The potential of Lepidium sativum L. for phytoextraction of Hg-contaminated soil assisted by thiosulphate

Abstract

Purpose: The possibility of using higher plants to extract mercury from contaminated sites is dependent on both the concentration of Hg and its bioavailability. To increase the solubility of Hg in soil, some chemical compounds can be used. The aim of this study was to evaluate the effectiveness of Hg soil cleaning with the use of Lepidium sativum L. and sodium thiosulphate, as well as the leach ability of Hg from soil after phytoextraction. Materials and methods: The experiment was conducted on soil artificially polluted by Hg, wherein sodium thiosulphate was tested as a phytoextraction promoter. The L. sativum L. plants were used for phytoextraction. The leaching of Hg was assessed by determination of Hg concentration in water extracts. All determinations of Hg in soil, plant and water extracts were analysed by CV-AAS method after acid mineralization. Results and discussion: The result of the study showed that L. sativum L. accumulated Hg from contaminated soil mostly in belowground tissues. Even less than 8 % of Hg was translocated to the shoots of L. sativum L. Application of thiosulphate increased the total Hg accumulation over 238–272 %, depending on both the Hg and thiosulphate concentrations in soil. After thiosulphate treatment, translocation of Hg to shoots of L. sativum L. increased even 10 times relative to unassisted process. Thiosulphate did not negatively affect plant biomass; however, the increased leaching of Hg after thiosulphate treatment was observed. Conclusions: Lepidium sativum L. showed the potential of a non-hyperaccumulating plant that can be used during phytoextraction of Hg-contaminated soils in controlled conditions. Thiosulphate promoted the phytoextraction process by increasing the total Hg accumulation by whole plant and translocation of Hg to shoots of L. sativum L. Thiosulphate-mobilized Hg in soil, which increased the Hg leaching. This constitutes the limitation of applying the technique in the field due to risk of Hg transferring to deeper layers of soil or water. Applying the technique in the field should be preceded by further investigations.