Abstract
BACKGROUND AND AIM: Chlorination is globally used as a drinking water disinfectant, but chlorination by-products, like trihalomethanes (THM), are easily formed. There are indications that THM may increase the risk of certain adverse reproductive outcomes, although the results are inconsistent. We conducted a nation-wide register-based prospective study to assess whether gestational exposure to THM via drinking water was associated with risk of congenital malformations. METHODS: We included all births during 2005-2015 of mothers residing in Swedish localities with 10,000 inhabitants, ≤ two operating water treatment plants, adequate information on chlorination procedures and sufficient number of THM measurements from the municipal monitoring. Individual maternal exposure was obtained by linking THM measurements to residential history, and categorized into no chlorination, 5, 5-15 and 15 µg THM/L. We also stratified the analyses by chlorination procedure. Outcomes and covariates were obtained via linkage of several Swedish health and administrative registers. Odds ratios (OR) and 95% confidence interval (CI) were estimated by logistic regression. RESULTS:Based on ~600,000 births and after full multivariable adjustment, we observed indications of associations between prenatal THM exposure in areas using chloramine and malformations of the nervous system (OR 1.82, 95% CI: 1.07-3.12), urinary system (2.06: 1.53-2.78), genitals (1.77: 1.38-2.26) and limbs (1.34: 1.10-1.64), comparing the population exposed to 15 µg THM/L with the unexposed. No associations were observed in areas using hypochlorite alone. CONCLUSIONS:This is one of the largest studies assessing chlorination by-products and congenital malformations. In areas using chloramine, we observed that THM was associated with an increased the risk of malformations of the nervous system, urinary system, genitals, and limb. An association between chloramine related chlorination by-products and congenital malformations has not previously been highlighted and needs attention. KEYWORDS: Water quality, Birth outcomes
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