147
Photoinduced and Microbial Generation of Hydrogen Peroxide
More simply, “Peroxides SSC = produced peroxides—(decay by microbles
and any other processes + contribution to DOM photo degradation)”, where
SSC = Steady-State Concentration. Therefore, enzymes might be an important factor in regulating the occurrence of H 2 O 2 and ROOH compounds in natural waters.
The decay rates of H 2 O 2 and ROOH, expressed as half-life times (t 1/2 ), are
hours to days depending on the presence of enzymes in natural waters (Harvey
1925; Mostofa 2005; Richard et al. 2007; Cooper and Zepp 1990; Cooper and
Lean 1992). For example, the half-life of H 2 O 2 is gradually increased from unfiltered to filtered lake waters, from 4.4 h for unfiltered water to 4.7 h for 64 μm
filtered water (zooplakton removed), 6.4 h for 12 μm filtered water (large algae
removed), 19.1 h for 1.0 μm filtered water (small algae removed), and 58.7 h for
0.2 μm filtered water (bacteria removed) (Cooper and Lean 1992). Similarly, the
half-lives are approximately 3 h or less for highly biologically productive coastal
waters or freshwaters, and hundreds of hours for oligotrophic unfiltered waters
(Mostofa 2005; Fujiwara et al. 1993; Moore et al. 1993; Richard et al. 2007).
1.5 H 2 O 2 Acts as a Reductant and Oxidant-REDOX
H 2 O 2 acts as a reductant and oxidant (REDOX) in many reactions occurring in
natural waters (Moffett and Zika 1987a; b; Moffett and Zafiriou 1990; Zepp
et al. 1992; Jeong and Yoon 2005). When H 2 O 2 acts as a reductant, O from H 2 O 2
is transformed into O 2 . When H 2 O 2 acts as an oxidant, O from H 2 O 2 is converted
into H 2 O (Moffett and Zafiriou 1990). The chain reactions of H 2 O 2 as reductant
and oxidant are schematically depicted below (Fig. 5) (Moffett and Zafiriou 1990).
1.6 Concentration Levels of H 2 O 2 and ROOH Compounds
in Natural Water
The levels of H 2 O 2 and ROOH are greatly variable for a variety of natural waters
(Table 1) (van Baalen and Marler 1966; Sinel’nikov 1971; Sinel’nikov and
Demina 1974; Cooper and Zika 1983; Helz and Kieber 1985; Lazrus et al. 1985;
H 2 O 2
HO 2
•—
HO 2
O 2
—
O 2 : Reductant
H 2 O 2 → OH + OH —
H 2 O
↓
OH —
H 2 O
Oxidant
Fig. 5 Electron transfer and proton transfer reactions in the reduction of O 2 from H 2 O 2 to H 2 O,
demonstrating the intermediates involved Data source Moffett and Zafiriou (1990)
Photoinduced and Microbial Generation of Hydrogen Peroxide
More simply, “Peroxides SSC = produced peroxides—(decay by microbles
and any other processes + contribution to DOM photo degradation)”, where
SSC = Steady-State Concentration. Therefore, enzymes might be an important factor in regulating the occurrence of H 2 O 2 and ROOH compounds in natural waters.
The decay rates of H 2 O 2 and ROOH, expressed as half-life times (t 1/2 ), are
hours to days depending on the presence of enzymes in natural waters (Harvey
1925; Mostofa 2005; Richard et al. 2007; Cooper and Zepp 1990; Cooper and
Lean 1992). For example, the half-life of H 2 O 2 is gradually increased from unfiltered to filtered lake waters, from 4.4 h for unfiltered water to 4.7 h for 64 μm
filtered water (zooplakton removed), 6.4 h for 12 μm filtered water (large algae
removed), 19.1 h for 1.0 μm filtered water (small algae removed), and 58.7 h for
0.2 μm filtered water (bacteria removed) (Cooper and Lean 1992). Similarly, the
half-lives are approximately 3 h or less for highly biologically productive coastal
waters or freshwaters, and hundreds of hours for oligotrophic unfiltered waters
(Mostofa 2005; Fujiwara et al. 1993; Moore et al. 1993; Richard et al. 2007).
1.5 H 2 O 2 Acts as a Reductant and Oxidant-REDOX
H 2 O 2 acts as a reductant and oxidant (REDOX) in many reactions occurring in
natural waters (Moffett and Zika 1987a; b; Moffett and Zafiriou 1990; Zepp
et al. 1992; Jeong and Yoon 2005). When H 2 O 2 acts as a reductant, O from H 2 O 2
is transformed into O 2 . When H 2 O 2 acts as an oxidant, O from H 2 O 2 is converted
into H 2 O (Moffett and Zafiriou 1990). The chain reactions of H 2 O 2 as reductant
and oxidant are schematically depicted below (Fig. 5) (Moffett and Zafiriou 1990).
1.6 Concentration Levels of H 2 O 2 and ROOH Compounds
in Natural Water
The levels of H 2 O 2 and ROOH are greatly variable for a variety of natural waters
(Table 1) (van Baalen and Marler 1966; Sinel’nikov 1971; Sinel’nikov and
Demina 1974; Cooper and Zika 1983; Helz and Kieber 1985; Lazrus et al. 1985;
H 2 O 2
HO 2
•—
HO 2
O 2
—
O 2 : Reductant
H 2 O 2 → OH + OH —
H 2 O
↓
OH —
H 2 O
Oxidant
Fig. 5 Electron transfer and proton transfer reactions in the reduction of O 2 from H 2 O 2 to H 2 O,
demonstrating the intermediates involved Data source Moffett and Zafiriou (1990)