Development Of Biotic Ligand Models Predicting Nickel Toxicity To Barley

Heavy metal contamination in the soil becomes increasingly serious,which has caused serious damage to the ecological system,so legislative control and the further improvement of soil quality criteria have become an urgent tasks.The current soil quality criteria is based on total or soluble metal concentrations.However,a large body of evidence indicates that both total and soluble metals are unrelated to ecotoxicity,directly, and the relationships between bioavailability and operationally defined fractions of metals are often influenced by other soil property.Thus,it is important to study of the bioavailability of heavy metals and its influencing factors and the establishment of heavy metal toxicity prediction model.Recently,a Biotic Ligand Model(BLM) has been developed to predict metal toxicity in aquatic ecosystems.Though the BLM approach is used to predict metal toxicity in terrestrial systems.To explore the influence factors of heavy metals toxicity to biological and improve our ability to assessment risk of heavy metal,this paper study the bioavailable forms and its influence factors of Nickel(Ni) by ecotoxicology methods,to use the obtained toxicity data to develop a BLM that can predict Ni toxicity toward barley.The development(this study) of such a semimechanistic model could support efforts to improve the ecological relevance of presently applied risk assessment procedures.The extent to which Ca²⁺,Mg²⁺,Na⁺,K⁺ and pH independently mitigate Ni toxicity for the barley was examined under hydroponic condition.The results showed that:(1) The effects of pH on nickel toxicity to barley need to consider NiCO₃ and H⁺ competition when BLM was developed.The effect of pH on the acute toxicity of nickel to barley root elongation was investigated in solution culture.The results showed that the effective concentrations,which reduced root elongation by 50%,based on free Ni²⁺ activity(EC₅₀(Ni²⁺)) reduced about 10 times when pH was from 4.5 to 8.3.Based on biotic ligand model theory,the nonlinear relationship between EC₅₀(Ni²⁺) and H⁺ activity in this study indicated that the increased toxicity with increasing pH was not only due to decreasing H⁺ competition.The logistic dose-response curve showed that considering the H⁺ competition and NiCO₃ plus Ni²⁺ as the dose improved the data fit significantly (R²=0.95) than only the free Ni²⁺ activity was considered.(2) The Mg²⁺ concentration was a main factor that affected the Ni acute toxicity to barley root elongation.The EC₅₀(Ni²⁺) for barley root elongation increased from 18.53μM to 165.46μM with increasing Mg²⁺ activity(0.05-4mM),supporting the concept of competitive binding of these ions.(3) Ca²⁺ activity(0.18-7.45mM),K⁺ activity(0.08-8.90 mM),Na⁺ activity(2.44 -22.05mM)did not significantly affect EC₅₀(Ni²⁺).(4) Based on the biotic ligand model(BLM) concept,stability constants for the binding of Ni²⁺,NiCO₃,Wand Mg²⁺ to the biotic ligand were obtained as follows: 1OgK_NiBL=5.01,logK_NiCO3BL=4.79,log K_HBL=4.60,logK_MgBL=4.60.