## 3 Characterisation
### Characterising Released Nanomaterials  
The major obstacle in studying NMs release, transformation and exposure is the characterisation of the particles themselves especially in complex matrices like the ecological environment or in a living organism. Even discrimination between particles by general type, such as engineered (e.g., CNTs) or natural (e.g., volcanic) or incidental (e.g., traffic pollutants), is difficult but of great importance when assessing exposure and for analyses that interface with health studies. In real-life scenarios the researcher may be presented with a \"soup\" of diverse nanoparticles to analyse and understand. This problem increases as the specific NMs become ever more removed from the actual source (both in time and space).  
Certainly, in a defined workplace environment specific NMs may be expected and the release and exposure can be targeted using specific search criteria and protocols, and hence it is often possible to limit resources to stipulate parameters exactly fitting the purpose. Some strategies and techniques have been developed and tested in workplaces (reviewed in [PERSON] _et al._[41] However, severe limitations exist even for research purposes and the existing techniques cannot always be employed in routine workplace measurements. In the wider environment it becomes even more difficult or impossible to develop a reliable and feasible method as released NMs may undergo ageing and diverse transformations.  
The effect of such transformations--whether air, water, soil or biological media or systems--should ideally be taken into account in exposure modelling, where relevant. Examples of such changes include loss of coatings, change in coating composition, development of a \"corona\" (a fuzzy coating) which depends on the particle surface properties and the nature of the biomolecules and ions available in the surrounding milieu, and dissolution in liquid media. These changes are fast and dynamic and current technologies are not sufficiently well-developed to provide rapid assessments in a coherent manner.  
The main monitoring techniques currently employed do not necessarily give the kind of _in situ_ characterisation needed. They are either microscopic methods for partial information on particle morphology, state of aggregation and chemical composition, or methods discriminating particles by size in relevant media (water, air, _etc._). The latter sometimes allow subsequent separate analysis for chemical composition. Examples are an Aerosol Mass Spectrometer [42] or the Field Flow Fractionation technique coupled with mass spectrometry for liquids. Both methods provide information on particle-size dependent chemistry.  
**Recommendation 11**: Given the complexity, in the short term possible key release processes should be identified for particular products containing specific and characterisable NMs along the life-cycle. This would involve the identification of possible exposure routes and uptake paths of engineered NMs during the life-cycle, fate and behaviour of such materials in the environment, with exposure concentrations, and enabling a wider risk assessment. We need predictive models on how a nanomaterial will interact with and be transformed by its surroundings through time, and how these changes may influence subsequent transport, accumulation and reactivity. Such data generation would be complex and advanced computational techniques may be necessary to handle them for meaningful NM risk management.