F ax-on-D emand
Telephone: (202) 401-0527
Item No.: 6084
Pesticide Science Policy
STANDARD OPERATING PROCEDURE (SOP)
FOR INCORPORATING SCREENING-LEVEL
ESTIMATES OF DRINKING WATER EXPOSURE
INTO AGGREGATE RISK ASSESSMENTS
PUBLIC COMMENT DRAFT
September 1, 2000
Office of Pesticide Programs
Environmental Protection Agency

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EXECUTIVE SUMMARY
This document is the Standard Operating Procedure (SOP) which provides a step-by-step
process for staff to follow when incorporating screening-level estimates of drinking water exposure
into the Office of Pesticide Program's (OPP) human health aggregate risk assessments. It contains:
1) terms, definitions, descriptions, and calculations for use in incorporating estimates of pesticide
concentrations in surface water and groundwater from screening-level models into aggregate risk
assessments, 2) examples of specific language that may be used in health effects risk assessment
documents to characterize screening-level exposure estimates for drinking water, and 3) an
appendix containing example scenarios and calculations. This document provides the detailed
procedures for implementing OPP's overall policy as articulated in "Estimating the Drinking Water
Component of a Dietary Exposure Assessment" (See 64 FR 61346-61348, November 10, 1999).
Under the procedures outlined in this document, the resulting estimates of exposure
associated with a pesticide in drinking water are considered to be unrefined, high-end, upper-bound
values. However, since many compounds can be "cleared" of drinking water concerns using these
screening-level procedures, the process saves limited resources by providing an efficient means to
determine whether a more refined assessment of drinking water exposure for a specific compound
is warranted. This document is an updated version of the existing SOP for incorporating drinking
water exposure into aggregate risk assessment and replaces the previous SOP dated August 1, 1999
(HED SOP 99.5, 1999). For additional information regarding the drinking water exposure models
which OPP's Environmental Fate and Effects Division uses to provide the exposure estimates used
in this SOP, refer to the following document: "Drinking Water Screening Level Assessment, Part
A: Guidance for Use of the Index Reservoir in Drinking Water Exposure Assessments, Part B:
Applying a Percent Crop Area Adjustment to Tier 2 Surface Water Model Estimates for Pesticide
Drinking Water Exposure Assessments."

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Standard Operating Procedure (SOP) for Incorporating Screening-Level Estimates of
Drinking Water Exposure into Aggregate Risk Assessments
Introduction
This document provides guidance in the form of a standard operating procedure (SOP) for
incorporating screening-level estimates of exposure to pesticides in drinking water into the OPP's
aggregate human health risk assessments. It outlines the step-by-step process the Health Effects
Division (HED) and the Environmental Fate and Effects Division (EFED) have developed to date
to coordinate the necessary interactions between the two divisions. It describes in detail the
processes outlined in the OPP's policy on estimating exposures to pesticides in drinking water1.
This SOP describes a generic process for any of the various actions generated in the Registration
Division (RD) and the Special Review and Reregistration Division (SRRD), including reregistration
eligibility decisions (REDs), the application for registration of new chemicals and new/amended
uses, and emergency exemptions (Section 18s). The SOP also includes specific examples of
language to be used in the following situations: 1) when a risk assessment is not warranted because
of the use pattern or chemical characteristics of the pesticide, and 2) when screening-level models'
estimates do not exceed drinking water levels of comparison. All such language is set in italicized
typeface and indented. The SOP will evolve over time as HED and EFED refine their screening-
level process for assessing exposure to pesticide residues in drinking water.
To assess whether drinking water exposures could potentially contribute significantly to aggregate
risk, the OPP uses an approach that incorporates a series of tiers, or screening procedures. OPP's
tiered approach provides an efficient process for determining which pesticides warrant a more
detailed assessment of drinking water exposures. Progression through the tiers is expected to result
in progressively more accurate and realistic estimates of pesticide concentrations in drinking water.
This document describes the initial tiers of OPP's current screening-level assessment process. The
screening-level process assures that any potential drinking water exposure will not result in
unacceptable levels of aggregate risk. The goal of this process is to identify pesticides for which
there is no reason to suspect that drinking water exposure will contribute significantly to aggregate
risk.
The goal is reached by using estimates of exposure that are conservative enough that there is little
possibility that they will be significantly exceeded for anyone in the population. If there does
appear to be a possibility of unacceptable exposure, a more detailed and quantitative assessment of
aggregate exposure may be warranted on a case-by-case basis. However, if aggregate risk based on
conservative estimates of exposure under the screening-level process are below the level of
concern, there is no need to conduct a more refined exposure assessment for drinking water, and
resources are conserved.
This approach requires that the drinking water exposure assessment address two questions: 1) For
USEPA, "Estimating the Drinking Water Component of a Dietary Exposure Assessment," 64 FR 61346-61348,
November 10, 1999.

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what concentration of a pesticide in drinking water can OPP be confident that there is no one in
the exposed population receiving drinking water with the pesticide at a significantly higher
concentration, and 2) Is that a concentration that may cause concern in light of aggregate exposure?
Any estimate of drinking water exposure developed under this screening-level paradigm represents
an upper bound and should be characterized as such in the risk assessment.
In this approach, the resulting drinking water exposure provided to the risk manager does not
represent an accurate estimate of drinking water exposures for most of the population, although it
might be representative for some maximally exposed individual. The risk manager can be confident
that the resulting assessment will yield overestimates of risk. Procedures for a more quantitative
estimate of exposure to pesticides in drinking water yielding more accurate estimates of risk will be
the subject of a different paper.
EFED's prime responsibility in this screening-level process is to develop screening-level estimates
of pesticide (and significant degradation products) concentrations in ground and surface water for
comparison to a theoretical limit for the pesticide in drinking water. All such concentration
estimates are considered to be high end or upper bound estimates for the purposes of comparison
to drinking water limits. Basic environmental fate and transport data, e.g., a description of the
pesticide's (and degradation products') persistence and mobility should accompany the
concentration estimates. If an estimation is not possible, EFED provides a complete explanation
regarding deficiencies in the fate and transport data which preclude generation of a model estimate.
HED uses the screening-level estimates of pesticide concentrations in ground and surface water
sources to develop a screening-level drinking water exposure assessment that will be incorporated
into the overall risk assessment. The drinking water assessment process is an iterative process
between HED and EFED, where HED drives refinement of the estimates through an on-going
risk assessment process. If necessary, HED will refine its exposure and risk assessment from
residues in food to include anticipated residues (using percent of crop-treated information,
monitoring and field trial data, and probabilistic assessments where appropriate) before requesting
refinements to estimated pesticide concentrations in water from EFED.

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Step 1: Initial Meetings for REDs or New Chemicals.
•	Reregistration Eligibility Decisions (REDs)
For newly assigned REDs, it is suggested that SRRD initiate a meeting with members of HED,
EFED, and the Biological and Economic Analysis Division (BEAD) who have been assigned
responsibility for their divisions' RED chapter. This meeting would introduce the responsible staff
members from each division to one another and provide for discussing specific time-lines regarding
drinking water assessments. In addition, use patterns, toxicity issues, degradation
products/metabolite issues, and any other major issues affecting the risk assessment could be
discussed. SRRD sends a formal request (bean sheet) to EFED for pesticide concentration
estimates in surface and ground water.
For REDs in process, SRRD sends a bean sheet to EFED requesting pesticide concentration
estimates in surface and ground water. Where an initial meeting has not been held, HED and
EFED need to be proactive and take responsibility for coordinating their RED activities. In
general, HED staff will contact the appropriate EFED staff to initiate information exchange
relevant to the risk assessment for drinking water. SRRD/HED staff in the interdisciplinary
reregistration branches will take responsibility for keeping EFED staff informed of HED's
scheduled due dates for RED chapters, presentation dates of their risk assessments to the Science
Assessment Review Committees (SARCs), and setting up additional follow-up meetings with EFED
to discuss drinking water exposure assessments for REDs assigned to them.
Time Frame: ASAP after chemical assignments have been made.
•	New Chemicals
It is suggested that RD initiate a meeting after data review packages are sent to HED and EFED
for review and after HED and EFED assign team members to the new chemical. The purpose of
the meeting is to introduce HED and EFED team members to one another and to consider the
uses associated with the new chemical, and to discuss timelines for the drinking water assessments.
RD should provide any important use and label information to HED and EFED as soon as
possible. RD sends a bean sheet to EFED for pesticide concentration estimates in drinking water.
RD/HED staff in the interdisciplinary registration branches will take responsibility for keeping
EFED staff informed of HED's scheduled due dates for risk assessment documents, presentation
of their risk assessments to SARCs, and setting up additional follow-up meetings with EFED to
discuss drinking water exposure assessments for new chemicals assigned to them.
Time Frame: ASAP after new chemical assignments have been made.
•	Emergency Exemptions - Section 18s
RD sends a bean sheet simultaneously to HED and EFED for the Section 18 action. RD
coordinates the due dates for EFED's assessment with HED's due date so that HED has time to
incorporate EFED's information into their risk assessment, i.e., EFED's memo must be sent to
HED a few days prior to HED's due date. EFED sends their finished assessment directly to HED

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and sends one copy to RD to close out the action. Under the Food Quality Protection Act
(FQPA), all uses of the chemical may need to be considered, not just the emergency exemption use.
•	Other Actions
RD uses the same general process, as described above for new chemicals, for new and amended
uses, and time-limited tolerances. However, under the FQPA, all uses of the chemical may need to
be considered, not just the new/amended use or the time-limited tolerance.
Step 2: HED Invites EFED to Metabolism Assessment Review Committee (MARC)
Meetings (All Actions)
•	I [I 'D takes responsibility for inviting EFED to the HED Metabolism Assessment Review
Committee (MARC) meeting where a decision is made to include or exclude the soil/water
degradation products in the tolerance expression or risk assessment. During the MARC
meeting plant/livestock metabolites are compared with soil/water degradation products.
The MARC determines whether soil/water degradation products are of toxicological
concern and present in significant concentrations to warrant inclusion into the drinking
water exposure assessment. EFED should provide a comprehensive fate profile of the
degradation products including their chemical identification, patterns of formation and
decline in terrestrial and aquatic environments, and relative concentrations and mobility in
soil and water. HED informs SRRD/RD of any issues relating to soil/water degradation
products that may impact the human health risk assessment.
•	As soon as possible, HED staff provide the EFED staff with as much information as is
available on the selected toxicity endpoints. This will enable EFED and HED to discuss
toxicity endpoints relative to available exposure numbers early in the process. This can be
done during the MARC meetings.
Step 3: Determine if a Drinking Water Exposure Assessment is Needed
•	A drinking water exposure assessment is not always needed. For instance, if the use pattern
associated with the action meets the following conditions:
—Active registrations exist for only the following types of uses: baits, greenhouse
uses, seed treatments, potato seed piece treatments, crack and crevice treatments,
food handling establishment uses, other indoor uses, or uses related to import
tolerances only — EFED states this in a brief memo to HED and completes the
bean sheet associated with the initial request for drinking water concentration
estimates. HED makes a statement such as the following in the risk assessment
document:
"OPP has considered the registered uses and the available data
on persistence and mobility for [chemical]. OPP has
determined through a qualitative assessment that the use

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pattern associated with [chemical] [specify use pattern
parenthetically] is not expected to impact water resources
through labeled uses. In light of this finding, OPP believes
that [chemical] use will not impact ground water or surface
water resources, and therefore is not expected to lead to
exposure to humans through drinking water. If new uses are
added in the future, OPP will reassess the potential impacts of
[chemical] on drinking water as a part of the aggregate risk
assessment process."
AND/OR
— EFED determines that the pesticide and its toxicologically significant degradation
products are neither persistent nor mobile and there is clearly no concern regarding
the impact of the pesticide's use on drinking water. In this case, EFED states this
in a brief memo to HED, which includes a brief description of the chemical's (and
its toxicologically significant degradation products) persistence and mobility
characteristics, and completes the bean sheet associated with the initial request for
drinking water concentration estimates. HED makes a statement such as the
following in the risk assessment document:
"OPP has considered the registered uses and the available data
on persistence and mobility for [chemical(s)]. OPP has
determined through a qualitative risk assessment that the
physical and chemical characteristics of [chemical(s)] are such
that they are not expected to impact water resources.
[Chemical(s)] is/ are neither persistent nor mobile. [Place
persistence and mobility characteristics here.] In light of these
findings, OPP believes that [chemical] use will not impact
ground water or surface water resources, and, therefore, is not
expected to lead to exposure to humans through drinking
water. If new uses are added in the future, OPP will reassess
the potential impacts of [chemical] on drinking water as a part
of the aggregate risk assessment process."
•	A drinking water exposure and risk assessment is usually needed if the pesticide is expected or
known to impact water resources based on usage pattern, persistence and mobility criteria,
or monitoring data, and thereby could result in exposure through drinking water.
Step 4: EFED Provides Screening-Level Estimates of Pesticide Concentrations in Drinking
Water from Surface and Ground Water to HED
•	Once it has been determined that a drinking water exposure assessment is needed, EFED
provides screening-level estimates of the pesticide's concentration in drinking water from
surface and ground water, and a brief description of the chemical's persistence and mobility
to HED. If any degradation products were included in the risk assessment as a result of the

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MARC meeting, screening-level estimates for those degradation products and their
persistence and mobility should also be included. HED needs estimates of the maximum
(peak), average annual, and multi-year mean concentration values for a pesticide for use in
acute and chronic exposure assessments. EFED provides the requested estimates and
persistence and mobility information in a memo to HED and completes the bean sheet
associated with the initial request for drinking water estimates. EFED copies the memo to
RD/SRRD.
•	To provide HED with the required estimates, EFED initially conducts a screening-level
assessment using tier 1 computer simulation models: Generic Estimated Environmental
Concentrations (GENEEC) or First Index Reservoir Screening Tool (FIRST) for surface
water estimates, and Screening Concentration In Groundwater (SCI-GROW) for
groundwater estimates2. EFED's screening-level assessments with GENEEC or FIRST and
SCI-GROW use the highest labeled application rate for a pesticide to provide estimates of
the pesticide's concentrations in surface and ground water, respectively. These
concentration estimates are considered to be upper bound for comparison to theoretical
concentration limits for the pesticide in drinking water (discussed in Step 5), and considered
adequate for screening-level purposes. From GENEEC, EFED provides a maximum
concentration value, and the 56-day average concentration value to HED. From FIRST,
EFED provides a maximum concentration value, and an average annual concentration value
to HED. Concentration estimates from GENEEC or FIRST are used for the surface water
exposure assessments. From SCI-GROW, EFED provides a single concentration value (a
90-day average) to be used for groundwater assessments. Because residues of pesticides in
groundwater do not fluctuate as widely over time as they do in surface water, one value is
considered adequate for screening-level assessments. Adequate data for a screening-level
assessment include all or most of the following: application rates, data on the soil and water
degradation products, solubility, soil-water adsorption coefficients, and rates of decay
associated with hydrolysis, soil/water photolysis, and aerobic/anaerobic soil and water
degradation processes.
•	In general, in a screening-level assessment for surface water, EFED will use a tier 1 model
(GENEEC or FIRST) before using a tier 2 surface water model: Pesticide Root Zone
Model/Exposure Analysis Modeling System (PRZM/EXAMS). The GENEEC and FIRST
models are subsets of the PRZM/EXAMS model that use a specific high-end runoff
scenario for pesticides. GENEEC incorporates a pond farm scenario, while both FIRST
and PRZM/EXAMS incorporate an index reservoir environment in place of the previous
farm pond scenario. The tier 2 PRZM/EXAMS model includes a percent crop area (PCA)
factor as an adjustment to account for the maximum percent crop coverage within a
watershed or drainage basin defined as an eight-digit Hydrologic Unit Code (HUC).
Specific PCAs have been developed for some crops. For all other crops, a default PCA of
0.87 has been recommended. The default PCA represents the highest percentage of land
within an eight-digit HUC in agricultural production, but is not specific to a particular crop
2
Currently, OPP uses GENEEC as the tier 1 screening-level model for surface water-sourced drinking water
assessments. OPP expects to replace GENEEC with FIRST as the tier 1 screening-level model for surface water-sourced drinking
water assessments in the future.

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(Effland, et al., 1999).
•	As a part of a screening-level assessment, EFED also briefly considers available monitoring
data from any of a variety of sources. These can include USEPA's STORET and National
Pesticide Survey databases, USGS' National Water Quality Assessment Program (NAWQA)
data, the Pesticides in Groundwater Database, data collected under the Safe Drinking Water
Act (SDWA), state monitoring programs, small-scale prospective groundwater studies, and
runoff studies. Results from the monitoring studies are compared to the model estimates to
ensure that the models are not underestimating a chemical's potential concentrations in
surface and ground waters. Once EFED has verified that the model estimates do not
underestimate concentrations reported in ground and surface waters from monitoring data,
EFED provides the concentration estimates to FLED.
•	If all or a geographic subset of the monitoring data consistently exceed the model values,
EFED conducts an in-depth review of the monitoring data and disregards the model
estimates. EFED provides a comparison of the monitoring data to the model values. If
the monitoring data are judged to be reliable and appropriate for a drinking water
assessment, HED uses these data to prepare the required exposure and risk assessments.
(See Step 10).
Step 5: Using Drinking Water Levels of Comparison Values (DWLOCs) in a Screening-
Level Exposure Assessment for Drinking Water
What is a DWLOC?
HED uses Drinking Water Level of Comparison (DWLOCs) values as a surrogate measure of
exposure and risk. The models currently used to estimate pesticide concentrations in drinking
water are very conservative and used as screening tools in the risk assessment process. HED does
not use concentration estimates from current models (GENEEC, FIRST, PRZM/EXAMS, and
SCI-GROW) to quantify risk as a percentage of the reference dose (%RfD) or population
adjusted dose (%PAD). [The PAD is the RfD after adjustment by a FQPA safety factor and can
be considered the target exposure not to be exceeded for a given pesticide.] Instead, HED
compares the model estimates to DWLOC values. This comparison provides a semi-quantitative
risk assessment for drinking water until the drinking water exposure estimates can be refined.
In calculating a DWLOC, HED determines how much of the acceptable exposure (i.e., the RfD or
PAD) is available for exposure through drinking water. Simply, if 10 mg/kg/day is the chronic RfD
or PAD, and chronic exposure through average food residues is 6 mg/kg/day, and there are no
residential uses, or other exposures, then 4 mg/kg/day is "allowed" or "available" for exposure
through drinking water. This allowable exposure through drinking water is used to calculate a
concentration that is considered a theoretical limit for the pesticide in drinking water. The
DWLOC takes into account estimates of aggregate exposure to a pesticide through food and home
uses. It is considered a theoretical limit because the calculation uses default assumptions about
body weight and drinking water consumption, and there is some uncertainty associated with the

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estimates of exposure from food and home uses. The body weights and consumption rates used are
the standard default values used by the Office of Ground Water and Drinking Water in calculating
drinking water standards (US EPA, OGWDW, 1989)3.
How many DIVLOCs are calculated?
Generally, a DWLOC will need to be calculated for each type of risk assessment required: acute,
short-term, intermediate-term, chronic, and cancer. This could require calculations for:
DWLOCacute, DWLOCSHOrt-termj DWLOCintermediate_term, DWLOCCHROnicj and
DWLOCcancer.
Under each type of required risk assessment, DWLOCs should be calculated for the following
populations in the Dietary Exposure Estimate Model (DEEM) using the assumed default values for
body weight and consumption as noted:
U.S. Population/48 states or highest exposed adult male subgroup (70 kg body weight and 2
liters/day consumption)
Females* (60 kg body weight and 2 liters/day consumption)
Infants* (10 kg body weight and 1 liter/day consumption)
Children* (10 kg body weight and 1 liter/day consumption)
* In the case of females, infants, and children, DEEM provides the exposure from food for various
population subgroups. There are four subgroups for females listed in the standard DEEM analysis
(13+ pregnant, 13+ nursing, 13-19 not pregnant or nursing, 20+ not pregnant or nursing). There
are also four subgroups for infants and children. In these instances, the DEEM subgroup with the
highest food exposure should be used when calculating the DWLOC specific to that population.
For example, DEEM provides the following results for four subgroups of the female population:
Population Subgroup	Exposure
Females (13+ years, pregnant)	0.000126
Females (13+ years, nursing)	0.000161
Females (13-19 years, not pregnant or nursing)	0.000157
Females (20 years, not pregnant or nursing)	0.000120
In the example above, a DWLOC representing the population "females" should be calculated for
"females 13+ years, nursing" since this is the subgroup for the female population with the highest
exposure. In addition, if any of the subgroups for adult males is higher than the exposure of the
OPP acknowledges that there are differences in body weights and consumption across population subgroups, and
although OPP does not consider them in the initial tiers of our screening-level process for estimating drinking water exposure
as described in this document, these differences are real, and OPP will be taking them into account in subsequent refinements
to the screening-level process. OPP will be using records containing covariant data linking individual drinking water
consumption and body weights for specific individuals within population subgroups as defined in the dietary exposure program
(DEEM). Additional refinements to the screening process will be the subject of another document on quantitative procedures to
assess exposure to pesticides in drinking water.

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general U.S. population, a DWLOC for the adult subgroup with the highest exposure should also
be calculated. Typically, then, a different DWLOC for each of 4 populations will be calculated: U.S.
population, females (the highest exposed subgroup within this population), infants and children (the
highest exposed subgroups within these populations), and the highest exposed adult subgroup if
any subgroup has an exposure that is greater than that for the U.S. population.
It should be noted that in some cases, a specific risk assessment is required for one specified
population subgroup only. For example, for a chemical, an acute risk assessment is required only for
females 13+ because the endpoint selected as the basis of the acute risk assessment is
developmental toxicity. In this case, a DWLOC ACute should be calculated for the specific
population subgroup for which the risk assessment is required, i.e., females 13+. No other
DWLOC calculations for the acute risk assessment would be necessary. Generally, the population
subgroups of interest for any required risk assessment are clearly stated in the Hazard Identification
Assessment Review Committee (HIARC) document.
[Note: the RfD or PAD may be different for different populations. For example, a FQPA safety
factor of 10X may be applied to females 13+ only for the acute dietary risk assessment. In this
case, the appropriate PAD reflecting the additional 10X safety factor must be carried through the
DWLOCacute calculations for this population only.]
Step 6: Calculating Drinking Water Level of Comparison (DWLOCs) Values.
In general, the DWLOCacute is the concentration in drinking water as a part of the aggregate acute
exposure that occupies no more than 100% of the acute RfD or PAD. The DWLOCCHRONiC is the
concentration in drinking water as a part of the aggregate chronic exposure that occupies no more
than 100% of the chronic RfD or PAD. The DWLOCcancer is the concentration in drinking water
as a part of the aggregate chronic exposure that results in a negligible cancer risk. Currently default
daily consumption and body weight values (as used by the Office of Ground Water and Drinking
Water) are used to calculate DWLOCs: 2L/70 kg (for adult males), 2L/60 kg (for adult females),
and 1L/10 kg (for infants and children). For aggregate risk assessments that include short- and
intermediate-term residential exposures, it may be necessary to calculate values for the DWLOC
short-term and the DWLOCintermediate_term . The necessary calculations are discussed later in this
step. The necessary calculations for each type of risk assessment follow:
A cute Risk Assessment
• The DWLOC for acute risk, is calculated as given in the equation below. It is assumed that
the acute RfD or PAD are known for an acute dietary risk assessment, that the acute food
exposures (at the 95th percentile of exposure for deterministic assessments or at the 99.9th
percentile of exposure for probabilistic assessments) from an acute DEEM run are known,
and that there is no residential exposure. Use default body weight and consumption rates,
accordingly.

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DWLOCacute (ug/L) = \ฐne~day water exposure (mg/kg bwlday) x body weight (A-g)]
\water consumption (L/dav) x 10~3 mg/ug]
one-day water exposure (mg/kg bwldav) = [AcutePAD - {one-day) food exposure (mg/kg bwldav)
Chronic Risk Assessment
• The DWLOC for chronic risk is calculated as given in the equation below. It is assumed
that the chronic RfD or PAD, and chronic food and residential (if any) exposures are
known. Where chronic residential exposure is expressed as the average daily dose (ADD).
Use default body weight and consumption rates, accordingly.
r\nrr rtn t..„n\ _ chronic water exposure (mg/kg bwldav) x body weight (kg)
chronic^ ^ /
water consumption (L/dav) x 10-3 mg/ug
chronic water exposure (mglkglday) = [Chronic PAD - (average food + chronic residential exposure (ADD)) (mglkglday)]
Cancer Risk Assessment
• To calculate DWLOC for cancer risk, (assuming the MOE or q+, and chronic food and
residential (if any) exposures are known),
(A) If the risk is quantified using the MOE approach, calculate DWLOCcancer as above under acute
risk, except include the chronic food and residential exposures in the aggregate exposure term when
calculating the water exposure value.
[NOAEL/MOE (mg/kg/day)] - ([chronic food + chronic residential exposure (ADD))
(mg/kg/day)] = chronic water exposure (mg/kg/day)

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(B) If the risk is quantified using a q* approach, where chronic residential exposure is expressed as the
LADD or lifetime average daily dose. Generally, a DWLOCcancer based on a q+ is calculated for
the US population only4.
Short- and Intermediate - Term Risk Assessments
As a part of aggregate risk assessment, short-term and intermediate-term risk assessments requiring
the incorporation of drinking water exposure and the calculation of DWLOC values, can be
handled either through:
1)	the reciprocal MOE equation ("1/MOE approach") for calculating an aggregate MOE and
solving for the term MOEwater, or
2)	the Aggregate Risk Index (ARI) method.
The reciprocal MOE equation using the 1/MOE approach can be used only if the acceptable
MOEs are identical for all routes of exposure included in the calculation, otherwise, use the ARI
method. Examples of DWLOC calculations using both methods are given in Appendix I.
Use the following guidance taken directly from the "Guidance for Performing Aggregate Exposure
and Risk Assessments" when incorporating screening-level estimates of short- and intermediate-
term drinking water exposure into aggregate risk assessments5.
"Since short- and intermediate-term, single-source risk assessments are typically only done
for worker and residential assessments, oral endpoints may not always be selected. If an
4
OPP acknowledges that the current cancer risk assessment process does not consider estimates of less-than-lifetime
exposures that may be warranted to cover early life effects. However, as cancer exposure assessment policy develops, future
exposure assessments may include consideration of cancer risk for other population subgroups.
DWLOCcancer (ug/L)
[chronic water exposure (mg/kg bw/day) x body weight (&g)]
[water consumption (LIday) x 10~3 mg/ug\
chronic water exposure (mg/kg/day)
Negligible risk
Q*
[(average food+chronic * residential exposure (LADD)) (mg/kg/day)]
^ US EPA, "Guidance for Performing Aggregate Exposure and Risk Assessments," 64 FR 61343-61346, November 10,
1999.

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endpoint and NOAEL from an oral study are selected for either short- or intermediate-
term dermal or inhalation risk assessment, this oral NOAEL and endpoint should be used
to calculate the non-dietary, inadvertent hand-to-mouth exposure and the dietary (food and
water) exposure components of the aggregate risk assessment. If an oral endpoint is needed
for short- or intermediate-term assessment, yet only dermal and or inhalation endpoints
have been selected for these assessments, the following default rules apply:
1)	If an oral endpoint is needed for short term risk assessment for incorporation of
dietary (food or water), or oral hand-to-mouth-type (non-dietary, inadvertent) exposures
into aggregate assessment, and only dermal and/or inhalation endpoints have been selected,
the acute oral endpoint (basis of the acute RfD or PAD) should be used to incorporate the
oral component into the aggregate risk.
2)	If an oral endpoint is needed for intermediate term risk assessment for
incorporation of dietary (food or water), or oral hand-to-mouth-type (non-dietary,
inadvertent) exposures into aggregate assessment, and only dermal and/or inhalation
endpoints have been selected, the chronic oral endpoint (basis of the chronic RfD or PAD)
should be used to incorporate the oral component into the aggregate risk."
Short-Term Risk Assessment Using the Reciprocal MOE Method
Whenever a short-term risk assessment is required for a pesticide with residential uses and the
acceptable Margins of Exposure (MOEs) are identical for all MOEs in the calculation, the following
equations should be solved for the term "MOEwater,". The acceptable MOE is the product of
the selected uncertainty factors (UFs) for the short-term risk assessment.
Aggregate MOE
1 + _J_ +	1
MOEoral MOEdermal moeinhalation
MOEw
1 -
MOE,
Where the aggregate MOEAGG is equal to the acceptable MOE for the short-term risk assessment:
the MOEFood is based on the dietary exposure from average food residues (chronic exposure) compared to the short-
term oral NOAEL or the acute dietary NOAEL,
the MOEwatbr is based on "allowable short-term water exposure" from average drinking water residues compared to
the short-term oral NOAEL or the acute dietary NOAEL,

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15
the MOEqral is based on the calculated short-term oral hand-to-mouth residential exposures compared to the short-
term oral NOAEL or the acute dietary NOAEL,
the MOEdermal is based on the calculated short-term residential dermal exposures compared to the NOAEL selected
for short-term dermal exposures,
and the MOEinhalation is based on the calculated short-term residential inhalation exposures compared to the
inhalation NOAEL (any time period).
After calculating the value for the term "MOEwater", solve the following equation for the allowable
short-term water exposure, calculated as follows:
MOEWAIBR =	Short-term oral or acute dietary NOAEL
Allowable Short-Term Water Exposure
Allowable Short-Term Water Exposure =	Allowable short-term oral or acute dietary NOAEL
moewatbr
Using the Allowable Short-Term Water Exposure value, the Short-term DWLOC is calculated as
follows using the appropriate default values for body weights and consumption rates:
DWLOCsHORT TBRM^g/L) = Allowable Short-Term Water Exposure (mg/kg/dav) x Body Wt fcg)
(IE-3 mg//ig) x Daily Drinking Rate (L/day)
Intermediate-Term Risk Assessment Using the Reciprocal MOE Method
Whenever, an intermediate-term risk assessment is required for a pesticide with residential uses the
following equations should be solved for the term "MOEwater":
Aggregate MOE
1 + _J_ +	1
MOEoral MOEdermal moeinhalation
moewater
1
1
MOE,
Where the aggregate MOEAGG is equal to the acceptable MOE for the intermediate-term risk assessment:
the MOEFood is based on the dietary exposure from average food residues (chronic dietary exposure) compared to the
intermediate-term oral NOAEL or the chronic dietary NOAEL,

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16
the MOEWAIBR is based on "allowable intermediate-term water exposure" from average drinking water residues
compared to the intermediate-term oral NOAEL or the chronic dietary NOAEL,
the MOEqral is based on the calculated intermediate-term oral hand-to-mouth residential exposures compared to the
intermediate-term oral NOAEL or the chronic dietary NOAEL,
the MOEdermal is based on the calculated intermediate-term residential dermal exposures compared to the NOAEL
selected for intermediate-term dermal exposures,
and the MOEinhalation is based on the calculated intermediate-term residential inhalation exposures compared to the
inhalation NOAEL (any time period).
After calculating the value for the term "MOEwater," the "allowable intermediate-term water
exposure" is calculated as follows:
MOEWAIBR =	Intermediate-term oral or chronic dietary NOAEL
Allowable Intermediate-Term Water Exposure
Allowable Intermediate-Term Water Exposure	—	Intermediate-term oral or chronic dietary NOAEL
moewatbr
Using the Allowable Intermediate-Term Water Exposure value, the Intermediate-term DWLOC is
calculated as follows using the appropriate default body weights and consumption rates:
DWLOCnsnBRMSDiATE-TERMCwg/L) = Allowable Intermediate -Term Water Exposure (mg/kg/dav) x Body Wt fcg)
(IE-3 mg/^ig) x Daily Drinking Rate (L/day)
Short- and Intermediate-term Risk Assessments Using the ARI Method
When Short- and Intermediate-term risk assessments cannot be conducted with the reciprocal
MOE method, the equations below for the ARI method can be used.
l
Aggregate ARI = 	
1	+ 1 + 1 + 1 +	1
ARIpooD ARTwater ARIoral ARIdermal	ARIinhalation
ARIW
1 -
ARL
1 + 1 + 1
+ 1
ARIr
Where ARI — [MOEcalcljlated (ie
(i.e., FOOD, WATER, DERMAL, INHALATION, ORAL)
- MOE
'ACCEPTABLE],

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17
Sample calculations using the reciprocal MOE and ARI methods are given in Appendix I.
Step 7: Comparing DWLOC Values to Concentration Estimates from Surface and Ground
Water Screening-Level Models
In general, maximum (peak) concentration estimates from the tier 1 or 2 screening-level models for
surface water (GENEEC, FIRST or PRZM/EXAMS) are compared only to acute DWLOC values
for the acute portion of the aggregate risk assessment. All other DWLOC values (short-term,
intermediate-term, chronic, and cancer) are compared to the long-term average concentration
estimates from the models for the short- and intermediate-term, chronic, and cancer portions of
the aggregate risk assessment.
Because GENEEC only provides a 56-day average value, and not a longer-term average value, (i.e.,
an annual average or multi-year mean), the 56-day concentration value from GENEEC is divided
by 3 for comparison to short-term, intermediate-term, chronic, and cancer DWLOC values.
Because the groundwater model, SCI-GROW, only provides one concentration estimate (a 90-day
average value), compare it to all DWLOC values, regardless of exposure scenario (acute dietary,
short- or intermediate-term, chronic, or cancer). Table 1 provides a summary. Specifics regarding
the comparison of model estimates to DWLOC values are given in steps 8 and 9.
Table 1. DWLOCs Compared to Model Estimates of Pesticide Concentrations in Ground and Surface Water.
DWLOC Values
GENEEC
FIRST
PRZM/EXAMS
SCI-GROW
DWLOC Acute
maximum
concentration
maximum
concentration
maximum concentration
90-day average
concentration
DWLOCchrohic
56-day average 3
annual
average
annual average and 36-year mean
90-day average
concentration
DWLOC CANCER
56-day average 3
annual
average
annual average and 36-year mean
90-day average
concentration
DWLOC SHORT-TERM
56-day average 3
annual
average
annual average and 36-year mean
90-day average
concentration
DWLOC INTERMEDIATE-TERM
56-day average 3
annual
average
annual average and 36-year mean
90-day average
concentration
Step 8: Characterizing the Results of the Screening-Level Assessment Using GENEEC or
FIRST and SCI-GROW
• If the models' estimates of a pesticide's concentration in ground and surface water (inclusive
of relevant degradation products) are less than HED's levels of comparison for drinking
water (DWLOCs), HED concludes with reasonable certainty that the exposure to the
pesticide in drinking water is likely to be insignificant, and the associated human health risks
are not of concern. Qualitative risk language should be used to characterize the risk, and/or

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a table of DWLOC values for comparison to the model estimates can be provided. An
example table comparing acute DWLOC values to the appropriate model concentration
estimates is provided below. Similar tables can be prepared for the chronic, cancer, short-
and intermediate portions of the aggregate risk assessment.
Population Subgroup
aPAD
(mg/kg)
1-Day Food
Exposure
(mg/kg/day)
Allowable
One-Day Water
Exposure
(mg/kg/day)
%
aPAD
GW
Cone.*
(PP^
SW
Cone.*
(Ppb)
Acute
DWLOC
(wg/L)
US population







Female Subgroup







Children's Subgroup







Infant's Subgroup







* Groundwater (GW) concentration from SCI-GROW represents a 90-day average. Surface water (SW) concentration from
GENEEC or FIRST represents an estimated maximum concentration.
• The following standard language provides an example of qualitative risk language that could
be used for a pesticide with food uses, but no residential uses, for which acute, chronic and
cancer risk assessments are required, and where the estimated concentrations in surface and
ground water are less than HED's levels of comparison for drinking water for all risk
assessments required.
"OPP has calculated drinking water levels of comparison (DWTOCs) for acute exposure
to [chemical} in surface and ground water for [papulation subgroups]. They are [X, Y,
...]ppb, respectively. For chronic (non-cancer) exposure to [chemical} in surface and
ground water, the drinking water levels of comparison are [X, Y,...] ppb for [pcpulation
subgroup], respectively. For chronic (cancer) exposure to [chemical] in surface and ground
water, the drinking water levels of comparison are [X, Y,..] ppb, respectively for
[population subgroups]. To calculate the DWLOCfor acute exposure relative to an acute
toxicity endpoint, the acute dietay food exposure from the DEEM analysis) was
subtractedfrom the acute RfD or PAD to obtain the allowable acute (1 -day) exposure to
[chemical] in drinking water. To calculate the DWEOCfor chronic (non-cancer)
exposure relative to a chronic toxicity endpoint, the chronic dietaiy food exposure from
DEEM) was subtracted from the chronic RfD or PAD to obtain the allowable chronic
(non-cancer) exposure to [chemical] in drinking water. To calculate the DWEOCfor
chronic exposures relative to a carcinogenic toxicity endpoint, the chronic (cancer) dietay
food exposure from the DEEM analysis) was subtractedfrom the ratio of the negligible
cancer risk to the q* to obtain the allowable chronic (cancer) exposure to [chemical] in
drinking water. DWLOCs were then calculated using default body weights and drinking
water consumption rates.
Estimated maximum concentrations of [chemical] in surface and ground water are [X]
and [Y] ppb, respectively. Estimated average concentrations of [chemical] in surface and
ground water are [X] and [Y] ppb, respectively. [Note: For the puposes of the screening-

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19
level assessment, the maximum and average concentrations in ground water are not believed
to vaiy significantly.] The maximum estimated concentrations of [chemical] in surface and
ground water are less than OPP's levels of comparison for [chemical] in drinking water
(DWTOC acutej as a contribution to acute aggregate exposure. The estimated average
concentrations of [chemical] in surface and ground water are less than OPP's levels of
comparison for [chemical] in drinking water (DWTOC chronic and cancer) as a
contribution to chronic aggregate exposure for cancer and non-cancer effects. Therefore,
taking into account the present uses and uses proposed in this action, OPP concludes with
reasonable certainty that residues of [chemical] in drinking water (when considered along
with other sources of exposure for which OPP has reliable data) would not result in
aggregate risk estimates that exceed HED's levels of concern at this time.
OPP bases this determination on a comparison of estimated concentrations of [chemical] in
surface waters and ground waters to back-calculated "levels of comparison"for [chemical]
in drinking water. These concentration estimates from screening-level models are considered
to be upper boundfor the puposes of comparison to drinking water levels of comparison.
These levels of comparison in drinking water were determined after OPP had considered all
other non-occupational human exposures for which it has reliable data, including all
current uses, and uses considered in this action. The estimates of [chemical] in surface and
ground waters are derivedfrom water quality models that use conservative assumptions
(health-protective) regarding the pesticide tranportfrom the point of application to surface
and ground water. Because OPP considers the aggregate risk resultingfrom multiple
exposure pathways associated with a pesticide's uses, levels of comparison in drinking
water may vaiy as those uses change. If new uses are added in the future, OPP will
reassess the potential impacts of [chemical] on drinking water as a part of the aggregate
risk assessment process.
• If the models' estimates of pesticide concentrations in surface and ground water are greater
than HED's levels of comparison for drinking water (DWLOCs), HED notifies EFED that
a refined screening-level assessment is needed. HED may initiate a meeting with EFED
and invites RD/SRRD to discuss the necessary refinement.
Step 9: Characterizing the Results of the Screening-Level Assessment Using
PRZM/EXAMS and SCI-GROW
For surface water, when the maximum concentration estimate from the GENEEC or FIRST
models are greater than the DWLOCacute, and/or the longer-term concentration estimates from the
tier 1 models are greater than the DWLOCcancer or DWLOCchromc values, HED requests refined
estimates from the PRZM/EXAMS surface water model from EFED. HED requests a maximum
(peak), the annual average, and 36-year mean concentration estimates from EFED for the pesticide
(inclusive of relevant degradation products) in surface water. HED compares the refined model
estimates to the appropriate DWLOC values. An annual average concentration may be appropriate
for comparison against DWLOC chronic values and a multi-year mean may be more appropriate
for comparison to cancer DWLOC values when a q* is used to quantify cancer risks. HED requests
both values from EFED. If the tier 2 model estimates from PRZM/EXAMS are less than the
DWLOCs, HED will use a similar approach as above in Step 8 for a qualitative risk assessment.

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20
•	For surface water, if the screening-level model estimates from PRZM/EXAMS are still
greater than HED's levels of comparison for drinking water (DWLOCs), HED again
notifies EFED, and EFED may conduct a detailed review and analysis of all available
monitoring data, and determines if they are reliable and appropriate to use for an
assessment of the pesticide's impacts on drinking water or EFED refines the screening-level
drinking water concentration estimates as much as possible.
•	For ground water, a tier 2 model is not yet available. EFED will review all monitoring data
to determine if they are appropriate for a human health exposure and risk assessment.
Step 10: EFED and HED Work Cooperatively to Prepare a Screening-Level Exposure
Assessment using Monitoring Data.
•	Once EFED determines the appropriateness and reliability of available ground and surface
water monitoring data, EFED provides maximum, annual average, and multi-year mean
concentrations from monitoring data for all regions /states /counties for which monitoring
data are available, appropriate, and reliable to HED.
•	EFED provides the concentrations requested and characterizes the monitoring data in a
memo to HED. The characterization includes as much of the following information as
possible:
Source of Data (STORET, Pesticides in Groundwater Database, USGS,
other)
Location of monitoring (the region/state/county where samples were taken,
and an indication as to whether the monitoring data is for ground or surface
water, and whether or not it represents drinking water sources (raw water at
intakes versus treated drinking water) or ambient water quality)
Sampling Dates
Total Number of Samples Analyzed
Total Number of Samples with Detects
The maximum concentration, average annual, and multi-year mean
concentrations, and the range of concentrations.
Limits of Detection (LOD) and Limits of Quantification (LOQ)
Spatial overlap of monitoring data with potential use areas
Depth of well water sampled for ground-water monitoring
Water sources (lake, river, stream, etc.) for surface-water monitoring
A clear statement regarding the level of confidence in monitoring data (the
confidence level associated with the monitoring data, i.e., high, medium or
low),
A statement regarding what the monitoring data represent (e.g., an upper
bound, lower bound, or something in between).
Estimates of populations living in the areas sampled.
•	HED may elect simply to compare the concentration estimates derived from available
monitoring data to the appropriate DWLOC values, and present the information in a table

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21
comparing DWLOC values to concentration estimates from the monitoring data. From the
monitoring data, estimates of maximum concentrations are compared to DWLOCacute
values, and estimates of long-term average concentrations (annual averages or multi-year
means) are compared to all other DWLOC values (as described in Step 7 for model
estimates).
Alternatively, HED may calculate the drinking water exposure using values from monitoring
data in the following equations for adult males, adult females, infants/children, respectively :
,, . ,, i i \ concentration water (u.s/L) x 10 3 (mg/ lie) x 2 LI day
Exposure (mglkglday) = 	 —		v 	—
70 kg for adults (male)
,, , ,, , 7 n concentration water (u.s/L) x 10 3 (mg/ug) x 2 LI day
Exposure (mglkglday) = 	 —		v 	—
60 kg for adults (female)
,, . ,, i i \ concentration water (u.s/L) x 10 3 (mg/ug) x 1 L/day
Exposure (mg!kg/day) = 	 —		v 	—
10 kg for children
In the above equations, for acute exposure calculations, HED uses maximum concentration
values for surface and ground water from EFED. For chronic (non-cancer) exposure
calculations, HED may use average annual concentration values for surface and ground
water from EFED. For cancer (q* approach) exposure calculations, HED may use multi-
year mean concentration values for surface and ground water if available.
The risk metrics (% RfD or PAD, and MOE) provided in HED's "Guidance for
Performing Aggregate Exposure and Risk Assessments" can be used to estimate the risk
inclusive of the screening-level estimate of drinking water exposure based on monitoring
data.
HED characterizes the drinking water exposure in light of EFED's characterization of the
data and confirms their understanding of the characterization with EFED. HED indicates
if the monitoring data represent drinking water (treated or raw) or ambient water quality,
and if pesticide use is associated with the areas monitored. HED states the level of
confidence in the data. HED states if the screening-level risk estimate is associated with a
specific region or regions of the country or a specific state or states. If population estimates
are provided for specific regional monitoring data, HED discusses exposure in terms of

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population potentially exposed.
•	If the concentration estimates from the monitoring data are less than the DWLOC values,
OR
the aggregate risk estimates inclusive of drinking water exposure are below HED's level of
concern (i.e., less than 100% of the RfD or PAD), HED finalizes its risk characterization,
and concludes with reasonable certainty that residues of the pesticide in drinking water are
not expected to result in aggregate risk estimates that exceed HED's levels of concern.
•	If the concentration estimates from the monitoring data are greater than the DWLOC
values or the aggregate risk estimates are above HED's levels of concern (i.e., greater than
100% of the RfD or PAD), and HED has refined its exposure assessment as to residues in
food as much as possible, HED may in consultation with EFED elect to further refine the
drinking water exposure assessment by using distributions of monitoring data in the DEEM
program and where applicable probabilistic techniques of exposure analysis. This step adds
another refinement to the screening-level process allowing incorporation of specific
information on body weights and drinking water consumption available through the DEEM
program into the drinking water exposure assessment. The need for more refined
screening-level assessments and/or quantitative estimates of drinking water exposure for a
compound will be determined on a case-by-case basis. The procedures, models, and
monitoring data needed to develop more refined screening-level assessments and/or
quantitative estimates of drinking water exposures to pesticides are beyond the scope of this
document; they will be discussed in future documents.
•	If the models' concentration estimates are greater than the DWLOC values, and adequate
monitoring data are not available, interim risk management and monitoring data or other
sources of information on the pesticide's impact on water may be required as a part of
reregistration for RED chemicals, as a condition of registration for new chemicals, or as a
condition of extending a tolerance or adding a new use. In general, chemicals needing
interim risk mitigation will be handled on a case-by-case basis.
Policy Not Rules
The policy document discussed in this notice is intended to provide guidance to EPA
personnel and decision-makers, and to the public. As a guidance document and not a rule, the
policy in this guidance is not binding on either EPA or any outside parties. Although this guidance
provides a starting point for EPA risk assessments, EPA will depart from its policy where the facts
or circumstances warrant. In such cases, EPA will explain why a different course was taken.
Similarly, outside parties remain free to assert that a policy is not appropriate for a specific pesticide
or that the circumstances surrounding a specific risk assessment demonstrate that a policy should
be abandoned.

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APPENDIX I
EXAMPLE CALCULATIONS FOR SHORT- AND INTERMEDIATE-TERM
DWLOCS AND DRINKING WATER EXPOSURE
Case 1: Calculating DWLOCshort.teem using the Reciprocal MOE Equation
An example summary of the endpoints selected by the HIARC are included as Table 1.
Table 1. Toxicology Endpoints for Lamda-cyhalothrin*
Exposure Route
Dose (mg/kg/day)
Endpoint Selected/study
Acute Dietary
N OAEL= 0.5 mg/kg/ day
RfD= 0.005 mg/kg/day, UF= 100**
MOE = 100
Gait abnormalities in dogs in a chronic toxicity study.
Chronic Dietary
N OAEL= 0.1 mg/kg/ day
RfD= 0.001 mg/kg/day, UF= 100
MOE = 100
Neurotoxicity, ataxia and convulsions in dogs in a
chronic toxicity study .
Short-term Dermal
NOAEL=10.0 mg/kg/day, UF = 100
MOE = 100
Mortality, clinical signs and effects on body weight and
food consumption in a 21-day dermal rat study.
Intermediate-term Dermal
NOAEL=10.0 mg/kg/day, UF = 100
MOE = 100
Mortality, clinical signs and effects on body weight and
food consumption in a 21-dermal study in rats
Chronic-term Dermal
NOAEL=0.1 mg/kg/ day, UF = 100
MOE = 100
Neurotoxic clinical signs in both sexes of dogs in a
chronic toxicity study.
Inhalation
(any time period)
NOAEL=0.3 jig/L, UF = 100
(0.08 mg/kg/day)
MOE = 100
Neurotoxic clinical signs, alterations in clinical
pathology and alveolitis in rats in a 21-day inhalation
study
* Taken from memo S. Weiss, 11/16/98, D249214, T:\HED\REVIEWS\128897\SEC18. Aggregate assessment is appropriate
because of similarity in systemic toxicity observed in rats via all routes. ** Uncertainty Factor (UF) is equivalent to the acceptable
Margin of Exposure (MOE).
To use the following equations, the following conditions must apply: all acceptable MOEs must be
identical for all MOEs to be included in the short-term risk assessment. Based on the toxicity
endpoint information above, all acceptable MOEs are 100, and no oral endpoint for hand-to-
mouth residential exposure was identified. In this case, use the acute dietary endpoint (NOAEL) to
incorporate dietary (food and water), and residential hand-to-mouth exposures in the aggregate risk
assessment. A short-term residential exposure scenario was identified and includes a dermal and
inhalation exposure route, but no oral exposure route. To complete the aggregate short-term
exposure and risk assessment, chronic dietary (food and drinking water) and residential (1 to 7 day)
dermal and inhalation exposures must be included.

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For infants, the pertinent short-term exposure routes are:
the short-term residential high-end dermal exposure of 1.28 E-3 mg/kg/day,
the short-term residential high-end inhalation exposure of 1.68 E-5 mg/kg/day, and
the average (chronic) exposure from food of 7.3 E-5 mg/kg/day.
Solve the reciprocal MOE equation below for MOEwater to determine the DWLOCshort_term for
infants.
Aggregate MOE
1 + _J_ +	1
MOEoral MOEdermal moeinhalation
MOEw
1 -
MOE,
Where Aggregate MOE = 100 (based on all acceptable MOEs being equal to 100),
MOEFood = 0.5 mg/kg/day7.3 E-5 mg/kg/day = 6850,
MOE dermal = 10 mg/kg/day ^ 1.28 E-3 mg/kg/day = 7800,
MOEinhalation = 0.08 mg/kg/day 1.68 E-5 mg/kg/day = 4760,
MOEoral = Not applicable to this risk assessment and the term is removed from equation.
Substituting these calculated MOEs into the equations above and solving for MOEwater gives:
l
100 = 	
l	+ l + l +	l
6850 MOEw,,tbr	7800 4760
MOEw
1
100
1
6850
7800
1
4760
MOEwater = 1 9.5 E-3 = 105
105 — Short-term oral or acute dietary NOAEL
Allowable Short-Term Water Exposure
4.76 E-3 mg/kg/day —	0.5 mg/kg/dav
105

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Substituting the Water Exposure value, the Short-term DWLOC for infants was calculated as
follows:
DWLOC(//g/L) = 4.76 E-3 (mg/kg/dav) x 10 (kg) = 48 ug/L (ppb)
(IE-3 mg///g) x 1 (L/day)
Compare the DWLOCshort.teem to the appropriate model estimates given below.
DWLOC Values (ppb)
GENEEC
FIRSL (ppb)
PRZM/EXAMS
(Ppb)
SCI-GROW (ppb)
DWLOC short-term (48 ppb)
56-day average 3
annual average
annual average and
36-year mean
90-day average
concentration
[Note: DWLOCintermediate_term is calculated similarly, but the intermediate-term oral or chronic
dietary NOAEL is used, and the appropriate intermediate-term dermal exposure, endpoint and UFs
are used.]
Case 2: Calculating DWLOCshort.teem using an Alternative Approach
For the case where the allowable exposure (the RfD or PAD) for all pertinent routes of exposure
(dietary (food and water) oral exposures, non-dietary residential dermal, inhalation or oral hand-to-
mouth type exposures) included in the short-term or intermediate-term risk assessment are the
same (i.e., the NOAELs and UFs selected for each pertinent route of exposure are identical), the
simplified equation given below can be used. For example, this situation occurs when the
endpoints selected for any short-term residential dermal, inhalation, and non-dietary, inadvertent
oral (hand-to-mouth) exposures are the same as those selected for the acute dietary oral (food and
water) exposures. This is also the case for the DWLOCintermediate_term when the endpoints
selected for any intermediate-term dermal, inhalation, and non-dietary, inadvertent oral (hand-to-
mouth) exposures are the same as those selected for the chronic dietary oral (food and water)
exposures.
Such a case is given in Table 2 showing hypothetical results from a HIARC meeting. Note that in
this case, the acute dietary NOAEL, the short-term dermal and inhalation NOAELs (endpoints)
and UFs are all identical.

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DWLOCst (ug/L)
[ST water exposure (mg/kg bw/day) x body weight (A'g)]
[consumption (LI day) x 10~3 mg/ug]
ST water exposure (mglkglday) = [AcuteP*4D - ( avg. food + high-end residential exposure) (mglkglday)
Table 2. Toxicology Endpoints for Chemical X*
Exposure Route
Dose (mg/kg/day)
Endpoint Selected/study
Acute Dietary
NOAEL=10.0 mg/kg/day
RfD= 0.01 mg/kg/day, UF= 100
MOE = 100
General neurotoxic effects (gait abnormalities).
Chronic Dietary
N OAEL= 0.1 mg/kg/ day
RfD= 0.001 mg/kg/day, UF= 100
MOE = 100
Neurotoxicity, ataxia and convulsions in dogs in a
chronic toxicity study .
Short-term Dermal
NOAEL=10.0 mg/kg/day, UF = 100
MOE = 100
General neurotoxic effects (convulsions).
Intermediate-term Dermal
NOAEL=10.0 mg/kg/day, UF = 100
MOE = 100
Mortality, clinical signs and effects on body weight and
food consumption in a 21-dermal study in rats
Inhalation
(any time period)
NOAEL= 10 mg/kg/day, UF = 100
MOE = 100
General neurotoxic effects (clinical signs, weight
gain/loss).
* Hypothetical values for purposes of example used.
Based on the toxicity endpoint information above, all acceptable MOEs are 100, and no oral
endpoint for hand-to-mouth residential exposure was identified. In this case, use the acute dietary
endpoint (NOAEL) to incorporate dietary (food and water), and residential hand-to-mouth
exposures in the aggregate risk assessment. A short-term residential exposure scenario was
identified and includes a dermal and inhalation exposure route, but no oral exposure route. To
complete the aggregate short-term exposure and risk assessment, chronic dietary (food and drinking
water) and short-term (1 to 7 day) residential exposures must be included.
For infants, the pertinent short-term exposure routes are:
the short-term residential high-end dermal exposure of 1.28 E-3 mg/kg/day,
the short-term residential high-end inhalation exposure and 1.68 E-5 mg/kg/day, and
the average (chronic) exposure from food of 7.3 E-5 mg/kg/day.
The short-term aggregate risk including drinking water exposure can be calculated using the

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27
equations and approach in Case 1 by solving the reciprocal MOE equation below for MOEwater to
determine the DWLOCshort_tenn for infants. It can also be solved using the simpler equation below
for calculating DWLOCshort_tenn values. The alternative approach is only valid for cases where all
endpoints and UFs included in the calculation for incorporating food, water, and residential
exposures are identical. If in doubt regarding the use of the approach in Case 2, use the reciprocal
MOE method to check the result. Either approach should lead to the same result.
Solving for the short-term (ST) water exposure and the DWLOCST for infants, gives:
Where, the Acute RfD = 0.01 mg/kg/day, given the information above on exposure, then
Short-term water exposure = 0.01 mg/kg/day - [(7.3 E-5 + 1.28 E-3 + 1.68 E-5) mg/kg/day]
Short-term water exposure = 0.01 mg/kg/day - 0.0013 mg/kg/day = 0.0086 mg/kg/day
DWLOCst = [0.0086 mg/kg/day x 10 kg bwt] + [1 L/day x 1 E-3 mg/ug] = 86 ug/L (ppb)
Compare the DWLOCshort.teem to the appropriate model estimates given below.
DWLOC Values (ppb)
GENEEC
FIRST (ppb)
PRZM/EXAMS (ppb)
SCI-GROW (ppb)
DWLOC short-term (86 ppb)
56-day average 3
annual average
annual average and 36-
year mean
90-day average
concentration
[Note: in this example, to calculate the intermediate-term DWLOC, the reciprocal MOE method is
needed because the chronic dietary NOAEL (0.1 mg/kg/day) is not equal to the intermediate
dermal and inhalation endpoints (10 mg/kg/day, each).]
Case 3: Calculating DWLOCshort.teem using the ARI Method
Based on the toxicity endpoint information below in Table 3, not all of the acceptable MOEs are
identical. The short-term dermal endpoint has a UF/MOE of 1000 because of the FQPA 10X
safety factor applied for infants and children, while the assessments for incorporating food, water,
and inhalation exposures have UFs/MOEs of 100. In this case, use the ARI method to calculate
DWLOCshort_term values for the short-term risk assessments. No oral endpoint for hand-to-
mouth residential exposure was identified, therefore, use the acute dietary endpoint (NOAEL) to
incorporate dietary (food and water), and residential hand-to-mouth exposures in the aggregate risk
assessment. A short-term residential exposure scenario was identified and includes a dermal and
inhalation exposure route, but no oral exposure route. To complete the aggregate short-term
exposure and risk assessment, chronic dietary (food and drinking water) and short-term (1 to 7 day)
residential dermal and inhalation exposures must be included.
Table 3. Toxicology Endpoints for Chemical X*
Exposure Route
Dose (mg/kg/day)
Endpoint Selected/study
Acute Dietary
N OAEL= 0.5 mg/kg/ day
RfD= 0.005 mg/kg/day, UF= 100
MOE = 100
Gait abnormalities in dogs in a chronic toxicity study.

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Table 3. Toxicology Endpoints for Chemical X*
Exposure Route
Dose (mg/kg/day)
Endpoint Selected/ study
Chronic Dietary
N OAEL= 0.1 mg/kg/ day
RfD= 0.001 mg/kg/day, UF= 100
MOE = 100
Neurotoxicity, ataxia and convulsions in dogs in a
chronic toxicity study .
Short-term Dermal
NOAEL=10.0 mg/kg/day, UF =
100, FQPA Factor = 10
MOE = 1000
Mortality, clinical signs and effects on body weight and
food consumption in a 21-day dermal rat study.
Intermediate-term Dermal
NOAEL=10.0 mg/kg/day, UF = 100
MOE = 100
Mortality, clinical signs and effects on body weight and
food consumption in a 21-dermal study in rats
Chronic-term Dermal
NOAEL=0.1 mg/kg/day, UF = 100
MOE = 100
Neurotoxic clinical signs in both sexes of dogs in a
chronic toxicity study.
Inhalation
(any time period)
NOAEL= 0.3 mg/kg/day, UF = 100
(0.08 mg/kg/day)
MOE = 100
Neurotoxic clinical signs, alterations in clinical
pathology and alveolitis in rats in a 21-day inhalation
study
* Hypothetical values for purposes of example used.
For infants, the pertinent short-term exposure routes are:
the short-term residential high-end dermal exposures of 1.28 E-3 mg/kg/day,
the short-term residential high-end inhalation exposures of 1.68 E-5 mg/kg/day, and
the average exposure from food of 7.3 E-5 mg/kg/day.
The short-term aggregate risk including drinking water exposure can be calculated using the ARI
method for aggregating exposure. The equations below can be solved for MOEwater to determine
the DWLOC^q^-Term for infants.
1
Aggregate ARI =		
1	+ 1 + 1 + 1 +	1
ARIpooc) ARIwater ARIqral ARIdermal	ARIiwhalatiow
ARIwater ~~
1 -
1 + 1 + 1 +
1

ARIagg
ฆ ARIpooD ARIdermal ARIinhalation
ARIqral -
Where, ARI — [MOEcalcijlated ฆ MOEacceptable],
ARIagg —
ARIpood = [MOEpooD + MOE (acceptable)] = [(0.5 - 7.3 E-5) (mg/kg/day)] - 100 = 69,
ARIdermal = [MOEDErmal + MOE (acceptable)] = [(10 - 1.28 E-3) (mg/kg/day)] - 1000 = 8 ,
ARIinhalation = [MOEINHalation + MOE (acceptable)] = [(0.08 - 1.68 E-5) (mg/kg/day)] - 100 = 48, and
ARIoral= not applicable to this risk assessment and the term is removed from the equation.

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Substituting the calculated and acceptable MOEs into the equations above and solving for
ARTwater gives:
ARIw
1 + 1 +
69
1
48
\ RIฆ/ : : — 1.19 — |\I() I . v : : \[() I. : : : ]; Where the acceptable MOE for water is 100.
MOEฎAtee = 1.19 x 100 = 119
119 = Short-term oral or acute dietary NOAEL
Short-term Water Exposure
Short-term Water Exposure (mg/kg/day) = 0.5 mg/kg/dav = 4.2 E-3 mg/kg/day
119
Substituting the ST Water Exposure value, the Short-term DWLOC for infants:
DWLOC(//g/L) = 4.2 E-3 (mg/kg/dav) x 10 (kg) = 42 ug/L
(IE-3 mg///g) x 1 (L/day)
Compare the DWLOCshort_term to the appropriate model estimates given below.
DWLOC Values (ppb)
GENEEC
FIRSL (ppb)
PRZM/EXAMS
(PP^
SCI-GROW (ppb)
DWLOC short-term (42 ppb)
56-day average 3
annual average
annual average and
36-year mean
90-day average
concentration
[Note: DWLOCintermediate_term is calculated similarly, but the intermediate-term oral or chronic
dietary NOAEL is used, and the appropriate intermediate-term dermal exposure, endpoint and UFs
are used.]
* Other examples of calculations can be found in the Bensulide and Iprodione REDs, and the
Section 18 for Lamda-Cyhalothrin on Flax in North Dakota (T:\hed\reviews\122897\secl8).

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