Development of a biotic ligand model for acute zinc toxicity to barley root elongation

The effects of pH and some cations on the acute toxicity of zinc (Zn) to barley (Hordeum vulgare) root elongation were investigated to aid the development of an appropriate biotic ligand model (BLM). The results showed that Zn toxicity decreased with increased activity of Mg2+, K+ and Ca2+ but not Na+. The effect of pH on Zn toxicity to barley root elongation could be explained by H+ competition with Zn2+ bound to a biotic ligand (BL) at pH≤6 and by the concomitant toxicity of ZnHCO3+ in solution culture at pH≥6. Stability constants were obtained for the binding of Zn2+, ZnHCO3+, Mg2+, K+, Ca2+ and H+ with BL: log KZnBL 4.06, log KZnHCO3BL+ 5.15, log KMgBL 3.72, log KKBL 2.62, log KCaBL 1.99 and log KHBL 4.27. On the basis of these estimated parameters, a BLM was successfully developed to predict Zn toxicity to barley root elongation as a function of solution characteristics.