The effect of 2,5,2′,5′-tetrachlorobiphenyl (TcBP) on cell death was investigated in the cyanobacterium Anabaena flos-aquae (Lyngb.) Bréb grown in a P-limited, semicontinuous culture under N₂-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 × 10⁵ 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 × 10⁵ 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 × 10⁵.

Keywords: Cell death, Cyanobacteria, Phytoplankton, Tetrachlorobiphenyl