A03007: Migration test protocols for electroplated and dipped metalware intended for food contact
Wednesday 18 June 2003
This research project investigates the extent of metal migration into food from plated metal products used in the kitchen, in order to produce recommendations for testing metalware cooking products.
Background
Metal products, such as pans and trays, used in the kitchen may be covered with a layer of metal or non-stick coating. Metal layers are applied by either electroplating or dipping. During use of the metal-coated utensils or cookware, metals can migrate into food. The conditions of use will influence the levels of metal migrating. For example, more migration may be observed when the article is exposed to an acidic foodstuff (metal ions will be most soluble in acidic foods). Longer contact times and higher exposure temperatures will also result in increased migration. Currently no migration tests are recommended for these food contact materials.
The testing of plated articles has long posed a problem to laboratories as there is no defined methodology for this class of food contact materials. In general testing is carried out into either 3 per cent acetic acid, as recommended to test plastics in contact with acidic foods, or 4 per cent acetic acid as recommended to test for metal release from ceramics. One aim of this project was to establish whether or not acetic acid is a suitable simulant for metalware products (in that it closely approximates or over-estimates migration into food), or if other simulants are more suitable. Another objective was to make recommendations that would provide a sound basis for the development of a protocol to test metalware for potential metal release (migration) to foods. Combinations of simulants and exposure conditions (e.g. time, temperature, number of exposures) were studied in order to obtain a reliable indication of the migration (which metals and at which levels) that may be expected to occur into foods.
Research Approach
Twenty-seven metalware items covering a range of cookware, kitchen tools and gadgets for use in the home were purchased from retail outlets and the metals present in their outer layer were identified. From these, nine products were selected for the migration studies. These included tin, chromium and nickel-containing products. The migration of metal ions into foods on single and repeat use (with scouring between use) was recorded. The foodstuffs and exposure conditions to which the metalware articles were exposed depended on the use of the product. For each application the most acidic food that the product may be exposed to and the worst foreseeable conditions of use were investigated.
Results were compared with migration into a range of potential simulants; acetate buffers pH 3.5-6.0, citrate buffers pH 4.0-6.5, phosphate buffers pH 3.0-8.0, water, aqueous acetic acid (3 and 4 per cent), aqueous citric acid (3 and 4 per cent) and aqueous phosphoric acid (0.1 per cent). The most appropriate simulant (i.e. the one whose use led to the best estimate of migration) was selected from the data obtained. This allowed recommendations for testing metalware food articles to be derived.
Results and findings
The migration of metal ions depended on the exposure conditions and the class of foodstuff. Of all the simulants investigated, 4 per cent acetic acid was the most suitable potential simulant for the prediction of migration into acidic foodstuffs under worst case exposure conditions (elevated temperatures and repeat use). Exposure to 4 per cent acetic acid has been demonstrated to be very severe, with respect to both the dissolution of the surface layer and subsequent attack of the underlying substrate. Therefore exposure to this simulant should determine, in all cases, the worst case migration of any toxic metals (e.g. lead, cadmium, mercury) which should not be released into foods under any exposure conditions. However this was not the case for the other foodstuffs investigated. In some cases the migration into four per cent acetic acid overestimated migration into food. This is thought to be due to the less acidic foodstuff to which the products were exposed and the temperature conditions that were applied. Acetic acid is not a suitable simulant for these applications.
Initial exposure to the acidic simulants resulted in considerable migration of those metal ions present in the outer metal layer of the products, with subsequent exposure resulting in increasing migration of the base metal. The same trend was observed with exposure to foodstuffs on repeat use. Between-specimen variability of coating thickness and coverage resulted in differences in the migration for duplicate specimens of a given product. Therefore it is proposed that any recommendations for migration testing should investigate replicate test specimens.
The results from this project enable recommendations to be made which should allow the establishment of a protocol for testing metalware articles for metal release (migration) to foods. In summary, the recommendations are:
- Four specimens of any article are tested and the average result calculated.
- For articles that are intended for contact only with dry foods, no migration testing may be required.
- For articles that are not intended for contact with acidic foods, no migration testing may be required.
- For articles which may be used with acidic foodstuffs, testing for the release of toxic metal ions (eg lead, cadmium, mercury) should use 4 per cent acetic acid in distilled water under test conditions of 24 hours at 25°C.
- For articles which may be used with acidic foodstuffs, the results for release of other metal ions (e.g. tin, iron, chromium) should be the average of those for the first three exposures to 4 per cent acetic acid in distilled water (24 hours at 25°C).
Dissemination information
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).
See Also