Tris (2-chloroethyl) phosphate (TCEP) is a typical phosphate flame retardant.Its potential adverse health effects have recently aroused conc.We investigated the seasonal variations of TCEP concentrations in the raw,finished and tap water samples from two drinking water treatment plants (DWTPs) in China,and evaluated the cytotoxicity and apoptosis/necrosis of organic extracts (OEs) in water samples.We enriched TCEP and OEs in water samples by solid-phase extraction method.The TCEP concentrations in water samples were determined by gas chromatography-mass spectrometry.Normal human liver cell line L02 was treated with OEs in the water samples,and then the cytotoxicity and apoptosis/necrosis were measured by 3-(4,5-dimethyithiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay and flow cytometry,respectively.The results showed that cytotoxicities of OEs in raw water samples from both DWTPs in summer and winter were stronger than those in spring and autumn,cytotoxicity of OEs in finished and tap water samples from both DWTPs in summer and autumn were stronger than those in spring and winter.In all seasons,the maximal concentrations (100 mL water/mL cell culture) of OEs in the raw water samples from both DWTPs induced late apoptosis/necrosis.The reasons for seasonal variations of TCEP in water samples and potential toxic effects of other pollutants in the water samples need to be further investigated.