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Scientific Advisory Panel
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- SOPs for Residential Exposure Assessments: Residential Lawns
Scientific Advisory Panel
Prior to the development of an exposure assessment for a turf scenario, the assessor should consult the pesticide label to determine whether the scenario is appropriate based on the usage characteristics of the product. Specific labeling considerations for residential lawns are as follows:
Registered for Use on Turfgrass: Determine whether the labeling contains directions for use on "turfgrass," "lawns," or "ornamental turf," or on specific species of turfgrasses, such as "bluegrass," "zoysia," "bentgrass," etc. Be sure that the product is intended to be applied at turfgrass sites and is not an herbicide intended to kill turfgrass species growing at other sites, such as gardens, landscape plants, and industrial sites.
Limitation and Descriptive Statements: Look for statements describing or limiting the use on turfgrass. These statements may be on the front panel of the label associated with the brand or trade name or in the use-directions section of the labeling. Assume that a product registered for use on turfgrass is used on home lawns, unless a specific labeling statement indicates otherwise. Restricted-Use Pesticide classification and statements such as "For use by commercial or professional applicators only" indicate that the product cannot be bought or applied by homeowners (no residential handler exposure/risk assessment required), but it may be applied by commercial applicators to residential sites, therefore a post-application exposure/risk assessment may be required. Statements such as "Golf course use only," "For use only on commercial sod farms," or "For use in commercial plantings only," and the more specific "Not for use on home lawns" indicate that the product cannot be used on residential turf and no residential handler or post-application exposure/risk assessment is required.
Introduction
This SOP provides a standard method to be used for estimating potential doses that homeowners may receive during turf applications from inhalation and dermal contact when chemical specific data are unavailable. This scenario assumes that pesticides are available to be inhaled or have the potential to come in contact with the skin of adults and youth during the mixing/loading and application of lawn chemicals. The method to determine handler inhalation and dermal exposure to pesticides from turf applications 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 Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The data required for estimating handler exposures to pesticides when treating turfgrass are the application method specific data (i.e., use scenario, formulation types, and unit exposures), application rates, and usage data (e.g., acreage or gallons). The maximum application rate specified on the label should be used, except in cancer assessments when the typical application rates should be used. However, it should be noted that the typical residential use rate is often the maximum residential use rate. The following assumptions are also needed for estimating daily inhalation and dermal mixer/loader/applicator doses.
-Application methods for granulars will include drop-type spreaders, whirly-bird spreaders, shaker cans, and dispersed by hand (spot treatment). Application methods for liquid formulations will include hose-end sprayers, typical garden sprinkler/watering can (spot treatment), low pressure handwands (spot treatment), and backpacks (spot treatment). Dermal and inhalation unit exposures and data confidence descriptions are available for all of these application methods in the Appendix B, except for shaker cans (refer to Section 9.1.1) and for the sprinkler/watering can scenario (use hose-end sprayers as a high-end estimate for this scenario). The current version of PHED uses measures of central tendency to estimate the best-fit unit exposure.
-The amount handled is based on 20,000 ft2 (i.e., approximately 1/2 acre) lawns for full treatments and 1,000 ft2 or 5 gallons of diluted spray for spot treatments. The mean lawn size is estimated to be 0.3 acre (Vinlove and Torla, 1995). Thus, 1/2 acre is assumed to be within the mean to upper-percentile range of the distribution of lawn size. One thousand ft2 or five gallons are the amounts typically used to represent an upper-percentile value by OPP/HED in risk assessments because it represents two 2-1/2-gallon low pressure handwand containers.
-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, 18 years and older) and is the value recommended in EPA's Exposure Factors Handbook (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 and/or dermal potential dose rates are calculated as
follows: PDR = UE * AR * A
where:
PDR = potential dose rate (mg/day)
UE = unit exposure (mg/lb ai)
AR = maximum application rate (lb ai/acre or lb ai/gal)
A = maximum area treated (acres/day) or (gal/day)
Inhalation and/or dermal potential doses normalized to body weight
are calculated as: PDRnorm = PDR / BW
where:
PDRnorm = potential dose rate, normalized to
body weight
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 dermal dose to an adult homeowner loading/applying a granular lawn chemical. A complete assessment would include inhalation and dermal dose for all registered application methods that might include whirly-bird spreaders, shaker cans, and dispersed by hand (spot treatment). For the purpose of this example, the application rate is assumed to be 1 lb ai/acre.
The estimated dermal potential dose rate using a push-type granular spreader would be as follows:
PDR = UE * AR * A
PDR = 2.9 mg/lb ai * 1 lb ai/acre * 0.5 acre/day
PDR = 1.45 mg/day
Finally, the estimated potential dermal dose rate, normalized to body weight for an adult with a body weight of 71.8 kg would be:
PDRnorm = PDR / BW
PDRnorm = (1.45 mg/day) / (71.8 kg)
PDRnorm = 0.02 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 estimates of the unit exposure, area treated, and body weight, and a central to upper-percentile assumption for the application rate and are considered to be representative of central tendency exposures. The uncertainties associated with this assessment stem from the use of surrogate exposure data (e.g., differences in the use scenarios and data confidence - see Surrogate Exposure Table) and assumptions regarding amount of chemical handled. These estimated doses 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.
Vinlove, F.K., Torla, R. (1995) Comprehensive Estimation of U.S. Home Lawn Area. Journal of Turfgrass Management. 1(1):83-97.
Introduction
This SOP provides a standard method for estimating potential doses among adults and/or toddlers from dermal contact with turf that has previously been treated with pesticides. Inhalation exposure is considered minimal due to the air exchange in the outdoor scenarios. This scenario assumes that pesticide residues are transferred to the skin of adults/toddlers that enter treated yards for recreation, yardwork, or other homeowner activities. The method for estimating postapplication dermal exposure to pesticide residues on turf is based on assumptions applicable when adequate chemical specific field data are unavailable. 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 Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The only datum required for estimating postapplication doses to pesticide residues on turfgrass is the application rate (e.g., lb ai/acre). The maximum application rate specified on the label should be used as the residential lawn application rate. One exception is for cancer assessments where the typical application rates should be used. It should be noted that the typical residential use rate is often the maximum residential use rate. The following assumptions are also needed for estimating daily pesticide postapplication doses.
-On the day of application, it may be assumed that 20 percent of the application rate is available from the turfgrass as dislodgeable residue. This value is based on the professional judgement and experience of the OPP/HED staff from the review of company-submitted data, and is assumed to represent an upper-percentile input value.
-Postapplication must be assessed on the same day the pesticide is applied since it is assumed that the homeowner could be exposed to turfgrass immediately after application. Therefore, postapplication exposures are based on day 0. For subsequent days after application, an assumed pesticide dissipation rate should be used, based on chemical-specific data.
-The mean dermal transfer coefficient is assumed to be 43,000 cm2/hr for adults and 8,700 cm2/hr for toddlers. (Cal EPA, 1996 reported a transfer coefficient of 43,000 for adults and 8,700 for children on carpet. The children's value was corrected from the adult transfer coefficient using the ratio of an adult body surface area to a child's surface area.)
-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, 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). 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).
-The duration of exposure for toddlers and adults is assumed to be 2 hours per day. The 95th percentile value for playing on grass is 121 minutes per day for both age groups 1-4 years and 18-64 years (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 dose (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 lb ai/acre)
F = fraction of ai retained on foliage (unitless)
D = fraction of residue that dissipates daily (unitless)
t = postapplication day on which exposure is being assessed
CF2 = weight unit conversion factor to convert the lbs ai in the application rate to ug for the DFR value (4.54E8 ug/lb)
CF3 = area unit 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 24.7E-9 acre/cm2 if the application rate is per acre)
Dermal potential dose rates, normalized to body weight, are calculated as:
PDRt-norm = PDRt / BW
where:
PDRt-norm = potential dose rate on day "t", normalized to body weight
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/cm 2
DFR0 = 2.16 ug/cm 2
The estimated potential dose rate for the day of application would be as follows:
PDRt = DFRt * CF1 * Tc * ET
PDR0 = 2.16 ug/cm2 * 0.001 mg/ug * 8,700 cm2/hr * 2 hours/day
PDR0 = 37.6 mg/day
Finally, the estimated potential dose rate, normalized to body weight, for a child with a body weight of 15 kg would be:
PDRt-norm = PDRt / BW
PDR0-norm = (37.6 mg/day) / (15 kg)
PDR0-norm = 2.51 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 some central tendency (i.e., body weight and transfer coefficient) and some upper-percentile assumptions (i.e., duration of exposure, and maximum application rate for acute assessments) and 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 turf, 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
Cal EPA (1996) Memorandum from T. Formoli (California EPA, Department of Pesticide Regulation, Worker Health and Safety Branch) to M. Mason (California EPA, Department of Pesticide Regulation, Pesticide Regulation Branch), October 17, 1996.
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.
Introduction
This SOP provides a standard method for estimating postapplication doses among toddlers from incidental ingestion of pesticide pellets and granules that have been applied to lawns and gardens when adequate site-or chemical-specific field data are unavailable. This scenario assumes that dry pesticide materials are ingested by toddlers that play in treated areas (i.e., yards, gardens, playgrounds). The doses estimated using this method may be combined with toxicity data to estimate the risks associated with incidental ingestion exposure from pesticide granules or pellets used to treat outdoor residential areas.
Methods for Estimating Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The data required for estimating postapplication doses from dry pesticide pellets and granules is the percent ai content of the dry formulation. The following assumptions are also needed for estimating daily pesticide postapplication doses.
-The assumed ingestion rate for dry pesticide formulations (i.e., pellets and granules) is 0.3 gram/day for children (age 3 years). This is based on the assumption that if 150 pounds of product were applied to a 1/2-acre lawn, the amount of product per square foot would be approximately 3 g/ft2, and a child would consume one-tenth of the product available in a square foot. This is believed to be an upper-percentile assumption, based on the experience and professional judgement of OPP/HED staff..
-Toddlers (age 3 years), used to represent the 1 to 6 year old age group, are assumed to weigh 15 kg. This is a mean of the median values for male and female children (U.S. EPA, 1996).
Potential dose rates from ingestion are calculated as follows: PDR
= IgR* F * CF1
where:
PDR = potential dose rate (mg/day)
IgR = ingestion rate of dry pesticide formulation (g/day)
F = fraction of ai in dry formulation (unitless)
CF1 = weight unit conversion factor to convert g units in the ingestion rate value to mg for the daily exposure (1,000 mg/g)
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)
Example Calculations
The following is an example calculation to determine the potential dose rate based on an assumed quantity of active ingredient per dry weight of pesticide pellets or granules. For the purpose of this example, the percent ai in the dry pesticide formulation is 0.5 percent (0.005). Thus, the estimated potential dose rate among toddlers from dry pesticide materials would be as follows:
PDR = IgR * F * CF1
PDR = 0.3 g/day * 0.005 * 1,000 mg/g
PDR = 1.5 mg/day
Finally, the estimated potential dose rate normalized to body weight for a toddler with a body weight of 15 kg would be:
PDRnorm = PDR / BW
PDRnorm = (1.5 mg/day) / (15 kg)
PDRnorm = 0.1 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 some central tendency (i.e., body weight) and some upper-percentile assumptions (i.e., ingestion rate of dry pesticide formulation, and maximum application rate for acute assessments) and are considered to be representative of high-end exposures. The uncertainties associated with this assessment stem from the use of an assumed ingestion rate of dry pesticide formulation. The dose estimates are considered to be reasonable high-end estimates based on 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.
Introduction
This SOP provides a standard method for estimating potential dose among toddlers from incidental ingestion of pesticide residues from previously treated turf. This scenario assumes that pesticide residues are transferred to the skin of toddlers playing on treated yards and are subsequently ingested as a result of hand-to-mouth transfer. It does not include residues ingested as a result of soil ingestion (see Section 2.3.4). The method for estimating postapplication incidental ingestion dose from pesticide residues on turf is based on assumptions when adequate chemical specific field data are unavailable.
Methods for Estimating Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The only datum required for estimating postapplication doses to pesticide residues on turfgrass is the application rate (e.g., lb ai/acre). The maximum application rate specified on the label should be used, except in cancer assessments when the typical application rates should be used. It should be noted, however, that the typical residential use rate is often the same as the maximum rate. The following assumptions are also needed for estimating pesticide postapplication doses.
- On the day of application, it may be assumed that 20 percent (i.e., 0.20) of the application rate is available on the turfgrass as dislodgeable residue. This value is based on the professional judgement and experience of the OPP/HED staff from the review of company-submitted data and is believed to be an upper-percentile value. P> - Postapplication activities must be assessed on the same day that the pesticide is applied since it is assumed that toddlers could play on the lawn immediately after application. For subsequent days after application, an assumed pesticide dissipation rate should be used, based on chemical-specific data.
- The median surface area of both hands is 350 cm2 for a toddler (age 3 years). This value represents the mean of the 50th percentile total surface area values for males and females in the 2<3 year and 3<4 year age groups, multiplied by the mean percentage of the total body represented by hands for males and females. (U.S. EPA, 1996a). The 3 year old age group was selected for use in this scenario because this is the youngest age group for which data on hand-to-mouth activity data were available.
- The mean rate of hand-to-mouth activity is 0.026 events/minute (i.e., 1.56 events/hr) for toddlers (3 to 5 year olds) (U.S. EPA, 1996b).
- Toddlers (age 3 years), 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, 1996a).
Potential dose rates from ingestion are calculated as follows: PDRt = DFRt * SA * FQ * ET * CF1
where:
PDRt = potential dose rate on day "t" (mg/day)
DFRt = dislodgeable foliar residue on day "t" (ug/cm2 turf)
SA = surface area of the hands (cm2/event)
FQ = frequency of hand-to-mouth activity (events/hr)
ET = exposure time (hr/day)
CF1 = weight unit conversion factor to convert ug units in the DFR value to mg for the daily exposure (0.001 mg/ug)
and DFRt = AR * F * (1-D)t * CF2 * CF3
where:
AR = application rate (lbs ai/ft2 or lb ai/acre)
F = fraction of ai available on turf (unitless)
D = fraction of residue that dissipates daily (unitless)
t = postapplication day on which exposure is being assessed
CF2 = weight unit conversion factor to convert the lbs ai
in the application rate to ug for the DFR value (4.54E8 ug/lb)
CF3 = area unit 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 = potential dose rate normalized to
body weight on day "t" (mg/kg/day)
BW = body weight (kg)
Example Calculations
The following is an example calculation to determine the dose based on an assumed dislodgeable foliar residue. For the purpose of this example, the application rate is assumed to be 2.2E-5 lbs ai/ft2 (approximately 1 lb/acre). Thus, the dislodgeable foliar residue on day 0 (i.e., the day of application) 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 incidental ingestion dose for a toddler on the day of application would be as follows:
PDRt = DFRt * SA * FQ * ET * CF1
PDR0 = 2.16 ug/cm2 * 350 cm2/event
* 1.56 events/hr * 2 hr/day * 0.001 mg/ug
PDR0 = 2.36 mg/day
Finally, the estimated potential dose rate, normalized by body weight, for a toddler with a body weight of 15 kg would be:
PDRt-norm = PDRt / BW
PDR0-norm = (2.36 mg/day) / (15 kg)
PDR0-norm = 0.16 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 some upper-percentile (i.e., available residues, duration of exposure) and some central tendency (i.e., surface area, hand-to-mouth activity, and body weight) assumptions and 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 available from turf, and assumptions regarding dissipation and hand-to-mouth activity. The estimated doses are believed to be reasonable high-end estimates based on observations from chemical-specific field studies and professional judgement.
References
U.S. EPA (1996a) Exposure Factors Handbook. [Draft]. U.S. Environmental Protection Agency, National Center for Environmental Assessment, Washington, DC. EPA/600/P-95/002Ba.
U.S. EPA (1996b) Time location activity pattern methodology: the creation of Bayesian distributions for the field investigations of exposure of infants and children to toxic substances. EPA-007-2. (To be included in an EPA Project Report entitled "Protocol for dermal exposure assessment in residential and non-occupational environments" which is currently in preparation and subject to EPA/ORD peer review).
Introduction
This SOP provides a standard method for estimating doses among toddlers from incidental ingestion of residential turfgrass that has been previously treated with pesticides. This scenario assumes that turf is ingested by toddlers that play on treated areas (i.e., yards, playgrounds). The method for estimating postapplication ingestion dose from pesticide residues on grass is based on assumptions when adequate site-or chemical-specific field data are unavailable. Thus, this method should be used in the absence of actual field data.
Methods for Estimating Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The only datum required for estimating postapplication doses from pesticide residues on grass is the application rate for the treatment areas (e.g., lb ai/acre). The maximum application rate specified on the label should be used, except in cancer assessments when the typical application rates should be used. It should be noted that the typical residential use rate is often also the maximum residential use rate. The following assumptions are also needed for estimating daily pesticide postapplication doses.
- On the day of application, it may be assumed that 20 percent of the application rate is ingested. Based on the experience and professional judgement of the OPP/HED staff, this is assumed to represent an upper-percentile input.
- Postapplication must be assessed on the same day the pesticide is applied since it is assumed that toddlers could play on the lawn immediately after application. For subsequent days after application, an assumed pesticide dissipation should be used, based on chemical-specific data.
- The assumed ingestion rate for grass for toddlers (age 3 years) is 25 cm2/day area of grass (i.e., 2 x 2 inches or 4 in2). This value is intended to represent the approximate area from which a child may grasp a handful of grass. Based on the experience and professional judgement of the OPP/HED staff, this is assumed to represent an upper-percentile input.
- Toddlers (age 3 years), 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).
Potential dose rates from ingestion are calculated as follows:
PDRt = GRt * IgR* CF1
where:
PDRt = potential dose rate on day "t" (mg/day)
GRt = grass (and plant matter) residue on day "t"
(ug/cm2)
IgR = ingestion rate of grass (cm2/day)
CF1 = weight unit conversion factor to convert the ug of residues
on the grass to mg to provide units of mg/day (1E-3 mg/ug)
and
GRt = AR * F * (1-D)t * CF2 * CF3
where:
AR = application rate (lbs ai/ft2 or lb ai/acre)
F = fraction of ai available on the grass (unitless)
D = fraction of residue that dissipates daily (unitless)
t = postapplication day on which exposure is being assessed
CF2 = weight unit conversion factor to convert the lbs ai
in the application rate to ug for the grass residue value (4.54E8
ug/lb)
CF3 = area unit conversion factor to convert the surface area
units (ft2) in the application rate to cm2
for the grass residue 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 = potential dose rate, normalized to
body weight, on day "t" (mg/kg/day)
BW = body weight (kg)
Example Calculations
The following is an example calculation to determine the dose based on an assumed residue on the grass. 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 turf residue on day 0 (i.e., the day of application) is as follows:
GRt = AR * F * (1-D)t * CF2 * CF3
GR0=(2.2E-5 lb ai/ft2) * (1.0) * (1-D)0
* (4.54E8 ug/lb) * (1.08E-3 ft2/cm2)
GR0 =10.8 ug/cm2
The estimated dose to toddlers from grass ingestion for the day
of application would be as follows: PDRt = GRt
* IgR * CF1
PDR0 = 10.8 ug/cm2 * 25 cm2
* 1E-3 mg/ug
PDR0 = 0.27 mg/day
Finally, the estimated potential dose rate, normalized to body weight, for a toddler with a body weight of 15 kg would be: PDRt-norm = Et / BW
DPR0-norm = (0.27 mg/day) / (15 kg)
PDR0-norm = 0.018 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 upper-percentile assumptions (except body weight which is an average value) and 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 on the turf, assumptions regarding dissipation of chemical residues on the grass, and the ingestion rate. The estimated doses are believed to be reasonable high-end estimates based on 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.
Introduction
This SOP provides a standard method for estimating dose among toddlers from incidental ingestion of soil containing pesticide residues. This scenario assumes that pesticide residues in soil are ingested by toddlers that play on treated areas (i.e., yards, gardens, playgrounds) as a result of normal mouthing activities (i.e., these estimates do not represent exposure among toddlers who exhibit pica, an abnormal ingestion behavior). The method for estimating postapplication ingestion exposure to pesticide residues in soil is based on assumptions when adequate site-or chemical-specific field data are unavailable. Thus, this method should be used in the absence of actual field data.
Methods for Estimating Potential Dose
Label information is important for selecting appropriate data inputs for the exposure assessment (see Section 2.0). The only datum required for estimating postapplication exposures to pesticide residues in soil is the application rate for the treatment areas (e.g., lb ai/acre). The maximum application rate specified on the label should be used, except in cancer assessments when the typical application rates should be used. However, it should be noted that the typical residential use rate is often the maximum residential use rate. The following assumptions are also needed for estimating daily pesticide postapplication doses.
Potential dose rates from ingestion are calculated as follows:
PDRt = SRt * IgR * CF1
where:
PDRt = potential dose rate on day "t" (mg/day)
SRt = soil residue on day "t" (ug/g)
IgR = ingestion rate of soil (mg/day)
CF1 = weight unit conversion factor to convert the ug of residues on the soil to grams to provide units of mg/day (1E-6 g/ug)
and SRt = AR * F * (1-D)t * CF2 * CF3
* CF4
where:
AR = application rate (lbs ai/ft2 or lb ai/acre)
F = fraction of ai available in uppermost cm of soil (fraction/cm)
D = fraction of residue that dissipates daily (unitless)
t = postapplication day on which exposure is being assessed
CF2 = weight unit conversion factor to convert the lbs ai
in the application rate to ug for the soil residue value (4.54E8
ug/lb)
CF3 = area unit conversion factor to convert the surface
area units (ft2) in the application rate to cm2
for the SR value (1.08E-3 ft2/cm2 or 2.47E-8
acre/cm2 if the application rate is per acre)
CF4 = volume to weight unit conversion factor to convert the
volume units (cm3) to weight units for the SR value (U.S.
EPA, 1992) (0.67 cm3/g soil)
Potential dose rates, normalized to body weight, are calculated
as: PDRt-norm = PDRt / BW
where:
PDRt-norm = potential dose rate, normalized to body weight, on day "t" (mg/kg/day)
BW = body weight (kg)
Example Calculations
The following is an example calculation to determine the dose
based on an assumed soil residue concentration. 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 soil residue
on day 0 (i.e., the day of application) is as follows:
SRt = AR * F * (1-D)t * CF2 * CF3 * CF4
SR0 = 2.2E-5 lb ai/ft2 * 1.0/cm * (1-D)0 * 4.54E8 ug/lb * 1.08E-3 ft2/cm2 * 0.67 cm3/g soil
SR0 = 7.2 ug/g
The estimated incidental soil ingestion dose among toddlers for the day of application would be as follows:
PDRt = SRt * IgR * CF1
PDR0 = 7.2 ug/g * 100 mg/day * 1E-6 g/ug
PDR0 = 0.0007 mg/day
Finally, the estimated potential dose rate, normalized to body weight, for a toddler with a body weight of 15 kg would be:
PDRt-norm = PDRt / BW
PDR0-norm = (0.0007 mg/day) / (15 kg)
PDR0-norm = 4.8E-5 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 some central (i.e., soil ingestion rate and body weight) tendency and some upper-percentile (i.e., availability of residues) assumptions and 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 available in the uppermost 1 cm of soil, and assumptions regarding dissipation of chemical residues in the soil and soil ingestion. The estimated doses are believed to be reasonable high-end estimates based on 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.
U.S. EPA (1992) Dermal Exposure Assessment: Principles and Applications. Office of Health and Environmental Assessment. EPA/600/8-9/011F.