title: Temporal variability in urinary concentrations of phthalate metabolites, phytoestrogens and phenols among minority children in the United States.
abstract: BACKGROUND
  Exposure to endocrine disruptors (EDs), including some phthalates, phytoestrogens and phenols can be quantified using biomarkers of exposure. However, reliability in the use of these biomarkers requires an understanding of the timeframe of exposure represented by one measurement. Data on the temporal variability of ED biomarkers are sparse, especially among children.
  
  
  OBJECTIVE
  To evaluate intraindividual temporal variability in 19 individual urinary biomarkers (eight phthalate metabolites from six phthalate diesters, six phytoestrogens (two lignans and four isoflavones) and five phenols) among New York City children.
  
  
  METHODS
  Healthy Hispanic and Black children (N=35; 6-10 years old) donated several urine samples over 6 months. To assess temporal variability we used three statistical methods: intraclass correlation coefficient (ICC), Spearman correlation coefficients (SCC) between concentrations measured at different timepoints, and surrogate category analysis to determine how well the tertile categories based on a single measurement represented a 6-month average concentration.
  
  
  RESULTS
  Surrogate category analysis indicated that a single sample provides reliable ranking for all analytes; at least three of four surrogate samples predicted the 6-month mean concentration. Of the 19 analytes, the ICC was >0.2 for 18 analytes and >0.3 for 10 analytes. Correlations among sample concentrations throughout the 6-month period were observed for all analytes; 14 analyte concentrations were correlated at 16 weeks.
  
  
  CONCLUSIONS
  The reasonable degree of temporal reliability and the wide range of concentrations of phthalate metabolites, phytoestrogens and phenols suggest that these biomarkers are appropriate for use in epidemiologic studies of environmental exposures in relation to health outcomes in children.
authors.affiliation: Mount Sinai School of Medicine, Department of Community and Preventive Medicine, 1 Gustave Levy Place, P.O. Box 1043, New York, NY 10029, USA. susan.teitelbaum@mssm.edu
authors.forename: S L
authors.initials: SL
authors.lastname: Teitelbaum
authors.forename: J A
authors.initials: JA
authors.lastname: Britton
authors.forename: A M
authors.initials: AM
authors.lastname: Calafat
authors.forename: X
authors.initials: X
authors.lastname: Ye
authors.forename: M J
authors.initials: MJ
authors.lastname: Silva
authors.forename: J A
authors.initials: JA
authors.lastname: Reidy
authors.forename: M P
authors.initials: MP
authors.lastname: Galvez
authors.forename: B L
authors.initials: BL
authors.lastname: Brenner
authors.forename: M S
authors.initials: MS
authors.lastname: Wolff
mesh_terms: D015415:Biomarkers / Q000652:urine; D002648:Child; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D004784:Environmental Monitoring / Q000379:methods; D062665:Epidemiological Monitoring; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D009519:New York City / Q000453:epidemiology; D010636:Phenols / Q000652:urine; D010795:Phthalic Acids / Q000652:urine; D048789:Phytoestrogens / Q000652:urine; D015203:Reproducibility of Results; D016482:Urinalysis / Q000592:standards*
chemical_list: D015415:Biomarkers; D010636:Phenols; D010795:Phthalic Acids; D048789:Phytoestrogens