Mature glochidia were stripped from the gills of gravid mussels and exposed to low pH (3 – 6.5), aluminum (150 – 3000 μg/L), aluminum (300 μg/L) at low pH (3–6.5), zinc (5 – 30 000 μg/L), cadmium (50–3000 μg/L), or copper (5 – 1500 μg/L) for 6 days. Viability was tested after 24, 48, 72, and 144 h by observing the ability of the glochidia to close when exposed to an irritant, 2.5 M KCl. Effective concentrations needed to reduce the closure response to 50% (EC50) under the experimental conditions were calculated using probit analysis. The relative toxicities (based on 48-h EC50s) of the metals to Anodonta cygnea glochidia were Cu (EC50 = 5.3 μg/L) > Cd (EC50 = 46.8 μg/L) > Zn (EC50 = 69.1 μg/L) > Al. The EC50 for pH was 4.34 for A. cygnea and 4.69 for Anodonta anatina. In 300 μg/L Al, the EC50 for pH for A. cygnea was 4.46. The ability of glochidia to close their valves is considered a reliable measure of viability, as this action is necessary for the larvae to complete the obligate ectoparasitic stage of their life cycle. Decrease in glochidial viability is suggested as a possible explanation for the disappearance of unionids from acid- and metal-contaminated waters.

The freshwater unionids Anodonta anatina, Anodonta cygnea and Unio pictorum were examined with respect to the distribution of calcium concretions among the various organs, and to a possible role of concretions in heavy metal detoxification. Gills of all three species contain large amounts of concretions, up to 55% of the tissue dry weight in A. cygnea. Smaller amounts are present in the mantle and the midgut gland, and also in granulocytes. The other organs, including the kidney, are practically devoid of concretion material. By electron-microprobe analysis, the concretions appear to be of the phosphatic type, and also contain manganese, iron and zinc. When animals were exposed to CdClz, cadmium was bound to the concretion fraction of the various organs. But, in almost all cases, Cd concentrations in the concretion material were lower than those in the whole organ. Furthermore, the contribution of the concretion fractions in Cd accumulation decreased over the course of exposure. It is concluded that calcium (pyro)phosphate concretions do not function as preferential sequestration sites for cadmium.

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