176
K. M. G. Mostofa et al.
further oxidized M (n+2)+ ion (Eq. 3.27). Therefore, formation of O 2
•− is an important step in the generation of organic peroxides in natural waters.
3.2 Microbial Formation of H 2 O 2 and ROOH
H 2 O 2 and ROOH compounds are typically produced under dark incubation by microbial
activity in natural waters (Fig. 2) (Palenic and Morel 1988; Moffett and Zafiriou 1990;
Vermilyea et al. 2010a, b). They are susceptible to be formed by several biological processes. Biota is thought to be the main source of dark H 2 O 2 and ROOH production in
natural waters (Fig. 2b) (Paradies et al. 2000; Forman and Boveris 1982). For instance,
dark production of H 2 O 2 in seawater is particle-dependent and the production rates are in
the range of 0.8–2.4 nM h −1 (Moffett and Zafiriou 1990). Recent studies demonstrate the
high dark production rate (29–122 nM h −1 ) of H 2 O 2 in several lake waters (Vermilyea
et al. 2010). Moreover, H 2 O 2 and ROOH may be formed extracellularly by marine phytoplankton or cyanobacteria (Palenic and Morel 1988; Zepp et al. 1986). Extracellular
H 2 O 2 can be produced under dark conditions by enzymatic reduction of oxygen at the
cell surface (Palenic et al. 1987) and upon oxygen reduction by other electron transport chains. The latter include the mitochondrial reduction of oxygen followed by H 2 O 2
diffusion out of the cell (Forman and Boveris 1982; Frimer et al. 1983). Also the autooxidation of organic material may produce H 2 O 2 and ROOH in the aquatic environment
(Stevens et al. 1973). In seawater, H 2 O 2 may be produced by particle-dependent and
light-independent microbial processes (Moffett and Zafiriou 1990). For example, a net
H 2 O 2 production (dark production minus dark consumption) of 1–3 nM h −1 has been
observed at 40–60 m in an in situ experiment conducted in the Sargasso Sea (Palenic
and Morel 1988). Finally, ROOH compounds are produced in bulk natural-water DOM
by light-independent microbial processes (Fig. 2) (Sakugawa et al. 2000). For example,
net ROOH production has been observed in both filtered and unfiltered river waters (2b),
while H 2 O 2 is merely produced in filtered river waters (Fig. 2a). ROOH compounds are
typically more concentrated in deep seawaters than in surface waters (Sakugawa et al.
2000).
4 Factors Controlling the Production and Decay of H 2 O 2
and ROOH in Natural Waters
Concentration levels of H 2 O 2 and ROOH as well as production rates of H 2 O 2 differ in a variety of natural waters (Table 1). The magnitude of the H 2 O 2 production
decreases from coastal waters to open oceans (Zika et al. 1985a, b; Fujiwara et al.
(3.25)
M
n+ + O 2 → M
(n + 1) + O 2
•− (M = Fe
2+ , Cu
+ , etc)
(3.26)
O 2
•− + R
+ → RO 2
• (R = H
+ /CH
+
3 , etc)
(3.27)
RO 2
• + M
(n+1)+ + H
+ → ROOH + M
(n+2)+ (R = H
+ /CH
+
3 )
K. M. G. Mostofa et al.
further oxidized M (n+2)+ ion (Eq. 3.27). Therefore, formation of O 2
•− is an important step in the generation of organic peroxides in natural waters.
3.2 Microbial Formation of H 2 O 2 and ROOH
H 2 O 2 and ROOH compounds are typically produced under dark incubation by microbial
activity in natural waters (Fig. 2) (Palenic and Morel 1988; Moffett and Zafiriou 1990;
Vermilyea et al. 2010a, b). They are susceptible to be formed by several biological processes. Biota is thought to be the main source of dark H 2 O 2 and ROOH production in
natural waters (Fig. 2b) (Paradies et al. 2000; Forman and Boveris 1982). For instance,
dark production of H 2 O 2 in seawater is particle-dependent and the production rates are in
the range of 0.8–2.4 nM h −1 (Moffett and Zafiriou 1990). Recent studies demonstrate the
high dark production rate (29–122 nM h −1 ) of H 2 O 2 in several lake waters (Vermilyea
et al. 2010). Moreover, H 2 O 2 and ROOH may be formed extracellularly by marine phytoplankton or cyanobacteria (Palenic and Morel 1988; Zepp et al. 1986). Extracellular
H 2 O 2 can be produced under dark conditions by enzymatic reduction of oxygen at the
cell surface (Palenic et al. 1987) and upon oxygen reduction by other electron transport chains. The latter include the mitochondrial reduction of oxygen followed by H 2 O 2
diffusion out of the cell (Forman and Boveris 1982; Frimer et al. 1983). Also the autooxidation of organic material may produce H 2 O 2 and ROOH in the aquatic environment
(Stevens et al. 1973). In seawater, H 2 O 2 may be produced by particle-dependent and
light-independent microbial processes (Moffett and Zafiriou 1990). For example, a net
H 2 O 2 production (dark production minus dark consumption) of 1–3 nM h −1 has been
observed at 40–60 m in an in situ experiment conducted in the Sargasso Sea (Palenic
and Morel 1988). Finally, ROOH compounds are produced in bulk natural-water DOM
by light-independent microbial processes (Fig. 2) (Sakugawa et al. 2000). For example,
net ROOH production has been observed in both filtered and unfiltered river waters (2b),
while H 2 O 2 is merely produced in filtered river waters (Fig. 2a). ROOH compounds are
typically more concentrated in deep seawaters than in surface waters (Sakugawa et al.
2000).
4 Factors Controlling the Production and Decay of H 2 O 2
and ROOH in Natural Waters
Concentration levels of H 2 O 2 and ROOH as well as production rates of H 2 O 2 differ in a variety of natural waters (Table 1). The magnitude of the H 2 O 2 production
decreases from coastal waters to open oceans (Zika et al. 1985a, b; Fujiwara et al.
(3.25)
M
n+ + O 2 → M
(n + 1) + O 2
•− (M = Fe
2+ , Cu
+ , etc)
(3.26)
O 2
•− + R
+ → RO 2
• (R = H
+ /CH
+
3 , etc)
(3.27)
RO 2
• + M
(n+1)+ + H
+ → ROOH + M
(n+2)+ (R = H
+ /CH
+
3 )