Chlorinated effluent organic matter causes higher toxicity than chlorinated natural organic matter by inducing more intracellular reactive oxygen species.

•EOM formed more N-DBPs and TOX than NOM during chlorination.•ROS damaged DNA, RNA and proteins then led to cell cycle arrest, necrosis and apoptosis.•Chlorinated EOM caused higher oxidative stress, cytotoxicity and genotoxicity.•Oxidative stress especially ROS was the major cause of toxicity.