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A recent study by UC Davis researchers calls into question the widespread use of two active ingredients — triclocarban and triclosan — in personal hygiene products, including antibacterial bar and liquid soaps. Using human and animal cell lines, researchers found that triclocarban disrupts reproductive hormone activity and triclosan interferes with a type of cell signaling that occurs in brain, heart and other cells.
"Americans spend nearly $1 billion dollars a year on these products even though recent studies show that they are no better than regular soap and water at reducing the spread of illness. Now we have added evidence that, in some cases, the benefits may not be worth the risks," said Dan Chang, professor emeritus of civil and environmental engineering.
"Manufacturers of products containing triclosan and triclocarban should consider providing cautionary labels. There are new health-related data on these chemicals that consumers should know about, even if the research is in its early stages," Chang said.
The current study was published online in Environmental Health Perspectives, a publication of the National Institute of Environmental Health Sciences.
The authors of the study are part of the UC Davis Superfund Basic Research Program. The group, part of a national network, is charged with assessing and understanding the effects that exposure to environmental substances have on human health.
"We decided to take a look at triclocarban and triclosan because these compounds appeared to be building up in the environment," said Bruce Hammock, a Superfund Basic Research Program investigator and professor of entomology. The compounds are also increasingly being detected in human breast milk and urine, he said.
Triclosan and triclocarban were first introduced for use by surgeons and other operating room personnel to prevent bacterial infections. Today they are inexpensive and readily available, in part because the patents on them have expired. "We are not concerned about limited use in settings with clearly edvident high-value such as in surgical settings. It's the widespread use that is of concern," Hammock said.
Superfund researchers use bioassays to measure the kind of effects a substance might have on living organisms, using animal or human cell lines as proxies for human exposure. The four assays in this study looked at the effects of triclocarban and triclosan. One assay tests a second messenger system broadly used by cells in the peripheral and central nervous systems, a second examines another pathway important in protein synthesis and two assays evaluate the activity of male and female sex hormones (androgens and estrogens).
The first assay involved observing the impact of the chemicals on ryanodine receptors, proteins that serve to keep calcium levels in balance. Calcium is needed for proper cell signaling, especially in brain, heart and muscle cells where these receptors are found. Disrupting these levels could lead to alterations in cell function. Triclosan significantly increased resting calcium levels in the mouse cells used in the assay.
The second assay looked at the impact on aryl hydrocarbon receptors (AhR). Normally, this cell-surface receptor binds a protein that leads to changes in gene expression, the process by which information encoded in the DNA is translated into proteins. Binding of this receptor by the environmental toxin dioxin has been shown to cause everything from birth defects to tumor production. Triclosan exhibited weak activity in the AhR bioassay. Triclocarban exhibited no activity.
Triclocarban had been previously implicated as a new kind of endocrine disruptor in a paper published in December 2007 in Endocrinology by co-author Bill Lasley, professor of obstetrics and gynecology. Lasley's group concluded that, unlike classical endocrine disrupters that bind to cell receptors, triclocarban amplifies the response of naturally occurring sex hormones.
Because of feedback loops in the body, amplification of these hormones could have the effect of depressing natural estrogen and androgen production, potentially impacting fertility and other hormone-dependent processes. In the current study, besides carrying out the AhR assays, co-author Michael Denison repeated Lasley's experiments using a different human cell line. Denison, a professor of environmental toxicology, observed a similar amplification effect.
Given these results, the question for regulators is whether these compounds should be restricted until further testing can be done. To help answer that question, the National Institute of Environmental Health Sciences and the Environmental Protection Agency are sponsoring a scientific meeting for researchers, regulators and industry representatives in October at UC Davis. "We're all getting together to explore where to go from here," Chang said.
Chang said he feels strongly that consumers be provided information about potential hazards, though he is quick to point out that those who are not in high-risk groups may decide to continue their use of triclosan- and triclocarban-containing products. "I have not stopped using my gingivitis-fighting toothpaste. However, if I were a pregnant woman or the parent of a small child, I might check the labels of the products that I use and stop using any that contain those chemicals until we can work this out," Chang said.
Other study authors, all of whom are at UC Davis, include Ki Chang Ahn, of the Departments of Entomology and Cancer Research Center; Bin Zhao, of the Department of Environmental Toxicology; Jiangang Chen, of the Department of Environmental Health; Gennady Cherednichenko, of the Department of Molecular Biosciences and Center for Children's Environmental Health and Disease Prevention; Enio Sanmart, of the Department of Animal Science; Michael S. Denison of the Department of Environmental Toxicology; Bill Lasley, of the Department of Environmental Health; Isaac N. Pessah, of the Center for Children's Environmental Health and Disease Prevention; Dietmar Kültz of the Department of Animal Science; Daniel P. Y. Chang, of the Department of Civil and Environmental Engineering; and Shirley J. Gee1 and Bruce D. Hammock, of the Departments of Entomology and Cancer Research Center.
Funding for the research was provided by the NIEHS Superfund Basic Research Program, the NIEHS Center for Environmental Health Sciences, the UC Davis Center for Children's Environmental Health and Disease Prevention, the U.S. Environmental Protection Agency through the Science to Achieve Results (STAR) program, and the National Institute for Occupational Safety and Health Center for Agricultural Disease and Research, Education and Prevention.