Docket Number EPA-HQ-OPP-2009-0160 

www.regulations.gov 

Fluridone Final Work Plan for 

Registration Review 

March 2010 

Case Number 7200 

Approved by: ___________________________

 Richard P. Keigwin, Jr. 

Director, Pesticide Re-evaluation Division 

Date: ___________________________
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Introduction:

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) 

for the registration review of fluridone. The Final Work Plan includes the expected registration 

review timeline. The FWP also addresses public comments received concerning the Preliminary 

Work Plan (PWP) in the Summary Document which was posted in the fluridone registration 

review docket (EPA-HQ-OPP-2009-0160) and any other comments concerning the initial docket 

postings. The Summary Document provided information on what EPA knows about the 

pesticide and what additional risk analyses and data or information the Agency believes are 

needed to make a registration review decision. 

The Agency is implementing the registration review program and will review each registered 

pesticide every 15 years to determine whether it continues to meet the Federal Insecticide, 

Fungicide, and Rodenticide Act (FIFRA) standard for registration. Changes in science, public 

policy, and pesticide use practices occur over time. The registration review program is intended 

to make sure that, as the ability to assess risk evolves and as policies and practices change, all 

registered pesticides continue to meet that statutory standard. The public phase of registration 

review begins when the initial docket is opened for each case. Information on this program is 

provided at http://www.epa.gov/oppsrrd1/registration_review/. 

Fluridone is a systemic aquatic herbicide used to manage aquatic weeds in ponds, lakes, 

reservoirs, irrigation canals, drainage canals, and rivers. It has two degradates of concern: Nmethyl formamide (NMF) and 3-trifluoromethyl benzoic acid. Fluridone is registered for 

residential use on ponds. It is particularly useful for the control of hydrilla in the southern states 

and Eurasian milfoil in the northern states. Fluridone was the subject of a September 2004 

“Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk 

Management Decision (TRED),” (available at 

http://www.epa.gov/oppsrrd1/REDs/fluridone_tred.pdf). Since fluridone was first registered in 

1986, it was not subject to a Reregistration Eligibility Decision, but a tolerance reassessment was 

required under the 1996 Food Quality Protection Act (FQPA). 

On September 23, 2009, EPA opened a 60-day public comment period for the registration review 

of fluridone. The Agency received comments from 30 parties, which included community 

groups, registrants, state and local governments, and commercial applicators. After reviewing 

acceptable studies that were submitted after the PWP’s publication, the Agency no longer 

anticipates requesting four studies for the fluridone technical grade active ingredient (TGAI): an 

environmental chemistry method in soil (Guideline 835.6100), a freshwater early-life stage study 

(Guideline 850.1400), a freshwater fish life cycle study (Guideline 850.1500), and an acute 

toxicity study for freshwater fish (Guideline 850.1075). However, the Agency has not altered 

the six-year timeline detailed in the fluridone PWP. 

In addition, the registrants may submit waiver requests for the required acute freshwater aquatic 

toxicity studies (Guidelines 850.1075 and 850.1010) for the fluridone typical end-use product 

(TEP) if the end-use product(s) tested in previous studies (MRIDs 000103297 & 000103309) are 

still representative of use. The registrants should submit these waiver requests in their 90-day 
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response to the fluridone data call-in (DCI). The Agency will review these waiver requests at 

that time. 

In the PWP, EPA also solicited comments on three specific topics: environmental justice, water 

body impairment and trade irritants. No comments or information were received during the 

public comment period concerning these issues.

An overview of comments is presented in the “Summary of Comments Received during Docket 

Opening” section of this document. A more detailed description of the comments received and 

the Agency’s response to these comments are available in the separate response memoranda 

from the Agency’s Environmental Fate and Effects Division (EFED) and Health Effects Division 

(HED) located in the fluridone registration review docket (EPA-HQ-OPP-2009-0160).

Summary of Comments Received During Docket Opening:

During the public comment period, the Agency received comments from various stakeholders, 

which included commercial applicators who apply fluridone, state and county agencies, the 

FIFRA Endangered Species Task Force, the Withlacoochee Area Residents, Inc., and the 

registrants – SePRO Corporation and Tessenderlo KERLEY, Inc. 

Commercial applicators and state and county government parties commented that fluridone is a 

highly valued tool for reducing dense populations of aquatic weeds as part of integrated longterm pest management. In addition, these parties noted that fluridone is selective and does not 

impair non-target, desirable aquatic plants. State and county commenters included Lee County, 

Florida Hyacinth Control District, Washington State Department of Ecology, Louisiana 

Department of Wildlife and Fisheries, Southwest Florida Water Management District, Lake 

County Mosquito/Aquatic Plant Management Division, Seminole County, Florida, California 

Department of Boating and Waterways, Florida Fish and Conservation Commission, and 

California Department of Food and Agriculture. The Agency will consider these comments and 

fluridone’s benefits, pursuant to FIFRA, as appropriate, through registration review. 

The FIFRA Endangered Task Force (FESTF) commented that SePRO Corporation and Kerley 

Trading, Inc, the registrants for fluridone, are not FESTF members, and therefore must offer to 

pay FESTF to rely on FESTF submitted data or develop substantially similar data on their own. 

Withlacoochee Area Residents Inc. described some of the environmental and ecological 

deleterious effects it witnessed after fluridone application and urged EPA to fully consider 

effects to estuarine ecosystems during registration review. 

Some specific comments and Agency responses are addressed below. Comments relevant to 

human health have been addressed by the Health Effects Division’s document, Fluridone, 

Response to Comments on the Preliminary Work Plan for the Registration Review of Fluridone 

(2/22/2010). Comments regarding the ecological fate or effects of fluridone have been addressed 

by the Response to Comments on Registration Review – Problem Formulation for the 
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Environmental Fate, Ecological Risk, and Endangered Species Assessment in Support of the 

Registration Review of Fluridone (2/24/2010). 

The Agency has also revised the following registration review supporting documents for 

fluridone: Registration Review: Preliminary Problem Formulation for Ecological Risk, 

Environmental Fate, and Endangered Species Assessment for Fluridone, California Department 

of Pesticide Regulation Usage Data, and Appendix A: Food/Feed & Non-Food/Non-Feed Uses 

Considered in Registration Review Work Planning (Appendix A) to reflect changes identified in 

OPP’s responses. These supporting documents, public comments, and data evaluation records 

completed after publication of the PWP are available in docket EPA-HQ-OPP-2009-0160 at 

www.regulations.gov. 

SePRO Corporation

Comment 1: 

 SePro notes that the PWP states that there are tablet and emulsifiable concentrate (EC) 

formulations of fluridone currently registered. However, SePRO clarified that there are no 

tablet or EC forms of fluridone currently registered, only pellets if in a solid state and aqueous 

suspension or soluble concentrate if in a liquid state. 

Response: 

EPA thanks SePRO for clarifying the current formulations of fluridone registered for use and has 

revised Appendix A to more accurately reflect registered formulations. 

Comment 2: 

SePRO commented that other than applications that are made to dewatered aquatic sites (2 

lbs/Acre) or recommended rates for static canals (40 lbs/Surface Acre), it is not possible to 

calculate a maximum application rate for formulated fluridone (i.e., Sonar®) in pounds/acre or 

gallons/acre. In EPA’s Appendix A: Food/Feed & Non-Food/Non-Feed Uses Considered in 

Registration Review Work Planning (Appendix A), it is unclear how the maximum application 

rates were calculated for individual applications (e.g., 1.22 gal/A, 0.865 lb/A, or 0.2085 gal/A) 

and for the total maximum application rate allowed per one growing season (e.g., 1 ppb/yr, 8.34 

ppb/yr, or 16.68 ppb/yr). For example, in Appendix A, some of the listed maximum application 

rates per application are greater than the maximum rate that can be applied per growing season. 

Fluridone (Sonar®) is applied to a 3-dimensional environment, and the water depth must be 

considered when determining how much product to apply per acre. Unless an assumption is 

made on the average depth used in this comparison, the amount of product applied will vary 

across sites depending on the water depth, even when the in-water concentration will be the 

same. For example, to apply 90 ppb in a pond with an average depth of 3 feet would require 0.18 

gallons of Sonar A.S. (67690-4), while applying 90 ppb in a pond with an average depth of 5 feet 

would require approximately 0.3 gallons. In other words, 1 pound of fluridone in 3 acre feet of 

water is approximately 124 ppb, but in 5 feet of water that 1 pound of fluridone would result in 

approximately 74 ppb. 
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Response: 

The Agency thanks SePRO for its comment and has revised Appendix A to reference applicable 

concentrations instead of application rates. 

Comment 3: 

 According to SePRO, there are no minimum retreatment intervals (MRIs) listed on any of the 

registered labels. Appendix A lists 45 days for some of the Use Sites. Retreatment intervals are 

determined by the need to maintain the active ingredient level in water at a predetermined 

concentration. This interval can vary depending on many conditions, but dilution of the treated 

water is the main determining factor. 

Response: 

The Agency thanks SePRO for its comment. There are no MRIs for any fluridone products; 

Appendix A has been revised accordingly. 

Comment 4: 

SePRO notes that in Appendix A, for the “Human Drinking Water Systems” use site, the EC and 

liquid formulations are allowed in New York due to the 24(c) that is active in the state for these 

formulations. SePRO also noted that the Section 3 label in Georgia includes the “Aquatic 

Areas/Water” use site. Finally SePRO noted that under the “Streams/Rivers/Channeled Water” 

use site, for the EC formulation for fluridone, the Geographic Restriction column in the 

spreadsheet should indicate that this use is allowed for Georgia due to the 24(c) that is active in 

the state. 

Response: 

EPA thanks SePRO for clarifying geographic restrictions for fluridone use patterns and has 

revised appendix A accordingly. 

Comment 5: 

 SePRO queried usage data from the California Department of Pesticide Regulation Pesticide 

Information Portal (PIP), and noted the following differences between its query results and 

EPA’s document entitled, “Fluridone (112900), California Department of Pesticide Regulation 

Usage Data” : 

- For year 2007, the value of 40.95 pounds active ingredient applied for the commodity 

“unknown” did not appear. 

- For year 2005, the following data were available: 

Commodity 2005 Pound Applied 

Landscape Maintenance 586.43 

Regulatory Pest Control 1677.83 

Rights of Way 186.76 

Structural Pest Control 207.54 

Unknown 25.97 

Water Area 858.85 

Recreational Areas, Tennis Courts, Parks, etc 0.9986 
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Response: 

EPA thanks SePRO for identifying this usage data. This data was not available on January 9, 

2009 when it was first queried by the Agency. Fluridone (112900), California Department of 

Pesticide Regulation Usage Data has been revised to incorporate this updated information. 

Tessenderlo KERLEY

Comment 6: 

According to Tessenderlo KERLEY, there were several errors and incorrect assumptions in the 

application rates specified Appendix A. Fluridone is applied to obtain a desired concentration, 

not a specific application rate per Acre. The actual application rate per Acre can vary 

tremendously depending on the depth of the water body being treated, the desired concentration 

of fluridone, and the flow rate of the water body being treated. Therefore, it would be virtually 

impossible to determine the maximum rate per Acre being treated without a hypothetical water 

body with specific dimensions. It would be more appropriate to specify the maximum single 

application rate of 90 or 150 ppb, depending on the water body being treated, and a maximum 

rate per annual growth cycle (i.e. sum of all applications) of 90 or 150 ppb, depending on the 

water body being treated. In addition, the maximum application rate of 4.88 lb ai/A identified for 

EC products for certain water bodies is calculated from 156.2 fl. oz. of a 4 lb SC product per 

Acre. However, the rate of 156.2 fl. oz. is based on treating a water body with an average depth 

of 20 feet at 90 ppb, not at the allowed maximum of 150 ppb. 

Response: 

Please see EPA’s response to comment 2 above. 

Comment 7: 

Tessenderlo KERLEY notes that in Appendix A, the MRI for several use sites is listed as 45 days. 

This is incorrect. There is no minimum retreatment interval specified on the labeling.

 

Response: 

Please see EPA’s response to comment 3 above. 

Endocrine Disruptor Screening Program:

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by 

a “naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 
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testing is designed to identify any adverse endocrine related effects caused by the substance, and 

establish a quantitative relationship between the dose and the E, A, or T effect. 

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first 

group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

This list of chemicals was selected based on the potential for human exposure through pathways 

such as food and water, residential activity, and certain post-application agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors. 

Fluridone is not among the group of 58 pesticide active ingredients on the initial list to be 

screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide 

chemicals. Accordingly, EPA anticipates issuing future EDSP orders/data call-ins for all 

Registration Review cases, including those for which EPA has already opened a Registration 

Review docket for a pesticide active ingredient. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: 

http://www.epa.gov/endo/. 

Risk Assessment and Data Needs:

The Agency anticipates conducting a comprehensive ecological risk assessment, including an 

endangered species risk assessment, for all uses of fluridone. The Agency also anticipates 

conducting an occupational handler assessment for all fluridone products. In addition, once new 

hazard data is received (neurotoxicity and immunotoxicity), the Agency may reexamine points of 

departure and safety factors for fluridone and revise the human health risk assessment if 

necessary. Additional data that the Agency anticipates needing to complete these assessments 

are included below. 

 

Ecological Risk: 

• The Agency has not conducted a risk assessment that supports a complete endangered 

species determination for the current use and usage of fluridone. The ecological risk 

assessment planned during registration review will allow the Agency to reexamine 

whether fluridone’s current use has “no effect” or “may affect” federally listed threatened 

or endangered species (listed species) or their designated critical habitats. When an 

assessment concludes that a pesticide’s use “may affect” a listed species or its designated 

critical habitat, the Agency will consult with the FWS and/or National Marine Fisheries 

Service (the Services), as appropriate. 

• The Agency anticipates needing the following data in order to conduct a complete 

ecological risk assessment, including an endangered species assessment, for fluridone and 

its metabolites: N-methyl formamide (NMF) and 3-trifluoromethyl benzoic acid: 
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Fluridone Technical Grade Active Ingredient (TGAI) 

o GDLN 850.1025 Acute toxicity estuarine/marine organisms: oyster shell deposition 

o GLDN 850.1075 – Acute toxicity estuarine/marine fish 

o GDLN 850.1300 – Aquatic invertebrate life-cycle: daphnid 

o GDLN 850.1500 – Fish life-cycle: estuarine/marine 

o GDLN 850.2100 – Avian oral toxicity: Passerine species 

o GDLN 850.2300 – Avian reproduction: upland game bird and waterfowl species 

o GDLN 850.3020 – Honeybee acute contact toxicity 

o GDLNs 850.4400 and 850.5400 – Aquatic plant growth, tier II aquatic plant growth (TGAI 

or TEP) 

o Special Study – whole sediment chronic freshwater invertebrate 

Fluridone Typical End-Use Product (TEP)

o GDLN 850.1010 – Acute toxicity freshwater invertebrates1

o GDLN 850.1025 Acute toxicity estuarine/marine organisms: oyster shell deposition 

o GLDN 850.1075 – Acute toxicity estuarine/marine fish 

o GLDN 850.1075– Acute toxicity freshwater fish: coldwater and warmwater species, 

preferably walleye and minnow2

 

o GDLNs 850.4100, 850.4150 – Terrestrial plant toxicity test, tier II seedling emergence and 

vegetative vigor 

o GDLNs 850.4400 and 850.5400 – Aquatic plant growth, tier II aquatic plant growth (TGAI 

or TEP) 

N-methyl formamide (NMF) 

o GDLN 850.1010 – Acute toxicity freshwater invertebrates

o GLDN 850.1075– Acute toxicity freshwater fish: coldwater and warmwater species, 

preferably walleye and minnow

o GDLN 850.1300 – Aquatic invertebrate life-cycle: daphnid 

o GDLN 850.1400 – Freshwater fish early-life stage 

o GDLN 850.2100 – Avian oral toxicity: Passerine species 

o GDLN 850.2300 – Avian reproduction: upland game bird and waterfowl species 

3-trifluoromethyl benzoic acid 

o GDLN 850.2100 – Avian oral toxicity: Passerine species 

o GDLN 850.2300 – Avian reproduction: upland game bird and waterfowl species 

Please refer to the document, Registration Review: Preliminary Problem Formulation for 

Ecological Risk, Environmental Fate, and Endangered Species Assessment for Fluridone, August 

20, 2009 for a detailed discussion of the Agency’s anticipated ecological risk and environmental 

fate assessment needs.

 

1

 The study submitted to fulfill this guideline (MRID 000103297) is acceptable. Therefore, the registrants may 

request a waiver for this data requirement if the end-use product used in the submitted study is still representative of 

current end use products. 

2

 The study submitted to fulfill this guideline (MRID 000103297) is acceptable. Therefore, the registrants may 

request a waiver for this data requirement if the end-use product used in the submitted study is still representative of 

current end use products. 
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Human Health Risk: 

• The Agency does not expect to conduct a drinking water assessment (DWA) as part of 

registration review for fluridone because maximum application rates to waters near 

drinking water inputs have not increased since the 2004 TRED. 

• The dietary exposure database for fluridone is complete, and EPA does not anticipate 

conducting additional dietary assessments for the registration review of fluridone unless 

endpoints or safety factors change as a result of new toxicity data. 

• Residue chemistry data are adequate to support all tolerances; however, the tolerance 

expression in 40 CFR § 180.420 should be revised during registration review to ensure 

that it appropriately addresses the metabolites and degradates of fluridone. The proposed 

revisions are to the chemical description rather than the individual tolerance levels. (See 

the “Tolerances and International Harmonization” section of the Fact Sheet for more 

detail). 

• Residential application exposures from all fluridone products have been assessed, and no 

risks of concern have been identified; therefore, EPA does not anticipate conducting 

additional residential exposure assessments in registration review unless endpoints or 

safety factors change as a result of new toxicity data. 

• The Agency estimated aggregate exposure and risk from dietary exposure (food and 

water) and exposures from swimming in treated water bodies in 2004. However, after 

2004, EPA issued the first fluridone registration with a residential use. Nevertheless, EPA 

does not anticipate conducting a new aggregate assessment, unless endpoints or safety 

factors change as a result of new toxicity data, because the most recent aggregate 

assessment showed risks considerably below the level of concern, and the new 

registration would not result in significantly different exposures. 

• Most fluridone products have not been assessed for occupational exposure; therefore, 

EPA anticipates completing an occupational handler assessment in registration review. 

Post-application exposure to workers from previously treated water bodies is negligible; 

therefore, the Agency does not anticipate conducting a post-application exposure 

assessment. 

• The fluridone toxicity database is largely complete except for new studies required under 

the revised 40 CFR part 158. EPA anticipates requiring the following guideline studies: 

o GDLN 870.6200 Neurotoxicity Battery (acute and subchronic neurotoxicity) 

o GDLN 870.7800 Immunotoxicity Study 
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• Please refer to Fluridone. Human Health Assessment Scoping Document in Support of 

Registration Review, July 16, 2009, available in the docket, for a detailed discussion of 

the anticipated risk assessment and data needs for completing the human health risk 

assessment. 

Other Data Needs: 

• GLDN 830.750 UV/Visible Light Absorption – this study is a new data requirement 

under 40 CFR part 158 (Product Chemistry Data Requirements) for registration of a 

pesticide (food and non-food uses). The Agency anticipates requiring this study to obtain 

basic information about the compound’s identity/composition and the wavelengths at 

which the compound may be susceptible to photochemical degradation.

Timeline:

 

The Agency has created the following estimated timeline for the completion of the fluridone 

registration review. 

Registration Review for Fluridone – Projected Registration Review Timeline 

Activities Estimated 

Year/Month 

Opening the Docket 

Open Docket and Public Comment Period September 2009 

Close Public Comment November 2009 

Case Development 

Issue Final Work Plan (FWP) March 2010 

Issue Data Call-in (DCI) October – December 

2010 

Data Submission October – December 

2012 

Open Public Comment Period for Preliminary Risk Assessments April – June 2014 

Close Public Comment Period July – September 

2014 

Registration Review Decision 

Open Public Comment Period for Proposed Registration Review 

Decision 

October – December 

2014 

Close Public Comment Period January – March 

2015 

Final Registration Review Decision & Begin Post-Decision 

Follow-up 2015 

Total (years) 6 
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Next Steps:

As noted previously, the Agency anticipates requiring several ecological effects and human 

health studies through a Data Call-In Notice, expected to be issued in 2010. This new 

information will be used to conduct the risk assessments outlined in this FWP for all fluridone 

uses.