The effects of pH, temperature, concentrations of Cd2+ and P43-, and density of algal suspension on the uptake of cadmium by C.pyrenoidosa were studied. Uptake occurred in at least two phases: fast (8 min) and slow (24 h). The slow uptake was dependent on pH (greater at pH 8.0 than 6.5) and temperature (faster at 25 than 4�C) whereas the fast uptake was not. Both phases of uptake were affected by the density of the algal suspension. Dependence on the concentration of Cd2+, at pH 8.0, was limited by the concentration of PO43- and also possibly by the concentration of CO3-2. Results were generally consistent with the model of initial ion-exchange uptake onto the cell wall and much slower transport across the cell membrane.

The effects of the cations calcium, iron, manganese and zinc on the uptake of cadmium by the alga C. pyrenoidosa and on the toxicity of cadmium were studied. Calcium at a level of 16 mg 1-1 reduced the short- term uptake and, in dilute cultures, the long-term uptake as well and caused a modest reduction in cadmium toxicity. Iron at a level of 1 mg I-1 greatly reduced cadmium toxicity and reduced both phases of uptake in dilute cultures. Manganese at a concentration of 0.5 mg I-1 had no consistent effect on uptake and tended to enhance cadmium toxicity. Zinc at a concentration of 3 mg I-1 reduced short-term uptake, had no consistent effect on long-term uptake, and exerted a toxic effect that was additive to that of cadmium. Factors such as coprecipitation and the physiological state of the culture were found to have an important bearing on the nature of the interaction of nutrient cations with cadmium.

No abstract

The development of an experimental system which can be used for demonstrating population studies in Chlorella vulgaris, and which is appropriate for use in secondary schools, is described. A culture medium was prepared on the basis of established inorganic nutrient requirements, and several cultures were set up to test the effects of variations in nutrient compo sition, temperature, pH, light and aeration. A satis factory system was eventually found which produced an ideal (sigmoidal) population-growth curve within three weeks. A similar pattern of results, though with different growth rates and maximum population levels, was obtained both for controlled and ambient con ditions of light and temperature, and for aerated tube and non-aerated flask cultures. Non-aerated tube cultures were relatively ineffective. Two methods were used, the counting of cells and the measurement of optical density, for estimating population density, and comparative results were obtained for serial dilutions of a standard culture.