Antimony in brake pads - a carcinogenic component?

Antimony trisulfide (Sb2S3) is used as a lubricant in friction material. X-ray diffraction analysis revealed Sb in 3/3 disc brake pads (range 41,000–46,000 mg/kg) and in 2/2 disc brake dust samples (21,000 and 17,000 mg/kg) from trucks. Considerably lower concentrations were found in drum brake pads (3/5, 59–6400 mg/kg) and in drum brake dust (4/18, 78–2800 mg/kg). Other toxic metals were also detected in pads and dust. The health risk of Sb in particulate brake emissions should be dependent on particle size and chemical entity, in particular solubility. A significant amount of the emitted dust was shown by size-fractionated optical particle counting to be inhalable in environmental (>90% mass) and occupational (>50% mass) exposure situations. Differentiation via selective solubility showed a considerable amount of Sb2S3 to oxidize during the braking process, likely leading to the formation of Sb2O3, a suspected human carcinogen. Sb in brake dust was soluble in calf serum (8:5 � 1:2%, 8:9 � 1: 7m g= la t 37 v