## 5 General Recommendations for Various Stakeholders
### Governmental Agencies and Funders  
The authors helped to identify a number of limitations of the OECD Technical Guidance Document (TGD) for Risk Assessment of Chemicals in relation to environmental exposure: a lack of information on physico-chemical properties relevant for NMs; a lack of access to information on production, emissions throughout the life-cycle, _etc._; fundamental limitations of the various assumptions made such as Kow being a good descriptor for processes like sorption and bioconcentration; and fundamental limitations of the various models of fate and degradation of NMs since they are developed for organic chemicals and for non-particulates. We propose the development of three interacting models: one for dissolved ions, one for NMs and one for aggregates and agglomerates.  
**Recommendation 33**: Government agencies fund and/or conduct more exposure monitoring at workplaces along the process of production, use and elimination and recycling in order to make more data available for risk assessors and researchers. They should set up registries of potentially exposed workers and if possible add information about exposure measurements and health assessments.  
**Recommendation 34**: Specific public funding is required for the development of material-specific analytical methods, such as routine analytical methods for characterisation of NMs in complex matrices; interaction of specific NMs and cellular energy metabolism (with the generation of Reactive Oxygen Species as a side product); the establishment of clear Structure-Property Relationships which govern the interaction with, uptake by, trafficking within and response of biological systems.  
**Recommendation 35**: One of the highest priorities must be funding to develop routine methods for the measurement of NMs in tissues. For example, information on tissue concentrations would be used to link cause and effect (dose-response), used to calculate key parameters in environmental risk assessments like bioconcentration factors (see [PERSON] _et al._, 2012 [64] for concerns regarding these tests), or be needed for the pharmacokinetics that are an absolute requirement for the registrations of new medicines. These are potential bottlenecks that can prevent a product being registered, and therefore prevent innovation.  
**Recommendation 36**: The kinetics of NMs in biological systems need funded research. Particle systems of well-defined and systematically variable physico-chemical properties should be employed. Some problems areas needing urgent study are as follows: The role of NMs and 'Trojan horse' uptake of contaminants (see Recommendation 1 above); and the relation between the ageing of NMs and the kinetics of NMs in biological systems. There is a need for funding of research on discrete body systems (cardiac, renal, neural, hormone system, _etc._) where they have been given little attention so far. Regarding human related hazard assessment only data from animal studies are accepted so far but _in vitro_ human models and co culture human models are crucially important to be further developed and considered in near future in combination with high throughput technologies and use of quality assurance and nano-specific reference standards following good laboratory practice.  
**Recommendation 37**: Regional and global environmental agencies should consider funding in a number of areas where knowledge is negligible, such as organisms that are not standard OECD test organisms and searching for new end-points for NM interactions. Nearly all our existing knowledge comes from a few organisms used mainly in regulatory tests from freshwater. Risk assessors currently cannot construct species sensitivity distributions (no data on different species) and we are a long way from the notion of 'protecting most of the organisms most of the time' in ecosystems. Gaps include amphibians, birds, reptiles, and most of the marine phyla, and non-crop plants. Data on tropical ecosystems are also lacking.