Nanotechnology and the production of nanomaterials have been expanding rapidly in recent years. Since many types of engineered nanoparticles are suspected to be toxic to living organisms and to have a negative impact on the environment, the process of designing new nanoparticles and their applications must be accompanied by a thorough risk analysis. (Quantitative) Structure-Activity Relationship ([Q]SAR) modelling creates promising options among the available methods for the risk assessment. These in silico models can be used to predict a variety of properties, including the toxicity of newly designed nanoparticles. However, (Q)SAR models must be appropriately validated to ensure the clarity, consistency and reliability of predictions. This paper is a joint initiative from recently completed European research projects focused on developing (Q)SAR methodology for nanomaterials. The aim was to interpret and expand the guidance for the well-known “OECD Principles for the Validation, for Regulatory Purposes, of (Q)SAR Models”, with reference to nano-(Q)SAR, and present our opinions on the criteria to be fulfilled for models developed for nanoparticles.

Conclusions
(Quantitative) Structure-Activity Relationship ([Q]SAR) modelling is one possibility for estimating hazard or exposure related characteristics, either in the context of a risk assessment or as part of a “safe-by-design” approach. It might be used for predicting a variety of properties, including toxicity of newly designed nanoparticles. However, every nano-(Q)SAR must be appropriately validated, which is crucial for ensuring its predictive accuracy.

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