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Mercury content of mussels from the St. Lawrence Estuary and northwestern Gulf of St. Lawrence, Canada
Volume 7/Number 12/December 1976 serum and plasma proteins. The interaction of human serum albumin with plumous ions. J. Am. Chem. Soc., 76, 187. Kinrade, 3. D. & Van Loon, J. C. (1974). Solvent extraction for use with flame atomic absorption spectrometry. Anal Chem., 46, 1894. Melbourne Metropolitan Board Works (1973). Environmental study of Port Phillip Bay. Report on Phase I: 1968-1971. M.M.B.W. Melbourne. NOel-Lambot, F. (1976). Distribution of cadmium, zinc and copper in the mussel Mytilus edulis. Existence of cadmium-binding proteins similar to metallo thioneins. Experientia, 32, 324-326. Olafson, R. W. & Thompson, J. A. J. (1974). Isolation of heavy metal binding protein from marine vertebrates. Mar. Biol., 28, 83. Pulido, P., Kagi, J. H. R. & Vallee, B. L. (1966). Isolation and some properties of human metallothionein. Biochem., 5, 1768. Rugstad, H. E. & Norseth, T. (1975). Cadmium resistance and content of cadmium binding protein in cultured human ceils. Nature, Lond., 257, 136.
Schroeder, H. A. (1974). The Poisons Around Us. Indiana Univ. Press. Suda, T., Horiuchi, N., Ogata, E., Ezawa, I., Otaki, N. & Kimura, M. (1974). Prevention by metallothionein of cadmium-induced inhibition of vitamin D activation reaction in kidney FEBS Lett., 42, 23. Talbot, V. W., Magee, R. J. & Hussain, M. (1976). Cadmium in Port Phillip Bay mussels. Mar. Pollut. Bull., 7, 84-85. Ulmer, D. D. & Vallee, B. L. (1969). Trace substances in Environmental Health--II. Proc. Univ. Missouri Ann. Conf. Trace substances Environ. Health, 2nd ed. D. D. Hemphill, 7. Columbia: Univ. Missouri. Valley, L. B. & Ulmer, D. D. (1972). Biochemical effects of mercury, cadmium and lead. Ann Rev. Biochem., 41,91-128. Victorian Parliamentary Hansards (1975). Trace metals in sea food of Victorian waters. 46th Parl. 2nd session, 27,7881. Zirino, A. & Yamamoto, S. (!972). A pH dependent model for the chemical speciation of copper, zinc, cadmium and lead in seawater. LimnoL Oceanogr., 17,661-671.
Mercury Content of Mussels from the St. Lawrence Estuary and Northwestern Gulf of St. Lawrence, Canada A first survey o f the mercury content o f intertidal mussels in the St. Lawrence Estuary and part o f the Gulf of St. Lawrence shows means values ranging from 0.160 to 0.629 ppm (dry weight). Highest values (grand mean 0.430 ppm) were f o u n d in the upper part o f the lower estuary, lowest values (grand mean 0.172 ppm) on the north shore o f the estuary and Gulf, and intermediate values along the Gasp~ Peninsula. The results indicate a decreasing gradient in mercury levels from the m o u t h of the Saguenay Fjord seaward. T h e St. L a w r e n c e E s t u a r y receives f r e s h w a t e r d r a i n a g e f r o m t h e G r e a t L a k e s a n d the St. L a w r e n c e Basin t h r o u g h the St. L a w r e n c e River. T h e e s t u a r y ' s d i s c h a r g e is i n c r e a s e d b y the i n f l o w o f t h e S a g u e n a y F j o r d a n d a n u m b e r o f rivers, p a r t i c u l a r l y t h o s e f r o m the M a n i c o u a g a n - O u t a r d e s - B e t s i a m i t e s c o m p l e x (Fig. 1). A l l these w a t e r s r u n t h r o u g h t h e m o s t i n d u s t r i a l i z e d a r e a o f E a s t e r n C a n a d a a n d a r e r e c e i p i e n t o f m a n y effluents i n c l u d i n g c h l o r a l k a l i p l a n t s a n d p a p e r mills ( F i m r e i t e , 1970). R e c e n t studies in the S a g u e n a y F j o r d s h o w t h a t m e r c u r y levels a r e p a r t i c u l a r l y high in the w a t e r , suspended particles, sediments and animals. For instance m e r c u r y levels as high as 12 a n d 15 p p m were f o u n d in s e d i m e n t s ( L o r i n g , 1975) a n d s h r i m p s ( G u b e l i et al., 1976) respectively. In the St. L a w r e n c e E s t u a r y , m e r c u r y levels in the s e d i m e n t r e a c h 0.9 p p m ( L o r i n g , 1975) b u t no results a r e a v a i l a b l e for a n i m a l s . Studies c a r r i e d o u t so far s h o w t h a t an i m p o r t a n t s o u r c e o f m e r c u r y c o n t a m i n a t i o n o f the e s t u a r y is l o c a t e d n e a r the h e a d o f the S a g u e n a y River. T h e p r e s e n t survey was c a r r i e d o u t to e v a l u a t e the a c t u a l levels o f c o n t a m i n a t i o n o f the l o w e r e s t u a r y ( f r o m the m o u t h o f the S a g u e n a y to G r o s s e s - R o c h e s ) a n d p a r t
o f the G u l f o f St. L a w r e n c e (Fig. 1). T h e l o w e r e s t u a r y is p a r t i c u l a r l y i m p o r t a n t e c o l o g i c a l l y as a source o f n u t r i e n t (Steven, 1974; Sinclair et al., 1976) w h e r e a s the n o r t h - w e s t e r n p a r t o f the G u l f is r e c o g n i z e d t o be a highly p r o d u c t i v e a r e a ( P l a t t , 1972; Steven, 1974).
Materials and M e t h o d s D u e to its w i d e d i s t r i b u t i o n in the s t u d y a r e a a n d its w i d e s p r e a d a c c e p t a n c e as a n i n d i c a t o r o f p o l l u t i o n ( G o l d b e r g , 1975), the mussel M y t i l u s edulis L. was c h o s e n in this survey. In o r d e r t o r e d u c e p o s s i b l e p h y s i o l o g i c a l effects o n m e t a l levels (De W o l f , 1975), all s a m p l e s were collected w i t h i n a s h o r t p e r i o d o f 2 weeks at the e n d o f M a y 1976. A d u l t s p e c i m e n s r a n g i n g f r o m 2.5 to 4.0 c m were collected o n r o c k y s h o r e at m i d tide level at 30 s t a t i o n s d i s t r i b u t e d o v e r 1000 k m a l o n g t h e e s t u a r y a n d G u l f c o a s t s (Fig. 1). A t P o i n t e - M 6 t i s , h o w e v e r , s a m p l e s were also collected o n m u d d y a n d r o c k y s u b s t r a t a at e x t r e m e (lowest) h i g h - w a t e r o f n e a p tides a n d m e a n low w a t e r o f n e a p tides. In the l a b o r a t o r y , a n i m a l s were m e a s u r e d a n d freed f r o m their shells. T h e s o f t p a r t s were f r e e z e - d r i e d a n d weighed. E a c h s a m p l e a n a l y s e d (0.5 to 1.0 g, d r y wt) included 3-5 individuals. A n a l y s e s were p e r f o r m e d using flameless a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y ( C o l e m a n M A S 50) as initially d e s c r i b e d b y H a t c h & O t t (1968) a n d s u b s e q u e n t l y m o d i f i e d b y U t h e et al. (1970) a n d T h i b a u d (1975). T h e sensibility o f the m e t h o d (1 °7o a b s o r b a n c e ) is 0.020 p p m a n d d e t e c t i o n limit 0.004 p p m . T h e s t a n d a r d e r r o r for 105 d e t e r m i n a t i o n s was 0.008 p p m . F o r v e r i f i c a t i o n o f the a n a l y t i c a l m e t h o d t w o h o m o g e n i z e d s a m p l e s were f r a c t i o n e d a n d sent for analysis to t w o o t h e r l a b o r a t o r i e s . T h e results p r e s e n t e d in T a b l e 1 s h o w 237
Marine Pollution Bulletin ,o~
Jacques-Cartier Passage
G u l f of St-Lawrence 0
e¢ ,,b
\
O-
\ Gaspe
peninsura
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
St. Andr4 ~ not obNrvld 16 N.D.-du-Portage ~ or sample too 17 Rivk~re~lu-Loup J )rmdlforam4ysis 18 Grol-C~couna 19 Trois-Pistoles 20 St. Simon--,ur-mer 21 St. Fabien-sw-mer 22 Anu-lmx-Sables 23 Pointe-eu-P~e 24 Ste. Flavie 26 Pointe-M~is 26 Eaie
b~te,Anr~de~Monts Rivk]~r~i-Marthe Mo~.Louis Rivi4re-Madeleine Pointe-Frigate Aale-t-Vadluu Cap~ll4~Rosiers St. Gdmrges-d4-1e-M~bale An I~-B411ufi|| Grand4-Rivi~fll
TEIoomg Grand~Beqlerorme B~Con,,oau Baie<:l~Homards Porte.artier
Fig. 1 Mean mercury content in the soft parts of intertidal Mytilus edulis (ppm, dry weight) along the coast of the Lower St. Lawrence Estuary and Northwest Gulf of St. Lawrence. Values represent the mean of three determinations.
that the means o f the three determinations are not significantly different and indicate the reliability o f our analytical method.
Results and Discussion The results presented throughout are means of three analyses and are expressed in ppm i.e./~g Hg g -' (dry wt). The mercury concentrations were first analysed to determine the extent o f the variation between determinations. The results are presented in the form o f an analysis o f variance in Table 2. It will be seen that either substrata, shore levels, localities or a combination o f these factors have a significant effect on the determinations. The data obtained at Pointe-M6tis were further analysed in Table 3 into influence o f the substratum and shore level on mercury content o f the mussels. Variance TABLE 1 Comparison of results of analyses of fractions of two homogenized samples of whole Mytilus edulis. Mean of determinations in ppm (dry wt). Laboratories
Number of Sample A determinations mean s.d.
Sample B mean s.d.
ratios (F) show that neither substratum nor shore level have a significant effect on mercury levels in mussle tissue within the range 2.5-4.0 cm. Mean mercury concentrations from samples collected on rocky substratum at mid tide level in the estuary and Gulf are presented in Fig. 1. Mercury levels are examined here on an overall basis. Mercury values from place to place are irregular but on the whose a decrease is observed along the South Shore from Rivi~re-du-Loup down the Gasp6 Peninsula. The mean values range from 0.160 to 0.629 ppm (dry wt). Highest values are found upstream at the mouth o f the Saguenay Fjord and on the South Shore o f the Lower Estuary (to Grosses-Roches, Station 14) (grand mean 0.430_+0.023 ppm). Lowest values are observed on the eastern part o f the North Shore (grand mean 0.172_+0.062 ppm) whereas intermediate mean mercury concentrations (grand mean 0.306-+0.029 ppm) are found along the coast o f the Gasp6 Peninsula. TABLE 2 Variation in the mercury content (ppm, dry wt) of the soft parts of Mytilus edulis from different shore levels, substratum and localities (Fsignificant atp <0.001).
Environment Canada Research and Development (Halifax Laboratory)
3
0.290 0.017 0.020 0.006
Sourceof variation
2
0.265 0.007 0.020 0.000
Between groups from different localities shore levels and substratum
34
InstitutScientifique et technique des P~ches Maritimes, (France)
0.280 0.033 0.015 0.008
Between determinations within each group
70
0.5247
Total
104
15.8418
Laboratoire oc~anographique de Rimouski (Qu6bec, Canada)
238
Degreesof freedom
Sumof squares
Mean square
F ratio
15.3171
0.4505
60.10
0.0075
Volume 7/Number 12/December 1976 TABLE 3
Influence of the level of collection and substratum on the mercury content (ppm, dry wt) of Mytilus edulis collected at Pointe-M6tis ( F n o t significant a t p < 0.10). Source of variation Between shore levels
Degrees of freedom
Sum of squares
Mean square
F ratio
2
0.0376
0.0188
1.59
Between substrata
1
0.0013
0.0013
0.072
Interaction
2
0.0070
0.0035
0.297
Error
12
0.1417
0.0118
Total
17
0.0187
scientifique et techniques de P~ches maritimes (France) and Mr G. Shum from Environment Canada (Halifax Laboratory) who analysed replicate samples. This work was supported by DGES-FCAC grant from the Quebec department of Education. We thank our colleages who critically reviewed the manuscript.
EDWIN BOURGET*
Institut National de la Recherche Scientifique INRS-Oc~anologie DANIEL COSSA
Mean values
*E(L)HWN MTL MLWN
Rocky 0.438ppm 0.311 ppm 0.375 ppm
Muddy 0.383ppm 0.295 ppm 0.395 ppm
Section d'Oceanographie de I'Universit~ du Quebec ~ Rimouski (SOUQAR ) 310Ave. de Ursulines Rimouski, Quebec, Canada *Present address: D~partement de biologie, Universit~ Laval, Quebec, Canada.
*E(L)HWN: extreme (lowest) high water of neap tides; MTL: mean tide level; MLWN: mean low water of neap tides.
These results are in agreement with previous studies showing that waters of the Saguenay are an important source of mercury contamination in the study area (Loring, 1975; Gubeli et al., 1976). The concentrations reflect the fate of the surface waters of the Fjord in the St. Lawrence Estuary. the flow of the Saguenay is directed on the South Shore. There, these water mix with waters originating from the Upper Estuary, before being directed seaward mainly along the South Shore (Nadeau, 1938; Farquharson, 1966; Trites, 1972). It appears that the mercury content of the mussles in the estuary merely reflect the overall seaward dilution of mercury from terrigenous sources. Since bivalves can accumulate metals from food and solution, mussels should ingest much more metal per unit volume of water filtrated towards the upper estuary. Relatively low concentrations were observed on the North Shore at stations 28, 29 and 30. An explanation for these low mercury values is the direct influence of marine water masses, probably with a lower mercury content, coming through Jacques Cartier Passage (Dawson, 1913; E1 Sabh, 1976) and the presence of an upwelling on the North Shore of the Lower Estuary (Gaudry, 1938; Steven, 1974) (Fig. 1). Intermediate values along the Gasp6 Peninsula coast probably reflect a residual influence of estuarine water masses through the Gasp~ current which flows along the entire length of the Gasp6 coast. Comparison of our results with those reported by Mytilus sp. from the Canadian Pacific coast (Parsons et aL, 1973) and from the European coast (Establier, 1973; Thibaud, 1973; Anderson & Neelakantan, 1974; De Wolf, 1975) indicate similar mercury levels with the exception of a few sites reported for the English coast (De Wolf, 1975).
The authors acknowledge the assistance of Mile D. Messiere and Mr J. Sylvian for collection of specimens and Mr G. Canuel for analysis of the samples. Special thanks are due to Dr Y. Thibaud from lnstitut
Anderson, A. T. & Neelakantan, B. B. (1974). Mercury in some marine organisms from the Oslofjord. Norw. J. Zool., 22, 231-235. Dawson, W. N. (1913). The currents in the Gulf o f St. Lawrence. Department of the Naval Service, Ottawa, Canada, 44 pp. DeWolf, P. (1975). Mercury content of mussels from west European coast. Mar. Pollut. Bull., 6, 61-63. EI-Sabh, M. I. (1976). Surface circulation pattern in the Gulf of St. Lawrence. J. Fish Res. Bd Can., 33, 124-138. Establier, R. (1973). Mercury content of the mussel Mytilus edulis growing free and under cultivation in Northwest Spain. Inv. Pesq., 37, 101-106. Farquharson, W. I. (1966). St. Lawrence Estuary current surveys. Unpublished manuscript. Bedford Institute of Oceanography, Report 66-6, 1-84. Fimreite, N. (1970). Mercury used in Canada and their possible hazards as sources of mercury contamination. Environ. Pollut., 1, 119-131. Gaudry, R. (1938). Les temp6ratures de l'estuaire du Saint-Laurent Contrib. Sta. Biol. St-Laurent, Univ. Lava113: 1-14. Goldberg, E. D. (1975). The mussel watch--a first step in global marine monitoring. Mar. Pollut. Bull., 6, 111. Gubeli, O., Alain. G. & Chateauneuf, R. (1976). D~termination des m6taux en traces toxiques et non toxiques des eaux, suspenso'ides et s6diments du Saguenay. P. 84. In: Groupe, de recherches oc6anographiquesdu Quebec, 4/~me rapport annuel, 141 pp. Hatch, W. R. & Ott, W. L. (1968). Determination of submicrogram quantities of mercury by atomic absorption spectrophotometry. Anal. Chem., 40, 2085-2087. Loring, D. H. (1975). Mercury in the sediments of the gulf of St. Lawrence. Can. J. Earth Sci., 12, 1219-1237. Nadeau, A. (1938). Salinit~ des eaux de l'estuaire du Saint-Laurent. Contrib. Sta. Biol. St-Laurent, Univ. Laval, 11: 1-19. Parsons, T. R., Bawden, C. A. & Heath, W. A. (1973). Preliminary survey of mercury and other metals contained in animals from the Fraser River mudflats. J. Fish Res. B d Can., 30, 1014-1016. Platt, T. (1972). The feasibility of mapping chlorophyl distribution in Gulf of St. Lawrence. Fish Res. Bd Can., Tech. Report Series No. 332. Sinclair, M., EI-Sabh, M. 1. & Brindle, J. R. (1976). Seaward nutrient transport in the Lower St. Lawrence Estuary. J. Fish Res. Bd Can., 33, 1271-1277. Steven, D. M. (1974). Primary and secondary production in the Gulf of St. Lawrence. McGill University, Mar. Sci. Centre, Report No. 26, 116pp. Thibaud, Y. (1973). Teneur en mercure dans les moules du littoral franeais. Science et P~che, Bull. Inst. P#ches Marit., 22 !, 1-6. Thibaud, Y. (1975). Analyse du mercure par un proced~ semiatomatique. Science et P~che, Bull. Inst. P~ches marit., 250, 1-8.
Trites, R. W. (1972). The Gulf of St. Lawrence from a pollution viewpoint. In Marine Pollution and Sea Life, ed. M. Ruivo, pp. 59-72. London: Fishing News (Books). Uthe, J. F., Armstrong, F. A. J. & Stainton, M. P. (1970). Mercury determination in fish samples by wet digestion and flameless atomic absorption spectrophotometry J. Fish Res. Bd Can., 27, 805-811.
239
Schroeder, H. A. (1974). The Poisons Around Us. Indiana Univ. Press. Suda, T., Horiuchi, N., Ogata, E., Ezawa, I., Otaki, N. & Kimura, M. (1974). Prevention by metallothionein of cadmium-induced inhibition of vitamin D activation reaction in kidney FEBS Lett., 42, 23. Talbot, V. W., Magee, R. J. & Hussain, M. (1976). Cadmium in Port Phillip Bay mussels. Mar. Pollut. Bull., 7, 84-85. Ulmer, D. D. & Vallee, B. L. (1969). Trace substances in Environmental Health--II. Proc. Univ. Missouri Ann. Conf. Trace substances Environ. Health, 2nd ed. D. D. Hemphill, 7. Columbia: Univ. Missouri. Valley, L. B. & Ulmer, D. D. (1972). Biochemical effects of mercury, cadmium and lead. Ann Rev. Biochem., 41,91-128. Victorian Parliamentary Hansards (1975). Trace metals in sea food of Victorian waters. 46th Parl. 2nd session, 27,7881. Zirino, A. & Yamamoto, S. (!972). A pH dependent model for the chemical speciation of copper, zinc, cadmium and lead in seawater. LimnoL Oceanogr., 17,661-671.
Mercury Content of Mussels from the St. Lawrence Estuary and Northwestern Gulf of St. Lawrence, Canada A first survey o f the mercury content o f intertidal mussels in the St. Lawrence Estuary and part o f the Gulf of St. Lawrence shows means values ranging from 0.160 to 0.629 ppm (dry weight). Highest values (grand mean 0.430 ppm) were f o u n d in the upper part o f the lower estuary, lowest values (grand mean 0.172 ppm) on the north shore o f the estuary and Gulf, and intermediate values along the Gasp~ Peninsula. The results indicate a decreasing gradient in mercury levels from the m o u t h of the Saguenay Fjord seaward. T h e St. L a w r e n c e E s t u a r y receives f r e s h w a t e r d r a i n a g e f r o m t h e G r e a t L a k e s a n d the St. L a w r e n c e Basin t h r o u g h the St. L a w r e n c e River. T h e e s t u a r y ' s d i s c h a r g e is i n c r e a s e d b y the i n f l o w o f t h e S a g u e n a y F j o r d a n d a n u m b e r o f rivers, p a r t i c u l a r l y t h o s e f r o m the M a n i c o u a g a n - O u t a r d e s - B e t s i a m i t e s c o m p l e x (Fig. 1). A l l these w a t e r s r u n t h r o u g h t h e m o s t i n d u s t r i a l i z e d a r e a o f E a s t e r n C a n a d a a n d a r e r e c e i p i e n t o f m a n y effluents i n c l u d i n g c h l o r a l k a l i p l a n t s a n d p a p e r mills ( F i m r e i t e , 1970). R e c e n t studies in the S a g u e n a y F j o r d s h o w t h a t m e r c u r y levels a r e p a r t i c u l a r l y high in the w a t e r , suspended particles, sediments and animals. For instance m e r c u r y levels as high as 12 a n d 15 p p m were f o u n d in s e d i m e n t s ( L o r i n g , 1975) a n d s h r i m p s ( G u b e l i et al., 1976) respectively. In the St. L a w r e n c e E s t u a r y , m e r c u r y levels in the s e d i m e n t r e a c h 0.9 p p m ( L o r i n g , 1975) b u t no results a r e a v a i l a b l e for a n i m a l s . Studies c a r r i e d o u t so far s h o w t h a t an i m p o r t a n t s o u r c e o f m e r c u r y c o n t a m i n a t i o n o f the e s t u a r y is l o c a t e d n e a r the h e a d o f the S a g u e n a y River. T h e p r e s e n t survey was c a r r i e d o u t to e v a l u a t e the a c t u a l levels o f c o n t a m i n a t i o n o f the l o w e r e s t u a r y ( f r o m the m o u t h o f the S a g u e n a y to G r o s s e s - R o c h e s ) a n d p a r t
o f the G u l f o f St. L a w r e n c e (Fig. 1). T h e l o w e r e s t u a r y is p a r t i c u l a r l y i m p o r t a n t e c o l o g i c a l l y as a source o f n u t r i e n t (Steven, 1974; Sinclair et al., 1976) w h e r e a s the n o r t h - w e s t e r n p a r t o f the G u l f is r e c o g n i z e d t o be a highly p r o d u c t i v e a r e a ( P l a t t , 1972; Steven, 1974).
Materials and M e t h o d s D u e to its w i d e d i s t r i b u t i o n in the s t u d y a r e a a n d its w i d e s p r e a d a c c e p t a n c e as a n i n d i c a t o r o f p o l l u t i o n ( G o l d b e r g , 1975), the mussel M y t i l u s edulis L. was c h o s e n in this survey. In o r d e r t o r e d u c e p o s s i b l e p h y s i o l o g i c a l effects o n m e t a l levels (De W o l f , 1975), all s a m p l e s were collected w i t h i n a s h o r t p e r i o d o f 2 weeks at the e n d o f M a y 1976. A d u l t s p e c i m e n s r a n g i n g f r o m 2.5 to 4.0 c m were collected o n r o c k y s h o r e at m i d tide level at 30 s t a t i o n s d i s t r i b u t e d o v e r 1000 k m a l o n g t h e e s t u a r y a n d G u l f c o a s t s (Fig. 1). A t P o i n t e - M 6 t i s , h o w e v e r , s a m p l e s were also collected o n m u d d y a n d r o c k y s u b s t r a t a at e x t r e m e (lowest) h i g h - w a t e r o f n e a p tides a n d m e a n low w a t e r o f n e a p tides. In the l a b o r a t o r y , a n i m a l s were m e a s u r e d a n d freed f r o m their shells. T h e s o f t p a r t s were f r e e z e - d r i e d a n d weighed. E a c h s a m p l e a n a l y s e d (0.5 to 1.0 g, d r y wt) included 3-5 individuals. A n a l y s e s were p e r f o r m e d using flameless a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y ( C o l e m a n M A S 50) as initially d e s c r i b e d b y H a t c h & O t t (1968) a n d s u b s e q u e n t l y m o d i f i e d b y U t h e et al. (1970) a n d T h i b a u d (1975). T h e sensibility o f the m e t h o d (1 °7o a b s o r b a n c e ) is 0.020 p p m a n d d e t e c t i o n limit 0.004 p p m . T h e s t a n d a r d e r r o r for 105 d e t e r m i n a t i o n s was 0.008 p p m . F o r v e r i f i c a t i o n o f the a n a l y t i c a l m e t h o d t w o h o m o g e n i z e d s a m p l e s were f r a c t i o n e d a n d sent for analysis to t w o o t h e r l a b o r a t o r i e s . T h e results p r e s e n t e d in T a b l e 1 s h o w 237
Marine Pollution Bulletin ,o~
Jacques-Cartier Passage
G u l f of St-Lawrence 0
e¢ ,,b
\
O-
\ Gaspe
peninsura
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
St. Andr4 ~ not obNrvld 16 N.D.-du-Portage ~ or sample too 17 Rivk~re~lu-Loup J )rmdlforam4ysis 18 Grol-C~couna 19 Trois-Pistoles 20 St. Simon--,ur-mer 21 St. Fabien-sw-mer 22 Anu-lmx-Sables 23 Pointe-eu-P~e 24 Ste. Flavie 26 Pointe-M~is 26 Eaie
b~te,Anr~de~Monts Rivk]~r~i-Marthe Mo~.Louis Rivi4re-Madeleine Pointe-Frigate Aale-t-Vadluu Cap~ll4~Rosiers St. Gdmrges-d4-1e-M~bale An I~-B411ufi|| Grand4-Rivi~fll
TEIoomg Grand~Beqlerorme B~Con,,oau Baie<:l~Homards Porte.artier
Fig. 1 Mean mercury content in the soft parts of intertidal Mytilus edulis (ppm, dry weight) along the coast of the Lower St. Lawrence Estuary and Northwest Gulf of St. Lawrence. Values represent the mean of three determinations.
that the means o f the three determinations are not significantly different and indicate the reliability o f our analytical method.
Results and Discussion The results presented throughout are means of three analyses and are expressed in ppm i.e./~g Hg g -' (dry wt). The mercury concentrations were first analysed to determine the extent o f the variation between determinations. The results are presented in the form o f an analysis o f variance in Table 2. It will be seen that either substrata, shore levels, localities or a combination o f these factors have a significant effect on the determinations. The data obtained at Pointe-M6tis were further analysed in Table 3 into influence o f the substratum and shore level on mercury content o f the mussels. Variance TABLE 1 Comparison of results of analyses of fractions of two homogenized samples of whole Mytilus edulis. Mean of determinations in ppm (dry wt). Laboratories
Number of Sample A determinations mean s.d.
Sample B mean s.d.
ratios (F) show that neither substratum nor shore level have a significant effect on mercury levels in mussle tissue within the range 2.5-4.0 cm. Mean mercury concentrations from samples collected on rocky substratum at mid tide level in the estuary and Gulf are presented in Fig. 1. Mercury levels are examined here on an overall basis. Mercury values from place to place are irregular but on the whose a decrease is observed along the South Shore from Rivi~re-du-Loup down the Gasp6 Peninsula. The mean values range from 0.160 to 0.629 ppm (dry wt). Highest values are found upstream at the mouth o f the Saguenay Fjord and on the South Shore o f the Lower Estuary (to Grosses-Roches, Station 14) (grand mean 0.430_+0.023 ppm). Lowest values are observed on the eastern part o f the North Shore (grand mean 0.172_+0.062 ppm) whereas intermediate mean mercury concentrations (grand mean 0.306-+0.029 ppm) are found along the coast o f the Gasp6 Peninsula. TABLE 2 Variation in the mercury content (ppm, dry wt) of the soft parts of Mytilus edulis from different shore levels, substratum and localities (Fsignificant atp <0.001).
Environment Canada Research and Development (Halifax Laboratory)
3
0.290 0.017 0.020 0.006
Sourceof variation
2
0.265 0.007 0.020 0.000
Between groups from different localities shore levels and substratum
34
InstitutScientifique et technique des P~ches Maritimes, (France)
0.280 0.033 0.015 0.008
Between determinations within each group
70
0.5247
Total
104
15.8418
Laboratoire oc~anographique de Rimouski (Qu6bec, Canada)
238
Degreesof freedom
Sumof squares
Mean square
F ratio
15.3171
0.4505
60.10
0.0075
Volume 7/Number 12/December 1976 TABLE 3
Influence of the level of collection and substratum on the mercury content (ppm, dry wt) of Mytilus edulis collected at Pointe-M6tis ( F n o t significant a t p < 0.10). Source of variation Between shore levels
Degrees of freedom
Sum of squares
Mean square
F ratio
2
0.0376
0.0188
1.59
Between substrata
1
0.0013
0.0013
0.072
Interaction
2
0.0070
0.0035
0.297
Error
12
0.1417
0.0118
Total
17
0.0187
scientifique et techniques de P~ches maritimes (France) and Mr G. Shum from Environment Canada (Halifax Laboratory) who analysed replicate samples. This work was supported by DGES-FCAC grant from the Quebec department of Education. We thank our colleages who critically reviewed the manuscript.
EDWIN BOURGET*
Institut National de la Recherche Scientifique INRS-Oc~anologie DANIEL COSSA
Mean values
*E(L)HWN MTL MLWN
Rocky 0.438ppm 0.311 ppm 0.375 ppm
Muddy 0.383ppm 0.295 ppm 0.395 ppm
Section d'Oceanographie de I'Universit~ du Quebec ~ Rimouski (SOUQAR ) 310Ave. de Ursulines Rimouski, Quebec, Canada *Present address: D~partement de biologie, Universit~ Laval, Quebec, Canada.
*E(L)HWN: extreme (lowest) high water of neap tides; MTL: mean tide level; MLWN: mean low water of neap tides.
These results are in agreement with previous studies showing that waters of the Saguenay are an important source of mercury contamination in the study area (Loring, 1975; Gubeli et al., 1976). The concentrations reflect the fate of the surface waters of the Fjord in the St. Lawrence Estuary. the flow of the Saguenay is directed on the South Shore. There, these water mix with waters originating from the Upper Estuary, before being directed seaward mainly along the South Shore (Nadeau, 1938; Farquharson, 1966; Trites, 1972). It appears that the mercury content of the mussles in the estuary merely reflect the overall seaward dilution of mercury from terrigenous sources. Since bivalves can accumulate metals from food and solution, mussels should ingest much more metal per unit volume of water filtrated towards the upper estuary. Relatively low concentrations were observed on the North Shore at stations 28, 29 and 30. An explanation for these low mercury values is the direct influence of marine water masses, probably with a lower mercury content, coming through Jacques Cartier Passage (Dawson, 1913; E1 Sabh, 1976) and the presence of an upwelling on the North Shore of the Lower Estuary (Gaudry, 1938; Steven, 1974) (Fig. 1). Intermediate values along the Gasp6 Peninsula coast probably reflect a residual influence of estuarine water masses through the Gasp~ current which flows along the entire length of the Gasp6 coast. Comparison of our results with those reported by Mytilus sp. from the Canadian Pacific coast (Parsons et aL, 1973) and from the European coast (Establier, 1973; Thibaud, 1973; Anderson & Neelakantan, 1974; De Wolf, 1975) indicate similar mercury levels with the exception of a few sites reported for the English coast (De Wolf, 1975).
The authors acknowledge the assistance of Mile D. Messiere and Mr J. Sylvian for collection of specimens and Mr G. Canuel for analysis of the samples. Special thanks are due to Dr Y. Thibaud from lnstitut
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239