QUANTIFICATION OF BIOLOGICAL EFFECTIVENESS OF UV RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 59

step of cutaneous vitamin D3 synthesis. Only low doses of UV are required at
wavelengths below 315 nm. The photoconversion of 7 DHC to pre D3 is determined
spectrophotometrically 48 or by HPLC 49 . This in vitro vitamin D dosimeter was utilized
to determine the seasonal and latitudinal changes on the potential of sunlight to initiate
cutaneous production of vitamin D3.
Cellular biological UV dosimeters
Bacteria as dosimeters . Bacterial systems have been frequently used as
biodosimeters which measure lethality as the prime cellular UV effect that essentially
reflects unrepaired DNA damage 18 . They include cells of E. coli in suspension 39,50-52 or
spores of B. subtilis in suspension 53 , as dry layers 35,54-57 , or immobilised in a
biofilm 7,40,58,59 . Due to their exponential inactivation kinetics repair deficient strains are
especially suited for biological dosimetry. They respond highly sensitive to low doses of
UV-light, because they accumulate the DNA photoproducts and consequently are killed
at relatively low numbers of lesions in their DNA. The E. coli CSR 603 uvrA6 recA1
phr-1 strain which is deficient in all dark repair as well as in photorepair is a kind of
"worst case" indicator, because it quantifies the incidence of primary lethal damage by
sunlight 51 . However, due to its extremely high UV sensitivity - it is inactivated by 3
orders of magnitude within 30 sec of insolation, it is too difficult to be used as field
dosimeter. Its rec + variant E. coli CSR 06 uvrA6 phr-1 39 and spores of B. subtilis
uvrA10 ssp-1 35,50,54-56 or of B. subtilis uvrA10 ssp-1 polA151 57 are the most frequently
used bacterial systems in biological dosimetry. The BED is determined either from the
inactivation rate constant 14,35,50,54-57 as number of lethal hits 35,54-55 or as % lethality 39 .
Because of their spectral responses 14 , their long shelf-life, their resistance against other
environmental parameters such as heat and humidity, the availability of repair-deficient
mutants with exponential inactivation curves and the lack of a photoreactivation system,
spores of B. subtilis especially meet many of the criteria for reliable biological
dosimetry of sunlight. The spore dosimeter has been utilized at different latitudinal and
seasonal conditions, in South America 50 in Japan 14,35,54,55,60 , and in Antarctica 57 as well
as in quality control of water disinfection by UV (254 nm) 61 . The E. coli cell dosimeter
has mainly been used in aquatic environments in Antarctica 39 and in freshwater lakes in
USA 62 .
DLR-biofilm dosimeter . The DLR-Biofilm dosimeter consists of a monolayer of
dry spores of B. subtilis immobilized in agarose on a transparent polyester plastic
sheet 40 . After exposure to sunlight and calibration at 254 nm, the biofilm is incubated in
nutrient broth medium and the proteins synthesized after spore germination and cell
growth are stained. Figure 6 shows the DLR-Biofilm after insolation, calibration, and
processing. The UV effect measured in this system is inhibition of biological activity, as
expressed by the amount of protein synthesized inside the biofilm in a given incubation
time. This amount of stained protein is determined by image analytic/photometric
measurements. The BED H eff in ( J/m²) eff is obtained according to Eq. 5 from the linear
quadratic calibration curve determined at 254 nm from a calibration source. It relates the
dose equivalent to that of the calibration source producing the same effect 63 . Its action
spectrum deviates from the CIE MED curve by less than a factor of 2 over a wide range
from UV-B to UV-A 7 . The response of the biofilm to UV is additive and follows the