User manual

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:

2.1.1 Product

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 use 
  • The size of the aerosol that acts as a carrier of the nanomaterial

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 truncated. 

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 unknown.
  • 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.

2.1.2 Nanomaterial
 

  • Nanomaterial diameter Primary diameter of the nanomaterial.
  • Density nanomaterial The mass density of the nanomaterial.
  • Shape nano particle  Used to define the shape of the nanoparticle. There are three options:

 Spherical: the particle geometry is defined by its diameter
 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.)

2.1.3 Room

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.

2.1.4 Usage

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 are:

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.

2.1.5 Simulation
 

  • 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 dose.

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.

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