Development of a Terrestrial Biotic Ligand Model(t-BLM): Alleviation of the Rhizotoxicity of Copper to Wheat by Magnesium
陆地生物配体模型(t-BLM)初探:镁离子降低铜离子对小麦根的毒性

By incorporating metal chemical speciation and the protective effects of competing cations on the BL, the Biotic Ligand Model(BLM)had been developed to predict aquatic metal bioavailability and toxicity. Recently, the BLM concept was applied to the soil environment. Developing the terrestrial biotic ligand model(t-BLM)which can effectively predict the ecotoxicity of heavy metals to soil organisms became a hot issue. At different concentrations of magnesium, which is one of the major cations in soil solution, copper toxicity affecting root growth of wheat(Triticum aestivum)was quantitatively discussed, by independent factor controlling-nutrient solution culture with constant pH-root elongation inhibition test of terrestrial plant. Results showed that higher concentrations of Mg2 decreased the toxicity of Cu2 to the wheat root significantly, which confirmed that the protective effects of cations to the plant metal toxicity exists in the terrestrial ecosystem, and held out the BLM hypothesis that cations compete with metal ion for the bound to the BL, i.e. the BLM concept applies to the terrestrial plants. Quantitative analysis showed a good relationship between the toxicity response index EC50(expressed as free copper ion activities) and free magnesium ion activities: pEC50(Cu2 )= -0.36(Mg2 ) 6.47(r2 = 0.9976),which meant the extent of magnesium influencing copper toxicity could be predicted by the equation. The conceptual model and modeling methodology of the t-BLM were discussed too. The t-BLM which combined the soil physicochemical property, metal speciation and organisms bioaccumulation/toxicity response, might provide a new tool to develop the more rational soil quality criteria and risk assessment of heavy metals.