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Metals in baby food and infant formulae - Cr speciation

Project Code: C02068

23/02/2007

Central Science Laboratory
Lewis, D

The FSA requested information regarding the speciated forms of arsenic and mercury in samples collected, as part of Project CO2072 (survey of metals and other elements in weaning foods and formula for infants). Determination of total and inorganic arsenic was performed by CSL, and total and methylmercury performed by the University of Pau, France.

27 samples were analysed for total and inorganic arsenic, and 11 samples were analysed for total and methylmercury . 7 samples were analysed for both analytes.

The data was as expected; samples containing fish products had the highest levels of methylmercury; samples containg rice of rice-derived product contained the highest percentage of inorganic arsenic.

The speciation of the toxic form of chromium, Cr(^VI), is not widely reported in solid food matrices. In the study reported here, the FSA requested the development of a methodology, suitable for the analysis of Cr(^VI) in samples from the *Survey of Metals in Weaning Foods and Formulae for Infants (2006)*.

Two methods, based on procedures for the speciation of Cr(^VI) in environmental matrices, plus two in-house methods were assessed, and modified for use with a range of solid foodstuffs, typically consumed by infants. The criteria by which they were assessed were:

Extraction efficiency
Preservation of the Cr(^VI) chemical form
Multi-matrix capability
Sensitivity

Of the four methods assessed, one, based on a strong alkaline digestion using NaOH (0.5M) met the above criteria, giving 82 to 103% recovery of spike from reagents and 2 food matrices. However, data obtained from a range of other spiked foods showed that added Cr(^VI) was immediately converted to another, unidentified, chemical form. Timebased studies showed that this conversion occurred within the time required to achieve an analysable extraction, i.e., less than 2 hours. The mechanism of this reaction was not established, but is expected to be due to the reduction of the hexavalent species in the presence of organic material. However, why this effect is not observed with all food matrices is not known.

The conclusion from the overall data was that; although the developed method itself did not affect the speciation of Cr(^VI) (as established from spiked reagent solutions), the behaviour of the analyte was highly unpredictable when the extraction included certain foods. Therefore, as meaningful data was unlikely to be obtained from the methodology, it should not be used with the Infant Foods survey.

The Fod Survey Information Sheet for this survey can be found at: http://www.food.gov.uk/multimedia/pdfs/fsis1706.pdf

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