RE: The two questions the current board have to answer22 Dec 2020 10:47
Physicochemical determinants of toxicity
The following physical and chemical properties are likely to be important in determining the hazardous potential of engineered nanomaterials. This list is not exhaustive. Future research may identify other physical or chemical properties that are important.
Size
There is no clear evidence for a step change in hazardous properties relating to the specific dimensions of a particle. However, it has been reported that particles with dimensions below 20 - 30 nm are less thermodynamically stable and undergo dramatic changes in their crystalline structure compared to larger particles with the same chemical composition . These changes will influence the way these very small particles interact with their environment and biological media. Consequently it is harder to predict their toxicological behaviour based on information obtained for larger sized particles, including those at the nano scale, even where the chemical composition is the same.
The size cut-off of 100 nm that has been used within the Commission definition has been chosen because many of the specified effects of nanomaterials occur with particles with dimensions in the range 1 – 100 nm. Also this ensures consistency with definitions that are used elsewhere. It should not be assumed that a particle that has no dimensions below 100 nm is free from hazard and it should not be assumed that a particle that has at least one dimension that is below 100 nm is highly hazardous. There will be a wide variation in the hazard potential of nano-sized particles just as there is a wide variation in the hazard potential of other substances.
Aggregation/agglomeration state
When nanomaterials are released, in nearly all situations they will rapidly form aggregates and agglomerates so that exposure in practice is to a much larger secondary particle than a nano-sized primary particle. The size of aggregates/ agglomerates will influence the residence time of the material in workroom air and may reduce the potential for a nanomaterial to be inhaled. The aggregation/agglomeration behaviour of nanomaterials is heavily influenced by the external environment i.e. workroom air, dispersion media, etc. It is therefore useful to understand the aggregation/agglomeration behaviour in the environment for which the risk assessment is being conducted.
Aggregates/agglomerates
Aggregates/agglomerates of nanoparticles are not necessarily stable and when the external environment changes e.g. the transition from workroom air to inhaled air, the aggregation/agglomeration state may change. So although a nanomaterial may be present in comparatively large aggregates/ agglomerates in the workroom air, there is the potential for disaggregation and disagglomeration to occur within the respiratory tract allowing smaller primary particles to penetrate to the deep lung. For this reason, although the aggregation/agglomeration state may reduce the potential to inhale a nanomaterial, it