The Thirst for Safe Water: Part 2 - Water Quality and Disinfection
Air Date: Week of April 10, 1998
Before reaching our homes, most tap water has gone through treatment plants where it is filtered and disinfected. The process is designed to make the water safe. But, research shows that the most common way to treat water adds chemicals that can get turned into cancer-causing agents. The Environmental Protection Agency is taking steps to reduce this danger, but some health experts say the agency isn't doing enough. Daniel Grossman has the second in our series, "The Thirst for Safe Water."
CURWOOD: This is Living on Earth, I'm Steve Curwood. Our bodies contain about 60 percent water, and to stay healthy, we need to drink about two quarts of water every day. Most of us assume that the tap water we get from our municipal supplies is okay. Before reaching us, most tap water has gone through treatment plants where it is filtered and disinfected. The process is designed to make the water safe. But, research shows that the most common way to treat water adds chemicals that can get turned into cancer-causing agents. The Environmental Protection Agency is taking steps to reduce this danger, but some say the agency isn't doing enough. Daniel Grossman has the second in our series, "The Thirst for Safe Water."
(Sounds of birds cawing)
GROSSMAN: The drinking water plant for Cambridge, Massachusetts is a low-slung brick building on the shores of Fresh Pond. Whatever the water’s quality when this reservoir was named, its not so fresh now. And it needs a lot of cleaning before it can be consumed.
MACDONALD: Could we get a filter backwash?
GROSSMAN Inside, the sprawling complex the city’s water quality chief, Timothy MacDonald, is inspecting the plant’s filters.
(Sounds of a valve opening and water spilling out)
GROSSMAN: A few steps away, Mr. MacDonald enters a room with three huge plastic tanks.
MACDONALD: This is where we feed the chlorine chemicals to do the disinfection in the water treatment plant. The chemical we use is sodium hypochlorite. It is a stronger form of the same thing you use at home in your laundry for bleach.
GROSSMAN: Timothy MacDonald says the chlorine compound plays a critical role.
MACDONALD: There are organisms in the water. bacteria, protozoa and other organisms that are harmful to our health. And we need to rid the water of those harmful organisms.
(Sound of a closing door inside of the plant).
GROSSMAN: The invention of disinfection at the turn of the century was largely responsible for ending epidemics of deadly diseases like cholera, that ravaged American cities.
OZONOFF: The purification of drinking water, disinfection of drinking water with chlorination is one of the great public health triumphs in this century.
GROSSMAN: But David Ozonoff, Chair of Boston University’s School of Public Health, says that like other powerful technologies, this one has a down side.
OZONOFF: And as it turns out, natural waters have lots of other things in them--natural products--that can react with the chlorine, and produce a whole suite of other chemicals. And it turns out that some of those chemicals that are produced inadvertently by chlorinating drinking water can also be harmful to human beings.
GROSSMAN: They’re called disinfection byproducts. Researchers have discovered that dozens of such chemicals are formed by water treatment. The most common are called trihalomethanes. They’re molecules created when carbon and hydrogen from decayed plant matter and other naturally occurring elements, combine with chlorine. It's long been known that some trihalomethanes cause cancer in laboratory animals. And recently, researchers have found links to cancer in humans as well. Ken Cantor, a researcher at the National Cancer Institute, headed a study comparing people who drank unchlorinated and chlorinated water from lakes and streams in Iowa. The results were sobering.
CANTOR: People drinking this type of water for thirty or forty or more years have maybe a one-and-a-half to two-fold risk of bladder cancer. And this translates to maybe ten percent of the bladder cancers in the United States. We’re talking in the realm of 4,000 to 4,500 new cases of bladder cancer a year.
GROSSMAN: Doctor Cantor says bladder cancer is fatal about 20 percent of the time. Other researchers have reported similar results. And some scientists have linked cancer of the rectum and colon to chlorinated water. One controversial study by a respected researcher indicated that about one percent of all the country’s cancers are linked to disinfection byproducts consumed in tap water. And there’s more bad news. Research has tied disinfection byproducts to problems such as birth defects, low birth weight and most recently, miscarriage. Doctor Shanna Swan of California’s Department of Health Services heads a team that recently published a study on disinfection byproducts in the journal Epidemiology.
SWAN: Women who drank at least five glasses of tap water a day that had seventy-five parts per billion of trihalomethanes or more had a nearly doubled rate of miscarriage compared to women who either drank less water or water with less trihalomethane in it.
GROSSMAN : Seventy-five parts per billion is significantly lower than the level which the Environmental Protection Agency considers safe. But not everyone is convinced of the danger of disinfection byproducts. Fred Hauchmann is a top official at the EPA’s Health and Environmental Effects Research laboratory. He has doubts about the evidence linking the chemicals to reproductive problems and cancer.
HAUCHMANN: While there is some indication that there may be a slight association between exposure to disinfection byproducts and these endpoints, for the most part the data are still inconclusive with respect to causality. And you really cannot draw a causal association between exposure and effect.
GROSSMAN: The dispute comes down to the level of proof. Epidemiological studies like Shanna Swan’s have shown a clear association between chlorination byproducts and cancer and birth defects. But no one has been able to demonstrate that the substances cause health problems in humans. For many scientists, though, the case against these disinfection byproducts is convincing.
OZONOFF: I don’t know what kind of evidence people who say that would have to have.
GROSSMAN: Boston University Professor David Ozonoff.
OZONOFF: There are many more studies now showing that there’s a causal relationship between disinfection byproducts and cancer than there was in 1949 when we showed that asbestos caused lung cancer, and was generally accepted by the medical community.
(Sound of a faucet opening and water coming out into a glass)
GROSSMAN: Virtually every American drinks water that's disinfected with chlorine every day . And the debate about the health effects of that process is heating up because the EPA is slated to tighten its safety rules this fall. The agency is expected to cut the current trihalomethane standard of 100 parts per billion to 80 parts per billion, and to set standards for another common class of byproducts as well. But Professor David Ozonoff says the agency should go even further.
OZONOFF: If this were a chemical that were leaked into the drinking water supply, contaminated by a barrel back in the back forty somewhere, it would never be set at a hundred, it would be set at 5 or less.
GROSSMAN: But some caution that the concern about the risks of chlorination should not obscure the very real and much larger benefits. Jack Sullivan is a top official at the American Water Works Association.
SULLIVAN: There must be a backstop. You cannot do anything that is going to increase the microbial risk. We must at all costs take what steps are necessary to prevent the microbial disease and do everything we can about balancing the tradeoffs associated with the disinfection byproduct risks.
GROSSMAN: Many experts though say the choices are not so stark: that we don’t have to choose between cancer on the one hand and germs on the other. The city of Cambridge has begun to reduce the level of disinfection byproducts in its water without increasing the risks of microbial contamination. Water quality supervisor Timothy MacDonald says a decade ago byproduct levels at his plant were among the worst in the country.
MACDONALD: The problem was that this plant was putting out elevated THM levels that ultimately I guess got up to 320 parts per billion.
GROSSMAN: Trihalomethane levels in Cambridge were three times the standard in 1989. Its 65 year old plant was dilapidated and poorly run.
MACDONALD: The filter media was in poor shape, the backwash system was not effective.
GROSSMAN: A year and only about a million dollars in changes later, trihalomethane levels had been cut to half the federal standard without violating disinfection requirements.
(Sound of Cambridge plant)
GROSSMAN: Of course simple changes won’t work everywhere. And many experts are calling for dramatic cuts in byproduct levels which would require a completely different approach like using the alternative disinfectant ozone, a gas widely used in Europe. Ozone also creates disinfection byproducts, but so far they don’t appear to be harmful. Better filters with activated carbon which cut down on organic matter can also help reduce byproducts. Of course all of these technologies cost a lot of money, and communities and governments need to decide whether the benefits are worth the costs. Here in Cambridge they’ve made the decision. Next year the city is breaking ground on a new fifty million dollar treatment plant using both activated carbon and ozone. It will be the largest public works project in the city’s history. For Living on Earth, this is Daniel Grossman.
CURWOOD: Next month, our series "The Thirst for Safe Water" continues with a look at how farm chemicals contaminate drinking water supplies in the Midwest.
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