Researchers at University of California reported that titanium dioxide nanoparticles (TiO2), found in everything from cosmetics and sunscreens to paint and vitamins, caused DNA damage when fed to mice. They induced breaks in DNA, damaged chromosomes, and caused inflammation of tissues; all of which increase the risk of cancers.

A team of researchers in Taiwan showed that exposing mammalian cells to TiO2 nanoparticles at 10 ppm in the short-term and long-term exposure resulted in enhancement of cell growth and a dramatic increase in transformed (cancerous) cells , resulting from a disturbance of cell division and genome instability. Similar toxicities have been found for other nanoparticles often used with TiO2, such as ZnO2 and SiO2.
Nano-silver, even more widely used than nano-TiO2, is toxic to beneficial bacteria that break down wastes and recycle nutrients in the soil.Fullerenes, which finds applications in electronics, electro-optics and much more besides, including cosmetics are being considered for drug delivery and cancer therapy also.

Fullerenes caused oxidative brain damage (through lipid peroxidation) in juvenile largemouth bass via the olfactory nerve.

Carbon nanotubes, long thin structures derived from fullerenes and often compared to asbestos, caused inflammation and granulomas when instilled into the lungs of mice. These results have now been confirmed in a study in which the mice inhaled aerosols of multiwall carbon nanotubes. Inflammation and granulomas were found in the lungs even at the lowest concentration.
Quantum dots are nanosized semi-conductors that generate electron-hole pairs confined in all three dimensions (quantum confinement), and hence behave like giant molecules rather than bulk semiconductors. They have numerous applications in light emitting diodes, transistors, solar cells etc., and are also being developed for drug delivery, cancer therapy and cell imaging. Unfortunately, most quantum dots contain highly toxic metals such as cadmium, which tends to be released when the quantum dots enter the cells or organisms. This was thought to be the main reason why CdSe/ZnSe quantum dots at nanomolar (10-9mol) concentrations were toxic to Daphnia magna, but much less toxic than the equivalent concentration of cadmium ions. However, CdTe quantum dots coated with hydrophilic sodium thioglycolate caused disruption in a cultured monolayer of Caco-2 human intestinal cells and cell-death at 0.1 ppm, which was thought to be caused by the quantum dots, rather than cadmium. In another study, CdSe/ZnS quantum dots injected intravenously into mice caused marked vascular thrombosis in the lungs at 0.7 to 3.6 nanomol per mouse, especially when the quantum dots had carboxylate surface groups. Three out of four mice injected at the higher concentration died immediately. The injected quantum dots were mainly found in the lungs, liver and blood; and it was hypothesized that the quantum dots activated the coagulation cascade through contact. In fact, many kinds of nanoparticles enhance the formation of insoluble fibrous protein aggregates (amyloids), which are associated with human diseases including Alzheimer’s, Parkinson’s and Creutzfeld-Jacob disease.