Drinking chlorinated water and congenital anomalies

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The rates of pregnancy loss and congenital defects are increasing. Several researches have been conducted in order to find a valid reason behind these elevated rates, but very few experiments have tried to assess the role of drinking water in these disorders.

The population of interest encompasses births (still and alive) at the Saint Georges Hospital between 1 January 2011 and 31 December 2013. The newborns' medical record should be available along with information about the mother, especially residence area and the source of potable water at the periconceptional period and during pregnancy.

Chlorination is by far the best methods for eliminating water borne pathogens. It is mainly the addition of chlorine in various forms to the drinking water. Chlorine kills the pathogens by reacting with their outer membrane, which is mainly constituted of lipids. The by-products of this reaction, the trihalomethanes (THM), constitute a major risk for human health. However, it was not until recently that the consumption of these byproducts has been linked to adverse pregnancy outcomes. Still, a lot of work is needed especially in finding a clear association and the mode of action for these byproducts. Proving that these byproducts have congenital effects, along with their already proven association with gastrointestinal cancer, will force scientists to search for a safer way to disinfect water.

In the article entitled as "Pregnancy Loss in the RAT Caused by Bromodichloromethane" (Bielmeier, 2001), scientists tried to assess the effect of bromodichloromethane (BCDM), which is a member of the THM family, on pregnant rats. The scientists tested the BCDM on rats for loss of pregnancy and for deviations in progesterone and luteinizing hormone (LH) levels. They gave the rats doses of 0, 75, or 100mg/Kg/day of BCDM. The results showed that there was a full-litter resorption in about 50% of rats that had taken the 75mg dose, and the percentage increases to reach 90% in rats taking the 100mg dose. Although these doses are much higher than those found in potable water, nevertheless, an association could be established.

In another article, "Chlorination Byproducts and Nitrate in Drinking Water and Risk for Congenital Cardiac Defects" (Cedergen, 2002), scientists tried to investigate the existence of a relationship between congenital heart defects and maternal exposure to chlorinated water. They included 71,978 Swedish infants in the study whose mothers consumed public chlorinated water during the periconceptional period or in early pregnancy. The levels of chlorine added to disinfect water were obtained from the municipalities' water supplies, as well as physical and chemical status of the potable water. Eighty-two percent of the participating mothers used the municipality as their primary source of drinking water while the rest (18%) retrieved their drinking water from private wells. A total of 937 infants were born with cardiac defects, 753 (80.36%) of them their mothers was drinking water from the Swedish water supplied, while the others (n=184) were drinking from private water wells.

Low birth weight (LBW) and preterm delivery might are also adverse pregnancy outcomes that might be related to consumption of chlorinated water. The article "Drinking water chlorination and adverse birth outcomes in Taiwan" (Yang, 2004), the scientists searched for a relation between drinking chlorinated water and (LWB) or preterm delivery. The scientists used information of 182,796 births in Taiwan over a period of two years, and divided their sample geographically; those whose mothers were living in areas in which more that 95% of the population was using chlorinated water were considered as chlorine-exposed infants, while those living in areas in which less than 5% of the population was using chlorinated water were considered chlorine-none exposed infants. They then defined an infant with LWB as an infant whose weight was less than 2500g, and an infant with preterm delivery as an infant who was born before the 37th week of the gestation period. The results showed that in chlorine-using communities, 4.51% of newborns had LBW and 4.55% had a preterm delivery. On the other hand, 4.52% of births in the other communities had LWB and 3.40% where born preterm. Thus, there is an association between drinking chlorinated water and preterm delivery, but not with LWB. Nevertheless, not all studies approve on such a relationship, as in the article "Foetal growth and duration of gestation relative to water chlorination" (Jaakkola, 2001). This study was done in Norway, and the scientists gathered information of 137,145 Norwegian born-alive children with the same outcomes of interest as the previous article (LWB and preterm delivery). They assessed the amount of the maternal exposure to chlorine by-products by using the water color scale, where dark colors inform the existence of high levels of dissolved organic carbon. The results showed that for mothers drinking non-chlorinated water, 4.5% of newborn had LWB and 6.7% were born preterm, however, 4.7% of newborn had LWB and 6.4% were born preterm in the population consuming chlorinated water. Thus, there is no relationship between exposure to chlorination by-products and such adverse pregnancy outcomes.

In another study, entitled as "Relation between Stillbirth and Specific Chlorination By-Products in Public Water Supplies" (King, 2000), the scientists conducted a retrospective cohort study on stillbirth embryos of known gestation age and of weight greater than 500g, and used normal births that occurred at the same time as a control. The conclusion was that as the consumption of THMs (especially bromodichloromethane) increases, the rate of stillbirth increases. This conclusion was based on the results that showed that the rate of stillbirth in pregnant women drinking chlorinated water with THM concentration less than 50µg/L was 0.33%, while the rate increases to 0.56% if the THM concentration was 100µg/L.

As it is clear, the authors of the above articles tried to find a relationship between drinking chlorinated water and a specific pregnancy disorder, without looking at the general picture. My future research will try to detect the relationship between drinking chlorinated water and congenital abnormalities in general, without focusing on one anomaly and discarding the others. Such congenital abnormalities may be neural, respiratory, and even urinary in addition to the previous studied outcomes. The future research should find a more specific way of measuring the amount of chlorine by-products since the water color scale that is used in most of the above articles is not specific to the THMs, but to all organic molecules dissolved in water.

Keywords: Chlorination, disinfection by-products, drinking water, congenital abnormalities, pregnancy loss, low birth weight, stillbirth.


  • Bielmeier S., Best D. (2001). Pregnancy Loss in the Rat caused by bromodichloromethane. Toxicological Sciences, 59, 309-315.
  • Cedergren M., Selbing A. (2002). Chlorination Byproducts and Nitrate in Drinking Water and Risk for Congenital Cardiac Defects. Environmental Research, 89, 124-130.
  • Jaakkola J., Magnus A. (2001).Foetal growth and duration of gestation relative to water chlorination. Occupational Environment, 58,437-442.
  • King W., Dodds L., Allen A. (2000). Relation between Stillbirth and Specific Chlorination By-Products in Public Water Supplies. Environmental Health Perspectives, 108, 883-886.
  • Yang C. (2004). Drinking Water chlorination and adverse birth outcomes in Taiwan. Toxicology, 198, 249-254.