Modelling uptake and toxicity of nickel in solution to Enchytraeus crypticus with biotic ligand model theory

Protons and other cations may inhibit metal uptake and alleviate metal toxicity in aquatic organisms, but less is known about these interactions in soil organisms. The present study investigated the influence of solution chemistry on uptake and toxicity of Ni in Enchytraeus crypticus after 14 days exposure. Ca²⁺, Mg²⁺ and Na⁺ were found to exert significant effects on both uptake and toxicity of Ni. An extended Langmuir model, which incorporated cation competition effects, well predicted Ni uptake. The LC50{Ni²⁺} predicted by a developed Biotic Ligand Model matched well with observed values. These suggest that cation competition needs to be taken into account when modelling uptake and effects. The binding constants of Ni²⁺, Mg²⁺ and Na⁺ on the uptake and toxic action sites were similar, but for Ca²⁺ they differed. This indicates that the effect of Ca²⁺ on Ni²⁺ toxicity cannot simply be explained by the competition for entry into organism.