Ecological Systems and Devices Annotation << Back DEPENDENCE OF THE TOXICITY OF K2CR2O7 ON THE TIME OF THE EXPERIMENT IN PHYTOTESTING ON CHLORELLA VULGARIS A.M. Lazareva, M.A. Mikhailina, K.E. Dobrovolskaya, V.S. Petrunina, I.A. Prokhorov, A.M. Mozgovaya The dependence of potassium dichromate K2Cr2O7 toxicity on the time of day during its addition to the algologically pure culture of Chlorella vulgaris was studied. The effect of the toxicant was evaluated at concentrations of 0,1, 1, and 5 mg/L by indices of the cell number and photosynthetic efficiency in the culture. Two experiments were carried out – in a luminostat and in a cultivator, in which we studied the effect of the time of day at the moment of adding the toxicant to the Chlorella vulgaris culture – in the morning, at 9.00 (the beginning of the light period in the luminostat) and in the evening, at 21.00 (the end of the light period in the luminostat). The sensitivity of the culture to K2Cr2O7 was established. The time of day at the moment of the toxicant addition found to have an effect on the bioassay results. A stimulation was noted when toxicant with 0,1 mg/L concentration was added in the evening, while with the morning adding at the same concentration the cell abundance was at the control level. The calculated ЕC50 values for two experiments confirm that the toxicity of potassium dichromate increases when the experiment is carried out in the morning compared to those for the evening experiment. Keywords: potassium dichromate, Chlorella vulgaris, toxicity, time of the toxicant addition, bioassay, circadian rhythms. DOI: 10.25791/esip.5.2023.1367 Pp. 03-10.