The Transfer of Trichloroethyene (TCE) from a Shower to Indoor Air: Experimental Measurements and Their Implications

Abstract

Experiments were performed to measure the transfer of trlchloroethylene (TCE), a volatile organic compound (VOC), from tap water In showers to Indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between Influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there Is no statistically significant difference between the transfer efficiency measured with hot (37°C) or cold (22°C) shower water and that there Is no statistically significant change In transfer efficiency with time during a 20-mln shower. The implications for exposure assessment are considered.Estimation of human exposure to organic chemicals transferred from tap water in showers to indoor air requires answers to several questions, among them- (1) what is the contaminant concentration in the water supply, (2) what fraction of the dissolved contaminant is transferred from water to air in the shower stall, (3) how much water is used in a typical shower, (4) what is the resulting concentration in Implications Efforts to assess human exposure to contaminated tap water have revealed that significant exposures to volatile organic compounds (VOCs) can occur from the indoor inhalation pathway-primarily in showers. At air-water interfaces, mass transfer of chemicals reflects the resistance through both the liquid and gas phases and is difficult to predict from first principles. However, basic mass transfer properties, such as diffusion coefficients, can be accurately estimated. The theoretical dependence of transfer efficiency on these properties makes plausible estimates of relative transfer efficiency through the scaling of mass transfer parameters from one chemical to another. The lack of temperature dependence in our measurements of transfer efficiency supports the premise that for volatile compounds transfer efficiency is limited by liquid-phase mass transfer (which is more temperature insensitive) and not by gas-phase mass transfer (which is more sensitive). For households using tap water contaminated with TCE, the results here indicate that inhalation exposures in showers could be as large as or larger than a conservative estimate of ingestion exposure. The assumption that 70-kg adult consumes 2 L per day of tap water is considered a conservative estimate of ingestion exposure. Our experimental results suggest that inhalation exposures in showers could be equivalent to an ingestion contact of 1 to 4 L. the shower stall and bathroom air, and (5) how much time is spent in contact with th...

In-home formation and emissions of trihalomethanes: The role of residential dishwashers

“…Measured stripping efficiencies ranged from 42% to 63% for chloroform. Similar findings have been reported for chemicals with similar chemical properties to chloroform, for example, trichloroethene, ethylbenzene, and toluene (McKone and Knezovich, 1991;Tancrede et al, 1992;Giardino and Andelman, 1996;Moya et al, 1999). While numerous researchers have studied chemical stripping from showers for various chemicals, recent research also suggests significant chemical stripping from water devices other than showers, for example, dishwashers , wash basins (Howard and Corsi, 1996) and washing machines (Howard and Corsi, 1998).…”

Inter- and intra-ethnic variation in water intake, contact, and source estimates among Tucson residents: Implications for exposure analysis

“…Additionally, Hispanics in this sample shower considerably longer than subjects in other studies (Shimokura et al, 1998 ). Showering and bathing represents a significant source of inhalation exposure to VOCs found in the water (Jo et al, 1990;McKone, 1989;McKone and Knezovich, 1991;Weisal and Jo, 1996 ). Given the southside's history of VOC (i.e., TCE; 1,1 -DCE; TCA; MEK ) contamination, it is reasonable to suggest that behaviors related to potential inhalation exposures should be investigated more thoroughly.…”

“…Tap water used for showering and bathing is a source of inhalation exposure to VOCs found in the water ( Jo et al, 1990;McKone, 1989;Weisal and Jo, 1996 ). McKone and Knezovich (1991 ) measured the transfer efficiency of TCE from shower water into air as 61% ( SD = 9% ). However, there are relatively few studies of exposures related to showering and bathing activities.…”

Applying the two-resistance theory to contaminant volatilization in showers

“…Although the relationship was only 'intended to be approximate it does not adequately account for gas-phase resistance (9). More recently, however, the results of four experimental studies on full-scale showers have become available (6,10,11,12). These results present an opportunity to detennine mass transfer coefficients for the various shower systems and then to use these to account in a consistent fashion for variation in contaminant volatility.…”

“…He points out the need for refining present estimates of indoor air exposure to VOCs derived from potable water sources by, inter alia, more accurately accounting for the chemical characteristics that affect the rate and extent of volatilization. In order to account for the different properties of VOCs, McKone (3,5,6) proposed a relationship which adjusts the measured transfer 2 ,it efficiency (the fraction volatilized) for radon (7,8) to that for any VOC using the Henry's law constant and liquid and gas diffusivities. Although the relationship was only 'intended to be approximate it does not adequately account for gas-phase resistance (9).…”