- Email: [email protected]
Trace metals in the common porpoise, Phocoena phocoena
Marine Environmental Research 8 (1983) 119-127
Trace Metals in the Common Porpoise, Phocoena
phocoena
C. R. Falconer, I. M. Davies & G. Topping DAFS, Marine Laboratory, PO Box 101, VictoriaRoad, AberdeenAB9 8DB, Scotland, Great Britain (Received: 3 September,1982) ABSTRACT Mercury, cadmium, copper and zinc concentrations in brain, lirer, kidney, heart and spleen of twenty-six specimens of the common porpoise (Phocoena phocoena) are presented. Mercury and cadmium levels in liver and kidneys tended to increase with length of animal, but copper and zinc levels show no such trends. The proportion of methylmercury to total mercury (9 %-57 %) in the liver decreased with increasing total mercury concentrations. Lead, chromium, nickel and cobalt levels were below the analytical detection limits (0"5, 1"0, 1"0 and 2.5 ltg g -l, respectively).
INTRODUCTION Apart from two species of seal, the porpoise Phocoena phocoena is the most abundant marine mammal in UK coastal waters. Porpoise are terminal carnivores feeding mainly upon gadoid and clupeoid fish (Rae, 1965; 1973) and therefore may have the capacity to accumulate high concentrations of certain contaminants which are present at much smaller concentrations in organisms at lower trophic levels. Although porpoise are not commonlyconsumed by man in the UK, it is appropriate to consider their contaminant burdens in the interest of the protection of the species. In the North Atlantic area, the most comprehensive investigations of metals in porpoise have been carried out in Canadian coastal waters (Gaskin et al., 1972; 1979) and have concentrated on mercury. This paper 119 Marine Environ. Res. 0141-1136/83/0008-0119/$03.00 © Applied Science Publishers Ltd, England, 1983. Printed in Great Britain
120
C. R. Falconer, I. M. Davies, G, Topping
reports measurements of a range of metals (Hg, Cd, Pb, Cu, Zn, Cr, Ni, Co) in porpoise from UK coastal waters and discusses the data in relation to body length.
MATERIALS AND METHODS Twenty-six common porpoise were collected on the east coast of Scotland during 1974, the majority having been entangled in cod nets. Each specimen was measured, and samples taken of brain, liver, kidney, heart and spleen. Tissues were stored deep-frozen, and thawed, chopped and sub-sampled prior to analysis. Total mercury was determined by a dry-ashing/cold vapour atomic absorption method (Topping et al., 1975) and methylmercury following Davies (1978). All other elements were determined by flame atomic absorption after digestion in concentrated nitric acid. These methods have been validated through participation in intercomparison exercises organised by the International Council for the Exploration of the Sea (Topping & Holden, 1978; Holden & Topping, 1981).
RESULTS
Lead, chromium, nickel and cobalt Concentrations of these elements in all tissues were below the detection limits of the method employed (0.5, 1.0, 1.0 and 2.5 #g g- 1, respectively).
Mercury All tissues showed a considerable range of mercury concentrations (Table 1). In general, levels were higher in the liver than in the other organs analysed. Concentrations in liver and kidney (Figs IA and 13) appeared to show an increase with body length. Methytmercury concentrations were measured in the liver of selected specimens. The proportion of methylmereury varied between 9 9/0 and 57 ~ of the total mercury, the higher proportions being found in samples containing lower total mercury levels (Fig. 1C).
Trace metals in the common porpoise, P h o c o c n a
1/.
phocoena
121
x
A. LI V ER
x
10
o o x
6
0
ox
Z
o_
X
2 X
X
xX 0
0 X
X,
nr
3
X
B. KIDNEY x
2
x
o
>-
x
x
x x
0 Of. UJ
1
x
x x
o
x x
xo
x x
x
o o
%
i
1£0
160 cm I_ENGTH
120== I--
60 2O
6
o
C. LIVER
o
x x D
2
o
x
nx x
2o
~x
x .
~
% METHYLMERCURY
x
60
Fig. I. Relationship between total mercury concentration (pg g- 1wet weight) and body length in porpoise liver (A) and kidney (B). Circles represent females; crosses, males. (C) Relationship between total mercury and the percentage of methylmercury in porpoise livers. Data from Gaskin et al. (1979) is shown as squares.
Cadmium Cadmium residues (Table 1) were considerably higher in kidney tissue than in liver, heart and spleen, whilst levels in the brain samples were mainly below the detection limit (0.05 pg g- 1). Cadmium concentrations in both liver and kidney appeared to show increase with body length (Figs 2A and B) but no such pattern was found in the heart or spleen analyses. Copper Copper was detected in all tissues analysed, with generally higher
0.1 I-046 0.29- IO.6 0.47-2.82 0.20-I .20 0~13-1~85
@08-3.04 0.2a- IS.9 0.23-I .79 044- I @8 0~12-1~01
17 17 17 16 13
6
6 6 6 5
Raft@
n
1004 97.7 61.8 36.4
53.3 97. I 53.4 52.5 86.8
O-30 3.42 I .23 0.59 o.s3
1.30 6.03 I.02 0.77 0.57’
CV%’
Metal
f
h4ercury
=Mostresults
--
Trace
Range
Concentrations
86.7 72.1 -
125.9 1056 -
CV% -
co.05 0.15' I.11 <0,05’
Cadmium f
1
3.93-6.69 2.65- IO.30 3.16-3.88 3.77-4.79 0.56-1.39
369-744 2,74- 12.80 2.64-4.77 3.77 5.19 099- 443
Range
._
5.12 7.21 3.59 4.35 I.10
24.X 36.6 7.2 9.2 30.0
20.4 40.3 13.6 IO.4 58.2
CV%
Porpoise
5-29 7.29 3.83 4.52 1.53
Copper i
wet weight) in Common -
TABLE (pcgg-’
13.3.. 16.1 36.7 51.9 20.3-25.3 24.3-28.7 18.1. 45.0
13,4-2OGO 18.4-67.6 19.5-33.1 23.1-2X.2 144 59.6
Range
ir
14-x 43.7 23, I 26.5 36.6
16.2 43.2 23.8 26.3 42.7
LiflC
?&2 12.5 4.Y 30.7
13.3
(‘I’ “;
Trace metals in the common porpoise, Phocoena phocoena 7 1'0 m08
A.
123
LIVER x x
~ 0-~ .<
0 x
~ 0.2
OX X
Z m
X X
X
x X o ~x
x
X
x
X
Z O
Ig
7 B
KIDNEY O
3
O X Xx
1 X
110
0 X
o ~X~o
~
~
150
150
X 0
'
'
1")'0
BODY LENGTH cm. Fig. 2. Relationship between porpoise body length and cadmium concentrations (#g g- ~wet weight) in liver (A) and kidney (B). Circles represent females; crosses, males.
concentrations in liver than in the other organs. Copper concentrations in liver and kidney displayed considerably less variability than did mercury and cadmium levels in the same organs. Also, no systematic variation of concentration with body length could be found. Zinc The concentrations of zinc also show no clear variation with size of porpoise, and relatively small differences between specimens. Higher concentrations were found in the liver and spleen (Table I) than in other organs. DISCUSSION Mercury concentrations in selected porpoise tissues have been reported by Gaskin et al. (1972; 1979) and Harms et al. (1977). The distribution of mercury between organs is similar for samples from both the east and west sides of the North Atlantic (Table 2); however, some Canadian porpoise contained relatively high mercury concentrations, particularly in the
M F
M F M F
0"89-18-3 0-55-91-3 3-38 3-37 0"70-28"0 0"29-10"6 0'28-15'9
° Gaskin et al. (1972). Gaskin et al. (1979). 5-year old adults. c Harms et al. (1977). Three specimens. d This study.
Baltic and North Sea r North Sea d
West Atlantic b
West Atlantic*
Liver Range
15-7 16'2 10-4 3"4 6"0
Y~
0.47-2"82 0'23-1.79
0"8-5"2 1.5-4.5
Kidney Range
1'23 1"02
2.00 2.77
"2
0' 11-0-46 0.08-3-04
Brain Range
TABLE 2 Mercury Concentrations (/~g g - t wet weight) in Porpoise
0"30 1"30
0'38 0-42
f~
0-21 - 1.92 0"26 2.58 0-6-2'6 0-7 -2-5
Muscle Range
0.75 1-02 1.12 i .46
Y~
q~
.t..x
Trace metals in the common porpoise, Phocoena phocoena
125
liver. The liver of porpoise from the Bay of Fundy (Gaskin et al., 1972) and in this study both show increasing mercury levels with body length. However, whilst concentrations are similar in small animals (up to about 140cm), in larger animals concentrations are considerably greater in Canadian samples. This length (140cm) corresponds to an age of 4-5 years (Gaskin et al., 1979) above which, due to increasing variance of weight in older animals, estimation of age from length becomes unreliable. The greater variance of mercury concentrations in large specimens noted by Gaskin et al. (1979), and the generally lower concentrations in large North Sea porpoise, may reflect difference in the age structure of the two sets of samples. The pattern of decreasing proportion of methylmercury in liver with increasing total mercury confirms and amplifies the trend reported by Gaskin et al. (1972; 1979). A similar pattern has been more widely established in seals (e.g. Reijnders, 1979). The most important uptake route of mercury to seals and porpoises is probably through the diet, i.e. fish. Mercury in fish is present almost entirely as methylmercury (Holden, 1973) and there is general agreement that a mechanism for the demethylation of organic mercury exists in seals, probably in the liver (Roberts et al., 1976). It may well be, therefore, that a similar mechanism occurs in the common porpoise. The only other measurements of cadmium in porpoise known to us are by Harms et al. (1977) who found 0.02-0.19/~g g - ~ and 0.08-0.95/tg gin liver and kidney, respectively, which agree reasonably with our data. The distribution of cadmium between organs is similar to that in the grey seal (Hepplestone & French, 1978; Caines, 1978; McKie et al., 1980) and, generally, increases in concentration with age or length were also found. The general levels and distribution of copper and zinc agree with those reported by Harms et al. (1977). However, the lack of any accumulation of these elements during growth, and the relatively small variance between animals, contrasts markedly with the results for mercury and cadmium. This suggests that the common porpoise can, at least partially, regulate copper and zinc concentrations. Coet~cients of linear correlation were calculated for the variation of mercury concentration with length in liver (r = 0-65) and kidney (r = 0.42), and found to be significant at the 0.1% and 5 % levels, respectively. The data for cadmium in liver (r = 0.57) and kidney (r = 0.69) were similarly treated, and the regressions were significant at the 1% and 0.1% levels, respectively. Whilst these regressions are significant, the correlation
('. R. Falconer, 1. M. Dat, ies, G. Topping
126
coefficients are fairly low. This may, to some extent, be due to length being a poor analogue of age (particularly for larger animals) as previous studies of marine mammals (e.g. Hepplestone & French, 1978; Gaskin et al., 1979) had found closer correlation between age and metal concentration. It may also be noted that the large variance in mercury and cadmium concentration obtained from a sample of porpoise from a small part of the North Sea implies that porpoise would be of limited usefulness as an indicator of environmental quality.
ACKNOWLEDGEMENTS The authors wish to thank members of the Demersal Section of the Marine Laboratory, Aberdeen, for the collection, measurement and sampling of the specimens.
REFERENCES Caines, L. A. (1978). Heavy metal residues in grey seals (Halichoems grypus)from the Farne Islands. International Council for the Exploration of the Sea, Statutory Meeting 1978, CM1979/E:40. Davies, I. M. (1978). Determination of methylmercury in the muscle of marine fish by cold vapour atomic absorption spectrophotometry. Anal. Chim. Acta, 102, 189-94. Gaskin, D. E., Ishida, K. & Frank, R. (1972). Mercury in harbour porpoises (Phocoena phocoena) from the Bay of Fundy region. J. Fish. Res. Bd Can., 29(11), 1644-6. Gaskin, D. E., Stonefield, K. I., Suda, P. & Frank, R. (1979). Changes in mercury levels in harbour porpoises from the Bay of Fundy, Canada and adjacent waters during 1969-1977. Arch. Environm. Contam. Toxicol., 8, 733-62. Harms, U., Drescher, H. E. & Huschenbeth, E. (1977). Further data on heavy metals and organochlorines in marine mammals from German coastal waters. International Council for the Exploration of the Sea, Statutory Meeting, 1977, CMI977/N:5, 14pp. Hepplestone, P. B. & French, M. C. (1978). Mercury and other metals in British seals. Nature, Lond., 243, 302-4. Holden, A, V. (1973). Mercury in fish and shellfish. A review. J. Fd Technol., 8, 1-25.
Holden, A. V. & Topping, G. (1981). Report on further intercalibration analysis in ICES pollution monitoring and baseline studies. International Council for the Exploration of the Sea, Co-operative Research Report No, 108.
Trace metals in the common porpoise, Phocoena phoccena
127
McKie, J. C., Topping, G. & Davies, I. M. (1980). Trace elements in grey seals Halichoerus grypus from the east coast of Scotland. International Council for the Exploration of the Sea, Statutory Meeting 1980, CMI980/E:41. Rae, B. B. (1965). The food of the common porpoise (Phocoena phocoena). J. Zool., 146, 114-22. Rae, B. B. (1973). Additional notes on the food of the common porpoise (Phocoena phocoena). J. Zool., 164, 127-31. Reijnders, P. J. H. (1979). Organochlorine and heavy metal residues in harbour seals of Schleswig Holstein plus Denmark and the Netherlands: Their possible effects in relation to the reproduction in both populations. International Council for the Exploration of the Sea, Statutory Meeting 1979, CMI979/N:I8. Roberts, T. M., Hepplestone, P. B. & Roberts, R. D. (1976). Distribution of heavy metals in tissues of the common seal. Mar. Poll. Bull., 7(10), 194-6. Topping, G. (1973). Heavy metals in fish from Scottish waters. Aquaculture, 1, 373-7. Topping, G. & Holden, A. V. (1978). Report on intercalibration analysis in ICES North Sea and North Atlantic baseline studies. International Council for the Exploration of the Sea, Co-operative Research Report No. 80. Topping, G., Pirie, J. M., Graham, W. C. & Shepherd, R. J. (1975). An examination of the heavy metal levels in muscle, kidney and liter of saithe in relation to year class, area of sampling and season. International Council for the Exploration of the Sea, Statutory Meeting 1975, CMI975/E:37.
Trace Metals in the Common Porpoise, Phocoena
phocoena
C. R. Falconer, I. M. Davies & G. Topping DAFS, Marine Laboratory, PO Box 101, VictoriaRoad, AberdeenAB9 8DB, Scotland, Great Britain (Received: 3 September,1982) ABSTRACT Mercury, cadmium, copper and zinc concentrations in brain, lirer, kidney, heart and spleen of twenty-six specimens of the common porpoise (Phocoena phocoena) are presented. Mercury and cadmium levels in liver and kidneys tended to increase with length of animal, but copper and zinc levels show no such trends. The proportion of methylmercury to total mercury (9 %-57 %) in the liver decreased with increasing total mercury concentrations. Lead, chromium, nickel and cobalt levels were below the analytical detection limits (0"5, 1"0, 1"0 and 2.5 ltg g -l, respectively).
INTRODUCTION Apart from two species of seal, the porpoise Phocoena phocoena is the most abundant marine mammal in UK coastal waters. Porpoise are terminal carnivores feeding mainly upon gadoid and clupeoid fish (Rae, 1965; 1973) and therefore may have the capacity to accumulate high concentrations of certain contaminants which are present at much smaller concentrations in organisms at lower trophic levels. Although porpoise are not commonlyconsumed by man in the UK, it is appropriate to consider their contaminant burdens in the interest of the protection of the species. In the North Atlantic area, the most comprehensive investigations of metals in porpoise have been carried out in Canadian coastal waters (Gaskin et al., 1972; 1979) and have concentrated on mercury. This paper 119 Marine Environ. Res. 0141-1136/83/0008-0119/$03.00 © Applied Science Publishers Ltd, England, 1983. Printed in Great Britain
120
C. R. Falconer, I. M. Davies, G, Topping
reports measurements of a range of metals (Hg, Cd, Pb, Cu, Zn, Cr, Ni, Co) in porpoise from UK coastal waters and discusses the data in relation to body length.
MATERIALS AND METHODS Twenty-six common porpoise were collected on the east coast of Scotland during 1974, the majority having been entangled in cod nets. Each specimen was measured, and samples taken of brain, liver, kidney, heart and spleen. Tissues were stored deep-frozen, and thawed, chopped and sub-sampled prior to analysis. Total mercury was determined by a dry-ashing/cold vapour atomic absorption method (Topping et al., 1975) and methylmercury following Davies (1978). All other elements were determined by flame atomic absorption after digestion in concentrated nitric acid. These methods have been validated through participation in intercomparison exercises organised by the International Council for the Exploration of the Sea (Topping & Holden, 1978; Holden & Topping, 1981).
RESULTS
Lead, chromium, nickel and cobalt Concentrations of these elements in all tissues were below the detection limits of the method employed (0.5, 1.0, 1.0 and 2.5 #g g- 1, respectively).
Mercury All tissues showed a considerable range of mercury concentrations (Table 1). In general, levels were higher in the liver than in the other organs analysed. Concentrations in liver and kidney (Figs IA and 13) appeared to show an increase with body length. Methytmercury concentrations were measured in the liver of selected specimens. The proportion of methylmereury varied between 9 9/0 and 57 ~ of the total mercury, the higher proportions being found in samples containing lower total mercury levels (Fig. 1C).
Trace metals in the common porpoise, P h o c o c n a
1/.
phocoena
121
x
A. LI V ER
x
10
o o x
6
0
ox
Z
o_
X
2 X
X
xX 0
0 X
X,
nr
3
X
B. KIDNEY x
2
x
o
>-
x
x
x x
0 Of. UJ
1
x
x x
o
x x
xo
x x
x
o o
%
i
1£0
160 cm I_ENGTH
120== I--
60 2O
6
o
C. LIVER
o
x x D
2
o
x
nx x
2o
~x
x .
~
% METHYLMERCURY
x
60
Fig. I. Relationship between total mercury concentration (pg g- 1wet weight) and body length in porpoise liver (A) and kidney (B). Circles represent females; crosses, males. (C) Relationship between total mercury and the percentage of methylmercury in porpoise livers. Data from Gaskin et al. (1979) is shown as squares.
Cadmium Cadmium residues (Table 1) were considerably higher in kidney tissue than in liver, heart and spleen, whilst levels in the brain samples were mainly below the detection limit (0.05 pg g- 1). Cadmium concentrations in both liver and kidney appeared to show increase with body length (Figs 2A and B) but no such pattern was found in the heart or spleen analyses. Copper Copper was detected in all tissues analysed, with generally higher
0.1 I-046 0.29- IO.6 0.47-2.82 0.20-I .20 0~13-1~85
@08-3.04 0.2a- IS.9 0.23-I .79 044- I @8 0~12-1~01
17 17 17 16 13
6
6 6 6 5
Raft@
n
1004 97.7 61.8 36.4
53.3 97. I 53.4 52.5 86.8
O-30 3.42 I .23 0.59 o.s3
1.30 6.03 I.02 0.77 0.57’
CV%’
Metal
f
h4ercury
=Mostresults
--
Trace
Range
Concentrations
86.7 72.1 -
125.9 1056 -
CV% -
co.05 0.15' I.11 <0,05’
Cadmium f
1
3.93-6.69 2.65- IO.30 3.16-3.88 3.77-4.79 0.56-1.39
369-744 2,74- 12.80 2.64-4.77 3.77 5.19 099- 443
Range
._
5.12 7.21 3.59 4.35 I.10
24.X 36.6 7.2 9.2 30.0
20.4 40.3 13.6 IO.4 58.2
CV%
Porpoise
5-29 7.29 3.83 4.52 1.53
Copper i
wet weight) in Common -
TABLE (pcgg-’
13.3.. 16.1 36.7 51.9 20.3-25.3 24.3-28.7 18.1. 45.0
13,4-2OGO 18.4-67.6 19.5-33.1 23.1-2X.2 144 59.6
Range
ir
14-x 43.7 23, I 26.5 36.6
16.2 43.2 23.8 26.3 42.7
LiflC
?&2 12.5 4.Y 30.7
13.3
(‘I’ “;
Trace metals in the common porpoise, Phocoena phocoena 7 1'0 m08
A.
123
LIVER x x
~ 0-~ .<
0 x
~ 0.2
OX X
Z m
X X
X
x X o ~x
x
X
x
X
Z O
Ig
7 B
KIDNEY O
3
O X Xx
1 X
110
0 X
o ~X~o
~
~
150
150
X 0
'
'
1")'0
BODY LENGTH cm. Fig. 2. Relationship between porpoise body length and cadmium concentrations (#g g- ~wet weight) in liver (A) and kidney (B). Circles represent females; crosses, males.
concentrations in liver than in the other organs. Copper concentrations in liver and kidney displayed considerably less variability than did mercury and cadmium levels in the same organs. Also, no systematic variation of concentration with body length could be found. Zinc The concentrations of zinc also show no clear variation with size of porpoise, and relatively small differences between specimens. Higher concentrations were found in the liver and spleen (Table I) than in other organs. DISCUSSION Mercury concentrations in selected porpoise tissues have been reported by Gaskin et al. (1972; 1979) and Harms et al. (1977). The distribution of mercury between organs is similar for samples from both the east and west sides of the North Atlantic (Table 2); however, some Canadian porpoise contained relatively high mercury concentrations, particularly in the
M F
M F M F
0"89-18-3 0-55-91-3 3-38 3-37 0"70-28"0 0"29-10"6 0'28-15'9
° Gaskin et al. (1972). Gaskin et al. (1979). 5-year old adults. c Harms et al. (1977). Three specimens. d This study.
Baltic and North Sea r North Sea d
West Atlantic b
West Atlantic*
Liver Range
15-7 16'2 10-4 3"4 6"0
Y~
0.47-2"82 0'23-1.79
0"8-5"2 1.5-4.5
Kidney Range
1'23 1"02
2.00 2.77
"2
0' 11-0-46 0.08-3-04
Brain Range
TABLE 2 Mercury Concentrations (/~g g - t wet weight) in Porpoise
0"30 1"30
0'38 0-42
f~
0-21 - 1.92 0"26 2.58 0-6-2'6 0-7 -2-5
Muscle Range
0.75 1-02 1.12 i .46
Y~
q~
.t..x
Trace metals in the common porpoise, Phocoena phocoena
125
liver. The liver of porpoise from the Bay of Fundy (Gaskin et al., 1972) and in this study both show increasing mercury levels with body length. However, whilst concentrations are similar in small animals (up to about 140cm), in larger animals concentrations are considerably greater in Canadian samples. This length (140cm) corresponds to an age of 4-5 years (Gaskin et al., 1979) above which, due to increasing variance of weight in older animals, estimation of age from length becomes unreliable. The greater variance of mercury concentrations in large specimens noted by Gaskin et al. (1979), and the generally lower concentrations in large North Sea porpoise, may reflect difference in the age structure of the two sets of samples. The pattern of decreasing proportion of methylmercury in liver with increasing total mercury confirms and amplifies the trend reported by Gaskin et al. (1972; 1979). A similar pattern has been more widely established in seals (e.g. Reijnders, 1979). The most important uptake route of mercury to seals and porpoises is probably through the diet, i.e. fish. Mercury in fish is present almost entirely as methylmercury (Holden, 1973) and there is general agreement that a mechanism for the demethylation of organic mercury exists in seals, probably in the liver (Roberts et al., 1976). It may well be, therefore, that a similar mechanism occurs in the common porpoise. The only other measurements of cadmium in porpoise known to us are by Harms et al. (1977) who found 0.02-0.19/~g g - ~ and 0.08-0.95/tg gin liver and kidney, respectively, which agree reasonably with our data. The distribution of cadmium between organs is similar to that in the grey seal (Hepplestone & French, 1978; Caines, 1978; McKie et al., 1980) and, generally, increases in concentration with age or length were also found. The general levels and distribution of copper and zinc agree with those reported by Harms et al. (1977). However, the lack of any accumulation of these elements during growth, and the relatively small variance between animals, contrasts markedly with the results for mercury and cadmium. This suggests that the common porpoise can, at least partially, regulate copper and zinc concentrations. Coet~cients of linear correlation were calculated for the variation of mercury concentration with length in liver (r = 0-65) and kidney (r = 0.42), and found to be significant at the 0.1% and 5 % levels, respectively. The data for cadmium in liver (r = 0.57) and kidney (r = 0.69) were similarly treated, and the regressions were significant at the 1% and 0.1% levels, respectively. Whilst these regressions are significant, the correlation
('. R. Falconer, 1. M. Dat, ies, G. Topping
126
coefficients are fairly low. This may, to some extent, be due to length being a poor analogue of age (particularly for larger animals) as previous studies of marine mammals (e.g. Hepplestone & French, 1978; Gaskin et al., 1979) had found closer correlation between age and metal concentration. It may also be noted that the large variance in mercury and cadmium concentration obtained from a sample of porpoise from a small part of the North Sea implies that porpoise would be of limited usefulness as an indicator of environmental quality.
ACKNOWLEDGEMENTS The authors wish to thank members of the Demersal Section of the Marine Laboratory, Aberdeen, for the collection, measurement and sampling of the specimens.
REFERENCES Caines, L. A. (1978). Heavy metal residues in grey seals (Halichoems grypus)from the Farne Islands. International Council for the Exploration of the Sea, Statutory Meeting 1978, CM1979/E:40. Davies, I. M. (1978). Determination of methylmercury in the muscle of marine fish by cold vapour atomic absorption spectrophotometry. Anal. Chim. Acta, 102, 189-94. Gaskin, D. E., Ishida, K. & Frank, R. (1972). Mercury in harbour porpoises (Phocoena phocoena) from the Bay of Fundy region. J. Fish. Res. Bd Can., 29(11), 1644-6. Gaskin, D. E., Stonefield, K. I., Suda, P. & Frank, R. (1979). Changes in mercury levels in harbour porpoises from the Bay of Fundy, Canada and adjacent waters during 1969-1977. Arch. Environm. Contam. Toxicol., 8, 733-62. Harms, U., Drescher, H. E. & Huschenbeth, E. (1977). Further data on heavy metals and organochlorines in marine mammals from German coastal waters. International Council for the Exploration of the Sea, Statutory Meeting, 1977, CMI977/N:5, 14pp. Hepplestone, P. B. & French, M. C. (1978). Mercury and other metals in British seals. Nature, Lond., 243, 302-4. Holden, A, V. (1973). Mercury in fish and shellfish. A review. J. Fd Technol., 8, 1-25.
Holden, A. V. & Topping, G. (1981). Report on further intercalibration analysis in ICES pollution monitoring and baseline studies. International Council for the Exploration of the Sea, Co-operative Research Report No, 108.
Trace metals in the common porpoise, Phocoena phoccena
127
McKie, J. C., Topping, G. & Davies, I. M. (1980). Trace elements in grey seals Halichoerus grypus from the east coast of Scotland. International Council for the Exploration of the Sea, Statutory Meeting 1980, CMI980/E:41. Rae, B. B. (1965). The food of the common porpoise (Phocoena phocoena). J. Zool., 146, 114-22. Rae, B. B. (1973). Additional notes on the food of the common porpoise (Phocoena phocoena). J. Zool., 164, 127-31. Reijnders, P. J. H. (1979). Organochlorine and heavy metal residues in harbour seals of Schleswig Holstein plus Denmark and the Netherlands: Their possible effects in relation to the reproduction in both populations. International Council for the Exploration of the Sea, Statutory Meeting 1979, CMI979/N:I8. Roberts, T. M., Hepplestone, P. B. & Roberts, R. D. (1976). Distribution of heavy metals in tissues of the common seal. Mar. Poll. Bull., 7(10), 194-6. Topping, G. (1973). Heavy metals in fish from Scottish waters. Aquaculture, 1, 373-7. Topping, G. & Holden, A. V. (1978). Report on intercalibration analysis in ICES North Sea and North Atlantic baseline studies. International Council for the Exploration of the Sea, Co-operative Research Report No. 80. Topping, G., Pirie, J. M., Graham, W. C. & Shepherd, R. J. (1975). An examination of the heavy metal levels in muscle, kidney and liter of saithe in relation to year class, area of sampling and season. International Council for the Exploration of the Sea, Statutory Meeting 1975, CMI975/E:37.