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REDUCTION OF INGESTION EXPOSURE TO TRIHALOMETHANES DUE TO VOLATILIZATION. (R825362)
Citation:
Batterman, S., A. T. Huang, S. Wang, AND L. Zhang. REDUCTION OF INGESTION EXPOSURE TO TRIHALOMETHANES DUE TO VOLATILIZATION. (R825362). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 34:4418-4424, (2000).
Description:
Ingestion of tap water is one of the principal exposure
pathways for disinfection byproducts (DBPs). One major
class of DBPs, trihalomethanes (THM), are highly volatile,
and volatilization will tend to lower ingestion exposures.
This study quantifies volatilization rates of the four THM
species that occur while drinking tap water, specifically,
losses during the preparation, storage, and serving of water.
A mass transfer model based on two-resistance theory
and quiescent conditions is presented, and parametrizations
of all variables are provided. Volatilization rate constants
are estimated in experiments representing common patterns
of tap water consumption, i.e., storage of tap water in
pitchers, pouring, and serving in glasses and mugs
at temperatures from 4 to 100 
C. Predicted and experimental
results show comparable loss rates for the four THMs.
Observed volatilization rates declined exponentially,
as expected, and greatly exceeded model predictions that
assumed quiescent conditions in the liquid. Loss rates
increased with temperature and mixing that resulted from
temperature gradients and air currents. Overall, storage,
pouring, and serving of tap water at temperatures below 30C caused minor (<20%) volatilization of THMs. Rapidly
heating water to 60 or 80 C also is not expected to result
in significant volatilization. However, volatilization losses
approached 75% when water was boiled even for brief periods
of time and reached 90% when boiled water was poured
and served. For the typical adult who drinks nearly half of
their water as hot beverages, volatilization will reduce
ingestion exposures of THMs by nearly a factor of 2. To
account for these losses, exposure estimates for THMs and
other volatile chemicals should separate the consumption
of heated and unheated tap water.