Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
1
Exposure Dose Guidance for Water Ingestion
Citation:
[ATSDR] Agency for Toxic Substances and Disease Registry. 2023. Exposure Dose
Guidance for Water Ingestion. Atlanta, GA: U.S. Department of Health and Human
Services, Public Health Service, Jan 31.
Content
This guidance contains the following topics:
Topic
See
Page
Purpose 2
Background 2
Definitions 2
Exposure Dose Equation
4
Summary Tables of Water Intake Rates 4
Cancer 6
Noncancer (Annual) Dose and Cancer (Lifetime) Dose Estimates 7
Central Tendency and Upper Percentile Dose Estimates (CTE/
RME)
9
Public Health Assessment Site Tool (PHAST) 9
Impact
10
References 10
Appendices 11
Appendix A—Exposure Dose Calculations 11
Appendix B—Mutagenic Mode of Action (MOA)
14
Appendix C—Derivation of Intake Rates for Standard Age Groups
and Special Groups
14
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Purpose
Based on the availability of updated exposure parameters, many from the
2019 update of drinking water ingestion values in the Exposure Factors
Handbook (EFH) published by the U.S. Environmental Protection Agency
(EPA), it is necessary that parameters used in calculating doses in our public
health evaluations be updated to reflect the best available science.
This water exposure dose guidance (EDG) provides health assessors with
updated guidance on how to estimate water-ingestion related exposures to
potential contaminants of concern (COCs). The guidance document for the
Shower and Household Water-use Exposure (SHOWER) model addresses
inhalation of volatile and semi-volatile organic compounds during household
water use, such as while showering (ATSDR 2020).
Background
After a release of chemicals into the environment, health assessors evaluate
all relevant human exposure pathways; water ingestion is usually one of the
more commonly evaluated pathways.
In ATSDR’s 2005 Public Health Assessment Guidance Manual (PHAGM),
default daily water intake rates were 2 L/day for adults and 1 L/day for
children (ATSDR 2005). This guidance document provides updated age-
specific drinking water intake rates for ATSDR’s standard and special age
groups using the 2019 update of EPA’s 2011 Exposure Factor Handbook,
Chapter 3, (EPA 2019). ATSDR’s standard age groups are based on age
ranges for residential scenarios. We also developed intake rates for special
groups, such as infants, school age children, workers, pregnant women, and
breastfeeding women.
Definitions
Any discussion of water ingestion needs to start with several important
definitions:
Intake rate (IR). IR refers to all forms of tap water intake from either
municipal or private wells (direct and indirect ingestion). It does not include
intake from bottled water.
Direct ingestion is drinking plain water as a beverage at home and away
from home from all sources, including
• Tap/fountain water from a community water supply,
• Household well or rain cistern,
• Household or public spring, and
• Bottled.
Direct ingestion does not include water used for preparing beverages such as
coffee or tea.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Indirect ingestion includes drinking water added during food preparation but
does not include drinking any water included with prepackaged, purchased
foods. Thus, indirect ingestion includes water added to prepare, for example,
baby formula, cake mix, and concentrated orange juice but does not include
the water that is part of, say, pasta sauce.
Community water includes tap water from a community or municipal water
supply.
Central tendency exposure (CTE). CTE refers to persons who have average
or typical water intake rate. For water ingestion, the dose calculation uses
CTE water intake.
Reasonable maximum exposure (RME). RME refers to persons who are at
the upper end of the exposure distribution (approximately the 95th
percentile). The RME scenario assesses exposures that are higher than
average but still within a realistic exposure range.
Exposure factor (EF): An expression of how often (frequency) and how
long (duration) a person may be contacting a substance in the environment. In
many instances, the exposure factor (EF) will equal 1, representing a daily
exposure to the contaminant. However, some exposures may occur on an
intermittent or irregular basis. For these exposures, an EF can be calculated
by averaging the dose over the exposure interval. The EF is calculated by
multiplying the exposure frequency (F) by the exposure duration (ED) and
dividing by the time period during which the dose is to be averaged
(averaging time - AT). The EF for occupational, school, trespassing, and
swimming scenarios is likely to be different than 1 (see examples).
Exposure duration (ED): The period over which the exposure takes place.
Exposure frequency (F): How frequently exposure occurs. This parameter is
often measured in days per week and weeks per year.
Averaging time (AT): The period over which the exposure is averaged to
arrive at a time-weighted exposure factor. For assessing cancer risks, AT is
averaged over a lifetime (78 years); for assessing noncancer risks, AT is
averaged over the exposure duration (days, weeks, or years), which may or
may not be a lifetime.
Residential occupancy period (ROP): The time in years between when a
person moves into a residence and when the person moves out or dies.
Chronic exposures: Exposures greater than 365 days. Exposure doses
derived for chronic exposure scenarios should be evaluated using chronic
ATSDR Minimal Risk Levels (MRLs). If MRLs are not available, EPA
Reference Doses (RfD), EPA Reference Concentrations (RfC) or another
suitable health guidance values may be used for the evaluation.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Intermediate exposures: Exposures of 15 to 364 days. Exposure doses
derived for intermediate exposure scenarios should be evaluated using
intermediate MRLs or appropriate toxicity information (e.g., utilizing studies
of similar duration, if available).
Acute exposures: Exposures up to 14 days. Exposure doses derived for acute
exposure scenarios should be evaluated using acute MRLs or appropriate
toxicity information (e.g., utilizing studies of similar duration, if available).
Exposure
Dose Equation
where
D = exposure dose (mg/kg-day)
C = contaminant concentration (mg/L)
IR = intake rate of contaminated water (L/day)
EF
chronic
= exposure factor (unitless) = (F x ED)/AT
• F = exposure frequency (d/wk x wk/yr)
• ED = exposure duration (yr)
• AT = averaging time
o noncancer = ED (yr) x F (d/wk x wk/yr)
o cancer: 78 yr x F (7 d/wk x 52.14 wk/yr)
BW = body weight (kg)
Sou
rce: Public Health Assessment Guidance Manual, Estimating Site-Spe
cific
Ingestion Doses (ATSDR 2022a).
Summary
Tables of
Water Intake
Rates
EDG and updated the intake rates using data from the 2019 update to
Chapter 3 in EPA’s 2011 Exposure Factors Handbook (EFH) (EPA 2019).
The 2019 EFH update has information about adult and child water intake
rates based on recent data from the National Health and Nutrition
Examination Survey (NHANES) IV (CDC 2012). Unless site-specific
conditions warrant using other rates, ATSDR recommends using the default
water intake rates in Table 1 to estimate site-specific doses. Table 1 also
contains associated time-weighted body weights (For further information,
see the EDG for body weight) (ATSDR 2023).
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Standard Age Groups
a
Age Range
Mean
(mL/day)
95
th
Percentile
(mL/day)
Body
Weight
(kg)
Birth to < 1 years 595 1,106 7.8
1 to < 2 years 245 658 11.4
2 to < 6 years
b
337
852
17.4
6 to < 11 years
455
1,258
31.8
11 to < 16 years 562 1,761 56.8
16 to < 21 years 722 2,214 71.6
Adult (21 to 78 years)
b
1,313 3,229 80
a
Intake rates for combined direct and indirect water from community water supply (EPA
2019,
b
See Appendix C for derivation of intake rates.
Children, pregnant and breastfeeding women: Table 2 has the recommended
water ingestion values for infants and for children in kindergarten as well as
for grade school children. Table 2 also provides recommended water
ingestion values for pregnant and breastfeeding women. If a review of
ATSDR toxicological profiles for potential COCs indicates a critical
outcome is based on developmental effects, include the pregnant woman
scenario in the health evaluation. Similarly, if information in the
toxicological profiles indicates potential COCs might affect breast milk,
include breastfeeding women in the health evaluation. For specific questions
regarding the evaluation of pregnant and breastfeeding women, contact the
Associate Director for Science (ADS).
If needed, EPA’s EFH contains more detailed information about water
ingestion for specific groups (e.g., sex, region, activity levels) (EPA 2019).
Use the default intake parameters in this guidance when calculating
contaminant exposure doses. If you modify default intake parameters using
site- or scenario-specific information, explain the basis of those
modifications in your public health documents.
Appendix A has sample water-exposure dose calculations. See Appendix C
for an explanation of how intake rates were calculated for each age group.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Table 2: Recommended Water Intake Rates for Special Groups
Age Range Special Group
Mean
(mL/day)
95
th
Percentile
(mL/day)
Body
Weight
a
(kg)
Birth to < 1 month
b
Infant 581 938 4.8
1 to < 3 months
b
Infant 785 1,224 5.9
3 to < 6 months
b
Infant
649
1,125
7.4
6 to < 12 months
b
Infant 554 1,104 9.2
3 to < 5 years
c
Pre-
Kindergarten
324 866 17.2
5 to < 6 years
c
Kindergarten 364 1,006 20.6
6 to < 11 years 1
st
-5
th
455 1,258 31.8
11 to < 14 years
c
6
th
-8
th
grade 553 1,655 50.6
14 to < 16
years
c
9
th
-10
th
grade 621 1,886 63.7
16 to < 18 years
c
11
th
-12
th
grade 675 2,072 67.3
18 ≤ 67 years
c
Full, part-time
worker/educator
1,276 3,270 80.6
15 < 45 year
d
Pregnant
Women
1,158 2,935 73
15 < 45 year
d
Breastfeeding
Women
1,495 3,061 73
a
See Exposure Dose Guidance for Body Weight (ATSDR 2023);
b
EPA 2019 EFH (update),
Chapter 3, Table 3-1;
c
See Appendix C for derivation of intake rates;
d
EPA 2019 EFH
(update), Chapter 3, Table 3-3 (EPA 2019)
Cancer
EPA’s approach to quantitative cancer risk estimates includes a cancer slope
factor (CSF). It involves multiplying a carcinogen-specific CSF by a
duration-specific estimated dose. This approach allows estimation of cancer
risk for adults and children as a function of exposure duration.
Special Cancer Considerations
EPA also has proposed that risk calculations for chemicals that act with a
mutagenic mode of action (MOA) for carcinogenesis can be quantified
using one of two possible approaches (EPA 2005):
• For some MOA chemicals, sufficient data are available to derive
age-specific cancer slope factors. These age-specific CSFs can be
used to estimate age-specific and total cancer risk. An example is
vinyl chloride which has two CSFs: one for early life exposure and
one for adult only exposure. These two CSFs account for differences
in susceptibility between exposure that begins in childhood and
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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exposure that begins in adulthood. Therefore, age-dependent
adjustment factors (ADAFs) should not be used for vinyl chloride.
• For MOA chemicals without age-specific CSFs, ADAFs should be
applied. EPA suggests using the following ADAFs:
Children 0 < 2 years 10
Children 2 to < 16 years 3
Children and adults 16 and older 1
Mutagenic chemicals are identified in PHAST and in the EPA’s Regional
Screening Levels (RSL) table [https://www.epa.gov/risk/regional-screening-
levels-rsls-generic-tables-may-2016] and include chemicals commonly found
at waste sites, such as polycyclic aromatic hydrocarbons, trichloroethylene,
and chromium compounds. Additional information about EPA’s approach to
evaluating early life exposure to mutagenic carcinogens can be found at
https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf.
Noncancer
(Annual) Dose
and Cancer
(Lifetime)
Dose
Estimates
1-year of exposure) are calculated. This allows for the doses to be directly
compared with the chronic MRL, which has been developed to be protective
for exposures of one year or greater.
Lifetime doses, used to evaluate cancerous effects, can differ depending on
exposure duration and are averaged over a lifetime of exposure (i.e., 78
years). For cancer risk evaluations, you can assume either lifetime exposure
or some fraction of a lifetime exposure.
You can convert the 1-year annual dose to a lifetime cancer dose by
multiplying the annual dose by the site-specific or default exposure
duration/averaging time (ED/AT). For default residential scenarios, RME
(33 years) and CTE (12 years) residential occupancy periods are used to
calculate the RME and CTE cancer risk, respectively. Health assessors have
several options available for the presentation of cancer risk estimates, which
are discussed below.
Unknown Exposure Duration
When the residential exposure duration is unknown, the 95
th
percentile
residential occupancy period (i.e., 33 years) may be incorporated into the
report and presented in several ways:
• Most commonly, adult and childhood cancer risk are presented
separately. Calculate and present the combined cancer risk for
children (birth to 21 years) using an ED/AT term of 21 yr/78 yr and
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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• Combined childhood and adulthood cancer risk can be presented as
one cancer risk estimate. This is only appropriate if you are assessing
exposures that began at birth and continue into adulthood at the same
house or in a house with similar contaminant levels. To incorporate
the 33 year default residential occupancy period into this scenario,
you should calculate the cancer risk for children exposed from birth
to 21 years (using an ED/AT term of 21/78) and calculate an
additional 12 years of exposure for adults (using an ED/AT term of
12/78). The childhood and adult cancer risk should be added together
to account for 33 years of total exposure.
When occupational exposure duration is unknown, health assessors should
use the values reported in Table 3. The basis for these values is described in
more detail in the EDG for determining life expectancy and exposure factor
(ATSDR 2016).
Table 3. Default assumptions for occupational scenarios
a
Typical workday, all
(hours/day)
Work year (weeks) Work tenure (years)
Full time: 8.5
RME: 50.0
CTE: 50.0
RME: 20.0
CTE: 5.0
Part time: 5.1
CTE: 50.0
CTE: 3.1
a
ATSDR 2016
Known Exposure Duration
When an exposure duration is known, you can incorporate the site-specific
exposure duration and present cancer risk (1) separately for children and
adults (most common scenario) or (2) combine them (if exposures are
occurring from childhood through adulthood and site-specific information
warrants), as discussed above.
Lifetime Exposure Duration
When site-specific information indicates that exposures may have occurred
over an entire lifetime (e.g., a small rural or tribal community), the cancer
risk for children (birth to 21 years; ED/AT of 21/78) and adults (additional
57 years; ED/AT of 57/78) should be added together to account for an entire
lifetime of exposure. Please note that there should be reliable site-specific
information available when considering the presentation of cancer risk with
a lifetime exposure duration.
For more information about exposure factors, review the EDG for
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Central
Tendency and
Reasonable
Maximum
Exposure
Dose
Estimates
(CTE/ RME)
To represent persons with typical and high-end exposures, estimate typical
exposure doses for receptors using CTE intake values and rates and high-end
doses for receptors using a combination of CTE and RME values and rates.
When feasible, you can present the results as a range of doses in the target
population. The EPA’s EFH is the primary source for CTE and RME tap
water intake rates in children and adults (EPA 2019).
Discussion in the public health implications section of your document should
include your explanation for estimates for both children and adults. For
example, if the risk of harmful effects is only for children with high intake
rates (RME), describe the risk of harm for that group and explain that children
with typical intake rates (CTE) are not at risk. Likewise, if the risk of harmful
effects is for both groups, your estimate explanation should reflect both
scenarios.
When evaluating noncancer endpoints, you should estimate doses for the
most highly exposed group (e.g., for drinking water, usually children birth to
1 yr) or for the most sensitive group. If the estimated dose for these groups
exceeds the health guideline (e.g., MRL, RfD), then evaluate doses for other
groups. Remember that when evaluating cancer risk, you should use site-
specific information to identify the age ranges for which you need cancer risk
estimates, whenever possible.
Public Health
Assessment
Site Tool
(PHAST)
Health assessors should use the public health assessment site tool (PHAST) to
estimate drinking water doses. PHAST provides a quick summary with the
maximum hazard quotient for chronic, intermediate, and acute exposure as
well as the maximum cancer risk for the typical residential exposure scenario
involving children and adults.
If the HQ exceeds one, review the age-specific dose and hazard quotient
calculations to evaluate risk of noncancerous effects in children and adults.
If no MRL or RfD is available, compare the maximum age-specific dose
directly to NOAELs and LOAELs to determine the possibility of harmful
effects. If you decide harmful effects are possible, consider doses for all age
ranges to determine who is at risk of noncancerous harmful effects.
The default cancer risk calculation in the quick summary assumes 33 years of
residential exposure—the 95
th
percentile residential-occupancy period. The
default 33-year cancer risk assumes 21 years of exposure as a child, followed
by 12 years of exposure as an adult at the same residence. If the maximum
cancer risk in the quick summary exceeds 1E-6, review the cancer risks for
children and adults from the more detailed cancer risks in the results table.
Remember that the quick summary cancer risk is a screen – you should not
include it in PHAs/HCs unless you have an exposure scenario where children
grow up in a house or area and continue to have the same exposure as adults.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Impact
Using the best available science to update the parameters to calculate
exposure doses for water ingestion will improve the consistency of exposure
dose estimates in ATSDR- and state-prepared health assessments and
consultations.
References
[ATSDR] Agency for Toxic Substances and Disease Registry. 2022a. Public
health assessment guidance manual. Atlanta: US Department of Health
and Human Services. Available at: https://www.atsdr.cdc.gov/pha-
guidance/index.html.
[ATSDR] Agency for Toxic Substances and Disease Registry. 2022b.
Exposure dose guidance for body weight. Atlanta, GA: US Department of
Health and Human Services, Public Health Service, Dec 1.
[ATSDR] Agency for Toxic Substances and Disease Registry. 2020.
Exposure dose guidance for the Shower and Household Water-use
Exposure (SHOWER) model v2.0. Atlanta, GA: US Department of Health
and Human Services, Public Health Service, Feb 3.
[ATSDR] Agency for Toxic Substances and Disease Registry. 2016.
Exposure Dose Guidance for Determining Life Expectancy and Exposure
Factor. Atlanta, GA: US Department of Health and Human Services, Public
Health Service, October 26.
[ATSDR] Agency for Toxic Substances and Disease Registry. 2005. Public
health assessment guidance manual (previous version). Atlanta: US
Department of Health and Human Services, Public Health Service.
[CDC] Centers of Disease Control and Prevention. 2012. National Health and
Nutrition Examination Survey. Available at:
http://www.cdc.gov/nchs/nhanes.htm [accessed 2022 August 11].
[EPA] US Environmental Protection Agency. 2019. Exposure Factors
Handbook Chapter 3 (Update): Ingestion of Water and Other Select
Liquids. U.S. EPA Office of Research and Development, Washington, DC,
EPA/600/R-18/259F. Available at:
https://cfpub.epa.gov/ncea/efp/recordisplay.cfm?deid=343661 [accessed
2022 August 17].
[EPA] US Environmental Protection Agency. Exposure Factors Handbook
2011 Edition (Final Report). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/R-09/052F, 2011.
[EPA] US Environmental Protection Agency. 2005. Supplemental Guidance
for Assessing Susceptibility from Early-Life Exposure to Carcinogens.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Washington, DC, EPA/630/R-03/003F. Available at:
https://www.epa.gov/risk/supplemental-guidance-assessing-susceptibility-
early-life-exposure-carcinogens [accessed 2016 Oct 19].
Appendices
Appe
ndix A: Exposure Dose Calculations
As discussed previously, health assessors should use PHAST to calculate water ingestion doses, hazard
quotients, and cancer risk estimates.
The examples in the appendices detail the dose calculations included in PHAST. We show examples
here for children and adults and for noncancer and cancer using the following dose formula for drinking
water ingestion:
D = dose in mg/kg/day
C = water concentration in mg/L
IR = tap water intake rate in L/day
EF = exposure factor
BW = body weight in kg
F = exposure frequency (d/wk x wk/yr)
ED = exposure duration (yr)
AT = averaging time
• noncancer = ED (yr) x F (d/wk x wk/yr)
• cancer = 78 yr x F (7 d/wk x 52.15 wk/yr)
F = exposure frequency (d/wk)
ED = exposure duration (wk)
AT = averaging time
• noncancer = ED (wk) x F (d/wk)
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
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Dose Calculation Examples
What follows are several examples showing how drinking water doses are calculated and the role
exposure factor (EF) and intermittent exposure plays in estimating doses. Sample dose calculations are
shown for chronic, intermediate, and acute durations.
Scenario #1. Children ages 2 to 6 years old attend preschool 5 days a week for 9 months of the year.
Tap water at the school contains 10 mg/L bromoform. What is the chronic dose for children at this
school from four years of exposure?
Chronic Dose
Table A1 shows the parameters used to calculate the chronic, noncancer doses for children and
adults at the daycare who drank water containing 10 mg/L bromoform. Compare these doses to
the chronic, oral MRL of 0.02 mg/kg/day to calculate a hazard quotient (HQ).
Age Group
CTE
Intake
Rate
L/day
RME
Intake
Rate
L/day
Exposur
e Factor
Unitless
Body
Weight
Kg
Chronic
CTE Dose
mg/kg/day
Chronic
RME Dose
mg/kg/day
Chronic
CTE
Hazard
Quotient
Chronic
RME
Hazard
Quotient
2 to < 6 yr
0.337
0.852
0.493
17.4
0..095
0.24
5
12
Adult (21 to 78 yr)
1.313
3.229
0.493
80
0.081
0.20
4
10.5
Pregnant Women
1.158
2.935
0.493
73
0.08
0.20
4
10
Breastfeeding Women
1.495
3.061
0.493
75
0.10
0.20
5
10
When exposure occurs every day throughout the year, the chronic, intermediate, and acute EF are 1.
However, when exposure is intermittent, which is the case for this scenario, the EF for chronic,
intermediate, and acute durations are different as can be seen in the examples below. For more
information about determining the EF for chronic, intermediate, and acute exposures, review the EDG
for determining life expectancy and exposure factor (ATSDR 2016).
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
13
Intermediate Dose
EF
intermediate
= 0.714 =
Table A2 shows the parameters used to calculate the intermediate, noncancer doses for children
and adults at the daycare who drank water containing 10 mg/L bromoform. Compare these doses
to the intermediate, oral MRL of 0.2 mg/kg/day.
Age Group
CTE
Intake
Rate
L/day
RME
Intake
Rate
L/day
Exposur
e Factor
Unitless
Body
Weight
Kg
Chronic
CTE Dose
mg/kg/day
Chronic
RME Dose
mg/kg/day
Chronic
CTE
Hazard
Quotient
Chronic
RME
Hazard
Quotient
2 to < 6 yr
0.337
0.852
0.714
17.4
0.14
0.35
0.69
1.8
Adult (21 to 78 yr)
1.313
3.229
0.714
80
0.12
0.29
0.59
1.4
Pregnant Women
1.158
2.935
0.714
73
0.11
0.29
0.57
1.4
Breastfeeding Women
1.495
3.061
0.714
75
0.14
0.29
0.71
1.5
Acute Dose
When evaluating acute exposures for drinking water, the EF always will be one.
Table A3 shows the parameters used to calculate the acute, noncancer doses for children and
adults at the daycare who drank water containing 10 mg/L bromoform. Compare these doses to
the acute, oral MRL of 0.7 mg/kg/day.
Age Group
CTE
Intake
Rate
L/day
RME
Intake
Rate
L/day
Exposur
e Factor
Unitless
Body
Weight
Kg
Chronic
CTE Dose
mg/kg/day
Chronic
RME Dose
mg/kg/day
Chronic
CTE
Hazard
Quotient
Chronic
RME
Hazard
Quotient
2 to < 6 yr
0.337
0.852
1
17.4
0.19
0.49
0.28
0.70
Adult (21 to 78 yr)
1.313
3.229
1
80
0.16
0.42
0.23
0.60
Pregnant Women
1.158
2.935
1
73
0.16
0.40
0.23
0.57
Breastfeeding Women
1.495
3.061
1
75
0.20
0.41
0.28
0.58
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
14
Appendix B: Exposure Dose Calculations — Mutagenic Mode of Action (MOA)
Typically, when calculating the cancer risk for a carcinogen, the chronic dose is adjusted for a lifetime
exposure by multiplying the chronic (annual) dose by the number of years of exposure divided by 78
years (the average human life span).
As mentioned previously, EPA has classified certain chemicals as having a mutagenic MOA; therefore,
the cancer risk estimates for MOA chemicals include age-dependent adjustment factors (ADAF) (EPA
2005).
EPA suggests using these ADAFs for chemicals with a mutagenic mode of action that do not have age-
specific CSFs:
• Children 0 < 2 years 10
• Children 2 to < 16 years 3
• Children and adults 16 and older 1
Appendix C: Derivation of Intake Rates for Standard Age Groups and Special
Groups
Standard Age Group (Table 1, pg 5)
2 to < 6 years
The intake rates for children 2 to < 6 years were derived by taking a time-weighted average
(TWA) of children 2 to < 3 years and children 3 to < 6 years as reported in the 2019 update of
the 2011 EFH, Chapter 3, Table 3-1 (EPA 2019).
Adult (21 to 78 years)
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
15
Special Age Groups (Table 2, pg 6)
ATSDR derived intake rates for the following special age groups using intake rates from the
standard age groups to generate a slope that describes the intake rate across the entire age range:
• 3 to < 5 years
• 5 to < 6 years
• 11 to < 14 years
• 14 to < 16 years
• 16 to < 18 years
To derive the mean and 95
th
percentile intake rates for these special age groups, ATSDR first
assigned a midpoint age value to each of ATSDR's standard exposure groups for persons aged 1
to 18. The midpoint age value for the 1 to < 2 years exposure group was 1.5 years, the midpoint
age value for the 2 to < 6 years exposure groups was 4 years, and so on. Next, ATSDR used
Excel to develop linear regression relationships between the midpoint age values for the standard
exposure groups and their mean and 95 percentile intake rates. Both relationships were highly
linear and had R-squared coefficients greater than 0.99. Finally, ATSDR used the linear
regression equations to estimate the mean and 95th percentile intake rates for the special
exposure groups, based on the midpoint age value of each group.
Figure 1 shows the regression plots for the mean and 95
th
percentile intake rates for ATSDR’s
standard age groups along with the regression equation used to estimate the drinking water intake
rate for special age groups reported in Table 2.
Exposure Dose Guidance for Water Ingestion, V1 – Jan 31, 2023
16
Table C1, Children
Age Group Mid-point Mean, mL/day 95
th
Percentile, mL/day
3 to < 5 years
4
324
866
5 to < 6 years
5
364
1,006
11 to < 14 years
12.5
553
1,655
14 to < 16 years
15
621
1,866
16 to < 18 years
17
675
2,072
Sample calculation for 3 to < 5 years
Table C2, Adults (21 to 78 year)
The mean and 95
th
percentile intake rates for adults are based on the following intake rates
reported in EPA 2019 EFH, Chapter 3, Table 3-1.
Age Range Mean, mL/day 95
th
Percentile, mL/day
21 to < 30 years
1,183
3,407
30 to < 40 years
1,277
3,278
40 to < 50 years
1,356
3,374
50 to < 60 years
1,419
3,388
60 to < 70 years
1,394
3,187
70 to < 80 years
1,214
2,641
Average
1,307
3,213
Table C3, Adult Workers (18 ≤ 64), full and part-time
The mean and 95
th
percentile intake rates for adult workers are based on the following intake
rates reported in EPA 2019 EFH, Chapter 3, Table 3-1.
Age Range Mean, mL/day 95
th
Percentile, mL/day
18 to < 21 years
722
2,214
21 to < 30 years
1,183
3,407
30 to < 40 years
1,277
3,278
40 to < 50 years
1,356
3,374
50 to < 60 years
1,419
3,388
60 to < 67 years
1,394
3,187
Time-weighted Average*
1,284
3,270
*