Relation between stillbirth and specific chlorination by-products in public water supplies

During water treatment, chlorine reacts with naturally occurring organic ma tter in surface water to produce a number of by-products. Of the by-product s formed, trihalomethanes (THMs) are among the highest in concentration. We conducted a retrospective cohort study to evaluate the relationship betwee n the level of total THM and specific THMs in public water supplies and ris k for stillbirth. The cohort was assembled from a population-based perinata l 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 leve ls of specific THMs monitored in public water supplies. Analysis was conduc ted for all stillbirths and for cause-of-death categories based on the phys iologic process responsible for the fetal death. Total THMs and the specifi c THMs were each associated with increased stillbirth risk. The strongest a ssociation was observed for bromodichloromethane exposure, where risk doubl ed for those exposed to a level of greater than or equal to 20 mu g/L compa red to those exposed to a level < 5 mu g/L (relative risk = 1.98, 95% confi dence interval, 1.23-3.49). Relative risk estimates associated with THM exp osures were larger for asphyxia-related deaths than for unexplained deaths or for stillbirths overall. These findings suggest a need to consider speci fic chlorination by-products in relation to stillbirth risk, in particular bromodichloromethane and other by-product correlates. The finding of a stro nger effect for asphyxia deaths requires confirmation and research into pos sible mechanisms.