LEACHING OF COPPER, CHROMIUM, AND ARSENIC THROUGH SOME FREE-DRAINING NEW-ZEALAND SOILS

Concentrated toxic solutions of copper, chromium, and arsenic (CCA) ar e used extensively in the New Zealand timber preservation industry. A 2% w/v solution containing cupric, dichromate, and arsenate ions was l eached through undisturbed soil monolith lysimeters containing the sur face and subsurface horizons of 2 free-draining New Zealand soils. The resulting breakthrough curves were successfully modelled using the Go mpertz equation for biomass growth Differences between soil horizons i n the fitted Gompertz parameter values were related to differences in soil physical and chemical properties affecting leaching. Results were compared to those from a previous study investigating pulse leaching of a concentrated CCA solution of similar ion ratio using the same soi ls. Generally, solution leaching produced breakthrough curves influenc ed more by the soil's physical structure and less by kinetic processes (i.e. sorption and diffusion). This was in part due to the high metal concentrations of the CCA solution and the decreased contact time bet ween soil and solute in the solution leaching experiment. The relative ease of solute ion breakthrough increased in the order copper < arsen ate < dichromate. The study suggests that further research is required to assess management implications for spills of these heavy metal ion s to soils to prevent leaching or runoff to ground and surface water.