UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

PC Code: 061402 

DP Barcode: D418766 

Date: April23, 2014 

MEMORANDUM 

SUBJECT: Response to Public Comments on the Acibenzolar-S-methyl Registration Review 

Problem Formulation 

TO: 

FROM: 

Dana Friedman, Chemical Review Manager 

Cathryn Britton, Team Leader 

Risk Management and Implementation Branch II 

Pesticide Re-Evaluation Division 

Office ofPesticide Programs (7508P) 

MichaelLowit,Ph.D.,Ecologist /~ ~i;/f Stephen Wente, Ph.D., Biologist~ ' ~ Lf ~J' f;y 

Meghan Radtke, Ph.D., Acting RAPL ~ 'f(~JL'f/' 

Sujatha Sankula, Ph.D., Branch Chief~~ 6.., t.n' J..c, ~ '1/J.J//'f 

Environmental Risk Branch I f D'O• 

Environmental Fate and Effects Division (7507P) 

Office ofPesticide Programs 

In response to the "Registration Review: Preliminary Problem Formulation for Environmental 

Fate, Ecological Risk, Endarigered Species, and Drinking Water Exposure Assessments for 

Acibenzolar-S-methyl" (DP413831), the registrant, Syngenta Crop Protection, and the Center for 

Biological Diversity submitted comments during the public comment period. The purpose of 

this memorandum is to address these comments. 

Comments by Syngenta Crop Protection 

Comment#l: 

The preliminary work plan issued in December 2013 requests an Environmental Chemistry 

Method for analysis of acibenzolar-S-methyl and CGA-21007 in water and a corresponding 

independent laboratory validation (ILV) of the method(s). Presumably, the origin of this 

requirement stems from Guideline Number 835.6200 for Aquatic Field Dissipation Studies. 

Guideline Number 835.6200 states that an independent laboratory validation should be provided 

for the method used to actually generate the aquatic dissipation data submitted. However, no 

aquatic dissipation studies were conducted or submitted based upon the use pattern; therefore, 

provision of a water method and an independent laboratory validation (IL V) should not apply. 
2

Therefore, Syngenta respectfully requests a waiver of the requirement to provide an applicable 

Environmental Chemistry Method and ILV for analysis of acibenzolar-S-methyl and CGA21007 

in water. (Syngenta Crop Protection, p. 2). 

EPA Response #1: 

Both the soil and water environmental chemistry methods (ECMs) are required for monitoring 

and enforcement purposes. If, for example, a spill of acibenzolar-S-methyl were to occur, a 

responsible agency would have an immediate need for methods for measuring residues in 

affected soils and surface and/or groundwater. The methods that registrants submit can be found 

at: http://www.epa.gov/pesticides/methods/ecm-a.html. This website has soil ECMs for 

acibenzolar-S-methyl and CGA-2100007, but no water ECMs for either chemical. The 

independent laboratory validation (ILV) studies ensure that the methods can be used as written in 

the ECM. 

Comment #2: 

EPA statements: Anticipated Data Needs for the CGA-210007 Degradate Avian reproduction 

test (bobwhite quail) (PWP Page 5, Table 1) 

“For instance, recent risk assessments stated that there would be a chronic risk concern if CGA210007 is about 2-15X more toxic than acibenzolar-S-methyl which caused effects to birds in one 

of the available reproduction studies. On the other hand, chemical structures suggest that CGA210007 is more likely than acibenzolar-S-methyl to be excreted in urine.” (PWP Page 21, 

Paragraph 2) 

Animal metabolism data for birds (Rumbeli 1996) and mammals (MRID 44014250) indicate that 

once ingested, acibenzolar-S-methyl is rapidly metabolized to CGA-210007 and therefore data 

from experiments conducted with acibenzolar-S-methyl are applicable for evaluating the 

biological effects of CGA-210007. This conclusion is based on the fact that internal exposure 

would be expected to be the same whether birds and mammals directly ingest CGA-210007 or 

alternatively ingest acibenzolar-S-methyl and then rapidly metabolize it to CGA-210007. The 

similar metabolic pathways and rapid breakdown of acibenzolar-S-methyl to CGA-210007 in 

birds and mammals, coupled with consistent findings that demonstrate markedly lower biological 

activity of CGA-210007 relative to acibenzolar-S-methyl in aquatic organisms (Table 4 of PPF), 

provide a strong basis that CGA-210007 poses no greater potential risk to birds and mammals 

compared to acibenzolar-S-methyl. 

Screening level evaluations using T-REX v.1.5.2 for foliar applications indicate that the avian 

chronic reproduction NOEC value for CGA-210007 would have to be markedly lower to cause 

any screening level exceedances for ecological risk assessment. For instance, output from TREX v.1.5.2 indicated that the highest predicted exposure on dietary items for foliar labelled 

uses is based on 4 applications at 0.0625 lb/A with 7-day intervals (default foliar half-life of 35 

days assumed). Relative to the avian reproduction NOEC value for bobwhite quail exposed to 

acibenzolar-S-methyl (600 mg/kg-diet; MRID 44537009), estimates of screening level exposure 

for this use indicate that the NOEC value for CGA-210007 would have to be 12 – 100 X lower 

(more sensitive) in order to exceed listed species LOC values. 
3

The highest predicted exposure based on a screening level evaluation of seed treatments is 

associated with the sunflower seed treatment. Using the seed treatment module of T-REX 

v.1.5.2, calculations indicate that the NOEC value for bobwhite quail with CGA-210007 would 

have to be 2 X lower (more sensitive) than the respective value for the parent acibenzolar-Smethyl (600 mg/kg-diet; MRID 44537009). It is important to note that assumptions of exposure 

associated with the seed treatment module of T-REX v.1.5.2 are highly conservative as it 

assumes terrestrial organisms ingest the entire seed treatment dose (mg ai/kg seed), and subsist 

for 5 months exclusively on a diet treated with the test item. Literature studies demonstrate that 

many small birds and mammals display a dehusking behavior, in which only the internal fruit is 

extracted and ingested, whereas the outer fibrous protective seed coat of sunflower seeds are 

discarded (Avery et al. 1997, Bruhl, et al. 2011). Minimal exposure may occur as animals handle 

treated seeds during the dehusking process, studies reported in the peer-reviewed literature 

indicate that the amount of active ingredient ingested is only a small fraction of that applied to a 

sunflower seed. During studies examining potential exposure associated with seed treatments to 

granivourous birds, Avery et al. 1997 determined that > 65% of the chemical that is applied to 

sunflower seed is left on the husks after birds handle the seed. 

The rapid metabolism of ingested acibenzolar-S-methyl to CGA-210007 by birds provides strong 

evidence that additional toxicity testing with CGA-210007 is unlikely to prove valuable to the 

ecological risk assessment of acibenzolar-S-methyl. Available data for acute oral (MRID 

44537005, MRID 44537004) and acute dietary toxicity studies (MRID 44537006, MRID 

44537008) indicate that acibenzolar-S-methyl is practically non-toxic to birds. Chronic 

reproductive studies with acibenzolar-S-methyl also show no effects to mallard ducks at 1000 

mg/kg-diet, the highest concentration tested (MRID 44537010). Effects to bobwhite quail were 

reported only at the highest dietary exposure concentration tested (1000 mg/kg-diet; MRID 

44537009), with a NOEC of 600 mg/kg-diet. While these studies were all initiated with 

acibenzolar-S-methyl, data from metabolism studies provide strong evidence that the test 

material is rapidly converted to CGA-210007 after birds were administered doses or consumed 

treated-diets. Given the transient nature of acibenzolar-S-methyl in birds, coupled with the fact 

that avian NOEC values for CGA-210007 would have to be markedly lower than those for 

acibenzolar-S-methyl in order to demonstrate risk based on highly conservative screening level 

assessments, there is strong evidence that avian chronic reproductive studies with CGA-210007 

will not provide additional information of value for the acibenzolar-S-methyl ecological risk 

assessment. Syngenta respectively requests that the Agency not include the bobwhite 

reproduction study with CGA-210007 as a data gap on the GDCI. (Syngenta Crop Protection, p. 

3-4). 

EPA Response #2: 

The registrant suggests that internal exposure would be expected to be the same whether birds 

and mammals directly ingest CGA-210007 or alternatively ingest acibenzolar-S-methyl and then 

rapidly metabolize it into CGA-210007. This assumes that acibenzolar-S-methyl is rapidly 

metabolized to CGA-210007 relative to the CGA-210007 excretion rate (alternatively, slow 

metabolism and rapid excretion would lead to lower exposure to CGA-210007). The cited rat 

metabolism study (MRID 44014250) and the physical-chemical properties of acibenzolar-Smethyl support the idea that acibenzolar-S-methyl should be metabolized to CGA-210007. 

However, blood concentrations were reported in terms of total radioactivity rather than 

individual chemicals and a time series was not presented showing the formation of CGA-210007. 
4

This type of information or other lines of evidence (e.g., the rate of hydrolysis of the thiol ester) 

would be useful for evaluating the amount of exposure to CGA-210007 from direct ingestion of 

acibenzolar-S-methyl. If the registrant has other data pertinent to this issue then EFED will take 

it into consideration. 

Mammals and birds may show differences in metabolism so EFED will consider whether or not 

the avian metabolism study (Rumbeli, 1996) provides sufficient information about avian 

exposure to CGA-210007 from direct ingestion of acibenzolar-S-methyl. 

The seed treatment exposure scenario does not assume that terrestrial organisms subsist for 5 

months exclusively on a diet treated with the test item. The exposure scenario assumes the peak 

concentration and that reproductive effects could occur from either a short or long duration 

exposure (reproductive effects may occur from a short duration exposure based on the timing of 

the exposure within the reproductive period). EFED acknowledges that some birds and 

mammals may de-husk seeds; however, this may not be the case for all species and the degree to 

which exposure may be reduced will vary by species and perhaps individual. 

Comment #3: 

EPA statement: Referenced endpoint for aquatic non-vascular plant studies was presented as 

cell density. (PF Page 11, Table 3) 

Effect concentrations (ECx) calculated based on growth rate are considered more robust than 

those based on standing crop (cell density and biomass) for a given time-point because growth 

rate is independent of exposure time (US EPA 2012). For aquatic plants, study duration, 

conditions of temperature, light, and nutrients, and reported endpoints can vary considerably 

among studies. In addition, other resource-limiting factors, such as nutrient depletion and selfshading, can complicate the interpretation of reported plant ECx values. These factors may affect 

study results, which could result in misleading estimates in certain cases for some species (US 

EPA 2012). Using cell density or absolute biomass can potentially result in particularly 

misleading ECx values when growth rates are modest, and a departure from exponential growth 

will be most pronounced in the treatments with the highest growth rates (US EPA 2012). With 

respect to toxicity testing, differences in design of the study can result in complicated growth 

dynamics and relationships that are difficult to interpret (US EPA 2012). 

As indicated by Bergtold and Dohmen (2011), growth rate is the appropriate endpoint in the 

Lemna and algal toxicity test guidelines (OECD 2006a,b). Specifically, in the OECD 221 

guideline for testing growth inhibition in freshwater alga and cyanobacteria (OECD 2006a), it 

states: 

“ECx values based upon average specific growth rate (ErCx) will generally be higher 

than results based upon yield (EyCx) if the test conditions of this Guideline are adhered 

to, due to the mathematical basis of the respective approaches. This should not be 

interpreted as a difference in sensitivity between the two response variables, simply that 

the values are different mathematically. The concept of average specific growth rate is 

based on the general exponential growth pattern of algae in non-limited cultures, where 

toxicity is estimated on the basis of the effects on the growth rate, without being 
5

dependent on the absolute level of the specific growth rate of the control, slope of the 

concentration-response curve or on test duration. In contrast, results based upon the yield 

response variable are dependent upon all these other variables. Yield is dependent on the 

specific growth rate of the algal species used in each test and on the maximum specific 

growth rate that can vary between species and even different algal strains. This response 

variable should not be used for comparing the sensitivity to toxicants among algal species 

or even different strains.” 

Based on the aforementioned information, Syngenta suggests that relative growth rate results are 

more scientifically appropriate and should be used for ecological risk assessment of aquatic 

plants. (Syngenta Crop Protection, p. 4-5). 

EPA Response #3: 

EFED will consider this approach in future risk assessments. 

Comment #4: 

EPA statement: “CGA-210007 toxicity to birds and mammals is unknown and will be assumed equal to 

that of acibenzolar-S-methyl in the absence. However, there is no basis at this time for characterizing a 

level of confidence in the assumption that CGA-210007 is not more toxic than acibenzolar-S-methyl to 

birds and mammals.” (PF Page 17, Paragraph 3) 

It is important to consider the available animal metabolism data while evaluating the ecological 

risk associated with environmental exposure of CGA-210007 to birds and mammals. CGA210007 has been identified as a degradate in both environmental fate and animal metabolism 

studies. Once ingested, acibenzolar-S-methyl parent is rapidly metabolized to CGA-210007, and 

therefore data from experiments conducted with acibenzolar-S-methyl are applicable for 

evaluating the biological effects of CGA-210007. This conclusion is based on the fact that 

internal exposure would be expected to be the same whether birds and mammals directly ingest 

CGA-210007 or alternatively ingest acibenzolar-S-methyl and then rapidly metabolize it to 

CGA-210007. 

A previously-submitted study on the metabolism of acibenzolar-S-methyl (MRID 44014250) is 

particularly relevant for evaluating dietary routes of exposures as the results demonstrate that 

acibenzolar-S-methyl is rapidly and completely absorbed in the gastrointestinal tract of rats. In 

this metabolism study with adult rats, 99+% of acibenzolar-S-methyl is absorbed, while small 

amounts, not exceeding 1% of the dose, are excreted unchanged with the feces. The dose 

absorbed is hydrolyzed to yield the corresponding carboxylic acid derivative (CGA-210007) and 

readily excreted (82-96% of the dose received) renally. A small amount of the acid, less than 3% 

of the dose, is eliminated via feces. A second minor portion (<2%) of the acid is conjugated with 

glycine and then renally eliminated. The metabolic fate of acibenzolar-S-methyl is quantitatively 

independent of gender and dose level and is not influenced by pretreatment of the compound. 

In a metabolism study with birds (Rumbeli 1996), laying hens administered oral doses of 

acibenzolar-S-methyl demonstrated the same rapid metabolism of acibenzolar-S-methyl to CGA210007 as rats. Syngenta will submit the laying hen metabolism study for EPA review. The 

aforementioned similar metabolic pathways and rapid breakdown of acibenzolar-S-methyl to 

CGA-210007 in birds and mammals, coupled with consistent findings that demonstrate markedly 
6

lower biological activity of CGA-210007 relative to acibenzolar-S-methyl in aquatic organisms 

(Table 4 of PPF), provide a strong basis that CGA-210007 poses no greater potential risk to birds 

and mammals compared to acibenzolar-S-methyl. (Syngenta Crop Protection, p. 5-6). 

EPA Response #4: 

Please see EPA Response #2. 

Comment #5: 

EPA statement: “This assessment will be conducted in accordance with the Overview Document 

(USEPA, 2004), provisions of the ESA, and the Services’ Endangered Species Consultation 

Handbook (USFWS and NMFS, 1998).” (Page 18) 

Simple deterministic screening level assessments, which are highly conservative by design, can 

facilitate rapid initial screening/exclusion criteria for a pesticide active ingredients’ potential to 

adversely affect listed (threatened or endangered species) and non-listed species. If a pesticide 

exposure results in a risk quotient (RQ) below a predefined level of concern (LOC), which are 

additionally conservative with respect to endangered (listed) species assessments (e.g. 5x to 10x 

lower than already conservative non-listed LOCs), then the potential risks are considered de 

minimis and unlikely to jeopardize the existence of a listed species. Thus by design, such 

compounded layers of conservatism are intended to minimize potential type II errors (failure to 

reject a false null hypothesis of de minimus risk) but correspondingly compound unrealistic 

conditions and assumptions. If, however, an RQ is generated that exceeds the highly 

conservative LOC, additional higher-tier scientific information must be incorporated in order to 

refine the risk assessment and more accurately and realistically reflect potential exposures and 

effects, and reducing potential type I errors (falsely rejecting the null hypothesis of de minimus 

risk). This information includes community-level effects data, environmental fate and exposure 

data, monitoring data, geospatial location and proximity data, species biology data, and a variety 

of refined modelling and assessment analysis, and other pertinent species-specific and pesticidespecific data. Given that ‘risk’ requires estimation of likelihood, higher tier risk assessments 

need to consider and employ probabilistic techniques in order to more accurately and realistically 

characterize risk. Moreover, where possible and appropriate, risk assessments should consider 

assemblage level effects (populations, communities, and ecosystems) rather than singular 

deterministically oriented single species approaches. A summary of the types of higher-tier data 

and assessment refinements available to more accurately and realistically evaluate potential risks 

to endangered species is provided in MRID# 49200601. (Syngenta Crop Protection, p. 6). 

EPA Response #5: 

EFED will conduct the risk assessment on acibenzolar-S-methyl in accordance with policies and 

guidelines pertinent at that time; this includes refinements to the screening level assessment, if 

applicable. 

Comment #6: 

EPA statement: “The most recent drinking water assessment (DWA) in support of human health 

risk assessment was conducted to support the registration of acibenzolar-S-methyl for use on the 

low growing berry subgroup 13-07G (DP 386365).” (Page 4) 
7

A more recent EPA DWA was conducted in support of human health risk assessment (DP 

392519; 12/13/11) to support registration of an Experimental Use Permit on grapefruit, apple and 

pear. Estimated Drinking Water Concentrations from this assessment were used in a 2012 

Human Health risk assessment (DP 396885, 4/25/12) which was cited in the 2013 AcibenzolarS-methyl: Human Health Risk Scoping Document in Support of Registration Review (Syngenta 

Crop Protection, p. 6). 

EPA Response #6: 

EFED should have referred to the drinking water assessment (DWA) referenced by Health 

Effects Division (HED) and Syngenta. Since the completion of the Problem Formulation and 

Human Health Risk Scoping Document, another drinking water assessment was completed – 

“Tier II Drinking Water Assessment for the Proposed Seed Treatment Use of Acibenzolar-Smethyl on Sorghum Seed” (DP 414662; 1/27/14). The Agency will use the most recent DWA at 

the time of the Registration Review risk assessments. 

Comment #7: 

Syngenta provided a list of edits to several chemical and fate properties listed in the problem 

formulation (Syngenta Crop Protection, p. 7). 

EPA Response #7: 

Thank you for the corrections and additional references. EFED will include as appropriate. 

Comments by the Center for Biological Diversity 

Comment #8: 

EPA Has an Independent Duty Under the Endangered Species Act to Consult with the U.S. Fish 

and Wildlife Service and National Marine Fisheries Service on the Reregistration of Acibenzolar 

(Center for Biological Diversity, p. 1). 

...the EPA should begin this review process with the Services immediately after the work plan is 

finalized. (Center for Biological Diversity, p. 2) 

The EPA Must Make Defensible “Not Likely to Adversely Affect” and “Likely to Adversely 

Affect” Determinations as a Prerequisite for Defensible “Jeopardy” and “No Jeopardy” 

Determinations (Center for Biological Diversity, p. 5). 

EPA and the Services Must Assess the Adverse Impacts of Acibenzolar in Critical Habitat 

(Center for Biological Diversity, p. 7). 

EPA Has an Independent Duty Under the Endangered Species Act to Consult with the U.S. Fish 

and Wildlife Service and National Marine Fisheries Service on the Approval of All Acibenzolar 

End-use Product Labels (Center for Biological Diversity, p. 8). 

EPA Response #8: 

EPA plans to address many of the concerns raised in the comments from Center for Biological 

Diversity as part of the implementation plan for assessing the risks of pesticides to listed species 
8

based on the recommendations of the April 2013 National Academy of Sciences (NAS) report. 

EPA will address concerns specific to acibenzolar-s-methyl in connection with the development 

of its registration review decision for acibenzolar-s-methyl. 

 

The NAS report, available at http://www.nap.edu/catalog.php?record_id=18344, outlines 

recommendations on specific scientific and technical issues related to the development of 

pesticide risk assessments that are compliant with the Endangered Species Act and the Federal 

Insecticide, Fungicide, and Rodenticide Act. In November, the EPA, along with the U.S. Fish & 

Wildlife Service (USFWS), the National Marine Fisheries Service (NMFS) (collectively, the 

Services), and the U.S. Department of Agriculture (USDA), released a summary of their joint 

Interim Approaches for assessing risks to listed species from pesticides. The Interim Approaches 

were developed in response to the NAS’ recommendations and reflect a common approach to 

risk assessment shared by the Agencies as a way of addressing scientific differences between 

EPA and the Services. The joint Interim Approaches were released prior to the stakeholder 

workshop held on November 15, 2013. EPA presented the joint Interim Approaches at the 

December 2013 PPDC and SFIREG meetings, allowing additional opportunities for stakeholders 

to comment on the Interim Approaches. The Agencies will consider public comments on the 

Interim Approaches prior to implementing them. The Agencies intend to jointly implement these 

approaches as part of a phased iterative process. EPA will refine its listed species risk 

assessments based on these interim approaches. The details of the joint Interim Approaches are 

contained in the white paper “Interim Approaches for National-Level Pesticide Endangered 

Species Act Assessments Based on the Recommendations of the National Academy of Sciences 

April 2013 Report,” dated November 1, 2013, available at 

http://www.epa.gov/espp/2013/nas.html. 

Regarding the Center for Biological Diversity's request for EPA to begin informal consultation 

with the Services immediately after the workplan for acibenzolar-s-methyl is finalized, EPA 

plans to follow the March 2013 stakeholder engagement paper (“Enhancing Stakeholder Input in 

the Pesticide Registration Review and ESA Consultation Processes and Development of 

Economically and Technologically Feasible Reasonable and Prudent Alternatives”) to identify 

the appropriate time for initiation of consultation, either formal or informal, with the Services. 

The stakeholder engagement paper, jointly developed by the EPA, USDA, and the Services and 

available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0442-0038, 

allows for early interaction with the Services under informal consultation. EPA and the Services 

acknowledge that early interaction as part of informal consultation may result in refinements to 

EPA’s effects determinations that can improve the efficiency of the ESA compliance process. 

For example, EPA may involve the Services at the earliest stages of registration review. In 

general, EPA plans to initiate formal ESA consultation, if necessary, at the final decision stage in 

the registration review process. Consulting later in the process allows the EPA to develop more 

refined ecological risk assessments and to engage stakeholders in discussions that should result 

in more focused consultation packages that may include risk mitigation for listed species. 

References 

Avery, M.L., D.L. Fischer, and T.M. Primus. 1997. Assessing the hazard to grainivorous birds 

feeding on chemically treated seeds. Pestic. Sci. 49: 362-366. 
9

Bruhl, C.A., B. Guckenmus, M. Ebeling, and R. Barfknecht. 2011. Exposure reduction of seed 

treatments through dehusking behaviour of the wood mouse (Apodemus sylvaticus). 

Environ. Sci. Pollut. Res. 18: 31-37. 

Bergtold, M. and G.P. Dohmen. 2011. Biomass or growth rate endpoint for algae and aquatic 

plants: Relevance for the aquatic risk assessment of herbicides. Integr Environ Assess 

Manag 7(2) 237-247. 

OECD (Organization for Economic Cooperation and Development). 2006a. OECD Guideline 

201: Freshwater alga and cyanobacteria, growth inhibition test. Adopted 23 March 2006. 

Paris. 

OECD (Organization for Economic Cooperation and Development). 2006b. OECD Guideline 

221: Lemna sp. growth inhibition test. Adopted 23 March 2006. Paris. 

Rumbeli, R. 1996. Metabolism of [Phenyl-(U)14C]CGA 245705 after multiple oral 

administration to laying hens. Unpublished report by Ciba-Geigy Ltd., Basel, 

Switzerland. 

US EPA, 2012. Proposed Methodology for Specifying Atrazine Levels of Concern for Protection 

of Plant Communities in Freshwater Ecosystems. Report To: Environmental Fate and 

Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency, 

Washington, DC. EPA/600/R-12/019. Mid-Continent Ecology Division, National Health 

and Ecological Effects Laboratory, Office of Research and Development, U.S. 

Environmental Protection Agency, Duluth, MN. March 5, 2012.