Characterization of exposure to trihalomethanes in a distribution system using modelling and epidemiologic methods: Preliminary analysis and descriptive statistics

Risk assessment of disinfection by-product (DBP) exposure from potable water has been limited by difficulties with exposure characterization. To address the need for improved exposure characterization, an investigation of exposure to 4 regulated DBPs, trihalomethane (THM) species, was conducted in a large public water distribution system. The source water was a groundwater that received chlorine disinfection prior to distribution. Concentrations of the four THM species were measured in household water samples and in samples of whole blood taken from one household member at each of 54 sites in the distribution system. Median concentrations of total THMs in paired water and whole blood samples taken from study participants and their household tap water at 54 households were 41.8 μg/L tap water and 28.1 pg/ml whole blood, respectively. A questionnaire was used to assess the water-use behavior of individual subjects; results will be incorporated into a total exposure measure that includes activities that contribute to ingestion, dermal absorption, and inhalation exposure routes. Tracer tests were performed in the distribution system concurrently with hydraulic and water quality monitoring. The tracer tests and hydraulic monitoring data were used to minimally calibrate an existing distribution system model. Measured THM concentrations were within the range of the model-predicted values 70% of the time.