We conducted a field study in Corpus Christi, Texas, and Cobb County, Georgia, to evaluate exposure measures for disinfection by-products, with special emphasis on trihalomethanes (THMs). Participants were mothers living in either geographic area who had given birth to healthy infants from June 1998 through May 1999. We assessed exposure by sampling blood and water and obtaining information about water use habits and tap water characteristics. Two 10-mL whole blood samples were collected from each participant before and immediately after her shower. Levels of individual THM species (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) were measured in whole blood [parts per trillion (pptr)] and in water samples (parts per billion). In the Corpus Christi water samples, brominated compounds accounted for 71% of the total THM concentration by weight; in Cobb County, chloroform accounted for 88%. Significant differences in blood THM levels were observed between study locations. For example, the median baseline blood level of bromoform was 0.3 pptr and 3.5 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). Differences were most striking in blood obtained after showering. For bromoform, the median blood levels were 0.5 pptr and 17 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). These results suggest that blood levels of THM species vary substantially across populations, depending on both water quality characteristics and water use activities. Such variation has important implications for epidemiologic studies of the potential health effects of disinfection by-products.

Water disinfection is extremely important for the protection of public health; however, it also forms by-products, including trihalomethanes (THMs). Previous studies of health effects from disinfection by-products have lacked accurate methods to quantify exposure over time. As a first step in establishing a better system for exposure assessment, the authors investigated which household water use activities cause a significant increase in internal dose concentrations of THMs. In this study, 7 subjects in 2 different cities carried out 12 common activities that involved water use. In 3 of these activities-bathing, showering, and washing dishes by hand-the blood concentrations of THMs increased substantially. Further analysis of the data suggested that tap water concentrations primarily controlled the blood concentrations from bathing exposure, whereas tap water concentrations and ambient air concentrations resulting from water use affected the blood concentrations from showering exposure. Further studies will focus on variables in these activities that can alter exposure.

It has been shown that bathroom-type water uses dominate personal exposure to water-borne contaminants in the home. Therefore, in assessing exposure of specific population groups to the contaminants in the water, understanding population water-use behavior for bathroom activities as a function of demographic characteristics is vital to realistic exposure estimates. In this article, shower and bath frequencies and durations are analyzed, presented, and compared for various demographic groups derived from analyses of the National Human Activities Pattern Survey (NHAPS) database and the Residential End Uses of Water Study (REUWS) database as well as from a review of current literature. Analysis showed that age and level of education significantly influenced shower and bath frequency and duration. The frequency of showering and bathing reported in NHAPS agreed reasonably well with previous studies; however, durations of these events were found to be significantly longer. Showering frequency reported in REUWS was slightly less than that reported for NHAPS; however, durations of showers reported in REUWS are consistent with other studies. After considering the strengths and weaknesses of each data set and comparing their results to previous studies, it is concluded that NHAPS provides more reliable frequency data, while REUWS provides more reliable duration data. The shower- and bath-use behavior parameters recommended in this article can aid modelers in appropriately specifying water-use behavior as a function of demographic group in order to conduct reasonable assessments of exposure to contaminants that enter the home via the water supply.

Humans are exposed daily to complex mixtures of chemicals, including drinking water disinfection by-products (DBPs) via oral, dermal, and inhalation routes. Some positive epidemiological and toxicological studies suggest reproductive and developmental effects and cancer are associated with consumption of chlorinated drinking water. Thus, the U.S. Environmental Protection Agency (EPA) conducted research to examine the feasibility of evaluating simultaneous exposures to multiple DBPs via all three exposure routes. A cumulative risk assessment approach was developed for DBP mixtures by combining exposure modeling and physiologically based pharmacokinetic modeling results with a new mixtures risk assessment method, the cumulative relative potency factors (CRPF) approach. Internal doses were estimated for an adult female and an adult male, each of reproductive age, and for a child (age 6 yr) inclusive of oral, dermal, and inhalation exposures. Estimates of the daily internal doses were made for 13 major DBPs, accounting for activity patterns that affect the amount of human contact time with drinking water (e.g., tap water consumed, time spent showering), building characteristics (e.g., household air volumes), and physicochemical properties of the DBPs (e.g., inhalation rates, skin permeability rates, blood: air partition coefficients). A novel cumulative risk assessment method, the CRPF approach, is advanced that integrates the principles of dose addition and response addition to produce multiple-route, chemical mixture risk estimates using total absorbed doses. Research needs to improve this approach are presented.