Contribution to the ecotoxicological study of cadmium, copper and zinc in the mussel Mytilus edulis. II. Experimental study. C. Amiard-Triquet, B. Berthet, ...
Marine BiOlOgy
Marine Biology 92, 7-13 (1986)
=
............
9 Springer-Verlag 1986
Contribution to the ecotoxicological study of cadmium, copper and zinc in the mussel Mytilus edulis II. Experimental study C. Amiard-Triquet, B. Berthet, C. Metayer and J. C. Amiard Universit6 de Nantes, Centre de Dosage des El6ments Traces; l, rue Gaston Veil, F-44035 Nantes c6dex, France
Abstract A regulation of internal levels of some essential metals has been observed in various animals, whereas the bioaccumulation of several non-essential metals parallels their overloads in water. In the mussel Mytilus edulis L., we have attempted to determine if such a phenomenon exists by comparing the patterns of accumulation of copper and zinc vs cadmium. With this aim, mussels collected in the Bay of Bourgneuf (France) in November 1983 were exposed to these metals for 16 d. At external levels of zinc as high as 100/~g 1-1, mussels were able to maintain a normal concentration in all groups of organs for 4 d. The ability of mussels to limit the bioaccumulation of copper and zinc varied from organ to organ, and decreased with higher levels of contamination and longer periods of exposure. In contrast, at the lowest experimental concentration and the lowest period of exposure, a significant increase of cadmium in mussel tissues was generally observed. Even at the highest sub-lethal doses, the levels of copper and zinc in mussel tissues were not much higher than the natural levels (contaminated:background ratios = 2.3 to 6.1), whereas the bioaccumulation of cadmium was less well restricted (contaminated:background ratios= 136 to 192). The use of mussels as a bioindicator of pollution seems doubtful for essential metals, particularly as regards short-term pollution, since the levels of these trace elements in the organisms are largely independent of their concentration in the ambient seawater.
Introduction The use of mussels as a biological indicator of metal pollution (National Academy of Sciences, 1980; Goldberg et al., 1983) assumes that a simple relation (linear, exponential, power) exists between metal concentrations in
water and in living organisms. According to Bryan (1984), there is little evidence that organisms actively prevent metal absorption, and he suggests that the internal concentration may be determined by storage and excretion efficiency. Bryan proposes three types of relationships that could exist between metal levels in the biota and the natural environment: (1) an organism excretes a metal at a rate proportional to its body burden (e.g. lead in Mytilus edulis L.); (2) an organism has limited powers of excretion and tends to detoxify and store metals; (3) in response to increased absorption, an organism increases its excretion efficiency. Radoux and Bouquegneau (1979) demonstrated that HgC12 intoxication induced increased mucus production by the gills of Serranus cabrilla, and a similar phenomenon was observed in Mytilus edulis exposed to copper by Scott and Major (1972). Coombs et al. (1972) established that cations can be complexed by mucous secretions. The combination of these two mechanisms and subsequent mucus delamination could limit the rate of entry of the pollutant in fish (Bouquegneau et al., 1982). Clearing of internal copper by transfer via excreted ligands, for example by increased mucous secretion from the gills of M, edulis, may be a mechanism of regulation in this species (Scott and Major, 1972). The ability of animals to maintain their internal chemical composition at a steady level when variations in the chemical composition of the external medium occur, varies from species to species and according to the physiological functions of trace elements. The best regulation is generally observed in the more highly evolved forms (fishes, decapod crustaceans) for the essential metals (Co, Cu, Mn, Zn). Among the molluscs, Haliotis tuberculata and Scrobicularia plana are able to regulate their level of zinc (Bryan et al., 1977; Bryan, 1979, 1984; Amiard et al., 1985). Consequently, the aim of the present study was to establish for Mytilus edulis the patterns of uptake of the essential trace metals copper and zinc compared to the non-essential cadmium.
C. Amiard-Triquet et al.: Experimental study of metals in Mytilus edulis
8 Material and m e t h o d s
Results
Experimental contamination
For each metal, we recorded its concentration in Mytilus edulis as a function of its level in the ambient seawater. For clarity, only mean concentrations are shown in Figs. 1-3. The coefficient of variation was an average of 35% for cadmium for all groups of organs and all periods of exposure. For copper, the mean coefficient of variation varied from 25% for the gills and palps to 36% for the "remainder" and 40% for the visceral mass; it was significantly lower for the gills and palps than for the other organs (paired-sample t test). For zinc, the coefficient of variation increased with the length of exposure from 23 to 32 in the gills and palps, 22 to 42 in the visceral mass and 35 to 42 in the "remainder". These differences between the "remainder" and the other two groups of organs are significant (paired-sample t test). In order to make comparison between metals easier, we used a concentration index (CI) w h i c h was the ratio between the concentration factors of the metal in contaminated organisms (CF 1) and in controls (CF 2), expressed as percent (Fig. 1-3):
Mytilus edulis L. were selected from a natural population according to their size (initial mean dry weight of soft tissues = 0.223 g) and maintained under cultivation in the bay of Bourgneuf for more than one year. These mussels were purged and acclimatized to laboratory conditions for 4 d. They were then placed in groups of twenty into polyethylene buckets containing 5 litres of continuouslyaerated artificial seawater (35%0 S) and were kept in an airconditioned room (15.5 ~ + 0.5 C ~ with a nychthemeral rhythm of 12 h: 12 h. They did not receive any food during the whole of the experiments, which were made in November 1983 during a period when the low availability of food in the natural environment induces a decrease in the soft-tissue weight (Amiard et al., 1986). Mussels were exposed to a large range of concentrations of cadmium (2.5 to 2 500 /~g1-1), copper (10 to 1 000 ktg 1-x) and zinc (50 to 5 000/~g 1-1), for 4, 8 or 16 d. In all experiments, seawater and pollutants were renewed every two days: decreases of metal concentrations in the culture medium were negligible. For each contamination time, ten mussels were sampled in the controls and for each concentration of each metal. Gills plus labial palps, visceral mass and the "remainder" (mantle, muscles, gonads) were dissected out. Trace-element analysis
The Mytilus edulis tissues were oven-dried (80~ to constant weight. The "remainder" was then pulverized and the analysis performed on an aliquot of about 100 mg of this powder. For the gills plus palps and the visceral mass, whole samples were analysed. The samples were digested with concentrated nitric acid at 90 ~ for 1 h, and were then brought to constant volume with deionized water. Metals were determined in this acid solution by means of flame or flameless atomic absorption spectrophotometry using Zeeman-effect background-correction. The validity of this method was established previously using US National Bureau Standard Materials (SRM 1566, oyster powder) and Canadian National Research Council Standards (TORT-1 lobster hepatopancreas) (Table 1). Table 1. Results of standard reference-material analysis
Reference material
Cadmium Copper
Oyster powder SRM 1566 Certified value 3.5 __0.4 Value obtained in our 3.6 + 0.1 laboratory Lobster hepatopancreas TORT- 1 Certified value 26.3 • 2.1 Value obtained in our 27.8 _+1.5 laboratory
Zinc
63.0+ 3.5 852-t-14 63.4__ 1.0 731_+ 8
439 +22 434 _+13
177_+10 148_+ 2
CI
CF1 x 100 CF2
,
(1)
where CF 1 = Conc in contaminated organisms (rag kg -1 dry wt) Conc in contaminated seawater (mg 1-1) and CF 2 = Conc in control organisms (mg kg -1 dry wt) Conc in normal seawater (mg 1-1) The metal concentrations in the various organs as a function of level of contamination in the seawater or length of exposure were statistically compared using an analysis-of-variance (F test of Snedecor, described in Rao, 1973)
Cadmium contamination The cadmium concentration inducing 50% mortality in 96 h (LC50/96 h) was 1 550ktg Cd 1-x, and all the mussels exposed to the highest experimental concentration (2 500 ktg Cd 1-1) died within 8 d. Consequently, at this latter concentration, the level of cadmium in mussels was established only for the 4 d exposure time. Experimental cadmium additions to the seawater induced increases in the cadmium concentration in the mussels. The pattern of cadmium accumulation in the gills plus palps and in the visceral mass is illustrated in Fig. 1, and was identical to that observed for the "remainder" (Table 2). The differences between concentrations recorded for contaminated mussels and controls were generally significant, even at the lowest experimental concentration (2.5/~g 1-1) and the lowest length of exposure (4 d). In the
C. Amiard-Triquet et al.: Experimental study of metals in Mytilus edulis
9
Cd Concentration
conc.
rag. k g "~
Concentration
index 4d
- - o - -
- - 4 . ~
8d 16 d
........ 9 . . . . . . . . . . . . . . .
+ ........
C d conc, m g k g -1
CI
Too 100i % Visceral
Gills
mass
+ Palps e-
"T
tI :'.
!
E !
i i
/ ? .?
50-
O
~ .... i: I
o L)
e.
E
I
it
i
:"
"'..
:"
".%
o
1/
-
l I
/ ." t ............ ~ ,
8 E E
i
."1"
t
10,
0.25
i
i
!
;"
"%
i
/
":9
9
i
,+ I
.g..L
2~5
.-
25 Cadmium
2go
2 00
concentration
in
o25 water
' ( ~lg
2500
1-1 )
Fig. 1. Mytilus edulis. Experimental contamination by cadmium. For clarity, only mean concentrations are shown here and in following figures; coefficients of variation are given in "Results". Concentration index = ratio between concentration factors in contaminated organs (CF l) and in controls (CF2), in percent: CI=CF l x 100/CF2 (see "Results" for further details). Data for "remainder" (mantle, muscles, gonads) for all metals are given in Table 2 gills plus palps, an overload of 25/~g 1-1 was necessary to induce an increase in cadmium after 4 or 8 d exposure. For the two lowest experimental concentrations of cadmium in the seawater (2.5 and 25 #g 1-1), the level of this metal remained steady in all groups of organs between 4 and 8 d exposure, whereas the highest addition of 250 #g 1-1 induced significant accumulation in the different organs during the same period. At this highest concentration and after the longest contamination period (16 d), the cadmium level in the "remainder" was 136 times greater than under natural conditions (0.25/~g 1-1). This ratio was 186 and 192 in the gills plus palps and the visceral mass, respectively. For mussels exposed to water containing 25/~g Cd 1-1, the concentration index decreased from control values in all organs and for all periods of exposure (Fig. 1 and Table 2). At the two highest experimental concentrations, the concentration index decreased very slightly or remained steady.' Applying Eq.(1) revealed that the mean cadmium concentrations in the organisms and the seawater were not proportional at the lowest contamination level, but became quasi-proportional at experimental concentra-
tions higher than 25/~g 1-1. For identical experimental concentrations in seawater, the concentration index was higher in all groups of organs after 16 d exposure than after 4 or 8 d (Fig. 1 and Table 2). Table 3 presents cadmium ratios between different groups of organs: cadmium was accumulated at increasing levels by the "remainder" =< visceral mass < gills plus palps. The level of accumulation were not very different and the ratios were generally < 1.5. Copper contamination (Fig. 2) The LC5o/96 h was at 480/~g C u l 1. It was therefore not possible to maintain mussels alive for 16 d after exposure to the two highest experimental concentrations (500 and 1 000/~g Cu 1-1 ). In the visceral mass of mussels exposed to copper for 4 d, the level of this metal did not vary significantly at external concentrations < 100#g 1-1; it then increased, attaining a new steady state (26 to 35 mg kg -1 dry wt) at external concentrations of 100 to 1 000/~g 1-1. After 8 and 16d exposure, experimental inputs of 50#g1-1 had be-
C. Amiard-Triquet et al.: Experimental study of metals in Mytilus edulis
10 Table 2. Mytilus edulis. Effect on "remainder" (pool of mantle, muscles and gonads) of experimental contamination by cadmium, copper and zinc for various periods of time. CI: concentration index (%). sl: sample lost Pollutant and experimental cone ~ug 1-1)
CI after: 4d
8d
16d
Cd Control (0.25 ~) 2.5 25 250 2 500
100 18.3 4.6 2.6 2.7
100 21.0 6.4 8.6 _b
100 28.0 10.8 7.6 _
Cu Control (6") 10 50 100 500 1 000
100 44.4 16.9 14.0 6.8 6.8
100 54.7 37.6 30.3 _c
100 93.4 42.3 22.9 _
_d
_
100 10.0 5.5 1.5 1.1 0.3
100 6.5 3.9 1.3 0.9 sl
100 11.0 7.6 1.5 1.2 -~
Zn
Control (5 ") 50 100 500 1 000 5 000
a Concentration (pg 1-1) in artificial seawater b 63% mortality observed at 4 d, so no measurements made at 8 and 16 d c 50% mortality observed at 4 d (LCs0 96 h) d 57% mortality observed at 4 d 100% mortality observed at 16 d
Table 3. Mytilus edulis. Ratios of metal concentrations between groups of organs in mussels exposed to experimental contamination Pollutant and experimental cone
Gills + palps: visceral mass
Visceral mass: "remainder"
(~g 1-~) 4d
8d
16d
4d
8d
16d
Cd Control (0.25") 2.5 25 250 2500
2.01 1.55 1.11 1 . 2 7 1.15 1 . 2 8 1.33 1 . 1 2 1.17 -
1.14 1.34 1.16 1.10 -
0.99 1.35 1.36 1 . 0 3 2.08 1 . 4 3 1.90 1 . 4 5 1,37 -
Cu Control (6") 10 50 100 500 1 000
1.22 1.15 2.61 1.66 5.91 7.62
1.55 2.41 2.25 2.21 -
1.75 2.10 1.86 3.34 -
1.94 2.20 1.40 1.48 1 . 4 1 1.19 1.26 1 . 4 4 1.63 2.30 1 . 6 0 0.97 0.81 0.55 -
1.64 1.35
1 . 0 6 0.87 1 . 9 6 1.37
0.92 0.97
0.80 0.69 1 . 0 1 1.08
1.56
1.64
1.00
1.39
Zn Control (5~) 50 100 500 1 000 5000
1.22
1.25 1 . 0 7 1.46 1.30 1 . 2 4 1.06 1.66 2.32 -
a Concentration ~ g 1-1) in artificial seawater
0.88 1.17 1.44 1.24 -
1.09
1.39 1 . 5 6 1.60 1.43 2.00 1.49 1.32 1.21 -
come sufficient to induce an increase o f copper in the visceral mass. The concentrations o f copper recorded in the gills and palps of mussels exposed for 4 or 8 d increased significantly at an experimental input o f 50 ktg 1-1; at 10/~g1-1, a similar effect was achieved only after 16 d. The pattern o f accumulation in t h e " r e m a i n d e r " was similar, and therefore is not illustrated in Fig. 2. The concentration index generally decreased for all groups o f organs with increasing concentrations o f copper in the seawater (Fig. 2 a n d Table 2). This decrease was more m a r k e d in the visceral mass than in the gills plus palps and " r e m a i n d e r " . However, in all three groups o f organs, the CI r e m a i n e d almost constant after 4 d exposure to experimental overloads from 500 to 1 000/~g 1-1 or after 16 d exposure to concentrations from 6/~g 1-1 (control) to 10/~g 1-1; i.e., in these instances, the increase of copper in the mussels paralleled the increase o f this metal in the seawater. However, at the end of the experiment, the level o f copper in the gills plus palps o f mussels exposed to the highest sub-lethal exposure (100 # g 1-1) was only five times higher than in controls. These ratios were 2.6 for the visceral mass and 3.8 for the " r e m a i n d e r " . C o p p e r was accumulated in increasing levels by the " r e m a i n d e r " =< visceral mass < gills plus palps. The ratios between copper concentrations in the visceral mass and the " r e m a i n d e r " (Table 3) were generally lower than 2. The difference between gills plus palps a n d visceral mass was more marked, m a i n l y at the highest exposure levels. Zinc c o n t a m i n a t i o n The L C s o / 9 6 h for zinc was higher than 5 000ktg1-1. However, after 16d, all the mussels exposed to this concentration were dead. Fig. 3 shows zinc uptake by the gills plus palps a n d the visceral mass. U p t a k e b y the " r e m a i n d e r " was very similar (Table 2). After 4 d contamination, zinc levels in the three groups o f organs had not increased significantly at external concentrations =< 100 ktg 1-1. At the same concentration, this steady state was m a i n t a i n e d in the visceral mass and " r e m a i n d e r " during 8 d exposure, and in the "rem a i n d e r " alone for 16 d. At this longest contamination time, even the lowest experimental i n p u t o f zinc (50 p g 1-1) was sufficient to induce a significant increase o f this metal in the gills plus palps and the visceral mass. At this time, at the highest assayed concentration (1 000/~g 1-1), which is 200 times higher than the control level in natural seawater, the zinc concentration in the " r e m a i n d e r " was 2.3 times greater than the natural one. This ratio was 5 for the visceral mass and 6.1 for gills plus palps. Concomitantly, the concentration index decreased rapidly with increasing external levels ranging from control values to 500/~g1-1; CI then decreased more slowly at higher experimental concentrations o f zinc. On the other hand, at external concentrations --- 500 # g 1-1, the zinc level in the various groups of organs r e m a i n e d steady between 4 and 8 d o f exposure; for the " r e m a i n d e r " this " e q u i l i b r i u m " was m a i n t a i n e d at 1 000 ktg 1-1.
C. Amiard-Triquet et aL: Experimental study of metals in Mytilus edulis
Concentration index 4d 8d 16d
Concentration
,.__
- - + - -
___ 9 . . . . . . ........ ~ ........
Gills. Palps
+--....... + .......
Cu conc. mg kg -~
CI %
lO~
~oo i\
,...,.....,
t-
Visceral mass
,+
._m
,+
E
"....
k
l
./"
.+,
..9
..." \
~."
,,.,,..,/...":" "'-..
:':i t
50
;
,i"~
;/" "'"'.,
50
50
9.
1
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"/
);.
'"
i
/',.
t
~+ "~.~
y;
E ..'""
s
.E 8
10
6
10
5'0
500
1~) Copper
|
6
000
concentration
;0
in water
I
I
50
100
5()0
1000
(/ug I-~ )
Fig. 2. Mytilus edulis, Experimental contamination by copper
Concentration Zn cone.
4 d 8d 16 d
I mg kg "1) 4-
Concentration
index ~o --+ ---o--- - - + _ _ _ ....... 9 ................ + ........
/,+ : t
Visceral mass
C I %
100
...~
:
\_ J /
"o
._c
50
4-"
~,'. ....... , -
}"
,..
I,oo
Gills + Palps
100
i~..
..'
".
O0
/+
ci;.
/
/ ,'/
100
i/
,.~ ,.,'"' r
*.
5 0 84
.,'
,+
i
300~
o
E .E
o_ =
....... c o
~\~"
5
loo ~ 8
so
10
r N
10 50
100
500
1000
Zinc
50O0
concentration
Fig. 3. Mytilus edulis. Experimental contamination by zinc
E
5 water
50 OJg
I "1 )
100
500 1000
5000
12
C.Amiard-Triquet et al.: Experimental study of metals in Mytilus edulis
The ratios of zinc concentrations between different groups of organs (Table 3), reveal that this metal was accumulated at increasing levels by the "remainder" =< visceral mass < gills plus palps. However, accumulation levels were not very different between these organs (ratios generally < 2).
Discussion and conclusions
At the lowest experimental concentration and the lowest exposure period, a significant increase of cadmium in Mytilus edulis tissues was generally observed. At the two lowest cadmium additions, the tissue levels of this metal remained steady between 4 and 8 d of exposure. George and Coombs (1977) also observed a lag period of 1.5 to 2 d in the kidneys of mussels exposed to 200 ktg Cd 1-1. A steady state between the water and the mussels had not been reached by the end of our experiment, and several authors have reported that such a steady state is still not achieved after 2 mo (Fowler and Benayoun, 1974) or more (Westernhagen etal., 1978; Ritz etal., 1982). At higher experimental concentrations (50 to 200/zg Cd 1-1) and/or longer periods of exposure, linear accumulation has been recorded by George and Coombs (1977), Westernhagen et al. (1978), Scholz (1980), Poulsen et al. (1982), Ritz et al. (1982) and present study. In situ, we observed no significant differences between the cadmium levels in different groups of organs (Amiard etal., 1986), whereas Theede et al. (1979), using mussels from a more polluted area, demonstrated preferential accumulation in the digestive gland compared to the gills. According to Scholz (1980), at the beginning of experimental contamination, the gills played the most important part in cadmium accumulation; after longer exposure the digestive gland accumulated most cadmium. In experimentally contaminated mussels, George and Coombs (1977) observed comparable accumulation of cadmium by the gills and the visceral mass whereas, in our study, the highest levels of cadmium were recorded in the gills plus palps. This discrepancy could result from initial differences in the degree of cadmium pollution in the areas where the biological materials were sampled. We have shown that the ability of mussels to regulate the bioaccumulation of copper varies from organ to organ and decreases with higher levels of contamination and increasing period of exposure. In long-term experiments (35 to 86 d) at low levels of exposure (5 to 20 ktg Cu 1-1) several authors also have observed a linear accumulation of copper (D'Silva and Kureishy, 1978; Ritz et al., 1982). After acute exposure (300/zg 1-1), an early and temporary increase of copper in Mytilus edulis was reported by Scott and Major (1972). These authors put forward several theories to explain the clearing of the initial influx of copper, e.g. detoxification of seawater by increased mucous secretion and subsequent binding, excretion of internal copper via mucus or faeces. Moreover, mussels can detect copper in seawater (0.5 to 10 mg 1-~) and close their
valves for periods of several hours (Scott and Major, 1972; Davenport, 1977). Consequently, in short-term contaminations, the accumulation and noxious effects of copper can be restricted. On the other hand, in field studies, the levels of copper in M. edulis, M. edulisplanulatus and the mussel Septifer bilocularis do not vary considerably between polluted and unpolluted areas (Phillips, 1976; Phillips and Yim, 1981; Cooper etal., 1982). These observations corroborate the hypothesis of copper regulation by these species. At external zinc levels as high as 100 r 1-1, the present study has demonstrated the ability of mussels to maintain a normal concentration in all groups of organs for 4 d; in the visceral mass, and the "remainder" (mantle, muscles and gonads) for 8 d; and in the "remainder" alone for up to 16 d. These results are similar to those obtained previously for the bivalve Scrobicularia plana (Amiard et al., 1985). With increasing length of exposure, lower doses become sufficient to disturb the regulatory mechanism, and in mussels exposed to 100-200 #g Zn1-1 over 35 to 86 d, zinc accumulation increases linearly (D'Silva and Kureishy, 1978; Ritz etal., 1982). Field studies have indicated that the concentration of zinc in mussels is closely related to the level of pollution of the sampling area (e.g. Phillips, 1976; Cooper et al., 1982). However, in the closely related species Septifer bilocularis, Phillips and Yim (1981) observed uniform concentrations of zinc in specimens from collection areas with different levels of pollution. In situ, the concentration of zinc in the digestive gland (or visceral mass), is similar to or higher than that of the gills (Brooks and Rumsby, 1965; Pentreath, 1973; Amiard et al., 1986). In experimentally contaminated mussels, Pentreath (1973) demonstrated that the gills accumulated much more zinc (radioactive 6SZn) than in natural conditions. In the present study, we observed preferential accumulation of zinc in the gills plus palps compared to the visceral mass and "remainder" (mantle, muscles and gonads) for experimentally exposed mussels. In Table 4, the highest concentrations recorded in the mussels have been calculated in g-#at kg -1 in order to compare the metal levels in terms of binding-sites of the organisms. Except for copper in gills plus palps, these concentrations are ~ 1 for cadmium and copper, whereas they are markedly higher for zinc (3 to 4.76 g-/~at kg-X). Even at the highest sub-lethal doses, the levels of copper and zinc in mussel tissues are not much higher than in controls (2.3 to 6.1), whereas the bioaccumulation of cadmium is less restricted (Table 4). The ratio between experimental inputs tolerated by mussels after 16 d exposure and normal concentrations in seawater are much higher for cadmium than for zinc and above all for copper (Table 4). Consequently, the range between safe and noxious concentrations is not very large for zinc and narrower for copper. In natural environments, differences between minimum and maximum values of copper and zinc concentrations in the mussels which result from seasonal factors (National Academy of Sciences, 1980; Amiard
C. Amiard-Triquet et al.: Experimental study of metals in Mytilus edulis Table 4. Mytilus edulis. Comparative increases of cadmium, copper and zinc levels in different groups of organs of mussels exposed to metal contamination for 16 d
LC5o/96 h (pg 1-1) Highest experimental contamination over 16 d exposure (#g 1 1) Ratio contamined" control water gills + palps visceral mass "remainder" Highest concentrations reached (g-#at kg 1) gills + palps visceral mass "remainder"
Cd
Cu
Zn
1 550
480
> 5 000
250
100
1 000
1 000 186 192 136
1.38 1.25 1.0l
17 5.0 2.6 3.8
2.76 0.83 0.85
200 6.1 5.0 2.3
4.76 4,47 3.00
a Ratio between metal concentrations in water or in organisms exposed for 16 d to highest experimental concentrations and control concentrations
et al., 1986) are of the same order o f m a g n i t u d e as those observed between experimentally c o n t a m i n a t e d and control mussels. F o r zinc, in situ studies have generally revealed c o n t a m i n a t e d : b a c k g r o u n d ratios lower than 10, even in heavily polluted areas (Bloom and Ayling, 1977; C o o p e r et aL, 1982). Regulation o f essential metals could result in s u b - n o r m a l levels o f these metals being encountered in mussels collected from areas with noxious levels in the water. Acknowledgements. This study was partly s u p p o r t e d b y G r a n t No. 83187 from the French Ministry of Environment. Thanks are due to Mr. P61ote, oyster farmer in Bouin (Vend6e), a n d his personnel who kindly supplied us with biological material, and to Mrs Racineux who t y p e d the text. Literature cited Amiard, J. C., C. Amiard-Triquet and C. M6tayer: Experimental study of bioaccumulation, toxicity and regulation of some trace metals in various estuarine and coastal organisms. In: Proceedings of Symposium on Heavy Metals in Water Organisms (Balatonfi~red 2-8 Sept. 1984). Symp. Biol. Hung. 29, 313-323 (1985) Amiard, J. C., C. Amiard-Triquet, B. Berthet and C. M6tayer: Contribution to the ecotoxicological study of cadmium lead copper and zinc in the mussel Mytilus edulis. I. Field study. Mar. Biol. 90, 425-431 (1986) Bloom, H. and G. M. Ayling: Heavy metals in the Derwent estuary. Envir. Geol. 2, 3-22 (1977) Bouquegneau, J. M., F. No~l-Lambot, C. Verthe and A. Disteche: The accumulation of heavy metals in marine organisms. Int. Counc. Explor. Sea Comm. Meet. (Pelagic Fish Comm.) E41, 140-156 (1982) Bryan, G. W.: Bioaccumulation of marine pollutants. Phil. Trans. R. Soc. (Ser. B) 286, 483-505 (1979) Bryan, G. W.: Pollution due to heavy metals and their compounds. In: Marine ecology, pp 1289-1431. Ed. by O. Kinne. London: John Wiley & Sons Ltd 1984
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