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Dana B. Barr,¹ Roberto Bravo,¹ Gayanga Weerasekera,¹ Lisa M. Caltabiano,¹ Ralph D. Whitehead, Jr.,¹ Anders O. Olsson,¹ Samuel P. Caudill,¹ Susan E. Schober,² James L. Pirkle,¹ Eric J. Sampson,¹ Richard J. Jackson,¹ and Larry L. Needham¹

¹National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA; ²National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland, USA

Abstract
We report population-based concentrations, stratified by age, sex, and racial/ethnic groups, of dialkyl phosphate (DAP) metabolites of multiple organophosphorus pesticides. We measured dimethylphosphate (DMP) , dimethylthiophosphate (DMTP) , dimethyldithiophosphate (DMDTP) , diethylphosphate (DEP) , diethylthiophosphate (DETP) , and diethyldithiophosphate (DEDTP) concentrations in 1,949 urine samples collected in U.S. residents 6-59 years of age during 1999 and 2000 as a part of the ongoing National Health and Nutrition Examination Survey (NHANES) . We detected each DAP metabolite in more than 50% of the samples, with DEP being detected most frequently (71%) at a limit of detection of 0.2 µg/L. The geometric means for the metabolites detected in more than 60% of the samples were 1.85 µg/L for DMTP and 1.04 µg/L for DEP. The 95th percentiles for each metabolite were DMP, 13 µg/L ; DMTP, 46 µg/L ; DMDTP, 19 µg/L ; DEP, 13 µg/L ; DETP, 2.2 µg/L ; and DEDTP, 0.87 µg/L. We determined the molar sums of the dimethyl-containing and diethyl-containing metabolites ; their geometric mean concentrations were 49.4 and 10.5 nmol/L, respectively, and their 95th percentiles were 583 and 108 nmol/L, respectively. These data are also presented as creatinine-adjusted concentrations. Multivariate analyses showed concentrations of DAPs in children 6-11 years of age that were consistently significantly higher than in adults and often higher than in adolescents. Although the concentrations between sexes and among racial/ethnic groups varied, no significant differences were observed. These data will be important in evaluating the impact of organophosphorus pesticide exposure in the U.S. population and the effectiveness of regulatory actions. Key words: biologic monitoring, dialkyl phosphate, general population, organophosphate, organophosphorus, reference range, urine. Environ Health Perspect 112:186-200 (2004) . doi:10.1289/ehp.6503 available via http://dx.doi.org/ [Online 4 November 2003]

Address correspondence to D.B. Barr, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-17, Atlanta, GA 30341 USA. Telephone: (770) 488-7886. Fax: (770) 488-0142. E-mail: dbarr@cdc.gov

We thank the people at the National Center for Health Statistics (NCHS) and Westat who were responsible for planning and conducting the National Health and Nutrition Examination Study (NHANES) , especially B. Lewis, C. Johnson, B. Lindstrom, A. Jeffries, and C. Humbertson. We thank E. Gunter and C. Pfeiffer for managing the National Center for Environmental Health's involvement in NHANES and for serving as liaisons with NCHS, and C. Fernandez for technical assistance. We also thank the Fairview University Medical Center for providing creatinine measurements.

The authors declare they have no competing financial interests.

Received 6 June 2003 ; accepted 4 November 2003.