PHYTOREMEDIATION OF FERRO- AND POTASSIUM CYANIDE IN GROUNDWATER WITH WILLOWS

A hydroponic uptake study with willow (Salix eriocephala) was conducted to demonstrate the efficacy of cyanide phytoremediation. The uptake of 15N-labeled free cyanide and ferrocyanide from solution was examined under conditions that maintained cyanide availability in solution. Cyanide speciation and concentration in the hydroponic solution were monitored with time to demonstrate the chemical stability of cyanide compounds. Cyanide uptake was monitored through analysis of the plant root, stem, and leaf tissue samples for 15N and cyanide content. Sorption to the root cell wall was also investigated to distinguish between biological uptake and physical association with the cell wall.The hydroponic solution and tissue results indicate uptake and assimilation of free cyanide and ferrocyanide by willow plants. Over the 20-day experiment, free cyanide and ferrocyanide levels in the hydroponic solutions decreased from initial values of > 9.0 mg to 0.56 and 7.41 mg as CN. Plant tissue results showed a significant increase in 15N relative to controls for both free cyanide and ferrocyanide-exposed plants. Root, stem, and leaf 15N concentrations increased by 488, 115, and 102 mg/kg-FW as CN for KCN-exposed tissue and 114, 6.33, and 21.9 mg/kg-FW as CN for ferrocyanide-exposed tissue relative to natural abundance levels. Analysis of caustic extracts from plant tissues showed a large discrepancy between the cyanide detected by analysis and predicted based upon the 15N content. Only ferrocyanide-treated roots showed cyanide levels comparable to the amount predicted by the 15N data with 128 mg/kg-FW as CN. The discrepancy, larger for free cyanide compared with ferrocyanide, suggests that cyanide is being taken into the plant and assimilated.