1

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

June 1, 2016

PC Codes: 085601, 108209, 118601, 118602, 119009, 119011, 122009, 122010, 122011,

122020,122021, 128721, 128820, 128845, 128887, 128901, 128969, 128973, 129002, 129008,

129009, 129031

MEMORANDUM DP Barcode: 431618

SUBJECT: Response to Comments on Preliminary Risk Assessment for 22 Sulfonylurea 

Herbicides

FROM: Brian D. Kiernan

Gregory Orrick

Hannah Yingling

Mary Clock-Rust 

William P. Eckel

R. David Jones

Brian Anderson

Environmental Fate and Effects Division (7507P)

REVIEWED Kristina Garber, M.S.

BY: Melissa Panger, Ph.D.

Environmental Fate and Effects Division (7507P)

TO: Margaret Hathaway

Pesticide Re-evaluation Division (7508P)

The Environmental Fate and Effects Division has received public comments on the registration 

review preliminary risk assessment (PRA) for 22 sulfonylurea (SU) herbicides. EFED appreciates 

the comments, has considered all of them, and has addressed them as appropriate below. Several 

types of comments were received, including:

• Error correction and differences in interpretation of studies and associated fate or toxicity 

endpoints and editorial comments

• Comments on the methodology used to assess exposure and risk including:

o Requests to further refine risk estimates

o Comments on the models and risk metrics used to assess, interpret, and compare 

potential risks

o Comments on the general conceptual model and risk metrics

• Comments requesting an endangered species consultation

• Comments supportive of the methods and approaches
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Each of these categories of comments is discussed below. This document does not include a detailed

response to every comment received on the risk assessment, apart from the comments on the Audrey 

III model, but does provide responses to the amalgam of comments across the SUs. It also serves as 

a risk assessment addendum with updates to specific endpoints, and error corrections.

1. Error Correction

EFED received several comments on toxicity and fate endpoints and choice of using alternative 

endpoints from multiple studies (Master Record Identifications or MRIDs). In response to these 

comments, EFED re-evaluated data evaluation records (DERs) to verify information and made 

corrections where warranted. This document serves as an addendum to the risk assessment and 

documents the changes made to the risk quotients (RQs). Updated information includes:

• verified plant endpoints and MRID numbers (Table 1); 

• corrections to the TerrPlant aerial application table (Table 2); 

• inclusion of a TerrPlant ground application table (Table 3); 

• modeled application rates (Table 4). 

A number of comments were submitted that recommended use of endpoints that were different from 

ones used in the PRA. Reasons for the differences in endpoints included:

• Submission of newer studies;

• Inconsistencies in endpoints used in study reports or in problem formulations relative to 

those used in the PRA; and

• Recommendation to use studies conducted on TEP (typical end use products) instead of 

TGAI (technical grade active ingredient). 

Responses to these types of comments are in the following sections. 

1.1. Terrestrial Plants

Use of IC25 as an endpoint and its relevance.

Comments regarding the relevance of the IC25 have been submitted, including a suggestion that the 

use of an IC50 may be more appropriate for SUs given the variability within chemicals at the IC25

level. The 850.4100 (Seedling Emergence) and 850.4150 (Vegetative Vigor) guidelines are 

designed to capture the 25% effect level for sublethal growth endpoints (biomass and shoot length). 

As the study design and the associated statistical methodology are optimized for determining a 25% 

effect, confidence in a derived 50% endpoint is likely to be rather low. For terrestrial plants, the IC25

level is used as described in the guidance memo “Clarification of Plant Evaluation Guidance” (2005; 

attachment 1).

The use of IC25 endpoints are considered protective, but not especially conservative, for terrestrial 

plant species. Given that, typically, 10 crop species are used as surrogates for all terrestrial plants, it 
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is important to consider the implications of that surrogacy. Some plants, particularly weedy species,

have a development and growth strategy that promotes rapid growth, early flowering and large 

numbers of seeds produced per individual. These species focus most of their energy resources to 

grow and reproduce quickly and cheaply (low energy resources to produce each seed), and are 

known as r-strategists. Possibly because of their energy allocation towards rapid growth and low 

investment in each seed, these species may be more likely outgrow or mitigate a 25% impact on 

growth early in a growing season, without appreciable change to the reproductive output. Other 

plants focus more of their resources on growth, long term survival and expend more energy 

resources on each seed than r-strategy species, and are referred to as k-strategists. These species, 

including many perennial herbs, shrubs and trees, may not be able to recover from 25% effects on 

growth in a single growing season. The affected k-strategy plants may maintain below normal 

growth throughout the season and would thus have fewer resources for their resource demanding 

reproduction cycle; therefore, they may survive the growth reduction impacts, but could have equal 

or greater reductions in fruit and seed yield. Therefore, the use of the IC25 based on growth 

parameters is considered protective but not unreasonably conservative.

Regulatory endpoints

EFED’s current practice for evaluating potential risk to non-listed terrestrial plants is to use the most 

sensitive IC25 value (concentration causing 25% inhibition in plants) from scientifically sound 

studies for both seedling emergence (850.4100) and vegetative vigor (850.4150). These values are 

used as inputs to the model TerrPlant (v1.2.2) and are then compared to estimated environmental 

concentration (EECs) that are based on an application rate, adjusted by solubility, application 

method and size of receiving area. EECs are divided by the IC25, and the resulting ratios are the risk 

quotients (RQs). RQs are then compared to a level of concern (LOC), which for plants is 1.0 based 

on the IC25. It is therefore critical for risk assessment that both the IC25 and the modeled application 

rate be correct. In addition to using the most sensitive IC25 values from the available seedling 

emergence and vegetative vigor studies for RQ calculations, the endpoints derived for other plant 

species in those studies are used to characterize an area of potential effect using the AgDRIFT 

(v2.1.1) model. 

In some cases, the commenters revealed errors in the reporting of the IC25; in other cases differences 

in statistical methodologies or in study selection were cause for comment. In either case, EFED 

reviewed all comments and revisited all DERs in response. The most sensitive IC25 values identified 

as a result of these reviews are presented in Table 1. These endpoints were subsequently used to 

recalculate RQs in TerrPlant. 

Submission of newer studies may confirm previous endpoints or be used to characterize variability 

in toxicity across studies, but will not generally supplant more sensitive endpoints from reliable 

older studies. This document is not recommending waiving previously requested data. Submission 

of studies conducted on Typical End Use Products (TEP) are very useful to determine if materials in 

the TEP impact toxicity. However, if TEP and TGAI studies produce a similar IC25, then the most 

sensitive endpoint across the two studies will be used. Also, ingredients of specific formulations can 
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vary across products, and there are often multiple formulated products for a given active ingredient. 

Therefore, the extent to which one TEP study relates to other registered products is often uncertain. 

Table 1 (Revised Table 7.1 from the PRA). Summary of Most Sensitive IC25s for Seedling 

Emergence (SE) and Vegetative Vigor (VV).

Chemical name Species Effects 

endpoints VV/SE IC25 (lbs a.i./Acre) MRID

bensulfuron-methyl oilseed rape height SE 0.000154 46290101

bensulfuron-methyl soybean biomass VV 0.000145 46290102

chlorimuron-ethyl onion biomass SE 0.000011 43777201

chlorimuron-ethyl oilseed rape height VV 0.000033 43777201

chlorsulfuron pea biomass SE 0.00022 46361801

chlorsulfuron oilseed rape height VV 0.00001 46326801

flazasulfuron cabbage biomass SE 0.00107 46930003

flazasulfuron radish height VV 0.00004 46930002

foramsulfuron lettuce biomass SE 0.00883 45483802

foramsulfuron radish biomass VV 0.0000517 45483801

halosulfuron-methyl lettuce biomass SE 0.000022A 42661424

halosulfuron-methyl radish biomass VV 0.000057 42661425

imazosulfuron onion biomass SE 0.034 47305211

imazosulfuron radish survival VV 0.08 47305211

iodosulfuron-methylNa tomato height SE 0.0000035 45109132

iodosulfuron-methylNa lettuce height VV 0.00000037B 45109131

mesosulfuron-methyl lettuce height SE 0.00082 45386316

mesosulfuron-methyl soybean biomass VV 0.00014 46688201

metsulfuron-methyl sugar beet biomass SE 0.000322 49154310

metsulfuron-methyl sugar beet biomass VV 0.0000887 49154308
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Chemical name Species Effects 

endpoints VV/SE IC25 (lbs a.i./Acre) MRID

nicosulfuron sorghum biomass SE 0.000954 49169704

nicosulfuron oilseed rape biomass VV 0.00208 49169705

orthosulfamuron radish biomass SE 0.04 46578941

orthosulfamuron carrot biomass VV 0.00012 46578942

primisulfuron-methyl cucumber height SE 0.000132 40856505

primisulfuron-methyl cucumber height VV 0.000127 40856506

prosulfuron lettuce biomass SE 0.000071 42974701

prosulfuron onion biomass VV 0.00041 42949710

rimsulfuron sorghum biomass SE 0.000164 49368401

rimsulfuron oilseed rape height VV 0.000274 49368402

sulfometuron-methyl tomato biomass SE 0.000031C 43538501

sulfometuron-methyl soybean biomass VV 0.000018 43538501

sulfosulfuron radish biomass SE 0.007D 44295783

sulfosulfuron radish biomass VV 0.00009 44295784

thifensulfuron-methyl onion biomass SE 0.000555E 48037903

thifensulfuron-methyl sugar beet biomass VV 0.0000019E 43158101

triasulfuron lettuce height SE 0.000085 40728321

triasulfuron lettuce height VV 0.000034 40728323

tribenuron sugar beet height SE 0.0018 42571301

tribenuron sugar beet height VV 0.00002F 47748203

trifloxysulfuron-Na lettuce biomass SE 0.0006 45371734

trifloxysulfuron-Na radish biomass VV 0.000009G 45371734

triflusulfuron-methyl oilseed rape height SE 0.0095H 42991417

triflusulfuron-methyl oilseed rape biomass VV 0.000087 42991417

A Halosulfuron SE endpoint changed from 0.000099 to 0.000022 lbs a.i./Acre

B Iodosulfuron vegetative vigor endpoint changed from 0.00000000037 to 0.00000037 lbs a.i./Acre
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C Sulfometuron SE endpoint changed from 0.000078 to 0.000031 lbs a.i./Acre

D Sulfosulfuron SE endpoint changed from >0.001 to 0.007 lbs a.i./Acre

E Thifensulfuron SE endpoint changed from 0.0000347 to 0.000555 lbs a.i./Acre and the VV 

endpoint changed from 0.0000302 to 0.0000019 lbs a.i./Acre

F Tribenuron VV endpoint changed from 0.018 to 0.00002 lbs a.i./Acre

G Trifloxysulfuron VV endpoint changed from 0.00001 to 0.000009 lbs a.i./Acre

H Triflusulfuron SE endpoint changed from >0.125 to 0.0095 lbs a.i./Acre

The ecological PRA for the SUs reported TerrPlant values only for aerial application methods, with 

a default drift assumption of 5% (Table 2). This was done intentionally to facilitate a rapid 

comparison of the potential upper-bound risks (at a selected high end application rate) across the 

SUs as a class. Several commenters correctly pointed out that not all SUs allow aerial application. 

Hence, a new table (Table 3) was generated from TerrPlant using the default ground application

drift assumption (1%). It should be mentioned that a post-hoc analysis using AgDRIFT default 

values demonstrates that both the aerial 5% and ground 1% values are associated with drift fractions 

roughly 200 feet from the edge of the use site.

Additionally, EFED typically uses the maximum labeled rate for a single application as the input for 

TerrPlant. However, for the SUs, the maximum single application rates are often associated with 

smaller non-agricultural use patterns (e.g. commercial premises, although ‘non-agricultural areas’ is 

often poorly defined, but can include industrial areas and other areas not related to agriculture use) 

that have very high per-unit-area use rates relative to wider-area agricultural or pasture/rangeland 

uses. Using these rates would be considered representative of the potential effect on non-target 

plants adjacent to these use sites, but may not adequately represent the overall potential area of effect 

based on more general use patterns. Therefore, in conjunction with PRD and BEAD, EFED selected

the maximum labeled application rates associated with wide area applications, not spot treatments,

and recalculated the RQs (Table 4). It should be kept in mind that the RQs for higher use rates 

would result in similarly higher RQs.

Table 2 (Revised Table 7.3.1. from the SU ecological PRA). TerrPlant RQs for the most 

sensitive species for each chemical (aerial application).

Chemical Name

RQs

Dry Areas Semi-Aquatic Areas Drift Only

Bensulfuron-methyl 41 225 22

Chlorimuron-ethyl 727 4000 364

Chlorsulfuron 28 155 310
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Chemical Name

RQs

Dry Areas Semi-Aquatic Areas Drift Only

Flazasulfuron* 4.2 23 56

Foramsulfuron* 0.59 3.2 50

Halosulfuron-methyl 427 2350 214

Imazosulfuron 0.88 4.8 0.44

Iodosulfuron-methyl-Na 254 1399 1203

Mesosulfuron-methyl 1.6 8.7 4.6

Metsulfuron-methyl 47 258 85

Nicosulfuron 6.9 38 3.5

Orthosulfamuron 0.17 0.91 28

Primisulfuron-methyl 27 150 14

Prosulfuron 51 279 25

Rimsulfuron 38 211 19

Sulfometuron-methyl

(high rate) 1226 6742 1056

Sulfometuron-methyl 

(low rate) 91 499 78

Sulfosulfuron 1.3 7.4 52

Thifensulfuron-methyl 33 181 737

Triasulfuron 33 181 41

Tribenuron-methyl 1.7 9.5 78

Trifloxysulfuron-Na* 4.7 26 156

Triflusulfuron-methyl 0.33 1.8 18

*do not have aerial applications; included for reference
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Table 3. (new table; not provided in the SU ecological PRA) TerrPlant RQs for the most 

sensitive species for each chemical (ground application).

Chemical Name

RQs

Dry Areas Semi-Aquatic Drift Only

Bensulfuron-methyl 25 209 4.3

Chlorimuron-ethyl 436 3709 73

Chlorsulfuron 17 144 62

Flazasulfuron 2.5 21 11

Foramsulfuron 0.35 3.0 10

Halosulfuron-methyl 256 2179 43

Imazosulfuron 0.53 4.5 <0.1

Iodosulfuron-methyl-Na 153 1297 240

Mesosulfuron-methyl 0.95 8.1 0.93

Metsulfuron-methyl 28 239 17

Nicosulfuron 4.2 35 0.69

Orthosulfamuron <0.1 0.84 5.5

Primisulfuron-methyl 16 139 2.8

Prosulfuron 30 258 5.1

Rimsulfuron 23 196 3.8

Sulfometuron-methyl

(high rate) 735 6252 211

Sulfometuron-methyl 

(low rate) 54 462 16

Sulfosulfuron 0.81 6.8 10

Thifensulfuron-methyl 20 168 147

Triasulfuron 20 168 8.3

Tribenuron-methyl 1.0 8. 8 16

Trifloxysulfuron-Na 2.8 24 21
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Chemical Name

RQs

Dry Areas Semi-Aquatic Drift Only

Triflusulfuron-methyl 0.20 1.7 3.6

Table 4 (Revised Table 4.1. from the PRA) SU Application Rates Used for Risk Assessment a

Chemical Lowest Max 

Application 

Rate

Highest Max 

Application 

Rate

Rate for Modeling Application 

Methods

Notes

Bensulfuron-methyl 0.047 0.063 0.063 - only used on rice Ground or Air Labeled only for rice

Chlorimuron-ethyl 0.0039 0.08 0.08 - soybean Ground or Air –

Chlorsulfuron 0.0012 0.14 0.062 - rangeland/fallow Ground or Air –

Flazasulfuron 0.045 0.093 0.045 - Grapes Ground only –

Foramsulfuron 0.0009 0.052 0.052 - Turf Ground only 

for turf

The draft PRA 

assessed corn which 

has since been 

canceled

Halosulfuron-methyl 0.03 0.14 0.094 – corn (most uses 

at 0.047)

Ground or air Most uses are ground 

only, but some allow 

aerial applications

Imazosulfuron - 0.66 0.3 - melons, vegetables, 

rice

Ground or air Uses are ground 

only, except aerial 

applications are 

allowed on rice

Iodosulfuron-methylNa0.00013 0.0089 0.0089 - wheat Ground only –

Mesosulfuron-methyl 0.0028 0.013 0.013 - triticale and 

wheat

Ground or air –

Metsulfuron-methyl 0.00023 0.15 0.15 - ag uncultivated 

areas and some forestry 

uses

Ground or air Labeled for mainly 

non-ag uses with 

several agricultural 

uses

Nicosulfuron 0.012 0.07 0.066 - corn Ground or air –

Orthosulfamuron 0.066 0.066 0.066 - rice Ground or air Labeled only for rice

Primisulfuron-methyl 0.018 0.036 0.036 - corn Ground or air Labeled only for 

bluegrass and corn

Prosulfuron 0.0089 0.036 0.036 – corn (most uses 

at 0.018)

Ground or air No non-ag uses 

labeled

Rimsulfuron 0.0078 0.063 0.063 - most uses Ground or air Numerous ag and 

non-ag uses; some 

uses only allow 

ground applications
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Chemical Lowest Max 

Application 

Rate

Highest Max 

Application 

Rate

Rate for Modeling Application 

Methods

Notes

Sulfometuron-methylb 0.0281 0.38 0.38 and 0.0281 Ground or air Numerous ag and 

non-ag uses; some 

uses only allow 

ground applications, 

but most allow both

Sulfosulfuron 0.03 0.125 0.094 - pastures Ground or air Most uses are noncropped areas; most 

uses allow only 

ground applications

Thifensulfuronmethyl0.0023 0.028 0.028 - almost all uses Ground or air Labeled mainly for 

agricultural uses

Triasulfuron 0.022 0.028 0.028 - most uses were 

0.0275 or 0.028

Ground or air –

Tribenuron-methyl 0.0012 0.0313 0.031 - field corn, 

blueberries

Ground or air Labeled mainly for 

agricultural uses

Trifloxysulfuron-Na 0.007 0.036 0.028 – sugarcane Ground only –

Triflusulfuron-methyl 0.016 0.031 0.031 - sugar beets (all 

other uses at 0.016)

Ground or air Labeled only for 

beets, sugar beets, 

chicory, and endive a All rates are in units of pounds of active ingredient per acre (lbs a.i./A). “Ag” means 

“agricultural” and “Non-ag” means “non-agricultural.”

b both 0.38 and 0.0281 were modeled in the terrestrial analysis as the most commonly applied 

rate is unclear.

1.2.Aquatic Plants, Environmental Fate Endpoints, and Application Rates

Comments were provided on several aquatic plant endpoints. EFED updated some aquatic plant 

endpoints and revised Table 6.1 in the PRA (Table 6 in this document) based on public 

comments to accurately reflect the available data. 

1.2.1. Imazosulfuron

The PRA indicated that sufficient data were not available for an aquatic assessment. This 

appears to be an error. Table 5 summarizes the available aquatic toxicity data for imazosulfuron.

The most recent risk assessment on imazosulfuron (DP402202, 2012) identified risks of concern 

only to sensitive aquatic vascular plants with RQs that ranged from approximately 0.6 to 3.6. 

Risks to terrestrial plants were considerably greater. These general conclusions are consistent 

with conclusions for other SUs. The Tier 1 peak EEC in the combined SU document was 

approximately 11.8 ug/L, which would result in a vascular plant RQ of approximately 26. RQs 

from the 2012 assessment are more specific to the labeled imazosulfuron uses. 
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Also, a comment suggested that an application rate of 0.66 lbs a.i./Acre be used instead of 0.74 

lbs a.i./Acre. EFED acknowledges that 0.66 lbs a.i./Acre is the highest application rate for 

imazosulfuron and not 0.74 lbs a.i./Acre. However, an application rate of 0.38 lbs a.i./Acre was 

used for modeling to represent labeled wide-area uses in the risk assessment and will continue to 

be used for this purpose (see Table 4). 

Table 5. Imazosulfuron Toxicity Values for Aquatic Organisms

Species EC50 Reference

Duckweed

(Lemna gibba)

EC50 = 0.00146 mg/L ECOTOX 104861

Lemna minor 0.00046 mg/L MRID 47639701

Green algae

(Pseudokirchneriella 

subcapitata)

EC50 = 0.206 mg/L ECOTOX 104861

Marine Diatom

Skeletonema costatum

>100 mg/L MRID 47035214

Blue-green Algae

Anabaena flos-aquae

11 mg/L MRID 47035215

Nitzschia palea >97 mg/L MRID 47035216

Selenastrum >5 mg/L MRID 47035217

1.2.2. Rimsulfuron

The PRA used 29 ug/L and 11.6 ug/L as the most sensitive non-vascular and vascular plant 

IC50s, respectively. These values are from MRIDs 42471308 (Lemna gibba, EC50 of 11.6 ug/L) 

and 42471305 (Selenastrum capricornutum, EC50 >29 ug/L). EPA acknowledges that additional 

studies were submitted in 2014 that evaluated toxicity to Lemna gibba G3 (MRID 49528803), 

Pseudokirchneriella subcapitata (MRID 49221701), and Anabaena flosaquae (MRID 9522805). 

Results of the studies do not alter conclusions reached in this assessment, but will be 

incorporated quantitatively as appropriate into future assessments. 
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1.2.3. Foramsulfuron

The registrant noted that the correct value to use for the vascular plant IC50 is 0.65 ug/L instead 

of 0.56 as used in the PRA. EFED agrees that 0.65 ug/L is the correct value. However, use of 

this value will have no impact on risk conclusions, therefore, the correction is captured in Table 

6, but additional modeling will not be done. 

An application rate of 0.031 (corn) was used in the risk assessment to represent foramsulfuron 

uses. However, the corn use was recently removed from all foramsulfuron labels. The 

remaining maximum application rate is 0.052 lbs a.i./Acre on golf courses and lawns. Therefore, 

0.052 lbs a.i./Acre will be used for the revised analysis provided in the addendum to the PRA. 

1.2.4. Triasulfuron

The PRA used a non-vascular plant EC50 of 35 ug/L from MRID 40728325. The registrant 

suggested using an EC50 value of 79 ug/L from MRID 49126701. MRID 40728325 is classified 

as supplemental, but is still considered to be scientifically sound, is adequate for RQ 

calculations, and produced the most sensitive non-vascular plant EC50. Therefore, it will 

continue to be used. 

The registrant noted that the vapor pressure of triasulfuron is 7.5 x 10-13 torr (20°C, MRID 

40271903) rather than the reported value of 7.5 x 10-11 torr. EPA agrees that the value reported 

in the draft PRA was in error. However, the use of the correct vapor pressure of triasulfuron in

modeling is not expected to change exposure estimates. Therefore, this correction will be 

captured in future assessments.

1.2.5. Halosulfuron

The registrants suggested that a newer study be used to calculate RQs for aquatic plants (Jenkins, 

2005; MRID 49031305) than was used in the PRA. The newer study produced an EC50 that is 

roughly 5 times higher (less sensitive) than the value used in the PRA. EFED’s policy is to use 

the most sensitive endpoint from scientifically sound studies. The Jenkins, 2005 study will be 

reviewed and included in future assessments on halosulfuron; however, the more sensitive 

endpoint from the scientifically sound MRID 43330701 will still be used for RQ calculations.

The registrant indicated that they are submitting two studies to show that the degradates of 

halosulfuron-methyl are much less toxic than the parent compound. The studies have not yet 

been reviewed. Regardless, exposure and risk based on parent-only exposure was shown to be 

substantially similar to that of any residues of concern. Therefore, the potential toxicity or lack 

thereof of the degradates is not important to the risk assessment.

The registrant suggested that the aerobic soil metabolism model input of 330 days (1489 days for 

residues of concern; based on MRID 42139410) is too long and was not used previously by EPA. 

Additionally, a study of four UK soils (MRID 49031306) was not considered. The 330-day 
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model input is the 90th percentile of the mean half-lives for two soils studied in MRID 42139410 

(the calculation follows EFED’s Input Parameter Guidance; USEPA 2009). Half-lives were 

recalculated for the SU PRA to be consistent with the current NAFTA-harmonized kinetics 

calculation guidance (USEPA, 2015). These aerobic soil metabolism half-lives are consistent 

with indications of persistence of halosulfuron-methyl residues at some field sites of up to two or 

three years (discussed in the Problem Formulation for Registration Review; USEPA, 2012). The 

results of the UK study (MRID 49031306; currently in review) were not included because the 

taxonomy of the UK soils was not compared to that of domestic soils where halosulfuron-methyl 

may be applied. In summary, EPA asserts that the aerobic soil metabolism half-life model inputs 

used in the assessment are consistent with current guidance and are appropriate.

1.2.6. Sulfometuron-methyl

The application rate used in the risk assessment was 0.38 lbs a.i./Acre. A commenter suggested 

that 0.28 lbs a.i./Acre be used instead. The 0.38 lbs a.i./Acre is listed in the LUIS report

(Appendix A of the PRA) as the maximum application rate labeled for a number of 

sulfometuron-methyl uses including agricultural fallow land, agricultural and non-agricultural 

uncultivated areas, and several forest trees. Therefore, the 0.38 lbs a.i./Acre application rate is 

appropriate. 

1.2.7. Sulfosulfuron

The application rate used in the risk assessment was 0.094 lbs a.i./Acre. A commenter suggested 

that 0.03 lbs a.i./Acre be used instead. The 0.094 lbs a.i./Acre is the maximum application rate 

labeled for a number of uses including agricultural fallow land, pastures, ornamentals, turf, and 

rights of ways. The lowest application rate is on wheat at approximately 0.03 lbs a.i./Acre. The 

application rates used in the risk assessment were chosen as the highest application rate 

associated with large use areas (not spot treatments). 

Table 6.1 from the PRA was updated based on the comments received on the aquatic toxicity 

endpoints and is summarized as Table 6 below.
14

Table 6 (Revised Table 6.1 from the PRA). Most sensitive endpoints for aquatic nonvascular and 

vascular plants.

Chemical Non-Vascular Plant IC50

(μg/L)

Vascular Plant IC50 (μg/L)

Bensulfuron-methyl 7.8 8.3

Chlorimuron-ethyl 0.77 0.27

Chlorsulfuron 50 0.35

Flazasulfuron 4.1 0.076

Foramsulfuron 3300 0.65 A

Halosulfuron-methyl 4.1 0.042

Imazosulfuron 206 B 0.46 B

Iodosulfuron-methyl-Na 41 0.7

Mesosulfuron-methyl 2400 0.64

Metsulfuron-methyl 31 0.36

Orthosulfamuron 80 0.7

Primisulfuron-methyl 98 0.8

Prosulfuron 10.6 1.22

Rimsulfuron 29 11.6

Rimsulfuron 0.0116 11.6

Sulfometuron-methyl 4.3 4.5

Sulfosulfuron 310 0.985

Thifensulfuron-methyl 2.63 1.59

Triasulfuron 35 0.19

Tribenuron-methyl 22 2

Trifloxysulfuron-Na 5.6 0.24

Nicosulfuron 18,000 C 2.6 C

A Data were changed from 0.56 to 0.65 per public comments

B Endpoints were added per public comments

C Data were not available at the time of risk assessment; preliminary review shows that addition of 

this data will not alter the overall risk picture, although the Tier 1 EECs were slightly higher than the 

vascular plant IC50. 
15

2. Spray Drift Models

Several comments regarding the use of AgDRIFT rather than AgDISP or RegDISP were 

received. EFED’s currently vetted model for evaluating the potential for effect at distances from 

the use site is AgDRIFT. While EFED has evaluated the spray drift deposition data submitted

by Crop Life America (i.e., the “Canadian data” or “Wolf data”), issues with the completeness

of these data prevent EFED from using the information for quantitative purposes. EFED is

in the process of evaluating all spray drift data that have been submitted to the Agency and

developing a policy for the use of existing and future deposition data in the conduct of its

assessments. Until this policy has been finalized, EFED will continue to use methods developed

in its Guidance on Modeling Offsite Deposition of Pesticides Via Spray Drift for Ecological

and Drinking Water Assessments document in the quantitative assessment of spray drift, while

using supplemental data submitted to the Agency for characterization purposes. The only

exception would be for spray drift deposition data, generated specifically for the active

ingredient/formulated product being assessed. Such data could be used for quantitative purposes,

if found to be acceptable to the Agency.

Although it is true that higher tier modeling can be performed in AgDRIFT, the specificity of 

inputs on labels are usually insufficient for such modeling to be meaningful. However, it should 

be noted that AgDRIFT default settings, except for droplet size spectra, were used in modeling. 

These default inputs are not necessarily conservative. The defaults include the following, all of 

which would need to be on the label for the current risk assessment to be protective:

• For aerial applications, the standard spray drift mitigation language assumed in the model 

(for water mixtures) is:

o 3-10 mph wind speed

o 10 ft release height above canopy

o 1/2 swath offset upwind at the edge of the field

o no sprays made during temperature inversions (the 3 mph low wind speed 

restriction is essentially equivalent

o spray boom length 75% of the wing or rotor length or less

• For ground boom sprays where the spray is to the ground or over top of the crop and 

sprayed downward, the standard mitigation language assumed in the model is:

o 3-10 mph wind speed

o no sprays during temperature inversions

o spray boom no more than 4 ft above the crop canopy

Additionally, some endpoints have changed, as noted above. These changes, with some 

exceptions, would result in mostly small changes in the distance of effect estimates and would 

have little impact overall on the number of plant species impacted by spray drift at a given 

distance described in the SU ecological PRA. Therefore, additional spray drift modeling for the 

SUs will not be conducted at this time.
16

3. Comments on the general methodology used to assess exposure and risk

Some commenters expressed concern that the comparative nature of the risk assessment was 

inappropriate. Reasons cited included that use sites were different (non-agricultural versus 

various agricultural crops), and that particular SUs are intended to control different weed species, 

and thus will have different effects on the Guideline-recommended test species.

EPA’s purpose in conducting the comparative spray drift analysis for 22 SU herbicides was to 

quantify the proportion of non-target plants that might be at risk from SU exposure as a function 

of distance from the application site. The submitted Guideline data, usually ten plant crop 

species, were used to represent all non-target plants. EPA understands that the ten tested plant 

species do not necessarily encompass the entire diversity of wild plants. However, use of all the 

submitted Guideline data to extrapolate to wild species was the most complete approach given 

the available data. 

Use patterns that cover large areas (e.g., major crops such as wheat) were considered in the spray 

drift analysis since these uses are most likely to cause actual exposure across the landscape. 

Simple metrics such as the proportion of species (>50%) with LOC exceedances at a particular 

distance, or the various distances off-site that LOCs were exceeded for each test species, serve to 

gauge possible landscape-scale effects. However, EPA acknowledges that the ecological 

significance of any proportion of plant species exceeding an LOC based on the 10 common test 

species is uncertain.

Comments on the toxicity of degradates of concern – Some commenters expressed concern 

that available data were not considered when determining which degradates are considered 

residues of concern (e.g., Bayer’s comments on iodosulfuron). At the time of writing the PRA, 

many submitted studies were in review and some pending studies were not yet submitted to EPA. 

Regardless, the ecological PRA analysis indicated that aquatic exposure and risk estimates were 

not substantially different when based on exposure to parent compounds versus a conservative 

selection of residues of concern. Therefore, the available data regarding the potential toxicity or 

lack thereof of SU degradates are of negligible consequence.

4. Requests to further refine risk estimates

4.1. Aquatic Risk Assessment

Several commenters requested that a Tier 2 risk assessment be performed for risk to aquatic 

plants. The analysis in the SU assessment was at Tier 1, using the GENEEC 2.0 model. 

Exposure and risk were calculated for both parent-only and for total toxic residues (TTR) as 

anticipated in the Problem Formulations for the individual active ingredients. This analysis 

demonstrated that there is little difference in the calculated risk for parent-only versus TTR, and 

that even degradates with intact sulfonylurea bridges did not contribute measurably to the overall 

risk. 
17

Determination of the level of refinement is made with both risk assessors and risk managers. In 

this case, the Tier 1 analysis showed that, although risk to aquatic plants may exceed concern 

levels for some SU active ingredients, the predominant risks for this group of herbicides are 

clearly to terrestrial plants. Because the terrestrial plant risk assessment (conducted with 

TerrPlant and AgDrift) indicated that there was some level of risk to terrestrial plants for all of 

the SUs, it was decided to focus risk refinement efforts on those rather than on the aquatic plants. 

It is anticipated that any mitigations required for protection of terrestrial plants will decrease 

exposures to aquatic plants from both spray drift and runoff and therefore potentially decrease 

risk. Therefore, Tier 2 aquatic exposure modeling is unnecessary and will not be conducted. 

Some commenters noted that the aquatic RQs cannot be directly compared with each other 

across chemicals. EFED agrees that RQs cannot be used as a comparative risk metric without 

additional characterization. 

4.2. Terrestrial Plant Assessment

EPA’s focus in the SU risk assessment was on plants in general, and terrestrial plants in 

particular, based on the results of past risk assessments for the individual SUs. The approach 

taken represents a more refined terrestrial plant risk assessment than is typically conducted for 

pesticide registrations. For instance, it included the use of the range of plant toxicity data for 

each chemical, not only the most sensitive species. It used the spray drift model AgDrift with

various spray droplet qualities to better define the magnitude of risk to plants by calculating how 

many of the ten tested species were exposed above the risk metric, 25% inhibition concentration 

or IC25, as a function of distance. The spray drift analysis also included different droplet size 

distributions so that the effect of coarser sprays on distance to effect was considered. Overall, 

the SU terrestrial plant risk assessment is believed to provide a good foundation for the 

exploration of risk mitigation options. However, the potential effect to any given taxon beyond 

those for which there are guideline data has not been determined.

4.3. Drinking Water Exposure Assessment

EPA’s focus in the SU drinking water exposure assessment was to expeditiously use coarse, 

tiered screens to show that conservative, high-end estimates of human drinking water exposure 

are not of concern for all SUs. Because the conservative exposure values are expected to be 

much higher than what would be found in drinking water and no risks to humans from drinking 

water were found, additional assessment is unnecessary and will not be conducted. Monitoring 

data were not collected for this assessment because of its screening, conservative approach that is 

not meant to estimate actual exposures at drinking water intake facilities. More refined drinking 

water exposure assessments may be available in support of proposed actions for individual SUs

that EPA assessed in the past. 

Syngenta requested the use of the sorption value for triasulfuron rather than that of its degradate 

CGA-195660, since the triasulfuron residues of concern are unclear, in order to be consistent 
18

with the approach for other SUs. The use of the sorption value for CGA-195660 appears 

inconsistent because triasulfuron is the only SU with unclear residues of concern for which 

degradate data were used for this parameter. However, the approach used was to make use of 

available degradate data if the degradates were of concern or potentially of concern when the 

residues of concern were uncertain. This approach was consistently applied to all of the SUs. 

Triasulfuron was the only SU with both unclear residues of concern and sorption data available 

for a major degradate that is a potential residue of concern. Ultimately, this issue is moot 

because exposure estimates based on the sorption value for CGA-195660, which are more 

conservative than exposure estimates based on the sorption value for triasulfuron, were found by 

the Health Effects Division not to be a risk concern, making additional exposure refinement 

unnecessary.

5. Endangered Species Act

The Center for Biological Diversity, US Dept. of Agriculture, and the FIFRA Endangered 

Species Task Force (FESTF) submitted comments related to EPA’s obligation to perform a risk 

assessment for endangered species. EPA recognizes this obligation. The SU assessment did not 

include an ESA analysis because the interim scientific methods, developed collaboratively with 

the Services (USFWS and NMFS) are currently being vetted in the context of draft Biological 

Evaluations (BEs) for three organophosphate insecticides. The expectation is that these 

additional approaches can be incorporated into the risk assessment process on a "day forward 

approach." This means that the shared scientific approaches, once fully developed and vetted, 

will be applied to pesticide reviews from that point in time. Given that the interim methods for 

the draft BEs are still being vetted and refined, they were not used in the SU risk 

assessment. However, EPA has applied some concepts incorporated in the pilot BEs, including 

the use of “toxicity data arrays” to more fully characterize risk to plants. Thus, instead of using 

only the most sensitive plant to calculate a single risk quotient, EPA used additional submitted 

plant toxicity tests (up to ten species per SU active ingredient) in the spray drift analyses.

Although EPA has not yet completed effects determinations for specific species or habitats, for 

this preliminary assessment, EPA conducted a screening-level assessment for all taxa of nontarget wildlife and plants that assumes for the sake of the assessment that listed species and 

designated critical habitats may be present in the vicinity of the herbicide application. This 

screening level assessment will allow EPA to focus its future evaluations on the types of species 

where the potential for effects exists once the scientific methods being developed by the agencies 

have been fully vetted. This screening-level risk assessment indicates potential risks of direct 

effects to listed plants. Listed species may also be affected through indirect effects because of 

the potential for direct effects on listed and non-listed species upon which such species may 

rely. Potential direct effects on listed plants from the use of SU herbicides may be associated 

with modification of Primary Constituent Elements (PCEs) of designated critical habitats, where 

such designations have been made. Once the agencies have fully developed and implemented 

the scientific methods necessary to complete risk assessments for endangered and threatened 
19

(listed) species and their designated critical habitats, these methods will be applied to subsequent 

analyses for SU herbicides as part of completing this registration review.

6. Comments on the Audrey III Model

Major comments on the use of the Audrey III model to further characterize risks identified with 

TerrPlant and AgDrift came from three sources, Crop Life America1, the United States 

Department of Agriculture2, and a Technical Workgroup of Sulfonylurea Registrants3. These 

comments and responses are below.

Comment 1

Crop Life America (page 2)

Technical Work Group (page 15)

USDA (page 5)

Audrey III is not validated and OPP should not use unvalidated models in risk assessment.

Response: As noted by the commenters, Audrey III is not yet validated, but it has already gone 

through extensive internal vetting. OPP intends to do a validation as part of an ongoing approval 

process. Numerous public presentations have been made on the conceptual model and 

implementation of the algorithms at American Chemical Society national meetings, Society for 

Environmental Toxicology and Chemistry, and the Environmental Model Public Meeting. While 

Audrey III itself has not been fully vetted, all of its algorithms have been taken from previously 

existing and approved models (PRZM, AgDrift, EXAMS) and have been combined to describe 

the exposure to plants immediately adjacent to pesticide application site rather than on the 

application site. It is unlikely that the validation portion of Audrey III’s evaluation process will be 

completed before the risk assessment process for the sulfonylureas is completed.

As noted in the sulfonylurea ecological risk assessment, and the submitted comments, Audrey III 

is only being used provisionally to provide additional risk characterization – all decisions regarding 

risk exceedances are being made using the currently approved tool TerrPlant. Provisional use of 

 1

Collins, Janet E., 2015. letter to the docket signed December 24, 2015 on behalf of Crop Life America. 2

Kunickis, Sheryl. 2015. USDA Comments on the Ecological Risk Assessment for the Registration Review of 22 Sulfonylurea Herbicides. Letter to 

Rick Keigwin, dated December 16, 2015 on behalf of the United States Department of Agriculture. 3

Vukich, Jay. 2015. Submission of Comments on the Ecological Risk Assessment and Drinking Water Exposure Assessment Posted to the 

Dockets for Sulfonylurea (SU) Herbicides on September 25, 2015. Letter to Kevin Costello, dated December 21, 2015.
20

Audrey III is intended to augment TerrPlant as that tool cannot account for multiple applications 

or any dissipation pathways so that risks identified with TerrPlant can be more fully characterized. 

Provisional use of models in risk assessments during model development is considered a routine 

part of the approval process and helps identify the strengths and deficiencies of the model and to 

show how best to use the model in the risk assessment process. 

Comment 2

Crop Life America (page 2)

“EPA should explain why its risk assessment tools have not been subject to the 

basic requirements of sound science.”

Response: EPA is required to use the ‘best available science’ in its risk assessments. While the 

evaluation of Audrey III is not complete, it is readily apparent that it is a superior tool to TerrPlant, 

and using it to augment TerrPlant for risk characterization would certainly fall under the rubric 

‘sound science’.

Comment 3

USDA, Page 3

“EPA should explain how exactly Audrey III will be used in the assessment of 

sulfonylurea herbicides and other pesticides, and how Audrey III differs from 

previous EPA approaches such as SWCC.”

Response: Audrey III was used to estimate the exposure to terrestrial plants in the sulfonylurea 

ecological risk assessment. The SWCC, or Surface Water Concentration Calculator, is a shell for 

generating input and collating output from the agricultural field model PRZM and the water model, 

VVWM. As such, it is designed to estimate the exposure to aquatic organisms and also exposures 

that occur in drinking water. The SWCC was used to run the PRZM component of Audrey III. The 

PRZM simulations output is the source of the pesticide, runoff, eroded sediment, and precipitation 

loading used by Audrey III to estimate the exposure to plants. It will be used to assess exposure 

for terrestrial, semi-aquatic and aquatic environments. However, in the sulfonylurea risk 

assessment, only the terrestrial exposure component was used. A module that estimates exposure 

to semi-aquatic plants is functioning and is available for future risk assessments. SWCC and its 

update, PWC, will continue to be used to estimate exposure to aquatic plants.

Comment 4

USDA, page 4
21

“A second example is chlorimuron where the Audrey III simulation was conducted 

for a soybean scenario on silt loam soil in Mississippi, pH or % organic matter 

(OM) in soil were not specified, with an application rate of 0.08 lb ai/a. According 

to the CanopyTM label, the highest application rate allowed for a preemergence 

treatment on a silt loam soil with OM of 3-5% in Mississippi is 10 oz/a of Canopy 

(0.067 lb chlorimuron ai/a). A third example is where chlorsulfuron was modeled 

for a rangeland application using a Florida turf scenario for Audrey III. Most 

chlorsulfuron is applied for weed control in Midwestern wheat production 

according to BEAD documents posted on the docket (EPA-HQ-OPP-2012-0878).”

Response: The organic carbon content in the soil used for Mississippi soybeans was 1.28%, which 

corresponds to 2.2% organic matter. The soil is a Loring silt loam, which tends to be strongly acid, 

so the pH restrictions for Canopy herbicide would not apply to this scenario. The explanations for 

the selection of parameters to describe each standard scenario are on the Office of Pesticide 

Program’s modeling web page4. The crops assessed with Audrey III for each sulfonylurea pesticide 

were chosen based both on the amount of use and the maximum application rate. Therefore the 

use pattern that was assessed for each chemical was not necessarily the one with the highest annual 

usage.

Comment 5

USDA, page 5

“Likewise, in the TerrPlant model used to derive EECs for runoff (plus a drift 

fraction) for terrestrial and semi-aquatic plants near where pesticides have been 

applied, there is no indication (e.g. on page 33) that this model accounts for any 

use restrictions related to applications within a given period of predicted rainfall. 

The same question arises for the provisional version or future versions of the 

Audrey III model for estimating exposure to terrestrial plants as described on pp. 

47-48 and 51-55.”

Response: No current or provisional EPA model for assessing pesticides can account for 

restrictions on applications due to predicted storm events. The extent to which these restrictions 

reduce runoff to adjacent habitant is currently not well characterized.

Comment 6

Technical Work Group Comments, page 9

“Section 3.1 indicates for terrestrial plants that only the parent compound is 

considered to be of concern. However, the Kf/Koc and aerobic soil (ASM) half-life 

inputs listed in Table 7.6.3 for Audrey III (the model used to estimate exposure to 

 4

https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/models-pesticide-risk-assessment#aquatic
22

terrestrial plants) are for the parent combined with degradates, not for the parent 

compound alone.” 

Response: The model used to estimate exposure to terrestrial plants was TerrPlant; Audrey III 

was only used to further characterize the risk. TerrPlant does not consider the degradation of the 

parent compound, hence, it can only consider parent. Audrey III does consider the degradation 

of the compound, so in order to properly estimate risk, it is necessary to consider toxic 

degradates. Justifications for the residues of concern for sulfonylureas were in Appendix A of 

the preliminary ecological risk assessment. The input parameters used in Audrey III to 

characterize the fate and transport of each compound were the same as those used for GENEEC, 

and chosen for the same reasons.

Comment 7

Technical Work Group comments page 18

“Seeding emergence, SE values in Table 7.1, p.30-31 of the “Preliminary 

Ecological Risk Assessment for Registration Review of 22 Sulfonylurea 

Herbicides” listed for each of the 22 SUs were adjusted to units “kg a.i./ha” for 

use in Audrey III Table 7.6.4. Chlorimuron-ethyl endpoint conversion appears to 

be transposed incorrectly to kg /ha. In addition, Registrants’ believes that the SE 

endpoint selected for mesosulfuron, foramsulfuron, and iodosulfuron is incorrect 

as discussed in the active ingredient specific comments. These endpoints should be 

incorporated into this table, once updated. Table 1.1 should also reflect the correct 

endpoints, revised RQs and exceedance time values.”

Response: The direct response to this comment is included in the general comments on the 

sulfonylurea PRA, above in this document. Based on the revisions proposed by the registrants, 

and accepted by OPP, the revised results are in Table 7 below. This replaces Table 7.6.4 in the 

Preliminary Risk Assessment. This table also reflects corrections in use rate, soil water content, 

and curve number as discussed in specific comments below.
23

Table 7. Results of Audrey III simulations for estimation of risk to seedling emergence of 

terrestrial plants from selected uses.

Sulfonylurea

Seedling Emergence 

EC25

(kg/ha)

1 in 10 

Year 

EECA

RQ

% Years 

with 

exceedance

% Time 

with 

Exceedance

Chlorimuron-ethyl4 1.2 x 10-5 (onion) 0.036 2929 100 61.4

Chlorsulfuron1 2.47 x10-4 (tomato) 0.033 132 100 27.3

Flazasulfuron2 1.2 x 10-3 (cabbage) 0.010 8.5 100 57.2

Foramsulfuron3 9.9 x 10-3 (lettuce) 0.004 0.40 0 0

Halosulfuron-methyl*4 2.5 x 10-5 (lettuce) 0.036 1471 100 37.0

Imazosulfuron 3.8 x 10-2 (onion) 0.079 2.1 73 7.5

Iodosulfuron-methyl-Na 3.9 x 10-6 (tomato) 0.0009 219 100 56.6

Mesosulfuron-methyl 9.2 x 10-4 (lettuce) 0.0048 5.2 100 42.3

Metsulfuron-methyl 3.6 x 10-4 (sugar beet) 0.11 315 100 39.6

Nicosulfuron*2 1.07 x 10-3 (sorghum) 0.024 22.8 100 16.6

Primisulfuron-methyl 1.48 x 10-4 (cucumber) 0.011 72.4 100 11.1

Prosulfuron* 8.0 x 10-5 (lettuce) 0.011 138.4 100 14.3

Rimsulfuron* 1.84 x 10-4 (sugar beet) 0.017 94.1 100 16.5

Sulfometuron-methyl*4 3.5 x 10-5 (tomato) 0.011 304 100 25.1

Sulfosulfuron*4 7.8 x 10-4 (radish) 0.033 42.6 100 16.9

Thifensulfuron-methyl4 5.55 x 10-4 (onion) 0.013 21.1 100 9.1

Triasulfuron 9.5 x 10-5 (lettuce) 0.010 105.8 100 20.7

Tribenuron-methyl*2 no toxicity data 0.0094 NA NA NA

Trifloxysulfuron-Na* 6.8 x 10-4 (lettuce) 0.018 26.7 100 16.0

Triflusulfuron-methyl*4 1.1 x 10-2 (rape seed) 0.020 1.83 100 6.1

* Values reflect corrected curve numbers. The EECs in the PEZ are not sensitive to curve 

number. Only the EECs of tribenuron methyl changed.
24

1) The application rate in the Audrey III spreadsheet was corrected.

2) The field capacity and/or wilting point value was corrected in the Audrey III spreadsheet.

3) Foramsulfuron was re-simulated for turf using the FL turf scenario as the corn use had been 

canceled.

4) The seedling emergence toxicity data has been updated and corrected according to the public 

comments received.

Comment 8

Technical Work Group comments page 15

“The introduction of a new model like Audrey III should be accompanied by 

validation, version control, input assumption guidance (and justification) along 

with discussion of use and areas of refinement in a tiered process. Although EPA 

has presented the conceptual model of Audrey III in scientific meetings, scientific 

evaluation of the model has not been conducted by a Science Advisory Panel (SAP) 

or in other scientific venues, nor is it clear that a thorough EPA-internal evaluation 

of the model was performed before using it for risk assessment.”

Response: Audrey III is a provisional model that is currently under development in the Office of 

Pesticide Programs. The terrestrial component of Audrey III, the component used for the 

sulfonylurea assessment has been internally reviewed to make sure that implemented equations 

were the same as those described in the documentation and that those equations worked as intended 

in the model. The semi-aquatic component which was not used in the SU ecological risk 

assessment has also completed its vetting process since the completion of the SU assessment. 

While the operational code for Audrey III has been stable, the Agency is continuing to consider 

alternative methods for output presentation in order to best take advantage of the capabilities of 

the model. In addition, changes to the format for model input are being considered in order to ease 

data entry. It should be noted that the final version of Audrey III is expected to be imbedded in the 

Pesticide Water Calculator (PWC) and not in a spreadsheet. The PWC (further discussed in the 

next response) is an updated version of the Surface and Ground Water Calculator (SGWC) and 

Surface Water Concentration Calculator (SWCC) shells.

Validation against field data has not been completed for Audrey III and OPP agrees that this step 

should be a part of the evaluation and approval process for Audrey III. In addition, some sort of 

external review will also be completed before full implementation of Audrey III, though the 

nature of this review and has not yet been decided – options may include one or a combination 

of: a Science Advisory Panel, a public workshop, a peer-reviewed literature publication, or some 

other external panel review.
25

Comment 9

Technical Work Group comments page 15

“A similar concern applies to the SGWC model (Surface and Ground Water 

Calculator), which was used to run PRZM and generate input data required by 

Audrey III. The Surface & Ground Water Calculator Version 1.25 is not publically 

available. It is not clear if it has been evaluated and undergone any EPA QA/QC 

process. EFED released the Pesticide Water Calculator 1.5 on Dec 9th, 2015. The 

Pesticide Water Calculator 1.5 was able to open the .swi files, although the .zts file 

(used as an Audrey III input) generated by running Pesticide Water Calculator 1.5 

did not match the .zts file provided in the Audrey spreadsheets.”

The PWC includes an update of the PRZM 5, which has had minor revisions and bug fixes 

to the code. The version log file for the PWC and PRZM 5 is attached. PRZM 5 has been 

updated in accordance with OPP policies for new model versions. Small differences in the 

.zts file are due to the changes in PRZM 5. In most cases, they are on the order of a few 

parts per thousand or less and do not affect the overall estimation of risk with PRZMdependent assessments.

Comment 10

Technical Work Group page 16

“Given the status of the Audrey and SGWC models, the SU registrants believe it is 

inappropriate to use and publish the output of these two models in the registration 

review of the SU’s or other compounds. Models that have not been fully 

scientifically evaluated or peer reviewed, with no descriptions of the limitations of 

the model or explanation of the role in risk assessment should not be used to support 

risk management decisions.”

Response: The use of Audrey III in sulfonylurea risk assessment is discussed in the response to 

Comment 1. The SGWC is not a model itself, but rather a shell around the PRZM and VVWM 

(Variable Volume Water Model) models. These two models have been fully evaluated for use in 

risk assessment. Various versions of PRZM have been used in aquatic risk assessments for 

pesticides since 1991. VVWM is a reduced version of EXAMS with addition of varying the water 

body depth. It was evaluated and approved for use in 2014. EXAMS has been in use since 1991. 

The Surface Water Concentration Calculator (SWCC), SGWC, and PWC are all versions of the 

same shell. They are used to collate input, run, and display output from PRZM and VVWM. Like 

other EFED tools, the initial inputs using default assumptions provide upper bound risk estimates 

as a screening exercise. Reviewing more realistic variations on assumptions, looking at additional 

environmental and use conditions, along with addressing uncertainties in parameters will lead to a 
26

more complete view of potential exposure and the probabilities and distributions that allow risk 

managers to make informed decisions. 

Comment 11:

Technical Work Group page 16

“Conceptually, Audrey III is not capable of characterizing chemical reductions in 

runoff and erosion due to movement within PEZ and the buffer setback mitigation 

allowed in the model. The chemical loading in runoff and erosion from the treated 

field to Plant Exposure Zone (PEZ) at varied distances from the edge of the field 

are considered the same by the model. The difference of exposure concentration at 

varied distances of PEZ is driven by spray drift only. This is also the case when the 

buffer setback option is used in the model. Registrants recommends the agency 

consider incorporating available and validated models, such as VFSMOD, into 

Audrey III to quantify the runoff buffer efficiency to reflect more realistic exposure 

conditions, which is very important for making risk management decisions.”

Response: The conceptual model for Audrey III puts the PEZ at the field edge. This is because 

field borders usually contain plants. A vegetated filter strip (VFS) used as a ‘buffer’, in effect, 

becomes the new PEZ as it is now the area closest to the field where there are plants. Thus, it is 

not conceptually sound to buffer a vegetated area with another vegetated area.

Comment 12:

Technical Work Group page 16

“The assumption that wind is always blowing towards the same PEZ which is 

always sloped away from the field topographically, and this occurs every year for 

30 years should be varied and evaluated in higher tier refinements to the tool. It is 

important in that presentation of results indicates the numbers of years with 

exceedances of LOC exceedances or time of an exceedance, but these results are 

heavily dependent on assuming the same high drift exposure event every year.” 

Response: We agree that varying the exposure with wind direction and wind speed is an 

appropriate refinement to current practice, which assumes constant wind speed at a default upper 

limit, (or for aerial applications, an upper limit specified on the label.) However, a properly 

working tool to do this has not yet been developed for use with the PWC. All current risk 

assessments, aquatic and terrestrial, that evaluate drift for pesticide make this same assumption.
27

Comment 13:

Technical Work Group page 16

“The runoff component is heavily outweighed by the drift loading, so using 

identical drift inputs every year reduces the power in evaluating annual results for 

a 30-year simulation. Like varying weather patterns, it would be reasonable to 

assume variation in wind direction or wind velocity in different application years.” 

Response: The Agency disagrees with this conclusion. An evaluation across chemicals and 

scenarios indicates that some sulfonylureas assessed with Audrey III are runoff dominated (e.g.

flazasulfuron) and some spray drift driven (e.g. chlorimuron). The relative importance of runoff 

versus spray drift can easily be assessed in the concentration versus time graph that is on the 

‘Audrey Daily Results’ page of the Audrey III spreadsheet. This graph shows the chemograph at 

the near edge and far edge of the PEZ. In cases where runoff dominates, these two lines will be 

very close together since Audrey III assumes that runoff and eroded sediment borne pesticide are 

evenly spread across the PEZ. In cases where spray drift dominates, the two lines will be far apart 

as spray drift deposition varies with distance across the PEZ.

Comment 14

Technical Work Group page 17

“A higher tier spray drift refinement option is not available.” 

Response: An update to Audrey III produced subsequent to the SU assessment allows input of 

user generated drift curves, which can be generated from higher tier AgDrift runs or other 

sources.

Comment 15

Technical Work Group page 17

“The summation of foliar and soil residues used in output summaries does not 

correspond well to the different environmental compartments and how plant studies 

are conducted. Soil (with loading from runoff, drift deposition, or wash-off and 

reduced over time with leaching, continued downslope runoff, and degradation) 

would be the correct compartment to compare to seedling emergence studies.”

Response: We agree that Audrey III does not reflect the nature of exposure in the tests. It does, 

however, better reflect the nature of exposure around agricultural fields and other application 
28

sites, where exposure can and does occur both as sprays onto foliar surfaces and through uptake 

through roots in soil solution. The best ways to use the available toxicity data with Audrey III is 

an active area of discussion and this comment will considered in that context.

Comment 16

Technical Work Group page 17

“As configured, the loading from runoff is uniform within the PEZ and impacted 

greatly by several assumptions like the sheet flow zone width and exposure zone 

depth. Given the goals of the model, it seems a differentiation in concentrations 

down gradient from the field would be valuable to include. This may be achievable 

using existing tools like VFSMOD or a sequential implementation of the PRZM 

model where segments receive input from the up gradient compartment.”

Response: VFSMOD makes the same assumption with regard to sheet flow of pesticides, that is, 

that the pesticide is uniformly distributed over the ‘buffer’, but it is also unable to account for 

differences in pesticide concentration with distance due to spray drift deposition, which Audrey 

III is capable of doing. We agree that the capability to assess differences in pesticide deposition 

from runoff and eroded sediment would significantly improve the utility of the model, but the 

technology is not yet available.

Comment 17

Technical Work Group, page 17

“The width and depth of PEZ are sensitive parameters in runoff driven exposure 

scenarios. In the SU assessment, a depth of 15cm and width of 30 m were used. It 

is unclear how these parameters are derived, and we will appreciate a clarification 

from the agency. A sensitivity analysis of the two [parameters] is necessary prior 

to the use of the model.”

Response: A sensitivity analysis has been completed for the terrestrial component of Audrey III 

and has found that it is indeed sensitive to these parameters. The depth of 15 cm represents the 

typical rooting depth from which the majority of soil water is removed by plants and is a 

somewhat standard assumption used for agricultural simulations. The width of 30 m is thought to 

represent the greatest distance at which distributed or sheet flow can be maintained. Beyond this 

distance concentrated flow would have initiated and deposition of pesticide from runoff and 

eroded sediment will be substantially reduced. OPP is interested in any data or rationales that 

could support other appropriate distances or depths.
29

Comment 18

Technical Work Group page 17, 19

“The criteria used in selecting curve number values in PEZ needs to be clarified. 

According to the notation of the Audrey III spreadsheet, the selection of the curve 

number in PEZ was based on the land cover of meadow and the hydrologic group 

of the soil used in standard PRZM crop scenario. However for the same land use 

cover and hydrologic soil group combinations, the curve number values used in the 

Audrey III model are not consistent. The table below summaries the curve numbers 

used in the SU simulations. For the FL turf scenario, 71 and 86 were used for 

different compounds. For the KS corn scenario, 71, 77, and 86 were used for 

different compounds”

“This assumes the soil type of adjacent areas match that of the agricultural field. 

Additionally, the values in the distributed spreadsheet vary for the same SWCC 

scenario soils and do not always match meadow CNs found in TR-55 or the PRZM 

manuals”

Response: The meadow curve numbers are from Table 9-1 in USDA’s Part 630: National 

Engineering Handbook. The full entry reads “Meadow- continuous grass, protected from 

grazing and general mowed for hay, as this is a reasonable surrogate for a grass field border 

which may be mowed. The curve numbers are for Hydrologic Group A: 30, B: 58, C: 71, and D: 

78. The Audrey III simulations have been reviewed and Table 1 above has been revised to reflect 

corrected curve numbers.

The assumption that the same soil underlies the whole agricultural field is implicit in PRZM and 

is carried into Audrey III. The meadow curve numbers are taken from the current USDA 

guidance for curve number selection – USDA’s National Engineering Handbook, Part 630: 

Hydrology. These values supersede those previously cited in TR-55 and the PRZM manuals. The 

EECs in the PEZ are not sensitive to curve number. Only the EECs of tribenuron-methyl 

changed, which may have been due to concurrent changes in available water capacity. Note that 

this contrasts with pesticide loading in PRZM which is quite sensitive to curve number 

(FEMVTF, 20055

). 

 5

http://femvtf.com/femvtf/index.htm
30

Comment 19

Technical Work Group page 18

“A hydrological parameter, initial soil water content (cell L6 in sheet “Audrey 

Daily Results”), is assumed a fixed value (0.097) for all soils. This is not a 

reasonable assumption. By looking at the scenarios used for the SU assessment, 

this value is lower than the wilting point (0.139) in the KS corn scenario, and higher 

than the field capacity (0.086) in the FL turf scenario.”

Response: We agree the 0.097 is not the best value to use for all scenarios. In response to this 

comment, Audrey III for future use has been modified so that the initial water soil water capacity 

for the simulation is equal to that at field capacity. It is worth noting that this change has no 

significant effect on the exposure estimates for the sulfonylureas as it is an insensitive parameter. 

Comment 20

Technical Work Group page 18

“Appendix H (following the Audrey III equation Appendix J) describes the use of 

IORE in deriving spray drift regression curves. There is no explanation of the 

intended use of this methodology. No details were given on how the drift was 

derived at each distance interval. Clarification on the interpolation method should 

be provided as values are given in the SDF tab as interpolated values. It is unclear 

how EPA generated spray drift values at distances less than 6 ft.”

Response: The spray drift description in the equation documentation was not properly 

updated to reflect a revised spray drift methodology. A description of the revised 

algorithms is in Appendix B.

Comment 21

Technical Work Group page 18

“The annual peak concentration was compared with the lowest non-target plant 

endpoint. This is the worst case scenario. It does not capture the variation of 

exposure concentrations throughout the year, or the range of effect endpoints. 

Given the availability of daily concentration output, the risk assessment should 

make use of all of the data provided to refine the assessment for a better risk 

characterization. This comment applies also for species affected exceedance 

probability characterization.” 
31

Response: The risk quotients tabulated in the sulfonylurea risk assessment were based on 1-in-10 

year peak values and were intended to reflect the level of concern represented by the TerrPlant 

assessment. They are not worst case (1-in-30 year, and 1-in-100 years are worse), and they are not 

a ‘scenario’ so the description is not appropriate. The Audrey III characterization for the SUs also 

looked at the fraction of the time over the level of concern (which utilizes the whole chemograph) 

and graphs were developed to look at the exceedance of risk for the distribution of species tested 

versus the annual maximum series. Given that Audrey III provides opportunities for a variety of 

new ways to evaluate risk to plants, OPP encourages interested parties to recommend alternative 

risk measurement endpoints for use with Audrey III.

Comment 22

Technical Work Group page 18

EPA pointed out that “In some cases EECs on the PEZ exceeded the single 

application rate.” We agree with EPA’s statement: “...suggest caution in 

interpreting the results of Audrey until the tool is better validated against field 

results.” 

Response: With the corrections discussed above, particularly those for use rates, no EECs 

exceed the application rate. While we still believe caution is warranted in interpreting Audrey 

results given the current status of the model, we believe that the results represent a reasonable 

representation of reality given the main fate and transport algorithms have all been in use for 

decades.

Comment 23

Technical Work Group page 20

“The application rate inputted into the Audrey spreadsheet and application rate 

used for running PRZM5 were different for Chlorsulfuron, sulfometuron, 

foramsulfuron and nicosulfuron Audrey runs. The application rates in the 

spreadsheet and PRZM5 should be the same. The discrepancies in the rates, will 

affect the final concentrations. For example for chlorsulfuron, using the correct 

application rates in the spreadsheet, will result reducing the final peak EEC’s by 

half (EPA-HQ-OPP-2012-0625-0006, Figure 7.6.2). 

Audrey spreadsheet uses field capacity and wilting point inputs, which are taken 

from the standard scenario that is being used in running PRZM5. For 

Flazasulfuron and tribenuron Audrey runs, the field capacity and wilting point 

values used in the spreadsheet did not match the values from the standard 

scenarios.” 
32

Response: The discrepancies in application rate between the PWC input file and the Audrey III 

spreadsheet have been addressed as have discrepancies in the field capacity and wilting point. 

These changes are reflected in Table 7 above. 

Foramsulfuron was reassessed using the Florida turf scenario as the corn use has been canceled 

since the publication of the SU ecological risk assessment. Two applications were modeled in 

Audrey III as occurring 6 days apart, starting on July 1, and were applied using a fine to mediumcoarse high boom spray. Foramsulfuron no longer exceeds risk thresholds as estimated using the 

Audrey III.

Comment 24

Technical Work Group, page 20

"The Audrey spreadsheet uses a relatively straight forward set of environmental 

fate inputs like soil half-life, foliar half-life, Koc, application data and several 

parameters setting the geometry of the PEZ that the user enters in the spreadsheet 

along with importing a .zts file. A guidance will be helpful that explains the inputs 

and what values should be used as a standard practice. There should also be a 

guidance available for refining inputs in cases of tiered assessments, if needed. 

Response: Guidance for selecting inputs will be prepared before Audrey III is finalized. 

We will consider including guidance on how to do refinements when we prepare that 

document.
33

Appendix A

Modification Log for SWCC, PRZM-GW, SGWC, PWC, PRZM, and VVWM

SWCC

1.093 : added error detection on Run Button when application method is not 

specified. Allowed a read of a file with incomplete application methods 

specified (previously would throw error and not read remaining input file.) 

Added filter to prevent multiple error messages during a multi run.

1.10 :

1. In GUI, added help info upon mouse hover on application method labels and 

assorted other areas.

2. In GUI, deleted msessage boxes that appeared during batch application 

window runs. These were inadvertently left over from prior debugging work.

3. In VVWM in the volatilzation routine, set some temporary arrays to form on 

the heap instead of stack by making them allocatable. This now allows for use 

of larger weather files (tested to 100 years).

4. In VVWM, set all real variables to "real" instead of "real(8)". Then set 

the default compiler option of real to double precision. This now allows 

concentration calculations with near zero degradation. previous versions 

threw NaN.

5. In GUI, Added capability to perform NAFTA Groundwater simulations. (hidden 

to users)

6. In GUI, the water-body-type highlighting when an incorrect input in drift 

of efficiency is made now remains on until corrected. previously when both 

reservoir and pond were run, the first error indicator would be cleared when 

the second water body was run.

7. Freundlich capabilities are now present, but currently hidden from users 

(until fully tested).

8. Ability to specify sorbed or aqueous only is present, but currently hidden 

from user.

9. Fixed misread of the transfer file affected the mass transfer rate (this 

bug only occurred since 1.092)

10. Added a 4th column in the daily output file for daily peak 

concentrations.

11. Installer: removed dependency on VisualBasicPowerPacks.dll, restructered 

folders so that applications are in "bin" subfolder and example files are in 

"Example" folder.

1.101 :
34

Made corrections in help file

corrected spelling errors on water body tab

additional tool tips on mouse hover

added long-term averages to batch output

1.102

For application widow labels: changed the word "skip" to "step" to better 

clarify the function

Added error catching for application widow runs: "step" must be an integer 

greater than zero

1.103

Added base flow option (hidden to users)

Corrected groundwater breakthrough day calculation (very minor). Total number 

of days was misestimated by 3 days as header lines in zts file were 

inadvertently included in the count.

Added last directory recognition to scenario dircetory and weather file 

directory

Fixed batch scenario runs so that custom water bodies could be run together 

with reservoir and pond

Established initial directories for weather and scenario files

1.104

Now produces DEEM and Calendex input files

Added last directory recognition to batch scenario directory,

In batch scenario mode, cheked state of water body selection now remains 

unchanged, regardless of scenario upload; Flow through time lag option 

however is determined by scenario (typically 30 days)

Added a warning to prevent use of slashes or semicolons in scenario ID. This 

was problematic because ID is used in output file naming.

1.105

First year of data is now removed from Calendex and DEEM file per HED 

request.

PCA (Fractional Cropped Area) is now on the Watershed Tab and saved with the 

input file. \
35

1.106 ******************* USEPA RELEASE VERSION (Pushed on or around 

6/6/2014) ***************

Recorded the Cropped Area Fraction in the main output file and in the Word 

document. Added application schedule and methods to Word file.

*****************************************************************************

****************

1.107 Corrected spelling on tool tip for Relative Dates radio button.

1.10

Added Erosion Efficiency

Heat of Henry in Joules/mol changed from kcal/mol (not the units for PRZM)

1.12 and so on

Daily time series output is now a csv file.

Added volatilization

VP, Sol are no longer required, but must have Henry Law Const

Henry's Constan Estimator added

revealed efficiency and drift on all water bodies all time.

Changed Molar Product: Reactant Ratio terminology

Batch runs can now be performed with scenario and app date simultaneously

reorganized Application Method buttons

Volatilization boundary layer thickness is an input parameter

Old input files are backwards compatible

Erosion Efficiency is now included.

Ability to do only PRZM Runs (without water body)

New Output page for PRZM-Only output

Node Examiner added

Added a header to input file to track Version Numbers. (made to be backward 

comaptible)

Corrected order of parent degradate delivery to PRZM5 (order was wrong when 

degradates included)
36

Corrected order of output (4-day and Overall avg were transposed under batch 

runs)

Run Button says "Wait" during run time and "Try Again" after an error.

Option for No HED Files

No longer supporting PE5 files

Added ESA batch run capability

restructured file naming for VVWM, Now all vvwm output files are named in the 

GUI and sent to VVWM by input file

this eliminates having to simultaneoulsy coordinate changes both GUI files 

and VVWM files.

Addtional capability to do alternate Return Frequency output

Coordinated Batch runs (non ESA) so that they can also do different frequency 

of return

Fixed Word file output for degradates so that graph will be displayed

Added error catch when depth of incorp is not specified

Added application method for mass increasing with depth. Decreasing with 

depth (7 methods total)

Updated GW output: now has degradates and data

Added baseflow to ESA inputs, hooked up PCA also

Brought irrigation depth to user interface

Fixed backwards compatible bug with scenarion read (1.25 to 1.26)

Added nonequilibrium inputs to PRZM

Added the option to define flow averaging for constant volume with flow. 

(requires ESA input file revision as well)

Curve Number optimization and USLE-C optimization with calibration data.

Added 1-day averages to the ESA batch output file

Name changed to PWC

******************************************************************

VERSION 1.50 Official Release *******12/10/15*********************

******************************************************************

Version 1.5001

 Made an Install Shield project

 Enlarged interface so that application slide control is acccessible
37

******************************************************************

VERSION 1.52 Official Release *******4/4/16*********************

******************************************************************

1.52 Added a relative ssq residual option for calibration (this option 

available on advanced), formerly it was just absolute ssq

 All degradate output is in absolute chemical mass of respective 

chemical

 Removed paralle1ization requirement from compiler (required dll that 

some may not have).

 Previously (except for runoff and erosion) they were in terms of 

parent.

 Changed the name of the help document to PWC_help.rtf

 Fixed Word document to recognize new application methods (see above)

*****************************************************************************

*******************

PRZM5:

Separated volatilization into its own module

Volatilization boundary thickness is now an input

Added erosion efficiency as a variable

eliminated erosion dependency on deltaX(1) embedded in enhanced Kd 

calculations

Eroded solids are now removed with a Kd appropriate for each layer, rather 

than assuming the Kd at the top layer only.

SPESTR and RESTR have been reanmed conc_porewater and conc_total respectively

Eliminated ELTERM as it was not intuitive replaced with 

enriched_eroded_solids and Kd

Rearranged order of aqueous, solid, gas degradation in Record C8

Time series Output no longer limited to 12.

Number of time series is no longer fixed at 12. Can do up to 100 now.

"MaxTimeSeries" parameter added to Constants_and_ Variable module to address 

time series number (currently set to 50).
38

soil temperature call moved to before chemical calcs

added a reference temp for henry, previously implied to be 25

okh and kh renamed old_henry and new_henry

Flux calculations separated from tridiagonal setup calculations and placed in 

new routine "flux_calculations"

new module "Tridiagonal"

Predictor Corrector added for better Freundlich Calculations 

Added Subdaily time step option

Fixed volatilization bug, C coefficient incorrectly had the Henry constant 

set to the node 1 instead of node 2. Big mass balance issues resulted. Has 

gone undetected since beginning of volatilization in PRZM 3.

Whole array operations on total concentration have been switched to partial 

arrays to avoid nan caused by 0 delx in denominator

 --think about making these allocatable so whole arrays could be used

In print buffer for zts file, any number less than 1.0e-99 is now equated to 

zero (seems as though numbers with exponents greater than 99 leave out the 

"E" and caused problems on rereading the data)

variable TEMP renamed to air_temp

Volatilization interface length is brought out as a user input

Eliminated variables ttrflx and tsrcfx as they were ununsed, TRFLUX is now 

local instead of in module

BUG FIX: Pesticide decay flux was incorrectly calculated, it subtracted added 

parent degraded and then subtracted degradate produced,changed to chemical 

specific

Changed variable dkr12 13, 23 to molarconvert_aq12 etc.

Added a solid phase molar conversion -- this was necessary for NAFTA-GW in 

which both hydrolysis and biodeg can occur in PRZM and for which biodeg \

is both aqueous and sorbed degradation.

Fixed an initialization problem with the subdaily steps for 

volatilization(thair_old wasnt initialzed)

NC is now "max_num_crops"

Increased maximum applications to 6000

Corrected double counting irrigation for Method 6 (not available in SWCC)

Preserved metfile precipitation, defined 2 new variables: precipitation and 

precip_rain (previously precip was overwritten)

ZTS PRCP output is now actual precipitation

Fixed units problem for Freundlich (PRZM concentration internally is g/cm3)
39

Added nonequilibrium 

Variable WP changed to wiltpoint

Following variables are made allocatable: soil_depth, wiltpoint,

replaced tridiag routine with numerical recipes version (checked ok).

Fixed temperature/frozen ground miscalculation (now takes average temperature 

simply to runoff moisture zone 10cm).

Adding new variables for all depth dependent inputs so that input parameters 

are not overwritten.

Soil parameters are now allocatable, rather than fixed at 2000 compartments.

eliminated error notification for water content over saturation (can be for 

hypothetical work and conceptual overrides)

No longer supply thermal conductivity as an input, all is calculated 

intenally based on texture.

Modified records 13 and 19 accordingly

Eliminated frozen soil adjustements. There is a bug in PRZM 3 that 

incorrectly estimated the nodes in the top 10 cm when determining if the 

ground was frozen

(PRZM3 after statement #15 in subscript delx() should be TLIN not MLIN). 

Essentially no possiblility of freezing in PRZM3.

Bug fix: degradation temperature adustment for top layer was referenced to 

2nd layer temperature.

Dispersion is now not chem specific, It is a 1-D array with distance.

Added version number as a parameter, Version number now appears on zts and 

kecho.

Option to have no soil moisture modification to curve number.

zts output now has three place exponent just in case low data show up and 

exponent is left off by fortran default

added ability to specify the calibration output file name

Corrected bug regarding harvest application (occurred sometime after last 

official release)

***********PRZM5 Version 5.02 Official 

Release*********12/10/15*********************

****************************************************************
40

VVWM: Version 1 Official release

Henry Constant now a function of temperature

Now takes unitless Henry

Vapor pressure and Solubility are no longer used (but kept for now as inputs)

Changed volatilization routine to read chemical parameters from variables 

module instead of as dummy variables.

Output File names are no longer constructed in vvwm, instead they are entered 

in the input file

Added flexibility to have another return frequency analysis (e.g. 15 year 

return in addition to the 10 year return)

Fixed bug with sediment input from zts file: Sediment in zts file is now 

recognized as tonnes (not tonnes/ha)

Added version number as a parameter. Version number on output file.

Daily output can be represented with 3 exponents

1-day avg with return frequency added to output

*****Version 1.02 Official Release *********12/10/15*************
41

Appendix B

Spray Drift Estimates for Audrey 3

Spray drift deposition data were exported from AgDRIFT 2.1.1 for the various Tier 1 application 

methods (i.e., aerial, ground, and airblast). The data were imported into the Audrey 3 model as a 

worksheet and used to estimate the average deposition across a terrestrial area a 30 meters wide, 

using 1 meter increments, similar to methods used in the Terrestrial Deposition Tool in 

AgDRIFT.

In short, the average deposition is estimated as the summation of the product of the distance 

times the average deposition across the distance divided by 1 m, the width of the terrestrial area. 

Distances and point deposition estimates were pulled from the AgDRIFT worksheet. For 

instance, the average deposition for an aerial, fine to medium spray application, from 0-1 m is 

estimated as such:

Distance (ft) Deposition 

Fraction

Distance 

Difference 

(ft)

Average 

Deposition 

Fraction

Product of Average 

Deposition Fraction and 

Distance Difference

0 0.4999

0.102525 0.4975 0.102525 0.498985 0.051158

0.20505 0.4952 0.102525 0.497 0.050955

0.4101 0.4904 0.20505 0.49405 0.101305

0.8202 0.4809 0.4101 0.4882 0.200211

1.6404 0.4619 0.8202 0.47645 0.390784

3.2808 0.424 1.6404 0.4529 0.742937

Average deposition fraction from 0-1 meter (0-3.2808 ft) 0.46859
42

References

FIFRA EXPOSURE MODEL VALIDATION TASK FORCE (FEMVTF). 

http://femvtf.com/femvtf/index.htm

USDA. 2015. National Engineering Handbook Hydrology chapters.

http://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/?cid=stelprdb1043063

USEPA. Models for Pesticide Risk Assessment. https://www.epa.gov/pesticide-science-andassessing-pesticide-risks/models-pesticide-risk-assessment#aquatic

USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides. Version 2.1. U.S. Environmental Protection Agency, Office 

of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009.

USEPA. 2012. Barrett, M. and A. Solliday. Registration Review: Preliminary Problem 

Formulation for Environmental Fate and Ecological Risk, Endangered Species, and 

Drinking Water Assessments for Halosulfuron-methyl. DP barcode 394807. Office of 

Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. 

Memorandum to Pesticide Re-evaluation Division. Mar. 8, 2012.

USEPA. 2013. White, K., F. Khan, C. Peck, and M. Corbin. Guidance on Modeling Offsite 

Deposition of Pesticides Via Spray Drift for Ecological and Drinking Water Assessments

USEPA. 2015. Standard Operating Procedure for Using the NAFTA Guidance to Calculate 

Representative Half-life Values and Characterizing Pesticide Degradation, Version 2. 

U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental 

Fate and Effects Division. Internal memorandum. Mar. 23, 2015.
43

Attachment 1. Clarification of Plant Evaluation Guidance
44
45
46
47
48
49