UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

PC Code: 125601

DP Barcode: 393895

March 26, 2013

MEMORANDUM

Subject: Registration Review –Ecological Risk Assessment and Effects Determination 

of Paclobutrazol

To: Khue Nugyen, Chemical Review Manager

Laura Parsons, Risk Manager

Pesticide Re-evaluation Division

Office of Pesticide Programs (7508P)

From: Meghan Radtke, Ph.D., Biologist

Faruque Khan, Ph.D., Senior Scientist

Environmental Risk Branch 1

Environmental Fate and Effects Division

Office of Pesticide Programs (7507P)

Approved 

by:

Edward Odenkirchen, Ph.D., Acting Branch Chief

Sujatha Sankula, Ph.D., Lead Biologist

Environmental Risk Branch 1

Environmental Fate and Effects Division

Office of Pesticide Programs (7507P)

Attached is the ecological risk assessment and effects determination for the registration 

review of the plant growth regulator, paclobutrazol.

In general, most of the registered uses of paclobutrazol were found to potentially adversely 

affect listed and non-listed species. The exception was the seed treatment use. Cucurbit, 

tomato, pepper, cabbage, broccoli, and cauliflower seed treatments are not expected to cause 

adverse direct or indirect effects for any species. For the other uses (potted ornamentals 

drench and spray, tree injection, turf, soil injection/basal drench), the following taxonomic 

groups of listed and non-listed organisms were found to be potentially of concern for direct

toxic risk from the registered uses of paclobutrazol:
• Mammals (acute and chronic)

• Birds, reptiles, and land-phase amphibians (chronic)

• Freshwater fish and aquatic-phase amphibians (chronic)

• Estuarine/marine fish (chronic)

• Freshwater invertebrates (acute and chronic)

• Estuarine/marine invertebrates (acute and chronic)

• Aquatic vascular plants

• Terrestrial plants

Mammals

• Risk quotient analysis indicates potential acute risks of concern from turf applications 

and soil injection/drench

• Risk quotients range from 0.10 to 0.11 for turf and 0.13 to 0.34 for soil 

injection/drench.

• Risk quotient analysis indicates chronic risk concerns for all uses but the seed 

treatments.

Birds, Reptiles, and Land-Phase Amphibians

• Risk quotient analysis indicates potential chronic risk concerns from the soil 

injection/drench use.

• Risk quotients range from 1.1 to 2.3.

• Risks from tree injection, seed treatment, and potted ornamental drench and spray are 

not expected to be of concern.

Freshwater Fish and Aquatic-Phase Amphibians

• Risk quotient analysis indicates potential chronic risk concerns from the turf and 

potted ornamentals drench.

Estuarine/Marine Fish

• Risk quotient analysis indicates potential acute risk concerns from the potted 

ornamental drench.

• Risk quotient analysis indicates potential chronic risk concerns from the turf and 

potted ornamentals drench.

Freshwater Invertebrates

• Risk quotient analysis indicates potential acute and chronic risk concerns from the 

turf and potted ornamental drench uses.

• The highest RQs for turf are 0.28 (acute) and 7.6 (chronic).

• The highest RQs for potted ornamental drench are 1.4 (acute) and 37 (chronic).
Estuarine/Marine Invertebrates

• Risk quotient analysis indicates potential acute and chronic risks from the turf and 

potted ornamental drench uses.

• The highest RQs for turf are 0.28 (acute) and 1.1 (chronic).

• The highest RQs for potted ornamental drench are 1.4 (acute) and 9.5 (chronic).

Aquatic Vascular Plants

• Risk quotient analysis indicates potential risk concerns from the turf and potted 

ornamental drench uses.

Terrestrial Plants

• Risk quotient analysis indicates potential risk concerns from the turf and soil 

injection/basal drench uses.

Groups that were not found to be of concern for direct toxic risk include:

• Birds and reptiles (acute)

• Freshwater mollusks (acute)

• Freshwater fish (acute)

• Estuarine/marine fish (acute)

• Amphibians (acute)

• Non-vascular plants

• Terrestrial invertebrates

Given that there are possible direct effects to mammals, birds, aquatic organisms, and plants, 

indirect effects to all other organisms could occur. Indirect effects may include, but are not 

necessarily limited to, food, shelter, seed dispersal/pollination, or other habitat alterations. 
REGISTRATION REVIEW

ECOLOGICAL RISK ASSESSMENT AND EFFECTS 

DETERMINATION

PACLOBUTRAZOL

CAS Number 76738-62-0

USEPA PC CODE 125601

(αR,βR)-rel-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-

triazole-1-ethanol

Prepared by:

Meghan Radtke, Ph.D., Biologist

Faruque Khan, Ph.D. Senior Scientist

Environmental Risk Branch I

Reviewed by:

Anita Ullagaddi, M.S., Biologist

Christopher Koper, M.S., Chemist

Environmental Risk Branch I

Environmental Fate and Effects Division

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460
v

Executive Summary

E.1 Nature of Stressor

Paclobutrazol is a systemic plant growth regulator that is used to modify the physical 

structure of vegetation. It inhibits cell elongation and internode extension by interfering with 

gibberellins biosynthesis. It is used to produce denser, more compact plants – ranging from 

vegetables to turf to ornamental trees. It is currently registered for application to turf grass

and a number of ornamentals (trees, shrubs, bulbs) to produce more compact plants and 

reduce mowing and trimming. It is also registered for use as a seed treatment for tomatoes, 

peppers, cucurbits, broccoli, cauliflower, and cabbage. Formulated products vary in 

concentration and form, according to their use. For turf, products range from 0.018 to 22.3 

percent active ingredient in a granular form. For outdoor trees and ornamental uses 

(greenhouse and outdoors), paclobutrazol is sold as a ready-to-use solution (2.51% ai), an 

emulsifiable concentrate (0.4 to 22.3% ai), a concentrated liquid (0.13 to 21.8% ai), or a 

wettable powder (50% ai). For seed treatments, paclobutrazol is available as an emulsifiable 

concentrate at a concentration of 22.3 to 22.9 percent active ingredient. Registered 

application methods for paclobutrazol are foliar spray (greenhouse and outdoors), soil drench

(greenhouse and outdoors), soil injection, tree injection, bulb soak, plug/liner soak, and seed 

treatment. 

Two major environmental degradates, the ketone analog of the parent (CGA 149907) and 

1H-1,2,4-triazol-3-ol (NOA457654), were identified in the environmental fate and terrestrial 

field dissipation studies. Paclobutrazol and these major degradates are considered as 

stressors for this risk assessment.

E.2 Assessment of Risk

E.2.1 Physico-Chemical and Environmental Fate Properties

Paclobutrazol is a racemic mixture of the (2R, 3R)- and (2S, 3S)-enantiomers but the

physiochemical and fate properties of each enantiomer were not investigated in the submitted 

studies. Therefore, it is assumed that each enantiomer of paclobutrazol has similar 

physiochemical and fate properties based on submitted studies. Paclobutrazol has a low 

solubility (25.9 mg/L) in water. The vapor pressure (1.28 x 10-9 mm Hg @25.0°C) and 

Henry's Law Constant (8.09 x 10-10 atm m3/mol) indicate that the compound is relatively 

non-volatile under field conditions. Paclobutrazol is stable to hydrolysis and photolysis.

Under aerobic conditions, paclobutrazol appears to be generally quite persistent in acidic 

soils, with half-lives greater than 300 days. However in soils with neutral or higher pH, 

estimated half-lives were as short as 25 days. Batch equilibrium results indicate that the 

mobility of paclobutrazol is quite variable; ranging from mobile to slightly mobile; terrestrial 

field dissipation studies in various regions suggest that paclobutrazol is persistent and 
vi

mobile. Two major environmental degradates, ketone analog of parent (CGA 149907, ≤ 

40.0%) and 1H-1,2,4-triazol-3-ol (NOA457654, ≤ 25.1%) were identified in the 

environmental fate and terrestrial field dissipation studies. Selected environmental fate 

studies indicate that NOA457654 is not a persistent chemical but that it is mobile. 

Laboratory and field studies suggest that paclobutrazol and its degradates have the potential 

to move into groundwater via leaching and surface water, mainly through runoff.

E.2.2 Ecological Risk Conclusions

The Agency assessed risk to a number of taxa, including:

• Birds (which are also used as surrogates for reptiles and terrestrial-phase amphibians)

• Mammals

• Fish (freshwater and estuarine/marine; freshwater fish are used as surrogates for

aquatic-phase amphibians)

• Aquatic invertebrates (freshwater and estuarine/marine)

• Terrestrial invertebrates

• Terrestrial plants

• Aquatic plants (vascular and non-vascular)

A direct (adverse) effect to an organism is considered to be that which occurs from exposure 

to paclobutrazol. An indirect (adverse) effect to an organism is an adverse modification to a 

resource used by that organism, such as loss of prey or habitat, which is caused by the use of 

paclobutrazol. This distinction is important when considering risks to species that are 

federally listed as endangered or threatened (referred to as “listed species”).

The specific taxa that may be at risk from paclobutrazol are highly dependent on the specific 

registered paclobutrazol use. For example, risk is unlikely from paclobutrazol use on seed 

treatments (pepper, tomato, cucurbit, cabbage, cauliflower, broccoli), which represent the 

lowest application rate of paclobutrazol products. Alternatively, for applications to turf, 

which have a higher application rate and exposure potential, this assessment identifies 

chronic risk for all size classes of mammals, as well as risk to terrestrial plants and aquatic 

invertebrates (chronic and acute).

In general, registered uses of paclobutrazol may cause direct adverse effects to some 

mammals, birds, reptiles, amphibians, fish, aquatic invertebrates, and plants. Birds may be at 

risk from chronic dietary exposures from the soil injection/drench use. Mammals may be at 

acute risk from turf applications (short grass only) and soil injection/drench (vegetation); 

chronic risks span all uses but the seed treatments and include diets of short grass, tall grass,

broadleaf plants/small insects, and fruits/pods/seeds/large insects. Direct risks to terrestrial 

invertebrates are not expected. 
vii

Risks were identified for direct effects to freshwater or estuarine-marine fish and

invertebrates from the current registered uses of paclobutrazol. Freshwater fish and mollusks 

are unlikely to be at acute risk from the registered paclobutrazol uses; however, risks were 

identified for chronic exposures to freshwater and estuarine/marine fish, and acute and 

chronic exposures to freshwater and estuarine/marine invertebrates. In particular, turf and 

potted ornamental drenches triggered these risks. Acute risks to estuarine/marine fish were 

also identified, but only for the potted ornamental drench use.

Direct effects are expected for aquatic vascular plants for the turf and potted ornamentals 

uses. Direct effects also are expected for terrestrial plants – both terrestrial and semi-aquatic 

– as a result of spray drift (turf only) and runoff. 

Given that there are possible direct effects to mammals, birds, aquatic organisms, and plants, 

indirect effects to other organisms could occur. Indirect effects could take the form of food, 

shelter, seed dispersal/pollination, or other alterations of habitat. 

The level of concern (LOC) from acute exposure is different for listed (endangered and/or 

threatened; LOC = 0.1), and non-listed (LOC = 0.5) terrestrial animals; and for listed (LOC = 

0.05), and non-listed (LOC = 0.5) aquatic organisms. For chronic exposure, the LOC is the 

same for listed and non-listed animals and is 1.0. The LOC is also 1.0 for both listed and 

non-listed plants (aquatic or terrestrial). As the LOCs are different for listed and non-listed 

species, evaluation of potential risk from direct exposure to paclobutrazol for non-listed and 

listed species are summarized separately. Tables E.1 – E.4 list the potential direct and 

indirect effects to listed species as well as the organism group and size classes potentially at 

risk from use of paclobutrazol.
viii

Table E.1. Potential risks to non-listed and listed species associated with direct or 

indirect effects from paclobutrazol

Taxonomic 

Group Effects Endpoint1 Direct Effects Indirect Effects from Direct Effects to:1 Non-listed Listed

Aquatic vascular 

plants

Measures of biomass –

Vascular plant –EC50 (Lemna 

spp.)

Non-vascular plant –EC50

(green algae) (surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect

Terrestrial plants

Aquatic nonvascular plantsNo;

RQs<LOC

No Effect;

RQs<LOC

Currently no listed non-vascular 

plants

Terrestrial plants -

dicots

Measures of biomassVegetative vigor EC25 and 

NOAEC (tomato)

Seedling emergence EC25 and 

NOAEC (surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect

Mammals, birds, terrestrial 

invertebrates

Terrestrial plants -

monocots

Measures of biomassVegetative vigor EC25 (nondefinitive) and NOAEC (corn, 

onion, ryegrass, wheat)

Seedling emergence EC25

(wheat) and NOAEC 

(surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect

Freshwater 

fish/amphibians

Acute: Mortality- LC50 (grass 

carp)

Mortality – LC50 (Asiatic toad)

No; 

RQs<LOC

No Effect;

RQs<LOC Terrestrial invertebrates, aquatic 

invertebrates, terrestrial and 

Chronic: Chronic early life- aquatic plants

stage-NOAEC (rainbow trout) Yes

May 

Affect/Likely 

to Adversely 

Affect

Estuarine/marine 

fish

Acute: Mortality -LC50

(sheepshead minnow)

(surrogate data)

No;

RQs<LOC

May 

Affect/Likely 

to Adversely 

Affect Terrestrial and aquatic plants, 

terrestrial invertebrates, birds 

Chronic: Early-life stage and/or mammals 

NOAEC (sheepshead minnow)

(surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect

Freshwater 

invertebrates

Acute: Mortality- EC50

(D.magna)

Mortality- LC50 (Chinese 

mystery snail)

No;

RQs<LOC

May 

Affect/Likely 

to Adversely 

Affect;

No Effect 

(freshwater 

mollusks only)

Terrestrial and aquatic plants 

Chronic: Growth and 

Reproduction- NOAEC (D. 

magna) (surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect

Estuarine/marine 

invertebrates

Acute: EC50 (Eastern oyster

and mysid shrimp) (surrogate 

data)

No;

RQs<LOC

May 

Affect/Likely 

to Adversely 

Affect Terrestrial and aquatic plants

Chronic: chronic toxicity 

NOAEC (mysid shrimp) 

(surrogate data)

Yes

May 

Affect/Likely 

to Adversely 

Affect
ix

Taxonomic 

Group Effects Endpoint1 Direct Effects Indirect Effects from Direct Effects to:1 Non-listed Listed

Mammals

Acute: Oral LD50 (rat) Yes

May Affect, 

Likely to 

Adversely 

Affect; Terrestrial invertebrates, birds, 

reptiles, land-phase amphibians; 

Chronic: Growth, survival, and terrestrial plants

reproduction - Multi-gen rat 

study

Yes

May Affect, 

Likely to 

Adversely 

Affect

Birds 

(surrogate for 

reptiles and landphase amphibians)

Acute: Oral LD50 (mallard 

duck) 

Acute: Dietary LC50 (bobwhite 

quail)

No;

RQs<LOC

No;

RQs<LOC

Terrestrial invertebrates, 

mammals, terrestrial plants Chronic: Growth, survival, 

and reproduction- (bobwhite 

quail)

Chronic 

dietary - Yes

May Affect, 

Likely to 

Adversely 

Affect

Terrestrial 

invertebrates

Acute: Contact LD50

(honeybee) (surrogate data) No No Terrestrial plants

1 Direct effects to species may result in indirect effects to other species by changing availability of prey and modification to 

habitat.

Table E.2. Potential direct effects to listed and non-listed terrestrial organisms from 

exposure to paclobutrazol1

Paclobutrazol Listed Terrestrial Species Non-listed Terrestrial Species

Birds2 Mammals Plants Birds2 Mammals Plants

Acute Chronic Acute Chronic Acute Chronic Acute Chronic

Turf N N Y 

(S,M)

Y

(S,M,L)

Y N N N Y 

(S.M.L)

Y

Potted 

ornamental 

spray

N N N Y 

(S,M,L)

N N N N Y 

(S,M,L)

Y

Tree injection N N N Y 

(S,M,L)

N/A N N N Y 

(S,M,L)

N/A

Soil 

injection/basal 

drench

N Y Y 

(S,M,

L)

Y 

(S,M,L)

Y N Y N Y 

(S,M,L)

Y

Potted 

ornamental 

drench

N N N Y 

(S,M,L)

N N N N Y 

(S,M,L)

Y

Tomato seed 

treatment

N N N N N N N N N N

Pepper seed 

treatment

N N N N N N N N N N

Cucurbit seed 

treatment

N N N N N N N N N N

Broccoli seed 

treatment

N N N N N N N N N N

Cauliflower 

seed treatment

N N N N N N N N N N
x

Paclobutrazol Listed Terrestrial Species Non-listed Terrestrial Species

Birds2 Mammals Plants Birds2 Mammals Plants

Acute Chronic Acute Chronic Acute Chronic Acute Chronic

Cabbage seed 

treatment

N N N N N N N N N N

1 Y= Potential direct effects (RQ ≥ LOC); N = Potential direct effects not expected (RQ < LOC);; N/A = not 

available (incomplete exposure pathway, thus it was not analyzed); S, M or L indicate which size class is 

potentially affected; S = small bird (20 g) or mammal (15 g); M = medium bird (100 g) or mammal (35 g); L = 

large bird (1000 g) or mammal (1000 g). For mammals, chronic size classes are for dose-based exposure only. 

Dietary-based acute and chronic exposure for birds and mammals is not evaluated using body weights. RQ 

values were determined for these specific weights only, therefore, it is expected that potential direct effects may 

exist between two size classes in which the lower size class exceeded the LOC but the next size class did not. 

Therefore, for example, if small birds (20 g) exceeded the LOC but medium birds (100 g) did not, then potential 

direct effects may exist for all birds less than 100 g at any life stage until can be shown otherwise.

2 Birds are surrogates for terrestrial reptiles and terrestrial-phase amphibians.

Table E.3. Potential direct effects to listed aquatic organisms from exposure to 

paclobutrazol1

Paclobutrazol

Freshwater Fish Estuarine/Marine 

Fish

Vascular 

Aquatic 

Plants

Freshwater 

Invertebrates

Estuarine/Marine 

Invertebrates

Acute Chronic Acute Chronic Acute Chronic Acute Chronic

Turf N Y N Y Y Y Y Y Y

Potted 

ornamental 

drench

N Y Y Y Y Y Y Y Y

1 Y= Potential direct effects; N = Potential direct effects not expected

Table E.4. Potential direct effects to non-listed aquatic organisms from exposure to 

paclobutrazol1

Paclobutrazol

Freshwater Fish Estuarine/Marine 

Fish

Vascular 

Aquatic 

Plants

Freshwater 

Invertebrates

Estuarine/Marine 

Invertebrates

Acute Chronic Acute Chronic Acute Chronic Acute Chronic

Turf N Y N Y Y N Y N Y

Potted 

ornamental 

drench

N Y N Y Y Y Y Y Y

1 Y= Potential direct effects; N = Potential direct effects not expected
xi

E.3 Uncertainties

Certain data and other supporting information were not available to the Agency as it 

conducted the preliminary risk assessment for paclobutrazol. As such, certain assumptions

were made and conclusions were based on the information that was available. For some 

taxa, this may have resulted in the use of overly conservative approaches for evaluating risk. 

EFED has identified the information it believes may help best resolve these uncertainties, 

such as toxicity data for plants. Additional information may allow EFED to refine its risk 

conclusions for certain species. Below is a summary of the uncertainties associated with the 

risk assessment of paclobutrazol.

E.3.1 Ecotoxicity Data Gaps

Data for the following fate and eco-toxicity studies were not available. The Final Work Plan 

for paclobutrazol requested seedling emergence and vegetative vigor data, but the studies 

submitted in response to this request were found to have major deficiencies that, in some 

cases, resulted in an “invalid” classification. Data for the other studies were not requested in 

the Final Work Plan. Open literature searches were performed, but even with the addition of 

information from these sources, data suitable for quantitative use in the risk assessment still 

were not available for estuarine/marine fish (acute and chronic), freshwater invertebrates 

(chronic), estuarine/marine invertebrates (acute and chronic), seedling emergence (monocots 

and dicots), vegetative vigor (monocots), honey bees (acute contact), and vascular aquatic 

plants. 

To address each gap, toxicity data were used from other triazoles that were similar in 

structure to paclobutrazol (Appendix F)

1

. Crystal Ball (2000 version 5.0) was used to create 

a fitted lognormal distribution of toxicity endpoints running a Monte Carlo sampling scheme 

(10,000 trials). The 5th percentile of the data was calculated and used in the risk assessment. 

Not every triazole had a complete set of data, so the chemicals and number of data points 

varied for each paclobutrazol data gap. This approach was chosen as it was thought to be 

conservative. The following bulleted list contains a brief description of how each data gap 

was filled. 

• Estuarine/Marine Fish (Acute) OPPTS 850.1075. Definitive LC50 data from six 

triazoles (cyproconazole, fenbuconazole, hexaconazole, metconazole, myclobutanil, 

tebuconazole, triticonazole) were available. A surrogate toxicity value for 

paclobutrazol acute effects on estuarine/marine fish was developed based on the 5th

percentile of the distribution of data. 

 1 In situations where paclobutrazol data were available, the toxicity values for chemically similar triazoles were 

compared with the paclobutrazol data. There were no consistent patterns of toxicity. Paclobutrazol was the 

most toxic of the triazoles for terrestrial plants, but not the most toxic in other scenarios. No single triazole 

emerged as being consistently toxicologically similar to paclobutrazol, and thus an appropriate surrogate in 

itself.
xii

• Estuarine/Marine Fish (Chronic) OPPTS 850.1400. Definitive NOAEC/NOEC data 

from three triazoles (metconazole, tebuconazole, triticonazole) were available. A 

surrogate toxicity value for paclobutrazol chronic effects on estuarine/marine fish was 

developed based on the 5th percentile of the distribution of data.

• Freshwater Invertebrates (Chronic) OPPTS 850.1300. Definitive NOAEC/NOEC 

data from eight triazoles (cyproconazole, fenbuconazole, hexaconazole, metconazole, 

tebuconazole, triadimefon, triadimenol, triticonazole) were available. A surrogate 

toxicity value for paclobutrazol chronic effects on freshwater invertebrates was 

developed based on the 5th percentile of the distribution of data.

• Estuarine/Marine Invertebrates (Acute) OPPTS 850.1025 and OPPTS 850. 1035. 

Definitive LC50/EC50 data from seven triazoles (cyproconazole, fenbuconazole, 

hexaconazole, metconazole, myclobutanil, tebuconazole, triticonazole) were 

available. A surrogate toxicity value for paclobutrazol acute effects on 

estuarine/marine invertebrates was developed based on the 5th percentile of the 

distribution of data. In addition, acute toxicity data were available for a freshwater 

mollusk.

• Estuarine/Marine Invertebrates (Chronic) OPPTS 850.1350. Definitive 

NOAEC/NOEC data were available for only one triazole – tebuconazole. 

Consequently, tebuconazole’s toxicity value was used as a surrogate for paclobutrazol 

chronic effects on estuarine/marine invertebrates.

• Seedling Emergence (Monocots and Dicots) OPPTS 850.4225. Definitive monocot 

NOAEC/NOEC data from four triazoles (cyproconazole, metconazole, tebuconazole, 

triticonazole) were available. A surrogate toxicity value for paclobutrazol effects on 

monocot seedling emergence was developed based on the 5th percentile of the 

distribution of data. Definitive dicot EC25 data from three triazoles (cyproconazole, 

tebuconazole, triticonazole) and definitive dicot NOAEC/NOEC data from three 

triazoles (cyproconazole, metconazole, triticonazole) were available. Surrogate 

toxicity values for paclobutrazol effects on dicot seedling emergence were developed 

based on the 5th percentile of these two data distributions. 

• Vegetative Vigor (Monocots) OPPTS 850.4250. Definitive monocot NOAEC/NOEC 

data from three triazoles (cyproconazole, metconazole, tebuconazole) were available. 

A surrogate toxicity value for paclobutrazol effects on monocot vegetative vigor was 

developed based on the 5th percentile of the distribution of data.

• Honey Bee (Acute Contact) OPPTS 850.3020. Only non-definitive LD50 data were 

available for five triazoles (cyproconazole, fenbuconazole, metconazole, triadimefon, 

triticonazole). Consequently, the most conservative value (triticonazole) was used in 

the risk assessment.

• Aquatic Vascular Plants (EC50) OPPTS 850.4400. Definitive EC50 data were 

available for four triazoles (cyproconazole, metconazole, tebuconazole, triticonazole). 
xiii

A surrogate toxicity value for paclobutrazol effects on aquatic vascular plants was 

developed based on the 5th percentile of the distribution of data.

• Aquatic Non-Vascular Plants (EC50) OPPTS 850.5400. Toxicity data were not 

available for algal species. Open literature provided some toxicity information on 

paclobutrazol to green algae.

• Passerine Birds (Acute) OPPTS 850.2100. Data were not available; therefore, the 

acute oral toxicity of paclobutrazol to the mallard duck was used to evaluate risk. 

E.3.2 Application Rates

Many of the labels did not contain application information in pounds of active ingredient per 

acre (Table E.5). Tree injection, and soil injection/basal drench for ornamental trees 

provided application rates in grams of paclobutrazol per tree diameter. To evaluate exposure, 

assumptions (based on open literature) on the number of trees expected to be present in one 

acre as well as a conservative application rate in pounds of paclobutrazol per acre were made. 

These assumptions may be overestimating or underestimating exposure.

Greenhouse seed treatments for cucurbits, peppers, tomatoes, broccoli, cauliflower, and 

cabbage were stipulated in terms of micrograms of paclobutrazol per seed. To evaluate 

environmental exposure, the number of transplants per acre was derived from open literature 

sources. These assumptions may be overestimating or underestimating exposure.

Pre-plant plug and liner soak labels did not provide specific use rates because the rate is 

influenced by varying soak times, the extent of rooting of each plant, the media moisture

levels, the differing sensitivities of cultivars and species being treated, cultural practices, and 

environmental factors. Consequently, it was not possible to calculate a per-acre application 

rate for these uses. It was assumed that the pre-plant plug and liner soak application rate 

would not exceed the soil drench and/or bench spray for greenhouse ornamental transplants 

(see below). This assumption may be overestimating or underestimating exposure.

Soil drench and bench spray application rates for greenhouse ornamental transplants were 

described in terms of parts per million per various size pot or bench area. To evaluate 

exposure, assumptions (based on open literature) were made to estimate the application rate 

per acre. These assumptions may be overestimating or underestimating exposure.
xiv

Table E.5. Summary of missing label information and approaches used in risk 

assessment

Use Missing Label Information Risk Assessment Approach

Tree injection (ornamental 

trees)

lb ai/A Convert ppm per tree DBH 

into lb ai/A, making 

assumptions about the 

number and size of trees in 

an urban acre

Soil injection/basal drench 

(ornamental trees)

lb ai/A Convert ppm per tree DBH 

into lb ai/A, making 

assumptions about the 

number and size of trees in 

an urban acre

Seed treatment (cucurbit, 

tomato, pepper, cabbage, 

cauliflower, broccoli)

lb ai/A Use high-end seeding rates 

for each crop to determine 

the lb ai/A

Soil drench and bench spray 

application (greenhouse 

ornamental transplants)

lb ai/A after plants have been 

moved outside of the 

greenhouse setting

Multiplied the ppm per pot 

application rate times the 

number of “can tight” pots 

found in an acre of nursey 

land to derive lb ai/A

E.3.3 Rate of Paclobutrazol Uptake into Plants

Spray, drench, and seed treatment applications assume that paclobutrazol will be absorbed 

into plants in one of two ways: directly through the leaves, stem, or seed coat; or taken up 

through the roots from the soil. Information was not available on the rate at which this 

occurred. This posed a challenge for assessing risk to terrestrial and aquatic organisms. For 

example, in the tree drench scenario, the most conservative assumption for assessing risk to 

terrestrial animals is to assume 100 percent of the paclobutrazol is taken up into the plant. 

Conversely, the most conservative assumption for assessing risks to aquatic organisms or 

other terrestrial plants (via runoff) is to assume that none of the paclobutrazol was taken up 

into the plant and is all still available in the soil. This approach of using the most 

conservative assumptions for each organism group assessed essentially “double counts” the 

amount of paclobutrazol available to non-target organisms and over-estimates risk to some 

groups, if not all. However, without data to show how quickly paclobutrazol is absorbed into 

plants, it is difficult to choose realistic exposure scenarios. Consequently, the following 

plant-to-soil scenarios were considered: 100%:100%, 50%:50%, 25%:75%, and 75%:25%.
xv

E.3.4 Distribution of Paclobutrazol in Plants

The application methods for paclobutrazol rely on its translocation to internodes and dividing 

cells within the plant. In particular, drenches and tree/soil injections rely on the chemical 

being transported from the roots or trunk of the tree to the leaves and stems. No information 

is available about whether all of the paclobutrazol concentrates in the leaves of the tree or if 

it remains equally distributed throughout the entire tree (roots, trunk, branches, fruit, leaves, 

etc.) or its translocation rate. In the risk assessment, the conservative assumption was made 

that paclobutrazol concentrates in the leaves of the plant (leaves are used as a surrogate for 

fruit, seeds, or other edible non-woody food items) and that it does so very quickly after 

being applied. This may have resulted in overly conservative estimates of paclobutrazol 

exposure through the consumption of treated foliage.

E.3.5 Fate Data Gaps

Data for the following fate study were not available. 

• OPPTS 850.1730 – Fish Bioconcentration Factor (BCF). In lieu of data, KABAM 

was used to model the bioaccumulation potential of paclobutrazol. Results indicated 

that the likelihood of bioaccumulation in aquatic food web was low.

E.3.6 Incomplete Life Histories of Listed Species

Currently, a database of life histories for each of the listed animals and plants is not available

for use by EFED. These life histories would include information such as body size at each 

life stage, food sources, relationships with other taxa, habitat, and reproductive habits. As 

such, conservative (protective) assumptions were made concerning the potential relationships 

between species in that each species was assumed to have a relationship with the other taxa. 

This is assumed to be an overestimation of the actual species that have a species dependent 

relationship. 

E.3.7 Locations of Listed Species

In addition, the specific occurrences of listed species are not known in some cases beyond the 

county-level. If the location of a species was not known in greater detail than the county 

level, the species was assumed to occur anywhere within that county at any time. This 

assumption may lead to an overestimation of co-occurrence with paclobutrazol exposure and 

overestimation of the number of species potentially at risk.

E.3.8 Seasonal Carryover in Plants

Paclobutrazol is a systemic and is known to persist for years in trees (based on label 

information and application intervals). It is unknown if for grasses and perennials, 

paclobutrazol levels are maintained across seasons and expressed in subsequent 

“generations” of foliage.
xvi

E.3.9 Information on Crop Locations, Actual Use Rates, and Application 

Methods

While the assessment was based on the maximum application rates and methods stated on the 

registered labels, information on the actual use rates and application methods employed in 

residential settings, golf courses, right-of-ways, athletic fields, and in agricultural fields were 

not available to refine the risk characterization of paclobutrazol. In addition, sub-county 

information on where treated tomatoes, peppers, cucurbits, broccoli, cauliflower, and 

cabbage are grown would allow for greater confidence in estimates of crop co-occurrences

with listed species.

E.3.10 Greenhouse Discharges

Paclobutrazol is applied as a liquid to potted plants within greenhouses, as well as a bulb and 

plug/liner soak. It is possible that paclobutrazol may be present in the runoff water. This is a 

scenario that was not assessed and a point of uncertainty.
xvii

Table of Contents

Introduction............................................................................................................................ 23

 Purpose of assessment..................................................................................................... 23

Problem formulation ............................................................................................................... 24

Previous risk assessments................................................................................................ 25

Stressor source and distribution....................................................................................... 25

Mechanism of action...............................................................................25

Overview of pesticide use and usage.............................................................26

Tree injection....................................................................................30

Soil injection....................................................................................31

Basal drench ....................................................................................31

Seed treatment...................................................................................32

Pre-plant plug/liner soak and pre-plant bulb soaks ........................................33

Soil drench and bench sprays (potted ornamentals).......................................33

Environmental fate and transport .................................................................................... 35

Summary of environmental fate...............................................................35

Degradation......................................................................................39

Mobility and transport ............................................................................................40

Field studies .....................................................................................40

Degradates.......................................................................................40

Bioaccumulation................................................................................42

Receptors......................................................................................................................... 43

Effects to organisms...............................................................................43

Registrant submitted studies for paclobutrazol .............................................43

Open literature studies ........................................................................43

Incident database review..........................................................................43

Data gaps identified................................................................................44

Ecosystems potentially at risk....................................................................44

Degradates.......................................................................................46

 Conceptual model ....................................................................................................... 46

Risk hypothesis........................................................................................................... 48

Terrestrial environment........................................................................48

Aquatic environment...........................................................................49

Analysis plan............................................................................................................... 49

Measures to evaluate the risk hypothesis and conceptual model.........................49

Measures of effect..............................................................................49

Integration of exposure and effects...........................................................50

Analysis of co-occurance of federally listed species with paclobutrazol...............50

Exposure assessment............................................................................................................... 52

Aquatic exposure assessment.............................................................................................. 52

Monitoring data....................................................................................52

PRZM/EXAMS.................................................................................52

Aquatic exposure modeling results.................................................................................. 55

Terrestrial exposure............................................................................................................. 57

Dietary-based paclobutrazol residue levels..................................................................... 57
xviii

EEC estimates for tree injection, soil injection, tree drench, and potted ornamentals 

(drench)..............................................................................................60

Tree injection, soil injection/tree drench, and woody potted ornamental drench leaf 

biomass estimates...............................................................................61

Non-woody potted ornamental drench application.........................................66

 EEC estimates for seed treatment to tomato, pepper, cucurbit, broccoli, cauliflower, 

 cabbage..............................................................................................68

Off-field terrestrial and wetland/riparian plant paclobutrazol exposure ......................... 70

Effects characterization........................................................................................................... 74

Terrestrial vertebrate toxicology ......................................................................................... 75

Effects on birds................................................................................................................ 77

Effects on mammals ........................................................................................................ 78

Terrestrial invertebrate toxicology...................................................................................... 78

Surrogate data approach .................................................................................................. 79

Aquatic vertebrate (fish) toxicology ................................................................................... 80

Effects to freshwater fish and aquatic-phase amphibians................................................ 80

Effects to estuarine-marine fish....................................................................................... 82

Surrogate data approach........................................................................82

Aquatic invertebrate toxicology.......................................................................................... 82

Effects to freshwater invertebrates.................................................................................. 83

Surrogate data approach........................................................................85

Effects to estuarine-marine invertebrates........................................................................ 85

Surrogate data approach........................................................................85

Terrestrial plant toxicology ................................................................................................. 85

Surrogate data approach .................................................................................................. 87

Aquatic plant toxicology ..................................................................................................... 88

Surrogate data approach .................................................................................................. 88

Results: risk characterization ................................................................................................. 90

Risk estimation.................................................................................................................... 90

Direct effects to non-target terrestrial vertebrates........................................................... 90

Direct effects to birds, reptiles, and (land-phase) amphibians...............................90

Direct effects to mammals........................................................................92

Acute effects............................................................................................................92

Chronic effects..................................................................................92

Direct effects to non-target terrestrial invertebrates........................................................ 95

Direct effects to terrestrial and wetland/riparian plants................................................... 95

Direct effects to freshwater fish (amphibians), invertebrates and estuarine-marine fish 

(amphibians) and invertebrates and aquatic plants.......................................................... 97

Freshwater fish and aquatic-phase amphibians - acute risk...............................97

Freshwater fish and aquatic-phase amphibians - chronic risk............................98

Estuarine/marine fish - acute risk............................................................99

Estuarine/marine fish - chronic risk..........................................................99

Freshwater invertebrates - acute risk........................................................100

Freshwater invertebrates - chronic risk.....................................................100

Estuarine/marine invertebrates - acute risk.................................................101

Estuarine/marine invertebrates - chronic risk.............................................102
xix

Aquatic vascular and non-vascular plants.................................................103

Probit slope response analysis of LOC values and acute RQ values............................. 104

Risk description................................................................................................................. 105

Exposure uncertainties................................................................................................... 106

Direct effects to terrestrial birds, reptiles and amphibians..................................108

Acute risk.......................................................................................108

Chronic risk....................................................................................108

Summary of risks from direct effects.......................................................109

 Direct effects to terrestrial mammals...........................................................110

Acute risk.......................................................................................110

Chronic risk....................................................................................111

Summary of risks from direct effects.......................................................114

 Direct effects to terrestrial invertebrates.......................................................115

Summary of risks from direct effects.......................................................115

 Direct effects to terrestrial plants...............................................................115

Summary of risks from direct effects.......................................................119

 Direct effects to aquatic fish, invertebrates, and plants......................................120

Freshwater fish and amphibians (aquatic-phase), and estuarine-marine fish.........120

Acute risk.................................................................................120

Chronic risk..............................................................................121

Freshwater and estuarine-marine invertebrates...........................................124

Acute risk.................................................................................124

Chronic risk..............................................................................126

Aquatic plants - vascular and non-vascular................................................128

Summary of risk from direct effects........................................................130

Listed species effects analysis....................................................................................... 130

Action area.........................................................................................136

Effects area determination.......................................................................136

Direct effects.......................................................................................136

Indirect effects....................................................................................137

Uncertainties............................................................................................141

Effects and risk assessment uncertainties.......................................................................... 141

Ecotoxicity data gaps..................................................................................................... 141

Application rates............................................................................................................ 143

Rate of paclobutrazol uptake into plants ....................................................................... 143

Distribution of paclobutrazol in plants.......................................................................... 144

Fate data gaps ................................................................................................................ 144

Incomplete life histories of listed species...................................................................... 144

Locations of listed species............................................................................................. 144

Information on crop locations, actual use rates, and application methods.................... 145

Other routes of exposure................................................................................................ 145

Foliar dissipation half-life ............................................................................................. 145

Species sensitivities..............................................................................145

Endocrine disrupter........................................................................................................ 146

Seasonal carryover in plants.......................................................................................... 147

Greenhouse discharges.................................................................................................. 147
xx

Spatial analyses.............................................................................................................. 147

References...............................................................................................148

Appendix A - Bibliography of MRIDs................................................................152

Appendix B – Half-life calculations of total toxic residues........................................157

Appendix C – Chemical structures..........................................................................161

Appendix D – KABAM inputs and outputs...............................................................162

Appendix E – ECOTOX literature search..........................................................168

Appendix F – Surrogate chemicals..........................................................................205

Appendix G – SIP and STIR model output.................................................................208

Appendix H – Risk quotient method and levels of concern..............................................211

Appendix I – Surface water model results and sample input and outputs.......................213

Appendix J – TerrPlant output.......................................................................218

Appendix K – Terrestrial EEC calculations..........................................................230
xxi

List of Abbreviated Terms and Symbols

@ symbol for “at”

% symbol for “percent”

> symbol for “greater than”

< symbol for “less than”

μg/L symbol for “micrograms per liter”

oC symbol for “degrees Celsius”

ai active ingredient

Acc# accession number

BEAD Biological and Economical Analysis Division

bw body weight

CI confidence interval

CL confidence limit

DP# data package

EC emulsifiable concentrate

EC25 25% effect concentration

EC50 50% (or median) effect concentration

ECOTOX EPA managed database

EEC estimated environmental concentration

EFED Environmental Fate and Effects Division

e.g. Latin exempli gratia (“for example”)

et al. Latin et alii (“and others”)

etc. Latin et cetera (“and the rest” or “and so forth”)

FESTF FIFRA Endangered Species Task Force

FIFRA Federal Insecticide Fungicide and Rodenticide Act

FQPA Food Quality Protection Act

ft feet

g gram

GENEEC Generic Estimated Exposure Concentration model

IC50 50% (or median) inhibition concentration

i.e. Latin for id est (“that is”)

IMS information management system

Kg kilogram(s)

Km kilometer(s)

Koc symbol for the organic carbon partitioning coefficient

LAA likely to adversely affect

Lbs pounds

lb ai/A pound(s) of active ingredient per acre

LC50 50% (or median) lethal concentration

LD50 50% (or median) lethal dose

LOAEC lowest observable adverse effect concentration

LOAEL lowest observable adverse effect level

LOC level of concern

LOD level of detection

LOEC lowest observable effect concentration

Kow symbol for the octanol water partitioning coefficient
xxii

LOQ level of quantitation

LUIS label use information system

m meter(s)

MA may affect

mg milligram(s)

mg/kg milligrams per kilogram (equivalent to ppm, except in the 

case of discussing dose such as mg/kg-bw)

mg/L milligrams per liter (equivalent to ppm)

mi mile(s)

MM may modify primary constituent element

MM/NSF may modify primary constituent element/no shapefile

mmHg millimeter of mercury

MRID master record identification number

MW molecular weight

NASS National Agricultural Statistics Service

NAWQA National Water Quality Assessment

NE no effect

NLAA not likely to adversely affect

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

NOAEC no observable adverse effect concentration

NOAEL no observable adverse effect level

NOEC no observable effect concentration

OCSPP Office of Chemical Safety and Pollution Prevention

OPP Office of Pesticide Programs

OPPTS Office of Prevention, Pesticides and Toxic Substances

pH symbol for the negative logarithm of the hydrogen ion 

activity in an aqueous solution, dimensionless

pKa symbol for the negative logarithm of the acid dissociation 

constant, dimensionless

ppb parts per billion (equivalent to μg/L or μg/kg)

ppm parts per million (equivalent to mg/L or mg/kg)

SLUA screening level usage analysis

USDA United States Department of Agriculture

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

USGS United States Geological Survey

Wt weight
23

Introduction

Purpose of Assessment

The purpose of this assessment is to evaluate the potential risks of paclobutrazol’s registered 

use and pending registrations on federally listed endangered and threatened (“listed”) species 

and all other non-target plant and animal (“non-listed”) species. This risk assessment 

incorporates the available effects data, modeling, and risk methodologies, some of which

may not have been available at the time when previous paclobutrazol registration actions 

occurred. Risks from direct and indirect effects are derived and evaluated in accordance with 

the risk assessment methodology described in the Agency’s Overview Document (US EPA,

2004). These risk findings are then used as part of an “effects determination” for listed 

species. The Agency will reach one of the following three conclusions regarding the 

potential for the registered paclobutrazol use on food and non-food crops to affect federally 

listed species:

• “No effect”; 

• “May affect, but not likely to adversely affect”; or

• “May affect, and likely to adversely affect”. 

If the results of the risk assessment show no indirect effects and the levels of concern (LOC) 

are not exceeded for direct effects for a given listed species taxonomic grouping (e.g., 

freshwater fish, small herbivorous mammal), a “no effect” (NE) determination is made, 

based on paclobutrazol’s use within the action area for a species within the given taxonomic 

group. If, however, there is a potential for indirect effects and/or exposure exceeds the listed 

species LOC values for direct effects for a given group, the Agency concludes a preliminary 

“may affect” (MA) for a species within the taxonomic group. The Agency then considers 

additional lines of evidence such as the geographical nature of the exposure, as well as more 

in-depth evaluations of the toxicological and ecological requirements to determine a rationale 

for a “not likely to adversely affect” (NLAA) or “likely to adversely affect” (LAA) 

determination.

Similarly the Agency will reach one of the following conclusions regarding the potential for 

paclobutrazol uses to result in destruction or adverse modification of critical habitat:

• “No effect”; 

• “May Modify Primary Constituent Elements”

The Agency uses the risk assessment analysis for direct effects to categories of biological 

resource requirements to draw conclusions about effects to principle constituent elements of 
24

critical habitat. The Agency is limited in a practical sense to those principle constituent

elements of critical habitat that are of a biological nature. If the results of the risk assessment 

show that no LOC is exceeded for all taxonomic groups a “no effect” (NE) determination for 

habitat modification is made. If an LOC is exceeded for one or more taxonomic groupings 

the Agency then considers additional lines of evidence such as the type and degree of effect 

on the taxonomic groupings, expected resultant effects on biologically mediated 

environmental processes (e.g., increased sedimentation from loss of vegetation) as compared 

to baseline environmental conditions, co-occurrence of the action area with critical habitat, 

the type of principle constituent elements associated with critical habitat for listed species in 

a taxonomic grouping to determine a rationale for a “may modify primary constituent 

elements”.

Problem Formulation

The problem formulation for this assessment and effects determination was provided in the

USEPA Registration Review – EFED Problem Formulation for Paclobutrazol Registration 

Review March 13, 2007 document. Data were requested for five studies:

• 850.7050 – UV/Visible absorption (“acceptable” classification)

• 850.1400 – Fish early-life stage toxicity test (“acceptable” classification)

• 850.2300 – Avian reproduction test (“acceptable classification)

• 850.4100 – Terrestrial plant toxicity – seedling emergence (“invalid” classification)

• 850.4150 – Terrestrial plant toxicity – vegetative vigor (“supplemental” 

classification)

Additional information on paclobutrazol was extracted from the scientific open literature. 

All submitted data and other information for paclobutrazol are listed in the MRID 

bibliography in Appendix A.

There were several modifications to the risk assessment process originally proposed in the 

problem formulation.

• Seed treatments (cucurbits, tomatoes, peppers, cabbage, cauliflower, broccoli) and 

plant/plug liner soaks were registered after the completion of the problem formulation 

and are thus considered in this risk assessment.

• Two paclobutrazol major degradates (CGA 149907 and 1H-1,2,4-triazol-3-ol 

(NOA457654) were identified as being stressors of concern. Since there are no 

toxicity and environmental fate data available for these degradates at this time, a total 

toxics residue approach was taken rather than solely considering paclobutrazol.
25

• A 5th percentile surrogate toxicity data approach was used to fill in data gaps rather 

than the proposed acute-to-chronic-ratio because paired datasets (e.g., same species 

and same chemical) were not available in most instances.

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), all pesticides 

distributed or sold in the United States generally must be registered by the United States 

Environmental Protection Agency (U.S. EPA). To determine whether a pesticide can be 

registered, EPA evaluates its safety to non-target species based on a wide range of 

environmental and health effects studies. In 1996, FIFRA was amended by the Food Quality 

Protection Act (FQPA), and EPA was mandated to implement a new program for the 

periodic review of pesticides, i.e., registration review2

. The registration review program is 

intended to ensure that as the ability to assess risk evolves and as policies and practices 

change, all registered pesticides continue to meet the statutory standard of no unreasonable 

adverse effects to human health and the environment. Changes in science, public policy, and 

pesticide use practices will occur over time. Through the new registration review program, 

the Agency periodically reevaluates pesticides to make sure that as change occurs, products 

in the marketplace can be used safely.

Previous Risk Assessments

The three most recent completed screening level risk assessments for use on tomatoes, 

peppers, and cucurbits seeds (DP Barcode D329407, June 4, 2007), use for pre-plant plug 

and liner soaks (DP Barcode D338570, June 12, 2007), and use on broccoli, cauliflower, and 

cabbage seeds (DP Barcode D398449, August 17, 2012) did not identify any adverse risks to 

listed species. However, there were a number of data gaps where assumptions were made. 

Of significance was the lack of plant data (terrestrial and aquatic) for these risk assessments.

The risk assessments available in the docket, and which serve as the basis for this problem 

formulation, include the following:

• June 12, 2007 assessment of pre-plant and liner soaks 

• June 4, 2007 and August 17, 2012 assessments of seed treatments

• Assessments for a variety of turf, ornamental, and tree uses in the 1980s

The risk assessments did not identify any risks to any specific taxa. 

Stressor Source and Distribution

MECHANISM OF ACTION

Paclobutrazol is a plant growth regulator that inhibits gibberellin biosynthesis. Gibberellin 

promotes cell elongation in plants; thus, inhibiting it decreases cell length and results in more 

 2 http://www.epa.gov/oppsrrd1/registration_review/
26

compact plants. Paclobutrazol enters the plant through leaves (foliar application), root 

uptake (soil drenches and injections), seed coat (seed treatment) or by direct injection into the 

tree, depending on the application method. The compound is then systemically transported 

through the plant via the xylem. Depending on the plant, paclobutrazol levels can persist 

within the plant from 8 weeks (turf) to several years (trees) with physical effects still visible. 

Paclobutrazol and its two major degradates (see “Degradates” section, below) are considered 

stressors of concern.

OVERVIEW OF PESTICIDE USE AND USAGE

Paclobutrazol, also known by the trade names Clipper, Bonzi, Paczol, and others, is a plant

growth regulator that is currently registered for application to a number of food and non-food 

crops to induce compact plant growth. Registered application methods for paclobutrazol are 

foliar spray, soil injection, soil drench, bulb soak, seed treatment, plug/liner soak, and tree 

injections. It is used to control the size of numerous plants including turf, trees in right-ofways, ornamental trees and shrubs, and bulbs (cut flower trade). Ten different companies 

currently have registered products with paclobutrazol concentrations ranging from 0.018 to 

50 percent. Current registrations for formulated products and uses of paclobutrazol are 

shown in Table 1, below. Uses of paclobutrazol are shown in Table 2, below. 

An average of 31,500 pounds of paclobutrazol (averaged from 2002, 2004, and 2006) is 

applied in the United States each year with the majority being applied to turf (24,500 lb). 

Paclobutrazol also was used as a growth regulator in nurseries/greenhouses (6000 lb) and 

landscape settings (1,000 lb). Specific usage information from the California Pesticide Use 

Report indicated that 1140 pounds of paclobutrazol were used in 2009 with the following 

breakdown: landscape maintenance (815 lb), greenhouse flowers/greens (3 lb), greenhouse 

container plants (55 lb), greenhouse grown transplant material (6 lb), outdoor container 

plants (24 lb), outdoor flowers/greens (7 lb), outdoor grown transplant material (2 lb),

ornamental turf (31 lb), rights of way (194 lb), and structural pest control3 (3 lb). 

 3 According to BEAD, this use may be 1) a mistake in the California database; or 2) a non-standard term used 

by applicators (e.g., a tree that is close to a building that has potential to cause structural damage may be 

recorded as “structural pest control” rather than “landscape maintenance”).
27

Table 1. Current registrations for paclobutrazol

Product Name Registrant

EPA 

Registration #

(latest label 

date)

Active 

Ingredient

(% w/w)

Form Use(s)

Bonzi 50 WP Syngenta Crop 

Protection, Inc.

000100-00992

(2/24/86) 50 Wettable powder

Ornamental herbaceous plants, ornamental nonflowering plants, ornamental woody shrubs and vines

Bonzi II Ornamental 

Growth Regulator

Syngenta Crop 

Protection, Inc.

000100-01079

(1/9/04) 0.13 Soluble concentrate

Ornamental herbaceous plants, ornamental woody 

shrubs and vines

Bonzi Ornamental 

Growth Regulator

Syngenta Crop 

Protection, Inc.

000100-00996

(8/18/10) 0.4 Soluble concentrate

Ornamental herbaceous plants, ornamental woody 

shrubs and vines,

Cambistat

Rainbow Treecare 

Scientific 

Advancements

74779-3

8/17/10 22.3 Emulsifiable concentrate Ornamental and/or shade trees

Clipper 20 UL Syngenta Crop 

Protection, Inc.

000100-00995

(1/17/86) 2.51 Ready-to-use solution Ornamental and/or shade trees

Clipper 50 WP Syngenta Crop 

Protection, Inc.

000100-00991

(6/6/85) 50 Wettable powder Ornamental and/or shade trees

Clipper E 20 UL Tree 

Growth Regulator

Syngenta Crop 

Protection, Inc.

000100-01037

(4/3/89) 2.51 Ready-to-usesolution

Nonagricultural uncultivated areas/soils, ornamental 

and/or shade trees

Cutdown

Phoenix 

Environmental 

Care, LLC.

81943-31

10/7/08 22.3 Emulsifiable concentrate Turf grass and trees

ETI 107 01 G Etigra 000228-679

(5/6/08) 0.4 Emulsifiable concentrate Ornamental herbaceous plants

Fertilizer with TGR 

Poa annua control

The Andersons 

Lawn Fertilizer 

Division, Inc.

009198-00196

(6/18/10) 1.38 Granular Golf course turf, ornamental lawns and turf

High K Fertilizer 

with TGR Poa annua

control

The Andersons 

Lawn Fertilizer 

Division, Inc.

009198-00201

(6/10/09) 0.34 Granular Golf course turf 

Paclo 2 SC

Fine 

Agrochemicals, 

Ltd.

62097-24

(11/7/08) 22.3 Soluble concentrate Ornamental and/or shade trees

Paclobutrazol 2 SC Syngenta Crop 

Protection, Inc.

000100-01014

(8/13/10) 22.3 Soluble concentrate

Turf, ornamental and/or shade trees, seeds (tomato, 

pepper, cucurbit, broccoli, cauliflower, and cabbage)

Paczol Ornamental 

Growth Regulator

Chemtura 

Corporation

000400-00515

(11/6/08) 0.4 Emulsifiable concentrate

Ornamental herbaceous plants, ornamental woody 

shrubs and vines

Piccolo

Fine 

Agrochemicals, 

Ltd.

062097-00011

(8/29/07) 0.4 Emulsifiable concentrate

Ornamental herbaceous plants, ornamental woody 

shrubs and vines
28

Product Name Registrant

EPA 

Registration #

(latest label 

date)

Active 

Ingredient

(% w/w)

Form Use(s)

Piccolo 10x

Fine 

Agrochemicals, 

Ltd.

62097-25

8/24/11 4 Flowable concentrate Ornamental herbaceous plants

Profile 2 SC Tree 

Growth Regulator

SePRO

Corporation

067690-00022

(11/2/10) 21.8 Soluble concentrate Turf, ornamental and/or shade trees, 

Scotts Turf Manager 

II

The Scotts 

Company

000538-00201

(3/24/86) 0.066 Granular Ornamental lawns and turf

Scotts Turf Manager 

for St. Augustine 

Grass

The Scotts 

Company

000538-00199

(8/26/93) 0.018 Granular Ornamental lawns and turf

TGR Turf Enhancer 

2SC

The Andersons 

Lawn Fertilizer 

Division, Inc.

009198-00205

(8/31/11) 22.3 Solubleconcentrate Golf course turf

TGR Winter 

Overseeding 

Enhancer

The Andersons 

Lawn Fertilizer 

Division, Inc.

009198-00199

(7/10/09) 1.38 Granular Golf course turf, ornamental lawns and turf

The Andersons 

Fertilizer with 0.25% 

Paclobutrazol

The Andersons 

Lawn Fertilizer 

Division, Inc.

009198-00215

(1/30/09 0.25 Granular Golf course turf

Tide Paclo 0.4% 

Liquid

Zhejiang Tide 

Cropscience 

Company, Ltd.

080697-00003

(12/30/10) 0.4 Soluble concentrate

Ornamental herbaceous plants, ornamental woody 

shrubs and vines

Tide Paclo 2 SC

Zhejiang Tide 

Cropscience 

Company, Ltd.

80697-4

8/13/10 22.3 Emulsifiable concentrate Turf grass and trees

Trimtect

Rainbow Treecare 

Scientific 

Advancements

74779-7

5/24/11 8 Emulsifiable concentrate Ornamental and/or shade trees
29

Table 2. Current registrations of paclobutrazol

Crop

Maximum 

Application 

Rate

Number of

Applications

Application 

Method

Shortest 

Application 

Interval

(days)

Reg. #*

Broccoli, cauliflower, and 

cabbage

2 μg ai/seed 1 Seed 

treatment**

N/A 000100-1014

Cucurbit 6.5 μg/seed 1 Seed 

Treatment**

N/A 000100-01014

Herbaceous and 

ornamentals 

(greenhouse)***

5.7 mg ai/ft2 NS Spray, Drench, 

Bulb Soak, 

Plug/Liner 

Soak

As needed 000100-00992

000100-00996

000100-01079

000400-00515

062097-00011

080697-00003

000228-679

62097-25

Pepper 16 μg ai/seed 1 Seed 

Treatment**

N/A 000100-01014

Tomato 12.5 μg

ai/seed

1 Seed 

Treatment**

N/A 000100-01014

Trees (shade and 

ornamental)

0.009 lb ai 

per inch 

DBH

1 Soil Injection, 

Basal Drench, 

Tree Injection

3 years or as 

needed

000100-01037

000100-00991

000100-00995

000100-01014

067690-00022

000228-680

74779-3

74779-7

80697-4

81943-31

62097-24

Turf 0.75 lb ai/A 3 Spray, 

Broadcast

14 009198-00196

009198-00199

009198-00201

009198-00205

009198-00215

000100-01014

067690-00022

000538-00201

000538-00199

000228-680

80697-4

81943-31

NS - not specified on label

*Application rates represent maximum application rate for a least one of the EPA Reg. # listed. Other labels may 

have slightly different application rates.

**Seeds are germinated in greenhouses and seedlings are later transplanted outdoors.

***May be planted outdoors after cultivation in a nursery or greenhouse.
30

Many of the labels for registered products did not contain application information in pounds 

of active ingredient per acre. The Biological and Economic Analysis Division (BEAD) 

calculated rates in pounds of paclobutrazol per acre, making a number of assumptions about 

the application method (US EPA, 2011a).

Tree Injection

For tree injection application rates, BEAD used the Clipper 20 UL label. Clipper is a tree 

growth retardant for ornamental trees. Injections should be made at every 8 inches around 

the circumference of the trunk. The amount of paclobutrazol injected depends on the number 

of holes and the size of the tree. The following table is presented on the label (Table 3):

Table 3. Tree size and use parameters for Clipper 20 UL (2.51% ai)

Tree Diameter 

(inches)1

Number of 

Injection Holes

Volume of 

Clipper 20 UL 

per Injection 

Site (ml)

Total Volume 

of Clipper 20 

UL per Tree 

(ml)

Total Grams of 

Paclobutrazol 

per Tree2

8 3 50 150 4.6

12 5 50 250 7.7

16 6 75 450 13.8

20 8 75 600 18.4

24 9 75 675 20.7

28 11 75 825 25.3

32 13 75 975 29.9

1

Assumed to be equivalent to the diameter at breast height (DBH)

2

Total grams ai per tree = total volume (ml) per tree*density (1.22 grams per ml [Tomlin 

2003]*percent product concentration (2.51%)

To calculate a “pounds of paclobutrazol per acre” rate based on the label directions, the 

density and sizes of trees in urban settings is necessary. Urban forest information was taken 

from Nowak et al. (2001). They characterize urban forests as ecosystems with trees and 

other vegetation in association with people and their developments. Nowak et al. (2001 

through 2011) conducted a series of studies assessing the effects and values of urban forests 

in 24 cities in the United States and Canada. They report the overall density of trees per acre 

and the distribution of tree size (diameter at breast height – DBH) for each city. Using this 

information, BEAD calculated the median value for density and DBH. These values were 

used to calculate tree injection, tree basal drench, and tree soil injection rates for 

paclobutrazol (see Table 1 in US EPA, 2011a).

Total grams ai per tree (4.6g)*number of trees per acre (36)*conversion factor (1 lb/453.59g) 

= 0.36 lb ai/A for tree injections.
31

This is considered a conservative estimate because: 1) applications using soil injections or 

basal drench around the base of the tree are much easier and faster to accomplish than tree 

injections (Chaney 2005); 2) soil injection around the base of the tree and basal drench also 

control the growth rate of grass around the tree (Chaney 2005); 3) the formulation contains 

methanol which has resulted in cracks, weeping injection holes, and internal wood 

discoloration and has reduced the use of alcohol-containing products in forestry (Chaney 

2005).

Soil Injection

For soil injections, BEAD used the Paclobutrazol 2SC label (2 pounds ai/gallon). The label 

calculates an application rate based on tree size and species. The dose for a 6-inch DBH tree 

ranges from 25 to 100 ml of formulation per tree. 

Using the median values for the number of trees planted per acre, tree DBH (see tree 

injection description), and the maximum application for a 6-inch DBH tree, BEAD calculated 

the following rate:

Formulation per tree (100 ml)*(1 gallon formulation/3785.4ml)*(2 lb ai/gallon)*number of 

trees per acre (36) = 1.9 lb ai/A

This is considered a conservative estimate because the maximum amount of active ingredient 

per tree is used and many small trees in urban forests are not treated with growth regulators.

Basal Drench

For tree basal drenches, BEAD used the Profile 2SC label (2 pounds ai/gallon). The label 

groups various species of trees and states the following application rates:

1 to 2 g ai/in DBH (e.g., sweetgum)

2 to 3 g ai/in DBH (e.g., elm, maple, oak)

3 to 4 g ai/in DBH (e.g., Bradford pear, ash)

Using the maximum application rate listed above, and the median values for number of trees 

per acre and tree diameter, the following application rate was calculated:

Grams ai applied per inch DBH (4) * median DBH (6) * (1 lb/453.59g) * number of trees per 

acre (36) = 1.9 lb ai/A

This is considered a conservative estimate because the maximum amount of active ingredient 

per tree is used and many small trees in urban forests are not treated with growth regulators.
32

Seed Treatment

For seed treatments (tomato, pepper, cucurbits, cabbage, broccoli, cauliflower), BEAD used 

the Paclobutrazol 2SC label (2 lb ai/gallon). Paclobutrazol 2SC is applied to seeds using 

slurries, film coatings, and direct application at the following rates:

Tomato – 1 to 12.5 μg ai/seed

Pepper – 1 to 16 μg ai/seed

Cucurbits – 1 to 6.5 μg ai/seed

Broccoli – 0.1 to 2 μg ai/seed

Cauliflower – 0.1 to 2 μg ai/seed

Cabbage – 0.1 to 2 μg ai/seed

Seeding rates vary by seed size; usually larger seeds, like pumpkin, have wider spacing 

intervals in fields. To be conservative for cucurbits, the crop that was thought to have the 

largest seeding rate (i.e., smallest seed) was chosen as a representative for the other cucurbits. 

Using seeding rates provided by BEAD (US EPA 2011b) the following equation was used to 

calculate paclobutrazol application rates in pounds of active ingredient per acre, for each of 

the six crops:

(μg ai/seed)(1 lb ai/ 453,592,370 μg ai)*(seed or transplants/A) = lb ai/A

Using the seeding/transplant rates provided by BEAD (US EPA 2011b), the following rates 

are calculated:

Tomato = (12.5 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(14,400 seeds/A) = 0.00040 lb ai/A

Pepper = (16 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(22,400 seeds/A) = 0.00079 lb ai/A

Cucurbits = (6.5 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(20,200 seeds/A) = 0.00029 lb ai/A

Broccoli = (2 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(21,780 seeds/A) = 0.000096 lb ai/A

Cauliflower = (2 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(14,520 seeds/A) = 0.000064 lb 

ai/A

Cabbage = (2 μg ai/seed)*(1 lb ai/453,592,370 μg ai)*(29,040 seeds/A) = 0.00012 lb ai/A

These estimates are characterized as conservative because: 1) the maximum application rate 

per seed is used for all six crops; 2) it includes mean maximum planting densities across the 

U.S. for all end uses of the crop. Often crops intended for processing are planted at higher 

densities than that intended for fresh markets; 3) the range of the number of seeds per acre 

given in US EPA 2011b is upwardly biased because the presented values are based on the 

minimum row width and the maximum number of seeds per row foot. Growers plant to an 

overall density per acre based on local conditions, so as the row width shrinks, the distance 

between seeds increases; 4) in the case of cucurbits, only the seeding rates for cucumbers and 
33

summer squash were considered. If pumpkins and melons were to be included, the mean 

number of seeds per acre would be substantially lower as these crops have more widely 

spaced plantings.

Pre-Plant Plug/Liner Soak and Pre-Plant Bulb Soaks

BEAD examined the Paczol label for information about pre-plant plug/liner soaks and preplant bulb soaks. Specific use rates are not given for these methods because the rate is 

influenced by varying soak times, the extent of rooting for each plant, the media moisture 

levels, the differing sensitivities of cultivars and species being treated, cultural practices, and 

environmental factors. BEAD did not have additional information to be able to calculate a 

per container application rate and therefore could not calculate an equivalent per acre 

application rate.

Although application rates for these methods could not be calculated, it is not expected that 

they would exceed the rates calculated for the soil drench or bench spray applications under 

greenhouse conditions, based on the label. Further, the registrant indicated that the bulb 

soaks are mainly for the cut flower trade and BEAD states that pre-plant soaks for plug/liners 

are most frequently used when preparing containers for the retail market, which would result

in negligible environmental exposures.

Soil Drench and Bench Sprays (Potted Ornamentals)

BEAD used the Bonzi II label (0.036 g ai/fluid ounce of product) to calculate application 

rates for bench sprays and soil drenches. The label provides general information about the 

concentration of product to be used in spray or drench scenarios for specific types of plants

(Table 4).

Table 4. Types of ornamentals and recommended concentrations on the Bonzi II label

Plant Type Concentration of Spray 

(ppm)

Concentration of Drench 

(ppm)

Azaleas (florist) 100 to 200 5 to 15

Bedding plants 5 to 90 1

Bedding plant plugs 1 to 20 Not recommended

Bulb crops “least desirable method” 5 to 200

Pot chrysanthemums 50 to 200 1 to 4

Flowering and foliage plants 30 to 50 1 to 2

Geraniums 10 to 30 “make with caution”

Hibiscus 30 to 150 4 

Poinsettias 10 to 30 (15 to 45 in Florida) 2 to 4

Woody landscape plants 100 4
34

For bench spray calculations, plants in containers are placed as closely together as possible 

and two to three quarts of spray volume per 100 ft2 are applied. Four-hundred 6-inch 

diameter containers can be packed onto a 100 ft2 bench (5 ft x 20 ft). Approximately 79 

percent of the applied spray will be deposited in the containers (area of containers 

[400*π*r2

(78.5 ft2) ÷ area sprayed (100 ft2) = 78.53 percent]. This produces an application 

volume per 6-inch container of 0.188 fluid ounces per pot (0.785*3 quarts spray per 100 ft2 * 

32 fluid ounces per quart * 100 ft2 per 400 pots). Similarly, assuming that 224 8-inch 

containers can be placed on a 100 ft2 bench (4 ft x 25 ft), the application volume per 8-inch 

container is 0.337 fluid ounces per pot. Finally, assuming that 88 liner trays may be placed 

on a 100 ft2 bench, the application volume per tray is 1.1 fluid ounces (3 quarts spray per 100 

ft2 * 32 fluid ounces per quart * 100 ft2 per 88 trays). All of the applied spray is assumed to 

be deposited in the tray containers.

For drenches, the label includes a table of volumes based on the size of the container. For 

example, 4 fluid ounces is applied to a 6-inch pot and 10 fluid ounces is applied to an 8-inch 

pot.

To calculate the application rates, assumptions about the most likely pot sizes needed to be 

made. There is considerable variation in the sizes of containers used in ornamental 

productions. For example, a “#1” container, as designated by the American Nursery and 

Landscape Association (ANLA), is specified to contain between 152 and 251 in3 (0.65 to 

1.08 gallons) (ANLA, 2004). Dimensions of a #1 container vary, with top diameters ranging 

from 6 inches to 8 inches. “Azalea pots” contain 132 in3 and typically measure 5’ 7/8” 

(diameter) by 4’ 7/8” (height). The dimensions of propagation liner trays are 18’ 3/8” 

(width) by 9’ 3/16” and contain either 18 (i.e., 3 x 6) or 32 (i.e., 4 x 8) square cavities 

(Nursery Supplies 2011). Approximately 88 trays can be placed on a 100 ft2 bench (6 ft x 16 

and 2/3 ft).

BEAD also characterized the layout and density of pots in a typical nursery setting. 

Nurseries are designed to allow for an orderly movement of plants into and out of areas by 

workers and to allow access for the care of the plants. Yeager and Ingram (2010) describe a 

typical layout as having plant beds that are 8 ft wide, separated by 2 ft walkways. Equipment 

access is provided by a narrow road (10 to 20 ft wide) every 100 ft between the plant beds 

and by a 30 ft wide perimeter road. This layout results in approximately 50 percent of the 

area consisting of plant beds, with the remaining area in service roads and access paths. 

Based on this layout, the highest density possible (“can tight”) of 6-inch containers in the 

plant bed area (50 percent of the total area) is 87,120 containers per acre. If 8-inch 

containers are used instead, the overall density would be about 49,000 containers per acre; 9 

x 18 inch propagation trays yields 19,360 containers per acre.
35

BEAD used the following generic equation to calculate application rates:

(oz spray/container)*(1 gallon spray/128 oz spray)*(oz formulation/gallon spray)*(1 gallon 

formulation/128 oz formulation)*(1 g ai/gallon formulation)*(1 lb ai/453.59 g 

ai)*(containers/A) = lb ai/A

BEAD calculated rates for the following scenarios using the maximum application rate of 

paclobutrazol (200 ppm solution – spray and drench):

6-inch pot (spray application) – (0.188 oz spray/6-inch pot)*(1 gallon spray/128 oz)*(20 oz 

formulation/gallon spray)*(1 gallon formulation/128 oz formulation)*(4.608 g ai/gallon 

formulation)*(1 lb/453.59 g)*(87,120 6-inch pots/A) = 0.20 lb ai/A

6-inch pot (drench) – (4 oz drench/6-inch pot)*(1 gallon drench/128 oz drench)*(20 oz 

formulation/gallon drench)*(1 gallon formulation/128 oz formulation)*(4.608 g/gallon 

formulation)*(1 lb/453.59 g)*(87,120 6-inch pots/A) = 4.3 lb ai/A

8-inch pot (spray) – (0.337 oz spray/8-inch pot)*(1 gallon spray/128 oz spray)*(20 oz 

formulation/gallon spray)*(1 gallon formulation/128 oz formulation)*(4.608 g/gallon 

formulation)*(1 lb/453.59 g)*(49,000 8-inch pots/A) = 0.2 lb ai/A

8-inch pot (drench) – (10 oz drench/8-inch pot)*(1 gallon drench/128 oz drench)*(20 oz 

formulation/gallon drench)*(1 gallon formulation/128 oz formulation)*(4.608 g/gallon 

formulation)*(1 lb/453.59 g)*(49,000 8-inch pots/A) = 6.1 lb ai/A

18-inch by 9-inch propagation trays (spray) – (1.1 oz spray/18-inch by 9-inch tray)*(1 gallon 

spray/128 oz spray)*(20 oz formulation/gallon spray)*(1 gallon formulation/128oz 

formulation)*(4.608 g/gallon formulation)*(1 lb/453.59 g)*(19,360 18-inch by 9-inch 

trays/A) = 0.26 lb ai/A

These are characterized as conservative estimates because of the use of the maximum 

application rate per container and the highest density of containers in the plant beds.

Environmental Fate and Transport

SUMMARY OF ENVIRONMENTAL FATE

Paclobutrazol is a racemic mixture of the (2R, 3R)- and (2S, 3S)-enantiomers, but the 

submitted physiochemical and fate properties of each enantiomer were not investigated in the 

submitted studies. Therefore, it is assumed that each enantiomer of paclobutrazol has similar 

physiochemical and fate properties based on the submitted studies. Paclobutrazol has a low 

solubility (25.9 mg/L) in water. The vapor pressure (1.28 x 10-9 mm Hg at 25.0oC) and 

Henry’s Law Constant (8.09 x 10-10 atm m3/mol) indicate that the compound is relatively 
36

non-volatile under field conditions. The log Kow of 3.2 indicates the potential for this 

chemical to bioaccumulate in aquatic organisms.

Paclobutrazol is stable to hydrolysis and photolysis. Under aerobic conditions, paclobutrazol 

appears to be generally quite persistent in acidic soils, with half-lives greater than 300 days. 

However, in soils with neutral or higher pH, estimated half-lives were as short as 25 days. In 

anaerobic aquatic metabolism studies, paclobutrazol variably partitioned to the sediment and 

degraded with a half-life of more than one year in flood loam and silt loam soils. Since the 

extrapolated half-lives were beyond the duration of the experiment, paclobutrazol was 

considered stable in the anaerobic aquatic system. Paclobutrazol residues were persistent and 

mobile in terrestrial field dissipation studies in California, West Virginia, Florida, North 

Carolina, Illinois, and Mississippi. Half-lives of paclobutrazol residues ranged from 450 to 

950 days for orchard soils in California, West Virginia, and Florida, and 175 to 252 days in 

agricultural soils in Mississippi, North Carolina, and Illinois. The potential mobility of this 

compound is quite variable, ranging from highly mobile to moderately mobile in soil, 

according to the mobility classification of the Food and Agriculture Organization (FAO, 

2000). Two major environmental degradates, ketone analog of parent (CGA 149907, ≤ 

40.0%) and 1H-1,2,4-triazol-3-ol (NOA457654, ≤ 25.1%) were identified in the 

environmental fate and terrestrial field dissipation studies. Based on laboratory and field 

studies, paclobutrazol has the potential to migrate into groundwater via leaching and surface 

water, mainly through runoff. Table 5 summarizes the physiochemical and environmental 

fate and transport properties of paclobutrazol.

Table 5. Summary of physical, chemical, and fate properties of paclobutrazol

Parameter Value Reference Comments

Chemical Paclobutrazol MRID 456625-01 ---

Chemical Class Triazole ---

CAS No. 76738-62-0 ---

Empirical Formula C15H20ClN3O MRID 456625-01 ---

IUPAC (2RS,3RS)-1-(4-

chlorophenyl)-4,4-dimethyl2-(1H-1,2,4-triazol-1-

yl)pentan-3-ol

MRID 456625-01

---

CAS Name (αR,βR)-rel-β-[(4-

chlorophenyl)methyl]-α-

(1,1-dimethylethyl)-1H1,2,4-triazole-1-ethanol

MRID 456625-01

---

Structure MRID 456625-01

---
37

Parameter Value Reference Comments

Selected Physical/Chemical Parameters

Molecular mass 293.8 g/mol MRID 456625-01 ---

Solubility (20.0°C) 25.9 mg/L (water)

2.8 g /L (n-Octanol)

79.8 g/L (methanol)

5.22 g/L (xylene)

MRID 456625-05

MRID 456625-03 ---

Vapor pressure (25.0°C) 1.7 x 10-7 Pa

(1.28 x 10-9 mm Hg)

MRID 456625-05 ---

Henry’s law constant (25°C) 8.2 x 10-7 Pa M3 mol-1

(8.09 x 10-12 atm M3 mol-1)

MRID 456625-05 ---

Octanol-water partition coefficient

(LogKOW) (25°C)

3.18 MRID 456625-05 ---

Persistence

Hydrolysis

pH 4: stable

pH 7: stable

pH 9: stable

MRID 00132698 ---

Aqueous Photolysis (t 1⁄2 ) Stable MRID 00132699 ---

Soil Photolysis (t 1⁄2 ) Stable MRID 40685002 After 33 days 

paclobutrazol decrease 

to 86.4 % of applied 

radioactivity

Aerobic Soil Metabolism 

(t 1⁄2 )

Sandy clay loam

19 (21 and 17) months1,2

[47 (58 and 36) months]

3

MRID 40685003 Major metabolite

(CGA 149907 (≈18.7%)

Sandy clay loam

301 days 

[385 days]

MRID 47338504 Supplemental 

No major metabolites 

detected above 10%.

Sandy loam

26 days4

[75.3 days]

Major metabolites

NOA 457654(25.1%)

CGA 149907(13.3%)

Sandy loam

25 days4

[55.9 days]

Major metabolites

NOA 457654 (20.5%)

CGA 149907(26.3%)

Anaerobic Soil Metabolism No data

Anaerobic Aquatic Metabolism (t 1⁄2 ) Stable MRID 40685003 After a year of 

incubation, 

paclobutrazol decrease 

to ≤79% of applied 

radioactivity 

Major transformation 

product:

(CGA 149907 (≈16.8%)

Aerobic Aquatic Metabolism

No data --

Mobility
38

Parameter Value Reference Comments

Soil Partition Coefficient Adsorption Kd (mL/g)

9.5 (Clay loam)

10.2 (Sandy Clay loam)

7.6 (Silty clay loam)

17.3 (Silt loam)

5

4.1 (sandy loam)

2.4 (loamy sand)

5.8 (Silty clay)

1.4 (Sand)

MRID 40685005 There was no significant 

correlation (r2 = 0.12) 

between Kd and % 

organic carbon. 

Soil Partition Coefficient Desorption Kdes (mL/g)6

15.6 (Clay loam)

18.1 (Sandy Clay loam)

14.0 (Silty clay loam)

34.0 (Silt loam)

5

5.1 (sandy loam)

10.4 (loamy sand)

2.7 (Silty clay)

6.1 (Sand)

MRID 40685005

---

Adsorption Kd (mL/g)

1.7 (Sandy loam) 5

0.8 (Sandy loam)

2.4 (Silty clay loam)

1.8 (Clay loam)

Desorption Kdes (mL/g)6

10.9 (Sandy loam) 5

3.81 (Sandy loam)

2.66 (Silty clay loam)

11.7 (Clay loam)

MRID 47338504 Supplemental

Leaching Aged methine 14C- labeled 

paclobutrazol residues were 

relatively immobile

Aged trizole 14C-labeled 

paclobutrazol residues were 

mobile in loamy sand and 

clay loam soils and low 

mobility in sands and sandy 

loam soils 

MRID 40685004 Major transformation 

product 

CGA 149907 (≈12.6%)

Field Dissipation

Terrestrial Field Dissipation (t 1⁄2 )

450 to 973 days

(CA, WV, FL)

MRID 

40685006-

406850012

Supplemental

Major transformation 

product

CGA 149907

88 days (CA)

133 days (NY) MRID 47338505

Supplemental

Major transformation 

product - CGA 149907 

(40%)
39

Parameter Value Reference Comments 1 Calculated half-lives are based on 14C labeled triazole and methane of paclobutrazol 2 Extrapolated half-lives exceeded beyond the study period except soils with pH > 7.0 3 Italic half-lives are calculated based on paclobutrazol and its major degradates (CGA 149907 and NOA 457654). 

Calculation can be found in Appendix B. 4 High Soil pH (≥ 7.0) may have contributed faster degradation rates for aerobic soil metabolism 

5 Japanese soils, excluded during exposure assessment 6 Reported values are based on second desorption step

a. Degradation

In the terrestrial environment, paclobutrazol appears to be generally quite persistent in acidic 

soils, with half-lives greater than 300 days; however, under certain conditions (soils with 

neutral or higher pH) estimated half-lives are as short as 25 days. Triazole- and methinelabeled paclobutrazol degraded with a half life of more than a year in loam soil (18 acres, pH 

6.6, organic matter 4.6%). By the end of an entire incubation year, 54 percent of triazolelabeled and 50.4 percent of methine-labeled parent were not degraded (MRID 40685003). 

Two transformation products were identified: CGA 149907 (ketone analog of parent) and

1,2,4-triazol. The major degradate of both test substances was CGA 149907 at a maximum 

concentration of 15.0 and 16.8% of the applied. 

The biotransformation of the triazole ring was also studied in three other soils (MRID 

43455801): a sandy clay loam soil (18 acres, pH 5.0, organic matter 4.5%), a sandy loam 

soil (Gartenacker, pH 7.1, organic matter 3.8%), and a sandy loam soil (Pappelacker, pH 7.0, 

organic matter 2.3%). Paclobutrazol degraded with half-lives of 301 days in the 18 acres of 

sandy clay loam soil, 25 days in the Gartenacker sandy loam soil, and 26 days in the 

Pappelacker sandy loam soils. Two transformation products were identified: CGA 149907 

and H-1,2,4-triazol-3-ol (NOA 457654). Both compounds were minor transformation 

products in the 18 acres of sandy clay loam soil, but major products (13.3 to 26. 3%) in the 

Gartenacker and Pappelacker sandy loam soils (Table 5). Up to four unidentified minor 

transformation products were also detected; each accounted for ≤1.8% of the applied. 

In aquatic systems, paclobutrazol is stable to hydrolysis and photolysis (MRIDs 00132698, 

00132699). In anaerobic aquatic metabolism studies, paclobutrazol variably partitioned to 

the sediment. Both triazole and methane labeled paclobutrazol degraded with a half-life of 

more than one year in flood loam and silt loam. The estimations of half-lives of 

paclobutrazol were not calculated because estimates involve extrapolation beyond the 

duration of experiment. At 1 year post treatment, 72.4 percent of triazole-labeled and 60.5 

percent of methine-labeled parent were still present (MRID 40685003). 
40

b. Mobility and Transport

Batch equilibrium studies resulted in adsorption coefficients (Kads) ranging from 0.8 to 17.3

ml/g with a median value of 3.74 ml/g for a wide range of soil textures (MRID 4188113 and 

47338503). Values for Kdes ranged from 2.66 to 34.0 ml/g with a median value of 10.7 ml/g 

(Table 5). Batch equilibrium results indicate that the mobility of paclobutrazol is quite 

variable, ranging from mobile to slightly mobile (FAO, 2000).

Soil column leaching experiments involving aged (9 week) residues of methine-labeled 

paclobutrazol determined that the compound was relatively immobile in 30 cm columns of 

sand, sandy loam, loamy sand, and clay loam soils leached with 66 cm of calcium chloride 

solution over 9 weeks. In contrast, aged residues of triazole-labeled paclobutrazol 

determined the compound to be of low mobility in 30 cm columns of sand and sandy loam 

soils, and mobile in loamy sand and clay loam soils. In all cases, the majority (58.6-90.7 

percent of the applied) of aged residue did not leach out of the upper 10 cm of the treated soil 

columns.

c. Field Studies

Paclobutrazol residues were persistent and mobile in terrestrial field dissipation studies in 

California, West Virginia, Florida, North Carolina, Illinois, and Mississippi (Supplemental 

MRID 00155854, 40685007, 40685009, 40685010, 40685011, 4068512 and 40685006; and 

Pearson, 1985 no MRID). Paclobutrazol residues include paclobutrazol and its ketone 

metabolite. Half-lives of paclobutrazol residues ranged from 450-950 days for orchard soils 

in California, West Virginia, and Florida, and 25 weeks to 36 weeks in agricultural soils in 

Mississippi, North Carolina, and Illinois. Although it was characterized as mobile in some 

soils in laboratory studies, no significant movement of paclobutrazol was detected in the 

agricultural soils. In the orchard studies, paclobutrazol residues (parent plus degradate) were 

detected at 10 percent or less of total applied, in a soil depth of 48 inches in the California 

study, 24 inches in the West Virginia study, and 48 inches in the Florida study. Note that 

these depths are the maximum depths sampled at each study. The CGA149907 metabolite 

was predominately detected in the subsurface soil layers, also at insignificant levels.

d. Degradates

Two major environmental degradates, ketone analog of parent (CGA 149907, ≤ 40.0%) and 

1H-1,2,4-triazol-3-ol (NOA457654, ≤ 25.1%) of paclobutrazol, were identified in the 

environmental fate and terrestrial field dissipation studies. Two minor degradates: CGA 

710191(1H-1,2,4-Triazole) and CGA 142856 (1,2,4-Triazol-1-yl-acetic acid) were also 

detected in environmental fate studies. NOA 457654 as well as these minor metabolites are 

common degradates of many triazole containing fungicides. Structures of major and minor 

degradates formed in various environmental fate studies were provided in Appendix C.
41

Selected environmental fate studies suggest that NOA-457654 is not persistent under aerobic 

soil conditions but highly mobile to mobile (Table 6). The estimated DT50 values for 

NOA457654 of 8.5 days in the 18 acres sandy clay loam soil, 4.0 days in the Gartenacker silt 

loam soil, 10.4 days in the Borstel loamy sand soil, and 3.5 days in the Pappelacker sandy 

loam soil were based on single first-order (SFO) reaction kinetics. Batch equilibrium studies 

resulted in adsorption coefficients (Kads) ranging from 0.13 to 0.30 ml/g with corresponding 

Koc values ranging from 8.1 to 13.0 ml/g (MRID 47338502). Values for Kdes ranged from 

1.0 to 1.8 ml/g with corresponding KOC values ranging from 66.5 to 74.6 ml/g. These results 

indicate that NOA-457654 is highly mobile to mobile according to the mobility classification 

of FAO (2000). The time-dependent sorption of NOA457654 was also investigated in four 

soils. It was determined that the amount of radioactivity recovered in the soil pore water 

decreased constantly over time and ultimately reached amounts that were similar to those 

recovered in the desorption solutions. A rapid decrease in the amount of radioactivity 

recovered during the initial 3 days was likely because complete equilibrium had not been 

achieved, and to the rapid biodegradation of NOA457654 (MRID 47338501).

Table 6. Selected physical, chemical, and fate properties of NOA-457654

Parameter Value Reference Comments

Chemical NOA-457654 MRID 473385-01 ---

Chemical Class Triazole MRID 473385-01 ---

CAS No. 122442-66-4 MRID 473385-01 ---

CAS Name 4H-1,2,4-Triazol-3-ol MRID 473385-01 ---

IUPAC Name 1H-1,2,4-Triazol-3-ol. MRID 473385-01 ---

Synonyms Hydroxytriazole, Triazole 

hydroxy, J7140/45/2

MRID 473385-01 ---

Empirical Formula C2H3N3O MRID 473385-01 ---

Molecular Weight 85.07 g/mole MRID 473385-01 ---

Aerobic Soil Metabolism 

(t 1⁄2 )

Sandy clay loam soil

8.5 days 

MRID 473385-01 No major degradate 

except CO2

Silt loam soil

4.0 days

Loamy sand soil

10.4 days

Sandy loam soil

3.5 days
42

Parameter Value Reference Comments

Soil Partition Coefficient

Adsorption Kads (mL/g)

0.13 (Loamy Sand)

0.25 (Loam)

0.19 (Sandy loam)

0.30 (Sandy loam)

Adsorption KOC (mL/g)

8.9 (Loamy Sand)

10.7 (Loam)

8.1 (Sandy loam)

13.0 (Sandy loam)

MRID 47338502 Calculated r2 value for 

Kads vs. % organic 

carbon content was 

0.93and Kads vs. % clay 

was 0.8

Desorption Kdes (mL/g)

1.0 (Loamy Sand)

1.7 (Loam)

1.5 (Sandy loam)

1.8 (Sandy loam)

Adsorption KOC (mL/g)

72,7 (Loamy Sand)

74.6 (Loam)

72.0 (Sandy loam)

66.5 (Sandy loam)

---

e. Bioaccumulation

The log Kow of 3.2 indicates the potential for paclobutrazol to bioaccumulate in aquatic 

organisms; however, no acceptable bioaccumulation study is available at this time. KABAM 

(KOW (based) Aquatic BioAccumulation Model, Version 1.0) is used to estimate potential 

bioaccumulation of paclobutrazol in freshwater aquatic food webs and subsequent risks to 

mammals and birds via consumption of contaminated aquatic prey. Estimated 

bioconcentration factor (BCF) ranges from 40 to 77 μg/L (Table 12 of Appendix D), and 

suggests that the potential bioaccumulation of paclobutrazol in aquatic species is low. 

Estimated chronic RQ values for mammals and birds consuming fish contaminated by 

paclobutrazol are well below the LOC (Table 16, Appendix D). Model inputs and outputs 

are provided in Appendix D. Detailed model description can be obtained from following 

URL.

http://www.epa.gov/oppefed1/models/water/kabam/kabam_user_guide.html#Section1_1
43

Receptors

EFFECTS TO ORGANISMS

Registrant Submitted Studies for Paclobutrazol

The registrant(s) submitted studies include two fish acute toxicity studies, one acute aquatic 

invertebrate study, a fathead minnow early life-stage study, one avian acute oral toxicity 

study, two avian acute dietary studies, two avian reproduction studies, and one vegetative 

vigor terrestrial plant toxicity study (dicots only). Also submitted were an acute oral rat 

study and a two-generation reproductive rat study. The acute toxicity studies testing fish, 

freshwater invertebrates, and mammals demonstrated that paclobutrazol is slightly toxic to 

these organisms; paclobutrazol is practically non-toxic to birds. The vegetative vigor study 

demonstrated toxicity to dicots, with the tomato as the most sensitive species. 

Open Literature Studies

Open literature studies from the ECOTOX database were reviewed for inclusion in the risk 

assessment. Five open literature papers on paclobutrazol were included in this risk 

assessment: effects to water flea (Daphnia magna), green algae (Selenastrum 

capricornutum), mollusk (Cipangopaludina chinensis), aquatic worm (Limnodrilus 

hoffmeisteri), toad (Bufo bufo gangarizas), predatory mites (Neoseiulus cucumeris and Orius 

insidiosus), and two vascular aquatic plants (Myriophyllum spicatum L. and Hydrilla 

verticillata). All acceptable and non-acceptable papers and rationales of why they were not 

included in the risk assessment are listed in Appendix E.

The paclobutrazol effects data and the values used in the risk assessment and effects 

determination are summarized in the Effects Characterization Section.

INCIDENT DATABASE REVIEW

A review of the Ecological Incident Information System on September 23, 2011 (EIIS, 

version 2.1), which is maintained by the Agency’s Office of Pesticide Programs, the 

Aggregate Summary Module of OPP’s Incident Database, and the Avian Monitoring 

Information System (AIMS), which is maintained by the American Bird Conservancy, 

indicated several incidents associated with the use of paclobutrazol.

According to Office of Pesticides Program Ecological Incident Information System (EIIS), 

the incident (Incident # I016555-001) was reported on 8/22/05 for three dead squirrels in 

Okeechobee County, Florida. Paclobutrazol (formulated product Profile 2SC) was applied 

via soil injection to ornamental and woody plants, a registered use. It was assumed that the 

squirrels had ingested the material after it had been applied; the application rate was not 

specified in the incident report. The incident was listed as “unlikely” to have been caused by 

paclobutrazol. 
44

There were two minor incidents listed in the Aggregate Summary Module of OPP’s Incident 

Database. The formulation, Profile 2SC, was associated with both of them. The first 

incident occurred between 4/1/05 and 6/30/05 and was classified as a minor fish and wildlife 

incident. The second occurrence was between 10/1/09 and 12/31/09 and was classified as a 

minor plant incident. There were no paclobutrazol incidents reported in the AIMS database 

and EFED is unaware of other incidents outside of these three databases.

DATA GAPS IDENTIFIED

The following toxicity data gaps have been identified:

• OPPTS 850.1025- Oyster Acute Toxicity Test

• OPPTS 850.1035- Mysid Acute Toxicity Test

• OPPTS 850.1075- Acute Estuarine/Marine Fish Toxicity Test

• OPPTS 850.1300- Freshwater (Aquatic) Invertebrate Life Cycle

• OPPTS 850.1350- Mysid Chronic Toxicity Test

• OPPTS 850.1400- Estuarine/Marine Fish Early-Life Toxicity Test 

• OPPTS 850.2100- Acute Oral Toxicity Test with a Passerine Species

• OPPTS 850.3020- Honey Bee Acute Contact Toxicity

• OPPTS 850.4225- Seedling Emergence Tier II (ninety percent of the species tested in 

the submitted study exhibited a solvent effect)

• OPPTS 850.4250- Vegetative Vigor Tier II – monocots only (monocots in the 

submitted toxicity study exhibited a solvent effect)

• OPPTS 850.5400- Algal Toxicity – Tiers 1 and 2

ECOSYSTEMS POTENTIALLY AT RISK

The ecosystems at risk are often extensive in scope, and as a result it may not be possible to 

be specific at the screening level. Paclobutrazol is mainly registered for non-food uses (turf, 

ornamental trees, shade trees, greenhouse transplants). It is also registered as a seed 

treatment for tomatoes, peppers, cucurbits, broccoli, cauliflower, and cabbage. In general 

terms, terrestrial ecosystems potentially at risk could include the treated trees/right-of-ways, 
45

golf courses, residences, treated fields, and areas immediately adjacent to these that may 

receive drift or runoff. Areas adjacent to the treated areas could include cultivated fields, 

fencerows and hedgerows, meadows, fallow fields or grasslands, woodlands, riparian habitats 

and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to or downstream from

the treated area and might include impounded bodies such as ponds, lakes and reservoirs, or 

flowing waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also 

includes marine ecosystems and estuaries. 

The previous problem formulation identified the areas with the greatest potential concern for 

effects to non-target organisms to be golf courses, plant nurseries, urban landscape areas, 

residential landscapes, road right-of-ways, and water bodies directly adjacent to treated areas 

that may receive chemical residues via drift and/or runoff. An additional use as a seed 

treatment for tomato, pepper, cucurbit, broccoli, cauliflower, and cabbage was registered 

after the problem formulation was assembled.

For turf uses (golf course, parks, sports fields, etc.), paclobutrazol is applied either as a spray 

or in granular form from a drop spreader at rates ranging from 0.1 to 0.75 lb ai/A. It is 

expected that potential candidate sites for this paclobutrazol use extend to most areas of the 

United States.

Tree applications involve urban environments, utility right-of-ways, residential areas, and 

other non-crop areas. The compound may be applied as a basal drench in a trench 

surrounding the tree trunk-soil intersection, soil injection to a depth of 3 to 6 inches around 

the base of the tree, or direct injection into the tree trunk. Application rates for basal and soil 

injection range from 1 to 4 g ai per inch of diameter at breast height (DBH) and is tree 

species dependent. Tree trunk injections are similar. Given that the pesticide is transported 

through the plant via the xylem, it is presumed that all or some of the applied pesticide will 

reach portions of the treated trees that are considered edible for wildlife. To evaluate the 

potential exposure to wildlife, assumptions of the concentrations of paclobutrazol in tree 

parts (e.g., mature leaves, buds, flowers, or fruits/seeds) following tree treatment will be 

important to the risk assessment. Given that no such data have been provided, a range of 

simplifying assumptions for the concentrations of paclobutrazol in above ground structural 

parts of the tree will be assumed (i.e., concentration in the leaves as a surrogate for other nonwoody food items). It is expected that potential candidate sites for this paclobutrazol use 

extends to most areas of the United States. 

For potted ornamental uses, the pesticide is applied as an indoor or outdoor foliar spray, bulb 

soak, pre-plant plug and liner soak, and indoor soil drench. Labeling does not present the 
46

application rates in terms of pounds of active ingredient per unit area for these uses, but the 

Biological and Economic Analysis Division (BEAD) has calculated rates (described in 

Terrestrial Exposure section) based on the labels’ descriptions (Becker, 2011). The rates 

applied to greenhouse plants may be conservatively used to assess potential exposures in the 

field once plants are transplanted. Such an assessment is accompanied by the conservative 

assumption that 100 percent of the applied pesticide is retained in soils prior to transplant and 

that plants are placed in the field to cover the entirety of the target landscape.

For tomato, pepper, cucurbit, broccoli, cauliflower, and cabbage uses, the labeled use 

involves treatment of the seeds before planting in greenhouses. Specific rates are designated 

for each type of seed. Ecosystems near transplanted peppers, cucurbits, tomatoes, broccoli, 

cauliflower, and cabbage treated with paclobutrazol could be at risk.

Degradates

As discussed in the environmental fate section, paclobutrazol has two major degradates. 

Toxicity information specific to these degradates is not available; consequently, the 

assumption has been made that the degradates are as toxic as the parent, paclobutrazol. 

Conceptual Model

For a chemical to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in 

the environment from a source to an ecological receptor. For an ecological exposure 

pathway to be complete, it must have a source, a release mechanism, an environmental 

transport medium, a point of exposure for ecological receptors, and a feasible route of 

exposure.

The conceptual model (Figures 1 and 2) depicts the potential pathways for ecological risk 

associated with paclobutrazol use. The conceptual model provides an overview of the 

expected exposure routes for organisms within the paclobutrazol action area. For terrestrial 

organisms, the major route of exposure considered is the dietary route; consumption of food 

items such as plant leaves or insects that have paclobutrazol residues as a result of spraying, 

seed treatment, drift, and translocation from soil or plant injection through xylem flow. It is 

important to note that since current screening risk assessment processes for wildlife exposure 

via treated vegetation do not address systemic pesticides, additional risk assessment 

characterization is needed to discuss interplant, and soil to plant transfer. Paclobutrazol 

exposure to wildlife from tree injection, soil drench, root area injection, etc. could explore 

pesticide residues as either a uniform translocation to all above ground biomass, or 

translocation concentrating the material in fruits, seeds, and leaves of vegetation. Either 

approach could be employed to establish co-exposure to herbivorous wildlife. Exposure 

through inhalation is unlikely given paclobutrazol’s low vapor pressure and the results of 
47

EFED’s Screening Tool for Inhalation Risk (STIR v. 1.0). EFED’s Screening Imbibition 

Program (SIP v. 1.0) indicated a potential chronic risk to mammals through the consumption 

of drinking water, but the actual concern for this exposure pathway is low because of 

paclobutrazol’s tendency to adhere to the soil substrate, with only a fraction of it being 

available for leaching (Appendix G). Exposure could occur through guttation water, which 

would primarily be a concern for terrestrial invertebrates.

For aquatic animal species, the major routes of exposure are considered to be via the 

respiratory surface (gills) or the integument.

Direct contact and/or root uptake is the major route of exposure for terrestrial and wetland 

(riparian) plants, while aquatic plants may be exposed via direct uptake and adsorption. 

Estimated exposure concentrations for all organisms are obtained through the use of several 

Agency exposure models.

** Route of exposure includes only ingestion of fish and aquatic invertebrates

Stressor

Source

Receptors

Attribute

Change

Paclobutrazol Applications to Turf, Trees, Ornamentals, Tomatoes, Peppers, 

and Cucurbits

Spray drifta

Aquatic animals

Invertebrates 

Vertebrates

**Piscivorous mammals 

and birds

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae and 

vascular plants

Reduction in prey

Modification of PCEs 

related to prey availability

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Modification of PCEs related to 

habitat

Surface water/

Sediment

Runoffb

Aquatic Animals

Invertebrates

Vertebrates

Exposure

Media

Uptake/gills 

or integument

Ingestion Ingestion

Atmospheric 

transport

Wet/dry deposition

Soil Leaching to

Groundwater

Uptake/gills 

or integument

Aquatic Plants

Non-vascular

Vascular

Uptake/cell, 

roots, leaves Riparian plants

terrestrial 

exposure 

pathways see 

Figure 2

Injection into 

Plantc

Figure 1. Conceptual model for the aquatic effects of paclobutrazol applications. Dotted 

lines indicate the pathway is not expected to be significant. aNot expected for tree injection, 

soil injection, greenhouse soil drench, or seed treatments. bNot expected for tree injection. c

Injection to plant will require an estimate of translocation to edible portions of the plant.
48

Stressor

Source

Attribute

Change

Paclobutrazol Applications to Turf, Trees, Ornamentals, Tomatoes, Peppers, 

and Cucurbits

Direct

application Spray drift

Terrestrial 

vertebrates

Terrestrial 

Inverts

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey and food

Modification of PCEs 

related to prey availability

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Modification of PCEs related

to habitat

Terrestrial plants

grasses/forbs, fruit, seeds 

(trees, shrubs)

Runoff

Terrestrial 

vertebrates 

Exposure Media 

& Receptors Soil

Ingestion

Ingestion

Dermal uptake/Ingestion

Atmospheric 

transport

Root uptake/contact

Wet/dry deposition

Ingestion

Leaching to

Groundwater Irrigation 

water

Figure 2. Conceptual model for the terrestrial effects of paclobutrazol applications.

Risk Hypothesis

For paclobutrazol, the following ecological risk hypotheses are being tested in the risk 

assessment: 

Terrestrial Environment

• Exposure to paclobutrazol residues on insects, seeds, foliage, and other plant parts

from direct deposition, tree injection, seed treatment, or spray drift from labeled use 

of the pesticide has the potential to cause reduced survival, growth and reproduction 

to terrestrial vertebrates (birds, mammals, reptiles, terrestrial-phase amphibians) and 

terrestrial invertebrates.

• Exposure to paclobutrazol residues on foliage, roots, or other plant parts from spray 

drift alone or from runoff from labeled use of the pesticide has the potential to result 

in reduced survival and biomass to upland plants and riparian/wetland plants in areas 

adjacent to a treated area. 
49

Aquatic Environment

• Exposure to paclobutrazol residues in water from spray drift, soil drenches/injections, 

or runoff from labeled uses of the herbicide has the potential to cause reduced 

survival, growth and reproduction to aquatic invertebrates and fish in surface waters 

adjacent to a treated area.

• Exposure to paclobutrazol residues in water from spray drift, soil drenches/injections,

or runoff from labeled uses of the pesticide has the potential to cause reduced survival 

and biomass to aquatic vascular and non-vascular plants in surface waters adjacent to 

a treated area.

Analysis Plan

In registration review, pesticide ecological risk assessments will follow the Agency’s 

Guidelines for Ecological Risk Assessment and will be in compliance with the paper titled 

“Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs, 

U.S. Environmental Protection Agency” (US EPA, 2004).

The focus of an ecological risk assessment is on both the toxic effects of a pesticide to nontarget organisms and the potential routes of the pesticide’s exposure to non-target organisms. 

In addition to addressing a pesticide’s toxic effects and potential routes of exposure, an 

ecological risk assessment addresses the uncertainties associated with a pesticide’s risk to 

non-target organisms.

MEASURES TO EVALUATE THE RISK HYPOTHESIS AND CONCEPTUAL MODEL

Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of paclobutrazol using maximum labeled application 

rates and methods of application. The models used to predict aquatic EECs are the PRZM

[Pesticide Root Zone Model (PRZM v3.12.2)] and EXAMS [EXposure Analysis Modeling 

System (v2.98.4.6)] models. The model used to predict terrestrial EECs on food items is TREX [Terrestrial Residue Exposure Model version 1.4.1 (Oct. 9, 2008)]. The model used to 

derive EECs relevant to terrestrial and wetland plants is TerrPlant [Version 1.2.2 (10/29/09)].

MEASURES OF EFFECT

Data identified in the Effects Characterization Section are used as measures of effect for 

direct and indirect effects to non-target organisms. Data were obtained from registrant 

submitted studies or from open literature studies identified by ECOTOX. The 

ECOTOXicology database (ECOTOX) was searched to provide more ecological effects data 

and to bridge existing data gaps. ECOTOX is a source for locating single chemical toxicity 

data for aquatic life, terrestrial plants, and wildlife and is maintained by the USEPA, Office 
50

of Research and Development, and the National Health and Environmental Effects Research 

Laboratory's Mid-Continent Ecology Division.

The acute measures of effect used for animals in this screening level assessment are the LD50, 

LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, given all 

at once, that is estimated to cause the death of 50% of the test organisms. LC stands for 

“Lethal Concentration” and LC50 is the concentration of a chemical that is estimated to kill 

50% of the test organisms. EC stands for “Effective Concentration” and the EC50 is the 

concentration of a chemical that is estimated to produce a specific effect in 50% of the test 

organisms. Endpoints for chronic measures of exposure for listed and non-listed animals are 

the NOAEL/NOAEC and NOEC. NOAEL stands for “No Observed-Adverse-Effect-Level” 

and refers to the highest tested dose of a substance that has been reported to have no harmful 

(adverse) effects on test organisms. The NOAEC (i.e., “No-Observed-Adverse-EffectConcentration”) is the highest test concentration at which none of the observed effects were 

statistically different from the control. The NOEC is the No-Observed-EffectsConcentration. For non-listed plants, only acute exposures are assessed (i.e., EC25 for 

terrestrial plants and EC50 for aquatic plants). 

INTEGRATION OF EXPOSURE AND EFFECTS

Risk characterization is the integration of exposure and ecological effects characterization to 

determine the potential ecological risk from agricultural and non-agricultural uses of 

paclobutrazol, and the likelihood of direct and indirect effects to non-target organisms in 

aquatic and terrestrial habitats. The exposure and toxicity effects data are integrated to 

evaluate the risks of adverse ecological effects on non-target species. For the assessment of 

paclobutrazol risks, the risk quotient (RQ) method is used to compare exposure and measured 

toxicity values. EECs are divided by acute and chronic toxicity values. The resulting RQs 

are then compared to the Agency’s levels of concern (LOCs) (US EPA, 2004). 

There is no established acute listed or non-listed LOC for terrestrial invertebrates. The LOCs 

currently in use for birds, mammals and aquatic species are based on 1975 regulations for the 

enforcement of FIFRA (40 CFR Part 154: 49005; 49007; 49016). Refer to Appendix H for 

addition information on the LOCs.

ANALYSIS OF CO-OCCURANCE OF FEDERALLY LISTED SPECIES WITH PACLOBUTRAZOL

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the

Agency will evaluate risks to federally-listed threatened and/or endangered (listed) species 

from registered uses of paclobutrazol. This assessment will be conducted in accordance with 

the Overview Document (US EPA, 2004), provisions of the ESA, and the Services’ 

Endangered Species Consultation Handbook (U.S. FWS/NMFS, 1998).
51

In the case of a nationwide risk assessment conducted under Registration Review, the action 

area will encompass the entire U.S. and its territories to ensure that the initial area of 

consideration encompasses all areas where the pesticide may be used now and in the future, 

including the potential for off-site transport via spray drift and downstream dilution. 

Additionally, the concept of a nationwide action area takes into account the potential for 

direct and indirect effects and any potential modification to critical habitat based on 

ecological effect measures associated with reduction in survival, growth, and reproduction, as 

well as the full suite of sub-lethal effects available in the effects literature. 

It is important to note that the nationwide action area does not imply that direct and/or 

indirect effects and critical habitat modification are expected to or are likely to occur over the 

full extent of the action area, but rather to identify all listed species and critical habitat that 

may potentially be affected by the action. The Agency will use more rigorous analysis 

including consideration of available land cover data, toxicity data, and exposure information 

to determine areas where individual listed species and designated critical habitat may be 

affected or modified via endpoints associated with reduced survival, growth, or reproduction. 

The Information Management System (IMS), a work product of the industry-based FIFRA 

Endangered Species Task Force (FESTF) will be used to evaluate the co-occurrence of listed 

species and critical habitat within the paclobutrazol action area. FESTF was formed to fulfill 

data requirements relative to species/pesticide use proximity. 
52

Exposure Assessment

Aquatic Exposure Assessment

Monitoring Data

Paclobutrazol is not included as one of the analytes monitored in the U.S. surface and 

groundwater under the USGS’s National Water Quality Assessment (NAWQA) program. 

There were no available monitoring data at the time of this assessment (January 2012).

Aquatic Exposure Modeling

Screening-level surface water exposures for aquatic risk assessment were conducted for all of

the registered uses except seed treatments. It is assumed that aquatic exposure from 

paclobutrazol’s agricultural uses would be insignificant since the application rates of seed 

treatments are several orders of magnitude lower than ornamentals and turf uses. Modeled 

application rates represent the maximum use pattern of the proposed label for use on 

ornamentals and turf. The aquatic exposure estimates presented in this assessment were 

based on the use of models because no surface or groundwater monitoring data are available 

for paclobutrazol within the continental U.S. Two major environmental degradates, CGA 

149907 (maximum of 40.4%) and NOA457654 (maximum of 25.1%) were identified in the 

environmental fate and terrestrial field dissipation studies. There are no toxicity data related 

to aquatic species as well as no environmental fate properties for these major degradates to 

exclude any of the degradates listed above. Therefore, a total toxic residue (parent plus 

degradates of concern) approach is included and expected to provide protective exposure 

estimation for aquatic organisms exposed to the major degradates of paclobutrazol. In 

addition, aquatic exposure was also estimated for parent (paclobutrazol) only.

PRZM/EXAMS 

The model Pesticide Root Zone Model (PRZM v3.12.2) linked with EXposure Analysis 

Modeling System (EXAMS v2.98.4.6) via the model shell PRZM/EXAMS (PE v5.0, Nov. 

15, 2006) was run to estimate baseline-level exposures for representative crop scenarios. The 

PRZM model simulates pesticide movement and transformation on and across the 

agricultural field resulting from crop applications. The EXAMS model simulates pesticide 

loading via runoff, erosion, and spray drift assuming a “standard” 1-ha pond, 2-m deep 

(20,000 m3

) with no outlet that borders a 10-ha treated field. Simulations are run for multiple 

(usually 30) years, and the Agency estimates peak and running mean values that are expected 

once every ten years based on the daily values generated during the simulation. The coupled 
53

PE models and users manuals are available from the U.S. Environmental Protection Agency 

Water Models web-page (U.S. EPA, 2011).

Exposure estimates generated using this “standard” pond are intended to represent a wide 

variety of vulnerable water bodies that occur at the top of watersheds including prairie pot 

holes, playa lakes, wetlands, vernal pools, man-made and natural ponds, and intermittent and 

first-order streams. As a group, there are factors that make these water bodies more or less 

vulnerable than the standard surrogate pond. Static water bodies that have larger ratios of 

pesticide-treated drainage area to water body volume would be expected to have higher peak 

EECs than the standard pond. These water bodies will be either smaller in size or have large 

drainage areas. Smaller water bodies have limited storage capacity and thus may overflow 

and carry pesticide in the discharge, whereas the standard pond has no discharge. As 

watershed size increases, it becomes increasingly unlikely that the entire watershed is planted 

with a non-major single crop that is all treated simultaneously with the pesticide. Headwater 

streams can also have peak concentrations higher than the standard pond, but they likely 

persist for only short periods of time and are then carried and dissipated downstream.

Paclobutrazol can be applied as either a spray or as a drench. The Overview of Pesticide Use and 

Usage section described earlier provided various application methods and application rates for 

paclobutrazol. A summary of inputs used to estimate paclobutrazol concentrations in the 

aquatic systems for ecological risk assessment are listed in Table 7.

Table 7. PRZM-EXAMS input parameter values for paclobutrazol

Parameter Value Source Comments

Application Rate 

(lb ai/A)

2.50 lb ai/A (based 

on 59% retention of 

parent in soil 

column)1

0.55 lbs/A (based on 

91% retention of 

parent in soil column

2.0 lbs/A for turf2

Memo from the 

Biological and 

Economic Analysis 

Division (BEAD) (US 

EPA, 2011)

Product Label

Maximum application rate was estimated 

based on information provided by BEAD 

(US EPA 2011) and adjusted with the 

retention of paclobutrazol in a soil 

column leaching study (MRID 40685004)

EPA Reg No. 100-1079

Number of 

Applications

1 (Nursery)

3 (Turf)

Product Label EPA Reg No. 100-1079

Application 

frequency (days)

Drench –None

Foliar-14

Product Label

EPA Reg No. 100-1079
54

Parameter Value Source Comments

Scenarios Ornamentals

CA Ornamentals 

STD

FL Ornamentals 

STD

MI Ornamentals 

STD

NJ Ornamentals 

STD 

OR Ornamentals 

STD 

TN Ornamentals 

STD

Turf

FL Turf STD

PA Turf STD

Selected ornamental scenarios were 

chosen to represent various regions of the 

Continental United States

Application Date Ornamentals–01 

(Mar –Sept) 3

Turf 

FL Turf -15 (FebSept)4

PA Turf 15 (AprSept)5

---

Spray Drift 

Fraction

Drench - 0

Ground foliar-0.1

Model input guidance 

(US EPA, 2010) ---

Application 

Efficiency

Drench- 1.0

Ground Foliar -0.99

Model input guidance 

(US EPA, 2010) ---

Soil Partitioning 

Coefficient (Kd

ml/g)

4.5 MRIDs 4188113 and 

47338503

Mean value 

Aerobic Soil 

Metabolism t1/2

(d)

1003.2 (Total 

residue)6

444.2 (Parent)6

MRIDs 40685003 and

47338504

90th percentile upper confidence bound 

on the mean.

Method of 

Application

Drench

Ground Paclobutrazol labels ---

Spray Drift 

Fractions

0 (drench)

6.4 (ground foliar)

Paclobutrazol labels Model input guidance 

(US EPA, 2010)

Solubility in 

Water (mg/L)

25.9 MRID 456625-05 ---

Aerobic Aquatic 

Metabolism t1/2

(days)

2006.4 (Total 

Residue)

888.4 (Parent)

2X of Aerobic soil 

metabolism half-life

Model input guidance 

(US EPA, 2010)

Hydrolysis t1/2 0 MRID 00132698 Stable to hydrolysis

Aquatic 

Photolysis t1/2

(days)

0 MRID 0013299 Stable to aquatic photolysis
55

Parameter Value Source Comments

1 Example of application rate calculation: 6.1 lbs/A- (6.1lbs/A*0.59) 

 Where

 6.1 lbs/A is application rate for drench application for 8-inch container grown ornamentals (US EPA, 2011)

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

40685004)

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

rate of 2.0 lbs/A due to Tier I model limitation. Model accepts only uniform rate for multiple applications. 3 In absence of application date from the label, model simulations were performed from March to September 

with date of application first of the month

4 In absence of application date in label, model simulations were performed from February to September with 

date of application 15th of the month 5 In absence of application date in label, model simulations were performed from March to September with date 

of application 15th of the month 6 Some of the estimated half-lives (Table 5) are beyond the study period and can be considered as stable. 

However, to use 90th percentile of the degradation rate in the modeling, all estimated half-lives were considered

Aquatic Exposure Modeling Results

The aquatic EECs for the various scenarios and application methods are listed in Table 8. In 

the absence of a specific application schedule for ornamentals and turf, the “MultiRun” 

function of the PE5 model was used to generate EECs for multiple application dates. Table 8

below provides a range of EECs for the parent only, and total toxic residues; Appendix I

provides detailed results. 

Table 8. Range of estimated environmental concentrations (EECs) of total residue

(paclobutrazol plus degradates) and paclobutrazol for surface water

Aquatic 

Exposure

(model)

Use

Scenario 

(modeled rate)

Environmental 

Column

Peak EEC 

(μg/L)

21-Day

EEC (μg/L)

60-Day 

EEC

(μg/L)

Total Toxic Residue (Paclobutrazol plus CGA149907 and NOA457654)

1

Surface Water 

(PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD 

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals 

STD(1app. X 2.50 lbs 

ai/acre)

Water

0.04-13

146-333

198-301

-143-247

52-103

146-258

0.04-13

145-332

197-301

143-256

52-103

145-257

0.04-13

140-331

197-197

142-255

52-103

144-256
56

Aquatic 

Exposure

(model)

Use

Scenario 

(modeled rate)

Environmental 

Column

Peak EEC 

(μg/L)

21-Day

EEC (μg/L)

60-Day 

EEC

(μg/L)

Total Toxic Residue (Paclobutrazol plus CGA149907 and NOA457654)

1

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD 

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1app. X 0.56 lbs 

ai/acre)

0.01-2.8

32-74

44-67

32-57

12-23

32-57

0.01-2.8

32-74

44-67

32-57

12-23

32-57

0.01-2.8

32-73

44-66

32-57

12-23

32-57

Turf

FL Turf STD

PA Turf STD

(3app. [2 app.x 

0.75lbs and 1app x 

0.5lbs ] ai/acre)

39-21

68-35

39-21

68-35

39-21

68-35

Parent Paclobutrazol only2

FL Ornamentals STD 

(1app. X 2.50 lbs 

ai/acre)

Water

187 184 184

PA Turf STD

(3app. [2 app.x 

0.75lbs and 1app x 

0.5lbs ] ai/acre)

51 51 51

1

Total toxic simulation includes two degradates, CGA 149907 and NOA457654) 2

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) 

identified from total toxic residue simulations

The ecological pond modeled with EXAMS is a static water body of fixed volume with no 

outlet. Since paclobutrazol is persistent in aquatic environments and the ecological pond has 

no outlet, there was a modeled accumulation of paclobutrazol in the pond throughout the 30 

year simulation (as shown in Figure 1) for paclobutrazol applied to FL Nursery. Exposure 

endpoints, in this assessment, are based on yearly peak concentrations. In the case of 

persistent compounds, a 1-in-10 year EEC from PRZM/EXAMS does not reflect varying 

meteorological conditions that are expected once every 10 years, since the yearly peaks are 

not independent but are actually correlated to the previous year’s peak concentration. The 

linked PRZM/EXAMS model runs simulate the effect of daily weather on the treated 

agricultural field over a period of thirty years. During this time, pesticide is washed-off of 

the field into the water body by twenty to forty rainfall/runoff events per year. Each new 

addition of pesticide to the water body adds to the pesticide which has arrived earlier either 

through previous runoff events or through spray-drift and begins degrading on the day it 

reaches the water. 
57

Figure 3. PRZM/EXAMS acute EECs for paclobutrazol applied to Florida nursery 

with selected aquatic toxicity assessment endpoints

Terrestrial Exposure

Dietary-Based Paclobutrazol Residue Levels

The Agency uses the T-REX model (v1.4.1, USEPA, Oct. 9, 2008) to estimate the terrestrial 

animal exposure values resulting from possible dietary ingestion of paclobutrazol residues on 

vegetative matter and insects present on non-food and food crops from exposure to 

paclobutrazol. In all screening-level assessments, the organisms are assumed to consume 

100% of their diet as one food type. This model incorporates the Kenaga nomograph, as 

modified by Fletcher et al. (1994), which is based on a large set of actual field residue data. 

The upper limit values from the nomograph represented the 95th percentile of residue values 

from actual field measurements (Hoerger and Kenaga, 1972). The Terrestrial Residue 

Exposure Model version 1.4.1 (T-REX) was employed to estimate (1) EECs for different 

food items for birds and mammals, (2) dose/diet based risk to birds as well as dose based risk 

to mammals, and (3) EECs for small insects were used to estimate risk to terrestrial 

invertebrates from direct contact (Table 9). 

Results of the T-REX v1.4.1 modeling of paclobutrazol residue levels on those dietary food 

items which potentially occur on some treated fields, for mammals, birds4

, and terrestrial 

 4 Birds are also used as a surrogate for reptiles and terrestrial-phase amphibians.
58

invertebrates are provided in Tables 10 – 12. Residue levels for dietary items were 

calculated for the turf, and spray applications to potted ornamentals.

Results include dietary-based values [i.e., milligrams of paclobutrazol per kilogram of diet 

(mg/kg-diet)], and both an upper-bound and mean estimate of these exposure levels. The 

upper-bound values are derived using the upper-bound Kenaga nomogram which used the 

highest of the highest normalized residue values from a number of studies, as a tolerance 

limit approach.

As birds are also used as a surrogate for reptiles and terrestrial-phase amphibians within this 

assessment, it is assumed that dose-based exposure levels for these animals are the same as 

birds (i.e., food ingestion rate per body weight for a bird is the same as for an amphibian and 

reptile). However, reptiles and amphibians have a lower ingestion rate for a given body 

weight than birds (US EPA, 1993). Therefore, the dose-based EECs presented here represent 

an overestimate of exposure for reptiles and amphibians of a given body size.

Table 9. Input parameters for T-REX modeling scenarios

Use Maximum 

Application 

Rate (lb ai/A)

Number of 

Applications 

(Interval 

between 

Applications, 

days)

Source (other 

labels have 

same or lower 

application 

rates)

Other Parameters

Herbaceous 

and 

ornamentals 

(greenhouse)

0.26 (spray) 1 Bonzi II 100-

1079 Foliar half life = 35 days

Avian NOAEC – 453 

mg ai/kg-diet (bobwhite 

quail)

Mammal LD50 = 1336 

mg ai/kg-bw (rat)

Mammal NOEL = 2.5 

mg ai/kg-bw (rat)

Turf 0.75 3 (28)1 Profile 2SC

67690-00022

1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb 

ai/A. A T-REX scenario was run with 3 applications at 0.66 lb ai/A. Risk quotients were 

~12% lower, but none of the exceeding risk quotients were reduced below the level of 

concern. Thus the higher application rate was used for this assessment to ensure that it was 

maximally protective.
59

Table 10. Avian paclobutrazol upper bound EEC values for spray applications to turf 

and potted ornamentals

Feeding Category

Dietarybased EECs 

(mg/kg-food 

item)

Dose-based EECs (mg/kg-bw)

Small

(20 g)

Medium

(100 g) Large

(1000 g)

Profile 2SC on Turf – 3 applications at 0.75 lb ai/A (28 day interval)1

Short grass 342.76 390.37 222.61 99.66

Tall grass 157.10 178.92 102.03 45.68

Broadleaf plants/small 

insects 192.80 219.58 125.22 56.06

Fruits/pods/seeds/large 

insects 21.42 24.40 13.91 6.23

Granivores - 5.42 3.09 1.38

Bonzi II Spray for Potted Ornamentals – 1 application at 0.26 lb ai/A

Short grass 62.40 71.07 40.53 18.14

Tall grass 28.60 32.57 18.57 8.32

Broadleaf plants/small 

insects 35.10 39.98 22.80 10.21

Fruits/pods/seeds/large 

insects 3.90 4.44 2.53 1.13

Granivores - 0.99 0.56 0.25

1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb 

ai/A. A T-REX scenario was run with 3 applications at 0.66 lb ai/A. Risk quotients were 

~12% lower, but none of the exceeding risk quotients were reduced below the level of 

concern. Thus the higher application rate was used for this assessment to ensure that it was 

maximally protective.

Table 11. Mammalian paclobutrazol upper bound EEC values for spray applications to 

turf and potted ornamentals

Feeding Category

Dietarybased EECs 

(mg/kg-food 

item)

Dose-based EECs (mg/kg-bw)

Small

(15 g)

Medium

(135 g) Large

(1000 g)

Profile 2SC on Turf – 3 applications at 0.75 lb ai/A (28 day interval)1

Short grass 342.76 326.80 225.86 52.37

Tall grass 157.10 149.78 103.52 24.00

Broadleaf plants/small 

insects 192.80 183.82 127.05 29.46

Fruits/pods/seeds/large 

insects 21.42 20.42 14.12 3.27

Granivores - 4.54 3.14 0.73

Bonzi II Spray for Potted Ornamentals – 1 application at 0.26 lb ai/A
60

Feeding Category

Dietarybased EECs 

(mg/kg-food 

item)

Dose-based EECs (mg/kg-bw)

Small

(15 g)

Medium

(135 g) Large

(1000 g)

Short grass 62.40 59.49 41.12 9.53

Tall grass 28.60 27.27 18.85 4.37

Broadleaf plants/small 

insects 35.10 33.47 23.13 5.36

Fruits/pods/seeds/large 

insects 3.90 3.72 2.57 0.60

Granivores - 0.83 0.57 0.13

1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb 

ai/A. A T-REX scenario was run with 3 applications at 0.66 lb ai/A. Risk quotients were 

~12% lower, but none of the exceeding risk quotients were reduced below the level of 

concern. Thus the higher application rate was used for this assessment to ensure that it was 

maximally protective.

Table 12. Adult insect foliar spray upper-bound EEC values 

Use EEC (based on arthropod)

(mg/kg-diet) (dose in μg ai/bee*)1

Profile 2SC on Turf

1 app at 0.75 lb ai/A2 101.25 (12.9)

Bonzi II Spray for Potted Ornamentals

1 app at 0.26 lb ai/A 35.10 (4.5)

*Conversion made by multiplying EEC by body weight of adult bee (0.128 g)

1

Based on single app at the highest single application rate because application interval is >5 

days

2

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb 

ai/A. A T-REX scenario was run with 3 applications at 0.66 lb ai/A. Risk quotients were 

~12% lower, but none of the exceeding risk quotients were reduced below the level of 

concern. Thus the higher application rate was used for this assessment to ensure that it was 

maximally protective.

EEC Estimates for Tree Injection, Soil Injection, Tree Drench, and Potted 

Ornamentals (Drench)

T-REX could not be used to calculate EECs for tree injection, basal (tree) drench, and potted 

ornamental drenches. T-REX assumes that the chemical is applied over the tops of the plants 

and that terrestrial organisms are exposed to the chemical via the residues left on plant parts. 

The residues will degrade over time as they are exposed to environmental conditions. For 

injections and drenches, paclobutrazol is taken up into the plant via the roots or direct 

injection into the tree. Terrestrial organisms can still be exposed to paclobutrazol through 

eating leaves or other plant parts, but the chemical is contained within the vegetation 
61

(systemic) rather than on the vegetation’s surface. Therefore, different methods were 

employed to estimate the concentrations of paclobutrazol in plants, based on the application 

method.

Tree Injection, Soil Injection/Tree Drench, and Woody Potted Ornamental Drench Leaf 

Biomass Estimates

An EEC is the concentration of paclobutrazol that is expected to be present in a unit of food. 

Therefore, to calculate an EEC, it is necessary to determine the biomass of the food item and 

the amount of paclobutrazol it is expected to contain. 

For tree injection, soil/injection/tree drenches, and woody potted ornamental drenches, it is 

assumed that paclobutrazol will accumulate in the leaves of the plant (a surrogate for other 

non-woody food items such as fruit). Both hardwoods and softwoods were considered in this 

scenario. Leaf biomass (dry weight) for hardwoods and softwoods were estimated using 

general hardwood and softwood leaf biomass equations from Jenkins et al. (2003). 

General hardwood equation for dry weight (Sollins et al., 1973)

ln leaf biomass (kg) = -3.862 + 1.74*(ln(dbh1

))

For the tree injection and soil injection/tree drench scenario, a diameter at breast height 

(DBH) of 6 inches (15.24 cm) is used. This DBH was selected based on BEAD’s assumption 

that the average sized tree in an acre of urban trees has a DBH of 6 inches (Becker, 2011).

ln leaf biomass (kg) = -3.862 + 0*15.24 + 1.74*(ln(15.241))

ln leaf biomass (kg) = -3.862 + 0 + 4.74

ln leaf biomass (kg) = 0.878

Leaf biomass = e0.878 = 2.4 kg

The correction for bias when converting from ln to arithmetic units = 1.34 (Sollins et al.,

1973). Therefore:

Leaf biomass = 2.4*1.34 = 3.216 kg dry weight

For leaves, 85 percent (mean) of the wet weight is water (USEPA, 1993); therefore, the 

general equation to convert leaf dry weight into wet weight is:

Leaf wet weight = (100% total leaf weight) *(kg of leaf dry weight) / (% leaf dry weight) 

Hardwood leaf wet weight = (100%)*(3.216 kg) / (15%)
62

Hardwood (6-inch DBH) leaf wet weight = 21.44 kg wet weight

A similar calculation is performed for the woody potted ornamental drench scenario; 

however, a DBH of 1 inch (2.54 cm) is assumed because woody potted ornamentals are 

small.

ln leaf biomass (kg) = -3.862 + 0*2.54 + 1.74*(ln(2.541))

ln leaf biomass (kg) = -3.862 + 0 + 1.621

ln leaf biomass (kg) = -2.241

Leaf biomass = e-2.241 = 0.106 kg

The correction for bias when converting from ln to arithmetic units = 1.34 (Sollins et al., 

1973). Therefore:

Leaf biomass = 0.106*1.34 = 0.142 kg dry weight

For leaves, 85 percent of the wet weight is water (USEPA, 1993); therefore, the general 

equation to convert leaf dry weight into wet weight is:

Wet weight = (100% total weight) *(kg of dry weight) / (% dry weight) 

Hardwood leaf wet weight = (100%)*(0.142 kg) / (15%)

Hardwood (1-inch DBH) leaf wet weight = 0.95 kg wet weight

General softwood equation for dry weight (Sollins et al., 1973)

ln leaf biomass (kg) = -2.907 + 0*dbh + 1.674*(ln(dbh1

))

For the tree injection and soil injection/tree drench scenario, a DBH of 6 inches (15.24 cm) is 

used. This DBH was selected based on BEAD’s assumption that the average sized tree in an 

acre of trees has a DBH of 6 inches (Becker, 2011).

ln leaf biomass (kg) = -2.907 + 0*15.24 + 1.674*(ln(15.241))

ln leaf biomass (kg) = -2.907 + 0 + 4.56

ln leaf biomass (kg) = 1.653

Leaf biomass = e1.653 = 5.222 kg

The correction for bias when converting from ln to arithmetic units = 1.34 (Sollins et al.,

1973). Therefore:

Leaf biomass = 5.222*1.34 = 7 kg dry weight
63

For leaves, 85 percent of the wet weight is water (USEPA, 1993); therefore, the general 

equation to convert leaf dry weight into wet weight is:

Wet weight = (100% total weight) *(kg of dry weight) / (% dry weight) 

Softwood leaf wet weight = (100%)*(7 kg) / (15%)

Softwood (6-inch DBH) leaf wet weight = 47 kg wet weight

A similar calculation is performed for the woody potted ornamental drench scenario; 

however, a DBH of 1 inch (2.54 cm) is assumed because woody potted ornamentals are 

small.

ln leaf biomass (kg) = -2.907 + 0*2.54 + 1.674*(ln(2.541

))

ln leaf biomass (kg) = -2.907 + 0 + 1.56

ln leaf biomass (kg) = -1.347

Leaf biomass = e-1.347 = 0.26 kg

The correction for bias when converting from ln to arithmetic units = 1.34 (Sollins et al., 

1973). Therefore:

Leaf biomass = 0.26*1.34 = 0.35 kg dry weight

For leaves, 85 percent of the wet weight is water (USEPA, 1993); therefore, the general 

equation to convert leaf dry weight into wet weight is:

Wet weight = (100% total weight) *(kg of dry weight) / (% dry weight) 

Softwood leaf wet weight = (100%)*(0.35 kg) / (15%)

Softwood (1-inch DBH) leaf wet weight = 2.3 kg wet weight

Table 13. Summary of hardwood and softwood leaf biomass wet weights

6-Inch DBH 

(kg)

1-Inch DBH

(kg)

Hardwood

(wet weight)

21.44 0.95

Softwood 

(wet weight)

47 2.3

Using the information in Table 13, EECs can be calculated for tree injection, soil 

injection/tree drench, and woody potted ornamental drench applications.

Tree Injection
64

Becker (2011) established that the application rate for tree injection or tree drench treatments 

as 0.36 lb ai/A. He made the assumption that on average, there would be 36 trees per acre. 

Thus:

(0.36 lb ai/A) / (36 trees/A) = 0.01 lb ai/tree

Conversion to mg = (0.01 lb ai)*(453592 mg ai/lb) = 4536 mg ai/tree

It is assumed that the entire application of paclobutrazol will accumulate in the leaves (a 

surrogate for other non-woody food items such as seeds) of the tree. To determine the 

dietary concentration (EEC) of paclobutrazol in the leaves of hardwoods and softwoods, the 

paclobutrazol application per tree is divided by the leaf biomass (Table 13).

Hardwoods = (4536 mg ai/tree) / 21.44 kg = 212 mg ai/kg-leaves

Softwoods = (4536 mg ai/tree) / 47 kg = 9.4 mg ai/kg-leaves

The EECs must be adjusted for mammal body weight. The T-REX analysis uses three size 

classes for mammals: 15, 35, and 1000g. According to the T-REX User’s Manual, a 15 g 

mammal consumes 95 percent of its body weight daily, a 35 g mammal consumes 66 percent 

of its body weight daily, and a 1000 g mammal consumes 15 percent of its body weight 

daily. Consequently, the general equation for determining the dose of paclobutrazol received 

per day is:

EEC mg ai/kg-bw = (dietary concentration mg ai/kg-diet)*(body weight consumption kgdiet/kg-bw)

Hardwoods

15 g mammal EEC = (212 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 201 mg ai/kg-bw

35 g mammal EEC = (212 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 140 mg ai/kg-bw

1000 g mammal EEC = (212 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 32 mg ai/kg-bw

Softwoods

15 g mammal EEC = (9.4 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 9 mg ai/kg-bw

35 g mammal EEC = (9.4 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 4.2 mg ai/kg-bw

1000 g mammal EEC = (9.4 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 1.4 mg ai/kg-bw

Soil Injection and Tree Drench Risk

Becker (2011) established that the application rate for tree injection or tree drench treatments 

as 1.9 lb ai/A. He made the assumption that on average, there would be 36 trees per acre. 

Thus:
65

(1.9 lb ai/A) / (36 trees/A) = 0.5 lb ai/tree

Conversion to mg = (0.5 lb ai)*(453592 mg ai/lb) = 22680 mg ai/tree

It is assumed that the entire application of paclobutrazol will accumulate in the leaves (a 

surrogate for other non-woody food items such as fruit) of the tree. To determine the dietary 

concentration (EEC) of paclobutrazol in the leaves of hardwoods and softwoods, the 

paclobutrazol application per tree is divided by the leaf biomass (see Table 13 for values).

Hardwoods = (22680 mg ai/tree) / 21.44 kg = 1058 mg ai/kg-leaves

Softwoods = (22680 mg ai/tree) / 47 kg = 483 mg ai/kg-leaves

The EECs must be adjusted for mammal body weight. The T-REX analysis uses three size 

classes for mammals: 15, 35, and 1000 g. According to the T-REX User’s Manual, a 15 g 

mammal consumes 95 percent of its body weight daily, a 35 g mammal consumes 66 percent 

of its body weight daily, and a 1000 g mammal consumes 15 percent of its body weight 

daily. Consequently, the general equation for determining the dose of paclobutrazol received 

per day is:

EEC mg ai/kg-bw = (dietary concentration mg ai/kg-diet)*(body weight consumption kgdiet/kg-bw)

Hardwoods

15 g mammal EEC = (1058 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 1005 mg ai/kg-bw

35 g mammal EEC = (1058 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 698 mg ai/kg-bw

1000 g mammal EEC = (1058 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 159 mg ai/kg-bw

Softwoods

15 g mammal EEC = (483 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 459 mg ai/kg-bw

35 g mammal EEC = (483 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 319 mg ai/kg-bw

1000 g mammal EEC = (483 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 72 mg ai/kg-bw

Woody Potted Ornamental Drench

Becker (2011) established that the highest application rate for drench applications to potted 

ornamentals is 6.1 lb ai/A. He made the assumption that on average, 49,000 8-inch pots 

would fit into an acre of outdoor storage space at a nursery. Thus:

(6.1 lb ai/A) / (49,000 pots/A) = 0.00012 lb ai/tree
66

Conversion to mg = (0.00012 lb ai)*(453592 mg ai/lb) = 56 mg ai/tree

It is assumed that the entire application of paclobutrazol will accumulate in the leaves (a 

surrogate for other non-woody food items such as flowers) of the tree. To determine the 

dietary concentration (EEC) of paclobutrazol in the leaves of hardwoods and softwoods, the 

paclobutrazol application per tree is divided by the leaf biomass (see Table 13 for values).

Hardwoods = (56 mg ai/tree) / 0.95 kg = 59 mg ai/kg-leaves

Softwoods = (56 mg ai/tree) / 2.3 kg = 24 mg ai/kg-leaves

The EECs must be adjusted for mammal body weight. The T-REX analysis uses three size 

classes for mammals: 15, 35, and 1000 g. According to the T-REX User’s Manual, a 15 g 

mammal consumes 95 percent of its body weight daily, a 35 g mammal consumes 66 percent 

of its body weight daily, and a 1000 g mammal consumes 15 percent of its body weight 

daily. Consequently, the general equation for determining the dose of paclobutrazol received 

per day is:

EEC mg ai/kg-bw = (dietary concentration mg ai/kg-diet)*(body weight consumption kgdiet/kg-bw)

Hardwoods

15 g mammal EEC = (59 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 56 mg ai/kg-bw

35 g mammal EEC = (59 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 39 mg ai/kg-bw

1000 g mammal EEC = (59 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 9 mg ai/kg-bw

Softwoods

15 g mammal EEC = (24 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 23 mg ai/kg-bw

35 g mammal EEC = (24 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 16 mg ai/kg-bw

1000 g mammal EEC = (24 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 3.6 mg ai/kg-bw

Non-Woody Potted Ornamental Drench Applications

Leaf biomass equations were not available for non-woody plants. Therefore, the assumption 

was made that the entire application of paclobutrazol would concentrate in the plant. 

Becker (2011)’s 6.1 lb ai/A was used to calculate the concentration (EEC) of paclobutrazol 

per plant. 49,000 8-inch pots are expected to fit into an acre of storage area at a typical 

nursery. Thus,

(6.1 lb ai/A) / 49,000 = 0.0012 lb ai/plant
67

Conversion to mg = (0.00012 lb ai)*(453592 mg ai/lb) = 56 mg ai/plant

It is assumed that the entire application of paclobutrazol will accumulate in the plant and that 

the average weight of a plant is 0.5 kg. Thus, to calculate the dietary concentration (EEC) of 

paclobutrazol in a plant, the paclobutrazol application per plant is divided by its weight (0.5 

kg).

(56 mg ai/plant) / 0.5 kg = 112 mg ai/kg-plant

The EECs must be adjusted for mammal body weight. The T-REX analysis uses three size 

classes for mammals: 15, 35, and 1000 g. According to the T-REX User’s Manual, a 15 g 

mammal consumes 95 percent of its body weight daily, a 35 g mammal consumes 66 percent 

of its body weight daily, and a 1000 g mammal consumes 15 percent of its body weight 

daily. Consequently, the general equation for determining the dose of paclobutrazol received 

per day is:

EEC mg ai/kg-bw = (dietary concentration mg ai/kg-diet)*(body weight consumption kgdiet/kg-bw)

15 g mammal EEC = (112 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 106 mg ai/kg-bw

35 g mammal EEC = (112 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 74 mg ai/kg-bw

1000 g mammal EEC = (112 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 17 mg ai/kg-bw

Table 14. Summary of mammalian and avian EECs for tree injection, soil 

injection/tree drench, potted woody ornamental drench, and potted non-woody 

ornamental drench uses

Bird Mammal

Dietary 

(mg ai/kg-plant)

Acute Dose 

(mg ai/kg-bw)

15 g 35 g 1000g

Tree Injection

Hardwood

212 201 140 32

Tree Injection

Softwood

9.4 9 4.2 1.4

Soil 

Injection/Drench

Hardwood

1058 1005 698 159

Soil 

Injection/Drench

Softwood

483 459 319 72

Potted Woody 

Ornamental Drench

59 56 39 9
68

Bird Mammal

Dietary 

(mg ai/kg-plant)

Acute Dose 

(mg ai/kg-bw)

15 g 35 g 1000g

Hardwood

Potted Woody 

Ornamental Drench

Softwood

24 23 16 3.6

Potted Non-Woody 

Ornamental Drench

112 106 74 17

EEC Estimates for Seed Treatment to Tomato, Pepper, Cucurbits, Broccoli, 

Cauliflower, Cabbage

Treated seeds remain in greenhouse settings until they are large enough to be transplanted to 

commercial agricultural fields. To evaluate potential risks to terrestrial species from this use, 

the assumption is being made that the entire treatment of paclobutrazol that was applied to 

the seed before planting is still present in the plant when a bird or mammal might consume it 

in the field. It is not expected that terrestrial organisms would have direct access to the 

treated seed because the seeds are being planted in a greenhouse.

It is assumed that the entire application of paclobutrazol will accumulate in the plant. 

Latimer (1992) reports the average dry weight of a 7-week old tomato transplant as 1120 mg. 

Data specific to cucurbits, peppers, broccoli, cauliflower, and cabbage were not available, so 

the tomato data were used to approximate the weight of these other crops, as well. 

For plants, 80 percent of the wet weight is water (USEPA, 1993); therefore, the general 

equation to convert leaf dry weight into wet weight is:

Wet weight = (100% total weight) *(kg of dry weight) / (% dry weight) 

Transplant wet weight = (100%)*(1120 mg) / (20%)

Transplant = (5600 mg)*(1g / 1000 mg)*(1 kg / 1000 g) = 0.0056 kg wet weight

To calculate the dietary concentration (EEC) of paclobutrazol in a plant, the paclobutrazol 

application per plant is divided by its weight (0.0056 kg). Maximum paclobutrazol 

applications per seed (and thus, per plant) are: tomato – 0.0125 mg ai/seed; cucurbit –

0.0065 mg ai/seed; pepper – 0.016 mg ai/seed. Thus:

Tomato EEC = (0.0125 mg ai/plant) / (0.0056 kg) = 2.2 mg ai/kg-plant

Cucurbit EEC = (0.0065 mg ai/plant) / (0.0056 kg) = 1.2 mg ai/kg-plant

Pepper EEC = (0.016 mg ai/plant) / (0.0056 kg) = 2.9 mg ai/kg-plant
69

Broccoli EEC = (0.002 mg ai/plant) / (0.0056 kg) = 0.36 mg ai/kg-plant

Cauliflower EEC = (0.002 mg ai/plant) / (0.0056 kg) = 0.36 mg ai/kg-plant

Cabbage EEC = (0.002 mg ai/plant) / (0.0056 kg) = 0.36 mg ai/kg-plant

The EECs must be adjusted for mammal body weight. The T-REX analysis uses three size 

classes for mammals: 15, 35, and 1000 g. According to the T-REX User’s Manual, a 15 g 

mammal consumes 95 percent of its body weight daily, a 35 g mammal consumes 66 percent 

of its body weight daily, and a 1000 g mammal consumes 15 percent of its body weight 

daily. Consequently, the general equation for determining the dose of paclobutrazol received 

per day is:

EEC mg ai/kg-bw = (dietary concentration mg ai/kg-diet)*(body weight consumption kgdiet/kg-bw)

Tomato

15 g mammal EEC = (2.2 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 2.1 mg ai/kg-bw

35 g mammal EEC = (2.2 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 1.5 mg ai/kg-bw

1000 g mammal EEC = (2.2 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.33 mg ai/kg-bw

Cucurbit

15 g mammal EEC = (1.2 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 1.1 mg ai/kg-bw

35 g mammal EEC = (1.2 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 0.79 mg ai/kg-bw

1000 g mammal EEC = (1.2 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.18 mg ai/kg-bw

Pepper

15 g mammal EEC = (2.9 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 2.8 mg ai/kg-bw

35 g mammal EEC = (2.9 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 1.9 mg ai/kg-bw

1000 g mammal EEC = (2.9 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.44 mg ai/kg-bw

Broccoli

15 g mammal EEC = (0.36 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 0.34 mg ai/kg-bw

35 g mammal EEC = (0.36 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 0.24 mg ai/kg-bw

1000 g mammal EEC = (0.36 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.05 mg ai/kg-bw

Cauliflower

15 g mammal EEC = (0.36 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 0.34 mg ai/kg-bw

35 g mammal EEC = (0.36 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 0.24 mg ai/kg-bw

1000 g mammal EEC = (0.36 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.05 mg ai/kg-bw
70

Cabbage

15 g mammal EEC = (0.36 mg ai/kg-diet)*(0.95 kg-diet/kg-bw) = 0.34 mg ai/kg-bw

35 g mammal EEC = (0.36 mg ai/kg-diet)*(0.66 kg-diet/kg-bw) = 0.24 mg ai/kg-bw

1000 g mammal EEC = (0.36 mg ai/kg-diet)*(0.15 kg-diet/kg-bw) = 0.05 mg ai/kg-bw

Table 15. Summary of mammalian and avian EECs for seed treatments

Bird Mammal

Dietary 

(mg ai/kg-plant)

Acute Dose 

(mg ai/kg-bw)

15 g 35 g 1000g

Tomato 2.2 2.1 1.5 0.33

Cucurbit 1.2 1.1 0.79 0.18

Pepper 2.9 2.8 1.9 0.44

Broccoli 0.36 0.34 0.24 0.05

Cauliflower 0.36 0.34 0.24 0.05

Cabbage 0.36 0.34 0.24 0.05

Off-Field Terrestrial and Wetland/Riparian Plant Paclobutrazol Exposure 

TerrPlant 1.2.2 (10/29/09) was used as a Tier 1 model for screening level assessments of 

pesticides. The model provides estimates of exposure to terrestrial plants from single 

pesticide applications; however, the model does not consider exposures to plants from 

multiple pesticide applications. TerrPlant derives pesticide EECs in runoff and in spray drift, 

and develops risk quotients for non-listed and listed species of monocots and dicots 

inhabiting dry and semi-aquatic areas. 

Paclobutrazol can be applied a number of different ways, depending on its use. See 

Appendix J for TerrPlant’s input for each scenario.

For turf, it was assumed that the application would take place in situ (i.e. on lawns) via 

ground application. Spray drift is assumed and soil incorporation is expected to be less than 

1 inch. 

For the soil injection/basal drench for ornamental trees, paclobutrazol is injected directly into 

the soil at depths of 3 to 6 inches (soil injection) or can be applied via a drench around the 

base of the tree (basal drench). For the latter, the label stipulates that if there is a risk for 

runoff, the paclobutrazol should be applied via a shallow trench around the base of the tree. 

Clean soil should be used to cover the trench. Based on these application methods, a soil 

incorporation depth of 3-inches and zero spray drift were incorporated into the TerrPlant 

model.
71

For the seed treatments (tomato, pepper, cucurbits, broccoli, cauliflower, cabbage), the label 

implies that seeds are treated in greenhouses with the intention to transplant young plants for 

commercial agriculture. To model this, the assumption has been made that the paclobutrazol 

applied to the seed coat was not absorbed by the seed and is now evenly dispersed in the pot 

of soil. Exposure occurs when the seedling is transplanted into an agricultural field. For this 

scenario, TerrPlant assumed no risk of spray drift and a paclobutrazol incorporation depth of 

3-inches (the depth of a transplant pot).

For the spray and drench treatments to potted ornamentals, plants are treated in a greenhouse 

setting. Many of the varieties listed on the label are commonly planted outdoors as 

ornamentals. For both the spray and drench scenarios, zero spray drift is expected because: 

1) applications take place within greenhouses; and 2) drift is not expected for a drench 

application method.

Tree injections were not modeled because paclobutrazol is injected directly into the plant and 

there is no opportunity for exposure via runoff or spray drift.

The estimated exposure concentrations of paclobutrazol for terrestrial plants are presented 

below (Table 16). The most protective application scenarios for each use were selected, 

based on information from the label. 

Table 16. Terrestrial plant exposure concentration estimates for paclobutrazol

Description Equation EEC (lb ai/A)

Profile 2SC on Turf – 1 ground application at 0.75 lb ai/A

Runoff to dry areas (A/I)*R 0.0055

Runoff to semi-aquatic areas (A/I)*R*10 0.055

Spray drift A*D 0.0055

Total for dry areas ((A/I)*R)+(A*D) 0.011

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.0605

Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees – 1 application at 3 

inches deep at 1.9 lb ai/A

Runoff to dry areas (A/I)*R 0.012666667

Runoff to semi-aquatic areas (A/I)*R*10 0.126666667

Total for dry areas ((A/I)*R)+(A*D) 0.012666667

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.126666667

Paclobutrazol 2SC Seed Treatment for Cucurbits – 1 application at 3 inches deep at 

0.00029 lb ai/A

Runoff to dry areas (A/I)*R 0.0000019

Runoff to semi-aquatic areas (A/I)*R*10 0.000019

Total for dry areas ((A/I)*R)+(A*D) 0.0000019

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000019
72

Description Equation EEC (lb ai/A)

Paclobutrazol 2SC Seed Treatment for Pepper – 1 application at 3 inches deep at 0.00079 

lb ai/A

Runoff to dry areas (A/I)*R 0.0000053

Runoff to semi-aquatic areas (A/I)*R*10 0.000053

Total for dry areas ((A/I)*R)+(A*D) 0.0000053

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000053

Paclobutrazol 2SC Seed Treatment for Tomato – 1 application at 3 inches deep at 0.00040 

lb ai/A

Runoff to dry areas (A/I)*R 0.0000027

Runoff to semi-aquatic areas (A/I)*R*10 0.000027

Total for dry areas ((A/I)*R)+(A*D) 0.0000027

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000027

Paclobutrazol 2SC Seed Treatment for Broccoli – 1 application at 3 inches deep at 

0.000096 lb ai/A

Runoff to dry areas (A/I)*R 0.00000064

Runoff to semi-aquatic areas (A/I)*R*10 0.0000064

Total for dry areas ((A/I)*R)+(A*D) 0.00000064

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.0000064

Paclobutrazol 2SC Seed Treatment for Cauliflower – 1 application at 3 inches deep at 

0.000064 lb ai/A

Runoff to dry areas (A/I)*R 0.00000043

Runoff to semi-aquatic areas (A/I)*R*10 0.0000043

Total for dry areas ((A/I)*R)+(A*D) 0.00000043

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.0000043

Paclobutrazol 2SC Seed Treatment for Cabbage – 1 application at 3 inches deep at 

0.00012 lb ai/A

Runoff to dry areas (A/I)*R 0.0000008

Runoff to semi-aquatic areas (A/I)*R*10 0.000008

Total for dry areas ((A/I)*R)+(A*D) 0.0000008

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000008

Bonzi II Spray for Potted Ornamentals for Transplant – 1 application at 0.26 lb ai/A

Runoff to dry areas (A/I)*R 0.0052

Runoff to semi-aquatic areas (A/I)*R*10 0.052

Total for dry areas ((A/I)*R)+(A*D) 0.0052

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.052

Bonzi II Drench for Potted Ornamentals for Transplant – 1 application at 6.1 lb ai/A

Runoff to dry areas (A/I)*R 0.122

Runoff to semi-aquatic areas (A/I)*R*10 1.22

Total for dry areas ((A/I)*R)+(A*D) 0.122

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 1.22

A = application rate

I = incorporation
73

Description Equation EEC (lb ai/A)

R = runoff fraction

D = drift fraction
Chapter 3 Effects Characterization

74

Effects Characterization

Several paclobutrazol toxicity studies were submitted by the registrant since the Registration 

Review Revised Paclobutrazol Final Work Plan (US EPA, 2007): fish early-life stage, avian 

reproduction (mallard duck and bobwhite quail), vegetative vigor, and seedling emergence. 

The fish early-life stage and two avian studies were classified as “acceptable” and filled data 

gaps in the ecotoxicological risk picture. The plant studies both exhibited solvent effects and 

only the dicot data from the vegetative vigor were determined to be reliable enough to be 

used in a risk assessment

There were three open literature studies on the effects of paclobutrazol that were used 

quantitatively in this assessment: an acute water flea study, an aquatic vascular plant study 

(hydrilla and Eurasian watermilfoil), and an acute aquatic organisms study (water flea, green 

algae, aquatic tubificid worm, Asiatic toad, and neonate grass carp). In addition, there was a 

predatory mite study that was used qualitatively in this assessment. There were other open 

literature studies and articles referencing paclobutrazol, but these were not included in this 

assessment because toxicity results were less sensitive than registrant submitted data, or the 

information was not appropriate for inclusion for a variety of reasons including the venue 

provided insufficient scientific information to evaluate and validate findings (e.g., abstract, 

review), the doses were not convertible into units used in risk assessment models, or the 

article was not pertinent to toxicity and effects (e.g., analytical methods). Paclobutrazol

results that were found in the open literature and passed the initial screen but which were not 

used in the assessment and the reasons for their exclusion are provided in Appendix E.

Finally, even with the additional information from the open literature, a number of toxicity 

data gaps still remain. These include: estuarine/marine fish and invertebrates (acute and 

chronic), freshwater invertebrate (chronic), seedling emergence (monocot and dicot), 

vegetative vigor (monocot), honeybee (acute contact), and vascular aquatic plants. To 

address each gap, toxicity data were used from other triazoles that were similar in structure to 

paclobutrazol (Appendix F). In situations where paclobutrazol data were available, the 

toxicity values for chemically similar triazoles were compared with the paclobutrazol data. 

There were no consistent patterns of toxicity. Paclobutrazol was the most toxic of the 

triazoles for terrestrial plants, but not the most toxic in other scenarios. No single triazole 

emerged as being consistently toxicologically similar to paclobutrazol, and thus an 

appropriate surrogate in itself. 

Crystal Ball (2000 version 5.0) was used to create a fitted lognormal distribution to the 

surrogate data running a Monte Carlo sampling scheme (10,000 trials). The 5th percentile of 

the data was calculated and used in the risk assessment. Not every triazole had a complete 

set of data, so the chemicals and number of data points varied for each paclobutrazol data 

gap. This approach was chosen as it was thought to be conservative; however, it is possible 
Chapter 3 Effects Characterization

75

that for any given endpoint, the triazole-calculated paclobutrazol surrogate could have 

underestimated the risk. 

Terrestrial Vertebrate Toxicology

Information is available on acute oral dose and dietary-based effects of and chronic toxicity 

of paclobutrazol in birds. Paclobutrazol is classified as practically non-toxic to birds, based 

on the LD50; however a passerine acute oral toxicity study was not available. Reproduction 

studies were conducted for both the mallard duck and the bobwhite quail. The bobwhite 

quail was twice as sensitive to paclobutrazol compared with the mallard duck. The most 

sensitive bobwhite quail toxicity value was adult female body weight gain while the most 

sensitive parameters for the mallard duck were the ratio of live 3-week embryos to viable 

embryos, the ratio of hatchlings to eggs set, the ratio of hatchlings to live 3-week embryos, 

and the ratio of hatchling survivors to eggs set. 

Information is available on the acute oral dose and chronic effects of paclobutrazol on 

mammals. An acute oral toxicity study with rats established LD50 values for both male and 

female rats. Chronic toxicity values were based on increased liver weights and on fatty 

change in the liver of female rats; and increased incidence of chromodacryorrhea and 

thickened eyelids, dental malocclusion, increased liver weights, mottling or accentuation of 

the lobular structure, liver enlargement, pallor and discoloration in male and female pups. 

No information was available on effects of paclobutrazol on reptiles or to terrestrial-phase 

amphibians. Effects and effect levels in birds will be used as a surrogate for reptiles and the 

terrestrial-phase of amphibians in this assessment. Toxicological endpoints selected for 

terrestrial animal assessment endpoints are contained in Table 17. 

Table 17. Summary of specific measurement endpoint values selected to evaluate risk 

for birds and mammal assessment endpoints

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s)

Chemical /

Source /

Study

Classification

Survival and 

Reproduction of 

Birds, Reptiles 

and Amphibians

Mortality: acute oral 

avian LD50

Mallard duck

(Anas 

platyrynchos)

LD50 > 7913 mg/kg-bw Paclobutrazol 

technical grade, % 

purity not reported

MRID 00117484

Acceptable
Chapter 3 Effects Characterization

76

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s)

Chemical /

Source /

Study

Classification

Mortality: subacute 

avian LC50

Mallard duck 

(Anas

platyrhynchos) 

8-day LC50 > 20,000 mg ai/kg-diet 

No mortality, but slight decrease in food 

consumption at 11,000 and 20,000 mg ai/kgdiet.

Paclobutrazol 

technical grade, 

92.4% ai

MRID 00117485 

(mallard)

Acceptable

Mortality: subacute 

avian LC50

Bobwhite quail 

(Colinus 

virginianus)

11-day LC50 > 5000 mg ai/kg-diet

Erratic mortalities were reported, some of 

which were likely from bullying behavior of 

the birds. Other sub-lethal effects that were 

observed were loss of balance, quietness, and 

unsteadiness.

Paclobutrazol 

technical grade, 

92.4% ai

MRID 00117486

Acceptable

Reproduction: 

chronic 

reproduction 

NOAEC

Mallard duck 

(Anas

platyrhynchos) 

NOAEC = 995 mg ai/kg-diet

LOAEC = 3010 mg ai/kg-diet

(10 weeks diet exposure to adults)

The most sensitive parameters were a reduced 

ratio of live 3-week embryos to viable 

embryos, reduced ratio of hatchlings to eggs 

set, reduced ratio of hatchlings to live 3-week 

embryos, and reduced ratio of hatchling 

survivors to eggs set.

Other effects included a reduction in 

hatchability in the 995 and 3010 mg ai/kg-diet 

groups.

Paclobutrazol 

technical grade, 

95.1%

MRID 48270602

Acceptable

Reproduction: 

chronic 

reproduction 

NOAEC

Bobwhite quail 

(Colinus 

virginianus)

NOAEC = 453 mg ai/kg-diet

LOAEC = 888 mg ai/kg-diet

(14 weeks diet exposure to adults)

The most sensitive parameter was a decrease in 

female body weight gain. No other treatmentrelated effects were observed.

Paclobutrazol

technical grade 

95.6% ai

MRID 48270601

Acceptable

Survival and 

Reproduction of 

Mammals

Mortality: acute oral 

LD50

Rat (Rattus 

norvegicus)

Male LD50 = 1954 mg/kg-bw

Female LD50 = 1336 mg/kg-bw

Unsteady gait, loss of righting reflex, 

piloerection, coma, hypothermia, respiratory 

stress, and urinary incontinence appeared after 

1-hour of dosing.

Paclobutrazol 

technical grade, % 

purity not reported

MRID 117478; 

Acc# 248688

Acceptable
Chapter 3 Effects Characterization

77

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s)

Chemical /

Source /

Study

Classification

Reproduction: 

chronic 

reproduction 

NOAEC

Rat (Rattus 

norvegicus)

NOEL = 50 mg/kg-diet (2.5 mg/kg-bw/ day)

LOEL = 250 mg/kg-diet (12.5 mg/kg-bw/ day)

(2 generation reproduction study)

Based on increased liver weights and on fatty 

change in the liver of females; increased 

incidence of chromodacryorrhea and thickened 

eyelids, dental malocclusion, increased liver 

weights, mottling or accentuation of the 

lobular structure, liver enlargement, pallor and 

discoloration in male and female pups.

Paclobutrazol 

technical grade, 

92.4%

MRID 40734303

Acceptable

Effects on Birds

There was one acute avian oral toxicity study with technical grade paclobutrazol (MRID 

00117484). The acute oral LD50 of paclobutrazol was >7913 mg/kg-bw in the mallard duck. 

Only one mortality (7913 mg ai/kg-bw group) was reported during the study, but it was 

attributed to “bullying” rather than as a response to the dosing. No changes in food 

consumption, body weight gain or other effects were observed. 

There were two avian subacute dietary studies with technical grade paclobutrazol. One study 

was conducted with mallard ducks and the other with bobwhite quail. The dietary 8-d5 LC50

value for the bobwhite quail was > 5000 mg ai/kg-diet (MRID 00117486) and the value for 

the mallard duck was > 20,000 mg ai/kg-diet (MRID 00117485). For the mallard dietary 

exposure study, no mortalities were observed, but there was a slight decrease in food 

consumption and weight gain in the 11,000 and 20,000 mg ai/kg-diet groups. The bobwhite 

quail study was extended by 3 days (total of 11 days) because of an erratic dose-response 

curve and a high amount of “bullying” among birds. The bullying behavior was felt to 

contribute to some of the mortalities at different dose levels, but was not thought to be 

induced by the paclobutrazol dosing. However, even when bullied birds were excluded from 

the mortality count, the dose-response curve was still erratic [mortalities: 2 controls (out of 

30), 0 at 554 ppm, 2 at 1007 ppm, 7 at 1830 ppm, 0 at 3328 ppm, 1 at 6050 ppm, 1 at 11,000 

ppm, and 2 at 20,000 ppm]. These results are not in line with the range finding test which 

demonstrated no mortality up to 20,000 ppm. The study also reported “quieting” and loss of 

balance in some birds in the 1007, 1830, and 20,000 ppm. Two “unsteady” birds in groups 

1830 and 20,000 ppm were found dead on days 4 and 9 of the experiment. Given these 

results, and the fact that the LC50 for the mallard duck was so high, it was determined that a 

conservative estimate for the bobwhite quail was LC50 > 5000 mg ai/kg-diet. 

 5 Study duration consists of 5 days exposure plus 3 days post-exposure.
Chapter 3 Effects Characterization

78

There were two chronic reproduction studies with technical grade paclobutrazol. The 

bobwhite quail study yielded a NOAEC of 453 mg ai/kg-diet and a LOAEC of 888 mg ai/kgdiet (MRID 48270601). The values were based on adult female body weight gain; no other 

treatment-related effects were observed. Four mortalities occurred during the experiment 

(two in the control and two in the 900 mg/kg group), but these were attributed to mate 

aggression rather than paclobutrazol. The mallard duck was less sensitive to chronic 

exposures of paclobutrazol with a NOAEC of 995 mg ai/kg-diet and a LOAEC of 3010 mg 

ai/kg-diet (MRID 48270602). A single incidental mortality occurred in the control group and 

two incidental mortalities occurred in the 1000 mg ai/kg treatment group, but they were not 

considered treatment-related (one showed no behavior or physiological signs of problems 

upon necropsy and the other had a prolapsed uterus). There were no treatment-related effects 

observed for any reproductive endpoint at levels up to and including 995 mg ai/kg. There 

were statistically significant reductions in several reproductive ratios at the 3010 mg ai/kg 

diet level: percentage of live 3-week embryos to viable embryos (4% lower than control), 

ratio of hatchlings to eggs set (27% lower than control), ratio of hatchlings to live 3-week 

embryos (26% lower than control), and the ratio of hatchling survivors to eggs set (27% 

lower than control). No statistically significant treatment related effects were observed for 

any other reproductive endpoints, including egg shell thickness or offspring body weights.

Effects on Mammals

An acute oral mammal toxicity study yielded LD50s of 1954 and 1336 mg ai/kg-bw for male 

and female rats, respectively (MRID 00117478). Paclobutrazol was assigned a toxicity class 

of III, based on these data. The study also reported that an unsteady gait, loss of righting 

reflex, piloerection, coma, hypothermia, respiratory stress, and urinary incontinence appeared 

within the first hour after doses were given. A two-generation rat reproduction study yielded 

a NOEL of 2.5 mg ai/kg-bw and a LOEL of 12.5 mg ai/kg-bw. At 250 ppm and above, an 

increased incidence of chromodacryorrhea and thickened eyelids was observed in both 

generations (parents and pups). At 1250 ppm, increases in liver weights were observed in 

females of both generations (23% absolute, 26% relative F0; 7% absolute, 14% relative F1) 

and fatty change in the liver was observed in F0 females (76% versus none of the controls). 

Increased liver weights, mottling or accentuation of the lobular structure, liver enlargement 

and pallor and discoloration were observed in male and female pups from both generations. 

In addition, dental malocclusion was observed in both generations and thickening of the 

urinary bladder wall was observed in one F0 and in three F1 high dose females. 

Terrestrial Invertebrate Toxicology

There were no toxicity data suitable for quantitative use in risk assessments for exposures of 

terrestrial invertebrates to paclobutrazol available. There was one open literature study that 

was classified as “qualitative,” meaning that it provided useful information but did not meet

the requirements for toxicity values to be used quantitatively in the risk assessment. Oetting 
Chapter 3 Effects Characterization

79

and Latimer (1995) conducted a residue exposure study on predatory mites using the 

formulated product, Bonzi (0.4% paclobutrazol). Two species of predatory mites 

(Neoseiulus cucumeris and Orius insidiosus) were exposed to three concentrations of Bonzi 

(40, 80, and 160 ppm). In the first scenario, mites were exposed to “wet” foliage (foliage 

that had just been dipped into a concentration of Bonzi). In the second scenario, mites were 

exposed to foliage that had been allowed to dry for one hour. For both scenarios, mortality 

was recorded at 24 and 48 hours after exposure to the treated foliage. In three instances, 

mortality in the negative control groups was greater than 20 percent (“wet” and “dry” 

scenarios for N. cucumeris, and “wet” scenario for O. insidiosus); thus information from 

these trials is not valid for this risk assessment. For the remaining scenario (“dry” scenario 

for O. insidiosus), the 48-hour NOAEC was determined to be 160 ppm, based on a visual 

inspection of the mortality data reported in the publication. In addition to the high mortality 

rate in three of the control groups, the experiment only used five individuals per replicate 

(compared with 25 individuals per replicate for the guideline honeybee test). Sub-lethal 

effects also were not reported in the study; however, it should not be assumed that such 

effects were not present.

SURROGATE DATA APPROACH

Honey bee toxicity data were collected from triazoles that were similar in structure to 

paclobutrazol. Only non-definitive acute contact LD50 data were available for five triazoles 

(cyproconazole, fenbuconazole, metconazole, triadimefon, triticonazole), thus, it was not 

possible to calculate a toxicity value based on the 5th percentile of data. To fill this data gap, 

the most conservative toxicity value – triticonazole (i.e., the chemical with the lowest nondefinitive value) – was used in the risk assessment (Table 18).

Table 18. Summary of specific measurement endpoint values selected to evaluate risk 

for honey bees

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s) (μg ai/bee)

Chemical /

Source /

Acute Contact 

Toxicity

Mortality: acute 

contact LD50

Honey Bee

(Apis mellifera)

LD50 > 24 Triticonazole

MRID 44802122
Chapter 3 Effects Characterization

80

Aquatic Vertebrate (Fish) Toxicology

Table 19. Summary of specific measurement endpoint values selected to evaluate risk 

for fish and amphibian assessment endpoints

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s) (mg ai/L)

Chemical/

Source /

Study

Classification

Survival and 

reproduction of 

freshwater fish

Acute mortality: 

most sensitive acute 

freshwater fish 48-

hour LC50

Grass carp 

(Ctenopharyngodon 

idellus)

48-hour LC50 = 15.92 Paclobutrazol

MRID 48605402 

Quantitative

Chronic Early Life 

Stage:

most sensitive 

NOAEC

Rainbow trout 

(Salmo gairdneri)

NOAEC = 0.049 Paclobutrazol

MRID 47918901

Acceptable

Survival and 

reproduction of 

estuarine/marine 

fish

Acute mortality: 

most sensitive acute 

estuarine/marine 

fish 48-hour LC50

Sheepshead 

minnow 

(Cyprinodon 

variegatus)

48-hour LC50 = 1.581 Cyproconazole, 

fenbuconazole, 

hexaconazole, 

metconazole, mycobutanil, 

tebuconazole

N/A

N/A

Chronic Early Life 

Stage: most 

sensitive NOAEC

Sheepshead 

minnow 

(Cyprinodon 

variegatus)

NOAEC = 0.0041 Metconazole, 

tebuconazole, triticonazole

N/A

N/A

Survival of 

amphibians

Acute mortality: 

most sensitive acute 

amphibian 96-hour

LC50

Asiatic toad (Bufo 

bufo gangarizas)

96-hr LC50 = 8.9 Paclobutrazol

MRID 48605402

Quantitative3

1

The 5th percentile as calculated from a distribution of data from structurally-similar triazoles. 2 Normally a 96-hour LC50 would be used. The duration of this study was only 48 hours. At 24 hours, the LC50 was 

determined to be 19.1 mg ai/L. It is expected that the toxicity value would have continued to decrease with a longer 

exposure period. Thus, it was determined that the grass carp is more sensitive than rainbow trout (96-hour LC50 = 27.8 mg 

ai/L) and bluegill sunfish (96-hour LC50 = 23.6 mg ai/L) for which registrant-submitted studies are available. 3

Open literature source.

Effects to Freshwater Fish and Aquatic-Phase Amphibians

Information is available for three acute and one chronic toxicity studies of paclobutrazol with

freshwater fish; no studies are available for estuarine/marine fish. One study is available for 

the acute effects to amphibians. Paclobutrazol is classified as slightly toxic to freshwater fish 

and moderately toxic to amphibians on an acute basis. All studies for paclobutrazol were 

completed using the technical grade. 
Chapter 3 Effects Characterization

81

Data are available for acute effects of paclobutrazol to warm and cold water species of 

freshwater fish. There are three acute freshwater fish studies using technical grade 

paclobutrazol. Based on the toxicity data available, paclobutrazol is classified as slightly

toxic to freshwater fish. The 96-hour LC50 values for bluegill sunfish (warm water species) 

and rainbow trout (cold water species) are 23.6 mg ai/L and 27.8 mg ai/L, respectively 

(MRIDs 00117488, 00117487); the 48-hour LC50 for grass carp (warm water species) is 15.9 

mg ai/L (MRID 48605402). The rainbow trout study reported hyperactivity followed by 

keeling and distension of the abdomen. Darkened pigmentation was noted at the 13.5 mg/L 

treatment level and higher. After the 96-hour exposure to paclobutrazol concentrations, fish 

in the 28 and 32 mg/L treatment groups were removed from the test water and placed in 

clean freshwater. Observations continued for a period of 144 hours. After 48 hours, most of 

the fish were no longer showing signs of keeling and distension in their abdomens, although 

pigmentation still remained dark. At 144 hours, one fish in the 32 mg/L group and three in 

the 28 mg/L group were still dark in color, but all others had recovered to a normal physical 

state. The bluegill sunfish test reported quiescence, darkened pigmentation, and loss of 

balance. Darkened pigmentation was reported for all concentrations above and including the 

17.3 mg/L treatment group. 

An open literature study provided acute toxicological information for the grass carp 

(Ctenopharyngodon idellus). Approximately 12 hours after hatching, grass carp were placed 

in solutions of paclobutrazol, including a negative control. LC50 values were calculated at 24 

and 48 hours after exposure; a 96-hour LC50 was not available. Therefore, the LC50 from this 

study may be underestimating toxicity to the grass carp. No sub-lethal effects were reported 

in the study; however, this does not rule out the possibility that sub-lethal effects were 

present.

There is one chronic toxicity study for freshwater fish. The NOAEC and LOAEC for the 

fathead minnow (Pimphales promelas) were established as 0.049 mg ai/L and 0.087 mg ai/L, 

respectively. Growth was the most sensitive endpoint (length and weight). Average length 

at the 0.087 mg ai/L treatment level was 19.7 mm versus 26.1 mm in the control (p < 0.05). 

Likewise, the average dry weight for the 0.087 mg ai/L treatment level was 0.0213 g 

compared with 0.0363 g for the control (p<0.05). Post-hatch larval survival also was 

affected but was less sensitive than the aforementioned growth effects; post-hatch larval 

survival effects were first observed at 0.180 mg ai/L (10% survival versus the control at 75% 

survival).

The amphibian study (MRID 48605402) was conducted with Bufo bufo gangarizas (Asiatic 

toad) tadpoles. Tadpoles less than 3-days old were placed in several different concentrations 

of paclobutrazol. LC50s were calculated at 24, 48, 72, and 96 hours; the 96-hour LC50 was 
Chapter 3 Effects Characterization

82

reported as 8.9 mg ai/L. No sub-lethal effects were reported in the study, however, this does 

not rule out the possibility that sub-lethal effects were present.

Effects to Estuarine-Marine Fish

There were no toxicity data for the effects of paclobutrazol on estuarine/marine fish. 

SURROGATE DATA APPROACH

Toxicity data were collected from triazoles that were similar in structure to paclobutrazol. 

For acute effects to estuarine/marine fish, definitive LC50 data from six triazoles 

(cyproconazole, fenbuconazole, hexaconazole, metconazole, myclobutanil, tebuconazole, 

triticonazole) were available. A surrogate toxicity value for paclobutrazol acute effects on 

estuarine/marine fish was developed based on the 5th percentile of the distribution of data. 

For chronic effects to estuarine/marine fish, definitive NOAEC/NOEC data from three 

triazoles (metconazole, tebuconazole, triticonazole) were available. A surrogate toxicity 

value for paclobutrazol chronic effects on estuarine/marine fish was developed based on the 

5th percentile of the distribution of data.

Aquatic Invertebrate Toxicology

There are five freshwater invertebrate acute toxicity studies; no data were available for 

chronic freshwater invertebrate effects or estuarine-marine acute and chronic effects for 

paclobutrazol. Information is available for three studies conducted with D. magna, an 

aquatic tubificid worm (Limnodrilus hoffmeisteri), and a freshwater mollusk 

(Cipangopaludina chinensis). Paclobutrazol is classified as slightly toxic to highly toxic to 

D. magna, slightly toxic to the aquatic tubificid worm and freshwater mollusk. All the 

studies were conducted with technical grade paclobutrazol. Toxicological endpoints selected 

for freshwater and estuarine-marine assessment endpoints are contained in Table 20. 
Chapter 3 Effects Characterization

83

Table 20. Summary of specific measurement endpoint values selected to evaluate risk 

for aquatic invertebrate assessment endpoints

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s) (mg ai/L)

Chemical/

Source /

Study

Classification

Survival and 

reproduction of 

freshwater 

invertebrates

Acute mortality: 

most sensitive acute 

freshwater 

invertebrate 48-hour

EC50

Water flea (D. 

magna)

1

48-hour EC50 = 0.24

48-hour LOEC = 0.05

Paclobutrazol

MRID 48605401

Quantitative2

Chronic effects: 

most sensitive 

NOAEC

Water flea (D. 

magna)

NOAEC = 0.0093 Cyproconazole, 

fenbuconazole, 

hexaconazole, 

metconazole, 

tebuconazole, 

triadimefon, 

triadimenol, 

triticonazole

N/A

N/A

Survival of 

freshwater 

mollusks

Acute mortality: 

most sensitive acute 

freshwater mollusk

48-hour LC50

Chinese mystery 

snail

(Cipangopaludina 

chinensis)

48-hour LC50 = 12.6 Paclobutrazol

MRID 48605401

Quantitative2

Survival and 

reproduction of 

estuarine/marine 

invertebrates

Acute mortality: 

most sensitive 

estuarine/marine 

invertebrate 48-hour 

EC50/LC50

Eastern oyster 

(Crassostrea 

virginianus)

Mysid shrimp 

(Americamysis 

bahia)

EC50 = 0.243 Cyproconazole, 

fenbuconazole, 

hexaconazole, 

metconazole, 

myclobutanil, 

tebuconazole, 

triticonazole

N/A

N/A

Chronic effects: 

most sensitive 

NOAEC

Mysid shrimp 

(Americamysis 

bahia)

NOAEC = 0.035 Tebuconazole

MRID 42038201

N/A

1

Conducted on the embryo part of the life-stage. 2

Open literature source.

3

The 5th percentile as calculated from a distribution of data from structurally-similar triazoles.

Effects to Freshwater Invertebrates

Information is available for three acute paclobutrazol toxicity studies conducted using D. 

magna. Paclobutrazol is classified as slightly to highly toxic to D. magna on an acute basis. 
Chapter 3 Effects Characterization

84

Two studies using first instar daphnids yielded a 48-hour LC50 of 28.2 mg ai/L and a 48-hour 

EC50 of 33.2 mg ai/L (MRIDs 48605402, 00117489). MRID 00117489 tested five different 

concentrations of paclobutrazol; however, the highest one exhibited precipitate that was 

observed to stick to the daphnids. All test solutions were verified and samples were 

centrifuged before analysis. A number of statistical analyses were performed and it was 

determined that the EC50 calculation was valid, despite being based on four concentrations 

rather than five. This test also established an EC50 (94 mg ai/L) for a formulated product –

GFU 0 29 (50% wettable powder). MRID 48605402 was an open literature study that tested 

daphnia that were less than 25 hours old. Individuals were exposed to five different 

concentrations of paclobutrazol and monitored every 24 hours to detect mortality. No sublethal effects were documented; however, this does not mean that sub-lethal effects did not 

occur.

A third open literature study (MRID48605401) was conducted on neonate and embryo 

daphnia. Toxicity values ranged from 48-hour EC50 = 25.6 mg ai/L (neonate) to 48-hour 

EC50 = 0.24 mg ai/L (embryo). In general, the study followed EPA 850.1010 guidelines; 

however, the guidelines do not usually test daphnia at the embryo stage. For this part of the 

test, embryos were exposed to various concentrations of paclobutrazol and observed daily to 

detect developmental abnormalities and premature death. No sub-lethal effects were reported 

for the neonate study. For the embryo study, malformation of several organs was visible at 

48 hours including: the second antenna, rostrum, malpighian tube, sensory bristles, and tail 

spine. In addition, embryonic development was inhibited at 48 hours and deformed growth 

was noted at 72 hours.

MRID 48605402 also derived acute toxicity values for the Chinese mystery snail 

(Cipangopaludina chinensis) and an aquatic tubificid worm (Limnodrilus hoffmeisteri). As 

with the daphnid study, Chinese mystery snails (average weight - 2.06 g) and aquatic 

tubificid worms (average length – 13.7 mm) were subjected to five different paclobutrazol 

concentrations, including a control. The 48-hour LC50 for the Chinese mystery snail was 

12.6 mg ai/L and the 48-hour LC50 for the aquatic tubificid worm was 49.9 mg ai/L. Toxicity 

values for the aquatic tubificid worm were calculated at the 72 and 96 hour marks as well. 

These values were lower than the 48 hour value (72-hour LC50 = 41.5 mg ai/L and 96-hour 

LC50 = 34.9 mg ai/L); however, the aquatic models used to generate EECs are sufficiently 

conservative making it overly conservative to use a 96-hour toxicity value when the norm is 

48 hours. Sub-lethal effects were not reported in the study, but this does not preclude the 

possibility that sub-lethal effects were present.

There were no chronic studies available for freshwater invertebrates.
Chapter 3 Effects Characterization

85

SURROGATE DATA APPROACH

Chronic toxicity data for freshwater invertebrates were collected from triazoles that were 

similar in structure to paclobutrazol. Definitive NOAEC/NOEC data from eight triazoles 

(cyproconazole, fenbuconazole, hexaconazole, metconazole, tebuconazole, triadimefon, 

triadimenol, triticonazole) were available. A surrogate toxicity value for paclobutrazol 

chronic effects on freshwater invertebrates was developed based on the 5th percentile of the 

distribution of data.

Effects to Estuarine-Marine Invertebrates

There are no data for the effects of paclobutrazol on estuarine/marine invertebrates available.

SURROGATE DATA APPROACH

Toxicity data were collected from triazoles that were similar in structure to paclobutrazol. 

For acute effects to estuarine/marine invertebrates, definitive LC50/EC50 data from seven 

triazoles (cyproconazole, fenbuconazole, hexaconazole, metconazole, myclobutanil, 

tebuconazole, triticonazole) were available. A surrogate toxicity value for paclobutrazol 

acute effects on estuarine/marine invertebrates was developed based on the 5th percentile of 

the distribution of data. 

For chronic effects to estuarine/marine invertebrates definitive NOAEC/NOEC data were 

available for only one triazole – tebuconazole. Consequently, tebuconazole’s toxicity value 

was used as a surrogate for paclobutrazol chronic effects on estuarine/marine invertebrates.

Terrestrial Plant Toxicology

Toxicity data involving exposures of terrestrial plants to paclobutrazol are available from a 

registrant submitted study; only dicot vegetative vigor data are available because of 

methodological issues with the other guideline studies. Surrogate data were calculated from 

other structurally-similar triazoles. The available data are described below and summarized 

in Table 21.
Chapter 3 Effects Characterization

86

Table 21. Effects to plants from paclobutrazol

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s) (lb ai/A)

Chemical/

Source /

Study

Classification

Effects to 

terrestrial plants

Vegetative vigor: 

dicot EC25 and 

NOAEC (based on 

shoot length)

Tomato 

(Lycopersicon 

esculentum)

EC25 = 0.032

NOAEC <0.0090

Paclobutrazol

MRID 47918903

Supplemental

Vegetative vigor: 

monocot EC25

Corn (Zea mays), 

onion (Allium 

cepa), ryegrass 

(Lollium perenne), 

wheat (Triticum 

aestivum)

EC25 > 0.097 Metconazole

MRID 46902215

Vegetative vigor: 

monocot NOAEC

N/A NOAEC = 0.0591 Cyproconazole, 

metconazole, 

tebuconazole

N/A

N/A

Effects to 

terrestrial plants

Seedling 

emergence: dicot 

EC25

N/A EC25 = 0.0091 Cyproconazole, 

tebuconazole, 

triticonazole

N/A

N/A

Seedling 

emergence: dicot 

NOAEC

N/A NOAEC = 0.0021 Cyproconazole, 

triticonazole, 

metconazole

N/A

N/A

Seedling 

emergence: 

monocot EC25

Wheat (Triticum 

aestivum)

EC25 > 0.098 Metconazole

MRID 46902214

Seedling 

emergence: 

monocot NOAEC 

N/A NOAEC = 0.0711 Cyproconazole, 

metconazole, 

tebuconazole, 

triticonazole

N/A

N/A

1

The 5th percentile as calculated from a distribution of data from structurally-similar triazoles.
Chapter 3 Effects Characterization

87

The registrant submitted two plant studies (seedling emergence and vegetative vigor) in 

support of registration review for paclobutrazol. Initially, these studies were classified as 

“supplemental” because they were performed with technical grade active ingredient (TGAI)

rather than a formulated product. Subsequently, it was discovered that there was a solvent 

control response in both studies. In the seedling emergence study (MRID 47918902), nine of 

the ten species tested reacted to the solvent. In some species, growth was promoted while in 

others, growth was inhibited. The only species that did not react to the solvent was the 

tomato (Lycopersicon esculentum). Thus, this study was re-classified as “invalid.” For the 

vegetative vigor study (MRID 47918903), three of the four monocots (ryegrass, onion, and 

oat) tested exhibited a growth promotion effect by the solvent; corn was not affected. None 

of the dicots appeared to be affected by the solvent; therefore it was determined that only the 

dicot data were reliable enough to be used in risk assessments. Of the dicots tested, the 

tomato (Lycopersicon esculentum) was the most sensitive with an EC25 of 0.032 lb ai/A and a 

NOAEC of < 0.0090 lb ai/A (based on shoot length).

SURROGATE DATA APPROACH

For seedling emergence, only non-definitive EC25 data were available for monocots. 

Consequently, the most conservative endpoint (metconazole) was used in the risk 

assessment. Definitive monocot NOAEC/NOEC data from four triazoles (cyproconazole, 

metconazole, tebuconazole, triticonazole) were available. A surrogate toxicity value for 

paclobutrazol effects on monocot seedling emergence (NOAEC) was developed based on the 

5th percentile of the distribution of data. 

Definitive dicot EC25 data from three triazoles (cyproconazole, tebuconazole, triticonazole) 

and definitive dicot NOAEC/NOEC data from three triazoles (cyproconazole, metconazole, 

triticonazole) were available. Surrogate toxicity values for paclobutrazol effects on dicot 

seedling emergence were developed based on the 5th percentiles of these two data 

distributions. 

For vegetative vigor, only non-definitive EC25 data were available for monocots. 

Consequently, the most conservative endpoint (metconazole) was used in the risk 

assessment. Definitive monocot NOAEC/NOEC data from three triazoles (cyproconazole, 

metconazole, tebuconazole) were available. A surrogate toxicity value for paclobutrazol 

effects on monocot vegetative vigor was developed based on the 5th percentile of the 

distribution of data.
Chapter 3 Effects Characterization

88

Aquatic Plant Toxicology

Aquatic plant toxicity data (Table 22) are available for paclobutrazol from two open 

literature studies. MRID 48605402 tested the effects of five different concentrations of 

technical grade paclobutrazol on green algae (Selenastrum capricornutum). The EC50 was 

determined by observing which of the five concentrations of paclobutrazol reduced algal 

productivity by 50 percent after 96 hours of exposure. The 96-hour EC50 was determined to 

be 40.8 mg ai/L. A 120-hour EC50 also was reported (32.9 mg ai/L), but was not used in this 

risk assessment because the PRZM/EXAMS peak EEC estimates are conservative making it 

overly conservative to use the more sensitive endpoints obtained from the longer testing 

intervals.

MRID 48637501 examined the effects of paclobutrazol (end use product) on two vascular 

aquatic plants: a dicot – Eurasian watermilfoil (Myriophyllum spicatum L.) and a monocot –

hydrilla (Hydrilla verticillata). 4-inch segments of each plant were exposed to 

concentrations of paclobutrazol for 4 weeks (hydrilla – 0, 75, 375, and 750 μg ai/L; milfoil –

0, 0.75, 7.5, 37, and 75μg ai/L). Measurements were taken at 0, 1, 2, and 4 weeks for: main 

stem length, lateral stem length and number, root length and number, fresh and dry weights, 

and chlorophyll concentration. The NOAEC and LOAEC for hydrilla were <75 μg ai/L and 

75 μg ai/L, based on main stem length and number of lateral stems. The milfoil NOAEC and 

LOAEC were <0.75 μg ai/L and 0.75 μg ai/L, based on main stem length, total stem length 

(main + laterals) and fresh weight. 

In addition, MRID 48637501 examined the amount of time needed for hydrilla and milfoil to 

recover from various paclobutrazol exposure durations. 4-inch apical segments of hydrilla 

and milfoil were exposed to concentrations of paclobutrazol (hydrilla = 750μg ai/L; milfoil = 

75 μg ai/L) for a period of 1, 3, 7, and 14 days. Following the exposure to paclobutrazol, the 

plant segments were rinsed in distilled, autoclave water and the returned to a fresh untreated 

medium for the duration of the experiment. Plants were measured for re-growth at 2, 4, and 

6 weeks following the paclobutrazol exposure period. The results of the study showed that 

hydrilla recovered to untreated stem lengths after a 6 week period, regardless of the initial 

paclobutrazol exposure duration. Milfoil was more sensitive and remained suppressed after 6 

weeks, even when the initial paclobutrazol exposure was only one day. These results 

indicate potential differences in the sensitivities of aquatic vascular monocots and dicots to 

paclobutrazol. 

SURROGATE DATA APPROACH

Acute toxicity data from structurally-similar triazoles were collected for aquatic vascular 

plants. Definitive EC50 data were available for four triazoles (cyproconazole, metconazole, 
Chapter 3 Effects Characterization

89

tebuconazole, triticonazole). A surrogate toxicity value for paclobutrazol effects on aquatic 

vascular plants was developed based on the 5th percentile of the distribution of data.

Table 22. Summary of specific measurement endpoint values selected to calculate risk 

quotient values to evaluate risk for aquatic plant assessment endpoints

Assessment

Endpoint

Measurement

Endpoint

Selected Measurement Endpoint Value and Source

Species Toxicological Endpoint

and Effect(s) (μg ai/L)

Chemical/

Source /

Study

Classification

Survival and 

biomass of 

aquatic vascular 

and non-vascular 

plants

Non-vascular species: the 

most sensitive productivity 

EC50 

Green algae

(Selenastrum 

capricornutum)

96-hour EC50 = 40,800 Paclobutrazol

MRID 48605402

Quantitative1

Vascular species: the 

NOAEC and LOAEC 

based on the most sensitive 

growth parameter 

Freshwater 

Eurasian 

watermilfoil

(Myriophyllum 

spicatum L.)

28-day NOAEC <0.75

28-day LOAEC = 0.75

Most sensitive endpoint was 

main stem length, total stem 

length (main + laterals), and 

fresh weight.

Paclobutrazol

MRID 48637501

Quantitative1

Vascular species: 

endpoints based on 

mortality EC50

Duckweed 

(Lemna gibba)

EC50 = 82 Cyproconazole, 

metconazole, 

tebuconazole, 

triticonazole

1 Open literature source. 

2

The 5th percentile as calculated from a distribution of data from structurally-similar triazoles.
90

Results: Risk Characterization

Risk Estimation

As described in the Paclobutrazol Work Plan, estimates of exposure and ecotoxicity of 

paclobutrazol are integrated using standard risk quotient (RQ) methods to evaluate the 

potential for adverse ecological effects to mammalian, avian, and other non-target species. 

Risk quotient results represent expected direct effects to organisms (i.e. effects from direct 

toxicity to paclobutrazol exposure) in contrast to indirect effects to an organism resulting 

from a modification of a resource such as loss of their prey or habitat.

Direct Effects to Non-Target Terrestrial Vertebrates

DIRECT EFFECTS TO BIRDS, REPTILES, AND (LAND-PHASE) AMPHIBIANS

Chronic risk quotients were calculated for the maximum usage rates of paclobutrazol for turf, 

seed treatments (tomato, pepper, cucurbits, broccoli, cauliflower, cabbage), tree 

injection/drench, potted ornamentals – spray, and potted ornamentals – drench (Tables 23 

and 24). Chronic-based risk quotients were calculated based on a bobwhite quail avian 

reproduction study (MRID 48270601) using technical grade paclobutrazol. Risk quotients 

were not calculated for acute dose-based or acute dietary-based risks because all of the 

toxicity data were non-definitive. Risks from these potential exposure pathways were 

evaluated and discussed in the Risk Description Section.

T-REX was used to calculate chronic dietary risk quotients for turf and spray applications to 

potted ornamentals. For turf, the risk quotients ranged from 0.05 to 0.79 and did not exceed 

the LOC of 1. The spray application for potted ornamentals yielded risk quotients from 0.01 

to 0.14 (Table 23). 

Chronic dietary risk quotients for tree injection, soil injection/drench, potted ornamental 

drench, and seed treatments were based on non-T-REX EEC calculations. Risk quotients for 

tree injection did not exceed the LOC. Risk quotients for soil injection/drench exceeded the 

LOC of 1 for both hardwoods (2.3) and softwoods (1.1). Consequently, there may be a 

chronic dietary risk to birds that consume leaves, fruit, seeds, or other vegetative items for 

this use. None of the other uses (seed treatment, woody and non-woody potted ornamental 

drench) exceeded the LOC; risk quotients ranged from 0.0008 to 0.25 (Table 24).
91

Table 23. Upper bound chronic dietary-based risk quotients for birds derived from TREX for applications of paclobutrazol on turf and potted ornamentals (spray)

Risk Quotients Based on Kenaga Upper 

Bound EEC

Chronic Dietary-Based Risk Quotients

Profile 2SC on Turf – 3 applications at 0.75 lb ai/A (28 day interval)1

Short grass 0.79

Tall grass 0.36

Broadleaf plants/small insects 0.44

Fruits/pods/seeds/lg insects 0.05

Bonzi II Spray for Potted Ornamentals – 1 application at 0.26 lb ai/A

Short grass 0.14

Tall grass 0.07

Broadleaf plants/small insects 0.08

Fruits/pods/seeds/lg insects 0.01

1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb 

ai/A; however, risk quotients did not exceed the LOC even at this higher rate. 

Table 24. Chronic dietary-based risk quotients for birds for tree injection, soil 

injection/drench, potted ornamental drench, and seed treatments (see Appendix K for 

RQ calculations)

Avian Chronic Dietary RQ (mg ai/kg-diet)

Tree injection at 0.36 lb ai/A

Hardwoods 0.47

Softwoods 0.02

Soil injection/drench at 1.9 lb ai/A

Hardwoods 2.3***

Softwoods 1.1***

Woody potted ornamental drench at 6.1 lb ai/A

Hardwoods 0.13

Softwoods 0.05

Non-woody potted ornamental drench at 6.1 lb ai/A

Non-woody plants 0.25

Seed treatments

Tomato <0.01

Cucurbit <0.01

Pepper <0.01

Broccoli <0.01

Cauliflower <0.01

Cabbage <0.01

***Exceeds chronic LOC of 1.
92

DIRECT EFFECTS TO MAMMALS

For mammalian species, acute dose-based risk quotients were calculated for the maximum 

usage rates of paclobutrazol on turf, tree injection/drench, potted ornamentals – spray, and 

potted ornamentals – drench, and seed treatments (Tables 25 and 26). Acute dose-based risk 

quotients were calculated based on the acute oral toxicity study using technical grade 

paclobutrazol with the female rat (MRID 117478, Accession Number 248688) and dosebased EECs were calculated from estimated paclobutrazol residues on dietary items. A 

chronic two-generation rat reproduction study (MRID 40724303), where paclobutrazol was 

mixed into the rat diet, was used to calculate both the dietary- and dosed-based chronic risk 

to mammals (Tables 25 and 26). 

Acute Effects

The highest risk quotients resulted from soil injection/drench applications. Risk quotients 

ranged from 0.07 to 0.34; 15, 35, and 1000 g mammals consuming leaves (leaves were used 

as a surrogate for other non-woody food items) from hardwood trees injected or drenched 

with paclobutrazol may be at risk (LOC of 0.1 for listed species). Small and medium-sized 

mammals consuming leaves from softwoods also exceeded the LOC (0.1). For turf, the acute

dose-based risk quotients ranged from <0.01 to 0.11 and exceeded the acute listed LOC (0.1) 

for 15 and 35 g mammals consuming a diet of short grass. For tree injections, risk quotients 

ranged from 0.001 to 0.07 and did not exceed the LOC. For spray applications to potted 

ornamentals, risk quotients ranged from <0.01 to 0.02 and did not exceed the LOC. Drench 

applications to potted ornamentals (woody and non-woody) yielded risk quotients from 

<0.003 to 0.04 and did not exceed the LOC. For seed treatments, risk quotients ranged from 

0.00005 to 0.001 and did not exceed the LOC. 

Chronic Effects

For turf, the chronic dose-based risk quotients ranged from 0.38 to 59.5 and exceeded the 

LOC of 1. All size classes of mammals were affected (15, 35, and 1000 g) that consumed a 

diet of short grass, tall grass, broadleaf plants, small insects, fruits, pods, seeds, and large 

insects; “granivore” was the only dietary class to not exceed an LOC. The highest risk 

quotients were found in small and medium sized mammals consuming an exclusive diet of 

short grass. Chronic dietary-based risk quotients were exceeded for diets of short grass, tall 

grass, broadleaf plants, and small insects; risk quotients ranged from 0.43 to 6.86.

For spray applications to potted ornamentals, chronic dose-based risk quotients ranged from 

0.07 to 10.8. The LOC of 1 was exceeded for small, medium, and large mammals (15, 35, 

and 1000 g) consuming short grass, tall grass, and broadleaf/small insects. The chronic 

dietary risk quotients ranged from 0.08 to 1.25. An exclusive diet of short grass was the only 

diet to exceed the LOC of 1.
93

For tree injection applications to trees, chronic dose-based risk quotients ranged from 17 to 

37 for hardwoods and 0.73 to 1.6 for softwoods. The LOC of 1 was exceeded for all size 

classes of mammals consuming hardwood leaves (used as a surrogate for other non-woody 

food items) and for the smallest mammal size class (15 g) with a diet of softwood leaves. 

These results indicate that mammals may be at risk from the chronic consumption of leaves 

from paclobutrazol-treated trees.

For soil injection/drench applications to trees, chronic dose-based risk quotients ranged from 

83 to 183 for hardwoods and 38 to 87 for softwoods. The LOC of 1 was exceeded for both 

of the scenarios in small, medium, and large mammal size classes. These results indicate that 

mammals may be at risk from the chronic consumption of leaves of paclobutrazol-treated 

trees.

For drench applications to potted ornamentals, chronic dose-based risk quotients ranged from 

5 to 11 for woody hardwoods, 2 to 4 for woody softwoods, and 9 to 19 for non-woody 

species. The LOC of 1 was exceeded for all of these scenarios in all size classes indicating 

that mammals with diets of non-woody plants or leaves of woody plants may be at risk from 

the chronic consumption of paclobutrazol-treated potted ornamentals. 

For seed treatments to tomato, cucurbit, pepper, broccoli, cauliflower, and cabbage, chronic 

dose-based risk quotients ranged from 0.03 to 0.51. These values do not exceed the LOC of 

1, thus mammals are not expected to be at chronic risk from consuming seed-treated 

transplants in the field.

Table 25. T-REX upper bound risk quotients for mammals for paclobutrazol turf and 

spray applications to potted ornamentals

Risk Quotients 

Based

on Kenaga

Upper Bound EEC

Dose-Based RQs Chronic 

DietaryBased RQs

15 g 35 g 1000 g

Acute Chronic Acute Chronic Acute Chronic

Profile 2SC on Turf – 3 applications at 0.75 lb ai/A (28 day interval)1

Short grass 0.11* 59.5*** 0.10* 50.8*** 0.05 27.2*** 6.86***

Tall grass 0.05 27.3*** 0.04 23.3*** 0.02 12.5*** 3.14***

Broadleaf 

plants/small insects 0.06 33.5*** 0.05 28.6*** 0.03 15.3*** 3.86***

Fruits/pods/seeds/lg 

insects 0.01 3.72*** 0.01 3.18*** <0.01 1.70*** 0.43

Granivores <0.01 0.83 <0.01 0.71 <0.01 0.38 -

Bonzi II Spray for Potted Ornamentals – 1 application at 0.26 lb ai/A

Short grass 0.02 10.8*** 0.02 9.25*** 0.01 4.96*** 1.25***

Tall grass 0.01 4.96*** 0.01 4.24*** <0.01 2.27*** 0.57
94

Risk Quotients 

Based

on Kenaga

Upper Bound EEC

Dose-Based RQs Chronic 

DietaryBased RQs

15 g 35 g 1000 g

Acute Chronic Acute Chronic Acute Chronic

Broadleaf 

plants/small insects 0.01 6.09*** 0.01 5.20*** 0.01 2.79*** 0.70

Fruits/pods/seeds/lg 

insects <0.01 0.68 <0.01 0.58 <0.01 0.31 0.08

Granivores <0.01 0.15 <0.01 0.13 <0.01 0.07 - 1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of 2 lb ai/A by 0.25 lb ai/A. A 

T-REX scenario was run with 3 applications at 0.66 lb ai/A. Risk quotients were ~12% lower, 

but none of the exceeding risk quotients were reduced below the level of concern. Thus the 

higher application rate was used for this assessment to ensure that it was maximally protective.

*Exceeds the acute listed LOC of 0.1

***Exceeds the chronic LOC of 1

Table 26. Risk quotients for mammals for paclobutrazol tree injection, soil 

injection/drench, potted ornamentals drench, and seed treatment applications (see 

Appendix K for RQ calculations)

Mammal Dose-Based RQs

Acute Chronic

15 g 35 g 1000 g 15 g 35 g 1000 g

Tree injection at 0.36 lb ai/A

Hardwoods 0.07 0.06 0.03 37*** 31*** 17***

Softwoods 0.003 0.001 0.001 1.6*** 0.94 0.73

Soil injection/drench at 1.9 lb ai/A

Hardwoods 0.34* 0.29* 0.15* 183*** 157*** 83***

Softwoods 0.16* 0.13* 0.07 87*** 72*** 38***

Woody potted ornamental drench at 6.1 lb ai/A

Hardwoods 0.02 0.02 0.01 11*** 9*** 5***

Softwoods 0.01 0.01 0.003 4*** 4*** 2***

Non-woody potted ornamental drench at 6.1 lb ai/A

Non-woody plants 0.04 0.03 0.02 19*** 17*** 9***

Seed treatments

Tomato 0.0007 0.0006 0.0003 0.38 0.34 0.17

Cucurbit 0.0004 0.0003 0.0002 0.20 0.18 0.09

Pepper 0.001 0.0008 0.0004 0.51 0.43 0.23

Broccoli 0.0001 0.0001 0.00005 0.06 0.05 0.03

Cauliflower 0.0001 0.0001 0.00005 0.06 0.05 0.03

Cabbage 0.0001 0.0001 0.00005 0.06 0.05 0.03

*Exceeds acute listed species LOC of 0.1

***Exceeds chronic LOC of 1
95

Direct Effects to Non-Target Terrestrial Invertebrates

Honeybee toxicity data were not available for paclobutrazol. Consequently, a non-definitive 

toxicity value was used based on other structurally similar chemicals. The risks to terrestrial

insects are discussed in the Risk Description Section of this document. 

Direct Effects to Terrestrial and Wetland/Riparian Plants

TerrPlant was used to model potential runoff and spray drift effects from the different 

paclobutrazol uses (Table 27). The maximum application rates for turf, ornamental tree soil 

injection/basal drench, seed treatment (pepper, cucurbits, tomato, broccoli, cauliflower, 

cabbage), potted ornamentals – spray, and potted ornamentals – drench were used to 

calculate risk quotients for semi-aquatic and upland terrestrial plants. Insufficient data were 

available to calculate risk quotients for non-listed monocots; thus this group will be discussed 

in the Risk Description Section.

For turf, risk quotients ranged from 0.13 to 78.75. LOCs were exceeded for listed monocots 

(semi-aquatic), listed dicots (dry and semi-aquatic), and non-listed dicots (dry and semiaquatic).

For ornamental tree soil injection and basal drench, risk quotients ranged from <0.1 to 63.33. 

LOCs were exceeded for listed monocots (semi-aquatic), listed dicots (dry and semi-aquatic), 

and non-listed dicots (dry and semi-aquatic).

For the seed treatments (cucurbits, pepper, tomato, broccoli, cauliflower, cabbage), risk 

quotients were all <0.1. Consequently, none of the seed treatments exceeded the LOC. 

For the potted ornamentals spray treatment, risk quotients ranged from <0.1 to 26. LOCs 

were exceeded for listed dicots (dry and semi-aquatic) and non-listed dicots (semi-aquatic 

only). 

For the potted ornamentals drench application, risk quotients ranged from <0.1 to 610. Risk 

quotients exceeded the LOC for dry and semi-aquatic monocots (listed) and dicots (listed and 

non-listed).

Table 27. Summary of risk quotient values for plants in dry and semi-aquatic areas 

exposed to paclobutrazol through runoff and/or spray drift

Plant Type Listed Status Dry Semi-Aquatic Spray Drift4

Profile 2SC on Turf – 1 ground application at 0.75 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 0.32 2.22*** 0.13

Dicot non-listed2 2.50*** 17.50*** 0.83
96

Plant Type Listed Status Dry Semi-Aquatic Spray Drift4

Dicot listed3 11.25*** 78.75*** 3.75***

Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees – 1 application 

at 3 inches deep at 1.9 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 0.18 1.78*** N/A

Dicot non-listed2 1.41*** 14.07*** N/A

Dicot listed3 6.33*** 63.33*** N/A

Paclobutrazol 2SC Seed Treatment for Cucurbits – 1 application at 3 inches deep at 

0.00029 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A

Dicot listed3 <0.1 <0.1 N/A

Paclobutrazol 2SC Seed Treatment for Pepper – 1 application at 3 inches deep at 

0.00079 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A

Dicot listed3 <0.1 <0.1 N/A

Paclobutrazol 2SC Seed Treatment for Tomato – 1 application at 3 inches deep at 

0.00040 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A

Dicot listed3 <0.1 <0.1 N/A

Paclobutrazol 2SC Seed Treatment for Broccoli – 1 application at 3 inches deep at 

0.000096 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A

Dicot listed3 <0.1 <0.1 N/A

Paclobutrazol 2SC Seed Treatment for Cauliflower – 1 application at 3 inches deep at 

0.000064 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A

Dicot listed3 <0.1 <0.1 N/A

Paclobutrazol 2SC Seed Treatment for Cabbage – 1 application at 3 inches deep at 

0.000012 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 <0.1 N/A

Dicot non-listed2 <0.1 <0.1 N/A
97

Plant Type Listed Status Dry Semi-Aquatic Spray Drift4

Dicot listed3 <0.1 <0.1 N/A

Bonzi II Spray for Potted Ornamentals for Transplant – 1 application at 0.26 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 <0.1 0.73 N/A

Dicot non-listed2 0.58 5.78*** N/A

Dicot listed3 2.60*** 26.00*** N/A

Bonzi II Drench for Potted Ornamentals for Transplant – 1 application at 6.1 lb ai/A

Monocot non-listed N/A N/A N/A

Monocot listed1 1.72*** 17.18*** N/A

Dicot non-listed2 13.56*** 135.56*** N/A

Dicot listed3 61.00*** 610.00*** N/A

***Exceeds LOC of 1.

1

The vegetative vigor NOAEC used in the risk quotient calculation was based on the 5th

percentile as calculated from a distribution of data from cyproconazole, metconazole, and 

tebuconazole.

2

The seedling emergence EC25 used in the risk quotient calculation was based on the 5th

percentile as calculated from a distribution of data from cyproconazole, tebuconazole, 

and triticonazole.

3

The seedling emergence NOAEC used in the risk quotient calculation was based on the 

5th percentile as calculated from a distribution of data from cyproconazole, triticonazole, 

and metconazole.

4

Spray drift was only a potential exposure route for the turf use.

Direct Effects to Freshwater Fish (Amphibians), Invertebrates and EstuarineMarine Fish (Amphibians) and Invertebrates and Aquatic Plants

Fish, aquatic invertebrates, and aquatic plant risk quotients are calculated using aquatic EECs 

derived as described in the exposure analysis using PRZM/EXAMS in conjunction with 

selected acute and chronic fish and aquatic invertebrate toxicity values. A range of months 

were considered, thus the risk quotients are presented as a range instead of a single value. 

Paclobutrazol is persistent in aquatic environments, thus an accumulation of paclobutrazol

was modeled during the 30 year pond simulations, as described earlier for paclobutrazol

applied to FL Nursery. The calculated risk quotients are based on total toxic residue

exposure from the parent (paclobutrazol) and its major degradates (CGA149907 and 

NOA457654) for the aquatic environment.

Freshwater Fish and Aquatic-Phase Amphibians – Acute Risk

For freshwater fish, acute risk quotients ranged from <0.1 to 0.02 and did not exceed the 

listed species acute LOC of 0.05 for any of the uses. Freshwater aquatic-phase amphibian 

acute risk quotients ranged from <0.01 to 0.04 and also did not exceed the listed acute LOC

of 0.05 for any of the uses (Table 28). 
98

Freshwater Fish and Aquatic-Phase Amphibians – Chronic Risk

For freshwater fish, risk quotients ranged from <0.1 to 6.8 for ornamentals assuming an 

application rate of 2.5 lb ai/A. All but the RQs from the California scenario exceeded the 

LOC of 1. Risk quotients ranged from <0.1 to 1.5 for ornamentals assuming an application 

rate of 0.56 lb ai/A. Depending on the month and application location, the high end risk 

quotients exceeded the LOC of 1. For turf, risk quotients ranged from 0.43 to 1.4 with only 

the high end Pennsylvania scenario exceeding the LOC of 1 (Table 28).

Table 28. Acute and chronic risks from paclobutrazol to freshwater fish and 

amphibians

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Freshwater 

Fish Acute 

RQ (Peak 

EEC/LC50) 

LC50 = 15,900 

μg ai/L

Freshwater 

Fish Chronic 

RQ (60-Day 

EEC/ 

NOAEC) 

NOAEC = 49 

μg ai/L

Freshwater 

Amphibian 

Acute RQ 

(Peak 

EEC/LC50) 

LC50 = 8900 

μg ai/L

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

1

Surface Water 

(Tier 2 

PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.01-<0.01

0.01-0.02

0.01-0.02

<0.01-0.02

<0.01-0.01

0.01-0.02

<0.1-0.26

2.9-6.8***

4.0-6.1***

2.9-5.2***

1.1-2.1***

3.0-5.2***

<0.01-<0.01

0.02-0.04

0.02-0.03

0.02-0.03

0.01-0.01

0.02-0.03

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01

<0.1-0.1

0.65-1.5***

0.90-1.3***

0.65-1.2***

0.24-0.47

0.7-1.2***

<0.01-0<0.01

<0.01-0.01

<0.01-0.01

<0.01-0.01

<0.01-<0.01

<0.01-0.01

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

<0.01-<0.01

<0.01-<0.01

0.43-0.80

0.71-1.4***

<0.01-<0.01

<0.01-0.01

 Parent Paclobutrazol Only2

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

0.01 3.8*** 0.02

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

<0.01 1.0*** 0.01

1

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

2

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified 

from total toxic residue simulations.
99

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Freshwater 

Fish Acute 

RQ (Peak 

EEC/LC50) 

LC50 = 15,900 

μg ai/L

Freshwater 

Fish Chronic 

RQ (60-Day 

EEC/ 

NOAEC) 

NOAEC = 49 

μg ai/L

Freshwater 

Amphibian 

Acute RQ 

(Peak 

EEC/LC50) 

LC50 = 8900 

μg ai/L

***Exceeds chronic LOC (1)

Estuarine/Marine Fish – Acute Risk

For estuarine/marine fish, risk quotients ranged from <0.01 to 0.21 for ornamentals, 

assuming an application rate of 2.5 lb ai/A. Specifically, all but the California scenario and 

the lower bound estimate in the Oregon scenario exceeded the acute listed species LOC of 

0.05. In addition, the upper bound estimate of the 0.56 lb ai/A ornamentals in the Florida

scenario (risk quotient = 0.05) equaled the acute listed species LOC of 0.05. The turf 

scenarios did not yield risk quotients that exceeded the LOC (Table 29).

Estuarine/Marine Fish – Chronic Risk

For estuarine/marine fish, risk quotients ranged from <1 to 83 for the ornamental scenario 

with a 2.5 lb ai/A application rate, <1 to 18 for ornamentals with a 0.56 lb ai/A application 

rate, and 5 to 17 for turf scenarios. All of the risk quotients except some of the California 

scenarios were above the LOC of 1 (Table 29).

Table 29. Acute and chronic risks from paclobutrazol to estuarine/marine fish

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Estuarine / 

Marine Fish 

Acute RQ 

(Peak 

EEC/LC50) 

LC50 = 1580 

μg ai/L1

Estuarine / 

Marine Fish 

Chronic RQ 

(60-Day EEC/ 

NOAEC) 

NOAEC = 4 

μg ai/L2

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

3,4

Surface Water 

(Tier 2 

PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A) Water

<0.01-0.01

0.09-0.21*

0.12-0.19*

0.09-0.16*

0.03-0.07*

0.09-0.16*

<1-3.2***

35-83***

49-75***

36-64***

13-26***

36-64***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.001-0.002

0.02-0.05*

0.03-0.04

0.02-0.04

0.008-0.01

0.02-0.04

<1-0.7

8-18***

11-17***

8-14***

3-6***

8-14***
100

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Estuarine / 

Marine Fish 

Acute RQ 

(Peak 

EEC/LC50) 

LC50 = 1580 

μg ai/L1

Estuarine / 

Marine Fish 

Chronic RQ 

(60-Day EEC/ 

NOAEC) 

NOAEC = 4 

μg ai/L2

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.01-0.02

0.02-0.04

5-10***

9-17***

 Parent Paclobutrazol Only5

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

0.11* 46***

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

0.03 13***

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a 

distribution of data from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, 

and tebuconazole.

2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from 

a distribution of data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs. 4 Total toxic residue simulation includes two metabolites (CGA 149907and NOA 457654) 5

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf 

STD) identified from total toxic residue simulations.

*Exceeds acute listed species LOC (0.05)

***Exceeds chronic LOC (1)

Freshwater Invertebrates – Acute Risk

For freshwater mollusks, risk quotients ranged from <0.01 to 0.03 and did not exceed the 

LOC of 0.05; therefore, acute risks to freshwater mollusks are not anticipated. For 

freshwater invertebrates, the acute LOC of 0.5 (non-listed species) was exceeded for the 2.5 

lb ai/A Florida ornamental, Michigan ornamental, and New Jersey ornamental scenarios. All 

other ornamental and turf scenarios had risk quotients that exceeded the acute listed species

LOC of 0.05 (Table 30).

Freshwater Invertebrates – Chronic Risk

For chronic risk, risk quotients ranged from <0.01 to 37. All but some of the California 

scenarios exceeded the LOC of 1, regardless of the month of application, the application rate, 

or the inclusion of major paclobutrazol degradates (Table 30).

Table 30. Acute and chronic risks from paclobutrazol to freshwater invertebrates

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Freshwater 

Invertebrate 

Acute RQ 

Freshwater 

Invertebrate 

Chronic RQ 

Freshwater 

Mollusk 

Acute RQ 
101

(Peak 

EEC/EC50) 

EC50 = 240 μg 

ai/L

(60-Day EEC/ 

NOAEC) 

NOAEC = 9 

μg ai/L1

(Peak 

EEC/LC50) 

LC50 = 12600 

μg ai/L

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

2,3

Surface Water 

(Tier 2 

PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals 

STD(1 app. X 2.5 lb 

ai/A)

Water

<0.01-0.05*

0.61-1.4**

0.83-1.3**

0.60-1.1**

0.22-0.43*

0.61-1.1**

<0.01-1.4***

16-37***

22-33***

16-28***

5.8-11***

16-28***

<0.01-<0.01

0.01-0.03

0.02-0.02

0.01-0.02

<0.01-0.01

0.01-0.02

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.01-0.01

0.13-0.31*

0.18-0.28*

0.13-0.24*

0.05-0.10*

0.13-0.24*

<0.01-.031

3.6-8.1***

4.9-7.3***

3.6-6.3***

1.3-2.6***

3.6-6.3***

<0.01-<0.01

<0.01-0.01

<0.01-0.01

<0.01-0.01

<0.01-<0.01

<0.01-0.01

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.09-0.16*

0.15-0.28*

2.3-4.3***

3.9-7.6***

<0.01-<0.01

<0.01-0.01

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

0.78** 20*** 0.01

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

0.21* 5.7*** <0.01

1

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from cyproconazole, fenbuconazole, hexaconazole, metconazole, tebuconazole, triadimefon, triadimenol, and 

triticonazole.

2

Multiple months were modeled; the range of RQs represents the highest and lowest EECs. 3 Total toxic residue simulation includes two metabolites (CGA 149907and NOA 457654) 4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified 

from total toxic residue simulations.

*Exceeds acute listed species LOC (0.05)

**Exceeds acute non-listed species LOC (0.5)

***Exceeds chronic LOC (1)

Estuarine/Marine Invertebrates – Acute Risk

For estuarine/marine invertebrates, risk quotients ranged from <0.01 to 1.4 for all uses of 

paclobutrazol. The acute non-listed species LOC (0.5) was exceeded for the Florida, 

Michigan, and New Jersey 2.5 lb ai/A application to ornamentals as well as the Florida 

ornamentals 2.5 lb ai/A parent paclobutrazol-only scenario. With the exception of some of 
102

the California scenarios, the acute listed species LOC (0.05) was equaled or exceeded (Table 

31).

Estuarine/Marine Invertebrates – Chronic Risk

For estuarine/marine invertebrates, risk quotients ranged from <0.1 to 9.5 for ornamental 

scenarios at 2.5 lb ai/A. All of these risk quotients exceeded the LOC of 1. The risk 

quotients for the lower ornamental application rate (0.56 lb ai/A) ranged from <0.1 to 2.1. 

The Florida, Tennessee, and New Jersey scenarios each had one risk quotient that exceeded 

the LOC (1), whereas all of the risk quotients generated in the Michigan scenario exceeded 

the LOC. Turf risk quotients ranged from 0.60 to 2.0 with both scenarios having at least one 

risk quotient that exceeded the LOC of 1 (Table 31).

Table 31. Acute and chronic risks from paclobutrazol to estuarine/marine 

invertebrates

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Estuarine / 

Marine 

Invertebrates 

Acute RQ 

(Peak 

EEC/EC50) 

EC50 = 240 μg 

ai/L1

Estuarine / 

Marine 

Invertebrates 

Chronic RQ 

(60-Day EEC/ 

NOAEC) 

NOAEC = 35 

μg ai/L2

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

3,4

Surface Water 

(Tier 2 

PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.01-0.05*

0.61-1.4**

0.83-1.3**

0.60-1.1**

0.22-0.43*

0.61-1.1**

<0.1-0.4

4.0-9.5***

5.6-8.6***

4.1-7.3***

1.5-2.9***

4.1-7.3***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.01-0.01

0.13-0.31*

0.18-0.28*

0.13-0.24*

0.05-0.10*

0.13-0.24*

<0.1-0.1

0.91-2.1***

1.3-1.9***

0.91-1.6***

0.34-0.66

0.9-1.6***

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.09-0.16*

0.15-0.28*

0.60-1.1***

1.0-2.0***

 Parent Paclobutrazol Only5

FL Ornamentals STD

(1 app. X 2.5 lb ai/A) Water

0.78** 5.3***

PA Turf STD 0.21* 1.5***
103

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Estuarine / 

Marine 

Invertebrates 

Acute RQ 

(Peak 

EEC/EC50) 

EC50 = 240 μg 

ai/L1

Estuarine / 

Marine 

Invertebrates 

Chronic RQ 

(60-Day EEC/ 

NOAEC) 

NOAEC = 35 

μg ai/L2

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A 1

The EC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a 

distribution of data from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutranil, 

tebuconazole, and triticonazole.

2

The NOAEC used in the risk quotient calculation was based on tebuconazole, the only structurallysimilar triazole available with chronic estuarine/marine invertebrate toxicity data.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Total toxic residue simulation includes two metabolites (CGA 149907and NOA 457654) 5

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf 

STD) identified from total toxic residue simulations.

*Exceeds acute listed species LOC (0.05)

**Exceeds acute non-listed species LOC (0.5)

***Exceeds chronic LOC (1)

Aquatic Vascular and Non-vascular Plants 

For aquatic vascular plants, risk quotients ranged from <0.1 to 42. All of the values, except 

some of the California scenarios, exceeded the LOC of 1, indicating potential risk of 

registered paclobutrazol applications to aquatic vascular plants. For aquatic non-vascular 

plants, risk quotients ranged from <0.01 to 0.01 and did not exceed the LOC of 1 (Table 32).

Table 32. Risks from paclobutrazol to aquatic vascular and non-vascular plants

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

Aquatic 

Vascular 

Plant RQ 

(Peak 

EEC/EC50) 

EC50 = 8 μg 

ai/L1

Aquatic NonVascular 

Plant RQ 

(Peak EEC/ 

EC50) EC50 = 

40800 μg ai/L

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

2,3

Surface Water 

(Tier 2 

PRZM/EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.1-1.6***

18-42***

25-38***

18-32***

6.5-13***

18.3-32.3***

<0.01-<0.01

<0.01-0.01

<0.01-0.01

<0.01-0.01

<0.01-<0.01

<0.01-0.01

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

<0.1-0.4

4.0-9.3***

5.5-8.4***

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01
104

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

4.0-7.1***

1.5-2.9***

4.0-7.1***

<0.01-<0.01

<0.01-<0.01

<0.01-<0.01

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

2.7-4.9***

4.4-8.5***

<0.01-<0.01

<0.01-<0.01

 Parent Paclobutrazol Only3

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

23*** <0.01

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

6.4*** <0.01

1

The EC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a 

distribution of data from cyproconazole, metconazole, tebuconazole, and triticonazole. 2

Multiple months were modeled; the range of RQs represents the highest and lowest EECs. 3

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf 

STD) identified from total toxic residue simulations.

***Exceeds LOC (1)

Probit Slope Response Analysis of LOC Values and Acute RQ Values

As part of the risk estimation, the probability of mortality associated with the listed acute 

LOC values is estimated along with the probability of acute mortality occurring if exposure 

at the EEC takes place. The probability of mortality calculations are based on the probit 

slope dose-response relationship. The probability of mortality for an exposed individual is

calculated using an Excel spreadsheet tool IECV1.1 (Individual Effect Chance Model 

Version 1.1) developed by EFED of the U.S. EPA, OPP, Environmental Fate and Effects 

Division (June 22, 2004).

The model provides the option of inserting taxa-specific probit slopes and confidence 

intervals. If specific information is not available, the model uses a default value of 4.5 for 

the probit slope and 2 and 9 for the upper and lower 95% confidence interval bounds. For 

paclobutrazol, taxa-specific data were not available. For birds, the acute oral toxicity study 

yielded non-definitive values, thus a probit slope could not be calculated. The mammal acute 

oral study did not calculate a probit slope. The freshwater fish and invertebrate toxicity 

information was taken from the open literature and did not provide enough information to 

calculate a probit slope. Finally, the estuarine/marine fish and invertebrate data were taken 

from the 5th percentile of structurally-similar triazoles, thus probit slopes were not available 

for these groups either. The default values were used for all of the modeled scenarios.

Risk quotient values for comparison were chosen based on the results of the risk assessment. 

For freshwater fish and estuarine/marine fish, the LOC of 0.05 was chosen because none of 
105

risk quotients calculated from the paclobutrazol uses exceeded the LOC. Likewise, the LOC 

of 0.1 was chosen for birds as the EECs did not exceed the non-definitive toxicity value. For 

freshwater invertebrates and estuarine/marine invertebrates, the highest calculated risk 

quotient was chosen – 0.35 for both cases. Several risk quotients were considered for 

mammals. They were chosen based on application scenario and represent the highest RQ 

and the lowest RQ that exceeded the LOC (0.1) (Table 33).

Table 33. Odds of mortality for an individual bird, mammal, fish, or aquatic

invertebrate at selected acute risk quotient values for paclobutrazol

RQ Slope 

(default)

95% Confidence 

Interval (default)

Odds

(1 in...)

95% Confidence 

Interval (odds)

Mammal (turf 

app.)

0.11 4.5 2, 9 125,000 36.2 – 3.19 x 1017

Mammal (soil 

injection)

0.34 4.5 2, 9 57 5.73 – 80,700

Mammal (soil 

injection)

0.13 4.5 2, 9 29,900 26.2 – 1.31 x 1015

Bird 0.1 4.5 2, 9 294,000 44 – 8.86 x 1018

Freshwater fish 0.05 4.5 2, 9 4.18 x 108 216 – 1.75 x 1031

Estuarine/marine 

fish

0.05 4.5 2, 9 4.18 x 108 216 – 1.75 x 1031

Freshwater 

invertebrates

0.35 4.5 2, 9 49.8 5.53 – 4.91 x 104

Estuarine/marine 

invertebrates

0.35 4.5 2, 9 49.8 5.53 – 4.91 x 104

Risk Description

The following section explains the overall effect conclusions regarding the potential 

ecological risk from the various uses of paclobutrazol. The risk conclusions take into 

consideration all lines of evidence, such as the risk estimates (risk quotient results);

information on the odds of mortality for the acute risk quotient values; comparisons of nondefinitive endpoints (i.e., limit tests) to EECs; information such as monitoring data, field 

studies, and incident data that may provide additional insights into the likelihood of 

exposure; and other factors that modify the likelihood of exposure such as timing of 

application, overlap of area affected and the degree of effect with the presence/absence of 

taxa, species sensitivity distribution, and presence/absence of dietary items.
106

Exposure Uncertainties

There were a number of exposure uncertainties that are applicable to most or all of the 

scenarios that were considered. Rather than repeat them for each section, they are described 

below. 

There is uncertainty concerning the expected exposure of paclobutrazol in the environment. 

For all uses but turf, the amount of paclobutrazol that could be applied within a geographical

area is unclear. BEAD estimated a paclobutrazol application rate in pounds of active 

ingredient per acre, based on labels for tree injection, soil injection/drench, potted 

ornamentals drench, and seed treatments. A number of assumptions were made in these 

scenarios to derive an environmentally protective estimate of the amount of paclobutrazol 

that could be applied within an acre (see Pesticide Use Overview Section for details). For 

terrestrial scenarios, the concentration of paclobutrazol in leaves could have been more 

directly calculated from the directions on the label (grams of ai/tree); however, it was 

decided for consistency sake to use the same application rates in lb ai/A for both the 

terrestrial and aquatic analyses.

For many of the endpoints typically used in risk assessments, no paclobutrazol-specific data 

were available. In these instances, surrogate data from structurally-similar triazoles were 

used in lieu of paclobutrazol data (see the Effects Characterization Section for details). In 

some instances, the surrogate data may have overestimated the toxicity threshold for certain 

groups of organisms, resulting in risk quotients that exceed the level of concern. Surrogate 

data were employed for the following endpoints: honey bee acute contact toxicity, seedling 

emergence, vegetative vigor (monocots only), estuarine/marine fish acute and chronic 

toxicity, estuarine/marine invertebrates acute and chronic toxicity, aquatic vascular plants. 

Where appropriate, changes to the RQs from using the most sensitive toxicity value from the 

structurally similar triazoles are discussed in the taxa specific sections below.

There is also uncertainty regarding the concentration of paclobutrazol that would be available 

in edible plant parts. Paclobutrazol is a systemic chemical and is transported throughout the 

entire plant. This characteristic is what makes tree injections, drenches, etc. efficient 

applications methods. When estimating the concentration of paclobutrazol that would be 

present in tree leaves (tree injection, soil injection/drench, and potted ornamental drench), it 

was assumed that the entire application of paclobutrazol would concentrate in the leaves. 

This may be an overestimate as paclobutrazol may be distributed throughout the tree, or it 

may more slowly “time release” than immediately concentrate in the leaves of the plant, or it 

may be metabolized by the tree. For seed treatments, it was assumed that the entire 

application of paclobutrazol would be equally distributed throughout the transplanted pepper, 
107

tomato, cucurbit, broccoli, cauliflower, or cabbage and that an organism would have the 

ability to consume the entire plant.

There is uncertainty regarding the biomass estimates for trees and seedlings. For trees, 

general hardwood and softwood equations were used along with the size assumptions that 

BEAD used in its calculations of paclobutrazol application rates. These are general 

equations/assumptions and may over or underestimate biomass, depending on the tree species 

and its geographical location. For seeds, tomato transplant data were used and applied to 

cucurbits, peppers, broccoli, cauliflower, and cabbage as well. 

There is uncertainty regarding the percent uptake of paclobutrazol from soil drench, soil 

injection, and seed treatment applications. The basic premise for paclobutrazol applications 

made to soil is that most of the chemical will be taken up into the plant via its roots; however, 

few data are available that document the efficiency of this mechanism. Sharma and Awasthi 

(2005) demonstrate for soil drenches of paclobutrazol to mango trees, that residues in the soil 

range from 1 to 3% for a single yearly application, ~25% for an application in year 2, and 30 

to 54% for an application in year 3. For exposure pathways considered in the risk assessment

that depend on paclobutrazol being available in the soil (i.e. runoff scenarios), it was 

assumed that 100 percent of the applied paclobutrazol was in the soil and that none of it had 

been taken up into the plant; however, alternative scenarios (75%, 50%, and 25%) uptake are 

also presented. Likewise, when considering paclobutrazol exposure through soil from the 

seed treatments, it was assumed that all of the paclobutrazol was available in the soil and that 

none of it had been absorbed into the seed through the seed coat. These are very 

conservative assumptions that were made in the absence of data; they may over-estimate risk 

to non-target terrestrial plants and aquatic organisms. 

Since paclobutrazol is persistent in aquatic environments, there was a modeled accumulation 

of paclobutrazol in the PRZM/EXAMS standard farm pond throughout the 30 year 

simulations, as demonstrated by the daily EECs for applications to FL nursery in the Figure 

3. Accumulation reached the plateau within a few years during the model simulation. Based 

on the non-linear accumulation as predicted in the Figure 3, the 1-in-10-year concentrations 

are expected to occur with continuing use of paclobutrazol; however, the time required to 

reach the chronic risk to animals or risk to plants (level of concern = 1) may occur with the 

first application depending on application rate, management practices, location, and 

meteorological conditions (e.g. potential adverse effects may occur to listed vascular plants 

and on a chronic basis immediately following the first season of paclobutrazol use in 

nurseries in Florida). Potential risks to many aquatic organisms from various paclobutrazol 

uses are expected to increase with continued paclobutrazol applications. 
108

For the spray and drench applications to ornamental plants, it is unclear how many 

applications may take place. These treatments occur in nursery/greenhouse settings. The 

applications may be made indoors, but then the potted plants are set outdoors to mature 

before shipping to market. This presents two levels of uncertainty. First, if potted plants are 

stored outdoors for an extended period of time, they may warrant additional applications of 

paclobutrazol. Second, if the turnover rate of potted plants in outdoor storage areas is high, a 

discreet geographical area may be exposed to maximum paclobutrazol application rates many 

times within a growing season. These points were not taken into consideration in the risk 

assessment; it was assumed that only one application of paclobutrazol would occur when 

modeling spray and drench applications to potted ornamentals.

 DIRECT EFFECTS TO TERRESTRIAL BIRDS, REPTILES, AND AMPHIBIANS

Acute Risk

Acute dose-based and dietary-based risk quotients could not be calculated to evaluate the 

risks to birds because only non-definitive acute toxicity data were available. Instead, the 

non-definitive toxicity values were directly compared to the EECs (Table 34). In all cases, 

none of the dietary EECs were larger than the non-definitive toxicity values for bobwhite 

quail and mallard duck, thus, the potential for acute risk is considered to be low for acute 

dose-based and dietary-based exposure of non-listed birds, reptiles, and land-phase 

amphibians from paclobutrazol for all registered uses. Likewise, the probit slope response 

analysis indicated a 1 in 294,000 chance of mortality with exposure to paclobutrazol.

Table 34. Comparison of the highest calculated dietary EEC for each use of

paclobutrazol to the most sensitive avian toxicity value

Application Rate

(Crop)

Dietary 

Item EEC (mg ai/kg-bw) LD50 (mallard) > 7913 mg ai/kg-bw

EEC (mg

ai/kg-diet)

LC50 (bobwhite) > 

5000 mg ai/kg-diet

3 ground spray applications at 

0.75 lb ai/A (turf) Short grass 390 390 <7913 343 343 <5000

1 tree injection at 0.36 lb ai/A Leaves N/A N/A 212 212 <5000

1 soil injection/drench at 1.9 

lb ai/A Leaves N/A N/A 1058 1058 <5000

1 spray application at 0.26 lb 

ai/A (potted ornamentals) Short grass 71 71 <7913 62.4 62.4 <5000

1 drench application at 6.1 lb 

ai/A (potted ornamentals) Leaves N/A N/A 112 112 <5000

1 seed treatment (pepper) Transplant N/A N/A 2.9 2.9 <5000

Chronic Risk

Chronic risk quotients were calculated for dietary-based chronic risks. The soil 

injection/drench application of 1.9 lb ai/A to trees was the only use to exceed the LOC (1). 

Risk quotients for both hardwoods (2.3) and softwoods (1.1) exceeded the LOC. These 

numbers indicate that there is a potential chronic risk for birds consuming non-woody 
109

vegetative items (leaves were used a surrogate for fruit, flowers, seeds, and other non-woody 

foods) that have been treated with paclobutrazol via soil injection or basal drench; however, 

they are based on the very conservative assumption that 100 percent of the paclobutrazol 

application has been taken up by the tree and has concentrated in the edible parts that a bird 

may eat (e.g., fruit, seeds, flowers). Less conservative assumptions of 75, 50, and 25 percent 

uptake by the tree were also modeled (Table 35).

Table 35. Paclobutrazol uptake scenarios for birds based on a hardwood EEC of 1058 

mg ai/kg-leaves, a softwood EEC of 483 mg ai/kg-leaves, and a NOAEC of 453 mg ai/kgdiet

Paclobutrazol Uptake Tree Type EEC Risk Quotient

100% Hardwood 1058 2.3***

Softwood 483 1.1***

75% Hardwood 794 1.75***

Softwood 362 0.80

50% Hardwood 529 1.17***

Softwood 242 0.53

25% Hardwood 265 0.58

Softwood 121 0.27

***Exceeds the LOC of 1.

Based on the alternative paclobutrazol uptake scenarios, avian risk from the consumption of 

softwood leaves falls below the LOC when 75 percent uptake is assumed while the risk from 

hardwood leaf consumption is reduced below the LOC at 25 percent uptake. Data are not 

available that describe the rate of uptake by a tree, but given that the chemical’s efficacy

relies on the uptake of paclobutrazol from the soil into the tree, it is possible that more than 

25% of the chemical is absorbed into the tree.

The chronic risk concern for birds is probably most relevant to a scenario where a large 

number of trees have been treated in an area (e.g., right-of-ways, large landscaping 

operations). Such scenarios may be limited in their occurrence because paclobutrazol, 

although registered for use in right-of-ways, is probably not the most cost effective way of 

controlling growth. Furthermore, use in landscapes would probably be targeted to specific 

trees, leaving many trees untreated. 

Summary of Risks from Direct Effects

A summary of the potential for acute and chronic risks to birds (surrogates for reptiles and 

land-phase amphibians) is listed below:
110

• The potential for acute risk to non-listed birds (surrogates for reptiles and land-phase 

amphibians) is low, based on comparisons between dose-based and dietary-based 

EECs and toxicity data. For all uses, the EECs are much lower than the toxicity 

value. 

• The potential for chronic risk to birds (reptiles and land-phase amphibians) exists as 

the risk quotients for soil injection/drench applications to trees exceeded the LOC.

 DIRECT EFFECTS TO TERRESTRIAL MAMMALS

Acute Risk

Soil injection/drench at 1.9 lb ai/A dose-based risk quotients exceeded the acute listed LOC 

of 0.1 for small (15 g), medium (35 g) and large (1000 g) sized mammals. Risk quotients 

were calculated for both hardwoods and softwoods for this use. All of the risk quotients for 

the hardwoods exceeded the LOC (0.34, 0.29, and 0.15) while the risk quotients for the 

softwoods only exceeded for small and medium-sized mammals (0.16 and 0.13). The turf 

scenario also exceeded the acute listed LOC (0.1) for 15 and 35 g mammals consuming a 

strict diet of short grass. No other acute dose-based risk quotients exceeded the LOC for any 

other use. It was only possible to calculate dietary risk quotients for the turf and potted 

ornamental spray uses; neither of these exceeded the LOC.

For the soil injection/drench the risk quotients indicate that there is a potential acute risk for 

mammals consuming the leaves of trees that have been treated with paclobutrazol via soil 

injection or basal drench. The probit slope response analysis further characterizes this risk 

by indicating a 1 in 57 chance of mortality with exposure to paclobutrazol. However, these

risk quotients are based on the very conservative assumption that 100 percent of the 

paclobutrazol application has been taken up by the tree and has concentrated in the edible 

parts that a mammal may eat. Less conservative assumptions of 75, 50, and 25 percent 

uptake by the tree were also modeled (Table 36).

Table 36. Paclobutrazol uptake scenarios based on adjusted mammal LD50s of 2936 mg 

ai/kg-bw (15 g), 2376 mg ai/kg-bw (35 g), and 1028 mg ai/kg-bw (1000 g) 

Paclobutrazol 

Uptake

Tree Type EEC Risk Quotient

15 g 35 g 1000 g 15 g 35 g 1000 g

100% Hardwood 1005 698 159 0.34* 0.29* 0.15*

Softwood 459 319 72 0.16* 0.13* 0.07

75% Hardwood 754 524 119 0.26* 0.22* 0.12*

Softwood 344 239 54 0.12* 0.10* 0.05

50% Hardwood 503 349 80 0.17* 0.15* 0.08

Softwood 230 160 36 0.08 0.07 0.04

25% Hardwood 251 175 40 0.09 0.07 0.04

Softwood 115 80 18 0.04 0.03 0.02
111

*Exceeds the LOC of 0.1 (listed species).

Based on the alternative paclobutrazol uptake scenarios, mammal risk from the consumption

of softwood leaves falls below the LOC when 50 percent uptake is assumed while the risk 

from hardwood leaf consumption is reduced below the LOC at 25 percent uptake. Data are 

not available that describe the rate of uptake by a tree, but given that chemical’s efficacy

relies on the uptake of paclobutrazol from the soil into the tree, it is likely that more than 

25% of the chemical is absorbed into the tree.

For turf, the acute dose-based risk quotients for small and medium-sized mammals slightly 

exceeded the listed species LOC of 0.1. Supporting this, the probit slope response analysis 

(using the highest risk quotient of 0.11) indicated a 1 in 125,000 chance of mortality with 

paclobutrazol exposure. The scenario used to calculate the risk quotients was overly 

conservative because 0.75 lb ai/A was applied 3 times, thus exceeding the seasonal 

maximum application rate of 2 lb ai/A. T-REX’s limitations do not allow for uneven 

applications. Running the scenario with an application rate of 0.66 lb ai/A slightly reduces 

the risk quotients to 0.1 for small mammals and 0.08 for medium mammals. One limitation 

of this scenario is that it does not apply the maximum single application rate of paclobutrazol 

(Table 37). 

Table 37. Alternative turf scenarios for acute mammal exposure using T-REX

Scenario Food Item Acute Dose Risk Quotient

15 g 35 g 1000g

3 applications at 

0.75 lb ai/A 

(28-day 

interval)

Short grass 0.11* 0.10* 0.05

Tall grass 0.05 0.04 0.02

Broadleaf plants/small insects 0.06 0.05 0.03

Fruits/pods/seeds/lg insects 0.01 0.01 <0.01

Granivores <0.01 <0.01 <0.01

3 applications at 

0.66 lb ai/A 

(28-day 

interval)

Short grass 0.10* 0.08 0.04

Tall grass 0.04 0.04 0.02

Broadleaf plants/small insects 0.06 0.05 0.03

Fruits/pods/seeds/lg insects 0.01 0.01 <0.01

Granivores <0.01 <0.01 <0.01

*Exceeds the LOC of 0.1 (listed species)

Chronic Risk

Seed treatments to tomatoes, cucurbits, peppers, broccoli, cauliflower, and cabbage were the 

only paclobutrazol uses to not produce risk quotients that exceeded the LOC. Only dosebased chronic risk quotients were calculated for the seed treatments.
112

Paclobutrazol was applied to turf at 0.75 lb ai/A with an application interval of 28 days. 

Three applications were made (this exceeds the maximum application rate of 2 lb ai/A per 

season by 0.25 lb ai/A because of restrictions to T-REX, but the results were not substantially 

different when lower application rates were used). Chronic dose-based risk quotients 

exceeded the chronic LOC of 1 for all size classes of mammals that feed on short grass (27.2 

– 59.5), tall grass (12.5 – 27.3), broadleaf plants/small insects (15.3 – 33.5), and 

fruits/pods/seeds/large insects (1.70 – 3.72). Granivores was the only dietary class that did 

not exceed dose-based chronic risk quotients. For chronic dietary-based risk, risk quotients 

exceeded the LOC for short grass (6.86), tall grass (3.14) and broadleaf plants/small insects 

(3.86). 

Paclobutrazol was applied as a spray to potted ornamentals in a single application of 0.26 lb 

ai/A. Chronic dose-based risk quotients exceeded the LOC of 1 for all size classes of 

mammals that feed on short grass (4.96 – 10.8), tall grass (2.27 – 4.96), and broadleaf 

plants/small insects (2.79 – 6.09). Fruit/pod/seed/large insect eaters and granivores were not 

at risk, based on chronic dose-based risk quotients. Short grass eaters were the only dietary 

class that was at risk based on dietary-based risk quotients (1.25).

Only chronic dose-based risk quotients were calculated for the remaining uses. 

Paclobutrazol was applied as a tree injection at an equivalent rate of 0.36 lb ai/A. 

Applications to both hardwoods and softwoods were considered. Risk quotients for 

hardwoods exceeded the LOC for all mammal size classes (17 to 37). For softwoods, only 

the 15 g mammal size class exceeded the LOC of 1 (1.6). 

Paclobutrazol was applied to trees via soil injection/drench at rate of 1.9 lb ai/A. 

Applications to both hardwoods and softwoods were considered. Chronic dose-based risk 

quotients exceeded the LOC of 1 for both classifications of trees as well as all mammal size 

classes. Hardwood risk quotients ranged from 83 to 183 and softwood risk quotients ranged 

from 38 to 87. These numbers are based on the very conservative assumption that 100 

percent of the paclobutrazol application has been taken up by the tree and has concentrated in 

the edible parts that a mammal may eat. Less conservative assumptions of 75, 50, and 25 

percent uptake by the tree were also modeled (Table 38).

Table 38. Paclobutrazol soil injection/drench uptake scenarios based on adjusted 

mammal NOAECs of 5.49 mg ai/kg-bw (15 g), 4.45 mg ai/kg-bw (35 g), and 1.92 mg 

ai/kg-bw (1000 g)

Paclobutrazol 

Uptake

Tree Type EEC Risk Quotient

15 g 35 g 1000 g 15 g 35 g 1000 g

100% Hardwood 1005 698 159 183*** 157*** 83***

Softwood 459 319 72 87*** 72*** 38***
113

Paclobutrazol 

Uptake

Tree Type EEC Risk Quotient

15 g 35 g 1000 g 15 g 35 g 1000 g

75% Hardwood 754 524 119 137*** 118*** 62***

Softwood 344 239 54 63*** 54*** 28***

50% Hardwood 503 349 80 92*** 78*** 42***

Softwood 230 160 36 42*** 36*** 19***

25% Hardwood 251 175 40 46*** 39*** 21***

Softwood 115 80 18 21*** 18*** 9***

***Exceeds the LOC of 1

Based on the alternative paclobutrazol uptake scenarios for the soil injection/drench, none of 

them result in risk quotients that are below the level of concern. This indicates that 

regardless of the exposure scenarios, the potential exists for chronic risk to all size classes of 

mammals that feed on non-woody vegetative food items.

Paclobutrazol can be applied as a drench to potted ornamentals at 6.1 lb ai/A. For this 

scenario, woody hardwoods, woody softwoods, and non-woody potted plants were 

considered. All scenarios yielded chronic dose-based risk quotients above the LOC of 1 for 

all mammal size classes. Woody hardwoods risk quotients ranged from 5 to 11, woody 

softwoods risk quotients ranged from 2 to 4, and non-woody risk quotients ranged from 9 to 

19. As with the soil injection/drench use, these scenarios assume 100 percent uptake of the 

paclobutrazol into the plant leaves (woody species) or entire plant (non-woody species). 

Less conservative assumptions of 75, 50, and 25 percent uptake by the tree were also 

modeled (Table 39).

Table 39. Paclobutrazol drench uptake scenarios based on adjusted mammal NOAECs 

of 5.49 mg ai/kg-bw (15 g), 4.45 mg ai/kg-bw (35 g), and 1.92 mg ai/kg-bw (1000 g) 

Paclobutrazol 

Uptake

Tree Type EEC Risk Quotient

15 g 35 g 1000 g 15 g 35 g 1000 g

100%

Hardwood 59 39 9 11*** 9*** 5***

Softwood 23 16 3.6 4*** 4*** 2***

Non-woody 106 74 17 19*** 17*** 9***

75%

Hardwood 44 29 7 8*** 6.5*** 3.6***

Softwood 17 12 2.7 3.1*** 2.7*** 1.4***

Non-woody 80 56 13 15*** 13*** 6.8***

50%

Hardwood 30 20 4.5 5.5*** 4.5*** 2.3***

Softwood 12 8 1.8 2.2*** 1.8*** 0.94

Non-woody 53 37 8.5 9.7*** 8.3*** 4.4***

25% Hardwood 15 10 2 2.7*** 2.2*** 1.0***
114

Paclobutrazol 

Uptake

Tree Type EEC Risk Quotient

15 g 35 g 1000 g 15 g 35 g 1000 g

Softwood 6 4 0.9 1.1*** 0.90 0.47

Non-woody 27 19 4.3 4.9*** 4.3*** 2.2***

*Exceeds the LOC of 1

Based on the alternative paclobutrazol uptake scenarios for the potted ornamental drench, 

only three of them result in risk quotients that are below the level of concern: 50% uptake in 

softwoods – large mammals; 25% uptake in softwoods – medium and large mammals. This 

indicates that there is the potential of chronic risk to all size classes of mammals that feed on 

tree leaves.

Summary of Risks from Direct Effects

A summary of the potential for acute and chronic risks to mammals is listed below:

• There is the potential for acute and chronic risk to mammals for soil 

injection/drenches to trees at a 1.9 lb ai/A application rate. Acute dose-based risk 

quotients exceeded the listed LOC for all mammals in hardwoods and small and 

medium-sized mammals in softwoods; reduced uptake scenarios lowered the risk 

quotients and eliminated all of them at 25 percent paclobutrazol uptake. Chronic 

dose-based risk quotients exceeded the LOC for all mammal size classes in 

hardwoods and softwoods. 

• The potential for acute and chronic risk to mammals exists for turf uses. Acute dosebased risk quotients exceeded the listed LOC for small and medium-sized mammals; 

assuming a lower application rate (0.66 lb ai/A) reduced the magnitude of the risk 

quotients, but did not substantially alter the risk picture. Chronic dose-based and 

dietary-based risk quotients exceeded the LOC for all size classes of mammals on 

several varieties of food.

• The potential for chronic risk to mammals exists for potted ornamental spray uses. 

Chronic dose-based and dietary-based risk quotients exceeded the LOC for multiple 

size classes of mammals and dietary items (dose-based only).

• The potential for chronic risks to mammals exists from tree injection uses. Chronic 

dose-based risk quotients exceeded the LOC for hardwoods (all mammal size classes) 

and softwoods (15 g mammals).

• The potential for chronic risks to mammals exists from drenches to ornamental potted 

plants at 6.1 lb ai/A. Chronic dose-based risk quotients exceeded the LOC for 

hardwoods, softwoods, and non-woody plants for all mammal size classes; for most 

cases, alternative paclobutrazol uptake scenarios did not reduce their magnitude 

enough to preclude risk.
115

DIRECT EFFECTS TO TERRESTRIAL INVERTEBRATES

Risk quotients could not be calculated for terrestrial invertebrates because only nondefinitive data were available (from a surrogate chemical). In lieu of this, the EEC 

(converted to a dose) was compared directly with the toxicity value for honeybees. For both 

the turf and potted ornamental plant uses, the EEC was less than the contact LD50, thus direct 

effects to terrestrial invertebrates are not expected for contact exposures (Table 40). Acute 

oral toxicity could not be assessed because data were not available and the results of the 

contact analysis were used as a surrogate for this route of exposure. 

Table 40. Comparison of Small and Large Insect EECs from Foliar Application of 

Paclobutrazol to the Extrapolated Acute Contact Honeybee Concentration

Application Rate

(Crop) Dietary Item EEC(μg ai/bee)

Contact LD50

1

(

μg ai/bee)

Turf Large insects 12.9 24

Spray to potted 

ornamentals Large insects 4.5 24

1

This value was extrapolated from triticonazol because toxicity data were not available 

for paclobutrazol.

There was an open literature paper identified in ECOTOX that examined the effects of 

paclobutrazol residues on predatory mites (Oetting and Latimer 1995). Based on mortality 

rates, a 48-hour NOAEC was established of 160 ppm for Orius insidiosus. This supports the 

risk quotient analysis that risks from acute contact exposure are not expected. 

Summary of Risks from Direct Effects

A summary of the potential for acute risks terrestrial invertebrates is listed below:

• The potential for acute risk to terrestrial invertebrates is not expected for terrestrial 

invertebrates, based on a comparison of EECs and honey bee acute contact LD50

toxicity data from a surrogate triazole, and the mite data.

 DIRECT EFFECTS TO TERRESTRIAL PLANTS

Paclobutrazol data (EC25 and NOAEC) were not available for monocot seedling emergence 

and vegetative vigor, and dicot seedling emergence. Therefore, data from other structurallysimilar triazoles were used as surrogates for these data. In addition, risk quotients were not

calculated for non-listed monocots because the available data were non-definitive. In lieu of 

a risk quotient, the EECs for each use were compared directly to the most sensitive toxicity 

value (Table 41).
116

Turf was the only use that considered spray drift as a potential route of exposure in addition 

to runoff. A single ground application of 0.75 lb ai/A scenario was modeled and resulted in 

risk quotients that exceeded the LOC of 1 for listed semi-aquatic monocots (2.22), non-listed 

dry and semi-aquatic dicots (2.50 – 17.50), and listed dry, semi-aquatic, and spray drift dicots 

(3.75 – 78.75). The comparison of the most sensitive non-definitive monocot EC25 to EECs 

for dry, semi-aquatic, and spray drift yielded no instances in which the EEC was greater than 

the EC25 (Table 41).

Paclobutrazol soil injection/basal drench was modeled because of the potential for runoff 

from soil injection or drench application. A single injection/drench scenario of 1.9 lb ai/A at 

3 inches in depth was modeled and resulted in risk quotients that exceeded the LOC of 1 for 

listed semi-aquatic monocots (1.78), non-listed dry and semi-aquatic dicots (1.41 to 14.07) 

and listed dry and semi-aquatic dicots (6.33 – 63.33). For the comparison of the most 

sensitive non-definitive monocot EC25 to EECs for dry and semi-aquatic monocots, the semiaquatic EEC was greater than the EC25 (Table 41). This indicates a potential risk to nonlisted semi-aquatic monocots from soil injection/basal drench.

Paclobutrazol seed treatments were modeled for tomato (0.00040 lb ai/A), cucurbit (0.00029 

lb ai/A), pepper (0.00079 lb ai/A), broccoli (0.000096 lb ai/A), cauliflower (0.000064 lb 

ai/A), and cabbage (0.00012 lb ai/A). Seed treatments occur within the greenhouse and 

seedlings are assumed to be transplanted into outdoor fields when they are about 7 weeks old. 

For the terrestrial plant model, it is assumed that the entire application of paclobutrazol to the 

seed coat ends up in the soil rather than the plant. Thus, paclobutrazol in runoff could be a 

concern. Each seed treatment application rate was modeled with an incorporation depth of 3 

inches. None of the risk quotients that were produced exceeded the LOC of 1. None of the 

comparisons between the most sensitive non-definitive EC25 for monocots and the 

corresponding EECs for dry and semi-aquatic monocots yielded EECs that were greater than 

the EC25 (Table 41).

The model for paclobutrazol spray on potted ornamentals considered runoff, but not spray 

drift as a potential exposure pathway. Spray drift was not considered a potential exposure 

pathway because spray applications take place within greenhouse settings. Environmental 

exposure is expected to occur when treated potted plants are set or planted outside, usually in 

a commercial setting. A single spray application of 0.26 lb ai/A was modeled and resulted in 

risk quotients that exceeded the LOC of 1 for non-listed semi-aquatic dicots (5.78) and listed 

dry and semi-aquatic dicots (2.60 – 26.00). The comparison between the most sensitive nondefinitive monocot EC25 and the EECs for dry and semi-aquatic monocots did not yield EECs 

that were greater than the EC25 (Table 41).
117

Paclobutrazol drench on potted ornamentals was modeled with a single application of 6.1 lb 

ai/A. Drenches take place within greenhouses and environmental exposure occurs when 

plants are stored or planted outdoors. Risk quotients exceeded the LOC of 1 for listed dry 

and semi-aquatic monocots (1.72 – 17.18), non-listed dry and semi-aquatic dicots (13.56 –

135.56), and listed dry and semi-aquatic dicots (61.00 – 610.00). The comparison between 

the most sensitive non-definitive monocot EC25 and the EECs for dry and semi-aquatic 

monocots yielded EECs that were greater than the EC25 in both instances (Table 41). These 

results indicate that paclobutrazol drenches to ornamental potted plants may pose risks to 

non-listed dry and semi-aquatic monocots.

Table 41. Comparison of EECs to the most sensitive non-listed monocot toxicity value

Application Rate

(Crop)

“Dry” EEC 

(lb ai/A)

EC25 > 0.0971

lb ai/A

“Semi-aquatic” 

EEC (lb ai/A)

EC25 > 0.0971

lb ai/A

“Spray drift” 

EEC (lb ai/A)

EC25 > 0.0971

lb ai/A

1 ground spray 

application at 0.75 lb 

ai/A (turf)

0.011 EEC < 0.097 0.0605 EEC < 0.097 0.0055 EEC < 0.097

1 soil 

injection/drench at 

1.9 lb ai/A

0.0127 EEC < 0.097 0.127 EEC > 0.097 N/A N/A

1 spray application 

at 0.26 lb ai/A 

(potted ornamentals)

0.0052 EEC< 0.097 0.052 EEC < 0.097 N/A N/A

1 drench application 

at 6.1 lb ai/A (potted 

ornamentals)

0.122 EEC > 0.097 1.22 EEC > 0.097 N/A N/A

1 seed treatment 

(pepper) 0.0000053 EEC < 0.097 0.000053 EEC < 0.097 N/A N/A

1

This value was used from metconazole because toxicity data were not available for paclobutrazol.

Some uncertainty is introduced into the RQ analysis because surrogate data were used for 

many of the toxicity endpoints. Alternatively, the toxicity value from the most sensitive 

chemical could be used instead of basing the toxicity value on the 5th percentile value. For 

this approach, most of the toxicity values are slightly higher than those predicted by the 5th

percentile (Table 42). In two instances (veg vigor and seed emergence monocot EC25), only 

non-definitive data were available and the most sensitive of these were used in the risk 

assessment anyway. For veg vigor monocot NOAEC, the most sensitive actual value was a 

“less then” value, thus the 5th percentile estimate may have offered a less sensitive toxicity 

value than real febuconazole NOAEC. Re-running TerrPlant using the values (excluding the 

non-definitives) in the “most sensitive endpoint” column (Table 42), the risk quotients are 

lowered for all scenarios. However, only the soil injection/basal drench for ornamental trees 

experiences a change in the overall risk conclusions. With the alternate approach, listed 

semi-aquatic monocots and non-listed dry dicots, are no longer expected to be potentially at 

direct risk from this application method. The overall risk conclusions for the other modeled 

scenarios do not change, supporting the premise that the 5th percentile approach is a 

reasonably conservative method to fill in toxicity datagaps.
118

Table 42. Comparison of 5th percentile data points and the most sensitive endpoint 

available for triazoles

Endpoint1 5th Percentile (lb ai/A) Most Sensitive Endpoint (lb 

ai/A)

Veg vigor monocot EC25 N/A >0.097 (metconazole)

Veg vigor monocot NOAEC 0.059 <0.061 (febuconazole)

Seed emerg dicot EC25 0.009 0.015 (triticonazole)

Seed emerg dicot NOAEC 0.002 0.004 (triticonazole)

Seed emerg monocot EC25 N/A >0.098 (metconazole)

Seed emerg monocot NOAEC 0.071 0.098 (metconazole)

1

Vegetative vigor dicot endpoints were available for paclobutrazol

N/A Only non-definitive data were available and 5th percentile could not be calculated. In lieu 

of this, the most sensitive non-definitive value was used in the risk assessment.

All of the original scenarios assumed that 100 percent of the paclobutrazol in runoff would 

be taken up by non-target plants. This is a conservative assumption; less conservative 

scenarios of 75, 50, and 25 percent uptake were also considered (Table 43). Seed treatments 

were not considered because the risk quotients did not exceed the LOC even with the 

conservative assumption of 100 percent uptake.

Table 43. Risk quotients for alternative paclobutrazol uptake scenarios for terrestrial 

plant runoff using TerrPlant

100% 75% 50% 25%

Dry SemiaquaticDry SemiaquaticDry SemiaquaticDry Semiaquatic

Profile 2SC on Turf – 1 ground application at 0.75 lb ai/A

Monocotlisted 0.32 2.22*** 0.16 1.58*** 0.11 1.06*** <0.1 0.53

Dicotnon-listed

2.50*** 17.50*** 1.24*** 12.44*** 0.83 8.33*** 0.42 4.18***

Dicotlisted

11.25*** 78.75*** 5.60*** 56.00*** 3.75*** 37.50*** 1.88*** 18.80***

Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees – 1 application at 3 inches 

deep at 1.9 lb ai/A

Monocotlisted0.18 1.78*** 0.13 1.34*** <0.1 0.89 <0.1 0.45

Dicot-nonlisted

1.41*** 14.07*** 1.06*** 10.56*** 0.70 7.04*** 0.35 3.52***
119

100% 75% 50% 25%

Dry SemiaquaticDry SemiaquaticDry SemiaquaticDry Semiaquatic

Dicot-listed 6.33*** 63.33*** 4.75*** 47.50*** 3.17*** 31.67*** 1.58*** 15.83***

Bonzi II Spray for Potted Ornamentals for Transplant – 1 application at 0.26 lb ai/A

Monocotlisted<0.1 0.73 <0.1 0.55 <0.1 0.37 <0.1 0.18

Dicot-nonlisted0.58 5.78*** 0.43 4.33*** 0.29 2.89*** 0.14 1.44***

Dicot-listed 2.60*** 26.00*** 1.95*** 19.50*** 1.30*** 13.00*** 0.65 6.50***

Bonzi II Drench for Potted Ornamentals for Transplant – 1 application at 6.1 lb ai/A

Monocotlisted

1.72*** 17.18*** 1.29*** 12.89*** 0.86 8.59*** 0.43 4.30***

Dicot-nonlisted

13.56*** 135.6*** 10.2*** 101.7*** 6.78*** 67.78*** 3.39*** 33.89***

Dicot-listed 61.00*** 610.0*** 45.8*** 457.5*** 30.5*** 305.0*** 15.3*** 152.50***

***Exceeds the LOC of 1.

Based on the alternative uptake scenarios, even when it is assumed that only 25 percent of 

the available paclobutrazol will be incorporated into a plant, risk quotients exceed the LOC 

of 1 for all modeled uses. Paclobutrazol is a plant growth regulator, thus risk to non-target 

plants is expected.

Summary of Risks from Direct Effects

A summary of the potential for risks terrestrial plants is listed below:

• The potential for direct effects to listed and non-listed terrestrial plants is unlikely 

from the seed treatments.

• The potential for direct effects to listed and non-listed terrestrial plants is likely for all 

other application scenarios (turf, potted ornamental drench, potted ornamental spray, 

soil injection/basal drench), even when reduced uptake scenarios are considered.
120

DIRECT EFFECTS TO AQUATIC FISH, INVERTEBRATES, AND PLANTS

Paclobutrazol exposure to aquatic environments was modeled for drenches to potted plants 

and turf applications. These application methods were considered the most likely to result in 

a complete exposure pathway to the aquatic environment. The PRZM/EXAMS model 

explored a number of different timing and geographical location scenarios. In addition, the 

drench scenario explored a conservative and more liberal concentration of available 

paclobutrazol in the water column, based on leaching experiments. Paclobutrazol studies 

indicated a range of mobility in soil. Scenarios were modeled using a total toxic residues 

approach (i.e., paclobutrazol plus its two major degradates.

Freshwater Fish and Amphibians (Aquatic-Phase), and Estuarine-Marine Fish

Acute Risk

Freshwater fish and aquatic-phase amphibian acute toxicity data were available. Risk 

quotients for these groups did not exceed the LOCs for listed or non-listed species. 

Paclobutrazol data were not available for acute toxicity to estuarine/marine fish; therefore, 

data from structurally-similar triazoles were used as a surrogate. Applications to turf did not 

yield risk quotients that exceeded the LOCs but ornamental drenches at the higher 

application rate (2.5 lb ai/A) did. As an alternative approach, the most sensitive surrogate 

toxicity value for structurally similar triazoles was used for RQ calculation rather than the 

value generated from the 5th percentile method. The most sensitive LC50 was 1800 μg ai/L 

(fenbuconazole) compared with the 5th percentile generated LC50 of 1580 μg ai/L. Recalculating RQs, with the fenbuconazole value, the RQs are lower, but the overall risk 

conclusions for each use does not change

The risk quotients are based on the assumption that 100 percent of the applied paclobutrazol 

is available in the soil (i.e., none of it was taken up by the plant to which it was applied). 

This is a conservative assumption and several less conservative scenarios that assumed 75, 

50, and 25 percent availability in the soil were considered (Table 44).

Table 44. Alternative paclobutrazol soil availability scenarios for acute toxicity to 

estuarine/marine fish

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

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

3

Surface 

Water 

(Tier 2 

PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.01-0.01

0.09-0.21*

0.12-0.19*

0.09-0.16*

0.03-0.07*

0.09-0.16*

<0.001-

0.008

0.07-0.16*

0.09-0.14*

0.07-0.12*

0.02-0.05*

0.07-0.12*

<0.001-

0.005

0.05-0.11*

0.06-0.10*

0.05-0.08*

0.02-0.04

0.05-0.06*

<0.001-

0.003

0.02-0.05*

0.03-0.05*

0.02-0.04

0.008-0.02

0.02-0.04
121

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

Ornamentals:

CA Ornamentals STD 

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.001-

0.002

0.02-0.05*

0.03-0.04

0.02-0.04

0.008-0.01

0.02-0.04

<0.001-

0.002

0.02-0.04

0.02-0.03

0.02-0.03

0.006-0.008

0.015-0.03

<0.001-

0.001

0.01-0.03

0.02-0.02

0.01-0.02

0.004-0.005

0.1-0.02

<0.01-0.001

0.005-0.01

0.008-0.01

0.005-0.01

0.002-0.003

0.005-0.01

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A) Water 0.11* 0.08* 0.06* 0.03

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified 

from total toxic residue simulations.

*Exceeds acute listed species LOC (0.05)

The alternative soil availability scenarios indicate that less than 25% of the applied 

paclobutrazol would need to be available in the soil to lower the risk quotients below the 

level of concern.

Chronic Risk

Chronic freshwater fish data were available and used to represent aquatic-phase amphibians 

in addition to fish. Risk quotients calculated from these data exceeded the LOC of 1 for 

almost every scenario that was tested. Likewise, risk quotients calculated for 

estuarine/marine fish exceeded the LOC for every situation. Paclobutrazol toxicity data were 

not available for chronic effects to estuarine/marine fish, thus the 5th percentile method was 

used to estimate the chronic value from structurally similar triazoles. An alternative 

approach of using the most sensitive triazole value (NOAEC = 11μg ai/L metconazole) 

versus the 5th percentile value (NOAEC = 4 μg ai/L) was explored. There were no changes

to the overall risk conclusions, even though the RQs were slightly lowered.

The chronic freshwater and estuarine/marine fish risk quotients are based on the assumption 

that 100 percent of the applied paclobutrazol is available in the soil (i.e., none of it was taken 

up by the plant to which it was applied). This is a conservative assumption and several less 

conservative scenarios that assumed 75, 50 and 25 percent availability in the soil were 

considered (Tables 45 and 46).
122

Table 45. Risk quotients for alternative paclobutrazol soil availability scenarios for 

chronic toxicity to freshwater fish

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environment

al Column

100% 75% 50% 25%

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

3

Surface 

Water 

(Tier 2 

PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.1-0.26

2.9-6.8***

4.0-6.1***

2.9-5.2***

1.1-2.1***

3.0-5.2***

<0.1-0.20

2.2-5.1***

3.0-4.6***

2.2-3.9***

0.83-1.6***

2.3-3.9***

<0.1-0.13

1.5-3.4***

2.0-3.1***

1.5-2.6***

0.6-1.1***

1.5-2.6***

<0.01-0.07

0.73-1.7***

1.0-1.5***

0.73-1.3***

0.28-0.53

0.8-1.3***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.1-0.1

0.65-1.5***

0.90-1.3***

0.65-1.2***

0.24-0.47

0.7-1.2***

<0.01-0.08

0.49-1.1***

0.68-0.98

0.49-0.90

0.18-0.35

0.53-0.9

<0.01-.05

0.33-0.75

0.45-0.65

0.33-0.60

0.12-0.24

0.35-0.6

<0.01-0.03

0.16-0.38

0.22-0.33

0.16-0.3

0.06-0.12

0.18-0.3

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.43-0.80

0.71-1.4***

0.32-0.60

0.53-1.1***

0.22-0.40

0.36-0.70

0.11-0.20

0.18-0.35

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

3.8*** 2.9*** 1.9*** 0.95

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

1.0*** 0.75 0.50 0.25

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs. 4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified 

from total toxic residue simulations.

***Exceeds chronic LOC (1)

The alternative soil availability scenarios for chronic effects to freshwater fish indicate that 

less than 25 percent of the applied paclobutrazol (i.e. 75 percent of the paclobutrazol was 

taken up into the plant to which it was applied), would need to be present in the soil to lower

the risk quotients below the level of concern for potted ornamentals. For turf, the RQs are 

below the LOC at 50% uptake.
123

Table 46. Risk quotients for alternative paclobutrazol soil availability scenarios for 

chronic toxicity to estuarine/marine fish

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environment

al Column

100% 75% 50% 25%

Total Toxic Residue (Paclobutrazol plus 149907and NOA 457654)

3

Surface 

Water (Tier 

2 PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.1-3.2***

35-83***

49-75***

36-64***

13-26***

36-64***

<0.1-2.4***

26-62***

37-56***

27-48***

9.8-20***

27-48***

<0.01-1.6***

18-42***

25-38***

18-32***

6.5-13***

18-32***

<0.01-0.8

8.8-21***

12-19***

9.0-16***

3.3-6.5***

9-16***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.1-0.7

8-18***

11-17***

8-14***

3-6***

8-14***

<0.1-0.53

6.0-14***

8.3-13***

6.0-11***

2.3-4.5***

6.0-11***

<0.1-0.35

4.0-9.0***

5.5-8.5***

4.0-7.0***

1.5-3.0***

4-7***

<0.1-0.18

2.0-4.5***

2.8-4.3***

2.0-3.5***

0.75-1.5***

2.0-3.5***

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

5-10***

9-17***

3.8-8.0***

6.8-13***

2.5-5.0***

4.5-8.5***

1.3-2.5***

2.3-4.3***

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

46*** 35*** 23*** 12***

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

13*** 9.8*** 6.5*** 3.3***

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified from 

total toxic residue simulations.

***Exceeds chronic LOC (1)

Even with the assumption that only 25 percent of the applied paclobutrazol is available in the 

soil (i.e. 75 percent was taken up by the plant), the risk quotients exceed the LOC of 1, 

indicating chronic risk to estuarine/marine fish.
124

Freshwater and Estuarine-Marine Invertebrates

Acute Risk

Acute paclobutrazol toxicity data for freshwater invertebrates and mollusks were available. 

Risk quotients did not exceed the LOCs for freshwater mollusks; however, LOCs were 

exceeded for all of the scenarios considered for freshwater invertebrates. The acute LOC of 

0.5 was exceeded for 75 percent of the drench applications to potted ornamentals at the 2.5 lb 

ai/A level. The acute listed LOC of 0.05 was exceeded for the remaining potted ornamental 

application, and turf scenarios. For estuarine/marine invertebrates, acute toxicity data for 

paclobutrazol were not available. Therefore, surrogate data from structurally-similar 

triazoles was used instead. This resulted in a 5th percentile estimate that was equivalent to 

the most sensitive triazole endpoint (mycobutanil EC50 = 240μg ai/L); thus, there was no 

difference between the 5th percentile approach and the most sensitive triazole endpoint 

approach. Risk quotients followed the same pattern as the freshwater invertebrates with the 

acute LOC (0.5) being exceeded for most potted ornamental applications at 2.5 lb ai/A and 

all other uses exceeding the acute listed LOC (0.05). A probit slope response analysis 

indicated a 1 in 49.8 chance of mortality with exposure to paclobutrazol for both freshwater 

and estuarine/marine invertebrates; the highest risk quotient was the same for both groups. 

These results indicate that there is acute risk to listed and non-listed freshwater and 

estuarine/marine invertebrates, excluding freshwater mollusks.

Data for an aquatic tubificid worm (Limnodrilus hoffmeisteri) were available from an open 

literature study identified by ECOTOX (Liu et al. 1996). The study indicated an acute 96-

hour LC50 was 34.9 mg ai/L (34900 μg ai/L). Compared with the Daphnia EC50 that was 

used in the risk quotient calculations, the tubificid worm is much less sensitive. Using the 

highest peak EEC of 333 (Total Toxic Residue approach – Florida Ornamentals at 2.5 lb 

ai/A), the risk quotient is 0.01, well below the LOCs.

In all scenarios, the assumption was made that 100 percent of the applied paclobutrazol is 

available in the soil (i.e., none of it was taken up by the plant to which it was applied). This 

is a conservative assumption and several less conservative scenarios that assumed 75, 50 and 

25 percent availability in the soil were considered for acute risks to freshwater and 

estuarine/marine invertebrates (Table 47).
125

Table 47. Risk quotients for alternative paclobutrazol soil availability scenarios for 

acute toxicity to freshwater and estuarine/marine invertebrates (RQs were the same for 

both groups, thus they are combined in one table)

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

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

3

Surface 

Water (Tier 

2 PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.01-0.05*

0.61-1.4**

0.83-1.3**

0.60-1.1**

0.22-0.43*

0.61-1.1**

<0.01-0.04

0.46-1.1**

0.62-0.98**

0.45-0.83**

0.17-0.32*

0.46-0.83**

<0.01-0.03

0.31-0.70**

0.42-0.65**

0.30-0.55**

0.11-0.22*

0.31-0.55**

<0.01-0.01

0.15-0.35*

0.21-0.33*

0.15-0.28*

0.06-0.11*

0.02-0.28*

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.01-0.01

0.13-0.31*

0.18-0.28*

0.13-0.24*

0.05-0.10*

0.13-0.24*

<0.01-0.01

0.10-0.23*

0.14-0.21*

0.10-0.18*

0.04-0.08*

0.1-0.2*

<0.01-0.01

0.07-0.16*

0.09-0.14*

0.07-0.12*

0.03-0.05*

0.07-0.12*

<0.01-<0.01

0.03-0.08*

0.05-0.07*

0.03-0.06*

0.01-0.03

0.3-0.06*

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.09-0.16*

0.15-0.28*

0.07-0.12*

0.11-0.21*

0.05-0.08*

0.08-0.14*

0.02-0.04

0.04-0.07*

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

0.78** 0.59** 0.39* 0.20*

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

0.21* 0.16* 0.11* 0.05*

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified from 

total toxic residue simulations.

*Exceeds the acute listed species LOC (0.05)

**Exceeds the acute non-listed species LOC (0.5)

Even with the assumption that only 25 percent of the applied paclobutrazol is available in the 

soil (i.e. 75 percent was taken up by the plant), the majority of the risk quotients exceed the 

LOC of 1, indicating acute risk to freshwater and estuarine/marine invertebrates.
126

Chronic Risk

Paclobutrazol chronic toxicity data for freshwater invertebrates were not available; thus 

surrogate data from structurally similar triazoles were used instead. This resulted in risk 

quotients that exceeded the LOC of 1 for all uses. As an alternative, the most sensitive 

endpoint from the triazoles (febuconazole NOAEC = 13 μg ai/L) was considered instead of 

the NOAEC generated by the 5th percentile approach. Using the 13 μg ai/L value, RQs were 

lowered; however, the risk conclusions remained the same. This indicates that paclobutrazol 

applications to potted ornamentals and turf present chronic risks to freshwater invertebrates. 

Paclobutrazol toxicity data were not available for estuarine/marine invertebrates; therefore,

surrogate data from structurally-similar triazoles was used instead. In this case, there was 

only one surrogate chemical available (tebuconazole), thus the most sensitive triazole 

NOAEC was used in the analysis by default. The risk quotients exceeded the LOC of 1 for 

the majority of the modeled scenarios. The exceptions included several scenarios in the 0.56 

lb ai/A drench to ornamental potted plants; however, there were several scenarios within this 

category that exceeded the LOC of 1. These results indicate that paclobutrazol applications 

to potted ornamental plants and turf present chronic risks to freshwater and estuarine/marine 

invertebrates. 

In all scenarios, the assumption was made that 100 percent of the applied paclobutrazol is 

available in the soil (i.e., none of it was taken up by the plant to which it was applied). This 

is a conservative assumption and several less conservative scenarios that assumed 75, 50 and 

25 percent availability in the soil were considered for acute risks to freshwater and 

estuarine/marine invertebrates (Tables 48 and 49).

Table 48. Risk quotients for alternative paclobutrazol soil availability scenarios for 

chronic toxicity to freshwater invertebrates 

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

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

3

Surface 

Water (Tier 

2 PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A) Water

<0.1-1.4***

16-37***

22-33***

16-28***

5.8-11***

16-28***

<0.1-1.1***

12-30***

17-25***

12-21***

4.4-8.3***

12-21***

<0.1-0.7

8.0-19***

11-17***

8.0-14***

2.9-5.5***

8.0-14***

<0.1-0.4

4.0-9.3***

5.5-8.3***

4.0-7.0***

1.5-2.8***

4.0-7.0***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

<0.1-0.31

3.6-8.1***

4.9-7.3***

3.6-6.3***

1.3-2.6***

<0.01-0.02

2.7-6.1***

3.7-5.5***

2.7-4.7***

0.98-2.0***

<0.01-0.02

1.8-4.1***

2.5-3.7***

1.8-3.2***

0.65-1.3***

0.0-0.001

0.9-1.0***

1.2-1.8***

0.9-1.6***

0.33-0.65
127

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

Ornamentals STD

(1 app. X 0.56 lb ai/A)

3.6-6.3*** 2.7-4.7*** 1.8-3.2*** 0.9-1.6***

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

2.3-4.3***

3.9-7.6***

1.7-3.2***

2.9-5.7***

1.2-2.2***

2.0-3.8***

0.58-1.1***

0.98-1.9***

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

20*** 15*** 10*** 5***

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

5.7*** 4.3*** 2.9*** 1.4***

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole. 3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified from 

total toxic residue simulations.

***Exceeds the chronic LOC (1)

Even with the assumption that only 25 percent of the applied paclobutrazol is available in the 

soil (i.e. 75 percent was taken up by the plant), the majority of the risk quotients exceed the 

LOC of 1, indicating chronic risk to freshwater invertebrates.

Table 49. Risk quotients for alternative paclobutrazol soil availability scenarios for 

chronic toxicity to estuarine/marine invertebrates 

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

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

3

Surface 

Water (Tier 

2 PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A) Water

<0.1-0.4

4.0-9.5***

5.6-8.6***

4.1-7.3***

1.5-2.9***

4.1-7.2***

<0.1-0.3

3.0-7.1***

4.2-6.5***

3.1-5.5***

1.1-2.2***

3.1-5.5***

<0.1-0.2

2.0-4.8***

2.8-4.3***

2.1-3.7***

0.75-1.5***

2.1-3.7***

<0.1-0.1

1.0-2.4***

1.4-2.2***

1.0-1.8***

0.38-0.73

1.0-1.8***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

<0.01-0.01

0.91-2.1***

1.3-1.9***

0.91-1.6***

0.34-0.66

<0.01-.01

0.68-1.6***

0.98-1.4***

0.68-1.2***

0.26-0.50

<0.01-0.01

0.46-1.1***

0.65-0.95

0.46-0.80

0.17-0.33

<0.01-<0.01

0.22-0.53

0.33-0.48

0.22-0.40

0.09-0.17
128

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

0.9-1.6*** 0.7-1.2*** 0.5-0.8 0.2-0.4

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

0.60-1.1***

1.0-2.0***

0.45-0.83

0.75-1.5***

0.30-0.55

0.5-1.0***

0.15-0.28

0.25-0.50

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

5.3*** 4.0*** 2.7*** 1.3***

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

1.5*** 1.1*** 0.75 0.38

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs. 4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified from 

total toxic residue simulations.

***Exceeds the acute listed LOC (1)

Even with the assumption that only 25 percent of the applied paclobutrazol is available in the 

soil (i.e. 75 percent was taken up by the plant), the potted ornamentals RQs do not fall below 

the level of concern. However, the turf concern is eliminated with a 25 percent soil 

availability. 

Aquatic Plants – Vascular and Non-vascular

Paclobutrazol toxicity data were available for aquatic non-vascular plants. A limited set of 

non-definitive data were available for aquatic vascular plants; thus the 5th percentile was used 

as an endpoint from structurally-similar triazoles. None of the risk quotients for aquatic nonvascular plants exceeded the LOC; however, all of the risk quotients for aquatic vascular 

plants exceeded the acute LOC of 0.5. To verify that the 5th percentile approach for 

generating an endpoint was not too conservative, the most sensitive EC50 (22 μg ai/L –

metconazole) was used to calculate RQs as well. The resulting RQs were lower; however it 

did not change the risk conclusion for any of the uses. The assumption was made that 100 

percent of the applied paclobutrazol is available in the soil (i.e., none of it was taken up by 

the plant to which it was applied). This is a conservative assumption and several less 

conservative scenarios that assumed 75, 50 and 25 percent availability in the soil were 

considered for risks to aquatic vascular plants (Table 50).
129

Table 50. Risk quotients for alternative paclobutrazol soil availability scenarios for 

toxicity to aquatic vascular plants 

Aquatic 

Exposure

(model)

Use Scenario 

(modeled rate)

Environmental 

Column

100% 75% 50% 25%

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

3

Surface 

Water 

(Tier 2 

PRZM/

EXAMS)

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

<0.1-1.6***

18-42***

25-38***

18-32***

6.5-13***

18-32***

<0.1-1.2***

14-32***

19-29***

14-24***

4.9-9.8***

13.7-24***

<0.1-0.8

9.0-21***

13-19***

9.0-16***

3.3-7.5***

9.0-16***

<0.1-0.4

4.5-11***

6.3-9.5***

4.5-8.0***

1.6-3.3***

4.5-8.0***

Ornamentals:

CA Ornamentals STD

FL Ornamentals STD

MI Ornamentals STD

NJ Ornamentals STD

OR Ornamentals STD

TN Ornamentals STD

(1 app. X 0.56 lb ai/A)

<0.1-0.4

4.0-9.3***

5.5-8.4***

4.0-7.1***

1.5-2.9***

4.0-7.1***

<0.1-0.3

3.0-7.0***

4.1-6.3***

3.0-5.3***

1.1-2.2***

3.0-5.3***

<0.1-0.2

2.0-4.7***

2.8-4.2***

2.0-3.6***

0.75-1.5***

2.0-3.6***

<0.1-0.1

1.0-2.3***

1.4-2.1***

1.0-1.8***

0.38-0.73

1.0-1.8***

Turf:

FL Turf STD

PA Turf STD

(3 app. [2 app. X 0.75 

lb and 1 app. X 0.5 lb] 

ai/A)

2.7-4.9***

4.4-8.5***

2.0-3.7***

3.3-6.4***

1.4-2.5***

2.2-4.3***

0.68-1.2***

1.1-2.1***

 Parent Paclobutrazol Only4

FL Ornamentals STD

(1 app. X 2.5 lb ai/A)

Water

23*** 17*** 12*** 6.3***

PA Turf STD

(3 app. [2 app. X 0.75 

and 1 app. X 0.5 lb] 

ai/A

6.4*** 4.8*** 3.2*** 1.6***

1

The LC50 used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of data 

from cyproconazole, fenbuconazole, hexaconazole, metconazole, mycobutanil, and tebuconazole. 2

The NOAEC used in the risk quotient calculation was based on the 5th percentile as calculated from a distribution of 

data from metconazole, tebuconazole, and triticonazole.

3

Multiple months were modeled; the range of RQs represents the highest and lowest EECs.

4

Exposure of parent only based on highest exposure scenarios (FL Ornamentals STD and PA Turf STD) identified 

from total toxic residue simulations.

***Exceeds the aquatic plant LOC (1)

Even with the assumption that only 25 percent of the applied paclobutrazol is available in the 

soil (i.e. 75 percent was taken up by the terrestrial plant), the majority of the risk quotients 

exceed the LOC of 1, indicating chronic risk to aquatic vascular plants.

The ECOTOX literature search identified one study on aquatic vascular plants (MRID 

48637501) that examined the effects of paclobutrazol on a dicot (Eurasian watermilfoil –

Myriophyllum spicatum L.) and a monocot (hydrilla – Hydrilla verticillata). In particular, the 
130

study examined the duration of time necessary for Eurasian watermilfoil and hydrilla to 

recover from a single exposure to paclobutrazol. Recovery was characterized by comparing 

the total stem length (i.e., length of main stem plus lateral stems) of controls to the treated 

groups. Exposures ranged from 0 to 14 days, depending on the treatment group. The study 

found that hydrilla recovered to a normal total stem length after 6-weeks, regardless of the 

initial exposure duration. In contrast Eurasian milfoil did not reach normal total stem lengths 

by 6-weeks, even when the paclobutrazol exposure period was limited to a single day. 

Overall, this study indicates that the Eurasian watermilfoil was more sensitive to 

paclobutrazol exposures than hydrilla. If this study can be extrapolated more broadly, it may 

indicate that aquatic dicots are likely to be more sensitive to paclobutrazol than aquatic 

monocots.

Summary of Risk from Direct Effects

A summary of the potential for risks to aquatic organisms is listed below:

• There are no acute risks for freshwater fish, aquatic-phase amphibians, and freshwater 

mollusks.

• Estuarine/marine fish are not at acute risk from the turf use, but are potentially at risk 

from the potted ornamental drench application. 

• There are potential chronic risks to freshwater fish and aquatic-phase amphibians; 

however, if only 50 percent, rather than 100 percent, of the paclobutrazol application 

remains in the soil, the potted ornamental use risk quotients fall below the LOC.

• There is potential risk for all application scenarios, including the reduced percentage 

of paclobutrazol in soil scenarios for: chronic estuarine/marine fish, acute freshwater 

invertebrates, acute estuarine/marine invertebrates, and chronic freshwater 

invertebrates.

• There are potential chronic risks to estuarine/marine invertebrates, even when 

reduced percents of paclobutrazol in the soil are considered for the potted 

ornamentals use; the risk quotients for turf use fall below the LOC with a 25 percent 

soil availability assumption.

• There are potential risks to vascular aquatic plants, even when reduced percents of 

paclobutrazol in the soil are considered.

• There are no risks to non-vascular plants from the application scenarios that were 

considered.

 

Listed Species Effects Analysis

The direct and indirect effects analysis for general taxa of listed species is summarized in

Table 51, for paclobutrazol uses. The analysis is based on the direct and indirect effects 

concluded from the analysis of risk estimates. 
131

Table 51. Summary of indirect and direct effects to listed species and preliminary effects determination for paclobutrazol uses 

Listed species 

group(1)

Direct Effect 

Assessment Endpoints

Direct Effects Indirect

Effects

Effects Determination

Non-vascular 

Aquatic Plant 

Species

Primary productivity No Effect – risk 

quotients below 

LOC. 

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

could affect non-vascular plant habitat by changing the water temperature, 

dissolved oxygen levels, sedimentation, etc. Therefore, indirect effects to 

aquatic non-vascular plants from effects to terrestrial plants may occur.

However, currently, there are no listed non-vascular aquatic plant species, 

therefore adverse effects to listed non-vascular plants is not expected. 

No Effect

Vascular 

Aquatic Plant 

Species

Primary productivity 

assessed from effects on

main stem length, total 

stem length (main + 

laterals), and fresh 

weight

May Affect, Likely 

to Adversely Affectrisk quotients above 

the LOC (using 

surrogate data).

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

could affect vascular plant habitat by changing the water temperature, 

dissolved oxygen levels, sedimentation, etc. Therefore, indirect effects to 

aquatic vascular plants from effects to terrestrial plants may occur.

May affect and likely affected based on direct effects and indirect effects 

from direct effects on terrestrial plants.

May Affect, Likely to 

Adversely Affect 

Freshwater 

Fish and 

Amphibians

Acute mortality No Effect – risk 

quotients below

LOC.

Adverse direct effects may be expected to aquatic organisms (fish, 

invertebrates, vascular plants) as potential food sources. 

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

May Affect, Likely to 

Adversely Affect
132

Listed species 

group(1)

Direct Effect 

Assessment Endpoints

Direct Effects Indirect

Effects

Effects Determination

Chronic survival, growth 

and reproduction 

May Affect, Likely 

to Adversely Effectrisk quotients above

LOC.

could affect freshwater fish and amphibian habitat by changing the water 

temperature, dissolved oxygen levels, sedimentation, etc. Therefore, indirect 

effects to freshwater fish and amphibians from effects to terrestrial plants 

may occur.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then freshwater fish and amphibians may be adversely affected by 

changes in prey populations.

Likely to adversely affect would be based on direct chronic effects to 

freshwater fish and amphibians as well as indirect effects from direct effects 

on aquatic organisms (fish, invertebrates plants), if the species is dependent

on them as a food source and from adverse effects on terrestrial plants which 

may affect habitat and and/or aquatic prey populations

Freshwater 

Invertebrates

Acute mortality May Affect, Likely 

to Adversely Affect –

risk quotients above 

LOC (except for 

freshwater mollusks).

Adverse direct effects to vascular aquatic plants are expected and could affect 

food sources or habitat for freshwater invertebrates. 

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

could affect freshwater invertebrate habitat by changing the water 

temperature, dissolved oxygen levels, sedimentation, etc. Therefore, indirect 

effects to freshwater invertebrates from effects to terrestrial plants may occur.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then freshwater invertebrates may be adversely affected by 

changes in prey populations. 

May affect and likely to adversely affect based on direct acute and chronic 

effects to freshwater invertebrates and indirect effects from direct effects on 

terrestrial plants which may affect habitat and and/or aquatic prey 

populations.

May Affect, Likely to 

Adversely Affect 

Chronic survival and 

reproduction 

May Affect, Likely 

to Adversely Affect –

risk quotients above

LOC.
133

Listed species 

group(1)

Direct Effect 

Assessment Endpoints

Direct Effects Indirect

Effects

Effects Determination

Estuarine/ 

Marine Fish

Acute mortality May Affect, Likely 

to Adversely Affect–

risk quotients above 

LOC (based on 

surrogate data).

Adverse direct effects are expected for aquatic vascular plants and 

invertebrates that may serve as a food source for the fish. 

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

could affect estuarine/marine fish habitat by changing the water temperature, 

dissolved oxygen levels, sedimentation, etc. Therefore, indirect effects to 

estuarine/marine fish from effects to terrestrial plants may occur.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then estuarine/marine fish may be adversely affected by changes 

in prey populations. 

May affect and likely to adversely affect based on direct effects to acute and 

chronic estuarine/marine fish and indirect effects from direct effects on 

terrestrial plants and aquatic organisms, which may affect habitat and and/or 

aquatic prey populations.

May Affect, Likely to 

Adversely Affect

Assessment of chronic 

growth and survival

May Affect, Likely 

to Adversely Affect –

risk quotients above

LOC (based on 

surrogate data).

Estuarine/ 

Marine 

Invertebrates

Acute mortality May Affect, Likely

to Adversely Affectrisk quotients above

LOC (based on 

surrogate data)

Adverse direct effects are expected for aquatic vascular plants that may serve 

as a food source or habitat to the estuarine/marine invertebrates.

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift (turf application) or runoff from drench and soil 

May Affect, Likely to 

Adversely Affect
134

Listed species 

group(1)

Direct Effect 

Assessment Endpoints

Direct Effects Indirect

Effects

Effects Determination

Assessment of chronic 

growth and reproductive 

effects

May Affect, Likely 

to Adversely Affect –

risk quotients above 

LOC (based on 

surrogate data).

injection applications. This could result in reduced growth of non-target 

plants and modify the structural habitat near aquatic environments. This 

could affect estuarine/marine invertebrate habitat by changing the water 

temperature, dissolved oxygen levels, sedimentation, etc. Therefore, indirect 

effects to estuarine/marine invertebrates from effects to terrestrial plants may 

occur.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then estuarine/marine invertebrates may be adversely affected by 

changes in prey populations.

May affect and likely to adversely affect based on direct acute and chronic 

risks to estuarine/marine invertebrates and indirect effects from direct effects 

on terrestrial plants which may affect habitats and/or aquatic prey populations

Non-target 

plants in 

terrestrial and 

semi-aquatic 

areas

Primary productivity 

assessed from effects on 

biomass as measured 

using survival and dry 

weight; incident data.

May Affect and 

Likely to Adversely 

Affect –

Evidence that direct 

foliar exposure or 

exposure to roots via 

runoff to 

paclobutrazol causes 

direct toxicity which 

may result in reduced 

biomass (based on 

surrogate and 

paclobutrazolspecific data).

Potential adverse effects to terrestrial invertebrates. As terrestrial 

invertebrates are foragers and/or pollinators for terrestrial plants, indirect 

effects to terrestrial plants may occur if a plant is dependent on a particular

species. Also, there is the potential for adverse direct effects to birds and 

mammals which may be seed dispersers for terrestrial plants. Therefore,

indirect effects on terrestrial plants from paclobutrazol are likely to have 

adverse effects if a species is dependent on another species for pollination. 

There are also potential adverse effects from habitat modification. 

Paclobutrazol modifies plants by promoting a more compact growth form. 

Any plant, animal, bird, or insect that depends on plants for shelter may be 

affected by a change in plant structure.

May Affect, Likely to 

Adversely Affect

Birds, 

Reptiles, and 

Land-Phase 

Amphibians

Acute mortality No Effect – risk 

quotients below 

LOC.

Potential for direct effects to mammals and other birds, reptiles and 

amphibians, therefore, indirect effects could occur from a reduction in prey 

populations.

May Affect, Likely to 

Adversely Affect
135

Listed species 

group(1)

Direct Effect 

Assessment Endpoints

Direct Effects Indirect

Effects

Effects Determination

Chronic reproduction May Affect, Likely 

to Adversely Affect –

risk quotients above 

LOC.

Direct effects to non-listed and listed terrestrial may occur from 

paclobutrazol spray drift and runoff exposure; therefore, indirect effects 

could occur from an alteration in habitat in which a species relies on for 

forage, shelter, and/or reproduction needs.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then birds, reptiles, and land-phase amphibians may be adversely 

affected by changes in prey populations. 

Likely to have adverse indirect effects depending on the relationship with 

prey and predator populations, plants as food source and habitat reliance.

Mammals Acute mortality May Affect, Likely 

to Adversely Affect –

risk quotients above 

LOC.

Potential for direct effects to other mammals and birds, reptiles and 

amphibians, therefore, indirect effects could occur from a reduction in prey 

populations.

Direct effects to non-listed and listed terrestrial may occur from 

paclobutrazol spray drift and runoff exposure; therefore, indirect effects 

could occur from an alteration in habitat in which a species relies on for 

forage, shelter, and/or reproduction needs.

If indirect effects to aquatic habitats from terrestrial plants occur, which then 

indirectly affect aquatic organism availability as a food source for other 

organisms, then mammals may be adversely affected by changes in prey 

populations. 

Likely to have adverse indirect effects depending on the relationship with 

prey and predator populations, plants as food source and habitat reliance.

May Affect, Likely to 

Adversely Affect 

Chronic Reproduction May Affect, Likely 

to Adversely Affect –

risk quotients above 

LOC.

Terrestrial 

Insects

Acute mortality based on 

contact

No Effect – based on 

surrogate data.

Direct effects to non-listed and listed terrestrial plants may occur from 

paclobutrazol spray drift and runoff exposure; therefore, indirect effects 

could occur from an alteration in habitat in which a species relies on for 

forage, shelter, and/or reproduction needs.

Likely to have adverse indirect effects depending on the relationship with 

prey and predator populations, plants as food source and habitat reliance.

May Affect, Likely to 

Adversely Affect
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ACTION AREA

In the case of a nationwide risk assessment conducted under registration review, the action 

area will encompass the entire U.S. and its territories. The purpose of defining the action 

area as the entire U.S. and its territories is to ensure that the initial area of consideration 

encompasses all areas where the pesticide may be used now and in the future, including the 

potential for off-site transport via spray drift and downstream dilution. Additionally, the 

concept of a nationwide action area takes into account the potential for direct and indirect 

effects and any potential modification to critical habitat based on ecological effect measures 

associated with reduction in survival, growth, and reproduction, as well as the full suite of 

sub-lethal effects available in the effects literature. 

It is important to note that the nationwide action area does not imply that direct and/or 

indirect effects and critical habitat modification are expected to or are likely to occur over the 

full extent of the action area, but rather to identify all listed species and critical habitat that 

may potentially be affected by the action. The Agency will use more rigorous analysis 

including consideration of available land cover data, toxicity data, and exposure information 

to determine areas where individual listed species and designated critical habitat may be 

affected or modified via endpoints associated with reduced survival, growth, or reproduction.

 

 EFFECTS AREA DETERMINATION

The potential for direct and/or indirect effects is possible to listed species from exposure to 

paclobutrazol. 

Direct Effects

There are potential direct effects to the listed species for the following taxa:

• Birds, Reptiles, and Land-phase Amphibians (based on chronic risk quotients 

exceeding the LOC)

• Mammals (based on acute and chronic risk quotients exceeding the LOC)

• Terrestrial Plants (based on risk quotients exceeding the LOC)

• Estuarine/Marine Fish (based on acute and chronic risk quotients exceeding the LOC)

• Freshwater Fish (based on chronic risk quotients exceeding the LOC)

• Freshwater Invertebrates (based on acute and chronic risk quotients exceeding the 

LOC)

• Estuarine/Marine Invertebrates (based on acute and chronic risk quotients exceeding 

the LOC)

• Vascular Aquatic Plants (based on risk quotients exceeding the LOC)
137

Indirect Effects

As there are potential direct effects to birds, reptiles, amphibians, mammals, terrestrial plants, 

estuarine/marine fish, freshwater fish, freshwater invertebrates, estuarine/marine 

invertebrates, and vascular aquatic plants, indirect effects could occur to other taxa.

• Indirect effects to listed fish, aquatic invertebrates, amphibians, reptiles, and other 

terrestrial organisms (e.g. birds, mammals and other invertebrates) that are dependent

on aquatic invertebrates and plants for food.

• Indirect effects to terrestrial plants for which terrestrial animals (e.g. birds and 

mammals) are needed for reproduction (e.g. pollination, seed dispersal) as there may 

be a potential change in terrestrial animal communities/populations. 

• Indirect effects to a listed species that is dependant to a bird, reptile, amphibian, 

mammal, fish, aquatic invertebrate, or aquatic vascular plant during some phase of 

their life-cycle.

• Indirect effects to listed species that are dependent on a plant in terrestrial or semiaquatic areas during some phase of their life-cycle for things such as food, shelter, 

reproductive habitats. 

The following table shows the potential taxa indirectly affected by direct effects (Table 52)

Table 52. Organism groups that are potentially indirectly affected by direct effects to 

other organisms

Taxon Directly Affected Taxon Indirectly Affected Reason for Indirect Effect

Birds, Reptiles, Amphibians Mammals, Plants, Reptiles, other 

Birds, Fish

Change in prey population (food 

source); Reduction in potential 

pollinators/seed dispersers

Mammals Reptiles, Birds, Plants, Amphibians Change in prey population (food 

source); Reduction in potential 

pollinators/seed dispersers

Aquatic Invertebrates Fish, Reptiles, Amphibians, Plants,

Mammals

Change in prey population (food 

source)

Fish Reptiles, Fish, Amphibians, 

Mammals, Birds

Change in prey population (food 

source)

Plants All taxa (birds, mammals, reptiles, 

amphibians, fish, aquatic and 

terrestrial invertebrates)

Change in food sources; change in 

habitats

Based on this screening-level assessment, there are potential concerns for direct toxic effects 

to listed and non-listed mammals, terrestrial plants, freshwater invertebrates, 

estuarine/marine invertebrates, freshwater fish, estuarine/marine fish, vascular aquatic plants, 

birds, reptiles, and amphibians from the use of paclobutrazol on some of its registered use 

sites. Listed species of all taxa may also be affected through indirect effects because of the 

potential for direct toxic effects on listed and non-listed species. Potential direct toxic effects 

on these species may be associated with modification of primary constituent elements of 
138

designated critical habitats, where such designations have been made. However, at this 

current stage of the Registration Review process, it is premature to make effects 

determinations for listed species until further refinements are conducted. To make effects 

determinations for individual species, useful refinements may include analyses of 1) more 

detailed, species-specific ecological and biological data; 2) more detailed and accurate 

information on paclobutrazol use patterns and application rates; and 3) sub-county level 

spatial proximity data for the co-occurrence of potential effects areas and listed species and 

any designated critical habitat. Examples of such refinements are described below.

EFED is currently developing tools that are expected to further refine the assessment and are 

designed to support effects determinations for individual federally listed species and their 

designated critical habitats (where applicable). Scientific information obtained from the U.S. 

Fish & Wildlife Service (USFWS), the National Marine Fisheries Service (NMFS), and other 

reliable sources is being collated by EFED to address all currently listed species. The 

information will be stored in an Office of Pesticide Programs Pesticide Registration 

Information SysteM (PRISM) knowledgebase. The listed species knowledgebase will 

consist of an information repository that houses biological and behavioral information 

relevant to individual species (e.g., habitat, diet, and life history, including specific temporal 

and spatial associations) and a document repository that contains supporting documents (e.g., 

USFWS recovery plans) and electronic information (e.g., GIS data files). For terrestrial taxa, 

the biological information relevant to risk quotient (RQ) calculations (e.g., diet and body 

weight) will be used to parameterize exposure estimates to derive species-specific RQs using 

a method consistent with currently used methods in the T-REX and T-HERPS models. 

Refinements may also include more detailed analyses of the registered uses and their use 

patterns that result in LOC exceedances for federally listed species in the screening-level 

assessment. The analyses may include more information on where, when, and how 

paclobutrazol is used on all use sites. Actual usage data (when available) and national landcover datasets that indicate potential use sites [e.g., national land cover dataset (NLCD), crop 

data layer (CDL)] may be used to support a more refined analysis of where paclobutrazol is 

reasonably expected to be used. Similarly, refinements for the timing of applications and 

how paclobutrazol is used may be based on the analysis of additional usage data, beyond 

what were available at the time of the screening-level assessment, and a more in-depth 

exploration of agronomic practices. 

In addition, a committee of the National Research Council (NRC) has been tasked with 

providing advice on ecological risk assessment tools and scientific approaches under ESA 

and FIFRA (Project Identification Number DELS-BEST-11-01). The committee has been 

asked to review the use of “best available data;” methods for evaluating sub-lethal, indirect, 

and cumulative effects; the state of the science regarding assessment of mixtures and 
139

pesticide inert ingredients; the development, application, and interpretation of results from 

predictive models; uncertainty factors; and what constitutes authoritative geospatial and 

temporal information for the assessment of individual species and habitat effects. The 

Agency anticipates that this NRC report, tentatively expected in Spring 2013, will provide 

recommendations to ensure the scientific soundness and maximize the utility of risk 

assessment refinements for listed species.

The refinements based on individual species data; additional, detailed usage information, 

when available; and further recommendations from the NRC report are expected to help to 

more accurately identify potential areas of effect and to better inform effects and habitat 

determinations for listed species and any designated critical habitats. For example, if 

paclobutrazol is used when a particular species of concern is not present (e.g., it is migratory) 

or is not co-located in space, then risk of potential direct effects to the species may often be 

precluded. If LOCs are still exceeded for terrestrial plants, mammals, freshwater 

invertebrates, estuarine/marine invertebrates, freshwater fish, estuarine/marine fish, birds, 

reptiles, amphibians, and vascular aquatic plants after conducting the refined analyses, 

further analyses of the potential spatial and temporal co-occurrence of listed species of 

concern (and any designated critical habitat) may be conducted. The extent of possible 

refinement in the analyses of spatial/temporal co-occurrence will largely depend on the scale 

and quality of the available sub-county level use site (e.g., NLCD, CDL) and species location 

data.

The Agency has refined the list of endangered and threatened species that may be affected by 

paclobutrazol uses based on the best available information to date. For the seed treatment 

uses (tomato, cucurbit, pepper, cabbage, cauliflower, broccoli) no direct or indirect effects 

are expected for listed species because these uses did not result in risk quotients that 

exceeded the level of concern for any taxonomic group. The remaining uses (potted 

ornamental drench and spray, tree injection, soil injection/basal drench, turf) will need to be 

considered in more depth before effects calls are made. At this time, the Agency does not 

have a spatial data layer that captures turf, ornamental plants, and shade tree uses. Further, 

the biological, geographical, and use pattern information outlined above will be necessary to 

refine the assessment. The following taxa will need to be considered for each use (Table 53).
140

Table 53. List of uses and taxa that need further consideration for direct effects calls

Taxa for further consideration

Potted ornamental drench Mammals, freshwater fish, estuarine/marine fish, freshwater 

invertebrates, estuarine/marine invertebrates, and vascular 

aquatic plants

Potted ornamental spray Mammals

Tree injection Mammals

Soil injection/basal drench Birds, mammals, and terrestrial plants

Turf and golf courses Mammals, terrestrial plants, freshwater fish, estuarine/marine 

fish, freshwater invertebrates, estuarine/marine invertebrates, 

and vascular aquatic plants
141

Uncertainties

A description of assumptions, uncertainties, strengths, and limitations of the basic risk 

assessment performed is described in Chapter 6 of the Agency’s Overview Document (EPA, 

2004) and includes those related to exposure for all taxa, those related to exposure for aquatic 

species, those related to exposure for terrestrial animals, those related to the effects 

assessment, and those associated with the acute LOC values. This Chapter discusses 

additional uncertainties associated with refinements made to the basic risk assessment.

Effects and Risk Assessment Uncertainties

Ecotoxicity Data Gaps

Data for the following fate and eco-toxicity studies were not available. The Final Work Plan 

for paclobutrazol requested seedling emergence and vegetative vigor data, but the studies 

submitted in response to this request were found to be partially or completely invalid. Data 

for the other studies were not requested in the Final Work Plan. Open literature searches 

were performed, but even with the addition of information from these sources, data still were 

not available for estuarine/marine fish (acute and chronic), freshwater invertebrates (chronic), 

estuarine/marine invertebrates (acute and chronic), seedling emergence (monocots and 

dicots), vegetative vigor (monocots), honey bees (acute contact), and vascular aquatic plants. 

To address each gap, toxicity data was used from other triazoles that were similar in structure 

to paclobutrazol (Appendix F). Crystal Ball (2000 version 5.0) was used to create a fitted 

lognormal distribution running a Monte Carlo sampling scheme (10,000 trials). The 5th

percentile of the data was calculated used in the risk assessment. Not every triazole had a 

complete set of data, so the chemicals and number of data points varied for each 

paclobutrazol data gap. This approach was chosen as it was thought to be conservative; 

however, it is possible that for any given endpoint, the triazole-calculated paclobutrazol 

surrogate could have underestimated the risk. The following bulleted list contains a brief 

description of how each data gap was filled. 

• Estuarine/Marine Fish (Acute) OPPTS 850.1075. Definitive LC50 data from six 

triazoles (cyproconazole, fenbuconazole, hexaconazole, metconazole, myclobutanil, 

tebuconazole, triticonazole) were available. A surrogate toxicity value for 

paclobutrazol acute effects on estuarine/marine fish was developed based on the 5th

percentile of the distribution of data. 

• Estuarine/Marine Fish (Chronic) OPPTS 850.1400. Definitive NOAEC/NOEC data 

from three triazoles (metconazole, tebuconazole, triticonazole) were available. A 

surrogate toxicity value for paclobutrazol chronic effects on estuarine/marine fish was 

developed based on the 5th percentile of the distribution of data.
142

• Freshwater Invertebrates (Chronic) OPPTS 850.1300. Definitive NOAEC/NOEC 

data from eight triazoles (cyproconazole, fenbuconazole, hexaconazole, metconazole, 

tebuconazole, triadimefon, triadimenol, triticonazole) were available. A surrogate 

toxicity value for paclobutrazol chronic effects on freshwater invertebrates was 

developed based on the 5th percentile of the distribution of data.

• Estuarine/Marine Invertebrates (Acute) OPPTS 850.1025 and OPPTS 850. 1035. 

Definitive LC50/EC50 data from seven triazoles (cyproconazole, fenbuconazole, 

hexaconazole, metconazole, myclobutanil, tebuconazole, triticonazole) were 

available. A surrogate toxicity value for paclobutrazol acute effects on 

estuarine/marine invertebrates was developed based on the 5th percentile of the 

distribution of data. In addition, acute toxicity data were available for a freshwater 

mollusk.

• Estuarine/Marine Invertebrates (Chronic) OPPTS 850.1350. Definitive 

NOAEC/NOEC data were available for only one triazole – tebuconazole. 

Consequently, tebuconazole’s toxicity value was used as a surrogate for paclobutrazol 

chronic effects on estuarine/marine invertebrates.

• Seedling Emergence (Monocots and Dicots) OPPTS 850.4225. Definitive monocot 

NOAEC/NOEC data from four triazoles (cyproconazole, metconazole, tebuconazole, 

triticonazole) were available. A surrogate toxicity value for paclobutrazol effects on 

monocot seedling emergence was developed based on the 5th percentile of the 

distribution of data. Definitive dicot EC25 data from three triazoles (cyproconazole, 

tebuconazole, triticonazole) and definitive dicot NOAEC/NOEC data from three 

triazoles (cyproconazole, metconazole, triticonazole) were available. Surrogate 

toxicity values for paclobutrazol effects on dicot seedling emergence were developed 

based on the 5th percentile of these two data distributions. 

• Vegetative Vigor (Monocots) OPPTS 850.4250. Definitive monocot NOAEC/NOEC 

data from three triazoles (cyproconazole, metconazole, tebuconazole) were available. 

A surrogate toxicity value for paclobutrazol effects on monocot vegetative vigor was 

developed based on the 5th percentile of the distribution of data.

• Honey Bee (Acute Contact) OPPTS 850.3020. Only non-definitive LD50 data were 

available for five triazoles (cyproconazole, fenbuconazole, metconazole, triadimefon, 

triticonazole). Consequently, the most conservative value (triticonazole) was used in 

the risk assessment

• Aquatic Vascular Plants (EC50) OPPTS 850.4400. Definitive EC50 data were 

available for four triazoles (cyproconazole, metconazole, tebuconazole, triticonazole). 

A surrogate toxicity value for paclobutrazol effects on aquatic vascular plants was 

developed based on the 5th percentile of the distribution of data.

• Aquatic Non-Vascular Plants (EC50) OPPTS 850.5400. Toxicity data were not 

available for algal species. Open literature provided some toxicity information on 

paclobutrazol to green algae.
143

• Passerine Birds (Acute) OPPTS 850.2100. Data were not available, therefore, the 

acute oral toxicity of paclobutrazol to the mallard duck was used to evaluate risk. 

Application Rates

Many of the labels did not contain application information in pounds of active ingredient per 

acre. Tree injection, and soil injection/basal drench for ornamental trees provided application 

rates in grams of paclobutrazol per tree diameter. To evaluate exposure, assumptions (based 

on open literature) on the number of trees expected to be present in one acre as well as a 

conservative application rate in pounds of paclobutrazol per acre were made. These 

assumptions may be overestimating or underestimating exposure.

Greenhouse seed treatments for cucurbits, peppers, tomatoes, broccoli, cauliflower, and 

cabbage were stipulated in terms of micrograms of paclobutrazol per seed. To evaluate 

environmental exposure, the number of transplants per acre was derived from open literature 

sources. These assumptions may be overestimating or underestimating exposure.

Pre-plant plug and liner soak labels did not provide specific use rates because the rate is 

influenced by varying soak times, the extent of rooting of each plant, the media moisture

levels, the differing sensitivities of cultivars and species being treated, cultural practices, and 

environmental factors. Consequently, it was not possible to calculate a per-acre application 

rate for these uses. It was assumed that the pre-plant plug and liner soak application rate 

would not exceed the soil drench and/or bench spray for greenhouse ornamental transplants 

(see below). This assumption may be overestimating or underestimating exposure.

Soil drench and bench spray application rates for greenhouse ornamental transplants were 

described in terms of parts per million per various size pot or bench area. To evaluate 

exposure, assumptions (based on open literature) were made to estimate the application rate 

per acre. These assumptions may be overestimating or underestimating exposure.

Rate of Paclobutrazol Uptake into Plants

Spray, drench, and seed treatment applications assume that paclobutrazol will be absorbed 

into plants in one of two ways: directly through the leaves, stem, or seed coat; or taken up 

through the roots from the soil. Information was not available on the rate at which this 

occurred. This posed a challenge for assessing risk to terrestrial and aquatic organisms. For 

example, in the tree drench scenario, the most conservative assumption for assessing risk to 

terrestrial animals is to assume 100 percent of the paclobutrazol is taken up into the plant. 

Conversely, the most conservative assumption for assessing risks to aquatic organisms or 

other terrestrial plants (via runoff) is to assume that none of the paclobutrazol was taken up 

into the plant and is all still available in the soil. This approach of using the most 

conservative assumptions for each organism group assessed essentially “double counts” the 
144

amount of paclobutrazol available to non-target organisms and over-estimates risk to some 

groups, if not all. However, without data to show how quickly paclobutrazol is absorbed into 

plants, it is difficult to choose realistic exposure scenarios. Consequently, the following 

plant-to-soil scenarios were considered: 100%:100%, 50%:50%, 25%:75%, and 75%:25%.

Distribution of Paclobutrazol in Plants

The application methods for paclobutrazol rely on its translocation to internodes and dividing 

cells within the plant. In particular, drenches and tree/soil injections rely on the chemical 

being transported from the roots or trunk of the tree to the leaves and stems. No information 

is available about whether all of the paclobutrazol concentrates in the leaves of the tree or if 

it remains equally distributed throughout the entire tree (roots, trunk, branches, fruit, leaves, 

etc.) or its translocation rate. In the risk assessment, the conservative assumption was made 

that paclobutrazol concentrates in the leaves of the plant and that it does so very quickly after 

being applied. This may have resulted in overly conservative estimates of paclobutrazol 

exposure through the consumption of treated foliage.

Fate Data Gaps

The following fate study is not available. 

• OPPTS 850.1730 – Fish Bioconcentration Factor (BCF). To evaluate 

bioaccumulation, the model, KABAM, was employed. Results indicated that the 

potential for bioaccumulation in aquatic food web is low.

Incomplete Life Histories of Listed Species

Currently, an approved database of the complete life histories for each of the listed animals 

and plants is not available. These life histories would include information such as body size 

at each life stage, food sources, relationships with other taxa, habitat, and dietary and 

reproductive habits. As such, conservative assumptions were made concerning the potential 

relationships between species in that each species was assumed to have a relationship with 

the other taxa. This is assumed to be an overestimation of the actual species that have an 

species dependant relationship. 

Locations of Listed Species

In addition, the locations of listed species are not known in some cases beyond the countylevel. If the location of a species was not known beyond county level, the species was 

assumed to occur anywhere within that county at any time. This assumption may lead to an 

overestimation of co-occurrence with paclobutrazol exposure and overestimation of the 

number of species potentially at risk.
145

Information on Crop Locations, Actual Use Rates, and Application Methods

While the assessment was based on the maximum application rates and methods stated on the 

registered labels, information on the use rates and application methods actually used in 

residential settings, golf courses, right-of-ways, athletic fields, and in fields were not 

available to refine the risk characterization of paclobutrazol. In addition, sub-county 

information on where treated tomatoes, peppers, cucurbits, broccoli, cauliflower, and 

cabbage are grown would have been helpful when determining co-occurrences with listed 

species.

Other Routes of Exposure

Screening-level risk assessments for applications of pesticides consider dietary exposure 

alone. Other routes of exposure, not considered in this assessment, are discussed below:

Incidental soil ingestion exposure - This risk assessment does not consider incidental soil 

ingestion. Available data suggests that up to 15% of the diet can consist of incidentally 

ingested soil depending on the species and feeding strategy (Beyer et al., 1994). This route 

of exposure may be important for applications of paclobutrazol as a soil drench or soil 

injection.

Dermal Exposure - The screening assessment does not consider dermal exposure, except as it 

is indirectly included in calculations of risk quotient’s based on lethal doses per unit of 

pesticide treated area. Dermal exposure may occur through three potential sources: (1) direct 

application of spray to terrestrial wildlife in the treated area or within the drift footprint, (2) 

incidental contact with contaminated vegetation, or (3) contact with contaminated water or 

soil. As foliar application and drenches are primary application routes on the registered 

labels for paclobutrazol, dermal contact with paclobutrazol to non-target animals may occur.

Foliar Dissipation Half-life

An additional source of uncertainty is the foliar dissipation half-life, which is useful for spray 

applications to foliage. No half-life data were provided, thus a default of 35 days was used. 

It is not known if this half-life over or under-estimates the true half-life for paclobutrazol.

Species Sensitivity

Although the screening-level risk assessment relies on a selected toxicity endpoint from the 

most sensitive species tested, it does not necessarily mean that the selected toxicity endpoints 

reflect the sensitivity of the most sensitive species existing in a given environment. The 

relative position of the most sensitive species tested in the distribution of all possible species 

is a function of the overall variability among species to a particular chemical. In the case of 

listed species, there is uncertainty regarding the relationship of the listed species’ sensitivity 

and the most sensitive species tested.
146

The Agency is not limited to a base set of surrogate toxicity information in establishing risk 

assessment conclusions. The Agency also considers toxicity data on non-standard test 

species when available.

Endocrine Disruptor Screening Program (EDSP)

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential 

adverse outcomes from exposure to chemicals. Collectively, these studies include acute, 

subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, 

developmental, reproductive, and general or systemic toxicity. These studies include 

endpoints which may be susceptible to endocrine influence, including effects on endocrine 

target organ histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, 

pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard 

assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental 

and reproductive effects in different taxonomic groups. As part of its decision, EPA 

reviewed these data and selected the most sensitive endpoints for relevant risk assessment 

scenarios from the existing hazard database. However, as required by FFDCA section 

408(p), paclobutrazol is subject to the endocrine screening part of the Endocrine Disruptor 

Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the 

Administrator may designate.” The EDSP employs a two-tiered approach to making the 

statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to 

identify the potential of a chemical substance to interact with the estrogen, androgen, or 

thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are 

found to have the potential to interact with E, A, or T hormonal systems will proceed to the 

next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests are 

necessary based on the available data. Tier 2 testing is designed to identify any adverse 

endocrine-related effects caused by the substance, and establish a dose-response relationship 

between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 

67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

Paclobutrazol is not among the group of 58 pesticide active ingredients on the initial list to be 

screened under the EDSP. Accordingly, as part of registration review, EPA will issue future 

EDSP orders/data call-ins, requiring the submission of EDSP screening assays for
147

paclobutrazol. For further information on the status of the EDSP, the policies and 

procedures, the list of 67 chemicals, future lists, the test guidelines and the Tier 1 screening 

battery, please visit our website: http://www.epa.gov/endo/.

Seasonal Carryover in Plants

Paclobutrazol is a systemic and is known to persist for years in trees (based on label 

information and application intervals). It is unknown if for grasses and perennials, 

paclobutrazol levels are maintained across seasons and expressed in subsequent 

“generations” of foliage.

Greenhouse Discharges

Paclobutrazol is applied as a liquid to potted plants within greenhouses, as well as a bulb and 

plug/liner soak. It is possible that paclobutrazol may be present in the runoff water. This is a 

scenario that was not assessed and a point of uncertainty.

Spatial Analysis

Data are not available for the percent of cropped areas and changes in crops (e.g., crop 

rotation or permanent shifts) over time. This remains an uncertainty, particularly for the 

proximity analysis for listed species. 
148

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Appendix A – Bibliography of MRIDs

Ecological Effects Studies

117478 Barber, J., G. Parkinson, G. Oliver, et al. 1982. PP333: acute oral, dermal, and 

intraperitoneal toxicity: report number CTL/P/748. Final report. (Unpublished study 

received October 28, 1982 under 10182-77; prepared by Imperial Chemical Industries 

PLC, England, submitted by ICI Americas, Inc., Wilmington, DE; CDL 248688-B).

117484 Ross, D., N. Roberts, and C. Phillips. 1979. The acute oral toxicity (LD50) of 

PP333 to the mallard duck. ICI 252WL/781176; CTL/C/ 686. (Unpublished study 

received October 28, 1982 und 10182-77; prepared by Huntingdon Research Centre, 

England, submitted by ICI Americas, Inc., Wilmington, DE; CDL: 248689-B).

117485 Roberts, N., C. Fairley, and R. Almond. 1982. The subacute dietary toxicity (LC50) 

of PP333 to the mallard duck. ICI 417WL/82629; CTL/C/1173. Final report. 

(Unpublished study received October 28, 1982 under 10182-77; prepared by Huntingdon 

Research Centre, England, submitted by ICI Americas, Inc., Wilmington, DE; CDL: 

248689-C).

117486 Roberts, N., C. Fairley, and R. Almond. 1982. The subacute dietary toxicity (LC50) 

of PP333 to the bobwhite quail. ICI 418/82661; CTL/?/1172. Final report. 

(Unpublished study received October 28, 1982 under 10182-77; prepared by Huntingdon 

Research Centre, England, submitted by ICI Americas, Inc., Wilmington, DE; CDL: 

248689-D).

117487 Hill, R., B. Young, and S. Cornish. 1978. Determination of the acute toxicity of 

PP333 to rainbow trout. BL/B/1935. (Unpublished study received October 28, 1982 

under 10182-77, prepared by Imperial Chemical Industries Ltd., England, submitted by 

ICI Americas, Inc., Wilmington, DE; CDL: 248689-E.

117488 Hill, R., and B. Maddock. 1982. PP333: determination of the acute toxicity to 

bluegill sunfish. BL/B/2209. Final report. (Unpublished study received October 28, 

1982 under 10182-77; prepared by Imperial Chemical Industries PLC, England, 

submitted by ICI Americas, Inc., Wilmington, DE; CDL: 248689-F.

117489 Hamer, M., I. Hill, and S. Walker. 1982. PP333: toxicity of the technical material 

and formulation GFU 029 to first instar Daphnia magna. Report series RJ 0282B. Final 

report. (Unpublished study received October 28, 1982 under 10182-77; prepared by 

Imperial Chemical Industries, Ltd., England, submitted by ICI Americas, Inc., 

Wilmington, DE; CDL: 248689-G.
153

40734303 Wickramaratne, G. A. 1987. Paclobutrazol: two generation reproduction study 

in rats including individual animal data. Unpublished study performed by ICI Central 

Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK. Study sponsored by 

ICI Americas Inc., Agricultural Products, Wilmington DE. Report submitted February 

27, 1987.

47918901 Martin, J. A. 2009. Paclobutrazol – early life-stage toxicity test with fathead 

minnow (Pimephales promelas). Unpublished study performed by Springborn Smithers 

Laboratories, Wareham, MA. Laboratory report number: 1781.6743. Study sponsored 

by Syngenta Crop Protection, Inc., Greensboro, NC. Study initiated July 16, 2009 and 

submitted November 23, 2009.

47918903 Martin, J. A. 2009. Paclobutrazol technical – vegetative vigor test following U.S. 

EPA OPPTS Draft Guideline 850.4250 and OECD Draft Guideline 208, Part B. 

Unpublished study performed by Springborn Smithers Laboratories, Wareham, MA. 

Laboratory report number: 1781.6742. Study sponsored by Syngenta Crop Protection,

Inc., Greensboro, NC. Study completed November 23, 2009.

48270601 Stafford, J. 2010. Paclobutrazol- reproductive toxicity test with northern 

bobwhite (Colinus virginianus) following FIFRA Guideline 71-4, OPPTS 850.2300 and 

OECD 206. Unpublished study performed by Springborn Smithers Laboratories (CRC), 

Snow Camp, NC. Laboratory Project No. 1781.4110. Study sponsored and submitted by 

Syngenta Crop Protection, Inc., Greensboro, NC. Study initiated September 29, 2009 and 

completed October 19, 2010.

48270602 Mitchell, L., K.H. Martin, J.B. Beavers, and M. Jaber. 2002. Paclobutrazole: A 

Reproduction Study with the Mallard. Unpublished study performed by Wildlife 

International, Ltd, Easton, Maryland. Laboratory Project No. 528-113. Study sponsored

by Syngenta Crop Protection AG, Basel, Switzerland and submitted by Syngenta Crop 

Protection, Inc. Greensboro, NC. Study initiated November 26, 2001 and completed July 

19, 2002.

48605401 Wang, K-S., C-Y Lu, and S-H Chang. 2011. Evaluation of acute toxicity and 

teratogenic effects of plant growth regulators by Daphnia magna embryo assay. Journal 

of Hazardous Materials. 190: 520-528.

48605402 Liu, Z. T., Z. M. Kong, F. Zhou, and L. S. Wang. 1996. Bioconcentration and 

toxicity effect on lipid content of aquatic organisms. Bulletin of Environmental 

Contamination and Toxicology. 56: 135-142.
154

48637501 Lembi, C.A., and M. D. Netherland. 1990. Bioassy of plant growth regulator 

activity on aquatic plants. Technical Report A-90-7, U.S. Army Waterways Experiment 

Station, Vicksburg, MS.

Environmental Fate Studies

132698 Woods, T.; Leahey, J. (1983) PP333: Hydrolysis in Water at pH 4, 7 and 9: 

Report Series RJ 0316B. (Unpublished study received Nov 10, 1983 under 

10182-82; prepared by Imperial Chemical Industries Ltd., Eng., submitted by ICI 

Americas, Inc., Wilmington, DE; CDL:251748-B) 

132699 Woods, T.; Leahey, J. (1983) PP333: Photolysis in Aqueous Solution: Report 

Series RJ 0317B. (Unpublished study received Nov 10, 1983 under 10182-82; 

prepared by Imperial Chemical Industries Ltd., Eng., submitted by ICI Americas, 

Inc., Wilmington, DE; CDL:251748-C) 

40685003 Harvey, B.; Hill, I. (1985) Paclobutrazol: Degradation in Aerobic and Flooded 

Soils: Laboratory Project ID: RJ0370B. Unpublished study prepared by ICI Plant 

Protection Division. 45 p. 

47338504 Oliver, R.; Webb, J. (2005) Paclobutrazol: Rate of Degradation in Three Soils 

Under Laboratory Conditions: Final Report. Project Number: RJ3677B, 04JH025, 

T008689/07. Unpublished study prepared by Syngenta Jealotts Hill International. 

77 p.

40685003 Harvey, B.; Hill, I. (1985) Paclobutrazol: Degradation in Aerobic and Flooded 

Soils: Laboratory Project ID: RJ0370B. Unpublished study prepared by ICI Plant 

Protection Division. 45 p. 

40685005 Takacs, M.; White, B. (1986) Paclobutrazol: Adsorption and Desorption 

Equilibria in Soils: Laboratory Project ID: TMJ2377B. Un- published study 

prepared by ICI Plant Protection Division. 26 p. 

47338503 Shaw, D. (2002) Paclobutrazol: Adsorption and Desorption Properties in Four 

Soil: Final Report. Project Number: GZR/007/014132, GZR/007, T008688/07. 

Unpublished study prepared by Huntingdon Life Sciences, Ltd. 71 p. Relates to 

L0001128.

40685004 Mistry, R.; Hill, I. (1986) Paclobutrazol: Mobility of Paclobutrazol and Its 

Degradation Products in Soil Columns: Laboratory Project ID: RJ0495B. 

Unpublished study prepared by ICI Plant Protection Division. 64 p. 

40685006 Mak, C.; Crook, S.; Atreya, N. (1987) Paclobutrazol: Field Dissipation following 

Subsurface Applications in US Orchard Soils Up to 12 Months: Laboratory 

Project ID: RJ0574B. Unpublished study prepared by ICI Plant Protection 

Division. 74 p. 

40685007 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--California Site--
155

Report of Field Data: Laboratory Project ID: TMU3304/B. Unpublished study 

prepared by ICI Biological Research Center. 19 p. 

40685008 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--California Site--

Second Follow-up Report of Field Data: Laboratory Project ID: TMU3346/B. 

Unpublished study pre- pared by ICI Biological Research Center. 20 p. 

40685009 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--Florida Site--

Follow-up Report of Field Data: Laboratory Project ID: TMU3303/B. 

Unpublished study prepared by ICI Biological Research Center. 18 p. 

40685010 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--Florida Site--

Second Follow-up Report of Field Data: Laboratory Project ID: TMU3345B. 

Unpublished study pre- pared by ICI Biological Research Center. 19 p. 

40685011 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--West Virginia Site-

-Follow-up Report of Field Data: Laboratory Project ID: TMU3305B. 

Unpublished study pre- pared by ICI Biological Research Center. 18 p. 

40685012 Hendley, P.; Davis, L.; Oliver, B. (1987) Paclobutrazol: Field Dissipation and 

Leaching following Subsurface Application in Orchard Soils--West Virginia Site-

-Second Follow-up Report of Field Data: Laboratory Project ID: TMU3347/B. 

Unpublished study prepared by ICI Biological Research Center. 19 p.

47338501 Adam, D. 2007. 14C-NOA457654: rate of degradation and time-dependent 

sorption in four soils. Unpublished study performed by RCC Ltd., Itingen, 

Switzerland; sponsored by Syngenta Ltd., Berkshire, UK and submitted by 

Syngenta Crop Protection, Inc., Greensboro, NC. Report Number B26763. Task 

Number T011573-06. Experimental start date March 20, 2007 and completion 

date June 19, 2007 (p. 13). Final report issued July 13, 2007.

47338502 Lin, Y. 2006. NOA457654 (degradate of paclobutrazol): adsorption/desorption 

properties in four soils. Unpublished study performed, sponsored and submitted

by Syngenta Crop Protection, Inc., Greensboro, NC. Report Number T000759-

06. Task Number T000759-06. Experimental start date May 15, 2006 and 

completion date August 11, 2006 (p. 5). Final report issued October 26, 2006.

47338503 Paclobutrazol adsorption and desorption properties in four soils. Unpublished 

study performed by Huntingdon Life Sciences Ltd., Cambridgeshire, England; 

sponsored by Syngenta, Bracknell, Berkshire, UK; and submitted by Syngenta 

Crop Protection, Inc., Greensboro, NC. Report Number GZR 007/014132. Study 

Number GZR 007. Task Number T008688-07. Experimental start date July 19, 

2001 and completion date September 18, 2001 (p. 31). Final report issued 

January 2, 2002.
156

47338504 Oliver, R.G. and J. Webb. 2005. Paclobutrazol rate of degradation in three soils 

under laboratory conditions. Unpublished study performed by Syngenta Jealott’s 

Hill International, Berkshire, UK; sponsored and submitted by Syngenta Crop 

Protection, Inc., Greensboro, North Carolina. Report Number RJ3677B. Study 

Number 04JH025. Task Number T008689-07. Experimental start data January 

11, 2005 and completion date July 12, 2005 (p. 21). Final report issued October 

3, 2005.

47338505 Bewick, B.; Hendley, P.; Hoag, R.; et al. (1989) Paclobutrazol: The Fate of 

(Carbon-14)-Paclobutrazol in Soil Under Field Conditions: Final Report. Project 

Number: RJ0710B, PP333AD02, T000229/08. Unpublished study prepared by 

ICI Agrochemicals. 212 p. 
157

Appendix B – Half-Life Calculations of Total Toxic Residues

Aerobic Soil Metabolism (MRID 40685003)

y = -0.0332x + 4.486

R2 = 0.9921

4.05

4.10

4.15

4.20

4.25

4.30

4.35

4.40

4.45

4.50

4.55

0 2 4 6 8 10 12 14

LN (% of Applied)

Months

Dissipation of paclobutrazol in 18 Acre sandy 

clay loam soil system (12 Months)

y = -0.0398x + 4.5257

R2 = 0.9726

4

4.1

4.2

4.3

4.4

4.5

4.6

0 2 4 6 8 10 12 14

LN (% of Aplied) 

Months

Dissipation of paclobutrazol in 18 Acre sandy 

clay loam soil system (12 Months)

DT50 = 21 months

DT50 = 17 months
158

y = -0.012x + 4.5088

R2 = 0.8271

4.34

4.36

4.38

4.40

4.42

4.44

4.46

4.48

4.50

4.52

4.54

0 2 4 6 8 10 12 14

LN (% of Applied)

Months (Post -treatment)

Dissipation of paclobutrazol in 18 Acre sandy clay 

loam soil system (12 Months)

y = -0.0195x + 4.5422

R2 = 0.9652

4.25

4.3

4.35

4.4

4.45

4.5

4.55

4.6

0 2 4 6 8 10 12

LN (% of Applied)

Months (Post -Treatment)

Dissipation of paclobutrazol in 18 Acre sandy clay 

loam soil system (12 Months)

DT50 = 58 months

DT50 = 36 months
159

y = -0.0018x + 4.4919

R2 = 0.4736

4.20

4.25

4.30

4.35

4.40

4.45

4.50

4.55

4.60

0 20 40 60 80 100 120 140

LN (% of Applied)

Days (Post-Treatment)

Dissipation of paclobutrazol in 18 Acres sandy clay loam soil 

system (0-120 days)

y = -0.0124x + 4.5691

R2 = 0.9886

0.00

1.00

2.00

3.00

4.00

5.00

0 20 40 60 80 100

LN (% of Applied)

Days

Dissipation of paclobutrazol in Pappelacker sandy loam soil 

system (0-120 days)

Half-Life = 56 days

Half-life = 385 days
160

y = -0.0092x + 4.5731

R2 = 0.9755

0.00

1.00

2.00

3.00

4.00

5.00

0 20 40 60 80 100 120 140

LN (% of Applied)

Days

Half-life = 75 Days
161

Appendix C - Chemical Structures

Structures of parent and identification of degradates in environmental fate 

studies

Common 

Name/Code

Chemical Name

(IUPAC)

Chemical Structure

Paclobutrazol

(2RS,3RS)-1-(4-Chlorophenyl)-

4,4-dimethyl-2-(1H-1,2,4-

triazol-1-yl)pentan-3-ol.

CGA 149907

Ketone analog

[CGA 132263, 

R 079105]

(2RS)-1-(4-Chlorophenyl)-4,4-

dimethyl-2-(1H-1,2,4 triazol-1-

yl) pentan-3-one.

Triazole [CGA 

71019] 

[J7140/44/3, 

Compound V]

1H-1,2,4-Triazole.

CGA 142856 

[Triazole acid, 

J7140/44/4, 

Compound VII]

1,2,4-Triazol-1-yl-acetic acid.

NOA 457654

[Triazole 

hydroxy, 

J7140/45/2, 

Compound IX]

1H-1,2,4-Triazol-3-ol.

1 Bolded degradates are major metabolites of 

N

N

N

Cl

OH

CH3

CH3

CH3

N

N

N

Cl

O

CH3

CH3

CH3

N N

N

H

N N

N

HO

O

HN N

N

OH
162

Appendix D – KABAM Inputs and Outputs

Table 1. Chemical characteristics of Paclobutrazol.

Characteristic Value Comments/Guidance

Pesticide Name Paclobutrazol Required input

Log KOW 3.2

Required input 

Enter value from acceptable or supplemental study submitted 

by registrant or available in scientific literature.

KOW 1585 No input necessary. This value is calculated automatically 

from the Log KOW value entered above.

KOC (L/kg 

OC)

530

(Estimated 

0.35xKow)

Required input

Input value used in PRZM/EXAMS to derive EECs. Follow 

input parameter guidance for deriving this parameter value 

(USEPA 2002).

Time to steady 

state (TS; days) 3 No input necessary. This value is calculated automatically from the Log KOW value entered above.

Pore water EEC 

(μg/L) 338

Required input 

Enter value generated by PRZM/EXAMS benthic file. 

PRZM/EXAMS EEC represents the freely dissolved 

concentration of the pesticide in the pore water of the 

sediment. The appropriate averaging period of the EEC is 

dependent on the specific pesticide being modeled and is 

based on the time it takes for the chemical to reach steady 

state. Select the EEC generated by PRZM/EXAMS which has 

an averaging period closest to the time to steady state 

calculated above. In cases where the time to steady state 

exceeds 365 days, the user should select the EEC 

representing the average of yearly averages. The peak EEC 

should not be used. 

Water Column EEC 

(μg/L) 330

Required input 

Enter value generated by PRZM/EXAMS water column file. 

PRZM/EXAMS EEC represents the freely dissolved 

concentration of the pesticide in the water column. The 

appropriate averaging period of the EEC is dependent on the 

specific pesticide being modeled and is based on the time it 

takes for the chemical to reach steady state. The averaging 

period used for the water column EEC should be the same as 

the one selected for the pore water EEC (discussed above). 
163

Table 2. Input parameters for rate constants. "calculated" indicates that model will calculate 

rate constant. 

Trophic level

k1 

(L/kg*d)

k2 

(d-1)

kD 

(kg-food/kgorg/d)kE 

(d-1)

kM* 

(d-1)

phytoplankton calculated calculated 0* 0* 0

zooplankton calculated calculated calculated calculated 0

benthic 

invertebrates calculated calculated calculated calculated 0

filter feeders calculated calculated calculated calculated 0

small fish calculated calculated calculated calculated 0

medium fish calculated calculated calculated calculated 0

large fish calculated calculated calculated calculated 0

* Default value is 0. 

k1 and k2 represent the uptake and elimination constants respectively, through 

respiration.

kD and kE represent the uptake and elimination constants, respectively, through diet.

kM represents the metabolism rate constant. 

Table 3. Mammalian and avian toxicity data for Paclobutrazol. These are required inputs.

Animal

Measure of 

effect (units) Value Species

If selected 

species is 

"other," 

enter body 

weight (in 

kg) here.

Avian LD50 (mg/kg-bw) mallard duck

LC50 (mg/kgdiet) Northern bobwhite quail

NOAEC (mg/kgdiet) 453 mallard duck

Mineau Scaling 

Factor 1.15

Default value for all species is 

1.15 (for chemical specific 

values, see Mineau et al.

1996).

Mammalian LD50 (mg/kg-bw) 1336 laboratory rat

LC50 (mg/kgdiet) N/A other

Chronic 

Endpoint 50

laboratory rat

units of chronic 

endpoint*

mg/kg-bw

*ppm = mg/kg-diet

OUTPUTS
164

Table 11. Estimated concentrations of Paclobutrazol in ecosystem components.

Ecosystem Component

Total 

concentration 

(μg/kg-ww)

Lipid 

normalized 

concentration 

(μg/kg-lipid)

Contribution 

due to diet 

(μg/kg-ww)

Contribution 

due to 

respiration 

(μg/kg-ww)

Water (total)* 330 N/A N/A N/A

Water (freely dissolved)* 330 N/A N/A N/A

Sediment (pore water)* 338 N/A N/A N/A

Sediment (in solid)** 7,166 N/A N/A N/A

Phytoplankton 24,730 1236485 N/A 24,729.70

Zooplankton 18,176 605867 10.20 18,165.83

Benthic Invertebrates 19,833 661103 29.66 19,803.43

Filter Feeders 13,152 657592 19.27 13,132.58

Small Fish 25,493 637329 109.37 25,383.77

Medium Fish 25,575 639364 206.59 25,367.96

Large Fish 25,683 642076 369.14 25,313.92

* Units: μg/L; **Units: μg/kg-dw

Table 12. Total BCF and BAF values of Paclobutrazol in aquatic 

trophic levels.

0

5000

10000

15000

20000

25000

30000

Zooplankton Benthic 

Invertebrates

Filter Feeders Small Fish Medium Fish Large Fish

Concentration (μg/kg)

Trophic Level

Figure 1. Total pesticide concentration 

per trophic level

Contribution due to respiration (μg/kg-ww)

Contribution due to diet (μg/kg-ww)
165

Trophic Level

Total BCF 

(μg/kgww)/(μg/L)

Total BAF 

(μg/kgww)/(μg/L)

Phytoplankton 77 75

Zooplankton 55 55

Benthic Invertebrates 60 60

Filter Feeders 40 40

Small Fish 77 77

Medium Fish 77 77

Large Fish 77 78

Table 13. Lipid-normalized BCF, BAF, BMF and BSAF values of Paclobutrazol in aquatic 

trophic levels.

Trophic Level

BCF 

(μg/kglipid)/(μg/L)

BAF 

(μg/kglipid)/(μg/L)

BMF 

(μg/kglipid)/(μg/kglipid)

BSAF 

(μg/kglipid)/(μg/kgOC)

Phytoplankton 3849 3747 N/A 7

Zooplankton 1835 1836 0.49 3

Benthic Invertebrates 2001 2003 1.09 4

Filter Feeders 1990 1993 1.08 4

Small Fish 1924 1931 1.01 4

Medium Fish 1924 1937 0.98 4

Large Fish 1922 1946 1.00 4

Table 14. Calculation of EECs for mammals and birds consuming fish contaminated by Paclobutrazol.

Wildlife Species Biological Parameters EECs (pesticide intake)

Body

Weight

(kg)

Dry Food 

Ingestion 

Rate (kg-dry 

food/kgbw/day)

Wet Food 

Ingestion 

Rate (kg-wet 

food/kgbw/day)

Drinking 

Water

Intake

(L/d)

Dose Based 

(mg/kgbw/d)

Dietary 

Based 

(ppm)

Mammalian

fog/water shrew 0.02 0.140 0.585 0.003 11.655 19.83

rice rat/star-nosed 

mole 0.1 0.107 0.484 0.011 9.475 19.50

small mink 0.5 0.079 0.293 0.048 7.537 25.57

large mink 1.8 0.062 0.229 0.168 5.892 25.57

small river otter 5.0 0.052 0.191 0.421 4.914 25.57

large river otter 15.0 0.042 0.157 1.133 4.060 25.68

Avian
166

sandpipers 0.0 0.228 1.034 0.004 20.2852 19.55

cranes 6.7 0.030 0.136 0.211 2.6713 19.58

rails 0.1 0.147 0.577 0.010 13.1315 22.66

herons 2.9 0.040 0.157 0.120 3.5873 22.70

small osprey 1.3 0.054 0.199 0.069 5.1178 25.57

white pelican 7.5 0.029 0.107 0.228 2.7504 25.68

Table 15. Calculation of toxicity values for mammals and birds consuming 

fish contaminated by Paclobutrazol.

Wildlife Species

Toxicity Values

Acute Chronic

Dose 

Based 

(mg/kgbw)

Dietary 

Based 

(mg/kg-diet)

Dose Based 

(mg/kg-bw)

Dietary 

Based 

(mg/kg-diet)

Mammalian

fog/water shrew 2805.47 N/A 105.00 1000

rice rat/star-nosed 

mole 1903.13 N/A 71.22 1000

small mink 1254.64 N/A 46.96 1000

large mink 887.17 N/A 33.20 1000

small river otter 687.20 N/A 25.72 1000

large river otter 522.16 N/A 19.54 1000

Avian

sandpipers 0.00 0.00 N/A 453

cranes 0.00 0.00 N/A 453

rails 0.00 0.00 N/A 453

herons 0.00 0.00 N/A 453

small osprey 0.00 0.00 N/A 453

white pelican 0.00 0.00 N/A 453
167

Table 16. Calculation of RQ values for mammals and birds consuming fish 

contaminated by Paclobutrazol.

Wildlife Species

Acute Chronic

Dose 

Based

Dietary 

Based

Dose Based Dietary 

Based

Mammalian

fog/water shrew 0.004 N/A 0.111 0.020

rice rat/star-nosed 

mole 0.005 N/A 0.133 0.019

small mink 0.006 N/A 0.161 0.026

large mink 0.007 N/A 0.177 0.026

small river otter 0.007 N/A 0.191 0.026

large river otter 0.008 N/A 0.208 0.026

Avian

sandpipers #DIV/0! #DIV/0! N/A 0.043

cranes #DIV/0! #DIV/0! N/A 0.043

rails #DIV/0! #DIV/0! N/A 0.050

herons #DIV/0! #DIV/0! N/A 0.050

small osprey #DIV/0! #DIV/0! N/A 0.056

white pelican #DIV/0! #DIV/0! N/A 0.057
168

Appendix E – ECOTOX Literature Search

Papers That Were Accepted

Al-Nimri, L. F. and Coolbaugh, R. C. (1990). Inhibition of Abscisic Acid Biosynthesis in 

Cercospora rosicola by Triarimol. J. Plant Growth Regul. 9: 221-225.

EcoReference No.: 94586

Chemical of Concern: ACM,CMZ,PBZ; Habitat: T; Effect Codes: BCM,POP; 

Code: LITE EVAL CODED (ACM,CMZ,PBZ).

Not evaluated because units were not transferrable into lb ai/A.

Benjawan, C., Chutichudat, P., Boontiang, K., and Chanaboon, T. (2006). Effect of Chemical 

Paclobutrazol on Fruit Development, Quality and Fruit Yield of Kaew Mango 

(Mangifera indica L.) in Northeast Thailand. Pak. J. Biol. Sci. 9: 717-722.

EcoReference No.: 111578

Chemical of Concern: PBZ; Habitat: T; Effect Codes: GRO,PHY,POP; Code: 

LITE EVAL CODED (PBZ).

Not evaluated because units were not transferrable into lb ai/A.

Bigot, J. and Boucaud, J. (1998). Effects of Synthetic Plant Growth Retardants and Abscisic 

Acid on Root Functions of Brassica rapa Plants Exposed to Low Root-Zone 

Temperature. New Phytol. 139: 255-265.

EcoReference No.: 66797

Chemical of Concern: ASA,MFD,PBZ; Habitat: T; Effect Codes: PHY; Code: 

LITE EVAL CODED (ASA,MFD,PBZ).

Not evaluated because units were not transferrable into lb ai/A.

Chorbadjian, R. (2009). Phenotypic Variation in Host Quality of Pines for the European Pine 

Sawfly (Neodiprion sertifer). Ph.D. Thesis, The Ohio State University, OH 169 p. 

(UMI# 3345826).

EcoReference No.: 152510

Chemical of Concern: PBZ; Habitat: T; Effect Codes: BCM,GRO,PHY; Code: 

LITE EVAL CODED (PBZ).

Not evaluated because units were not transferrable into lb ai/A.

Dawson, I. A. and King, R. W. (1993). Effect of Environment and Applied Chemicals on the 
169

Flowering and Form of Geraldton Wax (Chamelaucium uncinatum Schauer). Sci. 

Hortic. 54: 233-246.

EcoReference No.: 151275

Chemical of Concern: BAD,CQTC,DMZ,EPH,MLH,PBZ; Habitat: T; Effect 

Codes: GRO,PHY,REP; Code: LITE EVAL CODED (BAD,PBZ), NO ENDPOINT 

(CQTC,DMZ,EPH,MLH).

Not evaluated because units were not transferrable into lb ai/A.

Ding, F., Song, W. H., Guo, J., Gao, M. L., and Hu, W. X. (2009). Oxidative Stress and 

Structure-Activity Relationship in the Zebrafish (Danio rerio) Under Exposure to 

Paclobutrazol. J. Environ. Sci. Health Part B: Pestic. Food Contam. Agric. Wastes

44: 44-50.

EcoReference No.: 120224

Chemical of Concern: PBZ; Habitat: A; Effect Codes: BCM,MOR; Code: LITE 

EVAL CODED (PBZ).

Evaluated, but classified as “invalid” because it was unclear if the purity of the 

material had been adjusted for in the reported results.

Dubois, V., Moritz, T., and Garcia-Martinez, J. (2011). Comparison of the Role of 

Gibberellins and Ethylene in Response to Submergence of Two Lowland Rice 

Cultivars, Senia and Bomba. J. Plant Physiol. 168: 233-241.

EcoReference No.: 152434

Chemical of Concern: 1MCP,ETL,GIB,PBZ; Habitat: AT; Effect Codes: 

BCM,CEL,GRO; Code: LITE EVAL CODED (1MCP,ETL,GIB,PBZ), NO EFED 

CHEM (1MCP).

Not evaluated because units were not transferrable into lb ai/A.

Escalona, M., Lorenzo, J. C., Gonzalez, B., Daquinta, M., Gonzalez, J. L., Desjardins, Y., 

and Borroto, C. G. (1999). Pineapple (Ananas comosus L. Merr) Micropropagation in 

Temporary Immersion Systems. Plant Cell Rep. 18: 743-748.

EcoReference No.: 108781

Chemical of Concern: BAD,GIB,PBZ; Habitat: T; Effect Codes: REP; Code: 

LITE EVAL CODED (PBZ), NO MIXTURE (BAD,GIB).

Not evaluated because units were not transferrable into lb ai/A.

Fagerness, M. J. and Yelverton, F. H. (2001). Plant Growth Regulator and Mowing Height 
170

Effects on Seasonal Root Growth of Penncross Creeping Bentgrass. Crop Sci. 41: 

1901-1905.

EcoReference No.: 111282

Chemical of Concern: PBZ,TXE; Habitat: T; Effect Codes: POP; Code: LITE 

EVAL CODED (PBZ,TXE).

Not evaluated because duration of measurement was not transferable to EPA risk 

assessments.

Gandiaga, S. (2007). Effects of Hydrology and Applied Gibberellic Acid and Paclobutrazol 

on the Growth of the Invasive Exotic Lygodium microphyllum (Old World Climbing 

Fern). M.S. Thesis, Florida Atlantic University, FL 40 p. (UMI# 1443672).

EcoReference No.: 152512

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: GRO,PHY,REP; Code: 

LITE EVAL CODED (GIB,PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Gandiaga, S., Volin, J. C., Kruger, E. L., and Kitajima, K. (2009). Effects of Hydrology on 

the Growth and Physiology of an Invasive Exotic, Lygodium microphyllum (Old 

World Climbing Fern). Weed Res. 49: 283-290 Publlished from MS Thesis EcoRef 

#152512.

EcoReference No.: 152582

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: GRO,PHY; Code: 

LITE EVAL CODED (GIB,PBZ).

Not evaluated because the units could not be convereted into lb ai/A.

Gocal, G. F. W., Sheldon, C. C., Gubler, F., Moritz, T., Bagnall, D. J., MacMillan, C. P., Li, 

S. F., Parish, R. W., Dennis, E. S., Weigel, D., and King, R. W. (2001). GAMYBLike Genes, Flowering, and Gibberellin Signaling in Arabidopsis. Plant Physiol.

127: 1682-1693.

EcoReference No.: 108777

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: BCM,CEL,GRO,REP; 

Code: LITE EVAL CODED (GIB,PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Guoping, Z. (1997). Gibberellic Acid3 Modifies Some Growth and Physiologic Effects of 

Paclobutrazol (PP333) on Wheat. J. Plant Growth Regul. 16: 21-25.
171

EcoReference No.: 105433

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: BCM,GRO,POP; Code: 

LITE EVAL CODED (PBZ), NO MIXTURE (GIB).

Not evaluated because the units could not be converted in lb ai/A.

Hajihashemi, S., Kiarostami, K., Enteshari, S., and Saboora, A. (2006). The Effects of Salt 

Stress and Paclobutrazol on Some Physiological Parameters of Two Salt-Tolerant and 

Salt-Sensitive Cultivars of Wheat. Pak. J. Biol. Sci. 9: 1370-1374.

EcoReference No.: 111577

Chemical of Concern: Halides,NaCl,PBZ; Habitat: T; Effect Codes: BCM; Code: 

LITE EVAL CODED (Halides,NaCl,PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Hamid, M. M. and Williams, R. R. (1997). Translocation of Paclobutrazol and Gibberellic 

Acid in Sturt's Desert Pea (Swainsona formosa). Plant Growth Regul. 23: 167-171.

EcoReference No.: 100708

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: GRO; Code: LITE 

EVAL CODED (GIB,PBZ).

Not evaluated because it was not the most sensitive plant.

Hutchinson, M. J., Krishnaraj, S., and Saxena, P. K. (1997). Inhibitory Effect of GA3 on the 

Development of Thidiazuron-Induced Somatic Embryogenesis in Geranium 

(Pelargonium x hortorum Bailey) Hypocotyl Cultures. Plant Cell Rep. 16: 435-438 .

EcoReference No.: 111020

Chemical of Concern: ACM,GIB,PBZ,TDZ; Habitat: T; Effect Codes: REP; Code: 

LITE EVAL CODED (ACM,GIB,PBZ), NO MIXTURE (TDZ).

Not evaluated because the units could not be converted into lb ai/A.

Isgrigg III, J. (1999). Ecological Adaptations of Annual Bluegrass to Plant Growth 

Regulators and Herbicides. Ph.D.Thesis, North Carolina State Univ, NC 162 p. (UMI 

#9960156).

EcoReference No.: 121125

Chemical of Concern: 

ATZ,BFL,CPZ,DQT,DTP,FPD,FRM,GYP,MBZ,NONA,ODZ,OYZ,PBZ,PCZ,PDM,

PRM,PZM,SFZ,SZ,TXE; Habitat: T; Effect Codes: BCM,GRO,PHY,POP; Code: 
172

LITE EVAL CODED 

(ATZ,BFL,DQT,FPD,FRM,GYP,MBZ,OYZ,PBZ,PDM,PRM,PZM,SFZ,SZ,TXE), 

NO EFED CHEM (CPZ,DTP,ODZ), NO MIXTURE (NONA,PCZ).

Not evaluated because it was a mixture.

Kumar, S., Kashyap, M., and Sharma, D. R. (2005). In Vitro Regeneration and Bulblet 

Growth from Lily Bulbscale Explants as Affected by Retardants, Sucrose and 

Irradiance. Biol. Plant. (Praha) 49: 629-632.

EcoReference No.: 110006

Chemical of Concern: CQTC,DMZ,PBZ; Habitat: T; Effect Codes: GRO,REP; 

Code: LITE EVAL CODED (CQTC,DMZ,PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Lembi, C. A. and Netherland, M. D. (1990). Bioassay of Plant Growth Regulator Activity on 

Aquatic Plants. Technical Report A-90-7, U.S.Army Corp Eng.Waterways Exp.Stn., 

Vicksburg, MS 36 p. (NTIS/02971610_a).

EcoReference No.: 107916

Chemical of Concern: BSFM,FPD,PBZ; Habitat: A; Effect Codes: 

BCM,GRO,PHY; Code: LITE EVAL CODED (FPD,PBZ), NO EFED CHEM 

(BSFM).

Study was evaluated and used in the risk assessment.

Manivannan, P., Abdul Jaleel, C., Kishorekumar, A., Sankar, B., Somasundaram, R., and 

Panneerselvam, R. (2008). Protection of Vigna unguiculata (L.) Walp. Plants from 

Salt Stress by Paclobutrazol. Colloids Surf. B Biointerfaces 61: 315-318.

EcoReference No.: 152518

Chemical of Concern: Halides,NaCl,PBZ; Habitat: T; Effect Codes: BCM,GRO; 

Code: LITE EVAL CODED (Halides,NaCl,PBZ).

Not evaluated because the endpoint was not useful.

Marshall, J. G. and Dumbroff, E. B. (1999). Turgor Regulation via Cell Wall Adjustment in 

White Spruce. Plant Physiol. 119: 313-319.

EcoReference No.: 108741

Chemical of Concern: PBZ; Habitat: T; Effect Codes: BCM,PHY; Code: LITE 

EVAL CODED (PBZ).

Not evaluated because the units could not be converted into lb ai/A.
173

Nagano, S., Mori, G., and Oda, M. (2010). Promotion of Seed Germination in Musa velutina 

Wendl. & Drude by Scarification and GA3. J. Hortic. Sci. Biotechnol. 85: 267-270.

EcoReference No.: 152445

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: BCM,REP; Code: 

LITE EVAL CODED (GIB,PBZ).

Not evaluated because the endpoint was not useful.

Netherland, M. D. and Lembi, C. A. (1992). Gibberellin Synthesis Inhibitor Effects on 

Submersed Aquatic Weed Species. Weed Sci. 40: 29-36.

EcoReference No.: 9710

Chemical of Concern: FPD,PBZ; Habitat: A; Effect Codes: BCM,GRO,PHY; 

Code: LITE EVAL CODED (FPD,PBZ).

Evaluated and used in the risk assessment.

Ochoa, J., Franco, J. A., Banon, S., and Fernandez, J. A. (2009). Distribution in Plant, 

Substrate and Leachate of Paclobutrazol Following Application to Containerized 

Nerium oleander L. Seedlings. Spanish J.Agric.Res. 7: 621-628.

EcoReference No.: 152345

Chemical of Concern: PBZ; Habitat: T; Effect Codes: ACC,GRO; Code: LITE 

EVAL CODED (PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Oetting, R. D. and Latimer, J. G. (1995). Effects of Soaps, Oils, and Plant Growth Regulators 

(PGRs) on Neoseiulus cucumeris (Oudemans) and PGRs on Orius insidiosus (Say). 

J. Agric. Entomol. 12: 101-109.

EcoReference No.: 81074

Chemical of Concern: ACM,ALSV,CQTC,DMZ,MOIL,MSO,PBZ; Habitat: T; 

Effect Codes: MOR; Code: LITE EVAL CODED 

(ACM,ALSV,CQTC,DMZ,MOIL,MSO,PBZ), TARGET (ALSV,MOIL).

Evaluated and used in the risk assessment.

Ozmen, A. D., Ozdemir, F., and Turkan, I. (2003). Effects of Paclobutrazol on Response of 

Two Barley Cultivars to Salt Stress. Biol. Plant. (Praha) 46: 263-268.

EcoReference No.: 105666
174

Chemical of Concern: Halides,NaCl,PBZ; Habitat: T; Effect Codes: BCM,GRO; 

Code: LITE EVAL CODED (Halides,NaCl,PBZ).

Not evaluated because the units could not be converted in lb ai/A.

Rohwer, C. (2008). Jasmonate-Induced Defense Against Tetranychus urticae Koch. in 

Greenhouse Crops. Ph.D. Thesis, University of Minnesota, St. Paul, MN 189 p. 

(UMI# 3321929).

EcoReference No.: 152515

Chemical of Concern: DMZ,PBZ; Habitat: T; Effect Codes: 

BCM,BEH,GRO,MOR,POP; Code: LITE EVAL CODED (DMZ,PBZ).

Evaluated and found to be invalid because of an aphid infestation during the 

experiment.

Seymour, M. (1996). Response of Narrow-Leafed Lupin (Lupinus angustifolius L.) to Foliar 

Application of Growth Regulators in Western Australia. Aust. J. Exp. Agric. 36: 

473-478.

EcoReference No.: 70689

Chemical of Concern: BAD,CPR,CZE,DU,IZT,MBZ,MQC,NAA,PBZ,SZ; Habitat: 

T; Effect Codes: GRO,POP,REP; Code: LITE EVAL CODED 

(BAD,DU,MBZ,PBZ,SZ), NO EFED CHEM (CPR,CZE,IZT,MQC,NAA).

Not evaluated because the duration of the experiment was not comparable to OPP 

guideline studies.

Steffens, B., Wang, J., and Sauter, M. (2006). Interactions Between Ethylene, Gibberellin 

and Abscisic Acid Regulate Emergence and Growth Rate of Adventitious Roots in 

Deepwater Rice. Planta 223: 604-612.

EcoReference No.: 94888

Chemical of Concern: ASA,EPH,GIB,PBZ; Habitat: A; Effect Codes: GRO; Code: 

LITE EVAL CODED (ASA,EPH,GIB,PBZ).

Not evaluated because the units could not be converted into lb ai/A.

Tanimoto, T. (2007). Modification of Sex Expression in Sagittaria latifolia by the 

Application of Gibberellic Acid and Paclobutrazol. J. Jpn. Soc. Hortic. Sci. 76: 47-

53.

EcoReference No.: 96445

Chemical of Concern: GIB,PBZ; Habitat: A; Effect Codes: REP; Code: LITE 
175

EVAL CODED (GIB,PBZ).

Not evaluated because the duration unit of the experiment was not convertible into 

days.

Tari, I. and Nagy, M. (1996). Abscisic Acid and Ethrel Abolish the Inhibition of 

Adventitious Root Formation of Paclobutrazol-Treated Bean Primary Leaf Cuttings. 

Biol. Plant. (Praha) 38: 369-375.

EcoReference No.: 100154

Chemical of Concern: ASAM,CoCl,EPH,PBZ; Habitat: T; Effect Codes: 

BCM,GRO; Code: LITE EVAL CODED (ASAM,EPH,PBZ), NO EFED CHEM 

(CoCl).

Not evaluated because the units could not be converted into lb ai/A.

Vergieva, T. (1998). Single Day Treatment - a Feasible Tool in Revealing not Dependent on 

Maternal Toxicity Teratogenic Potential. Adv. Exp. Med. Biol. 444: 191-199.

EcoReference No.: 105597

Chemical of Concern: BMY,PBZ; Habitat: T; Effect Codes: CEL,GRO,PHY,REP; 

Code: LITE EVAL CODED (BMY,PBZ).

Not evaluated because it was not the most sensitive endpoint.

Wang, K. S., Lu, C. Y., and Chang, S. H. (2011). Evaluation of Acute Toxicity and 

Teratogenic Effects of Plant Growth Regulators by Daphnia magna Embryo Assay. 

J. Hazard. Mater. IN PRESS: 9 p.

EcoReference No.: 152403

Chemical of Concern: CTK,EPH,GIB,MNPNa,PBZ; Habitat: A; Effect Codes: 

GRO,MOR; Code: LITE EVAL CODED (CTK,EPH,GIB,MNPNa,PBZ), NO EFED 

CHEM (CTK).

Evaluated and used in the risk assessment.

Weiland, J. E., Nelson, A. H., and Hudler, G. W. (2009). Effects of Mefenoxam, 

Phosphonate, and Paclobutrazol on In Vitro Characteristics of Phytophthora cactorum 

and P. citricola and on Canker Size of European Beech. Plant Dis. 93: 741-746.

EcoReference No.: 152439

Chemical of Concern: MFX,PBZ,RMLX; Habitat: T; Effect Codes: POP,REP; 

Code: LITE EVAL CODED (MFX,PBZ,RMLX), TARGET (MFX,RMLX).

Not evaluated because the units could not be converted into lb ai/A.
176

Wiesman, Z. and Lavee, S. (1995). Enhancement of IBA Stimulatory Effect on Rooting of 

Olive Cultivar Stem Cuttings. Sci. Hortic. 62: 189-198.

EcoReference No.: 114107

Chemical of Concern: INDBA,PBZ; Habitat: T; Effect Codes: GRO; Code: LITE 

EVAL CODED (INDBA,PBZ).

Not evaluated because the units coult not be converted into lb ai/A.

Papers That Were Not Accepted

Accepted for EcoTox but not OPP

Alabadi, D., Gil, J., Blazquez, M. A., and Garcia-Martinez, J. L. (2004). Gibberellins Repress 

Photomorphogenesis in Darkness. Plant Physiol. 134: 1050-1057.

EcoReference No.: 120141

Chemical of Concern: BLD,GIB,PBZ; Habitat: T; Effect Codes: CEL,GRO; Code: 

NO EFED CHEM (BLD), NO ENDPOINT (GIB,PBZ), TARGET (PBZ) .

Ascough, G. D., Erwin, J., and Van Staden, J. (2007). In Vitro Propagation of Four Watsonia 

Species. Plant Cell, Tissue Organ Cult. 88: 135-145.

EcoReference No.: 115053

Chemical of Concern: 24D,24DXY,BAD,IAA,INDBA,NAA,PBZ; Habitat: T; 

Effect Codes: GRO,MOR; Code: NO EFED CHEM (NAA), NO ENDPOINT 

(PBZ), OK (24D,24DXY,BAD,IAA,INDBA).

Baker, E. A., Hayes, A. L., and Butler, R. C. (1992). Physicochemical Properties of 

Agrochemicals: Their Effects on Foliar Penetration. Pestic. Sci. 34: 167-182 .

EcoReference No.: 70752

Chemical of Concern: 

ACP,ATZ,BTN,CQTC,DFP,FXP,GYP,MLH,MLX,NYP,PBZ,SZ,TDF,TDM; 

Habitat: T; Effect Codes: ACC; Code: NO CONTROL 

(ACP,ATZ,CQTC,GYP,MLH,MLX,PBZ,SZ,TDF), NO EFED CHEM 

(BTN,DFP,FXP,NYP,TDM), NO ENDPOINT 

(ACP,ATZ,CQTC,GYP,MLH,MLX,PBZ,SZ,TDF).

Cohen, R., Pivonia, S., Shtienberg, D., Edelstein, M., Raz, D., Gerstl, Z., and Katan, J. 

(1999). Efficacy of Fluazinam in Suppression of Monosporascus cannonballus, the 

Causal Agent of Sudden Wilt of Melons. Plant Dis. 83: 1137-1141.
177

EcoReference No.: 108337

Chemical of Concern: 

BMY,CBD,DCNA,FNZ,FRM,FTF,HCZ,IPD,MYC,Maneb,OTQ,OXC,PBZ,PNB,TC

M,TCMTB,TDM,THM,TPM; Habitat: T; Effect Codes: POP; Code: NO EFED 

CHEM (HCZ,OTQ,OXC,TCM,TDM,TPM), NO ENDPOINT 

(BMY,CBD,DCNA,FRM,FTF,IPD,MYC,Maneb,PBZ,PNB,TCMTB,THM), NO 

MIXTURE (THM), TARGET 

(BMY,CBD,DCNA,FNZ,FRM,FTF,IPD,MYC,Maneb,PNB,TCMTB,THM).

Costa, G., Spinelli, F., Sabatini, E., and Rademacher, W. (2004). Incidence of Scab (Venturia 

inaequalis) in Apple as Affected by Different Plant Growth Retardants. Acta Hortic. 

(Wagening.) 653: 133-137.

EcoReference No.: 99893

Chemical of Concern: CQTC,PBZ,PHDCa,TXE; Habitat: T; Effect Codes: 

GRO,POP; Code: NO EFED CHEM (PHDCa), NO ENDPOINT (CQTC,PBZ,TXE).

Frear, D. S., Swanson, H. R., and Tanaka, F. S. (1993). Metabolism of Flumetsulam (DE498) in Wheat, Corn, and Barley. Pestic. Biochem. Physiol. 45: 178-192.

EcoReference No.: 106957

Chemical of Concern: FTS,PBZ,PPB; Habitat: T; Effect Codes: ACC; Code: NO 

CONTROL (FTS,PBZ,PPB), NO ENDPOINT (FTS,PBZ,PPB).

Huarte, H. R. and Benech-Arnold, R. L. (2010). Hormonal Nature of Seed Responses to 

Fluctuating Temperatures in Cynara cardunculus (L.). Seed Sci.Res. 20: 39-45.

EcoReference No.: 152436

Chemical of Concern: FDE,GIB,PBZ,PCB; Habitat: T; Effect Codes: REP; Code: 

NO EFED CHEM (PCB), NO ENDPOINT (FDE,PBZ), OK (GIB).

Jasik, J., Boggetti, B., Caricato, G., and Mantell, S. (1997). Characterisation of Morphology 

and Root Formation in the Model Woody Perennial Shrub Solanum aviculare Forst. 

Expressing rolABC Genes of Agrobacterium rhizogenes. Plant Sci. 124: 57-68.

EcoReference No.: 113943

Chemical of Concern: CTK,GIB,INDBA,PBZ; Habitat: T; Effect Codes: GRO; 

Code: LITE EVAL CODED (INDBA), NO EFED CHEM (CTK), NO MIXTURE 

(GIB,PBZ).

Khaimov, A. and Mizrahi, Y. (2006). Effects of Day-Length, Radiation, Flower Thinning 

and Growth Regulators on Flowering of the Vine Cacti Hylocereus undatus and 

Selenicereus megalanthus. J. Hortic. Sci. Biotechnol. 81: 465-470.
178

EcoReference No.: 151299

Chemical of Concern: BAD,EPH,GIB,PBZ; Habitat: T; Effect Codes: 

GRO,POP,REP; Code: NO ENDPOINT (BAD,EPH,GIB,PBZ).

Khan, M. S. H., Wagatsuma, T., Akhter, A., and Tawaraya, K. (2009). Sterol Biosynthesis 

Inhibition by Paclobutrazol Induces Greater Aluminum (Al) Sensitivity in AlTolerant Rice. Am. J. Plant Physiol. 4: 89-99.

EcoReference No.: 152400

Chemical of Concern: AlCl,PBZ; Habitat: A; Effect Codes: ACC,BCM,GRO; 

Code: NO EFED CHEM (AlCl), NO ENDPOINT (PBZ).

Kostenyuk, I., Oh, B. J., and So, I. S. (1999). Induction of Early Flowering in Cymbidium 

Niveo-marginatum Mak In Vitro. Plant Cell Rep. 19: 1-5.

EcoReference No.: 108745

Chemical of Concern: BAD,GIB,NAA,PBZ,TDZ; Habitat: T; Effect Codes: 

GRO,REP; Code: NO EFED CHEM (NAA), NO ENDPOINT (PBZ), OK 

(BAD,GIB,TDZ).

Koukourikou-Petridou, M. and Porlingis, I. (1997). Presowing Application of Gibberellic 

Acid on Seeds Used for the Mung Bean Bioassay, Promotes Root Formation in 

Cuttings. Sci. Hortic. 70: 203-210.

EcoReference No.: 113951

Chemical of Concern: GIB,INDBA,PBZ; Habitat: T; Effect Codes: GRO; Code: 

NO ENDPOINT (PBZ), OK (GIB,INDBA).

Lee, E. H., Kramer, G. F., Rowland, R. A., and Agrawal, M. (1992). Antioxidants and 

Growth Regulators Counter the Effects of O3 and SO2 in Crop Plants. Agric. 

Ecosyst. Environ. 38: 99-106.

EcoReference No.: 119873

Chemical of Concern: FPD,PBZ,SO2; Habitat: T; Effect Codes: BCM,PHY; Code: 

LITE EVAL CODED (SO2), NO MIXTURE (FPD,PBZ).

Liu, Y., Xu, Y., Xiao, J., Ma, Q., Li, D., Xue, Z., and Chong, K. (2011). OsDOG, a 

Gibberellin-Induced A20/AN1 Zinc-Finger Protein, Negatively Regulates 

Gibberellin-Mediated Cell Elongation in Rice. J. Plant Physiol. IN PRESS: 8 p.

EcoReference No.: 152444

Chemical of Concern: GIB,PBZ; Habitat: T; Effect Codes: CEL,GRO; Code: NO 

ENDPOINT (GIB,PBZ).

Pennucci, A. and Jagschitz, J. A. (1984). Preemergent Herbicides for Crabgrass and Spurge 
179

Control in Lawn Turf. Proc. Northeast. Weed Sci. Soc. 38: 265-270.

EcoReference No.: 44111

Chemical of Concern: 

24D,24DXY,BFL,BS,BTC,BTL,DCPA,DEE,EFS,FNPE,FPD,MCPP1,MSMA,NPP,

ODZ,PBZ,PDM,SID,TFN; Habitat: T; Effect Codes: POP; Code: NO EFED 

CHEM (BTC,BTL,DEE,EFS,MSMA,NPP,ODZ), NO ENDPOINT 

(24D,24DXY,BFL,BS,DCPA,FNPE,FPD,MCPP1,PBZ,PDM,SID,TFN), NO 

MIXTURE (24D,24DXY,MCPP1,TFN).

Price, C. E. and Anderson, N. H. (1985). Uptake of Chemicals from Foliar Deposits: Effects 

of Plant Species and Molecular Structure. Pestic. Sci. 16: 369-377 .

EcoReference No.: 103298

Chemical of Concern: 24DIO,24DXY,FSF,NaDPA,PBZ,PIRM,PMR; Habitat: T; 

Effect Codes: ACC; Code: NO CONTROL (FSF,NaDPA,PBZ,PIRM,PMR), NO 

EFED CHEM (24DIO,24DXY), NO ENDPOINT (FSF,NaDPA,PBZ,PIRM,PMR).

Ramoutar, D. (2009). Pyrethroid Resistance in the Annual Bluegrass Weevil, Listronotus 

maculicollis (Coleoptera: Curculionidae), from Southern New England Golf Courses. 

Ph.D. Thesis, University of Rhode Island, RI 161 p. (UMI# 3415505).

EcoReference No.: 152514

Chemical of Concern: BFT,CTD,FPD,FRM,GCYH,PBZ,PCZ,PPB,SS,TBF,TXE; 

Habitat: T; Effect Codes: MOR; Code: NO EFED CHEM (CTD,SS), NO 

MIXTURE (CTD,FPD,FRM,PBZ,PCZ,PPB,TBF,TXE), TARGET (BFT,GCYH).

Ramoutar, D., Cowles, R. S., Requintina, E. Jr., and Alm, S. R. (2010). Synergism Between 

Demethylation Inhibitor Fungicides or Gibberellin Inhibitor Plant Growth Regulators 

and Bifenthrin in a Pyrethroid-Resistant Population of Listronotus maculicollis 

(Coleoptera: Curculionidae). J. Econ. Entomol. 103: 1810-1814 Chapter 5 in Thesis 

EcoRef# 152514.

EcoReference No.: 152401

Chemical of Concern: BFT,FPD,FRM,PBZ,PCZ,TXE; Habitat: T; Effect Codes: 

MOR; Code: NO ENDPOINT (BFT,FRM,TXE), NO MIXTURE (PBZ), OK 

(FPD,PCZ), TARGET (BFT).

Rosado, A., Schapire, A. L., Bressan, R. A., Harfouche, A. L., Hasegawa, P. M., Valpuesta, 

V., and Botella, M. A. (2006). The Arabidopsis Tetratricopeptide Repeat-Containing 

Protein TTL1 is Required for Osmotic Stress Responses and Abscisic Acid 

Sensitivity. Plant Physiol. 142: 1113-1126.
180

EcoReference No.: 119582

Chemical of Concern: ASA,CTK,GIB,Halides,KCl,NAA,NaCl,PBZ; Habitat: T; 

Effect Codes: CEL,GRO,REP; Code: NO EFED CHEM (CTK,KCl,NAA), NO 

ENDPOINT (ASA,GIB,Halides,NaCl,PBZ).

Salaita, L., Kar, R. K., Majee, M., and Downie, A. B. (2005). Identification and 

Characterization of Mutants Capable of Rapid Seed Germination at 10(Degrees)C 

from Activation-Tagged Lines of Arabidopsis thaliana. J. Exp. Bot. 56: 2059-2069.

EcoReference No.: 104465

Chemical of Concern: ASAM,PBZ; Habitat: T; Effect Codes: PHY,REP; Code: 

NO ENDPOINT (ASAM,PBZ).

Sharma, D., Shalini, L., and Raja, M. E. (2008). Uptake and Persistence of Soil Applied 

Paclobutrazol in 'Alphonso' Mango and Soil in the Konkan Region of Maharashtra, 

India. Toxicol. Environ. Chem. 90: 577-583.

EcoReference No.: 152519

Chemical of Concern: PBZ; Habitat: T; Effect Codes: ACC; Code: NO 

CONTROL (PBZ), NO ENDPOINT (PBZ).

Spinelli, F., Sabatini, E., Costa, G., and Rademacher, W. (2010). Reduction of Scab 

Incidence (Venturia inaequalis) in Apple with Prohexadione-Ca and TrinexapacEthyl, Two Growth Regulating Acylcyclohexanediones. Crop Prot. 29: 691-698.

EcoReference No.: 152402

Chemical of Concern: CQTC,KRSM,MEM,PBZ,TXE; Habitat: T; Effect Codes: 

GRO,POP,REP; Code: NO EFED CHEM (KRSM), NO ENDPOINT (PBZ), NO 

MIXTURE (KRSM), OK (CQTC,MEM,TXE).

Tukey, L. D. (1983). Vegetative Control and Fruiting on Mature Apple Trees Treated with 

PP333. Acta Hortic. (Wagening.) 137: 103-109.

EcoReference No.: 44150

Chemical of Concern: PBZ; Habitat: T; Effect Codes: BCM,GRO,PHY,POP; 

Code: NO CONTROL (PBZ), NO ENDPOINT (PBZ).

White, C. N. and Rivin, C. J. (2000). Gibberellins and Seed Development in Maize. II. 

Gibberellin Synthesis Inhibition Enhances Abscisic Acid Signaling in Cultured 

Embryos. Plant Physiol. 122: 1089-1097.

EcoReference No.: 98439

Chemical of Concern: ASA,PBZ; Habitat: T; Effect Codes: BCM,REP; Code: NO 

ENDPOINT (ASA,PBZ).

Wiesman, Z. and Riov, J. ( 1994). Interaction of Paclobutrazol and Indole-3-Butyric Acid in 
181

Relation to Rooting of Mung Bean (Vigna radiata) Cuttings. Physiol. Plant. 92: 608-

612.

EcoReference No.: 120336

Chemical of Concern: GIB,INDBA,PBZ; Habitat: T; Effect Codes: GRO,PHY; 

Code: NO ENDPOINT (GIB,INDBA,PBZ).

Ziv, M. and Ariel, T. (1991). Bud Proliferation and Plant Regeneration in Liquid-Cultured 

Philodendron Treated with Ancymidol and Paclobutrazol. J. Plant Growth Regul. 10: 

53-57.

EcoReference No.: 152455

Chemical of Concern: PBZ; Habitat: T; Effect Codes: GRO; Code: NO 

ENDPOINT (PBZ).

Excluded

Adriansen, E. and Odgaard, P. (1997). Residues of Paclobutrazol and Uniconazole in 

Nutrient Solutions From Ebb and Flood Irrigation of Pot Plants. Scientia 

Horticulturae, 69 (1-2) pp. 73-83, 1997.

Chem Codes: Chemical of Concern: PBZ Code: FATE.

Al-Badawy, A. A., Barrett, J. E., and Nell, T. A. (1995). Growth of Begonia as Influenced by 

Paclobutrazol Residue in Compost-Amended Media. 92nd annual meeting of the 

american society for horticultural science and the 40th annual congress of the 

canadian society for horticultural science, montreal, quebec, canada, july 30-august 

3, 1995. Hortscience 30: 802.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Aldrich, J. H. and Norcini, J. G. (1996). Effect of Growth Retardants on Production of 

Containerized 'barbara Karst' Bougainvillea. 93rd annual conference of the american 

society for horticultural science, lexington, kentucky, usa, october 6-10, 1996. 

Hortscience 31: 679.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Amini AnicĚ§a, GleĚ varec GaeĚll 

JoeĚ l (2009). Low Levels o 

Ajmalicine in Catharanthus Roseus Cell Suspension Cultures. Planta Medica, vol. 

75, no. 2, pp. 187-191, 2009.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Anon ( Pesticide Fact Sheet Number 62: Clipper (Paclobutrazol). Govt reports 
182

announcements &amp; index (gra&i), issue 02, 1987.

Chem Codes: Chemical of Concern: PBZ Code: NO TOX DATA.

Appleford, N. E. J., Wilkinson, M. D., Ma, Q., Evans, D. J., Stone, M. C., Pearce, S. P., 

Powers, S. J., Thomas, S. G., Jones, H. D., Phillips, A. L., Hedden, P., and Lenton, J. 

R. (2007). Decreased Shoot Stature and Grain (Alpha)-Amylase Activity Following 

Ectopic Expression of a Gibberellin 2-Oxidase Gene in Transgenic Wheat. Journal 

of Experimental Botany, 58 (12) pp. 3213-3226, 2007.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Bai, S. and Chaney, W. (2001). Gibberellin Synthesis Inhibitors Affect Electron Transport in 

Plant Mitochondria. Plant Growth Regulation 35: 257-262.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Bangerth K.F. (2009). Floral Induction in Mature, Perennial Angiosperm Fruit Trees: 

Similarities and Discrepancies With Annual/Biennial Plants and the Involvement of 

Plant Hormones. Scientia Horticulturae, vol. 122, no. 2, pp. 153-163, 2009.

Chem Codes: Chemical of Concern: PBZ Code : BENEFICIAL EFFECT.

Barratt, D. H. P. (1986). Modulation by abscisic acid of storage protein accumulation in 

Vicia Faba L. cotyledons cultured in vitro. Plant Science 46: 159-167.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Bellerby, John M., Morris, John H., and Smith, W. Ewen (1985). An aromatic schiff base 

stabilised as a coordinated enol iminium zwitterion by complex formation with a 

series of divalent metal ions. Inorganica Chimica Acta 96: 203-207.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Ben-Cheikh, W., Perez-Botella, J., Tadeo, F. R., Talon, M., and Primo-Millo, E. (1997). 

Pollination Increases Gibberellin Levels in Developing Ovaries of Seeded Varieties 

of Citrus. Plant Physiology, 114 (2) pp. 557-564, 1997.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Berghage, R. D., Macneal, E. P., Wheeler, E. F., and Zachritz, W. H. (1999). "Green" Water 

Treatment for the Green Industries: Opportunities for Biofiltration of Greenhouse and 

Nursery Irrigation Water and Runoff With Constructed Wetlands. Hortscience 34: 

50-54.

Chem Codes: Chemical of Concern: PBZ Code: FATE.

Black, S. N., Williams, L. J., Davey, R. J., Moffatt, F., Jones, R. V. H., McEwan, D. M., and 
183

Sadler, D. E. (1989). The preparation of enantiomers of paclobutrazol: A crystal 

chemistry approach. Tetrahedron 45: 2677-2682.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Bo Nielsen, J., Ahm SØ, Rensen, J., and Nielsen, F. ( The Usual Suspects-Influence of 

Physicochemical Properties on Lag Time, Skin Deposition, and Percutaneous 

Penetration of Nine Model Compounds. J toxicol environ health a. 2009; 72(5):315-

23. [Journal of toxicology and environmental health. Part a]: J Toxicol Environ 

Health A.

Chem Codes: Chemical of Concern: PBZ Code: HUMAN HEALTH.

Breceda, A., Ortiz, V., and Scrosati, R. (2005). Mauto (Lysiloma Divaricatum, Fabaceae) 

Allometry as an Indicator of Cattle Grazing Pressure in a Tropical Dry Forest in 

Northwestern Mexico. Rangeland Ecology & Management [Rangeland Ecol. 

Manage.]. Vol. 58, no. 1, pp. 85-88. Jan 2005.

Chem Codes : Chemical of Concern: PBZ Code: SURVEY.

Burden, R. S., Carter, G. A., Clark, T., Cooke, D. T., Croker, S. J., Deas, A. Hb, Hedden, P., 

James, C. S., and Lenton, J. R. (1987). Comparative Activity of the Enantiomers of 

Triadimenol and Paclobutrazol as Inhibitors of Fungal Growth and Plant Sterol and 

Gibberellin Biosynthesis. Symposium on gibberellin and sterol synthesis inhibitors, 

london, england, uk, march 5, 1987. Pestic sci 21: 253-268.

Chem Codes: Chemical of Concern: PBZ Code: REVIEW.

Burden, R. S., Cooke, D. T., and Carter, G. A. ( 1989). Inhibitors of Sterol Biosynthesis and 

Growth in Plants and Fungi. Phytochemistry (oxf) 28: 1791-1804.

Chem Codes: Chemical of Concern: PBZ Code: REVIEW.

Burden, R. S., Deas, A. Hb, and Clark, T. (1987). Separation of Enantiomers of Fungicidal 

and Plant Growth Regulatory Triazole Alcohols Using Chiral Derivatization and 

Capillary Gas Chromatography. J chromatogr 391: 273-279.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Burpee, L. L. (1996). Interactions Among Plant Growth Regulators and Fungicides on Dollar 

Spot of Creeping Bentgrass. Meeting of the american phytopathological society, 

southern division, greensboro, north carolina, usa, february 3-7, 1996. 

Phytopathology 86: S104.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Calvo, A. P., Nicola(acute)s, C., Nicola(acute)s, G., and Rodri(acute)guez, D. (2004). 
184

Evidence of a Cross-Talk Regulation of a Ga 20-Oxidase (Fsga20ox1) by 

Gibberellins and Ethylene During the Breaking of Dormancy in Fagus Sylvatica 

Seeds. Physiologia Plantarum, 120 (4) pp. 623-630, 2004.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Canivenc, M. C., Cagnac, B., Cabanne, F., and Scalla, R. (1989). Induced Changes of 

Chlorotoluron Metabolism in Wheat Cell Suspension Cultures. Plant physiol 

biochem (paris) 27: 193-202.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Cerco(acute)s, M., Urbez, C., and Carbonell, J. (2003). A Serine Carboxypeptidase Gene 

(Pscp), Expressed in Early Steps of Reproductive and Vegetative Development in 

Pisum Sativum, Is Induced by Gibberellins. Plant Molecular Biology, 51 (2) pp. 165-

174, 2003.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Chen, Run tao, Deng, Ying yu, and Chen, Xiao yan (2008). Study on the two-generation 

reproductive toxicity of paclobutrazol in SD rats. Toxicology Letters 180: S165.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Chen, T., Dwyre-Gygax, C., Hadfield, S. T., Willetts, C., and Breuil, C. (1996). 

Development of an Enzyme-Linked Immunosorbent Assay for a Broad Spectrum 

Triazole Fungicide: Hexaconazole. Journal of agricultural and food chemistry 44: 

1352-1356.

Chem Codes: Chemical of Concern: PBZ Code: METHODS.

Ciferri, Claudio, Pasqualato, Sebastiano, Screpanti, Emanuela, Varetti, Gianluca, Santaguida, 

Stefano, Dos Reis, Gabriel, Maiolica, Alessio, Polka, Jessica, De Luca, Jennifer G., 

De Wulf, Peter, Salek, Mogjiborahman, Rappsilber, Juri, Moores, Carolyn A., 

Salmon, Edward D., and Musacchio, Andrea (2008-). Implications for KinetochoreMicrotubule Attachment from the Structure of an Engineered Ndc80 Complex. Cell

133: 427-439.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Clark, T. and Deas, A. Hb (1985). Separation of Enantiomers of Fungicides and Some 

Analogs by Capillary Gas Chromatography Using Chirasil Val. J chromatogr 329: 

181-185.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Cohen, S., Svrjcek, A., Durborow, T., and Barnes, N. L. (1999). Water Quality Impacts by 
185

Golf Courses. Journal of environmental quality 28: 798-809.

Chem Codes: Chemical of Concern: PBZ Code: FATE.

Cross, J. V. and Berrie, A. M. (1990). Efficacy of Reduced Volume and Reduced Dose Rate 

Spray Programmes in Apple Orchards. Crop Prot. 9: 207-217.

Chem Codes: Chemical of Concern: PBZ,VCZ Code: MIXTURE.

Davidson, S. E., Smith, J. J., Helliwell, C. A., Poole, A. T., and Reid, J. B. (2004). The Pea 

Gene Lh Encodes Ent-Kaurene Oxidase. Plant Physiology, 134 (3) pp. 1123-1134, 

2004.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Dewar, D. E. and Hume, D. J. (1995). Effects of Paclobutrazol Seed Treatments on Canola 

Yield and Quality. 1994 annual meeting of the canadian society of agronomy, 

regina, saskatchewan, canada. Canadian journal of plant science 75: 211.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Dugardeyn, Jasper and Van Der Straeten, Dominique (2007). Ethylene: Fine-tuning plant 

growth and development by stimulation and inhibition of elongation. Plant Science

175: 59-70.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Elmore, C. L., Gibeault, V. A., and Cudney, D. W. (1997). Invasion Resistance of Tall 

Fescue (Festuca Arundinaceae) and Perennial Ryegrass (Lolium Perenne) to 

Kikuyugrass (Pennisetum Clandestinum). Weed Technology, 11 (1) pp. 24-29, 1997.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Fatland, B. L., Nikolau, B. J., and Wurtele, E. S. (2005). Reverse Genetic Characterization of 

Cytosolic Acetyl-Coa Generation by Atp-Citrate Lyase in Arabidopsis. Plant Cell, 

17 (1) pp. 182-203, 2005.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Faust, M. and Miller, A. N. (1989). Effect of Bioregulators and Herbicides on Calcium and 

Phosphorus Content of Fruits. Sixth international symposium on growth regulators in 

fruit production, penticton, british columbia, canada, july 25-29, 1988. Acta hortic 

(wageningen) 0: 409-416.

Chem Codes : Chemical of Concern: PBZ Code: REVIEW.

Ferracini, Vera Lúcia, de Queiroz, Sonia Claudia Nascimento, and Rosa, Maria Aparecida 

(2008-). Determination of paclobutrazol in mango by LC/MS/MS system. Toxicology 
186

Letters 180: S166.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Fidanza, M. A., Wetzel III, H. C., Agnew, M. L., and Kaminski, J. E. (2006). Evaluation of 

Fungicide and Plant Growth Regulator Tank-Mix Programmes on Dollar Spot 

Severity of Creeping Bentgrass. Crop Prot. 25: 1032-1038.

Chem Codes: Chemical of Concern: AZX,CTN,FDX,PBZ,PCZ,TXE Code: 

MIXTURE.

Fos, M., Proan(tilde)o, K., Alabadi(acute), D., Nuez, F., Carbonell, J., and Garci(acute)aMarti(acute)nez, J. L. (2003). Polyamine Metabolism Is Altered in Unpollinated 

Parthenocarpic Pat-2 Tomato Ovaries. Plant Physiology, 131 (1) pp. 359-366, 2003.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Gao, Y., Zhao, Y., Li, T., Liu, Y., Ren, C., and Wang, M. ( Molecular Cloning and 

Expression Analysis of an F-Box Protein Gene Responsive to Plant Hormones in 

Brassica Napus. Mol biol rep. 2010, feb; 37(2):1037-44. [Molecular biology 

reports]: Mol Biol Rep.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

German Society of Food Chemistry Southeastern Chapter (1998). 7th Workshop of the 

Southeastern Chapter of the German Society of Food Chemistry (Koethen, Germany; 

April 16-17, 1998). Lebensmittelchemie 52: 128-132.

Chem Codes: Chemical of Concern: PBZ Code: HUMAN HEALTH.

Ghosh, S., Penterman, J. N., Madey, E., Baird, L. M., Frederick, J. M., Cummings, D. J., 

Hall-Glenn, F., De Giacomo, A., Volk, S., and Dumbroff, E. B. (2003). 

Paclobutrazol: Its Physiological Effects and Biochemical Functions During Plant 

Stress. Physiology and Molecular Biology of Plants 9: 163-173.

Chem Codes: Chemical of Concern: PBZ Code: REVIEW.

Gogoláková, Anna and Strba, Peter (2009). The impact of retardant Bonzi on growth and 

flowering of Hibiscus rosa-sinensis L. Comparative Biochemistry and Physiology -

Part A: Molecular & Integrative Physiology 153: S199.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Gong, P., Sun, T. H., Beudert, G., and Hahn, H. H. (1997). Ecological Effects of Combined 

Organic or Inorganic Pollution on Soil Microbial Activities. Water Air Soil Pollut.

96: 133-143.

Chem Codes: Chemical of Concern: As,Cu,PBZ,PHE,Zn Code: 
187

BACTERIA,MIXTURE.

Gong, P., Sun, T. H., Beudert, G., and Hahn, H. H. (1997). Ecological Effects of Combined 

Organic or Inorganic Pollution on Soil Microbial Activities. Water Air Soil Pollut.

96: 133-143.

Chem Codes: Chemical of Concern: PBZ Code : BACTERIA,MIXTURE.

Gong, P., Sun, T. H., Beudert, G., and Hahn, H. H. (1997). Ecological Effects of Combined 

Organic or Inorganic Pollution on Soil Microbial Activities. Water air and soil 

pollution 96: 133-143.

Chem Codes: Chemical of Concern: PBZ Code: BACTERIA, MIXTURE.

Gong Ping and Beudert, G. (1996). Ecological Effects of Multi-Effects-Triazole on Soil 

Microbe. Huanjing kexue 17: 36-38, 92.

Chem Codes: Chemical of Concern: PBZ Code: NON-ENGLISH.

Gong Ping, Sun Tieheng, Beudert, G., and Hahn, H. H. (1996). Side-Effects of Organic and 

Inorganic Pollutants on Soil Nitrification and Respiration. Journal of environmental 

sciences (china) 8: 66-76.

Chem Codes: Chemical of Concern: PBZ Code: FATE.

Gonza(acute)lez-Garci(acute)a, M. P., Rodri(acute)guez, D., Nicola(acute)s, C., 

Nicola(acute)s, G., and Lorenzo, O. (2006). A Protein Phosphatase 2a From Fagus 

Sylvatica Is Regulated by Ga and Okadaic Acid in Seeds and Related to the 

Transition From Dormancy to Germination. Physiologia Plantarum, 128 (1) pp. 153-

162, 2006 128: 153-162.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Gonçalves, I. C. R., Araújo, A. S. F., Carvalho, E. M. S., and Carneiro, R. F. V. (2005). 

Effect of paclobutrazol on microbial biomass, respiration and cellulose decomposition 

in soil. European Journal of Soil Biology 45: 235-238.

Chem Codes: Chemical of Concern: PBZ Code: FATE.

Gopi, R., Jaleel, C. Abdul, Sairam, R., Lakshmanan, G. M. A., Gomathinayagam, M., and 

Panneerselvam, R. ( Differential effects of hexaconazole and paclobutrazol on 

biomass, electrolyte leakage, lipid peroxidation and antioxidant potential of Daucus 

carota L. Colloids and Surfaces B: Biointerfaces In Press, Accepted Manuscript: 148.

Chem Codes: Chemical of Concern: PBZ Code: NO SOURCE.

Gray, William M and Estelle, Mark (1998). Biochemical genetics of plant growth. Current 
188

Opinion in Biotechnology 9: 196-201.

Chem Codes : Chemical of Concern: PBZ Code: IN VITRO.

Gutie(acute)rrez-Man(tilde)ero, F. J., Ramos-Solano, B., Probanza, A., Mehouachi, J., 

Tadeo, F. R., and Talon, M. (2001). The Plant-Growth-Promoting Rhizobacteria 

Bacillus Pumilus and Bacillus Licheniformis Produce High Amounts of 

Physiologically Active Gibberellins. Physiologia Plantarum, 111 (2) pp. 206-211, 

2001.

Chem Codes: Chemical of Concern: PBZ Code: BACTERIA.

Harrison, J., Marshall, C., and Baylis, A. D. (1994). Studies on a Tillering Inhibitor Pps889.

Annual meeting of the society for experimental biology, swansea, wales, uk, april 11-

15, 1994. Journal of experimental botany 45: 56.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Haughan, Penny A., Burden, Raymond S., Lenton, John R., and Goad, L. John (1989). 

Inhibition of celery cell growth and sterol biosynthesis by the enantiomers of 

paclobutrazol. Phytochemistry 28: 781-787.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Haughan, Penny A., Lenton, John R., and Goad, L. John (1988). Sterol requirements and 

paclobutrazol inhibition of a celery cell culture. Phytochemistry 27: 2491-2500.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Haughan, Penny A., Lenton, John R., and John Goad, L. (1987). Paclobutrazol inhibition of 

sterol biosynthesis in a cell suspension culture and evidence of an essential role for 

24-ethylsterol in plant cell division. Biochemical and Biophysical Research 

Communications 146: 510-516.

Chem Codes: Chemical of Concern: PBZ Code : IN VITRO.

Holloway, P. J. and Stock, D. (1990). Factors Affecting the Activation of Foliar Uptake of 

Agrochemicals by Surfactants. Karsa, d. R. (Ed.). Royal society of chemistry special 

publication, no. 77. Industrial applications of surfactants ii. Symposium, manchester, 

england, uk, april 19-20, 1989. Viii+403p. Royal society of chemistry: cambridge, 

england, uk; crc press, inc.: Boca raton, florida, usa. Illus. Maps. Isbn 0-85186-617-

4.; 303-337.

Chem Codes : Chemical of Concern: PBZ Code: REVIEW.

Horowitz, M., Smith, E. M., and Gorski, S. F. (1990). Slow-Release Tablets as Carriers for 

Herbicides and Growth-Regulators. 11th conference of the weed science society of 
189

israel, bet dagan, israel, february 26-27, 1990. Phytoparasitica 18: 255-256.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Hsueh, W., Li, R., and Pei, Y. (1986). Separation of 1 2 4 Triazole Derivatives by HighPerformance Liquid Chromatography. J chromatogr 356: 433-437.

Chem Codes: Chemical of Concern: PBZ Code: CHEM METHODS.

Huang, Q., Li, W., and Hartung, J. S. (2003). Association of Xylella Fastidiosa With Leaf 

Scorch in Japanese Beech Bonsai. Canadian Journal of Plant Pathology, 25 (4) pp. 

401-405, 2003.

Chem Codes: Chemical of Concern: PBZ Code: BACTERIA, IN VITRO.

Huett, D. O., George, A. P., Slack, J. M., and Morris, S. C. (1997). Diagnostic Leaf Nutrient 

Standards for Low-Chill Peaches in Subtropical Australia. Australian Journal of 

Experimental Agriculture, 37 (1) pp. 119-126, 1997.

Chem Codes: Chemical of Concern: PBZ Code: SURVEY.

Huey Jen Chen, Mubarack, M. M., Naess, S. K., Stover, E., and Swartz, H. J. (1996). 

Technique Development Towards Production of an in Vitro Graft Chimera in Rubus.

Fruit Varieties Journal, 50 (2) pp. 105-113, 1996.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Hunter, D. M. and Proctor, J. Ta (1987). Effect of Paclobutrazol on Photosynthesis in 

Grapes. 84th annual meeting of the american society for horticultural science and 

the 34th annual congress of the interamerican society for tropical horticulture, 

orlando, florida, usa, november 6-12, 1987. Hortscience 22: 1109.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Illing, H. Pa (1997). Is Working in Greenhouses Healthy? Evidence Concerning the Toxic 

Risks That Might Affect Greenhouse Workers. Occupational medicine (london) 47: 

281-293.

Chem Codes: Chemical of Concern: PBZ Code: HUMAN HEALTH.

Inagaki Soichi, Miura-Kamio Asuka, Saze Hidetoshi, Kakutani Tetsuji, Nakamura Yasukazu, 

Lu Falong, Cui, X. i. a., Cao Xiaofeng, Kimura Hiroshi, and Inagaki Soichi (2010). 

Autocatalytic Differentiation of Epigenetic Modifications Within the Arabidopsis 

Genome. EMBO Journal, vol. 29, no. 20, pp. 3496-3506, 2010.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Jacyna, T. and Dodds, K. G. (1992). Effect of Various Methods of Paclobutrazol Application 
190

on Cherry Tree Performance and Soil Residue. 52nd annual meeting of the ashs 

(american society for horticultural science) southern region, lexington, kentucky, usa, 

february 1-3, 1992. Hortscience 27: 1168.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Jarvis, T. D., Earley, F. Gp, and Rees, H. H. (1994). Inhibition of the Ecdysteroid 

Biosynthetic Pathway in Ovarian Follicle Cells of Locusta Migratoria. Pesticide 

biochemistry and physiology 48: 153-162.

Chem Codes: Chemical of Concern: PBZ Code : IN VITRO.

Jennings, J. C., Coolbaugh, R. C., Nakata, D. A., and West, C. A. (1993). Characterization 

and Solubilization of Kaurenoic Acid Hydroxylase from Gibberella fujikuroi. Plant 

Physiol. 101: 925-930.

Chem Codes: Chemical of Concern: PBZ,SFZ Code: IN VITRO.

Jennings, J. C., Coolbaugh, R. C., Nakata, D. A., and West, C. A. (1993). Characterization 

and Solubilization of Kaurenoic Acid Hydroxylase From Gibberella Fujikuroi. Plant 

Physiol. 101: 925-930.

Chem Codes: Chemical of Concern: PBZ,SFZ Code: IN VITRO.

Jiménez, Jesús ngel, onso-Ramírez, Ana, and Nicolás, Carlos (2008-). Two cDNA clones 

(FsDhn1 and FsClo1) up-regulated by ABA are involved in drought responses in 

Fagus sylvatica L. seeds. Journal of Plant Physiology 165: 1798-1807.

Chem Codes: Chemical of Concern: PBZ Code: NO TOXICANT.

Jonsson, C. M., Ferracini, V. L., Paraiba, L. C., Rangel, M., and Aguiar, S. R. (2002). 

Biochemical Changes and Accumulation in "Pacu" Fish (Metynnis Argenteus) 

Exposed to Paclobutrazol (Alteracoes Bioquimicas E Acumulo Em Pacus (Metynnis 

Argenteus) Expostos Ao Paclobutrazol). Sci. Agric. 59: 441-446(POR) (ENG ABS).

Chem Codes: Chemical of Concern: PBZ Code: NON-ENGLISH.

Kato, H. (1987). 1986 Evaluation of Candidate Pesticides: B-1 Fungicides Rice and Other 

Cereals. Jpn. Pestic. Inf. 50: 29-32.

Chem Codes: Chemical of Concern: CuO,PBZ Code: NO DURATION.

Kawabata, O. and Defrank, J. (1993). Purple Nutsedge Suppression With Soil-Applied 

Paclobutrazol. Hortscience 28: 59.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Kenna, M. and Curry, K. (1989). Growth Regulation of Four Bermudagrass Cultivars. 86th 
191

annual meeting of the american society for horticultural science, tulsa, oklahoma, 

usa, july 29-august 3, 1989. Hortscience 0: 70.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Kishor Arun, Srivastav Manish, Dubey A.K., Singh A.K., Sairam R.K., Pandey R.N., Dahuja 

Anil, and Sharma R.R. (2009). Paclobutrazol Minimises the Effects of Salt Stress in 

Mango (Mangifera Indica L.). Journal of Horticultural Science and Biotechnology, 

vol. 84, no. 4, pp. 459-465, 2009.

Chem Codes: Chemical of Concern: PBZ Code : BENEFICIAL EFFECTS.

Kobayashi, M., Nagayama, T., Hashimoto, T., Haneishi, N., Ito, M., Tamura, Y., and 

Tomomatsu, T. (1998). Survey of Pesticides Residues in Vegetable Products 

Collected From 1994 Through 1997. Journal of the food hygienic society of japan

39: 233-239.

Chem Codes: Chemical of Concern: PBZ Code: HUMAN HEALTH.

Kozlowski, T. T., Kramer, P. J., and Pallardy, S. G. (1991). Physiological Ecology the 

Physiological Ecology of Woody Plants. Kozlowski, t. T., P. J. Kramer and s. G. 

Pallardy. Physiological ecology: the physiological ecology of woody plants. 

Xix+657p. Academic press, inc.: San diego, california, usa London, england, uk. 

Illus. Maps. Isbn 0-12-424160-3.; 0: Xix+657p.

Chem Codes: Chemical of Concern: PBZ Code: REVIEW.

Krizek, D. T., Mirecki, R., and Semeniuk, P. (1987). Influence of Paclobutrazol Pretreatment 

and Sulfur Dioxide Dose Rate on Sulfur Dioxide Sensitivity and Transpiration Rate in 

Coleus. 84th annual meeting of the american society for horticultural science and the 

34th annual congress of the interamerican society for tropical horticulture, orlando, 

florida, usa, november 6-12, 1987. Hortscience 22: 1155.

Chem Codes: Chemical of Concern: PBZ Code : ABSTRACT.

Kuehny, J. S., Chang, W. C., and Branch, P. (1996). Influence of Plant Growth Regulators on 

Postharvest Quality of Zantedeschia and Preplant Treatment for Preventing Erwinia 

Infection. 93rd annual conference of the american society for horticultural science, 

lexington, kentucky, usa, october 6-10, 1996. Hortscience 31: 597.

Chem Codes: Chemical of Concern: PBZ Code : ABSTRACT.

Kutzner, B. and Buchenauer, H. (1986). Effect of Various Triazole Fungicides on Growth 

and Lipid Metabolism of Fusarium Moniliforme as Well as on Gibberellin Contents 

in Culture Filtrates of the Fungus (Wirkung Verschiedener Triazolfungizide Auf 

Wachstum Und Lipidstoffwechsel Von Fusarium Moniliforme Sowie Auf Die 
192

Gibberellingehalte in Kulturfilitraten Des Pilzes). Z. Pflanzenkrankh. Pflanzenschutz

93: 597-607(GER) (ENG ABS).

Chem Codes: Chemical of Concern: BTN,PBZ Code: NON-ENGLISH.

Latimer, J. G. and Oetting, R. D. (1995). Conditioning Treatments Affect Growth and Spider 

Mite Infestation of Greenhouse-Grown Bedding Plants. 92nd annual meeting of the 

american society for horticultural science and the 40th annual congress of the 

canadian society for horticultural science, montreal, quebec, canada, july 30-august 

3, 1995. Hortscience 30: 829.

Chem Codes: Chemical of Concern: PBZ Code : ABSTRACT.

Lee, E. H., Byun, J. K., and Steffens, G. L. (1985). Increased Tolerance of Plants to Sulfur 

Dioxide Chilling and Heat Stress by a New Gibberellin Biosynthesis Inhibitor 

Paclobutrazol Pp-333. Annual meeting of the american society of plant physiologists, 

providence, r.i., Usa, june 23-28, 1985. Plant physiol (bethesda) 77: 135.

Chem Codes: Chemical of Concern: PBZ Code : ABSTRACT.

Lee, E. H., Rowland, R., and Mulchi, C. (1989). Use of Antioxidant Compounds to 

Overcome Air Pollution Stress in Crop Plants. Annual meeting of the american 

society of plant physiologists held jointly with the canadian society of plant 

physiologists, toronto, ontario, canada, july 30-august 3, 1989. Plant physiol 

(bethesda) 89: 182.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Lee, S., Lee, S., Yang, K. Y., Kim, Y. M., Park, S. Y., Kim, S. Y., and Soh, M. S. (2006). 

Overexpression of Pre1 and Its Homologous Genes Activates Gibberellin-Dependent 

Responses in Arabidopsis Thaliana. Plant and Cell Physiology, 47 (5) pp. 591-600, 

2006.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Leon-Kloosterziel, K. M., Gil, M. A., Ruijs, G. J., Jacobsen, S. E., Olszewski, N. E., 

Schwartz, S. H., Zeevaart, J. A. D., and Koornneef, M. (1996). Isolation and 

Characterization of Abscisic Acid-Deficient Arabidopsis Mutants at Two New Loci.

Plant Journal 10: 655-661.

Chem Codes: Chemical of Concern: PBZ Code: NO TOX DATA.

Leshem, B., Ronen, R., and Lurie, S. (1994). Thidazuron and Paclobutrazol Appear to Mimic 

Cytokinin and Auxin Influences on Organ Regeneration and Protein Profiles in 

Cultured Melon Cotyledons. Journal of Plant Physiology, 143 (3) pp. 344-348, 1994.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.
193

Liao, W. B., Ruan, M. B., Cui, B. M., Xu, N. F., Lu, J. J., and Peng, M. (2009). Isolation and 

Characterization of a Gai/Rga-Like Gene From Gossypium Hirsutum. Plant Growth 

Regulation, 58 (1) pp. 35-45, 2009.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Libal-Weksler, Y., Vishnevetsky, M., Ovadis, M., and Vainstein, A. (1997). Isolation and 

Regulation of Accumulation of a Minor Chromoplast-Specific Protein From 

Cucumber Corollas. Plant Physiology 113: 59-63.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Liu, K., Lee, X. S., and Qiu, W. (1989). Chemical Pruning of Pittosporum-Tobira With 

Caprylic Acid and Paclobutrazol and the Physiological Effect. Acta hortic sin 16: 51-

56.

Chem Codes: Chemical of Concern: PBZ Code: NON-ENGLISH.

Lorenzo, J. C., Gonzalez, B. L., Escalona, M., Teisson, C., Espinosa, P., and Borroto, C. 

(1998). Sugarcane Shoot Formation in an Improved Temporary Immersion System.

Plant Cell, Tissue Organ Cult. 54: 197-200.

Chem Codes: Chemical of Concern: PBZ Code: REFS CHECKED,REVIEW.

Lurie, S., Ronen, R., Lipsker, Z., and Aloni, B. (1994). Effects of Paclobutrazol and Chilling 

Temperatures on Lipids, Antioxidants and Atpase Activity of Plasma Membrane 

Isolated From Green Bell Pepper Fruits. Physiologia Plantarum, 91 (4) pp. 593-598, 

1994.

Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

Marangoni, A. G. and Stanley, D. W. (1991). Studies on the Long-Term Storage of Mature, 

Green Tomato Fruit. J hortic sci 66: 81-84.

Chem Codes: Chemical of Concern: PBZ Code: NO SPECIES (DEAD).

Mathews, S. (2009). Use of a Tree Growth Regulator to Manage Vegetation Near Overhead 

Power Lines. M.S. Thesis, Oklahoma Oklahoma State University, OK 25 p. (UMI# 

1469173).

Chem Codes: Chemical of Concern: PBZ Code: NO CONC .

Mathis, P. (1995). Photosynthesis: From Light to Biosphere. In: P.Mathis (Ed.), Proc.10th 

Int.Photosynthesis Congr., Aug.20-25, 1995, Montpellier, France, Photosynthesis: 

From Light to Biosphere, Kluwer Acad.Publ., Dordrecht, Netherlands 4: (Table of 

Contents).
194

Chem Codes: Chemical of Concern: 

AlS,CaCl2,CdN,HOX,Halides,NaCl,PBZ,PQT,PbN Code: SKIMMED .

Mathis, P. (1995). Photosynthesis: From Light to Biosphere. In: P.Mathis (Ed.), Proc.10th 

Int.Photosynthesis Congr., Aug.20-25, 1995, Montpellier, France, Photosynthesis: 

From Light to Biosphere, Kluwer Acad.Publ., Dordrecht, Netherlands 4: (Table of 

Contents).

Chem Codes: Chemical of Concern: 

AlS,CaCl2,CdN,HOX,Halides,NaCl,PBZ,PQT,PbN Code: SKIMMED .

Meilan, R. (1997). Floral Induction in Woody Angiosperms. New Forests 14: 179-202.

Chem Codes : Chemical of Concern: PBZ Code: REVIEW.

Mercier, J., Stienstra, W. C., and Krupa, S. V. (1998). Reduction in Dollar Spot of Turf 

Associated With Applications of the Growth Regulator Paclobutrazol. Annual 

meeting of the american phytopathological society, las vegas, nevada, usa, november 

8-12, 1998. Phytopathology 88: S62.

Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

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Chem Codes: Chemical of Concern: 

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Code: NON-ENGLISH.
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Chem Codes: Chemical of Concern: PBZ Code : CHEM METHODS.

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Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

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Chem Codes: Chemical of Concern: PBZ Code: MODELING.

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Chem Codes: Chemical of Concern: PBZ Code: BIOLOGICAL TOXICANT.

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Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

Pennucci, A. and Jackson, N. (1986). Distinguishing Phytotoxicity and Pathogenicity by 

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Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

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Chem Codes: Chemical of Concern: PBZ Code: NO SPECIES (DEAD).

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Chem Codes: Chemical of Concern: PBZ Code: HUMAN HEALTH.

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Chem Codes: Chemical of Concern: PBZ Code: IN VITRO.

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ACR,ADC,AMTR,AND,ATZ,BDC,BMY,BTC,BTY,CBF,CBL,CHD,CPP,CPY,DD

T,DFP,DLD,DMT,DS,DU,DZ,DZE,EN,EP,EPRN,EPTC,ES,FNF,FNTH,HCCH,HP

T,HXZ,Hg,IFP,LNR,MBZ,MCB,MDT,MLN,MOM,MP,MRX,MTL,MTZ,MVP,MX

C,NPM,NPP,OML,OXT,OYZ,PBZ,PDM,PPCP,PPN,PPZ,PRN,PRT,Pb,SZ,TBF,TB

O,TFN Code: NO DURATION,SURVEY.

Reeder, A. L., Foley, G. L., Nichols, D. K., Hansen, L. G., Wikoff, B., Faeh, S., Eisold, J., 

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ACR,ADC,AMTR,AND,ATZ,BDC,BMY,BTC,BTY,CBF,CBL,CHD,CPP,CPY,DD

T,DFP,DLD,DMT,DS,DU,DZ,DZE,EN,EP,EPRN,EPTC,ES,FNF,FNTH,HCCH,HP

T,HXZ,Hg,IFP,LNR,MBZ,MCB,MDT,MLN,MOM,MP,MRX,MTL,MTZ,MVP,MX

C,NPM,NPP,OML,OXT,OYZ,PBZ,PDM,PPN,PPZ,PRN,PRT,Pb,SZ,TBF,TBO,TFN 

Code: NO DURATION,SURVEY.

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Chem Codes: Chemical of Concern: PBZ Code: ABSTRACT.

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Zhang Li-Ying, Bai Ming-Yi, Zhu Jia-Ying, Wang, H. a. o., Wang Wenfei, Zhao, J. u. n., 

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Appendix F - Surrogate Chemicals

Paclobutrazol toxicity data were not available for estuarine/marine fish and invertebrates 

(acute and chronic), freshwater invertebrates (chronic), seedling emergence, vegetative vigor 

(monocots), honey bees, and aquatic vascular plants. In lieu of these data, the triazole 

chemical family was examined to identify other triazoles that were similar in structure to 

paclobutrazol. In all, 13 triazoles were identified; however, four of them (diclobutrazol, 

ipconazole, penconazole, simeconazol) lacked ecotoxicity data. Data from the remaining 

nine were used to construct toxicity distributions for each endpoint gap. Data were analysed 

in Crystal Ball (2000, version 5.0); first they were fit to a lognormal distribution and then a 

Monte Carol sampling scheme was implemented with 10,000 trials. Finally, the 5th

percentile of the simulated distribution curve was calculated and used in lieu of paclobutrazol 

data in the risk assessment. The structures of the nine triazoles with toxicity data are below.

Cyproconazole

Fenbuconazole

Hexaconzole
206

Metconazole

Mycobutanil

Tebuconazole

Triadimefon
207

Triadimenol

Triticonazole
208

Appendix G – SIP and STIR Model Output

SIP

Table 1. Inputs

Parameter Value

Chemical name Paclobutrazol

Solubility (in water at 25oC; mg/L) 25.9

Mammalian LD50 (mg/kg-bw) 1336

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Mammalian NOAEL (mg/kg-bw) 2.5

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Avian LD50 (mg/kg-bw) 7913

Avian test species mallard duck

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 995

Bobwhite quail NOAEC (mg/kg-diet) 453

NOAEC (mg/kg-diet) for other bird species

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird 

species

Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 4.4548 4.4548

Adjusted toxicity value (mg/kg-bw) 1027.5985 1.9229

Ratio of exposure to toxicity 0.0043 2.3167

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Exposure through 

drinking water alone is a 

potential concern for 

mammals

Table 3. Avian Results

Parameter Acute Chronic
209

Upper bound exposure (mg/kg-bw) 20.9790 20.9790

Adjusted toxicity value (mg/kg-bw) 4108.6307 48.1531

Ratio of exposure to acute toxicity 0.0051 0.4357

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Drinking water exposure 

alone is NOT a potential 

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. 

Therefore, when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through 

drinking water may contribute to a total exposure that has potential for effects to non-target animals.

STIR

Input

Application and Chemical Information

Enter Chemical Name Paclobutrazol

Enter Chemical Use Drench

Is the Application a Spray? (enter y or n) n

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 293.8

Enter Chemical Vapor Pressure (mmHg) 1.28E-09

Enter Application Rate (lb a.i./acre) 6.1

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 7913

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 1.58

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 1336

Enter Lowest Rat Inhalation LC50 (mg/L) 250

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at 

Saturation (mg/m3) 2.02E-05

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.54E-06

Adjusted Inhalation LD50 5.95E+03

Ratio of Vapor Dose to Adjusted Inhalation LD50 4.28E-10

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose 

(mg/kg)

not 

applicable

Ratio of Droplet Inhalation Dose to Adjusted 

Inhalation LD50

not 

applicable not applicable
210

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at 

Saturation (mg/m3) 2.02E-05

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.20E-06

Adjusted Inhalation LD50 1.49E+04

Ratio of Vapor Dose to Adjusted Inhalation LD50 2.15E-10

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose 

(mg/kg)

not 

applicable

Ratio of Droplet Inhalation Dose to Adjusted 

Inhalation LD50

not 

applicable not applicable
211

Appendix H – Risk Quotient Method and Levels of Concern

The Risk Quotient Method is the means by which the Environmental Fate and Effects 

Division (EFED) integrates the results of exposure and ecotoxicity data. In this method, both 

acute and chronic risk quotients are calculated by dividing exposure estimates by the most 

sensitive ecotoxicity values derived from the studies. Calculated risk quotients are then 

compared to OPP's levels of concern. The levels of concern are the criteria used by OPP to 

indicate potential risk to non-target organisms and the need to consider regulatory action. 

EFED has defined levels of concern for acute risk, potential restricted use, and for listed 

species. Risk presumptions, along with the corresponding risk quotients and levels of concern 

are summarized in the table below.

Levels of Concern for Assessed Taxa

Risk Presumption Risk Quotient Level of 

Concern

Birds

Acute Risk EEC/LC50 or LD50/sqft or LD50/day 0.5

Acute Restricted Use EEC/LC50 or LD50/sqft or LD50/day (or LD50 < 

50 mg/kg)

0.2

Acute Listed Species EEC/LC50 or LD50/sqft or LD50/day 0.1

Chronic Risk EEC/NOAEC 1

Mammals

Acute Risk EEC/LC50 or LD50/sqft or LD50/day 0.5

Acute Restricted Use EEC/LC50 or LD50/sqft or LD50/day (or LD50 < 

50 mg/kg)

0.2

Acute Listed Species EEC/LC50 or LD50/sqft or LD50/day 0.1

Chronic Risk EEC/NOAEC 1

Aquatic Animals

Acute Risk EEC/LC50 or EC50 0.5

Acute Restricted Use EEC/LC50 or EC50 0.1

Acute Listed Species EEC/LC50 or EC50 0.05

Chronic Risk EEC/NOAEC 1

Terrestrial and Semi-Aquatic Plants 

Acute Risk EEC/EC25 1
212

Risk Presumption Risk Quotient Level of 

Concern

Acute Listed Species EEC/EC05 or NOAEC 1

Aquatic Plants

Acute Risk EEC/EC50 1

Acute Listed Species EEC/EC05 or NOAEC 1
213

Appendix I – Surface Water Model Results and Sample Input and Outputs

Range of estimated environmental concentrations (EECs) of total residue (paclobutrazol plus degradates) 

and paclobutrazol for surface water

Month California Florida Michigan New Jersey Oregon Tennessee

Estimated Exposure Concentrations (μg/L) based on total toxic residue1 and 2.5 lbs/Acre application rate2

Peak 21-day 60-

Day

Peak 21-day 60-

Day

Peak 21-day 60-

Day

Peak 21-day 60-

Day

Peak 21-day 60-

Day

Peak 21-day 60-

Day

April 12.7 12.7 12.5 156 155 154 198 197 197 143 143 142 52 52 52 187.4 186.5 185.6

May 8.1 8.0 8.0 260 260 258 211 211 210 145 145 144 68 68 68 169.8 168.9 168.8

June 0.04 0.04 0.04 333 332 331 208 208 207 169 169 168 92 92 92 144.0 143.0 142.9

July 0.3 0.3 0.3 146 145 140 200 199 199 180 180 179 97 97 97 179.3 179.3 178.4

August 3.5 3.5 3.5 212 211 208 239 238 237 219 218 218 103 103 103 172.8 171.8 171.7

September 7.2 7.2 7.1 207 206 205 301 301 300 257 256 255 96 96 96 255.0 254.0 253.0

Estimated Exposure Concentrations (μg/L) based on total toxic residue and 0.57lbs/Acre application rate3

April 2.8 2.8 2.8 34 34 34 44 44 44 32 32 32 12 12 11 41.4 41.3 41.1

May 1.8 1.8 1.8 58 57 57 47 47 46 32 32 32 15 15 15 37.5 37.4 37.3

June 0.01 0.01 0.01 74 74 73 46 46 46 37 37 37 20 20 20 31.9 31.8 31.6

July 0.1 0.1 0.1 32 32 32 44 44 44 40 40 40 21 21 21 39.8 39.6 39.4

August 0.8 0.8 0.8 47 47 46 53 53 52 48 48 48 23 23 23 38.2 38.1 38.0

September 1.6 1.6 1.6 46 46 45 67 67 66 57 57 57 21 21 21 56.4 56.3 56.0

Estimated Exposure Concentrations (μg/L) based on parent (paclobutrazon) only and 2.50 lbs/Acre application rate4

June4 187 184 183 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 1 Paclobutrazol plus its major degradates, CGA 149907 and NOA 457654

2

Application rate estimated based on minimum amount of parent retention (58.6 %)in a column leaching study (MRID 40685004)

3

Application rate estimated based on maximum amount of parent retention (90.7 %)in a column leaching study (MRID 0685004) 4 Exposure of parent only based on highest exposure scenario identified from total toxic residue simulations

NA Not Analyzed

Red high-lighted values are the highest exposure for nursery scenario

Green high-lighted values are the lowest exposure for nursery scenario
214

Sample Input and Output of PRZM/EXAMS: FL Ornamental

stored as FL_NURS_H_01-04_01-06.out

Chemical: Paclobutrazol

PRZM 

environme

nt: 

FLnursery

STD_V2.t

xt

modified Tueday, 27 May 2008 at 11:22:34

EXAMS 

environme

nt: 

pond298.e

xv

modified Tueday, 26 August 2008 at 06:14:08

Metfile: 

w12839.dv

f

modified Tueday, 26 August 2008 at 06:14:20

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 36.9 36.8 36.4 35.7 35.0 18.8

1962 56.7 56.5 56.0 55.0 54.3 42.7

1963 57.9 57.8 57.6 57.3 56.9 53.0

1964 117.0 117.0 116.0 113.0 111.0 84.0

1965 119.0 119.0 118.0 117.0 116.0 108.0

1966 161.0 160.0 159.0 157.0 155.0 133.0

1967 195.0 195.0 193.0 191.0 189.0 165.0

1968 222.0 222.0 221.0 218.0 217.0 195.0

1969 231.0 231.0 230.0 228.0 227.0 212.0

1970 217.0 217.0 217.0 215.0 214.0 210.0

1971 226.0 225.0 225.0 223.0 221.0 209.0

1972 255.0 255.0 253.0 250.0 248.0 226.0

1973 242.0 242.0 241.0 240.0 239.0 232.0

1974 294.0 294.0 292.0 288.0 285.0 254.0

1975 266.0 266.0 265.0 264.0 263.0 256.0

1976 263.0 263.0 263.0 260.0 259.0 248.0

1977 410.0 409.0 405.0 398.0 393.0 322.0

1978 362.0 361.0 361.0 359.0 358.0 350.0

1979 335.0 335.0 334.0 333.0 332.0 325.0

1980 312.0 312.0 311.0 310.0 309.0 301.0

1981 288.0 288.0 287.0 286.0 285.0 280.0

1982 298.0 297.0 296.0 295.0 293.0 277.0

1983 316.0 316.0 315.0 311.0 309.0 288.0

1984 295.0 295.0 294.0 292.0 290.0 285.0

1985 276.0 276.0 276.0 275.0 274.0 267.0
215

1986 287.0 287.0 285.0 283.0 281.0 265.0

1987 264.0 264.0 263.0 262.0 261.0 256.0

1988 288.0 288.0 286.0 283.0 281.0 260.0

1989 275.0 275.0 274.0 273.0 271.0 262.0

1990 257.0 257.0 256.0 255.0 254.0 249.0

Sorted results

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

0.03 410.0 409.0 405.0 398.0 393.0 350.0

0.06 362.0 361.0 361.0 359.0 358.0 325.0

0.10 335.0 335.0 334.0 333.0 332.0 322.0

0.13 316.0 316.0 315.0 311.0 309.0 301.0

0.16 312.0 312.0 311.0 310.0 309.0 288.0

0.19 298.0 297.0 296.0 295.0 293.0 285.0

0.23 295.0 295.0 294.0 292.0 290.0 280.0

0.26 294.0 294.0 292.0 288.0 285.0 277.0

0.29 288.0 288.0 287.0 286.0 285.0 267.0

0.32 288.0 288.0 286.0 283.0 281.0 265.0

0.35 287.0 287.0 285.0 283.0 281.0 262.0

0.39 276.0 276.0 276.0 275.0 274.0 260.0

0.42 275.0 275.0 274.0 273.0 271.0 256.0

0.45 266.0 266.0 265.0 264.0 263.0 256.0

0.48 264.0 264.0 263.0 262.0 261.0 254.0

0.52 263.0 263.0 263.0 260.0 259.0 249.0

0.55 257.0 257.0 256.0 255.0 254.0 248.0

0.58 255.0 255.0 253.0 250.0 248.0 232.0

0.61 242.0 242.0 241.0 240.0 239.0 226.0

0.65 231.0 231.0 230.0 228.0 227.0 212.0

0.68 226.0 225.0 225.0 223.0 221.0 210.0

0.71 222.0 222.0 221.0 218.0 217.0 209.0

0.74 217.0 217.0 217.0 215.0 214.0 195.0

0.77 195.0 195.0 193.0 191.0 189.0 165.0

0.81 161.0 160.0 159.0 157.0 155.0 133.0

0.84 119.0 119.0 118.0 117.0 116.0 108.0

0.87 117.0 117.0 116.0 113.0 111.0 84.0

0.90 57.9 57.8 57.6 57.3 56.9 53.0

0.94 56.7 56.5 56.0 55.0 54.3 42.7

0.97 36.9 36.8 36.4 35.7 35.0 18.8

0.1 333.1 333.1 332.1 330.8 329.7 319.9

Average of 

yearly 

averages:

221.1

Inputs generated by pe5.pl - Novemeber 2006
216

Data used for this run:

Output File: FL_NURS_H_01-04_01-06

Metfile: w12839.dvf

PRZM 

scenario:

FLnurserySTD_V2.txt

EXAMS 

environme

nt file:

pond298.exv

Chemical

Name:

Paclobutrazol

Descriptio

n

Variable 

Name

Value Units Comments

Molecular 

weight

mwt 293.8 g/mol

Henry's 

Law 

Const.

henry 8.09E-12 atm-m^3/mol

Vapor 

Pressure

vapr 1.28E-09 torr

Solubility sol 25.9 mg/L

Kd Kd 4.5 mg/L

Koc Koc mg/L

Photolysis 

half-life

kdp 0 days Half-life

Aerobic 

Aquatic 

Metabolis

m

kbacw 2006.4 days Halfife

Anaerobic 

Aquatic 

Metabolis

m

kbacs 0 days Halfife

Aerobic 

Soil 

Metabolis

m

asm 1003.2 days Halfife

Hydrolysis

:

pH 7 0 days Half-life

Method: CAM 1 integer See PRZM manual

Incorporati

on Depth:

DEPI 0 cm

Applicatio

n Rate:

TAPP 2.8 kg/ha

Applicatio

n 

Efficiency:

APPEFF 1 fraction

Spray Drift DRFT 0 fraction of application rate applied to pond

Applicatio

n Date

Date 6-Jan dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5
217

Flag for 

Index Res. 

Run

IR EPA Pond

Flag for 

runoff 

calc.

RUNOFF none none, monthly or total(average of entire run)
218

Appendix J – TerrPlant Output

Profile 2SC on Turf – 1 ground application at 0.75 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Turf

Application Method Broadcast

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.75

Incorporation I 1 none

Runoff Fraction R 0.02 none

Drift Fraction D 0.01 none

EECs for Paclobutrazol.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.015

Runoff to semi-aquatic areas (A/I)*R*10 0.15

Spray drift A*D 0.0075

Total for dry areas ((A/I)*R)+(A*D) 0.0225

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.1575

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x
219

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed 0.32 2.22 0.13

Dicot non-listed 2.50 17.50 0.83

Dicot listed 11.25 78.75 3.75

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees – 1 

application at 3 inches deep at 1.9 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Ornamental Tree

Application Method Soil Injection/Basal Drench

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 1.9

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.012666667

Runoff to semi-aquatic areas (A/I)*R*10 0.126666667

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.012666667

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.126666667
220

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed 0.18 1.78 <0.1

Dicot non-listed 1.41 14.07 <0.1

Dicot listed 6.33 63.33 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Paclobutrazol 2SC Seed Treatment for Cucurbits – 1 application at 3 

inches deep at 0.00029 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Cucurbits

Application Method Seed Treatment

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.00029

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none
221

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.0000019

Runoff to semi-aquatic areas (A/I)*R*10 0.000019

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.0000019

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000019

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Paclobutrazol 2SC Seed Treatment for Pepper – 1 application at 3 inches 

deep at 0.00079 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Pepper

Application Method Seed Treatment

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.00079

Incorporation I 3 none

Runoff Fraction R 0.02 none
222

Drift Fraction D 0 none

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.0000053

Runoff to semi-aquatic areas (A/I)*R*10 0.000053

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.0000053

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000053

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Paclobutrazol 2SC Seed Treatment for Tomato – 1 application at 3 inches 

deep at 0.00040 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Tomato

Application Method Seed Treatment

Application Form liquid 

Solubility in Water 

(ppm) 27
223

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.0004

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.0000027

Runoff to semi-aquatic areas (A/I)*R*10 0.000027

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.0000027

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000027

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
224

Paclobutrazol 2SC Seed Treatment for Broccoli – 1 application at 3 inches 

deep at 0.000096 lb ai/A

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Broccoli

Application Method Seed treatment

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.000096

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.00000064

Runoff to semi-aquatic areas (A/I)*R*10 0.0000064

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.00000064

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.0000064

Plant survival and growth data used for RQ derivation.

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic

Spray 

Drift

Monocot non-listed #VALUE! #VALUE! #DIV/0!

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
225

Paclobutrazol 2SC Seed Treatment for Cauliflower – 1 application at 3 

inches deep at 0.000064 lb ai/A

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Broccoli

Application Method Seed treatment

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.000064

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol.

Description Equation EEC

Runoff to dry areas (A/I)*R 4.26667E-07

Runoff to semi-aquatic areas (A/I)*R*10 4.26667E-06

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 4.26667E-07

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 4.26667E-06

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic

Spray 

Drift

Monocot non-listed #VALUE! #VALUE! #DIV/0!

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
226

Paclobutrazol 2SC Seed Treatment for Cabbage – 1 application at 3 inches 

deep at 0.00012 lb ai/A

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Broccoli

Application Method Seed treatment

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.00012

Incorporation I 3 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.0000008

Runoff to semi-aquatic areas (A/I)*R*10 0.000008

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.0000008

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.000008

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic

Spray 

Drift

Monocot non-listed #VALUE! #VALUE! #DIV/0!

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
227

Bonzi II Spray for Potted Ornamentals for Transplant – 1 application at 

0.26 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Ornamental Potted Plants for Transplant

Application Method Spray

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 0.26

Incorporation I 1 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.0052

Runoff to semi-aquatic areas (A/I)*R*10 0.052

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.0052

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.052

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed <0.1 0.73 <0.1

Dicot non-listed 0.58 5.78 <0.1

Dicot listed 2.60 26.00 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
228

Bonzi II Spray for Potted Ornamentals for Transplant – 1 application at 

6.1 lb ai/A

Chemical Identity.

Parameter User Inputs

Chemical Name Paclobutrazol

PC code 125601

Use Ornamental Potted Plants for Transplant

Application Method Drench

Application Form liquid 

Solubility in Water 

(ppm) 27

Input parameters used to derive EECs.

Input Parameter Symbol

Value (user 

inputs) Units

Application Rate A 6.1

Incorporation I 1 none

Runoff Fraction R 0.02 none

Drift Fraction D 0 none

EECs for Paclobutrazol. 

Description Equation EEC

Runoff to dry areas (A/I)*R 0.122

Runoff to semi-aquatic areas (A/I)*R*10 1.22

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.122

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 1.22

Plant survival and growth data used for RQ derivation. 

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot x 0.071 x 0.059

Dicot 0.009 0.002 0.032 x
229

RQ values for plants in dry and semi-aquatic areas exposed to Paclobutrazol through runoff and/or 

spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed 1.72 17.18 <0.1

Dicot non-listed 13.56 135.56 <0.1

Dicot listed 61.00 610.00 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
230

Appendix K – Terrestrial EEC Calculations

Profile 2SC on Turf – 3 applications at 0.75 lb ai/A (28 day interval) (TREX)

Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 0.00 390.37 N/A 178.92 N/A 219.58 N/A 24.40 N/A 5.42 N/A

100 0.00 222.61 N/A 102.03 N/A 125.22 N/A 13.91 N/A 3.09 N/A

1000 0.00 99.66 N/A 45.68 N/A 56.06 N/A 6.23 N/A 1.38 N/A

Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

0 342.76 N/A 157.10 N/A 192.80 N/A 21.42 N/A

Size class not used for dietary risk quotients 
231

Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

435 342.76 0.79 157.10 0.36 192.80 0.44 21.42 0.05

Size class not used for dietary risk quotients

Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 2936.30 326.80 0.11 149.78 0.05 183.82 0.06 20.42 0.01 4.54 <0.01

35 2375.78 225.86 0.10 103.52 0.04 127.05 0.05 14.12 0.01 3.14 <0.01

1000 1027.60 52.37 0.05 24.00 0.02 29.46 0.03 3.27 <0.01 0.73 <0.01

Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

0 342.76 N/A 157.10 N/A 192.80 N/A 21.42 N/A

Size class not used for dietary risk quotients
232

Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

50 342.76 6.86 157.10 3.14 192.80 3.86 21.42 0.43

Size class not used for dietary risk quotients 

Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 5.49 326.80 59.48 149.78 27.26 183.82 33.46 20.42 3.72 4.54 0.83

35 4.45 225.86 50.80 103.52 23.29 127.05 28.58 14.12 3.18 3.14 0.71

1000 1.92 52.37 27.23 24.00 12.48 29.46 15.32 3.27 1.70 0.73 0.38

Bonzi II Spray for Potted Ornamentals – 1 application at 0.26 lb ai/A (TREX)

Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 0.00 71.07 N/A 32.57 N/A 39.98 N/A 4.44 N/A 0.99 N/A

100 0.00 40.53 N/A 18.57 N/A 22.80 N/A 2.53 N/A 0.56 N/A

1000 0.00 18.14 N/A 8.32 N/A 10.21 N/A 1.13 N/A 0.25 N/A
233

Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

0 62.40 N/A 28.60 N/A 35.10 N/A 3.90 N/A

Size class not used for dietary risk quotients 

Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

435 62.40 0.14 28.60 0.07 35.10 0.08 3.90 0.01

Size class not used for dietary risk quotients

Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 2936.30 59.49 0.02 27.27 0.01 33.47 0.01 3.72 <0.01 0.83 <0.01

35 2375.78 41.12 0.02 18.85 0.01 23.13 0.01 2.57 <0.01 0.57 <0.01

1000 1027.60 9.53 0.01 4.37 <0.01 5.36 0.01 0.60 <0.01 0.13 <0.01
234

Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

0 62.40 N/A 28.60 N/A 35.10 N/A 3.90 N/A

Size class not used for dietary risk quotients

Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

50 62.40 1.25 28.60 0.57 35.10 0.70 3.90 0.08

Size class not used for dietary risk quotients 

Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 5.49 59.49 10.83 27.27 4.96 33.47 6.09 3.72 0.68 0.83 0.15

35 4.45 41.12 9.25 18.85 4.24 23.13 5.20 2.57 0.58 0.57 0.13

1000 1.92 9.53 4.96 4.37 2.27 5.36 2.79 0.60 0.31 0.13 0.07

Clipper 20 UL Ornamental Tree Injection – 1 application at 0.36 lb ai/A

Risk Quotient = EEC / Toxicological Value

Birds

The following definitive data are available for birds:

NOAEC = 453 mg/kg-diet
235

Chronic Dietary Risk Quotients = EEC/NOAEC

Hardwoods = (212 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 0.47

Softwoods = (9.4 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 0.02

Mammals

The following definitive data are available for mammals:

LD50 = 1336 mg/kg-bw

NOEL = 2.5 mg/kg-bw

Adjusted toxicity values were calculated for mammal size classes by T-REX

15 g mammal LD50 = 2936 mg/kg-bw

35 g mammal LD50 = 2376 mg/kg-bw

1000 g mammal LD50 = 1028 mg/kg-bw

15 g mammal NOEL = 5.49 mg/kg-bw

35 g mammal NOEL = 4.45 mg/kg-bw

1000 g mammal NOEL = 1.92 mg/kg-bw

Acute Dose-Based Risk Quotients = EEC/LD50

Hardwoods 

15 g mammal = (201 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.07

35 g mammal = (140 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.06

1000g mammal = (32 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.03

Softwoods

15 g mammal = (9 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.003

35 g mammal = (4.2 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.001

1000 g mammal = (1.4 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.001

Chronic Dose-Based Risk Quotients = EEC/NOEL

Hardwoods

15 g mammal = (201 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 37

35 g mammal = (140 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 31

1000 g mammal = (32 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 17

Softwoods

15 g mammal = (9 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 1.6
236

35 g mammal = (4.2 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 0.94

1000g mammal = (1.4 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 0.73

Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees – 1 

application at 1.9 lb ai/A

Risk Quotient = EEC / Toxicological Value

Birds

The following definitive data are available for birds:

NOAEC = 453 mg/kg-diet

Chronic Dietary Risk Quotients = EEC/NOAEC

Hardwoods = (1058 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 2.3

Softwoods = (483 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 1.1

Mammals

The following definitive data are available for mammals:

LD50 = 1336 mg/kg-bw

NOEL = 2.5 mg/kg-bw

Adjusted toxicity values were calculated for mammal size classes by T-REX

15 g mammal LD50 = 2936 mg/kg-bw

35 g mammal LD50 = 2376 mg/kg-bw

1000 g mammal LD50 = 1028 mg/kg-bw

15 g mammal NOEL = 5.49 mg/kg-bw

35 g mammal NOEL = 4.45 mg/kg-bw

1000 g mammal NOEL = 1.92 mg/kg-bw

Acute Dose-Based Risk Quotients = EEC/LD50

Hardwoods 

15 g mammal = (1005 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.34

35 g mammal = (698 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.29

1000g mammal = (159 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.15

Softwoods

15 g mammal = (459 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.16
237

35 g mammal = (319 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.13

1000 g mammal = (72 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.07

Chronic Dose-Based Risk Quotients = EEC/NOEL

Hardwoods

15 g mammal = (1005 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 183

35 g mammal = (698 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 157

1000 g mammal = (159 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 83

Softwoods

15 g mammal = (459 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 87

35 g mammal = (319 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 72

1000g mammal = (72 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 38

Bonzi II Drench for Potted Ornamentals – 1 application at 6.1 lb ai/A

Woody Potted Ornamentals

Risk Quotient = EEC / Toxicological Value

Birds

The following definitive data are available for birds:

NOAEC = 453 mg/kg-diet

Chronic Dietary Risk Quotients = EEC/NOAEC

Hardwoods = (59 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 0.13

Softwoods = (24 mg ai/kg-leaves) / (453 mg ai/kg-diet) = 0.05

Mammals

The following definitive data are available for mammals:

LD50 = 1336 mg/kg-bw 

NOEL = 2.5 mg/kg-bw 

Adjusted toxicity values were calculated for mammal size classes by T-REX

15 g mammal LD50 = 2936 mg/kg-bw

35 g mammal LD50 = 2376 mg/kg-bw

1000 g mammal LD50 = 1028 mg/kg-bw

15 g mammal NOEL = 5.49 mg/kg-bw
238

35 g mammal NOEL = 4.45 mg/kg-bw

1000 g mammal NOEL = 1.92 mg/kg-bw

Acute Dose-Based Risk Quotients = EEC/LD50

Hardwoods 

15 g mammal = (59 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.02

35 g mammal = (39 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.02

1000g mammal = (9 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.01

Softwoods

15 g mammal = (23 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.01

35 g mammal = (16 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.01

1000 g mammal = (3.6 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.003

Chronic Dose-Based Risk Quotients = EEC/NOEL

Hardwoods

15 g mammal = (59 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 11

35 g mammal = (39 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 9

1000 g mammal = (9 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 5

Softwoods

15 g mammal = (23 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 4

35 g mammal = (16 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 4

1000g mammal = (3.6 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 2 

Non-Woody Potted Ornamentals

Risk Quotient = EEC / Toxicological Value

Birds

The following definitive data are available for birds:

NOAEC = 453 mg/kg-diet

Chronic Dietary Risk Quotients = EEC/NOAEC

Non-woody plants = (112 mg ai/kg-plant) / (453 mg ai/kg-diet) = 0.25

Mammals
239

The following definitive data are available for mammals:

LD50 = 1336 mg/kg-bw 

NOEL = 2.5 mg/kg-bw 

Adjusted toxicity values were calculated for mammal size classes by T-REX

15 g mammal LD50 = 2936 mg/kg-bw

35 g mammal LD50 = 2376 mg/kg-bw

1000 g mammal LD50 = 1028 mg/kg-bw

15 g mammal NOEL = 5.49 mg/kg-bw

35 g mammal NOEL = 4.45 mg/kg-bw

1000 g mammal NOEL = 1.92 mg/kg-bw

Acute Dose-Based Risk Quotients = EEC/LD50

15 g mammal = (106 mg ai/kg-bw) / (2936 mg ai/kg-bw) = 0.04

35 g mammal = (74 mg ai/kg-bw) / (2376 mg ai/kg-bw) = 0.03

1000g mammal = (17 mg ai/kg-bw) / (1028 mg/kg-bw) = 0.02

Chronic Dose-Based Risk Quotients = EEC/NOEL

15 g mammal = (106 mg ai/kg-bw) / (5.49 mg ai/kg-bw) = 19

35 g mammal = (74 mg ai/kg-bw) / (4.45 mg ai/kg-bw) = 17

1000g mammal = (17 mg ai/kg-bw) / (1.92 mg ai/kg-bw) = 9

Paclobutrazol 2SC Seed Treatment for Tomato, Cucurbit, and Pepper – 1 

application at 0.0040, 0.00029, and 0.0079 lb ai/A, respectively

Risk Quotient = EEC / Toxicological Value

Birds

The following definitive data are available for birds:

NOAEC = 453 mg/kg-diet

Chronic Dietary Risk Quotients = EEC/NOAEC

Tomato = (2.2 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.005

Cucurbit = (1.2 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.003

Pepper = (2.9 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.006

Broccoli = (0.36 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.0008
240

Cauliflower = (0.36 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.0008

Cabbage = (0.36 mg ai/kg-diet) / (453 mg ai/kg-diet) = 0.0008

Mammals

The following definitive data are available for mammals:

LD50 = 1336 mg/kg-bw

NOEL = 2.5 mg/kg-bw

Adjusted toxicity values were calculated for mammal size classes by T-REX

15 g mammal LD50 = 2936 mg/kg-bw

35 g mammal LD50 = 2376 mg/kg-bw

1000 g mammal LD50 = 1028 mg/kg-bw

15 g mammal NOEL = 5.49 mg/kg-bw

35 g mammal NOEL = 4.45 mg/kg-bw

1000 g mammal NOEL = 1.92 mg/kg-bw

Acute Dietary Risk Quotients = EEC/LD50

Tomato

15 g mammal = (2.1 mg ai/kg-diet) / (2936 mg ai/kg-diet) = 0.0007

35 g mammal = (1.5 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0006

1000 g mammal = (0.33 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.0003

Cucurbit

15 g mammal = (1.1 mg ai/kg- diet) / (2936 mg ai/kg-diet) = 0.0004

35 g mammal = (0.79 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0003

1000 g mammal = (0.18 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.0002

Pepper

15 g mammal = (2.8 mg ai/kg-diet) / (2936 mg ai/kg-diet) = 0.001

35 g mammal = (1.9 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0008

1000 g mammal = (0.44 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.0004

Broccoli

15 g mammal = (0.34 mg ai/kg-diet) / (2936 mg ai/kg-diet) = 0.0001

35 g mammal = (0.24 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0001

1000 g mammal = (0.05 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.00005

Cauliflower

15 g mammal = (0.34 mg ai/kg-diet) / (2936 mg ai/kg-diet) = 0.0001
241

35 g mammal = (0.24 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0001

1000 g mammal = (0.05 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.00005

Cabbage

15 g mammal = (0.34 mg ai/kg-diet) / (2936 mg ai/kg-diet) = 0.0001

35 g mammal = (0.24 mg ai/kg-diet) / (2376 mg ai/kg-diet) = 0.0001

1000 g mammal = (0.05 mg ai/kg-diet) / (1028 mg ai/kg-diet) = 0.00005

Chronic Dietary Risk Quotients = EEC/NOEL

Tomato

15 g mammal = (2.1 mg ai/kg-diet) / (5.49 mg ai/kg-diet) = 0.38

35 g mammal = (1.5 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.34

1000 g mammal = (0.33 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.17

Cucurbit

15 g mammal = (1.1 mg ai/kg-diet) / 5.49 mg ai/kg-diet) = 0.20

35 g mammal = (0.79 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.18

1000 g mammal = (0.18 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.09

Pepper

15 g mammal = (2.8 mg ai/kg-diet) / (5.49 mg ai/kg-diet) = 0.51

35 g mammal = (1.9 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.43

1000 g mammal = (0.44 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.23

Broccoli

15 g mammal = (0.34 mg ai/kg-diet) / (5.49 mg ai/kg-diet) = 0.06

35 g mammal = (0.24 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.05

1000 g mammal = (0.05 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.03

Cauliflower

15 g mammal = (0.34 mg ai/kg-diet) / (5.49 mg ai/kg-diet) = 0.06

35 g mammal = (0.24 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.05

1000 g mammal = (0.05 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.03

Cabbage

15 g mammal = (0.34 mg ai/kg-diet) / (5.49 mg ai/kg-diet) = 0.06

35 g mammal = (0.24 mg ai/kg-diet) / (4.45 mg ai/kg-diet) = 0.05

1000 g mammal = (0.05 mg ai/kg-diet) / (1.92 mg ai/kg-diet) = 0.03