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Consumer Exposure Model (CEM)
Version 3.2
User Guide
Prepared for EPA Office of Pollution Prevention and Toxics
by ICF
October 2023
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Table of Contents
Executive Summary 5
Introduction 7
1. Downloading and Operating CEM 10
1.1. CEM Main Menu 11
1.2. Hiding Access Task Bar 11
1.3. Single Analysis Mode 12
CEM Heading Bar 12
1. Scenario tab 13
2. Inputs tab 15
2.a. Chemical Properties Input tab 15
2.b. Product/Article Properties Input tab 16
2.c. Environment Inputs tab 17
2.d. Receptor Exposure Factors Input tab 18
2.e. Activity Patterns Input tab 19
3. CEM Models tab 19
4. Results tab 20
5. Reports tab 21
1.4. Sensitivity Analysis Mode 21
1. Setup tab 22
2. Results tab 23
2. Summary of Models within CEM 25
El: Emission from Product Applied to a Surface Indoors Incremental Source Model 25
E2: Emission from Product Applied to a Surface Indoors Double Exponential Model 25
E3: Emission from Product Sprayed 26
E4: Emission from Product Added to Water 26
E5: Emission from Product Placed in Environment 26
E6: Emission from Article Placed in Environment 26
P_INH1: Inhalation of Product Used in Environment 26
P_INH2: Inhalation of Product Used in Environment (Near-Field / Far-Field) 27
A_INH1: Inhalation from Article Placed in Environment 27
P_ING1: Ingestion of Product Swallowed 27
P_ING2: Ingestion of Product Applied to Ground Outdoors 27
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A_ING1: Ingestion after Inhalation (Article Model) 27
A_ING2: Ingestion of Article Mouthed 28
A_ING3: Incidental Dust Ingestion (Article Model) 28
P_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin 28
P_DER2a: Dermal Dose from Product Applied to Skin, Fraction Absorbed Model 28
P_DER2b: Dermal Dose from Product Applied to Skin, Permeability Model 28
P_DER3: Dermal Dose from Soil where Skin Contact with Soil, Dust, or Powder Occurs 28
A_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin (Article Model) 29
A_DER2: Dermal Dose from Article where Skin Contact Occurs 29
A_DER3: Dermal Dose from Skin Contact with Dust 29
3. Detailed Descriptions of Models within CEM 30
Two-zone Mass Balance Model for Estimating Inhalation Exposure from Product Use 30
Near-field option for Estimating Product Exposure During Use 32
El: Emission from Product Applied to a Surface Indoors Incremental Source Model 33
E2: Emission from Product Applied to a Surface Indoors Double Exponential Model 36
E3: Emission from Product Sprayed 37
E4: Emission from Product Added to Water 38
E5: Emission from Product Placed in Environment 39
P_INH1 and PJNH2: Calculation of Inhalation Dose from Product Usage 40
E6: Emission from Article Placed in Environment 44
Model Description 45
Estimation of Chemical Parameters from Basic Physical-Chemical Properties 51
A_INH1: Calculation of Inhalation Dose from Article Exposure 54
P_ING1: Ingestion of Product Swallowed 55
P_ING2: Ingestion of Product Applied to Ground Outdoors 56
A_ING1: Ingestion after Inhalation (Article Model) 58
A_ING2: Ingestion of Article Mouthed (Migration Rate Method) 59
A_ING3: Incidental Dust Ingestion (Article Model) 60
P_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin 62
P_DER2a: Dermal Dose from Product Applied to Skin (Fraction Absorbed Model) 65
P_DER2b: Dermal Dose from Product Applied to Skin (Permeability Method) 68
P_DER3: Dermal Dose from Soil where Skin Contact with Soil, Dust, or Powder Occurs 70
A_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin (Article Model) 72
A_DER2: Dermal Dose from Skin Contact with Article 73
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A_DER3: Dermal Dose from Skin Contact with Articles using Dust Concentration 75
4. Areas for Future Enhancements 76
Glossary 80
References 90
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Executive Summary
OPPT aims for CEM to be a flexible, user-friendly, and scientifically rigorous tool to rapidly assess exposure to consumer
products and articles across a range of exposure scenarios and pathways. To this end, OPPT sought feedback on both the
performance and ease of use of the tool through beta testing and peer review. The scenarios, chemicals, and defaults
currently included in CEM are based on available data and professional judgment and are present in order for model
users to have the ability to use all parts of the model without requiring the model user to determine all model inputs for
each model run. At any time, defaults, chemicals, or use scenarios could be deleted, added, or refined based on newly
available information. In addition, generic scenarios are available which are blank and can be populated with user-
defined inputs.
CEM retains six existing models from the E-FAST model and adds fifteen additional models - these consist of six emission
models, three inhalation models, five ingestion models, and seven dermal models. All CEM models are used to estimate
chemical concentrations in exposure media, including indoor air, airborne particles, settled dust, and soil. The model
also evaluates dermal flux of a chemical through the skin and the migration of a chemical from an article to saliva. These
are combined with media contact rates and various exposure factors to determine the single daily dose, chronic and
lifetime average daily dose of a chemical resulting from product and article use scenarios associated with 73 specific
product and article categories and several generic categories that can be user-defined for any product or article.
Additionally, the model is parameterized for a variety of indoor use environments, including residences and specific
rooms within residences, offices, schools, automobiles, and limited outdoor scenarios.
Notably, models to estimate exposure to semi-volatile organic compounds (SVOCs) from consumer articles have been
incorporated, including a mass-balanced model for estimating emissions and indoor fate and transport of SVOCs.
Inhalation of airborne gas- and particle-phase SVOCs, ingestion of previously inhaled particles, dust ingestion via hand-
to-mouth contact, ingestion exposure via mouthing, and direct and gas-to-skin dermal exposure of SVOCs are
incorporated.
In addition, CEM also has the option to model higher exposure associated with product use near the breathing zone. The
option, called the "near field option" creates a small personal breathing zone around the user during product use in
which concentrations are higher, rather than employing a single well-mixed room. This option should be applied with
discretion as it is better used for product use categories associated with stationary rather than mobile use.
CEM has been developed to be a flexible tool that can assess both data-rich and data-poor chemicals. CEM requires that
the chemical molecular weight, vapor pressure, Kow, and Koa be provided. These values can be estimated from EpiSuite.
All other input variables, including mass transfer, partition, and diffusion coefficients can either be estimated within
CEM from these baseline physical-chemical parameters and model defaults or, if data are available, can be supplied by
the modeler.
Version 2.1 incorporated changes based on feedback from Beta reviewers, external peer reviewers, and EPA feedback.
The specific details of changes implemented are available in the User Guide of CEM 2.1. Briefly:
Product and article categories were harmonized with OECD categories. Ten new product and article categories
were added to CEM. To allow for greater flexibility, 11 generic product categories and one generic article
categories were added.
Additional product/scenario combinations that were not in previous versions were added.
New dermal models were added and existing dermal models were updated.
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A model considering ingestion of inhaled particles that are trapped in the upper airway was added.
The product applied to the ground outdoors model was revised to account for multiple product applications and
an abrasion term was added to the SVOC article model.
Prepopulated scenarios were added and some default values, estimators, and activity patterns were updated.
Models within CEM were ground-truthed against existing monitoring data, where available.
Multiple options for naming, outputting, formatting, and saving reports were added/revised.
Multiple options to increase the user-friendliness of the model were added, including additional help screens,
default parameters, parameter estimators, and search functions.
Version 3.0, a sensitivity analysis mode has been added to CEM that allows up to 27 variations of an analysis to be run at
once. In addition, modeling functions have been refined and consolidated into a single executable file for improved
performance and a faster runtime.
Version 3.1 and 3.2 include minor refinements and corrections. In addition, version 3.2 includes updates resulting from a
comprehensive quality assurance review of default parameter assumptions, as well as a comparison and analysis of
exposure estimates obtained from versions 2.1 and 3.1. Version 3.2 also includes an updated user guide. Appendix B to
the user guide, which documents default parameter values, has been updated for version 3.2 as well.
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Introduction
Under the Frank R. Lautenberg Chemical Safety in the 21st Century Act amendments to (TSCA), the U.S. Environmental
Protection Agency's (EPA) Office of Pollution Prevention and Toxics (OPPT) assesses potential exposures of new and
existing chemicals. When evaluating chemical uses, OPPT uses available measured data together with modeling tools to
provide scientifically based estimates of exposures and doses.
This guidance document describes the Consumer Exposure Model (CEM), which OPPT developed to estimate human
exposure to chemicals contained in consumer products and articles:
Products are generally consumable liquids, aerosols, or semi-solids that are used a given number of times before
they are exhausted.
Articles are generally solids, polymers, foams, metals, or woods, which are always present within indoor
environments for the duration of their useful life, which may be several years.
CEM contains 53 product categories and 20 article categories along with 11 generic product categories and one generic
article categories. Although there are existing definitions of consumer products and articles, they are distinguished from
each other in a more general way here. Certain chemicals may only be added to articles, others only used to formulate
products, and others could be used for both. For the purposes of exposure assessment, products and articles are treated
differently. Formulations, anticipated use patterns, and available approaches to estimate exposure are different.
CEM was originally developed as a module within EPA's Exposure and Fate Assessment Simulation Tool (E-FAST).
Compared with the original version, the updated version contains all existing models but also evaluates a wider range of
products and articles, use scenarios, and exposure estimation methods. The updated CEM can assess exposures from:
Inhalation - from vapors emitted from products that are sprayed, products that applied to surfaces, products placed
in a room, products that are added to water, and to vapors and particulates containing SVOCs from articles present
within an indoor environment;
Non-Dietary Ingestion - to chemical adsorbed to dust or soil or present on the surface of articles and incidentally
ingested through mouthing, swallowing, or hand-to-mouth contact; and
Dermal contact - to liquids present on skin after using consumer products, powdered products and products mixed
with soil, direct contact with articles, transfer of residue from the surface of articles, and transfer from vapor-phase
air to skin.
CEM includes several distinct models appropriate for evaluating specific product and article types and use scenarios. For
example, models for products recognize that emissions are generally highest for a shorter period during use(s), and
generally lower or non-existent when products are not being used. Product-use models include exposures from direct
use and/or close proximity. Models for articles assess migration of additive chemicals out of the articles and subsequent
exposure through ingestion of dust particles, inhalation of vapor-phase or particle phase chemicals in the air, mouthing
of chemicals present on an article's surface, dermal absorption through skin contact, or mouthing of chemical's present
on hands or other parts of the body after contact with articles.
Product use categories define various kinds of products and articles. Examples include aerosol spray paints, laundry
detergent, foam-based furniture, hard-plastic toys, and motor oil. Chemicals are present in products and articles for
many different reasons. The reason why a chemical is included in a product-its specific job-is referred to as its
functional use. Examples include propellants, flame retardants, solvents, surfactants, plasticizers, and repellants.
Functional uses are important to help define generic formulations within a product or article category. Harmonized
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nomenclature of product and article use categories along with functional use categories can help inform exposure
scenarios over time through development of generic formulations that provide typical weight fraction values or ranges
that a given chemical is present.
Exposure scenarios combine information needed to estimate consumer exposures for a given product use. A product
use category can vary in specificity of the product and its application. An exposure scenario developed for a specific
product use category will have a scope focused on activities with a common exposure source and associated
parameters. Exposure scenarios contain documented information needed to perform exposure calculations, including:
Formulations (e.g., weight fraction),
Use patterns (e.g., frequency, duration, and amount used),
Human exposure factors (e.g., body weight, inhalation rate),
Environmental conditions (e.g., air exchange rates and room size), and
Chemical or product-specific properties (e.g., product density, vapor pressure, molecular weight, diffusion
coefficient, overspray fraction, transfer coefficients, dilution factor).
There are a range of simple to complex models within CEM. The models are deterministic and appropriate for use in
OPPT chemical assessments. To facilitate the ability to run scenarios quickly, each product-use category is mapped to
the appropriate exposure models within CEM as shown in Table B-l. The model has been pre-parameterized with
default inputs (described in Section 1) for each product use category (see Appendix B for more details). The product use,
users, and use environment can be modified but not all inputs have complete user flexibility, such as the user and
bystander activity patterns.
Based on the data available, OPPT will consider variability and uncertainty associated with model inputs and overlap
model outputs. Variation has been incorporated (high, medium, and low choices) for many of the parameters that allow
for estimation of central tendency and reasonable worst-case exposure estimates. Chemicals can be used in many
different ways. How much of a product is used (amount), how often (frequency), and for how long (duration) vary. This
information, when combined with human and built environment exposure factors, can be used for consumer exposure
assessments. For articles, additional information on diffusion rates and other physical-chemical properties are needed to
estimate emissions and subsequent exposures. Other consumer models such as ConsExpo, MCCEM, IAQX, iSVOC, IECCU,
and CONTAM provide more robust estimates of exposure, including probabilistic ranges, but also require measured data
such as emission rates and emission factors derived from chamber studies. Default values are available in CEM, but the
model can be run with user-defined inputs based on measured data as well. The use of measured values informed by
current and robust collection of exposure data is preferred. See Section 3 for a detailed discussion of the individual
consumer exposure models contained within the CEM and associated data requirements.
There are some limitations that should be considered prior to using CEM. There are a range of simple to complex models
with CEM, so chemical and use specific considerations and relative data availability should be considered when selecting
a model with CEM or other consumer exposure models. CEM was designed to be user friendly, with prepopulated
scenarios that users can modify, however the scenarios reduce the flexibility of the model. Because CEM aims to be able
to be a flexible, easy-to-access model, that can be applied to a broad suite of chemicals, as well as consumer product
and article use scenarios, in both data-rich and data-poor simulations, some trade-offs were required. Notably, CEM is
deterministic, rather than population-based, and gives point estimates of exposure for populations of interest. Within
CEM, it is only possible to estimate exposure to one chemical from one product or article category in a single CEM run.
Additionally, CEM is not equipped to model complex emission profiles or activity patterns of residents other than those
pre-populated within CEM.
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While CEM is designed to appropriately model many kinds of consumer exposure scenarios, certain fields within CEM do
not have restrictions and are left to user discretion. For example, CEM does not restrict volatile organic compound (VOC)
models from being used with non-VOC chemicals. Because of this, some knowledge of exposure and exposure modeling
is recommended when using CEM.
This guidance document contains information previously included in the Consumer Exposure Module of E-FAST's User
Guide, and information previously included in the AMEM polymer migration model. To the extent possible, this
information has also been incorporated directly into the model through use of help screens.
The contents of this user guide include the following:
Directions for downloading and operating CEM
Summary of models contained within CEM (including domain scenarios and chemicals)
Detailed equations and description of models contained within CEM
Summary of sensitivity analyses and ground-truthing of models contained within CEM
Areas for future enhancement
Glossary of definitions of model parameters used in CEM
Additional CEM appendices are available on the EPA website:
Appendix A provides further information on the mass-balanced article and particle model within CEM
Appendix B documents model inputs used in CEM
Appendix C describes a sensitivity analysis results
Appendix D discusses ground-truthing results
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1. Downloading and Operating CEM
To use CEM, you will need to save three program files to your computer. These include a Microsoft Access database file,
which is the main CEM program file, and one "executable file" that supports the main program file. You will not use the
executable file directly, but it must be present in the same folder location as the main CEM program file for the model to
function.
The main program file and the executable file are provided together in a "zip" file (i.e., a file format commonly used for
compression and transmission of large computer files).1 You must "unzip" the CEM files before the first use. CEM will not
run if you attempt to open and use it from within the zip file (i.e., without unzipping the CEM files). The CEM files may be
unzipped to a computer hard drive, network folder, or other storage location. For best performance, it is recommended
to unzip CEM to your computer hard drive. Follow the steps below to download, unzip, and open CEM.
Download zip file titled "CEM Version 3.2.zip" to your hard drive or other storage location (see above). You may
need to copy or move the file from "downloads" into the folder location of your choice. Opening CEM without first
saving the zip file may result in errors. CEM must be downloaded to a directory in which you have write permission,
such as My Documents. It is recommended to download to and use CEM from a hard drive folder instead of a
network or cloud location.
2. Right click on file and select "Extract AN" or "Extract to here" or similar command. The specific command to
unzip/extract the file may differ depending on which file compression utility you use (e.g., WinZip, 7-zip).
3. Click "Extract". A new folder will appear where you downloaded the original zip file.
Double click the folder to open it and double click the main CEM file titled "CEM Version 3.2.accdr". This folder also
includes a copy of this User Guide and the CEM executable file (pycem_Runner_multi.exe).
The first time you open the main CEM file, Windows security will disable the model code. You must click "Enable
Content" near the menu bar at the top of the screen to enable the model programming to run. At the top right of
the screen, to the right of the CEM logo, select 'View a Saved Analysis' or 'New Analysis' to begin.
CEM generates external files that document the inputs and outputs of each model run. These files are stored in
folders named "Inputs" and "Outputs" that must be created in the same folder where CEM and the
pycem_runner_multi executable file are stored. You must create those two folders before using CEM for the first
time.
1 You will need a file compression/archival utility to open the zip file. Several free compression utilities are available, and many new
computers come with a compression utility pre-installed. Examples common compression utilities include WinZip and 7-Zip.
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1.1. CEM Main Menu
CEM opens to a Main Menu with buttons for the options shown below.
Analysis for a Single
Product or Article
Run CEM for a new or existing product or article scenario
Sensitivity Analysis
Run a sensitvity analysis by varying selected input
values for an existing product or article scenario
User Guide
Open the CEM user guide (PDF fomat)
Quit
Exit CEM
The functions associated with each button include:
1 Analysis for a Single Product or Article (Single Analysis Mode) - This mode runs CEM for a single product or article
use scenario. Users can choose from 84 pre-defined analyses or create and save new analyses. The analysis setup
with this option allows the user to modify use scenarios (e.g., location, time, and duration), chemical and product or
article properties, modeling options (e.g., emission estimation methods), and exposure factors.
2 Sensitivity Analysis (Sensitivity Analysis Mode) - This mode runs up to 27 variations of a product or article scenario.
Variations are created by choosing up to three values for up to three modeling parameters (e.g., frequency of use).
3 User Guide - The user guide can be exported from CEM as a pdf file.
4 Quit-This button closes CEM.
Instructions for navigating the heading bar and each of the tabs are presented in the following sections. Definitions of
terms and parameters are included in the glossary and the detailed descriptions in Section 3 include more discussion of
certain model parameters.
1.2. Hiding Access Task Bar
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When CEM is opened, the Access Taskbar (that includes, File, Home, Create, External Data, and Database Tools and
subheading options underneath each) may be visible. These controls are not used by CEM. To hide these and maximize
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CEM viewing, click the "down" caret on the bottom right side of the Access Task Bar and select Show tabs only. This
action will need to be taken only upon opening CEM.
1.3. Single Analysis Mode
Within the Single Analysis Mode, there is a heading bar that contains application-wide commands, and tabs for entering
required inputs, running the model, and viewing results.
CEM Heading Bar
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When the CEM Single Analysis Mode is opened, all controls beneath the heading bar are locked. To begin using CEM,
first choose either:
1 View a saved analysis. CEM is pre-loaded with 53 product-specific scenarios, 11 generic product scenarios, 20
article-specific scenarios, and one generic article scenario. Each scenario has defaults already saved within the
scenario. Once users create and save their own analyses, they are accessible via the "view a saved analysis"
dropdown.
2. Create a new analysis. A new analysis can be created based on a generic product or article or an existing analysis.
Currently CEM is populated with one scenario for every product and article category. These scenarios are in turn
fully populated with default inputs for that scenario. The modeler can select a chemical to be modeled and change
any of the pre-populated inputs. The product and article selections cannot be altered and then saved for pre-
populated scenarios. Users can make changes to other defaults associated with pre-populated scenarios and save
over them. Users can restore defaults to the original defaults included for a pre-populated scenario by using the
"Restore Defaults" button.
Additional controls on the heading bar include:
Use the 'Delete Analyses' button to delete one or more previously saved analyses.
2. 'Main Menu' returns the user to the main menu of CEM.
3. 'Save' allows users to save changes they make to the current analysis.
'Restore Defaults' restores all fields to the preprogrammed defaults for the current analysis.
The 'User Guide' button opens the CEM User Guide.
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CEM is built in Microsoft Access. As a default, Access orients to the bottom of a tab. To see the entire contents of a tab,
use the scroll bar to return to the top. A note to this effect is included on the heading bar.
1. Scenario tab
1. Scenario 2. Inputs 3. CEM Models 4. Results 5. Reports
This tab includes basic information about the exposure scenario, and choices made on this tab affect which inputs will
be required for the remaining tabs. Scenario features specified on the Scenario tab include:
1 Chemical of Interest - Enter the name of a chemical. Chemical specific information and defaults for a preselected
set of chemicals can be viewed by clicking the "View Chemicals Properties" button directly above the Chemical of
Interest.
2. Product or Article Used - First select whether to model a product or article. Then choose the product or article and
choose whether to use the default use environment for that particular item. When a product/article is selected,
CEM pre-populates with known default values, pre-selects the applicable exposure models, and identifies required
inputs. There are 53 product categories and 20 article categories, which should cover the range of expected uses.
However, in the event that a product or article is not explicitly included, an existing category could be adapted
noting that product- or article-specific defaults would need to be adjusted and are not provided up front as defaults.
There are also 11 generic product and one generic article categories that can be used to select different models for
user defined scenarios.
3. Product User(s) and Receptor(s) - CEM may be run for multiple product users and receptors including adults, youths
(aged 11-20 years), and children (aged 1-10 years). A product user is defined as receptor who uses a product
directly. A bystander is a receptor who is a non-product user that is incidentally exposed to the product or article.
Some products may be used more typically by adults and/or by children. The model user should carefully consider
who is likely to use a given product when making this choice. Choices about whether the users typically spend most
of their time at their residence, school, or other non-residence environment determine default activity patterns.
4 Activity Patterns - CEM is populated with three activity patterns. One in which the receptor primarily spends time
within the home; one in which the receptor works or attends school out of the home part-time; and one in which
the receptor works or attends school out of the home full-time. Only one activity pattern can be selected for a given
CEM run. The activity patterns were developed based on Consolidated Human Activity Database (CHAD) data of
activity patterns and are detailed on the Activity Pattern tab.
5 Product/Article Use Environment- The room or other location where the product/article is used. Choose from the
existing pick-list options and select only one environment for a given scenario. Additional options are available in
subsequent tabs to edit the default values pre-populated for the environment of use.
6 Weight Fraction of Chemical in Product/Article - If the selected scenario calculates exposure from the use of a
product or presence of an article, enter the level of chemical in the product initially.
7 Initial Concentration of SVOC in Article - If the selected scenario calculates exposure from the presence of an
article, either enter the level of chemical in the article initially or use the estimator button to calculate the initial
concentration from the weight fraction and density.
8 Background Air or Dust Concentrations - In order to quickly compare exposure attributed to consumer products
and articles to background exposures, user-defined background air, dust, soil, and drinking water concentrations can
be specified for certain models. Background air concentrations are only associated with product inhalation models
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(those that utilize emission models E1-E5). Dust ingestion exposure is only associated with articles; therefore,
background dust concentrations are only associated with article models (E6, A_ING3, A_DER3). The chronic exposure
to these media are calculated and reported separately from pathway-specific exposures. These are set to zero as
default.
9. Available Models for the Selected Product or Article - This menu lists the models that apply to the selected product
or article and a general indication of the domain of applicability as denoted by VOC, SVOC, or SVOC/VOC.
10. Exposure Pathway - The checked boxes show which exposure model pathways will be included in the CEM run.
IJnchecking the box for a pathway turns off the model pathway even if it is listed in the 'Available Models' above.
This allows for greater flexibility and the ability to only run a single model at a time if that is of interest,
11. Scenario Description/Notes - An optional free-text field to enter a scenario description for later reference. This field
is output with the final report and can be used in various ways, including to track the purpose of a run, whether
inputs were user supplied or estimated with CEM, data sources used for modeling runs, and other information that
would be useful in later interpreting model results.
12. Modeling Options - Options provided for relevant models (models that do not apply will not appear). Choose the
appropriate options pertaining to emission rate, near-field zones, and dermal absorption, as applicable. Further
information can be found in the model descriptions in Sections 2 and 3.
13. Help Buttons - Clicking the mouse on a question-mark button will show a help screen with instructions for each
feature.
1 Consumer
ฆ Exposure
ฆฆModel
View a Saved Analysis: ^u(Msซaiant)J
Current Analysis Name: Caulk (sealant)
| 1. Scenario 2. Inputs 3. CEM Models 4. Results S. Reports
1 Chemical of Interest: View Chemical Properties
Benzyl Alcohol
0 Adult (221 years)
0 Stay-At-Home
CAS Number: 100516
0 Youth (11-20 years)
U Part-Time
Q Use a Product or Article?: Product
D Child (<1-10 years) G
CD Full-Time
0 Which Product or Article it Used? 2
Glues and Adheslves (small scale)
Glues and Adhesives (large scale)
Caulk (Sealant)
Fillers and Putties
Fertilizers
Instant action air fresheners
Continuous action air fresheners
Crafting paint (direct and incidental contact)
Spray Fixative and finishing spray coatings
liquid-based concrete, cement, plaster (prior to hardening)
Anti-Freeze liquids
De-king liquids
De-king solids
Shoe polish, shoe wax
Anti-stalk Spray Fabric Protector
Textile and Leather finishing products (stain remover, waterp
Textile and Fabric Dyes
Exterior Car Wax and Polish
Exterior Car Wash and Soaps
Interior Car Care Cleaning and Maintenance Products
Touch up Auto Paint
All-Purpose Spray Cleaner
All-purpose Liquid Cleaner (note, diluted or not-diluted)
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Product/Article Use Environment:
Residence - Living room
Weight Fraction of Chemical In Product/Article:
05 0
Initial Concentration of SVOC in Article (mg/cmS):
Estimate
Background Air Concentration (mg/mS):
0
Background Dutt Concentration (ug/mg):
G Available Models for the Selected Product or Article:
VOC El: Emission from Product Applied to a Surface Indoors In
PJNH1: Calculation of Inhalation Dose from Product Usag
PJNH2: Cakulation of Inhalation Dose from Product Usag
SVOC/VOC P_DER2a: Dermal Dose from Product Applied to Skin, Frac
SVOC/VOC P_DER2b: Dermal Dose from Product Applied to Skin, Perr
G Select Pathway(i) for Selected Product or Article: 10
0 Inhalation ~ Ingestion 0 Dermal
G Scenario Description/notes: 11
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Modeling Options:
User-defined Emission Rates
ฎ Let CEM Estimate Emission Rate
O Use a User-Defined Emission Rate
Use Near-field Zone? (El, E2, E3 only) G
<ง> Do Not Use Near-field Area in Zone 1 (PJNH1)
O Use Near-field Area in Zone 1 (PJNH2)
Dermal Absorption or Permeability? G -13
Oa. Absorption Fraction Method (P_DER2a)
b. Permeability Method (P_DER2b)
Emission Factor Method (El only) G
O Use Emission Factor Method
ฎ Use Evaporation Time Method
14
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2. Inputs tab
The Inputs tab is where details such as chemical properties and product use details are entered. The Inputs tab includes
five subtabs ("a" - "e"), each of which is described below.
Because CEM includes several distinct models, not all inputs are required for every scenario. CEM automatically
identifies inputs required for the current scenario and disables unneeded inputs. Required inputs can be identified by
labels with blue text; inputs that are not required have gray labels and input boxes and may not be entered for the
current scenario.
CEM is pre-populated with default values associated with chemicals, products and articles, and receptors. In many cases,
high, medium, and low defaults are provided. The user should exercise caution when selecting defaults to ensure that
the scenario modeled is reasonable. Any defaults in CEM may be overwritten by the user. CEM includes a "Restore All
Default Inputs" button along with the five subtabs. If this button is selected, the defaults are restored across all five tabs.
Inputs that are not populated by a default are reset to blank.
2.a. Chemical Properties Input tab
1. Scenario
2. Inputs
3. CEM Models
4. Results
5. Reports
a. Chemical Properties
b. Product/Article Properties
c. Environment Inputs
d. Receptor Exposure Factors e. Activity Patterns
The Chemical Properties Input tab includes information on the physical-chemical properties of the chemical-of-interest
chosen in the Scenario tab. Examples include:
Vapor pressure,
Molecular weight,
Saturation concentration in air,
Octanol-water partition coefficient,
Octanol-air partition coefficient,
Water solubility,
Henry's Law coefficient, and
Emission factor.
Additionally, this tab contains data on the parameters required to estimate emissions from articles and transfer to dust.
More details concerning these parameters and how they are incorporated into CEM are presented in the Section 3
description of model E6. Examples include:
Solid-phase diffusion coefficient,
Partition coefficients between air and dust, respirable particles (RP), sources, and interior surfaces (sinks), and
Mass transfer coefficients to RP, dust, and interior surfaces (sinks).
When estimating chemical exposures, measured data are preferred over estimates whenever available. Because
measured data are often unavailable, however, estimation tools are available for several inputs. For chemicals within
the domain of the training sets used for Quantitative Structure-Activity Relationship (QSAR) development, EPA
recommends the use of EPI-Suite Version 4.11 (U.S. EPA. 2012a) to estimate physical-chemical properties if empirical
data are not available. EPI-Suite requires either the simplified molecular-input line-entry system (SMILES) code or CAS
number/chemical name to estimate parameters needed to CEM.
CEM incorporates many parameter estimators in the Inputs subtabs. To explore a parameter estimator, click on the
"Estimate" button. This will provide background on the parameter, the estimator equation, equation inputs, and the
15
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estimated parameter. Click "Copy to Form" to close the estimator and paste the estimated parameter to the Input tab.
To estimate all parameters on a tab at once, click the "Estimate AN" button. This will not show the individual estimator
equations.
All properties required by CEM are shown on the Chemical Properties tab, even though not all properties are required by
each model. Properties not required by the model selected are presented in gray and are inactivated.
1 Click the 'Estimate' button next to an input field to use an estimator.
1. Scenario 2. Inputs 3. CEM Models 4. Results 5. Reports
a. Chemical Properties b. Product/Article Properties c. Environment Inputs d. Receptor Exposure Factors e. Activity Patterns
Estimate All
Benzyl Alcohol
100516
Chemical Property/Attribute
Chemical Name:
CAS No.:
Vapor Pressure (torr):
Molecular Weight (g/mol):
Saturation Concentration in Air (mg/m3):
Log Octanol-water Partition Coefficient (-):
Log Octanol-air Partition Coefficient (-):
Required
Water Solubility (mg/mL):
Henry's Law Coefficient (atm/M):
Emission Factor (ug/m2/hr):
Not Required
O
o
>ฃ>
108.1
1
5.45e+02
Estimate
1.10E+00
5.96E+00
d
[3.30E+01
3.37E-07
[1.60E+06
| Estimate
2.b. Product/Article Properties Input tab
1. Scenario
2. Inputs
3. CEM Models
4. Results
5. Reports
a. Chemical Properties b. Product/Article Properties c. Environment Inputs d. Receptor Exposure Factors e. Activity Patterns
The Product/Article Properties Input tab is used to enter required data to describe the product or article and how a
receptor could interact with it. Examples include:
Density of product/article,
Surface area of article,
Thickness of article surface layer,
Duration of article contact, and
Area of article mouthed.
This tab also contains data on the parameters required for dermal and ingestion exposure. More details concerning
these parameters and how they are incorporated into CEM are presented in the Section 3. Examples include:
Film thickness on skin,
Amount retained on skin,
Skin permeability coefficient,
Chemical migration rate,
Surface loading,
Mouthing transfer efficiency,
16
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Fraction of chemical that is dislodgeable,
Product dilution fraction,
Transdermal permeability coefficient,
Absorption fraction (chronic and acute),
Ingestion fraction (RP, dust, abraded particle),
Chemical half-life in soil,
Average molecule diffusion per contact,
Frequency of article contact, and
Adherence factor.
Additionally, this tab contains other input parameters specifically for chronic or acute assessments:
Frequency of use,
Duration of use, and
Mass of product used,
Aerosol fraction (all assessments).
Default values are available for many inputs and non-default values can be entered for most inputs. Not all information
is required for all models. Inputs required by the model(s) applicable to the selected product or article are highlighted in
blue text and must be entered before moving to the next tab.
2.c. Environment Inputs tab
1. Scenario
2. Inputs
3. CEM Models
4. Results
5. Reports
a. Chemical Properties
b. Product/Article Properties c. Environment Inputs d. Receptor Exposure Factors e. Activity Patterns
Use the Environment Inputs tab to enter required inputs about the environment(s) where the product or article is used.
Examples include:
Use environment,
Building volume,
Use environment volume,
Yard area,
Air exchange rate, Zone 1,
Air exchange rate, Zone 2,
Interzonal ventilation rate,
Area of interior surface, and
Thickness of interior surface.
This tab also contains dust parameter inputs (RP, dust, and abraded particle). Examples include:
Deposition rate (RP, dust, abraded particles),
Resuspension rate (RP, dust, abraded particles),
Mass generation rate, suspended (RP, dust, abraded particles),
Mass generation rate, floor (RP, dust, abraded particles),
Radius of particle (RP, dust, abraded particles),
17
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Density of particle (RP, dust, abraded particles),
Ambient RP concentration,
Cleaning frequency,
Cleaning efficiency, and
HVAC filter penetration.
Other inputs on this tab include near field environment inputs and soil properties which include:
Near-field volume,
Far-field volume,
Air exchange rate at near-field boundary,
Soil mixing depth,
Soil density,
Soil porosity, and
Concentration in soil/powders (chronic, acute).
Default values are available for many inputs and non-default values can be entered for most inputs. Not all information
is required for all models. Required inputs are highlighted in blue text and must be entered before moving to the next
tab.
2.d. Receptor Exposure Factors Input tab
1. Scenario 2. Inputs 3. CEM Models
4. Results
5. Reports
a. Chemical Properties b. Product/Article Properties
c. Environment Inputs d. Receptor Exposure Factors e. Activity Patterns
The Receptor Exposure Factors Input tab is used to provide information on product or article users and incidentally
exposed humans (receptors). All exposure factors are presented by receptor age group.
2 Required exposure factors are listed in the box on the left.
3 The box on the right shows the values for the factor selected to the left.
4 Default values are shown alongside the values entered for the current analysis.
5 Enter non-default values for the specific analysis under Analysis Value. For skin surface area to body weight (SA-BW)
ratio exposure factors, a drop-down menu is provided for 5th percentile, 50th percentile, and the 95th percentile
values. User-specified values can also be entered. An additional table on this screen presents SA-BW Ratios for
differing areas of skin exposure (e.g., whole body versus both hands), for reference.
Choose an Exposure Factor
Body Weight (kg)
Receptor-specific Exposure Factors Values for this Analysis
la
Exposure Duration - Chronic (years)
Exposure Duration - Acute (days)
Averaging Time - Chronic (years)
Averaging Time - Acute (days)
Inhalation Rate During Use (m3/hr)
Inhalation Rate After Use (m3/hr)
SA-BW Ratio
Receptor
Adult (>21 years)
Youth (16-20 years)
Youth (11-15 years)
Child (6-10 years)
Small Child (3-5 years)
Infant (1-2 years)
Infant (<1 year)
Default Value *
3 80
71.6
56.8
31.8
18.6
12.6
7.8
Analysis Value
4 HE
71.6
56.8
31.8
18.6
12.6
7.8
Restore Defaults
18
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I.e. Activity Patterns Input tab
1. Scenario
2. Inputs 3. CEM Models
4. Results
5. Reports
a. Chemical Properties
b. Product/Article Properties
c. Environment Inputs
d. Receptor Exposure Factors e. Activity Patterns
CEM employs three default activity patterns, one corresponding to a person who spends most of their time at home,
one corresponding to a person who works or attends school part of the day, and one corresponding to a person who
works or attends school all day. These activity patterns are presented for reference on the Activity Patterns tab. Only
one activity pattern can be selected for ail receptors for a single model run in CEM
The activity patterns were developed based on human activity diaries included in CHAD. The diaries were used to
develop average time spent sleeping and awake, as well as time spent in commercial buildings, government buildings,
schools, child occupied facilities (COFs), automobiles, outdoors, and rooms within residences. The diaries were grouped
into three bins based on the time spent in residences versus commercial, government, schools, and COFs; average times
spent from these three grouping were used to develop the three default activity patterns.
For receptors who are also product users, the default activity pattern will be overridden to place the user in the room of
use beginning at the Use Start Time specified. The user will remain in the room of use for the duration of product use
selected. The start time and duration of use should be selected so that product use occurs within one 24-hr day. This
logic applies only to product use, not article exposure.
3. CEM Models tab
1. Scenario
2. Inputs
3. CEM Models
4. Results
5. Reports
Model Selection
E1
PJNH1
P_DER2b
Click the CEM Models tab after completing the Scenario and Inputs tabs. This tab allows users to review the scenario and
input selections and to run the applicable exposure models.
1. The Model Selection subtab summarizes the models applicable to the selected product or article. These models are
selected by CEM and cannot be edited.
11. Scenario
2. Inputs
3. CEM Models
4. Results
5. Reports
Model Selection El
PJNH1
P_DER2b
i zr
After reviewing inputs, click the 'Run CEM Models' button to run the applicable exposure models. If required model
inputs have not been provided, a message will appear instructing the modeler to enter those values. An additional
message will appear when all model runs are complete.
19
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Model Selection
For this scenario, emission rates, exposure concentrations, and exposure doses will be estimated using the listed model(s).
|E1: Emission from Product Applied to a Surface Indoors incremental Source Model
PJIMHl: Calculation of Inhalation Dose from Product Usage
P_DER2b: Dermal Dose from Product Applied to Skin, Permeability Model
Run CEM Models
2 Equations and inputs for each model are displayed on separate subtabs for transparency and model evaluation. Each
model subtab provides the relevant equations necessary to run the model and the inputs for those equations.
Clicking on an input will populate information in the Parameter Information pane, on the right side of the page. This
text provides an explanation of the clicked variable, sources of automated inputs, and relevant assumptions applied
to the input.
Model Selection El PJNH11 P_DER2b
Emission from Product Applied to a Surface Indoors Incremental Source Model
ER(t) = M * WF ~ CF / ta * (1 - e*-k(t - tstart)) - (1 - e*-k(t - (tstart + ta)) * Ht)
ER(t)
= Emission rate at time t (mg/min)
Varies
M
= Mass of product used (g)
150
WF
=Weight fraction of chemical in product (-)
0.5
CF
Conversion factor (mg/g)
1000
ta
= Duration of Use (min/use)
a
qir
k
= First-order rate constant for emissions decline (1/min
0.002421
t
= Time (min)
Varies
Ht
= 0 if t-(tstart + ta) < 0; 1 if t-(tstart + ta) > 0
Varies
tstart
= Application start time (min)
Varies
First-order rate constant, k (Eq 3-43)
k [1/min] = ln(10) / (EvapTime * 60)
Evaporation time, (Eq 3-42)
EvapTime [hr] = 145 / (MW x VP)A0.9546
MW = Molecular Weight (g/mol)
VP = Vapor Pressure (torr)
15.85368
108.1
0.094
Parameter Information
Description:
The amount of time that a
product or article is used each
time it is used (i.e., per use event).
CEM provides default values of
this input for many
products/articles. Different use
durations can be used for the
acute and chronic exposure
assessments.
Primary sources of data, methods or
assumptions:
Please see the "Product Properties
Sources" lookup table on the Lookup
Tables and VBA Code tab for further
information on parameter source
information specific to each product.
4. Results tab
1. Scenario 2. Inputs 3. CEM Models 4. Results 5. Reports
Product/Article: All-purpose Spray Cleaner
Cover Page Inhalation Ingestion Dermal
20
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The results tab is empty until 'Run CEM Models' on the CEM Models tab is clicked.
The Cover Page sub-tab summarizes the exposure estimate by route and presents the total exposure for each
receptor age group. The exposure attributed to inhalation of background air concentrations and incidental ingestion
of background dust concentrations are also reported on this page for reference.
Cover Page Inhalation Ingestion Dermal
l 2
Product/Article: Caulk (Sealant)
Chemical Name: Benzyl Alcohol
Lifetime LADD/LADC
Adult (221 years)
Youth (16-20 years)
Youth (11-15 years)
Child (6-10 years)
Small Child (3-5 years)
Infant (1-2 years)
Infant (<1 year)
0.00E+00
8.49E+00
1.00E+01
1.17E+01
1.66E+01
2.38E+01
2.93E+01
3.11E+01
2.09E-02
2.85E-02
3.37E-02
3.93E-02
5.58E-02
8.01E-02
9.85E-02
1.05E-01
0.00E+00
0.00E+00
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
0.00E+00
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
2.73E+01
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
8.19E-02
1.12E-01
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
O.OOE+OO
3.57E+01
1.00E+01
1.17E+01
1.66E+01
2.38E+01
2.93E+01
3.11E+01
1.41E-01
3.37E-02
3.93E-02
5.58E-02
8.01E-02
9.85E-02
1.05E-01
0 Adult (*21 years) D Youth (11-20 years; Q Child (<1-10 years'
2, The Results tab also includes subtabs for each of the exposure routes, and each subtab contains acute and chronic
exposure estimates. These are labeled Acute Dose Rate (ADR) and Chronic Average Daily Dose (CADD), respectively.
5. Reports tab
1 Scenjrio 2 inputs 3 CIMModols 4 Result 5. Reports
ฆ
Choose a Report to View
1 The Reports tab allows for the viewing and exportation of various reports as PDFs. Two report options are available,
including the CEM Results, CEM Results and Inputs. The CEM Results report includes the results on the Cover Page
and then depending on which models were run, the report includes Dermal Results, Inhalation Results, and
Ingestion Results. The CEM Results and Inputs report includes all information in the CEM Results report and includes
the Scenario Summary.
a. Clicking on the Preview button opens the selected report with Access.
b. Selecting the Export button allows for the selected reports to be saved to a select location. A prompt will open
that allows for selection of the file location. The following prompt allows for the user to enter the file name.
1.4. Sensitivity Analysis Mode
The Sensitivity Analysis Mode includes two tabs.
1. Setup
2. Results
21
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The Setup tab is used to select a base analysis (either preloaded in CEM or user-defined with the single analysis mode),
select parameters to vary for the sensitivity analysis, and run the analysis. The Results tab is used to view or export
results.
1. Setup tab
Setup
Step 1. Choose the base analysis:
Step 2. Choose up to 3 parameters and up to 3 comma-separated values for each
Parameters to vary Values
1. | PI
2- I R1
3. f^l~
Acute Analysis Values
Step 3. Create Variations of the Base Analysis
The setup tab allows the user to structure multiple variations of a base analysis (Steps 1 through 4) and run the analysis
(Step 5).
Step 1 - Select a base analysis for the sensitivity analysis using a drop-down menu. The drop-down menu includes all
analyses built-in to CEM, as well as any custom analyses defined and saved with the Single Analysis Mode. After
selecting a base analysis, Step 1 is disabled until a model run is completed (Step 5) or the Reset button is clicked.
Step 2 - Select parameter fields to vary. The available options provided in the three parameter drop-down menus
depend on the type of base analysis selected (i.e., product or article). Available product parameter fields include:
Weight fraction of chemical in product (unitless)
Frequency of use (events/day)
Mass of product used (g/day)
Building volume (m3)
Use environment volume (m3)
Air exchange rate, zone 1 (per hour)
Air exchange rate, zone 2 (per hour)
Available article parameter fields include:
Initial concentration in article (mg/cm3)
Use environment volume (m3)
Density of article (g/cm3)
Surface area of article (m2)
Duration of article contact (min/day)
Up to three parameters may be selected to vary. After selecting a parameter from the down-down menu, up to
three comma separated values can be entered in the Values field for that parameter. Default values for the
parameter are automatically loaded. These can be replaced or retained as one of the three values for the sensitivity
analysis.
When applicable, the user entry field for Acute/Chronic Analysis Values will also be available for users to enter
values. The Acute/Chronic Analysis Value fields must have the same number of values entered.
22
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Parameter values must include numbers only (e.g., do not include units), and percentage values must be entered as
fractions (e.g., 0.25 instead of 25%). A leading zero is recommended, but not required, for decimal values. For
example, CEM will recognize ".25" as meaning "0.25".
Step 3 - Click the 'Create Variations of the Base Analysis' button to generate the unique combination of parameter
values that will be individually run by CEM for the sensitivity analysis. A sensitivity analysis may include up to 27
variations, which is equal to the total number of unique input combinations when there are three values for each of the
three parameters. Each variation is given an identifying number (i.e., Analysis ID). The IDs consist of the CEM Base
Analysis ID and sequential variation IDs.
Step 4 - In this optional step, review the variations for the sensitivity analysis within the table generated from the
selection of the Step 3. Use this step to review the variations and inputs. If modifications are needed, return to Step 2
and make the necessary changes and then repeat Step 3.
Step 4 (optional). Review variations for the sensitivity analysis
AnalysisJD -f
Description
Weight Frac - Mass Used
(i ป Mass Used
3.01
0.5
150
400
3.02
0.5
200
500
3.03
0.6
15oP
400
3.04
0.6
200
500
ฆฆIf \
Record: H 1 of 4
1 ~ M ป# | S2 No
Search
Step 5 -Click the 'Run the Sensitivity Analysis' button to run CEM for each of the analysis variation and generate results.
Progress status is shown to the right of the button. These status messages include: Preparing Inputs, Running CEM,
Processing Analysis, and Sensitivity Analysis Complete.
Step 5. Run the Sensitivity Analysis
After the completion of the run, the view will switch to the Results tab.
2. Results tab
Setup Results
After CEM completes a sensitivity analysis, the results are displayed on the Results tab. Use the results tab to view and
export the results. If changes to the sensitivity analysis setup are desired, return to the Setup tab, modify the parameter
values, regenerate the variations, and rerun the analysis.
23
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Select a vacation to view the result* below
H j, < ;i ~ 1. H .
show lesulti foe:
Selected Receptor(t)
Amlyjis lO Description
ฆ weight Frac
Mass Used ( - Ma-
is Used (<
ฎ The selected variation
uptime LAOO
USE
0.5
150
400
O All variations
vooth I
0.5
200
500
Adult
3.03
0.6
150
400
Child a
3.04
0.6
200
500
Child 1
X *'lcM "1 ปฆ H * J ^
Search
upon muiu loom
infant 2
Inhalation
Ingestion
Dermal
Total
Acute
Chronic Average
Acuta
Chronic Average
Acute
Chronic Average
Acuta
Chronic Average
Dose Bate
Da'ly Dote
Dose Sate
Daily Dove
Dote Rate
Oa
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2. Summary of Models within CEM
El: Product Emissions,
Applied to Surfaces
(Incremental Source Model)
E2: Product Emissions,
Applied to Surfaces
(Double Exponential Model)
E3: Product Emissions,
Sprays
E4: Product Emissions,
Products added to Water
E5: Product Emissions,
Products Placed
*-p
o
Q.
Partition to Air
03
H
o3
_ Partition to Airborne
QJ
Particulates
o
o
Partition to Settled
c
Particulates
AJNHl: Inhalation
of Airborne
Emissions from
Articles (Gas&
Particulate)
Swallowing
Application to Skin
Application to Soil
PJNH2: Inhalation
of Airborne
Emissions
from Products
(Near Field-Far
AJNG1: Ingestion
of Airborne
Emissions from
Articles
(Particulates)
P_DER2a: Dermal
absorption of
product applied to
skin
(Fraction
Absorbed)
PRODUCT SOURCE
HUMAN RECEPTOR
Figure 1. Schematic relationship showing exposure models included in CEM
Figure 1 shows the 21 models within CEM. There are six emission models, three inhalation models (purple), five
ingestion models (red), and seven dermal models (green). Model names that begin with a "P" are product models and
model names beginning with an "A" are article models. The following section includes brief summaries of each model
included in CEM. See Section 3 for further details on model equations and parameters.
El: Emission from Product Applied to a Surface indoors Incremental Source Model
This model assumes a constant application rate over a user-specified duration of use. Each instantaneously applied
segment has an emission rate that declines exponentially over time, at a rate that depends on the chemical's molecular
weight and vapor pressure. This model is generally applicable to liquid products applied to surfaces that evaporate from
the surfaces, such as cleaners. There is a near-field model option that can be selected that seeks to capture the higher
concentration in the breathing zone of a product user during use. Alternately, if the near-field option is not selected,
Zone 1 is modeled as a homogeneous, well-mixed room. (U.S. EPA, 2007)
E2: Emission from Product Applied to a Surface Indoors Double Exponential Model
This model accounts for an initial fast release by evaporation, followed by a slow release dominated by diffusion, and is
generally appropriate for liquid products that are applied to a surface and dry or cure over time, such as paints. Only
25% of the applied mass is released because a substantial fraction of the mass becomes trapped in the cured substrate
when it dries. (Note: 10% of the emissions are associated with the first of the double exponential.) Empirical studies
25
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support the assumption of 25% mass released and estimate a relationship between the fast rate of decline and vapor
pressure, and between the slow rate of decline and molecular weight. There is a near-field model option that can be
selected that seeks to capture the higher concentration in the breathing zone of a product user during use. Alternately,
if the near-field option is not selected, Zone 1 is modeled as a homogeneous, well-mixed room. (U.S. EPA. 2007)
E3: Emission from Product Sprayed
This model assumes a small percentage of a product is aerosolized and therefore immediately available for uptake by
inhalation. The percent of a product that is overspray is not well characterized. A recent study recommends values
ranging from 1 to 6% based on a combination of modeled and empirical data (Jayjock, 2012). The remainder is assumed
to contact the target surface, and to later volatilize at a rate that depends on the chemical's molecular weight and vapor
pressure. The aerosolized portion is treated using a constant emission rate model. The remaining (non-aerosolized) mass
is treated in the same manner as products applied to a surface, combining a constant application rate with an
exponentially declining rate for each instantaneously applied segment. There is a near-field model option that can be
selected that seeks to capture the higher concentration in the breathing zone of a product user during use. Alternately,
if the near-field option is not selected, Zone 1 is modeled as a homogeneous, well-mixed room. (U.S. EPA. 2007)
E4: Emission from Product Added to Water
This model assumes emission at a constant rate over a duration that depends on the chemical's molecular weight and
vapor pressure. If this duration is longer than the user-specified duration of use, then the chemical emissions are
truncated at the end of the product-use cycle (i.e., in the case of a washing machine, the remaining chemical mass is
assumed to go down the drain). This model is appropriate for use scenarios such as laundry and dishwashing detergent.
The potential duration of emissions in this case is determined from the chemical's 90% evaporation time. (U.S. EPA.
2007)
E5: Emission from Product Placed in Environment
This model is mathematically similar to E4, but is appropriate for products that are placed in the environment, but not
added to water, such as air fresheners. The model assumes emission at a constant rate over a duration that depends on
its molecular weight and vapor pressure. If this duration exceeds the user specified duration of use, then the chemical
emissions are truncated at the end of the product-use period, because the product is assumed to be removed from the
house after the use period (U.S. EPA. 2007).
E6: Emission from Article Placed in Environment
This model assumes emissions of SVOC additives from articles and subsequent partitioning between indoor air, airborne
particles, settled dust, and indoor sinks over time. Multiple articles can be incorporated into one room over time based
on the total exposed surface area of articles present within a room. Quasi-steady state concentrations are estimated
over time as the fugacity based model (Little et al.. 2012) was modified to account for removal mechanisms through air
exchange and routine cleaning (i.e., vacuuming or dry sweeping).
PJNHl: Inhalation of Product Used in Environment
CEM predicts indoor air concentrations from product use by implementing a deterministic, mass-balance calculation
utilizing an emission profile determined by implementing El through E5. The model uses a two-zone representation of
the building of use (e.g., residence, school, office) with Zone 1 representing the room where the consumer product is
used (e.g., a kitchen) and Zone 2 being the remainder of the building. The product user is placed within Zone 1 for the
duration of use. Otherwise, product users and bystanders follow prescribed activity patterns as described in Section 1
and inhale airborne concentrations of those zones.
26
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PJIMH2: Inhalation of Product Used in Environment (Near-Field / Far-Field)
In some instances of product use, a higher concentration of product is expected very near the product user. To model
this elevated exposure, the near-field / far-field option can be selected within CEM. In this model, Zone 1 of the mass-
balance model described in P_INH1 is further divided into the near-field, with a default volume of lm3, and far-field, the
remainder of the room of use. Each zone is considered well-mixed with an air exchange between them as suggested by
Keil et al.. 2009. The near-field can be envisioned as a bubble surrounding the user that moves throughout the room
with the user, such as in the case of painting. Product users inhale airborne concentrations estimated within the near-
field during the time of use and otherwise follow their prescribed activity pattern. Bystanders follow their prescribed
activity pattern and inhale far-field concentrations when they are in Zone 1.
Currently, each age grouping (adult, youth, child) can only be modeled as a user or bystander within CEM. P_INH1 and
PJNH2 can each be modeled for the same scenario and the results compared to estimate exposure by, for example, an
adult user and an adult bystander.
AJNHl: Inhalation from Article Placed in Environment
CEM predicts indoor air concentrations from article exposure by implementing a deterministic, mass-balance calculation
utilizing an emission profile determined by implementing E6. The model uses a one-zone representation of the building
of use (e.g., residence, school, office.) As opposed to the product inhalation models, the article inhalation model tracks
chemical transport between the source, air, airborne and settled particles, and indoor sinks by accounting for emissions,
mixing within the gas phase, transfer to particulates by partitioning, removal due to ventilation, removal due to cleaning
of settled particulates and dust to which the SVOC has partitioned, and sorption or desorption to/from interior surfaces.
All receptors are considered bystanders that follow prescribed activity patterns and inhale Zone 1 concentrations when
they are present within the building of use.
PJNG1: Ingestion of Product Swallowed
Model assumes that the product is directly ingested as part of routine use and the mass is dependent on the weight
fraction and use patterns associated with the product (ACI. 2010).
PJNG2: Ingestion of Product Applied to Ground Outdoors
A shallow mixing model provides equations and inputs to assess a number of scenarios where products such as fertilizers
are applied to soil. The populations considered in this model are those individuals who are potentially exposed during
routine outdoor-work, including residential lawns, playgrounds, parks, recreation areas, schools, and golf courses. Note,
the amount of product, and the size of the application area can be adjusted. The model assumes ingestion of outdoor
particles adhered to soil (U.S. EPA. 2012b).
AJNG1: Ingestion after Inhalation (Article Model)
AJNHl model assumes emissions of SVOC additives from articles and subsequent partitioning between indoor air,
airborne particles, and settled dust over time. A_ING1 calculates incidental ingestion of airborne particles estimated
using AJNHl that are inhaled and trapped in the upper airway (U.S. EPA. 2011)
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AJNG2: Ingestion of Article Mouthed
Chemicals present in articles can be ingested by direct object-to-mouth contact, termed mouthing. The mouthing
methodology relies on a migration rate of the chemical of interest from the article of interest to saliva. When the
migration rate is known, the model assumes that the amount of a chemical transferred into the saliva is dependent of
the migration rate and estimates the amount transfers into the body through duration and frequency of mouthing
patterns (U.S. CPSC. 2014).
AJNG3: Incidental Dust Ingestion (Article Model)
A_INH1 model assumes emissions of SVOC additives from articles and subsequent partitioning between indoor air,
airborne particles, and settled dust over time. A_ING3 calculates incidental ingestion of dust contaminated with levels of
SVOCs as predicted by A_INH1 using the Tracer methodology (U.S. EPA. 2011).
P_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin
Dermal exposure can also occur from gas-phase chemical deposition directly onto the skin from the air, with subsequent
absorption. The potential skin loading is calculated as the product of the gas-phase chemical concentration as estimated
by P_INH1 and the partitioning between air and skin lipids, which in turn is dependent on the octanol-air partitioning
coefficient, Henry's Law coefficient (or air-water partitioning coefficient), the ideal gas law constant, and temperature
(Weschlerand Nazaroff, 2012).
P_DER2a: Dermal Dose from Product Applied to Skin, Fraction Absorbed Model
For products that come in direct contact with the skin, the dermal portion of the User-Defined scenario allows modeling
of dermal exposure based on potential or absorbed doses using either a permeability coefficient or fraction absorbed.
This model uses a fraction absorbed to estimate dermal dose. Potential dose is the amount of a chemical contained in
bulk material that is applied to the skin, that represents an upper bound of exposure, and can be estimated using this
model and the fraction absorbed estimator (U.S. EPA. 2007; Frasch and Bunge, 2015).
P_DER2b: Dermal Dose from Product Applied to Skin, Permeability Model
For products that come in direct contact with the skin, the dermal portion of the User-Defined scenario allows modeling
of dermal exposure based on potential or absorbed doses. In this model, the user can specify a skin permeability
coefficient if known or use the provided permeability estimator if the user is interested in the amount of chemical that is
absorbed (ten Berge, 2010).
P_DER3: Dermal Dose from Soil where Skin Contact with Soil, Dust, or Powder Occurs
Dermal contact with residues of products applied to soils, such as soil amendments, and to powdered products such as
powdered laundry detergent, may occur. For skin contact with chemicals in soil, the potential dermal dose is estimated
by multiplying the chemical concentration in the soil (mass/mass) by an age-specific soil adherence factor describing the
transfer of the chemical from the soil to the hands, fraction absorbed, and age-specific activity patterns to estimate
potential loading on the skin (Pawar et al. 2016). For skin contact with powdered chemicals, the potential dermal dose is
estimated by multiplying the chemical concentration in the product (mass/mass) by an age-specific adherence factor
describing the transfer of the chemical from the powder to the hands, fraction absorbed, and age-specific activity
patterns to estimate potential loading on the skin.
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A_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin (Article Model)
Similar to P_DER1, this model describes dermal exposure from gas-phase chemical deposition directly onto the skin from
the air, with subsequent absorption. A_INH1 model assumes emissions of SVOC additives from articles and subsequent
partitioning between indoor air, airborne particles, and settled dust over time. The potential skin loading is calculated as
the product of the gas-phase chemical concentration as estimated by A_INH1 and the partitioning between air and skin
lipids, which in turn is dependent on the octanol-air partitioning coefficient, Henry's Law coefficient (or air-water
partitioning coefficient), the ideal gas law constant, and temperature (Weschlerand Nazaroff, 2012).
A_DER2: Dermal Dose from Article where Skin Contact Occurs
For articles that come into direct contact with the skin, chemical can migrate from the article to the skin. This is
described by the migration rate to the skin, which is governed by the solid phase diffusion coefficient, in combination
with age-specific activity patterns to estimate potential loading on the skin. The amount of skin exposed will vary
depending on the type of article a receptor comes into contact with, for example mattresses versus toys (Delmaar et al..
2013).
A_DER3: Dermal Dose from Skin Contact with Dust
Dermal contact with chemicals in dust that settle on articles may occur. This model is similar to P_DER3, for skin contact
with chemicals in soil and powders. The potential dermal dose is estimated by multiplying the chemical concentration in
the dust (mass/mass) by an age-specific soil adherence factor describing the transfer of the chemical from dust to the
hands, fraction absorbed, and age-specific activity patterns to estimate potential loading on the skin (Pawar et al. 2016).
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3. Detailed Descriptions of Models within CEM
CEM predicts exposure via three pathways: inhalation, ingestion, and dermal. Exposure can occur via direct contact with
a product or article or by contact with an exposure medium (e.g., air, dust, soil.) Exposure media concentrations,
particularly air, can be dynamic in time. CEM predicts indoor air concentrations resulting from product use by
implementing a deterministic, mass-balance calculation. (Indoor concentrations of air and dust from article usage in
model E6 are determined in an alternate manner and are described in section E6.)
How a product's chemical emissions are represented in CEM depends on how the product is used and its chemical
makeup. Emissions from each incidence of product usage are estimated over a period of 60 days using the following
equations and methods that account for how a product is used or applied, the total applied mass of the product, the
weight fraction of the chemical in the product, and the molecular weight and vapor pressure of the chemical. The 60-day
modeling period for each incidence of usage was chosen after it was determined that airborne concentrations returned
to background levels well within the 60-day window. This methodology allows for overlaying multiple 60-day windows,
each associated with one incident of product usage to determine elevated concentrations associated with repeated use
while maintaining rapid model run times. Sections El through E5 describe the emission equations used by different
product categories. Emissions from articles and associated media concentrations are estimated over a one-year period
in models E6, AJNG3, AJNG1, and A_DER1.
Two-zone Mass Balance Model for Estimating Inhalation Exposure from Product Use
CEM predicts indoor air concentrations by implementing a deterministic, mass-balance calculation. The model uses a
two-zone representation of a house, school, and office building with Zone 1 representing the area where the consumer
product is used (e.g., a kitchen) and Zone 2 being the remainder of the building of use. The modeled concentrations in
the two zones are a function of the time-varying emission rate in Zone 1, the volumes of Zones 1 and 2, the air flows
between each zone and outdoors, and the air flows between the two zones. For a conservative estimate of exposure,
indoor sinks are assumed not to exist except in the case of SVOC emissions from articles (E6). The model requires the
conservation of pollutant mass as well as the conservation of air mass. CEM uses a set of differential equations whereby
the time-varying concentration of the chemical in each zone is a function of the rate of pollutant loss and gain for that
zone. These relationships can be expressed as shown in Figure 2 and the equations for Zone 1 and Zone 2:
C2 (Zone 2 cone)
(Zone 2 volume)
Zone 2
Oo2
C0
Zone 1
E (emission to air)
Ql2 = Q21
Figure 2. Schematic of two-zone model of indoor environment
Zone 1:
Q 12Xt-l _|_ _|_ Ql2Xt-2
(1)
30
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Zone 2: ^ = -AER2 x C2 + (2)
dt z z V2 V2 v '
Where:
^ = Change in concentration with time (|a,g/m3/hr)
AER = Air exchange rate in Zone 1 or 2, equivalent to Qdx/Vx (hr1)
C = Airborne concentration in Zone 1 or 2 (|a,g/m3)
Q12 = Interzonal air flow rate (m3/hr)
E(t) = Emission rate at time, t (jag/hr)
V = Volume of Zone 1 or 2 (m3)
The flow rates are input as constants. The pollutant mass balance is used in conjunction with the flow rates to predict
the time-varying pollutant concentrations in each of the two indoor zones. The differential equations are solved using
the linear solver for ordinary differential equations (LSODE) on the Python software platform.
Air exchange rates and interzonal air flow are variables that can be edited. Default air exchange rates for the building are
from the Exposure Factors Handbook (U.S. EPA. 2011). The default interzonal air flows are a function of the overall air
exchange rate and volume of the building, as well as the "openness" of the room itself. Kitchens, living rooms, garages,
schools, and offices are considered to be more open to the rest of the home or building of use; bedrooms, bathrooms,
laundry rooms, and utility rooms are usually accessed through one door and are considered more closed. The default
interzonal air flow equations are based on a regression analysis by (U.S. EPA. 1995) and are as follows:
Closed rooms: Q12 = (0.078 + 0.31 X AER) X (3)
Open rooms: Q12 = (0.046 + 0.39 X AER) X V (4)
Where:
AER = Air exchange rate of building (hr1)
V = Volume of building (m3)
Default volumes for buildings and individual room sizes are taken from the Exposure Factors Handbook (U.S. EPA. 2011).
Two default use environments are presented that differ from the two-zone model: automobile and outside. The
automobile is modeled as a one-zone model with a high (12.5 hr"1) air exchange rate. Product-specific scenarios that
have a default use environment of outside are: fertilizers, touch up auto paint, de-icing solids, and liquid-based concrete,
cement, plaster. There are no product-specific scenarios that have a default use environment of automobile.
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Near-field option for Estimating Product Exposure During Use
To account for scenarios which deviate from the assumption of inhalation exposure occurring in one of two well-mixed
zones, the CEM model offers the option of a "Near Field-Far Field" (NFFF) model. The near-field option should be
selected with care, generally only when a product user is stationary rather than mobile during the duration of product
use. The NFFF model accounts for imperfect mixing by conceptually dividing the room containing the emission source
into two separate zones: the near-field zone, in which the product is assumed to be used and the product user's
exposure occurs, and the far-field zone, which exchanges air with the near-field zone as well as the second well-mixed
zone and the outdoors. The NFFF option can be selected on the Scenario tab for any product with an inhalation model.
Figure 3 illustrates the assumed air exchange mechanics within the NFFF model. Chemical dispersion in the model is
described by means of a system of first-order, first-degree differential equations that maintain chemical mass balance.
Table 1 lists the symbols, and their corresponding definitions, used in Figure 3 and in the derivation of the governing
differential equations.
Q02
Co
Figure 3. Air flows in the near-field far-field model
Table 1. Guide to Symbols Used in NFFF Model Equations
Symbol
Definition
Vnf
Volume of the near-field in Zone 1 (m3)
VFF
Volume of the far-field in Zone 1 (m3)
Vr2
Volume of Zone 2 (m3)
Qof
Ventilation rate of Zone 1 to external environment (m3/hr)
Qj32
Ventilation rate of Zone 2 to external environment (m3/hr)
Qf2
Ventilation rate between Zone 1 and Zone 2 (m3/hr)
Qnf
Ventilation rate between the near field and far field (m3/hr)
AERri
Air exchange rate of Zone 1 computed as Qri/(VNf+VFf) (/hr)
aerR2
Air exchange rate of Zone 2 computed as Qr2/(VR2) (/hr)
AERnf
Air exchange rate between near-field and far-field computed as Qnfff/Vnf (/hr)
t
Time (hr)
The following equations define the chemical mass exchange dynamics in the near-field of Zone 1, the far-field of Zone 1,
and Zone 2, respectively.
Far Field
Cff
Qnf
Zone 2
c2
Near Field
(w source)
Cnf
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Near Field, Zone 1
= -AERnf x CNF + AERnf xcff+g (5)
Far Field, Zone 1
= AERnf X CFF X + AERnf X CNF X + QR1R2 X AERr1 X CFF X W^FF'> (?rir2 x (ฎ)
Zone 2
= Qr1R2 x AERr2 x CR2 Qr1R2 X (7)
The CEM model solves this system of equations to derive instantaneous estimates of chemical concentrations in each
zone of the model, i.e., in the near-field of Zone 1, the far-field of Zone 1, and in Zone 2. When solving these equations
using an ordinary differential equation solver in Python, the CEM model applies a concentration ceiling corresponding to
the chemical's saturation vapor pressure. The CEM model allows users to define emission rates according to five
alternative emission scenarios, or according to a user-specified constant emission rate.
The model only exposes the user to the near-field concentration when the product is in use. When the product is no
longer in use, the user is exposed to concentration in far-field zone until they change locations based on their activity
pattern. For example, if a product is used from 9:00am to 9:20am, the user is in the near-field during use and in the far-
field from the end of use until changing locations at 10:00am.
A two-zone model is used only for products that are used in a specific room within the house. For these products, a
person is in Zone 1 only when they are in the room of use, either during or after use. A person is in Zone 2 whenever
they are in any room other than the room of use. The "whole house" use environment is modeled as a single zone, and a
person is in Zone 1 if they are anywhere in the house. If they are not in the house they are neither in Zone 1 nor Zone 2.
For products used outdoors or any other non-residence location, a person is in Zone 1 when in the use environment, and
they are never in Zone 2. The outdoor use environment is unique in that it is not an enclosed space. Because CEM is not
designed to model air dispersion outdoors, non-users are assumed to be bystanders who receive the same exposure as
users.
El: Emission from Product Applied to a Surface Indoors Incremental Source Model
For a product that is applied to surface, such as a general purpose cleaner or a latex paint, an incremental source model
is used. This model assumes a constant application rate over the specified duration of use; each instantaneously applied
segment has an emission rate that declines exponentially over time, at a rate that depends on the chemical's molecular
weight (MW) and vapor pressure (VP). This model is dependent solely on the mass of chemical, rather than the amount
of product used. Therefore, dilution is not calculated in this model as it is in dermal models. There is an option to model
near-field exposure which determines whether to use the near-field use area directly around the product user for
exposure (Use Near-Field Area in Zone 1) or a homogenous concentration for the entire room (Do Not Use Near-Field
Area in Zone 1). The equation for exponentially declining emissions for each instantaneously applied segment is as
follows:
ER(t) = ER(0) X e~kt (8)
Where:
33
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ER(jt) = Emission rate at time t (mg/min)
ER(0) = Initial emission rate at time 0 (mg/min)
k = First-order rate constant for emissions decline (min1)
t = Elapsed time (min)
The value of k is determined from an empirical relationship, developed by (Chinn, 1981), between the time required for
90% of a pure chemical film to evaporate (EvapTime) and the chemical's molecular weight (MW) and vapor pressure
(VP):
EvapTime = (9)
The value of k is determined from the 90% evaporation time as follows:
k = (10)
EvapTImeX60
Users may also estimate k using another method shown in Equations 11 and 12, based on a model to estimate spills
using a chemical's gas-phase mass transfer coefficient and parameters of the spill (Guo et al., 2008):
k = ^ (11)
M0
Eo= kg x Csat (12)
Where,
E0
kg
r
ฐsat
M0
Where,
Emission factor (ng/m2/hr)
Gas-phase mass transfer coefficient (m/hr)
Saturation concentration based on the vapor pressure of chemical (mg/m3)
Mass of chemical per unit area (ng/m2)
M0 = p x thickness x CF1 x CFZ
(13)
P
thickness
CF1
cf2
Density of the chemical (g/cm3)
Thickness of the spill/puddle (assumed to be 0.01 cm)
Conversion factor, 104 cm2/m2
Conversion factor, 10s ng/g
Equations 11-13 are used when a user wants to model the emission from a chemical or product spill using an emission
factor. If the user selected "Use Emission Factor Method" on the Scenario page, then when a user selects "Estimate AN"
on the Chemical Properties page, a dialogue box will appear that askes if you want to estimate the emission factor. If
you want to use your own emission factor, select no and then manually enter the emission factor in the input box. If you
34
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do not want to use an emission factor, the emission factor input will be set to 0 and CEM will calculate k using Equation
10.
a. Chemical Properties b. Product/Article Properties | c. Environment Inputs | d. Receptor Exposure Factors | e. Activity Patterns
Values initially shown are default values. Override the default values by using the picklist or entering user-defined values.
Estimate All
Chemical Property/Attribute
Chemical Name:
Ethylene glycol
Microsoft Access
Do you want to use the Emission Factor to calculate the decay rate
constant for El?
ER(0) can be determined from the fact that the integral of the above ER(t) equation, which accounts for all chemical
mass released (i.e., applied mass X chemical weight fraction), is equal to ER(0) h- k. However, the equation for the
time-varying emission rate resulting from the combination of constant application and exponentially declining emissions
(Evans. 1996) requires knowledge of only the total mass released and k.
ER(t) =
Where:
ER(t)
M
WF
CF
t start
ta
k
t
Hit)
MXWFXCF
tn
X ^(l e fc(t tstart)) ^(l e kfetart+ta))^ x
(14)
Emission rate at time t (mg/min)
Mass of product used (g)
Weight fraction of chemical in product (unitless)
Conversion factor (1000 mg/g)
Time of start of application (min)
Application time (min)
First-order rate constant for emissions decline (min-1)
Time (min)
0/1 value used to indicate if product is actively in use
0 if t- (tstart + ta) < 0
1 if t- (tstart + ta) > 0
Because the saturation vapor pressure concentration (Csat) is the highest concentration that could be present in air,
CEM uses it as an upper-bound cap to estimated or user-defined zone air concentrations. The gas-phase saturation
concentration can be estimated with the following equation, where R = universal gas constant (8.314 Pa/mol-K) and T =
temperature in Kelvin (298), if an experimentally derived value is not available:
(VPXMWXCF^CFz)
r
ฐsat
(.RXT)
(15)
35
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Where:
r
ฐsat
= Saturation concentration in air (mg/m3)
VP
= Vapor pressure (Torr)
MW
= Molecular weight (g/mol)
CFt
= Conversion factor, 133 Pa/Torr
CF2
= Conversion factor, 103 mg/g
R
= Universal gas constant, 8.314 m3-Pa/mol-K
T
= Temperature (K)
At each time step CEM checks whether the current value for the emission rate results in an indoor concentration that
exceeds the Csat. If so, then the emission rate is reduced to a value that results in the indoor concentration equaling
Csat. In such a case, CEM keeps track of the cumulative mass that has been subtracted to meet the Csat constraint.
Release of this accumulated excess mass is initiated at a later point in time, when the modeled concentration otherwise
would be below the Csat value. This procedure is continued until all excess mass has been release, unless the model run
period of 60 days ends first (or the product is removed or goes down the drain).
E2: Emission from Product Applied to a Surface Indoors Double Exponential Model
Products with an initial fast release governed by evaporation and a later slower release dominated by diffusion have
their exposure estimated via the double exponential model. Latex paint is an example of this type of consumer product.
Empirical studies reported by (Wilkes et al.. 1996) have estimated a relationship between the fast rate of decline (k5) and
vapor pressure (VP), and between the slow rate of decline (k2) and molecular weight (MW), leading to the equation
below for the time-varying emission rate (Evans. 1996). Additionally, a fraction of the chemical mass in the product may
become trapped in the product substrate when it dries or cures. This fraction will vary based on the chemical and
product combination. Wilkes et al.. 1996 reports approximately 25% of the original VOC mass is released from latex
paint. To account for this, the weight fraction (WF) of chemical or mass of product used can be adjusted to reflect the
chemical mass that is available for release. This model is dependent solely on the mass of chemical, rather than the
amount of product used. Therefore, dilution is not calculated in this model. There is an option to model near-field
exposure which determines whether to use the near-field use area directly around the product user for exposure (Use
Near-Field Area in Zone 1) or a homogenous concentration for the entire room (Do Not Use Near-Field Area in Zone 1).
ER(t) = M XWFXCF X {[/ X (1 - + (1 - /) X (l - e"fe2(t-tstart))] _
[/ x (1 - e"fel(t-(tstart+ta))) + (1 - f) x (l - e"fe2(t-(tstart + ta)))] X H(t)} (16)
Where:
ER(t) = Emission rate at time t (mg/min)
M = Mass of product used (g) containing chemical available for release (chemical that is assumed not
trapped within the substrate)
WF = Weight fraction of chemical in product (unitless)
CF = Conversion factor (1000 mg/g)
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tstart = Time of start of application (min)
ta = Application time (min)
/ = Fraction of mass emitted from first exponential (0.1) (unitless)
t = Time (min)
H(t) = 0/1 value used to indicate if product is actively in use
= 0 if t- (tstart + ta) < 0
= 1 if t - + ta)> 0
/q = 233.25 X (VP -h 24) -h 60 (min1)
k2 = 0.0000584 X (MW h- 24) h- 60 (min-1)
VP = Vapor pressure (Torr)
MW = Molecular weight (g/mol)
The equation for the resultant emission profile requires estimates of the total mass released, /q and k2, and the fraction
of released mass associated with the first exponential (Evans. 1996). As the empirical studies reported by (Wilkes et al..
1996) report a variable fraction of mass released depending on the product and chemical (ranging up to 80%), CEM
assumes a total of 100% chemical mass is available for release and associates 10% of the released mass with the first
exponential. Users wishing to assume a smaller fraction of chemical mass available for release should proportionally
adjust the mass of product used term in Equation 16.
At each time step CEM checks whether the current value for the emission rate results in an indoor concentration that
exceeds the Csat. If so, then the emission rate is reduced to a value that results in the indoor concentration equaling
Csat. See El for further details.
E3: Emission from Product Sprayed
Model assumes a small percent of product is aerosolized and therefore immediately available for uptake by inhalation.
The remainder is assumed to contact the target surface, and to later volatilize at a rate that depends on the chemical's
molecular weight and vapor pressure. The aerosolized portion is treated using a constant emission rate model. The
amount of mass aerosolized varies by product type and updated defaults from ConsExpo (Delmaar et al.. 2005) have
been incorporated. The remaining (non-aerosolized) mass is treated in the same manner as products applied to a
surface, combining a constant application rate with an exponentially declining rate for each instantaneously applied
segment. There is an option to model near-field exposure which determines whether to use the near-field use area
directly around the product user for exposure (Use Near-Field Area in Zone 1) or a homogenous concentration for the
entire room (Do Not Use Near-Field Area in Zone 1) (U.S. EPA. 2007).
ERl(t) = MxWFxCFxf x [1 - H(t)] (17)
ta
Where:
ER1(t') = Emission rate at time t from initial aerosolized product (mg/min)
M = Mass of product used (g)
WF = Weight fraction of chemical in product (unitless)
37
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CF = Conversion factor (1000 mg/g)
/ = Fraction of product emitted to air (unitless)
ta = Application time (min)
H(t) = 0/1 value used to indicate if product is actively in use
= 0 if t- (tnan + ta)< 0
= 1 if t - (tstart + ta)> 0
ER2(t) = MXWFXCF x |^(l e fe(t tstซrt)) _ e fetart+ta))) x H(t))] (18)
Where:
ER2(f)
= Emission rate at time t from secondary surface-contacted product (mg/min
M
= Mass of product used (g)
WF
= Weight fraction of chemical in product (unitless)
CF
= Conversion factor (1000 mg/g)
tstart
= Time of start of application (min)
ta
= Application time (min)
k
= First-order rate constant for emissions decline (min1)
t
= Time (min)
Hit)
= 0/1 value used to indicate if product is actively in use
= 0 if t - (tstart + ta) < 0
= 1 if t - (tstart + fa) > 0
ERfinalit) = ER^t) + ฃK2(t) (19)
Where:
ERfinalit) = Final emission rate at time t (mg/min)
ฃ'i?1(t) = Emission rate at time t from initial aerosolized product (mg/min)
ER2(t) = Emission rate at time t from secondary surface-contacted product (mg/min)
At each time step CEM checks whether the current value for the emission rate results in an indoor concentration that
exceeds Csatฆ If so> then the emission rate is reduced to a value that results in the indoor concentration equaling Csat-
See El for further details.
E4: Emission from Product Added to Water
Model assumes emission at a constant rate over a duration that depends on its molecular weight and vapor pressure. If
this duration is longer than the user-specified duration of use, then the chemical emissions are truncated at the end of
38
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the product-use cycle (i.e., in the case of a washing machine, the remaining chemical mass is assumed to go down the
drain). The potential duration of emissions in this case is determined from the chemical's 90% evaporation time.
145
EvapTime = rrr--x 60 (20)
F {MW XVP)0-9546 V '
Where:
EvapTime = Evaporation time (min)
MW = Molecular weight (g/mol)
VP = Vapor pressure (Torr)
Where:
ER(t)
M
WF
CF
H{t)
^start
ta
tm n v
ER(t) = MXWFXCF x H(t)
EvapTime
Emission rate at time t (mg/min)
Mass of product used (g)
Weight fraction of chemical in product (unitless)
Conversion factor (1000 mg/g)
0/1 value used to indicate if product is actively in use
1 if t ([Pstart "i" tmax) ^ ^
0 if t ([Pstart "i" ^max) ^ 0
Time of start of application (min)
Application time (min)
Minimum between EvapTime and ta (min)
(21)
At each time step CEM checks whether the current value for the emission rate results in an indoor concentration that
exceeds the Csat. If so, then the emission rate is reduced to a value that results in the indoor concentration equaling
Csat. See El for further details.
E5: Emission from Product Placed in Environment
Model assumes emission at a constant rate over a duration that depends on its molecular weight and vapor pressure, as
shown in Equations 20 and 21. If this duration exceeds the user specified duration of use, then the chemical emissions
are truncated at the end of the product-use period, because the product is assumed to be removed from the house after
the use period (U.S. EPA. 2007).
In certain cases, the source models could lead to predicted concentrations that exceed the chemical's saturation
concentration in air. However, the model adjusts the time-varying emission rate so that the saturation concentration is
never exceeded. In such cases, the chemical mass will be released at a slower rate than implied by the source models,
once the saturation concentration is reached. The same chemical mass ultimately will be released, except in cases where
emissions are truncated at the end of the product use period.
39
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At each time step CEM checks whether the current value for the emission rate results in an indoor concentration that
exceeds the Csat. If so, then the emission rate is reduced to a value that results in the indoor concentration equaling
Csat. See El for further details.
PJNHl and PJIMH2: Calculation of Inhalation Dose from Product Usage
Two different inhalation concentration calculations are performed in CEM: Potential Lifetime Average Daily
Concentration (LADC), and Potential Peak Concentration (Cp). They are defined as follows:
LADC = CatiXFQXED
ATXCFi
Where:
LADC
= Potential Lifetime Average Daily Concentration (mg/m3)
r .
uati
= Time-integrated air concentration for an event (mg-day/m3-event)
FQ
= Frequency of product use (events/year)
ED
= Exposure duration (years of product usage)
AT
= Averaging time (years), assumed to an entire lifetime (78 years) for LADC
CFt
= Conversion factor (365 days/year)
The time-integrated air concentration is estimated using the following equation:
Cati ZFtCuXM (23)
Where:
Cati = Time-integrated, air concentration for an event (mg-day/m3-event) from start time (ST) to end time (ET),
where ET = ST + 60 days.
Ci t = Concentration in Zone i at time t (mg/m3)
At = Time interval (0.00035 days)
For cases where the evaporation time exceeds 60 days, the model will truncate the emissions at 60 days. Conversely, for
cases where the evaporation time is less than 60 days, emissions will be set to zero between the end of the evaporation
time and 60 days.
Peak concentration is the highest concentration experienced at any point during the day of use in the use environment.
The potential peak concentration (Cp) provided in the model output is defined as the highest instantaneous air
concentration that is calculated by the model during any 30-second time step, and should not be interpreted as a daily
maximum concentration.
Cp = MaxjQ (24)
Where:
Cp = Potential Peak Concentration (mg/m3), evaluated as the maximum Cufrom t=0 to t=ET
40
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Ci,t
Concentration in Zone i at time t (mg/m3
Two different inhalation dose calculations are performed in CEM: the Potential Chronic Average Daily Dose (CADD) and
the Potential Acute Dose Rate (ADR). The general expression for the Potential Chronic Average Daily Dose (CADD) is as
follows:
CADD =
CairX-Inh XFQXDcrXED
BW XATXCF1XCF2
(25)
Where:
CADD
= Potential Chronic Average Daily Dose (mg/kg-day)
r ฆ
wair
= Concentration of chemical in air (mg/m3)
lnh
= Inhalation rate (m3/hr)
FQ
= Frequency of use (events/year)
DCr
= Duration of use (min/event), chronic
ED
= Exposure duration (years of product usage)
BW
= Body weight (kg)
AT
= Averaging time (years)
CFr
= Conversion factor (365 days/year)
cf2
= Conversion factor (60 min/hr)
CEM uses two different inhalation rates, one when the receptor is using the product and another after the use has
ended. Table 2 shows the inhalation rates by receptor age category for during and after product use.
Table 2. Inhalation rates used in CEM product models.
Receptor category Inhalation Rate Inhalation Rate
During Use (m3/hr)a After Use (m3/hr)b
Adult (>21 years)
0.74
0.61
Youth (16-20 years)
0.72
0.68
Youth (11-15 years)
0.78
0.63
Child (6-10 years)
0.66
0.5
Small Child (3-5 years)
0.66
0.42
Infant (1-2 years)
0.72
0.35
Infant (<1 year)
0.46
0.23
aTable 6-2, light intensity values (EPA, 2011)
"Table 6-1 (EPA, 2011)
Within CEM, the inhalation dose is calculated iteratively, at 30-second time step intervals during the first 24 hours and
every hour after that for 60 days, taking into account the chemical emission rate over time, the volume of the house and
each zone, the air exchange rate and interzonal airflow rate, and the exposed individual's locations and inhalation rates
41
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during and after product use. Because of this iterative process, CADD cannot be calculated directly from the LADC
presented in the model results. Therefore, CADD is calculated using the following expression:
Doseati XFQXED
Where:
CADD
Doseati
FQ
ED
BW
AT
CFt
CADD =
BW XATXCF1
(26)
Potential Chronic Average Daily Dose (mg/kg-day)
Time-integrated, air dose for an event, presented in following equation (mg/event)
Frequency of product use (events/year)
Exposure duration (years of product usage)
Body weight (kg)
Averaging time (years)
Conversion factor (365 days/year)
;ati - Time-integrated, air dose for an event (mg/event) from start time (ST) to end time (ET), where ET = ST +
For CADD calculations, the averaging time is 1 year. In turn, the time-integrated air dose is calculated as follows:
Doseati = Y.st Q.t X At X Inhi t X CF2 (27)
Where:
Doseati
60 days
Ci t = Concentration in Zone i at time t (mg/m3)
Inhi t = Inhalation Rate for Zone i at time t (m3/hr)
At = Time interval (0.00035days)
CF2 = Conversion factor (24 hs/day)
For cases where the evaporation time estimated exceeds 60 days, the model will truncate the emissions at 60 days.
Conversely, for cases where the evaporation time is less than 60 days, emissions will be set to zero between the end of
the evaporation time and 60 days.
The Lifetime Average Daily Dose (LADD) represents chronic exposures over a lifetime and can also be calculated in CEM.
Users can calculate the LADD by changing the chronic exposure duration to a value for the specific product or article of
interest and change the chronic averaging time to the 78 years (an entire lifetime). The LADD should be used for adult
only.
LADD uses an averaging time of a lifetime, which is typically 78 years. Suggested LADD exposure durations for products
used regularly are 57 years, for products used intermittently are 12 years, and for those used less often are 5 years. The
suggested exposure durations were based on an exposure starting at 21 years old and continuing each year of an adult's
lifetime (78-21 = 57), an exposure starting at 18 years old and occurring every 5 years (78-18 = 60/5 = 12), and an
exposure occurring for only 5 years throughout a lifetime. Note, articles can generally be assumed to have a continuous
exposure duration in that exposure duration and averaging time are likely to match.
42
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The general expression for the Potential Acute Dose Rate (ADR) is as follows:
CgirX-Inh X-FQxDacXED (28)
~~ BW XATXCF1 * '
Where:
ADR
= Potential Acute Dose Rate (mg/kg-day)
r
ฐair
= Concentration of chemical in air (mg/m3)
lnh
= Inhalation rate (m3/hr)
FQ
= Frequency of product use (events/day)
Dac
= Duration of use (min/event), acute
ED
= Exposure duration (days of product usage)
BW
= Body weight (kg)
AT
= Averaging time (days)
CF1
= Conversion factor (60 min/hr)
For the ADR calculations, an averaging time of 1 day is used; the ADR therefore represents the maximum time-
integrated dose over a 24-hour period during the exposure event. As was the case with the CADD, ADR cannot be
calculated directly. Instead, the following expression for Doseati is used:
Doseati = Zงr ci.t X At X Inhi t X CF2 (29)
Where:
Doseati = Time-integrated, air dose for an event (mg/event) from start time (ST) to end time (ET), where ET = ST +
60 days.
Cit = Concentration in Zone i at time t (mg/m3)
Inhi t = Inhalation Rate for Zone i at time t (m3/hr)
At = Time interval (0.00035 days)
CF2 = Conversion factor (24 hrs/day)
For cases where the evaporation time estimated exceeds 60 days, the model will truncate the emissions at 60 days.
Conversely, for cases where the evaporation time is less than 60 days, emissions will be set to zero between the end of
the evaporation time and 60 days.
CEM provides the ADR, Peak Concentration (mg/m3), and Peak Dose (mg/day) in the reports. Peak Dose is calculated by
multiplying the ADR by the receptor body weight.
The airborne concentration in the above equation is calculated differently for ADR than for CADD. For the CADD
calculations, CEM uses the central tendency consumer product weight fraction, duration of use, and mass of product
used. In the ADR calculation, it uses the high-end consumer product weight fraction, duration of use, and mass of
43
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product used. CEM calculates all possible ADRs, over the 60-day modeling period, as running 24-hour integrations (i.e.,
hours 1-24, 2-25, etc.), and then reports the highest of these computed values as the ADR.
Owing to the relative complexity of the P_INH_1 and 2 models, additional details are provided here on how these
equations are computed within the computer code. To ensure speed of computation, a vectorized approach was used in
which activity pattern data were systematically mapped onto the time series concentration output from the differential
equation solver in the following steps:
Step 1: Mapping Indicators of Product Use and Occupant Location
Obtain time series concentration output for Zone 1 and Zone 2 (and near-field and far-field concentrations, if
applicable) from the differential equation solver
Add binary variables to indicate whether each time point occurs during a use-day or a non-use day
Add binary variables to indicate whether each time point occurs during a use-hour or a non-use hour
Add activity pattern data (room location as a categorical variable) depending on work status (full time/part
time/stay-at-home) on use days and non-use days at each time point
Step 2: Mapping Indicators of Zone 1 and Zone 2 Presence
Map different locations in the house to Zones 1 and 2. Regardless of user status, add binary variables to the time-series
indicating whether person present in:
Zone 1 on use day and non-use days
Zone 2 on use days and non-use days
Step 3: Compute Zone 1 and Zone 2 Exposure Point Concentrations
Separately assign person presence in Zone 1 and Zone 2 depending on user status for all age groups
First assume non-use day patterns for each zone. If a user only, assign use day patterns for zone 1 and zone 2
Assign zone 1 and zone 2 concentrations. If the near-field far-field option is selected, the user experiences near-
field concentration during active use, and far-field concentrations if present in zone 1.
Compute zone 1 and zone 2 exposure point concentrations based on presence in zone 1 and zone 2 and zone 1
and zone 2 concentrations (by vector multiplication of the two series)
Compute zone 1 and 2 concentration average time product based on exposure point concentrations and time
step
Step 4: Compute Intake in Each Time Step
Compute intakes from each receptor based on exposure point concentration of each receptor in each zone
accounting for variable inhalation rates during product use for users only
Step 5: Compute Concentrations and Dose for Acute and Chronic Exposure
Compute acute peak concentration and dose for each receptor, and chronic concentration and dose for each
receptor by performing appropriate arithmetic operations on previously computed time series concentration
average time and intake metrics.
E6: Emission from Article Placed in Environment
The mechanisms that control SVOC behavior in an indoor environment are shown in Figure 4. These include SVOC
emissions, article abrasion, mixing within the gas phase, transfer to particulates by partitioning, removal due to
ventilation, removal due to cleaning of settled particulates and dust to which the SVOC has partitioned, and sorption or
desorption to/from interior surfaces.
44
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V (room volume) H[NT (Partitioning to Indoor Surfaces)
Q (air flow rate),
RPa (ambient RP),
DustA (ambient Dust),
P (Penetration rate)
Assume ambient SVOC
concentration = 0
y (room air SVOC cone)
Hrp (Partitioning to RP)
E (SVOC emission
from source to air)
AA
I
Hdust
(Partitioning
to Dust
o o
o
IT
11 11
lulling ^ -
\n
RP& Dust
Kdepป Kres'
K (Deposition,
Resuspension,
Sorption, &
Desorption
from RP &
AO. A-
FAA
(Settled AA)
RP = respirable particle
AA = abraded article
SVOC in air phase
Particles
SVOC sorbed to particles
Srp & Sdust
(Generation of RP
& Dust)
Q
RP
Dust
y
FRP & FDust
(Settled RP & DUST)
KCi
(Removal due to
cleaning)
Figure 4. Schematic of fate and transport of SVOC in indoor environment
Model Description
The model provides time-varying estimates of indoor gas-phase, suspended particulate, and settled particulate SVOC
concentrations based on SVOC emissions from an article located in a hypothetical indoor environment. The main
features of the model include:
SVOC emissions from the article are estimated based on a first order source decay methodology described in
(ASTM. 2010).
The model comprises an air compartment (including gas phase, suspended particulates) and a floor
compartment (containing settled particulates).
A bimodal distribution is used to account for variable particle sizes in indoor environments: coarse
particulates (>10 pim - 100 pim in diameter, referred to as "dust"); and fine particulates (10 pim in diameter
or smaller, referred to as RP).
Particulates may exist in the suspended phase in the air compartment or in the settled phase within the
floor compartment of the model.
The two distinct forms of particulates are assumed to have differential partitioning behavior with respect to
air.
Particulates, both in the suspended and settled phases, are not assumed to be in equilibrium with the air
phase; chemical transfer between particulates and the air phase is kinetically modeled in terms of two-
phase mass transfer theory.
The interface area between particulate and air available for mass transfer is calculated assuming absence of
agglomeration and assuming that 100% of the area is available for suspended particulates while only 50% is
available for settled particulates.
Particulate settling and resuspension processes, which act as a means for chemical mass transfer between
the floor and air compartments, are incorporated into the model.
45
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The model tracks both the chemical inventory of SVOC in all phases of the room as well as the physical
inventory of particulates in both compartments.
The effect of periodic room cleaning, which allows depletion of the settled particulate inventory and its
associated SVOC burden, is accounted for.
The model accounts for sorption (and potentially desorption) of gas phase SVOC to other indoor surfaces
(sinks) using the two-phase mass transfer methodology.
Abrasion of the emitting article is modeled as a first order physical decay process. Abrasion is assumed not
to change the area of the emitting surface; as a result, the article's physical mass balance is not maintained.
Provided the abrasion rate is low, as may be reasonably expected, this assumption is a justifiable
simplification. Chemical mass balance is strictly preserved, however, in all respects.
Abraded particles are distinct from dust and respirable particles and constitute a third particle species in the
model. Abraded particles are first emitted to the air and thereafter may deposit on and resuspend from the
floor; like other particulates in the model, these particles are subject to cleaning and ventilation losses.
Abraded particles, both in the suspended and settled phases, are not assumed to be in equilibrium with the
air phase; chemical transfer between particulates and the air phase is kinetically modeled in terms of two-
phase mass transfer theory. Abraded particles settled on the floor are assumed to have a hemispherical area
available for emission, whereas those suspended in the air have a spherical area available for emission.
The approach summarized above effectively advances the (Little et al.. 2012) screening approach to a fully mass-
balanced model.
Exposure to SVOCs will occur via inhalation of both gas-phase and particle-bound SVOCs within the inhalable size range
(defined as <10 pim), as well as incidental ingestion of SVOCs partitioned to settled dust. As such, while the model treats
these entities separately based on mechanistic behavior, the values are combined as appropriate to estimate exposure
as described in Appendix A. SVOC exposure can also occur via direct contact with articles, by either direct mouthing or
dermal contact. The contribution of these exposure pathways to total exposure is captured in other models within CEM.
Calculations of exposure dose from chronic exposure to SVOC emissions from articles require slightly different
assumptions than when calculating exposure due from acute exposure from products. These considerations are put
forth in Appendix A.
Model Parameters
Table 3 itemizes the chemical and physical parameters and their representational symbols that feature in the set of 10
differential equations that define the model.
Table 3. Physical-Chemical Parameters Referenced in Model Equations
Symbol
Property
Units
Physical Parameters
V
Volume of the room
m3
Q
Ventilation rate of the room
m3/hr
As
Area of emitting article surface
m2
L-Art
Thickness of emitting article surface
m
PArt
Density of emitting article
mg/m3
kdepRP
RP deposition rate constant
1/hr
kdepoust
Dust deposition rate constant
1/hr
kdepAbArt
Abraded article particle deposition rate constant
1/hr
kresRP
RP resuspension rate constant
1/hr
46
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Symbol
Property
Units
kresDust
Dust resuspension rate constant
1/hr
kresAbArt
Abraded article particle resuspension rate constant
1/hr
gabr
Mass generation rate of abraded article particles
mg/hr
gARP
Mass generation rate of RP into indoor air
mg/hr
gADust
Mass generation rate of dust into indoor air
mg/hr
gFRP
Mass generation rate of RP onto indoor floor
mg/hr
gFDust
Mass generation rate of dust onto indoor floor
mg/hr
AmbRPConc
Concentration of RP in ambient air
mg/m3
FilterPen
Air Filter Penetration Ratio
None
Clpr
Cleaning Periodicity
1/hr
Cleff
Cleaning Efficiency
None
kd(t)
Binary switch representing whether cleaning is ongoing (based on Clpr)
None
Z(t)
Binary switch representing whether product is present in room
None
Prp
Density of RP particle
mg/m3
PDust
Density of dust particle
mg/m3
Trp
Radius of RP particle
m
TDust
Radius of dust particle
m
rAbArt
Radius of abraded article particles
m
A|nt
Area of interior surfaces
m2
Lint
Thickness of sorbing portion of interior surfaces
m
Chemical Parameters
h
SVOC gas phase mass transfer coefficient
m/hr
Krp
SVOC RP-air partition coefficient
m3/mg
KDust
SVOC dust-air partition coefficient
m3/mg
KArt
SVOC article-air partition coefficient
None
K|nt
SVOC -air partition coefficient
None
Hrp
RP overall gas-phase mass transfer coefficient
m/hr
HDust
Dust overall gas-phase mass transfer coefficient
m/hr
Hint
Interior surfaces overall gas-phase mass transfer coefficient
m/hr
HAbArt
Abraded article particle overall gas-phase mass transfer coefficient
m/hr
CoArt
Initial concentration of SVOC in emitting article
Hg/m3
Inventory Terms
Nair
SVOC mass in the gas phase in air
Mg
Narp
SVOC mass sorbed to suspended RP in the air
Mg
NADust
SVOC mass sorbed to suspended dust in the air
Mg
Nfrp
SVOC mass sorbed to settled RP on the floor
Mg
NFDust
SVOC mass sorbed to settled dust on the floor
Mg
N|t
SVOC mass sorbed to interior surfaces
Mg
Na AbArt
Air (suspended) abraded article SVOC mass
Mg
Nf AbArt
Floor (settled) abraded article SVOC mass
Mg
Arp
Mass of RP suspended in the air
mg
Aoust
Mass of dust suspended in the air
mg
AAbArt
Mass of abraded article suspended in the air
mg
Frp
Mass of RP settled on the floor
mg
Foust
Mass of dust settled on the floor
mg
F AbArt
Mass of abraded article settled on the floor
mg
aThe thickness of emitting article surface value can impact emissions. EPA is considering article-specific thicknesses.
47
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Default model inputs are provided in Table B-15. A description of inputs that are estimated via physical-chemical
properties is presented in the following section. The area of interior surfaces is estimated using the following equation
from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
Aint = 2.08 X V (30)
Where:
Aint = Area of Interior Surfaces (m2)
V = Volume of Room (m3)
Model Equations
The following set of 14 differential equations mathematically describe the model discussed above. Each equation has an
indicative title describing the entity for which a mass balance is being carried out. When these 10 equations are solved
simultaneously using an ordinary differential equation solver in Python, the model is able to produce time-varying
estimates of SVOC mass in various media as well as dust and RP mass in air and on the floor. Cleaning periodicity, or the
frequency that cleaning is conducted, is incorporated as a switch and is not shown explicitly in the equations below. That
is, if cleaning is conducted weekly, at a given time-step each week, mass of settled chemical will be removed, as
governed by the cleaning efficiency and mass of settled particles.
Mass Balance for SVOC in Gas Phase
dNAir _ z(t) xhx A x^Aฃt-xe
-------
Mass Balance for SVOC Sorbed to Suspended RP
d2^ = HRp x^x _L2_)
dt ppj,
rRP V Arp
+ kres^ x NPRP kdeppp x NAKP x NAKP
Mass Balance for SVOC Sorbed to Suspended Dust
^^ADust rj ^ ^Dust ^ ^ ^ Nair ^ADust ^ ^ \
Dust V TZ ซ y
PDust ^Dust Dust Dust
+ kresDust x - kdepDust x ^ x
Mass Balance for SVOC Sorbed to Settled RP
Mass Balance for SVOC Sorbed to Settled Dust
FDust IJ Dusi ^ ^air ^FDust ^ ^ \
= hDust X X X ( X )
Mass Balance for SVOC Sorbed to Interior Surfaces (Sinks)
dt
Mass Balance for Suspended RP
dN= H,n, ><
'Kr Nlm x1.0A
V ^ ^Int X Lint Kint J
Mass Balance for Settled Dust
dFr
(32)
(33)
- = Hrp x^xMx(^2ปi-^ฎLxi^-)
dt pRP
rTR ^ FKP Krp (34)
kres^ x Nppp + kdeppp x N^p kcl (t) x CI^ x Nppp
dt PDust rDust I' FDust KDust (35)
- kresDust x NFDust + kdepDust X NADust - kcl(/)x Cleff x Nmp
X Ant 06)
^ = Sarp + Q x AmbRPConc x FilterPen - x - kdep,,,, x + kresR/, x (37)
c# F
Mass Balance for Suspended Dust
^ x 4** " kdePDust x 4^, + kresDust x (38)
dt V
Mass Balance for Settled RP
dF;
7 ^ + kdepRP x App kreSpp xFpp kcl(t)xCle^- x FRP (39)
dt
= S FDust + X 4** " X FDust ~ kcl if) X CI eff X (40)
49
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Mass Balance for SVOC in Suspended Abraded Article Particles
dN -( -
A AbArt __ C xpKArt>
&abr ' PArt ^0 Art ^
dt
AbArt V t 7- j ~t y '
V (41)
AbArt
-kdePAbArl-xNAAbArl
- xN
y A _ AbArt
Mass Balance for SVOC in Settled Abraded Article Particles
dN AbArt _ x ^AlArl x x ^F AbArt ^ PArt \
^ ^ Pa, r V FAbA, K., , ,
,4Mซ yli/irf ,4K (42)
-kresA,A, xiV ,
ylMrZ .F
+ kdePAbArt XN A _ AbArt
-ke,{t)xCl.xN,
Mass Balance for Suspended Abraded Article Particles
dA-AbArl _
c> abr
dt
+ kres,^xF^ (43)
AbArt AbArt
~kdePAbAr, X AbArt
- X AAhA,
y AbArt
Mass Balance for Settled Abraded Article Particles
sj FT
AbArt = kres x
^4.b^4.rt ^4.b^4.rt
dt
-+- kcJap ih 1/v x AAbArt (44)
k (/ ) x CI ,, x F1...
cl V S ejy ^4.b^4.rt
Note: In Equations 32, 33, and 41, the value of 3/r is used to describe the surface area to volume ratio of a sphere. In
Equations 34, 35, and 42, the value of 1.5/r indicates that for settled particles, only half of the surface area is available
for mass transfer.
50
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A series of terms from the mass balance calculations are required for calculating dose. The following equations (45-54)
present the outputs from the mass balance equations that are used in the dose equations.
Caas = ^ (45)
SVOCRPair = (46)
SVOCDustair=^f^ (47)
SVOCAbArtair = (48)
Dustair = ^ (49)
RPaii^^f1 (50)
AbArtair=^fฑ (51)
SVOCfloorRP = ZZSL (52)
Frp
SVOCfloorDust = (53)
t Dust
SVOCfloorAbArt = (54)
r AbArt
Estimation of Chemical Parameters from Basic Physical-Chemical Properties
As noted in Table 3, the model depends on a number of chemical parameters that users have the freedom to specify. In
situations where users may not have access to sources of values for those parameters, the model can deploy "default"
equations that depend on basic physical and chemical properties to estimate the required parameters. This section
describes the default estimating equations.
Estimating the gas phase mass transfer coefficient
The gas phase mass transfer coefficient can be estimated using the relationships applied in the AMEM model. These
include mass transfer from vertical surfaces, mass transfer from horizontal surfaces, and mass transfer dominated by
thermal convection. While the authors consider each case, they conclude that mass transfer in indoor environments is
dominated by thermal convection. Equations 4-35 and 4-21 from the AMEM guidance (U.S. EPA, 1990) are combined,
along with constants necessary to convert from cm/s to m/hr (lm/lOOcm and 3600s/hr), to result in the following
estimation for mass transfer:
h = 46.8 X J (55)
(2.5+MW1/3)
Where:
h = Gas phase mass transfer coefficient for SVOC between bulk air and surface (m/hr)
MW = Molecular weight (g/mol)
The AMEM methodology for estimating the mass transfer coefficient was incorporated. PARAMS is another EPA model
that can estimate the mass transfer coefficient. We selected this simple empirical model (Equation 55) to create the
default value and, at the same time, give the users the option of entering their own value by using external models.
51
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Estimating Krp and Koust
The particle-air partitioning coefficient (Kp, expressed in units of mg/m3) can be estimated using the following general
equation, where 'part' refers to either RP or Dust as appropriate (Little et al.. 2012):
Kp=fompartXj2S- (56)
Ppart
Where:
Kp = SVOC partition coefficient for RP (KRP) or dust (KDust) (m3/mg)
fom part = Volume fraction organic matter in airborne particles; suggested value 0.4 (unitless)
Koa = Partitioning coefficient between octanol and air (unitless)
Ppart = Density of airborne particles; suggested value 1 x 109 (mg/m3)
The particle-air and dust-air partitioning coefficients can also be estimated using the vapor pressure. However, this
methodology is specific to each additive-solid combination and relies on experimentally determined empirical constants
that are available for a limited number of combinations. This methodology for estimating partitioning is available in
PARAMS (U.S. EPA. 2005) and we recommend using PARAMS if additional partitioning estimates are required.
We recommend estimating the particle-air partitioning coefficient based on the octanol-air partition coefficient (Koa)
rather than vapor pressure for the following reasons: (1) While several empirical models are available for estimating the
particle-air partitioning coefficients of VOCs based on their vapor pressure, few are available for SVOCs. (2) Unlike VOCs,
the vapor pressures for SVOCs are difficult to determine experimentally at normal temperature. Consequently, there is a
dearth of reliable vapor pressure data for SVOCs at normal temperature. (3) The octanol-air partition coefficient (Koa) for
both VOCs and SVOCs can be determined either experimentally or from QSAR models. Currently, at least three QSAR
models are available for estimating Koa (Fu et al., 2016).
Estimating Kart and Kint
Solid-air SVOC partition coefficients, such as Kart and Kint, are used to describe partitioning from the source to the air (art)
and from air to an indoor sink (int). These parameters may be estimated based on SVOC vapor pressure using the
following relationship, where 'solid' refers to either Art or Int as appropriate (U.S. EPA. 2005):
In 0ซsolid) = 8.86 - 0.785 X ln(Vp) (57)
Where:
Ksoud = The solid-air SVOC partition coefficient (dimensionless)
Vp = The vapor pressure of the SVOC (Torr)
Estimating Hint, HDust, HRP and HAbArt
_ 3X10-11
Ds = (58)
s (Mffv 292)6-5 v '
Where:
Ds = Solid-phase diffusion coefficient (m2/hr)
MW = Molecular weight (g/mol)
(59)
52
-------
Where:
Ksoud = Solid-air partition coefficient (unitless)
VP = Vapor pressure (Torr)
ha = 46.8 X (3.3 -h (2.5 + MW?)2 (60)
Where:
ha = SVOC gas phase mass transfer coefficient (m/hr)
MW = Molecular weight (g/mol)
The overall gas phase SVOC mass transfer coefficient between solid phases (such as interior surfaces, dust particles and
RP) and the air can be estimated based on the following relationship, where 'solid' refers to Int, RP, or Dust as
appropriate (U.S. EPA. 2005):
H solid
1- ฆ
~Ksolid
(61)
Where:
solid
H.
ha
Ds
L
Ksolid.
Overall mass transfer coefficient for interior surface (Hint), RP (HRP), or dust (HDust) (m/hr)
The SVOC gas phase mass transfer coefficient (m/hr), which is estimated earlier in Equation (60)
The SVOC solid-phase diffusion coefficient (m2/hr)
The thickness of the solid layer (m)
The SVOC solid-air partition coefficient (unitless)
Estimating D
The solid phase diffusion coefficient for the SVOC may be computed based on a reference compound (U.S. EPA. 2005),
as follows:
/ฃo\ =
VDi/ \MW0)
(62)
Where:
D0
Dt
MW0
MW,
3x10 11 (m2/hr) is the diffusion coefficient for the reference compound (PCB-52)
Diffusion coefficient for compound of interest (m2/hr)
292 (g/mol) is the molecular weight for the reference compound
Molecule weight for compound of interest (g/mol)
The thickness of the solid layer may be assumed to be 0.005 m for interior surfaces and equal to the radius of the
particle for particulates (Little et al.. 2012; ASTM, 2010; U.S. EPA. 2005).
The diffusion coefficient can also be estimated using the molar volume of the SVOC. However, this methodology is
specific to the molecular structure of each SVOC additive. This methodology for estimating diffusion is available in
PARAMS (U.S. EPA. 2005) and we recommend using PARAMS if additional partitioning estimates are required.
53
-------
Note, measured values are preferred over estimated values as inputs for use of this model. A select set of measured
partitioning and diffusion coefficients are presented in Tables B-17 and B-18, respectively. EPA is also considering
supplementing available measured values with a small number of estimated values for parameters above from the
AMEM and PARAMS models.
AJNHl: Calculation of Inhalation Dose from Article Exposure
Similar to inhalation exposure associated with product usage, two different inhalation dose calculations are performed
in CEM: the Potential CADD and the Potential ADR. Both gas-phase and airborne RP-bound SVOCs are assumed to be
available for inhalation. The general expression for the Potential CADD is as follows:
CADD
Air
Where:
CADDAir
CA D DParticuiate
CADDtotai
r
wgas_avg
SVOCRP,
air_avg
p p
rvr air_avg
ifrp
FracT ime
InhalAfter
CFt
BW
cf2
Cgas avgXFracTimeXlnhalAfterxCF^
BWXCF2
CADD
Particulate
SVOCRPair avgXRPair avgX(l-IF^p)FracTimeXlnhalAfterxCF1
BWXCF2
CADDtotai CADDAir + CAD Dparticuiate
Potential Chronic Average Daily Dose, air (mg/kg-day)
Potential Chronic Average Daily Dose, particulate (mg/kg-day)
Potential Chronic Average Daily Dose, total (mg/kg-day)
Average gas phase concentration (ng/m3)
Average SVOC in RP concentration, air (ng/mg)
Average RP concentration, air (mg/m3)
RP ingestion fraction (unitless)
Fraction of time in environment (unitless)
Inhalation rate after use (m3/hr)
Conversion factor (24 hrs/day)
Body weight (kg)
Conversion factor (1000 ng/mg)
(63)
(64)
(65)
The general expression for the Potential Acute Dose Rate (ADR) is as follows:
Cnae marXFracTimexInhalAfterxCF-i
ADRMr = 8as-max 1 1 66
A" bwxcf2
Ann SVOCRPair maxXRPair aVgXFracTimeXlnhalAfterxCF^
AL> Kparticuiate BWxCF2
ADRtotal ADRAir "I" ADRparticulate (ฎฎ)
54
-------
Where:
ADRAir = Potential Acute Dose Rate, air (mg/kg-day)
ADRParticulate = Potential Acute Dose Rate, particulate (mg/kg-day)
ADRtotai = Potential Acute Dose Rate, total (mg/kg-day)
Cgas max = Maximum gas phase concentration (ng/m3)
SVOCRPair max = Maximum SVOC in RP concentration, air (ng/mg)
RPair max = Maximum RP concentration, air (mg/m3)
FracTime = Fraction of time in environment (unitless)
InhalAfter = Inhalation rate after use (m3/hr)
CF1 = Conversion factor (24 hrs/day)
BW = Body weight (kg)
CF2 = Conversion factor (1000 ng/mg)
PJNG1: Ingestion of Product Swallowed
Model assumes that the product is directly ingested as part of routine use and the mass is dependent on the weight
fraction and use patterns associated with the product (ACI, 2010).
^ ^ FQcr X MXWFXFinaXCFi XEDcr
CADD = m -
BWXATcrXCF2
Where:
CADD
= Potential Chronic Average Daily Dose (mg/kg-day)
FQcr
= Frequency of use, chronic (events/year)
M
= Mass of product used (g)
WF
= Weight fraction of chemical in product (unitless)
p.
1 ing
= Fraction of product ingested (unitless)
CFt
= Conversion factor (1000 mg/g)
EDcr
= Exposure duration, chronic (years)
BW
= Body weight (kg)
ATcr
= Averaging time, chronic (years), 78 years for LADD
cf2
= Conversion factor (365 days/year)
ac'XMXWFXFingXCFiXEDac (70)
_ BWXATr
Where:
ADR = Potential Acute Dose Rate (mg/kg-day)
55
-------
PQac
= Frequency of use, acute (events/day)
M
= Mass of product used (g)
WF
= Weight fraction of chemical in product (unitless)
F-
1 ing
= Fraction of product ingested (unitless)
CF1
= Conversion factor (1000 mg/g)
EDac
= Exposure duration, acute (days)
ATac
= Averaging time, acute (days)
BW
= Body weight (kg)
PJNG2: Ingestion of Product Applied to Ground Outdoors
Model assumes ingestion of chemical mixed with soil particles after the product, such as fertilizer, is applied directly to
the ground. The model divides the mass of chemical (mass of product multiplied by weight fraction of chemical) by the
volume of soil (area of application multiplied by the soil mixing depth, density, and porosity) to get the concentration in
the soil. Chemical decay and physical transport away from the surface soil, as well as repeat applications, are accounted
for in the frequency and soil half-life terms. As currently incorporated, the CADD reports the average dose over 1 year,
resulting in the value of 365 multiplied by the natural log of 2, in the half-life terms of the equation. This is multiplied by
the soil ingestion rate, exposure duration, averaging time, and body weight to calculate dose (U.S. EPA. 2012b).
/ \ / /365in(2)U
M XWFxFreqxDxl 365ln^ X 1-e \ (l/2 ' \xSoilIngxEDcrXCF1
It
CADD = ^ /tl/2/ \ ^ (71)
AreaxDe-pthXpx{l-0)xATcrXBW
Where:
CADD
= Potential Chronic Average Daily Dose (mg/kg-day)
M
= Mass of product used (g/use)
WF
= Weight fraction of chemical in product (unitless)
Freq
= Frequency of use/application (use/year)
D
= Duration of application (1 year)
tl/2
= Chemical half-life in soil (days)
Soiling
= Incidental soil ingestion rate (mg/day)
EDcr
= Exposure duration, chronic (years)
CFt
= Conversion factor (1 kg/1000 g)
Area
= Area of yard product is applied (m2)
Depth
= Soil mixing depth (m)
P
= Soil density (kg/m3)
56
-------
0
AT
BW
Where:
ADR
M
WF
Freq
D
tl/2
Soiling
EDac
CF1
Area
Depth
P
0
ATac
BW
Soil porosity (unitless)
Averaging time, chronic (years), 78 years for lifetime
Body weight (kg)
M XWFxFreqxDxt
ln(2)/
in( 2)
x| 1-e V'l/z/ |xSoilIngxEDcrXCF1
ADR =
1/2 J
AreaxDe-pthXpx{l-0)xATcrXBW
(72)
Potential Acute Dose Rate (mg/kg-day)
Mass of product used (g)
Weight fraction of chemical in product (unitless)
Frequency of use/application (use/day)
Duration of application (1 day)
Chemical half-life in soil (days)
Incidental soil ingestion rate (mg/day)
Exposure duration, acute (days)
Conversion factor (1 kg/1000 g)
Area of yard product is applied (m2)
Soil mixing depth (m)
Soil density (kg/m3)
Soil porosity (unitless)
Averaging time, acute (days)
Body weight (kg)
Users may enter the chemical half-life in CEM, if known. If unknown, ECHA provides the following guidance in Table 4
based on Kp, soil and standard biodegradation test results (ECHA, 2016). For Kp values above 10,000, the half-life scales
according to the pattern listed in the table.
Table 4. Chemical half-life in soil (in days)
Kp, soil
Readily biodegradable
Readily biodegradable,
failing 10-d window
Inherently
biodegradable
<100
30
90
300
>100, <1000
300
900
3,000
>1000, <10,000
3,000
9,000
30,000
57
-------
A_ING1: Ingestion after Inhalation (Article Model)
The Article Model described in E6 estimates SVOC concentrations in small and large airborne particles. While these
particles are expected to be inhaled, not all will be able to penetrate to the lungs, but will be trapped in the upper
airway and subsequently swallowed. The model estimates the mass of SVOC bound to airborne small particles (RP) and
large particles (Dust) that will be inhaled and trapped in the upper airway. The fraction that is trapped in the airway is
termed the ingestion fraction (IF). The mass trapped is assumed to be available for ingestion.
CADDiai
| (^SVOCRP airavcj X/?P airaVg x/F/^p j + ^51/ OCDustairaVgXDustairav^ XlFj)UStj+(^SV OCAbrair_aVgXAbrair_aVgXlFAbr)\xInhalAfterxCFi
Where:
CADDiai
SVOCRPair avg
RPair_avg
IFrp
SVOC Dust,
air_avg
Dust
ls wot air_avg
I^Dust
SVOCAbrairavg
AbTair_avg
IF?Abr
InhalAfter
CF1
BW
cf2
bwxcf2
Potential Chronic Average Daily Dose from ingestion after inhalation (mg/kg-day)
Average SVOC in RP concentration, air (ng/mg)
Average RP concentration, air (mg/m3)
RP ingestion fraction (unitless)
Average SVOC dust concentration, air (ng/mg)
Average dust concentration, air (mg/m3)
Dust ingestion fraction (unitless)
Average SVOC in abraded particle concentration, air (ng/mg)
Average abraded particle concentration, air (mg/m3)
Abraded particle ingestion fraction (unitless)
Inhalation rate after use (m3/hr)
Conversion factor (24 hrs/day)
Body weight (kg)
Conversion factor (1000 mg/g)
(73)
ADRiai
[(Sl^OCRPgir maxXRPairjnax*!Fp>p^+(SVOCDusta[r maxx,Dusta[r maxxJF[)Us^+(SVOCAbra[r maxx,Abra[r maxxJFfii]r^ \ xlnhalAfte)'XCF\ . 7 .
BWXCF2 * '
Where:
ADRiai = Potential Acute Dose Rate from Ingestion and Inhalation (mg/kg-day)
SVOCRPair max = Maximum SVOC in RP concentration, air (ng/mg)
RPairjnax = Maximum RP concentration, air (mg/m3)
IFtsp = RP ingestion fraction (unitless)
58
-------
SVOCDustair max = Maximum SVOC in dust concentration, air (ng/mg)
Dustairmax = Maximum dust concentration, air (mg/m3)
I^Dust = Dust ingestion fraction (unitless)
SVOCAbrair avg = Maximum SVOC in abraded particle concentration, air (ng/mg)
Abrairavg = Maximum abraded particle concentration, air (mg/m3)
IFAbr = Abraded particle ingestion fraction (unitless)
InhalAfter = Inhalation rate after use (m3/hr)
CF1 = Conversion factor (24 hrs/day)
BW = Body weight (kg)
CF2 = Conversion factor (1000 mg/g)
AJNG2: Ingestion of Article Mouthed (Migration Rate Method)
Model assumes that a fraction of the chemical present in the article is ingested via object-to-mouth contact, or
mouthing where the chemical of interest migrates from the article to the saliva. When the migration rate is known,
model assumes that the amount of a chemical transferred into the saliva is dependent of the migration rate and
estimates the amount transfers into the body through duration and frequency of mouthing patterns (U.S. CPSC, 2014)
MRXCAXDmX EDcrXCF1
CADD =
BWXATcrXCF2
(75)
Where:
CADD
Potential Chronic Average Daily Dose (mg/kg-day)
MR
Migration rate of chemical from article to saliva (mg/cm2/hr)
CA
Contact area of mouthing (cm2)
Dm ~
Duration of mouthing (min/hr)
Cl
II
Exposure duration, chronic (years)
CF,
Conversion factor (24 hrs/day)
ATcr =
Averaging time, chronic (years)
BW
Body weight (kg)
= Conversion
factor (60 min/hr)
MRXCAXDmX EDacXCFi (76)
~~ BWXATacXCF2 * '
Where:
ADR = Potential Acute Dose Rate (mg/kg-day)
MR = Migration rate of chemical from article to saliva (mg/cm2/hr)
59
-------
CA
= Contact area of mouthing (cm2)
Dm
= Duration of mouthing (min/hr)
EDac
= Exposure duration, acute (days)
CF1
= Conversion factor (24 hrs/day)
BW
= Body weight (kg)
ATac
= Averaging time, acute (days)
= Conversion factor (60 min/hr)
The migration rate of the chemical from the article to saliva is a user defined input that is used in Equations 75 and 76 to
calculate the dose from ingestion of an article mouthed. CEM provides guidance (Table 5) as to what value should be
used, but there is no estimator equation. The migration rate suggestions depend on the concentration range and are
independent of the chemical's physicochemical properties. This means that the dose resulting from ingestion of an
article mouthed will not scale with the amount of chemical used. Using an extremely low chemical weight fraction also
requires using a correspondingly low migration rate.
Table 5. Suggested migration rates based on chemical concentration
Migration Rate Concentration Range
10 mg/cm2/hr
>10,000 ppm
0.1 mg/cm2/hr
100-10,000 ppm
1 x 10"3 mg/cm2/hr
1-100 ppm
1 x 10"4 mg/cm2/hr
<1 ppm
AJNG3: Incidental Dust Ingestion (Article Model)
The Article Model described in E6 calculates SVOC concentration in small particles (termed RP) and large particles
(termed Dust) that are settled on the floor. The model assumes these particle-bound SVOCs are available via incidental
dust ingestion assuming a daily dust ingestion rate and a fraction of the day that is spent in the zone with the SVOC-
containing dust. The model uses a weighted dust concentration, shown in Equations 77 and 78 for chronic and acute,
respectively.
Di icf
is ^^crwgt
Where:
Dust r
(Rpfloor_avgxSVOCRPfloor_avg) + (Dustfloor_avgxSVOCDustfloor_avg) + (AbArtfloor_avgxSVOCAbArtfloor_avg)
{RPfloor_avg+Dustfioor_avg+AbArtfioor_avg)
(77)
Lcr_wgt
RPi
floor_avg
SVOCRP,
floor_avg
Dust
ฆfloor_avg
SVOC Dust
floor_avg
Chronic weighted dust concentration (ng/mg)
Average RP mass, floor (mg)
Average SVOC in RP concentration, floor (ng/mg)
Average dust mass, floor (mg)
Average SVOC in dust concentration, floor (ng/mg)
60
-------
AbArt
ฆfloor_avg
SVOCAbArt
ฆfloor_avg
Average abraded particles mass, floor (mg)
Average floor dust SVOC concentration (ng/mg)
Dustacwgt
Where:
Dust
(Rpfloor_max>
-------
CF
= Conversion factor (1000 ng/mg)
The above equations assume the SVOCs are volatilized from the SVOC-containing article to the air and then partition to
dust. Alternately, SVOCs can partition directly from the article to dust in direct contact with the article. This is also
estimated in A_ING3 model assuming the original SVOC concentration in the article is known, and the density of the dust
and dust-air and solid-air partitioning coefficients are either known or estimated as presented in E6. The model assumes
partitioning behavior dominates, or instantaneous equilibrium is achieved. This is presented as a worst-case or upper
bound scenario.
C =
Where:
Q
r
ฐ0 _art
Kdust
CF
Ksolid.
Cp_art x^dust
Ksolid
(81)
Concentration of SVOC in dust (mg/mg)
Initial SVOC concentration in article (mg/cm3)
SVOC dust-air partition coefficient (m3/mg)
Conversion factor (10s cm3/m3)
Solid air partition coefficient (unitless)
Once the SVOC concentration in the dust is estimated, the acute dose rate can be calculated. In this scenario, there is no
difference between chronic and acute exposure, as both would rely on the same upper end dust concentration.
C^xFracTime xDustlng
ADRdtd
BW
(82)
Where:
ADRdtd
Q
FracT ime
Dusting
BW
Potential Acute Dose Rate from direct transfer to dust (mg/kg-day)
Concentration of SVOC in dust (mg/mg)
Fraction of time in environment (unitless)
Dust ingestion rate (mg/day)
Body weight (kg)
P_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin
Chemicals within the vapor phase can partition directly to the skin, resulting in dermal exposure. In this model, this
process is captured by first calculating the steady state dermal load or skin surface lipid loading of the chemical of
interest that would be reached if the skin were in equilibrium with the gas phase concentration. This is based on the gas-
lipid partitioning coefficient that can be estimated from the Kow, Henry's law constant, the Universal Gas Law constant,
and temperature. This loading is then used to estimate the average daily dose, using methodology adapted from
(Weschlerand Nazaroff, 2012):
is _ -I n(0.7XLogKow-0.0722XMW3-5.252)
p_cw
(83)
62
-------
Kva = ( + ) (86)
V-9 \Vd Kp_b) v '
Where:
Kp cw = Permeability coefficient through stratum corneum of a chemical when the species concentration is
measured in water in contract with skin (m/hr)
K0w = Octanol-water partition coefficient (unitless)
MW = Molecular weight (g/mol)
Kp_w = Permeability coefficient through the stratum corneum/viable epidermis composite of a chemical when
the species concentration is measured in water in contact with skin (m/hr)
Kpj, = Permeability coefficient that describes the transport of a gas-phase chemical from the boundary layer at
the skin surface (b) through the stratum corneum/viable epidermis composite to dermal capillaries
(m/hr)
H = Henry's law coefficient (atm/M)
Kp_g = Indoor air transdermal permeability coefficient that describes transport of a gas-phase chemical from air
in the core of a room through the boundary layer adjacent to skin and then through the stratum
corneum/viable epidermis composite to dermal capillaries (m/hr)
Vd = Deposition velocity (m/hr)
Because the concentration varies between Zone 1 and Zone 2, and the receptor can be present in either room, it is
necessary to calculate the flux that would occur in each of the zones as well as the time spent in each of the zones, as
shown in the following calculations.
DerFluxzlc = Kp~g^fl,zlc (87)
DerFluxz2c = Kv-3*C^3'Z2C (88)
Where:
DerFluxzl c = Chronic dermal flux in Zone 1 (ng/cm2-hr)
DerFluxz2iC = Chronic dermal flux in Zone 2 (ng/cm2-hr)
Kp_g = Transdermal permeability coefficient (m/hr)
Cg,zic = Average chronic gas phase concentration for Zone 1 (ng/cm3)
Cg,z2c = Average chronic gas phase concentration for Zone 2 (ng/cm3)
CF = Conversion factor (10,000 cm2/m2)
63
-------
log (Ki_g) = 0.74 + log (Kow) + log(H) + log (RT)
Where:
Ki
K0
H
R
T
1-9
Gas-phase to skin lipid partitioning coefficient (unitless)
Octanol-water partitioning coefficient
Henry's Law Coefficient (unitless)
Universal Gas Law constant (0.0821 atm/M/K)
Temperature (K)
SA
(DerFluxzl c x FracTimezl c + DerFluxz2iC x FracTimez2jC) x -nrrr x EDcr x CF1
CADD =
BW
ATcr X CF2
Where:
CADD
DerFluxzlc
FracTimezlc
DerFluxz2:C
FracTimez2 iC
SA
BW
EDcr
CF-l
A Trr
CF7
Potential Chronic Average Daily Dose (mg/kg-day)
Chronic dermal flux for Zone 1 (ng/cm2-hr)
Fraction of time in Zone 1 during one year (unitless)
Chronic dermal flux for Zone 2 (ng/cm2-hr)
Fraction of time in Zone 2 during one year (unitless)
Surface area to body weight ratio (cm2/kg)
Exposure duration, chronic (years)
Conversion factor (24 hrs/day)
Averaging time, chronic (years)
Conversion factor (1000 ng/mg)
Where:
DerFluxzla
DerFlux.
z2,a
K,
P-3
-g,zla
DerFluxzla = Kp~gXCg'zla
DerFluxz2ia =
CF
Kn (jXC,
V -9 9>z2a
CF
Dermal flux for Zone 1 (ng/cm2-hr)
Dermal flux for Zone 2 (ng/cm2-hr)
Transdermal permeability coefficient (m/hr)
Acute average gas phase concentration in Zone 1 (ng/cm3)
64
-------
r
ug,z2a
CF
SA
(DerFluxzla x FracTimezljfl + DerFluxz2 a x FracTimez2a) x x EDac x CF-,
ADR =
BW
ATac X CF2
(93)
Where:
ADR
DerFluxzla
FracTimezla
DerFluxz2a
FracTimez2 a
SA
BW
EDac
CFi
A Tac
CF7
Potential Acute Dose Rate (mg/kg-day)
Dermal flux for Zone 1 (ng/cm2-hr)
Fraction of time in Zone 1 during one day (unitless)
Dermal flux for Zone 2 (ng/cm2-hr)
Fraction of time in Zone 2 during one day (unitless)
Surface area to body weight ratio (cm2/kg)
Exposure duration, acute (days)
Conversion factor (24 hrs/day)
Averaging time, acute (days)
Conversion factor (1,000 ng/mg)
CEM includes six prepopulated generic product scenarios that include this model. They are listed in the existing analyses
as "Generic PI El + VS" and there is one for each emission model.
Note, the user will need to consider what the appropriate the surface area to body weight ratio default value should be
considering the specific scenario modeled. See Table B-3 in the Appendix for more guidance.
P_DER2a: Dermal Dose from Product Applied to Skin (Fraction Absorbed Model)
For products that come in direct contact with the skin, the dermal portion of the User-Defined scenario allows modeling
dermal exposure based on potential or absorbed doses. Potential dose is the amount of a chemical contained in bulk
material that is applied to the skin. (U.S. EPA. 2007). Absorbed dose is the amount of substance penetrating across the
absorption barriers of an organism. The absorbed dose can be calculated by multiplying the potential dose by the user-
specified fraction absorbed. The amount of product that is retained on the skin (grams of product per square centimeter
of skin surface per event or g/cm2-event) is the product of the film thickness of the liquid on the skin's surface and the
density of the formulation.
AR = FT x p x (1 - FracRemove) (94)
Where:
AR
FT
P
Amount retained on the skin (g/cm2 -event)
Film Thickness (cm)
Density of formulation (g/cm3)
65
-------
FracRemove = Fraction of product removed by washing or wearing (unitless)
Where
CADD
AR
SA
BW
PQcr
FRabs
Dil
WF
EDcr
CF1
ATcr
cf2
Where
ADR
AR
SA
BW
FQac
FRabs
Dil
WF
EDac
CF1
SA
AR X^^xFQcrXFRajjsXDilxWFxEDcfXCF-i
ATcrXCF2
Potential Chronic Average Daily Dose (mg/kg-day)
Amount retained on the skin (g/cm2-event)
Surface area to body weight ratio (cm2/kg)
Frequency of use, chronic (events/year)
Absorption fraction (unitless)
Product dilution fraction (unitless)
Weight fraction of chemical in product (unitless)
Exposure duration, chronic (years)
Conversion factor (1000 mg/g)
Averaging time, chronic (years)
Conversion factor (365 days/year)
SA
.4R X-g^XFQacXFRabsXDilxWFxEDacXCF-L
ATar
Potential Acute Dose Rate (mg/kg-day)
Amount retained on the skin (g/cm2-event)
Surface area to body weight ratio (cm2/kg)
Frequency of use, acute (events/day)
Absorption fraction (unitless)
Product dilution fraction (unitless)
Weight fraction of chemical in product (unitless)
Exposure duration, acute (days)
Conversion factor (1000 mg/g)
Averaging time, acute (days)
The fraction absorbed (FRabs) can be chosen by one of two methods:
Entering a fraction absorbed,
66
-------
2. Using the "Estimate" button and having the model calculate the fraction absorbed using the following equation
(Frasch and Bunge, 2015):
3 +
+-exp(-aW^7)]
FRabs = 1 , 7 ^ (97)
3(l+x)
X = Ratio of the evaporation rate from the SC surface to the dermal absorption rate through the SC (unitless)
a = Constant (2.906)
Dcr = Duration of use (min)
tlag = Lag time for chemical transport through the SC (hr)
CFt = Conversion factor (60 min/hr)
Where t|ag is defined as:
(6 x 10
hsc = Stratum corneum thickness (assumed to be 15 pim)
MW = Molecular weight (mg/mmol)
^la9 /V v 1n-2.8-0.0056MMA (^ฎ)
Where x is defined as:
= (99)
A KpXSwXRXT v '
h
= Gas phase mass transfer coefficient (m/hr)
p
1 vap
= Vapor Pressure (Torr)
MW
= Molecular weight (mg/mmol)
Kv
= Permeability coefficient for chemical transport through the SC from an aqueous vehicle (cm/hr)
sw
= Water solubility (mg/mL)
R
= Real gas constant (62.37 mL-Torr/K-mmol)
T
= Temperature (Kelvin)
CF1
= Conversion factor (100 cm/m)
The permeability coefficient (Kp) in Equation 99 is estimated using the built in CEM estimator from P_DER2b (Equation
100). The gas phase mass transfer coefficient (h) is estimated using Equation 55.
The user should take note that there is the potential for this model methods overestimate the dermal absorption, as the
product mass does not explicitly enter the model equations.
67
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Note, the user will need to consider what the appropriate the surface area to body weight ratio default value should be
considering the specific scenario modeled. See Table B-3 in the Appendix for more guidance.
P_DER2b: Dermal Dose from Product Applied to Skin (Permeability Method)
Absorbed dermal exposure can also be calculated using the permeability coefficient method and assuming a constant
supply of the product on the skin throughout the exposure duration. The current version of CEM provides an estimator
for a chemical-specific permeability coefficient. A permeability coefficient can be chosen by one of two methods:
Entering a permeability coefficient
2. Using the "Estimate" button and having the model calculate the permeability coefficient using the following
equation (ten Berge, 2010):
1
(100)
Where
Permeability coefficient for chemical transport through the SC from an aqueous vehicle (cm/hr)
Permeation coefficient of the lipid medium
Kpoi = Permeation coefficient of the protein fraction of the SC
K,
aq
Permeation coefficient of water (epi)dermal layer
Where K|ip, Kpoi and Kaq are defined in Equations 101-103, respectively,
ft _ ^q(2.96+0.981 Xlog(Kow)-0.0079 XMW)
lip
(101)
K,
_ 0.0552
P0' MW138
(102)
K,
1121
(103)
acl MW1-96
68
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Where
CADD
Kv
Dcr
Dil
P
SA
BW
FQcr
WF
EDcr
CF1
ATcr
cf2
cf3
Where
ADR
Kp
Dac
Dil
P
SA
BW
FQac
WF
EDac
CFi
ATac
cf2
SA
Kr, XDcrXDilXpX-XFQcrXWFxEDcrXC
CADD = bw ซ 1 (1Q4)
ATcrXCF2XCF3
Potential Chronic Average Daily Dose (mg/kg-day)
Permeability coefficient (cm/hr)
Duration of use (min/event), chronic
Product dilution fraction (unitless)
Density of formulation (g/cm3)
Surface area to body weight ratio (cm2/kg)
Frequency of use, chronic (events/year)
Weight fraction of chemical in product (unitless)
Exposure Duration, chronic (years)
Conversion factor (1000 mg/g)
Averaging time, chronic (years)
Conversion factor (60 min/hr)
Conversion factor (365 days/year)
SA
K-yj XDacXDilXpX--XFQacXWFxEDacXCFi
ADR = BW (105)
ATacXCF2
Potential Acute Dose Rate (mg/kg-day)
Permeability coefficient (cm/hr)
Duration of use (min/event), acute
Product dilution fraction (unitless)
Density of formulation (g/cm3)
Surface area to body weight ratio (cm2/kg)
Frequency of use, acute (events/day)
Weight fraction of chemical in product (unitless)
Exposure Duration, acute (days)
Conversion factor (1000 mg/g)
Averaging time, acute (days)
Conversion factor (60 min/hr)
69
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The user should take note that there is the potential for this model methods overestimate the dermal absorption, as the
product mass does not explicitly enter the model equations. For P_DER2b, it is possible that more chemical is absorbed
than was originally present. The assumption that any chemical penetrating the skin is replaced by more from an
unlimited source may need to be checked. Also, P_DER2b is effectively for "occluded" contact and will overestimate the
absorption if the contact is intermittent.
Note, the user will need to consider what the appropriate the surface area to body weight ratio default value should be
considering the specific scenario modeled. See Table B-3 in the Appendix for more guidance.
P_DER3: Dermal Dose from Soil where Skin Contact with Soil, Dust, or Powder Occurs
The model for exposure to products mixed with soil and powdered products is similar to the model of dermal exposure
of settled dust (A_DER3). The equation models general exposure to chemicals from powdered solids such as soil, dust or
powdered chemicals (Pawar et al. 2016). For scenarios with powdered products, the user must provide the
concentration of the chemical in the products.
CEM has a built in estimator to calculate the concentration of the chemical in soil for scenarios with products added to
soil. The estimator takes into account chemical decay in the soil. Equations 106 and 107 estimate the concentration of a
chemical in soil to be used in CADD and ADR:
M XWFX CFm X
J /
It
1/2
x 1-e V'1/2
-soil,cr
AreaxDepthxpx(l-0)
(106)
Where:
^soil.cr
M
WF
CF
tl/2
Area
Depth
P
0
Concentration of chemical in soil (mg/kg), chronic
Mass of product used per application (g)
Weight fraction (unitless)
Conversion factor (1000 mg/g)
Chemical half-life in soil
Area of yard product is applied (m2)
Soil mixing depth (m)
Soil density (kg/m3)
Soil porosity (unitless)
M XWFX CFmX
Csoil,ac
y/
It
1/2
x i-e Vri/2
AreaxDepthxpx(l-0)
(107)
Where:
r
ฐsoil,ac
M
WF
CF
v-r i rn
Concentration of chemical in soil (mg/kg), acute
Mass of product used per application (g)
Weight fraction (unitless)
Conversion factor (1000 mg/g)
70
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^1/2
Area
Depth
P
0
Chemical half-life in soil
Area of yard product is applied (m2)
Soil mixing depth (m)
Soil density (kg/m3)
Soil porosity (unitless)
CADD
CFt X CF2 XATcr
(108)
CADD
r
ฐsoil,cr
SA
BW
AF
FRabs
FQcr
EDcr
CFt
cf2
ATrr
Potential Chronic Average Daily Dose (mg/kg-day)
Concentration in soil, dust or powder (mg/kg)
Surface area to body weight ratio (cm2/kg)
Adherence factor of dust to hand (mg/cm2-event)
Fraction absorbed (unitless)
Frequency of use (events/year)
Exposure duration, chronic (years)
Conversion factor (1,000,000 mg/kg)
Conversion factor (365 days/yr)
Averaging time, chronic (years)
ADR =
Csoil,acX--g^X"AFXFRabsX-FQacX-EDac
CFiXATac
(109)
ADR
r
ฐsoil.ac
SA
BW
AF
FRabs
FQac
EDac
CFi
ATnr
Potential Acute Dose Rate (mg/kg-day)
Concentration in soil, dust, or powder (mg/kg)
Surface area to body weight ratio (cm2/kg)
Adherence factor of soil or product to hand (mg/cm2-event)
Fraction absorbed (unitless)
Events per day (events/day)
Exposure duration, acute (days)
Conversion factor (1,000,000 mg/kg)
Averaging time, acute (days)
71
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Note, the user will need to consider what the appropriate the surface area to body weight ratio default value should be
considering the specific scenario modeled. See Table B-3 in the Appendix for more guidance.
A_DER1: Dermal Dose from Direct Transfer from Vapor Phase to Skin (Article Model)
Chemicals within the vapor phase can partition directly to the skin, resulting in dermal exposure. In this model, this
process is captured by first calculating the steady state dermal load or skin surface lipid loading of the chemical of
interest that would be reached if the skin were in equilibrium with the gas phase concentration. This is based on the gas-
lipid partitioning coefficient that can be estimated from the Kow, Henry's law constant, the Universal Gas Law constant,
and temperature. This loading is then used to estimate the average daily dose, using methodology adapted from
(Weschlerand Nazaroff, 2012). This model is identical to P_DER1 with the exception that the calculations are based on a
one zone, versus a two-zone model.
Where:
DerFlux
K,
V-9
^a
CF
DerFlux = Kp-gXCa
CF
Dermal flux (ng/cm2-hr)
Transdermal permeability coefficient (m/hr)
Average gas phase concentration (ng/m3)
Conversion factor (10000 cm2/m2)
(110)
log OO = 0.74 + log {Kow) + log(tf) + log(S70 (111)
Where:
Kt g = Gas-phase to skin lipid partitioning coefficient (unitless)
K0w = Octanol-water partitioning coefficient
H = Henry's Law Coefficient (unitless)
R = Universal Gas Law constant (0.0821 atm/M/K)
T = Temperature (K)
Where:
CADD
DerFlux
SA
BW
DerFlux X-^xFracTimexEDrrXCF-t
CADD = bk ฃ1^1
ATcr^-C F2
Potential Chronic Average Daily Dose (mg/kg-day)
Dermal flux (ng/cm2-hr)
Surface area to body weight ratio (cm2/kg)
(112)
72
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FracTime =
Fraction of time in environment (unitless)
Cl
II
Exposure duration, chronic (years)
CF,
Conversion factor (24 hrs/day)
ATcr =
Averaging time, chronic (years)
cf2
Conversion factor (1000 ng/mg)
DerFluxX-^XFracTimexEDurXCF-t
ADR = SK 1
ATac^CF2
(113)
Where:
ADR
DerFlux
SA
BW
FracTime
EDac
CF1
A Tac
CF7
Potential Acute Dose Rate (mg/kg-day)
Dermal flux (ng/cm2-hr)
Surface area to body weight ratio (cm2/kg)
Fraction of time in environment (unitless)
Exposure Duration, acute (days)
Conversion factor (24 hrs/day)
Averaging time, acute (days)
Conversion factor (1000 ng/mg)
A_DER2: Dermal Dose from Skin Contact with Article
This model calculates the dermal exposure due to migration of a chemical within an article to the skin via direct article
contact. The model is based on a simplified diffusion model employed by Delmaar et al. 2013 to estimate dermal dose
after the diffusion of substances in articles to the surface of the article. This equation is a physically-based emission
model, grounded in the well-established theory of diffusion of substances in materials. The chemical is modeled as
emitted from the source to the skin directly, driven by diffusion through the material. The model estimates dermal
loading on the skin, or potential dose, rather than absorbed dose. Based on Delmaar et al. 2013, the average distance, /,
a diffusing molecule will travel during contact, Dur, is calculated by the equation:
I = (y 2 x (D x 60) x Dur) x CF1 (114)
Where:
I = Average distance a diffusing molecule travels per contact (cm/day)
D = Solid phase diffusion coefficient (m2/hr)
Dart = Duration of article contact (min/day)
CFt = Conversion factor (100 cm/m)
73
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Once the average distance per contact is calculated then the chronic dose rate can be calculated.
Where:
CADD
r
ฐart
SA
BW
FRabs_art
EDcr
A Trr
r a r> r> CartxBwxlxFRabs_artxEDcr
LRUU
A Trr
Potential Chronic Average Daily Dose (mg/kg-day)
Chemical concentration in article (mg/cm3)
Surface area to body weight ratio (cm2/kg)
Fraction absorbed (unitless)
Exposure duration, chronic (years)
Averaging time, chronic (years)
(115)
Where:
ADR
r
ฐart
SA
BW
FRabs_art
EDac
ATnr
^artxBwxlxFRabs_artxEDac
ATnr
Potential Acute Dose Rate (mg/kg-day)
Chemical concentration in article (mg/cm3)
Surface area to body weight ratio (cm2/kg)
Fraction absorbed (unitless)
Exposure duration, acute (days)
Averaging time, acute (days)
(116)
Where fraction absorbed is calculated using Equation 117,
3 + x\ 1-expl -a
X
a
Dart
EvD
hag
CFt
FR
abs art
(EvDxtlagxCFl)
:)]
3(1+*)
(117)
Ratio of the evaporation rate from the SC surface to the dermal absorption rate through the SC (unitless)
Constant (2.906)
Duration of use (min/day)
Frequency of article contact per day (events/day)
Lag time for chemical transport through the SC (hr)
Conversion factor (60 min/hr)
74
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Where is calculated using Eq 99 and x is calculated using Eq 100.
A_DER3: Dermal Dose from Skin Contact with Articles using Dust Concentration
Chemicals from articles can partition to the dust that lies on article surface. This can result to dermal exposure through
contact with dust settled on top of articles. The equation uses the concentration of the chemical in settled dust
calculated from the SVOC Model (see Equation 40). The CADD equation uses the average floor dust concentration, while
for ADR the maximum floor dust concentration is used.
SA
Duster WatX-Z777XAFxFAxEvDxEDrr
CADD = - 3 BW (118)
CF^XATcr v '
CADD = Potential Chronic Average Daily Dose (mg/kg-day)
Dustcr wgt = Chronic weighted dust concentration (ng/mg)
= Surface area to body weight ratio (cm2/kg)
AF = Adherence factor of dust to hand (mg/cm2-event)
FA = Fraction absorbed (unitless)
EvD = Frequency of article contact per day (events/day)
EDcr = Exposure duration, chronic (years)
CFt = Conversion factor (1000 ng/mg)
ATcr = Averaging time, acute, chronic (years)
SA
Dustac watX-=rXAFXFAXEvDXEDar
ADR = ~ 3 BW (119)
CF^ATac
SA
BW
SA
BW
ADR = Potential Acute Dose Rate (mg/kg-day)
Dustac wgt = Acute weighted dust concentration (ng/mg)
= Surface area to body weight ratio (cm2/kg)
AF = Adherence factor of dust to hand (mg/cm2-event)
FA = Fraction absorbed (unitless)
EvD = Frequency of article contact per day (events/day)
EDac = Exposure duration, acute (days)
CFt = Conversion factor (1000 ng/mg)
ATac = Averaging time, acute (days)
75
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4. Areas for Future Enhancements
CEM has been enhanced to include additional exposure pathways and scenarios. However, there are still several
exposure pathways that are not yet considered.
Exposure Metrics for Short-term Exposure
Throughout the User Guide of CEM, EPA provides metrics of Acute Dose Rates that are averaged over one day, Chronic
Average Daily Doses that are averaged over one year, and Lifetime Average Daily Doses and Concentrations that are
averaged over a lifetime (78 years). Further consideration could be given to additional short-term exposure metrics. One
or more metrics may be more appropriate depending on the exposure scenario and chemical of interest.
For short-term metrics, one approach could be to define a standard time period or to allow the length of an exposure
event to vary. Some products may result in relatively higher and shorter-lived concentrations during use. In such
instances, an averaging time of <24 hours may be appropriate. A per event average or an 8-hour time-weighted average
could be considered. Other products may result in relatively lower and longer-lived concentrations during and after use.
In such instances, a per-event averaging time could be considered that is longer than one day. However, for both shorter
and longer emitting products, some consideration could be given as to when to "stop" an event. Modeled air
concentrations will continue to be estimated over time getting closer and closer to zero and likely below the level of
quantification in air for many chemicals (for example,
-------
Q = Amount of water used per event (gallons/event) for bathing and rate of water use for showering
and handwashing (gallons/min) x event duration (min/event)
ATcr = Averaging time, chronic (years)
CF2 = Conversion factor (0.000264172 cm3/gaNons)
CF3 = Conversion factor (365 days/yr)
FQcr = Frequency of use, chronic (events/year), where
FQcr = EV X EF (121)
EV = Event frequency (events/day)
EF = Exposure frequency (days/year)
Articles in Routine Contact with Water
Water generally facilitates migration of chemicals from articles (i.e., additives in PVC drinking water pipes, bath and pool
toys, etc.). However, the migration rate and environmental conditions influencing migration are not well known. Human
interaction with these articles may result in exposure through hand-to-mouth and object-to-mouth contact with the
surface of the article or through ingestion of water into which the chemical additive has leached. In addition, there is
potential for release to the environment through down-the-drain applications. Other models such as l-SVOC or use of
empirically-based approaches can be considered for these exposure pathways.
Products Intended to go Down the Drain
EPA currently incorporates a top-down approach based on national production volume to estimate releases from
products that are intended to go down the drain by assuming that 100% of the intended production volume goes down
the drain. An alternative approach is to consider the mass per use, frequency of use, fraction of the population that uses
the product, per capita wastewater flow, POTW removal rate, and river dilution factors. In the future, EPA could
incorporate both of these approaches for down-the-drain estimates into CEM. The mass of product per use, weight
fraction of chemical in the product, and frequency per use are common inputs used in other consumer exposure models
to estimate human exposure. The per capita wastewater flow and river dilution factors are highly variable across the
country while the fraction of the population that uses a given product is not well characterized.
C = [MxtyFx^XJVxCF] xRx SDF (122)
C = Concentration in river water (unitless)
M = Mass per use (grams)
WF = Fraction of chemical in the product (unitless)
F = Frequency (uses/day/person)
N = Fraction of population that uses the product (unitless)
CF = Conversion factor (1000 mg/g)
77
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Q = Per capita wastewater flow (L/person/day)
R = POTW Removal Rate
SDF = Stream Dilution Factor
Vector-Facilitated Releases from Articles Not Intended to go Down the Drain
There is emerging literature that suggests that additives that are released from articles may be transported within
indoor environments and these airborne or settled particles may become entrained on vectors like clothing and other
textiles before being washed down the drain through routine laundering activities. This exposure pathway requires
further investigation of the greywater of buildings as an integrated source of chemicals released down the drain.
Detected chemicals that are not present in products and only present in articles present an opportunity to consider
source apportionment. One potential source could be the loading (mass per surface area) of textiles and estimates of
total mass of chemical per wash and number of washes per week. Another potential source could be mopping or wet-
vacuuming floors that contain settled dust of the chemical. Another potential source is the excretion of chemicals from
individuals after intake occurs (for example through dust ingestion). There may be other sources that have not been
considered as well. It should be noted that literature is emerging in this area and all exposure pathways are presented as
potential in nature.
Products that Spill or Leak Over Time
Some liquid products intended to be applied within machinery or other appliances may get spilled during application.
Additionally, some amount of the liquid may leak from the equipment over time. Examples include refrigerants or
cooling agents used in appliances and motor oils that are used for vehicles and other machinery. These spills and leaks
could be considered both in the context of potential human exposure as well as releases to the environment. There are
existing industrial hygiene models that quantify exposures after small spills, however, how various liquid consumer
products may spill or leak over time based on routine use patterns associated with equipment or appliance maintenance
are not well characterized. It should be noted that the majority of these exposures are expected to be occupational.
However, a small number of do-it-yourselfers and bystanders may also potentially be exposed.
Elevated Temperatures During Application and Use
Temperature is an important variable that can have a large effect on emission and migration of chemicals. For example,
increased temperatures may increase the emission rate of chemicals into air leading to a faster, higher rate of emissions
and using body temperature, rather than room temperature provides a better estimate of migration through mouthing.
Some products and articles are heated as a routine part of use while others have variable temperatures depending on
site-specific conditions of use. Temperature gradients between zones or rooms within a building can also influence
interzonal air flow and air exchange rates. EPA could consider incorporating temperature within existing models or
providing more guidance on how temperature influences emissions and migration in the future.
Consideration of Multiple Zones in the SVOC Article Model
While the product use models include multiple zones, the SVOC Article model does not. Given the uncertainty and
variability associated with quantifying interzonal air flow and tracking of particulates across rooms, the SVOC Article
model was limited to one zone at this time, under the assumption that this zone is representative of other rooms within
the building. Should additional information on interzonal air flow across zones within a building and resuspension of
dust across zones within a building become available, EPA could consider incorporating multiple zones.
78
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Consideration of Chemical and/or Age-Specific Transfer Efficiencies from Surface-to-Hand,
Hand-to-Mouth, and Object-to-Mouth
Transfer efficiencies are highly variable given the chemical, substrate, and human activity patterns of interest. Additional
empirical data characterizing these transfer efficiencies for both children and adults would help improve model accuracy
and reduce uncertainty. At present, high-end estimates based on SHEDS have been incorporated for all age groups, even
though for many chemical-product and chemical-article combinations it is likely that these transfer efficiencies will be
lower.
Consideration of Chemical or Material-Specific Migration Rates
Migration rates into saliva from sustained mouthing behavior are highly variable and understudied. EPA is aware of a
few dozen studies that have quantified migration rates using units similar to (ig/cm2/hr. EPA has compiled these into a
spreadsheet along with chemical concentration in the article to provide a range of possible values to select for this
parameter. Measurements of all three parameters: mass migrated, surface area, and time are important. The reported
values span several orders of magnitude and covers a range of different chemicals and substrates/materials in contact
with real or artificial saliva. EPA prefers to use experimental data for chemical of interest or a closely related analog.
Additional information is needed to be better characterize this important parameter. Factors that may influence the
migration rate into saliva may include: size of chemical additive (molecular weight and/or molar volume); water
solubility of chemical additive; chemical structure, concentration and/or loading of the chemical within the material;
temperature (~37ฐ C for human mouth), pH (~6.5 for human mouth), and composition (presences of salts, enzymes, etc.)
of saliva or simulated saliva; and the type of material in contact with saliva or simulated saliva.
Consideration of Total Ingestion Rates of Indoor Dust and Particles
There is uncertainty and variability associated with quantifying the total ingestion rate of dust from all surfaces for
children and adults. The total ingestion rate is variable and includes ingestion of settled dust on the floor as well as
ingestion of settled dust on the surface of articles through hand-to-mouth or object-to-mouth contact, as well as
ingestion of resuspended particles that are not respirable and are swallowed rather than being coughed out. In order to
not overestimate, EPA is considering methodology to mechanistically capture dust ingestion across a variety of indoor
sources and surfaces.
Consideration of Additional Exposure Scenarios and Exposure Defaults
EPA can always consider additional information to modify an existing exposure scenario or add new exposure scenarios
as use patterns change. How exposure scenarios are defined for consumer products and articles are varied in exposure
models from around the world. How consumer products are used has changed over time as formulations and methods
of application evolve. Some materials are formulated directly in a home environment rather than in an industrial facility.
EPA can consider newly available information on consumer exposure defaults as such information becomes available. An
effort was made to review available information from multiple sources. EPA expects that additional information to
better inform and refine consumer exposure scenarios will become available overtime.
79
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Glossary
Note - Values and data sources for Product and Article specific parameters are presented in Appendix B.
Absorption Fraction; FRabs (unitless) Fraction of chemical that is applied to the skin that is absorbed into the skin. Used
to estimate dermal exposure to products.
Activity Pattern Description of where the receptor spends their time during a 24-hour day. CEM has three different
activity patterns: stay-at-home, part-time out-of-the home (daycare, school, or work), and full-time out-of-the-home.
The activity patterns were developed based on Consolidated Human Activity Database (CHAD).
Acute Dermal Flux in Zone 1; DerFluxzl a (ng/cm2-hr) The rate of chemical flux from the air to the skin in Zone 1
resulting from product use in Zone 1 on the day of use.
Acute Dermal Flux in Zone 2; DerFluxz2 a (ng/cm2-hr) The rate of chemical flux from the air to the skin in Zone 2
resulting from product use in Zone 1 on the day of use.
Acute Average Gas Phase Concentration for Zone 1; Cg zla (ng/cm3) One-day average concentration in Zone 1.
Acute Average Gas Phase Concentration for Zone 2; Cg z2a (ng/cm3) One-day average concentration in Zone 2.
Acute Dose Rate; ADR (mg/kg-day) The average daily dose calculated for the 24-hour day on which the product is used.
ADR is calculated with age-group specific exposure factors.
Aerosol Fraction (overspray fraction) (unitless) The portion of the product (e.g., fabric protector) that is released as an
aerosol upon use. Values must be between 0 and 1. The defaults have been updated in this version of CEM to reflect
newer data. Updated defaults show a 1.0 to 4.5% overspray value for aerosols (3% central tendency and 4.5% high-end)
and a 3-6% overspray value for trigger sprays (4.5% central tendency and 6% high-end) (Jayjock, 2012)
Airborne Concentration (|xg/m3) Estimated or user-supplied concentration of the chemical in the room (Zone 1) or in the
portion of the building that is not the room (Zone 2) in which the product or article is used.
Air Exchange Rate (air exchanges/hr) The rate of the volume of air being replaced in a room divided by the volume of
the room for the room or other environment where the product or article is being used (Zone 1) or for the portion of the
building where the product or article is not in use (Zone 2) [(U.S. EPA. 2011) Table 19-24],
Air exchange rate between the near-field and far-field (m3/min) This input is the air exchange rate between near- and
far-field areas in Zone 1 and governs the concentration of the chemical in the air of the far-field portion of the use
environment.
Ambient Particulate Concentration (mg/m3) Level of particulates in the outdoor environment of use or surrounding the
indoor environment of use. EPA monitoring data summary information was chosen because it makes use of 570
monitors in numerous locations around the United States and represents the national trend. The central tendency value
is the mean value for 2012 as presented in the Excel data that can be downloaded from the website. The low and high
values are the 10th and 90th percentiles, respectively (U.S. EPA. 2014a).
Amount Retained on Skin; AR (g/cm2-event) The amount of product remaining on skin after use in the units of grams of
product per square centimeter of skin area. This value is a function of film thickness (m) * density (g/cm3).
Application time; ta (min) The time of product use. This value is calculated from the duration of product use and is used
in the model to estimate airborne emission rates.
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Area of Interior Surfaces; A/t(m2) The surface area of interior surfaces such as furnishings and building materials that
are potential sinks for airborne SVOCs.
Area of Yard (m2) The area of yard that a product can be applied to the ground outdoors.
Articles Generally solids, polymers, foams, metals, or woods, which are always present within indoor environments for
the duration of their useful life, which may be several years.
Average Chronic Gas Phase Concentration for Zone 1; Cg z2c (ng/cm3) The airborne concentration of the chemical in
Zone 1 resulting from product use in Zone 1 averaged over one year. This could include multiple uses of the same
product.
Average Chronic Gas Phase Concentration for Zone 2; Cg z2c (ng/cm3) The airborne concentration of the chemical in
Zone 2 resulting from product use in Zone 1 averaged over one year. This could include multiple uses of the same
product.
Averaging Time, Acute; ATac (days) The period over which exposures are averaged. For acute exposure assessments in
CEM, the default averaging is one day for all receptors.
Averaging Time, Chronic; ATcr (years) The period over which exposures are averaged. For chronic exposure
assessments in CEM, the default averaging time for adults is 1 years. For children, default averaging times vary by age
group.
Background ADR (mg/kg/d) Acute Dose Rate resulting from exposure to background concentration in air and/or dust.
Background Air Concentration (mg/m3) User specified concentration of chemical of interest within the air.
Background Chronic Dose (mg/kg-day) Chronic Dose resulting from exposure to background concentration in air and/or
dust.
Body Weight; BW (kg) The body weight of the receptor. Default values are from EPA's Exposure Factors Handbook
(EFH).
Building Volume (m3) The total volume of all rooms in the home or other building where the product or article is used.
Building volume is use to estimate air concentrations of the chemical in Zone 2 (i.e., rooms where the product or article
is not in use) [(U.S. EPA. 2011). Table 19-6],
Bystander A receptor who is a non-product user that is incidentally exposed to the product or article.
CAS number A unique numerical identifier assigned to chemicals by the Chemical Abstracts Service. This field is
automatically populated based on the chemical selected in the Scenario tab.
Change in Concentration with Time; ^ (ng/m3/hr) The change in the chemical concentration in air over time within a
zone.
Chronic Average Daily Dose; CADD (mg/kg-day) The annual average daily dose calculated with age-group-specific
exposure factors.
Chronic Dermal Flux in Zone 1; DerFluxzl c (ng/cm2-hr) The rate of chemical flux from the air to the skin in Zone 1
resulting from product use in Zone 1 averaged over the course of one year.
Chronic Dermal Flux in Zone 2; DerFluxz2 c (ng/cm2-hr) The rate of chemical flux from the air to the skin in Zone 2
resulting from product use in Zone 1 averaged over the course of one year.
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Chronic Dose; (mg/day) The receptor specific chronic dose, which is calculated by multiplying the receptor Chronic
Average Daily Dose (CADD) by the receptor body weight.
Cleaning Efficiency (unitless) The time period for one-half of the original product mass applied to the ground to decay
due to environmental fate processes. Cleaning efficiency has a wide range of values in the literature. A literature search
was conducted and values ranged from 0.05 [(Qian et al.. 2008); carpets] to 0.95 [(Ewers et al.. 1994); wood floors]. The
values selected are:
Low: 0.05 from (Qian et al.. 2008) (carpets)
Medium: 0.46 from (Yiin et al.. 2002) (midpoint of range, carpets)
High: 0.95 from (Ewers et al.. 1994) (wood floors)
NOTE: the high value corresponds to the most efficient cleaning (the least dusty home) Midpoint in (Yiin et al.. 2002);
alternate value is midpoint in (Roberts et al.. 1994); all are for carpet.
Cleaning Periodicity (hr"1) The rate at which the floor of a room is either vacuumed or swept. The Exposures Factors
Handbook provides estimates of cleaning frequency based on self-reported cleaning frequencies. However, the mean
value is very high (2 cleanings per week). For that reason, other sources of information were sought to complement this
data source. After examining the data, frequencies of twice a week, once a week, and once a month were selected as
default values and converted to units of "cleanings per hour." NOTE: the high value corresponds to the most frequent
cleaning (the least dusty home).
Professional judgment using data from NHAPS (Klepeis et al.. 2001), the Westat survey (U.S. EPA. 1987), and "Healthy
Homes" asthma intervention study (Largo et al.. 2011). Also (Little et al.. 2012).
Concentration (mg/m3) Measure of chemical in units of mass per volume either in the product or article or exposure
media (air, particles, dust, soil.)
Contact Area of Mouthing; CA, (cm2) The area of an article that comes into contact with mouth.
Density of Airborne Particles; ppart (mg/m3) Airborne particles density based on value recommended in (Little et al..
2012).
Density of Dust; Poust (mg/m3) Dust density based on value recommended in (Little et al.. 2012).
Density of Formulation or Product; p (g/cm3) The density of the product formulation or article material. This is used by
CEM for other calculations.
Density of RP; pRP (mg/m3) Density of respirable particles based on value recommended in (Little et al.. 2012).
Deposition Rate, Dust; kdepDust (hr"1) The rate at which large particulates settle from the air. The Exposure Factors
Handbook provided a few different sources for deposition rates. The (Thatcher and Layton, 1995) study was chosen
because it measured both deposition and resuspension rates for particles in the same house. For dust, the deposition
rates for particles greater than 10 pim (10-25 and >25) were averaged and rounded to the nearest tenth [(U.S. EPA.
2011); Table 19-33],
Deposition Rate, RP; kdepRP (hr-1) The rate at which fine particulates settle from the air. The Exposure Factors
Handbook provided a few different sources for deposition rates. The (Thatcher and Layton, 1995) study was chosen
because it measured both deposition and resuspension rates for particles in the same house. For RP, the deposition
rates for particles less than 10 um (1-5 and 5-10) were averaged and rounded to the nearest tenth [(U.S. EPA. 2011);
Table 19-33],
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Dermal Absorption Dermal modeling option (P_DER2a) where dermal exposure is modeled using a fraction absorbed
method.
Dermal Flux (g/cm2-hr) Rate of transfer of a chemical through the skin per unit area.
Dermal Permeability Dermal modeling option (P_DERMlb) where dermal exposure is modeled using a permeability
method.
Diffusion Coefficient (m2/hr) Proportionality constant between the molar flux due to molecular diffusion and the
concentration gradient that describes the rate of diffusion of a chemical from a substrate. Used to model chemical
behavior, specifically its migration from areas of higher concentration to areas of lower concentration consistent with
Fick's Law of diffusion. If this is used in the applicable models, this value will always need to be entered by the user
based on the chemical of interest.
Duration of Mouthing; Dm(min/hr) The amount of time that an article is mouthed.
Duration of Use, acute; Dac(min/use) The amount of time that a product or article is used each time it is used (i.e., per
use event). CEM provides default values of this input for many products/articles. Different use durations can be used for
the acute and chronic exposure assessments. For acute assessments, the duration of use must be less than 24 hours.
The minimum use duration for CEM is 0.5 minutes.
Duration of Use, chronic; Dcr (min/use) The amount of time that a product or article is used each time it is used (i.e.,
per use event). CEM provides default values of this input for many products/articles. Different use durations can be used
for the acute and chronic exposure assessments.
Duration of article contact; Dart (min/day) The amount of time the user is in direct contact with the article throughout
the day.
Dust Ingestion Fraction; IFDust (unitless) An estimate inhaled airborne particles in the dust size range that are ingested.
Values must be between 0 and 1. The default value is 1 and should be used unless data are available.
Dust Ingestion Rate (mg/day) Daily dust ingestion rate. Dust is defined as particles that exist within the home, and may
be comprised of soil. Default values by age group are from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
Emission Rate; ER (mg/hr) The rate of release of the chemical to air upon use of the product. CEM calculates the
emission rate for each 30-second time step. Users have the option to enter a constant emission rate.
Evaporation Time; EvapTime (min) The time required for 90% of a pure chemical film to evaporate. CEM estimates
EvapTime based on the molecular weight and vapor pressure in an empirical formula developed by (Chinn, 1981).
Exposure Duration, Acute; EDac (days) The duration of product use. Not to be confused with duration of use per event.
For acute assessments in CEM, the default exposure duration is one day.
Exposure Duration, Chronic; EDcr (years) The duration of product use. Not to be confused with duration of use per
event. For example, a spray cleaner might be used for 30 minutes per use, weekly.
Film Thickness; FT (cm) For products, the thickness of the layer of product remaining on the skin after use.
First-Order Emissions Decline, k (min"1) First-order rate constant for the emissions decline. Calculated using the
estimated time required for 90% of a film of pure chemical to evaporate (see Evaporation Time).
For the "Product Applied to a Surface Indoors Double Exponential Model" (E2), empirical studies reported by (Wilkes et
al.. 1996) support the assumption of 25% mass released and have estimated a relationship between the fast rate of
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decline (/q) and vapor pressure, and between the slow rate of decline (k2) and molecular weight, leading to the
following "fast" and "slow" values for the rate of decline (Evans. 1996):
/q = 233.25 x (VP -h 24) -h 60
k2 = 0.0000584 X (MW h- 24) h- 60
Fraction Absorbed (unitless) Fraction of product that is applied to the skin that is absorbed through the skin.
Fraction of Contact (unitless) Fraction of touches of all surfaces that are in contact with the article of interest.
Fraction Dislodgeable (unitless) Fraction of chemical on the surface of an object that can be dislodged and transferred
to the skin by touching.
Fraction of Mass Emitted; f (unitless) An estimate of the portion of the chemical mass that is emitted. Values must be
between 0 and 1. The default value is 0.1 and should be used unless data are available.
Fraction Organic Matter Dust (unitless) Fraction of organic matter in dust (large particles.)
Fraction Organic Matter RP (unitless) Fraction of organic matter in respirable (small) particles.
Fraction of Time Spent (unitless) Fraction of day spent in a given microenvironment by receptor and activity pattern.
Frequency of Use/Application, Acute; FQac (events/day) The number of product or article use events per day. For
acute exposure assessments, CEM estimates exposure for a single use of a product or article.
Frequency of Use/Application, Chronic; FQcr (events/year) The number of product or article use events per year. For
chronic exposure assessments, CEM provides high, medium, and low default values for many products and articles.
These can be modified by the user.
Frequency of Mouthing; FQ (events/day) The number of times an object is mouthed (or mouth to object contact is
made) daily.
Henry's Law Coefficient (atm/M) Measure of the partitioning of a chemical between air and water at equilibrium.
HVAC Penetration Efficiency for Dust (unitless) Fraction of large particulates removed from the air by the HVAC
filtration system. Limited information could be found about typical HVAC filtrations. Information indicates what filtration
is needed for a given rating, but the average efficiency is not usually reported. The reference was selected because it
reported a typical efficiency for panel filters for small particles (0.3 to 6 pim) (Creech et al.. 1996).
HVAC Penetration Efficiency for RP (unitless) Fraction of small particulates removed from the air by the HVAC filtration
system. Limited information could be found about typical HVAC filtrations. Information indicates what filtration is
needed for a given rating, but the average efficiency is not usually reported. The reference was selected because it
reported a typical efficiency for panel filters for "large" particles (Creech et al.. 1996).
Incidental Soil Ingestion Rate (mg/day) Daily incidental soil ingestion rate. Soil is comprised of particles that exist
outdoors. Default values by age group are from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
Inhalation Rate (m3/hr) The age-group-specific air inhalation rate. CEM uses separate inhalation rates for the periods
during and after product use. Default values by age group are from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
Inhalation Rate After Use (m3/hr) The air inhalation rate when the user is not using the product. Default values by age
group are from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
Inhalation Rate During Use (m3/hr) The air inhalation rate during use of the product. Default values by age group are
from EPA's Exposure Factors Handbook (U.S. EPA. 2011).
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Initial Concentration of SVOC in Article (mg/cm3) The SVOC additive concentration in a consumer article.
Interzonal Air Flow Rate (m3/hr) The volumetric air flow between Zones 1 and 2 during and after product usage.
Lifetime Average Daily Concentration; LADC (mg/kg-day) Estimated average daily airborne concentration of a chemical
averaged over both use and non-use days.
Lifetime Average Daily Dose; LADD (mg/kg-day) The average daily dose calculated over a lifetime.
Mass Generation Rate, Floor Dust (mg/hr) Amount tracked in and collected on doormat. This value is based on a study
by von Lindern et al. (2016) that measured the amount of dirt deposited on a floor mat in homes near a Superfund site.
Although Superfund sites are expected to have higher contaminant concentrations, the assumption is made that the
amount of dirt (not the amount of contaminant) is roughly the same across the United States as it is near this site. The
geometric mean and geometric standard deviation across the different study regions was estimated to be 248
mg/m2/day and 2.5, respectively. The mat used in the study for dirt collection was 0.318 m2, so multiplying gives a
geometric mean estimate of 79 mg/day in each home.
The von Lindern study estimates the amount of dirt on an entryway floor mat, but additional dirt will be tracked to the
rest of the home. Thatcher and Layton (1995) provide an estimate of the rate of accumulation of dirt on a mat versus
the "trackable" areas in the home. Using the relative areas of the home to get the total amount of dirt tracked per week
and taking the ratio, it was estimated that 13% of the tracked dirt is on the mat and 87% is in the rest of the house.
To make the final calculation, the von Lindern geometric mean of 79 mg/day was divided by 0.13 to estimate the total
amount tracked into the house (610 mg/day or 25.3 mg/hr). The central tendency value is based on this estimate. The
low and high values are then the 10th and 90th percentile values in the distribution using the GSD of 2.5 (von Lindern et
al.. 2003; Thatcher and Layton, 1995).
Mass Generation Rate, Floor RP (mg/hr) Amount tracked in and collected on doormat. Track-in likely includes both
smaller (<10 pim) and larger particles. However, the smaller particles likely stick better the shoe through electrostatic
forces. At this time, all track-in is assumed to occur in the larger (dust) size.
Mass Generation Rate, Suspended Dust (mg/hr) Rate at which large airborne particulates are generated in an indoor
environment. Dander is considered the primary dust source for particles greater than PM10. A literature search returned
no scientific sources for how much dander a person sheds per day; however, several websites anecdotally quoted a
number of 1.5 in 24 hours. To calculate the values for the model, we assumed a home included 2 adults that spend the
median amount of time in the house (low), 2 adults and 2 children that spend the median amount of time in the house
(medium), and 2 adults and 2 children that spend time in the house at the 90th percentile level (high).
The CHAD database was used to estimate the amount of time adults and children spend in the house (U.S. EPA. 2014b).
Because dander is based on surface area, we assumed the "children" were under 5 years old; older children will begin to
have the same surface area as their parents and should be treated as adults. These values are:
Median: adults: 16.25 hr; children under 5: 21.5 hr
90th percentile: adults: 23 hr; children under 5: 24 hr
The relative surface areas of children and adults were used to estimate the typical child dander shed mass per day. The
Exposure Factors Handbook provides estimates for children in different age groups and adults for each decade (U.S. EPA.
2011). The values were used to estimate the average childhood (<5) and adult (18-49) surface area by taking time-
weighted averages of the values in the Handbook. The resulting values are:
Adults: 2.1m2
Children: 0.6 m2
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The final dander shed rates are found by using the equations:
a 1 days in o
Adults: 1.5 x fraction time spent x number of adults x x 1000
day 24 hour g
r- Q child surf ace area r , . , 1 days
Children: 1.5 x x fraction time spent x number of adults x x 1000
day adult surface area 24 hour g
Then, low, mid, and high values are estimated by the equations:
Low = 2 x adult median
Medium = 2 x adult median + 2 x child median
High = 2 x Adult 90th + 2 x child 90th
Where "median" and "90th" refer the time spent value used. Multiple secondary sources (Bijlsma, 2015; Trimarchi,
2010).
Mass Generation Rate, Suspended RP (mg/hr) Generation rate for fine particulates inside the home. The PMi0 particles
generated inside the home were assumed to come from two dominant sources: cooking and smoking. Other sources
(e.g., candles) were not considered at this time.
For cooking, the CARB study was used because it looked at emission rates (rather than just particulate concentrations)
across a wide range of cooking activities for PM10 [(CARB, 2001), Table 3-32], The cooking rates for the different
activities were averaged to give an emission rate of 352 mg/hr during the cooking event.
The Department of Energy 2009 RECS survey provides information about how many times a day a person uses a stove
[(U.S. EIA, 2009), Table HC3.1], The distribution is wide with most respondents using once a day, a few times a week, or
once a week. "Low" assumes once a week and "medium" and "high" assume once a day. The duration of use per event
was assumed to be one hour. The average emission rate was normalized for duration and frequency of use to give an
average emission rate of 2.1 mg/hr (low) and 14.7 mg/hr (medium and high).
For the "high" case, cigarette smoke was added as an additional source. (Klepeis et al.. 2003) reports an average
emission rate of 0.7 to 0.9 mg/min for fine particulate. We used the midpoint, 0.8 mg/min. For frequency and duration,
we assumed 12 smoking events each lasting 15 minutes. Normalizing for frequency and duration gave an emission rate
of 6 mg/hr. This was added to the "medium" cooking emission rate to give 20.7 mg/hr.
NOTE: Mass Generation Rate of dust and RP into air and onto floor is in mg/hr (Qatsp'> 9ADust'> 9ftsp> dFDust)
Mass of Product Used; M (g/use) The amount of chemical-containing product used per event. CEM provides high,
medium, and low default estimates for many products. The mass of product used is multiplied by the weight fraction of
the chemical in the product to calculate the amount of chemical used per event.
Migration Rate of Chemical from Article to Saliva; MR (mg/cm2/hr) a measure of the flux in mass per area per time of
a chemical from an article containing the chemical to the saliva during mouthing. This is a function of the chemical and
the article itself and, along with mouthing behaviors such as frequency, area, and duration, governs mouthing exposure.
Molecular Weight; MW (g/mol) The mass of one mole of a chemical. This is needed to model chemical behavior,
including emission rates. If this is used in the applicable models, this value will always need to be entered by the user
based on the chemical of interest.
Near Field Modeling option within CEM where the model account for a small personal breathing zone around the user
during product use in which concentrations are higher, rather than employing a single well-mixed room.
Octanol-Air Partition Coefficient; Koa (unitless) A physical chemical property that is used to estimate the partitioning of
a chemical between a source material and air. If this is used in the applicable models, this value will always need to be
entered by the user based on the chemical of interest or the user can calculate this value using EpiSuite.
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Octanol-Water Partition Coefficient; Kow (unitless) The ratio of concentrations of the chemical between octanol and
water at equilibrium. If this is used in the applicable models, this value will always need to be entered by the user based
on the chemical of interest or the user can calculate this value using EpiSuite.
Peak Concentration (mg/m3) The highest concentration experienced at any point during the day of use in the use
environment.
Peak Dose (mg/day) This is calculated by multiplying the receptor average daily rate (ADR) by the receptor body weight.
Potential Peak Concentration (mg/m3) The highest instantaneous air concentration that is calculated by the model
during any 30-second time step, and should not be interpreted as a daily maximum concentration.
Products are generally consumable liquids, aerosols, or semi-solids that are used a given number of times before they
are exhausted.
Product Dilution Fraction; Dll (unitless) The ratio of the product that is diluted for use, for example, cleaning products
that are diluted in water. Values must be between 0 and 1. This is only use for dermal exposure models.
Product User A receptor who uses a product directly.
Radius of RP; rAbArt (m) Radius of abraded particles (Little et al.. 2012)
Radius of Dust Particles; rDust (m) Radius of dust particles (Little et al.. 2012).
Radius of RP; rRP (m) Radius of respirable particles (Little et al.. 2012).
Receptor The population of interest, also known as the receptor population and may be described by specific age ranges
or other characteristics (e.g., gender, ethnicity, geographic location). In CEM, the receptor is limited to three age ranges,
adult, youth, and child.
Resuspension Rate, Dust (per hour) The rate at which large particulates are resuspended from settled to the airborne
phase. The Exposure Factors Handbook recommends resuspension rates from the Thatcher and Layton 1995 study. For
dust, the deposition rates for particles greater than 10 mm (10-25 and >25) were averaged and rounded to two
significant digits [(U.S. EPA. 2011); Table 19-33],
Resuspension Rate, RP (per hour) The rate at which small particulates are resuspended from settled to the airborne
phase. The Exposure Factors Handbook recommends resuspension rates from the (Thatcher and Layton, 1995) study.
For RP, the resuspension rates for particles less than 10 mm (0.3 to 0.5, 0.6 to 1, 1-5 and 5-10) were averaged and
rounded to two significant digits [(U.S. EPA. 2011); Table 19-33],
RP Ingestion Fraction; IFRP (unitless) An estimate inhaled airborne particles in the respirable particle size range that
are ingested. Values must be between 0 and 1. The default value is 0 and should be used unless data are available.
Saturation Concentration in Air (mg/m3) The concentration at which exchange between the gas and liquid phases of the
chemical are at equilibrium. Air concentrations estimated by CEM or entered by the user may not be greater than the
saturation air concentration. If the user does not enter a saturation air concentration, it may be estimated within CEM
using the chemical's molecular weight and vapor pressure. CEM estimates the saturation air concentration at standard
temperature and pressure.
Scenario User defined name for specific analysis within CEM.
Skin Partitioning Coefficients (unitless) Multiple coefficients are used to describe the portioning of a chemical between
air, lipids, and multiple layers of the skin. Each is employed within the dermal air-to-skin model (A_DER1).
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Skin Permeability Coefficient; Kp (cm/hr) A measure of the chemical's absorption through skin. Enter an empirical value
or click the "Estimate" button to estimate the coefficient based on the chemical's molecular weight and octanol-water
partition coefficient.
Soil Density (kg/m3) Density of soil used by CEM in calculating exposure from products applied to ground.
Soil Mixing Depth; Depth, (m) Maximum depth in which a chemical can be expected to be mixed in soil after application
of the chemical to the surface of the soil. For example, tilled soiled will have a greater mixing depth and a lower resulting
soil concentration than soiled that are not mechanically mixed.
Soil Porosity; 0 (unitless) A measure of the porosity, or air spaces, in soil.
Surface Area of Article (m2) The surface area of articles containing the SVOC. CEM provides default values for many
products and articles. These can be modified by the user. Note, the model user can assume that multiple articles are
present within a single room. For example, 50 toys instead of 1 toy; 2 sofas instead of 1 sofa. However, caution should
be exercised and the model user is encouraged to think through how many articles of a given type are likely to be
present throughout a building. Using a high-end number of articles and surface area exposed may provide an upper
bound, but an average number of articles and surface area exposed is likely to provide more realistic exposure
estimates.
Surface Area of the Near-Field Geometry (m2) Surface area of the hemispherical bubble surrounding the product user.
Surface area for a use area with a radius of r is l/2*pi. 2*pi*rA2 (Keil and Nicas, 2003).
Surface Area of the Indoor Environment (m2) Surface area of the indoor environment, calculated as a function of the
zone volume and the surface area to volume ratio from the Exposure Factors Handbook.
SA
Surface Area to Body Weight Ratio; (cm2/kg) For products, the ratio of the surface area of the body in contact with
BW
the product to body weight. For articles, the ratio of exposed skin area to body weight. Six categories are included (i.e.,
all body surface area; half of body surface area; 25% of face, arms, and hands; all surface area of both hands; palms and
fingers of both hands; palm and fingers of one hand). The most representative category is matched to the article
category.
SVOC Gas-Phase Concentration in Contact with Article Surface (ng/m3) For materials with an SVOC additive present at
greater than 15% on a per weight basis, (Little et al.. 2012) recommends using the saturation vapor pressure
concentration. When the additive concentration is less than 15%, (Little et al.. 2012) recommends using monitoring data
to back calculate this value. Because the saturation vapor pressure concentration is the highest concentration that could
be present, using this value will potentially lead to over predictions of migration. CEM uses the saturation vapor
pressure in the absence of any monitoring data.
SVOC in RP Concentration; SVOCRP (|ig/mg) The ratio of the mass of SVOC sorbed to respirable particles to the mass of
the respirable particle. Used to estimate inhalation and ingestion exposure of particle-bound SVOCs.
SVOC in Dust Concentration; SVOCDust (ng/mg) The ratio of the mass of SVOC sorbed to large particles to the mass of
the respirable particle. Used to estimate inhalation and ingestion exposure of particle-bound SVOCs.
SVOC Gas Phase Mass Transfer Coefficient; h (m/hr) The mass transfer coefficient for SVOCs between bulk air and
surface. If this is used in the applicable models, this value will either need to be entered by the user based on the
chemical of interest or estimated by CEM based on the molecular weight of the SVOC.
SVOC Dust-Air Partition Coefficient; KDust (m3/mg) The ratio of concentrations of the chemical between dust and air at
equilibrium, specific to SVOCs. If this is used in the applicable models, this value will either need to be entered by the
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user based on the chemical of interest or estimated by CEM based on the volume fraction of organic matter in settled
dust, the octanol-air partition coefficient for the particular SVOC, and the density of airborne particles. This value can
also be estimated in the PARAMS model using vapor pressure.
SVOC RP-Air Partition Coefficient; KRP (m3/mg) The ratio of concentrations of the chemical between total suspended
particulate matter and air at equilibrium, specific to SVOCs. If this is used in the applicable models, this value will either
need to be entered by the user based on the chemical of interest or estimated by CEM based on the volume fraction of
organic matter in airborne particles, the octanol-air partition coefficient for the particular SVOC, and the density of
airborne particles. This value can also be estimated in the PARAMS model using vapor pressure.
Thickness of the Solid Layer; (L) (m) The thickness of the solid layer may be assumed to be 0.005 m for interior surfaces
and equal to the radius of the particle for particulates. Solid refers to where 'solid' refers to indoor sink (int), respirable
particles (RP), or dust.
Time; t (min) The time of the current time step.
Temperature (K) The temperature of the indoor environment.
Use Environment The room or other location where the product/article is used.
Use Environment Volume (m3) The total volume of the room of product use in the home or other building where the
product or article is used. Room volume is use to estimate air concentrations of the chemical in Zone 1 (i.e., room where
the product or article is in use) [(U.S. EPA. 2011), Table 19-6],
User-defined Emission Rate (mg/hr) See Emission Rate. Enter a value to prevent CEM from calculating emission rates
for use in exposure estimation (inhalation exposures only).
Vapor Pressure; VP (Torr) A chemical property that represents the saturation pressure of the chemical above a solid or
liquid substance. If this is used in the applicable models, this value will always need to be entered by the user based on
the chemical of interest.
Ventilation Rate; #(m3/hr) Volumetric rate of air exchange between building zones or between a building zone and the
outdoors. Used in conjunction with the zone volume to calculate air exchange rates.
Volume of Far-Field (m3) The portion of the use environment (Zone 1) that excludes the immediate area of product use.
The concentration of the chemical in air is governed by exchange with the near-field volume. Calculated based on other
values.
Volume of Near-Field (m3) The near-field volume is the portion of the use environment (Zone 1) that includes the
product user and where the air concentration of the chemical is governed by emissions from product use (Keil et al..
2009: Keil and Nicas. 2003).
Water Solubility; Sw (mg/mL) A physical/chemical property defined as the amount of chemical that can be dissolved in a
volume of water.
Weight Fraction; WF (unitless) The fraction of chemical present within a product or article. The sum of all chemicals
present would equal 1. For example, if a fragrance is present at 1% within a cleaning product, the weight fraction input
would be 0.01. This value is user defined.
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References
The reference list includes references from the CEM User Guide document and CEM Appendices.
Abt. (Abt Associates Inc.). (1992). Methylene chloride consumer products use survey findings. Bethesda, MD: U.S.
Consumer Product Safety Commission.
ACI (American Cleaning Institute). (2010). Consumer product ingredient safety: Exposure and risk screening methods for
consumer product ingredients, 2nd Edition. Washington, DC: American Cleaning Institute.
http://www.aciscience.org/docs/Consumer Product Ingredient Safety v2.0.pdf.
AISE. Consumer safety exposure assessment: A.I.S.E. REACT consumer tool. International Association for Soaps,
Detergents and Maintenance Products, http://www.aise.eu/our-activities/product-safety-and-
innovation/reach/consumer-safety-exposure-assessment.aspx#REACT.
ASTM. (2010). D5116-10 Standard guide for small-scale environmental chamber determinations of organic emissions
from indoor materials/products. West Conshohocken, PA: ASTM International.
http://www.astm.org/Standards/D5116.htm.
Better Homes and Gardens. (2015). Lawn fertilizer calculator. Available online at
http://www.bhg.com/gardening/yard/lawn-care/lawn-fertilizer-calculator/ (accessed March 2015).
Bijlsma, N. (2015). Dust. Available online at http://www.buildingbiology.com.au/index.php/Biologv/Dust.html (accessed
Bodalal, A., Zhang, J.S., Plett, E.G., 2000. A method for measuring internal diffusion
and equilibrium partition coefficients of volatile organic compounds for
building materials. Build. Environ. 35, 101-110
Brown, TN; Armitage, JM; Egeghy, P; Kircanski, I; Arnot, JA. (2016). Dermal permeation data and models
for the prioritization and screening-level exposure assessment of organic chemicals. Environment International.
94, 424-435.
CARB (California Air Resources Board). (2001). Indoor air quality: residential cooking exposures. Sacramento, CA:
Prepared for the State of California Air Resources Board by ARCADIS Geraghty & Miller, Inc.
http://www.arb.ca.gov/research/indoor/cooking/cooking.htm.
Chinn, KSK. (1981). A simple model for predicting chemical agent evaporation. Alexandria, VA: U.S. Department of
Defense, Defense Technical Information Center, Cameron Station.
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