Environmental Engineering Reference
In-Depth Information
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 pho-
toexperiments 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 decom-
posed and correspondingly generated, so that they reach a steady-state concentra-
tion in natural waters. (iii) ROOH compounds might be important transformation
intermediates of DOM and may be chemically converted into stable DOM com-
ponents 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.
1
a, b). It suggests that the formation rate
is higher than the transformation one. (ii) Photogenerated H
2
O
2
is gradually con-
sumed in aqueous media in the absence of solar radiation (Fig.
2
a). It suggests that
H
2
O
2
in aqueous solution is presumably decomposed by chemical and/or enzy-
matic reactions. (iii) The rate of H
2
O
2
photoproduction is higher in filtered than in
unfiltered natural waters samples (Fig.
2
a), suggesting that particulate matter may
rapidly consume H
2
O
2
in aqueous solution. (iv) The photoinduced generation of
