Docket Number: EPA-HQ-OPP-2008-0190 

www.regulations.gov 

 

Glufosinate Summary Document 

Registration Review: Initial Docket 

March 2008 

Case # 7224 

 

Page 3 of 71 

TABLE OF CONTENTS 

Page # 

I. Preliminary Work Plan................................................................................................ 4

II. Fact Sheet..................................................................................................................... 9

III. Ecological Risk Assessment Problem Formulation.............................................. 14

IV. Human Health Effects Scoping Document............................................................ 58

V. Glossary of Terms and Abbreviations .................................................................... 70
Page 4 of 71 

I. PRELIMINARY WORK PLAN 

Introduction:

The Food Quality Protection Act of 1996 mandated a new program: registration review. All 

pesticides distributed or sold in the United States generally must be registered by EPA, based on 

scientific data showing that they will not cause unreasonable risks to human health, workers, or 

the environment when used as directed on product labeling. The new 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 the statutory standard of no 

unreasonable adverse effects. Changes in science, public policy, and pesticide use practices will 

occur over time. Through the new registration review program, the Agency periodically 

reevaluates pesticides to make sure that as change occurs, products in the marketplace can be 

used safely. Information on this program is provided at: 

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

The Agency has begun to implement the new registration review program, and will review each 

registered pesticide every 15 years to determine whether it continues to meet the FIFRA standard 

for registration. The public phase of registration review begins when the initial docket is opened 

for each case. The docket is the Agency’s opportunity to state what it knows about the pesticide 

and what additional risk analyses and data or information it believes are needed to make a 

registration review decision. After reviewing and responding to comments and data received in 

the docket during this initial comment period, the Agency will develop and commit to a final 

work plan and schedule for the registration review of glufosinate-ammonium, which is the only 

active ingredient in the case. 

Glufosinate-ammonium (C15H15N2O4P) is a non-selective foliar herbicide that is used for preplant and post-emergent control of broadleaf weeds. Glufosinate-ammonium acts by inhibiting 

glutamine synthetase, which leads to poisoning in plants via the overproduction of ammonia. 

Glufosinate-ammonium was first registered for use in 2000. It is registered for use on the 

following crops: apples, berries, canola, corn, cotton, currants, grapes, grass grown for seed, 

potatoes, rice, soybeans, sugar beets, and tree nuts. Registrations for non-crop areas include golf 

course turf, residential lawns, ornamentals, and a variety of industrial, residential, and public 

areas. 

Anticipated Risk Assessment and Data Needs:

The Agency anticipates conducting comprehensive human health and ecological risk 

assessments, including an endangered species assessment for all uses of glufosinate-ammonium. 
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Ecological Risk 

• Based upon the information gathered to date, the risks of concern are mainly to nontarget plants as well as chronic risk to mammals, with potential indirect effects on 

terrestrial animals possible due to alterations in aquatic plant communities. Acute and 

chronic risk quotients for birds slightly exceeded the LOCs. However, the LOCs were 

based on the highest dose tested in the subacute dietary study and the two avian 

reproduction studies. There is also concern for effects on species listed under the 

Endangered Species Act, including mammals and birds. 

• Preliminary review of the available plant toxicity studies indicates that there are 

insufficient data on terrestrial plant toxicity to complete the ecological assessment. 

Because sufficient data were not reported, EPA cannot determine the no observed 

adverse effect concentration (NOAEC) for seedling emergence, making determination of 

an action area for an endangered species assessment difficult. Furthermore, EPA cannot 

verify the assessment endpoints, creating uncertainties with regard to the effect of 

glufosinate-ammonium on non-target terrestrial plants. 

• The Agency anticipates requiring terrestrial seedling emergence and vegetative vigor 

studies using typical end-use product (TEP). Only technical grade active ingredient 

(TGAI) was tested in the terrestrial plant studies. There are concerns that the herbicide 

formulations are enhanced with the addition of surfactant to improve their efficacy, and, 

therefore, toxicity to non-target plants might have been underestimated in the studies 

because the TGAI, rather than the TEP was tested. 

• The Agency does not anticipate that additional fate data will be needed. However, the 

analytical methods for residues in water and soil that were submitted have not been 

validated in an independent laboratory. Independent laboratory validation will be 

required to provide confidence in the quantification level of the submitted analytical 

method. 

• The planned ecological risk assessment will allow the Agency to determine whether 

glufosinate-ammonium use has “no effect” or “may affect” federally listed threatened or 

endangered species (listed species) or their designated critical habitat. If the assessment 

indicates that glufosinate-ammonium “may affect” a listed species or its designated 

critical habitat, the assessment will be refined. The refined assessment will allow the 

Agency to determine whether the use of glufosinate-ammonium is “likely to adversely 

affect” the species or critical habitat or “not likely to adversely affect” the species or 

critical habitat. 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 U.S. Fish 

and Wildlife Service and National Marine Fisheries Service (the Services), as 

appropriate. 

• The Ecological Fate and Effects Division has indicated that the nonvascular aquatic plant 

data may possess uncertainties, given that only one of the five nonvascular aquatic plant 
Page 6 of 71 

species were tested. However, given the low risk quotients, the Agency does not 

anticipate asking for additional nonvascular aquatic plant data. 

Human Health Risk: 

• In a previous glufosinate-amonium risk assessment (August 2003), EPA determined that 

the toxicology database lacked both a developmental neurotoxicity (DNT) study and a 

28-day inhalation study in rats that measure glutamine synthetase activity levels in 

organs. The submitted DNT and inhalation studies did not measure glutamine synthetase 

activity levels. The registrant has submitted a proposal requesting that the Agency accept 

the DNT and inhalation studies without the glutamine synthetase activity level 

measurements due to technical constraints on their ability to conduct such measurements. 

If this proposal is accepted, it is likely that the toxicity doses, endpoints, and uncertainty 

factors previously selected for glufosinate-ammonium would require revisions. This 

would necessitate revisions to the dietary, residential, occupational, and aggregate risk 

assessments. If the proposal is not accepted, the toxicology database for glufosinateammonium could be considered incomplete and additional data may be required. EPA’s 

decision on the glutamine synthetase proposal will be explained in the Final Work Plan. 

Timeline:

EPA has created the following estimated timeline for the completion of the glufosinateammonium registration review. 

Registration Review of Glufosinate – Projected Registration Review Timeline 

Activities Estimated 

Year/Month 

Phase 1: Opening the docket 

Open Public Comment Period for Glufosinate-Ammonium 2008 – March 

Close Public Comment Period 2008 – June 

Phase 2: Case Development 

Final Work Plan (FWP) 2008 – July-Sept. 

Issue DCI 2009 – Apr.-June 

Data Submission 2011 – Apr.-June 

Preliminary Risk Assessment and Public Comment 2012 – Oct.-Dec. 

Close Public Comment Period 2013 – Jan.-March 

Phase 3: Registration Review Decision 

Proposed Registration Review Decision 2013 – Apr.-June 

Public Comment Period 2013 – July-Sept. 

Final Registration Review Decision 

and Begin Post-Decision Follow-up 

2013 

Total (years) 5 
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Guidance for Commenters:

The public is invited to comment on EPA’s preliminary registration review work plan and 

rationale. The Agency will carefully consider all comments as well as any additional 

information or data provided in a timely manner prior to issuing a final work plan for the 

glufosinate-ammonium case. 

Through the registration review process, the Agency intends to solicit information on trade 

irritants and, to the extent feasible, take steps toward facilitating irritant resolution. Growers and 

other stakeholders are asked to comment on any trade irritant issues resulting from lack of 

Maximum Residue Levels (MRLs) or disparities between U.S. tolerances and MRLs in key 

export markets, providing as much specificity as possible regarding the nature of the concern. 

Please see page 8, Table 1, Human Health Effects Scoping Document, for a listing of the 

differences among the U.S., Canada, Codex, and Mexico tolerances for glufosinate-ammonium. 

Glufosinate-ammonium 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://oaspub.epa.gov/tmdl/waters_list.impairments?p_impid=3. The Agency invites submission 

of water quality data for this pesticide. To the extent possible, data should conform to the quality 

standards in Appendix A of the “OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process” (see: http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-

sop.pdf), in order to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments. 

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

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

and enforcement of environmental laws, regulations, and policies. To help address potential 

environmental justice issues, the Agency seeks information on any groups or segments of the 

population who, as a result of their location, cultural practices, or other factors, may have 

atypical, unusually high exposure to glufosinate-ammonium, compared to the general population. 

Please comment if you are aware of any sub-populations that may have atypical or unusually 

high exposure compared to the general population. 

Stakeholders are also specifically asked to provide information and data that will assist the 

Agency in refining the human health and ecological risk assessments, including any speciesspecific effects determinations. The Agency is interested in the following information: 

1. Confirmation on the following label information. 

a. Sites of application 

b. Formulations 

c. Application methods and equipment 

d. Maximum application rates in units related to mass per unit area of treatment zone 

e. Frequency of application, application intervals, and maximum number of 

applications per season, and 
Page 8 of 71 

f. Geographic limitations on use. 

2. Use or potential use distribution (e.g., acreage and geographical distribution of relevant 

uses). 

3. Use history. 

4. Median and 90th percentile reported use rates (lbs. a.i./acre) from usage data—national, 

state, and county. 

5. Application timing (date of first application and application intervals) by use—national, 

state, and county. 

6. Sub-county crop location data. 

7. Usage/use information for non-agricultural uses (e.g., golf courses, athletic fields, 

ornamentals). 

8. Directly acquired county-level usage data (not derived from state level data). 

a. Maximum reported use rate (lbs. a.i./acre) from usage data – county 

b. Percent crop treated—county 

c. Median and 90th percentile number of applications – county 

d. Total pounds per year—county 

e. The year the pesticide was last used in the county/sub-county area 

f. The years in which the pesticide was applied in the county/sub-county area. 

9. Typical application interval (days). 

10. State or local use restrictions. 

11. Ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian and 

mammalian mortalities) not already reported to the Agency. 

12. Monitoring data. 

Next Steps:

After the comment period closes, the Agency will review the comments received, and then issue 

a Final Work Plan for glufosinate-ammonium. 
Page 9 of 71 

II. FACT SHEET

 

Background Information:

• Glufosinate-ammonium Registration Review Case Number: 7224 

• Glufosinate-ammonium PC Code: 128850; CAS#: 7182-82-2 

• Technical Registrant: Bayer CropScience LP. 

• First product registered in 2000, therefore not subject to reregistration. 

• Special Review and Reregistration Division (SRRD), Chemical Review Manager: Karen 

Santora; santora.karen@epa.gov. 

• Registration Division (RD), Product Manager: Joanne Miller; miller.joanne@epa.gov. 

Use & Usage Information: 

• Glufosinate-ammonium is a non-selective foliar herbicide that is used for pre-plant and 

post-emergent control of broadleaf weeds. 

• It acts by inhibiting glutamine synthetase, which leads to poisoning in plants via the 

overproduction of ammonia. 

• It is registered for use on the following crops: apples, berries, canola, corn, cotton, 

currants, grapes, grass grown for seed, potatoes, rice, soybeans, sugar beets, and tree nuts. 

Registrations for non-crop areas include golf course turf, residential lawns, ornamentals, 

and a variety of industrial, residential, and public areas. 

• Both aerial and ground spray are allowed for most uses, although some applications are 

limited to methods using hand wands and backpack sprayers. 

• Application rates vary considerably by use pattern, with the highest rate (1.5 lb ai/A) for 

use patterns including orchard nuts and fruits, grapes, grasses grown for seed, and golf 

course turf. Multiple applications are allowed by most labels, with an annual maximum 

application rate of 4.5 lbs ai/A for orchards and vineyards. 

• The majority of agricultural uses occur in corn (900,000 lb ai/A), followed by cotton 

(300,000 lb ai/A), canola (60,000 lb ai/A), almonds (30,000 lb ai/A), and grapes (20,000 

lb ai/A). 

Recent Actions:

• The most recent and comprehensive human health risk assessment was conducted in 

2003, when acute, short-term, and chronic aggregate risk assessments were conducted for 

glufosinate-ammonium as a part of Section 3 registrations for transgenic cotton and 

cotton, transgenic rice, and bushberry.

• In 2002, EPA conducted an occupational and updated residential exposure risk 

assessment for the use of glufosinate-ammonium on rice, cotton, and bushberry. 

• In 2002, 2006, and 2007, environmental fate and effects studies were submitted to 

support FIFRA Section 3 New Use registrations for cotton, rice, blueberry, corn, 

soybeans, and canola. 

• In 2002 an environmental fate and effects study was also submitted to support a FIFRA 

Section 18 emergency exemption for blueberries in Mississippi.
Page 10 of 71 

• In 2007, new uses for non-transgenic canola, corn, and soybean were approved. 

• There are no pending new registrations for this chemical. 

Ecological Risk Assessment Status: 

Please refer to Section III of this document, Ecological Risk Assessment Problem Formulation, 

for a detailed discussion of the anticipated ecological risk assessment needs. The following 

ecological outcomes and anticipated data needs are based on the limited data and risk 

assessments currently available: 

• The Agency anticipates conducting comprehensive human health and ecological risk 

assessments, including an endangered species assessment for all uses of glufosinateammonium. 

• Based upon the information gathered to date, the risks of concern are mainly to nontarget plants as well as chronic risk to mammals, with potential indirect effects terrestrial 

animals possible due to alterations in aquatic plant communities. Acute and chronic risk 

quotients for birds slightly exceeded the LOCs. However, the LOCs were based on the 

highest dose tested in the subacute dietary study and the two avian reproduction studies. 

There is also concern for effects on species listed under the Endangered Species Act, 

including mammals and birds. 

• Preliminary review of the plant toxicity studies indicates that there are insufficient data 

on terrestrial plant toxicity to complete the ecological assessment. Because sufficient data 

were not reported, EPA cannot determine a NOAEC for seedling emergence, making 

determination of an action area for an endangered species assessment difficult. 

Furthermore, EPA cannot verify the assessment endpoints, creating uncertainties with 

regard to the effect of glufosinate-ammonium on non-target terrestrial plants. 

• The Agency anticipates requiring additional terrestrial plant seedling emergence and 

vegetative vigor studies using typical end-use product (TEP). Only technical grade active 

ingredient (TGAI) was tested in the terrestrial plant studies. There are concerns that the 

herbicide formulations are enhanced with the addition of surfactant to improve their 

efficacy, and, therefore, toxicity to non-target plants might have been underestimated in 

the studies because the TGAI, rather than the TEP was tested. 

• The environmental fate and transport data set submitted for glufosinate-ammonium is 

adequate. However, the analytical methods for residues in water and soil that were 

submitted have not been validated in an independent laboratory. Independent laboratory 

validation will be required to provide confidence in the quantification levels of the 

submitted analytical methods. 

Human Health Risk Assessment Status:

Please refer to Section IV of this document, Human Health Effects Scoping Document, for a 

detailed discussion of the anticipated risk assessment needs for human health. The following is a 

summary of those anticipated needs: 

Dietary (Food and Water): 

• The dietary exposure database for glufosinate-ammonium is complete. 
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• The Agency recently issued a document updating its estimated drinking water 

concentrations (EDWCs) for glufosinate-ammonium in groundwater sources. This update 

does not change the water values that were used in the most recent risk assessment for 

glufosinate-ammonium (August 2003). 

• The Agency anticipates that the acute and/or chronic dietary exposure analysis will be 

reassessed and include estimates of glufosinate-ammonium levels in drinking water as 

well as changes based on the Agency’s decision on the proposal regarding the glutamine 

synthetase. 

Residential: 

• A previous risk assessment (August 2003) identified potential residential exposures 

relating to residential handler and residential post application exposures to glufosinateammonium as a result of broadcast application to residential lawns (i.e., lawn renovation 

use). To mitigate the risk, the technical registrant, Bayer Environmental Science, 

voluntarily canceled the lawn renovation use. All labels for Bayer Environmental Science 

currently bear directions only for spot treatment of lawns, not the lawn renovation use. 

However, some end-use registrants still have the broadcast lawn renovation use on their 

labels. The Agency sent a letter to these registrants, which informed them of Bayer 

Environmental Science’s voluntary cancellation of all lawn renovation uses and requested 

that they submit draft labels deleting the lawn renovation use. Once the lawn renovation 

use is cancelled, the Agency does not anticipate that a residential risk assessment will be 

needed for glufosinate-ammonium. 

Occupational: 

• The Agency believes the current occupational risk assessments and the resulting exposure 

levels are adequate, but if the registrant’s proposal on glutamine synthetase (discussed 

earlier) is accepted, it is likely the MOEs will need to be revised. 

Aggregate: 

• The Agency anticipates that the aggregate risk assessments for glufosinate-ammonium 

may need to be revised to include the following: (1) the addition of water levels directly 

into the dietary analysis, thus obviating the need for Drinking Water Level of 

Comparison (DWLOC) analysis, and (2) reconsideration of the uncertainty factors and 

dose/endpoint selection based on a complete toxicity database for glufosinate. 

Incidents:

• The Agency has received 48 ecological incident reports that have been linked to the use 

of glufosinate-ammonium. The majority of the incidents (45) involved damage to corn. 

Another of these incidents involved a ‘massive’ fish kill in a farm pond in Maryland after 

application of glufosinate-ammonium to plants surrounding the farm pond. 

• A summary report listing the human health-related incidents reported for glufosinateammonium is pending and will be provided for the docket. The reported incidents will be 

provided during the development of the Final Work Plan. 
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Data Call-In Status:

• No Data Call-In has been issued for glufosinate-ammonium. 

Tolerances: 

For a list of the current U.S. tolerances and Mexican, Canadian, and Codex maximum residue 

limits (MRLs) for glufosinate-ammonium, please refer to Table 1 of Section IV of this 

document, Human Health Effects Scoping Document. 

• U.S. tolerances for glufosinate-ammonium are listed under 40 CFR 180.467. 

• Except for tree nuts, almond hulls, banana, and soybean, the U.S. tolerances and Codex 

MRLs are not in harmony with respect to numerical levels. 

• The U.S. tolerances and the Canadian MRLs are harmonized for field grain and soybeans 

but no other crops. 

• All Mexican MRLs are harmonized with U.S. tolerances. 

Labels: 

A list of registration numbers is included below and the labels can be obtained from the Pesticide 

Product Label System (PPLS) website: http://oaspub.epa.gov/pestlabl/ppls.home. 

Glufosinate-Ammonium Registration Numbers:

Registration 

# Product name Company Name Active Ingredient % Active Ingredient 

264-645 Ignite ManufacturingUse Product 

Bayer CropScience 

LP Glufosinate-ammonium 50.00 

264-646 Ignite Technical Bayer CropScience 

LP Glufosinate-ammonium 95.00 

264-652 Rely Herbicide Bayer CropScience 

LP 

Glufosinate-ammonium 11.33 

264-660 Liberty Herbicide Bayer CropScience 

LP 

Glufosinate-ammonium 18.19 

264-663 Remove Herbicide Bayer CropScience 

LP 

Glufosinate-ammonium 18.19 

264-668 Liberty ATZ Herbicide Bayer CropScience 

LP 

Glufosinate-ammonium 10.00 

264-829 Liberty 280 SL 

Herbicide 

Bayer CropScience 

LP 

Glufosinate-ammonium 24.5 

270-317 

AEH Concentrate 

Weed, Grass and Brush 

Killer 

Farnum Companies, 

Inc. 

Glufosinate-ammonium 5.78 
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270-318 AEH Ready-To-Use 

Weed and Grass Killer 

Farnum Companies, 

Inc. 

Glufosinate-ammonium 1.00 

270-319 

AEH Super Concentrate 

Weed, Grass and Brush 

Killer 

Farnum Companies, 

Inc. 

Glufosinate-ammonium 11.33 

432-875 

AEH 315 

Manufacturing 

Concentrate 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 18.19 

432-954 

FINALE Super 

Concentrate Weed, 

Grass and Brush Killer 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 11.33 

432-955 Finale Ready-To-Use 

Weed and Grass Killer 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 1.00 

432-956 

Finale Concentrate 

Weed, Grass and Brush 

Killer 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 5.78 

432-960 Derringer F Herbicide 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 11.33 

432-1228 Derringer Herbicide 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 11.33 

432-1229 Finale Herbicide 

Bayer 

Environmental 

Science 

Glufosinate-ammonium 11.33 
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III. ECOLOGICAL RISK ASSESSMENT PROBLEM FORMULATION

Page 16 of 71 

REGISTRATION REVIEW 

ECOLOGICAL RISK ASSESSMENT PROBLEM 

FORMULATION FOR: 

Glufosinate-ammonium 

ammonium-(2RS)-2-amino-4-(methylphosphinato)butyric acid 

CAS Registry Number: 71182-82-2 

PC Code: 128850

O

P

O

OH

O

NH2

NH4

+

Prepared by:

 

Brian Kiernan, Biologist 

Greg Orrick, Environmental Scientist

Reviewed by: 

Melissa Panger, Ph.D., Biologist 

Marietta Echeverria, Environmental Scientist 

Elizabeth Behl, Branch Chief

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch IV 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460
Page 17 of 71 

 I. Problem Formulation

 

The purpose of this problem formulation is to provide the foundation for an ecological 

risk assessment to be conducted for glufosinate-ammonium (glufosinate). As such, it articulates 

the purpose and objectives of the risk assessment, evaluates the nature of the problem, and 

provides a plan for analyzing the data and characterizing the risk (EPA, 1998). 

A. Nature of Regulatory Action

 The risk assessment will be conducted as part of the Agency’s registration review process 

established under the Food Quality Protection Act (FQPA; 1995). Previous risk assessments that 

serve as the basis for this problem formulation include the following (for details, see Appendix 

A): 

• 1 Section 3 New Chemical (S3NC) Risk Assessment of proposed uses on corn, soybeans, 

nut trees, vine crops, and non-agricultural areas (DP Barcode 203178+; Dec. 7, 1988) 

• 5 Section 3 New Use (S3NU) Risk Assessments of proposed uses on corn, soybeans, and 

non-agricultural areas (DP Barcode 260482+; Dec. 20, 1990); canola, potatoes, and sugar 

beets (DP Barcode 240586; Apr. 26, 2000); cotton, rice, and blueberries (DP Barcode 

280453; Jul. 18, 2002); cotton (DP Barcode 318746+; Feb. 28, 2006); and corn, 

soybeans, and canola (DP Barcode 344652; Oct. 2, 2007) 

• 8 Drinking Water Assessments from 1998 through 2007 

• 4 Section 18 Risk Assessments for uses on canola, sweet corn, and blueberries from 1998 

to 2002 

• 1 Response to Comments (DP barcode 287073; Jan. 6, 2003) that was received from the 

Sierra Club 

These previous assessments identify potential adverse effect to non-target plants. 

Previous assessments noted that the listed species LOC was exceeded for birds, mammals and 

aquatic invertebrates. 

B. Stressor Source and Distribution 

1. Nature of the Chemical Stressor

Glufosinate-ammonium [HOE 039866; ammonium-(2RS)-2-amino-4-

(methylphosphinato)butyric acid] is a non-selective foliar herbicide that acts by inhibiting 

glutamine synthetase, which leads to poisoning in plants via the overproduction of ammonia. 

Glufosinate-ammonium salt dissolves to produce ammonia and glufosinate acid, a racemic 

mixture of ionic isomers; only the L-isomer (or (S)-enantiomer) mimics the enzyme glutamine 

synthetase and is, therefore, herbicidally active. The product labels and most submitted studies 

refer to the salt racemate as the active ingredient. In this problem formulation, all glufosinateammonium residues are loosely referred to as “glufosinate” unless clarification is warranted. 
Page 18 of 71 

The chemical profile of glufosinate-ammonium is provided in Table 1. Chemical names and 

structures of the isomeric mixtures of glufosinate-ammonium and its degradates, as they are 

formulated in standards used in submitted environmental fate studies, are listed in Appendix B. 

Table 1. Chemical Profile of Glufosinate-ammonium.

Common name Glufosinate-ammonium 

IUPAC name ammonium-(2RS)-2-amino-4-(methylphosphinato)butyric 

acid 

CAS name (RS)-2-amino-4-(hydroxymethylphosphinyl)butanoic acid 

monoammonium salt 

Structure 

O

P

O

OH

O

NH2

NH4

+

Pesticide type, such as 

herbicide or insecticide, 

Herbicide 

Chemical class Glutamine synthetase inhibitor 

CAS number 77182-82-2 

Empirical formula C5H15N2O4P 

Molecular mass 198.2 g/mol 

Glufosinate inhibits the glutamate synthetase enzyme needed for the ammonification of 

glutamate to glutamine. This disruption in the production of key amino acids leads to disruption 

of the cell membrane, excess ammonium and death of the cell. Although this metabolic pathway 

exists in animals, the lack of acute toxicity is thought to be due the capacity for animals to 

supplement glutamine needs from their diet. Although neurotoxic effects (seizures) in mammals 

have been reported in Health Effects Divison (HED) studies, glufosinate is not thought to be a 

cholinesterase inhibitor. 

 2. Overview of Pesticide Uses and Usage

 Glufosinate-ammonium is an active ingredient in several formulated products registered 

for preplant and postemergent control of broadleaf weeds in a variety of crops and non-crop 

areas. Products include Liberty®, Ignite®, Rely®, RemoveTM, AEH®, Derringer® and Finale®. 

Crops for which glufosinate is registered include apples, berries, canola, corn, cotton, currants, 

grapes, grass grown for seed, potatoes, rice, soybeans, sugar beets, and tree nuts. Registrations 

for non-crop areas include golf course turf, residential lawns, ornamentals, and a variety of 

industrial, residential, and public areas. Both aerial and ground spray is allowed for most uses, 

although some applications are limited to methods using hand wands and backpack sprayers. 

Application rates vary considerably by use pattern. The highest rate for broadcast spray (ground) 
Page 19 of 71 

is 1.5 lbs ai/A for use patterns including orchard nuts and fruits (e.g. almonds, apples, hickory), 

grapes, grasses grown for seed and golf course turf. The maximum rate for cotton applications is 

0.79 lbs ai/A (also labeled at 0.52 lbs ai/A), for rice is 0.73 lbs ai/A, and for sugar beets is 0.55 

lbs ai/A. Corn and soybean broadcast applications are a maximum of 0.44 lbs ai/A. There are 

numerous other applications, including turf and patio applications, labeled for 0.03 lbs ai/A. 

Multiple applications are allowed by most labels, although the interval is not generally specified, 

with an annual maximum rate of up to 4.5 lbs ai/A for orchards and vineyards. This problem 

formulation will focus on the highest application rates and broadcast (aerial and ground) spray, 

because they are expected to result in the highest off-target exposure. 

 According to the Screening Level Usage Analysis (SLUA) provided by the Biological 

and Economic Analysis Division (BEAD), the majority of glufosinate is used on corn (900,000 

lbs ai/yr), followed by cotton (300,000), canola (60,000), almonds (30,000) and grapes (20,000). 

Potatoes, rice and soybeans account for 10,000 lbs ai/yr per crop. No other use pattern exceeded 

4000 lbs ai/A. The SLUA reports a maximum of 25% of canola crops treated and 15% of the 

almond crop, 10% of the potato crop; 5% or less of all other crops are treated; however, these 

data do not included non-agricultural uses. 

 C. Receptors 

 1. Aquatic and Terrestrial Effects 

The receptor is the biological entity that is exposed to the stressor (EPA, 1998). Aquatic 

and terrestrial receptors that live or forage on or adjacent to application sites may be exposed to 

glufosinate, such as birds, mammals, terrestrial plants, freshwater fish, etc. 

Consistent with the process described in the Overview Document (EPA, 2004), the risk 

assessment will use a surrogate species approach in its evaluation of glufosinate. Toxicological 

data generated from surrogate test species, which are intended to be representative of broad 

taxonomic groups, are used to extrapolate to potential effects on a variety of species (receptors) 

included under these taxonomic groupings. 

Acute and chronic toxicity data from studies submitted by pesticide registrants along with 

the available open literature are used to evaluate the potential direct effects of glufosinate to the 

aquatic and terrestrial receptors identified in this section. This includes toxicity data on the 

technical grade active ingredient, degradates, and when available, formulated products (e.g. “SixPack” studies). The open literature studies are identified through EPA’s ECOTOX database 

(http://cfpub.epa.gov/ecotox/), 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 glufosinate on biotic 

communities from loss of species that are sensitive to the chemical and from changes in structure 

and functional characteristics of the affected communities. 

Table 2 provides a summary of the taxonomic groups and the surrogate species tested to 

help understand potential acute ecological effects of pesticides to these non-target taxonomic 
Page 20 of 71 

groups. In addition, the table provides a preliminary overview of the potential acute toxicity of 

glufosinate by providing the acute toxicity classifications. 

Table 2. Test Species Evaluated for Assessing Potential Ecological Effects of Glufosinateammonium and the Associated Acute Toxicity Classification.

Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification 

Birds1 Mallard (Anas platyrhynchos) 

Bobwhite (Colinus virginianus) Practically non-toxic 

Mammals Laboratory rat (Rattus norvegicus) Practically non-toxic 

Insects Honey bee (Apis mellifera L.) Practically non-toxic 

Freshwater fish2 Bluegill sunfish (Lepomis macrochirus) Slightly non-toxic 

Freshwater invertebrates Water flea (Daphnia magna) Moderately toxic 

Estuarine/marine fish Sheepshead minnow (Cyprinodon 

variegatues) Slightly toxic 

Estuarine/marine 

invertebrates Mysid shrimp (Americamysis bahia) Moderately toxic 

Terrestrial plants3 Monocots – corn (Zea mays) 

Dicots – soybean (Glycine max) Not classified 

Aquatic plants and algae 

Duckweed (Lemna gibba) 

Green algae (Selenastrum 

capricornutum) 

Not classified 

1

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

 Freshwater fish may be surrogates for aquatic-phase amphibians. 3

 Four species of two families of monocots, of which one is corn; six species of at least four dicot families, of which one is 

soybeans. 

Ecological effect endpoints are derived from registrant-submitted guideline studies as 

required for registration under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA; 

40 CFR Part 158), as well as a review of data available through acceptable open literature 

(ECOTOX; www.epa.gov/ecotox), when available. The most sensitive endpoints (described 

below) from testing of surrogate species are used to estimate risk to the taxonomic group(s) 

represented by the surrogate tested. Toxicity testing reported in this document is intended to 

represent all terrestrial and aquatic organisms. However, only a few surrogate species are used 

to represent all freshwater fish (2000+), bird (680+) and plant (19,000+) species in the United 

States. In addition, neither reptiles nor amphibians are routinely tested. Bird data are used as 

surrogates for reptiles and terrestrial-phase amphibians; fish data are used as surrogates for 

aquatic-phase amphibians. The Norway rat is typically the surrogate for all mammals. 

Neither reptiles nor amphibians are tested. The risk assessment assumes that avian and reptilian 

and terrestrial-phase amphibian sensitivities to the chemical are similar. The same assumption is 

made for fish and aquatic-phase amphibians. Terrestrial plant data are derived from the 

vegetative vigor and seedling emergence tests, typically on 10 agricultural crop species, and do 

not account for potential chronic or reproductive effects. Typically, five aquatic plant species are 

used to represent potential toxicity to all aquatic plant species. 

 Most of the studies with non-target organisms were conducted with glufosinate technical. 

The typical end-use product (TEP), EF-1343, was the test material in the terrestrial plant seedling 

emergence and vegetative vigor studies. These studies provide the effects basis for risk 
Page 21 of 71 

estimation. A summary of the endpoints that will be used in the risk assessment are presented in 

Table 3. 

Further characterization will be possible because the TEP was used in several toxicity 

studies, including freshwater and estuarine/marine fish and invertebrates and mammals. In many 

of these studies, the formulated product is considerably more toxic than glufosinate technical, an 

important point which will be explored in the risk assessment. 

Table 3. The Endpoints Used in Glufosinate Risk Estimation. 

Environ

ment Taxa Species Type of Risk 

Type of 

Endpoint Endpoint Units MRID 

Aquatic Freshwater 

Fish 

Rainbow 

trout 

Acute LC50 >320 mg ai/L 001424-54 

001424-55 

 Chronic NOAEC No data -- 

 Freshwater 

Invertebrates 

Daphnid Acute EC50 668 mg ai/L 001424-56 

 Daphnid Chronic NOAEC 32 mg ai/L 405010-10 

 Estuarine 

/marine Fish 

Sheepshead 

minnow 

Acute LC50 >1000 mg ai/L 413961-04 

 Chronic NOAEC No data -- 

 Estuarine 

/marine 

Invertebrates 

Mysid Acute EC50 7.5 mg ai/L 413961-07 

 Chronic NOAEC No data -- 

 Plants Duckweed Acute EC50 1.47 mg ai/L 422624-04 

 Duckweed Listed NOAEC 0.80 mg ai/L 422624-04 

Terrestrial Avian Mallard Acute LD50 >2000 mg ai/kg-bw 001424-50 

 Mallard Chronic NOAEC 400 mg ai/kg-diet 403456-49 

 Mammalian Rat Acute LD50 3030 mg ai/kg-bw 001424-30 

 Rat Chronic NOAEC 6.0 mg ai/kg-diet 403456-12 

 Plants Carrot Acute EC25 0.063 lb ai/A 413961-13 

 Carrot Listed NOAEC 0.05 lb ai/A 413961-13 

Many pesticides have potential impacts to the growth, reproduction and survival of 

receptors via chronic exposure. For chronic assessments, the Agency typically evaluates longer 

duration studies on species similar to those used in acute studies; however, the assessment 

endpoints derived from these studies is not a median lethal dose, but a no adverse effect 

concentration/level (NOAEC/L). At this time, the Agency does not evaluate chronic risk to 

plants. Chronic exposure to avian species did not result in any effects at the highest 

concentration tested. Chronic effects were observed at the highest concentration in the chronic 

mammal study. 

For glufosinate, the only evaluation of chronic exposure in aquatic organisms is in a lifecycle study with freshwater invertebrates (i.e., daphnids), in which effects were seen only at the 
Page 22 of 71 

highest concentrations in the study. Potential chronic effects to fish and estuarine/marine 

invertebrates are uncertain due to lack of data. Consistent with the Agency’s agreement with the 

Services, an acute-to-chronic ratio will be used in the absence of other data to estimate potential 

risk to these taxa and to help define an action area for listed entities. 

 

2. Ecosystems Potentially at Risk 

The ecosystems at risk are often extensive in scope, and as a result it may not be possible 

to identify specific ecosystems during the development of a baseline risk assessment. However, 

in general terms, terrestrial ecosystems potentially at risk could include the treated field and 

areas immediately adjacent to the treated field that may receive drift or runoff. Areas adjacent to 

the treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow 

fields or grasslands, woodlands, riparian habitats and other uncultivated areas. 

 Aquatic ecosystems potentially at risk include water bodies adjacent to, or down stream 

from, the treated field and might include impounded bodies such as ponds, lakes and reservoirs, 

or flowing waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also 

includes marine ecosystems, including estuaries. Within water bodies, the water column, 

sediments, and pore water are all compartments of concern. Organisms of concern include birds, 

mammals, reptiles, fish, amphibians, terrestrial and aquatic invertebrates, and plants. The 

assessment endpoints are intended to reflect population sustainability and community structure 

within ecosystems and hence relate back to ecosystems at risk. If risks are expected for given 

species/taxa based on the screening-level assessment, then risks might be expected to translate to 

higher levels of biological organization. 

 

For glufosinate these areas would include agricultural areas growing apples, berries, 

canola, corn, cotton, currants, grapes, grass grown for seed, potatoes, rice, soybeans, sugar beets, 

or tree nuts, as well as fallow crop land, public and private non-agricultural areas including 

farmsteads, industrial areas, Christmas tree farms, ornamental areas, forests, golf courses, lawns, 

parks, paths, paved areas, recreational areas, residential areas, rights-of-way, and schools, and 

water bodies directly adjacent to use sites that may receive chemical residues via drift, runoff, 

and/or discharged ground water. 

D. Assessment Endpoints 

Assessment endpoints represent the actual environmental value that is to be protected, 

defined by an ecological entity and its attributes or characteristics (EPA, 1998). For glufosinate, 

the ecological entities may include the following: birds, mammals, freshwater fish and 

invertebrates, estuarine/marine fish and invertebrates, terrestrial plants, insects, and aquatic 

plants and algae. The attributes for each of these entities may include growth, reproduction, and 

survival. The ecological entity can be a species, a functional group of species, a community, an 

ecosystem, or another entity of importance or concern. An attribute is the characteristic of the 

entity that is important to protect and is potentially at risk. 
Page 23 of 71 

Defining an assessment endpoint involves two steps: 1) identifying the valued attributes of 

the environment that are considered to be at risk, and 2) operationally defining the assessment 

endpoint in terms of an ecological entity (e.g., a community of fish and aquatic invertebrates) 

and its attributes (i.e., growth, survival and reproduction). Therefore, selection of the assessment 

endpoints is based on valued entities (i.e., ecological receptors), the ecosystems potentially at 

risk and the routes by which ecological receptors are exposed to the pesticide. The selection of 

clearly defined assessment endpoints is important because they provide direction and boundaries 

in the risk assessment for addressing risk management issues of concern. 

Typical assessment endpoints for screening-level pesticide ecological risk assessments 

include reduced survival and/or reproductive impairment for both aquatic and terrestrial animal 

species from direct acute or direct chronic exposures. Aquatic animal groups that are typically 

characterized in the risk assessment include: freshwater and estuarine/marine fish and 

invertebrates. Terrestrial animal groups include birds, mammals, and, qualitatively, beneficial 

insects. All assessment endpoints are characterized at the individual level in order to protect 

threatened and endangered species. However, risks to higher biological levels (i.e., populations 

and communities) can be inferred from this approach (e.g., pesticide effects on individual 

survival and fecundity may impact population stability, growth, and/or habitat carrying capacity). 

If warranted, a species-specific assessment containing characterization of the potential for direct 

and indirect effects to listed species and the potential for adverse effects to designated critical 

habitat is the next step following completion of the screening-level risk assessment. 

For terrestrial and semi-aquatic plants, the baseline assessment endpoint is the perpetuation 

of populations of non-target species (crops and non-crop plant species). Existing test 

requirements only evaluate the seedling emergence and vegetative vigor of annuals. Although it 

is recognized that the endpoints of seedling emergence and vegetative vigor may not address all 

terrestrial and semi-aquatic plant life cycle components, it is assumed that impacts on plant 

emergence and/or on active growth have the potential to impact individual competitive ability 

and reproductive success, from which population effects can be inferred. 

For aquatic plants, the assessment endpoint is the maintenance and growth of standing crop 

or biomass. Measurement endpoints for this assessment focus on nonvascular, e.g., algae, and 

vascular plants, e.g., duckweed (Lemna gibba), growth rates and biomass measurements. 

 E. Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in 

biologically significant concentrations. An exposure pathway is the means by which a pesticide 

moves in the environment from a source to an ecological receptor. For an ecological pathway to 

be complete, it must have a source, a release mechanism, an environmental transport medium, a 

point of exposure for ecological receptors, and a feasible route of exposure. 

A conceptual model provides a written description and visual representation of the 

predicted relationships between glufosinate, potential routes of exposure, and the predicted 
Page 24 of 71 

effects for the assessment endpoint. A conceptual model consists of two major components: risk 

hypothesis and a conceptual diagram (EPA, 1998). 

 1. Risk Hypothesis 

 For glufosinate, the following ecological risk hypothesis will be employed for the 

ecological risk assessment: 

Based on the mode of action, use of glufosinate according to label directions is not 

expected to result in direct acute adverse effects to non-listed animal species; however, its use as 

directed may cause acute effects to listed entities and chronic effects are possible. Adverse 

effects to nontarget plant species are expected. Indirect effects on aquatic and terrestrial 

animals may occur due to alterations in plant communities.

 

 2. Conceptual Diagram 

The conceptual model used to depict the potential ecological risk associated with the use 

of glufosinate (the stressor) assumes that as a pesticide, glufosinate can adversely affect 

terrestrial and aquatic organisms (the receptors) if environmental concentrations exceed toxic 

thresholds as a result of application according to the label directions (Figure 1). Ecological 

receptors that may potentially be exposed to glufosinate include terrestrial and semi-aquatic 

wildlife (e.g., mammals, birds, amphibians and reptiles), terrestrial and semi-aquatic plants, 

terrestrial invertebrates (e.g., honey bees), and terrestrial soil and aquatic sediment invertebrates. 

Additionally, given the mobility of glufosinate, aquatic organisms (i.e., freshwater and 

estuarine/marine fish and invertebrates, amphibians, and aquatic plants) are potential receptors in 

adjacent water bodies through off-site transport of glufosinate from the application site through 

runoff, erosion and/or spray drift. 

 Routes of exposure to terrestrial and aquatic organisms can occur from direct application, 

spray drift and/or runoff. Exposure may be through ingestion of contaminated food or water 

sources, dermal contact or absorption, and/or inhalation. 

 This assessment does not take into account potential atmospheric transport in estimating 

environmental concentrations or potential exposure via groundwater, nor does it account for 

ingestion of glufosinate residues by animals in contaminated grit, ingestion through preening 

activities, or uptake through inhalation or dermal absorption by terrestrial animals. Exposure to 

terrestrial animals is based primarily on dietary consumption of foliar (and insect) residues. 

Aquatic assessments assume that all potential routes of direct exposure are accounted for. 
Page 25 of 71 

Figure 1. Conceptual Model for a Screening Level Assessment of Glufosinate. Dashed lines 

indicate exposure routes not evaluated; bold lines indicate routes of exposure 

hypothesized to be of greatest importance. 

Stressor 

Stressor 

Glufosinate Applied as Aerial or Ground Spray to Target Crops 

Source/ 

Transport 

Pathways 

Volatilization 

/ Wind 

Suspension 

Direct 

Deposition 

Spray 

Drift 

Runoff / 

Erosion 

Leaching 

(infiltration / 

Percolation) 

Source/ 

Exposure 

Media 

Terrestrial Food 

(foliage, 

fruits, insects) 

Receiving 

Water Body/ 

Sediment 

Ground water 

Irrigation water 

on crops 

Exposure 

Route 

Ingestion Uptake / 

Absorption 

Gill / 

Integument 

Uptake 

Receptors Terrestrial Vertebrates

Birds, Mammals, Reptiles, 

Terrestrial Phase Amphibians 

Aquatic Plants 

Aquatic 

Animals Non-target Crop

Attribute 

Changes 

Individual Animals

Reduced survival 

Reduced growth 

Reduced reproduction 

Plant Population

Reduced survival, 

growth 

Individual Vertebrates 

and Invertebrates

Reduced survival 

Reduced growth 

Reduced reproduction 

Reduced survival 

Reduced growth 

Foliage/Roots/Seeds 

Terrestrial 

Plants

Bold lines indicate pathways of primary concern in this risk assessment
Page 26 of 71 

 F. Analysis Plan and Preliminary Analysis 

The proposed label maximum application rates for the use of glufosinate will be selected 

for modeling environmental concentrations for this screening level, deterministic (risk-quotient 

based) assessment. The most sensitive toxicity endpoints from surrogate test species will be 

used to estimate treatment-related effects on growth, reproduction and survival assessment 

endpoints. Estimated environmental concentrations (EECs) used in terrestrial and aquatic 

ecological risk assessments will be based on glufosinate parent residues, as the toxicity of the 

degradates to ecological entities is not known. 

A risk quotient-based approach will be used in the assessment, comparing the ratio of 

exposure concentrations to effects endpoints with predetermined levels of concern (LOCs). The 

use, laboratory environmental fate and laboratory ecological effects data, all of which provide 

the basis for these risk quotients, are characterized in the assessment. Although risk is often 

defined as the likelihood and magnitude of adverse ecological effects, the risk quotient-based 

approach does not provide a quantitative estimate of likelihood and/or magnitude of an adverse 

effect. 

Additionally, consideration of potential risk from formulated product to the taxa for 

which data are available will be considered. Available data suggest that formulations of 

glufosinate exhibit greater toxicity than the parent alone. Exposure to formulations of 

glufosinate may result in great risk to nontarget taxa. This will be explored in detail in the risk 

assessment. 

 1. Conclusions from Previous Risk Assessments 

Previous risk assessments have identified potential acute risk to listed terrestrial and 

aquatic invertebrate species and chronic avian risk. Potential risk to nontarget plants was also 

identified. 

 

 2. Preliminary Identification of Data Gaps 

 Only one (Selanastrum capricornutum) of the five guideline nonvascular aquatic plant 

species studies is available to evaluate potential effects to nonvascular aquatic plants. The 

submission of the remaining guideline studies would allow a better characterization of potential 

indirect effects, especially within aquatic ecosystems. Since these non-vascular plant species are 

representative of important links in the aquatic food chain, a better understanding of the effect of 

glufosinate on these taxa could be important. 

 Uncertainty regarding potential chronic risk to freshwater fish and estuarine/marine 

organisms could be reduced with the submission of additional data. Consistent with the 

Agency’s agreement with the Services, an acute-to-chronic ratio will be used in the absence of 

other data to estimate potential risk to these taxa and to help define an action area for listed 

entities. 
Page 27 of 71 

 Because sufficient data were not reported, a determination of a NOAEC for seedling 

emergence is not possible. Therefore, determining an action area for an endangered species 

assessment will be difficult and subject to conservative assumptions. Data are insufficient in all 

studies to allow verification of the assessment endpoints, leading to heightened uncertainty 

regarding the effect of glufosinate on nontarget terrestrial plants. If these endpoints cannot be 

verified, they may not be sufficient for a risk assessment. Additionally, only the TGAI was 

tested in the terrestrial plant studies. Guideline studies conduct testing with the TEP. Since most 

herbicide formulations are enhanced with the addition of surfactants, toxicity to plants may have 

been greatly underestimated in the studies in-house. Given that glufosinate is an herbicide, these 

issues are critical to the completion of a risk assessment. 

Given the greater toxicity of formulated glufosinate to some taxa, avian toxicity data on 

the formulated product would allow for better characterization of potential risk to these taxa. 

Environmental fate submissions for each guideline requirement and any additional data 

needs are listed in Table C.1 in Appendix C. The submitted environmental fate data are 

sufficient to fulfill most data requirements for glufosinate-ammonium. However, the submitted 

analytical method for residues in water and soil has not been validated in an independent 

laboratory. Submission of an independent laboratory validation is necessary for confidence in 

the quantification level of the submitted analytical method. 

3. Measures of Exposure and Effect 

The screening level environmental fate and ecological risk assessments use the risk 

quotient (RQ) deterministic method of evaluating potential risk. The RQ, an integration of effect 

and exposure estimation (Table 4 ) is calculated by dividing the estimated environmental 

concentration (EEC) by the measure of effects (e.g. LD50). The resulting quotient is then 

compared to a predetermined level of concern (LOC; Table 5) 

Table 4. Measures of Ecological Effects and Exposure for Glufosinate.

Assessment Endpoint Surrogate Species and 

Measures of Ecological Effect1 

Measures of Exposure 

Survival 

Bobwhite acute oral LD50

Bobwhite and mallard subacute 

dietary LC50

Birds2 

Reproduction and growth 

Bobwhite and mallard chronic 

reproduction NOAEC and 

LOAEC 

Mammals 

Survival Laboratory rat acute oral LD50

Maximum residues on food 

items (foliar) 
Page 28 of 71 

Assessment Endpoint Surrogate Species and 

Measures of Ecological Effect1 

Measures of Exposure 

Reproduction and growth 

Laboratory rat oral reproduction 

chronic NOAEC and 

LOAEC 

Survival 

Rainbow trout and bluegill 

sunfish acute LC50 Peak EEC4 

Freshwater fish3

Reproduction and growth 

No Data 

60-day average EEC4 

Survival Water flea (or other freshwater 

invertebrates) acute EC50 

Peak EEC4 

Freshwater invertebrates 

Reproduction and growth Water flea chronic (life cycle) 

NOAEC 21-day average EEC4 

Survival Sheepshead minnow acute 

LC50)

Peak EEC4 

Estuarine/marine fish 

Reproduction and growth No Data 60-day average EEC4 

Survival Eastern oyster acute EC50 and 

mysid acute LC50

Peak EEC4 

Estuarine/marine 

invertebrates 

Reproduction and growth No Data 21-day average EEC4 

Terrestrial plants5 

Survival and growth 

Monocot and dicot seedling 

emergence and vegetative 

vigor EC25 and NOAEC 

values

Estimates of runoff and spray 

drift to non-target areas 

Insects 

Survival (not Honeybee acute contact LD50 Maximum application rate 
Page 29 of 71 

Assessment Endpoint Surrogate Species and 

Measures of Ecological Effect1 

Measures of Exposure 

quantitatively assessed) 

Aquatic plants and algae 

Survival and growth 

Algal and vascular plant (i.e., 

duckweed) EC50 and 

NOAEC values for growth 

rate and biomass 

measurements

Peak EEC4

1 If species listed in this table represent most commonly encountered species from registrant-submitted studies, risk assessment 

guidance indicates most sensitive species tested within taxonomic group are to be used for baseline risk assessments. 

2 Birds represent surrogates for amphibians (terrestrial phase) and reptiles. 3 Freshwater fish may be surrogates for amphibians (aquatic phase). 4 One in 10-year return frequency. 

5 Four species of two families of monocots - one is corn, six species of at least four dicot families, of which one is soybeans. 

LD50 = Lethal dose to 50% of the test population; NOAEC = No observed adverse effect concentration; LOAEC = 

Lowest observed adverse effect concentration; LC50 = Lethal concentration to 50% of the test population; EC50/EC25

= Effect concentration to 50%/25% of the test population.

Table 5. Levels of concern (LOCs) for various taxa. 

Risk Presumption RQ LOC

Birds and Mammals 

Acute Risk EEC/LC50 or LD50/sqft or LD50/day 0.5 

Acute Restricted Use EEC/LC50 or LD50/sqft or LD50/day (or LD50 < 50 mg/kg) 0.2 

Acute Endangered Species EEC/LC50 or LD50/sqft or LD50/day 0.1 

Chronic Risk EEC/NOAEC 1 

Aquatic Animals 

Acute Risk EEC/LC50 or EC50 0.5 

Acute Restricted Use EEC/LC50 or EC50 0.1 

Acute Endangered Species EEC/LC50 or EC50 0.05 

Chronic Risk EEC/NOAEC 1 

Terrestrial Plants 

Acute Risk EEC/EC25 1 

Acute Endangered Species EEC/NOAEC or EC05 1 

Aquatic Plants 

Acute Risk EEC/EC50 1 
Page 30 of 71 

Risk Presumption RQ LOC

Acute Endangered Species EEC/NOAEC or EC05 1 

4. Measures of Exposure 

a. Environmental Fate Characteristics

 The environmental fate and transport data set submitted for glufosinate-ammonium is 

adequate. These data indicate that residues of glufosinate-ammonium are hydrophilic and 

mobile in soil. The residues are not likely to persist in aerobic, surface soils; however, they do 

not hydrolyze and can readily move to surface water via spray drift and runoff. Chemical 

properties and environmental fate parameters of glufosinate are listed in Table 6. 

Table 6. General Chemical Properties and Environmental Fate Parameters of Glufosinateammonium. 

Parameter Value Reference

Selected Physical/Chemical Parameters

Molecular mass 198.2 g/mol Accsn # 263025 

Vapor pressure (25°C) <7.5 x 10-9 torr MRID 44032901 

Water solubility (22°C) 1.37 x 106 mg/L Accsn # 263025 

Octanol-water partition coefficient (KOW) <0.1 Accsn # 263025 

Fish Bioconcentration Factor (28 d) None MRID 41323130 

Persistence

Hydrolysis half-life pH 5 

(25°C) pH 7 

 pH 9 

No significant degradation 

No significant degradation 

No significant degradation 

MRID 40345656 

Aqueous photolysis half-life No significant degradation MRID 41323115 

Soil photolysis half-life 17 d MRID 41920102 

Aerobic soil metabolism half-life range 8.54-8.83 d (1.62 ppm applied) 

20.6-23.0 d (7.23 ppm applied) 

MRID 41323119 

MRID 40345659A

Anaerobic soil metabolism half-life 36.9 d MRID 40501014 

Anaerobic aqueous metabolism half-life No significant degradation MRID 46258601 

Aerobic aqueous metabolism half-lives 38.5, 51.8 d MRID 40345660 

Mobility

Freundlich organic carbon distribution 

coefficient (KFOC)

9.41 L/kgOC (sand) 

156 L/kgOC (silt loam) 

352 L/kgOC (silt loam) 

1230 L/kgOC (volcanic ash clay) 

MRID 40345662 

Field Dissipation

Terrestrial field dissipation half-life range 8-23 d MRID 43110402, 

MRID 43766915, 

MRID 43766916 
Page 31 of 71 

i. Transport and mobility 

Glufosinate residues are readily miscible in water (Accsn # 263025) and will not 

volatilize significantly due to a low vapor pressure of <7.5 x 10-9 torr (25°C; MRID 44032901). 

Glufosinate is hydrophilic, with an octanol-water partition coefficient of <0.1 (Accsn # 263025) 

and does not bioconcentrate in fish (MRID 41323130). 

Due to its hydrophilicity, glufosinate is mobile to highly mobile (KFOC of 9.41 to 352 in 

soils representative of use sites; MRID 40345662). Mobility of glufosinate residues may be 

explained by affinity to organic matter, as the coefficient of variation (CV) across four soils for 

the Freundlich organic carbon partition coefficient (99.7%) is less than that for the Freundlich 

soil-water partition coefficient (116%). 

Regarding degradates of glufosinate, HOE 061517 (3-methylphosphinico-propionic acid) 

is mobile to highly mobile, similar to glufosinate parent (KFOC range = <10 to 158 in soils 

representative of use sites; MRID 40345662). However, HOE 064619 (2-methylphosphinicoacetic acid) appears to be less mobile than the parent compound (KOC = 3260; MRID 41323121). 

ii. Degradation 

Glufosinate does not significantly degrade under the abiotic processes of hydrolysis and 

photolysis (MRID 40345656, 41323115). The compound is moderately biodegraded in aerobic 

soils, with an apparent sensitivity to concentration. Applied at 7.23 μg/g soil, glufosinate was 

biodegraded with a half-life range of 20.6-23.0 days (MRID 40345659A). Applied at 1.62 μg/g 

soil, glufosinate biodegraded with shorter half-lives of 8.54-8.83 days (MRID 41323119). 

Biodegradation occurs less readily in anaerobic soils (t1/2 = 36.9 days; MRID 40501014) and 

aerobic water bodies (t1/2 range = 38.5-51.8 days; MRID 40345660) and is insignificant in 

anaerobic water bodies (MRID 46258601). 

iii. Field studies 

 Several terrestrial field dissipation studies of glufosinate have been submitted. In these 

studies, glufosinate dissipates from the upper 6 inches of soil with half-lives of 1-4 weeks. This 

range of dissipation rates is generally consistent with those expected from the submitted fate and 

transport studies. Rates of aerobic soil metabolism, which is the sole major route of degradation, 

are similar. Glufosinate is expected to be mobile, but did not appear to leach further than 6 

inches in loam or clay soils or further than 24 inches in a sand soil. Leaching may have been 

attenuated by the presence of 2-3% soil organic matter. Analytes in the submitted studies 

include degradates HOE 061517 and HOE 064619. HOE 061517 exhibits a faster rate of 

formation and decline and greater mobility than HOE 064619. HOE 061517 also exhibits 

greater mobility than glufosinate parent (MRID 43110402, 43766915, 43766916). 
Page 32 of 71 

iv. Degradates 

Major degradates of glufosinate include HOE 061517 (MPP, 3-methylphosphinicopropionic acid), HOE 064619 (MPA, 2-methylphosphinico-acetic acid), HOE 085355 (NAG, 2-

acetamido-4-methylphosphinico-butanoic acid), and carbon dioxide (chemical names and 

structures are tabulated in Appendix B). Two minor degradates have been identified, HOE 

086486 [3-methylphosphinico-3-oxo-propionic acid] and HOE 065594 [4-methylphosphinico-2-

oxo-butanoic acid]. 

 Submitted studies have not reported toxic effects resulting from exposure to the major 

degradates. Therefore, exposure is assessed in terms of residues of the parent compound only for 

ecological assessments of glufosinate. 

b. Aquatic Exposure 

The Tier I screening model (GEN)eric (E)stimated (E)nvironmental (C)oncentration 

(Version 2.0, Aug. 1, 2001) was used to generate preliminary upper-bound EECs for glufosinate 

that may occur in surface waters adjacent to use sites. GENEEC simulates a vulnerable scenario 

run by the Tier II coupled exposure models PRZM and EXAMS, which simulate pesticide 

movement and transformation from crop application through soil residue processes and loading 

into an adjacent pond via runoff and spray drift. These models assume a standard pond scenario 

in which a 10-hectare field drains into an adjacent 1-hectare pond of 2-meter depth (EPA 2006). 

The exposure estimates listed in Table 7 reflect upper-bound concentrations of 

glufosinate residues in surface water based on the highest use patterns, e.g. tree nuts, apples, 

grapes (3 applications at 1.5 lbs ai/A each, unspecified interval). GENEEC is not sensitive to 

application timing; therefore, the screening-level estimated exposure concentrations (EEC) 

below represent all application timings at the modeled application rates. These EECs are 

considered conservative values relative to many of the registered glufosinate use patterns. 

Further crop- and area-specific refinements may be conducted using Tier II modeling. The 

model input parameters used to generate these EECs are presented in Table 8. 

Table 7. Tier I surface water upper-bound exposure estimates of glufosinate from the highest 

label use patterns. 

Crop 

Annual 

App. Rate 

(lbs ai/A) 

Peak EEC 

(ppb)

4-Day Avg 

EEC (ppb)

21-Day Avg 

EEC (ppb)

60-Day Avg 

EEC (ppb)

Tree nuts, 

apples, grapes 4.5 158 156 148 131 
Page 33 of 71 

Table 8. Tier I input parameter values for aquatic ecological exposure modeling of glufosinate 

using GENEEC. 

Input Parameter Value Justification Source

Application Rate in 

lbs a.i./A 

1.5 Maximum single application rate Current labels 

Applications per Year 3 Label directions for maximum rate Current labels 

Application Interval (days) 5 Assumption in absence of stated interval Current labels 

Organic Carbon Partition 

Coefficient (KOC) 

156 Represents the lowest non-sand KOC. MRID 40345662 

Aerobic Soil Metabolism 

Half-life (days) 

19.5 Represents the 90th percentile 

confidence bound on the mean half-life. 

MRID 41323119 

MRID 40345659A 

Wetted In? No Label directions Current labels 

Application Method Ground Label directions Current labels 

Nozzle Height (inches) 20 to 50 Label directions Current labels 

Droplet size distribution Medium to coarse Label directions Current labels 

Width of No-Spray Zone 

(ft) 

0 Label directions Current labels 

Depth of incorporation 

(inches) 

0 Value for broadcast spray Current labels 

Solubility in Water (mg/L) 1.37 x 106 Study value Accsn # 263025

Aerobic Aquatic 

Metabolism Half-life (days) 

65.6 Represents the 90th percentile 

confidence bound on the mean half-life. 

MRID 40345660 

Aqueous Photolysis 

Half-life (days) 

Stable Study value MRID 41323115 

i. Aquatic Exposure Monitoring 

A cursory review of currently available ground water and surface water monitoring data 

on glufosinate was conducted. No analyses of glufosinate were located. The compound is an 

upcoming analyte in the USGS NAWQA program, but no analyses have been reported through 

September 30, 2006 (USGS 2007). Glufosinate was not analyzed in monitoring conducted for 

the USGS NASQAN program (USGS 2006) or the California Department of Pesticide 

Regulation (DPR) Surface Water Database (CDPR 2006). Glufosinate is not an analyte listed in 

STORET (EPA 2007), in the EPA Pesticides in Ground Water Database (EPA 1992), or on the 

Safe Water Drinking Act (SWDA) Contaminant Candidate Lists. The compound is not listed in 

the EPA Safe Drinking Water Information System (SDWIS/FED) database (EPA 2007a), and 

not found in the EPA Unregulated Contaminants Monitoring Rules (UCMR) chemical 

monitoring database (EPA 2006a). 

ii. Drinking Water Exposure 

Separate from this ecological risk assessment, drinking water exposure assessment will 

be conducted as part of the Agency’s registration review process in support of the Health Effects 

Division’s human health risk assessment. For drinking water, the residues of concern include 

glufosinate, HOE 061517, HOE 064619, and HOE 099730 (a.k.a. 085355) (EPA 2002). 

Exposure estimates of previous drinking water assessments are listed in Table A.2 of Appendix 

A. 1-in-10-year peak and annual average estimates in surface water (e.g. 823 ppb) and ground 
Page 34 of 71 

water (e.g. 30.7 ppb) from the maximum use patterns listed in the latest drinking water exposure 

assessment (EPA 2007b) are expected to be used in support of assessment under registration 

review. 

b. Terrestrial Exposure 

i. Animals 

Terrestrial wildlife exposure estimates are typically calculated for birds and mammals 

emphasizing a dietary uptake of pesticide through residues on vegetative and insect forage items. 

Avian terrestrial EECs are considered representative of potential exposure for terrestrial-phase 

amphibians and reptiles as well, unless more appropriate data are available through ECOTOX. 

For exposure to terrestrial organisms, pesticide residues on food items are estimated, based on 

the assumption that organisms are exposed to a single pesticide residue in a given exposure 

scenario. Exposure was evaluated using EECs generated from a spreadsheet-based screening 

model (TREX v.1.3.1) that calculates the dissipation of a chemical applied to foliar surfaces for 

single or multiple applications. The terrestrial animal exposure assessment is based on the 

methods of Hoerger and Kenaga (1972) as modified by Fletcher et al. (1994). When data are 

absent, as in this case, EFED assumes a 35-day foliar dissipation half-life. The predicted 

maximum residues of glufosinate that may be expected to occur on selected avian or mammalian 

food items immediately following application at the maximum rate for a single growing season 

are presented in Table 10. 

Table 9. Unadjusted dietary-based estimated environmental concentrations (EECs) on terrestrial 

animal forage items following application of glufosinate based on TREX (version 1.3.2). 

Application Rate Food Items Upper-bound EEC 

(ppm)a

Mean EEC 

(ppm)a

Short grass 981 348 

Tall grass 450 147 

Broadleaf plants/small insects 552 184 

1.5 lbs ai/A 

3 applications 

5d interval 

Fruits, pods, seeds, and large insects 61 29 a Predicted residues based on Hoerger and Kenaga (1972) as modified by Fletcher et al. (1994). 

ii. Plants 

Exposure to upland and wetland plants is estimated using the TerrPlant (v1.2.2) screening 

model. TerrPlant estimates potential exposure from a single application using default 

assumptions for runoff and spray drift (Table 11). For runoff plus drift, TerrPlant incorporates 

two similar conceptual models for depicting dry and semi-aquatic areas of terrestrial habitats. 

For both models, a non-target area is adjacent to the treated field. Pesticide exposures to plants 

adjacent to the treated field are estimated to include runoff and drift from the treated field. For a 

dry area adjacent to the treated field, runoff exposure is estimated as sheet runoff. In the model, 

sheet runoff is defined as the amount of pesticide in water that runs off of the soil surface of a 

treated field which is equal in size to the non-target area (1:1 ratio of areas). For semi-aquatic 
Page 35 of 71 

areas, runoff exposure is estimated as channelized runoff. In the model, channelized runoff is the 

amount of pesticide that runs off of a treated field 10 times the size of the area adjacent to the 

treated field (10:1 ratio of areas). The drift component is calculated as 1% of applied mass (for 

ground spray) or 5% of applied mass (for aerial spray). Estimated exposures through runoff plus 

drift and drift alone are then compared to measures of plant survival and growth (e.g. effects to 

seedling emergence and vegetative vigor) to develop RQ values. 

Table 10. Estimated environmental concentrations (EECs) on plants following label-specified 

applications of glufosinate determined using the TerrPlant model (lbs ai/A).

Rate Application 

Method

Adjacent Upland 

Loadinga

Adjacent Wetland 

Loading

Drift Only

1.5 lbs ai/A Aerial 0.15 0.825 0.075 

Ground 0.09 0.765 0.015 a

Loading is runoff plus drift (lbs ai/A) 

5. Measures of Effect 

 Most of the studies with non-target organisms were conducted with glufosinate technical. 

The typical end-use product (TEP), EF-1343, was the test material in the terrestrial plant seedling 

emergence and vegetative vigor studies. These studies provide the effects basis for risk 

estimation. Further characterization is possible due the submission of non-guideline toxicity 

studies, as the TEP was tested in several aquatic studies. A summary of the endpoints used in 

this risk assessment were presented in Table 2. 

a. Aquatic Effects 

i. Freshwater Fish 

 

In two 96-hour acute static toxicity studies, rainbow trout (Oncorhynchus mykiss; 

MRID001424-54) and pumpkinseed sunfish (Lepomis gibbosus; MRID 001424-55) were 

exposed to glufosinate TGAI at nominal concentrations of 0 (control), 100, 180 and 320 mg ai/L. 

No mortality or other adverse effects were observed. The 96-h LC50 and NOAEC values for the 

technical glufosinate were >320 and 320 mg ai/L, respectively. Glufosinate technical is 

classified as practically non-toxic to the rainbow trout on an acute exposure basis. 

In a 96-hr study, bluegill sunfish (Lepomis macrochirus; MRID 001443-38) were 

exposed to formulated glufosinate (19% ai) at nominal concentrations of 0 (control), 1.8, 2.4, 

3.2, 4.2, 5.6, 7.5, 10, 13.5, 18, 24, 32, 42, 56 and 75 mg ai/L. There was 100% mortality at the 

highest concentration within 24 hrs, and there was 30 % mortality in the second highest 

concentration at 48 hrs. No other clinical signs of toxicity were noted. The NOEC and LC50

values for this study were 42 and 60 mg ai/L. 

A second acute toxicity study of formulated glufosinate with the bluegill (MRID 001599-

14) was conducted at nominal concentrations of 0 (control), 10, 13.5, 18, 24, 32, 42, 56, 75, 100 
Page 36 of 71 

mg ai/L. There was 100% mortality in the two highest concentrations after 24 hrs. No other 

clinical signs were reported. The study resulted in a NOEC and LC50 of 56 and 65 mg ai/L 

A study with formulated glufosinate (16.22%) was conducted with rainbow trout 

(formerly Salmo gairdneri; MRID 001599-13). Rainbow trout were exposed at nominal 

concentrations of 0 (control), 5.6, 10, 18, 56 and 100 mg ai/L. After 24 hrs, there was 100% in 

the two highest concentrations after 48 hrs. There was 10% mortality at the 32 mg ai/L 

concentration after 48 hrs, and by 72 hrs, there was 80% mortality. Signs of toxicity at the 32 

mg ai/L concentration included surface and head-down swimming and slow reaction to stimuli. 

The NOEC and LC50 for formulated glufosinate was 18 and 26.7 mg ai/L, respectively. Based 

on these studies, formulated glufosinate is classified as slightly toxic to freshwater fish. 

 

The chronic toxicity of glufosinate to freshwater fish cannot be estimated due to lack of 

data. 

ii. Freshwater Invertebrates 

 

An acute 48-hour static toxicity study was conducted to determine the effect of 

glufosinate technical on first instar water fleas (Daphnia magna; MRID 001424-56). The 

nominal test concentrations were 0 (control), 100, 135, 180, 240, 320, 420, 560, 750 and 1000 

mg ai/L. At 48 hours, there was 100% mortality at the highest concentration, 80% at 750 mg 

ai/L, and 10% at 560 mg ai/L. No effects were observed at test concentrations of 420 mg ai/L 

and lower. Therefore, the 48-h EC50 value was 668 mg ai/L and the 48-h NOAEC was 420 mg 

ai/L. Glufosinate is classified as practically non-toxic to daphnids on an acute exposure basis. 

Three studies evaluating the toxicity to daphnids of the formulated glufosinate are 

available, two at 19% ai and one 16.3% ai. The LC50s for these studies ranged from 15 to 79.5 

mg ai/L, with 20% mortality noted as low as 1.0 mg/L. Formulated glufosinate is classified as 

slightly toxic to daphnids on an acute exposure basis. 

 A chronic 21-day (life-cycle) static renewal toxicity study (MRID 405010-10) was 

conducted to determine the effects of glufosinate technical on daphnids. The nominal test 

concentrations were 0 (control), 10, 18, 32, 56, 64.8 and 100 mg ai/L, to which first instars were 

exposed. Seven beakers of one daphnid each were used to evaluate effects on reproduction and 

growth, and three replicates of five daphnids each were used to evaluate effects on mortality. 

The 21-day NOAEC was 32 mg ai/L based on reproductive rate. 

iii. Estuarine/Marine Fish 

 

In a 96-hour acute static toxicity study, sheepshead minnow (Cyprinodon variegatus; 

413961-04) were exposed to glufosinate technical at nominal concentrations of 0 (control), 100, 

180, 320, 560 and 1000 mg ai/L, prepared with reconstituted sea water. No mortality or other 

adverse reactions were reported. The 96-hour LC50 and NOAEC values were >1000 and 1000 
Page 37 of 71 

mg ai/L, respectively, and glufosinate is classified as practically non-toxic to estuarine/marine 

fish on an acute exposure basis. 

 In a 96-hour acute static toxicity study, sheepshead minnow (Cyprinodon variegatus; 

413961-08) were exposed to formulated glufosinate at nominal concentrations of 0 (control), 7.0, 

11.7, 19.4, 32.4 and 54.0 mg ai/L. Mortality was 100% at the two highest concentration after 24 

hours and 100% at the 19.4 mg ai/L at 48 hours. Mortality was 30% at 11.7 mg ai /L after 24 

hours, but no further mortality was recorded. There was no mortality in the control or at the 

lowest concentration tested. The 96-hour LC50 and NOAEC values were 13.5 and 7 mg ai/L, 

respectively, and glufosinate is classified as slightly toxic to estuarine/marine fish on an acute 

exposure basis 

iv. Estuarine/Marine Invertebrates 

 

A 96-hour acute toxicity study was conducted under static conditions to determine the 

effect of glufosinate technical on the mysid shrimp (Mysidopsis bahia; MRID 413961-07). The 

shrimp were exposed to nominal concentrations of 0 (control), 1.0, 1.8, 3.2, 5.6, 10.0, 18.0 and 

32.0 mg ai/L. Mortality ranged from 0 at the 1.0 mg ai/L to 100% at the 32.0 mg ai/L 

concentration. There was 10% mortality in the control after 24 hours. The 96-hour LC50 and 

NOAEC were 7.5 and 1.0 mg ai/L, respectively. Glufosinate is classified as moderately toxic to 

mysid shrimp on an acute exposure basis. 

 A 48-hour acute toxicity study was conducted under static conditions to determine the 

effect of glufosinate technical on the larvae of the Eastern oyster (Crassostrea virginica; MRID 

413961-05). The larvae were exposed to nominal concentrations of 0 (control), 4.9, 8.1, 13.5, 

22.8, 37.4, 62.3 and 104.0 mg ai/L. Hormesis was reported at the lowest test concentration, with 

20% more normal larvae compared to the control. Mortality ranged from 66% at the 8.1 mg ai/L 

to 100% at the 104.0 mg ai/L concentration. There was 10% mortality in the control after 24 

hours. The 48-hour calculated LC50 and NOAEC were 8.0 and 4.9 mg ai/L, respectively. 

Glufosinate is classified as moderately toxic to Eastern oyster on an acute exposure basis. 

 

A 48-hour acute toxicity study was conducted under static conditions to determine the 

effect of glufosinate technical on the larvae of the quahog clam (Mercenaria mercenaria; 

413961-06). The larvae were exposed to nominal concentrations of 0 (control), 16, 27, 45, 75 

and 125 mg ai/L. Mortality ranged from 0% at the 16 mg ai/L to 31% at the 125 mg ai/L 

concentration. The 48-hour calculated LC50 and NOAEC were >125 and 75 mg ai/L, 

respectively. Glufosinate is classified as slightly toxic to quahog clam on an acute exposure 

basis. 

A second study with the quahog clam was conducted with formulated product (MRID 

422624-02), at mean-measured concentrations of 0.52, 0.90, 1.54, 2.62, 4.22 and 7.12 mg ai/L. 

Reduction in normal larvae ranged from 100% at the three highest test concentrations to 24% at 

the lowest test concentration. The 48-hr EC50 was 0.69 mg ai/L with a NOAEC <0.52 mg ai/L. 
Page 38 of 71 

 A 96-hour acute toxicity study (MRID 413961-10) was conducted under static conditions 

to determine the effect of formulated glufosinate on the mysid shrimp. The shrimp were exposed 

to nominal concentrations of 0 (control), 1.4, 2.7, 5.4, 10.8, 21.6 and 43.2 mg /L (whole product). 

No mortality was reported in the 1.4, 2.7 or 5.4 mg ai/L concentrations, but there was 15%, 5% 

and 50% mortality in the 10.8, 21.6 and 43.2 mg ai/L concentrations. Partial loss of equilibrium 

was reported in some shrimp at all but the lowest concentration. The 96-hour LC50 and NOAEC 

were 43.2 and 1.4 mg ai/L, respectively. Formulated glufosinate is classified as slightly toxic to 

mysid shrimp on an acute exposure basis. 

Two studies examining the effect of formulated glufosinate on the Eastern oyster have 

been submitted. In one study (MRID 413961-09), larvae were exposed to nominal 

concentrations of 0 (control), 0.21, 0.35, 0.58, 0.97, 1.62 and 2.7 mg/L (whole product). 

Hormesis (9%-33%) was reported at all but the highest test concentrations, with 52% reduction 

in normal larvae at the highest dose compared to the control. The 48-hour calculated LC50 and 

NOAEC were >1.62 and 1.62 mg/L, respectively. Formulated glufosinate is classified as 

moderately toxic to eastern oyster on an acute exposure basis. 

The second study evaluated the effect of formulated glufosinate on shell deposition 

(MRID 422624-03). Eastern oysters were exposed to nominal concentrations of 0 (control), 

0.29, 0.50, 0.76, 1.32, 2.26 and 3.98 mg ai/L. Shell deposition was inhibited at the two highest 

test concentrations (45 and 55% respectively). The 48-hour calculated LC50 and NOAEC were 

2.9 and 1.32 mg ai/L, respectively. Formulated glufosinate is classified as moderately toxic to 

eastern oyster on an acute exposure basis. 

a. Aquatic Plants 

 

In a static laboratory toxicity test, the freshwater unicellular green alga, Selenastrum 

capricornutum (MRID 403456-53), was exposed to glufosinate ammonium technical at nominal 

concentrations of 0 (control), 2.5, 5.0, 10.0, 20.0, 40.0 and 80.0 mg ai/L. Significant reduction in 

cell counts, compared to those of the control, ranged from 10% at 5 mg ai/L to 71% at 80 mg 

ai/L. The 5-day NOEC and EC50 values, based on cell count, were 2.5 and 7.8 mg ai/L, 

respectively. 

 In a 14-day static toxicity test, duckweed (Lemna gibba; MRID 422624-04) was exposed 

to glufosinate ammonium technical at nominal concentrations of 0 (control), 0.78, 1.3, 2.2, 3.6, 

6.0 and 10 mg ai/L. After 14 days, inhibition of growth ranged from 11% at 0.78 mg ai/L (not 

statistically significant) to 100% at the two highest doses, relative to the control. The NOEC and 

EC50 values, based on frond number, were 0.80 and 1.5 mg ai/L, respectively. 
Page 39 of 71 

b. Terrestrial Effects 

i. Avian Acute Oral, Dietary and Chronic 

 

The acute oral toxicity of glufosinate to bobwhite quail (Colinus virginianus; MRID 

001424-51) and mallard duck (Anas platyrhynchos; MRID 001424-50) was assessed in separate 

studies. Glufosinate was administered to the birds in gelatin capsules as a single oral dose at 

nominal concentrations of 0 (control), and 2000 mg ai/kg-bw. No mortalities were observed in 

the studies. Sublethal effects, including passivity and diarrhea were reported in the bobwhite 

quail study; no sublethal effects were reported in the mallard duck study. The LD50 was >2000 

mg ai/kg-bw in both studies. Based on these results, glufosinate is classified as practically nontoxic to birds on an acute oral exposure basis.

 The subacute dietary toxicity of glufosinate to bobwhite quail and mallard duck was 

assessed over 8 days (MRIDs 001509-88; 001424-50). Glufosinate was administered to the birds 

in the diet at nominal levels of 0 (control), 1250, 2500 and 5000 mg ai/kg-diet for the bobwhite 

quail and at nominal levels of 0 (control), 312.5, 625, 1250, 2500 and 5000 mg ai/kg-diet for the 

mallard ducks. Bobwhite mortalities were 0, 10, 20 and 40 percent, respectively. There were no 

compound-related toxic effects to the mallards. The LC50 in both studies is >5000 mg ai/kg diet. 

Based on these studies, glufosinate is classified as practically non-toxic to bobwhite quail and 

mallard duck on a subacute dietary exposure basis. 

 The chronic toxicity of glufosinate to 5-month-old bobwhite quail and 23-week-old 

mallard duck was assessed (MRIDs 403456-49, 403456-50). The birds were fed diets containing 

glufosinate at nominal concentrations of 0 (control), 25, 100 and 400 mg ai/kg diet. At the end 

of the studies, there were no compound-related toxic effects at any of the concentrations tested. 

The NOAEC for chronic toxicity to birds is 400 mg ai/kg diet. 

ii. Mammalian Acute and Chronic 

Glufosinate is classified as practically nontoxic to rats (Rattus norvegicus) with acute oral 

LD50 value of 3030 mg ai/kg-bw in a study reviewed by HED (MRID 00142430). HED reports 

an LD50 for formulated product (24.3% ai) of 1000 mg/kg-bw. 

After reviewing a 2-generation rat reproduction study (MRID 40345612) HED reported a 

NOAEL of 6.0 mg ai/kg-bw/d for offspring and reproductive effects (decreased number of viable 

pups). Glufosinate-ammonium (HOE 039866 Technical, 95.3% ai) was administered to groups 

of 30 male and 30 female Wistar/Han rats in the diet at concentrations of 0 (control), 40, 120 or 

360 ppm (approximately 2.0, 6.0, 18.0 mg/kg) for two generations. 

At 360 ppm there was a significant (p<0.05) reduction in the mean number of viable 

pups/litter in all generations (-21% to -37%) with the exception of the F2a generation where the 

reduction (-11%) was not statistically significant. Surviving pups and the weight of survivors 
Page 40 of 71 

were unaffected by treatment. No other reproductive or developmental effects were reported. 

There were no dose- or treatment-related clinical signs of toxicity in the offspring of either 

generation. On June 4, 2002, the HIARC considered that the increased kidney weights seen in 

both sexes and generations as an adaptive response and not an adverse effect. The LOAEL for 

reproductive/developmental toxicity is 360 ppm (18 mg/kg/day) based on decreased number of 

viable pups in all generations. The NOAEL is 120 ppm (6.0 mg/kg/day). 

iii. Non-target Invertebrates 

 In an acute oral and an acute contact toxicity study, honey bees (Apis mellifera) were 

exposed to glufosinate at the rate of 345.5 μg ai/bee. No mortalities or sublethal symptoms were 

observed in either study. The LC50 was >100 μg ai/bee; therefore, glufosinate technical is 

classified as practically non-toxic to honeybees on an acute oral exposure basis. 

 In an acute oral and an acute contact toxicity study, honey bees (Apis mellifera) were 

exposed to formulated glufosinate (Basta) at a rate of 100 μg ai/bee. No mortalities or sublethal 

symptoms were observed in either study. The LC50 was >100 μg ai/bee; therefore, this 

glufosinate formulation is classified as practically non-toxic to honeybees on an acute exposure 

basis. 

iv. Terrestrial Plants 

 

In a seedling emergence laboratory toxicity test (MRID 41396-11), a total of four 

monocotyledonous species [corn (Zea mays), oat (Avena sativa), onion (Allium cepa) and 

ryegrass (Lolium spp.)] and six dicotyledonous species [carrot (Daucus carota), cucumber 

(Cucumis sativus), cabbage (Brassica oleracea), soybean (Glycine max), lettuce (Lactuca sativa) 

and tomato (Lycopersicon esculentum)] were exposed to nominal concentrations of 0 (control), 

0.09, 0.38, 0.75 and 1.5 lbs ai/A. Percent emergence was not affected for any of the test species 

except for onion, which demonstrated an EC25 of 0.85 lbs ai/A and a NOEC of 0.38. Seedling 

dry weight was affected at all test concentrations. The affect on dry weight was greatest in 

lettuce and cabbage, with EC25s of 0.15 and 0.16 lbs ai/A, respectively, and least affected in 

soybean with an EC25 of 1.24 lbs ai/A. Plant height was affected the most in onion and least in 

soybean with EC25s of 0.23 and 1.4 lbs ai/A, respectively. The dicotyledonous endpoints used 

for risk estimation are the dry weight EC25 (0.15 lbs ai/A) and NOEC (<0.15 lbs ai/A) for lettuce. 

The most sensitive monocot endpoints are the onion height EC25 (0.23 lbs ai/A) and NOEC 

(<0.23 lbs ai/A.). The data reported in the study are not sufficient to calculate an EC05. 

In a vegetative vigor study (MRID413961-12), four monocotyledonous species [corn 

(Zea mays), oat (Avena sativa), onion (Allium cepa) and ryegrass (Lolium spp.)] and six 

dicotyledonous species [carrot (Daucus carota), cucumber (Cucumis sativus), cabbage (Brassica 

oleracea), soybean (Glycine max), lettuce (Lactuca sativa) and tomato (Lycopersicon 

esculentum)] were exposed to nominal concentrations of 0 (control), 0.025, 0.05, 0.1, 0.2 and 0.4 

lbs ai/A. A continuation study was conducted on ryegrass at rates of 0.005, 0.01, 0.02 and 0.04 
Page 41 of 71 

lbs ai/A. Oat, corn and onion were unaffected at the highest test concentration, but ryegrass dry 

weight was significantly reduced, with an EC25 of 0.61 lbs ai/A and a NOEC of 0.04 lbs ai/A. 

The most sensitive dicot endpoint, based on an EC25 of 0.137 lbs ai/A, was lettuce, which had a 

NOEC of 0.05 lbs ai/A. 

A second vegetative vigor study (MRID 413961-13) was conducted on corn (Zea mays), 

oat (Avena sativa), onion (Allium cepa), carrot (Daucus carota), cucumber (Cucumis sativus), 

cabbage (Brassica oleracea), soybean (Glycine max) and tomato (Lycopersicon esculentum). In 

that study, carrot was the most sensitive dicot with a dry weight EC25 of 0.063 lbs ai/A and a 

NOEC of 0.05 lbs ai/A, while onion was the most sensitive monocot with a dry weight EC25 of 

0.11 and a NOEC of 0.10. All test species were affected at the highest concentration except oat, 

which demonstrated a NOEC of 0.8, the highest dose tested. 

Based on the results of the two vegetative vigor studies, the risk estimation endpoints are 

carrot (EC25 = 0.063 lbs ai/A; NOEC = 0.05 lbs ai/A) and onion (EC25 = 0.11; NOEC = 0.10). 

c. ECOTOX 

 The Agency’s publicly-available ECOTOX database (www.epa.gov/ecotox) was 

reviewed for toxicological endpoints. There were no additional data on glufosinate in the 

database when accessed 10/15/2007. Some of the terrestrial plant endpoints reported in the 

database are more sensitive than those used in this assessment, however, those endpoints were 

either from seedling germination studies, which are not considered reliable for pesticides, or 

were from phytotoxic scoring. Phytotoxicity scores are highly subjective and are not used 

quantitatively in the risk assessment. 

d. INCIDENT REPORTS 

The Agency has received 48 reports of adverse field effects to plants that have been 

linked to the use of glufosinate. Most of these incidents (45) involved damage to corn. The 

Agency considered the cause to be ‘possible’ or ‘likely’ in all but one incident, which was 

considered ‘unlikely’. A ‘massive’ fish kill was reported in a farm pond in Maryland after 

application of glufosinate to plants surrounding a farm pond; this incident was classified as 

‘probable’. 

A lack of reported incidents does not necessarily mean that such incidents have not 

occurred. In addition, incident reports for non-target plants and animals typically provide 

information on mortality events only. Reports for other adverse effects, such as reduced growth 

or impaired reproduction, are rarely received. 
Page 42 of 71 

5. Preliminary Risk Estimation 

Based on the most sensitive endpoint for each of the taxa evaluated and the highest rate 

(1.5 lbs ai/A, 3 applications, 5 day interval) the acute RQ values for may be exceeded for some 

birds and for non-target terrestrial plants exceed the LOC for the use of glufosinate. The listed 

species LOC may be exceeded for some mammals and the chronic LOC is exceeded for both 

birds and mammals. There are no exceedances for aquatic plants or animals, although chronic 

risk to fish is uncertain due to lack of data.. Consideration of various use patterns and potential 

risk will be explored in the risk assessment. 

Additionally, consideration of potential risk from formulated product to the taxa for 

which data are available will be considered in the risk assessment. Available data suggest that 

formulations of glufosinate exhibit greater toxicity to fish, aquatic invertebrates and mammals 

than the parent alone. Exposure to formulations of glufosinate may result in great risk to 

nontarget taxa, including avian species. 

a. Aquatic Species 

i. Freshwater Fish

Glufosinate is classified as practically nontoxic on an acute exposure basis to freshwater 

fish, i.e. the LC50 is greater than 100 mg ai/L, and the potential for acute risk to freshwater fish is 

presumed to be low. An RQ calculated using 320 mg/L (the highest dose tested) is several 

orders of magnitude below (calculated RQ <0.0005) even the acute risk to listed species LOC of 

0.05. The RQ for chronic exposure to freshwater fish is unknown due to lack of data. 

ii. Freshwater Invertebrates 

Glufosinate is classified as practically nontoxic on an acute exposure basis to freshwater 

invertebrates (LC50 =668 mg ai/L), and the potential for acute risk to freshwater invertebrates is 

presumed to be low. The RQ is several orders of magnitude below (RQ=0.0002) even the acute 

risk to listed species LOC of 0.05. The RQ for chronic effects to freshwater invertebrates is also 

orders of magnitude below (calculated RQ=0.007) the chronic risk LOC of 1.0. 

iii. Estuarine/Marine Fish 

Glufosinate is classified as practically nontoxic on an acute exposure basis to 

estuarine/marine fish, i.e. the LC50 is greater than 100 mg ai/L, and the potential for acute risk to 

freshwater fish is presumed to be low. An RQ calculated using 1000 mg/L (the highest dose 

tested) is several orders of magnitude below (calculated RQ <0.0002) even the acute risk to listed 

species LOC of 0.05. The RQ for chronic exposure to freshwater fish is unknown due to lack of 

data. 
Page 43 of 71 

iv. Estuarine/Marine Invertebrates 

Glufosinate is classified as moderately toxic on an acute exposure basis to 

estuarine/marine invertebrates (most sensitive LC50 =7.5 mg ai/L); however, the acute risk and 

listed species LOCs are not exceeded by the RQ of 0.02. The RQ for chronic exposure to 

estuarine/marine invertebrates is unknown due to lack of data. 

v. Aquatic Plants 

 

Neither the acute risk nor the listed species RQ for aquatic plants exceed the LOC. The 

RQ for listed vascular aquatic plants is 0.2 and is well below the acute risk to listed species LOC 

of 1.0. The RQ for nonlisted vascular aquatic plants is 0.11 and is again below the acute risk 

LOC of 1.0. 

b. Terrestrial 

i. Avian Acute and Chronic 

When both dose-based and dietary-based toxicity estimates are available for birds, acute 

risk quotients are calculated using both a dose-based and dietary-based approach. The dosebased RQs are calculated using a body weight-adjusted and consumption-weighted equivalent 

dose. The adjustments account for the fact that smaller-sized animals have to consume more 

food in terms of their body weight than larger animals and that differential amounts of food have 

to be consumed depending on the water content and nutritive value of the food. By expressing 

the Kenaga nomogram (Fletcher et al. 1994) estimated residues in terms of daily equivalent dose, 

estimated environmental concentrations can then be compared to the dose-based LD50. 

Glufosinate is classified as practically nontoxic to birds on both an acute and subacute dietary 

exposure basis; therefore, the potential for risk is presumed low. Although the avian acute oral 

studies tested up to the Agency’s limit doses (e.g. 2000 mg ai/kg-bw), definitive endpoints were 

not derived. Using the highest doses tested, three applications of 1.5 lbs ai/A potentially results 

in acute risk exceedances for small birds foraging on small grass (‘RQ’<1.08) and broadleaf 

plants/small insects (‘RQ’<0.61). The listed species LOC would be potentially exceeded for 

small birds foraging on tall grass (‘RQ’<0.49), medium sized birds foraging on short grass, tall 

grass and broadleaf plants/small insects (‘RQ’<0.48, 0.22 and 0.27) and large birds foraging on 

short grass (‘RQ’ <0.15). Using the highest dose tested in the subacute dietary study 

(LC50>5000 mg ai/kg-diet) would result in possible exceedances for birds foraging on short grass 

and broadleaf plants/small insects (‘RQ< 0.20 and 0.11). 

No effects on any adult, offspring or reproductive parameter were observed at the highest 

dose tested in the two submitted avian reproduction studies (NOAEC = 400 mg/kg-diet). 

However, based on the highest dose tested, chronic RQ values would be 2.45 for birds foraging 

on short grass, 1.12 for birds foraging on tall grass and 1.38 for birds foraging on broadleaf 

plants/small insects. 
Page 44 of 71 

ii. Mammalian Acute and Chronic 

The RQ based on the LC50 from the rat acute oral toxicity study is 3030 mg ai/kg-bw, and 

glufosinate is classified as practically nontoxic to mammals on an acute oral exposure basis; 

therefore, risk is presumed to be low. However, given the potential exposure, the RQs for smalland medium-sized mammals foraging on short grass (RQ=0.14 and 0.12) exceed the listed 

species LOC. 

Reduced litter size was observed in rats following chronic exposure to glufosinate. Using 

the NOAEL (120 mg ai/kg-diet), all dose-based chronic mammalian RQs (except large and 

medium-sized granivores) exceed the LOC of 1.0. Dose-based RQs exceedances range from 1, 

for small-sized granivores, to 71 for small-sized mammals foraging on short grass. Dietary 

based chronic RQs range from 8.2 for mammals foraging on short grass to 0.5 for mammals 

foraging on fruits/pods/large insects. 

iii. Nontarget Plants 

RQs for nontarget plants exceed the LOC for plants inhabiting wetlands adjacent to 

glufosinate use sites (RQs 3.3-5.1). Because NOECs could not be calculated for the seedling 

emergence study, it is not possible to determine listed plant species RQs. RQs for nonlisted 

upland plants exposed via run-off and plants exposed to spraydrift alone do not exceed the LOC. 

Because the RQ for nonlisted plants in wetlands is exceeded, there will be potential concerns for 

indirect effects to some terrestrial species. However, because the TGAI was used in the studies, 

toxicity of glufosinate to plants may be greatly underestimated. 

G. Other Information Needs 

There is specific information that will assist the Agency in refining the ecological risk 

assessment, including any species-specific effects determinations. The Agency is interested in 

obtaining the following information: 

1. confirmation on the following label information 

a. sites of application 

b. formulations 

c. maximum application rates 

d. frequency of application, application intervals, and maximum number of 

applications per season 

e. geographic limitations on use 

2. use or potential use distribution (e.g., acreage and geographical distribution of relevant 

uses) 

3. use history 
Page 45 of 71 

4. median and 90th percentile reported use rates (lbs. ai/acre) from usage data – national, 

state, and county 

5. application timing (date of first application and application intervals) by use – national, 

state, and county 

6. sub-county crop location data 

7. usage/use information for non-agricultural uses (e.g., golf courses, athletic fields, 

ornamentals) 

8. directly acquired county-level usage data (not derived from state level data) 

a. maximum reported use rate (lbs. ai/acre) from usage data – county 

b. percent crop treated – county 

c. median and 90th percentile number of applications – county 

d. total pounds per year – county 

The analysis plan will be revisited and may be revised depending upon the data available 

in the open literature and the information submitted by the public in response to the opening of 

the Registration Review docket. 
Page 46 of 71 

II. Bibliography 

CDPR. 2006. Surface Water Database. California Department of Pesticide Regulation, Surface 

Water Protection Program. Last updated: May 12, 2006. Online at: 

http://www.cdpr.ca.gov/docs/sw/surfdata.htm

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on 

plants. Environ. Toxicol. Chem. 13: 1383-1391. 

Hoerger, F. and E.E. Kenaga. 1972. Pesticide residues on plants: correlation of representative 

data as a basis for estimation of their magnitude in the environment. Environmental 

Quality and Safety. 1: 9-28. 

Urban D.J. and N.J. Cook. 1986. Hazard Evaluation Division Standard Evaluation Procedure 

Ecological Risk Assessment. EPA 540/9-85-001. U.S. Environmental Protection Agency, 

Office of Pesticide Programs, Washington, DC. 

USEPA. 1992. Pesticides in Ground Water Database: A Compilation of Monitoring Studies: 

1971-1991: National Summary. U.S. Environmental Protection Agency, Washington, 

DC. 

USEPA. 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum. EPA/630/R95/002F, April 1998. 

USEPA. 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and 

Effects Division. Feb. 28, 2002. Online at: 

http://www.epa.gov/oppefed1/models/water/input_guidance2_28_02.htm/

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs, U.S. Environmental Protection Agency. Endangered and Threatened Species 

Effects Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of 

Pesticide Programs, Washington, D.C. January 23, 2004. Online at: 

http://www.epa.gov/oppfead1/endanger/consultation/ecorisk-overview.pdf

USEPA. 2006. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and 

Policy. Last updated May 2, 2006. Online at: 

http://www.epa.gov/oppefed1/models/water/

USEPA. 2006a. Unregulated Contaminant Monitoring Rules (UCMR). U.S. Environmental 

Protection Agency, Unregulated Contaminant Monitoring Program. Last updated: Nov. 

24, 2006. Online at: http://www.epa.gov/safewater/data/ucmrgetdata.html
Page 47 of 71 

USEPA. 2007. STORET Data Warehouse. U.S. Environmental Protection Agency. Last Updated 

Jun. 20, 2007. Online at: http://www.epa.gov/storet/dw_home.html

USEPA. 2007a. Safe Drinking Water Information System/Federal Version (SDWIS/FED). U.S. 

Environmental Protection Agency. Last updated: May 7, 2007. Online at: 

http://www.epa.gov/safewater/data/getdata.html

USEPA. 2007b. Glufosinate-ammonium New Uses (Pre-plant Application for Corn, Canola, and 

Soybeans): Drinking Water Exposure Assessment. DP Barcode 335331, 335333. U.S. 

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

Effects Division, Memorandum to RD. Sep. 7, 2007. 

USGS. 2006. Kelly, V., R. Hooper, B. Aulenbach, and M. Janet. Concentrations and Annual 

Fluxes for Selected Water-Quality Constituents from the USGS National Stream Quality 

Accounting Network (NASQAN), 1996-2000. U.S. Geological Survey. Last updated: 

Nov. 13, 2006. Online at: http://pubs.usgs.gov/wri/wri014255/results/detect.htm 

USGS. 2007. National Water-Quality Assessment (NAWQA) Program. U.S. Geological Service. 

Last updated: Dec. 12, 2007. Online at: 

http://infotrek.er.usgs.gov/traverse/f?p=136:1:1779537078393353::NO::: 

Willis, Guye H., and Leslie.L. McDowell. 1987. Pesticide Persistence on Foliage. in Reviews of 

Environmental Contamination and Toxicology. 100:23-73 

A. Submitted Environmental Fate Studies 

Accsn # 263025. Willms, Klockner, Rochling, Albrecht, K. Rexer, G. Gorlitz, W. Bartsch, E. Dorn, Heinrich. 1985. 

Petition for Multi-Use Experimental Use Permit and Temporary Tolerance. Unpublished product chemistry 

studies perfomed by Pflanzenschutzforschung-Chemie, Pflanzenschutzforschung-Formulierung, and 

Analytisches Laboratorium; submitted by Hoechst. Jul. 15, 1981 to Oct. 9, 1985. 

MRID 40345656. Goerlitz, G.; Kloeckner, C.; Eyrich, U. 1986. Abiotic Hydrolysis as a Function of pH and 

Amendment and Separation of Potential Hydrolysis Products of HOE 039866 from the Active Ingredient 

by HPLC: Project Nos. (B)277/85 and (B)110/86. Unpublished study prepared by Hoechst AG. 48 p. 

MRID 40345659. Gildemeister, H.; Jordan, H.; Stumpf, K.; et al. 1987. Aerobic Soil Metabolism Studies with HOE 

039866-[carbon 14] and Amendment and Degradation in Soil Study with HOE 061517-[carbon 14]: Project 

Nos. CB066/85, CB060/86 and CB065/86. Unpublished study prepared by Hoechst AG. 152 p. 

MRID 40345660. Gildemeister, H.; Jordan, H.; Schink, C. 1987. HOE 039866-[carbon 14]: Aerobic Aquatic 

Metabolism Study: Project No. CB064/86. Unpublished study prepared by Hoechst AG. 56 p. 

MRID 40345662. Goerlitz, G. 1985. Adsorption/Desorption in the System--Soil/Water for HOE 039866 and HOE 

061517: Project Nos. CP055/85 and CP062/ 85. Unpublished study prepared by Hoechst AG. 81 p. 

MRID 40345666. Specht, W.; Kunzler, K.; Idstein, H. 1986. Method Verification of the Analytical Method for the 

Analysis of HOE 039866 and HOE 061517 in Crops and Soil and Validation of the Analytical Method AL 
Page 48 of 71 

38/85 for the Residue Analysis of HOE 039866 in Plant Mate- rials, Water and Soil: Project Nos. 31-A and 

(B)104/86. Unpub- lished study prepared by Institut fur Ruckstandsanalytik. 300 p. 

MRID 40501014. Gildemeister, H. 1987. Hoe-039866-?Carbon 14|--Anaerobic Soil Me- tabolism Study: Study No. 

CB008/86. Unpublished study prepared by Hoechst Ag. 31 p. 

MRID 41323115. Stumpf, K. 1989. HOE 039866-?Carbon 14|: Photodegradation in Water at pH 5, 7, and 9: Lab 

Project Number: A40989: CB/89/88. Unpublished study prepared by Hoechst AG. 73 p. 

MRID 41323119. Stumpf, K. 1989. HOE 039866-3,4-?Carbon 14|: Degradation and Meta- bolism in Different Soils 

Under Aerobic and Anaerobic Conditions at an Application Rate of 1.6 mg/kg: Lab Project Number: 

CB019- 88: A41299. Unpublished study prepared by Hoechst AG. 92 p. 

MRID 41323130. Schwalbe-Fehl, M.; Fischer, R. 1988. HOE 039866: Bioaccumulation in Fish: Lab Project 

Number: A39698. Unpublished study prepared by Hoechst AG. 14 p. 

MRID 41920102. Stumpf, K. 1990. Photolysis of HOE 039866-14C (Glufosinate-Ammoni- um) on Soil: Lab 

Project Number: CB90/097: A44730. Unpublished study prepared by Hoechst Aktiengesellschaft. 76 p. 

MRID 43110402. Mayasich, J.; Czarnecki, J. 1994. Terrestrial Field Dissipation of Ignite Herbicide Applied to a 

Citrus Grove in Florida: Lab Project Number: 89-0093: 90-0008: 90-0081 HOE. Unpublished study 

prepared by Hoechst Celenese Corp. 346 p. 

MRID 43766915. Novak, R. 1995. Terrestrial Field Dissipation of Ignite Herbicide Applied to Transgenic Corn: 

Lab Project Number: HRAV 93-0014: F93-1929: H93-04R. Unpublished study prepared by Heartland 

Technologies; En-Cas Analytical Labs and NPC, Inc. 962 p. 

MRID 43766916. Novak, R. 1995. Terrestrial Field Dissipation of Ignite Herbicide Applied to Transgenic Soybean: 

Lab Project Number: HRAV 93-0015: F93-1930: A54506. Unpublished study prepared by Stewart 

Agricultural Research Services, Inc.; En-Cas Analytical Labs; and NPC, Inc. 956 p. 

MRID 44032901. Miklautz, H. 1995. The Vapor Pressure of Glufosinate-Ammonium (Hoe 039866) at 25 (degrees) 

C: Lab Project Number: 0910: A55227: APC 126/95. Unpublished study prepared by Schering AG, 

Institute of Physical Chemistry. 16 p. 

MRID 46258601. Stupp, H. 2003. Degradation and Metabolism of Glufosinate Ammonium in Soil Under Anaerobic 

Conditions. Project Number: M1261285/5, MEF/367/03, C038925. Unpublished study prepared by Bayer 

Ag, Institute of Product Info. 62 p. 
Page 49 of 71 

APPENDIX A. Past Ecological Risk and Drinking Water Exposure Assessments for 

Glufosinate-ammonium. 

TABLE A.1. Past Ecological Risk Assessments for Glufosinate-ammonium. 

DATE TYPE 

OF 

ACTION

USE(S) 

ASSESSED

POTENTIAL 

RISK 

IDENTIFIED

SUMMARIZED ECOLOGICAL CONCLUSIONS

12/12/1984 EUP Soybeans, 

tree/vine, nonag, homeowner 

No Risk assessment was not conducted due to a lack of data. 

11/20/1986 EUP Soybeans, 

tree/vine, nonag 

Yes No acute risk to birds. Chronic exposure to birds not 

expected. Hazard to aquatic organisms not assessed due to 

lack of data. Should not result in hazard to listed birds. 

Sites should be kept away from habitats of listed aquatic 

animals and listed plants. 

12/7/1988 S3NC Corn, soybean, 

nut/vine, non-ag 

Yes Minimal acute risk to terrestrial and aquatic animals. EUP 

12X more toxic than tech product to rainbow trout; 44X 

more toxic to Daphnia magna. Lack of chronic toxicity 

data. No listed species risk exceedances, but conclusions 

pend submission of data. 

12/20/1990 S3NU Corn, soybean, 

non-ag 

 Yes Little acute risk to terrestrial or aquatic animals or algae. 

Risk to terrestrial plants, including all listed plant species. 

12/3/1998 §18 Canola-MN Yes Little acute risk to terrestrial and aquatic animals. No 

chronic risk to birds. No chronic toxicity data for aquatic 

animals. No toxicity data on aquatic plants. Risk to 

terrestrial plants. Risk to listed plant, Western Prairie 

Orchid. 

12/3/1998 §18 Canola-ND Yes Little acute risk to terrestrial and aquatic animals. No 

chronic risk to birds. No chronic toxicity data for aquatic 

animals. No toxicity data on aquatic plants. Risk to 

terrestrial plants. No risk to listed species. 

4/26/2000 S3NU Canola, potato, 

sugar beet 

Yes Little acute risk to terrestrial and aquatic animals. No 

chronic risk to terrestrial animals. No chronic toxicity data 

for aquatic animals. Risk to terrestrial plants. Risk to 

listed plants, but not to other listed species. 

1/18/2002 §18 Blueberry-MS Yes Little acute risk to birds or mammals; no acute risk to 

aquatic animals. Lack of chronic toxicity data for animals. 

Risk to plants. Listed LOCs slightly exceeded for birds 

and mammals, but species not affected. 

7/18/2002 S3NU Cotton, rice, 

blueberry 

Yes Little acute risk to birds or mammals; no acute risk to 

aquatic animals. Lack of chronic toxicity data for animals. 

Risk to plants. Listed LOCs slightly exceeded for birds 

and mammals and exceeded for aquatic invertebrates. 

1/6/2003 RTC Not applicable Yes Likely to impact terrestrial insect species. 

2/28/2006 S3NU Cotton Yes Acute risk to terrestrial plants. Chronic risk to terrestrial 

and aquatic animals in absence of data. 
Page 50 of 71 

TABLE A.2. Past Drinking Water Exposure Assessments for Glufosinate-ammonium.

DATE TYPE 

OF 

ACTION

USE(S) 

ASSESSED

Surface Water 1-in10-year Peak 

EDWCs (ppb)

Surface Water 1-in10-year Annual 

Avg. EDWCs (ppb)

Ground Water 1-

in-10-year EDWCs 

(ppb)

10/23/1998 S3NU Canola 69.5 52.3 0.34 

12/1/1998 S3NU Potatoes 209 158 1.16 

12/1/1998 S3NU Canola, sugar 

beets 

237 178 1.16 

12/3/1998 §18 Canola-MN 69.5 52.3 0.34 

12/3/1998 §18 Canola-ND 69.5 52.3 0.34 

2/22/1999 §18 Sweet cornWI 209 158 1.16 

6/30/1999 S3NU Apples, sugar 

beets 

34.1 0.79 1.16 

1/18/2002 §18 Blueberry-MS 234 40.5 0.406 

7/18/2002 S3NU Cotton, rice, 

blueberry 

1168 (rice) 

356 (other uses) 

1168 (rice) 

56 (other uses) 

0.855 

4/22/2003 S3NU Not reported 823 (rice) 

94 (other uses) 

823 (rice) 

43 (other uses) 

9.0 

2/28/2006 S3NU Cotton 823 (rice) 

94 (other uses) 

823 (rice) 

43 (other uses) 

30.7 

9/7/2007 DWA Corn, canola, 

soybean 

823 (rice) 

94 (other uses) 

823 (rice) 

43 (other uses) 

30.7 
Page 51 of 71 

APPENDIX B. Chemical Names, Structures, and Maximum Reported Amounts of 

Glufosinate-ammonium and its Degradates. 

Table B.1. Maximum Reported Amounts of Glufosinate Degradation Products (Major Amounts 

in Bold). 

Degradate Maximum % of Applied Study Type MRID 

HOE 085355, NAG 19.6 (8 d) Soil photolysis MRID 41920102 

HOE 061517, MPP 70.8 (30 d) 

55.4 (64 d) 

47.7 (7 d) 

69.1 (33 d) 

42.2 (60 d) 

55.1 (64 d) 

50 (10 d) 

47 (42 d) 

52 (14 d) 

Soil photolysis 

Aerobic soil metabolism 

Aerobic soil metabolism 

Anaerobic soil metabolism 

Anaerobic soil metabolism 

Aerobic aquatic metabolism 

Terrestrial field dissipation 

Terrestrial field dissipation 

Terrestrial field dissipation 

MRID 41920102 

MRID 40345659A 

MRID 41323119 

MRID 41323119 

MRID 40501014 

MRID 40345660 

MRID 43110402 

MRID 43766915 

MRID 43766916 

HOE 064619, MPA 11.4 (30 d) 

18.5 (95 d) 

28.2 (14 d) 

24.4 (18 d) 

5.8 (60 d) 

17.8 (94 d) 

39 (183 d) 

24 (296 d) 

34 (45-65 d) 

Soil photolysis 

Aerobic soil metabolism 

Aerobic soil metabolism 

Anaerobic soil metabolism 

Anaerobic soil metabolism 

Aerobic aquatic metabolism 

Terrestrial field dissipation 

Terrestrial field dissipation 

Terrestrial field dissipation 

MRID 41920102 

MRID 40345659A 

MRID 41323119 

MRID 41323119 

MRID 40501014 

MRID 40345660 

MRID 43110402 

MRID 43766915 

MRID 43766916 

HOE 086486 5.9 (32 d) 

5.7 (60 d) 

5.0 (94 d) 

Aerobic soil metabolism 

Anaerobic soil metabolism 

Aerobic aquatic metabolism 

MRID 40345659A 

MRID 40501014 

MRID 40345660 

HOE 065594 5.7 (8 d) Aerobic soil metabolism MRID 40345659A 

CO2 5.0 (30 d) 

60.6 (120 d) 

7.5 (78 d) 

Soil photolysis 

Aerobic soil metabolism 

Anaerobic soil metabolism 

MRID 41920102 

MRID 41323119 

MRID 41323119 

Unextracted residues 13.9 (16 d) 

19.9 (4 d) 

45.2 (60 d) 

13.7 (7 d) 

Soil photolysis 

Aerobic soil metabolism 

Aerobic soil metabolism 

Anaerobic soil metabolism 

MRID 41920102 

MRID 40345659A 

MRID 41323119 

MRID 41323119 
Page 52 of 71 

Table B.2. Chemical Names and Structures of Glufosinate-ammonium and its Degradates 

(MRID 45204401, 45204403). 

Chem. 

Group 

Chemical Name Description Structure 

HOE 039866, AE F039866, 

Glufosinate-ammonium 

IUPAC: ammonium-(2RS)-2-amino-4-

(methylphosphinato)butyric acid 

ammonium-DL-homoalanin-4-

yl(methyl)phosphinate 

CAS: (RS)-2-amino-4-

(hydroxymethylphosphinyl)butanoic 

acid monoammonium salt 

CAS Reg. No. 77182-82-2 

Racemic 

salt

O

P

O

OH

O

NH2

NH4

+

HOE 035956, AE F035956, 

Glufosinate 

IUPAC: (RS)-2-amino-4-

[hydroxy(methyl)phosphinoyl]butyric 

acid 

DL-homoalanin-4-

yl(methyl)phosphinate 

CAS: (RS)-2-amino-4-

(hydroxymethylphosphinyl)butanoic 

acid 

CAS Reg. No. 51276-47-2 

Racemic 

free acid

P

OH

O

O

OH

NH2

1 

HOE 058192, AE F058192 

IUPAC: (S)-2-amino-4-

[hydroxy(methyl)phosphinoyl]butyric 

acid 

L-homoalanin-4-

yl(methyl)phosphinate 

L-isomeric 

free acid

P

OH

O

O

OH

NH2
Page 53 of 71 

Chem. 

Group 

Chemical Name Description Structure 

HOE 099730, AE F099730 

IUPAC: disodium-(S)-2-acetamido-4-

methylphosphinico-butanoic acid 

L-isomeric 

salt

O

P

O

O

O

NH O

Na+

2

HOE 099729, AE F099729, N-acetyl 

glufosinate, NAG 

IUPAC: (S)-2-acetamido-4-

methylphosphinico-butanoic acid

L-isomeric 

free acid

O

P

OH

O

NH O

HO

2 

HOE 085355, AE F085355, N-acetyl 

glufosinate, NAG 

IUPAC: 2-acetamido-4-

methylphosphinico-butanoic acid

Racemic 

free acid

O

P

OH

O

NH O

HO

3 HOE 061517, AE F061517, MPP, 

MPPA 

IUPAC: 3-methylphosphinicopropionic acid 

CAS: 3-

(hydroxymethylphosphinyl)propanoic 

acid 

CAS Reg. No. 15090-23-0

Free acid 

O

P

HO

OH

O
Page 54 of 71 

Chem. 

Group 

Chemical Name Description Structure 

4 HOE 064619, AE F064619, MPA, 

MPAA 

IUPAC: 2-methylphosphinico-acetic 

acid 

CAS: 

(hydroxymethylphosphinyl)acetic acid

CAS Reg. No. 72651-25-3 

Free acid 

O

P

HO O

OH

5 HOE 086486, AE F086486 

IUPAC: 3-methylphosphinico-3-oxopropionic acid

Free acid 

O

P OH

HO

O O

6 HOE 065594, AE F065594 

IUPAC: 4-methylphosphinico-2-oxobutanoic acid

Free acid 

O

P

O

O

HO

OH

HOE 042231, AE F042231 

IUPAC: disodium-2-hydroxy-4-

methylphosphinico-butanoic acid 

Racemic 

salt

O

P

O

O

O

OH

Na+

2

7 

HOE 053705, AE F053705 

IUPAC: 2-hydroxy-4-

methylphosphinico-butanoic acid

Racemic 

free acid

O

P

O

OH

HO

OH

8 HOE 039046, AE F039046 

IUPAC: 4-methylphosphinicobutanoic acid

Free acid

O

P

HO O

OH
Page 55 of 71 

Chem. 

Group 

Chemical Name Description Structure 

HOE 084658, AE F084658 

IUPAC: disodium-methylphosphinicoformic acid 

Salt 

O

P

O

O

O

Na+

2

9 

HOE 130947, AE F130947 

IUPAC: methylphosphinico-formic 

acid 

Free acid

O

P

O

HO

OH

10 HOE 130948, AE F130948 

IUPAC: methylphosphonic acid

Free acid

O

P

HO OH

11 HOE 078091, AE F078091 

IUPAC: methylphosphinic acid 

Free acid

O

HO

P

H
Page 56 of 71 

APPENDIX C. Submitted Data for Glufosinate-ammonium.

Table C.1 identifies studies by MRID or Accession Number that offer data for each 

guideline requirement. Also listed are study classifications, whether or not the studies are 

collectively sufficient for the data requirement, and whether or not the current action necessitates 

data submission in support of guideline requirement completion. Table C.2 lists the same 

information for ecological effects. 

TABLE C.1. Environmental fate data submitted for glufosinate-ammonium. 

Subdivision N 

Guideline # 

Data 

Requirement 

Sufficient 

for EFED?

Submitted Studies 

(MRID/Acc. #) 

Classification Current Additional 

Data Need 

161-1 Hydrolysis Yes 40345656 Acceptable None 

161-2 Aqueous 

photolysis 

Yes 40345657 

41323115 

Supplemental 

Acceptable 

None 

161-3 Soil photolysis Yes 40345658 

41323116 

41323117 

41920102 

Supplemental 

Unacceptable 

Unacceptable 

Acceptable 

None 

162-1 Aerobic soil 

metabolism 

Yes 40345659A,C,D 

40345659B 

40501018 

41323118 

41323119 

41920103 

Supplemental 

Supplemental 

Unacceptable 

Supplemental 

Supplemental 

Supplemental 

None 

162-2 Anaerobic soil 

metabolism 

Yes 40501014 

41323119 

41323120 

41920103 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

None 

162-3 Anaerobic aquatic 

metabolism 

Yes 45215401 

46258601 

(Under review) 

Supplemental 

None

162-4 Aerobic aquatic 

metabolism 

Yes 40345660 

45204401 

45204402 

Acceptable 

(Under review) 

(Under review) 

None 

163-1 Aged leaching/ 

adsorption/ 

desorption 

Yes 40345661 

40345662 

41323121 

Unacceptable 

Acceptable 

Supplemental 

None

163-2 Volatility - lab Yes 41323122 

41920104 

Unacceptable 

Supplemental 

None 

164-1 Terrestrial field 

dissipation 

Yes 40345663 

40345664 

40345665 

41323123 

41323124 

41920106 

43110402 

43766915 

43766916 

Supplemental 

Supplemental 

Supplemental 

Unacceptable 

Supplemental 

Unacceptable 

Acceptable 

Acceptable 

Acceptable 

None 

164-2 Aquatic field 

dissipation 

Yes 45204403 (Under review) None 
Page 57 of 71 

Subdivision N 

Guideline # 

Data 

Requirement 

Sufficient 

for EFED?

Submitted Studies 

(MRID/Acc. #) 

Classification Current Additional 

Data Need 

165-4 Fish 

bioaccumulation 

Yes 40501017 

41323130 

Supplemental 

Acceptable 

None 

(OPPTS 

850.7100) 

Data Reporting 

for Environmental 

Chemistry 

Methods 

No 40345666 Not classified Independent laboratory 

validation of submitted 

analytical method for 

residues in soil and water

TABLE C.2. Ecological effects data submitted for glufosinate-ammonium. 

Subdivision J 

Guideline # 

Data 

Requirement 

Sufficient 

for EFED?

Submitted Studies 

(MRID/Acc. #) 

Classification Current Additional 

Data Need 

71-1 Avian Oral Yes 00142450 

00142451 

Acceptable 

Acceptable 

None 

71-2 Avian Dietary Yes 00150988 

00150989 

Acceptable l 

Acceptable 

None 

71-4 Avian 

Reproduction 

Yes 40345650 

40345650 

Acceptable 

Acceptable 

None 

72-1 Acute FW Fish Yes 00142454 

00142455 

Acceptable 

Acceptable 

None 

72-2 Acute FW 

Invertebrates 

Yes 00142456 Acceptable None 

72-3 Acute E/M 

Organisms 

Yes 00128850 

41396107 

Acceptable 

Acceptable 

None

72-4 Fish 

ELS/Invertebrate 

Life Cycle 

Yes 00128850 Acceptable None 

123-1a,b Seedling 

Emergence/Veget

ative Vigor 

No 41396111 

41396112 

41396113 

Supplemental 

Supplemental 

Supplemental 

Seedling emergence 

NOEC 

123-2 Aquatic Plants No 40345653 

42262404 

Acceptable 

Acceptable 

Four nonvascular plants 
Page 58 of 71 

IV. HUMAN HEALTH EFFECTS SCOPING DOCUMENT 

Page 60 of 71 

Introduction. The HED Glufosinate Ammonium Registration Review Team has evaluated the 

status of the human health risk assessments for the herbicide glufosinate ammonium to determine 

whether sufficient data are available and whether new human health risk assessments are needed 

to support Registration Review. The primary sources for the status update were the most recent 

human health risk assessment (August 2003), Agency memoranda, and an OPPIN bibliography 

of submitted studies (MRIDs). Memoranda regarding proposed label amendments were also 

considered (February 2005, September 2007). Incident databases were also reviewed. 

 

Technical glufosinate ammonium is a racemic mixture of the D and L enantiomers; only the L 

enantiomer is herbicidally active. The compound is a non-selective herbicide and acts as an 

inhibitor of glutamine synthetase which leads to poisoning of the plant by ammonia. Glufosinate 

ammonium is currently registered for use on both transgenic and nontransgenic crops. The 

transgenic plants currently registered (canola, sugar beet, corn, soybean, rice, and cotton) have 

been genetically engineered to express phosphiothrion-acetyltransferase (PAT) which enables 

the plant to metabolize glufosinate ammonium into N-acetylglufosinate. 

Although the current glufosinate ammonium tolerance listing in 40 CFR 180.473 distinguishes 

between nontransgenic (40 CFR 180.473(a)(1)) and transgenic crops (40 CFR 180.473(a)(2)), 

HED concurs with a recent recommendation that this distinction be removed (D335330, T. 

Bloem, 12-SEP-2007). This recommendation was based on a determination by the Metabolism 

Assessment Review Committee (MARC) that a single tolerance expression (glufosinate 

ammonium, N-acetyl-glufosinate, and 3-methylphosphinico-propionic acid) applies to both 

transgenic and nontransgenic crops. 

Hazard Characterization and Toxicology. Contingent on conclusions of the HED HASPOC 

regarding a waiver request for determination of glutamine synthetase levels, the toxicity 

database for glufosinate ammonium is substantially complete for the purpose of assessing 

human health risks. 

No acute reference dose was selected for the general population because an endpoint attributable 

to a single exposure was not available from the toxicity studies. However, an acute reference 

dose applicable to females 13-50 years old was selected from a rabbit developmental toxicity 

study based on reduced fetal body weights and increased fetal deaths. 

Chronic toxicity testing has revealed a variety of effects including increased mortality, inhibition 

of brain glutamine synthetase and increased liver and kidney weights. In dogs, 

electrocardiogram (EKG) alterations were also observed. The database for carcinogenicity is 

considered complete. Glufosinate ammonium has been classified as not likely to be a human 

carcinogen (Group E). The mutagenicity/genetic toxicity database is considered complete and 

indicates no mutagenicity concern. 
Page 61 of 71 

Previous assessments have concluded that the special FQPA safety factor should be reduced to 

1x for the following reason: There was no quantitative or qualitative evidence of increased 

susceptibility following in utero exposure in the prenatal developmental study in rats. There is 

qualitative evidence of increased susceptibility in the prenatal developmental study in rabbits 

and quantitative evidence of increased susceptibility in the 2-generation reproduction study in 

rats. In this study, a decrease in the number of viable pups was observed in the absence of 

parental toxicity at any dose. Since there is qualitative evidence of increased susceptibility of 

the young following exposure to glufosinate ammonium, the HED Hazard Identification 

Assessment Review Committee (HIARC) performed a degree of concern analysis to: (1) 

determine the level of concern for the effects observed when considered in the context of all 

available toxicity data; and (2) identify any residual uncertainties after establishing toxicity 

endpoints and traditional uncertainty factors to be used in the risk assessment of this chemical. 

Based on the data gaps listed above, the HIARC did not identify any other residual 

uncertainties. The established endpoints are protective of pre-pre/postnatal toxicity following 

acute and chronic exposures. 

In an April 2003 report of the HIARC, it was concluded that a 10X database uncertainty factor 

(UFDB) should be applied to all exposure scenarios to account for the lack of a DNT study with 

comparative glutamine synthetase activity measurements in organs. 

The previous glufosinate ammonium risk assessment (August 2003) identified two primary 

toxicology data gaps: a developmental neurotoxicity (DNT) study in rats, and a 28-day 

inhalation study in rats with glutamine synthetase activity measurements in brain, kidney, liver 

and lung for both studies. HED subsequently received the following two toxicological 

submissions: 

1) MRID 46455701. Developmental Neurotoxicity Study in Rats. 

This study was reviewed recently (TXR# 0053106, R.J. Mitkus, 8/24/2005) and found adequate 

to satisfy the registration requirement of a developmental neurotoxicity study. However, the 

review noted that the study did not measure glutamine synthetase levels in organs. 

2) MRID 47058101. 28-Day Inhalation Toxicity Study in Rats. 

This study was reviewed recently (TXR# 0053314, L. Austin, 9/6/2007) and was classified as 

Acceptable/Non-guideline. However, the review noted that the study did not measure glutamine 

synthetase levels in organs. While this study did not determine a NOAEL, the LOAEL was 

established at 0.056 mg a.i./L based on lung/bronchial congestion in female rats. 

Dietary Exposure. With respect to the assessment of dietary risks, the dietary exposure 

database is complete. There are adequate residue data reflecting the use of all existing 

formulations on representative commodities. Acute and chronic dietary exposure analyses have 

been conducted using DEEM-FCID (version 1.30) (D292560, T. Bloem, 07-AUG-2003). HED 
Page 62 of 71 

identified a reference dose for chronic exposure (cRfD) of 0.006 mg/kg/day from a “weight-ofevidence” approach from three studies based upon glutamine synthetase inhibition and 

alterations in the electrocardiogram found in the studies. The NOAEL from the three studies was 

6.0 mg/kg/day and the cRfD was derived by applying a 1000X uncertainty factor (10x database 

UF, 100X inter-/intra-species UF). Because the FQPA SF was determined to be 1X, the cRfD 

and the cPAD are numerically equivalent. Chronic dietary exposure estimates greater than 100% 

of the cPAD would exceed HED’s level of concern. Chronic dietary (food only) risk estimates 

were less than 30% of the cPAD for all populations using a partially refined exposure assessment 

(tolerance or average field trial residue levels, percent crop treated information for several crops, 

and processing factors when available). Any update of the chronic dietary exposure analysis 

should include recommendations of the HASPOC regarding the glutamine synthetase waiver 

request and estimates of glufosinate ammonium levels in drinking water. 

HED identified a reference dose for acute exposure (aRfD) of 0.0063 mg/kg for females 13-49 

years old only. The NOAEL of 6.3 mg/kg was based on reduced fetal body weights and 

increased fetal deaths seen at the LOAEL of 20 mg/kg. A 1000x uncertainty factor (10x 

database UF, 100X inter-/intra-species UF) was incorporated in the aRfD. Because the FQPA 

SF was determined to be 1X, the aRfD and the aPAD are numerically equivalent. Acute dietary 

exposure estimates greater than 100% of the aPAD would exceed HED’s level of concern. 

Acute dietary (food only) risk estimates were less than 50% of the aPAD for females 13-49 years 

old using a partially refined exposure assessment (tolerance, highest or average field trial residue 

levels depending on the level of blending of a given commodity, 100% crop treated information 

for all crops, and processing factors when available). Any update of the acute dietary exposure 

analysis should follow recommendations of the HASPOC regarding the glutamine synthetase 

waiver request and should include estimates of glufosinate ammonium levels in drinking water. 

 

Water Considerations. The Environmental Fate and Effects Division (EFED) recently issued a 

memo updating its estimated drinking water concentrations (EDWCs) for glufosinate ammonium 

in ground water sources (D335331, J. Stone, 07-SEP-2007). However, this update does not 

change the water values used in HED’s 2003 risk assessment since the surface water EDWCs 

exceed the ground water EDWCs, and the surface water values were made use of in the HED 

risk assessment. 

Residential Exposure. 

Residential Handlers

According to a previous human health risk assessment (August 2003), potential residential (nonoccupational) exposures were anticipated as a result of applications of glufosinate ammonium to 

residential lawns. Risks were estimated for both residential handler exposures (adults) and 

residential postapplication exposures (adults and toddlers). Residential exposure was of concern 

for adults and toddlers for several exposure scenarios as a result of broadcast application of 

glufosinate ammonium to residential lawns according to the lawn renovation section of the 

Finale Super Concentrate label (EPA Reg. No. 45639-191). However, according to OPPIN 

Query, EPA Reg. No. 45639-191 was transferred from Agrevo USA to Bayer Environmental 
Page 63 of 71 

Science as EPA Reg. No. 432-954. The last accepted label in PPLS for this registration, Finale 

Super Concentrate Weed, Grass and Brush Killer, only bears directions for spot treatment in 

lawns (personal communication, James Stone, 10-DEC-2007). 

The available residential exposure and risk assessment for homeowner handlers/applicators 

combined the short-term inhalation and short-term dermal exposure estimates since the same 

toxicological endpoint was selected for both routes of exposure. An ARI approach was used to 

estimate risk to account for the different target MOEs for residential dermal (>1000) and 

inhalation (>3000) exposures. These calculations showed spot treatments to result in exposure 

levels below HED’s level of concern (ie ARIs >1) and only to exceed HED’s level of concern for 

the lawn renovation use, which is no longer supported. Once the glutamine synthetase issue is 

resolved by the HASPOC, the residential handler risk assessment will likely need revisions to 

reflect any updates to the NOAELs and UFs, but the exposure levels should not change. 

Residential Post Application

The 2003 risk assessment mentions lawn renovation uses of glufosinate ammonium which 

exceeded HED’s level of concern and that the registrant will voluntarily cancel the lawn 

renovation use. Indeed, a residential assessment of the lawn renovation use from Finale Super 

Concentrate label (EPA Reg. No. 45639-191) showed risks of concern for incidental oral and 

dermal exposures for children, and for dermal exposures for adults (D284811, J.T. 

Swackhammer, 09-AUG-2002). However, according to OPPIN Query, EPA Reg. No. 45639-

191 was transferred from Agrevo USA to Bayer Environmental Science EPA Reg. No. 432-954. 

The last accepted label in PPLS for this registration, Finale Super Concentrate Weed, Grass and 

Brush Killer, only bears directions for spot treatment in lawns (personal communication, James 

Stone, 10-DEC-2007). In accordance with the HED Exposure Science Advisory Committee 

(ExpoSAC) guidance, the registered spot treatment use is not expected to result in significant 

post application exposure and thus no residential post application risk assessment is necessary. 

Aggregate Risk Assessment. Acute, short-term, and chronic aggregate risk assessments were 

conducted for glufosinate ammonium in the 2003 assessment. Drinking water risks were 

included in the aggregate assessments using the Drinking Water Level of Comparison (DWLOC) 

approach. In the 2003 risk assessment, the acute surface water EEC (94 ppb; provided by the 

Ecological Fate and Effects Division/EFED 2003) was nearly equal to the acute DWLOCs for 

females 13-49 years old (98 ppb). The chronic surface water EEC of 43 ppb was considerably 

less than the short-term DWLOCs of 156-187 ppb for the population subgroups included in the 

short-term aggregate analysis, indicating risk levels below HED’s level of concern. However, 

the chronic surface water EEC of 43 ppb was nearly equal to the DWLOC values determined for 

the infant and children population subgroups (44-51 ppb for all infants < 1 year old, children 1-2 

years old, children 3-5 years old and children 6-12 years old). 

Revisions to the aggregate risk assessments for glufosinate ammonium should include the 

following: 1) the addition of water levels directly into the dietary analysis, thus obviating the 

need for DWLOC analysis, and 2) reconsideration of UFs and dose/endpoint selection to include 
Page 64 of 71 

recommendations of the HASPOC based on the complete toxicity database for glufosinate 

ammonium. 

 

Occupational Exposure. The 2003 glufosinate ammonium assessment presented an 

occupational risk assessment based on the highest supported use rates for cotton, bushberry, and 

rice. Subsequent to the 2003 risk assessment, Bayer CropSciences requested an amendment to 

the registered product Liberty Herbicide for an increase in the rate of a single application to 

cotton from 0.52 to 0.786 lb ai/A. Consequently, the occupational handler risk assessment for 

the cotton scenario was updated to reflect the higher use rate (D318745, M.I. Dow, 07-FEB2006). While the exposure levels from these assessments are adequate, the MOEs are likely to 

need revision, contingent on the decision of the HASPOC with regards to the glutamine 

synthetase waiver request. Once this determination is made, and the relevant toxicity endpoints 

and doses are updated, the occupational risk assessment may be revised accordingly. 

Public Health and Pesticide Epidemiology Data. A summary report listing reported incidents 

for glufosinate ammonium will be provided for the docket. The reported incidents will be 

screened in more detail during the development of the Preliminary Work Plan (PWP) for 

glufosinate ammonium. 

Cumulative Risk Assessments. The Agency has not determined whether glufosinate 

ammonium shares a common mechanism of toxicity with other chemical substances, and 

whether a cumulative assessment is warranted. The following reference contains information 

regarding determination of common mechanisms of toxicity: “Guidance for Identifying Pesticide 

Chemicals and Other Substances that have a Common Mechanism of Toxicity” (January 29, 

1999). To date, the Agency has assessed the potential for a common mechanism of toxicity for 

four groups of chemicals: organophosphates, N-methyl carbamates, S-triazines, and 

chloroacetanilides. If glufosinate ammonium is determined to share a common mechanism of 

toxicity with other substances, then methods for aggregating exposures and risks will be 

developed. Until glufosinate ammonium is scheduled for a common mechanism determination 

and a decision is made, the Agency would not a priori assume a common mechanism of toxicity 

exists for glufosinate ammonium and other substances. 

Environmental Justice. Potential areas of environmental justice concerns, to the extent 

possible, were considered in the human health risk assessment, in accordance with U.S. 

Executive Order 12898, "Federal Actions to Address Environmental Justice in Minority 

Populations and Low-Income Populations," 

http://www.eh.doe.gov/nepa/tools/guidance/Volume1/2-6-EO_12898envjustice.pdf). The Office 

of Pesticide Programs (OPP) typically considers the highest potential exposures from the legal 

use of a pesticide when conducting human health risk assessments, including, but not limited to, 

people who obtain drinking water from sources near agricultural areas, the variability of diets 

within the U.S. (including different ages), and people who may be exposed when harvesting 

crops. Should these highest exposures indicate potential risks of concern, OPP further refines the 

risk assessments to ensure that the risk estimates are based on the best available information. 
Page 65 of 71 

Registration Review Conclusions: HED has determined that toxicity and exposure databases 

for glufosinate ammonium are substantially complete. However, due to recent submissions of 

DNT and inhalation studies, it is likely that the toxicity doses and endpoints previously selected 

for glufosinate ammonium may require revisions, as well as the uncertainty factors. This would 

necessitate revisions to the dietary, residential, occupational, and aggregate risk assessments. 

However, prior to making these revisions, the issue of glutamine synthetase measurements 

should be resolved. The HED HASPOC will be consulted on this issue. 

Harmonization Issues. The Codex Alimentarius Commission has established several maximum 

residue limits (MRLs) for residues of glufosinate ammonium and its metabolites in/on various 

raw agricultural and processed commodities. The Codex MRLs are expressed in terms of 

glufosinate ammonium and its metabolites and are presented in Table 1 below. Except for tree 

nuts, almond hulls, banana, and soybean, the U.S. tolerances and Codex MRLs are not in 

harmony with respect to numerical levels. The U.S. tolerances and the Canadian MRLs are 

harmonized for field corn grain and soybeans but not other crops. All Mexican MRLs are 

harmonized with U.S. tolerances. 
Page 66 of 71 

Table 1. Comparison of U.S., Canadian, and Mexican tolerances to Codex MRLs for glufosinate 

ammonium. 

US Canada Mexico Codex 

Residue Definition: 

40CFR 180.473 

butanoic acid, 2-amino-4-

(hydroxymethylphosphinyl)-

monoammonium salt and its 

metabolites, 2-acetamido-4-

methylphosphinico-butanoic acid 

and 3-methylphosphinico-propionic 

acid, expressed as 2-amino-4-

(hydroxymethylphosphinyl)butanoic 

acid equivalents 

As an inadvertent residue: 

butanoic acid, 2-amino-4-

(hydroxymethylphosphinyl)-, 

monoammonium salt and its 

metabolite, 3-

methylphosphinicopropionic acid 

ammonium(±)-2-amino4-

(hydroxymethylphosphinyl) 

butanoate, 

including the metabolite 

propanoic acid, 3- 

(hydroxymethylphosphinyl) 

Glufosinate 

ammonium 

Sum of glufosinate-ammonium, 3-

[hydroxy(methyl)phosphinoyl]propionic 

acid, and N-acetyl-glufosinate, 

calculated as glufosinate (free acid).

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg) 

Commodity US Canada Mexico Codex 

Almond, hulls 0.50 0.5 

Apple 0.05 

Asparagus - 0.05 (*) 

Banana 0.30 0.3 0.2 

Banana, pulp 0.20 

Beans, dry white - 0.5 

Beet, sugar, molasses 5.0 

Beet, sugar, roots 0.9 0.05 (*) 

Beet, sugar, tops (leaves) 1.5 

Bushberry subgroup 13B 0.15 0.1 

(Berries and other small fruits) 

Broad bean (dry) 2 

Canola, meal 1.1 

Canola, seed 0.40 3 

(rape seed) 

 5 

(rape seed) 

Canola oil (rape seed oil), 

crude - 0.05 (*) 

Carrot - 0.05 (*) 

Cattle, fat 0.40 0.1 
Page 67 of 71 

US Canada Mexico Codex 

Cattle, meat 0.15 

0.1 0.05 (*) 

meat (from mammals other than 

marine) 

Cattle, meat byproducts 6.0 0.1; 1 (liver, kidney) 0.1 (*) 

(edible offal, mammalian) 

Citrus fruits - 0.1 

Common bean (dry) - 2 

Common bean (pods 

and/or immature seeds) - 0.05 (*) 

Corn, field forage 4.0 5 

Corn, field, grain 0.20 0.2 0.2 

(maize) 

0.1 (maize) 

Corn, field, stover 6.0 10 

(maize, fodder (dry)) 

Corn salad - 0.05 (*) 

Cotton, gin byproducts 15 

Cotton, undelinted seed 4.0 

Cottonseed oil - 3.5 

Currants, black and red - 0.5 

Egg 0.15 0.1 0.05 (*) 

Goat, fat 0.40 0.1 

Goat, meat 0.15 0.1 

Goat, meat byproducts 6.0 0.1; 1 (liver, kidney) 

Grain aspirated fractions 25 

Grape 0.05 0.05 

Hog, fat 0.40 0.1 

Hog, meat 0.15 0.1 

Hog, meat byproducts 6.0 0.1; 1 (liver, kidney) 

Horse, fat 0.40 

Horse, meat 0.15 

Horse, meat byproducts 6.0 

Lentils - 6 

Juneberry 0.10 

Lingonberry 0.10 

Milk 0.15 0.04 0.02 (*) 

Nut, tree, group 14 0.10 0.1 

Onion, bulb - 0.05 

Peas, dry - 3 3 

Pistachio 0.10 

Pome fruits - 0.05 (*) 

Potato 0.80 0.4 0.5 

Potato, chips 1.6 
Page 68 of 71 

US Canada Mexico Codex 

Potato granules/flakes 2.0 

Poultry, fat 0.15 0.1 

Poultry, meat 0.15 0.1 0.05 (*) 

Poultry, meat byproducts 0.60 0.1; 1 (liver, kidney) 0.1 (*) 

(edible offal) 

Rice, grain 1.0 1 

Rice, hull 2.0 

Rice, straw 2.0 

Salal 0.10 

Sheep, fat 0.40 0.1 

Sheep, meat 0.15 0.1 

Sheep, meat byproducts 6.0 0.1; 1 (liver, kidney) 

Soybean 2.0 2 2 2 

Soybean, hulls 5.0 

Stone fruits - 0.05 (*) 

Sunflower seed - 5 

Sunflower seed oil, crude - 0.05 (*) 

Tropical fruit and subtropical fruits, assorted – 

inedible peel- 

 0.05 (*) 

Wheat - 0.2 

Inadvertent Residues 

Barley, hay 0.40 

Barley, straw 0.40 

Buckwheat, fodder 0.40 

Buckwheat, forage 0.40 

Oat, forage 0.40 

Oat, hay 0.40 

Oat, straw 0.40 

Rye, forage 0.40 

Rye, straw 0.40 

Teosinte 0.40 

Triticale 0.40 

Wheat, forage 0.40 

Wheat, hay 0.40 

Wheat, straw 0.40 
Page 69 of 71 

Referenced Memoranda 

Glufosinate Ammonium (PC Code 128850). Section 3 Registrations for Transgenic Cotton and 

Cotton (ID# 0F06140), Trasgenic Rice (ID#0F06210), and Bushberry (ID# 2E06404). Human 

Health Risk Assessment. DP# 290086, T. Bloem, PV Shah, and M. Dow, August 7, 2003. 

Glufosinate Ammonium. Label Amendment to Increase the Registered Cotton Application Rate 

and Reduce the Plant-Back Intervals Following Application to Cotton. DP#s 318744 & 319568, 

T. Bloem, February 22, 2005. 

Glufosinate Ammonium (PC Code 128850). Label Amendment for Pre-Plant Application of 

Glufosinate Ammonium to the Transgenic and Non-Transgenic Varieties of Field Corn, Canola, 

and Soybean. Residue Chemistry Summary. DP#s 335330, 335332, and 339226, T. Bloem, 

September 12, 2007. 

 Glufosinate Ammonium – Review of Developmental Neurotoxicity Study in Rats (MRID 

46455701). DP# 312684, R.J. Mitkus, August 24, 2005. 

Glufosinate Ammonium – Review of 28-Day Inhalation Toxicity Study (MRID 47058101). DP# 

337298, L Austin, September 6, 2007. 

Glufosinate Ammonium – 3rd Report of the Hazard Identification Assessment Review Committee. 

TXR# 0051833, B. Tarplee, April 17, 2003.

Glufosinate-Ammonium – Exposure/Risk Assessment for the Use of Glufosinate-ammonium on 

Cotton at Higher Rates. DP# 318745, M.I. Dow, February 7, 2006.

Occupational and Updated Residential Exposure Risk Assessment for the use of Glufosinate 

Ammonium on Rice, Cotton, and Bushberry. DP# 284811, J.T. Swackhammer, 09-AUG-2002. 
Page 70 of 71 

V. GLOSSARY OF TERMS AND ABBREVIATIONS 

A Acre 

ai Active Ingredient 

aPAD Acute Population Adjusted Dose 

aRfD Acute Reference Dose 

BEAD Biological and Economic Analysis Division 

CDPR California Department of Pesticide Regulation 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

DCI Data Call-In 

DEEM-FCID Dietary Exposure Evaluation Model software with Food Commodity 

Intake Database 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison. 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EFED Ecological Fate and Effects Division 

EPA Environmental Protection Agency 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FQPA Food Quality Protection Act 

FWP Final Work Plan 

GENEEC Tier I Surface Water Computer Model 

HED Health Effects Division 

HIARC Hazard Identification Assessment Review Committee 

LC50 Median Lethal Concentration. A statistically derived concentration of a 

substance that can be expected to cause death in 50% of test animals. It is 

usually expressed as the weight of substance per weight or volume of 

water, air or feed, e.g., mg/l, mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be 

expected to cause death in 50% of the test animals when administered by 

the route indicated (oral, dermal, inhalation). It is expressed as a weight of 

substance per unit weight of animal, e.g., mg/kg. 

LOC Level of Concern 

LOAEL Lowest Observed Adverse Effect Level 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording and 

tracking studies submitted. 

MRL Maximum Residue Level 

NAWQA USDA’s National Water-Quality Assessment Program 

NOAEC No Observed Adverse Effect Concentration 
Page 71 of 71 

NOAEL No Observed Adverse Effect Level 

NOEC No Observed Effect Concentration 

OPP EPA Office of Pesticide Programs 

OPPIN Office of Pesticide Programs Information Network 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 

ppb Parts Per Billion 

PPLS Pesticide Product Label System 

PRZM/EXAMS Tier II Surface Water Computer Model 

RD Registration Division 

RfD Reference Dose 

SDWIS/FED Safe Drinking Water Information System/Federal 

SLUA Screening Level Usage Analysis 

SRRD Special Review and Reregistration Division 

TEP Technical End-Use Product 

TGAI Technical Grade Active Ingredient 

TREX Terrestrial Residue EXposure model 

USGS United States Geological Survey 

UF Uncertainty Factor