UNITED STATES ENVIRONMENTAL PROTECTION AGE CY WASHINGTON, D. C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENT l ON

ENVIRONMENTAL RISK BRANCH Ill ENVIRONMENTAL FATE & EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS

PC CODE 1 28968

MEMORANDUM DP BARCODE : 396343 DATE: OX/21/20 1 2

SUBJECT: D ri nk ing Water Assess m en t f o r New Use of Fluroxypyr in R ice (Padd i es)

TO: Seyed Tadayon, Risk A ssesso r Mi c h a el Metzger

, Branch C hi ef Regi s tr a tion Ac ti on Bra nc h 7 H ea l th Effects Di v i sio n

FROM:

THRU : Bethany Benbow

, Reviewer K athryn Montague, Product Manager 23 H erbicide Bran c h Registration Di vis ion ( 75 05P) 

# (\**l\ aoe?~**  o C?.( ")..\

## :-1_ Ronald Parker, P h .D.**\!....-~, ~V'-**  Sen i or Env i ronmenta l En g in eer Envi r onmental Risk Branch 3 Env i ro nmental Fate and Effects Divi s ion (75 07P)

Exe cutive Summary

. GF -2764 (fluroxypy r

- MHE) i s an h e rbi c ide intended for p ost-e m ergent

se l ec tive co ntrol of broadl eaf weeds. It is cur r e ntly re g i ste red for u se on whea 1 t, b a rl ey, oat s,
com, so rghum

, fallow c ropland

, non-crop l and (i.e., rangeland), and others. Tbi s memorandum evaluates the pr opose d new flur oxypyr use on rice, and the potentia l result in g re s idues th at may

occur in drinkin g wate r r eso ur ces. The propo se d new u se l abel for applicat i o n to rice p ermits a si n gle maximum application of 0.34 l b ai per ac re p er year a nd allow s for two applications with a maximum total of 0 .5 68 lb a i per acre per y ea r wit h a minimum retr ea tment i n terval (RTI) of ten day s.

1

### 2 The fluroxypyr estimated drinking water concentrat ion (EDWC) value is 540 μg/L (ppb) for both acute and chronic exposure. Details of the EFED Tier 1 Rice Model can be found at http://www.epa.gov/oppefed1/m odels/water/rice_tier_i.htm

. A screening assessment for the impact of fl uroxypyr on potential groundw ater drinking water sources, using the Tier 1 groundwater model SCI-GROW, was also conducted. EDWC values based on use of the EFED SCI-GROW model ar e 0.055 μg/L (ppb) for both acute and chronic exposures. SCI-GROW model details can be found at: http://www.epa.gov/oppefed1/models/water/#scigrow . Tables A1 and A2 in Appendix A of this report provide a summary of the inputs of values used in the Tier 1 Rice model. Tables A3 and A4 in Appendix A provide a summary of the inpu ts of values used in the SCI-GROW model and a copy of the SCI-GROW output file, respectively.

Previous Drinking Water Exposure Assessments . Results from this evaluation for use on paddy rice can be compared with previous drinking water assessments (DWA) – including uses for rangeland and permanent grass pastur e (8/13/03, DP Barcode #292471), and for onion (5/30/06, DP Barcode #314020). Previously, the highest modeled EDWC for surface water drinking water resulted from uses on rangeland, with a peak value of 32.9 μg/L (ppb), annual mean value of 3.28 μg/L (ppb), and a 36-year overall mean of 1.76 μg/L (ppb). Previous drinking water assessments for fluroxypyr were based on the OPP/EFED linked Tier 2 PRZMEXAMS surface water models. See http://www.epa.gov/oppefed1/models/water/#przm and http://www.epa.gov/oppefed1/models/water/#exams for information on these two models. Percent Cropped Area (PCA) corrections of 87% were applied for these crops. Also see: http://www.epa.gov/pesticides/science/efed/mode ls/water/archives/pca_adjustment_dwa_9sep20 10.pdf for information on use of PCA values for drinking water exposure modeling.

Environmental Fate. Once fluroxypyr MHE is applied to th e environment, it is expected to degrade to its herbicidal activ e ingredient, fluroxypyr acid. The fate of fluroxypyr-MHE in the environment is complicated by uncertainty in the formation rate and distribution of the initial degradate fluroxypyr acid following spray applic ation. Fluroxypyr-MHE application rates are established based upon acid equivale nts (ae) pursuant to fluroxypyr acid as the active ingredient (ai). However, the solubility of fluroxypyr-MHE is much lower (~0.1 mg/L) than fluroxypyr acid (~8,000 mg/L); according to mixing/application inst ructions, the tank must be agitated before and during applications to allow undissolved materi al to remain in suspension. In neutral or low pH aqueous conditions, fluroxypyr-MHE is sufficien tly stable such that spray distributed on a target zone will initially contain mostly the fl uroxypyr-MHE form. Under field conditions it is likely that most of the MHE will convert to the ac tive ingredient (fluroxypyr acid) in the course of a few days. In the EFED models, it is assume d that the initial spray contains all the active ingredient, and that degradation rates for th e active ingredient commence immediately after spraying. However, there may be initial on-site exposure to the MHE after spraying, with degradation occurring first from the MHE to aci d form, then to other forms. Actual exposure could then potentially be longer than assessed. Conversely, this effect may also attenuate the impact of the active ingredient, as it will be introduced onto the si te more gradually (according to degradation rates). In high-p H conditions, though, degradation of both MHE and acid forms are expected to occur more rapidly. For the purpos e of EFED assessments, the most conservative fate and effects input parameters are used wh ere available; in this instance, it is more

### 3 conservative to use the values for fluroxypyr acid . Furthermore, in the case of potential drinking water exposure, fate parameters for fluroxypyr aci d were selected also because this compound is both more soluble in water and more likely to be transported in an aquatic medium. Physical/ chemical properties of fluroxypyr-MHE and fluroxypyr acid are listed in Ta bles 1 & 2. Chemical structures of fluroxypyr-MHE and its degr adates are provided in Appendix A5.

Table 1. General Environmental Fate & Phys ico-chemical Properties of Fluroxypyr-MHE

CAS Number 8140637-3

Molecular Formula C 15 H 21 Cl 2 FN 2 O 3

Parameter Value Source

Molecular Weight 367 g/mol OPP/Pesticide Fact Sheet/1998

Melting Point 56-57 o C

log K ow 3.788 OPP/Pesticide Fact Sheet/1998

Water Solubility 0.9 mg/L @ pH 7 OPP/Pesticide Fact Sheet/1998

Vapor Pressure (25 o C) 1.07 X 10 -7 mm Hg OPP/Pesticide Fact Sheet/1998

Henry’s Law Constant 5.75 X 10 -7 atm m 3 /mol Calculated Hydrolysis Half-life (25 o C) (days) pH 5 pH 7 pH 9 pH 8.3 (Natural Water-Dark) pH 8.3 (Natural Water-Lighted) stable 454 days 3.2 days 20 days 63 days (photo-inhibition) MRID 40244539

Aqueous Photolysis Half-life (days) 550 days 197 days (buffered) MRID 44080342

Aerobic Soil Metabolism Half-life (days) Total: (Fluroxypyr-MHE + Fluroxypyr) silt loam: 12.26 days sandy loam: 23.43 days loam: 11.65 days

clay: 7.44 days MRID 42137317

Anaerobic Aquatic Metabolism Half-life (days) (Under Review) MRID 44080344

Aerobic Aquatic Metabolism Half-life (days) (Under Review) MRID 44080345

Soil Photolysis Half-life (days) 152.7 days MRID 44080343

Adsorption Kd / Koc K ads K oc loam 190 6,200 sandy loam 95 43,000 silt loam 260 12,000 clay 210 17,000 MRID 42137319

### 4 Table 2. General Environmental Fate and Physic o-chemical Properties of Fluroxypyr Acid

CAS Number 69377-81-7

Molecular Formula C 7 H 5 Cl 2 FN 2 O 3

Parameter Value Source

Molecular Weight 255.03 g/mol OPP/Pesticide Fact Sheet/1998

Melting Point 57.5 0 C OPP/Pesticide Fact Sheet/1998

log K ow 0.04 @ pH 7 IUPAC Pesticide Properties Database

Water Solubility 7950 mg/L OPP/Pesticide Fact Sheet/1998

Vapor Pressure (25 o C) 9.5x10 -11 mm Hg MERCK

Henry’s Law Constant 4.01 x10 -15 ( atm m 3 /mol ) Calculated Hydrolysis Half-life (25 o C) (days) pH 5 pH 7 pH 9 Stable stable stable MRID 40244539

Aqueous Photolysis Half-life (Natural Water) (days) 429 days (buffered) MRID 44080342

Aerobic Soil Metabolism Half-life (days) Total: (Fluroxypyr-MHE + Fluroxypyr) silt loam: 12.26 days sandy loam: 23.43 days loam: 11.65 days

clay: 7.44 days MRID 42137317

Anaerobic Aquatic Metabolism Half-life (days) (Under Review) MRID 44080344

Aerobic Aquatic Metabolism Half-life (days) (Under Review) MRID 44080345

Soil Photolysis Half-life (days) 152.7 days MRID 44080343

Adsorption Kd / Koc K ads K oc loam 1.9 62 sandy loam 0.11 51 silt loam 1.7 78 clay 1.0 81 MRID 42137319

### 5 Drinking Water Exposure Modeling . Fluroxypyr-MHE is formulated as an emulsifiable concentrate that is mixed with water and appl ied as ground or aerial spray. GF-2764 is used for post-emergent broadleaf weed suppression. Applica tions to rice may be made after the paddy has been flooded.

Estimation of Exposure Concentrations for Surfa ce Water in Rices Paddies (Tier 1 Rice Model)

The proposed new use label for application to ri ce permits a single maximum application of 0.34 lb ai per acre per year and allows for two appl ications with a maximum total of 0.568 lb ai per acre per year with a minimum retreatment interval (RTI) of ten days. The label also requires a pre-harvest interval (PHI) of 60 days of harv est. This assessment reflects a high-exposure scenario by assuming the maximum application am ount of 0.568 lb ai/A (0.64 kg/ha) is used per
year.

Tier 1 Rice Model (v1) When using the Tier 1 rice model, EFED assumes pesticide application to a static rice paddy with no inflow from rain fall or outflow from seepage, overflow or evaporation. The only process simulated by the m odel is partitioning of the applied chemical between the 10-centimeter deep water column and the 1-centimeter deep sediment layer of the paddy. The partitioning is based on the pesticide’s K d 

### . Degradation in the paddy is not calculated by the model so the pesticide is assumed to rema in at the initial concentration in the water indefinitely. Results of the tie r 1 rice modeling are presented in Table 3. Acute and chronic values are equal because the model does not simu late degradation of the pesticide in the paddy.

Table 3. Summary of Tier 1 Rice Model EDWC for Use on Rice Assessment Type Acute EDWC Chronic EDWC Tier 1 Rice Model (conc in paddy) 540 μg/L (ppb) 540 μg/L (ppb)

### 6 Appendix A. Model Inputs and Outputs.

Table A1 is a summary of the input values used in the Tier 1 Rice Model.

Table A1. Summary of EFED Tier 1 Rice Model Input Values for Fluroxypyr

Environmental Fate Parameter Value Justification Source

Adsorption Coefficient (Kads) (mL/g ) 1.0 Lowest Non-sand Kd MRID 42137319



### Appendix 2. Physical Values of the Tier I Rice Model v1.0.

Table A2. Physical Values of the Tier I Rice Model v1.0.
Parameter Symbol Value Reference Water column depth d w 

### 0.10 m USDA (1998, 2002) Sediment depth d sed 

### 0.01 m Calibration described in Section III C of this document. Organic content of sediment f oc 

### 0.01 Justification provided in Section III B of this document. Sediment bulk density ρ b 

### 1300 kg/m 3 

### Brady (1984), Hillel (1982)

Grain density ρ g 

### 2650 kg/m 3 

### Density of quartz, typical assumption; Brady(1984), Hillel (1982) Sediment porosity θ sed 

### 0.509 θ sed = 

### 1- ( ρ b 

### / ρ g 

### )

Most of the assumptions used in this model help ensure that th e outputs are protective of most environments associated with rice agriculture. The following is a summary of the Tier 1 EECs resulting from application of fluroxypyr on rice . The model assumptions include the following:

1. Movement of pesticide on suspe nded sediment is not considered. 2. Degradation does not occur. 3. Volatilization and other dissipat ion processes are not considered. 4. Partitioning to sedi ment is instantaneous. 5. Water is available for human or wildlife exposure instantaneously. 6. Water column depth is 10 cm. 7. Sediment depth is 1 cm. 8. All pore space is saturated with water. 9. Organic carbon fraction is 0.01. 10. Bulk density is 1300 kg/m 3



### . 11. Grain density is 2650 kg/m 3



### .

### 7 Appendix 3. SCI-GROW Model Input Values

Table A3: Summary of Input Values Used in SCI-GROW Tier 1 Groundwater Model.

Table A3. Summary of EFED SCI-GROW Model Input Values for Fluroxypyr

Environmental Fate Parameter Value Justification Source

Organic Carbon Normalized Adsorption Coefficient (Koc) 68 Mean of 4 Values (Table 2) MRID 42137319

Aerobic Soil Metabolism Half-life (days)
Total: (Fluroxypyr-MHE + Fluroxypyr) 13.7 Mean of 4 Values (Table 2) MRID 42137317



### Appendix 4. SCI-GROW Model Output File.

SCIGROW VERSION 2.3 ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY SCREENING MODEL FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3 chemical:Fluroxypyr time is 8/15/2012 14:45:32

------------------------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------------------------- 0.568 1.0 0.568 6.80E+01 13.7

------------------------------------------------------------------------------------------- groundwater screening cond (ppb) = 5.47E-02 ************************************************************************

### 8 Appendix 5. Structure of Fluroxypyr and Related Degradation Products