UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: January 24, 2013 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

Subject: Glufosinate Ammonium. Human Health Risk Assessment for Registration Review. 

PC Code: 128850 

Decision No.: 471210 

Petition No.: NA 

DP Barcode: 0406360 

Registration No.: NA 

Regulatory Action: Registration Review 

Risk Assessment Type: Single Chemical Aggregate Case No.: NA 

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

MRIDNo.: NA 40 CFR: 180.437 

From: 

Through: 

To: 

William H. Donovan, Ph.D., Chemist lfd. ~~D~ CH ... /) nh 

Ana Rivera-Lupianez, Chemist W~Jl. t~ F..____ 

Risk Assessment Branch V (RABV) 

Health Effects Division (HED) (7509P) 

Michael 

Risk Assessment 

S. Metzger, 

Branch 

Branch 

V (RABV) 

Chief U' ~~ (} (} ;{ /} ' Jl f ~ '\. 

Health Effects Division (7509P) 

Katie Weyrauch, Chemical Review Manager 

Risk Management and Implementation Branch V 

Pesticide Re-evaluation Division (PRD) (7508P) 

The PRD requested that HED prepare a human-health risk assessment for glufosinate ammonium 

in support of registration review. To address this request, HED cites the most recent glufosinate 

ammonium risk assessment (D3874 13, W. Donovan, J. Doherty, and A. Rivera-Lupiafiez, 

07/25/12) and has prepared this memo, which updates and expands appropriate sections of the 

July 25, 2012 assessment. Recent changes in occupational assessment policies (e.g. , unit 

exposures, TCs and new guidance for requiring/waiving Turf Transferrable Residue (TTR) and 

Dislodgeable Foliar Residue (DFR) studies) have triggered the need for an updated occupational 

assessment for glufosinate ammonium. To take into account this new information, the following 

sections are provided: 

1) Updated occupational handler exposure and risk estimates for spot/directed treatments to 

Page 1 of 10 
Page 2 of 10

citrus, pome, and stone fruits; and olives.

2) New occupational handler exposure and risk assessment for the representative crops of 

corn, cotton, sorghum, and canola.

3) New summary of estimated occupational post-application risks for application of 

glufosinate ammonium to representative crops.

HED concludes that, based on currently registered uses, the following studies have been 

identified as data gaps for glufosinate ammonium:

Dislodgeable Foliar Residue (DFR) studies for corn, canola, cotton, and soybeans.

Finally, HED reiterates that all glufosinate ammonium labels allowing residential turf uses or 

park/recreational field uses must restrict lawn/turf uses to spot treatments only. The maximum 

application rate for residential lawn treatments should not exceed 4 fl ounces per gallon of water 

per 1,000 square feet. 

No other changes to the July 25, 2012 glufosinate ammonium risk assessment are needed.
Page 3 of 10

Detailed Considerations

The updated and new sections of this document supersede the previous glufosinate-ammonium 

risk assessment (D387413, W. Donovan, et al., 07/25/12). The present analysis includes a 

revision to the mixer/loader/applicator (M/L/A) scenario utilizing mechanically-pressurized 

handgun for spot/directed treatments on citrus fruit, pome fruit, stone fruit, and olives, to account 

for the Exposure Science Advisory Committee (ExpoSAC) revision of the unit exposure value 

assigned for this particular M/L/A scenario (ExpoSAC Meeting Minutes, 09/13/2012).

Also, an updated occupational assessment was performed for registered uses of glufosinate to

account for changes in occupational assessment policies (e.g., unit exposures, TCs and new 

guidance for requiring/waiving Turf Transferrable Residue (TTR) and Dislodgeable Foliar 

Residue (DFR) studies). Several high-acreage field crops that represent worst-case scenarios for 

exposure to glufosinate-ammonium were assessed (i.e., corn, canola, cotton, and soybeans).

1) Revised Occupational Exposure and Risk Estimates for Spot/Directed Treatments on 

Citrus Fruit, Pome Fruit, Stone Fruit, and Olives

The previous assessment (D387413, 07/25/12) identified risk concerns for M/L/A scenarios 

utilizing mechanically-pressurized handgun for spot/directed treatments on citrus fruit, pome 

fruit, stone fruit, and olives; however, results of the current revised assessment indicate that 

short- and intermediate-term dermal risks are not of concern to the HED (MOEs ≥ 1000) at the 

level of personal protection recommended on the label (double layer clothing and gloves). 

Likewise, results from the updated assessment indicate that short- and intermediate-term 

inhalation risks are not of concern to the HED (MOEs ≥ 300) at baseline levels of respiratory 

protection (i.e., no respirator). A summary of short- and intermediate-term agricultural handler 

exposure and risk estimates for glufosinate ammonium for spot/directed spray applications is 

presented in Table 1. This table supersedes Table 9.1c from the July 2012 risk assessment.

2) Occupational Exposure and Risk Estimates for Representative Registered Agricultural

Uses

Results from the assessment of occupational handler scenarios on representative high-acreage 

crops (corn, canola, cotton and soybeans) indicate that short- and intermediate-term dermal risks 

for mixer/loader scenarios are not of concern to HED (MOEs ≥ 1000) at some level of risk 

mitigation (e.g., gloves, or other engineering control measures such as closed systems).

Likewise, results from the assessment of all occupational handler scenarios indicate that shortand intermediate-term inhalation risks are not of concern to HED (MOEs ≥ 300) at the baseline 

level of respiratory protection (i.e., no respirator). Aerial and groundboom applicator risks do 

not exceed HED’s level of concern (MOEs ≥ 1000 for dermal exposures and MOEs ≥300 for 

inhalation exposures) at some level of risk mitigation or engineering control measures (i.e.,

gloves, enclosed cockpit, or closed cab). A summary of short-/intermediate term agricultural 

handler exposure and risk estimates for glufosinate ammonium applications on corn, canola, 

cotton and soybeans is presented in Table 2.

3) Occupational Post-Application Exposure and Risk

A summary of post-application risk estimates for glufosinate ammonium applications on corn, 

canola, cotton and soybeans is presented in Table 3.
Page 4 of 10

Short- and intermediate-term post-application risk estimates were not a concern on day 0 (12 

hours following application) following glufosinate treatments on cotton.

For scouting activities on corn (unspecified type), an MOE >1,000 is achieved on day 2 after 

treatment at the highest label rate (see EPA Reg 264-663). For irrigation activities, an acceptable 

MOE is not achieved until day 4 for sweet corn, day 5 for field corn, and day 7 for corn 

(unspecified type at the highest label rate). Therefore, these post-application activities are of 

concern to the HED. 

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

for scouting activities on canola indicate an MOE of 990 on day 1; an MOE>1000 is achieved on 

Day 2 after treatment. Likewise, for scouting activities on soybeans, an MOE >1,000 is achieved 

on day 4 after glufosinate treatment. Therefore, these post-application activities are of concern 

to the HED. 

It should be noted that glufosinate labels indicate an REI of 12 hours. HED recommends that the 

REI be revised to address the risk concerns identified.

Residue Data Requirements

In accordance with the updated Part 158 data requirements (2007), one or more DFR studies are

required when a pesticide has residential or occupational uses that could result in postapplication dermal exposure. As part of the recent revision to the Health Effects Division’s 2012 

Standard Operating Procedures for Residential Pesticide Exposure Assessment,

http://www.epa.gov/pesticides/science/residential-exposure-sop.html, HED analyzed a number 

of DFR studies and selected a new default value for the fraction of the application rate available 

to be dislodged after a foliar application (FAR). This default value is 25% and is based on an 

analysis of 19 DFR studies where the FAR value ranged from 2% to 89%. This value is 

recommended for use in both residential and occupational post-application assessments. Of the 

analyzed DFR studies, the maximum FAR value seen was 89% or 3.6 times higher than the 

default residue transfer value. Therefore, HED has decided that a calculated MOE of 

approximately 4 times higher than the level of concern (e.g., an MOE > 4000 if the LOC = 1000) 

using the default dislodged residue values would provide an adequate margin of safety for any 

potentially higher residues seen in a chemical-specific DFR study (Guidance for 

Requiring/Waiving Turf Transferrable Residue (TTR) and Dislodgeable Foliar Residue (DFR) 

Studies. 6/7/2012, Exposure Science Advisory Council). DFR studies for corn, canola, cotton 

and soybeans are required for glufosinate ammonium since the post-application dermal MOEs 

are lower than 4000 (i.e. 4 X LOC) on Day 0 (scouting and or irrigation mature/high foliage 

plants) based on default values for the fraction of application rate available for transfer after a 

foliar application.
Page 5 of 10

Table 1. Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium 

(Updated M/L/A Scenario for 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)

Baseline 

Inhalation s

(ug/lb ai)

Baseline 

Dermald,h

PPE

Dermalj

Baseline 

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 1.3

2.160

0.390 

(SL/G)

0.290

(DL/G)

3.9 0.0526

0.0158 

(SL/G)

0.0117

(DL/G)

0.00151 270

890

(SL/G)

1,200

(DL/G)

8,300

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 x inhalation absorption 

(100%) / 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),
Page 6 of 10

Table 2. Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium 

(Representative crops)

Exposure 

Scenario

Crop or 

Target

App 

Ratea

(lb 

ai/A)

Acres 

Treate

d

Dailyb

Unit Exposurec Dose (mg/kg/Day)

MOEs

(Dermal LOC = 1000

Inhalation LOC = 300)

Baseline

Dermal 

(mg/lb 

ai)

PPEDermal 

(mg/lb ai)

Inhalatio

n

(ug/lb ai)

Baseline 

Dermald,

h

PPE 

Dermali

Inhalatio

n

e

Baselin

e 

Dermal

f

PPEDermalInhalation

g,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

Corn (Field), 

Canola, 

Soybean

0.6615 1200 0.228

0.0389

(SL/G)

0.0301

(DL/G)

0.00891

(EC)

0.00218 61

360

(SL/G)

470

(DL/G)

1600

(EC)

5,700

Cotton 0.7901 1200 0.273

0.0464

(SL/G)

0.036

(DL/G)

0.0106

(EC)

0.0026 51

300

(SL/G)

390

(DL/G)

1300

(EC)

4,800

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

Corn (Field), 

Canola, 

Soybean

0.6615 200 0.038 0.00648

(SL/G) 0.000363 370 2,200

(SL/G)

34,000

Cotton 0.7901 200 0.0454 0.00775

(SL/G) 0.000433 310 1,800SL/G) 29,000
Page 7 of 10

Table 2. Short-/Intermediate Term Agricultural Handler Exposure and Risk Estimates for Glufosinate Ammonium 

(Representative crops)

Exposure 

Scenario

Crop or 

Target

App 

Ratea

(lb 

ai/A)

Acres 

Treate

d

Dailyb

Unit Exposurec Dose (mg/kg/Day)

MOEs

(Dermal LOC = 1000

Inhalation LOC = 300)

Baseline

Dermal 

(mg/lb 

ai)

PPEDermal 

(mg/lb ai)

Inhalatio

n

(ug/lb ai)

Baseline 

Dermald,

h

PPE 

Dermali

Inhalatio

n

e

Baselin

e 

Dermal

f

PPEDermalInhalation

g,i

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)

Corn (Field), 

Canola,

Soybean

0.6615 1200 No Data 0.00518

(EC)

0.000675

(EC) No Data 2,700(EC)

19,000

(EC)

Cotton 0.7901 1200 No Data 0.00618

(EC)

0.000806

(EC) No Data 2,300(EC)

16,000

(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) 100,000

Corn (Field), 

Canola, 

Soybean

0.6615 200 0.0136 0.00278

(SL/G) 0.000563 1,000 5,000 22,000

Cotton 0.7901 200 0.0162 0.00331

(SL/G) 0.000671 860 4,200 19,000

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

Flagging for 

Aerial Sprays

High Acreage 

Crops 0.7901 0.00397 NA 0.00121 3,500 - 10,000
Page 8 of 10

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 x inhalation absorption 

(100%) / 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 9 of 10

Table 3. Summary of Estimated Post-application Risks for glufosinate ammonium (Representative crops)

EPA Reg. 

Number

Maximum 

Application 

Ratea

(lb ai/A).

ExpoSAC 

Policy 3 TC 

Crop 

Group

DATb

DFR c

(μg/cm2)

TC d

Activity d Short-/IntTerm MOEe

Corn(Sweet)

279-3313, 

279-3108 0.365 Field / row crop, tall

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 1,050

Corn (Field)

264-829 0.4042 Field / row 

crop, tall

0 1.13 1,100 Scouting mature/high 

foliage plants 1,100

0 1.13 1,900 Irrigation mature/high 

foliage plants

630

5 0.669 1,900 1,100

Corn (Unspecified)

264-663 0.5218 Field / row 

crop, tall

0 1.46

1,100 Scouting mature/high 

foliage plants

830

2 1.46 1,000

0 1.46

1,900 Irrigation mature/high 

foliage plants

480

7 0.70 1000

Canola

264-660 0.4435

Field / row 

crop, low / 

medium

0 1.24 1,100

Scouting mature/high 

foliage plants

990

1 1.12 1,100 1,100
Page 10 of 10

Table 3. Summary of Estimated Post-application Risks for glufosinate ammonium (Representative crops)

EPA Reg. 

Number

Maximum 

Application 

Ratea

(lb ai/A).

ExpoSAC 

Policy 3 TC 

Crop 

Group

DATb

DFR c

(μg/cm2)

TC d

Activity d Short-/IntTerm MOEe

Cotton

264-829 0.7901

Field / row 

crop, low / 

medium

0 2.22 210 Scouting low/ full 

foliage plants 2,900

0 2.22 70 Hand weeding low/ full 

foliage plants 8,600

Soybeans

264-829 0.6615

Field / row 

crop, low / 

medium

0 1.86

1,100 Scouting low/ full 

foliage plants

660

4 1.22 1000

a) Maximum application rate (lb ai/A) indicated on registered labels

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).