Minimising data needs to support the safer design of multicomponent nanomaterials – Application of grouping

There is an ongoing demand to develop options to reduce hazard testing of substances and materials on a case-by-case basis. Grouping approaches offer a way to share or re-use safety-related information between similar substances, providing insights that can inform the Safe and Sustainable by-Design (SSbD)² of new materials.

Here, an existing grouping hypothesis template for single-component nanomaterials (NMs)³ is expanded to facilitate systematic consideration of grouping for multicomponent nanomaterials (MCNMs)⁴ relevant to SSbD. Modifications to the template include additional information on a) the complexity of physical and chemical composition; b) the emerging properties driving the MCNM functionality; c) the potential for MCNM components to transform with different rates, leading to complex exposure scenarios; d) prioritisation and simplification of grouping decisions related to material properties (what they are), fate/toxicokinetics (where they go) and the hazard mechanisms (what they do).

Existing information and data are used to formulate a matrix of sub-hypotheses that individually relate one (or more) indicators of ‘what they are’ to a single indicator of either ‘where they go’ or ‘what they do’. The resultant sub-hypotheses are easier to assess than the all-encompassing over-arching hypothesis required for regulatory application of grouping. The estimated level of impact of each indicator is used to prioritise the sub-hypothesis assessment. Accepting or rejecting each prioritised sub-hypothesis is facilitated by the application of tiered testing strategies promoting the use of relevant existing data, new approach methodologies and machine learning-based models. A case study of SiO₂@ZnO MCNM is provided to demonstrate the template’s usefulness in an SSbD context.