Environmental Engineering Reference
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The analysis of the speed distribution demonstrated that the fraction of cells
swimming at speed lower than 0.1 mm/s (slow cells) showed a decrease immediately
after the end of irradiation and a subsequent increase. Nevertheless, at the longest
irradiation time (120 min) the fraction of slow cells increased immediately after the end
of irradiation (from 0.05 before irradiation to 0.08 immediately after irradiation) (see
Fig. 6). This result could indicate that at long irradiation time a part of the cell
population was damaged and swam at very low speed, whereas the majority of
population increased its swimming speed. A possible explanation of this result is the
existence of a subpopulation of cells more sensitive to UV-B radiation 19 .
0,15
0,15
a
b
0,10
0,10
0,05
0,05
0,00
0,00
0,0
0,1
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Cell speed [mm/s]
Cell speed [mm/s]
Fig. 6. Histograms of the speed distributions of F. salina cells (a) before and (b) after 120 min with
UV-B, UV-A and visible light. After irradiation, we observe an increase of the fraction of cells
swimming at speed of 0.1 mm/s or less.
A preliminary action spectrum for the effect of the UV-B radiation on the
motility of Ophryoglena flava is shown in Fig. 7. Most of the damaging effect is due to
wavelengths shorter than 300 nm.
5e-22
4e-22
3e-22
2e-22
1e-22
0
270
280
290
300
310
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330
Wavelength (nm)
Fig. 7. Preliminary action spectrum for the effect of UV-B wavelength on the motility of Ophryoglena flava.
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