Challenges of Regulation and Risk Assessment of Nanomaterials

5. EXPOSURE ASSESSMENT
5.1. Summary record
Exposure is a central concept in risk assessment: if there is no exposure, there is no risk. Therefore,
exposure assessment studies for nanomaterials (NM) are a cornerstone to carry out reliable risk
assessment. However, there are very few studies so far and mostly concentrated in the occupational
area. The goal of this session was to present some examples of exposure measurement and
estimation, hoping to have more of these studies available in near future.
Among other exposure pathways, the consumer exposure via spray products is considered a priority,
since it could lead to significant acute exposure to NM. In the market there are several products to
treat surfaces obtaining a nanofilm inducing the loto effect (increased hydrophobic properties of the
surfaces). In general the goal is to simplify cleaning and to reduce the amount of cleaning substances
used. Not all of these products contain actual NM, but they were considered because of the
generation of a nanofilm. This case shows how it is somewhat difficult to define and identify
‘nanoproducts’ that are on the market: for example sometimes the content of a NM is not declared,
and sometimes the use of a NM in the product is not necessary to decide that we are dealing with a
nanoproduct. A case study presented during the session showed the amount and form of NM
released during the use of various spray products commercialized in Denmark. Exposure was
measured in laboratory, simulating the actual use. According to these results, nanoparticles are
formed in air, but after short time (few minutes) the number of particles decreased. During the
discussion it was suggested that decrease of particle number could be related to adsorption of
particles to the walls of the chamber used in the test, but this hypothesis was not checked. Anyway,
size development during and after exposure was monitored. Using the spray can, a high nucleation
was observed, with formation of bigger particles in short time, maybe due to the presence of O3. For
two of the products an inhalation toxicity test on mice was performed, and for one product it was
found an unacceptable risk at concentrations very near the concentrations found during normal use,
but related to a chemical compound which was not a NM. During the discussion it was highlighted
that besides inhalation also oral exposure could play a big role in consumer exposure. According to 1
study, oral intake is 1000 to 10000 higher than inhalation, and the translocation from gut to blood is
significant. Therefore there is the need to have more data about this route of exposure, especially
about transit time and translocation. However, if it is important to collect more experimental
exposure data measured in realistic conditions, it is not practical to expect that exposure will be
measured in all possible conditions and for all products. As it happened for conventional chemicals,
also for NM it is essential that modelling tools are made available to risk assessors and regulatory
bodies in order to screen the possible workers, consumers and environmental exposure. Current
models, e.g. ECETOC TRA, ConsExpo, Stoffenmanager, are still based on conventional chemical
parameters, and the identification of properties of NM that could influence the exposure and their
parameterization are lacking. To try to understand the applicability of the human exposure models to
NM, available models where applied to some exposure scenarios for workers, and brief
considerations where made for consumers. In this last case, both ECETOC TRA and ConsExpo are in
principle applicable to estimate the inhalation of NM, but there are some limitations due to the fact
that values for some parameters are defaults not addressing NM specificities, and that agglomeration
is not taken into account. For workers, a thorough assessment of suitability and performance check
was carried out. According to the results, the models' basic concepts are suitable, but there are issues
related to the variable categories (e.g. dustiness) that should be refined and adapted to NM, to
exposure metrics that probably are not always optimal. Finally, there is no calibration for NM. Models
were applied in few exposure scenarios using real conditions, and the results were compared to
experimental exposure data measured in the same conditions to check the model performance. The
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