Radionuclides and metals in freshwater mussels of the upper South Alligator River, Australia

During an inspection of the old Rockhole Mine area in Kakadu National Park in 1999, it was found that a small amount of tailings from the former South Alligator uranium (U) mill had been uncovered by wet season rain and road works. Samples of sediment, water and freshwater mussels, Velesunio angasi, were collected from the South Alligator River, near and at the confluence of Rockhole Mine Creek, and adjacent to the exposed tailings. The 228Ra/226Ra activity ratios in sediments and mussel tissue indicate a small influence from the tailings and from Rockhole Mine adit water on 226Ra concentrations. The uptake of 226Ra in mussels does not correlate with other alkaline-earth metals. Mussel U concentrations are higher immediately downstream of Rockhole Mine Creek, but there is no noticeable increase in the immediate vicinity of the tailings area. A hypothetical ingestion of 2 kg of mussels from the sites was used to estimate the committed effective dose for a 10-year-old child resulting in a figure of 0.23 mSv per annum, of this total dose, 69% is attributed to 210Po. Only 0.03 mSv per annum can be directly linked to impacts of the tailings.     

A study of radium uptake by the water-lily Nymphaea violacea (Lehm) from contaminated sediment

The rate and extent of radium-226 accumulation from sediment by the water-lily Nymphaea violacea (Lehm) were assessed. The plants were collected from Magela Creek, Northern Territory, Australia and grown in ²²⁶RaCl₂-labelled laboratory sediment over a period of 570 days. The nominal sediment activity of 5 Bq g⁻¹ dry weight was 100 times that of the naturally occurring concentration.In the roots and rhizomes, ²²⁶Ra accumulated on plant surfaces. This result was confirmed by autoradiographic studies which showed the presence of an iron-containing plaque on the surface of these tissues with which the radium was closely associated. Little radium reached the pith of the rhizomes and acropetal translocation was not detected. The average concentration ratio for growing rhizomes was 0·22. Assuming first order accumulation kinetics and likely incremental environmental concentrations, this Aboriginal dietary tissue could become dose-limiting within 50 years.The foliar accumulation of radium originating from the sediment was predominately due to contamination via the sediment-water-plant pathway. Differences in foliar radium concentrations in plants of different ages were due to differential biomass turnover rates. Plants with faster biomass turnover had higher average radium concentrations.     

Radium and uranium levels in vegetables grown using different farming management systems

Vegetables grown with phosphate fertilizer (conventional management), with bovine manure fertilization (organic management) and in a mineral nutrient solution (hydroponic) were analyzed and the concentrations of ²³⁸U, ²²⁶Ra and ²²⁸Ra in lettuce, carrots, and beans were compared. Lettuce from hydroponic farming system showed the lowest concentration of radionuclides 0.51 for ²²⁶Ra, 0.55 for ²²⁸Ra and 0.24 for ²³⁸U (Bq kg⁻¹ dry). Vegetables from organically and conventionally grown farming systems showed no differences in the concentration of radium and uranium. Relationships between uranium content in plants and exchangeable Ca and Mg in soil were found, whereas Ra in vegetables was inversely correlated to the cation exchange capacity of soil, leading to the assumption that by supplying carbonate and cations to soil, liming may cause an increase of U and a decrease of radium uptake by plants. The soil to plant transfer varied from 10⁻⁴ to 10⁻² for ²³⁸U and from 10⁻² to 10⁻¹ for ²²⁸Ra.     

Determination of 228Ra, 226Ra and 224Ra in natural water via adsorption on MnO2-coated discs

A fast procedure based on sorption of Ra on MnO2 coated polyamide discs is presented for determination of radium isotopes (i.e. 228Ra, 226Ra, 224Ra) in aqueous samples. The sample discs can be used directly for low-level alpha-spectrometry without the need for further separation and preparation methods to produce planar sample sources. While the activity of alpha-emitting 224Ra and 226Ra can be determined during a first measurement, beta-emitting 228Ra is obtained via ingrowth of the progeny 228Th on the same sample disc after a standing time of about six months. Calculations are presented for optimizing the analytical accuracy as well as for predicting the sorption yield or chemical recovery of radium on the sample disc as a function of exposure time because the sorption uptake proceeds with first-order kinetics. The analyses can be carried out on small samples of 0.5-11 and, for long counting times of one week and use of high-purity silicon surface barrier detectors, a detection limit of 0.15 mBq l-1 is obtained for 226Ra. Since the half-life of 224Ra is only 3.7 d and since 228Th (as a measure for 228Ra) is built up only partially on the sample disc, a slightly higher detection limit of 0.24 mBq l-1 results for the latter isotopes. The procedure is therefore sufficiently sensitive to allow the investigation of Ra isotope relationships in aquifers at typical environmental levels.     

Measuring the radium quartet (Ra, Ra, Ra, Ra) in seawater samples using gamma spectrometry

Radium isotopes are widely used in marine studies (eg. to trace water masses, to quantify mixing processes or to study submarine groundwater discharge). While ²²⁸Ra and ²²⁶Ra are usually measured using gamma spectrometry, short-lived Ra isotopes (²²⁴Ra and ²²³Ra) are usually measured using a Radium Delayed Coincidence Counter (RaDeCC). Here we show that the four radium isotopes can be analyzed using gamma spectrometry. We report ²²⁶Ra, ²²⁸Ra, ²²⁴Ra, ²²³Ra activities measured using low-background gamma spectrometry in standard samples, in water samples collected in the vicinity of our laboratory (La Palme and Vaccarès lagoons, France) but also in seawater samples collected in the plume of the Amazon river, off French Guyana (AMANDES project). The ²²³Ra and ²²⁴Ra activities determined in these samples using gamma spectrometry were compared to the activities determined using RaDeCC. Activities determined using the two techniques are in good agreement. Uncertainties associated with the ²²⁴Ra activities are similar for the two techniques. RaDeCC is more sensitive for the detection of low ²²³Ra activities. Gamma spectrometry thus constitutes an alternate method for the determination of short-lived Ra isotopes.     

Determination of 226Ra and 228Ra in slightly mineralised natural waters

A radiochemical method for simultaneous separation of ²²⁶Ra and ²²⁸Ra from natural waters by precipitating the radionuclides in the form of chromates that have low solubility in weak acetic acid has been described. For analytical purposes the change into soluble state was achieved through high-temperature melting the radium chromates precipitate with sodium and potassium carbonates at certain ratios. The chemical yield for radium-226 amounted to 87.1 ± 1.4% at the efficiency of counting 92.8 ± 0.7%. Calculated in series of 20 parallel determinations, reproducibility of the method was 7%. The chemical yield in separating radium-228 made up 63.8 ± 1.1%.     

Contamination of settling ponds and rivers as a result of discharge of radium-bearing waters from Polish coal mines

Saline waters from underground coal mines in Poland often contain natural radioactive isotopes, mainly 226Ra from the uranium decay series and 228Ra from the thorium series. Approximately 40% of the total amount of radium remains underground as radioactive deposits, but 225 MBq of 226Ra and 400 MBq of 228Ra are released daily into the rivers along with the other mine effluents from all Polish coal mines. Technical measures such as inducing the precipitation of radium in gobs, decreasing the amount of meteoric inflow water into underground workings, etc. have been undertaken in several coal mines, and as a result of these measures, the total amount of radium released to the surface waters has diminished by about 60% during the last 5-6 years. Mine water can have a severe impact on the natural environment, mainly due to its salinity. However, associated high levels of radium concentration in river waters, bottom sediments and vegetation have also been observed. Sometimes radium concentrations in rivers exceed 0.7 kBq/m3, which is the permitted level for waste waters under Polish law. The extensive investigations described here were carried out for all coal mines and on this basis the total radium balance in the effluents has been calculated. Measurements in the vicinity of mine settling ponds and in rivers have given us an opportunity to study radium behaviour in river waters and to assess the degree of contamination. Solid waste materials with enhanced natural radioactivity have been produced in huge amounts in the power and coal industries in Poland. As a result of the combustion of coal in power plants, low-radioactive waste materials are produced, with 226Ra concentration seldom exceeding a few hundreds of Bq/kg. A different situation is observed in coal mines, where, as a result of precipitation of radium from radium-bearing waters, highly radioactive deposits are formed. Sometimes the radioactivity of such materials is extremely high; precipitates from coal mines may have radium concentrations of 400,000 Bq/kg--equivalent to 3% uranium ore. Usually, such deposition takes place underground, but sometimes co-precipitation of radium with barium takes place on the surface, in settling ponds and in rivers. Therefore management of solid waste with technologically enhanced natural radioactivity (TENR) is a very important subject.     

Simultaneous measurement of (226)Ra and (228)Ra in natural water by liquid scintillation counting

Several types of bottled drinking water originating from three different areas in Egypt are studied through measurement of radium activity, assessment of related annual dose for adults and finally to define the role of water quality on radium levels. The mean levels of (226)Ra activity range from 0.44 to 0.92 Bq/L and the mean levels of (228)Ra from 0.30 to 0.78 Bq/L, with related (226)Ra/(228)Ra ratios ranging from 2.61 to 0.56. Water types originating from the Eastern Nile Delta area are characterized by low (226)Ra levels and relatively high (228)Ra activity, presumably due to the muddy agricultural nature of this area, which is subject to water from several surface resources for irrigation. In general, the mean activity levels for both (226)Ra and (228)Ra are within those in drinking water in several other countries and the annual ingested dose is comparable with the typical range reported by UNSCEAR. Also, the effect of TDS, pH, calcium, bicarbonate, sulphate and chloride ion concentrations on radium levels is studied and discussed.     

Source of radium in a well-water-augmented Florida lake

A study of the lake waters of Saddleback Lake, Florida was undertaken with the goal of determining the source of elevated radium activities in the lake. Four radium isotopes, (226)Ra, (228)Ra, (223)Ra and (224)Ra, were measured and activities of all the four radium isotopes were substantially greater in the well water used to augment the lake as compared to the lake waters. In the surface water, radium activities were highest close to the well used for augmentation in the initial sampling. Activities initially decreased with time after augmentation from the well ceased. The (223)Ra/(226)Ra activity ratio decreased during the first month of sampling and closely followed an exponential decay curve based on the (223)Ra decay constant. Trends in the activities and the (223)Ra/(226)Ra activity ratios support the conclusion that the well used to augment the lake was the dominant source of (223)Ra and (226)Ra to Saddleback Lake during this study. The (224)Ra/(226)Ra activity ratio did not follow the expected trend of exponential decay based on the (224)Ra decay constant. While the augmentation well supplied some (224)Ra, these results suggest that there must be an additional source of (224)Ra to the lake. The most likely additional source of (224)Ra appears to be the ingrowth of (224)Ra on the sediment within the lake from (228)Ra (via (228)Th).     

Environmental impact studies of barium and radium discharges by produced waters from the "Bacia de Campos" oil-field offshore platforms,Brazil

Produced water samples from different E&P offshore petroleum platforms, belonging to the Bacia de Campos oil field, Brazil, were analyzed for barium, 226Ra and 'Ra. The concentrations measured are in the range of 0.36-25.7 mg l(-1) for barium, 0.012-6.0 Bq l(-1) for 226Ra and <0.05-12.0 Bq l(-1) for 1Ra. A strong correlation between the concentration of barium and radium isotopes was observed (226Ra: r2=0.926: 228Ra: r2=0.785). Additionally, seawater and sediment samples were taken at different distances (from 250 to 1,000 m) from the two selected platforms. Water samples were analyzed for dissolved and particulate barium, 226Ra and 225Ra and the sediment samples for total and leachable barium, 226Ra and 228Ra. The results showed that even for the shortest sampling distance (250 m) from the discharge point, barium, 226Ra and 228Ra concentrations are similar to the local background, indicating that dispersion by local currents is enough to minimize environmental impacts.     

Environmental fate of Ra in cation-exchange regeneration brine waste disposed to septic tanks, New Jersey Coastal Plain, USA: migration to the water table

Fate of radium (Ra) in liquid regeneration brine wastes from water softeners disposed to septic tanks in the New Jersey Coastal Plain was studied. Before treatment, combined Ra (²²⁶Ra plus ²²⁸Ra) concentrations (maximum, 1.54 Bq L⁻¹) exceeded the 0.185 Bq L⁻¹ Maximum Contaminant Level in 4 of 10 studied domestic-well waters (median pH, 4.90). At the water table downgradient from leachfields, combined Ra concentrations were low (commonly ≤0.019 Bq L⁻¹) when pH was >5.3, indicating sequestration; when pH was ≤5.3 (acidic), concentrations were elevated (maximum, 0.985 Bq L⁻¹ - greater than concentrations in corresponding discharged septic-tank effluents (maximum, 0.243 Bq L⁻¹)), indicating Ra mobilization from leachfield sediments. Confidence in quantification of Ra mass balance was reduced by study design limitations, including synoptic sampling of effluents and ground waters, and large uncertainties associated with analytical methods. The trend of Ra mobilization in acidic environments does match observations from regional water-quality assessments.     

Abnormal high natural radium concentration in surface waters

Unexpected high 228Ra concentrations, up to 2 Bq 1(-1), were found in waters of a coastal lagoon close to a monazite sand separation plant. Due to their use as process waters in this plant, the initial supposition was a contamination related to its operation. However, it was concluded that these abnormal radium concentrations had a natural origin, springs at the lagoon head area with high 228Ra and 226Ra concentrations. The strong relationship among radium and light rare-earth elements (LREEs), the observed 228Ra/226Ra activity ratio and the rare-earth element pattern in the spring waters suggested that monazite is the main source of nuclides for water, indicating the disturbance of monazite chemical stability by the combined effects of low pH and high salinity. Both factors combined allow relatively low mobility of thorium, but, on the other hand, a relatively high mobility of radium and LREEs.     

226Ra bioavailability to plants at the Urgeiriça uranium mill tailings site

Large amounts of solid wastes (tailings) resulting from the exploitation and treatment of uranium ore at the Urgeiri?a mine (north of Portugal) have been accumulated in dams (tailing ponds). To reduce the dispersion of natural radionuclides into the environment, some dams were revegetated with eucalyptus (Eucalyptus globolus) and pines (Pinus pinea). Besides these plants, some shrubs (Cytisus spp.) are growing in some of the dams. The objective of this study is to determine the 226Ra bioavailability from uranium mill tailings by quantifying the total and available fraction of radium in the tailings and to estimate its transfer to plants growing on the tailing piles. Plant and tailing samples were randomly collected and the activity concentration of 226Ra in plants (aerial part and roots) and tailings was measured by gamma-spectrometry. The exchangeable fraction of radium in tailings was quantified using one single step extraction with 1 mol dm-3 ammonium acetate (pH = 7) or 1 mol dm-3 calcium chloride solutions. The results obtained for 226Ra uptake by plants show that 226Ra concentration ratios for eucalyptus and pines decrease at low 226Ra concentrations in the tailings and appear relatively constant at higher radium concentrations. For shrubs, the concentration ratios increase at higher 226Ra solid waste concentrations approaching a saturation value. Percentage values of 16.0 +/- 8.3 and 12.9 +/- 8.9, for the fraction of radium extracted from the tailings, using 1 mol dm-3 ammonium acetate or calcium chloride solutions, respectively, were obtained. The 226Ra concentration ratios determined on the basis of exchangeable radium are one order of magnitude higher than those based on total radium. It can be concluded that, at a 95% confidence level, more consistent 226Ra concentration ratios were obtained when calculated on the basis of available radium than when total radium was considered, for all the dams.     

Radium geochemistry in Na-Cl type groundwater in Niigata Prefecture, Japan

Radium isotopes in 23 Na-Cl type groundwater sampled mainly from deep wells in Niigata Prefecture, which is the site of the largest oil- and gas-fields in Japan, were measured along with U isotopes, chemical components and hydrogen and oxygen isotope ratios to elucidate the distribution and behavior of Ra in a brackish environment underground. Also analyzed were U and Th isotopes in 38 rock samples collected from outcrops at 17 locations. Ra-226 concentrations (8.86-1637 mBq kg⁻¹) of groundwater samples roughly correlated with total dissolved solid (TDS) concentrations and other alkaline earth contents. Their ²²⁸Ra/²²⁶Ra activity ratios (0.32-5.2) were similar to or higher than the ²³²Th/²³⁸U activity ratios (0.6-1.7) in the rocks. The most likely transport mechanism of Ra isotopes into groundwater was due to their α-recoil from the solid phase, probably from the water-rock interface where Th isotopes had accumulated, and adsorption/desorption reaction based on the increase in ²²⁶Ra contents with TDS.     

Soil radium, soil gas radon and indoor radon empirical relationships to assist in post-closure impact assessment related to near-surface radioactive waste disposal

Least squares (LS), Theil’s (TS) and weighted total least squares (WTLS) regression analysis methods are used to develop empirical relationships between radium in the ground, radon in soil and radon in dwellings to assist in the post-closure assessment of indoor radon related to near-surface radioactive waste disposal at the Low Level Waste Repository in England. The data sets used are (i) estimated ²²⁶Ra in the <2 mm fraction of topsoils (eRa226) derived from equivalent uranium (eU) from airborne gamma spectrometry data, (ii) eRa226 derived from measurements of uranium in soil geochemical samples, (iii) soil gas radon and (iv) indoor radon data. For models comparing indoor radon and (i) eRa226 derived from airborne eU data and (ii) soil gas radon data, some of the geological groupings have significant slopes. For these groupings there is reasonable agreement in slope and intercept between the three regression analysis methods (LS, TS and WTLS). Relationships between radon in dwellings and radium in the ground or radon in soil differ depending on the characteristics of the underlying geological units, with more permeable units having steeper slopes and higher indoor radon concentrations for a given radium or soil gas radon concentration in the ground. The regression models comparing indoor radon with soil gas radon have intercepts close to 5 Bq m⁻³ whilst the intercepts for those comparing indoor radon with eRa226 from airborne eU vary from about 20 Bq m⁻³ for a moderately permeable geological unit to about 40 Bq m⁻³ for highly permeable limestone, implying unrealistically high contributions to indoor radon from sources other than the ground. An intercept value of 5 Bq m⁻³ is assumed as an appropriate mean value for the UK for sources of indoor radon other than radon from the ground, based on examination of UK data. Comparison with published data used to derive an average indoor radon: soil ²²⁶Ra ratio shows that whereas the published data are generally clustered with no obvious correlation, the data from this study have substantially different relationships depending largely on the permeability of the underlying geology. Models for the relatively impermeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with lower indoor radon: soil ²²⁶Ra ratios, whilst the models for the permeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with higher than average indoor radon: soil ²²⁶Ra ratios.     

Ra and Ra in scale and sludge samples and their correlation with the chemical composition

In order to contribute to a future waste management policy related to the presence of technologically enhanced natural occurring radioactive material (TENORM) in the Brazilian petroleum industry, the present work presents the chemical composition and the ²²⁶Ra and ²²⁸Ra content of sludge and scales generated during the offshore E and P petroleum activities in the Campos Basin, the primary offshore oil production region in Brazil.The ²²⁶Ra and ²²⁸Ra content on 36 sludge and scales samples were determined by gamma-spectrometry. Based on X-ray diffractometry results, a chemical analysis schema for these samples was developed. The results have shown that scales are 75% barium and strontium sulfates, with a mean ²²⁶Ra and ²²⁸Ra content of 106 kBq kg⁻¹ and 78 kBq kg⁻¹, respectively. On the other hand, sludge samples have a much more complex chemical composition than the scales. The ²²⁶Ra and ²²⁸Ra content in sludge also varies much more than the content observed in the scales samples and ranged from 0.36 to 367 kBq kg⁻¹ and 0.25 to 343 kBq kg⁻¹, respectively.     

Radium and radium-daughter nuclides in carbonates: a brief overview of strategies for determining chronologies

Radium isotopes have been used extensively to trace the movement of groundwater as well as oceanic water masses, but these radionuclides (and their daughters) are also useful chronometers for the determination of the time scales of other Earth and environmental processes. The purpose of this overview is to present the application of Ra and Ra daughters in the dating of carbonates. We show that the choice of dating method (decay of excess radionuclide or ingrowth of daughter) depends strongly on the parent/daughter activity ratios in the water in which the carbonate was precipitated. Thus freshly precipitated carbonates uniformly show excesses of ²²⁶Ra relative to its parent ²³⁰Th, and ²²⁶Ra decay can provide ages of carbonates over Holocene time scales. In contrast, carbonates are precipitated in waters of greatly varying ²¹⁰Pb/²²⁶Ra. Corals, deep-sea hydrothermal vent clams and the shelled cephalopod Nautilus live in waters with significant dissolved ²¹⁰Pb and all show excesses of ²¹⁰Pb in their carbonate. Bivalve molluscs from nearshore and coastal waters, and carbonates deposited from groundwater environments (e.g. travertines) in which ²¹⁰Pb is efficiently scavenged from solution, show deficiencies of ²¹⁰Pb relative to ²²⁶Ra. In contrast, fish otoliths strongly discriminate against ²¹⁰Pb regardless of the environment in which the fish lives. Deficiencies of ²²⁸Th relative to ²²⁸Ra are common in all carbonates. Useful time ranges for the ²¹⁰Pb/²²⁶Ra and ²²⁸Th/²²⁸Ra chronometers are ∼100 y and ∼10 y, respectively.     

Biomagnification of 7Be, 234Th, and 228Ra in marine organisms near the northern Pacific coast of Japan

Enrichment of natural radionuclides of thorium, radium and beryllium in several kinds of marine organisms was investigated near the Pacific coast of Miyagi Pref., Japan. The radioactivity of 7Be, 210Pb, 234Th, 238U, 228Ra and 137Cs was measured using gamma spectrometry. High concentrations of 234Th were observed in ascidian livers (50-400 Bq/kg dry) and excrement (2000-2900 Bq/kg dry), although the parent 238U concentrations were less than 3 Bq/kg dry. Such extreme disequilibrium between 238U and 234Th activity was observed in other organisms (barnacles, mussels and brown algae). Relatively high concentrations of 228Ra were detected in ascidian livers and were observed to decrease according to its half-life (5.75 year), suggesting disequilibrium with its parent 232Th. High concentrations (about 1900-5000 Bq/kg dry) of 7Be were detected in ascidian liver. Possible mechanisms for the observed biomagnification and bioaccumulation of these radionuclides in the organisms analyzed were proposed.     

Natural radionuclides in Austrian mineral water and their sequential measurement by fast methods

Ten samples of Austrian mineral water were investigated with regard to the natural radionuclides (228)Ra, (226)Ra, (210)Pb, (210)Po, (238)U and (234)U. The radium isotopes as well as (210)Pb were measured by liquid scintillation counting (LSC) after separation on a membrane loaded with element-selective particles (Empore Radium Disks) and (210)Po was determined by alpha-spectroscopy after spontaneous deposition onto a copper planchette. Uranium was determined by ICP-MS as well as by alpha-spectroscopy after ion separation and microprecipitation with NdF(3). From the measured activity concentrations the committed effective doses for adults and babies were calculated and compared to the total indicative dose of 0.1 mSv/a given in the EC Drinking Water Directive as a maximum dose. The dominant portion of the committed effective dose was due to the radium isotopes; the dose from (228)Ra in most samples clearly exceeded the dose from (226)Ra.     

Radiological hazards of TENORM in the wasted petroleum pipes

Disposal petroleum pipes containing sludge and scale as a technically enhanced natural occurring radioactive material (TENORM) leads to internal and external radiation hazards and then a significant radiation dose to the workers. In order to contribute to a future waste management policy related to the presence of TENORM in the disposal sites of wasted petroleum pipes, scale and sludge as TENORM wastes are collected form these disposal pipes for radiometric analysis. These pipes are imported from onshore oilfields at south Sinai governorate, Egypt. The highest mean ²²⁶Ra and ²²⁸Ra concentrations of 519 and 50 kBq/kg respectively, were measured in scale samples. Sludge lies within the normal range of radium concentration. The average absorbed dose caused by the exposure to the wasted pipes equal to 4.09 μGy h⁻¹ from sludge and 262 μGy h⁻¹ from scale. This is much higher than the acceptable level of 0.059 μGy h⁻¹. Due to radon inhalation, important radon related parameters are calculated which advantage in internal dose calculation. Fairly good correlation between real radium content and radon exhalation rate for sludge samples is obtained. The hazards from sludge come from its high emanation power for radon which equal to 3.83%. The obtained results demonstrate the need of screening oil residues for their radionuclide content in order to decide about their final disposal.