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(70-70) Assessing bioavailable zinc and cadmium in soils using Lepidium heterophyllum. Zhao, Fangjie*,1, Song, Jing1,2, Zhang, Hao3, McGrath, Steve1, 1 IACR-Rothamsted, Herts, United Kingdom2 Institute of Soil Science, Nanjing, China3 University of Lancaster, Lancaster, United Kingdom ABSTRACT- Thirty-two soils from diverse geographical regions were used to study the solubility of Zn and Cd in soil pore water and their bioavailability to Lepidium heterophyllum. The properties of the soils studied that influence bioavailability varied greatly (pH 4.3 - 7.7, organic C 1.1 - 10.0%, total Zn 59 - 27413 mg/kg and total Cd 0.1 - 315 mg/kg). Solubility of Zn and Cd was controlled mainly by soil pH and organic C content, and the concentrations of soluble Zn and Cd in the pore water can be predicted using total metal concentration, pH and organic C content, with 86-91% of variability accounted for. Lepidium heterophyllum was found to be a suitable indicator plant for toxicity testing, because it readily took up and transported metals from roots to shoots and was sensitive to metal toxicity. The threshold concentration of Zn in the shoots for phytotoxicity was between 300 and 500 mg/kg. The concentrations of Zn and Cd extractable with 1 M ammonium nitrate and the DGT fluxes of the metals gave best correlation with the concentrations of the metals in plant shoots. This was followed by the concentrations of soluble Zn and Cd in soil pore water. In contrast, total, EDTA extractable or isotopically exchangeable metals correlated poorly with plant uptake. The results suggest that pore water concentration is an important determinant of the bioavailability of Zn and Cd to plant, but re-supply of the metals to the pore water during plant growth must also be considered. Key words: zinc, cadmium, bioavailability, Lepidium heterophyllum |
