238U series isotopes and 232Th in carbonates and black shales from the Lesser Himalaya: implications to dissolved uranium abundances in Ganga-Indus source waters

238U and (232)Th concentrations and the extent of (238)U-(234)U-(230)Th radioactive equilibrium have been measured in a suite of Precambrian carbonates and black shales from the Lesser Himalaya. These measurements were made to determine their abundances in these deposits, their contributions to dissolved uranium budget of the headwaters of the Ganga and the Indus in the Himalaya and to assess the impact of weathering on (238)U-(234)U-(230)Th radioactive equilibrium in them. (238)U concentrations in Precambrian carbonates range from 0.06 to 2.07 microg g(-1). The 'mean' U/Ca in these carbonates is 2.9 ng U mg(-1) Ca. This ratio, coupled with the assumption that all Ca in the Ganga-Indus headwaters is of carbonate origin and that U and Ca behave conservatively in rivers after their release from carbonates, provides an upper limit on the U contribution from these carbonates, to be a few percent of dissolved uranium in rivers. There are, however, a few streams with low uranium concentrations, for which the carbonate contribution could be much higher. These results suggest that Precambrian carbonates make only minor contributions to the uranium budget of the Ganga-Indus headwaters in the Himalaya on a basin wide scale, however, they could be important for particular streams. Similar estimates of silicate contribution to uranium budget of these rivers using U/Na in silicates and Na* (Na corrected for cyclic and halite contributions) in river waters show that silicates can contribute significantly (approximately 40% on average) to their U balance. If, however, much of the uranium in these silicates is associated with weathering resistant minerals, then the estimated silicate uranium component would be upper limits.Uranium concentration in black shales averages about 37 microg g(-1). Based on this concentration, supply of U from at least approximately 50 mg of black shales per liter of river water is needed to balance the average river water U concentration, 1.7 microg L(-1) in the Ganga-Indus headwaters. Data on the abundance and distribution of black shales in their drainage basin are needed to test if this requirement can be met. (234)U/(238)U activity ratios in both carbonates and black shales are at or near equilibrium, thus preferential mobilization of (234)U from these deposits, if any, is within analytical uncertainties. (230)Th is equivalent to or in excess of (238)U in most of the carbonates. (230)Th/(238)U>1 indicates that during weathering, uranium is lost preferentially over Th. (232)Th concentrations in carbonates are generally quite low, <0.5 microg g(-1), though with a wide range, 0.01-4.8 microg g(-1). The variation in its concentrations seem to be regulated by aluminosilicate content of the carbonates as evident from the strong positive correlation between (232)Th and Al.     

Radionuclides from past uranium mining in rivers of Portugal

During several decades and until a few years ago, uranium mines were exploited in the Centre of Portugal and wastewaters from uranium ore milling facilities were discharged into river basins. To investigate enhancement of radioactivity in freshwater ecosystems, radionuclides of uranium and thorium series were measured in water, sediments, suspended matter, and fish samples from the rivers Vouga, D?o, Távora and Mondego. The results show that these rivers carry sediments with relatively high naturally occurring radioactivity, and display relatively high concentrations of radon dissolved in water, which is typical of a uranium rich region. Riverbed sediments show enhanced concentrations of radionuclides in the mid-section of the Mondego River, a sign of past wastewater discharges from mining and milling works at Urgeiri?a confirmed by the enhanced values of (238)U/(232)Th radionuclide ratios in sediments. Radionuclide concentrations in water, suspended matter and freshwater fish from that section of Mondego are also enhanced in comparison with concentrations measured in other rivers. Based on current radionuclide concentrations in fish, regular consumption of freshwater species by local populations would add 0.032 mSv a(-1) of dose equivalent (1%) to the average background radiation dose. Therefore, it is concluded that current levels of enhanced radioactivity do not pose a significant radiological risk either to aquatic fauna or to freshwater fish consumers.     

Influences of natural and anthropogenic processes on the nitrogen and phosphorus fluxes of the Yangtze Estuary, China

Nutrient flux to the sea through the estuary is important to the health of the sea. Combining natural processes with anthropogenic activities, we discuss the influence on the nitrogen and phosphorus fluxes to the Yangtze River basin, to the estuary and to the sea. The fluxes of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) to the estuary through the river/estuary interface are obviously higher than those to the sea through to the estuary/sea interface of the Yangtze estuary. The changes in nutrient fluxes through different interfaces are largely due to the estuarine hydrological and biogeochemical processes. Household, livestock and agricultural runoff are major sources of nitrogen from human activities, and household and livestock contribute to an increase in the anthropogenic phosphorus. The fluxes of DIN and DIP from economic activities account for about one-third of DIN and DIP fluxes to the sea through the Yangtze estuary.     

Acid mine drainage pollution in the Tinto and Odiel rivers (Iberian Pyrite Belt, SW Spain) and bioavailability of the transported metals to the Huelva Estuary

The Tinto and Odiel rivers are seriously affected by acid mine drainage (AMD) from the long-term mining activities in Iberian Pyrite Belt (IPB). As a consequence, the Huelva estuary is heavily contaminated by metals and metalloids. This study presents an estimation of the seasonal variation, and the dissolved contaminant load transported by both rivers from February 2002 to September 2004. Besides, toxicity and bioaccumulation tests with the sediments of the estuary have been conducted in order to measure the mobility of the toxic metals. Results show that the Tinto and Odiel rivers transport enormous quantities of dissolved metals to the estuary: 7900 t yr(-1) of Iron (Fe), 5800 t yr(-1) Aluminium (Al), 3500 t yr(-1) Zinc (Zn), 1700 t yr(-1) Copper (Cu), 1600 t yr(-1) Manganese (Mn) and minor quantities of other metals and metalloids. These values represent 37% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 15% of the global gross flux of dissolved Cu. These metals and metalloids usually sink in the estuarine sediments due to pH and salinity changes. The increase of salinity in the estuary favours the adsorption and trapping of metals. For this reason, the mobility and bioavailability of metals such as Zn, Cd and Cu is higher in sediments located in the area of fresh water influence that in sediments located in the marine influenced area of the estuary, showing a higher percentage of fractionation and bioaccumulation of these metals in the station influenced by the fresh water environment.     

Investigation of dissolved uranium content in the watershed of Seine River (France)

A systematic survey of dissolved uranium activity was carried out in the Seine and the Marne over one year. A small watershed, the Grand Morin, included in the Seine one, was also investigated from stream to medium-sized rivers. The Melarchez stream exhibits low but variable dissolved 238U levels (3.3 +/- 2.0 mBq l(-1)). Thereafter, uranium activities show a rapid increase to reach, from the Grand Morin River, a rather constant range (8-11 mBq l(-1)). On the Marne before the confluence with the Seine, dissolved 238U is nearly invariable (9.1 +/- 0.8 mBq l(-1)), for flow rates comprised between 60 and 423 m3 s(-1). Dissolved 238U in the Seine corresponds to almost triple the global mean riverine uranium concentration. In the estuary of the Seine, uranium shows a gradual increase, resulting from conservative mixing of river with sea waters.     

Estimation of internal radiation dose to the adult Asian population from the dietary intakes of two long-lived radionuclides

Daily dietary intakes of two naturally occurring long-lived radionuclides, 232Th and 238U, were estimated for the adult population living in a number of Asian countries, using highly sensitive analytical methods such as instrumental and radiochemical neutron activation analysis (INAA and RNAA), and inductively coupled plasma mass spectrometry (ICP-MS). The Asian countries that participated in the study were Bangladesh (BGD), China (CPR), India (IND), Japan (JPN), Pakistan (PAK), Philippines (PHI), Republic of Korea (ROK) and Vietnam (VIE). Altogether, these countries represent more than 50% of the world population. The median daily intakes of 232Th ranged between 0.6 and 14.4 mBq, the lowest being for Philippines and the highest for Bangladesh, and daily intakes of 238U ranged between 6.7 and 62.5 mBq, lowest and the highest being for India and China, respectively. The Asian median intakes were obtained as 4.2 mBq for 232Th and 12.7 mBq for 238U. Although the Asian intakes were lower than intakes of 12.3 mBq (3.0 ug) 232Th and 23.6 mBq (1.9 ug) 238U proposed by the International Commission on Radiological Protection (ICRP) for the ICRP Reference Man, they were comparable to the global intake values of 4.6 mBq 232Th and 15.6 mBq 238U proposed by the United Nation Scientific Commission on Effects of Radiation (UNSCEAR). The annual committed effective doses to Asian population from the dietary intake of 232Th and 238U were calculated to be 0.34 and 0.20 microSv, respectively, which are three orders of magnitude lower than the global average annual radiation dose of 2400 microSv to man from the natural radiation sources as proposed by UNSCEAR.     

Environmental characterization and radio-ecological impacts of non-nuclear industries on the Red Sea coast

The Red Sea is a deep semi-enclosed and narrow basin connected to the Indian Ocean by a narrow sill in the south and to the Suez Canal in the north. Oil industries in the Gulf of Suez, phosphate ore mining activities in Safaga-Quseir region and intensified navigation activities are non-nuclear pollution sources that could have serious radiological impacts on the marine environment and the coastal ecosystems of the Red Sea. It is essential to establish the radiological base-line data, which does not exist yet, and to investigate the present radio-ecological impact of the non-nuclear industries to preserve and protect the coastal environment of the Red Sea. Some natural and man-made radionuclides have been measured in shore sediment samples collected from the Egyptian coast of the Red Sea. The specific activities of 226Ra and 210Pb (238U) series, 232Th series, 40K and 137Cs (Bq/kg dry weight) were measured using gamma ray spectrometers based on hyper-pure germanium detectors. The specific activities of 210Po (210Pb) and uranium isotopes (238U, 235U and 234U) (Bq/kg dry weight) were measured using alpha spectrometers based on surface barrier (PIPS) detectors after radiochemical separation. The absorbed radiation dose rates in air (nGy/h) due to natural radionuclides in shore sediment and radium equivalent activity index (Bq/kg) were calculated. The specific activity ratios of 228Ra/226Ra, 210Pb/226Ra, 226Ra/238U and 234U/238U were calculated for evaluation of the geo-chemical behaviour of these radionuclides. The average specific activity of 226Ra (238U) series, 232Th series, 40K and 210Pb were 24.7, 31.4, 427.5 and 25.6 Bq/kg, respectively. The concentration of 137Cs in the sediment samples was less than the lower limit of detection. The Red Sea coast is an arid region with very low rainfall and the sediment is mainly composed of sand. The specific activity of 238U, 235U and 234U were 25.3, 2.9 and 25.0 Bq/kg. The average specific activity ratios of 226Ra/228Ra, 210Pb/226Ra and 234U/238U were 1.67, 1.22 and 1.0, respectively. The relationship between 226Ra/228Ra activity ratio and sample locations along the coastal shoreline indicates the increase of this ratio in the direction of the Shuqeir in the north and Safaga in the south where the oil exploration and phosphate mining activities are located. These activities may contribute a high flux of 226Ra. The concentration and distribution pattern of 226Ra in sediment can be used to trace the radiological impact of the non-nuclear industries on the Red Sea coast.     

Distribution of long-lived radionuclides of the 238U series in the sediments of a small river in a uranium mineralized region of Spain

A study is presented on the distribution and mobilization of the natural U isotopes (238U and 234U), 230Th, and 226Ra in the sediments of a small river crossing an uranium mineralized zone where a disused uranium mine is located. Due to the preferential directions for surface run-off waters and to the mine's situation, one sampling point along the river bed was identified as a point of accumulation of radionuclides. The average values of the activity concentrations (Bq/kg) in this sediment sample were 5,025, 5,055, 5,915 and 1,694 for 238U, 234U, 230Th and 226Ra, respectively, while the respective average values of the activity concentrations (Bq/kg) for the sediment sample considered to give the background level were 125, 124, 131 and 370. Isotopic ratios between the descendants of 238U served to clarify some paths of distribution, involving the soils nearest to the sampling points and the location of these points with respect to the disused mine. The differences in behaviour found between the uranium, thorium and radium isotopes were associated to the mobility of these radionuclides in the fluvial system studied. Correlations between the radionuclide activity concentration ratios and stable element concentrations in the sediment samples were also investigated.     

Origin and transport of U and Ra in riverine,estuarine and marine sediments of the Krka River,Croatia

Spatial distribution of ²³⁸U and ²²⁶Ra activities in sediment columns along the Krka River and estuary, were studied using gamma spectrometry. Markedly different ²³⁸U and ²²⁶Ra activities between riverine, estuarine and marine sediments were observed. Distribution of these radionuclides, as well as their anthropogenic and natural origin, was evaluated by activity measurements, taking into account sedimentation rates estimated by ¹³⁷Cs distribution in sediment columns.     

Size-fractionated thorium isotopes (228Th, 230Th, 232Th) in surface waters in the Jiulong River estuary, China

Thorium isotopes (228Th, 230Th, 232Th and 234Th) are useful tracers for studying particle dynamics and trace element scavenging in marine environments. In this study, surface waters were collected along a salinity gradient from the Jiulong River estuary, China, for determination of activity concentrations of 228Th, 230Th and 232Th in different size fractions, namely, the >53 microm, 10-53 microm, 2-10 microm, 0.4-2 microm, 10 kDa-0.4 microm and the <10 kDa fractions. Our results indicated that the activity concentrations of 228Th, 230Th and 232Th in the Jiulong River estuarine waters were significantly higher than most of the previously reported values in coastal and oceanic seawaters, suggesting a higher lithogenic U and Th contribution from the Jiulong River Basin. When normalized to the particulate mass concentration, the activity concentrations of the three thorium isotopes decreased with increasing particle size, demonstrating the important role of surface areas of particles in controlling the scavenging of thorium from the water column. The partitioning of three thorium isotopes showed a common characteristic, i.e., the >53 microm fraction had the least share (0-1%), while the 10-53 microm fraction had the largest share of Th isotopes. The average value of the 230Th/232Th activity ratio (230Th/232Th)(A.R.) increased from 0.8 in the >53 microm fraction to 3.7 in the 10 kDa-0.4 microm fraction, indicating that the radiogenic Th isotopes are preferentially scavenged by the small size particles. (230Th/232Th)(A.R.) in the <10 kDa and 10 kDa-0.4 microm fractions were similar, however, suggesting a similar chemical composition and/or equilibrium partitioning between the low molecular weight and colloidal Th. It was very interesting to note that the geochemical behaviors of the three Th isotopes were different from each other. Dissolved 228Th had the highest concentration in the mid-salinity region, showing a non-conservative behavior with additional input. In contrast, dissolved 232Th showed a concave profile, indicating a net removal of 232Th during the mixing of fresh water with seawater. The behavior of Th isotopes in the <10 kDa fraction followed those in the dissolved phases. The difference in geochemical behaviors among three Th isotopes was ascribed to their different sources in the estuary.     

Soil to plant transfer of 238U, 226Ra and 232Th on a uranium mining-impacted soil from southeastern China

Both soil and plant samples of nine different plant species grown in soils from southeastern China contaminated with uranium mine tailings were analyzed for the plant uptake and translocation of 238U, 226Ra and 232Th. Substantial differences were observed in the soil-plant transfer factor (TF) among these radionuclides and plant species. Lupine (Lupinus albus) exhibited the highest uptake of 238U (TF value of 3.7x10(-2)), while Chinese mustard (Brassica chinensis) had the least (0.5x10(-2)). However, in the case of 226Ra and 232Th, the highest TFs were observed for white clover (Trifolium pratense) (3.4x10(-2)) and ryegrass (Lolium perenne) (2.1x10(-3)), respectively. 232Th in the tailings/soil mixture was less available for plant uptake than 226Ra or 238U, and this was especially evident for Chinese mustard and corn (Zea mays). The root/shoot (R/S) ratios obtained for different plants and radionuclides shown that Indian mustard had the smallest R/S ratios for both 226Ra (5.3+/-1.2) and 232Th (5.3+/-1.7), while the smallest R/S ratio for 238U was observed in clover (2.8+/-0.9).     

Natural radioactivity in some major rivers of coastal Karnataka on the southwest coast of India

Systematic studies on radiation level and distribution of radionuclides have been carried out in riverine environs of three major rivers of coastal Karnataka, viz. Kali, Sharavathi and Netravathi. The ambient gamma radiation levels along three rivers were measured using a portable plastic scintillometer. Activity concentrations of (226)Ra, (232)Th and (40)K in soil, sediment and rock were measured using a NaI(Tl) gamma-ray spectrometer. In the Kali, Sharavathi and Netravathi riverbanks, the median values of absorbed gamma dose rates in air were found to be 44 nGy h(-1), 35 nGy h(-1) and 57 nGy h(-1), respectively. The highest activity of (226)Ra was found in riverbank soil samples of Sharavathi River. The highest activities of (232)Th and (40)K were found in riverbank soil and sediment samples of Netravathi River. In Kali River, the highest (226)Ra activity was recorded for rock samples. To assess the radiological hazard of natural radioactivity in the samples, absorbed gamma dose rates in air, radium equivalent activity, representative level index, external hazard index and internal hazard index associated with the radionuclides were calculated and compared with internationally recommended values. The representative level index (I(gammar)) values are high in sediment samples of Netravathi River. The radium equivalent activity (Ra(eq)), external hazard index (H(ex)) and internal hazard index (H(in)) values are high in rock samples of Kali River. The results of these investigations are presented and discussed in this paper.     

Levels of elements in the surficial estuarine sediments of the Hugli River, northeast India and their environmental implications

The present paper is the first document of a detailed geochemical and mineralogical study of muddy to sandy mud estuarine sediments of the Hugli River collected from five different sites along its course in the coastal areas of West Bengal, northeast India. The present work attempts to establish the status of distribution and environmental implications of 52 elements in the surficial estuarine sediments and their possible sources of derivation. The level of both metallic and non-metallic elements shows a wide range of variation all along the course of the estuary and can be attributed to their differential derivation from the source rocks and differential discharge of untreated effluents originating from industrial, agricultural, aquacultural as well as domestic sewage. The element contents, particularly the heavy metal content in the sediments, are the lowest in the upstream part of the estuary at Diamond Harbor, whereas, these are slightly higher in the intermediate stretch of the estuary at Haldia to highest in the mouth of estuary at Gangasagar. These changes indicate that the metals that are carried from upstream find their ultimate depositional sink at the delta mouth near Gangasagar, where almost all the elements showed elevated values. The majority of the elements have their highest concentrations at Canning, a site within the tidal channel network of the Hugli-Matla drainage basin away from the direct influence of the Hugli River. This site is severely contaminated with huge organic load from domestic sewage, aquaculture, intensive trawling activities and agricultural runoff. Moreover, the site suffers from heavy siltation load causing an almost moribund condition of Matla River at this point. Equi-dimensional quartzo-feldspathic mineral grains are consistent components in the siliciclastic composition of the sediments and their sizes at each station are controlled by respective hydrodynamic conditions. Various flaky minerals (mica, chlorite, hornblende) are also present but show inconsistent patterns of distribution. These flaky minerals remain in suspension for a long time and do not follow the usual law of settling of particles depending on the hydrodynamic regime prevailing in the area. Presented data will serve as a baseline against which future anthropogenic effects may be assessed. A comprehensive account of heavy metal content in sediments from different coastal regions of peninsular India has also been presented for purpose of comparison.     

Behaviors of 323Th, 238U, 228Ra and 226Ra on combustion of crude oil terminal sludge

Crude oil terminal sludge contains technologically enhanced naturally occurring radionuclides such as (232)Th, (238)U, (228)Ra and (226)Ra, thus cannot be disposed of freely without proper control. The current method of disposal, such as land farming and storing in plastic drums is not recommended because it will have a long-term impact on the environment. Due to its organic nature, there is a move to treat this sludge by thermal methods such as incineration. This study has been carried out to determine the behaviors of (232)Th, (238)U, (228)Ra and (226)Ra present in the sludge during combustion at a certain temperature and time. The percentage of volatilization was found to vary between 2% and 70%, (238)U was the most volatile in comparison with (232)Th, (228)Ra and (226)Ra. (238)U is found to be significantly volatilized above 500 degrees C, and might reach maximum volatilization at above 700 degrees C. A mathematical model was developed to predict the percentage of volatilization of (232)Th, (238)U, (228)Ra and (226)Ra contained in the sludge. With this known percentage of volatilization, the concentration of (232)Th, (238)U, (228)Ra and (226)Ra present in the bottom and filter ashes can be calculated.     

Invariance of isotope ratios of lithogenic radionuclides: more evidence for their use as sediment source tracers

Activities of radionuclides in the 238U (230Th, 226Ra, 210Pb) and 232Th (232Th, 228Th, 228Ra) decay series were determined in sediments from an east Texas watershed and examined with isotope ratios and compared to particulate organic carbon (POC), % fines (<63 microm) and total concentrations of Al, Fe and Mn. The objective was to elucidate the presence or absence of relationships affecting the effectiveness of these radionuclides in modeling sediment transport. Strong positive correlations were observed between radionuclides and Mn (Th) and % fines (Ra and Th). Isotope ratios effectively reduce these influences, supporting the contention that isotope ratios offset extrinsic variability in terrestrial sediments. Strong associations of 210Pbxs (excess 210Pb) and 226Ra/230Th with POC agree with data from marine and terrestrial settings, indicating that the role of POC in isotope fractionation, transport and sequestration merits further investigation.     

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.     

Distribution of uranium isotopes in surface water of the Llobregat river basin (Northeast Spain)

A study is presented on the distribution of ²³⁴U, ²³⁸U, ²³⁵U isotopes in surface water of the Llobregat river basin (Northeast Spain), from 2001 to 2006. Sixty-six superficial water samples were collected at 16 points distributed throughout the Llobregat river basin. Uranium isotopes were measured by alpha spectrometry (PIPS detectors). The test procedure was validated according to the quality requirements of the ISO17025 standard. The activity concentration for the total dissolved uranium ranges from 20 to 261 mBq L⁻¹. The highest concentrations of uranium were detected in an area with formations of sedimentary rock, limestone and lignite. A high degree of radioactive disequilibrium was noted among the uranium isotopes. The ²³⁴U/²³⁸U activity ratio varied between 1.1 and 1.9 and the waters with the lowest uranium activity registered the highest level of ²³⁴U/²³⁸U activity ratio. Correlations between uranium activity in the tested water and chemical and physical characteristics of the aquifer were found.     

Thorium and uranium contents in human urine: influence of age and residential area

Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of (232)Th and (238)U in urine of unexposed Jordanian subjects living in six cities. The range of (232)Th excretion in all subjects was found to be 1.4-640 microBq d(-1) with an average of 34.8 microBq d(-1) (geometric mean 15.8 microBq d(-1)). Results showed no statistically significant correlation with age and residential area. The average value obtained is in agreement with levels considered normal in some recent publications. The average value of (238)U in all samples was found to be 3955 microBq d(-1) (geometric mean 1107 microBq d(-1)), which is higher than reported figures from Germany and India, but in agreement with those figures given in ICRP publication, number 23. The mean values of the different groups were found to be proportional to age up to 60 years. A noticeable drop is observed for subjects greater than 60 years old.     

Anthropogenic 236U at Rocky Flats,Ashtabula river harbor,and Mersey estuary: three case studies by sector inductively coupled plasma mass spectrometry

236U (t(1/2)=2.3 x 10(7) y) is formed as a result of thermal neutron capture by (235)U. In naturally occurring U ores, where a high neutron flux is present from spontaneous fission of (238)U, (236)U/(238)U atom ratios are approximately 10(-4) ppm. In the natural Earth's crust, unaffected by nuclear fallout, these ratios are expected to be on the order of 10(-8) ppm. Reactor-irradiated U, however, exhibits high (236)U/(238)U atom ratios approaching 10(4) ppm. As a result, the presence of very small quantities of reactor-irradiated U will significantly enhance the "background" (236)U/(238)U atom ratio. When sufficiently elevated (236)U/(238)U ratios are present, the determination of (236)U/(238)U by rapid inductively coupled plasma mass spectrometric (ICPMS) methods is attractive. We have used sector ICPMS at medium resolving power (R=3440) to measure (236)U/(238)U atom ratios with a determination limit of 0.2 ppm. The limiting factors in the measurement are the (235)U(1)H(+) isobar and background signal at m/z 236 arising from the (238)U(+) peak tail. Based upon the analysis of replicates and considerations of possible systematic errors, uncertainties of +/-5% are found for (236)U/(238)U atom ratios of 1-100 ppm. This procedure has been demonstrated in studies of anthropogenic (236)U in the environment at three locations: (a) offsite soils from the vicinity of the Rocky Flats Environmental Technology site (Golden, Colorado, USA); (b) sediments from the Ashtabula River (Ohio, USA); and (c) sediments from the Mersey estuary (Liverpool, UK). In each of these three locations, definite plumes of elevated (236)U/(238)U are identified and characterized. Maximum (236)U/(238)U atom ratios observed in RFETS-vicinity soils, the Ashtabula River, and the Mersey Estuary are 2.8, 140, and 4.4 ppm, respectively.     

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.