Environmental Engineering Reference
In-Depth Information
indicating both an increase in photosensitization and in
•
OH processes. Sing-
let oxygen formed during the photolysis reacts with dissolved organic matter
to form peroxide. It is possible that the peroxide formed may generate the hy-
droxyl radicals from the humic solution, which in turn causes dealkylation [52].
2-Methylthio-4-
tert
-butylamino-6-ethylamino-
s
-triazine (compound 4) was
also formed during these series of experiments, apart from the derivatives men-
tioned in distilled water (compounds 2, 3 and 5), showing that in the presence
of DOM both direct and indirect reactions can occur.
The product profile of irgarol photodegradation in natural waters was
very similar to that of the HA
FA system, which strongly suggests that DOM
present in natural waters sensitize the photolysis of irgarol 1051, as indicated
by the formation of the dealkylated derivative, diaminohydroxy-
s
-triazine.
However, in this case too, 2-methylthio-4-
tert
-butylamino-6-amino-
s
-triazine
was the main byproduct formed, proving its occurrence in surface waters.
Hall et al. [44] showed the presence of the irgarol 1051 metabolite
(GS26575), increasing from 0.4% at the start of the experiment to 3.6%ofthe
total concentration after 42 days. This good mass balance supports previous
reports that GS26575 is the major degradation product of irgarol 1051 [45].
An experiment to determine the rate of GS26575 removal showed only 74%of
the compound to be present after 42 days. Once again, if a first-order degrada-
tion reaction is applied then a seawater half-life of 82 days can be calculated.
This suggests that the rate of GS26575 degradation is much greater than
that of irgarol 1051 and that under the experimental conditions employed,
GS26575 is not as environmentally persistent as irgarol 1051. On the other
hand, Okamura [43] demonstrated that irgarol was rapidly photodegraded,
in contrast to its major metabolite under the same irradiation conditions.
The results indicated that 78-93% of GS26575 was degraded after exposure
to solar irradiation for 10 months, and thus that it is more persistent than the
parent compound.
In the study of Lam et al. [53] during the HgCl
2
-catalyzed hydrolysis of
irgarol-1051, a new degradation product was identified. The EI-MS of this
unknown product, hereby designated as M2, is similar to that obtained by
Ogawa et al. [54]. With careful chromatographic separation and purifica-
tion, M2 was successfully isolated and identified as 3-[4-
tert
-butylamino-6-
methylthiol-
s
-triazin-2-ylamino]-propionaldehyde - the
N
-propionaldehyde
derivative of M1. The presence of this compound was also detected in the
coastal waters of Hong Kong, indicating that the environmental degradation
of irgarol 1051 is more complicated than expected.
/
3.4
Sea-Nine 211
Sea-Nine 211 (4,5-dichloro-2-
n
-octyl-4-isothiazolin-3-one), degrades rapidly
both biologically and chemically in natural seawater [55]. Isothiazolone has
