Environmental Engineering Reference
In-Depth Information
Irgarol photodegradation has been studied in a variety of natural waters
under both natural and simulated solar irradiation [34, 47]. The data demon-
strate that photolysis of irgarol 1051 was lower in environmental waters
compared to distilled water, showing a strong dependence on the constitu-
tion of the irradiated media. After 66 calendar days of daylight exposure
66%, 60%, 57%, and 65% of irgarol 1051 was degraded in distilled, sea, river,
and lake water, respectively, while more than 66%, 57%, 55%, and 53%de-
graded within 48 h under simulated solar irradiation. The presence of DOM
in natural waters inhibits the degradation rate of irgarol 1051. The retarded
photodegradation indicate that organic matter absorbed most of the photons
emitted thereby slowing down direct photochemical reaction of irgarol 1051
(optical filter effect). Photoreaction of the colored dissolved organic matter
(cDOM) in sunlight caused a decrease mostly in the UV-B (280-315 nm) re-
gion. This is very important in the case of irgarol 1051 because it does not
absorb strongly above 320 nm. Another reason may be that irgarol 1051 was
partially bound to dissolved organic matter (log
K
oc
=3.0, log
K
ow
=3.9) by
hydrophobic partitioning or weak van der Waal forces, and so this fraction
was never available for photolysis action.
A recent study of Okamura and Sugiyama [48] investigated irgarol 1051
photolysis in the presence of some photosensitizers. Aqueous solutions con-
taining irgarol or its metabolite GS26575, with or without photosensitizers,
were irradiated using a light source from a UV-A fluorescent lamp for 48 h.
GS26575 was more stable than irgarol when irradiated in the presence of pho-
tosensitizers such as acetone, benzophenone, tryptophan, and rose bengal.
Four types of fulvic acids (FA) and two types of humic acids (HA) puri-
fied from natural soils and river waters were used as photosensitizers at
a concentration of 10 mg L
-1
. Degradation of irgarol 1051 and simultaneous
production of GS26575 were observed in the presence of each of the natu-
ral humic substances tested. The half-lives of irgarol ranged from 6.8 to 39 h
while the maximum concentration of GS26575 (0.35 mg L
-1
)wasobservedin
the presence of HA-I. This shows that the photochemical reaction assisted
by natural humic substances (NHS) may lead to accumulation of GS26575
in natural aquatic environments in agreement with Sakkas et al. [47], who
reported that GS26575 was a major photoproduct among five intermedi-
ates identified in HA
FA solutions under simulated solar light. NHS also
accelerated the photodegradation of irgarol. However, GS26575 was more per-
sistent than the parent compound, which was completely degraded. In the
same study [48] after 48 h of irradiation, irgarol 1051 in river water was de-
graded with simultaneous production of GS26575. On the other hand, when
irgarol 1051 was irradiated in pure water no significant degradation was
observed and GS26575 was not formed, which is in agreement with the ob-
servations of previous studies [42, 47]. Therefore, indirect photosensitized
reactions in natural waters may result in the accumulation of GS26575 in
aquatic environments.
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