Reload Index (ZRiChK UMCS)

STUDIES OF MIGRATION MECHANISM OF RADIOACTIVE ISOTOPES IN NATURAL ENVIRONMENT

Stanis³aw CHIBOWSKI, Andrzej KOMOSA, Jan SOLECKI,
Marek RESZKA, Jolanta ORZE£

DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY

Our study refers to Lublin region, especially preglacial valleys of the rivers: Wieprz, Bug and an artificial waterway Wieprz-Krzna canal. The samples of soil profiles and some usable plants and vegetables were subjected to study. The measuring methods consisted of alpha and gamma radiation spectrometry (PIPS and HPGe detectors, Genie-2000 Canberra’s software), beta radiation spectrometry (the liquid scintillation Beckman’s counter), and microcalorimetry.

The rate of vertical migration of 137Cs (calculated basing on the compartment model) was found depending on the ratio of adsorption / desorption distribution coefficients that are connected with organic matter content in the soil. The rate of cesium migration in soil of a medium organic matter level ranged from 0.8 to 1.8 cm/year, but in the case of organic soil the rate increases to 7-12 cm/year. Cesium retention in soil is controlled by the clay minerals and silica presence what irreversibly adsorb cesium ions.

The method of 90Sr determination in soil samples was elaborated. It was found that 90Sr in soil profiles is distributed rather homogeneously down to 30 cm, and average concentration in 5-cm layers was equal to 26 Bq/kg.

It was established that the rate of vertical migration of plutonium isotopes of the global fallout origin in forest soil of elevated organic matter content was 0.4 cm/year, and the Chernobyl plutonium 0.7 cm/year. In general, plutonium from river valleys revealed higher migration velocity. The rate of global fallout plutonium was 0.3 – 0.9 cm/year, and of Chernobyl one 0.9 – 2.5 cm/year. Plutonium concentration in sediment of natural river was about four times lower than in soil, taken from the riverbank, unlike to artificial waterway where the concentration in sediment and soil did not differ much.

Using a selective extraction of various geochemical forms of plutonium from soil it was found that usually a majority of plutonium was bound to organic and sesquioxide soil fractions. Other fractions, namely easily available, carbonate and residual one contained small amount of plutonium.

New method of plutonium separation from air dust and aerosols collected on Petrianov filter was also studied. A problem of polonium presence, which interferes with plutonium during alpha spectrometric determination, was overcome. Average plutonium concentration in ground-level air during the year 1998 and 1999 was equal to 9 nBq/kg (239,240Pu) and 0.7 Bq/kg (238Pu).

New procedures for determination of beta radiating plutonium (241Pu) were elaborated. They consisted of plutonium separation, alpha activity measurement, liquid extraction with trioctylphosphine oxide and finally measurement with liquid scintillation counter. Mean concentration of 241Pu in soil was equal to 5.4 Bq/kg.

Studies on radionuclide transfer from soil to usable plants and vegetables revealed that green parts of plant cumulated natural radionuclides such as 7Be, 40K and 210Pb, but only in a low extent anthropogenic 137Cs. The lowest concentration of radionuclides was observed in the plant roots. The calculated transfer factors of radionuclides from soil to edible parts of plant ranged from 0.001 to 0.5.

 

Grant KBN 3T09C 03415