Dr. Swan has led several investigations involving the evaluation of chlorinated chemicals in drinking water and the risk of spontaneous abortions during early pregnancy (first trimester). Dr. Swan initially became involved in these studies as a result of the Fairchild solvent tank leak that impacted groundwater in the Santa Clara area. The affected aquifer is used as a local drinking water supply. During the time that the solvent plume was being investigated, health officials became concerned about what appeared to be an increased rate in spontaneous abortions in the Santa Clara area.
Dr. Swan investigated the spontaneous abortion rate for the Santa Clara area and determined that the rate was higher than expected, but the cause was not determined. This initial study suffered because it was a retrospective study that relied on the recall of the participants. The questions asked by the investigators could have resulted in a "recall-bias" based on the responses of the women involved. That is, the women may not have remembered water supply sources and number of glasses consumed or provided a response in anticipation of what they thought the investigator wanted to hear. As such, interpretation of the results of the survey can be difficult.
To determine whether the water supply was the cause for the higher spontaneous abortion rate, Dr. Swan conducted a prospective study of more than 5,000 women who were in their first trimester. The study evaluated the spontaneous abortion rate based on the water supply and number of glasses of water consumed each day. The study population included pregnant woman living in Santa Clara, Walnut Creek, and Fontana. The results of the study indicated an increased rate of spontaneous abortions for women living in the Santa Clara area and consuming tap water, but less than expected for consuming bottled water. The spontaneous abortion rates for women living in Walnut Creek and Fontana were either near or less than the expected rate for women consuming either tap water or bottled water. The results of this second study indicated that there may be a substance in the tap water in the Santa Clara area that may have caused the observed increased rate of spontaneous abortions.
The next phase of the study was to determine what substance in the water sources, particularly that of Santa Clara, could be the cause of the observed increased rate of spontaneous abortions. Chemical analyses for trihalomethanes, which are typical chlorination (water purification) byproducts, showed higher concentrations of brominated compounds in the Santa Clara water supply. Dr. Swan stated that the groundwater in the Santa Clara area contains bromide compounds, a seawater influence, which could be the source for bromine in the trihalomethanes. Dr. Swan further evaluated the data and observed an increased risk of spontaneous abortions when the trihalomethane concentration exceeded 75 µg/L. The current MCL for trihalomethanes is 100 µg/L.
A study such as this one must evaluate, factor in, or eliminate a large number of potential causal factors that could produce the observed effect. For example,
can all affect the outcome of the study. Dr. Swan was able to evaluate many of these factors for importance in affecting the outcome of this study. Although it appears that brominated compounds may have caused the observed effect, other factors cannot be ruled out.
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