UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C., 20460

OFFICEOF • CHEMICAL SAFETY AND
POLLUTION PREVENTION



### MEMORANDUM

DATE:

SUBJECT:

FROM:

THRU:

TO: March 10, 2014

Registration Review- Preliminary Problem Formulation for the Ecological Risk**Assessm~nt** 

### and Drinking Water Exposure Assessment to be Conducted for Imazapyr and Imazapyr Isopropylamine (PC Code 128829 (isopropylamine salt)

and 

### 128821 (imazapyr acid); DP Barcode 

### 41 7327)

# ~ 

# a /I' 

# A**~** 

# /t ")

James A. Hetrick, Ph.D.,

# Se~**Adviso~** · / / ' 

# vf 

# 1

Tanja Crk, Biologist /

### ~**~~** 

## L/'t:.- 

# "Stl b 2/JIJj


### Environmental Risk Branch 3 · 

# J

Environmental Fate and Effects Division (7507P)

Dana Spatz,

# Chie~ , / ;. Melissa Panger, Ph.D., Senior Scientist 

# 3/ / 6 

# If

Rosanna Louie-Juzwiak, RAPL (})

_ Environmental Risk Branch 3**~** 

### Environmental Fate and Effects Division (7507P)

Joel Wolf, Chemical Review Manager

Kevin Costello, Chief

Risk Management and Implementation B"ranch 2

Pesticide Reevaluation Division (7508P)

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem

formulation for the ecological risk to be conducted as part ·of the Registration Review of imazapyr and imazapyr isopropylamine. At this time, EFED does not expect to conduct a new drinking water assessment given that the Health Effects Division (HED) does not anticipate conducting a dietary assessment. This document is intended to provide an overview of what is currently known regarding the environmental fate and ecological effects associated with imazapyr and imazapyr isopropylamine and their degradation products, and outlines

uncertainties regarding attributes of the parent compounds and their transformation products. It

describes the preliminary ecological risk hypothesis and the processes that will be used during

the completion ofihe ecological risk assessment in support of Registration Review.

### 2 1. INTRODUCTION

The active ingredient imazapyr is a systemic imid azolinone herbicide that is used for control of most annual and perennial broadleaf weeds a nd grasses, woody speci es, and riparian and emergent aquatic weeds species. It is formulated both as an acid (imazapyr) and as an isopropylamine salt (imazapyr IPA). The mode of action of imazapyr is to inhibit acetohydroxyacid synthase (ALS) wh ich interferes with plant cell growth and DNA synthesis.

The chemical structure of imazapyr along with the chemical identi fiers is provided in Table 1

.

Table 1. Imazapyr Chemical Identifiers

Chemical Name Imazapyr Imazapyr IPA

Chemical
Structure

Chemical
Abstracts Service (CAS) Registry

Number 81510-03-0 81334-34-1



### Imazapyr is currently registered for use in terrestrial (railroa ds and industrial right-of-ways, fencerows, wildlife habitats and forests) and aquatic (ponds, lake s, reservoirs, marshes, bayous, canals, streams, rivers, and water drainage syst ems) non-crop sites and for corn fields. Aqueous imazapyr formulations may be mixed with surfactan ts or oils for application, as well as mixed with other herbicides and fertilizers. Imazapyr is also available in a water dispersible granular
formulation and an emulsifiable concentrate. Typical terrestria l application met hods consist of ground and aerial spray, with granular broadcast applications for forestry uses, while surface waters including bogs, marshes, potholes, wetla nds, and intermittently fl ooded areas are treated directly with aqueous formulations. For more information on use and usage, please see the
BEAD Chemical Profile document.

2. PREVIOUS RISK ASSESSMENTS

An ecological risk assessment in support of th e re-registration eligibility decision (RED) for imazapyr (both acid and salt formulations; PC Codes: 128821 and 128829), he reafter referred to as imazapyr, was finalized by EFED on September 30, 2005 (DP Barcode: D313607) ( Table 2 ). The screening level risk assessmen t indicated risk to non-target terrestrial plants (monocots and dicots) and aquatic vascular plants from imazapyr use, based on the highest application rate from a variety of use patterns. Seedling emergence a nd vegetative vigor for both monocots and dicots would be impacted by exposure to both the imazapyr acid and th e isopropylamine salt. The
assessment indicated minimal risk of acute effect s to fish and aquatic i nvertebrates and minimal risks to aquatic non-vascular plants at maximum application rates. In addition, there were no
chronic risks to fish and invert ebrates, although there was an un certainty for estuarine/marine

### 3 fish and invertebrates, since no toxicity data we re available to observe the prolonged effects of imazapyr to these taxa. Likewise, acute and chro nic risks to mammals and birds consuming food types containing imazapyr residues are not expected from the labeled uses of the herbicide. EFED currently does not quantify risks to terrestrial non-target insects; ho wever, available data on honey bees indicate that the risk to terrestrial non-target insect s was likely to be low. The assessment indicated the potential for indirect ri sk to all taxa from direct effects on plants ( i.e.

, effects on habitat and/or primary productivity).

An assessment of risk to the list ed California Red-Legged Frog (CRLF, Rana aurora draytonii ) was completed on July 20, 2007. That assessment i ndicated no expected dire ct effects on either the aquatic or terrestrial phase CRLF. There were also no indirect effects expected for the CRLF through direct effects to either its terrestrial or aquatic food s ources. The assessment determined that the CRLF may be adversely affected thr ough direct effects on habitat and/or primary productivity ( i.e. , ecosystem structure and function for both the aquatic plant community and riparian vegetation). Critical ha bitat may also be adversely modi fied based on direct effects to aquatic vascular plants and terr estrial plants. The risks exceeded the level of concern (LOC) for non-listed non-target terrestrial plants (monocots a nd dicots) for all imazapyr uses. The risks to non-listed non-target aquatic va scular plants exceeded the LOC for aquatic, rangeland and forestry uses (aerial application) as well as ri ghts-of-way (assuming 50% pervious surfaces). No effects were expected for aquatic non-vascular plants.

A Special Local Needs 24(c) assessment was conducted in May 24, 2010 (DP Barcode D374578). The request was to allow broadcast application of imazapyr (Arsenal PowerLine EPA Reg. No. 241-431) on grass past ure for control of cogongrass ( Imperata cylindrica ) in areas that may be grazed or cut for hay. The assessm ent indicated no expected risks for effects to aquatic and terrestrial animals fr om the proposed broadcast spray a pplication of 0.75 lb a.e./A of imazapyr on pastures. Non-target terrestrial plants may be adversely affected from the proposed use. Off-site movement of imazapyr onto non-targ et terrestrial plants is associated with both runoff onto adjoining fields and spray drift deposition.

Finally, an assessment was conducted in August 2, 2010 (DP Barcode D379032). BASF petitioned to add aquatic use si tes to the Arsenal Powerline TM 

### herbicide (EPA Reg. No. 241-431) label to allow direct application of imazapyr to potable surface water, public waters, private waters, livestock watering ponds, recreational wate r areas at a maximum ra te of 1.5 lb a.e/A per

year.

Table 2. Summary of Previous Risk Asse ssments Conducted by EFED on Imazapyr

Use Reference
(DP Barcode) Max. Application Rate Taxa for which risk was identified at the Agency’s

concern levels

Various RED, 2005
(D313607) 1.5 lbs a.e./A Terrestrial plants, aquatic vascular plants; fish, aquaticinvertebrates, aquatic nonvascular plants

Various CRLF, 2007 1.5 lbs a.e./A CRLF assessment: Terrestrial plants and aquatic vascular plants

### 4 Table 2. Summary of Previous Risk Asse ssments Conducted by EFED on Imazapyr

Use Reference
(DP Barcode) Max. Application Rate Taxa for which risk was identified at the Agency’s

concern levels

Grass pasture SLN 24(c), 2010
(D374578) 0.75 lb a.e./A Terrestrial plants and aquatic vascular plants

Direct aquatic D379032 1.5 lbs a.e./A Terrestrial plants, aquatic vascular plants; fish, aquaticinvertebrates, aquatic nonvascular plants



### Previous Drinking Water Assessments

The drinking water assessment (DWA) for imazapyr was conducted on terrest rial (spot treatment on pasture) and aquatic uses (D275562, 2003). The DWA was based on an application rate of 1.5 lb a.e./A, which represents the maximum application rate for aquatic use sites ( Table 3 ).

Table 3. Estimated Drinking Water Concentrations (μg/L) for Imazapyr

Use Pattern Models Pea k Annual Avera g e 30-year Annual
Avera g e

Aquatic/Terrestrial@ 1.5 lb a.e./A (D275562, 2003) Tier I FIRST 137 81 N A

SCI-GROW 35.9 N A NA=not applicable for a Tier 1 drinking waters assessment



### Clean Water Act Programs

Imazapyr is not identified as a cause of impairment for any wa ter bodies listed as impaired under section 303(d) of the Clean Water Act ( http://water.epa.gov/lawsregs/law sguidance/cwa/tmdl/index.cfm ). No Total Maximum Daily Load (TMDL) criteria have been developed for imazapyr. Aquatic life benchmarks have published for imazapyr ( http://www.epa.gov/oppefed1/ecoris k_ders/aquatic_life_benchmark.htm ) ( Table 4 ). The aquatic life benchmarks represent ecotoxicity endpoints derived from risk assessments to support pesticide registrations.

Table 4: OPP Aquatic Life Benchmarks for Imazapyr

Compound Fish Invertebrate Non-Vascular
Plants Vascular
Plants Acute Chronic Acute Chronic μg/L Imazapyr >50000 43100 5 0000 97100 12000 24

### 5 3. ENVIRONMENTAL FATE AND TRANSPORT

The environmental fate database is complete for assessing the environmental fate and transport of imazapyr and imazapyr isopropylamine (Appendix A). Imazapyr is an an ionic, organic acid (pK
a 

### of about 3.8) that is non-volatile, degrades through photolysis in clear shallow waters, and is both persistent and mobile in soil. A summary of selected physical and chemical properties for imazapyr and imazapyr isopropylamine salt are presented in Table 5 . Imazapyr is mainly present in anionic form at typical environmental pHs, and the behavior of the acid and salt forms are expected to be similar, ther efore, the environmental fate of the imazapyr is evaluated in terms of acid equivalents. Most environmental fa te data available for imazapyr are based on dissociation of the isopropylamine salt in water. Imazapyr was e ssentially stable to aerobic and anaerobic soil metabolism, and no major transformation products were identified during the course of laboratory studies ( Table 6 ). Field study observations ar e consistent with imazapyr’s intrinsic ability to persist in so ils and move via runoff in surface water and leach to groundwater. Imazapyr did not bioconcentrate in submitted laborato ry studies. The relatively high solubility in water and low n-octanol to water partitioning rati o of imazapyr is also consistent with little
likelihood of bioconcentration.

Table 5. Physical and Chemical of Imazapyr and the Isopropylamine Salt of Imazapyr
Physical and Chemical Properties

Chemical name Imazapyr Imazapyr Isopropylamine Salt

2-[4,5-Dihydro-4-methyl-4-(1- methylethyl)-5-oxo-1 H -imidazol-2-yl]-3- pyridinecarboxylic acid 2-Propanamine, 2-(4,5-dihydro-4-methyl-4-(1- methylethyl)-5-oxo-1 H -imidazol-2-yl]-3- pyridinecarboxylate

Empirical
Formula C 13 H 15 N 3 O 3 C 13 H 15 N 3 O 3 ·C 3 H 9 N

Molecular Weight 293.16 g/mol 322.19 g/mol

Aqueous Solubility at 25

 C 11.1 g/L MRID 00145872

pK

a 3.8 MRID 00145872

Vapor Pressure

at 60  C <10 -7 mm Hg MRID 00145872

Henry’s Law
Constant at 25

 C <7 x 10 -17 atm x m3/mol Calculated

Log P

ow at pH 7

and 20  C 0.22 MRID 00145872

### 6 Table 6. Environmental Fate Data for Imazapyr and Imazapyr IPA

Guideline # Data Requirement (material) MRID # Values

835.2120 Hydrolysis (Imazapyr) 00132359 t 1⁄2= Stable

835.2240 Photodegradation in Water (Imazapyr) 00131617 t 1⁄2-= 2.3-3 days

835.2210 Photodegradation on Soil (Imazapyr) 40003713 t 1⁄2= 149 days

835.4100 Aerobic Soil Metabolism (Imazapyr) (Imazapyr) 41023201
45119701 t 1⁄2= 5.9 years

t 1⁄2= 296 days

835.4200 Anaerobic Soil Metabolism (Imazapyr) 00131619 t 1⁄2= Stable

835.4400 Anaerobic Aquatic Metabolism (Imazapyr) 40003712 t 1⁄2= Stable

835.4300 Aerobic Aquatic Metabolism (Imazapyr) (Photoproducts: CL 9140, CL 119060) 41002301
41891501
45119702 t 1⁄2 Stable-Parent

t 1⁄2= 5.7 days-CL9140 (Upper 90% CB of Mean)

t 1⁄2= 8 days-CL119060(Upper 90% CB of Mean)

835.1230

835.1240 Leaching-Adsorption/Desorption (Imazapyr + photoproducts) 45119705 Sand-K f =0.091 (1/N=0.733) Kfoc=19.4 (Parent)

Silt loam-K f =0.091 (1/N=0.887) Kfoc=19.4 (Parent)

Sand-K f =0.69 (1/N=0.811) Kfoc=149 (CL9140)

Silt loam-K f =31.6 (1/N=0.955) Kfoc=4940 (CL9140)

Sand-K f =0.551 (1/N=0.939) Kfoc=117 (CL119060)

Silt loam-K f =5.77 (1/N=0.962) Kfoc=902

(CL119060)
835.6100 Terrestrial Field Dissipation (Imazapyr) (Arsenal 2AS) (Arsenal 2AS) 45119706
42192101
42192102 t 1⁄2 =143 days – OR field study (soil)

t 1⁄2= 64 days – NC field study (soil)

t 1⁄2= 94 days-IA field study (soil)

t 1⁄2= 126 days-NE field study (soil)

835.6300 Aquatic Field Dissipation (Imazapyr) (Arsenal 2AS) 45119707
41891501 t 1⁄2 = 3 days- FL field study (water and sediment)

t 1⁄2= 4 days- LA field study (water and sediment)

835,6400 Forestry Dissipation (Arsenal) 40003714 t 1⁄2 =24 days- AL field study (soil)

t 1⁄2 =26 days- AL field study (soil)

850.1730
Accumulation in Fish

— No Data

Nonguideline Accumulation- aquatic nontarget (Imazapyr) (Imazapyr) 45119707
45119709 Fish/Crayfish- No detectable
bioaccumulation
Shrimp/Oysters- No detectable
bioaccumulation BCF<1

### 7 Transformation Products

Although imazapyr is stable to hydrolysis and mi crobial metabolism, photodegradation in water is an important route of dissipation. Major pho todegradation products of imazapyr (>10% of applied radiation) are CL11960 and CL9140. The degradation product CL252974 was a minor transformation product (<6.9% of applied radiati on) in hydrolysis and aerobic soil metabolism
studies. The transformation products CL11960 and CL9140 are prone to degrade through
oxidative mineralization to CO 2 

### . These transformation products are listed in APPENDIX A
with the maximum amounts of each observed in the various environmental fate studies.

4. RECEPTORS

The toxicity endpoints for imazapyr acid fo r use in the risk assessment are shown in Table 7. Available aquatic ecotoxicity study endpoints on imazapyr sa lt and acid are summarized in
Table 8 and Table 9. The available terrestrial ecotoxicity study endpoints on the isopropylamine salt of imazapyr, and its acid form, are in Table 10 and Table 11 . A summary of the ecotoxicity
data is shown in APPENDIX C . The endpoints from the toxicity tests with the isopropylamine salt of imazapyr are expressed in acid equivalents (a.e.).

Table 7. Toxicity Endpoints Used in Assessment of Risk in Acid Equivalents 

### Organisms Toxicity Endpoint MRID

Aquatic Organisms

Acute Freshwater fish LC 50 (mg ae/L) >100 00131629 thru
-631

Acute Freshwater invertebrate EC 50 (mg ae/L) >100 00131632

Acute Marine/estuarine fish LC 50 (mg ae/L) >184 41315801 Acute Marine/estuarine invertebrate (mollusk) EC 50 (mg ae/L) >132 45119710 Acute Marine/estuarine invertebrate (pink shrimp) LC 50 (mg ae/L) >189 41315803

Chronic Freshwater fish NOA EC (mg ae/L) 43.1 41315804

Chronic Freshwater invertebrate NOAEC (mg ae/L) 97.1 41315805 Aquatic nonvascular plants EC 50 /NOAEC (mg ae/L) 11.5/7.16 43889102 Aquatic vascular plants EC 50 /NOAEC (mg ae/L) 0.018/0.011 43889102 Terrestrial Organisms Acute Avian (oral dose-based) LD 50 (mg ae/kg-bw) >2150 00131633
00131634 Acute Avian (dietary) LC 50 (mg ae/kg-diet) >5000 00131635
00131636 Acute Mammal (oral dose-based) LC 50 (mg ae/kg-bw) >5000 00132030 Chronic Avian (dietary) NOAEC (mg ae/kg-diet) 1670 45119714 Chronic Mammal (dietary) NOAEC (mg ae/kg-diet) 10000 41039505 Chronic Mammal (dose-based) NOAEL (mg ae/kg-bw/day) 738 41039505 Acute Terrestrial Invertebrate (contact) LD 50 (  g a.e./bee) >100 00131637 Dicot Seedling Emergence (EC 25 )/(NOAEC/EC 05 ) (lbs ae/A) 0.0024/0.00017 40811801 Dicot Vegetative Vigor (EC 25 )/(NOAEC/EC 05 ) (lbs ae/A) 0.0009/0.000064 Monocot Seedling Emergence (EC 25 )/(NOAEC/EC 05 ) (lbs ae/A) 0.0046/0.00099 Monocot Vegetative Vigor (EC 25 )/(NOAEC/EC 05 ) (lbs ae/A) 0.012/0.0039

### 8 Receptors

Tables 8 through Table 11 provide a summary of the aquatic and terrestrial taxonomic groups, respectively, and most sensitive surrogate species tested to characterize the potential acute and chronic ecological effects of imazapyr.

Effects to Aquatic Animals

Table 8 provides a summary of endpoints from aquati c toxicity studies for imazapyr acid. The available toxicity data for th e salt are no more toxic than the acid and are summarized in Appendix C

.

Table 8. Summary of Endpoints from Aq uatic Toxicity Studies for Imazapyr Acid

Taxonomic

Group Study Type Species %

ae Endpoint Toxicity Category / Endpoint
Affected MRID No.
Author/Year Study
Classification

Freshwater
Fish Acute Bluegill
sunfish (Lepomis macrochirus) 93 96-hour

LC 50 : >100 mg/L Practically
non-toxic 00131630
ABC Laboratories,
1983 Acceptable

Rainbow trout (Oncorhynchus mykiss) 93 96-hour
LC 50 : >100 mg/L Practically
non-toxic 00131629
ABC Laboratories,
1983 Acceptable

Channel catfish (Ictalurus

punctatus ) 93 96-hour

LC 50 : >100 mg/L Practically
non-toxic 00131631
ABC Laboratories,
1983 Acceptable

Chronic: Early-life

stage study Rainbow Trout (Oncorhyncus mykiss) 99.5 NOAEC/LOAEC: 43.1/92.4 mg ae/L 1 Larval
survival 41315804 Ward, 1988 Supplemental

Fathead
Minnow ( Pimephales promelas ) 99.6 NOAEC/LOAEC: 118/>118 mg ae/L No treatmentrelated
effects 45119711

Drottar et al.

, 1998 Acceptable

Chronic:
Full life

cycle Fathead
Minnow (Pimephales promelas) 100
NOAEC/LOAEC: 120/>120 mg ae/L No treatmentrelated
effects 45119712

Drottar et al.

, 1999 Supplemental

Freshwater
invertebrates Acute Waterflea ( Daphnia

magna ) 93 48-hour

EC 50 : >100 mg/L Practically
non-toxic 00131632
ABC Laboratories,
1983 Acceptable

Chronic: Life cycle Waterflea (Daphnia magna) 99.5 21-day
NOAEC/LOAEC: 97.1/>97.1 mg/L No effects on growth or reproduction 41315805
Mannin g ,

1988 Acceptable

### 9 Table 8. Summary of Endpoints from Aq uatic Toxicity Studies for Imazapyr Acid

Taxonomic

Group Study Type Species %

ae Endpoint Toxicity Category / Endpoint
Affected MRID No.
Author/Year Study
Classification

Estuarine/
Marine Fish Acute Silverside
minnow (Menidia menidia) 99.5 96-hour

LC 50 : >184 mg
ae/L Practically
non-toxic 41315801 Manning ,
1988 Acceptable

Chronic* Data not
submitted N/A N/A N/A N/A N/A

Estuarine/

Marine
Invertebrates Acute Eastern oyster ( Crassostrea

virginica ) 99.6 96-hour

EC 50 >132 mg
ae/L Practically
non- toxic 45119710

Drottar et al

., 1997 Acceptable

Eastern oyster ( Crassostrea

virginica ) 99.5 96-hour

EC 50 : >173 mg
ae/L Practically
non- toxic 41315802 Ward, 1998 Supplemental

Pink shrimp

(Penaeus duorarum) 99.5 LC 50 >189 mg
ae/L Practically
non-toxic 41315803 Manning,

1988 Acceptable

Chronic* Data not
submitted N/A N/A N/A N/A N/A

* The EC 50 /NOAEC values from the toxicity tests with the is opropylamine salt of imazapyr are expressed in acid equivalents (a.e.). The toxicity values with the acid are not expressed in terms of acid equivalents.

1 Equation for calculating acid equivalents (a.e.): (molecular weight of acid / molecular weight of salt) x endpoint derived from study with isopropylamine salt as test compound.

Therefore, given the endpoint from a study conducted with the salt, to obtain the acid equivalent of the concentration, multiply the endpoint in terms of a.i. of salt by 0.9098 (i.e., 293.16 g/mol divided by 322.19 g/mol) to obtain the concentration in acid equivalents.



### *Estuarine and Marine Fish and Invertebrates, Chronic

Chronic studies on estuarine/marine fish and invertebrates were not submitted. Although acute
studies are available for freshwater and marine /estuarine fish and i nvertebrates and chronic
studies are available for freshwater fish and invertebrates, acute to chronic ratios could not be
estimated because all of the acute LC 50 

### /EC 50 

### values are greater than values. As a result, an assumption will be made that the marine/estuari ne fish and invertebrates will have a similar sensitivity to imazapyr as freshwater fish a nd invertebrates, especially since the acute LC 50 

### values of these taxa were all great er than 100 mg a.e./L. There is uncertainty associated with this assumption because quantifiable taxonomic sensitiv ity factors between the two broad categories
of fish and invertebrates do not exist. There is additional uncertainty associated with the
estimated chronic NOAEC for estuarine/marine fish and for estuarine/marine invertebrates because the acute toxicity data do not allow for a definitive determination of the relative sensitivity of freshwater and estuar ine/marine fish and invertebrates.

### 10 Effects to Aquatic Plants

Unlike the effect of the isopropylam ine salt to aquatic animals with respect to the imazapyr acid ( i.e. the salt is no more toxic than the acid), the t oxicity of the isopropylami ne salt is more toxic to aquatic vascular plants and non-vascular plants (based on du ckweed and green algae) than imazapyr acid ( Table 9 ).

Table 9. Non-target Aquatic Plant Toxicity for Imazapyr Acid and Isopropylamine Salt of Imazapyr

Species [Tier II] % ae EC 50 /NOAEC Endpoints
Affected MRID No. Author, Year Study
Classification

Isopropylamine Salt of Imazapyr *

Duckweed ( Lemna gibba ) 23.3 0.018/0.011 (mg ae/L) Frond production 43889102 Hughes et al ., 1995 Acceptable

Green Algae ( Selenastrum capricornutum) 23.3 11.5/7.16 (mg ae/L) Slight change in cell shape 43889102 Hughes et al ., 1995 Acceptable

Imazapyr Acid

Duckweed ( Lemna gibba ) 99.5 0.024/0.01 (mg a.i./L) Population growth Frond production 40811802 Hughes, 1987 Acceptable

Green Algae ( Selenastrum capricornutum ) 99.5 71/50.9 (mg a.i./L) Cell density 40811802 Hughes, 1987 Acceptable

Blue-green Algae ( Anabaena flos-aquae ) 99.5 12.2/9.6 (mg a.i./L) Cell density 40811802 Hughes, 1987 Acceptable

Diatom ( Navicula pelliculosa ) 99.5 >41/41 (mg a.i./L) Cell density 40811802 Hughes, 1987 Acceptable

Diatom ( Skeletonema costatum ) 99.5 92/15.9 (mg a.i./L) Cell density 40811802 Hughes, 1987 Acceptable

* The EC 50 /NOAEC values from the toxicity te sts with the isopropylamine salt of imazapyr are expressed in acid equivalents (a.e.)



### Terrestrial Effects Characterization

Terrestrial Animals

Table 10 provides a summary of endpoints from terrest rial toxicity studies for imazapyr. The available toxicity data (subacute dietary avian and rat acute studies) for the salt are no more toxic
than the acid and are summarized in Appendix C

.

### 11 Table 10. Summary of Endpoints from Terrestrial Animal To xicity Studies for Imazapyr Acid

Taxonomic

Group Study Type Species %

ae Endpoint Toxicity Category / Endpoint
Affected MRID No.
Author/Year Study
Classification

Birds Acute Oral Northern bobwhite quail (Colinus virginianus) 93 LD 50 : >2,150 mg ae/kg-bw Practically
non-toxic 00131633
Bio-Life Assoc., 1983 Acceptable

Mallard duck (Anas platyrhynchos) 93 LD 50 : >2,150 mg ae/kg-bw Practically
non-toxic 00131634
Bio-Life Assoc., 1983 Acceptable

Sub-acute

Dietary Northern bobwhite quail (Colinus virginianus) 93 8-day LC 50 :>5,000 mg ae/kgdiet Practically
non-toxic 00131635
Bio-Life Assoc., 1983 Acceptable

Mallard duck (Anas platyrhynchos) 93 8-day LC 50 :>5,000 mg ae/kgdiet Practically
non-toxic 00131636
Bio-Life Assoc., 1983 Acceptable

Chronic: Reproduction Northern bobwhite quail (Colinus virginianus) 100 NOAEC/LOAEC: 1,670/>1,670 mg ae/kg-diet No treatmentrelated toxicity 45119714
Ahmed et al.

, 1999 Acceptable

Northern bobwhite quail (Colinus virginianus) Tech NOAEC/LOAEC:
2000/>2000 mg ae/kg-diet No treatmentrelated toxicity 43831401
1987 Acceptable

Mallard duck (Anas platyrhynchos) Tech NOAEC/LOAEC:
1890/>1890 mg ae/kg-diet (2000 nominal) No treatmentrelated toxicity 43831402
1987 Acceptable

Mammals Acute Rat(SpragueDawley) 93 LD 50 >5,000 mg ae/kg bw (males/females) Mortality 00132030
American Cyanamid Co., 1983 Acceptable

Chronic: Developmental 2 Rat (Sprague Dawley) 93 NOAEL/LOAEL
= 300/1000 mg/kg bw/day Maternal tox 1 00131611
Salamon & Mayhew,

1983 Acceptable

NOAEL = 1000 mg/kg bw/day Developmental

Rabbit (New Zealand White) 93 NOAEL = 400 mg/kg bw/day No effects 00131613 Mayhew & Salamon,

1983 Acceptable

### 12 Table 10. Summary of Endpoints from Terrestrial Animal To xicity Studies for Imazapyr Acid

Taxonomic

Group Study Type Species %

ae Endpoint Toxicity Category / Endpoint
Affected MRID No.
Author/Year Study
Classification

Chronic: Reproduction Rat (Sprague Dawley) 99.5 NOAEL = 738 mg/kg bw/day -
Males

NOAEL = 933.3 mg/kg bw/day –
Females

10000 ppm for
both males and
females. No effects 41039505 Robinson,
1987 Acceptable

Terrestrial
invertebrates Acute contact Honey Bee (Apis mellifera) Tech LD 50 : >100 μg ae/bee Practically
non-toxic 00131637 Atkins, 1983 Acceptable

1 Maternal toxicity - Gravid dams exhibite d salivation during gestation days 8 - 15 (lik ely related to gavage route of administr ation).

2 Developmental toxicity - No treatment-related effects in developmental parameters; no treatment-related malformations



### Terrestrial Plants

Results of Tier II toxicity st udies with monocots and dicots in dicate that seedling emergence and vegetative vigor are severely impacted by expos ure to imazapyr acid and to the isopropylamine salt of imazapyr ( Table 11 ).

Table 11. Summary of En dpoints from Terrestrial Plant Toxici ty Studies for Imazapyr Acid and Isopropylamine Salt

Taxonomic

Group Study Type Species Compound EC 25 lbs
ae/A NOAEC /[EC 05 ] **

lbs ae/A Endpoint
Affected MRID No.
Author/Year Study
Classification

Monocot

Seedling Emergence Oat

Acid 0.054 0.0156 Height

40811801 Banks, 1988 Supplemental Onion 0.034 [0.01] Weight

Wheat 0.0046 [0.00099] Weight

Dicots Sugar
beet 0.0024 [0.00017] Weight

Tomato 0.008 0.0003 Weight

Monocots

Vegetative Vigor Corn >0.0156 0.0078 Weight

Oat 0.013 0.0039 Height

Wheat 0.012 0.0039 Weight

Dicots Sugar
beet 0.00097 [0.00039] Weight

Sunflower 0.0054 0.0039 Weight

Cucumber 0.0009 [0.000064] Height

### 13 Table 11. Summary of En dpoints from Terrestrial Plant Toxici ty Studies for Imazapyr Acid and Isopropylamine Salt

Taxonomic

Group Study Type Species Compound EC 25 lbs
ae/A NOAEC /[EC 05 ] **

lbs ae/A Endpoint
Affected MRID No.
Author/Year Study
Classification

Tomato >0.0156 0.00097 Weight

Monocots Onion

Salt * 0.012 [0.005] Dry weight 43889101
Feutz & Canez, 1995 Acceptable

Dicots Soybean 0.034 0.008 Shoot length

Sugar
beet 0.002 0.001 Dry weight

* The EC 50 /NOAEC values from the toxicity tests with the isopropylamine salt of imazapyr are expressed in acid equivalents (a.e.).

** If the NOAEC value is above the EC 25 , equal to the EC 25 , or below the lowest concentration, an EC 05 value is used instead.

Bold values are used in risk assessment

.



### Ecological Incidents

The ecological incident information system (EIIS ) is an OPP database that houses ecological incidents that have been repor ted to the Agency. When ava ilable, EIIS includes date and location of an incident, type and magnitude of effects observed in various species, use(s) of pesticides known or suspected of contributing to the inci dent, and results of any chemical residue analysis or other analyses conducted during in cident investigation. EIIS incidents are categorized according to the certai nty that the incident resulted from pesticide exposure. The Avian Monitoring System (AIMS) is a database administered by the Amer ican Bird Conservancy that contains publicly available data on reported avian incidents involving pesticides. Many of
the incidents listed in this database are also in the EIIS. However, there was only a single report in the AIMS database linked to the isopropylam ine salt of imazapyr (PC Code 128829) which was considered an unlikely factor in the death of 70 birds from a fence row multiple herbicide use in South Carolina in 1992 (#I000022-001).

In addition to the incidents reco rded in EIIS and AIMS, the Agen cy maintains a database (IDS) which stores counts of minor incidents that pestic ide registrants record in quarterly aggregated incident reports. Ecological incidents record ed in these aggregated reports include those categorized as ‘minor fish and wildlife’ (W-B), ‘minor plant’ (P-B), and ‘other non-target’ (ONT) incidents. ‘Other non-targ et’ incidents include reports of adverse e ffects to insects and
other terrestrial invertebrates. A review of this database in February 2014 indicates the following:

A total of 229 incidents for the imazapyr acid (PC Code 128821): all 229 P-B. A total of 61 incidents for the isopropyl amine salt (PC Code 128829): 6 W-B, 55 P-B.

Twelve incidents resulting from imazapyr and its isopropylamine salt use have been recorded in the Ecological Incident Information System (EIIS) as of April 25, 2005. Incidents reported include possible impacts to terrest rial and aquatic plants , fish and birds. The majority of reported incidents are damage to terrestrial plants, espe cially food crops as a result of exposure following

### 14 application of formulations containing imaza pyr and other active pesticide ingredients ( Table
12a and 12b ).

Table 12a. Incident Reports Involving Imazapyr Acid (04/20/1995 – 8/14/2013)

Location
and Incident # Organism

Involved Product Contact with Product/Symptoms Certainty Legality

Driveway CO
1006019-001 Willow and Spruce Imazapyr Driveway surface application/Mortality Probable Intentional
misuse

Chelan County

WA
1014406-001 Cherry and pear

trees Imazapyr Applied in irrigation
canal/Several dead or dying cherry and
pear tress. Possible Unknown

Dubuque County IA
1008079-001 Corn crop Mixture of

Hornet (unknown pesticide) and

Lightning (imazapyr) Post-emergent application/low yield
and death in 120

acres. Possible Registered Use

Whitman County/ Washington

State
1014407-017 Winter wheat Imazapyr Carryover residues from application to peas the previous Spring/damage. Complication assigning causes to the case concerning
detection limits for imazapyr. Probable Unlikely

Texas
1005972-001 Live oaks Imazapyr Application to neighbor’s property/injury to 3
live oaks. Probable Registered Use

Halifax County,
NC
1003826-008 Goldfish Arsenal (imazapyr) Aerially applied to nearby 145 acre area followed by rain 12 days later/mortality.
No residues found in
area. Cause of mortality not
determined. Possible Registered Use

Grant, WA
1020459-003 Potato Imazapyr Plant damage due to drift exposure. Possible Unknown

Montgomery,

IN
1012366-031 Corn Imazapyr Plant damage from
direct broadcast application to 203
acres of corn. Probable Misuse

Grant, WA
1013884-015 Birch and
Willow Imazapyr Mortality from spray
drift. Highly
Probable Misuse

Limestone, AL
1025684-001 Tomato Imazapyr Plant damage to 1,200 tomato plants Possible Unknown

### 15 from spray drift. Adams, WA
1020459-012 Wheat Imazapyr Plant damage to
wheat from runoff. Possible Unknown

Grant, WA 1020459-001 Wheat Imazapyr Plant damage to
wheat from drift and
runoff. Possible Unknown

Bolivar, MO
1025432-001 Green bean and

Tomato Imazapyr Mortality to green
beans and tomatoes from spray drift. Possible Registered Use

Leake, MS
1025563-001 Soybean Imazapyr Plant damage to 0.75

acres. Possible Unknown

Maricopa, AZ
1024071-369 Trees Imazapyr Mortality due to
direct treatment. Possible Unknown

Table 12b. Incident Reports Involving the Isopropylamine Salt of Imazapyr (05/26/1992 – 06/04/2004)

Location
and Incident # Organism

Involved Product Contact with Product/Symptoms Certainty Legality

Aiken County,

SC
1000022-001 Birds and Fish Arsenal (imazapyr)

Karmex (Diuron)

Escort (Metsulfuron methyl) Spray on fence row drifted onto adjacent
bird nest boxes located
from 2-85 feet of application site; runoff into a pond 60 foot away/bird kill of nesting and mature
birds and fish and algae kill in pond. Possible Unknown

Cass County,

Texas
1015265-001 Loblolly pine seedlings Hexazinone, glyphosate,

imazapyr Hexazinone in soil samples, Onestep (glyphosate and imazapyr) used in site preparation for planting of seedlings/mortality Possible Registered Use

AR
1015280-001 Tomatoes, Cantaloupes
Water-melons Krenite
Arsenal

Escort Glyphos (glyphosate,

imazapyr,
metsulfuron

methyl) Krenite/Arsenal/Escort mixture applied totransmission right-ofway (150 yards to 1/4 mile distance). Glyphos applied to pond levee 30-40 feet
from watermelon and cantaloupe fields./Severe curling
of oldest leaves on tomato plants with
interveinal chlorosis.

Mature tomatoes
rotted from stem side.
Watermelon and Possible Registered Use

### 16 cantaloupes aborted
blooms and fruit. Pattern of glyphosate
drift could be seen
across field. No residues of any of applied pesticides found in plant tissues.

Washington County Florida
1013550-007 Beans
Oak Trees Grape vines Garlon 4 Chopper Spraying to a forest
site 150-200 feet away/beans exhibited chlorosis and cupping; grapes were chlorotic,
and some oak leaves
turned brown. Probable Registered Use

### 17 5. EXPOSURE PATHWAYS OF CONCERN

The high persistence of imazapyr in terrestrial li mits potential routes of dissipation to leaching, runoff, and spray drift. In aquatic environm ents, imazapyr dissipation is expected to be controlled by photodegradation. Field dissipatio n studies show that imazapyr is moderately persistent under typical use conditions. Although the routes of dissipation of imazapyr were not clearly defined in field dissipation studies, there was discerni ble movement or leaching of imazapyr into the soil profile.

The exposure pathways for imazapyr may result in a wide range of potential aquatic and terrestrial exposure scenarios. For this problem formulation, th e drinking water and inhalation pathways were screened using the SIP (Screening Imbibition Program) and STIR (Screening Tool for Inhalation Risk) screening methods a nd were found to be exposure pathways of low concern. However, it is noted th at the screening analysis do not include aggregation with all other exposure pathways (dietary, dermal, inha lation, or drinking water), which together, may contribute to a total exposure that has a potenti al for effects to non-target animals. The risk
characterization section will discu ss the impact of the considerati on of other routes of exposure
that have been identified as potentially important, and the degree of certainty associated with screening-level risk assessment conclusions. SIP and STIR are described in detail at http://www.epa.gov/oppefed1/ models/terrestrial/index.htm and the SIP and STIR model outputs
are available in APPENDIX D and E , respectively.

6. ANALYSIS PLAN

Drinking Water Assessment

EFED does not expect to conduct a new drinking water assessment given that the Health Effects Division (HED) does not anticipate conducting a dietary assessment . A drinking water assessment may be updated if a human health diet ary risk assessments of imazapyr is conducted.

The current models available for conducting drin king water assessment for surface water include PRZM (Pesticide Root Zone Model, version 3.12.3, June 2006) and EXAMS (Exposure Analysis Modeling System, version 2.98.04.06, April 2005) models. PRZM will be used to simulate pesticide transport as a result of runoff and erosion from an agricultural field while EXAMS will
be used to estimate environmental fate and tran sport of pesticides in the index reservoir. Measures of exposure will be based on maximum single and year (including multiple seasons per year) labeled applicatio n rates, minimum retreatment interv als, and conservative methods of application.

Currently, groundwater modeling is completed using PRZM-Groundwater (PRZM-GW version 1.0, December 11, 2012), using the GW-GUI (Graphi cal User Interface, version 1.0, December 11, 2012) and SCI-GROW (Screening Concentra tion in Groundwater, version 2.3, August 8, 2003). SCI-GROW is an empirical model based on a linear best fit throu gh 13 single-application groundwater studies. PRZM-GW can be used to simu late vertical pesticid e transport through the

### 18 soil profile into an aquifer following applicati on to an agricultural field. The PRZM scenarios used in groundwater simulations are representative of vulnerable sites—shallow unconfined aquifers under an agricultural field with leaching prone soil—and output values represent pesticide concentrations that may be observed in drinking water resul ting from the use of groundwater vulnerable to pesticide contamination as source water. The results are expected to represent the upper bound va lues on the concentrations of to xic residues that might be found in drinking water supplied by groundwater.

Ecological Risk Assessment

Measures of Exposure

In order to estimate risks of imazapyr exposure to aquatic and terrest rial organisms, all exposure modeling and resulting risk conclusions will be made based on maximum application rates, application methods, and any mitigation measures specifically indicated on the label. The models that will be used to pr edict the EECs of imazapyr are discussed on OPP’s model website. 1 

### These models include: PRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling System), PRZM-groundwater (GW), AgDrift, AgDisp, T-REX, TerrPlant, SIP (Screening Imbibition Program), and STIR (Screening Tool for Inhalation Risk). Because imazapyr is applied through aerial and ground spray and is an herbicide, a comprehensive spray drift buffer zone analysis will be conducted.

For imazapyr, the predicted estimated environmental concentrations of imazapyr acid will be used to calculate risk quotients. For the T-REX model, we will assume that the default half-life value of 35 days for foliar residue dissipation will capture the parent and degradates, unless data becomes available to suggest that the 35-day half -life is inadequate. If the estimated environmental concentrations (EECs) generate d by T-REX with the default foliar dissipation half-life result in risk quotients (RQs) that are sufficient to exceed any levels of concern (LOCs),
then the risk assessor will obtain more data or alter the default value to characterize risk with alternative values. (It should be noted that in T-REX, the foliar dissipation half-life does not affect EECs when only one a pplication is simulated.)



## Measure of Effects

Ecological effects data are used as measures of di rect and indirect effect s to biological receptors. Data are typically obtained from registrant-submitte d studies or from literature studies identified by ECOTOX. The ECOTOX database provides more ecological effects data in an attempt to bridge existing data gaps. ECOTOX is a source fo r locating single chemical toxicity data and potential chemical mixture toxicity data for aqua tic life, terrestrial plants, and wildlife. ECOTOX was created and is maintained by the U.S. EPA, Office of Research a nd Development, and the
National Health and Environmental Effects Research Laboratory’s Mid-Continent Ecology
Division.

1 http://www.epa.gov/opp00001/science/models_pg.htm

### 19 

## Integration of Exposure and Effects

Risk characterization is the integration of e xposure and ecological effects to determine the potential ecological risk from the use of pestic ides and the likelihood of direct and indirect effects to non-target organisms in aquatic and terrestrial habitats. For the assessment of risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity values. EECs are divided by acute and chronic toxicity values. The resulting RQs are then compared to the Agency’s Levels of Concern (LOCs) (USEPA 20 04). These criteria will be used to indicate when imazapyr use, as directed on the label, has th e potential to cause adverse direct or indirect effects to non-target organisms. In addition, any incident data from the EIIS, IDS, and AIMS will be considered as part of the risk characterization.



## Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate exposure and potential risks to federally-listed threatened and/or endangered (listed) species from registered uses of pesticides in registration review.



## Endocrine Disruptor Screening Program
As required by FIFRA and FFDCA, EPA reviews num erous studies to asse ss potential adverse outcomes from exposure to chemicals. Collectiv ely, these studies includ e acute, subchronic and chronic toxicity, including asse ssments of carcinogenicity, ne urotoxicity, developmental, reproductive, and general or systemic toxicity. These studies include endpoints which may be susceptible to endocrine influe nce, including effects on endocri ne target organ histopathology, organ weights, estrus cyclicity, sexual maturatio n, fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess gr owth, developmental and reprod uctive effects in different taxonomic groups. As part of its most recent registration decision for imazapyr EPA reviewed these data and selected the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. However, as required by FFDCA section 408(p), imazapyr is subject to the endocrine screeni ng part of the Endocrine Disrup tor Screening Program (EDSP).

EPA has developed the EDSP to determine whet her certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estrogen, or ot her such endocrine effect s as the Administrator may designate.” The EDSP employs a two-tiered approach to making th e statutorily required
determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a chemical substance to interact with the estrog en, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go th rough Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stag e of the EDSP where EPA will determine which, if any, of th e Tier 2 tests are necessary base d on the available data. Tier 2 testing is designed to identify a ny adverse endocrine-related eff ects caused by the substance, and

### 20 establish a dose-response relationship between the dose and the E, A, or T effect.

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, which contains 58 pest icide active ingredient s and 9 inert ingredients. A second list
of chemicals identified for EDSP sc reening was published on June 14, 2013 2 

### and includes some pesticides scheduled for registration review and chemicals found in water

. Neither of these lists
should be construed as a list of know n or likely endocri ne disruptors.

For further information on the status of the ED SP, the policies and procedures, the lists of chemicals, future lists, the test guidelines and the Tier 1 screening ba ttery, please visit our
website. 3



### 7. PRELIMINARY IDENTIFICATIO N OF DATA GAPS

Table 13 identifies the environmental fate studies submitted by the registrant, as well as study
classifications and whether or not additional data are needed in order to support the registration review exposure assessments.

Table 13. Submitted Environmental Fate Data for Chemical Imazapyr and its Isopropylamine Salt

Guideline Data Requirement (material) MRID # Study
Classification Are data needed to conduct
risk assessment?

835.2120 Hydrolysis (Imazapyr a ) 00132359 Acceptable No

835.2240 Photodegradation in Water (Imazapyr) 00131617 Acceptable No

835.2210 Photodegradation on Soil (Imazapyr) 40003713 Acceptable No

835.2370 Photodegradation in Air — — —

835.4100 Aerobic Soil Metabolism (Imazapyr) (Imazapyr) 41023201
45119701 Acceptable Supplemental No

835.4200 Anaerobic Soil Metabolism (Imazapyr) 00131619 Acceptable No

835.4400 Anaerobic Aquatic
Metabolism (Imazapyr) 40003712 Acceptable

No

Aerobic Aquatic Metabolism (Imazapyr) (Photoproducts: CL 9140, CL 119060) 41002301
41891501
45119702 Acceptable Supplemental

Acceptable No

2 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of

chemicals.

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

### 21 Table 13. Submitted Environmental Fate Data for Chemical Imazapyr and its Isopropylamine Salt

Guideline Data Requirement (material) MRID # Study
Classification Are data needed to conduct
risk assessment?

835.4300 (Photoproducts: CL 9140, CL 119060)

835.1230

835.1240 LeachingAdsorption/Desorption (Imazapyr + photoproducts) 45119705 Acceptable

No b

835.1410 Laboratory Volatility — — —

835.8100 Field Volatility — — —

835.6100 Terrestrial Field Dissipation (Imazapyr) (Arsenal 2AS a ) (Arsenal 2AS) 45119706
42192101
42192102 Supplemental Upgradeable Upgradeable No

850.6100 ECM/ILV for Soil and Water 41891501 -- No

835.6300 Aquatic Field Dissipation (Imazapyr) (Arsenal 2AS) 45119707
41891501 Unacceptable Supplemental No

835,6400 Forestry Dissipation (Arsenal) 40003714 Acceptable No

850.1730 Accumulation in Fish No

850.1730 Accumulation- aquatic nontarget (Imazapyr) (Imazapyr) 45119707
45119709 Supplemental Supplemental

No

835.7100 Ground Water- small prospective — — —

a Imazapyr refers to the parent compound (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H -imidazol-2-yl]-3- pyridinecarboxylic acid); Arsenal 2AS is the isopropylamine salt (2-Propanamine, 2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-

oxo-1 H-imidazol-2-yl]-3-pyridinecarboxylate). CL 9140 is pyridine 2,3-dicarboxylic acid. CL 119060 is Furo[3,4]pyridine5(7 H ), one-7-hydroxy.

b Limited to two soils.



### Ecological Effects

Table 14 and Table 15 identify the ecological effects st udies (aquatic and terrestrial, respectively) submitted by the registrant, as we ll as study classifications and whether or not additional data are needed in order to suppor t the registration review risk assessments.

A passerine study is not available; however, given the low sensitivity of the quail and mallard duck to imazapyr, it is assumed that further tes ting on passerines will not be of great value to inform on the potential toxicity of imazapyr.

### 22 The terrestrial plant guidelines (850.4100 and 850.4150) are partially fulfill ed (four species of monocots, including corn; five species of dico ts, including soybean and sugar beet) (MRID 40811801; acid).

Table 14. Submitted Aquatic Toxicity Data for Ch emical Imazapyr and its Isopropylamine Salt

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) [Acid/Salt] Study
Classifications

[Acid/Salt] Are data needed
to conduct risk

assessment? Comments

850.1010 Freshwater
invertebrate acute toxicity 00131632

00147117 All acceptable No Although TEP data would address some uncertainty regarding potential toxicity of the formulations applie d directly to water, the TGAI data show that imazapyr is practically non-toxic and no aquatic animal incidents have been reported.

850.1025
850.1035
850.1045
850.1055 Saltwater
invertebrate acute toxicity 41315803
41315802
45119710

No salt Acceptable Supplemental

Acceptable No Although TEP data would address some uncertainty regarding potential toxicity of the formulations applie d directly to water, the TGAI data show that imazapyr is practically non-toxic and no aquatic animal incidents have been reported.

850.1075 Freshwater fish acute toxicity 00131630
00131629

00131631

45119713
00147116 All acceptable No Although TEP data would address some uncertainty regarding potential toxicity of the formulations applie d directly to water, the TGAI data show that imazapyr is practically non-toxic and no aquatic animal incidents have been reported.

850.1075 Saltwater fish acute toxicity 41315801

No salt Acceptable No Although TEP data would address some uncertainty regarding potential toxicity of the formulations applie d directly to water, the TGAI data show that imazapyr is practically non-toxic and no aquatic animal incidents have been reported.

850.1300 Freshwater
invertebrate life cycle 41315805

No salt Acceptable No
--

850.1350 Saltwater
invertebrates life cycle No data N/A No
--

850.1400 Freshwater fish early-life stage 41315804
45119711

No salt Supplemental Acceptable No --

### 23 Table 14. Submitted Aquatic Toxicity Data for Ch emical Imazapyr and its Isopropylamine Salt

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) [Acid/Salt] Study
Classifications

[Acid/Salt] Are data needed
to conduct risk

assessment? Comments

850.1400
Saltwater fish early-life stage No data N/A No While data are unavailable for this taxa, sensitivity of saltwater fish is assumed to be similar to that of the freshwater fish,
which in this case is low.

850.1500 Freshwater fish full life cycle 45119712

No salt Supplemental No --

850.4400 Aquatic plant growth:
Tier II vascular plants 40811802

43889102 All acceptable No --

850.5400 Aquatic Plant
Growth: Tier II algae 40811802

43889102 All acceptable No --

### 24 Table 15. Submitted Terrestrial Toxicity Data for Chemical Imazapyr and its Isopropylamine Salt

OCSPP
Guideline Data Requirement Submitted
Studies (MRID) [Acid/Salt] Study
Classifications

[Acid/Salt] Are data needed
to conduct risk

assessment? Comments

850.2100 Avian Oral Toxicity 00131633

00131634

No salt All acceptable No While data are unavailable for passerine (40 CFR, Part 158-Subpart G). acute oral studies on quail and mallard duck indicates low sensitivity to imazapyr.

850.2200 Avian Dietary Toxicity 00131635
00131636

00147115 All acceptable No
--

850.2400 Wild
Mammal Toxicity 00132030

00147049
44735301 All acceptable No
--

850.3020 Honeybee

Acute Contact Toxicity 00131637

No salt Acceptable No --

850.2300 Avian Reproduction

Toxicity 45119714a
43831401

43831402

No salt Acceptable Acceptable Acceptable No --

850.4100 Seedling Emergence

Tier II 40811801

No salt Supplemental No --

850.4150 Vegetative Vigor Tier II 40811801

40003711
43889101 Supplemental Supplemental

Acceptable No --

850.1735 Whole
sediment:

acute freshwater
invertebrates No data N/A No Half-life of the imazapyr in sediment is >10 days (aerobic aquatic metabolism study, MRID 41002301) but the log P

ow is 0.22. Furthermore, imazapyr is not expected to partition to sediment.

850.1740 Whole
sediment:
acute marine
invertebrates No data N/A No Half-life of imazapyr in sediment is >10 days (aerobic aquatic metabolism study, MRID 41002301), but the log P

ow is 0.22. Furthermore, imazapyr is not expected to partition to sediment.

Non-GLN Whole
sediment:
chronic
invertebrates

freshwater
and marine No data N/A No Half-life of the imazapyr in sediment is >10 days (aerobic aquatic metabolism study, MRID 41002301), but the log P

ow is 0.22. Furthermore, imazapyr is not expected to partition to sediment.

### 25 APPENDIX A- Summary of Environmental Fate Data

Hydrolysis (835.2120, MRID 00132359, St udy Status: Acceptable). Imazapyr is stable to hydrolysis at envir onmentally relevant pH values and temperatures. Imazapyr was stable in aqueous buffer solutions (pH 5 and 7) a nd distilled water (pH 5.2) for up to 30 days at

25±1  C. Imazapyr degraded slowly in an aque ous pH 9 buffer solution. The only identified degradate was 2-[(1-carbomyl- 1,2-dimethylpropyl)carbomyl] nicotin ic acid (CL 252974). Minor degradates were not identified.

Aqueous Photolysis (835.2240, MRID 00131617, Study Status: Acceptable). Imazapyr is susceptible to photolysis. Imazapyr degraded with a half-life of 2.5-5.3 days in

distilled water or buffer so lution at pH 5 or 9, at 25  C, irradiation with a xenon arc lamp (12 hours/day) for up to 10 days. Two major degrad ates were formed: 2,3-pyridinecarboxylic acid (CL 9140, 22.7%) and 7-hydroxy-furo[3,4-b]pyr idin-5(7H)-one (CL 119060, 9.7%). Unidentified degradates comprised up to 7.1% of the applied radioactivity. Imazapyr was stable in the dark during the 10-day incubation period.

Soil Photolysis (835.2210, MRID 40003712, Study Status: Acceptable). Imazapyr degraded slowly on irradiated soil. 14 

### C-pyridine-ring-labeled imazapyr applied at a rate of 1.5 lb ae/acre, degraded with an extrapolated half- life of 149 days on sandy loam soil irradiated a 4- week period. No degradate was >10% of the ap plied radioactivity. In dark controls, imazapyr was 95-98% of the applied radioactivity after 4 weeks. Unidentified residues were 2.9-4.9% of the applied radioactivity.

Aerobic Soil Metabolism (835.4100, MR ID 41023201, Study Status: Acceptable). Imazapyr is essentially stable to degradati on in soil maintained unde r aerobic conditions.

14 

### C/ 13 

### C-labeled imazapyr was added to Princeton sa ndy loam soil (soil moisture 75% of field capacity) at a concentration of 1.5 ppm. Samples were maintained at 25  C in the dark for up to 365 days. Volatiles and/or CO 2 

### were collected in traps. At 365 days, 88% of the applied radioactivity remained as pare nt imazapyr (calculate d half-life of 5.9 years). Unextractable residues averaged 4% of the applied radioac tivity during the study and accounted for 5% at 365 days. Cumulative 14 

### CO 2 

### accounted for up to 7% of the app lied radioactivity after 365 days. Material balance averaged 101%.

Aerobic Soil Metabolism (835.4100, MRID 45119701, Study Status: Supplemental).
The aerobic soil metabol ism of [pyridine-6- 14 

### C]-imazapyr was studied for 121 days in Sassafras sandy loam soil (pH 6.0, organic matter 2.0%; soil moisture content of 75% of 1/3 bar) from New Jersey. Samples were keep in the dark at 25±1  C. [ 14 

### C]Imazapyr was applied at the nominal rate of 0.22 mg ae./kg soil (equivalent to 0.44 lb ae/acre or 0.50 kg ae/ha with 15-cm soil incorporation). Because the 121-day study period was short compared to the persistence of [pyridine-6- 14 

### C]imazapyr, there was insufficient time for the full pattern of formation and decline of products to develop. At study end, approximately 72% of the amount of parent recovered at the beginning of th e study remained. A structurally similar transformation product,

### 26 2-[4-Isopropyl-4-methyl-5-oxo-2-imidazolin-2 -yl]-3-hydroxy pyridine, was present at approximately 7% of parent radioactivity rec overed at the beginning of the study and increased slowly for the duration of the study. Volatilized 14 

### CO 2 

### totaled approximately 6% of initial parent radioactivity at 121 days.

Two additional minor transformation products, 2-[(1-carbamoyl-1,2-dimethylpropyl)carbamoyl] nicotinic acid and 2-[4-isopropyl-4-methyl-5- oxo-2-imidazolin-2-yl]-3- carboxymethyl pyridine,

were each detected at  3% of the applied, but may have been artifacts produced during sample extraction and preparation. Orga nic volatiles were <0.1% of app lied at any sampling interval. Material balance ranged from approximately 100% to 97%.

The extrapolated first-order kinetics regression half-life for parent imazapyr for the 121-day period is 296 days (r 2 

### = 0.89, 95% confidence interval of 247 to 370 days). If the two putative artifact compounds are assumed to be parent ma terial and included in the regression, then the apparent half-life increases slightly to 313 days (r 2 

### = 0.90, 95% confidence interval of 264 to 387 days).

Anaerobic Soil Metabolism (835.4200, MR ID 00131619, Study Status: Acceptable). Imazapyr was stable in sandy loam soil. Sandy loam soil (1.8% organic matter, pH 5.3-6.5, CEC 8.5 meq/100 g) was treated with a 50:50 mixture of 14 

### C and 13 

### C-carboxy-labeled imazapyr at 1 lb ae/acre. Radioactivity in the water extract was three-fold that in the soil.

Anaerobic Aquatic Degradation (835.4400, MRID 40003712, Study Status: Acceptable). Imazapyr is resistant to an aerobic aquatic degradation. 14 

### C-pyridine-labeled imazapyr, applied at 1.5 lb/A, was incubated in an anaerobic sand sediment:water system in the

dark at 19-22  C for up to 4 months. Imazapyr comprised 96-98% of the rec overed radioactivity at all sampling intervals.

Aerobic Aquatic Metabolism (835.4300, MR ID 41002301, Study Status: Acceptable). Imazapyr did not degrade in water or sediment under aquatic conditions. 14 

### C-Imazapyr was added to a series of water and soil sediments (92% sand) collected from an irrigation pond at a rate equivalent to 1.5 lb/A. Sample containers were maintained under positive pressure in the

dark at 25  C. 14 

### CO 2 

### accounted for <2% of the applied ra dioactivity 4 weeks (there were no organic volatiles). Over the course of the study, >96% of the applied radi oactivity remained in the aqueous phase while <2% was bound to soil . Analysis by thin-layer chromatography determined that parent imazapyr accounted for >97% of the applied radio activity after 4 weeks.

Aerobic Aquatic Metabolism of Two De gradates of Imazapyr (835.4300, MRID 45119702, Study Status: Acceptable). The aerobic degradation of the imazapyr degradation products, [pyridine-6- 14 

### C]-labeled furo[3,4-b]pyridine-5-(7 H )-one-7-hydroxy (CL 119060) and pyridine 2,3-dicarboxylic acid (CL 9140), was studi ed in each of two pond water:sediment systems. A pond water:sediment system (water pH 8.2; sand sediment pH 7.7, organic matter 0.8%) from Florida, and a pond wate r:sediment system (water pH 7.9; silt loam sediment pH 6.6, organic matter 1.1%) from Missouri were st udied for 14 days in darkness at 25±1  C.

### 27 [ 14 

### C]furo[3,4- b ]pyridin-5( 7H )-one,7-hydroxy- and [ 14 

### C]pyridine 2,3-dicarboxylic acid was applied separately at the nomina l rate of 0.083 mg ae/L. The se diment:water ratio used was 175 g wet sediment:200 mL water. For both test compounds and systems, aerobic conditions were maintained in the water layers of the sediment:w ater systems, but the sediment layers remained anaerobic throughout the study. Levels of parent [ 14 

### C]furo[3,4- b ]pyridin-5( 7H)-one,7-hydroxyand [ 14 

### C]pyridine 2,3-dicarboxylic acid and transformation products were identified only in the water layers. To compensate for the failure to identify and quantify residu es extracted from the sediments and low material balances during late r sampling intervals, it was assumed that all
extracted sediment residues were unreacted starti ng materials. These extracted sediment residues were then added to parent materials identified an d quantified in the water phases to estimate total system (water + sediment phases) half-lives.

In the water layer, the major nonvolat ile transformation product of [pyridine-6- 14 

### C]furo[3,4-
b ]pyridin-5( 7H )-one,7-hydroxy-pyridine 2,3-dicarboxylic ac id. This compound was detected at maximums of 20% of applied at 1 day and 28% at 3 days, in the sand and silt loam sediment systems, respectively. Nicotinic acid was identified as a nonvol atile transformation product, and detected at maximums of 6% at 2 days and 10% at 1 day, in the sand and silt loam sediment systems, respectively. Unidentified polar product s increased to maximums of 33-41% of applied at 7 days in both systems. For bot h test systems, nonextractable [ 14 

### C]residues were  6% at any sampling interval. 14 

### CO 2 

### was a major volatile transforma tion product, totaling 45% for sand sediment:water systems. The first-order ki netics regression half- life for [pyridine-6-

14 

### C]furo[3,4- b ]pyridin-5( 7H )-one,7-hydroxy- in the Florida pond system (water + sediment) was 3.9 days (r 2 

### = 0.95, 95% confidence interval of 3.4 to 4.5 days). The Missouri pond system firstorder regression half-life (water + sediment) for [pyridine-6- 14 

### C]furo[3,4- b ]pyridin-5( 7H )-one,7- hydroxy- was 5.8 days (r 2 

### = 0.80, 95% confidence interval of 4.5 to 8.2 days). The average halflife for the Florida and Missouri systems for [pyridine-6- 14 

### C]furo[3,4- b ]pyridin-5( 7H )-one,7- hydroxy- was 5±1 days with an upper 90% confidence bound on the mean of 8 days.

No major nonvolatile transforma tion products of [pyridine-6- 14 

### C]pyridine 2,3-dicarboxylic acid were detected in the water layers. Minor nonvol atile transformation produc ts were unidentified polar products. For both se diments, nonextractable [ 14 

### C]residues were  3.9% at any sampling
interval. 14 

### CO 2 

### was a major volatile transformation product, totaling 53% for sand sediment:water systems and 23% for silt loam sediment:water systems at study termination. Organic volatiles were <0.1% of applied at any sampling interval. The first-order kinetics regression half-life for of [pyridine-6- 14 

### C]pyridine 2,3-dicarboxylic ac id for the Florida pond system (water + sediment) was 3 days (r 2 

### = 0.56, 95% confidence interv al of 1.9 to 5.9 days). The Missouri pond system first-order regression half-life (water + sediment) for pyridine 2,3- dicarboxylic acid was 4 days (r 2 

### = 0.88, 95% confidence interval of 3.5 to 5.5 days). The average half-life for the Florid a and Missouri systems for pyridin e 2,3-dicarboxylic acid is 4±1.0 days with an upper 90% confiden ce bound on the mean of 5.7 days.

### 28 Aerobic Aquatic Metabolism of Imazapyr Photodegradation Products (835.4300, MRID 41891501, Study Status: Supplemental). This study addressed the aerobic aquatic metabolism of the two major aqueous photodegradation products of imazapyr, 2,3- pyridinedicarboxylic acid (CL 9140) and 7-hydro xy-furo[3,4-b]pyridin-5(7H)-one (CL 119060) over a 4-week period. The photoproducts were generated by irradiating 10 mg of imazapyr in 50 mL of deionized water which yielded the major products CL 9140 and CL 119060 (22% and 24%, respectively). The photoprodu cts were added to pond water and sediment from a wetland in New Jersey. Evolved CO 2 

### was trapped and measured. The study presented evidence that CL 119060 is rapidly converted to CL 9140) which, in turn, is metabolized to CO 2



### .

Adsorption/Desorption (835.1230/8 35.1240, MRID 45119705, Study Status: Acceptable). The batch-equilibrium adsorpti on/desorption characteristics of 14 

### C-6-pyridinering-labeled- imazapyr and the metabolites ( photoproducts) pyridine 2,3-dicarboxylic acid and furo[3,4- b ]pyridin-5( 7H )-one,7-hydroxy- (both 14 

### C-6-labeled in the pyri dine ring) were each studied separately in a sand sediment from Fl orida [pH - 7.7, organic carbon - 0.47%] and a silt loam sediment from Missouri [pH - 6.6, organi c carbon - 0.64%]. The equilibrating solution
used was 0.01 M CaCl 2 

### , at a soil/solution ratios of 1:2 (w:v). The desorption phase of the study

was carried out at 20±1  C for 27.5 hours (imazapyr), 24 hours (pyridine 2,3-dicarboxylic acid) or 44 hours (furo[3,4- b ]pyridin-5( 7H )-one,7-hydroxy-). The desorption phase was conducted once. Supernatant solutions were analyzed us ing LSC and HPLC. Sediments were extracted with 0.1 M sodium hydroxide following desorption, analyzed by LSC. Radi oactivity in the soil
residue after extraction was determined by combustion.

Imazapyr : Freundlich adsorption parameters a nd average simple ad sorption/desorption coefficients are given in Ta ble A-1 below. The Freundlich adsorption coefficients (K f 

### ) were 0.091 (1/N=0.733; K foc 

### = 19.4) and 0.523 (1/N=0.887; K foc 

### =81.4) for the sand and silt loam sediments, respectively. Corresponding simple adsorption coefficients adjusted for organic carbon (K
oc 

### ) were 30.6 and 99.8 mL/g organic carbon.

Pyridine 2,3-dicarboxylic acid : Freundlich adsorption para meters and average simple adsorption/desorption coefficients are given in the results synopsis and in Table A-2 below. The Freundlich adsorption coefficients (K f 

### ) were 0.699 (1/N=0.811; K foc 

### = 149.4) and 31.6 (1/N=0.955; K foc 

### =4940) for the sand and silt loam se diments, respectively. Corresponding K
oc 

### values were 217 and 6053 mL/g organic carbon.

Furo[3,4- b ]pyridin-5( 7H )-one,7-hydroxy- : Freundlich adsorption para meters and average simple adsorption/desorption coefficients are given in the results synopsis and in Table A-3 below. The Freundlich adsorption coefficients (K f 

### ) were 0.551 (1/N=0.939; K foc 

### = 117) and 5.77 (1/N=0.962;

K foc 

### =902) for the sand and silt loam sedi ments, respectively. Corresponding K
oc 

### values were 134 and 1020 mL/g organic carbon.

### 29 Table B-1: Adsorption and desorption pa rameters for imazapyr in the sediments.

Soil Freundlich Adsorption Simple Ads/Des Coefficient Averages

Kf ads 1/N R 2 Kf ads oc Kads Kads oc Kdes Kdes oc

Sand sediment (FL) 0.091 0.733 0.976 19.4 0.144 30.6 0.338 71.9

Silt loam sediment (MO) 0.523 0.887 0.999 81.7 0.639 99.8 1.02 159
Kf ads – Freundlich adsorption coefficient; 1/ N – Slope of Freundlich adsorption isotherm. Subscript oc indicates sorption per unit organic carbon ([K x 100]/% organic carbon).

R 2 - Regression coefficient of Freundlich equation.



### Table B-2: Adsorption and desorption paramet ers for Pyridine 2,3-dicarboxylic acid in the
sediments

.

Soil Freundlich Adsorption Simple Ads/Des Coefficient Averages

Kf ads 1/N R 2 Kf ads oc Kads Kads oc Kdes Kdes oc

Sand sediment (FL) 0.699 0.811 0.998 149 1.02 217 1.60 340

Silt loam sediment (MO) 31.6 0.955 0.999 4940 38.7 6053 140 21,900
Kf ads – Freundlich adsorption coefficient; 1/ N – Slope of Freundlich adsorption isotherm. Subscript oc indicates sorption per unit organic carbon ([K x 100]/% organic carbon).

R 2 - Regression coefficient of Freundlich equation.



### Table B-3: Adsorption and desorption parameters for Furo[3,4- b ]pyridin-5( 7H )-one,7- hydroxy- in the sediments.

Soil Freundlich Adsorption Simple Ads/Des Coefficient Averages

Kf ads 1/N R 2 Kf ads oc Kads Kads oc Kdes Kdes oc

Sand sediment (FL) 0.551 0.939 0.998 117 0.628 134 1.89 402

Silt loam sediment (MO) 5.77 0.962 1.000 902 6.53 1020 16.9 2640
Kf ads - Freundlich adsorption coefficient; 1/N -Slope of Freundlich adsorption isotherm. Subscript oc indicates sorption per unit organic carbon ([K x 100]/% organic carbon).

R 2 - Regression coefficient of Freundlich equation.



### Terrestrial Field Dissipation (835.6100, MRID 42192101, Study Status: (Supplemental). Arsenal 2AS, the isopropylamine salt of imazapyr (22.6% ae in aqueous solution) dissipated with a calcu lated half-life of 143 days. Howe ver, the dissipation pathway(s) was not addressed. The test material was app lied by boom sprayer to a bareground plot of silt loam soil (2.6% organic matter, pH 5.1, CEC 16.9 meq/100 g) located in Hillsboro, Oregon. Application rate was 1.53 lb ae/acr e. Sprinkler irrigation was a pplied at 0.5 to 3.0 inches, 1-3 times/month. The temperature ranged from 6 to 100  F, total precipitation was 67 inches, and irrigation total was 29 inches. Imazapyr was f ound primarily in the 0-6-inch soil layer at a maximum concentration of 400 ppb. In the 6-12-inch layer, residues were  6 ppb at 1-30 days,

### 30 14-17 ppb at 240 days, and 6-13 ppb at 452 days. In the deeper soil layers residues were <8 ppb immediately posttreatment, and not detected at la ter sampling times. A half-life of 143 days was

calculated. Residues in a control plot were  4 ppb. Routes of dissipa tion were not provided.

T errestrial Field Dissipation ( 835.6100, MRID 42192102, Study Status: Supplemental). Arsenal 2AS, the isopropylamine salt of imazapyr (22.6% ae in aqueous solution) dissipated with a calcu lated half-life of 64 days. Howe ver, the mode(s) of dissipation was not addressed. The test material was app lied by backpack sprayer to a bareground plot of sandy loam soil (2.3% organic matter, pH 5.7, CE C 6.75 meq/100 g) located in Janesville, North Carolina. Application rate was 1.53 lb ae/acre. Sprinkler irrigation was applied at 0.58 to 2.0 inches, 3-5 times/month. The temperature ranged from 18 to 98  F, total precipitation was 67 inches and irrigation to taled 22 inches. Imazapyr residues were found primarily in the 0-6-inch soil layer, averaging 300-440 ppb immediately posttreatment and declining to 7-12 ppb at 240- 360 days. In the 6-12-inch layer, residues were at a maximum of 10-21 ppb at 14 days. In the 12-18 inch and 18-24 inch depths, residues reached a maximum of 8-14 ppb and 7-11 ppb, respectively, at 30 days. In the deeper soil layers, residues were  6 ppb at all sampling times. Residues in a control plot were  3 ppb. Routes of dissipa tion were not provided.

Terrestrial Field Dissipation ( 835.6100, MRID 45119706, Study Status: Supplemental). This study shows that imazapyr is prone to leach and is relatively long-lived. Cropped corn fields in Iowa and Ne braska were used as the study sites. Apparent, simple firstorder regression half-lives at all sampled dept hs (0-36 inches) were 94 days in Iowa (95% confidence limits 84-107 days, r 2 

### = 0.88) and 126 days in Nebras ka (95% confidence limits 113- 143 days, r 2 

### = 0.88). The degree to which the apparent loss/dispersal of imazapyr was due to transformation, plant uptake, volatilization, leachi ng, runoff, etc. was not determined. There was no analysis for transformation pr oducts (degradates or metabolit es), no measurement of plant uptake, or attempt to correlate daily rainfall/irri gation with pesticide disa ppearance or potential for movement in soil during the course of study. Therefore, disappearance half-lives represent only lower limits for what may be much longer ef fective half-lives, and cannot be assumed to be attributable to degradation or detoxification of parent (or any possible by-products).

For the present study, casual inspec tion of the soil concentration da ta shows quick infiltration of imazapyr into moist surface soil, and close correla tion between rainfall/irr igation events with eventual leaching of imazapyr into the lower soil depths (down to 30 or 36 inches). Rainfall/irrigation was said to be typical or av erage for the experimental sites in Iowa and Nebraska. These penetrations into soil are evid ence of high mobility. Furthermore, the leaching
occurred in soils with characteristics that ar e not usually associated with high potential for leaching. The soils had relatively high cation exch ange capacities, organic matter, and moisture retention capacity. Subsoil clay co ntent was approximately 25-30%.

Aquatic Field Dissipation (835.6300, MRID 41891501, Study Status: Supplemental). Arsenal 2AS rapidly dissipated from shallow ponds in Florida and Louisiana during summer months. Arsenal 2AS applied at the proposed ma ximum label rate of 1.5 lb ae/acre dissipated

### 31 with half-lives of 3 and 4 da ys in pond water and sediment, respectively. In a similar study carried out in Louisiana, Arsena l 2AS dissipated with half-lives of 2 and 4 days in pond water and sediment, respectively. The analytical de tection limits were too high to provide an understanding of the formation and decline kinetics of the degrad ation kinetics. Because these studies were conducted in shallow ponds duri ng the summer months, the rapid dissipation observed in these studies may not be represen tative of dissipation ra tes at other aquatic
environments.

Forestry Dissipation (835.6400, MRID 40003714, Study Status: Supplemental). Imazapyr applied by aerial spray to a forest dissip ated primarily by runoff, and to a lesser degree, by foliar absorption. Arsenal was applied by helicopt er at 2.24 kg/ha (2 lb ae/acre) with Igepal DM-710 as a surfactant, over tw o forested watersheds in Fayette and Randolph counties, Alabama, in May and June, 1985. Each site was divided into two water sheds, one treated and one control. Precipitation was measured at each site, and stream water levels were monitored. Samples were taken of water, suspended sediment , vegetation (composited), litter, and soil (up to 20 inches depth), the latter by area of ridge, mid-slope and lower slope.

Description, Fayette county site. This was a 121-ha site of mixed hardwoods. Pines in the plot had been harvested earlier. The application t ook place over 4 days due to weather conditions of intermittent fog and drizzle. The plot was drained by a single stream. The soil was sand loam (1.92% organic matter, CEC 3.7 meq/100 g).

Description, Randolph county site. This was a 40-ha area of lobl olly pine seedlings and mixed hardwoods. The plot was drained by a single stream. The underlying soil was loam (4.4% organic matter, CEC 4.17 meq.100 g).

Results, Fayette county. Imazapyr dissipated from vegetation w ith a half-life of 12 days (highest mean residue, about 100 ppb at 3 days post-treatm ent), from litter with a half-life of 44 days, from 0-4-inch depth of bare ground soil with a half-life of 24 days, a nd from 0-4-inch depth litter-covered soil with a calculated half-life of 19 days. Residues were found primarily in the 0- 12-inch soil depth. Residues in stream grab samples were highe st during application (up to 680 ppb) and following storm events. Stream residues declined to trace amounts at later sampling intervals. Only one stream sediment sample contained a detectable residue, 52 ppb.

Results, Randolph county. Imazapyr dissipated from vegeta tion with a half-life of 40 days (highest mean residue, 122 ppb immediately post- treatment), from litter w ith a half-life of 37 days, from 0-4-inch depth of bare ground soil wi th a half-life of 26 days, and from 0-4-inch depth litter-covered soil with a ca lculated half-life of 34 days. Residues were found primarily in the 0-12-inch soil depth. Visual observation indicat ed at least 99% kill of all targeted vegetation.

Bioconcentration in Aquatic Non-ta rget Organisms (850.1730, MRID 45119707. Study Status: Supplemental). Parent imazapyr did not biocon centrate appreciably in the fish and crayfish species tested (three fish and one crayfi sh species at each site, total of four different species). There were no tests for de gradates in any of the test speci es. It should be noted that the

### 32 reported limit of quantitation for parent in tissue was a relatively high 50 ppb. In several instances, for unknown or unverified reasons, ther e was some limited mortality of some test species and/or their partial disappearance, such that for some sampling intervals there were insufficient amounts of tissue for analysis. Howeve r, this does not signifi cantly alter the general conclusion of no appreciable bioconcentration of parent above a c oncentration of 50 ppb.

Bioconcentration in Aquatic Non -target Organisms (850.1730, MRID 45119709, Study Status: Supplemental). Under test conditions (28- day exposure periods at mean measured concentrations of 250 ppb for oyste rs and 260 ppb for shrimp followed by 14-day depuration periods), overall results for the two test species, oyster and shrimp, are essentially the same. There was no bioconcentration of pyridyl-6- 14 

### C-imazapyr [bioconcentration factor (BCF) <1)]. The study was deficient for both oyster and shrimp because of rela tively high levels of quantitation (LOQ; 72 ppb for oyster, 128 ppb for shri mp) compared to exposure concentrations. Consequently, because of the relatively low and va riable concentrations of residues compared to the LOQ, uptake and depuration rates of imazapyr could not be calculated meaningfully, and no
metabolite identification work was conducted. The information was considered supplemental,
but no additional st udies are needed.APPENDIX B-Transformation Productsin Environmental Fate StudiesStudy MRIDStudy TypeSystemImazapyrhalf-lifeMaximum transformation products(% of applied radiation)CL2882471CL 252974 CL 119060 CL9140CL252974 5CO200132359Hydrolysis (161-1)pH 5 at 25CStableND2ND ND ND ND NDpH 7 at 25CStableND ND ND ND ND NDpH 9 at 25CStableND 6.9 ND ND ND ND00131617Photolysis in water (161-2)pH 5 and 9 at 25C(12 hour exposure cycle)2.5 - 5.3 daysND ND 9.7 22.7 ND NA340003713Photolysis in soil (161-3) Loamy sand soil Stable(~149 days)ND ND ND ND ND NA41023201Aerobic Soil Metabolism (162-1)Loamy sand soilStableND ND ND ND ND 745119701Aerobic Soil Metabolism (162-1) (Supplemental) Loamy sand soil(~5.9 years)>296 daysND3NDNDND600131619Anaerobic Soil Metabolism (162-2)Loamy sand soilStable(>60 days)ND ND ND ND ND ND40003712Anaerobic Aquatic Metabolism (162-3)Total system>120 daysND ND ND ND ND ND4100230145119702Aerobic Aquatic Metabolism(162-4)Aerobic Aquatic Metabolism(162-4) - Degradate metabolismTotal systemTotal system(CL 119060 metabolism)(CL 9140 metabolism)>120 days4.9 days3.6 daysNDNANANDNANANDNANAND20.4NANDNDND1.144.95342192101Terrestrial field dissipation (164-1) Bare ground / Silt loam soilHillsboro, Oregon143 daysNA NA NA NA NA NA42192102Terrestrial field dissipation (164-1)Bare ground / Sandy loam soilJanesville, North Carolina64 daysNA NA NA NA NA NA40003714Forestry Dissipation (164-3) Aerial application,residues measured12-40 days(vegetation)37-44 days(litter)NA NA NA NA NA NA

### 34 APPENDIX C- 

## Ecological Effects Data

Studies are with imazapyr acid, unless otherwise noted

71-1 Avian Acute Oral (850.2100)

Bobwhite Quail. MRID 00131633 (Accep table). In a 14-day oral gavage study, imazapyr acid was determined to be practically no n-toxic to bobwhite quail with an LD 50 

### of >2,150 mg ae/kg. The study is scientifically sound and follows the guideline protocols.

Mallard Duck. MRID 00131634 (Acceptable). In a 14-day oral gavage study, imazapyr acid was determined to be practically non-t oxic to mallard ducks with an LD 50 

### of >2,150 mg ae/kg. The study is scientifically sound and fo llows the guideline protocols.

71-2 Avian Subacute Dietary (850.2200)

Imazapyr acid Bobwhite Quail. MRID 00131635 (Accep table). In an 8-day dietary study, imazapyr acid was determined to be practically non-toxic to upl and game birds (bobwhite quail) with an LC 50 

### >5000 ppm. The study is scientifically sound and generally followed guideline protocols; however, there was some unexplainable low wei ght gains and mortality at the 625 ppm test
concentration.

Mallard. MRID 00131636 (Acceptable). In an 8-day dietary study, imazapyr acid was determined to be practically non-toxi c to mallard ducklings with an LC 50 

### >5000 ppm.. The study is scientifically sound and genera lly followed guideline protocols.

Imazapyr isopropylamine salt Bobwhite Quail. MRID 00147115 (A cceptable). In an 8-day dietary study, the isopropylamine salt of imazapyr was determined to be practic ally non-toxic to upland game birds (bobwhite quail) with an LC 50 

### >5000 ppm. The study is scientif ically sound and generally followed guideline protocols. This st udy was conducted with the formulat ed product to ensure that isopropylamine did not affect the t oxicity of the active ingredient.

71-4 Avian Reproduction (850.2300)

Bobwhite Quail. MRID 45119714a (Acceptable). In a one-generation reproductive toxicity study, imazapyr acid produced no evidence of trea tment-related adverse effects on adult or reproductive parameters with an NOAEC of 1670 ppm. The study is scientifically sound and generally followed guideline protocols.

Mallard. MRID 45119714b (Invalid). In a one-gener ation reproductive toxi city study, imazapyr acid resulted in a significant reduction in the ratio of viab le embryos/eggs at the 1,670 ppm

### 35 treatment level. However, the study was determined to be invalid due to bacterial contamination and high embryonic mortality in the controls. EFED recomme nded that another study be conducted to determine the reproductive t oxicity of imazapyr to waterfowl.

Bobwhite Quail. MRID 43831401 (Originally Suppl emental; Reclassified Core). In a onegeneration reproductive toxicity study, imazapyr aci d resulted in reduced hatchlings/live embryo at 2000 ppm (LOEC; NOEC = 1000 ppm); however, the study was originally determined to be supplemental due to guideline deficiencies (pri marily, EECs would be higher than highest dose tested and control egg shell cr acking was 13%). EFED reevalua ted the studies and determined that the dosing did reflect the maximum EEC and that the handling and measurement
deficiencies did not reflect a dos e-response relationship; conseque ntly, the study was reclassified as core and the NOEC was changed to 2000 ppm.

Mallard. MRID 43831402 (Originally Supplemental; Reclassified Core). In a one-generation reproductive toxicity study, imazapyr acid produced no evidence of treatment-related adverse effects on adult or reproductive paramete rs with an NOAEC of 1890 ppm (measured concentration; 2000 ppm nomina l concentration). However, the study was originally determined to be supplemental due to guideline deficiencies (primar ily, EECs would be higher than highest dose tested, inaccurate measurement of egg shell thickness, and insufficient pre-egg laying period.) EFED reevalua ted the studies and determined that the dosing did reflect the
maximum EEC and that the measurement defi ciencies did not reflect a dose-response relationship; consequently, the study was reclassi fied as core and the NOAEC was established at 2000 ppm.

72-1 Freshwater Fish Acute (850.1075)

Imazapyr acid Rainbow Trout. MRID 00131629 (Acceptable). In a 96-hour acute test, imazapyr acid was determined to be practically non-t oxic to rainbow trout with an LC 50 

### of >100 mg/L. The NOEC was determined to be 100 mg/L. The study is sc ientifically sound and meet s guideline protocols.

Bluegill Sunfish. MRID 00131630 (Acceptable). In a 96-hour acute test, imazapyr acid was determined to be practically non-toxi c to bluegill sunfish with an LC 50 

### of >100 mg/L. The NOEC was determined to be 100 mg/L. The stud y is scientifically sound and meets guideline protocols.

Channel Catfish. MRID 00131631(Acceptable). In a 96-hour acute test, imazapyr acid was determined to be practically non-t oxic to channel catfish with an LC 50 

### of >100 mg/L. The NOEC was determined to be 100 mg/L. The stud y is scientifically sound and meets guideline protocols.

### 36 Imazapyr isopropylamine salt Rainbow Trout. MRID 45119713 (Acceptable). In a 96-hour flow-through test, imazapyr isopropylamine salt was determined to be practically non-toxic to rainbow trout with an LC 50 

### of >110 mg ae/L (mean measured concentration; nominal concentration 120 mg ae/L). The NOEC was determined to be 110 mg ae/L. The st udy is scientifically sound and meets guideline protocols.

Bluegill Sunfish. MRID 00147116 (Acceptable). In a 96-hour test, imazapyr isopropylamine salt was determined to be practically non- toxic to bluegill sunfish with an LC 50 

### of >818 mg ae/L (1000 mg ai/L). The study is scientifi cally sound and meets guideline protocols.

72-2 Freshwater Invertebrate Acute (850.1010)

Imazapyr acid Daphnia. MRID 00131632 (Core). In a 48-hour acute test, imazapyr acid was determined to be practically non-toxic to daphnids with an EC 50 

### of >100 mg/L. The study is scientifically sound and meets guideline protocols.

Imazapyr isopropylamine salt Daphnia. MRID 00147117 (Core). In a 48-hour st atic test, imazapyr isopropylamine salt was determined to be practically non-toxic to daphnids with an EC 50 

### of 614 mg ae/L (750 mg ai/L). The study is scientifically sound and meets guideline protocols.

72-3a Estuarine/Marine Fish Acute (850.1075)

Silverside Minnow. MRID 41315801 (Acceptable). In a 96-hour flow-through test, imazapyr acid was determined to be practically non- toxic to silverside minnow with an LC 50 

### of >184 mg ai/L (mean measured concentration; nominal concentration 200 mg ai/L). The NOEC was determined to be 184 mg ai/L. The study is scie ntifically sound and meet s guideline protocols.

72-3b Estuarine/Marine Invertebrate Acute (850.1025, 850.1045)

Eastern Oyster. MRID 45119710 (Acceptable). In a 96-hour flow-through test, imazapyr acid was determined to be practically non-t oxic to the eastern oyster with an EC 50 

### of >132 mg ai/L (mean measured concentration; nominal concentration 120 mg a i/L). No mortalities were
observed in either the treated or control groups. The control shell deposition during the study
was 2.46 mm. The NOAEC was determined to be 132 mg ai/L, the highest c oncentration tested. No significant adverse effects were observed on shell deposition for any treated group. The study is scientifically sound a nd meets guideline protocols.

Eastern Oyster. MRID 41315802 (Supplemental). In a 96-hour flow-through test, imazapyr acid was determined to be practically non-t oxic to the eastern oyster with an EC 50 

### of >173 mg ai/L (mean measured concentration; nominal concentration 200 mg a i/L; the highest concentration tested). No mortalities were observed in eith er the treated or contro l groups. There was a statistically significant decrease in mean shel l deposition at 173 mg/L when compared to the

### 37 control group (p  0.05). The NOAEC was determined to be 109 mg ai/L. Originally, this study
was classified as invalid because the control oyster growth (1.35 mm new shell deposition) did not meet the guideline requirement of 2 mm (ame ndment to SEP, dated 9/1990). In addition, the flow rate of the test solution was 1.05 L/oyste r/hour. The protocols recommended by the SEP (APHA, 1981 and EPA, 1976) state that each oyster should receive a minimum of 5 L/oyster/hour. This study was later upgraded to supplemental. The memorandum stated that shell growth in the control group may be used as an indicator of stress for the oysters. Less than 2 mm shell growth in the contro l group indicates that the oysters may be undergoing stress. The low flow-through rate with no supplemental food a dded in this study may have contributed to stress on the oysters. For this study, it appears that the seawater was trucked in from the ocean to Gainesville, Florida. During such time, the f ood organisms (such as algae) may have been inhibited during the tran sport and storage. The oysters in the study may not have fed well
because of the combination of the lower amount of available food organisms in the shipped sea water, the low flow rate and the lack of supplemental food ad ded; thereby, contributing to inadequate shell deposition. However, since there was some dose-re sponse, the study was upgraded to supplemental.

Pink Shrimp. MRID 41315803 (Acceptable). In a 96-hour flow-through test, imazapyr acid was determined to be practically non-toxic to pink shrimp with an LC 50 

### of >189 mg ai/L (mean measured concentration; nominal concentration 2 00 mg ai/L). There was one mortality at the second highest concentration level (111 mg/L), which does not appear to be related to treatment. No other signs of toxicity were observed. Th erefore, the NOAEC was determined to be 189 mg ai/L, the highest concentration tested. The study is scientifically sound and meets guideline protocols.

72-4a Freshwater Fish Early Life Stage (850.1400)

Fathead Minnow. MRID 45119711 (Acceptable). In an early life-stage flow-through test, imazapyr acid produced no treatment-related effect s on embryonic survival, time to hatch, alevin survival, terminal length, or wet and dry weight . The NOEC was determined to be 118 mg ai/L (mean measured concentration; nom inal concentration 120 mg ai/L). The study is scientifically sound and meets guid eline protocols.

Rainbow Trout. MRID 41315804 (Supplemental). In an early life-stage flow-through test, imazapyr acid resulted in significantly reduced percent hatch and an observed reduction on survival at 92.4 mg/L (mean measured concentration; nominal concentration 100 mg/L). No abnormalities in embryonic or juvenile developm ent were observed. The MATC was >43.1 and <92.4 mg/L; thus the geometric mean MATC was 63.1 mg/L. The study did not meet all guideline requirements (feeding limited the growth of replicates with higher fish densities).

72-4b Freshwater Invertebrate Life Cycle (850.1300)

Daphnia. MRID 41315805 (Acceptable). In a li fe cycle flow-through test, imazapyr acid produced no treatment-related effects on surviv al, growth and reproduction of first generation

### 38 daphnids. No physical or behavioral abnorma lities were observed. The MATC and NOEL were

determined to be  97.1 mg/L. The study is scientifically sound and meets guideline protocols.

72-5 Freshwater Fish Life Cycle (850.1500)

Fathead Minnow. MRID 45119712 (Supplemental). In a full life cycle flow-through test, imazapyr acid produced no treatment-related eff ects on growth, embryo survival, time to hatch, or larval and juvenile survival of the F 0 

### and F 1 

### generations. No treatme nt-related effects were observed on percent spawning frequency, mean numb er of eggs produced per female or mean percent fertilization su ccess. The NOEC was reported at the nominal concentration of 120 mg ai/L (mean measured concentration 118 mg ai/L). The study is scientific ally valid but did not meet all guideline requirements (F 1 

### generation was maintained for 4 weeks instead of 8 weeks).

81-1 Acute Mammalian Oral

Imazapyr acid Rat. MRID 132030 (Acceptable). In an acute oral study, imazapyr acid was determined to have a low toxicity (Toxicity Categor y III) to rats with an LD 50 

### >5000 mg/kg. The study is scientifically sound and meets guideline protocols.

Imazapyr isopropylamine salt Rat. MRID 00147049 (Acceptable). In an acute oral study, imazapyr isopropylamine salt was determined to exhibit no toxicity (Toxic ity Category IV) to rats with an LD 50 

### of >5000 mg/kg (>4090 mg ae/kg). The study is scientifica lly sound and meets guideline protocols.

Rat. MRID 44735301 (Acceptable). In an acute oral study, imazapyr isopropylamine salt was determined to exhibit no toxicity (Toxic ity Category IV) to rats with an LD 50 

### of >5000 mg/kg (>4090 mg ae/kg). The study is scientifica lly sound and meets guideline protocols.

83-3 Mammalian Developmental

Rat. MRID 00131611 (Acceptable). In a 2-generation developmental study, imazapyr acid produced maternal toxicity in Sprague Dawley rats at 1000 mg ai/kg/day (LOAEL), based on salivation in the gravid dams be tween gestation days 8-15. The fi ndings were determined to be treatment-related. The NOAEL was 300 mg /kg bw /day. No treatment-related effects were reported for developmental parameters. The stud y is scientifically sound and meets guideline protocols.

Rabbit. MRID 00131613 (Acceptable). In a 2-generation teratology study, imazapyr acid produced no treatment-related e ffects for maternal or developmental parameters; consequently, the NOAEL for both endpoints was  400 mg/kg bw/day in New Zealand white rabbits. The study is scientifically sound a nd meets guideline protocols.

### 39 83-4 Mammalian Reproduction

Rat. MRID 41039505 (Acceptable). In a 2-generation reproduction study, imazapyr acid produced no treatment-related e ffects for maternal or developmental parameters; consequently, the parental systemic, reproduc tive, and offspring NOAEL was  738 mg/kg bw/day in males and 933.3 mg/kg bw/day in females. The study is scie ntifically sound and meet s guideline protocols.

122-2 Aquatic Plant Nonvascular (850.5400)

Imazapyr acid Green algae. MRID 40811802 (Acce ptable). In a Tier II toxicity test with Selenastrum capricornutum , the 7 day EC 50 

### for cell density was 71 mg ai/L (NOEC = 50.9 mg ai/L). The study is scientifically sound and meets the guideline protocols.

Blue-green algae. MRID 40811802 (Acceptable). In a Tier II toxicity test with Anabaena flosaquae , the7-day EC 50 

### for cell density was 12.2 mg ai/L ( NOEC = 9.6 mg ai/L). The study is scientifically sound and meet s the guideline protocols.

Marine diatom. MRID 40811802 (Acceptable). In a Tier II toxicity test with Skeletonema

costatum , the 7-day EC 50 

### for cell density was 92 mg ai/L (NOEC = 15.9 mg ai/L). The study is scientifically sound and meet s the guideline protocols.

Diatom. MRID 40811802 (Acceptable). In a Tier II toxicity test with Navicula pelliculosa , the 7- day EC 50 

### for cell density was >41 mg ai/L (NOEC = 41 mg ai/L). The study is scientifically sound and meets the guideline protocols.

Imazapyr isopropylamine salt Green algae. MRID 43889102 (Acce ptable). In a Tier II toxicity test with green algae, the 7-day
EC 50 

### , based on slight changes in cell shape wa s 11.5 mg ae/L (NOEC = 7.16 mg ae/L). The study is scientifically sound and meets the guideline protocols.

123-1(a) Seedling Emergence - Tier II (850.4225)

Imazapyr Acid Monocots (4 species) and Dicots (4 species). MRID 40811801 (Supplemental). In a Tier II seedling emergence study, the most sens itive monocot tested was wheat (EC 25 

### 0.0046 lb ae/acre,

EC 05 

### 0.00099 lb ae/acre; shoot weight). The most sensitive dicot tested was sugarbeet (EC 25 

### 0.0024 lb ae/acre, EC 05 

### 0.00017 lb ae/acre; shoot weight). Du e to deficiencies in the study, the guideline requirements are only partially fulfilled; acceptable data endpoints were used in the
risk assessment.

### 40 Nontarget Terrestrial Plant Seedling Emergence Toxicity (Tier II)

Species % ai EC25 (lbs ai/A) NOEC /

[EC05] Endpoint Affected MRID No. Study Classification

22.6% 408118-01

Monocot- Corn 0.025 0.0156 height invalid 2

Monocot- Oat 0.054 0.0156 “ supplemental 3

Monocot- Onion 0.034 [0.01] A weight 4 supplemental 3

Monocot- Wheat 0.0046 [0.00099] A “ supplemental 3

Dicot- Sunflower 0.0027 [0.000021] A height invalid 2

Dicot- Soybean 0.012 0.0078 “ invalid 2

Dicot- Pea 0.093 0.0624 weight 4 invalid 2

Dicot-Cucumber 0.0043 [0.000005] A “ invalid 2

Dicot- Sugarbeet 0.0024 [0.00017] A “ supplemental 3

Dicot- Tomato 0.008 0.0003 “ supplemental 3

1 Determination of the most sensitive species is based on EC 25 values; results are based on the non-linear

regression analysis.

2 Large seedlings were subjected to overcrowding , 10 seeds were planted in a 4-in dixie cup.

3 Small seedlings could be subjected to overcrowding , 10 seeds were planted in a 4-in dixie cup.

4 Fresh weight was recorded instead of dry weight.

A The NOEC value is above the EC25, equal to the EC25, or below the lowest concentration, an EC05

value is used instead.



### .

123-1(b) Vegetative Vigor - Tier II (850.4250)

Imazapyr acid Monocots (4 species) and Dicots (4 species). MRID 40811801 (Supplemental). In a Tier II vegetative vigor study, the most sensitive monocot tested was wheat (EC 25 

### 0.012 lb ae/acre, NOEC 0.0039 lb ae/acre; shoot weight). The mo st sensitive dicot tested was cucumber (EC 25 

### 0.0009 lb ae/acre, EC 05 

### 0.000064 lb ae/acre; shoot height). Du e to deficiencies in the study, the guideline requirements are partially fulfilled; acceptable data e ndpoints were used in the risk

assessment.

### 41 Species % a.i. EC 25 (lbs

ae/A) NOEC [EC05]

(lbs ae/A) Endpoint

affected MRID No. Study

classification

22.6% 408118-01

Monocot-Corn >0.0156 A 0.0078 weight 2 supplemental 3

Monocot-Oats 0.013 0.0039 height supplemental 3

Monocot-Onion -- -- n/a C invalid

Monocot-Wheat 0.012 0.0039 weight 2 supplemental 3

Dicot-Soybean -- -- n/a C invalid

Dicot-Pea -- -- n/a C invalid

Dicot-Sugarbeet 0.00097 [0.00039] B weight 2 supplemental 3

Dicot-Sunflower 0.0054 0.0039 weight 2 supplemental 3

Dicot-Cucumber 0.0009 [0.000064] B height supplemental 3

Dicot-Tomato >0.0156 A 0.00097 weight 2 supplemental 3

1 Determination of the most sensitive species is based on EC 25 values.

2 Fresh weight was recorded instead of dry weight.

3 the toxicity values could be underestimated since the study was tested with older plants (28D) at a less

sensitive stage of growth (timing of application).

A The EC25 value is above the highest concentration tested.

B The NOEC value is above the EC25, equal to the EC25, or below the lowest concentration, an EC05

value is used instead.

C No data



### Imazapyr isopropylamine salt Monocots (3 species) and Dicots (2 species). MRID 43889101 (Core). In a Tier II vegetative vigor study, chlorosis, stunting, and plant deat h were observed. The most sensitive monocot tested was onion (EC 25 

### 0.010 lb ae/acre, NOEC 0.004 lb ae/ac re; shoot weight). The most sensitive dicot tested was sugar beet (EC 25 

### 0.0016 lb ae/acre, NOEC 0.0008 lb ae/acre; shoot weight). The study is scientifically sound and meets guid eline protocols.

Monocots (4 species) and Dicots (4 species). MRID 40003711 (Supplemental). This study was a modified Tier II vegetative vigor study that did not meet gui deline requirements. Only

### 42 descriptive summary data was presented; conseq uently effect levels were not determined. Observed effects included chlorosis, stunting, leaf tip burning, necrosis, and plant death.

123-2 Aquatic Plant Vascular (850.4400)

Imazapyr acid Duckweed. MRID 40811802 (Acceptable). In a 14- day toxicity test with duckweed, the EC 50 

### for frond production was 0.024 mg ai/L and the NOEC wa s 0.01 mg ai/L. Imazapyr is considered highly toxic and expected to exer t a detrimental effect on vascular aquatic plants. The study is scientifically sound and meets guideline protocols.

Imazapyr isopropylamine salt Duckweed. MRID 43889102 (Acceptable). In a 14- day toxicity test with duckweed, the EC 50 

### for frond production was 0.018 mg ai/L and the NOEC was 0.011 mg ai/L. The study is scientifically sound and meets guideline protocols.

### APPENDIX D

The S creening I mbibition P rogram (SIP v.1.0, Released June 15, 2010) was used to calculate an upper bound estimate of exposure using imazapyr’s solubility (acid: 11,100 mg/L), the most
sensitive acute and chronic avian to xicity endpoints (bobwhite quail LD 50 

### >2,150 mg ae/kg-bw, MRID 00131633; and bobwhite quail NOAEC of 1670 mg ae/kg-diet, MRID 45119714 as well as mallard duck NOAEC of 1890 mg ae/kg-diet , MRID 43831402) and the most sensitive acute
and chronic mammalian toxi city endpoints (rat LD 50 

### >5,000 mg ae/kg-bw, MRID 00132030; and, a rat NOAEL of 300 mg/kg-bw/day, MRID 00131611) . Drinking water exposure alone was determined to be a potential pathway of concer n for avian and mammalian species on an acute and chronic basis. However, given that most studies indicated no effect s (with the exception of the rat developmental study, MRID 00131611) it is possi ble that the result is largely due in part by the high solubility limit of imazapyr.

This pathway will be explored further with the development of SIP v.2.0 in the Ecological Risk Assessment for imazapyr. See table below for a sample of the output generated by SIP v.1.0. Detailed information about the SIP v.1.0, as well as the tool, can be found on the EPA’s website

at http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial

.

Table 1. Inputs

Parameter Value

Chemical name Imazapyr (acid)
Solubility (in water at 25 o C; mg/L) 11100

Mammalian LD 50 (mg/kg-bw) 5000 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 300 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg-bw) 2150 Avian test species northern bobwhite quail Body weight (g) of "other" avian species Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 1890 Bobwhite quail NOAEC (mg/kg-diet) 1670 NOAEC (mg/kg-diet) for other bird species Body weight (g) of other avian species NOAEC (mg/kg-diet) for 2nd other bird species Body weight (g) of 2nd other avian species

### 44 Table 2. Mammalian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 1909.2000 1909.2000 Adjusted toxicity value (mg/kg-bw) 3845.8028 230.7482 Ratio of exposure to toxicity 0.4964 8.2740

Conclusion* Exposure through drinking water alone is a

potential concern for
mammals Exposure through drinking water alone is a

potential concern for
mammals

Table 3. Avian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 8991.0000 8991.0000 Adjusted toxicity value (mg/kg-bw) 1548.9235 93.7677 Ratio of exposure to acute toxicity 5.8047 95.8859

Conclusion* Exposure through drinking water alone is a

potential concern for
birds Exposure through drinking water alone is a

potential concern for
birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated with other routes ( i.e ., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure that has potential for effects to non-target animals.

### 45 APPENDIX E

The S creening T ool for I nhalation R isk (STIR v.1.0, November 19, 2010) was used to calculate an upper bound estimate of exposure using imazapyr acid’s vapor pressure (<10 -7 

### mm Hg) and molecular weight (293.16 g/mol) for vapor phase exposure as well as the maximum application rate (1.5 lb a.i./A) and method of application for spray drift (i.e., ground and aerial spray). STIR incorporates results from several toxicity studie s including acute oral a nd inhalation rat toxicity endpoints obtained from the “six-pack” of core studies, which are a series of six guideline studies that are submitted to the Registration Division of the Office of Pesticide Programs for technical and formulated products of a pesticide. The t echnical grade acute inha lation study (Guideline 870.1300) data was obtained from an HE D risk assessment (US EPA 2010): LC 50 

### > 1.3 mg/L (MRID 00252004); the typical duration for these studies is 4 hours, which was assumed for this study as well. The most sensitive acute oral avian toxicity endpoi nt (bobwhite quail LD 50 

### >2,150 mg ae/kg-bw, MRID 00131633) and most sens itive acute mammalian endpoint (rat LD 50 

### >5,000 mg ae/kg-bw, MRID 00132030) were obtained from ecological toxicity studies submitted to
EFED. Based on the results of th e STIR model, inhalation exposur e alone was not determined to be a potential pathway of concern for avian and mammalian species on an acute basis.

Inhalation exposure via spray drift and/or vapor-phase of the pest icide alone does not appear to be of concern. The analysis of the inhalation ro ute in STIR does not cons ider that aggregation with other exposure pathways such as dietary, derm al, or drinking water may contribute to a total exposure that has a potential fo r effects to non-target animals. However, the Agency does consider the relative importance of other routes of exposure in situations where data indicate that pesticide exposures through other routes may be potentially signi ficant contributo rs to wildlife risk (USEPA, 2004). Detailed information about STIR v.1.0, as well as the tool, can be found on the EPA’s website at: http://www.epa.gov/pe sticides/science/models_pg.htm#terrestrial

.

References;

USEPA. 2004. Overview of the Ecological Risk Assessment Process in th e Office of Pesticide Programs. U.S. Environmental Protection Ag ency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Washington DC. January 23, 2004.

USEPA. 2010. Imazapyr: Revised Occupational and Residential Exposure/Risk Assessment Under 24(c) for the Proposed Use of Broad cast Application on Cogongrass in Areas that may be Grazed or Cut for Hay. U.S Envi ronmental Protection Agency, Office of Chemical Safety and Pollution Prevention, Office of Pesticide Programs, Washington DC. July 27, 2010.

### 46 Sample input/output:

Input

Application and Chem ical Information

Enter Chemical Name Imazapyr

Enter Chemical Use various Is the Application a Spray? (enter y or n) y If Spray What Type (enter ground or air) air

Enter Chemical Molecu lar Weight (g/mole) 261.28 Enter Chemical Vapor Pressure (mmHg) 1.00E-07 Enter Application Rate (lb a.i./acre) 1.5

Toxicity Properties

Bird

Enter Lowest Bird Oral LD 50 (mg/kg bw) 2150 Enter Mineau Scaling Factor 1.15 Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD 50 (mg/kg bw) 5000

Enter Lowest Rat Inhalation LC 50 (mg/L) 1.3 Duration of Rat Inhalation Study (hrs) 4 Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg ) Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.58E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.98E-04

Adjusted Inhalation LD 50 3.12E+0
0

Ratio of Vapor Dose to Adjusted Inhalation LD 50 6.36E-05 Exposure not Likely Significant Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.44E-01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation
LD 50 4.62E-02 Exposure not Likely Significant

Results Mammalian (0.015 kg ) Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.58E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.49E-04

Adjusted Inhalation LD 50 7.74E+0
1

Ratio of Vapor Dose to Adjusted Inhalation LD 50 3.22E-06 Exposure not Likely Significant Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.81E-01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation
LD 50 2.34E-03 Exposure not Likely Significant