Environmental Engineering Reference
In-Depth Information
slowed the rate of photolysis. For example, experiments performed with con-
centrations4,8,16,and24 mg L
-1
of HA produced rate constants of 0.0392,
0.0360, 0.0324, and 0.0281 h
-1
, respectively. The same tendency has been
observed for FA. The rate constants decreased as the concentration of FA in-
creased: 0.0277, 0.0233, 0.0195, and 0.0171 h
-1
at concentration of 4, 8, 16, and
24 mg L
-1
, respectively. The decrease in the rate of photodegradation could
be due to either DOM competing with dichlofluanid for the available pho-
tons or to binding between DOM and dichlofluanid. The very low solubility of
the compound in water (2 mg L
-1
)anditshighoctanol
water partition coef-
ficient (
K
ow
= 3.7), indicate that this biocide has a tendency to associate with
particulate matter.
The main degradation products occurred from photodegradation, hydro-
lysis, and anaerobic degradation were
N
,
N
-dimethyl-
N
-phenyl-sulfamide
(DMSA),
N
-dichlorofluoromethylthio-aniline, and aniline [34, 35, 37]. Their
structures are shown in Fig. 3.
DMSA is the major degradation product of dichlofluanid in biotic and
abiotic processes, arising from the N - Sbondcleavageandtherearrange-
ment of the
N
,
N
dimethyl sulfonyl group in the
para
position. In addition,
another minor peak was identified and associated to dichlorofluoromethane,
which arises from the N - S bond cleavage of dichlofluanid. Loss of the
N
,
N
dimethylsulfonamyl SO
2
N(CH
3
)
2
group from dichlofluanid results in the for-
mation of
N
-dichlorofluoromethylthio-aniline.
/
3.3
Irgarol 1051
Irgarol 1051(2-methylthio-4-
tert
-butylamino-6-cyclopropylamino-
s
-triazine)
is considered to be non-biodegradable [38] and its degradation in sea-
water and freshwater is slow, with a half-life of about 100 and 200 days,
respectively [39]. However, the detection of irgarol degradation product (2-
methylthio-4-
tert
-butylamino-6-amino-
s
-triazine, known also as GS26575)
demonstrates that it could undergo environmental transformation in aquatic
ecosystems. Solar photodegradation of irgarol 1051 has been proposed as
themostpossibleenvironmentalprocesswhilestudieshaveshownthat
this biocide undergoes direct or indirect photodegradation with the for-
mation of the
N
-dealkylated derivative (GS26575) as the major degrada-
tion product [40-43]. Irgarol 1051 and GS26575 are shown to demonstrate
a similar seawater half-life [44], suggesting that GS26575 has a greater en-
vironmental persistence than irgarol 1051 [45]. However, these data con-
flict with other studies which have shown that GS26575 was at gener-
ally lower concentrations than the parent compound [46], which suggests
that the environmental transformation rate of irgarol 1051 is relatively
slow and that the rate of GS26575 degradation is greater than that of its
formation.
