Cd tolerance and accumulation in the aquatic macrophyte, chara Australis: Potential use for charophytes in phytoremediation

We investigated the potential use of the alga Chara australis (R. Br.) forphytore mediation of Cd-contaminated sediments in aquatic systems. Chara tolerated up to 20 mg added Cd (kg soil)^-1 in laboratory culture. Chlorophyll a and b levels were not affected even at Cd concentrations that suppressed growth. Levels of glutathione were suppressed at 2-35 mg added Cd (kg soil)^-1 to 200-350 nmol GSH (g DW)^-1, while control levels were 660 nmol GSH (g DW)^-1). Histochemical studies showed Cd occurred throughout cell walls and cytoplasm in plants grown in 5-20 mg Cd (kg soil)^-1. Quantification using ICP-MS showed the maximum concentration in shoots was 72 mg Cd (kg DW)^-1 at 35 mg added Cd (kg soil) ^-1, while the maximum in rhizoids was 116 mg Cd (kg DW)^-1 at 25 mg added Cd (kg soil)^-1. The bioconcentration factor (BCF, concentration in plant/concentration in soil) exceeded 1.0, the critical value for hyperaccumulators, for shoots exposed to 35 mg Cd (kg soil)^-1 and rhizoids exposed to ≥25 mg Cd (kg soil)^-1. Translocation factors (TF, shoot concentration/rhizoid concentration) did not exceed 1.0 for any treatment. While Chara cannot be considered a hyperaccumulator, it shows promise for use in phytoremediation efforts.