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.     

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.     

Gamma-emitting natural and anthropogenic radionuclides in the terrestrial environment of Kongsfjord,Svalbard

This paper presents results obtained from a radiometric survey, conducted by the Norwegian Radiation Protection Authority, into the levels of gamma-emitting radionuclides, both anthropogenic and natural, in the terrestrial environment of Kongsfjorden, which lies on the North-Western Coast of Spitsbergen in the Arctic archipelago of Svalbard (79 degrees N, 12 degrees E). Samples of terrestrial matrices were taken during field campaigns conducted between 2000 and 2002 and analysed for a range of gamma-emitting radionuclides. The objectives of this study included an assessment of the levels of gamma-emitting radionuclides in the terrestrial environment of the region, identification of processes and activities that influence the accumulation and redistribution of such nuclides within the region and elucidation of the behaviour of such radionuclides within a high arctic environment. Results indicate a quite homogenous spatial distribution of such radionuclides within the study area and highlight the relatively low levels of contamination by the anthropogenic radionuclide, 137Cs, on Svalbard. Average values and ranges of the radionuclides activities in surface soils (0-3 cm) were: 238U 42 Bq/kg (17-134), 226Ra 43 Bq/kg (12-137), 232Th 21 Bq/kg (4-52), 40K 283 Bq/kg (31-564), 137Cs 35 Bq/kg (1-146). Average levels of these nuclides in avian faecal materials were 238U 63 Bq/kg, 226Ra 54 Bq/kg, 232Th 19 Bq/kg, 40K 365 Bq/kg, 137Cs 78 Bq/kg. Enrichment of radionuclides is apparent in soils taken from locations close to bird colonies in the locale, maximum levels of the radionuclides being found in samples associated with such colonies. The results indicate that this is due to concentration of such radionuclides within the faecal material of the birds and subsequent enrichment of the nearby soils either via direct incorporation of the faeces into the soil or by leaching processes. The results indicate that this process may result in contamination of non-related species, such as Svalbard reindeer (Rangifer tarandus playrhynchus), via pathways other than the traditionally accepted route of atmospheric deposition-vegetation-reindeer.     

Transport of fallout radiocesium in the soil by bioturbation: a random walk model and application to a forest soil with a high abundance of earthworms

It is well known that bioturbation can contribute significantly to the vertical transport of fallout radionuclides in grassland soils. To examine this effect also for a forest soil, activity-depth profiles of Chernobyl-derived 134Cs from a limed plot (soil, hapludalf under spruce) with a high abundance of earthworms (Lumbricus rubellus) in the Olu horizon (thickness=3.5 cm) were evaluated and compared with the corresponding depth profiles from an adjacent control plot. For this purpose, a random-walk based transport model was developed, which considers (i) the presence of an initial activity-depth distribution, (ii) the deposition history of radiocesium at the soil surface, (iii) individual diffusion/dispersion coefficients and convection rates for the different soil horizons, and (iv) mixing by bioturbation within one soil horizon. With this model, the observed 134Cs-depth distribution at the control site (no bioturbation) and at the limed site could be simulated quite satisfactorily. It is shown that the observed, substantial long-term enrichment of 134Cs in the bioturbation horizon can be modeled by an exceptionally effective diffusion process, combined with a partial reflection of the randomly moving particles at the two borders of the bioturbation zone. The present model predicts significantly longer residence times of radiocesium in the organic soil layer of the forest soil than obtained from a first-order compartment model, which does not consider bioturbation explicitly.     

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.     

Radiocaesium and natural gamma emitters in mushrooms collected in Spain

Mushrooms can accumulate heavy metals in general, including radionuclides found in the nature. However, little attention has been paid to the radioactive content of mushrooms collected in Spain and the dose for the population due to their ingestion. To address this, we analysed the contents of 137Cs, 40K, 226Ra and 7Be present in different species of mushrooms, according to their genus and nutritional mechanism. We observed that mycorrhizal mushrooms accumulate 137Cs more than saprophytes, and vice versa for 7Be. 40K and 226Ra are accumulated to the same degree by the two groups of mushrooms. We estimated the dose due to ingestion of mushrooms in Spain to be 2 microSv/year, and the contribution of 40K and 226Ra to be generally greater than that of 137Cs. The contribution of 137Cs to the dose was calculated by taking into account the results of an experiment carried out under the controlled laboratory conditions, which showed that approximately 98% of 134Cs was associated with the readily digestible fraction of the mushrooms.     

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth > 2000 m) and analysed for ^239,240Pu and ¹³⁷Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of ²¹⁰Pb, together with ¹⁴C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess ²¹⁰Pb inventory was used to normalize ^239,240Pu and ¹³⁷Cs inventories for variable sediment fluxes. The ^239,240Pu/²¹⁰Pb_xs ratio was uniform across the entire sea, with a mean value of 1.24 × 10^− 3, indicating homogeneous fallout of ^239,240Pu. The ¹³⁷Cs/²¹⁰Pb_xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of ^239,240Pu/¹³⁷Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of ^239,240Pu in the water column and major sedimentation of ¹³⁷Cs in the eastern basin. Although areas with water depths of > 2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the ^239,240Pu and 0.95% of the ¹³⁷Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments.     

The use of mosses as indicators of airborne radionuclides near a major nuclear installation

Samples of naturally growing moss (mainly Pseudoscleropodium purum and Hypnum cupressiforme ) were used to investigate the distribution of photon-emitting radionuclides, notably 129I , 137Cs, 144Ce and 241Am, at distances up to 12 km from the nuclear fuel reprocessing plant at Sellafield in West Cumbria . The relative activities of the naturally occurring radionuclides, 7Be and 210Pb, in moss and air indicated that the removal half-time of these radionuclides on moss is very long (best estimate of half-time, corrected for radioactive decay, was 240 days) and that the mosses are very efficient collectors of airborne particulates (product of deposition velocity and interception factor was 2.4 X 10(-2) ms-1). Hence the activities of artificially-produced radionuclides on the mosses present an effective record of local airborne radionuclide pollution integrated over a number of years. The activity of 210Pb in each sample was used to standardize the activities of artificial radionuclides in the samples. It was found that the activity ratio of 129I /210Pb, 137Cs/210Pb and 144Ce/210Pb declined with distance from Sellafield indicating that the major local source of these radionuclides has been material discharged to air from the site. The activity ratio of 241Am/210Pb declined with distance from the site and also with distance from the sea confirming that the resuspension of material originally discharged to sea is an important local source of 241Am.     

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.     

Atmospheric deposition and migration of artificial radionuclides in Alpine soils (Val Piora, Switzerland) compared to the distribution of selected major and trace elements

Artificial radionuclides (¹³⁷Cs, ⁹⁰Sr, Pu, and ²⁴¹Am) are present in soils because of Nuclear Weapon Tests and accidents in nuclear facilities. Their distribution in soil depth varies according to soil characteristics, their own chemical properties, and their deposition history. For this project, we studied the atmospheric deposition of ¹³⁷Cs, ⁹⁰Sr, Pu, ²⁴¹Am, ²¹⁰Pb, and stable Pb. We compared the distribution of these elements in soil profiles from different soil types from an alpine Valley (Val Piora, Switzerland) with the distribution of selected major and trace elements in the same soils. Our goals were to explain the distribution of the radioisotopes as a function of soil parameters and to identify stable elements with analogous behaviors. We found that Pu and ²⁴¹Am are relatively immobile and accumulate in the topsoil. In all soils, ⁹⁰Sr is more mobile and shows some accumulations at depth into Fe-Al rich horizons. This behavior is also observed for Cu and Zn, indicating that these elements may be used as chemical analogues for the migration of ⁹⁰Sr into the soil.     

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.     

Distribution of 7Be, 210Pb and 137Cs in watersheds of different scales in the Seine River basin: inventories and residence times

The activity of environmental radionuclides ((7)Be, (210)Pb and (137)Cs) was monitored in nested catchments, inside the Seine River basin. Suspended matter data was collected at 8 different watersheds, ranging from order 1 to order 7, and ranging in size over 4 orders of magnitude. Suspended matter was analyzed for (210)Pb, (137)Cs and (7)Be, and used to calculate the flux of sediments out of each watershed. Monthly atmospheric flux data of (210)Pb and (7)Be was analyzed to assess the input flux of each into the watersheds, taking into account the rainfall during sampling periods. Taking advantage of the different half-lives of (7)Be (53 days) and (210)Pb (22 years), a two-box model was built for each of the catchments following a methodology previously developed by Dominik et al. [Dominik J, Burrus D, Vernet JP. Transport of the environmental radionuclides in alpine watershed. Earth Planet Sci Letters 1987; 84: 165-180.]. The model divides the watershed into a soil box and a rapid reservoir and provides insight into the removal rate of suspended matter from the surrounding watershed. The model enables the assessment of the surface area and the residence time of slow and rapid reservoirs to describe the fate of contaminants of atmospheric origin inside the river basin. The model was improved by considering the dissolved fraction in the total flux and adding the (137)Cs inventory as an additional constraint. The effects of these changes are discussed. Residence times in the soil box, characterized by low transport velocity, range between 4800 years at Melarchez (order 1) to about 30000 years at Andresy and Poses (order 7). They remain constant in each watershed over a large range of variation of atmospheric fluxes of (7)Be and (210)Pb during the whole study, but are sensitive to SM variations. The residence time in the rapid box, which includes the surface of the river and immediate surroundings, is less than one year, while its surface area is in the range 0.6% to 2.2% of the total catchment area. They are sensitive to (7)Be atmospheric flux variations. The two-box model was used to estimate the amount of the radionuclides in each reservoir. Inventories appear to be constant from one watershed to the next. The (7)Be inventory ratio in the rapid and slow boxes expresses the rate of particle-reactive atmospheric pollutants that will be rapidly delivered to the river.     

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.     

The cumulative effect of three decades of phosphogypsum amendments in reclaimed marsh soils from SW Spain: (226)Ra, (238)U and Cd contents in soils and tomato fruit

Phosphogypsum (PG), a by-product of the phosphate fertiliser industries, has been applied as soil amendment to reduce Na saturation in soils, as in the reclaimed marsh area from SW Spain, where available PG has a typical fingerprint of 710+/-40 Bq kg(-1) of (226)Ra, 165+/-15 Bq kg(-1) of (238)U and 2.8+/-0.4 mg kg(-1) of Cd. This work was focussed on the cumulative effects of PG amendments on the enrichment of these pollutants in cultivated soils and plants (Lycopersicum esculentum Mill L.) from the area studied, where PG has been applied since 1978 at recommended rates of 20-25 Mg ha(-1) every 2-3 years. A field experiment was conducted over three years to compare activity concentrations of (226)Ra ((214)Pb) and (238)U ((234)Th) in non-reclaimed soils, reclaimed soils with no additional PG application, and reclaimed soils with two additional PG applications. A non-significant effect of two PG amendments (in three years) was observed when compared with non-amended reclaimed plots. Nevertheless, a significant (p<0.05) enrichment of (226)Ra was observed in the surface horizon (0-30 cm) of reclaimed plots relative to deeper horizons and also when compared with the surface horizon of non-reclaimed soil (p<0.05), thereby revealing the cumulative effect of three decades of PG applications. Furthermore, the effect of a continuous application of PG was studied by analysing soils and tomato fruits from six commercial farms with different cumulative rates of PG applied. Cadmium concentrations in tomatoes, which were one order of magnitude higher than those found in tomatoes from other areas in South Spain, were positively correlated (r = 0.917) with (226)Ra-concentration in soils, which can be considered an accurate index of the cumulative PG rate of each farm.     

Multitracer study of anthropogenic contamination records in the Camargue, Southern France

Contaminants are supplied to the coastal zone by the atmosphere, rivers and point sources like wastewaters or industrial area. Wetlands retain many of these contaminants and can be used to reconstruct sources and magnitudes of contaminant inputs. Radionuclides ((137)Cs, (210)Pb, (239)Pu and (240)Pu) and stable lead isotope ((206)Pb, (207)Pb) profiles were investigated in two cores collected in wetlands of the Rh?ne River delta, south of France (Camargue), to estimate the recent sediment accumulation rates and reconstruct the deposition of pollutants during the last century. One site was affected by storm or flood deposition from the Rh?ne river and showed the influence of Marcoule reprocessing plant releases on the plutonium isotopic ratios. The other site appears suitable for the reconstruction, even if mixing is evidenced at the surface by the radionuclides profiles. Plutonium isotopic ratios are characteristic of global fallout and the (210)Pb inventory of 4240 Bq m(-2) is approximately 30% higher than atmospheric deposit estimation. The pollutant lead inventory is 139 microg cm(-2), slightly higher than previous estimation from direct fallout. This difference can be partly due to an over-collection at this site (due to canopy cover) but also to variations with time in the deposition.     

Radioenvironmental survey of the Megalopolis lignite field basin

The Megalopolis lignite field basin in southern Greece, with Megalopolis-A and B lignite-fired power plants in operation (total 900 MW), has been repeatedly investigated during the past 25 years by the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA). The present work aims at an integrated radioenvironmental approach leading to the dose assessment to the public and to the plants staff. This approach includes systematic sampling of lignite and barren at the local lignite mines feeding the power plants and sampling of lignite, fly-ash and bottom ash at the power plants for the determination of the activity of the natural radionuclides 226Ra, 232Th, 40K, 234Th and 210Pb. Furthermore, the following measurements and samplings were conducted in 25 selected sites within 10 km around the power plants: soil sampling for the determination of the above radionuclides, radon concentration and exhalation rate measurements, soil gas radon concentration measurements, dose measurements and calculations, determination of air-particulate matter concentration, etc. The results obtained allowed for the mapping of the parameters studied which lead to useful conclusions. Dosimetric calculations for the population living around the power plants and the plants staff were also performed based on the guidance of UNSCEAR (1982 report).     

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.     

The use of 210Pb and 137Cs in the study of sediment pollution in the Lagoon of Venice

The activity of 137Cs per unit area in sediments of the central part of the Lagoon of Venice was determined with the aim of identifying boundaries of homogeneous depositional zones. The 210Pb dating technique was used to date vertical profiles of cores from the same area. A comparison of the total amounts of 137Cs and non-supported 210Pb present in each core and the atmospheric input allows us to identify different depositional areas inside the basin and to outline the possible drainage effect of industrial solid wastes used in past reclaiming operations.     

Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part I: activity-depth profiles of (134)Cs and (137)Cs

The temporal changes of the vertical distribution of (134)Cs (deposited by the Chernobyl fallout in 1986) and (137)Cs (deposited by the Chernobyl and the global fallout) in the soil were investigated at an undisturbed Bavarian grassland site in Germany. At ten sampling dates between 1986 and 2001, the activity density of (134)Cs and (137)Cs was determined in various soil layers down to 80 cm depth. In 2001, the small-scale spatial variability of the radiocaesium activity was determined by sampling five plots within 10 m(2) (coefficient of variation about 20% for the upper soil layers). Between 1987 and 1990, substantial changes of the activity-depth profiles were observed. The percentage depth distributions of (134)Cs and (137)Cs were rather similar. The 50%-depth of the accumulated activity increased from 2.4 cm in 1988 to 5.3 cm in 2001 for (134)Cs and from 2.7 to 5.8 cm for (137)Cs. This indicates that at the study site the migration data of Chernobyl-derived (137)Cs can be estimated by those of total (137)Cs. In the second part of this study, the activity-depth profiles will be evaluated by the convection-dispersion model [Schimmack, W, Feria Márquez, F. Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part II: Evaluation of the activity-depth profiles by transport models. Sci Total Environ 2006-this issue].     

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.