- Title
- Phytoremediation of heavy metal contaminated sites by mining in Thai Nguyen province Vietnam
- Creator
- Nguyen, Ngoc Son Hai
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Phytoremediation is a green remediation technology providing a cost-effective, aesthetic solution for remediation of contaminated soil. One of the phytoremediation strategies in the metal-contaminated soil is phytoextraction, which involves the uptake and accumulation of metals into harvestable biomass of plants (i.e. shoots). These can then be harvested and removed from the site. Another application of phytoremediation is phytostabilisation, where certain plant species are used to immobilise the metal in the contaminated soil. It is important to use native plants for phytoremediation because these plants are often better in terms of survival, growth and reproduction under local environmental conditions than plants introduced from other sites. This study evaluated the phytoremediation potential of two native plant species, Lau plant (EA) (Erianthus arundinaceus (Retz.) and Reed plant (PA), Phragmites australis (Cav.), for three contaminated mining sites in Vietnam, specifically the following: Ha Thuong lead-zinc mine, Trai Cau Iron mine, and Hich Village Lead-zinc mine in Thai Nguyen province. The ability of EA and PA to accumulate heavy metal(loid)s (HMs), including As, Cd, Cu, Pb, Zn) has been evaluated. Total metal(loid)s concentrations including As, Cd, Cu, Pb and Zn in the plants and corresponding soils were determined. Soil samples were subsequently characterised by XRD, SEM and EDS analysis. The concentrations of HMs were high in stem, leaves and roots, demonstrating the plants’ high metal bioaccumulation potential from the soils, which are also high in HM content. Total As, Cd, Cu, Pb and Zn concentration in soils varied from 4 to 2605, 0 to 124, 6 to 603, 45 to 5008 and 64 to 31789 mg/kg, respectively, while the corresponding concentrations in the plants ranged from 0.02 to 300, 0.1 to 33, 3 to 111, 1.19 to 982, 27 to 1346 mg/kg, respectively. There was a positive correlation between HM content in the soil and those in the plants. The accumulation factor for HMs in roots was higher than that in stems or leaves of the plants for all soils. Only EA had the ability to naturally survive, grow and generate high biomass in the presence of extremely high concentrations of multiple HMs in soils, especially As, Cd, Cu, Pb and Zn, the concentrations of which were as high as 2605 mg/kg, 124 mg/kg, 603 mg/kg, 5008 mg/kg, 31788 mg/kg, respectively. Lau plant (EA) accumulated HMs more efficiently than PA in the root, stem and leaves in all three mining sites. The phytoextraction capacity of PA and EA is relatively low. However, their high biomass yield led to a relatively large accumulation of HMs. Native EA species have high BCF (6.45) and low TF (0.74) in terms of Cd in the soils, thus indicating the EA has the potential for phytostabilisation of Cd contaminated sites. EA and PA growing on the sites have the potential for phytoremediation of the five metals, and consequently repair to some extent the metal-contaminated sites. They can help to stabilise soil and phytoremediate especially in extremely high concentrations of multiple HMs (As, Cd, Cu, Pb, Zn), and thereby reduce offsite pollution in the mining areas. Detailed mineral characterisation shows the presence of arsenopyrite (FeAsS) and franklinite (ZnFe³⁺₂O₄) in HT soils with these minerals contributing to high As, Zn and Fe content, especially in acid soil environment (pH <5). Dolomite CaMg(CO₃)₂ , calcite (CaCO₃) and calcium carbonate (CaCO₃) minerals were found in LH, contributing to an alkaline soil environment (pH 8.28) and high Pb, Zn. PA tolerates slightly acidic to strongly alkaline soil. In contrast, EA was tolerant of extremely acidic environment (pH 4.12 - 5.95) to strongly alkaline environment (pH (7.43 – 8.72) and high concentration of multiple HMs also. The effects of different chelates were investigated using different doses and methods of application to examine mobilisation of selected metals (loid)s (As, Cd, Cu, Pb and Zn) in soil and the potential for enhancing phytoaccumulation of in plants. Factors affecting plant metal uptake in mine sites, chelate mobilisation in soils and the applicability of enhanced phytoextraction were investigated. The application of EDTA, EDDS and NTA to three selected soils from the three sites significantly increased the concentrations of As, Cd, Cu, Pb and Zn in the shoots of rye grass (Lolium multiflorum). EDTA 0.5:1+0.5:1 was more effective at increasing the concentration of Pb in shoots than other chelates (NTA, EDDS) and controls. With the application of chelate treatments EDTA (0.5:1+0.5:1), the concentrations of Pb in the shoots of the ryegrass in LH reached 1,339 mg/kg DW which were 269.5-fold larger than that of the controls. Moreover, the concentrations of Zn in the shoots of ryegrass in LH significantly increased with the application of split dose (0.5:1+0.5:1). Additionally, Zn shoot concentration was significantly increased in chelate treatments (EDTA 1:1, NTA 1:1 and NTA 0.5:1+0.5:1) in HT; while EDTA 0.5:1+0.5:1 resulted in significant increased shoot Cd, Pb, Zn concentration at p<0.01 and NTA 0.5:1 +0.5:1 significantly increased shoot As, and EDDS 0.5:1 +0.5:1 significantly increased shoot Pb concentration in LH. Plant growth was significantly affected in soils treated with chelates, particularly sequential chelate treatment (EDTA 0.5:1+0.5:1; NTA 0.5:1+0.5:1; EDDS 0.5:1+0.5:1). The plants displayed symptoms of toxicity including yellow and necrotic leaves at the end of the experiment. The selected chelates (EDTA, EDDS and NTA) led to a significant decrease in plant biomass (yield) 28 days after transfer with a maximum decrease in EDTA treatment (0.5:1+0.5:1) soils. This decrease was 3.43-fold in HT, 3.00-fold in LH and 1.59–fold respectively, relative to the control. Fresh weight of shoot of the ryegrass (Lolium multiflorum) had a strong positive relationship with dry biomass, and negative correlation with Pb and Zn concentration in the shoot. There was strong positive correlation among As and Pb concentration with Zn concentration in the shoot. Combined with HMs concentration and DOC results in pore water this provided an explanation for why fresh weight was significantly reduced with application of chelates in sequential dose (EDTA 0.5:1+0.5:1 and NTA 0.5:1 +0.5:1). The different chelate treatments especially sequential addition are considered to have potential for enhancing phytoextraction of specific metals depending on soil properties of the contaminated soils. While a laboratory-based study demonstrates potential for phytoremediation of the metal contaminated mined soils, further research is needed in the field under controlled conditions. In particular, the extension of chelate-mobilised mining of metals by plants needs detailed anlaysis both in the laboratory and in the field. In conclusion, this research suggests more future work is required on phytoremediation of HMs, especially phytoextraction by assisted chelate moblisation at mining sites. Chelate-assisted mobilisation of HMs using the selected plants, namely native plant (EA and PA) and exotic plants using the single or split application is quite promising for HMs accumulation as well as phytoextraction of the HMs.
- Subject
- heavy metals; Erianthus arundinaceus (Retz.); Phragmites australis (Cav.); chelate-assisted; ryegrass (Lolium multiflorum); phytoremediation; contaminated sites
- Identifier
- http://hdl.handle.net/1959.13/1421278
- Identifier
- uon:37713
- Rights
- Copyright 2020 Ngoc Son Hai Nguyen
- Language
- eng
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