Research Stories

by Adelheid Fischer

When it comes to consumer products, today's germaphobe lives in a land of plenty. Want to avoid the "yuck factor" of grabbing handholds on the subway? No problem. Just stock up on a new line of antibacterial gloves designed especially for urban commuters.

Does touching the doorknobs in public restrooms give you pause? A new product called HYSO may be coming to a bathroom near you. The $60 gadget is timed to spritz hospital-grade disinfectant on doorknobs every 15 minutes.

Fretting about a salmonella outbreak in your own kitchen? Problem already solved. Antimicrobial cutting boards are available in just about any retail outlet. And for cleanup, there are antimicrobial sponges, dish detergents and hand soaps.

From socks and skin lotions to teddy bears, just about everything you buy today is antimicrobial, says Rolf Halden. Halden is an associate professor of civil and environmental engineering at Arizona State University and a researcher at The Biodesign Institute. Despite the glut of "protective" products, he is feeling far from reassured.

Halden's research is focused on two of the most popular antimicrobial additives. They are nonagricultural pesticides known as triclosan (TCS) and triclocarban (TCC). Created in the mid-20th century, these biocides were first used in surgical soaps. Considered safe and biodegradable, they quickly found their way out of the hospital and into consumer products.

Today, more than 1,500 products contain biocides, Halden says. That includes three-quarters of all liquid soaps and one-third of commercial bar soaps.

"In the last 10 years we've seen a proliferation of antimicrobial products," Halden observes. "The question we have to ask, first of all, is do these chemicals work? Second, what happens to them?"

On October 20, 2005, the U.S. Food and Drug Administration convened a panel to begin answering these questions. Public health experts reviewed evidence and heard testimony from researchers such as Halden. The panel concluded that there is no scientific evidence that washing hands with antimicrobial-laced products is any more effective against germs than using regular soap.

Halden explains that the use of these biocides is not a zero-sum game. New research has shown that antimicrobials imperil the very health of the people they purport to protect.

Halden and his colleagues are pioneering much of this research. In 2002, for example, they began sampling water from streams, wells, wastewater-treatment plants, and drinking water supplies around New York City and Baltimore, Md. At the time, there were no published data on the fate of TCC in the environment.

To carry out the work, Halden's group developed a new analytical method specifically designed for the environmental monitoring of antimicrobials. Aiding his quest was a research tool known as liquid chromatography (tandem) mass spectrometry.

Until recently, this technology largely had been confined to pharmaceutical laboratories. The device enables environmental scientists like Halden to sample water and fluids in the human body. It allows them to measure chemicals that don't show up in other kinds of tests.

"The technology has opened up a new window into chemistry," Halden says.

Among those contaminants is TCC. In 2004, Halden published the astonishing results of his initial environmental reconnaissance. TCC was widespread in soils and water resources. The problem, he reported, wasn't confined to the Eastern Seaboard. The problem was nationwide.

Most troubling was the presence of TCC in sewage sludge. On average, sewage-treatment processes remove most of the TCC from treated wastewater. That's because TCC is hydrophobic, it is "fearful of water." As a result, the compound doesn't linger in water. Instead, TCC attaches itself to organic particles such as the solids in sewage sludge.

Halden's group found that beneficial microbes degrade only 25 percent of the TCC that enters a typical municipal plant. The remainder becomes lodged in the leftover sludge.

This chemical persistence is not altogether surprising given the chemical structure of antimicrobials. Halden points out that TCS and TCC belong to a family of chemicals known as organochlorines. Included in this group are some of the most nefarious chemicals of all time: PCBs, DDT and dioxin.

Organochlorines were created in the heyday of chemical experimentation following World War II. To synthesize them, scientists started with a base molecule composed of carbon and hydrogen. By replacing some of the hydrogen atoms with chlorine atoms, they created new compounds. The substitutions increased the chemicals' toxicity–and durability. Organochlorines were purposely designed to resist breakdown by natural forces, including degradation by microbes.

Halden says that the persistence of biocides in sludge poses a number of hazards to human health and the environment. For example, sewage sludge routinely is used as fertilizer. According to Halden's calculations, one wastewater treatment plant alone can export more than one metric ton of TCC to the environment each year. Once spread out over the land, the biocide can migrate into waterways through runoff. Scientists currently are investigating their potential for contaminating food crops.

Biocides such as TCS and TCC also may turn sewage treatment plants or estuary sediments into incubators for deadly microbes. In one study, for example, Halden and his colleagues extracted sediments from the Chesapeake Bay around Baltimore and New York's Jamaica Bay. They detected antimicrobials in sediment layers dating back to the 1950s and 1960s.

"These products don't work on your hands because the microbes don't get exposed long enough to them," Halden explains. "But when antimicrobials sit in the environment, the microbes and all the other biota in the sediments experience exposures to the chemicals for a lifetime and over many generations. This provides opportunities for microbes to develop a resistance to TCC and TCS."

Laboratory studies show that such dangers are real. In 2004, scientists in the United Kingdom reported the results of one study in which a deadly strain of E. coli microbes was exposed to TCS. The microbes were then treated with 12 different life-saving antibiotics that are used in human medicine. Seven out of 12 antibiotics were shown to be less effective in combating these dangerous microorganisms after they had contact with TCS.

The danger to the health of people and the environment doesn't stop there. Recent studies have shown that TCS and TCC tamper with the endocrine systems of both aquatic and terrestrial animals in the wild.

In 2007, a group of researchers at the University of California, Davis, demonstrated that TCC had similarly ill effects in laboratory rodents and human cell lines. Most troubling was the finding that TCC interfered with hormonal signaling even at low doses.

Halden doesn't advocate an outright ban on antimicrobial agents. Research carried out in the developing world show that the use of antimicrobials can save lives.

In one study conducted in Nepal, the antimicrobial chlorhexidine was used to cleanse the umbilical cords of newborns. This simple procedure dramatically cut rates of life-threatening infection.

"Antimicrobials, including antibiotics, have really revolutionized medicine," Halden points out. "There are indisputable benefits to human health from the availability of antimicrobials. They're a great thing. If used imprudently, however, they can turn against you."

Research on the impact of antimicrobial chemicals is supported by the Johns Hopkins Center for a Livable Future and the National Institute of Environmental Health Sciences. For more information, contact Rolf Halden, Ph.D., Department of Civil and Environmental Engineering, Ira A. Fulton School of Engineering, 480.727.0893. Send email to Halden@asu.edu