2

use on alfalfa and pomegranate

. It is important to note that the modeled total residues of concern of saflufenacil included saflufenacil paren t, M01, M02, M07, M08, M15, M22, and Product 8, all of which are assumed to have similar toxicity to saflufenacil parent.

It is also noted that the results obtained from this assessment for crops other than rice are as

follows:

(1) For surface water EDWCs :

a. From use on pomegranate: 17.9 ppb acute and 10.9 ppb chronic ( Tier I FIRST modeling); and

b. From use on all other crops including the new use on alfalfa : 11.9 ppb acute and 7.4 ppb

chronic ( Tier I FIRST modeling

, Attachment 1 : DP Barcode: 413592 dated August 12,

2013 ) ; and

(2) For ground water EDWCs ( from use in all crops including new uses on alfalfa and

pomegranate ) : 94.6 ppb acute and 63.1 ppb chronic ( current 1.07 version of PRZM

- GW modeling using current NCCOASTAL_STD , this assessment ) increasing from 69.2 ppb

acute and 51.5 ppb chronic ( old version of PRZM

- GW modeling using old
WISANDS_STD scenario

, Attachment 1 : DP Barcode: 413592 dated August 12, 2013 ).

This increase in EDWCs is due to the PRZM

- GW model version/scenario changes in

addition to the higher a pplication rate suggested for pomegranate (a total of 0.175 lb a.i/A for pomegranate compared to the previous maximum rate of 0. 134 lb a.i/A for all other crops including rice).

Results stated in (1) and (2) above indicates that the previously obtained surface water EDWCs ( 133.1 ppb for acute and 120.4 ppb for chronic ) resulting from use on dry

- seeded rice represent

upper

- bound estimates of total concentrations that might be found in surface water . Ground

water EDWCs ( 94.6 ppb acute and 63.1 ppb chronic ) represent upper

- bound estimates of total concentrations that might be found in ground water due to the use of saflufenacil as a herbicide

on the current

/proposed use patterns. If more information or refinement is needed, please call

Mohammed A. Ruhman at (703) 605

- 0644 or email: ruhman.mohammed@epa.gov



### I. BACKGROUND

F ive drinking water exposure assessments were conducted :

The 1 st Assessment: A surface/ground drinking water exposure assessment for s ection 3 new chemical uses on agricultural and non

- agricultural areas ( DP Barcode: 349860 dated April 15,

2009 ): This assessment reported the modeled EDWCs for the stressor (i.e., residues of concern) in drinking water resulting labeled uses at that time

. This asse ssment was based on labeled uses on Christmas trees; citrus; conifer and hardwood plantations; c orn (field, sw eet, and pop); cotton,

f allow and post

- harvest applications; grape vines; legume vegetables; non

- agricultural areas; pome fruits; small grains; so rghum; soybeans and s unflower . The maximum label rate consisting

from a single application rate of 0.356 lb a.i/A for use on Christmas trees; citrus; conifer and hardwood plantations; and non

- agricultural areas. Tier 1 FIRST modeling for surface water and3

older version of PRZM

- GW for ground water were used . In this respect it is noted that input parameters for the current PRZM

- GW were changed following this assessment

.

The 2 nd Assessment : A surface d rinking water exposure assessment for section 3 new chem ical

use on rice “Pre

- plant burn

- down” ( DP Barcode: 384975 dated March, 03, 2011 )

. This

assessment was based o n pre

- plant/pre

- flood use on rice at a rate of 0.0445 lb a.i/A with specific

use restrictions. Tier 1 Rice Model (ver. 2) was used in modeling which allows aerobic soil degradation of the pre

- flood applied chemical in addition to partitioning and degradation in the rice paddy for the left over chemical residues.

The 3 rd Assessment: A Tier II Drinking Water Exposure Assessment for Saflufenacil ( Section 3 New Chemical Uses as a harvest aid on dry edible beans, dry peas, soybean, oilseeds “sunflower subgroup 20B”, oilseeds “cotton subgroup 20C”, and oilseeds canola “subgroup 20A” ( DP

Barcodes: 380641 and 381294 dated April 1, 2011)

.

The 4 th Asses sment (

Attached) : A surface drinking water exposure assessment for the proposed

new use pattern on r ice (EPA Reg. No. 7969

- 278) and the new master label for saflufenacil formulations (EPA R eg. No. 7969

- 323 ( DP Barcode: 413592 dated August 12, 2013 )

. This

assessment was b ased on these two labels which included the following changes :

(1) A maximum application rate for all crops, including rice, is 0.134 lb a.i/A instead of the previous maximum rate of 0.356 lb a.i/A ;

(2) T he aerobic soil half

- life and partitioning coefficient (K
oc ) were entered as per guidance to

the current version of PRZM

- GW (refer to referenced document for these changes)

(3) New c rop

- specific use restrictions/limitations for rice (refer to referen ced document for these changes).

The 5 th Assessment : Drinking Water Exposure Assessment for Saflufenacil: New Chemical Use pattern on Barley, Wheat and Triticale; Perennial forage grasses (grown in pastures and range land or in field grown for forage, silage and hay; and on Olive Trees ( DP Barcode 414007

, 414474 & 417504 dated May 16, 2014).4



### II. CURRENT ASSESSMENT

This current assessment is for the new use patterns on alfalfa and pomegranate trees . Important application parameters for the new use label s are summarized in Table 1

.

Table 1 New us e pattern for saflufenacil herbicide on alfalfa

, mixed Stands of alfalfa and cool

season forage grasses , and pomegranate trees for broadleaf weed control ( MSR= Maximum single application rate in lbs a.i/A; MNOA= Maximum number of applications; MS = Maximum seasonal application rate in lbs a.i/A;

and MAI= Minimum application intervals in days ; Note: Application procedure is not stated in the label but assumed to be ground and aerial)

Application Types /Purpose MSR MNOA MS MAI Notes

Alfalfa: Broad leaf weed control in season (crop planted in Fall or Spring) after 1 st cutting : One application OR

Alfalfa: Broad leaf weed control in dormant

season (Fall/Winter): One OR Two sequential application 0.0223 One 0.0 223

N/A Sharpen ® ; PA Reg. No. 7969

- 278 label for in season (between cutting)

0.0223 One 0.0 223 Sharpen ® ; PA Reg. No. 7969

- 278 label for dormant season 0.0223 Two 0.04 46 14

Mixed alfalfa and cool season grasses: in

season and dormant

- season applications 0.0223 One 0.0 223

Refer to

next
column Sharpen ® : O ne application in

the spring plus two applications in fall or winter 14 days apart 0.0223 One 0.0 223

0.0223 One 0.0 223 Pomegranate trees: Post

- emergence directed

Broad leaf weed control : (a) T ree b loom to har vest
OR (b) P ost

- harvest to tree bloom (dormant

T rees) Plus

Tree bloom to harvest 0.0438 Three 0.1313 21 Treevix ® : From one to four applications. Four applications can only be added if one or two of the applications were applied during the tree dormant period. 0.0438 Two

0.175 21

0.0438 Two 21

1 N/A= Not applicable (only one application)

II.1

. Surface Water Modeling

Tier 1 FIRST modeling is to be used to calculate surface EDWCs because previous assessments were based on this type of modeling. Data for the new use patterns ( Table 1 ) indicate that the

maximum total application rate s needed for Tier 1 FIRST modeling are as follows:

(1) for alfalfa: 0.066 9 lbs a.i/A ( 1+2= 3 application s at 0.0223 lbs a.i/A each at 14

- day intervals); and

(2) For pomegranate: 0.175 lbs a.i/A (4 applications at 0.0438 lbs a.i/A each: two during the growing period and two during the dormant period at 21

- day int ervals).

In case of the new use on alfalfa, the total maximum application rate is 0.066 lbs a.i/A which is almost half of the rate used in previous Tier 1 FIRST surface water modeling. Therefore,

surface water EDWCs for the new alfalfa use will be much l ower than that o btained in the attached EFED assessment which was based on an application rate of 0.132 lbs ( Attachment 1

,5

DP Barcode: 413592 dated August 12, 2013) . Therefore, surface water EDWCs reported earlier

can cover the use on alfalfa and mixed stands of alfalfa and cool

- season forage grasses.

In case of t he new use on pomegranate , the total maximum application rate is 0.175 lbs a.i/A

which is higher than before ( 0.175 lbs a.i/A )

. Therefore, a new Tier 1 FIRST modeling is

needed for the use on pomegranate . A Tier 1 FIRST model run was executed using the high

pomegranate application rate with the same parameters in the previous DW assessment (refer to

Table 5 in Attachment 1 ) . The application rate, used in this modeling run, was 0.044 lbs a.i/A in four applications for a total of 0.175 lbs a.i/A/year with 21

- day application intervals ) . The results, of this modeling run, suggest that use on pomegranate is expected to cause higher surface water exposure EDWCs compa red to all other crops, except rice. These results were: 17.9 ppb

acute EDWC and 10.9 ppb chroni c EDWC

.

II.2

. Ground Water Modeling

The new maximum use rate on pomegranate (a total of 0.175 lb a.i/A ) is higher than the previous

maximum rate of 0. 134 lb a.i/A for all other crops. Additionally, there were changes in PRZM

GW model version/scenario. Therefore, new modeling runs w ere executed for:

(1) The previous maximum rate 0.1 34 lb a.i/A to arrive at ground water EDWCs for all other crops (including the rice and new use on alfalfa); and

(2) The new maximum rate 0.175 lb a.i/A on pomegranate to arrive at ground water EDWCs for this crop; and

Two batch runs were executed for all scenarios: one for the use on all crops, except

pomegranate and the others for po megranate. The results obtained for the first run are

summarized in Table 2 while those for the second run are summarized in Table 3

.

T able 2 Modeled EDWCs resulting from use on all crops, except pomegranate

Scenario Highest Daily

Value (ppb) Post Breakthrough

Average (ppb) Overall Sim ulation

Av erage (ppb) Average Breakthrough

Time in Days ( Years )

NCCOASTAL_STD.SCN 73.1 48.5 38.6 2,175 (6.0)

DELMARVA_STD.SCN 54.4 38.4 32.1 1

, 358 (3.7)

WISANDS_STD.SCN 49.2 42.5 32.6 2 693 (1.9)

FLCITRUS_STD.SCN 45.2 35.2 32.4 957 (2.6)

FLPOTATO_STD.SCN 37.4 27 24.4 1

, 064 (2.9)

GACOASTAL_STD.SCN 20.1 15.8 13.7 1 ,611 (4.4)6

Table 3 Modeled EDWCs resulting from use on pomegranate

Scenario Highest Daily

Value (ppb) Post Breakthrough

Average (ppb) Overall Sim ulation

Av erage (ppb) Average Breakthrough

Time in Days (Years)

NCCOASTAL_STD.SCN 94.6 63.1 50 2,175 (6.0)

DELMARVA_STD.SCN 69 49.8 41.5 1

, 358 (3.7)

WISANDS_STD.SCN 63 53.9 41 2,693 ( 7.4 )

FLCITRUS_STD.SCN 59.5 45.7 41.8 957 (2.6)

FLPOTATO_STD.SCN 49.5 35.2 31.6 1

, 064 (2.9)

GACOASTAL_STD.SCN 25.6 20.5 17.8 1 ,611 (4.4)

Data in Tables 2 and 3 indicate that the maximum ground water EDWCs ( from use in all crops including new uses on alfalfa and pomegranate ) are 94.6 ppb acute and 63.1 ppb chronic (Table 3) and it also indicate that ground water EDWCs ( from use in all crops including new

uses on alfalfa and excluding the new use on pomegranate ) had changed from the previous DW

assessment to 73.1 ppb acute and 48.5 ppb chronic ( due t o the use of the current 1.07 version

of PRZM

- GW / scenarios )

.

Hereunder, is the results for the maximum EDWCs from running a single run using pomegranate application rate and the Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton s cenario :

Estimated ground water concentrations and breakthrough times for saflufenacil are presented in

Table 4 for the NC Eastern Coastal Plain

- Norfolk loamy sand

- Cotton groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1

. These values were generated with the PRZM

- GW (Version 1.07). Critical input values for the

model are summarized in Tables 5 and 6

.

Table 4

. Groundwater Results for saflufenacil and the NC Eastern Coastal Plain

- Norfolk loamy

sand

- Cotton Scenario.

Peak Concentration (ppb) 94.6

Post

- Breakthrough Mean Concentration (ppb) 63.1

Entire Simulation Mean Concentration (ppb) 50

Average Breakthrough Time (days) 2174.558

Throughputs 5.0401057

Table 5

. Chemical Properties for Groun dwater Modeling of saflufenacil

Koc (ml/g) 24 Surface Soil Half Life (days) 6833 Hydrolysis Half Life (days) 0

Diffusion Coefficent Air (cm2/day) 0.0 Henry's Constant 0.0 Enthalpy (kcal/mol) 0.0

Table 6

. Pesticide application scheme used for saflufenacil. This application scheme was appli ed every year of the simulation

Application Date (Month/Day) Application Method Application Rate (kg/ha)

04/15 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.0491

05/06 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.0491

11/15 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.0491

12/06 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.04918

Figure 1. Aquifer Breakthrough Curve for saflufenacil and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario

[

----------------------------- 30 Years

------------------------------- ]9 

### Attachment 1

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF PREVENTION, PESTICIDES, AND

TOXIC SUBSTANCES

PC Code: 118203

DP Barcode: 413592 August 12, 2013

MEMORANDUM

SUBJECT: Revised Drinking Water Exposure Assessment for Saflufenacil: New Chemical

Use pattern on Rice and Change in Label Application Rates for Other Crops.

TO: Bethany Benbow, Risk Manager Reviewer

Kathryn Montague, M.S., Risk Manager, Rm 23 Daniel Kenny, Branch Chief

Herbicide Branch Registration Division (RD) (7505P)

AND: George F. Kramer, Ph.D., Chemist

Charles Smith, Acting Branch Chief

Risk Assessment Branch I

Health Effects Division (7509P)

FROM: Mohammed Ruhman, Ph.D., Senior Agronomist

Environmental Risk Branch 5 Environmental Fate and Effects Division (7507P)

THROUGH: Mah Shamim, Ph.D., Branch Chief

Environmental Risk Branch 5

Environmental Fate and Effects Division (7507P)



### I. EXECUTIVE SUMMARY

This is a revision for previously calculated tier I screening level EDWCs for saflufenacil total toxic residues. The revision is necessary due to the proposed new use pattern on r ice (EPA Reg.

No. 7969

- 278) and the cha nges in label application rates for some uses (EPA R eg. No. 7969

- 323 ). These revised EDWCs may be used in support of human health risk assessment.

The revised highest maximum EDWCs are 13 3.1 ppb for acute and 12 0 .4 ppb for chronic resulting from use on dry

- seeded rice ( Tier I Rice m odeling)

.10

This conclusion is based on the following EDWC results: (4) For surface water : 13 3.1 ppb acute and 12 0.4 ppb chronic resulting from use on dry

seeded rice ( Tier I Rice modeling) and 11.9 ppb acute and 7.4 ppb chronic fr om application to crops other than rice ( Tier I FIRST modeling); and

(5) For ground water : 69.2 ppb acute and 51.5 ppb chronic ( PRZM

- GW modeling using WI SANDS scenario).

It is noted that the maximum of the previously calculated EDWCs was obtained from modeling using an older version of the current PRZM

- GW with input parameters that are different from

the current PRZM

- GW

. Table 1 contains a summar y of previous results notin g that reasons for the revision are detailed in section II (Background), below.

Table 1 Previously calculated 1

- in

- 10

- year EDWCs for the proposed saflufenacil uses contained

in EDWC Memo dated April, 15, 2009 (DP Barcode: 349860 )

Source (Tier: Model) Peak Exposure (μg/L) Annual Mean Exposure (μg/L)

Surface water (Tier I: FIRST) 37.3 23.8 Ground water (PRZM GW) 180 173

The above stated values represent upper

- bound estimates of total concentrations that might be

found in surface water and ground water due to the use of saflufenacil as a herbicide on the current/proposed use patterns. If more information or refinement is needed, please call Mohammed A. Ruhman at (703) 605

- 0644 or email: ruhman.mohammed@epa.gov



### II. BACKGROUND

Two drinking water exposure assessments were conducted :

(1) A surface/ground drinking water exposure assessment for s ection 3 new chemical uses on agricultural and non

- agricult ural areas ( Appendix 1 ): This assessment reported the modeled EDWCs for the stressor (i.e., residues of concern) in drinking water resulting labeled uses at
that time

. This assessment was based on the following:

a. Labeled uses : Christmas trees, Citrus, Conif er and hardwood plantations, Corn (field, sweet, and pop), Cotton, Fallow and post

- harvest, Grape vines, Legume vegetables, Non

agricultural areas, Pome fruits, Small grains, Sorghum, Soybeans and Sunflower;

b. F ive labels: BAS 800 04H (FiRoCrop: Saflufenaci l 29.74%); BAS 804 00H (LegVeg: Saflufenacil 17.80% + Imazethapyr 50.20%); BAS 781 02H (Saflufenacil 6.24% +

Dimethenamid

- P 55.04%); BAS 800 01H (TNV: Saflufenacil 70%); and BAS 800 02H (SharpenTM: Saflufenacil 12.27%);

c. A maximum label rate consisting from a single application rate of 0.356 lb a.i/A for use on Christmas tree, conifer, and hardwood plantat ions and non

- agricultural areas ( SharpenTM

label ) ; d. The maximum rate of 0.356 lb a.i/A used in all surface/ground water modeling; and

e. The stressor included parent compound and it ’ s degradates M800H01, M800H02, M800H07, M800H08, M800H15, M800H22 ; and11

f. Tier I FIRST modeling for surface water and older version of PRZM

- GW for ground water. In this respect it is noted that input parameters for the current PRZM

- GW a re different.

Reported EDWCs for this assessment is summarized in Table 2

.

Table 2 Previously calculated 1

- in

- 10

- year EDWCs for the proposed saflufenacil uses reported

in EDWC Memo dated April, 15, 2009 (DP Barcode: 349860, Appendix 1 )

Source (Tier: Mod

el) Peak Exposure (μg/L) Annual Mean Exposure (μg/L)

Surface water (Tier I: FIRST) 37.3 23.8 Ground water (Tier II: PRZM GW) 180 173

(2) A surface drinking water exposure a ssessment for section 3 new chemical use on rice “Pre

plant burn

- down” ( Appendix 2 ) This assessment was based on the following:

a. Labeled use : pre

- plant/pre

- flood use on rice only ; b. A suggested label amendment (Sharpen EPA Reg. No. 7969

- 278) ;

c. A maximum label rate consisting from single maximum application rate of 0.0445 lb a.i/A ; d. Crop

- specific use restrictions/limitations that include (1) DO NOT a pply after rice planting; (2) DO NOT i rrigate (flush) between application and rice seeding ; (3) DO NOT i nitiate

perma nent flood to rice fields until 30 days or more after planting ; and (4) DO NOT a p ply within 45 days of permanent flooding in water

- seeded rice paddies ;

e. The stressor included parent compound and it ’ s degradates M800H01, M800H02, M800H07, M800H08, M800H15, M800H22 ; and

f. Tier I Rice Model (ver. 2) modeling which allows aerobic so il degradation of the pre

- flood applied chemical in addition to partitioning and degradation in the rice paddy for the left over

chemical residues.

Reported EDWCs for this assessment is summarized in Table 3

.

Table 3 Surface water E DWCs f or the propos ed new use on rice as reported in EDWC Memo

dated March

, 03 , 20 11 (DP Barcode: 384975

, Appendix 2 )

Holding Time Peak (μg/L) Annual Mean (μg/L)

1

- day 45.57 41.22

3

- day 45.50 41.19

21

- day 45.04 40.78

This current revised assessment is based on the proposed new use pattern on r ice (EPA Reg. No.

7969

- 278) 1 and the master label for saflufenacil formulations (EPA R eg. No. 7969

- 323 ) 2

. Based on these two labels, this assessment took in consideration the following:

1 EPA Reg. No. 7969

- 278 (Sharpen ® Powered by KIXOR ® Herbicide) : A supplemental Label For broadleaf weed control in rice production

. 2 EPA Reg. No. 7969

- 323 (KIXOR ® Herbicide): A broad leaf herbicide for use in field and row agricultural crops, bearing and nonbearing tree and vine crops, and in non

- crop

.12

(6) The maximum application rate for all crops, including rice, is 0.134 lb a.i/A instead of 0.356

lb a.i/A ; (7) Changes in values for the aerobic soil half

- life and partitioning coefficient (K
oc ) which is

entered in the current version of PRZM

- GW (refer to Table 4 ).

Table 4 A summary of the dif ference in input parameters between older version of PRZM

- GW (strikethrough parameters) and the current PRZM

- GW version (parameters in normal text).

Parameter (units) Value Source and Calculation Procedure

Soil Metabolism

Half

- life (days) 6,833 90 th percentile half

- life using four soils with half

- life values of 987; 1,433; 1,822; and 9,613 ( MRID 47445901)

Koc (mL/g O.C) 5.9 (the

mean of the

lowest reported

K OC values)

24 Overall average value calculated for all of the constituents of the

stressor ( MRIDs 47127829 and 47127830) as shown in the following Table :

Stressor Constituents Soil 1 Soil 2 Soil 3 Soil 4 Soil 5 Soil 6

Parent 9.3 19 22 23 25 55

Metabolite M1 4.8 7 7.1 8.6 13 27

Metabolite M2 0 6.7 10 12 13 41

Metabolite M7 3.3 32 59 67 97 111

Metabolite M8 4.8 5.6 7.1 12 18 20

Metabolite M22 0 5.2 6.4 13 23 25

Overall Average 24

Overall Median 13

(8) The change in crop

- specific use restrictions/limitations for rice which includes:

a. The pesticide can be applied to drilled, dry and water

- seeded rice;

b. The 1 st application: A maximum of 0.089 lb a.i/A (0.1 kg/ha) is applied pre

- plant through pre

- emergence “within 3 days of rice planting”;

c. The 2 nd application: A maximum of 0.045 lb a.i/A (0.05 kg/ha) is applied as a

post

- emergence weed c ontrol that may be applied either before or after flooding only when rice has reached the 2

- leaf stage;

d. The 1 st and 2 nd application may be applied sequentially but the two applications should be separated by at least 14 days;

e. The maximum seasonal rate shou ld not exceed 0.134 lb a.i/A (0.150 kg/ha); and

f. Water may be released from treated fields after 7

- days following the “last?” pesticide application noting that t he life cycle of rice is assumed to be a minimum of 110 day. Thus, water is released is released after 110+7= 117 days which is 72 days after flooding in dry

- seeded rice and 117 days after flooding in water seeded

rice. In rice, the length for the recognized growth stages is highly dependent on variety, type of rice culture (i.e., dry or water seede d), temperature and other environmental conditions 3 . For example, germination occurs within two days when temperatures are between 70° to 97°F; below

3 Rice Growth and Development by Karen Moldenhauer and Nathan Slaton : URL http:/ / baegrisk.ddns.uark.edu/ test/ Books/ PDF/ chapter1sl3.pdf13

or above this temperature, germination requires more time. Therefore, the following variable time periods were reported for rice growth stages in the same reference:

g. From planting

, through germination/seedling emergence

, to the 2 nd leaf stage: 8

- 3 0 days ; h. From planting, through the 2 nd leaf stage to the start of internode elongation (the green ring stage) : 44 to 112 days ; and

i. L ife cycle of rice cultivars in Arkansas ranges from 110 to 150 days from germination to maturity

.

In the rice label, the 2 nd application ( post

- emergence weed control) may be applied before or after flooding when rice has reached the seco nd leaf stage up to internode elongation. This means that the window for the second application is from 45 to 112 days after planting. However, the

label states that the minimum time intervals between the 1 st and second application is 14 days

and that was the interval used in modeling.

Based on rice culture, growth stages and label specific use restrictions/limitations, the following may be stated:

(1) In dry seeded rice: the 1 st application within 3 days of planting and the 2 nd application within 14 days of the 1 st application with flooding occurring within 30 to 45 days of planting (normal agronomic practice in dry seeded rice). (2) In water seeded rice: the 1 st application within 3 days of planting and the 2 nd application within 14 days of the 1 st application w ith flooding occurring at planting (water

- seeded).

Saflufenacil and its residues (the stressor) is expected to be highly persistent in soils before flooding (t 1⁄2 ranges 987 to 9,613 days; 6,833 days is used in modeling “90 th % value”) but it is expected to be less persistent in the rice paddy after flooding (aerobic aquatic t 1⁄2= 415.7 days; 1,247 days is used in modeling “3x the single value”).

Based the fate properties of the stressor and all of the label and rice agronomic practices, the following may be considered as the most conservative exposure scenarios:

(1) For dry seeded rice: the 1 st application at planting, the second application 14 days after planting and flooding at 45 days after planting; and (2) For water seeded rice: the 1 st application at planting, the second application 14 days after planting and flooding at planting.14



### III. D RINKING WATER EXPOSURE MODLING

1. Surface Water Modeling

a. All Crops Except Rice

The FQPA Index Reservoir Screening Tool (FIRST v1.1.1, Mar. 25, 2008; USEPA, 2008 ) was used in modeling EDWCs for drinking water from surface water sources. FIRST is a Tier I screening model that simulates the upper

- end exposure of the standard water body, the Index Reservoir, to pesticide residues in runoff and spray drift from an application within the standard watershed. Peak and annual mean EDWCs are generated to estimate acute and chronic exposure. The Index Reservoir covers 5.2 hectares (ha) with an average depth of 2.74 meters (m) in a

standard watershed of 172 .8 ha. A more detailed description of the index reservoir watershed

can be found in Jones et al ., 1998. The FIRST model and user’s manual are available from the

EPA Water Models web

- page (USEPA, 2009). Input parameters, for modeling the stressor, are

sum marized in Table 5 and modeling results are summarized in Table 6

.

Table 5 FIRST input parameters for the total residues of saflufenacil based on the maximum

seasonal application among all use patterns

Input Parameter Value Comments Source

Application rate (lbs a.i./A) 0.134 Maximum proposed single application

rate. Proposed label.

Number of applications per

year 1 Maximum proposed number of applications per year at the maximum proposed single application rate. Proposed label. Percent cropped area 100% Default for non

- agricultural uses. Effland et al. , 1999 Organic Carbon Partition Coefficient (K OC ) (L/kg OC ) 24 Refer to Table 4, above for calculation procedure MRID 47127829

MRID 47127830

Aerobic soil metabolism

half

- life (days) 6,833 Represents the upper 90% confidence

bound on the mean of four half

- lives

for the residues of concern. MRID 47445901

Wetted in? No Not required. Proposed label.

Method of application Aerial Proposed application method of highest potential spray drift. Proposed label. Solubility in water (ppm) 2100 Solubility in pH 7 water. MRID 47127819 Aerobic aquatic metabolism

half

- life (days) 1,247 Represents 3x the single available

half

- life for the residues of concern. MRID 47127827

Aqueous photolysis half

- life (days) 90.9 Represents the maximum environmental photo transformation

half

- life for the residues of concern. MRID 47699901

Table 6 FIRST modeling output (ppb).

Peak EDWC (Acute) Annual Average (Chronic

11.873 7.34615

(b) Rice

Tier I v2.0 rice model was used to generate estimated drinking water concentrations (EDWC) of

saflufenacil residues of concern that may occur in surface water used as drinking water. The tier

I v2.0 rice model is a modification of the same model ( v1.0). The two versions of the model rely on an equilibrium partitioning concept to provide EDWCs resulting from application of pesticides to rice paddies. When a pesticide is applied to a rice paddy, the model assumes that it will instantaneously partition between a water phase and a sediment phase. Although v 1.0 of the model does not account for pesticide degradation, v2.0 accounts for degradation in the rice paddy using the aerobic aquatic half

- life. It is noted however, that both versions of the model produces the same peak concen tration in water on the day of treatment and may produce similar concentrations thereafter, depending on the aerobic aquatic degradation rate of the compound. Peak concentrations of rapidly degraded compounds in released tail

- water following a holding

per iod will be lower than those produced by v1.0 of the model, as will any chronic concentrations averaged over time.

Both versions of the model, do not account for mass transfer between the aqueous phase and the sediment, volatilization, dilution, drift or other dissipation processes. It should be stated that v01 of the model was calibrated to generate estimates that are consistent with or conservative for dissolved concentrations measured within rice paddies and in discharged paddy water. The

model was no t evaluated or calibrated for concentrations measured in sediment and does not

account for residues partitions to suspended sediment. Currently, v02 of the model is considered to be a provisional model.

Due to a range of envir onmental and other factors, v01 of the rice model is expected to generate conservative EDWCs that exceed peak measured concentrations of pesticides in water bodies well downstream of rice paddies by less than one order of magnitude to multiple orders of magnitude (USEPA, 2007b). Ric e paddies are likely to be planted and harvested on or near the same date suggesting that when paddy waters are released, an influx of saflufenacil residues from multiple locations to the waterways may be expected. Also, EDWCs are expected to be

more cons ervative downstream of rice paddies in California and inland areas of the Southeastern U.S. where dilution is expected to occur. Tidal influences in surface waters of the coastal areas of the Southeastern United States may effectively reduce dilution of s aflufenacil residues from discharged paddy water, lengthening the period of chronic saflufenacil exposure in waterways influenced by rice paddies. In contrast, v02 of the rice model is expected to generate after peak

concentrations that are lower than thos e generated by v01 for pesticides that are expected to degrade quickly in aquatic system s (short aerobic aquatic half

- lives). However, these

concentrations a re expected to be less conservative than those produced by v01 model but possibly more representati ve to actual conditions in the field where degradation is expected to take place. Tier I v1.0 rice model and associated users’ manuals may be downloaded from the

U.S. Environmen tal Protection Agency (EPA) w ater model s web

- page (USEPA, 2009).

E xposure wa s specifically assessed for the proposed use of saflufenacil on rice based on the following two conservative exposure scenarios (refer to II (2) BACKGROUND section above for details used in identifying these two scenarios):16

(1) The first scenario for dry seed ed rice: the 1 st application at planting, the second application 14 days after planting and flooding at 45 days after planting; and

(2) The second scenario for water seeded rice: the 1 st application at planting, the second application 14 days after planting and flooding at planting.

For dry seeded rice, M odeling was done in two stages:

(1) Stage 1: Field before flooding: to estimate the amount of pesticide left in the soil after the 45 day in which the rice paddy is not flooded

. The estimate was based on the aerobic soil degradation half

- life of 6,833 days for saflufenacil residues

. Stage 1 estimate that 99. 7 % of the appli ed pesticide was left, in the un

- flooded soil, after 45 days and two applications: one at 14 days from planting and the other after 45 days from planting ; and (2) Stage 2: Field after flooding (Rice paddy): to estimate daily concentrations using the tier I

v2. 0 rice model which takes into account degradation in the rice paddy. This degradation was based on 3 times the one aerobic aquatic half

- life of saflufenacil residues which was determined previously to equal 1,247 days (from 3 x 415.7). Other parameters use d in modeling included: maximum application rate s (1 st = 0.089 lb a.i/A and 2 nd = 0.045 lb a.i/A, the mean for partitioning coefficient (K
oc ) = 24 L/kg, water column depth of 0 .1 meter (m)

, sediment depth of 0.01 m, sediment organic fraction of 0.01, sedime nt bulk density of 1300 kg/m 3 , and sediment porosity of 0.509 (50.9%).

Modeling results are summarized in Table 7 , below.

Table 7 Tier I v2.0 R ice model output (EDWCs in ppb) for tail water following a 7 days holding period

Scenario Peak Annual Mean

The first scenario : dry seeded rice 13 3

. 1 12 0. 4

The second scenario for water seeded rice 129.8 117.5

Data in Table 7 show that the maximum EDWC is 138.0 ppb for peak and 125.4 ppb for the

annual mean

.17

Figure 1 Change in EECs with time following two applications in dry and water

- seeded rice (in dry seeded rice flooding is after 45 days of planting while it is at planting in water seeded rice) Aqueous Concentration (μg/L)

Days After Planting

EECs vs Time following Two Applications (Dry

- Seeded Rice)

Aqueous Concentration (μg/L)

Days After Planting EECs vs Time following Two Applications (Water

- seeded rice)18



### 2. Ground Water Modeling
As per current EFED policy, ground water exposu re was modeled using Tier I PRAZM

- GW

and SCI

- GROW models. Parameters used in modeling runs were as follows:

(1) Scenarios and application rates and associated parameters:

PRZM

- GW calls for using the six standard scenarios representing vulnerable ground water s, namely: (1) DELMARVA_STD GW, (2) FLCITRUS_STD GW, (3) FLPOTATO_STD, (4) GACOASTAL_STD GW, (5) NCCOASTAL _STD, and (6) WISANDS_STD GW. Table 8 contains a summary of the input parameters used in modeling.

Table 8 PRZM

- GW and SCI

- GROW input parameters us ed for modeling saflufenacil

Parameter (units) Input Values

Data Source/Comments PRZM

- GW SCI

- GROW

Application Rate 0.150 Kg a.i/Ha 0.134 lb a.i/A Suggested amendment to label: maximum rate is changed from 0.356 to 0.134 lb a.i/A

Hydrolysis Ha lf

- life Stable N/A MRID 47127823

Soil Metabolism

Half

- life (days) 6,833 1,628 90 th percentile half

- life for PRZM

- GW and

median half

- live for SCI

- GROW using four

soils with half

- life values of 987; 1,433; 1,822; and 9,613 ( MRID 47445901)

CAM (chemical Application Model) 2 N/A As per guidance 1

Koc (mL/g O.C) 24 13 Average for PRZM

- GW and Median for

SCI

- GROW ( MRIDs 47127829 and

47127830 refer to Table 4 , above)

1 URL: http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_guidance.htm

Modeling results are summarized in Figure 2 for PRZM

- GW and Table 9 for SCI

- GROW and

PRZM

- GW

.19

Figure 2 PRZM

- GW estimated drinking water concentrations (EDWCs μg/L ) in ground water resulting from the stressor (total toxic residues of saflufenacil)20

Table 9 PRZM

- GW and SCI

- GROW estimated drinking water concentrations (EDWCs μg/L )

in ground water resulting from the stressor (total toxic residues of saflufenacil)

PRZM

- GW SCI

- GROW

Application

Dates Scenario* Highest Daily

Value Post

Breakthrough Average Average Simulation

Breakthrough Time
(Days/Years) Peak and

Average

Mar 15 DELMARVA_STD 42.4 27.5 413.5849 (1.1)

160 ppb

SCI

- GROW

was developed using K OC values ranging from

32

- 180 mL

g OC - 1 and

half

- lives

from 13

- 1000 days. Extrapolation beyond these

values will

increase the uncertainty of the ground

water
concentration . Therefore,

the results for this modeling

exercise are

not used in

this risk

assessment Mar 15 FLCITRUS_STD 38.8 27.1 432.3471 (1.2 )

Mar 15 FLPOTATO_STD 28.4 19.2 749.658 (2 .1)

Mar 15 GACOASTAL_STD 19.7 15.2 1380.526 ( 3.8 )

Mar 15 NCCOASTAL_STD 39.6 30.9 1247.013 ( 3.4 )

Mar 15 WISANDS_STD 67.3 48.7 1248.434 ( 3.4 )

Apr 15 DELMARVA_STD 43 27.6 413.5849 (1.1)

Apr 15 FLCITRUS_STD 39.3 27.2 432.3471 (1.2 )

Apr 15 FLPOTATO_STD 28.1 19.2 749.658 (2 .1)

Apr 15 GACOASTAL_STD 19.6 15.3 1380.526 ( 3.8 )

Apr 15 NCCOASTAL_STD 39.6 30.8 1247.013 ( 3.4 )

Apr 15 WISANDS_STD 69.2 51.5 1248.434 (3.4)

Jan 15 DELMARVA_STD 44.2 27.4 413.5849 (1.1)

Jan 15 FLCITRUS_STD 40.9 27 432.3471 (1.2 )

Jan 15 FLPOTATO_STD 27.8 19.2 749.658 (2 .1)

Jan 15 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

Jan 15 NCCOASTAL_STD 38.7 31.2 1247.013 ( 3.4 )

Jan 15 WISANDS_STD 62.2 46.2 1248.434 ( 3.4 )

Jul 15 DELMARVA_STD 43.6 27.1 413.5849 (1.1)

Jul 15 FLCITRUS_STD 43.8 26.9 432.3471 (1.2 )

Jul 15 FLPOTATO_STD 26.4 19.2 749.658 (2 .1)

Jul 15 GACOASTAL_STD 20.2 15.2 1380.526 ( 3.8 )

Jul 15 NCCOASTAL_STD 40.3 30.8 1247.013 ( 3.4 )

Jul 15 WISANDS_STD 68 51 1248.434 (3.4 )

Jun 01 DELMARVA_STD 42.1 27.5 413.5849 (1.1)

Jun 01 FLCITRUS_STD 40.5 26.1 432.3471 (1.2 )

Jun 01 FLPOTATO_STD 27.4 19.2 749.658 (2 .1)

Jun 01 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

Jun 01 NCCOASTAL_STD 39.7 30.7 1247.013 ( 3.4 )

Jun 01 WISANDS_STD 68.2 51.2 1248.434 ( 3.4 )

May 15 DELMARVA_STD 43 27.5 413.5849 (1.1)

May 15 FLCITRUS_STD 40.1 27.4 432.3471 (1.2 )

May 15 FLPOTATO_STD 28.2 19.2 749.658 (2 .1)

May 15 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

May 15 NCCOASTAL_STD 39.9 30.7 1247.013 ( 3.4 )

May 15 WISANDS_STD 69 51.2 1248.434 (3.4 )

Oct 15 DELMARVA_STD 40.4 26.6 413.5849 (1.1)

Oct 15 FLCITRUS_STD 42 26.2 432.3471 (1.2 )

Oct 15 FLPOTATO_STD 29 19 749.658 (2 .1)21 PRZM

- GW SCI

- GROW

Application

Dates Scenario* Highest Daily

Value Post

Breakthrough Average Average Simulation

Breakthrough Time
(Days/Years) Peak and

Average

Oct 15 GACOASTAL_STD 19.8 15.2 1380.526 ( 3.8 )

Oct 15 NCCOASTAL_STD 39.9 30.6 1247.013 ( 3.4 )

Oct 15 WISANDS_STD 64.4 50.3 1248.434 ( 3.4 )

Sep 15 DELMARVA_STD 40.3 26.8 413.5849 (1.1)

Sep 15 FLCITRUS_STD 42.9 26.2 432.3471 (1.2 )

Sep 15 FLPOTATO_STD 27.5 19.1 749.658 (2 .1)

Sep 15 GACOASTAL_STD 19.7 15.2 1380.526 ( 3.8 )

Sep 15 NCCOASTAL_STD 39.9 30.6 1247.013 ( 3.4 )

Sep 15 WISANDS_STD 65 50.8 1248.434 (3.4 )

Nov 15 DELMARVA_STD 41.3 26.5 413.5849 (1.1)

Nov 15 FLCITRUS_STD 42.2 26.3 432.3471 (1.2 )

Nov 15 FLPOTATO_STD 28.2 19 749.658 (2 .1)

Nov 15 GACOASTAL_STD 20.1 15.2 1380.526 ( 3.8 )

Nov 15 NCCOASTAL_STD 39.1 30.6 1247.013 ( 3.4 )

Nov 15 WISANDS_STD 65.2 50 1248.434 (3.4 )

Data in Table 9 show that the maximum EDWC is 69.2 ppb for peak and 51.5 ppb for the post breakthrough average with an average breakthrough time of 3.4 years.

LITERATURE CITATIONS

USEPA. 2009. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and Policy. Last updated: Apr 23, 2008. Online at: http://www.epa.gov/oppefed1/models/water/

USEPA. 2007b. Bradbury, S. Guidance for Tier I Estimation of Aqueous Pesticide Concentrations in Rice Paddies. U.S. Environmental Protection Agency, Offi ce of Prevention, Pesticides and Toxic Substances, Environmental Fate and Effects Division. Internal Memorandum. May 8, 2007.