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Standard Operating Procedures (SOPs) for Residential Exposure Assessments


These Residential Exposure Assessment Standard Operating Procedures (SOPs) are designed for those who assess exposure to pesticides in a residential setting. The objective of these SOPs is to provide standard default methods for developing residential exposure assessments for both handler and postapplication exposures when chemical- and/or site-specific field data are limited (U.S. EPA, 1987, 1995). These methods may be used in the absence of, or as a supplement to, chemical- and/or site-specific data.

Handler and postapplication SOPs for developing assessments of dermal, inhalation, and/or incidental ingestion doses are provided in the following major residential exposure scenarios:

- residential lawns,
- garden plants,
- trees (e.g., fruit, ornamental),
- swimming pools,
- painting and wood preservative treatments,
- fogging,
- crack and crevice and broadcast treatments,
- pet treatments,
- detergent/hand soap,
- impregnated materials,
- termiticides,
- inhalation of residues from indoor treatments, and
- rodenticides.

Each SOP includes:

- a description of the exposure scenario,
- the recommended methods (i.e., algorithms and default parameters) for quantifying doses,
- example calculations,
- limitations and uncertainties associated with the use of the SOP, and
- applicable references.

This document also provides information on the general principles of exposure assessment (Section 1.1), background information on the development and use of these residential SOPs (Section 1.2), guidance for amortizing daily doses to obtain lifetime doses, and guidance on using labeling information to determine whether a pesticide is registered for use at residential sites, and to determine formulation type, application methods, use-rates, and use frequency (Section 1.4). General labeling considerations are provided in Section 1.4 and scenario-specific labeling information is provided at the beginning of each chapter. Section 1.5 provides information on many of the conversion factors used in the SOPs and Section 1.6 provides definitions for many of the common terms used. Appendix A summarizes the data inputs for the various scenarios.

The SOPs were prepared by EPA's Office of Pesticide Programs, Health Effects Division and Antimicrobial Division with input from EPA's Office of Pollution Prevention and Toxics, and Office of Research and Development. The Workgroup was also provided with technical support from Versar, Inc.

1.1 General Principles of Exposure Assessment

Exposure assessment is the process by which: (1) potentially exposed populations are identified; (2) potential pathways of exposure are identified; and (3) chemical intakes/potential doses are quantified. The populations being considered in these SOPs are those individuals who are potentially exposed to pesticides used in residential settings. Exposures to pesticides may occur from handling or postapplication via contact by oral, inhalation, or dermal absorption routes. Exposure is commonly defined as contact of visible external physical boundaries (i.e., external boundaries such as the mouth, nostrils, and skin) with a chemical agent (U.S. EPA, 1992). As described in the Guidelines for Exposure Assessment (U.S. EPA, 1992), exposure is dependent upon the intensity, frequency, and duration of contact. The intensity of contact is typically expressed in terms of the concentration of contaminant per unit mass or volume (i.e.,Fg/g, Fg/L, mg/m3, ppm, etc.) in the media to which humans are exposed (U.S. EPA, 1992).

Dose refers to the amount of chemical to which individuals are exposed that crosses the external boundary. Dose is dependent upon contaminant concentration and the rate of intake (i.e., inhalation or ingestion) or uptake (i.e., dermal absorption) and may be normalized to body weight as a function of time (i.e., mg/kg/day). Potential dose is the amount of chemical which could be ingested or deposited upon the skin. The absorbed dose is the amount of chemical absorbed into the body through the gastrointestinal tract, lung or skin. The toxicologic basis for risk assessment is typically either the potential dose from animal feeding studies or the absorbed dose from pharmacokinetic studies followed by intraperitoneal or other injected delivery into the test animal. Potential dose may be calculated as follows:


PDR = potential dose rate (mg/day);

C = contaminant concentration in the media of interest (mg/cm2; mg/m3, mg/g); and
CR = contact rate with that media (cm2/day; m3/day; day).

Absorbed doses may be calculated by including an absorption factor in the equation above.

The contaminant concentration is the amount of pesticide in the media to which humans are exposed. The contaminant concentration may be affected by dissipation of chemical over time by evaporation, degradation, or other fate processes. Contact rate may be defined as the rate of ingestion, inhalation, or dermal absorption or as the transfer coefficient (U.S. EPA, 1989).

Average, high-end, and/or bounding estimates may be made using this algorithm. These exposure descriptors account for individual and population variability and represent points on the distribution of exposures. Average potential dose rates represent the mean and may be estimated using central tendency values for all the parameters in the dose algorithm. The high-end potential dose rate (90th or 95th percentile) is a reasonable approximation of dose for individuals at the upper end of the distribution of exposures (U.S. EPA, 1992). High-end values are estimated by setting some, but not all, input parameters to the upper-end values. Finally, bounding potential dose rates are exposures that are estimated to be greater than the highest individual exposure in the population of interest. Bounding estimates use all upper-percentile inputs and are often used in screening-level assessments.

Inputs for the standard exposure calculations should be representative of the population/scenarios being evaluated. Contaminant concentration values may be generated based on residue and dissipation assumptions for the media of interest. Factors such as frequency and duration of use can be derived from actual data on the activities/uses associated with site/scenario-specific uses of a chemical, or from general population survey data on activity patterns and product usage. Other inputs to the exposure calculations such as contact rate (ingestion rate, inhalation rate, skin surface area), body weight, and lifetime may be based on standard exposure factors. Mean and upper-percentile exposure factors based on distributions of data collected from the scientific literature are reported in EPA's Exposure Factors Handbook (1996) and EPA's Risk Assessment Guidance for Superfund (1989).

Uncertainty may be introduced into the dose calculations at various stages of the exposure assessment process. Uncertainty may occur as a result of: (1) the techniques used to estimate chemical residues, (2) chemical dissipation assumptions, and (3) the selection of exposure scenarios and exposure factors. Variability can occur as a result of variations in individual day-to-day or event-to-event exposure factors or variations among the exposed population. Variability can be addressed by estimating exposure for the various descriptors of exposure [i.e., central tendency (mean or median), high-end (90th or 95th percentile), or bounding (100th percentile)] to represent points on the distribution of exposures.

1.2 Residential SOPs

These SOPs are for residential exposure assessments and rely on high-end scenarios. The residential lawn scenario, for example, is assumed to represent the upper end of the distribution of exposures that could occur from lawns, parks, playgrounds, recreational areas, athletic fields, and other turf areas. Also, these scenarios normally rely on one or more upper-percentile assumptions such as 90th percentile exposure duration values and/or 90th percentile skin surface area values. They are intended to represent Tier 1 assessments. If a Tier 1 assessment indicates a potential concern, a more detailed exposure assessment is warranted, possibly including chemical-specific or site-specific data (U.S. EPA, 1987, 1995).

The estimated doses resulting from using these SOPs are appropriate for use in developing estimates of human risks associated with residential exposures to pesticides. (The actual calculations of human health risks are not within the scope of this document.) Each SOP provides calculations for daily dose. The daily potential dose rate calculations are based on the amount of chemical to which an individual is exposed in a day and are expressed as milligrams per day. The daily potential dose rate, normalized to body weight, is a calculation of the amount of chemical to which an individual is exposed on a per-unit-body-weight basis and is expressed in units of milligrams per kilogram per day. The potential dose rate definition used here is consistent with EPA's Exposure Assessment Guidelines (U.S. EPA, 1992) which states that dose is defined as "the amount of a chemical contained in material ingested, air breathed, or bulk material applied to the skin." The dermal and inhalation dose values determined by these SOPs represent potential doses and do not, in general, include an adjustment for the amount of chemical likely to pass through the skin or lungs and be absorbed into the human system. Assessors will need to apply chemical-specific dermal and inhalation absorption rates, if available, to determine absorbed dose. See Section 1.6 for definitions of the terms used in exposure assessment.

Each SOP provides methods for estimating short-term or acute daily doses for a single route of exposure (e.g., dermal, inhalation, ingestion). These represent estimates of exposure that may need to be combined with estimates from other routes of exposure and other use sites to estimate aggregate exposures. Techniques for determining aggregate doses are not within the scope of this document. The assumptions in the SOPs do not include the distributions of inputs that would be necessary for a probability analysis (e.g., Monte Carlo).

For calculating exposures for many cancer assessments, the daily dose values estimated in the individual SOPs may have to be amortized to obtain lifetime average daily potential dose. Section 1.3 provides guidance for amortizing daily doses. In general, the daily doses estimated by these SOPs represent acute doses and use maximum application rates as input. Cancer assessments should use typical application rates.

The assumptions in these SOPs will be periodically updated as new data become available. In addition, these SOPs are designed to allow the assessor to substitute alternate inputs for the default assumptions when more specific data are available or when professional judgement indicates that alternative values are more appropriate. Currently, the SOPs do not include adjustments for exposure-reduction techniques, such as coatings on granules that reduce exposures to dusts, or specialized packaging that reduces exposure. Also, these SOPs do not attempt to discuss toxicity or selection of endpoints for use in calculating risk. The exposure assessor would need to consult with the toxicologist especially if dermal or inhalation endpoints have not been previously selected.

Most SOPs include body weights for adults and for children within specific age groups. When exposure assessments are conducted for age groups other than those specified in the SOP, standard body weights in EPA's Exposure Factors Handbook (1996) may be used to ensure consistency among the assessments prepared by OPP. The body weight for specific age groups are summarized in Table 1-1.

Table 1-1. Body Weight Values for Specified Age Groups

Age (Years) Body Weight (kg) Comments
Infants (0.5 to 1.5) 10 Mean of median values for males and females in the 6-11 month and 1 year age groups
Toddlers (3) 15 Mean of median values for male and female 3 year olds
Children (6) 22 Mean of median values for male and female 6 year olds
Youth (10 to 12) 39.1 Mean of median values for males and females age 10, 11, and 12 years
Adult Reproductive Females 60 Mean for females age 13 to 54 years
Adults 71.8 Mean for males and females 18 years and older
Source: U.S. EPA (1996)

Many of the postapplication exposure scenarios make assumptions regarding the amount of dislodgeable pesticide residues. Dislodgeable residues are those residues that may be transferred to the skin as a result of contact and are available for dermal absorption or ingestion. Assumptions regarding transfer of dislodgeable residues are generally based on the experience and professional judgement of OPP staff from the review of monitoring studies. Many of the handler SOPs use unit exposure values from the Pesticide Handlers Exposure Database (PHED) as inputs into the exposure assessment algorithms. PHED is a database containing surrogate handler data collected from field exposure studies. Assessors should refer to the Appendix B for these unit exposure values. (See Appendix B.) The Appendix B provides surrogate exposure information for various handler exposure scenarios as well as the confidence/grades associated with the data.

1.3 Amortizing Dose

Generally, the SOPs provided in this document provide methods for calculating the potential daily dose rates for pesticides to which individuals are exposed. These daily dose rate estimates are appropriate for assessing risk to human health from short-term exposure. However, further calculation may be required to obtain amortized doses that represent average doses over a lifetime. The lifetime average daily dose (LADD) is used for many assessments involving cancer effects. The LADD is calculated as follows:

LADD = (D * EF * ED) / (AT * CF)


D = dose (mg/kg-day)
EF = exposure frequency (i.e., frequency of product use) (days/year)
ED = exposure duration (years)
AT = averaging time (i.e., lifetime) (years)
CF = conversion factor (365 days/year)

For handler scenarios, estimated doses on the day of application may be amortized using this LADD algorithm and assumptions regarding the exposure frequency, exposure duration, and averaging time (i.e., lifetime). It should be noted that OPP/HED is currently in the process of developing information on exposure frequency on the scenarios provided in this document. These frequency data will be available in an update of these SOPs. For postapplication scenarios, exposures on the day of application and on subsequent days while residues are dissipating must first be summed and averaged within the scenario prior to amortizing the postapplication dose.

1.4 Labeling Considerations

Prior to conducting an exposure assessment using the SOPs in this document, several labeling issues should be considered, as follows.

Obtain End-Use Product Labels: Attempt to obtain copies of all end-use product labels (or at least representative labels for broad spectrum chemicals).

Determine Whether Registered for Use at Residential Sites: Assume that a product may be used at residential sites unless labeling statements indicates otherwise. (See site-specific labeling for more information.) Restricted-Use classification, statements such as "For use by commercial or professional applicators only," or liquid-concentrate formulations marketed only in large containers (e.g., 40 gallons) indicate that the product cannot be bought or applied by homeowners. No residential handler exposure/risk assessment is required for these products. However, it may be applied by commercial applicators to residential sites, therefore a post-application exposure/risk assessment may be required. Sometimes the Reference Files System (REFs) database will indicate whether the product is used at residential sites.

Determine Formulation Type: Often the label front panel will list the type of formulation as part of or associated with the brand name. For example, Pesto 3G indicates the product is a granular; whereas Pesto WP is a wettable powder and Pesto EC is an emulsifiable concentrate. Sometimes the formulation type is not listed on the front panel. For all liquid formulations, immediately before or after the active ingredient statement is a statement listing the number of pounds of active ingredient contained in a gallon of the liquid formulated product. The label use-directions also may provide an indication of the formulation type. Look at the mixing/loading instructions, application-equipment types, and dose-rates (in general, dry products are measured in ounces or pounds and liquid products are measured in pints, quarts, or gallons).

Determine Possible Methods of Application: The label use-directions often specify the methods of application for a product either by prohibiting specific application techniques (e.g., "do not apply in any type of irrigation equipment" or "spot treatment only") or by listing the application equipment to be used. Unless certain equipment or application techniques are specifically prohibited on the labeling or are obviously incompatible with the formulation or use-directions, assume any equipment or technique can be used.

Determine Use-Rates: Maximum Use-Rates: Determine the maximum label-permitted use-rate by comparing the use-directions for each use listed on the label. Often there are multiple use-directions with widely varying use-rates due to factors such as indoor/outdoor use, pests to be controlled, timing of application, and type of surface (e.g., plant, soil, carpet, hard-surface) being treated. Maximum use-rates may vary by formulation-type, so the maximum rate for each formulation must be determined. Typical Use-Rates: Determine the typical use-rates (needed only for cancer risk assessments) by studying the label use-directions and choosing the use-rate that would most commonly be used; do not select the rate for heavy infestations, severe conditions, etc. However, when a range of application rates is given for a routine pest or situation, choose the highest use-rate. Typical use-rates may vary by formulation-type, so the typical rate for each formulation must be determined.

Determine Use Frequency: For cancer risk assessments, it may be necessary to estimate the number of handler and post-application exposures per year. The pesticide label will often indicate how frequently the product may be applied. Look in the Directions-For-Use section for instructions about frequency. Examples of typical statements include "apply at 7-day intervals while pests are present," "apply in early Spring before first mowing," or "apply a second spray in 3 to 5 days."

1.5 Conversion Factors

Many of the SOPs require the use of weight, area, or volume unit conversion factors. These conversion factors are used to convert common units of measure to those needed to calculate dose. Table 1-1 provides a list of conversion factors that are frequently used in these SOPs.

Table 1-1. Conversion Factors

To Convert Multiply by To Obtain
acre 43,560 square feet (ft2)
acre 4.047E3 square meters (m2)
gram (g) 1,000 milligrams (mg)
milligrams (mg) 1,000 micrograms (Fg)
pound (lb) 454 grams (g)
square centimeter (cm2) 1.08E-3 square feet (ft2)
square centimeter (cm2) 2.47E-8 acre
gram (g) 2.2E-3 pound (lb)
liter (L) 2.64E-1 gallon (gal)
gallon (gal) 3.785 liter (L)
liter (L) 1,000 cubic centimeter (cm3)
square centimeter (cm2) 1E-4 square meter (m2)
square meter (m2) 1E4 square centimeter (cm2)
square feet (ft2) 2.29E-5 acre
square meter (m2) 2.47E-4 acre
milligram (mg) 1E-3 gram (g)
microgram (Fg) 1E-3 milligram (mg)
cubic centimeter (cm3) 1E-3 liter (L)

1.6 Definitions

This section provides definitions for many of the key terms used in these SOPs. Most of these definitions are taken directly from EPA's Guidelines for Exposure Assessment (U.S. EPA, 1992) or EPA's Draft Series 875 - Occupational and Residential Exposure Test Guidelines, Group B - Postapplication Exposure Monitoring Test Guidelines (U.S. EPA, 1997).

Absorbed Dose - The amount of a substance penetrating across the absorption barriers (the exchange boundaries) of an organism, via either physical or biological processes. This is synonymous with internal dose.

Bounding Dose Estimate - An estimate of dose that is higher than that incurred by the person in the population with the highest dose. Bounding estimates are useful in developing statements that doses are "not greater than" the estimated value.

Central Tendency Dose Estimate - An estimate of dose for individuals within the central portion (average or median) of a dose distribution.

Dislodgeable Residues - The portion of pesticide residues that are available for transfer to humans.

Dose Rate - Dose per unit time, for example in mg/day, sometimes also called dosage. Dose rates are often expressed on a per-unit-body-weight basis yielding such units as mg/kg/day. They are also often expressed as averages over some time period, for example a lifetime.

Exposure Assessment - The determination of the magnitude, frequency, duration, and route of exposure.

Exposure Concentration - The concentration of a chemical in its transport or carrier medium at the point of contact.

Exposure Pathway - The physical course a chemical or pollutant takes from the source to the organism exposed.

Exposure Route - The way a chemical or pollutant enters an organism after contact, e.g., by ingestion, inhalation, or dermal absorption.

Exposure Scenario - A set of facts, assumptions, and inferences about how exposure takes place that aids the exposure assessor in evaluating, estimating, or quantifying exposure.

Geometric Mean - The nth root of the product of n values.

High-end Dose Estimates - A plausible estimate of individual dose for those persons at the upper end of a dose distribution, conceptually above the 95th percentile, but not higher than the individual in the population who has the highest dose.

Mean Value - The arithmetic average of a set of numbers.

Median Value - The value in a measurement data set such that half the measured values are greater and half are less.

Potential Dose - The amount of a chemical contained in material ingested, air breathed, or bulk material applied to the skin.

Surrogate Data - Substitute data or measurements on one substance (or population) used to estimate analogous or corresponding values for another substance (or population).

Unit Exposure - The amount of residue to which individuals are exposed (based on monitoring data), normalized to the amount of active ingredient used.

Upper-Percentile Value - The value in a measurement data set that is at the upper end of the distribution of values (i.e., 90th to 95th percentile).

1.7 References

U.S. EPA (1987) Pesticide Assessment Guidelines. Subdivision U. Applicator Exposure Monitoring. Washington, DC: Office of Pesticide Programs. U.S. EPA Publication No. 540/9-87-127. NTIS Publication No. PB87-133286.

U.S. EPA (1989) Risk Assessment Guidance for Superfund. Washington, DC: Environmental Protection Agency, Office of Emergency and Remedial Response. EPA/540/1-89/002.

U.S. EPA (1992) Guidelines for Exposure Assessment. Washington, DC. Environmental Protection Agency. Federal Register Notice. Vol. 57. No. 104, pp. 22888-22938.

U.S. EPA (1995) Series 875: Occupational and Residential Exposure Test Guidelines, Group B - Post-Application Exposure Monitoring Test Guidelines (Working Draft, Version 5.1). Office of Prevention, Pesticides, and Toxic Substances. U.S. Environmental Protection Agency, Washington, DC.

U.S. EPA (1996) Exposure Factors Handbook, External Review Draft. U.S. Environmental Protection Agency, Office of Health and Environmental Assessment, Washington, DC. EPA/600/P-95/002B.

U.S. EPA (1997) Series 875 - Occupational and Residential Exposure Test Guidelines, Group B - Postapplication Exposure Monitoring Test Guidelines. Draft Document (Version 5.2). Office of Prevention, Pesticides, and Toxic Substances, Washington, DC.

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