The effects of the heavy metal ions copper, cadmium, mercury and lead on motility and photo-orientation have been assayed in the photosynthetic flagellate Euglena pcilis.
The first three elements were tested in both shortterm and long-term experiments, but lead was only tested in short-term experiments.
Copper significantly impairs growth, measured as cell division, at concentrations of greater than 5 PM and motility at concentrations of greater than 100 PM. Cadmium affects growth at greater than 3 PM and motility at 10 PM, and mercury is effective at greater than 1 PM (growth) and greater than 0.1 PM (motility). Lead decreases motilitjr on shortterm exposure at greater than 30 PM, but the effect decreases with time in the heavy metal solution. Phototaxis and swimming velocity are affected by all four heavy metals. Copper is effective at concentrations of greater than 50 PM with phototaxis being impaired more strongly in older cultures and velocity being affected more significantly in younger cultures. The same is true for mercury and cadmium; in addition, these heavy metals affect negative phototaxis at far lower concentrations than positive phototaxis. The results indicate that the effects of the pollutants in aquatic habitats strongly depend on the age of the culture and the time and duration of exposure to these ions, which must be taken into consideration when this system is used as a bioindicator for heavy metal pollution in aquatic habitats.