Kinetics of cadmium release from soils as influenced by organic acids: implication in cadmium availability

• Published in: Journal of environmental quality 1997-01, Vol.26 (1), p.271-277
• Main Authors: Krishnamurti, G. S. R., Cieslinski, G., Huang, P. M., Van Rees, K. C. J.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; cadmio; Cadmium; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; Mineral components. Ionic and exchange properties; Organic acids; Physics, chemistry, biochemistry and biology of agricultural and forest soils; pollution du sol; polucion del suelo; procesos de transporte en el suelo; soil pollution; Soil science; soil transport processes; transport dans le sol
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq1997.00472425002600010038x

The low-molecular-weight organic acids (LMWOAs) secreted by plant roots modify the mobility of Cd through formation of soluble complexes in the soil rhizosphere; the kinetics of Cd release as influenced by organic acids and its impact on Cd bioaccumulation remains to be established. The influence of LMWOAs (10(-3) and 10(-2) M), viz., acetic, citric, oxalic, fumaric, and succinic acids, which are present in the soil rhizosphere, on the kinetics of Cd release from selected soils (Luseland, Waitville, and Jedbergh) of Saskatchewan, Canada, was investigated at 25 degrees C and at an ionic strength of 0.1 M NaNO3. It was observed that the Cd release from the soils increased initially up to a reaction period of about 2 h and then slowly decreased with time. With time, the LMWOAs were apparently microbially degraded and the soil solution Cd2+, which was transformed from the Cd-LMWOA complexes by microbial degradation, was adsorbed onto the negatively charged soil particles. Increasing amounts of Cd were released from the soils to the soil solution with the renewal of LMWOAs after every 2 h. The short-term (reaction period of 0.25 to 1 h) kinetics of Cd release from the soils was described by a parabolic diffusion kinetic model. The overall diffusion coefficient of the Cd release from the soil and the Cd released by the renewal of LMWOAs followed the same trend as the Cd availability index of the soils: Luseland >> Waitville > Jedbergh. Thus, the results presented in this investigation indicate the importance of the kinetics of the Cd release from the soils by the LMWOAs excreted by root exudates in understanding the availability of soil Cd.