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 micrograms/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 micrograms Cd/liter and more than 50% of the specimens exposed to 0.2 micrograms Cd/liter, demonstrating that Dreissena cannot 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 d10 metals.