Absorption characteristics of vetiver grass to the heavy metals in the soil of a heavy metal compound-polluted mining area

Studying the adsorption effect of plants on heavy metals in composite heavy metal pollution soil is highly important in the prevention and control of heavy metal pollution. In this study, four densities of vetiver grass were grown in a composite heavy metal mining area to investigate the vetiver grass growth and its effect on soil heavy mental concentrations (Hg, As, Sb, Pb). The results showed that the vetiver grass root length, root surface area, and shoot and root biomass increased significantly with the planting density and harvest time; the contents of heavy metals in the shoots were significantly lower than those in the roots. With increases in planting density and harvest time, the soil concentrations of As, Pb, and Sb significantly decreased, especially for As, whereas the soil Hg was almost unchanged. Vetiver grass enriched Hg, As, Pb and Sb, and its enrichment potential ranged from Sb > Hg > Pb > As. Following 180 days of planting, the accumulations for As, Sb, Hg, and Pb per of vetiver grass were 7.24, 1.04, 9.24, and 13.9 mg, respectively. The accumulations of heavy metals significantly increased by 44% (As), 42% (Sb), 25% (Hg), and 44% (Pb) at 360 days after planting. Pearson’s correlation analysis showed that the accumulations of As, Sb, and Hg of vetiver grass were significantly correlated to the biomass, root length and root surface area. Vetiver grass enriched the four heavy metals in composite mining areas and the roots accumulated more heavy metals than the shoots. In conclusion, vetiver grass can accumulate four heavy metals (highest rate for Pb) in composite polluted mining areas and significantly reduce the heavy metals remaining in the soil. The accumulations of the heavy metals were positively correlated with the planting density and harvest time. The accumulations of heavy metals were also correlated to the root length, root area, and biomass.