143
Photoinduced and Microbial Generation of Hydrogen Peroxide
R can be CH 3 –, CH 3 –CH 2 –, etc. and H can be H or R. The organic peroxides are
ubiquitously distributed in air, cloud, dew, rain, mineral water, freshwater and
seawater (Sakugawa and Kaplan 1987; Lazrus et al. 1985; Hellpointner and Gäb
1989; Sauer et al. 2001; Kelley and Reddy 1986; Mostofa 2005; Sakugawa et al.
2006; Mostofa and Sakugawa 2009; Sakugawa et al. 2000; Gerringa et al. 2004).
The major ROOH compounds identified in the aquatic environments are methyl
hydroperoxide (CH 3 OOH), hydroxymethyl hydroperoxide (HOCH 2 OOH), ethyl
hydroperoxide (CH 3 CH 2 OOH), 1-hydroxyethyl hydroperoxide (CH 3 CH(OH)OOH),
2-hydroxyethyl hydroperoxide (CH 2 (OH)CH 2 OOH), 1-hydroxypropyl hydroperoxide
(CH 3 CH 2 CH(OH)OOH), 2-hydroxypropyl hydroperoxide (CH 3 CH(OH)CH 2 OOH),
3-hydroxypropyl hydroperoxide (CH 2 (OH)CH 2 CH 2 OOH), and bis(hydroxymethyl)
peroxide (HOCH 2 OOCH 2 OH) (Hellpointner and Gäb 1989; Hewitt and Kok 1991).
The concentration levels of ROOH compounds are commonly low (~<390 nM) in
natural waters, and their concentrations are also low when they are generated in photoexperiments conducted on natural waters or on aqueous solutions of standard DOM
components.
The various biogeochemical functions of ROOH can be categorized as follows:
(i) Production of ROOH compounds would be a marker of microbial changes in
bulk organic matter or DOM under dark conditions, which are usually occurring
in deeper layers of lake or seawater (Sakugawa et al. 1995, 2000; Hayase and
Shinozuka 1995; Mostofa et al. 2005). (ii) ROOH compounds are readily decomposed and correspondingly generated, so that they reach a steady-state concentration in natural waters. (iii) ROOH compounds might be important transformation
intermediates of DOM and may be chemically converted into stable DOM components in natural waters. (iv) The photoinduced and thermal decomposition of
organic peroxides generally yields organic peroxide radicals; they may combine
with other organic substances to form new compounds, or can form polymeric
compounds in aqueous solution (Mageli and Kolczynski 1966; Mill et al. 1980;
Kieber and Blough 1990; Faust and Allen 1992). Future research is expected to
further highlight the importance of ROOH in natural waters.
1.3 Nature and Characteristics of H 2 O 2 and ROOH
In natural waters, H 2 O 2 shows several characteristic properties that can be listed
as follows: (i) The photoinduced generation of H 2 O 2 follows a regular trend of
increasing concentration with increasing irradiation time, in photoexperiments
conducted under a solar simulator (Fig. 1a, b). It suggests that the formation rate
is higher than the transformation one. (ii) Photogenerated H 2 O 2 is gradually consumed in aqueous media in the absence of solar radiation (Fig. 2a). It suggests that
H 2 O 2 in aqueous solution is presumably decomposed by chemical and/or enzymatic reactions. (iii) The rate of H 2 O 2 photoproduction is higher in filtered than in
unfiltered natural waters samples (Fig. 2a), suggesting that particulate matter may
rapidly consume H 2 O 2 in aqueous solution. (iv) The photoinduced generation of
Photoinduced and Microbial Generation of Hydrogen Peroxide
R can be CH 3 –, CH 3 –CH 2 –, etc. and H can be H or R. The organic peroxides are
ubiquitously distributed in air, cloud, dew, rain, mineral water, freshwater and
seawater (Sakugawa and Kaplan 1987; Lazrus et al. 1985; Hellpointner and Gäb
1989; Sauer et al. 2001; Kelley and Reddy 1986; Mostofa 2005; Sakugawa et al.
2006; Mostofa and Sakugawa 2009; Sakugawa et al. 2000; Gerringa et al. 2004).
The major ROOH compounds identified in the aquatic environments are methyl
hydroperoxide (CH 3 OOH), hydroxymethyl hydroperoxide (HOCH 2 OOH), ethyl
hydroperoxide (CH 3 CH 2 OOH), 1-hydroxyethyl hydroperoxide (CH 3 CH(OH)OOH),
2-hydroxyethyl hydroperoxide (CH 2 (OH)CH 2 OOH), 1-hydroxypropyl hydroperoxide
(CH 3 CH 2 CH(OH)OOH), 2-hydroxypropyl hydroperoxide (CH 3 CH(OH)CH 2 OOH),
3-hydroxypropyl hydroperoxide (CH 2 (OH)CH 2 CH 2 OOH), and bis(hydroxymethyl)
peroxide (HOCH 2 OOCH 2 OH) (Hellpointner and Gäb 1989; Hewitt and Kok 1991).
The concentration levels of ROOH compounds are commonly low (~<390 nM) in
natural waters, and their concentrations are also low when they are generated in photoexperiments conducted on natural waters or on aqueous solutions of standard DOM
components.
The various biogeochemical functions of ROOH can be categorized as follows:
(i) Production of ROOH compounds would be a marker of microbial changes in
bulk organic matter or DOM under dark conditions, which are usually occurring
in deeper layers of lake or seawater (Sakugawa et al. 1995, 2000; Hayase and
Shinozuka 1995; Mostofa et al. 2005). (ii) ROOH compounds are readily decomposed and correspondingly generated, so that they reach a steady-state concentration in natural waters. (iii) ROOH compounds might be important transformation
intermediates of DOM and may be chemically converted into stable DOM components in natural waters. (iv) The photoinduced and thermal decomposition of
organic peroxides generally yields organic peroxide radicals; they may combine
with other organic substances to form new compounds, or can form polymeric
compounds in aqueous solution (Mageli and Kolczynski 1966; Mill et al. 1980;
Kieber and Blough 1990; Faust and Allen 1992). Future research is expected to
further highlight the importance of ROOH in natural waters.
1.3 Nature and Characteristics of H 2 O 2 and ROOH
In natural waters, H 2 O 2 shows several characteristic properties that can be listed
as follows: (i) The photoinduced generation of H 2 O 2 follows a regular trend of
increasing concentration with increasing irradiation time, in photoexperiments
conducted under a solar simulator (Fig. 1a, b). It suggests that the formation rate
is higher than the transformation one. (ii) Photogenerated H 2 O 2 is gradually consumed in aqueous media in the absence of solar radiation (Fig. 2a). It suggests that
H 2 O 2 in aqueous solution is presumably decomposed by chemical and/or enzymatic reactions. (iii) The rate of H 2 O 2 photoproduction is higher in filtered than in
unfiltered natural waters samples (Fig. 2a), suggesting that particulate matter may
rapidly consume H 2 O 2 in aqueous solution. (iv) The photoinduced generation of