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The Sponsorship Programme for the Testing of Manufactured Nanomaterials (further referred to as “the Testing Programme”) was concluded in March 2013, and the publication of the dossiers via the OECD website (www.oecd.org/science/nanosafety) started in June 2015. As indicated in the “Guidance manual for the testing of manufactured nanomaterials: OECD’s sponsorship programme”, after conclusion of the Testing Programme a next step is to consider “the status, need for, and coordination of further test development”. Parallel to concluding the final stages of the Testing Programme, a series of workshops have taken place, in which for different topics the applicability of existing OECD test guidelines for nanomaterials was discussed and the need for new ones analysed. One workshop focussed on physico-chemical methods, addressing in detail the relevance of each physico-chemical endpoint proposed in the Testing Programme for the regulation of nanomaterials. The methods were discussed in more general terms. However, as most of the proposed endpoints are new to the OECD Test Guidelines Programme, a much more detailed evaluation of the applied methods would
be highly relevant.
To this extent,the Netherlands volunteered to lead an initial detailed evaluation of the applicability of the test methods applied to determine the physico-chemical properties of different types of nanomaterials in the Testing Programme. This initial focus on physico-chemical properties was prompted by the essential need for an adequate and complete characterisation of nanomaterials to enable a further evaluation of their (toxicological) properties.
A number of experts from several delegations volunteered to review and evaluate the methods applied to determine the physico-chemical properties of the nanomaterials in the Testing Programme.
The primary crystallite size of titania powder relates to its properties in a number of applications. Transmission electron microscopy was used in this interlaboratory comparison (ILC) to measure primary crystallite size and shape distributions for a commercial aggregated titania powder. Data of four size descriptors and two shape descriptors were evaluated across nine laboratories. Data repeatability and reproducibility was evaluated by analysis of variance. One-third of the laboratory pairs had similar size descriptor data, but 83% of the pairs had similar aspect ratio data. Scale descriptor distributions were generally unimodal and were well-described by lognormal reference models. Shape descriptor distributions were multi-modal but data visualization plots demonstrated that the Weibull distribution was preferred to the normal distribution. For the equivalent circular diameter size descriptor, measurement uncertainties of the lognormal distribution scale and width parameters were 9.5% and 22%, respectively. For the aspect ratio shape descriptor, the measurement uncertainties of the Weibull distribution scale and width parameters were 7.0% and 26%, respectively. Both measurement uncertainty estimates and data visualizations should be used to analyze size and shape distributions of particles on the nanoscale.