OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

September 3, 2014

PC Code: 005100

MEMORANDUM DP Barcode: D422421

SUBJECT: Addendum to the Problem Formulation for the Environmental Fate and 

Ecological Risk, Endangered Species, and Drinking Water Assessments in 

Support of the Registration Review of Aminopyralid Regarding Tier I Honey Bee 

Toxicity Testing

FROM: Edward Scollon, PhD, Toxicologist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

REVIEWED

BY: Thomas Steeger, PhD, Senior Science Advisor

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

THROUGH: Sarah Winfield, Acting Branch Chief

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

TO: Veronica Dutch, Chemical Reviewer Manager

Lee Tanner, Acting Team Leader

Linda Arrington, Branch Chief

Risk Management and Implementation Branch V

Pesticide Re-Evaluation Division (7508P)

This addendum addresses changes to the registration review data gaps identified in the 

preliminary problem formulation1and Final Work Plan (FWP2) written in support of the 

Registration Review of aminopyralid. Specifically, this document identifies additional data gaps 

for aminopyralid with respect to toxicity tests on honey bees (Apis mellifera).

 

1 USEPA. 2014. Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and 

Human Health Drinking Water Exposure Assessments for Aminopyralid, Potassium salt of Aminopyralid, and Triisopropanolamine Salt of 

Aminopyralid. DP Barcode D415743. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2013-0749-0011

2USEPA. 2014 Aminopyralid Final Preliminary Work Plan. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2013-0749-0012
Since the preliminary problem formulation was completed, the Agency has issued guidance3

for 

assessing the potential risks of pesticides to bees and the data needed to support such 

assessments. The guidance document indicates that if exposure of bees to a pesticide is

expected, a Tier I screening-level risk assessment should be conducted. The Tier I assessment is 

intended to be sufficiently conservative such that chemicals which pass the screen represent a 

relatively low risk of adverse effects to bees. Tier I toxicity data that are generally needed to 

complete screening-level risk assessments include a suite of laboratory-based studies of 

individual bees and consists of the following tests: acute contact toxicity data to adult honey 

bees (honey bees serving as a surrogate for other Apis and non-Apis bees and other insect 

pollinators), acute and chronic oral toxicity to adult honey bees, and acute and chronic oral 

toxicity to honey bee larvae. If risk concerns are identified in the screening-level assessment, the 

assessment may be refined using data that further define exposure or through additional data 

including Tier II semi-field or full-field toxicity tests conducted with whole colonies.

Aminopyralid is registered for use on a variety of agricultural, forest, commercial, and residential 

areas and may be applied via aircraft, ground sprayer, hand-held sprayer, and boom sprayer. 

Aminopyralid may also be applied to forest plantings via broadcast, high volume spray, spot 

treatment, stump treatment, girdle treatment, frill treatment, tree wound treatment, and tree 

injection. These use patterns may result in exposure to blooming non-target plants and could 

result in residues in pollen and nectar (which could then be transported to the hive by adult 

forager bees). Additionally, aminopyralid is highly persistent and, like other members of the 

picolinic acid family, is systemic and can move in both xylem and phloem tissue. Although 

aminopyralid uptake is primarily through the foliage, root uptake is also possible. Therefore, in 

addition to direct contamination of pollen and/or nectar through foliar applications, aminopyralid

residues may be translocated to pollen and nectar either through transport from leaf tissues 

affected by spray drift or from root uptake in plants grown where aminopyralid was previously 

applied. Residues can in turn be brought back to bee colonies where in-hive bees including 

young adult and developing brood (i.e., eggs, larvae and pupae) may be exposed. Therefore, 

exposure at all bee life stages would be expected. 

Since exposure of bees to aminopyralid residues is expected, Tier I honey bee laboratory toxicity 

data are needed to conduct the screening-level risk assessment. Acute contact toxicity data are

available that indicate aminopyralid residues are practically non-toxic to honey bees on an acute 

contact exposure basis. However, no data are available to evaluate aminopyralid’s oral toxicity to 

either adult or larval bees from either acute or chronic exposure. 

Therefore, the Agency is requesting Tier I laboratory toxicity data on the technical grade active 

ingredient (TGAI) for acute and chronic oral toxicity for both adult and larval honey bees in 

order to complete the risk assessment for bees, as is further detailed in the attached data rationale 

tables. Should the screening level risk assessment identify that there are risk concerns to bees, 

mitigation measures may need to be considered or the registrant may be required to conduct 

more refined studies under semi-field or full-field conditions (e.g. 850.30404guideline studies) 

that reduce uncertainty by characterizing aminopyralid’s effects at the whole-colony level.

 

3 USEPA et al.. 2014. Guidance for Assessing Pesticide Risks to Bees. http://www2.epa.gov/sites/production/files/2014-

06/documents/pollinator_risk_assessment_guidance_06_19_14.pdf

4 USEPA. 2012. Ecological Effects Test Guidelines OCSPP 850.3040: Field Testing for Pollinators. Office of Chemical Safety and Pollution 

Prevention (7101). EPA 712-C-017 January 2012. file:///C:/Users/tsteeger/Downloads/EPA-HQ-OPPT-2009-0154-0018%20(3).pdf
References

USEPA, 2014. Preliminary Problem Formulation for the Environmental Fate and Ecological 

Risk, Endangered Species, and Human Health Drinking Water Exposure for Aminopyralid, 

Potassium salt of Aminopyralid, and Triisopropanolamine Salt of Aminopyralid. Environmental 

Fate and Effects Division, Office of Pesticide Programs, USEPA, Washington D.C. February 12, 

2014. D415743.

USEPA, PMRA and CDPR, 2014. Guidance for Assessing Pesticide Risks to Bees. Office of 

Pesticide Programs, USEPA, Washington D.C. Health Canada Pest Management Regulatory 

Agency, Ottawa, ON, Canada. California Department of Pesticide Regulation, Sacramento, CA. 

June 23, 2014.
Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Acute Oral Toxicity

Rationale for Requiring the Data

This study is needed to evaluate potential effects to adult honey bees from acute oral exposure to technical 

grade active ingredient (TGAI). Aminopyralid is registered for use on a variety of agricultural, forest, 

commercial, and residential areas and may be applied via aircraft, ground sprayer, hand-held sprayer, and 

boom sprayer. Aminopyralid may also be applied to forest plantings via broadcast, high volume spray, 

spot treatment, stump treatment, girdle treatment, frill treatment, tree wound treatment, and tree injection. 

Some of these uses may result in exposure to blooming non-target plants and could result in residues in 

pollen and nectar (which could then be transported to the hive). Additionally, aminopyralid is highly 

persistent and, like other members of the picolinic acid family, is systemic and can move in both xylem 

and phloem tissues into pollen and/or nectar and represent a route of exposure to bees. Although 

aminopyralid uptake is primarily through the foliage, root uptake is also possible. Therefore, 

aminopyralid residues may be present in pollen and nectar either through transport from leaf tissues 

affected by spray drift or from root uptake in plants grown where aminopyralid was previously applied. 

Residues can in turn be brought back to bee colonies where in-hive bees including young adult and 

developing brood (i.e., eggs, larvae and pupae) may be exposed. Therefore, exposure at all bee life stages 

would be expected. 

Since the preliminary Problem Formulation5 was completed, the Agency finalized its guidance6for

assessing the risk of pesticides to bees. EPA now requires this study for all use sites where potential 

exposure to pollinators may occur. Although EPA has not developed a guideline for this study, the 

Organization for Economic Cooperation and Development (OECD) has developed a formal test guideline 

for an acute oral toxicity study with adult honey bees (OECD TG2137) that may be used to assess the 

acute oral toxicity for adult bees.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The acute oral toxicity data are used in conjunction with acute contact data obtained through OCSPP 

850.30208to estimate the acute toxicity of technical grade active ingredient (TGAI) to individual young 

adult honey bees. The studies also provide slopes for the dose-response curves that can in turn be used for 

estimating the likelihood of individual effects, and sublethal effects observed in the study will be used to 

further characterize effects observed following a single exposure to TGAI. Data obtained from this study 

will be used in estimating acute risk to individual adult bees. Risk estimates based on these data will be 

considered along with other lines of evidence to determine whether higher-tier studies are needed at the 

whole colony level.

These data are needed for risk assessments written in support of Registration Review risk assessment as 

well as for future endangered species assessments. The data would allow the Agency better characterize 

 

5 USEPA. 2014. Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and 

Human Health Drinking Water Exposure Assessments for Aminopyralid, Potassium salt of Aminopyralid, and Triisopropanolamine Salt of 

Aminopyralid. DP Barcode D415743. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2013-0749-0011

6 USEPA et al.. 2014. Guidance for Assessing Pesticide Risks to Bees. http://www2.epa.gov/sites/production/files/2014-

06/documents/pollinator_risk_assessment_guidance_06_19_14.pdf

7 OECD. 1998. OECD Guidelines for the Testing of Chemicals Honeybees, Acute Oral Toxicity Test. OECD/OCDE 213 Adopted 21st

September 1998. http://www.oecdilibrary.org/docserver/download/9721301e.pdf?expires=1408726996&id=id&accname=guest&checksum=29D93505197D8AB40C63E8F0DFB4

47D0

8 USEPA. 2012. Ecological Effects Test Guidelines OCSPP 850.3020: Honey Bee Acute Contact Toxicity Test. Office of Chemical Safety and 

Pollution Prevention (7101). EPA-712-C-019. January 2012. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-

0016
Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Acute Oral Toxicity

Rationale for Requiring the Data

the potential for risk to insects (including beneficial pollinators) from the use of picolinic acids-class 

chemicals. These data may help the Agency determine whether any mitigations are needed. If the 

Registration Review and any future endangered species risk assessments are performed without these data, 

the Agency would have to assume that picolinic acids-class chemicals "may affect" insects, including bees 

and beneficial pollinators, directly (and endangered species from other taxa indirectly), and uses of 

aminopyralid might need to be restricted in areas where pollinators could be exposed. 

Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed to evaluate the potential effects of technical grade active ingredient (TGAI) on young 

adult honey bees from repeat exposure. Aminopyralid is registered for use on a variety of agricultural, 

forest, commercial, and residential areas and may be applied via aircraft, ground sprayer, hand-held 

sprayer, and boom sprayer. Aminopyralid may also be applied to forest plantings via broadcast, high 

volume spray, spot treatment, stump treatment, girdle treatment, frill treatment, tree wound treatment, and 

tree injection. Some of these uses may result in exposure to blooming non-target plants and could result 

in residues in pollen and nectar (which could then be transported to the hive). Additionally, aminopyralid

is highly persistent and, like other members of the picolinic acid family, is systemic and can be 

translocated to pollen and/or nectar via transport through both xylem and phloem tissues of plants. 

Although aminopyralid uptake is primarily through the foliage, root uptake is also possible. Therefore, 

aminopyralid residues may be present in pollen and nectar either through transport from leaf tissues 

affected by spray drift or from root uptake in plants grown where aminopyralid was previously applied. 

Residues can in turn be brought back to bee colonies where in-hive bees including young adult and 

developing brood (i.e., eggs, larvae and pupae) may be exposed. Therefore, exposure at all bee life stages 

may occur. 

Since the preliminary Problem Formulation9 was completed, the Agency finalized its guidance10 for 

assessing risks to bees. EPA now requires this study for all use sites where potential exposure to 

pollinators may occur. Although EPA has not developed a guideline for this study and OECD has yet to 

finalize test guidance for chronic studies, efforts are currently underway to develop standardized 

guidelines for assessing effects from chronic (10-day) exposures to adult bees in the laboratory. 

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The 10-day toxicity study with young adult bees provides data that will be used in estimating chronic risk 

to individual adult bees. Risk estimates based on these data will be considered along with other lines of 

evidence to determine whether higher-tier studies are needed at the whole colony level.

These data are needed for risk assessments written in support of Registration Review as well as for future 

endangered species assessments. These data would allow the Agency better characterize the potential for 

risk to insects (including beneficial pollinators) from the use of picolinic acids-class chemicals. These data 

may help the Agency determine whether any mitigations are needed. If the Registration Review and any 

future endangered species risk assessments are performed without these data, the Agency would have to 

 

9

Ibid USEPA 2014.

10 Ibid USEPA et al. 2014.
Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

assume that picolinic acids-class chemicals "may affect" insects, including bees and beneficial pollinators, 

directly (and endangered species from other taxa indirectly), and uses of aminopyralid might need to be 

restricted in areas where pollinators could be exposed. 

Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed to evaluate the potential effects of technical grade active ingredient (TGAI) honey 

bee larvae from repeat exposure. Aminopyralid is registered for use on a variety of agricultural, forest, 

commercial, and residential areas and may be applied via aircraft, ground sprayer, hand-held sprayer, and 

boom sprayer. Aminopyralid may also be applied to forest plantings via broadcast, high volume spray, 

spot treatment, stump treatment, girdle treatment, frill treatment, tree wound treatment, and tree injection. 

Some of these uses may result in exposure to blooming non-target plants and could result in residues in 

pollen and nectar (which could then be transported to the hive). Additionally, aminopyralid is highly 

persistent and, like other members of the picolinic acid family, is systemic and can be translocated to 

pollen and/or nectar via transport through both xylem and phloem tissues of plants. Although 

aminopyralid uptake is primarily through the foliage, root uptake is also possible. Therefore, 

aminopyralid residues may be present in pollen and nectar either through transport from leaf tissues

affected by spray drift or from root uptake in plants grown where aminopyralid was previously applied. 

Residues can in turn be brought back to bee colonies where in-hive bees including young adult and 

developing brood (i.e., eggs, larvae and pupae) may be exposed. Therefore, exposure at all bee life stages 

may occur. 

Since the preliminary Problem Formulation11 was completed, the Agency finalized its guidance12 for 

assessing risks to bees. EPA now requires this study for all use sites where potential exposure to 

pollinators may occur. Although EPA has not developed a guideline for this study, the 21-day larval 

toxicity study currently under development by OECD13 provides a draft guidance protocol for potentially 

assessing both the acute and chronic toxicity to developing brood (larvae and pupae) from repeat exposure 

to pesticides. 

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The 21-day toxicity study provides data on the effects of technical grade active ingredient (TGAI) on 

developing bees from acute (short-term) and chronic (longer term) exposure and will be used for estimating 

risk to individual (solitary) bees as well as bee colonies (social bees). Risk estimates based on these data 

will be considered along with other lines of evidence to determine whether higher-tier studies are needed at 

the whole colony level.

These data are needed for risk assessments written in support of Registration Review as well as for future 

endangered species assessments. These data would allow the Agency better characterize the potential for 

 

11 Ibid USEPA 2014.

12 Ibid USEPA et al. 2014.

13 OECD. 2013. OECD Draft Guidance Document Honey Bee (Apis mellifera) Larval Toxicity Test, Repeated Exposure. Revision of June 2013 

draft GD, 25 November 2013. http://www.oecd.org/env/ehs/testing/Draft_GD_honeybees_rep_exp_for_2nd_CR_25_November_2013.pdf
Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

risk to insects (including beneficial pollinators) from the use of picolinic acids-class chemicals. These data 

may help the Agency determine whether any mitigations are needed. If the Registration Review and any 

future endangered species risk assessments are performed without these data, the Agency would have to 

assume that picolinic acids-class chemicals "may affect" insects, including bees and beneficial pollinators, 

directly (and endangered species from other taxa indirectly), and uses of aminopyralid might need to be 

restricted in areas where pollinators could be exposed. 
Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Acute and Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed for the assessment to evaluate risks to honey bees if the registered uses will result in 

bee exposure. Aminopyralid is registered for use on a variety of agricultural, forest, commercial, and 

residential areas and may be applied via aircraft, ground sprayer, hand-held sprayer, and boom sprayer. 

Aminopyralid may also be applied to forest plantings via broadcast, high volume spray, spot treatment, 

stump treatment, girdle treatment, frill treatment, tree wound treatment, and tree injection. Some of these 

uses may result in exposure to blooming non-target plants and could result in residues in pollen and nectar 

(which could then be transported to the hive). Additionally, aminopyralid is highly persistent and, like 

other members of the picolinic acid family, is systemic and can move in both xylem and phloem. 

Although aminopyralid uptake is primarily through the foliage, root uptake is also possible. Therefore, 

aminopyralid residues may be present in pollen and nectar either through transport from leaf tissues 

affected by spray drift or from root uptake in plants grown where aminopyralid was previously applied. 

Residues can in turn be brought back to bee colonies where in-hive bees including young adult and 

developing brood (i.e., eggs, larvae and pupae) may be exposed. Therefore, exposure at all bee life stages 

would be expected. 

Since the Problem Formulation was completed, the Agency finalized its framework to assess risk to 

pollinators (USEPA, 2014). EPA now requires this study for all use sites where potential exposure to 

pollinators may occur. Registrants may request a waiver of the study if use practices significantly restrict 

exposure of the pesticide to bees.

Although EPA has not developed a guideline for this study, the 21-day larval toxicity study currently 

under development by OECD provides both acute and chronic oral toxicity data on developing bee brood 

and (when this guidance is finalized) may be used to satisfy the requirement for both acute and chronic 

oral toxicity to honey bee larvae. Registrants are at liberty though to submit a separate acute (single dose) 

larval toxicity study following OECD TG 237 as well as the 21-day repeat dose chronic toxicity study. 

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The 21-day larval toxicity study under development by OECD provides both acute and chronic toxicity 

data on developing bee brood and will yield a median lethal dose (LD50) for assessing acute toxicity 

during the early part of the study as well as a 21-day no-observed adverse effect level (NOAEL) and 

lowest-observed adverse effect level (LOAEL) for assessing chronic effects. Effects on survival and 

development (adult bee emergence) from repeat exposures to the active ingredient will be used in 

estimating chronic risk to individual brood. Risk estimates based on these data will be considered along 

with other lines of evidence to determine whether higher-tier studies are needed at the whole colony level.

These data are needed for the registration review risk assessment and for future endangered species 

assessments. The data would allow the Agency better characterize the potential for risk to insects 

(including beneficial pollinators) from the use of picolinic acids-class chemicals. This data may help the 

Agency determine whether any mitigations are needed. If the registration review and any future 

endangered species risk assessments are performed without these data, the Agency would have to assume 

that picolinic acids-class chemicals "may affect" insects, including bees and beneficial pollinators, directly 

(and endangered species from other taxa indirectly), and uses of aminopyralid might need to be restricted 

in areas where pollinators could be exposed.