Effect of cadmium toxicity on survival and phototactic behaviour of Daphnia magna.

Change in the phototactic behaviour of a positively Daphnia magna clone C1 34 was used as indicator of toxic stress. The phototactic behaviour was quantified using an experimental set-up which was described in a previous study. In flow-through experiments, animals exposed to 0.03 mg l(-1) Cd++ exhibited a significant effect of cadmium on the phototactic behaviour within a period of 1 h, either with starved or fed animals by approximately 2x10(5) Scenedesmus acutus cell.ml(-1). The results suggest also that cadmium can be adsorbed for 3- h exposure and became desorbed after 4.5 h period. Continuous flow-through protocol was described for measuring survival of strain of D. magna, using juveniles that have been exposed to 1 mg l(-1) Cd++ for: 0.25; 0.5; 1; 2; 4 and 6 h. In these experiments a significant reduction in survival was demonstrated and the effect was shown to be significant within the first 30 min of the test. It was also found that the inhibition rate I(n) of survival can be estimated by a logarithmic expression as a function of time: I(n) (%) = 26.348 Ln 54.352 x t.