Disinfection By-Products
Fate and Transport of DBPs in the Environment
Exposure Pathways, and Methods for Measuring Human Exposure to DBPs
It has not been definitively established whether or not there are adverse health effects caused by human exposure to DBPs. A large part of the problem in conducting studies in this area is that it is difficult to measure actual human exposure to these compounds. DBPs in water exist in low concentrations along with many other chemicals, and humans are exposed to them through multiple routes.(1) Sampling of the water supply as required by the USEPA Stage 1 Disinfectants and Disinfection Byproducts Rule is one method for monitoring exposure. All water utilities are required to prepare annual Consumer Confidence Reports about the quality of the water in that area. A consumer concerned about the level of DBPs in the local water supply should consult the report from the local water utility.
Unfortunately, knowing the DBP level in a particular water supply is not always an accurate method for assessing overall exposure. Ingestion is only one exposure pathway among many, including both inhalation and dermal contact during showers, baths, swimming, dishwashing, and clothes washing. There is a different metabolic process that occurs among all these routes, as well as a wide variation of exposure within a population.(1) One study measuring THM concentrations in tap water and blood levels of fifty women living in two separate counties found that concentrations of THMs in blood “rose significantly as a result of showering…and that THMs measured in the blood of women living in the two locations reflected species and concentration differences in their respective tap waters.” (2) Another study compared an individual’s exposure to THMs through showering for 10 minutes, bathing for 10 minutes in a bathtub and drinking 1 L of tap water during a 10-minute time period. The blood of the participants was analyzed using a purge-and-trap/gas chromatography/mass spectrometry method; the highest levels of THMs were found in the blood of those people who had taken 10-minute showers.(3) There is such a large variability over time, water source, temperature, temporal DBP levels, and daily activity that accurately measuring a population’s exposure to DBPs becomes a difficult problem. Epidemiological studies accurately assessing human exposure to DBPs at a population level will need to take into account all of these different variabilities.
Citations:
1. Vieuwenhuijsen, Mark J., Toledano, Mireille B., Eaton, Naomi E., Fawell, John, & Elliott, Paul. Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review. Occup Environ Med 2000; 57: 73-85.
2. Miles, A.M., Singer, P.C., Ashley, D.L., Lynberg, M.C., Mendola, P., Langlois, P.H., & Nuckols, J.R. Comparison of trihalomethanes in tap water and blood. Environmental Science & Technology 2002; 36(8): 1692-8.
3. Backer, L.C., Ashley, D.L., Bonin, M.A., Cardinali, F.L., Kieszak, S.M., & Wooten, J.V. Household exposures to drinking water disinfection by-products: whole blood trihalomethane levels. Journal of Exposure Analysis and Environmental Epidemiology 2000; 10(4): 321-6.