Linking Geographic Water Utility Data with Study Participant Residences from the National Birth Defects Prevention Study

image of tap water In 1998, the Centers for Disease Control and Prevention (CDC) and the U.S. Environmental Protection Agency (USEPA) entered into an Interagency Agreement to build a study of disinfection byproducts (DBPs) and birth defects into the existing National Birth Defects Prevention Study (NBDPS). Initiated in 1997, the NBDPS is a case-control study of birth defects risk factors; it is being conducted in eight geographic areas across the United States (Atlanta, Arkansas, California, Iowa, New Jersey, New York, Massachusetts, and Texas). Major study strengths include: 1) large population-based birth defects registries with populations on diverse water supplies; 2) a large sample size which provides unprecedented power to evaluate potential risk factors for specific birth defects; 3) improved birth defect case definition; and 4) an interview instrument which obtains information from mothers on relevant exposures and potential confounders.

The NBDPS provides a unique and unprecedented opportunity to study the relationship between birth defects and DBPs. Methods for assessing exposure to DBPs in the NBDPS include obtaining information on both personal water use habits (through telephone interview) and tap water characteristics. To obtain information on personal water use, a water module was developed for inclusion as an integral part of the NBDPS computer assisted telephone interview (CATI). As of February 2000, all NBDPS participants are asked about water consumption (at home and at work) and water use (bathing, swimming, household habits).

The NBDPS does not collect information on DBP levels in the water supplies of study participants. Such information is important for classifying exposure in conjunction with the data collected on water consumption and use. Information on tap water characteristics is most readily available from water utility monitoring data collected under the auspices of federal regulations pertaining to the Safe Drinking Water Act. However, using monitoring data to assign DBP levels to individual locations (residences) in a water distribution system requires knowledge of the hydraulic relationship between the sampling point and the residence location. Often times, such information is not available and system-wide averages or proximity relationships between the sampling point and the residence are used to assign a DBP concentration to the individual's water supply. Such an approach can lead to significant misclassification of exposure depending on the degree of spatial variation in DBP concentrations across the water distribution system.

Current research is being conducted to ascertain the extent of utility-based information on DBPs within the geographic areas covered by the NBDPS, researchers at Colorado State University and the CDC developed a relational database containing trihalomethanes (THMs) and haloacetic acids (HAAs) water quality and treatment records for water utilities, including development of software capable of querying the database and identifying those areas served by utilities where spatial variation in DBP level is minimal.

The goal of the current study is to determine the extent to which utility water quality monitoring data on THMs and HAAs can be linked with residential information of NBDPS participants. Ultimately, six of the 8 geographic areas covered by the NBDPS will be included in this analysis. California and New Jersey have been excluded from this geographic evaluation. By this project, we will develop and evaluate a prototype method for linking these data for use in the NBDPS Tap Water Study. The linkage algorithm will be developed in collaboration with the Texas Birth Defects Research Center (TBDRC) at the Texas Dept of Health, where we will evaluate linkage capability between water utility data and study participant data (including residential history) for 1,104 NBDPS cases and 640 NBDPS controls ascertained in Texas between the period 1997-2001. We will then assess the transferability of our findings to other geographic areas within the NBDPS.

Two reports detailing this research are published by the AWWA Research Foundation (AWWARF) http://www.awwarf.com and are titled:

Identifying Geographic Regions for Potential Future Epidemiology Research on Disinfection Byproducts.
Development of Exposure Assessment Methods for THM and HAA in Water Distribution Systems.