Migration factors of nanosilver in PVC packaging studied
The objective was to evaluate the migration of silver from plasticised polyvinyl chloride (PVC) nanocomposites to chicken meat following varying storage time and temperature conditions, according to Cushen et al.
They found a worst case scenario migration of 8.85mg/kg or 0.84mg/dm2, below what European Union (EU) legislation allows for general substances; no more than 60mg/kg, or 10mg/dm2.
However, they noted if silver at nanoscale is to be put on the positive list of substances permitted in food contact materials, its specific permitted migration are likely to be lower than that of general substances due to its increased surface area and reactivity and increased potential to induce toxic effects.
The researchers found nanosilver migration was influenced by nanomaterial fill percentage in the packaging material and storage duration but not temperature.
Writing about temperature, they said: “This relationship was unexpected because it is widely accepted in the scientific community that any mass transfer or migration increases with temperature and the relationship observed is notable different from other migration studies using other packaging materials (i.e. not PVC) where the effect of temperature is discussed.”
They said it could be explained because at higher temperature silver nanoparticles crosslink with the polymer chains.
Migrated nanosilver
It was concluded that because there was no difference between silver quantification of samples in contact with the PVC more of the smaller particles (10nm) had migrated than the 50nm particles.
“However, the exact extent of differing migration rates is difficult to determine without more knowledge on the behaviour of silver nanoparticles. This is because the migrating silver is likely to be made up of both nanoparticles and ions.”
The silver content of the chicken was quantified using inductively coupled plasma mass spectroscopy (ICPMS) and migration was found to occur within a range of 0.03–8.4 mg/kg.
An exposure assessment revealed that human exposure to silver (assuming a worst case scenario that all silver is in its most harmful nanoform), is likely to be below current migration limits for conventional migrants and a provisional toxicity limit; however it is acknowledged there is still considerable uncertainty about the potential harmful effects of particles at the nanoscale.
A sensitivity analysis revealed that silver migration from the nanocomposite to the food surface was influenced most by the percentage fill (p < 0.01), followed by storage time (p < 0.01) and storage temperature (p < 0.05).
Use of silver
The researchers cited a number of other studies outlining the antimicrobial effects, improved tensile properties, oxygen scavenging and improved light and gas barrier properties that nanoparticulate fillers in food packaging materials can achieve.
Assessments on nanosilver are in progress as adequate toxicological data is not yet available in the EU.
It was assumed that all silver was in its most harm causing state i.e. nanoparticles, because it is not known how readily silver nanoparticles produce silver ions or at what ratios to one another they co-exist and both processes are likely to vary according to pH, temperature and or time.
Source: Food Chemistry Volume 139, Issues 1–4, 15 August 2013, Pages 389–397
Online, ahead of print: 10.1016/j.foodchem.2013.01.045
“Migration and exposure assessment of silver from a PVC nanocomposite”
Authors: M. Cushen, J. Kerry, M. Morris, M. Cruz-Romero, E. Cummins
