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Standard Operating Procedures (SOPs) for Residential Exposure Assessments

13.0 INHALATION OF RESIDUES FROM INDOOR TREATMENTS

13.1 Handler Surrogate Inhalation Dose from Pesticides Applied Indoors as Crack & Crevice and Broadcast Treatments

Introduction

This SOP provides a standard method for estimating potential inhalation doses that homeowners may receive during crack & crevice (e.g., baseboard treatments) and broadcast treatments (e.g., carpets) indoors. This scenario assumes that pesticides are available to be inhaled by adults during the mixing/loading and application of pesticides used indoors. The method for estimating handler inhalation dose from pesticides during indoor treatments relies on using surrogate PHED data. Thus, this method should be used in the absence of actual field data, or as a supplement to estimates based on field data.

Methods for Estimating Dose

Prior to the development of an exposure assessment for this scenario, the assessor should consult the pesticide label to determine whether this scenario is appropriate based on the usage characteristics of the product. Label information is also important for selecting appropriate data inputs for the exposure assessment. The data required for estimating handler doses from pesticide when using pesticides indoors are the application method specific data (i.e., use scenario and unit exposures), application rates, and usage data (e.g., gallons). The maximum application rate specified on the label should be used. In the absence of actual data, the following assumptions are also needed for estimating daily inhalation mixer/loader/applicator doses.

- Application methods for indoor treatments will include crack and crevice or broadcast treatments using low pressure handwands, aerosol cans, and shaker cans (dust).

- Mixer/loader/applicator inhalation unit exposure values and data confidence descriptions for the low pressure handwand and aerosol cans are located in the Appendix B; for shaker cans refer to Section 9.1.1. The current version of PHED uses measures of central tendency to estimate the best fit unit exposures.

- The amount handled to treat baseboards or carpets are assumed to be one aerosol can of diluted solution (i.e., homeowner may potentially use the entire contents of the product for a single treatment), two gallons for low pressure handwands, and the entire contents of one shaker can (i.e., homeowner may potentially use the entire contents of the product for a single treatment). Based on the experience and professional judgement of the OPP/HED staff, this is assumed to be an upper-percentile value.

- Adults are assumed to weigh 71.8 kg (use 60 kg for females when the selected endpoint is from a reproductive or developmental study). A body weight of 71.8 kg represents the mean body weight for all adults (i.e., male and female, ages 18 years and older) and is the value recommended in U.S. EPA (1996). A body weight of 60 kg represents the mean body weight for females between ages 13 and 54 years (U.S. EPA, 1996). The average body weight for a 10 to 12 year old youth is 39.1 kg. This represents the mean of the median values for males and females at ages 10, 11, and 12 years.

Inhalation potential dose rates are calculated as follows: PDR = UE * AR * N

where:

PDR = potential dose rate (mg/day)
UE = unit exposure from Appendix B (mg/lb ai)
AR = amount of active ingredient applied per container of product or per gallon of diluted solution (lb ai/can or lb ai/gal)
N = maximum number of containers used per exposure day or number of gallons of diluted solution used per exposure day (cans/day) or (gal/day)

Inhalation potential dose rates, normalized to body weight, are calculated as: PDRnorm = PDR / BW

where:

PDRnorm = potential dose rate, normalized to body weight (mg/kg/day)
BW = body weight (kg)

The body weight used can be adjusted to fit any specific scenario (for example, exposure to male or female adults).

Example Calculations

The following is an example calculation to determine the inhalation dose based on a homeowner mixing/loading/applying a liquid broadcast application using a low pressure handwand. For the purpose of this example, the application rate is assumed to be 0.05 lb ai/gallon diluted spray. The estimated inhalation potential dose rate using a low pressure handwand would be as follows:

PDR = UE * AR * N

PDR = 0.031 mg/lb ai * 0.05 lb ai/gal * 2 gal/day

PDR = 0.0031 mg/day

Finally, the estimated inhalation potential dose rate, normalized to body weight for an adult with a body weight of 71.8 kg would be:

PDRnorm = PDR / BW

PDRnorm = (0.0031 mg/day) / (71.8 kg)

PDRnorm = 4.3E-05 mg/kg/day

This dose would be used in conjunction with toxicity data to assess risk.

Limitations and Uncertainty

The dose estimates generated using this method are based on central tendency and upper percentile assumptions. The uncertainties associated with this assessment stem from the use of surrogate exposure data (e.g., differences in use scenarios and data confidence) and assumptions regarding amount of chemical handled. The dose estimates are believed to be reasonable central tendency to high-end estimates based on observations from chemical-specific field studies and professional judgement.

References

U.S. EPA (1996) Exposure Factors Handbook [Draft]. U.S. Environmental Protection Agency, National Center For Environmental Assessment, Washington D.C. EPA/600/P-95/002Ba.

13.2 Inhalation Bystanders and Postapplication Dose Among Adults and Children from Pesticide Applications in and Around a Residence

Introduction

This SOP provides a standard method for completing postapplication inhalation exposure assessments for adults and children after a pesticide treatment in their residence. The basis for each scenario is that nonhandler inhalation exposure occurs while occupying living spaces within a residence during and after a pesticide treatment. This SOP addresses all types of pesticide use scenarios including short- and long-term emission sources in a treated residence. The method for completing exposure assessments for indoor residential inhalation exposure scenarios when surrogate data are not available is based on modeling. Thus, this method should only be used in the absence of adequate data. Two models developed by EPA/OPPTS serve as the basis for this SOP (SCIES and MCCEM). SCIES or the Screening-Level Consumer Inhalation Exposure Software and MCCEM or the Multi-Chamber Concentration and Exposure Model will be used to calculate concentration values to which individuals will be exposed. Further calculations are required to estimate dose. These calculations are also detailed in this SOP. This SOP provides standard model inputs for using SCIES and MCCEM in exposure assessments. Assessors should refer to the respective User's Manual for details on the operation of SCIES and MCCEM and for information concerning the underlying assumptions and limitations of each. All specific model inputs and calculations represented in this SOP are based are SCIES Version 3.0 and MCCEM Version 2.4.

General Methods for Estimating Dose

Methods for calculating exposure concentrations and dose are presented below using outputs from both models.

Methods For Calculating Exposure Concentrations

Screening Consumer Inhalation Exposure Software (SCIES)

SCIES has been developed to perform screening-level inhalation exposure assessments for 11 predetermined consumer product use scenarios and an "input your own" scenario. For the purposes of this SOP, SCIES is to be used only to complete calculations for a scenario similar to one of the predetermined consumer product use scenarios. Assessors are asked not to use the "input your own scenario" option for calculation. Any exposure scenarios not addressed by one of the 11 predetermined use scenarios are to be addressed through the use of MCCEM. The available consumer product categories included in SCIES are presented below:

- all-purpose liquid cleaner,
- machine wash laundry detergent (liquid),
- liquid fabric softener (semivolatile),
- liquid fabric softener (volatile),
- automobile vinyl upholstery cleaner,
- floor wax/polish,
- fabric protector,
- aerosol paints/clear coatings,
- latex paint,
- oil-based paint, and
- solid air freshener.

After a use scenario has been selected from the SCIES main menu, the following basic chemical-and product-specific parameters must be input for all calculations:

- chemical name (optional)

- molecular weight

- vapor pressure

- weight fraction in product

Each predetermined use scenario in SCIES includes default numerical values for the following input parameters. Although SCIES is also flexible in that these default input parameters can be modified, assessors are asked to accept the default values for all calculations within the SOP.

- room where the product is used
- user occupancy patterns
- the annual frequency of use
- the mass of the product used per event
- the air exchange rate
- the non-user inhalation rate
- the user inhalation rate
- the duration of use
- room volume
- the volume of the house

SCIES provides average and peak concentration values in the room of use and in the remainder of a house. These values will be used to calculate exposure and dose. SCIES also provides annualized dose rates for the product user and those passively exposed, but these will not be used for this SOP. An example SCIES report that includes both the input parameters and output (i.e., calculated concentrations) is presented in Figure 1.

The use of SCIES is straightforward as described in the User's Manual. However, an overview of the operation for the purposes of this SOP is provided. Once in the Main Menu a user selects the predetermined use scenario appropriate for the pesticide label use pattern. After this selection, the Defaults Submenu appropriate for the use scenario will appear. All default values are to be accepted. The user is required to enter chemical/product specific data under the Input Chemical Properties selection of the Defaults Submenu. Concentration calculations can then be completed. [Note: Room of use and start time menus appear in the Run the Model submenu. Assessors are asked to also accept the default options for the purposes of this SOP.]

Multi-Chamber Concentration and Exposure Model (MCCEM)

MCCEM is a model that is capable of calculating indoor air concentrations and the corresponding exposure assessments for both acute and chronic scenarios. The model can also calculate the "percent of cases" where the airborne concentration of a contaminant exceeds a toxicological level of concern. MCCEM should be used for residential exposure scenarios for which predetermined consumer product use scenarios are unavailable in SCIES. MCCEM contains a database of various default house data that are needed to complete each calculation such as air exchange rates, geographically based inter-room air flows, and house/room volumes. Chemical source emission rates of pollutants are entered into the model either as numbers or as formulas. MCCEM can account for chemical decay and the contribution of outdoor concentrations and is capable of performing sensitivity analyses and Monte Carlo analyses. However, because this SOP is focused on high-end assessments, only the aspects of MCCEM required by the SOP are addressed herein.

The essential aspects of MCCEM that must be defined to complete a high-end assessment include the following:

- type of house (selection based on construction type),
- definition of zones for selected house (single or multi-zone up to 4 indoor zones),
- selection of model (i.e., short or long-term scenarios/up to 1 week or 1 year),
- selection/calculation of appropriate emission rate inputs for chemical/product, and
- selection of a decay rate for the chemical/product.

Table 1 includes MCCEM inputs that are specific to each exposure scenario that are appropriate for a high-end calculation. MCCEM requires further input to operate the model. However, these additional inputs represent administrative functions (e.g., file handling). Example MCCEM input and output reports are presented in Figure 2.

Step-by-step procedures for completing a high-end assessment using MCCEM are presented below (refer to Table 1 during each step of process):

Step 1/Source of Input Menu: New users select "Specify New Inputs" option.

Step 2/Type of Residence Menu: Select the "Generic House" option (#4) and the defaults "Bedroom House GN001" and "S" (summer) that are presented by the system (i.e., this provides a conservative air exchange rate of 0.18 xch/hr).

Step 3/Multi or Single Chamber Model: Select multi- or single-chamber model depending upon the default inputs specified for the exposure scenario of interest. Input appropriate number of zones for the scenario (i.e., 1 for single- and 2 for multi-chamber model).

Step 4/Model Type: Select the long-term model option. The long-term model is appropriate for all high-end assessments to be completed as it is appropriate for durations from 24 hours to 1 year, in 2-hour steps. The duration the calculation encompasses is also input (i.e., 90 days is used except for termiticides where 365 days is used). Calculations using MCCEM can completed in 1 hour or 24 hour steps. For the purposes of this SOP, 1 hour steps should used for an acute endpoint while a 24 hour step should be used for a chronic endpoint.

Step 5/Emission Rate & Exposure Zone Inputs: For the high-end assessment requirement, two emission mechanisms have been selected as options. The first type is to be used to model "Instant Release" scenarios such as a house fogger (i.e., all chemical is "thrown up" in the air of a residence as an aerosol immediately -- less than 1 hour). Emissions for this scenario are calculated as the amount of product released times the percent of active ingredient (ai) in the product. For example, if a fogger can contains 1 lb (454 g) of pressurized spray at 50 percent ai (w/w), the mass applied (m) is 0.5 lb (227 g) of ai (i.e., 454 * 0.5). The second type of emission is the Chinn type or long-term emission (e.g., a crack and crevice treatment is completed and the pesticide offgasses from the treated surfaces for several weeks). The offgassing emission rate is calculated based on an empirical relationship between evaporation time, vapor pressure, and molecular weight (Chinn, 1981). The equations used to calculate a Chinn Type emission rate and an example calculation are presented in Figure 3. Example MCCEM emission input tables for both scenarios are presented in Figures 4 and 5. [Note: For all calculations including two zone scenarios, emissions will occur in Zone 1 (Column D). In Figure 5, the source is active for only 545 hours of the 2,160 hours of the run.]

Step 6/Decay Rate Input: "Nonreactive" or a value of 0 should be used for all calculations unless information is available to indicate otherwise.

Step 7/Outdoor Concentrations: No contributions from the outdoors will be assumed for this SOP (i.e., pass through to next screen with no inputs).

Step 8/Monte Carlo & Sensitivity Options: Neither of these options will be used in a high-end assessment (i.e., pass through to next screens by selecting "No").

Step 9/Level of Concern & LADD Inputs: Neither of these options will be used in a high-end assessment (i.e., pass through to next screens by selecting "No").

Step 10/Execute the Model: Run the model and save the output files for review purposes.

Calculating Exposure and Dose

Once a model has been used to calculate an exposure concentration, human inhalation exposure/dose must be calculated. Selection of the proper concentration value to be used in an exposure assessment depends on the inhalation toxicological endpoint (i.e., acute or chronic). If SCIES was used to complete the assessment, the " average concentration in the zone of release during the period of use" is selected for an acute scenario. If the endpoint is chronic, the "average concentration to which the non-user is exposed" is selected. (See Figure 1 for further information.) If MCCEM was used to complete the assessment, the "average concentration in the zone 1" is selected for an acute endpoint. This value is used even if a multi-chamber model run is completed because zone 1 will have slightly higher concentration values as it will always be designated as the release zone. If the endpoint is chronic, the "TWA or Time-Weighted-Average" value is selected for Zone 1.

In order to complete the calculation, current and/or proposed labeling should be consulted to define any remaining required information. The following assumptions are also used to calculate post application inhalation exposures in a residence after the use of pesticide containing products in and around the residence:

- Adults are assumed to weigh 71.8 kg (use 60 kg for females when the selected endpoint is from a reproductive or developmental study) A body weight of 71.8 kg represents the mean body weight for all adults (i.e., male and female, ages 18 years and older) and is the value recommended in U.S. EPA (1996). A body weight of 60 kg represents the average body weight for females between ages 13 and 54 years (U.S. EPA, 1996). Toddlers (3 years old), used to represent the 1 to 6 year old age group, are assumed to weigh 15 kg. This is the average of the median values for male and female toddlers (U.S. EPA, 1996).

- A mean inhalation rate of 13.3 m3/day for adults will be used to calculate daily exposures (U.S. EPA, 1996). A mean inhalation rate of 8.7 m3/day for toddlers will be used to calculate daily exposures (U.S. EPA, 1996).

- Five percent of termiticides applied by foundation/soil injection techniques penetrate the foundation of a house to become a source for offgassing in a Chinn type emission. This is based on the experience and professional judgement of the OPP staff based on the review of company-submitted data. All termiticides applied indoors are assumed to 100 percent available for emission.

- Table 1 includes various assumptions required for the use of MCCEM not addressed in this list. The default values in SCIES are not assumptions; they are based on actual data.

Inhalation potential dose rates for acute scenarios are calculated as follows: PDR = Ca * IR

where:

PDR = potential dose rate (mg/day)
Ca = modeled airborne concentration of pesticide in air (mg/m3)
IR = inhalation rate (m3/day)

Inhalation potential dose rates, normalized to body weight, are then calculated as: PDRnorm = PDR / BW

where:

PDRnorm = potential dose rate, normalized to body weight (mg/kg/day)
BW = body weight (kg)

The body weight used can be adjusted to fit any specific scenario (e.g., use of 65 kg for women when developmental endpoints are available).

Example Calculations

The following is an example calculation to determine the potential dose rates based on a single latex painting event using SCIES for an adult. Refer to Figure 1 for Ca value which is the "average concentration in zone of release during period of use."

PDR = Ca * IR

PDR = 0.947 mg/m3 * 13.3 m3/day

PDR = 12.6 mg/day

The estimated potential dose rate, normalized to body weight, for an adult with a body weight of 71.8 kg would be:

PDRnorm = PDR / BW

PDR = (12.6 mg/day) / (71.8 kg)

PDR = 0.18 mg/kg/day

Limitations and Uncertainty

The dose estimates generated using this method are based on some central tendency (i.e., inhalation rate and body weight) and some upper-percentile (i.e., model inputs and exposure concentrations) assumptions. The uncertainties associated with this assessment stem from the generic applicability for exposure scenarios, and assumptions regarding the model inputs. MCCEM may calculate concentrations that exceed the theoretical saturation value. A saturation concentration must be calculated using the ideal gas law for comparison to MCCEM results. If MCCEM calculated values exceed the saturation concentration, the saturation value must be used in the exposure assessment process. This is not an issue for SCIES. Other limitations of the SCIES model are that it is intended for use as a screening-level tool and is designed to use very limited data to generate high-end to bounding exposure estimates. Also, the Chinn relationship is based on the evaporation of pure substances under artificial conditions and may overestimate the emissions expected from substances in mixtures. These assumptions are believed to be reasonable to calculate high-end estimates based on observations from similar field studies.

References

Chinn, K.S.K. (1981) A simple method for predicting chemical agent evaporation. September 1981. Dugway, UT: U.S. Army Proving Ground. DPG Document No. DPG-TR-401.

U.S. EPA (1995) Multi-Chamber Concentration and Exposure Model (MCCEM): User's Guide, Version 2.4. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics, Economics, Exposure and Technology Division, Exposure Assessment Branch, Washington D.C.

U.S. EPA (1994) Screening-Level Consumer Inhalation Exposure Software (SCIES): Description and Users Manual, Version 3.0. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics, Exposure Assessment Branch, Washington D.C.

U.S. EPA (1996) Exposure Factors Handbook [Draft]. U.S. Environmental Protection Agency, National Center For Environmental Assessment, Washington D.C.

TABLE 1: SCENARIOS AND INPUT PARAMETERS FOR MCCEMa

Use Scenario House Type & Season Air Exchange Rate (xch/hr) Chamber Type (Number Zones) Model Type Calculation Durationb
(days)
Emission Typec Emission Ratec Product Use Scenarioa Room of Use MCCEM Decay Rate
Single Use Pressurized Fumigant Can Generic/
Summer
0.18 Single (1) Long-Term 90 Instant Release Total/hr 2 Cans Bedroom 0
Crack and Crevice Generic/
Summer
0.18 Single (1) Long-Term 90 Chinn Evaporation Chinn Rate All Rooms Bedroom 0
Carpet Broadcast Generic/
Summer
0.18 Multi (2) Long-Term 90 Chinn Evaporation Chinn Rate 1 Room Bedroom 0
Termiticides Generic/
Summer
0.18 Single (1) Long-Term 365 Chinn Evaporation Chinn Rate Entire House and 5 % Penetration Inside Bedroom 0
Pressurized or RTU Sprays Generic/
Summer
0.18 Multi (2) Long-Term 90 Instant Release Total/h 1 Can Bedroom 0
Carpet Dusting Generic/
Summer
0.18 Multi (2) Long-Term 90 Chinn Evaporation Chinn Rate 1 Room Bedroom 0
Pet Treatments Generic/
Summer
0.18 Single (1) Long-Term 90 Chinn Evaporation Chinn Rate 2 Pets Bedroom 0

a Use scenario provides basis for calculating the amount of chemical used in each type of use scenario and, for termiticides, the amount of applied chemical that penetrates a residence through the foundation in order to characterize the source.

b Calculation duration refers to the length of time that the chemical concentration is modeled. It is recommended that if a highly toxic compound is being modeled that the model outputs be saved and imported into a spreadsheet in order to review the data to ensure that the model was run for a sufficient period of time.

c See Figure 6 for details concerning the calculation of these emission rates.

Latex Paint

Annual Frequency of Use : 6 Events/Year

Mass of Product : 9.070E+03 grams

Duration of Use : 4.900 hours

Zone 1 Volume : 35.000 cubic meters

Whole House Volume : 408.000 cubic meters

House Air Exchange Rate : 0.200 air exchanges/hr

User Inhalation Rate : 1.300 cubic meter/hr (during use)

Non-User Inhalation Rate : 1.100 cubic meter/hr (& user after use)

Molecular Weight : 450.000 g/mole

Vapor Pressure : 4.000E-05 torr

Weight Fraction : 0.040

Starting Time : 9:00 AM

OUTPUT SUMMARY

Evaporation Time : 6.708E+03 hours

Release Time : 6.708E+03 hours (Evaporation Time)

Duration Following Each Use : 1.311E+04 hours

Interval Between Uses : 1.460E+03 hours

User Potential Dose Rate From Inhalation : 4.62435E+03 mg/yr

Non-User Potential Dose Rate From Inhalation : 4.61155E+03 mg/yr

---------------------------------------------------------------------------

Average (mg/m3 Peak (mg/m3)

Concentration in zone of release

During period of use 0.947 0.969

During period after use 0.893 0.969

Concentration in Zone 2

During period of use 0.220 0.302

During period after use 0.287 0.311

Concentration to which User and Non-User are exposed

Person Using Product (user) 0.479 0.969

Person Not Using Product (non-user) 0.479 0.969

HOURLY ACTIVITY PATTERN

User : 1 1 1 1 1 1 1 3 1 1 1 1 1 1 1 1 1 1 1 1 1 4 1 1

Non-User : 1 1 1 1 1 1 1 3 4 5 4 2 4 6 7 4 2 2 7 4 4 4 1 1

Hour : 03 06 ^ 12 15 18 21 24

START HOUR
Room of Use : Bedroom

FIGURE 1: EXAMPLE SCIES INPUT/OUTPUT REPORT

SUMMARY OF INPUTS FOR MODEL RUN

1. TYPE OF STRUCTURE: Generic House

2. GEOGRAPHIC AREA: (N/A)

3. HOUSE CODE: GN001 SEASON: Summer

4. NUMBER OF ZONES: 1 (Single-chamber)

5. SHORT/LONG TERM: Long-term

LENGTH OF RUN: 90 day(s) TIME STEP: 1 hour(s)

6. MAXIMUM INDOOR EMISSION RATE (g/hr): 227

Z1 = 227

7. DECAY RATE: 0:0

8. MAXIMUM OUTDOOR CONCENTRATION (mg/m^3: 0

9. MONTE CARLO OPTION: No

10. SENSITIVITY OPTION: No

11. CALCULATE % CASES >= 0 mg/m^3

12. LIFETIME AVG. DAILY DOSE OPTION: No

Specify screen to be updated (1-12): [ 0 ]

SINGLE RUN SUMMARY STATISTICS

ZONE 1 ZONE 2 ZONE 3 ZONE 4 EXPOSURE

Whole House (Single-chamber)

TWA, mg/m^3 1.43E+00 0.00E+00

STD. DEVIATION 1.99E+01 0.00E+00

MAXIMUM, mg/m^3 5.09E+02 0.00E+00

PERCENT OF CASES 100.0 0.0

>= 0 mg/m^3

PERCENT OF TIME IN RESIDENCE 0.0

LIFETIME AVG. DAILY DOSE, mg/kg-day (N/A)

FIGURE 2: EXAMPLE MCCEM INPUT/OUTPUT REPORT

FIGURE 3: CALCULATION OF CHINN RELEASE EMISSION RATES

File:GNS1L002 * Total of 2160 Time Steps *

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FIGURE 4: EXAMPLE MCCEM INSTANT RELEASE EMISSION TABLE

File:GNS1L002 * Total of 2160 Time Steps * Day: 1

Whole House (Single-chamber)

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Emission Rate [g/hr]

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FIGURE 5: EXAMPLE MCCEM CHINN RELEASE EMISSION TABLE

14.0 RODENTICIDES (REFER TO 2.3.1)

15.0 PICK YOUR OWN

15.1 Postapplication Dermal Potential Doses from Pesticide Residues on Pick Your Own Strawberries

Introduction

This SOP provides a standard method for estimating doses among adults and/or toddlers from dermal contact with strawberries that have previously been treated with pesticides. Inhalation dose is considered minimal due to the air exchange that occurs in outdoor scenarios. This scenario assumes that pesticide residues are transferred to the skin of adults/toddlers that enter treated strawberry fields during "pick your own" fruit harvesting. For the purposes of this SOP, "pick your own" facilities are considered commercial farming operations that allow public access for harvesting strawberries in large-scale fields treated with commercially labeled pesticides. The method for estimating postapplication dermal dose from pesticides on strawberries is based on assumptions when adequate chemical specific field data are unavailable. Thus, this method should be used in the absence of actual field data.

Methods for Estimating Potential Dose

Prior to the development of an exposure assessment for this scenario, the assessor should consult the pesticide label to determine whether this scenario is appropriate based on the usage characteristics of the product. Label information is also important for selecting appropriate data inputs for the exposure assessment. The only datum required for estimating postapplication doses from pesticide residues on "pick your own" strawberries is the application rate. The maximum application rate specified on the label should be used as the application rate. One exception is for cancer assessments where the typical application rates should be used. It should be noted that pesticide products not labelled for the residential/home garden market must be considered for this scenario as label stipulations do not typically preclude "pick your own access." It should also be noted that the typical use rate is often the maximum residential use rate. In the absence of actual data, the following assumptions can be used for estimating daily pesticide postapplication doses.

- On the day of application, it may be assumed that 20 percent of the application rate is available on the foliage as dislodgeable residue. This value is based on the professional judgement and experience of the OPP staff from the review of company-submitted data.

- Postapplication exposure must be assessed on the same day the pesticide is applied since it is assumed that individuals could enter a "pick your own location" immediately after application. For subsequent days after application, an assumed pesticide dissipation rate should be used, based on chemical-specific data.

- The duration of exposure is assumed to be 2.0 hours per day for youth (age 10-12 years) and 4.0 hours per day for adults (age 18-64 years), based on the 50th percentile values for time spent outdoors at a farm (U.S. EPA, 1996).

- The assumed dermal transfer coefficient is 10,000 cm2/hr for adults and 5,000 cm2/hr for youth (age 10-12 years). This value is based on the professional judgement and experience of the OPP staff from the reviewed company-submitted data.

- Adults are assumed to weigh 71.8 kg (use 60 kg for females when the selected endpoint is from a reproductive or developmental study). A body weight of 71.8 kg represents the mean body weight for all adults (i.e., male and female, ages 18 years and older) and is the value recommended in U.S. EPA (1996). A body weight of 60 kg represents the average body weight for females between ages 13 and 54 years (U.S. EPA, 1996). Toddlers (3 years old), used to represent the 1 to 6 year old age group, are assumed to weigh 15 kg. This is the mean of the median values for male and female children. (U.S.EPA, 1996).

Dermal potential dose rates are calculated as follows: PDRt = DFRt * CF1 * Tc * ET

where:

PDRt = potential dose rate on day "t" (mg/day)
DFRt = dislodgeable foliar residue on day "t" (ug/cm2)
CF1 = weight unit conversion factor to convert ug units in the DFR value to mg for the daily exposure (0.001 mg/ug)
Tc = transfer coefficient (cm2/hr)
ET = exposure time (hr/day)

and DFRt = (AR * F) * (1-D)t * CF2 * CF3

where:

AR = application rate (lbs ai/ft2 or lbs ai/acre)
F = fraction of ai retained on foliage (unitless)
D = fraction of residue dissipating daily (unitless)
t = postapplication day on which exposure is being assessed
CF2 = conversion factor to convert the lbs ai in the application rate to ug for the DFR value (4.54E8 ug/lb)
CF3 = conversion factor to convert the surface area units (ft2) in the application rate to cm2 for the DFR value (1.08E-3 ft2/cm2 or 2.47E-8 acre/cm2 if the application rate is per acre)

Potential dose rates, normalized to body weight, are calculated as: PDRt-norm = PDRt / BW

where:

PDRt-norm = dose on day "t" (mg/kg/day)
BW = body weight (kg)

The body weight used can be adjusted to fit any specific scenario (for example, exposure to adults or toddlers).

Example Calculations

The following is an example calculation to determine the dose based on an assumed DFR over time. For the purpose of this example, the application rate is assumed to be 2.2E-5 lbs ai/ft2 (approximately 1 lb ai/acre). Thus, the dislodgeable foliar residue on day 0 is as follows:

DFRt = (AR * F) * (1-D)t * CF2 * CF3

DFR0 = (2.2E-5 lb ai/ft2 * 0.2) * (1-D)0 * (4.54E8 ug/lb) * (1.08E-3 ft2/cm2)

DFR0 = 2.16 ug/cm2

The estimated dose for the day of application would be as follows:

PDRt = DFRt * CF1 * Tc * ET

PDR0 = 2.16 ug/cm2 * 0.001 mg/ug * 5,000 cm2/hr * 2 hours/day

PDR0 = 21.6 mg/day

Finally, the estimated dose for an adult with a body weight of 71.8 kg would be:

PDRt-norm = PDRt / BW

PDR0-norm = (21.6 mg/day) / (71.8 kg)

PDR0-norm = 0.30 mg/kg/day

Limitations and Uncertainty

The dose estimates generated using this method are based on upper-percentile assumptions for transfer coefficients and duration, and central tendency estimates for body weights. They are considered to be representative of high-end exposures. The uncertainties associated with this assessment stem from the use of an assumed amount of pesticide retained on strawberries, and assumptions regarding dissipation and transfer of chemical residues. The dose estimates are believed to be reasonable high-end estimates based on observations from chemical-specific field studies and professional judgement.

References

U.S. EPA (1996) Exposure Factors Handbook [Draft]. U.S. Environmental Protection Agency, National Center For Environmental Assessment, Washington D.C. EPA/600/P-95/002Ba.


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