APPENDIX E

BACKGROUND INFORMATION FOR THE

DEVELOPMENT OF REFERENCE GROUND-WATER

CONCENTRATION VALUES
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E-i

TABLE OF CONTENTS

Page

E-1 Shower Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-1

E-1.1 Shower Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-1

E-1.2 Shower Model Uncertainties and Limitations . . . . . . . . . . . . . . . . . . . . E-7

E-1.3 References for Section E-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-18

E-2 Constituent-specific Chemical and Physical Properties for the 

Shower Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-18

E-2.1 Data Collection Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-18

E-2.2 Solubility (Sol) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-19

E-2.3 Henry’s Law Constant (HLC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-19

E-2.4 Diffusion Coefficient in Water (Dw) . . . . . . . . . . . . . . . . . . . . . . . . . . . E-20

E-2.5 Diffusion Coefficient in Air (Da) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-21

E-2.6 References for Section E-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-27

E-3 Human Health Benchmarks used in the IWEM Tool . . . . . . . . . . . . . . . . . . . E-28

E-3.1 Methodology and Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-28

E-3.1.1 Integrated Risk Information System (IRIS) . . . . . . . . . . . . E-28

E-3.1.2 Superfund Provisional Benchmarks . . . . . . . . . . . . . . . . . . E-29

E-3.1.3 Health Effects Summary Tables (HEAST) . . . . . . . . . . . . E-29

E-3.1.4 ATSDR Minimal Risk Levels . . . . . . . . . . . . . . . . . . . . . . E-29

E-3.1.5 CalEPA Cancer Potency Factors and Reference 

Exposure Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-30

E-3.1.6 Other EPA Health Benchmarks . . . . . . . . . . . . . . . . . . . . . E-30

E-3.2 Human Health Benchmark Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-31

E-3.2.1 Benzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-43

E-3.2.2 Vinyl Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-43

E-3.2.3 Polychlorinated Biphenyls . . . . . . . . . . . . . . . . . . . . . . . . E-43

E-3.2.4 Dioxin-like Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . E-43

E-3.2.5 Superfund Technical Support Center 

Provisional Benchmarks . . . . . . . . . . . . . . . . . . . . . . . . . . E-45

E-3.2.6 Benchmarks From Other EPA Sources . . . . . . . . . . . . . . E-46

E-3.2.7 Air Characteristic Study Provisional Benchmarks . . . . . . E-47

E-3.2.8 Surrogate Health Benchmarks . . . . . . . . . . . . . . . . . . . . . E-47

E-3.2.9 Chloroform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-48

E-3.3 References for Section E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-49
E-ii

LIST OF TABLES

Page

Table E-1. Shower Model Input Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-4

Table E-2. Constituent-specific Chemical and Physical Properties . . . . . . . . . . . E-22

Table E-3. Human Health Benchmark Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-32

Table E-4. TEFs Used for Dioxin and Furan Congeners . . . . . . . . . . . . . . . . . . . . E-44

Table E-5. Provisional Human Health Benchmarks Developed by the 

Superfund Technical Support Center . . . . . . . . . . . . . . . . . . . . . . . . . . E-45

Table E-6. Provisional Inhalation Benchmarks Developed in the Air 

Characteristic Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-47
IWEM Technical Background Document Appendix E

E-1

BACKGROUND INFORMATION FOR THE

DEVELOPMENT OF REFERENCE GROUND-WATER

CONCENTRATION VALUES

E-1 Shower Model

E-1.1 Shower Model

The shower model calculates the incremental change in the concentration of a

constituent in air that results from the transfer of constituent mass from the water phase

(the shower water) to the vapor phase (the air in the shower stall) over time. The model

then estimates the concentration of the constituent in a bathroom that results from air

exchange within the bathroom and between the bathroom and the rest of the house over

time. After the model calculates the predicted air-phase constituent concentration in the

shower stall and bathroom, we use those concentrations to estimate the average air-phase

constituent concentration to which an individual is exposed over the course of an entire

day. We use this average daily concentration to calculate inhalation HBNs. 

The shower model is based on differential equations presented in McKone (1987)

and Little (1992a). We solved the differential equations using a mathematical technique

called “finite difference numerical integration,” to produce the equations that we use in

our analysis, Equations E-1 to E-11 in this Appendix. In reviewing the equations and

reading the following sections, it will help to keep in mind the following two concepts:

We calculate air-phase constituent concentrations for different “compartments.” 

The shower model is based on the understanding that there are two compartments

in the bathroom: 1) the shower stall and 2) the rest of the bathroom (outside of

the shower stall). We assume that an adult spends time: in the shower stall when

the shower is running; in the shower stall after the shower is turned off; and in the

rest of the bathroom after the shower is turned off (see Equations E-1 and E-2). 

We calculate air-phase constituent concentrations for different time steps. We

implement the shower model in time steps. That is, we estimate the air-phase

constituent concentration in each of the two compartments in 0.2-minute

increments or time steps. The air-phase constituent concentration at the

beginning of the 0.2-minute time step differs from the concentration at the end of

the 0.2-minute time step because of volatilization of constituent mass from the

shower water (which adds constituent mass) and the exchange of air between the

compartments in the bathroom and the rest of the house (which disperses the

mass). At the beginning of a time step, the air-phase concentration in each
IWEM Technical Background Document Appendix E

E-2

bathroom compartment is equal to the air-phase concentration that was estimated

for the compartment at the end of the previous time step.

The following is our basic procedure for implementing the shower model:

# Calculate a mass transfer coefficient for each constituent;

# Estimate the air-phase constituent concentration in the shower stall for

sequential 0.2-minute time steps;

# Estimate the air-phase constituent concentration in the bathroom (other

than in the shower stall) for sequential 0.2-minute time steps;

# Use the air-phase constituent concentrations calculated for the shower

stall, and the air-phase constituent concentrations calculated for the

bathroom, to calculate the average constituent concentration to which an

adult is exposed during the course of a day.

This procedure is explained in greater detail below. Table E-2 provides the

values for the constituent-specific properties used in the model. Table E-1 provides the

values we used for the parameters in the model.

Calculating a Mass Transfer Coefficient

The first step in estimating the concentration of a constituent in air is to quantify

the constituent’s “resistance” to movement between the water phase and the air phase. 

We quantify this resistance using the mass transfer coefficient presented in Equation E-4,

which incorporates variables calculated in Equations E-3 and E-5. The mass transfer

coefficient depends on properties specific to each constituent evaluated, as well as

physical properties of the water droplet. Specifically, the mass transfer coefficient

depends on:

# The constituent’s diffusivity in water (the molecular diffusion coefficient

for the constituent in water), which determines how readily the constituent

mass in the center of the water droplet will diffuse to the surface of the

water droplet. If a constituent’s diffusivity in water is low, then as the

constituent is emitted from the surface of the water droplet, the rate at

which the surface of the droplet is “supplied” with constituent from the

center of the water droplet will be slow, resulting in less constituent being

emitted from the droplet. Diffusivity influences the concentration gradient

across the droplet.
IWEM Technical Background Document Appendix E

E-3

# The Henry’s law constant for the constituent, which establishes how the

constituent will partition between the water phase and the air phase to

achieve equilibrium. Henry’s law states that, at equilibrium, the amount

of a constituent dissolved in water is proportional to the amount of the

constituent in the air phase that is in contact with the water. This

proportion is constituent-specific (each constituent has a different Henry’s

law constant). The Henry’s law constant influences the magnitude of the

air-phase constituent concentrations more than any other constituentspecific parameter.

# The constituent’s diffusivity in air (the molecular diffusion coefficient for

the constituent in air), which determines how readily the constituent will

migrate away from the droplet once it is released into the air surrounding

the droplet. Constituents with lower diffusivities in air will have

comparatively higher concentrations around the water droplet than in the

surrounding air. Therefore, because of Henry’s law, less constituent

would need to come out of solution into the air phase in order to achieve

equilibrium.

# The amount of time that the droplet is in contact with the air, which we

assume is equivalent to the time it takes for the droplet to fall to the floor

of the shower. We determine the time it takes the droplet to fall by

dividing distance that the droplet has to fall (which we assume is equal to

the height of the shower nozzle) by the velocity at which the water droplet

falls (which we assume is the terminal velocity of the droplet). For this

analysis, we set the nozzle height and the terminal velocity of the droplet

at fixed values, as presented in Table E-1.

# The ratio of the water droplet’s surface area to its volume. Because we

assume that the droplet is a sphere, its surface area to volume ratio is equal

to a value of 6 divided by the diameter of the droplet. For this analysis,

the diameter of the droplet, therefore its surface area to volume ratio, is a

fixed value (see Table E-1). 

Table E-2 presents the constituent-specific diffusivities and Henry’s law constants

that we used in our analysis.
E-4

Table E-1. Shower Model Input Parameters

Input Parameter Description Value Units Reference C

Bathroom Properties Vb Volume of the bathroom 10 m3 McKone, 1987 Exchange Rate Qbh Volumetric exchange rate between the bathroom and the house 300 L/min derived value Estimated from t

in McKone (198rate equals the vresidence time (e

Qsb Volumetric exchange rate between the shower and the bathroom 100 L/min derived value Estimated from t

in McKone (198rate equals the vresidence time (e

Exposure Time ShowerStallTime Time in shower stall after showering 5 min U.S. EPA, 1997c Table 15-23. 50T_bathroom Time spent in bathroom, not in shower 5 min U.S. EPA, 1997c Table 15-32. 50ShowerTime Shower time, 50th percentile 15 min U.S. EPA, 1997c Table 15-21. 50Shower Properties Vs Volume of shower 2 m3 McKone, 1987 NozHeight Height of shower head 1.8 m Little, 1992a Selected based o

reported in Tablsummary of five 

ShowerRate Rate of water flow from shower head 10 L/min derived value Value obtained b

reported in five Little (1992a) (Q

DropVel Terminal velocity of water drop 400 cm/s derived value Selected value b

data. DropDiam Diameter of shower water drop 0.098 cm derived value Estimated as a fuvelocity<=600cm

Groundwater Cin Constituent concentration in incoming water 0.001 mg/L NA Unit concentrati
IWEM Technical Background Document Appendix E

E-5

Calculating the Air-Phase Constituent Concentration in the Shower

Calculating the air-phase constituent concentration in the shower at the end of

each time step involves:

1. Calculating the fraction of constituent that can be emitted into the air from each

water droplet (Equation E-7);

2. Translating the fraction of constituent that can be emitted from each water droplet

(from step 1) into the mass of constituent that is emitted from the entire volume of

water that is coming into the shower during each time step (Equation E-6); and 

3. Determining the constituent concentration at the end of the time step by:

calculating the concentration added to the shower air during the time step

(dividing the constituent mass emitted from the water in step 2 by the volume of

the shower); adding this concentration to the concentration of the constituent that

was already in the shower air at the beginning of the time step; and subtracting

the concentration lost from the shower air due to the exchange of air with the rest

of the bathroom (Equation E-9). 

An important element of this analysis is the difference between the time in the

shower stall that is spent showering (15 minutes, Table E.1) and the time in the shower

stall that occurs after showering (5 minutes, Table E.1). The difference in these two time

periods involves how we handle the value for mass of constituent emitted from the

shower water (step 2, above). When we switch the model over from the time period

where the shower nozzle is turned on (the time spent showering), to the time period

where the shower nozzle is turned off (the time spent in the shower stall after showering),

we set the mass emitted from the water to zero. This means that during the 5-minute

period when the individual is in the shower after the shower is turned off, the air-phase

concentration of the constituent is only a function of the concentration of the constituent

in the air at the beginning of the time step and the air exchange between the shower stall

and the rest of the bathroom. The following paragraphs describe steps 1 and 2 in more

detail.

The fraction of the constituent mass that potentially can be emitted from a droplet

at any given time during the droplet’s fall through the air (Equation E-7) is a function of

the mass transfer coefficient (the constituent’s resistance to movement from the water

phase to the air phase, described previously) and the “fraction of gas phase saturation” in

the shower (calculated using Equation E-8). Inherent in this calculation is an assumption

that the concentration of the constituent in the air is constant over the time it takes the

droplet to fall. The fraction of gas phase saturation is an expression of how close the airphase constituent concentration is to the maximum possible (equilibrium) air-phase
IWEM Technical Background Document Appendix E

E-6

concentration. Stated another way, Henry’s law dictates that for a certain constituent

concentration in water, we can predict the maximum concentration of constituent in the

air that is in contact with the water (assuming the air and water are in equilibrium). 

Consequently, if there is already constituent in the air, then, to maintain equilibrium,

there is a limit to how much additional constituent can be emitted from the water to the

air (the less constituent already present in the air, the more constituent that theoretically

may be emitted). The fraction of gas phase saturation is an expression of how close the

air concentration is to that limit at the beginning of each time step. However, as

suggested at the beginning of this paragraph, even though Henry’s law influences the

maximum fraction of mass that could be emitted from the droplet, the mass transfer

coefficient also influences how much of the constituent will “free itself” from the water. 

Factors such as the constituent’s dispersivity (in water and air) and the surface area of the

droplet also influence the fraction of constituent mass that can be emitted from the

droplet.

In most cases, for each 0.2-minute time step we evaluate, the mass of a

constituent emitted from the shower water to the air is the product of: the concentration

of the constituent in the shower water; the volume of water emitted from the shower

during the time step; and the fraction of the constituent mass in the water that potentially

could be emitted from the water (discussed above). However, in certain cases (typically

rare), the mass transfer coefficient is of a magnitude that the concentration calculated in

this way exceeds the mass that possibly could be emitted when the water and the air

phases are at equilibrium. In this case, we “cap” the constituent mass that can be emitted

from the shower water during the time step. The cap is the maximum constituent mass

that could be emitted from the water at equilibrium (based on Henry’s law) minus the

constituent mass already in the shower stall at the beginning of the time step

Calculating the Air-Phase Constituent Concentration in the Bathroom (other than in

the Shower Stall)

The air-phase constituent concentration in the bathroom (Equation E-10) is a

function of the air-phase constituent concentration calculated for the shower, and the

exchange of air 1) between the shower and the bathroom and 2) between the bathroom

and the rest of the house. Specifically, for each time step, the air-phase constituent

concentration in the bathroom is equal to: the air-phase constituent concentration in the

bathroom at the beginning of the time step, plus the constituent concentration added as a

result of the exchange of air with the shower, minus the constituent concentration lost as

a result of the exchange of air with the rest of the house. Table E-1 presents the values

we used for the volumetric exchange rate between the shower and the bathroom; the

volumetric exchange rate between the bathroom and the house; and the volume of the

bathroom.
IWEM Technical Background Document Appendix E

E-7

Calculating the Average Daily Constituent Concentration to which an Individual is

Exposed

To calculate the average concentration of a constituent to which an individual is

exposed on a daily basis (24 hours per day) (Equation E-11), we:

1. Calculate the average constituent concentration in the shower air across all time

steps and multiply this concentration by the amount of time an individual spends

in the shower stall (Equation E-2);

2. Calculate the average constituent concentration in the bathroom air (not including

the shower air) across all time steps and multiply this concentration by the

amount of time an individual spends in the bathroom (not including the time spent

in the shower stall);

3. Sum the values calculated in steps 1 and 2, and divide the sum by the length of a

day. This calculation carries with it an assumption that an individual only is

exposed to the constituent in the shower, and in the bathroom after showering

(that is, that the concentration of the constituent in the rest of the house is zero).

E-1.2 Shower Model Uncertainties and Limitations

The primary limitations and uncertainties of the shower model are as follows:

# The model is constructed such that air-phase concentration of a constituent

in household air results solely from showering activity. Individuals are

exposed to emissions via inhalation for time spent in the shower while

showering, in the shower stall after showering, and in the bathroom after

showering. Other models calculate indoor air concentrations resulting

from emissions from household use of tap water and/or calculate

inhalation exposures for time spent in the remainder of the house. 

However, McKone (1987) found that the risk from inhalation exposures in

the remainder of the house was considerably lower than the risk from

inhalation exposures in the bathroom and during showering. In addition,

there are few data available to estimate the input parameters needed to

calculate exposure concentrations from other household activities,

including variables such as house volume, air exchange rate between the

house and outside air, and exposure time in the house. Given the expected

lower risk due to exposure in the remainder of the house, and the lack of

available data to estimate house constituent concentrations, we focused on

showering as the greatest source of inhalation exposure and risk due to use

of contaminated water.
IWEM Technical Background Document Appendix E

E-8

# The model currently only considers exposures to adults who shower, and

does not consider exposures to children who bathe in bathtubs. This

limitation of the model may be significant. A recent report by EPA’s

National Center for Environmental Assessment states that: “Because of

the longer exposure times, chemical emissions during the use of bathtubs

may be as, or more, significant than during showers, in terms of human

inhalation. This is particularly important given that small children are

typically washed in bathtubs rather than showers and are generally more

sensitive to chemical exposure than are healthy adults” (U.S. EPA, 2000).

# Our analysis does not consider an individual’s dermal exposure to water

or an individual’s incidental ingestion of water while showering.

# The model only considers emissions that result from falling droplets of

water in the shower. The model does not include algorithms that account

for emissions from water films on shower walls or puddles on the floor of

the shower. Use of the model also assumes that a droplet falls directly

from the shower nozzle to the shower stall floor, and is not intercepted by

the body of the individual who is showering. 

# The input parameter values are a source of uncertainty for the shower

model. To select values for the shower properties (shower and bathroom

volume, nozzle height, and flow rate), we generally used central tendency

values that were reported in the literature. Although fixing shower model

input parameters as constant does not capture variability in the results, the

results still compare favorably to experimental data for numerous organic

compounds of varying volatility (Coburn, 1996). The values for droplet

properties (diameter and velocity) are also constants, and are based on

correlation to existing data. The largest uncertainty is likely in the

volumetric exchange rates used between the shower and bathroom and the

bathroom and the rest of house. We derived these values, 300 L/min for

the exchange rate between the bathroom and house, and 100 L/min for the

exchange rate between the shower and bathroom, from McKone (1987). 

However, values reported in a five-study summary by Little (1992a)

ranged from 35 to 460 L/min for the exchange between the shower and

bathroom, and 38 to 480 L/min for the exchange between the bathroom

and the rest of the house. Such a large range of volumetric exchange rates

imparts uncertainty to the shower model’s estimation of constituent

concentrations.

# A constituent’s solubility in water depends on a number of factors

including the temperature of the water and the other chemicals (for
IWEM Technical Background Document Appendix E

E-9

example, other solvents) that are in the water. When the concentration of

a constituent in water exceeds the constituent’s solubility in that water, we

expect that at least some of the constituent will exist in the water as a nonaqueous (free) phase. Henry’s law, a basic principle of the shower model,

only applies to constituents dissolved in water, it does not apply to nonaqueous phase constituents (U.S. EPA, 1996). As a result, it would not be

appropriate to use the HBNs we developed for the inhalation pathway if

the shower water (which we assume is from a ground-water well)

contained non-aqueous phase constituent. More importantly, however,

EPACMTP, the ground-water fate and transport model that we use to

estimate constituent concentrations in the modeled ground water, cannot

be used to model non-aqueous phase liquids. Consequently, the IWEM

tool should not be used in cases where non-aqueous phase constituents are

present in leachate. In these situations, another tool must be used that is

capable of evaluating non-aqueous phase liquids.
IWEM Technical Background Document Appendix E

E-10

BSResTime ShowerTime ShowerStallTime T_ bathroom = + +

ShowerResTime ShowerStallTime ShowerTime = +

Equation E-1. Total time spent in shower and bathroom

Name Description Value

BSResTime Total time spent in shower and bathroom (min) Calculated above

ShowerTime Duration of shower (min) Provided in Table E-1

ShowerStallTime Time in shower stall after showering (min) Provided in Table E-1

T_bathroom Time spent in bathroom, not in shower (min) Provided in Table E-1

This equation calculates the total time that a receptor is exposed to vapors.

Equation E-2. Total time spent in shower stall

Name Description Value

ShowerResTime Total time spent in shower stall (min) Calculated above

ShowerStallTime Time in shower stall after showering (min) Provided in Table E-1

ShowerTime Duration of shower (min) Provided in Table E-1

This equation calculates the total time that a receptor is exposed to vapors in the shower stall.
IWEM Technical Background Document Appendix E

E-11

Hprime HLCcoef HLC

HLCcoef R Temp

= ×

= ×

1

N = Kol AVRatio DropResTim

DropResTime

× ×

=

= ×

e

AVRatio

DropDiam

NozHeight

DropVel

6

100

Equation E-3. Dimensionless Henry’s law constant

Name Description Value

Hprime Dimensionless Henry's law constant (dimensionless) Calculated above

HLCcoef Coefficient to Henry's law constant Mol/(atm-m3

) Calculated above

HLC Henry's law constant (atm-m3

/Mol) Chemical-specific

R Ideal Gas constant (atm-m3/K-Mol) 0.00008206

Temp Temperature (K) 298

This equation calculates the dimensionless form of Henry’s law constant.

Equation E-4. Dimensionless overall mass transfer coefficient

Name Description Value

N Dimensionless overall mass transfer coefficient (dimensionless) Calculated above

AVRatio Area-to-volume ratio for a sphere (cm2

/cm3) Calculated above

Kol Overall mass transfer coefficient (cm/s) Calculated in Equation E-5

DropResTime Residence time for falling drops (s) Calculated above

DropDiam Drop diameter (cm) Provided in Table E-1

NozHeight Nozzle height (m) Provided in Table E-1

DropVel Drop terminal velocity (cm/s) Provided in Table E-1

100 Conversion factor (cm/m) Conversion factor

This equation calculates the dimensionless overall mass transfer coefficient. The above equation is based

on Little (1992a; Equation 5), which provides the equation as N = Kol × A/Q1 where A is the total surface

area for mass transfer and Q1 is water flow in volume per time.
IWEM Technical Background Document Appendix E

E-12

Kol

D D Hprime w a

=× +

×





 





−

β

25 1

23 23

1

.

/ /

Equation E-5. Overall mass transfer coefficient

Name Description Value

Kol Overall mass transfer coefficient (cm/s) Calculated above

beta Proportionality constant (cm-s^-1/3) 216

Dw Diffusion coefficient in water (cm2

/s) Chemical-specific

Da Diffusion coefficient in air (cm2/s) Chemical-specific

Hprime Dimensionless Henry's law constant (dimensionless) Calculated in Equation E-3

This equation calculates the overall mass transfer coefficient. The above equation corresponds to Equation

17 in McKone (1987) and was modified to use the dimensionless Henry’s law constant. McKone (1987)

noted that the proportionality constant, beta, was a dimensionless value. Little (1992b) indicated that beta 

is not dimensionless. The correct units are noted above. The value for beta was derived using data for

benzene and verified for chemicals of varying volatility (Coburn, 1996).
IWEM Technical Background Document Appendix E

E-13

Es = Emax

Es Et =

( )

Et Cin ShowerRate ts fem

y y Vs eq s t

= × × ×

Emax 1000 = − ×× ,

Equation E-6. Constituent mass emitted in the shower for a given time step

For Et > Emax,

For Et # Emax,

Where,

Name Description Value

Es Constituent mass emitted in the shower for a given time step

(mg)

Calculated above

Emax Maximum possible mass of constituent emitted from shower

during time step (mg)

Calculated above

Et Potential mass of constituent emitted from shower during

time step (mg)

Calculated above

yeq Gas-phase constituent concentration in equilibrium between

water and air (mg/L)

Hprime x Cin

ys, t Gas-phase constituent concentration in the shower at the

beginning of time step (mg/L)

Calculated in Equation E-9 (As

ys, t+ts for previous time step)

Vs Volume of shower (m3

) Provided in Table E-1

Cin Liquid-phase constituent concentration in the incoming water

(mg/L)

Provided in Table E-1

ShowerRate Rate of flow from showerhead (L/min) Provided in Table E-1

ts Time step (min) 0.2

fem Fraction of constituent emitted from a droplet

(dimensionless)

Calculated in Equation E-7

Hprime Dimensionless Henry's law constant (dimensionless) Calculated in Equation E-3

1000 Conversion factor (L/m3

) Conversion factor

The above equations are used to determine the mass of constituent emitted for a given time step. The

equilibrium concentration in air (y_eq) is calculated from Equation 1 in Little (1992a). If the mass emitted

based on the mass transfer coefficient (Et) is greater than the amount emitted to reach equilibrium (Emax),

the mass is set to the amount that results in the air concentration at equilibrium.
IWEM Technical Background Document Appendix E

E-14

fem Fsat e ( ) ( ) N = − ×− − 1 1 

Fsat y

y

s t

eq

= ,

Equation E-7. Fraction of constituent emitted from a droplet

Name Description Value

fem Fraction of constituent emitted from a droplet

(dimensionless)

Calculated above

Fsat Fraction of gas-phase saturation (dimensionless) Calculated in Equation E-8

N Dimensionless overall mass transfer coefficient

(dimensionless)

Calculated in Equation E-4

This equation is used to calculate the fraction of a given chemical emitted from a droplet of water in the

shower. The equation is based on Equation 5 in Little (1992a). The above equation is obtained by

rearranging the equation in Little given that ys_max/m = Cin and Fsat = ys/ys_max = ys/(m × Cin).

Equation E-8. Fraction of gas-phase saturation in shower

Name Description Value

Fsat Fraction of gas-phase saturation in shower (dimensionless) Calculated above

yeq Gas-phase constituent concentration in equilibrium between

water and air (mg/L)

Hprime x Cin

ys, t Current gas-phase constituent concentration in air (mg/L) Calculated in Equation E-9 (as

ys, t+ts for previous time step)

Hprime Dimensionless Henry's law constant (dimensionless) Calculated in Equation E-3

Cin Constituent concentration in incoming water (mg/L) Provided in Table E-1

This equation is used to calculate the fraction of gas phase saturation in shower for each time step. The

equilibrium concentration in air (y_eq) is calculated from Equation 1 in Little (1992a).
IWEM Technical Background Document Appendix E

E-15

[ ( ( ) )] y y

E Q y y ts

V

s t ts s t

s sb s t b t

s

, ,

, ,

+ = +

−× − ×

× 1000

Equation E-9. Gas-phase constituent concentration in the shower at end of time step

Name Description Value

ys, t+ts Gas-phase constituent concentration in the shower at end of

time step (mg/L)

Calculated above

ys, t Gas-phase constituent concentration in the shower at the

beginning of time step (mg/L)

Calculated in Equation E-10 (as

yb, t+ts for previous time step)

yb, t Gas-phase constituent concentration in the bathroom at the

beginning of time step (mg/L)

Calculated from last time step

Es Mass emitted in the shower for a given time step (mg) Calculated in Equation E-6

Qsb Volumetric exchange rate between the shower and the

bathroom (L/min)

Provided in Table E-1

Vs Volume of shower (m3

) Provided in Table E-1

ts Time step (min) 0.2

1000 Conversion factor (L/m3

) Conversion factor

This equation is used to calculate the gas-phase constituent concentration in the shower at end of time step. 

The equation is derived from Equation 9 in Little (1992a). Es is set to 0 when the shower is turned off (i.e.,

at the end of showering) to estimate the reduction in shower stall air concentrations after emissions cease.
IWEM Technical Background Document Appendix E

E-16

[ ] ( ) ( )( )

y y

Qy y Q yy

V

b t ts b t ts

sb s t ts b t bh b t h t

b

, ,

, , ,,

+

+

= +

× − −× −

×

×

1000

Equation E-10. Gas-phase constituent concentration in the bathroom at end of time step

Name Description Value

yb, t+ts Gas-phase constituent concentration in the bathroom at end

of time step (mg/L)

Calculated above

yb, t Gas-phase constituent concentration in the bathroom at the

beginning of time step (mg/L)

Calculated from last time step

ys, t+ts Gas-phase constituent concentration in the shower at the end

of time step (mg/L)

Calculated in Equation E-9

yh, t Gas-phase constituent concentration in the house at the

beginning of time step (mg/L)

Assumed deminimus, zero

Qsb Volumetric exchange rate between the shower and the

bathroom (L/min)

Provided in Table E-1

Qbh Volumetric exchange rate between the bathroom and the

house (L/min)

Provided in Table E-1

Vb Volume of bathroom (m3

) Provided in Table E-1

ts Time step (min) 0.2

1000 Conversion factor (L/m3

) Conversion factor

This equation is used to calculate the gas-phase constituent concentration in the bathroom at end of time

step. The equation is derived from Equation 10 in Little (1992a).
IWEM Technical Background Document Appendix E

E-17

( ) ( )

[ ] ( )

[ ] ( )

C

C ShowerResTime C T bathroom

C

y y

n

C

y y

air indoor

air shower air bathroom

air shower

s t ts s t

s

air bathroom

b t ts b t

_

_ _

_

,

_

, ,

_

, /

/

= × +×

=

+ ×

=

+ ×

+

+

∑

∑

1440

1000

 1000

nb

2

2

Equation E-11. Average daily concentration in indoor air

Name Description Value

Cair_indoor Average daily concentration in indoor air (mg/m3

) Calculated above

Cair_shower Average concentration in shower (mg/m3

) Calculated above

Cair_bathroom Average concentration in bathroom (mg/m3

) Calculated above

ShowerResTime Total time spent in shower stall (min) Calculated in Equation E-2

T_bathroom Time spent in bathroom, not in shower (min) Provided in Table E-1

ys, t Gas-phase constituent concentration in the shower at the

beginning of time step (mg/L)

Calculated in Equation E-9 (as

ys, t+ts for previous time step)

ys, t+ts Gas-phase constituent concentration in the shower at the end

of time step (mg/L)

Calculated in Equation E-9

yb, t Gas-phase constituent concentration in the bathroom at the

beginning of time step (mg/L)

Calculated in Equation E-10 (as

yb, t+ts for previous time step)

yb, t+ts Gas-phase constituent concentration in the bathroom at the

end of time step (mg/L)

Calculated in Equation E-10

ns Number of time steps corresponding to time spent in the

shower (dimensionless)

Summed in model code

nb Number of time steps corresponding to time spent in the

bathroom (dimensionless)

Summed in model code

1440 Minutes per day (min) Adjustment factor

1000 Conversion factor (L/m3

) Conversion factor

The above equations are used to calculate the time-weighted average daily indoor air concentration to

which a receptor is exposed. The equation assumes that receptors are only exposed to constituents in the

shower and bathroom.
IWEM Technical Background Document Appendix E

E-18

E-1.3 References for Section E-1

Coburn, J., 1996. Memo to Dana Greenwood on Emission Flux Equations for

Showering, July 1.

Little, J.C., 1992a. Applying the two resistance theory to contaminant volatilization in

showers. Environmental Science and Technology 26(7):1341-1349.

Little, J.C., 1992b. Applying the two resistance theory to contaminant volatilization in

showers. Environmental Science and Technology 26(4); 836-837.

McKone, T.E., 1987. Human exposure to volatile organic compounds in household tap water:

The indoor inhalation pathway. Environmental Science and Technology 21:1194-1201.

U.S. EPA, 1996. Soil Screening Guidance: Technical Background Document. EPA/540/R95/128.

Office of Solid Waste and Emergency Response. May.

U.S. EPA, 1997a. Exposure Factors Handbook, Volume I, General Factors.

EPA/600/P-95/002Fa. Office of Research and Development, Washington, DC.

U.S. EPA, 2000. Volatilization Rates from Water to Indoor Air, Phase II. EPA/600/R-00/096. 

National Center for Environmental Assessment–Washington Office, Office of Research

and Development, Washington, DC. October.

E-2 Constituent-specific Chemical and Physical Properties for

the Shower Model

To calculate inhalation HBNs, the shower model requires input of several

chemical-specific properties, including solubility (Sol), Henry’s law constant (HLC), and

diffusion coefficients in air (Da) and water (Dw). This attachment describes the data

sources and methodologies used to collect and develop these properties. Table E.2 lists

by constituent the chemical-specific properties used to calculate inhalation HBNs, along

with the data source for each value.

E-2.1 Data Collection Procedure

To select data values available from multiple sources, we created a hierarchy of

references based on the reliability and availability of data in such sources. Our first

choice for data collection and calculations was EPA reports and software. When we

could not find data or equations from EPA publications, we consulted highly recognized

sources, including chemical information databases on the Internet. These on-line sources
IWEM Technical Background Document Appendix E

E-19

HLC

P

Sol

vp =

are compilations of data that provide the primary references for data values. The specific

hierarchy varied among properties as described in subsequent sections. 

For dioxins, the preferred data source in all cases was the Exposure and Human

Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related

Compounds, Part 1, Vol. 3 (Dioxin Reassessment) (U.S. EPA, 2000). We used the

Mercury Study Report to Congress (U.S. EPA, 1997a) as the preferred source for

mercury properties. If values were unavailable from these sources, we followed the same

reference hierarchy that was used for other constituents. 

All data entry for chemical and physical properties was checked by comparing

each entry against the original online or hardcopy reference. All property calculation

programs were checked using hand calculations to ensure that they were functioning

correctly. 

E-2.2 Solubility (Sol)

For solubility (Sol) values, we looked for data by searching the following sources

in the following order: 

1. Superfund Chemical Data Matrix (SCDM) (U.S. EPA, 1997b); 

2. CHEMFATE Chemical Search (SRC, 1999); 

3. Hazardous Substances Data Bank (HSDB) (U.S. NLM, 2001); 

4. ChemFinder (CambridgeSoft Corporation, 2001). 

For mercury, we obtained a solubility for elemental mercury from The Merck Index: An

Encyclopedia of Chemicals, Drugs, and Biologicals (Budavari, 1996).

E-2.3 Henry’s Law Constant (HLC)

Collection of Henry’s law constant (HLC) data proceeded by searching sources in

the following order: 

1. SCDM; 

2. CHEMFATE; 

3. HSDB. 

When we could not find data from these sources, we calculated HLC using

equation 15-8 from Lyman, Reehl, and Rosenblatt (1990):
IWEM Technical Background Document Appendix E

E-20

Dw = × MW − 0 00022 2 3 . /

where

HLC = Henry’s law constant (atm-m3/mole)

Pvp = vapor pressure (atm)

Sol = solubility (mol/m3

).

E-2.4 Diffusion Coefficient in Water (Dw)

For all chemicals, we calculated the diffusion coefficient in water (Dw) by hand

because few empirical data are available. The preferred calculation was equation 17-6

from the WATER9 model (U.S. EPA, 2001):

D T MW w =  +



 









 





−

0 0001518 27316

29816

0 6

. .

.

.

ρ

where

Dw = diffusion coefficient in water (cm2

/s)

T = temperature (degrees C)

MW = molecular weight (g/g-mol)

D = density (g/cc).

When we did not know chemical density, we used equation 3.16 from Process

Coefficients and Models for Simulating Toxic Organics and Heavy Metals in Surface

Waters (Process Coefficients) (U.S. EPA, 1987), which only requires molecular weight:

where

Dw = diffusion coefficient in water (cm2

/s)

MW = molecular weight (g/mol).
IWEM Technical Background Document Appendix E

E-21

( )

D

T

MW

MW

MW

a =

+ +−





 



 +

















0 0029 27316 0 034 1 1 0 000015

2 5

18

15 2

0 333 2

. ( .) . .

. .

.

.

ρ

E-2.5 Diffusion Coefficient in Air (Da)

All diffusion coefficients in air (Da) were calculated values because few empirical

data are available. Similar to Dw, we first consulted WATER9 and then used U.S. EPA

(1987). Equation 17-5 in WATER9 calculates diffusivity in air as follows:

where

Da = diffusion coefficient in air (cm2/s)

T = temperature (degrees C)

MW = molecular weight (g/g-mol)

D = density (g/cc).

When density was not available, we used equation 3.17 from Process Coefficients

(U.S. EPA, 1987):

where

Da = diffusion coefficient in air (cm2

/s)

MW = molecular weight (g/mol).

For dioxins and furans, we used an equation from the Dioxin Reassessment (U.S.

EPA, 2000) to estimate diffusion coefficients from diphenyl’s diffusivity:

D

D

MW

MW

a

b

b

a

= 



 





0 5.

where

Da = diffusion coefficient of constituent in air (cm2

/s)

Db = diffusion coefficient of diphenyl at 25 degrees C (0.068

cm2

/s)

MWa = molecular weight of constituent (g/mole)

MWb = molecular weight of diphenyl (154 g/mole).
IWEM Technical Background Document Appendix E

E-22

Table E-2. Constituent-specific Chemical and Physical Properties

Constituent CASRN

Da

(cm2/s)

(a)

Dw

(cm2/s)

(a)

HLC 

(atmm3

/mol)

(c)

Sol

(mg/L)

(c)

Acetaldehyde (ethanal) 75-07-0 0.128 0 7.89e-05 1.00e+06

Acetone (2-propanone) 67-64-1 1.06E-01 1.15E-05 3.88e-05 1.00e+06

Acetonitrile (methyl cyanide) 75-05-8 1.34E-01 1.41E-05 3.46e-05 1.00e+06

Acrolein 107-02-8 1.12E-01 1.22E-05 1.22e-04 2.13e+05

Acrylamide 79-06-1 1.07E-01 1.26E-05 1.00e-09 6.40e+05

Acrylic acid (propenoic acid) 79-10-7 1.03E-01 1.20E-05 1.17e-07 1.00e+06

Acrylonitrile 107-13-1 1.14E-01 1.23E-05 1.03e-04 7.40e+04

Aldrin 309-00-2 2.28E-02 5.84E-06 1.70e-04 1.80e-01

Aniline (benzeneamine) 62-53-3 8.30E-02 1.01E-05 1.90e-06 3.60e+04

Benz(a)anthracene 56-55-3 5.09E-02b 5.89E-06b 3.35e-06 9.40e-03

Benzene 71-43-2 8.95E-02 1.03E-05 5.55e-03 1.75e+03

Benzidine 92-87-5 3.55E-02 7.59E-06 3.88e-11 5.00e+02

Benzo(a)pyrene 50-32-8 2.55E-02 6.58E-06 1.13e-06 1.62e-03

Benzo(b)fluoranthene 205-99-2 4.76E-02b 5.51E-06b 1.11e-04 1.50e-03

Benzyl chloride 100-44-7 6.34E-02 8.81E-06 4.15e-04 5.25e+02

Bis(2-ethylhexyl)phthalate 117-81-7 1.73E-02 4.18E-06 1.02e-07 3.40e-01

Bis(2-chloroethyl)ether 111-44-4 5.67E-02 8.71E-06 1.80e-05 1.72e+04

Bis(2-chloroisopropyl)ether 39638-32-9 4.01E-02 7.40E-06 1.34e-04e 1.31e+03

Bromodichloromethane 75-27-4 5.63E-02 1.07E-05 1.60e-03 6.74e+03

Bromomethane (methyl bromide) 74-83-9 1.00E-01 1.35E-05 6.24e-03 1.52e+04

Butadiene, 1,3- 106-99-0 1.00E-01 1.03E-05 7.36e-02 7.35e+02

Carbon tetrachloride 56-23-5 5.71E-02 9.78E-06 3.04e-02 7.93e+02

Carbon disulfide 75-15-0 1.06E-01 1.30E-05 3.03e-02 1.19e+03

Chlordane 57-74-9 2.15E-02 0 4.86e-05 5.60e-02

Chloro-1,3-butadiene, 2-

(Chloroprene) 126-99-8 8.41E-02 1.00E-05 1.19e-02f 1.74e+03

Chlorobenzene 108-90-7 7.21E-02 9.48E-06 3.70e-03 4.72e+02

Chlorobenzilate 510-15-6 2.18E-02 5.48E-06 7.24e-08f 1.11e+01

Chlorodibromomethane 124-48-1 3.66E-02 1.06E-05 7.83e-04 2.60e+03

Chloroethane (ethyl chloride) 75-00-3 1.04E-01 1.16E-05 8.82e-03 5.68e+03

Chloroform 67-66-3 7.70E-02 1.09E-05 3.67e-03 7.92e+03
Table E-2. Constituent-specific Chemical and Physical Properties (continued)

IWEM Technical Background Document Appendix E

Constituent CASRN

Da

(cm2/s)

(a)

Dw

(cm2/s)

(a)

HLC 

(atmm3

/mol)

(c)

Sol

(mg/L)

(c)

E-23

Chloromethane (methyl chloride) 74-87-3 0.124 1.36E-05 8.82e-03 5.33e+03

Chlorophenol, 2- 95-57-8 0.0661 0 3.91e-04 2.20e+04

Chloropropene, 3- (allyl chloride) 107-05-1 9.36E-02 1.08E-05 1.10e-02 3.37e+03

Chrysene 218-01-9 2.61E-02 6.75E-06 9.46e-05 1.60e-03

Cresol, o- 95-48-7 7.59E-02 9.86E-06 1.20e-06 2.60e+04

Cresol, — 108-39-4 0.0729 0 8.65e-07 2.27e+04

Cresol, p- 106-44-5 7.24E-02 9.24E-06 7.92e-07 2.15e+04

Cresols (total) 1319-77-3 7.37E-02 9.48E-06 9.52e-07 2.34e+04

Cumene 98-82-8 6.02E-02 7.85E-06 1.16e+00 6.13e+01

Cyclohexanol 108-93-0 7.59E-02 9.35E-06 1.02e-04f 4.30e+04f

DDT, p,p'- 50-29-3 1.83E-02 4.44E-06 8.10e-06 2.50e-02

Dibenz(a,h)anthracene 53-70-3 0.0236 6.02E-06 1.47e-08 2.49e-03

Dibromo-3-chloropropane, 1,2- 96-12-8 0.0321 8.90E-06 1.47e-04 1.23e+03

Dichlorobenzene, 1,2- 95-50-1 0.0562 8.92E-06 1.90e-03 1.56e+02

Dichlorobenzene, 1,4- 106-46-7 0.055 8.68E-06 2.40e-03 7.38e+01

Dichlorobenzidine, 3,3'- 91-94-1 4.75E-02b 5.50E-06b 4.00e-09 3.11e+00

Dichlorodifluoromethane (Freon 12) 75-71-8 7.60E-02 1.08E-05 3.43e-01 2.80e+02

Dichloroethane, 1,1- 75-34-3 8.36E-02 1.06E-05 5.62e-03 5.06e+03

Dichloroethane, 1,2- 107-06-2 8.54E-02 1.09E-05 9.79e-04 8.52e+03

Dichloroethylene, 1,1- 75-35-4 8.63E-02 1.10E-05 2.61e-02 2.25e+03

Dichloropropane, 1,2- 78-87-5 7.33E-02 9.73E-06 2.80e-03 2.80e+03

Dichloropropene, trans-1,3- 10061-02-6 7.63E-02 1.01E-05 1.80e-03i 2.72e+03

Dichloropropene, 1,3- (isomer

mixture) 542-75-6 7.63E-02 1.01E-05 1.77e-02 2.80e+03

Dichloropropene, cis-1,3- 10061-01-5 7.65E-02 1.02E-05 2.40e-03i 2.72e+03

Dieldrin 60-57-1 2.33E-02 6.01E-06 1.51e-05 1.95e-01

Dimethyl formamide, N,N- (DMF) 68-12-2 9.72E-02 1.12E-05 7.39e-08i 1.00e+06f

Dimethylbenz(a)anthracene, 7,12- 57-97-6 4.71E-02b 5.45E-06b 3.11e-08 2.50e-02

Dinitrotoluene, 2,4- 121-14-2 3.75E-02 7.90E-06 9.26e-08 2.70e+02

Dioxane, 1,4- 123-91-1 8.74E-02 1.05E-05 4.80e-06 1.00e+06

Diphenylhydrazine, 1,2- 122-66-7 0.0343 7.25E-06 1.53e-06 6.80e+01

Epichlorohydrin 106-89-8 0.0888 1.11E-05 3.04e-05 6.59e+04
Table E-2. Constituent-specific Chemical and Physical Properties (continued)

IWEM Technical Background Document Appendix E

Constituent CASRN

Da

(cm2/s)

(a)

Dw

(cm2/s)

(a)

HLC 

(atmm3

/mol)

(c)

Sol

(mg/L)

(c)

E-24

Epoxybutane, 1,2- 106-88-7 9.32E-02 1.05E-05 1.80e-04f 9.50e+04f

Ethoxyethanol acetate, 2- 111-15-9 0.057 0 1.80e-06i 2.29e+05i

Ethoxyethanol , 2- 110-80-5 8.19E-02 9.76E-06 1.23e-07 1.00e+06

Ethylbenzene 100-41-4 6.86E-02 8.48E-06 7.88e-03 1.69e+02

Ethylene dibromide

(1,2-dibromoethane) 106-93-4 4.31E-02 1.05E-05 7.43e-04 4.18e+03

Ethylene glycol 107-21-1 1.17E-01 1.36E-05 6.00e-08 1.00e+06

Ethylene thiourea 96-45-7 8.69E-02 1.01E-05 3.08e-10 6.20e+04

Ethylene oxide 75-21-8 1.34E-01 1.46E-05 1.48e-04 1.00e+06g

Formaldehyde 50-00-0 1.67E-01 1.74E-05 3.36e-07 5.50e+05

Furfural 98-01-1 8.53E-02 1.07E-05 4.00e-06 1.10e+05

HCH, gamma- (Lindane) 58-89-9 2.74E-02 7.30E-06 1.40e-05 6.80e+00

HCH, beta- 319-85-7 0.0277 7.40E-06 7.43e-07 2.40e-01

HCH, alpha- 319-84-6 2.75E-02 7.35E-06 1.06e-05 2.00e+00

Heptachlor epoxide 1024-57-3 2.19E-02 5.58E-06 9.50e-06 2.00e-01

Heptachlor 76-44-8 2.23E-02 5.70E-06 1.10e-03 1.80e-01

Hexachloro-1,3-butadiene 87-68-3 2.67E-02 7.03E-06 8.15e-03 3.23e+00

Hexachlorobenzene 118-74-1 2.90E-02 7.85E-06 1.32e-03 5.00e-03

Hexachlorocyclopentadiene 77-47-4 2.72E-02 7.22E-06 2.70e-02 1.80e+00

Hexachlorodibenzo-p-dioxins

(HxCDDs) 34465-46-8 4.27E-02j 4.12E-06b 1.10e-05d 4.40e-06d

Hexachlorodibenzofurans (HxCDFs) 55684-94-1 4.36E-02j 4.23E-06b 1.10e-05d 1.30e-05d

Hexachloroethane 67-72-1 3.21E-02 8.89E-06 3.89e-03 5.00e+01

Hexane 110-54-3 7.28E-02 8.12E-06 1.43e-02 1.24e+01

Indeno(1,2,3-cd)pyrene 193-39-5 4.48E-02 5.19E-06 1.60e-06 2.20e-05

Isophorone 78-59-1 5.25E-02 7.53E-06 6.64e-06 1.20e+04

Mercury 7439-97-6 7.15E-02 3.01E-05 7.10e-03k 5.62e-02h

Methacrylonitrile 126-98-7 9.64E-02 1.06E-05 2.47e-04 2.54e+04

Methanol 67-56-1 1.58E-01 1.65E-05 4.55e-06 1.00e+06

Methoxyethanol acetate, 2- 110-49-6 6.59E-02 8.71E-06 3.11e-07e 1.00e+06i

Methoxyethanol, 2- 109-86-4 0.0952 1.10E-05 8.10e-08f 1.00e+06g

Methyl methacrylate 80-62-6 7.53E-02 9.25E-06 3.37e-04 1.50e+04
Table E-2. Constituent-specific Chemical and Physical Properties (continued)

IWEM Technical Background Document Appendix E

Constituent CASRN

Da

(cm2/s)

(a)

Dw

(cm2/s)

(a)

HLC 

(atmm3

/mol)

(c)

Sol

(mg/L)

(c)

E-25

Methyl tert-butyl ether (MTBE) 1634-04-4 0.0755 0 5.87e-04f 5.13e+04f

Methyl isobutyl ketone 108-10-1 0.0698 0 1.38e-04 1.90e+04

Methyl ethyl ketone 78-93-3 0.0917 0 5.59e-05 2.23e+05

Methylcholanthrene, 3- 56-49-5 2.41E-02 6.14E-06 9.40e-07 3.23e-03

Methylene chloride (dichloromethane) 75-09-2 9.99E-02 1.25E-05 2.19e-03 1.30e+04

N-Nitrosomethylethylamine 10595-95-6 8.41E-02 9.99E-06 1.40e-06i 1.97e+04

N-Nitrosodimethylamine 62-75-9 9.88E-02 1.15E-05 1.20e-06 1.00e+06

N-Nitrosopiperidine 100-75-4 6.99E-02 9.18E-06 2.80e-07 7.65e+04

N-Nitrosodiphenylamine 86-30-6 2.84E-02 7.19E-06 5.00e-06 3.51e+01

N-Nitrosodiethylamine 55-18-5 7.38E-02 9.13E-06 3.63e-06 9.30e+04

N-Nitroso-di-n-butylamine 924-16-3 4.22E-02 6.83E-06 3.16e-04 1.27e+03

N-Nitrosopyrrolidine 930-55-2 8.00E-02 1.01E-05 1.20e-08 1.00e+06

N-Nitroso-di-n-propylamine 621-64-7 5.64E-02 7.76E-06 2.25e-06 9.89e+03

Naphthalene 91-20-3 6.05E-02 8.38E-06 4.83e-04 3.10e+01

Nitrobenzene 98-95-3 6.81E-02 9.45E-06 2.40e-05 2.09e+03

Nitropropane, 2- 79-46-9 8.47E-02 1.02E-05 1.23e-04 1.70e+04

Pentachlorodibenzo-p-dioxins

(PeCDDs) 36088-22-9 0.0447j 4.38E-06b 2.60e-06d 1.18e-04d

Pentachlorodibenzofurans (PeCDFs) 30402-15-4 4.57E-02j 4.51E-06b 5.00e-06d 2.40e-04d

Pentachlorophenol 87-86-5 2.95E-02 8.01E-06 2.44e-08 1.95e+03

Phenol 108-95-2 8.34E-02 1.03E-05 3.97e-07 8.28e+04

Phthalic anhydride 85-44-9 5.95E-02 9.75E-06 1.63e-08 6.20e+03

Polychlorinated biphenyls (Aroclors) 1336-36-3 2.33E-02 5.98E-06 2.60e-03 7.00e-02

Propylene oxide (1,2-epoxypropane) 75-56-9 1.10E-01 1.21E-05 1.23e-04f 4.05e+05f

Pyridine 110-86-1 9.31E-02 1.09E-05 8.88e-06 1.00e+06

Styrene 100-42-5 7.13E-02 8.81E-06 2.75e-03 3.10e+02

Tetrachlorodibenzo-p-dioxin, 2,3,7,8-

(2,3,7,8-TCDD) 1746-01-6 4.70E-02j 4.68E-06b 3.29e-05d 1.93e-05d

Tetrachlorodibenzofurans (TCDFs)* 55722-27-5 4.82E-02j 4.84E-06b 1.40e-05d 4.20e-04d

Tetrachloroethane, 1,1,2,2- 79-34-5 4.89E-02 9.29E-06 3.45e-04 2.97e+03

Tetrachloroethane, 1,1,1,2- 630-20-6 4.82E-02 9.10E-06 2.42e-03 1.10e+03

Tetrachloroethylene 127-18-4 5.05E-02 9.45E-06 1.84e-02 2.00e+02
Table E-2. Constituent-specific Chemical and Physical Properties (continued)

IWEM Technical Background Document Appendix E

Constituent CASRN

Da

(cm2/s)

(a)

Dw

(cm2/s)

(a)

HLC 

(atmm3

/mol)

(c)

Sol

(mg/L)

(c)

E-26

Toluene 108-88-3 0.078 0 6.64e-03 5.26e+02

Toluenediamine 2,4- 95-80-7 7.72E-02b 8.94E-06b 7.92e-10 3.37e+04

Toluidine, o- 95-53-4 0.0724 0 2.72e-06 1.66e+04

Toxaphene (chlorinated camphenes) 8001-35-2 0.0216 0 6.00e-06 7.40e-01

Tribromomethane (bromoform) 75-25-2 3.58E-02 1.04E-05 5.35e-04 3.10e+03

Trichloro-1,2,2-trifluoro-ethane, 1,1,2- 76-13-1 3.76E-02 8.59E-06 4.81e-01 1.70e+02

Trichlorobenzene, 1,2,4- 120-82-1 3.96E-02 8.40E-06 1.42e-03 3.46e+01

Trichloroethane, 1,1,2- 79-00-5 6.69E-02 1.00E-05 9.13e-04 4.42e+03

Trichloroethane, 1,1,1- 71-55-6 6.48E-02 9.60E-06 1.72e-02 1.33e+03

Trichloroethylene (TCE) 79-01-6 6.87E-02 1.02E-05 1.03e-02 1.10e+03

Trichlorofluoromethane (Freon 11) 75-69-4 6.55E-02 1.01E-05 9.70e-02 1.10e+03

Trichlorophenol, 2,4,6- 88-06-2 3.14E-02 8.09E-06 7.79e-06 8.00e+02

Trichloropropane, 1,2,3- 96-18-4 5.75E-02 9.24E-06 4.09e-04 1.75e+03

Triethylamine 121-44-8 6.63E-02 7.84E-06 1.38e-04f 5.50e+04f

Vinyl acetate 108-05-4 8.51E-02 1.00E-05 5.11e-04 2.00e+04

Vinyl chloride 75-01-4 1.07E-01 1.20E-05 2.70e-02 2.76e+03

Xylene, p- 106-42-3 6.84E-02 8.45E-06 7.66e-03 1.85e+02

Xylene, o- 95-47-6 6.91E-02 8.56E-06 5.19e-03 1.78e+02

Xylene, m- 108-38-3 6.85E-02 8.47E-06 7.34e-03 1.61e+02

Xylenes (total) 1330-20-7 0.0687 0 6.73e-03 1.75e+02

Da = air diffusivity; Dw = water diffusivity; HLC = Henry’s law constant; Sol = aqueous solubility

CASRN = Chemical Abstract Service Registry Number

* Values used for 2,3,7,8-tetrachlorodibenzofuran (CAS #51207-31-9).

Data Sources:

a Calculated based on WATER9 (U.S. EPA, 2001). b Calculated based on U.S. EPA, 1987. c SCDM (U.S. EPA, 1997b). d U.S. EPA, 2000. e Calculated based on Lyman, Reehl, and Rosenblatt, 1990. f CHEMFATE (SRC, 1999). g ChemFinder.com (CambridgeSoft Corporation, 2001). h The Merck Index (Budavari, 1996). i HSDB (U.S. NLM, 2001).

j Calculated based on U.S. EPA, 2000. k U.S. EPA, 1997a.
IWEM Technical Background Document Appendix E

E-27

E-2.6 References for Section E-2

Budavari, S. (ed), 1996. The Merck Index: An Encyclopedia of Chemicals, Drugs, and

Biologicals. 12th edition. Whitehouse Station, NJ: Merck and Co. 

CambridgeSoft Corporation, 2001. ChemFinder.com database and internet searching.

http://chemfinder.cambridgesoft.com. Accessed July 2001.

Lyman, W.J., W.F. Reehl, and D.H. Rosenblatt, 1990. Handbook of Chemical Property

Estimation Methods: Environmental Behavior of Organic Compounds. 

Washington, DC: American Chemical Society.

Syracuse Research Corporation (SRC), 1999. CHEMFATE Chemical Search,

Environmental Science Center, Syracuse, NY. 

http://esc.syrres.com/efdb/Chemfate.htm. Accessed July 2001.

U.S. EPA, 1987. Process Coefficients and Models for Simulating Toxic Organics and

Heavy Metals in Surface Waters. Office of Research and Development. 

Washington, DC: U.S. Government Printing Office (GPO).

U.S. EPA, 1997a. Mercury Study Report to Congress. Volume IV: An Assessment of

Exposure to Mercury in the United States. EPA-452/R-97-006. Office of Air

Quality Planning and Standards and Office of Research and Development.

Washington, DC: GPO.

U.S. EPA, 1997b. Superfund Chemical Data Matrix (SCDM). SCDMWIN 1.0 (SCDM

Windows User’s Version), Version 1. Office of Solid Waste and Emergency

Response, Washington DC: GPO. 

http://www.epa.gov/superfund/resources/scdm/index.htm. Accessed July 2001.

U.S. EPA, 2000. Exposure and Human Health Reassessment of 2,3,7,8-

Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds, Part 1, Vol. 3. 

Office of Research and Development, Washington, DC: GPO. 

U.S. EPA, 2001. WATER9. Office of Air Quality Planning and Standards, Research

Triangle Park, NC. http://www.epa.gov/ttn/chief/software/water/index.html. 

Accessed July 2001.

U.S. NLM (U.S. National Library of Medicine), 2001. Hazardous Substances Data Bank

(HSDB). http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen/HSDB. Accessed July

2001.
IWEM Technical Background Document Appendix E

E-28

E-3 Human Health Benchmarks used in the IWEM Tool

Human health benchmarks for chronic oral and inhalation exposures are an

important component of the IWEM 1 tool. The EPA uses reference doses (RfDs) and

reference concentrations (RfCs) to evaluate noncancer risk from oral and inhalation

exposures, respectively. Oral cancer slope factors (CSFs), inhalation unit risk factors

(URFs), and inhalation CSFs are used to evaluate risk for carcinogens.

This section provides the toxicity benchmarks we used to develop the HBNs that

we will use in developing Reference Ground-Water Concentrations for IWEM. Section

E-3.1 describes the data sources and general hierarchy used to collect these benchmarks. 

Section E-3.2 provides the benchmarks along with discussions of individual human

health benchmarks extracted from a variety of sources.

E-3.1 Methodology and Data Sources

Several sources of health benchmarks are available. Human health benchmarks

were obtained from these sources in the following order of preference:

# Integrated Risk Information System (IRIS)

# Superfund Technical Support Center Provisional Benchmarks

# Health Effects Assessment Summary Tables (HEAST)

# Agency for Toxic Substances and Disease Registry (ATSDR) minimal risk

levels (MRLs)

# California Environmental Protection Agency (CalEPA) chronic inhalation

reference exposure levels (RELs) and cancer potency factors.

# EPA health assessment documents

# Various other EPA health benchmark sources.

For dioxins and dibenzofurans, World Health Organization (WHO) toxicity equivalency

factors (TEFs) from Van den Berg et al. (1998) were applied to the oral and inhalation

CSF for 2,3,7,8-TCDD to obtain CSFs for all other dioxins and furans (see Section E3.2.4). 

E-3.1.1 Integrated Risk Information System (IRIS)

Benchmarks in IRIS are prepared and maintained by EPA, and values from IRIS

were used to develop HBNs for the IWEM tool whenever IRIS benchmarks were

available. IRIS is EPA’s electronic database containing information on human health

effects (U.S. EPA, 2001a). Each chemical file contains descriptive and quantitative

information on potential health effects. Health benchmarks for chronic noncarcinogenic

health effects include RfDs and RfCs. Cancer classification, oral CSFs, and inhalation
IWEM Technical Background Document Appendix E

E-29

URFs are included for carcinogenic effects. IRIS is the official repository of Agencywide consensus of human health risk information. 

Inhalation CSFs are not available from IRIS, so they were calculated from

inhalation URFs (which are available from IRIS) using the following equation:

In this equation, 70 kg represents average body weight; 20 m3/d represents average

inhalation rate; and 1000 :g/mg is a units conversion factor (U.S. EPA, 1997). These

standard estimates of body weight and inhalation rate are used by EPA in the calculation

of the URF, and, therefore, the values were used to calculate inhalation CSFs.

E-3.1.2 Superfund Provisional Benchmarks

The Superfund Technical Support Center (EPA’s National Center for

Environmental Assessment [NCEA]) derives provisional RfCs, RfDs, and CSFs for

certain chemicals. These provisional health benchmarks can be found in Risk

Assessment Issue Papers. Some of the provisional values have been externally peer

reviewed, and some (e.g., trichloroethylene, tetrachloroethylene) come from previously

published EPA Health Assessment Documents. These provisional values have not

undergone EPA’s formal review process for finalizing benchmarks and do not represent

Agency-wide consensus information. Specific provisional values used in the IWEM tool

are described in Section E-3.2.5. 

E-3.1.3 Health Effects Summary Tables (HEAST)

HEAST is a listing of provisional noncarcinogenic and carcinogenic health

toxicity values (RfDs, RfCs, URFs, and CSFs) derived by EPA (U.S. EPA, 1997). 

Although the health toxicity values in HEAST have undergone review and have the

concurrence of individual EPA program offices, either they have not been reviewed as

extensively as those in IRIS or their data set is not complete enough to be listed in IRIS. 

HEAST benchmarks have not been updated in several years and do not represent

Agency-wide consensus information.

E-3.1.4 ATSDR Minimal Risk Levels

The ATSDR MRLs are substance-specific health guidance levels for

noncarcinogenic endpoints (ATSDR, 2001). An MRL is an estimate of the daily human

exposure to a hazardous substance that is likely to be without appreciable risk of adverse

noncancer health effects over a specified duration of exposure. MRLs are based on

noncancer health effects only and are not based on a consideration of cancer effects. 
IWEM Technical Background Document Appendix E

E-30

MRLs are derived for acute, intermediate, and chronic exposure durations for oral and

inhalation routes of exposure. Inhalation and oral MRLs are derived in a manner similar

to EPA’s RfCs and RfDs, respectively (i.e., ATSDR uses the no-observed-adverse-effectlevel/uncertainty factor (NOAEL/UF) approach); however, MRLs are intended to serve

as screening levels and are exposure duration-specific. Also, ATSDR uses EPA’s 1994

inhalation dosimetry methodology in the derivation of inhalation MRLs. A chronic

inhalation MRL for mixed xylenes was used as a surrogate for each of the xylene

isomers.

E-3.1.5 CalEPA Cancer Potency Factors and Reference Exposure Levels 

CalEPA has developed cancer potency factors for chemicals regulated under

California’s Hot Spots Air Toxics Program (CalEPA, 1999a). The cancer potency factors

are analogous to EPA’s oral and inhalation CSFs. CalEPA has also developed chronic

inhalation RELs, analogous to EPA’s RfC, for 120 substances (CalEPA, 1999b, 2000). 

CalEPA used EPA’s 1994 inhalation dosimetry methodology in the derivation of

inhalation RELs. The cancer potency factors and inhalation RELs have undergone

internal peer review by various California agencies and have been the subject of public

comment. A chronic inhalation REL for mixed cresols was used as a surrogate for each

of the cresol isomers.

E-3.1.6 Other EPA Health Benchmarks

EPA has also derived health benchmark values in other risk assessment

documents, such as Health Assessment Documents (HADs), Health Effect Assessments

(HEAs), Health and Environmental Effects Profiles (HEEPs), Health and Environmental

Effects Documents (HEEDs), Drinking Water Criteria Documents, and Ambient Water

Quality Criteria Documents. Evaluations of potential carcinogenicity of chemicals in

support of reportable quantity adjustments were published by EPA’s Carcinogen

Assessment Group (CAG) and may include cancer potency factor estimates. Health

toxicity values identified in these EPA documents are usually dated and are not

recognized as Agency-wide consensus information or verified benchmarks, however, and

as a result they are used in the hierarchy only when values are not available from IRIS,

HEAST, Superfund provisional values, ATSDR, or CalEPA. Section E-3.2.6 describes

the specific values from these alternative EPA sources that were used in the IWEM tool.
IWEM Technical Background Document Appendix E

E-31

E-3.2 Human Health Benchmark Values

The chronic human health benchmarks used to calculate the HBNs in the IWEM

tool are summarized in Table E-3, which provides the Chemical Abstract Service

Registry Number (CASRN), constituent name, RfD (mg/kg-d), RfC (mg/m3), oral CSF

(mg/kg-d-1), inhalation URF [(:g/m3)

-1], inhalation CSF (mg/kg-d-1), and reference for

each benchmark. A key to the references cited and abbreviations used is provided at the

end of the table.

For a majority of the IWEM constituents, human health benchmarks were

available from IRIS (U.S. EPA, 2001a), Superfund Provisional Benchmarks, or HEAST

(U.S. EPA, 1997). Benchmarks also were obtained from ATSDR (2001) or CalEPA

(1999a, 1999b, 2000). This section describes benchmarks obtained from other sources,

along with the Superfund Provisional values and special uses (e.g., benzene, vinyl

chloride) of IRIS benchmarks.
E-32

Table E-3. Human Health Benchmark Values Constituent Name CASRN RfD (mg/kg-d) RfD Ref CSFo (per mg/kg-d) CSFo Ref RfC (mg/m3) RfC Ref URF (per :g/m3) URF Ref 

Acenaphthene 83-32-9 6.0E-02 I Acetaldehyde (ethanal) 75-07-0 9.0E-03 I 2.2E-06 I Acetone (2-propanone) 67-64-1 1.0E-01 I 3.1E+01 A Acetonitrile (methyl cyanide) 75-05-8 6.0E-02 I Acetophenone 98-86-2 1.0E-01 I Acrolein 107-02-8 2.0E-02 H 2.0E-05 I Acrylamide 79-06-1 2.0E-04 I 4.5E+0 I 1.3E-03 I Acrylic acid (propenoic acid) 79-10-7 5.0E-01 I 1.0E-03 I Acrylonitrile 107-13-1 1.0E-03 H 5.4E-1 I 2.0E-03 I 6.8E-05 I Aldrin 309-00-2 3.0E-05 I 1.7E+01 I 4.9E-03 I Allyl alcohol 107-18-6 5.0E-03 I Aniline (benzeneamine) 62-53-3 5.7E-3 I 1.0E-03 I 1.6E-06 C99a Anthracene 120-12-7 3.0E-01 I Antimony 7440-36-0 4.0E-04 I Arsenic 7440-38-2 3.0E-04 I 1.5E+00 I Barium 7440-39-3 7.0E-02 I Benz{a}anthracene 56-55-3 1.2E+00 C99a 1.1E-04 C99a Benzene 71-43-2 5.5E-02 I 6.0E-02 C00 7.8E-06 I Benzidine 92-87-5 3.0E-03 I 2.3E+02 I 6.7E-02 I Benzo{a}pyrene 50-32-8 7.3E+00 I 1.1E-03 C99a Benzo{b}fluoranthene 205-99-2 1.2E+00 C99a 1.1E-04 C99a Benzyl chloride 100-44-7 1.7E-01 I 4.9E-05 C99a Benzyl alcohol 100-51-6 3.0E-01 H Beryllium 7440-41-7 2.0E-03 I Bis(2-chloroethyl)ether 111-44-4 1.1E+00 I 3.3E-04 I 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-33

Bis(2-chloroisopropyl)ether 39638-32-9 4.0E-02 I 7.0E-02 H 1.0E-05 H Bis(2-ethylhexyl)phthalate 117-81-7 2.0E-02 I 1.4E-02 I 1.0E-02 C99b 2.4E-06 C99a Bromodichloromethane 75-27-4 2.0E-02 I 6.2E-02 I 1.8E-05 AC Bromomethane (methyl bromide) 74-83-9 1.4E-03 I 5.0E-03 I Butadiene, 1,3- 106-99-0 2.0E-02 C00 2.8E-04 I Butanol 71-36-3 1.0E-01 I Butyl benzyl phthalate 85-68-7 2.0E-01 I Butyl-4,6-dinitrophenol,2-sec- (Dinoseb) 88-85-7 1.0E-03 I Cadmium 7440-43-9 5.0E-04 I Carbon tetrachloride 56-23-5 7.0E-04 I 1.3E-01 I 7.0E-03 SF 1.5E-05 I Carbon disulfide 75-15-0 1.0E-01 I 7.0E-01 I Chlordane 57-74-9 5.0E-04 I 3.5E-01 I 7.0E-04 I 1.0E-04 I Chloro-1,3-butadiene, 2- (Chloroprene) 126-99-8 2.0E-02 H 7.0E-03 H Chloroaniline, p- 106-47-8 4.0E-03 I Chlorobenzene 108-90-7 2.0E-02 I 6.0E-02 SF Chlorobenzilate 510-15-6 2.0E-02 I 2.7E-01 H 7.8E-05 H Chlorodibromomethane 124-48-1 2.0E-02 I 8.4E-02 I 2.4E-05 AC Chloroethane (ethyl chloride) 75-00-3 1.0E+01 I Chloroform 67-66-3 1.0E-02 I 1.0E-01 A Chloromethane (methyl chloride) 74-87-3 1.3E-02 H 9.0E-02 I 1.8E-06 H Chlorophenol, 2- 95-57-8 5.0E-03 I 1.4E-03 AC
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-34

Chloropropene, 3- (allyl chloride) 107-05-1 1.0E-03 I 6.0E-06 C99a Chromium (III) 16065-83-1 1.5E+00 I Chromium (VI) 18540-29-9 3.0E-03 I Chrysene 218-01-9 1.2E-01 C99a 1.1E-05 C99a Cobalt 7440-48-4 2.0E-02 SF Copper 7440-50-8 (only a drinking water action level is available for this metal) Cresol, p- 106-44-5 5.0E-03 H 6.0E-01 surr (C00) Cresol, o- 95-48-7 5.0E-02 I 6.0E-01 surr (C00) Cresol, m- 108-39-4 5.0E-02 I 6.0E-01 surr (C00) Cresols (total) 1319-77-3 5.0E-02 surr (I) 6.0E-01 C00 Cumene 98-82-8 1.0E-01 I 4.0E-01 I Cyclohexanol 108-93-0 1.7E-05 solv 2.0E-05 solv Cyclohexanone 108-94-1 5.0E+00 I DDD 72-54-8 2.4E-01 I DDE 72-55-9 3.4E-01 I DDT, p,p'- 50-29-3 5.0E-04 I 3.4E-01 I 9.7E-05 I Di-n-butyl phthalate 84-74-2 1.0E-01 I Di-n-octyl phthalate 117-84-0 2.0E-02 H Diallate 2303-16-4 6.1E-02 H Dibenz{a,h}anthracene 53-70-3 7.3E+00 TEF 1.2E-03 C99a Dibromo-3-chloropropane, 1,2- 96-12-8 1.4E+0 H 2.0E-04 I 6.9E-07 H 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-35E-35

Dichlorobenzene, 1,2- 95-50-1 9.0E-02 I 2.0E-01 HDichlorobenzene, 1,4- 106-46-7 2.4E-2 H 8.0E-01 I 1.1E-05 C99a Dichlorobenzidine, 3,3'- 91-94-1 4.5E-01 I 3.4E-04 C99a Dichlorodifluoromethane(Freon 12)

75-71-8 2.0E-01 I 2.0E-01 H

Dichloroethane, 1,2- 107-06-2 9.1E-2 I 2.4E+00 A 2.6E-05 I Dichloroethane, 1,1- 75-34-3 1.0E-01 H 5.0E-01 H 1.6E-06 C99a Dichloroethylene, 1,1- 75-35-4 9.0E-03 I 6.0E-1 I 7.0E-02 C00 5.0E-05 I Dichloroethylene, trans-1,2- 156-60-5 2.0E-02 I

Dichloroethylene, cis-1,2- 156-59-2 1.0E-02 HDichlorophenol, 2,4- 120-83-2 3.0E-03 IDichlorophenoxyacetic acid,2,4- (2,4-D)

94-75-7 1.0E-02 I

Dichloropropane, 1,2- 78-87-5 9.0E-02 A 6.8E-2 H 4.0E-03 IDichloropropene, trans-1,3- 10061-02-6 3.0E-02 I 1.0E-1 I 2.0E-02 surr (I) 4.0E-06 surr (I) 

Dichloropropene, cis-1,3- 10061-01-5 3.0E-02 I 1.0E-1 I 2.0E-02 surr (I) 4.0E-06 surr (I) 

Dichloropropene, 1,3- (mixtureof isomers)

542-75-6 3.0E-02 I 1.0E-01 I 2.0E-02 I 4.0E-06 I 

Dieldrin 60-57-1 5.0E-05 I 1.6E+01 I 4.6E-03 I Diethyl phthalate 84-66-2 8.0E-01 IDiethylstilbestrol 56-53-1 4.7E+03 HDimethoate 60-51-5 2.0E-04 IDimethoxybenzidine, 3,3'- 119-90-4 1.4E-02 HDimethyl formamide, N,N-(DMF)

68-12-2 1.0E-01 H 3.0E-02 I

Dimethylbenz{a}anthracene,7,12-

57-97-6 7.1E-02 C99a 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

Dimethylbenzidine, 3,3'- 119-93-7 9.2E+00 HDimethylphenol, 2,4- 105-67-9 2.0E-02 IDinitrobenzene, 1,3- 99-65-0 1.0E-04 IDinitrophenol, 2,4- 51-28-5 2.0E-03 IDinitrotoluene, 2,6- 606-20-2 1.0E-03 H 6.8E-01 surr (I)Dinitrotoluene, 2,4- 121-14-2 2.0E-03 I 6.8E-01 surr (I) 8.9E-05 C99a Dioxane, 1,4- 123-91-1 1.1E-2 I 3.0E+00 C00 7.7E-06 C99a Diphenylamine 122-39-4 2.5E-02 IDiphenylhydrazine, 1,2- 122-66-7 8.0E-1 I 2.2E-04 I Disulfoton 298-04-4 4.0E-05 IEndosulfan (Endosulfan I andII,mixture)

115-29-7 6.0E-03 I

Endrin 72-20-8 3.0E-04 IEpichlorohydrin 106-89-8 2.0E-03 H 9.9E-3 I 1.0E-03 I 1.2E-06 I Epoxybutane, 1,2- 106-88-7 2.0E-02 IEthoxyethanol acetate, 2- 111-15-9 3.0E-01 H 3.0E-01 C00Ethoxyethanol, 2- 110-80-5 4.0E-01 H 2.0E-01 IEthyl acetate 141-78-6 9.0E-01 IEthyl ether 60-29-7 2.0E-01 IEthyl methacrylate 97-63-2 9.0E-02 HEthyl methanesulfonate 62-50-0 2.9E+02 RQEthylbenzene 100-41-4 1.0E-01 I 1.0E+00 I 1.1E-06 SF Ethylene oxide 75-21-8 1.0E+0 H 3.0E-02 C00 1.0E-04 H Ethylene dibromide (1,2-dibromoethane)

106-93-4 8.5E+1 I 2.0E-04 H 2.2E-04 I 

Ethylene glycol 107-21-1 2.0E+00 I 4.0E-01 C00
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-37

Ethylene thiourea 96-45-7 8.0E-05 I 1.1E-01 H 1.3E-05 C99a Fluoranthene 206-44-0 4.0E-02 I Fluoride 16984-48-8 0.12 surr (I) Formaldehyde 50-00-0 2.0E-01 I 9.8E-03 A 1.3E-05 I Formic acid 64-18-6 2.0E+00 H Furfural 98-01-1 3.0E-03 I 5.0E-02 H HCH, beta- 319-85-7 1.8E+00 I 5.3E-04 I HCH, gamma- (Lindane) 58-89-9 3.0E-04 I 1.3E+00 H 3.1E-04 C99a HCH, alpha- 319-84-6 8.0E-03 A 6.3E+00 I 1.8E-03 I Heptachlor 76-44-8 5.0E-04 I 4.5E+00 I 1.3E-03 I Heptachlor epoxide 1024-57-3 1.3E-05 I 9.1E+00 I 2.6E-03 I Hexachloro-1,3-butadiene 87-68-3 3.0E-04 SF 7.8E-2 I 2.2E-05 I Hexachlorobenzene 118-74-1 8.0E-04 I 1.6E+0 I 4.6E-04 I Hexachlorocyclopentadiene 77-47-4 6.0E-03 I 2.0E-04 I Hexachlorodibenzo-p-dioxins (HxCDDs) 34465-46-8 1.56E+04 WHO98 3.3E+00 WHO98 Hexachlorodibenzofurans (HxCDFs) 55684-94-1 1.56E+04 WHO98 3.3E+00 WHO98 Hexachloroethane 67-72-1 1.0E-03 I 1.4E-02 I 4.0E-06 I Hexachlorophene 70-30-4 3.0E-04 I Hexane, n- 110-54-3 1.1E+01 SF 2.0E-01 I Hydrogen Sulfide 7783-06-4 3.0E-03 I Indeno{1,2,3-cd}pyrene 193-39-5 1.2E+00 C99a 1.1E-04 C99a Isobutyl alcohol 78-83-1 3.0E-01 I Isophorone 78-59-1 2.0E-01 I 9.5E-04 I 2.0E+00 C99b Kepone 143-50-0 5.0E-04 A
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-38

Lead 7439-92-1 (only a drinking water action level is available for this metal) Manganese 7439-96-5 4.7E-02 I Mercury 7439-97-6 1.0E-04 surr (I) 3.0E-04 I Methacrylonitrile 126-98-7 1.0E-04 I 7.0E-04 H Methanol 67-56-1 5.0E-01 I 4.0E+00 C00 Methoxychlor 72-43-5 5.0E-03 I Methoxyethanol, 2- 109-86-4 1.0E-03 H 2.0E-02 I Methoxyethanol acetate, 2- 110-49-6 2.0E-03 H 9.0E-02 C00 Methyl parathion 298-00-0 2.5E-04 I Methyl methacrylate 80-62-6 1.4E+00 I 7.0E-01 I Methyl isobutyl ketone 108-10-1 8.0E-02 H 8.0E-02 H Methyl ethyl ketone 78-93-3 6.0E-01 I 1.0E+00 I Methyl tert-butyl ether (MTBE) 1634-04-4 3.0E+00 I Methylcholanthrene, 3- 56-49-5 6.3E-03 C99a Methylene bromide (dibromomethane) 74-95-3 1.0E-02 H Methylene Chloride (dichloromethane) 75-09-2 6.0E-02 I 7.5E-03 I 3.0E+00 H 4.7E-07 I Molybdenum 7439-98-7 5.0E-03 I N-Nitroso-di-n-butylamine 924-16-3 5.4E+00 I 1.6E-03 I N-Nitroso-di-n-propylamine 621-64-7 7.0E+00 I 2.0E-03 C99a N-Nitrosodiethylamine 55-18-5 1.5E+02 I 4.3E-02 I N-Nitrosodimethylamine 62-75-9 8.00E-06 SF 5.1E+01 I 1.4E-02 I N-Nitrosodiphenylamine 86-30-6 2.00E-02 SF 4.9E-03 I 2.6E-06 C99a N-Nitrosomethylethylamine 10595-95-6 2.2E+01 I 6.3E-03 C99a 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-39

N-Nitrosopiperidine 100-75-4 2.7E-03 C99a N-Nitrosopyrrolidine 930-55-2 2.1E+00 I 6.1E-04 I Naphthalene 91-20-3 2.0E-02 I 3.0E-03 I Nickel 7440-02-0 2.0E-02 I Nitrobenzene 98-95-3 5.0E-04 I 2.0E-03 H Nitropropane, 2- 79-46-9 2.0E-02 I 2.7E-03 H Octamethyl pyrophosphoramide 152-16-9 2.0E-03 H Parathion (ethyl) 56-38-2 6.0E-03 H Pentachlorobenzene 608-93-5 8.0E-04 I Pentachlorodibenzo-p-dioxins (PeCDDs) 36088-22-9 1.56E+05 WHO98 3.3E+01 WHO98 Pentachlorodibenzofurans (PeCDFs) 30402-15-4 7.8E+04 WHO98 1.7E+01 WHO98 Pentachloronitrobenzene (PCNB) 82-68-8 3.0E-03 I 2.6E-01 H Pentachlorophenol 87-86-5 3.0E-02 I 1.2E-01 I 5.1E-06 C99a Phenol 108-95-2 6.0E-01 I 2.0E-01 C00 Phenyl mercuric acetate 62-38-4 8.0E-05 I Phenylenediamine, 1,3- 108-45-2 6.0E-03 I Phorate 298-02-2 2.0E-04 H Phthalic anhydride 85-44-9 2.0E+00 I 1.2E-01 H Polychlorinated biphenyls (Aroclors) 1336-36-3 2.0E-05 surr (I) 4.0E-01 I 1.0E-04 I Pronamide 23950-58-5 7.5E-02 I Propylene oxide (1,2- epoxypropane) 75-56-9 2.4E-01 I 3.0E-02 I 3.7E-06 I 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-40E-40

Pyrene 129-00-0 3.0E-02 IPyridine 110-86-1 1.0E-03 I 7.0E-03 EPA86Safrole 94-59-7 1.8E-01 RQSelenium 7782-49-2 5.0E-03 ISilver 7440-22-4 5.0E-03 IStrychnine and salts 57-24-9 3.0E-04 IStyrene 100-42-5 2.0E-01 I 1.0E+00 ITetrachlorobenzene, 1,2,4,5- 95-94-3 3.0E-04 ITetrachlorodibenzo-p-dioxin,2,3,7,8-(2,3,7,8-TCDD)

1746-01-6 1.56E+05 DA85 3.3E+01 H 

Tetrachlorodibenzofuran,2,3,7,8- (2,3,7,8-TCDF)

51207-31-9 1.56E+04 WHO98 3.3E+00 WHO98 

Tetrachloroethane, 1,1,2,2- 79-34-5 6.0E-02 SF 2.0E-01 I 5.8E-05 I Tetrachloroethane, 1,1,1,2- 630-20-6 3.0E-02 I 2.6E-02 I 7.4E-06 I Tetrachloroethylene 127-18-4 1.0E-02 I 5.2E-02 HAD 3.0E-01 A 5.8E-07 HAD Tetrachlorophenol, 2,3,4,6- 58-90-2 3.0E-02 ITetraethyl dithiopyrophosphate(Sulfotep)

3689-24-5 5.0E-04 I

Thallium 7440-28-0 8.0E-05 surr (I)Thiram (Thiuram) 137-26-8 5.0E-03 IToluene 108-88-3 2.0E-01 I 4.0E-01 IToluenediamine, 2,4- 95-80-7 3.2E+00 H 1.1E-03 C99a Toluidine, o- 95-53-4 2.4E-01 H 6.9E-05 AC Toluidine, p- 106-49-0 1.9E-01 HToxaphene (chlorinatedcamphenes)

8001-35-2 1.1E+00 I 3.2E-04 I 
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

E-41

Tribromomethane (bromoform) 75-25-2 2.0E-02 I 7.9E-03 I 1.1E-06 I Trichloro-1,2,2- trifluoroethane, 1,1,2- 76-13-1 3.0E+01 I 3.0E+01 H Trichlorobenzene, 1,2,4- 120-82-1 1.0E-02 I 2.0E-01 H Trichloroethane, 1,1,1- 71-55-6 2.8E-01 SF 2.2E+00 SF Trichloroethane, 1,1,2- 79-00-5 4.0E-03 I 5.7E-02 I 1.6E-05 I Trichloroethylene (1,1,2- trichloroethylene) 79-01-6 1.1E-02 HAD 6.0E-01 C00 1.7E-06 HAD Trichlorofluoromethane (Freon 11) 75-69-4 3.0E-01 I 7.0E-01 H Trichlorophenol, 2,4,5- 95-95-4 1.0E-01 I Trichlorophenol, 2,4,6- 88-06-2 1.1E-02 I 3.1E-06 I Trichlorophenoxy)propionic acid, 2-(2,4,5- (Silvex) 93-72-1 8.0E-03 I Trichlorophenoxyacetic acid, 2,4,5- 93-76-5 1.0E-02 I Trichloropropane, 1,2,3- 96-18-4 6.0E-03 I 7.0E+00 H 5.0E-03 SF Triethylamine 121-44-8 7.0E-03 I Trinitrobenzene, sym- (1,3,5-Trinitrobenzene) 99-35-4 3.0E-02 I Tris(2,3- dibromopropyl)phosphate 126-72-7 9.8E+00 RQ Vanadium 7440-62-2 7.0E-03 H Vinyl acetate 108-05-4 1.0E+00 H 2.0E-01 I Vinyl chloride 75-01-4 3.0E-03 I 7.2E-01 I 1.0E-01 I 4.4E-06 I Xylene, p- 106-42-3 2.0E+00 surr (H) 4.0E-01 surr (A)
Table E-3. Human Health Benchmark Values (continued)

Constituent Name CASRN

RfD

(mg/kg-d) RfD Ref

CSFo 

(per

mg/kg-d)

CSFo

Ref

RfC

(mg/m3) RfC Ref

URF

(per

:g/m3) URF Ref

Xylene, m- 108-38-3 2.0E+00 H 4.0E-01 surr (A)Xylene, o- 95-47-6 2.0E+00 H 4.0E-01 surr (A)Xylenes (total) 1330-20-7 2.0E+00 I 4.0E-01 AZinc 7440-66-6 3.0E-01 I

Key:CASRN = Chemical Abstract Service registry number. RfD = reference dose.CSFo = oral cancer slope factor. RfC = reference concentration.CSFi = inhalation cancer slope factor. URF = unit risk factor.a Sources:

A = ATSDR MRLs (ATSDR, 2001) H = HEAST (U.S. EPA, 1997)AC = developed for the Air Characteristic Study (U.S. EPA, 1999g) I = IRIS (U.S. EPA, 2001a)calc = calculated RQ = reportable quantity adjustments (U.S. EPA, 1998d

SF = Superfund Risk Issue Paper (U.S. EPA, 1998a,b; 1

2001b,c,d)

C99a = CalEPA cancer potency factor (CalEPA, 1999a) solv = 63 FR 64371-0402 (U.S. EPA, 1998c)C99b = CalEPA chronic REL (CalEPA, 1999b) surr = surrogate (source in parentheses; see section C.2.8C00 = CalEPA chronic REL (CalEPA, 2000) TEF = toxicity equivalency factor (U.S. EPA, 1993)DA85 = Dioxin Assessment (U.S. EPA, 1985) WHO98 = World Health Organization (WHO) 1998 toxicity 

scheme (Van den Berg et al., 1998)

EPA86 = Pyridine Health Effects Profile (U.S. EPA, 1986b)HAD = Health Assessment Document (U.S. EPA, 1986a, 1987)
IWEM Technical Background Document Appendix E

 1A twofold increase of the oral CSF to 1.4 per mg/kg-d to account for continuous

lifetime exposure from birth was also recommended but was not used for IWEM.

 2

A twofold increase to 8.8E-6 per :g/m3 for the inhalation URF, to account for

continuous lifetime exposure from birth, was also recommended but was not used for

IWEM.

E-43

E-3.2.1 Benzene

The cancer risk estimates for benzene are provided as ranges in IRIS. The oral

CSF for benzene is 1.5E-02 to 5.5E-02 (mg/kg/d)-1 and the inhalation URF is 2.2E-06 to

7.8E-06 (μg/m3)

-1 (U.S. EPA, 2001a). For IWEM, the upper range estimates were used

(i.e., 5.5E-02 (mg/kg/d)-1 and 7.8E-06 (μg/m3

)

-1 for the oral CSF and inhalation URF,

respectively).

E-3.2.2 Vinyl Chloride

Based on use of the linearized multistage model, IRIS recommends an oral CSF

of 7.2E-1 per mg/kg-d for vinyl chloride to account for continuous lifetime exposure

during adulthood; this value was used in the IWEM tool.1 Based on use of the linearized

multistage model, an inhalation URF of 4.4E-6 per :g/m3 to account for continuous,

lifetime exposure during adulthood was recommended for vinyl chloride and was used

for IWEM; an inhalation CSF of 1.5E-2 per mg/kg-d was calculated from the URF.2

E-3.2.3 Polychlorinated Biphenyls

There are two inhalation CSFs available from IRIS for polychlorinated biphenyls

(PCBs): 0.4 per mg/kg-d for evaporated congeners and 2.0 per mg/kg-d for dust or

aerosol (high risk and persistence). The inhalation CSF for evaporated congeners was

used for IWEM.

E-3.2.4 Dioxin-like Compounds

Certain polychlorinated dibenzodioxin, polychlorinated dibenzofuran, and

polychlorinated biphenyl (PCB) congeners are said to have “dioxin-like” toxicity,

meaning that they are understood to have toxicity similar to that of 2,3,7,8-

tetrachlorodibenzo(p)dioxin (2,3,7,8-TCDD). Although EPA has not developed health

benchmarks for each specific compound with dioxin-like toxicity, these compounds have

been assigned individual “toxicity equivalency factors” (TEFs; Van den Berg et al.,

1998). TEFs are estimates of the toxicity of dioxin-like compounds relative to the

toxicity of 2,3,7,8-TCDD, which is assigned a TEF of 1.0. TEF estimates are based on a
IWEM Technical Background Document Appendix E

E-44

knowledge of a constituent’s mechanism of action, available experimental data, and other

structure-activity information. We used the TEFs to calculate cancer slope factors for the

dioxin and furan congeners (and congener groups) in the IWEM tool. 

The dioxin-like congeners (and groups of congeners) included in IWEM are as

follows:

# 2,3,7,8-TCDD,

# 2,3,7,8-Tetrachlorodibenzofuran (2,3,7,8-TCDF)

# Pentachlorodibenzodioxins (PeCDDs)

# Pentachlorodibenzofurans (PeCDFs)

# Hexachlorodibenzodioxins (HxCDDs)

# Hexachlorodibenzofurans (HxCDFs).

2,3,7,8-TCDF has a TEF of 0.1. The dioxin-like PeCDD congener is 1,2,3,7,8-PeCDD,

which has a TEF of 1.0. The dioxin-like PeCDF congeners include 1,2,3,7,8-PeCDF and

2,3,4,7,8-PeCDF which have TEFs of 0.05 and 0.5, respectively. The dioxin-like

HxCDD congeners include 1,2,3,7,8,9-HxCDD, 1,2,3,4,7,8-HxCDD, and 1,2,3,6,7,8-

HxCDD, which have TEFs of 0.1. The dioxin-like HxCDF congeners include

1,2,3,7,8,9-HxCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, and 2,3,4,6,7,8-HxCDF,

which also have TEFs of 0.1. Table E-4 shows the TEFs that we used to calculate CSFs

for the dioxin and furan congeners (and congener groups) for the purpose of developing

HBNs for the Tier 1 tool. 

Table E-4. TEFs Used for Dioxin and Furan Congeners

Constituent Name TEF

CSFo

(mkd)-1

CSFo

Source

URF

(:g/m3

)

-1

URF

Source

CSFi

(mkd)-1 CSFi Source

Dioxins

Pentachlorodibenzodioxins 1 1.56+05 WHO 1998 3.3E+01 WHO 1998 1.56+05 WHO 1998

2,3,7,8-TCDD 1 1.56+5 EPA, 1985 3.3E+01 EPA, 1997 1.56+5 EPA, 1985

Hexachlorodibenzodioxins 0.1 1.56+4 WHO 1998 3.3E+00 WHO 1998 1.56+4 WHO 1998

Furans

Hexachlorodibenzofurans 0.1 1.56+4 WHO 1998 3.3E+00 WHO 1998 1.56+4 WHO 1998

Pentachlorodibenzofurans 0.5 7.8+4 WHO 1998 1.7E+01 WHO 1998 7.8+4 WHO 1998

2,3,7,8-TCDF 0.1 1.56+4 WHO 1998 3.3E+00 WHO 1998 1.56+4 WHO 1998

WHO 98 = TEFs presented in Van den Berg et al. (1998)

EPA, 1997 = HEAST (U.S. EPA, 1997).
IWEM Technical Background Document Appendix E

E-45

The human health benchmarks calculated using the TEFs for 1,2,3,4,7,8-

hexachlorodibenzo-p-dioxin and 1,2,3,4,7,8-hexachlorodibenzofuran were surrogates for 

hexachlorodibenzo-p-dioxins (HxCDDs) and hexachlorodibenzofurans (HxCDFs),

respectively. The human health benchmarks for 1,2,3,7,8-pentachlorodibenzo-p-dioxin

and 2,3,4,7,8-pentachlorodibenzofuran were used to represent pentachlorodibenzodioxins

(PeCDDs) and pentachlorodibenzofurans (PeCDFs), respectively. The human health

benchmarks for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and

2,3,7,8-tetrachlorodibenzofuran were used to represent tetrachlorodibenzo-p-dioxins

(TCDDs) and tetrachlorodibenzofurans (TCDFs), respectively. When TEFs varied

within a class of dioxin-like compounds (i.e., pentachlorodibenzofurans), the TEF most

protective of human health was used.

E-3.2.5 Superfund Technical Support Center Provisional Benchmarks

Table E-5 lists the provisional human health benchmarks from the Superfund

Technical Support Center that were used for some of the IWEM constituents. A

provisional subchronic RfC of 2.0E-2 mg/m3

 was developed by the Superfund Technical

Support Center (U.S. EPA, 1999a) for carbon tetrachloride; a provisional chronic RfC of

7.0E-3 mg/m3 was derived from this value by applying an uncertainty factor of 3 to

account for the use of a subchronic study.

Table E-5. Provisional Human Health Benchmarks Developed by the Superfund

Technical Support Center

CASRN Chemical Name

Benchmark

Type

Benchmark

Value Units Reference

108-90-7 Chlorobenzene RfC 6.0E-02 mg/m3 U.S. EPA, 1998a

7440-48-4 Cobalt (and compounds) RfD 2.0E-02 mg/kg-d U.S. EPA, 2001b

100-41-4 Ethylbenzene URF 1.1E-06 (:g/m3)-1 U.S. EPA, 1999b

87-68-3 Hexachlorobutadiene RfD 3.0E-04 mg/kg-d U.S. EPA, 1998b

110-54-3 Hexane RfD 1.1E+01 mg/kg-d U.S. EPA, 1999c

62-75-9 N-Nitrosodimethylamine 

(N-methyl-N-nitrosomethanamine)

RfD 8.0E-06 mg/kg-d U.S. EPA, 2001c

86-30-6 N-Nitrosodiphenylamine RfD 2.0E-02 mg/kg-d U.S. EPA, 2001d

79-34-5 Tetrachloroethane, 1,1,2,2- RfD 6.0E-02 mg/kg-d U.S. EPA, 2000

71-55-6 Trichloroethane, 1,1,1- RfD 2.8E-01 mg/kg-d U.S. EPA, 1999d

71-55-6 Trichloroethane, 1,1,1- RfC 2.2E+00 mg/m3 U.S. EPA, 1999e

96-18-4 Trichloropropane, 1,2,3- RfC 5.0E-03 mg/m3 U.S. EPA, 1999f
IWEM Technical Background Document Appendix E

E-46

E-3.2.6 Benchmarks From Other EPA Sources

For some IWEM constituents, human health benchmarks were not available from

IRIS, the Superfund Technical Support Center, HEAST, ATSDR, or CalEPA, but were

available from other EPA sources:

# The provisional oral CSF of 5.2E-2 per mg/kg-d, provisional inhalation

URF of 5.8E-7 per :g/m3

, and the provisional inhalation CSF of 2.0E-3

per mg/kg-d developed for tetrachloroethylene by EPA in a Health

Assessment Document (HAD) (U.S. EPA, 1986a) were used.

# For trichloroethylene, provisional cancer benchmarks developed by EPA

in a HAD (U.S. EPA, 1987) were used and include the oral CSF of 1.1E-2

per mg/kg-d, inhalation URF of 1.7E-6 per :g/m3

, and inhalation CSF of

6.0E-3 per mg/kg-d.

# A provisional RfD of 1.7E-5 mg/kg-d and a provisional RfC of 2.0E-5

mg/m3

 were derived for cyclohexanol in the final listing rule for solvents

(63 FR 64371) and were used (U.S. EPA, 1998c).

# An acceptable daily intake (ADI) of 2.0E-03 mg/kg-d from inhalation

(7.0E-3 mg/m3) was identified for pyridine (U.S. EPA, 1986b).

# EPA calculated an oral cancer potency factor of 293 per mg/kg-d for ethyl

methanesulfonate in a reportable quantity adjustment evaluation (U.S.

EPA, 1998d).

# EPA calculated an oral cancer potency factor of 0.18 per mg/kg-d for

safrole in a reportable quantity adjustment evaluation (U.S. EPA, 1998e).

# EPA calculated an oral cancer potency factor of 9.8 per mg/kg-d for

tris(2,3-dibromopropyl)phosphate in a reportable quantity adjustment

evaluation (U.S. EPA, 1998f).

# The cancer slope factor for dibenzo(a,h)anthracene was calculated using a

TEF approach developed for polycyclic aromatic hydrocarbons (U.S.

EPA, 1993). The TEF approach assigns dibenzo(a,h)anthracene a TEF of

1 relative to the toxicity of benzo(a)pyrene. The oral CSF for

dibenzo(a,h)anthracene is therefore the same as the IRIS (U.S. EPA,

2001a) value for benzo(a)pyrene: 7.3.E+00 (mg/kg-d)-1.
IWEM Technical Background Document Appendix E

E-47

E-3.2.7 Air Characteristic Study Provisional Benchmarks

Provisional inhalation health benchmarks were developed in the Air

Characteristic Study (U.S. EPA, 1999g) for several constituents lacking IRIS, HEAST,

alternative EPA, or ATSDR values. For 2-chlorophenol, a provisional RfC was

developed using route-to-route extrapolation of the oral RfD. Using route-to-route

extrapolations based on oral CSFs from IRIS and HEAST, the Air Characteristic Study

developed provisional inhalation URFs and inhalation CSFs for bromodichloromethane,

chlorodibromomethane, and o-Toluidine.

These provisional inhalation benchmark values are summarized in Table E-6

below. Additional details on the derivation of these inhalation benchmarks can be found

in the Revised Risk Assessment for the Air Characteristic Study (U.S. EPA, 1999g).

Table E-6. Provisional Inhalation Benchmarks Developed in the Air

Characteristic Study

CASRN Chemical Name

RfC

(mg/m3)

RfC Target

Effect

URF

(:g/m3)

-1

CSFi

(mg/kg-d)-1

75-27-4 Bromodichloromethane

(dichlorobromomethane)

1.8E-05 6.2E-02

124-48-1 Chlorodibromomethane

(dibromochloromethane)

2.4E-05 8.4E-02

95-57-8 2-Chlorophenol (o-) 1.4E-03 Reproductive,

developmental

95-53-4 o-Toluidine (2-methylaniline) 6.9E-05 2.4E-01

E-3.2.8 Surrogate Health Benchmarks

For several IWEM constituents, IRIS benchmarks for similar chemicals were used

as surrogate data. The rationale for these recommendations is as follows: 

# cis-1,3-Dichloropropylene and trans-1,3-dichloropropylene were based on

1,3-dichloropropene. The studies cited in the IRIS file for 1,3-

dichloropropene used a technical-grade chemical that contained about a

50/50 mixture of the cis- and trans-isomers. The RfD is 3E-02 mg/kg-d

and the RfC is 2E-02 mg/m3

. The oral CSF for 1,3-dichloropropene is 0.1

(mg/kg-d)-1 and the inhalation URF is 4E-06 (μg/m3

)

-1.
IWEM Technical Background Document Appendix E

E-48

# The IRIS oral CSF for the 2,4-/2,6-dinitrotoluene mixture (6.8E-01 per

mg/kg-d) was used as the oral CSFs for 2,4-dinitrotoluene and 2,6-

dinitrotoluene.

# The RfDs for o- and m-cresol (both 5E-02 mg/kg/d) are cited on IRIS. The

provisional RfD for p-cresol (5E-03 mg/kg/d) is from HEAST. Cresol

mixtures contain all three cresol isomers. Based on the hierarchy

described above (i.e., IRIS is preferred over HEAST because IRIS is

EPA’s official repository of Agency-wide consensus human health risk

information), the RfD for m-cresol (5E-02 mg/kg-d) was used as a

surrogate for cresol mixtures.

# Fluoride was based on fluorine. The IRIS RfD for fluorine (0.12 mg/kg-d)

is based on soluble fluoride and related to the endpoint of skeletal

fluorisis.

# The RfD for methyl mercury (1E-04 mg/kg-d) was used as a surrogate for

elemental mercury.

# The RfD for Arochlor 1254 (2E-05 mg/kg-d) was used as a surrogate for

PCBs.

# Thallium was based on thallium chloride. There are several thallium salts

that have RfDs in IRIS. The lowest value among the thallium salts (8E-05

mg/kg-d) is routinely used to represent thallium in risk assessments.

# p-Xylene was based on total xylenes. An RfD of 2 mg/kg-d is listed for

total xylenes, m-xylene, and o-xylene in IRIS. Total xylenes contain a

mixture of all three isomers; therefore, the RfD likely is appropriate for pxylene.

E-3.2.9 Chloroform

EPA has classified chloroform as a Group B2, Probable Human Carcinogen,

based on an increased incidence of several tumor types in rats and mice (U.S. EPA,

2001a). However, based on an evaluation initiated by EPA’s Office of Water (OW), the

Office of Solid Waste (OSW) now believes the weight of evidence for the carcinogenic

mode of action for chloroform does not support a mutagenic mode of action; therefore, a

nonlinear low-dose extrapolation is more appropriate for assessing risk from exposure to

chloroform. EPA’s Science Advisory Board (SAB), the World Health Organization

(WHO), the Society of Toxicology, and EPA all strongly endorse the nonlinear approach

for assessing risks from chloroform. 
IWEM Technical Background Document Appendix E

E-49

Although OW conducted its evaluation of chloroform carcinogenicity for oral

exposure, a nonlinear approach for low-dose extrapolation would apply to inhalation

exposure to chloroform as well, because chloroform’s mode of action is understood to be

the same for both ingestion and inhalation exposures. Specifically, tumorigenesis for

both ingestion and inhalation exposures is induced through cytotoxicity (cell death)

produced by the oxidative generation of highly reactive metabolites (phosgene and

hydrochloric acid), followed by regenerative cell proliferation (U.S. EPA, 1998g). 

Chloroform-induced liver tumors in mice have only been seen after bolus corn oil dosing

and have not been observed following administration by other routes (i.e., drinking water

and inhalation). As explained in EPA OW’s March 31, 1998, and December 16, 1998,

Federal Register notices pertaining to chloroform (U.S. EPA, 1998g and 1998h,

respectively), EPA now believes that “based on the current evidence for the mode of

action by which chloroform may cause tumorigenesis, ...a nonlinear approach is more

appropriate for extrapolating low-dose cancer risk rather than the low-dose linear

approach...”(U.S. EPA, 1998g). OW determined that, given chloroform’s mode of

carcinogenic action, liver toxicity (a noncancer health effect) actually “is a more sensitive

effect of chloroform than the induction of tumors” and that protecting against liver

toxicity “should be protective against carcinogenicity given that the putative mode of

action understanding for chloroform involves cytotoxicity as a key event preceding tumor

development” (U.S. EPA, 1998g). 

The recent evaluations conducted by OW concluded that protecting against

chloroform’s noncancer health effects protects against excess cancer risk. EPA now

believes that the noncancer health effects resulting from inhalation of chloroform would

precede the development of cancer and would occur at lower doses than would tumor

development. Although EPA has not finalized a noncancer health benchmark for

inhalation exposure (i.e., an RfC), ATSDR has developed an inhalation MRL for

chloroform. Therefore, ATSDR’s chronic inhalation MRL for chloroform (0.1 mg/m3

)

was used in IWEM.

E-3.3 References for Section E-3

ATSDR, 2001. Minimal Risk Levels (MRLs) for Hazardous Substances. 

http://atsdr1.atsdr.cdc.gov:8080/mrls.html

CalEPA, 1999a. Air Toxics Hot Spots Program Risk Assessment Guidelines: Part II. 

Technical Support Document for Describing Available Cancer Potency Factors.

Office of Environmental Health Hazard Assessment, Berkeley, CA. Available

online at http://www.oehha.org/scientific/hsca2.htm.

CalEPA, 1999b. Air Toxics Hot Spots Program Risk Assessment Guidelines: Part III. 

Technical Support Document for the Determination of Noncancer Chronic
IWEM Technical Background Document Appendix E

E-50

Reference Exposure Levels. SRP Draft. Office of Environmental Health Hazard

Assessment, Berkeley, CA. Available online at

http://www.oehha.org/hotspots/RAGSII.html.

CalEPA, 2000. Air Toxics Hot Spots Program Risk Assessment Guidelines: Part III. 

Technical Support Document for the Determination of Noncancer Chronic

Reference Exposure Levels. Office of Environmental Health Hazard Assessment,

Berkeley, CA. Available online (in 3 sections) at

http://www.oehha.org/air/chronic_rels/22RELS2k.html,

http://www.oehha.org/air/chronic_rels/42kChREL.html,

http://www.oehha.org/air/chronic_rels/Jan2001ChREL.html.

U.S. EPA, 1985. Health Assessment Document for Polychlorinated Dibenzo-p-Dixons. 

Office of Health and Environmental Assessment, EPA/600/8-84/94F.

U.S. EPA, 1986a. Addendum to the Health Assessment Document for

Tetrachloroethylene (Perchloroethylene). Updated Carcinogenicity Assessment

for Tetrachloroethylene (Perchloroethylene, PERC, PCE). External Review

Draft. EPA/600/8-82-005FA. Office of Health and Environmental Assessment,

Office of Research and Development, Washington DC.

U.S. EPA, 1986b. Health and Environmental Effects Profile for Pyridine. EPA/600/x86-168. Environmental Criteria and Assessment Office, Office of Research and

Development, Cincinnati, OH.

U.S. EPA, 1987. Addendum to the Health Assessment Document for Trichloroethylene. 

Updated Carcinogenicity Assessment for Trichloroethylene. External Review

Draft. EPA/600/8-82-006FA. Office of Health and Environmental Assessment,

Office of Research and Development, Washington DC.

U.S. EPA, 1993. Provisional Guidance for Quantitative Risk Assessment of Polycyclic

Aromatic Hydrocarbons. Office of Health and Environmental Assessment,

Environmental Criteria and Assessment Office, Cincinnati, OH. EPA/600/R-93-

089.

U.S. EPA, 1994. Methods for Derivation of Inhalation Reference Concentrations and

Application of Inhalation Dosimetry. EPA/600/8-90-066F. Environmental

Criteria and Assessment Office, Office of Health and Environmental Assessment,

Office of Research and Development, Research Triangle Park, NC.
IWEM Technical Background Document Appendix E

E-51

U.S. EPA, 1997. Health Effects Assessment Summary Tables (HEAST). EPA-540-R-97-

036. FY 1997 Update. Office of Solid Waste and Emergency Response,

Washington, DC. 

U.S. EPA, 1998a. Risk Assessment Issue Paper for: Derivation of a Provisional Chronic

RfC for Chlorobenzene (CASRN 108-90-7). 98-020/09-18-98. National Center

for Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 1998b. Risk Assessment Paper for: Evaluation of the Systemic Toxicity of

Hexachlorobutadiene (CASRN 87-68-3) Resulting from Oral Exposure. 98-

009/07-17-98. National Center for Environmental Assessment. Superfund

Technical Support Center, Cincinnati, OH.

U.S. EPA, 1998c. Hazardous waste management system; identification and listing of

hazardous waste; solvents; final rule. Federal Register 63 FR 64371-402.

U.S. EPA, 1998d. Evaluation of the Potential Carcinogenicity of Ethyl Methanesulfonate

(62-50-0) in Support of Reportable Quantity Adjustments Pursuant to CERLCA

Section 102. Prepared by Carcinogen Assessment Group, Office of Health and

Environmental Assessment, Washington, D.C.

U.S. EPA, 1998e. Evaluation of the Potential Carcinogenicity of Safrole (94-59-7) in

Support of Reportable Quantity Adjustments Pursuant to CERLCA Section 102. 

Prepared by Carcinogen Assessment Group, Office of Health and Environmental

Assessment, Washington, D.C.

U.S. EPA, 1998f. Evaluation of the Potential Carcinogenicity of Tris(2,3-

dibromopropyl)phosphate (126-72-7) in Support of Reportable Quantity

Adjustments Pursuant to CERLCA Section 102. Prepared by Carcinogen

Assessment Group, Office of Health and Environmental Assessment,

Washington, D.C.

U.S. EPA, 1998g. National primary drinking water regulations: disinfectants and

disinfection byproducts notice of data availability; Proposed Rule. Federal

Register 63 (61): 15673-15692. March 31.

U.S. EPA, 1998h. National primary drinking water regulations: disinfectants and

disinfection byproducts; final rule. Federal Register 63 (241): 69390-69476. 

December 16.
IWEM Technical Background Document Appendix E

E-52

U.S. EPA, 1999a. Risk Assessment Paper for: The Derivation of a Provisional

Subchronic RfC for Carbon Tetrachloride (CASRN 56-23-5). 98-026/6-14-99. 

National Center for Environmental Assessment. Superfund Technical Support

Center, Cincinnati, OH.

U.S. EPA, 1999b. Risk Assessment Issue Paper for: Evaluating the Carcinogenicity of

Ethylbenzene (CASRN 100-41-4). 99-011/10-12-99. National Center for

Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 1999c. Risk Assessment Paper for: An Updated Systemic Toxicity Evaluation

of n-Hexane (CASRN 110-54-3). 98-019/10-1-99. National Center for

Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 1999d. Risk Assessment Issue Paper for: Derivation of Provisional Oral

Chronic RfD and Subchronic RfDs for 1,1,1-Trichloroethane (CASRN 71-55-6).

98-025/8-4-99. National Center for Environmental Assessment. Superfund

Technical Support Center, Cincinnati, OH.

U.S. EPA, 1999e. Risk Assessment Issue Paper for: Derivation of Provisional Chronic

and Subchronic RfCs for 1,1,1-Trichloroethane (CASRN 71-55-6). 98-025/8-4-

99. National Center for Environmental Assessment. Superfund Technical

Support Center, Cincinnati, OH.

U.S. EPA, 1999f. Risk Assessment Paper for: Derivation of the Systemic Toxicity of

1,2,3-Trichloropropane (CASRN 96-18-4). 98-014/8-13-99. National Center for

Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 1999g. Revised Risk Assessment for the Air Characteristic Study. EPA-530-

R-99-019a. Volume 2. Office of Solid Waste, Washington, DC.

U.S. EPA, 2000. Risk Assessment Paper for: Derivation of a Provisional RfD for

1,1,2,2-Tetrachloroethane (CASRN 79-34-5). 00-122/12-20-00. National Center

for Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 2001a. Integrated Risk Information System (IRIS). National Center for

Environmental Assessment, Office of Research and Development, Washington,

DC. Available online at http://www.epa.gov/iris/
IWEM Technical Background Document Appendix E

E-53

U.S. EPA, 2001b. Risk Assessment Paper for: Derivation of a Provisional RfD for

Cobalt and Compounds (CASRN 7440-48-4). 00-122/3-16-01. National Center

for Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 2001c. Risk Assessment Paper for: Derivation of a Provisional RfD for NNitrosodimethylamine (CASRN 62-75-9). 00-122/3-16-01. National Center for

Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

U.S. EPA, 2001d. Risk Assessment Paper for: Derivation of a Provisional RfD for NNitrosodiphenylamine (CASRN 86-30-6). 00-122/3-16-01. National Center for

Environmental Assessment. Superfund Technical Support Center, Cincinnati,

OH.

Van den Berg, M., L. Birnbaum, A.T.C. Bosveld, et al, 1998. Toxic equivalency factors

(TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife. Environmental Health

Perspectives 106:775-792.