Chemistry Reference
In-Depth Information
higher concentrations (7 and 20 pmol/L in the Atlantic
and Pacifi c, respectively) in the deeper waters. The
concentrations of silver are closely correlated to silicate
concentrations (Flegal
et al
., 1995).
Silver is emitted into the aquatic environment from
photographic industries and mining activities and into
the atmosphere by combustion of fossil fuels, leading
to a relatively high mobilization factor of 83 (Lantzy
and Mackenzie, 1979).
The accumulation and toxicity of silver has been
reviewed by (Ratte, 1999).
during the 1970s and 1980s in many countries, and
they have, likewise, been used to prevent fouling of
equipment in marine aquaculture.
However, tributyltin (TBT) is a highly toxic chemi-
cal, and the adverse effects of the chemical reaches far
outside the ship hulls in the aquatic ecosystems.
8.15.2.2 Use and Dispersal of TBT
Organic tin compounds are used for many purposes,
but of the approximately 35,000 tons that were used
globally in the middle of the 1980s, 9% (in the form of
TBT) was used as antifouling chemical in paints for
ships. Approximately two thirds were used (mainly in
the form of dibutyltin) as additive in PVC (Fent, 1996).
The TBT is formulated in the ship's paint in a way
such that a gradual liberation to the water phase takes
place. In areas with intense leisure time boating, a
marked seasonal variation in the TBT concentrations
of the water and sediments is observed; the concentra-
tion increases during summer when the leisure time
boats are in the water (Blanck and Dahl, 1996). The TBT
concentrations are highest around harbors and major
shipping routes.
8.15 Tin
8.15.1 Inorganic Tin
Tin exists in seawater as Sn(II) and Sn(IV). Surface
and deep seawater concentrations of 0.5-5 and 0.2 ng/L,
respectively, have been reported (Bruland, 1983).
Tin has been discharged into the environment from
tin mining, and elevated concentrations of tin have
been registered in sediment dwelling organisms in
coastal areas affected by drainage from operating and
abandoned tin mines (Bryan
et al
., 1980). The anthro-
pogenic mobilization factor for tin is 8.3 (Lantzy and
Mackenzie, 1979).
However, the largest ecotoxicological problems
caused by tin compounds are associated with the use
of organic tin compounds and especially the use of
tributyltin in antifouling paints.
8.15.2.3 Uptake and Metabolization of TBT
The chemical character of TBT is dominantly non-
polar (the
n
-octanol/water partitioning coeffi cient is
approximately 5600), and the chemical is accumulated
in aquatic organisms to concentrations which for fi sh
typically are approximately 200 times higher than the
concentration in the ambient seawater, whereas mol-
luscs such as snails and mussels may concentrate the
compound to concentration factors as high as 50,000-
100,000. Equilibrium between TBT in the seawater
and the tissues is reached after 2-3 months (Bryan
et
al
., 1987). Snails and mussels have a low capacity to
metabolize TBT, and it is lost from dog whelks
Nucella
lapillus
with a half-life of 50-100 days.
Higher organisms may metabolize TBT by hydroxy-
lating and subsequently eliminating the butyl groups
one by one such that the TBT is metabolized to dib-
utyltin and further to monobutyltin and inorganic tin,
which are all less toxic than TBT (Lee, 1991).
In seawater, TBT is relatively quickly degraded by
bacteria and algae to mono- and dibutyltin (Lee
et al
.,
1989). The half-life for TBT in seawater is in the range of
days to weeks, whereas the half-life in sediments may
be up to 6 months or longer (Seligman
et al
., 1986).
8.15.2 Tributyltin (TBT)
8.15.2.1 TBT as Antifouling Agent
Since man began to use ships as means of transpor-
tation, seafarers have had to fi ght fouling of the water-
covered parts of the ships. The fouling with algae
and barnacles may affect speed and stability, whereas
attacks by shipworm (which is a mussel species) and
other boring animals might destroy the woodwork
of the ships. As far back as 300 years BC, there were
descriptions of ships that had the water-covered parts
protected against fouling with plates of lead. In the
17th and 18th century, copper plates were used for the
same purpose, and around 1830, painting of ships with
copper oxide-containing paints was initiated.
Many different toxic compounds (organic mercury
compounds, arsenic compounds, etc.) have been used
besides copper oxide, and in the 1960s, the use of
organic tin compounds—especially tributyltin oxide—
in ship painting was initiated.
Because of their broad versatility and high effi ciency,
the organic tin compounds have been the most wide-
spread components to protect ships against fouling
8.15.2.4 Adverse Effects of TBT in the Marine
Environment
Of the species investigated so far, molluscs (gastro-
pods, mussels) seem to be the most sensitive toward
TBT.
