Several effects have already been shown in animals. Among these, toxic effects have been identified in several organs (heart, lungs, kidneys, reproductive system ), as well as genotoxicity and cytotoxicity. For example, some particles cause granulomas, fibrosis and tumoural reactions in the lungs. Thus, titanium dioxide, a substance recognized as having low toxicity, shows high pulmonary toxicity on the nano-scale in some studies and no or almost no effects in other studies. In general, the toxicological data specific to nanoparticles remains limited, often rendering quantitative risk assessment difficult due to the small number of studies for most substances, the short exposure.
