Disinfection Byproducts — What are they? What can they do?

For more than 80 years, drinking water in the United States has been disinfected, primarily with chlorine. The use of chlorine has dramatically reduced the number of waterborne diseases, such as dysentery and cholera, in this country. Until 1974, the only concerns with using chlorine were how to apply it to all drinking water and how to use it efficiently.

Although a necessary component of water treatment, chlorine is now implicated in another major health issue. Chlorine and other disinfectants added to drinking water can react with naturally occurring organic matter in the water to form such substances as chloroform. Called disinfection byproducts (DBPs) or trihalomethanes (THMs), these substances have the potential to cause cancer in humans.

* Should water treatment plants stop using chlorine to disinfect water?
* What is EPA doing about DBPs?
* How do you detect DBPs in water?
* What can you do to protect yourself?

Should water treatment plants stop using chlorine to disinfect water?
Disinfection is key to eliminating bacteria, viruses, and parasites in water, making it safe to drink. Without disinfection, drinking water can cause such diseases as gastroenteritis, dysentery, cholera, hepatitis, and the flu; some of these diseases are potentially fatal. In countries that do not disinfect their drinking water, almost 20-25% of childhood deaths are attributed to diseases contracted from drinking contaminated water. This compares to a median child mortality rate of about 1% in countries that do disinfect their drinking water.
Chlorine is the most widely used and least expensive drinking water disinfectant. Since it is so cost effective, water treatment plants have few other alternatives to disinfect water. Moreover, many experts argue that the risks associated with waterborne pathogenic microorganisms outweigh the risks associated with DBPs. To meet these competing interests, water treatment plants must balance the need to disinfect water using chlorine with the need to protect against DBPs.

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What is EPA doing about DBPs?
In 1979, EPA set an interim maximum contaminant level (MCL) for total THMs at 0.10 mg/l. The agency based this standard on the need to balance the requirement for continued water disinfection to reduce pathogenic microorganisms while simultaneously lowering exposure to DBPs. However, this standard only applies to public water treatment systems that serve at least 10,000 people. States may extend this standard to smaller water treatment systems, but most states have found that these smaller systems use ground water, which is generally low in organic materials that can bond with chlorine to form THMs.

Since the THM MCL was established as an "interim" standard, EPA began to develop a more permanent standard. In 1992, the agency convened a commission to study the DBP problem. The commission realized that large amounts of information on DBPs was unavailable. Nevertheless, the commission agreed that EPA should propose a DBP rule to cover all water systems, small and large, that use disinfectants to treat water. The commission recommended that this proposed rule reduce the MCL for total THMs, regulate addition DBPs generated from the use of disinfectants other than chlorine, set limits for the use of disinfectants, and reduce the level of organic compounds in source water. The commission also recommended that EPA developthe DBP rule in separate stages.

On July 29, 1994, EPA proposed the Stage I Disinfectants/Disinfection Byproduct Rule. The proposed rule established a lower MCL for total THMs — 0.064 mg/l. But a fundamental principle of the proposed rule is that the new standard to control DBPs must not result in significant increases in microbial risk. Public water systems would have to meet the new THM MCL while ensuring that microbial pathogens are killed, or inactivated.

In November 1997, EPA made available new data for the Stage I disinfection byproducts proposed rule. Among the information available are studies that show disinfection needs at water treatment plants vary dramatically over the course of a year; therefore, ensuring that water treatment plants stay in compliance with the proposed reduced THM of 0.064 mg/l could bedifficult. These changes in disinfectant requirements relate to changing water temperature, flow rate (and thus contact time with the disinfectant), seasonal changes, pH, and disinfectant demand.

To address this, the commission suggested that water treatment plants plot or chart the inactivation of Giardia over time. This would provide a profile so a water treatment plant could develop a baseline or benchmark of bacteria inactivation against which to measure possible changes in disinfectant practice. The goal would be to ensure protection against microbial pathogens while complying with the lower total THM standard.
EPA plans on finalizing the stage I DBP rule in November 1998. It would likely not become effective until three years later, or November 2002.

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How do you detect DBPs in water?
Unfortunately, it is not easy to detect DBPs at your water tap. If you use water from a community water supply, call your water utility and request a water quality report. This report should contain information about THM levels in your drinking water.

Alternatively, you can make assumptions based on the source of your water or if it smells like chlorine. If your water comes from surface water sources (rivers, lakes, or reservoirs), there is a possibility it will contain THMs because surface water sources often contain organic matter. Also, if your water smells like chlorine, chances are some of this chlorine has bonded with naturally occurring organic material in your water to form THMs.

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What can you do to protect yourself?
Water filters that use carbon filter cartridges are effective at removing chlorine from drinking water. They are particularly effective at meeting the balance of pathogen risk versus DBP risk because they remove the chlorine after it has already inactivated the bacteria and viruses in your drinking water. If you are concerned about DBPs, you can easily install one of thesefilters in your home.

OMNI makes many filters that remove chlorine from your drinking water. You can select from a Whole House filter — Models U25 or BF7 (with a TO6 or CB6 filter cartridge) — to remove chlorine from the water going to all the faucets in your home. Alternatively, you can install a "point of use" water filter to remove chlorine from drinking water at your kitchen or bathroom sink. All OMNI Undersink, Faucet Mount/Countertop, and Refrigerator/Icemaker filters, and OMNI's water cooler filter are effective at removing chlorine.

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