Appendix G. TerrPlant Version 1.2.2 (December 26,2006): Model Description, Input, and 

Output for Spirotetramat 

1. Model Description 

TerrPlant was created by the Plant Technical Team and is used by the Environmental Fate and Effects 

Division (EFED) as a Tier 1 model for screening level assessments of pesticides. The model is 

implemented in Microsoft Excel. The purpose of TerrPlant is to provide screening level estimates of 

exposure to terrestrial plants from single pesticide applications. The model does not consider exposures 

to plants from multiple pesticide applications. TerrPlant derives pesticide EECs in runoff and in drift. 

RQs are developed for non-listed and listed species of monocots and dicots inhabiting dry and semiaquatic areas which are adjacent to treatment sites. 

2. Model History 

TerrPlant was originally used in EFED in 2002 as version 1 .O. The model was developed to automate 

existing methods for calculating RQ values for non-listed and listed terrestrial plants, including wetland 

species (USEPA 2002a). In 2005, TerrPlant was modified to v1.2.1 to remove an assumption that aerial 

applications result in 60% application efficiency. TerrPlant v1.2.1 assumed 100% efficiency in ground 

and aerial applications (USEPA 2005). The current model version (1.2.2) includes the same assumptions 

and equations as v1 .O, with the exception of the application efficiency assumption for aaial applications. 

TerrPlant v1.2.2 represents a cosmetic update of v1.2.1. No model assumptions or equations were altered 

from v1.2.1. Version 1.2.2 automates the calculation of EECs and RQ values according to current EFED 

guidance. 

3. Conceptual models 

TerrPlant incorporates two similar conceptual models for depicting dry and semi-aquatic areas of 

terrestrial habitats. For both models, a non-target area is adjacent to the target area. Pesticide exposures to 

plants in the non-target area are estimated to receive runoff and spray drift from the target area. For a dry 

area adjacent to the treatment area, runoff exposure is estimated as sheet runoff. Sheet runoff is the 

amount of pesticide in water that runs off of the soil surface of a target area of land which is equal in size 

to the non-target area (1 : 1 ratio of areas). For semi-aquatic areas, runoff exposure is estimated as channel 

runoff. Channel runoff is the amount of pesticide that runs off of a target area 10 times the size of the 

non-target area (10: 1 ratio of areas). Exposures through runoff and spray drift are then compared to 

measures of survival and growth (e.g. effects to seedling emergence and vegetative vigor) to develop RQ 

values. 

4. Calculation of EECs 

In TerrPlant v1.2.2, user inputs for EECs are indicated by green text and are located in Tables 1 and 2. 

Table 1 contains reference information for the user which is relevant to the identity and use of the 

pesticide but does not directly affect EEC calculations. Table 2 is used to input parameter values for 

deriving drift and runoff EECs. Inputs and results for spirotetramat are found in Tables 1-5, below. 

TEXT SEARCHABLE DOCUMENT
In cases where multiple application methods (ground and aerial/airblast/spray chernigation) and/or 

application forms (liquid and granule) are possible for a pesticide, multiple drift fractions are possible for 

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resulting RQs for the different possible drift fractions, the user should complete the following steps: 1) 

input all relevant data for the pesticide according to one relevant type of application method and form 

(Tables 1,2 and 4); 2) copy the worksheet within the Excel file; 3) alter the relevant application method 

andlor form to represent another application scenario; and 4) repeat as necessary. 

In Table 2, the application rate should be entered in units which are consistent with units of plant survival 

and growth data entered in Table 4 (e.g. lbs a.i./A, lbs a.e./A). This value represents the maximum rate 

per single application according to the label. If multiple applications are allowed by the label, only the 

application rate per single application should be entered, not the total annual application rate. 

The incorporation value is based on the depth of pesticide incorporation in inches. Incorporation depth is 

dependent upon label directions. In TerrPlant, this value is unitless and is related to the proportion of 

applied pesticide which is available for runoff. The default value for this parameter is 1, which is entered 

for ground applications with no incorporation and for aerial applications. When the incorporation depth is 

>1 inch, the specified value is entered. If the value is > 6 inches, 6 should be entered. In cases where 

labels give a range of incorporation depth, the user should model RQs resulting from both the minimum 

and maximum depths as indicated by the label. 

The magnitude of runoff is assumed to be dependent on the water solubility of the pesticide active 

ingredient. For pesticides with a solubility of 40, 10 to 100, or >I00 ppm, runoff fractions of 0.0 1,0.02 

or 0.05 respectively (Aquatic Effects Dialogue Group 1992), are selected by the model user. 

It is assumed that, for a liquid formulated pesticide applied by ground methods, 1% of the applied mass of 

pesticide per acre will drift to the non-target area. For a liquid formulated pesticide which is applied 

through aerial, airblast or spray chemigation methods, 5% of the applied mass of pesticide per acre will 

drift to the non-target area (USEPA 2002). In cases where a pesticide is in granular form, drift is assumed 

to be 0%. 

Runoff exposure is assessed in two scenarios: sheet and channel runoff. In the sheet runoff scenario, the 

treated area generating runoff is assumed to drain into an area with equal size containing seedlings, 

resulting in 1,2, or 5% of the application rate being deposited. In the channel runoff scenario, a ten-toone ratio of watershed area to receiving area results in 10,20, or 50% of the application rate being 

deposited on soil with emerging or emerged seedlings. With pesticides which are ground incorporated, 

the runoff EEC is decreased because the application rate is divided by the incorporation depth before 

being multiplied by the runoff value. For RQ derivation, EECs for dry and semi-aquatic areas combine 
runoff and drift exposures. Drift only EECs are also used for RQ derivation (Table 3). All EEC values are 

in units consistent with those entered by the user for application rate (Table 2). 

5. Toxicity Data 

Data from submitted seedling emergence and vegetative vigor studies are used to establish the toxicity of 

a pesticide to monocots and dicots. The ECz5 values of a pesticide for the most sensitive tested monocot 

and dicot species are used to define the toxicity of this pesticide to non-listed species. The corresponding 

NOAEC values (or ECo5 if a suitable NOAEC is unavailable) for the same species and endpoint are used 

to define the toxicity of the pesticide to listed plants (USEPA 2005b) (Table 4). Units for toxicity data 

must be consistent with application rate units. 

6. RQ values 

TerrPlant derives RQ values for non-listed and listed species of monocots and dicots inhabiting dry and 

semi-aquatic areas. The model compares the combined deposition estimates fiom runoff and spray drift 

to adverse effect levels measured in seedling emergence studies. RQs (Table 5) are derived by dividing 

the total EEC (Table 3) by the relevant seedling emergence value (Table 4). 

Monocot non-listed <0.1 <0.55 0.13 

I *If RQ > 1 .O, the LOC is exceeded, resulting in potential for risk to that plant group. I 

Monocot 

Dicot 

Dicot 

In addition, RQs are derived for plants with consideration for spray drift exposures. For monocots and for 

dicots, TerrPlant compares estimated spray drift deposition, without a runoff exposure component, to the 

more sensitive measure of effect, either seedling emergence or vegetative vigor (USEPA 2005b). The 

selection of the more sensitive measure of effect is automated by the model and is defined by the lowest 

EC25 value. The associated NOAEC value is selected to define RQ values for listed species exposed to 

listed 

non-listed 

listed 

0.1 

<0.1 

0.1 

0.55 

<0.55 

0.55 

0.40 

<0.1 

<0.1 
drift. In cases where the ECZ5 values for seedling emergence and vegetative vigor studies are equal, the 

lowest NOAEC value is selected in calculation of the RQ value. The results of these calculations are RQ 

values for non-listed and listed monocots and dicots inhabiting adjacent and semi-aquatic areas and 

exposed to drift only (Table 5). 

In TerrPlant v1.2.2, if a RQ value is <0.1, the model automatically indicates "<0.1" as the RQ. 

7. LOC 

EFED's LOC for non-listed and listed plant species is 1.0. RQ values exceeding 1.0 indicate potential risk 

to plants. RQ values less than or equal to 1.0 indicate that potential risk is minimal. In other words, if 

pesticide exposure (EEC) does not exceed the toxicity value (ECz5 or NOEC), the RQ is 51 .O. This places 

the RQ below EFED7s LOC and potential risk to that plant group is considered to be acceptable. 

8. Discussion of Assumptions and Uncertainties 

TerrPlant7s 10 to 1 ratio of target area to semi-aquatic non-target area is based on research indicating a 

pond located in Georgia with a 6-7 foot typical depth and a requirement of 2 acre drainage areas per foot 

of depth (USDA 1997). Although the data are derived from observations of aquatic areas (e.g. farm 

ponds), it is assumed that this ratio is relevant to low-lying semi-aquatic areas. There is some uncertainty 

associated with the depth of the ponds used for modeling purposes and the expected depth of a semiaquatic area. 

Consistent with a screening level approach, the application efficiency, which is the amount of applied 

pesticide reaching the target area, is assumed to be 100% for all applications. Application efficiency is 

considered separately from spray drift; where the sum of the two does not necessarily equal 100%. 

Spray drift is estimated based on application method alone, without consideration of other potentially 

influential factors related to application, such as droplet size, wind speed and release height. 

The model assumption that granular applications have 0% spray drift may result in an underestimation of 

exposure. 

TerrPlant assumes that drift and runoff concentrations are uniform/over the non-target area. In the field, 

decreasing concentration gradients would be expected for each of these exposure pathways as the distance 

increases from the application site. If the dimensions (i.e. length and width) of the target area and nontarget area where defined, the uncertainties associated with these assumptions could be explored. 

For pesticides that involve ground incorporation applications (> 1 in), less of the pesticide applied is 

vulnerable to runoff. In TerrPlant, the application rate is divided by the incorporation depth. The basis for 

calculation of effects of ground incorporation on pesticide runoff also originated fi-om former assumptions 

related to modeling aquatic EECs. The assumption is that the incorporation depth in inches is directly 

related to the proportion of runoff. For example, incorporation of a pesticide to a depth of 2 inches would 

result in % of the application rate being available for runoff. This proportion is considered relevant up to 6 

inches. Thus, the model assumes that the amount of pesticide in runoff is directly related to the depth to 

which the pesticide is incorporated into the ground. 

There are several assumptions related to temporal factors of exposure and effects. 1) The model assumes 

that pesticide contained in drift and runoff reaches the non-target area at the same time. This assumption 

is conservative because it is unlikely that a pesticide would move at equal rates in drift and runoff. 2) The 

model does not consider the coincidence of drift pesticide and runoff pesticide reaching the non-target 
area in time to reach the emergence portion of the plant's life cycle. If applied later in the plant's life 

cycle, it is possible that the pesticide will reach the non-target plants at stages of different sensitivities. It 

is uncertain whether or not an exposure which occurs at a different life stage of the plant is relevant to the 

RQ derived based on the early seedling stage of a plant's lifecycle (i.e. this may have greater or lesser 

effect than indicated by the RQ). 

Modeled pesticide concentrations in runoff are dependent solely upon solubility of the pesticide. The 

amount of pesticide in runoff does not consider other relevant transport properties of the pesticide (e.g. 

&). In addition, the model does not consider pesticide movement through the soil or contained in eroded 

soil. 

The model does not incorporate parameters that would allow for photolytic, hydrolytic or microbial 

degradation. In cases where degradation occurs, this leads to an uncertainty in the amount of pesticide that 

would be present in runoff and in drift. 

The RQ values which are currently derived by TerrPlant represent the risk of effects for single maximum 

applications. It is assumed that each single application would expose different plants (i.e. due to different 

drift patterns). The modeling of EECs from single pesticide applications rather than multiple applications 

could result in underestimating pesticide exposures to plants. 

For defining RQ values for plants exposed to runoff, measures of effect to seedling emergence are used; 

however, vegetative vigor could be affected by runoff (i.e. effects to plant roots). Due to limitations of 

testing methods, these effects are not measured and cannot be incorporated into RQ development. 

There is an absence of data comparing the field concentrations of pesticides to EECs generated by 

TerrPlant. Therefore, the relevance of TerrPlant predictions to pesticides concentrations in the field is 

unknown. 

9. References 

Aquatic Effects Dialogue Group. 1992. Improving Aquatic Risk Assessment Under FIFRA. Report of the 

Aquatic Effects Dialogue Group. RESOLVE, An Independent Program of World Wildlife Fund. 

SAP. 2001. Scientific Advisory Panel Briefing: Proposal to update non-target plant toxicity testing under 

NAFTA. Joint presentation by Health Canada and USEPA. June 27-29,2001. 

USDA. 1997. Ponds - Planning, design, construction. United States Department of Agriculture. Issued 

June 1992. Revised November 1997. Agriculture Handbook 590. Available online at: 

http://www.in.nrcs.usda.gov/pdfo/o20fdes/PONDS .PDF. 

USEPA. 1996. Ecological effects test guidelines. OPPTS 850.4000. Background - Nontarget plant 

testing. United States Environmental Protection Agency. EPA 712- 

C-96-151. Online at: 

http://www.epa.gov/oppts~s/publications/OPPTSHonize85OEcolocalEffects~Test~Guidelines 

/Drafts/850-4000.pdf. 

USEPA. 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides, Version II. US Environmental Protection Agency, Washington DC. 

Environmental Fate and Effects Division. Online at: http://www.epa.gov/oppefedl/models 

waterlinputsidance2-28-02. htm. 
USEPA. 2002a. EFED Policy Memorandum: automation of Environmental Exposure Concentrations 

(EECs) and Determinations of Risk Quotients (RQs) for Terrestrial Plants Using TerrPlant Model 

(version 1.0). United States Environmental Protection Agency, Office of Pesticide Programs. October 16, 

2002. 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. 

U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of 

Pesticide Programs, Washington DC. 100 pp. January 23,2004. 

USEPA. 2005. Memorandum: policy guidance to remove the 60% application efficiency factor from 

aerial applications exposure estimates in TerrPlant. United States Environmental Protection Agency, 

Office of Prevention, Pesticides and Toxic Substances. October 4,2005. 

USEPA. 2005a. Memorandum: clarification of plant evaluation guidance. United States Environmental 

Protection Agency, Office of Prevention, Pesticides and Toxic Substances. October 4,2005.