The National Nanotechnology Initiative in the United States defines nanomaterials generally as follows:

Nanomaterials: a term that includes all nanosized materials, including engineered nanoparticles, incidental nanoparticles and other nano-objects, like those that exist in nature.

When particles are purposefully manufactured with nanoscale dimensions, we call them engineered nanoparticles. There are two other ways nanoparticles are formed. Nanoparticles can occur as a byproduct of combustion, industrial manufacturing, and other human activities; these are known as incidental nanoparticles. Natural processes, such as sea spray and erosion, can also create nanoparticles.

Many important functions of living organisms take place at the nanoscale. The human body uses natural nanoscale materials, such as proteins and other molecules, to control the body’s many systems and processes. A typical protein such as hemoglobin, which carries oxygen through the bloodstream, is 5 nms in diameter.¹

Meanwhile, the American Chemistry Council Nanotechnology Panel has proposed a separate definition for Engineered Nanomaterials. “The ACC Nanotechnology Panel believes that definitions used to describe Engineered Nanomaterials are important because they will be used to guide the public when information requests are made by regulators and NGO’s. It is desirable that the definitions be as simple as possible yet not so broad that the collection of meaningless information is encouraged.”² For this reason, the ACC has proposed the following definition for Engineered Nanomaterials:

Engineered Nanomaterial: any intentionally produced material that has a size in 1, 2, or 3-dimensions of typically between 1-100 nanometers.

It is noted that neither 1 nm nor 100 nm is a “bright line” and data available for materials outside of this range may be valuable. Buckyballs are also included even though they have a size <1 nm.

Exclusions:

1. Materials that do not have properties that are novel/unique/new compared to the non-nanoscale form of a material of the same composition. 2. Materials that are soluble in water or in biologically relevant solvents. Solubility occurs when the material is surrounded by solvent at the molecular level. The rate of dissolution is sufficiently fast that size is not a factor in determining a toxicological endpoint. 3. For those particles that have a particle distribution such that exceeds the 1-100 nm range (e.g. 50-500 nm) if less than 10% of the distribution falls between 1-100 nm it may be considered as non an Engineered Nanomaterial. The 10% level may be on a mass or surface area basis, whichever is more inclusive. 4. Micelles and single polymer molecules.

Inclusions:

1. Aggregates and agglomerates with size >100 nm if breakdown may occur creating particles in the 1-100 nm range during the lifecycle.²

1. National Nanotechnology Initiative FAQ

2. Consideration for a Definition for Engineered Nanomaterials, ACC- Nanotechnology Panel (March 13, 2007)