Trace Metal Levels in Intertidal
Molluscs of California
Abstract
Determinations of Ag, Cd, Cr, Cu, Mn, Pb, and Zn were made by
atomic absorption spectrophotometry on 7 species of Mollusca in the
genera Acmaea, Tegula, Thais (gastropods), and Mytilus, Protothaca,
and Tapes (bivalves). Eleven regions along the California coast
from San Francisco Bay to Los Angeles were included. Separate
analyses were performed on shells, and on soft portions of whole
bodies. Highest levels, above 900 ppm Pb were found in bodies
of Acmaea digitalis, 570 ppm Cu and 1700 ppm Zn in bodies of
Thais emarginata.
Trace Metal Levels in Intertidal
Molluscs of California
Introduction
A growing number of observations of potentially toxic levels
of trace elements such as lead, cadmium, and zinc in fishes and shell¬
fish has focused concern on the matter of distribution of these materials
in marine organisms (Drinnan, 1966; Hardy, 1966; Houblouget al, 1954;
MeFarren et al, 1961). The interest in this field is not new. Since
the work of Cornec (1919), and Clark and Wheeler (1922), scientists have
been aware of concentration of trace metals in a variety of marine
plants and animals. Results of later studies have been compiled by
Vinogradov (1953) and Goldberg (1965); they cover many marine species,
though most of the data were obtained by analytical methods far less
accurate than those in current use.
Limited information is now available on the heavy metal content of
a number of marine molluscs in various parts of the world (e.g. Brooks
and Rumsby, 1965; Shuster and Pringle, 1968) but little has been done with
California species. In the present study, 7 species of molluscs from 11
locations in California were analyzed for their content of silver, cad-
mium, chromium, copper, manganese, lead, and zinc (Ag, Cd, Cr, Cug Mn,
Pb, Zn). While far from Comprehensive, the present survey represents an
attempt to establish baselines for existing levels, to relate these
levels to possible environmental sources, and to discover any molluscs
which exhibit particularly high levels of one or more metals.
Materials and Methods
Collecting stations are shown in Fig. 1. The species examined
-2-
included two herbivorous gastropods, one predatory snail, two bivalves
living on hard substrata, and two burrowing clams, as follows:
Acmaea digitalis Eschscholtz, 1833
Tegula funebralis (Adams, 1854)
Thais emarginata (Deshayes, 1839)
Mytilus californianus (Conrad, 1837
tilus edulis Linnaeus, 1758
Protothaca staminea (Conrad, 1837)
Tapes semidecussata (Reeve, 1864)
All species were collected alive, from the lowest portions of their
intertidal ranges. Animals were kept in filtered sea water for 24 hours
to purge sediments and gut contents. Before removal of soft parts, com¬
mensal organisms were removed, and the external surfaces of the shells
were cleaned with a non-metallic brush. Bivalves were placed in a 60°0.
oven for 15 minutes to cause opening, while gastropods were cracked
carefully in a vice. Bodies of both classes were then excised withaa
plastic knife, and both bodies and shells were washed with filtered sea
water and dried at 110°0. for 24 hours. The bodies of each species from
each location were pooled together to produce enough material for anal¬
ysis. From this, 3 aliquots were taken for triplicate analysis. The
same was done for shells.
Each aliquot of shell was crushed with mortar and pestle to.5-1cm
pieces. Samples of approximately .25g were used for analysis, as
experience showed that this small amount of sample, in the dilutions used,
caused less light scattering in analysis. These samples were then
placed in a 30ml pyrex beaker and weighed to the nearest .lmg. Five
196
to oml of concentrated HOlwere added and the beaker covered with a way
watch glass. After foaming subsided, 5-6ml of 90% HNO3 were added.
Samples were shaken gently and warmed at low heat (60-70°0.) When
solutions turned clear, they were diluted with distilled water to 25ml.
Dried bodies were ground to a fine powder. Aliquots of approx-
imately lg were weighed to the nearest .lmg in a 30ml pyrex beaker.
Then 5-6ml of 70% HNO, were added; samples were covered as above, and
heated to a slow boil. If lipids were not present (visible as droplets)
samples were allowed to cool, and 2-3ml of 30% H,0, were added dropwise
to oxidize remaining organic matter. When clear, solutions were diluted
with distilled water to 25ml. If lipids were present, samples were
evaporated to dryness, then charred at 250°0. They were then cooled to
room temperature, redissolved in 90% HNO, boiled, recooled, treated
as above with Ho0, then diluted to 25ml.
Controls were run in two different ways, all steps of treatment
being identical to those with samples. Type 1 controls were blank
beakers used to compensate for contamination of samples from procedures
(handling, drying, reagents, etc.). These readings were subtracted from
sample readings. Type 2 controls were beakers containing standard
solutions of mètals at known concentrations, to measure loss. Steps
of treatment were again identical to those with samples. Results, used
to adjust sample readings, are as follows: Ag-1% loss, Cd-no loss, Or-
7 gain, Cu-7% loss, Mn-5% loss, Pby11% loss, Zn-38 loss.
Gderk
All samples were analyzed using a Perkin-Elmer Atomic Absorption Spectro-
photometer, Model 303. Light scattering artifacts in Od, Pb, and Zn
were compensated for by running all samples with the Pb lamp at 222).
At this wavelength, the spectrophotometer read only background levels
of light scatter. Values from this procedure were treated as werettypell
controls, and subtracted from sample readings.
-H
Results and Discussion
Levels of metals found in shells and bodies appear in tables 1 and
2, and figs. 2 and 3, and are discussed below.
Silver and Copper
Of the metals studied, Ag was distributed most uniformly in the
shells of animals examined; the highest levels,210 ppm, were found in
Acmaea at Fort Point, San Francisco (location B, in figs. and tables);
Thais and Tegula at Mussel Point (G). Body values of Ag were highest in
Tapes from Coyote Point, San Mateo (A), 7.3 ppm. Detectable amounts
(21 ppm) were found in all Tegula bodies, and consistently higher values
in the shells. Nicholls et al. (1959) have found Ag in zooplankton;
Brooks and Rumsby (1965) suggest that Ag is introduced into the digestive
system of the animals they studied (bivalves Ostrea sinuata, Pecten
novae-zelandiae and Mytilus edulis) by ingestion of plankton and suspended
particles.
Copper levels on molluscan bodies examined were up to 90 times as
high as in the shells (viz. Thais). High Cu values in Tegula,175 ppm, and
Thais, 570 ppm, from Fisherman's Wharf at Monterey Harbor (F) are probably
related, at least in part, to the presence of nearly 300 small boats
docked in the area, some only 50 yards away; the hulls of many are coated
with a Cu-based anti-fouling paint. The almost three-fold increase in
hais over Tegula may be related to the fact that the former is a preda-
cious snail and may get part of its Cu from the ingestion of herbivores
(like Tegula) or filter feeders (like Mytilus) which already contain sig-
nificant levels of Cu. Copper is an important enzyme activator and is a
constituent of hemocyanins that are present in all of the molluscs studied.
A basic physiological level for Cu cannot now be suggested, owing to the
198
-5
likely possibility of Cu contamination at all localities in this study.
Chromium and Manganese
Chromium was found in relatively high amounts in bodies at two local-
ities, in Acmaea at Fort Point (B) and in Tegula at Fisherman's Wharf (F).
Shells were consistently highest at the Wharf. Body levels may relate to
possible contamination from automobiles at Fort Point (see lead, below), and
the presence of small craft in Monterey Harbor (see copper, above). Tapes
at Coyote Point (A) is also notable. tor high Cr.
High Mn levels in bodies and shells were found in animals from muddy
areas; in Mytilus and Tapes at Coyote Point (A) and in Mytilus at Elkhorn
Slough (D). Values were also high in Acmaea from Fort Point (B) and White's
Point (K). Manganese levels in shells of Tegula were first documented by
Krinsely (1959) who found 4-6 ppm in shells of live California animals, and
13-17 ppm in fossilized specimens. Most values in the present study are
above the range given for live animals. Manganese has a role as an activator
of enzyme systems that is well established.
Lead
Detection of Pb in shells was partially handicapped by high spectro-
photometric limits. High values were found in Mytilus californianus at
Half Moon Bay (C), both species of Mytilus at White's Point (K), and
especially in Acmaea at Fort Point (B), 931 ppm. These are animals which
live well up in the intertidal zone, and, near cities, they are exposed to
atmospheric fallout of Pb from automobile exhaust for much of the day.
Animals found at Half Moon Bay were in the vacinity of a sewer outfall.
White's Point, besides being directly inshore of the Los Angeles County
sewer outfall, is close to regions of heavy traffic in Los Angeles and
Long Beach. Fort Point attracts an estimated 60-100 tourist automobiles
199
-6-
per day on weekends, many of which have been seen to park within 5 feet
of the wall on which Acmaea were found. In addition, this locality is
situated directly under the Golden Gate Bridge. The very high levels
of Pb in Acmaea digitalis bodies at this point perhaps reflect not only
the high Pb fallout from auto exhaust, but also the fact that this species
lives on, and feeds from rock surfaces not thoroughly rinsed by their
submersion at high tides each day. Lead has no known usefulness in bio-
logical systems, and is known to inhibit certain enzymes.
Cadmium and Zinc
Cadmium in shells was highest in Mytilus at Carmel Bay (I), in Tapes
at Coyote Point (A), and Tegula at Fisherman's Wharf (F). Body values are
most sizable in Acmaea at White's Point (K) and Thais at the Wharf (F).
Cadmium is toxic to living systems because it can replace Zn, an important
component of metalloproteins such as carbonic anhydrase. Zinc metal in the
environment, however, often contains substantial amounts of Od as a contam¬
inant, which might explain the high correlations of Cd and Zn in bodies of
maea and Thais.
Zinc was the most abundant trace metal in the soft parts of molluscs,
as it is in seawater; values in the body were at least 20 times higher than
in the shell. High amounts of Zn in bodies of Thais at Fisherman's Wharf,
1700 ppm, and of Acmaea at White's Point (K), 763 ppm, may be correlated
with location. In motor-driven marine vessels, it is almost universal to
have Zn blocks fastened to the hull, near the propeller to protect it and
the drive shaft from electrolysis in sea water. These blocks, higher in
the electromotive-force series than iron and brass, slowly go into solution
and need replacement at regular intervals. Fisherman's Wharf, as noted
earlier, lies in a harbor, while at White's Point (K) the collecting siteer.
200
-7-
is less than 4 miles from the Los Angeles-Long Beach Harbor, where many
hundreds of boats are moored. Zinc has been found to be concentrated by
brown algae (Black and Mitchell, 1952) 40 times that in sea water.
Mytilus edulis
It is perhaps noteworthy that levels of trace metals in Mytilus edulis
from California show a number of agreements with those of the same species
in New Zealand (Table 3) as determined by Brooks and Rumsby (1965). Dif-
ferenceslocalities and methods of analysis, however, should be taken
into consideration in any comparisons made.
Summary
Determinations of Ag, Cd, Cr, Cu, Mn, Pb, and Zn were made by
atomic absorption spectrophotometry on 7 species of Mollusca in the
genera Acmaea, Tegula, Thais (gastropods), and Mytilus, Protothaca,
and Tapes (bivalves). Eleven regions along the California coast from
San Francisco Bay to Los Angeles were included. Separate analyses were
performed on shells and soft portions of whole bodies. Highest levels.
above 900 ppm Pb found in bodies of Acmaea digitalis, 570 ppm Cu in
Tegula funebralis and 1700 ppm Zn in Thais emarginata, have raised
the question of causes for these unusual levels.
20
-8
Figure Captions
Figure 1. Map of collection sites, coast of California.
A. Coyote Point, San Mateo, San Francisco Bay. Mud flats with some
rocks; wave action slight.
B. Fort Point, San Francisco. Animals collected from vertical concrete
sea wall below Golden Gate Bridge; moderate wave action.
Half Moon Bay. Animals collected from rocky area just north of
Pillar Point, not far from sewer outfall for towns of Princeton,
Miramar, and Half Moon Bay; moderate to strong wave action.
Sandy mud flats; no wave action.
Elkhorn Slough, Moss Landing.
Monterey Municipal Wharf, Monterey. Animals collected from rocks
immediately to right of wharf. Mixing with waters inside the
harbor present; moderate wave action.
Fisherman's Wharf, Monterey. Animals collected from rocks
immediately to the right of, and underneath, wharf. This region,
inside the small craft harbor, is in close proximity to some
300 boats; no wave action.
Mussel Point, Pacific Grove, site of Hopkins Marine Station.
Animals collected from intertidal rocks; moderate wave action,
H. Point Pinos, Pacific Grove, Animals collected within 30 ft. ofnt
mouth of Pacific Grove sewage treatment plant outfall; wave action
moderate to strong.
Carmel Bay. Animals collected from rocky-intertidal region, close
to City of Carmel sewage treatment plant outfall; moderate to
strong, wave action.
Point Sur, Monterey County. Animals collected from rocky-intertidal;
wave action moderate to strong.
K.
White's Point, Palos Verdes Peninsula, Los Angeles. Animals
collected on intertidal rocks directly inshore of mile-long
Los Angeles County sewer outfall; wave action moderate to strong.
Figure 2. Concentrations of trace elements in shells of California
molluscs (pom dry weight). Letters indicate collecting sites
shown in Fig. 1. Dashed lines indicate detection limits.
Figure 3. Concentrations of trace elements in bodies of California
molluscs (ppm dry weight). LLetters indicate collecting sites
shown in Fig. 1. Dashed lines indicate detection limits.
63
-9-
Table Captions
Table 1. Concentrations of trace elements in shells of California
molluscs (ppm dry weight). N - no. of individuals in pooled sample.
Values given for each sample are means and standard deviations for
analysis of 3 separate aliquots. Letters indicate collecting sites
shown in Fig. 1.
Table 2. Concentrations of trace elements in bodies of California m
molluscs (ppm dry weight). N - no. of individuals in pooled sample.
Values given for each sample are means and standard deviations for
analysis of 3 separate aliquots. Letters indicate collecting sites
shown in Fig. 1.
Table 3. Trace metals (ppm dry weight) in soft portions of whole bodies of
Mytilus edulis. Values show means followed by ranges in parentheses.
A. Levels found in present study. B. Levels found by Brooks and
Rumsby (1965) in New Zealand,
203
Pacitic
Ocean
A-Coyote Point
B-Fort Point
C-Half Moon Bay
D-Elkhorn Stough
E-Monterey Wharf +2
F-Fisherman's Wharf (Mty.)
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A-Point Pinos
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(c
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20
A.
-15
Table 3
—
—
Cu
Mn
Ag
Pb
Ca
28 (201-
Calif.
4 (2-8)
24
5 (3-7)
1.0(1-3)
7 (5-11)
16(6-28
5 (2-8)
31)
New
(50-
6 1(71-1.99 (8-11) 1669-24) 27(12-39 12(3-25) 10 ( 1091
180)
1Zealand
209
-16
The author wishes to express thanks to the faculty, staff, and


graduate students of Hopkins Marine Station, especially to Dr. Donald
P. Abbott for his encouragement and many indispensible suggestions
both during research and while writing the manuscript. Dr. John H.
Martin provided additional helpful criticism and a general knowledge
of the problems of trace metal analysis. Both to them and to Mr. George
Knauer and Mr. S. John Chang, I owe gratitude for inspiration furnished
during this study.
C
-17-
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21