UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 

MEMORANDUM

DATE: 25-JUL-2012

SUBJECT: Glufosinate Ammonium

Proposed New Use of 

Pome Fruit (Crop Group 11), Stone Fruit (Crop Group 12), Olives and Sweet 

Corn.

PC Code: 128850

Decision No.: 424395

Petition No.: NA

Risk Assessment Type: Single 

chemical aggregate

TXR No.: NA

MRID No.: NA

FROM: William Donovan, Ph.D., Chemist

John Doherty, Ph.D., Toxicologist

Ana Rivera

Risk Assessment 

Health Effects

THROUGH: Michael S. Metzger

Risk Assessment Branch V (RABV)

Health Effects Division (7509P)

TO: Kathryn Montague

Sidney Jackson/Barbara Madden, RM 05

Registration Division (7505P)

The most recent human-health risk assessment for 

potential risk concerns resulting from the 

al., 15-DEC-2010). This document 

providing updated toxicological, 

and post-application), residue chemistry, 

primary changes include the following:

 Revised residue of concern definition for drinking water.

 Revised chronic EDWC based on rice uses and PFAM modeling.

 Revised dietary exposure 

NHANES/WWEIA food consumption survey

 Revised ORE assessment according to updated SOPs

Page 1 of 45

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

 POLLUTION PREVENTION

Glufosinate Ammonium. Updated Human Health Risk Assessment 

Proposed New Use of Glufosinate Ammonium in/on Citrus Fruit (Crop Group 10), 

Pome Fruit (Crop Group 11), Stone Fruit (Crop Group 12), Olives and Sweet 

DP Barcode: D387413

Registration No.: NA

Regulatory Action: Section 3 Registration

Case No.: NA

CAS No.: 60168-88-9

40 CFR: §180.473

William Donovan, Ph.D., Chemist

John Doherty, Ph.D., Toxicologist

Ana Rivera-Lupiáñez, Chemist

Assessment Branch V (RABV)

Health Effects Division (7509P)

Michael S. Metzger, Branch Chief

Assessment Branch V (RABV)

Health Effects Division (7509P)

Kathryn Montague, RM 23

Sidney Jackson/Barbara Madden, RM 05

Registration Division (7505P)

health risk assessment for glufosinate ammonium identified 

potential risk concerns resulting from the established rice use (D372623, W. Donovan 

This document updates and supersedes previous assessments

updated toxicological, dietary (food and drinking water), residenti

residue chemistry, occupational, and aggregate assessments.

primary changes include the following:

Revised residue of concern definition for drinking water.

Revised chronic EDWC based on rice uses and PFAM modeling.

exposure analysis using updated EDWC with the 

NHANES/WWEIA food consumption survey data, 2003-2008.

Revised ORE assessment according to updated SOPs.

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF CHEMICAL SAFETY AND

POLLUTION PREVENTION

Health Risk Assessment for the 

Citrus Fruit (Crop Group 10), 

Pome Fruit (Crop Group 11), Stone Fruit (Crop Group 12), Olives and Sweet 

Section 3 Registration

identified 

rice use (D372623, W. Donovan et. 

assessments,

residential (handler 

and aggregate assessments. The 
Page 2 of 45

1.0. EXECUTIVE SUMMARY

Bayer Crop Science requested a Section 3 registration for application of glufosinate ammonium 

(butanoic acid, 2-amino-4-(hydroxymethylphosphinyl)-, monoammonium salt) to citrus fruit, 

pome fruit, stone fruit, and olives; and the Interregional Research Project Number 4 (IR-4) 

requested a Section 3 registration for application of glufosinate ammonium to sweet corn. A 

summary of the human-health risk estimates resulting from the requested and registered uses of 

glufosinate ammonium is provided in this document.

Technical glufosinate ammonium is a racemic mixture of the D and L enantiomers; with the L

enantiomer being responsible for its herbicidal activity. 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 (rice, cotton, canola, sugar beet, 

corn, soybean) have been genetically engineered to express phosphiothrion-acetyltransferase

(PAT) which enables the plant to metabolize glufosinate ammonium into N-acetylglufosinate.

Toxicology and Dose-Response

The toxicology database for glufosinate ammonium is complete for current risk assessment 

purposes, including the assessment of potential increased susceptibility of infants and children.

For acute exposure durations, glufosinate ammonium is not highly toxic: it was classified into 

toxicity category III or IV for all acute toxicity studies, including dermal and eye irritation. It is 

not a dermal sensitizer. 

In the subchronic rat study, inhibition of glutamate synthetase was evident and inhibition of this 

enzyme in the brain is considered a possible mode of action resulting in neurotoxicity. However, 

inhibition of this enzyme in the liver and kidney is considered adaptive. In the chronic studies in 

the rat, increased mortality, increased occurrence of retinal atrophy, and inhibition of brain 

glutamine synthetase were observed, as were increased liver and kidney weights. In the mouse, 

increased mortality was observed, as were changes in glucose levels consistent with changes in 

glutathione levels. Increased mortality and electrocardiogram (EKG) alterations were observed in 

dogs. 

Although there was no evidence of neurotoxicity in two acute neurotoxicity studies at doses up to 

500 mg/kg/day, clinical signs of neurotoxicity were seen in several studies, including the 

subchronic, developmental, and chronic studies in rats and dogs. In addition to a variety of 

clinical signs, retinal atrophy was also observed. The rat developmental neurotoxicity study

demonstrated altered brain morphometrics at dose levels that did not cause maternal toxicity. 

Since increased fetal mortality was observed in the presence of maternal toxicity in the rabbit 

developmental study, there is evidence of qualitative increased susceptibility in fetuses. The 

reproductive toxicity study in rats indicated postnatal developmental toxicity at the highest dose 

tested (HDT) in the form of decrease in viable pups. No parental toxicity was seen at the HDT. 

Since pup mortality was observed in the absence of parental toxicity, there is evidence of 

quantitative increased susceptibility in offspring. The rat developmental toxicity study

demonstrated dilated pelvis and/or hydroureter in the offspring at the same doses that the dams 

demonstrated hyperactivity and vaginal bleeding. 
Page 3 of 45

An acceptable 28-day inhalation toxicity study demonstrated toxicity at the lowest dose tested as 

indicated by lung and bronchial effects and slight behavioral changes. 

There is no concern for mutagenic activity based on the results of several mutagenicity studies.

Glufosinate ammonium was classified as “not likely to be a human carcinogen.” There was no 

evidence of a treatment-related increase in tumors in either rats or mice.

Additional testing was conducted with the L-isomer of glufosinate ammonium (HOE 058192), 

and degradates HOE 061517 (MPP) and HOE 099730 (NAG). These compounds, tested in 

subchronic rat, mouse, and dog studies, and in developmental toxicity studies in rat and rabbit, are 

generally less toxic than the parent compound. However, HOE 058192 was found to be slightly 

more toxic than the racemic parent compound. This finding is not a concern since this isomer is 

included in the toxicity testing of the parent compound at the levels in the technical material.

Endpoints for risk assessment were selected for dietary, dermal, and inhalation scenarios. The 

FQPA Safety Factor was reduced to 1× for acute dietary exposure only; thus a standard 

uncertainty factor of 100× was used for the acute dietary risk assessment. An additional 

uncertainty factor of 10× was used for other exposure scenarios (total uncertainty factor of 1000×) 

because the studies selected for endpoint setting used LOAELs (the developmental neurotoxicity

and the 28-day inhalation studies) and did not establish NOAELs.

Residue Chemistry

The nature of the residue in plants and livestock is understood. The residues of concern in plant 

and livestock commodities are parent, glufosinate propanoic acid, and N-acetylglufosinate.

The registration requirements for magnitude of the residue in plants have been evaluated and 

deemed fulfilled. The field trials on citrus fruits, pome fruits, stone fruits, olives, and sweet corn

are adequate. An adequate number of trials were conducted reflecting the proposed use patterns 

in the appropriate geographic regions, and the appropriate commodities were collected at the 

proposed PHIs. However, the proposed use directions should specify the maximum application 

rate, the maximum number of applications, and the retreatment intervals. Samples were analyzed 

using validated analytical methods. Processing studies were conducted on the appropriate 

commodities and these results were taken into consideration in the recommended tolerance levels.

Acceptable analytical methods are available for enforcement of residue tolerances of glufosinate 

ammonium and metabolites in/on plant and livestock commodities. 

No increase in dietary burden results from the proposed uses; established tolerance levels in meat, 

milk, poultry and egg commodities remain appropriate. 

Dietary Risk (Food and Drinking Water)

The Environmental Fate and Effects Division (EFED) provided a drinking water assessment for 

glufosinate ammonium. The assessment evaluated the maximum use patterns of the established 

and proposed new uses of glufosinate ammonium. Based on maximum use patterns, the peak and 

1-in-10-year annual mean estimated drinking water concentrations (EDWCs) are 390 and 95 ppb, 

respectively, driven by the rice use. The drinking water exposure estimates are lower for all other 

uses. 
Page 4 of 45

An acute dietary exposure assessment for glufosinate ammonium was conducted for the only 

relevant population subgroup, females 13-49 years old. A screening level assessment made use of 

tolerance level residues, 100% crop treated assumptions, default processing factors and an acute 

EDWC of 390 ppb. This acute dietary exposure estimate gave results below HED’s level of 

concern (LOC), with the females 13-49 year old population subgroup at 39% aPAD. 

The chronic dietary exposure assessment for glufosinate ammonium is refined using anticipated 

residues based on average residue levels from crop field trials. Percent crop treated (%CT) 

information and processing factors, where available, were used in the assessment. The chronic 

dietary risk assessment for glufosinate ammonium at an EDWC of 95 ppb showed that chronic 

dietary risk estimates are below HED’s LOC (<100% cPAD) for infants (<1 year old), the highest 

exposed population subgroup (98% of the cPAD), as well as for the general US population (39% 

of the cPAD). 

Non-Occupational and Residential Risk

The current petition for glufosinate ammonium results in no non-occupational/residential 

exposures. Post-application short-term dermal and inhalation exposures to adult homeowners are 

possible based on the existing spot treatments to turf; however, these exposures are expected to be 

low and current Agency practice does not routinely require these assessments. In contrast, 

residential handler assessments are needed for spot treatments to turf. The inhalation margins of 

exposure (MOEs) for all potential exposure scenarios are greater than 300, the inhalation LOC. 

Similarly, the dermal MOEs for all potential exposure scenarios related to turf spot treatments are 

greater than 1000, the dermal LOC. 

Aggregate Risk

An aggregate exposure risk assessment was conducted by incorporating drinking water directly

into the dietary exposure assessment for the following scenarios: acute, chronic, and short-term

aggregate exposure. The short-term aggregate exposure risk assessment also included residential 

exposure estimates. Intermediate- and long-term residential exposures are not anticipated; 

therefore intermediate-/long-term aggregate risk assessments were not performed. Cancer 

aggregate-risk assessments were not performed because glufosinate ammonium is not likely

carcinogenic. 

Acute aggregate risk estimates are identical to the acute dietary risk estimates and do not exceed 

HED’s LOC. Chronic aggregate risk estimates are identical to the chronic dietary risk estimates 

and do not exceed HED’s LOC.

Using average food and water exposures together with residential exposures from turf spot 

treatments, the short-term aggregate MOE is estimated as 1800, which is greater than the target 

MOE of 1000. For residential exposures, only the dermal route of exposure was included in the 

aggregate analysis since potential dermal exposures are higher than potential inhalation 

exposures; it is not appropriate to aggregate the dermal and inhalation exposures since the toxicity

endpoints are different. Therefore, the short-term aggregate risk exposure estimate is not of 

concern to the Agency as it does not exceed HED’s LOC (MOEs less than or equal to 1000). 
Page 5 of 45

Occupational Exposure and Risk

Results from the assessment of all occupational handler scenarios, with the exception of 

mixer/loader/applicator (MLAP) spot treatments scenarios with mechanically pressurized 

handgun, indicate that short- and intermediate-term dermal and inhalation risks are not of concern 

to HED. Short- and intermediate-term risks for spot treatment MLAP scenarios with 

mechanically pressurized handgun are of concern to HED even with the addition of personal 

protection and/or engineering controls.

Post Occupational Exposure and Risk

Results of the glufosinate ammonium post-application exposure and dermal risk assessment for 

sweet corn indicate that an MOE of 1,050 is not achieved until Day 4 for irrigation of mature/high 

foliage plants; therefore, this post-application activity is of potential concern to the Agency at 

shorter re-entry intervals (REIs). The proposed Liberty® Herbicide label indicates an REI of 12 

hrs. This timing needs revision to achieve an MOE above the target of 1000 based upon the postapplication exposure estimates obtained for sweet corn.

Review of Human Research

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These data, which include studies from the 

Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1); the Agricultural Handler 

Exposure Task Force (AHETF) database; the Outdoor Residential Exposure Task Force (ORETF) 

database; and the Agricultural Re-entry Task Force (ARTF) database; are subject to ethics review 

pursuant to 40 CFR 26, have received that review, and are compliant with applicable ethics 

requirements. For certain studies that review may have included review by the Human Studies 

Review Board. Descriptions of data sources as well as guidance on their use can be found at 

http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html

2.0 HED Recommendations

HED recommends for a registration and tolerances for the use of glufosinate ammonium in/on 

citrus fruit, pome fruit, stone fruit, olives, and sweet corn. The specific tolerance 

recommendations are provided in Section 2.2, and label modifications are listed in Section 2.3.

2.1 Data Deficiencies

 None

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

There are adequate residue analytical methods for tolerance enforcement. Also, the methods used 

for data collection were adequate based on the method recoveries, precision and the range of 

levels tested. 
Page 6 of 45

Two analytical methods have been validated by the Analytical Chemistry Branch (ACB) for 

enforcement of the currently established tolerances: (1) method HRAV-5A was validated by 

ACB for the determination of glufosinate ammonium and glufosinate propanoic acid in/on apple, 

grape, almond, soybean seed, corn grain, and corn forage (PP# 8F3607, J. Garbus, 14-Sep-1989) 

and (2) method BK/01/99 was validated by ACB for determination of glufosinate ammonium, Nacetyl-glufosinate, and glufosinate propanoic acid in/on canola seed and sugar beet root 

(D258420, T. Bloem, 19-Aug-2000). Both methods involve extraction with water, anionexchange chromatography, derivatization with trimethylorthoacetate, silica-gel column clean-up, 

and quantification via gas chromatography with flame photometric detection (residues expressed 

as glufosinate free acid equivalents). Method BK/01/99 includes a cation ion-exchange column 

prior to derivatization which fractionates glufosinate ammonium and N-acetyl-glufosinate and 

allows for speciation of these compounds (both compounds are derivatized to the same 

compound). This step can be eliminated if separation of these two compounds is unnecessary. 

The methods do not distinguish between the D and L enantiomers of glufosinate ammonium and 

N-acetyl-glufosinate. 

Based on the similarity in the two methods and the results from the petition method validations 

(PMVs), HED concludes that adequate enforcement methods are available for sweet corn, stone 

fruit, pome fruit, citrus fruit and olive. 

2.2.2 Recommended Tolerances

The tolerance expression under 40 CFR §180.473 should be revised to read as follows: 

Tolerances are established for residues of glufosinate ammonium, including its metabolites and 

degradates, in or on the commodities in the table below. Compliance with the tolerance levels 

specified below is to be determined by measuring the sum of glufosinate ammonium (butanoic 

acid, 2-amino-4-(hydroxymethylphosphinyl) monoammonium salt) and its metabolites, 2-

(acetylamino)-4-(hydroxymethyl phosphinyl) butanoic acid, and 3-(hydroxymethylphosphinyl) 

propanoic acid, expressed as 2-amino-4-(hydroxymethylphosphinyl)butanoic acid equivalents:

Table 2.2.2 Tolerance Summary for Glufosinate Ammonium.

Commodity Proposed 

Tolerance (ppm)

Recommended

Tolerance (ppm)

Comments

Citrus (CG 10) 0.05 0.15 Fruit, citrus, group 10-10

Pome Fruit (CG 11) 0.10 0.25 Fruit, pome, group 11-10

Stone Fruit (CG 12) 0.10 0.25 Fruit, stone, group 12-12

Olives 0.05 0.15

Corn, sweet, kernels plus cob 

with husks removed

0.2 0.30

Corn, sweet, forage 4.0 1.5

Corn, sweet, stover 6.0 6.0

Plum, prune, dried 0.20 None Covered by the Stone Fruit 

tolerance.

2.2.3 Revisions to Petitioned-For Tolerances

HED recommends higher tolerance levels for citrus, pome fruit, stone fruit, and olives due to 

summation of the full LOQ for each of the three residues of concern in situations where <LOQ 
Page 7 of 45

residue levels were found. The recommended sweet corn tolerances are based on the OECD 

tolerance calculation procedures. No separate prune tolerance was recommended as residues in 

this processed commodity are covered by the stone fruit group tolerance. 

2.2.4 International Harmonization

The Codex Alimentarius Commission has not established maximum residue limits (MRLs) for 

glufosinate ammonium in/on olives and sweet corn commodities. However, for glufosinate 

ammonium in/on citrus fruit, pome fruit and stone fruit, Codex has set MRLs of 0.1, 0.05, and 

0.05 ppm, respectively. The recommended US tolerances for citrus fruit, pome fruit, and stone 

fruit, are 0.15, 0.25 and 0.25 ppm, respectively. The US tolerance values for these commodities is 

higher than the Codex MRL; therefore, harmonization of the US tolerances with the Codex MRLs 

is not possible with this petition because MRLs could be exceeded with the proposed uses. There 

are no MRLs established in Mexico or Canada for the use of glufosinate ammonium on the 

commodities under the current petition.

2.3 Label Recommendations

2.3.1 Recommendations from Residue Reviews

 Crop use pattern information should include maximum single and seasonal use rates, retreatment intervals (RTIs), and pre-harvest intervals (PHIs).

2.3.2 Recommendations from Occupational Assessment

 Short- and intermediate-term risks for mixer/loader/applicator (MLAP) scenarios with 

mechanically pressurized handgun for spot treatments on olives, citrus, pome, and stone 

fruit are of concern to the Agency even with the addition of personal protection to 

mitigate exposure such as: extra layer of clothing (coveralls), gloves and PF10R 

respirator. 

 The proposed Liberty® Herbicide label indicates an REI of 12 hrs; however, this timing 

needs revision to 4 days based upon the post-application exposure estimates obtained for 

sweet corn in order to achieve an MOE which exceeds the target MOE = 1000.

2.3.3 Recommendations from Residential Assessment

 Since glufosinate ammonium is not a restricted use pesticide it is recommended that all 

labels that could potentially be used by homeowners clearly restrict lawn/turf uses to 

spot treatments only. The maximum application rate should not exceed 4 fl ounces per 

gallon of water per 1,000 square feet. 

3.0. Introduction

The nomenclature and physicochemical properties of glufosinate ammonium are presented below 

in Tables 3.1 and 3.2.

3.1. Chemical Identity
Page 8 of 45

TABLE 3.1. Test Compound Nomenclature.

Compound

P

NH2

O

OH

O

CH3-O

NH4+

Common name Glufosinate ammonium

Company experimental name AE F039866, HOE 039866

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

CAS name 2-amino-4-(hydroxymethylphosphinyl)butanoic acid monoammonium salt

CAS registry number 77182-82-2

End-use product (EP) RELY 200 SC

Compound

Common name Glu-PPA, AE F061517, Glufosinate propanoic acid, HOE 061517, MPP

Chemical name 3-methylphosphinico-propionic acid or

3-(hydroxymethylphosphinyl) propanoic acid

Compound

Common name Glu-NAG, AE F085355, N-acetylglufosinate, HOE 099730, NAG

Chemical name 2-(acetylamino)-4-(hydroxymethyl phosphinyl) butanoic acid

Compound

Common name HOE 064619, Glufosinate acetic acid, MPA

Chemical name 2-methyl phophinico acetic acid

3.2. Physical/Chemical Characteristics

Table 3.2. Physicochemical Properties of the Technical Grade Test Compound.

Parameter Value1

Melting point/range (°C) 215-218

pH 4.7

Density (g/cm3) 1.32

Water solubility (g/L at pH 5) 1370

Solvent solubility at room temp (g/L) methanol: 5.73; DMSO: 0.049; polyethylene glycol: 0.047;

acetonitrile, toluene, acetone, ethyl acetate, and hexane: <0.00025

P

HO

O CH3

OH

O

P

HO

O CH3

O

OH

NH

CH3

O
Page 9 of 45

Table 3.2. Physicochemical Properties of the Technical Grade Test Compound.

Parameter Value1

Vapor pressure at 25 °C (mPa) 0.031

Dissociation constant, pKa 9.15

Octanol/water partition coefficient (Log KOW) -4.01

UV/visible absorption spectrum (nm) >190

1

Source: 46573701.der.doc, T. Bloem, 2005

Based on its physical-chemical properties, glufosinate ammonium is highly water soluble, nonvolatile, and a weak acid. 

3.3 Pesticide Use Pattern

Table 3.3 summarizes the proposed use patterns for the new crop uses requested in the current 

petitions.

Table 3.3 Summary of Directions for Use of Glufosinate Ammonium (2.34 lb/gal; EPA Reg. No. 352-515).

1

Applic. 

Timing, Type, 

and Equip.

Applic. Rate 

(lb ai/A)

Retreat. 

Interval 

(days)

Max. No. 

Applic. Per 

Season

Max. Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days) Adjuvant Use Directions and Limitations

Broadcast, 

banded or 

spot treatment

Stone Fruit Do not apply this 

product through 

any type of 

irrigation system.

Do not apply this 

product aerially.

Do not graze, 

harvest, and/or 

feed treated 

orchard cover 

crops to livestock.

Do not make spot 

spray applications 

to suckers.

1.5 28 2 3.0 14 non-ionic 

antifoam2

Pome Fruit

1.5 14 3 4.5 14 non-ionic 

antifoam2

Citrus

1.5 14 3 4.5 14 non-ionic 

antifoam2

Olives

1.5 14 3 4.5 14 non-ionic 

antifoam2

Foliar 

treatment

Transgenic Sweet Corn

Must be applied 

with ammonium 

sulfate.

0.365 14 2 0.73 50 None

1 The listings in bold are not in the label but correspond to the field trial use patterns.

2 A non-ionic antifoam adjuvant may be added.

See Section 2.3 for recommended modifications to the proposed label.

3.4 Anticipated Exposure Pathways

The Registration Division has requested an assessment of human health risk to support the 

proposed new uses of glufosinate ammonium in/on a variety of crops. Humans may be exposed 

to glufosinate ammonium in food and drinking water, since it may be applied directly to growing 

crops and application may result in glufosinate ammonium reaching surface and ground water 

sources of drinking water. There are registered residential turf uses (limited to spot treatments) 
Page 10 of 45

that may lead to homeowner exposures. In an occupational setting, applicators may be exposed 

while handling the pesticide prior to application, as well as during application. There is a 

potential for post-application exposure for workers re-entering treated fields. 

Risk assessments have been previously conducted for glufosinate ammonium and the only new 

toxicity study received since the last risk assessment was the immunotoxicity study, which 

demonstrated effects only at higher doses than selected as points of departure in the earlier risk 

assessments. A detailed description of the toxicity data and metabolism information may be 

found in the risk assessment dated 12/15/2010 (W. Donovan et. al., D372623). The current risk 

assessment considers all of the aforementioned exposure pathways based on the proposed new 

uses of glufosinate ammonium, but also considers the existing new uses as well, particularly for 

the dietary and residential exposure assessments. 

3.5 Consideration of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

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://homer.ornl.gov/nuclearsafety/nsea/oepa/guidance/justice/eo12898.pdf).

As a part of every pesticide risk assessment, OPP considers a large variety of consumer subgroups 

according to well-established procedures. In line with OPP policy, HED estimates risks to 

population subgroups from pesticide exposures that are based on patterns of that subgroup’s food 

and water consumption, and activities in and around the home that involve pesticide use in a 

residential setting. Extensive data on food consumption patterns are compiled by the USDA 

under the National Health and Nutrition Examination Survey/“What We Eat in America” 

(NHANES/WWEIA), and are used in pesticide risk assessments for all registered food uses of a 

pesticide. These data are analyzed and categorized by subgroups based on age, season of the 

year, ethnic group, and region of the country. Additionally, OPP is able to assess dietary

exposure to smaller, specialized subgroups and exposure assessments are performed when 

conditions or circumstances warrant. Whenever appropriate, non-dietary exposures based on 

home use of pesticide products and associated risks for adult applicators and for toddlers, youths, 

and adults entering or playing on treated areas post-application are evaluated. Further 

considerations are currently in development as OPP has committed resources and expertise to the 

development of specialized software and models that consider exposure to bystanders and farm 

workers as well as lifestyle and traditional dietary patterns among specific subgroups.

4.0 HAZARD CHARACTERIZATION

The existing toxicological database for glufosinate ammonium is adequate to support the existing 

and proposed uses. The registrant recently submitted an acceptable immunotoxicity study that 

previously had been identified as a data gap (D390963, J. Doherty, 28-OCT-2011). The 

following information includes summaries of prior assessments (D372623, W. Donovan et. al., 

15-DEC-2010).

4.1 Summary of Toxicological Effects

There are several pharmacokinetic studies with glufosinate and they render similar results. 

Glufosinate is eliminated via the excreta with 95-98% in the first 24 hours. The feces is the major 

route of excretion with 88% in males and 84% in females of the administered dose recovered in 
Page 11 of 45

the feces. Parent compound (~88% in males and ~74% in females) was the principle compound 

found in the excreta indicated that glufosinate is poorly absorbed from the gastro intestinal tract. 

The only metabolite found at > 1% of the administered dose was HOE 061517 (representing < 2% 

of the dose) in both the urine and feces. Tissue retention of label resulting from administration of 

radio labeled glufosinate was not remarkable in the kidneys, liver, or gonads with residual values 

not much above background level following a single dose; more was found following repeated 

dosing. 

For subchronic toxicity in rats, inhibition of glutamate synthetase was noted at the LOAEL. The 

HED Hazard Identification Assessment Review Committee (HIARC, HED Document TXR No.: 

0051833, April 17, 2003) concluded that the changes in brain glutamine synthetase activity are of 

significant concern for possible neurotoxicity and/or expression of clinical signs. However, the 

alterations in liver and kidney glutamate synthetase are considered an adaptive response. The 

primary effects in the mouse subchronic study were increased liver and kidney weights with 

increases in serum aspartate amino transferase and alkaline phosphatase. 

In the chronic studies in the rat, inhibition of brain glutamine synthetase, increased mortality, 

and increased occurrence of retinal atrophy were noted, as were increased liver and kidney

weights. In the mouse, increased mortality was noted, as were changes in glucose levels 

consistent with changes in glutathione levels. Increased mortality and electrocardiogram (EKG) 

alterations were observed in dogs. There was no evidence of a treatment-related increase in 

tumors in the rat or mouse carcinogenicity studies.

The developmental toxicity study in the rat produced dilated renal pelvis and/or hydroureter in the 

fetuses at levels that produced significant increases in hyperactivity and vaginal bleeding in dams. 

In the rabbit, decreased fetal body weight and increased mortality were observed at 20 mg/kg/day, 

while in rabbit dams, decreased food consumption, body weight, and body weight gain were 

observed at 20 mg/kg/day. Since increased fetal mortality was observed in the presence of less 

severe maternal toxicity in the rabbit developmental study, there is evidence of qualitative

increased susceptibility in fetuses.

The reproductive toxicity study in rats indicated postnatal developmental toxicity at the highest 

dose tested (HDT) in the form of decrease in viable pups. No parental toxicity was seen at the 

HDT. Since pup mortality was observed in the absence of parental toxicity, there is evidence of 

quantitative increased susceptibility in offspring. However, the susceptibility was only observed 

at the highest dose tested, which is 3.3 times higher than the point of departure used for the risk 

assessment.

There were indications of neurotoxicity in several studies. Of particular concern is that the 

developmental neurotoxicity study demonstrated alterations in brain morphometrics in the adult 

offspring exposed in utero or during lactation at dose levels not associated with maternal toxicity. 

Retinal atrophy was observed in the rat oral subchronic study. In the 90-day dietary neurotoxicity

study, increases in the incidence of decreased exploratory activity, decreased alertness, and 

decreased startle response, increased incidence of fearfulness, increased pain response and 

meiosis were reported. The subchronic dermal toxicity study indicated aggressive behavior, a 

high startle response and piloerection. The 28-day subchronic inhalation study demonstrated 

tono-clonic convulsions at the high dose in at least some males. However, in a 37-day dietary

neurotoxicity study, there was no evidence of neurotoxicity at doses up to 143.3 mg/kg/day. 

There was no evidence of neurotoxicity in two acute neurotoxicity studies at doses up to 500 

mg/kg/day. Also, there was no evidence of neurotoxicity in White Leghorn hens following an 
Page 12 of 45

acute dose of up to 10000 mg/kg. Changes in glutamine synthetase levels were observed in liver, 

kidney, and brain in rats. The altered electrocardiograms seen in the dog studies imply a possible 

neuromuscular effect. 

A 28-day inhalation toxicity study with glufosinate ammonium generated from a powder 

technical grade product is available but it is classified as unacceptable due to the particle size 

exceeding guideline criteria. This study indicates a concern for exposure via the inhalation route 

because it suggested that animals are more sensitive to effects by the inhalation route. A later 

second 28-day inhalation toxicity study was provided but this study assessed an aerosol generated 

from an aqueous technical product. The study was determined to have atmospheric particles 

within the guideline criteria and was classified as Acceptable/Non-Guideline. It was considered 

non-guideline because it was for only 28 and not 90 days duration. The LOAEL was 

unexpectedly greater than the previous study with the unacceptable particle size. HED considers 

that differences in pH of each test material may contribute to the differences in expression of 

toxicity since the first study assessed a powder with near neutral pH and the second study

assessed an aqueous preparation with pH of 4.9. The pH conditions of the test material regulate 

the conversion of ammonium to ammonia; further, the potential for glufosinate to inhibit 

ammonia clearance may amplify the toxicity of inhaled ammonia.

There is no concern for mutagenic activity in several studies including: Salmonella E. Coli, in 

vitro mammalian cell gene mutation assays, mammalian cell chromosome aberration assays, in 

vivo mouse bone marrow micronucleus assays, and unscheduled DNA synthesis assays.

There is also no concern for immunotoxicity based on review of the series 870.7800 

immunotoxicity study. 

Consistent with the 2003 risk assessment (D290086, T. Bloem et. al., 07-AUG-2003) and 

ToxSAC recommendation (J. Kidwell, 29-JUN-2010), a dermal absorption factor of 9% was 

assumed, based on a dermal absorption study in male rats (D289836, B. Daiss, 17-JUN-2003). 

4.2 Safety Factor for Infants and Children (FQPA Safety Factor)

When the DNT study is used as an endpoint for risk assessment, an extra 10× database 

uncertainty (UFL) factor is applied because the DNT study did not demonstrate a NOAEL for 

altered brain morphometrics. This additional uncertainty factor will also account for indications 

of increased qualitative or quantitative sensitivity evident in the rat and rabbit developmental 

studies, and the rat multigenerational reproduction study. Similarly, a UFL was applied to the 

inhalation exposure scenarios because the 28-day inhalation study in the rat did not identify a 

NOAEL. The toxicity and exposure databases for glufosinate ammonium are otherwise complete. 

Acute, subchronic, and developmental neurotoxicity studies are available, and all endpoints used 

in this risk assessment are protective of neurotoxic effects when the extra 10× UFL is applied. 

The dietary, occupational, and residential assessments are based on reliable data and will not 

underestimate exposure. 

4.2.1 Completeness of the Toxicology Data Base 

The toxicity data base for the evaluation sensitivity/susceptibility to infants and children is 

complete. No additional studies are required at this time. The toxicity data base consists of acute 
Page 13 of 45

and subchronic neurotoxicity screen studies, a developmental neurotoxicity study, rat and rabbit 

developmental studies, a rat multi-generation reproduction study and an immunotoxicity study. 

4.2.2 Evidence of Neurotoxicity

A critical indication of neurotoxicity was evident in the developmental neurotoxicity study where 

alterations in brain morphometrics in the adult offspring were demonstrated. 

The clinical signs seen in rat or dog studies were varied and included hyperactivity, aggressive 

behavior, tonoclonic convulsion, piloerection, high startle response, and retinal atrophy. In a 90-

day dietary neurotoxicity study, increases in the incidence of decreased exploratory activity, 

decreased alertness, decreased startle response, increased incidence of fearfulness, increased pain 

response and meiosis were observed. 

4.2.3 Evidence of Sensitivity/Susceptibility in the Developing Young Animal

In the DNT, alterations in brain morphometrics in adults following in utero exposure was evident 

at the lowest dose tested and at a dose level where there was no maternal toxicity. Thus, there is 

evidence of quantitative increased sensitivity in the rat. 

In the multi-generational reproductive toxicity study in rats, pup mortality was observed in the 

absence of parental toxicity. Thus, there is further evidence of quantitative increased 

susceptibility in offspring in rats. However, the susceptibility was only observed at the highest 

dose tested, which is 3.3× higher than the point of departure used for the risk assessment.

In the rabbit, decreased fetal body weight and increased mortality were observed at 20 mg/kg/day, 

while in rabbit dams, decreased food consumption, body weight, and body weight gain were 

observed at 20 mg/kg/day. Since increased fetal mortality is more severe that the responses in the 

dams, there is evidence of qualitative increased susceptibility in the rabbit offspring.

The developmental toxicity study in the rat produced dilated renal pelvis and/or hydroureter in the 

offspring at levels that produced significant increases in hyperactivity and vaginal bleeding in 

dams. Since effects occurred in the pups and dams at the same dose, this study is not considered 

to demonstrate either increased qualitative or quantitative sensitivity in the rat. 

4.2.4 Residual Uncertainty in the Exposure Database. 

There are no residual uncertainties in the exposure database. Although the chronic dietary

exposure estimates are partially refined, HED does not believe that the exposure estimates are 

underestimated. These assumptions and refinements are detailed in Section 5.4.3. With limited 

monitoring data available, upper-bound assumptions were used to determine exposure through 

drinking water sources. 

4.3 Toxicity Endpoint and Point of Departure Selections

There have been no changes to the prior dose-response assessment, recommendations for 

combining routes of exposure, or the cancer classification. Table 4.3.1 presents a summary of the 

toxicological doses and endpoints used in the dietary, residential, and occupational risk 

assessments. A 10X uncertainty factor, attributable to the DNT study not demonstrating a 

NOAEL, should be applied to chronic dietary and residential dermal assessments. For 
Page 14 of 45

occupational and residential inhalation exposure assessments, a 10X database uncertainty factor 

should be applied due to the inhalation study not demonstrating a NOAEL.

Table 4.3.1 Summary of Toxicological Doses and Endpoints for Glufosinate Ammonium

for Use in Dietary and Non-Occupational and Occupational Human Health Risk 

Assessments

Exposure/

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Acute Dietary 

(General 

Population, 

including 

Infants and 

Children)

An endpoint attributable to a single exposure was not available from the toxicity studies, including 

the developmental toxicity and developmental neurotoxicity studies.

Acute Dietary

(Females 13-

49 years of 

age)

NOAEL = 

6.3 

mg/kg/day

UFA=10×

UFH=10×

FQPA SF= 1×

Total UF = 100×

Acute RfD = 

0.063 

mg/kg/day

aPAD=0.063 

mg/kg/day

Developmental Toxicity Study in Rabbits

LOAEL = 20 mg/kg/day based on 

increased fetal deaths.

Chronic 

Dietary 

(All 

Populations)

NOAEL= 6 

mg/kg/day

UFA=10×

UFH=10×

FQPA SF = UFL = 

10×

Total UF = 1000×

Chronic RfD = 

0.006 

mg/kg/day

cPAD = 0.006 

mg/kg/day

“Weight of evidence” approach from four 

studies. Rat subchronic and chronic 

studies with the LOAEL based on 

inhibition of brain glutamate synthetase. 

A dog chronic study with the LOAEL 

based on altered electrocardiogram and 

mortality. The rat developmental 

neurotoxicity study with a LOAEL

(without a NOAEL, basis for UFL) based 

on altered morphometrics in the offspring 

as adults.

Incidental Oral

Short-Term (1-

30 days) and 

Intermediate 

term (1-6 

months)

LOAEL= 14 

mg/kg/day

(LDT)

UFA=10×

UFH=10×

FQPA SF= UFL= 

10×

Total UF = 1000×

Residential 

LOC for MOE 

= 1000

Developmental Neurotoxicity Study in 

Rats

LOAEL = 14 mg/kg/day based on brain 

morphometric changes at PND 72. No 

NOAEL identified.

Dermal 

Short-Term (1-

30 days), and 

IntermediateTerm (1-6 

months) 

LOAEL= 14 

mg/kg/day

(LDT)

UFA=10×

UFH=10×

FQPA SF=UFL= 

10×

Total UF = 1000×

Residential and 

Occupational 

LOC for MOE 

= 1000 for 

short and 

intermediateterm exposures

Developmental Neurotoxicity Study in 

Rats

LOAEL = 14 mg/kg/day based on brain 

morphometric changes at PND 72. No 

NOAEL identified.
Page 15 of 45

Table 4.3.1 Summary of Toxicological Doses and Endpoints for Glufosinate Ammonium

for Use in Dietary and Non-Occupational and Occupational Human Health Risk 

Assessments

Exposure/

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Inhalation 

Acute, ShortTerm (1-30 

days), 

intermediate 

(1-6 months)

LOAEL=12.5 

mg/kg/day 

(56 mg/m3) 

UFA= 3×

UFH=10×

FQPA SF=UFL = 

10×

Total UF = 300×

Residential and 

Occupational 

LOC for MOE 

= 300 for short 

and 

intermediate 

term

28-day Inhalation Study (MRID 

47058101) 2007

LOAEL = 12.5 mg/kg/day based on 

lung/bronchial congestion and increased 

lung/bronchi weight in female rats and 

increased kidney and liver weights.

Cancer (oral, 

dermal, 

inhalation)

Classification: “Not likely to be Carcinogenic to Humans” based on the absence of significant 

tumor increases in two adequate rodent carcinogenicity studies.

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = 

uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity 

among members of the human population (intraspecies). UFL = use of a LOAEL to extrapolate a NOAEL. FQPA SF 

= FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = reference dose. MOE = 

margin of exposure. LOC = level of concern. N/A = not applicable.

5.0 Dietary Exposure and Risk Assessment

5.1 Residues of Concern Summary and Rationale

No plant or animal metabolism data were submitted with the subject petitions. The nature of the 

residue of glufosinate ammonium in livestock and plants has been adequately delineated. HED 

has previously reviewed metabolism studies conducted with nontransgenic (corn, soybean, apple, 

and lettuce; 8F3607, J. Garbus, 14-Oct-1988 & 8-Aug-1990) and transgenic (corn, soybean, sugar 

beet, canola, and rice; D227386, M. Rodriguez,7-Mar-1996; D257629, T. Bloem, 9-Jul-1999; 

45204405.der.wpd) crops. The transgenic corn, soybean, sugar beet, canola, and rice investigated 

in the metabolism studies were engineered to express PAT which acetylates glufosinate 

(herbicidally active) to form N-acetyl-glufosinate (not herbicidally active). 

Based on the metabolism and magnitude of the residue studies, the Metabolism Assessment Review 

Committee (MARC) concluded that the residues of concern in plants and livestock, for tolerance 

expression and risk assessment purposes, are glufosinate ammonium, N-acetyl-glufosinate, and 

glufosinate propanoic acid (D282757, T. Bloem, 9-May-2002). HED concludes that the results from 

the currently available metabolism studies may be translated to citrus fruit, pome fruit, stone fruit, 

olive, and sweet corn.

The residue of concern in drinking water was considered at a meeting of the Residue of Concern 

Knowledgebase Subcommittee (ROCKS) (D397644, I. Negrón-Encarnación, 29-MAR-2012). 

The ROCKS noted that MPP may have different toxicity than the parent and is likely to have a 

lower toxicity, but not so low that it could be definitely excluded from consideration. After the 
Page 16 of 45

ROCKS meeting, the team consulted with Health Effects Division Toxicology Science Advisory

Council (ToxSAC) regarding the toxicity of MPP (J. Kidwell, 02/21/2012). The consensus of the 

ToxSAC was that glufosinate ammonium and MPP show different toxicities, such that they

should not be aggregated. Because MPP is less toxic than glufosinate ammonium and should not 

be aggregated with it, if MPP EDWCs are not more than 4-5× greater than those for glufosinate, 

the risk assessment for the parent will be protective of any toxicity associated with exposure to 

MPP in drinking water. Indeed, the Environmental Fate and Effects Division has indicated that 

the acute and chronic concentrations of MPP are not likely to be more than twice the 

corresponding levels of glufosinate ammonium in drinking water (see Table 5.1). Therefore, a 

quantitative risk assessment for MPP in drinking water is not needed. Table 4.2.1 summarizes the 

nature of the residue decisions for glufosinate ammonium.

Table 5.1. Summary of Metabolites and Degradates to be included in the Risk 

Assessment and Tolerance Expression

Matrix Residues included in Risk 

Assessment

Residues included in 

Tolerance Expression

Plants Primary and 

Rotational Crops

Glufosinate ammonium,

glufosinate propanoic acid, 

and N-acetylglufosinate

Glufosinate ammonium,

glufosinate propanoic acid, 

and N-acetylglufosinate

Livestock Ruminant Glufosinate ammonium,

glufosinate propanoic acid, 

and N-acetylglufosinate

Glufosinate ammonium,

glufosinate propanoic acid, 

and N-acetylglufosinate

Swine

Poultry

Drinking Water Glufosinate ammonium 1 Not applicable

1

Since MPP has a different toxicity profile than the parent compound, it should not be aggregated with the parent. 

Because MPP EDWCs are not significantly greater than those for glufosinate, the risk assessment for the parent is

protective of any toxicity associated with exposure to MPP in drinking water, and a quantitative risk assessment for 

MPP is not required.

5.2 Food Residue Profile

A review of the residue chemistry data submitted in conjunction with the current petition is 

provided in D372625 (I. Negrón-Encarnación, 31-AUG-2010). Specific information regarding 

the magnitude of the residue data and tolerance derivations is provided in Appendix B. 

No adjuvant effects were discernible in any of the field trials, which are supported by adequate 

storage stability data. The trials were adequate with respect to number and location. 

Processing studies were performed for orange, plum and olive commodities. Details concerning 

the processing studies are in the following reviews: orange (47915706.der.wpd), plum 

(47915707.der.wpd) and olive (47915708.der.wpd). These studies are considered acceptable and 

demonstrated no concentration in any processed commodity except for prune, where concentration 

factors for GA, MPP, and NAG were <1.0×, 2.5×, and <1.0×, respectively. Multiplying the field 

trial HAFT values for plum by the concentration factors for prune gives: <0.05 ppm × <1.0 + 

0.0655 ppm × 2.5 + <0.05 ppm × <1.0 = <0.26 ppm. Because the residue concentration in prunes 

is covered by the plum RAC tolerance level of 0.25 ppm, no separate prune tolerance is needed. 
Page 17 of 45

Except for sweet corn, there are no livestock feedstuffs associated with the proposed new use 

crops. Inclusion of sweet corn does not result in an increase in the dietary burden from what was 

previously determined (D271110, T. Bloem, 20-June-2002). Accordingly, the established 

tolerances for livestock commodities remain adequate and no revisions to these values are needed.

Sweet corn is the only proposed crop to which plant back intervals (PBIs) apply. The Liberty 

Herbicide label indicates that plant rotation to other crops after treatment of sweet corn can occur 

with a PBI of 120 days with the exception of small cereal grains, for which a PBI of 70 days is 

allowed. Based on the results from the confined and field rotational studies, HED concludes that 

the proposed rotational crop restrictions are appropriate for sweet corn. 

5.3 Water Residue Profile

The following information was provided by EFED (D372624, C. Peck, 22-JUN-2010; D368799, 

C. Peck, 07-JUL-2010; D381992, C. Peck, 20-OCT-2010; and D387412, C. Peck, 30-MAY2012). 

Environmental Fate Assessment: Environmental fate studies indicate glufosinate-ammonium is 

relatively stable and is very mobile (Kd = 1.5; Koc = 173; water solubility 1370 g/liter). It 

dissipated with a first order half-life ranging from 4.3 – 10.3 days on bare ground and 8 – 30 days 

on cropped fields following a single application. The main degradation pathway in water and soil 

is via microbial action, metabolizing primarily to CO2, HOE 061517 [MPP], 2-methylphosphinico 

acetic acid (HOE 064619), and 2-acetamido-4-methylphosphinico-butanoic acid. Aerobic soil 

metabolism produced a half-life of approximately 4 – 23 days; metabolite concentrations peaked 

at 3 weeks and then began to decline. Anaerobic soil metabolism produced a half-life of 56 days. 

The aerobic aquatic metabolism half-life was 64 days in gravel pit water sand sediment. 

Glufosinate may leach to ground water under certain conditions (such as in areas of sandy soils 

with high permeability and shallow ground water). Degradates HOE 061517 (Kd = 0.7 and Koc = 

84) and N-acetyl-glufosinate (Kd = 0.8) are more mobile than the parent, and may also be 

expected to leach to ground water. However, the potential for degradate HOE 064619 to leach to 

ground water is much lower because of its higher adsorption coefficient (Kd = 24).

Ground and Surface Water Estimated Drinking Water Concentrations (EDWCs): EFED 

estimated acute EDWCs for glufosinate-ammonium and MPP using the refined Tier I Rice Model 

and Pesticide Flooded Application Model (PFAM) [version 0.70] without the index reservoir. To 

estimate chronic EDWCs, the acute concentrations from PFAM without the index reservoir were 

assumed to degrade over a 365-day period, using aerobic aquatic degradation half-lives; thus

allowing calculation of average concentrations over a one-year period. This method results in

chronic values approximately 76% and 3% lower than the acute values for glufosinate-ammonium 

and MPP, respectively. 

Previous analyses from EFED demonstrated that the maximum acute and chronic EDWCs for 

glufosinate ammonium arise from the rice uses; these values being nearly an order of magnitude 

higher than the values from any other crop use of glufosinate ammonium (DP 372624, C. Peck, 

6/22/2010 & DP 381992, C. Peck, 10/20/2010). Thus, EFED conducted a comprehensive 

refinement of the drinking water assessment for the rice use of glufosinate ammonium, with the 

expectation that the resulting values should be protective of other uses. 

Table 5.3 summarizes the PFAM EDWCs for glufosinate ammonium and MPP based on the rice 
Page 18 of 45

use patterns, as provided by EFED. Most of the application scenarios result in lower values for 

MPP than for glufosinate ammonium, although the maximum chronic EDWC for MPP is 

approximately 2x higher than the corresponding value for glufosinate ammonium: 177 and 95 

ppb, respectively. Because glufosinate ammonium is considerably more toxic than MPP, and 

these compounds have sufficient differences in toxicity that precludes aggregation, glufosinate 

ammonium EDWCs are protective of MPP EDWCs. Accordingly, for purposes of acute and 

chronic dietary analyses, the recommended glufosinate ammonium EDWCs are 390 and 95 ppb, 

respectively.

Table 5.3. EDWCs for glufosinate-ammonium and MPP from rice use derived using 

PFAM (maximum values appear in bold).

Use rate, Number of apps, retreatment 

interval, water holding period, application 

timing

Acute EDWC 

(μg/L)

Chronic EDWC1

(μg/L)

4” 8” 4” 8”

Glufosinate-ammonium

1.46 lbs ai/acre, 1, NA, 7 days, dry 173 86 42 21

0.73 lbs ai/acre, 2, 10, 30, dry and flooded2 NA 320 NA 78

0.73 lbs ai/acre, 2, 10, 55, dry and flooded2

390 NA 95 NA

0.89 lbs ai/acre, 1, NA, 7 days, dry 106 53 26 13

0.66 lbs ai/acre, 1, NA, 7 days, dry 74 38 18 9

0.44 lbs ai/acre, 2, 10 days, 7 days, dry 88 45 22 11

0.44 lbs ai/acre, 2, 10 days,7 days, flooded NA 375 NA 92

MPP

1.46 lbs ai/acre, 1, NA, 7 days, dry 5.7 2.9 5.5 2.8

0.73 lbs ai/acre, 2, 10, 30, dry and flooded2 NA 88 NA 85

0.73 lbs ai/acre, 2, 10, 55, dry and flooded2

183 NA 177 NA

0.89 lbs ai/acre, 1, NA, 7 days, dry 3.5 1.8 3.4 1.7

0.66 lbs ai/acre, 1, NA, 7 days, dry 2.2 1.1 2.1 1.1

0.44 lbs ai/acre, 2, 10 days, 7 days, dry 3.0 1.5 2.9 1.5

0.44 lbs ai/acre, 2, 10 days,7 days, flooded NA 45 NA 44

1. Chronic EDWC calculated by taking acute EDWC and allowing it to degrade for 365 days, using the aerobic aquatic 

degradation half-life, and then taking the average value over the 365-day period.

2. For this scenario the first application is made to a dry field, while the second application is made to a flooded field.

NA – not allowed.

5.4. Dietary Risk Assessment

Acute and chronic dietary (food + drinking water) exposure analyses for glufosinate ammonium 

were conducted by HED (D402741, W. Donovan, 19-JUN-2012). Glufosinate ammonium acute 

and chronic dietary exposure assessments were conducted using the Dietary Exposure Evaluation 

Model software with the Food Commodity Intake Database DEEM-FCIDTM, Version 3.10, which 

incorporates consumption data from USDA’s National Health and Nutrition Examination 

Survey/“What We Eat in America” (NHANES/WWEIA) dietary survey conducted in 2003-2008. 

The 2003-2008 data are based on the reported consumption of individuals over two nonconsecutive survey days. 

5.4.1 Acute Dietary Exposure/Risk
Page 19 of 45

Residue Data Used for Acute Assessment: Established and recommended tolerance level residues 

were used for the acute analysis, along with default processing factors, and 100% crop treated 

assumptions (unrefined analysis). 

Results of Acute Dietary Exposure Analysis: An unrefined acute dietary risk assessment for 

glufosinate ammonium at the EDWC of 390 ppb showed that acute dietary risk estimates are 

below HED’s level of concern (i.e. <100% aPAD) for the relevant population subgroup, females 

13-49 years old (39% aPAD). 

5.4.2 Chronic Dietary Exposure/Risk

The chronic dietary exposure assessment for glufosinate ammonium is refined using anticipated 

residues based on average residue levels from field trial studies. Average %CT information and 

processing factors, where available, were used in the assessment. There were no PDP monitoring 

data available for glufosinate ammonium.

Results of Chronic Dietary Exposure Analysis: The chronic dietary risk assessment for 

glufosinate ammonium at an EDWC of 95 ppb showed that chronic dietary risk estimates are 

below HED’s level of concern (i.e. <100% cPAD) for all population subgroups, with the highest 

exposed population subgroup [all infants (<1 year old)] at 98% of the cPAD, and the U.S. 

Population at 39% of the cPAD.

The results of the dietary exposure analyses are reported in Tables 5.4.2. 

Table 5.4.2. Summary of Dietary Exposure and Risk for Glufosinate Ammonium [Acute 

EDWC of 390 ppb, Chronic EDWC of 95 ppb]. 

Population Subgroup1

DEEM Acute Dietary Analysis,

95th Percentile

DEEM Chronic Dietary Analysis

Exposure 

(mg/kg/day)

% aPAD Exposure 

(mg/kg/day)

% cPAD

General U.S. Population

NA2 NA2

0.002324 39

All Infants (< 1 year old) 0.005887 98

Children 1-2 years old 0.004387 73

Children 3-5 years old 0.003447 57

Children 6-12 years old 0.002261 38

Youth 13-19 years old 0.001706 28

Adults 20-49 years old 0.002203 37

Adults 50-99 years old 0.002202 37

Females 13-49 years old 0.024401 39 0.002195 37

1 Values for the population with the highest risk for each type of risk assessment are bolded. 

2 NA = Not Applicable

5.4.3 Anticipated Residue and Percent Crop Treated (%CT) Information

The DEEM-FCID chronic analysis was performed using anticipated residues (ARs) from field 
Page 20 of 45

trial data, processing factors and updated %CT information. The DEEM default processing 

factors were used for all commodities except apple juice, pear juice, grape juice, and raisins, for 

which factors derived from the processing studies were used. 

Percent Crop Treated: One hundred percent crop treated values were used for all proposed new 

uses. The following average percent crop treated estimates (BEAD SLUA, 19-MAR-2012) were 

used in the chronic dietary analysis for crops that are currently registered for glufosinate 

ammonium: almond: 15%; blueberry: 5%; field corn, 5%; grape, 15%; pecan, 1%; potato, 10%; 

soybean, 1%; walnut, 10%; canola, 25%; cotton, 5%; filbert, 10%; pistachio, 20%; and rice, 1%.

6.0 Residential (Non-Occupational) Exposure/Risk Characterization

Glufosinate ammonium is not a restricted use pesticide (RUP). There are no proposed residential 

uses associated with this petition ; however, there are existing residential turf uses that have been 

reassessed in this document to reflect updates to HED’s 2012 Residential SOPs along with policy

changes for body weight assumptions. The revision of residential exposures will impact the 

human health aggregate risk assessment for glufosinate ammonium.

The quantitative exposure/risk assessment developed for residential handlers is based on the 

following exposure scenarios:

1. mixing/loading/applying liquids with a manually pressurized handgun,

2. mixing/loading/applying liquids with a hose-end sprayer,

3. mixing/loading/applying liquids with a backpack sprayer, and

4. mixing/loading/applying liquids with a sprinkler can.

Data and Assumptions for Residential Handler Exposure Scenarios

Unit Exposures and Area/Amount Treated

Unit exposure values and estimates for area treated were taken from HED’s 2012 Residential 

SOPs: Lawns/Turf. It was assumed that residential handlers would treat a maximum of 1000 ft2

(0.023 acres).

Application Rate

A maximum single application rate of 1.36 lb ai/Acre (4 fl. oz./ 1000 ft2) was used for all spot 

treatment scenarios (EPA Reg. No. 432-1229).

Body Weight

The average female adult body weight of 69 kg was used for estimating short-term dermal dose 

because the selected toxicological POD is based on developmental effects; the average male adult 

body weight of 80 kg was used for estimating short-term inhalation dose.

Absorption Factors

 A dermal absorption factor of 9% is used to estimate short-term dermal exposure since the 

point of departure is based on an oral study. 

 A route-specific study was used for the inhalation assessment.

6.1 Residential Handler Exposure
Page 21 of 45

Residential handler exposure is expected to be short-term. Intermediate-term exposures are not 

likely because of the intermittent nature of applications by homeowners. Summaries of the shortterm dermal and inhalation risk estimates for residential handlers are included in Table 4.5. The

maximum application rate for each exposure scenario is presented as the worst case scenario. 

All dermal scenarios for residential handlers performing spot treatment applications utilizing 

hose-end-sprayer and sprinkler can, resulted in MOEs greater than the LOC (i.e., MOEs ≥ 1,000) 

and, therefore are not of concern. 

All inhalation scenarios for residential handlers resulted in MOEs greater than the LOC (i.e., 

MOEs ≥ 300) and, therefore are not of concern. In this assessment, since the PODs selected for 

both dermal and inhalation routes of exposure are based on different endpoints; the MOEs for the 

dermal and inhalation exposure routes were not combined. 

Table 6.1 Updated Summary of Short-Term Residential Handler Exposures and Risks Estimates for 

Application of Glufosinate-Ammonium on Residential Turf.

Exposure 

Scenario

Application 

Rate a Area 

Treated 

Daily b

Unit Exposure c Dose d

MOE e

Dermal Inhalation Dermal Inhalation

lb ai

per 1000 ft2 mg/lb ai mg/kg/day Dermal Inhalation

Spot Treatments

Hose-end 

Sprayer

0.0312 1000 

ft2 13.4 0.022 0.0005 0.000009 26000 1,500,000

Manuallypressurized 

handwand 

0.0312 1000 

ft2 63 0.018 0.0026 0.000007 5400 1,800,000

Sprinkler 

can

0.0312 1000 

ft2 13.4 0.022 0.0005 0.000009 26000 1,500,000

Backpack

Sprayer

0.0312 1000 

ft2 130 0.14 0.0053f

0.0001 2600 230,000

a Application Rates based on maximum application rates of registered residential turf uses for glufosinate ammonium 4 fl oz per 

gallon of water to treat to treat 1000 ft2.

b Based on HED’s SOPs: Lawns/Turf (January 2012). Area treated daily: 0.023 A = 1000 ft2.

c Residential Handler Attire: no gloves, short pants, short-sleeved shirt, no respirator. 

d Dose (mg/kg/day) = daily unit exposure (mg/lb ai) × application rate (lb ai/A) × area treated (Acres/day) × absorption factor (%) 

÷ body weight (69 kg for dermal; 80 kg for inhalation). Dermal absorption factor = 9%.

e Dermal MOE = LOAEL (14 mg/kg/day) / dermal daily dose (mg/kg/day), where LOC = 1000

Inhalation MOE = LOAEL (12.5 mg/kg/day) / inhalation daily dose (mg/kg/day), where LOC = 300

f

 Residential exposure estimate recommended for use in aggregate assessment.

6.2 Residential Post-Application Exposure

Exposure is possible during post-application activities on treated turf. Children may experience 

exposure via incidental non-dietary ingestion (i.e., hand-to-mouth, object-to-mouth (turfgrass), 

and soil ingestion) during post-application activities on treated turf. Based on the Agency's 

current practices, post-application dermal assessments are not performed for spot treatment uses 

(HED’s SOPs: Lawns/Turf; January 2012). These types of uses can result in residues on turf but 

residential exposure is expected to be low.

Likewise, post-application inhalation exposure while engaged in activities on or around 

previously treated turf is generally not assessed. The combination of low vapor pressure for 

chemicals typically used as active ingredients in outdoor residential pesticide products and 
Page 22 of 45

dilution in outdoor air is likely to result in minimal inhalation exposure. Therefore, a quantitative 

post-application inhalation exposure assessment was not performed for glufosinate ammonium at 

this time primarily because it has very low vapor pressure (vapor pressure less than 1 x 10-8

mmHg). However, volatilization of pesticides may be a potential source of post-application 

inhalation exposure to individuals nearby to pesticide applications. The Agency sought expert 

advice and input on issues related to volatilization of pesticides from its Federal Insecticide, 

Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009. The Agency

received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html) and is in the process of 

evaluating the SAP report. The Agency may, as appropriate, develop policies and procedures to 

identify the need for and, subsequently, the way to incorporate post-application inhalation 

exposure into the Agency's risk assessments. If new policies or procedures are put into place, the 

Agency may revisit the need for a quantitative post-application inhalation exposure assessment 

for glufosinate ammonium. However, it should be noted that residential handler inhalation 

exposures result in high MOEs, ranging from approximately 230,000 to 1,800,000.

6.3 Spray Drift

Spray drift is always a potential source of exposure to residents nearby to spraying operations. 

This is particularly the case with aerial application but, to a lesser extent, could also be a potential 

source of exposure from the groundboom application methods additionally employed for 

glufosinate ammonium. The Agency has been working with the Spray Drift Task Force, EPA 

Regional Offices, and State Lead Agencies for pesticide regulation and other parties to develop 

the best spray drift management practices. The Agency is now requiring interim mitigation 

measures for aerial applications that must be placed on product labels/labeling. The Agency has 

completed its evaluation of the new data base submitted by the Spray Drift Task Force, a 

membership of U.S. pesticide registrants, and is developing a policy on how to appropriately 

apply the data and the AgDRIFT computer model to its risk assessments for pesticides applied by 

air, orchard airblast, and ground hydraulic methods. After the policy is in place, the Agency may

impose further refinements in spray drift management practices to reduce off-target drift and risk 

estimates associated with aerial as well as other application types where appropriate. 

Although a quantitative residential post-application inhalation exposure assessment was not 

performed as a result of pesticide drift from neighboring treated agricultural fields, an inhalation 

exposure assessment was conducted for residential handlers use on turf. This exposure scenario is 

representative of a worse case inhalation (drift) exposure and may be considered protective of 

most outdoor agricultural and commercial post-application inhalation exposure scenarios.

7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate glufosinate ammonium

pesticide exposures and risks from three major sources: food, drinking water, and residential 

exposures. In an aggregate assessment, exposures from relevant sources are added together and 

compared to quantitative estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves 

can be aggregated. When aggregating exposures and risks from various sources, HED has

considered both the route and duration of exposure. 

7.1 Acute Aggregate Risk
Page 23 of 45

The acute dietary assessment included food and water exposures for females 13-49 years old and 

represents the acute aggregate risk assessment for glufosinate ammonium (see Section 5.4.1). 

7.2 Short-Term Aggregate Risk 

The short-term aggregate risk assessment takes into account average exposure estimates from 

dietary consumption of glufosinate ammonium (food and drinking water) and residential/nonoccupational exposures. HED uses average (chronic) food and water exposure estimates when 

conducting short-term aggregate exposure assessments. Short-term exposure has been defined as 

from 1- 30 days and HED has concluded that average exposures to food and water will more 

accurately reflect actual exposure over these time periods than will high end exposures. The 

refined chronic dietary assessment incorporated percent crop treated information for several crops 

and assumed average residues levels from field trials. For livestock commodities, anticipated 

residues were also assumed. The residential handler dermal and inhalation exposure estimates 

were conducted using residential SOPs and ORETF data. The resulting exposures were less than 

HED’s level of concern (see Table 4.5) for all scenarios, with the backpack sprayer scenario 

giving the highest potential exposure. 

Short-term aggregate exposure to glufosinate ammonium is provided in Table 7.2. For average 

dietary exposure, the General U.S. Population was selected as it is protective for all other 

population subgroups except for infants and young children, who will not be applying glufosinate 

ammonium. For residential/non-occupational exposures, only the dermal route of exposure was 

included in the aggregate analysis since potential dermal exposures are higher than potential 

inhalation exposures (see Table 6.1); it is not appropriate to aggregate the dermal and inhalation

exposures since the toxicity endpoints are different. The backpack sprayer residential exposure 

scenario was chosen for aggregate analysis because it is protective for the other residential 

exposure scenarios. The point of departure (POD) selected for short-term aggregate exposure to 

glufosinate ammonium is 14 mg/kg/day. Based on these assumptions, the estimated short-term 

aggregate MOE of 1800 (LOC = 1000) is not of concern to HED. 

Table 7.2. Short-Term Aggregate Risk for Glufosinate Ammonium (backpack 

sprayer scenario for residential mixer/loader/applicator)

Population LOAEL

(mg/kg/day)

Food + Drinking 

Water Exposure 

(mg/kg/day)

Dermal Dose

(mg/kg/day)

Total Exposure 

(mg/kg/day) LOC MOE Agg

General 

U.S. 

Population

14 0.002324 0.0053 0.00762 1000 1800

LOC=Level of Concern

MOE= LOAEL/Exposure

MOE Aggregate= LOAEL/(Exposurefood and water + Exposuredermal)

Food + Drinking Water exposure: See Table 5.4.2.

Dermal exposure: See Table 6.1.

7.3 Intermediate/Long-Term Aggregate Risk

Intermediate/long-term exposures are not anticipated. Therefore an intermediate/long-term 

aggregate risk assessment was not performed. 
Page 24 of 45

7.4 Chronic Aggregate Risk

The chronic dietary assessment included food and water exposures and represents the chronic 

aggregate risk assessment for glufosinate ammonium (see Section 5.4.2).

8.0 Cumulative Exposure/Risk Characterization

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a common 

mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as to glufosinate 

ammonium and any other substances, and glufosinate ammonium does not appear to produce a toxic 

metabolite produced by other substances. For the purposes of this tolerance action, therefore, EPA 

has not assumed that glufosinate ammonium has a common mechanism of toxicity with other 

substances. For information regarding EPA’s efforts to determine which chemicals have a common 

mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the policy

statements released by EPA’s Office of Pesticide Programs concerning common mechanism 

determinations and procedures for cumulating effects from substances found to have a common 

mechanism on EPA’s website at http://www.epa.gov/pesticides/cumulative/.

9.0 Occupational Exposure/Risk Characterization

9.1 Occupational Handler

Occupational exposure to glufosinate ammonium is anticipated for handlers who apply the 

formulated products to the proposed new use sites. Based on application rate and label 

information, dermal and inhalation exposure is expected to occur for short- and intermediate-term 

durations. Chronic exposure is not expected for the proposed use patterns. 

Potential occupational exposure scenarios include: 

1) Mixer/Loader using open pouring of liquids in support of aerial, groundboom, and spot/ 

directed spray application operations; 

2) Aerial Applicators (enclosed cockpit);

3) Applicators using open-cab ground boom equipment; 

4) Flaggers in support of aerial applications; and

5) Mixer/Loader/ Applicator (MLAP) for mechanically pressurized handgun spray applications.

6) Mixer/Loader/ Applicator (MLAP) for Backpack sprayer applications.

Chemical-specific data were not submitted to the Agency in support of this Section 3 registration. 

It is the policy of HED to use the best available data to assess handler exposure. Sources of 

generic handler data, used as surrogate data in the absence of chemical-specific data, include the 

Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1), the Agricultural Handler 

Exposure Task Force (AHETF) database, or other registrant-submitted occupational exposure 

studies. Some of these data are proprietary (e.g., AHETF data), and subject to the data protection 

provisions of FIFRA. The standard values recommended for use in predicting handler exposure 

that are used in this assessment, known as “unit exposures”, are outlined in the “Occupational 
Page 25 of 45

Pesticide Handler Unit Exposure Surrogate Reference Table” 

(http://www.epa.gov/opp00001/science/handler-exposure-table.pdf), which, along with additional 

information on HED policy on use of surrogate data, including descriptions of the various 

sources, can be found at http://www.epa.gov/pesticides/science/handler-exposure-data.html.

The average adult weight of 80 kg was used for estimating inhalation exposure. For dermal risk 

assessments, a 69 kg body weight was used to calculate exposure to glufosinate ammonium since 

the point of departure was selected from a developmental toxicity study. A dermal absorption 

factor of 9% was applied during the conduct of the short- and intermediate-term dermal exposure 

assessments, based on a dermal penetration study (D289836, B. Daiss, 17-JUN-2003). For 

inhalation risk assessment, a route specific study was used.

In this assessment, since the Points of Departure (PODs) selected for both short- and 

intermediate-term dermal and inhalation routes of exposure are based on different endpoints and 

the toxicological effects are different; the MOEs for the dermal and inhalation exposure routes 

were not combined. 

Daily dermal or inhalation handler exposures are estimated for each applicable handler task with 

the application rate, the area treated in a day, and the applicable dermal or inhalation unit 

exposure using the following formula:

Daily Exposure (mg ai/day) = Unit Exposure (mg ai/lb ai handled) x Application Rate (lbs 

ai/area) x Daily Area Treated (area/day)

Where: 

Daily Exposure = Amount (mg ai/day) deposited on the surface of the skin that 

is available for dermal absorption or amount inhaled that is 

available for inhalation absorption;

Unit Exposure = Unit exposure value (mg ai/lb ai) 

Application Rate = Normalized application rate based on a logical unit 

treatment, such as acres; and

Daily Area Treated = Normalized application area based on a logical unit 

treatment such as acres (A/day). 

The daily dermal or inhalation dose is calculated by normalizing the daily exposure by body

weight and adjusting, if necessary, with an appropriate dermal or inhalation absorption factor 

using the following formula:

Average Daily Dose (mg/kg/day) = Daily Exposure (mg ai/day) x (Absorption Factor (%/100)) / 

Body Weight (kg)

Where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a 

given scenario (mg ai/kg body weight/day);

Daily Exposure = Amount (mg ai/day) deposited on the surface of the skin that 

is available for dermal absorption or amount inhaled that is 

available for inhalation absorption;

Absorption Factor = A measure of the amount of chemical that crosses a 
Page 26 of 45

biological boundary such as the skin or lungs (% of the total 

available absorbed); and

Body Weight = Body weight determined to represent the population of 

interest in a risk assessment (kg).

Non-cancer dermal and inhalation risks for each applicable handler scenario are calculated using a 

MOE, which is a ratio of the point of departure (POD) to the daily dose. All MOE values were 

calculated using the formula below:

MOE= POD (mg/kg/day) / Average Daily Dose (mg/kg/day)

See Tables 9.1a - 9.1c for a summary of estimated exposures and risks. Results from the 

assessment of all occupational handler scenarios, with the exception of mixer/loader/applicator 

(MLAP) spot treatments scenarios with mechanically pressurized handgun, indicate that shortand intermediate-term dermal risks are not of concern to the Agency (i.e., MOEs ≥ 1000) at level 

of personal protection recommended on the label (i.e., gloves). Short- and intermediate-term 

dermal risks MLAP scenarios with mechanically pressurized handgun for spot treatments on 

olives, citrus, pome, and stone fruit are of potential concern to the Agency (MOE= 160) even 

with the addition of personal protection to mitigate exposure such as an extra layer of clothing 

(coveralls) and gloves. 

Likewise, results from the assessment of all occupational handler scenarios, with the exception of 

MLAP spot treatments scenarios with mechanically pressurized handgun, indicate that short- and 

intermediate-term inhalation risks are not of concern to the Agency (i.e., MOEs ≥ 300) at baseline 

level of personal protection (i.e. no respirator). MLAP scenarios, for spot treatments on olives, 

citrus, pome, and stone fruit, result in short- and intermediate-term dermal risks of potential 

concern to the Agency (MOE= 82) even with the addition of a PF10R respirator. 

The formulated end use products labels involved in this assessment indicate user restrictions and 

state: “for retail sale to and use only by certified applicators or persons under their supervision 

and only for the uses covered by the certified applicator’s certification”. The proposed

glufosinate ammonium labels direct applicators and other handlers who might be exposed to the 

diluted chemical and anything that has been treated, such as plants, soil, or water to wear specific 

personal protection equipment (PPE). Handlers mixing, loading, and cleaning equipment are 

instructed to wear a chemical resistant apron. Applicators and other handlers must wear 

coveralls; chemical resistant gloves and footwear, plus socks, and protective eyewear (goggles, 

face shield or safety glasses). Mixers and loaders supporting aerial applications must wear a dust 

mist filtering respirator (MSHAINIOSH approval number prefix TG21 C), or a NIOSH approved 

respirator with any N, R, P or HE filter. PPE required for early entry to treated areas that is 

permitted under the Worker Protection Standard must be used. 

The minimum level of PPE for handlers is based on acute toxicity for the end-use product. The 

Registration Division (RD) is responsible for ensuring that PPE listed on the label is in 

compliance with the Worker Protection Standard (WPS) for agricultural pesticides. 
Page 27 of 45

Table 9.1a Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium

Exposure

Scenario

Crop or 

Target

App 

Ratea

(lb 

ai/A)

Acres 

Treated

Dailyb

Unit Exposurec Dose (mg/kg/Day)

MOEs

(Dermal LOC = 1000

Inhalation LOC = 300)

Baseline

Dermal 

(mg/lb ai)

PPEDermal 

(mg/lb ai)

Inhalation

(ug/lb ai)

Baseline 

Dermald,h

PPE 

Dermali Inhalatione Baseline Dermalf

PPEDermal Inhalationg,i

Mixer/Loader

Mixing/Loading to 

Support

Aerial treatments 

(PHED)

Sweet 

Corn 0.365 350 0.220 0.0376 

(SL/G)

0.219 0.0367

0.00626

(SL/G)

0.00485

(DL/G)

0.00035 380 2,200

(SL/G)

36,000

Mixing/Loading to 

Support Groundboom 

Applications (PHED)

Sweet 

Corn 0.365 80 0.220 0.0376 

(SL/G)

0.219 0.00837 0.00143

(SL/G)

0.000079 1,700 9,800

(SL/G)

160,000

Citrus 

Fruit, 

Pome 

Fruit, 

Stone 

Fruit, 

Olives

1.50 80 0.220 0.0376 

(SL/G)

0.219 0.0344 0.00588

(SL/G)

0.000329 410 2,400

(SL/G)

38,000

a) Application Rates based on proposed uses on label for Glufosinate -ammonium formulations Liberty Herbicide (EPA Reg. No. 264-660) and Liberty 280 SL Herbicide (EPA Reg. No. 264-

829). Units expressed in lb ai/Acre unless specified otherwise.

b) Exposure Science Advisory Council Policy # 9.1

c) Unit Exposures based on Unit Exposures based on “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (PHED)

(http://www.epa.gov/pesticides/science/handler-exposure-table.pdf), dated September 2011. Engineering control unit exposure for applying sprays via aerial equipment = enclosed cockpit. 

d) Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/acre) x acres treated x dermal absorption factor (9%) / body weight (69 kg adult female).

e) Inhalation Dose (mg/kg/day) = daily unit exposure (μg/lb ai) x conversion factor (1 mg/1,000 μg) x application rate (lb ai/acre) x acres treated/ body weight (80 kg). 

f) Dermal MOE = LOAEL (14 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 1000.

g) Inhalation MOE = LOAEL (12.5) mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 300.

h) Baseline Dermal: Long-sleeve shirt, long pants, and no gloves; 

i) Baseline Inhalation: no respirator

j) PPE: G (gloves), SL (Single Layer), DL (Double Layer), PF10R (respirator), E.C. (Engineering Control; Closed System). 
Page 28 of 45

Table 9.1b Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium

Exposure 

Scenario Crop or Target

App 

Ratea

(lb 

ai/A)

Acres 

Treated 

Dailyb

Unit Exposurec Dose (mg/kg/Day)

MOEs

(Dermal LOC = 1000

Inhalation LOC = 300)

Baseline 

Dermal h

(mg/lb 

ai)

PPE

Dermal j, g 

(mg/lb ai)

Inhalationg

(ug/lb ai)

Baseline 

Dermald,h

PPE-G 

Dermal Inhalatione Baseline Dermalf, h

PPE-G 

Dermal Inhalationi

Applicator

Applying Sprays 

via Aerial 

Equipment –

Enclosed Cockpit 

(PHED)

Sweet Corn 0.365 350 No Data 0.005

(EC)

0.068

(EC)

No Data 0.000833

(EC)

0.000109

(EC) No Data 17,000(EC)

110,000

(EC)

Applying Sprays 

via Groundboom 

Equipment Open 

Cab

Sweet Corn 0.365 80 0.0786 0.0161

(SL/G)

0.34 0.003 0.000613

(SL/G)

0.000124 4,700 23,000

(G) 100,00

Citrus Fruit, 

Pome Fruit, 

Stone Fruit, 

Olives

1.5 80 0.0786 0.0161

(SL/G)

0.34 0.0123 0.00252

(SL/G)

0.00057 1,100 5,600

(G) 25,000

Flagger

Flagging for Aerial 

Sprays Sweet Corn 0.365 350 0.011 0.012 0.35 .00183 0.0020 0.00064 7,600 7,000

(G) 19,000

a) Application Rates based on proposed uses on label for Glufosinate -ammonium formulations Liberty Herbicide (EPA Reg. No. 264-660) and Liberty 280 SL Herbicide (EPA Reg. No. 264-

829). Units expressed in lb ai/Acre unless specified otherwise.

b) Exposure Science Advisory Council Policy # 9.1

c) Unit Exposures based on Unit Exposures based on “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (PHED)

(http://www.epa.gov/pesticides/science/handler-exposure-table.pdf), dated September 2011. Engineering control unit exposure for applying sprays via aerial equipment = enclosed cockpit. 

d) Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/acre) x acres treated x dermal absorption factor (9%) / body weight (69 kg adult female).

e) Inhalation Dose (mg/kg/day) = daily unit exposure (μg/lb ai) x conversion factor (1 mg/1,000 μg) x application rate (lb ai/acre) x acres treated/ body weight (80 kg). 

f) Dermal MOE = LOAEL (14 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 1000.

g) Inhalation MOE = LOAEL (12.5) mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 300.

h) Baseline Dermal: Long-sleeve shirt, long pants, and no gloves; 

i) Baseline Inhalation: no respirator

j) PPE: G (gloves), SL (Single Layer), DL (Double Layer), PF10R (respirator), E.C. (Engineering Control; Closed System). 
Page 29 of 45

Table 9.1c Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium (Spot/Directed 

Spray Applications)

Exposure 

Scenario

App 

Ratea(lb 

ai/gal)

Acres 

Treated 

Dailyb

Unit Exposurec, j Dose (mg/kg/Day)

MOEs

(Dermal LOC = 1000

 Inhalation LOC = 300)

Baseline 

Dermal h (mg/lb 

ai)

PPE

Dermal j 

(mg/lb ai)

Inhalation 

(ug/lb ai)

Baseline 

Dermald,h

PPE

Dermalj Inhalatione Baseline Dermalf,h PPE Dermal j

Inhalationg,i

Citrus Fruit, Pome Fruit, Stone Fruit, Olives

Mixer/Loader/Applicator

Mixing/Loading/Applying 

(MLAP) with Mechanically 

Pressurized Handgun

(spot/ directed spray)

1.7 fl oz/gal

0.031 

lbai/gal

1,000

gallons 4.310 2.160(DL/G)

3931 

(No respirator)

393.1

(PF10R)

0.175 0.0874

(DL/G)

0.0004

0.153 (PF10R)

80 160

(DL/G)

8.2

82 (PF10R)

Mixing/Loading/Applying 

(MLAP) with Backpack 

Sprayer

(spot/ directed spray)

40

gallons 8.260 8.260 2.58 0.0133 0.0133 0.0004 1,100 1,100(SL/G)

310,000

a) Application Rates based on proposed uses on label for Glufosinate -ammonium formulations Liberty Herbicide (EPA Reg. No. 264-660) and Liberty 280 SL Herbicide (EPA Reg. No. 264-

829). Units expressed in lb ai/Acre unless specified otherwise.

b) Exposure Science Advisory Council Policy # 9.1

c) Unit Exposures based on Unit Exposures based on “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (PHED)

(http://www.epa.gov/pesticides/science/handler-exposure-table.pdf), dated September 2011. Engineering control unit exposure for applying sprays via aerial equipment = enclosed cockpit. 

d) Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/acre) x acres treated x dermal absorption factor (9%) / body weight (69 kg adult female).

e) Inhalation Dose (mg/kg/day) = daily unit exposure (μg/lb ai) x conversion factor (1 mg/1,000 μg) x application rate (lb ai/acre) x acres treated/ body weight (80 kg). 

f) Dermal MOE = LOAEL (14 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 1000.

g) Inhalation MOE = LOAEL (12.5) mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 300.

h) Baseline Dermal: Long-sleeve shirt, long pants, and no gloves; 

i) Baseline Inhalation: no respirator

j) PPE: G (gloves), SL (Single Layer), DL (Double Layer), PF10R (respirator), E.C. (Engineering Control; Closed System). 
Page 30 of 45

9.2 Occupational Post-Application Risk

Inhalation Post-Application Risk

Based on the Agency's current practices, a quantitative occupational post-application inhalation exposure 

assessment was not performed for glufosinate ammonium. However, there are multiple potential sources 

of post-application inhalation exposure to individuals performing post-application activities in previously

treated fields. These potential sources include volatilization of pesticides and resuspension of dusts and/or 

particulates that contain pesticides. The Agency sought expert advice and input on issues related to 

volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific 

Advisory Panel (SAP) in December 2009. The Agency received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in the process of 

evaluating the SAP report as well as available post-application inhalation exposure data generated by the 

Agricultural Reentry Task Force and may, as appropriate, develop policies and procedures, to identify the 

need for and, subsequently, the way to incorporate occupational post-application inhalation exposure into 

the Agency's risk assessments. If new policies or procedures are put into place, the Agency may revisit 

the need for a quantitative occupational post-application inhalation exposure assessment for glufosinate 

ammonium. Although a quantitative occupational post-application inhalation exposure assessment was 

not performed, an inhalation exposure assessment was performed for occupational/commercial handlers. 

Handler exposure resulting from mixing/loading pesticides is likely to result in higher exposure than postapplication exposure. Thus, handler inhalation exposure estimates would be protective of most 

occupational post-application inhalation exposure scenarios.

Dermal Post-Application Risk

A quantitative post-application dermal exposure assessment was not performed for glufosinate ammonium

uses on citrus fruit, pome fruit, stone fruit, and olives. There is a low potential for occupational postapplication exposure associated with the use of ground and spot-directed application of herbicides. Most 

of the proposed uses for glufosinate ammonium are ground-directed uses where crop foliage treatment 

should be avoided. Currently, HED has no transfer coefficients (TCs) or other data to assess postapplication dermal exposures to soil by occupational workers. Therefore, for the proposed soil-directed 

uses, post-application exposures and risks to occupational workers were not quantitatively assessed for 

these crops. In general, such exposures are considered to be minimal. 

Even though the proposed uses for glufosinate ammonium are for post-emergent applications when crop 

foliage is present, dislodgeable foliar residues are expected to be very low during post-application 

activities since the proposed label advises applicators to avoid contact of Liberty® 280 SL Herbicide with 

foliage or parts of trees, other than mature brown bark as serious injury may occur. The label specifies a 

preharvest interval of 14 days for citrus fruit, pome fruit, stone fruit, and olive crops.

There is potential for post-application dermal exposure to glufosinate ammonium following the proposed 

use on sweet corn. Occupational re-entry workers may experience short-/intermediate-term exposure to 

glufosinate ammonium while performing post-application activities such as scouting and irrigation of 

sweet corn. Post-application exposure resulting from detasseling activities was not assessed since it is 

estimated that this activity would occur too late after the last application permitted for the herbicide 

(ExpoSAC meeting August 5, 2010). Therefore, post-application dermal exposure scenarios for the 

proposed new uses of glufosinate ammonium on sweet corn were assessed for scouting and irrigation 

activities only. The post-application activity scenarios along with respective TCs and risk estimates for 

short-/intermediate-term MOEs are summarized in Table 9.2. 
Page 31 of 45

It is the policy of HED to use the best available data to assess post-application exposure. 

Since no chemical-specific dislodgeable foliar residue (DFR) data were submitted in support of this 

registration action, dermal transfer coefficients (TCs) were used to relate foliage residue values to activity

patterns (e.g., scouting) to estimate potential human exposure. Sources of generic post-application data, 

used as surrogate data in the absence of chemical-specific data, are derived from Agricultural Reentry 

Task Force (ARTF) exposure monitoring studies, and, as proprietary data, are subject to the data 

protection provisions of FIFRA. The standard values recommended for use in predicting post-application 

exposure that are used in this assessment, known as “transfer coefficients”, are presented in the “Science 

Advisory Council for Exposure (ExpoSAC) Policy 3” 

(http://www.epa.gov/pesticides/science/exposac_policy3.pdf), which, along with additional information 

about the ARTF data, can be found at http://www.epa.gov/pesticides/science/post-app-exposuredata.html. It is also assumed that a fraction of ai (25% of the rate of application) is available as 

dislodgeable foliar residue on day zero after initial treatment with a continued dissipation rate of 10% per 

day on following days.

The following equations were used to calculate risks for workers performing post-application activities:

Dislodgeable Foliar Residue

DFRt (μg/cm2)= AR (lb ai/acre) × F × (1-D)t× 4.54E8 μg/lb × 2.47E-8 acre/cm2

Where:

DFRt = dislodgeable foliage residue on day "t" (μg/cm2),

AR = application rate (lb ai/acre),

F = fraction of ai retained on foliage (unitless), and

D = fraction of residue that dissipates daily (unitless).

Daily Dose

Daily dose (dermal) is calculated by normalizing the daily exposure value by body weight and accounting 

for absorption factors:

DD t (mg/kg-day) = DFRt (μg/cm2) × 1E-3 mg/μg × TC (cm2/hr) × DA (9%) × ET (hrs)

BW (kg)

Where:

DD t = daily dermal dose on day “t,”

t = number of days after application day (days),

DFRt = dislodgeable foliage residue on day "t" (μg/cm2),

TC = transfer coefficient (cm2/hr),

DA = dermal absorption factor (unitless),

ET = exposure time (hr/day), and

BW = body weight (kg).

Margin of Exposure (MOE)

The daily dermal dose received by occupational handlers was compared to the appropriate PoD (i.e. 

LOAEL) to assess the risk to occupational handlers. All MOE values were calculated using the following 

formula:

MOE = LOAEL (mg/kg/day)

ADD (mg/kg/day)

Where:

MOE = Margin Of Exposure (unitless),

ADD = Average Daily Dose (mg/kg/day), and

LOAEL = Lowest Observed Adverse Effect Level (mg/kg/day)
Page 32 of 45

The results of the glufosinate ammonium post-application exposure and dermal risk assessment for sweet 

corn indicate that an MOE of 1,200 is achieved on Day 0 for scouting mature/high foliage plants. 

However, for irrigation activities, an acceptable MOE of 1,050 is not achieved until Day 4; therefore, this 

post-application activity is of potential concern to the Agency. The proposed Liberty® Herbicide label 

indicates an REI of 12 hrs; thus, this timing needs revision based upon the post-application exposure 

estimates obtained for sweet corn to achieve an MOE ≥ 1000. The proposed label states a preharvest 

interval of 50 days for sweet corn. The post-application activity scenarios along with respective TCs and 

risk estimates for short-/intermediate-term MOEs are summarized in Table 9.2. 

Table 9.2 Summary of Estimated Post-Application Risks for Glufosinate Ammonium 

(9 % absorption factor)

Crop Maximum 

Application 

Ratea

DAT b DFR c TC d Activity dShort-/IntTerm MOE e

Sweet 

corn

0.365 

0 1.024 1,100 Scouting mature/high 

foliage plants

1,200

0 1.024 1,900 Irrigation mature/high 

foliage plants

690

4 0.672 1,900 Irrigation mature/high 

foliage plants 1,050

a) Maximum application rate (lb ai/A) indicated on proposed labels Reg.No.279-3313, 279-3108. 

b) DAT = Days after treatment needed to reach the LOC of 1000; DAT 0 = the day of treatment, after sprays have dried; assumed to

be approximately 12 hours. 

c) DFR (μg/cm2) = Application rate (lb ai/A) x Fraction of ai retained on foliage on day zero (25%)× (1 - fraction of residue that 

dissipates daily 10%)t× 4.54E8 μg/lb × 2.47E-8 acre/cm2.

d) TC (cm2/hr) = Transfer coefficients and associated activities from ExpoSAC Policy 3” 

(http://www.epa.gov/pesticides/science/exposac_policy3.pdf)

e) MOE = MOE on the corresponding DAT. MOE = LOAEL / Daily Dose. 

Daily Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day × dermal absorption 9 %]  body weight (69 kg 

adult).

The toxicity categories of the active ingredient for acute dermal, eye irritation, and skin irritation potential 

are used to determine the interim REI (Restricted-entry Intervals). The glufosinate ammonium technical 

material has been classified in Toxicity Category III for acute dermal and primary eye irritation. It is not a 

dermal irritant (toxicity category IV) nor is it a dermal sensitizer. Per the Worker Protection Standard 

(WPS), a 12-hr restricted entry interval (REI) is required for chemicals classified under Toxicity Category

III or IV. Both labels indicate an REI of 12 hrs, which is in compliance with the WPS for most postapplication activities. However, an REI of 4 days is needed based upon the post-application exposure 

estimates obtained for sweet corn to achieve the target MOE ≥ 1000.

10.0 References

Endpoint Selection Documents

Glufosinate ammonium – 3

rd Report of the Hazard Identification Assessment Review Committee; B. 

Tarplee, 4/17/2003.

Glufosinate ammonium – Review of Developmental Neurotoxicity Study in Rats (MRID 46455701); DP#: 

312684, R.J. Mitkus, 8/24/2005.
Page 33 of 45

Glufosinate ammonium – Review of 28-Day Inhalation Toxicity Study (MRID 47058101); DP#: 337298, 

L. Austin, 9/6/2007.

Glufosinate ammonium – Request to Waive Requirement for Glutamine Synthetase Measurements and 

Other Data Requirements; DP#: 328229, L. Austin, TXR No. 0054838, 4/8/2008. 

Glufosinate ammonium – ToxSAC Meeting on June 10, 2010; J. Kidwell, 6/29/2010.

Risk Assessments

Glufosinate Ammonium (PC Code 128850). Section 3 Registrations for Transgenic Cotton

and Cotton (ID# - 0F06140), Transgenic Rice (ID# - 0F06210), and Bushberry (ID# -

2E06404). Human Health Risk Assessment. DP#: 290086; T. Bloem, PV Shah, and M. Dow, 8/7/2003.

Glufosinate Ammonium. Human Health Risk Assessment in Support for the Proposed New Use of

Glufosinate Ammonium in/on Citrus Fruits (Crop Group 10), Pome Fruits (Crop Group 11), Stone Fruits 

(Crop Group 12), Olives, and Sweet Corn; DP#: 372623, W. Donovan et. al., 12/15/2010. 

Dietary Exposure Memoranda

Glufosinate Ammonium. Update of the Revised Acute and Chronic Aggregate Dietary (Food and 

Drinking Water) Exposure Assessment in Support of the Petition Proposing Tolerances for Residues of 

Glufosinate Ammonium in/on Citrus Fruits (Crop Group 10), Pome Fruits (Crop Group 11), Stone Fruits 

(Crop Group 12), Olives, and Sweet Corn; DP#: 402741, W. Donovan, 6/19/2012.

Drinking Water Memoranda

Tier II Drinking Water Assessment for Glufosinate-ammonium on Stone Fruit, Citrus, Pome Fruit, and 

Olives; DP#: 372624; C. Peck; 6/22/2010.

Tier II Drinking Water Assessment for Glufosinate-ammonium on Sweet Corn; DP#: 368799; C. Peck; 

7/7/2010.

Refined Drinking Water Assessment for Glufosinate-ammonium Use on Rice; DP#: 387412; C. Peck; 

5/30/2012.

Residue Chemistry Data Review

Glufosinate Ammonium. Petitions for the Establishment of Permanent Tolerances in/on Citrus Fruits 

(Crop Group 10), Pome Fruits (Crop Group 11), Stone Fruits (Crop Group 12), Olives and Sweet Corn. 

Summary of Analytical Chemistry and Residue Data. DP#: 372625; I. Negrón-Encarnación; 8/31/2010.

Occupational and Residential Exposure Assessment

Glufosinate-Ammonium; Occupational and Residential Risk Assessment to Support Request for Section 3 

Registrations on Sweet Corn, Citrus Fruit, Pome Fruit, Stone Fruit, and Olives. DP#: 368798, A. RiveraLupiáñez, 8/31/2010.
Page 34 of 45

Appendix A

A.1 Toxicology Data Requirements

The requirements (40 CFR 158.340) for food uses of glufosinate ammonium are in Table 1. Use of the new guideline numbers 

does not imply that the new (1998) guideline protocols were used.

Study

Technical

Required Satisfied

870.1100 Acute Oral Toxicity.......................................................

870.1200 Acute Dermal Toxicity..................................................

870.1300 Acute Inhalation Toxicity..............................................

870.2400 Acute Eye Irritation.......................................................

870.2500 Acute Dermal Irritation .................................................

870.2600 Skin Sensitization..........................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 90-Day Oral Toxicity in Rodents..................................

870.3150 90-Day Oral Toxicity in Nonrodents.............................

870.3200 21/28-Day Dermal Toxicity ..........................................

870.3250 90-Day Dermal Toxicity ...............................................

870.3465 90-Day Inhalation Toxicity (28 days) ...........................

Yes

Yes

yes

No

Yes

Yes

See Chronic

Yes

--

Yes

870.3700a Prenatal Developmental Toxicity (rodent) ....................

870.3700b Prenatal Developmental Toxicity (nonrodent)..............

870.3800 Reproduction and Fertility Effects................................

Yes

Yes

yes

Yes

Yes

Yes

870.4100a Chronic Toxicity (rodent)..............................................

870.4100b Chronic Toxicity (nonrodent)........................................

870.4200a Carcinogenicity (rat)......................................................

870.4200b Carcinogenicity (mouse)...............................................

870.4300 Combined Chronic Toxicity/Carcinogenicity ...............

Yes.

Yes

Yes

Yes

Yes

See combined.

Yes 

Yes

Yes

Yes

870.5100 Mutagenicity—Bacterial Reverse Mutation Test..........

870.5300 Mutagenicity—Mammalian Cell Gene Mutation Test..

870.5395 Mutagenicity—Structural Chromosomal Aberrations ..

870.5395 Mutagenicity – in vivo mammalian cytogenetics

870.5500 Mutagenicity—bacterial DNA damage/repair test........

870.5550 Mutagenicity –unscheduled DNA synthesis

Yes

Yes

Yes

Yes

No

No

Yes

Yes

Yes1

Yes

Yes

Yes

870.6200a Acute Neurotoxicity Screening Battery (rat).................

870.6200b 90-Day Neurotoxicity Screening Battery (rat) ..............

870.6300 Developmental Neurotoxicity .......................................

Yes

Yes

Yes

Yes

Yes2

Yes

870.7485 Metabolism and Pharmacokinetics................................

870.7600 Dermal Penetration........................................................

870.7800 Immunotoxicity.............................................................

Yes

Yes

Yes

Yes

Yes

Yes

1 Although the structural chromosome aberration study is listed as being required, it is no longer considered necessary for 

glufosinate ammonium because there are two additional studies (bacterial DNA damage/repair test and unscheduled DNA 

synthesis) and because glufosinate is classified as "not likely" to be a carcinogen in humans. 

2 The submitted study was classified as unacceptable/guideline but demonstrated neurotoxicity at high doses. A developmental 

neurotoxicity study classified as acceptable set the LOAEL at a low level; thus, a repeat of the subchronic neurotoxicity 

screening study is unnecessary.
Page 35 of 45

A.2 Toxicology Profile

Table 1: Acute Toxicity of Glufosinate ammonium Technical

Guideline No. Study Type MRID No. Results Toxicity Category

81-1 Acute Oral 00142430, 00142431, 

00142432

LD50 = 4010 mg/kg in males

LD50 = 3030 mg/kg in females

III

81-2 Acute Dermal 00142436, 00142437 LD50 = >2000 mg/kg in males 

& females

III

81-3 Acute Inhalation 00151496, 00151497 LC50 = 4.42 m/liter estimated in 

males & females

III

81-4 Primary Eye Irritation 00142438 eye irritant, corneal opacity 

reversible within 72 hours

III

81-5 Primary Skin Irritation 00142438 not a dermal irritant IV

81-6 Dermal Sensitization 00142439 not a dermal sensitizer N/A
Page 36 of 45

Table 2: Toxicity Profile of Glufosinate Ammonium Technical

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3100

90-Day oral toxicity 

rodents-rat (rangefinding study)

45179103 (2000)

Acceptable/nonguideline

0, 100 or 1000 ppm, Glufosinate

0, 6.2-8.8, or 64-90 mg/kg/day 

(males only)

0, 1000 or 10,000 ppm, N.acetylL-glufosinate

0, 65-90, or 657-935 mg/kg/day 

(males only)

Glufosinate ammonium

NOAEL = 6.2-8.8 mg/kg/day in males

LOAEL = 64-90 mg/kg/day in males, based on 

glutamine synthetase inhibition in the brains 

N-acetyl-L-glufosinate disodium

NOAEL = 65-90 mg/kg/day in males

LOAEL = 657-935 mg/kg/day in males, based on 

glutamine synthetase inhibition in the brains 

870.3100

90-Day oral toxicity 

rodents-mouse

40345609 (1986) 

Acceptable/guideline 

0, 80, 320 or 1,280 ppm; 

0, 12, 48 or 192 mg/kg/day

NOAEL = 48 mg/kg/day in males, 192 mg/kg/day in 

females (HDT)

LOAEL = 192 mg/kg/day in males, not achieved in 

females; based on the changes in clinical biochemistry 

and liver weights in males 

870.3200 Repeated 

Dose Dermal 

Toxicity-rat

40345605 (1985)

Acceptable/guideline

0, 100, 300 or 1000 mg/kg/day

NOAEL= 100 mg/kg/day

LOAEL= 300 mg/kg/day based on clinical observations 

(aggressive behavior, piloerection, and a high startle 

response)

870.3465 

Subchronic 

inhalation- 28-day

repeat dosing - rat

40345606 (1985)

Supplementary

0, 8, 20 or 46 mg/m3

(estimated 0, 2.2, 5.5 or 12.6 

mg/kg/day). 

NOAEL = 8 mg/m3(estimated 2.2 mg/kg/day)

LOAEL = 20 mg/m3(estimated 5.5 mg/kg/day) based 

on clinical signs, decreased lung weight, increased body 

weight (female), tono-clonic convulsions (2 males). At 

the highest dose, 4 deaths. 

879.3465 

Subchronic 

inhalation- 28-day

repeat dosing - rat

47058101 (2007)

Acceptable/Non-guideline

0, 56 or 105 mg/m3, or an 

estimated 0, 12.5 or 25 

mg/kg/day

LOAEL = 0.56 mg/m3 (estimated 12.5 mg/kg/day) –

lung/bronchial congestion in females, some clinical 

signs (isolated and transient). Liver and kidney weights. 

870.3700a

Prenatal 

developmental in 

rodents- rat

00142445, 00142446 (1982)

0, 0.50, 2.24 or 10 mg/kg/day

00151499, 00151500 (1982)

0, 0.50, 2.24 or 10 mg/kg/day

0, 10, 50 or 250 mg/kg/day

40345610 (1986) 

0, 0.5, 2.24 or 10.0 mg/kg/day 

All three studies combined 

Acceptable/guideline

Maternal: NOAEL = 10 mg/kg/day

LOAEL = 50 mg/kg/day based on vaginal bleeding and 

hyperactivity

Developmental: NOAEL = 50 mg/kg/day 

LOAEL =250 mg/kg/day based on dilated renal pelvis

870.3700b Prenatal 

developmental in 

nonrodents- rabbit

40345611, 41144703 (1984)

Acceptable/guideline

0, 2.0, 6.3 or 20.0 mg/kg/day

Maternal: NOAEL = 6.3 mg/kg/day 

LOAEL = 20.0 mg/kg/day based on reduced food 

consumption, body weight and weight gains

Developmental: NOAEL = 6.3 mg/kg/day

LOAEL = 20.0 mg/kg/day based on decreased body 

weights and fetal death

870.3800 

Reproduction and 

fertility effects- rat

40345612 (1988)

Acceptable/guideline

0, 40, 120 or 360 ppm

0, 2.0, 6.0, or 18.0 mg/kg/day

Parental/Systemic NOAEL = 18.0 mg/kg/day (HDT).

LOAEL = not established

Reproductive NOAEL = 6.0 mg/kg/day

LOAEL = 18.0 mg/kg/day based on decreased number 

of viable pups
Page 37 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

Offspring NOAEL = 6.0 mg/kg/day 

LOAEL = 18.0 mg/kg/day based on decreased number 

of viable pups

870.3700b Prenatal 

developmental in 

nonrodents- rabbit

40345611, 41144703 (1984)

Acceptable/guideline

0, 2.0, 6.3 or 20.0 mg/kg/day

Maternal: NOAEL = 6.3 mg/kg/day 

LOAEL = 20.0 mg/kg/day based on reduced food 

consumption, body weight and weight gains

Developmental: NOAEL = 6.3 mg/kg/day

LOAEL = 20.0 mg/kg/day based on decreased body 

weights and fetal death

870.3800 

Reproduction and 

fertility effects- rat

40345612 (1988)

Acceptable/guideline

0, 40, 120 or 360 ppm

0, 2.0, 6.0, or 18.0 mg/kg/day

Parental/Systemic NOAEL = 18.0 mg/kg/day (HDT).

LOAEL = not established

Reproductive NOAEL = 6.0 mg/kg/day

LOAEL = 18.0 mg/kg/day based on decreased number 

of viable pups

Offspring NOAEL = 6.0 mg/kg/day 

LOAEL = 18.0 mg/kg/day based on decreased number 

of viable pups

870.4100b Chronic 

toxicity- dog

40345608 (1984)

Acceptable/guideline

0, 2.0, 5.0 or 8.5 mg/kg/day

NOAEL = 5.0 mg/kg/day 

LOAEL = 8.5 mg/kg/day based on mortality (week 2) 

and alterations in the electrocardiogram at 6 months

870.4200 

Carcinogenicity- rat

44539501 (1989)

Acceptable/guideline

0, 1000, 5000 or 10000 ppm

0/0, 45.4/57.1, 228.9/281.5, or 

466.3/579.3 mg/kg/day, M/F

NOAEL = 45.4 mg/kg/day in males, 57.1 mg/kg/day in 

females 

LOAEL = 228.9 mg/kg/day in males and 281.5 based on 

increased incidences of retinal atrophy

No evidence of carcinogenicity.

870.4300 Chronic/

Carcinogenicity- rat

40345607, 41144701 (1986)

Acceptable/guideline

0, 40, 140 or 500 ppm

0/0, 1.9/2.4, 6.8/8.2, or 24.4/28.7 

mg/kg/day, M/F

NOAEL = 24.4 mg/kg/day in males, 8.2 mg/kg/day in 

females 

LOAEL = not achieved in males and 28.7 based on 

inhibition of brain glutamate synthetase in females at 

130 weeks

No evidence of carcinogenicity.

870.4300 

Carcinogenicitymice

40345609, 41144702 (1986)

Acceptable/guideline

0, 20, 80, 160 (males only) or 

320 (females only) ppm

0/0, 2.83/4.23, 10.82/16.19 or 

22.60/66.96 mg/kg/day, M/F

NOAEL = 10.82 mg/kg/day in males, 16.19 mg/kg/day 

in females

LOAEL = 22.60 mg/kg/day in males, 63.96 mg/kg/day 

in females based on increased mortality and glucose 

levels and consistent changes in glutathione levels in 

males, increased glucose levels and decreased albumin 

and total proteins

No evidence of carcinogenicity. 

870.5265

Reverse Mutation 

Assay

Accession No. 072962 (1984)

Acceptable/guideline

0, 5, 10, 50, 100, 500, and 1000 

μg/plate

In a bacterial cell gene reverse mutation assay 

Salmonella typhimurium strains TA98, TA100, TA1535 

and TA1537 were exposed to glufosinate ammonium 

(92.1% a.i.) at concentrations of 0, 5, 10, 50, 100, 500, 

and 1000 μg/plate in the presence and absence of 

mammalian metabolic activation (S9-mix).

No increases in mutation frequencies, with or without 

metabolic activation, were noted in any of the test strains 
Page 38 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

at any of the doses tested. Virtually total inhibition of 

growth was noted in all strains at the highest dose, 1000 

μg/plate. Therefore, the requirement that chemicals be

tested to the limits of cytotoxicity was satisfied. The 

positive controls, 2-aminoanthracene, AF-2, 1-ethyl-2-

nitro-3-nitroso-guanidine, 9-amino-acridine, and 2-nitrofluorine, induced the appropriate responses. Therefore 

the test systems were sensitive to agents that induce gene 

mutation. Under the conditions of the test, glufosinateammonium failed to cause reverse mutations in bacteria 

with and without metabolic activation.

870.5300 Detection 

of gene mutations in 

somatic cells in 

culture

40445616 (1988)

Acceptable/guideline

50 to 5000 μg/mL 

300 to 5000 μg/mL (S9-

activated doses).

In a mouse lymphoma L5179Y forward mutation assay, 

HOE 039866 was tested at seven nonactivated doses of 

50 to 5000 μg/mL or at six S9-activated doses of 300 to 

5000 μg/mL.

HOE 39866 did not increase the mutation frequency at 

the thymidine kinase locus. The solvent controls gave 

acceptable values and the positive controls 

ethylmethanesulfonate (nonactivated) and 3-

methylcholanthrene (S9-activated) provided evidence 

that the assay had adequate sensitivity for detecting 

mutagenicity.

870.5395

In vivo mammalian 

cytogenetic tests

41144704 (1986)

Acceptable/guideline

100, 200, and 350 mg/kg by 

gavage

In a mouse micronucleus assay 13 groups of mice 

(5/sex/dose) received a single administration of HOE 

039866 at dose levels of 100, 200, and 350 mg/kg by 

gavage. A positive control group received 50 mg/kg of 

cyclophosphamide. After dosing, the animals were 

sacrificed at 24, 48, and 72 hrs., and the erythrocytes 

from the bone marrows were sampled at these times. 

The results indicated the test agent had no effect on 

micronucleus formation. 

870.5500

Bacterial DNA 

damage or repair test

Accession No. 072962 (1984)

Acceptable/guideline

0, 50, 100, 500, 1000, 5000 or 

10,000 μg/plate.

In a DNA damage/repair assay, glufosinate ammonium 

was exposed overnight to B. subtilis that lacks the 

capacity for repair (H45) at concentrations of 0, 50, 100, 

500, 1000, 5000 or 10,000 μg/plate. Glufosinate 

ammonium was also exposed, at the same dose levels, to 

an isogenic sister strain which has the capacity for DNA 

repair (H17).

Under the conditions of the study, no difference in the 

inhibition of growth between these two strains was noted 

at any of the doses tested. Since the test measures the 

inhibition of growth in response to the test article, the 

requirement that chemicals be tested to the limits of 

cytotoxicity was satisfied. The positive controls, 2-(2-

furyl)-3-(5-nitro-2-furyl)acrlamide (AF-2), caused a 

differential growth inhibition, whereas the negative 

controls (NaOH, HCL, and Kanamycin) produced no 

significant difference in growth inhibition. The test 

system was therefore sensitive to agents that damage 

DNA. Under the conditions of the test, the test article 

failed to cause damage to DNA that could be detected by 

this repair assay.

870.5550 

Unschedule DNA 

synthesis in 

40345614 (1984)

Acceptable/guideline

0.1 to 5240 μg/mL

In an unscheduled DNA synthesis assay (MRID 

40345614), primary rat hepatocyte cultures were 

exposed to HOE 039886 in deionized water at 15 
Page 39 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

mammalian cells in 

culture

concentrations ranging from 0.1 to 5240 μg/mL for 18 -

19 hours. HOE 039866 was tested up to cytotoxic 

concentrations as evidenced by decreased survival rate 

as low as 34% There was no evidence that unscheduled 

DNA synthesis was induced by the test material.

870.6200

Acute Neurotoxicity 

-rat

45190704 (1999)

Acceptable/nonguideline

0, 10, 100 or 500 mg/kg

NOAEL= 500 mg/kg in males and females

LOAEL= Not established in both sexes

870.6200

Acute Neurotoxicity 

-rat

45190703 (1999)

Acceptable/nonguideline

0, 10, 100 or 500 mg/kg

NOAEL= 500 mg/kg in males and females

LOAEL= Not established in both sexes

870.6200b Repeat 

Dose Neurotoxicityrat (37-day study)

45179101, 45179102, 45297001 

(2000)

Acceptable/nonguideline

0, 20, 200 or 2000 ppm

0/0, 1.5/1.8, 14.9/17.1 or 

143.3/161.5 mg/kg/day, M/F

NOAEL= 1.5 mg/kg/day in males, 1.8 mg/kg/day in 

females 

LOAEL= 14.9 mg/kg/day in males, 17.1 mg/kg/day in 

females, based on the inhibition of glutamate synthetase 

in the brain 

870.6200b Repeat 

Dose Neurotoxicityrat (90-day study)

42768201 (1993)

Unacceptable/guideline

0, 7500, 10000 or 20000 ppm

0/0, 521.45/573.79, 

685.95/740.57 or 

1351.09/1442.64 mg/kg/day, 

M/F

NOAEL= Not established

LOAEL= 521.45 mg/kg/day in males, 573.79 mg/kg/day 

in females based on increases in the incidence of 

decreased exploratory activity, decreased alertness, 

decreased startle response and meiosis

870.6300. 

Developmental 

Neurotoxicity study 

– rats. 

46455701 (2004) 

Acceptable/Non-guideline

0, 14, 69 or 292 mg/kg/day 

(during gestation) 

Maternal:

NOAEL = 69 mg/kg/day. 

LOAEL = 292 mg/kg/day based on decreased body 

weight, body weight gain and food consumption during 

gestation and lactation. 

Developmental:

NOAEL – Not established. 

LOAEL = 14 mg/kg/day based on altered brain 

morphogenics. 

870.7485 

Metabolism and 

pharmacokinetics -

rat

43766913 (1993)

Acceptable/nonguideline

2.0 mg/kg single dose

In a metabolism study (85-1), groups of Wistar rats 

(5/sex) received a single dose (2 mg/kg) of 14C-Hoe 

039866 (glufosinate ammonium) by gavage. The 

majority of the radioactivity (95-98% of the dose) was 

eliminated during the first 24 hrs after dosing. The

parent compound, Hoe 039866, accounted for most of 

the eliminated radioactivity in the urine and feces of 

both males (80% of the dose) and females (73% of the 

dose). The metabolite, Hoe 061517, was consistently 

found in both urine and feces of both sexes. Hoe 099730 

(7-8% of the dose) and Hoe 042231 (3% of the dose) 

were found in the feces of both male and female rats and 

none in the urine. 

870.7485 

Metabolism and 

pharmacokinetics -

rat

43766914, 43778402 (1995)

Acceptable/nonguideline

500 mg/kg single dose

In a metabolism study, groups of Wistar rats (5/sex or 

2/sex) received a single dose (500 mg/kg) of 14C-Hoe 

039866 (glufosinate ammonium) by gavage. Animals 

were sacrificed at various times (2, 6, 24, and 96 hrs) 

after dosing. The majority of the radioactivity was 

eliminated during the first 24 to 48 hrs after dosing. The 

parent compound, Hoe 039866, accounted for the 

majority of the radioactivity eliminated in the excreta of 

both males (80% of the dose) and females (88% of the 

dose). This finding is consistent with the results of a 
Page 40 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

previous metabolism studies (MRID No. 40345638 and 

MRID No. 43766913). The metabolite, Hoe 061517, 

was consistently found in both urine (0.22-1.20% of the 

dose) and feces (0.44-1.36% of the dose) of both sexes. 

Hoe 099730 was found in feces (0.28-1.72% of the dose) 

of both male and female rats and barely above or at the 

level of the detection in the urine of both sexes (0.02-

0.04% of the dose). Hoe 042231 was mainly found in 

the feces of both male and females (0.2-0.28% of the 

dose). Very little if any of administered Hoe 039866 

was sequestered in any tissues examined.

870.7485 

Metabolism and 

pharmacokinetics -

rat

40345640 (1985)

Acceptable/nonguideline

30 mg/kg single dose

Groups of Wistar rats (5/sex) were orally administered a 

single nominal dose (30 mg/kg) of 14C-HOE 039866. 

Rapid elimination during the first 24 hr for both males 

and females was observed. The major route of excretion 

was via feces (88% and 84% of the administered 

radioactivity for males and females, respectively). 

Within seven days of post dosing, greater than 94% of 

the dose was eliminated. Kinetics analysis indicated that 

the process of excretion was a two-phase process. The 

tissue radioactivity level for kidneys, liver and gonads 

was just above the background level.

870.7485 

Metabolism and 

pharmacokinetics -

rat

43766913 (1993)

Acceptable/nonguideline

2.0 mg/kg single dose

In a metabolism study (85-1), groups of Wistar rats 

(5/sex) received a single dose (2 mg/kg) of 14C-Hoe 

039866 (glufosinate ammonium) by gavage. The 

majority of the radioactivity (95-98% of the dose) was 

eliminated during the first 24 hrs after dosing. The 

parent compound, Hoe 039866, accounted for most of 

the eliminated radioactivity in the urine and feces of 

both males (80% of the dose) and females (73% of the 

dose). The metabolite, Hoe 061517, was consistently 

found in both urine and feces of both sexes. Hoe 099730 

(7-8% of the dose) and Hoe 042231 (3% of the dose) 

were found in the feces of both male and female rats and 

none in the urine.

870.7485 

Metabolism and 

pharmacokinetics -

rat

40345642 (1985)

Acceptable/nonguideline

2.0 mg/kg/day (repeat dose 14 

days)

Groups of Wistar rats (6/sex) were orally administered 

(gavage) unlabeled HOE 039866 for 14 days and 14CHOE039866 at the 15th day at a nominal dose of 2 

mg/kg. The majority of the radioactivity was excreted 

within 24 hr after the last dose. The major route of 

elimination was via feces. There was also a two-phased 

elimination process. More radioactivity was found in 

the tissues of animals dosed repeatedly than that of 

animals receiving a single dose.

870.7600

Dermal Penetrationrat

40345620 (1986)

Acceptable/guideline

0, 0.1, 1.0 or 10.0 mg/6cm2 

The results indicate that at the low dose (0.1 mg) 42.5 to 

50.8% of the applied radioactivity was absorbed whereas 

at the high dose (10 mg) 26% was absorbed. After 

removal and washing of the treated skin a substantial 

amount of the radioactivity still remained in the skin, 

and it was gradually absorbed and eliminated. 

Radioactivity was found in both feces and urine samples, 

but the majority of HOE 039866 was eliminated in the 

urine. In all organs/tissues examined, radioactivity was 

found to reach a maximum level either at four or 10 hr 

after exposure. Subsequently, the radioactivity dropped 

rapidly. The amount of radioactivity found in the brain 

was very minimal relative to that of kidneys and liver.
Page 41 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

870.7600. Dermal 

penetration – rat

45922103 (1995)

Acceptable/Guideline

12, 116 or 1218 μg/cm2 .

A dermal absorption factor of 9% can be supported 

based on similar total absorbed and remaining on the 

skin at 10 and 24 hours

HOE 061517 Metabolite

870.3100

90-Day oral toxicity 

rodents-rat

44076206 (1988)

Acceptable/guideline)

0, 400, 1600 or 6400 ppm

0/0, 30/32, 102/113 or 420/439 

mg/kg/day M/F

NOAEL = 102 mg/kg/day in males, 113 mg/kg/day in 

females

LOAEL = 420 mg/kg/day in males, 439 mg/kg/day in 

females based on increased in reticulocytes and 

increased in absolute and relative liver weights in males

870.3100

90-Day oral toxicity 

rodents-mice

44076207 (1989)

Acceptable/guideline)

0, 320, 1600, 3200 or 8000 ppm

0/0, 46/47, 209/220, 496/561 or 

1121/1340 mg/kg/day M/F

NOAEL = 1121 mg/kg/day in males, 1340 mg/kg/day in 

females

LOAEL = Not established

870.3700a

Prenatal 

developmental in 

rodents- rat

44076209 (1994)

Acceptable/nonguideline

0, 100, 300 or 900 mg/kg/day

Maternal: NOAEL = 300 mg/kg/day

LOAEL = 900 mg/kg/day based on one death and 

clinical findings (persistent piloerection and/or increased

urinary output)

Developmental: NOAEL = 300 mg/kg/day 

LOAEL =900 mg/kg/day based on increases in the 

incidences of total litter loss and in the fetal and litter 

incidences of wavy and/or thickened ribs

870.3700b Prenatal 

developmental in 

nonrodents- rabbit

44076210 (1994)

Unacceptable/guideline

0, 50, 100 or 200 mg/kg/day

Maternal: NOAEL = 50 mg/kg/day 

LOAEL = 100 mg/kg/day based on increased abortions, 

mortality, and reductions in food and water 

consumption, body weight gain, and fecal output

Developmental: NOAEL = 200 mg/kg/day

LOAEL = Not observed

HOE 099730 metabolite

870.3100

90-Day oral toxicity 

rodents-rat

44076201 (1994)

Acceptable/guideline

0, 400, 2000 or 10,000 ppm

0/0, 29/32, 147/162 or 738/800 

mg/kg/day M/F

NOAEL = 147 mg/kg/day in males, 162 mg/kg/day in 

females

LOAEL = 738 mg/kg/day in males, 800 mg/kg/day in 

females based on glutamine synthetase inhibition in the 

brain

870.3100

90-Day oral toxicity 

rodents-mice

44076202 (1994)

Acceptable/guideline

0, 500, 2000 or 8000 ppm

0/0, 83/110, 324/436 or 

1296/1743 mg/kg/day M/F

NOAEL = Not established for males, 110 mg/kg/day in 

females

LOAEL = 83 mg/kg/day in males, 436 mg/kg/day in 

females based on glutamine synthetase inhibition in the 

brain

870.3150 

Subchronic 

Nonrodent Oral 

Toxicity-dog

44076203 (1994)

Acceptable/guideline

0, 500, 2000 or 8000 ppm

0/, 19/21, 72/79 or 289/300 

mg/kg/day M/F

NOAEL = 19 mg/kg/day in males, 21 mg/kg/day in 

females

LOAEL = 72 mg/kg/day in males, 79 mg/kg/day in 

females based on glutamine synthetase inhibition in the 

brain

870.3700a

Prenatal 

developmental in 

rodents- rat

44076204 (1993)

Acceptable/guideline

0 or 1000 mg/kg/day

Maternal: NOAEL = 1000 mg/kg/day

LOAEL = Not observed

Developmental: NOAEL = 1000 mg/kg/day 

LOAEL = Not observed

870.3700b Prenatal 

developmental in 

nonrodents- rabbit

44076205 (1995)

Acceptable/guideline

0, 64, 160 or 400 mg/kg/day

Maternal: NOAEL = 64 mg/kg/day 

LOAEL = 160 mg/kg/day based on reduced feed 

consumption

Developmental: NOAEL = 64 mg/kg/day

LOAEL = 160 based on uni- or bilateral extra at the 13th
Page 42 of 45

Guideline No./ 

Study Type

MRID No. (year)/ 

Classification /Doses Results

thoracic vertebra

870.6200

Acute Neurotoxicity 

-rat

45190702 (1999)

Acceptable/nonguideline

0, 100, 1000 or 2000 mg/kg

NOAEL= 1000 mg/kg in males and females

LOAEL= 2000 mg/kg in males and females based on 

clinical signs of toxicity including sedation, ruffled fur, 

and diarrhea

870.6200

Acute Neurotoxicity 

-rat

45190701 (1999)

Acceptable/nonguideline

0, 100, 1000 or 2000 mg/kg

NOAEL= 100 mg/kg in males and females

LOAEL= 1000 mg/kg in males and females based on 

decreased body weight gain

870.6200b Repeat 

Dose Neurotoxicityrat

45179101, 45179102, 45297001 

(2000); Acceptable/nonguideline

0, 20, 200 or 2000 ppm

0/0, 1.6/1.75, 15.5/17.7 or 

158.9/179.4 mg/kg/day, M/F

NOAEL= 158.9 mg/kg/day in males, 179.4 mg/kg/day 

in females 

LOAEL= Not established in males and females

HOE 058192 (L-isomer of glufosinate ammonium)

870.3100

90-Day oral toxicity 

rodents-rat

44068501 (1989)

Acceptable/guideline

0, 25, 250, 1250 or 2500 ppm

0/0, 1.9/1.9, 18.5/19.8, 

91.8/100.3 or 186.4/194.3 

mg/kg/day M/F

NOAEL = 18.5 mg/kg/day in males, 19.8 mg/kg/day in 

females

LOAEL = 91.8 mg/kg/day in males, 100.3 mg/kg/day in 

females based on increased ammonia levels in the 

plasma and urine and slight kidney weight increases

870.3150 

Subchronic 

Nonrodent Oral 

Toxicity-dog

44068502 (1989)

Acceptable/guideline

0, 2, 5 or 8.5 mg/kg/day

NOAEL = 2 mg/kg/day 

LOAEL = 5 mg/kg/day based on increased plasma and 

kidney ammonia levels

870.3700b Prenatal 

developmental in 

nonrodents- rabbit

43829405 (1992)

Acceptable/guideline

0, 1.25, 2.50, or 5.00 mg/kg/day

Maternal: NOAEL = 1.25 mg/kg/day ; LOAEL = 2.50 

mg/kg/day based on decrease in body weight gains and 

food consumption, neurotoxic signs and abortions

Developmental: NOAEL = 1.25 mg/kg/day; LOAEL = 

2.50 mg/kg/day based on an increase in post 

implantation loss (fetal resorptions)
Page 43 of 45

Appendix B. Magnitude of the Residue Considerations

Citrus Fruit

For citrus fruits, a total of twenty three magnitude of the residue field trials were conducted for 

orange, lemon, and grapefruit. A summary of the residue data is presented in Table B.1. Eight of 

the 23 trials used a non-ionic antifoam adjuvant. Following three broadcast applications at a

target rate of 1.50 lb ai/A/application, with a 14-day RTI and a 14-day PHI, residues of 

glufosinate ammonium (GA) and its two metabolites, glufosinate propanoic acid (MPP) and Nacetylglufosinate (NAG) were not detected above the limit of quantitation (LOQ) (0.05 ppm) 

in/on oranges, lemons, or grapefruit. Residue decline studies performed on each of the three 

representative crop types at PHIs of 7, 11, 14, 17, and 21 days showed residues below the LOQ

for all residues of concern. Accordingly, the appropriate tolerance level for citrus fruit is 0.15 

ppm [computed as the sum of the LOQs for each of the three residues of concern].

Stone Fruit

For peach, nine crop field trials were conducted, all without adjuvant. Following two broadcast 

applications at a target rate of 1.50 lb ai/A/application, with a 28-day RTI and a 14-day PHI, there 

were no residues of GA, MPP or NAG detected above the LOQ (0.05 ppm) in/on peach samples. 

There were no residue decline studies performed for peach.

For plum and cherry, six crop field trials each were conducted. Five of the 12 trials for plum and 

cherries used a non-ionic antifoam adjuvant. Following two broadcast applications at a target rate 

of 1.50 lb ai/A/application, with a 28-day RTI and a 14-day PHI, residues of GA and NAG were 

not detected above the LOQ (0.05 ppm). One cherry trial and one plum trial showed MPP 

residues above the LOQ. Thus, for cherries, the highest average field trial (HAFT) was 0.083 

ppm with a maximum residue of 0.098 ppm MPP. For total glufosinate ammonium, the cherry

HAFT was 0.183 ppm with a maximum residue of 0.198 ppm. For plums, the HAFT was 0.0655

ppm with a maximum residue of 0.066 ppm MPP. For total glufosinate ammonium, the plum 

HAFT was 0.1655 ppm with a maximum residue of 0.166 ppm. Results from the residue decline 

studies performed on both crops at PHIs of 7, 11, 14, 17, and 21 days indicated that total 

glufosinate ammonium residues in cherry and plum were found to be near or below the LOQ at all 

PHIs; therefore, a trend was not observed. The recommended stone fruit tolerance level was 

based on the cherry data; the maximum total glufosinate ammonium residue of 0.198 ppm 

indicates a stone fruit tolerance level of 0.25 ppm is appropriate.

Pome Fruit

For pear, six crop field trials were conducted. In all trials, ammonium sulfate fertilizer was added 

to each tank mixture. Two sites received a non-ionic antifoam adjuvant. Following three

broadcast applications at a target rate of 1.50 lb ai/A/application, with a 14-day RTI and a 14-day

PHI, residues of GA and NAG in/on pear were less than the LOQ (0.05 ppm). However, one pear 

trial found MPP residues above the LOQ. Specifically, the pear HAFT for MPP was 0.081 ppm, 

and the maximum residue was 0.089 ppm. For total glufosinate ammonium, the pear HAFT was 

0.181 ppm with a maximum residue of 0.189 ppm. Results from the residue decline study with 

PHIs of 7, 9, 14, 16, and 21 days showed all residues of concern were below the LOQ at all 

sampling intervals. 

The established apple tolerance of 0.05 ppm is based on the same use pattern used in the pear 

trials. Accordingly, it is appropriate to recommend a pome fruit tolerance based on the pear trials. 

The maximum total glufosinate ammonium residues of 0.189 ppm indicates a pome fruit 

tolerance level of 0.25 ppm is appropriate.
Page 44 of 45

 

Olive

For olive, three crop field trials were conducted. In all trials, ammonium sulfate fertilizer was 

added to each tank mixture. In two of the trials, a non-ionic antifoam adjuvant was also added to 

the tank mixture. Following three broadcast applications at a target rate of 1.50 lb 

ai/A/application, with a 14-day RTI and a 14-day PHI, there were no residues of GA, MPP, or 

NAG detected above the LOQ (0.05 ppm) in/on olive samples. There were no residue decline 

studies performed for olive. The appropriate tolerance level for olive is 0.15 ppm [computed as 

the sum of the LOQs for each of the three residues of concern].

Sweet Corn

For sweet corn, twelve crop field trials were conducted (see Table B.2). Two of the trials in 

Arlington, Wisconsin were conducted in the same field in the same year, and therefore cannot be 

considered independent. In all trials, ammonium sulfate fertilizer was added to each tank mixture, 

but no adjuvant was used. Following two foliar applications at a rate of 0.375 lb ai/A, with a RTI

of 14 days and a PHI of 30-50 days, maximum total glufosinate ammonium residues in/on sweet 

corn ears, forage and stover were 0.19, 0.79, and 3.70 ppm, respectively. The tolerance levels for 

sweet corn commodities were determined using the Organization for Economic Cooperation and 

Development (OECD) tolerance calculation procedures. Thus, the recommended tolerance levels 

for sweet corn ears, forage, and stover are 0.30, 1.5, and 6.0 ppm, respectively. 

TABLE B.1. Summary of Total Glufosinate Ammonium Residues (sum of GA + MPP + NAG) in Fruits 

and Olive.

Commodity

Total Applic. Rate 

(lb ai/A) PHI 

(days)

Residue Levels (ppm)

n

1 Min. Max. HAFT Median Mean

Orange 4.38 to 4.61 14 24 <0.15 <0.15 <0.15 NA NA

Lemon 4.50 to 4.53 14 10 <0.15 <0.15 <0.15 NA NA

Grapefruit 4.47 to 4.58 14 12 <0.15 <0.15 <0.15 NA NA

Pear 4.45 to 4.57 14 12 <0.15 0.189 0.181 0.15 0.155

Cherry 3.00 to 3.11 14 12 <0.15 0.198 0.183 0.15 0.156

Plum 2.92 to 3.03 14 12 <0.15 0.166 0.1655 0.15 0.153

Peach 2.86 to 3.07 14 18 <0.15 <0.15 <0.15 NA NA

Olive 4.50 to 4.52 14 6 <0.15 <0.15 <0.15 NA NA

1

 Two values per field trial.
Page 45 of 45

TABLE B.2. Summary of Total Glufosinate Ammonium Residues (sum of GA + MPP + NAG) in Sweet Corn.

Commodity

Total Applic. Rate 

(lb ai/A)

PHI 

(days)

Residue Levels (ppm)

n

1 Min. Max. HAFT Median Mean

Sweet Corn, 

Ears 0.75 30-50 11 0.10 0.19 0.19 0.10 0.11

Sweet Corn, 

Forage 0.75 30-50 11 0.18 0.79 0.79 0.31 0.39

Sweet Corn, 

Stover 0.75 30-50 11 0.16 3.7 3.7 1.53 1.42

1 One value per field trial: replicate averages.