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 Eisenia veneta were investigated following 4 weeks of exposure to a nickel-chloride spiked loamy sand soil. The ability of a simple earthworm biomarker, the lysosomal membrane stability of coelomocytes, to reflect nickel exposure was also studied. Nickel caused a significant toxic effect on E.veneta at soil concentrations above 85 mg Ni/kg. Reproduction (cocoon production) was the most sensitive parameter being reduced at soil concentrations above 85 mg Ni/kg (EC10 = 85 mg Ni/kg). Survival of adults was only reduced at concentrations above 245 mg Ni/kg, while adult and cocoon wet weight were not affected by soil nickel concentrations up to 700 mg Ni/kg. The lysosomal membrane stability, measured as neutral-red retention time, was reduced at soil nickel concentrations similar to those that reduced reproduction, and demonstrated a dose-response relationship. The neutral-red retention time showed large individual variation for the earthworms within each exposure concentration. It was concluded that the lysosomal membrane stability, measured as neutral red retention time, has a potential role in risk assessment, but care should be taken conducting this test.