Water Research 37 (2003) 4553–4560 Endotoxin inactivation by selected drinking water treatment oxidants William B. Anderson a,b, *, Colin I. Mayfield b , D. George Dixon b , Peter M. Huck a a Department of Civil Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 b Department of Biology, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Received 17 May 2002; received in revised form 31 July 2003; accepted 1 August 2003 Abstract Exposuretoendotoxinsintreateddrinkingwatercanoccurthroughingestion,dermalabrasions,inhalationofwater vapor, intravenous injection or during dialysis. While the risks associated with endotoxin ingestion and entry through dermal abrasions are not well quantified, adverse effects of intravenous injection and dialysis are well known and some studies indicate that inhalation of moisture-laden air may impact human health. This study quantifies the inactivation of endotoxin derived from Escherichia coli O55:B5 by three substances used either as disinfectants or oxidants in drinkingwatertreatment:chlorine,monochloramineandpotassiumpermanganate.Inactivationrateswerefoundtobe 1.4, 1.0 and 0.7 endotoxin units (EU)/mLh, for free chlorine, potassium permanganate and monochloramine, respectively. These rates are relatively slow given that contact times in drinking water distribution systems are typically less than 48h. While small amounts of endotoxin may be removed by oxidation the observed removals are much less than those provided by physical removal processes. The significance of this finding is important for dialysis considerations but is as yet unclear with regard to inhalation, as the risk of inhaling sufficient quantities of endotoxin- containing aerosolized water droplets to adversely affect human health has not yet been adequately quantified. r 2003 Elsevier Ltd. All rights reserved. Keywords: Endotoxin; Lipopolysaccharide; Monochloramine; Potassium permanganate; Chlorine 1. Introduction Endotoxins are a component of the lipopolysacchar- ide (LPS) complexes which make up a part of the outer layerofthecellwallsofmostGram-negativebacteria [1] and some cyanobacteria (e.g. [2,3]). LPS complexes are macromolecules composed of three main regions: lipid A, core polysaccharide, and ‘‘O’’ antigens [4]. The lipid A component is critical for all biological responses to endotoxin [1,5]. Endotoxins are typically released either during cell lysis or multiplication [6] and are relatively heat stable (stable at 121  Cfor1h) [7]. Endotoxin concentrations are expressed in endotoxin units (EU) rather than in units of weight. This form of reporting reflects the fact that endotoxin potency depends on the genus of bacteria and, within species, on the specific lot or batch of bacteria from which the reference endotoxin is isolated. Much of the available literature does not use the newer terminology; on an approximate basis ng can be converted to EU, by multiplying by a factor of 5–10. To date, outbreaks of endotoxin-related illness associated with drinking water have been documented infrequently [8–12],likelysincemanyoutbreaksoffever- related illness from water are never identified by routine medical and bacteriological analyses, and since endo- toxin-related fever symptoms are typically short-lived. ARTICLE IN PRESS *Corresponding author. Department of Civil Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1. Tel.: +1-519-888-4567; fax: +1-519-746-7499. E-mail address: wbanderson@uwaterloo.ca (W.B. Anderson). 0043-1354/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2003.08.016