Tuesday, 11 July 2006

Bioaccumulation of Copper and Cadmium Ions by Cyanobacterium Spirulina Platensis.

Wenli Chen, State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Shizishan, Wuhan, China, Qiaoyun Huang, Key Laboratory of Subtropical Agriculture and Environment, Ministry of Agriculture, Huazhong Agricultural University, Wuhan, 430070, China, and Hongxia Huang, Huazhong Agricultural University, Shizishan, Wuhan, 430070, China.

Utilization of biological materials for the remediation of heavy metal-contaminated soils offers a potential alternative approaches to the conventional techniques. In order to search for available biomaterials with higher accumulation capacity of heavy metals, biosorption of Cu2+ and Cd2+ by 10 bacterial strains in 4 genera was investigated. Cyanobacterium Spirulina platensis FACHB439 showed the strongest ability to bind Cu2+ and Cd2+ ions with the adsorption capacity of 1993 and 2347 mmol/kg dry biomass for Cu2+ and Cd2+, respectively. This adsorption quantity is significantly greater than those reported for other microorganisms. The strain has a specific surface area of 214.4 m2/g dry weight and a zero point of charge at 5.0. Within the pH range from 1.8 to 10.3, the surface charge density of the strain was 9.19~-2.05 μmol/m2. In the presence of 20~180 mg/L of biomass, Cu (0.1mM) removed by the bacteria from solution was from 8.4% to 64.6%, while the Cd (0.1mM) immobilized was from 18.6% to 61.3%. The equilibrium sorption of both metals by the test strain followed the Langmuir model. Adsorption of copper reached equilibrium in 2 h, and that of cadmium in 4 h. The adsorption kinetics of Cu and Cd conformed to the Elovich equation.Adsorbability of the two metal ions by dead cells is considerably lower than that by viable cells. The release of biosorbed metals was 11.1~20.9% and 50.9~58.2% by H2O and 1M NH4NO3, respectively. The presence of companying heavy metal ions compete effectively with the adsorption of Cu and Cd by the test strain. The influence of competition on Cu was in the order of Zn >Pb >Cd > Cr, while that on Cd adsorption followed the sequence Cu > Cr > Pb > Zn. In the single-metal system, the percent adsorption was 66.8% and 69.4 % for Cu and Cd, respectively, at a metal concentration of 0.1mM. In the multiple-metal systems, the adsorption of Cu was 17.3% and that of Cd was 21.3%. The data obtained suggest that cyanobacterium Spirulina platensis has promising potential in the bioremediation of copper and cadmium-polluted soils and wastewaters. Studies on the binding mechanisms of heavy metals and genetic investigations on the organism merit further attention.

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