CHAPTER 8 • Quality Status, Appropriate Monitoring and Legislation of the North Sea
173
duced in some of the sediment bioassay data using bivalve larvae. There is a reversal
in this trend, at the most offshore station over the Dogger Bank, detected by a number
of techniques, whose coincidence suggests that they are significant.
Chemical data showing the concentrations of contaminants in sediments along the
transect demonstrate a decrease in concentration with distance offshore. This trend
could be seen most clearly in the whole sediment data for PCBs, PAHs, total hydrocarbons and some of the major metals (lead, arsenic, mercury, cadmium). However, when
analyses of the fine fraction «63 !lm) are considered, the spatial trends are markedly
different, often increasing progressively with distance offshore (total hydrocarbons),
increasing only at the most offshore stations (arsenic, lead), or decreasing offshore and
then increasing over the Dogger Bank (mercury, cadmium). Such distributions closely
match some of the biological data, indicating significant contamination. Inshore the
data shDw marked effects due to pollution of the estuarine plume by the contaminants
flowing out of the rivers Elbe and Weser. Effects are reduced progressively with distance offshore as concentrations of contaminants decrease due to dilution. Such data
lend support to the interpretation that the association of contaminants with the organic-rich fine fraction is the reason for their disproportionate effect on the biota
(Kempe et al. 1988).
Flatfish such as the dab possess a particularly vulnerable lifestyle under these circumstances, since they are likely to be exposed to high concentrations accumulated by
their benthic prey, as well as lying cryptically beneath the superficial layer of the fine
contaminant-rich floc found in depositional areas (e.g. Dogger Bank). Thus flatfish are
exposed to higher concentrations than other demersal fish and, as a consequence, show
the adaptive responses of enzyme systems that aid the degradation and excretion of
organic contaminants. At higher levels of exposure they are more vulnerable to disease and indeed show increased frequencies of some diseases in parts of the North Sea
(Fig. 8.5).
8.6.3
Fish Embryo Abnormalities
As part of the ICES/IOCBremerhaven Workshop, Cameron and Berg (1992) evaluated
the frequency of developmental abnormalities in dab embryos in surface plankton
across the German Bight (Fig. 8.5). Subsequently the technique was used for all fish
species in a survey of the North Sea. Such teratogenic and chromosomal abnormalities are determined in living embryos at sea. On a transect extending NE across the
German Bight frequencies of abnormalities were high at the most inshore stations (32%)
decreasing with distance offshore (9%) before increasing again over the Dogger Bank
(31%) (Cameron and Berg 1992). Similarly, chromosomal aberrations were highest inshore, lowest offshore, and increased over the Dogger Bank (Fig. 8.5).
It is concluded that the enhanced frequencies of developmental abnormalities and
chromosomal aberrations of dab embryos are at least partly due to organochlorines
which occurred at elevated concentrations in adult dab livers (see Stebbing et al. 1992,
Appendix 1). Experimental work has shown that elevated levels of chlorinated hydrocarbons (PCB, DDE, dieldrin) in flatfish result in malformations during embryonic
development which reduce hatching success (Westernhagen 1988). The possibility of
abnormalities being caused by the exposure of floating eggs and embryos to contami-
173
duced in some of the sediment bioassay data using bivalve larvae. There is a reversal
in this trend, at the most offshore station over the Dogger Bank, detected by a number
of techniques, whose coincidence suggests that they are significant.
Chemical data showing the concentrations of contaminants in sediments along the
transect demonstrate a decrease in concentration with distance offshore. This trend
could be seen most clearly in the whole sediment data for PCBs, PAHs, total hydrocarbons and some of the major metals (lead, arsenic, mercury, cadmium). However, when
analyses of the fine fraction «63 !lm) are considered, the spatial trends are markedly
different, often increasing progressively with distance offshore (total hydrocarbons),
increasing only at the most offshore stations (arsenic, lead), or decreasing offshore and
then increasing over the Dogger Bank (mercury, cadmium). Such distributions closely
match some of the biological data, indicating significant contamination. Inshore the
data shDw marked effects due to pollution of the estuarine plume by the contaminants
flowing out of the rivers Elbe and Weser. Effects are reduced progressively with distance offshore as concentrations of contaminants decrease due to dilution. Such data
lend support to the interpretation that the association of contaminants with the organic-rich fine fraction is the reason for their disproportionate effect on the biota
(Kempe et al. 1988).
Flatfish such as the dab possess a particularly vulnerable lifestyle under these circumstances, since they are likely to be exposed to high concentrations accumulated by
their benthic prey, as well as lying cryptically beneath the superficial layer of the fine
contaminant-rich floc found in depositional areas (e.g. Dogger Bank). Thus flatfish are
exposed to higher concentrations than other demersal fish and, as a consequence, show
the adaptive responses of enzyme systems that aid the degradation and excretion of
organic contaminants. At higher levels of exposure they are more vulnerable to disease and indeed show increased frequencies of some diseases in parts of the North Sea
(Fig. 8.5).
8.6.3
Fish Embryo Abnormalities
As part of the ICES/IOCBremerhaven Workshop, Cameron and Berg (1992) evaluated
the frequency of developmental abnormalities in dab embryos in surface plankton
across the German Bight (Fig. 8.5). Subsequently the technique was used for all fish
species in a survey of the North Sea. Such teratogenic and chromosomal abnormalities are determined in living embryos at sea. On a transect extending NE across the
German Bight frequencies of abnormalities were high at the most inshore stations (32%)
decreasing with distance offshore (9%) before increasing again over the Dogger Bank
(31%) (Cameron and Berg 1992). Similarly, chromosomal aberrations were highest inshore, lowest offshore, and increased over the Dogger Bank (Fig. 8.5).
It is concluded that the enhanced frequencies of developmental abnormalities and
chromosomal aberrations of dab embryos are at least partly due to organochlorines
which occurred at elevated concentrations in adult dab livers (see Stebbing et al. 1992,
Appendix 1). Experimental work has shown that elevated levels of chlorinated hydrocarbons (PCB, DDE, dieldrin) in flatfish result in malformations during embryonic
development which reduce hatching success (Westernhagen 1988). The possibility of
abnormalities being caused by the exposure of floating eggs and embryos to contami-