Relation of trihalomethane concentrations in public water supplies to stillbirth and birth weight in three water regions in England

Abstract

We investigated the association between total trihalomethanes (TTHMs) and risk of stillbirth and low and very low birth weight in three water regions in England, 1992-1998; associations with individual trihalomethanes (THMs) were also examined. Modeled estimates of quarterly TTHM concentrations in water zones, categorized as low (< 30 microg/L), medium (30-59 microg/L), or high (> or = 60 microg/L), were linked to approximately 1 million routine birth and stillbirth records using maternal residence at time of birth. In one region, where there was a positive socioeconomic deprivation gradient across exposure categories, there was also a positive, significant association of TTHM with risk of stillbirth and low and very low birth weight. Overall summary estimates across the three regions using a random-effects model to allow for between-region heterogeneity in exposure effects showed small excess risks in areas with high TTHM concentrations for stillbirths [odds ratio (OR) = 1.11; 95% confidence interval (CI), 1.00-1.23), low birth weight (OR = 1.09; 95% CI, 0.93-1.27), and very low birth weight (OR = 1.05; 95% CI, 0.82-1.34). Among the individual THMs, chloroform showed a similar pattern of risk as TTHM, but no association was found with concentrations of bromodichloromethane or total brominated THMs. Our findings overall suggest a significant association of stillbirths with maternal residence in areas with high TTHM exposure. Further work is needed looking at cause-specific stillbirths and effects of other disinfection by-products and to help differentiate between alternative (noncausal) explanations and those that may derive from the water supply.

Figure 1. Locations of the study water company supply regions in Great Britain.

Figure 2. Maps showing water-supply-zone-level TTHM exposure categories for each quarter: Northumbrian Water, 1997: (A) January–March; (B) April–June; (C) July–September; (D) October–December.

Figure 3. Maps showing water supply-zone-level TTHM exposure categories for each quarter, United Utilities Water, 1997: (A) January–March; (B) April–June; (C) July–September; (D) October–December.

Figure 4. Maps showing water supply-zone-level TTHM exposure categories for each quarter, Severn Trent Water, 1997: (A) January–March; (B) April–June; (C) July–September; (D) October–December.