TIME DEPENDENCE ON Tc, Mn, Sr AND Cs BEHAVIORS IN AGRICULTURAL SOILS UNDER AEROBIC AND ANAEROBIC CONDITIONS

摘要

In order to investigate the time dependence on behaviors of Tc, Mn, Sr and Cs in two soils (Andosol and Gray lowland soil) under two different water contents, corresponding to upland and paddy field condition, a radiotracer experiment was carried out. At 1, 3, 7, 14, 30, 60 and 180 days, three soil fractions, (a) water soluble and ion exchangeable, (b) specifically adsorption, and (c) organically bound fractions, were determined by selective extraction methods with 0.05M calcium chloride (CA), 0.5M acetic acid and 0.1M sodium pyrophosphate, respectively. The results showed that the relative amount (Q_(ra)) of CA extractable Cs decreased rapidly to almost zero within a few days after being freshly introduced to the soil samples. The Q_(ra) of CA extractable Sr in all the samples was almost the same during 6-month. For Mn, the Q_(ra) of CA-Mn in Gray lowland soils decreased throughout the experiment, but the soil redox conditions did not affect on the change, the Q_(ra) of CA-Mn in Andosol was much lower than that in Gray lowland soils. Interestingly, for Tc, the Q_(ra)s of CA-Tc was lower in the anaerobic condition than in the aerobic conditions in both soils. Due to the reduce of the amounts of water soluble and exchangeable forms of these elements in soils, the amounts of these elements entering the food chain probably decrease gradually with time.