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The Determination of Hexavalent Chromium in Airborne Particulate Matter in Presence of High Amounts of Trivalent Chromium


Chromium speciation is an extensively studied topic due to the pronounced difference of toxicity of the two most stable oxidation states Cr(III) and Cr(VI). While Cr(III) is considered to play a beneficial role in the metabolism of glucose, Cr(VI) is classified as Group 1 carcinogen. Since chromium is used in many industrial sectors, the potential risk associated with chromium exposure of workers call for critical attention. For a reliable risk assessment, accurate quantification of Cr(VI) in all media workers may be exposed to is mandatory. Unfortunately, accurate chromium speciation analysis is hampered by easy interconversion between Cr(III) and Cr(VI) during the different steps of analysis such as sample collection, extraction and separation. Such interconversion is especially critical, when samples do contain high amounts of Cr(III), which is the case in the leather industry where Cr(III) is used for tanning. Cr-tanned leather contains up to 3-5% Cr(III), resulting in high Cr content of air particulates resulting from leather shavings. Accurate determination of Cr(VI) in such samples is very challenging, since the slightest oxidation of Cr(III) during analysis might compromise the speciation analysis.   

In the framework of occupational safety and health, the classical approach for exposure assessment is based on the active personal sampling of airborne particles and subsequent analysis to determine the Cr(VI) levels. Within the EU the Occupational Exposure Limit set under Directive 2017/2398 is 10 µg/m3 (8-h time-weighted average) until January 17, 2025; after that period the OELV will be limited at 5 µg/m3. The current official methods for the determination of Cr(VI) in such samples are the ISO 16740:2005 standard, NIOSH 7600-7605, and OSHA ID-215. All three protocols are similar with respect to use PVC filters for sample collection, alkaline extraction at 95°C and colorimetric detection using 1,5-diphenylcarbazide. While the methods are meant to selectively leach Cr(VI), bias produced by interconversion of Cr(III) during extraction has been observed.

The new study:
In view of these problems, researchers from Italy and the UK aimed at the development of an alternative protocol. They started with the use of a liquid chromatography inductively coupled plasma mass spectrometry apparatus (LC-ICP-MS), adapting an original separation strategy based on Cr(OH)3 head-column stacking in order to tolerate high concentration of Cr(III) up to 10 mg/kg, followed by separation on an anionic column. A species-specific isotope-enriched spike addition technique for both oxidation states of chromium was used that allowed for the study of Cr(III)/Cr(VI) interconversions during the extraction step. Detection was based on ICP-MS operated in the Kinetic Energy Discrimination (KED) mode, using He as collision gas, resulting in limit of detection of 0.51 µg/kg.

Using this method, it was verified that the official extraction protocols always yield false positive values for samples collected in the leather industrial environment. In order to avoid interconversion during extraction as much as possible, a novel procedure was developed based on a 48-h extraction at room temperature using a pH-8 phosphate buffer. It was verified that even insoluble chromates are quantitatively extracted after 48 h. In order to avoid redox reactions induced by coextracted  reductants or oxidants, the authors added a Fe(II)/Fe(III) redox buffer to the extracts. Using the developed protocol, occupational exposure samples were analysed. All obtained results for Cr(VI) were below the limit of quantification.

The authors concluded that their method has been proven to be very robust in the challenging case study of leather industries.

The original study

Andrea Spinazzč, Davide Spanu, Pietro Della Bella, Cristina Corti, Francesca Borghi, Giacomo Fanti, Andrea Cattaneo, William Robert Wise, Stefan John Davis, Domenico Maria Cavallo, Sandro Recchia, On the Determination of Cr(VI) in Cr(III)-Rich Particulates: From the Failure of Official Methods to the Development of an Alternative Protocol. Int. J. Environ. Res. Public Health 19 (2022) 12111. DOI: 10.3390/ijerph191912111

Instrumentation used:

Thermo Scientific - ICAP Q ICP-MS

Related studies (newest first)

T. Santonen, S.P. Porras, B. Bocca, R. Bousoumah, R.C. Duca, K.S. Galea, L. Godderis, T. Göen, E. Hardy, T. Iavicoli, et al., HBM4EU chromates study-Overall results and recommendations for the biomonitoring of occupational exposure to hexavalent chromium. Environ. Res., 204 (2022) 111984. DOI: 10.1016/j.envres.2021.111984

D. Spanu, D. Monticelli, G. Binda, C. Dossi, L. Rampazzi, S. Recchia, One-minute highly selective Cr(VI) determination at ultra-trace levels: An ICP-MS method based on the on-line trapping of Cr(III). J. Hazard. Mater., 412 (2021) 125280. DOI: 10.1016/j.jhazmat.2021.125280

C.C. Alvarez, M.E. Bravo Gómez, A. Hernández Zavala, Hexavalent chromium: Regulation and health effects. J. Trace Elem. Med. Biol. 65 (2021) 126729. DOI: 10.1016/j.jtemb.2021.126729

L. Huang, C.H. Yu, P.K. Hopke, J.Y. Shin, Z. Fan, Trivalent chromium solubility and its influence on quantification of hexavalent chromium in ambient particulate matter using EPA method 6800. J. Air Waste Manag. Assoc., 64 (2014) 1439–1445. DOI: 10.1080/10962247.2014.951745

L. Huang, C.H. Yu, P.K. Hopke, P.J. Lioy, B.T. Buckley, J.Y. Shin, Z. Fan, Measurement of Soluble and Total Hexavalent Chromium in the Ambient Airborne Particles in New Jersey. Aerosol. Air Qual. Res., 14 (2014) 1939–1949. DOI: 10.4209/aaqr.2013.10.0312  

L. Huang, Z. Fan, C.H. Yu, P.K. Hopke, P.J. Lioy, B.T. Buckley, L. Lin, Y. Ma, Interconversion of Chromium Species During Air Sampling: Effects of O3, NO2, SO2, Particle Matrices, Temperature, and Humidity. Environ. Sci. Technol., 47 (2013) 4408–4415. DOI: 10.1021/es3046247

M.A. Torkmahalleh, L. Lin, T.M. Holsen, D.H. Rasmussen, P.K. Hopke, The Impact of Deliquescence and pH on Cr Speciation in Ambient PM Samples. Aerosol Sci. Technol., 46 (2012) 690–696. DOI: 10.1080/02786826.2011.654285

N. Fabregat-Cabello, P. Rodríguez-González, A. Castillo, J. Malherbe, A.F. Roig-Navarro, S.E. Long, J.I.G. Alonso, Fast and Accurate Procedure for the Determination of Cr(VI) in Solid Samples by Isotope Dilution Mass Spectrometry. Environ. Sci. Technol., 46 (2012) 12542–12549. DOI: 10.1021/es3022864

Q. Meng, Z. Fan, B. Buckley, L. Lin, L. Huang, C.-H. Yu, R. Stiles, L. Bonanno, Development and evaluation of a method for hexavalent chromium in ambient air using IC-ICP-MS. Atmos. Environ., 45 (2011) 2021–2027. DOI: 10.1016/j.atmosenv.2011.02.009

N. Zeiner, I. Rezic, D. Ujevic, I. Steffan, Determination of total chromium in tanned leather samples used in car industry. Coll. Antropol., 35 (2011) 89–92. available from https://www.researchgate.net

N. Fontaine, Y. Clement, N. Blanc, C. Demesmay, Hexavalent chromium release from leather over time natural ageing vs accelerated ageing according to a multivariate approach. J. Hazard. Mater., 368 (2019) 811–818. DOI: 10.1016/j.jhazmat.2018.12.112

N. Unceta, F. Séby, J. Malherbe, O.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

ISO 16740:2005; Workplace Air—Determination of Hexavalent Chromium in Airborne Particulate Matter—Method by Ion Chromatography and Spectrophotometric Measurement Using Diphenyl Carbazide. International Organization for Standardization: Geneva, Switzerland, 2005.

Y. Li, Selective determination of airborne hexavalent chromium using inductively coupled plasma mass spectrometry. Talanta, 57 (2002) 1143–1153. DOI: 10.1016/S0039-9140(02)00196-0

D. Huo, H.M. “Skip” Kingston, Correction of Species Transformations in the Analysis of Cr(VI) in Solid Environmental Samples Using Speciated Isotope Dilution Mass Spectrometry. Anal. Chem., 72 (2000) 5047–5054. DOI: 10.1021/ac000008r

J.M. Boiano, M.E. Wallace, W. Karl Sieber,J.H. Groff, J. Wang, K. Ashley, Comparison of three sampling and analytical methods for the determination of airborne hexavalent chromium. J. Environ. Monit., 2 (2000) 329–333. DOI: 10.1039/B002456M

O. Nygren, J.E. Wahlberg, Speciation of chromium in tanned leather gloves and relapse of chromium allergy from tanned leather samples. Analyst, 123 (1998) 935–937. DOI: 10.1039/A707458A

 Related EVISA Resources
Brief summary: Standard methods for chromium speciation analysis
Material Database: Certified reference materials for Cr(VI)

Related EVISA News

April 12, 2007: OSHA Agrees to Monitor Worker Exposure to Hexavalent Chromium-Containing Cement
October 4, 2006: OSHA Issues Hexavalent Chromium Guidance for Small Businesses
February 28, 2006: OSHA Issues Final Standard on Hexavalent Chromium

last time modified: November 7, 2022


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