Phytoremediation of Cu and Zn by vetiver grass in mine soils amended with humic acids

Abstract

Phytoremediation of contaminated mine soils requires the use of fast-growing, deep-rooted, high-biomass, and metal-tolerant plants with the application of soil amendments that promote metal uptake by plants. A pot experiment was performed to evaluate the combined use of vetiver grass (Chrysopogon zizanioides) and humic acid for phytoremediation of Cu and Zn in mine soils. Vetiver plants were grown in soil samples collected from two mine sites of Spain mixed with a commercial humic acid derived from leonardite at doses of 0, 2, 10, and 20 g kg(-1). Plant metal concentrations and biomass were measured and metal bioavailability in soils was determined by a low molecular weight organic acid extraction. Results showed that humic acid addition decreased organic acid-extractable metals in soil. Although this extraction method is used to estimate bioavailability of metals, it was not a good estimator under these conditions due to competition with the strong chelators in the added humic acid. High doses of humic acid also promoted root growth and increased Cu concentrations in plants due to formation of soluble metal-organic complexes, which enhanced removal of this metal from soil and its accumulation in roots. Although humic acid was not able to improve Zn uptake, it managed to reduce translocation of Zn and Cu to aerial parts of plants. Vetiver resulted unsuitable for phytoextraction, but our study showed that the combined use of this species with humic acid at 10-20 g kg(-1) could be an effective strategy for phytostabilization of mine soils.

Bioaccumulation and biochemical responses of Vetiveria zizanioides grown under Cadmium and Copper stresses

“…Noticeably the BCF for Cd was found to be higher compared to Cu exhibiting that the Cd accumulation potential V. zizanioides was higher than the Cu. Similar trend of metal accumulation and translocation was observed by several authors (Danh et al 2010;Banerjee et al 2016;Vargas et al 2016;Meyer et al 2017). …”

Effects of pH Conditions and Application Rates of Commercial Humic Substances on Cu and Zn Mobility in Anthropogenic Mine Soils

“…The results from the present study and from our previous pot experiment with plants [17] suggest that the addition of humic substances at high rates (about 2-10 g kg −1 ) could be a suitable tool to improve assisted-phytoextraction techniques in contaminated anthropogenic mine soils by the enhancement of metal uptake by plants due to a high metal mobility. However, the application of these rates under more alkaline conditions than natural soil pH could lead to an excessive Cu mobility, and therefore to an increasing risk of leaching to groundwater and its transfer to the trophic chain, as well as a greater toxicity for plants and soil microorganisms.…”

“…Our previous pot experiment using vetiver grass grown in contaminated soils with commercial humic substances [17] showed a greater uptake of Cu by plants with increasing rates of the humic product (10-20 g kg −1 ) in soils that had higher pH conditions. This greater Cu uptake was due to the mobilization of this metal by the formation of soluble metal-organic complexes.…”

“…In our previous work [17], we evaluated the use of a commercial humic product derived from American leonardite in combination with metal-tolerant plants (vetiver grass) for the phytoremediation of anthropogenic mine soils through pot experiments. In that study, we reported that humic substances exhibited different behaviors depending on the soil.…”

Study on the Application of Floating Beds of Macrophites (Vetiveria zizanioides and Phragmites australis) in Pilot Scale for the Removal of Heavy Metals from Água Forte Stream (Alentejo-Portugal)

“…They can be classified as submerged, floating and emerging macrophytes. In this study, the emerging macrophytes Vetiveria zizanioides and Phragmites australis were used, because both plants have high tolerance towards the elevated concentrations of heavy metals such as As, Cd, Cu, Cr, Pb, Hg, Ni, Se and Zn (Truong et al, 2010;Bonanno, 2011;Srivastava, Kalra, & Naraian, 2014;Vargas et al, 2016).…”