Phytoextraction of mercury-contaminated soils using legumes

J.N. Wünsche; N.J. Sommer

摘要

In Ghana, many soils are heavily contaminated with mercury (Hg) that is used in the amalgamation process of gold. This pollution has drastic effects not only on the environment but also on humans through direct exposure in areas close to illegal gold mining sites and consumption of contaminated food crops that are cultivated on those soils. Consequently, the objective of this study was to identify suitable plant species for phytoremediation of Hg-contaminated soils and to return the land to agricultural use for food production. Plants growing on Hg-contaminated sites need to possess some level of tolerance to Hg-toxicity in order to survive. It is postulated that Hg-tolerance of plants is due to a restricted Hg-uptake and/or translocation brought about for example by Hg-sequestration in certain cell compartments or by organic compounds. Consequently, native legumes, which grow near Hg-contaminated sites in Ghana, are presumed tolerant to Hg and improve the fertility of the degraded soils due to their ability to fix atmospheric nitrogen. The plant species that are currently evaluated for Hg-uptake efficiency in pot experiments under greenhouse conditions are Acacia mangium, Brassica juncea, Leucaena leucocephala, Mimosa pudica, Moringa oleifera and Senna siamea. Brassica juncea plant is a known metal-accumulating wild-type plant and serves as a positive control. Hg was provided at two concentrations (5, 10 mg kg~(-1)) as mercury chloride (HgCl_2) solution. To evaluate physiological reactions of the plant species to mercury exposure gas exchange (H_2O and CO_2) of all experimental plants was measured in order to determine assimilation. Plants which can accumulate high concentrations of mercury with a high tolerance level to Hg without visible or physiological phytotoxicity symptoms will be selected for further experiments in phytoremediation of Hg-contaminated soils in Ghana.

Phytoextraction of mercury-contaminated soils using legumes

摘要

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