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Chromium speciation in solid matrices


Chromium  (Cr)  is  widely used in industry for different applications such as pigments, metal plating, or leather tanning and in chemical production such as synthesis and as catalysts. As a result of its use and chemistry, different species of chromium can be released into the environment (soil, surface, and ground waters) and may lead to human exposure. Chromium can exist in several valency states between 0 and VI. However, only trivalent and hexavalent chromium species are stable enough to occur in the environment. Cr(III) is considered an essential micronutrient in the human diet and is widely used as a nutritional supplement for humans and animals. Nevertheless, it has been demonstrated that Cr(III) is capable of eliciting eczema at low concentrations and of causing DNA damage in cell-culture systems.

In contrast, Cr(VI) is much more toxic than Cr(III) for both acute and chronic exposure. It  is  suspected of being extremely toxic after inhalation and oral exposure with effects on the respiratory tract, liver, kidney, gastrointestinal and immune systems, and possibly the blood, and dermal exposure may cause contact dermatitis, sensitivity, and ulceration of the skin.  Cr(VI) has been recognised as a highly toxic species and classified as a human carcinogen by the EPA and as a class I human carcinogen by the International Agency for Research on Cancer (IARC).

Because of its toxicity and its high mobility in the environment, several directives have been adopted by the European Commission to limit the release of Cr(VI) into the environment, and to protect workers exposed to chromium and end-consumers of manufactured products. These directives have promoted the development of standard methods at the European and international levels that include the determination of hexavalent chromium.

Review of Speciation Analysis
A group of experts from France and Spain have now reviewed existing methodology for the speciation of chromium in solid matrices.  

Standard method
   EPA 3060A
   EPA 6800
   PD CEN/TR 14589
Workplace air
INRS (France)
TLV=0.05 mg Cr(VI)m-3
ISO 16740
TLV=0.05 mg soluble Cr(VI)m-3
TLV=0.01 mg insoluble Cr(VI)m-3
NIOSH 7604
 OSHA 2006 (USA)
PEL 5 µgm-3
NIOSH 7703
   NIOSH 7605
2 mg/kg soluble Cr(VI)
TRGS 613

EN 196-10
Cr(VI)+Pb+Cd+Hg < 100 mg kg-1
ICG (for glass only)
0.02 mg/kg Cr(VI) (dry materials)

0.005 mg/kg Cr(VI) (liquid materials)
Corrosion protection layers (end of life vehicles)
2 g Cr(VI)/vehicle
nothing after July 1st 2007
EN 15205
Electronic waste (WEEE/RoHS)
1 g/kg Cr(VI)
nothing in products produced after July 1st 2007

IEC 62321

Direct X-ray based techniques (XPS, XANES, XRD) are generally regarded as the reference methods for chromium speciation analysis since they are non-destructive, however their limited sensitivity (around 0.1 %) and the fact that often only the surface will be analysed is limiting their application.
While the speciation methodology applied for solutions often shows appropriate analytical capabilities, solid matrices call for an additional extraction (leaching) procedure that may alter the original species distribution. Unfortunately, a common standard method for each solid matrix does not always exist. The most widespread extraction procedure is using  NaOH-Na2CO3 solutions in combination with hot-plate extraction, minimizing but not fully avoiding method-induced oxidation and reduction.  Furthermore, for most matrices, no certified reference material is available for quality-control purposes.  Several studies  suggest  that  species-specific isotope dilution analysis (SIDMS)  could  be  a  suitable  tool  for correction of these interconversions when the equilibration between sample species and spike species is achieved.

 The original review

 N. Unceta, Fabienne Séby, J. Malherbe, Olivier F. X. Donard, Chromium speciation in solid matrices and regulation: a review, Anal. Bioanal. Cem., 2010, ahead of print. doi: 10.1007/s00216-009-3417-1

 EVISA Resources

Link database: Analytical methods for chromium speciation
Link database: Toxicity of chromium valency species
Link database: Legislation related to chromium
Materials database: Certified reference materials for Cr(VI)
Summary: The role of elemental speciation in legislation

EVISA News related to Chromium species

February 3, 2009: New Reference Material for Hexavalent Chromium in Contaminated Soil
September 16, 2008: New method for the determination of hexavalent chromium in anti-corrosion coating
January 15, 2008: Species-specific isotope dilution analysis has been adopted as an official method under US legislation
May 17, 2007: Hexavalent Chromium in Drinking Water Causes Cancer in Lab Animals
April 12, 2007: OSHA Agrees to Monitor Worker Exposure to Hexavalent Chromium-Containing Cement
November 8, 2006: Double spiking species-specific isotope dilution result calculations simplified
October 4, 2006: OSHA Issues Hexavalent Chromium Guidance for Small Businesses
June 8, 2006: Scientific journal adds fuel to ongoing chromium debate
February 28, 2006: OSHA Issues Final Standard on Hexavalent Chromium
November 15, 2005: NIST/EPA/NJ DEP embark on the preparation of a soil reference materials for chromium speciation
March 19, 2005: Phasing out of chromated copper arsenate as a wood preservative

last time modified: February 15, 2010


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