Environmental Engineering Reference
In-Depth Information
thus contribute to the good health and efficient growth of plants. However, high
concentrations of H
2
O
2
(50-100
μ
M) in the presence of iron (Fe) and oxalate can
generate HO
•
that would decrease the plant productivity and growth (Kobayashi et
al.
2002
). Furthermore, the ability of H
2
O
2
and ROOH compounds to act as anti-
bacterial and anti-fungal agents additionally suggests that an optimal level of per-
oxides could play a positive role toward good health and efficient growth of earth's
plants.
5.7 Role of H
2
O
2
in Oxygen Production by Photosynthesis
Photosynthetic O
2
evolution involves different stages that carry out a gradual accu-
mulation of oxidizing equivalents in the Mn-containing water-oxidizing complex
(WOC) (Samuilov et al.
2001
). The WOC can exist in different oxidation states
(S
n
, where high n indicates the most oxidised states), which can be probed by
addition of different redox-active molecules. The interaction of H
2
O
2
with the
S states of the WOC is depicted in the scheme below (Fig.
12
) (Samuilov et al.
2001
):
E
0
= 1.77 V
H
2
O
2
+ 2H
+
2H
2
O
S
2
S
-1
S
0
S
1
O
2
•
-
+ 2H
+
H
2
O
2
O
2
+ 2H
+
H
2
O
2
+ 2H
+
E
0
= 1.71 V
E
0
= 0.69 V
Fig. 12
Different oxidation states of H
2
O
2
and its interaction with the S states of the water-
oxidizing complex.
Data source
Samuilov et al. (
2001
)
6 Impacts of H
2
O
2
and ROOH in Natural Waters
H
2
O
2
and ROOH compounds are uncharged and non-radical active oxygen spe-
cies, and capable of acting as oxidants and reductants in chemical reactions
in natural waters. These properties have some impact on the aquatic organisms,
which can be listed as follows: (1) Acid rain; (2) Inhibition of photosynthetic elec-
tron transport in cells of cyanobacteria; (3) Effect of H
2
O
2
on bacterial growth
in waters; and (4) Impact of H
2
O
2
on microbial quality of recreational bathing
waters.
