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Guidance for the Development of Conceptual Models for a Problem Formulation Developed for Registration Review

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Guidance for the Development of Conceptual Models for a Problem Formulation Developed for Registration Review (PDF) (10 pp, 210K, About PDF)

On this page:

  1. Conceptual Model for Pesticide Effects on Aquatic Organisms
  2. Conceptual Model for Pesticide Effects on Terrestrial Organisms

Memorandum

March 10, 2011

SUBJECT: Guidance for the Development of Conceptual Models for a Problem Formulation Developed for Registration Review

FROM: Donald J. Brady, Ph.D., Director
Environmental Fate and Effects Division
Office of Pesticide Programs

TO: All Managers and Staff of the Environmental Fate and Effects Division

The Endangered Species Registration Review Workgroup is providing guidance for Environmental Fate and Effects Division's (EFED) scientists who are developing conceptual models for aquatic and terrestrial exposures in Problem Formulation for Registration Review and litigation-related assessments. The conceptual model is a graphic representation of the predicted relationships between the ecological entities, both listed (threatened and endangered) and non-listed species, and the stressors to which they may be exposed.

The conceptual model specifies the potential routes of exposure, biological receptor types, and effects endpoints of potential concern. Examples of conceptual models are provided in Figures 1 (generic aquatic exposure pathways), 2 (generic terrestrial exposure pathways), and 3 (terrestrial exposure specific for drinking water ingestion and inhalation). (An electronic copy of these figures can be found on the G Drive under Policies, Guidance, and Formats\Formats\Review Actions\Problem Formulation\Conceptual Model Formats.) These examples are intended to be generic in scope, and representative of major routes of potential exposure for aquatic and terrestrial receptors including runoff and spray drift. Further description of the major routes of aquatic and terrestrial exposure routinely considered in ecological risk assessments completed by EFED is provided in the Overview Document (USEPA,2004). Both models consider direct and indirect effects to listed and non-listed species, as well as consideration of the Primary Constituent Elements (PCEs) associated with designated critical habitat for listed species. Microsoft® PowerPoint files of the conceptual models, which should be modified prior to incorporation in the problem formulation, are provided as an attachment to this guidance memo.

In addition to the traditional exposure pathways identified in Figures 1 and 2, other potential aquatic and terrestrial exposure pathways that may need to be considered in the development of pesticide-specific conceptual models are addressed in Sections 1.1 and 2.1, respectively. The risk assessor should also consider any major degradate(s) of concern and unique types of application methods (e.g., direct application to water, soil injection, etc.) that may result in modification to the generic conceptual models. Figure 3 provides a conceptual diagram for consideration of drinking water and inhalation exposure pathways to terrestrial animals, both of which are discussed in Section 2.1.

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  1. Conceptual Model for Pesticide Effects on Aquatic Organisms

    Figure 1 provides a sample of a generic conceptual model for pesticide effects on aquatic organisms.

    Figure 1

    graphic depiction of generic aquatic exposure pathways

    Figure 1
    Conceptual model depicting stressors, exposure pathways, and potential effects to aquatic organisms from the use of CHEM X to CHEMX Use.
    Dotted lines indicate exposure pathways that have a low likelihood of contributing to ecological risk.


    Instructions for Modification to Generic Aquatic Conceptual Model

    • All stressors (e.g., parent compound and major degradate(s) of concern) should replace the term "pesticide" in the uppermost box.

    • Figure X in the "Riparian plant" receptor box should be changed to include the Figure # for the generic terrestrial conceptual model.

    • If risks to piscivorous mammals and birds via consumption of aquatic prey are not considered (see unique aquatic exposure below), delete this receptor (**) and associated footnote shown in green font.

    • Special considerations should be given to the ground water and atmospheric transport exposure pathways, which may represent significant routes of exposure for certain pesticides (i.e., the lines in the conceptual model should be solid for these pathways unless the risk assessor can justify why they should be "dotted").

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    • 1.1 Additional Aquatic Exposures

      For certain pesticides, sediment, ground water, and atmospheric transport may be significant exposure pathways for aquatic organisms; for other pesticides, these pathways represent a negligible route of exposure and may be neglected. Criteria are provided for determining whether these additional routes of exposure should be considered in developing a pesticide-specific conceptual model. In addition, criteria are also provided for the need to address consumption of aquatic food items by piscivorous birds and mammals.

      • Sediment

        To determine whether the sediment exposure pathway should be evaluated as part of the conceptual model for aquatic organisms, the partitioning of the pesticide and/or major degradate(s) of concern in the aquatic environment and its persistence should be considered. In general, the data requirements for sediment toxicity testing, which are specified in 40 CFR Part 158.630, are used to determine whether the sediment exposure pathway should be considered. Acute sediment exposures should be addressed if the half-life of the pesticide and/or major degradate(s) of concern in sediment is ≤ 10 days in either the aerobic soil or aquatic metabolism studies, and if any one of the following conditions exist:

        • Any soil-water distribution coefficient (Kd) is ≥ 50 L/kg;

        • The log octanol-water partition coefficient (Kow) is ≥ 3; or

        • Any organic carbon (OC) normalized distribution coefficient (Koc) is ≥ 1,000 L/kg OC.

        Acute and chronic sediment exposures should be addressed if the estimated acute environmental concentration (EEC) in sediment is > 0.1 of the acute LC50/EC50 values, the half-life of the pesticide and/or major degradate(s) of concern in the sediment is ≥ 10 days in either the aerobic soil or aquatic metabolism studies, and if any one of the following conditions exist:

        • Any Kd is ≥ 50 L/kg;

        • The log Kow is ≥ 3; or

        • Any Koc is ≥ 1,000 L/kg OC.

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      • Ground water

        The importance of the movement of the pesticide and/or major degradate(s) of concern into ground water is based on available laboratory, field, and/or monitoring data. The ground water route of exposure should be considered if any one of the four following criteria is met:

        • Detections in ground water are reported in the prospective ground water study conducted for registration, or in other reliable monitoring data found in the publicly available literature. Monitoring data are considered reliable when a reasonable presumption can be made that the residues found in ground water are from registered applications of the pesticide, rather than from a point source, for example a spill.

        • One or more terrestrial field dissipation studies show pesticide and/or major degradate(s) of concern movement to the depth sampled such that a prospective ground water study may become a data requirement. The absence of detected movement with soil core sampling in field dissipation studies is not necessarily an indication of the lack of pesticide leachability.

        • The pesticide and/or major degradate(s) of concern have a combination of environmental fate properties similar to other pesticides historically found in ground water as a result of normal label uses. The chemical(s), at a minimum, should have combined mobility (value of Kd < 5) and persistence (hydrolysis half-life > 30 days at any pH or aerobic soil metabolism half-life > 2 weeks) (USEPA, 2008a).

        • Uses of the pesticide of concern may be in areas characterized by karst topography or known to be vulnerable to ground water contamination (e.g. Long Island, New York).

        Currently, the Agency does not have a routine method for quantifying the exposure and risk associated with the ground water route of exposure to aquatic receptors. Therefore, consideration of the ground water exposure pathway would be limited to a qualitative assessment at this time.

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      • Atmospheric transport/volatilization

        See "atmospheric transport/volatilization" under Section 2.1. In addition, the "Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem Formulation for Registration Review" should be consulted for addressing potential atmospheric transport and volatilization exposure pathways for aquatic receptors.

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      • Consumption of aquatic food items by piscivorous mammals and birds

        In order to determine whether to evaluate consumption of aquatic food items by piscivorous mammals and birds in the conceptual model, the risk assessor should consult the User's Guide for KABAM (Kow (based) Aquatic BioAccumulation Model; version 1.0; available at: G:\Models\Aquatic\Miscellaneous\KABAM and KABAM. KABAM is used to estimate potential bioaccumulation of hydrophobic organic pesticides in freshwater aquatic food webs and subsequent risks to mammals and birds via consumption of contaminated aquatic prey when pesticides and/or major degradate(s) of concern have all of the following characteristics:

        • They are non-ionic and organic;

        • Log Kow values are between 4 and 8; and

        • They have the potential to reach aquatic habitats.

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  2. Conceptual Model for Pesticide Effects on Terrestrial Organisms

    Figures 2 and 3 provide generic conceptual models for pesticide effects on terrestrial organisms. Figure 2 focuses on exposure pathways for terrestrial plants, terrestrial invertebrates, and dietary routes of exposure for terrestrial vertebrates. Figure 3 considers drinking water and inhalation exposure pathways for terrestrial vertebrates and also ingestion of pesticide residues in dew by terrestrial invertebrates.

    Figure 2

    graphic depiction of generic terrestrial exposure pathways

    *See Figure x for drinking water and inhalation exposure pathways for terrestrial vertebrates and ingestion of residues in dew by terrestrial invertebrates.

    Figure 2
    Conceptual model depicting stressors, generic exposure pathways, and potential effects to terrestrial organisms (terrestrial plants, terrestrial invertebrates, and dietary routes of exposure for terrestrial vertebrates) from the use of CHEM X to CHEMX Use.
    Dotted lines indicate exposure pathways that have a low likelihood of contributing to ecological risk.


    Instructions for Modification to Generic Terrestrial Conceptual Model

    • All stressors (e.g., parent compound and major degradate(s) of concern) should replace the term "pesticide" in the uppermost box.

    • Special consideration should be given to exposure pathways including atmospheric transport and ground water used as irrigation water, which may represent significant routes of exposure for certain pesticides (i.e., the lines in the conceptual model should be solid for these pathways unless the risk assessor can justify why they should be "dotted").

    • Figure X in the footnote denoted by the asterisk (*) should be changed to include the Figure # for the terrestrial conceptual model specific for the drinking water and inhalation exposure pathways.

    Figure 3

    graphic depiction of terrestrial exposure specific for drinking water ingestion and inhalation

    Figure 3
    Conceptual model depicting stressors, drinking water and inhalation exposure pathways, and potential effects to terrestrial animals from the use of CHEM X to CHEMX Use.
    Dotted lines indicate exposure pathways that have a low likelihood of contributing to ecological risk.


    Instructions for Modification to Terrestrial Conceptual Model for Drinking Water and Inhalation Exposure Pathways

    • All stressors (e.g., parent compound and major degradate(s) of concern) should replace the term "pesticide" in the uppermost box.

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    • 2.1 Additional Terrestrial Exposures

      For some chemicals, atmospheric transport, volatilization, and inhalation may present exposure pathways for terrestrial organisms along with dermal and drinking water exposure. Guidelines are provided below for assessing these routes of exposure.

      • Atmospheric transport/volatilization/inhalation

        The "Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem Formulations for Registration Review, Registration Review Risk Assessments, Listed Species Litigation Assessments, New Chemical Risk Assessments, and Other Relevant Risk Assessments" should be consulted for addressing potential volatilization exposure pathways. Fate properties, such as vapor pressure and Henry's Law constant should be considered to characterize potential volatilization from dry and wet conditions. However, volatilization in air also depends on a variety of factors including soil properties (e.g., moisture content and organic matter content), farming practices (e.g., tillage and application rate and techniques), and meteorological factors (e.g., precipitation, temperature, humidity, and wind speed). Therefore, it is recommended that the following approach be used to determine whether atmospheric transport/volatilization/inhalation should be considered as viable exposure pathways.

        The Screening Tool for Inhalation Risk (STIR) should be used in all screening-level assessments to assess the potential risk of acute inhalation exposure through airborne droplets and vapor phase of a pesticide. The STIR model and associated User's Guide, which are currently in development, will be available to EFED staff on the following website upon completion: STIR.

        Atmospheric monitoring data from numerous studies suggest that semi-volatile pesticides have the potential to volatilize from fields long after treatment (USEPA, 2008b; Majewski and Capel, 1995; Lenoir et al., 1999; Majewski and Baston, 2002; McConnell et al., 1998). If monitoring data provides evidence of a pesticide in the atmosphere, a tiered screening approach can be used to estimate the concentrations of applied pesticide in air, which can be compared with acute mammalian and avian inhalation toxicity data to evaluate potential effects on terrestrial organisms. Currently, EFED is evaluating some of the existing models in an effort to develop tiered screening and refined approaches to determine the rate of volatilization (flux) for semi-volatile pesticides applications to bare soil and crop canopies and estimate the concentrations of applied pesticide in the atmosphere under varying environment conditions. This tiered approach was presented to the FIFRA Scientific Advisory Panel (SAP) in December 2009. EFED is in the process of developing tiered screening and refined methods, based on recommendations from the SAP, to address near field inhalation exposure resulting from the vapor phase of pesticide and monitoring data to address far field inhalation exposure.

        In order to address the long-range transport potential (LRTP), the atmospheric half-life of the pesticide and/or major degradate(s) of concern and its interaction with aerosol particles should be considered. LRTP should be considered as a potential route of exposure if the atmospheric half-life is greater than 2 days and if the chemical's vapor pressure suggests potential volatilization from treated surfaces. EFED is not able to quantify the extent to which a pesticide will undergo long-range transport once it has been released from a treatment site; therefore, it is not possible to quantify the amount of exposure that could potentially occur to non-target receptors distant from the use sites. However, the LRTP of a chemical may be qualitatively described by comparing model estimates of LRTP with those of chemicals that have been documented via monitoring data to be susceptible to long-range transport (e.g., DDT, aldrin, and endrin). At this time, EFED scientists may use the Organization of Economic and Cooperative Development (OECD) Screening Tool Pov and LRTP Screening Tool to characterize the LRTP of a pesticide. This tool is available at: (OECD Pov and LRTP Screening Tool). The use of this tool has been vetted and accepted as an available screening tool for long-range transport potential by the October 2008 FIFRA PBT SAP. In addition, any available monitoring data should be used to characterize the LRTP of a chemical.

        Several monitoring datasets are available for persistent organic pollutants, which are recognized to accumulate in the environment over time. Many of these datasets contain information on pesticide residues in air, soil, sediment, precipitation, animal and plant biota, and bodies of water. Historical air monitoring data collected by the California Air Resources Board is available on-line at Toxic Air Contaminant Program Monitoring Reports. Monitoring data in precipitation can be found in various open literature sources including Lenoir et al., 1999 and Majewski and Baston, 2002. Publications containing comprehensive monitoring data conducted in Western U.S. National Parks are available for 26 currently used and cancelled pesticides at WACAP - Western Airborne Contaminants Assessment Project. Another useful source of air monitoring data for eight currently used and cancelled pesticides studied in Western Canadian National Parks can be found in Daly et al., 2007.

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      • Dermal

        The dermal route of exposure for terrestrial wildlife can be divided into a few sub-routes. These include organisms exposed:

        • In the treated field at the time of application or in the areas adjacent to the treated field and within the aerial drift plume that may come in direct contact with applied material.

        • While conducting daily activities within treated or drift-impacted areas whereby exposure may occur via contact with dislodgeable residues of the pesticide on treated vegetation.

        • To the pesticide deposited on soil particles either through contact with contaminated soil through portions of the body contacting the ground, dust bathing, or through incidental contact with fugitive dust emissions from treated or drift-impacted areas.

        • Via dermal contact with the pesticide that is dissolved in puddles water on the treated field or in areas impacted by drift and run-off.

        • To volatile compounds in the vapor phase integument via direct absorbtion.

        At the present time, the Agency does not have a method to quantify these levels of exposure, and data are limited to quantify the contribution of such exposures to the toxic burden an organism experiences. The Agency is actively working on a screening method to quantify exposure from direct impingement of applied foliar sprays and from incidental contact with dislodgeable foliar pesticide residues from treated or drift-impacted vegetation. This guidance will be updated as those screening methods become available.

        In the interim, problem formulation documents and risk assessments should acknowledge the potential for this route of exposure for terrestrial wildlife, but state that no quantification of exposures and attendant risks is possible until the completion of initial screening models.

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      • Wildlife drinking water

        Drinking water for the purposes of terrestrial organism risk assessment is defined as that portion of an organism's daily water intake that is not met by dietary or metabolic sources and must be consumed in liquid form. Typical drinking water sources for wildlife in pesticide use areas may include on-field puddles, irrigation equipment (e.g ., drip irrigation in grape cultivation), dew deposited on treated plants, and off-field surface water exposures.

        The Screening Imbibition Program (SIP) should be used in all screening-level assessments to assess the potential risk to birds and mammals from both dew and on-field puddle sources of drinking water. The SIP model and associated User's Guide (found in a "READ ME" tab located within the tool) are available at: G:\Models_Repository\SIP\Current version and SIP. It should be noted that version 1.0 of SIP considers the potential for risk via exposure to drinking water for birds and mammals only. It is recognized that terrestrial invertebrates, such as honey bees (Apis mellifera), may also be exposed to pesticide residues in dew and/or leaf guttation drops; however, the current 1.0 version of SIP does not specifically address this exposure pathway. Further updates to SIP are expected to incorporate exposure to terrestrial invertebrates, as well as terrestrial amphibians and reptiles.

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Any questions should be directed to Anita Pease or other members of the Workgroup, which are identified at the end of this guidance.

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References

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Endangered Species Registration Review Workgroup

David Bays, AD
Shannon Borges, BPPD
James Breithaupt, AD
Mark Corbin, EFED
Kevin Costello, PRD
William Eckel, EFED
Catherine Eiden, PRD
Melissa Grable, EFED
Mark J. Huff, EFED
Stephanie Irene, EFED
Russell Jones, BPPD
Stephen Morrill, BPPD
Edward Odenkirchen, EFED (Co-Chair)
Melissa Panger, EFED
Anita Pease, EFED
Mohammed Ruhman, EFED
Dana Spatz, EFED
Thomas Steeger, EFED
Ingrid Sunzenauer, EFED (Co-Chair)
Michelle Thawley, EFED
Zigfridas Vaituzis, BPPD
Katrina White, EFED

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