Abstract
Paspalum distichum L. was tested to evaluate their phytoremediation capacity for Hg contaminated soil through analyzing the dissipation of Hg in soil through a greenhouse study by using self-made rhizos box. Original soil samples were collected at Hg mining site with serious Hg contamination and a control site, respectively. Planting of P. distichum. L last for 60 days. Soil and plant samples were collected from four periods (0 d, 20 d, 40 d, and 60 d) and soil samples were collected from five different rhizosphere distance in horizontal direction (0-2 cm, 2-4cm, 4-6cm, 6-8cm, 8-10cm). The results showed that the presence of P. distichum. L significantly accelerated the Hg dissipation in soil compared with control. Hg concentration in the rhizospheric soil was affected by the plant growth period and the distance to the plant roots. The closer of soil to the root of P. distichum. L, the lower mercury concentration in soil. During the 60-day growing period, the concentrations of total Hg (THg) and methylmercury (MeHg) reduced by 45% and 64%, respectively, in the rhizosphere (0-2cm) of Hg contaminated soil. However, MeHg concentration was increased near the roots (0-4 cm) during the initial growing period (0-20 d), which may be attributed to the influence of root exudates. Root is the major part for Hg accumulation in P. distichum. L. The low ratio between Hg concentrations in underground and aboveground tissues indicated that it seemed difficult for Hg translocation from root to shoot. The highest THg (9.71 ± 3.09 μg·g-1) and MeHg (26.97 ± 0.98 ng·g-1) value in root of P. distichum. L were observed at the 20th day when P. distichum. L grown in Hg contaminated soil. The results of chemical fractions analyses showed that elemental Hg and residual Hg were the two major speciations followed by organic bound Hg in the Hg contaminated soil, which indicated the high bioavailability and ecological potential risk of Hg in Hg contaminated soil.
Highlights
The high toxicity of mercury (Hg) is illustrated by its long residence times in the atmosphere, rapid bioaccumulative natures and wide distribution on the earth (Fitzgerald et al, 1998)
Root is the major part for Hg accumulation in P. distichum
Peak values of total Hg (THg) and MeHg were observed on the 20th day for GXS and decreased gradually, which indicated that accumulation of Hg by P. distichum
Summary
The high toxicity of mercury (Hg) is illustrated by its long residence times in the atmosphere, rapid bioaccumulative natures and wide distribution on the earth (Fitzgerald et al, 1998). The environmental problem of Hg pollution in soil is pretty serious to the safety of the local agricultural products. Anthropogenic Hg pollution has been brought about by the chloralkali process, cement production, mining and smelting, artisanal small-scale gold mining, coal burning, and oil refining, which together emit huge quantities of Hg to the environment (O'Connor et al, 2019). It is estimated 250–1000 Gg amount of Hg mass accumulated in soils (Obrist et al, 2018). Plants can reduce the concentrations or toxic effects of contaminants on account of their various natural features through accumulating heavy mental by their tissues to inactivate them (Gomes et al, 2016).The uptake of Hg by plants depends upon the plant species, Hg bioavailability in soil and soil properties
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