In recent years, the OECD has increasingly recognised the need to include considerations of environmental transformations into the risk assessment of nanomaterials.  Recent publications and activities emphasise the importance of understanding how these materials behave in dynamic environments, rather than relying solely on static characteristics as determined in laboratories. RIVM expects that this shift will improve regulatory risk assessments of advanced materials  like nanomaterials, although further guidance still needs to be developed. 

OECD encourages assessing nanomaterial transformations in the environment 

Recent activities within the Organisation for Economic Co-operation and Development (OECD) reflect a growing recognition of the need to consider environmental transformations of advanced materials in risk assessment. The OECD has recently published a Guidance on Sample Preparation and Dosimetry for Manufactured Nanomaterials, which complements its earlier Guidance Document on dissolution and dispersion stability of nanomaterials, and an evaluation of tools and models used for assessing environmental exposure to manufactured nanomaterials. These activities emphasise the importance of parameters like dissolution rate and dispersion stability in the risk assessment of nanomaterials, shifting the focus from static material characterisation to a more dynamic understanding of material behaviour over time. 

Transformations of nanomaterials in dynamic environments 

Traditional risk assessment approaches are typically based on the properties of pristine materials as characterised under laboratory conditions. However, growing evidence shows that this approach may not adequately capture the real-world behaviour of advanced materials like nanomaterials. In dynamic environments, these materials often undergo changes: they may dissolve, agglomerate, react, or interact with biological and environmental components, altering properties such as mobility, persistence, bioavailability and (eco)toxicity.  

Importance of transformation data in regulatory risk assessment 

Although transformation processes of nanomaterials have been described for more than a decade, their integration into regulatory risk assessment remains limited. Nevertheless, there is a growing awareness of the need to include explicit requirements for transformation data in regulatory dossiers. This need arises from discrepancies between laboratory-derived hazard data and actual environmental exposure conditions, which creates uncertainty in assessing environmental fate and effects. Such discrepancies can lead to either underestimation or overestimation of risks. However, developing harmonised approaches and guidance to assess environmental transformations is technically challenging. 

Reflections by RIVM 

The OECD's publications provide a valuable foundation for harmonisation. They represent an important step towards improving the robustness of risk assessment for nanomaterials and AdMa and support more informed decision-making. However, further guidance is needed to ensure that regulatory-relevant information on dissolution, stability and transformation products becomes available.  

For example, improved integration between experimental data and exposure modelling is required, so that models can more accurately reflect the dynamic nature of advanced materials. Additionally, guidance is needed on how to address aged forms of materials, which are more representative of environmental exposure than pristine materials.  

Furthermore, the coexistence of parent materials and their transformation products raise questions about mixture effects, which current frameworks do not fully address. Integrating these aspects into safe-and-sustainable-by-design approaches will help ensure that innovations in advanced materials can be made safer for human health and the environment.