect indoor radon co ncentrations. The passive radon detector is a chip of CR-39 polymer in a closed-end cup. This inexpensive device provides high detection eff iciency, and does not require highly skilled training for persons enga ged in the deployment and retrieval of the devices. The overall costs of a national survey of indoor radon can, therefore, be kept relativel y 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 rad on concentration levels was 50.6 Bq m(-3), which is most probably due to many houses having permanent openings to the outside.