To the Editor

Within the European Seventh Framework (FP7) Programme, there are 34 projects dedicated to nanomaterial toxicology worth over €100 million1. This investment was necessary to establish public confidence, but nanotoxicology studies have not yet provided any clear and unequivocal answers on the toxicity of nanomaterials, as was highlighted in your recent Editorial2.

At present, nanomaterial toxicity is assessed by following test protocols developed by the International Organization for Standardization (ISO) and/or the Organisation for Economic Co-operation and Development (OECD)3,4. These guidance documents were established based on results of early investigations into the toxicity of nanomaterials, where size, shape, chemistry, homogeneity and processing history of the nanomaterial were shown to be important. Consequently, the need to provide physicochemical data to support toxicological findings is increasingly important. Although current measurement guidelines will inform researchers as to which physicochemical characteristics should be measured, the quality of the data generated is being questioned. In particular, current techniques may not be suitable for all nanomaterial samples (for example, if the sample has a polydisperse shape and/or size, or if it is in a complex medium). Furthermore, imaging techniques such as transmission electron microscopy may give results that are either statistically not significant or highly operator dependent. The need to develop new and better measurement techniques is clear but it will take time and substantial research.

If our immediate goal is to effectively regulate without hampering public perception on the benefits of nano-related products, first, all stakeholders should agree on the definition of a nanomaterial, and the measurement methods that would support this definition. Second, the phases of the nanomaterial life cycle should be identified so the risk associated with each phase (from synthesis to product) can be assessed. For example, carbon nanotubes may be considered high risk in a factory setting where aerosol exposure can be problematic, but may be rendered medium or low risk when encapsulated in a composite matrix. Finally, simple test methods are needed to identify these risk categories. Instead of attempting to report a number of physicochemical properties at every phase of the nanomaterial life-cycle, we need to consider if there are some overarching parameters that can easily and rapidly categorize the risk of toxicity.