Reduction of ingestion exposure to trihalomethanes due to volatilization

Ingestion of tap water is one of the principal exposure pathways for disinf ection byproducts (DBPs). One major class of DBPs, trihalomethanes (THM), a re highly volatile, and volatilization will tend to lower ingestion exposur es. This study quantifies volatilization rates of the four THM species that occur while drinking tap water, specifically, losses during the preparatio n, storage, and serving of water. A mass transfer model based on two-resist ance 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., st orage of tap water in pitchers, pouring, and serving in glasses and mugs at temperatures from 4 to 100 degreesC. Predicted a nd experimental results s how 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 cu rrents. Overall, storage, pouring, and serving of tap water at temperatures below 30 degreesC caused minor (<20%) volatilization of THMs. Rapidly heat ing water to 60 or 80 <degrees>C also is not expected to result in signific ant volatilization. However, volatilization losses a pp ro a ch ed 75% when water was boiled even for brief periods of time and reached 90% when boile d water was poured and served. For the typical adult who drinks nearly half of their water as hot beverages, volatilization will reduce ingestion expo sures of THMs by nearly a factor of 2. To account for these losses, exposur e estimates far THMs and other volatile chemicals should separate the consu mption of heated and unheated tap water.