Relation between Stillbirth and Specific Chlorination By-Products in Public Water Supplies
King, Will D., Dodds, Linda, Allen, Alexander C., Environmental Health Perspectives
During water treatment, chlorine reacts with naturally occurring organic matter in surface water to produce a number of by-products. Of the by-products formed, trihalomethanes (THMs) are among the highest in concentration. We conducted a retrospective cohort study to evaluate the relationship between the level of total THM and specific THMs in public water supplies and risk for stillbirth. The cohort was assembled from a population-based perinatal database in the Canadian province of Nova Scotia and consisted of almost 50,000 singleton deliveries between 1988 and 1995. Individual exposures were assigned by linking mother's residence at the time of delivery to the levels of specific THMs monitored in public water supplies. Analysis was conducted for all stillbirths and for cause-of-death categories based on the physiologic process responsible for the fetal death. Total THMs and the specific THMs were each associated with increased stillbirth risk. The strongest association was observed for bromodichloromethane exposure, where risk doubled for those exposed to a level of [is greater than or equal to] 20 [micro]g/L compared to those exposed to a level [is less than] 5 [micro]g/L (relative risk = 1.98, 95% confidence interval, 1.23-3.49). Relative risk estimates associated with THM exposures were larger for asphyxia-related deaths than for unexplained deaths or for stillbirths overall. These findings suggest a need to consider specific chlorination by-products in relation to stillbirth risk, in particular bromodichloromethane and other by-product correlates. The finding of a stronger effect for asphyxia deaths requires confirmation and research into possible mechanisms. Key words: chlorination by-products, epidemiology, public water supplies, stillbirth, trihalomethanes. Environ Health Perspect 108:883-886 (2000). [Online 2 August 2000] http://ehpnet1.niehs.nih.gov/docs/2000/108p883-886king/abstract.html
In Canada, stillbirths occur at a rate of approximately 6 per 1,000 births (1). Despite the obvious importance of stillbirths as a health event, little is known about the risk factors that contribute to this event. In a recent study examining the relationship between chlorination by-products and several adverse birth outcomes, we reported an increase in stillbirth risk with high exposure to total trihalomethanes (THMs) (2). Several other studies have also implicated water chlorination by-products as a potential cause of spontaneous abortion and stillbirth (3-5), but this relationship requires confirmation.
During the water treatment process, natural organic substances can react with chlorine to produce a number of halogenated hydrocarbon compounds. By-products formed include THMs, halogenated acetic acids, halogenated acetonitriles, chlorinated ketones, and halogenated phenols (6). Quantitatively, the THMs are among the highest in concentration of the chlorination by-products and are the most consistently measured in treated water. THMs comprise four compounds: chloroform, bromodichloromethane, chlorodibromomethane, and bromoform. THM compounds as well as other by-products may occur in different concentrations in water supplies with a similar total THM level.
Five studies, including our own, have examined either stillbirth or spontaneous abortion in relation to chlorination by-products (2-5,7). Exposure in three of these was based on total THM level, and in another study, exposure was based on a chlorinated versus chloraminated water source. Only Waller et al. (3) examined risk in relation to specific THMs. They found a stronger association with bromodichloromethane than with THM compounds per se, which points to the need to examine risk in relation to specific THMs.
The etiology of stillbirths is multifactorial and likely differs depending on the specific pathophysiologic process responsible for the fetal death. Therefore, this study evaluated the relationship between specific THM compounds and stillbirth according to cause-of-death categories based on the physiologic process responsible for the fetal death. …