1 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

June 1 , 2016

PC Code s : 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 Greg ory 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. E FED appreciates the comments, has considered all of the m , 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, interpr et, and compar e potential risks

o Comments on the general conceptual model and risk metrics

• Comments requesting an endangered species consultation

• Comments supportive of the methods and approaches2 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 assessme nt 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 MRID s ) . 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 i n the following sections.

1.1. Terrestrial Plants

Use of IC 25 as an endpoint and its relevance.

Comments regarding the relevance of the IC 25 have been submitted, including a suggestion that the
use of an IC 50 may be more appropriate for SUs given the variability within chemicals at the IC 25 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 an d 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 IC 25 level is used as described in the guidance memo “Clarification of Plant Evaluation Guidance” (2005;
attachment 1 ).

The use of IC 25 endpoints are considered protective, but not especially conservative, for terrestrial plant species. Given that, typically, 10 crop species are use d as surro gates for all terrestrial plants, it3 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 produc ed 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 growin g 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 IC 25 based on growth parameters is considered protective but not unreasonably conservative.

Regulatory endpoints

EFED’s current practi ce for evaluating potential risk to non

- listed terrestrial plants is to use the most
sensitive IC 25 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 IC 25 , 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 IC 25 . It is theref ore critical for risk assessment that both the IC 25 and the modeled application
rate be correct. In addition to using the most sensitive IC 25 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 IC 25 ; in other cases differences
in st atistical 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 IC 25 values identified as a result of these reviews are presented in Table 1

. These e ndpoints 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 im pact toxicity. However, if TEP and TGAI studies produce a similar IC 25 , then the most sensitive endpoint across the two studies will be used. Also, ingredients of specific formulations can4 vary across products, and there are often multiple formulated pro ducts 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 IC 25 s for Seedling Emergence (SE) and Vegetative Vigor (VV)

.

Chemical name Species Effects endpoints VV/SE IC 25 (lbs a.i./A cre ) 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 0.000022 A 42661424

halosulfuron

- methyl radish biomass VV 0.000057 42661425

imazosulfuron onion biomass SE 0.034 47305211

imazosulfuron radish survival VV 0.08 47305211

iodosulfuron

- methyl

Na tomato height SE 0.0000035 45109132

iodosulfuron

- methyl

Na lettuce height VV 0.00000037 B 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 491543085 Chemical name Species Effects endpoints VV/SE IC 25 (lbs a.i./A cre ) 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 0.000031 C 43538501

sulfometuron

- methyl soybean biomass VV 0.000018 43538501

sulfosulfuron radish biomass SE 0.007 D 44295783

sulfosulfuron radish biomass VV 0.00009 44295784

thifensulfuron

- methyl onion biomass SE 0.000555 E 48037903

thifensulfuron

- methyl sugar beet biomass VV 0.0000019 E 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 0.00002 F 47748203

trifloxysulfuron

- Na lettuce biomass SE 0.0006 45371734

trifloxysulfuron

- Na radish biomass VV 0.000009 G 45371734

triflusulfuron

- methyl oilseed rape height SE 0.0095 H 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./Acre6 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 sh ould 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 max imum 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, al though ‘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

t he 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 3107 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 reference8 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 24 219 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

- methyl

Na 0.00013 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 applications10 Chemical Lowest Max Application Rate Highest Max Application Rate Rate for Modeling Application Methods Notes

Sulfometuron

- methyl b 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 non

cropped areas; most uses allow only ground applications Thifensulfuron

methyl 0.0023 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 Plant s, 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 in dicated 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 gener al 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 th e labeled imazosulfuron uses.11 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, a n 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 Aquati c Organisms Species EC50 Reference

Duckweed

( Lemna gibba ) EC 50 = 0.00146 mg/L ECOTOX 104861

Lemna minor 0.00046 mg/L MRID 47639701

Green algae

(Pseudokirchneriella subcapitata) EC 50 = 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
IC 50 s, respectively. These values are from MRIDs 42471308 ( L emna gibba , EC 50 of 11.6 ug/L) and 42471305 ( Selenastrum capricornutum , EC 50 >29 ug/L). EPA acknowledges that additional studies were submitted in 2014 that evaluated toxicity to Lemna gib ba 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 wi ll be incorporated quantitatively as app ro pr iate into future assessments.12 1.2.3. Foramsulfuron

The registrant noted that the correct value to use for the vascular plant IC 50 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, u se of
this value wil l 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 0.0 31 (corn) was used in the risk assessment to represent foramsulfuron uses. However, the corn use w as 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 EC 50 of 35 ug/L from MRID 40728325. The registrant suggested using an EC 50 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 EC 50 . 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 re ported 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 EC 50 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 hal osulfuron; 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 expo sure 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 inp ut 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

- day13 model input is the 90 th percentile of the me an 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 meta bolism 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 u sed 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 ar eas, 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./ A cre. The

app lication 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 sum marized 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 IC 50 (μg/L) Vascular Plant IC 50 (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 IC 50

.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 distance s from the use site i s AgDRIFT. While EFED has evaluated the spray drift depositio n 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 di stance 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

- agric ultural 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 anal ysis 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, w ere 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 give n 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 a vailable 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 su bmitted 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 a ctive 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 o f the level of refinement is made with both risk assessors and risk managers. In this case, t he 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 refineme nt 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 metr ic 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 approac h 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 IC 25 , 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 f oundation 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 ex posure 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 w hat would be found in drinking water and no risks to humans from drinking water were found, a dditional 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 reque sted 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 consistent18 with the approach for other SUs. The use of the sorption value for CGA

- 1956 60 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 relat ed 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 N MFS) 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

approac h." 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, E PA 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 calcu late 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 p reliminary assessment, EPA conducted a screening

- level assessment for all taxa of non

target 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 herbicid e 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 dev eloped and implemented the scientific methods necessary to complete risk assessments for endangered and threatened19 (listed) species and their designated critical habitats, these methods will be applied to subsequent analyses for SU herbicides as part of co mpleting 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 America 1 , the United States Dep artment of Agriculture 2 , and a Technical Workgroup of Sulfonylurea Registrants 3 . 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 p ublic 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 Departm ent 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 inte nded 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 c onsidered 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 as sessment 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 occ ur 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 b e used to assess exposure for terrestrial, semi

- aquatic and aquatic environments. However, in the sulfonyl urea 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 421 “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 O M 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 Midwes tern 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 l oam, 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 pa ge 4 . 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 highes t 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 habit ant 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#aquatic22 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 co nsider 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 appe ars 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
i ncorporated 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 th is document. Based on the revisions proposed by the registrants, and accepted by OPP, the revised results are in Table 7 below. This replaces T able 7.6.4 in the Preliminary Risk Assessment

. This table also reflects corrections in use rate, soil water cont ent, 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 EC 25
(kg/ha) 1 in 10
Year EEC A RQ % Years with
exceed

ance % Time
with
Exceed

ance

Chlorimuron

- ethyl 4 1.2 x 10

- 5 (onion) 0.036 2929 100 61.4

Chlorsulfuron 1 2.47 x10

- 4 (tomato) 0.033 132 100 27.3

Flazasulfuron 2 1.2 x 10

- 3 (cabbage) 0.010 8.5 100 57.2

Foramsulfuron 3 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

- methyl 4 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 10 0 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 Aud rey 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

Techn ical 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 ev aluation 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 implemente d 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, chan ges 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 discus sed in the next response) is an updated version of the Surface and Ground Water Calculator ( SGWC ) and Surface Water Concentration Calculator (SWCC) shell s

. Validation against field data has not been completed for Audrey III and OPP agrees that this step
sh ould 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 in clude 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 (Surfac e 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 wi th 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 PRZM

dependent asses sments.

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 A udrey 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
ris k assessment. Various versions of PRZM have been used in aquatic risk assessments for pesticides since 1991. VVWM is a reduced version of EXAMS with ad dition 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 assumpt ions 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 a26 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 pu ts 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 concept ually 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
hea vily 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 u pper 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 pes ticide 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 th at 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’ pag e 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 line s will be very close together since Audrey III assumes that runoff and eroded sediment born e pesticide are evenly spread across the PEZ. In case s where spray drift dominates, the two line s will be far apart as spray drift deposition varies with distance acr oss 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 downsl ope 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 aroun d agricultural fields and other application28 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 o f 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 exposur e 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 whe re 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
d ifferences in pesticide concentration with distance d ue 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 derive d, 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 combinatio ns, 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, an d 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 fo und 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
wh ich 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 t he 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 wi th pesticide loading in PRZM which is quite sensitive to curve number (FEMVTF, 2005 5 ).

5 http://femvtf.com/femvtf/index.htm30 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 (0.0 97) 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 th e 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 prov ided 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 f or 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 intend ed 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 S Us 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 Audre y 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 repr esent 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 run ning 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 t he 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 mediu m

coarse 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 wi th 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: Guidan ce 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 : a dded 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 mes sages 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 fr om 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 var iables 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 Ground water 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 t ransfer 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 ap plications 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 applicat ion 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 breakthrou gh 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 ru ns 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 b atch 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 sce nario 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 Effi ciency 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 support ing 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.

Addtion al 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 no t 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 ba ckwards 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 op timization 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 acccessible37 ******************************************************************

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

A ll 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.

Chan ged 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, ga s 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 a llocatable 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 re named 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 a dded 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 ca n 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 nonequi l ibrium

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 r ecords 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 MLI N). 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 paramet er, 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 ca libration 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 Dep osition 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 estim ates 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) 0.4685942 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

- and

assessing

- pesticide

- risks/models

- pesticide

- risk

- assessment#aquatic

USEPA. 20 09. 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. 2 012. Barrett, M. and A. So l liday. 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, Off ice of Pesticide Programs, Environmental Fate and Effects Division. Internal memorandum. Mar. 23, 2015.43 Attachment 1. Clarification of Plant Evaluation Guidance444546474849