Levels of Selected Potentially Carcinogenic Drinking Water Disinfection Byproducts in Whole Blood After Showering
Disinfection byproducts in drinking water (DBP) are inadvertently created when chlorine
interacts with organic compounds in the untreated water. DBP have been implicated in
elevated risk of several types of cancer. Until recently, ingestion was considered to be
the major route of exposure. However, an NCI collaborative study in Spain is now showing a
link between bladder cancer and exposure to DBP in water during showering or bathing.
However, little is known of the mechanisms of action. Almost all drinking water disinfected
with chlorine contains measurable levels of DBP. The DBP found in greatest concentration
are the trihalomethanes [(THM); chloroform, bromoform, bromodichloromethane, and
dibromochloromethane]. Previously, our collaborators from the CDC measured changes in blood
THM levels after showering and bathing, and ingesting water. Showering resulted in the
largest increases, with a wide range in the increase among subjects with similar exposures.
Enzyme variants due to genetic polymorphisms may be responsible for these differences.
We plan to assess the association between the presence of enzyme variants (genetic
polymorphisms) and the increase of trihalomethanes in the blood of people exposed to DBP
while showering. The study will be conducted at the General Clinical Research Center
(GCRC), Center for Clinical Pharmacology (CCP), University of Pittsburgh, Dr. Robert Branch,
Director. Approximately 250 volunteers will be identified from Dr. Branch's ongoing
research program. These subjects will have been pre-screened with a normal standard blood
panel and for genetic polymorphisms of interest. From this pool of pre-screened
individuals, we will recruit approximately 100 people who have enzyme variants of differing
We will ask the 100 volunteers to provide seven 10-mL blood samples and two urine samples,
and take a 10-minute shower at the study site (the CCP in Pittsburgh, PA). Blood samples
will be analyzed for trihalomethane concentrations, and red blood cell enzyme activities.
To study the activity of the enzyme CYP2E1, we will administer a single dose of
chlorzoxazone, a muscle relaxant metabolized by this enzyme. We will measure enzyme
activity by analyzing blood samples collected 2 hours post-administration. We will conduct
a brief interview with each volunteer to obtain demographic and other information that might
impact the dose of THM. We will collect ambient air samples before, during and after
showering for each participant and analyze them for levels of THMs. A water sample will be
collected during showering and analyzed for levels of THM and haloacetic acids. We will ask
10 randomly selected study subjects to repeat study activities for quality control purposes.
Levels of THM in blood before and after showering, and the rate of decrease in blood
concentration, will be analyzed with respect to the presence of genetic polymorphisms for
selected enzymes, or their phenotypic activity. Blood THM levels will also be compared with
various demographic and physiologic measurements. To test intra-individual variation in
several measures, ten randomly selected participants (stratified by sex, i.e. 5 males and 5
females) will be asked to conduct the study twice, with the two study appointments separated
by at least a week.
National Cancer Institute (NCI)
United States: Federal Government
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