Environmental Engineering Reference
In-Depth Information
Despite the universal and unique functions that H
2
O
2
and ROOH may play in
water ecosystems, their roles on some key biogeochemical functions in natural
waters have hardly been investigated. This chapter will provide a general overview
on the biogeochemical functions of H
2
O
2
and ROOH, their production mecha-
nisms and the controlling factors for formation and decay, as well as their signifi-
cance and impact in natural waters.
1.1 Hydrogen Peroxide and its Biogeochemical Functions
Hydrogen peroxide (H
2
O
2
) is a simple chemical compound (H-O-O-H) that
appears like water (H-O-H) in its chemical formula, with an additional oxygen
atom. Hydrogen peroxide can undergo dismutation into water and oxygen:
2H
2
O
2
→
2H
2
O
+
O
2
H
2
O
2
is a universal constituent of the hydrosphere and occurs in freshwater,
seawater, mineral water, rain, dew, cloud, snow, air, and in all living organisms.
H
2
O
2
also finds effective application in experiments as well as in treatment pro-
cesses. It acts as an useful indicator for a variety of photoinduced, biological and
abiotic processes in the aquatic environment.
The various biogeochemical functions of H
2
O
2
can be classified as follows:
(iii) H
2
O
2
is the most stable reactive oxygen species (ROS) and is used as an indi-
cator of photoinduced activity, because it is for instance photolytically generated
through irradiation of various dissolved organic matter (DOM) components in nat-
ural waters (Cooper and Zika
1983
; Zika et al.
1985a
,
b
; Mostofa and Sakugawa
2009
; Obernosterer et al.
2001
; Fujiwara et al.
1993
; Moore et al.
1993
; Scully et
al.
1996
). (iii) H
2
O
2
and its precursor superoxide (O
2
•
−
) can be both oxidising and
reducing agents and are, therefore, potentially important for a number of redox
reactions in natural waters (Moffett and Zika
1987a
,
b
; Petasne and Zika
1987
;
Moffett and Zafiriou
1990
; Zafiriou
1990
; Zepp et al.
1992
; Zafiriou et al.
1998
;
Voelker et al.
2000
; Jeong and Yoon
2005
). (iii) H
2
O
2
is a natural tracer of the
surface-water mixing zone or of stratification processes in lake and marine envi-
ronments (Johnson et al.
1989
; Sikorsky and Zika
1993a
,
b
; Sarthou et al.
1997
;
Scully and Vincent
1997
). (iv) H
2
O
2
is an indicator of the photodegradation of
dissolved organic matter (DOM) and of organic pollutants in surface natu-
ral waters (Gao and Zepp
1998
; Westerhoff et al.
1999
; Southworth and Voelker
2003
). (v) H
2
O
2
is involved in oxidative stress in biota/living cells, because of its
elevated reactivity by both oxidation and reduction (Berlett and Stadtman
1997
;
Paradies et al.
2000
; Blokhina et al.
2003
; Richard et al.
2007
). (vii) H
2
O
2
can be
helpful in the identification of biological activity, in particular in coastal waters
where higher biological activity with rapid decay of H
2
O
2
is commonly observed
compared to the open oceans (Fujiwara et al.
1993
; Moffett and Zafiriou
1990
;
Cooper and Zepp
1990
; Petasne and Zika
1997
). (vii) H
2
O
2
is a useful tracer of
the vertical advection transport or the convective overturn, which is usually caused