Experiments with Prorocentrum micans Ehrenberg were run over a period of 380 h in North Sea water containing 0.5 mg C 1-' of dissolved organic carbon. Dissolved Cd concentrations ranged from 0.08 to 10 pg l-'; Zn concentration was 0.1 pg 1-'. Cell density started with 35 000 1-'. Growth in terms of cell numbers, primary productivity, bacterial activity, and uptake of Zn and Cdmeasured by the radlo isotopes 6 5~n and ' OgCd -were followed in short intervals during exponential and stationary growth phases. Enrichment factors of the metals were highest at the lowest Cd concentration. On a daily basis, Cd and Zn concentrations increased during the day and decreased at night. The rhythm was most obvious during exponential growth. This indicates the special role of actively metabolising cells for uptake of Zn and Cd. Accumulation was more rapid for Zn (maxima every 24 h) than for Cd (maxima every 26 h), so that the daily rhythm of the metals was shifted.
ABSTIZACT: Water samples from different areas were investigated after addition of varying concentrations of heavy metals (Zn, Cd, Cu). Accumulation of metal by phytoplankton was measured, employing the radio isotopes Cd-109, Zn-65 and Cu-64. Influence of metal to carbon fixation rate of phytoplankton and to glucose incorporation by bacteria was determined. Accumulation of metal, expressed as enrichment factor, was highest at the lowest ambient metal concentration. At higher concentrations a constant value was reached. This change in enrichment was related to plankton activity. Corresponding data of metal content per chlorophyll a unit for the point when accumulation changes are compared for different samples. It is discussed that these concentrations vary for different organisms.
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