Exposure and respiratory tract deposition of particulate matter among teachers using chalkboards in selected public secondary schools in the Johannesburg region.

Particulate matter (PM4) was collected from teachers' breathing zones during classroom lessons using GilAir 3 personal pumps attached to a cyclone (cut-point: PM4) connected to a 25 mm cassette housing a polyvinyl chloride membrane filter. Sampling was conducted at 1.85 L/min from Monday to Friday between 08:00 and 14:35. Sixty samples were collected from 12 teachers (seven females and five males). A multipath particle dosimetry model was used to predict particle deposition in teachers' respiratory tracts at low, moderate, and high exertion levels during nasal and oronasal breathing. PM4 concentrations ranged from 0.019 to 0.761 mg/m3, with an average of 0.126 ± 0.134 mg/m3. Chalk use (β = 0.468, p < 0.001) and sampling duration (β = 0.305, p < 0.001) were positively associated with PM4 concentrations. Breathing route was the main determinant of particle deposition, and the deposition varied by sex, respiratory region, and exertion level. Males exhibited greater deposited mass than females across all breathing routes and exertion levels. Particle clearance was slower in the alveolar region than in the tracheobronchial region in both sexes, allowing prolonged particle retention. Teachers may be at risk of developing respiratory disorders even when exposed to PM4 concentrations below the relevant occupational exposure limit.