The aim of this work was to evaluate the ability of plants to remove bioavailable amount of mercury from contaminated soil. Three plant species were selected: Brassica juncea, Poa annua and Helianthus annuus. The trials were carried out in a greenhouse using pots prepared with mercury contaminated soil (mesocosms). The bioavailable contaminant stripping BCS, that has recently received renewed interest, can be safely applied if the soil ability to replenish the bioavailable pool in the long term is known. According to a precautionary principle we have modified the BCS remediation approach by adding a new step (enhanced bioavailable contaminant stripping EBCS), in which mercury bioavailability was increased with the use of a strong mobilizing agent, ammonium thiosulphate (NH4)2S2O3. The scheme of EBCS treatability test, followed also in this experiment can be summarized in the following steps: 1 - Determination of the original potentially bioavailable fraction directly in the soil solution or by mild chemical methods that extract metals actually in the soil solution. In this work: H2O and NH4Cl; 2 - Determination of all possible release of the metal from soil surfaces over time. This step is performed by extraction with a specific mobilizing agent. In this work: (NH4)2S2O3. The action of the mobilizing agent is much stronger than any natural process, thus the released amount can be considered the maximum available to plants and may be also used to define the clean up target 3 - Pot experiments. Plants are evaluated on the basis of their ability to remove the original and the new available fraction brought in solution by the mobilizing agent. In this step the most efficient species can be selected. 4 - Determination of the residual potentially bioavailable fraction in soil by both chemical extraction and further growing cycles. When metal concentrations in plant is negligible and no available fraction can be further extracted from soil by (NH4)2S2O3, the residual concentration of the metal can be considered safe, or introduced in a proper risk assessment procedure. In this way the amount of mercury releasable over time was considered. In our experiments after one growing cycle nearly all bioavailable mercury was removed while the metal remained in the soil can be considered inert since it was neither extractable by (NH4)2S2O3, nor uptaken by plants from a second growing cycle. If we move from current definition of remedial targets based on total metal concentrations, EBCS appears promising, since it removes the most dangerous metal forms while substantially shortening the cleanup time, with an elevated security. After EBCS the residue metal in soil will remain unavailable over time, since it was not released in mobile forms even with the use of strong mobilizing agents.
Enhanced bioavailable contaminant stripping approach to clean.up mercury contaminated soil
Francesca Pedron;Meri Barbafieri;Eliana Lanfranca Tassi;Irene Rosellini;Gianniantonio Petruzzelli
2011
Abstract
The aim of this work was to evaluate the ability of plants to remove bioavailable amount of mercury from contaminated soil. Three plant species were selected: Brassica juncea, Poa annua and Helianthus annuus. The trials were carried out in a greenhouse using pots prepared with mercury contaminated soil (mesocosms). The bioavailable contaminant stripping BCS, that has recently received renewed interest, can be safely applied if the soil ability to replenish the bioavailable pool in the long term is known. According to a precautionary principle we have modified the BCS remediation approach by adding a new step (enhanced bioavailable contaminant stripping EBCS), in which mercury bioavailability was increased with the use of a strong mobilizing agent, ammonium thiosulphate (NH4)2S2O3. The scheme of EBCS treatability test, followed also in this experiment can be summarized in the following steps: 1 - Determination of the original potentially bioavailable fraction directly in the soil solution or by mild chemical methods that extract metals actually in the soil solution. In this work: H2O and NH4Cl; 2 - Determination of all possible release of the metal from soil surfaces over time. This step is performed by extraction with a specific mobilizing agent. In this work: (NH4)2S2O3. The action of the mobilizing agent is much stronger than any natural process, thus the released amount can be considered the maximum available to plants and may be also used to define the clean up target 3 - Pot experiments. Plants are evaluated on the basis of their ability to remove the original and the new available fraction brought in solution by the mobilizing agent. In this step the most efficient species can be selected. 4 - Determination of the residual potentially bioavailable fraction in soil by both chemical extraction and further growing cycles. When metal concentrations in plant is negligible and no available fraction can be further extracted from soil by (NH4)2S2O3, the residual concentration of the metal can be considered safe, or introduced in a proper risk assessment procedure. In this way the amount of mercury releasable over time was considered. In our experiments after one growing cycle nearly all bioavailable mercury was removed while the metal remained in the soil can be considered inert since it was neither extractable by (NH4)2S2O3, nor uptaken by plants from a second growing cycle. If we move from current definition of remedial targets based on total metal concentrations, EBCS appears promising, since it removes the most dangerous metal forms while substantially shortening the cleanup time, with an elevated security. After EBCS the residue metal in soil will remain unavailable over time, since it was not released in mobile forms even with the use of strong mobilizing agents.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
