Distribution,cycling and mean residence time of 226Ra, 210Pb and 210Po in the Tagus estuary

Results for dissolved and particulate ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po in the Tagus river, estuary and coastal sea system show different distribution and chemical behaviour patterns for these radionuclides in the three aquatic environments. ²²⁶Ra from riverborne particles dissolves in the estuary and contributes to increased concentrations of dissolved ²²⁶Ra in estuarine water. In the estuary, dissolved ²¹⁰Pb and ²¹⁰Po from river discharge and atmospheric deposition are scavenged by suspended matter, which in turn becomes enriched in these nuclides in comparison with riverborne particles. As a result of these processes, the estuarine water flowing into the coastal sea contains enhanced concentrations of dissolved ²²⁶Ra, but is depleted in dissolved ²¹⁰Pb and ²¹⁰Po. Under average river flow conditions, mass balance calculations for dissolved ²¹⁰Po and ²¹⁰Pb in the estuary allowed their mean residence times to be estimated as 18 and 30 days, respectively. Due to the rapid sorption of these radionuclides on to settling particles, bottom sediments in the estuary represent a sink for ²¹⁰Pb and ²¹⁰Po from both natural sources and industrial waste releases. Results also suggest that partial re-dissolution of these radionuclides from bottom sediments and intertidal mudflats is likely to occur in the mid- and low-estuary zones. Nevertheless, box-model computations indicate that the discharge of ²¹⁰Pb and ²¹⁰Po into the coastal sea takes place mainly with the transport of sediment, whereas the discharge in the dissolved fraction can only account for one third of the activities entering the estuary in the soluble phase. Implications of these results to the cycling of radionuclides in phosphate waste releases into estuarine environments are discussed.     

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.     

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.     

Spatial distribution of radionuclides in soil around a coal-fired power plant: 210Pb, 210Po, 226Ra, 232Th, 40K emitted with the fly ash and 137Cs from the worldwide weapon testing fallout

To determine the effect of airborne emissions of radionuclides from coal-fired power plants on the environment, the concentrations of the most important radionuclides were measured in soil samples from the local environments (0.4–5.2 km) as well as in fly ash. The spatial distribution of the radionuclides in the soil did not indicate any significantly increased concentrations in the area downwind of the plant compared to other areas; the ratios ²¹⁰Pb/²²⁶Ra and ²¹⁰Po/²²⁶Ra were within the range observed for unaffected soils. The emissions from the plant, though present, are obviously too small to significantly change the natural local distribution pattern of the radionuclides in the soil. A highly significant correlation between ⁴⁰K and ²³²Th was observed which was independent of the different types of soils found in this area. The concentration of ¹³⁷Cs in topsoil, which is the result of worldwide fallout from nuclear weapons testing, varied at some places even within a small distance (～ 2 km) by up to one order of magnitude. Furthermore, it was observed that the concentration of ¹³⁷Cs in soils from cropland was on average a factor of 2 less than in those from grassland. This variability has to be considered in planning monitoring programs around nuclear power plants, which may also release this radionuclide.     

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.     

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.     

Pb and stable lead content in fungi: Its transfer from soil

The uptake and transfer of natural radionuclides, other than ⁴⁰K, from soil to mushrooms has been somewhat overlooked in the literature. Their contribution to the dose due to the consumption of mushrooms was considered negligible. But the contribution of ²¹⁰Pb in areas unaffected by any recent radioactive fallout has been found to be significant, up to 35% of the annual dose commitment in Spain. More than 30 species of mushrooms were analyzed, and the ²¹⁰Pb detected was in the range of 0.75-202 Bq/kg d.w. A slight difference was observed between species with different nutritional mechanisms (saprophytes ≥ mycorrhizae). The ²¹⁰Pb content was correlated with the stable lead content, but not with its predecessor in the uranium radioactive series, ²²⁶Ra. This suggested that ²¹⁰Pb was taken up from the soil by the same pathway as stable lead. The bioavailability of ²¹⁰Pb in soil was determined by means of a sequential extraction procedure (NH₄OAc, 1M HCl, 6M HCl, and residue). About 30% of the ²¹⁰Pb present in the soil was available for transfer to mushrooms, more than other natural radionuclides in the same ecosystem. Lycoperdon perlatum, Hebeloma cylindrosporum, and Amanita curtipes presented the highest values of the available transfer factor, ATF. As reflected in their ATF values, the transfer from soil to mushroom of some natural and anthropogenic radionuclides was in the following order:

^228,230,232Th ≈ ⁴⁰K ≥ ¹³⁷Cs ≥ ^234,238U ≈ ²²⁶Ra ≥ ⁹⁰Sr ≥ ²¹⁰Pb ≈ ^239 + 240Pu ≈ ²⁴¹Am.     

Anthropogenic and natural radionuclides in caribou and muskoxen in the western Alaskan Arctic and marine fish in the Aleutian Islands in the first half of 2000s

A number of caribou and muskoxen samples from the western Alaskan Arctic and fish samples from the Aleutian Islands were collected between 1998 and 2006 and analyzed for anthropogenic (⁹⁰Sr and ¹³⁷Cs) and natural radionculides (⁴⁰ K, ²¹⁰Pb and ²²⁶Ra), as part of the radiological assessment for the regional subsistence hunting communities in the first half of 2000s. We examined the relationship between the activities of these nuclides with the size of the fish. In caribou samples, concentration of ⁹⁰Sr in muscle was below the detection limit of 0.14 Bq kg^− 1 and ¹³⁷Cs concentration in bones was below the detection limit of 0.15 Bq kg^− 1.¹³⁷Cs activity varied over an order of magnitude in caribou muscle samples with an average value of 2.5 Bq/kg wet wt. Average ¹³⁷Cs activity in muskoxen muscle was found to be 9.7 Bq/kg wet wt. However, there were a little variation (less than 60%) in ²¹⁰Pb, ⁴⁰ K, and ²²⁶Ra in both muscle and bone of both caribou and muskoxen. The activities of total ²¹⁰Pb in caribou and muskox bones were found to be 1-2 orders of magnitude higher than that of parent-supported ²¹⁰Pb indicating the potential for dating of bones of terrestrial mammals (time elapsed since the death of the animal) based on the excess ²¹⁰Pb method exists. In fish muscle samples, ¹³⁷Cs activity varied from below detection limit to 154 mBq/kg wet wt. and its content increased with the size of the fish due to its transfer through the food chain. Among the seven fish species investigated, ²¹⁰Pb activities varied almost an order of magnitude; however, ⁴⁰K and ²²⁶Ra activities varied less than a factor of two. Total annual effective dose due to ⁹⁰Sr and ¹³⁷Cs from the ingestion of those terrestrial and marine meats was estimated to be negligible (ca. 9 μSV/a) compared to the natural radionuclides present thus posing negligible radiological threat to humans.     

Pre-operational environmental survey at the uranium mine and mill site,Poços de Caldas,Minas Gerais,Brazil

The first Brazilian uranium mine and mill are located on the Poços de Caldas plateau, in the Central State of Minas Gerais. The pre-operational environmental survey was carried out over a period of two years by the Brazilian Nuclear Energy Commission (CNEN), through the Instituto de Radioproteção e Dosimetria (IRD). The selection of the materials to be monitored, the sampling points and the radionuclides to be analysed were based on critical parameters taking into account the meteorological and hydrological characteristics of the site as well as land use. The results obtained are sufficient to characterize the environmental background of the area, and will allow an assessment of the environmental impact due to the operation of the facility and an evaluation of the adequacy of the effluent emmission control measures. In relation to their contribution to the population dose, the results indicated that ²²⁶Ra and ²¹⁰Pb will be the important radionuclides.     

Mesoscale variability of vertical profiles of environmental radionuclides (40K, 226Ra, 210Pb and 137Cs) in temperate forest soils in Germany

Vertical profiles of environmental radionuclides (40K, 226Ra, 210Pb and 137Cs) were investigated in several temperate forest soils in Germany to estimate heterogeneity of the soil horizon of interest. Absolute values of the activity concentrations of these nuclides varied to a large extent depending on the properties of individual forests as well as local geology. Several trends were generally observed independent of the location: (1) Activity concentrations of 40K increased with increasing soil density reflecting that most potassium is contained in mineral components of the soil. The variations in the 40K activity with depth may relate to biological activities in subsoil, such as root uptake of the nutrients. (2) Profiles of 226Ra with depth could be an indicator for evaluating soil heterogeneity within a horizon of interest. They are also useful to estimate anthropogenic 210Pb (210Pbexc) derived from the atmosphere via dry fallout or wet deposition. In several forests, there appeared surface enrichment of 210Pb down to a depth of approximately 10 cm, in which the 210Pb would have come from the atmosphere by combustion of fossil fuels. (3) Depth profiles of 137Cs were roughly divided into three types in which (a) the activity concentration decreased exponentially with soil depth, (b) small amounts of 137Cs existed only in the upper-most layer of the soil (0-5 cm) and (c) 137Cs disappeared at certain depths and appeared again at deeper portions of the soil. Consequences of bioturbation could be deduced from variability in vertical profiles of the environmental radionuclides. It is probable that a site showing an exponential decrease of the 137Cs activity with depth and also having a surface enrichment of 210Pb is not significantly influenced by bioturbation.     

The ratio of lead-210 to polonium-210 in U.K. diet

The levels of the natural radionuclides, ²¹⁰Pb and ²¹⁰Po, in U.K. diet have been measured previously. However, in the earlier measurements, the samples were sufficiently aged for ²¹⁰Pb and ²¹⁰Po to have attained secular equilibrium. In order to determine the extent of disequilibrium between these radionuclides in fresh food, measurements have been made on recently collected dietary samples. Disequilibrium has been observed in five food groups. The activity per unit mass of ²¹⁰Pb was found to be greater than that of ²¹⁰Po in bread, cereals, sugar and preserves, whereas the opposite was found to be true for eggs and beverages. When account is taken of consumption rates, however, the total intakes of ²¹⁰Pb and ²¹⁰Po from these food groups are approximately the same. The -annual effective dose equivalents from the ingestion of ²¹⁰Pb and ²¹⁰Po have been re-estimated at 41 and 12 μSv, respectively.     

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.     

(210)Po and (210)Pb in the tissues of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen field (Mid-Atlantic Ridge)

The hydrothermal deep-sea vent fauna is naturally exposed to a highly specific environment enriched in potentially toxic species such as sulfides, metals and natural radionuclides due to the convective seawater circulation inside the oceanic crust and its interaction with basaltic or ultramafic host rocks. However, data on radionuclides in biota from such environment are very limited. An investigation was carried out on tissue partitioning of ²¹⁰Po and ²¹⁰Pb, two natural radionuclides within the ²³⁸U decay chain, in Bathymodiolus azoricus specimens from the Mid-Atlantic Ridge (Menez Gwen field). These two elements showed different distributions with high ²¹⁰Pb levels in gills and high ²¹⁰Po levels in both gills and especially in the remaining parts of the body tissue (including the digestive gland). Various factors that may explain such partitioning are discussed. However, ²¹⁰Po levels encountered in B. azoricus were not exceptionally high, leading to weighted internal dose rate in the range 3 to 4 μGy h^− 1. These levels are slightly higher than levels characterizing coastal mussels (~ 1 μGy h^− 1).     

Sedimentation rates in Western Nipigon Bay,Lake Superior using the 210Pb method

²¹⁰Pb, ²²⁶Ra and ¹³⁷Cs profiles have been measured for sediment cores from three locations in western Nipigon Bay, Lake Superior, Canada. Compaction of the sediment with depth of burial was taken into account in calculating recent sedimentation rates and age profiles at these locations from the excess ²¹⁰Pb profiles. The rates at two of the locations were 0.85±0.03 mmy^?1 (16.7 mg cm^?2 y^?1) and 1.39±0.12 mmy^?1 (29.5 mg cm^?2 y^?1). The third core had an anomaly in the ²¹⁰Pb profile below a depth of 3.5 cm corresponding to the time that the outfall of a nearby pulp mill was relocated. The ¹³⁷Cs profiles of the two undisturbed cores were in accord with the corresponding age/depth curves derived from the ²¹⁰Pb measurements.     

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

A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from measurements.     

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.     

Pb and 210Pb in a tropical river environment

The Periyar River in south India receives the major share of Pb and ²¹⁰Pb from effluents released by factories along its bank that process monazite ore and rock phosphate. Their distribution in the river system is influenced by the rains during the monsoon and by salinity during the non-monsoon period. The concentration of both Pb and ²¹⁰Pb in the sediments from the backwater zone was observed to increase during the monsoon due to sediment transport from the upstream industrial zone. The water in the backwater zone showed increased levels of Pb and ²¹⁰Pb in the non-monsoon period, due possibly to solubilization from the sediments as a result of salinity changes. The levels of Pb and ²¹⁰Pb in the river water are much lower than the international standards for safe limits in drinking water. No significant concentration of Pb and ²¹⁰Pb above a background level was observed in fish obtained from the river.     

Concentrations of radionuclides in Lake Ontario water from measurements on water treatment plant sludges

The purpose of this investigation was to compare the results of indirect measurements of radionuclide concentrations in water with those measured directly. The levels of ¹³⁷Cs and ²²⁶Ra in western Lake Ontario nearshore waters were derived from high-resolution γ-spectrometric measurements on aluminum hydroxide sludge samples obtained from four water treatment plants. The concentrations of ¹³⁷Cs evaluated by this indirect technique averaged 0.036 compared with 0.023 pCi l⁻¹ measured directly, while those of ²²⁶Ra averaged 0.047 compared with the direct measurement of 0.03 pCi l⁻¹. The concentrations of a number of other radionuclides at these locations were also calculated from the sludge γ-ray measurements.     

Mineralogy-induced radiological aspects with characterization of commercial granites exploited in Turkey

This study deals with natural radioactivity levels of the ten most important commercial granites from various districts currently being exploited as dimension stone in Turkey. Determining the level of radioactivity is important for human health, particularly for indoor use of granites. This study shows that the relationship between the natural radioactivity and the radiogenic mineralogical contents of the granites exploited for commercial utilization in Turkey is variable. The natural radioactivity levels (i.e., activity concentrations of radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K) of granite samples were determined by high-resolution gamma-ray spectrometry. Using these activities, radiological hazard dose rates (absorbed and annual effective) and gamma-activity indexes were calculated using standard equations accepted by public health bodies, taking relevant international reports and guidelines into account. Three of the granites exploited in the Black Sea, Aegean, and Central Anatolia regions were found to be high in radium-equivalent activities and annual effective doses due to minerals bearing the radionuclides, including zircon, apatite, allanite, xenotime, uranothorite, K-feldspars, and biotite. Of those, uranothorite contains large amounts of radionuclides and is present in samples of granites collected from the Black Sea and Aegean regions. Radioactivity measurements using high-resolution gamma-ray spectroscopy serve as a rapid screening tool to evaluate natural radioactivity, whereas detailed petrographic, mineralogical, and elemental investigations can reveal the source of radioactive emissions in granites.     

An examination of groundwater discharge and the associated nutrient fluxes into the estuaries of eastern Hainan Island, China using 226Ra

The nutrient concentrations and stoichiometry in a coastal bay/estuary are strongly influenced by the direct riverine discharge and the submarine groundwater discharge (SGD). To estimate the fluxes of submarine groundwater discharge into the Bamen Bay (BB) and the Wanquan River Estuary (WQ) of eastern Hainan Island, China, the naturally occurring radium isotope (²²⁶Ra) was measured in water samples collected in the bay/estuary in August 2007 and 2008. Based on the distribution of ²²⁶Ra in the surface water, a 3-end-member mixing model was used to estimate the relative contributions of the sources to these systems. Flushing times of 3.9 ± 2.7 and 12.9 ± 9.3 days were estimated for the BB and WQ, respectively, to calculate the radium fluxes for each system. Based on the radium fluxes from groundwater discharge and the Ra isotopic compositions in the groundwater samples, the estimated SGD fluxes were 3.4 ± 5.0 m³ s⁻¹ in the BB and 0.08 ± 0.08 m³ s⁻¹ in the WQ, or 16% and 0.06%, respectively, of the local river discharge. Using this information, the nutrient fluxes from the submarine groundwater discharge seeping into the BB and WQ regions were estimated. In comparison with the nutrient fluxes from the local rivers, the SGD-derived nutrient fluxes played a vital role in controlling the nutrient budgets and stoichiometry in the study area, especially in the BB.