311
Photoinduced and Microbial Degradation
production of HO • (Vione et al. 2004) and leads to high photoinduced degradation
of DOM in iron-rich waters. Addition to the water of fluoride ion or deferoxamine
mesylate (DFOM) can form unreactive Fe 3+ complexes, inhibiting iron photoreduction and slowing down the photoinduced degradation of DOM (Gao and Zepp
1998; Wu et al. 2005). The photoinduced formation of DIC, CO and NH 4
+ has been
greatly affected by the addition of fluoride ion to the water of the River Satilla (Gao
and Zepp 1998). Thus, the photo-Fenton reaction plays an important role in natural
waters, especially in acidic waters. The photoinduced degradation rate constant of
humic acid is significantly decreased by the addition of fluoride, but that of fulvic
acid is not affected (Wu et al. 2005). Dissolved Fe is thus thought to play an important role in the photoinduced degradation of humic acid rather than fulvic acid. Due
to the higher aromaticity of humic acid as compared to fulvic acid (30–51 % of aromatic carbon vs. 14–20 %) (Malcolm 1985; Gron et al. 1996), humic acid is more
susceptible to react with HO
• which is generated from the photo-Fenton reaction (Fe
2+ + H 2 O 2 → HO
• + − OH + Fe 3+ ) (Zepp et al. 1992; Senesi 1990; Minakata et al.
2009; Chen and Pignatello 1997). Therefore, it is likely that humic acid is the DOM
component that undergoes the fastest photoinduced degradation in natural waters.
3.4 Occurrence and Quantity of NO 2
− and NO 3
− Ions
Photoinduced degradation of DOM can be affected by the occurrence and concentration levels of NO 2
− and NO 3
− ions, both of which are efficient in the production of HO
• upon photolysis in waters (see also chapter “Photoinduced Generation
of Hydroxyl Radical in Natural Waters”) (Zafiriou and True 1979a, b; Takeda
et al. 2004; Vione et al. 2006; Mack and Bolton 1999; Nakatani et al. 2004; Chin
et al. 2004). Contribution of HO
• production in sewage polluted rivers is 48–80 %
from NO 2
− and 2–19 % from NO 3
− , but the contribution is 6–26 % and 1–49 %,
respectively, in upstreams and clean rivers (Takeda et al. 2004; Nakatani et al.
2004). In anthropogenically polluted Rhône River Delta (S. France) and Lake
Piccolo (NW Italy) the contribution of HO
• production is accounted for by NO 2
−
(62–63 %) and NO 3
− (27–38 %), while in the unpolluted and remote Lake Goose
and Lake Divide (Wyoming, USA) the contribution of nitrate and nitrite is relatively lower, 0–11 % and <0.5 %, respectively (Minero et al. 2007). In seawater
NO 2
− is the major source of HO
• in Seto Inland Sea (7–75 %) and Yellow Sea
(10–44 %) compared to NO 3
− (<1 % and 0.4–8 %, respectively) (Takeda et al.
2004). The two anions (NO 2
− and NO 3
− ) collectively are dominant sources in
both river and seawater, while their role in lake water is less important (Vione
et al. 2006). Natural waters that include high concentration levels of NO 2
− and
NO 3
− could induce degradation of DOM by photoinduced production of HO
•
.
However, it has been found that the rate of mineralization of DOM in acidified lake
water far exceeds that rate of HO
• generation by all the sources, which suggests
that HO
•
-independent processes (tentatively, photolysis of Fe(III)-DOM complexes) may also play an important role in DOM mineralization (Vione et al. 2009).
Photoinduced and Microbial Degradation
production of HO • (Vione et al. 2004) and leads to high photoinduced degradation
of DOM in iron-rich waters. Addition to the water of fluoride ion or deferoxamine
mesylate (DFOM) can form unreactive Fe 3+ complexes, inhibiting iron photoreduction and slowing down the photoinduced degradation of DOM (Gao and Zepp
1998; Wu et al. 2005). The photoinduced formation of DIC, CO and NH 4
+ has been
greatly affected by the addition of fluoride ion to the water of the River Satilla (Gao
and Zepp 1998). Thus, the photo-Fenton reaction plays an important role in natural
waters, especially in acidic waters. The photoinduced degradation rate constant of
humic acid is significantly decreased by the addition of fluoride, but that of fulvic
acid is not affected (Wu et al. 2005). Dissolved Fe is thus thought to play an important role in the photoinduced degradation of humic acid rather than fulvic acid. Due
to the higher aromaticity of humic acid as compared to fulvic acid (30–51 % of aromatic carbon vs. 14–20 %) (Malcolm 1985; Gron et al. 1996), humic acid is more
susceptible to react with HO
• which is generated from the photo-Fenton reaction (Fe
2+ + H 2 O 2 → HO
• + − OH + Fe 3+ ) (Zepp et al. 1992; Senesi 1990; Minakata et al.
2009; Chen and Pignatello 1997). Therefore, it is likely that humic acid is the DOM
component that undergoes the fastest photoinduced degradation in natural waters.
3.4 Occurrence and Quantity of NO 2
− and NO 3
− Ions
Photoinduced degradation of DOM can be affected by the occurrence and concentration levels of NO 2
− and NO 3
− ions, both of which are efficient in the production of HO
• upon photolysis in waters (see also chapter “Photoinduced Generation
of Hydroxyl Radical in Natural Waters”) (Zafiriou and True 1979a, b; Takeda
et al. 2004; Vione et al. 2006; Mack and Bolton 1999; Nakatani et al. 2004; Chin
et al. 2004). Contribution of HO
• production in sewage polluted rivers is 48–80 %
from NO 2
− and 2–19 % from NO 3
− , but the contribution is 6–26 % and 1–49 %,
respectively, in upstreams and clean rivers (Takeda et al. 2004; Nakatani et al.
2004). In anthropogenically polluted Rhône River Delta (S. France) and Lake
Piccolo (NW Italy) the contribution of HO
• production is accounted for by NO 2
−
(62–63 %) and NO 3
− (27–38 %), while in the unpolluted and remote Lake Goose
and Lake Divide (Wyoming, USA) the contribution of nitrate and nitrite is relatively lower, 0–11 % and <0.5 %, respectively (Minero et al. 2007). In seawater
NO 2
− is the major source of HO
• in Seto Inland Sea (7–75 %) and Yellow Sea
(10–44 %) compared to NO 3
− (<1 % and 0.4–8 %, respectively) (Takeda et al.
2004). The two anions (NO 2
− and NO 3
− ) collectively are dominant sources in
both river and seawater, while their role in lake water is less important (Vione
et al. 2006). Natural waters that include high concentration levels of NO 2
− and
NO 3
− could induce degradation of DOM by photoinduced production of HO
•
.
However, it has been found that the rate of mineralization of DOM in acidified lake
water far exceeds that rate of HO
• generation by all the sources, which suggests
that HO
•
-independent processes (tentatively, photolysis of Fe(III)-DOM complexes) may also play an important role in DOM mineralization (Vione et al. 2009).