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Biswakarma J, Kang K, Schenkeveld WDC, Kraemer SM, Hering JG, Hug SJ. Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB. CHEMOSPHERE 2021; 263:128188. [PMID: 33297154 DOI: 10.1016/j.chemosphere.2020.128188] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 08/23/2020] [Accepted: 08/26/2020] [Indexed: 06/12/2023]
Abstract
Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5-15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10-40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3-5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.
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Affiliation(s)
- Jagannath Biswakarma
- Swiss Federal Institute of Technology (ETH) Zurich, IBP, CH-8092, Zürich, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Kyounglim Kang
- University of Vienna, Dept. of Environmental Geosciences, 1090, Vienna, Austria
| | - Walter D C Schenkeveld
- Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, 3584, CB Utrecht, the Netherlands
| | - Stephan M Kraemer
- University of Vienna, Dept. of Environmental Geosciences, 1090, Vienna, Austria
| | - Janet G Hering
- Swiss Federal Institute of Technology (ETH) Zurich, IBP, CH-8092, Zürich, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland; Swiss Federal Institute of Technology Lausanne (EPFL), ENAC, CH-1015, Lausanne, Switzerland
| | - Stephan J Hug
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.
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Biswakarma J, Kang K, Borowski SC, Schenkeveld WDC, Kraemer SM, Hering JG, Hug SJ. Fe(II)-Catalyzed Ligand-Controlled Dissolution of Iron(hydr)oxides. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:88-97. [PMID: 30571098 DOI: 10.1021/acs.est.8b03910] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Dissolution of iron(III)phases is a key process in soils, surface waters, and the ocean. Previous studies found that traces of Fe(II) can greatly increase ligand controlled dissolution rates at acidic pH, but the extent that this also occurs at circumneutral pH and what mechanisms are involved are not known. We addressed these questions with infrared spectroscopy and 57Fe isotope exchange experiments with lepidocrocite (Lp) and 50 μM ethylenediaminetetraacetate (EDTA) at pH 6 and 7. Addition of 0.2-10 μM Fe(II) led to an acceleration of the dissolution rates by factors of 7-31. Similar effects were observed after irradiation with 365 nm UV light. The catalytic effect persisted under anoxic conditions, but decreased as soon as air or phenanthroline was introduced. Isotope exchange experiments showed that added 57Fe remained in solution, or quickly reappeared in solution when EDTA was added after 57Fe(II), suggesting that catalyzed dissolution occurred at or near the site of 57Fe incorporation at the mineral surface. Infrared spectra indicated no change in the bulk, but changes in the spectra of adsorbed EDTA after addition of Fe(II) were observed. A kinetic model shows that the catalytic effect can be explained by electron transfer to surface Fe(III) sites and rapid detachment of Fe(III)EDTA due to the weaker bonds to reduced sites. We conclude that the catalytic effect of Fe(II) on dissolution of Fe(III)(hydr)oxides is likely important under circumneutral anoxic conditions and in sunlit environments.
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Affiliation(s)
- Jagannath Biswakarma
- Eawag , Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf , Switzerland
- Swiss Federal Institute of Technology (ETH) Zürich , IBP , CH-8092 Zürich , Switzerland
| | - Kyounglim Kang
- University of Vienna , Dept. of Environmental Geosciences , 1090 Vienna , Austria
| | - Susan C Borowski
- Eawag , Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf , Switzerland
| | | | - Stephan M Kraemer
- University of Vienna , Dept. of Environmental Geosciences , 1090 Vienna , Austria
| | - Janet G Hering
- Eawag , Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf , Switzerland
- Swiss Federal Institute of Technology (ETH) Zürich , IBP , CH-8092 Zürich , Switzerland
- Swiss Federal Institute of Technology Lausanne (EPFL) , ENAC , CH-1015 Lausanne , Switzerland
| | - Stephan J Hug
- Eawag , Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf , Switzerland
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Lin Y, Wei Y, Sun Y. Room-temperature synthesis and photocatalytic properties of lepidocrocite by monowavelength visible light irradiation. ACTA ACUST UNITED AC 2012. [DOI: 10.1016/j.molcata.2011.11.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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Han SK, Hwang TM, Yoon Y, Kang JW. Evidence of singlet oxygen and hydroxyl radical formation in aqueous goethite suspension using spin-trapping electron paramagnetic resonance (EPR). CHEMOSPHERE 2011; 84:1095-101. [PMID: 21561642 DOI: 10.1016/j.chemosphere.2011.04.051] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 04/13/2011] [Accepted: 04/16/2011] [Indexed: 05/11/2023]
Abstract
The generation of reactive species in an aqueous goethite suspension, under room light and aeration conditions, was investigated using the electron paramagnetic resonance (EPR) technique employing spin trap agents. The trap reagents, including 5,5-dimethylpyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP), were used for the detection of OH radicals (OH·) and singlet oxygen (1O2), respectively. On the addition of DMPO to the goethite suspended solution, a DMPO-OH adduct was formed, which was not decreased, even in the presence of the OH· scavenger, mannitol. This result implied a false positive interpretation from the DMPO-OH EPR signal. In the presence of TEMP reagent, a TEMP-O signal was detected, which was completely inhibited in the presence of the singlet oxygen scavenger, sodium azide. With both DMPO-OH and TEMP-O radicals in the presence and absence of radical scavengers, singlet oxygen was observed to be the key species formed in the room-light sensitized goethite suspension. In the goethite/H2O2 system; however, both OH· and singlet oxygen were generated, with significant portions of DMPO-OH resulting from both OH· and singlet oxygen. In fact, the DMPO-OH resulting from OH· should be carefully calculated by correcting for the amount of DMPO-OH due to singlet oxygen. This study reports, for the first time, that the goethite suspensions may also act as a natural sensitizer, such as fulvic acids, to form singlet oxygen.
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Affiliation(s)
- Sang Kuk Han
- Department of Marine Environmental Engineering, Mokpo National Maritime University, 91 Haeyangdaehag-ro, Mokpo, Jeollanam-do 530-729, Republic of Korea
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Samanta G, Clifford DA. Preservation of inorganic arsenic species in groundwater. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2005; 39:8877-82. [PMID: 16323789 DOI: 10.1021/es051185i] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The objective of this research was to develop a robust preservation method for stabilizing inorganic As(IlI/V) species in synthetic and actual groundwaters. Ethylenediaminetetraacetic acid (EDTA), H2SO4, H3PO4, and EDTA-acetic acid (HAc) were evaluated in synthetic groundwater containing 3 mg/L Fe(ll) in the pH range 6.5-8.4 and Eh range -100 to +200 mV at room temperature. In the absence of strong UV light, only EDTA-HAc was found to be an effective preservative under all the experimental conditions tested. A total of 89 samples (including 16 samples in triplicate) from 55 drinking waterwells in Minnesota, California, and North Dakota were preserved with a combination of EDTA-HAc and speciated to evaluate its effectiveness for preserving inorganic arsenic species in actual groundwater samples. The preserved and field-speciated samples were repeatedly speciated and analyzed in the laboratory for up to 85 days after collection. Field-speciated As(lll) concentrations were compared with the As(lll) concentrations in the preserved samples. The results were highly correlated (slope 0.9773, R2 = 0.9986), which indicates that during sample transportation and storage the distribution of arsenic species did not change for samples preserved with EDTA-HAc.
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Affiliation(s)
- Gautam Samanta
- Department of Civil and Environmental Engineering, University of Houston, N 107 Engineering Building 1, Houston, Texas, 77204-4003, USA
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Gómez-Gallego M, Pellico D, Ramírez-López P, Mancheño MJ, Romano S, de la Torre MC, Sierra MA. Understanding of the Mode of Action of FeIII-EDDHA as Iron Chlorosis Corrector Based on Its Photochemical and Redox Behavior. Chemistry 2005; 11:5997-6005. [PMID: 16052655 DOI: 10.1002/chem.200500286] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The very low reduction potential of the chelate Fe(III)-EDDHA (EDDHA = ethylenediamine N,N'-bis(2-hydroxy)phenylacetic acid) makes it unreactive in photochemically or chemically induced electron transfer processes. The lack of reactivity of this complex toward light invalidates photodegradation as an alternative mechanism for environmental elimination. However, in spite of its low reduction potential, the biological reduction of Fe(III)-EDDHA is very effective. Based on electrochemical measurements, it is proposed that Fe(III)-EDDHA itself is not the substrate of the enzyme ferric chelate reductase. Likely, at the more acidic pH in the vicinity of the roots, the ferric chelate in a closed form (FeL-) could generate a vacant coordination site that leads to an open hexacoordinate species (FeHL) where the reduction of the metal by the enzyme takes place.
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Affiliation(s)
- Mar Gómez-Gallego
- Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain.
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He J, Ma W, Song W, Zhao J, Qian X, Zhang S, Yu JC. Photoreaction of aromatic compounds at alpha-FeOOH/H2O interface in the presence of H2O2: evidence for organic-goethite surface complex formation. WATER RESEARCH 2005; 39:119-128. [PMID: 15607171 DOI: 10.1016/j.watres.2004.09.006] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 09/03/2004] [Accepted: 09/07/2004] [Indexed: 05/24/2023]
Abstract
The photoreactions of aromatic compounds were investigated in aqueous dispersions of alpha-FeOOH(goethite)/H(2)O(2) at neutral pHs. It was found that aromatic compounds could undergo rapid decomposition and mineralization (even to 100% yield) in the presence of both alpha-FeOOH and H(2)O(2) under UV irradiation, and the degradation rates of the organics were related to their sorption ability of the surface of alpha-FeOOH and were in the following order: salicylic acid approximately m-hydroxylbenzoic acid>p-hydroxylbenzoic acid approximately benzoic acid>p-biphthalic acid>phenol>benzenesulfonic acid. The interactions of salicylic acid and benzenesulfonic acid with goethite were examined by Fourier transform infrared spectroscopy (FTIR), and electron spin resonance (ESR) was applied to detect the intermediate radicals formed in the photoreaction. The effect of pH and foreign ligands on the degradation of salicylic acid, decomposition of H(2)O(2), and formation of dissolved iron was also examined.
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Affiliation(s)
- Ju He
- Laboratory of Photochemistry, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
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Metsärinne S, Rantanen P, Aksela R, Tuhkanen T. Biological and photochemical degradation rates of diethylenetriaminepentaacetic acid (DTPA) in the presence and absence of Fe(III). CHEMOSPHERE 2004; 55:379-388. [PMID: 14987936 DOI: 10.1016/j.chemosphere.2003.10.062] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2003] [Revised: 10/07/2003] [Accepted: 10/24/2003] [Indexed: 05/24/2023]
Abstract
The environmental fate of ethylenediaminetetraacetic acid (EDTA) has been extensively studied, while much less is known about the environmental behaviour of diethylenetriaminepentaacetic acid (DTPA). In this study, it was confirmed that DTPA is persistent toward biodegradation. The biodegradability of DTPA was investigated in the absence and in the presence of Fe(III) by using CO2 evolution test and Manometric respirometry test. The CO2 evolution and oxygen uptake of iron-free (DTPA was added as free acid) and Fe(III)DTPA were less than in inoculum blank. Possible inhibitor effect was analysed by testing biodegradation of sodium benzoate with and without iron-free or Fe(III)DTPA in the Manometric respirometry test. Only slight inhibition was observed when DTPA was added as free acid. Photodegradation of iron-free DTPA and Fe(III)-DTPA complex was studied by using sunlight and UV radiation at the range 315-400 nm emitted by black light lamps. The results indicate that DTPA added as free acid degrades photochemically in humic lake water. Fe(III)DTPA was shown to be very photolabile in humic lake water in the summer; the photochemical half-life was below one hour. Photodegradation products were identified by the mass spectrometric technique (GC-MS). It was shown that photodegradation of Fe(III)DTPA does not result in total mineralization of the compound. Diethylenetriaminetetraacetic acid, diethylenetriaminetriacetic acid, ethylenediaminetriacetic acid, N,N'- and/or N,N-ethylenediaminediacetic acid, iminodiacetate, ethylenediaminemonoacetic acid and glycine were identified as photodegradation products of Fe(III)DTPA. Based on these observations, we propose a photodegradation pathway for Fe(III)DTPA.
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Affiliation(s)
- Sirpa Metsärinne
- Department of Environmental Sciences, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland.
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9
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Nowack B. Environmental chemistry of aminopolycarboxylate chelating agents. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2002; 36:4009-16. [PMID: 12380068 DOI: 10.1021/es025683s] [Citation(s) in RCA: 258] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Aminopolycarboxylate chelating agents are under scrutiny due to their influence on metal availability and mobility and in particular due to their persistence in the environment. In this review chelate adsorption, metal-mobilization, metal-exchange, mineral dissolution, reactive transport, photodegradation, and chemical degradation are all shown to be substantially affected by the chelated metal ion. The different reactivities of the metal-complexes have to be considered when assessing the reactions of chelating agents in the environment because they occur in natural waters predominantly in the form of metal complexes. Knowing the speciation of chelating agents in natural waters is therefore crucial for predicting their environmental fate. Despite this importance, only a few speciation measurements have been reported for natural waters, and model calculations have been frequently used instead. These calculations are, however, complicated by slow metal-exchange reactions that result in a nonequilibrium speciation and by the presence of naturally occurring ligands that compete with the chelating agents for available metals. The basis for a refined risk assessment of aminocarboxylate chelates should be the actual speciation in the natural water directly determined by analytical methods. The discussion of the influence of chelates on metal availability and fate also has to include the potential presence of other aminopolycarboxylate chelating agents besides the well-known EDTA and NTA.
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Affiliation(s)
- Bernd Nowack
- Institute of Terrestrial Ecology (ITO), Swiss Federal Institute of Technology Zürich (ETH), CH-8952 Schlieren, Switzerland.
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Nowack B, Stone AT. Homogeneous and Heterogeneous Oxidation of Nitrilotrismethylenephosphonic Acid (NTMP) in the Presence of Manganese(II, III) and Molecular Oxygen. J Phys Chem B 2002. [DOI: 10.1021/jp014293+] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Ammann AA. Determination of strong binding chelators and their metal complexes by anion-exchange chromatography and inductively coupled plasma mass spectrometry. J Chromatogr A 2002; 947:205-16. [PMID: 11883654 DOI: 10.1016/s0021-9673(01)01607-7] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Based on the negative charge of polycarboxylic chelators, an anion-exchange separation has been developed that is compatible with sensitive metal detection by ICP-MS. A low capacity hydrophilic polymer (AS11) was used as the anion exchanger and ammonium nitrate as the eluent. The new procedure provided high selectivity in the isocratic mode as well as a large separation window and high separation efficiency in the gradient mode. This was demonstrated for different types of chelators and their metal complexes. The aminopolycarboxylates NTA, EDTA, CDTA, DTPA, EDDS and for the EDTA derivatives HEDTA, ED3A and EDTMP, the phosphonic acid analogue of EDTA were tested. Their retention times generally depended on the charge, which was lower in 1:1 metal chelator complexes. Evaluation of the separation mechanism demonstrated that they were all separated predominantly by an anion-exchange mechanism with only a minor contribution from hydrophobic attraction. The method is useful for species identification and for predicting the charge of unknown analogous species from retention times. A gradient separation procedure achieved on-column preconcentration and matrix removal for the interference-free detection of metal chelates down to low nanomolar concentration in samples from various fields of environmental research.
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Affiliation(s)
- Adrian A Ammann
- Swiss Federal Institute for Environmental Science and Technology (EAWAG), Dübendorf.
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Liu R, Tang H. Surface acid–base characteristics of natural manganese mineral particles. Colloids Surf A Physicochem Eng Asp 2002. [DOI: 10.1016/s0927-7757(01)00820-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Hug SJ, Canonica L, Wegelin M, Gechter D, Von Gunten U. Solar oxidation and removal of arsenic at circumneutral pH in iron containing waters. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2001; 35:2114-21. [PMID: 11393995 DOI: 10.1021/es001551s] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
An estimated 30-50 million people in Bangladesh consume groundwater with arsenic contents far above accepted limits. A better understanding of arsenic redox kinetics and simple water treatment procedures are urgently needed. We have studied thermal and photochemical As(III) oxidation in the laboratory, on a time scale of hours, in water containing 500 micrograms/L As(III), 0.06-5 mg/L Fe(II,III), and 4-6 mM bicarbonate at pH 6.5-8.0. As(V) was measured colorimetrically, and As(III) and As(tot) were measured by As(III)/As(tot)-specific hydride-generation AAS. Dissolved oxygen and micromolar hydrogen peroxide did not oxidize As(III) on a time scale of hours. As(III) was partly oxidized in the dark by addition of Fe(II) to aerated water, presumably by reactive intermediates formed in the reduction of oxygen by Fe(II). In solutions containing 0.06-5 mg/L Fe(II,III), over 90% of As(III) could be oxidized photochemically within 2-3 h by illumination with 90 W/m2 UV-A light. Citrate, by forming Fe(III) citrate complexes that are photolyzed with high quantum yields, strongly accelerated As(III) oxidation. The photoproduct of citrate (3-oxoglutaric acid) induced rapid flocculation and precipitation of Fe(III). In laboratory tests, 80-90% of total arsenic was removed after addition of 50 microM citrate or 100-200 microL (4-8 drops) of lemon juice/L, illumination for 2-3 h, and precipitation. The same procedure was able to remove 45-78% of total arsenic in first field trials in Bangladesh.
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Affiliation(s)
- S J Hug
- Swiss Federal Institute for Environmental Science and Technology (EAWAG), Postfach 611, Uberlandstrasse 133, CH-8600 Dübendorf, Switzerland.
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Bucheli-Witschel M, Egli T. Environmental fate and microbial degradation of aminopolycarboxylic acids. FEMS Microbiol Rev 2001; 25:69-106. [PMID: 11152941 DOI: 10.1111/j.1574-6976.2001.tb00572.x] [Citation(s) in RCA: 337] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Aminopolycarboxylic acids (APCAs) have the ability to form stable, water-soluble complexes with di- and trivalent metal ions. For that reason, synthetic APCAs are used in a broad range of domestic products and industrial applications to control solubility and precipitation of metal ions. Because most of these applications are water-based, APCAs are disposed of in wastewater and reach thus sewage treatment plants and the environment, where they undergo abiotic and/or biotic degradation processes. Recently, also natural APCAs have been described which are produced by plants or micro-organisms and are involved in the metal uptake by these organisms. For the two most widely used APCAs, nitrilotriacetate (NTA) and ethylenediaminetetraacetate (EDTA), transformation and mineralisation processes have been studied rather well, while for other xenobiotic APCAs and for the naturally occurring APCAs little is known on their fate in the environment. Whereas NTA is mainly degraded by bacteria under both oxic and anoxic conditions, biodegradation is apparently of minor importance for the environmental fate of EDTA. Photodegradation of iron(III)-complexed EDTA is supposed to be mostly responsible for its elimination. Isolation of a number of NTA- and EDTA-utilising bacterial strains has been reported and the spectrum of APCAs utilised by the different isolates indicates that some of them are able to utilise a range of different APCAs whereas others seem to be restricted to one compound. The two best characterised obligately aerobic NTA-utilising genera (Chelatobacter and Chelatococcus) are members of the alpha-subgroup of Proteobacteria. There is good evidence that they are present in fairly high numbers in surface waters, soils and sewage treatment plants. The key enzymes involved in NTA degradation in Chelatobacter and Chelatococcus have been isolated and characterised. The two first catabolic steps are catalysed by a monooxygenase (NTA MO) and a membrane-bound iminodiacetate dehydrogenase. NTA MO has been cloned and sequenced and its regulation as a function of growth conditions has been studied. Under denitrifying conditions, NTA catabolism is catalysed by a NTA dehydrogenase. EDTA breakdown was found to be initiated by a MO also which shares many characteristics with NTA MO from strictly aerobic NTA-degrading bacteria. In contrast, degradation of [S,S]-ethylenediaminedisuccinate ([S,S]-EDDS), a structural isomer of EDTA, was shown to be catalysed by an EDDS lyase in both an EDTA degrader and in a NTA-utilising Chelatococcus strain. So far, transport of APCAs into cells has only been studied for EDTA and the results obtained give strong evidence for an energy-dependent carrier system and Ca(2+) seems to be co-transported with EDTA. Due to their metal-complexing capacities, APCAs occur in the environment mostly in the metal-complexed form. Hence, the influence of metal speciation on various degradation processes is of utmost importance to understand the environmental behaviour of these compounds. In case of biodegradation, the effect of metal speciation is rather difficult to assess at the whole cell level and therefore only limited good data are available. In contrast, the influence of metal speciation on the intracellular enzymatic breakdown of APCAs is rather well documented but no generalising pattern applicable to all enzymes was found.
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Affiliation(s)
- M Bucheli-Witschel
- Swiss Federal Institute for Environmental Science and Technology, Department of Microbiology, Uberlandstrasse 133, CH-8600, Dübendorf, Switzerland
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Mazellier P, Bolte M. Heterogeneous light-induced transformation of 2,6-dimethylphenol in aqueous suspensions containing goethite. J Photochem Photobiol A Chem 2000. [DOI: 10.1016/s1010-6030(00)00198-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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