Solubility impact.

Depending on their chemical nature, some particles may dissolve more or less rapidly in biological fluids, thus promoting their transfer throughout the organism. Then they lose their structure of nanoparticles and their toxicity is that of a conventional chemical risk.

One might think that nanoparticles that dissolve very quickly probably have a toxicity close to that of particles of the same chemical nature but of a larger scale. 

In contrast, nanoparticles that dissolve slowly or do not dissolve will probably move more slowly from the lung to the rest of the organism. Specific effects related to the structure of nanoparticles will last longer.