Influence of diethyldithiocarbamate on cadmium and copper toxicity to freshwater macrophyte Spirodela polyrhiza

Toxic effects of two heavy metals, cadmium (Cd) and copper (Cu), and a fungicide, diethyldithiocarbamate, have been evaluated, alone and in association, on Spirodela polyrhiza duckweed cultivated in a synthetic mineral medium and in a distilled water medium. The composition of the culture medium influenced the toxicity of the three compounds and the effects of their associations were clearly shown in the distilled water medium. Copper has an antagonistic effect on Cd and reduced its absorption by duckweed. On the other hand, Cd in the culture medium increased Cu absorption. The most significant effect was observed with diethyldithiocarbamate simultaneously associated with Cu and Cd. The diethyldithiocarbamate association largely inhibited the absorption of Cd and Cu by duckweed and so appeared to have a complexant effect that reduced the toxicity of these two metals.