HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Supplement Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Schmidt, G. T. Articles by Kersten, M. PubMed PubMed Citation Articles by Schmidt, G. T. Articles by Kersten, M. GeoRef GeoRef Citation Agricola Articles by Schmidt, G. T. Articles by Kersten, M. Related Collections Batch Studies Toxic Trace Metals Geochemical Processes Heavy Metals Soil Pollution

TECHNICAL REPORTS

Heavy Metals in the Environment

Speciation and Mobility of Arsenic in Agricultural Lime

^a Environmental Geochemistry Group, Institute of Geosciences, Becherweg 21, Johannes Gutenberg-Univ., 55099 Mainz, Germany
^b present address: Karl Winnacker Institute, Dechema e.V., Theodor-Heuss-Allee 25, 60486 Frankfurt am Main, Germany

^* Corresponding author (kersten{at}uni-mainz.de).

Received for publication October 6, 2008. Agricultural liming materials are used to correct soil acidity and to improve plant growth and microbial functionality. A relatively low-grade agricultural lime was found to contain up to 125 mg kg^–1 arsenic (As), which is above any fertilizing materials code threshold. The color of the milled material is brown due to ample oxide dendrites. Microprobe elemental maps confirmed that these accessory oxide mineral phases are responsible for the elevated As concentrations in the limestone. The black Mn-bearing dendrites contain minor amounts of As, whereas the brown Fe-bearing dendrites contain the major part of the As inventory, with an Fe/As molar ratio around 100. Because the elemental maps represent only a few sample regions of interest (ROI), the results are corroborated by a bulk five-step sequential extraction of the lime, which suggests that a majority of the As is bound to acid-reducible phases. Because repartitioning of the As oxyanion during extraction cannot be ruled out, X-ray absorption spectroscopy with micrometer resolution (µ-XAS) was used as a solid-state speciation analysis approach. The µ-XAS results at the Fe K-edge for the selected ROIs revealed the brown dendrites to consist of ferrihydrite and goethite, whereas those at the As K-edge revealed that the pentavalent As species arsenate predominates, with As-Fe distance and coordination indicating binding as a mononuclear inner-spheric adsorbate complex. Batch experiments with soil exposed to submerged conditions of up to 41 d revealed a negligible As release rate from the lime (approximately 40 ng kg^–1 d^–1). The results of this study corroborate regulatory codes that set the permissible As content in agricultural lime relative to the respective Fe content.

Abbreviations: ALS, Advanced Light Source • E₀, edge energy in a X-ray absorption spectroscopy energy scan • EPMA, electron probe X-ray microanalysis • EXAFS, extended X-ray absorption fine structure spectroscopy • HG-AAS, hydride generation atomic absorption spectrometry • N, coordination number of EXAFS scattering path shells • ROI, region of interest • RSF, radial structure function • XANES, X-ray absorption near-edge structure • XAS, X-ray absorption spectroscopy • XRD, X-ray diffractometry • XRF, X-ray fluorescence spectroscopy • ², Debye Waller Factor of EXAFS scattering path shells