| The potential for phytoremediation of cyanide-contaminated groundwater with willow trees was investigated in this research. The objectives were to investigate the uptake and metabolism of dissolved free cyanide and iron cyanide by willow and to determine the major plant processes governing iron cyanide fate in the willow plant. Hydroponic uptake experiments were performed to demonstrate the uptake and fate of 15N-labeled CN− and Fe(CN)64− solutions containing 2 ppm cyanide. A novel extraction method was developed and used to analyze tissue cyanide content to separate cyanide uptake from metabolism. Willow was observed to take up and metabolize both free cyanide and ferrocyanide, with faster rates for free cyanide. Metabolism of the cyanide species by willow was demonstrated by the difference between measured cyanide species and cyanogenic- 15N concentrations in extracted plant tissue.; A process model was constructed to represent the physiological processes affecting the cyanide mass transfer and transformation processes in the willow plant. The model was fitted to the experimental hydroponic data to obtain the optimal parameter values and to examine the importance of the various processes. Consistent with the experimental observations, the uptake and metabolic rate constants were higher for free cyanide than for ferrocyanide. Also, free cyanide volatilization and root cell wall adsorption did not affect cyanide fate. Active uptake was applicable for free cyanide, but did not apply to ferrocyanide uptake. To achieve the observed solution cyanide concentration profiles, the plant must actively take up free cyanide while ferrocyanide must be excluded from entering the root. Predicted assimilate concentrations for the root and stem tissue were significantly underestimated. Predicted and actual tissue cyanide and leaf assimilate concentrations were of identical magnitude. In order to match the root, stem, and leaf assimilate concentrations in the plant, a means of removing assimilate from leaf tissue is required. This suggests that phloem redistribution may be important for determining uptake of cyanide from solution and fate within the willow plant.; Calculations pertaining to the applicability of ferrocyanide phytoremediation to the field-scale were conducted using the uptake rate data from the hydroponic experiments and operating parameters for an existing wetland treatment system. A conservative estimate ignoring photodissociation, surface volatilization, and biodegradation showed that a typical wetland system could remove an influent concentration of up to 0.2 ppm as CN of Fe(CN)64− via plant uptake. |
