220
K. M. G. Mostofa et al.
According to Eq. 2.7, the plot of 1/r P versus 1/[B] should be straight line (Takeda
et al. 2004) and k ′
SC
/k B can be calculated from the slope and intercept of the plot.
Thus, F B,HO can be calculated with Eq. 2.6 using the values of k ′
SC
/k B and [B].
2.5 Levels of Photoinduced Generation of HO
•
in Natural Waters
The production rates of HO
• that have been estimated in a variety of waters, in
the presence of standard chemical species (NO 2
– , NO 3
– and H 2 O 2 ) or of standard organic substances under sunlight are summarized in Table 2 (Mopper and
Zhou 1990; Takeda et al. 2004; Zepp et al. 1987; Haag and Hoigné 1985; White
et al. 2003; Arakaki and Faust 1998; Nakatani et al. 2007; Mostofa KMG and
Sakugawa H, unpublished data; Nakatani et al. 2004; Qian et al. 2001; Allen et
al. 1996; Mabury 1993; Grannas et al. 2006; Anastasio and Newberg 2007). The
rates are typically varied in a range from 10 –7 to 10 –10 M s –1 in aqueous solution (Table 2). Production rates in rivers are (0.6–7.5) × 10 –11 M s –1 in upstream
waters, (0.4–7.4) × 10 –8 M s –1 in upstream waters contaminated with AMD,
(1.0–2.9) × 10 –11 M s –1 in non-polluted river waters, 2.4 × 10 –11 M s –1 in
Ogeechee River, (2.0–6.0) × 10 –10 M s –1 in Wetland on Lake Erie and Artificial
Agricultural wetland, 6.4 × 10 –11 M s –1 in Rice field water, (2.0–17.0) × 10 –
10 M s –1 in Satilla River and Pine Barrens that have iron-rich waters (Table 2). It is
noticeable that the production rates of HO
• are higher by two to five orders of magnitude in stream waters contaminated with AMD (Allen et al. 1996) than in typical
river waters. Such an effect might be caused by the photo-Fenton reaction that is
considerably favored in the presence of elevated iron contents (Allen et al. 1996;
McKnight et al. 1988). Similarly, high production rates of HO
• have been observed
in Satilla River water (White et al. 2003), where more than 70 % of the total HO
•
production is accounted for by the photo-Fenton reaction. Therefore, the latter process is expected to be the main contributor to HO
• photo-production in iron-rich
waters. In contrast, upstream waters mainly contain DOM components (mostly fulvic and humic acids) that are the major contributors to HO
• photo-production in
these systems. A possible pathway that yields HO
• from DOM is the photoinduced
formation of H 2 O 2 (Eqs. 3.13–3.18, see chapter “Photoinduced and Microbial
Generation of Hydrogen Peroxide and Organic Peroxides in Natural Waters”),
which could induce the photo-Fenton reaction in the presence of Fe or produce
HO
• by direct photolysis (Nakatani et al. 2007; Mostofa KMG and Sakugawa
H, unpublished data). An alternative explanation for the production of HO • from
DOM is the oxidation of water by the excited triplet states ( 3 DOM*) (Brigante
et al. 2010).
In lake water the production rates of HO
• are very variable, ranging from
1.8 × 10 –13 to 4.6 × 10 –11 M s –1 (Table 2). The HO
• photo-production depends
on the irradiation wavelength. For instance, the formation rate of HO
• observed on
extracted lake DOM under sunlight is higher [(1.6–1.8) × 10 –10 Ms –1 at 308 nm]
K. M. G. Mostofa et al.
According to Eq. 2.7, the plot of 1/r P versus 1/[B] should be straight line (Takeda
et al. 2004) and k ′
SC
/k B can be calculated from the slope and intercept of the plot.
Thus, F B,HO can be calculated with Eq. 2.6 using the values of k ′
SC
/k B and [B].
2.5 Levels of Photoinduced Generation of HO
•
in Natural Waters
The production rates of HO
• that have been estimated in a variety of waters, in
the presence of standard chemical species (NO 2
– , NO 3
– and H 2 O 2 ) or of standard organic substances under sunlight are summarized in Table 2 (Mopper and
Zhou 1990; Takeda et al. 2004; Zepp et al. 1987; Haag and Hoigné 1985; White
et al. 2003; Arakaki and Faust 1998; Nakatani et al. 2007; Mostofa KMG and
Sakugawa H, unpublished data; Nakatani et al. 2004; Qian et al. 2001; Allen et
al. 1996; Mabury 1993; Grannas et al. 2006; Anastasio and Newberg 2007). The
rates are typically varied in a range from 10 –7 to 10 –10 M s –1 in aqueous solution (Table 2). Production rates in rivers are (0.6–7.5) × 10 –11 M s –1 in upstream
waters, (0.4–7.4) × 10 –8 M s –1 in upstream waters contaminated with AMD,
(1.0–2.9) × 10 –11 M s –1 in non-polluted river waters, 2.4 × 10 –11 M s –1 in
Ogeechee River, (2.0–6.0) × 10 –10 M s –1 in Wetland on Lake Erie and Artificial
Agricultural wetland, 6.4 × 10 –11 M s –1 in Rice field water, (2.0–17.0) × 10 –
10 M s –1 in Satilla River and Pine Barrens that have iron-rich waters (Table 2). It is
noticeable that the production rates of HO
• are higher by two to five orders of magnitude in stream waters contaminated with AMD (Allen et al. 1996) than in typical
river waters. Such an effect might be caused by the photo-Fenton reaction that is
considerably favored in the presence of elevated iron contents (Allen et al. 1996;
McKnight et al. 1988). Similarly, high production rates of HO
• have been observed
in Satilla River water (White et al. 2003), where more than 70 % of the total HO
•
production is accounted for by the photo-Fenton reaction. Therefore, the latter process is expected to be the main contributor to HO
• photo-production in iron-rich
waters. In contrast, upstream waters mainly contain DOM components (mostly fulvic and humic acids) that are the major contributors to HO
• photo-production in
these systems. A possible pathway that yields HO
• from DOM is the photoinduced
formation of H 2 O 2 (Eqs. 3.13–3.18, see chapter “Photoinduced and Microbial
Generation of Hydrogen Peroxide and Organic Peroxides in Natural Waters”),
which could induce the photo-Fenton reaction in the presence of Fe or produce
HO
• by direct photolysis (Nakatani et al. 2007; Mostofa KMG and Sakugawa
H, unpublished data). An alternative explanation for the production of HO • from
DOM is the oxidation of water by the excited triplet states ( 3 DOM*) (Brigante
et al. 2010).
In lake water the production rates of HO
• are very variable, ranging from
1.8 × 10 –13 to 4.6 × 10 –11 M s –1 (Table 2). The HO
• photo-production depends
on the irradiation wavelength. For instance, the formation rate of HO
• observed on
extracted lake DOM under sunlight is higher [(1.6–1.8) × 10 –10 Ms –1 at 308 nm]