C
Abst
Trace metal analysis of 23 species of common Pacific Coast marine
foods revealed high cadmium values for Bent-nosed clams (Macoma nasuta),
Bay mussels (Mytilus edulis), Bay oysters (Ostrea lurida), Pacific oysters
(Crassostrea gigas), and Littleneck clams (Protothaca staminea). Metals
were found to concentrate in the gills, heart, and visceral mass of all
10 species of bivalve mollusks examined. Swordfish (Xiphias gladius) and
Salmon (Oncorhynchus tshawytscha) demonstrated the highest cadmium values
for fish flesh.
Introduction
In light of the recent concern over contamination and toxicity of
cadmium (Nilsson, 1969), (Schroeder, et al, 1966, 1967, 1968), (Pringle, 1968),
an examination of cadmium, zinc, copper, and manganese concentrations in the
edible portions of bivalve mollusks, 10 species of fish, and 3 species of
crustaceans was undertaken. Particular attention was given to the soft
bodies and organs of the mollusks since other workers have reported that
they concentrate trace metals (Schroeder, 1967), (Brooks and Rumsby, 1965),
(Pringle, 1968).
Six species of mollusks and 2 species of fish were collected from
Elkhorn Slough, which flows into Monterey Bay near Moss Landing, California.
This area is particularly abundant in estuarine animals although it has
been condemned by the county health department as a health hazard due to
high E.coli counts. It is also the receptor of both the Pacific Gas & Electric
generator plant and the Kaiser Aluminum plant waste water effluents. No
attempt was made to determine the metal contents of the effluents. Accord-
ing to Veith (1971), Monterey Bay sewage effluents pour as much as 175 grams
of cadmium into the Bay per day.
Methods
Mollusks were collected and removed from shells, rinsed with dis-
tilled water and disected (where applicable). Fish and crustacean samples were
purchased at local fish markets. All samples were weighed, dried for about
12 hours at 1000C and reweighed. Digestion of dried material was accomplished
55.
563
by adding 90% nitric acid and heating in acid-cleaned 30ml Pyrex beakers.
Drops of capryl alcohol were added to minimize foaming where necessary,
(as in Middleton and Stuckey, 1953). Blanks were treated exactly as the
marine samples. Once the tissues were in solution, they were heated until
charred, on hot plates, in order to burn off lipid particles. Samples
were cooled, redisolved with 90% nitric acid, and cleared by adding
hydrogen peroxide dropwise with heat. Once clear, samples were diluted with
distilled water, covered, and analyzed within 3 days. Samples were analyzed
for metal concentrations by atomic absorption spectrophotometry (Perkin-Elmer 303),
using a triple slot burner head. The detection limits for cadmium, copper,
and manganese were 0.05 ug/g dry weight, and for zinc was 0.5 ug/g dry weight.
Results & Discussion
Tables of the results indicate the common and scientific names of
samples, which samples were disected, and which samples were analyzed whole
(since they are eaten whole). The right hand column of the tables lists the
dry to wet weight ratio. Multiplication of this value by the dry parts per
million (ppm or ug/g) figures gives the values for ppm wet weight.
Metals were clearly concentrated in bivalve mollusks of all species.
The highest concentrations were found in the heart, gills and visceral mass
of individual animals. The clams tended to concentrated the metals to a
lesser degree than did the non-siphoned bivalves, i.e. the scallop, oysters,
and mussels, in every case except for the Bent-nosed clams. Three Bent-nosed
clams (Nacoma nasuta) from Elkhorn Slough averaged 30 ppm dry weight of cadmium
and 1,076 ppm dry weight of zinc (See Table 1). This particularly hardy
species of clam has a separated siphon which acts as a "vacuum cleaner"
combing the surface of the slough bottom.
Whole oysters, and especially Ostrea lurida from San Francisco Bay,
were noted to have high concentrations of zinc (900 ppm dry) and copper
(173 ppm dry) (See Table 2). The nephridium of one scallop (Hinnites multi-
rugosus) taken from San Pedro Harbor in Los Angeles, contained the highest
cadmium level of the study (181 ppm dry) (See Table 4). Interestingly enough,
the nephridium corresponds in function to the mammalian kidneys, which are
also the site of cadmium concentration (Schroeder, 1967).
Although the Gaper clams (Tresus nuttalli) from Elkhorn Slough, had
low metal concentrations, the outer skin, covering the neck was found to
have the highest manganese content (1,200 ppm dry) (See Table 5). Since
manganese is a common metal component of sediments, it is possible that
the sample of neck skin included some clay particles, although it was thor-
oughly washed. Unfortunately a substrate analysis of the Slough sediment was
not taken.
Although cadmium values in fish flesh were relatively low,(less than
1.5 ppm dry) Swordfish and Salmon contained more cadmium than the crustaceans
and edible portions of the Gaper clam (Table 6).
The figures presented here should not be considered as representitive for
species from the entire Pacific Coast. Note, for example, that the cadmium
concentration was 5 times higher in Littleneck clams (Protothaca staminea)
from Elkhorn Slough than those from Canada (See Table 1).
54
According to Schroeder, a normal human intake of cadmium is 215 ug/ day
(Nilsson, 1969). Of this, 984 is excreted. Of the 24 retained, most is stored
in the kidneys and liver. Bowen (1966) indicated that 3mg of cadmium ingested
per day is "toxic" to humans. In order to achieve such an intake of cadmium
per day, one would have to eat 1½ pounds of Bent-nosed clams or 17 whole
oysters from Elkhorn Slough. Likewise, 84 pounds of scallop muscles from
San Pedro Harbor, or 174 pounds of Swordfish steak would account for such
a quantity of cadmium. (These amounts were calculated from the cadmium
concentrations in ppm wet weight.)
55
C
Acknowledgements
I would like to thank John Martin, Phd., and D.P. Abbott, Phd., both of
Hopkins Marine Station, for their aid and advice. I would also like to
thank Dr. and Mrs. Wm. Burget for making this research financially possible.
Special thanks goes to Prof. Hadley Kirkman and his bride.
566
10.
11.
12.
Bibliography
Bowen, H.J.M.: Trace Elements in Biochemistry, Academic Press, New York,
1966, p.116.
Brooks, R.R. & Rumsby, M.G.: "The Biogeochemistry of Trace Element Uptake
by Some New Zealand Bivalves", Jr. Limnol. Oceanog., 10: 521-527, 1965.
Christian, G.D. & Feldman,F.J.: Atomic Absorption Spectoscopy, Wiley-
Interscience, New York, 1970.
Middleton,G. & Stuckey, R.E.: "The Preparation of Biological Material
for the Determination of Trace Metals", Analyst, vol.79: 138-142, March 1954.
Pringle, B. et al: "Trace Metal Accumulation by Estuarine Mollusks",
Proc. Am. Soc. of Civil Eng., p.455-475, June 1968.
Ricketts, Ed & Calvin,J.: Between Pacific Tides, Stanford University Press,
Stanford, California, 1939.
Nilsson, Robert: Aspects on the Toxicity of Cadmium and its Compounds,
Nat. Science Research Council, Stokholm, Sweden, May 1969.
Schroeder,.H.A., et al.: "Trace Metals in Rat Tissues as Influenced
by Calcium in Water", Jr. of Nutrition 93: 331-335, 1967.
Schroeder, H.A., et al.: "Influence of Cadmium on Renal Ischemic
Hypertension in Rats", Jr. of Physiology, 214: 469-473, March 1968.
Schroeder, H.A., et al.: "Essential Trace Metals in Man: Zinc Relation
to Environmental Cadmium",J. chron. Dis., 20: 179-210, 1967.
Tipton,I.H.; "The.Distribution of Trace Metals in the Human Body"
in Seven,M.S, & Johnson,L.A. eds.: Metal Bindings in Medicine, Lippincott
pp. 27-42, 1960.
Veith, Rob: "Trace Metals in Monterey Peninsula Sewerage", unpublished,
Hopkins Marine Station of Stanford Univ., Pacific Grove Calif., 1971.
Legend for Graph 1
The following bar graph represents cadmium concentrations in
weight of edible samples. In the cases where the whole animal (shell-less)
is eaten, such as the smaller clams and oysters, whole body concentrations
are depicted. Samples listed as "ND" are the cleaned edible portions in
which the metal concentration was below the detection limit.
Tables i through 7 list the genus species names of the animals examined
along with the ppm dry weight values and the dry/wet weight ratios.
555
22
Bent-nosed Clamt
(Elkhorn Slough)
Pacific Oyster
(Elkhorn Slough)
181.18
Bay Musse.
(Elkhorn Slough
Pacific Oyster
(Shelton. Mash.
ittle Neck Clam
(Elkhorn Slough)
Scallop muscle
(L.A. Harbor)
Razor Clam
Sword
Little Neck Clam
(Canada)
Rosetta Clam
(East Coast
Dungenest
(canned)
Dungeness
(fresh)
Salmont
Prauns
Pacific Shrimp
Gaper Clam
Rock Codt ,Solet
Sableffish",
Red Snapper
CADMU TCONDON MARTNE FOOD
rgrwet weight ofsample (ppm wetwe
Cleaned edible portion
Deconcentrat
tdetect
565
pon
560
Table 1
Bivalve Mollusks
Concentrations of trace elements in whole individuals
(Average PPM dry weight)
Zinc Copper Manganese dry/wet"
Cadmium
Mercenaria mercenaria
Eastern Rosetta clams
.242
62.0
15.0
10.8
average of 3 whole bodies
1.2
(18.5) (2.5)
(.1)
(1.1) (standard deviation)
Protothaca staminea
Little Neck clams; Elkhorn Slough
.208
65.0
8.5
average of 5 whole bodies
5.1
6.2
(0.8)
(3.2)
(9.2)
(1.5)
.260
8.2
2.8
1.0
59.3
average of 3 whole bodies
from British Columbia
(44.4) (8.3)
(0.3)
Macoma nasuta
Bent-nosed clams; Elkhorn Slough
.177
30.0
1076.0 42.0
29.0
average of 3 whole bodies
(100.0) (15.0) (10.6)
(6.7)
Tresus nuttall
Gaper clam; Elkhorn Slough
.564
5.0
31.0
17.0
0.7
one whole body
Saxidomus nuttalli
Butter clam; Elkhorn Slough
.220
37.8
2.4
4.5
one whole body
1.3
Siliqua patula
Razor clams; Sunset Beach, Oregon
average of 3 by parts
63.0
1.5
3.0
Neck and mantle
.213
(10.0) (1.4)
(1.8)
(0.3)
nd*
.234
65.0
6.3
18.0
Visceral mass + contents
(16.5) (2.0)
(8.3)
2.0
144.7
25.0
3.1
.29
Gills
(36.0) (1.4)
(0.9)
(1.2)
(* ratio of grams dry weight/grams wet weight)
* concentration not detectable)
Table 2
Bivalve Mollusks
Concentrations of trace elements in whole individuals
(Average PPM dry weight)
Cadmium Zinc Copper Manganese dry/wet"
Ostrea lurida
Olympia Oysters;
San Francisco Bay
average of 3 whole bodies 6.2
906.0 173.0
21.7
.272
(.9)
(3.7)
(50.0) (40.0)
(Standard deviation)
Crassostrea gigas
Pacific Oysters; Shelton Wash.
Commercially harvested
124
average of 3 whole bodies 2.5
290.0 28.5
6.1
(50.0) (3.4) (1.0)
(0.4)
Mytilus edulis
Mussels; Elkhorn Slough
37.7
5.6
.248
average of 3 whole bodies
(1.2)
(16.7) (0.8)
(0.7
cont
Table 3
Bivalve Mollusks
Concentrations of trace elements in individual organs
(PPM dry weight)
drylwet
Cadmium
Zinc Copper Manganese
Crassostrea gigas
Pacific Oyster; Elkhorn Slough
Oyster fl
nd*
3.0
256.0
8.0
.172
Adductor muscle
ant
574.0
10.0
2.0
.167
65.0
Mantle + gonad
.240
3.0
320.0
31.0
25.0
Gonad
11.0
.190
Gills
660.0 96.0 52.0
uth
5.0 461.0 47.0
.272
Mouth palps
632.0
.250
50.0
nd
24.0
Heart
.228
23.0 477.0 87.0
10.0
Digestive gland
minus gonad
Oyster #2
.176
1.5 174.0
Adductor muscle
8.0
6.0
458.0
24.0
57.0
.213
Mantle + gonad
17.0
3.4
154.0 27.0
5.0
.250
Gonad
25.0 658.0 92.0
.195
Gills
96.0
.286
Mouth palps
12.0
10.5 377.0 74.0
64.0 415.0 84.0
13.0
Heart
.233
214
5.0
Digestive gland
16.7 271.0 41.0
plus gonad
263.0 40.0
10.6
11.0
.270
Whole oyster
63 grams wet--17 grams dry: Analyzed and dryed by parts.
(* ratio of grams dry weight/grams wet weight)
(** nd - concentration of element was not detectable)
Si
Table 3 cont.
Bivalve Mollusks
Concentrations of trace elements in individual organs
(PPM dry weight)
Cadmium
Copper Manganese dry/wet"
Zinc
Crassostrea gigas
Pacific Oyster; Shelton Wash.
Commercially harvested
419.0
29.0
Adductor muscle
5.0
9.0
.200
230.0
46.0
2.0
Mantle + gonad
.222
nd*
230
Gonad
387.0
74.0
7.5
167
197.0
6.0
15.0
Gills
628.0
5.6
287.0
34.0
nd
.250
Mouth palps
442.0
.200
7.0
130.0
nd
Heart
567.0
94.0
7.5
218
Digestive gland
10.0
minus gonad
56
Table 4
Bivalve Mollusks
Concentrations of trace elements in individual organs
(PPM dry weight)
Copper Manganese dry/wet"
Cadmium
Zinc
Hinnites multirugosus
Scallop; San Pedro Harbor, L.A.
Adductor muscle
3.5
1.4
83.0
1.0
.22
12.0
90.0
3.0
.195
Mantle
3.0
nd*
191.0
nd
.085
Foot
nd
Gills
467.0
105.0
.084
8.6
21.0
.065
Labial palps
304.0
75.0
13.0
54.0
41.0
7.3
.093
212.0
31.0
Heart
.104
53.0
25.0
181.0
311.0
Nephridium
.720
Visceral mass
77.0 87.0
37.6
5.5
plus gonad
564
Table !
Bivalve Mollusks
Concentrations of trace elements in individual organs
Values represent ugrams of metal/gram dry weight of tissue
Copper Manganese dry/wet
Cadmium
Zinc
Saxidomus nuttalli
Butter clam; Elkhorn Slough
.264
8.7
Anterior adductor muscle
0.1
21.0
0.8
37.0
1.0
1.8
0.5
Foot muscle
nat
.234
2.9
50.0
Neck muscle
0.5
40.0
.250
1.8
19.0
Mantle
0.7
.164
83.0
6.0
1.8
Gills + contents
1.7
2.4
.198
81.0
6.2
8.2
Heart, palps, alimentary
canal and contents
123.0
12.0
3.7
Visceral mass + contents
3.2
(* ratio of grams dry weight/grams wet weight of sample)
(* not detecable)
Tresus nuttalli
Gaper clam; Elkhorn S.
clam l
.23
58.0
Anterior adductor muscle nd
.139
nd
101.0
Foot muscle
.170
53.0
Neck muscle (skinless)
nd
.119
109.0
17.0
1.0
Gills
.144
59.0
81.0
16.0
15.0
Heart and alimentary
canal
38.0
33.0
5.8
0.75
.530
Visceral mass + contents
1200.0
.16
122.0
4.0
Neck skin
nd
Aié
566
Table 5 cont.
Bivalve Mollusks
Concentrations of trace elements in individual organs
(PPM dry weight)
Cadmium Zinc Copper Manganese dry/wet
resus nuttalli
Gaper clam; Elkhorn Slough
Clam +2
nd*
.149
87.0
nd
Anterior a ductor muscle
.135
4.0
73.0
Foot muscle
nd
nd
.149
47.0
4.0
0.9
Neck muscle (skinless)
18.0
.135
103.0
nd
nd
Mantle
.119
108.0
nd
nd
21.6
Gills

1.
Heart and alimentary
42.0
.108
190.0
8.5
18.0
canal
48.0
58.0
16.0
.192
Visceral mass + contents
0.9
* ratio of grams dry weight/grams wet weight of tissue sampled)
(* concentration of element was not detectable = nd)
566
Table 6
Fishes
Concentrations of trace elements in fish flesh
(Average PPM dry weight)
Zinc Copper Manganese dry/wet
Cadmium
Oncorhynchus tshawytscha
King Salmon
nd*
.308
19.0
2.9
Average from 2 fillets
0.6
(0.0)
(7.0)
(1.0)
(standard deviation)
Xiphias gladius
39.0
nd
25
1.5
1.25
Swordfish, one sample
Gadus macrocephalus
Rock Cod; Monterey Bay
1.0
.229
16.4
Average from 3 fillets
nd
0.2
(2.0)) (0.0)
(0.0)
Sebastodes miniatus
Vermillion Rockfish or Red Snapper
23.6
1.9
.221
nd
Average of 3 fillets
(0.6)
(7.0)
Anoploma fimbria
Black Cod; Sable fish
nd
2.5
Average from 2 fillets
.321
(225) (0.0)
62
Sole-species unknown
.155
2.0
23.0
1.2
Average of 3 fillets
(3.0) (0.4)
(0.9)
Atherinos affinis
Top Smelt; Pajaro River, Cal.
66.0
average of 3 fillets
(0.1)
(6.0) (0.1)
Cymatogaster aggregata
Shiner Perch; Elkhorn Slough
43.0
3.6
2.0
0.2
Average of 10 fillets
(13.0) (1.7)
(0.7)
(0.3)
Platichthys stellatus
Starry Flounder; Elkhorn Slough
1.
Average of 5 fillets
nd
(0.2) (0.2)
(0.2)
Roccus saxatilis
Striped Bass; Pajaro River
20.0
1.2
Average of 3 fillets
10.6)
(2.0) (0.4)
(* ratio of dry weight/wet weight of sample) (*concentration not detectable)
(4 data from Jim Prickett, Hopkins Marine Station, Pacific Grove, California)
56
68
Table 7
Crustaceans
Concentrations of trace elements in flesh
(Average PPM dry weight)
Manganese dry/wet"
Copper
Cadmium
Zinc
Pandalus jordani
Ocean Shrimp; fresh
18.5
(3:5)
(8.0)
0.5
(standard deviation)
Average of 7 shelled
(0.0)
tail portions
Prawns; species unknown
47.0
12.0
nd**
.221
Average of 3 shelled tails
0.2
(15.1) (2.2)
(0.0)
Cancer
magister
Dungeness Crab meat
16.0
fresh
73.0
(6.0) (1.6)
(0.8)
(0.1
93.0
7.2
0.8
.3
canned
(0.1)
(7.6) (1.5)
(0.1)
(* ratio of dry weight to wet weight of sample)
(** concentration of element, not detectable)