Research On Chelate-induced Phytoremediation Of Co Contaminated Soils

Radionuclide which comes from the exploitation and utilization of nuclear technology would cause the pollution of ecological environment when they enter into soil, They will affect the human health through the plants grown in the cotainmented soil and the food chains, and it has become a problem which was needed to be settled urgently. Phytoremediation, especially the phytoextraction is a kind of economic, easy and green technology in the remediation of the radionuclide and heavy metals cotainmented soil. Employing of chelating agent to increase phytoextraction efficiency is a kind of effective measure in the enhance contaminant uptake ability of plant species. In this study, a series of pot experiments were laid out and done by way of adding different concentrations(2.5 mmol/kg, 5.0 mmol/kg, 7.5 mmol/kg) of chelating agents, such as EDDS, NTA, the citric acid and oxalic acid to the imitated environment of the different concentrations(20 mg/kg, 40 mg/kg, 60 mg/kg) cobalt contaminated soil to find their effects on the growth, the uptake, transfer and accumulation of Co by the Arachis hypogaea L, AstragaLus sinicus L, LobuLaria maritima, as well as the capability of the chelating agent on the activating cobalt in the soil, which would afford academic and technological approach for improving phytoextraction efficiency. The main results were shown as follows:(1)In slightly(20 mg/kg) cobalt polluted soil, the effect of low concentrations of chelating treatments on the growth of three species were not significant, but high concentrations of chelating agents significantly inhibited the growth of LobuLaria maritima, and biomass of AstragaLus sinicus L was minimal in all chelating treatments. Under the treatment of 5.0 mmol/kg EDDS, cobalt concentration of aboveground parts of three species were reached its peak, while comparing with themselves aboveground parts bioaccumulation for cobalt: LobuLaria maritima>Arachis hypogaea L> AstragaLus sinicus L. At the same time, the translocation factor(TF) and transfer quantity factor(TQF) of LobuLaria maritima was significantly higher than that of Arachis hypogaea L. Therefore, LobuLaria maritima and 5.0 mmol/kg EDDS could be used as the most appropriate combination scheme for remediating slightly cobalt pollution soil.(2)In moderately(40 mg/kg) cobalt polluted soil, compared with total dry weight of three species under four different chelating agent treatments: Arachis hypogaea L> LobuLaria maritima>AstragaLus sinicus L. It was conducted to promote the cobalt absorption, translocation and accumulation capabilities of plant when treated with EDDS in moderately cobalt polluted soil. The bioaccumulation factor(BCF) of LobuLaria maritima was the highest among three species, and the bioaccumulation quantity(BCQ) and bioaccumulation quantity factor(BQF) of aboveground parts of LobuLaria maritime were the biggest. When treated with 5.0 mmol/kg EDDS, the capacity of accumulating cobalt by LobuLaria maritima was the highest, and the boaccumulation factor of cobalt in aboveground parts and roots were 1.83 and 1.62, respectively; while the total bioaccumulation factor and translocation factor reached 1.82 and 1.13 were higher than 1, meet the requirement of enrichment plants. Therefore, in moderately cobalt contamination in soil, LobuLaria maritima was a most suitable remediate plant, and 5.0 mmol/kg EDDS was most appropriate chelating agent type and concentration.(3)In heavily(60 mg/kg) cobalt polluted soil, the biomass of three species decreased with increasing chelating agent concentration, and the comparison of per plant biomass: Arachis hypogaea L>AstragaLus sinicus L>LobuLaria maritima. When treated with 2.5 mmol/kg EDDS, the biomass of Arachis hypogaea L aboveground parts and total bioaccumulation were the highest among three species. The absorptive and transferred capacity of Arachis hypogaea L for Co after using EDDS were obviously higher than the control. Besides, the translocation factor of Arachis hypogaea L could reach maximum value 0.916, which implied that the heavy metal contaminated soils enjoy the capability for self-remediating mechanism. Therefore, Arachis hypogaea L and 2.5 mmol/kg EDDS could be used as the most appropriate combination scheme for remediating heavily cobalt pollution soil.(4)The effect of chelating agent on plant physiological and biochemical characteristics in different levels of cobalt polluted soil showed that applying chelating agents could cause alteration or destruction of plant cell ultrastructure under the stress of cobalt, cell membranes and chloroplasts could be chelated heavy metals or heavy metal action site, increased levels of relative electric conductivity and MDA content of plant leaves, and decreased chlorophyll a, b content; The combined effects of Co pollution soil and chelating agent had toxic effects on the root of plants, and decreased root activity. Four types of chelating agent treatment led SOD, POD and CAT activity changed vary greatly in the leaves, the low concentration of cobalt and chelating treatment stimulated enzyme activity increased and under high concentration chelating treatment, overall activity of three enzymes were inhibited.(5) Adding Chelating agent, to some extent, increased the available cobalt content in soil solution, thereby promoting plant uptake in different levels of cobalt polluted soil. However, the form of high concentrations of chelating agent with metals would render difficult for plant to uptake macromolecules, indirectly to weaken its chelating effect, thereby reducing the bioavailability of cobalt in soil. Compared to the other three chelating agents, EDDS could promote the available cobalt increasing significantly, especially for the effect on absorbing Co among three species.