Distribution of uranium-238 in environmental samples from a residential area impacted by mining and milling activities

Abstract

Abstract The northern region of Karnes County, Texas, USA, has been the site of extensive mining/milling of uranium for over 30 years. A previous study in our laboratory indicates that residents living near these facilities have increased chromosomal aberrations and a reduced DNA repair capacity. In this study, the long-lived radionuclides uranium-238 (238U) and thorium-232 (232Th) were measured in order to evaluate the extent of contamination from mining/milling facilities. 232Th was quantified simultaneously and served as a reference. Soil samples (n = 70) were collected from the yards of previously studied households and adjacent areas near former mining and mining/milling sites at the surface and 30 cm subsurface. Additionally, samples from drinking water wells (n = 6) were collected from selected households. Sites located over 14 km from the study area with no known history of mining/milling served as the control. In the control area, 238U concentrations in soil were consistent between surface (0.13–0.26 mg/kg) and subsurface (0.13–0.23 mg/kg) samples. Near mining/milling sites, 238U in surface soil (0.34–15.71 mg/kg) was found to be consistently and statistically higher (p < 0.05) than corresponding subsurface samples (0.17–2.11 mg/kg). Near mining-only areas, 238U in surface soil (1.11–1.97 mg/kg), however, was not significantly increased over subsurface soil (0.96–1.68 mg/kg). As expected, 238U was much higher overall in the mining/milling and mining-only areas compared to the control sites. No trends were detected in the distribution of 232Th. The concentration of 238U was up to six times higher in a drinking water well near a former mining/milling operation, indicating possible leaching into the groundwater, while 232Th concentrations were low and uniform. Furthermore, lead isotope ratio analysis indicates contamination from the interstate shipping of ore by rail to and from a mining/milling facility. These data indicate contamination of the environment by the mining/milling activities in a residential area.