Fig 1. Cytotoxicity in normal and cystic fibrosis (CF) human bronchial epithelia (HBE) 24 h after exposure to seasonally sampled PM from either an urban roadside (Bern) or a rural alpine valley (Magadino).

(a) Cytotoxicity presented as percentage of total lactate dehydrogenase (LDH) released from damaged cells into the apical compartment. Low dose deposited on HBE = 0.9–2.5 μg per cm² of cell culture area, high dose = 8.8–25.4 μg/cm². The data are presented as mean values and error bars representing 1 standard deviation (SD) of three independent experiments with triplicate cell cultures (total n = 9 cell cultures). ANOVA, Dunnett’s multiple comparison). (b) Scatter plot and corresponding regression line for normal and CF HBE, evaluating the relationship of cytotoxicity and deposited particle dose (repeated measurements at the same dose are displayed for visualization). * p-value < 0.05 compared to filter blank. Abbreviation: R² = R-square linear coefficient of determination.