Using geophysics to locate elevated soil zinc and natural organic matter to influence metal bioavailability

Conductivity and chargeability data, obtained in the field by Time-Domain Induced Polarisation (TDIP), were employed as a non-invasive means of determining elevated soil zinc concentrations. A comparison of chargeability data with zinc concentration data, obtained by total soil digestion in the laboratory, showed soil with high chargeability were soils which also had elevated soil zinc concentrations (300 to 4, 750 mg/kg soil). Glasshouse phytoremediation experiments were conducted on these soils, as well as on lateritic soils with high nickel concentrations (2,250 to 4,000 mg/kg soil), in order to determine if natural organic amendments increased phytoextraction potential and biomass production of Lolium perenne. Zinc and nickel were shown to be extracted from the amended soils and accumulated into the aboveground parts of ryegrass in concentrations less than that of unamended control soils. In fact, the organic amendments decreased bioavailability of the metals. A plot of leaf dry weight versus leaf metal concentration showed the bioavailability of zinc and nickel to be lowest after the addition of Colac Peat.