Endotoxins: The Critical Risk Factor in Reclaimed Water via Inhalation Exposure

The use of reclaimed water for nonpotable uses requires consideration of potential adverse health effects. Considering that inhalation can be a significant route of transmission of microorganisms and inflammatory agents, this study used a mouse model to test the possible adverse effects of reclaimed water use during car washing where aerosols are generated. Intensive innate immune responses were found in the lungs after acute exposure, and the lavage polymorphonuclear cell proportion was the most sensitive end point. Four types of evidence are presented to demonstrate that the main risk factor that initiates innate inflammation is the free endotoxin. (1) Small molecules (<10 kDa) cannot induce inflammation. (2) The endotoxin levels of 11 water samples from five different plants showed positive correlations with inflammatory responses. (3) Actual water samples showed similar activities with free endotoxins other than bacterially bound endotoxins. (4) Specific removal of endotoxins with polymyxin B affinity chromatography further confirmed the role of free endotoxins. It is noteworthy that 62.9% of the investigated tertiary-treated water had endotoxin levels higher than the allowable acute threshold (120 endotoxin units/mL) under the hypothesized car wash condition, which strongly suggests the need to carefully consider the water treatment steps required to produce safe water for various reclaimed water end uses.