1 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

January 28, 2015 

PC Code: 128819 

MEMORANDUM DP Barcode: 422524 

SUBJECT: EFED Registration Review Problem Formulation for Forchlorfenuron 

FROM: Christina Wendel, Biologist 

Greg Orrick, Environmental Scientist 

 Environmental Risk Branch 2 

Environmental Fate and Effects Division (7507P) 

REVIEWED Ronald D. Parker, Senior Environmental Engineer

BY: Donna Reed Judkins, Ph.D., Biologist 

Environmental Risk Branch 2 

Environmental Fate and Effects Division (7507P) 

THROUGH: Brian Anderson, Branch Chief 

Environmental Risk Branch 2 

 Environmental Fate and Effects Division (7507P) 

 

TO: Wilhelmena Livingston, Chemical Review Manager 

 Kevin Costello, Acting Branch Chief 

Risk Management and Implementation Branch 4 

Pesticide Re-evaluation Division (7508P)

 
2 

Table	of	Contents	

1. Executive summary ................................................................................................................. 3

2. Introduction ............................................................................................................................. 4

a. Mode of Action .................................................................................................................... 4

3. Use Characterization ............................................................................................................... 4

4. Conclusions from Previous Risk Assessments ....................................................................... 5

a. Ecological Risk Assessment ................................................................................................ 5

b. Drinking Water Exposure Assessments ............................................................................... 7

c. Clean Water Act Programs .................................................................................................. 7

5. Environmental Fate and Transport.......................................................................................... 7

a. Transformation Products ...................................................................................................... 9

6. Receptors............................................................................................................................... 10

a. Effects to Aquatic Organisms ............................................................................................ 11

b. Effects to Terrestrial Organisms ........................................................................................ 11

c. Ecological Incidents ........................................................................................................... 13

7. Exposure Pathways of Concern ............................................................................................ 13

8. Analysis Plan ........................................................................................................................ 14

a. Stressors of Concern .......................................................................................................... 14

b. Measures of Exposure ........................................................................................................ 14

c. Measures of Effect ............................................................................................................. 15

d. Endangered Species Assessments ...................................................................................... 15

e. Endocrine Disruptor Screening Program ........................................................................... 15

9. Preliminary Identification of Data Gaps ............................................................................... 15

a. Environmental Fate ............................................................................................................ 15

b. Effects ................................................................................................................................ 16

10. References .......................................................................................................................... 24

a. Submitted Environmental Fate Studies .............................................................................. 25

b. Submitted Ecological Toxicity Studies .............................................................................. 26

APPENDIX A. Forchlorfenuron Ecotoxicity Data ....................................................................... 28

APPENDIX B. SIP & STIR Inputs and Outputs .......................................................................... 32
3 

1. Executive summary 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments to be conducted as part of the registration review of forchlorfenuron. The problem 

formulation describes the methods planned to be used during the completion of drinking water 

and ecological risk assessments in support of registration review and provides an overview of the 

environmental fate, ecological effects, potential risks associated with the use, and uncertainties 

unique to the risk assessment of forchlorfenuron. This document also identifies additional studies 

that would be beneficial to the conduct of an ecological risk assessment. 

Three ecological risk assessments have been conducted for forchlorfenuron FIFRA §3 actions: a 

new chemical assessment in 2004 (DP 301774) and new use assessments in 2008 (DP 341868+) 

and in 2013 (DP 406985). The assessments concluded that proposed uses of forchlorfenuron do 

not result in level-of-concern (LOC) exceedances for aquatic or terrestrial organisms. However, 

past risk assessments noted uncertainties in chronic risks to birds and aquatic organisms based on 

lack of chronic data, and risks to bees are uncertain in the absence of data. Previous conclusions 

remain unchanged; however, based on the current toxicity and exposure profile of 

forchlorfenuron, EFED believes that chronic effects to birds or aquatic animals are unlikely to be 

of concern. An updated, full ecological risk assessment is not needed for registration review, 

although EFED recommends that additional data be requested to allow for a more 

comprehensive evaluation of potential effects to honey bees and sediment dwelling invertebrates. 

EFED will evaluate those data when they are submitted and will work with the Pesticide Reevaluation Division (PRD) to address any risks of concern identified by those data. 

The following are the needed data and major uncertainties for forchlorfenuron: 

Data Needs 

 Environmental Fate Data 

o None (due to no currently identified risk LOC exceedances; however, if the 

requested data identify a risk concern, then additional environmental fate studies 

may be needed to further characterize the magnitude and duration of the risk) 

 Ecotoxicity Data 

o OECD TG 213 and Non-guideline special studies: Honey bee adult acute and 

chronic oral toxicity studies 

o OECD TG 237 and Non-guideline special studies: Honeybee larval acute and 

chronic oral toxicity studies 

o Special study OECD TG 75 and OSCPP 850.3040: Semi-field testing for 

pollinators and Field testing for pollinators (both studies that are conditionally 

required based on the results of the Tier I – laboratory based studies listed above; 

if needed these additional field studies will be discussed pending the results of the 

acute and chronic adult and larval oral toxicity studies to honey bees) 

o OSCPP 850.1760 or 850.1770: Whole Sediment Chronic Life-cycle Freshwater 

invertebrate toxicity testing 
4 

o Avian reproduction study (OSCPP 850.2300) (currently in review –the review 

will be finalized prior to issuance/publication of the DCI – status update 

forthcoming) 

o OSCPP 850.4150: Terrestrial plant, Tier II vegetative vigor data with the TEP is 

still an uncertainty, as the current available vegetative vigor study did not test the 

active ingredient, forchlorfenuron, at the highest application rate. 

Some data gaps are not identified as data needs at this time (see Section 9 for details) due to the 

low risks of forchlorfenuron uses in the United States. If a risk of concern is identified in the 

future, data needs for risk assessment may also change. 

2. Introduction 

Forchlorfenuron is a plant growth regulator that was first registered in 2005. It is registered for 

use on blueberries, bushberries (black currants, red currants, elderberries, gooseberries, and 

lingonberries), kiwifruit, and grapes, with applications pending for use on figs, sweet cherries, 

plums including prunes, pears, almonds, and pistachios. Forchlorfenuron was recently assessed 

in 2013 (USEPA, 2013). 

a. Mode of Action 

Forchlorfenuron is a phenylurea, cytokinin plant growth regulator. The compound acts 

synergistically with natural auxins to promote plant cell division and lateral growth, resulting in 

improved fruit size, fruit set, cluster weight, cold storage, and/or resistance to splitting from rain 

in a variety of fruits and nuts (USEPA, 2008). The mode of action in non-target organisms is 

unknown. 

3. Use Characterization 

Three end-use formulations containing forchlorfenuron are currently registered for use in the 

United States (EPA Reg. No. 71049-1, 71049-3, and 71049-4). Table 1 lists the maximum use 

patterns for the labeled use sites. There are no ambiguous label directions that require 

clarification for exposure assessment. 

Table 1. Forchlorfenuron Use Patterns 

Uses 

Max. Single 

App. Rate 

(lbs a.i./A) 

Max. Annual 

App. Rate 

(lbs a.i./A) 

App. 

Interval (d) 

Application 

Type 

Almonds, sweet cherries, figs, pears, 

pistachios, plums/prunes 0.022 0.022 n/a 

Ground/air-blast

Blueberries 0.022 A 0.044 B 14 

Black currants, red currants, elderberries, 

gooseberries, lingonberries (i.e., bushberries) 0.0044 0.0088 B 14 

Grapes 0.022 0.022 B n/a 

Kiwifruit 0.018 0.018 B n/a A This rate is used to delay harvest. Otherwise, the maximum single application rate is 0.0044 lbs a.i./A. B The labeled application rate is limited per crop cycle or per season. These crops have only one crop cycle or 

growing season per year (USEPA, 2007; USDA, 2000). Therefore, these rate limits were used as annual rate 

limits. 
5 

A Screening Level Usage Analysis conducted by the Agency indicates that annual 

forchlorfenuron usage from 2004 to 2012 was approximately 1,000 pounds on table grapes and 

less than 500 pounds each on raisin grapes, kiwifruit, and blueberries (USEPA, 2014). The 

treated fraction of crops was reported to be <1-25% on average, with a maximum of 50% on 

kiwifruit (USEPA, 2014). 

4. Conclusions from Previous Risk Assessments 

a. Ecological Risk Assessment 

Three ecological risk assessments have been conducted for forchlorfenuron FIFRA §3 actions: a 

new chemical assessment in 2004 (DP 301774) and new use assessments in 2008 (DP 341868+) 

and in 2013 (DP 406985). These assessments concluded that proposed uses of forchlorfenuron 

do not result in LOC exceedances for federally endangered and threatened (listed) and non-listed 

aquatic or terrestrial organisms. However, chronic risks to birds (also a surrogate for terrestrialphase amphibians and reptiles) and risks to honey bees are uncertain in the absence of data. It is 

also unclear how stimulative growth effects to terrestrial and aquatic plants could directly impact 

listed terrestrial and aquatic plant species, or indirectly impact species that rely on plants for 

shelter or sustenance. Therefore, due to this uncertainty, direct effects to listed plants and 

potential indirect risks to all listed species that depend on plants for food or shelter cannot be 

ruled out. Chronic risk to aquatic animals is uncertain in the absence of data, but unlikely to 

exceed concern levels based on toxicity estimates using acute-to-chronic ratios. A summary of 

LOC exceedances is listed in Table 2. Figure 1 and Table 3 summarize the potential risks and 

the supporting evidence. 

Table 2. LOC Exceedances for Recently Assessed Uses 

Effect 

Taxonomic Group 

Birds Mammals Terrestrial 

Plants 

Terrestrial

Inverts Fish Aquatic Inverts 

Aquatic 

Plants 

Direct Effect LOC Exceedance √A -- -- B -- -- -- -- B

Indirect Effect Potential C √ √ √ √ √ √ √ A Uncertain chronic risks to birds (surrogates for terrestrial-phase amphibians and reptiles) B Stimulative growth effects observed in both terrestrial and aquatic plant species, direct risks to listed plants cannot 

be dismissed. 

C Indirect risks to all listed species cannot be ruled out due to uncertainties of stimulative growth effects on both 

terrestrial and aquatic plant species. 
6 

Figure 1. Graphic Summary of Potential Risks of Recently Assessed Uses 

Table 3. Evidence of Risk to Taxonomic Groups from Forchlorfenuron Uses 

Predominant Evidence of Negligible Risk Predominant Evidence of Risk 

Mammals: No toxicity observed in acute studies. 

Chronic RQs <1.0. 

Limited Evidence of Negligible Risk Limited Evidence of Risk 

Fish & Aquatic Invertebrates: No toxicity was observed 

in acute studies with multiple species. Chronic risk is 

unlikely to exceed concern levels; toxicity would have to 

be 15,000 to 27,000 times greater than acute toxicity to 

trigger risk concerns. 

Terrestrial & Aquatic Plants: Observed stimulative 

growth effects could directly impact terrestrial and 

aquatic plants. However, the relationship between the 

stimulative effect and survival and reproduction of plant 

species or animals that depend on them for food or 

shelter is uncertain. 

Birds: No toxicity was observed in acute studies. 

Preliminary review of chronic toxicity data are 

available; chronic effects were observed at all test 

concentrations. In addition, drinking water was found to 

be an exposure pathway of potential concern on a 

chronic basis, based on the Screening Imbibition 

Program (SIP). 

Terrestrial Invertebrates: Risk is presumed in the 

absence of acute and chronic oral toxicity data for adults 

and larvae. Forchlorfenuron is systemic in plants so 

exposure via pollen and nectar is possible. 
7 

b. Drinking Water Exposure Assessments 

Three drinking water exposure assessments have been conducted for forchlorfenuron FIFRA §3 

actions: a new chemical assessment in 2004 (DP 301774) and new use assessments in 2008 (DP 

341630) and in 2013 (DP 407227). Maximum screening exposure estimates for forchlorfenuron 

(which is the only residue of concern) were 0.60 μg/L (1-in-10-year peak) and 0.21 μg/L (1-in10-year annual mean) for surface water and 8.8 μg/L (1-in-10-year peak) and 7.3 μg/L (1-in-10-

year annual mean) for ground water. 

c. Clean Water Act Programs 

The Clean Water Act requires the Agency to publish water quality criteria that accurately reflect 

the latest scientific knowledge on the kind and extent of all identifiable effects on health and 

welfare that might be expected from the presence of pollutants in any body of water, including 

ground water. While these recommended criteria do not, in themselves, impose any 

requirements, states and authorized tribes can use them to develop water quality standards. An 

Aquatic Life Ambient Water Quality Criteria document has not been published for 

forchlorfenuron (see url: http://www.epa.gov/waterscience/criteria/). 

The Office of Pesticide Programs (OPP) publishes aquatic life benchmarks for freshwater species 

based on toxicity values for the most sensitive species from the most recent risk assessments. 

However, aquatic life benchmarks have not been published for forchlorfenuron (see url: 

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm#benchmarks). Any data 

submitted or otherwise located as part of the registration review process may be used to update 

aquatic life benchmarks if applicable. 

Forchlorfenuron is not identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5. No Total Maximum Daily Load (TMDL) criteria have been developed for forchlorfenuron, 

based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES. 

5. Environmental Fate and Transport 

The available environmental fate data for forchlorfenuron are listed in Table 4. In summary, the 

compound persists in the environment, has moderate to slight mobility in soil, does not 

appreciably volatilize, is hydrophilic, and, therefore, does not appreciably bioconcentrate in fish. 

Sorption to soil correlates with soil clay content (r2

=0.97) and with soil organic carbon (r2=0.70), 

with the coefficient of variation (CV) for KFOC (0.61) less than that for KF (1.0). Major 

degradates other than carbon dioxide have not been found. Field data are not available. 

Forchlorfenuron may infiltrate to ground water in some soils and may move to surface water 

bodies via spray drift and/or runoff of dissolved and/or sorbed residues. 
8 

Table 4. Chemical Properties and Environmental Fate Parameters of Forchlorfenuron

Parameter Value Source

Selected Physical/Chemical Parameters 

Molecular mass (molecular formula) 247.69 g/mol (C12H10ClN3O) (Calculated) 

Vapor pressure (25 °C) 3.5 x 10-10 torr MRID 44359508 

Aqueous solubility (20-21C) 39 mg/L MRID 44359509 

Henry’s Law Constant (25 °C) 2.9 x10-12 atm-m3/mol (Calculated) 

Octanol-to-water partition coefficient (KOW);

log KOW (20 C) 1600; 3.20 MRID 44359512 

Dissociation constants (pKa, pKb) 2.5, 12.2 MRID 44394603 

Persistence

Hydrolysis half-life (25C) No substantial degradation 

(pH 5, 7, and 9) MRID 44394604 

Aqueous photolysis half-life (25C) No substantial degradation MRID 44394605 

Aerobic soil metabolism half-life (25°C) 577 d MRID 44359515/ 

45840119 

Anaerobic soil metabolism half-life (25C) 234 d MRID 44359514/ 

45840118 

Mobility

Freundlich soil-water partition coefficients 

(KF); Freundlich organic carbon-normalized 

coefficients (KFOC) 

2.13, 5.79, 17.2, 39.8 L/kg; 

852, 1430, 1,450, 3,320 L/kgOC

MRID 44359516/ 

45840121 

Field Dissipation 

Field data were not submitted. 

Fish Bioconcentration 

Fish bioconcentration factors (steady-state, 

total residues); depuration rate 

Not quantified 1 (edible), 16 (inedible), 

7.2 (whole fish); >88% in 3 days 

MRID 44359524/ 

45840120 1

 A BCF for fillet tissue was not quantified because residues were not present above the LOQ (75 μg/kg).
9 

a. Transformation Products 

Major degradates of forchlorfenuron other than carbon dioxide have not been found. Chemical names and structures 

and carbon dioxide are in Table 5. 

Table 5. Forchlorfenuron and Its Environmental Transformation Products 

Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID M

%A

PARENT

Forchlorfenuron N-(2-chloro-4-pyridinyl)-N’-phenylurea 

CAS No.: 68157-60-8 Formula: C12H10ClN3O 

MW: 247.68 g/mol SMILES:C1=CC(=CC=C1)NC(=O)NC2=CC(=NC=C2)Cl 

TRANSFORMATION PRODUCTS

Unextracted residues 

Not applicable 

Not applicable 

Aerobic soil 44359515/ 45840119 24

Anaerobic soil 44359514/ 45840118 31

Carbon dioxide Carbon dioxide 

Formula: CO2

MW: 44.1 g/mol 

O O

Aerobic soil 44359515/ 45840119 9.9

Anaerobic soil 44359514/ 45840118 1.
10 

6. Receptors 

The toxicity endpoints that will be used in risk assessment for aquatic and terrestrial organisms 

exposed to forchlorfenuron are presented in Table 6 and Table 7 below. A complete list of the 

ecotoxicity data available for forchlorfenuron can be found in Appendix A.

Forchlorfenuron is moderately toxic to freshwater fish and invertebrates; however, no effects 

were observed in the aquatic vascular or non-vascular plant toxicity studies. Forchlorfenuron is 

practically non-toxic to birds and mammals on an acute exposure basis. The acute mammalian 

toxicity study used in previous risk assessments was reclassified as unacceptable by HED; 

however, there was another acute oral mammalian study available using an end-use product 

(0.86% a.i.) that was classified as acceptable. The change in endpoint from the previously used 

endpoint to the new endpoint should not change any risk conclusions for mammals (the previous 

endpoint LD50 = 4889 mg/kg and the new endpoint LD50 >5050 mg/kg). Toxicity to terrestrial 

invertebrates has only been assessed for adult honey bees via an acute contact exposure. 

No chronic toxicity data for forchlorfenuron are available for fish or aquatic or terrestrial 

invertebrates. The chronic bird toxicity data with Bobwhite quail was recently submitted to the 

agency and is undergoing review. Based on an initial review of the data, there are indications of 

significant effects on 14-day survivor weight observed in all test concentrations (7-9%), resulting 

in a NOAEC of <170 mg a.i./kg-diet. There were, however, no other treatment related effects of 

forchlorfenuron on survival, abnormal behavior or reproductive endpoints. Although the effects 

indicate a NOAEC of less than the lowest test concentration, the NOAEC is likely being 

approached given the diminished magnitude of the effect observed at the lowest test 

concentration. It is reasonable to consider this LOAEC value from the submitted avian 

reproduction study to be sufficient. The chronic NOAEC for birds (a surrogate for reptiles and 

terrestrial-phase amphibians) would need to be approximately 30-fold lower than the LOAEC 

value (170 mg a.i./kg-diet) to result in LOC exceedances. The mammalian 2-generation 

reproduction study indicated effects to mammals based on decreased food consumption in F0 & 

F1 males, clinical signs of toxicity and lower body weight in F1 males & females, and growth 

retardation in F1 & F2 pups. 

There were no significant effects in reduction of growth observed for aquatic plant species 

exposed to forchlorfenuron at the treatment levels tested; however, there were stimulative, 

growth effects that were observed for both vascular and non-vascular aquatic plant species that 

were tested. The most substantial stimulative effect was observed in the freshwater green algal 

study (Pseudokirchneriella subcapitata), after 96 hours of exposure to 16 μg a.i./L of 

forchlorfenuron a 43% increase in growth (cell density) was observed (MRID 46753502). 

There were no ≥25% effects in reduction that were observed for terrestrial plant species exposed 

to forchlorfenuron at the treatment rates tested (i.e., 0.055 lbs a.i./A (seedling emergence, MRID 

45840111) or 0.022 lbs a.i./A (vegetative vigor, MRID 46753505)), although a reduction of 20% 

in dry weight was observed in cucumber in the vegetative vigor study. However, stimulative 

growth effects were observed for some terrestrial plant species that were tested, in both terrestrial 

plant toxicity studies. A 46% increase in shoot weight was observed in ryegrass in the seedling 

emergence study (MRID 45840111), and a 36% increase in shoot weight in turnip was observed 
11 

in the vegetative vigor study. The measured concentrations in the vegetative vigor study (based 

on spray solution recoveries) were 30.3% - 32.2% of nominal, which indicates that the study has 

not tested the active ingredient at the highest application rate. Based on the available data, there 

is uncertainty of risk to terrestrial plants at the maximum application rate. 

a. Effects to Aquatic Organisms 

Table 6. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 

Forchlorfenuron1 

Taxonomic 

Group 

Study 

Type Surrogate Species Toxicity Value (mg a.i./L) 

Acute Toxicity 

Classification 

MRID 

(Study 

Classification) 

Freshwater fish 

& Aquatic-phase 

amphibians 

Acute 

Bluegill 

(Lepomis macrochirus)/

(TGAI, 100% a.i.) 

96-h LC50 = 8.8 Moderately toxic 44359519 

(Acceptable) 

Freshwater 

invertebrates Acute 

Waterflea

(Daphnia magna)

(TGAI, 100% a.i.) 

96-h EC50 = 5.3 Moderately toxic 44359520 

(Acceptable) 

Aquatic plants2

Vascular 

Duckweed 

(Lemna gibba) 

(EP, 0.86% a.i.) 

7-d EC50 > 0.90 

7-d NOAEC = 0.90

Stimulated 

growth of 4%2 

45840110 

(Acceptable)

Nonvascular 

Marine diatom 

(Skeletonema costatum) 

(TGAI, 98.2% a.i.) 

96-h EC50 > 0.016 

NOAEC = 0.016 

No significant 

effects 

46753501 

(Acceptable)

Freshwater green algae 

(Pseudokirchneriella 

subcapitata) 

(TGAI, 98.2 % a.i.) 

96-h EC50 > 0.016 

NOAEC = 0.016 

No significant 

effects, but cell 

density had 

stimulated 

growth of 43%2 

46753502 

(Acceptable) 

1 No chronic freshwater toxicity data and no estuarine/marine acute or chronic toxicity are available for 

forchlorfenuron. 

2 No significant effects in reduction were observed for aquatic plant species exposed to forchlorfenuron at the 

treatment levels tested. However, there were stimulative, positive growth effects that were observed for some 

aquatic plant species that were tested. Stimulative growth was observed in the following aquatic non-vascular 

plants: the green algae (Pseudokirchneriella subcapitata; +43% growth), the freshwater diatom (Navicula 

pelliculosa; +4% growth), and stimulative growth was also observed in the vascular aquatic plant duckweed (L. 

gibba; +4% growth). 

b. Effects to Terrestrial Organisms 

Table 7. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 

Forchlorfenuron 

Taxonomic 

Group 

Study 

Type Species Toxicity Value (Endpoints) 

Acute Toxicity 

Classification 

MRID 

(Study 

Classification) 

Birds, 

Reptiles, & 

Terrestrialphase 

amphibians 

Acute 

Bobwhite quail 

(Colinus virginianus) 

(TGAI, 100% a.i.) 

LD50 > 2250 mg a.i./kgbw1 Practically nontoxic 

44359523 

(Acceptable) 

Sub-acute 

dietary Bobwhite quail LC50 > 5620 mg a.i./kgdiet1

Practically nontoxic 44359521 

(Acceptable) 
12 

Taxonomic 

Group 

Study 

Type Species Toxicity Value (Endpoints) 

Acute Toxicity 

Classification 

MRID 

(Study 

Classification) 

Repro Bobwhite quail 

NOAEC/LOAEC 

<170/170 mg a.i./kgdiet2 NA 49350901 

(IN REVIEW) 

Mammals 

Acute oral 

Laboratory rat 

(Rattus norvegicus) 

(EP, 0.86% a.i.) 

LD50 > 5,050 mg/kgbw (M&F)3 

Practically nontoxic; Toxicity 

category IV 

45794401 

(Acceptable) 

Chronic 

2-gen. 

Laboratory rat 

(TGAI, 98.5% a.i.) 

NOAEC/LOAEC = 

150/2000 ppm 

(9/115 mg/kg/day)4 

NA 44394616 

(Acceptable) 

Acute 

inhal. 

Laboratory rat 

(EP, 0.86% a.i.) 

LC50 > 2.14 mg/L 

(M&F)5

Toxicity 

category IV 

45794403 

(Acceptable) 

Terrestrial 

invertebrates 

Acute 

contact 

Honey bee 

(Apis mellifera) 

(TGAI, 98.5% a.i.) 

LD50 >25 ug a.i./bee6 Practically nontoxic 

44359525 

(Acceptable) 

 

Terrestrial 

plants7

 

Seedling 

Emergence 

Monocot and Dicot 

species 

EC25 > 0.055 lbs a.i./A

NOAEC = 0.055 lbs 

a.i./A 

NA 45840111 

(Acceptable) 

Vegetative 

Vigor 

(monocot) 

Oat 

(Avena sativa)

EC25 > 0.0067 lbs a.i./A 

NOAEC = 0.0067 lbs 

a.i./A 

NA 46753505 

(Supplemental) 

Vegetative 

Vigor 

(dicot)

Cucumber 

(Cucumis sativa)

EC25 > 0.0071 lbs a.i./A 

NOAEC < 0.0071 lbs 

a.i./A8 

NA 46753505 

(Supplemental) 

NA: Not Applicable 

1

 No mortality 

2 Significant (7-9%) dose-dependent reductions in 14-d survivor weight in all treatment levels when compared to the 

negative control.

3 No mortality was observed; the only clinical sign was diarrhea in males on the day of dosing. 

4 Endpoints affected included: decreased food consumption in F0 & F1 M; clinical signs of toxicity & lower BW in F1M & 

F and growth retardation in F1 & F2 pups); Concentrations tested: 0, 150, 2000, and 7500 ppm, Premating doses for the 

adult F0 males were 11, 144, and 544 mg/kg/day and for the F0 females were 13, 169, and 701 mg/kg/day, respectively. 

Premating doses for the adult F1 males were 13, 168, and 829 mg/kg/day and for the F1 females were 15, 202, and 926 

mg/kg/day, respectively. 

5 No mortality was observed; Clinical signs included activity decrease and piloerection in both sexes on the day of dosing 

only. 

6

 There were two (2) mortalities (4%) in the negative control and 25 μg a.i./bee (measured) test concentrations; and one 

(1) mortality (2%) in the solvent control at 48 hours. Immobility and lethargy were noted in a few instances, but this was 

largely the case in the two control groups. 

7 No significant effects in reduction were observed for terrestrial plant species exposed to forchlorfenuron at the treatment 

rate tested, i.e., 0.055 lbs a.i./A (seedling emergence, MRID 45840111) or 0.022 lbs a.i./A (vegetative vigor, MRID 

46753505). However, there were stimulative, positive growth effects that were observed for some terrestrial plant species 

that were tested. For the seedling emergence study, these stimulative effects were observed in cabbage (+11% shoot 

length), corn (+9% shoot weight), oat (+13% shoot weight), onion (+8% shoot weight), perennial ryegrasses (+4% shoot 

length and +46% shoot weight), and turnips (+3% shoot length); and for the vegetative vigor study, these stimulative 

effects were observed in corn (+4% shoot length and +8% dry weight), oat (+2% shoot length), onion (+1% shoot length 

and +6% dry weight), ryegrass (+4% shoot length and +15% dry weight), cabbage (+2% dry weight), lettuce (+19% shoot 

length dry weight), soybean (+6% dry weight), and turnips (+36% dry weight). For the vegetative vigor study, the 

measured concentrations were 30.3-32.2% of nominal, which was supposed to be set at the maximum application rate of 

0.022 lbs a.i./A. However, the study does provide some information on potential toxic effects to plants; but the study did 

not test forchlorfenuron at the highest application rate. 

8 Endpoints affected: None, but there was a 20% reduction in dry weight in cucumber. 
13 

c. Ecological Incidents 

The ecological incident information system (EIIS) is an OPP database that houses ecological 

incidents that have been reported to the Agency. When available, EIIS includes date and location 

of an incident, type and magnitude of effects observed in various species, use(s) of pesticides 

known or suspected of contributing to the incident, and results of any chemical residue analysis 

or other analyses conducted during incident investigation. EIIS incidents are categorized 

according to the certainty that the incident resulted from pesticide exposure. The Avian 

Monitoring System (AIMS) is a database administered by the American Bird Conservancy that 

contains publicly available data on reported avian incidents involving pesticides. Many of the 

incidents listed in this database are also in the EIIS. The Aggregate Incident Reports database is 

an Agency database that may contain minor wildlife and plant incidents for chemicals. 

As of November 24, 2014, there were no ecological incidents reported in EIIS or AIMS for 

forchlorfenuron. There were also no minor incidents reported in the Aggregate Incident Reports 

database for forchlorfenuron. However, an absence of incident reports does not necessarily 

equate to an absence of incidents given the nature of incident reporting. 

7. Exposure Pathways of Concern 

The environmental fate properties and use patterns of forchlorfenuron indicate that direct spray, 

spray drift, and runoff represent potential transport mechanisms to aquatic and terrestrial 

organisms. The conceptual model will consider forchlorfenuron as the residue of concern. 

Drinking water and inhalation exposure pathways were screened using the SIP (Screening 

Imbibition Program, version 1.0) and STIR (Screening Tool for Inhalation Risk, version 1.0) 

screening methods. Only one potential route of exposure (drinking water to birds on a chronic 

basis) was found to be an exposure pathway of potential concern (Table 8). Although, SIP 

suggests that exposure to contaminated drinking water could lead to LOC exceedances, a number 

of factors affect the likelihood that exposures will result in adverse effects, including pesticide 

concentrations in the contaminated puddles (SIP assumes the pesticide is present at the solubility 

limit) and duration of exposure relative to the duration of exposure needed to cause adverse 

effects. Refinements of these parameters are currently not available. A number of speciesspecific parameters, including water content of diet, size, and behavioral parameters will also 

influence the potential exposure levels that may occur from contaminated puddles. Although SIP 

was designed as a conservative screen, it may over- or under-estimate potential individual 

exposures based on varying behaviors of individual birds. The other screening methods found no 

other potential exposure routes of concern (outputs for each model are located in Appendix B). 

SIP and STIR are described in detail at: 

http://www.epa.gov/oppefed1/models/terrestrial/index.htm. 
14 

Table 8. SIP Avian Results

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 32 32 

Adjusted toxicity value (mg/kg-bw) 1621 18 

Ratio of exposure to acute toxicity 0.020 1.7 

Conclusion* 

Drinking water exposure 

alone is NOT a potential 

concern for birds 

Exposure through 

drinking water alone is a 

potential concern for birds 

8. Analysis Plan 

Three ecological risk assessments have been conducted for forchlorfenuron FIFRA §3 actions: a 

new chemical assessment in 2004 (DP 301774) and new use assessments in 2008 (DP 341868+) 

and in 2013 (DP 406985). The assessments concluded that proposed uses of forchlorfenuron do 

not result in level-of-concern (LOC) exceedances for aquatic or terrestrial organisms. However, 

chronic risks to birds (a surrogate for terrestrial-phase amphibians and reptiles) and risks to bees 

are uncertain in the absence of data. These conclusions remain unchanged and an updated, full 

ecological risk assessment is not needed for registration review. EFED recommends that 

additional data be requested to allow for a more comprehensive evaluation of potential effects to 

honey bees. EFED will evaluate those data when they are submitted and will work with PRD to 

address any risks of concern identified by those data. 

a. Stressors of Concern 

i. Ecological Risk Assessment 

Forchlorfenuron is the only residue of concern for terrestrial and aquatic organisms in the 

ecological risk assessment for forchlorfenuron. Major degradates of forchlorfenuron other than 

carbon dioxide have not been found. 

ii. Drinking Water 

Forchlorfenuron is the only residue of concern for the forchlorfenuron drinking water exposure 

assessment in support of human health dietary risk assessment, due to a lack of observed organic 

degradates. The results of the recent 2013 drinking water exposure assessment (DP 407227) will 

be used for registration review unless an update is warranted due to new data or assessment 

methodologies. 

b. Measures of Exposure 

Past assessments of forchlorfenuron EFED have used standard available models to evaluate 

potential exposures to aquatic and terrestrial organisms as described at 

http://www.epa.gov/oppefed1/models/water/index.htm and 

http://www.epa.gov/pesticides/science/models_db.htm. GENEEC or the Surface Water 

Concentration Calculator (SWCC) are currently the models that are typically used to estimate 
15 

aquatic exposure. T-REX, Bee-REX, and TerrPlant are currently the models that are typically 

used to estimate terrestrial exposure. 

i. Available Monitoring Data 

The Agency is not aware of monitoring conducted by federal and state agencies for 

forchlorfenuron, as of September 8, 2014. Monitoring will be considered in the assessment to 

the extent that data on forchlorfenuron are available. 

c. Measures of Effect 

Toxicity data presented in Section 6 of this problem formulation would be used to calculate risk 

quotients. Any additional information submitted by the registrant or found in the open literature 

prior to conduct of the risk assessment would also be considered. The open literature studies are 

identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 2007a), which employs 

a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, 

and wildlife. The evaluation of both sources of data can also provide insight into the direct and 

indirect effects of pesticides on biotic communities from loss of species that are sensitive to the 

chemicals and from changes in structure and functional characteristics of the affected 

communities. 

d. Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency would evaluate risks to federally listed, threatened and/or endangered (listed) species 

from registered uses of pesticides in registration review. The process for evaluating potential 

risks to listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm. 

e. Endocrine Disruptor Screening Program 

Forchlorfenuron was not included in the first group of 67 chemicals issued an order to conduct 

Tier 1 EDSP testing and is not on the second list of chemicals for Tier 1 screening. For 

additional information the EDSP program, visit http://www.epa.gov/endo/. 

9. Preliminary Identification of Data Gaps 

a. Environmental Fate 

Table 9 identifies environmental fate studies by MRID that offer data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in order 

to support risk assessment. Additional environmental fate studies and analytical methods are not 

needed at this time; however, if the requested ecotoxicity data identify a risk concern, then 

additional environmental fate studies and analytical methods may be needed to further 

characterize the magnitude and duration of the risk. 
16 

Table 9. Submitted Environmental Fate Data for Forchlorfenuron 

OCSPP 

Guideline Data Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Sufficient 

for risk 

assessment?

Current Additional Data Need 

835.2120 Hydrolysis 44394604 Acceptable Yes None 

835.2240 Aqueous photolysis 44394605 Supplemental Yes None 

835.2410 Soil photolysis (None) (Not applicable) Yes None: forchlorfenuron is not 

expected to photolyze

835.4100 Aerobic soil 

metabolism 

44359515/ 

45840119 Acceptable Yes None: a study of three additional soils 

is not needed due to the limited risks 

835.4200 Anaerobic soil 

metabolism 

44359514/ 

45840118 Acceptable Yes None 

835.4300 Aerobic aquatic 

metabolism (None) (Not applicable) Yes None: a study is not needed due to the limited risks 

835.4400 Anaerobic aquatic 

metabolism (None) (Not applicable) Yes None: a study is not needed due to 

the limited risks 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

44359516/ 

45840121 Acceptable Yes None 

835.6100 Terrestrial field 

dissipation (None) (Not applicable) Yes None: a study is not needed due to the limited risks 

850.1730 Fish 

bioconcentration 

44359524/ 

45840120 Acceptable Yes None

850.6100 

Analytical method 

in soil (None) (Not applicable)

Yes* 

*Analytical methods are not needed 

to address low risks. However, if the 

requested ecotoxicity data identify a 

risk concern, then an analytical 

method will be needed for the 

relevant environmental matrix. 

Analytical method 

in water (None) (Not applicable)

b. Effects 

Table 10 and Table 11 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether further data are needed in 

order to support risk assessment. The rationale for additional non-guideline data requested is 

presented below the tables. 
17 

Table 10. Submitted Aquatic Ecological Effects Data for Forchlorfenuron 

OCSPP 

Guideline Data Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Sufficient 

for risk 

assessment? 

Current Additional Data 

Need 

850.1010 

Freshwater 

invertebrate 

acute toxicity 

44359520 Acceptable Yes None

850.1025 

850.1035 

850.1045 

850.1055 

Saltwater 

invertebrate 

acute toxicity 

(None) (Not applicable) Yes 

An acute study with an 

estuarine/marine invertebrate 

species would allow for a more 

comprehensive evaluation of 

potential risks; however, 

freshwater data will be used as 

a surrogate in the absence of 

data. The margin of safety 

from use of freshwater 

invertebrate data as a surrogate 

is such that EFED is confident 

in the risk conclusions for 

saltwater invertebrates. 

850.1075 Freshwater fish acute 

toxicity 

44359518 Acceptable Yes None

44359519 Acceptable 

850.1075 Saltwater fish acute 

toxicity (None) (Not applicable) Yes

An acute study with an 

estuarine/marine fish species 

would be useful; however, 

freshwater data will be used as 

a surrogate in the absence of 

data. The margin of safety 

from use of freshwater fish 

data as a surrogate is such that 

EFED is confident in the risk 

conclusions for saltwater fish. 

850.1300 

Freshwater 

invertebrate 

life cycle 

(None) (Not applicable) Yes

None. Chronic effects to fish 

and aquatic invertebrates are 

unlikely because chronic 

NOAEC’s would need to be 

approximately 3 to 4 orders of 

magnitude lower than acute 

LC50s to result in chronic risk 

concern. Tier 1 EECs from 

past assessments were less 

than 1 ug/L, and acute LC50s 

are approximately 5,000 ug/L 

to 9,000 ug/L. 

850.1350 

Saltwater 

invertebrates 

life cycle 

(None) (Not applicable) Yes

850.1400 Freshwater fish 

early-life stage (None) (Not applicable) Yes

850.1400 Saltwater fish 

early-life stage (None) (Not applicable) Yes

850.1500 Fish life cycle (None) (Not applicable) Yes
18 

OCSPP 

Guideline Data Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Sufficient 

for risk 

assessment? 

Current Additional Data 

Need 

Either

850.1760 

Or 

850.1770 

Whole sediment 

(chronic) Life cycle 

freshwater 

invertebrate 

(None) (Not applicable) No

Yes, Forchlorfenuron has the 

potential to partition to the 

sediment (log Kow of 3.2; 

MRID 44359512 and remain 

for an extended amount of time 

(aerobic soil metabolism is 

577d; MRID 44359515/ 

45840119). One freshwater 

invertebrate chronic sediment 

toxicity study would allow us 

to characterize any potential 

difference in toxicity to 

invertebrates exposed via water 

column vs. sediment. 

850.1780 

Whole sediment 

Chronic (Life cycle) 

estuarine/marine 

invertebrate 

(None) (Not applicable) Yes

Although based on the fact that 

forchlorfenuron has the 

potential to partition to the 

sediment and remain for an 

extended amount of time; 

however, at this time 

estuarine/marine sediment 

toxicity data is not being 

requested, it may be requested 

at a later date. Freshwater data 

will be used as a surrogate in 

the absence of data. 

850.4400 

Aquatic plant 

Toxicity Test using 

Lemna spp. 

45840110 Acceptable Yes None 

850.4500 Algal toxicity 

46753501 Acceptable Yes None; (Marine diatom; 

Skeletonema costatum)

46753502 Acceptable Yes

None; (Freshwater green alga; 

Pseudokirchneriella 

subcapitata )

46753503 Acceptable Yes None; (Freshwater diatom; 

Navicula pelliculosa)

850.4550 Cyanobacteria 46753504 Acceptable Yes None; (Freshwater blue-green 

alga; Anabaena flos-aquae)
19 

Table 11. Submitted Terrestrial Ecological Effects Data for Forchlorfenuron

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Sufficient 

for risk 

assessment? 

Current Additional Data Need 

850.2100 Avian oral 

toxicity 44359523 Acceptable Yes

Yes – a second acute oral species is 

needed to fulfill guideline 

requirements - passerine or upland 

game species. However, Tier 1 

EECs from past assessments ranged 

from approximately 5-11 mg/kg, and 

acute LD50 was >2250 mg/kg-bw 

and acute LC50 was >5620 mg/kgdiet. The passerine LC50 would 

have to be 6 orders of magnitude 

lower than the other avian species to 

result in an acute listed species LOC 

exceedance of 0.1. Therefore, based 

on this, there is a margin of safety 

given the lack of acute effects to 

other birds and additional data 

would not likely add significantly to 

the risk assessment. 

850.2200 Avian dietary 

toxicity 

44359521 Acceptable Yes None

44359522 Acceptable 

850.2300 Avian 

reproduction 49350901 In Review In Review

Currently in review, at this time; 

however, the review will be finalized 

prior to publication of the DCI. A 

status update is forthcoming 

870.1100 Mammalian 

acute oral 45794401 Acceptable Yes None 

870.1300 Mammalian 

acute inhalation 45794403 Acceptable Yes None 

870. 

Mammalian 2- 

generation 

Reproduction 

 44394616 Acceptable Yes None

850.3020 

Honey bee adult 

acute contact 

toxicity 

44359525 Acceptable Yes None 

Special 

study 

OECD 213 

Honey bee adult 

acute oral 

toxicity 

(None) (Not applicable) No An acute oral toxicity study with the 

adult honey bee is needed. 

Special 

Study 

Honey bee adult 

chronic toxicity (None) (Not applicable) No A chronic oral toxicity study with the adult honey bee is needed. 

Special 

study 

OECD 237 

Honey bee larvae 

acute oral 

toxicity 

(None) (Not applicable) No An acute oral toxicity study with the 

honey bee larvae is needed. 

Special 

Study 

Honey bee larvae 

chronic toxicity (None) (Not applicable) No A repeat dose toxicity study with honey bee larvae is needed. 
20 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Sufficient 

for risk 

assessment? 

Current Additional Data Need 

Special 

Study 

Field trial of 

residues in pollen 

and nectar 

(None) (Not applicable) No 

A field trial measuring the residues 

of forchlorfenuron in pollen and 

nectar is needed 

850.3030 

Honey bee 

residue on 

foliage 

(None) (Not applicable) Yes

None. Acute contact LD50 >25 

μg/bee; study is not triggered, LD50 

is not < 0.11 μg/bee. 

Special 

Study 

OECD 75 

Semi-field 

testing for 

pollinators 

(None) (Not applicable) Maybe 

Need for this study depends on the 

results of the Tier I studies that are 

needed.

850.3040 Field testing for 

pollinators (None) (Not applicable) Maybe

Need for this study depends on the 

results of the Tier I studies that are 

needed.

850.4100 Seedling 

Emergence 45840111 Acceptable Yes None 

850.4150 Vegetative Vigor 46753505 Supplemental No 

Additional data is still needed. 

Measured concentrations (were 

based on spray solution recoveries) 

that were 30.3% - 32.2% of nominal. 

Therefore, based on this the study 

did not test at the highest application 

rate. Uncertainty of risk at maximum 

application rate. 

Honeybee Toxicity 

Although forchlorfenuron is categorized as practically non-toxic to adult honeybees on contact 

exposure basis, and by extension, to other beneficial terrestrial invertebrates on an acute 

exposure basis, there is considerable uncertainty regarding the potential effects of the compound 

on honeybee larval development and survival as well as potential for chronic effects. Therefore, 

additional data on pollinators are needed to fully characterize the risk associated with 

forchlorfenuron use to all developmental stages of honeybees, as sensitivity may vary according 

to life-stage and length of exposure (adult vs. larval and acute vs. chronic, respectively). 

Additional information is needed, but uncertainty associated with risks to honey bees need to be 

evaluated with more data to different life stages. Open literature data is needed to help better 

characterize some uncertainties regarding potential effects to bees and other non-target terrestrial 

invertebrates. In addition, higher tier effects toxicity tests (i.e., semi-field and/or field studies – 

Tier II and Tier III, respectively) may be needed, based on the results of the larval and chronic 

adult toxicity studies. Higher tier studies are recommended if the ratio of the EEC and larval or 

adult bee acute LD50>0.4 or the ratio of the EEC and the chronic NOAEC>1. Incident data 

and/or compelling open literature studies can also be used to support the need for higher tier 

studies. Should the screening level risk assessment identify that there are risk concerns to bees, 

mitigation measures may need to be considered or the registrant may need to conduct Tier II or 

Tier III effects studies (e.g. OECD Guideline 75 and/or 850.3040 guideline studies) that reduce 

uncertainty by characterizing forchlorfenuron’s effects at the whole-colony level1

. 

 

1 http://www2.epa.gov/pollinator-protection/pollinator-risk-assessment-guidance. 
21 

Study Title: Honey Bee Adult Acute Oral Toxicity Test; 

Guideline Number: Special Study – OECD 213; 

Test Substance: Forchlorfenuron – TGAI 

Rationale for Requiring the Data

No data are available with which to assess the toxicity of forchlorfenuron to honey bees on an acute 

oral exposure basis. Based on the registered use patterns, terrestrial invertebrates have the potential to 

be exposed by contacting and consuming forchlorfenuron residues. Therefore, the acute oral toxicity 

test is needed for EFED’s current screening-level process for assessing potential effects to terrestrial 

invertebrates. 

The Agency finalized its framework to assess risk to pollinators (USEPA, 2014). EPA now requires 

these studies for all use sites where potential exposure to pollinators may occur. Registrants may 

request a waiver of the studies if use practices significantly restrict exposure of the pesticide to bees. 

The Agency does not have a guideline for the acute oral honey bee study; however, the OECD 213 

guideline may be useful in protocol development. 

Practical Utility of the Data 

How will the data be used and how could the data impact the Agency’s future decisionmaking? 

Data will be used to assess hazard and characterize risk to non-target listed and non-listed terrestrial 

invertebrate species. See Guidance for Assessing Pesticide Risks to Bees (USEPA, 2014) for 

additional details. 

If future endangered species risk assessments are performed without these data, the Agency would 

have to assume that forchlorfenuron "may affect" endangered terrestrial insects directly (and 

endangered species from other taxa indirectly), and use of forchlorfenuron might need to be restricted 

in areas where endangered species could be exposed. The lack of these data will limit the flexibility 

the Agency and registrants have in coming into compliance with the Endangered Species Act and 

could result in use restrictions for forchlorfenuron which are unnecessarily severe. In addition, the 

lack of these data may result in an uncertain assumed risk and potential mitigation of forchlorfenuron 

formulations under FIFRA. 

 
22 

Study Title: Honey Bee Adult Chronic Oral Toxicity Study; 

Guideline Number: Special Study – Non-guideline; 

Test Substance: Forchlorfenuron – TGAI 

Rationale for Requiring the Data 

No data have been submitted on the chronic toxicity of forchlorfenuron to adult honey bees. A study 

is needed to determine the chronic toxicity of the compound to adult honey bees, including mortality 

and sub-lethal effects. This study is part of EFED’s current screening-level process for determining 

potential effects to terrestrial invertebrates. Therefore, a non-guideline honeybee larval toxicity study 

is recommended. Although EPA has not developed a guideline for this study and OECD has yet to 

finalize test guidance for chronic studies, efforts are currently underway to develop standardized 

guidelines for assessing effects from chronic (10-day) exposures to adult bees in the laboratory. The 

registrant should submit a proposed protocol for review and approval by EFED prior to initiation of 

the study. 

The Agency finalized its framework to assess risk to pollinators (USEPA, 2014). EPA now requires 

this study for all use sites where potential exposure to pollinators may occur. Registrants may 

request a waiver of the study if use practices significantly restrict exposure of the pesticide to bees.

Practical Utility of the Data 

How will the data be used and how could the data impact the Agency’s future decisionmaking? 

The 10-day toxicity study with young adult bees provides no-observed adverse effect level (NOAEL) 

and lowest-observed adverse effect level (LOAEL) for assessing chronic effects. Data obtained from 

this study will be used in estimating chronic risk to individual adult bees. Risk estimates based on 

these data will be considered along with other lines of evidence to determine whether higher-tier 

studies are needed at the whole colony level. 

These data are needed for the registration review risk assessment and for future endangered species 

assessments. The data would allow the Agency better characterize the potential for risk to insects 

(including beneficial pollinators) from the use of forchlorfenuron. This data may help the Agency 

determine whether any mitigations are needed. If the registration review and any future endangered 

species risk assessments are performed without these data, the Agency would have to assume that 

forchlorfenuron "may affect" insects, including bees and beneficial pollinators, directly (and 

endangered species from other taxa indirectly), and uses of forchlorfenuron might need to be 

restricted in areas where pollinators could be exposed. 

 
23 

Study Title: Honey Bee Acute and Chronic Larvae Oral Toxicity Study; 

Guideline Number: Special Study – OECD 237 and Non-Guideline; 

Test Substance: Forchlorfenuron – TGAI 

Rationale for Requiring the Data 

No data have been submitted on the toxicity of forchlorfenuron to honey bee larvae. Larval toxicity 

study are needed to determine the toxicity of the compound to developing brood (i.e., larvae and 

pupae), including mortality and adult emergence. This study is part of EFED’s current screeninglevel process for determining potential effects to terrestrial invertebrates. Although EPA has not 

developed a guideline for this study, the 21-day larval toxicity study currently under development by 

OECD provides both acute and chronic oral toxicity data on developing bee brood and (when this 

guidance is finalized) may be used to satisfy the requirement for both acute and chronic oral toxicity 

to honey bee larvae. Registrants are at liberty though to submit a separate acute (single dose) larval 

toxicity study following OECD TG 237 as well as the 21-day repeat dose chronic toxicity study. For 

the chronic toxicity study though, since no guideline is available, it is recommended that the 

registrant should submit a proposed protocol for review and approval by EFED prior to initiation of 

the study. 

The Agency finalized its framework to assess risk to pollinators (USEPA, 2014). EPA now requires 

these studies for all use sites where potential exposure to pollinators may occur. Registrants may 

request a waiver of the studies if use practices significantly restrict exposure of the pesticide to bees. 

Practical Utility of the Data 

How will the data be used and how could the data impact the Agency’s future decisionmaking? 

The 21-day larval toxicity study under development by OECD provides both acute and chronic 

toxicity data on developing bee brood and will yield a median lethal dose (LD50) for assessing acute 

toxicity during the early part of the study as well as a 21-day no-observed adverse effect level 

(NOAEL) and lowest-observed adverse effect level (LOAEL) for assessing chronic effects. Effects 

on survival and development (adult bee emergence) from repeat exposures to the active ingredient 

will be used in estimating chronic risk to individual brood. Risk estimates based on these data will be 

considered along with other lines of evidence to determine whether higher-tier studies are needed at 

the whole colony level. 

Data will be used to assess risk to non-target listed and non-listed terrestrial invertebrate species. This 

study would allow the Agency to refine the screening-level hazard assessment for beneficial 

terrestrial invertebrates. The effects data will be used to determine the potential for adverse effects on 

beneficial terrestrial invertebrates through direct effects on larval bees. See Guidance for Assessing 

Pesticide Risks to Bees (USEPA, 2014) for additional details. 

These data are needed for the registration review risk assessment and for future endangered species 

assessments. The data would allow the Agency better characterize the potential for risk to insects 

(including beneficial pollinators) from the use of forchlorfenuron. This data may help the Agency 

determine whether any mitigations are needed. If the registration review and any future endangered 

species risk assessments are performed without these data, the Agency would have to assume that 

forchlorfenuron "may affect" insects, including bees and beneficial pollinators, directly (and 

endangered species from other taxa indirectly), and uses of forchlorfenuron might need to be 

restricted in areas where pollinators could be exposed. 
24 

10. References 

U.S. Department of Agriculture (USDA). 2000. Crop Profile for Kiwi in California. NSF Center 

for Integrated Pest Management (host). U.S. Department of Agriculture, National 

Institute of Food and Agriculture. January, 2000. 

http://www.ipmcenters.org/cropprofiles/index.cfm

United States Environmental Protection Agency (USEPA). 2004. Overview of the Ecological 

Risk Assessment Process in the Office of Pesticide Programs. U.S. Environmental 

Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects 

Division. Available at http://www.epa.gov/espp/consultation/ecorisk-overview.pdf

USEPA. 2007. Kaul, M. 2007. Maximum Number of Crop Cycles per Year in California for 

Methomyl Use Sites. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides, and Toxic Substances, Biological and Economic Analysis Division. 

Memorandum to M. Panger, Environmental Fate and Effects Division. Feb. 28, 2007. 

USEPA. 2007a. ECOTOXicology Database. Office of Research and Development National 

Health and Environmental Effects Research Laboratory’s (NHEERL’s) Mid-Continent 

Ecology Division (MED). http://cfpub.epa.gov/ecotox/ 

USEPA. 2008. Borges, S., Wm. J. Shaughnessy, and D. Spatz. Ecological Risk Assessment for 

the Section 5 Experimental Use Permit for Forchlorfenuron on Almond, Cherry, Fig, 

Pear, Pistachio, and Plum/Prune, and the Section 3 Proposed New Use of 

Forchlorfenuron on the Bushberry Subgroup 13H. DP barcode 341868+. U.S. 

Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and 

Effects Division. Memorandum to the Registration Division. Feb. 15, 2008. 

USEPA. 2013. Wendel, C. and G. Orrick. Forchlorfenuron: Ecological Risk Assessment for the 

Section 3 Proposed New Uses on Almonds, Sweet Cherries, Figs, Pears, Pistachios, and 

Plums Including Prunes. DP barcode 406985. U.S. Environmental Protection Agency, 

Office of Chemical Safety and Pollution Prevention, Environmental Fate and Effects 

Division. Memorandum to the Registration Division. Apr. 24, 2013. 

USEPA. 2014. Screening Level Usage Analysis (SLUA): Forchlorfenuron. U.S.Environmental 

Protection Agency, Office of Chemical Safety and Pollution Prevention, Biological and 

Economic Analysis Division. May 20, 2014. 

USEPA. 2014a. Guidance for Assessing Pesticide Risks to Bees. U.S. Environmental Protection 

Agency, Office of Pesticide Programs; Health Canada Pest Management Regulatory 

Agency; and California Department of Pesticide Regulation. Jun. 23, 2014. Available at 

http://www2.epa.gov/pollinator-protection/pollinator-risk-assessment-guidance. 
25 

a. Submitted Environmental Fate Studies 

MRID Citation Reference 

44359508 Harteveld, J. (1992) The Vapor Pressure of SKW 20010: Lab Project Number: 132191310. 

Unpublished study prepared by Prins Maurits Laboratory TNO. 15 p. 

44359509 Treur, J. (1991) Determination of the Water Solubility of SKW 20010: Lab Project 

Number: 056622. Unpublished study prepared by RCC Notox B.V. 19 p. 

44359512 Treur, J. (1991) Determination of the Partition Coefficient (N-octanol/water) of SKW 

20010: Lab Project Number: 056644. Unpublished study prepared by RCC Notox B.V. 22 

p. 

44359514 Schmidt, J. (1992) Anaerobic Soil Metabolism of (carbon 14)-Forchlorfenuron: Lab 

Project Number: 38176: N-162-2. Unpublished study prepared by ABC Laboratories, Inc. 

674 p. 

44359515 Schmidt, J. (1992) Aerobic Soil Metabolism of (carbon 14)-Forchlorfenuron: (Final 

Report): Lab Project Number: 38175. Unpublished study prepared by ABC Laboratories, 

Inc. 885 p. 

44359516 Dykes, J. (1989) Soil Adsorption/Desorption with (carbon 14)-Forchlorfenuron: Lab 

Project Number: 38173: N-163-1. Unpublished study prepared by ABC Laboratories, Inc. 

360 p. 

44359524 Burgess, D. (1990) Uptake, Depuration and Bioconcentration of (carbon 14)-SKW 20010 

by Bluegill Sunfish (Lepomis macrochirus): Lab Project Number: 38137: 7701. 

Unpublished study prepared by ABC Laboratories, Inc. 327 p. 

44394603 Rozek, A. (1985) Determination of the Dissociation Constant, pka of CN-11-3183 (KT30): Lab Project Number: 411975. Unpublished study prepared by Velsicol Chemical Lab. 

10 p. 

44394604 Fostiak, W. (1986) Aqueous Hydrolysis of CN-11-3183 (KT-30): Lab Project Number: 

411978. Unpublished study prepared by Sandoz Crop Protection Corp. 12 p. 

44394605 Dykes, J. (1990) Determination of the Photolysis Rate of Forchlorfenuron: Lab Project 

Number: 38174. Unpublished study prepared by ABC Labs., Inc. 387 p. 

45840118 Siemer, S. (2002) Addendum to Anaerobic Soil Metabolism of (Carbon 14)-

Forchlorfenuron: Lab Project Number: 02-38176: 38176: 38175. Unpublished study 

prepared by Seimer and Associates, Inc. 172 p. 

45840119 Siemer, S. (2002) Addendum to Aerobic Soil Metabolism of (Carbon 14)-Forchlorfenuron: 

Lab Project Number: 02-38175: 38175: 38173. Unpublished study prepared by Seimer and 

Associates, Inc. 187 p. 

45840120 Siemer, S. (2002) Addendum to Uptake, Depuration and Bioconcentration of (Carbon 14)-

SKW 20010 by Bluegill Sunfish (Lepomis machrochirus): Lab Project Number: 02-38137: 

38137: 38173. Unpublished study prepared by Siemer and Associates, Inc. 74 p. 

45840121 Siemer, S. (2002) Addendum to Soil Adsorption/Desorption with (Carbon 14)-

Forchlorfenuron: Lab Project Number: 02-38173: 38173: 38175. Unpublished study 

prepared by Siemer and Associates, Inc. 49 p. 
26 

b. Submitted Ecological Toxicity Studies 

MRID Citation Reference 

44359523 Grimes, J.; Jaber, M. (1989) SKW 20010--An Acute Oral Toxicity Study with the 

Bobwhite: (Final Report): Lab Project Number: 248-103: 89-0032 WILTR. Unpublished 

study prepared by Wildlife International Ltd. 25 p. 

44359521 Grimes, J.; Jaber, M. (1989) A Dietary LC50 Study with the Bobwhite: (SKW 20010): 

(Final Report): Lab Project Number: 248-101: 89-0032: 89-0032 WILTL. Unpublished 

study prepared by Wildlife International Ltd. 26 p. 

44359522 Grimes, J.; Jaber, M. (1989) A Dietary LC50 Study with the Mallard: (SKW 20010): (Final 

Report): Lab Project Number: 248-102: 89-0032 WILTR. Unpublished study prepared by 

Wildlife International Ltd. 26 p. 

44359518 Bowman, J. (1990) Acute Toxicity of SKW 20010 to Rainbow Trout (Oncorhynchus 

mykiss): Lab Project Number: 37721: 7601-SEP: Unpublished study prepared by ABC 

Laboratories, Inc. 180 p. 

44359519 Bowman, J. (1990) Acute Toxicity of SKW 20010 to Bluegill (Lepomis macrochirus): Lab 

Project Number: 37720: 7601-SEP. Unpublished study prepared by ABC Laboratories, Inc. 

179 p. 

44359520 Forbis, A. (1989) Acute Toxicity of SKW 20010 to Daphnia magna: Lab Project Number: 

37722: 7806-SEP. Unpublished study prepared by ABC Laboratories, Inc. 158 p. 

45794401 Kuhn, J. (2001) Acute Oral Toxicity Study in Rats: KT-30: Final Report: Lab Project 

Number: 6243-01. Unpublished study prepared by Stillmeadow, Inc. 10 p. {OPPTS 

870.1100 

45794403 Carter, L. (2001) Acute Inhalation Toxicity Study in Rats: KT-30: Final Report: Lab Project 

Number: 6245-01. Unpublished study prepared by Stillmeadow, Inc. 20 p. {OPPTS 

870.1300} 

44394616 Nemec, M. (1997) Dietary Two-Generation Reproduction Study of SKW20010 in Rats: 

Final Report: Lab Project Number: WIL-171002: WIL-171002B: WIL-171002A. 

Unpublished study prepared by WIL Research Labs., Inc. 2573 p. 

45840111 Teixeira, D. (2002) ABG-3207--Determination of Effects on Seedling Emergence of Ten 

Plant Species: Lab Project Number: 13774.6100: 014123.IT-1. Unpublished study prepared 

by Springborn Laboratories, Inc. 130 p. {OPPTS 850.4100, 850.4225} 

45840110 Hoberg, J. (2002) ABG-3207--Toxicity to Duckweed, Lemna gibba: Lab Project Number: 

13774.6101: 014123.IT-2: 990106. Unpublished study prepared by Springborn Smithers 

Laboratories. 49 p. {OPPTS 850.4400} 

44359525 Hoxter, K.; Bernard, W.; Smith, G. (1993) SKW 20010: An Acute Contact Toxicity Study 

with the Honey Bee: Final Report: Lab Project Number: 248-106A: 079212. Unpublished 

study prepared by Wildlife International Ltd. 36 p 

46753505 Teixeira, D. (2005) CPPU - Determination of Effects on Vegetative Vigor of Ten Plant 

Species. Project Number: 13774/6107, 044123/1A/5, METH/171. Unpublished study 

prepared by Springborn Smithers Laboratories and Morse Laboratories, Inc. 124 p. 
27 

MRID Citation Reference 

46753501 Hoberg, J. (2005) CPPU - Acute Toxicity to the Marine Diatom, Skeletonema costatum. 

Project Number: 13774/6105, 044123/1A/1, METHH/171. Unpublished study prepared by 

Springborn Smithers Laboratories and Morse Laboratories, Inc. 51 p. 

46753502 Hoberg, J. (2005) CPPU - Acute Toxicity to the Freshwater Green Alga, 

Pseudokirchneriella subcapitata. Project Number: 13774/6104, 044123/1A/2, METH/171. 

Unpublished study prepared by Springborn Smithers Laboratories and Morse Laboratories, 

Inc. 51 p. 

46753503 Hoberg, J. (2005) CPPU - Acute Toxicity to the Freshwater Diatom (Navicula pelliculosa). 

Project Number: 13774/6103, 044123/1A/3, METH/171. Unpublished study prepared by 

Springborn Smithers Laboratories and KIM-C1, LLC and Morse Laboratories, Inc. 51 p. 

46753504 Hoberg, J. (2005) CPPU - Acute Toxicity to the Freshwater Blue-Green Alga, Anabaena 

flosaquae. Project Number: 13774/6106, 044123/1A/4, METH/171. Unpublished study 

prepared by Springborn Smithers Laboratories and Morse Laboratories, Inc. 51 p. 

49350901 Frey LT, Martin KH, Beavers JB, Jaber M. 2014. Forchlorfenuron: A Reproduction Study 

with the Northern Bobwhite. Unpublished study performed by Wildlife International, Ltd., 

Easton, Maryland. 180 p. 
28 

APPENDIX A. Forchlorfenuron Ecotoxicity Data 

Toxicity to Terrestrial Animals

Avian Toxicity 

Table A-1. Acute Oral Toxicity of Forchlorfenuron to Birds

Species % ai LD50 

(mg a.i./kg-bw) 

Toxicity 

Category 

MRID 

Author, Year 

Study 

Classification 

Northern bobwhite quail 

(Colinus virginianus) 100 >2250 1 Practically 

non-toxic 

44359523 

Grimes and Jaber, 1989 Acceptable

1 No mortality of toxicity occurred at the highest concentration tested 

Table A-2. Subacute Dietary Toxicity of Forchlorfenuron to Birds 

Species % ai LC50

(ppm a.i.) 

Toxicity 

Category 

MRID 

Author, Year 

Study 

Classification 

Northern bobwhite quail 

(Colinus virginianus) 100 >5620 1 Practically 

non-toxic 

44359521 

Grimes and Jaber, 1989 Acceptable 

Mallard duck 

(Anas platyrhynchos) 100 >56202 Practically 

non-toxic 

44359522 

Grimes and Jaber, 1989 Acceptable 

1

 One control bird out of fifty died on the first day of testing. The mortality was attributed to physical injuries 2

 No mortality. 

Table A-3. Avian Reproduction Toxicity of Forchlorfenuron to Birds 

Species % ai NOAEC/LOAEC 

(ppm a.i.) Endpoints MRID Author, Year 

Study 

Classification 

Northern bobwhite quail 

(Colinus virginianus) 96.95 <170/1701 14-d survivor 

weight 

49350901 

Frey, et al. 2014 In Review 

1

Significant (7-9%) dose-dependent reductions in 14-d survivor weight in all treatment levels when compared to the negative 

control 

Mammalian Toxicity 

Table A-4. Mammalian Toxicity of Forchlorfenuron

Species % ai Test 

Type Toxicity Value Most Sensitive Endpoints 

MRID No. 

Author, Year

(Study 

Classification)

Laboratory rat 

(Rattus norvegicus) 0.86 Acute Oral 

LD50 >5,501 

mg a.i./kg-bw None 

45794401 

Kuhn, 2001 

(Acceptable) 

Laboratory rat 0.86 Acute 

Inhal. LC50 > 2.14 mg/L1 None 

45794403 

Carter, 2001 

(Acceptable) 

Laboratory rat 98.5 2-gen 

repro. 

NOAEC/LOAEC = 

150/2000 ppm 

(11/144 mg/kg/day)

Decreased food consumption in F0 

& F1 M; clinical signs of toxicity & 

lower BW in F1M & F and growth 

retardation in F1 & F2 pups 

44394616 

Nemec, 1997 

(Acceptable) 

1

 Male and female; No mortality was observed; the only clinical sign was diarrhea in males on the day of dosing 2

 Male and female; No mortality was observed; Clinical signs included activity decrease and piloerection in both sexes on 

the day of dosing only. 

3

 Concentrations tested: 0, 150, 2000, and 7500 ppm, Premating doses for the adult F0 males were 11, 144, and 544 

mg/kg/day and for the F0 females were 13, 169, and 701 mg/kg/day, respectively. Premating doses for the adult F1

males were 13, 168, and 829 mg/kg/day and for the F1 females were 15, 202, and 926 mg/kg/day, respectively. 
29 

Terrestrial Invertebrate Toxicity 

Table A-5. Terrestrial Invertebrate Acute Contact Toxicity of Forchlorfenuron

Species % ai LD50

(μg a.i./bee) 

Toxicity 

Category 

MRID No. 

Author, Year 

Study 

Classification 

Honey bee 

(Apis mellifera) 98.5 LD50 >251 Practically 

non-toxic 

44359525 

Hoxter et. al., 1993 Acceptable 

1

 Sporadic mortalities noted were not believed to be treatment-related. 

Toxicity to Terrestrial Plants 

No significant effects in reduction were observed for terrestrial plant species exposed to 

forchlorfenuron at the treatment rates tested, i.e., 0.055 lbs a.i./A (seedling emergence, MRID 

45840111) or 0.022 lbs a.i./A (vegetative vigor, MRID 46753505). However, there were stimulative, 

positive growth effects that were observed for some terrestrial plant species that were tested (Table 

A-6 & A-7). 

Table A-6. Summary of Effects of Forchlorfenuron on Vegetative Vigor1 

Species EC25 

(lb a.i./acre) 

NOAEC 

(lb a.i./acre) Most Sensitive Endpoint 

MRID 

(Study 

Classification) 

Oat 

(Avena sativa)/ Monocot >0.0067 0.0067 No reductions, but a 2% stimulative growth in shoot length 

46753505 

Teixeira (2005) 

(Supplemental) 

Corn 

(Zea mays)/Monocot >0.0067 0.0067 

No reductions, but a 4% 

stimulative growth in shoot length 

and 8% in dry weight 

Onion 

(Allium cepa)/Monocot >0.0067 0.0067 

No reductions, but a 1% 

stimulative growth in shoot length 

and 6% in dry weight 

Ryegrass 

(Lolium perenne)/Monocot >0.0067 0.0067 

No reductions, but a 4% 

stimulative growth in shoot length 

and 15% in dry weight 

Cucumber 

(Cucumis sativa)/Dicot >0.0071 <0.0071 None, but there was a 20% 

reduction in dry weight 

Cabbage 

(Brassica oleracea) Dicot >0.0067 0.0067 No reductions, but a 2% 

stimulative growth in shoot length 

Lettuce 

(Latuca sativa)/Dicot >0.0067 0.0067 

No reductions, but a 19% 

stimulative growth in shoot length 

and dry weight 

Soybean 

(Glycine max)/Dicot >0.0069 0.0069 No reductions, but a 6% stimulative growth in dry weight 

Tomato 

(Solanum lycopersicum)/ 

Dicot 

>0.0067 0.0067 None, but there was a 16% 

reduction in dry weight 

Turnip 

(Brassica rapa)/Dicot >0.0067 0.0067 No reductions, but a 36% stimulative growth in dry weight 1 Stimulative effects were observed in corn (+4% shoot length and +8% dry weight), oat (+2% shoot length), onion (+1% shoot 

length and +6% dry weight), ryegrass (+4% shoot length and +15% dry weight), cabbage (+2% dry weight), lettuce (+19% 

shoot length & dry weight), soybean (+6% dry weight), and turnips (+36% dry weight). Vegetative vigor study measured 

concentrations were 30.3-32.2% of nominal, which was supposed to be set at the maximum application rate of 0.022 lbs a.i./A. 
30 

The study does provide some information on potential toxic effects to plants; however, the study has not tested the active 

ingredient, forchlorfenuron, at the highest application rate. 

Table A-7. Summary of Effects of Forchlorfenuron on Seedling Emergence1

Species EC25

(lb a.i./acre) 

NOAEC 

(lb a.i./acre)

Most Sensitive 

Endpoint

MRID 

(Study Classification)

Monocot and 

Dicot species >0.055 0.055 

No reductions, but 

stimulative effects in 

growth were observed 

for most species (both 

monocot and dicot 

species)1 

45840111 

Teixeira (2002) 

(Acceptable) 

1

Stimulative effects were observed in cabbage (+11% shoot length), corn (+9% shoot weight), oat (+13% shoot 

weight), onion (+8% shoot weight), perennial ryegrasses (+4% shoot length and +46% shoot weight), and turnips 

(+3% shoot length). 

Toxicity to Aquatic Animals

Aquatic Vertebrate Toxicity 

Table A-8. Freshwater Fish Acute Toxicity of Forchlorfenuron 

Species % ai 

96-hour LC50

(ppm a.i.) 

Toxicity 

Category 

MRID No. 

Author, Year 

Study 

Classification

Rainbow trout, 

(Oncorhynchus mykiss) 100 9.2 Moderately 

toxic 

44359518 

Bowman, 1990 Acceptable 

Bluegill sunfish, 

(Lepomis macrochirus) 100 8.3 Moderately 

toxic 

44359519 

Bowman, 1990 Acceptable

Freshwater Fish Chronic Toxicity 

No fish early-life stage or fish life cycle studies are available for forchlorfenuron. 

Estuarine/Marine Fish Toxicity 

No estuarine/marine fish toxicity studies are available for forchlorfenuron. 

Aquatic Invertebrate Toxicity 

Table A-9. Acute Toxicity of Forchlorfenuron to Freshwater Invertebrates

Species % ai 48-hour LC50

(ppm a.i.) Toxicity 

Category 

MRID No. 

Author, Year 

Study 

Classification 

Waterflea 

(Daphnia magna) 100 5.3 1 Moderately 

toxic 

44359520 

Forbis, 1989 Acceptable

Freshwater Aquatic Invertebrates Chronic Toxicity 

No chronic freshwater aquatic invertebrate studies are available for forchlorfenuron. 

Estuarine/Marine Aquatic Invertebrates Toxicity 

No estuarine/marine aquatic invertebrate toxicity studies are available for forchlorfenuron. 
31 

Aquatic Plant Toxicity

Table A-10. Toxicity of Forchlorfenuron to Aquatic Plants 

Species % ai 96 hr EC50

(mg a.i./L) 

EC05 or 

NOAEC 

(mg a.i./L) 

MRID No. 

Author (Year) 

Study 

Classification

Duckweed 

(Lemna gibba) 0.86 > 0.901 0.901 45840110 

Hoberg (2002) Acceptable3 

Marine diatom 

(Skeletonema costatum) 98.2 > 0.0162 0.0162 46753501 

Hoberg (2005) Acceptable3

Green algae 

(Pseudokirchneriella 

subcapitata)

98.2 > 0.0162

 0.0162 46753502 

Hoberg (2005) Acceptable3

Freshwater diatom 

(Navicula pelliculosa) 98.2 > 0.0172

 0.0172 46753503 

Hoberg (2005) Acceptable3

Blue-green cyanobacteria 

(Anabaena flos-aquae) 98.2 > 0.0172

 0.0172 46753504 

Hoberg (2005) Acceptable3 

1

 Based on frond numbers and growth rate; no significant effects were seen. 

2

 Based on cell density; no significant effects were seen. 

3

 No significant effects in reduction were observed for aquatic plant species exposed to forchlorfenuron at the treatment 

levels tested. However, there were stimulative, positive growth effects that were observed for some aquatic plant 

species that were tested. Stimulative growth was observed in the following aquatic non-vascular plants: the green algae 

(Pseudokirchneriella subcapitata; +43% growth), the freshwater diatom (Navicula pelliculosa; +4% growth), and 

stimulative growth was also observed in the vascular aquatic plant duckweed (L. gibba; +4% growth). 

 
32 

APPENDIX B. SIP & STIR Inputs and Outputs 

SIP Inputs/Outputs 

Table 1. Inputs

Parameter Value

Chemical name Forchlorfenuron

Solubility (in water at 25o

C; mg/L) 39

Mammalian LD50 (mg/kg-bw) 5050

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 9

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 2250

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 0

Bobwhite quail NOAEC (mg/kg-diet) 170

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) 6.7080 6.7080

Adjusted toxicity value (mg/kg-bw) 3884.2609 6.9224

Ratio of exposure to toxicity 0.0017 0.9690

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 31.5900 31.5900

Adjusted toxicity value (mg/kg-bw) 1620.9664 18.0707

Ratio of exposure to acute toxicity 0.0195 1.7481

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Exposure through drinking 

water alone is 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.
33 

STIR Inputs/Outputs 

Input

Application and Chemical Information

Enter Chemical Name Forchlorfenuron

Enter Chemical Use Blueberries

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) air

Enter Chemical Molecular Weight (g/mole) 247.69

Enter Chemical Vapor Pressure (mmHg) 3.50E-10

Enter Application Rate (lb a.i./acre) 0.022

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 2250

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 5050

Enter Lowest Rat Inhalation LC50 (mg/L) 2.14

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) 4.67E-06

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 5.86E-07

Adjusted Inhalation LD50 5.32E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.10E-07 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 2.11E-03

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 3.98E-04 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 4.67E-06

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 7.37E-07

Adjusted Inhalation LD50 1.27E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 5.79E-09 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 2.66E-03

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 2.09E-05 Exposure not Likely Significant

**NOTE**: When entering values, pres

in order to update linked cells.