Endotoxins are a component of the lipopolysaccharide complexes that make up a part ofthe outer layer of the cell walls of most gram-negative bacteria and some cyanobacteria.Laboratory filter column tests to identify conditions under which endotoxins can bereleased from biologically active drinking water treatment anthracite/sand filters showedthat endotoxin was produced in large quantities in the first few hours followingshutdown. However, accumulated endotoxin can be easily dealt with by immediatelybackwashing or running filters to waste following periods of shutdown. Free chlorine,monochloramine, and potassium permanganate were not particularly efficient atinactivating endotoxin, with the maximum inactivation rate being 1.4 endotoxin units(EU)/mL.h for free chlorine. Medium pressure ultraviolet irradiation was somewhateffective (~0.55 EU/mL per mJ/cmsup2/sup), although higher dosages than those currently beingemployed in drinking water treatment would be required to effectively remove higherconcentrations. Using a range of drinking water endotoxin concentrations measured inbiofilter shutdown experiments and from values recorded in the literature, endotoxinaerosolization associated with humidifiers was examined. A theoretical assessmentsuggests that ultrasonic humidifiers are able to produce quantities of aerosolizedrespirable endotoxin sufficient to easily induce adverse health impacts, including thoserequiring medical attention. In addition to being a health hazard on its own, endotoxinmay exacerbate existing medical conditions and may confuse physicians attempting todiagnosis multiple symptoms. Includes 22 references, table, figures.
Keywords: Health; Chlorine; Water Treatment; Filters; Risks; Bacteria; Ultraviolet Radiation
