Environmental Engineering Reference
In-Depth Information
and antifouling paints containing tar, grease, sulphur pitch and brimstone
were developed. One hundred years later, copper sheathing was used, which
prevented fouling through dissolution of the toxic metal ions. It was in the
mid-1800s that antifouling paints really began to develop. This was attributed
to the introduction of iron ships on which copper sheathing caused corro-
sion of the iron. Paints were prepared by adding toxicants such as copper
oxide, arsenic, and mercury oxide to resin binders. These proved to be effect-
ive. Following the Second World War, the introduction of petroleum-based
resins and health and safety concerns relating to organo-arsenicals and mer-
curials meant that synthetic copper based paints became most popular. In
the late 1950s and early 1960s, a new formulation using tributyltin (TBT)
proved to be excellent in the prevention of fouling. This is where our story
begins.
The efficiency of TBT, especially in “self-polishing” formulations, was re-
markable, and the application of TBT-based paints rapidly expanded. Added
bonuses also included the fact that it did not cause galvanic corrosion on
aluminium hulls, it was colourless, and periods between dry-docking were
extended. Whilst this appears ideal, unfortunately, the use of the compound
had environmental consequences. As the popularity of TBT grew, oyster pro-
ducers in France were reporting shell malformations, which rendered their
produce worthless. This effect was traced to TBT in the water. In Arca-
chon Bay (France) alone, it has been estimated that TBT provoked a loss in
revenue of 147 million US dollars through reduced oyster production [2].
Wild populations of other mollusc species were also found to be affected at
very low concentrations (
<
10 ng L
-1
) [3]. Female dog whelks (
Nucella
sp.)
were shown to develop male characteristics (termed imposex) at these lev-
els [4]. Imposex was also reported in the open North Sea [5]. Although
dealt with in more detail in a later section, national and international leg-
islation was introduced to restrict the use of TBT. In 1989, the European
Community introduced a directive to prevent the use of TBT on boats
under 25 m [6]. This provoked paint manufacturers and chemical compa-
nies to develop and sell a range of agents for new antifouling paints for
the “small boat” market. Although usually added to copper-based formu-
lations, they were also added to TBT-based paints to enhance efficacy for
larger vessels. These compounds have since been termed “booster biocides”.
Examples of the types of compounds that were used or promoted for use
included:
•
2-methylthio-4-tertiary-butylamino-6-cyclopropylamino-s-triazine
(Irgarol 1051);
•
1-(3,4-dichlorophenyl)-3,3-dimethylurea (diuron);
•
4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (SeaNine 211);
N
-dichlorofluoromethylthio-
N
,
N
-dimethyl-
N
-phenylsulphamide
(dichlofluanid);
•
