Saturday, 15 July 2006

Phytoextraction of Heavy Metal Contaminated Soil by Hyperaccumulator Sedum alfredii Hance with Mixed Chelant in a Co-Crop System.

Ze-Bin Wei1, Qi-Tang Wu1, Ying Ouyang2, and Jean Louis Morel3. (1) College of Natural Resource and Environment, South China Agricultural Univ, Wushan, Guangzhou, 510642, China, (2) Dept of Water Resources, St. Johns River Water Management District, Palatka, FL 1429, (3) INPL(ENSAIA)/INRA, Laboratoire Sols et Environnement, BP 172, 2 avenue de la forêt de Haye, F-54505 Vandoeuvre les Nancy Cédex, France

Phytoextraction is a promising technology that uses hyperaccumulating-plants to remove inorganic contaminants, primarily heavy metals, from soils and waters. A field experiment was conducted to evaluate impacts of a Mixed Chelant (MC) upon the growth and phytoextraction of heavy metals by the hyperaccumulator Sedum alfredii Hance in a co-crop system in a paddy land that has historically irrigated with Pb and Zn contaminated mining wastewaters. The co-crop system used in this study comprised of a Zn- and Cd-hyperaccumulator (S. alfredii) and a low-accumulating crop (Zea mays). Results showed that yields of the two plants were both increased with the addition of the MC. Concentrations of Zn, Pb and Cd were increased significantly in the aboveground parts of S. alfredii but not in those of Z. mays with the addition of the MC to the co-crop system. Results further revealed that concentrations of Zn, Pb and Cd in the corn grains of Z. mays conform to the Chinese hygiene standards for animal feeds and in the other parts of Z. mays conform to the Chinese organic fertilizer standards. When the MC was applied to the co-crop system in the soil contaminated with Zn, Cd and Pb, respectively, at the initial levels of 700, 2, and 750 mg kg-1, the highest phytoextraction rates were observed and were 9.87, 0.08, and 0.09 kg ha-1, respectively, for Zn, Cd, and Pb in one harvest. Our study suggested that the use of the hyperaccumulator S. alfredii and the low-accumulating crop Z. mays in the co-crop system with the addition of the MC was a more promising approach than the use of a single hyperaccumulator with the assistance of EDTA (ethylene diamine triacetic acid). This approach not only enhances the phytoextraction rates of the heavy metals but also simultaneously allows agricultural practices with safe products in the metal-contaminated soils.

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