URANIUM IN THE SURROUNDING ENVIRONMENT OF SAN MARCOS-SACRAMENTO VALLEY (CHIHUAHUA,MEXICO)

The Chihuahua valley is a north-south oriented basin with a dimension of 8 x 32 km², forming part of the Chihuahua hydrologic basin. This basin supplies most of the water for the Chihuahua City. First studies about surface water (San Marcos Dam), in the upper part of the basin, inform that water, enriched in organic matter, has up to 75% of the uranium content incorporated as suspended particles. Therefore, this study was carried out to assess whether uranium deposits located in the San Marcos outcrops (NW of Chihuahua City, Mexico) could be considered as a source of U-isotopes in its surrounding environment.

Activity concentration of U-isotopes was determined in groundwater, surface water and biota by either alpha-spectrometry or liquid scintillation spectrometry. For the determination of uranium activity in biota, specific parts were considered. Thus, muscles of fishes, and root, stem and leaves of vegetables were analyzed. Annual effective doses were also calculated.

The results have shown a possible lixiviation and infiltration of uranium from geological substrate into the ground and surface water, and consequently, a transfer to biota. Indeed, some uranifer species have been observed in these deposits and U-isotopes could move from mineral deposits into groundwater and surface water: the rivers and a water reservoir, which are within this region. A significant enhancement of U-isotopes determined in these samples could contribute to a no negligible dose in the neighboring population because these waters are finally consumed by the population of Chihuahua City.

By all these considerations it is concluded that in this zone there is natural enhancement of uranium in all environmental samples analyzed in the present work.