Exposure to silver via food reduces egg production and viability in herbivorous copepods and cladocerans

Most toxicity tests expose organisms to metals via the dissolved phase only. Marine copepods Acartia tonsa and Acartia hudsonica, and the freshwater cladoceran Simocephalus sp., were exposed to silver (Ag) via the dissolved phase and through phytoplankton food. Dissolved phase exposure caused no discernible acute or sublethal effects in either organism. When zooplankton were exposed to Ag via their phytoplankton food, egg production decreased by up to 75%. This toxic effect occurred when the phytoplankton are exposed to concentrations of 500 pM Ag for cladocerans and 1 nM Ag for copepods. These concentrations are realistic for polluted environments and are three orders of magnitude lower than concentrations at which lethal effects are seen in toxicity tests with dissolved Ag. We believe that Ag toxicity occurs via disruption of vitellogenin (Vtg) transport into the egg. Total protein content of the egg decreases by up to 50% as the parent is exposed to increasing concentrations of Ag, and Vtg is the dominant egg protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of yolk proteins is being conducted to more specifically quantify differences in the eggs proteins produced by control and exposed parents.