Environmental Engineering Reference
In-Depth Information
sea [16]. Studies on the global occurrence of organotins in the last few years
using biota and sediments as pollution markers demonstrate that the decrease
is only marginal in many places [98], but occurred in others [60, 82, 100]. TBT
water concentrations persist for years at levels considered as chronically toxic
to most susceptible organisms [55, 97, 98].
Highest TBT levels were and are still found in and near marinas and
ports due to the use of antifouling paints and painting and depainting op-
erations in docks. Levels in harbor and port waters were in the range of
100-500 ng L
-1
in the mid 1980s. They were significantly higher than in open
surface waters, bays and estuaries where commonly values of up to 50 ng L
-1
were observed. Recent surveys reported similar levels in developing coun-
tries, for instance 32 ng L
-1
in South Korea [101], but also 7 ng L
-1
in Japanese
coastal waters [94]. In general TBT concentrations in seawater are variable.
Much higher levels occur in the surface microlayer [102]. Contamination de-
creased slowly in countries, where TBT containing antifouling paints have
been regulated [54, 63], but the decrease is not significant [97, 103], or even
absent [94, 99]. Where no regulations have been implemented, levels are in-
creasing to the same range as in other countries prior to legislation, as shown
in Asia [70, 75, 84, 86, 87, 104], Oceanian countries, and South America [105].
It is a fact that TBT contamination occurs globally including Asian countries,
Eastern Europe [57], South America or Bahrain, where extremely high lev-
els of 14.7
gL
-1
were reported [64]. Larger vessels lead to contamination
of commercial ports and shipping straits [72], or even the Arctic [92] and
Antarctic [93]. Even after regulation of pleasure boats, large ships, icebrak-
ers and dry-docks may be sources. In 1992, TBT ranged up to 17 ng L
-1
in
estuaries, but in harbors and dry-dock areas the concentrations are often
high, exceeding 100 ng L
-1
. Recent surveys indicate that seawater concentra-
tions exceed the UK environmental quality standard value of 2 ng L
-1
[106].
TBT at levels of 2-7 ng L
-1
was also found in 15% of the offshore water sam-
ples in the North Sea, English Channel, Mediterranean, and off the coast of
Japan.
The TBT decrease is not, or to a lesser extent, observable in sediments and
biota. Temporal trends in a port indicate the decrease of TBT in water, sedi-
ment and biota, particularly for TPT, between 1989-1996 [63]. On the other
hand, data on harbor and estuarine sediments in pleasure boat harbors indi-
cate that TBT residues remain high (Fig. 4). Sediment levels are high in ports
and boat harbors, depending on the boat frequencies, but lower in coastal re-
gions and in some developing Asian countries (Fig. 5). However, this is not
a general rule. Larger Bays, estuarine and harbor areas may be contaminated
in the range of 0.1-2.71
µ
gg
-1
TBT (dry wt) [42]. Recent TBT levels are also
variable and range up to several
µ
gg
-1
(dry wt) in boat harbors, although
considerable variation occurs between different sites (Fig. 5). Most contam-
inated areas are harbors with high vessel activity. A mean of 54 ng g
-1
TBT
was found in 35 sediment samples in a US coastal survey [76]. The contam-
µ
