Environmental Engineering Reference
In-Depth Information
Table 13
Degradation of TBT by marine algae [97]
a
Concentration
b
,
µ
gL
-1
TBT
Algae species
DBT
Hydroxylated Polar
products
products
Diatoms-Bacillariophyta
Skeletonema costatum
0.1
0.2
0.1
0.04
Chaetoceros curvisetus
0.20
0.11
0.05
nd
Dinoflagellates-Pyrrhophyta
Procentrum triestinum
0.30
0.05
0.01
nd
Golden algae-Chrysophyta
Isochrysis galbana
0.40
nd
nd
nd
Cricosphaera ricoco
0.35
0.02
nd
0.01
Green algae-Chlorophyta
Dunaliella tertiolecta
0.40
0.05
nd
nd
a
Algae were cultured in seawater media. [
14
C] TBT was added to cultured algae to give
an initial concentration of 0.04
µ
gL
-1
. After 2 days the algae culture containing TBT was
extracted and analyzed for TBT and metabolites
b
nd, not detected (
<
0.01
µ
gL
-1
)
The fate of TBT with a subtropical seagrass bed including
Thalassia tes-
tudinum
and associated fauna was studied over 3 or 6 weeks by dosing weekly
for 24 hwith
14
C-labeled TBT. The TBT was rapidly removed from the wa-
ter column (half-life of 10-20 h), primarily through absorption onto sediment
and seagrass leaves. By contrast, 12 microcosms that received similar TBT
doses but that contained only seawater had TBT removal half-life of 2-7 days.
The accumulation of TBT in sediment and grasses was temporary, however, at
harvest, the seagrass microcosms contained just 20-30%ofthe
14
Cthathad
been adsorbed or assimilated during dose periods, and half of this label was
in degradation products. The principal mechanism of TBT loss from solids
was degradation followed by the desorption of degradation products (largely
monobutyltin and CO
2
which are more soluble than TBT) [136].
7
Conclusions
The organotin compounds have a high affinity to sediment and organisms.
Hence, the organotin compounds tend to be accumulated in the sediment and
organisms, though they are degraded relatively rapidly in seawater or fresh-
water mainly by microorganisms.
Many countries started to ban the use of the organotin antifoulants for
small vessels in the late 1980s. Consequently, in France, UK, USA, Canada,
Australia, Japan, Spain, Norway, Switzerland, etc., decreases in TBT have been
