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Accurate determination of hexavalent chromium in agricultural soil


Due to its carcinogenicity, hexavalent chromium is in the focus of environmental monitoring and different rules and legislation is meant to reduce its release to the environment. The determination of hexavalent chromium in soil is hampered by the potential reduction to Cr(III) occuring during the extraction from the solid sample.

The new study:
A group of researchers from Spain and Italy studied the effect of organic matter and iron content of different soils on the determination of hexavalent chromium. Using the conditions previously recommended by Fabregat, applying focused microwaves in an alkaline EDTA medium, complete reduction of Cr(VI) was observed when extracting chromium from real soil samples from Lombardia. The iron content of the soil was identified as one of the cause for the reduction. Fe(II) promotes the reduction of hexavalent chromium by acting as a redox catalyst in several reactions. The reduction of Cr(VI) by soil organic compounds is also facilitated by the presence of Fe(III): It is first reduced by humic substances and then oxidized by Cr(VI) in a redox cycle. Under strong alkaline extraction conditions, humic compounds are released from soils and sediments. At a pH of 10, the solubility of Fe(III) is also increased.

The researchers modified the extraction conditions in order to reduce the Cr(VI) reduction. Especially a second microwave heating step to 110°C lasting 12 min. was ommitted, leading to significantly lower Cr(VI) reduction.  Using the milder extraction conditions, speciated isotope dilution analysis could be applied to accurately determine the original Cr(VI) content.

The new study:

Laura Guidotti, Silvia Queipo Abad, Pablo Rodríguez-GonzálezJ. Ignacio García Alonso, Gian Maria Beone, Quantification of Cr(VI) in soil samples from a contaminated area in northern Italy by isotope dilution mass spectrometry, Environ. Sci. Pollut. Res. (2015) doi: 10.1007/s11356-015-4963-z

Related studies (newest first):

Mesay Mulugeta Wolle, G.M. Mizanur Rahman, H.M. Skip Kingston, Matt Pamuku, Optimization and validation of strategies for quantifying chromium species in soil based on speciated isotope dilution mass spectrometry with mass balance, J. Anal. At. Spectrom., 29 (2014) 1640-1647. DOI: 10.1039/c4ja00133h

Tea Zuliani, Janez Ščančar , Radmila Milačič , The use of stable isotopes for Cr(VI) determination in silty-clay soil solution, Anal. Bioanal. Chem., 405 (2013) 7231–7240. doi: 10.1007/s00216-013-7172-y  

J. Malherbe, M.P. Isaure, Fabienne Séby, R.P. Watson, P. Rodriguez-Gonzalez, P.E. Stutzman, C.W. Davis, C. Maurizio, N. Unceta, J.R. Sieber, S.E. Long, Olivier F.X. Donard, Evaluation of hexavalent chromium extraction method EPA method 3060A for soils using XANES spectoscopy, Environ. Sci. Technol., 45 (2011) 10492–10500. doi: 10.1021/es201002g

Ruth E. Wolf and Stephen A. Wilson, Evaluation of Extraction Methods for Hexavalent Chromium Determination in Dusts, Ashes, and Soils, U.S. Geological Survey, Open-File Report 2010–1243.  

N. Unceta, Fabienne Séby, J. Malherbe, Olivier F.X. Donard, Chromium speciation in solid matrices and regulation: a review, Anal. Bioanal. Chem., 397 (2010) 1097–1111. doi: 10.1007/s00216-009-3417-1

M. Pettine, S. Capri, Digestion treatments and risks of Cr(III)-Cr(VI) interconversions during Cr(VI) determination in soils and sediments—a review, Anal. Chim. Acta., 540 (2005) 231–238. doi: 10.1016/j.aca.2005.03.040

P.R. Wittbrodt, C.D. Palmer, Reduction of Cr(VI) in the presence of excess soil fulvic acid, Environ. Sci. Technol., 29 (1995) 255–263. doi: 10.1021/es00001a033

P.R. Wittbrodt, C.D. Palmer, Effect of temperature, ionic strength, background electrolytes, and Fe(III) on the reduction of hexavalent chromium by soil humic substances, Environ. Sci. Technol., 30(8) (1996) 2470–2477. doi: 10.1021/es950731c

 Related EVISA Resources

 Link Database: Toxicity of hexavalent chromium (chromate)
 Link Database: Methods for chromium speciation analysis
Link Database: All about hexavalent chromium
Link Database: US EPA Method 6800
Journals Database: Journals related to soil science
Brief summary: ICP-MS: A versatile detection system for trace element and speciation analysis
Brief summary: LC-ICP-MS - The most often used hyphenated system for speciation analysis
Brief summary: Standard methods for chromium speciation analysis
Material Database: Soil reference materials certified for chromium
Material Database: Certified reference materials for Cr(VI)

 Related EVISA News

February 15, 2010: Chromium speciation in solid matrices
February 3, 2009: New Reference Material for Hexavalent Chromium in Contaminated Soil
January 15, 2008: Species-specific isotope dilution analysis has been adopted as an official method under US legislation
November 15, 2005: NIST/EPA/NJ DEP embark on the preparation of a soil reference materials for chromium speciation

last time modified: June19, 2016


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