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Phytoremediation
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
The bioavailability of heavy metals enhances the process of phytoremediation. Employing chemicals such as chelating agents or surfactants can increase the mobility of ions in the medium, therefore increasing the accumulating potential of non-hyperaccumulating plants. 1,2-cyclohexylenedinitrilo tetraacetic acid (CDTA), ethylene diamine tetra-acetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), ethylene diamine disuccinate (EDDS), and ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) are some of the most commonly-used chelating agents (Muthusaravanan et al. 2018). Chelating agents enhance the process of phytoremediation by increasing the concentration of heavy metals in soil, destroying the root barriers by high levels of resultant complexes, increasing the metal-EDTA complex movement towards the roots, and enhancing the metal translocation from root to shoot by increasing the complex mobility in comparison to free ions (Kumar Yadav et al. 2018). One serious concern associated with use of chelating agents is that they can lead to the leaching of metals into groundwater, therefore contaminating it (Muthusaravanan et al. 2018). Furthermore, some chelating agents and their complexes, such as that of EDTA (non-biodegradable), can cause harm to the plants and microorganisms present in the soil. EDDS is produced by microorganisms and can increase the bioavailability of Ni, Cu, and Zn to a greater extent when compared to EDTA. NTA is another chelating agent which is easy to biodegrade and has no phytotoxic effects (Kumar Yadav et al. 2018).
Remediation of a metal-contaminated soil by chemical washing and repeated phytoextraction: a field experiment
Published in International Journal of Phytoremediation, 2021
Xian’an Yu, Tong Zhou, Jie Zhao, Changxun Dong, Longhua Wu, Yongming Luo, Peter Christie
Soil washing with chemical agents can give rapid and efficient removal of metals in a relatively short time (Meng et al. 2017; Yoo et al. 2018). Chelating agents such as ethylenediaminetetra-acetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS) and their derivatives have been frequently proposed because of their ability to chelate metals (Koopmans et al. 2008). However, the residual chelate-metal complexes remaining in the soil after washing are often harmful to soil biota and crops (Wu et al. 2004). Recent studies have proposed some alternative chemical washing agents such as citric acid (Schwab et al. 2008) and FeCl3 (Makino et al. 2006; Yoo et al. 2016). The citric acid and FeCl3 not only have high extraction efficiency of metals but also show high biodegradability, readily availability, cost-effectiveness, and less detrimental effects on soils and crops. Compared with the FeCl3 alone, the combining utilization of FeCl3 with citric acid significantly increased the removal efficiencies of Cd, Cu, Zn, and Pb from a neutral soil (Gao et al. 2018). However, chemical washing agents usually lead to some degradation of soil quality such as low pH, poor texture, and nutrient loss and may then negatively influence plant growth (Jelusic and Lestan 2014; Fedje and Stromvall 2016). After washing, a portion of residual metals may be also destabilized and shift to exchangeable fractions in the remediated soil (Tsang and Hartley 2014).
Evaluation method for the measuring comprehensive suitability of chelating agents: a study of the temporal dynamics of heavy metal activation
Published in International Journal of Phytoremediation, 2019
Xiaotao Mai, Dinggui Luo, Lezhang Wei, Yu Liu, Xuexia Huang, Qihang Wu, Guangchao Yao, Guowei Liu, Lirong Liu
Chelating agents are classified into aminopolycarboxylic acids and low molecular weight organic acids (LMWOAs) (Song et al.2016). The main chelating agents include ethylenediaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), [S,S]-stereoisomer of ethylenediaminedisuccinic acid (EDDS), nitrilotriacetic acid (NTA), N,N-bis(carboxymethyl)glutamic acid (GLDA), and citric acid (CA) (Pinto et al.2014). EDTA with activating effects on many heavy metals such as cadmium, zinc (Zn), and lead is widely used to induce phytoextraction (Sun et al.2001), during which its activation effects on Pb are especially outstanding (Zhao et al.2010; Qiao et al.2017). However, EDTA is difficult to biodegrade (Bucheli-Witschel and Egli 2001). Due to the toxicity of heavy metal-EDTA complexes and considering long-term risks of heavy metals leaching (Hadi et al.2010), researchers have started to examine chelating agents of less biological toxicity and that are more degradable such as EDDS, NTA, GLDA, and CA (Lan et al.2013).
Effects of plant growth regulators (DA-6 and 6-BA) and EDDS chelator on phytoextraction and detoxification of cadmium by Amaranthus hybridus Linn.
Published in International Journal of Phytoremediation, 2018
Zhangwei Li, Rushan Zhang, Huimin Zhang
Phytoextraction is an emerging technology that uses metal-accumulating plants to extract heavy metals from contaminated soils (Zhou et al.2015). The approach has attracted attention because it is cost-effective, environment friendly, and convenient (Zhao et al.2015). However, phytoextraction efficiency is often limited by plant uptake ability and aerial biomass yield. The compound [S,S]-Ethylenediaminedisuccinic acid (EDDS) is a biodegradable chelator that enhances Cd mobility of Cd-contaminated soil and improved its uptake and translocation to the plant shoot, thus increasing the plant shoot's Cd-uptake ability (Li et al.2013). However, applying EDDS can also have toxic effects on plants and can strain plant growth, reducing phytoextraction efficiency (Lan et al.2013; Hseu et al.2013).