Journal of Exposure Science and Environmental Epidemiology (2010) 20, 255–262; doi:10.1038/jes.2009.35; published online 24 June 2009

Public health interpretation of trihalomethane blood levels in the United States: NHANES 1999–2004

Judy S Lakinda,b, Daniel Q Naimanc, Sean M Haysd, Lesa L Aylwarde and Benjamin C Blountf

  1. aLaKind Associates, LLC, Catonsville, Maryland, USA
  2. bDepartment of Epidemiology and Preventive Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA
  3. cDepartment of Applied Mathematics and Statistics, The Johns Hopkins University, Baltimore, Maryland, USA
  4. dSummit Toxicology, LLP, Lyons, Colorado, USA
  5. eSummit Toxicology, LLP, Falls Church, Virginia, USA
  6. fDivision of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Correspondence: Dr. Judy S. LaKind, LaKind Associates, LLC, 106 Oakdale Avenue, Catonsville, MD 21228, USA. Tel./Fax: +1 410 788 8639; E-mail:

Received 21 February 2009; Accepted 20 May 2009; Published online 24 June 2009.



Trihalomethanes (THMs) can form as byproducts during drinking water disinfection, which is crucial for limiting human exposure to disease-causing pathogens. The US Environmental Protection Agency (USEPA), recognizing both the importance of water disinfection for public health protection and potential risks associated with THM exposure, developed disinfection byproduct rules with the parallel goals of ensuring safe drinking water and limiting the levels of THMs in public water systems. The National Health and Nutrition Examination Survey (NHANES) THM blood data can be used as a means for assessing US population exposures to THMs; biomonitoring equivalents (BEs) can provide human health risk-based context to those data. In this paper, we examine the blood THM levels in the 1999–2004 NHANES data to (i) determine weighted population percentiles of blood THMs, (ii) explore whether gender and/or age are associated with blood THM levels, (iii) determine whether temporal trends can be discerned over the 6-year timeframe, and (iv) draw comparisons between population THM blood levels and BEs. A statistically significant decrease in blood chloroform levels was observed across the 1999–2004 time period. Age-related differences in blood chloroform levels were not consistent and no gender-related differences in blood chloroform levels were observed. The concentrations of all four THMs in the blood of US residents from the 2003 to 2004 NHANES dataset are below BEs consistent with the current US EPA reference doses. For bromodichloromethane and dibromochloromethane, the measured median blood concentrations in the United States are within the BEs for the 10−6 and 10−4 cancer risk range, whereas measured values for bromoform generally fall below the 10−6 cancer risk range. These assessments indicate that general population blood concentrations of THMs are in a range considered to be a low to medium priority for risk assessment follow-up, according to the guidelines for interpretation of biomonitoring data using BEs.


THMs; blood; chloroform; biomonitoring equivalent; DBPs; NHANES


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