Environmental Engineering Reference
In-Depth Information
a half-life of 8.4 days according to Callow and Willingham [38] and has a res-
idence time of 5 days according to Ranke [56]. The hydrolytic half-life was
>
720 h for a pH 7 buffered solution while degradation in natural seawater
containing microorganisms showed a half-life of less than 24 h. Anaerobic
half life of
<
0.5 days was calculated by Thomas et al. [37], increasing when
the compound was introduced to sediments associated with paint particles.
A summary of Sea-Nine 211 half-lives in various environmental matrices was
reported by Willingham and Jacobson [57]. Biological degradation is consid-
ered to be over 200 times faster than hydrolysis and photolysis [57], which
contributes to a lesser extent to its degradation in the environment. Pho-
tolysis half-life experiments, conducted at pH 7, gave values of
t
1
/
2
= 322 h
and
t
1
/
2
= 315 h, respectively [34, 58]. The rapid degradation reduces the con-
centration to significantly below toxic levels. Its metabolites are ring-opened
structures and their toxicity is reduced by 4-5 orders of magnitude [59, 60].
Phototransformation of Sea-Nine 211 in natural waters under natural
sunlight [34, 60] was significantly enhanced following the order: lake water
>
river water
>
sea water
>
distilled water showing a strong dependence on
the composition of the irradiated media. Simulated solar irradiation for 30 h
resulted in a 77%, 87%, 92%, and 97% decline of Sea-Nine 211 concentration
in distilled, sea, river, and lake water, respectively. Experiments with concen-
trations of 4, 8, 16, and 24 mg L
-1
of HA produced rate constants of 0.0690,
0.0776, 0.0835, and 0.1008 h
-1
, respectively, resulting in 89%, 91%, 93%, and
96% decline in Sea-Nine 211 concentration. The same tendency has been
observed for FA. The rate constants increased as the concentration of FA in-
creased: 0.0624, 0.0664, 0.0726, and 0.0771 h
-1
at concentrations of 4, 8, 16,
and 24 mg L
-1
, respectively. As the DOM and nitrate concentration in natural
waters increases, a faster degradation rate is observed. This rapid photo-
transformation in all experiments is attributed to the presence of naturally
occurring photosensitizers in natural waters. Energy, electron, and hydrogen
atom transfer reactions as well as reactions with photochemically generated
free radicals may be very significant in the environmental phototransforma-
tion of Sea-Nine 211, which does not absorb strongly above 290 nm.
Two main transformation pathways are observed during the phototrans-
formation of Sea-Nine 211 according to the proposed reaction scheme
(Fig. 5). The first pathway (a) involves cleavage of the isothiazolone ring
and subsequent oxidation of the resulting alkyl metabolites [61] thus,
N
-
n
-
octyl acetamide is formed. The cleavage of the weakest bond of the molecule
(N - S) of Sea-Nine 211 and subsequent dechlorination and hydroxylation
results in
N
-
n
-octyl hydroxypropionamide. Further oxidation yields the for-
mation of
N
-
n
-octyl malonamic acid, which is then decarboxylated to give
the corresponding
N
-
n
-octyl acetamide. The presence
N
-
n
-octyl hydrox-
ypropionamide and
N
-
n
-octyl malonamic acid was not identified in either
sample [34, 60]. The above transformation pathway was also observed during
analysis of the dark control samples in an outdoor experiment, indicating that
