Bivalve mollusc Sunetla scripta is abundant in the inshore waters of Co chin and is a suitable indicator

species of metal pollution. The metal load in the bivalve showed an increase during the monsoon season

indicating the apparent influence of river run off and reduction in salinity in the seasonality of metal uptake. In

the case of copper, the smaller individuals recorded relatively higher load than that of larger ones

Pillai, V K

Valsala, K K

113-115Bivalve mollusc Sunetta scripta is abundant in the inshore waters of Cochin and is a suitable indicator species of metal pollution. The metal load in the bivalve showed an increase during the monsoon season indicating the apparent influence of river run off and reduction in salinity in the seasonality of metal uptake. In the case of copper, the smaller individuals recorded relatively higher load than that of larger ones

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Seasonal variations of some metals in bivalve mollusk Sunetta scripta from the Cochin coastal waters

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Indian Journal of Marine Sciences Vol. 24, June 1995, pp. 113-115 Seasonal variations of some metals in bivalve mollusc Sunetta scripta from the Cochin coastal waters V K Pillai & K K Valsala Central Marine Fisheries Research Institute. PO Box-1603. Cochin·682 014. India Received 16 December 1993, revised 22 February 1995 Bivalve mollusc Sunetla scripta is abundant in the inshore waters of Co chin and is a suitable indicator species of metal pollution. The metal load in the bivalve showed an increase during the monsoon season indicating the apparent influence of river run off and reduction in salinity in the seasonality of metal uptake. In the case of copper, the smaller individuals recorded relatively higher load than that of larger ones. Marine pollution monitoring programme known as mussel watch envisages analyses of trace metal and pesticide load of different species of bivalves from various localities l . Bivalve mollusc Sunella scripta is abundant in the inshore waters of Cochin. A pre-liminary survey carried out in May 1983, reported ' that population densiiy of 420 clams/m' vias found in the inshore waters of Cochin on the west coast of India, but the densities are likely to be higher during monsoon period. The objective of this study is to understand the seasonality and body size associated variations in metal load in the body tissue of the bivalve. Information on the seasonality of pollutants is important in designing monitoring programmes .using bioaccumulator species to understand the variations in toxicant levels in the area. Samples of S. scripta were collected from the landing-centre at Vypeen (Cochin: lat. 09°58'N; long. 76°11 'E) during 1989-90. Whole body tissues of 10 animals of similar size, ere analysed for Cu, Zn, Cd and Pb by wet digestion"" The digested samples were analysed on a Perkin Elmer AAS (Model 2380) in an air-acetylene flame. The precision and accuracy of the method followed and the instrument used was evaluated by recovery studies as well as inter-calibration exercises (with National Institute of Oceanography, Goa, India) . In general, the metal load in the bivalve increased during the monsoon season (Table I). The metal levels in molluscs are usually linked to size, sex, reproductive condition, seasonal variation and also on the available chemical form in the ambient water. Three major inter-related factors which may contribute to fluctuation of pollutants in aquatic biota are: pollutant delivery to the aquatic environ-ment, organism physiology, particularly sexual cycle and changes of ambient water quality parameters ... such as temperature or salinity'. It is known that river run off adds to the pollution input considerably. In the present study, the location of the sample collection is just outside the Cochin bar mouth. The changes in salinity and temperature are reported to be closely involved in the process of metal availability in water and intake by bivalves. The influence of salinity in the seasonality in this case is apparent since all the four metals studied showed sig.nificant increase in the metal load dur;ng monsoon season. (Cu: May-July; Zn: July-Nov. ; Cd: July-Oct.; Pb: Nov.). In case of Cu, the smaller individuals recoreded relatively higher load than that of the larger ones (Table 2). However, the levels of all the four metals in S. scripta were much below the levels recommended for seafood for human consumption. A review of copper in marine organisms indicated that, molluscs contained more copper in tissues and soft parts than any other group induding plants, Table I- Metal levels in bivalve Sunetta scripta Months Metals ( ± SD) (~gfg wet weight) Cu Zn Cd Pb Jan. 1989 5. 15±0.70 19.86 ± 0.94 0.18±0.10 0.26±0.11 Feb. 5.07±0.15 22.07 ±0.37 0.27 ±0.01 0.56±0.06 March . 4.99±O.O2 20.27 ± 0.42 O.18 ± O.O5 O.27 ± O.O7 May 6.74 ± 0.25 . 21.18±0.82 0.2r±0.OO5 0.26±0.11 July 6.80±0.90 22.45 ± o,o5 0.28±0.01 0.35±0.05 Aug. 4.28 ± 0.06 21.57 ± OJO 0.22±0.OO5 0.25±0.05 Sept. 4.22 ± 0.22 26.13 ± 2.18 0.30±0.05 0.44±0.17 Oct. 6.l5±0.02 30.07 ± 0.90 0.31 ±0.09 0.33 ± 0.26 Nov. 2.21 ± 0.06 33.48 ± 1.13 0.21 ±0.03 0.61,±0.O6 Jan. 1990 6.11 ± 0.24 32.40 ± 2.65 0.36 ± 0.01 0.44 ± 0.02 n = IO nos. of similar size and analysed in duplicate. 114 INDIAN J. MAR. SCI. VOL. 24 JUNE 1995 Table 2- Metallevels of SunettQ scripta in relation with size variations (10 samples in each size and analysed in duplicate) Month Size Metals (Ilgig wet weight) Cli Zn Cd Pb Feb. 1989 LS 3.73 ±O.41 46.71 ±O.26 I.35±O.04 O.75±O.O5 SS 5.07±0. 15 22.07 ±0.37 0.27±0.01 0.56±0.06 March 1989 LS 3.89±0.60 43.24±0.38 1.50±0.16 0.75±0.22 SS 4.99±O.02 20.27±0.42 1.1 8±0.05 0.27 ±O.07 May 1989 LS 4.13±0.23 51.83± 1.48 1. 14 ±0.06 0.4 1 ±0.16 SS 6.74 ±0.25 21. 18±0.82 0.27±0.OO5 0.26±0. 1I July 1989 LS 5.41 ±0.59 37.25±0.45 1.70±0.01 0.31 ±O. II SS 6.80±0.90 22.45±0.05 0.28±O.01 O.70±0.20 Aug. 1989 LS 3.72±0.45 35.92±1.4 0.96±0.08 0.28±0.01 SS 4.28 ± 0.06 21.57±0. 10 0.22±0.OO5 0.25±0.05 L S = Large aize (32.43 mm average): S S = Small size (8.31 mm average) other invertebrate groups or vertebrates·. It is also reported that copper accumulations. or rates of accumulation varied with age of tlie organism. but even within the same species the pa ttern was not always predictable'. Decreasing copper content and increasing body weight were documented for clams Piltar mOrrhall(lfla'7 and Mercenaria !1'1erCeflllricl". But copper was positively correlated with increasing body.weight for bivalve molluscs including My!illis '!dulis . Mercenaria m'ercellar;a and Venusupis decassUla'o It was proved that differences in rate of availability may not drastically Influence the pattern of distribution of heavy metals over the various tissues. but it can significantly increase the quantity accumulated in each tissuelI Variations in zinc content of soft tissues from individual shellfish species have been correlated with seasonal . as dist inct from thermal regimes" ·l.'. In general. hivalve molluscs residing in comparatively sal i ne wa ters can tai ned red uced zinc concen t ra ti ons in their tissue while those from lower salinity waters contained more zinc. But salinity of the medium was not an important factor governing uptake of zi nc in mussels Mytilus eduli~'4 . However, zinc content of marine molluscs tends to correlate positively with particulate matter produced as a result of dredging operations'". The location of the station from which samples are collected for the present study is exposed to dredge spoil deposited off Cochin regularly. The sa lt content of the medium was inversely associated with Cd body burdens' . At low salinities. comparatively high Cd resid ues were measured in M. edlllis'4 and M. mercl'llaria9 There appears to be considerable temperature salinity-Cd interactions in M. edlllis". It was also observed that the presence of other metals in solution such as Zn. Pb and Cu had no effect OIl the individual net uptake of Cd from the medium by mussels". Temperature of the ambient seawater made little difference in Pb residues in mussel M. edllli.i' 4. However. the salinily of the medium significantly affected Pb residues, with high Pb concentrations reported in mussels from lower salinity waters". The high Pb levels in mussels from low salinity waters are not co rrelated with higher levels of Pb in water. but att ri buted to the biological avai labi lity ofPb. which exists primari ly in particulate form in seawater1 s. It is significant to note that higher levels of Pb load was observed in the biva lve may be due to the above said fac tor. The apparent selectivity for Pb and other melals among va rio us molluscan species largely depends upon its availability in the environment, its chemical and physical properties, the kind of number of ligands available for chelation. its transport. storage and the stability of the complex formed ' . Bivalves are known for Iheircapabil ity of acting as efficient time integrated indicators of various metals over a wide range of environmenta l conditions'4. From the present study it is apparent that S. scripta possesses the requisite features to be used. as a bioaccumulator for metal pollution monitoring programme. Authors thank Dr PS B R James. former Director fo r his encouragement in the investigations and to Dr M S Rajagopalan for his helpful suggestions. References I Goldberg E D. Thc I1/lisse/11Y1t h. i:.illlirollnlclIllll ollSCrWlliol1 , 5(1978) 101. SHORT COMMUNICATION 115 2 Kattikaran C M. Studies olllhe biology oJ the clam, SUI/etta scripta (Lin.)from the sub-tidal lI 'o fers oJCochin. Ph.D. thesis. Cochin UniversilY of Science & Technology, India. 1989. 3 Dalziel J & Baker C, FAO Fish Tech Pap" , 212 (1984) 14, 4 Anon, FAO Fish Tech Paper, 150 ( 1976) 76 . . 5 Philips 0 G H. Quanfita/Ne aquatic biological indicators. (App Sc Publ . London) 1980. 458. 6 Eisler R. in Copper in Ihe f:'flviromnenr, PaTt-1 Ecological cycling, edited by J 0 Nriague, (John Wiley. New York) 1979. 351. 7 Eisler R. Trace metal concentration in marine organism.s. (Pergamon Press, Nell' York) 1981,685. fI Eisler R, Barry M M, Lapan R L. Telek G, OW1eY E W & Soper A E, Mar Bio/, 45 (1978) 31 1. 9 Larsen L. Estuaries. 2 ( 1979) I. 10 Boyden C R. Na,ure, 251 ( 1974) 3 11. II George S G & Coombs P L. Mar Bio/, 39 ( 1977) 261. 12 Patel B. Valanju P G. Mulay C D, Balani M C & Patel S, in Radioactive Conlaminaciono/rhe marine environment, (Atom Encrg Agen. Vienna, Austria) 307. 13 Philips J H. Mar Bio/, 3H (1976) 14, 14 Philips D J H. Mar Bio/, 46 (1978) 147. IS Bryan G W, J Mar Bio/ Assn UK. 53 (1973) 145, 16 Rosenberg R, Mar Poll Bull. 8 ( 1977) 102, 

Seasonal variations of some metals in bivalve mollusc Sunetta scripta from the Cochin coastal waters

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Seasonal variations of some metals in bivalve mollusc Sunetta scripta from the Cochin coastal waters

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