Laboratory accumulation and depuration of copper and cadmium in the freshwater mussel Dreissena polymorpha and the aquatic moss Rhynchostegium riparioides

This work assessed the potentialities of the zebra mussel Dreissena polymorpha and the aquatic moss Rhynchostegium riparioides as indicators of freshwater heavy metal contamination. Simultaneous exposure of the two species was performed in the same experimental system developed to fulfill the food requirements of the mussels. The exposure to Cu (4.5, 9, 21 and 50 μg L −1) and Cd (0.3, 6, 15 and 44 μg L −1) over a 27-day period was followed by a 14-day post-exposure phase. Accumulation of both metals was rapid in the mosses and reached a plateau after 18 days for Cu and 6 days for Cd; it was slower for the mussels and no steady state was observed, except for the lowest Cu treatment (9 μg L −1). The filtration rate of the bivalves and consequently bioaccumulation was reduced at the highest Cu concentration and in the absence of food. At the end of the depuration phase, the mosses had lost 50 ± 4 % of Cu and 88 ± 1 % of Cd, while the mussels had eliminated 18 ± 11 % of Cu and 5 ± 7 % of Cd. Highly significant linear relationships were observed at the end of both the accumulation and depuration phases (i) between the average aqueous Cu and Cd concentrations and the metal levels in the two organisms, and (ii) between the metal concentrations in the mussels and those in the mosses.