The effect of 2,5,2′,5′‐tetrachlorobiphenyl on growth and death of the cyanobacterium Anabaena flos‐aquae

The effect of 2,5,2′,5′‐tetrachlorobiphenyl (TcBP) on cell death was investigated in the cyanobacterium Anabaena flosaquae (Lyngb.) Bréb grown in a P‐limited, semicontinuous culture under N 2 ‐fixing conditions during a 17‐d period. The TcBP was supplied daily to yield final concentrations of 1, 10, and 100 ppb (or ng/ml). At 1 and 10 ppb, the population size of live cells (sum of live vegetative cells and live heterocysts) was not different from that of the TcBP‐free controls ( p > 0.1, t test) and remained constant both in its absolute value (9.6 × 10 5 cells/ml) and as a percentage of the total population (98.6%). However, at 100 ppb, the population size of live cells declined significantly after the 11th day (8.2 × 10 5 cells/ml, or 96.6% of total population; p < 0.01, t test). The decrease in viable cells was mostly found in vegetative cells. Bioconcentration factor in the cell ([pg TcBP/g dry wt cells]/[pg TcBP/ml]) was 1.23 × 10 5 .