UV – Radiation Properties at the Dead Sea

Résumé

The Dead Sea, a salt lake located between the Judean mountains in Israel and Moab mountains in Jordan, is one of the saltiest bodies of water known, containing 345 g mineral salts per liter. It is situated at the lowest terrestrial point on earth, approximately 400 m below mean sea level. The Dead Sea area is recognized as a natural treatment facility for patients with psoriasis, atopic dermatitis, vitiligo and other skin and rheumatic diseases. A research project was initiated in 1994 to determine if the Dead Sea basin is indeed characterized by a unique ultraviolet radiation spectrum, which contributes to the success of photoclimatherapy of psoriasis and other skin diseases. A meteorological station was established at the Dead Sea basin (Neve Zohar) to continuously monitor solar global, UVB and UVA radiation, measure spectral selectivity within the ultraviolet spectrum and investigate other relevant bio-climatological parameters. The same parameters were also monitored continuously at a second meteorological station in Beer Sheva, which is located in the southern Negev region of Israel at a distance of approximately 65 km west of the Dead Sea and an altitude of ~315 m above mean sea level, i.e., about a 700 m altitude differential between the two sites.

The results of this on-going study can be summarized as follows:

• The UVB and UVA solar radiation intensities at the Dead Sea are both attenuated relative to Beer Sheva; the UVB to much a greater extent than the UVA.
• The degree of attenuation is inversely proportional to the wavelength. The erythema wavelength range (ca. 300 nm) is attenuated to greatest extent, whereas the degree of attenuation is lower in the therapeutic wavelength range (ca. 311 nm) with regard to psoriasis.
• Consequently, the incident solar UVB has a higher ratio of therapeutic to erythema radiation relative to other sites.
• The ratio of the therapeutic to erythema radiation has a minimum value at solar noon (diurnal minimum optical path length).

These findings have been applied to revise the psoriasis treatment protocol at the Dead Sea with the goal of reducing the cumulative sun-exposure time without affecting treatment efficacy.