Environmental Engineering Reference
In-Depth Information
of the photolytic degradation of TPT. The microbial degradation of a radi-
olabeled TPT in soil or sediment samples was slow, with only 5%degraded
during a 14 day incubation period.
With regard to the organotins in aqueous systems, less is known about
the patterns of degradation. The reason for this is that, in general, with the
organotin compounds, their aqueous solubility decreases as the length of the
alkyl chain increases, and tributyl- and triphenyltin compounds have solu-
bility's typically of only a few ppm as shown in Table 2. Maquire et al. [45]
showed that the UV degradation of tributyl species in water occurs in nat-
ural sunlight and the environmental half-life of tributyltin oxide (TBTO) in
water was estimated to be approximately 89 days [45]. Hence, obviously, UV
degradation is only important in situations where the organotins are exposed
to sunlight and is important close to the surface of water because seawater
contains a large amount of suspended solid and the organotins have a high
affinity for the soil and sediment [24].
In Brest naval harbor water from September 1993 to December 1997, the
levels of contamination were more or less the same (14-75 ng L
-1
)during
the four-year study period. The variations of the DBT concentrations showed
a seasonal pattern and had a statistically significant relationship with those of
water temperature [46]. This lends support to the hypothesis of a dominant
effect of microbiological activity (favored by the increase in temperature) in
the degradation of TBT.
A colder temperature slowed the degradation as shown in Table 5 [47-51].
This evidence also shows that the degradation of TBT takes place by micro-
organisms.
Table 5
Degradation of TBT in the marine environment [47-51]
Comments
Initial TBT
Reaction
Half-life
Rate
Refs.
concentration
order
constant
gL
-1
)
(
µ
Natural water
radiolabeled TBT
0.615
First
3.5 days
0.20
/
day
[48]
ambient marine water
0.57
6 days
[49]
natural water
0.8
First
60 days
[49]
(at 5
◦
C)
filtered seawater
0.55
First
2.5 days
0.28
/
day
[50]
Sediment
sediment cores
0.3
First
1.85 years
0.375
/
y
[51]
from a marina
Biota
eelgrass grown in
0.14
First
9.6 days
0.072
/
d
[50]
TBT-spiked seawater
