Mobility of Cadmium‐109 and Zinc‐65 in Soil Influenced by Equilibration Time, Temperature, and Organic Matter

Abstract

Partitioning of 109Cd and 65Zn fractions in an alum shale soil as affected by time, temperature, and organic matter was investigated. The soil was extracted sequentially by H20 (F1), 1 M NH4OAc at pH 7 (F2), 1 M NH4OAc at pH 5 (F3), 0.04 M NH2OH HCl (F4), 30% H2O2 (F5), and finally by 7 M HNO3 (F6). Sequential extraction of metals was performed on soil samples collected at time intervals ranging from 0.5 to 8760 h (1 yr) after spiking the soil with 109Cd and 65Zn. The soil was placed incipiently in temperature controlled climate chambers at 9, 15, and 21°C. Before spiking, the soil was treated with 0 or 4% organic matter. Adsorption of 109Cd and 65Zn was rapid, but a subsequent slow diffusion of the metals toward chemisorbed fractions was also evident since the 109Cd and 65Zn concentrations decreased in the three mobile fractions (F1–F3) and increased in the inert fractions (F4, F5, F6 and F7) with time. Temperature elevation resulted in decreased concentrations of 109Cd and 65Zn in the F2 and F3 fractions, whereas the concentrations of these metals increased in the inert fractions. In the organic matter‐treated soil, 109Cd and 65Zn were increased significantly in the mobile fractions, with a corresponding reduction of 109Cd and 65Zn in the inert fractions. The effect of organic matter was more pronounced at 9°C than at 21°C. The results thus indicate that increasing time and temperature reduce the organic matter‐induced mobilization of 109Cd and 65Zn in soil.

Effects of rice straw on the speciation of cadmium (Cd) and copper (Cu) in soils

“…The result is contradictory to the finding that Cd was increased significantly in the mobile fractions in the soil with the addition of organic matter (Almas et al, 1999). The total soluble concentration of metal ions in soil solutions depends on the free metal ion concentration, the presence of inorganic and organic ligands and pH.…”

“…CaCl 2 -extractable Cu in some artificial soils, soluble and exchangeable Cu fractions in sandy soil and sandy loam were found to decrease over time (Han et al, 2001;Tom-Petersen et al, 2004; Daoust et al, 2006). In sequential chemical extraction experiment, Cd concentration decreased in the three mobile fractions with time (Almas et al, 1999). In this study, the effect of incubation time on free Cu 2+ and Cd 2+ concentrations showed different patterns for the four soils.…”

“…Contradictory results were found about the effect of organic matter on bioavailability and mobility of heavy metals in soils. Almas et al (1999) found that Cd in the mobile fractions decreased significantly in the soil treated with organic matter. Strobel et al (2005) found that dissolved organic carbon (DOC) had no effect on the amount of soluble Cu and Cd in soil with DOC addition.…”

Change of the Extractability of Cadmium Added to Different Soils: Aging Effect and Modeling

“…The processes of diffusion were slow aging processes. Almås et al [50] also found that the transfer of Cd from solution to stable forms were significantly slower processes. The slow processes were due to inner-sphere surface complexation via partial or complete dehydration of surface species [12].…”

Cádmio na cadeia alimentar: proveniente de vegetais e avaliação da sua disponibilidade no solo com auxílio do 109Cd

“…Segundo Muraoka (1991) 2 O elétron da camada K é puxado para dentro do núcleo e se transforma em nêutron (p + + e -k → n 0 ), e a vacância livre é ocupada por um elétron de outra camada, emitindo raio-X. Nas plantas, a atividade do radionuclídeo é representada pela atividade específica, dada por (DI; CONDRON; FROSSARD, 1997): O mais rigoroso método para avaliar a biodisponibilidade de íons metálicos no solo é pela medida direta da porção lábil, usando a técnica de diluição isotópica com traçadores radioativos (MURAOKA; NEPTUNE; NASCIMENTO FILHO, 1983a;1983b;NAKHONE;YOUNG, 1993;HAMON et al, 1998;SALBU, 1999;SMOLDERS et al, 1999;STANHOPE et al, 2000;SINGH, 2001 Figura 2 -Esquema de decaimento do 109 Cd ( 109m Ag). O número entre parênteses indica o valor da energia em keV.…”