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Mixed Cr(III)-Fe(III) (oxy)hydroxides are important Cr-bearing phases in natural, unpolluted soil. Fires frequently affect large areas of land around the world, causing the temporary development of elevated soil temperatures. This study examines the hypothesis that heating Cr(III)-Fe(III) (oxy)hydroxides at temperatures which occur in surface soils during fires can drive rapid oxidation of Cr(III) to hazardous Cr(VI). To test this, poorly-ordered Cr(III)x-Fe(III)1-x (oxy)hydroxides, with x spanning 0.1 to 0.9, were heated at up to 800 °C for 2 h. Heating at 400-800 °C produced a highly crystalline hematite-eskolaite solid-solution (FeIII2-nCrIIInO3, where n ranges from 0 to 2). Chromium K-edge X-ray absorption spectroscopy showed that during heating up to ∼40% of the initial Cr(III) was oxidized to Cr(VI), with the greatest extent of Cr(VI) formation occurring at 200-400 °C. At these temperatures, a substantial proportion (17%-70%) of the newly-formed Cr(VI) was exchangeable (i.e. extracted by a pH 7.2, 10 mM PO43- solution). This suggests that much of the Cr(VI) formed by heating of Cr(III)x-Fe(III)1-x (oxy)hydroxides at 200-400 °C is likely to be relatively mobile in fire-impacted soils. The results of this study provide new insights into a potentially-important pathway for the in-situ formation of Cr(VI) in soil.
Pubmed ID: 30716546
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Athena is a web-based application that warehouses disparate datatypes related to the control of gene expression. Athena provides several features to enable exploration of the regulatory mechanisms of Arabidopsis gene control. The first main tool we provide is visualization of promoter domains of selected genes. Database crossreference for these transcription factors is provided as well as a statistical test for enrichment of binding activity within the set of selected promoters. The data mining tools in Athena allow for selection of sets of genes based on two different factors. -Genes can be select by specifying a set of binding factors whose putative sites must be present within all of those genes'' promoter regions. -Alternatively, genes can be selected using Gene Ontology annotations. Both GO (Gene Ontology) Slim terms and Gene Ontology terms are available. One can select a set of genes by either choosing a union of the genes annotated by a selected set of Slim terms or Gene Ontology terms. The selected gene''s putative binding factors are listed, including enrichment data. Furthermore, enriched presence of Gene Ontology terms is given. The analysis suite provides both enhanced data mining tools for selecting genes as well as several data displays.
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