Health Stream Literature Summary - Issue 53 - March 2009

Impact of chlorination on the incidence of cancers and miscarriages in two different campus communities in India.
Goel S. (2008) Journal of Environmental Science and Engineering, 50(3); 175-178.

Chlorination has been an extremely effective disinfectant against some of the most common waterborne microbial pathogens, especially bacteria. However, the potential carcinogenicity of disinfection by-products (DBPs) in chlorinated drinking waters is now recognised as a secondary heath risk, and is a major concern in developed countries. Animal toxicology studies at high doses have shown that exposure to chlorinated by-products can cause neurotoxic, cytotoxic, genotoxic and mutagenic effects. Some epidemiological studies at low-dose exposure levels have shown statistically significant relationships between cancers and miscarriages in populations exposed to chlorinated drinking water while other studies have shown no or little adverse effects. Most studies examining chlorinated drinking water and adverse reproductive effects have shown little or no evidence of adverse reproductive outcomes such as low birth weight, preterm delivery, and neonatal death. However, no studies from less developed countries have been reported in the literature and it is possible that results in these countries may vary due to differences in location, water quality, population demographics and a greater incidence of other diseases. This population-based cross-sectional study was conducted to assess the impacts of drinking chlorinated water on the incidence of cancers and miscarriages in two campus communities in India.

The two campus communities included in this study were Indian Institute of Technology Kanpur (IITK) and Indian Institute of Technology Kharagpur (IITKgp). The IITK campus community has been using untreated ground water since its inception in 1963. The estimated resident population is around 5000. This community serves as the control group. The IITKgp campus community established in 1950 has been using chlorinated water which is mainly surface water mixed with some amount of ground water. Drinking water comes from open wells located on the bank of the river Kangsabati, tubewells at campus and in Balarampur village about 5 km away from campus. The resident population in this community is estimated at 4000, excluding students. Water from the three sources is combined in underground reservoirs at campus and supplied after disinfection with calcium hypochlorite.
House-to-house surveys were conducted in the two communities and included 230 households and 949 residents in IITK and 1191 households and 3914 residents in IITKgp. The questionnaire used in the survey gather information on family size, age and income, years of exposure to chlorinated drinking water, water treatment methods adopted at home, incidence of cancer and affected site/organ, age of mother at each pregnancy, number of miscarriages and other health concerns.

IITK residents were more likely to use their water without treatment - 62.6% of the total households surveyed compared with 20.2% of the total households in IITKgp. All of the other households were using some form of treatment in-house ranging from boiling to using various commercial systems based on filtration, adsorption and disinfection processes. There were 19 cases of cancer reported in IItKgp during the survey and for 9 of these major contributing factors were identified. Odds ratios (ORs) were calculated using the remaining 10 cases. Only four cancer cases were reported in IITK and no major contributing factors were identified for any of them. There were 60 cases of spontaneous abortions identified during the IITKgp survey of which the cause had been medically diagnosed in 27 cases. ORs were calculated based on the remaining 33 cases. In the IITK survey 24 cases of spontaneous abortions were identified and the cause was identified in only one case leaving 23 cases for calculation.

ORs were calculated based on the hypothesis that exposure to chlorinated drinking water may result in a higher incidence of cancers and miscarriages. The OR values were found to be 0.56 (95% CI = 0.18 - 1.81) for cancers and 0.33 (95% CI = 0.19 - 0.56) for miscarriages. The ORs imply no significant association was found here between exposure to chlorinated drinking water and the incidence of cancers and miscarriages. ORs were calculated based on the alternative hypothesis that chlorination (along with in-house treatment) decreases the risk of cancers and miscarriages. The OR values found were for cancers 1.77 (95% CI = 0.55 to 5.66) and for miscarriages, 3.07 (95% CI 1.78-5.29). These results show there is no association between exposure to chlorinated and treated drinking water and cancers, however there was a significant decrease in the incidence of miscarriages for those exposed to chlorinated drinking water which may have additional in-home treatment.

This study did not find an increased risk of cancers and miscarriages in those exposed to chlorinated drinking water. On the contrary, the results suggest a significant decrease in the incidence of miscarriages for those exposed to chlorinated drinking water compared to non-disinfected water.

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