A new study suggests there is more to nanoparticle toxicology than cell life and death. Immune cells treated with nano iron oxide particles appeared healthy in standard toxicology tests. However, when exposed to the pneumonia causing bacteria Streptococcus pneumoniae the immune cells struggled to destroy them.

These recent results are consistent with previous studies that found that mice that had inhaled copper nanoparticles or carbon nanotubes were less able to clear bacteria from their lungs. Similar effects have also been observed in people exposed to ultra-fine particles in air pollution.

The researchers have raised concerns that exposure to significant levels of the nanoparticles may adversely affect people’s immune systems.

Engineered nanoparticles are now used in everything from washing machines to cosmetics and in vitro (test tube) systems are increasingly used to assess their toxicity. This has led the authors of the study to warn that the potential health hazards associated with nanoparticles may be due to indirect effects rather than direct toxicity. Nanotoxicology screening strategies must therefore consider whether these emerging materials make our bodies less able to deal with other pollutants or pathogens.