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 g reen algae Chlorella vulgaris was tested in laboratory conditions. Chl orophyll a, number of cells, biomass and content of cadmium in the bio mass were utilized as measures of the influence. Enrichment factors (E Fs) 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 f rom 1.1.10(4) to 2.5.10(3) and from 1.5.10(4) to 6.2.10(3) when cadmiu m was accumulated from growth media containing 100 mu g Cd/dm(3) and 5 00 mu g Cd/dm(3), respectively. Taking into account the mechanism of c admium transport through cell membranes and limited complexing capacit y of the utilized humic substances, it is concluded that sorption of h umic substances to cell surface, rather than decreased concentration o f bioavailable forms of cadmium due to complexing with humic substance s, is responsible for the phenomenon. (C) 1998 Elsevier Science Ltd.