Abstract: Aiming at the combined pollution of low dose microcystins (MCs) and di sinfection by-products (DBPs) in drinking water, the individual and combined cy totoxic effects of two MCs (MCLR and MCRR) and two DBP compounds (CHClBr2 and CH Cl2Br) on the apoptosis of isolated grass carp (Ctenopharngodon idellus) lymphoc ytes were examined by using in vitro bioassays. The results showed that after 2 hours exposure to the four pollutants within the range of test concentrations, t he apoptosis of isolated lymphocyte occurred, and there existed significant dose -effect relationship. The combined cytotoxic effects of 1 nmol·L-1 MCLR or MCRR and 1〖KG-*2〗-〖KG-*7〗100 nmol·L-1 CHClBr2 or CHCl2Br were all of additive, and the apoptosis percent was highly correlated with the exposure dose. It was suggested that the apoptosis percent of grass carp lymphocytes could be used as an effective indicator to evaluate the cytotoxicity caused by the co mbined pollution of MCs and DBPs.

Key words: ecosystem, environmental management., alternative stable state, ecological threshold, regime shift