DISTRIBUTION OF U-238 IN ENVIRONMENTAL-SAMPLES FROM A RESIDENTIAL AREA IMPACTED BY MINING AND MILLING ACTIVITIES

The northern region of Kames County, Texas, USA, has been the site of extensive mining/milling of uranium for over 30 years. A previous stud y in our laboratory indicates that residents living near these facilit ies have increased chromosomal aberrations and a reduced DNA repair ca pacity. In this study, the long-lived radionuclides uranium-238 (U-238 ) and thorium-232 (Th-232) were measured in order to evaluate the exte nt of contamination from mining/milling facilities. Th-232 was quantif ied simultaneously and served as a reference. Soil samples (n = 70) we re collected from the yards of previously studied households and adjac ent areas near former mining and mining/milling sites at the surface a nd 30 cm subsurface. Additionally, samples from drinking n ater 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, U-238 concentrations in soil wer e consistent between surface (0.13-0.26 mg/kg) and subsurface (0.13-0. 23 mg/kg) samples. Near mining/milling sites, U-238 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). Ne ar mining-only areas, U-238 in surface soil (1.11-1.97 mg/kg), however , was not significantly increased over subsurface soil (0.96-1.65 mg/k g). As expected. U-238 was much higher overall in the mining/milling a nd mining-only areas compared to the control sites. No trends were det ected in the distribution of Th-232. The concentration of U-238 was up to six times higher in a drinking water well near a former mining/mil ling operation. indicating possible leaching into the groundwater, whi le Th-232 concentrations were low and uniform. Furthermore, lead isoto pe ratio analysis indicates contamination from the interstate shipping of ore by rail to and from a mining/milling facility. These data indi cate contamination of the environment by the mining/milling activities in a residential area.