The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated iron oxides, considering all toxicity endpoints. Publications and available unpublished studies are the basis for the evaluation.
Following exposure to iron oxide dusts (poorly soluble particles) effects on the lungs are considered to be the critical effects. However, although iron oxides are poorly soluble, it cannot be excluded that small amounts of soluble Fe(II) or Fe(III) ions are also present in the lungs after inhalation. Toxic effects of iron oxides are only expected when the homeostasis of iron in the body is deregulated or exceeded. Under these conditions iron ions may cause an increased formation of reactive oxygen species via the Fenton reaction. These ions can trigger genotoxic and carcinogenic changes.
Although an increased risk for lung cancer has been observed in employees at workplaces with exposures to dust containing iron oxides this is probably due to simultaneous exposure to other toxic compounds, and no final statement can be made on the carcinogenicity of iron oxides in humans. After intratracheal application of iron oxides in high doses an increased tumour incidence in the lungs of rats was observed. Therefore, and on the indication for a genotoxic effect of iron ions in in vitro studies, iron oxides are classified in Carcinogen Category 3B. Skin contact is not expected to contribute to systemic toxicity. Practically no risk of sensitization is to be expected, although the data to support this statement are scarce.