Effects of fluoride and chloride on the growth of Chlorella pyrenoidosa

摘要

To compare the toxic action of fluoride (F~-) and chloride (Cl~-) on freshwater algae, effects of F~- and Cl ~- on Chlorella pyrenoidosa growth were investigated by determination of the algal biomass and model analysis. Results showed that the exponential growth equation (D = D_0 + ae~(bT)) may be used to fit the relationship between cell density (D) of C. pyrenoidosa and exposure time (T), but F~- and Cl~- have significantly different effects on parameters a (initial quantity of algae at the exponential growth stage) and b (growth constant). In the range of experimental concentrations, F~- inhibited C. pyrenoidosa growth, and percent inhibition increased with increasing exposure time and F~- concentration. By contrast, Cl ~- either inhibited or enhanced C. pyrenoidosa growth depending on Cl~- concentration and exposure time, and percent inhibition increased with increasing Cl~- concentration but decreased with increasing exposure time. The dose-response equation: I = min + (max - min)/(1 + 10 ~(lgEC50-lgC)) may be used to fit the relationship between percent inhibition (I) and F~- or Cl~- concentration (C); however, F~- was distinct from Cl~- in terms of effects on parameter 'min'. The EC50 values of F~- and Cl~- ranged from 118 to 170 mg/L and 19.73 to 36.33 g/L, respectively; the latter is much higher than the former. Thus F~- has higher toxicity than Cl~-.