1 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460 

August 11, 2015 

PC Code: 128819 

DP Barcode: 316642, 417353, and 420428 

MEMORANDUM 

SUBJECT: Forchlorfenuron: Response to Data Waiver Requests for a Terrestrial Field 

Dissipation Study and an Avian Reproduction Study AND Summary of the 

Review of an Ecotoxicity Study on the Ecological Effects of Forchlorfenuron 

FROM: Christina Wendel, Biologist 

Greg Orrick, Environmental Scientist 

ERB2/Environmental Fate and Effects Division (7507P) 

THROUGH: Elyssa Arnold, Risk Assessment Process Leader (RAPL)

Brian Anderson, Branch Chief 

ERB2/EFED (7507P)

TO: Marcel Howard, Risk Manager Reviewer 

Tony Kish, Product Manager PM, Team 22 

Fungicide Branch/Registration Division (7505P) 

1. Waiver Requests

The Environmental Fate and Effects Division (EFED) has completed its review of the 

data waiver requests submitted to the Agency in a letter dated July 1, 2013 for a terrestrial field 

dissipation and an avian reproduction study that were requested to meet conditional registration 

requirements for the use on pears, plums, sweet cherries, figs, pistachios and almonds (a single 

application rate of 0.022 lb a.i./A). A supplementary component of the avian reproduction 

waiver request was submitted to EFED in March 2014 was a reproduction study with the 

bobwhite quail. The results of this study are discussed in combination with the review of the 

waiver request for avian reproduction. EFED’s responses are provided in Table 1 below. 

Table 1. Disposition of Waiver Requests for Forchlorfenuron

OCSPP 

Guideline 

Study Type DP 

Barcode 

Are Additional Data 

Needed for Risk 

Assessment? 

835.6100 Terrestrial Field Dissipation 316642 No 

850.2300 Avian Reproduction 417353 Yes 

2015.08.12 09:53:06 -04'00'
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Submissions: 

49165701 Weidenbach, P.C. (Ex

ponent®, Inc.). 2013. Forchlorfenuron: Waiver Request for 

 Avian Reproduction, OCSPP Guideline 850.2300. Unpublished report prepared 

 by Ex

ponent, Inc. for Sponsor KIM-C1, LLC. 9p. (DP barcode 417353). 

49165702 Weidenbach, P.C. (Ex

ponent®, Inc.). 2013. Forchlorfenuron: Waiver Request for 

 Terrestrial Field Dissapation, OCSPP Guideline 835.6100. Unpublished report 

 prepared by Exponent, Inc. for Sponsor KIM-C1, LLC. 9p. (DP barcode 316642). 

49350901 Frey L.T., Martin K.H., Beavers J.B., and Jaber M. 2014. Forchlorfenuron: A 

 Reproduction Study with the Northern Bobwhite. Unpublished study performed 

 by Wildlife International, Ltd., Easton, Maryland. Laboratory report number 248- 

 108. Study sponsored by Degussa AG, Product Line Agriculture, D-83308 

 Trostberg, Germany. Study completed on December 3, 2003 and report amended 

 on March 21, 2014. (DP barcode 420428). 

1.1. Request for a Waiver from the Requirement for a Terrestrial Field Dissipation 

Study for Forchlorfenuron (OCSPP 835.6100) 

1.1.1. Basis for Waiver Request 

The registrant’s basis for waiving the required terrestrial field dissipation study was that 

the maximum application rate is low, making quantitation of residues difficult. Further 

complications include that fruit and nut orchards will intercept residues, resulting in lower and 

non-homogeneous soil concentrations, and that soil adsorption and slow microbial degradation 

will further reduce concentrations over time. 

1.1.2. Response to Waiver Request 

The Agency currently recommends waiving additional environmental fate studies 

including the terrestrial field dissipation study on the basis of no risk level of concern 

exceedances from current or proposed uses using conservative assumptions in the absence of 

data (see DP411314; USEPA, 2013b). If a risk level of concern exceedance is identified, the 

following environmental fate studies of forchlorfenuron may be necessary: 

x Soil photolysis study 

x Aerobic soil metabolism study (3 additional soils) 

x Aerobic aquatic metabolism study 

x Anaerobic aquatic metabolism study 

x Terrestrial field dissipation study 

x Analytical methods in soil and water 

Since the Agency has not identified any exceedance of risk thresholds for the currently 

registered and proposed uses of forchlorfenuron, EFED recommends that RD grant a waiver 

request for a terrestrial field dissipation study for forchlorfenuron. 
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1.2. Request for a Waiver from the Requirement for an Avian Reproduction Study for 

Forchlorfenuron (OCSPP 850.2300) 

1.2.1. Basis for Waiver Request 

The registrant’s basis for waiving the required avian reproduction study was that the 

maximum application rate is low, and deposition on typical avian dietary items would be 

minimal (estimated to be 5.3 mg/kg on short grass) resulting in low exposure to birds. The 

registrant estimated for birds ingesting short grass containing forchlorfenuron residues 

immediately after an application, exposures for different weight classes of birds (20, 100 and 

1000 grams) were calculated to be 6.1, 3.5 and 1.5 mg/kg-bw/day, far less than the lowest 

reproductive NOAEL (144 mg/kg-bw/day) reported in a rat two-generation reproduction toxicity 

study. Coupled with the fact that forchlorfenuron is practically non-toxic to birds on an acute 

basis, the registrant believes an avian reproduction study is not necessary and seeks the 

concurrence of EPA. 

1.2.2. Response to Waiver Request 

With the submission of the avian reproduction study with bobwhite quail (Colinus 

virginianus) (MRID 49350901; DP420428), the response to the waiver request became 

dependent on the review of this study. Based on the review, there were significant reductions in 

14-d survivor body weight at all treatment levels relative to the negative control. These observed 

effects on 14-d survivor body weight, resulted in a NOAEC of <170 mg a.i./kg-diet (the lowest 

test concentration tested). Findings of the review are presented in Table 2 below. There were 

no treatment-related mortalities, abnormal signs of toxicity, or other treatment-related effects on 

any reproductive parameter analyzed. Therefore, the bobwhite quail avian reproduction study 

was determined to be scientifically sound; however, the study was classified as supplemental 

because a valid NOAEC could not be established, due to the effects on the offspring observed in 

all treatment levels. Without a definitive NOAEC, the study cannot be upgraded to acceptable, 

and the study does not satisfy the guideline requirement for avian reproduction. To meet 

guideline requirements additional data on birds (surrogate for terrestrial-phase amphibians and 

reptiles) are needed. It is recommended that lower doses be used when conducting the new 

bobwhite quail reproduction study. 

Table 2. Summary of the Submitted Toxicity Data for Forchlorfenuron

MRID 

Number 

OCSPP 

Guideline 

Study 

Description Toxicity Endpoint Study Classification Major Issues 

49350901 850.2300 

Avian 

Reproduction: 

Bobwhite quail 

(96.95% a.i.; 

TGAI) 

NOAEC <170 mg a.i./kg diet 

LOAEC = 170 mg a.i./kg diet 

Endpoint affected: reduction 

in 14-d survivor body weight 

Supplemental 

A definitive NOAEC 

could not be established, 

significant effects in 14d 

survivor body weight 

were observed at all 

treatment levels relative 

to the negative control. 1

TGAI = Technical Grade Active Ingredient 
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The exposure estimates associated with the evaluated uses (pears, plums, sweet cherries, 

figs, pistachios and almonds), represent one of the lowest annual application rates for 

forchlorfenuron, with a single application rate of 0.022 lb a.i./A. Whereas, the maximum use 

pattern for forchlorfenuron is the use on black and red currants, elderberries, gooseberries, and 

lingonberries (i.e., bushberries), and corresponds to an annual application rate of 0.088 lb a.i./A 

(0.044 lb a.i./A x 2 applications @ a 14d interval). Therefore, the exposure load in the 

environment is greater for these other uses of forchlorfenuron, with maximum estimated dosebased EECs of 21.1, 12.1 and 5.4 mg/kg-bw versus 6.1, 3.5 and 1.5 mg/kg-bw/day for the 

different weight classes of birds (20, 100 and 1000 grams, respectively). 

Reduction in body weight was the most sensitive endpoint seen in both the bobwhite 

quail study (reduction in 14-d survivor body weight; MRID 49350901), and the rat twogeneration study (reduction in body weight in F1 males & females, and growth retardation in F1 

& F2 pups, MRID 44394616). These studies suggest that there may be some consistencies in 

observed effects across vertebrate species, both birds and mammals. The observed body weight 

effects cannot be discarded as inessential to fitness or that they are not consistent with other 

longer term exposure studies in higher vertebrates, as effects were observed across multiple 

doses in a potentially dose responsive manner in multiple vertebrate species. Therefore, in 

addition to the bobwhite quail study, in order to fulfil the data requirement for avian reproduction 

and complete the risk picture for birds on a chronic basis, a mallard duck study is also needed

(Table 3). 

Table 3. Summary of Toxicity Data Needs for Forchlorfenuron 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID #) 

Study 

Classifications 

Sufficient for 

risk 

assessment? 

Current Additional Data Need 

850.2300 Avian 

Reproduction 

49350901 Supplemental 

No

The bobwhite quail study (MRID 

49350901) was classified as 

supplemental (not upgradable) 

because a definitive NOAEC 

could not be established 

(treatment-related effects were 

observed in all test 

concentrations). Toxicity data 

are needed for both the bobwhite 

quail and mallard duck to fulfill 

the data requirements. 

None Not applicable 

 
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References: 

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. MRID 44394616. 

USEPA. 2013a. Wendel, C., G. Orrick, R.D. Jones, J. Holmes, and B. Anderson. 

 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. Dated April 24, 2013. U.S. Environmental Protection Agency, Office of 

 Pesticide Programs, Environmental Fate and Effects Division. Memorandum to the 

 Registration Division. 

USEPA. 2013b. Wendel, C., G. Orrick, R.D. Jones, J. Holmes, and B. Anderson. Memorandum 

“Forchlorfenuron: Response to Data Waiver Requests for an Avian Reproduction Study 

 and a Soil Dissipation Study with KT-30 (Forchlorfenuron) AND Response to the 75-day 

 Deficiency Letter dated March 14, 2013.” DP barcode 411314. Dated May 14, 2013. 

 Office of Pesticide Programs, Environmental Fate and Effects Division. Memorandum to 

 the Registration Division.