The effects of heavy metals on the feeding rate of Euplotes mutabilis (Tuffrau, 1960)

The effects of the toxic metals cadmium, lead, copper, mercury and nickel on the feeding rate of well fed Euplotes mutabilis have been studied. Fluorescent latex beads in various sizes and concentrations have been tested as substitute food particles for the ciliates. After exposing standard cultures of the ciliates to a soluble compound of one of the metals at two selected concentrations close to the lethal limit for one hour, the beads were introduced to the cultures. At set time intervals over a period of ten minutes, representative cells were fixed, in order to determine the quantity of particles that had been ingested. Lead showed no significant effect on the feeding rate of the surviving ciliates, but copper, mercury and nickel depressed feeding rates significantly. In the case of cells exposed to 0.5 ppm of cadmium, the rate of uptake of particles was significantly higher than that of the control cells in the normal medium; however, it was observed in this case that the formation of food vacuoles was abnormal. The effects of some metal ions upon the feeding activity of Euplotes may affect the long-term survival of the ciliates in polluted environments.