Determination of 137Cs activities in surface sediments and derived sediment accumulation rates in Thessaloniki Gulf, Greece

Surficial and core samples collected from the eastern Thessaloniki Gulf, located in the NW Aegean Sea, were analyzed for their sedimentation rate and inventories of ¹³⁷Cs and ²¹⁰Pb. The study of the spatial radionuclide dispersion in the specific region is essential for the assessment of marine pollution levels. The sedimentation rates were calculated from the vertical distribution of ¹³⁷Cs and excess ²¹⁰Pb in the sediment cores. The spatial distribution of ¹³⁷Cs was studied with respect to sediment characteristics such as the grain size of the sample and the organic carbon content. The activity concentrations were measured by means of gamma ray spectrometry using HPGe detector for ¹³⁷Cs and gross alpha counting using alpha counter for ²¹⁰Pb. The average sedimentation rate along the sediment cores is characterized by a consistent pattern and varies from 0.18?±?0.02 to 0.22?±?0.03?cm?year^?1. The ¹³⁷Cs inventories varied from 205?±?15 to 602?±?39?Bq?m^?2, while the ²¹⁰Pb inventories of the studied cores exhibited average value of 140?±?9?Bq?m^?2. Elevated ¹³⁷Cs activities were observed compared to certain Mediterranean marine areas; however, they were lower than the reported values in the Black Sea.     

Estimate of the density of global fallout of cesium-137 according to the data of its content in closed geochemical arenas of southwestern Siberia

The density of global radioactive contamination was the most reliable estimated in marine regions and less accurate for intracontinental areas with semi-arid and arid climatic conditions. This work presents the results of using a new method developed for estimating the density of global radioactive contamination based on the calculation of ¹³⁷Cs concentration in closed lake catchments. An average density of of ¹³⁷Cs contamination in the model closed lake catchments of southwestern Siberian steppe landscapes is 0.80 ± 0.24 kBq m^–2 that is 2–3 times lower than the levels calculated on the basis of the published data.     

A model of radionuclide transfer by groundwater on the territory of the Russian Research Centre Kurchatov Institute

The convective transfer of ¹³⁷Cs and ⁹⁰Sr by groundwater on the territory of the Russian Research Centre Kurchatov Institute (RRCKI) was modeled. Geological data on the RRCKI site and possible sources of radionuclides show that the uppermost aquifer, composed of Quaternary sediments, is the most probable region of spreading of radioactive contamination. Since the lateral migration of radionuclides is predominant, a 2D horizontal model was used for the forecasting of spreading of radioactive contaminants in the subsurface medium. Transient or long-term repositories of radioactive materials at the RRCKI site (concentrated sources) and aquifer rocks contaminated in the course of removal of radionuclides from these repositories (distributed source) are responsible for groundwater pollution. The initial ¹³⁷Cs and ⁹⁰Sr distributions used in the forecasting of radionuclide migration were determined from their contents in core samples taken from wells drilled in contaminated areas of the RRCKI site. The zone of radionuclide migration is limited by poorly permeable moraine loam from below and by the water table from above. To determine the upper and lower boundaries, these surfaces were mapped in plan view. The data of meteorological observations over a long period were used to map the intensity of precipitation in the studied territory. The density of rocks in the uppermost aquifer and partition coefficients of radionuclides between rocks and groundwater were estimated from the data of laboratory examination of the core samples. The available data on the permeability of rock samples and the results of test pumping out of some wells were involved in the consideration. The results obtained and the data on the water table allowed us to define a gauge problem for determining the distribution of the filtration coefficient in the uppermost aquifer. This problem was solved taking the intensity of precipitation into account. The properties of the uppermost aquifer and the initial radionuclide distribution therein were used as initial data for modeling ¹³⁷Cs and ⁹⁰Sr migration on the territory of the RRCKI over 50 years.     

High-resolution historical records from Pettaquamscutt River basin sediments: 1. Pb and varve chronologies validate record of Cs released by the Chernobyl accident

Cesium-137 derived from the explosion of the Chernobyl reactor in 1986 was preserved in anoxic sediments from a coastal environment in southern Rhode Island. Although the radioactive plume was detected in surface air samples at several locations in the United States, this is the first known record of a Chernobyl ¹³⁷Cs peak in sediments from North America. The inventory of Chernobyl ¹³⁷Cs that was preserved in the Pettaquamscutt River is small compared to European counterparts and should only be detectable for the next 15-20 yr. However, the presence of two ¹³⁷Cs peaks (1963 and 1987) identifies a well-dated segment of the sediment column that could be exploited in understanding the decomposition and preservation of terrestrial and aquatic organic matter. Different methods for calculating the ²¹⁰Pb chronology were also evaluated in this study and checked against independent varve counting. The end result is a detailed chronology of a site well suited for reconstruction of historical records of environmental change.     

Comparative 210Pb, 137Cs,and pollen geochronologies of sediments from Lakes Ontario and Erie

The distribution of ²¹⁰Pb, ¹³⁷Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with ²¹⁰Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with ¹³⁷Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of ¹³⁷Cs and ²¹⁰Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on ²¹⁰Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of ²¹⁰Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both ²¹⁰Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated.     

Movement of radiocaesium fallout released by the 2011 Fukushima nuclear accident

The moment magnitude (M _w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of ¹³⁴Cs and ¹³⁷Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of ¹³⁴Cs and ¹³⁷Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs.     

Plutonium, 241Am and 137Cs ratios,inventories and vertical profiles in Washington and Oregon continental shelf sediments

Continental shelf sediments from nine locations off Washington and Oregon have ^239,240Pu inventories which average 8.0 ± 2.6 mCi/km². The Columbia River and seawaters advecting over the shelf supply Pu which is removed to underlying sediments, principally through scavenging by inorganic paniculate matter. Mass balance calculations argue that less than 20 percent of the advected Pu need be scavenged from the water column to balance river input and total shelf sediment inventories. The percentage of the Pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment/water distribution coefficients.No marked separation of Pu from ¹³⁷Cs is observed with depth in Pacific shelf sediments as has been reported in Atlantic coastal sediments. This interocean distinctness can be explained by differences in particle mixing and downward diffusion of Cs in sediments of varying porosities. The transuranic inventories and Pu/Cs ratios in the Pacific sediments do not support the hypothesis of Livingston and Bowen that Pu is remobilized within the sediment column by ‘complexone’ formation with (principally) organic substances.Excess ²¹⁰Pb/^239,240Pu inventory ratios in eight representative cores from the Washington shelf average 100 ± 19, even though absolute values of both inventories vary by much larger factors. This reasonably constant ratio, for a given water depth, permits estimation of total Pu inventories and prediction of sites of unusual Pu accumulation from data on the more easily measured natural radionuclide.     

长江河口水下三角洲137Cs地球化学分布特征

文章通过对长江口水下三角洲采集的10个柱状样放射性核素¹³⁷Cs的分析可以得知,长江口水下三角洲¹³⁷Cs剖面中均存在清晰的最大蓄积峰,其峰值比活度介于5.68±1.03～21.74±1.39Bq/kg之间,平均值为14.11±1.10Bq/kg,最大蓄积峰所处的深度为55～117cm。剖面中¹³⁷Cs最大蓄积峰应该与1963年的¹³⁷Cs散落沉降相对应。长江口水下三角洲的表层沉积物中的¹³⁷Cs比活度范围介于0～9.19±1.12Bq/kg之间,并且与长江流域其他地区的表层¹³⁷Cs比活度相一致。长江口水下三角洲可探测到的¹³⁷Cs比活度的最大深度范围在88～160cm的范围内变化,¹³⁷Cs蓄积总量为2361.30±174.38～17714.94±262.14Bq/m²,平均值为9664.97±100.05Bq/m²,¹³⁷Cs比活度的最大深度及¹³⁷Cs蓄积总量均表现出从岸向海逐渐增加的趋势。实测的¹³⁷Cs总量均大于长江流域的¹³⁷Cs背景值,说明了长江口水下三角洲的¹³⁷Cs蓄积既有大气散落直接沉降的来源,又有流域侵蚀带来的¹³⁷Cs输入,并且主要以后者为主。通过放射性核素示踪模型分析长江口水下三角洲¹³⁷Cs散落蓄积特征可以得知,长江口水下三角洲¹³⁷Cs的蓄积以长江流域来源为主,说明了放射性核素¹³⁷Cs在长江口水下三角洲沉积物中的蓄积主要受流域侵蚀因素的影响。     

Prediction of solid/liquid distribution coefficients of radiocaesium in soils and sediments. Part three: a quantitative test of a KID predictive equation

An equation is presented for predicting solid/liquid distribution coefficients of radiocaesium on soils and sediments (freshwater and marine). The equation is based on the value of the radiocaesium interception potential of the illitic frayed edge sites of the system and liquid phase composition (K, NH₄ and Na). The predictive potential of the equation is tested for some 130 combinations of soil/sediment and water composition covering a three-order-of-magnitude range in K_D^137_Cs values. On average, experimental K_D^137_Cs values exceed predicted values by a factor of 1.62 ± 0.75.     

137Cs reference site characteristics in Hong Kong — Some considerations

The distribution of ¹³⁷Cs is being assessed at input reference sites in Hong Kong. This work suggests that, in certain landscapes, difficulties in identifying potential reference sites and subsequently confirming site stability exert some constraints on ¹³⁷Cs measurement programmes. While the value of guidelines on site and sample selection has been reaffirmed, concern has emerged about the vertical distributions that may be taken to indicate reference site stability.The decline of ¹³⁷Cs concentrations down a reference soil profile are often reported to be exponential. Recently, a more complex profile with depleted ¹³⁷Cs totals at the soil surface has been reported and discussed. Thus there is no clear standard for a reference profile, though the profile has been the only empirical control on a reference site's suitability after selection.This study presents the depth distribution and spatial variation of ¹³⁷Cs areal activities at three reference sites in Hong Kong. The three sites have different spatial variability and different depth distributions, and serve to illustrate the difficulty of using vertical depth distributions as a confirmation of site stability. One possible independent check is the expected ¹³⁷Cs total from rainfall records; another is numerical modelling of the predicted profile given the physical and chemical controls on soil ¹³⁷Cs in reference site profiles.     

Reversible ion-exchange fixation of cesium-137 leading to mobilization from reservoir sediments

The radioactive fission product, ¹³⁷Cs, has been observed to mobilize from bottom sediments of two South Carolina reservoirs during summer thermal stratification and hypolimnetic anoxia. Mobilization is attributed to ion-exchange displacement of ¹³⁷Cs from sediments by cations such as NH⁺₄, Fe⁺² and Mn⁺² released under anaerobic conditions.Three types of ¹³⁷Cs binding sites to sediment clay minerals are identified: 1) surface and planar sites from which ¹³⁷Cs is generally exchangeable by all cations studied (Na⁺, NH⁺₄, H⁺, Cs⁺, Ca⁺², Mg⁺², Fe⁺², and Mn⁺²); 2) wedge sites where ¹³⁷Cs exchange is sterically limited to cations of similar size and charge (NH⁺₄, Cs⁺, K⁺, and perhaps H₃O⁺); 3) interlayer sites from which ¹³⁷Cs is not readily exchanged. More than 15 years after final ¹³⁷Cs inputs, the reservoir sediments we studied showed the following percentage distribution of sites: 2 to 9% surface sites, 6 to 13% wedge sites, and 78 to 85% interlayer sites. In contrast, lake and stream sediments near Oak Ridge, Tennessee receiving ¹³⁷Cs inputs more than 20 years earlier had greater than 99% of their ¹³⁷Cs associated with non-exchangeable interlayer sites. The difference is attributed to the paucity in the South Carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites. Such interlayer deficient clays are dominant in the Atlantic and Gulf coastal plains of the United States and elsewhere. This suggests that ¹³⁷Cs will be physically and chemically more mobile in such areas as well as more biologically available. Mobility will be enhanced in regimes where cation inputs favoring ¹³⁷Cs exchange occur. Subsurface waste disposal sites where anaerobic conditions develop with NH⁺₄ production and Fe⁺² and Mn⁺² release might be such a regime.     

Bestimmung sehr kleiner Verteilungskoeffizienten von Cs,Na und Ba zwischen Lösung und KCl-Einkristallen mit Hilfe radioaktiver Isotope

Distribution of Cs, Na, and Ba between great monocrystals of KCl and water solution was investigated. Impurity was either labelled by long-lived radioactive isotopes or was activated after growth of the crystals by neutrons in a nuclear reactor. No influence on partition coefficients was caused by using radioactive tracers, e.g. due to raised inclusion of mother liquor. Between impurity concentrations from 3·10^–4 to 10^–1 in the solution the partition coefficients were nearly constant and about 10^–3 for Na, about 10^–4 for Cs, and <5·10^–5 for Ba in KCl at temperatures of 40° C. If different impurity ions were built in simultaneously, the partition coefficients were independent of composition of solution. In case of Cs in KCl capture of Cs increased with increasing temperature.

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Meinem hoehverehrten Lehrer, Herrn Prof. Dr. W. von Engelhart, danke ieh für die freundliehe Überlassung des interessanten Themas. Für die stete Förderung und die zahlreichen fruehtbaren Diskussionen und Anregungen bin ich ihm und Herrn Dr. H. Puchelt zu großem Dank verpflichtet.Dem Bundesnlinisterium für wissensehaftliehe Forsehung danke ieh ffir die großzügige Unterstützung der Arbeit.Herrn Prof. Dr. W. Seelmann-Eggebert und Herrn Dr. V. Schneider vom Kernforsehungszentrum Karlsruhe und Herrn Dr. Bartel von der Kernforsehungsanlage Jülich danke ich für die Unterstützung bei der Neutronenaktivierung und Herrn Dr. J. Ottemann vom Mineralogischen Instigut der Universität Heidelberg für die Untersuchung mit der Elektronenmikrosonde.     

Clinopyroxene-matrix partitioning of K,Rb, Cs,Sr and Ba

Extremely pure samples of clinopyroxene phenocrysts from two volcanic rocks have been analyzed for K, Rb, Cs, Sr and Ba. In conjunction with matrix concentrations, partition coefficients are obtained which are in the range 0.001–0.004 for K, Rb, Cs and Ba. These values are lower than those in the literature by factors of 6–100 but are in good agreement with values determined experimentally at pressures of 15–30 kb by Shimizu (Geochim. Cosmochim. Acta38, 1974). Values for partition coefficients measured on separates of impure or cloudy pyroxenes from these same rocks were higher and similar to those in the literature. We suggest this effect is related to ‘trapping,’ during crystal growth, of liquid which is enriched in the larger ions (such as Rb and Cs) due to lack of diffusion equilibrium in the liquid. Partition coefficient values for olivine and plagioclase from one of these same rocks were also determined.     

Post‐deposition diffusion of 137Cs in lake sediment: Implications for radiocaesium dating

Peak activities of radiocaesium (¹³⁷Cs) in lake sediments have frequently been used to infer the ages of sediments deposited in the 1960s (¹³⁷Cs derived from nuclear bomb testing) or in 1986 (Chernobyl derived ¹³⁷Cs). Records of the vertical distribution of ¹³⁷Cs in sediments can thus be used to provide accurate dates for a critical period in which palaeoecological reconstructions often overlap contemporary monitoring data. However, knowledge regarding how the distribution of ¹³⁷Cs in sediments is affected by post‐depositional processes is limited to interpretations based on the ¹³⁷Cs distribution in sediments sampled at a single given date. This study assesses the extent to which the ¹³⁷Cs record in annually laminated (varved) lake sediments is affected by post‐depositional diffusion, using 11 archived sediment cores sampled between 1986 and 2007. The sediment record reveals how Chernobyl ¹³⁷Cs incorporated into the 1986 varve diffused downwards in the core at a decreasing rate over time, whereas the surface sediments continued to receive inputs of ¹³⁷Cs mobilized from the catchment soils or lake margin. In spite of these processes, all cores post‐dating the Chernobyl accident had a clear and well‐resolved peak in the 1986 varve, justifying the use of this feature as a fixed chronostratigraphic feature. Because of the very high levels of Chernobyl fallout at this site, downwards migration of Chernobyl ¹³⁷Cs has, however, completely masked the nuclear weapons ¹³⁷Cs fallout peak that had been clearly preserved in the 1964 varve of a pre‐Chernobyl core sampled just three weeks before the Chernobyl accident. In consequence, the weapons fallout marker is likely to be of little use for determining ¹³⁷Cs dates in areas strongly affected by high levels of Chernobyl fallout.     

Ways of investigating radionuclide migration processes in the lithosphere and hydrosphere

In Russia, until recently, it was considered that groundwater was protected from surface radioactive contamination by soil and rocks in the zone aeration. Groundwater was not a subject of radiation control. The accident at the Chernobyl Nuclear Power Plant showed, however, that groundwater is vulnerable to radioactive contamination. In this connection, the vulnerability of groundwater to and the problems of protecting groundwater from radioactive contamination became urgent. The assessment of natural protection of groundwater from radioactive contamination is now considered a top priority. The zone of aeration is generally considered to be the zone separating groundwater from surface contamination. In respect to radioactive contamination, soils that may fix a large quantity of radionuclides serve as a protection zone of a higher order. The mapping of protectibility was done for each radionuclide taking into consideration the specific structure of the flow medium and migration properties of a radionuclide.⁹⁰Sr and¹³⁷Cs have different mechanisms of transport; convective transport is characteristic of the former and diffusive transfer of the latter. This is conditioned by different physico-chemical properties of the radionuclides and principally by their sorption capacities. The coefficient of distribution of⁹⁰Sr is in many times less than the coefficient of distribution of¹³⁷Cs. The environmental protection problem in regions with nuclear power plants and in areas subjected to radioactive contamination may be solved using a monitoring, system including interrelated systems of observation and prediction of the lithosphere and the hydrosphere. The problem of mathematical modeling of migration processes is related to the complexities of modeling the processes of flow, mass transfer, and the accompanying physicochemical processes in zones of full and partial saturation, as well as difficulties in mathematical calculations.     

A geochemical investigation on overbank sediments in the Inari area,northern Finnish Lapland

Four overbank sediment profiles in the Inari area of northern Finnish Lapland were studied in detail by the collection of samples at one-centimetre intervals. The sample sites are situated along a line from northeast to southwest away from the industrial centre at Nikel in the Kola Peninsula. Total, aqua regia and ammonium acetate leachable concentrations were determined for more than 30 elements to study their vertical distribution, and to evaluate the results of the three analytical methods in environmental studies. Radioisotopes of ¹³⁷Cs and ¹³⁴Cs were measured on 34 samples to assess radioactive fallout. Radiometrie ¹⁴C-dating was determined in one profile to estimate the rate of sedimentation. Grain-size analysis was carried out for calculating the field weight to produce a minimum of 500 g of minus 125 μm material, required for analysis and storage, and to estimate the clay content, which affects leachable element concentrations, when partial or near-total analytical methods are used.It was found that the concentration of studied elements varies with depth. Airborne Ni and S contamination from the smelting plants in the Kola Peninsula was weakly detectable by ammonium acetate leachable contents.¹³⁷Cs and ¹³⁴ Cs isotope concentrations, originating from the nuclear weapon tests on the island of Novaya Zemlya and/or from the Chernobyl nuclear power plant accident, were clearly detectable in the topmost layer of overbank sediments. ¹⁴C dating has given a time-lag of 5000 years for the deposition of an overbank sediment sequence of 120 cm thickness. Thus, a very slow deposition rate of overbank sediments in northern Finnish Lapland is indicated.It is concluded that grain-size analysis and radiometric dating are necessary for a full interpretation of the geochemistry of overbank sediment sequences, and the selection of leaching methods should be done according to the character of the assumed contamination.     

Natural decrease of the intensity level of artificial radioactive isotopes in the Barents Sea

The results of radioecological investigations carried out within the framework of the Russian-Finnish high-latitude expedition in 2007 are presented. The characteristics of the present-day accumulation level of the significant radioecological isotopes ¹³⁷Cs, ⁹⁰Sr and ^239,240Pu in the Barents Sea are described. The comparative analysis is performed for the radiation pollution of the environment in the 1980s and 1990s and in the first decade of the 21st century. Natural purification processes in the marine environment are the main factors of the decrease in the intensity level of artificial radioactive isotopes. These processes include repeated dilution, nuclear decay, occlusion by sediments and suspended solid material, and accumulation by aquatic inhabitants. A stable decreasing trend is observed for the intensity level of artificial radioactive isotopes in the Barents Sea.     

Geochemistry of heavy metals and sedimentation rate in a bay adjacent to the Caspian Sea

In the present investigation down core variations of heavy metals such as; Zn, Ni, Co, Mn, Fe and Al in a sediment core from Bay of Gorgan adjacent to the Caspian Sea was studied. Inter-relationship amongst various parameters was brought out through correlation coefficients and cluster analysis. The results of present study reveals that Zn, Ni, Co and Mn possess both lithogenous and non-lithogenous sources. The increasing trend of Al towards top of sediment core is indicative higher erosion in the recent years. Interestingly, concentration of all studied metals increases toward core top (except for Fe) that might be indicative of influence of man’s activities residing in catchment area of Gorgan Bay and also oil exploration in the Caspian Sea. Further, ²¹⁰Pb and ¹³⁷Cs techniques were used to find out rate of sedimentation. The result of dating is indicative of sedimentation rate between 1.4 to 2.45 mm/yr. based on ²¹⁰Pb and ¹³⁷Cs activities respectively.     

Results of Marine Radioecological Study of Fjords of Western Spitsbergen

The patterns of the distribution of technogenic radionuclides ¹³⁷Cs and ⁹⁰Sr in the water mass and bottom deposits of three fjords of Western Spitsbergen (Isfjorden and its arms Grønfjorden and Billefjorden) were studied. The hydrological processes affecting migration of radionuclides in these water bodies were described. It was shown that the ice sheet of the archipelago that accumulates atmospheric precipitation is a source of radioactive contamination of the marine environment of the coast. Technogenic isotopes were accumulated during nuclear weapon testing in the second half of the twentieth century. The current climatic changes strengthen the role of glaciers in the contamination of arctic seas. It was noted that extrema of the ¹³⁷Cs and ⁹⁰Sr specific activity is mainly concentrated in the areas of glacier runoff discharge.

     

Annual cycle of radionuclide contamination on tide-washed pasture in the Mersey Estuary, NW England

The radionuclide burden of vegetation comprising a tide-washed pasture at Ince Marsh in the Mersey Estuary, U.K., derives mainly from adhered external particulates originating as suspended sediments in estuarine water. Radionuclide concentrations are dominated by the growth cycle of the vegetation, with the highest winter levels of contamination activity an order of magnitude greater than the lowest levels in mid-summer. A secondary effect due to sediment transfer during periods of severe flooding produces subsidiary features on this dominant seasonal profile. Radionuclide concentrations on vegetation are in the range¹³⁷Cs=8–191,¹³⁴Cs=0.3–0.9,²⁴¹Am=0.6–46,²³⁸Pu=0.1–1.5, and^239/240Pu=0.8–44 Bq kg⁻¹. These ranges reflect the relative concentrations of radionuclides in estuarine sediment (¹³⁷Cs=615,²⁴¹Am=202, and^239/240Pu=104 Bq kg⁻¹) rather than the values in filtered estuary water (¹³⁷Cs=0.4,²⁴¹Am=0.001, and^239/240Pu=0.001 Bq 1⁻¹). Median K_d values for these radionuclide species are Cs=1,400, Am=200,000, and Pu=80,000 1 kg⁻¹).