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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

 POLLUTION PREVENTION

MEMORANDUM

Date: August 31, 2010

Subject: 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.

PC Code: 128850 DP Barcode No.: D372625

Decision No.: 424397 Registration No.: 264-646

Petition No.: 9F7655 and 9E7604 Regulatory Action: Tolerance Petition 

Risk Assessment Type: Residue Chemistry Case No.: NA

TXR No.: NA CAS No.: 77182-82-2

MRID No.: 47915701, 47915702, 47915703, 

47915704, 47915705, 47915706, 47915707, 

47915708, 47828201, 47828202 and 47828203

40 CFR: §180.473

FROM: Ideliz Negrón-Encarnación, Ph.D., Chemist 

 Risk Assessment Branch V

 Health Effects Division (7509P)

THROUGH: William H. Donovan, Ph.D., Chemist 

Risk Assessment Branch V

 Health Effects Division (7509P)

 Jack Arthur, Chief

 Risk Assessment Branch V

 Health Effects Division (7509P)

TO: Sidney Jackson, Barbara Madden, RM Team 05

James Stone, RM Team 23

Registration Division (RD) (7505P)

Tom Myers, Risk Manager 

Pesticide Re-Evaluation Division (PRD) (7508P)
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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Executive Summary

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

enantiomer is herbicidally active. The compound is a non-selective herbicide and acts as an 

inhibitor of glutamine synthetase which leads to poisoning of the plant by ammonia. Glufosinate 

ammonium is currently registered for use on both transgenic and nontransgenic crops. The 

transgenic plants currently registered (canola, sugar beet, corn, soybean) and the transgenic plants 

requested for registration (rice and cotton) have been engineered to express phosphiothrionacetyl-transferase (PAT) which enables the plant to metabolize glufosinate ammonium into Nacetyl-glufosinate.

The petitioners have proposed application of Liberty® 280 SL (24.5% glufosinate ammonium; 

soluble concentrate; EPA Reg. No. 264-829) to Citrus Fruits (Crop Group 10), Pome Fruits 

(Crop Group 11), Stone Fruits (Crop Group 12) and Olives. However, the crop field trials were

performed with RELY 200SL (18.19% glufosinate ammonium; soluble concentrate; EPA Reg. 

No. 264-660). For the intended purpose of establishing tolerances, the RELY 200SL data will be 

considered acceptable to amend the Liberty label to included uses for the mentioned RACs. The 

Liberty® label may include use directions to support a three applications to the soil at a

maximum rate of 1.5 lb ai/A, 14-day retreatment interval (RTI), and 14-day pre harvest interval 

(PHI) for citrus fruits, pome fruits and olives for a maximum seasonal rate of 4.5 lb ai/A. For 

stone fruits, the studies submitted support two applications to the soil with a maximum rate of 

1.5 lb ai/A, 28-day RTI, and 14-PHI for a maximum seasonal rate of 3.0 lb ai/A. The product 

label prohibits application through irrigation equipment and by aircraft.

The Interregional Research Project No 4 submitted crop field trial data to support the use of 

glufosinate ammonium on transgenic sweet corn. Twelve crop field trials were conducted in 

EPA regions 1, 3, 5, 10 and 11. Two foliar applications of Liberty Herbicide at a rate of 0.375 lb 

ai/A for a total of 0.75 lb ai/A were performed with a retreatment interval (RTI) of 14-16 days. 

Ammonium sulfate was included in the tank mix. Sweet corn ears, forage and stover were 

harvested 30 to 50 days following the final application. Stover was dried for 5 to 13 days after 

harvest.

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

Committee (MARC) concluded that the residues of concern in the crops studied, 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 fruits, pome fruits, stone 

fruits, olives and sweet corn. 

Adequate enforcement and multiresidue analytical methods are available for glufosinate 

ammonium, N-acetylglufosinate, and glufosinate propanoic acid. In the current studies, residues 

of glufosinate ammonium, N-acetyl-glufosinate, and glufosinate propanoic acid were determined

using one of three methods. A Gas Chromatography (GC) with flame photometric detection

method currently used for enforcement purposes (BK/01/99) was used for the analysis of peach 

samples. A method very similar to the enforcement method HRVA-5 was used for the analysis 

of sweet corn samples. A Liquid Chromatography/Mass Spectrometry/Mass Spectrometry

(LC/MS/MS) method developed by Bayer was used for the analysis of orange, lemon, grapefruit, 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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prune, pear, cherry, olive, olive oil, orange oil and prunes. The method described in Bayer 

CropScience report number GL-001-P07-01, “An Analytical Method for the Determination of 

Residues of Glufosinate in Crop Matrices Using LC/MS/MS” residues were quantitated by liquid 

chromatography/mass spectroscopy/mass spectroscopy (LC/MS/MS). The limit of quantitation 

(LOQ) is reported to be 0.05 ppm for each analyte. The method was adequate for data collection 

based on concurrent method recoveries. Control samples were fortified with glufosinate 

ammonium, N-acetyl-glufosinate, and glufosinate propanoic acid at 0.05, 0.5 ppm for all 

commodities. All recoveries were between the acceptable range of 70-120%. 

With the current petition, frozen storage stability was demonstrated for glufosinate residues in 

peaches stored frozen for 730 days (24.3 months) and N-acetylglufosinate and 3-

methylphosphinico-propanoic acid residues stored frozen for 778 days (25.9 months). Previously

submitted and reviewed frozen storage stability data indicate that glufosinate ammonium and 

glufosinate propanoic acid are stable for 730 days on frozen apples, corn grain, and soybeans 

(PP#8F3607, J. Garbus, 8-Aug-1990), and for 24 months on oranges and 6 months on kiwi. 

Blueberry storage stability data results showed that glufosinate ammonium and glufosinate 

propanoic acid were stable in/on frozen blueberry samples for 693 days and 664 days, 

respectively (D271110, T. Bloem, 20/June/2002). Additional storage stability data indicated that 

glufosinate ammonium, N-acetylglufosinate, and glufosinate propanoic acid are stable for 12 

months on transgenic soybean seed, forage and hay; for 3 months on soybean oil and meal; for 6 

months on transgenic corn grain, fodder and forage; and for 24 months on transgenic sugar beet 

tops and roots (D211531 and D219069, M. Rodriguez, 7-Mar-1996; D257629, T. Bloem, 9-Jul1999). These data are adequate to validate the storage interval and conditions for the samples 

analyzed as part of the current study.

Regulatory Recommendations and Residue Chemistry Deficiencies

Provided revised Section B and F are submitted as specified below there are no residue chemistry

deficiencies that would preclude granting a registration for the requested uses of glufosinate 

ammonium on citrus fruits, pome fruits, stone fruits, olives and sweet corn. The submitted data 

support the following tolerances for glufosinate ammonium residues of concern in/on the 

following raw agricultural commodities: 

Citrus fruit (CG 10) ................................................... 0.15 ppm

Pome fruit (CG 11) ....................................................0.25 ppm

Stone fruit (CG 12) ................................................... 0.25 ppm

Olives .........................................................................0.15 ppm

Corn, sweet, kernels plus cob with husks removed ....0.25 ppm

Corn, sweet, forage .......................................................1.6 ppm

Corn, sweet, stover.........................................................10 ppm

A revised human health risk assessment including glufosinate ammonium uses on citrus fruits, 

pome fruits, stone fruits, olives and sweet corn is being prepared as a separate document.

Revised Section B - Label use directions should match crop field trial use pattern to include 

maximum application rates, RTI, and adjuvant uses.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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Revised Section F – Proposed crop commodity definitions and tolerance levels should be revised 

to those recommended in Table 9.

Background

The chemical structure and nomenclature of glufosinate ammonium, N-acetyl-glufosinate, and 

glufosinate propanoic acid are presented in Table 1 while the physicochemical properties are 

presented in Table 2.

TABLE 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-DL-homoalanin-4-yl-(methyl)-phosphinate

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

CAS registry number 77182-82-2

End-use product (EP) RELY 200 SC

Compound

P

HO

O CH3

OH

O

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

Chemical name 3-methylphosphinico-propionic acid or

3-(Hydroxymethylphosphinyl) propanoic acid

Compound

P

HO

O CH 3

O

OH

NH

CH 3

O

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

Chemical name 2-(Acetylamino)-4-(hydroxymethyl phosphinyl) butanoic acid
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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Table 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;

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

Vapor pressure at 25 °C (torr) <7.50 x 10-9

Dissociation constant, pKa 9.15 ± 0.07

Octanol/water partition coefficient (Log KOW) 9.77 x 10-5

UV/visible absorption spectrum (nm) >190

1

Source: DER for MRID 46573701, Tom Bloem, 2005

860.1200 Directions for Use

For the application of glufosinate ammonium in/on citrus, pome fruit, stone fruit and olives, the 

petitioner has submitted undated draft labels in conjunction with each petition for the 2.34 lb/gal 

SL formulation (Liberty® 280 SL Herbicide; EPA Reg. No. 264-829). A summary of the 

proposed/registered crop use patterns in this document is listed in Table 3.

Liberty® 280 SL Herbicide is presently registered for use on canola, field corn, silage corn, 

cotton, soybean, bushberries, lingonberry, juneberry, salal, tree nuts, grape vineyards and potato. 

The petitioner submitted residue field trials to establish tolerances for glufosinate ammonium and 

two metabolites in/on citrus, pome fruit, stone fruit and olives. For this RELY 200, a soluble 

concentrate formulation containing 1.64 lb ai/A was applied to the soil near the base of the trees.

IR-4 submitted field trials to support the use of glufosinate ammonium in/on transgenic sweet 

corn. With this purpose, foliar applications of Liberty® Herbicide on transgenic sweet corn were 

performed. End-use products equivalent to the Liberty® Herbicide may be registered for use on 

transgenic sweet corn based on the data generated in these crop field trials.
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Table 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 Do not use

1 The numbers in bold are not in the label but correspond to the use pattern proposed based on the field trials.

2 A non-ionic antifoam adjuvant may be added to the tank mixture at the application rate used in the field trials.

Conclusions. The proposed use directions should specify the maximum application rate and 

retreatment interval; therefore, the petitioner may revise the product label to specify the 

conditions used in the field trials studies. The Liberty® label may include use directions to 

support a three applications to the soil at a maximum rate of 1.5 lb ai/A, 14-day retreatment 

interval (RTI), and 14-day pre harvest interval (PHI) for citrus fruits, pome fruits and olives for a 

maximum seasonal rate of 4.5 lb ai/A. For stone fruits, the studies submitted support two 

applications to the soil with a maximum rate of 1.5 lb ai/A, 28-day RTI, and 14-PHI for a 

maximum seasonal rate of 3.0 lb ai/A. A non-ionic antifoam adjuvant was included in the 

herbicide mixture in some field trials for citrus fruits, peach, plum, pear and olives; therefore, the 

use directions may include the use of this adjuvant on the crops specified but the corresponding 

use rate should reflect the one used in the crop field trials. For transgenic sweet corn, the crop 

field trials support the following use pattern: two foliar applications of Liberty Herbicide at a 

maximum rate of 0.365 lb ai/A for a total seasonal maximum rate of 0.73 lb ai/A, a 14-day RTI, 

and a 50-day PHI following the final application. Moreover, as stated in the label use directions 

for sweet corn, ammonium sulfate must be added to the pesticide mixture.

860.1300 Nature of the Residue – Plants and Livestock

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, 
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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-Jul1999; 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 the crops studied, 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 and sweet corn. 

Glufosinate propanoic acid was the only metabolite identified in the nontransgenic studies (2-

40% total radioactive residue (TRR); only soybean leaf, corn stover, and apples were analyzed). 

The petitioner demonstrated that 40% of the TRR in nontransgenic corn stover was incorporated 

into protein, starch, cellulose, and lignin. Glufosinate ammonium, N-acetyl-glufosinate, and 

glufosinate propanoic acid were the major residues identified in the transgenic crops (40-98% of 

the TRR). The petitioner demonstrated that for transgenic sugar beet leaves, surface residues are 

composed of a nearly equal mixture of the D and L enantiomers of glufosinate ammonium while 

interior residues are composed of almost exclusively D enantiomer of glufosinate ammonium. 

This indicates that only the L enantiomer of glufosinate ammonium was acetylated to form Nacetyl-glufosinate. 

There are no feedstock items associated with this petition; however, the nature of the residue in 

livestock commodities has been assessed and have been determined to be the same as in plants 

(D271110, T. Bloem, 20/June/2002).

860.1340 Residue Analytical Methods

Enforcement methods

D335330, T. Bloem, 09/12/2007

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 derivitized to the same 
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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 method BK/01/99 is a suitable method for enforcement of sweet

corn, stone fruit, pome fruit, citrus fruit and olive tolerances. 

Data-collection methods

Three methods were used for quantitation of glufosinate ammonium and its two metabolites. For 

peach samples, residues of glufosinate ammonium and its two metabolites, 3-methylphosphinicopropanoic acid and N-acetylglufosinate were analyzed from their derivatives AE F064706 and 

AE F070951 by using a gas chromatograph equipped with a flame photometric detector operating

in the phosphorous mode. This method is equivalent to the enforcement method BK/01/99 but 

instead of following the general procedure, the optional speciation process (optional method, 

Section 3.2) is followed to quantify the parent and its two metabolites separately. Quantitation is 

based on the use of a calibration curve. The limit of quantitation for each analyte is 0.05 ppm. 

Concurrent recovery data was obtained for peach samples by spiking the samples with the 

corresponding standards before the extraction process.

For sweet corn, a similar method to the enforcement method HRVA-5 was used for quantitation. 

In this method the analytes were extracted from samples with deionized water, the sample was 

cleaned through an anion exchange resin, derivatized with trimethylorthoacetate/glacial acetic 

acid to AE F064706 and AE F070951, and cleaned through a silica solid phase extraction 

column. The parent and N-acetylglufosinate are derivatized to the same analyte, AE F064706, 

while glufosinate propanoic acid is derivatized to AE F070951. The residues were subsequently

measured by gas chromatography with flame photometric detection in phosphorous mode, and 

reported as glufosinate free acid equivalents. Modifications were performed to add clarity to the 

extraction procedure. To prove the extraction efficiency in sweet corn, this method was 

validated by obtaining recoveries of glufosinate ammonium and glufosinate propanoic acid but to 

support it use in transgenic sweet corn IR-4 submitted with the current petition recovery data for 

N-acetylglufosinate. The method was validated with triplicate samples of sweet corn ears at 

levels 0.0480 and 0.480 ppm, forage at 0.048 and 1.06 ppm, and stover at 0.048, 0.480 and 5.32 

ppm. The recoveries of N-acetylglufosinate in/on sweet corn were between 78% and 113% for 

all matrices. The method LOQ was determined to be 0.05 ppm for each analyte.

For orange, lemon, grapefruit, cherry, plum, pear and olive, residues were determined using a 

method described in Bayer Report Number GL-001-P07-01, “An Analytical Method for the 

Determination of Residues of Glufosinate in Crop Matrices Using LC/MS/MS”. Orange, lemon, 

grapefruit, cherry, plum, pear and olive raw agricultural commodities and processed samples 

were analyzed for residues of glufosinate ammonium and its two metabolites, glufosinate 

propanoic acid and N-acetylglufosinate using liquid chromatography with tandem mass-spectral 

detection (LC/MS-MS) (Method Number GL-001-P07-01). 
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Briefly, for extraction from orange, lemon, grapefruit, cherry, plum, pear and olive RACs and 

prunes process commodity, a sub-sample was extracted by shaking the sample in the presence of 

water for 30 minutes at room temperature. An internal standard was added to the sample vial and 

then an aliquot of the extract was mixed with methanol and purified through a SAX SPE column. 

The eluent was dried, reconstituted, and injected onto the LC/MS/MS for quantification of the 

residues. For extraction of the olive oil and citrus oil matrix, an oil aliquot was dissolved into 

hexane and shake in the presence of water at room temperature two separate times. The water 

layers were decanted and combined. An aliquot of the water extract was mixed with acetone and 

evaporated to dryness. The residue was reconstituted into 1 mL diluting solvent (85:15 mixture 

of acetonitrile/diluting buffer) and injected onto LC/MS/MS. An electrospray interphase in 

positive mode was used for ionization of the sample. Since the analytes elute at a similar 

retention time, specificity is achieved by multiple reaction monitoring of glufosinate ammonium 

(152.7/134.0 m/z), N-acetylglufosinate (223.7/117.0 m/z) and glufosinate propanoic acid 

(155.7/137.0 m/z). Quantification of the residues was based on the use of a calibration curve and 

the deuterated analytes as internal standards. Based on the lowest level of method validation 

(LLMV), the limit of quantitation (LOQ) was 0.05 ppm for each analyte. Concurrent method 

recovery data was obtained for citrus, pome fruit, stone fruit and olive raw agricultural and 

processed commodities. 

The recovery of the parent and its two metabolites was based on relative recovery studies in 

which a known amount of the analyte and deuterated analyte were added during the sample 

preparation process and the recovery was calculated by measuring the response of the analyte 

with respect to its deuterated form. For orange, lemon, grapefruit, cherry, plum, pear, peach and 

olive, the method was validated for glufosinate ammonium and its two metabolites at levels of 

0.05 ppm and 0.50 ppm. The average recoveries obtained from these commodities were between 

78.7% and 110%. For orange oil, olive oil and plums, the method was validated at 0.05 ppm and 

at 0.8 ppm only for plum. The average recoveries were within 80.3% and 112%. Average 

recoveries for all RAC and processed commodities were within the acceptable range of 70-120%. 

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

methods used for data collection was adequate based on the method recoveries, precision and the 

range of levels tested which included the LOQ and tolerance level. 

860.1360 Multiresidue Methods

Glufosinate ammonium, glufosinate propanoic acid, and N-acetyl-glufosinate were not 

quantitatively recovered from any of the FDA Multiresidue Testing Protocols. This information 

has been forwarded to FDA (PP#8F3607, J. Garbus, 14-Aug-1988; PP#5F4578, M. Rodriguez, 

10-Oct-1995).
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860.1380 Storage Stability

Reference DERs: 47828201.der.doc and 47915705.der.doc.

Previously submitted and reviewed frozen storage stability data indicate that glufosinate 

ammonium and glufosinate propanoic acid are stable for 24 months on frozen apples, corn grain, 

and soybeans (PP#8F3607, J. Garbus, 8-Aug-1990), for 24 months on oranges and 6 months on 

kiwi (study pending approval). Moreover, blueberry storage stability data was submitted with the 

petition for tolerances in the bushberries crop group (D271110, T. Bloem, 20/June/2002). The 

results showed that glufosinate ammonium and glufosinate propanoic acid were stable in/on 

frozen blueberry samples for 693 days and 664 days, respectively. Additional storage stability

data indicated that glufosinate ammonium, N-acetylglufosinate, and glufosinate propanoic acid

are stable for 12 months on transgenic soybean seed, forage and hay; for 3 months on soybean oil 

and meal; for 6 months on transgenic corn grain, fodder and forage; and for 24 months on 

transgenic sugar beet tops and roots (D211531 and D219069, M. Rodriguez, 7-Mar-1996; 

D257629, T. Bloem, 9-Jul-1999). 

Frozen storage stability for glufosinate residues was investigated in peaches stored frozen for 730 

days (24.3 months) and N-acetylglufosinate and 3-methylphosphinico-propanoic acid residues 

stored frozen for 778 days (25.9 months) under the same storage conditions as those of the field 

samples. The storage stability study started when the field samples arrived at the analytical 

laboratory the fortified samples were stored under the same conditions as the field samples. 

Average storage stability results ranged from 87% to 95% for glufosinate ammonium, from 70%

to 78% for 3-methylphosphinico-propanoic acid, and from 77% to 80% for N-acetylglufosinate. 

However, the storage stability period do not cover the actual storage duration for peaches, 791 

days (26 months). The number of days not covered by the storage stability studies was 61 for 

glufosinate ammonium and, 13 for 3-methylphosphinico-propanoic acid and N-acetylglufosinate. 

Since the storage stability recoveries for glufosinate ammonium were quite high and just a few 

days were not covered for the two metabolites, on this time HED will considered the peach 

storage period covered by the interval of demonstrated storage stability. 

Storage stability was also demonstrated in sweet corn ears (765 and 914 days)), forage (793 days) 

and stover (812 days) spiked with glufosinate ammonium and glufosinate propionic acid at < -10 

oC. Average storage stability results were from 64.2 to 92.4% while the results corrected for the 

mean concurrent recoveries were from 89.1 to 112% after over two years of frozen storage. This 

storage stability study support the stability of glufosinate and glufosinate propionic acid for 914 

days for ears, and 793 days for forage and 812 days for stover. Based on the storage stability

results the interval of demonstrated storage stability will be considered to cover the sweet corn 

storage period for ears (197-950 days), forage (146-788 days) and stover (143-810 days) samples. 

The stability of the N-acetylflufosinate was not assessed during this study which is a metabolite 

relevant to transgenic sweet corn. Previous storage stability studies performed up to 6 months on 

nontransgenic field corn show the stability of this residue but this interval do not covers the study

period. However, the stability of N-acetylglufosinate in peach samples was demonstrated up to 

778 days which covers the storage period of 10 of the 12 samples of sweet corn ears and most of 

the forage and stover samples; therefore, the sweet corn data will be considered acceptable for 

the current petition.
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To translate storage stability data to all RACs, HED guidelines require that stability is proven for

at least five diverse crops. Indeed, the data available covers this requirement: oilseed (transgenic 

soybean seed, 12 months), nonoily grain (transgenic corn grain for 6 months and nontransgenic 

corn grain for 24 months (N-acetylglufosinate not assessed)), fruit or fruiting vegetable (orange

for 24 months and blueberries for 21.8 months, N-acetylglufosinate not assessed), leafy vegetable 

(sugar beet tops, 24 months), and root crop (sugar beet root, 24 months).

Based on the available storage stability data and since acceptable percent recoveries were 

attained for fortified samples run concurrent to the treated samples, HED concludes that the 

storage intervals and conditions for the samples collected as part of the orange, lemon, grapefruit, 

cherry, plum, pear, peach and olive field trials are acceptable. The storage durations and 

conditions of samples from the crop field trials submitted to support these petitions are presented 

in Table 4.

The storage stability of glufosinate ammonium, glufosinate propanoic acid and Nacetylglufosinate has been established in some processed commodities. These are stable under 

frozen conditions for 3 months on soybean oil and meal, and for 9 months on sugar beet pulp, 

molasses, and sugar beet refined sugar (D211531 and D219069, M. Rodriguez, 7-Mar-1996; 

D286447, T. Bloem, 11-Dec-2002). Storage stability studies for olive oil, orange oil and prunes 

processed commodities haven’t been submitted with the current petition. These studies are 

recommended in OPPTS 860.1380 and OPPTS 860.1520 guidelines. However, under certain 

circumstances HED waives these studies. The storage intervals for olive oil (3.7 months) and 

prunes (4.4 months) can be supported based on the available storage stability studies for soybean 

oil and a wide variety of RACs. The orange oil commodity was stored for 9.2 months. Storage 

stability for orange oil will not be requested at this time based on the following: residue levels 

were <LOQ in the RAC and processed commodity after applying exaggerated rates (5x) of the 

end use product, and storage stability has been demonstrated on a wide variety of RACs for at 

least 2 years and some processed commodities for at least 9 months. 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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TABLE 4. Summary of Storage Conditions.

Matrix (RAC) Analytes Storage 

Temp (°C)

Actual Storage 

Duration1

Interval of Demonstrated Storage 

Stability (months)

Citrus, fruit

Glufosinate 

ammonium, and 

Glufosinate 

Propanoic Acid

<0

336 days

(11.2 months)

Concurrent storage stability data was 

submitted for residues in/on peach showing 

a stability period of 730 days for glufosinate 

ammonium, and 778 days for glufosinate 

propanoic acid, and N-acetylglufosinate

(MRID 47915705). In addition, concurrent 

studies in transgenic sweet corn were 

submitted showing stability of glufosinate 

and glufosinate propanoic acid for 914 days 

in ears, 793 days in forage and 812 days in 

stover (MRID 47828201).

Glufosinate ammonium and glufosinate 

propanoic acid: Apple, corn grain, and

soybean for 730 days (PP#8F3607, J. 

Garbus, 8-Aug-1990), blueberries for 664

days (D271110, T. Bloem, 20/June/2002), 

orange for 24 months and kiwi for 6 months 

(study pending approval).

Glufosinate ammonium, glufosinate 

propanoic acid, and N-acetylglufosinate: 12 

months on transgenic soybean seed, forage, 

and hay; for 3 months on soybean oil and 

meal; for 6 months on transgenic corn grain,

fodder, and forage; and for 24 months on 

transgenic sugar beet tops and roots; for 9 

months on sugar beet pulp, molasses, and 

sugar beet refined sugar (D211531 and 

D219069, M. Rodriguez, 7-Mar-1996; 

D257629, T. Bloem, 9-Jul-1999; D286447, 

T. Bloem, 11-Dec-2002).

Trans. Sweet 

Corn, Ears

197-950 days

(9.6-31.2 months)

Trans. Sweet 

Corn, Forage

146-788 days

(4.9-26.3 months)

Trans. Sweet 

Corn, Stover

143-810 days

(4.8-27 months)

Pear

Glufosinate 

ammonium, 3-

methylphosphinicopropanoic acid, and 

N-acetylglufosinate

224 days

(7.5 months)

Cherry 332 days

(11.1 months)

Plum 281 days

(9.4 months)

Olive 259 days

(8.6 months)

Orange, Fruit 

(Processing 

Studies)

176 days 

(5.9 months)

Orange, Oil 274-277 days 

(9.1-9.2 months)

Plum 

(Processing 

Studies)

135-146 days 

(4.5-4.9 months)

Prune 128-133 days 

(4.3-4.4 months)

Olive Fruit 

(Processing 

Studies)

122-125 days 

(4.1-4.2 months)

Olive Oil 109-111 days 

(3.6-3.7 months)

1Actual storage duration from harvest to extraction. 

Conclusions. There are adequate storage stability data available in a wide variety of crops which 

can be translated in the current petitions for orange, lemon, grapefruit, cherry, plum, pear, peach 

and olive RACs, and citrus oil, prunes and olive oil processed commodities to validate sample 

storage conditions and durations. However, the petitioner is reminded that storage stability

studies are recommended for processed commodities. In addition, these studies should cover the 

period of time in which the RAC or processed commodity was stored. For N-acetylglufosinate 

in/on transgenic sweet corn, the concurrent and previous storage stability studies do not cover the 

storage interval. This deficiency needs to be resolved.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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860.1400 Water, Fish, and Irrigated Crops

There are no proposed uses that are relevant to this guideline topic. However, glufosinate 

ammonium has uses registered for rice (D271110, T. Bloem, 20-June-2002).

860.1460 Food Handling

There are no proposed uses that are relevant to this guideline topic.

860.1480 Meat, Milk, Poultry, and Eggs

No new animal feeding studies were submitted with these petitions and only sweet corn forage 

and stover are associated with feedstuff items. In addition, glufosinate ammonium has uses 

registered for feedstuff (D271110, T. Bloem, 20-June-2002). In June 2008 an update to the 

Table 1 of OPPTS 860.1000 was issued. Therefore, the dietary burden to livestock was 

calculated based on the updated values of Table 1 and the use of sweet corn feedstuff.

Table 5. Calculation of Maximum Livestock Dietary Burden for Glufosinate Ammonium.

Feedstock Tolerance %Dry Matter % of Diet Burden (ppm)2

Dairy Cattle

Sweet Corn Stover (R) 10 83 15 1.81

Field Corn Forage (R) 4.0 40 30 0.03

Field Corn Grain (CC) 0.20 88 15 3.00

Beet Sugar Molasses (CC) 5.0 75 10 0.67

Rice Grain (CC) 1.0 88 20 0.45

Undelinted Cottonseed (PC) 4.0 88 10 0.23

TOTAL 100 6.19

Beef Cattle

Field Corn Forage (R) 4.0 40 10 1.00

Cotton Gin Byproducts (R) 15 90 5 0.83

Aspirated Grain Fractions (CC) 25 85 5 1.47

Beet Sugar Molasses (CC) 5.0 75 10 0.67

Field Corn Grain (CC) 0.2 88 45 0.10

Rice Grain (CC) 1.0 88 20 0.23

Soybean Seed (PC) 2.0 89 5 0.11

TOTAL 100 4.41

Poultry

Field Corn Grain (CC) 0.2 NA 55 0.11

Rice Grain (CC) 1.0 NA 20 0.20

Soybean Seed (PC) 2.0 NA 20 0.40

Soybean Meal (PC) 2.0 NA 5 0.10

TOTAL 100 0.81

Swine

Field Corn Grain (CC) 0.2 NA 65 0.13

Rice Grain (CC) 1.0 NA 20 0.20

Soybean Seed (PC) 2.0 NA 15 0.30

TOTAL 100 0.63

NA = Not Applicable

1

 As per Revised Table 1 (OPPTS Guideline 860.1000).

2

 For beef and diary cattle: Burden = [Tolerance  % DM] x % Diet; for poultry and swine: Burden = 

Tolerance x % Diet / 100.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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The dietary burden calculated with the % of dry matter and % of diet values from the updated 

Table 1 of OPPTS 860.0000 is shown in Table 5. The previously calculated dietary burden for 

beef cattle, dairy cattle, poultry and swine is 15.38, 15.22, 3.33 and 8.89 ppm, respectively

(D271110, T. Bloem, 20/June/2002). These values are higher than the dietary burden calculated 

for this new petition; therefore, currently the tolerances for livestock are covered by the feeding 

studies previously performed with diary cow and poultry.

860.1500 Crop Field Trials

Reference DERs: 47915701.der.doc, 47915702.der.doc, 47915703.der.doc, 47915704.der.doc, and 

47915705.der.doc.

Twenty three crop field trials were performed in the corresponding regions, according to OPPTS 

guidelines, to evaluate the magnitude of residue for orange, lemon and grapefruit. A summary of 

the residue data is presented in Table 6. Eight of the 23 trials used a non-ionic antifoam. Each 

trial consisted of one treated plot and one control plot. Following three broadcast applications of 

RELY at the target rate of 1.50 lb ai/A/application residues of glufosinate ammonium and its two 

metabolites, glufosinate propanoic acid and N-acetylglufosinate were not detected above the 

LOQ (0.05 ppm) in/on oranges, lemons and grapefruit harvested at a PHI of 14 (-1) days. No 

effect of the adjuvant on the residue levels was observed since the residues were below the 

method LOQ for applications with and without the non-ionic antifoam. Moreover, results from 

the residue decline study performed on each of the three crop types at five intervals 

corresponding to PHIs of 7, 11, 14, 17, and 21 days indicated that residues of glufosinate 

ammonium, glufosinate propanoic acid and N-acetylglufosinate were below the LOQ at all PHIs 

used. 

 

For plum commodities, six crop field trials were performed according to OPPTS guidelines. For 

cherries, sweet cherries or tart cherries can be selected as a Stone Fruit crop group representative. 

The registrant submitted data with both crops and the regions were selected to represent both 

commodities. Five of the 12 trials for plum and cherries used a non-ionic antifoam. Each trial 

consisted of one treated plot and one control plot. Following three broadcast applications of 

RELY at the target rate of 1.50 lb ai/A/application residues of glufosinate ammonium and Nacetylglufosinate in/on cherries and plum were not detected above the LOQ (0.05 ppm). 

However, 3-methylphosphinico-propanoic acid was at quantifiable levels in/on these 

commodities. One trial of the six field trials for cherries and for plum showed total residues 

above the LOQ. For cherries, the highest average field trial (HAFT) was 0.083 ppm with a 

maximum residue of 0.098 ppm. The HAFT for total glufosinate ammonium residue was 0.183 

ppm with a maximum residue of 0.198 ppm. For plums, the HAFT for 3-methylphosphinicopropanoic acid residue was 0.066 ppm with a maximum residue of 0.066 ppm. The HAFT for

total glufosinate ammonium residue was 0.166 ppm with a maximum residue of 0.166 ppm. Any

effect of the adjuvant (non-ionic antifoam) on the residue levels can not be established with this 

data; however, the tolerance for stone fruit commodities will be set based on the HAFT of the 

field trials with residues above the LOQ. Results from the residue decline study performed on 

both crop types at five intervals corresponding to PHIs of 7, 11, 14, 17, and 21 days indicated 

that total glufosinate ammonium residues in cherry and plum were found to below or close to the 

LOQ at all PHIs; therefore, a trend was not observed. 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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For peach, nine crop field trials were performed in the corresponding regions according to 

OPPTS guidelines. Each trial consisted of one treated plot and one control plot. No adjuvants 

were added to the herbicide mixture. Following two broadcast applications of RELY at the 

target rate of 1.50 lb ai/A/application there were no apparent residues of glufosinate ammonium, 

3-methylphosphinico-propanoic acid and N-acetylglufosinate detected above the LOQ (0.05 

ppm) in/on peach samples collected from the treated and untreated plots at a target PHI of 14 

days. There were no residue decline studies performed for this commodity but were performed 

for other stone fruits, plum and cherry.

For pear, six crop field trials were performed in the corresponding regions according to OPPTS 

guidelines. Each trial consisted of one treated plot and one control plot. In all trials, ammonium 

sulfate was added to each tank mixture and applied at a rate of 3 lb/A. Two sites received a nonionic antifoam adjuvant. Following three broadcast applications of RELY at the target rate of 

1.50 lb ai/A/application residues of glufosinate ammonium and N-acetylglufosinate in/on pear 

were not detected above the LOQ (0.05 ppm). However, 3-methylphosphinico-propanoic acid 

was at quantifiable levels in one of the six field trials. Any effect of the adjuvant (non-ionic 

antifoam) on the residue levels can not be established with this data; however, the tolerance for 

Pome Fruit crop group will be set based on the HAFT of the field trials with residues above the 

LOQ. Results from the residue decline study with five sampling intervals corresponding to PHIs 

of 7, 9, 14, 16, and 21 days indicated that residues of glufosinate ammonium, glufosinate 

propanoic acid and N-acetylglufosinate were below the LOQ at all PHIs. 

For olives, three crop field trials were performed in the corresponding regions according to 

OPPTS guidelines. Each trial consisted of one treated plot and one control plot. In all trials, 

ammonium sulfate was added to each tank mixture and applied at a rate of 3 lb/A. In two of the 

trials, a non-ionic antifoam was also added to the tank mixture. Following three broadcast 

applications of RELY at the target rate of 1.50 lb ai/A/application there were no apparent 

residues of glufosinate ammonium, 3-methylphosphinico-propanoic acid and N-acetylglufosinate 

detected above the LOQ (0.05 ppm) in/on olive samples collected from the treated and untreated 

plots at the PHI of 14 days. No effect of the adjuvant on the residue levels was observed since 

the residues were below the method LOQ for applications with and without the non-ionic 

antifoam. There were no residue decline studies performed for this commodity.

For sweet corn, twelve crop field trials were conducted in EPA regions 1, 3, 5, 10 and 11. Two 

of the field trials in region five were performed in the same location at Arlington, Wisconsin; 

therefore, eleven field trials would represent the geographic diversity recommended by HED. 

Each trial consisted of one treated plot and one control plot. In all trials at region 5, ammonium 

sulfate was added to each tank mixture. Stover was dried for 5 to 13 days after harvest. 

Following two foliar applications of Liberty Herbicide at a rate of 0.375 lb ai/A for a total rate of 

0.75 lb ai/A (one trial received an overapplication of 1.2 lb ai/A) with a retreatment interval 

(RTI) of 14-16 days and a PHI of 30-50 days, HAFT residue values in/on sweet corn ears, forage 

and stover were 0.06, 0.74 and 3.55 ppm for the glufosinate acid equivalent from glufosinate 

ammonium and N-acetylglufosinate, 0.135, 0.14, and 0.49 ppm for glufosinate acid equivalent 

from glufosinate propanoic acid and 0.185, 0.79, and 3.72 ppm for total glufosinate acid, 

respectively. No residue decline data was collected. 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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TABLE 6. Summary of Residue Data from Crop Field Trials with Glufosinate ammonium and its Two 

Metabolites.

Commodity

Total Applic. Rate 

(lb ai/A)

[kg ai/ha]

PHI 

(days)

Residue Levels1(ppm)

n Min. Max. HAFT2 Median Mean Std. Dev.

Glufosinate ammonium

Orange 4.38 to 4.61

[4.91 to 5.16] 14 24 <0.05 <0.05 <0.05 NA NA NA

Lemon 4.50 to 4.53

[5.05 to 5.07] 14 10 <0.05 <0.05 <0.05 NA NA NA

Grapefruit 4.47 to 4.58

[5.01 to 5.14] 14 12 <0.05 <0.05 <0.05 NA NA NA

Pear 4.45 to 4.57

[4.99 to 5.12] 14 12 <0.05 <0.05 <0.05 NA NA NA

Cherry 3.00 to 3.11

[3.37 to 3.49] 14 12 <0.05 <0.05 <0.05 NA NA NA

Plum 2.92 to 3.03

[3.27 to 3.40] 14 12 <0.05 <0.05 <0.05 NA NA NA

Olive 4.50 to 4.52

[5.05 to 5.07] 14 12 <0.05 <0.05 <0.05 NA NA NA

Glufosinate propanoic acid

Orange 4.38 to 4.61

[4.91 to 5.16] 14 24 <0.05 <0.05 <0.05 NA NA NA

Lemon 4.50 to 4.53

[5.05 to 5.07] 14 10 <0.05 <0.05 <0.05 NA NA NA

Grapefruit 4.47 to 4.58

[5.01 to 5.14] 14 12 <0.05 <0.05 <0.05 NA NA NA

Pear 4.45 to 4.57

[4.99 to 5.12] 14 12 <0.05 0.089 0.081 0.05 0.053 0.007

Cherry 3.00 to 3.11

[3.37 to 3.49] 14 12 <0.05 0.098 0.083 0.05 0.056 0.013

Plum 2.92 to 3.03

[3.27 to 3.40] 14 12 <0.05 0.066 0.066 0.05 0.053 0.007

Olive 4.50 to 4.52

[5.05 to 5.07] 14 12 <0.05 <0.05 <0.05 NA NA NA
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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TABLE 6. Summary of Residue Data from Crop Field Trials with Glufosinate ammonium and its Two 

Metabolites.

Commodity

Total Applic. Rate 

(lb ai/A)

[kg ai/ha]

PHI 

(days)

Residue Levels1(ppm)

n Min. Max. HAFT2 Median Mean Std. Dev.

N-Acetylglufosinate

Orange 4.38 to 4.61

[4.91 to 5.16] 14 24 <0.05 <0.05 <0.05 NA NA NA

Lemon 4.50 to 4.53

[5.05 to 5.07] 14 10 <0.05 <0.05 <0.05 NA NA NA

Grapefruit 4.47 to 4.58

[5.01 to 5.14] 14 12 <0.05 <0.05 <0.05 NA NA NA

Pear 4.45 to 4.57

[4.99 to 5.12] 14 12 <0.05 <0.05 <0.05 NA NA NA

Cherry 3.00 to 3.11

[3.37 to 3.49] 14 12 <0.05 <0.05 <0.05 NA NA NA

Plum 2.92 to 3.03

[3.27 to 3.40] 14 12 <0.05 <0.05 <0.05 NA NA NA

Olive 4.50 to 4.52

[5.05 to 5.07]] 14 12 <0.05 <0.05 <0.05 NA NA NA

Total Glufosinate ammonium

Orange 4.38 to 4.61

[4.91 to 5.16] 14 24 <0.15 <0.15 <0.15 NA NA NA

Lemon 4.50 to 4.53

[5.05 to 5.07] 14 10 <0.15 <0.15 <0.15 NA NA NA

Grapefruit 4.47 to 4.58

[5.01 to 5.14] 14 12 <0.15 <0.15 <0.15 NA NA NA

Pear 4.45 to 4.57

[4.99 to 5.12] 14 12 <0.15 0.189 0.181 0.15 0.155 0.013

Cherry 3.00 to 3.11

[3.37 to 3.49] 14 12 <0.15 0.198 0.183 0.15 0.156 0.013

Plum 2.92 to 3.03

[3.27 to 3.40] 14 12 <0.15 0.166 0.166 0.15 0.153 0.007

Olive 4.50 to 4.52

[5.05 to 5.07] 14 12 <0.15 <0.15 <0.15 NA NA NA
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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TABLE 7. Summary of Residue Data from Crop Field Trials with Glufosinate ammonium in/on Sweet Corn

Commodity

Total Applic. Rate 

(lb ai/A)

PHI 

(days)

Residue Levels1(ppm)

n Min. Max. HAFT2 Median Mean Std. Dev.

Glufosinate ammonium and N-Acetylglufosinate

Sweet Corn, 

Ears 0.75 30-50 24 <0.05 0.06* 0.06 0.05 0.513 0.003

Sweet Corn, 

Forage 0.75 30-50 24 0.08 0.74* 0.74 0.19 0.32 0.23

Sweet Corn, 

Stover 0.75 30-50 24 0.33 3.55* 3.55 1.12 1.20 1.12

Glufosinate propanoic acid

Sweet Corn, 

Ears 0.75 30-50 24 <0.05 0.135* 0.135 0.05 0.06 0.03

Sweet Corn, 

Forage 0.75 30-50 24 <0.05 0.14* 0.14 0.05 0.06 0.03

Sweet Corn, 

Stover 0.75 30-50 24 <0.05 0.49* 0.49 0.09 0.12 0.09

Total Glufosinate

Sweet Corn, 

Ears 0.75 30-50 24 0.10* 0.19* 0.19* 0.10 0.11 0.02

Sweet Corn, 

Forage 0.75 30-50 24 0.18* 0.79* 0.79* 0.28 0.44 0.23

Sweet Corn,

Stover 0.75 30-50 24 0.16* 3.7* 3.7* 1.43 1.16 1.05

*The average residue of each analyte in each field trial were added and the total residue value of each trial was used 

to select the maximum and minimum values. In a similar way the HAFT was selected from the sum of the average 

values of each analyte from each field trial. In the study provided, the residues from each field trial were reported in 

pairs; therefore, is not possible to identify the residue from each one of the duplicate samples analyzed in each field 

trial.

Conclusions. The number and location of field trials for orange, lemon, grapefruit, pear, cherry, 

plum and olive comply with the requirements of OPPTS 860.1500 guideline. The data are

adequate to establish tolerances for these RACs. The residue decline studies in all the 

commodities tested showed that residues were below or close (for plum) to the LOQ at all PHIs; 

therefore, residues are not expected to be higher at longer PHIs than those established for the 

RACs under this petition.

860.1520 Processed Food and Feed

Processing studies were performed for orange, plum and olive commodities. Detailed reviews 

concerning the processing studies submitted in support of the current petitions can be found in 

the following reviews: orange (47915706.der.wpd), plum (47915707.der.wpd) and olive

(47915708.der.wpd). A summary of the results obtained is summarized in Table 8.

Oranges were treated with three applications of RELY herbicide at 7.5 lbs ai/A (14-day RTI; 

22.73 lbs ai/A total; 5x the maximum proposed seasonal application rate). Oranges were

harvested 14 days after the last application and processed into dried pulp, oil, juice (pasteurized), 

peels, and peeled fruit. However, only the orange RAC and orange oil (the processed commodity
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 19 of 26

with the highest theoretical processing factor) were analyzed for residues of glufosinate 

ammonium, N-acetyl-glufosinate and glufosinate propanoic acid. After using exaggerated rates, 

the residues in the orange RAC were below the method LOQ. Under this condition tolerances 

and processing studies are not required with the exception of those for commodities with very

high processing factors, citrus oil (1000x) and mint oil (330x). The orange oil processed 

commodity resulted in combined residues of glufosinate ammonium, N-acetyl-glufosinate and 

glufosinate propanoic acid below the method LOQ; therefore, these didn’t concentrated in orange 

oil (1x). Orange juice and orange dried pulp were prepared by the registrant but not analyzed. 

Based on the guidelines, the analysis of these processed commodities is not required when the 

residues are below LOQ in the RAC after applying 5x exaggerated rates. 

Plums were treated with two applications of RELY herbicide at 7.5 lbs ai/A (28-day RTI; 15 lbs 

ai/A total; 5x the maximum proposed seasonal application rate). Plums were harvested 14 days 

after the last application and processed into prunes. Plums and prunes were analyzed for residues 

of glufosinate ammonium, N-acetyl-glufosinate and glufosinate propanoic acid. Only residue 

levels of glufosinate propanoic acid were above the method LOQ in the plums and prunes 

samples. The total average residue level in the prune samples was 0.433 ppm. After correction 

for the exaggerated application rate (5x) the residue level (0.0866 ppm) will be below the method 

total LOQ (0.15 ppm); therefore, no tolerance is required for the prune RAC. However, a 

processing factor of 1.8x can be set for the prunes RAC by assuming that glufosinate ammonium, 

N-acetyl-glufosinate and glufosinate propanoic acid are at LOQ levels when these were not 

detected. This processing factor is below the theoretical concentration factor of 3.4x which is 

based on loss of water. 

Olives were treated with three applications of RELY herbicide at 7.5 lbs ai/A (14-day RTI; 22.5 

lbs ai/A total; 5x the maximum proposed seasonal application rate). Olives were harvested 14 

days after the last application and processed into olive oil. Samples of olives and olive oil were 

analyzed for residues of glufosinate ammonium, N-acetyl-glufosinate and glufosinate propanoic 

acid. Only residue levels of glufosinate propanoic acid were above the method LOQ in the olive 

samples. The total average residue level in the olive oil sample was below the method LOQ; 

therefore, no tolerance is required for the olives RAC. However, a processing factor of 0.6x can 

be set for the olives by assuming that glufosinate ammonium, N-acetyl-glufosinate and 

glufosinate propanoic acid are at LOQ levels when these were not detected. This processing 

factor is below the theoretical concentration factor of 108x which is based on separation of 

components. 

The orange, prunes and olive oil processing studies will be considered adequate at this time but 

for future studies the registrant is recommended to analyze the washed RAC if this is washed 

during the processing studies. The current practice of using the unwashed RAC residue levels 

may result in a sub estimation of the processing factor.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

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TABLE 8. Residue Data from Orange, Plum and Olive Processing Study with Glufosinate Ammonium.

Trial: 

City, 

State; 

Year 

(Trial 

ID#)

Processed 

Commodity

Total 

Rate

(lb 

ai/A) 

PHI 

(days)

Glufosinate 

ammonium

Glu-NAG Glu-PPA Total3

Residues 

(ppm)1

Processing 

Factor2

Residues 

(ppm)1

Processing 

Factor2

Residues 

(ppm)1

Processing 

Factor2

Residues 

(ppm)1

Processing 

Factor2

Arroyo 

Grande, 

CA; 

2008 

(GL001-

08PA)

Orange, 

Fruit

22.73 14 <LOD -- <LOD -- <LOD -- <0.15 --

Orange, Oil <LOD ≤1x <LOD ≤1x <LOD ≤1x <0.15 ≤1x

Live 

Oak, 

CA; 

2008 

(GL025-

08PA)

Plum RAC 

(unwashed)

15.0 14 0.0704, 

<LOQ 

(0.0229), 

<LOD

Avg. 

<LOQ 

-- 0.142, 

0.126,

0.131

Avg. 

0.13

-- <LOQ 

(0.0358), 

<LOD, 

<LOD 

Avg. 

<LOQ 

-- 0.262

0.226

0.231

Avg. 

0.240

--

Prune <LOD, 

<LOD,

<LOD

Avg. 

<LOD

<1.0X 0.393, 

0.344, 

0.263

Avg. 

0.33

2.5X <LOD, 

<LOD,

<LOD

Avg. 

<LOD

<1.0X 0.493

0.444

0.363

Avg. 

0.433

1.8X

Corning, 

CA; 

2008 

(GL047-

08PA)

Olive RAC 22.5 14 <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

-- 0.132, 

0.142, 

0.134

Avg. 

0.136

-- <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

-- 0.232

0.242

0.234

Avg. 

0.236 

--

Olive Oil <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

<1.0x <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

<0.2x <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

<1.0x <LOD, 

<LOD, 

<LOD

Avg. 

<LOD

<0.6x

1

 LOQ = 0.05 ppm for glufosinate ammonium, Glu-PPA and Glu-NAG. Residues in parenthesis are values between the LOD 

and LOQ. 

2

 The processing factor was calculated by dividing the residues in the processed sample by the residues in the unprocessed RAC 

sample. Values <LOQ and <LOD were assigned a value of the LOQ (0.05 ppm) for calculations. 

3 The total glufosinate ammonium residue is the sum of the individual measured residue for the analytes of glufosinate 

ammonium, Glu-NAG and Glu-PPA. Values <LOQ and <LOD were assigned a value of the LOQ (0.05 ppm) for calculations.

Conclusions: The processed commodities required under OPPTS 860.1520 guidelines for the 

corresponding RACs were prepared and analyzed. These studies are considered acceptable. 

However, the petitioner is advised to wash the RAC before analysis if it will be washed during 

processing.

860.1850 / 860.1900 Confined / Field Accumulation in Rotational Crops

D271110, T. Bloem, 20/June/2002

A confined rotational crop study has been submitted and reviewed (D211531 and D219069, M. 

Rodriquez, 7-Mar-1996). Lettuce, radish, and spring wheat were planted 28 and 119 days after 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 21 of 26

the soil was treated with [3,4-

14C]-HOE-039866 at 0.9 lbs ai/acre (1.2x the maximum proposed 

application rate for sweet corn). All samples planted 28 days after treatment were analyzed. 

HOE 061517 (5-57% TRR) and HOE 064619 (6-10% TRR) were the only compounds identified 

(a total of 32-64% of the TRR was identified). Except for the wheat commodities, TRRs were 

0.02 ppm for the samples planted 120 days after treatment (wheat commodities 0.06-0.15 ppm). 

A wheat field rotational crop study has also been submitted and reviewed (P. Errico [RD], 6-

May-1998). Wheat was planted 73 - 90 days after the soil was treated with glufosinate 

ammonium at 0.8 lbs ai/acre (1.2x the maximum proposed application rate for sweet corn). 

Wheat forage, hay, straw, and grain were harvested at maturity and analyzed for residues of 

glufosinate ammonium and HOE 061517 (residues were < LOQ; LOQ = 0.05 ppm). 

Based on the confined and field rotational crop studies, the MARC determined that the residues 

of concern in rotational crops, for tolerance expression and risk assessment purposes, are 

glufosinate ammonium, HOE 061517, and HOE 064619 (D282757, T. Bloem, 9-May-2002). 

The Liberty Herbicide label indicates that plant rotation to other crops after treatment of sweet 

corn can occur with a Plant Back Interval (PBI) of 120 days with the exception of wheat, barely, 

buckwheat, millet, oats, rye sorghum, and triticale 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. 

860.1650 Submittal of Analytical Reference Standards

Analytical standards for the herbicide glufosinate ammonium, N-acetylglufosinate and 3-

methylphosphinico-propanoic acid are to be kept available in the EPA National Pesticide 

Standards Repository. These analytical reference standards must be replenished as requested by

the Repository. If requested, reference standards should be sent to the Analytical Chemistry

Laboratory located in Fort Meade to the attention of either Theresa Cole at the following address:

U.S. EPA

National Pesticide Standards Repository/ Analytical Chemistry Branch/OPP

701 Mapes Road

Fort George G. Meade, MD 20755-5350

Please note that mail will be returned if the entire extended zip code is not used when addressing 

correspondence to the Repository. 

860.1550 Proposed Tolerances

Glufosinate ammonium tolerances are established under 40 CFR §180.473 and are currently

expressed in terms of glufosinate ammonium and two of its metabolites. On 27-MAY-2009 

HED established interim guidance on writing tolerance expressions for enforcement purposes. In 

order to add clarity to the language used to establish the coverage of the tolerance expression and 

measurement of the level of the residue in the RACs the text in the 40 CFR § 180.533 should 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 22 of 26

read: “(a) General. (1) 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 

glufosinate ammonium (butanoic acid, 2-amino-4-(hydroxymethylphosphinyl)-monoammonium 

salt) and its metabolites, 2-acetamido-4-methylphosphinico-butanoic acid and glufosinate 

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

The residue values obtained in the A summary of the recommended tolerances for the crop 

commodities discussed in this Summary Document is presented in Table 9.

Table 9. Tolerance Summary for Glufosinate Ammonium.

Commodity Current §180.533

Tolerance (ppm)

Proposed 

Tolerance (ppm)

Recommended §180.533

Tolerance (ppm)

Comments

Citrus (CG 10) None 0.05 0.15 Fruit, citrus, group 10*

Pome Fruit (CG 11) None 0.10 0.25 Fruit, pome, group 11*

Stone Fruit (CG 12) None 0.10 0.25 Fruit, stone, group 12

Olives None 0.05 0.15

Corn, sweet, kernels 

plus cob with husks 

removed

None 0.2 0.25

Corn, sweet, forage None 4.0 1.6

Corn, sweet, stover None 6.0 10

Plum, prune, dried None 0.20 N/A Covered by the Stone 

Fruit tolerance.

* Or Group 10-10 and Group 11-10 when these new crop groups are officially established.

The NAFTA calculator was used to establish the tolerance for sweet corn forage and stover. The 

maximum residues from each field trial location were selected from each analyte and then 

summed to obtain the total residue value used to establish the tolerance. A lognormal 

distribution was assumed and the 95/99 rule was used to calculate the tolerance for sweet corn 

forage and the UPL median 95 method for sweet corn stover. The latter method is used as an 

alternative to the 95/99 rule when the standard deviation of the field trials is high. For the 

remaining commodities the tolerance was estimated based on the HAFT. 

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, Pome Fruit and Stone Fruit the Codex have set a MRL of 0.1, 0.05, and 

0.05 ppm, respectively. The US tolerance for Citrus, Pome Fruit and Stone Fruit, is 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, see Attachment 1. There are no MRLs established in Mexico or Canada for 

the use of glufosinate ammonium on the commodities under the current petition.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 23 of 26

References

Tom Bloem, Glufosinate Ammonium (PC Code: 128850). Label Amendment for Pre-Plant 

Application of Glufosinate Ammonium to Transgenic and Non-transgenic Field Corn, Nontransgenic Canola, and Non-transgenic Soybean. Residue Chemistry Summary., D335330, 

09/12/2007.

Tom Bloem, Glufosinate Ammonium (PC Code 128850). Section 3 Registrations for Transgenic 

Cotton (ID# - 0F06140), Transgenic Rice (ID# - 0F06210), and Bushberry (ID# - 2E06404). 

Summary of Analytical Chemistry and Residue Data., D271110, 20/June/2002.

M. Rodriguez, PP5G4466 & PP5F4578: Glufosinate-ammonium in/on Transgenic Corn and 

Soybeans. Experimental Use Permit, Temporary Tolerance and Permanent Tolerance Petitions. 

Evaluation of Analytical Method and Residue Data., D219069 and D211531, 03/07/1996.

Attachments

Attachment 1: International Residue Limit Status 

Attachment 2: NAFTA Calculator Results 
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 24 of 26

Attachment 1: International Residue Limit Status 

Glufosinate Ammonium (PC Code 128850; Aug 10, 2010)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition: 

US Canada Mexico2 Codex3

40 CFR 180.473

Plant and Livestock: glufosinate 

ammonium (butanoic acid, 2-amino-4-

(hydroxymethylphosphinyl)-

monoammonium salt) and its metabolites, 

2-acetamido-4-methylphosphinicobutanoic acid and 3-methylphosphinicopropionic acid, expressed as 2-amino-4-

(hydroxymethylphosphinyl)butanoic acid 

equivalents

ammonium(±)-2-

amino-4-

(hydroxymethylp

hosphinyl)butano

ate, including the 

metabolite 

propanoic acid, 3-

(hydroxymethylp

hosphinyl)

Sum of glufosinateammonium, 3-

[hydroxy(methyl)ph

osphinoyl]propionic 

acid and N-acetylglufosinate, 

calculated as 

glufosinate (free 

acid).

Commodity1 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex

Citrus (CG10) 0.15* Citrus fruits 0.1

Pome Fruit (CG 11) 0.25 Pome fruits 0.05 (*)

Stone Fruit (CG 12) 0.25 Stone fruits 0.05 ( *)

Olives 0.15*

Corn, Sweet, Ears 0.25

Corn, Sweet, Forage 1.6

Corn, Sweet, Stover 10

Completed: M. Negussie; 08/10/2010

1

Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and 

not those proposed by the applicant.

2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.

3 * = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = 

processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the 

fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 25 of 26

Attachment 2.1: NAFTA Calculator Results for Sweet Corn Forage

Regulator: EPA

Chemical: Glufosinate

Crop: Sweet Corn, Forage

PHI: 43 Days

App. Rate: 0.75 lb ai/A

Submitter: IR-4

n: 12

min: 0.10

max: 0.98

median: 0.34

average: 0.43

95th Percentile 99th Percentile 99.9th Percentile

0.90 1.1 1.3

(1.2) (1.5) (--)

1.1 1.6 3.0

(2.5) (4.0) (--)

#REF!

1.3

2.5

0.9641

p-value > 0.05 : Do not reject lognormality assumption

Approximate 

Shapiro-Francia

Normality Test 

EU Method I

Normal

UCLMedian95th

95/99 Rule

EU Method II

Distribution-Free

Mean+3SD

Lognormal Probability Plot

0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9

1.0000

0.5000

0.2500

0.1250

0.0625

y = 0.6651x - 1.0315

R

2

 = 0.9641

Percentiles

Concentrations

EPA Glufosinate Sweet Corn, Forage 43 Days 0.75 lb ai/A IR-4
Glufosinate Ammonium Summary of Analytical Chemistry and Residue Data D372625

Page 26 of 26

Attachment 2.2: NAFTA Calculator Results for Sweet Corn Stover

Regulator: EPA

Chemical: Glufosinate

Crop: Sweet Corn, Stover

PHI: 43 Days

App. Rate: 0.75 lb ai/A

Submitter: IR-4

n: 12

min: 0.19

max: 5.54

median: 1.61

average: 1.57

95th Percentile 99th Percentile 99.9th Percentile

4.0 5.0 7.0

(6.0) (8.0) (--)

6.0 13 30

(19) (55) (--)

#REF!

6.0

10

0.9137

p-value > 0.05 : Do not reject lognormality assumption

Approximate 

Shapiro-Francia

Normality Test 

EU Method I

Normal

UCLMedian95th

95/99 Rule

EU Method II

Distribution-Free

Mean+3SD

Lognormal Probability Plot

0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9

6.0000

3.0000

1.5000

0.7500

0.3750

0.1875

y = 1.0734x + 0.012

R

2

 = 0.9137

Percentiles

Concentrations

EPA Glufosinate Sweet Corn, Stover 43 Days 0.75 lb ai/A IR-4