Synthetic Musks May Enhance the Effects of Toxic Compounds

Newswise — Nontoxic synthetic musks, which are widely used as fragrances in a variety of products, may pose a hidden threat to human health by enhancing the effect of compounds that are toxic, according to a study published today in the January issue of the peer-reviewed journal Environmental Health Perspectives (EHP). Researchers found that musk compounds inhibited natural defenses against toxicants in California mussels and that the effect remained long after exposure ended.

Humans are exposed to musks through the skin when they use soaps and cosmetics, and wear clothes washed with scented detergents. People also inhale musks through cologne sprays. Every year, approximately 8,000 metric tons of synthetic musks are produced worldwide.

Under normal circumstances, cells resist toxicants through multidrug/multixenobiotic resistance (MDR/MXR) efflux transporters, proteins that keep foreign chemicals from entering cells. Using mussel gill tissue because its efflux transporters are particularly active, the researchers incubated tissue for 90 minutes in a solution of musk compounds and a fluorescent dye. Finding the dye in the tissue would indicate that the efflux transporters were failing.

Immediately after exposure, the fluorescent dye uptake was 38-84% higher in tissue treated with musk compounds than in controls. Twenty-four hours later, dye uptake was still 30-74% higher in tissue exposed to musks. The tissue remained compromised 48 hours after exposure for four of the six musk compounds tested.

"This study especially points to the need to screen musks and other environmental chemicals that accumulate in humans to determine if they are also chemosensitizers of MXR-related transporters. Especially critical will be to ascertain whether they cause long-term effects similar to those seen in our study," the study authors write. "Effects on efflux systems could result in unanticipated accumulation of toxicants in humans and confound safety predictions of seemingly innocuous chemicals."

Although the exposures tested in the study were several times higher than those found in the environment, musk compounds are known to concentrate in fats, including breast milk, and endure in human tissue long after exposure. As a result, the researchers expressed concern that, even if ambient concentrations are low, long-term exposure could lead to accumulated tissue burdens high enough to inhibit natural cellular defenses in humans.

"While other studies have shown that humans are constantly exposed to musk compounds, routine toxicology screens have always shown these compounds to be nontoxic. This study's suggestion that they could harm the body's ability to fight other toxicants certainly merits further examination," says Dr. Jim Burkhart, science editor for EHP.

The authors of the study were Till Luckenbach and David Epel of Hopkins Marine Station of Stanford University. The article is available free of charge at http://ehp.niehs.nih.gov/members/2004/7301/7301.html.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/.