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 activity.
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.
