Environmental Engineering Reference
In-Depth Information
Zika et al.
1985a
,
b
; Moffett and Zika
1987a
; Palenic and Morel
1988
; Cooper
and Lean
1989
; Hellpointner and Gäb
1989
; Johnson et al.
1989
). Starting from
the 1980's, organic peroxides (ROOH) have been detected in air (Sakugawa and
Kaplan
1987
; Lazrus et al.
1985
; Hellpointner and Gäb
1989
; Sauer et al.
2001
),
cloudwater and rain (Kelley and Reddy
1986
). The ROOH concentrations have also
been determined in freshwater (Mostofa
2005
; Sakugawa et al.
2006
; Mostofa and
Sakugawa
2009
) and seawater (Sakugawa et al.
2000
; Gerringa et al.
2004
).
Recent studies have demonstrated that natural sunlight or solar radiation is a
key factor for the generation of H
2
O
2
and ROOH in the atmosphere and in natural
waters. Microbial processes can produce small amounts of both H
2
O
2
and ROOH
in living organisms (Kim and Portis
2004
; Boveris et al.
2006
; Grivennikova et
al.
2008
; Roy and Atreja
2008
) as well as in the deeper water layers (i.e., under
dark conditions) of river, lake and marine environments (Komissarov
2003
).
H
2
O
2
is found to link with the occurrence of oxygenic photosynthesis in both
higher plants (Komissarov
1994
,
1995
,
2003
) and natural waters (Mostofa
et al.
2009a
,
b
). Therefore, H
2
O
2
generated mostly by solar radiation and microbial
processes could simultaneously be important for the occurrence of photosynthe-
sis in terrestrial higher plants and for the production of organic matter (ca. algae,
cyanobacteria, etc.) in water environments. There is evidence that the microbial
processing of vascular-plant spoils in the terrestrial soil environment can produce
humic substances (fulvic and humic acids), which are then released into river, lake
and marine waters (Mostofa et al.
2009a
). The action of sunlight on fulvic and
humic acids correspondingly produces H
2
O
2
that, by favoring photosynthesis in
the surface layer of rivers, lakes and oceans, would induce the generation of algae
and other aquatic organisms. These organisms are then able to produce autochtho-
nous DOM via photorespiration (or photo-assimilations) and microbial respira-
tion or processes (Mostofa et al.
2009b
; Collen et al.
1995
; McCarthy et al.
1997
;
Rosenstock and Simon
2001
; Medina-Sánchez et al.
2006
; Nieto-Cid et al.
2006
;
Zhang et al.
2009
; Fu et al.
2010
). The photoinduced reactions of autochthonous
DOM also yield H
2
O
2
in natural waters. The production of H
2
O
2
would mostly
depend on the amount of DOM and on solar irradiance. Global warming with the
associated increase in water temperature would enhance the production of H
2
O
2
,
simultaneously affecting both the photodegradation of DOM and the photosynthe-
sis (Mostofa et al.
2009b
). Photosynthesis in higher plants and in natural waters
can be significantly increased by rain, also because of the elevated concentration
of H
2
O
2
and ROOH in rainwater. Therefore, the photoinduced and microbial gen-
eration of H
2
O
2
is a key factor for the occurrence of many photoinduced, biologi-
cal, physical and geochemical processes. Such processes include the production
of hydroxyl radical and other free radical species, photosynthesis, production of
chlorophyll and of autochthonous DOM, photodegradation of DOM, CDOM and
FDOM, and complexation of DOM with trace elements in natural water environ-
ments. On the other hand, production of ROOH could be a marker of microbial
modification of bulk organic matter and of DOM under dark conditions. A few
studies have previously been conducted to examine the photoinduced and micro-
bial production of ROOH, their chemical nature and relationships with DOM.
