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Phytoremediation of Cyanide Contaminated
Soils High concentrations of cyanide in soil can result from runoff adjacent to storage areas for road salt, electroplating waste, and residuals from manufactured gas plants. The most toxic species of cyanide are the so-called free cyanides (HCN and CN-), but these species are generally rare in contaminated soil and groundwater. Iron cyanides are often predominant in environmental samples and have low toxicity. Unfortunately, thermodynamics predict that free cyanides are the favorable species in solution, and degradation of iron cyanide compounds to the free cyanides can be accelerated by sunlight and specific microorganisms. The objective of this project is to investigate the potential for phytoremediation of cyanide contaminated soils, particularly using cyanogenic plants. Cyanogenic plants are those species that synthesize cyanogenic glucosides, compounds that readily decompose to cyanide when the plant tissue is injured. Because cyanide is a natural component of these plants, they have enhanced capacities for degrading cyanide. Another objective will be to determine whether cyanide degradation in these systems occurs in the rhizosphere (soil immediately surrounding the root). Cyanogenic plants and other species will be evaluated for their potential for phytoremediation of cyanide using contaminated field soils obtained from a former manufactured gas plant site. Two experiments will be conducted: 1) a greenhouse evaluation study in which at least six species, including both cyanogenic and non-cyanogenic species, will be evaluated for degradation of cyanide compared to an unvegetated control and 2) a fully contained plant chamber study to determine whether cyanide is degraded in the rhizosphere or within the plant. This 14C tracer study will allow for a complete mass balance of the cyanide parent compound (Prussian blue) as well as examine the fate of the contaminant in the soil/water/plant/air continuum. Overall, this project will advance our knowledge of phytoremediation and may lead to the development of an exciting new field approach. |