Secondary organic aerosol (SOA) is
a major component of airborne
fine particulate matter (PM
2.5
) that contributes to adverse
human health effects upon inhalation. Atmospheric ozonolysis of α-pinene,
an abundantly emitted monoterpene from terrestrial vegetation, leads
to significant global SOA formation; however, its impact on pulmonary
pathophysiology remains uncertain. In this study, we quantified an
increasing concentration response of three well-established α-pinene
SOA tracers (pinic, pinonic, and 3-methyl-1,2,3-butanetricarboxylic
acids) and a full mixture of α-pinene SOA in A549 (alveolar
epithelial carcinoma) and BEAS-2B (bronchial epithelial normal) lung
cell lines. The three aforementioned tracers contributed ∼57%
of the α-pinene SOA mass under our experimental conditions.
Cellular proliferation, cell viability, and oxidative stress were
assessed as toxicological end points. The three α-pinene SOA
molecular tracers had insignificant responses in both cell types when
compared with the α-pinene SOA (up to 200 μg mL
–1
). BEAS-2B cells exposed to 200 μg mL
–1
of
α-pinene SOA decreased cellular proliferation to ∼70%
and 44% at 24- and 48-h post exposure, respectively; no changes in
A549 cells were observed. The inhibitory concentration-50 (IC
50
) in BEAS-2B cells was found to be 912 and 230 μg mL
–1
at 24 and 48 h, respectively. An approximate 4-fold
increase in cellular oxidative stress was observed in BEAS-2B cells
when compared with untreated cells, suggesting that reactive oxygen
species (ROS) buildup resulted in the downstream cytotoxicity following
24 h of exposure to α-pinene SOA. Organic hydroperoxides that
were identified in the α-pinene SOA samples likely contributed
to the ROS and cytotoxicity. This study identifies the potential components
of α-pinene SOA that likely modulate the oxidative stress response
within lung cells and highlights the need to carry out chronic exposure
studies on α-pinene SOA to elucidate its long-term inhalation
exposure effects.