Effect of chemical pollution on forms of 137Cs, 90Sr and 239,240Pu in arctic soil studied by sequential extraction

Effects of cattle manure compost application on crop growth and soil-to-crop transfer of cesium in a physically radionuclide-decontaminated field

Resuming crop production in physically decontaminated fields affected by radiocesium (134Cs and 137Cs) releases is crucial for restoring impacted areas. However, surface soil excavation to reduce radiocesium may lead to lower crop yield due to the loss of fertile topsoil. This study aimed to assess the effects of cattle manure compost (CMC) application on soil properties, crop growth, and 137Cs soil-to-crop transfer in a physically decontaminated field and pot experiment. Field trials were conducted during 2018-2022, with CMC (1 and 2 kg m-2 year-1) applied alongside conventional fertilization (CMC1 and CMC2 plots, respectively) in 2018-2019 and conventional fertilization alone in 2020-2022. Additionally, a pot experiment was used to evaluate the impact of CMC application in soil (1 kg m-2 year-1 for 5 years) on 137Cs transfer. In the field trial during 2018-2019, CMC1 and CMC2 plots exhibited higher soybean shoot dry weight (DW) compared with plots receiving conventional fertilization and additional K fertilizer (+K2O). CMC application also improved soil nutrient content. The transfer factor of 137Cs (TF-137Cs: plant 137Cs activity concentration/soil 137Cs activity concentration) followed the order CMC2 < CMC1 ≈ +K2O < conventional fertilization only (CF) and was negatively correlated with soil exchangeable K (Ex-K). During 2020-2022, when all plots received conventional fertilization alone, grain yields were higher in CMC1 and CMC2 plots than in the +K2O plot, with the lowest TF-137Cs in CMC2 plot followed by CMC1, +K2O, and CF plots. The pot experiment confirmed that CMC soil had a lower TF-137Cs and higher plant DW compared with CF soil with the same Ex-K level. Additionally, the soil exchangeable 137Cs (Ex-137Cs) level was significantly lower in CMC soil than CF soil. These findings demonstrate the potential of CMC application to improve crop growth and reduce 137Cs transfer in physically decontaminated fields.

Analysis of the vertical distribution of 137Cs and 239,240Pu in waterlogged and non-boggy soils by the sequential extraction method

Mobile capabilities of ¹³⁷Cs, ^239,240Pu and some stable element physicochemical forms were studied in soil layers at a depth of 6-8 cm (maximum concentrations of radionuclides) of non-boggy and waterlogged soil cores sampled on the shores of Lake Bedugnis (Lithuania). Soil samples were acidic with small amount of clay (muscovite). The radionuclide activity concentrations were about 2.5 times higher in non-boggy soil. It was explained by different conditions of deposition of radioactive fallout at these sampling sites and density of the soil samples. The value of the exchangeable fraction of radionuclides is shown to be an indicator of their migration capabilities in the soil. Under anaerobic conditions in waterlogged soil (stagnant pore water conditions) and due to the presence of clay admixture, ∼90% of ¹³⁷Cs was concentrated in the residual fraction and its mobility was low. ^239,240Pu was concentrated mainly in organic matter with rather large exchangeable fractions (∼9.6-∼13.9%). Under oxidizing conditions in non-boggy soil (dynamic pore water conditions in the case of rain), ^239,240Pu was mostly concentrated in the oxide fraction. Its exchangeable fractions were less than those in waterlogged soil and, respectively, its mobility was lower. In non-boggy soils, exchangeable fractions of ¹³⁷Cs were large and varied in the range of 10.1-12.2%, which indicated its high mobility. In the case, ¹³⁷Cs adsorption by clay materials was reduced and its residual fraction did not exceed 71.3%. The obtained data show that in the area of Lake Bedugnis, the migration capabilities of ¹³⁷Cs and ^239,240Pu change in antiphase.

Speciation of naturally occurring radionuclides in Mediterranean soils: bioavailabilty assessment

Knowledge of soil-to-plant transfer processes is a key element that can have a significant health impact. Much effort has been taken to characterize the speciation of anthropogenic radionuclides released into the environment. However, the information about naturally occurring radionuclides is scarce. This work evaluate the potential risks of transference, that is, the bioavailability of the ^234,238U, ²²⁶Ra, ^228,230,232Th, and ²¹⁰Po in three different soils collected in Mediterranean ecosystems. Chemical speciation of these radionuclides was carried out according to two different methods, Pavlotskaya and a modification of Tessier's protocol. Most of these radionuclides were associated to fractions strongly bound to soil particles and not able to be transferred. Increasing concentrations of U and Th extracted with increasing volume of NH₄OAc 1 M were observed, until it reached saturation. Readily bioavailable fraction in both methods (either exchangeable or water soluble + exchangeable) decreased in the following order: ²²⁶Ra > ^234,238 U > ^228,230,232Th > ²¹⁰Po. It was found that < 3% of the natural radionuclide concentration in soil are readily bioavailable for plant uptake in this region of Spain, and the resulting human health risk is negligible from natural radionuclide ingestion.

Evaluation of the possibility to use the plant-microbe interaction to stimulate radioactive 137Cs accumulation by plants in a contaminated farm field in Fukushima, Japan

Field experiments in a contaminated farmland in Nihonmatsu city, Fukushima were conducted to assess the effectiveness of the plant-microbe interaction on removal of radiocesium. Before plowing, 93.3% of radiocesium was found in the top 5 cm layer (5,718 Bq kg DW(-1)). After plowing, Cs radioactivity in the 0-15 cm layer ranged from 2,037 to 3,277 Bq kg DW(-1). Based on sequential extraction, the percentage of available radiocesium (water soluble + exchangeable) was fewer than 10% of the total radioactive Cs. The transfer of (137)Cs was investigated in three agricultural crops; komatsuna (four cultivars), Indian mustard and buckwheat, inoculated with a Bacillus or an Azospirillum strains. Except for komatsuna Nikko and Indian mustard, inoculation with both strains resulted in an increase of biomass production by the tested plants. The highest (137)Cs radioactivity concentration in above-ground parts was found in Bacillus-inoculated komatsuna Nikko (121 Bq kg DW(-1)), accompanied with the highest (137)Cs TF (0.092). Furthermore, komatsuna Nikko-Bacillus and Indian mustard-Azospirillum associations gave the highest (137)Cs removal, 131.5 and 113.8 Bq m(-2), respectively. Despite the beneficial effect of inoculation, concentrations of (137)Cs and its transfer to the tested plants were not very high; consequently, removal of (137)Cs from soil would be very slow.

Association of plutonium with sediments from the Ob and Yenisey Rivers and Estuaries

The present study applied sequential extraction techniques to investigate the binding and mobility of plutonium (Pu) in sediments from the rivers and estuaries of the Ob and Yenisey. As a study site, the Ob and Yenisey are particularly interesting as both rivers have weapons-grade Pu sources in their catchment areas, including the Russian Pu production and reprocessing plants at Mayak, Tomsk-7 and Krashnoyarsk, and the Semipalantinsk nuclear weapons testing site in Kazakhstan. Plutonium activity and (240)Pu/(239)Pu ratios were determined using accelerator mass spectrometry (AMS). Sequential extractions showed that between 47 and 80% of the Pu in Yenisey River sediments and 35-53% of the Pu in soils around the Techa River are mobilized with weak oxidising agents, which can indicate that Pu is bound to organic material. In contrast, Pu in Ob and Yenisey Estuarine sediments was more strongly bound, with 60-100% being found in the HNO(3)-extractable fraction. This change in speciation could reflect either that Pu bound to organic material in the Techa and Yenisey River sediments becomes more fixed to the sediments with time, or that organic-bound Pu is mobilized and released to the water when the sediments encounter the more saline water of the Ob and Yenisey estuaries. In general, (240)Pu/(239)Pu ratios were relatively consistent between different extraction fractions, although, in whole sediments, an increase in ratio was observed with distance from the source. This reflects the increased influence of weapon fallout from catchment runoff within the river systems, as compared to the weapons-grade sources close to the production and reprocessing plants. Knowledge of Pu speciation in the Ob and Yenisey Rivers, and the processes controlling its behaviour in estuarine systems, can improve predictions of its transfer and subsequent environmental impact to Arctic Seas.

Is there a future for sequential chemical extraction?

Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Distribution of 90Sr and 137Cs in Arctic soil profiles polluted by heavy metals

Effects of industrial pollution on the behaviour of radionuclides in spruce forest ecosystems were studied along a gradient from of a copper-nickel smelter in Monchegorsk, NW Russia. A reference site was situated in Lapland, Finland, 152 km west of Monchegorsk. Most of the total 137Cs activity in soil was in mineral (E and B) horizons, except at the reference site where the major part was still in the organic surface layer. Most of the total 90Sr activity still remaining in the soil profile was found in the surface layer, but the relative amount decreased with increasing level of industrial pollution. Pollutants from the smelter clearly affected the chemical speciation of radionuclides. Smaller amounts of exchangeable radionuclides were present in the organic surface layer at the most polluted sites. The decline of 137Cs with decreasing distance from the smelter correlated strongly with a similar depletion in exchangeable K and Mg. Total concentrations of 137Cs and 90Sr showed high correlations with exchangeable cations, particularly in the E and upper B horizon. A sudden change in behaviour of 137Cs in the lower B horizon may be associated with changes in clay mineralogy along the soil profile caused by weathering.

Effect of industrial pollution on the distribution of 137Cs in soil and the soil-to-plant transfer in a pine forest in SW Finland

The objective of this study was to evaluate the effect of industrial pollution on the distribution of radiocaesium in soil and on its transfer from soil to plants. The study was started in September 2000 in four Scots pine stands located at distances of 0.5, 2, 4 and 8 km along a transect running SE from the Cu-Ni smelter at Harjavalta in SW Finland. Annual emissions from the smelter in 1990 were 80 t of Cu, 31 t of Ni and 9000 t of SO(2), and in 1999 these were 5.9, 0.8 and 3400 t, respectively. At each site, soil profiles were sampled with a corer, and samples were separated into litter (L), organic soil layer (O) and mineral soil layers (B, E). Mushrooms, lichens (Cladina spp. and Cetraria islandica), lingonberry (Vaccinium vitis-idaea) and crowberry (Empetrum nigrum) plants were collected at each site, except at a distance of 0.5 km, where only mushrooms were available. In the organic soil layer, 137Cs activity decreased from 8000 Bq/m(2) at a distance of 8 km from the smelter to 1500 Bq/m(2) at a distance of 0.5 km; in litter, 137Cs concentration increased from 6300 Bq/m(2) at 8 km to 14000 Bq/m(2) at 0.5 km. 137Cs activity concentration decreased significantly in plants, mushrooms and lichens as the pollution load increased. In lichens, 137Cs activity decreased from 910 Bq/kg at 8 km to 170 Bq/kg at 2 km, while in lingonberry it decreased from 1470 to 20 Bq/kg and in crowberry from 310 to 20 Bq/kg. Aggregated transfer factors for 137Cs decreased in a similar way in lingonberry from 7.6x10(-2) m(2)/kg at 8 km to 7.7x10(-4) m(2)/kg at 2 km and in crowberry from 1.6x10(-2) to 7.9x10(-4) m(2)/kg.

Effect of industrial pollution on soil-to-plant transfer of plutonium in a Boreal forest

Plutonium in a forest ecosystem was studied at different distances from the copper and nickel smelter at Monchegorsk, Kola Peninsula, Russia. Soil and plant samples were collected 7 (site A), 16 (B), 21 (C) and 28 (D) km from the smelter and at a reference site situated in Finland, 152 km from Monchegorsk. The deposition of Cu in litter and in the organic layer decreased from 10700 mg/m2 at site A to 33 mg/m2 at the reference site, the deposition of Ni from 14300 to 29 mg/m2. From the reference site to site A, the volume of the litter layer increased almost five-fold. Most of the 239,241Pu in soil was found in the organic layer and in the litter layer. When industrial pollution increased, the content of 239,240Pu in the litter layer increased (from approx. 0.5 at site D to 15 Bq/m2 at site A) whereas, that in the organic layer decreased (from approx. 20 at site D to 5 Bq/m2 at site A). Four different plant species typical for the subarctic environment were collected at each sampling site: Deschampsia flexuosa (forest hair grass); Empetrum nigrum (crowberry); Vaccinium myrtillus (blueberry); and Vaccinium citis idaea (lingonberry). The concentration of 239,241Pu increased with pollution in Deschampsia flexuosa (from approx. 2 at site D to 7 mBq/kg at site A), Empetrum nigrum (from approx. 3 at site D to 14 mBq/kg at site A) and Vaccinium myrtillus (from approx. 1 at site D to 8 mBq/kg at site A). In Vaccinium vitis idaea, the Pu concentration did not have any clear trend of association with pollution. With the exception of Vaccinium vitis idaea, the aggregated transfer factors of plutonium (m2/kg) for the plants studied increased almost ten-fold from site D to site A, the range being 3 x 10(-5)-3 x 10(-4) m2/kg for Deschampsia flexuosa, 7 x 10(-5)-5 x 10(-4) m2/kg for Empetrum nigrum and 3 x 10(-5)-3 x 10(-4) m2/kg for Vaccinium myrtillus. The most likely explanation for the higher transfer factors of plutonium near the smelter is contamination of the plants by litter rather than root uptake.