Association of Chernobyl-derived 239+240Pu, 241Am, 90Sr and 137Cs with different molecular size fractions of organic matter in the soil solution of two grassland soils |
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Authors: | K Bunzl W Kracke G I Agapkina A Tikhomirov A I Shcheglov |
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Institution: | (1) GSF – National Research Center for Environment and Health, D-85764 Neuherberg, Germany Fax: (+49) 89 3187 3323 e-mail: bunzl@gsf.de, DE;(2) Moscow State University, Soil Science Faculty, Leninskie gory, 119899 Moscow, Russian Federation, RU |
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Abstract: | Radiocesium is normally bound only rather weakly and unspecifically by humic substances, in contrast to the actinides Pu
and Am. Recently, however, it was observed that fallout 137Cs in the soil solution from an Of-horizon of a podzol forest soil (slightly decomposed plant material) was associated essentially
only with one single size fraction of the humic substances. In deeper soil layers with well humified material (AOh-horizon),
radiocesium was associated with all size fractions of the dissolved organic matter (DOM). To examine whether this unexpected
behaviour is also observable for DOM isolated from other soils, we determined the association of fallout 137Cs,90Sr,238Pu, 239+240Pu and 241Am with various size fractions of DOM from in situ soil solutions isolated from two layers (0–2 cm and 2–5 cm) of two grassland
soils (a soddy podzolic soil and a peat soil) within the 10 km zone of the nuclear reactor at Chernobyl (Ukraine). The four
size fractions of DOM as obtained by gel filtration of the soil solution were (mean nominal molecular weight in daltons):
fraction I: ≥2000, fraction II: 1300; fraction III: 560, fraction IV: inorganic compounds. The results for the well humified
DOM (humus accumulation horizon of podzol, deeper layer of peat soil) showed that Pu and Am are essentially associated with
the high molecular weight fractions, while Sr is present only in the `inorganic' fraction. Radiocesium is found in all the
size fractions separated. A quite similar pattern was also found for Pu, Am, and Sr in the soil solution from only slightly
decomposed plant material (0–2 cm of peat soil), but not for radiocesium. This radionuclide was again essentially only observable
in one single low molecular weight fraction of DOM. The above results thus support our recent observations in the different
horizons of a forest podzol mentioned above, even though no reason for the different binding of radiocesium by well humified
soil organic matter and by only slightly decomposed plant material can be given at present. The data demonstrate, however,
that information on only the total amount of a radionuclide in the soil solution will not be sufficient to interpret or predict
its fate adequately in the soil.
Received: 13 February 1998 / Accepted in revised form: 14 July 1998 |
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