Transport and metabolism of free cyanide and iron cyanide complexes by willow

Abstract

Cyanide compounds are contaminants of growing importance that could be remediated biologically via phytoremediation, provided the plants possess suitable mechanisms for managing these pollutants without toxicity. The transport and metabolism of two cyanide compounds, potassium cyanide and potassium ferrocyanide, by willow ( Salix eriocephala L. var. Michaux) were compared using a hydroponic system that preserved cyanide speciation and solubility. The cyanide compounds were labelled with 15 N to quantify transport while a novel tissue extraction procedure was used to relate tissue 15 N to cyanide content and speciation. These analyses revealed that although little free cyanide was detected in the aerial tissues of plants exposed to either of these two cyanide compounds, significant enrichments in 15 N were observed, suggesting transport and subsequent metabolism of free cyanide as well as ferrocyanide. The results for ferrocyanide are of interest because this molecule is resistant to microbial degradation and if oxidized to ferricyanide is purportedly membrane impermeable. Nevertheless, these results and mass balance calculations for tissue 15 N and solution cyanide confirming 100% recovery for the added ferrocyanide are suggestive of ferrocyanide uptake and metabolism. This study provides new information describing the biological transport and metabolism of these two cyanide compounds in plants. Moreover, the data also suggest that phytoremediation of cyanide may be possible and ecologically safe due to the lack of cyanide bioaccumulation in aerial tissues.

Effect of Temperature on the Uptake and Metabolism of Cyanide by Weeping Willows

“…Loss from controls without plants was negligible, so most likely, all loss was due to metabolism by plant enzymes. This is consistent with earlier findings (Ebbs et al, 2003;Larsen et al, 2004Larsen et al, , 2005Yu et al, 2004). The calculated cyanide metabolism rates are shown in Table 1.…”

“…However, no cyanide above detection limit was trapped for willows exposed to 24 0 C over a 2-d test period using the test chamber with the gas trap (cyanide transpired at other treatment temperatures was not measured). The same result was also found in the study of Ebbs et al (2003). Trapp et al (2001) found small amounts (1.5%) of cyanide in air.…”

“…Ebbs et al (2003) used free and iron complexed cyanide labeled with 15 N. It was found that free cyanide was rapidly taken up by plants and subsequently metabolized. There was also evidence for an uptake of ferrocyanide, probably followed by metabolism inside plants.…”

“…The values of all v max were normally distributed with a mean of 13 mg CN/(kg·h). Bushey et al (2006aBushey et al ( , 2006b) developed a model for the calculation of uptake and metabolism of free and iron-complexed cyanide and fitted a parameter set to the experimental results of Ebbs et al (2003) and additional data. Larsen et al (2005) certain threshold (about 20 mg CN/L for willows grown in sand), the enzyme system of the plant is overloaded, and accumulation of cyanide followed by toxic effects occurs.…”

Effects of inhibitors on ferricyanide uptake and assimilation by plants

“…Although direct evidence of the plant-mediated uptake and assimilation of ferricyanide is still under investigation, several studies have been conducted to clarify the possible biological transport and fate involved (Ebbs et al 2003(Ebbs et al , 2008Larsen and Trapp 2006;Samiotakis and Ebbs 2004;Yu and Gu 2010). Unlike botanical uptake of small neutral chemical species, ferricyanide is unable to move through biological membranes by simple diffusion due to its physical-chemical properties (Ebbs et al 2003;Federico and Giartosio 1983).…”