Selected molluscs as monitors of metal pollution in coastal marine environments

Doctoral Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

The potential of bivalve molluscs as monitors of metal pollution in South African coastal marine environments has been investigated using the species Crassostrea gigas, Crassostrea margaritacea, Perna perna and Choromytilus meridionalis. Metal concentrations in these and other species living along an unpolluted coast have been determined by atomic absorption spectrometry following chemical oxidation of the biological tissues. Variations in concentrations within a population may depend upon the size or sex of the individual and on the season during which the sample is collected. Metal accumulation by the four study species has been investigated under controlled laboratory conditions for the elements zinc, cadmium, copper, lead, iron, manganese, nickel, cobalt and chromium. Rates of accumulation differ between species and for each element. Some of the factors affecting cadmium uptake have been studied. Rates of accumulation depend greatly upon the form of the cadmium in solution but are also affected by changes in environmental parameters. The accumulation rates of other elements are probably also affected by these factors, not necessarily in the same way. The solution concentrations tested for these accumulation experiments, and also those tested for their effects on the filtering rates of adults or on the development of larvae, are higher than those normally found in polluted areas. This implies that these species are sufficiently tolerant of the presence of metals in their environment to be able to act as monitoring organisms. However, adult oysters and mussels may react to the presence of metals or to the estuarine environment, where fluctuations in water salinity may occur regularly and where effluents may be discharged into the freshwater stream. The mollusc which has closed its valves for either of these reasons may avoid the pollutant. This reaction obviously affects the ability of molluscs to monitor such pollutant inputs. Theoretically, the four study species cannot be used to monitor metal pollution in coastal marine environments quantitatively, as metal accumulation is influenced by too many environmental variables. However, the results from field sampling surveys can be interpreted with greater confidence when the effects of these variables on metal accumulation are known. In practice, a semi-quantitative measure of metal pollution can be achieved.

Bibliography: pages 150-163.