Nanotechnology, lauded by enthusiasts in its 1990s heyday, has proved to be a mixed success. However, what has come with its inception is the finding that nano-particles are more toxic than considered previously.
These nanoparticles are all chemicals that range in particle size: 10 Angstroms to 250 Angstroms in diameter.
Many nanoparticles have been identified as toxic— with the following passage taken as representative from the article.
Toxicity of Nanoparticles in the journal (2014) Current Medicinal Chemistry
with Maria Antonietta Zoroddu as the lead author—
“Several adverse properties have been unveiled for nanomaterials that were previously regarded as safe in their bulk form. A few for all, silver that is known for its antibacterial activity, has cytotoxic effect higher than that of asbestos when in the nano form and it is now reported to be toxic to animal cells as well as to humans [160,161]; TiO2, that is quite inert as a bulk material, becomes extremely dangerous when designed in a long wire shape and as a fiber that is longer than a lung macrophage is capable of sequestering. In addition, it is noteworthy that low doses (10 mg/m3 ) of 20 nm diameter sized of inhaled TiO2 nanoparticles resulted in a greater lung tumor incidence than exposure to higher doses (250 mg/m3 ) of 300 nm diameter sized particles. TiO2 nanoparticles with diameter larger than 100 nm are considered inert material both in humans and animals.”
The two cited references in passage come from the following:
 Gatti, A. M. Biocompatibility of micro- and nano-particles in the colon. Part II. Biomaterials, 2004, 25(3), 385-392.
 Soto, K.F.; Carrasco, A.; Powell, T.G.; Garza, K.M.; Murr, L.E. Comparative in vitro cytotoxicity assessment of some manufactured nanoparticulate materials characterized by transmission electron microscopy. J. Nanopart. Res., 2005, 7(2-3), 145-169.
Nanoparticles are particles of the following size— 10 Angstroms to 250 Angstroms where the sizes of individual chemical bonds are approximately 2-3 Angstroms. (One Angstrom is 0.0000001 meters) The width of one human hair is approximately 0.00005 meters.
Part of the Nano-toxicology realization is the rush to market has proved to be the Achilles heel to the chemical sciences. Herbicides, insecticides, and many other chemical products have been rushed to market without proper toxicological analyses in the past.
Other representative references follow:
From the prestigious journal: Angewandte Chemie International English Edition devoted a single 2016 issue to the problem of Nanotoxicology.
A partial list of contents follows:
Physical Effects ENPs in Aquatic Toxicity Tests
The Influence of the Dissolved Fraction on the Aquatic Toxicity of ENPs
Uptake, Internalization, and Translocation of Engineered Nanoparticles in Aquatic Organisms
Known Mechanisms of ENP Ecotoxicity — The Question of Particle Properties
Implications of ENP Behavior in Guideline Tests for Assessment of Chemical Safety