Total concentrations of copper, cadmium, zinc and iron in the marine bivalve Macoma balthica have been measured every 2 months for 1 year by atomic absorption (AAS) and emission (ICP) spectrometry. In the sample treatment, the freeze-drying and the digestion procedure were studied in detail. Although the range of fluctuations for the four metals are different, they show a similar temporal pattern, with higher concentrations in winter and lower in summer, ranging from 16.8 to 32.1 mug . g-1 for Cu, from 0.19 to 1.13 mug . g-1 for Cd, from 377 to 692 mug . g-1 for Zn and from 506 to 1955 Ag . g-1 for Fe. The relationship between metal content and body weight varies from a highly significant straight line correlation (for copper and zinc) to no correlation at all (for cadmium). Thus, copper and zinc appear to be largely controlled by biological processes, while cadmium depends mostly on environmental levels, iron fluctuations being dependent on both factors.
