Environmental Engineering Reference
In-Depth Information
(Arakaki et al.
1998
,
1999a
,
b
; Arakaki and Faust
1998
; Nakatani et al.
2001
;
Kobayashi et al.
2002
). It is considered that the HO
•
formed in the liquid phase
on the needle surfaces of Japanese red pine, which are frequently present in
the dew on sunny mornings in the warm-temperate region, are the cause of
ecophysiological disorders in plants (Kobayashi et al.
2002
).These effects sub-
sequently affect to decrease in the maximum CO
2
assimilation rate, stomatal
conductance, minimal fluorescence and needle lifespan (Kume et al.
2000
).
7 Summary and Scope of the Future Challenges
•
The HO
radical is the most reactive among the many oxygen transient spe-
cies produced photolytically in natural waters. However, a few studies on HO
•
•
production have been conducted on fresh- and seawater as a whole. The HO
production in acidic lake waters is not well investigated, although it is known
that acidification enhances the formation of HO
•
•
production varies with the contents of DOM, which may be a key factor to
understand the photoinduced processes in a variety of natural waters. Moreover,
there is no study conducted about production of alkoxide radicals (RO
(Vione et al.
2009
). The HO
•
) and
•
their role in the photodegradation kinetics of DOM along with HO
. An example
of key possible research on free radicals needed for the future challenges are:
(i) Effect of pH and temperature on the production of HO
•
for a variation in qual-
ity and quantity of DOM in natural waters. (ii) Investigation on the sources of
free radicals (HO
•
•
), particularly from fluorescent dissolved organic
matter (FDOM) for a variety of waters. (iii) Photoinduced generation of alkoxide
radicals (RO
and RO
•
•
and other
solution components. (iv) Impacts of free radicals on specific biota in the aquatic
environment.
) and their relative reaction kinetics with respect to HO
Problems
•
(1)
List the various sources of HO
and their role in natural waters.
•
(2)
List three important free radical species except HO
and their importance in
natural waters.
•
(3)
How is the steady state concentration of HO
defined, and why does the
steady state concentration vary for a variety of natural waters?
•
(4)
Explain why the potential of HO
formation is low in surface waters com-
pared to those of deep lakes and the sea.
•
(5)
Mention the important processes of HO
formation in natural waters and
explain the mechanism of in situ generation of HO
•
from DOM via H
2
O
2
.
(6) Explain why the photo-Fenton reaction is more suitable than the Fenton
reaction in the degradation of organic pollutants in aqueous solution.
