UNITED STATES ENVIRONM

E NTAL PROTECTION AGENCY WASHINGTON D.C., 20460 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 125601 DP Barcodes: 395022 Date: January 05, 2012 MEMORANDUM SUBJECT: TO: FROM: Approved By: Tier
I Drinking Water Assessment for the Registration Review ofPaclobutrazol on Turf (commercial, ornamental and golf courses), Ornamental and Shade Trees, and Seed Treatment of Tomato, Pepper, and Cucurbit Khue Nguyen, Chemical Review Manager Laura Parsons, Risk Manager Risk Management and Implementation Branch

1 Pesticide Reevaluation Division (7508P) Faruque Khan, Ph.D., Senior **Scienti~**

{ **{~** t/J I 12_ Environmental Risk Branch

I Environmental Fate and Effects Division **(750~~ /~**  /ol; ;;J---. Nancy Andrews, Ph.D., Branch Chief **~/** flY'• /' Environmental Risk Branch

I Environmental Fate and Effects Division (7507P) Attached
is the drinking water exposure assessment for the registration review of paclobutrazol use on ornamentals grown in outdoor/indoor nurseries, turf (commercial, ornamental, and golf courses) and as seed treatment of tomato, pepper, and cucurbit. If additional refinements are necessary, please contact Faruque Khan at 703-305-6127

or khan

. faruque@epa.gov.Drinking Water Exposure Assessment for the Registration Review of P . aclobutrazol
on Ornamentals Grown in Outdoor/Indoor Nurseries, Turf (commercial, ornamental, and golf courses), and Seed Treatment of Tomato, Pepper, and Cucurbit Cl Paclo butrazol CAS Number 76738-62-0 CAS Name

- ( aR,JJR)-rel-JJ-

[ ( 4-chlorophenyl)methyl)-a.-(1 ,1-dimethylethyl)-1H-1 ,2,4-triazole-1-ethanol 2
Mail Washingto1_1 DC 20460 .J!;. **ll.;:.r.l',;:i:?.,1~· :P..>ez6f.~.A-l;..•.!:t~'::~.** 

l1 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. Tier
1 surface water and groundwater modeling were conducted with two highest application rates: 6.1 lbs/ A for nursery production of containergrown ornamentals through soil drench method (US EPA, 2011) and 2.0 lbs/A for foliar ground spray. Two major environmental degradates, CGA 149907 (maximum of 40.4%) and NOA457654 (maximum of25.1 %) were identified in the environmental fate and terrestrial field dissipation studies, and were included into the drinking water exposure assessment. However, there is no available recommendati<

, m to include these major metabolites from the Residues of Concern Knowledgebase Sub-committees (ROCKS) of the Health Effects Division (HED). The upper-bound estimated drinking water concentrations (EDWCs) for total residue (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 health risk assessment. -Table 1. Tier
I EDWCs for Paclobutrazol based on Soil Drench Application
to ContainerGrown Ornamentals Drinking Water Source Model Use rate Acute Chronic (lbs ai/A/season) (Jtg/L) (Jtg/L) Total Residue (Paclobutrazol plus CGA 149907 and NOA 457654) Surface water FIRST

133.8 46.7 Groundwater SCI-GROW

2.50

1

33

. 1
33

. 1 Parent only Surface water FIRST

133

. 5 43.5 Groundwater SCI-GROW

2.50

20

. 0 20.0 1 Maximum rate of6.llbs/A was normalized with the lowest fraction (0.59) ofpaclobutrazol retained in the soil column leaching study. Sample calculation

is provided in Table 4. 2 PROBLEMFORMULATION 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 Pesticide 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 3the human health dietary risk assessment and provides

a description of how those concentrations were determined. 3 ANALYSIS 3.1 Use Characterization Paclobutrazol, also known by the trade names Clipper, Bonzi, Paczol, and PP333, is a plant growth regulator that is currently registered for application
to a number of food (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 concentrations ranging from 0.018 to 50.0 percent. Currently registered uses and rates ofpaclobutrazol
are shown in Table 2. Table 2. Current Registered Uses and Application Rates of Paclobutrazol Maximum Application
Shortest Crop Rate

1 Number of Application Application Reg#

2 Applications Method Interval (days) Cucurbit

6.5 Jlg/seed

1 Seed N/A 000100-01014 0 . 00029/bs/A Treatment Herbaceous

5.7 mg ailff

· NS Spray, Drench, As needed 000 100-00992 and

Bulb Soak, 000100-00996 ornamentals Spray Application Plug/Liner 000100-01079 (greenhouse)

0 . 20 lbs!Afor 6'-8 pot
Soak 000400-00515 0 . 26/bs/Afor 18"x9" 062097-00011 propagation trays 080697-00003 drench application
000228-679 4.3 lbs!Afor 6" pot

62097-25 6.1/bs/AforB'pot Pepper

16 Jlg/seed

1 Seed N/A 000100-01014 0 . 00079 lbs/A Treatment Tomato

12

. 5 Jlg/seed

1 Seed N/A 000100-01014 0 . 00040 lbs!A Treatment Trees (shade 0.009 lb ai per inch DBH

1 Soil Injection,

3 years or as 000100-01037 and

Basal Drench, needed 000 100-00991 ornamental) Tree injection

: 0.36/bs/A
Tree Injection 000100-00995 Soil Injection

: 1 . 9/bs/A 000100-01014 Basel drench

: 1.9 lbs!A 067690-00022 000228-680 74779-3 74779-7 80697-4 81943-31 62097

- 24 4Table 2. Current Registered Uses and Application Rates of Paclobutrazol Maximum Application
Shortest Crop Rate

1 Number of Application Application

Reg#

2 Applications Method Interval (days) Turf 0.75lb ai!A

3 Spray,

14 009198-00196 Broadcast 009198-00199 00919 8-0020

1 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 represent maximum application rate for a least one of the EPA Reg# listed. Other labels may have slightly different application rates. 3.2 Environmental Fate and Transport Characterization Paclobutrazol

is a racemic mixture of the (2R, 3R)- and (2S, 3S)-enantiomers but the submitted physiochemical and fate properties of each enantiomer were not investigated
in the submitted studies. Therefore,

it is assumed that each enantiomer ofpaclobutrazol 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-Io atm m 3 /mol) indicate that the compound

is relatively non-volatile under field conditions. The log Kow of3.2 indicates the potential for this chemical to bioaccumulate

in aquatic organisms. Paclobutrazol

is stable to hydrolysis and photolysis. Under aerobic conditions, paclobutrazol appears to be generally quite persistent in acidic soils, with half-lives greater than 300 days. However in soils with neutral or higher pH, estimated half-lives were as short as 25 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 half-lives were beyond the duration 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 Mississippi Half-lives ofpaclobutrazol 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 lH-1,2,4-triazol-3-ol (NOA457654,:::; 25.1%) were identified in the environmental fate and terrestrial field dissipation studies.

5---- --- .
The potential mobility of this compound

is quite variable; ranging from highly mobile to moderately mobile in soil according
to the mobility classification
of the Food and Agriculture Organization
(F AO, 2000). Soil column leaching experiments involving aged (9 week) residues ofmethine-labeled paclobutrazol determined that the compound was relatively immobile in 30 em columns of sand, sandy loam, loamy sand except in clay loam soils, where it was leached with 66 em rain over 9 weeks. In contrast, aged residue studies oftriazole-labeled paclobutrazol determined the compound
to be oflow mobility in 30 em 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 em of the treated soil columns. Table
3 summarizes the physiochemical and environmental fate and transport properties of paclobutrazol. **'t, a~l** **tr~ fb.xsic~i,** 
**Ch** **~mi~IH~q!!~i*if.onmental**
**F~te** properties of P :. adobutrazch _..,.,. r,i<' •

t **J:i;i:'t,r;:.,,**

' .•!;:jil?

:a. ...: ··

) ,tl;

. ..:"!: **.,:~~~-::,~~~**

- '"4? **~''~'** Value

1<'\l Refer:ence Cf!miJ!.ents · J-::,..

"-· **Parameter** ,A!.·.·.,ri **:·',:i'-~;t~< -~?'** **.<#l.,;'t-.'7,~**

.Ji: ·:..,. .

**~~**
\ **.~.~1** ,tC' ... **~** ,]C.}

•

;- .i,'."'::,\, i;t:

. **·;~~~-3** Chemical Paclobutrazol MRID 456625-0

1 Chemical Class Triazole CAS No

. 76738-62-0 Empirical Formula C1sH2oCIN30 MRID 456625-01 IUPAC (2RS,3RS)-1-(4- MRID 456625-01 -

- chlorophenyl)-4,4-dimethyl-

- 2-(1H-1,2,4-triazol-1- yl)pentan-3-ol CAS Name (aR,pR)-rel-P-[(4- MRID 456625-01 chlorophenyl)methyl]-a.- (1, 1-dimethylethyl)-1H1 ,2,4-triazole-1-ethanol Structure

**~\\** MRID 456625-01 Cl '7
I N'N **~**

H **~" -·-·~r·**  **··-~"·'·ru,,~·dffl~f~;~~~~i**

**.i~! s~i~tfci**  **Pii li~ille**  **Wrdi~ii Parameters** 

... ·n **t'~~!J,;,JJ'~.ij~',~~~'** ·

.. **,t~,.,.··rj,**

< **~'71·, ·•"'··-**  **~- •··~·**  **•w~~~- -~**  **~** Molecular mass
293.8 g/mol MRID 456625-01 Solubility (20.0°C)

25.9 mg!L (water) MRID 456625-05 2
. 8 g fL (n-Octanol) MRID 456625-03 79

. 8 giL (methanol) **22** giL (xylene) 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 (25°C)
8.2 X 1 0' 7 Pa M 3 mor

1 (8.09 x 10-12 atm M 3 mol'

1 ) MRID 456625-05 Octanol-water partition coefficient 3.18 MRID 456625-05 (LogKow) (25°C) **:~t~'";,·**

... "Ji Persistence **~-~~N~'~:**

**;;;~!** 'l,<l;' **,~:1.!.**

i': :(_\ **~.i.'izel~-v.~~~.**

} .... · .. .,._

;:I!" 6Table 3. Physical, Chemical and Environmental Fate properties of Paclobutrazol Parameter Value Reference Comments pH4: stable MRlD 00132698 Hydrolysis

pH 7: stable pH 9: sqtble Aqueous Photolysis

(t **~** ) Stable MRID 00132699 Soil Photolysis

(t **~** ) Stable MRID 40685002 After 33 days paclobutrazol decrease to 86.4 %of applied radioactivity Aerobic Soil Metabolism Sandy clay loam MRID 40685003 Major metabolite (t **~)**

19 (21 and 17) months

1 • 2 (CGA 149907 (:::::18.7%) [47 (58 and 36) months/ \

MRID 47338504 Supplemental Sandy clay loam 301 days

No major metabolites [385 days]
detected above 10%. Sandy loam

Major metabolites 26 days
4

NOA 457654(25.1%) [75.3 days]

CGA 149907(13.3%) Sandy loam

Major metabolites 25 days
4 [55

. 9 days]

NOA 457654 (20.5%) CGA 149907(26.3%) Anaerobic Soil Metabolism

No data Anaerobic Aquatic Metabolism

(t **~** ) Stable MRID 40685003 After
a year of incubation, paclobutrazol decrease to :579% of applied radioactivity Major transformation product: (CGA 149907 (:::::16.8%) No data

-- Aerobic Aquatic Metabolism Mobility Soil Partition Coefficient AdsorJ!tion Kg (mL/g} MRID 4188113 There was no significant 9.5 (Clay loam) correlation (i = 0.12) 10.2 (Sandy Clay loam) between Kct and % 7.6 (Silty clay loam) 17.3 (Silt loam)

5 organic carbon

. 4.1 (sandy loam) 2.4 (loamy sand) 5.8 (Silty clay) 1.4 (Sand)

7Table3.Physical,ChemicalandEnvironmentalFatepropertiesofPaclobutrazolParameterValueReferenceCommentsSoilPartitionCoefficientDesorption(mL/g)6MRID418811315.6-(Clayloam)18.1(SandyClayloam)14.0(Siltyclayloam)34.0(Siltloam)55.1(sandyloam)10.4(loamysand)2.7(Siltyclay)6.1(Sand)Adsorution&{mL/2)MRID47338503Supplemental1.7(Sandyloam)50.8(Sandyloam)2.4(Siltyclayloam)1.8(Clayloam)Desorption{mL/gt10.9(Sandyloam)53.81(Sandyloam)2.66(Siltyclayloam)11.7(Clayloam)LeachingAgedmethine14C-labeledMRID40685004Majortransformationpaclobutrazolresidueswereproduct-relativelyimmobileCGA149907(:::::12.6%)Agedtrizole14C-labeledpaclobutrazolresiduesweremobileinloamysandandclayloamsoilsandlowmobilityinsandsandsandyloamsoilsFieldDissipationTerrestrialFieldDissipation(tYz)MRIDSupplemental450to973.days40685006-Majortransformation(CA,WV,FL)406850012productCGA149907Supplemental88days(CA)MRID47338505Majortransformation133days(NY)product-CGA149907(40%)1Calculatedhalf-livesarebasedon14Clabeledoftriazoleandmethaneofpaclobutrazol2Extrapolatedhalf-livesexceededbeyondthestudyperiodexceptsoilswithpH>7.03Italichalf-livesarecalculatedbasedonpaclobutrazolanditsmajordegradates(CGA149907andNOA457654).CalculationcanbefoundinAppendixA.4HighSoil7.0)mayhave contributedfasterdegradationratesforaerobicsoilmetabolism5Japanesesoils,excludedduringexposureassessment6Reportedvaluesarebasedonseconddesorptionstep83.3 Drinking Water Exposure Modeling Tier
1 modeling was used to estimate the drinking water exposure for use in the dietary risk assessment ofpaclobutrazol. The following
is a description ofthe 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, 2010a) 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 drinking 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 Pesticide Programs to assess drinking water exposure (Office of Pesticide Programs, 2010b).
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% of 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 is 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 (20 1 Oa). SCI GROW is a regression model used as a screening tool for ground water used as drinking water. SCI GROW 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 and the soil-water partition coefficient. The output of SCI GROW represents the concentrations that might be expected in shallow unconfined aquifers under sandy soils. 3.3.2 Modeling Approach and Input Parameters Tables
4 and 5 summarize the model input parameter values used in FIRST and SCIGROW, respectively. These parameters were selected in accordance with EFED's input parameter guidance (US EPA, 2010c). Half-lives (rate constants) listed in Table
3 were used for exposure modeling. Average soil-water partitioning coefficient was used in FIRST. For total residue, 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 Koc value was used in SCI GROW because there was greater than 3-fold variability in the available data.

9Table
4 . FIRST (v 1.0) input **i>~rameter v~lues**  for :Pacloti
u ffiazol . .

,

. "

' '.

' **:"'·~··' ~:·:"7**  .• , .. **q,,4fltf.''''~"·~'-' ~~if** 

, Parameter

-•.-.

· .Value

'

.

**~0**

. ;, . **~~~};~** Com m ents **-~:(~~**
"; .

'.

o r ce

**~1l** 1 ·;-

r

"

' **~·~?tv~**

! £""" .,

!\: ·,.•

,, ..

"

' **·c__.___j~** ...

- **;~.;....._:!L**

**-~·**

• ., P-.'.'1!. _\1;, ,..,.

-
Jl ....... "''· ... **~** Application Rate 2.50 lb a.i/ A (based on Memo from the Biological Maximum application rate was (lb a.i./A) 59% retention of parent and Economic Analysis estimated based on information in soil column)

1 Division (BEAD) (US EPA, provided by BEAD (US EPA 20II)

20 II) and adjusted with the 0.55 lbs/A (based on retention of paclobutrazol

in a soil 9I% retention of parent
column leaching study (MRID in soil column 40685004) 2.0 lbs/A for turf Number of Applications

I (nursery) Product Label 3(turf) Soil Partitioning

4.5 MRIDs 4I88113 and Mean value Coefficient (K.i mVg) 47338503 Aerobic Soil

1 003

. 2 (Total residue) MRIDs 40685003 and 90m percentile upper confidence Metabolism t112 (d) 444

. 2 (Parent) 47338504 bound on the mean. -

-

- -·
-
- Wetted in?

No

---

--- Depth of Incorporation

0

---

--- (inches) Method of Application Drench Paclobutrazollabels

-- Ground Spray Drift Fractions

0 (drench) Paclobutrazollabels Model input guidance 6 . 4 (ground foliar)

(US EPA, 2010) Percent Cropped Area 0.87 Nursery National Default 1.0
Turf

No PCA established for turf Solubility
in Water 25.9 MRID 456625-05

--- (mg!L) Aerobic Aquatic 2006.4 (Total Residue)
2X of Aerobic soil Model input guidance Metabolism

t 112 (days) 888.4 (Parent) metabolism half-life
(US EPA, 2010) Hydrolysis t112

0 MRID OOI32698 Stable to hydrolysis Aquatic Photolysis

t 112

0 MRID 0013299 Stable to aquatic photolysis (days) 1 Example of application rate calculation: 6.I lbs/A- (6

. 11bs/A *0.59) Where 6 . 1lbs/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 leaching study (MRID 40685004) 2 Maximum single application rate of0.67lbs/A was used instead of0.75 lbs/A to account maximum seasonal rate of 2.0 lbs/ A due to Tier
I model limitation

. Model accepts only uniform rate for multiple applications. 10Maximum Application Rate (lbs a.i./A) **M~um** Number of Applications per Year Aerobic Soil Metabolism Half-life Organic Carbon Partition Coefficient Koe
. LIK

2 See calculation
in Table 4 2.50 1 (Nursery) 230.2 (Total Residue) 163.5 (Parent) 40.4 Product Label MRIDs 40685003 and 47338504 MRIDs 4188113 and 47338503 median value Lowest value; > 1 OX variability
in data There is no significant correlation between 1<.! and organic carbon

. Since, model does not have an option to use 1<.!, ----1 the lowest value ofKoc was used in the model 3. 3 . 3 Modeling Results The FIRST and SCI-GROW output files are located in Appendix B. Based on the results of these simulations, EFED recommends acute surface water EDWC of 133.8 J.lg/L and a chronic EDWC of 46.7 J.lg/L for use in the human health risk assessment. These recommendations
are based on the use **ofp~clobutrazol**
on various uses at an annual application rate of2.50 lb a.i./A/season. The recommended EWDC for groundwater

is 33 f.lg/L and is also based on the use of paclobutrazol
on various uses at the previously stated rate. Modeling results are depicted in Table 6. Sample outputs of Tier
I FIRST and SCIGROW are provided in Appendix
B. No drinking water assessment was performed in the past to compare with current assessment

. Total Residue (Paclobutrazol plus CGA 149907 and NOA 457654) Nursery:

133.8 46.7 {lapp. X 2.50 lbs ailacre) Drench 29.4
10.3 Surface Water (lapp. X 0.55 lbs ailacre) (FffiST) Turf: X 0.0

. 67lbs ailacre) Ground 126.1

44

. 6 11.' f a bl e

**ie r**  tEs iiDi' ated D ri nkin g Water En vironmental Concentr

a tions (EDWCs) of Pa c lo6utiazol **for rface**  Water and Grouna Water '-"'--"'-

"'

.... _

'
u..

4

.. _._, **~"(_,** Groundwater (lapp

. X 2.50 lbs ai!acre) Drench

33

. 0 (SCIGROW) (lapp

. X 0.55lbs ailacre)

7.30 Parent only (paclobutrazol) Nursery:

133.5 (lapp

. X 2 . 50 lbs ai!acre) Drench
29.4 (lapp. X 0.55 lbs ai!acre) Turf: Ground 124.4 (3 app. X 0.67 lbs ailacre) Groundwater lapp. X 2.50 lbs ailacre) Drench

20

. 0 (SCI GROW) (lapp

. X 0 . 55 lbs ai!acre)

4.4 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 Paclobutrazol. 3.6 Uncertainties

33

. 0 7.30 43

. 5 9.6 41.1 20.0 4.4 In general, the 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 application of potted nursery.
It is assumed that treated pots would be placed outdoors immediately after drench application throughout the watershed of the index reservoir. If the treated pots remain indoors and/or the applied paclobutrazol

is taken up by the potted plants, the

· residual paclobutrazol would be less than the modeled 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 seasonal application rate for drench method. Indoor potted plants can be grown several times within

a year. If this chemical
is applied to multiple batches of potted plants and placed outdoors during the growing season, exposure would be higher than the reported values in Table 6. In addition, exposure would be higher or lower based on residence time of treated potted plants remain outdoors before planting or distributing
to retailers. 1 2REFERENCES Food and Agriculture Organization (FAO) ofthe United Nations. 2000. FAO Pesticide Disposal Series. Assessing Soil Contamination:

A Reference Manual. Appendix
2. Parameters of Pesticides that Influence Processes in the Soil. Editorial Group,
F AO Information Division: Rome. http://www.fao.org/DOCREP/003/X2570EIX2570EOO.htm US EPA. 2011. Per-Acre Application Rates for Ornamental Trees in Urban Forests, Seed Treatment and Container-Grown Ornamental Uses ofPaclobutrazol. Biological and Economic Analysis Division. November, 2011 US EPA. 2010a. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and Policy. Online at: http://www.epa.gov/oppefed1/models/water/ US EPA. 2010b

. Development 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, April15, 201 0. Online at: http:/ /www.epa.gov/oppefed 1/models/water/index.htm USEP A. 201 Oc. 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/oppefedl/models/water/input parameter guidance.htm 13Chemical: MRID: PC Code: Paclobutrazol 40685003 125601 Guideline: 835.4100 APPENDIX

A Distribution
of residues- 18 Acre loam soil Half Life 57.8 Months LN of %of Total total Months Residue residue 0
87

. 6

4
. 47 1 92.2

4
. 52 4
88

. 8 4.49 8 81.0 4.39 12
78

. 7

4
. 37 Chemical: Paclobutrazol MRID: 40685003 PC Code: 125601 Guideline: 835.4100 Dissipa_tion
of paclobutrazol

in 18 Acre loam loam soil system (12 Months) 4
. 55 - "g .! 4
. 50 Q. a. <C .... 4.45 0 **~** 4.40 3 •

y = -0

. 012x + 4.5088 R 2 = 0.8271 4.35 -1-- ----.--- --- ---,r-----

- --, 0

5

10

15 Months (Post -treatment) Distribution
of residues- 18 Acre **loam,:,..2.so~i!..l** ------------------------, Half Life
35

. 5 Months LN of % ofTotal total Months Residue residue 0 96.1 4.57 1 91.6 4.52 4 84

. 6

4
. 44 8 80.1 4.38 12 75.1 4.32 Dissipation
of paclobutrazol

in 18 Acre loam - 4.6 **~** 4.55 **·~** 4.5 :4.45 0 4.4 ?fl. 4.35 z 4.3 _, 4.25
0 14 loam soil system (12 Months) y = -0.0195x

+ 4.5422 = . 5 2
4

6

8 10 12 Months (Post -Treatment)Chemical: MRID: PC Code: Guideline: Half-Life Days (Posttreatment)
0 0 7 7 22 22 35 35 so so 70 70 91 91 120 120 Chemical: MRID: PC Code: Guideline: Half-Life Days (Posttreatment)
0 0 7 7 22 22 35 35 so so 70 70 91 91 120 120 Paclobutrazo

l 47338504 125601 835.4100 55 90 days Paclobutrazol,

LN Total CGA 149907, NOA457654 Residue 90

. 1 4.5 80.4
4.4 92.5
4.5 92.8
4.5 87.4
4.5 88

. 5 4.5 74.7
4.3 74.4
4.3 62.6
4.1 65.9
4.2 54
4.0 55

. 6 4.0 41
3.7 38

. 3 3.6 32.3
3.5 28.9
3.4 Paclobutrazol 47338504 125601 835

. 4100 75

. 34 days Paclobutrazol,

LN Total CGA 149907, NOA457654 Residue 85 4.4 93.4
4.5 91.9

4
. 5 92.6

4
. 5 85.5 4.4 84.9 4.4 69.5 4.2 70

. 3 4.3 61.4 4.1 59.2 4.1 53

. 3 4.0 51

. 9 3.9 45.3 3.8 39.2 3.7 29.3 3.4 32

. 6 3.5 Dissipation of paclobutrazol

in Pappelacker sandy loam soil system (0-120 days) ::g 6.00

y = -0.0124x

+ 4.5691 **~ ~~~** **== ~._~~~** 
**~0 .~98~8~6~**  **~ ·~**  4.00
1

.... **~** Q.

.... <( .... 2.00 0 e o.oo +-- -----r-

- --

- ----. 3

0
50 Days 100 Dissipation ofpaclobutrazol

in Gartenackersandyloam

soil system (0·120days) 5.00

y- **uu~ux**+ 4.5731 wa.. ...._.__.. :g 4.00

""

R 2 = 0.9755 .! --.---. Q. a. 3 . 00 < ... **~** 2.00 3 1.00 0.00

- 0
so 100 150 Days 15Chemical:MRID:PCCode:Guideline:Half-LifeDays(Posttreatment)007722223535505070709191120120Paclobutrazol47338504125601835.4100385.08daysPaclobutrazol,CGA149907,LNTotalNOA457654Residue87.64.4787.24.4792.84.5388.14.4893.34.54.95.34.5677.14.3580.84.3981.14.4074.64.3176.24.3370.74.2679.84.3890.24.5072.14.2870.04.25Dissipationofpaclobutrazolin18Acressandyclayloamsoilsystem{0-120days)=-0.0018x+4.4919::C4·604.50_____....._____Cl.Cl.<(4.40-1---.....0e4.3o34.20-1------.------r-------.050100150Days(Post-Treatment)16APPENDIXB Surface Water Drench Application RUN No.

1 FOR Paclobutrazol

ON Nursury

* INPUT VALUES

* RATE (#/AC) ONE(MULT) No.APPS

& INTERVAL SOIL SOLUBIL Kd (PPM

) APPL TYPE (%DRIFT) %CROPPED INCORP AREA (IN) 2.500( 2.500)

1
1 4.5 25

. 9 GRANUL ( . 0) 8 7 . 0

. 0 METABOLIC (FIELD) 1003

. 20 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) DAYS UNTIL RAIN/RUNOFF

2 HYDROLYSIS (RESERVOIR) N/A PHOTOLYSIS (RES. -EFF) .00- .00 METABOLIC (RESER.) ****** COMBINED (RESER.) 2006.40 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007 Application rate (lb/acre) 2.500 PEAK DAY (ACUTE) CONCENTRATION ANNUAL AVERAGE (CHRONIC) CONCENTRATION 133.759 Ground Water SCI GROW VERSION 2.3 46.658 ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY SCREENING MODEL FOR AQUATIC PESTICIDE EXPOSURE SciGrow version 2.3 chemical:Paclobutrazol time is 12/22/2011 14:19:32 Number of applications Total Use (lb/acre/yr)
Koc (ml/g) Soil Aerobic metabolism (days) 1.0 2.500 4.04E+01 230.2 groundwater screening cond (ppb) = 3.31E+01 17!I