Neurotoxicity of inhaled manganese: Public health danger in the shower? Robert J.F. Elsner, John G. Spangler * Wake Forest University School of Medicine, Department of Family and Community Medicine, Medical Center Blvd., Winston-Salem, NC 27157-1084, USA Received 24 January 2005; accepted 26 January 2005 Summary Context: Manganese (Mn) is an essential trace element but is neurotoxic at high doses. Showering with Mn-laden water has never been evaluated as a central nervous system (CNS) delivery vector for Mn, even though intranasally administered Mn in laboratory animals circumvents the blood–brain barrier and passes directly into the brain via olfactory pathways. Objective: To review the literature on Mn and attempt to quantify potential human CNS exposure to manganese from showering. Data sources: We systematically searched Medline 11/9/02 and again on 3/9/04. The following search terms were used: manganese, water, drinking water, shower, showering, bath, bathing and inhalation, then combined with ‘‘water or drinking water or showering or shower or bathing or inhalation.’’ Study selection: Animal experimental investigations, human epidemiological studies, and consensus and govern- mental reports were utilized. Data extraction: Data were extracted by both authors and extrapolations to humans were calculated by one of us (JGS) controlling for age, length of exposure and known respiratory differences between rats and humans. Data synthesis: During a decade of showering in Mn-contaminated water, models for children and adults show higher doses of aerosolized Mn (3-fold and 1 1 2 -fold greater, respectively) than doses reported to cause Mn brain deposition in rats. Conclusions: Long-term shower exposure to Mn-laden water may pose a significant risk for CNS neurotoxicity via olfactory uptake in up to 8.7 million Americans. If our results are confirmed, regulatory agencies must rethink existing Mn drinking water standards.  c 2005 Elsevier Ltd. All rights reserved. Introduction Manganese (Mn) is an essential element for many biological systems [1], but similar to iron, has spe- cific toxicity at high doses [2–4]. Because certain individuals are particularly at risk for the toxic 0306-9877/$ - see front matter  c 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2005.01.043 * Corresponding author. Tel.: +1 336 716 2238; fax: +1 336 716 3206. E-mail address: jspangle@wfubmc.edu (J.G. Spangler). Medical Hypotheses (2005) x, xxx–xxx http://intl.elsevierhealth.com/journals/mehy ARTICLE IN PRESS