AM Riederer, R Dhingra, K Blount, K Steenland. Predictors of Blood Trihalomethane Concentrations in NHANES 1999-2006. Environ Health Perspect. 2014 Mar 19.
BACKGROUND: Trihalomethanes (THMs) are water disinfection by-products that have been associated with bladder cancer and adverse birth outcomes. Four (bromoform, chloroform, bromodichloromethane, dibromochloromethane) were measured in blood and tap water of U.S. adults in 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 regression 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 1999-2006, geometric mean blood and water THM levels dropped in parallel-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=4,582 chloroform; N=4,080 bromoform; N=4,374 bromodichloromethane; N=4,464 dibromochloromethane). Statistically significant inverse associations were detected 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 sub-sample (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 which may be factors affecting their metabolism; potential health implications require further study.