150
A.R.D. Stebbing . R.I. Willows
used to interpret metal equilibria and behaviour in the marine environment, particularly those of radionuclides (IAEA 1985). For organic chemistry hydrophobic partitioning depends on the organic carbon content of suspended particulate matter; this partitioning can be calculated from the octonol-water partition coefficient (Kow) (Harris
et al. 1993). However, recent fmdings suggest that some polyaromatic hydrocarbons
(PAHs) detected on suspended marine and estuarine particles may not be subject to
particle-water equilibration and that for those important contaminants (see Sections 8.5.1 and 8.6.4 the partition coefficient is not adequately developed as a means of
describing and predicting contaminant behaviour in the environment (Zhou, pers.
comm.), let alone their use for management purposes.
This organic-rich fraction is highly mobile, settling to the bottom in calm conditions and low current speeds, providing a superficial covering of a few mm thickness
in .pepositional areas. However this layer is quickly remobilized and carried up into
the water column by storms and the turbulence they create, only to settle again through
the water column where currents weaken. It is during repeated deposition and
resuspension that particulate organic matter scavenges the water column of many contaminants. Deposited organic material provides the basis for production by benthic
ecosystems. Many species live by removing fine grained particles a few microns in diameter from suspension (e.g. filter feeding bivalves) or from within the sediment itself (e.g. polychaetes and ophiuroids). Since it is this fine fraction to which many contaminants are adsorbed or bound, even where it represents <1% of the total sediment,
these organisms will be exposed to much higher concentrations than those in the sediment as a whole (Kempe et al. 1988). Hence it is likely that organisms will take up and
may concentrate the associated contaminants.
The residence time of contaminants adsorbed to sediments in the North Sea is much
longer than for those in solution. The average residence time for adsorbed contaminants is likely to be decades (Lohse 1988), if inputs were to cease, it might take centuries for levels to return to those in pre-industrial times (Kempe et al. 1988). Although
there are temporary depositional areas on the Dogger Bank, and sedimentation occurs in the Wadden Sea and German Bight, it is predominately in the Norwegian Trench
(depth 225-700 m) that suspended sediments are deposited. Some 77-84% of the total
net accumulation of fine-grained material in the North Sea occurs here, together with
most of the persistent chemical contaminants which are bound to it (Skei 1981). Thus
Lohse (1988) speculated that, from sources in the southern North Sea to their sink in
the Norwegian Trench, organochlorine contaminants will, over a period of years, be
digested and excreted several times before final deposition.
8.2.2
Perceptions of the Health of the North Sea
The North Sea is rich in the variety of its natural habitats and the diversity and productivity of life that inhabit them. Regular "Quality Status of the North Sea" reports
review the monitoring effort by those countries that bound the North Sea, providing
an overall assessment of its health. The 1987 Quality Status Report concluded "In general deleterious effects, at present, can only be seen in certain regions, in the coastal
margins, or near identifiable pollution sources. There is as yet no evidence of pollution away from these areas".
A.R.D. Stebbing . R.I. Willows
used to interpret metal equilibria and behaviour in the marine environment, particularly those of radionuclides (IAEA 1985). For organic chemistry hydrophobic partitioning depends on the organic carbon content of suspended particulate matter; this partitioning can be calculated from the octonol-water partition coefficient (Kow) (Harris
et al. 1993). However, recent fmdings suggest that some polyaromatic hydrocarbons
(PAHs) detected on suspended marine and estuarine particles may not be subject to
particle-water equilibration and that for those important contaminants (see Sections 8.5.1 and 8.6.4 the partition coefficient is not adequately developed as a means of
describing and predicting contaminant behaviour in the environment (Zhou, pers.
comm.), let alone their use for management purposes.
This organic-rich fraction is highly mobile, settling to the bottom in calm conditions and low current speeds, providing a superficial covering of a few mm thickness
in .pepositional areas. However this layer is quickly remobilized and carried up into
the water column by storms and the turbulence they create, only to settle again through
the water column where currents weaken. It is during repeated deposition and
resuspension that particulate organic matter scavenges the water column of many contaminants. Deposited organic material provides the basis for production by benthic
ecosystems. Many species live by removing fine grained particles a few microns in diameter from suspension (e.g. filter feeding bivalves) or from within the sediment itself (e.g. polychaetes and ophiuroids). Since it is this fine fraction to which many contaminants are adsorbed or bound, even where it represents <1% of the total sediment,
these organisms will be exposed to much higher concentrations than those in the sediment as a whole (Kempe et al. 1988). Hence it is likely that organisms will take up and
may concentrate the associated contaminants.
The residence time of contaminants adsorbed to sediments in the North Sea is much
longer than for those in solution. The average residence time for adsorbed contaminants is likely to be decades (Lohse 1988), if inputs were to cease, it might take centuries for levels to return to those in pre-industrial times (Kempe et al. 1988). Although
there are temporary depositional areas on the Dogger Bank, and sedimentation occurs in the Wadden Sea and German Bight, it is predominately in the Norwegian Trench
(depth 225-700 m) that suspended sediments are deposited. Some 77-84% of the total
net accumulation of fine-grained material in the North Sea occurs here, together with
most of the persistent chemical contaminants which are bound to it (Skei 1981). Thus
Lohse (1988) speculated that, from sources in the southern North Sea to their sink in
the Norwegian Trench, organochlorine contaminants will, over a period of years, be
digested and excreted several times before final deposition.
8.2.2
Perceptions of the Health of the North Sea
The North Sea is rich in the variety of its natural habitats and the diversity and productivity of life that inhabit them. Regular "Quality Status of the North Sea" reports
review the monitoring effort by those countries that bound the North Sea, providing
an overall assessment of its health. The 1987 Quality Status Report concluded "In general deleterious effects, at present, can only be seen in certain regions, in the coastal
margins, or near identifiable pollution sources. There is as yet no evidence of pollution away from these areas".