Pergamon 0025-326X(94)E0032-4 Marine Pollution Bulletin. Vol. 28, No. 10, pp. 592-600, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved (/1125-326X/94 $7.00 + 11.111~ Accumulation and Subcellular Distribution of Metals (Cu, Fe, Mn, Pb and Zn) in the Mediterranean Mussel Mytilus galloprovincialis During a Field Transplant Experiment FRANCESCO REGOLI and ENZO ORLANDO Dipartimento di Biomedicina Sperimentale Infettiva e Pubblica, Universith di Pisa, Via A. Volta 4, 56100 Pisa, Italy Marine mussels are generally used as biomonitors of heavy metal pollution in coastal areas. However, the time-integration capacity of these molluscs may vary from different metals and this fact should be considered when interpreting heavy metal concentrations in natural mussel populations. The aim of this work was to investigate the uptake-excretion kinetics and the subcellular distribution of metals in field conditions: the results were expected to provide useful information on the different time-integration capacities of mussels for various elements. Mussels from a clean site were transplanted to a heavy metal polluted environment where they accumulated Pb, Fe, and Mn. The accumulation was not linear but a steady state was reached after only 2 weeks, indicating that mussels can rapidly equilibrate with enhanced environmental levels of these pollutants. Copper and zinc were not accumulated by transplanted mussels, suggesting a similar bioavailability in the two environments or a certain regulation capability of molluscs for these essential elements. Polluted mussels, allowed to depurate in clean seawater, showed excretion rates which were different between elements. Moreover the subcellular distribu- tion was characteristic for each metal but the patterns were similar in wild populations as well as in trans- planted and depurating mussels, indicating that the same subcellular fractions are involved in the uptake, storage and excretion of metals. From the results, the different time-integration capacities of mussels for various elements appear to be related to the cellular mechanisms involved in their detoxification and/or excretion. Several studies have demonstrated that the concentra- tion of heavy metals in mussels tissues can provide a time-integrated measure of the environmental bio- availability of these contaminants (Phillips, 1976, 1977, 1980). However, the time-integration capacity of mussels may vary for different metals and these biomonitors reflect the environmental condition over a period of time which increases if the biological half life of a particular metal is extended. Usually this aspect is not considered in monitoring studies, probably because the available data on heavy metal biological half lives in natural conditions are scanty and often contradictory (Phillips & Segar, 1986). In fact, important biological processes associated with metal exposures such as uptake, excretion and biological effects, have been generally studied under laboratory conditions and seldom in field experiments (Widdows et al., 1981; Roseijadi et al., 1984; Regoli, 1992). In this respect, a useful approach for a better understanding of metal accumulation in marine biota, may be represented by mussel transplantation. In fact, since the molluscs are easily available from commercial stocks, it is possible to use organisms with a low genetic and/or age variability (Phillips & Segar, 1986) and in the same phase of the reproductive cycle, so reducing the effects of these variables which have a strong influence when comparing data obtained from different wild populations (Regoli & Orlando, 1994a). According to Simkiss & Mason 11984), the uptake kinetics of metals should be initially characterized by a direct proportionality between the accumulated doses and the time of exposure, whereas the final concentra- tion in the organism is determined by the intracellular availability of metal-binding ligands and by the turnover of the formed complexes. A better knowledge of uptake-excretion kinetics and of the subcellular distribution of metals in field conditions may contribute to the understanding of the time-integration capacity of mussels for different elements, and provide useful information for inter- preting heavy metal levels in natural mussel popu- lations. 592