title: Temporal variability of pesticide concentrations in homes and implications for attenuation bias in epidemiologic studies.
abstract: BACKGROUND
  Residential pesticide exposure has been linked to adverse health outcomes in adults and children. High-quality exposure estimates are critical for confirming these associations. Past epidemiologic studies have used one measurement of pesticide concentrations in carpet dust to characterize an individual's average long-term exposure. If concentrations vary over time, this approach could substantially misclassify exposure and attenuate risk estimates.
  
  
  OBJECTIVE
  We assessed the repeatability of pesticide concentrations in carpet dust samples and the potential attenuation bias in epidemiologic studies relying on one sample.
  
  
  METHODS
  We collected repeated carpet dust samples (median = 3; range, 1-7) from 21 homes in Fresno County, California, during 2003-2005. Dust was analyzed for 13 pesticides using gas chromatography-mass spectrometry. We used mixed-effects models to estimate between- and within-home variance. For each pesticide, we computed intraclass correlation coefficients (ICCs) and the estimated attenuation of regression coefficients in a hypothetical case-control study collecting a single dust sample.
  
  
  RESULTS
  The median ICC was 0.73 (range, 0.37-0.95), demonstrating higher between-home than within-home variability for most pesticides. The expected magnitude of attenuation bias associated with using a single dust sample was estimated to be ≤ 30% for 7 of the 13 compounds evaluated.
  
  
  CONCLUSIONS
  For several pesticides studied, use of one dust sample to represent an exposure period of approximately 2 years would not be expected to substantially attenuate odds ratios. Further study is needed to determine if our findings hold for longer exposure periods and for other pesticides.
authors: Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA. dezielnc@mail.nih.gov
authors: Nicole C
authors: NC
authors: Deziel
authors: Mary H
authors: MH
authors: Ward
authors: Erin M
authors: EM
authors: Bell
authors: Todd P
authors: TP
authors: Whitehead
authors: Robert B
authors: RB
authors: Gunier
authors: Melissa C
authors: MC
authors: Friesen
authors: John R
authors: JR
authors: Nuckols
mesh_terms: D016902:Air Pollution, Indoor / Q000032:analysis*; D000818:Animals; D015982:Bias; D004391:Dust / Q000032:analysis*; D016021:Epidemiologic Studies; D006801:Humans; D010575:Pesticides / Q000009:adverse effects*; D012044:Regression Analysis
chemical_list: D004391:Dust; D010575:Pesticides