Accumulation of cadmium by green algae Chlorella vulgaris in the presence of marine humic substances

The influence of humic substances (HS) on accumulation of cadmium by green algae Chlorella vulgaris was tested in laboratory conditions. Chlorophyll a, number of cells, biomass and content of cadmium in the biomass were utilized as measures of the influence. Enrichment factors (EFs) of cadmium in algae grown in the medium containing 0.1-500 mu g Cd/dm(3) were in the range from 1.1.10(3) to 1.5.10(4). In the presence of HS (5 mg/dm(3)) isolated from the Baltic Sea water, EFs decreased from 1.1.10(4) to 2.5.10(3) and from 1.5.10(4) to 6.2.10(3) when cadmium was accumulated from growth media containing 100 mu g Cd/dm(3) and 500 mu g Cd/dm(3), respectively. Taking into account the mechanism of cadmium transport through cell membranes and limited complexing capacity of the utilized humic substances, it is concluded that sorption of humic substances to cell surface, rather than decreased concentration of bioavailable forms of cadmium due to complexing with humic substances, is responsible for the phenomenon. (C) 1998 Elsevier Science Ltd.