188
K. M. G. Mostofa et al.
concentrated H 2 O 2 in rainwater, where the measured levels are 0–110,600 nM
in Europe, 17,000–199,000 nM in Brazil, 30–120,000 nM in the USA, 500–
34,000 nM in Canada, 24–56,400 nM in Japan and 3,500–82,000 nM in marine
areas (Table 1) (Lazrus et al. 1985; Cooper and Lean 1989; Hellpointner and
Gäb 1989; Sakugawa et al. 1990, 1993, 2006; Hewitt and Kok 1991; Cooper and
Lean 1992; Yuan and Shiller 2000; Miller et al. 2008). ROOH concentrations in
rainwater are 400–1600 nM in Europe and 60–6500 nM in the USA (Table 1)
(Hellpointner and Gäb 1989; Sakugawa et al. 1993; Hewitt and Kok 1991). The
levels of H 2 O 2 and ROOH in rainwater (Table 1) usually show some common
trends. First, there are strong diel variations with highest concentrations in the
afternoon and lowest ones in the night time and in the early morning. Second,
high variations are observed between summer and winter, which are presumably
caused by high light intensity in summer that induces elevated H 2 O 2 production. Rain drops may scavenge H 2 O 2 and ROOH generated in the gas phase or
within cloud droplets. Because of the observed diel trend, daytime precipitation
might be a more important source of peroxides to natural waters compared to the
nighttime one.
5 Significance of H 2 O 2 and ROOH in the Aquatic
Environment
H 2 O 2 and ROOH compounds are uncharged, non-radical active oxygen species
that may act as oxidants and reductants in natural waters. These features of peroxides are also of importance for their use in chemical reactions and in our daily life.
The main effects of H 2 O 2 and ROOH can be distinguished as: (1) Natural purifiers in natural waters; (2) Photo-Fenton reaction for the decomposition of organic
pollutants; (3) Indicators of microbial changes in bulk DOM; (4) Function as a
redox agents in aqueous solution, (5) Medical treatment and commercial uses;
(6) Growth of terrestrial vegetation by rainwater H 2 O 2 and ROOH; and
(7) Oxygen evolution in photosynthesis.
5.1 Natural Purification in Aquatic Ecosystems
H 2 O 2 and ROOH compounds are powerful oxidants, which can directly oxidize the DOM or other reactants in natural waters (Draper and Crosby 1984; Ho
1986; Samuilov et al. 2001). Peroxides are formed photolytically from DOM in
natural water, and their productions reach maximum at noon time. The photoinduced generation of HO
• from peroxides can degrade organic pollutants or DOM
(Gao and Zepp 1998; Brezonik and Fulkerson-Brekken 1998; Goldstone et al.
2002), which accounts for the role of H 2 O 2 and ROOH as purifiers in natural
waters.
K. M. G. Mostofa et al.
concentrated H 2 O 2 in rainwater, where the measured levels are 0–110,600 nM
in Europe, 17,000–199,000 nM in Brazil, 30–120,000 nM in the USA, 500–
34,000 nM in Canada, 24–56,400 nM in Japan and 3,500–82,000 nM in marine
areas (Table 1) (Lazrus et al. 1985; Cooper and Lean 1989; Hellpointner and
Gäb 1989; Sakugawa et al. 1990, 1993, 2006; Hewitt and Kok 1991; Cooper and
Lean 1992; Yuan and Shiller 2000; Miller et al. 2008). ROOH concentrations in
rainwater are 400–1600 nM in Europe and 60–6500 nM in the USA (Table 1)
(Hellpointner and Gäb 1989; Sakugawa et al. 1993; Hewitt and Kok 1991). The
levels of H 2 O 2 and ROOH in rainwater (Table 1) usually show some common
trends. First, there are strong diel variations with highest concentrations in the
afternoon and lowest ones in the night time and in the early morning. Second,
high variations are observed between summer and winter, which are presumably
caused by high light intensity in summer that induces elevated H 2 O 2 production. Rain drops may scavenge H 2 O 2 and ROOH generated in the gas phase or
within cloud droplets. Because of the observed diel trend, daytime precipitation
might be a more important source of peroxides to natural waters compared to the
nighttime one.
5 Significance of H 2 O 2 and ROOH in the Aquatic
Environment
H 2 O 2 and ROOH compounds are uncharged, non-radical active oxygen species
that may act as oxidants and reductants in natural waters. These features of peroxides are also of importance for their use in chemical reactions and in our daily life.
The main effects of H 2 O 2 and ROOH can be distinguished as: (1) Natural purifiers in natural waters; (2) Photo-Fenton reaction for the decomposition of organic
pollutants; (3) Indicators of microbial changes in bulk DOM; (4) Function as a
redox agents in aqueous solution, (5) Medical treatment and commercial uses;
(6) Growth of terrestrial vegetation by rainwater H 2 O 2 and ROOH; and
(7) Oxygen evolution in photosynthesis.
5.1 Natural Purification in Aquatic Ecosystems
H 2 O 2 and ROOH compounds are powerful oxidants, which can directly oxidize the DOM or other reactants in natural waters (Draper and Crosby 1984; Ho
1986; Samuilov et al. 2001). Peroxides are formed photolytically from DOM in
natural water, and their productions reach maximum at noon time. The photoinduced generation of HO
• from peroxides can degrade organic pollutants or DOM
(Gao and Zepp 1998; Brezonik and Fulkerson-Brekken 1998; Goldstone et al.
2002), which accounts for the role of H 2 O 2 and ROOH as purifiers in natural
waters.