Uptake and toxicity of spiked nickel to earthworm Eisenia fetida in a range of Chinese soils

Abstract

Bioavailability and toxicity of metals to soil organisms varies among different soils, and knowledge of this variance is useful for the development of soil environmental quality guidelines. In the present study, laboratory experiments were performed to investigate the effects of variations in nickel (Ni) uptake and toxicity on growth, cocoon output, and juvenile production in the earthworm Eisenia fetida in 13 Chinese soils spiked with nickel chloride. Body weight development of E. fetida was rather insensitive to Ni, and significant inhibition of growth was observed only at high Ni concentrations, such as 560 and 1000 mg/kg. The 50% inhibition effect concentrations (EC50s) for cocoon and juvenile production, based on measured Ni concentrations in soils, varied from 169 to 684 mg/kg and from 159 to 350 mg/kg, respectively. The EC50s represented approximately fourfold variation for cocoon output and twofold variation for juvenile production among 13 Chinese soils. Juvenile production, compared to cocoon output, was a more sensitive endpoint parameter to Ni. Nickel uptake in E. fetida increased as simple linear functions of increasing soil Ni concentrations. Tissue Ni-based EC50s (based on Ni concentrations in earthworm tissues) for cocoon production varied from 37 to 121 mg/kg (threefold variation) in 12 of 13 soils, suggesting a similar variation to that of soil Ni-based EC50s. Relationship analysis between soil properties and Ni toxicity showed that neither the EC50s for cocoon output nor those for juvenile production presented significant correlation with soil properties (pH, organic matter content, cation exchange capacity, clay content, Ca²⁺ and Mg²⁺). This may be ascribed to the narrow range of properties of selected soils. The soil factors that determined Ni toxicity to earthworm reproduction remain undetermined in the present study, and these data should be used cautiously when developing toxicity prediction models because of the narrow selection of soil properties.