THE NATURAL BACKGROUND GAMMA RADIATION EXPOSURE IN THE METROPOLITAN AREA OF THE VALLEY OF MEXICO

Measurements of the natural background radiation have been made at numerous places throughout the world. Very little work in this field has been done in developing countries. In Mexico the natural radiation to which the population is exposed has not been assessed. This dissertation represents a pioneer study in this environmental area. The radiation exposure which occupants within buildings receive as a result of naturally occurring radionuclides present in construction materials is the principal focus.^ Data were collected between August 1979 and November 1980. Continuous monitoring was done with TLDs placed on site for periods of 3 to 6 months. The instrumentation used for "real-time" measurements was a portable NaI (Tl) scintillation detector. In addition, radiometric measurements were performed on construction materials commonly used in Mexican homes.^ Based on TLD readings taken within 75 dwellings, the typical indoor exposure for a resident of the study area is 9.2 (mu)Rh('-1). The average reading of the 152 indoor scintillometer surveys was 9.5 (mu)Rh('-1), the outdoor reading 7.5 (mu)Rh('-1). Results of one-way and multi-way analyses of the exposure data to determine the effect due to building materials type, geologic subsoil, age of dwelling, and elevation are also presented. The results of 152 indoor scintillometer surveys are described. ^

Catchment area of oral cleft cases for two major hospitals in Harris County

Background. Orofacial clefts are among the most common birth defects and considered to be of complex etiology with both genetic and environmental factors.^ Objectives. The purpose of this study was to describe maternal and infant characteristics, examine the catchment area, and determine if there are any geospatial patterns among infants with an orofacial cleft delivered at two major hospitals in Harris County, The Woman's Hospital of Texas and Memorial Hermann Hospital-Texas Medical Center, from January 1, 2003 through December 31, 2007.^ Methods. Data were obtained from two major hospitals in Harris County and included all babies delivered in the period from 2003 through 2007 with an orofacial cleft. Residential addresses were mapped using MapInfo GIS software and the cluster analysis performed with SaTScan software.^ Results. Ninety-nine cases were identified spanning nine counties. 26% of cases resided within a 5-mile radius of the Texas Medical Center. Birth rates ranged from 1.4 to 16.5 per 10,000 total births. A cluster was identified in southwest Harris County, however, it was not significant (p=0.066).^ Conclusion. This study encourages further focus on linking cleft cases to environmental factors in order to determine potential risks. ^