DBD plasma had a good inactivation effect on the bacteria examined in this study. However, the endotoxins that are released during the death and disintegration of gram-negative bacteria also directly affect the safety of water. Fig. 5 A shows the fate of endotoxin released by Escherichia coli in solution after inactiva- tion by plasma treatment. The activity of free-endotoxin generally decreased as the treatment duration increased, indicating that the plasma treatment had a good ability to remove free-endotoxin. However, both total-endotoxin and bound-endotoxin increased firstly and then decreased as the treatment duration increased. The maxima of total- and bound-endotoxin were reached after plasma treatment for 10 s and 30 s, respectively. The free-endotoxin and bound-endotoxin are two compotents of the total-endotoxin [15] . The free-endotoxin decreased from 262 EU/ml to 61 EU/ml dur- ing 0–30 s plasma treatment, thus the increase of total-endotoxin from 444 EU/ml to 461 EU/ml in the early stage of plasma treat- ment (0–30 s) was caused by the increase of bound-endotoxin ( Fig. 5 A). The increase of bound-endotoxin was due to the increas- ing number of bacteria being killed as treatment time increased; thus when the treatment duration was 30 s, the inactivation ratio of Escherichia coli was up to 7.0 log ( Fig. 2 A), resulting in a maxi- mum of bound-endotoxin (402 EU/ml) ( Fig. 5 A). During the course of bacteria disintegration, more endotoxins originally embeded in cell walls were exposed to the water. This part of endotoxins, which connected to the damaged bacterial wall, existed as the bacteria- bounded endotoxins and hence contributed to the increase in bound-endotoxin shown in Fig. 5 A. However, because the free- endotoxin decreased gradually as treatment time increased, the maximum of total-endotoxin appeared at 10 s, which was ear- lier than the occurrence time of the maximum bound-endotoxin. Notably, the concentration of bacteria used for illustration in Fig. 5 A was high compared to the real contaminants, which contributed to the high level of endotoxins in the bacterial suspension