Toxicity of nickel to the earthworm and the applicability of the neutral red retention assay

The toxic effects of nickel on survival, growth, and reproduction of Eiseni a veneta were investigated following 4 weeks of exposure to a nickel-chlori de spiked loamy sand soil. The ability of a simple earthworm biomarker, the lysosomal membrane stability of coelomocytes, to reflect nickel exposure w as also studied. Nickel caused a significant toxic effect on E.veneta at so il concentrations above 85 mg Ni/kg. Reproduction (cocoon production) was t he most sensitive parameter being reduced at soil concentrations above 85 m g Ni/kg (EC10 = 85 mg Ni/kg). Survival of adults was only reduced at concen trations above 245 mg Ni/kg, while adult and cocoon wet weight were not aff ected by soil nickel concentrations up to 700 mg Ni/kg. The lysosomal membr ane stability, measured as neutral-red retention time, was reduced at soil nickel concentrations similar to those that reduced reproduction, and demon strated a dose-response relationship. The neutral-red retention time showed large individual variation for the earthworms within each exposure concent ration. It was concluded that the lysosomal membrane stability, measured as neutral red retention time, has a potential role in risk assessment, but c are should be taken conducting this test.