Trace metals in the marine bivalve Macoma balthica in the westerschelde estuary, The Nertherlands. Part 3: Variability of the role of cytosol in metal uptake by the clams

Tellinid clams Macoma balthica were sampled every 2 months for 2.5 years at two locations from the Westerschelde estuary (The Netherlands) and submitted to in vitro short-term exposure to Cd, Cu and Zn. Total and heat-stable cytosolic metal concentrations have been measured before and after exposure to study the effects of the sampling season on metal uptake by the bivalve. We observed much higher uptakes of Cd and, to a lesser extent, Cu in winter than in summer, while Zn appears to be constantly regulated. These phenomena are amplified in the cytosol, especially for Cd, a non-essential element, for which the concentrations after exposure can reach 35–45 μg·g⁻¹ (dry wt.) in winter, but only a maximum of 0.5 μg·g⁻¹ in summer, all natural values being between 0.01 and 0.1 μg·g⁻¹ on average. The contents (μg) of the various elements, either at the total or at the cytosolic level, are not constant, hence showing that the seasonal body weight fluctuation of the clams (dilution or concentration effect) is not the only parameter responsible for the metal uptake variability. Furthermore, we have shown that the proportion of cytosolic metal is not constant, but increases with the absolute cytosolic concentration up to 35–40. Therefore, the cytosolic phase of the cells plays a growing role in Cd, Cu and Zn storage as long as their total concentration increases.     

Metallothionein and metal levels in cytosol of liver, kidney and brain in relation to growth parameters of Mullus surmuletus and Liza aurata from the Eastern Adriatic Sea

Two wild fish populations (Mullus surmuletus (striped red mullet) as a bottom, and Liza aurata (golden grey mullet) as a pelagic species, were sampled in Kastela Bay, Middle Dalmatia. Metallothionein (MT) and metal content (Cu, Zn, Cd) was determined in heat-treated supernatants (S50) of fish tissues. MT levels were statistically different in liver and kidney of sampled species, with highest value in kidney of M. surmuletus (31.1 +/- 7.96 micrograms mg-1 proteins). Metal levels are statistically different between all tissues. Highest metal concentrations are in liver cytosols, especially of Cu in L. aurata (6.46 +/- 3.45 micrograms ml-1 S50). High positive correlation of MT and cytosolic metals is established with Zn in liver of M. surmuletus (0.95) and with Cu in liver of L. aurata (0.69). Total length, body weight and age are mostly correlated biometric parameters with MT and soluble metal concentrations. MT and metal levels increase with age in liver cytosol of both species.