Glass packaging is a combination of different materials: a glass container (made of silica glass) and a closure (made of glass, metal, cork, or plastic). The closure material depends on the type of foodstuff. For example, foods that require sterilization after filling by heat and pressure application will be closed with a gasket-type seal, i.e. a rubbery, heat resistant rim that is airtight. Such gaskets are typically made with PVC, rubber or alternative materials.
Glass contaminants (also see Table):
- Migration of elements from different types of glass food contact materials has been studied by the UK Central Science Laboratory
- Lead has been shown to migrate from glass into drinking water. The highest level documented was 417 ng/L. The current WHO drinking water standard is 10’000 ng/L. The sources of lead in glass packaging are diverse and to a certain extent unknown. Lead is naturally present at very low levels in the raw material of glass manufacture, silica sand. Additional known sources are recycled glass, where crystal glass or other glass with higher lead content is mixed with container glass.
- Plasticizers like phthalates and epoxidised soy bean oil (ESBO) have been found to migrate from glass container closures containing PVC gaskets (Pedersen et al. 2008 ; Biedermann et al. 2008, Graubardt et al. 2009).
Chemical diffusion from within the glass is thought to be hindered due to glass’ structure. This also applies to compounds from the outside (e.g. printing inks, adhesives). Glass’ inertness is assumed due to its chemical structure, an amorphous non-crystal solid with pore sizes that are too small to allow molecules or single atoms to pass through. In a commentary letter and its reply in the scientific journal Applied Geochemistry, this issue has been discussed in more detail.
The EU Framework Regulation EC 1935/2004 on materials and articles intended to come into contact with food generally regulates glass as a food packaging material. Additionally, polymer-based gaskets used to seal glass packaging are regulated under the EU regulation EC 10/2011 on plastic materials and articles intended to come into contact with food (Art 2).