{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T21:21:15Z","timestamp":1790803275196,"version":"4.1.0"},"reference-count":51,"publisher":"Public Library of Science (PLoS)","issue":"10","license":[{"start":{"date-parts":[[2025,10,24]],"date-time":"2025-10-24T00:00:00Z","timestamp":1761264000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100016764","name":"Fred and Pamela Buffett Cancer Center","doi-asserted-by":"publisher","award":["P30CA036727"],"award-info":[{"award-number":["P30CA036727"]}],"id":[{"id":"10.13039\/100016764","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS One"],"abstract":"<jats:p>Malathion has the reputation of being a safe pesticide. There are no reported cases of cholinergic toxicity in people exposed to low environmental doses of malathion. Our goal was to explain the safety of malathion in terms of the mechanism of malathion detoxication. The structure of malathion includes a built-in safety feature, specifically two ethyl esters. The ethyl esters are decarboxylated by human esterases to negatively charged malathion which does not react with acetylcholinesterase. Acetylcholinesterase is the toxicologically relevant target for organophosphates such as malathion. A toxic form of malathion is produced by Cytochrome P450 enzymes which convert malathion to malaoxon. Malaoxon is toxic because it inhibits acetylcholinesterase. We used high pressure liquid chromatography on a Prodigy 5 \u00b5m ODS column to monitor the production of enzyme-catalyzed decarboxylation of the malathion ethyl esters. The products of malathion decarboxylation were identified by mass spectrometry using a Thermo RSLC Ultimate 3000 ultra-high pressure chromatography system with a Thermo Easy-Spray PepMap RSLC C18 separation column attached to an Orbitrap Fusion Lumos Tribrid mass spectrometer. Decarboxylation and enzyme inhibition were assayed with recombinant human acetylcholinesterase (rHuAChE), human butyrylcholinesterase (HuBChE), and recombinant human liver carboxylesterase (rHuCE1). A trace contaminant in 98.5% pure malathion was identified by mass spectrometry. Consistent with the fact that negatively charged compounds are not inhibitors of HuAChE, HuBChE, or HuCE1, we found that negatively charged, decarboxylated malathion did not inhibit the activity of rHuAChE, HuBChE, or rHuCE1. Carboxylesterase detoxified malathion 100,000-fold faster compared to rHuAChE and HuBChE. Low dose exposures to malathion are not directly toxic The toxic metabolite, malaoxon, is produced very slowly. By comparison, detoxified malathion acids are formed rapidly. In conclusion, our data suggest that the safety of low dose environmental exposures to malathion is explained by the fact that malathion is detoxified faster than it is activated to the toxic malaoxon. Our review of the literature finds no convincing evidence that low dose malathion exposure causes cancer.<\/jats:p>","DOI":"10.1371\/journal.pone.0335361","type":"journal-article","created":{"date-parts":[[2025,10,24]],"date-time":"2025-10-24T17:34:43Z","timestamp":1761327283000},"page":"e0335361","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":7,"title":["Kinetic analysis suggests that malathion at low environmental exposures is not toxic to humans"],"prefix":"10.1371","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1785-9247","authenticated-orcid":true,"given":"Lawrence M.","family":"Schopfer","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2772-5226","authenticated-orcid":true,"given":"Ozden","family":"Tacal","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7837-3662","authenticated-orcid":true,"given":"Patrick","family":"Masson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Oksana","family":"Lockridge","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2025,10,24]]},"reference":[{"key":"pone.0335361.ref001","unstructured":"Overstreet J. Malathion interium registration review decision case number 0248. Environ Protect Agen. 2024;Docket EPA-HQ-OPP-2009-0317-0175:18."},{"key":"pone.0335361.ref002","doi-asserted-by":"crossref","first-page":"1527","DOI":"10.1016\/B978-0-12-374367-1.00071-9","article-title":"Malathion: A review of toxicology.","volume-title":"Hayes\u2019 Handbook of Pesticide Toxicology","author":"IM Jensen","year":"2010","edition":"3"},{"issue":"1","key":"pone.0335361.ref003","doi-asserted-by":"crossref","first-page":"126","DOI":"10.1016\/0041-008X(74)90137-9","article-title":"Percutaneous penetration of some pesticides and herbicides in man","volume":"28","author":"RJ Feldmann","year":"1974","journal-title":"Toxicol Appl Pharmacol"},{"issue":"1","key":"pone.0335361.ref004","doi-asserted-by":"crossref","first-page":"182","DOI":"10.1093\/toxsci\/kfg061","article-title":"A toxicokinetic model of malathion and its metabolites as a tool to assess human exposure and risk through measurements of urinary biomarkers","volume":"73","author":"M Bouchard","year":"2003","journal-title":"Toxicol Sci"},{"issue":"5","key":"pone.0335361.ref005","first-page":"503","article-title":"Safety of malathion dusting powder for louse control","volume":"22","author":"WJ Hayes","year":"1960","journal-title":"Bull World Health Organ"},{"issue":"4","key":"pone.0335361.ref006","doi-asserted-by":"crossref","first-page":"546","DOI":"10.1007\/s002449910071","article-title":"Malathion deposition, metabolite clearance, and cholinesterase status of date dusters and harvesters in California","volume":"38","author":"RI Krieger","year":"2000","journal-title":"Arch Environ Contam Toxicol"},{"issue":"1","key":"pone.0335361.ref007","doi-asserted-by":"crossref","first-page":"116","DOI":"10.1016\/0041-008X(83)90360-5","article-title":"Malathion percutaneous absorption after repeated administration to man","volume":"68","author":"RC Wester","year":"1983","journal-title":"Toxicol Appl Pharmacol"},{"issue":"6","key":"pone.0335361.ref008","doi-asserted-by":"crossref","first-page":"1342","DOI":"10.1021\/jf60214a002","article-title":"Malathion exposure studies. Determination of mono- and dicarboxylic acids and alkyl phosphates in urine","volume":"25","author":"DE Bradway","year":"1977","journal-title":"J Agric Food Chem"},{"issue":"2","key":"pone.0335361.ref009","first-page":"353","article-title":"Assessment of exposure to organophosphate insecticides during spraying in Haiti: monitoring of urinary metabolites and blood cholinesterase levels","volume":"63","author":"M Warren","year":"1985","journal-title":"Bull World Health Organ"},{"issue":"10","key":"pone.0335361.ref010","first-page":"2393","article-title":"Increased frequency of specific genomic deletions resulting from in vitro malathion exposure","volume":"56","author":"JM Pluth","year":"1996","journal-title":"Cancer Res"},{"issue":"3","key":"pone.0335361.ref011","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1124\/dmd.104.001693","article-title":"Malathion bioactivation in the human liver: the contribution of different cytochrome p450 isoforms","volume":"33","author":"FM Buratti","year":"2005","journal-title":"Drug Metab Dispos"},{"issue":"2","key":"pone.0335361.ref012","doi-asserted-by":"crossref","first-page":"255","DOI":"10.1042\/bj0840255","article-title":"Hydrolysis of malathion by ali-esterases in vitro and in vivo","volume":"84","author":"A Main","year":"1962","journal-title":"Biochem J"},{"issue":"6","key":"pone.0335361.ref013","doi-asserted-by":"crossref","first-page":"406","DOI":"10.1002\/jbt.20106","article-title":"Malathion detoxification by human hepatic carboxylesterases and its inhibition by isomalathion and other pesticides","volume":"19","author":"FM Buratti","year":"2005","journal-title":"J Biochem Mol Toxicol"},{"issue":"1","key":"pone.0335361.ref014","doi-asserted-by":"crossref","first-page":"36","DOI":"10.1021\/jf60107a009","article-title":"Insecticide Metabolism, Metabolism of Malathion by Rat Tissue Preparations and Its Modification by EPN","volume":"8","author":"FW Seume","year":"1960","journal-title":"J Agric Food Chem"},{"key":"pone.0335361.ref015","unstructured":"Blondell J, Spann MF. Review of Malathion Incident Reports. Environ Protect Agen. 1998;US EPA Malathion PcCode 057701-122:1-39."},{"key":"pone.0335361.ref016","unstructured":"Britton W, Piper S, Britt A. Malathion Updated draft human health risk assessment for registration. Environ Protect Agen. 2024;Docket EPA-HQ-OPP-2009-0317-0161:38."},{"issue":"2","key":"pone.0335361.ref017","doi-asserted-by":"crossref","first-page":"168","DOI":"10.1002\/pros.21232","article-title":"Prostate cancer risk and exposure to pesticides in British Columbia farmers","volume":"71","author":"PR Band","year":"2011","journal-title":"Prostate"},{"issue":"9","key":"pone.0335361.ref018","doi-asserted-by":"crossref","first-page":"1023","DOI":"10.1093\/aje\/kwm182","article-title":"Malathion exposure and the incidence of cancer in the agricultural health study","volume":"166","author":"MR Bonner","year":"2007","journal-title":"Am J Epidemiol"},{"issue":"2","key":"pone.0335361.ref019","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1093\/aje\/kwi022","article-title":"Pesticide Use and Breast Cancer Risk among Farmers\u2019 Wives in the Agricultural Health Study","volume":"161","author":"LS Engel","year":"2005","journal-title":"Am J Epidemiol"},{"issue":"11","key":"pone.0335361.ref020","first-page":"1155","article-title":"Non-Hodgkin\u2019s lymphoma and specific pesticide exposures in men: cross-Canada study of pesticides and health","volume":"10","author":"HH McDuffie","year":"2001","journal-title":"Cancer Epidemiol Biomarkers Prev"},{"issue":"10","key":"pone.0335361.ref021","doi-asserted-by":"crossref","first-page":"736","DOI":"10.1136\/oemed-2014-102798","article-title":"Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study","volume":"72","author":"CC Lerro","year":"2015","journal-title":"Occup Environ Med"},{"issue":"4","key":"pone.0335361.ref022","doi-asserted-by":"crossref","first-page":"238","DOI":"10.1080\/10937404.2012.632358","article-title":"Occupational pesticide exposures and cancer risk: a review","volume":"15","author":"MCR Alavanja","year":"2012","journal-title":"J Toxicol Environ Health B Crit Rev"},{"issue":"16","key":"pone.0335361.ref023","doi-asserted-by":"crossref","first-page":"7560","DOI":"10.1021\/jf800910q","article-title":"DNA damage after acute and chronic treatment with malathion in rats","volume":"56","author":"GZ R\u00e9us","year":"2008","journal-title":"J Agric Food Chem"},{"issue":"5","key":"pone.0335361.ref024","doi-asserted-by":"crossref","first-page":"471","DOI":"10.1289\/ehp.01109471","article-title":"A rat mammary tumor model induced by the organophosphorous pesticides parathion and malathion, possibly through acetylcholinesterase inhibition","volume":"109","author":"G Cabello","year":"2001","journal-title":"Environ Health Perspect"},{"key":"pone.0335361.ref025","doi-asserted-by":"crossref","first-page":"109131","DOI":"10.1016\/j.envres.2020.109131","article-title":"Malathion induced cancer-linked gene expression in human lymphocytes","volume":"182","author":"R Anjitha","year":"2020","journal-title":"Environ Res"},{"issue":"8","key":"pone.0335361.ref026","doi-asserted-by":"crossref","first-page":"1046","DOI":"10.1289\/ehp.7311","article-title":"Differential gene expression in normal human mammary epithelial cells treated with malathion monitored by DNA microarrays","volume":"113","author":"MR Gwinn","year":"2005","journal-title":"Environ Health Perspect"},{"key":"pone.0335361.ref027","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1016\/j.tiv.2017.06.013","article-title":"\u201cExposure to the insecticides permethrin and malathion induces leukemia and lymphoma-associated gene aberrations in vitro\u201d","volume":"44","author":"MP Navarrete-Meneses","year":"2017","journal-title":"Toxicol In Vitro"},{"issue":"1","key":"pone.0335361.ref028","doi-asserted-by":"crossref","DOI":"10.1371\/journal.pone.0209795","article-title":"Purification of human butyrylcholinesterase from frozen Cohn fraction IV-4 by ion exchange and Hupresin affinity chromatography","volume":"14","author":"LM Schopfer","year":"2019","journal-title":"PLoS ONE"},{"key":"pone.0335361.ref029","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/0006-2952(61)90145-9","article-title":"A new and rapid colorimetric determination of acetylcholinesterase activity","volume":"7","author":"GL Ellman","year":"1961","journal-title":"Biochem Pharmacol"},{"issue":"3","key":"pone.0335361.ref030","doi-asserted-by":"crossref","first-page":"193","DOI":"10.1385\/MB:16:3:193","article-title":"Comparison of Escherichia coli, Saccharomyces cerevisiae, Pichia pastoris, Spodoptera frugiperda, and COS7 cells for recombinant gene expression. Application to a rabbit liver carboxylesterase","volume":"16","author":"CL Morton","year":"2000","journal-title":"Mol Biotechnol"},{"issue":"10","key":"pone.0335361.ref031","doi-asserted-by":"crossref","first-page":"1897","DOI":"10.1021\/acs.chemrestox.7b00209","article-title":"Immunopurification of Acetylcholinesterase from Red Blood Cells for Detection of Nerve Agent Exposure","volume":"30","author":"AJ Dafferner","year":"2017","journal-title":"Chem Res Toxicol"},{"issue":"4","key":"pone.0335361.ref032","doi-asserted-by":"crossref","first-page":"582","DOI":"10.1021\/tx0101806","article-title":"Retrospective detection of exposure to organophosphorus anti-cholinesterases: mass spectrometric analysis of phosphylated human butyrylcholinesterase","volume":"15","author":"A Fidder","year":"2002","journal-title":"Chem Res Toxicol"},{"issue":"10","key":"pone.0335361.ref033","doi-asserted-by":"crossref","first-page":"918","DOI":"10.1038\/nbt.2377","article-title":"A cross-platform toolkit for mass spectrometry and proteomics","volume":"30","author":"MC Chambers","year":"2012","journal-title":"Nat Biotechnol"},{"issue":"4","key":"pone.0335361.ref034","doi-asserted-by":"crossref","first-page":"256","DOI":"10.1556\/1326.2019.00713","article-title":"Rapid resolution liquid chromatography method for determination of malathion in pesticide formulation","volume":"32","author":"L Velkoska-Markovska","year":"2020","journal-title":"Acta Chromatog"},{"issue":"1","key":"pone.0335361.ref035","doi-asserted-by":"crossref","first-page":"136","DOI":"10.1093\/toxsci\/kfm215","article-title":"Aging Pathways for Organophosphate-Inhibited Human Butyrylcholinesterase, Including Novel Pathways for Isomalathion, Resolved by Mass Spectrometry","volume":"100","author":"H Li","year":"2007","journal-title":"Toxicol Sci"},{"issue":"2","key":"pone.0335361.ref036","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1006\/taap.2001.9279","article-title":"Identification of butyrylcholinesterase adducts after inhibition with isomalathion using mass spectrometry: difference in mechanism between (1R)- and (1S)-stereoisomers","volume":"176","author":"JA Doorn","year":"2001","journal-title":"Toxicol Appl Pharmacol"},{"issue":"7","key":"pone.0335361.ref037","doi-asserted-by":"crossref","first-page":"807","DOI":"10.1021\/tx015501s","article-title":"Probing the active sites of butyrylcholinesterase and cholesterol esterase with isomalathion: conserved stereoselective inactivation of serine hydrolases structurally related to acetylcholinesterase","volume":"14","author":"JA Doorn","year":"2001","journal-title":"Chem Res Toxicol"},{"key":"pone.0335361.ref038","doi-asserted-by":"crossref","first-page":"579","DOI":"10.1016\/0163-7258(79)90066-4","article-title":"Mode of action of anticholinesterases","volume":"6","author":"AR Main","year":"1979","journal-title":"Pharmac Ther"},{"issue":"2","key":"pone.0335361.ref039","doi-asserted-by":"crossref","first-page":"238","DOI":"10.1007\/BF01688646","article-title":"Assimilation of malathion in the Indian River estuary, Florida","volume":"47","author":"T Wang","year":"1991","journal-title":"Bull Environ Contam Toxicol"},{"issue":"43","key":"pone.0335361.ref040","doi-asserted-by":"crossref","first-page":"11606","DOI":"10.1021\/bi00094a018","article-title":"Glycosylation-dependent activity of baculovirus-expressed human liver carboxylesterases: cDNA cloning and characterization of two highly similar enzyme forms","volume":"32","author":"DL Kroetz","year":"1993","journal-title":"Biochemistry"},{"issue":"2","key":"pone.0335361.ref041","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1016\/0378-1119(92)90134-B","article-title":"Production and secretion of high levels of recombinant human acetylcholinesterase in cultured cell lines: microheterogeneity of the catalytic subunit","volume":"121","author":"C Kronman","year":"1992","journal-title":"Gene"},{"issue":"1","key":"pone.0335361.ref042","doi-asserted-by":"crossref","DOI":"10.1371\/journal.pone.0280380","article-title":"Human butyrylcholinesterase in Cohn fraction IV-4 purified in a single chromatography step on Hupresin","volume":"18","author":"L M. Schopfer","year":"2023","journal-title":"PLoS ONE"},{"key":"pone.0335361.ref043","first-page":"113","article-title":"Pesticides and susceptible populations: people with butyrylcholinesterase genetic variants may be at risk","volume":"21","author":"O Lockridge","year":"2000","journal-title":"Neurotoxicology"},{"issue":"5","key":"pone.0335361.ref044","doi-asserted-by":"crossref","first-page":"1909","DOI":"10.1046\/j.1471-4159.1995.64051909.x","article-title":"Anticholinesterases: medical applications of neurochemical principles","volume":"64","author":"CB Millard","year":"1995","journal-title":"J Neurochem"},{"issue":"2","key":"pone.0335361.ref045","doi-asserted-by":"crossref","first-page":"408","DOI":"10.1016\/0041-008X(66)90137-2","article-title":"Relationship between acute toxicity and in vitro inhibition and hydrolysis of a series of carbalkoxy homologs of malathion","volume":"9","author":"WC Dauterman","year":"1966","journal-title":"Toxicol Appl Pharmacol"},{"key":"pone.0335361.ref046","unstructured":"Mackinson FN, Shincoff RS, Partridge LJ. Occupational health guidelines for chemical hazards. 1981;NIOSH\/OSHA 81-123:20."},{"key":"pone.0335361.ref047","unstructured":"Keigwin RP. Reregistration eligibility decision for malathion. 2009;EPA HQ-OPP 2004-0348-0057 revision. 2009:18."},{"issue":"2","key":"pone.0335361.ref048","doi-asserted-by":"crossref","first-page":"216","DOI":"10.1124\/dmd.116.072652","article-title":"Age-Dependent Absolute Abundance of Hepatic Carboxylesterases (CES1 and CES2) by LC-MS\/MS Proteomics: Application to PBPK Modeling of Oseltamivir In Vivo Pharmacokinetics in Infants","volume":"45","author":"M Boberg","year":"2017","journal-title":"Drug Metab Dispos"},{"issue":"1","key":"pone.0335361.ref049","doi-asserted-by":"crossref","first-page":"24","DOI":"10.1124\/dmd.121.000623","article-title":"Ontogeny of Scaling Factors for Pediatric Physiology-Based Pharmacokinetic Modeling and Simulation: Microsomal Protein Per Gram of Liver","volume":"50","author":"JS Leeder","year":"2022","journal-title":"Drug Metab Dispos"},{"issue":"8054","key":"pone.0335361.ref050","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/S0140-6736(78)90375-6","article-title":"Epidemic malathion poisoning in Pakistan malaria workers","volume":"1","author":"EL Baker","year":"1978","journal-title":"Lancet"},{"issue":"4","key":"pone.0335361.ref051","doi-asserted-by":"crossref","first-page":"946","DOI":"10.1021\/jf60212a008","article-title":"Effect of impurities on the mammalian toxicity of technical malathion and acephate","volume":"25","author":"N Umetsu","year":"1977","journal-title":"J Agric Food Chem"}],"container-title":["PLOS One"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/dx.plos.org\/10.1371\/journal.pone.0335361","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,24]],"date-time":"2025-10-24T17:34:49Z","timestamp":1761327289000},"score":1,"resource":{"primary":{"URL":"https:\/\/dx.plos.org\/10.1371\/journal.pone.0335361"}},"subtitle":[],"editor":[{"given":"Farooq Ahmed","family":"Wani","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"editor"}]}],"short-title":[],"issued":{"date-parts":[[2025,10,24]]},"references-count":51,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2025,10,24]]}},"URL":"https:\/\/doi.org\/10.1371\/journal.pone.0335361","relation":{},"ISSN":["1932-6203"],"issn-type":[{"value":"1932-6203","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,10,24]]}}}