SCIENCE FINDINGS 

SUMMARY SCIENCE STATEMENTS 

Acute toxicity data indicate that has low toxicity via oral, dermal and 

inhalation routes of exposure. The technical product is classified in toxicity 

category I [DANGER] based on an acute eye irritation study conducted with the free 

acid. The formulated end-use product ( has low toxicity and is classified in 

toxicity category IV [Caution]. 

In an acute neurotoxicity study in rats with there were no 

treatment-related effects on Functional Observation Battery (FOB), motor activity, or 

neuropathological observations. The systemic No Observed Adverse Effect Level 

(NOAEL) was 1000 mg/kg based on transient clinical observations of fecal soiling in 

males and urine soiling in females observed at 2000 mg/kg bw, the highest dose tested 

[HDT]. In a chronic neurotoxicity study in rats the NOAEL was equal to or greater than 

1,000 mg/kg/day [HDT]. 

 was negative in all mutagenicity studies, except for an in vitro 

chromosome aberration assay utilizing rat lymphocytes. In this assay, 

induced chromosome aberrations without S9 activation, but only at cytotoxic 

concentrations. The clastogenic response was induced secondary to toxicity. 

In a rat developmental study the NOAEL for maternal and developmental toxicity was 

equal to or greater than 1,000 mg/kg/day [HDT]. In a developmental toxicity study in 

rabbits with the NOAEL for maternal toxicity was 250 mg/kg/day and the 

-2-
developmental NOAEL was equal or greater than 500 mg/kg/day. Maternal toxicity was 

observed at 500 and 750 mg/kg/day [HDT] in the form of decreased body weights and 

clinical observations of uncoordinated gait. Ulcers and erosions of the glandular 

mucosa of the stomach were observed in the 500 and 750 mg/kg/day dose groups. 

Similar toxic effects were also observed in a developmental study in rabbits with 

 the formulated triisopropanolamine (TIPA) salt of 

Developmental toxicity could not be determined in rabbit study since the 

750 mg/kg/day group was removed from the study due to the severity of the clinical 

signs (body weight changes, decreased food consumption and a decreased amount of 

feces). However, in the rabbit developmental study with developmental 

toxicity was demonstrated by a decrease in fetal body weights at 520 mg acid 

equivalents (ae)/kg/day. In a 2-generation reproduction study in rats, there was no 

evidence of parental, reproductive, or offspring toxicity observed after exposure to 

up to 1000 mg/kg/day [HDT]. The developmental toxicity studies and the 

2-generation reproduction study did not exhibit quantitative or qualitative susceptibility. 

There were no systemic toxic effects observed at 1000 mg/kg/day [HDT] in a 28-day 

dermal toxicity study in rats with However, dermal toxicity was indicated 

by slight epidermal hyperplasia in males at the HDT. 

The database on indicates that the stomach, ileum and cecum are targets 

for this compound. In a 90-day toxicity study in dogs the NOAEL was 282 mg/kg/day for 

males and 232 mg/kg/day for females based on slight diffuse hyperplasia and 

hypertrophy of the mucosal epithelium of the stomach at 1070 mg/kg/day in males and 

929 mg/kg/day in females. In the 1-year chronic toxicity study in dogs, the NOAEL was 

99 mg/kg/day for males and 93 mg/kg/day for females based on thickening of the 

stomach, slight lymphoid hyperplasia of the gastric mucosa, and slight chronic mucosal 

inflammation at the HDT. In a 90-day mouse dietary study, no toxicity was observed at 

1000 mg/kg/day [HDT]. In a 90-day rat feeding study the NOAEL was 1000 mg/kg/day 

[HDT] for females and 500 mg/kg/day for males based on hyperplasia of the mucosal 

epithelium of the ileum and the cecum at 1000 mg/kg/day [HDT]. 

In the mouse chronic feeding study the NOAEL was 1000 mg/kg/day [HDT] for males 

and 250 mg/kg/day for females. In the rat chronic feeding study the NOAEL was 50 

mg/kg/day based on cecal enlargement, slight mucosal hyperplasia (males) and slightly 

decreased body weights at 500 mg/kg/day. 

 has been classified as "not likely" to be carcinogenic to humans. No 

increases in any tumors were found in carcinogenicity studies in rats and mice. 

In a metabolism study in rats, was rapidly absorbed, distributed, and 

excreted following oral administration. Tissue distribution and bioaccumulation were 

minimal; <0.73% of administered dose [AD] was recovered in tissues after 7 days for all 

dosing groups. The highest levels of radioactivity were found in the skin and carcass. 

 was excreted unchanged, indicating an absence of metabolism. The AD 

-3-
was recovered as parent compound in 100% of the feces and = 96% of the urine. 

Three unknown components found in urine (= 4 %) were also detected in similar 

quantities in dose formulations, suggesting that they were trace impurities. 

Based on aminopyralid's low toxicity, an acute Reference Dose (RfD) for the general 

population is not required. 

The chronic RfD for is 0.5 mg/kg/day. This value is based on the NOAEL 

of 50 mg/kg/day in the rat combined chronic toxicity/carcinogenicity study with a 

100-fold uncertainty factor to account for interspecies extrapolation (10X) and 

intraspecies variability (10X). An additional safety factor to protect infants and children 

is not required, due to the toxicity properties of the material and the conservative nature 

of the exposure estimates. 

A DEEM chronic exposure analysis was conducted using the tolerance levels for wheat 

grain and meat commodities and assuming 100% of crops treated with 

The estimated exposures to US-population and relevant sensitive sub-population 

groups were all at least 3 orders of magnitude below the RfD (< 1% RfD). 

Based on the PRZM/EXAMS model, the estimated environmental concentrations (EECs) of

for

chronic exposures are estimated to be 1.937 parts per billion (ppb) for surface water and 0.630

ppb for ground water. The chronic estimated water concentrations derived from surface water

modeling results were significantly higher than the modeled ground water concentrations, and

therefore protective of potential exposures via ground water sources of drinking water when

LifeLineTM Version 2.0 to determine aggregate pesticide exposures from pesticide residues in 

incorporated into aggregate exposure estimates. The EEC’s were incorporated into 

There are no requested uses for that are considered residential and neither handler

nor post-application residential exposures from uses around homes are expected to occur.

However, the use on campgrounds and other recreation areas to control vegetation has the

potential to result in short-term post-application incidental oral exposures for infants and

children via hand-to mouth transfer of residues and ingestion of contaminated

grass and soil. For children with a 15-kg body weight exposed via the hand-to-mouth route, the

potential MOE was 150,000. Post-application exposure via inhalation is not expected to occur.

The source of human exposure results from dietary exposure from food and drinking water, and

short term incidential oral exposure, a short term oral exposure of children to treated

campgrounds.. Aggregating these exposure estimates gives a combined potential level of 0.0033

mg/kg/day, for the highest exposed group, children 1-2 years of age. The margin of exposure

(MOE) associated with this Tier I exposure estimate is 32,000, greatly above the acceptable limit

(MOE = 100). EPA thus concludes that there is reasonable certainty that no harm will come

from aggregate exposure to residues.

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Based on labeled uses, the occupational exposure is expected to be short- to intermediate-term 

and no long-term exposure is expected. Based on the available toxicological information, 

dermal exposures do not result in any adverse systemic effect; therefore, dermal exposures were 

not included into the estimation of occupational risk to workers. Short- and intermediate-term 

oral and inhalation exposures are being regulated based on the effects seen in the developmental 

rabbit toxicity study, which showed a NOAEL of 104 mg/kg/day. 

The highest potential exposure was estimated to Mixer-Loaders working on aerial applications of 

0.11 lb ae/A, for up to 1200 acres applied per day. The corresponding MOE is 40,000. 

Dietary tolerances are established for free and conjugated residues in the following crop 

food/feed commodities: 

Commodity Parts per million 

Grass, forage 

25 

Grass, hay 50 

Wheat, bran 0.1 

Wheat, forage 2.0 

Wheat, grain 0.04 

Wheat, hay 4.0 

Wheat, straw 0.25 

Aspirated grain fractions 0.2 

Tolerances also listed for the parent in or on the following animal commodities: 

Commodity Parts per Million 

Cattle, fat 0.02 

Cattle, meat 0.02 

Cattle, meat byproducts, 

excluding kidney 

0.02 

Cattle, kidney 0.3 

Goat, fat 0.02 

-5-
Goat, meat 0.02 

Goat, meat byproducts, 

excluding kidney 

0.02 

Goat, kidney 0.3 

Horse, fat 0.02 

Horse, meat 0.02 

Horse, meat byproducts, 

excluding kidney 

0.02 

Horse, kidney 0.3 

Milk 0.03 

Sheep, fat 0.02 

Sheep, meat 0.02 

Sheep, meat byproducts, 

excluding kidney 

0.02 

Sheep, kidney 0.3 

In aquatic systems, the primary route of degradation is photolysis, where a laboratory 

experiment yielded a half-life of 0.6 days. In addition to CO2, oxamic and 

 were identified as major degradates. was stable to direct hydrolysis 

and in anaerobic sediment-water systems. In aerobic sediment-water systems, 

degradation proceeded slowly, with observed total system half-lives of 462 to 990 days. 

The degradation resulted in the formation of non-extractable residues and no other 

major products. 

Under aerobic conditions, degradation of in five different soils resulted in 

the production of CO2 and non-extractable residues. Half-lives ranged from 31.5 to 

533.2 days in 5 soils. For risk assessment purposes, EPA used a half-life of 103.5 

days. 

 photolyzed moderately slowly on a soil surface. The half-life was 72 days 

and CO2, non-extractable residues and small amounts of acidic volatiles were the 

degradates. 

 is weakly sorbed to soil. A laboratory Freundlich adsorption isotherm 

study with 8 US and European soils yielded 48-hour Kd values of 0.03 to 0.72 mL/g; 

adsorption Koc values were 1.05 to 24.3 mL/g. 

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Two field dissipation studies were performed (in California and Mississippi). The results 

indicate that is likely to be non-persistent and relatively immobile in the 

field. Half-lives of 32 and 20 days were determined, with minimal leaching below the 15 

to 30 cm soil depth. 

 has been shown to be practically non-toxic to birds, fish, honeybees, 

earthworms, and aquatic invertebrates. is slightly toxic to eastern oyster, 

algae and aquatic vascular plants. The log Kow is less than 3 and thus is 

not expected to bioaccumulate in fish tissue. 

There are no acute or chronic risks to non-target endangered or non-endangered fish, 

birds, wild mammals, terrestrial and aquatic invertebrates, algae or aquatic plants. 

TECHNICAL CHEMICAL CHARACTERISTICS 

Empirical Formula:

Molecular Weight: 

Color; Off-white 

Physical State: Powder 

Odor: Odorless 

Melting Point: 161.75 - 165.23o C 

Density: 1.72 (20o C, relative to water at 4o C) 

Solubility: 

Water 212 g/L (pH 5) 

205 g/L (pH 7) 

203 g/L (pH 9) 

2.48 g/L (unbuffered) 

Acetone 29.2 g/L

Ethyl Acetate 4 g/L

Methanol 52.2 g/L

1,2-dichloroethane 0.189 g/L

Xylene 0.043 g/L

Heptane less than 0.010 g/L

Vapor

Pressure: 7.14 x 10-11 mm Hg at 20o C

-7-
1.92 x 10-10 mm Hg at 25o C 

Dissociation

Constant: pKa = 2.56 at 20o C

Octanol/Water

Partition

Coefficient: logP = 0.201 (Unbuffered at 20o C)

LogP = -1.75 (pH 5 at 20o C) 

LogP = -2.87 (pH 7 at 20o C) 

LogP = -2.96 (pH 9 at 20o C) 

pH: 2.31 (1% w/w solution/suspension)

Oxidizing or

Reducing

Action: none

Mobility: Kd = 0.03 - 0.72 

TOXICOLOGY CHARACTERISTICS 

(formulated end-use product)

Acute Oral

Toxicity

(rats):

Toxicity LD 50 Males and Females > 5000 mg/kg

Category: IV

Acute Dermal

Toxicity

(rats):

Toxicity LD 50 Males and Females > 5000 mg/kg

Category: IV

Acute Inhalation

Toxicity

(rats):

Toxicity LC 50 Males and Females > 5.79 mg/L

Category: IV

Primary Eye

-8-
Irritation

(rabbits):

Toxicity No irritation

Category: IV

Primary Skin

Irritation

(rabbits):

Toxicity Slight erythema at 24 and 72 hours, resolving by day 7

Category: IV

Dermal

Sensitization

(guinea pigs): Not a sensitizer

90-day dietary

(rats): NOAEL = 1000 mg (TIPA) salt of kg/day (520 mg acid 

equivalents (ae)/kg/day) 

LOAEL = not determined 

Developmental

Toxicity

(rabbit): Maternal NOAEL = 200 mg TIPA salt of /kg/day (104

mg ae/kg/day)

Maternal LOAEL = 500 mg TIPA salt of /kg/day (260

mg ae/kg/day) based on severe inanition and body weight loss,

decreased fecal output, and mild clinical observations of

uncoordinated gait

Developmental NOAEL = 500 mg TIPA salt of /kg/day

(260 mg ae/kg/day)

Developmental LOAEL = 1000 mg TIPA salt of kg/day

(520 mg ae/kg/day) based on decreased fetal body weights

Developmental

Toxicity

(rat): Maternal NOAEL = 1000 mg TIPA salt of kg/day (520

mg ae/kg/day)

Maternal LOAEL = not determined

Developmental NOAEL = 1000 mg TIPA salt of kg/day

(520 mg ae/kg/day)

Developmental LOAEL = not determined 

Mutagenicity: The mutagenicity studies submitted for satisfy the 

-9-
mutagenicity test battery. was negative in all 

mutagenicity studies. 

Metabolism 

(Non-guideline): 14C- and 14C-aminopryalid TIPA salt, when 

administered orally to rats, were bioequivalent in terms of 

absorption, distribution, metabolism, and excretion of the 

amino-dichloro-picolinate portion of the molecule(s). 

Technical 

(manufacturing use product)

Acute Oral

Toxicity

(rats):

Toxicity LD 50 Males and Females > 5000 mg/kg

Category: IV

Acute Dermal

Toxicity

(rabbits):

Toxicity LD 50 Males and Females >5000 mg/kg

Category: IV

Acute Inhalation

Toxicity

(rats):

Toxicity LC 50 Males and Females >5.5 mg/L

Category: IV

Primary Eye

Irritation

(rabbits):

Toxicity Corneal opacity in 1/3 through day 35

Category: I

Primary Skin

Irritation

(rabbits):

Toxicity No irritation

Category: IV

Dermal

Sensitization

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(guinea pigs): Not a sensitizer

Acute Neurotoxicity

Screening

Battery

(rat): NOAEL = 1000 mg/kg

LOAEL = 2000 mg/kg based on fecal soiling in males and urine 

soiling in females 

90-day dietary 

(rats): NOAEL Male = 500 mg/kg/day, Female = 1000 mg/kg/day 

LOAEL Male = 1000 mg/kg/day based on hyperplasia of the 

mucosal epithelium of ileum and cecum, Female = not determined 

90-day dietary 

(dogs): NOAEL Male = 282 mg/kg/day, Female = 232 mg/kg/day 

LOAEL Male = 1070 mg/kg/day, Female = 929 mg/kg/day based on 

stomach histopathology (slight diffuse hyperplasia and hypertrophy 

of the mucosal epithelium) 

28-day dermal 

(rats): Systemic NOAEL = 1000 mg/kg/day 

LOAEL = not determined 

Dermal NOAEL Male = 100 mg/kg/day, Female = 1000 mg/kg/day 

LOAEL Male = 500 mg/kg/day based on histopathological changes 

(slight epidermal hyperplasia), Female = no 

Developmental

Toxicity

(rabbit): Maternal NOAEL = 250 mg/kg/day

Maternal LOAEL = 500 mg/kg/day based on decrease in body 

weight (GD 7-10), decreased food consumption, clinical 

observations of uncoordinated gait and ulcers and erosions of the 

stomach 

Developmental NOAEL = 500 mg/kg/day 

Developmental LOAEL = not determined 

Developmental

Toxicity

(rat): Maternal NOAEL = 1000 mg/kg/day

Maternal LOAEL = not determined 

Developmental NOAEL = 1000 mg/kg/day 

-11-
Developmental LOAEL = not determined 

Two-Generation

Reproduction

(rat): Paternal NOAEL = 1000 mg/kg/day

Paternal LOAEL = not determined 

Reproductive NOAEL = 1000 mg/kg/day 

Reproductive LOAEL = not determined 

Offspring NOAEL = 1000 mg/kg/day 

Offspring LOAEL = not determined 

1 Year Chronic

Feeding

(dog): NOAEL Male = 99 mg/kg/day, Female = 93 mg/kg/day

LOAEL Male = 967 mg/kg/day, Female = 1038 mg/kg/day based on 

thickening of stomach mucosa (females), and stomach 

histopathology in all animals (slight diffuse hyperplasia and 

hypertrophy of the mucosal epithelium, slight lymphoid hyperplasia 

of the gastric mucosa and very slight/slight chronic mucosal 

inflammation) 

Chronic Neurotoxicity 

(rat): NOAEL = 1000 mg/kg/day 

LOAEL = not determined 

Chronic Feeding/

Carcinogenicity

(rat): NOAEL = 50 mg/kg/day

LOAEL = 500 mg/kg/day based on cecal enlargement, slight 

mucosal hyperplasia (males) and slightly decreased body weights 

Carcinogenicity 

(mouse): NOAEL Male = 1000 mg/kg/day, Female 250 mg/kg/day 

LOAEL Male = not determined, Female = 1000 mg/kg/day based 

on increased mortality 

Mutagenicity: The mutagenicity studies submitted for satisfy the 

mutagenicity test battery. was negative in all 

mutagenicity studies, except for an in vitro chromosome aberration 

assay utilizing rat lymphocytes. In this assay, induced 

chromosome aberrations, but only at cytotoxic concentrations. The 

clastogenic response was induced secondary to toxicity. 

-12-
Metabolism: Low dose = 50 mg/kg 

High dose = 1000 mg/kg 

Repeated dose = 50 mg/kg/day (unlabeled) for 14 days, 50 

mg/kg/day (labeled) on day 15 

Recovery after 168 hrs: 96% in low dose (urine - 50%, feces - 43%, 

tissues - 0.1%, cage wash - 10%), and 95% in the repeated low 

dose (urine 59%, feces - 33%, tissues - 0.1%, cage wash - 3%). 

 represented = 96% of administered dose (AD) in urine 

and 100% AD in feces. Three unknown components (= 4 %) found 

in urine were also found in dose formulations. 

ECOLOGICAL CHARACTERISTICS 

Avian Acute Toxicity: 

Bobwhite Quail: LD50>2250 mg a.e./kg bw 

Avian Dietary Toxicity: 

Bobwhite Quail: 5-day LC50 >5556 mg a.e./kg diet 

Mallard Duck: 5- day LC50 >5496 mg a.e./kg diet 

Avian Reproduction: 

Bobwhite Quail: No Observed Effect Concentration 

(NOEC) = not determined 

Lowest Observed Effect Concentration 

(LOEC) = 640 mg a.e./kg diet 

Mallard Duck: No Observed Effect Concentration 

(NOEC) = 2623 mg a.e./kg diet 

Lowest Observed Effect Concentration 

(LOEC) > 2623 mg a.e./kg diet 

Acute Mammalian Toxicity:

Rattus rattus: LD50 >5000 mg a.e./kg bw

Chronic Mammalian Toxicity:

Rattus norvegicus: NOEL >1000 mg a.e./kg bw/day

Freshwater fish and amphibian

Acute Toxicity:

Bluegill Sunfish: 96-hour LC50 >100 mg a.e./L

Rainbow Trout: 96-hour LC50 >100 mg a.e./L

Northern leopard frog: 96-hour LC50 >95.2 mg a.e./L

Estuarine/marine fish 

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Acute Toxicity:

Sheepshead minnow: 96-hour LC50 >120 mg a.e./L

Freshwater Fish

Early life-stage

Toxicity:

Fathead Minnow: NOEC = 1.36 mg a.e./L

LOEC = 2.44 mg a.e./L 

MATC** = 1.82 mg a.e./L 

** Defined as the geometric mean of the NOEC and LOEC 

Freshwater Invertebrate

Toxicity:

Daphnia magna: 48-hour EC50 >98.6 mg a.e./L

Freshwater Invertebrate

Life-Cycle Toxicity:

Daphnia magna: NOEC = 102 mg a.e./L (highest concentration tested)

LOEC > 102 mg a.e./L 

Estuarine/Marine

Invertebrate Acute

Toxicity:

Eastern Oyster: 48-hour EC50 >89 mg a.e./L

Mysid: 96-hour LC50 >100 mg a.e./L

Non-Target Insects

Toxicity:

Honey Bee

Acute Contact: LD50 >100 :g a.e./bee

Acute Oral: LD50 >117 :g a.e./bee 

Seedling Emergency and Vegetative Vigor For 

Seedling Emergence:

Species EC25 (g a.i./ha) Most Sensitive Parameter

Monocot - Barnyardgrass >230.8 None

Monocot - Corn >230.8 None

Monocot - Onion 29.0 Fresh weight (Most Sensitive Monocot)

Monocot - Wheat >230.8 None

Dicot - Cucumber >57.7 None

Dicot - Soybean 2.7 Fresh weight (Most Sensitive Dicot)

Dicot - Sugar Beet 14.0 Fresh weight

Dicot - Lettuce 20.0 Fresh weight

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Dicot - Oilseed Rape 49.0 Fresh weight 

Dicot - Radish >230.8 None

Vegetative Vigor:

Species EC25 (g a.i./ha) Most Sensitive Parameter

Monocot - Barnyardgrass >230.8 None

Monocot - Corn >230.8 None

Monocot - Onion 53.0 Fresh weight 

Monocot - Wheat >230.8 None

Dicot - Cucumber 12.0 Shoot length

Dicot - Soybean 0.75 Shoot length

Dicot - Sugar Beet 8.4 Fresh weight

Dicot - Lettuce 3.3 Fresh weight

Dicot - Oilseed Rape >230.8 None

Dicot - Radish 54.0 Fresh weight

Non-target Aquatic Plant Toxicity (Tier II):

Vascular Plants

Duckweed

Lemna gibba: EC50 > 88 mg a.e./L NOEC = 44 mg a.e./L 

Nonvascular Plants

Green algae

Pseudokirchneriella subcapitata: ErC50 = 30 mg a.e./L NOEC = 23 mg a.e./L

Marine diatom:

Skeletonema costatum: EbC50 = 70 mg a.e./L NOEC = 13 mg a.e./L

Freshwater diatom:

Navicula pelliculosa: EC50 = 18 mg a.e./L NOEC = 6 mg a.e./L

Blue-green algae:

Anabaena

Flos-aquae: not determined

 has been shown to be practically non-toxic to birds, fish, honeybees,

earthworms, and aquatic invertebrates. is slightly toxic to eastern oyster,

algae and aquatic vascular plants. The log Kow is less than 3, indicating that

is not expected to bioaccumulate in fish tissue. Tier II seedling emergence

and vegetative vigor studies were conducted using the formulated product, 

Seedling emergence testing indicated that onion was the most sensitive monocot (fresh

shoot weight EC25 = 29 g a.i./ha), while soybeans were the most sensitive dicot (fresh

shoot weight EC25 = 2.7 g a.i./ha). Vegetative vigor testing indicated that onion was

-15-
again the most sensitive monocot (fresh shoot weight EC25 = 53 g a.i./ha). Similarly, 

soybeans were the most sensitive dicot (shoot length EC25 = 0.75 g a.i./ha). Grass 

species (barnyardgrass, corn and wheat) were among the least sensitive species tested 

in both the seedling emergence and vegetative vigor tests and had EC25 values that 

exceeded the maximum application rate tested. There are no acute or chronic risks to 

non-target endangered or non-endangered fish, birds, wild mammals, terrestrial and 

aquatic invertebrates, algae or aquatic plants. 

ENVIRONMENTAL CHARACTERISTICS 

In aquatic systems, the primary route of degradation is photolysis, where a laboratory 

experiment yielded a half-life of 0.6 days (corrected for natural sunlight conditions). In 

addition to CO2, oxamic and were identified as major degradates, along 

with a number of minor 2-3 carbon chain length acid amides. was stable 

to direct hydrolysis and in anaerobic sediment-water systems. In aerobic 

sediment-water systems, degradation proceeded slowly, with observed total system 

half-lives of 462 to 990 days. The degradation resulted in the formation of 

non-extractable residues and no other major products. 

Under aerobic conditions, degradation of in five different soils resulted in 

the production of no significant degradation products beyond CO2 and non-extractable 

residues. Half-lives ranged from 31.5 to 533.2 days, although material balance criteria 

were not met for 4 of the 5 soils; the soil meeting these criteria yielded a half-life of 

103.5 days. By the end of the study, CO2 accounted for 66 to 73% of the applied 

(except in a Barnes Clay Loam soil at 27-30% of applied). Non-extractable residues 

were detected at 0 to 16% of applied radioactivity at the end of the study, except for the 

test with a Houston Black Clay soil, where the non-extractable residues were 23-24% of 

applied. 

 photolyzed moderately slowly on a soil surface. The half-life was 72 days 

(corrected for natural sunlight and soil metabolism) and CO2, non-extractable residues 

and small amounts of acidic volatiles were the degrates.. 

 is weakly sorbed to soil. A laboratory Freundlich adsorption isotherm 

study with 8 US and European soils yielded 48-hour Kd values of 0.03 to 0.72 mL/g; 

adsorption Koc values were 1.05 to 24.3 mL/g. 

Two field dissipation studies were performed (in California and Mississippi). The results 

indicate that is likely to be non-persistent and relatively immobile in the 

field. Half-lives of 32 and 20 days were determined, with minimal leaching below the 15 

to 30 cm horizon depth. 

The nature of the residue in plants and animals is well understood. Based on the nature 

of residue studies (NOR) on grass and wheat, the tolerance expression in or on grass 

forage, grass hay, wheat raw agricultural commodities and wheat processed products is 

-16-
the total parent both free and conjugated. Based on the NOR study on

lactating goat, the tolerance expression in milk, meat and meat-byproducts is the

unchanged parent, 

Tolerances are established for residues of as described in the Summary

Science Statements of this Fact Sheet.

AGGREGATE EXPOSURES

As indicated by the Food Quality Protection Act (FQPA), 1996, the potential for 

concurrent exposure to via oral, dermal and inhalation routes must be 

assessed by EPA. This aggregate exposure considers every possible non-occupational 

exposure route, including residues in food, in drinking water and residential exposure 

from indoor/outdoor non-crop uses. 

However, based on the available toxicological information, dermal exposures do not 

result in any adverse systemic effect; therefore, dermal exposures are not included into 

the estimation of aggregate risk for any duration of exposure. Short- and 

intermediate-term oral and inhalation exposures are being regulated based on the 

effects seen in the developmental rabbit toxicity study. However, the non-crop uses do 

not include any indoor uses; therefore, both handler and post-application inhalation 

exposures are expected to be negligible. 

1. From Food and Feed Uses 

Based on aminopyralid's low toxicity profile, an acute Reference Dose (RfD) for the 

general population or any of the population sub-groups is not required. 

The chronic Reference Dose (RfD) for is 0.5 mg/kg/day. It is based on the 

NOAEL of 50 mg/kg/day from the rat combined chronic toxicity/ carcinogenicity study, 

the lowest NOAEL observed in any of the chronic studies. A 100-fold uncertainty factor 

to account for interspecies extrapolation (10X) and intraspecies variability (10X) was 

applied over the selected NOAEL in order to establish the RfD. 

An extra safety factor (SF) to protect infants and children is not needed based on the 

following considerations: 

a) the toxicity data showed no increase in susceptibility in fetuses and pups with 

in-utero and post-natal exposure; b) the dietary food exposure assessment was 

done with tolerance-level residues and 100% crop treated for all commodities, 

which results in very high-end estimates of dietary exposure; c) the drinking 

water assessment was based on values generated by models which are 

designed to provide conservative, high-end estimates of water concentrations; d) 

exposures due to recreational activities are based on default EPA assumptions 

that result in high-end estimates of exposure. 

A DEEM chronic exposure analysis was conducted using the tolerance levels for wheat 

-17-
grain and meat commodities and assuming 100% of crops treated with 

The estimated exposures to US-population and relevant sensitive sub-population 

groups were all at least 3 orders of magnitude below the level of the RfD (< 1% RfD). 

2. From Potable Water 

Drinking water estimated concentrations were estimated with the SCI-GROW model for 

ground water and with the Index Reservoir model for surface water. The set of 

assumptions included the maximum seasonal use rate of 0.11 lb a.e./A, Koc of 1.05 and 

a half-life of 38.7 days. does not have an acute RfD established; therefore, 

an acute assessment is not needed for drinking water. A chronic exposure assessment 

considering the highest chronic concentrations from surface drinking water has shown 

levels of exposure which are four orders of magnitude below the RfD of 0.5 

mg/kg-bw/day, both for adults and children 1-6 years of age. 

3. For Non-Dietary Uses 

At this time, there are no requested uses for that are considered home 

uses and neither handler nor post-application residential exposures from uses around 

home are expected to occur. However, the use on campgrounds and other recreation 

areas to control vegetation has the potential to result in short-term post-application 

incidental oral exposures for infants and children via hand-to mouth transfer of residues 

and ingestion of contaminated grass and soil. Post-application exposure 

via inhalation is not expected to occur. 

Short-term residential exposure to children with 15 kg body-weight from the three routes 

mentioned above was estimated using the HED Draft Standard Operating Procedures 

(SOP's) for Residential Exposure Assessments (12/18/97) and the Revisions to the 

Standard Operating Procedures (SOP's) for Residential Exposure Assessment (Science 

advisory Council for Exposure Policy 12, Revised February 22, 2001) for Hand-to-Mouth 

Transfer, Ingestion of Turfgrass and Ingestion of Soil, from uses on lawn broadcast 

application. The lowest MOE was 150,000 for this tier-I post-application residential 

assessment and it corresponds to children exposed via the hand-to-mouth route. 

AGGREGATE RISK CONCLUSIONS 

Since the only source of residential exposure would result from oral exposure, an 

aggregate exposure assessment was performed adding the estimated chronic dietary 

exposure to the estimated short-term oral residential exposure. Totaling the two oral 

exposure estimates gives a combined potential level of 0.0033 mg/kg/day, for the 

highest exposed group, children 1-2 years of age. The margin of exposure (MOE) 

associated with this Tier I exposure estimate is 32,000 and it is much above the 

acceptable limit (MOE = 100). EPA thus concludes that there is reasonable certainty 

that no harm will come from aggregate exposure to residues. 

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CUMULATIVE EXPOSURE TO SUBSTANCES WITH COMMON MECHANISM OF 

TOXICITY 

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

a common mechanism of toxicity, EPA has not made a common mechanism of toxicity 

finding for and any other substances. Furthermore, does not 

appear to have a toxic metabolite that is produced by other substances. For the time 

being, EPA has assumed that does not have a common mechanism of 

toxicity with other substances. For information regarding EPA's efforts to determine 

which chemicals have a common mechanism of toxicity and to evaluate the cumulative 

effects of such chemicals, see the policy statements released by the Office for 

Pesticides Programs concerning common mechanism determinations and procedures 

for cumulating effects from substances found to have a common mechanism on EPA's 

website at http: //www/epa.gov/pesticides/cumulative/ 

OCCUPATIONAL EXPOSURE 

Based on labeled uses, the occupational exposure is expected to be short- to 

intermediate-term and no long-term exposure is expected. The application of 

to control weeds in wheat, rangeland, pastures, non-cropland areas and natural 

recreation areas is recommended by using broadcast treatment with ground and aerial 

equipment on wheat and also hand-spray and spot treatments for all other uses. 

Based on the available toxicological information, dermal exposures do not result in any 

adverse systemic effect; therefore, dermal exposures were not included into the 

estimation of occupational risk to workers. Short- and intermediate-term oral and 

inhalation exposures are being regulated based on the effects seen in the 

developmental rabbit toxicity study, which showed a NOAEL of 104 mg/kg/day. 

The highest potential exposure was estimated to Mixer-Loaders working on aerial 

applications of 0.11 lb ae/A, for up to 1200 acres applied per day. The corresponding 

MOE is 40,000. 

SUMMARY OF DATA GAPS 

No major data gaps have been identified with the registrant-submitted data, although 

uncertainties were noted in the determinations of soil half-life, chronic effects on birds 

and effects upon cyanobacteria. 

1. Submit completed enforcement method of analysis to show that analytical method 

differentiates between picloram and clopyralid. 

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 2. The analytical method must be submitted to EPA Fort Meade Laboratory for validation. 

3, Submit storage stability data for grass forage and hay reflecting up to approximately 15 

months of frozen storage. 

4. Submit a repeated Aerobic Soil Metabolism Study (EPA Guidelines No. 162-1). 

5. Submit a repeated Avian Reproduction study in bobwhite quail (EPA Guideline No. 71-

4(a). 

6. Submit a repeated Tier II Aquatic Plant Growth: Blue-Green Algae, Anabaena flos aquae 

(EPA Guideline No. 123-2). 

PUBLIC INTEREST FINDING 

 is a Reduced Risk herbicide that provides reliable control of a broad

spectrum of difficult-to control noxious weeds and invasive plants on rangeland and

pastures, rights-of-way, and wildlife habitat areas. is particularly effective

for the control of tropical soda apple, musk thistle, Canada thistle, spotted knapweed,

diffuse knapweed, yellow starthistle and Russian knapweed. has a

favorable human health toxicity profile when compared to the registered alternatives for

these use sites and will be applied at a lower rate. Its residual action should alleviate

the need for repeat applications, resulting in a reduction in the amount of herbicides

applied to the environment for the control of these weeds. has been

determined to be practically non-toxic to non-target animals at the registered application

rates, compared to the alternatives, and is less likely to impact both terrestrial and

aquatic plants.

GOVERNMENT PERFORMANCE AND RESULTS ACT (GPRA)

Registration of will meet the objectives of GRPA title 3.1.1 by assuring

new pesticides that enter the market are safe for humans and the environment and title

4.1.2 by reducing environmental exposure to herbicides.

CONTACT PERSON AT EPA

Joanne Miller, 

Project Manager, Team 23

Herbicide Branch

Registration division (7505C)

E-Mail Address: 

miller.joanne@epamail.epa.gov 

Mailing Address: 

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US Environmental Protection agency

Office of Pesticide Programs (7505C)

Ariel Rios building

1200 Pennsylvania Ave., N.W.

Washington, D.C. 20460

Office Location and Telephone Number

Room 241, Crystal Mall building #2

1801 south Bell Street

Arlington, VA 22202

(703) 305-6224

Disclaimer: The information presented in this Pesticide Fact Sheet is for informational

purposes only and may not be used to fill data requirements for pesticide registration

and reregistration.

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