The multiplicity of ENM variants makes material-by-material assessment impractical. That heterogeneity in nanomaterials, characterized by distributions of properties, has spurred efforts to generalize about exposure and hazard potential in relation to these properties, rather than considering risks for specific types of materials. Initial attempts point to complexities in understanding risks of ENMs (Dreher 2004). For example, the size range used to describe ENMs—1-100 nm— has relatively little bearing itself in determining the risk to people or the environment (see, for example, Auffan et al. 2009; Drezek and Tour 2010). Risk “problems” associated with ENMs have been formulated in terms of established “technologic” characteristics of ENMs (such as particle size) that do not appropriately reflect the potential for harm.

Framing risks associated with an ENM in terms of established definitions provides some insight into emergent risks. For example, exposure potential may be enhanced as particle size decreases to the point where novel physicochemical properties begin to dominate behavior. At the same time, a focus on particle size may highlight issues that are not relevant while shifting attention from such properties as reactivity that may be more relevant to determining risks (for example, Maynard 2011; Maynard et al. 2011a). Consequently, there is substantial uncertainty in understanding of the risks associated with the products of nanotechnology, leading to confusion on prioritizing, and addressing these risks— a confusion that is illustrated in many reports on risk. (See discussion in Chapter 1.)

In making risk-based decisions—whether translating an innovative idea into a new product, crafting new regulations, or developing a risk-research strategy—effective problem formulation is essential (NRC 2009). Formulating the environmental, health, and safety (EHS) “problems” presented by ENMs has proved challenging, as documented by research efforts over the last decade.

DEVELOPING A STRATEGY AND A CONCEPTUAL FRAMEWORK

In addressing the challenges presented by ENMs, the committee notes that there is a distinction between a research strategy and a research agenda. The committee has developed a strategy that provides a principle-based approach to sustaining an agenda for EHS research that will be accountable and adaptive as ENMs change, diversify, and expand in use. In this chapter, the committee describes the research framework for its strategy; later chapters identify data gaps to be addressed by the research strategy. The generation of findings for risk assessment is considered here as an evolving process based on the integration of various research efforts rather than as a static “deliverable.” There will be an ongoing need to inform decision-making in advance of product development and to consider uncertainty coming from incomplete information on future production quantities, ENM properties, and uses of nanomaterials. An evolving and iterative process provides feedback for adjusting research priorities and provides



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