BIOPESTICIDES REGISTRATION ACTION DOCUMENT

Homobrassinolide

PC Code 067700

U.S. Environmental Protection Agency

Office of Pesticide Programs

Biopesticides and Pollution Prevention Division

(last updated April 28, 2010)

This document is for informational purposes only and is representative of the Agency’s justification in registering 

products containing this active ingredient. This is not a legal document. 
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TABLE OF CONTENTS

I. BACKGROUND:.................................................................................................................. 4

II. ACTIVE INGREDIENT OVERVIEW............................................................................... 5

III. REGULATORY BACKGROUND..................................................................................... 5

A. Classification ........................................................................................................................ 5

B. Food Clearances and Tolerances........................................................................................ 5

IV. RISK ASSESSMENT........................................................................................................... 6

A. Active Ingredient Characterization.................................................................................... 6

B. Human Health Assessment.................................................................................................. 6

1. Toxicity............................................................................................................................... 6

2. Dose Response Assessment............................................................................................... 6

3. Food Quality Protection Act (FQPA) Considerations................................................... 7

 4. Occupational, Residential, School and Day Care Exposure and Risk 

Characterization.............................................................................................8

 5. Cumulative Effects.................................................................................8

 6. Risk Characterization..............................................................................8

C. ENVIRONMENTAL ASSESSMENT................................................................................ 9

1. Nontarget Organism Toxicology ..................................................................................... 9

2. Environmental Fate and Ground Water Data ............................................................... 9

3. Ecological Exposure and Risk Characterization ........................................................... 9

 4. Endangered Species Assessment................................................................10

D. PRODUCT PERFORMANCE DATA (EFFICACY)..................................................... 10

V. RISK MANAGEMENT DECISION................................................................................. 10

A. Determination of Eligibility for Registration .................................................................. 10

B. Regulatory Decision........................................................................................................... 11

VI. TERMS AND CONDITIONS OF THE REGISTRATION(S)....................................... 11

VII. APPENDIX A. Data Requirements (40 CFR Part 158)................................................... 13

VIII. APPENDIX B. Product Specific Information..................................................16

IX. APPENDIX C. References................................................................................................... 16
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BIOPESTICIDES REGISTRATION ACTION DOCUMENT TEAM

Office of Pesticide Programs:

Biopesticides and Pollution Prevention Division

Biochemical Pesticides Branch (BPB)

John Fournier Regulatory Action Leader

Linda Hollis Branch Chief

Miachel Rexrode, Ph.D. Senior Biologist
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I. BACKGROUND:

The active ingredient, homobrassinolide, is a plant growth regulator and a synthesized 

homologue of brassinolide, a naturally occurring brassinosteroid. Brassinosteroids are a group of 

steroidal plant hormones first discovered in 1973, when it was shown that pollen from Brassica 

napus could promote stem elongation and cell divisions and that the biologically active molecule 

was a steroid. They are ubiquitously distributed in the plant kingdom. Since their discovery, 

over 70 brassinosteroids have been isolated from plants. The occurrence of these steroids have 

been demonstrated in various plant parts, such as pollen, flower buds, fruits seeds, vascular 

cambium, leaves, shoots and roots. Studies on higher plants suggest that these steroids play a

critical role in a range of developmental processes (i.e. stem elongation, root growth, floral 

initiation, etc. Homobrassinolide is a white to pale yellow powder that gives off a mild, 

characteristic odor. This application is for uses as a plant growth regulator includes all 

agronomic and horticultural crops such as agricultural crops, greenhouse food uses and non-food 

crops, and aquatic food and non-food crops. 

The Biopesticides and Pollution Prevention Division (BPPD) has reviewed the data required to 

support the registration of this biochemical active ingredient, under Section 3(c)(5) of the Federal 

Insecticide, Fungicide and Rodenticide Act (FIFRA). Product chemistry data requirements were 

satisfied by acceptable guideline studies. Acceptable mammalian toxicology waivers and 

information from scientific literature were submitted to support registration of homobrassinolide. 

Acceptable acute toxicity guideline studies were submitted for the active ingredient. Ecological 

effects data requirements for homobrassinolide are fulfilled by acceptable guideline studies and 

acceptable waivers to support the remaining Tier I and Tier II requirements.

Based on the data available, EPA determined that no unreasonable adverse effects to the U.S. 

population and the environment will result from the use of the active ingredient when label 

instructions are followed and good agricultural practices are employed. Laboratory studies 

indicate that the active ingredient is not toxic following oral, inhalation or dermal exposure. 

Brassinosteroids are found in all plants and there are no reports of adverse effects following 

human exposure. Moreover, the pesticidal usage of this biochemical will not have any harmful 

environmental effects. Since brassinosteroids are ubiquitous in the plant kingdom, mammals, 

birds, fish, aquatic invertebrates, insects, and non-target plants all have a long history of exposure

to them. 

Due to the negligible risk concerns when used as a plant growth regulator, homobrassinolide 

meets the criteria as specified in §3(c)(5) of the Federal Insecticide, Fungicide and Rodenticide 

Act (FIFRA), as amended, and is thus eligible for unconditional registration. It was determined 

that the data/information submitted adequately satisfy applicable data requirements at 40 C.F.R. 

Subpart U §158.2000.
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II. ACTIVE INGREDIENT OVERVIEW

Common Name: Homobrassinolide

Chemical Names: Homobrassinolide (2α,3α,22S,23S,24S)-2,3,22,23-tetrahydroxy-24- 

 ethyl-β-homo-7-oxa-5α-cholestan-6-one)

Trade & Other Names: Homobrassinolide

CAS Registry Number: 80483-89-2

OPP Chemical Code: 067700

Type of Pesticide: Plant Growth Regulator

III. REGULATORY BACKGROUND

On November 16, 2007, Repar Corporation of Silver Spring, Maryland, submitted an application 

for the registration of the manufacturing-use product (MP) Homobrassinolide Technical (69361-

RT) containing 80% homobrassinolide. A notice of receipt of the application for registration of 

homobrassinolide as a new active ingredient was published in the Federal Register on February

13, 2008 (73 FR 8312), with a 30-day comment period. Two comments were received following 

this publication, but neither was related to the registration of homobrassinolide as a new active 

ingredient. Neither comment opposed the registration of homobrassinolide or provided any

substantive basis supporting that position. The comments both referenced an unrelated pesticide 

product not related to homobrassinolide. The comment also did not provide any data or 

information calling into question EPA's risk assessment. All comments have been included in 

the docket. 

Consistent with the Agency’s new policy for making pesticide registration actions more 

transparent, EPA will provide a 30-day public comment period on the decision to register

Homobrassinolide.

A. Classification

On April 9, 2002, the Biochemical Classification Committee determined that Homobrassinolide

is a biochemical pesticide due to its mode of action as a plant growth regulator and natural 

occurrence in the environment.

B. Food Clearances/Tolerances 

The applicant filed a petition (PP 7F7296) proposing to establish an exemption from the 

requirement of a tolerance for residues of Homobrassinolide in or on all food commodities. A 

notice of filing was published on February 13, 2008 (73 FR 8312).
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IV. RISK ASSESSMENT

A. Active Ingredient Characterization

Homobrassinolide(2α,3α,22S,23S,24S)-2,3,22,23-tetrahydroxy-24-ethyl-β-homo-7-oxa-5αcholestan-6-one) is a synthesized homologue of brassinolide, a naturally-occuring 

brassinosteroid. Brassinosteroids are a class of plant polyhydroxysteroids that are ubiquitously

distributed in the plant kingdom. These compounds, when applied to plants, improve plants’

quality and yield. They have been further researched for stress-protective properties (i.e. cold, 

heat, salt, and heavy metal exposure). Homobrassinolide is a plant growth regulator that can

control or regulate the growth and development of all higher and lower plants. The proposed 

uses include all agronomic and horticultural crops such as agricultural crops, greenhouse food 

uses and non-food crops, and aquatic food and non-food crops.

The descriptions of the product formulation and production process, as well as the formation of 

impurities, were examined by the Agency and found to meet current standards. A preliminary

analysis was conducted to determine homobrassinolide content in five batches of the product, 

and the results were determined to be acceptable by the Agency. The analytical method used to 

determine the content of the active ingredient is also acceptable. Physical and chemical 

properties submitted for the active ingredient were found to be adequate. Refer to Table 1 in 

Appendix A for a summary of product chemistry data requirements. Refer to Table 2 in 

Appendix A for the summary of physical and chemical characteristics of homobrassinolide. 

All product chemistry data requirements for registration of homobrassinolide have been 

satisfied.

B. Human Health Assessment

1. Toxicity 

Adequate mammalian toxicology data/information are available to support registration of

homobrassinolide. All toxicology data requirements for homobrassinolide have been satisfied.

For more information regarding the toxicity data requirements, refer to Table 3 in Appendix A. 

2. Dose Response Assessment

No toxicological endpoints were identified; therefore, a dose response assessment was not 

required.
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3. Food Quality Protection Act (FQPA) Considerations

a. Dietary Exposure and Risk Characterization

The applicant provided information on the risk of homobrassinolide to humans. Although the 

metabolism of brassinosteroids is poorly understood, these plant steroids appear to be 

metabolized in plants to produce inactive forms through transformation in the side chain or in the 

steroid skeleton. Brassinosteroids are present in all plants, resulting in ubiquitous exposure to 

humans and other organisms through the food chain without causing harm. The endogenous 

levels are in parts per million (ppm) to parts per billion (ppb) levels (i.e. brassinosteroids levels 

in pollen have measured at 200 ppb). The applicant claims that the small quantity (less than 20 

grams per acre) of homobrassinolide that is proposed for application as a plant growth stimulant 

is unlikely to increase levels of brassininosteroids in the treated plants. They reason that the 

amount of exogenenous brassinosteroid that is applied to a crop plant will be metabolized as the 

plant grows. Levels in the human diet are, therefore, unlikely to be affected. Calculations 

suggests that human exposure to homobrassinolide is expected to be low, with 20 grams per acre 

equivalent to 0.459 milligrams per square foot. Potential toxicity is low with an acute oral 

toxicity value of less than five grams per kilogram of bodyweight and acute inhalation value of 

2.2 milligrams per liter. This suggests that risk from exposure is very low at 20 grams per acre. 

Even if the entire acre of exposed plants were consumed (unlikely) by an individual, the toxicity

from homobrassinolide is more than ten times below the toxicity values noted above. The 

applicant has requested tolerance exemption for residues of homobrassinolide in or on crops and 

use sites. The registrant also requests waivers for all tests for determining the residues including 

the analytical method. 

Based on the available data, the Agency determined that there are reasonable grounds (as noted 

above) for tolerance exemption for the proposed uses of homobrassinolide in/on all raw 

agricultural commodities. The Agency also accepts the registrant’s argument that for low 

homobrassinolide toxicity and exposure to humans and feels that exemption from the required 

tolerance of residues in or on raw commodities is warranted.

b. Drinking Water Exposure and Risk Characterization

No significant drinking water exposure or residues are expected to result from the usage of 

homobrassinolide as a plant growth regulator. The active ingredient (AI) is intended for use as a 

foliar application on food commodities and not to be applied directly to water. If used in 

accordance with EPA-approved labeling, the AI is not likely to accumulate in drinking water. In 

the unlikely event that exposure via drinking water occurs from accidental spraying, the health 

risk would be minimal, based on the low acute oral toxicity and the long history of human 

exposure to brassinosteroids without adverse effects. It also seems unlikely that 

homobrassinolide concentrations would exceed levels that are currently ubiquitous to plants. 

Although environmental fate information is not available, the compound is not soluble in water 

(water solubility 3.18%), and the log Pow = 3.96, which suggests moderate binding to soil and a 

low probability of ground water contamination.

As a result, dietary and drinking water exposure to residues of homobrassinolide are expected to 

be minimal.
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c. Acute and Chronic Dietary Risks for Sensitive Subpopulations, Particularly Infants 

and Children

FFDCA section 408 provides that the Agency shall apply an additional tenfold margin of 

exposure (safety) for infants and children in the case of threshold effects to account for pre- and 

post-natal toxicity and the completeness of the database, unless the Agency determines that a 

different margin of exposure (safety) will be safe for infants and children. Margins of exposure 

(safety) are often referred to as uncertainty (safety) factors. In this instance, based on all the 

available information, the Agency has concluded that there is reasonable certainty that no harm to 

infants and children or adults will result from the use of homobrassinolide when label 

instructions are followed. 

4. Occupational, Residential, School and Day Care Exposure and Risk Characterization

a. Occupational Exposure and Risk Characterization

The potential for dermal, eye, and inhalation exposure to homobrassinolide for handlers and 

applicators is mitigated as long as products are used according to label directions. The Agency

will require labels to include the appropriate signal word, re-entry interval and precautionary

statements, including the requirement for personal protective equipment, to mitigate any risk of 

exposure.

b. Residential, School and Day Care Exposure and Risk Characterization

No indoor residential, school, or day care uses are currently approved for products containing 

homobrassinolide.

Section 408(b)(2)(D)(v) of the FFDCA requires that, when considering whether to establish an 

exemption from a tolerance, the Agency consider “available information concerning the 

cumulative effects of [a particular pesticide's] residues and other substances that have a common 

mechanism of toxicity.'' These considerations include the possible cumulative effects of such 

residues on infants and children.

5. Cumulative Effects

EPA has considered the potential for cumulative effects of homobrassinolide and other 

substances in relation to a common mechanism of toxicity. However, because of its low toxicity

to mammals and because it is readily metabolized by plants into inactive forms, the Agency does 

not expect any cumulative or incremental effects from exposure to residues of homobrassinolide 

when applied/used as directed on the label and in accordance with good agricultural practices.

6. Risk Characterization

The Agency considered human exposure to homobrassinolide in light of the relevant safety

factors in FQPA and FIFRA. EPA determined that no unreasonable adverse effects to the U.S. 

population in general, and to infants and children in particular, will result from the use of 

homobrassinolide when label instructions are followed.
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C. ENVIRONMENTAL ASSESSMENT

1. Nontarget Organism Toxicology 

Adequate non-target toxicology data/information are available to support registration of 

homobrassinolide. All non-target toxicology data requirements for homobrassinolide have been 

satisfied.

There are no concerns for any non-target organisms when homobrassinolide is applied in 

accordance with EPA-approved label use directions. Toxicity studies on mammals show 

practically no toxicity, and avian species have been environmentally exposed to the active 

ingredient since brassinosteroids are found in all plants. Application of the product in the 

environment is expected to be low at twenty grams per acre, with potential exposure to avian 

species at less than one milligram per square foot. Additionally, the product will be sprayed, not 

applied as a granular, resulting in decreased exposure. No toxic effects have been identified for 

non-target birds, non-target plants, and non-target soil organism such as earthworms. Although 

homobrassinolide is slightly toxic to fish and moderately toxic to aquatic invertebrates in 

laboratory testing, as a result of the rapid metabolism of homobrassinolide by crop plants under 

approved conditions of use, calculated Risk Quotients (RQs) for fish and aquatic invertebrates 

are well below any Levels of Concern (LOCs) for threatened and endangered species. There are 

no concerns for non-target insects. Only insects that feed directly on treated plant foliage or roots 

will be directly exposed to homobrassinolide at levels that will be pesticidal. These insects, 

however, also have been environmentally exposed to the active ingredient since it is ubiquitous 

in all plants and plant products (i.e. pollen). Due to the rapid metabolization of 

homobrassinolide by crops, honey bees and other pollinators that feed on nectar, and predators of 

insect pests are unlikely to consume enough of the active ingredient to cause adverse effects.

For more information regarding the non-target toxicity data requirements, refer to Table 4 in 

Appendix A.

2. Environmental Fate and Ground Water Data 

Homobrassinolide is a plant growth regulator that is ubiquitous in the plant kingdom and rapidly

metabolized by crop plants, making it unlikely that concentrations of the active ingredient would 

exceed levels naturally found in plants. As a result, homobrassinolide is not likely to persist in 

the environment. The compound is not soluble in water and binds moderately to soil, resulting in 

a low probability of ground water contamination. 

3. Ecological Exposure and Risk Characterization

The potential for exposure to non-target wildlife is minimal. Based on the results/information 

presented in the Environmental Fate and Groundwater Data section above, it is highly unlikely

that non-target organisms, particularly aquatic organisms, would be exposed to potentially toxic 

levels of homobrassinolide via runoff and/or movement through the soil. The active ingredient 

in ubiquitous in the plant kingdom and plants rapidly metabolize homobrassinolide into inactive 

forms when it is applied. No unreasonable adverse effects to the environment are expected from 

the use of homobrassinolide when label instructions are followed.
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4. Endangered Species Assessment

A non-target organism hazard assessment and an Endangered Species Assessment have been 

conducted to support registration of Homobrassinolide Technical (80% homobrassinolide 

manufacturing-use product). There are no concerns for non-target mammals and birds, including 

threatened and endangered species. Toxicity to mammals is in the slight to practically non-toxic 

range (LD50 >1000 to 5000 mg/kg). Moreover, as brassinosteroids are ubiquitous in the plant 

kingdom and are readily metabolized by plants when applied as a plant growth regulator, they are 

not likely to persist in the environment. Due to the ubiquitous nature of the active ingredient in 

the natural world, birds, mammals, and insects have all been environmentally exposed with no 

reported adverse effects. Based on submitted laboratory studies, no concerns were identified for 

non-target aquatic organisms, including threatened and endangered species. Calculated Risk 

Quotients (RQs) fish and aquatic invertebrates are well below any Levels of Concerns (LOCs) 

for threatened and endangered species. Using the acute endangered species level of concern 

(LOC) of 0.05 and the default slope of 4.5, the chance of an individual mortality for aquatic 

endangered species is ~ 1 in 410,000,000 and for terrestrial endangered species is ~ 1 in 294,000. 

Because homobrassinolide is not toxic to non-target organisms based on its use pattern and use 

instructions, EPA has determined it will have "No Effect" on any currently listed threatened or 

endangered species or any designated critical habitat.

D. PRODUCT PERFORMANCE DATA (EFFICACY)

Submission of product performance data (OPPTS 810.3000) is listed as a requirement for all 

pesticide products. Customarily, the Agency requires efficacy data to be submitted for review 

only in connection with the registration of products directly pertaining to the mitigation of 

disease bearing human health organisms and certain designated quarantine pests, i.e., ticks, 

mosquitoes, fleas, Mediterranean fruit flies, gypsy moths, Japanese beetles, etc. For a list of 

organisms considered by the Agency as “public health pests”, please refer to Pesticide 

Registration Notice 2002-1 (http://www.epa.gov/PR_Notices/pr2002-1.pdf). 

V. Risk Management Decision

A. Determination of Eligibility for Registration

Section 3(c)(5) of FIFRA provides for the registration of new active ingredients if it is 

determined that (A) its composition is such as to warrant the proposed claims for it; (B) its 

labeling and other materials required to be submitted comply with the requirements of FIFRA; 

(C) it will perform its intended function without unreasonable adverse effects on the 

environment; and (D) when used in accordance with widespread and commonly recognized 

practice, it will not generally cause unreasonable adverse effects on the environment. 

The four criteria of the Eligibility Determination for Pesticidal Active Ingredients are satisfied by

the science assessments supporting products containing homobrassinolide. Such products are not 

expected to cause unreasonable adverse effects, and are likely to provide protection as claimed 

when used according to label instructions. Therefore, homobrassinolide is eligible for registration 

for the labeled uses. 
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B. Regulatory Decision

EPA has determined that homobrassinolide presents no issues of toxicological, ecological, or 

environmental concern. As discussed above, acute toxicity data for homobrassinolide 

demonstrate that it is either toxicity category IV or III. Homobrassinolide does not demonstrate 

subchronic or developmental toxicity, and it is not mutagenic or genotoxic. EPA has no 

concerns for any non-target organisms exposed to homobrassinolide in accordance with approved 

label directions. EPA has not identified any toxic effects for non-target mammals, birds, plants, 

aquatic, or soil organisms. There are no concerns for any threatened and endangered species. 

Given that homobrassinolide has very low toxicity and presents little if any risk to non-target 

organisms, EPA concludes that it is in the best interests of the public and the environment to 

issue the registration for homobrassinolide without delay. 

Consistent with the Agency’s new policy for making these registration actions more transparent, 

EPA will provide a 30-day public comment period on the decision to register homobrassinolide.

The data submitted fulfill the requirements of registration of homobrassinolide for use on all 

agricultural commodities (including vegetables, fruits, nuts, outdoor and greenhouse ornamental 

and food crops) as a plant growth regulator. Refer to Appendix B for product-specific 

information. 

1. Conditional/Unconditional Registration

All data requirements have been met and EPA has determined that unconditional registration of 

homobrassinolide is appropriate.

C. Environmental Justice

EPA seeks to achieve environmental justice - the fair treatment and meaningful involvement of 

all people, regardless of race, color, national origin, or income - in the development, 

implementation, and enforcement of environmental laws, regulations, and policies. At this time 

EPA does not believe that use of pesticide products containing homobrassinolide will cause harm 

or a disproportionate impact on at-risk communities.

For additional information regarding environmental justice issues, please visit EPA’s website at:

http://www.epa.gov/compliance/environmentaljustice/index.html.

VI.TERMS AND CONDITIONS OF THE REGISTRATION(S)

The Agency evaluated all of the data submitted in connection with the initial registration of 

homobrassinolide and determined that these data are sufficient to satisfy current registration data 

requirements. No additional data are required to be submitted to the Agency at this time. For 

new uses and/or changes to existing uses, additional data may be required. 

Not withstanding the information stated in the previous paragraph, it should be clearly

understood that certain, specific, data are required to be reported to the Agency as a requirement 

for maintaining the Federal registration for a pesticide product. A brief summary of these types of 

data are listed below.
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A. Reporting of Adverse Effects

Reports of all incidents of adverse effects to the environment must be submitted to the Agency

under the provisions stated in FIFRA, Section 6(a)(2).

B. Reporting of Hypersensitivity Incidents

Additionally, all incidents of hypersensitivity (including both suspected and confirmed incidents) 

must be reported to the Agency under the provisions of 40 CFR Part 158.2050(d).
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VII. Appendix A. Data Requirements (40 CFR Part 158-Subpart U)

*NOTE: Master Record Identification (MRID) numbers listed in the following tables are 

representative of supporting data for the original registration of the product containing this active 

ingredient. Subsequent to this registration, there may be additional MRIDs that support 

registration of other products containing this active ingredient. 

TABLE 1. Product Chemistry Data Requirements for homobrassinolide (40 CFR § 158.2030)

OPPTS Guideline No. Study Results MRID

830.1550

to

830.1670

Product identity;

Manufacturing process;

Discussion of formation of 

unintentional ingredients

Submitted data satisfy the 

requirements for product identity, 

manufacturing process, and discussion 

of formation of impurities.

47185101-04

830.1700 Analysis of samples Submitted data satisfy the requirements 

for analysis of samples.

47185106-08

830.1750 Certification of limits Limits listed in the CSF are adequate / 

acceptable.

47185110-17

830.1800 Analytical method Acceptable. 47208901-02
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TABLE 2. Physical and Chemical Properties of homobrassinolide (40 CFR § 158.2030)

OPPTS Guideline No. Property Description of Result MRID

830.6302 Color White to pale yellow 47185104

830.6303 Physical State Powder 47185104

830.6304 Odor Mild, characteristic odor (1% 

suspension in ultrapure water)

47208901

830.6313 Stability to Normal and Elevated 

Temperatures, Metals and Metal Ions

Not applicable

830.6315 Flammability Not flammable at 

temperatures up to 1000 C

47185114

830.6317 Storage Stability Stable for 14 days at 54+2

0 C 

and 62% relative humidity.

47185113

830.6319 Miscibility Not applicable, product is not 

to be mixed with petroleum 

solvents.

830.6320 Corrosion Characteristics Calculated corrosion rates 

based on mean weight loss of 

coupons exposed to the 

product for 14 days: Copper -

0.00142 mm/year

Aluminum - 0.0540 mm/year.

47185115

830.7000 pH 7.65

(1g in 100 ml of water)

47185112

830.7050 UV/Visible Light Absorption ^max = 1.2458 at 202 nm 

(10 mg in 50 ml methanolHCL)

47185116

830.7100 Viscosity Not applicable, product is a 

solid

830.7200 Melting Point/Range 116-1180 C 47175106

830.7220 Boiling Point/Range Not applicable, product is a 

solid

830.7300 Density Density = 0.7 g/ml at ambient 

temperature

47185107

830.7520 Particle Size, Fiber Length and 

Diameter Distribution

830.7550

830.7560

830.7570

Partition Coefficient (nOctanol/Water)Log Pow = 3.96 47185111

830.7840 Water Solubility 3.18% in water

95.89% in acetone

99.89% in ethanol

47185108

830.7950 Vapor Pressure N/A, product is a solid and 

does not vaporize

47208902
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TABLE 3. Mammalian Toxicology Data Requirements for homobrassinolide (40 CFR § 158.2050)

Study/OPPTS Guideline No. Results Toxicity 

Category/Description

MRID

Acute oral toxicity (rat)

(870.1100)

> 5,000 mg/kg

Acceptable

IV

47185118

47208903

Acute dermal toxicity (rat)

(870.1200)

> 2,000 mg/kg

Acceptable

III 47185120

Acute inhalation toxicity (rat)

(870.1300)

>2.26 mg/L

Acceptable

IV

47185121

Primary eye irritation (rabbit)

(870.2400)

Mild irritation

Acceptable

III 47185122

Primary dermal irritation (rabbit)

(870.2500)

Not an irritant

Acceptable

IV 47185123

Dermal sensitization (guinea pig)

(870.2600)

Not a sensitizer

Acceptable

IV 47185124

Hypersensitivity incidents

(885.3400)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185131

90-Day oral toxicity 

(870.3100)

> 1,000 mg/L

Acceptable

III 47208906

90-Day dermal toxicity

(870.3250)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185136

90-Day inhalation toxicity

(870.3465)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185137

Developmental toxicity

(870.3700)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185139

Bacterial Reverse Mutation Assay

(870.5100)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185139

In vivo Mammalian CytogeneticsErythrocyte Micronucleus Assay

(870.5395)

Not Cytotoxic Acceptable 47185127

In vitro Mammalian Cell Gene 

Mutation Testing

(870.5300)

No potential for genotoxicity Waiver Request 

Acceptable

47185132

Mammalian Bone Marrow 

Chromosomal Aberration Test 

(870.5385)

No chromosome aberrations in mice treated 

up to a single oral dose of 2000 mg/kg body 

weight.

Acceptable

No Chromosomal 

Aberrations

47208905

DNA Synthesis in Mammalian Cells 

in Culture

(870.5550)

Not required Waiver not needed 47185133

In vitro Mammalian Chromosomal 

Aberration Test

(870.5375)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185134

Immunotoxicity

(880.3550)

No changes in organ weights or differential 

white blood cell counts of the treated animals 

which would indicate potential interference 

with normal immune function.

Waiver Request 

Acceptable

47185135

Immune Response

(880.3800)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185140

Chronic Exposure Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185141

Carcinogenicity

(870.4200)

A carcinogenicity test is not required. Waiver not needed 47185142
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VIII. Appendix B.

Product specific information is not available at this time as there are no currently registered 

products containing this active ingredient. When products containing homobrassinolide are 

registered with EPA, this document will be amended to include links to product specific 

information.

IX.Appendix C.

REFERENCES

Bajguz, A., 2000. Effect of brassinosteroids on nuclear acids and protein content in cultured

cells of chlorella vulgaris. Plant Physiol. Biochem. 38, 209-215.

Catterou, M., F. Dubois, H. Schaller, L. Aubanella, B. Vilcol, B. S. Sangwan-Norrel, R.S. 

Sangwan, 2001. Brassinosteroids microtubules and cell elongation in Arabidopsis thaliana. II.

Effects of brassinosteroids on microtubules and cell elongation in the bull mutant. Planta, 212, 

673-683.

IECVI.I – Individual Effects Chance Model Version 1.1. 2004. USEPA/OPP/EFED

Seeta S.R.R., B.V.Vardhini, E. Sujatha, S. Anuradha. 2002. Brassinosteroids-A new class of 

phytohormones. Current Science, 82:12391245.

TABLE 4. Nontarget Organism Toxicity Requirements for active ingredient (40 CFR § 158.2060)

Study/OPPTS Guideline No.

/MRID No.

Results Toxicity 

Category/Description

MRID

Avian acute oral toxicity

Colinus virginianus

(850.2100)

Sufficient information has been submitted to 

support the waiver.

Practically non-toxic 

based on waiver 

information

47185143

Avian dietary toxicity

Colinus virginianus

(850.2200)

Sufficient information has been submitted to 

support the waiver.

Practically non-toxic 

based on waiver 

information

47185144

Aquatic invertebrate acute toxicity

(Daphnia magna)

(850.1010)

48-hr EC50 = 8.9 mg/L Moderately Toxic 47185130

Freshwater fish LC50

(Oncorhynchus mykiss)

(850.1075)

96-hr LC50 = 24.56 mg/L

96-hr LC50 = 14.38 mg/L

Slightly Toxic 47185129

Non-target plant studies

(850.4000-4800, as applicable)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185145

Non-target insect testing

(880.4350)

Sufficient information has been submitted to 

support the waiver.

Waiver Request 

Acceptable

47185146

Acute oral (mouse) toxicity

(870.1100)

LD50 = >5000 mg/kg for female IV 47208903

90-Day Oral Feeding (rat)

(870.3100)

NOAEL 1000 mg/kg/day No subchronic oral 

toxicity

47208906