Distribucija Cs137 u obradivom zemljištu

Abstract

Usled padavina koje su usledile nakon Černobilskog akcidenta 1986. godine, proizvedeni radionuklid 137Cs je deponovan u zemljištu. S obzirom na njegovo dovoljno dugo vreme poluraspada (30,05 godina), posebno je važna radiološka zaštita kultivisanog (obradivog) zemljišta jer se postavlja pitanje da li se ovaj radionuklid zadržava u površinskim slojevima zemljišta, da li biva usvojen od strane biljaka ili se spušta u dublje slojeve zemljišta. U ovom radu prikazani su rezultati merenja specifične aktivnosti 137Cs metodom gama-spektrometrije u zemljištu 15 godina starog voćnjaka pod zasadom breskvi. Priprema zemljišta za sadnju bresaka izvršena je rigolovanjem, posle čega je usledila 12 godina duga nega voćnjaka, a zatim uzorkovanje zemljišta je izvršeno tri godine nakon prestanka svih poljoprivrednih tretmana. U radu je prikazan pregled rezultata analize uticaja dugogodišnje kultivacije (obrađivanja) zemljišta na preraspodelu 137Cs duž profila dubine 0-80 cm. Linearna i višestruka regresiona analiza primenjene su da bi se procenilo u kojoj meri su nivoi radioizotopa cezijuma povezani sa: nivoima izotopa kalijuma 40K detektovanim u zemljištu; zatim, osnovnim osobinama koje karakterišu zemljište (pH, sadržaj humusa, sadržaj karbonata, granulometrijski sastav, sadržaj higroskopske vlage); mineralnim sastavom glinovite frakcije zemljišta i dostupnim sadržajima mikroelemenata (Zn, Cu, Mn, Fe). Obrasci distribucije 137Cs sa dubinom ukazivali su da je cezijum bio mehanički prenesen iz površinskih ka nižim slojevima zemljišta tokom kultivacije. Rezultati analiza su pokazali da na zatečenu distribuciju izotopa cezijuma sa dubinom glavni uticaj imaju varijacije sadržaja humusa i minerala glinovite frakcije zemljišta, vermikulita, ilita i smektita.

Due to the fallout followed by Chernobyl accident in 1986 anthropogenic radionuclide 137Cs was deposited in the soil. Given long half-life of 137Cs (30.05 years), cultivated soils in particular are subject of radiological protection because the question is whether this radionuclide would be retained in the surface layers of the soil, adopted by plants or transferred to the deeper soil layers. This paper presents an overview of the results of 137Cs specific activity measurements by gamma-spectrometry method in cultivated anthrosol soil of a 15-year old peach tree plantation at the experimental field “Radmilovac”. Preparing the land for planting peach trees deep ploughing was conducted followed by 12-year-long cultivation, and soil sampling was carried out three years after the termination of all agricultural treatments. Overview of the analyzes of the long-term cultivation impact on 137Cs redistribution in the soil along the 0-80 cm profile depth is presented. Linear and multiple regression analysis was applied to assess to what extent the levels of cesium radioisotopes are associated with a) levels of potassium isotope 40K detected in the soil; b) the basic features that characterize the soil (pH, humus content, carbonate content, grain size distribution, moisture content of hygroscopic); c) mineral composition of the clay fraction of soil and d) available DTPA-extracted microelements Zn, Cu, Mn and Fe. Patterns of 137Cs distribution with depth indicated that radiocesium was mechanically transferred from the surface to the lower layers of soil during the cultivation. The results of the statistical analysis showed that on radiocesium variations with depth a major impact had the contents of humus and the main minerals of the clay fraction of soil – vermiculite, illite, and smectite.