### 2 

# Drinking Water Exposure Assessment for the Registration Review

of Paclobutrazol on Ornamentals Grown in Outdoor/Indoor Nurseries, Turf (commercial, ornamental, and golf courses) , and

Seed Treatment of Tomato, Pepper, and Cucurbit

Paclobutrazol

CAS Number 76738

- 62

- 0

CAS Name

- (α R ,β R )

- rel

- β

- [(4

- chlorophenyl)methyl]

- α

- (1,1

- dimethylethyl)

- 1 H

- 1,2,4

- triazole

- 1

- ethanol



### Prepared by:

Faruque Khan, Ph.D. Senior Scientist

Environmental Risk Branch I U. S. Environmental Protection Agency 

### Office of Pesticide Programs

Environ mental Fate and Effects Division

Environmental Risk Branch I 1200 Pennsylvania Ave., NW

Mail Code 7507P Washington, DC 20460 Reviewed by: Stephen Wente, Ph.D. Biologist Christopher Koper, M.S ., Chemist

Environmental Risk Branch I

Environmental Fate an d Effects Division

### 3 1 EXECUTIVE SUMMARY

This document reports the drinking water exposure assessment for paclobutrazol to support the human health risk assessment for the registration review

. Paclobutrazol is a plant growth regulator that is currently registered for application to turf grass and a number of ornamentals (trees, shrubs, bulbs). It is also registered for use as seed treatment for tomatoes, peppers, and cucurbits. Registered application methods for paclobutrazol are foliar spray (greenhouse and outdoors) , soil drench (greenhouse and outdoors)

, soil injection, tree injection, bulb soak, plug/liner soak, and seed treatment. Revised T ier 1 surface water and groundwater modeling w ere conducted for the highest application rate of 6.1 lbs/A for nu rsery production of

container

- grown ornamentals through soil drench method (US EPA, 2011). Two major environmental degradates , CGA 149907 ( maximum of 40. 4 %) and NOA457654 ( maximum of 25.1%) were identified in the environmental fate and terrestrial field di ssipation studies

, and

were included in to the d rinking water exposure assessment . However, there is no available

recommendation to include these major metabolites from the Residues of Concern Knowledgebase Sub

- committees (ROCKS) of the Health Effects Divis ion (HED)

. The upper

bound estimated drinking water concentrations (EDWCs) for total toxic residue ( TTR

paclobutrazol plus two major degradates (CGA 149907 and NOA 457654) as well as for paclobutrazol ( parent only ) are provided in Table 1 for the human hea lth risk assessment

.

Table 1

. Estimated Maximum Drinking Water Environmental Concentrations (E DWC s) of

Paclobutrazol for Surface Water and Ground Water

Drinking Water Source (model) Use (modeled rate) a Application

Method Acute
( 

### μg/L ) Chronic
( 

### μg/L )



### Parent only (paclobutrazol)

Surface Water (FIRST) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 153.3 b 49.0 b

Groundwater (SCIGROW) Nursery : (1 app. X 2.50 lbs ai/acre) Drench 26.9 26.9 b

Groundwater (PRZM

- GW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 29.1 6.7



### Total Toxic Residue (Paclobutrazol plus CGA 149907 and NOA 457654)

Surface Water (FIRST) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 255.3 b 166.2 b

Groundwater (SCIGROW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 25.0 25.0

Groundwater (PRZM

- GW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 945.0 b 622.0 b

### 4 Table 1

. Estimated Maximum Drinking Water Environmental Concentrations (E DWC s) of

Paclobutrazol for Surface Water and Ground Water

Drinking Water Source (model) Use (modeled rate) a Application

Method Acute
( 

### μg/L ) Chronic
( 

### μg/L )

a Example of application rate calculation: 6.1 lbs/A

- (6.1lbs a.i. /A* (1.0

- 0.59) = 2.50 lbs a.i./A

Where

6.1 lbs a.i. /A is application rate for drench application for 8

- inch containe r grown ornamentals (US EPA, 2011) 0.59 is the minimum fraction of retention of parent (paclobutrazol) in column leaching study (MRID 40685004)

b Bolded values are recommended for human health concerns



### Tier I FIRST model concentra tions represent untreated surface water concentrations. The

SCIGROW and PRZM

- GW concentrations represent groundwater concentration that might be expected in shallow unconfined aquifers under sandy soils. For TTR, EFED recommends acute

surface water EDWC of 255.3 μg/L and a chronic EDWC of 166.2 μg/L for use in the human health risk assessment. For parent, EFED recommends acute surface water EDWC s of 153.3 μg/L and a chronic EDWC of 49.0 μg/L for use in the human health risk assessment. The

recommended EWD Cs for groundwater are 945 μg/L for acute and 622 μg/L for chronic and 29.1 μg/L for acute and 26.9 μg/L for chronic for TTR and parent respectively. These recommendations are based on the use of paclobutrazol on nursery at an annual application rate

of 6. 1 lbs a.i./A/season. The simulated concentrations provided in this assessment are upper

bound estimates of concentrations for drinking water.

2 PROBLEM FORMULATION

This is a Tier I drinking water assessment that uses modeling and available monitoring

data to estimate the groundwater and surface water concentrations in drinking water sources (pre

- treatment) resulting from pesticide use on sites that are vulnerable. This initial tier screens out chemicals with low potential risk and allows the Office of Pesti cide Programs ( OPP ) to focus resources on more refined risk assessments for chemicals which potentially present more significant risks. This drinking water assessment reports potential exposure concentrations for the human health dietary risk assessment an d provides a description of how those concentrations

were determined.

3 ANALYSIS

3.1 Use Characterization

Paclobutrazol, also known by the trade name s Clipper, Bonzi, Paczol, and PP333 , is a plant growth regulator that is currently registered for application to a number of foo d (seed treatments)

and non

- food crops (ornamentals and turf) to induce compact plant growth . Registered application methods for paclobutrazol are foliar spray, soil injection , soil drench, bulb soak, seed

treatment

, plug/liner soak, and tree injections. It is used to control the size of numerous plants including turf, trees in right

- of

- ways, ornamental trees and shrubs, and bulbs (flower trade). Ten different companies currently have registered products with paclobutrazol concentration s ranging

### 5 from 0.018 to 50 .0 percent. Current ly regist e r ed u ses and rates of paclobutrazol are shown in

Table 2

.

Table 2. Current Registered Uses and Application Rates of Paclobutrazol

Crop Maximum Application

R ate 1 Number of Applications Application

Method Shortest Application

Interval

(days) Reg # 2

Cucurbit 6.5 μ g/seed

0.00 0 29 lbs/A 1 Seed

Treatment N/A 000100

- 01014

Herbaceous

and

ornamentals (greenhouse) 5.7 mg ai/ft 2

Spray Application 0.20 lbs/A for 6’

- 8 pot 0.26 lbs/A for 18”x9” propagation tr ays drench application 4.3 lbs/A for 6” pot 6.1 lbs/A for 8’ pot NS Spray, Drench, Bulb Soak, Plug/Liner

Soak As needed 000100

- 00992

000100

- 00996

000100

- 01079

000400

- 00515

062097

- 00011

080697

- 00003

000228

- 679

62097

- 25

Pepper 16 μ g/seed

0.00 07 9 lbs/A 1 Se ed

Treatment N/A 000100

- 01014

Tomato 12.5 μ g/seed

0.00 040 lbs/A 1 Seed

Treatment N/A 000100

- 01014

Trees (shade

and ornamental) 0.009 lb ai per inch DBH

Tree injection: 0.36 lbs/A Soil Injection: 1.9 lbs/A

Basel drench: 1.9 lbs/A 1 Soil Injection,

Basal Drench, Tree Injection 3 years or as

needed 000100

- 01037

000100

- 00991

000100

- 00995

000100

- 01014

067690

- 00022

000228

- 680

74779

- 3

74779

- 7

80697

- 4

81943

- 31

62097

- 24

Turf 0.75 lb ai/A 3 Spray,

Broadcast 14 009198

- 00196

009198

- 00199

009198

- 00201

009198

- 00205

009198

- 00215

000100

- 01014

067690

- 00022

000538

- 00201

000538

- 00199

000228

- 680

80697

- 4

81943

- 31
NS=not specified on label N/A Not Applicable

1 Italic rates are provided by the Biological and Economic Analysis Division (US EPA, 2011)

2 Application rates repr esent maximum application rate for a least one of the EPA Reg# listed. Other labels may have slightly different application rates.

### 6 3.2 Environmental Fate and Transport Characterization

Paclobutrazol is a racemic mixture of the (2 R , 3 R )

- and (2 S , 3 S )

- enant iomers but the submitted physiochemical and fate properties of each enantiomer w ere not investigated in the

submitted studies . Therefore, it is assumed that each enantiomer of paclobutrazol has similar physiochemical and fate properties based on submitted studies. Paclobutrazol has a low solubility (25.9 mg/L) in water. The vapor pressure ( 1.28 x 10 - 9 

### mm Hg @ 25.0°C ) and Henry's Law Constant (8.09 x 10 - 10 

### atm m 3 

### /mol) indicate that the compound is relatively non

- volatile under field conditions. The log K

ow 

### of 3.2 indicates the potential for this chemical to bioaccumulate in aquatic organisms.

Paclobutrazol is stable to hydrolysis and photolysis. Degradation rates of aerobic soil metabolism were revised based on the NAFTA Guidance for evaluating degradation k inetics in environmental media (U.S. EPA, 2012a). Under aerobic conditions, paclobutrazol appears to be generally quite persistent in acidic soils, with half

- lives less than 471 days. However in soils with neutral or higher pH, estimated half

- lives were as short as 19 days. In anaerobic aquatic metabolism studies, paclobutrazol variably partitioned to the sediment and degraded with a half

life of more than one year in flood loam and silt loam soils. Since, the extrapolated h alf

- li ves were beyond the dura tion of experiment, paclobutrazol was considered stable in the anaerobic aquatic system

. Paclobutrazol residues were persistent and mobile in terrestrial field dissipation studies in California, West Virginia, Florida, North Carolina, Illinois, and Mississ ippi Half

- lives of paclobutrazol residues ranged from 450

- 950 days for orchard soils in California, West Virginia, and Florida, and 175 days to 252 days in agricultural soils in Mississippi, North Carolina, and Illinois. Two major environmental degradates, ketone analog of parent ( CGA

149907

, ≤ 40.0%) and 1H

- 1,2,4

- triazol

- 3

- ol ( NOA457654

, ≤ 25.1%) were identified in the environmental fate and terrestrial field dissipation studies.

The potential mobility of this compound is quite var i able; ranging from highly mob i le to moderately mobile in soi l according to the mobility classification of the Food and Agriculture Organization ( FAO

, 200 0 )

. Soil column leaching experiments involving aged (9 week) residues

of methine

- labeled paclobutrazol determined that the compound was relatively immobile in 30

c m columns of sand, sandy loam, loamy sand except in clay loam soils , where it was leached

with 66 cm rain over 9 weeks . In contrast, aged residue s tudies of triazole

- labeled paclobutrazol determined the compound to be of low mobili t y in 30 cm columns of sand and sandy loam soils, and mobile in loamy sand and clay loam soils. In all cases, the majority (58.6

- 90.7 percent of the applied) of aged residue did not leach out of the upper 10 cm of the treated soil columns. Table 3

summarizes the physiochemical and environmental fate and transport properties of paclobutrazol

.

Table 3. Physical, C hemical and Environmental Fate properties of Paclobutrazol

Parameter Value Reference Comments

Chemical Paclobutrazol MRID 456625

- 01

Chemical Class Tria zole

CA S No. 76738

- 62

- 0

Empirical Formula C 15 H 20 Cl N 3 O MRID 456625

- 01

### 7 Table 3. Physical, C hemical and Environmental Fate properties of Paclobutrazol

Parameter Value Reference Comments

IUPAC 

### ( 2 RS, 3 RS )

- 1

- (4

- chlorophenyl)

- 4,4

- dimethyl

2

- (1 H

- 1,2,4

- triazol

- 1

- yl)pentan

- 3

- ol MRID 456625

- 01

CAS Name (α R ,β R )

- rel

- β

- [(4

- chlorophenyl)methyl]

- α

- (1,1

- dimethylethyl)

- 1 H

1,2,4

- triazole

- 1

- ethanol MRID 456625

- 01

Structure MRID 456625

- 01

Selected Physical/Chemical Parameters

Molecular mass 293.8 g/mol MRID 456625

- 01

Solubility ( 20.0 °C) 25.9 m g/L (water) 2.8 g /L ( n

- Octanol )

79.8 g/L ( methanol ) 5.22 g/L (xylene) MRID 456625

- 05

MRI D 456625

- 03

Vapor pressure (25 .0 °C) 1.7 x 10 - 7 Pa (1.28 x 10 - 9 mm Hg) MRID 456625

- 05

Henry’s law constant (2 5 °C ) 8.2 x 10 - 7 Pa M 3 mol - 1

(8.09 x 10

- 12 atm M 3 mol - 1 ) MRID 456625

- 05

Octanol

- water partition coefficient (LogK OW ) (25°C) 3.18 MRID 4566 25

- 05

Persistence

Hydrolysis pH 4 : stable pH 7: stable pH 9: stable MRID 00132698

Aqueous Photolysis (t 1⁄2 ) Stable MRID 00132699

Soil Photolysis (t 1⁄2 ) Stable MRID 40685002 After 33 days paclobutrazol decrease to 86.4 % of applied radioactivity

A erobic Soil Metabolism (t 1⁄2 ) @ 25°C 1 Sandy clay l oam ,2
443.4 days f or triazole

label [950.4 days f or triazole label] 3
470.9 days for methane

label 1020.4 days for methane

label 3 MRID 4 0685003 Major metabolite (CGA 149907 (≈18.7%)

### 8 Table 3. Physical, C hemical and Environmental Fate properties of Paclobutrazol

Parameter Value Reference Comments

Sandy clay loam

2 0 0 .1 days
[ 277.9 days] 3 MRID 47338504 Supplemental

No major metabolites

detected above 10%.

Sandy loam

16.7 days 4

[ 33.2 days] 3,4 Major metabolites NOA 457654(25.1%) CGA 149907(13.3%)

Sandy loam 19 days 3

[ 24.0 days ] 3,4 Major metabolites NOA 457654 (20.5%) CGA 149907(26.3%)

Anaerobic Soil Metabolism No data

Anaerobic Aquatic Metabolism (t 1⁄2 ) Stable MRID 40685003 After a year of incubation, paclobutrazol decrease to ≤79% of applied radioactivity Major transfo rmation product: (CGA 149907 (≈16.8%)

Aerobic Aquatic Metabolism No data

--

Mobility

Soil Partition Coefficient Adsorption K d (mL/g)

9.5 ( Clay loam )

10.2 ( Sandy Clay loam )

7.6 ( Silty clay loam )

17.3 ( Silt loam ) 5
4.1 (sandy loam) 2.4 (loamy sand) 5.8 ( Silty clay) 1.4 (Sand) MRID 4188113 There was no significant

correlation (r 2 = 0.12)

between K d and % organic carbon.

Soil Partition Coefficient Desorption K des (mL/g) 6

15.6 ( Clay loam )

18.1 ( Sandy Clay loam )

14.0 ( Silty clay loam )

34.0 ( Silt l oam ) 5
5.1 (sandy loam) 10.4 (loamy sand) 2.7 (Silty clay) 6.1 (Sand) MRID 4188113

### 9 Table 3. Physical, C hemical and Environmental Fate properties of Paclobutrazol

Parameter Value Reference Comments

Adsorption K d (mL/g) 1.77(Sandy loam) 5
0.8 (Sandy loam) 2.66 (Silty clay loam) 1.8 (Clay loam) Desorption K des (mL/g) 6
10.9 (Sandy loam) 5
3.81 (Sandy loam)

14.2 (Silty clay loam) 11.7 (Clay loam) MRID 47338503 Supplemental

NOA 457654 Adsorption K d (mL/g)

Borstel Loamy Sand

- 0.09

Gartenaker Loam

- 0.25 Pappelacker San d y loam

0.19

18 Acres Sandy loam

- 0.30 MRID 47338502 NOA 457654 is a major degrradate of paclo butrazol Supplemental

Leaching Aged methine 14 C

- labeled paclobutrazol residues were relatively immobile

Aged trizole 14 C

- labeled paclobutrazol residues were mobile in loamy sand and clay loam soils and low mobility in san d s and sandy

loam soils MRID 40685004 Major transformation product CGA 149907 (≈12.6%)

Field Dissipation

Terrestrial Field Dissipation (t 1⁄2 ) 450 to 973 days (CA, WV, FL) MRID

40685006

- 406850012 Supplemental Major transformation product

CGA 149907

88 days (CA) 133 days (NY) M RID 47338505 Supplemental Major transformation product

- CGA 149907 (40%)

1 DT 50 value were recalculated using the NAFTA Guidance for evaluating and calculating d egradation k inetics in

e nvironmental media (U.S. EPA, 2012) and the estimated DT 50s were adju sted to 25°C using Arrhenius equation

. Calculation s can be found in Appendix A.

2 Calculated half

- lives are based on 14 C labeled of triazole and methane of paclobutrazol

3 Italic half

- lives are calculated based on paclobutrazol and its major degradates (CG A 149907 and NOA 457654). Calculation can be found in Appendix A.

4 High Soil pH (≥ 7.0) may have contributed faster degradation rates for aerobic soil metabolism

5 Japanese soils, excluded during exposure assessment

6 Reported values are based on second desorption step

### 10 3.3 Drinking Water Exposure Modeling

Tier 1 modeling was used to estimate the drinking water exposure for use in the dietary

risk assessment of paclobutrazol . The following is a description of the models used, the selection of the model input parameters, and a characterization of the output from these simulations.

3.3.1 Models

Tier 1 EDWCs for surface water were generated using FIRST, dated August 5, 2001. FIRST is a screening model designed by the Environmental Fate and Effects Division (EFED,

20 10 a) of the Office of Pesticide Programs to estimate the concentrations found in drinking water from surface water sources for use in human health risk assessment. As such, it provides upper bound values on the concentrations that might be found in drinki ng water due to the use of a pesticide. FIRST is a single

- event model (one runoff event), but can account for spray drift from multiple applications. FIRST is hardwired to represent the Index Reservoir, a standard water body used by the Office of Pestici de Programs to assess drinking water exposure (Office of Pesticide Programs, 20 10b ). It is based on a real reservoir, Shipman City Lake in Illinois, that is known to be vulnerable to pesticide contamination. The single runoff event moves a maximum

of 8% o f the applied pesticide into the reservoir. This amount can be reduced due to degradation on the field and the effects of binding to soil in the field. FIRST also uses a Percent Cropped Area (PCA) factor to adjust for the area within the watershed that i s planted to the modeled crop.

The national default PCA of 1.0 and 0.87 was applied for turf and nursery assessment

, respectively

.

Tier 1 EDWCs for groundwater were generated with SCIGROW 2.3, dated July 29, 2003 ( 2010a ). SCIGROW is a regression model u sed as a screening tool for ground water used as drinking water. SCIGROW was developed by regressing the results of Prospective Ground Water studies against the Relative Index of Leaching Potential (RILP). The RILP is function of

aerobic soil metabolism a nd the soil

- water partition coefficient. The output of SCIGROW represents the concentrations that might be expected in shallow unconfined aquifers under sandy

soils.

In addition, Tier 1 groundwater EDWCs for paclobutrazol and TTR , resulting from use for nursery were also derived using the PRZM

- GW model (Pesticide Root Zone Model for Groundwater, version 1.0, August 31, 2012), with the GW

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

- GW is a one

- dimensional, fi nite

- 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 agricu ltural 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 contaminations, are

available f or use with PRZM

- GW for risk assessment purposes. In PRZM

- GW simulations, each

of these standard scenarios was used. PRZM

- GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agric ultural field following many years of pesticide application. Descriptions of all executable

### 11 versions of current models used in drinking water exposure can be obtained from URL link ( http://www.epa.gov/ oppefed1/models/water/ ).

3.3.2 Modeling Approach and Input Parameters

Tables 4 , 5 and 6 summarize the model input parameter values used in FIRST

, SCI

GROW and PRZM

- GW

, respectively. These parameters were selected in accordance with EFED’s input parameter gui dance ( US EPA, 2010c and US EPA

, 2012c ). H alf

- lives (rate constants) listed in Table 3 were used for exposure modeling. The a verage soil

- water partitioning

coefficient was used in FIRST. For TTR , half

- lives were estimated by accounting the percent of applied parent (paclobutrazol) , CGA 149907 and NOA 457654 present on each sampling period

of fate studies ( Appendix A ). The lowest K

oc 

### value was used in SCI

- GROW because there was a greater than 3

- fold variability in the available data.

Table 4 . FIRST (v 1.0) I nput P arameter V alues for Paclobutrazol and Total Toxic Residues (TTR) of Paclobutrazol

Parameter Value Source Comments

Application

Rate (lb a.i./A) 2.5 0 lb a.i/A (based on

59 % retention of parent in soil column) 1

0.55 lbs/A ( based on 91 % retention of parent in soil

column

2.0 lbs/A for turf 2 Memo from the Biological and Economic Analysis Division (BEAD) (US EPA, 2011) Maximum application rate w as estimated based on information provided by BEAD (US EPA 2011)

and adjusted with the re tention of

paclobutrazol in a soil column leaching study (MRID 40685004)

Number of Applications 1 ( nursery ) 3 (turf) 

### Product Label

Soil Partitioning Coefficient (K d ml/g) 4.5 (Parent)

0.16 (NOA) MRID s 4188113 and 47338503 Mean value

Aerobic Soil

Meta bolism t 1/2 (d) 791 (T TR )

381 (Parent) MRID s 40685003 and

47 338504 90 th percentile upper confidence

bound on the mean.

Wetted in? No

--- ---

Depth of Incorporation (inches) 0

--- ---

Method of Application Drench

Ground Paclobutrazol labels ---

Spray Drift

Fractions 0 (drench) 6.4 (ground foliar) Paclobutrazol labels Model input guidance (US EPA, 2010)

Percent Cropped Area 0.87

1.0 Nursery

Turf National Default

No PCA established for turf

### 12 Table 4 . FIRST (v 1.0) I nput P arameter V alues for Paclobutrazol and Total Toxic Residues (TTR) of Paclobutrazol

Parameter Value Source Comments

Solubility in Water (mg/L) 25.9 (Parent)

336000 (TTR) MRID 4 56625

- 05

EPISUITE Estimated value

Aerobic Aquatic

Metabolism t 1/2 (days) 1594 (T TR

762 (Parent) 2X of Aerobic soil metabolism

half

- life Model input guidance (US EPA, 2010)

Hydrolysis t 1/2 0 MRID 00132698 Stable to hydrolysis

Aquatic Photolysis t 1/2 (da ys) 0 MRID 0013299 Stable to aquatic photolysis

1 Example of application rate calculation : 6.1 lbs/A

- (6.1lbs/A* (1.0

- 0.59)

Where

6.1 lbs/A is a pplication rate for drench application for 8

- inch container grown ornamentals (US EPA, 2011)

0.59 is the minimum fraction of retention of parent (paclobutrazol) in column leaching study (MRID 40685004)

2 Maximum single application rate of 0.67 lbs/A was used instead of 0.75 lbs/A to account maximum seasonal rate of

2.0 lbs/A due to Tier I model l imitation. Model accepts only uniform rate for multiple application s

.



### Table 5. SCIGROW 2.3 I nput P arameter V alues for Paclobutrazol and Total Toxic Residues (TTR) of Paclobutrazol

Parameter Value Source Comments

Maximum Application Rate (lbs a.i./A) 1 2. 50 Maximum application rate w ere estimated based on information provided by BEAD (US EPA 2011 and adjusted with the retention of chemicals in a soil column leaching study (MRID 40685004)

Maximum Number of Applications per

Year 1 (Nursery) Product L abel #s of application were based on information provided in the submitted labels for vegetables, grape, hops, and ornamentals and

flower bulbs

Aerobic Soil

Metabolism Half

- life (d ays ) 277.9 (Total Residue)

200.1 (Parent) MRID s 40685003

and 47 338504 medi an value

Organic Carbon

Partition Coefficient (K

oc , L/Kg) 2 40.4 (Parent)

0. 16 (NOA) MRID s 4188113

and 47338503

MRID 47338501 Lowest value; > 10X variability in

data

Average of four values

1 See calculation in Table 4

2 There is no significant corre lation between K d and organic carbon. Since , model does not have an option to use

K d , the lowest value of Koc was used in the model

### 13 Table 6

. PRZM

- GW (v 1.0 ) Input Parameter Values for Paclobutrazol and Total Toxic Residues (TTR) of Paclobutrazol

Parame ters 1 Value Data Source Comments

Application Method Ground Table 4 Same as input for FIRST Model

Maximum Application

Rate (lbs a.i./A) 2.50 Table 4 Same as input for FIRST Model

Application Frequency 1 Table 4 Same as input for FIRST Model

Hydrolysis (DT 50 ) d 0 (Parent and TTR) Table 4 Same as input for FIRST Model

Aerobic soil metabolism (DT 50 ) d 381 (Parent) 791 (TTR) Table 4 Same as input for FIRST Model

K

oc 40.4 (Parent)

0.16 L/Kg (NOA) Table 4 Same as input for FIRS T Model

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



### Modeling Results

Revised m odeling r esults are depicted in Table 6. Tier I FIRST model concentrations represent untreated surface water concentrations. The SCIGROW and PRZM

- GW concentrations represent groundwater concentration that might be expected in shallow unconfined aquifers

under san dy soils. For TTR, EFED recommends acute surface water EDWC of 255.3 μg/L and a

chronic EDWC of 166.2 μg/L for use in the human health risk assessment. For parent, EFED

recommends acute surface water EDWC of 153.3 μg/L and a chronic EDWC of 49.0 μg/L for

use in the human health risk assessment. The recommended EWDC s for groundwater are 945 μg/L for acute and 622 μg/L for chronic and 29.1 μg/L for acute and 26.9 μg/L for chronic for TTR and parent re s pectively. These recommendations are based on the use o f paclobutrazol on

nursery at an annual application rate of 6.1 lbs a.i./A/season. The simulated concentrations provided in this assessment are upper

- bound estimates of concentrations for drinking water. If dietary risks require refinement, higher

- tiered , crop

- specific and location

- specific models and modeling scenarios can be used. Sample ou t puts of Tier I FI R ST and SCIGROW a s well as Results and sample output PRZM

- GW are provided in Appendix B.

### 14 Table 6

. Estimated Maximum Drinking Water Environmental Concentrations (E DWC s) of

Paclobutrazol for Surface Water and Ground Water

Drinking Water Source (model) Use (modeled rate) a Application

Method Acute
( 

### μg/L ) Chronic
( 

### μg/L )



### Parent only (paclobutrazol)

Surface Water (FIRST) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 153.3 49.0

Groundwater (SCIGROW) Nursery : (1 app. X 2.50 lbs ai/acre) Drench 26.9 26.9

Groundwater (PRZM

- GW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 29.1 6.7



### Total Toxic Residue (Paclobutrazol plus CGA 149907 and NOA 457654)

Surfac e Water (FIRST) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 255.3 166.2

Groundwater (SCIGROW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 25.0 25.0

Groundwater (PRZM

- GW) Nursery : ( 1 app. X 2.50 lbs ai/acre ) Drench 945.0 622.0

a Example of application ra te calculation: 6.1 lbs/A

- (6.1lbs/A*(1.0

- 0.59)

Where

6.1 lbs/A is application rate for drench application for 8

- inch container grown ornamentals (US EPA, 2011) 0.59 is the minimum fraction of retention of parent (paclobutrazol) in column l eaching study (MRID 40685004)



### 3.4 Monitoring Data

There were no national

- scale monitoring data available for this assessment.

3.5 Drinking Water Treatment

There is no available information on the drinking water treatment effects on

Paclobu trazol

.

3.6 Uncertainties

In general, t he EDWCs provided in this assessment are upper bound estimates of paclobutrazol concentrations in untreated drinking water. A major source of uncertainty is the leaching of paclobutrazol from indoor drench applic ation of potted nursery. It is assumed that treated pots would be placed outdoors immediately after drench application throughout the

watershed of the i ndex r eservoir . If the treated pots remain indoor s and /or the applied paclobutrazol is taken up by the p otted plant s , the residual paclobutrazol would be less than the

model ed application rate and consequently exposure in surface water and groundwater would be less than the reported values. Additionally , exposure assessments were performed based on one

seas onal application rate for drench method

. Indoor potted plants can be grown several times

### 15 within a year. If this chemical is applied to multiple batches of potted plants and placed outdoor s during the growing season

, exposure would be higher than the report ed values in Table 6

. In addition, exposure would be higher or lower based on residence time of treated potted plants

remain outdoor s before planting or distributing to retailers.

### 16 R EFERENCES

Food and Agriculture Organization (FAO) of the United Nation s. 2000. FAO Pesticide Disposal Series. Assessing Soil Contamination: A Reference Ma nual . Appendix 2. Parameters of Pesticides that Influence Processes in the Soil. Editorial Group, FAO Information

Division: Rome. http://www.fao.org/DOCREP/003/X2570E/X2570E00.htm

US EPA. 2011. Per

- Acre Application Rates for Ornamental Trees in Urban Forests, Seed

Treatment and Container

- Grown Ornamental Uses of Pac1obutrazol. Biological and Economic Analysis D ivision. November, 2011



### US EPA. 2010a . Water Models. U.S. Environmental Protection Agency, Pesticides: Scienc e and Policy. Online at: http://www.epa.gov/oppefed1/models/water/

US EPA. 2010 b

. Devel opment and Use of the Index Reservoir in Drinking Water Exposure

Assessments. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects Division, April 15, 2010 . Online at: http://www.epa.gov/oppefed1/models/water/index.htm

USEPA. 2010c . 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

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

US EPA . 20 12a. Memorandum: NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media. Environmental Fate and Effects Division, Of fice of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.

US EPA . 20 12b

. 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/water/pca_adjustment_dwa.html

### 17 APPENDIX A

Degradation Kinetic Estimates of Paclobutrazol

DT 50 

### = 20.9 months = 627 days @ 20°C

DT 50 

### = 443.4 days @ 2 5 °C

Es timated DT 50 

### value was adjusted to tem perature of 25°C using Arrhenius equation below

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

### 18 DT 50 

### = 22.2 months = 666 days @ 20°C

DT 50 

### = 470.9 days @ 2 5 °C

DT 50 

### = 283 days @ 20°C

DT 50 

### = 200.1 days @ 2 5 °C

### 19 DT 50 

### = 23.6 days @ 20°C

DT 50 

### = 16.7 days @ 2 5 °C

DT 50 

### = 26.8 days @ 20°C

DT 50 

### = 19.0 days @ 2 5 °C

### 20 Degradation Kinetic Estimates of total Toxic Residue of Paclobutrazol @ T emp 20°C

DT 50 

### = 44.8 months = 1344 days @ 20°C

DT 50 

### = 950 .4 days @ 2 5 °C

DT 50 

### = 4 8

. 1 months = 1 433 days @ 20°C

DT 50 

### = 102 0.4 days @ 2 5 °C

DT 50 

### = 950.4 days @ 2 5 °C

### 21 DT 50 

### = 393 days @ 20°C

DT 50 

### = 277.9 days @ 2 5 °C

DT 50 

### = 47.1 days @ 20°C

DT 50 

### = 33.2 days @ 2 5 °C

### 22 DT 50 

### = 34 days @ 20°C

DT 50 

### = 24.0 days @ 2 5 °C

### 23 APPENDIX B

Surface Water

Drench Application

RUN No. 1 FOR Paclobutrazol ON Nurnery * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- 2.500( 2.500) 1 1 4.5 25.9 GRANUL( 0.0) 100.0 0.0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

------------------------------------------------ -------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/RUNOFF (RESERVOIR) (RES.

- EFF) (RESER.) (RESER.)

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

381.00 2 0.00 0.00

- 0.00 762.00 762.00

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- 153.399 49.020

RUN No. 1 FOR Paclobutazol _TTR ON Nursery * INPUT VA LUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

------------------------------ -------------------------------------- 2.500( 2.500) 1 1 0.2******* GRANUL( 0.0) 100.0 0.0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

--------------------------------------------------------------------
METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/RUNOFF (RESERVOIR) (RES.

- EFF) (RESER.) (RESER.)

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

797.10 2 0.00 0.00

- 0.00 ****** 1 595.20

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONC ENTRATION

-------------------------------------------------------------------- 255.337 166.243

### 24 Ground Water **SciGrow version 2.3**

chemical:Paclobutrazol
time is 2/10/2014 10:27:26

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

------------------------------------------- ----------------------------- 2.500 1.0 2.500 4.04E+01 200.1

------------------------------------------------------------------------ groundwater screening cond (ppb) = 2.69E+01

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

chemical:Paclobutrazol_TTR
time is 2/10/2014 10:28: 5

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

------------------------------------------------------------------------ 2.500 1.0 2.500 6.06E+01 277.9

------------------------------------------------------------------------ groundw ater screening cond (ppb) = 2.52E+01

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

### 25 PRZM

- GW



### Table B

- 1 . PRZM

- GW Generated E stimated D rinking Water C concentration s of

Paclobutrazol and it’s Total Toxic Residue

Application Rate and Frequency S cenario 1 Highest Daily Value ( μ g/L) Post Breakthrough

A verage ( μ g/L) Average S imulation Breakthrough Time (days)

2.50 lbs a.i./ A x 1applications 

### Parent

FL Citrus 29.1 6.69 274

FL Potato 15.2 4.07 338 GA peanut 0.01 0.001 1064

NC Cotton 0.03 0.003 1089

Delmarva sweet corn 0.25 0.03 252

WI corn 9.33E

- 11 6.88E

- 12 938

Total Toxic Residue of Paclobutrazol

FL Citrus 635 458 238 FL potato 447 328 246 GA peanut 312 246 993

NC cotton 615 437 1054

Delmarva sweet corn 632 426 217

WI corn 945 622 868

1 These scenarios are regional vulnerable sites for groundwater evaluation.



### Sample outpu t of PRZM

- GW