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TECHNICAL REPORTS

Heavy Metals in the Environment

Prediction of Zinc, Cadmium, Lead, and Copper Availability to Wheat in Contaminated Soils Using Chemical Speciation, Diffusive Gradients in Thin Films, Extraction, and Isotopic Dilution Techniques

^a CSIRO Land and Water, PMB 2, Glen Osmond, SA 5064, Australia
^b Soil and Land Systems, School of Earth and Environmental Sciences, University of Adelaide, PMB 1, Glen Osmond, SA 5064, Australia
^c Current address: National Measurement Institute, PO Box 385, Pymble, NSW 2073, Australia

^* Corresponding author (Annette.Nolan{at}measurement.gov.au)

Received for publication June 3, 2004. To predict the availability of metals to plants, it is important to understand both solution- and solid-phase processes in the soil, including the kinetics of metal release from its binding agent (ligand and/or particle). The present study examined the speciation and availability of Zn, Cd, Pb, and Cu in a range of well-equilibrated metal-contaminated soils from diverse sources using several techniques as a basis for predicting metal uptake by plants. Wheat (Triticum aestivum L.) was grown in 13 metal-contaminated soils and metal tissue concentrations (Zn, Cd, Pb, and Cu) in plant shoots were compared with total soil metal concentrations, total soluble metal, and free metal activities (pM²⁺) in soil pore waters, 0.01 M CaCl₂–extractable metal concentrations, E values measured by isotope dilution, and effective metal concentrations, C_E, measured by diffusive gradients in thin films (DGT). In the DGT technique, ions are dynamically removed by their diffusion through a gel to a binding resin, while E values represent the isotopically exchangeable (labile) metal pools. Free metal activities (Zn²⁺, Cd²⁺, and Pb²⁺) in soil pore waters were determined using a Donnan dialysis technique. Plant Zn and Cd concentrations were highly related to C_E, while relationships for Zn and Cd with respect to the other measures of metals in the soils were generally lower, except for CaCl₂–extractable Cd. These results suggest that the kinetically labile solid-phase pool of metal, which is included in the DGT measurement, played an important role in Zn and Cd uptake by wheat along with the labile metal in soil solution. Plant Pb concentrations were highly related to both soil pore water concentrations and C_E, indicating that supply from the solid phase may not be so important for Pb. Predictions of Cu uptake by wheat from these soils by the various measures of Cu were generally poor, except surprisingly for total Cu.

Abbreviations: C_E, effective concentration • DGT, diffusive gradients in thin films • E, isotopically exchangeable (labile) metal pool • EC, effect concentration • GF-AAS, graphite furnace atomic absorption spectroscopy • ICP, inductively coupled plasma • MS, mass spectrometry • MWHC, maximum water holding capacity • OES, optical emission spectroscopy

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This Issue in Journal of Environmental Quality

JEQ 2005 34: 403-407. [Full Text]