CHAPTER 2: The Devil is in the Definition

Nanomaterials are explicitly or implicitly addressed in a variety of legislative provisions worldwide. For legal clarity it is necessary to define the term ″nanomaterial″ in a regulatory context. This chapter discusses the challenges in finding an appropriate definition that fits in with hazard neutral or with hazard related contexts. Approaches to find appropriate defining criteria can involve specifying quantitative, semi-quantitative and qualitative identifiers. Whereas size is used as criterion to identify nanomaterials in hazard neutral as well as in hazard related contexts, other identifiers (certain physicochemical, novel or unique properties) are used more in hazard-driven regulatory contexts. The practical implementation of nanomaterial definitions leads to further challenges regarding the measurement of quantitative identifiers and particularly the specification of semi-quantitative and qualitative criteria. In addition, clear and open communication between all stakeholders is essential to establish and implement regulatory definitions of the term nanomaterial in specific contexts and to generate and communicate a broad understanding of the term.