Assessment of Prenatal Exposure to Trihalomethanes in Tap Water. N. E. Stone, L. Y. Wong, B. K. Lin, C. A. Gotway, and A. Correa, NCEH, CDC, Atlanta, GA
Adverse pregnancy outcomes may be associated with exposure to disinfecftion by-products in tap water such as trihalomethanes (THMs). To date, assessment of exposure to THMs in tap water has been based on data averaged over 3 months and over water systems. Since critical exposure windows may be fewer than 3 months and since THM levels in tap water may vary by season and residence in the water system, exposure assessment methods that reflect such variations are needed. We developed and evaluated a method for assessing exposure to THMs in tap water with spatial and temporal specificity. Monthly THM monitoring data were used to assess exposure to THMs for a sample of infants born between 1993 and 1996 in metropolitan Atlanta. Exposure indices were assigned to each infant: a general index based on the average of all system samples taken up to 3 months before and 3 months after conception, and a specific index based on samples taken a month before and after conception and closest to the infant’s residence at the time of birth. Monitoring data revealed that THM levels were higher in the fall and were higher and were higher further away from the treatment plant. For study subjects, the distribution of exposures based on the specific index reflected the temporal and spatial variation in THM monitoring levels with more resolution than did the distribution of exposures based on the less specific index. These findings underscore the need for the development and use of more specific exposure methods when assessing exposure to THMs in tap water.
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