A quantitative definition for poorly soluble particles

A new ECETOC study provides a clearer way to define “poorly soluble particles” (PSPs) – a group of materials that can persist in the lungs after inhalation and are widely discussed in chemical safety assessment. In it, the authors introduce a quantitative approach that links particle dissolution rates with lung burden and clearance mechanisms.

By analysing existing inhalation studies, the researchers show that adverse effects are consistently associated with exceeding a defined lung burden threshold, rather than the specific chemistry of the particle. The framework also enables the use of laboratory-based (abiotic) dissolution data to predict in vivo behaviour, supporting the move towards non-animal methods. Overall, the work offers a more robust and transparent basis for identifying PSPs and could improve consistency in hazard assessment and regulatory decision-making.