Natural UV-protective organic matter in thermal water.

Medical significance of the organic fractions of natural waters is still poorly understood. Nevertheless, there are putative biologically active organic compounds found in natural medical waters and related clay or mud samples. Organic fractions of five thermal (spa) water samples of different geochemical origin were tested for photo-biological effects. To study possible effects on the UV sensitivity of Salmonella typhimurium TA strains, the organic isolates were applied in the "plate incorporation" Ames test combined with UV-irradiation. Four samples showed measurable survival of TA100 his+ revertants following exposure to a normally lethal UV dose. Metabolic activation with a mammalian microsomal fraction (S9) elevated the effect detected (up to 61% survival). This is the first study to demonstrate the UV-protective property of organic matter in natural thermal water samples used in balneotherapy.