Although polystyrene nanoparticles are generally considered nontoxic, a study shows that ingesting them can influence iron uptake and transport (Nat. Nanotechnol., DOI: 10.1038/nnano.2012.3). The finding, by Cornell University’s Michael L. Shuler and colleagues, suggests there may be a mechanism by which ingested nanoparticles exert a subtle yet harmful effect. The researchers examined how carboxylated polystyrene particles just 50 nm in diameter behaved in an in vitro model of the human intestinal epithelium and in tests with live chickens given doses that mimic potential human exposure. Intestinal cells in the in vitro model showed increased iron transport because of disruptions to the cell membrane. Chickens with acute nanoparticle exposure had lower iron absorption than either unexposed or chronically exposed chickens. The researchers found that the villi—tiny projections in the intestinal walls—of chickens subjected to chronic exposure remodeled themselves to increase the surface area for iron absorption. People don’t typically eat polystyrene nanoparticles, but the researchers wonder whether nanoparticles commonly used as food additives, such as titanium dioxide and silicates, might have similar effects.