Quantification of the biological effectiveness of environmental UV radiation

To determine the impact of environmental UV radiation on the critical processes of our biosphere demands accurate and reliable monitoring systems that weight the spectral irradiance according to the biological responses under consideration. The need for a biological weighting of solar UV irradiance derives from the highly wavelength-specific absorption characteristics of atmospheric ozone and the wavelength specificity of the biological action spectra in the UVB range. The degree to which the biological effectiveness of solar UV radiation increases with stratospheric ozone depletion is determined by the shape of the action spectrum of the biological phenomenon under consideration. In principle, three different approaches for quantifying biologically effective solar irradiance are available: (1) weighted spectroradiometry where the biologically weighted radiometric quantities are derived from spectral data by multiplication with an action spectrum of a relevant photobiological reaction, e.g. erythema formation, DNA damage, skin cancer or reduced productivity of terrestrial plants and aquatic ecosystems; (2) wavelength-integrating chemical or physical dosimetric systems with spectral sensitivities similar to a biological response curve; (3) biological dosimeters that weight directly the incident UV components of sunlight in relation to the effectiveness of the different wavelengths and the interactions between them. In most cases, simple biological dosimeters are applied, such as bacteria, bacteriophages or biomolecules. Induction rates for lethality, mutagenesis or photoproduct formation are used, which reflect directly the UV sensitivity of DNA. Biological dosimeters are potentially reliable field dosimeters for measuring the integrated biologically effective irradiance for key targets, provided that a direct intercalibration with spectroradiometric-based measurements is applied.