Metals in shellfish
Metals in fish
Organochlorines in shellfish
Organochlorines in fish liver
Organochlorines and mercury in gannet
Data summarised from the 'National
Monitoring Programme Survey of the Quality of UK
Metals in shellfish
Two shellfish species were specified for use in
the NMP survey, the common mussel Mytilus edulis
(L.) and the horse mussel Modiolus modiolus.
Data were submitted for metals in shellfish for
26 NMP sites around the UK coasts and estuaries.
The NMP survey concluded that, while there were
some gaps in the available dataset, on the basis
of the available data, contamination by the metals
examined was not a significant problem in UK estuaries.
Median cadmium concentrations ranged from 0.96
mg kg-1 dry weight at two sites on the
Welsh side of the Dee estuary to 9.78 mg kg-1
dry weight in the Severn estuary. The range of median
concentrations reported in the NMP survey was stated
to be consistent with those previously reported
for UK estuaries and coastal sites.
The Joint Monitoring Programme (JMP) of the Oslo
and Paris Commissions has adopted arbitrary descriptive
guidelines for cadmium in mussels of up to 2 mg
kg-1 dry weight as in the "lower"
level, between 2-5 mg kg-1 as the "medium"
level, and >5 mg kg-1 as the "upper"
level (MAFF, 1987). In this context, the highest
cadmium concentrations reported for the UK NMP survey,
in the Severn estuary, fall into the Aupper"
category. Results for one site in each of the Clyde,
Mersey, and Severn estuaries fall into the "medium"
category, while results for the remaining 11 sites
are in the "lower" category.
In Scotland, a recommended standard of 15 mg kg-1
dry weight has been set for cadmium in mussels under
the terms of the EC Shellfish Growing Waters Directive,
specifically to ensure that "the concentration
in the shellfish water or in the flesh must not
reach or exceed a level which gives rise to harmful
effects on the shellfish or their larvae" (ADRIS,
1982). The NMP survey concluded that the results
presented by the NMP survey suggested that harmful
effects due to cadmium contamination were unlikely
in any of the UK estuaries surveyed.
Median mercury concentrations ranged from 0.084
mg kg-1 dry weight in Southampton Water
to 0.804 mg kg-1 at the intermediate
site off the Lune and Wyre estuaries. These concentrations
are lower than levels reported for contaminated
estuaries elsewhere in the UK (0. 12-2.3 mg kg-1)
and for European shores (0.012-1.02 mg kg-1),
but similar to levels found at UK coastal sites
(0.11-0.38 mg kg-1).
The ADRIS (Association of Directors and River Inspectors
in Scotland) recommended standard set under the
EC Shellfish Growing Waters Directive is 3 mg kg-1,
well above the highest reported concentration. The
NMP survey concluded from the results presented
that harmful effects on mussels from mercury contamination
Median lead concentrations ranged from 3.01 mg
kg-1 dry weight at the intermediate site
in the Firth of CIyde to 13.5 mg kg-1
at Broughty Castle near Dundee in the Tay estuary.
The elevated concentrations in the Tay estuary mussels
were said to be consistent with high lead levels
reported for sediments collected at the mid-channel
NMP site off Broughty Castle. Concentrations above
10 mg kg-1 were also recorded for one
site in each of the Forth and Clyde estuaries, which
have been subject to historical industrial contamination.
Lead levels at the NMP sites were found to be slightly
lower than median concentrations previously reported
for contaminated estuaries in the UK (3.5-39 mg
kg-1) but similar to levels reported
for UK coastal sites (<3.0-29 mg kg-1)
and European shores (0.6-27.6 mg kg-1).
Standards are not available for lead in mussels,
although the ADRIS recommended standard for shellfish
growing waters has been set at 50 mg kg-1
dry weight which the NHP survey suggests /indicates
that shellfish are not at risk.
Median zinc concentrations ranged from 84-90 mg
kg-1 dry weight at Selsey Bill and in
the Solent to 204-209 mg kg-1 at the
outer most sites in the Tyne and Humber estuaries.
The NMP survey reports these to be broadly similar
to levels reported at coastal sites in the UK (58-303
mg kg-1) and Europe (55-294 mg kg-1),
and to results for UK estuaries (91-330 mg kg-1).
The NMP survey suggests that the high concentrations
reported for mussels in the Mersey should be investigated
since they approach the ADRIS recommended level
of 500 mg kg-1 set under the terms of
the EC Directive on Shellfish Growing Waters to
protect shellfish and their larvae.
Metals in fish
The NMP determinands were mercury and arsenic in
fish muscle tissue and cadmium and lead in fish
liver. The coverage achieved in the survey, particularly
for intermediate and offshore sites, was considered
to represent the best attempt to date to obtain
a synoptic survey across the whole of the UK. Only
in some estuaries are there significant gaps.
The NMP survey states that the results are reassuring
in that they generally confirm those from previous
surveys, which have demonstrated that contamination
is confined to a few well known geographical locations.
Mercury in fish muscle
Results were generally as would have been expected
from previous surveys, with highest concentrations
found in Liverpool Bay and Morecambe Bay, areas
that have been subject to considerable inputs of
mercury via discharges from the chloro-alkali industry.
The results presented confirm those from more specific
local studies, e.g. the Mersey.
Levels were relatively high in some other inshore
areas, e.g. the Thames estuary, with an observed
general reduction in concentrations offshore. One
unexpected result was the mercury concentrations
in dab from inshore Cardigan Bay, which were relatively
high in both CEFAS and Environment Agency samples.
Concentrations were generally low around the coast
of Scotland, with only one value, from the Minches,
exceeding 0.1 mg kg-1 wet weight. This
was for megrim, which cannot be compared directly
with other species. Plaice from the same station
contained low concentrations of mercury (0.03 mg
Median mercury concentrations in dab ranged from
0.01- 0.02 mg kg-1 in Dundrum Bay and
off the Tamar in the English Channel, to 0.26 mg
kg-1 in the Burbo Bight off the Mersey.
No median values therefore fell in the "higher"
level category (>0.3 mg kg-1) designated
by the Joint Monitoring Group of the Oslo and Paris
Commissions and virtually all were 50% or less of
the maximum limits for mercury in fishery products
(0.5 mg kg-1) designated in European
Community Commission Decision 93/351/EEC.
The range of the mean concentrations of mercury
in those dab samples collected from North Sea NMP
stations during the present survey was 0.03-0.11
mg kg-1 wet weight, generally similar
to that (0.05-0.12 mg kg-1) found in
dab samples collected in the 1989-91 period under
the Monitoring Master Plan designed to provide data
for the North Sea Quality Status Report.
Median concentrations in the essentially estuarine
samples of flounder ranged from <0.01 to 0.08
Arsenic in fish muscle
There appeared to be little obvious spatial pattern
in the concentrations observed. The highest levels
in dab (~20 mg kg-1) were found off the
Tees, Tay and Forth estuaries. However, concentrations
were almost as great in the Moray Firth area, indicating
that the levels found are not likely to be entirely
due to anthropogenic inputs. The highest arsenic
concentration found in fish muscle was in the Minches,
which would be expected to be relatively free of
anthropogenic contamination. This was, however,
in non-recommended species, megrim, and it is known
that very considerable differences occur between
species in the accumulation of arsenic in fish (Falconer
et al., 1983).
Concentrations of arsenic in flounder were
relatively low, with a maximum concentration of
~6 mg kg-1.
Unfortunately, arsenic has not yet been included
in most international programmes, so data for comparison
purposes from previous monitoring are limited.
Cadmium in fish liver
Concentrations appear to be highest off the east
coast of Scotland, with a maximum median of around
0.8 mg kg-1 wet weight off the Tay. The
maximum median concentration in English waters (0.37
mg kg-1) was offshore of the Tyne-Humber
, previously identified in the sampling carried
out under the North Sea Monitoring Master Plan as
an area where cadmium concentrations were above
the upper quartile of the survey results.
The maximum values found in the earlier North Sea
survey was 0.96 mg kg-1 cadmium, with
the median concentration 0.18 mg kg-1.
Cadmium concentrations were relatively low in the
Northern Irish samples and in all samples of flounder.
Lead in fish liver
The range of concentrations of lead found in dab
liver was relatively small, from 0.03 mg kg-1
in the Moray Firth to a maximum of 0.58 mg kg-1
off the coast of Northern Ireland. Generally low
concentrations were recorded in dab taken from Scotland,
but plaice taken off the Tay had the highest level
for all the fish sampled 0.62 mg kg-1.
There are unfortunately few earlier data that could
be used for comparative purposes, since in previous
years, the methods generally employed were rarely
able to provide low enough detection limits to yield
positive results. In the early 1990s, for example,
concentrations in dab liver in the samples collected
under the North Sea Monitoring Master Plan were
all <0.6-< 1.0 mg kg-1.
Organochlorines in shellfish
NMP specified the determination of dieldrin, aldrin,
endrin and isodrin. The most common compound in
biological samples is dieldrin. Other drins tend
to revert to dieldrin in the natural environment
and are unlikely to be found unless the organism
has been recently exposed.
Only data for dieldrin were reported at concentrations
greater than the limit of detection. Dieldrin was
detected at five sites at concentrations ranging
from 0.006 to 2 mg kg-1. All data were below the ADRIS
"no harmful effects" concentration of
100 mg kg-1.
More than half the data reported for pp-DDT was
below the limit of detection of the analysis. Positive
data for pp-TDE were reported at both sites in the
Forth and one site in the Humber. The concentration
found in the Forth is approximately an order of
magnitude less than that found in the Humber. Data
for pp-DDE were reported at eight sites at concentrations
ranging from 0.007-6.5 mg
kg-1. All data were below the ADRIS "no
harmful effects" concentration of 100 mg kg-1.
Data greater than the limit of detection were reported
at five sites for gamma-HCH . Concentrations were
low (0.25-5.5 mg
kg-1) and well below the ADRIS "no
harmful effects" concentration of 30 mg kg-1. Positive data for %-HCH
were reported at only one site (Selsey Bill).
NMP specified a range of congeners for analysis.
Data are presented for PCB 153 as this is the congener
for which most data were available. Positive data
were reported at seven sites, two in the Forth,
two in the Humber and three in Belfast Lough.
The highest concentrations occurred in the Humber
kg-1). Concentrations reported in Belfast
Lough (0.006 mg kg-1) were below the limit of detection of all other
sites. Belfast Lough and the Forth samples fall
into the lower contamination range for PCBs in molluscs
(JMP guideline values) whereas the Humber sites
fall into the medium range.
Positive data were only reported in the Humber
(26.9 mg kg-1)
and the Forth (0.31 mg
kg-1). The sediments of the Forth have
been shown to be contaminated with HCB as a result
of past discharges (Harper et al, 1992) and
provide a source of HCB to the resident biota.
Only two sets of data were returned for PCP and
both sets had more than 50% of data less than the
limit of detection. PCP is known to metabolise rapidly
and is consequently difficult to analyse for in
Organochlorines in fish liver
The NMP determinands were 11 individual polychlorinated
biphenyl congeners (PCBs 28, 52, 101, 105, 118,
128, 138, 153, 156, 170 and 180), dieldrin,
aldrin and endrin and three DDT group compounds
(pp-DDT, pp-TDE and pp-DDE). As with the metals
the first choice species was dab with flounder as
PCB 153 (2,2',4,4',5,5'- hexachlorobiphenyl) is
generally considered to be highly persistent in
marine biota and therefore is most often the dominant
congener in a typical chlorobiphenyl profile. This,
coupled with the relative ease of measurement, results
in it often being used as an indicator chlorobiphenyl
and this is the case for the purposes of the NMP
PCB 153 was detected at more than 90'% of the 39
stations for which data were presented, with more
than 50% of the stations having values exceeding
20 mg kg-1. Seven stations exceeded 50 mg kg-1, while the highest median values
(in excess of 100 mg
kg-1) were reported for the three stations;
the Forth at Kingston Hudds Liverpool Bay at Burbo
Bight and Liverpool Bay, offshore with values of
120, 160 and 170 mg
kg-1 respectively. The last two values
are consistent with previous data that have put
contamination in the medium and upper categories
of the JMP guideline levels for PCBs in fish tissue.
Although concentrations generally declined offshore,
PCB 153 was present at all stations. The relatively
high levels in Liverpool Bay are consistent with
the results of more localised studies in that area.
Dieldrin was detected in more than 90% of the stations
for which data were reported. Highest median values
were reported for Liverpool Bay; Off Lune/ Wyre
; Thames and offshore Moray Firth, with median values
of 35, 22, 50 and 72 mg
The results for the nine stations for which data
were presented were all less than the limit of detection,
which is not surprising as aldrin is readily converted
to dieldrin in many environmental compartments.
The coverage for endrin was wider than for aldrin,
with data for 13 stations being produced. However,
only two stations, Moray Firth and Belfast Lough
yielded positive results, with median values of
5 and 6 mg kg-1
respectively . Although endrin is highly toxic,
it is much less persistent than dieldrin and its
occurrence was not expected to be widespread.
DDT group compounds
Three DDT compounds were required to be determined,
namely, pp-DDE , pp-TDE and pp-DDT. The highest
median level concentrations for all three compounds
were found at the sites off the north- west of England
with median values of 15-91 mg
kg-1 for pp-DDE; 23-130
mg kg-1 for pp-TDE and 13-28
mg kg-1 for pp-DDT. These values
are within the "expected range" for these
compounds in fish liver, with the stable metabolite
pp-DDE being the dominant component. The concentrations
of these compounds generally decreased at offshore
sites, with stations off Wales and the south-west
coast of England being close to or below the limit
of detection. The concentration patterns
were similar for pp-DDE and pp-TDE. However, four
stations off the east coast of England appear to
have higher levels with median values ranging from
6.5 to 20 mg kg-1 for pp-DDT. No corresponding
data were presented for the estuarine sites in this
Organochlorines and mercury in
During 1971-1997, eggs have been obtained from
up to eight different gannet colonies around Britain
and Ireland as part of an on-going monitoring programme
funded by the Joint Nature Conservation Committee
(JNCC). Although residues of DDE, HEOD and PCB have
generally declined, some sites have shown an increase
in residues, particularly of PCBs and mercury, at
least over part of this period (Newton et al