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.     

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.     

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.     

Variations of organic carbon stock in reclaimed estuarine soils (Villaviciosa estuary, NW Spain)

A study was carried out in the Villaviciosa Estuary (Asturias, NW Spain) to determine the effects of polderization on soil properties and soil organic carbon content. The results showed that the polderized soils were more acidic and contained less carbonates and a higher soil organic carbon (SOC) content than the natural soils. The organic carbon stock in the reclaimed soils ranged from 83.2 to 91.8 t ha(-1), whereas in natural soils was approximately 43.7 t ha(-1). The degree of humification of the surface humic acids also indicated that the stability and degree of decomposition of the organic matter was higher in the reclaimed soils than in natural soils.     

Spatial and temporal variations of plutonium isotopes (238Pu and 239,240Pu) in sediments off the Rhone River mouth (NW Mediterranean)

The dispersion and fate of the Rhone River inputs to the Gulf of Lions (Northwestern Mediterranean Sea) have been studied through the spatial and temporal distributions of plutonium isotopes in continental shelf sediments. Plutonium isotopes ((238)Pu and (239,240)Pu) are appropriate tracers to follow the dispersion of particulate matter due both to their high affinity for particles and their long half-lives. In the Rhone River valley, plutonium isotopes originate from both the weathering of the catchment basin contaminated by global atmospheric fallout, and the liquid effluents released from the Marcoule reprocessing plant since 1961. This work presents a first detailed study on (238)Pu and (239,240)Pu distributions in sediments from the Rhone prodelta to the adjacent continental shelf, since the decommissioning of Marcoule in 1997. The vertical distribution of Pu isotopes has been analysed in a 4.75 m long core sampled in 2001 at the Rhone mouth. Despite this length, plutonium is found at the last 10 cm, manifesting the high sedimentation rate of the prodeltaic area and its ability for trapping fine-grained sediments and associated contaminants. The highest (238)Pu and (239,240)Pu concentrations reached 1.26 and 5.97 Bq kg(-1) respectively and were found within the layer 280-290 cm. The (238)Pu/(239,240)Pu activity ratios (AR) demonstrated an efficient and huge trapping of the Pu isotopes derived from Marcoule. The fresh sediments, located on the top of the core, show lower plutonium activity concentrations and lower (238)Pu/(239,240)Pu ratios. This decrease is in close relation with the shut down of the Marcoule reprocessing plant in 1997. In 2001, plutonium isotopes were also analysed in 21 surface sediments located offshore and concentrations ranged from 0.03 to 0.17 Bq kg(-1) for (238)Pu and from 0.33 to 1.72 Bq kg(-1) for (239,240)Pu. The (238)Pu/(239,240)Pu AR ranged from 0.24 close to the river mouth to 0.06 southwards, indicating the decreasing influence of the Marcoule releases (global fallout AR 0.03-0.05 and Marcoule AR 0.30). This is in good agreement with the main direction spread of the Rhone River plume and the bottom current. This dataset has been compared to those obtained in the same area in 1984 and 1990 in order to follow the time trend in Pu concentrations. This comparison highlights the decrease with time in plutonium concentrations close to the Rhone River mouth, but further away this reduction is not so evident.     

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.     

Background arsenic concentrations in Southeastern Spanish soils

The arsenic content in the province of Granada (SE Spain) was quantified, based on 93 soils at two different depths and their corresponding parent materials. The arsenic concentrations fit a log-normal distribution. Four different statistical procedures to estimate the arsenic background range in the region were tested. Upper background limits clearly exceeded limits reported for natural soils when based on the Tukey box plot or means and standard deviations of the dataset (M+/-2sdev) or of the calculated distribution function (Mf+/-2sigma) but not when based on median values (Md+/-2MAD). The relative cumulative frequency curve not only adequately estimates the background range but also delivers a clear and detailed visualisation of the data distribution and identifies subpopulations with specific background ranges related to combinations of parent materials and degree of soil development.     

Mineralization rate of eroded organic C in Andosols of the Canary Islands

The aim of this paper is to determine the biological dynamism of the organic C forms bonded to soil particles mobilized by water erosion in Andosols of the Canary Islands, to evaluate their susceptibility towards mineralization processes and the role of sediments as sources or sinks of atmospheric CO(2) in these soils. The study was carried out in Tenerife (Canary Islands) on three 200 m(2) experimental plots of the RESEL Programme on silic Andosols under forest, 3 years after being subjected to clear-cutting. Eroded sediments were collected for analysis from five significant winter rainfall episodes. For each event, samples of surface (0-5 cm) soil in situ were also collected. CO(2)-C was measured by incubation in all the samples, as well as microbial biomass-linked C. The results obtained show an enrichment in the eroded sediments of microbial biomass (7.5+/-1.6 g kg(-1) vs. 3.8+/-1.5 g kg(-1)) and of potentially mineralizable C (1419 mg CO(2)-C kg(-1) vs. 386 mg CO(2)-C kg(-1)). In addition, there was twice as much mineralization of C compounds in eroded sediments as in the soil surface horizon.     

Radiocaesium (137Cs) in marine mammals from Svalbard, the Barents Sea and the North Greenland Sea

Specific activities of the anthropogenic radionuclide, 137Cs, were determined in marine mammals from Svalbard and the Barents and North Greenland Seas. Muscle samples were collected from 12 polar bears, 15 ringed seals, 10 hooded seals, 7 bearded seals, 14 harp seals, one walrus, one white whale and one blue whale in the period 2000-2003. The mean concentrations (+/-SD) of 137Cs were: 0.72+/-0.62 Bq/kg wet weight (w.w.) for polar bears; 0.49+/-0.07 Bq/kg w.w. for ringed seals; 0.25+/-0.10 Bq/kg w.w. for hooded seals; 0.22+/-0.11 Bq/kg w.w. for bearded seals; 0.36+/-0.13 Bq/kg w.w. for harp seals; 0.67 Bq/kg w.w. for the white whale sample; 0.24 Bq/kg w.w. for the blue whale; and below detection limit for the walrus. Significant differences in 137Cs specific activities between some of the species were found. Ringed seals had higher specific activities than the other seal species in the study. Bearded seals and hooded seals had similar values, which were both significantly lower than the harp seal values. The results in the present study are consistent with previous reported results, indicating low specific activities of 137Cs in Arctic marine mammals in the Barents Sea and Greenland Sea region during the last 20 years. The species specific differences found may be explained by varying diet or movement and distribution patterns between species. No age related patterns were found in specific activities for the two species (polar bears and hooded seals) for which sufficient data was available. Concentration factors (CF) of 137Cs from seawater were determined for polar bears, ringed, bearded, harp and hooded seals. Mean CF values ranged from 79+/-32 (SD) for bearded seals sampled in 2002 to 244+/-36 (SD) for ringed seals sampled in 2003 these CF values are higher than those reported for fish and benthic organisms in the literature, suggesting bioaccumulation of 137Cs in the marine ecosystem.     

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

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

Occurrence and degradation characteristics of dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) in typical agricultural soils of China

In this study, we analyze the pollution and degradation characteristics of two kinds of phthalate esters (PEs), dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), in two kinds of soils collected from non-cultivated, crop, greenhouse, and vegetable fields from the Harbin and Handan Districts, China. The results demonstrate that DBP has relatively high residual levels in the soils, ranging from 3.18 to 29.37 mg/kg in fluvo-aquic soils of the Handan District (average 14.06 mg/kg) and 2.75-14.62 mg/kg in black soils of the Harbin District (average 7.60 mg/kg). Residual levels of DEHP reach 1.15-7.99 mg/kg in fluvo-aquic soils of the Handan District (average 4.86 mg/kg) and 0.44-4.20 mg/kg in black soils of the Harbin District (average 2.35 mg/kg). All non-cultivated soils contain the lowest contents of PEs, suggesting that the kinds of pollutants are largely derived from human agricultural activities. Laboratory experiments verify that the degradations of two kinds of PEs are mainly via microbial processes. The microbial populations are higher and reduce more slowly in black soils than those in fluvo-aquic soils. These observations might partially explain the lower levels of residuals and higher degradation rates of PEs pollutants in black soils than those in fluvo-aquic soils. The detection of DBP metabolites indicates that DBP biodegradation might begin by ester hydrolysis to form monobutyl phthalate (MBP) and corresponding alcohol. The MBP then degrades to phthalic acid or butyl benzoate, which might be possibly caused by microbial decarboxylation. The two derivatives of MBP degrade to form protocatechuate through ring cleavage.     

Distribution of 137Cs, 238Pu and 239+240 Pu in sediments of the southeastern Brazilian shelf-SW Atlantic margin

In this work levels of 137Cs, 238Pu and 239+240 Pu as well as activity ratios of anthrophogenic radionuclides in sediment samples from the southeastern Brazilian shelf are presented. Instrumental gamma spectrometry was used to determine 137Cs and alpha spectrometry to determine 238Pu and 239+240 Pu after a radiochemical procedure. The levels ranged from 0.30 to 1.79 Bq kg(-1) for 137Cs, from 15 to 150 mBq kg(-1) for 238Pu and, from 18 to 117 mBq kg(-1) for 239+240 Pu. There was a bathymetric differentiation in the radionuclides distribution. 137Cs values were generally higher in the samples collected at water depths of less than 100 m. On the other hand, plutonium isotopes exhibit higher values at greater depths. The mean ratio of 239+240 Pu/137Cs obtained was 0.112+/-0.072 which is in agreement with the value reported for the Atlantic from atmospheric fallout of nuclear explosions in the past. The 238Pu/230+240 Pu ratios varied widely (from 0.339 to 2.088) and showed the influence of the SNAP-9A accident in the 238Pu levels for this area. The main goal of this work was to present unpublished anthropogenic radionuclide levels and activity ratios related to the contamination of the southeastern Brazilian shelf.     

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

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

Effect of biodegradable amendments on uranium solubility in contaminated soils

Chelate-assisted phytoextraction has been proposed as a potential tool for phytoremediation of U contaminated sites. In this context, the effects of five biodegradable amendments on U release in contaminated soils were evaluated. Three soils were involved in this study, one with a relatively high background level of U, and two which were contaminated with U from industrial effluents. Soils were treated with 5 mmol kg(-1) dry weight of either citric acid, NH(4)-citrate/citric acid, oxalic acid, S,S-ethylenediamine disuccinic acid or nitrilotriacetic acid. Soil solution concentration of U was monitored during 2 weeks. All amendments increased U concentration in soil solution, but citric acid and NH(4)-citrate/citric acid mixture were most effective, with up to 479-fold increase. For oxalic acid, S,S-ethylenediamine disuccinic acid and nitrilotriacetic acid, the increase ranged from 10-to 100-fold. The highest concentrations were observed 1 to 7 days after treatment, after which U levels in soil solution gradually decreased. All amendments induced a temporary increase of soil solution pH and TOC that could not be correlated with the release of U in the soil solution. Thermodynamic stability constants (log K) of complexes did not predict the relative efficiency of the selected biodegradable amendments on U release in soil solution. Amendments efficiency was better predicted by the relative affinity of the chelate for Fe compared to U.     

Uranium contents and (235)U/(238)U atom ratios in soil and earthworms in western Kosovo after the 1999 war

The uranium content and (235)U/(238)U atom ratio were determined in soils and earthworms of an area of Kosovo (Djakovica garrison), heavily shelled with depleted uranium (DU) ammunition during the 1999 war. The aim of the study was to reconstruct the small-scale distribution of uranium and assess the influence of the DU added to the surface environment. The total uranium concentration and the (235)U/(238)U ratio of topsoils showed great variability and were inversely correlated. The highest uranium levels (up to 31.47 mg kg(-1)) and lowest (235)U/(238)U ratios (minimum 0.002147) were measured in topsoils collected inside, or very close to, the clusters of DU penetrator holes. Regarding the fractionation of uranium in the surface soils, the uranium concentrations in the soluble and exchangeable fractions increased as the total uranium concentration of the topsoils increased. High and rather uniform percentage contents of uranium (24-36%) were associated with the poorly crystalline iron oxide phases of soils. In the U-enriched soils the elevated levels of the element were probably due to the presence of very small, unevenly distributed oxidized DU particles. The total uranium concentration in earthworms was in the range 0.142-0.656 mg kg(-1), with the highest concentrations in Lumbricus terrestris. The juveniles of all three studied species seemed to accumulate uranium more than adults, probably due to age-related differences in metabolism. The (235)U/(238)U ratio in the earthworms was variable (0.005241-0.007266) and independent of both the total uranium contents in soils and the absolute uranium levels in the animals. Bioconcentration was greater at lower U concentrations in soil, probably due to an increasing rate of elimination of uranium by the earthworms as the soil contents of the element increase. The results of this study clearly indicate that DU was added to the soil of the study area. Nevertheless, the phenomenon was very limited spatially and the total uranium concentrations fell within the natural range of the element in soils. Moreover, the absolute uranium concentrations indicate that there was no contamination of the earthworm species studied.     

Trends of radionuclide sorption by estuarine sediments. Experimental studies using 133Ba as a tracer

Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced 226Ra concentrations. 133Ba was used as a tracer since it is a gamma emitter and a good analogue of the environmental behaviour of 226Ra. Laboratory experiments have been carried out to quantify the uptake kinetics of 133Ba by sediments in aqueous suspensions and by sediment cores under a water column at rest. Depth distributions of 133Ba in sediments have been studied with different contact times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l(-1) suspension) and sediment cores (up to 70% in a few minutes). The kinetics of the uptake by suspended sediments could be reasonably described by a model of two parallel and reversible reactions followed by a weakly-reversible reaction. The total uptake and the rate of reaction decreased with the increment of grain size. Furthermore, uptake following diffusion through the interstitial water was hardly detectable beyond 1 cm depth. For the case with more experimental results, the depth distribution could be reasonably described by the analytical solution based on the use of an effective diffusion coefficient (4.2 x 10(-12) m2 s(-1)) and the measured intrinsic distribution coefficient (kd = 63 +/- 6 l kg(-1)).     

Ambient trace element background concentrations in soils and their use in risk assessment

The definition of ambient background concentrations (ABCs) is used in this study to assess the potential environmental risk of trace elements in soils and parent materials from Granada, Spain. Two different layers of soil (0-20 and 20-40 cm) and parent material samples were collected at 93 sites. From cumulative frequency distribution curves, ABCs for As, Co, Cu, Cr, Ni, Pb and Zn were estimated at 3.5-20, 7-23, 13-25.6, 29-66, 7-20, 15-36, and 5.5-76 mg kg^− 1, respectively. Tukey box-plots were used to discriminate different concentration classes and identify potentially contaminated sites. Weakly-weathered soils (Entisols) over carbonate materials showed the lowest background contents, the most developed soils (Alfisols) over metamorphic rocks the highest ones. Outliers were mainly found near a former iron mine where arsenic concentrations were by far exceeding the corresponding regional ABC. These soils were however, not toxic to Escherichia coli and Vibrio fischeri. The prediction of site-specific ABCs together with bioavailability and toxicity assessment is a valuable tool for giving further insight into the risk of trace elements in soils.     

Impact of mercury atmospheric deposition on soils and streams in a mountainous catchment (Vosges, France) polluted by chlor-alkali industrial activity: the important trapping role of the organic matter

Total atmospheric Hg contamination in a French mountainous catchment upstream from a chlor-alkali industrial site was assessed using Hg concentrations in the deepest soil horizon, in the stream bottom sediments, in river waters and in bryophytes. The natural background level of Hg content deriving from rock weathering was estimated to 32 ng g(-1) in the deepest soil layers. The soils appear to be Hg contaminated in two stages: atmospheric deposition and leaching through the soil profiles of Hg-organic matter complexes. The Hg enrichment factor (EF(Hg)(Sc)) which could be calculated by normalization to a conservative element like Sc, allows to estimate the major contribution (63% to 95%) of the atmospheric inputs, even in the upper part of the basin. This contribution may be attributed to diffuse regional atmospheric deposition of Hg and is mainly due to the geographic location of the chlor-alkali plant. This study shows for the first time that the mercury enrichment is proportional to the carbon content indicating that most of the atmospheric mercury deposition is trapped by the organic matter contained in the soils and in the stream sediments. The Hg stock in the soils of the upper catchment and the soil erosion contribution to the riverine Hg fluxes are estimated for the first time and allow to assess the Hg residence time. It indicates that Hg is trapped in the soils of such a polluted catchment for probably several thousand years.     

Organic matter in degraded agricultural soils amended with composted and thermally-dried sewage sludges

The cumulative and residual effects of composted and thermally-dried sewage sludge (CSS and TSS, respectively) on soil organic matter and its humified fraction were evaluated in a field experiment under Mediterranean conditions. The experimental design included soil plots either unamended (control) or amended with mineral fertilizer, CSS and TSS at rates of 20 and 80 t ha(-)(1). After the first year of sewage sludge application, each plot was divided into two subplots. In one subplot group, no additional application of SS was made in the following 3 years, and the residual effect of the first applications was evaluated. In the second subplot group, the cumulative effect of sludge amendments was evaluated by applying CSS and TSS also in the following three consecutive years. Nine months after the yearly sludge and mineral fertilizer applications, surface soil samples from control and amended soils were collected and analyzed for total organic C (TOC), total extractable C (TEC), and humified C fractions, both humic acid C (HAC) and fulvic acid C (FAC) fractions. Compared with the control and mineral treatments, which showed similar results, the repeated application to soil of TSS, and specially CSS, induced an increase on the content of the organic fractions examined, as well as HA percentage (%HA=HAC/TOC) and degree of polymerisation (DP=HAC/FAC). In the residual experiment, the TOC, TEC, HAC and FAC content of soils amended once with CSS and TSS decreased slightly when increasing the time from the amendment, whereas the %HA and DP tended to increase. Further, three years after the sludge applications, with respect to the control soil, the soils amended once with CSS exhibited similar TOC, TEC, and FAC content, and slightly larger HAC content, %HA and DP; whereas those amended once with TSS, featured still larger TOC, TEC, HAC content, similar FAC content, and slightly larger %HA and DP values. As a whole, the results obtained suggested that both kind of sludges contribute to improved soil organic matter levels and humified fractions, although the CSS contribution can be considered as a more efficient organic amendment than the TSS, which may present problems of maturity and degradability.     

Accumulation of radiocesium in wild mushrooms collected from a Japanese forest and cesium uptake by microorganisms isolated from the mushroom-growing soils

Mushrooms and soils samples collected from a sub-alpine forest of Mt. Fuji in Japan were measured for 137Cs and stable Cs. The ranges of 137Cs specific activities and stable Cs concentrations in the mushrooms were 291-7950 Bq kg(-1) dry weight and 4.69-58.1 mg kg(-1) dry weight, respectively. Both 137Cs specific activities and stable Cs concentrations in the mushrooms were higher than those in common agricultural plants. The 137Cs specific activities and stable Cs concentrations in the soils were 3.18-149 Bq kg(-1) dry weight and 0.618-2.18 mg kg(-1) dry weight, respectively. The appearance frequencies of filamentous actinomycetes and planktonic bacteria from the soils decreased according to increasing Cs contents in the medium. No relationship was observed between the appearance frequencies of those and the stable Cs concentrations in the soils. The filamentous actinomycetes from any soil sample could not grow in the presence of 25 mM Cs, although the planktonic bacteria from the soil samples could grow with up to 50 mM Cs in YM agar. In addition, the planktonic bacteria from approximately 70% of the soil samples could grow even in the presence of 100 mM Cs. Filamentous actinomycetes were more sensitive to Cs than planktonic bacteria. In in vitro experiments, Cs uptake by these strains of filamentous actinomycetes and planktonic bacteria was high in the presence of 5 mM CsCl and the strains accumulated Cs, the same as in mushrooms. Our results indicate that filamentous actinomycetes in the soils have higher sensitivity to Cs than planktonic bacteria, and several strains of filamentous actinomycetes have a high Cs accumulation in the presence of 5 mM Cs.