Physico-chemical characteristics and toxicity of nanomaterials

"Physico-chemical characteristics" and toxicity of nanomaterials

By AVICENN Team – Last Added June 2022

At the nanoscale, we can no longer consider that "It's the dose that makes the poison", this sentence of the doctor and alchemist Paracelsus who founded toxicology and is very often invoked to assess the risks associated with synthetic chemical substances. Scientifically, it is now called into question, in particular by the specific case of the toxicity of nanomaterials on which the physico-chemical characteristics of the nanomaterials considered have a strong influence.

Each of the parameters mentioned below influences the toxicity of nanomaterials. And each of them is itself subject to variation during the life cycle of nanomaterials. Hence the complexity, for researchers, of ruling on the toxicity of nanomaterials.

– Their chemical composition:

• This is the identity of the substance, for example "silver" or "titanium dioxide"

• One can extrapolate knowledge that we have on the substance in the macro state, whose known properties (and sometimes toxicity) can be increased tenfold due to surface reactivity.
  
• De new properties (or a new toxicity) can also appear specifically at the nanometric scale; they are much more difficult to predict, and we often still know too little about them.
  
• Please note, however, that nanomaterials from the same family can not be considered as a “monosubstance”: within the same family, different substances can exhibit toxicity and genotoxicity different¹Results of the European program Nanogenotox on the genotoxicity of nanomaterials, presented in French at ANSES, during the Restitution of the national environmental and occupational health research program: Chemical substances and nanoparticles: models for the study of exposure and health effects: Participant's file et Slideshow, November 2013. And "The toxicological assessment of nanomaterials must evolve, according to a European research project", APM International, 14 November 2013. On the genotoxicity of nanomaterials, see also: Genotoxicity of Manufactured Nanomaterials: Report of the OECD expert meeting, OECD, December 2014.

– Their dimension (size and size distribution):

Their nanometric size allows nanomaterials to penetrate the cell and cause harmful effects²See for example Size determines how nanoparticles affect biological membranes, Dunning, H., Imperial College London, September 17, 2020 (press release) and Size dependency of gold nanoparticles interacting with model membranes, Contini, C et al., Nature Communications Chemistry, 130, 2020, but the size of the nanomaterials is not the only one that comes into play; the following list is also decisive.

– Their shape (or morphology):

There is a wide variety of forms of nanoparticles: nanotubes, nanowires, nanosheets, nanocubes, etc. it seems that structures in tubes, fibrous or with multiple facets present a higher toxicity than smooth structures (such as spheres), in connection with the surface reactivity³See for example: The influence of surface coatings of silver nanoparticles on the bioavailability and toxicity to elliptio complanata mussels, Auclair J et al., Journal of Nanomaterials, 2019: Silver nanoparticles harm mussels: High silver levels in freshwater mussels are linked to reduced survival time in air, weight loss during air exposure and DNA damage. ; the toxic action may also prove to be greater on one of the facets, for example for nanomaterials of complex shape and nature (but here again, this will depend on the type of nanomaterial).

– Their specific surface:

it's about the surface of a particle or material in relation to its volume; it has an important role in explaining certain changes in the behavior of the same material (for example powdered sugar will melt more quickly in hot tea than a large lump of sugar)

– Their surface reactivity / surface chemistry (and if applicable, their coating: coating or encapsulation)

– Their state of charge

– Their degrees of agglomeration / aggregation:

• Note: Research conducted in Belgium published in 2020 shows that aggregates larger than 100 nm should not be considered necessarily less toxic than their nanoscale counterparts, whether silica nanoparticles⁴See Assessing the Toxicological Relevance of Nanomaterial Agglomerates and Aggregates Using Realistic Exposure In Vitro, Murugadoss S et al, Nanomaterials, 11, 1793, 2021 and Is aggregated synthetic amorphous silica toxicologically relevant?, Murugadoss S et al., Particle and Fiber Toxicology, 17 (1), 2020 or titanium dioxide nanoparticles⁵See Agglomeration of titanium dioxide nanoparticles increases toxicological responses in vitro and in vivo, Murugadoss S et al., Particle and Fiber Toxicology, 17 (10), 2020.

– Their solubility (in water, biological fluids, etc.)

– Their crystallinity

– Their dustiness