Trace contamination of foods by migration from plastics packaging—A review

Abstract

Plastic packaging often contains many components in addition to the base polymer. Additives are required both for the manufacturing process to give acceptable results and for the finished product to have the desired characteristics. Furthermore, decomposition products may arise from these additives, while the base polymer itself will contain monomer and oligomers in addition to traces of constituents of the polymerisation mixture (such as catalysts) and any decomposition products arising from these. Printing inks, laminates and their adhesives further complicate the picture. Consequently, the final product can contain a multitude of components at all levels from traces to perhaps 20–30% by weight. Where these components are of low molecular weight, a potential exists for their migration into packaged foods. It is essential, therefore, that manufacturers and users of plastic packaging intended for food contact be aware of the chemical nature of the range of potential migrants expected from a given polymer/additive/food system and have some understanding of the underlying mechanisms and kinetics of migration. This paper presents an overview of current knowledge of migration. After an outline of the physical basis of migration, the concept of—and problems inherent in—measuring overall migration are described, followed by a discussion of selected specific migrants. Although information on contamination from residual monomers forms the bulk of the available literature on specific migrants, migration of other base polymer constituents and of non-volatile plastics additives and their decomposition products can be of importance and is reviewed here.