A Mathematical Model for 137Cs Uptake and Release by Filamentous Algae

A mathematical model of the dynamics of radiocaesium transport in the aquatic phase—algae system is suggested in this work. Allowance is made for algae growth and for both reversible and irreversible absorption of this radionuclide by the algae. The algae biomass is divided hypothetically into two compartments with different exchange kinetics. The parameters of the model are time dependent. The model is quantified using experimental data for the concentrations of ¹³⁷Cs in Cladophora glomerata filamentous algae and in water, obtained in situ in the environment of a nuclear power station. The model fits the data reasonably well and can be applied, for example, in bioindication of radioactivity in aquatic recipients in the environment of nuclear power stations.     

Determination of soil-to-plant transfer factors of 137Cs and 90Sr in the tropical environment of Bangladesh

Soil-to-plant transfer factors (TF) of ¹³⁷Cs and ⁹⁰Sr have been determined for different plants/crops, such as rice, beans, peanuts, pineapple, cabbage, tomato, spinach and grass. They were obtained from radioisotope experiments on plants grown in pots under outdoor ambient tropical conditions for three growing seasons (1994–1996). In the case of ¹³⁷Cs and concerning the above mentioned plants/crops, the average TFs were found to be 0.28, 0.25, 0.77, 0.19, 0.23, 0.28, 0.59 and 0.18, respectively. In the case of ⁹⁰Sr, the average TFs were found to be 0.82, 0.51, 0.20, 0.82, 0.69, 0.59, 0.91 and 0.84, respectively. A minor seasonal variation was observed. This study provides a database of TFs for tropical environments to be used, e.g., for radiological safety assessment models. Received: 14 October 1997 / Accepted in revised form: 9 February 1998     

Uptake of arsenic by mushrooms from soil

ABSTRACT

Graphite furnace atomic absorption spectrometry (standard addition method) was used to determine the total arsenic in wild-growing mushrooms after digestion with nitric acid, then with perchloric acid and in associated soils after digestion with mixtures of nitric and hydrofluoric acids in a microwave system. Among 83 species of mushrooms the highest concentrations of arsenic on a dry mass basis were found in Laccaria amethystea (26–125 mg kg^?1), Laccaria laccata (11–33 mg kg^?1), Thelephora terrestris (38 mg kg^?1), Boletus cavipes (11.6 mg kg^?1) and Ramaria botrytis (10 mg kg^?1). Mushroom caps of L. laccata, L. amethystea, and B. cavipes had approximately double the arsenic concentrations found in stems. The arsenic concentrations in caps of L. amethystea and L. laccata were directly proportional to the concentrations in the soils. The concentrations of arsenic in the soils were in the range 6.5–65 mg kg^?1. Among the 19 mushroom caps with arsenic concentrations above the method detection limit of 0.2 mg As/kg dry mass, only L. amethystea and L. laccata had arsenic concentration ratios ‘cap/soil’ higher than 1 (between 1.1 and 1.9). Thelephora terrestris had a ratio of 2.37.     

Phytoremediation of 137Cs: factors and consequences in the environment

Radionuclide contamination is a concerning threat due to unexpected nuclear disasters and authorized discharge of radioactive elements, both in the past and in present times. Use of atomic power for energy generation is associated with unresolved issues concerning storage of residues and contaminants. For example, the nuclear accidents in Chernobyl 1986 and Fukushima 2011 resulted in considerable deposition of cesium (Cs) in soil, along with other radionuclides. Among Cs radioactive variants, the anthropogenic radioisotope ¹³⁷Cs (t_½?=?30.16 years) is of serious environmental concern, owing to its rapid incorporation into biological systems and emission of β and γ radiation during the decaying process. To remediate contaminated areas, mostly conventional techniques are applied that are not eco-friendly. Hence, an alternative green technology, i.e., phytoremediation, should in future be considered and implemented. This sustainable technology generates limited secondary waste and its objectives are to utilize hyper-accumulating plants to extract, stabilize, degrade, and filter the radionuclides. The review highlights plant mechanisms for up-taking radionuclides and influences of different environmental factors involved in the process, while considering its long-term effects.

     

The analysis of coefficient of 137Cs transfer from soil into potato in relationship with 137Cs content in soil and plant mineral feed

The soil-potato transfer factor for 137Cs (TF) was estimated by using results of 137Cs activity concentration measurements in 214 samples of soil and potato taken at fields with various level of contamination with 137Cs. The relationships between the coefficient TF and soil characteristics (acidity pH (KCl), content of K2O, P2O5, CaO and MgO in soil) and soil contamination with 137Cs have been analysed. The results show that the TF values tend to decrease with increasing concentration of 137Cs, K2O, P2O5, and CaO in considered sod-podsolic sandyloam soil. The regression function describing the TF dependence of 137Cs, K2O, P2O5, and CaO content in soil has been derived.     

Uptake of natural and man-made radionuclides by lichens and mushrooms

Summary Due to the large absorbing surface of the mycelium that grows in the upper parts of the soil mushrooms take up higher amounts of¹³⁷Cs and⁴⁰K than lichens. Besides these nuclides only the long-lived radionuclides¹²⁵Sb and⁶⁰Co could be measured; but not the short-lived fission-products¹⁴⁴Ce,⁹⁵Zr and⁹⁵Nb which probably decayed before absorption into the mycelium. These nuclides, however, are present in lichens because of their surface structures which enable high foliar deposition.The¹³⁷Cs-content of lichens is probably due to absorption by the mycobiont and seems to be used to satisfy their potassium-requirements. Mushrooms on the other hand are characterized by a relatively stable potassium-content and a wide ranging¹³⁷Cs-content which depends on the availability in different substrates. Occasionally the natural radionuclides²³⁸U and²²⁶Ra could be detected in mushroom and lichen samples, showing no correlation with the natural radionuclide content of the soil.     

Comparison of the post-Chernobyl 137Cs contamination of mushrooms from eastern Europe, Sweden, and North America.

A comparison was made of 134Cs and 137Cs contamination in fungi from eastern Europe and eastern North America. Mean activities of 25 Ukrainian, 6 Swedish, and 10 North American collections were 4,660, 9,750, and 205 Bq/kg (dry weight), respectively. Additional measurements were made on samples from the Moscow, southern Belarus, and Yugoslavia/Bulgaria regions. Activity values were found to vary by several orders of magnitude within all geographic areas, even for the same mushroom species. Significantly higher specific activities were observed in mycorrhizal species than in saprophytic and parasitic fungi. Unfortunately, many of the European mycorrhizal species considered as prized edibles contained unacceptably high levels of 137Cs (> 1,000 Bq/kg [dry weight]) and should be used sparingly as food. By contrast, no mushrooms collected in Ontario or northern Michigan exceeded 1,000 Bq of 137Cs per kg (dry weight). The excessive 137Cs contamination was evident in mushrooms from areas that had substantial fallout from the 1986 accident in reactor 4 at the Chernobyl nuclear power station. However, observations suggest that about 20% of the 137Cs in eastern Europe (Moscow area, Belarus, and Ukraine) is of non-Chernobyl origin.     

Uptake of Carrier-free Cs by Ramalina reticulata

The uptake of carrier-free ¹³⁷Cs by Ramalina reticulata Kremp. does not appear to be directly linked to metabolism. The results indicate the presence of a barrier to entry of ¹³⁷Cs. The barrier is stabilized by Ca ions. Removal of Ca by pretreatment of the tissue in monovalent salt solutions increases the uptake of ¹³⁷Cs. Uptake under anaerobiosis is also greater than normal, but in this case, Ca displaced from the barrier membrane is not lost from the tissue and normal permeability is rapidly re-established when aerobic conditions are restored. Under anaerobiosis Ca²⁺ increases damage to the respiratory mechanism presumably by increasing retention of toxic products.     

Uptake and translocation of 134Cs by maize roots as affected by heterogeneous distribution of 134Cs

Structure-induced non-uniform water flow induces a heterogeneous distribution of surface-applied radionuclides in the soil profile. This study was conducted to assess the amount of ¹³⁴Cs which can be taken up by a single root growing in an area enriched in ¹³⁴Cs relative to the total amount of ¹³⁴Cs that can be taken up by the whole root system growing in an area homogeneously contaminated with ¹³⁴Cs. A split-root experiment was used to simulate the heterogeneous distribution of ¹³⁴Cs and roots. Seedlings of maize (Zea mays L. cv Corso) were grown for 14 days in solution culture and then transferred to a two-compartment pot system, where a single root was grown in a ¹³⁴Cs contaminated compartment while the rest of the root system was grown in an uncontaminated compartment. Plants with the whole root system growing in a solution contaminated with ¹³⁴Cs were used as control. We tested the effect of the competition between Cs and K on the uptake and translocation of ¹³⁴Cs by using two K concentrations, 0.2 and 1.05 mM. At the K concentration of the nutrient solution of 0.2 mM the single root representing 21% of the total root weight was able to take up 47% of the ¹³⁴Cs taken up by the entire root system, while at 1.05 mM the single root, representing 15% of the total root weight, took up 15% of the ¹³⁴Cs taken up by the entire root system. The translocation of ¹³⁴Cs from the root to the shoots did not depend on the external K concentration in the nutrient solution, but it was lower in the split root treatment than in the control treatment at both K concentrations. Section Editor: R. W. Bell     

Analysis of factors determining the biological availability of 137Cs in forest ecosystem soils

On five forest plots varying in species composition of woody plants and soil properties, 137Cs accumulation by vegetation of the forest understorey has been studied. Differences in 137Cs availability for root uptake are shown to be dependent on a vertical distribution of 137Cs content over the soil profile, percentage of exchangeable 137Cs and distribution of plant root systems (fungous mycelium) in soil. A 137Cs-bioavailability index is suggested and its non-linear relationship with 137Cs transfer factors to different plant species in the understorey is shown.     

Mechanisms and models of 137Cs migration in soils

The most spread mechanisms and models of 137Cs migration in soil were considered and the advantage of the models, which take into account the kinetics of sorption-desorption above the models with two components were presented.     

Distribution and dynamic of 137Cs in arboreal plants

Dynamics of 137Cs specific activity (SA) in woody plants was examined. It was found that interseasonal variations of SA are connected mainly with precipitations and related oxygen in soil as well as Eh level. The rate of daily variation in SA in an individual tree can reach 19%. Acropetal or basipetal 137Cs distribution in the bole depends on physiological condition category (PCC) of a tree, weather and environment; SA ratio of higher and lower PCC depends on the same factors. In winter compared to summer higher SA correlation of tree separate parts was observed. Trees with 137Cs acropetal distribution in bark had proven lower general CA level.     

Dynamics of the factors of 137Cs transfer to natural and sown grasses in the long term after the accident at the Chernobyl power plant

The regularities of changes in factors of 137Cs transfer to natural and sown grasses in the longterm period after the Chernobyl accident are described. The dynamics of changes in factors of 137Cs transfer to sown grasses over the period of 1993 to 1999 was of a non-uniform character. On average, these transfer factors (TF) tended to decrease in that period. A significant tendency for an increase in TF to sown grasses was noted for 1997-1999. The half-life periods of decrease in TF to natural grasses in the period 1993-1999 were shown to be ranged from 4.6 to 24.6 years. It was demonstrated that the differences in the TF dynamics between sown and natural grasses were related to the peculiarities of their development and application of countermeasures.     

Concentration of 137Cs, 65Zn,and 85Sr by fresh-water algae

Differences in the concentration and retention of ¹³⁷Cs by unicellular diatoms, filamentous green algae, and filamentous blue-green algae were demonstrated under both batch and continuous-flow culture conditions. ¹³⁷Cs concentration factors were generally higher by a factor of 2 in batch tests than in continuous flow tests. In retention studies, ¹³⁷Cs was desorbed more rapidly from algae under continuous-flow conditions. Studies with blue-green algae indicate that ¹³⁷Cs concentrations in the various species were more closely related to the surface-to-volume ratios of algal cells than to the systematic relationships of the three species. Continuous-flow studies indicated no differences among three species of filamentous green algae in the concentration of ¹³⁷Cs, ⁶⁵Zn, and ⁸⁵Sr. However, the average concentration factors of the radionuclides were considerably different: 3800 for ⁶⁵Zn, 460 for ¹³⁷Cs, and 230 for ⁸⁵Sr. These radionuclides were rapidly desorbed following the transfer of algae to nonradioactive media. The desorption rate was inversely related to the concentration rate.     

An estimation of 137Cs accumulation in forest fungi by the soil properties

A method of calculation of radiocaesium uptake by forest mushrooms as a function of soil properties is presented. Calculated value of 137Cs transfer factor for Xerocomus badius in the contaminated area of Bryansk Province of Russia is in a good agreement with experimental data.     

Comparison of the accumulation of 137Cs and 90Sr by six spring wheat varieties

The uptake of ¹³⁷Cs and ⁹⁰Sr by six varieties of spring wheat (Triticum aestivum) was compared in field trials on land contaminated by the Chernobyl accident. All the experimental varieties are officially adopted for agricultural use in Belarus and are used in large-scale production. Under identical conditions of nutrition, the productivity of the varieties varied significantly by a factor of 1.3. The extent of ¹³⁷Cs and ⁹⁰Sr accumulation by wheat grain, quantified as the concentration ratio, differed between the varieties by as much as a factor of 1.6, for both radionuclides. There was a significant linear positive correlation between the ⁹⁰Sr activity concentration in grain and straw, and the calcium concentration. The correlation between ¹³⁷Cs and potassium was not significant. The results suggest that certain varieties of spring wheat used in normal agricultural practice accumulate less ¹³⁷Cs and ⁹⁰Sr into grain than others. Some spring wheat varieties accumulated relatively less ¹³⁷Cs, but did not accumulate less ⁹⁰Sr. One variety, Quattro, had a significantly lower uptake of both ⁹⁰Sr (for grain) and ¹³⁷Cs (for both grain and straw) than that of the other varieties tested. The reduction efficiency achieved by the use of these varieties, however, is not as high as that achieved by soil amelioration techniques in the past. Nevertheless, since there are no additional costs or production losses associated with these varieties, their use in the contaminated areas is worth considering as a simple, practical, and effective contribution to reducing the uptake of both ⁹⁰Sr and ¹³⁷Cs and allowing farmers to produce food-grade grain.