A mass spectrometry-based method to measure dialkylphosphate degradation products of organophosphorous insecticides in dust and orange juice† Gayanga Weerasekera, a Kimberly D. Smith, a Lesliam Quir os-Alcal a, bc Carolina Fernandez, a Asa Bradman, b Brenda Eskenazi, b Larry L. Needham a and Dana B. Barr * a Received 8th December 2008, Accepted 1st April 2009 First published as an Advance Article on the web 23rd April 2009 DOI: 10.1039/b821841b Dialkylphosphates (DAPs) are urinary metabolites and breakdown products of organophosphorous (OP) pesticides. Urinary DAPs are widely used to assess exposure to OP pesticides in epidemiologic studies. Recent evidence suggests that preformed DAPs are present in food and that they may also be present in other parts of the environment. Thus, DAP concentrations observed in urine may reflect a person’s exposure to both parent OP pesticides and preformed DAPs in food and other environmental media. The presence of preformed DAPs in multiple media may indicate that previous studies have overestimated exposure to OP pesticides and that the use of urinary DAPs as biomarkers of exposure for OP pesticides may not accurately characterize exposure in non-acute settings. To establish the presence of DAPs in environmental and food media, we developed analytical methods to measure six DAPs in dust and orange juice. The limits of detection (LOD) for the dimethyl phosphates (dimethylphosphate (DMP), dimethylthiophosphate, and dimethyldithiophosphate) ranged from 2.8–9.9 ng g 1 and 0.2–0.4 ng mL 1 in dust and juice, respectively. The LODs for the diethyl phosphates (diethylphosphate (DEP), diethylthiophosphate, diethyldithiophosphate) ranged from 5.2–10.4 ng g 1 and 0.5–3.0 ng mL 1 in dust and juice, respectively. The extraction efficiencies for the analytes ranged from 23% to 91% and from 41% to 85% in dust and orange juice, respectively. DMP was detected in about half of the dust samples whereas DEP was detected in 80% of the dust samples tested. Other DAPs were less frequently detected in dust. Less than 3% of intact pesticide present in the matrices was converted to their respective DAPs during the pre-analytic and analytic process. Evaluation of the conversion of intact pesticides in the samples to DAPs will help us to better understand the contribution of preformed DAPs to urinary DAP concentrations. Introduction Urinary dialkylphosphates (DAPs) have been widely used to assess human exposure to organophosphorus (OP) pesticides, both in the general population 1–7 and in occupational settings. 3,8–11 Approximately 75% of the OP pesticides (O,O-dimethyl and O,O-diethyl substituted OP pesticides) registered with the United States Environmental Protection Agency (EPA) can be metab- olized to form one or more DAPs that are excreted in urine. 12 DAPs consist of three diethyl (DE) and three dimethyl (DM) alkylphosphate species: diethylphosphate (DEP), diethylth- iophosphate (DETP), diethyldithiophosphate (DEDTP), dimethylphosphate, dimethylthiophosphate (DMTP), and dimethyldithiophosphate (DMDTP). DAPs are class-specific metabolites, and urinary DAP concentrations reflect cumulative exposure to OP pesticides and potentially the preformed metabolites present in the environment, rather than to specific OP pesticides. These biomarkers of exposure are commonly used because they integrate exposure to OP pesticides from multiple routes, 2,13–16 there are existing validated laboratory methods to measure DAPs in urine at low levels of detection, 2,17 and collection of urine is relatively simple and noninvasive, especially when one is assessing OP pesticide exposure in children. 10,12 Historically, urinary DAP concentrations have been attributed solely to OP pesticide exposure. 10,16 However, recent evidence suggests that people may be exposed to preformed DAPs present in their diet and environment. 18–21 Rodent studies have shown that DAPs are excreted unchanged after oral exposure, 22 thus urinary DAPs would represent exposure to both OP pesticides and preformed DAPs. Lu et al. 19 reported concentrations of DAPs in both organic and conventional fresh fruit juices purchased from local grocery stores, with conventional juices having higher DAP concentrations than organic juices. The authors also found that OP pesticides degraded in refrigerated juices to form DAPs after only 72 hours of storage. The authors concluded that the presence of DAPs in fresh fruit juices casts doubts on the usefulness of urinary DAPs as biomarkers of a National Center for Environmental Health, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-17, Atlanta, Georgia, USA. E-mail: dbarr@cdc.gov; Fax: +1 (770) 488-0142; Tel: +1 (770) 488-7886 b Center for Children’s Environmental Health Research, School of Public Health, University of California, Berkeley, CA, USA c EPA STAR Fellow, US Environmental Protection Agency, USA † Disclaimer: The results and conclusions in this manuscript are those of the authors, and they do not necessarily represent the official views of the Centers for Disease Control and Prevention. The research described in this manuscript has been funded in part by the United States Environmental Protection Agency (EPA) under the Science to Achieve Results (STAR) Graduate Fellowship Program. The EPA has not officially endorsed this publication and the views expressed herein may not reflect the views of the EPA. This journal is ª The Royal Society of Chemistry 2009 J. Environ. Monit., 2009, 11, 1345–1351 | 1345 PAPER www.rsc.org/jem | Journal of Environmental Monitoring Published on 23 April 2009. Downloaded by University of California - Berkeley on 16/03/2015 16:48:31. View Article Online / Journal Homepage / Table of Contents for this issue