Long-UV light may cause cancer ....

Long-UV light may cause cancer . . .

In recent years, suntanning salons have sprung up in the United States and Europe claiming to use "safe' wavelengths of ultraviolet (UV) light. Their tanning lamps emit wavelengths primarily in what is known as the longer, or "A,' portion of the UV spectrum. But a new Food and Drug Administration (FDA) study indicates these lamps may not be safe after all.

The study found that UV-A--the most prevalent form of UV in sunlight penetrating to earth's surface--can cause mutations in cultured mouse lymphoma cells, a standard screening test for potential human carcinogens. According to C. David Lytle, acting director of the biophysics division at FDA's Center for Devices and Radiological Health, in Rockville, Md., "We interpret these findings as indicating the potential of the radiation to cause skin cancer.' Unlike shorter-wavelength UV-B--which is also present in sunlight and is believed to play an active role in skin cancer formation--UV-A has generally been considered virtually benign.

The tests, conducted at the FDA laboratory in Rockville by Victoria Hitchins, exposed the cells to pure UV-A, using only wavelengths in excess of 340 nanometers. Mutation rate increased with dose, based on single exposures of up to 60 joules per square centimeter. In fact, Hitchins told SCIENCE NEWS, at the highest dose--one comparable to what manufacturers of their lamp suggest for humans seeking a tan--90 percent of the cells died. However, Lytle adds, the cells used in this test were growing fast and were unprotected by an outer skin layer, the stratum corneum. As a result, he says, one would expect the test cells "to be much more sensitive than the [vulnerable] cells in somebody's skin.'

Recent studies at Argonne (Ill). National Laboratory have shown that UV-A can damage DNA in both bacteria and human cells via mechanisms quite different from those of shorter-wavelength UV (SN: 11/30/85, p. 342). In fact, Lytle says, Hitchins's new data "are very consistent with that [the Argonne findings], and are basically a continuation of that type of work.'

Lytle says it's not yet clear whether such data will have much effect on UV-A tanning salons, since their lamps already must carry timers and labels warning that the light may contribute to aging and cancer. But it's possible, he says, that these new data may provide ammunition "for the Federal Trade Commission to keep people from advertising these devices as "safe.''