title: The implications of using a physiologically based pharmacokinetic (PBPK) model for pesticide risk assessment.
abstract: BACKGROUND
  A physiologically based pharmacokinetic (PBPK) model would make it possible to simulate the dynamics of chemical absorption, distribution, metabolism, and elimination (ADME) from different routes of exposures and, in theory, could be used to evaluate associations between exposures and biomarker measurements in blood or urine.
  
  
  OBJECTIVE
  We used a PBPK model to predict urinary excretion of 3,5,6-trichloro-2-pyridinol (TCPY), the specific metabolite of chlorpyrifos (CPF), in young children.
  
  
  METHODS
  We developed a child-specific PBPK model for CPF using PBPK models previously developed for rats and adult humans. Data used in the model simulation were collected from 13 children 36 years of age who participated in a cross-sectional pesticide exposure assessment study with repeated environmental and biological sampling.
  
  
  RESULTS
  The model-predicted urinary TCPY excretion estimates were consistent with measured levels for 2 children with two 24-hr duplicate food samples that contained 350 and 12 ng/g of CPF, respectively. However, we found that the majority of model outputs underpredicted the measured urinary TCPY excretion.
  
  
  CONCLUSIONS
  We concluded that the potential measurement errors associated with the aggregate exposure measurements will probably limit the applicability of PBPK model estimates for interpreting urinary TCPY excretion and absorbed CPF dose from multiple sources of exposure. However, recent changes in organophosphorus (OP) use have shifted exposures from multipathways to dietary ingestion only. Thus, we concluded that the PBPK model is still a valuable tool for converting dietary pesticide exposures to absorbed dose estimates when the model input data are accurate estimates of dietary pesticide exposures.
authors.affiliation: Exposure, Epidemiology, and Risk Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA. cslu@hsph.harvard.edu
authors.forename: Chensheng
authors.initials: C
authors.lastname: Lu
authors.forename: Christina M
authors.initials: CM
authors.lastname: Holbrook
authors.forename: Leo M
authors.initials: LM
authors.lastname: Andres
mesh_terms: D000328:Adult; D000818:Animals; D015415:Biomarkers / Q000652:urine; D002648:Child; D002675:Child, Preschool; D004390:Chlorpyrifos / Q000493:pharmacokinetics / Q000633:toxicity; D003430:Cross-Sectional Studies; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005506:Food Contamination / Q000032:analysis; D006801:Humans; D008954:Models, Biological; D010573:Pesticide Residues / Q000652:urine; D010575:Pesticides / Q000493:pharmacokinetics* / Q000633:toxicity*; D011728:Pyridones / Q000652:urine; D051381:Rats; D018570:Risk Assessment
chemical_list: D015415:Biomarkers; D010573:Pesticide Residues; D010575:Pesticides; D011728:Pyridones; C012587:3,5,6-trichloro-2-pyridinol; D004390:Chlorpyrifos