Linearity assumption in soil-to-plant transfer factors of natural uranium and radium in Helianthus annuus L

The linearity assumption of the validation of soil-to-plant transfer factors of natural uranium and (226)Ra was tested using Helianthus annuus L. (sunflower) grown in a hydroponic medium. Transfer of natural uranium and (226)Ra was tested in both the aerial fraction of plants and in the overall seedlings (roots and shoots). The results show that the linearity assumption can be considered valid in the hydroponic growth of sunflowers for the radionuclides studied. The ability of sunflowers to translocate uranium and (226)Ra was also investigated, as well as the feasibility of using sunflower plants to remove uranium and radium from contaminated water, and by extension, their potential for phytoextraction. In this sense, the removal percentages obtained for natural uranium and (226)Ra were 24% and 42%, respectively. Practically all the uranium is accumulated in the roots. However, 86% of the (226)Ra activity concentration in roots was translocated to the aerial part.     

Deposition of Ra on surfaces during precipitation and leaching of (Ba, Ra)SO4

Formation of a barium-radium sulphate precipitate occurs during the treatment of uranium tailings decants with barium chloride to remove ²²⁶Ra. This note presents results from experiments designed to identify the importance of radium adsorption onto the (Ba, Ra)SO₄ precipitate as a mechanism for removal. Adsorption was investigated indirectly by forming a precipitate and then measuring radium release during leaching.In the conduct of the precipitation/leaching experiments serious difficulties were encountered initially in obtaining satisfactory mass balances—radium recoveries were quite low. EDTA extractions of apparatus revealed that significant quantities of ²²⁶Ra were adhering to apparatus surfaces during both precipitation and leaching. This has important implications for treatment process design, the behaviour of radium in the environment and for the conduct of experimental work. Although the amounts of radium adhering to surfaces were significant relative to levels in solution, the total release of radium from sludge during distilled water leaching was not large. The results of the leaching tests indicated that during precipitation the radium is incorporated into the precipitate rather than adsorbed on its surface.     

Deposition of 226Ra on surfaces during precipitation and leaching of (Ba,Ra)SO4

Formation of a barium-radium sulphate precipitate occurs during the treatment of uranium tailings decants with barium chloride to remove ²²⁶Ra. This note presents results from experiments designed to identify the importance of radium adsorption onto the (Ba, Ra)SO₄ precipitate as a mechanism for removal. Adsorption was investigated indirectly by forming a precipitate and then measuring radium release during leaching.In the conduct of the precipitation/leaching experiments serious difficulties were encountered initially in obtaining satisfactory mass balances—radium recoveries were quite low. EDTA extractions of apparatus revealed that significant quantities of ²²⁶Ra were adhering to apparatus surfaces during both precipitation and leaching. This has important implications for treatment process design, the behaviour of radium in the environment and for the conduct of experimental work. Although the amounts of radium adhering to surfaces were significant relative to levels in solution, the total release of radium from sludge during distilled water leaching was not large. The results of the leaching tests indicated that during precipitation the radium is incorporated into the precipitate rather than adsorbed on its surface.     

Daily intakes of 238U, 234U, 232Th, 230Th, 228Th and 226Ra in the adult population of central Poland.

Activity concentration of the uranium and thorium series radionuclides was determined in foodstuffs and drinking water in central Poland. Annual and daily intake for the adult population was estimated from the concentrations determined and average annual consumption of food and water. The daily intakes (in mBq) were 22.1 (238U), 26.5 (234U), 2.38 (232Th), 4.06 (230Th), 11.2 (228Th) and 42.2 (226Ra). The intake of uranium isotopes occurred mainly with water; the main intake of thorium isotopes was with animal products, vegetables, cereals and potatoes, whereas 226Ra entered mainly with animal products, cereals and vegetables. From the intake and dose coefficients, the annual effective doses for the ingested radionuclides were calculated. The annual effective dose was 5.95 microSv, of which 72.4% originated from 226Ra.     

Radium migration through clay liners at waste disposal sites

The migration of 226Ra through the bottom compacted clay liner of the wastewater disposal reservoirs of an industrial plant that processes uranium ore was evaluated. An instrumental method for 226Ra analysis in soils, consisting of detector calibration, the determination of detector counting efficiency, cumulative counting of both background and soil samples in regular counting intervals, and photo-peak smoothing was developed. The 226Ra was analyzed by means of its granddaughter 214Bi, at a photo-peak of 609 keV. The results showed that most of the 226Ra which diffused from the solution into the soil was retained in the upper layer of the sample, and that just a small percentage migrated to the subjacent layers. This methodology is adequate for the assessment of the migration of radionuclides through soil layers and for environmental impact studies related to contamination of soils by radionuclides.     

Estimated dose to man from uranium millling via the beef/milk food-chain pathway

One of the major pathways of radiological exposure to man from uranium milling operations is through the beef/milk food chain. Studies by various investigators have shown the extent of uptake and distribution of ²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²¹⁰Pb, and ²¹⁰Po in plants and cattle. These long0lived natural radioisotopes, all nuclides of the uranium decay series, are found in concentrated amounts in uranium mill tailings. In this paper, data from these investigations are used to estimate the dose to man from consumption of beef and milk from cattle that have fed on forage contaminated with the tailings. The estimated doses from this technologically enhanced source are compared with those resulting from average dietary intake of these radionuclides from natural sources.     

Radioactivity of fertilizers in Finland

Concentrating of ²³⁸U, ²²⁶Ra, ²²⁸Th, ²³⁵U and ⁴⁰K in 81 samples of Finnish fertilizer were measured with Ge (Li) spectrometers. The samples represented 28 different types of fertilizer including those for agriculture, forests and gardens. The ratios of activity concentrations of ²³⁸U to ²²⁶Ra in the samples varied from 1.0 to 67 with a geometric mean of 3.6 and the ratios of ²²⁸Th ²²⁸Ra varied from 0.95 to 9.5 with a geometric mean of 2.4. The weighted means of radionuclide concentrations per unit weight of phosphorus in fertilizers were estimated to be 3800 Bq/kgP of ²³⁸U, 1100 Bq/kgP of ²²⁶Ra, 78 Bq/kgP of ²²⁸Ra, 190 Bq/kgP of ²²⁸Th and 210 Bq/kgP of ²³⁵U. The weighted mean of the ⁴⁰K concentrations in fertilizers was 3500 Bq/kg. The estimated total activities spread on tilled soils during the 1982–1983 season were 260 GBq of ²³⁸U, 72 GBq of ²²⁶Ra, 5.3 GBq of ²²⁸Ra, 13 GBq of ²²⁸Th, 14 GBq of ²³⁵U and 3800 GBq of ⁴⁰K. The amounts of the uranium isotopes correspond to about 21 000 kg of natural uranium.     

Estimation of ionizing radiation impact on natural Vicia cracca populations inhabiting areas contaminated with uranium mill tailings and radium production wastes

Industrial areas in proximity to the Vodny settlement in the Komi Republic, Russia, have been contaminated by uranium mill tailings and radium production wastes. These areas, exhibiting high activity concentrations of naturally occurring radionuclides in soils, constitute a field laboratory where the effects of combined chronic exposures to α-, β- and γ-emitting radionuclides on natural plant populations can be studied. The aim of the present work was to determine dose–effect relationships and the range of doses that cause biological effects in natural Vicia cracca L. populations inhabiting the study area. The studied plant species is native to the area and is found ubiquitously. Soil and vegetation samples were taken at a reference location and six contaminated sites characterized by distinct floodplain depositional units with different enhanced levels of naturally occurring radionuclides. A large fraction of the dose at the study sites (including the reference location) was attributable to internal irradiation and ²²⁶Ra was found to be an important contributor to this component of dose. The relationship between the frequency of chromosome aberrations in seedlings' root tip cells and the absorbed dose was found to be quadratic. An exponential model provided the best result in describing the empirical dependence between the absorbed dose and both the germination capacity of seeds and the survival rate of sprouts of V. cracca. For V. cracca plants inhabiting areas contaminated with uranium mill tailings and radium production wastes, a weighted absorbed dose of 0.2 Gy (weighting factor for alpha particles = 5) during the vegetation period could be considered to be a level below which no increase in genetic variability and decrease in reproductive capacity might be observed above background.     

Contamination and restoration of an estuary affected by phosphogypsum releases

The Huelva Estuary in Huelva, Spain, has been one of the most studied environmental compartments in the past years from the point of view of naturally occurring radioactive material (NORM) releases. It has been historically affected by waste releases, enriched in radionuclides from the U-decay series, from factories located in the area devoted to the production of phosphoric acid and phosphate fertilizers.Nevertheless, changes in national regulations forced a new waste management practice in 1998, prohibiting releases of phosphogypsum into the rivers. The input of natural radionuclides from phosphate factories to rivers was drastically reduced. Because of this there was a unique opportunity for the study of the response of a contaminated environmental compartment, specifically an estuary affected by tidal influences, after the cessation of the contaminant releases to, in this case, the Huelva Estuary (henceforth referred to as the Estuary).To investigate the environmental response to this new discharge regime, the specific activities of radionuclides ²²⁶Ra and ²¹⁰Pb in water and sediment samples collected in four campaigns (from 1999 to 2005) were determined and compared with pre-1998 values.From this study it is possible to infer the most effective mechanisms of decontamination for the Estuary. Decontamination rates of ²¹⁰Pb and ²²⁶Ra in the sediments and water have been calculated using exponential fittings and corresponding half-lives have been deduced from them. The cleaning half-life in the whole area of the Estuary is about 6 and 3.5 years for ²²⁶Ra and ²¹⁰Pb respectively.The observed trend clearly shows that contamination of the Estuary by natural radionuclides is now decreasing and radioactive levels in waters and sediments are approaching the natural background references. This work attempts to evaluate whether it can be expected that the decontamination of the enhanced levels of natural radioactivity in the Estuary can be performed via natural processes.     

Multidisciplinary analysis of Finnish esker sediment in radon source identification

In order to define the naturally-occurring radioactive materials that are the source of radon in natural environments, a comprehensive analytical (geochemical, physical and chemical) methodology was employed to study sand samples from the Hollola esker in the city of Hollola (Lahti area, Finland). Techniques such as gamma-spectrometry, emanation measurements, sequential chemical extraction, scanning electron microscopy (SEM), electron probe microanalyses (EPMA) and inductively-coupled plasma mass spectrometry (ICP-MS) were used to determine the potential source of radon. Monazite and xenotime, uranium- and thorium-bearing minerals and potential radon sources, occurred in significant amounts in the samples and were also the main reason for the distribution of uranium and thereby radium in separate grain-size fractions. Following deposition, the esker sand has been exposed to no significant weathering, and radium has not therefore been much separated from uranium. However, considering its non-compatibility with crystal lattices, it was recognized rather in easily leachable species (44% of the total (226)Ra) than uranium (21% of the total (238)U) in our analyses. The smallest grain-size fraction of the esker sand had a higher emanation power (0.24) than the other fractions (around 0.17). Due to the small relative proportion of this fraction, however, it contributed only slightly to the total emanation (4%). The emanation power of the leachable species was about three times higher (ca. 0.20) than that of the species tightly bound to the crystal lattice (ca. 0.07).     

Evolution of pH, organic matter and (226)radium/calcium partitioning in U-mining debris following revegetation with pine trees

Natural attenuation processes resulting from the afforestation of some U-waste rock piles have the potential to limit the linkage of radioelements and other trace pollutants, thereby minimizing exposure risks. We determined the evolution of pH and organic matter and compared the (226)Ra and Ca extractability in pyrite-containing mining debris which was revegetated 35 years ago with Scots pine. Oxidation of sulphidic minerals remaining in the substrate appeared to dominate over acidification processes due to vegetation inputs and litter decomposition. The accumulation of organic matter in forest floor had a negligible effect on the (226)Ra upward recycling compared to the migration losses observed mainly from decarbonatation of the surface mining debris. (226)Ra was overall less soluble than Ca in the soil profile but NH(4)Ac-pH 5 had the capacity to extract a (226)Ra fraction of 31.1-41.5%, i.e. at least twice as much as for Ca. In deeper layers, a majority of both Ca and (226)Ra were extractable from the same non-specific adsorption pool, which mainly involved carbonate. In the upper acidified layer, the incorporation of organic matter had no effect on (226)Ra extractability. A further specific adsorption pool for (226)Ra was attributed to the formation of sparingly soluble Fe-Al oxyhydroxides. However, that specific (226)Ra-bearing phase was readily dissolved in NH(4)Ac-pH 5, indicating a relatively reversibility of the precipitation reaction of (226)Ra with amorphous oxide. Trees are effective at reducing hydrological release of many pollutants but in the mining debris studied, four decades of pine growth did not significantly promote (226)Ra remediation in the soil.     

Natural radionuclides in mineral waters

Concentration levels of natural radionuclides in mineral waters have been studied in several European countries. In the Federal Republic of Germany in recent years a nationwide investigation was carried out by several institutions.The concentrations of ²²⁶Ra, uranium isotopes, ²¹⁰Pb and ²¹⁰Po found are similar to those in other European countries. While for adults the health risk from drinking mineral water is comparable to the risk from terrestrial radiation, special consideration has to be given to the risk of infants when mineral water is used for preparing their food.     

About the assumption of linearity in soil-to-plant transfer factors for uranium and thorium isotopes and 226Ra

The linearity assumption for soil and plant concentrations of radionuclides is usually a good approximation for use in food-chain models. To verify this assumption, different samples of plant and substrate were collected from a granitic zone located near a disused uranium mine in order to cover a large range of concentrations. In all of the samples, the activity concentration of 226Ra and of different isotopes of uranium (238U and 234U) and thorium (232Th, 230Th and 228Th) were determined. The results indicate that the linearity assumption can be considered valid when the range of concentrations taken into account is large (approx. two orders of magnitude). Otherwise, there is a clear deviation from linearity. Also, the influence of different stable elements on the soil-plant transfer factors was studied by using multivariate regression methods. The uptake of uranium, thorium and radium was found to be mainly associated with the concentration of iron in the plant and the phosphorus and alkaline earths in the substrate.     

Effect of water purification on its radioactive content

We have analyzed the dissolved activity of various radionuclides of natural origin (226Ra and (234,235,235)U) and artificial origins (90Sr and (239+240)Pu), together with other non-radioactive physico-chemical parameters (pH, conductivity, dry residue, [Ca2+], [Mg2+], [K+] and [Fe(2+,3+)], in both pre-potable and potable water from 17 treatment plants in Extremadura (Spain). We have established a series of criteria and complementary techniques to the traditional methods of purification, aimed at the quantitative elimination of the presence in solution of the mentioned radionuclides. We highlight: (a) the increment of the mineral content of the water in its treatment succeeds in eliminating 226Ra, until reaching values close to 70%; (b) the increment of the mineralization of the water by addition of chemical reagents, conducted within the pH values 7.1 and 7.8, succeeds in eliminating up to 90% of the total uranium in dissolution; (c) the elimination of 90Sr during the purification is poor, in general, reaching average levels of only 15% when the purification process is practiced within concrete ranges for potable water (pH > 7, conductivity > 150 microS/cm, dry residue > 150 mg/l, [Ca2+] > 10 mg/l and [Mg2+] > 1.2 mg/l), and finally, (d) the decrease of the solubility of the iron, as low as it can get during the purification process, together with an increase of the conductivity associated, in principle, to parallel increments of other variables not analyzed in this work, such as SO4(2-), CO3(2-), etc., the activity of dissolved (239+240)Pu decreases to 90%. The application of the traditional processes of water purification outside the ranges and criteria formulated can increase the presence in dissolution up to 400%, for some radionuclides, largely the consequence of its redissolution from the non-soluble fraction of the water.     

Natural radionuclides in industrial and rural soils

Radium-226, lead-210, uranium and thorium are dispersed in the environment by fly ash emitted by coal fuelled power stations. Concentrations of these nuclides have been determined in fly ash from three power stations and in soils collected in six industrial and twenty rural regions. In industrial areas the concentrations of natural radionuclides, in a 5 cm thick surface soil layer, were found to be higher than in lower layers. With the exception of lead-210 this effect was not observed in rural soils, which contained less of radium-226, uranium and thorium. It was found that the type of coal, or combustion technology, influences the amount of radium-226 dispersed in the environment which is accessible to plants.     

Heterogeneous distribution of radionuclides, barium and strontium in phosphogypsum by-product

Phosphogypsum (PG) is a high volume by-product of the phosphate fertilizer industry which is composed mainly of CaSO₄·2H₂O. Impurities in PG include F, trace elements and naturally-occurring radionuclides. Radium-226 content is sufficiently high in some PGs that it has limited PG usage in building materials and as an amendment to agricultural soils. Radium likely exists in PG as a sulfate solid solution with Ba, and possibly Sr. This study determined the distribution of ²²⁶Ra, Ba, Sr, U, Th and ²¹⁰Pb among three size fractions (fine: <20 μm; medium: 20–53 μm; coarse: >53 μm) in PGs derived from three different phosphate rock sources. All chemical species, except for Sr in PG derived from Idaho rock, were enriched in the <20-μm fraction relative to the other size fractions and relative to unfractionated PG. On average, fine fraction ²²⁶Ra and ²¹⁰Pb contents were enriched approximately sixfold over unfractionated PG. ²²⁶Ra was enriched in the fine fraction to a greater degree than were Ba or Sr, indicating that Ra behavior in PG is distinct from these other elements. The combination of (i) particle sorting during PG deposition, and (ii) non-uniform distribution of radionuclides in PG, may contribute to radionuclide heterogeneity at PG repositories.     

Natural radionuclide distribution in quartzite sands of East Mediterranean Region (Turkey)

The study examined 15 sites in the Ovacik-Kargicak (Mersin, Turkey) open pit mines and obtained two quartzite samples from each. Gamma-ray spectrometric measurements were undertaken on the quartzite rocks and sands to quantify the concentrations of the natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K. In addition, the mean radioactivity concentrations of these natural nuclides were calculated to be 6.94, 7.34 and 140.05 Bqkg⁻¹. Also the mean radioactivity concentrations of the natural nuclides in old Ovacik quartzite sands ²²⁶Ra, ²³²Th and ⁴⁰K were calculated to be 9.85, 10.54, and 226.40 Bqkg⁻¹, respectively.     

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements

The estuary of the Odiel River has been affected by both direct discharges of phosphogypsum (radium enriched industrial waste) and dissolution and weathering of the exposed piles where this radium enriched waste was stored. In 1998 the waste management policy for industries changed. The direct discharges stopped and the new phosphogypsum piles were well protected against dissolution processes, avoiding any transference of radium into the environment. This work presents a study of the evolution with time (1999-2002) of the levels of 226Ra in river water and sediment samples with the new waste management policy. A liquid scintillation technique was used to measure the 226Ra activity concentration in sediment samples. A gas-proportional counter was also used to measure the 226Ra activity concentration in river water samples. The main conclusion is that a systematic and continuous decrease of the activity concentration of 226Ra with time in the Odiel River estuary is occurring. Thus, a possible self-cleaning in the estuary, once the direct waste discharges were avoided, can be inferred.     

Radioactivity of anthropogenic origin in the Tejo Estuary and need for improved waste management and environmental monitoring

The Tejo Estuary is a large water body surrounded by seven municipalities and industries with liquid effluent discharges containing contaminants that reach the estuary. This is the case for man-made radionuclides used in nuclear medicine, present in liquid effluents discharged by medical facilities. Radionuclide measurements in seaweeds, mussels, fish, water and sediments sampled along the North bank of the estuary revealed the presence of ¹³¹I and ^99mTc, originating from nuclear medicine facilities in Lisboa. Concentrations reached 90 Bq kg^?1 (wet weight) of ^99mTc in fish, and 18 Bq kg^?1 (wet weight) of ¹³¹I in mussels, and were even higher in the water. Another anthropogenic source of radionuclides is industrial waste, such as phosphogypsum the by-product of phosphoric acid production stockpiled at the South bank of the estuary. Main radionuclides present in phosphogypsum are ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po and uranium. Concentrations of ²²⁶Ra in phosphogypsum are about 1000 Bq kg^?1, which is a high value in comparison with ²²⁶Ra in soils of the Tejo valley, <100 Bq kg^?1. ²²⁶Ra, in particular, is dissolved by rainwater from phosphogypsum stacks and seeps into the estuary. Other potential sources of radioactivity are discharges from naval nuclear powered vessels and merchant ships transporting radioactive materials that berth in the Lisboa harbour. A whole survey of the estuary indicated low concentrations of ¹³⁷Cs in sediments, mostly attributed to radioactive fallout. Since waste discharges are undergoing deep modifications due to enhanced urban waste treatment, but economic activities have changed and the use of radiopharmaceuticals increases, the periodic radioactivity monitoring of the Tejo Estuary is advised and should provide feedback to enhanced waste management.     

Distribution of radionuclides in different parts of a mushroom: influence of the degree of maturity

Mushrooms are known to be bioaccumulators of radionuclides, but little is known about their distribution within the fruiting bodies or the influence of the degree of maturity on uptake. We carried out a series of cultures of the species Pleurotus eryngii under controlled laboratory conditions to analyze these variables. The maximal uptake of 134Cs and 85Sr was found to occur in mature fruiting bodies, and with the growth of the mushroom the distribution of radionuclides within the fruiting bodies became inhomogeneous. In particular, there was an exponential increase in the percentage of the total activity of 134Cs, 85Sr, and 60Co in the cap+gills as the fruiting bodies matured, accompanied by a complementary decrease in the stem. Radiocaesium, potassium, calcium, (239+240)Pu, (234,238)U, (228,230,232)Th, and 226Ra were assayed in the cap, gills, and stem of fruiting bodies of Tricholoma equestre collected in a natural ecosystem and cultured P. eryngii. Potassium and radiocaesium were mainly located in the cap+gills, and 226Ra in the gills. There was a disequilibrium between (230,232)Th and 228Th in the different parts of the fungi, probably due to uptake of 228Ra and subsequent decay to 228Th. Finally, the distribution pattern of (239+240)Pu, (234,238)U, and (230,232)Th seemed to be species dependent.