Assess risk from nano-pollution and antimicrobials in packaging - IFST

The Institute of Food Science and Technology (IFST) has called for greater appraisal of the potential risks from the release into the environment of nanomaterials used in food packaging.

The possibility that wider exposure to anti-microbial agents in food contact materials (FCMs) may contribute to heightened bacterial resistance was highlighted as an area of concern for the UK-based body. It also said the accumulation of nanosilver in the environment should be scrutinised and the development of bespoke recycling procedures considered.

The IFST made its comments in its response to the European Food Safety Authority’s (EFSA) guidelines on the potential risks of nano-applications in food and feed published in January 2011.

The independent group said it was important that the EFSA document suggest the need for full toxicity data on engineered nanomaterials (ENM) used as composites in FCMs even where there is no evidence for migration of these particles into food, or where levels of migration are low, it said.

The body added: “IFST considers that this is important because, although the direct use of these materials may not lead to significant ingestion of the particles, knowledge of the level of toxicity, or lack of toxicity, may be needed in order to assess the acceptable levels of migration.”

Antimicrobial issues

The organisation said it was “concerned” that a number of mineral ENMs were being used, or put forward for use, as anti-microbial agents in food contact materials. It called for more research on the consequences of their release into the environment and declared this should be evaluated when considering their use in food applications.

The IFST said the use of antimicrobial agents was potentially important in the future – particularly in light of the spread of antimicrobial resistant microorganisms.

“If there is to be a use for such antimicrobials in the medical area in dressings, treatment of wounds, or generally in coating of medical implants, surgical instruments or hospital surfaces, then the IFST believes one should avoid widespread low-level exposure, which could lead to bacterial resistance to these materials,” said the body.

This issue should also be taken into account when considering the use of antimicrobials in supplements, or in directly-applied coatings for natural food products to prevent spoilage

Whole life concerns and specialised recycling

Crucially it raised the issue that production and disposal of these materials may eventually lead to increased exposure to the nanoparticles and urged that the possible consequences of this be explored.

Consideration of the ‘whole life’ aspects of encapsulated nanoparticles should be taken into account in their use or regulation, said the IFST.

It noted there was already evidence that the increased commercial use of nanosilver had led to a rise in the level of silver in streams and rivers. But it added that most nanosilver particles were removed during sewage treatment and converted into less reactive and more stable silver sulphite nanoparticles.

The IFST raised the possibility that disposal of food contact materials containing nanoparticles – and their subsequent breakdown - could lead to the release of more reactive forms into the environment.

The body cited evidence that nanoparticles can be transferred up the food chain once released into the environment and suggested the development of specialised recycling procedures be considered as part of the risk assessment

The World´s Smallest Pipettes: Capillary Action in Carbon Nanotubes

Encapsulated metal nanoparticles can be extracted from carbon nanotubes through reverse capillary action.

It helps plants to transport water from their roots to their leaves. It is the reason why a sponge can be used for cleaning. It allows for the separation of different substances by chromatographic techniques like thin layer chromatography. Capillarity is the fundament of many biological and physical processes. However, this phenomenon is relevant not only on the macroscopic scale; with an increasing interest in nanofluidic devices, the effects of capillarity on the nanoscale have become an important topic, too. Possible applications of nanofluidic devices include promising areas like the separation of biomolecules, single-molecule analysis, or drug-delivery systems, and it is crucial to understand if the balance of capillary forces on the nanoscale resembles the one in the bulk material. Kirsten Edgar et al. from Wellington, New Zealand, now demonstrated for the first time that it is possible to withdraw an encapsulated metal particle from a multi-walled carbon nanotube via reverse capillary action, a fact that could make carbon nanotubes suitable for the use as pipettes. 

Carbon nanotubes present an ideal material to study nanoscale capillarity – they are among the smallest capillaries currently known, and they can absorb particles of even non-wetting metals if the Laplace pressure of the free droplet exceeds its meniscus pressure in the nanotube. But then shouldn´t it also be possible to extract an encapsulated particle if, the other way around, its meniscus pressure is higher than its Laplace pressure? The New Zealand research group gave it a try with silver-filled multi-walled carbon nanotubes: They chopped the ends of the nanotubes off using a silver-assisted oxidation method by which, simultaneously, silver nanoparticles were produced. The opened nanotubes then absorbed those silver particles that were small enough while the larger particles remained dispersed in the sample randomly – and larger particles that abutted on the open end of a metal-filled nanotube actually started to extract the internal particle. This process could be observed via electron microscopy: Within two minutes, an encapsulated particle was released completely from the nanotube and absorbed by the large particle, leaving the walls of the nanotube partially collapsed.

Molecular dynamics simulations for a liquid silver particle supported the experimental observations: an encapsulated metal droplet will be released from a carbon nanotube if the external particle has at least twice the radius of the droplet. However, unlike in the experiment, the simulated droplet did not shrink in diameter during extraction and the nanotube walls remained unaffected, indicating that the dynamics of the experimental process might differ from those in the model. Still, the results from the simulations and the experiments confirm that the ratio of a particle´s Laplace pressure and meniscus pressure determine if it will be absorbed or released from a capillary, showing that carbon nanotubes indeed could be applied as nanopipettes one day.