170
A.R.D. Stebbing . R.I. Willows
was incorporated in antifouling paints as a broad spectrum biocide, to keep vessels
free of the full range of sessile communities (algae, barnacles, hydroids etc.). It was also
used as an antifoulant on salmon rearing pens. It proved toxic to marine life at such
low concentrations that it was probably the first compound for which it was clear that
the sea had no assimilative capacity. It is unfortunate therefore that the research programme initiated in the UK was almost exclusively autoecological; the effect of TBT
on communities in polluted waters was overlooked, although anecdotal evidence for a
wider impact was strong.
Since legislation has effectively controlled the use of TBT on small vessels and the
impact ofTBT in coastal and estuarine waters has been controlled, attention has turned
to the effect of TBT originating from large vessels through studies of imposex in dog
whelks around the North Sea. The species was once very widespread and the effects
ohserved during a survey of the entire North Sea coastline in 1992 are likely to prove
catastrophic for the species. Offshore, in the German Bight, TBT has been shown to
occur in the sea surface microlayer at concentrations in excess of the UK EQS of 2 ng 1-1
(Hardy and Cleary 1992), while in the southern North Sea high incidences of imposex
have been found in benthic whelk (Buccinum undatum) populations living in a
deepwater offshore shipping lane (Mensink et al. 1996).
The contribution to the depression of scope for growth in mussels due to TBT
(Widdows et al. 1990) is significant in increasing the taxonomic breadth of organisms
known to be affected in the environment. The results also show the biological impact
of TBT in areas (Thames estuary) where dog whelks no longer occur. In the case of
TBT, no case needs to be made for the deployment of biological indices with appropriate chemistry, as it has already been established that imposex is a specific biomarker
for TBT pollution, to the extent that the degree and frequency of imposex is widely
used as a proxy for chemical analyses of TBT.
8.6
Biological Evidence for Pollution Gradients in the North Sea
We now consider examples from the North Sea where the use of biological techniques
has demonstrated pollution gradients in terms of the biological impact of contaminants. At the same time these examples demonstrate the extent to which the capacity
of the North Sea to assimilate anthropogenic inputs of wastes and effluents is being
approached or exceeded.
8.6.1
Gradients Related to Oil Rigs
The North Sea not only accepts inputs of contaminants from the bordering riparian states,
it also receives direct inputs from certain offshore activities such as the disposal of sewage sludge, the use of incinerator ships, and as a consequence of the offshore oil and
gas industry. While the first two sources of input are now subject to stringent control, oil
and gas production and exploration will continue for the foreseeable future. At first it was
believed that the major environmental impact of this industry would be a consequence
of oil inputs from production platforms. In the event, the largest impacts have resulted
from the disposal around the rigs of discharg~d drill-cuttings (Kingston 1992). Initial
A.R.D. Stebbing . R.I. Willows
was incorporated in antifouling paints as a broad spectrum biocide, to keep vessels
free of the full range of sessile communities (algae, barnacles, hydroids etc.). It was also
used as an antifoulant on salmon rearing pens. It proved toxic to marine life at such
low concentrations that it was probably the first compound for which it was clear that
the sea had no assimilative capacity. It is unfortunate therefore that the research programme initiated in the UK was almost exclusively autoecological; the effect of TBT
on communities in polluted waters was overlooked, although anecdotal evidence for a
wider impact was strong.
Since legislation has effectively controlled the use of TBT on small vessels and the
impact ofTBT in coastal and estuarine waters has been controlled, attention has turned
to the effect of TBT originating from large vessels through studies of imposex in dog
whelks around the North Sea. The species was once very widespread and the effects
ohserved during a survey of the entire North Sea coastline in 1992 are likely to prove
catastrophic for the species. Offshore, in the German Bight, TBT has been shown to
occur in the sea surface microlayer at concentrations in excess of the UK EQS of 2 ng 1-1
(Hardy and Cleary 1992), while in the southern North Sea high incidences of imposex
have been found in benthic whelk (Buccinum undatum) populations living in a
deepwater offshore shipping lane (Mensink et al. 1996).
The contribution to the depression of scope for growth in mussels due to TBT
(Widdows et al. 1990) is significant in increasing the taxonomic breadth of organisms
known to be affected in the environment. The results also show the biological impact
of TBT in areas (Thames estuary) where dog whelks no longer occur. In the case of
TBT, no case needs to be made for the deployment of biological indices with appropriate chemistry, as it has already been established that imposex is a specific biomarker
for TBT pollution, to the extent that the degree and frequency of imposex is widely
used as a proxy for chemical analyses of TBT.
8.6
Biological Evidence for Pollution Gradients in the North Sea
We now consider examples from the North Sea where the use of biological techniques
has demonstrated pollution gradients in terms of the biological impact of contaminants. At the same time these examples demonstrate the extent to which the capacity
of the North Sea to assimilate anthropogenic inputs of wastes and effluents is being
approached or exceeded.
8.6.1
Gradients Related to Oil Rigs
The North Sea not only accepts inputs of contaminants from the bordering riparian states,
it also receives direct inputs from certain offshore activities such as the disposal of sewage sludge, the use of incinerator ships, and as a consequence of the offshore oil and
gas industry. While the first two sources of input are now subject to stringent control, oil
and gas production and exploration will continue for the foreseeable future. At first it was
believed that the major environmental impact of this industry would be a consequence
of oil inputs from production platforms. In the event, the largest impacts have resulted
from the disposal around the rigs of discharg~d drill-cuttings (Kingston 1992). Initial