A03053: Monomer and other chemical migrant levels in food grade plastic

Study Duration: September 2005 to January 2008

Contractor: Pira International

Year one of an ongoing three year survey entitled ‘Chemicals used in plastic materials and articles in contact with food: compliance with statutory limits on composition and migration,’ identified the need for work on the variation of monomer levels in food contact plastics. Inter-sample variation is a source of uncertainty in estimating exposure to chemical migrants in food, but there are few hard data on actual variation. This new project looked at the variation in levels of selected chemical substances in plastics and considered the main factors leading to such variation.

The investigation was divided into 2 phases. In the first phase of the project, variations in levels of 1,3-butadiene, styrene and acrylonitrile in polystyrene were investigated in a range of articles including cups, trays and containers. In the second phase, variations in levels of melamine, formaldehyde and hexamethylenetetramine in melamine-ware were investigated. The levels of monomers measured were correlated with factory conditions.

Conclusions

Polystyrene:

• Levels of monomers for articles from a given factory line were found to be relatively consistent both within and between batches. For polymers made using butadiene and styrene, the level of monomers in the finished product was found to be directly influenced by the levels of monomer in the feed polymer
• Storage had most influence on the levels for butadiene but was found to be minimal for styrene levels
• Samples made using acrylonitrile/butadiene/styrene polymer gave the highest residual levels of monomers. One example, purchased from a catering supplier, contained butadiene at levels up to 3 mg/kg. Another example, supplied directly from a factory line, contained butadiene at 1.9 mg/kg. These values are above the maximum permitted quantity of butadiene in finished material or article (QM). However the Specific Migration Limit (SML) was not exceeded for either sample when tested using the most appropriate worst case migration conditions
• The largest inter-sample variation of monomer levels was found in ABS pipes obtained from a catering supplier, which had butadiene levels ranging from 0.84 to 1.69 mg/kg; and in an AS food container bought from a retail outlet, which had acrylonitrile levels ranging from 12.5 to 23.4 mg/kg. These findings echo the 1,3-butadiene variations found in the Agency survey (FSIS 43/03) in polystyrene cups

Melamine-ware:

• Several peaks were detected in the chromatograms for melamine and it was observed that extracted melamine reacted in solution giving rise to increased levels of these additional peaks. These compounds were tentatively identified as being addition reaction products of melamine with formaldehyde
• There was little variation of melamine content in the different articles tested. It was found that even when stored in a freezer, levels of melamine decreased. A standard stock solution of melamine was stable under the same conditions
• Levels of formaldehyde increased during storage of the filtered extract. A solution of formaldehyde stored under the same conditions was found to be stable
• Residual levels of formaldehyde were found to be scattered. The scatter exceeded the precision of the method so is likely to be caused by differences between the samples. This is possibly because formaldehyde is very volatile and could be lost during manufacture. Based on these findings it may be difficult to provide a homogenous reference sample of melamine-ware for formaldehyde determinations
• Analysis for HMTA proved inconsistent giving lower values than for formaldehyde alone

In general, monomer levels were found to be relatively consistent from given factory lines, greater variation was found across some retail purchases where the manufacturing history was unknown. Migration of butadiene was not detected from a sample of ABS found to contain a greater level of butadiene than the maximum quantity permitted (QM). This result could call into question the usefulness of QMs as a restriction. Residual levels of formaldehyde in melamine samples were scattered and this may be problematic in the provision of a homogeneous reference sample of melamine ware for formaldehyde determinations. This information will be used to inform future EU discussions on monomer limits and the provision of melamine-ware reference materials for proficiency tests or collaborative trials.