Environmental Engineering Reference
In-Depth Information
(3) Photoinduced degradation can regulate water-quality parameters. In particular:
(i) Photoinduced degradation changes the physical, chemical and optical properties
of water (Kopacek et al.
2003
; Vahatalo et al.
2000
; Twardowski and Donaghay
2002
; Mostofa et al.
2005
; Mostofa et al.
2007a
,
b
; Moran et al.
2000
), the struc-
ture of DOM (Kramer et al.
1996
; Kulovaara
1996
; Bertilsson and Allard
1996
)
as well as its molecular weight (Twardowski and Donaghay
2002
; Allard et al.
1994
; Kaiser and Sulzberger
2004
; Yoshioka et al.
2007
); (ii) Photoinduced deg-
radation processes can affect the acidity-alkalinity balance and the consumption
of dissolved oxygen at the epilimnion level in both lacustrine and oceanic envi-
ronments (Kopacek et al.
2003
; Amon and Benner
1996
; Gao and Zepp
1998
);
(iii) Photoinduced degradation decreases the absorbance of CDOM (and/or
FDOM), which can result in water discoloration (Reche et al.
1999
) and increases
the water-column transparency. A notable consequence is the increased penetra-
tion of photosynthetically active radiation (PAR, 400-700 nm) but also of damag-
ing UV radiation (280-400 nm) in the water column (Laurion et al.
2000
). These
effects have also an influence on the photoinduced degradation of deep-water
DOM (Morris and Hargreaves
1997
; Siegel and Michaels
1996
); (iv) Photoinduced
processes can induce the degradation of organic pollutants or contaminants. A wide
variety of photogenerated transients is involved (HO
•
•
−
,
1
O
2
,
3
CDOM*)
(Maddigapu et al.
2011
; Minella et al.
2011
; Arsene C
2011
), but the hydroxyl rad-
ical is the reactive species that is less likely to produce secondary toxic pollutants.
Therefore, HO
, CO
3
•
-induced processes are most likely to achieve efficient decontami-
nation. The photo-Fenton reaction or photo-ferrioxalate/H
2
O
2
reactions are par-
ticularly effective to this purpose (Safarzadeh-Amiri et al.
1997
; Southworth and
Voelker
2003
; Brezonik and Fulkerson-Brekken
1998
); (v) Photoinduced degrada-
tion of DOM can interact with eutrophication by increasing the phosphate concen-
tration upon decomposition of organic phosphorus present in DOM (Reche et al.
1999
; Carpenter et al.
1998
; Kim and Kim
2006
; Li et al.
2008
); (vi) Production of
CO
2
as well as other dissolved inorganic carbon (DIC) species upon photoinduced
degradation of DOM can potentially influence the carbon cycling, and may have an
impact on climate change (Salonen and Vähätalo
1994
; Graneli et al.
1996
,
1998
);
(vii) The decomposition of DOM affects directly or indirectly the distribution of
trace elements in natural waters (Kopacek et al.
2003
; Kieber et al.
1989
).
(4) Photoinduced degradation of DOM can be beneficial to the water ecosystem and
provides energy for microbial loops. Its effects include: (i) Supply of nutrients,
which are naturally important for plankton productivity in natural waters (Kim
and Kim
2006
; Kirchman et al.
1991
; Salonen et al.
1992
; Wetzel
1992
); (iii)
Increase in the pool of bioavailable carbon substrates, which are essential foods
for microorganisms (Bertilsson and Allard
1996
; Lindell et al.
1996
; Wetzel et
al.
1995
; Benner and Biddanda
1998
; Bertilsson and Tranvik
1998
; Bertilsson et
al.
1999
); (iii) Photo-production of reactive species by CDOM or FDOM, such
as hydrogen peroxide (H
2
O
2
), organic peroxides (ROOH) and HO
•
. These spe-
cies can contribute damage to macromolecules such as DNA, proteins and lipids
(O'Sullivan et al.
2005
; Samuilov et al.
2001
; Blokhina et al.
2003
; Zhao et al.
2003
). (iv) The simultaneous generation of H
2
O
2
, CO
2
and DIC from DOM
