Distribution of radionuclides in the guano sediments of Xisha Islands, South China Sea and its implication

Several natural and anthropogenic radionuclides (²¹⁰Pb, ²²⁶Ra and ¹³⁷Cs) in guano-phosphatic coral sediments and pure guano particles collected from Ganquan, Guangjin, Jinqing and Jinyin Islands of the Xisha archipelago, South China Sea, were analyzed. The Constant Initial Concentration (CIC) model and the Constant Rate of Supply (CRS) model were applied for age calculation. The average supply rate of ²¹⁰Pb was 126 Bq m⁻² a⁻¹, very close to the flux of northern hemisphere average (125 Bq m⁻² a⁻¹). The activities of anthropogenic radionuclides in the sediments were very low, indicating that human nuclear tests did not notably impact this region. The main source of radionuclides in the sediments was from atmospheric precipitation, and the organic matter derived from plant and produced by nutrient-rich guano could further enhance them.     

Anthropogenic influence on the water quality in Guanabara Bay, Rio de Janeiro, Brazil

Guanabara Bay is a 384-km² coastal bay with 70% of the population of the metropolitan area of Rio de Janeiro located within its drainage basin. The water quality of the Bay is impacted by domestic and industrial runoff, of which only 15% has been adequately treated. However, based on a 14-year monitoring program, the water quality for most of Guanabara Bay remains acceptable because of intense tidal flushing, and we failed to find a worsening of conditions during the 14-year study. The inner shallow regions of the Bay, the western and northwestern parts, receive most of the drainage from metropolitan Rio de Janeiro. It is here that the water quality is alarmingly poor, characterized by hypertrophic conditions and occasional hypoxic events. Fecal coliform counts in these inner reaches of the Bay are 4–100 times higher than the maximum acceptable count for recreational waters. Hypertrophic conditions prevail in Guanabara Bay, which is characterized by low dissolved oxygen, high biochemical oxygen demand, peaks in fecal coliform, and extremely high chlorophyll-a concentrations, which reflect high quantities of nutrients entering the system. These anthropogenic pressures are a threat to planktonic and benthic communities and are reminiscent of San Francisco Bay 30 years ago. The Guanabara Bay water quality could be returned to pre-1950 conditions, but it would require sufficient political will and economic investment to ensure that at least 80–90% of the domestic and industrial sewage were treated adequately. Electronic Publication     

Long-term investigation of anthropogenic and naturally occurring radionuclides at reference sites in western Sweden

In case of an accidental release of radioactive substances into the environment, it is important to quickly and reliably estimate the radiation dose received by people in the affected area, and to determine the extent of the contamination. Measurements of the extent of the release and the subsequent contamination can be facilitated if there are predetermined reference sampling sites with known background radiation and inventory of radionuclides. Since 1996, 34 reference sites for soil sampling, field gamma, and intensimeter measurements have been established in western Sweden. Time series data for dose rates and radioisotope inventory have been collected at these sites, allowing for the investigation of changes in these parameters over time. The mass activity densities for the uranium and thorium series elements varied approximately between 10 and 50 Bq/kg and between 10 and 40 Bq/kg, respectively. The mass activity density of ⁴⁰K was approximately in the range 300–800 Bq/kg. The radiation exposure due to ¹³⁷Cs was rather small in this area. The dose rates calculated from in situ measurement data showed that the contribution to the total dose rate was almost entirely due to naturally occurring radionuclides. The measured dose rate was about twice as high as the calculated rate, even after subtracting the contribution from cosmic radiation. This may be explained by the fact that intensimeters generally are calibrated to measure the quantity ambient dose equivalent, which should not underestimate the effective dose.     

Natural and anthropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring ⁷Be, ²¹⁰Pb, ⁴⁰K, ²¹⁴Bi, ²¹⁴Pb, ²¹²Pb, ²²⁸Ac and ²⁰⁸Tl and anthropogenic ¹³⁷Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The ²¹²Pb and ²⁰⁸Tl, ²¹⁴Bi and ²¹⁴Pb, ⁷Be and ²¹⁰Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The ⁷Be and ²¹⁰Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the ⁷Be, ²¹⁰Pb, ⁴⁰K and ¹³⁷Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides.     

210Pb as a tool for establishing sediment chronologies: examples of potentials and limitations of conventional dating models

For aquatic sediments, the use of ²¹⁰Pb originating from the decay of atmospheric ²²²Rn is a well-established methodology to estimate sediment ages and sedimentation rates. Traditionally, the measurement of ²¹⁰Pb in soils and sediments involved laborious and time-consuming radiochemical separation procedures. Due to the recent development of advanced planar (‘n-type’) semi-conductors with high efficiencies in the low-energy range which enable the gamma-spectrometric analysis of the 46.5 keV decay line of ²¹⁰Pb, sediment dating using this radionuclide has gained renewed interest.In this contribution, potentials and limitations of the ²¹⁰Pb methodology and of the models used for estimating sediment ages and sedimentation rates are discussed and illustrated by examples of freshwater and marine sediments. Comparison with the use of ¹³⁷Cs shows that the information which may be gained by these two tracers is complementary. As a consequence, both radionuclides should be used in combination for dating of recent sediments. It is shown that for various sedimentation regimes additional information from other sources (e.g. sediment lithology) may be needed to establish a reliable chronology. A strategy for sediment dating using ²¹⁰Pb is recommended.     

Recent Cs deposition in sediments of Admiralty Bay, Antarctica

Cesium-137, radium-226 and lead-210 profiles of a 25 cm sediment core give an indication of recent changes in land-ocean interactions at a polar coastal environment (Admiralty Bay, King George Island, Antarctica). The linear sedimentation accumulation rate at the study site calculated from the unsupported ²¹⁰Pb profile was 6.7 mm/year from 1965 to 2005. A 3.5-fold increase in ¹³⁷Cs concentrations was observed in the top layer of this sediment core. This sharp increase seems to indicate a recent redistribution of fallout radionuclides previously deposited on soil, vegetation and snow. These results imply enhanced land-ocean interactions at this site likely as a result of climate change. Because our results are based on a single core, additional investigations are needed to confirm our observations.     

Modelling the reworking effects of bioturbation on the incorporation of radionuclides into the sediment column: implications for the fate of particle-reactive radionuclides in Irish Sea sediments

A microcosm laboratory experiment was conducted to determine the impact of biological reworking by the ragworm Nereis diversicolor on the redistribution of particle-bound radionuclides deposited at the sediment-water interface. Over the course of the 40-day experiment, as much as 35% of a ¹³⁷Cs-labelled particulate tracer deposited on the sediment surface was redistributed to depths of up to 11 cm by the polychaete. Three different reworking models were employed to model the profiles and quantify the biodiffusion and biotransport coefficients: a gallery-diffuser model, a continuous sub-surface egestion model and a biodiffusion model. Although the biodiffusion coefficients obtained for each model were quite similar, the continuous sub-surface egestion model provided the best fit to the data. The average biodiffusion coefficient, at 1.8 ± 0.9 cm² y⁻¹, is in good agreement with the values quoted by other workers on the bioturbation effects of this polychaete species. The corresponding value for the biotransport coefficient was found to be 0.9 ± 0.4 cm y⁻¹. The effects of non-local mixing were incorporated in a model to describe the temporal evolution of measured ⁹⁹Tc and ⁶⁰Co radionuclide sediment profiles in the eastern Irish Sea, influenced by radioactive waste discharged from the Sellafield reprocessing plant. Reworking conditions in the sediment column were simulated by considering an upper mixed layer, an exponentially decreasing diffusion coefficient, and appropriate biotransport coefficients to account for non-local mixing. The diffusion coefficients calculated from the ⁹⁹Tc and ⁶⁰Co cores were in the range 2-14 cm² y⁻¹, which are consistent with the values found by other workers in the same marine area, while the biotransport coefficients were similar to those obtained for a variety of macrobenthic organisms in controlled laboratories and field studies.     

Inventories of Pu, Cs, and excess Pb in sediments from freshwater and brackish lakes in Rokkasho, Japan, adjacent to a spent nuclear fuel reprocessing plant

We investigated the vertical profiles of ^239+240Pu, ¹³⁷Cs, and excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples obtained from two freshwater lakes and two brackish lakes situated near the first commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan, before the final test of the plant using actual spent nuclear fuel. The inventory of ^239+240Pu in those lakes was larger than that in soil in Rokkasho, which indicated the inflow of ^239+240Pu from the catchment area in addition to direct deposition on the lake surfaces. The ¹³⁷Cs inventory in sediments of the brackish lakes was lower than that in the soil, which showed that part of the ¹³⁷Cs was removed from the sediments by the brackish water or that it was not deposited into the sediments, because of the high solubility of Cs in brackish water. The ¹³⁷Cs inventory in sediments of the freshwater lakes was higher than that of the brackish lakes, and comparable with that in soil except for one core sample out of four. The ^239+240Pu/¹³⁷Cs ratio in freshwater lake sediments was higher than that in soil, and that indicated that part of the ¹³⁷Cs was lost from the sediments. The low inventory of ¹³⁷Cs may be attributable to competition for absorption sites in sediments with ammonium ions formed in the reducing environment which occurs from summer to fall in the sediments. Those data will be used as background data on the artificial radionuclides in the lakes to assess the effect of released radionuclides on their concentrations.     

137Cs in marine samples from the Brazilian southeastern coastal region

The present work presents the results of ¹³⁷Cs concentration in seawater, fish and sediments samples collect in 11 sampling points, crossing the Brazilian Southeastern coastal region, from Vitória (ES) to Santos (SP), on a routine basis from 1997 to 2002. This monitoring program was carried out by the Instituto de Radioproteção e Dosimetria (IRD/CNEN/MCT), in cooperation with the Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM/Brazilian Navy), aiming at determining artificial radionuclides in marine samples. Additionally to the ¹³⁷Cs results, ⁹⁰Sr concentrations in fish samples from 1998 to 2002 are also reported.The ¹³⁷Cs in seawater follows a lognormal distribution, with a geometric mean of 1.8 Bq m^-3 and a geometric standard deviation of 1.4 (n=54), decay corrected to June/2002. For ¹³⁷Cs levels in fish samples a geometric mean of 0.19 Bq kg⁻¹ and a geometric standard deviation of 2.9 (n=39), decay corrected to June/2002, with a range of 0.03 to 1.7 Bq kg⁻¹, were obtained. Based on the ¹³⁷Cs mean concentration in fish as well as in seawater, a transfer factor of 1 × 10² was calculated, which is quite in agreement with the recommended value found in the Safety Report Serie 19.     

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides ²¹⁰Pb and ¹³⁷Cs. The anthropogenic radionuclide, ¹³⁷Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with ²¹⁰Pb geochronology. However, while ¹³⁷Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of ¹³⁷Cs in the southern hemisphere was only 25% that of the north and the low activities of ¹³⁷Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low ¹³⁷Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator.This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding ¹³⁷Cs profiles and ²¹⁰Pb geochronologies. We find that Pu has significant advantages over ¹³⁷Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to ¹³⁷Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the ²³⁸Pu/^239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over ¹³⁷Cs due to its enrichment in bottom sediment relative to ¹³⁷Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.     

Accumulation of Cs in puddle sediments within urban ecosystem

The role of puddle sediments as a final depot of ¹³⁷Cs horizontal migration within the urban landscape is studied using the example of Ekaterinburg city, Russia. Radioactive contamination in the city appeared due to fallout after atmospheric testing of nuclear weapons and nuclear accidents. Contamination density of ¹³⁷Cs in the region was assessed from archive data to be about 5.1 kBq/m², of which the maximum activity concentration (<30 Bq/kg) is associated with the upper 15 cm soil layer. Results of the survey reported here indicate a mean ¹³⁷Cs activity concentration in puddle sediments of 80 Bq/kg, with a maximum value of 540 Bq/kg. It is estimated that horizontal migration has led to about a fourfold concentration of ¹³⁷Cs in puddle sediments.     

Artificial radionuclides in the atmosphere over Lithuania

Measurements of airborne radioactive aerosol concentration were carried out on the basis of 1-3 days samples after the Chernobyl disaster and during the period of 1992-2003. Transport of "hot" particles of different composition resulted in the high activity concentrations of (137)Cs, (238)Pu, (239,240)Pu and (241)Am in the atmosphere in Vilnius at the end of April 1986. The (240)Pu/(239)Pu atom ratio showed clear evidence of non-global plutonium originating from the Chernobyl accident in the atmosphere over Lithuania. The (240)Pu/(239)Pu atom ratio ranged from 0.14 to 0.40 in monthly samples in Vilnius in 1995-2003. An increase in activity concentration of (137)Cs by a factor of 100 (up to 300 microBq/m(3)) was found following forest fires in the Ukraine and Belarus. However, no transport of the Chernobyl plutonium was observed and the (240)Pu/(239)Pu atom ratio in samples collected during the forest fires was found to be 0.229 and 0.185, respectively. The exponential decrease in the (240)Pu/(239)Pu atom ratio from 0.30 to 0.19 (mean values) was observed in 1995-2003.     

Determining floodplain sedimentation rates using Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout ¹³⁷Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of ¹³⁷Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total ¹³⁷Cs inventories calculated from the detailed profile data. Information on the rates of ¹³⁷Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of ¹³⁷Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for ¹³⁷Cs being known and without having to assume that ¹³⁷Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total ¹³⁷Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, ¹³⁷Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.     

Recent changes in Red Lake (Romania) sedimentation rate determined from depth profiles of Pb and Cs radioisotopes

This work presents a first estimation of the sedimentation rate for the Red Lake (Romania). The sediment accumulation rates were determined by two well-known methods for recent sediment dating: ²¹⁰Pb and ¹³⁷Cs methods. Both techniques implied used the gamma emission of the above-mentioned radionuclides. The ²¹⁰Pb and ¹³⁷Cs concentrations in the sediment were measured using a gamma spectrometer with a HpGe detector, Gamma-X type. Activities ranging from 41 ± 7 to 135 ± 34 Bq/kg were found for ²¹⁰Pb and from 3 ± 0.5 to 1054 ± 150 Bq/kg for ¹³⁷Cs. The sediment profile indicates acceleration in sedimentation rate in the last 18 years. Thus, the sedimentation process for the Red Lake can be divided in two periods, the last 18 years, and respectively, the period before that. Using the Constant Rate of ²¹⁰Pb Supply method values between 0.18 ± 0.04 and 1.85 ± 0.5 g/cm² year (0.32 ± 0.08 and 2.83 ± 0.7 cm/year) were obtained. Considering both periods, an average sedimentation rate of 0.87 ± 0.17 g/cm² year (1.17 cm/year) was calculated. Considering an average depth of 5.41 m for the lake and the sedimentation rate estimated for the last 18 years, it could be estimated that the lake will disappear in 195 years.     

Deposition of artificial radionuclides from atmospheric Nuclear Weapon Tests estimated by soil inventories in French areas low-impacted by Chernobyl

Soil inventories of anthropogenic radionuclides were investigated in altitudinal transects in 2 French regions, Savoie and Montagne Noire. Rain was negligible in these 2 areas the days after the Chernobyl accident. Thus anthropogenic radionuclides are coming hypothetically only from Global Fallout following Atmospheric Nuclear Weapon Tests. This is confirmed by the isotopic signatures (²³⁸Pu/^239+240Pu; ¹³⁷Cs/^239+240Pu; and ²⁴¹Am/^239+240Pu) close to Global Fallout value. In Savoie, a peat core age-dated by ²¹⁰Pb_ex confirmed that the main part of deposition of anthropogenic radionuclides occurred during the late sixties and the early seventies. In agreement with previous studies, the anthropogenic radionuclide inventories are well correlated with the annual precipitations. However, this is the first time that a study investigates such a large panel of annual precipitation and therefore of anthropogenic radionuclide deposition. It seems that at high-altitude sites, deposition of artificial radionuclides was higher possibly due to orographic precipitations.     

Recent atmospheric lead deposition recorded in an ombrotrophic peat bog of Great Hinggan Mountains, Northeast China, from Pb and Cs dating

Radioactive markers are useful in dating lead deposition patterns from industrialization in peat archive. Peat cores were collected in an ombrotrophic peat bog in the Great Hinggan Mountains in Northeast China in September 2008 and dated using ²¹⁰Pb and ¹³⁷Cs radiometric techniques. The mosses in both cores were examined systematically for dry bulk density, water and ash content. Lead also was measured using atomic emission spectroscopy with inductively coupled plasma (ICP-AES). Both patterned peat profiles were preserved well without evident anthropogenic disturbance. Unsupported ²¹⁰Pb and ¹³⁷Cs decreased with the depth in both of the two sample cores. The ²¹⁰Pb chronologies were established using the constant rate of supply model (CRS) and are in good agreement with the ¹³⁷Cs time marker. Recent atmospheric ²¹⁰Pb flux in Great Hinggan Mountains peat bog was estimated to be 337 Bq m⁻² y⁻¹, which is consistent with published data for the region. Lead deposition rate in this region was also derived from these two peat cores and ranged from 24.6 to 55.8 mg m⁻² y⁻¹ with a range of Pb concentration of 14-262 μg g⁻¹. The Pb deposition patterns were consistent with increasing industrialization over the last 135-170 y, with a peak of production and coal burning in the last 50 y in Northeast China. This work presents a first estimation of atmospheric Pb deposition rate in peatlands in China and suggests an increasing trend of environmental pollution due to anthropogenic contaminants in the atmosphere. More attention should be paid to current local pollution problems, and society should take actions to seek a balance between economic development and environmental protection.     

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

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

Time-dependency of the Cs contamination of wild boar from a region in Southern Germany in the years 1998 to 2008

Following the Chernobyl accident, ¹³⁷Cs contamination levels of wild boar in some districts of Southern Germany are still exceeding thousands of Bq kg⁻¹. While the long term ¹³⁷Cs concentration in forest plants, mushrooms, and roe deer meat has decreased significantly, for wild boar it has remained constant during the last decade. Between 1998 and 2008, we analysed the muscle meat of 656 wild boars shot in the district (“Landkreis”) Ravensburg. The ¹³⁷Cs activity concentration showed considerable variability from less than 5 up to 8266 Bq kg⁻¹ and it followed a seasonal pattern, which is attributed to changes in dietary habits, fodder availability, meteorological conditions and specific behaviour of ¹³⁷Cs in wild boar organism. T_ag values for wild boars from the district Ravensburg varied from 0.008 to 0.062 m² kg⁻¹ during 2000–2008.     

Pu/Cs ratios in the water column of the North Pacific: a proxy of biogeochemical processes

Anthropogenic radionuclides in seawater have been used as transient tracers of processes in the marine environment. Especially, plutonium in seawater is considered to be a valuable tracer of biogeochemical processes due to its particle-reactive properties. However, its behavior in the ocean is also affected by physical processes such as advection, mixing and diffusion. Here we introduce Pu/¹³⁷Cs ratio as a proxy of biogeochemical processes and discuss its trends in the water column of the North Pacific Ocean. We observed that the ^239,240Pu/¹³⁷Cs ratio in seawater exponentially increased with increasing depth (depth range: 100–1000 m). This finding suggests that the profiles of the ^239,240Pu/¹³⁷Cs ratios in shallower waters directly reflect biogeochemical processes in the water column. A half-regeneration depth deduced from the curve fitting the observed data, showed latitudinal and longitudinal distributions, also related to biogeochemical processes in the water column.     

Comparative trends and seasonal variation of ⁷Be, ²¹⁰Pb and ¹³⁷Cs at two altitude sites in the central part of France

The atmospheric concentrations of ¹³⁷Cs, ²¹⁰Pb, and ⁷Be were measured over a three-year period at two research stations located less than 12 km apart and at different altitudes (puy de Dôme, 1465 m a.s.l. and Opme, 660 m a.s.l., France). Seasonal trends in all radionuclides were observed at both stations, with high concentration measured during the summer and low concentrations during the winter. The ²¹⁰Pb concentrations at both stations were similar to each other. Higher concentrations of both ⁷Be and ¹³⁷Cs were measured at puy de Dôme than at Opme. These observations can be explained by the stratospheric and upper tropospheric sources of ⁷Be and the long-range transportation of ¹³⁷Cs at high altitudes. Air mass origins during sampling periods were classified into several groups by their route to the stations (marine, marine modified, continental and mediterranean). We observed that ⁷Be concentrations were constant regardless of the air mass origins, unlike ¹³⁷Cs and ²¹⁰Pb concentrations that increased when influenced by continental air masses. Higher ⁷Be concentrations were observed when air masses were arriving from the upper troposphere than from the boundary layer, the opposite was observed for ¹³⁷Cs. The temporal trend in concentrations of ⁷Be shows good agreement with previous modelling studies suggesting that there is a good understanding of its sources and the atmospheric vertical mixing of this radionuclide. The sources and mixing of ²¹⁰Pb, however, seem to be more complex than it appeared to be in previous modelling studies.