Assessment of the radiological impact of gamma and radon dose rates at former U mining sites in Tajikistan.

An assessment of the radiological situation due to exposure to gamma radiation, radon ((222)Rn) and thoron ((220)Rn) was carried out at former uranium (U) mining and processing sites in Taboshar and at Digmai in Tajikistan. Gamma dose rate measurements were made using various field instruments. (222)Rn/(220)Rn measurements were carried out with field instruments for instantaneous measurements and then discriminative (222)Rn/(220)Rn solid state nuclear track detectors (SSNTD) were used for longer representative measurements. The detectors were exposed for an extended period of time in different outdoor and indoor public and residential environments at the selected U legacy sites. The results showed that gamma, (222)Rn and (220)Rn doses were in general low, which consequently implies a low to relatively low radiological risk. The radiation doses deriving from external radiation (gamma dose rate), indoor (222)Rn and (220)Rn with their short-lived progenies did not exceed national or international standards. At none of the sites investigated did the average individual annual effective doses exceed 10 mSv, the recommended threshold value for the general public. A radiation hazard could be associated with exceptional situations, such as elevated exposures to ionizing radiation at the Digmai tailings site and/or in industrial facilities, where gamma and (222)Rn/(220)Rn dose rates could reach values of several 10 mSv/a. Current doses of ionizing radiation do not represent a hazard to the health of the resident public, with the exception of some specific situations. These issues should be adequately addressed to further reduce needless exposure of the resident public to ionizing radiation.

Environmental impact assessment of radionuclides and trace elements at the Kurday U mining site, Kazakhstan.

The Kurday uranium mining site in Kazakhstan operated from 1954 to 1965 as part of the USSR nuclear weapon programme. To assess the environmental impact of radionuclides and trace elements associated with the Kurday mining site, field expeditions were performed in 2006. In addition to in situ gamma and (220)Rn dose rate measurements, sampling included at site fractionation of water as well as sampling of water, fish, sediment, soils and vegetation. The concentrations of U and associated trace metals were enriched in the Pit Lake and in the artesian water (U exceeding the WHO guideline value for drinking water), and decreased downstream from the mining area. Uranium, As, Mo and Ni were predominantly present as mobile low molecular mass species in waters, while a significant proportion of Cr, Mn and Fe were associated with colloids and particles. Due to oxidation of divalent iron in the artesian ground water upon contact with air, Fe served as scavenger for other elements, and peak concentrations of U-, Ra-isotopes, As and Mn were seen. Most radionuclides and trace elements were contained in minerals in soils and sediments, and good correlations were obtained between U and As, Cd, Mo and (226)Ra. Based on sequential extractions, a significant fraction of U, Pb and Cd could be considered mobile. Radioactive particles carrying significant amount of trace metals may represent a hazard during strong wind events. The transfer of radionuclides and metals from soils or sediments to water was in general low. The Kd levels varied with the element in question, ranging from 0.5 to 3 × 10(2) L/kg d.w. for (238)U being relatively mobile, 10(3) for (226)Ra, As, Cd, Ni, to 10(4) L/kg d.w. for Cu, Cr and Pb being rather inert The transfer of radionuclides and metals from soils to vegetation (TF) was low, while higher if the transfer to vegetation, especially underwater mosses, occurred via water (e.g., BCF 37 L/kg w.w. for (238)U and 3 × 10(3) L/kg w.w. for (226)Ra). The transfer of Cd, Pb and As from water to fish liver (BCF) was rather high, showing BCFs in the range of 10(2)-10(3) L/kg w.w., and may, if eaten, represent a health risk. Furthermore, the high Hg level in fish filet reaching 0.3 mg/kg w.w. muscle and the tendency of biomagnification call for dietary restrictions. Total gamma and Rn dose rate to man amounted to about 6 mSv/y, while the highest calculated dose rate for non-human species based on the ERICA Assessment Tool were obtained in aquatic plants, with calculated mean doses of 700 µGy/hr, mostly due to the U exposure. Overall, it is concluded that measures such as restricted access to the Pit Lake as well as dietary restrictions with respect to drinking water and intake of fish should be taken to reduce the environmental risk to man and biota.