Respiratory deposition and health risk of inhalation of particle-bound heavy metals in the carbon black feeding area of a tire manufacturer

The health effects of metal-containing carbon black (CB) particles obtained from the CB feeding area of a tire manufacturing plant were investigated. Atmospheric samples were collected over 24 h for 20 working days in 2016 using the 12 impaction stages of micro-orifice uniform deposit impactor, and metal-containing particles were analyzed using an inductively coupled plasma optical emission spectrometer. The concentration of total particulate matter in the CB feeding area was 944.8 +/- 456.4 mu g/m(3), and the most abundant elements in the samples include Zn (8622.0 +/- 5679.0 ng/m(3)), Al (3113.3 +/- 2017.1 ng/m(3)), and Fe (1519.1 +/- 875.0 ng/m(3)). Carcinogenic metals (Cd, Co, Cr, and Ni) with the mass median diameter were incorporated in submicron particles. The mean total deposition flux in the head airway (HA) region was approximately 16-30 times higher than that in the tracheobronchial (TB) region and alveolar region (AR). The most abundant deposition flux of heavy metals in the AR and TB region was distributed in particles of less than 3.2 mu m. The cancer risk presented by carcinogenic metals (Cd, Co, Cr, and Ni) in total particles to CB feeding workers ranged from 5.52 x 10(-4) to 5.65 x 10(-2), which is substantially higher than the acceptable cancer risk range 10(-6)-10(-4). In particular, the cancer risk presented by these four metals in ultrafine particles (UFPs) exceeded the 10(-6) benchmark level. These results demonstrate the high health risk presented by particle-bound heavy metals to workers in a CB feeding area via inhalation exposure.