UPTAKE OF NICKEL AND ZINC BY THE ZEBRA MUSSEL DREISSENA-POLYMORPHA

Short-term experiments with nickel and zinc radioisotopes showed that the zebra mussel Dreissena polymorpha takes up both ''dissolved'' (<0. 45 mu m) and particulate fractions of these metals in water. Uptake of particulate nickel was significant (despite a relatively low affinity of nickel for particulate matter), though less important than uptake of dissolved nickel. The relative importance of dissolved and particul ate zinc varied from an almost exclusive uptake of dissolved zinc to u ptake of particulate zinc only. This variability may reflect a depende nce on the composition of the suspended particulate material, in line with the observation that zinc uptake and bioaccumulation were higher in high-turbidity water than in low-turbidity water. Metal excretion d iffered between the two metals; more than half of the accumulated zinc was excreted in twenty four hours, while no nickel excretion was evid ent. The mussels removed a larger proportion of total watercolumn zinc than of total watercolumn nickel. Of the metal removed from the water column, a majority of the zinc was biodeposited (as feces/pseudofeces) while most of the nickel was bioaccumulated. These results indicate t hat the introduction of the zebra mussel will result in element-specif ic decreases of watercolumn metal levels, increases in metal bioaccumu lation and increases in metal biodeposition. Results also indicate tha t D. polymorpha tissue metal levels obtained in biomonitoring programs will generally reflect both dissolved and particulate metal levels.