UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

DATE: January 21, 2015 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Paclobutrazol: Revised Preliminary Occupational and Residential Exposure/Risk 

Assessment for Registration Review 

PC Code: 125601 

Decision No.: 455061 

Petition No.: 

DP Barcode: D427481 

Registration No.: 

Regulatory Action: Registration Review 

Risk Assessment Type: Single Case No.: 7002 

Chemical/ Aggregate 

TXRNo.: 

MRID No.: 

FROM: 

CAS No.: 76738-62-0 

40 CFR: 

Monica 

Risk Assessment 

Hawkins, 

Branch 

Ph.D., M.P 

6 

.H., Environmental Health Scientist Jr'l ~~ 

Health Effects Division (7509P) 

THROUGH: Donna Davis, Acting Chief 

Risk Assessment Branch 6 

Health Effects Division (7509P) 

TO: Khue Nguyen 

Risk Management and Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

and 

Sheila Piper, Risk Assessor 

Risk Assessment Branch 6 

Health Effects Division (7509P) 

Page I of 44 
INTRODUCTION

As part of Registration Review, the Pesticide Re-evaluation Division (PRD) of OPP requested 

that HED conduct a revised occupational and residential exposure/risk assessment for 

paclobutrazol for application as a foliar spray for turf (including parks, athletic fields, and golf 

courses); a foliar spray for ornamentals in greenhouses and nurseries; as a tree injection; as a tree 

root drench; and as a seed treatment (on cucurbit, pepper, tomato, broccoli, cauliflower, and 

cabbage seeds). As part of Registration Review, the paclobutrazol hazard assessment was 

revisited by HED.

The revised occupational and residential exposure assessment is based on the previous 2013 risk 

assessment (D394230, S. Piper, C. Smith, M. Hawkins, and N. McCarroll, 9/11/13). The 

document was revised to incorporate data from the acceptable/guideline acute neurotoxicity and 

to account for the data waivers granted for the subchronic inhalation and the immunotoxicity 

studies by the Hazard and Science Policy Council on February 27, 2014. As a result of the 

meeting, the 10X database uncertainty factor was removed. In addition, the dermal absorption 

factor was updated to be consistent with current HED policy. 

It is HED policy to use the best available data to assess exposure. Several sources of generic 

data were used in this assessment as surrogate data in the absence of chemical-specific data, 

including Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1); the Agricultural 

Handler Exposure Task Force (AHETF) database; the Outdoor Residential Exposure Task Force 

(ORETF) database; the Agricultural Reentry Task Force (ARTF) database; ExpoSAC Policy 14 

(SOPs for Seed Treatment); the Residential SOPs (Lawns/Turf), a chemical-specific turf 

transferable residue study (MRID 45214201), and a chemical-specific dislodgeable foliar residue 

study (MRID 45310801 and 45336601). Some of these data are proprietary, and subject to the 

data protection provisions of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).

Page 2 of 44
Table of Contents

1.0 Executive Summary........................................................................................................... 4

2.0 Risk Assessment Conclusions and Recommendations.................................................... 6

2.1 Summary of Risk Estimates.......................................................................................... 6

2.2 Label Recommendations from Occupational Assessment.......................................... 7

2.3 Label Recommendations from Residential Assessment ............................................. 7

2.4 Data Deficiencies and Requirements............................................................................ 7

3.0 Hazard Characterization................................................................................................... 7

4.0 Use Profile......................................................................................................................... 11

5.0 Residential Exposure and Risk Estimates ..................................................................... 12

5.1 Residential Handler Exposure/Risk Estimates...........Error! Bookmark not defined.

5.2 Residential Post-application Exposure/Risk Estimates............................................ 12

5.3 Residential Risk Estimates for Use in Aggregate Assessment.................................. 15

5.4 Spray Drift.................................................................................................................... 15

5.5 Residential Bystander Post-Application Inhalation Exposure ................................ 16

6.0 Occupational Exposure and Risk Estimates.................................................................. 16

6.1 Occupational Handler Exposure/Risk Estimates...................................................... 16

6.2 Occupational Post-application Exposure/Risk Estimates ........................................ 28

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates.................. 28

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates....................... 29

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms............. 34

Appendix B. Paclobutrazol DFR and TTR Study Results..................................................... 41

Page 3 of 44
1.0 Executive Summary

Paclobutrazol, is a triazole plant growth regulator that slows vegetative growth by inhibiting 

gibberilin biosysthesis creating more compact plants. 

Use Profile

There are a number of existing uses for paclobutrazol with formulations including liquids, 

wettable powders, and granulars. Paclobutrazol is currently registered for use as a foliar spray 

for turf (including parks, athletic fields, and golf courses); a foliar spray for ornamentals in 

greenhouses and nurseries; as a tree injection; as a tree root drench; and as a seed treatment (on 

cucurbit, pepper, tomato, broccoli, cauliflower, and cabbage seeds). 

Hazard Profile

Paclobutrazol is classified as Toxicity Category III via the dermal route and or skin irritation 

potential based on studies submitted in 2012. It is not a skin sensitizer. Quantification of shortterm (1-30 days) and intermediate-term (1-6 months) dermal and inhalation risks for 

paclobutrazol was performed using a developmental oral toxicity study. The Lowest Observed 

Adverse Effect Level (LOAEL) from this study was 40 mg/kg/day based on partial ossification 

of the 7th vertebra and an increased incidence of 14th rib on a fetal and litter basis at a dose that 

was not maternally toxic (LOAEL = 40 mg/kg/day). The No Observed Adverse Effect Level 

(NOAEL) from this study was 10 mg/kg/day. Based on a dermal absorption study in male rats, 

absorption of paclobutrazol was deemed to be 18.7% after 10 hours. Since both the dermal and 

inhalation endpoints were based on the same toxicological effects, these routes may be combined 

to result in a total margin of exposure (MOE). Since the dermal and inhalation points of 

departure (PODs) are based on developmental and/or fetal effects, the body weight appropriate 

for dermal and inhalation assessments is 69 kg. Quantification of an incidental oral risk was 

performed using a reproductive rat toxicity study. The offspring LOAEL from this study was 

116.9 mg/kg/day based on the increased incidence of chromodacryorrhea, thickened eyelids and 

dental malocclusion, increased liver weights, mottling or accentuation of the lobular structure of 

the liver along with liver enlargement, pallor and discoloration in male and female pups of both 

generations. The NOAEL from this study was 23.2 mg/kg/day. A target MOE of 100 is 

considered adequate for all exposure scenarios (10X for interspecies extrapolation, 10X for 

intraspecies variability). 

There are no proposed or currently registered food uses for paclobutrazol. Carcinogenicity 

studies are not required for non-food use chemicals. Carcinogenicity studies in mice and rats 

are available. The Agency was unable to determine the potential carcinogenicity of 

paclobutrazol because the maximum tolerated dose (MTD) was not achieved in the 2-year 

carcinogenicity/ chronic study in rats and the carcinogenicity/chronic study in mice. The 

carcinogenic potential will be re-evaluated if the use pattern changes (i.e., food uses are 

proposed). 

Residential Exposure and Risk

Page 4 of 44
Paclobutrazol is currently not registered for homeowner use on residential lawns. Therefore, a 

residential handler exposure assessment was not conducted. Paclobutrazol is applied 

commercially to parks and golf courses; therefore residential post-application exposure was 

assessed. A chemical-specific turf transferable residue (TTR) study was available and was used 

to estimate transferable residues from turf treated with liquid formulations. Dermal postapplication risks were assessed for adults, and children 11 to 16 years old. All adult and older 

children golfing dermal risk estimates for both liquid and granular formulations are greater than 

HED’s level of concern (MOEs ≥ 100). All adults on treated turf dermal risk estimates for both 

liquid and granular formulations MOEs range from 170 to 1,100. All children 1 – 2 years old 

oral non-dietary ingestion risk from hand-to-mouth activity on treated turf estimates for both 

liquid and granular formulations MOEs range from 210 to 1,400,000. 

A quantitative spray drift assessment for paclobutrazol is not required because the maximum 

application rate to a crop/target site multiplied by the adjustment factor for drift of 0.26 is less 

than the maximum direct spray residential turf application rate (0.75 lb ai/A)

1 for the 

paclobutrazol products. The turf post-application MOEs are protective for any potential 

exposures related to spray drift for paclobutrazol. 

Occupational Exposure and Risk

The occupational handler assessment was completed assuming the maximum label application 

rate for each crop. Based on the activity use pattern, the duration of exposure is expected to be 

short-term (1 to 30 days) and intermediate-term (1 to 6 months). Long-term exposures (greater 

than 6 months) are not anticipated based on the existing use pattern. For the dermal and 

inhalation routes of exposure, the same points of departure were chosen for short-term and 

intermediate-term exposures; therefore, risks are the same for both durations of exposure. 

Occupational handler exposures to the existing turf, ornamental, and tree uses of paclobutrazol 

may occur via the dermal and inhalation route. The short- and intermediate-term risk estimates 

for the occupational handler scenarios are greater than HED’s LOC (MOEs ≥100) with the 

exception of mixing/loading/applying liquids via a backpack sprayer. The MOEs range from 29 

to 19,000,000. The backpack sprayer equipment scenario is still not greater than HED’s LOC 

(MOEs < 100) even with the use of personal protective equipment PPE of a double layer and 

gloves (MOE = 58).

Occupational handler exposures to the existing seed uses of paclobutrazol may occur via the 

dermal and inhalation route for both primary handlers (i.e., those who treat the seed in 

commercial seed treatment facilities) and secondary handlers (i.e., those who plant paclobutrazol 

treated seeds). The short- and intermediate-term risk estimates for all primary and secondary 

handler scenarios are greater than HED’s LOC (MOEs ≥ 100) at varying levels of PPE. The 

short- and intermediate-term risk estimates for all primary and secondary handler scenarios 

MOEs range from 16,000 to 13,000,000.

Occupational post-application exposures to the existing uses of paclobutrazol may occur via the 

dermal route. The results indicate that occupational post-application risks are greater than 

HED’s LOC (MOEs ≥100) on day zero after application for all post-application activities that 

1 0.59 lb ai/A x 0.26 ≤ 0.75 lb ai/A

Page 5 of 44

 
were assessed. The occupational post-application risks MOEs range from 110 to 2,800.

Paclobutrazol is classified as Toxicity Category III via the dermal route and or skin irritation 

potential based on studies submitted in 2012. It is not a skin sensitizer. Short- and intermediateterm post-application risk estimates were not a concern on day 0 (12 hours following application) 

for all post-application activities. Under 40 CFR 156.208 (c) (2) (iii), ai’s classified as Acute 

Toxicity Category III chemicals require a 12-hr restricted entry interval (REI). The occupational 

post-application assessment, dermal risk estimates do not exceed HED’s level of concern (MOEs 

>100). Based on the acute dermal toxicity, the 12-hour REI that appears on the current 

paclobutrazol labels is supported by the acute toxicity data.

Based on the Agency's current practices, a quantitative non-cancer occupational post-application 

inhalation exposure assessment was not performed for paclobutrazol at this time. If new policies 

or procedures are put into place, the Agency may revisit the need for a quantitative occupational 

post-application inhalation exposure assessment for paclobutrazol.

Review of Human Research

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These data, which include studies from 

PHED 1.1; the AHETF database; the Outdoor Residential Exposure Task Force (ORETF) 

database; the ARTF database; ExpoSAC Policy 14 (SOPs for Seed Treatment); the Residential 

SOPs (Lawns/Turf); a chemical-specific turf transferable residue study (MRID 45214201), and a 

chemical-specific dislodgeable foliar residue study (MRID 45310801 and 45336601). are (1) 

subject to ethics review pursuant to 40 CFR 26, (2) have received that review, and (3) are 

compliant with applicable ethics requirements. For certain studies, the ethics review may have 

included review by the Human Studies Review Board. Descriptions of data sources, as well as 

guidance on their use, can be found at the Agency website2

. 

2.0 Risk Assessment Conclusions and Recommendations

2.1 Summary of Risk Estimates

All adult and older children golfing dermal risk estimates for both liquid and granular 

formulations are greater than HED’s level of concern (MOEs ≥ 100). All adults on treated turf 

dermal risk estimates for both liquid and granular formulations MOEs range from 170 to 1,100. 

All children 1 – 2 years old oral non-dietary ingestion risk from hand-to-mouth activity on 

treated turf estimates for both liquid and granular formulations MOEs range from 210 to 

1,400,000. 

The short- and intermediate-term risk estimates for the occupational handler scenarios are greater 

than HED’s LOC (MOEs ≥100) with the exception of mixing/loading/applying liquids via a 

backpack sprayer. The MOEs range from 29 to 19,000,000. The backpack sprayer equipment 

2 http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html

Page 6 of 44

 
scenario is still not greater than HED’s LOC (MOEs < 100) even with the use of personal 

protective equipment PPE of a double layer and gloves (MOE = 58).

The short- and intermediate-term risk estimates for all primary and secondary handler scenarios 

are greater than HED’s LOC (MOEs ≥ 100) at varying levels of PPE. The short- and 

intermediate-term risk estimates for all primary and secondary handler scenarios MOEs range 

from 16,000 to 13,000,000.

The occupational post-application risks are greater than HED’s LOC (MOEs ≥100) on day zero 

after application for all post-application activities that were assessed. The occupational postapplication risks MOEs range from 110 to 2,800.

2.2 Label Recommendations from Occupational Assessment 

None.

2.3 Label Recommendations from Residential Assessment

None.

2.4 Data Deficiencies and Requirements

None. 

3.0 Hazard Characterization

Paclobutrazol has low toxicity in the rat, rabbit, and guinea pig via the oral (category III) route of 

exposure, the dermal route (category III) in rats and rabbits, and via the inhalation route 

(category III to IV) in rats. It is slightly to mildly irritating to the skin and the eye and is 

negative for dermal sensitization. Table 3.1 presents a summary of the acute toxicity information 

for paclobutrazol.

Acute Toxicity

Table 3.1.: Acute Toxicity of Paclobutrazol Technical Grade

Guideline No/Study Type MRIDs Results Toxicity Category

870.1100 Acute Oral (97% ai)

Alderley Park Rat

00117478 (1983) LD50 = 1954 mg/kg (M)

 1336 mg/kg (F)

III

870.1100 Acute Oral (97% ai)

Alderley Park Mouse

00117478 (1982) LD50 = 490 mg/kg (M) 1219 mg/kg (F) 

 II

870.1100 Acute Oral (97% ai)

Dunkin Hartley Albino Guinea pig

00117478 (1982) LD50 = 542 mg/kg (M) >400 and <640 mg/kg (F) III

870.1100 Acute Oral (97% ai) 00117478 (1982) LD50 = 835 mg/kg (M)

 937 mg/kg (F)

III

Page 7 of 44
NZW Rabbit

870.1200 Acute Dermal (97% ai) 

Alderley Park Rat

00117478 (1982) LD50 = >1000 mg/kg (M F) II

870.1200 Acute Dermal (97% ai) 

NZW Rabbit 00117478 (1982) LD50 = >1000 mg/kg (M F) II

870.1300 Acute Inhalation (97% ai)

50% ai 

Alderley Park Rat

00117482 (1982) LC50 = >766 mg/m3 (M)

359-766 mg/m3 (F)

III

870. 2400 Primary Eye Irritation (97% ai)

NZW Rabbit 00117479 (1982) 5/6 rabbits with unwashed eyes 

had slight corneal opacity, 

which cleared within 7 days; 

3/6 rabbits with washed eyes 

had slight redness of the 

conjunctiva, with some 

chemosis and discharge, which 

was not apparent by 3 days. 

IIIa

870.2500 Primary Skin Irritation 

(97% ai) NZW Rabbit

00117479 (1982) Mild irritation that persisted for 

72 hours III

870.2500 Primary Skin Irritation 

(97% ai) Alderley Park Albino Rat

00117479 (1982) 3/5 M showed erythema; 2/5 (F) 

showed desquamation and 

scabbing. Effects did not 

persist in either sex.

III

870.2600 Dermal Sensitization (Guinea pig) Dunkin Hartley Albino 00117479 (1982) Not a skin sensitized

a Reclassified in 1995, based on additional data provided by the registrant (HED Document 011460). 

Toxicological PODs Used for Risk Assessment

Short-term Dermal: Quantification of dermal risks was performed using a developmental rat 

study with a NOAEL of 10 mg/kg/day based on partial ossification of the 7th vertebra and an 

increased incidence of 14th rib on a fetal and litter basis at a dose that was not maternally toxic

(LOAEL = 40 mg/kg/day). Since an oral dose was selected, a dermal absorption factor of 18.7% 

should be used in estimating dermal risks. A Margin of Exposure (MOE) of 100 is required 

which includes an interspecies extrapolation (10X) and an intraspecies variability (10X).

Short-term Inhalation: Quantification of inhalation risks was performed using a developmental 

rat study with a NOAEL of 10 mg/kg/day based on partial ossification of the 7th vertebra and an 

increased incidence of 14th rib on a fetal and litter basis at a dose that was not maternally toxic 

(LOAEL = 40 mg/kg/day). Since an oral dose was selected absorption via inhalation is 

presumed to be equivalent to oral absorption. A MOE of 100 is required which includes an 

interspecies extrapolation (10X) and an intraspecies variability (10X).

Short-term Incidental Oral: Quantification of incidental oral ingestion risks was performed using 

a reproductive rat study with a NOAEL of 23.2 mg/kg/day based on the increased incidence of 

chromodacryorrhea, thickened eyelids and dental malocclusion, increased liver weights, mottling 

Page 8 of 44
or accentuation of the lobular structure of the liver along with liver enlargement, pallor and 

discoloration in male and female pups of both generations (Offspring LOAEL = 116.9

mg/kg/day). A MOE of 100 is required which includes an interspecies extrapolation (10X) and 

an intraspecies variability (10X).

HED reviewed the full toxicological database for paclobutrazol in an attempt to select endpoints 

for the dermal children 1 < 2 years old and 6 to < 11 years old scenarios; however no appropriate 

endpoint was available because in a three-week dermal toxicity test paclobutrazol was not 

systemically toxic up to the limit dose. An inhalation endpoint for the children 1 < 2 years old 

and 6 < 11 years old scenario was not selected because there is no exposure to them via the 

inhalation route.

The need for a subchronic inhalation study for paclobutrazol was discussed by the Hazard and 

Science Policy Council (HASPOC) (Leshin, 2014, TXR # 0056914). The HASPOC concluded 

that based on a weight-of-evidence approach, considering all the available hazard and exposure 

information for paclobutrazol, a subchronic inhalation study is not needed at this time.

There are no proposed or currently registered food uses for paclobutrazol. Carcinogenicity 

studies are not required for non-food use chemicals, however, carcinogenicity studies in mice 

and rats are available. In 1994, the RfD Peer Committee evaluated the potential carcinogenicity 

of paclobutrazol (TXR 0011081). At that time it was determined that the Agency was unable to 

determine the potential carcinogenicity of paclobutrazol because the maximum tolerated dose 

(MTD) was not achieved in the 2-year carcinogenicity/chronic study in rats and the 

carcinogenicity/chronic study in mice. The carcinogenic potential will be re-evaluated if the use 

pattern changes (i.e., food uses are proposed).

The Agency’s level of concern for risks (i.e., target level for MOEs) is defined by the uncertainty 

factors that are applied to the assessment. The Agency typically applies a factor of 10X to 

account for interspecies extrapolation to humans from the animal test species and another factor 

of 10X to account for intra-species sensitivity. In the case of paclobutrazol, the total uncertainty 

factor that has been applied to occupational and residential risk assessments is 100 for short- and 

intermediate-term dermal, inhalation and incidental oral exposures. 

A summary of the toxicological doses and endpoints for use in the occupational and residential 

exposure and risk assessment are provided in Table 3.2.

Table 3.2.: Summary of Toxicological Doses and Endpoints and Points of Departure for 

Paclobutrazol 

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern for 

Risk Assessment Study and Toxicological Effects

Acute Dietary

General Population

NOAEL = 30 

mg/kg UFA=10x

UFH=10x

30 mg/kg NOAEL 

 100 (UF)

aRfD = 0.3 mg/kg

Acute Neurotoxicity Study (Rats)

MRID 49211902

LOAEL = 150 mg/kg, based on transient 

alterations in motor activity (decreased rearing 

and decreased subsession distances in females 

3-4 hours after dosing)

Page 9 of 44
Table 3.2.: Summary of Toxicological Doses and Endpoints and Points of Departure for 

Paclobutrazol 

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern for 

Risk Assessment Study and Toxicological Effects

Acute Dietary

Females 13-49

NOAEL = 10

mg/kg/day

UFA=10x

UFH=10x

10 mg/kg/day NOAEL 

 100 (UF)

aRfD = 0.1 mg/kg 

Developmental Toxicity in Rats

MRID 00143158)

Developmental LOAEL = 40 mg/kg/day, based 

on partial ossification of the 7th vertebra and an 

increased incidence of 14th rib on a fetal and 

litter basis at a dose that was not maternally 

toxic. 

Chronic Dietary

All Populations

NOAEL = 

10.8 mg/kg/day

UFA=10x

UFH=10x

10.8 mg/kg/day NOAEL 

 100 (UF)

cRfD = 0.11 mg/kg/day 

Chronic (2-Year Rat) Feeding Toxicity MRID 

40734301

LOAEL = 54.2 mg/kg/day , based on increased 

liver weights (both sexes), hypertrophy, and 

steatosis (both sexes) and decreased 

triglycerides (females)

Incidental Oral 

Short- and IntermediateTerm (Young children1-

2 years old)

NOAEL = 

23.2 mg/kg/day

UFA=10x

UFH=10x Residential LOC = 100

Reproductive Toxicity Study in Rats

MRID 40734303/47338506

Offspring LOAEL = 116.9 mg/kg/day, based 

on the increased incidence of 

chromodacryorrhea, thickened eyelids and 

dental malocclusion; increased liver weights; 

mottling or accentuation of the lobular structure 

of the liver along with liver enlargement, 

pallor and discoloration in male and female 

pups of both generations. 

Dermal

Short- and IntermediateTerm (Young Children 1-

2 years old)

No dermal risk assessment because in a 3-week dermal toxicity test (MRID 00132688), paclobutrazol was 

not systemically toxic up to the limit dose.

Inhalation

Short- and IntermediateTerm (Young Children 1-

2 years old)

There is no exposure to young children via the inhalation route.

Cancer (oral, dermal, 

inhalation) Not required for non-food use pesticides.

Dermal

Short- and IntermediateTerm (Females 13-49)

Oral NOAEL = 10

mg/kg/day

(Dermal 

Absorption Rate = 

18.7%; (MRID 

41048202)

UFA=10x

UFH=10x Residential/Occupational 

LOC = 100

Developmental Toxicity in Rats

MRID 00143158)

Developmental LOAEL = 40 mg/kg/day, based 

on partial ossification of the 7th vertebra and an 

increased incidence of 14th rib on a fetal and 

litter basis at a dose that was not maternally 

toxic. 

Inhalation 

Short- and IntermediateTerm (Females 13-49)

Oral NOAEL = 10 

mg/kg/day

Inhalation Rate = 

100%

UFA=10x

UFH=10x Residential/Occupational 

LOC = 100

Developmental Toxicity in Rats

MRID 00143158)

Developmental LOAEL = 40 mg/kg/day, based 

on partial ossification of the 7th vertebra and an 

increased incidence of 14th rib on a fetal and 

litter basis at a dose that was not maternally 

toxic. 

NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = 

extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human 

population (intraspecies). MOE = margin of exposure. LOC = level of concern. 

Note: A FQPA factor was not applied because the currently registered use patterns are all non-food uses. 

Page 10 of 44
Absorption

A dermal absorption factor of 18.7 % was used for the exposure assessment and is based on a 

dermal penetration study. Since no inhalation absorption data are available, toxicity by the 

inhalation route is considered to be equivalent to the estimated toxicity by the oral route of 

exposure.

Body Weight

Since the dermal and inhalation PODs are based on developmental and/or fetal effects, the body 

weight appropriate for dermal and inhalation assessments is 69 kg.

4.0 Use Profile 

Paclobutrazol is currently registered for use as a foliar spray to turf (including parks, athletic 

fields, residential lawns, and golf courses), ornamental plants in nurseries and greenhouses, as a 

tree injection, as a soil injection, as a bulb soak treatment, as pre-plant plugs/liners, and as a seed 

treatment (on cucurbit, pepper, tomato, broccoli, cauliflower, and cabbage seeds). Specific 

details related to the existing use pattern are summarized in Table 4.1. 

Table 4.1.: Paclobutrazol Use Patterns and Formulations

Formulation Use Sites Maximum 

Application Rate

Application 

Equipment REI Notes

Soluble 

Concentrate Turf 0.75 lb ai/A Ground and 

handheld

24 hrs or 12 

hrs depending 

on label

Although paclobutrazol turf 

products do not appear to be 

specifically marketed towards 

residential handler use (i.e., 

homeowners); residential handler 

use was assumed to be protective 

of any such use

Granular Turf 0.5 lb ai/A Ground and 

handheld 12 hrs

Although paclobutrazol turf 

products do not appear to be 

specifically marketed towards 

residential handler use (i.e., 

homeowners); residential handler 

use was assumed to be protective 

of any such use

Soluble 

Concentrate

Tree Injection 

(Soil injection at 

base of tree)

0.352 lb ai/tree Soil injection 

equipment N/A

Emulsifiable 

Concentrate

Pre-plant 

plugs/liners 0.000051 lb ai/gal Plug/liner soak N/A

Emulsifiable 

Concentrate Bulbs 0.00255 lb ai/gal Bulb soak N/A

Application rate represents 

highest application rate for a 

bulb (freesia)

Emulsifiable 

Concentrate

Ornamental 

Plants in 

Greenhouses 

and Nurseries

0.59 lb ai/A Ground and 

handheld 12 hours

Application rate represents 

highest application rate for an 

ornamental (chrysanthemums)

Soluble 

Concentrate

Tree Injection

(8 inch tree) 0.0099 lb ai/tree Pressurized injection system

N/A

Application rates on labels are 

presented for multiple diameter 

trees; two application rates were 

selected to be representative of 

those on the labels

Tree Injection 

(35 inch tree) 0.07 lb ai/tree Pressurized 

injection system

Page 11 of 44
Table 4.1.: Paclobutrazol Use Patterns and Formulations

Formulation Use Sites Maximum 

Application Rate

Application 

Equipment REI Notes

Soluble 

Concentrate

Cucurbit Seed 0.00027 lb ai/lb seed

Commercial seed 

treatment equipment N/A On-farm seed treatment is prohibited

Tomato Seed 0.00414 lb ai/lb seed

Pepper Seed 0.00247 lb ai/lb seed

Broccoli Seed 0.000661 lb ai/seed

Cauliflower 

Seed 0.000635 lb ai/seed

Cabbage Seed 0.000639 lb ai/seed

Wettable

Powder

Tree Injection 

(6-16 inches in 

diameter)

0.000059 lb ai/tree Pressurized 

injection system

N/A

Application rates on labels are 

presented for multiple diameter 

trees; two application rates were 

selected to be representative of 

those on the labels

Tree Injection 

(>16 inches in 

diameter)

0.00024 lb ai/tree Pressurized 

injection system

5.0 Residential Exposure and Risk Estimates

Paclobutrazol is currently registered for use as a foliar spray for turf (including parks, athletic 

fields, and golf courses). Paclobutrazol is currently not registered for homeowner use on 

residential lawns. Therefore, a residential handler exposure assessment was not conducted. A 

residential post-application assessment was performed as use of paclobutrazol in parks and golf 

courses is expected to result in residential post-application exposure. In assessing these 

exposures, HED’s 2012 Residential SOPs3 for Residential Pesticide Exposure Assessment: 

Lawns/Turf was used. Some of the data included in the Lawns/Turf SOP are proprietary and 

thus are subject to the data protection provisions of the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA).

5.1 Residential Post-application Exposure/Risk Estimates

There is the potential for post-application exposure for individuals exposed as a result of being in 

an environment that has been previously treated with paclobutrazol. The quantitative 

exposure/risk assessment for residential post-application exposures is based on the following 

scenarios:

• Physical activities on turf: adults (dermal) and children 1 < 2 years old (incidental oral)

• Golfing: adults (dermal), children 11 < 16 years old (dermal)

The lifestages selected for each post-application scenario are based on an analysis provided as an 

Appendix in the 2012 Residential SOPs4. While not the only lifestage potentially exposed for 

these post-application scenarios, the lifestage that is included in the quantitative assessment is 

health protective for the exposures and risk estimates for any other potentially exposed lifestage.

Residential Post-application Exposure Data and Assumptions

3 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html 4 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html

Page 12 of 44

 
A series of assumptions and exposure factors served as the basis for completing the residential 

post-application risk assessment. Each assumption and factor is detailed in the 2012 Residential 

SOPs5

.

In addition, the following assumptions were used to calculate post-application risk estimates:

Assumptions:

• A TTR study was used to assess the liquid formulation scenarios (Turf Enhancer® 2SC 

Plant Growth Regulator Transferable Turf Residue Study – MRID No.: 45214201). Data 

were collected at three sites in the TTR study including New York, California, and North 

Carolina. Data from the California site was used in this assessment as it resulted in the 

highest predicted Day 0 residues (see Appendix B for more details).

Application Rate: Refer to the currently registered use pattern table in Table 4.1. 

Exposure Duration: Residential post-application exposure is expected to be short-term in 

duration. While multiple applications may be possible, it is anticipated that these applications 

will be intermittent in nature and dissipation due to rainfall/irrigation, grass growth, and grass 

mowing is expected.

Residential Post-application Non-Cancer Exposure and Risk Equations

The algorithms used to estimate residential post-application exposure and dose can be found in 

Appendix A and/or the 2012 Residential SOPs5. 

Combining Exposure and Risk Estimates

The incidental oral scenarios (i.e., hand-to-mouth and object-to-mouth) should be considered 

inter-related and it is likely that they occur interspersed amongst each other across time. 

However, combining these scenarios would be overly-conservative because of the conservative 

nature of each individual assessment. Therefore, the post-application exposure scenarios that 

represents the highest exposure for children 1 to < 2 years old is the hand-to-mouth scenario. 

This scenario should be considered a protective estimate of children’s exposure to pesticides 

used outdoors. 

Summary of Residential Post-application Non-Cancer Exposure and Risk Estimates

A summary of the adult and children short-term dermal exposure and risk estimates is shown in 

Table 5.1.1. All adult and children golfing dermal risk estimates for both liquid and granular 

formulations are greater than the LOC (MOEs ≥ 100). All adults on treated turf dermal risk 

estimates for both liquid and granular formulations are greater than the LOC (MOEs ≥ 100). 

Page 13 of 44
Table 5.1.1. Residential Post-application Non-cancer Exposure and Risk Estimates for Paclobutrazol

Lifestage Post-application Exposure Scenario

Application Rate a

(lb ai/A)

TTR 

(ug/cm2)

Dermal Dose b

(mg/kg/day)

Dermal MOEs c

Liquid Formulations

Adult Dermal 

Physical Activities on Turf

0.75 0.080 d,

0.058 170

Golfing 0.0046 2,200

Child 11 < 16 years old Dermal Golfing 0.75 0.080 d 0.0046 2,200

Granular Formulations

Adult

Dermal 

Physical Activities on Turf

0.5 0.01e

0.01 1,100

Golfing

0.0006 16,000

Child 11 < 16 years old 0.0006 16,000

a. Application rates = maximum application rates from labels.

b. Dose (mg/kg/day) equations provided in Appendix A. 

c. Dermal MOE = NOAEL (10 mg/kg/day) / Dermal Dose (mg/kg/day)

d. Representative of California TTR data taken from MRID No.: 45214201; the site that resulted in the highest TTR values.

e. Turf Transferable Residues (TTR) = Application Rate x 0.2% x 11.2.

A summary of the children short-term oral non-dietary ingestion exposure and risk estimates is 

shown in Table 5.1.2. All children oral non-dietary ingestion risk estimates for both liquid and 

granular formulations do not exceed HED’s level of concern (MOEs ≥ 100). 

Table 5.1.2. Short-Term Oral Non-dietary Ingestion Residential Post-application Exposure and Risk Estimates for 

Paclobutrazol

Lifestage Post-application Exposure Scenario Application Rate a

(lb ai/A)

TTR 

(ug/cm2)

Oral Dose b

(mg/kg/day)

Oral 

MOEs c

Liquids

Child 1 < 2 year old Oral 

Hand-to-Mouth

0.75 0.080 d

0.011 2,100

Object-to-Mouth 0.00033 70,000

Soil Ingestion 0.000025 910,000

Granulars

Child 1 < 2 year old Oral 

Hand-to-Mouth

0.5 0.01e

0.0008 31,000

Object-to-Mouth 0.00005 500,000

Soil Ingestion 0.000017 1,400,000

Episodic Granular Ingestion

(1.4% ai) 0.05 210

a. Application rates = maximum application rates from labels.

b. Dose (mg/kg/day) equations provided in Appendix A.

c. Oral MOE = NOAEL (23.2 mg/kg/day) / Oral Dose (mg/kg/day).

d. Representative of California TTR data taken from MRID No.: 45214201; the site that resulted in the highest TTR values.

e. Turf Transferable Residues (TTR) = Application Rate x 0.2% x 11.2.

Page 14 of 44
5.3 Residential Risk Estimates for Use in Aggregate Assessment

Table 5.3 reflects the residential risk estimates that are recommended for use in the aggregate 

assessment for paclobutrazol.

• The recommended residential exposure for use in the adult short-term aggregate 

assessment reflects dermal exposure from post-application exposure from physical 

activities on turf.

• The recommended residential exposure for use in the children 1 to <2 years old shortterm aggregate assessment reflects hand-to-mouth exposures from post-application 

exposure to turf applications.

Table 5.3. Recommendation for the Residential Exposures for the Paclobutrazol Aggregate Assessment

Lifestage Exposure 

Scenario

Dose (mg/kg/day)1 MOE2

Dermal Inhalation Oral Total Dermal Inhalation Oral Total

Adult

Turf

(Liquids)

0.058 N/A N/A 0.058 170 N/A N/A 170

Child 1 to <2 

yrs old

Hand-toMouth

(Liquids)

N/A N/A 0.011 0.011 N/A N/A 2,100 2,100

1 Dose = the highest dose for each applicable lifestage of all residential scenarios assessed. Total = dermal + inhalation + incidental oral (where 

applicable).

2 MOE = the MOEs associated with the highest residential doses. Total = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE) + (1/Incidental Oral 

MOE), where applicable.

5.4 Spray Drift

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtrget and can lead to exposures to those it may directly contact. They can also deposit on surfaces 

where contact with residues can eventually lead to indirect exposures (e.g., children playing on 

lawns where residues have deposited next to treated fields). The potential risk estimates from 

these residues can be calculated using drift modeling coupled with methods employed for

residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessment is based 

on a premise of compliant applications which, by definition, should not result in direct exposures 

to individuals because of existing label language and other regulatory requirements intended to 

prevent them.5

 Direct exposures would include inhalation of the spray plume or being sprayed 

directly. Rather, the exposures addressed here are thought to occur indirectly through contact 

with impacted areas, such as residential lawns, when compliant applications are conducted. 

Given this premise, exposures for children (1 to 2 years old) and adults who have contact with 

turf where residues are assumed to have deposited via spray drift thus resulting in an indirect 

5 This approach is consistent with the requirements of the EPA’s Worker Protection Standard which, 

when included on all labels, precludes direct exposure pathways.

Page 15 of 44

 
exposure are the focus of this analysis analogous to how exposures to turf products are 

considered in risk assessment. 

Several paclobutrazol products have existing labels for use on turf, thus it was considered 

whether the risk assessment for that use may be considered protective of any type of exposure 

that would be associated with spray drift. The currently registered maximum single application 

rate of paclobutrazol for foliar sprays on ornamentals in nurseries is 0.59 lb ai/A which is less 

than the direct turf application rate of 0.75 lbs ai/A, therefore the registered residential uses on 

turf result in exposure greater than potential exposure from spray drift; and no new spray drift 

residential assessment needs to be completed. The turf post-application MOEs are protective for 

any potential exposures related to spray drift for paclobutrazol. 

5.5 Residential Bystander Post-Application Inhalation Exposure

Volatilization of pesticides may be a source of post-application inhalation exposure to 

individuals nearby pesticide applications. The agency sought expert advice and input on issues 

related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act 

Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on 

March 2, 2010 (http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The 

agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a

subsequent Volatilization Screening Analysis 

(http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219). During Registration 

Review, the agency will utilize this analysis to determine if data (i.e., flux studies, route-specific 

inhalation toxicological studies) or further analysis is required for paclobutrazol.

6.0 Occupational Exposure and Risk Estimates

6.1 Occupational Handler Exposure/Risk Estimates

HED uses the term handlers to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct job functions or tasks related to 

applications and exposures can vary depending on the specifics of each task. Job requirements 

(amount of chemical used in each application), the kinds of equipment used, the target being 

treated, and the level of protection used by a handler can cause exposure levels to differ in a 

manner specific to each application event. 

Based on the anticipated use patterns and current labeling, types of equipment and techniques 

that can potentially be used, occupational handler dermal and inhalation exposure is expected 

from the existing uses. 

The quantitative exposure/risk assessment developed for occupational handlers is based on the 

following scenarios:

Page 16 of 44
• Mixing/loading liquids for groundboom applications

• Mixing/loading liquids for tree injection

• Mixing/loading liquids for soil injection

• Mixing/loading wettable powders for tree injections

• Loading granules for open cab solid broadcast spreader applications

• Mixing/loading liquid concentrations via dip (bulb soak)/liner soaks

• Applying sprays for open cab groundboom equipment

• Applying granules for open cab solid broadcast spreader

• Loading/applying granules for belly grinder applications

• Loading/applying granules for push type spreader applications

• Mixing/loading/applying liquids for backpack sprayer applications

• Mixing/loading/applying liquids for manually pressurized handwand applications

• Mixing/loading/applying liquids for mechanically pressurized handgun sprayer 

applications

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

handler risk assessments. Each assumption and factor is detailed below on an individual basis.

Application Rate: Refer to the currently registered use pattern table in Section Table 4.1.

Unit Exposures: It is the policy of HED to use the best available data to assess handler exposure. 

Sources of generic handler data, used as surrogate data in the absence of chemical-specific data, 

include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force 

(ORETF) database, or other registrant-submitted occupational exposure studies. Some of these 

data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. 

The standard values recommended for use in predicting handler exposure that are used in this 

assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit 

Exposure Surrogate Reference Table6

”, which, along with additional information on HED policy 

on use of surrogate data, including descriptions of the various sources, can be found at the 

Agency website7

. 

Area Treated or Amount Handled: 

The daily areas treated or amounts handled were defined for each handler scenario (in 

appropriate units) by determining the amount that can be reasonably treated by an individual in a 

single day. When possible, the assumptions for daily areas treated or amounts handled are taken 

from the HED’s ExpoSAC Policy #9.1: “Standard Values for Daily Acres Treated in 

Agriculture”. Values used for area treated or amount handled include: 

• 40 acres for groundboom application for golf courses and nurseries;

• 40 acres for tractor drawn spreader application for golf courses;

6 Available: http://www.epa.gov/opp00001/science/handler-exposure-table.pdf 7 Available: http://www.epa.gov/pesticides/science/handler-exposure-data.html

Page 17 of 44

 
• 50 trees/day for tree injection applications (see note below);

• 50 trees/day for soil injection applications (see note below); 

• 100 and 1000 gallons for mixing/loading liquids concentrations via dip (bulb soak)/liner 

soaks;

• 5 acres for mixing/loading/applying with a mechanically pressurized handgun sprayer to 

turf and golf courses and 25 acres to nurseries and greenhouses;

• 5 acres for mixing/loading/applying with a manually pressurized handwand to nurseries 

and greenhouses;

• 5 acres for mixing/loading/applying with a backpack sprayer to turf, golf courses, 

nurseries, and greenhouses; and 

• 5 acres for push-type spreader application to turf and golf courses.

Note: HED received written information from several paclobutrazol registrants that for 

occupational applicators, about 50 trees per day are treated for tree injection applications and soil 

injection applications. The data ranged from 10 trees per day to 70 trees per day. HED selected 

50 trees per day for tree and soil injection applications because it was the most typical number 

from the available information.

Exposure Duration: 

HED classifies exposures from 1 to 30 days as short-term and exposures 30 days to six months 

as intermediate-term. Exposure duration is determined by many things, including the exposed 

population, the use site, the pest pressure triggering the use of the pesticide, and the cultural 

practices surrounding that use site. For most agricultural uses, it is reasonable to believe that 

occupational handlers will not apply the same chemical every day for more than a one-month 

time frame; however, there may be a large agribusiness and/or commercial applicators who may 

apply a product over a period of weeks (e.g., completing multiple applications for multiple 

clients within a region). 

For paclobutrazol, based on the proposed use, short- and intermediate-term exposures are

expected. The short- and intermediate-term PODs are the same; therefore, short-term risk 

estimates are protective of longer-term exposures.

Mitigation/Personal Protective Equipment: Estimates of dermal and inhalation exposure were 

calculated for various levels of personal protective equipment (PPE). Results are presented for 

“baseline,” defined as a single layer of clothing consisting of a long sleeved shirt, long pants, 

shoes plus socks, no protective gloves, and no respirator, as well as baseline with various levels 

of PPE as necessary (e.g., gloves, respirator, etc). The paclobutrazol product labels direct 

mixers, loaders, applicators and other handlers to wear long-sleeved shirt and long pants, 

chemical-resistant gloves, and shoes plus socks. In addition, some of the labels also state that 

chemical-resistant aprons should also be used. 

Occupational Handler Non-Cancer Exposure and Risk Estimate Equations

The algorithms used to estimate non-cancer exposure and dose for occupational handlers can be 

found in Appendix A.

Page 18 of 44
Combining Exposures/Risk Estimates:

Dermal and inhalation risk estimates were combined in this assessment, since the toxicological 

effects for these exposure routes were similar. Dermal and inhalation risk estimates were 

combined using the following formula:

Total MOE = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE)

Summary of Occupational Handler Non-Cancer Exposure and Risk Estimates

The short- and intermediate-term risk estimates for occupational handlers are included in Table 

6.1.1. The short- and intermediate-term risk estimates for the occupational handler scenarios are 

greater than HED’s LOC (MOEs ≥100) with the exception of mixing/loading/applying liquids 

via a backpack sprayer. The backpack sprayer equipment scenario is still not greater than HED’s 

LOC (MOEs < 100) even with the use of PPE of a double layer and gloves (MOE = 58).

Page 19 of 44
Table 6.1.1. Occupational Handler Exposures and Risks for Paclobutrazol Turf, Ornamental, and Tree Uses

Activity Use Site

PPE-G Dermal 

Unit Exposure 

(mg/lb ai)a

Baseline 

Inhalation Unit 

Exposure 

(mg/lb ai)a

Application 

Rate b

Area 

Treated 

Daily c

PPE-G Baseline Inhalation

Total MOE (PPE-G + 

Baseline Inhalation) Dermal 

Dose 

(mg/kg/day)d

MOEf Dose (mg/kg/day)e MOEg

Mixer/Loader

Mixing/Loading Liquids

Groundboom 

Applications on 

Ornamentals in 

Nurseries

0.0376 0.000219

0.59 lb ai/A 40 A 0.0024 4,200 0.000075 130,000 4,000

Groundboom 

Applications on 

Golf Courses

0.75 lb ai/A 40 A 0.0031 3,300 0.000095 110,000 3,200

Tree Injection (8 

diameter Inch 

Trees)

0.0099 lb 

ai/tree 50 trees 0.00005 200,000 0.0000016 6,400,000 190,000

Tree Injection (35 

diameter Inch 

Trees)

0.07 lb 

ai/tree 50 trees 0.00036 28,000 0.000011 900,000 27,000

Tree Soil Injection 0.352 lb 

ai/tree 50 trees 0.0018 5,600 0.000056 180,000 5,400

Dips for 

Plug/Liner Soaks

0.000051 lb 

ai/gal 100 gals 0.00000052 19,000,000 1.60E-08 620,000,000 19,000,000

0.000051 lb 

ai/gal

1000 

gals 0.0000052 1,900,000 1.60E-07 62,000,000 1,900,000

Dips for Bulb 

Soaks (Freesia)

0.00255 lb 

ai/gal 100 gals 0.000026 380,000 8.1E-07 12,000,000 370,000

0.00255 lb 

ai/gal

1000 

gals 0.00026 38,000 0.0000081 1,200,000 37,000

Mixing/Loading Wettable 

Powders

Tree Injection (6-

16 inches in 

diameter) 0.17 0.043

0.000059 lb 

ai/tree 50 trees 0.0000014 7,400,000 0.0000018 5,400,000 3,100,000

Tree Injection 

(>16 inches in 

diameter)

0.00024 lb 

ai/tree 50 trees 0.0000055 1,800,000 0.0000075 1,300,000 770,000

Page 20 of 44
Table 6.1.1. Occupational Handler Exposures and Risks for Paclobutrazol Turf, Ornamental, and Tree Uses

Activity Use Site

PPE-G Dermal 

Unit Exposure 

(mg/lb ai)a

Baseline 

Inhalation Unit 

Exposure 

(mg/lb ai)a

Application 

Rate b

Area 

Treated 

Daily c

PPE-G Baseline Inhalation

Total MOE (PPE-G + 

Baseline Inhalation) Dermal 

Dose 

(mg/kg/day)d

MOEf Dose (mg/kg/day)e MOEg

Loading Granulars

Tractor Drawn 

Spreader 

Applications on 

Golf Courses

0.0069 0.0017 0.5 lb ai/A 40 A 0.00037 27,000 0.00049 20,000 12,000

Applicator

Applying Liquid Sprays 

via Groundboom

Golf Courses

0.0161 0.00034

0.75 lb ai/A 40 A 0.0013 7,600 0.00015 68,000 6,900

Ornamentals in 

Nurseries 0.59 lb ai/A 40 A 0.001 9,700 0.00012 86,000 8,700

Applying Granulars via 

Tractor Drawn Spreader Golf Courses 0.0072 0.0012 0.5 lb ai/A 40 A 0.00039 26,000 0.00035 29,000 14,000

Mixer/Loader/Applicator

Mixing/Loading/Applying 

Liquids via Backpack 

Sprayer

Turf

8.26 0.00258

0.75 lb ai/A 5 A 0.084 120 0.00014 71,000 120

Golf Course 0.75 lb ai/A 5 A 0.084 120 0.00014 71,000 120

Drench Tree 

Treatments (8 inch 

Tree)

0.07 lb 

ai/tree 50 trees 0.078 130 0.00013 76,000 130

Drench Tree 

Treatments (35 

inch Tree)

0.31 lb 

ai/tree 50 trees 0.35 29 0.00058 17,000 29

Drench Tree 

Treatments

(35 inch Tree)

4.12

(PPE G-DL)

0.00258 0.31 lb 

ai/tree 50 trees 0.17 58 0.00058 17,000 58

(PPE G-DL + baseline 

Inhalation)

Foliar Sprays on 

Ornamentals in 

Nurseries and 

Greenhouses

11200 140 0.00423 lb 

ai/gallon

40 

gallons 0.00515 1,900 0.000343 29,000 1,800

Mixing/Loading/Applying 

Liquids via Manually 

Pressurized Handwand

Foliar Sprays on 

Ornamentals in 

Nurseries and 

Greenhouses 0.43 30

0.00423 lb 

ai/gallon

40 

gallons 0.000197 51,000 0.0000736 140,000 37,000

Drench Tree 

Treatments (8 inch 

Tree)

0.07 lb 

ai/tree 50 trees 0.0041 2,500 0.0015 6,600 1,800

Page 21 of 44
Table 6.1.1. Occupational Handler Exposures and Risks for Paclobutrazol Turf, Ornamental, and Tree Uses

Activity Use Site

PPE-G Dermal 

Unit Exposure 

(mg/lb ai)a

Baseline 

Inhalation Unit 

Exposure 

(mg/lb ai)a

Application 

Rate b

Area 

Treated 

Daily c

PPE-G Baseline Inhalation

Total MOE (PPE-G + 

Baseline Inhalation) Dermal 

Dose 

(mg/kg/day)d

MOEf Dose (mg/kg/day)e MOEg

Drench Tree 

Treatments (35 

inch Tree)

0.31 lb 

ai/tree 50 trees 0.018 550 0.0067 1,500 400

Loading/Applying 

Granulars via Push-type

Spreader

Turf

0.24 0.01

0.5 lb ai/A 5 A 0.0016 6,100 0.00036 28,000 5,000

Golf Course 0.5 lb ai/A 5 A 0.0016 6,100 0.00036 28,000 5,000

Mixing`/Loading/Applying 

Liquids via Mechanically 

Pressurized Handwand

Turf 0.88 0.0019 0.75 lb ai/A 5 A 0.0089 1,100 0.0001 97,000 1,100

Golf Course 0.75 lb ai/A 5 A 0.0089 1,100 0.0001 97,000 1,100

Foliar Sprays on 

Ornamentals in 

Nurseries

390 3.9 0.00423 lb 

ai/gallon

1,000 

gallons 0.00447 2,200 0.000239 42,000 2,100

Foliar Sprays on 

Ornamentals in 

Greenhouses

2,500 120 0.00423 lb 

ai/gallon

1,000 

gallons 0.0287 350 0.00736 1,400 280

a. Unit Exposures taken from Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (http://www.epa.gov/opp00001/science/handler-exposure-table.pdf)

b. Application rates = maximum application rates from labels.

c. Exposure Science Advisory Council Policy #9.1.

d. Dermal Dose (mg/kg/day) = Dermal Unit exposure (mg/lb ai) × Conversion Factor (0.001 mg/μg) x Application Rate x Area Treated or Amount Handled x % Dermal 

Absorption Factor (18.7%) /Body weight (69 kg). 

e. Inhalation Dose (mg/kg/day) = Inhalation Unit Exposure (mg/lb ai) x Conversion Factor (0.001 mg/μg) x Application Rate x Area Treated x %Absorption (100% inhalation ) / 

Body weight (69 kg). 

f. Dermal MOE = Dermal NOAEL (10 mg/kg/day) / Dermal Dose (mg/kg/day). LOC = 100. 

g. Inhalation MOE = Inhalation NOAEL (10 mg/kg/day) / Inhalation Dose (mg/kg/day). LOC = 100

Page 22 of 44
Short-/Intermediate-Term Handler Risk for Seed Treatments

Paclobutrazol is currently registered for commercial seed treatment use on tomato, pepper, and 

cucurbit, broccoli, cauliflower, and cabbage seeds. The paclobutrazol labels do not permit onfarm seed treatment. Based on the existing seed treatment use pattern, there is a potential for 

exposure to paclobutrazol to primary handlers (i.e., activities related to treating the seed) and 

secondary handlers (i.e., planting treated seed). Primary and secondary handler exposure is 

expected to be short- or intermediate-term in duration based on the information provided on the 

existing labels. The short- and intermediate-term toxicological endpoints are the same for the 

respective routes of exposure; therefore, the estimates of risk for short-term duration exposures 

are protective of those for intermediate-term durations.

Primary Handler (Treating Seed)

Potential primary occupational handler exposure scenarios from the use of paclobutrazol as a 

commercial seed treatment include:

• Mixing, loading, applying liquid formulations;

• Bagging treated seed;

• Sewing bags; and

• Multiple activities.

Typically, for large-scale commercial seed treatments, workers perform only those specific 

individual tasks listed above; however, it is assumed that workers also may perform multiple 

activities throughout the day. As a result a “multiple activities” scenario (i.e. where one worker 

performs all seed treatment tasks such as loading/applying, sewing, bagging, cleaning, 

calibration, repair, forklift driver, etc.) was addressed. No assessment was performed for onfarm seed treatment as the paclobutrazol labels do not permit on-farm seed treatment. 

Secondary Handler (Planting Treated Seed)

Potential secondary occupational handler exposure scenarios from the use of paclobutrazol as a 

commercial seed treatment include planting treated seed.

It is the policy of HED to use the best available data to assess handler exposure. Sources of 

generic handler data for seed treatment are incorporated in HED ExpoSAC Policy 14: SOPs for 

Seed Treatment. The amount of active ingredient handled depends on the application rate (lb 

ai/lb seed or lb ai/seed), the pounds of seed treated in a day, and the pounds of seed that can be 

planted in a day, all of which vary depending upon the seed type. Values for the amount of seed 

treated and planted per day were obtained from HED ExpoSAC Policy 15.

Summaries of the risk estimates for primary and secondary handlers are included in Tables 6.1.2 

and 6.1.3. The short- and intermediate-term risk estimates for all primary and secondary handler 

scenarios are greater than HED’s LOC (MOEs ≥100) at some level of PPE.

Page 23 of 44
Table 6.1.2 Summary of Short- and Intermediate-Term Handler Exposures and Risks for Paclobutrazol Seed Treatment

Seed Type

Max Application 

Ratea

Unit Exposureb

(mg/lb ai)

Amount of Seed 

Treatedc

Absorbed Dose

(mg/kg/day)d MOEe

lb ai/lb seed Dermal Inhal. lb seed/day Dermal Inhal. Dermal Inhal.

LOADER/APPLICATOR (single layer, gloves)

Cucurbit

(Cucumber) 0.000229

0.00023 0.00034 3,000

0.000043 0.000003 230,000 3,000,000

Cucurbit

(Cantaloupe) 0.00027 0.000050 0.000004 200,000 2,500,000

Cucurbit

(Pumpkin) 0.000107 0.000020 0.000002 500,000 6,300,000

Cucurbit

(Squash) 0.000172 0.000032 0.000003 310,000 3,900,000

Cucurbit

(Watermelon) 0.000157 0.000029 0.000002 340,000 4,300,000

Pepper 0.00247 0.000462 0.000037 22,000 270,000

Tomato 0.00414 0.000774 0.000061 13,000 160,000

Broccoli 0.000661 0.000124 0.000010 81,000 1,000,000

Cauliflower 0.000635 0.000119 0.000009 84,000 1,100,000

Cabbage 0.000639 0.000119 0.000009 84,000 1,100,000

SEWER (single layer, no gloves)

Cucurbit

(Cucumber) 0.000229

0.0062 0.00023 3,000

0.000012 0.000002 870,000 4,400,000

Cucurbit

(Cantaloupe) 0.00027 0.000014 0.000003 730,000 3,700,000

Cucurbit

(Pumpkin) 0.000107 0.000005 0.000001 1,900,000 9,300,000

Cucurbit

(Squash) 0.000172 0.000009 0.000002 1,200,000 5,800,000

Cucurbit

(Watermelon) 0.000157 0.000008 0.000002 1,300,000 6,400,000

Pepper 0.00247 0.000125 0.000025 80,000 400,000

Tomato 0.00414 0.000209 0.000041 48,000 240,000

Broccoli 0.000661 0.000033 0.000007 300,000 1,500,000

Cauliflower 0.000635 0.000032 0.000006 310,000 1,600,000

Page 24 of 44
Table 6.1.2 Summary of Short- and Intermediate-Term Handler Exposures and Risks for Paclobutrazol Seed Treatment

Seed Type

Max Application 

Ratea

Unit Exposureb

(mg/lb ai)

Amount of Seed 

Treatedc

Absorbed Dose

(mg/kg/day)d MOEe

lb ai/lb seed Dermal Inhal. lb seed/day Dermal Inhal. Dermal Inhal.

Cabbage 0.000639 0.000032 0.000006 310,000 1,600,000

BAGGER (single layer, no gloves)

Cucurbit

(Cucumber) 0.000229

0.0091 0.00016 3,000

0.000017 0.000002 590,000 6,300,000

Cucurbit

(Cantaloupe) 0.00027 0.000020 0.000002 500,000 5,300,000

Cucurbit

(Pumpkin) 0.000107 0.000008 0.000001 1,300,000 13,000,000

Cucurbit

(Squash) 0.000172 0.000013 0.000001 790,000 8,400,000

Cucurbit

(Watermelon) 0.000157 0.000012 0.000001 860,000 9,200,000

Pepper 0.00247 0.000183 0.000017 55,000 580,000

Tomato 0.00414 0.000306 0.000029 33,000 350,000

Broccoli 0.000661 0.000049 0.000005 200,000 2,200,000

Cauliflower 0.000635 0.000047 0.000004 210,000 2,300,000

Cabbage 0.000639 0.000047 0.000004 210,000 2,200,000

MULTIPLE ACTIVITIES (combination of loader/applicator with gloves and no coveralls, sewer without gloves, stacker without gloves)

Cucurbit

(Cucumber) 0.000229

0.042 0.0016 3,000

0.000078 0.000016 130,000 630,000

Cucurbit

(Cantaloupe) 0.00027 0.000092 0.000019 110,000 530,000

Cucurbit

(Pumpkin) 0.000107 0.000037 0.000007 270,000 1,300,000

Cucurbit

(Squash) 0.000172 0.000059 0.000012 170,000 840,000

Cucurbit

(Watermelon) 0.000157 0.000054 0.000011 190,000 920,000

Pepper 0.00247 0.000843 0.000172 12,000 58,000

Tomato 0.00414 0.001414 0.000288 7,100 35,000

Broccoli 0.000661 0.000226 0.000046 44,000 220,000

Cauliflower 0.000635 0.000217 0.000044 46,000 230,000

Cabbage 0.000639 0.000218 0.000044 46,000 220,000

Page 25 of 44
a Application Rates based on existing labels for paclobutrazol.

b Unit Exposures from HED Exposure Science Advisory Council Policy 14.

c HED default for lb seed treated per day from HED Exposure Science Advisory Council Policy 15.

d Dermal Dose (mg/kg/day) = dermal unit exposure (mg/lb ai) x application rate (lb ai/lb seed) x amount treated (lb seed/day) x absorption factor (18.7%) / body weight (69 kg 

adult). Dermal MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Dermal Dose (mg/kg/day). Level of concern = 100.

e Inhalation Dose (mg/kg/day) = inhalation unit exposure (mg/lb ai) x application rate (lb ai/lb seed) x amount treated (lb seed/day) x absorption factor (100%) / body weight (69

kg adult). Inhalation MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Inhalation Dose (mg/kg/day). Level of concern = 100.

Table 6.2.3. Summary of Secondary Handler (Planter) Exposures and Risks for Paclobutrazol (Single Layer, Gloves during 

Loading Only)

Seed Type

Max

Application 

Rate a

(lb ai/lb 

seed)

Dermal Unit 

Exposureb

(mg/lb ai)

Inhalation Unit 

Exposureb

(mg/lb ai) 

Amount 

of Seed 

Planted 

Per 

Dayc

(lb 

seed/day)

Absorbed 

Dermal 

Dosed

(mg/kg/day)

Absorbed 

Inhalation 

Dosed

(mg/kg/day)

Dermal 

MOEe

Baseline 

Inhalation 

MOEe

Cucurbit Seed 

(Cucumber) 0.000229 0.25 0.0034 3,000 0.00046547 0.0000339 21,000 300,000

Cucurbit Seed 

(Cantaloupe) 0.00027 0.25 0.0034 3,000 0.00054880 0.0000399 18,000 250,000

Cucurbit Seed 

(Pumpkin) 0.000107 0.25 0.0034 3,000 0.00021749 0.0000158 46,000 630,000

Cucurbit Seed 

(Squash) 0.000172 0.25 0.0034 3,000 0.00034961 0.0000254 29,000 390,000

Cucurbit Seed 

(Watermelon) 0.000157 0.25 0.0034 3,000 0.00031912 0.0000232 31,000 430,000

Pepper 0.00247 0.25 0.0034 3,000 0.00502054 0.0003651 2,000 27,000

Page 26 of 44
Tomato 0.00414 0.25 0.0034 3,000 0.00841500 0.0006120 1,200 16,000

Broccoli 0.000661 0.25 0.0034 3,000 0.00134355 0.0000977 7,400 100,000

Cauliflower 0.000635 0.25 0.0034 3,000 0.00129071 0.0000939 7,700 110,000

Cabbage 0.000639 0.25 0.0034 3,000 0.001298837 0.0000945 7,700 110,000

a Application Rates based on existing labels for paclobutrazol.

b Unit Exposures from HED Exposure Science Advisory Council Policy 14: Standard Operating Procedures for Seed Treatment.

c HED default for lb seed planted per day from HED Exposure Science Advisory Council Interim Policy 15 and the BEAD memo “Acres Planted Per Day and Seeding Rates of 

Crops Grown in the United States” (J. Becker, March 2011).

d Daily Absorbed Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/lb seed) x amount treated (lb seed/day) x absorption factor (18.7% for dermal, 100% 

for inhalation) / body weight (69 kg adult). Level of concern = 100.

e MOE = NOAEL (dermal and inhalation = 10.0 mg/kg/day for short- and intermediate-term exposure) /Absorbed Dose (mg/kg/day). Level of concern = 100.

Page 27 of 44
6.2 Occupational Post-application Exposure/Risk Estimates

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production, such as scouting for pests 

or harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post-application inhalation exposure to individuals 

performing post-application activities in previously treated fields. These potential sources 

include volatilization of pesticides and resuspension of dusts and/or particulates that contain 

pesticides. The agency sought expert advice and input on issues related to volatilization of 

pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel 

(SAP) in December 2009, and received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The agency has 

evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent 

Volatilization Screening Analysis (http://www.regulations.gov/#!docketDetail;D=EPA-HQOPP-2014-0219). During Registration Review, the agency will utilize this analysis to determine 

if data (i.e., flux studies, route-specific inhalation toxicological studies) or further analysis is 

required for paclobutrazol.

In addition, the Agency is continuing to evaluate the available post-application inhalation 

exposure data generated by the Agricultural Reentry Task Force. Given these two efforts, the 

Agency will continue to identify the need for and, subsequently, the way to incorporate 

occupational post-application inhalation exposure into the agency's risk assessments.

Although a quantitative occupational post-application inhalation exposure assessment was not 

performed, an inhalation exposure assessment was performed for occupational/commercial 

handlers. Handler exposure resulting from application of pesticides outdoors is likely to result in 

higher exposure than post-application exposure. Therefore, it is expected that these handler 

inhalation exposure estimates would be protective of most occupational post-application 

inhalation exposure scenarios.

The Worker Protection Standard for Agricultural Pesticides contains requirements for protecting 

workers from inhalation exposures during and after greenhouse applications through the use of 

ventilation requirements.[40 CFR 170.110, (3) (Restrictions associated with pesticide 

applications)].

Page 28 of 44
A post-application inhalation exposure assessment is not required as exposure is expected to be 

negligible. Seed treatment assessments provide quantitative inhalation exposure assessments for 

seed treaters and secondary handlers (i.e., planters). It is expected that these exposure estimates 

would be protective of any potential low-level post-application inhalation exposure that could 

result from these types of applications.

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

Occupational Post-application Dermal Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

post-application risk assessments. Each assumption and factor is detailed below on an individual 

basis.

Exposure Duration: HED classifies exposures from 1 to 30 days as short-term and exposures 30 

days to six months as intermediate-term. For paclobutrazol, based on the currently registered 

use, short- and intermediate-term exposures are expected. The short- and intermediate-term 

PODs are the same; therefore, short-term risk estimates are protective of longer-term exposures.

Transfer Coefficients: It is the policy of HED to use the best available data to assess postapplication exposure. Sources of generic post-application data, used as surrogate data in the 

absence of chemical-specific data, are derived from ARTF exposure monitoring studies, and, as 

proprietary data, are subject to the data protection provisions of FIFRA. The standard values 

recommended for use in predicting post-application exposure that are used in this assessment, 

known as “transfer coefficients”, are presented in the ExpoSAC Policy 38

” which, along with 

additional information about the ARTF data, can be found at the Agency website9. Table 6.2.2.1 

provides a summary of the anticipated post-application activities and associated transfer 

coefficients for the proposed crops/use sites.

Table 6.2.2.2. provides a summary of the transfer coefficients and activities associated with turf

and ornamentals in greenhouse and nurseries.

Table 6.2.2.1. Post-application Activities and Dermal Transfer Coefficients.

Crops Crop Height Foliage

Density

Transfer Coefficients 

(cm2/hr) Activities

Turf Low Full 2,500 Golf course maintenance, 

greens only

Turf Low Full 3,700 Maintenance

Ornamentals in 

Nurseries

Low Min 230 Grafting, Propagating, 

Transplanting

Low Full 230

Hand harvesting, Hand 

pruning, Scouting, Hand 

Weeding , Transplanting, 

Pinching, Tying/Training

8 Available: http://www.epa.gov/pesticides/science/exposac_policy3.pdf 9 Available: http://www.epa.gov/pesticides/science/post-app-exposure-data.html

Page 29 of 44

 
Table 6.2.2.1. Post-application Activities and Dermal Transfer Coefficients.

Crops Crop Height Foliage

Density

Transfer Coefficients 

(cm2/hr) Activities

High Min 230 Hand harvesting, Hand 

pruning, Transplanting

High Full 230

Hand harvesting, Hand 

pruning, Scouting, 

Container Moving, Hand 

weeding, Transplanting, 

Pinching

Low/High Full 1900 Hand set irrigation

Ornamentals in 

Greenhouses

Low Min

230

Grafting, Propagating, 

Transplanting

Low Full Hand harvesting, Hand 

pruning, Scouting, Hand 

weeding, Transplanting, 

Pinching, Tying/Training

High Min Hand harvesting, Hand 

pruning, Transplanting

High Full Hand harvesting, Hand 

pruning, Scouting, 

Container Moving, Hand 

weeding, Transplanting, 

Pinching

Application Rate: 

• Application Rate = 0.75 lb ai/A for turf 

• Application Rate = 0.13 lb ai/A for poinsettas

• Application Rate = 0.59 lb ai/A for chrysanthemums

Exposure Time: The average occupational workday is assumed to be 8 hours. 

In addition, the following assumptions and data were used in the paclobutrazol dermal postapplication assessment:

• Chemical-specific TTR data submitted in support of the paclobutrazol turf uses (MRID 

45214201). In the study, Turf Enhancer 2SC Plant Growth Regulator was applied to turf

at three test sites located in Madera, California, North Rose, New York, and Creedmoor, 

North Carolina. Each test site consisted of one untreated control plot (containing 50 

subplots) and one treated plot (containing 60 subplots). The first application was made at 

an application rate of 0.5 lb ai/A and the remaining applications were made at 0.75 lb 

ai/A. The turf application was made in California with a 60-gallon tank pressure sprayer. 

The turf application was made in New York with a 30-gallon cone shaped tank with a 

commercial tractor-mounted boom. The turf application was made in North Carolina 

with a commercial tractor-mounted sprayer equipped with a 5-foot boom. The Modified 

California Roller technique was used to evaluate the amount of transferable residues from 

Page 30 of 44
turf grass. For the California test site, the average paclobutrazol TTR value was 0.0821 

ug/cm2 following the third application. The residues dropped below the level of detection 

fourteen days after treatment, third application. For the New York test site, the average 

paclobutrazol TTR value was 0.0212 ug/cm2 following the third application. The 

residues dropped below the level of detection eight days after treatment three. For the 

North Carolina test site, the average paclobutrazol TTR value was 0.156 ug/cm2

following the fourth application. The residues dropped below the level of detection 

twenty-two days after treatment four. The TTR level used in this assessment (0.080 

ug/cm2) is based on the California data as it resulted in the highest predicted Day 0 

residues. Appendix B has more specific information regarding the TTR study. 

• Chemical-specific dislodgeable foliar residue (DFR) data submitted in support of the 

paclobutrazol poinsettia uses (MRID 45336601). In the study, BONZI Ornamental 

Growth Regulator was applied to chrysanthemums in a greenhouse. A single application 

was made to chrysanthemums in separate greenhouses by a hand-held boom powered by 

CO2. Leaf discs were collected using a Birkestrand 1.784 cm (0.702 inch) diameter leaf 

punch. The average total paclobutrazol DFR on chrysanthemums was 0.755 ug/cm2

twenty-four hours after the application. By day thirty-five, the average total 

paclobutrazol residues declined to 0.202 ug/cm2. The DFR values did not drop below the 

limit of quantitation (0.005 ug/cm2

) during the timeframe of the study. Appendix B has 

more specific information regarding this DFR study.

• Chemical-specific DFR data submitted in support of the chrysanthemum uses (MRID 

45310801). In this study, Bonzi Ornamental Growth Regulator was applied to poinsettias 

in shadehouses. Three applications were made to poinsettias at 7-day intervals in a 

commercial shadehouse in Stuart, Florida. The three applications were made at a rate of 

0.13 lb ai/Acre with a backpack sprayer with a hand-held boom powered by CO2. The 

field trial consisted of one treated plot and one untreated plot. Leaf discs were collected 

using a Birkestrand 2.54 cm (1 inch) diameter leaf punch. The average total 

paclobutrazol DFR value on poinsettias was 0.439 ug/cm2 after the third (final) 

application. By thirty-five days after the last application, the total paclobutrazol residue 

declined to <LOQ (0.005 ug/cm2). Appendix B has more specific information regarding 

this DFR study.

Daily dermal exposures were calculated on each post-application day after application using the 

following equation:

DE(t) (mg/day) = (TR(t) (μg/cm2) x TC (cm2/hr) x Hr/Day)/1000 (μg/mg)

Where:

DE(t) = Daily exposure or amount deposited on the surface of the skin at 

time (t) attributable for activity in a previously treated area, also referred 

to as potential dose (mg ai/day);

TR(t) = Transferable residues that can be dislodgeable foliar residue at 

time “t” (μg/cm2);

TC = Transfer Coefficient (cm2/hour); and

Hr/day = Exposure duration meant to represent a typical workday (hours).

Page 31 of 44
Occupational Post-application Non-Cancer Dermal Exposure and Risk Estimate Equations

The algorithms used to estimate non-cancer exposure and dose for occupational post-application 

workers can be found in Appendix A.

Occupational Post-application Non-Cancer Dermal Risk Estimates

A summary of the estimated occupational post-application risks are provided in Table 6.2.2.2. 

The short- and intermediate-term risk estimates for golf course maintenance activities are greater 

than HED’s LOC (MOEs ≥ 100) using predicted Day 0 residue values from the TTR study. The 

short- and intermediate-term risk estimates for ornamentals in greenhouses and nurseries are 

greater than HED’s LOC (MOEs ≥ 100) using predicted Day 0 residue values from either the 

Chrysanthemum or Poinsettia DFR data for all activities. 

Table 6.2.2.2. Occupational Post-application Non-Cancer Exposure and Risk Estimates for Paclobutrazol.

Crop/Site Activities Transfer Coefficient 

(cm2/hr) DFR/TTR1 Dermal Dose (mg/kg/day)2 MOE3

Short- and Intermediate-term

Turf4

Golf course 

maintenance, greens 

only

2,500 0.080 0.004 2,300

Turf4 Maintenance 3,700 0.080 0.006 1,600

Ornamentals in 

Nurseries using 

Chrysanthemum DFR 

Data5

Hand harvesting, 

Hand pruning, 

Scouting, Container 

moving, Hand 

Weeding, 

Transplanting, 

Grafting, 

Propagating, 

Pinching, 

Tying/Training

230 0.73 0.004 2,800

Hand set irrigation 1,900 0.73 0.030 330

Ornamentals in 

Greenhouse using 

Chrysanthemum DFR 

Data5

Hand harvesting, 

Hand pruning, 

Scouting, Container 

moving, Hand

Weeding, 

Transplanting, 

Grafting, 

Propagating, 

Pinching, 

Tying/Training

230 0.73 0.004 2,800

Ornamentals in 

Nurseries using 

Poinsettia DFR Data6

Hand harvesting, 

Hand pruning, 

Scouting, Container 

moving, Hand 

Weeding, 

Transplanting, 

Grafting, 

Propagating, 

Pinching, 

Tying/Training

230 2.20 0.011 910

Page 32 of 44
Table 6.2.2.2. Occupational Post-application Non-Cancer Exposure and Risk Estimates for Paclobutrazol.

Crop/Site Activities Transfer Coefficient 

(cm2/hr) DFR/TTR1 Dermal Dose (mg/kg/day)2 MOE3

Short- and Intermediate-term

Hand set irrigation 1,900 2.20 0.091 110

Ornamentals in

Greenhouse using 

Poinsettia DFR Data6

Hand harvesting, 

Hand pruning, 

Scouting, Container 

moving, Hand 

Weeding, 

Transplanting, 

Grafting, 

Propagating, 

Pinching, 

Tying/Training

230 2.20 0.011 910

1 (See MRID 45214201, MRID 45310801, MRID 45336601).

2 Daily Dermal Dose = [DFR or TTR (μg/cm2

) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day × dermal absorption (18.7 %)] ÷ BW (69 kg).

3 MOE = POD (mg/kg/day) / Daily Dermal Dose. Daily Dermal Dose = [DFR/TTR (μg/cm2

) × TC × 0.001 mg/μg × 8 hrs/day × dermal 

absorption factor (18.7 %)] ÷ BW (69 kg).

4 TTR data represents CA which was the test site with the highest residues (MRID 45214201).

5 Chrysanthemum DFR data represents use in a greenhouse in Oregon (MRID 45310801).

6 Poinsettia DFR data represents use in a shadehouse in Florida (MRID 45336601).

Restricted Entry Interval

Paclobutrazol is classified as Toxicity Category III via the dermal route and or skin irritation 

potential based on studies submitted in 2012. It is not a skin sensitizer. Short- and intermediateterm post-application risk estimates were not a concern on day 0 (12 hours following application) 

for all post-application activities. Under 40 CFR 156.208 (c) (2) (iii), ai’s classified as Acute 

Toxicity Category III chemicals require a 12-hr REI. The occupational post-application 

assessment, dermal risk estimates do not exceed HED’s level of concern (MOEs >100). Based

on the acute dermal toxicity, the 12-hour REI that appears on the current paclobutrazol labels is 

supported by the acute toxicity data.

Page 33 of 44
Appendix A. Summary of Occupational and Residential Non-cancer Algorithms

Residential Non-cancer Handler Algorithms

Handler dermal and/or inhalation exposures are estimated by multiplying the application 

method-specific unit exposure by an estimate of the amount of active ingredient handled in a 

day, using the following algorithm:

E = UE*AR *A

where:

E = exposure (mg/day);

UE = unit exposure (mg/lb ai);

AR = application rate (e.g., lb ai/ft2, lb ai/gal); and

A = area treated or amount handled (e.g., ft2/day, gal/day).

Dermal and/or inhalation doses are estimated using the following algorithm:

BW

E *AF D =

where:

D = dose rate (mg/kg-day);

AF = absorption factor (dermal and/or inhalation); and

BW = body weight (kg).

Dermal and inhalation risks were combined in this assessment, since the toxicological effects for 

these exposure routes were similar. Dermal and inhalation risks were combined using the 

following formula:

Total MOE = Point of Departure (mg/kg/day) / Combined dermal + inhalation dose (mg/kg/day)

Residential Non-cancer Post-application Algorithms

Dermal exposure:

E = TTRt * CF1 * TC * ET

where:

E = exposure (mg/day); 

TTRt = turf transferable residue on day "t" (μg/cm2

);

CF1 = weight unit conversion factor (0.001 mg/μg);

TC = transfer coefficient (cm2/hr); and

Page 34 of 44
ET = exposure time (hr/day).

Assumptions:

• A TTR study was used to assess the liquid formulation scenarios (Turf Enhancer® 2SC 

Plant Growth Regulator Transferable Turf Residue Study – MRID No.: 45214201). Data 

were collected at three sites in the TTR study including New York, California, and North 

Carolina. Data from the California site was used in this assessment as it resulted in the 

highest predicted Day 0 residues (see Section 4.2.1 and Appendix A for more details).

• Transfer coefficients:

o Physical activities on turf: 180,000 cm2

/hr for adults and 49,000 cm2/hr for 

children 1 < 2 years old for liquids and 200,000 cm2/hr for adults and 54,000 

cm2/hr for children for granulars

o Mowing: 5,500 cm2/hr for adults and 4,500 cm2/hr for children 11 < 16 years old

o Golfing: 5,300 cm2

/hr for adults, 4,400 cm2/hr for children 11 < 16 years old, and 

2,900 cm2/hr for children 6 < 11 years old

• Exposure time (hr):

o Physical activities on turf: 1.5 hr for adults and children

o Mowing: 1 hr

o Golfing: 4 hr

Hand-to-Mouth: 

E = [HR * (FM * SAH) * (ET * N_Replen) * (1- (1- SE)

(Freq_Replen/N-Replen))]

where:

E = exposure (mg/day);

HR = hand residue loading (mg/cm2

);

FM = fraction hand surface area mouthed / event (fraction/event);

SAH = typical surface area of one hand (cm2

);

ET = exposure time (hr/day);

N_Replen = number of replenishment intervals per hour (intervals/hour);

SE = saliva extraction factor (i.e., mouthing removal efficiency); and

Freq_Replen = number of hand-to-mouth contacts events per hour (events/hour).

and

SA * 2

Faihands*DE HR

H

=

where:

HR = hand residue loading (mg/cm2);

Faihands = fraction ai on hands compared to total surface residue from dermal 

transfer coefficient study (unitless);

DE = dermal exposure (mg); and

SAH = typical surface area of one hand (cm2).

Page 35 of 44
Object-to-Mouth: 

E = [OR* CF1 * SAMO * (ET * N_Replen) * (1- (1- SEO)

(Freq_Replen/N_Replen))]

where:

E = exposure (mg/day);

OR = chemical residue loading on the object on day “t” (ug/cm2);

CF1 = weight unit conversion factor (0.001 mg/μg);

SAMO = area of the object surface that is mouthed (cm2/event);

ET = exposure time (hr/day);

N_Replen = number of replenishment intervals per hour (intervals/hour);

SE = saliva extraction factor (i.e., mouthing removal efficiency); and

Freq_Replen = number of object-to-mouth contact events per hour (events/hour).

and

OR = AR * FO * CF2 * CF3

where:

OR = chemical residue loading on the object (μg/cm2);

AR = application rate (lbs ai/ft2 or lb ai/acre);

FO = fraction of residue available on the object (unitless);

CF2 = weight unit conversion factor (4.54 x 108 μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3 ft2/cm2 or 2.47 x 10-8

acre/cm2).

Soil Ingestion: 

E = SRt * SIgR * CF1

where:

E = exposure (mg/day);

SRt = soil residue on day "t" (μg/g);

SIgR = ingestion rate of soil (mg/day); and

CF1 = weight unit conversion factor (1 x 10-6 g/μg).

and

SRt = AR * FS * (1-FD)

t * CF2 * CF3 * CF4

where:

SRt = soil residue on day "t" (μg/g);

AR = application rate (lbs ai/ft2 or lb ai/acre);

FS = fraction of ai available in uppermost cm of soil (fraction/cm);

FD = fraction of residue that dissipates daily (unitless);

t = post-application day on which exposure is being assessed;

Page 36 of 44
CF2 = weight unit conversion factor (4.54 x 108 μg/lb);

CF3 = area unit conversion factor (1.08 x 10-3 ft2/cm2 or 2.47 x 10-8 acre/cm2); and

CF4 = soil volume to weight unit conversion factor (0.67 cm3

/g soil).

Mowing:

E = TTRt * CF1 * TC * ET

where:

E = exposure (mg/day);

TTRt = turf transferable residue on day "t" (μg/cm2

);

CF1 = weight unit conversion factor (0.001 mg/μg);

TC = transfer coefficient (cm2

/hr); and

ET = exposure time (hr/day).

and

TTRt = AR * F * (1-FD)

t * CF2 * CF3

where:

TTRt = turf transferable residue on day "t" (μg/cm2);

AR = application rate (lbs ai/ft2 or lb ai/acre);

F = fraction of ai retained on turf (unitless);

FD = fraction of residue that dissipates daily (unitless);

t = post-application day on which exposure is being assessed;

CF2 = weight unit conversion factor (4.54 x 108 μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3 ft2

/cm2 or 2.47 x 10-8 acre/cm2).

Golfing:

E = TTRt * CF1 * TC * ET

where:

E = exposure (mg/day); 

TTRt = turf transferable residue on day "t" (μg/cm2

);

CF1 = weight unit conversion factor (0.001 mg/μg);

TC = transfer coefficient (cm2/hr); and

ET = exposure time (hr/day).

and

TTRt = AR * F * (1-FD)

t * CF2 * CF3

where:

TTRt = turf transferable residue on day "t" (μg/cm2);

AR = application rate (lbs ai/ft2 or lb ai/acre);

Page 37 of 44
F = fraction of ai retained on turf (unitless)’

FD = fraction of residue that dissipates daily (unitless);

t = post-application day on which exposure is being assessed;

CF2 = weight unit conversion factor (4.54 x 108 μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3 ft2/cm2 or 2.47 x 10-8 acre/cm2).

For each scenario, absorbed dose (normalized to body weight) was calculated as:

BW

E*AF D =

where:

D = dose (mg/kg-day);

E = exposure (mg/day); 

AF = absorption factor (dermal only; 24.5 %); and

BW = body weight (79.5 kg for adults; 56.8 kg for children 11 < 16 years old, 31.8 

kg for children 6 < 11 years old, 11.4 kg for children 1 < 2 years old).

Dermal and incidental oral risk estimates were calculated using the following formula:

MOE = Point of Departure (mg/kg/day) / Dermal or incidental oral dose (mg/kg/day)

where:

Dermal NOAEL = 10 mg/kg/day, and 

Incidental oral NOAEL =18.8 mg/kg/day 

Occupational Non-cancer Handler Algorithms

Potential daily exposures for occupational handlers are calculated using the following formulas:

E=UE * AR * A * 0.001 mg/ug

where:

E = exposure (mg ai/day),

UE = unit exposure (μg ai/lb ai),

AR = maximum application rate according to proposed label (lb ai A or lb ai/gal), and

A = area treated or amount handled (e.g., A/day, gal/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

Page 38 of 44
ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and inhalation dose received by occupational 

handlers are compared to the appropriate POD (i.e., NOAEL) to assess the risk to occupational 

handlers for each exposure route. All MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).

Occupational Non-cancer Post-application Algorithms

Potential daily exposures for occupational post-application workers are calculated using the 

following formulas:

DFRt=AR * F* (1-D)t

* �4.54E8 ug

lb� * �2.47E-8

A

cm2�

where:

DFRt = dislodgeable foliage residue on day "t" (μg/cm2

),

AR = application rate (lb ai/acre),

F = fraction of ai retained on foliage or 25% (unitless),

D = fraction of residue that dissipates daily or 10% (unitless), and

t = number of days after application day (days).

E=TC * DFR t* ET * 0.001 mg

ug

where:

E = exposure (mg ai/day),

TC = transfer coefficient (cm2/hr),

DFRt = dislodgeable foliar residue on day “t” (μg/cm2

), and

ET = exposure time (hours/day).

Page 39 of 44
The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each scenario are calculated using a Margin 

of Exposure (MOE), which is a ratio of the toxicological endpoint to the daily dose of concern. 

The daily dermal dose received by occupational post-application workers is compared to the 

appropriate POD (i.e., NOAEL) to assess the risk to occupational post-application workers. All 

MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).

Page 40 of 44
Appendix B. Paclobutrazol DFR and TTR Study Results

Summary of the TTR Study: Determination of Transferable Residues of Paclobutrazol 

Turf Treated with Turf Enhancer 2SC Plant Growth Regulator (MRID 45214201)

The study was designed to determine the total transferable residues (TTR) of paclobutrazol 

dislodged from turf treated with Turf Enhancer 2SC Plant Growth Regulator, a liquid soluble 

concentrate formulation containing 22.3% paclobutrazol as the active ingredient. The test site 

consisted of three fields located in Madera, California, North Rose, New York, and Creedmoor, 

North Carolina. Each test site consisted of one untreated control plot (containing 50 subplots) 

and one treated plot (containing 60 subplots). The first application was made at an application 

rate of 0.5 lb ai/A and the remaining applications were made at 0.75 lb ai/A. Applications were 

made in California (60-gallon tank pressure sprayer was used) and New York (30-gallon cone 

shaped tank was used) with a commercial tractor-mounted boom and in North Carolina with a 

commercial tractor-mounted sprayer equipped with a 5-foot boom. The Modified California 

Roller technique was used to evaluate the amount of transferable residues from turf grass. 

First-order dissipation kinetics were assumed to generate dissipation curves for paclobutrazol at 

all three test sites. The individual residue data was collected after the last application through the 

first day when all triplicate TTR levels were less than the level of quantitation (LOQ). For 

values that were less than the LOQ, a value was used that is one-half of the LOQ. A linear 

regression analysis was conducted using the natural logarithm of the individual TTR values from 

cloth dosimeters. 

For the California test site, the average paclobutrazol TTR value was 0.0821 ug/cm2 following 

the third application. The residues dropped below the level of detection fourteen days after 

treatment, third application. For the New York test site, the average paclobutrazol TTR value 

was 0.0212 ug/cm2 following the third application. The residues dropped below the level of 

detection eight days after treatment three. For the North Carolina test site, the average 

paclobutrazol TTR value was 0.156 ug/cm2 following the fourth application. The residues 

dropped below the level of detection twenty-two days after treatment four. 

The overall average low and high level field fortification recoveries for California were >90%. 

The overall average low and high level field fortification recoveries for New York and North 

Carolina were both <90%. The raw field residue samples were corrected using the 

corresponding average low or high fortification level recovery for each test site when the 

recoveries were <90%. For New York, the field residue samples that had the average low level 

field fortification were corrected for an 83.7% low level average recovery. All of the field 

samples from the North Carolina test site were corrected for either the average low level 

recovery of 81.5% or the average high level recovery of 83.5%. 

Based on the results, the half-life was determined to be 1.77 days (R2

=0.916) for California, 1.50 

days (R2

=0.983) for New York and 2.56 days (R2=0.815) for North Carolina.

The results of the study are acceptable for risk assessment purposes.

Page 41 of 44
Table B1. Summary of TTR Values and Regression Analysis Results for Turf Enhancer 2SC Plant Growth 

Regulator Transferable Turf Residue Study (MRID# 45214201).

Input/Parameter New York California North Carolina

Application Rate (lb ai/A)

0.51 

(1st application)

0.76 

(2nd application)

0.77 

(3rd application)

0.51 

(1st application)

0.76 

(2nd application)

0.77 

(3rd application)

0.51 

(1st application) 

0.75 

(2nd application)

0.76 

(3rd application)

0.75 

(4th application) 

Spray Volume (GPA) †

44.0 

(1st application)

44.4 

(2nd application)

44.9 

(3rd application)

44.4 

(all applications)

44.0 

(1st, 2nd, & 3rd

application)

43.6 (4th application)

Measured Average Day 0 

Residue (μg/cm2

)

0.212 

(1st application)

0.0821 

(1st application)

0.0373 

(1st application)

Predicted Day 0 Residue 

(μg/cm2) ‡ 0.018 0.077 0.050

Slope -0.4616 -0.39084 -0.2703

Half-life (days) 1.50 1.77 2.56

R2 0.983 0.916 0.815

Page 42 of 44
Summary of the DFR Study for Treated Chrysanthemums with Bonzi Ornamental Growth 

Regulator (MRID# 45310801)

The study review was designed to determine the dissipation of dislodgeable foliar residues 

(DFR) of paclobutrazol from chrysanthemums treated with BONZI Ornamental Growth 

Regulator, a liquid formulation containing 0.4% paclobutrazol as the active ingredient (ai). The 

test site consisted of commercial greenhouses located in Aurora, Oregon. The field trial 

consisted of one treated plot and one untreated plot that were located in separate greenhouses. A 

single application was made to chrysanthemums by a hand-held boom powered by CO2. The 

application was made at an application rate of 0.56 lb ai/A. Leaf discs were collected using a 

Birkestrand 1.784 cm (0.702 inch) diameter leaf punch.

The DFR samples were collected prior to and immediately after the application, and on days 1, 2, 

4, 7, 10, 14, 21, 28, and 35 after the application. The average total paclobutrazol DFR on 

chrysanthemums was 0.755 ug/cm2 twenty-four hours after the application. By day thirty-five, 

the average total paclobutrazol residues declined to 0.202 ug/cm2. The DFR values did not drop 

below the limit of quantitation (0.005 ug/cm2

) during the timeframe of the study.

The DFR values were not corrected because the average low level field fortification recovery 

was >90%. The midpoint was used between the two fortification concentrations (1.25 ug/cm2) as 

the break point and all of the DFR values were below the midpoint. 

Based on the results, the half-life was determined to be 22.7 days (R2=0.774).

The study was found to be acceptable for use in exposure and risk assessments. 

Table B2. Summary of DFR Values and Regression Analysis Results for Treated Chrysanthemums with Bonzi 

(MRID# 45310801).

Input/Parameter Oregon

Application Rate (lb ai/A) 0.56 lb ai/A bench space

Spray Volume (GPA) † 2.87 qt/100 sq ft of bench space (1st application)

Measured Average Day 0 Residue (μg/cm2)

0.467 (1st application)

0.755(2nd application)

0.623(3rd application)

Predicted Day 0 Residue (μg/cm2) ‡ 0.684

Slope -0.03053

Half-life (days) 22.7

R2 0.774

Page 43 of 44
Summary of the DFR Study for Treated Poinsettas with Bonzi Ornamental Growth 

Regulator (MRID# 45336601)

The study was designed to determine the dissipation of dislodgeable foliar residues of 

paclobutrazol applied to poinsettias with Bonzi Ornamental Growth Regulator, a liquid 

formulation containing 0.4 % paclobutrazol as the active ingredient (ai). Three applications were 

made to poinsettias at 7-day intervals in a commercial shadehouse in Stuart, Florida. The three 

applications were made at a rate of 0.13 lb ai/Acre with a backpack sprayer with a hand-held 

boom powered by CO2. The field trial consisted of one treated plot and one untreated plot. Leaf 

discs were collected using a Birkestrand 2.54 cm (1 inch) diameter leaf punch.

The DFR samples were collected prior to and following each application, and on days 1, 2, 4, 7, 

10, 14, 21, 28, and 35 following the last application. The average total paclobutrazol DFR value 

on poinsettias was 0.439 ug/cm2 after the third (final) application. By thirty-five days after the 

last application, the total paclobutrazol residue declined to <LOQ (0.005 ug/cm2).

The DFR values were corrected using the average percent recovery of the field fortification 

samples (88%). The midpoint between the two fortification concentrations (1.25 ug/cm2) was 

used as the break point. 

The DFR residue values were not corrected that were below the LOQ (0.005 ug/cm2). For 

residue values that were less than the level of quantification (LOQ) (0.005 ug/cm2

), 1⁄2 LOQ was 

used in the calculations. 

Based on the results, the half-life was determined to be 4.55 days (R2=0.911).

The study was found to be acceptable for use in exposure and risk assessments. 

TableB3. Summary of DFR Values and Regression Analysis Results for Treated Poinsettias with Bonzi (MRID# 

45336601).

Input/Parameter Florida

Application Rate (lb ai/A) 0.13 (all applications)

Spray Volume (GPA) †

2.9 qt/100 sq ft of bench space (1st application)

3.0 qt/100 sq ft of bench space (2nd application)

3.0 qt/100 sq ft of bench space (3rd application)

Measured Average Day 0 Residue (μg/cm2)

0.292 (1st application)

0.326(2nd application) 

0.439 (3rd application)

Predicted Day 0 Residue (μg/cm2) ‡ 0.471

Slope -0.1522

Half-life (days) 4.55

R2 0.914

Page 44 of 44