High-resolution characterization of magnetite nanoparticles
(MNPs)
derived from coal combustion activities is crucial to better understand
their health-related risks. In this study, size distribution and elemental
composition of individual MNPs from various coal fly ashes (CFAs)
collected from a representative coal-fired power plant were analyzed
using a single-particle inductively coupled plasma time-of-flight
mass spectrometry technique. Majority (61–80%) of MNPs were
identified as multimetal (mm)-MNPs, while the contribution of single
metal (sm)-MNPs to the total increased throughout all the CFAs, reaching
the highest in fly ash escaped through the stack (EFA). Among Fe-rich
MNPs, Fe-sole and Fe–Al matrices were predominant, and Fe-sole
MNPs were identified as the important carrier for toxic metals, with
the highest mass contributions of toxic metals therein. Toxic potency
results showed that the oxidative stress induced by MNPs was 1.2–2.2
times greater than those of <1 μm fractions in CFAs, while
the reduction in cell viability showed no significant difference,
elucidating that these MNPs can induce more distinct oxidative stress
compared to cell toxicity. Based on structural equation model, MNP
size can both directly and indirectly regulate the toxic potency,
and the indirect regulation is through a size-dependent elemental
composition of MNPs, including toxic metals. sm-MNPs and Fe-rich MNPs
with Fe-sole, Fe–Cr, and Fe–Zn matrices can regulate
the oxidative stress, whereas Cr, Zn, and Pb associated with Fe-sole,
Fe–Al, Si–Fe, and Al–Fe MNPs showed significant
effects on cell viability.