The ConsExpo nano tool can be used to estimate inhalation exposure to nanomaterials in consumer spray products. To run the model, user input on different exposure determinants such as the product and its use, the nanomaterial and the environmental conditions is required. Exposure is presented in different measures.
2.1 User input
The tool requires user input on the following aspects:
In the product section of the input the parameters of the spray
that determine exposure are specified. There are two aspects of the
product that have a large impact on the potential exposure:
- The amount of nanomaterial that is released into air during
- The size of the aerosol that acts as a carrier of the
The amount released from a spray is determined by its mass
generation rate and the time duration of the use of the spray (i.e.
how long the product is sprayed.) The emitted product will be a
mixture of various compounds such as propellants, solvents and the
nanomaterial itself. Only the nonvolatile components of the product
will end up as airborne aerosol particles as the volatile
components will vaporize and be released as a gas. In ConsExpo
nano, it is assumed that the nanomaterial is the dominant
non-volatile component and the contribution of other compounds to
the aerosol particle is neglected. Finally, if a spray is used on a
surface only a fraction will become airborne as most of the product
is expected to land on the surface.
The size of the aerosol is important for two reasons. First it
determines how long the aerosol will be airborne. A smaller aerosol
will be airborne for a longer stretch of time and thus have a
higher potential for inhalation. Second, once inhaled, the aerosol
size will determine its deposition in the respiratory tract and
therefore its potential to reach the alveoli.
To specify the product the following input is required:
- Mass generation rate The amount of
product released per unit time. The product will generally contain
different components (e.g. propellant gas, solvents, the
(non-volatile) nanomaterial itself.) The mass generation refers to
the mass of this complete mixture. It is the value that would be
measured when measuring the spray before use and after use divided
by the time it was operated.
- Aerosol The aerosol is assumed to consist
of spherical particles, the geometry of which is uniquely
determined by its (aerodynamic) diameter.
- The type of distribution The
diameter of the sprayed aerosol may be represented by a single
number or as a (mass-based) lognormal distribution. In the case of
a ‘monodisperse’ distribution, the aerosol diameter is specified by
the value of the parameter ‘Aerosol diameter (median)’. In case of
a ‘log normal’ distribution, the distribution is specified by the
‘Aerosol diameter (median)’, the ‘arithmetic coefficient of
variation’ (defined as the arithmetic standard deviation divided by
the mean). The distribution is taken to range from 0 to the
‘Maximum aerosol diameter’, above which the distribution is
In addition, the aerosol particle has a mass density, specified
using the parameter:
- Density aerosol particle The mass density
of the airborne aerosol particle generated by the product. It
depends on the mass density of the nanomaterial itself and the
stacking of nanoparticles (or their aggregates) in the aerosol
particle. Could be set to the density of the nanomaterial if
- Weight fraction nanomaterial The fraction
of the nanomaterial mass of the total product mass (as it is
contained in the spray can).
- Airborne fraction The fraction that
accounts for the fact that in using a spray on a surface, only part
of the spray will end up as airborne aerosol, as the bulk of the
material will end up on the treated surface. For an air space
application (e.g. spray against flying insects, air freshener) the
fraction will be close to 1. For a surface spray (e.g. a plant
spray, all purpose cleaner), this fraction will be much lower. See
[ref to spray report] for estimated values for this parameter.
- Nanomaterial diameter Primary diameter of
- Density nanomaterial The mass density of
- Shape nano particle Used to define
the shape of the nanoparticle. There are three options:
Spherical: the particle geometry is defined by its
Cylindrical: the particle geometry is determined by the
radius and height
Sheet: the particle geometry is specified by the
‘nanoparticle thickness’ and the single sided ‘nanoparticle surface
area’. The volume is taken to be the thickness times the single
sided surface area. The particle surface is assumed to be twice the
single sided surface area (i.e. negligible thickness.)
- Nanomaterial soluble The user can specify
whether the nanomaterial is soluble in the alveolar macrophages.
Only materials with a low rate of dissolution can be modelled using
the ConsExpo nano tool as the deposition model is valid only for
poorly soluble particles.
- Dissolution rate The fraction of
materials that dissolves in the macrophage per unit of time. The
tool allows only moderate dissolution rates (between 0.0001 per day
and 1 per day.)
Consumer sprays are assumed to be used indoors. Features of the
indoor environment such as room size and ventilation determine to a
large extent the resulting aerosol air concentrations. The
following parameters need to be specified:
Room volume The volume of the room where the spray is used.
The sprayed aerosol is assumed to be homogeneously distributed
throughout the room after spraying.
- Room height The height of the room. The
sprayed aerosol is assumed to be distributed homogeneously over
this height. It may be more appropriate in cases where the spray is
not directed upwards, to use the release height of the spray rather
than the actual height of the room itself.
- Ventilation rate The number of
times the air in the room is refreshed per hour.
Conditions of use of the spray include information on how long
and how often the spray is used, and how long the exposure takes
place after use.
- Spray duration The period during which
the spray is used.
- Exposure duration The period a person is
present in the room where the spray was used. In this period the
person is potentially exposed to the aerosol (and nano-) particles
released from the spray.
- Spraying towards exposed
person This option allows to account for the
situation in which the spray is used directly in the breathing zone
of the exposed person (e.g. for a hair spray or deodorant.)
- Cloud volume In case the spray is
used on a person, the distribution volume of the aerosol is reduced
during spraying. The cloud volume is the volume after 1 second of
spraying. For each second of spraying the distribution volume of
the aerosol is assumed to increase by this volume.
- Exposure pattern This parameter defines
whether the exposure takes place repeatedly or not. Options
Single event: exposure takes place only once
Repeated (unlimited): exposure takes place with a fixed
frequency (to be specified by the user.)
Repeated (fixed number of times): exposure is repeated with a
user-specified frequency for a number of times and then stops. User
specifies the ‘number of exposure events’ parameter.
- Simulation duration The total period the
load in the alveoli is to be estimated. Note that the clearance of
non-soluble particulate matter from the lung is generally slow and
residues of inhaled material may be present in the alveoli for
substantial time after the actual exposure has taken place.
- Deposition model The user has a choice
between two parameterisations of the ICRP deposition model: ‘male
(light exercise)’ and ‘female (light exercise)’
- Inhalation rate Volume of inhaled air per
hour. Combined with the air concentration this gives the inhaled
2.2 Model output
- Inhaled dose per event The total dose of
aerosol that is inhaled during a single exposure event. The dose is
expressed in different dose measures <link: dose metrics
1.3>. For repeated exposure events, the same inhaled dose for
each event is assumed.
- Alveolar dose per event The dose of
aerosol that, after inhalation in a single exposure event, deposits
in the alveoli.
- Distributions In this section the
dependence of a number of exposure measures on the diameter of the
inhaled aerosol is shown. The plots include the inhaled dose during
an exposure event versus the diameter, the deposition fraction in
different regions of the respiratory tract as a function of the
aerosol diameter and finally, the deposited mass in different
regions of the respiratory tract as a function of the aerosol
diameter. These graphs are only shown in case the aerosol diameter
is represented by a (log normal) distribution.
- Dose-time plots In this section of the
output, important exposure estimates are displayed as a function of
time. The first graph plots the inhaled and alveolar dose during a
single exposure event versus time. The time ranges from zero (the
start of the exposure event) to the exposure duration. The second
graph shows the alveolar load over the simulation duration. For
both graphs the dose measure may be chosen from a drop-down list.
Finally, if the solubility of the material is simulated, a graph
will appear that shows the (cumulative) amount of nanomaterial that
has dissolved in the alveoli since the start of the simulation.
Note that the fate (e.g. interstitialisation or systemic uptake) of
the dissolved nanomaterial is not considered in the ConsExpo nano
tool. The graph is not to be interpreted as the amount of material
that is present in the alveoli at any particular time.