QUANTIFICATION OF BIOLOGICAL EFFECTIVENESS OF UV RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 62

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hole

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Figure 7. Ozone data and BED H eff of solar UV-B and UV-A radiation determined with the biofilm
dosimeter at the Georg von Neumayer Station (70°37'S, 8°22'W) in Antarctica (modified from ref.
58.

following period in 1991 58 . In the latter case, the ratio of biologically effective UV-B to
biologically effective UV-A was raised by a factor of 2 during the ozone depletion
period, from 0.1-0.3 to 0.5-0.6 58 .
Sensitivity of the biologically effective solar irradiance to ozone . In a space
experiment, extraterrestrial sunlight was used as natural radiation source, filtered
through a set of different cut-off filters to simulate the terrestrial UV radiation climate at
different ozone concentrations down to very low values 63 . The biologically effective
irradiance E eff as a function of simulated ozone column thickness was directly measured
with the biofilm technique and compared with expected data from model calculations
using the biofilm action spectrum. Figure 8 shows a dramatic increase in E eff with
decreasing (simulated) ozone concentration. The full spectrum of extraterrestrial solar
radiation led to an increment of E eff by nearly three orders of magnitude compared with
the solar spectrum at the surface of the Earth for average total ozone columns. These
data have been used to assess the history of the UV radiation climate of the Earth from
the very beginning up to today 71 .
Vertical attenuation of biologically effective UV irradiance in natural water . The
spectral transmission of UV radiation in natural waters may vary substantially from one
water body to another in response to the concentration of colored dissolved organic
matter (CDOM) and other dissolved component. To assess the risks from enhanced
UV-B radiation for aquatic ecosystems, it is important to determine the vertical profile
of the biologically effective UV radiation within the water column, separately for each
habitat of concern. Vertical attenuation coefficients of biologically effective UV
irradiance have been determined for various freshwater and marine environments on the
base of DNA, bacteriophage 47 or bacterial dosimeters. It is interesting to note that the
biological attenuation coefficients, integrated over the whole spectral range of sunlight,
correspond to spectroradiometrically determined attenuation coefficients in the range of
320 to 340 nm 62 . This suggests a substantial contribution of UV-A to the harmful effect