OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION 

### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

August 12 , 201 5

PC Code: 085601, 108209, 118601, 118602, 119009, 119011, 122001, 122009, 122010, 122020, 122021, 128721, 128820, 128845, 128887, 128901, 128969, 128973, 129002, 129008, 129009, 129031
MEMORANDUM DP Barcode: 427429

SUBJECT : Drinking Water Exposure Assessment for the Registration Review of 22 Sulfonylurea Herbicides

FROM : Greg ory Orrick, Environmental Scientist
ERB1 /EFED (7507P)

THROUGH: Rochelle F. H. Bohaty, Ph.D., Chemist ERB3/EFED (7507P)

Brian Anderson

, ERB2 Branch Chief
ERB2 /EFED (7507P)

TO : Julie Van Alstine, MPH

, Environmental Health Scientist
Donna Davis

, Acting Branch Chief
RAB 6 /HED (7509 P)

Margaret Hathaway , Chemical Review Manager Kevin Costello, Branch Chief RMIB2/PRD (7508P)

1. Executive Summary

This Environmental Fate and Effects Division (EFED) memorandum is an abbreviated
drinkin g water exposu re assessment based on labeled u ses of the 22 currently active sulfonylureas (SU) in support of registration review. Coarse and refined s creening drinking water exposure estimates were generated with PRZM

- GW (v.1.07) and FIRST (v1.1.1) for use in the SU dietary risk assessments in support of human health assessment. A tiered approach was used in this assessment beginning with coarse
- screen estimates that should exceed upper

- bound
chemical

- specific estimated d rinking water concentrations ( EDWC ) for all SUs. This was achieved by using model inputs that represent the use pattern of highest potential exposure from any SU, the highest soil mobility of any SU residue of concern, and stability to any route of degrad ation over time. The resulting highest coarse

- screen EDWC s from PRZM

- GW were proposed in all S U dietary risk assessments as a conservative estimate of exposure. Due to the

### 2 screening nature of this assessment, EFED does not expect that the EDWCs reflect a ctual potential exposures. However, i f the resulting dietary exposure was not of concern, then exposure modeling refinements, including chemical

- specific modeling, were unnecessary. If the resulting dietary exposure was of concern, then simple chemical

- s pecific refinements were made to generate lower refined

- screen EDWCs that remained conservative for the chemical ( i.e. , the
refined

- screen EDWCs are still coarse, but a step more refined than the coarse

- screen EDWCs)

. For both screens, the SUs were conser vatively treated as stable to all routes of degradation, making consideration of degradates of concern irrelevant. Table 1.1 lists the coarse

- and
refined

- screen EDWCs for the SUs. Due to the conservative nature of these screens, the EDWCs presented in t his assessment are not expected to occur in drinking water.

Table 1.1

. Screening

- level Maximum EDWCs for Sulfonylureas

Sulfonylurea (Use) PRZM

- GW
Scenario Screen
Level Max. Daily Conc. (μg/L) Post

breakthrough Mean (μg/L) Mean Breakthrough

Time (yrs)
Chlorsulfuron (non

- ag areas) NC cotton Refined 78 52 5.9

Halosulfuron

- methyl (fallow) NC cotton Refined 74 53 8.1
Nicosulfuron (rights

- of

- way) NC cotton Refined 39 26 6.2
Prosulfuron (corn) NC cotton Refined 15 13 12
Rimsulfuron (commercial areas) NC cotton Refined 105 71 6.5
Triasulfuron (rangeland) NC cotton Refined 21 19 16

Tribenuron

- methyl (corn) NC cotton Refined 35 23 6.1

Triflusulfuron

- methyl (sugarbeet) FL citrus Refined 23 20 9.5
All other sulfonylureas NC cotton Coarse 751 492 5.7

- 8.7



### 2. Use Characterization

The uses and use patterns of the assessed sulfonylureas (SU) are generally described by the LUIS reports that were prepared and posted to the dockets during the problem formulation phase of registration review. The risk managers assi gned to the SUs were consulted to update the use patterns for this assessment to reflect any label changes that occurred after the LUIS reports were prepared. Table 2 .1 lists the resulting lowest, average, and maximum single application rates labeled for the SUs. Maximum agricultural single application rates are listed separately from maximum non

- agricultural single application rates.

Table 2 .2 lists the maximum seasonal or annual application rates for agricultural uses of SUs that were assessed to estimate drinking water exposure using the Tier I screening drinking water exposure models, PRZM

- GW and FIRST. Maximum single application rates were often the same as maximum seasonal or annual application rates. Uses with single application rates less than seasonal or annual application rates generally did not provide a minimum reapplication interval, as indicated in Table 2 .2 . Upper

- boun d usage rates provided by the Biological and
Econo mic Analysis Division (BEAD) were used to estimate maximum annual application rates
for uses without maximum annual application rates on the label. Clarification of the maximum annual application rate and minimum reapplication interval is recommended for all labeled SU use sites for which these directions are not currently provided on the label.

### 3 Table 2 .1 Sulfonylurea Single Application Rates A

Chemical Lowest
Max Application
Rate Highest
Max Application
Rate Rate to Model

- Ag Rate to Model

- Non

- Ag Average Rates
Across Uses
W here Available

(S upplied by BEAD) Application
Methods Notes

Bensulfuron

- methyl 0.047 0.063 0.063

- only used on rice none 0.032 ; up to 2 apps Ground or Air Labeled only for rice

Chlorimuron

- ethyl 0.0039 0.08 0.08

- soybean 0.0313

- several

non

- ag uses 0.004 to 0.017 Ground or Air

–

Chlorsulfuron 0.0012 0.14 0.062

- rangeland/fallow 0.14 0.007 to 0.047 Ground or Air

–

Flazasulfuron 0.047 0.093 0.045 0.093 0.045 Ground only

–

Foramsulfuron 0.0009 0.052 0.038

- corn 0.052

- all non Ag 0.029 to 0.032 Ground only for tur and ground
or air for corn –

Halosulfuron

- methyl 0.03 0.14 0.094

– corn (most uses at 0.047) 0.136 0.016 to 0.077 Ground or air Most uses are ground only, but some allow aerial applications

Imazosulfuron

- 0.66 0.3

- melons, vegetables,
rice 0.66 Not available Ground or air Uses are ground only, except aerial applications are allowed
on rice
Iodosulfuron

- methyl

Na 0.00013 0.0089 0.0089

- wheat 0.0089

- most turf 0.002 Ground only

–

Mesosulfuron

- methyl 0.0028 0.013 0.013

- triticale and wheat none 0.002 to 0.011 Ground or air

–

Metsulfuron

- methyl 0.00023 0.15 0.15

- ag uncultivated areas and some forestry

uses 0.15

- several

non

- ag uses 0.002 to 0.024 Ground or air Labeled for mainly non

- ag uses with several agricultural uses

Nicosulfuron 0.012 0.07 0.066

- corn 0.07

- several

non

- ag areas 0.011 to 0.043 Ground or air

–

Orthosulfamuron 0.066 0.066 0.066

- rice none 0.061 Ground or air Labeled only for rice

Primisulfuron

- methyl 0.018 0.036 0.036

- corn 0.036

- bluegrass 0.009 to 0.022 Ground or air Labeled only for bluegrass and

corn

Prosulfuron 0.0089 0.036 0.036

– corn (most uses at 0.018) none 0.003 to 0.018 Ground or air No non

- ag uses labeled

### 4 Chemical Lowest
Max Application
Rate Highest
Max Application
Rate Rate to Model

- Ag Rate to Model

- Non

- Ag Average Rates
Across Uses
W here Available

(S upplied by BEAD) Application
Methods Notes

Rimsulfuron 0.0078 0.063 0.063

- most uses 0.0625

- most

uses 0.01 to 0.062 Ground or air Numerous ag and non

- ag uses; some uses only allow ground applications

Sulfometuron

- methyl 0.0281 0.0281 0.38

– fallow,
uncultivated areas 0.281

- forestry
and more 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 0.094

- almost all

uses 0.008 to 0.07 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 none 0.002 to 0.015 Ground or air L abeled for mainly agricultural

uses

Triasulfuron 0.022 0.028 0.028

- most uses were 0.0275 or 0.028 none 0.013 to 0.019 Ground or air

–

Tribenuron

- methyl 0.0012 0.0313 0.031

- field corn,
blueberries none 0.002 to 0.017 Ground or air Labeled main ly for agricultural

uses
Trifloxysulfuron

- Na 0.007 0.036 0.028

– sugarcane 0.036

- turf 0.006 to 0.017 Ground or air

–

Triflusulfuron

- methyl 0.016 0.031 0.031

- sugar beets (all other uses at 0.016) none 0.008 to 0.012 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”; “Non

- ag” means “non

- agricultural”.

### 5 Table 2 .2

. Sulfonylurea Application Rate Patterns of Highest Expected Exposure A
Sulfonylurea Maximum Rate Pattern

Bensulfuron

- methyl 0.0625 lbs/A/yr

Chlorimuron

- ethyl 0.080 lbs/A/yr

Chlorsulfuron 0.14 lbs/A x ?/yr B

Flazasulfuron 0.15 lbs/A/yr

Foramsulfuron 0.052 lbs/A x ?/yr B

Halosulfuron

- methyl 0.125 lbs/A/yr

Imazosulfuron 0.66 lbs/A x 2/ yr A

Iodosulfuron

- methyl

- Na 0.009 lbs/A/yr

Mesosulfuron

- methyl 0.013 lbs/A x ?/yr B

Metsulfuron

- methyl 0.15 lbs/A x ?/yr B

Nicosulfuron 0.070 lbs/A x ?/yr B

Orthosulfamuron 0.067 lbs/A/yr

Primisulfuron

- methyl 0.036 lbs/A x ?/yr B

Prosulfuron 0.036 lbs/A x ?/yr B

Rimsulfuron 0.0625 lbs/A x ?/yr B

Sulfometuron

- methyl 0.375 lbs/A x 1/yr

Sulfosulfuron 0.125 lbs/A/yr

Thifensulfuron

- methyl 0.031 lbs/A/yr

Triasulfuron 0.039 lbs/A/yr

Tribenuron

- methyl 0.031 lbs/A x 1/yr
Trifloxysulfuron

- Na 0.080 lbs/A/yr

Triflusulfuron

- methyl 0.078 lbs/A/yr

A The highest maximum rate pattern is bolded and in red.

B Question marks indicate application rate patterns for which maximum annual application rates and maximum numbers of applications per year are not stated on the label.



### 3. Environmental Fate Characterization

Sulfonylurea s tend to be anions. Therefore, the compounds tend to be hydrophilic and do not bioaccumulate in the environment. Water solubility limits range from 26 (trifloxysulfuron) to 3,180,000 mg/L (chlorsulfuron). The highest available whole fish bioconcentration fact or (BCF) is 3.0x (tribenuron

- methyl).

Based on the soil mobility data presented in Table 5 .1 , the SU s as a class may be characterized as “mobile” to “moderately mobile” on the FAO scale (USEPA, 2006) . This

means they will have some tendency for leaching into ground water and for transport aw ay from the site of application diss olved in runoff.

Aerobic soil metabolism (ASM) half

- lives for the SUs indicate a wide range of stability to metabolism by soil microbes, ranging from 3.6 days ( shortest half

- life fo r iodosulfuron

methyl ) to 240 days (longest half

- life for metsulfuron

- methyl) . Bensulfuron

- methyl and
chlorsulfuron are assumed stable to ASM in the absence of acceptable data

. Iodosulfuron

- methyl

### 6 degrades with a half

- life of 3.6

- 51 days to a nother SU, m etsulfuron

- methyl, that degrades slower
with a half

- life of 26

- 240 days . Thus, SU half

- lives for ASM range from several days up to many months , for the same compound in some cases

.

Aerobic aquatic metabolism (AAM) half

- lives for the SUs indicate a wide range of stability to metabolism by aquatic microbes, similar to ASM half

- lives, ranging from 9.1 days (shortest half

- life for triflusulfuron

- methyl) to 187 days (longest half

- life for sulfometuron

methyl)

. Bensulfuron

- methyl a nd chlorsulfuron are assumed stable to AAM in the absence of acceptable data.

Aquatic photolysis i s not a significant degradation process for the SUs

, except for a few SUs whose photolysis half

- lives were on the order of a few days ( flazasulfuron, imazo sulfuron, sulfosulfuron, and thifensulfuron

- methyl).

Overall, the data for the SUs indicate that their mobility and stability to degradation are
conducive to leaching into ground water and off

- site transport via runoff, resulting in the
contamination of water resources.

4. Residues of Concern

The drinking water residues of concern (ROC) are clearly defined for eight SU s (see
Table 4 .1 ). For the 14 remaining SUs, the ROCs are unclear for a variety of reasons, e.g. , studies with new degradates may have been submitted after the ROCs were determined or the ROCs may not have been clearly determined in past assessments. The drinking water ROCs are irrelevant in this assessment, however, because the SUs are treated as completely stable to degradation in the scre ening approach used. Therefore, there was no need to clarify for this assessment the drinking water ROCs for any SUs.

Table 4 .1. Status of SU Drinking Water Residues of Concern (ROC)

Pesticide DW ROCs Citation/Rationale SUs with Clearly Defined ROCs

Chlorimuron

- ethyl Demethylated parent Only deg with SU group ( DP 358796, 2009 HHRA)

Flazasulfuron DTPU, DTPP, HTPP, TPSA, ADMP, and GTF (all major degs) ROCKS decision (DP 386767)

Imazosulfuron HMS, IPSN, ADPM, UDPM, and SDPM DEREK flags (DP 377141)

Mes osulfuron

- methyl AE F154851, AE F160459, AE F160460 2004 MARC decision (DP 298760+)

Nicosulfuron IN

- 37740, IN

- HYY21 DP 414505 (DWA) (1 new study w/ no new degradates)

Orthosulfamuron DBS acid, DOP urea, DB amine, o

desmethyl orthosulfamuron HHRA (DP 319264 )

Tribenuron

- methyl None SU deg radate s not major or not prominent (USEPA 2009

- DEA )

Trifloxysulfuron

- Na CGA

- 053052, CGA

- 382997, CGA

368732 2003 MARC decision (DP 293085 )

### 7 Pesticide DW ROCs Citation/Rationale
SUs with Unclear ROCs
Bensulfuron

- methyl

Unclear -- Chlorsulfuron

-- Foramsulfuron

-- Halosulfuron

- methyl

-- Iodosulfuron

- methyl

- Na

-- Metsulfuron

- methyl

-- Primisulfuron

- methyl

-- Prosulfuron

-- Rimsulfuron

-- Sulfometuron

- methyl

-- Sulfosulfuron

--

Thifensulfuron

- methyl 2004 MARC included IN

- L9226

- but 2 new SU deg radate s ID'ed since
Triasulfuron

-- Triflusulfuron

- methyl

--



### 5. Exposure Modeling

5.1. Ground Water ( PRZM

- GW )

Screening ground water

- sourced drinking water exposure estimates were generated with
PRZM

- GW (v.1.07) for use in the SU dietary risk assessments in support of human health assessment. Rather than produce chemical

- specific EDWCs following the usual assessment procedures a tiered approach was used in this assessment beginning with coarse
- screen
est imates that should exceed upper

- bound chemical

- specific EDWCs for all SU s . This was achieved by using model inputs that represent the use pattern of highest potential exposure from any SU, the highest soil mobility of any SU residue of concern, and stabil ity to degradation over time. The resulting highest coarse

- screen EDWC s from PRZM

- GW were proposed in all SU dietary risk assessments as a conservative estimate of exposure. Due to the screening nature of this assessment, EFED does not expect that the EDWCs reflect actual potential exposures. However, i f the resulting dietary exposure was not of concern, then exposure modeling refinements, including chemical

- specific modeling , were unnecessary. If the resulting dietary exposure was of concern, then simple chemical

- specific refinements were made to generate
lower refined

- screen EDWCs that remained conservative for the chemical ( i.e. , the refined

screen EDWCs are still coarse, but a step more refined than the coarse

- screen EDWCs). Due to the conservative nature of these screens, the EDWCs presented in this assessment are not expect ed to occur in drinking water.

5.1.1. Coarse Screen

For the coarse screen, the application rate pattern of highest expected exposure ( i.e.

, maximum rate pattern) of any SU was modeled with PRZM

- GW to produce coarse

- screen EDWCs. The maximum application rate pattern for each SU is summarized above in Table 2 .2

. Many current labels do not provide maximum an nual application rate limits, resulting in uncertainty in the maximum rate pattern for the individual SU in the product. Despite this uncertainty, the maximum rate pattern from all SUs appears to be for imazosulfuron use on turf (0.66 lbs/A x 2 applicatio ns/year).

### 8 The lowest sorption coefficients for any SU, considering the available data for residues of concern, were used as model inputs for PRZM

- GW (representing orthosulfamuron’s degradate DBS acid and primisulfuron

- methyl). Table 5

. 1 lists the SU

- spec ific mean sorption coefficients
for the residues of concern. K d 

### or K F 

### was used when the coefficient of variation (CV) for the parameter was less than the CV for K OC 

### or K FOC 

### . Otherwise, K OC 

### or K FOC 

### was used. Freundlich parameters were used when available and when less than similar non

- Freundlich parameters, if available. The representative compound was the residue of concern with the lowest mean sorption coefficient if sorption coefficient data were available. Therefore, the parent compound was the repr esentative compound for one of three reasons: 1) the mean sorption coefficient for the parent compound was less than that for the degradates of concern, 2) data were not available for degradates of concern, or 3) there were no degradates of concern.

Table 5

. 1

. Sulfonylurea Mean Sorption Coefficients for Residues of Concern A

Sulfonylurea Mean K d or K F Mean K OC or K F OC Representative Compound Source

Bensulfuron

- methyl K OC =315 P arent compound Acc# 73657

Chlorimuron

- ethyl K OC =91 P arent compound MRID 143120

Chlorsulfuron K F OC =21 P arent compound MRID 42156705

Flazasulfuron K OC =29 TPSA MRID 4 6930001, 49030002 (in review )

Foramsulfuron K F OC =78 P arent compound MRID 45109723

Halosulfuron

- methyl K F OC =109 P arent compound MRID 42139411

Imazosulfuron K OC =242 P arent compound MRID 47305117

Iodosulfuron

- methyl

- Na K F OC =21 Metsulfuron MRID 49154301

Mesosulfuron

- methyl K F OC =78 AE F154851 MRID 45386433

Metsulfuron

- methyl K F OC =21 Metsulfuron MRID 49154301 (in review )

Nicosulfuron K OC =35 P arent compound MRID 40924222

Orthosulfamuron K F =0.11 DBS acid MRID 49308108 (in review )

Primisulfuron

- methyl K FOC = 12 P arent compound MRID 41869304

Prosulfuron K F =0.22 P arent compound MRID 42685257

Rimsulfuron K F OC =47 P arent compound MRID 41356336

Sulfometuron

- methyl K F OC =63 P arent compound MRID 42789301

Sulfosulfuron K F =0.29 P arent compound MRID 44295728

Thifensulfuron

- methyl K F OC =28 P arent compound MRID 161290

Triasulfuron K F =0.34 CGA

- 195660 MRID 42782002

Tribenuron

- methyl K F OC =31 P arent compound MRID 46101501
Trifloxysulfuron

- Na K F =0.26 CGA

- 382997 MRID 45371821

Triflusulfuron

- methyl K F =0.64 P arent compound MRID 42496861

A The lowest mean sorption coefficient inputs are bolded and in red.



### The PRZM

- GW inputs for the coarse

- screen EDWCs are listed in Table 5

. 2 . Application inputs represent the maximum rate pattern for imazosulfuron, which is the highest of any SU

### 9 (two applications per year at 0.66 lbs/acre, with a 21

- day reapplication interval )

. The initial application date (7 days since emergence) is a post

- emergence date within the application season. Alternative initial application dates of 37 and 67 days post

- emergence were also explored with
the North Carolina scenario.

Chemical inputs ( i.e. , sorption coefficients) for the sulfonylurea residues of concern
follow the PRZM

- GW Input Parameter Guidance (USEPA, 2012). The chemicals were modeled as stable to degradation (hydrolysis and aerobic soil metabolism) as part of the coarse

- screen approach

. Sorption coefficients reflect the highest soil mobility of any SU residue of concern,
consistent with the coarse

- screen approach.

Table 5

. 2 . PRZM

- GW Input Parameters for Sulfonylurea Coarse

- Screen EDWCs
Input Parameter Value Justification Source

Application Rate (kg a.i./ha) 0.74 Maximum labeled single application
rate for use of imazosulfuron on turf (see Table 2 .2 ) EPA Reg. No.
59639

- 155 (Mar. 29, 2011) Applications per Year 2; every year

Reapplication Interval (days) 21 Minimum labeled interval

Initial Application Date (days since emergence) 7 Post

- emergence application date (calculated)

Chemical Application
Method 2 Foliar application EPA Reg. No.
59639

- 155
Hydrolysis Half

- life (days) 0 Stability was modeled as a screen Screening assumption

Surface Soil Half

- life (days) 0 Stability was modeled as a screen Screening assumption

Sorption Coefficient (ml/g) K d = 0.11 or
K OC =12 Represent the lowest mean K d and
K FOC values for sulfonylurea
residues of concern in Table 5

. 1 MRID 49308108 (in
review ); MRID
41869304



### All six standard scenarios were modeled as surrogates for the use site (turf) with maximum app lication rates. PRZM

- GW outputs are listed in Table 5

. 3

. The K OC 

### of 12 produced shorter mean breakthrough times than the K d 

### of 0.11. Coarse

- screen EDWCs were higher with the K OC 

### input as well, with two exceptions. The North Carolina scenario produced the highest daily and post

- breakthrough mean EDWCs . The highest daily concentration was produced with the K OC 

### input and the 3 7

- days post

- emergence initial application date. The highest post

- breakthrough mean concentration was produced with the K d 

### input and the 7

- day s post

- emergence initial application date. The initial application date input was not as sensitive as the sorptio n coefficient, which is expected due to the assumptions that the residues are stable and are not allowed (by the PRZM

- GW conceptual model) to run

- off, leaving them available for leaching whenever precipitation or irrigation events occur

.

### 10 Table 5

. 3 . PRZM

- G W Coarse

- Screen EDWCs for Sulfonylureas A

Modeled Scenario K d or K OC Initial Application Dates (days post

emergence) Max. Daily Conc. (μg/L) Mean Breakthrough

Time (yrs) Post

breakthrough Mean (μg/L)

Wisconsin ( WI )

corn K d 7 449 11.5 415

K OC 7 504 6.9 425

Delmarva ( DMV )

corn K d 7 489 5.3 369

K OC 7 560 3.3 378

Florida ( FL ) citrus K d 7 429 3.2 351

K OC 7 467 2.3 349

Florida ( FL ) potato K d 7 375 2.6 272

K OC 7 407 2.2 275
Georgia ( GA ) peanut K d 7 197 5.2 156

K OC 7 206 3.9 158

North Carolina

( NC ) cotton K d 7 640 8.7 492

K d 37 641 8.7 491

K d 67 637 8.7 490

K OC 7 742 5.7 484

K OC 37 751 5.7 483

K OC 67 744 5.7 482

A Maximum values are bold ed.



### Figure 5 .1 displays ground water concentrations over time for the North Carolina
scenario with the K d 

### input and the 7

- days post

- emergence initial application date.

Figure 5 .1 Sulfonylurea Coarse

- screen Ground Water EDWCs (μg/L) per Time (years) for
the North Carolina Scenario , K d 

### of 0.11, and 7

- days post

- emergence initial application date

### 11 5.1.2. Refined Screen

Refined

- screen exposure estimates were generated for 8 sulfonylureas (chlorsulfuron,
halosulfuron

- methyl, nicosulfuron, prosulfuron, rimsulfuron, triasulfuron, tribenuron

- methyl, and
triflusulfuron

- methyl) for which the coarse

- screen EDWCs ( i.e. , a cute EDWC of 751 μg/L and chronic EDWC of 492 μg/L) were problematic. The PRZM

- GW inputs for refined

- screen EDWCs are listed in Table 5

. 4 . Application inputs represent the maximum application rate pattern for the chemical, considering the maximum single application rate first, then the maximum seasonal application rate, using national

- scale upper

- bound usage rates provided by BEAD if the labels do not provide a maximum seasonal rate

. The modeled sorption coefficient
is also chemical

- specific. All other inputs, including the screening assumptions of stability to degradation and application every year, remained the same as for the coarse screen.

Table 5

. 4 . PRZM

- GW Input Parameters for Sulfonylurea Refined

- Screen EDWCs

Sulfonylurea (Use) App. Rate (kg a.i. /ha) App.

per Year Reapp.
Interval

(days) Initial App

. Date (days
since emergence) App.
Method Hydrolysis
and Surface
Soil Half

- life (days) Sorption
Coefficient (ml/g)

Chlorsulfuron (non

- ag areas) 0.157 1 N/A

7 2 0 K OC =21

Halosulfuron

- methyl (fallow) 0.157 1 A N/A K OC =109 Nicosulfuron (rights

- of

- way) 0.078 1 N/A K OC =35 Prosulfuron (corn) 0.040 1 N/A K d =0.22 Rimsulfuron (commercial areas) 0.071 3 B 7 C K OC =47 Triasulfuron (rangeland) 0.031 2 D 7 C K d =0.34

Tribenuron

- methyl (soybeans) 0.035 2 E 7 C K OC =31

Triflusulfuron

- methyl (sugarbeet) 0.035 3 F 7 C K d =0.64 A One application per year was assumed in the absence of label directions based on national

- scale usage data
collect ed by BEAD indicating halosulfuron

- methyl was not applied more than once to 27,303 acres of fallow land. B Three applications per year were assumed in the absence of label directions , based on national

- scale usage data collected by BEAD indicating that rimsulfuron was not applied more than three times pe r year to any crop

. C A 7

- day reapplication interval was assumed in the absence of label directions , based on the assumption that herbicides are not applied more often, giving time to evaluate the impact of the previous application before the next

. D The 2 nd application is at 0.013 kg a.i./ha to reach the seasonal maximum rate of 0.039 lbs a.i./A. E Two applications per year were assumed in the absence of label directions based on usage data provided by BEAD
that indicates tribenuron

- methyl was never applie d more than twice to 4,831,149 acres of soybeans. F The 2nd and 3rd applications are at 0.026 kg a.i./ha each to reach the seasonal maximum rate of 0.078 lbs a.i./A.



### All six standard scenarios were modeled as surrogates for the use sites listed in Table
5

. 4

. PRZM

- GW outputs for the most vulnerable scenario are listed in Table 5

. 5 . The North Carolina scenario produced the highest daily and post

- breakthrough mean EDWCs for each modeled use pattern except that for triflusulfuron

- methyl on sugarbeets, for wh ich the Florida citrus scenario provided the highest EDWCs. Additional EDWC refinements were not pursued
because the refined

- screen EDWCs were found by the Health Effects Division not to be a risk

concern

.

### 12 Table 5

. 5 . PRZM

- G W Refined

- Screen EDWCs for Sulf onylureas

Sulfonylurea (Use) PRZM

- GW
Scenario Max. Daily Conc. (μg/L) Post

- breakthrough Mean (μg/L) Mean Breakthrough Time (yrs)
Chlorsulfuron (non

- ag areas) NC cotton 78 52 5.9

Halosulfuron

- methyl (fallow) NC cotton 74 53 8.1

Nicosulfuron (rights

- of

- way) NC cotton 39 26 6.2
Prosulfuron (corn) NC cotton 15 13 12
Rimsulfuron (commercial areas) NC cotton 105 71 6.5
Triasulfuron (rangeland) NC cotton 21 19 16

Tribenuron

- methyl (corn) NC cotton 35 23 6.1

Triflusulfuron

- methyl (sugarbeet) FL citrus 23 20 9.5



### 5.2. Surface Water ( FIRST )

5.2.1. Coarse Screen

Screening surface water

- sourced drinking water exposure estimates were generated with
FIRST (v.1.1.1) to confirm that estimated exposure to SUs via surface water sources is less than that via ground water sources. Rather than produce chemical

- specific EDWCs

, a coarse

- screen estimation approach was used that should exceed upper

- bound chemical

- spe cific EDWCs for all
SUs

, similar to the coarse

- screen assessment approach used for ground water exposure . This was achieved by using model inputs that represent the use pattern of highest exposure from any SU, the highest soil mobility of any SU residue o f concern, and stability to any r oute of degradation
over time.

The FIRST inputs for the coarse

- screen EDWCs are listed in Table 5 .6

. Application inputs represent the maximum rate pattern for imazosulfuron, which is the highest of any SU (two application s per year at 0.66 lbs/acre, with a 21

- day reapplication interval )

. A conservative Percent Cropped Area (PCA) of 100% was used. Chemical inputs ( i.e. , sorption coefficients) for
the SU ROCs were prepared follow ing the Water Models Input Parameter Guidance (USEPA,
2009 ). The chemicals were modeled as stable to degradation (hydrolysis, photolysis, and metabolism processes) as part of the coarse

- screen approach

. Sorption coefficients reflect the highest soil mobility of any SU residue of concern, consistent with the coarse

- screen approach.

Table 5

. 6

. FIRST Input Parameters for Sulfonylurea Coarse

- Screen EDWCs
Input Parameter Value Justification Source

Application Rate (lbs a.i./ A ) 0 .66 Maximum labeled single application
rate for use of imazosulfuron on turf (see T able 2 .2 ) EPA Reg. No.
59639

- 155 (Mar. 29, 2011) Applications per Year 2

Reapplication Interval (days) 21 Minimum labeled interval

PCA Decimal 1.0 Conservative value for screen Screening assumption

K d or K OC value (L/kg) K d =0.11 or
K OC =12 Represent the lowest mean K d and
K FOC values for sulfonylurea
residues of concern in Table 5

. 1 MRID 49308108 (in
review ); MRID
41869304
Method of Application Aerial Conservative value for screen Screening assumption

### 13 Input Parameter Value Justification Source

Solubility (ppm) 26 Lowest SU value (input is well above and does not impact EDWCs) MRID 45371702

Aerobic Soil Metabolism
Half

- life (days) 0 Stability was modeled as a screen Screening assumption

Aerobic Aquatic Metabolism
Half

- life (days) 0 Stability was modeled as a screen Screening assumption

Hydrolysis Half

- life (days) 0 Stability was modeled as a screen Screening assumption

Phot olysis Half

- life (days) 0 Stability was modeled as a screen Screening assumption



### The resulting coarse

- screen EDWC s from FIRST using a K d 

### o f 0.11 were 13 8 μg/L (1

- in

- 10

- year peak used for acute exposure ) and 9 8 μg/L (1

- in

- 10

- year annual mean used for chronic exposure)

. Respective EDWCs using a K OC 

### of 12 were slightly less, at 137 μg/L and 97 μg/L. These values (using either K d 

### or K OC 

### ) are 18

- 20 % of the c oarse

- screen ground water EDWCs, indicating that the coarse

- screen ground water exposure assessment is prote ctive of surface water exposure for SU s with dietary exposure not of concern at the coarse screen.

5.2.2. Refined Screen

Screening surface water EDWCs were generated with FIRST (v.1.1.1) for the 8 SUs for
which refined

- screen ground water EDWCs were generated, in order to further confirm that
estim ated exposure to SUs via surface water sources is less than that via ground water sources.
The same s imple che mical

- specific refinements as were made for ground water assessment were
made for surface water assessment to generate lower refined

- screen EDWCs that remained
conservative for the chemical (see Table 5 .7 )

. Application inputs represent the maximum application rate pattern for the chemical, considering the maximum single application rate first, then the maximum seasonal application rate, using national

- scale upper

- bound usage data provided by BEAD if the labels do not provide a maximum seasonal rate

. The modeled sorption
coefficient is also chemical

- specific. All other inputs, including the screening assumption of stability to degradation, rem ained the same as for the coarse screen.

Table 5.7

. FIRST Input Parameters for Sulfonylurea Refined

- Screen EDWCs

Sulfonylurea (Use) App. Rate (lbs a.i./ A ) App.

per Year Reapp.
Interval

(days) Solubility (ppm) PCA
Decimal App.
Method Degradation
Half

- lives (days) Sorption
Coefficient (ml/g) Chlorsulfuron (non

- ag areas) 0.14 1 N/A

26 1.0 Aerial 0 K OC =21

Halosulfuron

- methyl (fallow) 0.14 1 A N/A K OC =109 Nicosulfuron (rights

- of

- way) 0.07 0 1 N/A K OC =35 Prosulfuron (corn) 0.036 1 N/A K d =0.22 Rimsulfuron (commercial areas) 0.063 3 B 7 C K OC =47 Triasulfuron (rangeland) 0.028 2 D 7 C K d =0.34

Tribenuron

- methyl (corn ) 0.031 2 E 7 C K OC =31

Triflusulfuron

- methyl (sugarbeet) 0.031 3 F 7 C K d =0.64 A One application per year was assumed in the absence of label directions based on national

- scale usage data provided by BEAD indicat ing halosulfuron

- methyl was not applied more than once to 27,303 acres of fallow land.
B Three applications per year were assumed in the absence of label directions, based on national

- scale usage data collected by BEAD indicating that rimsulfuron was not applied more than three times per year to any crop.

### 14 C A 7

- day reapplication interval was assumed in the absence of label directions, based on the ass umption that herbicides are not applied more often, giving time to evaluate the impact of the previous application before the next.
D The two applications (0.056 lbs a.i./A total) exceed the seasonal maximum rate of 0.039 lbs a.i./A because FIRST

cannot ac cept multiple application rate values

. E Two applications per year were assumed in the absence of label directions based on usage data provided by BEAD
that indicates tribenuron

- methyl was never applied more than twice to 4,831,149 acres of soybeans.
F The three applications (0.093 lbs a.i./A total) exceed the seasonal maximum rate of 0.078 lbs a.i./A because FIRST cannot accept multiple application rate values

.



### FIRST outputs are listed in Table 5 .8

. As expected, acute and chronic surface water
EDWCs are less than respective ground water EDWCs for each SU. Therefore, screening ground water exposure estimates rather than surface water exposure estimates are used to screen for exposure concerns in this assessment.

Table 5 .8

. FIRST Refined

- Screen EDWCs for Sulfonylureas

Sulfonylurea (Use) 1

- in

- 10

- year Peak (μg/L) 1

- in

- 10

- year Annual
Mean (μg/L)
Chlorsulfuron (non

- ag areas) 14 10

Halosulfuron

- methyl (fallow) 13 7.2
Nicosulfuron (rights

- of

- way) 7.0 4.7
Prosulfuron (corn) 3.7 2.6

Rimsulfuron (commercial areas) 19 12
Triasulfuron (rangeland) 5.7 3.9

Tribenuron

- methyl (corn) 6.2 4.2

Triflusulfuron

- methyl (sugarbeet) 9.0 5.8



### 6. Exposure Summary

T able 6

. 1 summarizes the maximum coarse

- screen and refined

- screen exp osure model
results for the sulfonylureas , which are not expected to occur in drinking water due to the
conservative nature of these screens. Monitoring data were not collected for this assessment because of its screening approach that is not meant to estimate actual exposures at drinking water
intake facilities.

Table 6.1

. Coarse

- and Refined

- Screen Maximum EDWCs for Sulfonylureas

Sulfonylurea (Use) PRZM

- GW
Scenario Screen
Level Max. Daily Conc. (μg/L) Post

breakthrough Mean (μg/L) Mean Breakthrough

Time (yrs)

Chlorsulfuron (non

- ag areas) NC cotton Refined 78 52 5.9

Halosulfuron

- methyl (fallow) NC cotton Refined 74 53 8.1
Nicosulfuron (rights

- of

- way) NC cotton Refined 39 26 6.2
Prosulfuron (corn) NC cotton Refined 15 13 12
Rimsulfuron (commercial areas) NC cotton Refined 105 71 6.5
Triasulfuron (rangeland) NC cotton Refined 21 19 16

Tribenuron

- methyl (corn) NC cotton Refined 35 23 6.1

Triflusulfuron

- methyl (sugarbeet) FL citrus Refined 23 20 9.5
All other sulfonylureas NC cotton Coarse 751 492 5.7

- 8.7

### 15 7. References

USEPA. 2006. Standardized Soil Mobility Classification Guidance. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Internal memorandum. Apr. 21, 2006.

USEPA. 2009. Guidance for Selecting Input P arameters 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. http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

USEPA. 2012. Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model. Version 1.0. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects
D ivision; Health Canada, Pesticide Management Regulatory Agency, Environmental Assessment Directorate. Oct. 15, 2012.

Appendix A. Aquatic Model Calculations

Aquatic model input and output files are contained in the attached WinZip file.

Appendix B. Environmental Fate Data

In support of this assessment, environmental fate data regarding the sulfonylureas and their degradates were collected from the problem formulations for registration review and, in some cases, directly from studies submitted to EPA . The data are tabulated in the attached
Microsoft Excel workbook.

SU PRA Fate Data FINAL.xls



### Appendix C. Chemical Structures

In support of this assessment, the chemical structures of the sulfonylureas and their degradates were collected from the problem formulations for registration review and from studies submitted to EPA after the problem formulations were prepared. The data are tabulated
in the attached Microsoft Word document.

SU PRA Chemical

Structures.doc