A03016: Investigation of the migration of metals from glazed ceramic ware

Study Duration: April 1998 to September 2003

Contractor: Central Science Laboratory

A wide range of glazed ceramic ware products is commercially available today from countries within the EC and as imports from the rest of the world. The diversity of these products, in terms of their colours and designs, is vast. The clays, and particularly the coloured glazes used in the manufacture of this type of ware, contain a variety of metals. Metals used in the glazes include cobalt for blue colours, chromium for green, cadmium, selenium and sulphur for red/yellow/orange, copper, magnesium, antimony and vanadium to give stability or depth to a colour and calcium and lead to adjust the tone of the colour. Little information is available with regard to the potential for migration of these metals when ceramic ware products are used in contact with food and drink.

Current UK legislation specifies limits for cadmium and lead migration from ceramics into foods, based upon the use of 4% acetic acid as a food simulant.

The aims of this project are to:

• Establish compliance with current legislation for the migration of lead and cadmium into the simulant 4% acetic acid (Directive 84/500/EEC) from a range of ceramic articles
• Identify which other elements migrate into this simulant
• Establish the validity of the current method of test by comparison of the results obtained using the simulant with those obtained for migration into foods under 'normal' and 'worst foreseeable' conditions of use

One hundred and eleven ceramic ware products will be purchased in duplicate and the standard migration test with 4% acetic acid applied. The acidic extracts will be subjected to multi-element analysis by inductively coupled plasma-mass spectrometry to measure the migration of metals. The elements migrating at relatively high levels (by comparison with 50 times the median value) will be identified and these elements selected for analysis in subsequent investigations. Those products showing higher levels of metal ions leaching into the acetic acid solution will be selected for further studies. Additional specimens will be purchased so that in total four test specimens of each article type were exposed to the 4% acetic acid.

Ceramic ware products are repeat use articles and the migration of the selected elements into a fresh portion 4% acetic acid will be determined to establish the effect of repeat use on the exposure. Also migration into acidic foods will be determined and the effects of the worst foreseeable conditions of use (e.g. marinating, baking, microwaving, dishwashing, scouring and thermal shock; any of which may result in cracking and crazing of glaze) investigated.

Compliance with current legislation for the migration of lead and cadmium into the simulant 4% acetic acid (EU Directive 84/500/EEC and BS 6748 (Clause 4 and Appendix)) was confirmed for each of the 111 products tested in duplicate. The migration into 4% acetic acid identified heterogenous test specimens of a given product.

Releaching studies showed variable product specific results, with some ceramic articles exhibiting increased migration on re-use, some lower levels and for several of the products the migration results obtained were at approximately the same level. Not all products exhibited the same pattern for all of the ions analysed.

For most of the elements and products studied migration into the acetic acid was observed to be either a good approximation or an overestimation of the migration of metal ions into acidic foodstuffs (not direct comparisons of exactly the same item). There were some exceptions, but follow-up studies revealed an overestimation of migration into acetic acid relative to foodstuffs.

All products tested complied with existing legislation. However, migration into 4% acetic acid identified heterogenous test specimens of a given product. As a result this work endorsed a recommendation that migration from more than one test specimen is investigated (n = 4) to confirm the suitability of a given product for contact with foodstuffs. This is addressed in the 'new' draft standard that has been produced since this project was commissioned. This draft states that the migration from four test specimens must be investigated in all cases in order to determine compliance and that each specimen (not only the average) must not release lead or cadmium above the limit value.

The migration into acetic acid and foods on repeat use increased for some of the ceramic products investigated. These results stress the importance of repeat use studies, in particular with migration into foods, to determine the suitability of a given product intended to be used in food contact applications. A product deemed acceptable on first use analysis may subsequently show greater migration levels such that it is deemed unacceptable following repeat use.

Migration studies into foods were carried out and in several cases clear differences existed between the migration into foods and into acetic acid simulant. Initial work suggested that migration into the foodstuff was underestimated by migration into acetic acid for several of the products. Additional work was carried out to compare the migration from four test specimens into acetic acid with that into tomato soup (n = 4) and apples (n = 4). In all cases although there was little migration, the migration into 4%acetic acid overestimated migration into the foods. Four percent acetic acid is therefore considered to be a suitable test simulant for the migration of metal ions from ceramic ware.

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk