Effects of ozonation on the activity of endotoxin and its inhalation toxicity in reclaimed water

Abstract

Aerosolized reclaimed water can cause inflammatory responses in lung after inhalation, and endotoxin has been identified as the main inducer. Since the effects of disinfection treatments on endotoxins had conflicting results, this study explored the changes of endotoxin activity and inflammation inducing ability of reference endotoxin, gram-negative bacteria solutions and reclaimed water after ozonation respectively, and found that LAL assay based endotoxin activity and mouse inhalation exposure based inflammation examination had inconsistent results. The excessive ozone could not remove the endotoxin activity, but was able to reduce the inflammation inducing ability of free endotoxin. When treating on gram-negative strains, ozone first released the cell-bound endotoxin and caused the dramatic increase of endotoxin activity. But for the inflammatory response, despite the rapid increase at the very beginning, it immediately dropped back with further ozonation. The endotoxin aggregate size was proposed as a key regulator of the toxicity of endotoxin, which was modified by ozone oxidation. In real reclaimed water, insufficient ozone significantly enhanced the inflammatory response, but when the ozone dosages were large enough, the inflammation could be drawn back to the original level, which was consistent with the observations from pure endotoxin and bacteria. This work demonstrates that the endotoxin activity cannot predict the endotoxin-induced toxicity of ozone treated water, and low dosage of ozone treatment may even increase the health risk of reclaimed water.