Some further considerations on the use of repair-defective organisms as biological dosimeters for broad-band ultraviolet radiation sources

The extreme variation in biological effectiveness of the various components of solar ultraviolet radiation (solar UV) which reaches the earth's surface, especially photons of wavelengths between 295 and 330 nm, makes the dosimetry of solar UV a complex problem. A proper weighting of the components of solar UV would permit expression of exposure as a single parameter (dose). Weighting could compensate for the variations in composition of solar UV which might occur during exposure or the differences in sources of UV radiations; weighting would permit comparison of exposures at various locations on the earth and extrapolation of laboratory observations to field situations where wavelength composition might be different. Various radiation-sensitive microorganisms have been proposed as biological dosimeters. Biological dosimeters automatically weight the subcomponents of solar UV differently than a purely physical irradiance meter. The available evidence regarding the weighting which repair-defective mutants provide was examined in comparison with response of a number of wild-type organisms. For broad-band UV sources, repair-sensitive mutants may improperly weight the components, leading to errors of dosimetry and of interpretation of results of solar UV exposure of wildtype organisms. (author)