Guidance on providing additional data requirements

This section gives guidance on the physico-chemical characterisation and reporting requirements for additional data requirements (above that normally required for the notification category).

The recommended test methods identified for the physico-chemical data are informed by the International Organization for Standardisation's (ISO) technical report (ISO/PDTR 13014) on Nanotechnologies—Guidance on physico-chemical characterisation for manufactured nano-objects submitted for toxicological testing[1] and the Organisation for Economic Co-operation and Development (OECD) sponsorship program Guidance manual for the testing of manufactured nanomaterials OECD's sponsorship programme.[2] Refer to these documents for further details and alternative methods.

Where NICNAS asks for specific physico-chemical data and/or test results but it is not feasible or not considered applicable to provide it, you must provide a scientific rationale for not doing so.

You need to supply physico-chemical data for the nanomaterial as manufactured (that is, at the point on completion of manufacture or as the sample is removed from the manufacturer's container) and, where data is available, in the end-use product formulation.

In general, all physico-chemical data should specify the:

  • grade of the nanomaterial tested, including its purity
  • testing authority or organisation
  • method of preparing the test sample
  • physical conditions used for all test data (for example, agitation method (dispersing aids), pH, ionic strength, ionic composition, temperature or pressure).

You need to ensure that the standard of testing used to obtain data complies with the OECD Principles of Good Laboratory Practice.

Note:

The OECD Working Party on Manufactured Nanomaterials (WPMN) reviewed all 22 OECD test guidelines for physico-chemical properties for their applicability to the testing of nanomaterials.[3] The review concluded that all but two of the current tests may provide information applicable to nanomaterials. The two tests not considered to provide useful information are TG 103 Boiling Point and TG 114 Viscosity of Liquids.

It was also recognised that some tests would only be applicable to a sub-set of nanomaterials depending on their physical form and chemical composition. For example, it was concluded that the three test guidelines for physico-chemical properties of polymers (OECD TG 118 to 120) would only apply to polymeric manufactured nanomaterials.

The key physico–chemical properties requiring characterisation when considering aquatic environmental exposure of chemicals are water solubility, water-soil and water-oil partitioning, hydrolysis and dissociation constants. All standard test guidelines for these properties potentially apply to nanomaterials. However, it is noted that this applicability depends in part on the presence of colloidal dispersions of nanomaterials in water which may complicate both the conduct and/or interpretation of studies.

Particle size and size distribution

You need to provide the mean primary particle size and number weighted primary particle size distribution with number fraction <100 nm. In addition, provide a representative microscopy image at a magnification capable of resolving features <100 nm, to validate the particle sizing method.

When measuring the particle size distribution, effort should be made to break down loose agglomerates, including those of fibres (for example, through sonication or the use of dispersing aids to fully disperse the nanomaterial).  Report the method of dispersion and sample preparation.

Where you have not provided the size distribution and number weighted percentage of particles <100 nm, the chemical will be assumed to be a nanomaterial under the NICNAS definition if there is evidence of primary particles of <100 nm in the representative microscopy image.

Fibre-like nanomaterials

For fibre-like nanomaterials, such as carbon nanotubes, provide the aspect ratio (fibre length range and diameter range). For guidance on measurement refer to the OECD's technical guidance document No. 10—Particle Size Distribution/Fibre Length and Diameter Distributions[4].

Recommended test methods are: Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Atomic force microscopy (AFM), Dynamic Light Scattering (DLS)*, Laser Diffraction, Disk centrifugation and Scanning Mobility Particle Sizer (SMPS).

*DLS, although suitable for monodisperse materials, should not be solely relied upon for measuring the primary particle size distribution of nanomaterials with broad size distributions as this method is strongly biased towards larger particles or aggregates which may obscure the presence of nanoparticles.

Method of production

You must describe the method of production, including the methods used for purification as these may affect key properties of the nanomaterial, including the type and level of impurities and surface chemistry.

Shape

You must describe in detail the physical shape of the nanomaterial, using terms such as spheres, fibres, tubes or plates.

Recommended test methods are: SEM and TEM.

Agglomeration/aggregation state

You must provide the agglomeration/aggregation state of a dispersion of the nanomaterial in an aqueous medium. NICNAS recommends that you do so using two techniques—a direct observational technique such as TEM or SEM, and a DLS technique.

The electron microscopic techniques provide information on the structure and size of primary nanoparticles whereas light scattering provides information on the average hydrodynamic radius of agglomerates and aggregates of nanoparticles dispersed in the water phase. The information derived from both techniques is complementary and important to fully characterise the state of nanomaterial aggregation in aqueous media used for environmental fate and effects testing.

You must also provide a qualitative assessment of the degree of aggregation and agglomeration in the end-user or finished product and, where feasible, a representative microscopy image.

Agglomerate (definition from the International Organization for Standardisation's ISO TS27687 2008 - www.iso.org/iso/catalogue_detail?csnumber=44278):

… collection of loosely bound particles or aggregates or mixtures of the two where the resulting external surface area is similar to the sum of the surface areas of the individual components.

Notes:

  1. The forces holding an agglomerate together are weak forces, for example van der Waals forces, as well as simple physical entanglement.
  2. Agglomerates are also termed secondary particles.

Aggregate (definition from ISO TS27687 2008 - www.iso.org/iso/catalogue_detail?csnumber=44278):

… particle comprising strongly bonded or fused particles where the resulting external surface area may be significantly smaller than the sum of calculated surface areas of the individual components.

Notes:

  1. The forces holding an aggregate together are strong forces, for example covalent bonds, or those resulting from sintering or complex physical entanglement.
  2. Aggregates are also termed secondary particles and the original source particles are termed primary particles.

Recommended test methods are: SEM, TEM and DLS.

Crystalline phase

Crystalline phase refers to the specific space group for a given crystal structure.  In certain cases it is possible to have multiple crystalline phases, such as with silica (that is, amorphous and different crystalline forms) and titanium dioxide (that is, rutile phase and anatase phase).

You need to describe the average crystalline phase.Recommended test methods are: X-ray diffraction, electron diffraction and TEM.

Composition (purity/impurities)

You must provide the percentage purity of the nanomaterial and the identity and percentage of all impurities. Impurities may arise from incomplete reactions, from reagents used for production (for example, catalysts) or from post-production handling (such as absorption of endotoxins).

Recommended test methods are:

  • Metallic impurities: atomic absorption spectroscopy, Inductively coupled plasma mass spectroscopy and Inductively coupled plasma atomic emission spectroscopy.
  • Organic impurities: UV/VIS (Ultraviolet-visible spectroscopy), GC-MS (Gas chromatography–mass spectrometry) or LC-MS (Liquid chromatography–mass spectrometry).

Surface area

You must provide the exposed surface area per unit mass of the nanomaterial presented as m2/g.

The recommended test method is: BET[5] gas-absorption method.

Surface charge

Due to their extremely high specific surface area, aqueous dispersions of nanoparticles can easily lose their colloidal stability as a result of changes in the chemistry of the dispersion medium (for example, ionic strength, pH, level of dissolved organic carbon). Agitation conditions and changes in concentration of the particles can also lead to agglomeration or aggregation.

An important predictor of colloidal stability is the surface charge of particles. The surface charge is usually characterised by measurements of the zeta potential. You must provide the measurement of this electrokinetic parameter over a wide range of pH and ionic strengths in water. This is valuable information on the tendency of particle size and size distribution to change with time and solution chemistry.

The zeta potential of the nanomaterial in aqueous dispersion should be measured over as wide a pH range as practicable, but measurements must span the environmentally relevant pH range of 4 to 9. You must fully describe the test methodology, including details of the dispersion medium (such as ionic strength and identity and concentration of any added electrolytes or stabilisers). You must submit a full plot of the measured zeta potential versus pH profile of the nanomaterial. You must also provide an estimate of the pH for the point of zero charge of the nanomaterial if there is no net charge on the particles in the measured pH range.

The recommended test method is: Measure electrophoretic mobility and calculate zeta potential.

Surface chemistry (for example, coating or modification)

Surface chemistry plays a key role in determining fate in natural aqueous systems, colloidal stability and exposure. For a given functionalisation or coating it will affect other physico-chemical properties such as agglomeration, surface charge, surface area and water solubility.

You must provide the chemical nature of the outermost layers of the nanomaterial, if different to the rest of the material, including the identity of any coatings or stabilisers and/or surfactants and intentional functionalisation. If the nanomaterial has a functionalised surface, you need to identify the treating agent. You must also identify, if feasible, the unintended functional groups on the surface, such as those induced by purification processes.


[1] ISO 2010, ISO/PDTR 13014, The International Organization for Standardization, <www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_tc_browse.htm?commid=381983&development=on>, accessed 17 November 2010.

[2] OECD 2009a,  first revision, ENV/JM/MONO(2009)20/REV. In: OECD Environment, Health and Safety Publication, series on the safety of manufactured nanomaterials, OECD Paris, Organisation for Economic Co-operation and Development, no. 25, p. 92, <www.oecd.org/document/53/0,3343,en_2649_37015404_37760309_1_1_1_1,00.html>, accessed 17 November 2010.

[3] OECD 2009b, 'Preliminary review of OECD test guidelines for their applicability to manufactured nanomaterials', OECD Environment, Health and Safety Publication, series on the safety of manufactured nanomaterials, no. 15, ENV/JM/MONO(2009)21, OECD Paris, Organisation for Economic Co-operation and Development, p. 71, <www.oecd.org/document/53/0,3343,en_2649_37015404_37760309_1_1_1_1,00.html>, accessed 17 November 2010.

[4] See: tsar.jrc.ec.europa.eu/documents/Testing-Methods/Guidance_Document_on_Granulometry.pdf

[5] Method expounded by Stephen Brunauer, Paul Hugh Emmett, and Edward Teller.


Last update 29 July 2018