Physicochemical Characteristics

"Unlike gases, liquids and many solid materials, the desirable properties of Engineered Nanomaterials closely depend on size, shape and structure (both physically and chemically) at the nanoscale. Similarly, there is a strong likelihood that biological activity will depend on physicochemical parameters not usually considered in toxicity screening studies. Although quantitative toxicity studies on Engineered Nanomaterials are still relatively sparse, published data on fullerenes, single walled carbon nanotubes, nanoscale metal oxides such as TiO2 and nanometer-diameter low solubility particles, support the need to carefully consider how nanomaterials are characterized when evaluating potential biological activity. Respirable fibers present perhaps the closest analogy to a material that is not fully characterized by mass and chemical composition alone. However, the diversity and complexity of nanomaterials suggests that the level of characterization appropriate to toxicity screening tests will be commensurately more sophisticated."¹

• Particle Size and Size Distribution

"The unusual properties of nanomaterials are predominantly associated with their nanometer-scale structure, size and structure-dependent electronic configurations and an extremely large surface-to-volume ratio relative to bulk materials. Particles in the nanosize range can deposit in all regions of the respiratory tract including the distal lungs. Due to their small size, nanoparticles may pass into cells directly through the cell membrane or penetrate between or through cells and translocate to other parts of the body. Limited data have suggested possible translocation of inhaled nanoparticles to the nervous system and other organs/tissues . . . ."²

• Surface Area

"The size of nanoparticles alone may not be the critical factor determining their toxicity; the overall number and thus the total surface area may also be important. As a particle decreases in size, the surface area increases (per unit mass only; if you normalize to number of particles, the surface area decreases) and a greater proportion of atoms/molecules are found at the surface compared to those inside. Thus, nanoparticles have a much larger surface area per unit mass compared with larger particles. The increase in the surface-to-volume ratio results in the increase of the particle surface energy which may render them more biologically reactive."³

• Surface Chemistry (or Activity)
• Other

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1. G. Oberdörster, A. Maynard, K. Donaldson, et al, “Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy,” Particle and Fibre Toxicology 2005, 2:8, § 4.1.1 (footnotes omitted).

2. G. Oberdörster, A. Maynard, K. Donaldson, et al, “Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy,” Particle and Fibre Toxicology 2005, 2:8, § 4.1.3 (footnotes omitted).

3. G. Oberdörster, A. Maynard, K. Donaldson, et al, “Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy,” Particle and Fibre Toxicology 2005, 2:8, § 4.1.3.