Assessment of radon and gamma in Kurday mining site, Kazakhstan.

Abstract

The present work is based on the data obtained from expeditions to Kurday, Kazakhstan in 2006 performed by Joint Norwegian- Kazakhstan – Kyrgyzstan- Tajikistan project in collaboration with the NATRO RESCA project. The former uranium mining and processing site Kurday, located in Zambyl region in southern Kazakhstan is rich in naturally occurring radioactive materials (NORMs) and technologically enhanced naturally occurring radioactive materials (TENORMs). It has been recognized as one of the earliest uranium legacy production sites in Central Asia. In addition, the area is not only contaminated with uranium and its daughters, but also from associated trace metals which may pose a risk to man and the environment. The objectives of the thesis were to use the available outdoor and indoor radon concentrations as well as gamma dose rates/doses to estimate public annual effective doses from gamma and radon exposure in selected area of the site. The corresponding doses estimated from gamma and radon obtained in Kurday, Kazakhstan and Taboshar, Tajikistan were also compared. The risk of human stochastic effects (excess cancer) from the estimated total doses was also evaluated. The absorbed gamma dose rates in air were measured at every sampling sites and also in the dwellings, using different dosimeters like Geiger Muller type (DKS-96 Automess) and scintillation type (SRP-68, Radiagem) dosimeters. For every measurement points, the detectors were positioned 1m above the ground and occasionally at ground. In addition, simulteneous outdoor and indoor radon concentrations measurements were conducted around the Pit Lake, at the hills around the lake and in a grid pattern at the mountain plateau. Radon detectors were also placed indoor in the dwellings of Kurday, and outdoor in the garden of the dwellings. Indoor and outdoor concentration of Rn in air were measured using both active and passive devices. The screenings of preliminary level of radon concentration were done by RAMON-01, RRA AND PRM-145. The track detectors were then placed for a longer period (2-9 months). All the data were analyzed using windows office EXCEL 2007 and minitab 16. For all analyisis, p values <<0.05 were considered statistically significant. Annual average effective doses were estimated by extrapolating the abosorbed doses in air over the measured period and using the conversion factor 1 Sv/Gy. Indoor occupancy of 6000 hours per year was used, while 350 hours and 700 hours per year were applied for tailing piles and for gardens of houses, respectively, to estimate doses. In case of radon doses, equilibrium factor 0.4 was used, while the dose conversion factor applied was 9 nSv/Bq/m3/hour. The occupancy factor used in radon calculations was similar to that of gamma doses for corresponding locations. Similarly, the risk of developing cancer in human was estimated using the risk factor of 5×10-2 per Sv. As a summary, the gamma dose rates were found to vary within the studied areas; highest at the Pit lake (0.11-1.07 μGy/h) and waste rock piles (0.7-1.05 μGy/h), inside dwellings (0.131-0.254 μGy/h) and lowest in the gardens (0.07-0.21 μGy/h). The calculated mean annual effective doses of gamma radiation at different areas of Kurday were; Pit lake (0.31±0.26 mSv), waste rock piles (0.36±0.05 mSv) inside room (1.40±1.80 mSv) and garden (0.11±0.02 mSv). One way ANOVA analysis showed the variation of mean dose rates for all the four areas investigated. The mean dose rate measured in waste rock piles was significantly higher (p<<0.05) than that in Pit Lake, inside dwellings and in gardens. The radon concentrations also varied according to the sites investigated. Peak radon concentrations were found in the living rooms and bedrooms of two selected houses exceeding 1000 Bq/m3. The mean radon concentrations of indoor environment (inside rooms) were found to be significantly higher (p<<0.05) than that in outdoor conditions (gardens). The regression analyses of outdoor gamma dose rate and outdoor radon concentrations, and indoor gamma dose rates and indoor radon concentrations conditions showed that both of the combinations have p<<0.05 and R2 around 76%. The mean effective doses due to outdoor radon exposures at Kurday area was found to be 0.13±0.05 mSv whereas, the mean effective dose due to indoor radon exposure was estimated to be 3.91±1.80 mSv. Similarly, the mean concentration of uranium in drinking water from Muzbell dwelling area was found to be 26 μg/L and the annual effective dose was estimated to be 0.25 mSv. The total dose calculated was 6.31 mSv/year where indoor radon was the largest dose contributor. The dose could potentially contribute to health injuries to the individuals to develop one cancerous case to ionizing radiation- at a risk factor of 5×10-2 per Sv. In conclusion, the present study based on the summary report obtained in the NATO RESCA project and JNKKT project showed that the Kurday area of Kazakhstan represent sources of potential contamination of the living environment i.e. gamma radiation, radon exposure and the uranium concentration in drinking water sources. The outdoor gamma dose rates (0.078- 1.226 μGy/h) were found to be higher than the indoor gamma dose rates (0.013-0.69 μGy/h), whereas the indoor radon concentrations inside dwellings (70-330 Bq/m3) were recorded to be higher than the outdoor radon concentrations (30-90 Bq/m3). The values of outdoor gamma dose rates, indoor and outdoor radon concentrations are considerably higher than global average corresponding values. The mean uranium concentration in drinking water from Muzbel dwelling area (26 μg/L) was also found to be higher than the recommended value by WHO. The highest dose contribution to humans was obtained from indoor radon concentration (0.18-7.13 mSv) in the houses of Kurday area. The doses from indoor gamma radiation was also significantly high (0.14-4.14 mSv), while that from drinking water (0.25 mSv) was quite low (within the recommended value) compared to indoor radon and gamma radiation doses. The outdoor annual gamma doses obtained in Kurday, Kazakhstan were found to be similar to the outdoor gamma doses observed in Taboshar, Tajikistan (around 0.6 mSv). However, the outdoor radon in Taboshar was found to be five times higher than that in Kurday, both the values were lower than the global recommended values. Similarly, the indoor radon dose and indoor gamma dose in Kurday and that in Taboshar were in the comparable range. However, the peak values for indoor gamma doses were found to be higher in Kurday than those in Taboshar region. The radiological risk to human (cancer) from the total dose was estimated to be one cancerous case in Kurday with 3000 population. Therefore, on the basis of the present findings, it can be recommended that interventions should be made at the high doses sites in Kurday region in order to minimize the probability of human stochastic effects and thereby limit the public doses as low as reasonably achievable.