A generic biotic ligand model quantifying the development in time of Ni toxicity to Enchytraeus crypticus

Biotic ligand models (BLMs) predicting metal toxicity for a fixed exposure time are available, but it is uncertain how to extrapolate predictions to a dynamic environment with time-variable exposure. Three BLM-based models were developed to describe change of Ni toxicity to Enchytraeus crypticus in time. These models assumed that: (a) biotic ligand binding constants of Ni and competing cations (K_NiBL and K_CBL) and the fraction of biotic ligands occupied by Ni to produce 50% mortality (f₅₀) are fixed with time, (b) K_NiBL and K_CBL remain constant while f₅₀ varies with time, and (c) K_NiBL, K_CBL, and f₅₀ are all time-dependent. Model (a) successfully described the 7-d toxicity of Ni but failed in explaining Ni toxicity at longer exposure times. Both models (b) and (c) well described Ni toxicity, within a factor of 2, at varying solution chemistries and different exposure times. This shows that the acute BLM cannot directly be applied for predicting chronic metal toxicity and that some BLM parameters may vary with time. Our findings provide plausible explanations for differences in mechanisms of acute and chronic toxicity, offering a framework for incorporating toxicokinetic and toxicodynamic processes in describing Ni toxicity in time.