Spatial distribution of uranium and thorium in the surface soil around proposed uranium mining site at Lambapur and its vertical profile in the Nagarjuna Sagar Dam

The understanding and evaluation of the possible interactions of various naturally occurring radionuclides in the world's third largest man-made dam, Nagarjuna Sagar located in Andhra Pradesh, India and built on river Krishna assumed significance with the finding of uranium deposits in locations near the dam. For the present work, surface soil samples from the mineralized area of Lambapur, Mallapuram, Peddagattu and sediment core samples from the Nagarjuna Sagar dam were analyzed for naturally occurring radionuclides namely uranium and thorium using gamma spectrometric technique. Also toxic elements lead and chromium were analysed by the Energy Dispersive X-ray Fluorescence Spectrometer (EDXRF) technique. Surface soil samples show a variation from 25 to 291 Bq/kg (2.02–23.5 mg/kg) for ²³⁸U and 32–311 Bq/kg (7.9–76.9 mg/kg) for ²³²Th. U/Th concentration ratio in surface soil samples ranged from 0.19 to 0.31 and was found comparable with the nation wise average of 0.26. The study of sediment core samples reflected higher U/Th concentration ratio of 0.30–0.33 in the bottom section of the core as compared to 0.22–0.25 in the upper section. The concentration ratio in the upper section of the core was similar to the ratio 0.23 found in the western Deccan Basalt region through which the river originates. A higher concentration of lead and chromium was observed in the upper section of the core compared to bottom section indicating the impact of river input on the geochemical character of dam sediment.     

Distribution of radionuclides in surface soils, Singhbhum Shear Zone, India and associated dose

Gamma emitters were estimated in surface soils from a mineralized zone in Eastern India using high purity Germanium detector-based high resolution gamma spectrometry system. Activities of ²³⁸U, ²²⁶Ra, ²³²Th, ²³⁵U, ²²⁷Th, ^234mPa, ²¹⁰Pb, ⁴⁰K, and ¹³⁷Cs were 79?±?50, 81?±?53, 65?±?23, 4?±?2, 5?±?4, 92?±?50, 97?±?45, 517?±?201, and 4?±?2 Bq/kg, respectively. Most radionuclides were observed to follow log-normal distribution. The correlation between physicochemical properties of the samples, like pH, organic matter content, particle size, and moisture content were also studied. Activity ratios of ²²⁶Ra/²³⁸U, ²¹⁰Pb/²²⁶Ra, and ²²⁷Th/²³⁵U indicated deviation from secular equilibrium in some samples. The associated annual effective dose ranged from 0.07 to 0.24 mSv and the mean was calculated to be 0.12?±?0.04 mSv for this region, indicating it to be one of normal natural background radiation.     

Inverse Modeling for Aquatic Source and Transport Parameters Identification and its Application to Fukushima Nuclear Accident

Inverse modeling technique based on nonlinear least square regression method (LSRM) is developed for the identification of aquatic source and transport parameters. Instantaneous line source release model in two-dimensional domain and continuous point source release model in three-dimensional domain are used for the purpose. Case studies have been carried out for both types of releases to illustrate their application. Error analysis has been carried out to identify the maximum error that can be tolerated in the input concentration data used in the inverse model and to specify the minimum number of sampling points to generate such input data. The LSRM is compared with the well-established correlation coefficient optimization method for instantaneous line source release model, and good comparison is observed between them. The LSRM is used to quantitatively estimate the releases of different radionuclides into the Pacific Ocean which has resulted due to the discharge of highly radioactive liquid effluent from the affected Daiichi Nuclear Power Station at Fukushima in Japan. The measured concentrations of these radionuclides in seawater samples collected from two sampling points near Fukushima are used for the estimation. The average release works out to be 1.09?×?10¹⁶ for ¹³¹I, 3.4?×?10¹⁵ Bq for ¹³⁴Cs, and 3.57?×?10¹⁵ Bq for ¹³⁷Cs. Very good agreement is observed between the releases estimated in this study and those estimated by other different agencies.     

Intake of ²³⁸U and ²³²Th through the consumption of foodstuffs by tribal populations practicing slash and burn agriculture in an extremely high rainfall area

The concentration of naturally occurring radionuclides ²³²Th, ²³⁸U was determined using Instrumental Neutron Activation Analysis (INAA) in different food groups namely cereals, vegetables, leafy vegetables, roots and tubers cultivated and consumed by tribal population residing around the proposed uranium mine. The study area is a part of rural area K. P. Mawthabah (Domiasiat) in the west Khasi Hills District of Meghalaya, India located in the tropical region of high rainfall that remains steeped in tribal tradition without much outside influence. Agriculture by Jhum (slash and burn) cultivation and animal husbandry are the main occupation of the tribal populations. A total of 89 samples from locally grown food products were analyzed. The concentration of ²³⁸U and ²³²Th in the soil of the study area was found to vary 1.6-15.5 and 2.0-5.0 times respectively to the average mean value observed in India. The estimated daily dietary intake of ²³⁸U and ²³²Th were 2.0 μg d⁻¹ (25 mBq d⁻¹) and 3.4 μg d⁻¹ (14 mBq d⁻¹) is comparable with reported range 0.5-5.0 μg d⁻¹ and 0.15-3.5 μg d⁻¹ respectively for the Asian population.     

Long-term leaching of uranium from different waste matrices

A semi-dynamic leaching test was carried out for metallurgical wastes and ore samples from the uranium and copper mining industry over a 142 day period using distilled water and 0.1N NaNO(3) as solvents. Laser fluorimetry was used as the analytical technique to determine the total uranium content in the leachates. The cumulative leach fraction (CLF) of uranium release from the samples was calculated to be 0.22, 0.22, 0.07 and 0.39% for rock, uranium tailings, copper kinker ash samples and copper tailings respectively using distilled water as solvent and 0.31, 0.27, 0.05 and 0.59% for the same matrices using 0.1N NaNO(3). The release of mobile uranium fraction was very slow, being faster in the initial stage and then attained a near steady state condition. The diffusion coefficient and bulk release of uranium from the samples have been calculated. The processes governing the release of uranium from these matrices have been identified to be surface wash-off and diffusion. Hence the use of weak solvents (leach out the mobile/exchangeable fraction of uranium) under semi-dynamic conditions aids the determination of leaching parameters and identification of the leaching mechanism for mobile uranium fraction from different matrices by slow leaching processes.     

Dispersion of pollutants over land–water–land interface: Study using CALPUFF model

The CALMET/CALPUFF modeling system is used to study atmospheric dispersion of pollutant over land–water–land interface. It is shown that the default scheme used by CALMET/CALPUFF to handle inhomogeneous surfaces does not take care of the different turbulence characteristics over such surfaces. An alternative method is suggested to incorporate different turbulent characteristics over inhomogeneous surfaces by using the appropriate atmospheric stability category over different surfaces. The results show that the presence of water body can increase the ground level concentration by a factor of up to 50 for the width of water body varying from 1 km to 5 km. It is also shown that the effect of water body on the ground level concentration decreases as the distance from the water body increases. The present study showed that for land–water interface, the realistic specification of turbulence characteristics over inhomogeneous surfaces significantly changes the estimation of ground level concentration as compared to the default scheme available in the CALMET/CALPUFF modeling system and is expected to give realistic results.     

Exchange of polycyclic aromatic hydrocarbons across the air-water interface at the creek adjoining Mumbai harbour, India

Concentration levels of polycyclic aromatic hydrocarbons (PAHs) have been determined in air and water in order to estimate the magnitude and direction of gas flux across the air-water interface at the creek adjoining the Mumbai harbour, India. The range of total PAHs was found to be 4.1-30.4 ng/m3 in air and 84.3-377.5 ng/l in seawater, respectively. The lower molecular weight PAHs revealed positive values of the fluxes indicating the tendency for transfer of these contaminants from water to air. In contrast, fluxes of less volatile compounds like benzo(k)fluoranthene and benzo(a)pyrene were always from the atmosphere into the surface water of the creek at all locations and sampling periods. While the fugacity ratio ranged from 0.12 to 6.97, it was found greater than 1 for the lower molecular weight PAHs and less than 1 for higher molecular weight PAHs. The present study suggests the active transfer of lower molecular weight dissolved PAHs into the atmosphere due to volatilization and deposition of higher molecular weight gas-phase PAHs into the surface water.     

Trace element concentration in groundwater of Pesarlanka Island, Krishna Delta, India

There is a growing concern over the potential accumulation of trace element concentration in groundwater of coastal aquifer owing seawater encroachment in the last several decades. A total of 29 groundwater samples collected from Pesarlanka Island, Krishna delta, Andhra Pradesh, India were analyzed for 13 trace elements (B, V, Mn, Fe, Ni, Co, Cu, Zn, As, Sr, Cd, Ba, and Pb) using inductively coupled plasma mass spectrometry. The results reveal that B, Fe, Ni, As, Sr, and Pb vary from 11.22 to 710.2, 1.25 to 684.6, 0.02 to 37.33, 27.8 to 282.3, 164.1 to 7,009, and 1.97 to 164.4 μg/l, respectively. Ba, Cd, Co, Cu, Ni, V, and Zn are almost within permissible limits for drinking water, but As, Fe, Mn, Pb, B, and Sr are above the permissible limit. The toxic element Pb is 1.64 times more than the maximum permissible limits of drinking water. The minimum value of As is also 2.78 times more, whereas the maximum is 28.2 times the permissible limit. The spatial distributions of alkaline earths (Sr, Ba), transition metals (V, Co, Ni, Fe), metallic elements (Cu, Pb), and (As) were found in considerable variation in the entire Island. Good cross-correlations were found between As, B, Co, and Sr with total dissolved solids and among other trace elements such as B, As, Co, and Sr. The variability observed within the groundwater samples is closely connected to the sea spray input; hence, it is primarily a consequence of geographical and meteorological factors, such as distance from the ocean and time of year. The trace element levels, in particular those of heavy metals, are very low, suggesting an origin from natural sources rather than from anthropogenic contamination. A few trace elements (Sr and B) are found as sensitive parameters responding to changes in fresh to saline groundwater environment. The highly elevated trace elements in this area which may be attributed to marine sediments or death and decay of plants are presented in this paper.     

Distribution and fate of persistent organochlorine pesticides in coastal marine environment of Mumbai

Multi-compartment monitoring of residue levels of OCPs in coastal marine environment of Mumbai has been studied. The concentration of total HCHs in seawater varied from 0.16 to 15.92 ng/L and concentrations of total DDT varied from 3.01 to 33.21 ng/L. The total HCH concentration in the sediment samples was in the range of 3.8 to 16.2 ng/g. Gamma-HCH contributed almost 55% to the total HCH. In sediment samples the DDT has higher mean concentration in comparison to its metabolite DDE and DDD. The concentration of total HCHs in different marine species varied from 0.87 to 33.73 ng/g and concentrations of total DDT varied from 0.38 to 34.1 ng/g. The variation in the beta-HCH in different compartments is not significant and this could be due to the high persistence and metabolically inactive nature of this isomer. The alpha-HCH is found to be more dominant in fish samples whereas the gamma-HCH is major contributor in the sediment samples.     

Radiological assessment of surface water quality around proposed uranium mining site in India

The gross alpha and gross beta activities were estimated for radiological assessment of surface water quality around the proposed uranium mining site Kylleng Pyndengsohiong Mawthabah (Domiasiat), West Khasi Hills District, Meghalaya situated in a high rainfall area (12,000 mm) in India. 189 Surface water samples were collected over different seasons of the year from nine different locations covering around 100 km². Gross beta activities were found to vary from 144 to 361 mBq/L which is much below the prescribed WHO limit of 1000 mBq/L for drinking water. Gross alpha activities varied from 61 to 127 mBq/L. These values are much below the reported gross alpha values by other countries. In about 7% of the samples the alpha activities remain exceeded the WHO guideline limit of 100 mBq/L. Surface water samples collected during the summer season of the year show higher activity whereas low activity was found from samples collected during monsoon season. Results show that all water sources are acceptable as drinking water for human consumption from the radiological point of view, the higher gross alpha concentrations in a few locations remains so only for short duration during the summer season.