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Granular Activated Carbon (GAC)
February 1999
Heterotrophic menace: Fact or fiction? Scientists place bacteria under microscope to see if it causes health problems.
Summary: Heterotrophic bacteria, amplified by water treatment equipment, are being scrutinized for possible health risks. Consumers will shun residential water treatment devices if these microscopic bugs are found to cause health problems.
By James Denn, Executive Editor
A new battle is raging in government and scientific circles regarding the health effects of heterotrophic bacteria. The fight could affect every water treatment dealer in the United States.
Heterotrophic micro-organisms, single-celled creatures that may cause gastrointestinal illness and pneumonia in some people, multiply in point-of-use/point-of-entry (POU/POE) equipment. Granular activated carbon (GAC) filters, the most popular form of filtration, creates an ideal home for these bacteria.While most heterotrophic bacteria are harmless, mounting evidence shows that some members of this microscopic family are a health threat. The problem for water treatment dealers is that their equipment may be exacerbating the contamination.Heterotrophic micro-organisms similarly grow in on-the-shelf bottled water, well water pressure tanks and in water in household plumbing. Heterotrophic bacteria also is found in food.If heterotrophic bacteria are dangerous, federal and state regulators might require dealers to install additional treatment devices, such as ultraviolet or reverse osmosis (RO) systems, to prevent bacterial proliferation.If standard water treatment equipment in homes and offices - filters, softeners, pressure tanks and RO units - are a breeding ground for heterotrophic bacteria, the industry will have trouble convincing consumers to buy it.
The heart of the argument
While the US Environmental Protection Agency (EPA) does not have a maximum contaminant level (MCL) for heterotrophic bacteria, key players in the debate say an MCL may be needed."Heterotrophic bacteria clearly do pose a danger, the degree of which is poorly characterized,'' says National Drinking Water Advisory Council member Dr. Jeffrey K. Griffiths, associate director, Graduate Programs in Public Health, Tufts University School of Medicine, Boston, MA.Griffiths says a contaminant standard may be required for some heterotrophic bacteria. Setting an MCL, or any step to create a formal standard to gauge or classify heterotrophic bacteria as a contaminant, is exactly what the water treatment industry does not want.Nearly all heterotrophic bacteria have historically been presumed to be non-pathogens. Scientists say there is a need to make sure.A new study by Joan B. Rose, Department of Marine Science, University of South Florida, says not enough is known about heterotrophic bacteria and the levels that may be associated with human health risk.Some research suggests people experience less gastrointestinal illness when drinking water from POU/POE equipment where heterotrophic bacteria have colonized.
Rose notes conflicting reports regarding the relationship between specific heterotrophic bacteria in water to disease. While there are heterotrophic pathogens, overall the probability of disease from ingesting the bacteria is low.
Battles lines are forming
The EPA uses an informal standard of 500 colony forming units (CFU) of heterotrophic bacteria per milliliter to measure water quality and turbidity.
EPA standard is five times less strict than European standards, but high enough to fail most water treatment devices. A typical carbon filter that sits overnight contains between 1,000 to 10,000 CFUs.
The traditional method of measuring heterotrophic bacteria is now being challenged by new assay methods that result in higher bacteria counts. Paul Berger, senior microbiologist at the EPA, has been looking at the heterotrophic issue for more than two decades. He championed the need to set an MCL for the bacteria in the late 1980s, but lost to utility and water industry opposition.Despite his defeat, Berger advocates the need for additional studies "for the sake of safety.''Timothy E. Ford, associate professor of Environmental Microbiology, Harvard School of Public Health, is calling on the EPA to finance it.
GAC is a problem
Gerald N. Stelma Jr., an EPA scientist at the National Exposure Research Lab, Cincinnati, says heterotrophic bacteria growth is amplified in granular activated carbon (GAC) filters and hot water tanks.
"Although these bacteria are not hazardous to healthy individuals, it is possible that some of them - in addition to Legionellae and nontuberculosis mycobacteria - are opportunistic pathogens and could be hazardous to those whose body defenses are compromised,'' he says.Stelma says a cadre of high-ranking EPA officials would like to set an MCL for heterotrophic bacteria but lack evidence about the danger. One thing is clear. Water treatment equipment, especially carbon filters, will be the focus of an investigation.Bruce E. Rittmann, professor of Environmental Engineering at Northwestern University, Evanston, IL, says concern about HPCs and carbon filters is a hot topic.
"Carbon filters become a very friendly environment for microorganisms,'' he says. "You are creating a perfect environment for [bacteria] to grow. It raises the issue in the mind of the consumer if the water that comes out is safe. [As a result] the issue of home units will become more controversial.''
Gail Gerono, spokeswoman for Pittsburgh-based Calgon Carbon Corp., the world's largest producer of activated carbon, says the company is monitoring the heterotrophic debate.
"We know bacteria will grow on GAC filters,'' says Gerono. "All the information we have is that the bacteria is non-pathogenic.''
The US is the only developed country without an MCL for measuring heterotrophic bacteria. Federal regulators may choose to adopt a recommended standard found in Europe of 100 total bacteria counts per milliliter. "Those low numbers will kill the industry,'' says Beauman.Meanwhile, WQA is rushing ahead to counter negative findings by proving the benefits of heterotrophic bacteria. EPA's Berger says WQA's study will not stop the agency's quest to find out if the bugs are harmful.
Significant Industry Impact
In addition to naming some types of heterotrophic bacteria as a contaminant, the EPA may develop treatment standards to lower levels of heterotrophic bacteria in municipal systems. It also may formalize an HPC measurement to monitor heterotrophic bacteria.
Bacterial contamination of POU/POE treatment devices occurs because municipal water plants remove most bacteria, but do not produce sterile water. Once a carbon filter removes chlorine, bacteria can multiply.
Though heterotrophic bacteria colonizes in yogurt and milk, regulators only seem concerned about bacteria in drinking water, says WQA's Harrison. "The only place where you hear there is a problem is the in-home water treatment system,'' he says.
Wakem does not foresee a burden if an MCL is set. The industry will meet demands of the regulation by creating new technology to protect the consumer.
"The dealer will pay more for the product and that will be passed on to the consumer,'' he says. "It's insignificant based on the benefits."
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