1 © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com small 2011, X, No. XX, 1–12 On the Lifecycle of Nanocomposites: Comparing Released Fragments and their In-Vivo Hazards from Three Release Mechanisms and Four Nanocomposites Wendel Wohlleben,* Sandra Brill, Matthias W. Meier, Michael Mertler, Gerhard Cox, Sabine Hirth, Bernhard von Vacano, Volker Strauss, Silke Treumann, Karin Wiench, Lan Ma-Hock, and Robert Landsiedel 1. Introduction Nanocomposites are internally nanostructured mate- rials, [1] generated spontaneously or by nanofillers (nanopar- ticles, -platelets, or -fibers) dispersed in a continuous matrix material. The combination of seemingly adverse properties (scratch resistance and elasticity, conductivity and transpar- ency, etc.) enables nanocomposites to cannibalize traditional materials such as metals and polymers. [2,3] The high annual growth rates at a market size of around $28 billion in 2009 [4] are evidence of the fast spread of nanocomposites. But are they safe? Consumer contact with nanocomposites has received limited attention by science and regulators. [5] Hazard assessment has focused on nanoparticles and nanofibers, ori- ented towards occupational safety. [6,7] In-vitro [8] and in-vivo DOI: 10.1002/smll.201002054 Dr. W. Wohlleben, S. Brill, Dr. V. Strauss, Dr. S. Treumann, Dr. L. Ma-Hock, Dr. R. Landsiedel Experimental Toxicology GV/T BASF SE 67056 Ludwigshafen, Germany E-mail: wendel.wohlleben@basf.com Dr. W. Wohlleben, Dr. G. Cox, Dr. S. Hirth, Dr. B. von Vacano Polymer Physics GKC BASF SE 67056 Ludwigshafen, Germany Dr. M. W. Meier, Dr. M. Mertler Aerosol Technology GCP/T BASF SE 67056 Ludwigshafen, Germany Dr. K. Wiench Product Safety GUP/PC BASF SE 67056 Ludwigshafen, Germany Nanocomposites are the dominating class of nanomaterials to come into consumer contact, and were in general assumed to pose low risk. The first data is now emerging on the exposure from nanocomposites, but little is yet known about their hypothetical nanospecific physiological effects, giving ample room for speculation. For the first time, this comprehensive study addresses these aspects in a systematic series of thermoplastic and cementitious nanocomposite materials. Earlier reports that ‘chalking’, the release of pigments from weathered paints, also occurs for nanocomposites, are confirmed. In contrast, mechanical forces by normal consumer use or do-it-yourself sanding do not disrupt nanofillers (nanoparticles or nanofibers) from the matrix. Detailed evidence is provided for the nature of the degradation products: no free nanofillers are detected up to the detection threshold of 100 ppm. Sanding powders measuring 1 to 80 μm in diameter are identified with the original material, still containing the nanofillers. The potential hazard from aerosols generated by sanding nanocomposites up to the nuisance dust limit is also investigated. In-vivo instillation in rats is used to quantify physiological effects on degradation products from abraded nanocomposites, in comparison to the abraded matrix without nanofiller and to the pure nanofiller. In this pioneering and preliminary evaluation, the hazards cannot be distinguished with or without nanofiller. Nanocomposites