Nov. 15, 2000—A Canadian study has found an association between disinfection byproducts and stillbirths, the sixth study to reach such a conclusion. The study, by three Canadian epidemiologists, was reported in the September/October WWEMA Washington Analysis newsletter. The study also found a dose-response relationship, meaning the larger the dose the greater the risk.
Environmental Health Perspectives, a peer-reviewed monthly journal from the National Institute of Environmental Health Sciences is scheduled to publish the study, "Relation Between Stillbirth and Specific Chlorination By-Products in Public Water Supplies," this Fall.
The authors analyzed data on 49,756 babies delivered between 1988 and 1995 in Nova Scotia. Of those deliveries, 214 were stillbirths.
The authors estimated exposure by reviewing water monitoring data between 1988 and 1995 from publicly owned treatment works that served most of the homes of the families in the study group. The authors presented data on the concentrations of to tal trihalomethanes-byproducts of chlorine-as well as the two trihalomethanes detected most frequently: chloroform and bromodichloromethane.
Mothers who were estimated to be exposed to concentrations of 100 ug/L or more total trihalomethanes had a 1.7 times greater risk of having a stillbirth than mothers with exposures less than 50 ug/L, the authors found. The risk increased 0.5 percent with each 10 ug/L increase of total trihalomethanes, they said.
Increasing exposure to chloroform and bromodichloromethane also increased risk, the authors said. The risk of a stillbirth doubled when mothers were estimated to be exposed to 20 ug/L or more of bromodichloromethane, the authors said. At exposures greater than 100 ug/L of chloroform, stillbirths were 1.6 times more likely.
The authors then reviewed data on the association between chlorine byproducts and unexplained stillbirths and asphyxiation. Those two categories accounted for 73 percent of the deaths. The risk of asphyxiation was nearly five times greater for mothers estimated to be exposed to 100 or more ug/L total trihalomethanes. The risk that they would deliver a baby who had died due to a lack of oxygen was more than three times higher among mothers estimated to be exposed to 100 or more ug/L chloroform.
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