The European Food Safety Authority established the following table to characterize engineered nanomaterials prior to use in food/feed related applications. That said, the guidance provided in this table should be of assistance in other applications:
“Parameters for characterization and identification of ENM”1
|Chemical composition/ identity||Essential||Information on chemical composition of the ENM including purity, nature of any impurities, coatings or surface moieties, encapsulating materials, processing chemicals, dispersing agents and/or other formulants e.g.stabilisers.|
|Particle size (Primary/Secondary)||Essential(two methods, one being electron microscopy)||
Information on primary particle size, size range and number size distribution (indicating batch to batch variation “ if any). The same information would be needed for secondary particles (e.g. agglomerates and aggregates) if present. .
|Physical form and morphology||Essential||Information on the physical form and crystalline phase/shape. The information should indicate whether the ENM is present in a particle-, tube-, rod-/shape, crystal or amorphous form, and whether it is in free particulate form or in an agglomerated/aggregated state as well as whether the preparation is in the form of a powder, solution, suspension or dispersion.|
|Particle and mass concentration||Essential for dispersions and dry powders||Information on concentration in terms of particle number and particle mass per volume when in dispersion and per mass when as dry powder.|
|Specific surface area||Essential for dry powders||Information on specific surface area of the ENM.|
|Surface chemistry||Essential (for ENM with surface modifications)||
Information on ENM surface “ including any chemical/ biochemical modifications that could modify the surface reactivity, or add a new functionality.
|Surface charge||Essential||Information on zeta potential of the ENM.|
|Redox potential||Essential for inorganicENMs||Information on redox potential. Conditions under which redox potential was measured need to be documented.|
|Solubility and partition propertiesa||Essential||
Information on solubility of the ENM in relevant solvents and their partitioning between aqueous and organic phase (e.g. as log Kow if appropriate).
|pH||Essential for liquiddispersions||pH of aqueous suspension.|
|Viscosity||Essential for liquid dispersions||Information on viscosity of liquid dispersions.|
|Density and pour density||Essential for granular materials||Information on density/porosity of unformulated ENM and pour density.|
|Dustiness||Essential for dry powders||Information on dustiness of powder products such as spices, creamers and soup powders.|
|Chemical reactivity/catalytic activityb||Essential||Information on relevant chemical reactivity or catalytic activity of the ENM and of any surface coating of the ENM.|
|Photocatalytic activity||Essential for photocatalytic materials||Information on photocatalytic activity of relevant materials used in food packaging, coatings, and printing inks and internal reactions.|
a) Dispersion, solution, dissolved: An insoluble ENM introduced to a liquid form a ˜dispersion™ where the liquid and the ENM coexist. In a true solution the ENM is dissolved (and thus not present) (see OECD ENV/JM/MONO(2010)25)
b) If an ENM has catalytic properties, it may catalyse a redox or other reaction that may perpetuate resulting in a much larger biological response even with small amounts of the catalytically active ENM. Thus, compared to a conventional biochemical reaction that uses up the substrate, ENM reaction centres may perpetuate catalytic reactions.
1. European Food Safety Authority, “EFSA Scientific Committee; Scientific Opinion on Guidance on the risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain,” EFSA Journal 2011;9(5):2140 (36 pp.) doi:10.2903/j.efsa.2011.2140, at 13 (see appendix A for characterization methods).