No abstract

Shell weight of molluscs is introduced as alternative parameter for biological monitoring of heavy metals. Variability of metal concentration due to variations in soft-body weight can be eliminated by relating metal body burden to shell weight. A reformed 'Mussel Watch' concept IS outlined. Detailed investigation of Cd in mussels exemplifies advantages of the new approach. The relation of Cd body burden to shell weight is constant in relation to environmental Cd concentration. In contrast, conventional Cd concentration values of soft tissues, in general, are related to the physical condition of mussels. The dependency of condition and Cd concentration on individual size, tidal exposure, spawning, and nutrient supply is documented. Accumulation of Cd in soft tissues and formation of the calcareous shell are discussed in terms of influx of environmental ions and organismic immobilisation, together with their respective organic ligands.

Juvenile mussels Mytilus edulis L. were culhvated in controlled flow-through aquana to investigate the influence of environmental temperature, salinity, and dissolved oxygen on cadmium balance. (1) Inverse relations between Cd concentration of soft tissues and physical condition of mussels were observed in response to temperature. The relation between Cd body burden and shell weight (Cd/shell-wt index) is independent of temperature between 7 and 25°C. (2) Reducing salinity (mg kg-'), while keeping dissolved Cd (pg I-') constant, increases the molar ratio of Cd and seawater salts. Accumulation of Cd in the soft tissues and of Ca in the shells of mussels is determined by Cd and Ca concentrations within the range of 15 to 30 960 salinity. Residues of Cd in mussels, therefore, are hlgher in samples from lower salinity. Below 15 %a the Cd/shell-wt index is disproportionately higher, corresponding to reduced shell growth In lower salimtles. Slightly lower index values were observed in 35 %. (3) Dissolved oxygen concentrahons between 2.5 and 6.5 m1 1-' have no influence on the Cd balance of mussels. (4) Experimental results were reproducible and corresponded to field observations. (5) Modifications of growth and performance were In accordance with the literature Lowest expenmental temperature, salinity, and oxygen tested inhibited both growth of mussels and Cd uptake withn a small laboratory gradlent. Growth in the concerned environment is discussed as an essenhal aspect of research on metals and molluscs, and in relation to the mussel watch concept.

No abstract

Juvenile blue mussels Mytilus edulis were cultivated in flow-through aquaria to investigate the influence of dissolved cadmium on cadmium accumulation (in terms of the Cd/shell-wt index). Where the ratio (by weight) of dissolved Zn to Cd remains within the range 25:l to 60:1, accumulation of Cd is not significantly influenced by dissolved Zn. Higher levels of concomitant Zn reduce the Cd/shellwt index. A lower ratio of Zn to Cd may slightly increase Cd accumulation. The Cd/shell-wt index is proportional to ambient levels of dissolved Cd up to 100 yg 1-' There were no significant effects on growth up to ca 30 pg 1-' Cd. Results corresponded to earlier experimental work and to field surveillance data reported in the literature. A procedure is suggested by which the concentration of dissolved Cd In natural environments may be estimated from 'mussel watch' data (Cd body burden, shell weight) and salinity. Cd accumulation in the mussel is described by the integral of the Cd/shell-rut index with growth of shells by weight. A model of biochemical accumulation of metals requires laboratory and field transplant experiments to be designed such that considerable growth is allowed in a new environment in order to approximate a new balance of metal residues in organisms in relation to ambient levels.