Joint toxicity of copper and zinc to a terrestrial nematode community in an acid sandy soil

Heavy metal toxicity to an indigenous nematode community was examined following the addition of Cu and Zn, alone or in combination, to agricultural soil. The dissolved Cu or Zn concentrations measured after equilibrating soil samples with a 0.01 M solution of CaCl2, showed that the metal concentrations found in soils with combined metal additions were not significantly different from those with single metal additions. After an exposure period of six months, many nematode community parameters and individual nematode taxa were significantly affected by increasing concentrations of Cu and Zn up to 200 mg kg(-1). Some nematode taxa, such as Thonus, Alaimus and Aporcelaimellus were very sensitive and disappeared at Cu and Zn concentrations exceeding 50 mg kg(-1). For several nematode community parameters and nematode taxa, EC50 values for single metal exposures were used to calculate TU50 values for the joint toxicity of Cu and Zn. Based on these calculations, it is concluded that the effects of a combined exposure to Cu and Zn were additive or less than additive. Before this conclusion can be generalised, however, more data are needed on other types of soil, other pH values and other combinations of pollutants.