adsorption of arsenic on soil under different soil moisture conditions

the adsorption study was conducted on three japanese soils with different soil properties to characterize the adsorption pattern of arsenic (as). double tube method was used to find out the effect of soil moisture levels on as adsorption. for this study, besides double tube method, conventional batch method also was used. the as adsorption showed two phase kinetics. an initial and rapid adsorption was found at first hour and then gradually preceded before equilibrium in all the three soils in the case of double tube method and in clay loam and light clay soil in the case of batch method. adsorption seemed to reach equilibrium at 24 h in both methods, though the initial adsorbate load was not the same at the same applied concentration in the methods. adsorption activity differed according to soil and as well as to the methods. the highest adsorption was found in clay loam soil followed by light clay and sandy loam soil. the linear model of freundlich adsorption was found better fitted in the case of double tube method than batch method. suggesting that, under the experimental conditions stated here, the double tube method is more appropriate to describe the adsorption of as in the three japanese soils under normal field condition. the concentration of as in soil water was slightly increased at different moisture levels from 50%-80% which may contribute significantly to the bioavailability of as at the moisture level below maximum filed capacity.