177
Photoinduced and Microbial Generation of Hydrogen Peroxide
1993). The influence of riverine fluxes having high DOM plays an important role
in the production of H 2 O 2 in coastal seawaters. The lowest H 2 O 2 concentration
was seasonally detected in southern oceans (5–25 nM), which was 10 to 20 times
lower compared to other oceanic environments (Table 1). The major factors behind
the low H 2 O 2 concentration in the southern ocean are thought to be: (i) Low incident solar intensity and penetration efficiency in the surface water layer (Zika et
al. 1985), solar irradiance being a major factor for the photoinduced formation of
H 2 O 2 in natural waters. (ii) Water temperature that is normally below <5 °C in the
southern ocean. (iii) Vertical mixing (Johnson et al. 1989). (iv) DOC concentration
(Zika et al. 1985a, b). (v) Distinct latitude or solar zenith angle, considering that
H 2 O 2 photoproduction decreases with increasing apparent-noon solar zenith angle
(Sikorsky and Zika 1993a, b).
Therefore, the production and decay of H 2 O 2 and ROOH and their lifetimes
in the aquatic environment (Table 1) generally depend upon a complex set of factors, which can be distinguished as: (1) Effects and variation of solar radiation;
(2) Contents and molecular nature of DOM; (3) Presence of phytoplankton, algae
and microbes; (4) Photodegradation; (5) Photosynthesis; (6) Photolytic and chemical processes; (7) Physical processes; and (8) Precipitation (e.g. rain).
4.1 Effects and Variation of Solar Radiation
Solar radiation is one of the key factors in the generation of H 2 O 2 and ROOH in
natural waters (Mostofa and Sakugawa 2009; Obernosterer et al. 2001; Richard
et al. 2007; Rusak et al. 2010; Holm-Hansen et al. 1993). The diurnal cycle of
H 2 O 2 , where an increase of solar radiation intensity increases the production of
H 2 O 2 and vice versa, is a typical example of the strong dependence between solar
intensity and H 2 O 2 generation (Fig. 6). It has been estimated that the production of
H 2 O 2 and ROOH is usually higher by several times in the summer season than in
the winter one. Production of H 2 O 2 is higher in summer by 55–79 % in upstream
waters, 162–364 % in polluted waters, and 137–146 % in clean river waters. In
the case of ROOH the summer production is higher by 116–240 %, 521–1322 %,
and 244–550 %, respectively, compared to the winter one. Such effects are mostly
considered to be the effect of variation in solar intensity, which is much higher in
the summer season (by 84 %, 32 %, and 216 %, respectively) compared to winter during a sampling day (Fig. 9) (Mostofa and Sakugawa 2009). Therefore, an
increase in solar intensity would enhance the production of H 2 O 2 in aqueous solution (Mostofa and Sakugawa 2009).
The solar intensity is highly variable in different regions. In the subtropical
zone, ultraviolet (UV) B radiation (280–320 nm) is stable, but it is much higher
(≈ten fold) than that in the Antarctica (Holm-Hansen et al. 1993). Depletion of the
stratospheric ozone layer increases the ground-level UV B radiation in the polar
regions (Crutzen 1992) as well as at temperate latitudes (Stolarski et al. 1992).
H 2 O 2 formation is largely dependent on the radiation wavelengths (Obernosterer
Photoinduced and Microbial Generation of Hydrogen Peroxide
1993). The influence of riverine fluxes having high DOM plays an important role
in the production of H 2 O 2 in coastal seawaters. The lowest H 2 O 2 concentration
was seasonally detected in southern oceans (5–25 nM), which was 10 to 20 times
lower compared to other oceanic environments (Table 1). The major factors behind
the low H 2 O 2 concentration in the southern ocean are thought to be: (i) Low incident solar intensity and penetration efficiency in the surface water layer (Zika et
al. 1985), solar irradiance being a major factor for the photoinduced formation of
H 2 O 2 in natural waters. (ii) Water temperature that is normally below <5 °C in the
southern ocean. (iii) Vertical mixing (Johnson et al. 1989). (iv) DOC concentration
(Zika et al. 1985a, b). (v) Distinct latitude or solar zenith angle, considering that
H 2 O 2 photoproduction decreases with increasing apparent-noon solar zenith angle
(Sikorsky and Zika 1993a, b).
Therefore, the production and decay of H 2 O 2 and ROOH and their lifetimes
in the aquatic environment (Table 1) generally depend upon a complex set of factors, which can be distinguished as: (1) Effects and variation of solar radiation;
(2) Contents and molecular nature of DOM; (3) Presence of phytoplankton, algae
and microbes; (4) Photodegradation; (5) Photosynthesis; (6) Photolytic and chemical processes; (7) Physical processes; and (8) Precipitation (e.g. rain).
4.1 Effects and Variation of Solar Radiation
Solar radiation is one of the key factors in the generation of H 2 O 2 and ROOH in
natural waters (Mostofa and Sakugawa 2009; Obernosterer et al. 2001; Richard
et al. 2007; Rusak et al. 2010; Holm-Hansen et al. 1993). The diurnal cycle of
H 2 O 2 , where an increase of solar radiation intensity increases the production of
H 2 O 2 and vice versa, is a typical example of the strong dependence between solar
intensity and H 2 O 2 generation (Fig. 6). It has been estimated that the production of
H 2 O 2 and ROOH is usually higher by several times in the summer season than in
the winter one. Production of H 2 O 2 is higher in summer by 55–79 % in upstream
waters, 162–364 % in polluted waters, and 137–146 % in clean river waters. In
the case of ROOH the summer production is higher by 116–240 %, 521–1322 %,
and 244–550 %, respectively, compared to the winter one. Such effects are mostly
considered to be the effect of variation in solar intensity, which is much higher in
the summer season (by 84 %, 32 %, and 216 %, respectively) compared to winter during a sampling day (Fig. 9) (Mostofa and Sakugawa 2009). Therefore, an
increase in solar intensity would enhance the production of H 2 O 2 in aqueous solution (Mostofa and Sakugawa 2009).
The solar intensity is highly variable in different regions. In the subtropical
zone, ultraviolet (UV) B radiation (280–320 nm) is stable, but it is much higher
(≈ten fold) than that in the Antarctica (Holm-Hansen et al. 1993). Depletion of the
stratospheric ozone layer increases the ground-level UV B radiation in the polar
regions (Crutzen 1992) as well as at temperate latitudes (Stolarski et al. 1992).
H 2 O 2 formation is largely dependent on the radiation wavelengths (Obernosterer