Environmental Engineering Reference
In-Depth Information
polymer backbone by ester links (
Figure 2.15
) [66]. TBT kills settling organisms and
also makes the surface smoother [29]. Originally zinc oxide was used as the soluble
pigment particle. This was later replaced by cuprous oxide. When immersed in water,
the soluble pigment particles start to dissolve. Because TBT methacrylate and methyl
methacrylate (MMA) in the paint are hydrophobic, they stop the seawater from
piercing the paint, and therefore only ill the pores generated after the dissolution of
the soluble pigments. In slightly alkaline conditions, the TBT portion gets cleaved
by slow hydrolysis of the carboxyl-TBT linkage, and thus, releases the biocide into
the water. Gradually, the seawater dissolves more pigments and expands the region
(the leached layer) (
Figure 2.16
) [2, 67, 29].
The partially reacted brittle polymer backbone gets easily eroded by the ocean currents
and exposes the less reacted paint surface. This is called the SP effect [2, 67].
TBT is rapidly taken up by the bacterial cells because TBT is extremely lipid-soluble.
Within the cells TBT inhibits respiration and photosynthesis [29]. Although TBT-SPC
paints were extremely successful, evidence of environmental side effects on marine life
led to a worldwide ban of the application of these paints to any ship from 2003 [68].
TBT at very low concentrations have been shown to affect non-targeted organisms,
including shellish. The disappearance of
Nucella lapillus
from rocky shores and the
imposition of male sexual characters on females at very low concentrations of 1 ng/l
has been attributed to the extensive use of TBT-SPC paints [29].
H
2
H
2
C
C
C
C
O
C
O
C
O
O
CH
3
CH
2
Sn
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
CH
2
CH
2
CH
2
CH
3
Figure 2.15
Chemical formula of a repeating unit of a copolymer of TBT
methacrylate and MMA
