Biotic Ligand Model Development Predicting Acute Cu Toxicity To The Algae Scenedesmus Obliquus:Construction And Validation

Recently,the biotic ligand model?BLM?,which considering metal chemical speciation,metal interaction,and cation competition,has been widely used to predict metal toxicity?e.g.Cu,Zn,Cd,Ag,Ni,Pb?to a variety of aquatic organisms.However,no application of the BLM in predicting Cu toxicity to Scenedesmus obliquus was developed.As a common metal in life,most of the established BLM of other aquatic organisms are about Cu,which can provide a reference value for developing S.obliquus-BLM in this study.The eukaryotic green algae S.obliquus is widely distributed in freshwater and occupies an important position in the aquatic ecosystem.Green algaes are the primary producer of the aquatic ecosystems.So,any effects of contaminants on green algae like S.obliquus will incur far more expanded effects on the whole aquatic ecosystems.Therefore,it is very important to develop a S.obliquus-BLM to predict the Cu toxicity to S.obliquus depending on site-specific water characteristics.The objectives of the present study were to develop a biotic ligand model?BLM?to predict acute Cu toxicity to Scenedesmus obliquus and to verify the practicability of this model in laboratory and freshwater.In this study,the individual effects of calcium,magnesium,potassium,sodium and pH on copper toxicity to the green alga Scenedesmus obliquus and the adsorption effect of copper on Scenedesmus obliquus were investigated.Higher activities of Ca²⁺,Mg²⁺,and Na⁺?but not K⁺?linearly increased the 72h-EC²⁺_50Cu,proving the BLM concept of competitive binding of these cations and copper ions on algal cells.However,the positive correlation between H⁺and 72h-EC²⁺_50Cu seemed to be caused by toxicity of copper hydroxide rather than proton competition.The results of this study also demonstrate that the adsorption effect of copper on Scenedesmus obliquus is substantially according with van den Berg equation.Based on the BLM concept,stability constants for the binding of Cu²⁺,CuOH⁺,Ca²⁺,Mg²⁺,Na⁺and H⁺to the biotic ligand and the metal accumulation on membranes associated with 50%effective concentrations(EA₅₀)were estimated by the methodology described below.Following values were derived:logK_CuBL=5.90,log K_CaBL=3.25,logK_MgBL=3.86,logK_NaBL=2.81,logK_CuOHBL=6.64,logK_HBL?5.4 and EA₅₀=2.985 nmol/gw.Using all of the parameters,a initial S.obliquus-BLM was developed which can predict acute copper toxicity to S.obliquus depending on site-specific water characteristics.After validation with laboratory and natural water of Shangtang River,the developed S.obliquus-BLM will contribute to improve the current copper criterion which consider site-specific water characteristics and could be applied in environmental risk assessment.