Table 1: Comparison of the lowest observed effect levels (LOELs) for nanoparticles exposure of cells exposed at ALI and submerged conditions.

ReferenceParticle typeHuman epithelial cell typeTime at ALI prior to exposureExposure
time
Postincubation
time
Exposure
time
Postincubation
time
Biological parameterDose for the lowest observed effect level (LOEL)1
ALIALISubmergedSubmergedSubmerged
( g/cm2)
ALI
(μg/cm2)
ALI more sensitive than submerged

IL-8 (mRNA) 12.5–25≤2.0yes
[26]Coarse urban PMBronchial
(primary)
3 d3 h0 h0 h1 hHOX-1 (mRNA) 25–65≤2.0yes
COX-2 (mRNA) ≤7.0≤2.0unclear

[24]Diesel sootBronchial (16HBE14o)?26 h20 h6 h20 hIL-8 (protein) 0.25–1.88>0.1unclear

IL-8 (mRNA) 0.7–2.5<0.7yes
GM-CSF
(mRNA)
>2.50.73yes
This studyAgglomerated ZnO nanoparticlesAlveolar type II (A549)1 h3 h0 h1 h0 hIL-6 (mRNA) >2.5 <0.7yes
HMOX1 (mRNA) >2.5>2.2unclear
SOD-2 (mRNA) >2.5>2.2unclear
GCS
(mRNA)
>2.50.7–2.5yes

1LOEL: lowest dose in μg/cm2 at which a statistically significant effect ( ) was observed relative to the control.
2Not stated in publication.
3Here: 0.7 μg/cm2 showed a significant effect, while 2.2 μg/cm2 was not statistically significant due to larger variability in the data. Hence, we assume that 0.7 μg/cm2 is a good estimate for LOEL.