Differential sensitivity of Anabaena doliolum to Cu and Zn in batch and semicontinuous cultures.

Elevated concentrations of Cu and Zn inhibited Anabaena doliolum more severely in semicontinuous culture than in batch culture with growth and protein, chlorophyll a, and carotenoid contents generally more than two-fold more sensitive in the former culture system. The greater sensitivity of A. doliolum to test metals in semicontinuous culture was associated with their greater accumulation. The level of inhibition of various parameters of the test organism remained almost constant in semicontinuous culture, but considerable alleviation of the inhibitory effect occurred in batch culture with time concomitant with a regular decline in metal content of cells. However, metal content of cells in semicontinuous culture remained more or less constant with time, thereby causing no change in the level of inhibition. Unlike semicontinuous culture, batch culture showed considerable depletion of phosphate from the medium and a rise in pH (from 7 to 7.8). In conclusion, batch culture is not appropriate for long-term assessment of metal toxicity as it might substantially underestimate toxic effects of heavy metals.