Phytoremediation of metals using vetiver (Chrysopogon zizanioides (L.) Roberty) grown under different levels of red mud in sludge amended soil

Globally, 120 million tonnes of red mud is generated whose disposal and storage occupy large areas of potentially important arable lands. Red mud dumps are physically, nutritionally and biologically poor in nature. Vetiver (Chrysopogon zizanioides (L.) Roberty), a medicinally important perennial plant, known to control soil erosion, tolerates a wide range of pH and elevated levels of toxic metals. This information prompted to make use of red mud with sewage sludge, a nutrient rich bio-waste for growing vetiver. An experimental study was conducted using red mud at four rates (0, 5, 10 and 15% w/w) in soil amended with sewage sludge (soil: sludge: 2:1 w/w) to evaluate the effects on physico-chemical properties, plant growth performance, biomass and metal contents in vetiver under control (without sewage sludge and red mud) and different soil treatments. Application of red mud with sludge enhanced the levels of organic matter and nutrient status of the soil which offered suitable substrata to support plant growth. Heavy metal contents (Fe, Mn, Mg, Zn, Cu, Ni, Pb, Cd and Cr) increased with increase in red mud levels, however, their phytoavailable contents decreased. Addition of red mud resulted in significant improvement in root-shoot lengths, number of tillers culm− 1, root-shoot ratio and biomass compared to the control. However, maximum improvement occurred in root (125.27%), shoot (79.91%) and total plant biomass (88.07%) under 10% red mud treatment compared to control. Vetiver is found to be a potential metal tolerant plant as tolerance index was > 100%. Based on translocation and bioconcentration factors, the plant was found efficient in translocation of Mn and Cu from roots to shoot, whereas it acted as a potential phytostabilizer for Fe, Zn, Mg, Cd, Pb, Ni and Cr. The study suggests utilization of 10% red mud in sludge amended soil to sustain maximum plant growth coupled with enhanced phytoremediation potential of vetiver.