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To identify potential chemicals in pigments and dyes that could migrate into foodstuffs and measure migration of these chemicals into food simulants
Project Code: A03045
The purpose of this project was to obtain information about substances most likely to migrate from pigments and dyes used in food contact plastics, to help inform decisions on how best to control these substances.
There are many colourants (pigments and dyes) that can be used in plastics intended for food contact applications. Several different grades of a colourant may be available, all of which can nominally be described using the same identifying name, for example Pigment White 6. In addition, to achieve a desired effect colourants can be blended with each other so that a particular plastic may contain several different colourants.
The use of substances in the manufacture of food contact plastics is governed by the provisions of the Plastic Materials and Articles in Contact with Food Regulations 1998, as amended. These Regulations implement the requirements of EU-harmonised rules contained in EC Directive 2002/72/EC as amended. The use of substances as colourants is not specifically restricted in these EU-harmonised rules other than where colourants are prepared by diazo-coupling. In this case, primary aromatic amines (excluding those listed in Directive 2002/72/EC as amended) shall not be detectable in food or food simulants. Colourants are subject, along with all other substances that might migrate from the plastic, to the overall migration limit laid down in Article 2 of the Directive. Otherwise, colourants have to comply with the health and food nature/quality requirements of Article 3 of Regulation (EC) No. 1935/2004. Guidance is also given in the Council of Europe Resolution AP(89)1 on colourants. This lays down similar health requirements to the European Regulation, but adds that there should be no visible migration of the colourant from the material by analysis. This requirement is adhered to by companies who are members of ETAD, the Ecological and Toxicological Association of Dyes and Organic Pigment Manufacturers.
Industry support was obtained from two masterbatch manufacturers and Members of the British Colourants Manufacturers Association (BCMA). In total based on industry advice, 22 samples of colourant were tested, this included 16 of the most commonly used colourants in the UK. Of these, 4 were designated Colour Index (C.I.) Pigment White 6 and 2 as C.I. Pigment Black 7. In addition 2 of the samples originated in Asia, these were identified as having the same C.I. generic name as those colourants supplied by European manufactures, and were obtained for comparative purposes.
The first step of the work centred on attempting to identify potential migrants, that is impurities and intentionally added substances such as surface treatment chemicals, in the colourants. This was done by extracting each of the colourants using dichloromethane (DCM), acetone and methanol. The extracts were analysed by gas chromatography mass spectrometry (GCMS), high temperature gas chromatography (HTGC) and high pressure liquid chromatography (HPLC). To simulate severe processing conditions the colourants were heated, under nitrogen, for 5 minutes at 280 °C and were re-extracted with all three solvents.
The extracts were analysed to determine if any further compounds had been formed during the pseudopolymer processing. This was the case for one sample (CO115/9, C.I. Pigment Yellow 181).
A semi-quantitative, 45 element scan of the colourants was undertaken by inductively coupled plasma-atomic excitation spectroscopy. Of the eight metals for which guidance is given on maximum limits in the CoE Resolution, only barium was detected in two samples. Levels were well below the maximum limits.
A limited comparison was made on the 2 colourants, having the same C.I. generic name but in each case comparing one from the European market and one from the Asian market. In both cases the chromatograms were more complex for the samples obtained from Asia.
Based on the extraction results, some of the colourants were used to prepare test articles of compounded plastics. Migration tests were conducted using food simulants or recommended fatty simulant substitutes under worst case test conditions, according to Directive 97/48/EC. Exposed simulants were analysed using GCMS, HTGC and HPLC. Some migration of the substances identified in the extraction test was found but in general at concentrations of less than 50 micrograms/kg. The limit of detection was 35 micrograms/kilogram or better for all substances identified. (Such compounds included phthalimide, decamethylcyclopentasiloxane, trimethylol propane, o-phenetidine).
Migration of 4-chloro-2,5-dimethoxyaniline, a primary aromatic amine (PAA), was found at a concentration of 109 micrograms/kg from 1 plastic test article (CO115/11) prepared using C.I. Pigment Yellow 83. This equates to a migration of 54 micrograms/kg of aniline. The specific migration limit for PAAs expressed as aniline, in 2002/72/EC is non detectable with a limit of detection of 20 micrograms/kg. It must be noted that this work was undertaken on specially prepared plastics, not real-use articles, using worst case migration conditions. However, evidence of such migration demonstrates that care must be taken over the use of such colourants, the choice of plastics, the processing conditions and the possible migration issues attendant on their use, particularly with respect to compounds such as PAAs.
Some colour leaching was noted from one of the polyester test articles into 95 per cent ethanol simulant. However, this was not repeated when a colour leaching test was undertaken as described in the CoE Resolution AP (89) 1 using simulant D (olive oil) at 50°C.
The effect of abrasion on the migration of substances was investigated for two of the plastic test articles. In general this effect was found to be minimal. However, migration of trimethyol propane (TMP) was found to increase by 40% from a polypropylene test article containing a titanium dioxide colourant.
Finally, based on the initial concentrations of migrants in the test articles (determined experimentally or from information supplied by the colourant manufacturer) a migration model was used to predict levels of migration. Results were compared with those obtained from the migration work conducted into simulants. On the basis of the work carried out to date, which encompasses the range of colourants so far examined, the model was found to considerably overpredict migration. It is suggested that the cause of these over predictions is due to the adsorption of the migrating substances (impurities and intentionally added substances) onto the colourants. The model is based on the principal that the substance is present as a free agent and not bound to another material.
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