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 follo wing the addition of Cu and Zn, alone or in combination, to agricultural so il. The dissolved Cu or Zn concentrations measured after equilibrating soil samples with a 0.01 M solution of CaCl2, showed that the metal concentrati ons found in soils with combined metal additions were not significantly dif ferent 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 t o 200 mg kg(-1). Some nematode taxa, such as Thonus, Alaimus and Aporcelaim ellus were very sensitive and disappeared at Cu and Zn concentrations excee ding 50 mg kg(-1). For several nematode community parameters and nematode t axa, EC50 values for single metal exposures were used to calculate TU50 val ues 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 additi ve or less than additive. Before this conclusion can be generalised, howeve r, more data are needed on other types of soil, other pH values and other c ombinations of pollutants.