title: Predictors of blood trihalomethane concentrations in NHANES 1999-2006.
abstract: BACKGROUND
  Trihalomethanes (THMs) are water disinfection by-products that have been associated with bladder cancer and adverse birth outcomes. Four THMs (bromoform, chloroform, bromodichloromethane, dibromochloromethane) were measured in blood and tap water of U.S. adults in the National Health and Nutrition Examination Survey (NHANES) 1999-2006. THMs are metabolized to potentially toxic/mutagenic intermediates by cytochrome p450 (CYP) 2D6 and CYP2E1 enzymes.
  
  
  OBJECTIVE
  We conducted exploratory analyses of blood THMs, including factors affecting CYP2D6 and CYP2E1 activity.
  
  
  METHODS
  We used weighted multivariable regressions to evaluate associations between blood THMs and water concentrations, survey year, and other factors potentially affecting THM exposure or metabolism (e.g., prescription medications, cruciferous vegetables, diabetes, fasting, pregnancy, swimming).
  
  
  RESULTS
  From 1999 to 2006, geometric mean blood and water THM levels dropped in parallel, with decreases of 32%-76% in blood and 38%-52% in water, likely resulting, in part, from the lowering of the total THM drinking water standard in 2002-2004. The strongest predictors of blood THM levels were survey year and water concentration (n = 4,232 total THM; n = 4,080 bromoform; n = 4,582 chloroform; n = 4,374 bromodichloromethane; n = 4,464 dibromochloromethane). We detected statistically significant inverse associations with diabetes and eating cruciferous vegetables in all but the bromoform model. Medications did not consistently predict blood levels. Afternoon/evening blood samples had lower THM concentrations than morning samples. In a subsample (n = 230), air chloroform better predicted blood chloroform than water chloroform, suggesting showering/bathing was a more important source than drinking.
  
  
  CONCLUSIONS
  We identified several factors associated with blood THMs that may affect their metabolism. The potential health implications require further study.
authors.affiliation: Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Riederer
authors.forename: Radhika
authors.initials: R
authors.lastname: Dhingra
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Blount
authors.forename: Kyle
authors.initials: K
authors.lastname: Steenland
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics / Q000378:metabolism; D004202:Disinfectants / Q000032:analysis / Q000097:blood*; D060766:Drinking Water / Q000032:analysis*; D004781:Environmental Exposure; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D022882:Trihalomethanes / Q000032:analysis / Q000097:blood*; D014481:United States; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000097:blood; D055815:Young Adult
chemical_list: D004202:Disinfectants; D060766:Drinking Water; D004785:Environmental Pollutants; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical; D019392:Cytochrome P-450 CYP2E1; D019389:Cytochrome P-450 CYP2D6