An improved biotic ligand model (BLM) for predicting Co(II)-toxicity to wheat root elongation: The influences of toxic metal speciation and accompanying ions

Abstract

In order to explore the effects of pH and accompanying ions on divalent cobalt (Co(II)) toxicity to the wheat root elongation, an improved biotic ligand model (BLM) to predict Co(II) toxicity was developed in solution culture. The results showed that the Co(II)-toxicity decreased with the increases of K+, Ca2+ and Mg2+ activities, and the activity of Na+ had no impact on the Co(II)-toxicity. High H+ activity reduced the Co(II)-toxicity by the competitive effect of H+, while low H+ activity affected the toxicity by the change in the type of Co(II) in culture medium. Co2+ and CoOH+ were toxic to wheat root elongation, and Co(OH)2 was not. On the basis of BLM theory, the conditional equilibrium constants for Co2+, CoOH+, H+, Mg2+, Ca2+, K+ were obtained: logKCoBL = 4.65, logKCoOHBL = 6.62, logKHBL = 4.53, logKMgBL = 3.65, logKCaBL = 2.36 and logKKBL = 2.17. Free Co2+ and CoOH+, and the competitions of K+, Mg2+ and Ca2+ were suggested to be considered when developing the Co(II)-BLM.