Nanomaterials are understood as chemicals in the REACH directive and approaches of “classical” toxicology generally applied. Nevertheless, some properties of nanomaterials differ from compounds, e.g. size of basic unit, transport properties, corona etc. Growing use of nanomaterials will lead to their release to the environment and potential, even today unknown behaviour may appear. Human society has wide range of experience with unexpected or unknown toxic effects of engineered compounds (molecules), which may have parallel in nanoscale and which may demand development of new methods. Some examples are: Global pollution by lead in petrol anti-knock. Need of monitoring techniques for NMs in environment distinguishing ENM from natural NM is challenge arising from this parallel. Persistence, long-distance transport and bioaccumulation of POPs show us the necessity to understand and to measure transport properties, behaviour in living organisms an life cycle of ENMs. Mercury transformation to more toxic methylmercury (e.g. Minamata disease) is an example of environmental transformation with increased hazard and its parallel may be transformation of ENM to other, more toxic particles in environment, and even their ”invisibility”. Environmental fate studies will need both identification and monitoring technics, only rarely present today. New forms of toxicity and gaps in testing may be recognized in nanoscale, similarly as endocrine disruption or thalidomide effects were unexpected before their discovery. Since the questions about behaviour of nanomaterials in environment will be understood enough, already existing precautionary technics as life cycle analysis and cleaner production may be applied to minimize exposure to nanomaterials throw environment.Keywords: Engineered nanomaterials, toxicity, persistence, bioaccumulation, transformation
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