Environmental Engineering Reference
In-Depth Information
short-wavelengths edge of the solar spectrum. Although nearly all action spectra for
biologically adverse effects of sunlight decrease with increasing wavelength, the rate of
decline varies considerably (Figure 4). Especially the tail of the action spectra in the
UV-A or visible waveband has to be checked carefully, since it may be different for
different species or even strains, even for the same endpoint. This phenomenon reflects
the complex interplay of a variety of cellular mechanisms for processing UV-induced
damage (reviewed in
7
).
Most biological dosimeters are easy to use, at least by a trained technician. They
are of low cost, which allows for a broad distribution. Some of them can be miniaturized
so that they are suitable for personal dosimetry or to measure the distribution of the
biologically effective UV in endangered ecosystems, cultivars, trees etc.
On the other hand, as every biological system, biological dosimeters may be
sensitive to factors other than UV and their dynamic range may be restricted. In any
case, a careful calibration and intercomparison with spectroradiometric data is needed.
3. Quantification of biologically effective dose using biological UV dosimeters
Biomolecules and viruses as biological UV dosimeters
Uracil dosimeter
. The dimerization of uracil monomers in a polycrystalline layer
is determined spectrophotometrically by a decrease in the absorption characteristics in
the wavelength range 250-400 nm (Table 1). The effective dose for uracil bleaching is
given in absolute values of
H
eff
(called
H
U
), which is equal to the exposure that
decreases the optical density of the uracil layer to the e-th part of the difference between
the original (non-irradiated) and the saturated values, i.e. on the average 1 hit per
molecule
36
. Uracil dosimeters have been utilized at several sites for long-term
UV monitoring.
DNA Dosimeter
. The formation of cyclobutane pyrimidine dimers and other UV
lesions in DNA (Table 1) is analyzed by a radiochromatographic assay
38
, by PCR
44
, or
by an immunochemical reaction
45
. The BED is given in
(J/m²)
eff
, equivalent to a dose of
254 nm producing the same effect. The DNA dosimeter was tested as solution in marine
waters at different depths
38
and as dried film
44,45
.
T7 Dosimeter
. The inactivation of bacteriophage T7 (Table 1) is determined
either by the plaque test or photometrically from the lysis of the host cells
34
.
H
eff
is given
as
H
T7
, which equals to the absolute value of the term ln (
N/N
0
), with
N
= number of
viable individuals after irradiation and
N
0
= number of viable individuals without
irradiation. The term ¸ln (
N/N
0
)¸ gives the average amount of UV damage in one
bacteriophage particle
46
. T7 dosimeters have been utilized at different land sites and in
different aquatic environments.
47
.
Vitamin D Dosimeter
. The endogenous synthesis of vitamin D under solar UV
radiation is a widespread process and indicates one of the beneficial effects of solar
UV-B radiation. The
in vitro
process of vitamin D synthesis by UV has been developed
as a biological UV dosimeter (Table 1)
37
: 7-Dehydrocholesterol (7 DHC), the precursor
of vitamin D3 in methanol, has been used as biomarker for UV exposure indicating the
photoisomerisation of provitamin D3 (7 DHC) to previtamin D3 which is the initiating
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