Determination of Cadmium–Metallothioneins in Zebra Mussels Exposed to Subchronic Concentrations of Cd2+

Metallothioneins have been detected and investigated in zebra mussels (Dreissena polymorpha) using high-performance liquid chromatography (size exclusion) coupled with microatomization–AAS or inductively coupled plasma mass spectrometry. The mussels were exposed to 0.2, 2, and 20 μg/liter Cd2+(as CdCl2) for 1 month under controlled temperature and dietary conditions. Elevated (relative to control) concentrations of tissue Cd2+were detected in all specimens exposed to 2 μg Cd/liter and more than 50% of the specimens exposed to 0.2 μg Cd/liter, demonstrating thatDreissenacannot regulate Cd2+at trace exposure concentrations. In most specimens, at least 85% of the measured Cd2+was bound to metallothioneins. After reduction and exposure to excess Cd2+, the metallothionein fraction of all extracts adsorbed similar quantities of Cd2+, indicating that the physiological concentration of metallothionein in the exposed specimens remained similar to the basal concentration in the control specimens. Thus, a short-term exposure to environmentally relevant concentrations of Cd2+did not produce a genetic induction of metallothionein biosynthesis as generally observed in specimens exposed to higher concentrations of d10metals.