Summary
Seasonal measurement of natural radionuclides in drinking water and sediments in Darbandikhan lake water with their resources were carried out. During the period May, 2014 – February, 2015 a total of forty-one locations were selected for taking water and sediment samples in each season for the analysis of naturally occurring primordial radionuclides using spectrometry techniques of Peg, Nail(Tl), RAD7-H 2O and X- Ray Fluorescence.
The mean activity concentrations for U238, THz232 and k40 in the water samples were found to be 1.544±0.215, 2.395±0.0.337 and 77.943±1.700 Bq/L in spring; 1.225±0.184, 2.386±0.311 and 63.791±1.487 Bq/L in summer; 1.187±0.182, 1.896±0.304 and 51.299±1.325 Be/L in autumn; 1.340±0.204, 2.306±0.321 and 68.143±1.557 Be/L in winter, respectively. THz was approximately two times higher than the recommended values for drinking water by WHO.
The mean specific activity for U238, THz232 and k40 in the sediment samples were found to be 11.612±1.004, 8.091±1.08 and 210.762±3.414 Be/kg in spring; 9.232±1.189, 7.663±0.977 and 181.365±3.063 Be/kg in summer; 12.706±1.523 , 8.157±1.04 and 186.098±3.095 Be/kg in autumn; 11.914±1.553, 9.132±1.028 and 212.144±3.04 Be/kg in winter, respectively. values of the natural radionuclide’s ( U238, THz232 and k40) are below the recommended level, which is reported by (UNSCEAR, 2000) (35 Bq/Kg for 238 232 40U, 30 Bq/Kg for Th and 400 Bq/Kg for K).
For water and sediment samples the average specific activity are higher in wet seasons (spring and winter) compared with the dry seasons (summer and autumn).
For water samples the health hazard impact of the (outdoor &indoor annual effective dose), the committed effective dose, the (external & internal hazard index), the (outdoor & indoor cancer risk) and cancer risk due to ingestion of water were computed as (0.0056 & 0.0434)mSv/y, 0.703 mSv/y, (0.0254& 0.029), (0.020×10-3 & 0.152×10-3 ) and 2.461×10-3 , respectively.
All the calculated health hazard indices are below the average world values except the committed annual effective dose and cancer risks due to water ingestion.
For sediment samples the health hazards of the Ra eq. , (outdoor & indoor annual affective dose), the annual gonadal dose equivalent, the (external , internal hazard index& representative level index), activity Utilization Index and outdoor and indoor cancer risks were computed as 37.941 Bq/kg, (0.022 and 0.173) mSv/y, 130.347 ?Svy , (0.102, 0.133& 0.287), 0.217, 0.076×10-3 and 0.604×10-3 respectively.
All the calculated health hazard indices of the sediments are below the average world values indicating their safe usage in building and constructing activities.
Statistics of multivariate analysis (descriptive statistics, Pearson correlation coefficient, principal component analysis and cluster analysis) were applied to water and sediment samples in order to determine the relationships between primordial radionuclide’s itself and radiological hazards on the other hand. It was observed that all three primordial radionuclides contribute to the derived 232 40 radiological hazards; especially the loads were on Th and K.
Contour maps for water and sediments of U238, Th232 and K40 have been made which can be used as a first baseline data maps for the study area. The solid-liquid distribution coefficients between sediments and water were calculated and have average values of 8.329, 3.612 and 3.124 for U238, Th232 and K40 respectively.
Using the direct method of RAD7-H 2O to determine the radon concentration in water samples, the mean Rn activity concentrations in the water samples were found to be 1.793±0.199, 2.364±0.312, 1.964±0.224 and 1.854±0.252 Bq/L in spring, summer, autumn and winter, respectively. Only two samples (S8 & S12) for each season exceeds the maximum contamination level of 11.1 Bq/L recommended by EPA.
The estimation of average annual committed effective dose from ingestion of drinking water was calculated for three different age groups which are infant (1-2 years), children (7-12 years) and adults (>17 years). The average annual committed effective dose for first group is 11.543 ?Svy , for the second group is 3.986 ?Svy and for third group is 4.932 ?Svy . The first groups are more sensitive than both the children and adults whom exposed to radon.
The study also shows that there is a strong positive correlation between the radon concentration with both conductivity (R =0.87) and water temperature (R =0.8) and a negative correlation (R = – 0.539) with pH for spring water samples; no correlation of radon concentration with physiochemical parameter for lake and streams was observed.
The cancer risk due to ingestion of water (ELCR) for radon concentration was calculated for adult age groups for both stomach and lungs and have the average values of 0.00142 ×10 for stomach and 0.01702 ×10 for lungs and the total average values of 0.01844 ×10 for (stomach plus lungs). All values were below the average worldwide value of (0.29×10 ) suggested by (UNSCEAR, 2000) except for sample (S12).
The activity concentration of primordial radionuclides and the concentration of major elements were found using Energy Dispersive X-ray fluorescence techniques for 25 sediment samples in summer seasons. The average specific activity of K was found to be 202.27 Bq/kg, while the activity concentration for both uranium and thorium was beyond the detection limits. Statistics of multivariate analysis were applied to sediment samples, which show that there is a strong positive correlation coefficient between K and Ti, Mn and Fe and a weak negative correlation between K and Mg, Si, P, Ca was observed. RESRAD BUILD CODE for low, high and medium activity of three primordial radionuclides was used to estimate the indoor dose rate and cancer risks for dwellers inside the buildings.
posted:7/5/2017