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Tributyltin (TBT)
Risk Assessment Document |
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ABSTRACT
This risk assessment report provides an evaluation of
the risk from TBT to giant Pacific oysters and short-neck
clams in Tokyo Bay.
TBT has been found to have adverse effects not only on
organisms attached to vessel hulls, but also on marine
organisms in general. Because TBT may also affect the
environment and enter the human food chain, many countries
have enforced regulations which have led to a decrease
in TBT concentration in the aquatic environment.
However, as Cardwell et al. (1999) indicated, it is unclear
whether this decrease in TBT concentrations has led to
a reduction in risk sufficient to protect marine organisms.
In this risk assessment, Tokyo Bay was selected as the
study area because it is one of the most congested maritime
areas in Japan. It has an estimated annual traffic volume
of 240,000 vessels. The short-neck clam (Ruditapes philippinarum),
which is the main fishery resource in the Tokyo Bay area,
and the giant Pacific oyster (Crassostrea gigas), which
is very sensitive to TBT and an important species inhabiting
the study area were selected as the assessment organisms.
The risks posed by TBT to these organisms were quantitatively
assessed for the past (1990), the present (2000), and
the period before complete regulation (2007).
This risk assessment report does not address the TBT risk
to marine mammals and humans.
The assessment endpoint was established at the level at
which TBT has no effect on giant Pacific oysters and short-neck
clams. These effects were "abnormal calcification" and
"growth reduction" respectively.
The no observed effect concentration (NOEC) used for this
assessment was estimated using previously published values
of the least observed effect concentration (LOEC) for
the giant Pacific oyster and the short-neck clam based
on the LOEC/NOEC ratio of Mercenaria mercenaria –
a closely related species. The estimated NOEC values were
1.0 ng/L and 4.1 ng/L, respectively, as a TBT group. The
risk was assessed using the margin of exposure (MOE),
which is the ratio of the NOEC to the estimated environmental
concentration (EEC), as calculated by gthe chemical fate
model.h
Assessment results for the short-neck clams for 1990,
suggested that growth reduction was occurring throughout
the year in the Ara River estuary and during winter in
other habitats. In the case of the giant Pacific oysters
it is highly likely that abnormal calcification occurred
throughout the year in all habitats.
While the risk of growth reduction in short-neck clams
had decreased by 2000, the results for the giant Pacific
oyster indicated that there were still some habitats where
abnormal calcification could occur.
The risk assessment model predicted that both growth reduction
in the short-neck clam and abnormal calcification in the
giant Pacific oyster are highly unlikely in 2007.
As for the alternatives to TBT, some paints are now under
development by various manufacturers but little information
is yet available on any possible harmful effects. Therefore,
the function, toxicity, bioaccumulative properties, economic
trade-offs and environmental impacts of these TBT alternatives
still need to be examined.
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This Tributylin (TBT) Risk Assessment Document
was produced by the Development of Chemical Substance
Risk Assessment and the Risk Assessment Procedure Program
by the New Energy and Industrial Technology Development
Organization. |
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full text in English [zip file, 8MB]
27.April.2005 |
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