Effects of deionized water on viability of the zebra mussel, Dreissena polymorpha.

1. Zebra mussels exposed to deionized water (DW, changed daily) begin to die within several days. More than half the animals die in DW within a week. 2. Animals allowed to reattach themselves prior to exposure to DW live somewhat longer than detached animals exposed to DW but are still sensitive to the toxic effects of DW. 3. Small animals die in response to DW faster than large animals. 4. The toxic effect of DW can be suppressed by addition of 0.5 mM NaCl, 0.25 mM MgSO4, or small amounts of aquarium water. 5. KCl is about 10 times more toxic to zebra mussels when applied in DW than when applied in aquarium water. 6. The toxic effects of 37 mg KCl/l DW are not prevented by the addition of 0.5 mM NaCl or 0.25 mM MgSO4. 7. Stimulation of potassium transport mechanisms by DW may account for the increased toxicity of KCl in DW. Toxic effects of DW and increased toxicity of potassium in DW may have applications in controlling zebra mussel infestations.