Volatilization Rates From Water To Indoor Air Phase II

Contaminated water can lead to volatilization of chemicals to residential indoor air. Previous research has focused on only one source (shower stalls) and has been limited to chemicals in which gas-phase resistance to mass transfer is of marginal significance. As a result, attempts to extrapolate chemical emissions from high-volatility chemicals to lower volatility chemicals, or to sources other than showers, have been difficult or impossible.

This study involved the development of two-phase, dynamic mass balance models for estimating chemical emissions from washing machines, dishwashers, and bathtubs. An existing model was adopted for showers only. Each model required the use of source- and chemical-specific mass transfer coefficients. Air exchange (ventilation) rates were required for dishwashers and washing machines as well. These parameters were estimated based on a series of 113 experiments involving 5 tracer chemicals (acetone, ethyl acetate, toluene, ethylbenzene, and cyclohexane) and 4 sources (showers, bathtubs, washing machines, and dishwashers). Each set of experiments led to the determination of chemical stripping efficiencies and mass transfer coefficients (overall, liquid-phase, gas-phase), and to an assessment of the importance of gas- phase resistance to mass transfer. Stripping efficiencies ranged from 6.3% to 80% for showers, 2.6% to 69% for bathtubs, 18% to 100% for dishwashers, and 3.8% to 100% for washing machines. Acetone and cyclohexane always defined the lower and upper bounds, respectively, of these ranges.

Results for shower experiments were reasonably consistent with those reported by other researchers. An important conclusion of this study was that bathtubs may be more significant than showers with respect to human exposure to chemicals dissolved in water. Dishwashers were determined to be very effective at removing chemicals from water to air, with low but continuous emissions during operation and significant storage within the dishwasher headspace. Chemical stripping efficiencies for washing machines were observed to be highly sensitive to system operating conditions. Water temperature was an important variable that affected stripping efficiencies and mass transfer coefficients for all sources.

A set of protocols was defined for estimating emission rates for chemicals other than those used in this study. Example applications are provided and illustrate the dynamic behavior of emissions and importance of chemical properties on such emissions. The results of this study should be of value to those interested in improved tools for risk-based corrective action, human exposure to disinfection by-products and other water contaminants, or the general issue of human exposure to toxic chemicals through routine daily activities.

Additional Information

This report was submitted in fulfillment of #CR 824228-01 by The University of Texas at Austin under the sponsorship of the United States Environmental Protection Agency. It covers a period from June 1, 1995, to August 31, 1997, and work was completed as of August 31, 1997.