Soil fertilisation with 137Cs-contaminated and uncontaminated wood ash as a countermeasure to reduce 137Cs uptake by forest plants.

The purpose of present study was to find out whether wood ash with a high pH value and neutralizing capacity reduces 137Cs uptake by forest plants many years after the radionuclide fallout. The effects of one-time point fertilisation with 137Cs-contaminated and uncontaminated wood ash alone or in combination with KCl on 137Cs transfer from soil to young leaves and green shoots of various dwarf shrubs and tree species were examined in a long-term fertilisation experiment (2012-2021) conducted in Bazar mixed forest, around 70 km from Chernobyl nuclear power plant. The results indicated minor effects of soil fertilisation, although there were differences between 137Cs uptake by species and years. Soil amendment with 137Cs-contaminated wood ash generally did not affect 137Cs uptake by young shoots and leaves of plants over the growing season in the first year and only slightly decreased Tag for 137Cs in the following years. The effect of a single application of 137Cs-uncontaminated wood ash on reducing 137Cs uptake by plants was generally negligible. Application of 137Cs-contaminated wood ash in combination with KCl reduced plant 137Cs uptake by about 45%, however, such reduction was only significant in some years for bilberry berries, young leaves and green shoots of lingonberry and alder buckthorn. Thus application of wood ash to 137Cs-contaminated forest soil many years after radionuclide fallout generally does not reduce 137Cs uptake by forest vegetation in a mixed forest ecosystem and this countermeasure should be applied with caution.

The grain storage of wet-deposited caesium and strontium by spring wheat - A modelling study based on a field experiment.

The aims of this study were to extend the Tracey model in order to quantify and to analyse spring wheat's grain storage dynamics of wet-deposited radionuclides. Tracey, a dynamic model of trace element cycling in terrestrial ecosystems, was extended with descriptions of wet-deposition, interception, foliar uptake and radioactive decay. Radionuclide fluxes were set proportional to corresponding water or carbon fluxes, simulated with CoupModel. The extended Tracey was calibrated against experimental data, where 134Cs and 85Sr were deposited on spring wheat at six growth stages in 2010 and 2011. Sensitivities of grain storage to wheat's and radionuclide properties were assessed, using the Eikos software, by 1000 Monte Carlo simulations for each of the 48 scenarios (combination of 2 radionuclides, 1 foliar uptake, 2 root uptake approaches, 6 deposition treatments and 2years). Simulations were accepted if simulated grain storage values were within 95% confidence intervals (CI) of measurements. We found that 15% of 134Cs and 85Sr simulations for 2011, and 6% of the 2010 simulations met the CI-criterion. Foliar uptake accounted for 99% and 90% of total plant uptake of 134Cs and 85Sr, respectively. Mean simulated grain storage at harvest increased with lateness of deposition, as the stored proportion of radionuclide deposited was 0.02% when deposition was before flowering, 2% between flowering and ripening, and 5% (2010) or 10% (2011, late harvest) after ripening, respectively. Similarly, the property that governed grain storage depended on the growth stage at time of deposition; stem and leaf fixation rates (deposition before flowering), grain fixation rates (between flowering and ripening) and grains' interception capacity (after ripening). We conclude that grains' interception capacities can be used to predict grain storage of radionuclides deposited in the riskiest period, i.e. close to harvest.

Modelling (137)Cs concentrations in moose (1986-2012) from areas highly contaminated by the Chernobyl fallout.

Data from long term annual monitoring of (137)Cs concentrations in harvested moose (Alces alces) were empirically modelled by applying multivariate data analysis that is able to from relatively raw datasets show how the many various impact variables are related (Principal component analysis, PCA). In the later stage regression modelling (Partial least squares, PLS) was applied to analyse which environmental and physiological factors were significant (i.e. of predictive value) based on the measured (X) activity concentrations in moose meat. The data sets originate from two different forest dominated areas in Sweden. One area is located inland (Heby municipality) and the other borders to the Baltic Sea (Gävle municipality). In inland with 20% farmland, GIS-software was used to calculate the proportion of different habitat types and (137)Cs deposition around individual killing spots. This model reveals that the proportions of farmland and forest around the killing spot were significant parameters, second to deposition and years since fallout. Significance was also obtained for the proportions of mire and water bodies, the amount of rain in summer and the age of the moose. In the other model based on data from the coastal area with only about 4% farmland, the coordinates of the moose killing spots were not recorded in the data sets. In the resulting model the temperature in July was the most important parameter, second to years since fallout. Significance was also found for the following parameters: temperature and rainfall in several summer months, the approximate north- and eastward location of the killing spot and to which age category (adult/calf) the harvested moose belonged.

Interception and retention of wet-deposited radiocaesium and radiostrontium on a ley mixture of grass and clover.

The aims of this study were to assess the potential radioactive contamination of fodder in the case of accidental radionuclide fallout, and to analyse the relationship between interception and retention of radionuclides as a function of biomass and Leaf Area Index (LAI). The interception and the retention of wet deposited (134)Cs and (85)Sr in ley (a mixture of grass and clover) were measured after artificial wet deposition in a field trial in Uppsala (eastern central Sweden). The field trial had a randomised block design with three replicates. (134)Cs and (85)Sr were deposited at six different growth stages during two growing seasons (2010 and 2011) using a rainfall simulator. The biomass was sampled in the center of each parcel 2 to 3h after deposition and at later growth stages (1 to 5) during the growing season. The above ground biomass and LAI were measured as well. The interception of radionuclides by the ley was largest at the late growth stages; the spike and tassel/flowering (code 5:6) in the 1(st) year, and at flowering/initial flowering (code 6:5) in the 2(nd) year. There was a correlation between radionuclide interception and above ground plant biomass, as well as with LAI, for both radionuclides in both years. The highest activity concentrations of both radionuclides were measured after deposition at the late growth stages and were found to be higher in the 2(nd) year. The weathering half-lives were shorter at the earlier growth stages than at the later growth stages for both radionuclides. For the magnitude of deposition chosen in our experiment, it can be concluded that the above ground biomass is a good predictor and the LAI a more uncertain predictor of the interception of radiocaesium and radiostrontium by ley grass and clover.

Accumulation of wet-deposited radiocaesium and radiostrontium by spring oilseed rape (Brássica napus L.) and spring wheat (Tríticum aestívum L.).

The accumulation of (134)Cs and (85)Sr within different parts of spring oilseed rape and spring wheat plants was investigated, with a particular focus on transfer to seeds after artificial wet deposition at different growth stages during a two-year field trial. In general, the accumulation of radionuclides in plant parts increased when deposition was closer to harvest. The seed of spring oilseed rape had lower concentrations of (85)Sr than spring wheat grain. The plants accumulated more (134)Cs than (85)Sr. We conclude that radionuclides can be transferred into human food chain at all growing stages, especially at the later stages. The variation in transfer factors during the investigation, and in comparison to previous results, implies the estimation of the risk for possible transfer of radionuclides to seeds in the event of future fallout during a growing season is still subject to considerable uncertainty.

Effects of ageing and microbial component on chemical availability of (137)Cs in a long-term experimental site.

A loamy soil contaminated with (137)CsCl 40 years ago was investigated by a sequential extraction technique to determine the effect of ageing on chemical availability of (137)Cs. The soil samples were sequentially extracted with H(2)O, NH(4)Ac, NH(2)OH x HCl, H(2)O(2), and HNO(3). Extractability of (137)Cs decreased in the order: HNO(3) > Residual > H(2)O(2) > NH(4)Ac > NH(2)OH x HCl > H(2)O. Only 0.94% in labile fractions (H(2)O and NH(4)Ac), while more than 96% was found in the strongly bound fraction (HNO(3) and residual). However, the activity percentage in labile fractions was increased to 1.34% after autoclaving treatment, while those in the other fractions did not significantly differ. This indicates that the microbial activity played a role in the (137)Cs retention. In the subsequent pot experiments with ryegrass and leek, specific activities in both plants were significantly higher in autoclaved soil than in non-autoclaved soil, and uptake of (137)Cs in the five cuts by ryegrass was 25% of the labile (137)Cs in the soil. In addition, a positive correlation was found between the amount of (137)Cs in labile fractions and that by plant uptake.

Arbuscular mycorrhizal fungi mediated uptake of 137Cs in leek and ryegrass.

In a first experiment of soil contaminated with 137Cs, inoculation with a mixture of arbuscular mycorrhizae enhanced the uptake of 137Cs by leek under greenhouse conditions, while no effect on the uptake by ryegrass was observed. The mycorrhizal infection frequency in leek was independent of whether the 137Cs-contaminated soil was inoculated with mycorrhizal spores or not. The lack of mycorrhizae-mediated uptake of 137Cs in ryegrass could be due to the high root density, which was about four times that of leek, or due to a less well functioning mycorrhizal symbiosis than of leek. In a second experiment, ryegrass was grown for a period of four cuts. Additions of fungi enhanced 137Cs uptake of all harvests, improved dry weight production in the first cut, and also improved the mycorrhizal infection frequencies in the roots. No differences were obtained between the two fungal inoculums investigated with respect to biomass production or 137Cs uptake, but root colonization differed. We conclude that, under certain circumstances, mycorrhizae affect plant uptake of 137Cs. There may be a potential for selecting fungal strains that stimulate 137Cs accumulation in crops. The use of ryegrass seems to be rather ineffective for remediation of 137Cs-contaminated soil.

Role of the fungal mycelium in the retention of radiocaesium in forest soils.

The aim of this work was to study possible binding of 137Cs to various organic components in the soil and fungi, by using various sequential extraction procedures. The retention and binding of 137Cs has been studied in two horizons Of/Oh and Ah/B of a Ukrainian forest soil. The exchangeable fractions 137Cs from soil (sum of H2O and 1 M NH4OAc fraction) were found to be 12% in the organic-rich layer (range 11-14%) and 23% in the organic-poor (range 20-29%). The hydrolysis with 10% H2SO4 resulted in an additional release of 30% of 137Cs from the organic-rich soil (range 30-35%) and 38% from the organic-poor soil horizon (range 27-53%). Extraction with 30% H2O2 released 11 and 15% of the 137Cs activity from organic-rich and organic-poor soil horizons. The corresponding values for treatment with 98.8% NaOCl were about 27% in both types of soil. About 11% of the total 137Cs activity was found in the humic acid fraction, about 5% in the fulvic fraction and 46% in the residue fraction. Relatively high level of 137Cs activity in soil (ca. 50%) was thus still left unsolved in the residue fraction. About 29% of 137Cs activity concentration in fungal mycelia was found as water soluble with a range of 11 to 41%. Additionally 24% of the 137Cs activity from mycelia was released by 1 M ammonium acetate extraction. Together, water and 1 M ammonium acetate extraction released about 53% of the total 137Cs activity in the mycelia. In fruit bodies of mycorrhizal fungi, 68% of the total 137Cs inventory was found to be water soluble at room temperature and 93% at 80 degrees C.