Residual effects of EDDS leachates on plants during EDDS-assisted phytoremediation of copper contaminated soil

Phytoremediation of Toxic Metals: A Sustainable Green Solution for Clean Environment

Contamination of aquatic ecosystems by various sources has become a major worry all over the world. Pollutants can enter the human body through the food chain from aquatic and soil habitats. These pollutants can cause various chronic diseases in humans and mortality if they collect in the body over an extended period. Although the phytoremediation technique cannot completely remove harmful materials, it is an environmentally benign, cost-effective, and natural process that has no negative effects on the environment. The main types of phytoremediation, their mechanisms, and strategies to raise the remediation rate and the use of genetically altered plants, phytoremediation plant prospects, economics, and usable plants are reviewed in this review. Several factors influence the phytoremediation process, including types of contaminants, pollutant characteristics, and plant species selection, climate considerations, flooding and aging, the effect of salt, soil parameters, and redox potential. Phytoremediation’s environmental and economic efficiency, use, and relevance are depicted in our work. Multiple recent breakthroughs in phytoremediation technologies are also mentioned in this review.

Assessment of biodegradable chelating agents in the phytoextraction of heavy metals from multi-metal contaminated soil

A pot incubation experiment under natural conditions was designed to investigate the effects of three biodegradable chelating agents, namely; the [S,S]-isomer of ethylenediamine disuccinate (EDDS), citric acid (CA), and tetrasodium N,N-Bis(carboxymethyl)-L-glutamate acid (GLDA), on two plant species (Brassica juncea and Brassica rapa) in terms of plant foliar growth, dry matter yield, and heavy metal (HM) accumulation. Both plant species exhibited diminished growth and symptoms of phytotoxicity under HM stress. The application of EDDS and CA affected plant foliar growth, biomass production, and led to the development of chlorotic lesions on leaves. EDDS and CA also decreased the shoot length by 38.5% and 45.2% in B. juncea, and 60.1% and 100% in B. rapa, respectively. In contrast, GLDA relieved HM stress by significantly increasing plant growth (P > 0.05) and was shown to be well tolerated (tolerance index [TI]; B. juncea = 99% and B. rapa = 123%). Among both plants, B. juncea displayed the ability to accumulate a wider range of HMs at higher concentrations. Amongst the three chelators, EDDS induced the highest bioconcentration (BCF) of Pb (2.45), Zn (2.68), and Cd (3.36) while CA achieved better results for Ni (4.01) and Cr (1.45). However, the current results showed that even with the application of chelating agents, HMs were predominantly accumulated in roots and translocation factor was generally <1. The findings of this investigation emphasize that chelate-assisted phytoextraction with Brassica spp. is highly limited in multi-metal settings, making it an unsuitable option for severely contaminated sites.

Formation of disinfection byproducts from sulfamethoxazole during sodium hypochlorite disinfection of marine culture water

The fates of the antibiotic sulfamethoxazole (SMX) in the chlorination of fresh water, simulated brackish marine culture water, and marine water were investigated. SMX was oxidized by sodium hypochlorite (NaClO) at different reaction rates in the different samples. The oxidation of SMX followed pseudo-first-order kinetics, and the rate constant was the largest in marine water (3.44 min^-1), as Br^- ions promote the oxidation reaction. Moreover, the kinds of disinfection byproducts (DBPs) were also affected by Br^- ions. Br-DBPs were found in the simulated brackish marine culture water and marine water disinfection systems. The structures of the DBPs indicated that S-C cleavage, polymerization, S-N hydrolysis, chlorine/bromine substitution, and desulfonation reactions occurred on SMX during the disinfection process. EPI (Estimation Programs Interface) Suite™ and absorbable organic halogen (AOX) analysis were used to evaluate the toxicity of the DBPs. The results suggested that DBPs in the simulated brackish marine culture water and marine water systems were more toxic than those in the fresh water system.

Effects of plant growth regulators (DA-6 and 6-BA) and EDDS chelator on phytoextraction and detoxification of cadmium by Amaranthus hybridus Linn

In this study, pot experiments were carried out to investigative the effects of growth-promoting hormone diethyl aminoethyl hexanoate (DA-6), 6-Benzylaminopurine (6-BA), and chelator [S,S]-Ethylenediaminedisuccinic acid (EDDS) when applied to soil contaminated with cadmium (Cd). The substances were applied alone and in combination to assess their impact on biomass, Cd phytoextraction, subcellular distribution, and chemical forms in Cd hyperaccumulator Amaranthus hybridus Linn. (A. hybridus). Results showed that the treatment of EDDS alone inhibited plant growth, and raised the Cd concentration in the plant shoot and root. Treatments with DA-6 and 6-BA combined with EDDS alleviated the negative effect of EDDS on plant growth, resulting in a synergistic effect on Cd phytoaccumulation and translocation. At the subcellular level, DA-6 and 6-BA detoxified the Cd toxicity in the plant by retaining the Cd in the cell wall. On the distribution of the chemical form of Cd in plant shoot, DA-6 and 6-BA significantly decreased Cd mobility in the plant compared to EDDS. These results confirmed that combining DA-6 and 6-BA with EDDS can counteract the adverse effect of EDDS on plant growth. The treatment of 5.0 mmol kg^-1 EDDS + 1 μM DA-6 was optimal for improving the remediation of A. hybridus Linn. growing in Cd contaminated soil.

Ethylenediamine disuccinic acid enhanced phytoextraction of nickel from contaminated soils using Coronopus didymus (L.) Sm

In a screenhouse, the applicability of biodegradable chelant ethylenediamine disuccinic acid (EDDS) to enhance Ni-phytoextraction by Coronopus didymus was tested for the first time. This study assayed the hypothesis based upon the role of EDDS on physiological and biochemical alterations and ameliorating phytoextraction capacity of C. didymus under nickel (Ni) stress. Pot experiments were conducted for 6 weeks and C. didymus plants were cultivated in soil artificially contaminated with 30, 50, and 70 mg kg^-1 Ni treatments. Soil was amended with EDDS (2 mmol kg^-1). Plants were harvested, 1 week after EDDS application. At 70 mg kg^-1 Ni level, EDDS application dramatically enhanced the root and shoot Ni concentration from 665 and 644 to 1339 and 1338 mg kg^-1, respectively. Combination of Ni + EDDS induced alterations in biochemical parameters of plants. EDDS addition posed pessimistic effects on growth, biomass, photosynthetic activity and protein content of the plants. Besides, application of EDDS stimulated the generation of superoxide anion, H₂O₂ content and MDA level. However, EDDS assisted mount in antioxidant activities (superoxide dismutase, catalase and glutathione peroxidase) considerably neutralised the toxicity induced by reactive oxygen species in plant tissues. The results revealed EDDS efficacy to ameliorate the performance of antioxidant enzymes and improved Ni translocation in plant tissues, thus strongly marked its affinity to be used together with C. didymus for Ni-phytoextraction.

Sequential application of soil washing and phytoremediation in the land of fires

This paper presents an experimental study aimed at verifying the efficiency of a double-stage remediation process to be applied in former agricultural sites contaminated by illegal dumping of industrial wastes. The process, which includes an EDDS (Ethylenediamine-N,N'-disuccinic acid) enhanced washing, followed by a phytoremediation treatment, is applied at the lab scale for the remediation of a soil sampled in a territory known as Land of Fires (Italy) contaminated with Cu (∼400 mg kg^-1) and Zn (∼250 mg kg^-1). Phytoremediation is conducted using Lactuca sativa to verify, together with process efficiency, the potential risks due to metal accumulation in edible species. The results of the washing process show the possibility of removing the potential toxic metals from 44% to 77% for Cu and from 18% to 47% for Zn. The removal is well distributed among all soil fractions. There is almost no removal of other components which are fundamental for an agricultural soil. Results of the subsequent phytoremediation treatment indicate that both the contaminants and the residual EDDS/EDDS-chelates adsorbed into the soil generally negatively affect plant growth, reducing the number of germinated seeds up to 43%, and the shoot length up to 63%. Nonetheless, whenever the efficiency of the washing stage is high enough, no adverse effect is obtained on the plants. The efficiency of the phytoremediation stage mainly relies on leaf uptake, which accounts for up to 88% of the total removed Cu and up to 95% of the total removed Zn. Stabilization in the underground part of the plant is more contained because of the limited mass of the roots.

Improvement effects of cytokinin on EDTA assisted phytoremediation and the associated environmental risks

Soil samples containing excess Cd (0.82 mg kg^-1), Pb (92.7 mg kg^-1) and Cu (72.7 mg kg^-1) relative to their corresponding safe thresholds (0.3, 80 and 50 mg kg^-1, respectively) from a notorious e-waste disposing and recycling place in southern China were phytoremediated with EDTA addition to evaluate the promotion effects of cytokinin on the remediation efficiency of Eucalyptus globulus. Biomass production of the plant, evapotranspiration amount of the soil, metals accumulation in plant organs and the volume of leachate under various treatments were compared. Relative to the planting control, EDTA application shortened the time required for Cd, Pb and Cu decontamination by 1.7-5.5 times but led to significantly more leachate (996 vs 1256 mL), indicating the negative influence of the chelate treatment on the species and the surrounding environment. The foliar application of cytokinin can expand the advantage and alleviate the adverse impact of individual EDTA application simultaneously as manifested by the increased biomass yield, less time consumption for purification and decreased leachate volume. Cytokinin accelerated the transpiration rate of the plant proved by the least volume of leachate in individual cytokinin treatment. The major factors for effective phytoremediation were the resistance of species to high concentrations of contaminants and less environmental risks generation during the remediation processes. Therefore, synergistic use of such components provides more efficient decontamination of metals and more security for the environment.

Appraising the role of environment friendly chelants in alleviating lead by Coronopus didymus from Pb-contaminated soils

In a screenhouse experiment, we investigated the role of two environment friendly chelants, Ammonium molybdate and EDDS for Pb mobilisation and its extraction by Coronopus didymus under completely randomized controlled conditions. Seedlings of C. didymus were grown in pots having Pb-contaminated soil (1200 and 2200 mg kg^-1) for 6 weeks. Plants were harvested, 1 week after the addition of A. molybdate and EDDS. Results revealed that A. molybdate and EDDS enhanced the uptake and accumulation of Pb in roots and shoots of C. didymus. At 2200 mg kg^-1 Pb level, compared to Pb-alone treatment, the maximal concentration of Pb was increased upto ∼10% and ∼19%, in roots whereas ∼8% and ∼18%, respectively, in shoots on addition of 2 mmol kg^-1 A. molybdate and EDDS. Additionally, Pb + EDDS treatments enhanced the plant biomass and triggered strong antioxidative response, more efficaciously than Pb + A. molybdate and Pb-alone treated plants. In this study, EDDS relative to A. molybdate was more efficient in mobilising and extracting Pb from soil. Although, EDDS followed by A. molybdate had good efficacy in mitigating Pb from contaminated soils but C. didymus itself has the inherent affinity to tolerate and accumulate Pb from contaminated soils and hence in future, can be used either alone or with some other eco-friendly amendments for soil remediation purposes.

Effects of [S,S]-ethylenediaminedisuccinic acid and nitrilotriacetic acid on the efficiency of Pb phytostabilization by Athyrium wardii (Hook.) grown in Pb-contaminated soils

Chelate-assisted phytoextraction with biodegradable chelants has been demonstrated as an efficient method to enhance heavy metal remediation efficiency by plants, while there is little available information on phytostabilization. A pot experiment was conducted to investigate the effects of biodegradable [S,S]-ethylenediaminedisuccinic acid (EDDS) and nitrilotriacetic acid (NTA) on plant growth and Pb accumulation of Pb phytostabilizer Athyrium wardii (Hook.) grown in Pb contaminated soils and to explore the feasibility of chelate-assisted phytostabilization. Greater adverse effects on plant biomass under high EDDS treatments were observed than NTA treatments. Significant increase of shoot Pb concentrations of A. wardii was noticed with increasing NTA and EDDS dosages, while EDDS induced higher shoot Pb concentrations than NTA. Moreover, root Pb concentrations of A. wardii under NTA treatments were 1.18-1.28-time higher than EDDS treatments, and a peak value of root Pb concentrations was observed at 2 mmol kg(-1) of NTA. Shoot Pb accumulations significantly increased with increasing dosages, and EDDS treatments caused a 1.44-1.6-time increase of shoot Pb accumulation than NTA. Root Pb accumulations under NTA treatments were 1.18-1.28-time higher than EDDS treatments. Maximum root Pb accumulation (155.5 mg plant(-1)) was found at 2 mmol kg(-1) of NTA on the 14th day. Higher BCF values and lower TF values were found under NTA treatments as compared to EDDS treatments. Available Pb concentrations in soil significantly increased on the 7th day with increasing NTA and EDDS dosages, then gradually decreased on the 14th day. Soil pH slightly decreased with increasing NTA and EDDS dosages. Therefore, chelate-assisted phytostabilization could be a feasible way to enhance the efficiency of Pb phytostabilization by A. wardii.

Assessment of amendments for the immobilization of Cu in soils containing EDDS leachates

In this study, the effectiveness of six soil amendments (ferrihydrite, manganese dioxide, gibbsite, calcium carbonate, biochar, and organic fertilizer) was investigated to assess the feasibility of minimizing possible environmental contaminant leaching during S,S-ethylenediaminedisuccinic acid (EDDS)-enhanced phytoextraction process based on 0.01-M CaCl2 extraction. Results showed that the application of EDDS could significantly increase Cu concentrations in the leaching solution. Compared with control, incorporation of six amendments (excluding organic fertilizer) significantly decreased CaCl2-extractable Cu concentrations in both soils. When EDDS-containing solutions leached from the soil columns (mimicking the upper soil layers) were added to soils with different amendments (mimicking the subsoil), CaCl2-extractable Cu in the soils amended with ferrihydrite, manganese dioxide, gibbsite, and calcium carbonate was significantly lower than that in the control soil (no amendments) and remained relatively constant during the first 14 days. Incorporation of biochar or organic fertilizer had no positive effect on the immobilization of Cu in EDDS leachates in soils. After 14 days, CaCl2-extractable Cu concentration decreased rapidly in soils incorporated with various amendments. Integrating soil washing with biodegradable chelating agents or chelant-enhanced phytoextraction and immobilization of heavy metals in subsoil could be used to rapidly reduce the concentration of bioavailable metal fractions in the upper soil layers and minimize environmental risks of secondary pollution.

Enhanced efficiency of cadmium removal by Boehmeria nivea (L.) Gaud. in the presence of exogenous citric and oxalic acids

Boehmeria nivea (L.) Gaud. is a potential candidate for the remediation of Cd contaminated sites. The present investigation aims to explore Cd tolerance threshold and to quickly identify the role of exogenous organic acids in Cd uptake and abiotic metal stress damage. Elevated Cd levels (0-10mg/L) resulted in an obvious rise in Cd accumulation, ranging from 268.0 to 374.4 in root and 25.2 to 41.2mg/kg dry weight in shoot, respectively. Citric acid at 1.5 mmol/L significantly facilitated Cd uptake by 26.7% in root and by 1-fold in shoot, respectively. Cd translocation efficiency from root to shoot was improved by a maximum of 66.4% under 3 mmol/L of oxalic acid. Citric acid exhibited more prominent mitigating effect than oxalic acid due to its stronger ligand affinity for chelating with metal and avoiding the toxicity injury of free Cd ions more efficiently. The present work provides a potential strategy for efficient Cd remediation with B. nivea.

Influence of the application of chelant EDDS on soil enzymatic activity and microbial community structure

The present study evaluated the effects of a biodegradable chelant, S,S-ethylenediaminedisuccinic acid (EDDS), on enzyme activities and microbial community composition in copper (Cu)-contaminated soils, planted with either corn or beans. Results showed that the application of EDDS did not affect urease and acid phosphatase activities in the soil, but greatly reduced catalase and saccharase activities, and increased β-glucosidase activity on the seventh day after EDDS application. On the 28th day, no significant difference was observed in the enzyme activities (except for β-glucosidase) of EDDS-treated soils compared to the controls. Analysis of phospholipid fatty acids (PLFAs) showed that the application of 3 mmol kg(-1) EDDS did not cause significant stress to soil microbial communities. However, PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint revealed that EDDS influenced the bacterial communities in the soils, and the effects on bean soils were more significant than that with corn. In general, the enzyme activities and bacterial communities were influenced by the application of EDDS, but the impact became weaker or even disappeared with the biodegradation of EDDS.