Reload Index (ZRiChK UMCS)

 

 

STUDY ON THE HORIZONTAL TRANSPORT OF SOME RADIONUCLIDES IN THE WIEPRZ RIVER VALLEY

 

ST. CHIBOWSKI, A. KOMOSA, M. RESZKA, J. SOLECKI,

J. ZYGMUNT

DEPT. OF RADIOCHEMISTRY AND COLLOID CHEMISTRY

 

 

        A horizontal transport of radionuclides was studied by the analysis of surface soil samples from preglacial valleys of Wieprz river and its bottom sediments. Along the river 34 sampling sites were selected, where soil (points B and C) and sediment samples (point A) from river bed were collected. Measured isotopes were g-radiating 40K and other, coming from 238U and 232Th series (natural origin), antropogenic 134Cs and 137Cs and a-emitting 238Pu and 239,240Pu ones.

        The concentrations of natural radioactive isotopes in all points do not differ much. Small exceptions were noticed along the river. A slight increase in radioactivity, observed for samples at the lowlands, was because the isotopes are carried by many tributaries and spread by frequent floods. The increase of their concentration at the upper course of the river results from the difference in the morphology of this area. Bottom sediments, specially these taken below the tributaries show higher radioactivity.

        Potassium isotope 40K concentrations are much higher than other isotopes of the natural series while the differences of activity between points B and C, in the same site, are smaller because the relatively substantial concentrations of the potassium in the environment and fertilization of the fields in vicinity of the sampling points.

        The concentrations of the 137Cs isotope in surface samples, (Fig. 1), are similar to natural isotopes. In sediment samples (point A) its concentration is definitely lower and more uniform than in the soil samples from the same site (points B and C).

Fig. 1.  137Cs activity in collected samples [Bq/kg]

 

        Caesium is adsorbed in the soil very strongly and this hinders isotope horizontal migration from the soil to water as well as its desorption from the bottom sediments. Such behavior is confirmed by lack of the cumulation of this isotope in bottom sediments along the river. The concentration of radiocaesium from Chernobyl fallout was calculated from 134Cs content that originate from the Chernobyl fallout only. Using T1/2 values of 134Cs and 137Cs, the ratio of the two nuclides at the time of sampling was estimated to be 0.01228 and the activity of 137Cs of the Chernobyl origin was as follows

Acs-137 =Acs-134 / 0.01228

        In our samples it ranges from 83 to 99%,bearing with a high error that comes from the low measured activity of 134Cs In soil samples collected in Eastern Poland this value ranges from 50% to 80% [1, 2].

        Measurements of a-emitting isotopes are presented in Fig. 2 for 239,240Pu.

Fig. 2. 239,240 Pu activity in collected samples [Bq/kg]

 

        Detected amount of plutonium in soil is low and there is no distinct difference between samples collected near the river bank (B) and the remote (C). In sediment samples, the activity is usually about 4-times lower than in soil and does not vary with a distance along the river. Plutonium activity in soil samples reveals more distinct variability along the river that correlate with higher concentration of natural g-radiating nuclides. Plutonium concentrations in soil samples are of the same level as determined earlier in the region of Eastern Poland [3]. From the ratio of 238Pu to 239,240Pu a Chernobyl fraction (PuCh) of total activity of  Pu was calculated using formula:

PuCh = (Rs-0.04) / (0.50 - 0.04)

where: Rs is the 238Pu/239,240Pu ratio in the measured sample, 0.04 is the ratio in global fallout and 0.50 in Chernobyl one.

 

References:

[1] J. Zygmunt, St. Chibowski, Z. Klimowicz, Polish J. Environ. Studies, 6 (1997) 57

[2] J. Zygmunt, S. Chibowski, Z. Klimowicz, J. Radioanal. Nuclear Chem.,231 (1998)

[3] A. Komosa, Sci. Total Environ., 188 (1996) 59

 

Grant IAEA (International Atomic Energy Agency, Wien, Austria)