Predicting Toxicity of Metal Mixtures to Pseudomonas Fluorescens Using Fixed Ratio Rays And Central Composite Experimental Designs

ABSTRACT 

The toxicities of binary (Ni(II) + Co(II) and Zn(II) + Cd(II)), ternary (Zn(II) + Cd(II) + Ni(II) and Ni(II) + Co(II) + Cd(II)) and quaternary (Ni(II) + Co(II) + Zn(II) + Cd(II)) mixtures of metals, as well as the individual metal ions to Pseudomonas fluorescens, were assessed by using inhibition of dehydrogenase activity as an endpoint. Uniform design concentration ratio (UDCR) and equieffect concentration ratio (EECR) mixtures were designed to evaluate the combined toxicities of these heavy metal ions. All the dose-response relationships of the UDCR and EECR mixtures and the individual metals ions could be described by a logistic function. The EC50s of the individual metal ion and their mixtures were estimated using logistic function. The Duncan test indicated significantly different EC50 values for each of the metal ions. Isobolographic and Toxic index analyses showed possible interaction among the metal mixtures. Toxicities predicted by concentration addition (CA) and independent action (IA) models were compared with the observed toxicities. The CA and IA models predicted similar toxicities of the binary and Zn(II) + Cd(II) + Ni(II) ternary mixtures. Generally, Zn(II) + Cd(II) + Ni(II) ternary mixtures were synergistic while Ni(II) + Co(II) + Cd(II) ternary mixtures were antagonistic. The equieffect and quaternary mixtures were generally synergistic. The response surface methodology using central composite design indicated synergistic effect for Ni(II) + Co(II) and antagonistic effect for Zn(II) + Cd(II) binary mixtures. Synergistic, antagonistic and additive interactions of the mixtures are possible from the viewpoint of these analyses.