Accumulation, assimilation and growth inhibition of copper on freshwater alga (Scenedesmus subspicatus 86.81 SAG) in the presence of EDTA and fulvic acid

Accumulation and growth inhibition of Cu to fresh water alga (Scenedesmus subspicatus 86.81 SAG) and the influences of ethylenediaminetetraacetic acid (EDTA) and fulvic acid (FA) were examined. These results demonstrated that both EDTA and FA could reduce toxicity of Cu to alga by the way of preventing Cu from being adsorbed by cell wall of alga. When dissolved Cu (Cu_dissolved), extracellular Cu (Cu_{extracellular}), and intracellular Cu (Cu_{intracellular}) were differentiated, our results showed that the concentration level of extracellular Cu ([Cu_{extracellular}]) was a good indicator for measuring the toxic effects of Cu on alga growth in complex matrix. Either in the absence or in the presence of EDTA and FA, the concentration of intracellular Cu increased to 0.6-1.5×10^-8 μM per cell when the growth inhibition reached to about 50%. We found that the acute toxicity of copper on unicellular alga could be interpreted by its accumulation at a discrete site or biotic ligand at alga cell wall and critical accumulation of Cu associated with EC₅₀ was determined to be 1×10^-8 μM per cell. Therefore, the Biotic Ligand Model (BML) could be extended to predict the influence of copper on growth inhibition of alga.