Marine Environmental Research 17 (t985) 277-280

Some Responses of Transplanted Mytilus edulis to Metal-Enriched Sediments and Sewage Sludge

Derek Johnson & T imothy J. Lack

Water Research Centre, PO Box 16, Marlow, Buckinghamshire SL7 2HD, Great Britain

Approximately 25 °/o of the sewage sludge produced in the United Kingdom (about 10 million wet tonnes anually) is disposed of to British coastal waters at 15 sites. A series of tests is being et'aluated in order to determine the effects of this practice in relation to the effects due to other polluting inputs, both natural and man-made, to the marine environment. The results presented here are for one site on the south-west coast o f Britain. They indicate that the increased metal content o f the tissue and the presence o_[ sulphydryl-rich metal-binding prote#zs in the lysosornes of digestive cells in transplanted mussels can be correlated with exposure at sites overlying metal-rich sediments and to a lesser extent an area used for the disposal o f sewage sludge containing metallic contaminants.

Mussels (Mytilus edulis) were collected from Whitsand Bay to the west of Plymouth Sound and placed in baskets suspended 4m below the surface and 4 m above the sea bed at sites along a transect from Plymouth Sound to the Eddystone Rocks (Fig. 1). The line included sites in shallow water (10 m) overlying metal-enriched sediments (sites 1 and 2) and a deep water (50 m) sewage disposal ground (sites 5 and 6). The mussels were exposed for about 60 days after which they were recovered and returned to the laboratory for a range of physiological and cytochemical measurements, to study general condition and the effects of exposure to enhanced metal concentrations. Among these were some designed to determine the effects of exposure to metals. A small portion of the digestive gland was dissected out of each of five mussels from each site and

277

Marine Enciron. Rt,s. 014 I- 1136/85~$03 -30 ~ Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain

2 7 8 Derek Johnson, Timothy J. Lack

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Fig. 1. Sketch map showing the positions of the monitoring sites in relation to Plymouth Sound and the Sewage Disposal Ground.

this was mounted on a cryostat chuck by supercooling in hexane at - 70 °C. The presence of SH-rich metal-binding protein was determined using the Shikata-Orcein test. 1 Additional soft tissue was dissected out for metal analysis by X-ray fluorescence spectrometry.

The tissue analysis showed that, in almost every case, the mussels held in the lower cages had higher concentrations of metals than those in the upper cages at the same site. The mussels at site 1 had the highest levels and these decreased until close to the disposal ground where a second peak occurred. The concentrations of metals in the sediments along the

Response oJ mussels to metal-enriched sediments and sewage sludge 279

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Fig. 2. Upper graph shows the zinc content of the soft tissue of the muscles; centre, the presence of metal-binding protein in the digestive cells; and lower, the concentration of

zinc in the coarse and fine sediment fraction along the monitoring line.

280 Derek Johnson, Timothy J. Lack

line have been determined-" and show high concentrations in the shallow water adjacent to the Sound. These are due to the weathering of naturally metal-rich rock in the catchment of the River Tamar which flows into the Sound, a peak also occurs in the region of the disposal ground. As an example the concentrations or" zinc in the soft tissue and sediments are given in Fig. 2. It is suggested that the mussels at the shallow site are exposed to resuspended natural sediment particles and those in the area o( the disposal ground to particles derived (rom sewage sludge.

Also shown in Fig. 2 is analysis of" the digestive cells for metal-binding protein which shows a pattern similar to that of the metal content of the tissue. The mussels in the upper cages gave a 60 ~o response at site 1 while at all other sites no positive reactions. The mussels in the louver cages showed maxima at sites 1 and 6 with no positive reactions at site 3. There is a significant correlation (r~ = 0.9: P = 0.05) between the metal-binding proteins in the digestive cell lysosomes and the zinc content of the tissue.

R E F E R E N C E S

1. Viarengo, A., Moore, M. N., Partica, M., Mancinelli, G., Zanicchi, G. & Pipe, R. K. Sci. Total,Era'iron., 44. 135-45 (1985).

2. Eagle, R. A., Hardiman, P. A., Norton, M. G. & Nunny, R. S. Fish. Res. Tech. Report, No. 50, MAFF Direct. Fish. Res., Lowestoft, t979.