Effect of temperature on removal of iron cyanides from solution by maize plants

Abstract

Cyanide is commonly found in soils and groundwater complexed with iron as ferro- and ferri-cyanide. It is evident that plants are capable of tolerating, transporting, and assimilating iron cyanides. The objectives of this study were to investigate the influence of temperatures on the removal and bioaccumulation of two chemical forms of iron cyanides by maize seedlings. Maize (Zea mays L. var. ZN 304) seedlings were grown hydroponically and treated with ferro- or ferri-cyanide in solution for 5 days. Six different temperatures were tested ranging from 12 to 27 degrees C. Total cyanide in solution phase and plant tissues was analyzed spectrophotometrically. The temperature coefficient (Q (10)) was also determined for maize exposed to both iron cyanides. The dissociation of both iron cyanides to free cyanide in solution was below the detection limit. Maize seedlings showed a significantly higher removal potential for ferro-cyanide than ferri-cyanide at all treatment temperatures. Analysis of mass balance revealed that the majority of these iron cyanides taken up from the hydroponic solutions was assimilated by maize, and roots were the major sink for cyanide accumulation. The Q (10) values were determined for ferro- and ferri-cyanide to be 2.31 and 2.75, respectively. Due to the significant difference in the removal rate between the two species of iron cyanides by plant, the conversion of ferri- to ferro-cyanide in aqueous solution prior to uptake is unlikely. Compared to the treatments amended with ferro-cyanide, more cyanide was recovered in plant materials of maize when exposed to ferri-cyanide, implying that ferri-cyanide is less sensitive to degradation than ferro-cyanide. Although the velocity of botanical assimilation of ferro-cyanide was faster than that of ferri-cyanide at any of the treatment temperatures, the removal of ferri-cyanide by maize was more sensitive to changes in temperature than that of ferro-cyanide. Removal of both iron cyanides by maize seedlings was observed to be positive in response to temperatures. Changes in temperatures have a substantial influence on not only the uptake and assimilation of ferro- and ferri-cyanide by maize but also cyanide accumulation in plant tissues. As one of the crucial abiotic factors involved in phytoremediation, temperature shows a positive influence on the removal of iron cyanides by plants. Further investigation on the fate of ferro- and ferri-cyanide in plant tissues would have helped distinguish the differences in the botanical assimilation pathways between the two iron cyanides. The ability of maize to remove iron cyanides has important implications on the vegetation management of environmental contamination.