Unattached Fraction of Radon Progeny as an Experimental Tool in the Assessment of the Risk of Nanoparticles* - Aerosols: Measurement, Dosimetry, and Health Effects - page 423

16.1.7 c ellular e ntering M ecHanisMs
A review of literature on existing knowledge and uncertainties regarding nanoparticles into cell
penetration is presented in IOM report CBO407.
Nanoparticles into cell penetration have been observed to be size and temperature dependent
(IOM, CBO407).
It was shown that after inhalation 25 nm particles of TiO 2 has been observed in greater amount
in lung interstitium than 250 nm particles.
The uptake of nano- and microparticles of polylactic polyclycolic acid copolymer of 100 nm was
2.5-fold greater than that of 1,000 nm and 6-fold greater than 10,000 nm particles. The uptake rate
was greater at 37°C than at 4°C (Desal et al., 1997).
In a study (Rejman et al., 2004) it was observed that the uptake of 50 nm beads was three- to
fourfold greater than for 100 nm and 8-10 times greater than for 1000 nm.
There is very limited work in published literature on the interaction of nanoparticles with cell
membranes and their behavior within the cells.
As it was underlined in IOM, CBO407, it is clear from the review of literature that many studies
on nanoparticles into cell penetration did not investigate systematically the physicochemical factors
which control these processes. Therefore, it is dificult to understand the role of each of the factors
from these studies where many factors and variables are reported (size, surface coating, and charge).
Moreover, such properties of nanoparticles as surface chemistry or aggregation in biological or
other luids cannot be in equilibrium or even at steady state and these properties may well change
as a function of time.
In Bhabra et al. (2009) it was reported that nanoparticles of chromium, 29.5 ± 6.3 nm in diameter,
can damage human ibroblast cells even without having to cross the barrier.
16.1.7.1 Conclusions
Assessment of the dose and correspondent risk associated with nanoaerosols is a very complicated
process consisting of many individual steps and parameters which should be determined by
measurement or calculation.
Unfortunately the strategy for this process is not developed and as a result it is not clear exactly
what kind of physical values determining the dose as a cause of health effect should be measured.
In this chapter we presented the possible strategy for the dose assessment of nanoaerosols in the
form of dosimetric road map that allows analyzing the gaps between available and necessary infor-
mation on every dosimetric parameter in the case of nanoaerosols.
Dosimetric road map consists of two main branches:
1. Parameters related to nanoaerosols airborne concentration measurement
2. Parameters of lung deposition and lung dosimetry for nanoaerosols
A review of the literature suggested that in the case of nanoparticles not the mass concentration
but rather the particle surface area and particle concentration are better metric especially for health
effect characterization. Generally speaking aerosol mass concentration cannot be used as a measure
of the health effect in the case of nanoaerosols.
As a result, the calculation of the exposure based on measured concentration and time cannot be
considered as a measure of the health effect in the case of nanoaerosols. So, at a present time it is
not possible to get a valuable quantitative assessment of the exposure in the case of nanoaerosols. In
practice, it is dificult to ind studies with the assessment of the exposure in occupational setting or
other types of contacts between human and nanoaerosols.
In principle, there cannot be a correlation between exposure and effect in the case of nanoaerosols,
especially because we can see from dosimetric road map in this case so many different factors will
affect the inal assessment of the dose.