CHAPTER 8 • Quality Status, Appropriate Monitoring and Legislation of the North Sea
149
(5000 shipping movements at anyone time), from oil exploitation activities and platforms (approx. 150 presently in the North Sea). In recent years there has been an improved awareness of the importance of diffuse atmospheric inputs (Quality Status
Report for the North Sea 1993). The accuracy of riverine load estimates is much greater
(+20-30%) compared to those for atmospheric inputs (+50-100%). Nevertheless, estimates of the proportions of different classes of contaminants indicate that those entering the North Sea by atmospheric wet or dry deposition represent a significant proportion of the total inputs (Nitrate 34-51% (QSR 1993); cadmium 11-108%, mercury
20-42%, copper 13-36%, lead 31-58%, zinc 17-43%, chromium 2-11%, nickel 43-63%
(Kersten et al. 1988); PCBs 96% (Huiskes and Rozema 1988); PAHs 50-1300% (van Aalst
1988». There seems to be agreement that elevated lead levels in North Sea sediments
are due to atmospheric inputs (Kersten et al. 1988), probably from motor vehicles, and
that the relationship with PAHs (Preston et al. 1992) implicates a similar route. However at the time of the Quality Status Report (1993) there were no input data for PAHs.
Inputs to the sea surface from the atmosphere tend to be held in the sea surface
microlayer, where concentrations of contanIinants (e.g. metals) are elevated by one or
two orders of magnitude, and may be toxic (Hardy and Cleary 1992) to life exposed to
the microlayer.
Contaminants entering the marine environment most often disperse, dilute and
become degraded, such that their toxicity is decreased. Some may be accumulated preferentially by organisms in their food or because they filter large volumes of water
(e.g. bivalve molluscs). Bio-accumulation of contaminants may cause toxic effects due
to bio-magnification of concentrations in higher trophic levels. However, it is also useful in monitoring, since concentrations are not only higher, but tissue levels can be
expected to relate to toxicity and assist in establishing causality (Stebbing et al. 1980;
Chapman 1997). Many other contaminants become partitioned to particles, when it is
the movement of suspended particulate matter that becomes responsible for contaminant flux. South of a line from Hull to the Skagerrak the North Sea is significantly more
turbid (1-10 mg 1- 1 ) than to the north (0.1-1 mg 1- 1 ) (Eisma and Irion 1988). Fine-grained
suspended matter in the North Sea is the most important phase for heavy metals and
synthetic organic contaminants. It consists of a clay fraction (illite, mectite, kaolinite)
with large surface areas, for adsorption relative to volume, and complex ion exchange
properties. The fine fraction is also rich in Particulate Organic Matter (POM) derived
from plankton, such as faecal pellets of copepods and the degradation products of
planktonic production in the water column. The high adsorption capacity of clay minerals and the complexation of organic compounds by POM, scavenges the water column of contaminants. Thus the concentrations of heavy metals and organic contaminants on particles (Jlg g-1 dry weight) is much higher than their concentrations in solution (Jlg 1- 1 ), and the fine fraction accumulates contaminants preferentially. The interpretation of contaminant flux, and the capacity of the North Sea to assimilate wastes,
depends critically on the behaviour and movement of fine-grained, organic-rich suspended particulate matter (Kempe et al. 1988).
The partitioning of contaminants between particulate matter and solution is defined by a partition coefficient (Kd), i.e. the ratio of concentrations at steady state in
particulate and dissolved phases. Since KdS vary with salinity and the concentrations
of contaminants and particles, their use in estuaries and near-shore waters is complex
and their utility constrained where they could be, most useful. KdS have been widely
149
(5000 shipping movements at anyone time), from oil exploitation activities and platforms (approx. 150 presently in the North Sea). In recent years there has been an improved awareness of the importance of diffuse atmospheric inputs (Quality Status
Report for the North Sea 1993). The accuracy of riverine load estimates is much greater
(+20-30%) compared to those for atmospheric inputs (+50-100%). Nevertheless, estimates of the proportions of different classes of contaminants indicate that those entering the North Sea by atmospheric wet or dry deposition represent a significant proportion of the total inputs (Nitrate 34-51% (QSR 1993); cadmium 11-108%, mercury
20-42%, copper 13-36%, lead 31-58%, zinc 17-43%, chromium 2-11%, nickel 43-63%
(Kersten et al. 1988); PCBs 96% (Huiskes and Rozema 1988); PAHs 50-1300% (van Aalst
1988». There seems to be agreement that elevated lead levels in North Sea sediments
are due to atmospheric inputs (Kersten et al. 1988), probably from motor vehicles, and
that the relationship with PAHs (Preston et al. 1992) implicates a similar route. However at the time of the Quality Status Report (1993) there were no input data for PAHs.
Inputs to the sea surface from the atmosphere tend to be held in the sea surface
microlayer, where concentrations of contanIinants (e.g. metals) are elevated by one or
two orders of magnitude, and may be toxic (Hardy and Cleary 1992) to life exposed to
the microlayer.
Contaminants entering the marine environment most often disperse, dilute and
become degraded, such that their toxicity is decreased. Some may be accumulated preferentially by organisms in their food or because they filter large volumes of water
(e.g. bivalve molluscs). Bio-accumulation of contaminants may cause toxic effects due
to bio-magnification of concentrations in higher trophic levels. However, it is also useful in monitoring, since concentrations are not only higher, but tissue levels can be
expected to relate to toxicity and assist in establishing causality (Stebbing et al. 1980;
Chapman 1997). Many other contaminants become partitioned to particles, when it is
the movement of suspended particulate matter that becomes responsible for contaminant flux. South of a line from Hull to the Skagerrak the North Sea is significantly more
turbid (1-10 mg 1- 1 ) than to the north (0.1-1 mg 1- 1 ) (Eisma and Irion 1988). Fine-grained
suspended matter in the North Sea is the most important phase for heavy metals and
synthetic organic contaminants. It consists of a clay fraction (illite, mectite, kaolinite)
with large surface areas, for adsorption relative to volume, and complex ion exchange
properties. The fine fraction is also rich in Particulate Organic Matter (POM) derived
from plankton, such as faecal pellets of copepods and the degradation products of
planktonic production in the water column. The high adsorption capacity of clay minerals and the complexation of organic compounds by POM, scavenges the water column of contaminants. Thus the concentrations of heavy metals and organic contaminants on particles (Jlg g-1 dry weight) is much higher than their concentrations in solution (Jlg 1- 1 ), and the fine fraction accumulates contaminants preferentially. The interpretation of contaminant flux, and the capacity of the North Sea to assimilate wastes,
depends critically on the behaviour and movement of fine-grained, organic-rich suspended particulate matter (Kempe et al. 1988).
The partitioning of contaminants between particulate matter and solution is defined by a partition coefficient (Kd), i.e. the ratio of concentrations at steady state in
particulate and dissolved phases. Since KdS vary with salinity and the concentrations
of contaminants and particles, their use in estuaries and near-shore waters is complex
and their utility constrained where they could be, most useful. KdS have been widely