Chlorine disinfection reduces the exposure risks of inhaled reclaimed water

The increasing application of reclaimed water in urban areas is a rising health concern. For instance, the inhalation of reclaimed water induces polymorphonuclear cell-dominant inflammation in the lung, and prefibrosis can develop after subchronic exposure. The major toxic source, free endotoxins, could be inhibited by chlorination, yet whether the chlorination can increase or reduce the inhalation toxicity of reclaimed water is still unclear. Here, we treated secondary effluent samples with different doses of chlorine, and then mice were exposed to these samples via inhalation. We studied inflammatory markers such as polymorphonuclear cell, proinflammatory cytokines in lung lavage, induced bronchus-associated lymphoid tissue, and immunohistochemical analysis of fibrotic markers. Results show that endotoxin activities increased slightly from 951 endotoxin units per milliliter to the highest activity of 1133 endotoxin units per milliliter after disinfection. However, pulmonary inflammation was reduced after 5 and 10 mg/L chlorine treatment. The aggregate size of endotoxin displayed a decline after chlorination. Furthermore, the potential cytotoxicity of the disinfection byproducts after chlorination was not observed in the lungs after subchronic exposure. This study demonstrates that sufficient chlorination can prevent acute and subchronic pulmonary damage caused by the reclaimed water. In addition, endotoxin activity should not be used as an index for acute and subchronic toxicity control.

Automated summary

The increasing use of reclaimed water in urban areas raises health concerns. This study found that sufficient chlorination can reduce the pulmonary damage caused by reclaimed water and prevent acute and subchronic health effects. It also suggests that endotoxin activity should not be used as an index for toxicity control.