Dangers of chlorinated water

August 6, 1998

By Peter Montague

There were just over 4 million live births in the US in 1992. There were 30,000 foetal deaths. A foetal death is one that occurs after at least 20 weeks of gestation but prior to birth.

In actuality, there were very likely more than 30,000 foetal deaths in 1992. The Statistical Abstract says, "There is substantial evidence that not all foetal deaths for which reporting is required are reported".

In addition, there are spontaneous abortions — pregnancies that terminate spontaneously before the end of the 20th week. These are far more common than foetal deaths, though the exact number is not known. Various studies estimate that spontaneous abortions occur in somewhere between 6.5% and 21% of all pregnancies.

Together, spontaneous abortions and foetal deaths are termed "miscarriages".

Recent studies indicate that some miscarriages — as well as some serious birth defects — may be caused by chlorine added to drinking water as a disinfectant.

In the US, chlorine is added to public drinking water to kill harmful bacteria. The chlorine reacts with naturally occurring organic matter in the water, creating a host of chlorinated chemicals as by-products.

Health agencies, including the federal Environmental Protection Agency, simply ignore most of these by-products and know almost nothing about them.

Instead, they focus on four by-products, allowing these four to act as surrogates for all the others. The four that EPA pays attention to are chloroform, bromoform, bromodichloromethane and chlorodibromomethane. Together, these four are called "trihalomethanes" or THMs.

According to federal drinking water regulations, if a public water supply serving more than 10,000 people contains over 100 parts per billion of total THMs, the water is unacceptable. However, since there are usually no other available sources of drinking water, EPA is usually not in a position to do anything except urge the water supplier to clean up its act.

Pregnancy study

A study by the California Department of Health published in March 1998 tracked the drinking water consumption and the pregnancy outcomes of 5144 pregnant women in a prepaid health plan during 1989-1991. The drinking water consumption of the women was ascertained as soon as their pregnancy was registered in the study's database. Later, the outcome of their pregnancy was compared with the amount of water they drank and the total amount of THMs they received by drinking water (information received from the water companies).

The study found that 16% of women drinking five or more glasses of water per day containing more than 75 ppb THMs had miscarriages, whereas only 9.5% of women drinking less water, or water lower in THMs, had miscarriages.

Thus, among women with high exposure to THMs in drinking water, the likelihood of spontaneous abortion was 1.8 times as great as it was among women with low exposure.

The strength of this study was its prospective nature: it did not rely on women to remember how much water they drank in the past.

To see if their results represented a real effect, the researchers compared women who filtered their water, or who let the water stand before drinking it, with women who drank it straight from the tap. (THMs are volatile and will slowly leave water that is allowed to stand.) The results were consistent with THMs causing spontaneous abortion.

Birth defects

In January, the Agency for Toxic Substances and Disease Registry published a case-control study showing that serious birth defects — spina bifida, or neural tube defects — are associated with total trihalomethanes ingested in drinking water. Neural tube defects are serious birth defects in which the spinal cord is not properly enclosed by bone.

This statewide study in New Jersey found a doubled risk of neural tube defects among those with the highest exposures to THMs in drinking water.

This study pointed out that exposure to THMs can also occur through the contamination of indoor air. Flushing toilets, showering and washing dishes and clothes can inject THMs into household air.

The study examined public water company records and compared pregnancy outcomes to the amounts of THMs delivered to the home in drinking water. It did not examine the amount of water ingested. The study found no relationship to foetal deaths, but the likelihood of neural tube defects was tripled by exposure to THMs at levels exceeding 80 parts per billion.

This study provoked a letter to the editor of the American Journal of Epidemiology, in which the authors suggested a biological mechanism by which trihalomethanes might cause neural tube defects. Neural tube defects are known to be associated with vitamin B12 deficiency, and the letter pointed to studies showing that vitamin B12 use by the body can be disrupted by chloroform, one of the four main trihalomethanes in chlorinated drinking water.

An earlier case-control study reported on pregnancy outcomes among women in Boston during the years 1977-1980. Stillbirths were 2.6 times as common among women exposed to chlorinated surface water, compared to controls whose water was disinfected with chloramine instead of chlorine.

More recently, a study of drinking water and pregnancy outcomes in central North Carolina reported a 2.8-fold increased likelihood of miscarriage among women in the highest exposure group for trihalomethanes in drinking water.


Very recently, a second study from the California Department of Health has shown that, in one area of California, women who drank cold tap water had nearly a five-fold increased risk of miscarriage, compared to women who drank mostly bottled water very low in trihalomethanes.

Bottled water is often disinfected by a process called ozonation instead of chlorination. Bubbling ozone through water kills bacteria effectively, avoids the distinctive taste and odour of chlorine in the treated water and produces no dangerous trihalomethanes.

US EPA is currently setting new standards for THMs in drinking water. The new regulations would apply to all water companies, not just those serving 10,000 people or more, and would limit total THMs to 80 ppb, down from the present 100 ppb.

Still, since several studies link trihalomethanes at 75 ppb or even less to increased miscarriages, EPA's new standard seems dubious even before it has been established.

Many European cities, and some Canadian cities, long ago turned away from chlorination in favour of ozonation to disinfect their water. In recent years, a few smaller US cities have begun to use ozonation.

Still, the vast majority of water supplies in the US remain chlorinated. And water quality experts remain in the dark about trihalomethane levels in water delivered to customers.

Kellyn S. Betts, writing in Environmental Science & Technology, quotes the EPA official in charge of the new THM regulations as saying that no-one knows how many US water systems deliver water with THMs exceeding 75 ppb.

Erik Olson, a water quality expert with the Natural Resources Defense Council, an environmental group in New York City, points out that THM levels in water supplies typically increase by as much as a factor of 1.5 to 2 during the summer months. He says short-term exposures may be very important in producing spontaneous abortions, foetal deaths and serious birth defects. "We may be totally overlooking the risk of short-term exposure", Olson said.

[From Rachel's Environment & Health Weekly. Like Green Left Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]

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