Levels of Trihalomethanes in Tap Water and Human Blood in a Representative US Population, National Health and Nutrition Examination Survey 1999–2004

Abstract

S-31B8-2 Background/Aims: Water disinfection reduces infectious disease outbreaks, but can also form potentially harmful disinfection byproducts such as trihalomethanes (THMs). Improved exposure assessment tools and data are needed to better understand THM exposure prevalence, magnitude, and its potential health impact. Methods: Household tap water and blood samples were collected from 3229 adult participants of the US National Health and Nutrition Examination Survey from 1999 to 2004. THM levels in these samples were quantified based on stable isotope internal standard response generated by analysis with solid phase microextraction coupled with GC-MS. Results: We found detectable levels of 4 THMs in the following percent of blood samples: chloroform: 100%, 97%, 92%; bromodichloromethane: 97%, 98%, 73%; dibromochloromethane: 87%, 76%, 48%, and bromoform: 74%, 81%, 40% collected during 1999–2000, 2001–2002, and 2003–2004, respectively. These detection frequencies suggest widespread exposure to THMs in the US population. Tap water originating from private wells had significantly lower levels of all 4 THMs compared with tap water originating from other sources. Implementation of more stringent regulatory limits in 2001 corresponded to decreased tap water chloroform levels from 1999 to 2004; blood chloroform levels also decreased over this same time frame. The median levels of the other 3 THMs decreased slightly over the 6 years in both water and blood. The adjusted geometric mean bromodichloromethane was significantly higher in non-Hispanic whites than non-Hispanic Blacks (P < 0.002) and higher in non-Hispanic Blacks than Mexican-Americans (P < 0.006). Additional variables associated with increased blood bromodichloromethane levels included the following: recent water-related activity (showering and bathing), having body mass index >25, and time of day of sample collection. Conclusion: These population data for THM exposure establish a nationally representative baseline for THM exposure in the United States and provide data for evaluating the efficacy of regulatory changes designed to reduce human exposure.