Halloysite is a natural clay mineral that can occur in nature as rolled-up sheets of aluminum and silica, then called halloysite nanotubes (HNTs). HNTs can be used in food packaging. Loading of HNTs with essential oils and the subsequent incorporation into food packing material can increase the food shelf life, since essential oils have antimicrobial properties.
A group from the National Research Centre for the Working Environment in Denmark did experiments on two types of HNTs to examine possible toxicity, genotoxicity and induction of inflammation. The toxicological response to HNTs following airway exposure is important as people can be exposed to high quantities of HNTs during mining, processing and handling. These tests were not performed for HNTs fixed in a food packaging.
Both a pristine HNT and a HNT with modified surface were assessed:
- None of the HNTs showed signs of being cytotoxic, inducing genotoxicity or affecting the mouse body weight (in vitro and in vivo on mice).
- Some results suggest that HNTs with modified surface induce inflammation, which is linked to a risk of cardiovascular disease (lung and liver tissue).
The results indicate that modification of pristine material can increase toxicity, probably due to an increase in surface area of the particles. Hence, the etching increases surface area of the HNTs, and the toxicity data indicated that the observed toxicity depended on surface area of the particles, so that the higher the particle surface area that was deposited in the mouse lungs, the higher the toxicity. These tests were performed in animal models under direct exposure to the HNTs and cannot be directly transferred to the use of HNTs in a food packaging. They do however show that it is important to reduce exposure of workers to the lowest level possible, so inhalation is avoided.
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