VO: Hello, everyone.
Welcome to the tutorial on the Probabilistic Aggregate Consumer Exposure Model...
or PACEM for short.
This video will provide an explanation...
of the underlying methodology used in PACEM.
In addition, an illustrative example will be given...
of how to perform a risk assessment with this model.
But first, let's get a quick overview of the applicability of PACEM...
and why to use it in the first place.
Some chemical substances, for example fragrances and preservatives...
are used in many different consumer products.
To estimate the total daily exposure of a person or population...
exposures to the chemical from all products used on that day...
need to be considered.
PACEM has been developed for this purpose.
PACEM is designed to estimate aggregate exposure to chemicals...
in various consumer products...
by considering various factors, including usage patterns in a population...
product types, and chemical concentrations in the products.
It uses a probabilistic approach...
to provide a comprehensive exposure assessment of a population of interest.
To perform such a probabilistic exposure assessment, PACEM uses information...
about product-use frequencies and product-usage amounts...
of hundreds to thousands of individuals. This information is gathered in surveys.
The individuals questioned in the surveys form the basis of the simulated population.
Specifically, the product-use frequencies and product amounts...
reported by the individual are used to simulate product-usage diaries.
These describe which products are used on each day of a 14-day period.
For each product used on a given day...
a product amount is sampled from the usage information as well.
Once the usage diary has been created, substance concentrations are sampled...
for each product and each individual in the usage diary.
These concentrations are based on input provided by the user of PACEM.
To calculate an individual's exposure to a particular substance...
the product amount used...
is multiplied by the substance concentration in that particular product.
Then, all exposures within a given day of the usage diary are summed...
such that an aggregated exposure is estimated for each 24-hour time frame...
for an individual in a two-week period.
PACEM supports two endpoints of exposure:
short-term exposure and long-term exposure.
When selecting short-term exposure...
the day with the highest aggregate exposure is taken from the 14-day diary.
When selecting long-term exposure...
the average aggregate exposure is taken from the 14 days.
This allows users to select an endpoint...
that fits their exposure and risk assessment best.
Now that you have a global idea of the methodological concepts of PACEM...
let's take a look at the steps required to perform an exposure assessment.
In the first panel of PACEM, the user can select the product groups of interest...
being personal care products and/or household cleaning products.
Then, two types of exposure assessments can be selected:
dermal load and systemic exposure.
Finally, the population needs to be selected.
Currently, France, Germany, Spain, the Netherlands and the UK...
are included in PACEM...
which refers to the product usage surveys...
conducted for individuals of those countries.
Then, in the next panel, relevant product groups need to be selected.
Here, we select aftershave spray, after-sun cream, and liquid all-purpose cleaner.
For each selected product group...
substance concentrations need to be provided...
as well as the percentage of products containing the substance.
This user input is needed to link substance concentrations...
to the product usage diaries that are created based on the surveys.
The last step on this panel is to provide exposure fractions...
or retention factors if performing dermal load assessment.
These fractions are needed to account for situations...
where not all the used products lead to actual exposure...
for example due to rinsing off.
Exposure fractions and retention factors...
are represented by a value between 0 and 1...
with 0 representing no exposure...
and 1 representing exposure to all of the substance used during an event.
The fractions implicitly comprise information on the exposure duration...
the release of the substance from the product...
contact between user and product and the relevant exposure routes.
User input can be provided as point values, but also as distributions.
This can be done by clicking on the button with the distribution symbol.
This will open a panel...
where users can select the type of distribution they want to use...
and provide the necessary input to define that distribution.
By clicking on 'Apply', the selected distribution will be used by PACEM.
Once the product exposure settings have been provided...
one can specify the absorption fractions for each exposure route.
For this example, we assume 50% inhalation and dermal absorption.
In the next panel of PACEM, the Simulation Settings panel...
users can choose the product sample size.
This number reflects the number of times...
an individual is sampled from the information in the survey.
Higher numbers will give more precise results...
but the simulation will take longer to run.
Upon clicking on the submit button...
the exposure assessment will be sent to the PACEM server...
and the calculations will start.
Information on the status of the computations are provided.
Once the status of the computations turns to 'Success'...
users can click on the Analysis button to analyse the results.
We can now take a look at the results and select the endpoints that we want to see.
In this example...
we will take a look at short-term exposure of all females in the population.
You can also see the option to select exposed individuals only...
or the entire population.
By clicking on 'Create Output'...
we can now see the estimated aggregate exposure for the selected population.
Since we selected systemic exposure in the assessment settings of this example...
an aggregate exposure will be shown for each exposure route...
as well as the total aggregate exposure.
If dermal load was selected, only the dermal load would have been shown.
For each exposure route...
various percentiles of the population exposure are given.
In addition, a visualisation of the cumulative exposure is shown below.
Finally, PACEM offers various options to export the results...
by clicking on this symbol with the three horizontal lines.
To summarise, you now hopefully understand...
how to perform an exposure assessment with PACEM...
and have a global understanding of the underlying principles.
We hope this tutorial has helped you to familiarise yourself with PACEMWeb.
Our support does not end here.
Visit the PACEM website to find help pages that provide information on PACEMWeb...
and a user manual.
You can also access the 'i' and '?' icons within the software...
which are there to give you extra help when needed.
If you still have questions or need assistance...
please contact us at pacemweb@rivm.nl.