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.Objectives: 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.Citation: Riederer AM, Dhingra R, Blount BC, Steenland K. 2014. Predictors of blood trihalomethane concentrations in NHANES 1999–2006. Environ Health Perspect 122:695–702; http://dx.doi.org/10.1289/ehp.1306499

Blood Biomarkers of Late Pregnancy Exposure to Trihalomethanes in Drinking Water and Fetal Growth Measures and Gestational Age in a Chinese Cohort

“… Silva et al (2013) also found that blood THM concentrations dropped rapidly during the first 30 min after showering among 100 study participants following a controlled showering exposure. Consistent with two previous reports, TCM was the main component of blood TTHMs in our study population (> 70%) ( Miles et al 2002 ; Riederer et al 2014 ). The median concentrations of blood THM were higher than reported for a representative sample of U.S. adults (National Health and Nutrition Examination Survey participants in 1999–2006) ( Riederer et al 2014 ) and a group of 150 U.S. women ( Rivera-Núñez et al 2012 ), but were similar to levels reported for 401 men from Wuhan, China ( Zeng et al 2013 ).…”

“…Although it has been suggested that blood concentrations at a single point in time may reflect steady-state levels ( Blount et al 2011 ), high-exposure events such as showering, bathing, and swimming can have a substantial effect on blood concentrations ( Nuckols et al 2005 ; Silva et al 2013 ). Changes in routine water-use activities in late pregnancy, and dietary changes (e.g., fasting) before delivery, also may cause blood THM concentrations to fluctuate, both within and between days ( Ashley et al 2005 ; Riederer et al 2014 ). Thus, future studies should collect multiple blood samples to provide a more accurate measure of steady-state levels, and use longer-lived exposure biomarkers (e.g., protein or DNA adducts) to avoid this limitation ( Blount et al 2011 ).…”

“…Although the elimination half-life of THMs in blood is short (minutes–hours), there are believed to be steady-state concentrations due to repeated and relatively consistent exposure to THMs ( Blount et al 2011 ). Several factors have been associated with blood THM levels including THM concentrations in water distribution systems, water-use activities (e.g., bathing/showering, swimming), personal sociodemographic characteristics (e.g., age, body mass index, education, household income), and genetic and physiological differences ( Aggazzotti et al 1998 ; Backer et al 2008 ; Caro and Gallego 2007 ; Lynberg et al 2001 ; Nuckols et al 2005 ; Riederer et al 2014 ; Rivera-Núñez et al 2012 ; Zeng et al 2014b ).…”

Trihalomethane exposure and biomonitoring for the liver injury indicator, alanine aminotransferase, in the United States population (NHANES 1999–2006)

“…Overall, TTHM exposures in this sample were relatively low; only ~5% of the study population had household tap water TTHM levels that exceeded the MCL. These levels are consistent with previously published values among NHANES participants during the same time frame (Riederer et al, 2014). …”

Overview of Disinfection By-products and Associated Health Effects

“…Levels in exhaled air are useful in evaluating short-term exposure [41], and levels in the blood have been used in evaluations at the population level [42,43]. However, these biomarkers are of limited use for evaluating risks associated with cancer, reproductive outcomes, and other health effects that require longer exposure periods.…”