12/06/2020 4 mins

Review of analytical methods available for characterising nano-objects and their aggregates and agglomerates, in order to meet regulatory requirements

Ahead of the European Commission's revision of the definition of nanomaterials, ANSES is publishing a review of the analytical methods available for characterising these materials

When the particles making up a material are at the nanoscale (of the order of a billionth of a metre), its physico-chemical properties are likely to be modified. These different behaviours are sought after for many applications, but the nanometric size of particles can also modify their toxicity, both for humans and the environment. Today, due largely to the enormous diversity of nanoscale particles, there is still not enough knowledge of their potential effects on human health and the environment to be able to assess the risks associated with the multiple routes of exposure.

In the absence of a consensus on the definition of the term "nanomaterial" in the scientific, regulatory and legal fields that would enable these objects' characteristics to be defined, bodies such as the International Organization for Standardization (ISO) have suggested harmonising the vocabulary used (nano-objects, aggregates, agglomerates, engineered nanomaterials, etc.) and then establishing a definition and criteria for characterising these substances, such as their size, distribution, specific surface area, etc. At the European level, the European Commission's Recommendation on the definition of nanomaterial (2011/696/EU) has been used several times as a reference in the various legislative texts. This recommendation was based on the SCENIHR's work on this topic, published in 2010 [1].

At the moment, the definition of the term "nanomaterial" may differ from one industrial sector to another (biocidal products, cosmetics, food). There are differences and varying levels of precision in the proposed definitions, for example concerning the particle number or size threshold to be taken into account, or notions of insolubility or biopersistence, etc.

After several phases of discussions that began in 2012, the European Commission is considering a 14-week public consultation on a revised definition. This revision should make it possible to obtain a harmonised definition that can be applied to all the different industry sectors. The date of publication of the draft definition, originally planned for the summer of 2018, is currently unknown.

In this context, ANSES received a formal request to prepare a contribution for the Commission's public consultation. It was specifically asked:

  • to assess the existence of measurement methods that are compatible with the proposed definition;
  • and to present in an opinion the adaptations it feels are necessary to the current definition proposed in Recommendation (2011/696/EU).

Review of existing measurement methods for characterising nanomaterials

In response to the first part of the formal request, a review of the analytical methods available for characterising nanomaterials, based on several reference documents, was carried out. This included:

  • a description of the techniques generally used to characterise the eight physico-chemical parameters essential to the characterisation of nanomaterials;
  • and a summary of their respective advantages and limitations, including their accessibility.

In its opinions associated with the numerous published expert appraisals on the health risks of exposure to nanomaterials, the Agency had recommended improving the analytical methods used for characterising nanomaterials. The review published today by the Agency shows that real progress has been made:

  • techniques are now available for measuring each of the eight physico-chemical parameters;
  • none of these techniques can be regarded as most suitable for characterising a physico-chemical parameter for all nanomaterials. They need to be selected on a case-by-case basis, considering:
    • the analytical strengths and limitations of these methods;
    • the limitations introduced by sample preparation.
  • cross-checking the analytical data helps ensure the relevance of the physico-chemical characterisation. This means that if certain techniques are not relevant as such, they may nevertheless provide information of interest with regard to other analyses (e.g. dynamic light scattering, which is unsuitable for measuring the sizes of primary particles except in special cases, may provide information on the agglomeration state and stability of a suspension);
  • although many analytical methods are available for characterising size and size distributions, only electron microscopy techniques provide access to primary particles.

This analysis is an essential prerequisite for the response to the European Commission's public consultation on the proposed definition.

See the ANSES SCIENTIFIC AND TECHNICAL SUPPORT REPORT on the review of analytical methods available for characterising nano-objects and their aggregates and agglomerates, in order to meet regulatory requirements (in French)