### 2

sugar beet 1.98 lbs a.i/A . Terbufos application s are limited to one application per year for each

crop

.

This drinking water assessment was performed using a parent only approach ( terbufos ) as well as

a total toxic residue approach (TTR; i.e. parent plus terbufos sulfoxide and terbufos sulfone)

, as

recommend ed by the Residues of Concern Know ledgebase Subcommittee (ROCKS) of the

Hea l th Effects Division (US EPA 2014 ; DP417464 )

. T he s urface water and groundwater

modeling w ere conducted according to label ed use directions

, which listed a maximum annual

application rate of 1. 30 lbs. a.i./A to 1.98 lbs a.i/A for various crops

. Modeling for the ground

application us ed the coupled models PRZM and EXAMS for surface water and SCI

- GROW as

well as PRZM

- GW for groundwater

. Recommend ed EDWCs for terb u fos and total toxic

residue s of terbufos in surface water and groundwater are summarized in Table 1.

Table 1

. Recommended EDWCs for Drinking Water R isk A ssessment for Terbufos and

its Degradates

Source of Drinking

Water Estimated Drinking Water C oncentration (μg/L)

1

- in

- 10

- year Peak

Exposure 1

- in

- 10

- year Annual

Mean Exposure 30

- year Mean

Exposure

Total Toxic Residue s of Terbufos (Terbufos plus Terbufos Sulfoxide and Terbufos Sulfone)



### Surface Water a,b 

### 63.06 11.53 6.13

Groundwater c 

### 33.54

-- 14.02

Terbufos (Parent only)



### Surface Water b,d 

### 46.02 0.28 0.12

Groundwater e 

### 0.02 0.02 0.02

a EDWCs based on PRZM/EXAMS model and residue summation method for TX Sorghum OP Scenario

b PCA adjusted modeled values

c Highest EDWCs based summation of terbufos, terbufos sul f oxide and terbufos sulfone derived from PRZM

- GW

model for Delmarva scenario

d EDWCs based on PRZM/EXAMS model for parent terbufos alone for MS corn STD Scenario

e EDWCs for parent terbufos were derived from SCI

- GROW model



### Drinking Water Exposure Modeling

Surface Water

A Tier II d rinking water assessment was performed using PRZM (v3.12.2)/EXAMS (v.

2.98.04.06) modeling with the index reservoir scenario. The EDWCs were generated for the

parent only and for terbufos parent plus its two major degradates, terbufos sulfoxide and terbufos

sulfone (TTR approach)

. Available environmental fate data for terbufos and individual

degradates were used in exposure assessments

. For the TTR approach

, the residue summation

method was used in estimating concentration s for individual residue s of concern

, which were

then summated to represent the TTR s

. Description of the r esidue summation m ethod can be

found in the document related to the m ethods for assessing ecological risks of pesticides with

persistent, bioaccumulative and toxic characteristic s (USEPA, 2008). Application rates for

transformation products were ad justed to account for the parent and the normalized maximum

percentage of transformation product formed as well as for molecular weight ratios of parent to

the metabolite

. T he t wo scenarios with the highest EDWCs for the parent (i.e. MS corn STD and

TX Sorghum OP scenarios) were simulated to generate EDWCs for the TTR. P ost

- processing of

### 3

estimated EDWCs generated for terbufos and its degradates was applied using EXCEL

spreadshee t software in estimating the 1

- in

- 10 year exposure concentrations for TTR

.

T he Pesticide Root Zone Model, (PRZM, Carsel et al . 1997) and the Exposure Analysis

Modeling System (EXAMS, Burns 2000) were used in tandem to generate surface water

EDWCs . PRZM (3.12.2 dated May 12, 2005) simulates fate and transport on the agricultural

land whereas EXAMS (2.98.04.06, dated April 25, 2005) simulates the fate and resulting daily

concentrations in the water body. Simulations wer e carried out with the linkage program shell,

PE5V01.pl (dated November 15, 2006), which incorporates the standard agricultural scenarios

developed by the Environmental Fate and Effects Division ( EFED )

. The PRZM model s imulates

pesticide movement and transformation from crop applicatio n through soil residue processes.

The EXAMS model simulates pesticide loading via runoff, erosion, and spray drift assuming a

standard watershed of 172.8 ha that drains into an adjacent standard drinking water index

reservoir of 5.26 ha with an average de pth of 2.74 m. A more detailed description of the index

reservoir watershed can be found in Jones et al. , 1998. Standard percent cropped areas (PCA)

were used for proposed uses as estimates of the extent of watershed on which crops are grown.

The default PCA of 0.91 was used for the proposed uses because currently terbufos can be used

in agricultural settings only (USEPA 2012 b ).

PRZM/EXAMS input parameters are shown in Table s 3

, 4 and 5 for the parent, terbufos

sulfoxide and terbufos sulfone

, respective ly. Simulations are run for multiple (usually 30) years,

and the E DWCs represent peak values that are expected once every ten years based on the thirty

years of daily values generated during the simulation. Sample output s and results o f

PRZM/EXAMS modeling are provided in Appendix B

. The EDWCs for the parent and TTR s are provided in Table 6

. P RZM/EXAMS generated “t ime series ” files of terbufos for MS corn

STD and TTR for TX sorghum OP scenario s are also attached in Appendix B

. Additional

information on these models can be found at: http://www.epa.gov/oppefed1/models/water

/index.htm

.

Table 3 . PRZM/EXAMS Input Parameters for Terbufos

Parameter Input Value Source Comment

Application Rate Corn: 1.30 lbs a.i/A

Sorghum: 1.68 lbs a.i./

Sugar beet: 1.98 lbs a.i/A EPA Reg # 241

- 314

EPA Reg# 5481

- 562 These are maximum

application rates for

specified crops

Number of

application / year 1 EPA Reg # 241

- 314

EPA Reg# 5481

- 562 Label directions

Application method Ground Current Label s Label directions

CAM 6 PRZM Manual To simulate subsurface

incorporation of applied

terbufos

Depth of Incorporation 1 inch Current labels Label direction for corn.

For sorghum and sugar beet,

incorporation depths were

assumed based on seeding

depths.

### 4

Table 3 . PRZM/EXAMS Input Parameters for Terbufos

Parameter Input Value Source Comment

Use Site

Scenario and

Application Date

(Month

- Date) Corn

CA corn OP (04

- 01)

IA corn STD (05

- 25

IL corn STD (05

- 01)

IN corn STD (05

- 15)

KS corn STD (05

- 10)

MN corn STD (05

- 15)

MS corn STD (04

- 10)

NC CornE STD (04

- 15)

NC CornW OP (04

- 25)

ND Corn OP (05

- 05)

NE corn STD (05

- 25)

OH corn STD (05

- 01)

PA corn STD (04

- 16)

TX corn OP (03

- 16)

FL sweetcorn OP (10

- 16)

OR Sweetcorn OP (05

- 16)

Suger beets

CA Sugar Beet Wirrg OP (02

- 01)

MN Sugar Beet STD (05

- 16)

Sorghum

KS Sorghum STD (05

- 20)

TX Sorghum OP (05

- 10) Label directions

and available

scenarios The f ollowing scenarios

were used in generating

EDWCs.

Corn

11 standard and 5 organo

phosphate specific scenarios

Suger beets

1 standard and 1 organo

phosphate specific scenarios

Sorghum

1 standard and 1 organo

phosphate specific scenarios

Spray drift fraction Not applicable EFED Guidance (US

2013) ---

Molecular weight 288.4 g/mole MRID 4104495

- 02

--- Solubility in water

25 °C) 5.4 mg/L MRID 4104495

- 02

---

Vapor pressure 6.6E

- 04 (mmHg @25°C) MRID 4104495

- 02 Additional parameters such

as DAIR and Enthalpy

were used for semi

- volatile

characteristic of terbufos Henry’s Law constant

(20 °C) 2.46E

- 05 atm.m 3 /mol Footprint

DAIR 3372 cm 2 /s Estimated Schwarzenbach et al, 1993

Enthalpy 12.88 http://www.chemical

book.com/ MSDS for terbufos

Hydrolysis (t 1/2 ) 1 1.5 days @ 25°C @ pH 7 MRID 44862501 Appendix A contains DT 50

calculations

Aquatic photoly sis

(t 1/2 ) 1 1.77 days MRIDs 00161567

and 41181101 Appendix A contains DT 50

calculations

Aerobic soil

metabolism (t 1/2 ) 1 1 4.7 days MRIDs 00156853

and 41749801 Appendix A contains DT 50

calculations. The 90% of the

upper confidence limit ( UCL )

of the mean metabolism half

life 2

. Aerobic aquatic

metabolism (t 1/2 ) 1 36.2 days MRID 44672004

### 5

Table 3 . PRZM/EXAMS Input Parameters for Terbufos

Parameter Input Value Source Comment

Anaerobic aquatic

metabolism (t 1/2 ) Stable 2

--- Since terbufos is sensitive to

hydrolytic degradation,

anaerobic aerobic aquatic

metabolism was assumed

stable according to Input

Parameter Guidance

(USEPA 2009) 2

Partition coefficient K d 11.11 mL/g MRID 41373604 Represent average K d for 4

soils

1 DT 50s were recalculated using NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in

Environmental Media (USEPA 2012). Appendix A contains revised estimated half

- lives.

2 http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm



### Table 4 . PRZM/EXAMS Input Parameters for Terbufos Sulfoxide

Parameter Input Value Source Comment

Use Site

Scenario 1 and

Application (Month

Day) Corn

MS corn STD ( 0 5

- 10)

Sorghum

TX Sorghum OP ( 0 6

- 10) --- Application dates were

adjusted based on maximum

terbufos sulfoxide formation

in laboratory study

Application Rate Corn: 0.72 lbs

Sorghum: 0.93 lbs

Sugar beet: 1.08 lbs Estimated See sample calculations

below 2

Number of applications

per year 1 EPA Reg # 241

- 314

EPA Reg# 5481

-
562 ---

Application method G round

---

Degradation product of

terbufos CAM 1

---

Spray drift fraction Not applicable

--- Molecular weight 304.42 g/mole EPISUITE 4.1

--- Solubility in water

25 °C) 3214 mg/L MRIDS 44672001

and 44672002 Solubility of terbufos

sulfoxide is higher terbufos

Vapor pressure 3.42E

- 05 (mmHg @25°C) EPISUITE 4.1

Estimated using EPISUITE

model Henry’s Law constant

(25 °C) 9.13E

- 08 atm.m 3 /mol EPISUITE 4.1

Hydrolysis (t 1/2 ) 65.1 days @ 25°C MRID 44862501

---

Aquatic photolysis (t 1/2 ) Stable

--- In absence of data, a ssumed

stable according to Input

Parameter Guidance

(USEPA 2009) 3

Aerobic soil

metabolism (t 1/2 ) 136 x 3 (408 days ) MRIDs 00156853 Single value is available. 3X

was used according to Input

Parameter Guidance

(USEPA 2009) 3

### 6

Table 4 . PRZM/EXAMS Input Parameters for Terbufos Sulfoxide

Parameter Input Value Source Comment

Aerobic aquatic

metabolism (t 1/2 ) Stable

--- In absence of data, a ssumed

stable

Anaerobic aquatic

metabolism (t 1/2 ) Stable

--- Since terbufos sulfoxide is

sensitive to hydrolytic

degradation, anaerobic

aerobic aquatic metabolism

was assumed stable

according to Input

Parameter Guidance

(USEPA 2009) 3

Partition coefficient K d 1.12 mL/g MRID 41373604 Represent average K d for 4

soils

1 The highest EDWCs for parent (i.e. MS corn STD and TX Sorghum OP scenarios) were used for generating

TTR EDWCs

2 Terbufos Sulfoxide application rate = Terbufos application rate of [1 .30 lbs x (0.523, the maximum conversion

rate from the degradation of terbufos to terbufos sulfoxide in laboratory studies) x (1.05 5, the molecular weight

ratio of terbufos sulfoxide to terbufos]

3



### = http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm



### Table 5 . PRZM/EXAMS Input Parameters for Terbufos Sulfo ne

Parameter Input Value Source Comment

Use Site

Scenario 1 and Application

(Month

- Day) Corn

MS corn STD (0 6

- 10)

Sorghum

TX Sorghum OP (0 7

- 10) --- Application dates were

adjusted based on maximum

terbufos sulfone formation

in the laboratory study

Application Rate 1 Corn: 0.29 lbs

Sorghum: 0.38 lbs

Sugar beet: 0.44 lbs Estimated See a sample calculations

below 2

Number of applications

per year 1 EPA Reg # 241

-
314

EPA Reg# 5481

- 562

Application method G round

--- Degradation product of

terbufos CAM 1

Spray drift fraction Not applicable

--- Molecular weight 320.42 g/mole EPISUITE 4.1

---

Solubility in water

25 °C) 407 mg/L MRIDS

44672001 and

44672002 More soluble than terbufos

Vapor pressure 7.88E

- 06 (mmHg @25°C) EPISUITE 4.1

Estimated using EPISUITE

model Henry’s Law constant

(25 °C) 4.10E

- 08 atm.m 3 /mol EPISUITE 4.1

Hydrolysis (t 1/2 ) 43.8 days @ 25°C MRID

444862501

Aquatic photolysis (t 1/2 ) Stable

--- Assumed stable

### 7

Table 5 . PRZM/EXAMS Input Parameters for Terbufos Sulfo ne

Parameter Input Value Source Comment

Aerobic soil metabolism

(t 1/2 ) 174 x 3 (522 days ) MRIDs

00156853 Single value is available. 3X

was used according to Input

Parameter Guidance

(USEPA 2009) 2

Aerobic aquatic

metabolism (t 1/2 ) Stable ---- In absence of data, a ssumed

stable according to Input

Parameter Guidance

(USEPA 2009) 3

Anaerobic aquatic

metabolism (t 1/2 ) Stable

--- Since terbufos sulfoxide is

sensitive to hydrolytic

degradation, anaerobic

aerobic aquatic metabolism

is assumed stable according

to Input Parameter

Guidance (USEPA 2009) 3

Partition coefficient K d 1.26 mL/g MRID 41373604 Represent average K d for 4

soils

1 The highest EDWCs for parent (i.e. MS corn STD and TX Sorghum OP scenarios) were used for generating

TTR EDWCs

2 Terbufos Sulfo ne application rate = Terbufos application rate of [1 .30 lbs x (0. 201 , the maximum conversion

rate from the degradation of terb ufos to terbufos sulfo ne in laboratory studies) x (1. 11, the molecular weight ratio

of terbufos sulfoxide to terbufos]

3 http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm



### Table 6

. Surface Water EDWCs for Drinking Water R isk A ssessment for Terbufos and

its Total Toxic Residue

Senarios Estimated Drinking Water C oncentration (μg/L)

1

- in

- 10

- year Peak

Exposure 1

- in

- 10

- year Annual

Mean Exposure 30

- year Mean

Exposure

Parent only

CA corn OP 2.49 0.02 0.00

IA corn STD 15.58 0.12 0.04

IL corn STD 10.42 0.08 0.04

IN corn STD 11.50 0.08 0.03

KS corn STD 15.65 0.12 0.06

MN corn STD 4.97 0.04 0.02

MS corn STD 46.02 0.28 0.12

NC CornE STD 16.14 0.10 0.02

NC CornW OP 12.37 0.09 0.05

ND Corn OP 5.84 0.05 0.02

NE corn STD 28.95 0.22 0.10

OH corn STD 11.01 0.11 0.05

PA corn STD 4.32 0.04 0.02

TX corn OP 8.63 0.07 0.03

FL sweetcorn OP 22.99 0.17 0.09

OR Sweetcorn OP 1.18 0.01 0.00

KS Sorghum STD 14.59 0.12 0.06

TX Sourghum OP 36.71 0.23 0.09

### 8

Table 6

. Surface Water EDWCs for Drinking Water R isk A ssessment for Terbufos and

its Total Toxic Residue

Senarios Estimated Drinking Water C oncentration (μg/L)

1

- in

- 10

- year Peak

Exposure 1

- in

- 10

- year Annual

Mean Exposure 30

- year Mean

Exposure

CA Sugarbeet OP 10.52 0.08 0.02

MN Sugarbeet STD 7.31 0.05 0.03

Total Toxic Residue 1

MS corn STD 60.25 6.84 3.61

TX Sorghum OP 63.06 11.58 6.13

1 Total Toxic residues are based on two scenarios with the highest EDWCs for parent (i.e. MS corn STD and TX

Sorghum OP scenarios)



### Ground w ater

Screening Concentration in Ground Water (SCI

- GROW v2.3, Jul. 29, 2003) is a regression

model used as a screening tool to estimate pesticide concentrations found in groundwater used as

drinking water. The SCI

- GROW model and user’s manual may also be downloaded from the

EPA Water Models web

- page ( http://www.epa.gov/oppefed1/models/water/#scigrow ). A

summary of the model input parameter values used in the SCI

- GROW m odel is listed in Table 7

. SCI

- GROW EDWCs are presented in Table 8

.

Table. 7

. SCI

- GROW Input Parameters for T erbufos, T erbu fos S ulfoxide and

T erbufos S ulfone

Model Input Variable Input Values Sources Comments

The following input parameters are applicable to parent terbufos

Application Rate 1 Corn: 1.30 lbs a.i/A

Sorghum: 1.68 lbs a.i./A

Sugar beet: 1.98 lbs

a.i/A EPA Reg # 241

-
314

EPA Reg# 5481

-
562 Label d irections

Number of Applications 1 Product Label as

above Label d irections

Aerobic Soil Metabolism

H alf

- L ife 8.03 days MRIDs 00156853

and 41749801 Mean value

K

oc 1460 mL/g MRID 41373604 Median value

The following input parameters are applicable to terbufos sulfoxide

Application Rate 1 Corn: 0.72 lbs A

Sorghum: 0.93 lbs /A

Sugar beet: 1.08 lbs /A Estimated See a sample calculation in

Table 4

Number of Applications 1 EPA Reg # 241

- 314

EPA Reg# 5481

- ---

### 9

Table. 7

. SCI

- GROW Input Parameters for T erbufos, T erbu fos S ulfoxide and

T erbufos S ulfone

Model Input Variable Input Values Sources Comments

Aerobic Soil Metabolism

H alf

- L ife 136 x 3 ( 408 days ) MRID 00156853 Single value is available. 3X

was used according to Input

Parameter Guidance

(USEPA 2009) 2

K

oc 112 mL/g MRID 41373604 Median value

The following input parameters are applicable to terbufos sulfone

Application Rate s 1 Corn: 0.29 lbs /A

Sorghum: 0.38 lbs /A

Sugar beet: 0.44 lbs /A Estimated See a sample calculation in

Table 5

Aerobic Soil Metabolism

H alf

- L ife 174 x 3 (522 days ) MRIDs 00156853 Single value is available. 3X

was used according to Input

Parameter Guidance

(USEPA 2009) 2

K

oc 141 mL/g MRID 41373604 Median value

1 SCI

- GROW modeling was performed based on the highest application rates for terbufos and its degradates

2 http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm



### Table 8. SCI

- GROW Simulated Groundwater EDWCs for Drinking Water R isk

A ssessment for Terbufos and it s Total Toxic Residue s

Residue of Concern Estimated Drinking Water concentration (μg/L) 1



### Peak Exposure Chronic Exposure

Terbufos 0.02 0.02

Terbufos Sulfoxide 7.28 7.28

Terbufos Sulfone 2.76 2.76

Total toxic Residue 2 10.06 10.06

1 EDWCs were generated for the highest application rate of 1.98 lbs a.i./ A for suga r beet

2 Sum of residues of concern (i.e. terbufos, terbufos sulfoxide and terbufos sulfone)



### In addition, Tier 1 groundwater EDWCs for terbufos and its to t al toxic residue s , resulting from

its use on sug a r beet for its highe st application rate of 1.98 lbs a.i./A were estimated using the

PRZM

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

- GUI (Graphical User Interface, version 1.0,

August 31, 2012 a ). PRZM

- GW is a one

- dimensional, fini te

- 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 agricult ural field. PRZM

- GW permits the assessment of multiple years of pesticide

application (up to 100 years) on a single site. Six standard scenarios, each representing a

different region known to be vulnerable to groundwater contamination, are available for use with

PRZM

- GW for risk assessment purposes. E ach of these standard scenarios was used for PRZM

GW simulations . PRZM

- GW output values represent pesticide concentrations in a vulnerable

groundwater supply that is located directly beneath a rural agricult ural field following many

years of pesticide application. B reakthrough s were observed in all modeled scenarios. A

### 10

summary of the model input parameter values used in PRZM

- GW m odel is listed in Table 9

.

PRZM

- GW values are presented in Table 10

. 

### A sample output of PRZM

- GW model can be found

in Appendix B

.

Table 9 . PRZM

- GW Input Parameters 1 

### for Terbufos, Terbufos S ulfoxide and Terbufos

Sulfone

Variable Name Data Value Data Source

MRID(s) Comment

The following input parameters are applicable to parent Terbufos

Application Method Ground ( Granular) potato Current labels See Table 4

Application Rate

(lbs a.i./acre) [kg/ha] 1.98 [ 2.22 ] Sugar beet Current labels Used highest

application rate

Application Frequency 1 time/year Current labels See Table 4

Application Interval (days) Not Applicable Current labels See Table 4

Hydrolysis, DT 50 (Days) 1.5 days @ 25°C MRID 46902201

---

Aerobic Soil Metabolism

DT 50 (Days) 14.7 days MRIDs 00156853

and 41749801 The 90% of the upper
confidence limit ( UCL )

of the mean metabolism

half

- life

.

Partition C oefficient K d 11.11 mL/g MRID 41373604 Represent s average

K d for 4 soils

The following input parameters are applicable to Terbufos Sulfoxide

Application Method Ground (Granular) potato Current labels Application Method

Application Rate

(lbs a.i./acre) [kg/ha] 1. 08 [ 1.21 ] Sugar beet Current labels Application Rate

(lbs a.i./acre) [kg/ha]

Application Frequency 1 time/year Current labels Label Directions

Hydrolysis, DT 50 (Days) 65.1 MRID 46902201

---

Aerobic Soil Metabolism

DT 50 (Days) 136 x 3 (408 days) MRID 00156853 Single value is

available. 3X was

used according to

Input Parameter

Guidance (USEPA

2009) 1

Partition coefficient K d 11.11 mL/g MRID 41373604 Represent s average

K d for 4 soils

The following input parameters are applicable to Terbufos Sulfone

### 11

Table 9 . PRZM

- GW Input Parameters 1 

### for Terbufos, Terbufos S ulfoxide and Terbufos

Sulfone

Variable Name Data Value Data Source

MRID(s) Comment

Application Method Ground (Granular) potato Current labels Application Method

Application Rate

(lbs a.i./acre) [kg/ha] 0.44 [ 0.49 ] Sugar beet Current labels Application Rate

(lbs a.i./acre) [kg/ha]

Application Frequency 1 time/year Current labels Application

Frequency

Hydrolysis, DT 50 (Days) 43.8 MRID 46902201

---

Aerobic Soil Metabolism

DT 50 (Days) 174 x 3 (408 days) MRID 00156853 Single value is

available. 3X was

used according to

Input Parameter

Guidance (USEPA

2009) 2

Partition coefficient K d 11.11 mL/g MRID 41373604 Represent s average

K d for 4 soils

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



### Table 10

. PRZM

- GW Simulated Groundwater EDWCs for Drinking Water R isk

A ssessment for Terbufos and it s Total Toxic Residue s

Crop Scenario Highest

Daily

Value ( μ g/L) A verage ( μ g/L) Average S imulation

Breakthrough Time

(days)

Terbufos (Parent only)

Sugar beet

( 1.98 lbs a.i./ A x 1

application) D elmarva sweet corn 3.16E

- 14 2.56E

- 15 475

FL citrus 0 0 1170

FL potato 1.61E

- 17 2.63E18 306

GA peanut 3.10E

- 13 1 2.53E

- 14 328

NC cotton 0 0 1142

WI corn 0 0 1043

Terbufos Sulfoxide

Sugar beet

( 1.08 lbs a.i./ A x

1 application) Delmarva sweet corn 27.3 11.6 224

FL citrus 17.9 9.48 246

FL potato 10.8 6.11 266

GA peanut 0.952 0.0454 1007

NC cotton 0.563 0.233 1062

WI corn 0.658 0.00768 885

Terbufos Sulfone

Sugar beet

( 0.44 lbs a.i./ A x

1application) Delmarva sweet corn 6.24 2.42 226

FL citrus 3.36 1.61 246

FL potato 2.08 1.04 269

GA peanut 0.00324 0.00145 1010

NC cotton 0.0366 0.0146 1063

### 12

Table 10

. PRZM

- GW Simulated Groundwater EDWCs for Drinking Water R isk

A ssessment for Terbufos and it s Total Toxic Residue s

Crop Scenario Highest

Daily

Value ( μ g/L) A verage ( μ g/L) Average S imulation

Breakthrough Time

(days)

WI corn 0.00455 0.000502 885

Total Toxic Residue (EDWCs Summation of terbufos, terbufos sulfoxide and t erbufos sulfone)

Not applicable Delmarva sweet corn 33.54 14.02

Not applicable FL citrus 21.26 11.09

FL potato 12.88 7.15

GA peanut 0.10 0.05

NC cotton 0.60 0.25

WI corn 0.07 0.01

1 Bolded values are the highest EDWCs for parent, terbufos sulfoxide, terbufos sulfone and total toxic residue s

.



### Monitoring Data

A surface water an d groundwater monitoring study was conducted for terbufos and its

degradates

, terbufos sulfoxide and terbufos sulfone. The study was required by USEPA's Interim

Reregistration Eligibility Decision (IRED) to confirm exposures of terbufos and its degradates

terbufos sulfoxide and terbufos sulfone in drinking water sources (USEPA, 2008 ) . For the

surface water, a total of 502 samples were collected from 33 sites between 1999 and 2005. For

the groundwater, 73 samples were collected from 2003 to 2005. From 1999 t o 2003, samples

from numerous watersheds were provided by the NAWQA (National Water Quality Assessment)

program. In surface water, terbufos and terbufos oxon were not detected above the reporting

limits in any samples. Terbufos sulfoxide was detected in f our samples at 0.092 to 0.205 μg/L,

with an additional nine estimated detections of 0.045 to 0.262 μg/L. Terbufos sulfone was

detected in six samples at 0.046 to 0.114 μg/L, with 30 additional estimated detections of 0.012

to 0.034 μg/L. There were no dete ctions of terbufos or any degradates in any of the groundwater

samples.

Monitoring data from 2006 to up

- to

- date data from the USGS

- NAWQA program were accessed

o n March 18 , 201 4 to evaluate the current trend of terbufos and its degradates concentration s in

surface water and groundwater. All data of filtered surface water and groundwater was

downloaded since the evaluation of a monitoring study of terbufos and its degradates in drinking

water issued 200 8 (USEPS, 2008) . For surface water, a total of 6740 water samples were

analyzed for terbufos

. Terbufos was detected in only one sample and the concentration was 0.02

μg/L. There were two detections of 0.07 μg/L and 0.17 μg/L terbufos sulfone in surface water

samples out of 6198 water samples

. For groundwa ter, a total of 3582 water samples were

analyzed for terbufos

. Terbufos was detected in one sample with a concentration of 0.01 μg/L

. There were no detections of terbufos sulfone in any of the groundwater samples.

The National Water

- Quality Assessment Program of the U.S. Geological Survey began

monitoring the quality of source water and finished water of aquifers and major rivers used by

### 13

some of the larger community water systems in the United States (USGS 2010). The 295

anthropogenic organic compounds (AOCs) including terbufos and terbufos sulfone were

monitored for the Source Water

- Quality Assessments (SWQAs) studies during 2002

– 20 10

( Carter et al., 2010). The SWQA studies are intended to complement drinking

- water monitoring

required by Federal, State, and local programs, which focus primarily on post

- treatment

compliance monitoring. A total of 221 surface water samples were analyzed for terbufos and its

oxygen analog

, terbufos sulfone. There were no detections of terbufos and terbufos sulfone in

any samples.

Monitoring data for surface water, groundwater, and sediment from the California Department of

Pesticide Regulation (CDPR) were searched on March 18 , 201 4

. Terbufos was detected in only

one sam ple and the concentration was 0.04 μg/L out of 2538 surface water sample s

. There were

no detections of terbufos or its degradates in any of the groundwater samples

Uncertainties

Current labels of terbufos require certain setback distance s or vegetative buffer s between treated

area s and the bodies of surface water. A well maintained vegetative buffer could potential ly

intercept sediment laden pesticides via runoff from terbufos applied to the field. However, the

current s urface water model does not have the capability to account for prescribed setbacks or

vegetative buffer distances, thus the PRZM/EXAMS model generated EDWCs are considered

upper bound exposure s . In addit i on, a lack of the full suite of environmental fate data for major

degradates of terbufos is an uncertainty in this assessment. S elected persistence and mobility of

terbufos sulfoxide and terbufos sulfone were estimated from registrant submitted environmental

fate data . However, several fate parameters were assumed stable in absence of data

. Selected

physicochemical parameters w ere also estimated usi ng the EPISUITE, which is a Windows ®



### - based suite of physical/chemical propert ies and environmental fate estimation programs

developed by the EPA’s Office of Pollution Prevention Toxics and Syracuse Research

Corporation (SRC). Additional e nvironmental fate and physicochemical properties of major

degradates can reduce the uncertainties in the drinking water assessment

.

Conclusions

This assessment provides estimated drinking water concentrations (EDWCs) of terbufos and its

major metabolite s, terbufos sulfoxi de and terbufos sulfone

, in surface water and groundwater in

support of human health risk assessment for use of terbufos in various crops. The surface water

and groundwater modeling were conducted according to a label

- recommended maximum annual

appl icatio n rate of 1.3 0 to 1.98 lbs a.i./A for granular application s using the coupled models

PRZM and EXAMS for surface water and SCI

- GROW for ground water. In addition, the PRZM

GW model was used in determining groundwater EDWCs for terbufos and its total toxic

residue s

.

Recommended EDWCs for terbufos and total toxic residue of terbufos in surface water and

groundwater are summarized in Table 1. The maximum acute concentration of 63.06 μg/L and

chronic concentration of 6.13 μg/L for surface water were associated with application to

sorghum. T he maximum acute and chronic estimated concentrations of TTR in shallow

### 14

groundwater using PRZM

- GW model a r e 33.54 and 14.02 μg/L

, respectively. For parent

terbufos, the maximum acute concentration of 46.02 μg/L and chronic concentration of 0.12

μg/L for surface water were associated with application to corn. The maximum acute and

chronic estimated concentrat ions of terbufos in shallow groundwater i s 0.02 μg/L

, derived from

SCIGROW model.

Since the review of terbufos and its degradates terbufos sulfoxide and terbufos sulfone in

drinking water sources (USEPA, 2008 ) , l imited numbers of terbufos and terbufos su lfone have

been detected in surface water and groundwater samples collected for NAWQA and CDPR

. However, NAWQA monitoring data were not targeted specifically to terbufos use areas or during times of known terbufos use. Terbufos was not detected in sediment monitoring of the

NAWQA program. For SQWA, a total of 221 surface water samples were analyzed for terbufos

and its oxygen analog

, terbufos sulfone. There were no detections of terbufos and terbufos

sulfone i n any samples.

### 15 References

Carter, J.M ., Kingsbury, J.A., Hopple, J.A., and G.C. Delzer. 20 10

. Concentration data for

anthropogenic organic compounds in groundwater, surface water, and finished water of

selected community water systems in the United States, 2002

– 10: U.S. Geological

Survey Data Series 544

.

Jones, R. D., S. Abel, W. R. Effland, R. Matzner, R. Parker. 1998. An Index Reservoir for Use

in Assessing Drinking Water Exposure. Proposed Methods for Basin

- scale Estimation of

Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment.

Presentation to FIFRA Science Advisory Panel, June 29

- 30, 1998. Online at:

http://www.epa.gov/scipoly/sap/1998/index.htm

Schwarzenbach R.P., Gschwend P.M. and D.M. Imboden. 1993. Environmental Organic

Chemistry, Wiley

- Interscience, N J

USEPA, 2008. White Paper on Methods for Assessing Ecological Risks of Pesticides with

Persistent, Bioaccumulative and Toxic Characteristics. Office of Chemical Safety and

Pollution Pre vention. U. S. Environmental Protection Agency.

http://www.epa.gov/scipoly/sap/meetings/2008/october/sap_pbt_whitepaper_final_Oct_7

_08d.pdf

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,

Environmental Fate and Effects Division, October 22, 2009

.

USEPA. 2010 . Water Models. U.S. Environment al Protection Agency, Pesticides: Scienc e and

Policy. Online at: http://www.epa.gov/oppefed1/models/water/

US EPA

. 20 12 a

. Development and Use of Percent Cropped Area and Percent Turf Area

Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update

http://www.epa.gov/oppefed1/models/wat er/pca_adjustment_dwa.html

US EPA

. 20 12b . Memorandum: Approval of PRZM

- GW for use of Drinking Water Exposure

Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and

Pollution Prevention. U. S. Environmental Protection Agency.

U S EPA . 20 14. Terbufos. Report of the Residues of Concern Knowledge base S ubcommittee

(ROCKS) Office of Chemical Safety and Pollution Prevention. U. S. Environmental

Protection Agency. (DP 417464)



### US EPA . 20 13b. Guidance on Modeling offsite 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. De cember 20, 2013.

### 16 APPENDIX A

Terbufos

Hyd ro lysis (MRID 44862501

Temperature adjusted DT 50 

### @ 25o C 1.5 days

Following guidance was used in calculating temperature adjusted DT50s.

http://www.epa.gov/oppefed/models/water/input_parameters_guidance.html

### 17

Aquatic Photolysis (MRID 41181101

Estimated DT 50 

### is 1.77 days @ 25o C

### 18

Aerobic Soil Metabolism (MRID 00156853)

Aerobic Soil Metabolism (MRID 41181101)

90 th 

### %tile DT 50 

### 14.7 days

### 19

Aerobic Aquatic Metabolism (MRID 44672204)

Temperature adjusted 90 th 

### %tile DT 50 

### @ 25o C 36.2 days

### 20 Terbufos Sulfoxide

Hydrolysis (MRID 44862501

Temperature adjusted DT 50 

### @ 25o C 65.1 days

Aerobic Soil Metabolism (MRID 00156853)

### 21

Terbufos Sulfon e



### Hydrolysis (MRID 44862501

Temperature adjusted DT 50 

### @ 25o C 43.8 days

Aerobic Soil Metabolism (MRID 00156853)

### 22

APPENDIX B

Table 6. Surface Water EDWCs for Drinking Water for Terbufos and its Total Toxic

Residue

Scenario Peak 96 hr 21 Day 60 Day 90 Day Yearly Average

of

yearly

averages

Estimated Drinking Water concentration (μg/L)

Terbufos

CA corn OP 2.49 1.08 0.29 0.10 0.07 0.02 0.00

IA corn STD 15.58 6.88 2.08 0.73 0.49 0.12 0.04

IL corn STD 10.42 4.48 1.23 0.47 0.32 0.08 0.04

IN corn STD 11.50 4.89 1.34 0.50 0.34 0.08 0.03

KS corn STD 15.65 7.58 1.93 0.72 0.49 0.12 0.06

MN corn STD 4.97 2.09 0.73 0.27 0.18 0.04 0.02

MS corn STD 46.02 19.49 4.25 1.71 1.14 0.28 0.12

NC CornE STD 16.14 6.91 1.59 0.59 0.40 0.10 0.02

NC CornW OP 12.37 5.60 1.42 0.53 0.35 0.09 0.05

ND Corn OP 5.84 3.52 0.91 0.33 0.22 0.05 0.02

NE corn STD 28.95 13.89 3.52 1.34 0.90 0.22 0.10

OH corn STD 11.01 5.57 1.78 0.66 0.45 0.11 0.05

PA corn STD 4.32 1.84 0.67 0.24 0.16 0.04 0.02

TX corn OP 8.63 4.02 1.14 0.42 0.29 0.07 0.03

FL sweetcorn OP 22.99 10.25 2.71 0.99 0.67 0.17 0.09

OR Sweetcorn OP 1.18 0.66 0.20 0.07 0.05 0.01 0.00

KS Sorghum STD 14.59 6.19 1.52 0.74 0.49 0.12 0.06

TX Sourghum OP 36.71 15.63 4.03 1.42 0.95 0.23 0.09

CA Sugarbeet OP 10.52 5.01 1.28 0.48 0.32 0.08 0.02

MN Sugarbeet STD 7.31 3.79 0.91 0.32 0.22 0.05 0.03



### Total Toxic Residue 1

MS corn STD 60.25 56.74 33.15 23.69 18.58 6.84 3.61

TX Sorghum OP 63.06 60.59 53.58 38.54 30.85 11.58 6.13

1 Total Toxic residues are based on two scenarios with the highest EDWCs for parent (i.e. MS corn STD and

TX Sorghum OP scenarios)

### 23

An Example of Non

- Adjusted PCA PRZM/EXAMS modeling Output

stored as MScornDW.out

Chemical: Terbusfos

PRZM environment: MScornSTD.txt, modified Tueday, 29 May 2007 at 2:57:40

EXAMS environment: ir298.exv, modified Tueday, 26 August 2008 at 05:14:08

Metfile: w03940.dvf, modified Tueday, 26 August 2008 at 05:14:14

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 3.44 1.48 0.33 0.16 0.12 0.03

1962 41.63 19.19 4.43 1.59 1.06 0.26

1963 4.71 1.99 0.54 0.19 0.15 0.04

1964 20.89 8.69 2.89 1.03 0.69 0.17

1965 0.94 0.40 0.09 0.03 0.02 0.01

1966 8.42 4.20 1.29 0.59 0.39 0.10

1967 7.61 3.25 1.10 0.54 0.36 0.09

1968 4.19 1.94 0.76 0.30 0.20 0.05

1969 30.06 12.66 3.95 1.40 0.93 0.23

1970 3.10 1.30 0.40 0.24 0.16 0.04

1971 16.51 8.07 2.35 0.93 0.62 0.15

1972 4.00 1.70 0.50 0.20 0.13 0.03

1973 40.85 18.26 4.09 1.51 1.01 0.25

1974 41.50 17.40 4.08 1.47 0.98 0.24

1975 6.43 2.96 1.09 0.47 0.32 0.08

1976 3.38 1.44 0.62 0.29 0.20 0.05

1977 6.59 3.89 1.08 0.39 0.26 0.07

1978 4.29 1.82 0.73 0.50 0.34 0.08

1979 88.51 48.86 11.28 4.20 2.81 0.70

1980 76.11 45.88 11.28 4.09 2.73 0.67

1981 3.30 1.59 0.44 0.18 0.12 0.03

1982 17.91 8.44 2.09 0.75 0.51 0.13

1983 51.56 21.67 4.69 1.91 1.28 0.32

1984 4.19 1.76 0.60 0.23 0.16 0.04

1985 1.20 0.59 0.15 0.06 0.04 0.01

1986 1.99 0.97 0.53 0.22 0.15 0.04

1987 1.81 0.81 0.34 0.15 0.10 0.03

1988 8.81 3.74 0.91 0.32 0.22 0.05

1989 9.57 4.17 1.17 0.45 0.31 0.08

1990 6.12 2.60 0.92 0.38 0.25 0.06

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.03 88.51 48.86 11.28 4.20 2.81 0.70

### 24

0.06 76.11 45.88 11.28 4.09 2.73 0.67

0.10 51.56 21.67 4.69 1.91 1.28 0.32

0.13 41.63 19.19 4.43 1.59 1.06 0.26

0.16 41.50 18.26 4.09 1.51 1.01 0.25

0.19 40.85 17.40 4.08 1.47 0.98 0.24

0.23 30.06 12.66 3.95 1.40 0.93 0.23

0.26 20.89 8.69 2.89 1.03 0.69 0.17

0.29 17.91 8.44 2.35 0.93 0.62 0.15

0.32 16.51 8.07 2.09 0.75 0.51 0.13

0.35 9.57 4.20 1.29 0.59 0.39 0.10

0.39 8.81 4.17 1.17 0.54 0.36 0.09

0.42 8.42 3.89 1.10 0.50 0.34 0.08

0.45 7.61 3.74 1.09 0.47 0.32 0.08

0.48 6.59 3.25 1.08 0.45 0.31 0.08

0.52 6.43 2.96 0.92 0.39 0.26 0.07

0.55 6.12 2.60 0.91 0.38 0.25 0.06

0.58 4.71 1.99 0.76 0.32 0.22 0.05

0.61 4.29 1.94 0.73 0.30 0.20 0.05

0.65 4.19 1.82 0.62 0.29 0.20 0.05

0.68 4.19 1.76 0.60 0.24 0.16 0.04

0.71 4.00 1.70 0.54 0.23 0.16 0.04

0.74 3.44 1.59 0.53 0.22 0.15 0.04

0.77 3.38 1.48 0.50 0.20 0.15 0.04

0.81 3.30 1.44 0.44 0.19 0.13 0.03

0.84 3.10 1.30 0.40 0.18 0.12 0.03

0.87 1.99 0.97 0.34 0.16 0.12 0.03

0.90 1.81 0.81 0.33 0.15 0.10 0.03

0.94 1.20 0.59 0.15 0.06 0.04 0.01

0.97 0.94 0.40 0.09 0.03 0.02 0.01

0.10 50.57 21.42 4.67 1.88 1.26 0.31

Average

of yearly

averages: 0.14

Inputs generated by pe5.pl

- Novemeber 2006

Data used for this run:

Output File: MScornDW

Metfile: w03940.dvf

PRZM

scenario: MScornSTD.txt

EXAMS

environm

ent file: ir298.exv

### 25

Chemical

Name: Terbusfos

Descripti

on Variable

Name Value Units Comments

Molecula

r weight mwt 288.4 g/mol

Henry's

Law

Const. henry 2.46E

- 05 atm

- m^3/mol

Vapor

Pressure vapr 6.60E

- 04 torr

Solubility sol 5.4 mg/L

Kd Kd 11.11 mg/L

Koc Koc mg/L

Photolysi

s half

- life kdp 1.77 days Half

- life

Aerobic

Aquatic

Metabolis

m kbacw 36.2 days Halfife

Anaerobi

c Aquatic

Metabolis

m kbacs 0 days Halfife

Aerobic

Soil

Metabolis

m asm 14.7 days Halfife

Hydrolysi

s: pH 7 1.5 days Half

- life

Method: CAM 6 integer See PRZM manual

Incorpora

tion

Depth: DEPI 2.56 cm

Applicati

on Rate: TAPP 1.46 kg/ha

Applicati

on

Efficienc

y: APPEFF 1 fraction

Spray

Drift DRFT fraction of application rate applied to pond

Applicati

on Date Date 4

- Oct dd/mm or dd/mmm or dd

- mm or dd

- mmm

Record

17: FILTRA

IPSCND 1

UPTKF

Record

18: PLVKRT

PLDKRT

FEXTRC 0.5

### 26

Flag for

Index

Res. Run IR Reservoir

Flag for

runoff

calc. RUNOFF total none, monthly or total(average of entire run)



### Time Series Files

### 27 Groundwater

SciGrow version 2.3

chemical:Terbufos

time is 2/28/2014 9:53:25

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

1.980 1.0 1.980 1.46E+03 8.0

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

groundwater screening cond (ppb) = 1.95E

- 02

************************************************************************

SciGrow version 2.3

chemical:Terbufos SO

time is 2/28/2014 9:55:31

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

1.080 1.0 1. 080 1.12E+02 408.0

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

groundwater screening cond (ppb) = 7.28E+00

************************************************************************

SciGrow version 2.3

chemica l:Terbufos SO

time is 2/28/2014 9:56: 3

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism ( days)

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

0.440 1.0 0.440 1.41E+02 522.0

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

groundwater screening cond (ppb) = 2.76E+00

************************************************************************

### 28

Example Output of PRZM

- GW modeling for Terbufos Sulfoxide for Delmarva Scenario