Association of fallout radiocesium with soil constituents: effect of sterilization of forest soils by fumigation with chloroform

Abstract

The effect of soil sterilization by chloroform fumigation on the release of fallout radiocesium incorporated in the fungal biomass of the organic layer of two forest soils was investigated by applying a sequential extraction procedure for radiocesium. The amount of the biomass in all soil samples was estimated by determination of the dissolved organic carbon (DOC) before and after fumigation, and qualitatively also by the ergosterol test. The five fractions obtained by sequential extraction (modified Tessier procedure) were: (I) easily exchangeable, (II) bound to oxides, (III) bound to organic matter, (IV) persistently bound, (V) residual. For the samples from the soil under spruce trees, no significant effects were apparent in any of these five fractions as a result of chloroform fumigation, indicating that the amount of radiocesium in the biomass of this soil was obviously negligibly small compared with the radiocesium associated with other soil constituents. The results obtained for the soil samples from the beech stand, however, reveal that the destruction of the biomass by chloroform fumigation modified considerably the extent of the association (i.e., binding) of radiocesium with the various other soil constituents (especially the clay minerals). As a result of this rapid redistribution of radiocesium released by the fungal biomass, it is not possible, in general, to attribute the observed increase of radiocesium in fraction I (easily exchangeable) after soil sterilization quantitatively to radiocesium released by the biomass. A reliable method to determine the amount of radiocesium incorporated in the fungal biomass of the soil samples which also contain clay minerals has, therefore, still to be developed.

Availability and immobilization of 137Cs in subtropical high mountain forest and grassland soils

“…The latter solid species are more resistant in the soil. Compared to results of relatively short-term deposition (Baumann et al, 1996;Rigol et al, 1999), our soils showing long-term deposition had lower amounts of 137 Cs bound to exchangeable, microbial biomass or organic matter fractions but higher amounts as persistent and residual fractions, which might be due to the well-known ''aging effect'' (Absalom et al, 1996;Spezzano, 2005). Recent study of soils affected by the Chernobyl accident indicate that most of the 137 Cs is in the residual fraction (Hou et al, 2003), which supports this aging phenomenon.…”

“…Several studies have reported the upward movement of 137 Cs in forest soil, where fungal activities play key role in translocation of 137 Cs (Brückmann and Wolters, 1994;Rafferty et al, 1997). Being aware of the importance of the availability of 137 Cs retained by fungi, some investigators tried to determine the fraction of nuclear fallout 137 Cs in fungal hyphae in soil (Brückmann and Wolters, 1994;Baumann et al, 1996). Recent study indicates that a critical part of fungal mycelia and fruit bodies of mycorrhizal fungi are water soluble (Vinichuk et al, 2005), which contributes to the mobility of 137 Cs in the forest soils.…”

“…The procedure basically followed that of Tessier et al (1979), but the extraction for the carbonate-bound fraction was omitted because of the low pH of the studied soils. The selective sequential extraction procedure was modified according to Baumann et al (1996).…”

“…Most studies (Shand et al, 1994;Baumann et al, 1996;Rigol et al, 1999;Sanchez et al, 2000) investigated the fate of 134 Cs or 137 Cs in different soil phases only in the short-term, or a few years after the Chernobyl deposition. Some other studies looked at local 137 Cs contamination, such as the release of 137 Cs due to accidents at nuclear facilities (Wasserman et al, 2002).…”

Chemical Speciation in Soils and Related Materials by Selective Chemical Extraction

“…The changes in plutonium and americium speciation with depth have been studied in grassland soil (Bunzl et al, 1995b) and of plutonium and caesium in forest soil . The effect of soil sterilisation on 137 Cs partitioning was also investigated and found to be soil dependent (Baumann et al, 1996). A four-stage sequential extraction has been used to partition Chernobyl-derived 137 Cs in a coniferous forest soil in Sweden (Fawaris and Johanson, 1995).…”