efsa-opinion-chromium-food-drinking-water

Chromium in food and drinking water
percentage of conversion from Cr(III) (LOD of 0.4 µg/L) to Cr(VI) (LOD of 0.04 µg/L) increased
from 5.9 % to 9.3 % with increase of the concentration of Cr(VI) and Cr(III) from 1 to 100 µg/L,
while the reverse conversion from Cr(VI) to Cr(III) was observed within a range between 0.9 % and
1.9 %. The equilibrium constant for the conversion was found to be independent of the initial
concentrations of Cr(III) and Cr(VI) and in the range of 1.0 (at pH 3) to 1.8 (at pH 10).
3.2.3. Analytical quality assurance: performance criteria, reference materials, validation and
proficiency testing
Some performance criteria (limits of detection and quantification (LOD/LOQ), method bias and
recovery, measurement uncertainties and analytical quality assurance) for the determination of total
chromium and chromium species content in food are laid down in the EN 13804, 2013. The LOD and
LOQ will vary with the analytical technique, the sample mass, the laboratory and the food matrix.
For the determination of chromium in water intended for human consumption, EU Council Directive
98/83/EC indicates that the performance characteristics for the method of analysis used must, as a
minimum, be capable of measuring concentrations equal to the parametric value with a trueness,
precision and limit of detection that must not exceed 10 % of the parametric value (i.e. 5 μg/L).
To demonstrate the trueness (i.e. systematic error) and precision (i.e. random error) of trace element
data, one of the important criteria is the reporting of correct (and precise) data for the chromium
content of certified reference materials that closely match the matrix of the samples under
investigation (Jorhem, 2004). Several standard or certified reference materials (SRMs and CRMs) are
available for total chromium (Appendix B, Table B1). There is a current need for CRMs certified for
different chromium species in water and other foodstuffs.
Two fully validated, European standardised methods are available for the determination of total
chromium in food by graphite furnace atomic absorption spectrometry (GFAAS) after pressure
digestion wih a LOQ of about 0.04 to 0.16 mg/kg according to the sample weight (EN 14083:2003) or
by atomic absorption spectrometry (FAAS or GFAAS), but GFAAS is recommended) after ash drying
(EN 14082:2003). Four standardised methods are available for the determination of total chromium in
water by flame or graphite furnace atomic absorption spectrometry (FAAS or GFAAS (EN 1233:1996
or ISO 9174:1998, EN ISO 15586: 2004), by inductively coupled plasma optical emission
spectrometry (ICP-OES) (EN ISO 11885:2009) or mass spectrometry (ICP-MS) (EN ISO 17294-
2:2003). Similar sensitivity can be obtained by GFAAS, ICP-OES and ICP-MS methods (LOD of
0.5 µg/L).
No standardised methods are available for determination of Cr(VI) in food while two methods are
suitable for various types of water and based on colorimetric reactions with 1,5-diphenylcarbazide.
Namely, the continuous flow analysis (CFA) and spectrometric detection method
(EN ISO 23913:2006) and the photometric method (EN ISO 18412:2006) can be applied for drinking
water in the concentration range of 2 to 20 µg/L and 2 to 50 µg/L, respectively.
A number of proficiency testing schemes (PTS) are regularly organised by several providers for total
chromium in food and for both total chromium and Cr(VI) in water to demonstrate and maintain
analytical quality assurance. However, no PTS are available for Cr(VI) in food.
Between 2010 and 2012, Food Analysis Performance Assessment Scheme (FAPAS) organized several
proficiency tests on the determination of total chromium in food e.g. in infant cereal (FAPAS ® reports
07183, 07165), infant formula (FAPAS ® report 07177, 07159), soft drinks (FAPAS ® report 07155)
and milk powder (FAPAS ® report 07138). The results indicate that most of the participating
laboratories, although applying different methods, are capable of reliably analysing total chromium
(range 67-98 % satisfactory results, 42 to 60 participants) at the level of interest.
Between 2012 and 2013, FAPAS organized several proficiency tests on the determination of total
chromium in potable water (LEAP ® Scheme reports CHEM107, 109, 111V2 and 112). 88-95 % of
17 to 25 participants obtained satisfactory results at the level of interest (range 9.91-41.4 µg/L).
EFSA Journal 2014;12(3):3595 30