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Figure 4: Critical specific growth ( ) as a function of primary particle size of TiO2 in terms of EC20 and EC50. Lines are a five-parameter modified log normal empirical fitting (7) from SigmaPlot ver. 9.01 for EC20 (dotted) and EC50 (solid). Error bars are ±1 standard deviation. Experimental conditions: initial algae concentration =  cell/mL, test duration = 4 days, and initial test volume = 200 mL.