UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

DATE: September 18,2013 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Paclobutrazol: Preliminary Occupational and Residential Exposure/Risk 

Assessment for Registration Review 

PC Code: 125601 

Decision No.: &./SS0"1 

Petition No.: 

DP Barcode: D399496 

Registration No.: 

Regulatory Action: Registration Review 

Risk Assessment Type: Single Case No.: 7002 

Chemical/ Aggregate 

TXRNo.: 

MRIDNo.: 

CAS No.: 76738.:.62-0 

40 CFR: 

FROM: Monica Hawkins, Ph.D., M.P.H., Environmental Health Scientist IV1 TC ~ K:-AllJ 

Risk Assessment Branch 6 Jl ~ Health Effects Division (7509P) 

THROUGH: Felecia Fort, Chief ~ 0 Risk Assessment Branch 6 fA-

~C:: A . ~ 

Health Effects Division (7509P) 

and 

Charles Smith, Chief C 

Risk Assessment Branch I 

Health Effects Division (7509P) 

TO: Khue Nguyen/Laura Parsons 

Risk Management and Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

Page 1 of39 
INTRODUCTION 

This memorandum contains HED's (Health Effects Division) occupational and residential 

exposure and risk assessment required during registration review. As part of Registration 

Review, the Pesticide Re-evaluation Division (PRD) of OPP requested that HED conduct an 

occupational exposure/risk assessment for paclobutrazol for application as a foliar spray to turf 

(including parks, athletic fields, residential lawns, and golf courses), for application as a foliar 

spray to ornamental plants in nurseries and greenhouses, use as a tree injection, use as a soil 

injection, use as a bulb soak treatment, use as a pre-plant plug/liner soak, and for use as a seed 

treatment (on cucurbit, pepper, and tomato seeds). As part of Registration Review, the 

paclobutrazol hazard assessment was revisited by HED. Based on the occupational 

exposure/risk assessment, HED has determined that there are potential occupational dermal risk 

estimates for mixer/loader/applicators that use handheld equipment even with the use of personal 

protective equipment (PPE). There are also potential risk estimates of concern for workers 

entering nurseries to perform handset irrigation activities. The dermal plus inhalation risk 

estimates of concern for residential handlers is a concern for homeowners that are 

mixing/loading/applying paclobutrazol with a belly grinder. There are also potential residential 

dermal risk estimates for adults and children playing on treated turf for both liquid and granular 

formulations. 

Page 2 of39 
Page 3 of 39

Table of Contents

1.0 EXECUTIVE SUMMARY ................................................................................................. 4

2.0 HAZARD PROFILE............................................................................................................ 6

3.0 USE PROFILE..................................................................................................................... 9

4.0 OCCUPATIONAL EXPOSURE/RISK CHARACTERIZATION ................................... 10

4.1 Short- and Intermediate- Term Handler Exposure and Risk.......................................... 10

4.2 Occupational Post-application Exposure and Risk ........................................................ 21

5.0 RESIDENTIAL (NON-OCCUPATIONAL) EXPOSURE.................................................... 24

5.1 Residential (Non-Occupational) Handler Exposure and Risk............................................. 25

5.2 Residential Post-Application Exposure and Risk............................................................... 27

5.3 Spray Drift .......................................................................................................................... 33
Page 4 of 39

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, residential lawns, and golf courses), a foliar spray for 

ornamentals in greenhouses and nurseries, as a bulb soak treatment, as a tree injection treatment, 

as a soil injection, as a pre-plant plug/liners treatment, and as a seed treatment for cucurbit, 

pepper, and tomato seeds. 

Hazard Profile

Paclobutrazol is classified as Toxicity Category III for the acute oral route, Toxicity Category II 

for the acute dermal, and Toxicity Category III for the acute eye and skin irritation route. 

Quantification of short-term (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 Affect Level (LOAEL) from this study was 40 mg/kg/day based on renal 

dilation, hydroureter, and minor skeletal defects or variations. 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 24.5% after 24 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). Quantification of an incidental oral risk 

was performed using a 90-day oral toxicity study. The LOAEL from this study was 93 

mg/kg/day based on elevated liver weights and changes in clinical chemistry parameters 

associated with the liver. The NOAEL from this study was 18.8 mg/kg/day. Since the 

toxicological effects from the oral route of exposure are different than those from the dermal and 

inhalation routes of exposure, these routes should not be combined. A target MOE of 1000 is 

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

intraspecies variability, and a 10X database uncertainty factor for lack of an acute and 

subchronic nuerotoxicity). 

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). 
Page 5 of 39

Occupational Handler

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 all 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 most occupational handler scenarios do not exceed HED’s level of concern (MOEs ≥1000) at 

some level of PPE. However, there are some handheld equipment scenarios that exceed HED’s 

level of concern (MOEs < 1000) even with the use of PPE.

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 do not exceed HED’s level of concern (MOEs ≥ 1000) at some level of PPE.

Occupational Post-application

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

dermal route. The results indicate that occupational post-application risks, as calculated per 

HED default values, do not exceed HED’s level of concern (an MOE ≥1000) on day zero after 

application for all post-application tasks that were assessed except for hand set irrigation in 

nurseries.

The restricted entry interval (REI) listed on the existing paclobutrazol labels are based on the 

acute toxicity of the technical material. Paclobutrazol is classified as Toxicity Category III for 

the acute oral route, Toxicity Category II for the acute dermal toxicity route, and Toxicity 

Category III for eye and skin irritation. It is not a skin sensitizer. In accordance with the Worker 

Protection Standard (WPS), acute Toxicity Category III and II chemicals require a 12- or 24-

hour REI, respectively. Based on the acute dermal toxicity, the 12-hour REI that appears on the 

current paclobutrazol labels may not be adequate and should be revisited. Special consideration 

should also be given to use of hand set irrigation in nurseries.

Residential Handler

Although, paclobutrazol products do not appear to be specifically marketed towards residential 

handler use (i.e., homeowners); a residential handler assessment was performed to be protective 

of any such use. HED assumes that only short-term exposures are applicable to residential risk 

assessments; therefore, intermediate-term and chronic exposures were not assessed for 

residential handler risk assessments. The residential handler assessment was completed 

assuming the maximum label application rate allowed for residential turfgrass. The combined 

residential handler dermal plus inhalation MOEs do not exceed HED’s level of concern for all 
Page 6 of 39

scenarios (i.e., MOEs ≥ 1000) except for mixing/loading/applying with a belly grinder (MOE =

790).

Residential Post-application

HED determined that there is a potential for exposure from entering paclobutrazol-treated 

residential areas, such as lawns, sports fields, and golf courses that could lead to postapplication exposures to adults and children. A chemical-specific turf transferable residue 

(TTR) study was available and was used to estimate transferable residues from turf treated with 

liquid formulations. 

Dermal post-application risks were assessed for adults and children 1 < 2 years old while oral 

post-application risks were assessed for children 1 < 2 years old. All adult and children mowing 

and golfing dermal risk estimates for both liquid and granular formulations do not exceed HED’s 

level of concern (MOEs ≥ 1000). All adult and children playing on treated turf dermal risk 

estimates for both liquid and granular formulations exceed HED’s level of concern (MOEs < 

1000). All children 1 < 2 years old oral non-dietary ingestion risk estimates for both liquid and 

granular formulations do not exceed HED’s level of concern (MOEs ≥ 1000).

Review of Human Research

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

were intentionally exposed to a pesticide or other chemical to determine their dermal and 

inhalation exposure. These data, which include studies from the Pesticide Handlers Exposure 

Database Version 1.1 (PHED 1.1); the Outdoor Residential Exposure (ORETF) Database; the 

Agricultural Handlers Exposure Task Force (AHETF) database; and the Agricultural Reentry 

Task Force (ARTF) database and a number of studies used in the 2012 Standard Operating 

Procedures for Residential Pesticide Assessment: Lawns/Turf are subject to ethics review 

pursuant to 40 CFR Part 26, have received that review, and are compliant with applicable ethics 

requirements. For certain studies that 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 

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

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

2.0 HAZARD PROFILE 

Paclobutrazol is classified as Toxicity Category III for the acute oral route, Toxicity Category II 

for acute dermal, and Toxicity Category III for acute eye and skin irritation. It is not a dermal 

sensitizer. Table 1 presents a summary of the acute toxicity information for paclobutrazol.
Page 7 of 39

Table 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)

NZW Rabbit

00117478 (1982) LD50 = 835 mg/kg (M)

937 mg/kg (F) III

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) II

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 sensitizer

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

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

study with a NOAEL of 10 mg/kg/day based on renal dilation, hydroureter and minor skeletal 

defects or variations (LOAEL = 40 mg/kg/day). Since an oral dose was selected, a dermal 

absorption factor of 24.5% should be used in estimating dermal risks (see Section 3.2.1). A 

Margin of Exposure (MOE) of 1000 is required which includes interspecies extrapolation (10X), 

intraspecies variability (10X), and the database uncertainty factor for lack of a neurotoxicity 

battery.

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

rat study with a NOAEL of 10 mg/kg/day based on renal dilation, hydroureter and minor skeletal 

defects or variations (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 1000 is required which 

includes to account for interspecies extrapolation (10X), intraspecies variability (10X), and the 

database uncertainty factor for lack of a neurotoxicity battery.
Page 8 of 39

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

a 90-day oral rat study with a NOAEL of 18.8 mg/kg/day based on elevated liver weights, and 

changes in clinical chemistry parameters associated with the liver (LOAEL = 93 mg/kg/day). A 

MOE of 1000 is required which includes interspecies extrapolation (10X), intraspecies 

variability (10X), and the database uncertainty factor for lack of a neurotoxicity battery.

Exposures from the short-term and intermediate-term dermal and inhalation routes were 

combined because the points of departure for these routes are based on the same toxicological 

effects. Exposures from the short-term and intermediate-term oral route were not combined with 

the dermal and inhalation routes of exposure because the points of departure for these routes are

not based on the same toxicological effects. 

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. 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, a 10x database 

uncertainty factor (UFDB) has also been applied due to lack of acute and subchronic

neurotoxicity studies. These studies are required for paclobutrazol because paclobutrazol is a 

member of the triazole chemical class which in general appear to be neurotoxic. There is not 

sufficient data that evaluated the neurotoxic potential of paclobutrazol. As a result, the total 

uncertainty factor that has been applied to occupational and residential risk assessments is 1000

for short- and intermediate-term dermal, inhalation and incidental oral exposures. 

Table 2 presents the selected points of departure for Paclobutrazol.
Page 9 of 39

Table 2: Summary of Revised Toxicological Points of Departure and Endpoints for Paclobutrazol from 

Supplemental Data Provided By the Registrant (2007)1

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern for 

Risk Assessment Study and Toxicological Effects

Acute Dietary

No endpoints identified from the available developments toxicity studies (rat and rabbit) 

appropriate for an acute dietary assessment for paclobutrazol.

Incidental Oral 

Short-Term (1-30 

days) NOAEL = 

18.8 mg/kg/day

UFA=10x

UFH=10x

UFDB =10x

Residential LOC for 

MOE = 1000 

Occupational = NA

90-Day Oral Toxicity Study in 

Rats

MRID 00132689

LOAEL = 93 mg/kg/day, based 

on elevated liver weights, and 

changes in clinical chemistry 

parameters associated with the 

liver

Incidental Oral 

Intermediate-Term 

(1-6 months)

Dermal

Short-Term (1-30 

days)

Oral NOAEL = 

10 

mg/kg/day

(Dermal 

Absorption rate 

= 24.5%)

UFA=10x

UFH=10x

UFDB =10x

Residential/ 

Occupational LOC 

for MOE = 1000

Developmental (Rat) Toxicity 

Study 

MRID 00143158 

LOAEL = 40 mg/kg/day, based 

on renal dilation, hydroureter 

and minor skeletal defects or 

variations

Dermal 

Intermediate-Term 

(1-6 months)

Inhalation ShortTerm (1-30 days) Oral NOAEL = 

10 mg/kg/day) UFA=10x

UFH=10x

UFDB =10x

Residential/ 

Occupational LOC 

for MOE = 1000

Developmental (Rat) Toxicity 

Study 

MRID 00143158 

LOAEL for this study is 40 

mg/kg/day, based on renal 

dilation, hydroureter and minor 

skeletal defects or variations

Inhalation 

Intermediate-term 

(1-6 months)

Cancer (oral, 

dermal, inhalation) Not required for non-food use pesticides.

Explanation of Abbreviations: Point of Departure (PoD) = A data point or an estimated point that is derived from 

observed dose-response data and used to mark the beginning of extrapolation to determine risk associated with 

lower environmentally relevant human exposures. 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). UFDB = database 

uncertainty, lack of neurotoxicity (acute and subchronic)studies. MOE = margin of exposure. LOC = level of 

concern. 

3.0 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, and tomato seeds). Specific details related to the existing use

pattern are summarized in Table 3. 
Page 10 of 39

Table 3: 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

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

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

4.0 OCCUPATIONAL EXPOSURE/RISK CHARACTERIZATION

4.1 Short- and Intermediate-Term Handler Exposure and Risk

Short-/Intermediate-Term Handler Risk for Turf, Ornamental, and Tree Uses

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 11 of 39

Mixing/loading liquids for groundboom applications

Mixing/loading wettable powders for tree injections

Mixing/loading granules for open cab solid broadcast spreader applications

Mixing/loading liquid concentrations via dip

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

For pesticide handlers, HED presents estimates of dermal exposure for “baseline” (i.e., workers 

wearing a single layer of work clothing consisting of a long sleeved shirt, long pants, shoes plus 

socks and no protective gloves), as well as for “baseline” and the use of protective gloves or 

other PPE, as might be necessary. 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. 

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 the 

PHED 1.1, the AHETF database, the 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 Table” 

(http://www.epa.gov/opp00001/science/handler-exposure-table.pdf), which, along with 

additional information on HED policy on use of surrogate data, including descriptions of the 

various sources, can be found at http://www.epa.gov/pesticides/science/handler-exposuredata.html.

Typically, HED completes short- and intermediate-term assessments for occupational scenarios 

in all cases because these kinds of exposures are likely and acceptable use/usage data are not 

available to justify deleting intermediate-term scenarios. Based on use data and label 

instructions, HED believes that occupational exposures may occur over a single day or up to 

weeks at a time for many of the use-patterns and that intermittent exposure over several weeks 

may also occur. Some applicators may apply these products over a period of weeks, because 

they are commercial applicators who are completing multiple pesticide applications for multiple 

clients. Long-term exposures are not expected; therefore, a long-term assessment was not 

conducted. 

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 
Page 12 of 39

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;

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;

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.

Daily dermal or inhalation handler exposures are estimated for each applicable handler task with 

the application rate, the amount handled or area treated in a day, and the applicable dermal or 

inhalation unit exposure using the following formula:

Daily Exposure = Unit Exposure x Application Rate x Daily Area Treated

Where: 

Daily Exposure = Amount (mg/day) deposited on the surface of the skin that is available for 

dermal absorption or amount inhaled that is available for inhalation absorption;

Unit Exposure = Unit exposure value (mg/lb ai);

Application Rate = Normalized application rate based on a logical unit treatment, such as acres (A); 

and

Daily Area Treated = Normalized application area based on a logical unit treatment such as acres 

(A/day). 

The daily dermal or inhalation dose is calculated by normalizing the daily exposure by body 

weight and adjusting, if necessary, with an appropriate dermal or inhalation absorption factor 

using the following formula:

Average Daily Dose = Daily Exposure x Absorption Factor / Body Weight

Where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given scenario 

(mg/kg/day);

Daily Exposure = Amount (mg/day) deposited on the surface of the skin that is available for 

dermal absorption or amount inhaled that is available for inhalation absorption;
Page 13 of 39

Absorption Factor = A measure of the amount of chemical that crosses a biological boundary such as 

the skin or lungs (% of the total available absorbed); and

Body Weight = Body weight determined to represent the population of interest in a risk 

assessment (kg).

Margin of Exposure (MOE): The daily dermal dose and daily inhalation dose received by 

occupational handlers are compared to the appropriate point of departure (i.e., NOAEL) to assess 

the risk to occupational handlers for each exposure route. All MOE values are calculated 

separately for dermal and inhalation exposure levels using the following equation:

MOE = NOAEL (mg/kg/day) / Average Daily Dose (mg/kg/day)

Where:

MOE = Margin of exposure value used by HED to represent risk or how close a 

chemical exposure is to being a concern (unitless),

ADD = Average daily dose is the absorbed dose received from exposure to pesticide (mg/kg/day)

NOAEL = No Observable Adverse Effect Level (mg/kg/day)

Combined Risks: Dermal and inhalation risks for short- and intermediate-term exposures were 

combined in this assessment, since the toxicological effects for the dermal and inhalations routes 

were the same. Dermal and inhalation risks were combined using the following equation:

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

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

4. The short- and intermediate-term risk estimates for most occupational handler scenarios do 

not exceed HED’s level of concern (MOEs ≥1000) at some level of personal protective 

equipment (PPE). However, there are some handheld equipment scenarios that exceed HED’s 

level of concern (MOEs < 1000) even with the use of PPE.
Page 14 of 39

Table 4. Occupational Handler Exposures and Risks for Paclobutrazol Turf, Ornamental, and Tree Uses

Activity Use Site

PPE-G 

Dermal 

Unit 

Exposure 

(mg/lb ai)a

PPE-DL 

Dermal 

Unit 

Exposure 

(mg/lb ai)a

Baseline 

Inhalation 

Unit 

Exposure 

(mg/lb ai)a

Application 

Rate b

Area 

Treated 

Daily c

PPE-G PPE-G, DL Baseline Inhalation Total MOE 

(PPE-G + 

Baseline 

Inhalation)

Total MOE 

(PPE G-DL 

+ Baseline 

Inhalation)

Dermal 

Dose 

(mg/kg/day)d

MOEf

Dermal 

Dose 

(mg/kg/day)d

MOEf Dose 

(mg/kg/day)e MOEg

Mixing/Loading Liquids

Groundboom 

Applications on 

Ornamentals in 

Nurseries

0.0376 0.0291 0.000219

0.59 lb ai/A 40 A 0.0027 3,700 0.0021 4,800 0.000065 150,000 3,600 4,600

Groundboom 

Applications on Golf 

Courses

0.75 lb ai/A 40 A 0.0035 2,900 0.0027 3,700 0.000082 120,000 2,800 3,600

Tree Injection (8 

diameter Inch Trees)

0.0099 lb 

ai/tree 50 trees 0.000057 180,000 0.000044 230,000 0.0000014 7,400,000 170,000 220,000

Tree Injection (35 

diameter Inch Trees) 0.07 lb ai/tree 50 trees 0.0004 25,000 0.00031 32,000 0.0000096 1,000,000 24,000 31,000

Tree Soil Injection 0.352 lb 

ai/tree 50 trees 0.002 4,900 0.0016 6,400 0.000048 210,000 4,800 6,200

Dips for Plug/Liner 

Soaks

0.000051 lb 

ai/gal 100 gals 0.00000059 17,000,000 0.00000045 22,000,000 1.40E-08 720,000,000 17,000,000 21,000,000

0.000051 lb 

ai/gal 1000 gals 0.0000059 1,700,000 0.0000045 2,200,000 1.40E-07 72,000,000 1,700,000 2,100,000

Dips for Bulb Soaks 

(Freesia)

0.00255 lb 

ai/gal 100 gals 0.000029 340,000 0.000023 440,000 0.0000007 14,000,000 330,000 430,000

0.00255 lb 

ai/gal 1000 gals 0.00029 34,000 0.00023 44,000 0.000007 1,400,000 33,000 43,000

Mixing/Loading Wettable 

Powders

Tree Injection (6-16 

inches in diameter)

0.17 0.13 0.043

0.000059 lb 

ai/tree 50 trees 0.0000015 6,500,000 0.0000012 8,500,000 0.0000016 6,300,000 3,200,000 3,600,000

Tree Injection (>16 

inches in diameter)

0.00024 lb 

ai/tree 50 trees 0.0000062 1,600,000 0.0000048 2,100,000 0.0000065 1,600,000 790,000 890,000

Loading Granulars

Tractor Drawn 

Spreader 

Applications on Golf 

Courses

0.0069 0.0034 0.0017 0.5 lb ai/A 40 A 0.00042 24,000 0.00021 48,000 0.00043 24,000 12,000 16,000

Applying Liquid Sprays 

via Grounboom

Golf Courses

0.0161 0.0126 0.00034

0.75 lb ai/A 40 A 0.0015 6,800 0.0012 8,600 0.00013 78,000 6,200 7,800

Ornamentals in 

Nurseries 0.59 lb ai/A 40 A 0.0012 8,600 0.00091 11,000 0.0001 100,000 7,900 9,900
Page 15 of 39

Table 4. Occupational Handler Exposures and Risks for Paclobutrazol Turf, Ornamental, and Tree Uses

Activity Use Site

PPE-G 

Dermal 

Unit 

Exposure 

(mg/lb ai)a

PPE-DL 

Dermal 

Unit 

Exposure 

(mg/lb ai)a

Baseline 

Inhalation 

Unit 

Exposure 

(mg/lb ai)a

Application 

Rate b

Area 

Treated 

Daily c

PPE-G PPE-G, DL Baseline Inhalation Total MOE 

(PPE-G + 

Baseline 

Inhalation)

Total MOE 

(PPE G-DL 

+ Baseline 

Inhalation)

Dermal 

Dose 

(mg/kg/day)d

MOEf

Dermal 

Dose 

(mg/kg/day)d

MOEf Dose 

(mg/kg/day)e MOEg

Appyling Granulars via 

Tractor Drawn Spreader Golf Courses 0.0072 0.0042 0.0012 0.5 lb ai/A 40 A 0.00044 23,000 0.00026 39,000 0.0003 33,000 13,000 18,000

Mixing/Loading/Applying 

Liquids via Backpack 

Sprayer

Turf

8.26 4.12 0.00258

0.75 lb ai/A 5 A 0.095 110 0.047 210 0.00012 83,000 110 210

Golf Course 0.75 lb ai/A 5 A 0.095 110 0.047 210 0.00012 83,000 110 210

Drench Tree 

Treatments (8 inch 

Tree)

0.07 lb ai/tree 50 trees 0.089 110 0.044 230 0.00011 89,000 110 230

Drench Tree 

Treatments (35 inch 

Tree)

0.31 lb ai/tree 50 trees 0.39 26 0.2 51 0.0005 20,000 25 51

Foliar Sprays on 

Ornamentals in 

Nurseries and 

Greenhouses

11.2 6.23 0.14 0.59 lb ai/A 5 A 0.1 99 0.056 180 0.0052 1,900 94 160

Mixing/Loading/Applying 

Liquids via Manually 

Pressurized Handwand

Foliar Sprays on 

Ornamentals in 

Nurseries and 

Greenhouses

0.43 0.365 0.03

0.59 lb ai/A 5 A 0.0039 2,600 0.0033 3,000 0.0011 9,000 2,000 2,300

Drench Tree 

Treatments (8 inch 

Tree)

0.07 lb ai/tree 50 trees 0.0046 2,200 0.0039 2,600 0.0013 7,600 1,700 1,900

Drench Tree 

Treatments (35 inch 

Tree)

0.31 lb ai/tree 50 trees 0.02 490 0.017 580 0.0058 1,700 380 430

Mixing/Loading/Applying 

Liquids via Mechanically 

Pressurized Handwand

Turf 0.88 0.45 0.0019 0.75 lb ai/A 5 A 0.01 990 0.0052 1,900 0.000089 110,000 980 1,900

Golf Course 0.75 lb ai/A 5 A 0.01 990 0.0052 1,900 0.000089 110,000 980 1,900

Foliar Sprays on 

Ornamentals in 

Nurseries

0.39 0.29 0.0039 0.59 lb ai/A 25 A 0.018 570 0.013 760 0.00072 14,000 550 720

Foliar Sprays on 

Ornamentals in 

Greenhouses

2.5 1.6 0.12 0.59 lb ai/A 25 A 0.11 89 0.072 140 0.022 450 74 110

Loading/Applying 

Granulars via Push-type 

Spreader

Turf

0.24 0.13 0.01

0.5 lb ai/A 5 A 0.0018 5,400 0.001 10,000 0.00031 32,000 4,700 7,600

Golf Course 0.5 lb ai/A 5 A 0.0018 5,400 0.001 10,000 0.00031 32,000 4,700 7,600

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. Amount handled per day values are HED estimates of acres treated or gallons applied per day based on Exposure SAC SOP #9 “Standard Values for Daily Acres Treated in Agriculture,” industry 
Page 16 of 39

sources, and HED estimates.

d. Dermal Dose (mg/kg/day) = Dermal Unit exposure (mg/lb ai) x App Rate x Area Treated x %Absorption (24.5% dermal) / Body weight (80 kg). 

e. Inhalation Dose (mg/kg/day) = Inhalation Unit exposure (mg/lb ai) x App Rate x Area Treated x %Absorption (100% inhalation ) / Body weight (80 kg). 

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

g. Inhalation MOE = NOAEL (10 mg/kg/day) / Inhalation Dose (mg/kg/day) 
Page 17 of 39

Short-/Intermediate-Term Handler Risk for Seed Treatments

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

cucurbit seeds (see Table 3). The paclobutrazol labels do not permit on-farm 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 5 and 

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

scenarios do not exceed HED’s level of concern (MOEs > 1000) at some level of PPE.
Page 18 of 39

Table 5: Summary of Short- and Intermediate-Term Occupational Handler Exposure and Risk Estimates for Paclobutrazol Seed Treatment Uses

Seed Type

lbs seed 

treated/day

a

Application 

Rate b

(lb ai/lb seed)

Amount 

Handled 

per day

(lb ai/day)

Baseline 

Dermal Unit 

Exposure c

(mg/lb ai)

Baseline 

Inhalation Unit 

Exposure c

(ug/lb ai)

PPE-G 

Dermal 

Unit 

Exposure c

(mg/lb ai)

Baseline 

Dermal 

MOE d

PPE-G 

Dermal 

MOE

d

Baseline 

Inhalation 

MOE e

Total 

Baseline 

MOE

Total MOE 

(Baseline 

Inhalation + 

Gloves)

Loader/Applicator

Cucurbit

(Cucumber) 5512 0.000229 1.3

No Data 0.34 0.023

N/A 110000 1900000 N/A 100000

Cucurbit 

(Cantaloupe) 5512 0.00027 1.5 N/A 95000 1600000 N/A 90000

Cucurbit (Pumpkin) 5512 0.000107 0.6 N/A 240000 4000000 N/A 230000

Cucurbit (Squash) 5512 0.000172 0.9 N/A 150000 2500000 N/A 140000

Cucurbit 

(Watermelon) 5512 0.000157 0.9 N/A 160000 2700000 N/A 150000

Pepper 5512 0.00247 13.6 N/A 10000 170000 N/A 9400

Tomato 5512 0.00414 22.8 N/A 6200 100000 N/A 5800

Broccoli 5512 0.000661 3.65 N/A 39000 650000 N/A 37000

Cauliflower 5512 0.000635 3.5 N/A 41000 670000 N/A 39000

Cabbage 5512 0.000639 3.52 N/A 40000 670000 N/A 38000

Sewer

Cucurbit

(Cucumber) 5512 0.000229 1.3

0.0062 0.23 No Data

420000 N/A 2800000 360000 N/A

Cucurbit 

(Cantaloupe) 5512 0.00027 1.5 350000 N/A 2300000 300000 N/A

Cucurbit (Pumpkin) 5512 0.000107 0.6 890000 N/A 5900000 770000 N/A

Cucurbit (Squash) 5512 0.000172 0.9 560000 N/A 3700000 490000 N/A

Cucurbit 

(Watermelon) 5512 0.000157 0.9 610000 N/A 4000000 530000 N/A

Pepper 5512 0.00247 13.6 39000 N/A 260000 34000 N/A

Tomato 5512 0.00414 22.8 23000 N/A 150000 20000 N/A

Broccoli 5512 0.000661 3.65 140000 N/A 950000 120000 N/A

Cauliflower 5512 0.000635 3.5 150000 N/A 990000 130000 N/A

Cabbage 5512 0.000639 3.52 150000 N/A 990000 130000 N/A
Page 19 of 39

Table 5: Summary of Short- and Intermediate-Term Occupational Handler Exposure and Risk Estimates for Paclobutrazol Seed Treatment Uses

Seed Type lbs seed 

treated/day a

Application 

Rate b

(lb ai/lb seed)

Amount 

Handled 

per day

(lb ai/day)

Baseline 

Dermal Unit 

Exposure c

(mg/lb ai)

Baseline 

Inhalation Unit 

Exposure c

(ug/lb ai)

PPE-G 

Dermal 

Unit 

Exposure c

(mg/lb ai)

Baseline 

Dermal 

MOE d

PPE-G 

Dermal 

MOE d

Baseline 

Inhalation 

MOE e

Total 

Baseline 

MOE

Total MOE 

(Baseline 

Inhalation 

+ Gloves)

Bagger

Cucurbit

(Cucumber) 5512 0.000229 1.3

0.0091 0.16 No Data

280000 N/A 4000000 260000 N/A

Cucurbit 

(Cantaloupe) 5512 0.00027 1.5 240000 N/A 3400000 220000 N/A

Cucurbit (Pumpkin) 5512 0.000107 0.6 610000 N/A 8500000 570000 N/A

Cucurbit (Squash) 5512 0.000172 0.9 380000 N/A 5300000 350000 N/A

Cucurbit 

(Watermelon) 5512 0.000157 0.9 410000 N/A 5800000 380000 N/A

Pepper 5512 0.00247 13.6 26000 N/A 370000 24000 N/A

Tomato 5512 0.00414 22.8 16000 N/A 220000 15000 N/A

Broccoli 5512 0.000661 3.65 98000 N/A 1400000 91000 N/A

Cauliflower 5512 0.000635 3.5 100000 N/A 1400000 93000 N/A

Cabbage 5512 0.000639 3.52 100000 N/A 1400000 93000 N/A

Multiple Activities

Cucurbit

(Cucumber) 5512 0.000229 1.3

No Data 1.6 0.042

N/A 62000 400000 N/A 54000

Cucurbit 

(Cantaloupe) 5512 0.00027 1.5 N/A 52000 340000 N/A 45000

Cucurbit (Pumpkin) 5512 0.000107 0.6 N/A 130000 850000 N/A 110000

Cucurbit (Squash) 5512 0.000172 0.9 N/A 82000 530000 N/A 71000

Cucurbit 

(Watermelon) 5512 0.000157 0.9 N/A 90000 580000 N/A 78000

Pepper 5512 0.00247 13.6 N/A 5700 37000 N/A 4900

Tomato 5512 0.00414 22.8 N/A 3400 22000 N/A 2900

Broccoli 5512 0.000661 3.65 N/A 21000 140000 N/A 18000

Cauliflower 5512 0.000635 3.5 N/A 22000 140000 N/A 19000

Cabbage 5512 0.000639 3.52 N/A 22000 140000 N/A 19000

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

b Application Rates based on existing labels for paclobutrazol.

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

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 (24.5%) / body weight (80 kg 

adult). Dermal MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Dermal Dose (mg/kg/day). Level of concern = 1000.

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 (80 

kg adult). Inhalation MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Inhalation Dose (mg/kg/day). Level of concern = 1000.
Page 20 of 39

Table 6: Summary of Secondary Handler (Planter) Exposures and Risks for Paclobutrazol

Crop

Application 

Rate a

(lb ai/lb seed)

Seeds/lb b seeds 

planted/acre b

lbs 

seed/acre

Amount 

Handled per 

day c

(lb ai/day)

PPE-G Dermal 

Unit Exposure 

(mg/lb ai) d

Baseline 

Inhalation Unit 

Exposure

(ug/lb ai) d

PPE-G 

Dermal 

MOE e

Baseline 

Inhalation 

MOE f

Total MOE 

(Baseline 

Inhalation + 

Gloves)

Cucurbit Seed 

(Cucumber) 0.000229 12000 139392 11.6 0.21 0.25 3.4 61000 1100000 58000

Cucurbit Seed 

(Cantaloupe) 0.00027 16000 38848 2.4 0.052 0.25 3.4 250000 4500000 240000

Pepper 0.00247 50000 69696 1.4 0.28 0.25 3.4 47000 850000 45000

Cucurbit Seed 

(Pumpkin) 0.000107 1600 7260 4.5 0.039 0.25 3.4 340000 6100000 320000

Cucurbit Seed 

(Squash) 0.000172 1920 15374 8.0 0.11 0.25 3.4 120000 2100000 110000

Cucurbit Seed 

(Watermelon) 0.000157 4800 43560 9.1 0.11 0.25 3.4 110000 2100000 100000

Tomato 0.00414 120000 130680 1.1 0.36 0.25 3.4 36000 650000 34000

Broccoli 0.000661 80000 210845 2.6 0.1394 0.25 3.4 94000 1700000 89000

Cauliflower 0.000635 80000 23232 0.3 0.0148 0.25 3.4 890000 16000000 840000

Cabbage 0.000639 45000 98010 2.2 0.1113 0.25 3.4 120000 2100000 110000

a Application Rates based on existing labels for paclobutrazol.

b Taken from a Biological and Economic Analysis Division memo entitled, “Acres Planted per Day and Seeding Rates of Crops Grown in the United States” (J. Becker and S. 

Ratnayake; 3/24/11).

c Amount Handled per Day = Application Rate (lb ai/seed) * lbs seed/acre * 80 acres.

d Unit Exposures from HED Exposure Science Advisory Council Policy 14. No data is available for baseline dermal exposure (i.e., no gloves).

e 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 (24.5%) / body weight (80 kg 

adult). Dermal MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Dermal Dose (mg/kg/day). Level of concern = 1000.

f 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 (80 

kg adult). Inhalation MOE = NOAEL (10.0 mg/kg/day for short- and intermediate-term exposure) / Inhalation Dose (mg/kg/day). Level of concern = 1000.
Page 21 of 39

4.2 Occupational Post-application Exposure and Risk

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. 

4.2.1 Dermal Post-Application Risk

In the case of paclobutrazol, there is a potential for post-application dermal exposure to workers 

following foliar applications of paclobutrazol to turf, golf courses, and ornamentals in 

greenhouse and nurseries. 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 Agricultural Reentry Task Force (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 

“Science Advisory Council for Exposure (ExpoSAC) Policy 3”

(http://www.epa.gov/pesticides/science/exposac_policy3.pdf), which, along with additional 

information about the ARTF data, can be found at http://www.epa.gov/pesticides/science/postapp-exposure-data.html. 

Table 7 provides a summary of the transfer coefficients and activities associated with turf and 

ornamentals in greenhouse and nurseries.

Table 7. Post-application Activities and Dermal Transfer Coefficients.

Use Site Transfer Coefficients (cm2/hr) Activities

Turf 3,700 golf course maintenance

Ornamentals in 

Greenhouse and 

Nurseries

230

transplanting, irrigation (hand watering), 

hand harvesting, container moving, hand 

weeding, pinching, tying/training, 

propagating, hand pruning

1900 irrigation

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

• 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 Duration = 8 hours per day

• Body Weight = 80 kg

• 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
Page 22 of 39

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 

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/cm2following 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 (0.077

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

residues. Appendix A 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 A 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/cm2after the third (final) 

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

declined to <LOQ (0.005 ug/cm2). Appendix A 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)
Page 23 of 39

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).

A summary of the estimated occupational post-application risks are provided in Table 8. The 

short- and intermediate-term risk estimates for golf course maintenance activities do not exceed 

HED’s level of concern (MOEs ≥ 1000) using predicted Day 0 residue values from the TTR 

study. The short- and intermediate-term risk estimates for ornamentals in greenhouses and 

nurseries do not exceed HED’s level of concern (MOEs ≥ 1000) using predicted Day 0 residue 

values from either the Chrysanthemum or Poinsettia DFR data for all activities except for hand 

set irrigation. Hand set irrigation would not be performed in greenhouses and thus this issue 

only applies to nursery situations.

Table 8: Summary of Short-and Intermediate-term Occupational Post-Application Risks for Paclobutrazol

Crop/Site Activities

Transfer 

Coefficient 

(cm2/hr)

Application 

Rate

(lb ai/A)

Predicted 

Day 0 TTR 

or DFR 

(ug/cm2)

Day 0 Dermal 

Dose

(mg/kg/day) d

Day 0 

MOE e

Day X at 

which MOE 

>= LOC

Turf a golf course 

maintenance 3,700 0.75 0.077 0.007 1500 N/A

Ornamentals in 

Greenhouse and 

Nurseries using 

Chrysanthemum DFR 

Data b

transplanting, 

irrigation, hand 

harvesting, container 

moving, hand 

weeding, pinching, 

tying/ training, 

propagating, hand 

pruning

230 0.59 0.68 0.0041 2,500 N/A

Irrigation (hand set) f1900 0.59 0.68 0.034 300 40

Ornamentals in 

Greenhouse and 

Nurseries using 

Poinsettia DFR Data c

transplanting, 

irrigation, hand 

harvesting, container 

moving, hand 

weeding, pinching, 

tying/ training, 

propagating, hand 

pruning

230 0.59 0.47 0.0027 3800 N/A

Irrigation (hand set) f1900 0.59 0.47 0.022 460 6

a. TTR data represents CA which was the test site with the highest residues.

b. Chrysanthemum DFR data represents use in a greenhouse in Oregon.

c. Poinsettia DFR data represents use in a shadehouse in Florida

d. Dermal Dose = [DFR or TTR (ug/cm2) x Tc (cm2/hr) x 0.001 mg/ug x 8 hrs/day x DAF (24.5%)] body weight (80 kg)

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

f. Hand set irrigation only applies to nursery settings.
Page 24 of 39

Restricted Entry Interval: The REI listed on the existing paclobutrazol labels is based on the 

acute toxicity of the technical material. Paclobutrazol is classified as Toxicity Category III for 

the acute oral route, Toxicity Category II for the acute dermal toxicity route, and Toxicity 

Category III for eye and skin irritation. It is not a skin sensitizer. In accordance with the WPS, 

acute Toxicity Category III and II chemicals require a 12- or 24- hour REI, respectively. Based 

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

may not be adequate and should be revisited. Special consideration should also be given to use 

of hand set irrigation in nurseries.

4.2.2 Occupational Post-application Inhalation

Based on the Agency's current practices, a quantitative post-application inhalation exposure 

assessment was not performed for paclobutrazol at this time primarily because paclobutrazol’s 

vapor pressure (1.28 x 10-9 mm Hg @ 25.0°C) and Henry's Law Constant (8.09 x 10-10 atm 

m

3

/mol) indicate that the compound is relatively non-volatile under field conditions. However, 

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 is in the 

process of evaluating the SAP report as well as available post-application inhalation exposure 

data generated by the Agricultural Reentry Task Force and may, as appropriate, develop policies 

and procedures, to identify the need for and, subsequently, the way to incorporate occupational 

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

5.0 RESIDENTIAL (NON-OCCUPATIONAL) EXPOSURE

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

fields, residential lawns, and golf courses). Although, paclobutrazol products do not appear to be 

specifically marketed towards residential handler use (i.e., homeowners); a residential handler 

assessment was performed to be protective of any such use. A residential post-application

assessment was also performed as use of paclobutrazol in parks, residential lawns, and golf 

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

exposures, the Health Effects Division’s 2012 Standard Operating Procedures 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).
Page 25 of 39

5.1 Residential Handler Exposure and Risk

Assessing exposures and risks resulting from residential uses is very similar to assessing 

occupational exposures and risks, except that residential handler exposure scenarios do not use a 

tiered approach for personal protection using increasing levels of PPE in residential handler risk 

assessments. Homeowner handler assessments are based on the assumption that individuals are 

wearing shorts, short-sleeved shirts, socks, and shoes, and homeowner handlers are expected to 

complete all tasks associated with the use of a pesticide product including mixing/loading if 

needed as well as the application. Residential handler exposure scenarios are considered to be 

short-term only, due to the infrequent use patterns associated with homeowner products.

It has been determined that exposure to pesticide handlers is likely during the residential use of 

paclobutrazol on lawns. The quantitative exposure/risk assessment developed for residential 

handlers is based on the following scenarios:

Mixing/Loading/Applying Liquids with Manually-Pressurized Handwand;

Mixing/Loading/Applying Liquids with Hose End Sprayer;

Mixing/Loading/Applying Liquids with Backpack Sprayer;

Loading/Applying Granules with Push Type Spreader; and 

Loading/Applying Granules with Belly Grinder

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 the 

Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1), the Outdoor Residential 

Exposure Task Force (ORETF) database, or other registrant-submitted occupational exposure 

studies. Some of these data are proprietary (e.g., ORETF data), and subject to the data protection 

provisions of FIFRA. The standard values recommended for use in predicting residential handler 

exposure that are used in this assessment, known as “unit exposures”, are outlined in the 2012 

Lawns/Turf SOP.

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
Page 26 of 39

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)

Short-term risks for residential handlers are presented in Table 9. Intermediate-term exposures 

are not likely because of the intermittent nature of applications by homeowners. Short-term 

combined dermal plus inhalation risk estimates to residential handlers do not exceed HED’s level

of concern for all scenarios (i.e., MOEs ≥ 1000) except for belly grinder application (MOE=790).

Table 9. Residential Handler Baseline Dermal and Inhalation Exposures

Crop 

Grouping

Application 

Ratea

Area 

Treated 

Dailyb

Dermal 

Unit 

Exposure 

(mg/lb ai)

Inhalation 

Unit 

Exposure 

(mg/lb ai)

Baseline Baseline Inhalation Total

(lb ai/A) (acres/day) Baseline Baseline

Dermal 

Dosec

(mg/kg/day)

Dermal 

MOEd

Dosee

(mg/kg/day) MOEf

Baseline 

Dermal + 

Baseline 

Inhalation 

MOEg

Mixer/Loader/Applicator (Liquids) - Manually Pressurized Handwand Application

Turf 0.75 0.023h

63 0.018 0.0033 3000 0.0000039 2600000 3000

Mixer/Loader/Applicator (Liquids) - Hose End Sprayer Application

Turf 0.75 0.5 13.4 0.022 0.024 2500 0.000048 1200000 2500

Mixer/Loader/Applicator (Liquids) - Backpack Sprayer Application

Turf 0.75 0.023h

130 0.14 0.0069 1500 0.00003 330000 1400

Mixer/Loader/Applicator (Granules) - Push Type Spreader Application

Turf 0.5 0.5 0.81 0.0026 0.00062 16000 0.0000081 1200000 16000

Mixer/Loader/Applicator (Granules) - Belly Grinder Application

Turf 0.5 0.023h

360 0.039 0.013 790 0.0000056 1800000 790

a. Application rates based on existing labels. 

b. Based on HED’s Standard Operating Procedures for Residential Exposure Assessment; Lawns/Turf (January 2012).

c. Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/acre or lb ai/gal) x acres or gal treated x 24.5% dermal 

absorption / body weight (80 kg).

d. Inhalation Dose (mg/kg/day) daily unit exposure (μg/lb ai) x application rate (lb ai/acre or lb ai/gal) x acres or gal treated x 100% 

inhalation absorption / body weight (80 kg). 

e. Dermal MOE = NOAEL (10 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 1000.

f. Inhalation MOE = NOAEL (10 mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 1000.

g. Combined Dermal + Inhalation MOE = NOAEL (10 mg/kg/day) / Combined dermal + inhalation dose (mg/kg/day).

h. 0.023 acres is equivalent to 1,000 ft2
Page 27 of 39

5.2 Residential Post-Application Exposure/Risk

Paclobutrazol can be used in many areas that can be frequented by the general population 

including residential areas (e.g., home lawns). As a result, individuals can be exposed by 

entering these areas if they have been previously treated.

5.2.1 Post-application Inhalation

Based on the Agency's current practices, a quantitative residential post-application inhalation 

exposure assessment was not performed for paclobutrazol at this time primarily because 

paclobutrazol’s vapor pressure (1.28 x 10-9 mm Hg @ 25.0°C) and Henry's Law Constant (8.09 x 

10-10 atm m3/mol) indicate that the compound is relatively non-volatile under field conditions. 

The Agency sought expert advice and input on issues related to volatilization of pesticides from 

its Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel 

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

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in the 

process of evaluating the SAP report and may, as appropriate, developing policies and 

procedures, to identifying the need for and, subsequently, the way to incorporate post-application 

inhalation exposure into the Agency's risk assessments. If new policies or procedures are put 

into place, the Agency may revisit the need for a quantitative post-application inhalation 

exposure assessment for paclobutrazol.

5.2.2 Residential Post-Application Dermal and Incidental Oral

Short-term dermal and incidental oral exposure and risk estimates have been assessed for 

paclobutrazol. Dermal and oral exposures were not combined as the toxicological effects from 

the dermal and oral routes of exposure are different.. The scenarios, routes of exposure and 

lifestages assessed include:

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

incidental oral);

Mowing: adults (dermal) and children 11 < 16 years old (dermal); and

Golfing: adults (dermal), children 11 < 16 years old (dermal), and children 6 < 11 years 

old (dermal).

The lifestages (i.e., adults,children 1<2 years old, children 11 < 16 years old, and children 6 < 11 

years old) selected for each post-application scenario are based on an analysis provided as an 

Appendix in the 2012 Residential SOPs. These lifestages are not the only lifestages that could 

be potentially exposed for these post-application scenarios; however, the assessment of these 

lifestages is health protective for the exposures and risks for any other potentially exposed 

lifestages.

The following equations and assumptions were used to calculate post-application risk estimates:

Dermal exposure:
Page 28 of 39

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).

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 

cm

2

/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
Page 29 of 39

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).

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/ft2or lb ai/acre);

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

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

CF3 = area unit conversion factor (1.08 x 10-3ft2/cm2or 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 10-6g/μg).

and

SRt = AR * FS * (1-FD)

t

* CF2 * CF3 * CF4
Page 30 of 39

where:

SRt = soil residue on day "t" (μg/g);

AR = application rate (lbs ai/ft2or 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;

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

CF3 = area unit conversion factor (1.08 x 10

-3

ft2/cm2 or 2.47 x 10-8acre/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/ft2or 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 108μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3ft2/cm2or 2.47 x 10-8acre/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
Page 31 of 39

TTRt = AR * F * (1-FD)

t

* CF2 * CF3

where:

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

AR = application rate (lbs ai/ft2or 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 108μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3ft2/cm2or 2.47 x 10-8acre/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 

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

Table 10. All adult and children mowing and golf dermal risk estimates for both liquid and 

granular formulations do not exceed HED’s level of concern (MOEs ≥ 1000). All adult and 

children playing on treated turf dermal risk estimates for both liquid and granular formulations 

exceed HED’s level of concern (MOEs < 1000). 

Table 10. Short-Term Dermal Residential Post-application 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 0.077 d

0.064 160

Mowing 0.0013 7700

Golfing 0.005 2000

Child 11 < 16 years old Mowing 0.0015 6700

Golfing 0.0058 1700

Child 6 < 11 years old Golfing 0.0069 1500
Page 32 of 39

Table 10. Short-Term Dermal Residential Post-application 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

Child 1 < 2 year old Physical Activities on Turf 0.12 82

Granular Formulations

Adult

Dermal 

Physical Activities on Turf

0.5 0.011 e

0.010 970

Mowing 0.00019 53000

Golfing 0.00073 14000

Child 11 < 16 years old Mowing 0.00022 46000

Golfing 0.00084 12000

Child 6 < 11 years old Golfing 0.00099 10000

Child 1 < 2 year old Physical Activities on Turf 0.019 520

a. Application rates = maximum application rates from labels.

b. Dermal Dose (mg/kg/day) = TTR (μg/cm2) x 0.001 (mg/μg) x short-term TC (cm2/hr) x ET (hr/day) x DAF (40%)

BW (kg) 

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 11. All children oral non-dietary ingestion risk estimates for both liquid and 

granular formulations do not exceed HED’s level of concern (MOEs ≥ 1000). 

Table 11. Short-Term Oral Non-dietary Injestion 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, c, d

(mg/kg/day)

Oral 

MOEs e

Liquids

Child 1 < 2 year old Oral 

Hand-to-Mouth

0.75 0.077 f

0.010 1800

Object-to-Mouth 0.00032 59000

Soil Ingestion 0.000025 770000

Granulars

Child 1 < 2 year old Oral 

Hand-to-Mouth

0.5 0.011 g

0.00074 25000

Object-to-Mouth 0.00023 82000

Soil Ingestion 0.000016 1200000

Episodic Granular Ingestion N/A h

a. Application rates = maximum application rates from labels.

b. Hand-to-Mouth Dose (mg/kg/day) = E = [HR * (FM * SAH) * (ET * N_Replen) * (1- (1- SE)

(Freq_Replen/N-Replen))]

c. Object-to-Mouth Dose (mg/kg/day) = E = [OR* CF1 * SAMO * (ET * N_Replen) * (1- (1- SEO)

(Freq_Replen/N_Replen))]

d. Soil Ingestion Dose (mg/kg/day) = E = SRt * SIgR * CF1

e. Oral MOE = NOAEL (18.8 mg/kg/day) / Oral Dose (mg/kg/day)

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

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

g. No endpoints identified from the available developments toxicity studies (rat and rabbit) appropriate for an acute dietary 

assessment for paclobutrazol and thus no assessment is required for episodic granular ingestion.

5.3 Combined Exposure

HED combines risk values resulting from separate exposure pathways when it is likely they can 

occur simultaneously based on the use pattern, the behavior associated with the exposed

population, and the hazard associated with the points of departure. HED reviewed all residential 

sources of exposure to determine which residential exposure scenarios would be appropriate to 

combine with dietary exposure for an aggregate risk assessment. 

HED did not combine exposure resulting from adult handler and post-application exposure 
Page 33 of 39

resulting from treated lawns and/or golfing because of the conservative assumptions and inputs 

within each estimated exposure scenario. HED believes that combing exposures resulting from 

handler and post-application activities would result in an overestimate of adult exposure. 

Therefore, HED selected the most conservative adult residential scenario, dermal postapplication exposure (MOE = 160) as the contributing source of residential exposure to be 

combined with the dietary exposure for the aggregate assessment.

The children’s oral exposure is based on post-application hand-to-mouth exposures only (MOE= 

1800). To include exposure from object-to-mouth and soil ingestion in addition to hand-tomouth could result in a very conservative estimation of exposure, as it would overestimate the 

potential for oral exposure. Furthermore, although there is the potential for co-occurrence of 

dermal and oral exposure, the toxicological effects from the dermal and oral routes of exposure 

are different. As a result, a combined residential exposure assessment is not possible for 

children. Therefore, two independent children’s aggregate assessments are required (postapplication dermal combined with dietary exposure and post-application oral combined with 

dietary exposure) to ensure no unacceptable risk will result to children when combining 

residential and dietary exposure for purposes of estimating an aggregate risk.

Table 12 summarizes the residential exposure scenarios that are to be used for estimating 

aggregate exposure. 

Table 12. Combined Residential Exposure and Risk Estimates for Paclobutrazol

Use Site

Handler 

Dermal a

Handler

Inhalation a

Post-application 

Dermal MOE b

Hand-to-Mouth 

MOE c

Dose MOE Dose MOE Dose MOE Dose MOE

Adults – Turf (Granulars) 0.013 790 0.0000056 1800000 0.010 970 N/A

Adults – Turf (Liquids) 0.0069 1500 0.00003 330000 0.064 160 N/A

Children 1 < 2 Years Old 

- Turf (Granulars) N/A N/A 0.019 520 0.00074 25000

Children 1 < 2 Years Old 

- Turf (Liquids) N/A N/A 0.12 82 0.010 1800

a. See Table 9: Residential Handler Dermal Exposure and Risk (granulars represents belly grinder and liquids represents 

backpack sprayer)

b. See Table 10: Dermal Post-application Exposure and Risk

c. See Table 11: Hand-To-Mouth Exposure and Risk

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 offtarget 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 
Page 34 of 39

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.1 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 

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

considered in risk assessment.

Paclobutrazol is not registered on use sites that are likely to result in spray drift outside of the 

currently registered turf uses. Since post-application exposure from the direct turf applications is 

already assessed for paclobutrazol (see above in Section 5.2), quantitative assessment of spray 

drift is not required for paclobutrazol at this time.

 

1 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 35 of 39

Appendix A: Paclobutrazol DFR and TTR Study Results
Page 36 of 39

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 tranferable 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/cm2following 

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/cm2following 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/cm2following 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 37 of 39

Table A1. 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

R

2

0.983 0.916 0.815
Page 38 of 39

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/cm2twenty-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 A2. 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

R

2

0.774
Page 39 of 39

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/cm2after 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. 

TableA3. 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

R

2

0.914