### 1 OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460



### PC Code: 108201
DP Barcode: 423330

Date: April 20

, 2015

MEMORANDUM

SUBJECT: D rinking W ater E xposure A ssessment in Support of the New Use Registration

of Diflubenzuron Formulated Product on Alfalfa

, Carrot, Cottonseed s Subgroup 20C, Peach S ubgroup 12

- 12B, Plum Subgroup 12

- 12

- C Peppers/Eggplant Subgrou p 8

- 10B and Conversion for Tree Nuts Group 14

- 12.

TO: Carmen Rodia , Risk Manager Reviewer

Barbara Madden, Risk M anager Deborah McCall , Branch Chief Registration Division (7505 P )

Thurston Morton , Chemist
Elissa Reaves , Branch Chief
Risk Assessment Branch IV
Health Effects Division (750 9 P )

FROM: Faruque Khan, Ph.D., Senior Fate Scientist

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

APPROVED
BY : Sujatha Sankula

, Ph.D., Branch Chief,

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

This assessment provides estimated drinking water concentrations (EDWC s ) of dif lubenzuron and its major metabolite, 4

- chlorophenyl urea ( CPU ) in surface water and groundwater in support of hu man health risk assessment on the I nterregional Research Project Number 4 ( IR4 ) proposed new uses on alfalfa, carrot, cottonseed Subgroup 20C, peach Subgroup 12

- 12B, Plum

### 2

Subgroup 12

- 12

- C, p eppers/ e ggplant Subgroup 8

- 10B, and conversion of t ree Nut Group 14

- 12

. Proposed a pplication rate information is provided in Table 1

.

Table 1. Proposed New Use Application Rates for Diflubenzuron

Use Single max app rate (lb ai/A) Max yearly

app rate (lb ai/A) Min interval

between applications (days) Additional Notes

Alfalfa/Alfalfa grown
for seed 0.03 25 0.09 75 14 For use West of the Mississippi

Carrot 0.1 25 0.25 7 Not for use in CA
Cottonseed S ubgroup
20C 0.1 25 0. 3 75 5

---

Peach S ubgroup 12

- 12B
Plum S ubgroup 12

- 12B 0.25 0.50 14

---

Peppers/Eggplant
S ubgroup 8

- 10B 0.1 25 0. 3 75 7

---



### T he Metabolism Assessment Review Committee ( MARC ) of the Health Effects Division (HED) suggested to include CPU as a residue of concern for drinking water (USEPA, 20 01 , D P
D 272976 ) and recommended to assess the concentration s of CPU and diflubenzuron in drinking water sources independently. Therefore, t his drinking water assessment was performed for both
diflubenzuron and CPU in support of the proposed Section 3 new uses

. Foliar spray applications ( aerial

, air

- blast and ground spr ay application s) are being proposed for these crops

.

The EDWCs of dif

lubenzuron and CPU were generated using the annual maximum application
rates of 0.098 to 1.00 lb a.i./A with the Surface Water Concentration Calculator model (SWCC)
for surface water an d the Pesticide Root Zone Model

- Groundwater (PRZM

- GW) model for ground water. Conversely, the a pplication rates for CPU were adjusted based on maximum
formation of CPU in the submitted environment fate studies and molecular ratio of CPU and
diflubenzuron. Since additional environmental fate data became available and the implementation of SWCC and PRZM

- GM models, the previously recommended EDWCs were reevaluated for citrus crop , for which the highest water concentrations were reported earlier . The maximum ap plication rate of 0.312 lbs a.i./A X 3 application s /year for citrus as well as 0.25 lbs a.i./A X 4 application s /year for tree nut were also modeled with the SWCC and PRZM

- GW
models. M odel input parameters were chosen according to current guidance (USEPA, 2 00 9 and USEPA, 2013 a )

. For surface water sources of drinking water , the recommended peak (acute)
concentration of 4.61 μg/L , annual mean (non

- cancer chronic) concentration of 0. 41 μg/L and the 30 year annual average concentration (cancer chronic) of 0. 38 μ g/L based on LV application
of diflubenzuron for c itrus use

. For CPU, the recommended surface water conc e ntrations are 6.83 μg/L for acute

, 0. 89 μg/L for non

- cancer chronic and 0. 5 1 μg/L for cancer chronic also
based on aeial application representative of citrus use

.

For groundwater sources of drinking water, the maximum acute and chronic estimated concentrations of
CPU in shallow groundwater from PRZM

- GW model for applications to citrus were 8.62 μg/L and 8.02 μg/L , respectively. However, the concentratio ns of diflubenzuron in groundwater were negligible

. 

### Recommended surface water and groundwater EDWCs for human health are listed in Table 2

.

### 3

Table 2 . Drinking Water Exposure Estimates for Diflubenzuron and its Major Degradate, CPU for Use on Various Crops

.

Source Residue Peak Exposure (μg/L) Annual Mean

Exposure (μg/L) 30

- year Average

Exposure (μg/L)



### Surface water 1 Diflubenzuron 2 4.61 0. 41 0. 38

CPU 2 6.83 0.89 0. 5 1



### Groundwater 1 Diflubenzuron 0

--- 0

CPU 8.62

--- 8.02

1 EDWCs generated using SWCC and PRZM

- GW model s for aerial LV application of 0. 312 lbs a.i./A X 3 applications for c itrus use

2 Estimated in FL Citrus scenario



### Environmental Fate and Transport Properties

The physicochemical properties suggest that diflubenzuron has a low solubility in water (0.8 mg/L )

. The vapor pressure ( 9.0 × 10

- 10 

### mm Hg ) and Henry's L aw C onstant ( 1.19 x 10

- 11 

### atm

m 3 

### /mol) indicate that diflubenzuron is a non

- volatile chemical. Based on registrant

- submitted data, diflubenzuron appears to be relatively non

- persistent and slightly mobile under normal use
conditions. Diflubenzuron is relatively stable to hydrolysis and photolysis. The major route of dissipation appears to be biotic processes (half

- life of approximately ≤ 14 days for aerobic soil metabolism). T wo major degradates, a maximum of 48 % of 4

- chlorophenylurea (CPU or p

CPU ) and a maximum of 31% of 2,6

- diflubenzoic acid (DFBA) were identified in the submitted environmental fate studies for diflubenzuron. However, there is insufficient data on the majo r degradate s of diflubenzuron to adequately assess their persistence and mobility. Detailed environmental fate properties can be obtained from the Registration Review Problem
Formulation document (USEPA 2012 a)

.

Residues of Concern

T wo major degradates, a maximum of 48 % of 4

- chlorophenylurea (CPU or p

- CPU ) and a maximum of 31% of 2,6

- diflubenzoic acid (DFBA) were identified in the submitted
environmental fate studies for diflubenzuron. The Residues of Concern Knowledgebase Subcommittee (ROCKS) of the Hea lth Effects Division (HED) suggested to include CPU as a residue of concern for drinking water (USEPA, 20 01, DP D 272976 ) and recommended to assess
the concentrations of CPU and diflubenzuron in drinking water sources independently.

Drinking Water Exposure Modeling Approach and Input Parameters

Models

The EDWCs were generated using EFED’s standard suite of models. Most surface water EDWCs and groundwater EDWCs were determined in previous assessments using older models

. In this assessment, SWCC and PRZM

- GW ( current ly approved models) were used to estimate
surface water and g roundwater EDWCs. Since additional environmental fate data became available, the previously recommended EDWCs were reevaluated for citrus scenario.

### 4

I nformation concerning the model can be found on the EPA Water Models web

- page 1 

### (USEPA,
2015 ) . The maximum application rate of 0.312 lbs a.i./A X 3 application/year for citrus was also modeled with the SWCC (Surface Water Concentration Calculator) and PRZM

- GW (Pesticide
Root Zone Model

- Groundwater) models. The highest predicted EDWCs for diflubenz ur on scenarios were used in estimating EDWCs for CPU for surface water and groundwater.

Surface Water

The Surface Water Concentration Calculator (SWCC v 1.106) model was used to generate

E DW Cs for the Tier II aquatic exposure assessment. The SWCC is a graphical user interface that runs the Pesticide Root Zone Model (PRZM, v 5, November 15, 2006) and the Variable Volume Water Body Model (VVWM, 3/6/2014) (USEPA, 20 06b). Simulations are run for multiple (usually 30) years and the E DW Cs represent peak values that are expected once every ten years based on the thirty years of daily values generated during the simulation. The default P ercent Crop Area (P CA ) of 1.0 was u sed for the proposed uses because dif lubenzuron can be used in both agricultural and non

- agricultural settings (USEPA 2014 ).

Groundwater

Tier I groundwater EDWCs for dif lubenzuron and CPU , resulting from its use on various crops
estimated using the PRZM

- GW model ( USEPA, 2012 b ), with the GW

- GUI (Graphical User Interface, version 1.0, August 31, 2012 b ). PRZM

- GW is a one

- dimensional, finite

- difference model that estimates the concentrations of pesticides in groundwater. It accounts for pesticide
fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field. PRZM

- GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site. PRZM

- GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agricultural field following many years of pesticide application. PCAs are not applicable for the PRZM

- GW model.

In put Parameters

There is no environmental fate data available for CPU at this time. The aerobic soil metabolism
and aerobic aquatic input values for CPU used in SWCC and PRZM

- GW were estimated from
diflubenzuron submitted environmental fate studies. Assumed the highest fraction of CPU forming in the diflubenzuron stud ies for “ D ay 0” then adjust ed the subseque n t sampling day s for
CPU accordingly. The NAFTA degra dation Kinetics tool, PestDF v0. 8 .13 tool 2 

### was used in estimating representative de gradation half

- lives for aerobic soil and aerobic aquatic metabolisms.

T he calculation can be found in Appendix A . The EPISUITE 4.1 was also used in estimating selected physicochemical properties of CPU for model inputs

.

Summaries of the model input parameter values for diflubenzuron and CPU used in SWCC are presented in Tables 3 and 4 respectively

. Summaries for PRZM

- GW input parameter values for
diflubenzuron and CPU used are presented in Table 5

. Input parameters were s elected in

1 http://www.epa.gov/oppefed1/models/water /index.htm

2 http://www.epa.gov/oppefed1/ecorisk_ders/degradation_kinetics/NAFTA_Degradation_Kinetics.htm

### 5

accordance with EFED’s “Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides ,” Version 2.1 ( USEPA, 200 9 ) and “G uidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the
Pesticide Root Zone Model ,” Version 1 ( USEPA 2013 a )

.

Table 3

. SWCC Input Parameters for Diflubenzuron Modeling

Parameter Value Source Comments
Crops
Citrus Scenario
CACitrus STD
FLCitrusSTD

All available standard crop
scenarios of SWCC were used except
for alfalfa. Alfalfa CAalfalfa WirrigOP
MNalfalfaOP

T XalfalfaOP Regional Restriction west of Mississippi River. No standard
scenario available for alfalfa. Surrogate scenarios from west of Mississippi River were used for
alfalfa

Carrot FLCarrotSTD

Cottonseed Subgroup
20C CAcotton_WirrigSTD
MScottonSTD
NCCottonSTD

Peach and Plum Subgroup (12

- 12B) CAFruits Wirrig STD
GAPeachSTD

Peppers/Eggplant Subgroup 8

- 10B

Tree Nut Subgroup 14

- 12 FLPeppersSTD

CAalmond_WirrgSTD
GAPecanSTD

Crops M ax single application

rate lb a.i./A x Max # of application

Dimilin ® 2L

(EPA Reg # 400

- 461) Citrus 0.312 lbs a.i./A X 3 Low

- and high

- volume (LV and HV) application applicable to citrus

Alfalfa 0.0325 lbs a.i./A x 3 ---

---

Carrot 0.125 lbs a.i./A x 2

---

Cottonseed subgroup
20C 0.125 lbs a.i./A x 3

---

Peach and Plum subgroup (12

- 12B) 0.25 lbs a.i./A x 2

---

### 6

Table 3

. SWCC Input Parameters for Diflubenzuron Modeling

Parameter Value Source Comments

Peppers/Eggplant subgroup 8

- 10B 0.125 lbs a.i./A x 3

---

Tree Nut Subgroup 14

-

12 0.25 lbs a.i./A x 4

---

Crop

Scenario: Application
date and minimum
interval between applications (days) Citrus

CA citrus : Dec 10 ( 7 )

FL Citrus: Dec 10 (7) Dimilin ® 2L (EPA Reg # 400

- 461) and SWCC
Scenario Based on pre

- harvest
recommendation

Alfalfa
CAalfalfa : Feb 02 (30)
MNalfalfaOP :May 25(30)
TXalfalfaOP : Apr 15 (30) Dimilin ® 2L

, SWCC Scenario and USDA, 2010 Based on three harvests of alfalfa

per year. Harvest dates for the states (USDA 2010) and maturation of 30 days for successive harvest

Carrot
FL Carrot : Jan 08 (7) Dimilin ® 2L and SWCC Crop
Scenario Based on pre

- harvest
recommendation

Cottonseed subgroup
20C CA Cotton: July 01 (5) MS Cotton: July 01 (5) NC Cotton: August 15 (5) Dimilin ® 2L Assumed 1 st application at fully bloomed (USDA, 2006)

USDA Cotton crop profile

Peach Subgroup (12

- 12B)
CA Fruit: July 01 (14) GA Peach: Aug 01 (14) Dimilin ® 2L and
SWCC Scenario Based on pre

- harvest
recommendation

Pepper/Eggplant
FL Peppers Nov 10 (7)

Tree Nuts CA Almond: July 26 (7) GA Pecan: Aug 06 (7)

Depth of Incorporation (inches) 0 Dimilin ® 2L For foliar application according to Input parameter guidance (USEPA,

200 9 )

Method of Application

and

crops Aerial

Alfalfa, c itrus, c otton seed, pepper/eggplant

Ground

Alfalfa, carrot, cottonseed, pepper/eggplant

Air

- blast spray

Citrus p each, plum and

tree nut Dimilin ® 2L

---

### 7

Table 3

. SWCC Input Parameters for Diflubenzuron Modeling

Parameter Value Source Comments

Application Efficiency 1

, 2 Aerial: 0.95 (Default)

Aerial LV: 0.69 (Est.))

Ground: 0.99 (Default) Input parameter guidance (USEPA,
200 9 ) For LV, application efficiency was

estimated from AgDRIFT model

output.

Spray Drift Fraction Citrus scenario

Aerial (default) 0.04

Aerial (LV) 0.21

Air

- blast : 0 .01 AgDRIFT modeling Based on LV and DV0.5 = 90 um
and 150 ft buffer.

Based on 25 ft buffer for ground

application.

Generic Default

Aerial: 0.135

Ground: 0.066 Spray Drift

Guidance (USEPA, 2013b) Based on AgDRIFT Default
Scenarios

Air

- blast : 0 .025 (Orchard) Based on orchard scenario due to active growing season for peach/plum and nut trees

Molecular Mass (g/mol) 311 MRID 485969

- 01 Product chemistry data

Vapor Pressure (Torr) 9.0 x 10

- 10 MRID 485969

- 01 Product chemistry data

Henry’s Law Constant (atm m3/mol) 1.19 x 10

- 11 Estimated EPISUITE 4.1

Solubility in Water (mg/L) 0.08 MRID 485969

- 01 Product chemistry data

Hydrolysis t 1/2 at pH 7.0 (days) 119 MRID 014355 --

Aquatic Photolysis t 1/2 (d ays ) 80 MRID 40816301

MRID 41087802 --

Aerobic Soil
Metabolism t 1/2 (d ays ) 5.1 MRID 41722801

MRID 46888703
MRID 46888708 90 th percentile upper confidence

bound on the mean half

- life of
diflubenzuron

Aerobic Aquatic
Metabolism t 1/2 (d ays ) 25.2 MRID 44895001

MRID 46888707 90 th percentile upper confidence

bound on the mean half

- life of total
toxic residue of diflubenzuron

Anaerobic Aquatic
Metabolism t 1/2 (d ays ) 102 (34 x 3 ) 3 MRID 41837601 Input parameter guidance (USEPA,
200 9 )

Soil Partitioning Coefficient (K
oc ; ml/g
oc ) 4862.1 MRID 00157842

MRID 46895401 A verage K oc from 7 soils

### 8

Table 3

. SWCC Input Parameters for Diflubenzuron Modeling

Parameter Value Source Comments

1 L ow volume application is restricted in Cal ifor n i a

. FL C itrus STD was used for LV application.

2 Spray drift fraction was estimated using AgDRIFT 2.1.1 model

– Tier I Air

- blast scenario (citrus, aerosol to fine droplet) and the Guidance on Development and Use of the Index Reservoir in Drinking Water Exposure
Assessments. http://www.epa.gov/oppefed1/models/water/index_reservoir_dwa.html#memo

3 Due to reported half

- life for a single anaerobic aquatic metabolism study

, the input half

- life was multiplied by 3

accor ding to Guidance for Selecting Input Parameters in Modeling for Environmental Fate and Transport of

P esticides. Version 2.1 October 22 , 200 9

.



### Table 4

. SWCC Input Parameters for CPU Modeling

Parameter Value Source Comments

Crops M ax single application

rate lb a.i./A x Max # of application

Estimated from
label rate Maximum CPU formation of 48%

in aerobic aquatic system (MRID
46888707 was used in application
rate calculation 1 Citrus 0.0 81 X 3 (Aerial Default)

Cotton 0. 033 X 3 (Aerial Default )

Method of Application Ground application Assumed Contribution from degradation

Application Date Same as Table 2

Depth of Incorporation (inches) 0 Assumed Contribution from degradation

Application Efficiency Ground: 1.0 Assumed Contribution from degradation

Spray Drift Fraction 0 Assumed Contribution from degradation

Molecular Mass (g/mol) 177.6

TOXNET Estimated value

http://chem.sis.nlm.nih.gov/chemid plus/rn/140

- 38

- 5#physical Vapor Pressure (Torr) 1.65 x 10

- 04

Henry’s Law Constant (atm m3/mol) 1.49 x 10

- 10

Solubility in Water (mg/L) 1770

Hydrolysis t 1/2 at pH 7.0 (days) 0 Assumed No data

Aquatic Photolysis t 1/2 (d ays ) 0 Assumed No data

Aerobic Soil
Metabolism t 1/2 (d ays ) 65.4 MRID 41722801

MRID 46888703
MRID 46888708 90 th percentile upper confidence

bound on the mean half

- life derived from diflubenzuron study.

MRID 41722801 is the same study

as MRID 46888708.

### 9

Table 4

. SWCC Input Parameters for CPU Modeling

Parameter Value Source Comments

Aerobic Aquatic
Metabolism t 1/2 (d ays ) 41.9 MRID 44895001

MRID 46888707 90 th percentile upper confidence

bound on the mean half

- life derived from diflubenzuron study

Anaerobic Aquatic
Metabolism t 1/2 (d ays ) 0 Assumed No data

Soil Partitioning Coefficient (K
oc ; ml/g
oc ) 246 Van Dijk, N.R.M.
1992 Cited from previous assessment

(USEPA, 2002; D279732+)

1 Diflubenzuron application rate ( 0.312 lb/ A) x [(0. 48 , the maximum conversion rate from the aerobic aquatic degradation of diflubenzuron to CPU in laboratory stud y ) x ( [177.6/311]) , the molecular weight ratio of CPU to diflubenzuron ) x (Application Efficiency, 0.95 for default).



### Table 5 . PRZM

- GW Input Parameters 1 

### for Diflubenzuron and its Major Degradate, CPU

Variable Name Data Value Data Source MRID(s) Comment

Diflubenzuron

Application Method Aerial and ground

Dimilin®2L EPA Reg# 400

- 461 ---

Maximum Single Application Rate (lbs. a.i./acre) [kg/ha] X Maximum # of application Citrus:0.312 [0.349] x 3 Carrot: 0.125 [0.14] x 2 Tree Nuts: 0.25 [0.28] x 4 Since the highest application rate for
citrus has never been modeled, it was also included in modeling

Crop Scenario Carrot
Delmarva sand
FL Jacksonville
WI Sand
Citrus FL Central ridge
Tree Nuts
GA Coastal
NC Coastal Specific scenario for FL
carrot. In addition potential sites to grow

carrot

Citrus site specific

Specific scenario for
GA Coastal. In addition potential sites to grow

tree nuts

Application Interval (days) 7 (Citrus and tree nuts) 7 (Carrot) 7(Tree Nuts) No specification for tree

nuts.

Hydrolysis, DT 50 (Days) 119 MRID 014355

---

Aerobic Soil Metabolism

DT 50 (Days) 5.1 days MRIDs.:
41722801
4688703
4688708 The 90% of the upper

confidence limit ( UCL ) of
the mean metabolism half

life

.

### 10

Table 5 . PRZM

- GW Input Parameters 1 

### for Diflubenzuron and its Major Degradate, CPU

Variable Name Data Value Data Source MRID(s) Comment

K oc ( mL/g oc ) 4862.1 MRID s: 00157842 and
46895401 A verage K oc from 7

soils

CPU

Application Method Ground

--- Assumed for degradation product

Maximum Single Application Rate X Maximum # of application (lbs. a.i./acre) [kg/ha] 0.086[ 0.096] x 3 (Citrus) 0.034[0.038] x 2 (Carrot) 0.069[0.077] x 4 (Tree nut) Estimated 2

---

Crop Scenarios and Application Interval (days) Same as diflubenzuron Dimilin®2L EPA Reg# 400

- 461 ---

Hydrolysis, DT 50 (Days) 0

--- No study related to CPU

Aerobic Soil Metabolism

DT 50 (Days) 65.4 MRID
41722801
4688703
4688708 The 90% of the upper

confidence limit ( UCL ) of
the mean metabolism half

life

.

K oc ( mL/g oc ) 246 Van Dijk, N.R.M. (1992) Cited from previous

assessment (USEPA, 2002;D279732+)

1 EFED input parameter guidance: http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.htm

2 Diflubenzuron application rate ( 0.312 lb/ A) x [(0. 48 , the maximum conversion rate from the aerobic aquatic degradation of diflubenzuron to CPU in laboratory stud y ) x ( [177.6/311])

, the molecular weight ratio of CPU to diflubenzuron )



### Modeling Results

Estimated diflubenzuron and CPU concentrat ions in surface water used for drinking water are
summarized in Table 6

. Values in bold are recommended for use in the human health risk assessment. 

### For surface water, the recommended peak (acute) concentration of 5.18 μg/L , annual mean (non

cancer chronic ) concentration of 0.63 μg/L and the 30 year annual average concentration (cancer chronic) of 0.49 μg/L based on LV application of d iflubenzuron applications representative of

cotton

. The default Percent Crop Area (PCA) of 1.0 was used for the proposed uses because diflubenzuron can be used in both agricultural and non

- agricultural settings (USEPA 201 4 ).

For CPU, the recommended surface water concentrations are 6.83 μg/L for acute

, th e 0. 89 μg /L
for non

- cancer chronic and 0.55 μg/L for cancer chronic also based on LV applications representative of citrus and cotton. Sample outputs with the highest EDWCs from the SWCC model runs is provided in Appendix B

. The Percent Crop Area is not applicable for groundwater.

### 11

Table 6

. EDWCs of Diflubenzuron and its Major Degradate, CPU for Surface Water

Crop Crop Scenario Application
Method 

### Peak (Acute)

Exposure Annual Mean

(chronic) Exposure 30

- year Mean

(cancer chronic) Exposure

----------------------- (μg/L)

-----------------------

Citrus 1 CA Citrus 1 Aerial (Default) 0.95 0.14 0.12

Air

- blast 0.41 0.04 0.03

FL Citrus 1 Aerial (Default) 1.52 0.12 0.09

Aerial LV 4.61 0.41 0.38

Air

- blast 1.2 0.07 0.04

Alfalfa CA Alfalfa Aerial 0.23 0.04 0.04

Ground 0.11 0.02 0.02

MN Alfalfa Aerial 0.23 0.05 0.05

Ground 0.11 0.02 0.02

TX Alfalfa Aerial 0.61 0.05 0.04

Ground 0.58 0.04 0.03

Carrot FL Carrot Ground 1.38 0.08 0.04

Cotton CA Cotton Aerial (Default) 1.52 0.15 00.14

Ground 0.86 0.10 0.09

MS Cotton Aerial (Default) 3.37 0.26 0.19

Ground 2.81 0.22 0.15

NC Cotton Aerial (Default) 4.22 0.51 0.33

Ground 4.11 0.47 0.27

Peach Subgroup
12

- 12B CA Fruit Air

- blast 0.42 0.03 0.03

GA Peach 0.77 0.05 0.04

Peppers /Eggplant Subgroup
8

- 10B FL Peppers Aerial 2.36 0.16 0.12

Ground 2.02 0.12 0.08

Tree Nut Subgroup
14

- 12 CA Almond Air

- blast 0.52 0.08 0.07

GA Pecan 2.91 0.22 0.14

CPU 3

Aerial LV 5.00 (R) 4 0.64 (R) 0.28(R)

FL Citrus 1.83 (D) 4 0.25 (D) 0.23 (D)
6.83 (T) 4 0.89 (T) 0.51 (T)

Cotton MS Cotton Aerial (Default) 3.96 0.39 0. 16

NC Cotton 3.66 0. 79 0.46

1 For citrus scenarios EDWCs were generated using 150 ft and 25 ft buffer as prescribed in the diflubenzuron label
for aerial and air

- blast applications respectively

2 Bolded values are the highest EDWCs observed among various scenarios

### 12

Table 6

. EDWCs of Diflubenzuron and its Major Degradate, CPU for Surface Water

Crop Crop Scenario Application
Method 

### Peak (Acute)

Exposure Annual Mean

(chronic) Exposure 30

- year Mean

(cancer chronic) Exposure

----------------------- (μg/L)

-----------------------

3 CPU EDWCs were estimated for selected high concentration of diflubenzuron scenarios (i.e. FL Citrus, MS Cotton and NC cotton) observed during SWCC modeling

4 CPU EDWCs generated from Runoff (R) and drift (D) for citrus UL application . The summation of EDWCs from runoff and drift is designated as Total (T) CPU

.



### Estimated diflubenzuron and CPU concentrations in groundw ater used for drinking water are
summarized in Table 6

. Values in bold are recommended for use in the human health risk assessment. For groundwater sources of drinking water, the maximum acute and chronic estimated concentrations of CPU in shallow groundwa ter from PRZM

- GW model for applications to citrus are 8.61 μg/L and 8.02 μg/L , respectively. However, the concentrations of diflubenzuron in groundwater were negligible (Table
7 ). Sample outputs with the highest EDWCs from the PRZM

- GW model runs is provide d in Appendix B

.

Table 7

. Results from PRZM

- GW Modeling B ased on Diflubenzuron U se s on Citrus and Proposed New Uses

Crop (Application Rate) Scenario Highest Daily Value ( μ g/L) A verage ( μ g/L) Average S imulation Breakthrough Time (days)

Citrus 1 ( 0. 312 lbs a.i./ A x 3 applications)

Other Crops ( 0. 25 lbs a.i./ A x 3 applications) Diflubenzuron

FL

- Central Ridge 0

--

Incomplete 3 FL

- Jacksonville 0 0

GA Coastal 0 0

NC Coastal cotton 3.04E

- 18

-- DELMARVA Sandy 6.59E

- 20

WI Sand 0 0

CPU

FL

- Central Ridge 8.61 8.02 3191

FL

- Jacksonville 0.0 1 0.0 0 5942

GA Coastal 2.07 1.94 5291

NC Coastal cotton 4.26 3.81 4228
DELMARVA Sandy 1.07 0.94 3970

WI Sand 3.85 3.47 5665

1 PRZM

- GW modeled the highest diflubenzuron application rate of 0.312 lbs a.i/A for diflubenzuron uses using FL Central ridge scenario known for growing citrus crops.

2 Bolded concentrations are the highest EDWCs determined for groundwater

3 Incomplete with 30 and 100

- y ears simulation

### 13

Monitoring Data

Monitoring data for dif

lubenzuron are available from the United States Geological Survey ( USGS ) National Water

- Quality Assessment ( NAWQA ) P rogram Data Warehouse 3 

### , searched on April 06, 2015

. No diflubenzuron was detected in 11 surface water samples from Texas. However, the study design of NAWQA is not targeted to account for all diflubenzuron use areas ; timing of application and other factors which may more accurately represent spatially and

t emporally dependent variables influencing runoff vulnerability. No groundwater and sediment
data are available at this time.

Monitoring data for surface water, groundwater

, and sediment from the California Department of Pesticide Regulation (CDPR) 4 

### were a lso searched on April 06

, 201 5

. No diflubenzuron was detected in 66 surface water samples from California. No groundwater and sediment data are
available at this time. No monitoring data related to CPU is available at this time.

3 ( http://infotrek.er.usgs.gov/nawqa_queries/jsp/swmaster.jsp

4 http://www.cdpr.ca.gov/docs/emon/ehap.htm

### 14 References

USEPA, 2001. Health Effects Division (HED) Metabolism Assessment Review Committee (MARC) Meetings of 2/20/01 & 5/8/01. Diflubenzuron

. Residues of Concern for Cancer
Risk Assessment. Chemical 108201. Barcode D272976. Case 239100. Submission
S590172.

USEPA. 2009 . Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides , Version 2.1 . U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs,

E nvironmental Fate and Effects Division, October 22, 2009

.

US EPA . 20 12 a

. Registration Review : Problem Formulation for the Environmental Fate, Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for
Diflubenzuron. Environmental Fa te and Effects Division, Office of Chemical Safety and
Pollution Prevention. U. S. Environmental Protection Agency (D398815)

.

US EPA

. 20 12b . Memorandum: Approval of PRZM

- GW for use of Drinking Water Exposure
Assessment. Environmental Fate and Effects Divi sion, Office of Chemical Safety and
Pollution Prevention. U. S. Environmental Protection Agency.

USEPA, 2 013 a . Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model. Version 1. October 15, 2012. Environmental Fate and Effects Division. Office of Pesticide Programs. United States
Environm ental Protection Agency. Available at http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.ht

m

USEPA, 2013 b . Guidance on modeling off

- site deposition of pesticides via spray drift for ecological and drinking water assessments. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency

.

USE PA. 2014. Guidance on Development and Use of Community Water System Drinking Water
Intake Percent Cropped Area Adjustment Factors for Use in Drinking Water Exposure
Assessments :2014 Update . Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention, United States Environmental Protection Agency.

Van Dijk, N.R.M. 1992. Adsorption test with 4

- chlorophenylurea with four soil types. SOLVAY DUPHAR B.V., Environmental Research department, Graveland, The Netherlands (preliminary EFED review).

USDA, 2006. Fruits and Tree Nuts: Blooming, Harvesting, and Marketing Dates. USDA, National Agricultural Statistics Service, Agriculture Handbook No. 729 http://www.nass.usda.gov

### 15

USDA, 2010. Field Crops Usual Planting and Harvesting Dates

. USDA, National Agricultural Statistics Service, Agriculture Handbook No. 628. http://www.nass.usda.gov

### 16 APPENDIX A

Note: DT50 cannot be calculated for Clay loam soils from French and UK. Not enough data points to regress.

### 17

### 18 

# Appendix B

Sample Output s :

Summary of Water Modeling of Diflubenzuron and the USEPA Standard Reservoir

Estimated Environmental Concentrations for Diflubenzuron are presented in Table 1 for the USEPA standard reservoir with the FLcitrusSTD field scenario. A graphical presentation of the

year

- to

- year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are
summarized in Tables 2 and 3.

Table 1. Estimated Environmental Concentrations (ppb) for Diflubenzuron.

Peak (1

- in

- 10 yr) 4.61

4

- day Avg (1

- in

- 10 yr) 3.83

21

- day Avg (1

- in

- 10 yr) 2.75

60

- day Avg (1

- in

- 10 yr) 1.61

365

- day Avg (1

- in

- 10 yr) 0.410

Entire Simulation Mean 0.376

Table 2. Summary of Model Inputs for Diflubenzuron.

Scenario FLcitrusSTD

Cropped Area Fraction 1.0

Koc (ml/g) 4862.1

Water Half

- Life (days) @ 25 °C 25.2

Benthic Half

- Life (days) @ 25 °C 102

Photolysis Half

- Life (days) @ 40 °Lat 80

Hydrolysis Half

- Life (days) 119

Soil Half

- Life (days) @ 25 °C 5.1

Foliar Half

- Life (days)

Molecular Wt 311

Vapor Pressure (torr) 9.0E

- 10

Solubility (mg/l) 0.08

Table 3. Application Schedule for Diflubenzuron.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

12/10 Foliar 0.35 0.69 0.21

12/17 Foliar 0.35 0.69 0.21

12/24 Foliar 0.35 0.69 0.21

### 19

Figure 1. Yearly Peak Concentrations



### Summary of Water Modeling of CPU and the USEPA Standard Reservoir

Simulated Concentration from Runoff Contribution only

Estimated Environmental Concentrations for CPU are presented in Table 1 for the USEPA standard reservoir with the FLcitrusSTD field scenario. A graphic al presentation of the year

- to

year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are
summarized in Tables 2 and 3.

Table 1. Estimated Environmental Concentrations (ppb) for CPU.

Peak (1

- in

- 10 yr) 5.00

4

- day Avg (1

- in

- 10 yr) 4.73

21

- day Avg (1

- in

- 10 yr) 3.81

60

- day Avg (1

- in

- 10 yr) 2.69

365

- day Avg (1

- in

- 10 yr) 0.639

Entire Simulation Mean 0.284

Table 2. Summary of Model Inputs for CPU.

Scenario FLcitrusSTD

Cropped Area Fraction 1.0

### 20

Koc (ml/g) 246

Water Half

- Life (days) @ 25 °C 41.9

Benthic Half

- Life (days) @ 25 °C 0

Photolysis Half

- Life (days) @ 40 °Lat 0

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 65.4

Foliar Half

- Life (days)

Molecular Wt 177.6

Vapor Pressure (torr) 1.65E

- 04

Solubility (mg/l) 1770

Table 3. Application Schedule for CPU.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

12/10 Ground 0.066 1 0

12/17 Ground 0.066 1 0

12/24 Ground 0.066 1 0



### Figure 1. Yearly Peak Concentrations

Simulated concentrations from Drift Contribution only

Estimated Environmental Concentrations for CPU are presented in Table 1 for the USEPA standard reservoir with the FLcitrusSTD field scenario. A graphical presentation of the year

- to

year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are
summarized in Tables 2 and 3.

### 21

Table 1. Estimated Env ironmental Concentrations (ppb) for CPU.

Peak (1

- in

- 10 yr) 1.83

4

- day Avg (1

- in

- 10 yr) 1.73

21

- day Avg (1

- in

- 10 yr) 1.42

60

- day Avg (1

- in

- 10 yr) 1.04

365

- day Avg (1

- in

- 10 yr) 0.248

Entire Simulation Mean 0.232

Table 2. Summary of Model Inputs for CPU.

Scenario FLcitrusSTD

Cropped Area Fraction 1.0

Koc (ml/g) 246

Water Half

- Life (days) @ 25 °C 41.9

Benthic Half

- Life (days) @ 25 °C 0

Photolysis Half

- Life (days) @ 40 °Lat 0

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 65.4

Foliar Half

- Life (days)

Molecular Wt 177.6

Vapor Pressure (torr) 1.65E

- 04

Solubility (mg/l) 1770

Table 3. Application Schedule for CPU.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

12/10 Ground 0.020 0 1

12/17 Ground 0.020 0 1

12/24 Ground 0.020 0 1



### Figure 1. Yearly Peak Concentrations

### 22

Groundwater Analysis for Diflubenzuron and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Diflubenzuron are presented
in Table 1 for the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations in the aq uifer 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 2 and
3.
Table 1. Groundwater Results for Diflubenzuron and the Florida Citrus

- FL Central Ridge, Pol k County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 1.6E

- 12

Post

- Breakthrough Mean Concentration (ppb) Incomplete

Entire Simulation Mean Concentration (ppb) 2.74E

- 13

Average Breakthrough Time (days) Incomplete

Throughputs 0.2207278

Table 2. Chemical Properties for Groundwater Modeling of Diflubenzuron.

Koc (ml/g) 4862.1

Surface Soil Half Life (days) 5.2

Hydrolysis Half Life (days) 116

### 23

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Diflubenzuron. This application scheme was applied every year of the simulation.

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

12/10 Ground application with mass distribution increasing proportionally with depth to 4

cm 0.349

12/17 Ground application with mass distribution increasing proportionally with depth to 4

cm 0.349

12/24 Ground application with mass distribution increasing proportionally with de pth to 4

cm 0.349



### Figure 1. Aquifer Breakthrough Curve for Diflubenzuron and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A
Scenario

Groundwater Analysis for CPU and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for CPU are presented in Table 1
for the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met Fi le (12842.dvf)

- Astatula sand, hrgb A 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 2 and 3.

### 24

Table 1. Groundwater Results for CPU and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 8.61

Post

- Breakthrough Mean Concentration (ppb) 8.02

Entire Simulation Mean Concentration (ppb) 6.25

Average Breakthrough Time (days) 3191.4

Throughputs 3.434229

Table 2. Chemical Properties for Groundwater Modeling of CPU.

Koc (ml/g) 246

Surface Soil Half Life (days) 65.4

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for CPU. This application scheme was applied every year of the
simulation.

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

12/10 Ground application with mass distribution increasing proportionally with depth to 4

cm 0.096

12/17 Ground application with mass distribution increasing proportionally with depth to 4

cm 0 .096

12/24 Ground application with mass distribution increasing proportionally with depth to 4

cm 0.096



### Figure 1. Aquifer Breakthrough Curve for CPU and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

### 25