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      The Effect of pH and Biogenic Ligands on the Weathering of Chrysotile Asbestos: The Pivotal Role of Tetrahedral Fe in Dissolution Kinetics and Radical Formation

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          Abstract

          Chrysotile asbestos is a soil pollutant in many countries. It is a carcinogenic mineral, partly due to its surface chemistry. In chrysotile, Fe II and Fe III substitute Mg octahedra (Fe[6]), and Fe III substitutes Si tetrahedra (Fe[4]). Fe on fiber surfaces can generate hydroxyl radicals (HO .) in Fenton reactions, which damage biomolecules. To better understand chrysotile weathering in soils, net Mg and Si dissolution rates over the pH range 3.0–11.5 were determined in the presence and absence of biogenic ligands. Also, HO . generation and Fe bulk speciation of pristine and weathered fibers were examined by EPR and Mössbauer spectroscopy. Dissolution rates were increased by ligands and inversely related to pH with complete inhibition at cement pH (11.5). Surface‐exposed Mg layers readily dissolved at low pH, but only after days at neutral pH. On longer timescales, the slow dissolution of Si layers became rate‐determining. In the absence of ligands, Fe[6] precipitated as Fenton‐inactive Fe phases, whereas Fe[4] (7 % of bulk Fe) remained redox‐active throughout two‐week experiments and at pH 7.5 generated 50±10 % of the HO . yield of Fe[6] at pristine fiber surfaces. Ligand‐promoted dissolution of Fe[4] (and potentially Al[4]) labilized exposed Si layers. This increased Si and Mg dissolution rates and lowered HO . generation to near‐background level. It is concluded that Fe[4] surface species control long‐term HO . generation and dissolution rates of chrysotile at natural soil pH.

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          Rhizosphere carboxylates and morphological root traits in pasture legumes and grasses

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            Author and article information

            Contributors
            w.d.c.schenkeveld@uu.nl
            Journal
            Chemistry
            Chemistry
            10.1002/(ISSN)1521-3765
            CHEM
            Chemistry (Weinheim an Der Bergstrasse, Germany)
            John Wiley and Sons Inc. (Hoboken )
            0947-6539
            1521-3765
            04 February 2019
            01 March 2019
            : 25
            : 13 ( doiID: 10.1002/chem.v25.13 )
            : 3286-3300
            Affiliations
            [ 1 ] Department of Environmental Geosciences University of Vienna Althanstrasse 14 (UZA II) 1090 Vienna Austria
            [ 2 ] Institute of Solid State Physics TU Wien Wiedner Hauptstrasse 8–10 1040 Vienna Austria
            [ 3 ] Institute of Pharmacology and Toxicology University of Veterinary Medicine, Vienna Veterinärplatz 1 1210 Vienna Austria
            [ 4 ] Current address: Copernicus Institute of Sustainable Development Faculty of Geosciences Utrecht University Princetonlaan 8A 3584 CB Utrecht The Netherlands
            Author information
            http://orcid.org/0000-0002-1531-0939
            Article
            CHEM201804319
            10.1002/chem.201804319
            6582442
            30417458
            b97b9b46-056b-4258-a322-78397d425e79
            © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

            This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

            History
            : 24 August 2018
            : 08 November 2018
            Page count
            Figures: 8, Tables: 3, References: 100, Pages: 15, Words: 0
            Funding
            Funded by: University of Vienna
            Award ID: uni:docs program
            Categories
            Full Paper
            Full Papers
            Redox Chemistry
            Custom metadata
            2.0
            chem201804319
            March 1, 2019
            Converter:WILEY_ML3GV2_TO_NLMPMC version:5.6.2.1 mode:remove_FC converted:17.04.2019

            Chemistry
            asbestos,iron,radical reactions,redox chemistry,silicates
            Chemistry
            asbestos, iron, radical reactions, redox chemistry, silicates

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