() Effects of aging and toxic cations on Cu bioavailability and toxicity in soils.
Lombi, E1, Hamon, R1, Ma, Y1, Nolan, A1, McLaughlin, M1, 1 CSIRO Land and Water, Glen Osmond, South Australia, Australia
ABSTRACT- The bioavailability and toxicity of Cu in soils is controlled by a number of soil properties and processes. Some of these such as pH, adsorption/desorption and competition with beneficial cations have been extensively studied. However, the effects of aging (or natural attenuation) and of co-toxicants, such as Al and Mn, have not been thoroughly investigated. Both these processes are important in terms of risk assessment. The effect of aging on Cu availability was investigated in 19 European soils covering the major soil types found in Europe. These soils were spiked with Cu at two levels, incubated outdoors and sampled several times during a period of one year. Natural attenuation of Cu was investigated using isotopic dilution techniques (E and L-values), which measure the lability or chemical reactivity of metals in soil. Lability of Cu rapidly decreased after spiking especially in high pH soils, probably due to precipitation reactions. After this rapid initial reaction phase, metal ageing continued with a slower rate. Soil pH and organic matter content were the principal parameters controlling the rate of aging. In a separate study rhizotoxicity of Al, Mn and Cu to wheat seedlings was studied in well-defined nutrient solutions, with these elements present singly, or in combination. Toxicity was expressed on a solution metal activity basis. There was no interaction between Mn2+ and Cu2+ toxicity, but Cu2+ was significantly less toxic, on a relative basis, in the presence of Al3+. Thus, critical thresholds for soil solution Cu2+ activity determined in acidic soils will be underprotective compared to soils which contain low concentrations of soluble Al (e.g. limed or non-acidic soils).
Key words: aging, Copper, bioavailability, interactions