Metals in oysters from the Arnhem Land coast, northern Territory, Australia

Marine Pollution Bulletin 0025 326X/89 SJ.00+0.()() © 1989 Pergamon Press plc

Marine Pollution Bulletin, Volume 20, No. 3, pp. 144-145, 1989 Printed in Great Britain.

from Darwin region were relatively small (3-4 cm long, 2-3 cm wide), a composite sample of 26 individuals were used for analysis. When defrosted, the oysters were shucked, drained and weighed into 150 ml beakers and

Metals in Oysters from the Arnhem Land Coast, Northern Territory, Australia The concentration of heavy metals in oysters is a function of water quality, seasonal factors, temperature, salinity, diet, spawning, and individual variation (Forstner & Wittman, 1981). The concentration of metals can increase in oysters many orders of magnitude above background concentration (Talbot, 1985; Forstner & Wittman, 1981; Longhurst, 1981), thus demonstrating the potential of oysters as sentinel accumulators of heavy metals. Recently the Fisheries Division of the Northern Territory has shown keen interest in developing the oyster culture industry in the Northern Territory of Australia (Nathan, 1988). This has prompted us to carry out a preliminary survey of the Arnhem Land coast and some areas of Darwin Harbour for suitability of location with respect to metal contamination. Two oysters occur in the Northern Territory waters, the blacklip, Saccostrea echinata, and the milky oyster, Saccostrea cucullata. Of these, the blacklip is the larger, growing to 15 cm shell width (Arnhem Land coast) and is favoured as an aquaculture prospect (Griffith, 1979). No heavy metal data are available from Arnhem Land coast to establish natural background levels in the oysters. This paper reports the values for lead, zinc, copper, cadmium, nickel, and iron in the oysters from Arnhem Land coast and Port Darwin area. Samples of oysters (Saccostrea echinam, S. cucullata) from seven locations were collected before the spawning period (February-April) from sites as shown in Fig. 1; their identification is given in Table 1. The oysters (shell plus flesh) were placed in separate, labelled plastic bags and kept frozen prior to being transported to Darwin and stored at -10°C until analysis. As most of the oysters were large (Amhem Land coast: 5-9 cm long, 3-9 cm wide), twelve individuals from each location were used for analysis. Oysters

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Fig. 1 Location of sampling sites.

TABLE 1

Metal concentration (gg g-l, wet wt) in oysters. Range (i +- s.d.). Site number

1

Location

Gove Harbour

Date

Pb (2.5 ggg-~)*

Ni

Zn (1000 ggg-1),

Cu (70.0 ~tgg-t) *

Cd (2.0 gg g-~)*

Fe

June 86

nd

nd

337-556 (430 _+84) 0.63-36.2 (13_+10.7) 2.6-7.3 (4.9 ± 1.5) 8.1-17.1 (13.3_+2.4) 488-787 (611 _+83) 180-305 (245 _+40) 625-150 (109_+28) 0.01

22.l-38.2 (29 _+7.9) 6.4-27.8 (14.5_+5.6) 1.8-7.7 (5.2 _+ 1.9) 6.1-18.6 (9.7_+3.5) 17.3-39.8 (30.4_+7.2) 45.2-70.2 (58.3 -+ 9.4) 16.8-37.5 (27.0+-6.2) 0.05

1.0-2.5

(1.6 _+0.59) 2.5-5.7 (4.1 _+ t.l) 3.5-18.0 (10.6_+4.2) 1.3-4.4 (2.3 _+ 1.0) 0.17-0.29 (0.25 _+0.04) 0.34-0.53 (0.44 _+0.07) 0.41-0.88 (0.58_+0.13) 0.01

35-90 (53+_22) 10-23 (15_+4) 15-51 (31 _+ 10)

2

Marchinar Island

June 86

nd

nd

3

Raragala Island

June 86

nd

nd

4

Coburg Peninsula

June 86

nd

nd

5

Rapid Creek, Darwin

Oct 86

nd

6

East Point, Darwin

Oct 86

nd

7

Channel Island

Oct 86

nd

Detection Limit

0.05

0.42-0.44 (0.43_+0.01) 0.44-1.06 (0.82 -+ 0.43) 0.36-0.73 (0.49-+0.13) 0.05

*National Health and Medical Research Council recommended standard (Anon., 198(/) for metal in molluscs.

144

11-55

(28 + 12) 122-1228 (352+_361) 32-151 (84 _+4(3) 21-139 (62+-35) 0.20

Volume 20/Number 3/March 1989 their wet weight was recorded. 30 ml of 6 M nitric acid (Aristar) was added to each beaker and to two blanks. Watch glasses were placed over beakers and the oysters were left to digest overnight. The digests were slowly evaporated to near dryness on a hotplate at 70°C. The residues were dissolved in 20 ml of 1 M nitric acid (Aristar) and when cool, m a d e up to 50 ml in volumetric flasks with deionized water; filtration of the digests was unnecessary. Samples were placed in acid-washed polyethylene screw-top sample bottles and analysed within 24 hours by flame spectroscopy using a Varian AA1475. The accuracy of the method used was established using SRM 1566 oyster tissue and recovery trials. Duplicate analysis gave the following results: Sample

Pb

Zn

Cu

Cd

RecoveryTrial % 100% 95% 95% 100% SRM Oyster Tissue Certified Values ggg-1 0.48_+0.04 852_+14 63.0_+3.5 3.5_+0.4 Conc. found p.gg-~ n.d. 795 _+16 59 _+2.1 3.5 _+0.1 The cadmium concentrations were extremely high in the oysters from A r n h e m Land Coast and all exceeded the r e c o m m e n d e d N H M R C limit; Raragala Island (Location 3) being the highest (3.5-18.0 ~tg g-l). The A r n h e m Land Coastal area of the N o r t h e r n Territory is very sparsely populated, has no anthropogenic source of cadmium, pollution-free and virtually no industry with exception of Gove H a r b o u r (Site 1). Naturally high concentrations of the cadmium has also recently been reported at a similar tropical site, pollution-free, remote and isolated location of Shark Bay, Western Australia (McConchie et al., 1988). The elevated level of cadmium (Pinctada carchariarium 37.8 ~tg g-1 and P i n n a dollabrata 48.8 ~tg g-l) could be due to variation in the heavy metal concentration in the groundwater in the supratidal zone, variation in substrate sediment composition, variation in turbulence between sites or a combination of these possibilities (McConchie, 1988). The concentation of zinc in the oyster was highest ( 4 8 8 - 7 8 7 5'g g-l) at Rapid Creek (Location 5). Rapid Creek is a treated sewage and storm water discharge site. It has consistently shown higher levels of zinc around that area (Peerzada & Dickenson, 1988). The concentration of zinc was also high at Gove H a r b o u r ( 3 3 7 - 5 5 6 ~tg g-l).

~,larine Pollution Bulletin, Volume 20, No. 3. pp. 145-147, 1989 Printed in Great Britain.

Marine Environmental Quality Attended by 67 participants from five countries (Canada, United States, England, Ireland, and Greece), the Oslo and Paris Commissions, and the United Nations Environment P r o g r a m m e (UNEP), the Canadian Conference on Marine Environmental Quality was held in Halifax, N o v a Scotia, 29 F e b r u a r y - 3 March,

Gove H a r b o u r mainly received input from the bauxite industry operating at its shores. Elevated values of zinc are still within the r e c o m m e n d e d N H M R C limit of 1000 ~tg g-1. The highest level of copper (45.2-70.2 gg g-i) was found at East Point which is a wildlife reserve including Race Course Creek into which treated sewage is discharged, emptying into a base close to the sampling site. The oysters from A r n h e m Land Coast were large but contained higher levels of cadmium and zinc with exception of the Coburg Peninsula (Location 4) which showed lower concentrations of zinc, copper and cadmium and may be considered as a suitable site for oyster culture as attempts to cultivate oysters in Darwin H a r b o u r were not successful, probably due to the large tidal range and silt load in the waters (Griffith, 1979). NASEEM PEERZADA CHRISTINE DICKINSON Faculty o f A p p l i e d Science, Darwin Institute o f Technology, Casuarina, Darwin, Northern Territory, 0810 Australia

Anon. (1979). Report on the 90th Session of the National Health and Medical Research Council, Australian Government Publication Service, Canberra. Forstner, J. & Wittman, G. T. M. (1981). Metal Pollution in the Aquatic Environment. Springer, Berlin & New York. Griffith, R. K. (1979). Aquaculture Potential in the Northern Territory, Extension Leaflet, Department of Fisheries. DPP, Northern Territory, Australia. Harris, J. E., Fabris, G. J., Statham; E J. & Tavdik. E 11979). Biogeochemistryof Selected Heavy Metals in Western Port, Victoria, and Use of Invertebrates as Indicators with Emphasis on Mytilus edulis planulatus. Aust. J. Mar. FreshwaterRes. 30, 159-178. Longhurst, A. R. (1981). Analysis of Marine Ecosystems. Academic Press, New York. McConchie, D. M., Mann, A. W., Lintern, M. J., Longman, D., Talbot, V. & Gabelish, M. J. (1988). Heavy Metals in Marine Biota, Sediments and Waters from the Shark Bay Area, Western Australia. J. Coastal Res. 4, 37-58. Nathan, S. (1988). Director of Aquaculture, Division of fisheries, DID; Workshop on Water Quality in Aquaculture, 27 February 1988, Darwin N.T., Australia. Peerzada, N. & Dickinson, C. (1988). Heavy Metal Concentration in Oysters from Darwin Harbour. Mar. Pollut. Bull. 19, 182-184. Talbot, V. 11985). Heavy Metal Concentrations in the Oysters 5"accostrea cucullata and Sacostrea sp. from the Dampier Archipelago, Western Australia. Aust. J. mar. Freshwat. Res. 36, 169-175.

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1988. Organizers and sponsors were Environment Canada, Dalhousie University, Canada D e p a r t m e n t of Fisheries and Oceans, D e p a r t m e n t of External Affairs for Canada, Nova Scotia D e p a r t m e n t of Environment, Federation of c a n a d i a n Municipalities, Canadian Water and Wastewater Association, and the Canadian Association on Water Pollution Research and Control. It was coordinated and facilitated by the International 145