Determination of Characteristic vs Anomalous 135Cs/137Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples.

A contamination with the ubiquitous radioactive fission product 137Cs cannot be assigned per se to its source. We used environmental samples with varying contamination levels from various parts of the world to establish their characteristic 135Cs/137Cs isotope ratios and thereby allow their distinction. The samples included biological materials from Chernobyl and Fukushima, historic ashed human lung tissue from the 1960s from Austria, and trinitite from the Trinity Test Site, USA. After chemical separation and gas reaction shifts inside a triple quadrupole ICP mass spectrometer, characteristic 135Cs/137Cs isotope signatures (all as per March 11, 2011) were obtained for Fukushima- (∼0.35) and Chernobyl-derived (∼0.50) contaminations, in agreement with the literature for these contamination sources. Both signatures clearly distinguish from the characteristic high ratio (1.9 ± 0.2) for nuclear-weapon-produced radiocesium found in human lung tissue. Trinitite samples exhibited an unexpected, anomalous pattern by displaying a low (<0.4) and nonuniform 135Cs/137Cs ratio. This exemplifies a 137Cs-rich fractionation of the plume in a nuclear explosion, where 137Cs is a predominant species in the fireball. The onset of 135Cs was delayed because of the longer half-life of its parent nuclide 135Xe, causing a spatial separation of gaseous 135Xe from condensed 137Cs, which is the reason for the atypical 135Cs/137Cs fractionation in the fallout at the test site.

Uptake of Radionuclides by Bryophytes in the Chornobyl Exclusion Zone.

The "Chernobyl nuclear disaster" released huge amounts of radionuclides, which are still detectable in plants and sediments today. Bryophytes (mosses) are primitive land plants lacking roots and protective cuticles and therefore readily accumulate multiple contaminants, including metals and radionuclides. This study quantifies 137Cs and 241Am in moss samples from the cooling pond of the power plant, the surrounding woodland and the city of Prypiat. Activity concentrations of up to 297 Bq/g (137Cs) and 0.43 Bq/g (241Am) were found. 137Cs contents were significantly higher at the cooling pond, where 241Am was not detectable. Distance to the damaged reactor, amount of original fallout, presence of vascular tissue in the stem or taxonomy were of little importance. Mosses seem to absorb radionuclides rather indiscriminately, if available. More than 30 years after the disaster, 137Cs was washed out from the very top layer of the soil, where it is no more accessible for rootless mosses but possibly for higher plants. On the other hand, 137Cs still remains solved and accessible in the cooling pond. However, 241Am remained adsorbed to the topsoil, thus accessible to terrestrial mosses, but precipitated in the sapropel of the cooling pond.

Survival of the basidiomycete Schizophyllum commune in soil under hostile environmental conditions in the Chernobyl Exclusion Zone.

Radioactive contamination resulting from major nuclear accidents presents harsh environmental conditions. Inside the Chernobyl exclusion zone, even more than 30 years after the accident, the resulting contamination levels still does not allow land-use or human dwellings. To study the potential of basidiomycete fungi to survive the conditions, a field trial was set up 5 km south-south-west of the destroyed reactor unit. A model basidiomycete, the lignicolous fungus Schizophyllum commune, was inoculated and survival in the soil could be verified. Indeed, one year after inoculation, the fungus was still observed using DNA-dependent techniques. Growth led to spread at a high rate, with approximately 8 mm per day. This shows that also white-rot basidiomycetes can survive the harsh conditions in soil inside the Chernobyl exclusion zone. The unadapted fungal strain showed the ability to grow and thrive in the contaminated soil where both stress from radiation and heavy metals were present.

Caesium inhibits the colonization of Medicago truncatula by arbuscular mycorrhizal fungi.

Contamination of soils with radioisotopes of caesium (Cs) is of concern because of their emissions of harmful ß and γ radiation. Radiocaesium enters the food chain through vegetation and the intake of Cs can affect the health of organisms. Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with plants through colonization of the roots and previous studies on the influence of AM on Cs concentrations in plants have given inconsistent results. These studies did not investigate the influence of Cs on AM fungi and it is therefore not known if Cs has a direct effect on AM colonization. Here, we investigated whether Cs influences AM colonization and if this effect impacts on the influence of Rhizophagus intraradices on Cs accumulation by Medicago truncatula. M. truncatula was grown with or without R. intraradices in pots containing different concentrations of Cs. Here, we present the first evidence that colonization of plants by AM fungi can be negatively affected by increasing Cs concentrations in the soil. Mycorrhizal colonization had little effect on root or shoot Cs concentrations. In conclusion, the colonization by AM fungi is impaired by high Cs concentrations and this direct effect of soil Cs on AM colonization might explain the inconsistent results reported in literature that have shown increased, decreased or unaffected Cs concentrations in AM plants.

137Cs and 40K in fruiting bodies of different fungal species collected in a single forest in southern Poland.

Fruiting bodies of fungi belonging to more than 70 species were collected within a few thousand square meter area of one forest during 2006 and 2007. The soil profile was collected to check the cumulative deposition of (137)Cs, which was relatively high, equal to 64 +/- 2 kBq/m(2) (calculated for October 2006). The majority of this activity was in the first 6 cm. Fruitbodies were analyzed for radiocesium and (40)K by means of gamma-spectrometry. The highest (137)Cs activity was 54.1 +/- 0.7 kBq/kg (dry weight) for a sample of Lactarius helvus collected in 2006. The results for 2006 were higher than those for 2007. In a few cases the traces of short-lived (T(1/2) = 2.06 a) (134)Cs were still found in samples. The importance of mycorrhizal fungi for radiocesium accumulation is confirmed. The differences in activity among the species are discussed in relation to observations and predictions from previous studies, where the change in relative accumulation between fruiting bodies of different species was at least partially explained by the differences in the depth of the mycelium localization in a litter/soil system. It is concluded that in some cases, such as Boletus edulis and Xerocomus badius, this prediction is fulfilled and therefore this explanation confirmed.