RESPONSE TO UV-B RADIATION: WEIGHTING FUNCTIONS AND ACTION SPECTRA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 82

RESPONSE TO UV-B RADIATION: WEIGHTING FUNCTIONS AND ACTION
SPECTRA
FRANCESCO GHETTI, COSTANZA BAGNOLI AND GIOVANNI
CHECCUCCI
CNR Istituto di Biofisica
Via G. Moruzzi 1, I-56100 Pisa, Italy
1. Introduction
In the last twenty years, the presence in the atmosphere of ozone-depleting
substances (CFCs, HCFCs, halons, carbon tetrachloride, etc.) has been reducing the
ozone concentration in the stratosphere over high and mid-latitudes of both
hemispheres. Notwithstanding ozone concentration in the atmosphere is very low, the
stratospheric layer, which contains approximately 90% of the total ozone, has the
function of a protective filter for the Earth's surface, cutting-off solar radiation under
280 nm and greatly reducing UV-B radiation (280-315 nm).
The reduction of stratospheric ozone has been recognized as the main cause of
the increase of UV-B irradiance at the Earth's surface. This increase has been estimated
in the range 6-14% in the last twenty years. Also spectral measurements performed at
various sites located in Europe, North and South America, Antarctica and New Zealand
have correlated UV-B radiation increase with the ozone decline. 1
UV-B has various direct adverse effects on human health (skin cancer,
immunosuppression, eye disorders), terrestrial plants and aquatic organisms (DNA
alterations, photosynthesis inhibition, reduced growth). Moreover, due to the differences
in UV-B sensitivity and adaptation among the various species, shifts in species
composition may occur as a consequence of increased UV-B radiation, thus leading
indirectly to alterations in ecosystems. 2-4
As the enhancement of solar UV-B is highly wavelength specific and increases
when the wavelength decreases, action spectroscopy plays a central role in assessing the
effects of ozone depletion on the biosphere. 5,6
2. Action spectroscopy
Action spectroscopy is a non-destructive technique for studying in vivo the
absorption properties and, in some cases, the primary reactions of photoreceptors
involved in triggering biological photoresponses. Action spectroscopy can be used in
the investigation of any light-dependent phenomenon for which a standard response can
be defined. It consists in the quantitative analysis of the response of the system as a
function of the wavelength of the stimulating light and the outcome of this analysis, the
action spectrum, is a measure of the relative efficiency of light of different wavelengths
in inducing a defined effect on the examined biological system.