A multi-scale methodology was used to characterize the long-term behavior and chemical stability of a CeO2-based nanocomposite used as UV filter in wood stains. ATR-FTIR and 13C NMR demonstrated that the citrate coated chelates with Ce(IV) through its central carboxyl- and its α-hydroxyl- groups at the surface of the unaged nanocomposite. After 42 days under artificial daylight, the citrate completely disappeared and small amount of degradation products remained attached to the surface even after 112 days. Moreover, the release/desorption of the citrate layer led to a surface reorganization of the nano-sized CeO2 core observed by XANES (Ce L3-edge). Such a surface and structural transformation of the commercialized nanocomposite could have implications in term of fate, transport, and potential impacts towards the environment.

Two common sorrel (Rumex acetosa) accessions, one from a Zn–Pb contaminated site (CS accession) and the other from an uncontaminated site (UCS accession), were hydroponically exposed to a mixture of heavy metals (Pb2+ + Zn2+ + Cd2+) with and without EDTA at an equimolar rate. The metallicolous CS accession showed a higher tolerance to metal treatment in the absence of the chelating agent, whereas the UCS accession was especially tolerant to EDTA treatment alone. Combination of metal and EDTA treatment resulted in a higher Pb accumulation in shoots of both accessions although plants hardly showed phytotoxic symptoms. Cd and Zn uptake was not augmented by EDTA addition to the polymetallic medium. Chelant-assisted Pb accumulation was 70% higher in the CS accession than in the UCS accession, despite the fact that the former accession evapotranspired less water than the UCS accession. These results support the existence of a non-selective apoplastic transport of metal chelates by R. acetosa roots, not related to transpiration stream.

Cement-solidification and chelator-stabilisation of municipal solid waste incineration fly ash (MSWI-FA) are two main treatment techniques to immobilise heavy metals. Differences in the long-term stabilities of those two methods of heavy-metal immobilisation were explored to aid in determining the better MSWI-FA treatment. However, few comparative studies have been conducted on 6-year-old cement-solidified FA (Ce-6-FA) and chelator-stabilised FA (Ch-6-FA). In this study, we compared the physicochemical and heavy metal leaching characteristics of Ce-6-FA and Ch-6-FA. The chemical speciation of heavy metals was modelled using geochemical software to assess long-term stability. The results showed weaker long-term stability in Pb immobilisation under the chelating system. The leaching concentrations of target heavy metals, acetic acid leaching tests, acid neutralising capacity, and pH-dependent leaching results indicated that Ce-6-FA had higher long-term stability than Ch-6-FA. A column experiment indicated that the cumulative release rates of Pb in Ce-6-FA and Ch-6-FA were 2.49% and 4.72%, respectively. The phase-controlled leaching of Pb in Ce-6-FA mainly occurred through Pb2(OH)3Cl and chloropyromorphite (Pb5(PO4)3Cl), whereas that in Ch-6-FA mainly occurred through Pb5(PO4)3Cl. The decomposition of heavy metal chelates in Ch-6-FA and salt generation in this process led to the release of Pb via the inorganic complex.

Cadmium uptake in rice is believed to be mediated by the Fe transport system. Phyto-available Cd can be changed by Fe fertilization of substrates. This work investigated whether and how Fe fertilization affects mitigation of Cd accumulation in paddy rice. A 90-d soil column experiment was conducted to study the change of Cd and Fe availability in soil after Fe fertilization (ionic and chelated Fe). A low-Cd accumulating cultivar (TY116) and a high-Cd accumulating cultivar (JY841) were grown in two Cd-polluted paddy soils amended with chelated Fe fertilizers. Additionally, both cultivars were grown in hydroponics to compare Fe-related gene expression in EDDHAFe-deficient and EDDHAFe-sufficient roots.The column experiment showed that EDTANa2Fe(II) and EDDHAFe(III) fertilization had a better mitigation effect on soil Cd availability compared to FeSO4·7H2O. Moreover, the field experiment demonstrated that these two chelated fertilizations could reduce Cd concentrations in brown rice by up to 80%. Iron concentrations in the brown rice were elevated by Fe chelates. Compared to EDDHAFe(III), EDTANa2Fe(II) fertilization had a stronger mitigation effect by generating more EDTANa2Cd(II) in the soil solution to decrease phyto-available Cd in the soil. While EDDHAFe(III) fertilization could increase soil pH and decrease soil Eh which contributed to decreasing phyto-available Cd in a contaminated soil. In the hydroponic experiment, Fe sufficiency significantly reduced Cd concentrations in above-ground organs. In some cases, the expression of OsIRT1, OsNRAMP1 and OsNRAMP5 was inhibited under Fe sufficiency relative to Fe deficiency conditions. These results suggest that mitigation of rice Cd by Fe chelate fertilization results from a decrease in available Cd in substrates and the inhibition of the expression of several Fe-related genes in the IRT and NRAMP families.

Chelates, used to increase the uptake of heavy metals in phytoremediation, can also increase the mobility of metals. If plants fail to uptake or stabilize all the mobilized metals, then subsurface soil or groundwater can be contaminated. Therefore, the type and concentration of chelate used and proper site management are important for chelate-aided phytoremediation. In this study, we evaluated potential metal leaching from the soil after applying three different chelates. The readily soluble and exchangeable metal (RSEM) and plant-available metal (PAM) of Pb, Zn, Cu, Cd, and Ni in soil amended with ethylene diamine tetra acetic acid (EDTA), ethylene diamine disuccinate (EDDS), or humic acid (HA) were analyzed, and the potential leaching factor (PLF) of the heavy metals was estimated. Results showed that the effects of chelates and their concentration on RSEM and PAM of heavy metal in soil were different. The addition of EDTA increased the CRSEM and CPAM of all heavy metals, although its effects varied with the concentration added. EDDS application increased CRSEM and CPAM of Cu, Ni, and Zn, but EDDS was more effective than EDTA for Cu and Ni. HA did not show a significant impact due to the short duration of the experiment. In most cases with chelates effects, the increase of RSEM was greater than PAM, and the potential of metal leaching increased. Therefore, application of chelates for remediation of metal-contaminated soil should consider not only the capacity of metal uptake in plants but also the potential metal leaching from the system. Additionally, this process should be accompanied by proper water management to minimize leachate in chelate-aided phytoremediation applications.

This study compares the efficiency of a synthetic chelate (ethylenediaminetetraacetic acid-EDTA), a natural low-molecular-weight organic acid (citric acid), and their combination for phytoremediation of Cu-pyrene co-contaminated soils. Zea mays was grown in each soil and amended with citric acid and/or EDTA to understand the effect of chelates during phytoremediation of contaminated soils. In Cu or pyrene-contaminated soil, plant growth was negatively affected by EDTA (43 %) and citric acid (44 %), respectively, while EDTA + citric acid promoted (41 %) plant growth in co-contaminated soil. EDTA and EDTA + citric acid increased the phytoextraction of Cu in Cu-contaminated and co-contaminated soils, respectively. In pyrene-contaminated soil, all tested chelates increased the dissipation of pyrene reaching 90.4 % for citric acid, while in co-contaminated soil, only citric acid or EDTA + citric acid enhanced pyrene dissipation. These results show that Z. mays can be effective with the help of chelates in phytoextraction of Cu and dissipation of pyrene in co-contaminated soil.

The effects of one of the most toxic heavy metals, lead (Pb), applied in two different concentrations and combined with chelate application were investigated on the water macrophyte (Pistia stratiotes L.) physiology. The influences were observed by the chlorophyll and free amino acid content determination. Also the lead accumulation in macrophyte biomass was investigated to assess the potential efficiency of this plant for rhizofiltration of highly Pb-polluted water. Na EDTA and Na citrate were used as chelates and Pb(NO3)2 as lead supplement. The application of organic chelates simulated conditions of an induced phytoextraction process. Statistical analyses were performed as a one-way ANOVA with a subsequent Tukey HSD test at a level of P < 0.05. Pb contents in both root and leaf tissues gradually increased with increasing Pb concentrations in the nutrient solution. More lead was accumulated in leaves than in roots within all treatments. The total chlorophyll content decreased with increased Pb concentration and with a higher content of chelates. The chelate addition increased the total amino acid content in leaves but decreased the total amino acid content in roots. The addition of lead with chelates decreased the dry biomass weight. However, water macrophyte showed extremely high lead accumulation in biomass in the short term (up to 8 days) and this accumulation potential could be used for relatively fast and effective decrease of high concentration of this risk element in contaminated water or sewage.

Phytoextraction is a promising technology that uses hyperaccumulating plants to remove inorganic contaminants, primarily heavy metals, from soils and waters. A field experiment was conducted to evaluate impacts of a mixture of chelators (MC) upon the growth and phytoextraction of heavy metals by the hyperaccumulator Sedum alfredii Hance in a co-planting system in a paddy soil that was historically irrigated with Pb and Zn contaminated mining wastewaters. The co-planting system used in this study was comprised of a Zn- and Cd-hyperaccumulator (S. alfredii) and a low-accumulating crop (Zea mays). Results showed that yields of S. alfredii were significantly increased with the addition of the MC and by co-planting with Z. mays. Our study further revealed that concentrations of Zn, Pb, and Cd in the corn grains of Z. mays conform to the Chinese hygiene standards for animal feeds and in the other parts of Z. mays conform to the Chinese organic fertilizer standards. The uptake of Zn, Cd, and Pb by S. alfredii was significantly increased with the addition of MC. The uptake of Zn by S. alfredii was also significantly enhanced by co-planting with Z. mays, but the interaction between MC and co-planting was not significant, meaning the effects of the two types of treatments should be additive. When the MC was applied to the co-planting system in the soil contaminated with Zn, Cd, and Pb, the highest phytoextraction rates were observed. This study suggested that the use of the hyperaccumulator S. alfredii and the low-accumulating crop Z. mays in the co-planting system with the addition of the MC was a more promising approach than the use of a single hyperaccumulator with the assistance of EDTA (ethylenediaminetetraacetic acid). This approach not only enhances the phytoextraction rates of the heavy metals but also simultaneously allows agricultural practices with safe feed products in the metal-contaminated soils.

Siderophores are small molecular weight extracellular organic compounds secreted by microorganisms under iron-starved conditions, used by them to chelate and solubilize iron. Though they are specific ferric iron chelator, but is reported that they bind other metals also, such as divalent heavy metals and actinides because of potentially high metal-siderophore stability constants. Thus metal contaminant fate and transport in subsurface environment can be heavily influenced by siderophores. This approach can be successfully used in removing many toxic metals off the soil which poses a serious health threat. Our research focuses on the correlation between cell growth and siderophore production and chemical characterization of the siderophore type. Its also documents the development of an assay method for the screening of different metals for complexation with siderophores based on the Chrome Azurol S (CAS) assay. The present research aims at batch scale mobilization of arsenic from arsenic contaminated soils using siderophore produced by P. azotoformans and thus evaluating its efficiency as compared to Ethylene Diamine Tetra Acetic Acid (EDTA), Citric Acid (CA) for the same. FT-IR spectroscopic studies were carried out to determine the interaction between soil, arsenic and siderophore. Results have shown that the cell growth and siderophore production are inversely related. Characterization of siderophore produced by P. azotoformans has revealed that it is of mixed-type catecholate and hydroxamate. Siderophore was found to complex with heavy metals like Cadmium, Lead, Nickel, Arsenic (III, V), Aluminium, Magnesium Zinc, Copper, Cobalt, Strontium other than Iron. Five washings by siderophore, EDTA, CA removed almost 92.8%, 77.3%, 70.0% arsenic respectively as compared to only 33.8% removal by control. Washing of arsenic contaminated soil with tap water revealed that ≈ 65.8% of arsenic in contaminated soil is in freely available or weakly bound form. The IR spectra revealed that hydrogen bonding exists between siderophore, arsenic and soil. Encouraging results of arsenic removal by biomolecule-siderophore can lead to an emerging tool brimming with opportunities for environmental clean up.

In this paper, we report on a field experiment being carried out in a Typic Eutrorthox. The experiment was initiated in the 1997–98 agricultural season as a randomized block design with four treatments (0, 5, 10, and 20 t ha⁻¹) of sewage sludge and five replicates. Compound soil samples were obtained from 20 subsamples collected at depths of 0–0.1 and 0.1–0.2 m. Cu, Fe, Mn, and Zn concentrations were extracted with DTPA pH 7.3; 0.1 mol L⁻¹ HCl, Mehlich-I, Mehlich-III, and 0.01 mol L⁻¹ CaCl₂. Metal concentrations were determined via atomic absorption spectrometry. Diagnostic leaves and the whole above-ground portion of plants were collected to determine Cu, Fe, Mn, and Zn concentrations extracted by nitric–perchloric digestion and later determined via atomic absorption spectrometry. Sewage sludge application caused increases in the concentrations of soil Cu, Fe, and Mn in samples taken from the 0–0.1 m depth evaluated by the extractants Mehlich-I, Mehlich-III, 0.01 mol L⁻¹ HCl and DTPA pH 7.3. None of the extractants provided efficient estimates of changes in Mn concentrations. The acid extractants extracted more Cu, Fe, Mn, and Zn than the saline and chelating solutions. The highest concentrations of Cu, Fe, and Zn were obtained with Mehlich-III, while the highest concentrations of Mn were obtained with HCl. We did not observe a correlation between the extractants and the concentrations of elements in the diagnostic leaves nor in the tissues of the whole maize plant (Zea mays L.).