VO: Welcome to the tutorial...
for using ConsExpo Web's 'emission from solid materials' model...
to estimate the inhalation of substances evaporating from solid materials...
in an indoor environment.
The tutorial includes an introduction, a description of the model concept...
descriptions of the input fields...
for which the user needs to insert values that fit the exposure scenario...
and a demonstration on how to interpret the model outcomes.
The 'emission from solid materials' is one of the inhalation exposure models...
that ConsExpo Web has to offer.
It is most suitable for consumer exposure scenarios...
for volatile or semi-volatile substances...
that are slowly released from solid materials in an indoor environment...
such as furniture, floors, walls or objects.
'Emission from solid materials' can be selected...
in the model dropdown menu at ConsExpo Webs 'inhalation' tab.
The consumer is assumed to reside in the room with the solid material...
from which substances are emitted for a prolonged period of time...
leading to a long term exposure duration of days, months or even years.
The 'emission from solid materials' model consists of three stages...
that simulate the diffusion of the substance in the solid material matrix...
the partitioning behaviour at the interface of the material surface...
and a stagnant layer of air...
and the mass transfer of substance from the stagnant air to the room air.
The following animation visualizes the fate of the evaluated substance...
expressed here as purple dots.
Inside the solid material...
the substance moves in randomly directed patterns driven by diffusion.
Once the substance hits the interface with the stagnant layer of air...
it can leave the solid material.
Here the substance is driven by partitioning behaviour...
searching for thermodynamic equilibrium...
between the concentration in stagnant air and the material.
As such, the substance may travel back into the material.
Finally, the substance mass is transferred from the stagnant air...
into the room air in which the inhalation exposure scenario takes place.
Here, the input fields are described...
so that the model user knows how to insert appropriate values...
fit for the consumer exposure scenario.
'The product surface area' refers to the area of the product material...
that is in contact with air.
The unit varies from square centimetres for small objects...
to square meters for large surfaces, such as floors or walls.
The 'product thickness' describes how thick the layer of the product material is...
in which the substance is formulated.
It may range, for example...
from micrometres in the case of a layer of dried paint...
millimetres for a piece of paper...
or centimetres for wooden boards or window panes.
The 'product density' refers to the density of the product material...
in which the substance of interest is formulated.
It is expressed as a unit of mass per unit of volume...
such as grams per cubic centimetre or kilograms per litre.
The diffusion coefficient is an input parameter...
that describes how fast the evaluated substance diffuses...
within the product material.
As such, it depends on the properties of the substances...
as well as the product material.
The faster a substance diffuses...
the less time it will take before it reaches the interfacial area...
from which it can evaporate into the stagnant air above the material.
Consequentially, substances with high diffusion coefficients...
are more prone to rapid evaporation.
Collecting the accurate data for the diffusion coefficient...
can be a challenging task...
because diffusion coefficients may vary within orders of magnitude...
between substances and between product materials.
The unit for diffusion coefficient...
is expressed as the squared distance per unit of time...
and is typically referred to as square meter per second.
The input field 'weight fraction'...
refers to the amount of substance formulated in the product...
per unit of product amount.
Here, the product amount is the sum of the substance mass...
and the mass of the material it is formulated in.
Typically weight fraction is unitless...
because it refers to the amount of substance in grams...
divided by the amount of product in grams...
but it can also be inserted as a weight percentage.
The product-air partition coefficient...
refers to the ratio of the substance concentration in the product material...
to the substance concentration of the product in air...
at thermodynamic equilibrium.
Typically, partitioning coefficients are symbolized by the letter K...
and by the two media between the substances partitions...
expressed in subscript.
The partitioning coefficients don't depend...
on the initial concentration of the substance in the product...
because it refers to a state of thermodynamic equilibrium.
Substances with low product-air partitioning coefficients...
have little tendency to remain in the product...
and are as such driven to equilibrium at the air side.
As a consequence, these substances are more prone to rapid evaporation...
from the solid product material.
Just as with diffusion coefficients...
collecting accurate data for the product-air partitioning coefficient...
can be a challenging task...
because it may vary within orders of magnitude...
between substances and between product materials.
The unit of the partitioning coefficient can be inserted as linear...
but also as loglinear...
because the concentrations across the two media can vary within orders of magnitude.
The emission from solid materials model...
is designed to simulate exposure scenarios over a long period of the time.
As such, the exposure dose of the substance inhaled by the consumer...
does not only depend on the concentration of the substance in the room air...
but also on the timeframe in which the consumer is present in the room.
Some consumer products...
such as, for example, flooring agents and drain openers...
advise that a period of time should elapse before entering the room...
after the product has been applied.
This timeframe can be inserted in ConsExpo Web...
using the 'start exposure' and 'exposure duration' input fields.
The start exposure input field refers to the amount of time...
between application of the product and entering the room.
'Exposure duration' refers to the amount of time the consumer then stays in the room.
The intensity of the exposure is calculated in ConsExpo...
as the air concentration in the room over time...
for which graphs and data tables are available.
Here, it can be seen that the air concentration changes over time...
so that the inhaled dose depends on the moments...
the consumer enters and leaves the room.
This is to be inserted as 'start exposure'...
and the period of the time in which the consumer then stays in the room...
is to be inserted as 'exposure duration'.
The mass transfer coefficient expresses the velocity...
at which the substance in the stagnant layer of air above the product...
is transferred to the room air.
Such transfer depends on a number of factors...
such as the substance's molecular weight, the air flow over the product...
and the surface roughness of the product.
The most recent ConsExpo Web fact sheets...
suggest a default value for the mass transfer coefficient of 10 meters per hour.
The 'emission from solid materials' model also includes 'room volume'...
'ventilation rate', 'inhalation rate' as input fields...
and the 'absorption' model to calculate internal exposure doses.
These are not explained in this tutorial...
but are covered in the 'introduction to inhalation models tutorial'...
which explains the input fields and models that are common to all inhalation models.
We would like to acknowledge all partners in the ConsExpo project:
Health Canada...
the French Agency for Food, Environmental and Occupational Health and Safety...
the German Federal Institute for Risk Assessment...
the Swiss Federal Office of Public Health...
the Netherlands Food and Consumer Product Safety Authority...
and the Dutch Ministry of Health, Welfare and Sport.
(SILENCE)