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UNITED STATES EI\VIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C..20460

PC Code: 080803

DP Barcode: 415839

MEMORANDUM December 6,2013

Subject:

To:

From:

Environmental Fate and Effects Division's Response to Public Comments on

the Registration Review Preliminary Problem Formulation for Atrazine

Kaitlin Keller, Chemical Review Manager

Patricia Parrott, Branch Chief

Risk Management and Implementation Branch III

Pesticide Re-evaluation Division (7508P)

Frank Famrggia, Ph.D., Biologist

Amy Blankinship, M.S., Chemist

James Hetrick, Ph.D., Senior Advisor

Environmental Risk Branch III

Environmental Fate and Effects Division (7507P)

Through: te-lalzDr s

Environmental fusk Branch III

Environmental Fate and Effects Division (7507P)

This document contains the Environmental Fate and Effects Division's (EFED's) responses to

comments received on the Atrazine Registration Review Preliminary Problem Formulation

(EPA-HQ-OPP-2013-0266). Comments have been organized according to the following

topic areas; 1) effects on aquatic plants, 2) ecotoxicity to animals, 3) bias factors, and 4)

endangered species risk assessment and protection. Comment summaries and EPA's

response to comments are shown below.

Effects on Aquatic Plants

1. Comment Summary (Syngenta): There is research available demonstrating the

recovery of aquatic plants from atrazine exposure. A list of publications was

provided.

EFED Response: As described in the 2012 FIFRA Scientific Advisory Panel (SAP)

white paper (USEPA 2012) and in the addendum to the Problem Formulation

(USEPA 2013) for the Preliminary Risk Assessment, EFED intends to consider the

Dana Spatz, Branch Cfti.f$

Rosanna Louie-Juzwiak, Ri sk Asse3sment Process
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potential for recovery of individual species after exposure to atrazine has stopped, and 

considers the recovery of communities to be quite different than that of the individual 

species. EFED will consider the literature that was cited by Syngenta in their 

comments as part of the preliminary risk assessment.

2. Comment Summary (Syngenta): A comprehensive scientific evaluation of the 

micro/mesocosm dataset was completed by Giddings in 2012 and provided several 

conclusions that Syngenta and Giddings presented to the SAP in 2012. 

EFED Response: As stated in the Addendum to the Problem Formulation (USEPA 

2013), EPA will consider the information presented during the SAP, including the 

Giddings 2012 report, and will also evaluate and include, as appropriate, additional 

studies prior to conducting the preliminary risk assessment. 

3. Comment Summary (Syngenta): An evaluation of the sensitivity of the EPA’s 

methodology for specifying an LOC for atrazine using the PATI model indicated that 

the model is sensitive to the cosm studies included and their scoring. Additionally, 

assessment periods in the initial dataset identified by EPA were sometimes outside of 

the assessment window. The Giddings 2012 report provides the most accurate 

representation of the toxicity data. 

EFED Response: As stated in the Addendum to the Problem Formulation (USEPA 

2013), EPA will consider the information presented during the SAP, including the 

Giddings 2012 report regarding the sensitivity of the CE-LOC methodology to cosm 

study selection, duration and scoring. 

4. Comment Summary (Syngenta): A few additional community-scale research 

projects are underway or have been completed: research on periphyton, aquatic 

macrophytes, benthic communities, and physical habitats of midwestern streams have 

been conducted; ongoing research investigating the sensitivity and potential recovery 

of native periphyton communities following an atrazine exposure.

EFED Response: EPA will be conducting a literature search prior to writing the 

preliminary risk assessment, and will also evaluate and include, as appropriate,

submitted studies.

Ecotoxicity of Atrazine to Animals

1. Comment Summary (Anonymous commenter (1jx-8792-ton7); Center for 

Biological Diversity; Beyond Pesticides; Public commenter, L. Markham; 

Syngenta): There were numerous comments that included open literature citations 

regarding testing of atrazine on aquatic and terrestrial organisms.

EFED Response: EFED will consider these studies for inclusion in the preliminary 

risk assessment for the registration review of atrazine.
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2. Comment Summary (Syngenta): Syngenta supports the approach proposed by the 

EPA (pg 11 of Addendum to the Atrazine Problem Formulation) regarding a 

comprehensive evaluation of the large data set of amphibian studies using atrazine. A 

publication manuscript regarding an analysis based on a quantitative weight of 

evidence approach of the available atrazine testing with amphibians will be provided 

to the EPA. 

EFED Response: EFED will evaluate and consider the weight of evidence approach 

presented by Syngenta as EFED develops an integrated and comprehensive approach 

for evaluating the large set of toxicity data available for amphibians.

3. Comment Summary (Syngenta): An analysis of available amphibian data was 

provided to evaluate potential differences in sensitivities with regard to Xenopus 

laevis and native species of North American amphibians (topic discussed on pg 13 of 

Addendum to the Atrazine Problem Formulation). These analyses included 

discussion of the relative sensitivity to estradiol, sex ratio, and other metrics 

considered as part of the Weight of Evidence analysis that will be submitted to EPA.

EFED Response: EFED will consider these data provided in the sensitivity analyses 

and will continue to gather information by searching the open literature for papers 

that may be useful in elucidating relevant pathways in amphibian species, as well as 

potential differences between them.

Development and Use of Bias Factors

1. Comment Summary (Syngenta): Bias factor estimation should account for 

watershed characteristics, toxicity endpoint, and sampling design. Syngenta has 

conducted research to show that the magnitude of bias factors is dependent on 

normalize flow (reservoirs vs. flowing water), size of watershed, averaging time of 

the toxicity endpoint, and sampling design (Mosquin et al., 2011 a, b; Chen and 

Mosquin, 2012; Chen et al., 2013). 

EFED Response: EFED’s proposed approach for the development of bias factors is 

to consider the hydrology (reservoirs versus flowing water), data interpolation 

methods, sampling strategy (systematic versus stratified random), and averaging time 

of the toxicity endpoint (60-day average). EFED also will evaluate the referenced 

research papers (Mosquin et al., 2011 a, b; Chen and Mosquin, 2012; Chen et al., 

2013) on the relationship of bias factors to watershed size and flow to consider as part 

of the development of bias factors. 

2. Comment Summary (Syngenta): Bias factor-estimated concentrations should be 

compared to the upper confidence bounds of the highest percentile (e.g., 99%) values 

statistically inferred from relevant historical multiple year and site data (Mosquin et 

al., 2012). This comparison provides a ground-truth of bias factor estimates with 

quantified uncertainty. 
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EFED Response: EFED will evaluate the proposed statistical methods in Mosquin et 

al., 2012 for attempting to quantify the uncertainty in the bias factor-adjusted

concentration.

3. Comment Summary (Syngenta): Bias factor-estimated concentrations should not 

be used to identify vulnerable watersheds for atrazine runoff. Syngenta recommends 

that the use of models (e.g., PRZM Hybrid) incorporating environmental and 

agronomic factors in conjunction with extensive monitoring data (USGS and AEMP) 

is the most appropriate approach for selection of vulnerable watersheds.

EFED Response: EFED proposed that watershed vulnerability be determined using 

the same criteria used in selection of Atrazine Ecological Monitoring Program 

(AEMP) monitoring sites. As noted in the Addendum to the Problem Formulation, if 

watershed properties are outside the range of the criteria used for selection of AEMP 

monitoring sites, then an evaluation of available monitoring data using appropriate 

bias factor adjustments or modeling approaches (Corn Belt WARP, National WARP, 

SEAWAVE) are proposed for assessing the need for additional monitoring within the 

watershed. These monitoring data would provide appropriate data to assess watershed 

vulnerability. 

4. Comment Summary (Syngenta): Data based regression models (such as 

SEAWAVE, WARP, etc.) are a valid approach for estimating daily atrazine

concentrations from monitoring data or non-monitored watersheds. However, the 

regression models need to be thoroughly evaluated and validated against all available 

measured data from the AEMP, AMP, and other monitoring programs. Syngenta

recommends that 10 to 20 data points for each parameter are needed to provide a 

statistically robust estimate from regression models (Harrell, 2000). 

EFED Response: EFED agrees and will explore the potential use of regression 

models (SEAWAVE, Corn Belt WARP, National WARP) for estimating daily 

atrazine concentrations. 

EFED Response to Comments Related to Endangered Species Risk Assessment and 

Protection

EPA has reviewed the comments from Center for Biological Diversity, Environmental Law 

and Policy Center, Center for Regulatory Effectiveness, and Syngenta on the registration 

review docket openings for atrazine and plans to address many of the concerns raised as part

of the implementation plan for assessing the risks of pesticides to listed species based on the 

recommendations of the April 2013 National Academy of Sciences (NAS) report. EPA will 

address concerns specific to atrazine in connection with the development of its registration 

review decision for atrazine. 

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 
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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 jointly by the Agencies 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 is presenting 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 atrazine 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.
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Literature Cited

Chen, Wenlin and, Paul Mosquin, Impact of Alternative Monitoring Frequencies on Estimation of 

Atrazine Rolling Average Environmental Concentrations. Addendum to MRID 48550601. Final 

Report Addendum 2. May 29, 2012.

Chen, Wenlin, Paul Mosquin, and Clint Truman. 2013. Sampling Bias Factors: Compensation for 

“Missing the Peak”. CropLife America RISE Spring Conference. Washington, DC.

Harrell, F.E. Jr. 2001. Regression Modeling Strategies. Springer. New York

Giddings, J.M. 2012. Atrazine: Review of Mesocosm and Microcosm Studies. Project Report 

Number: 12709. Compliance Services International (CSI).

Mosquin, Paul, Roy Whitmore, and Wenlin Chen. 2012. Estimation of Upper Centile Concentrations 

Using Historical Atrazine Monitoring Data from Community Water Systems. J. Environmental 

Quality. 41:834-844.

Mosquin, Paul, Roy Whitmore, and Wenlin Chen. Impact of Alternative Monitoring Frequencies on 

Estimation of Atrazine Rolling Average Environmental Concentrations. Report No. TK0038002, 

Task No. : TK0038002. April 29, 2011a.

Mosquin, Paul, Roy Whitmore, and Wenlin Chen. Impact of Alternative Monitoring Frequencies on 

Estimation of Atrazine Rolling Average Environmental Concentrations. Addendum to MRID 

48470008. Report No. TK0038002, Task No. : TK0038002. Final Report Addendum. July 19, 

2011b.

U.S. Environmental Protection Agency (USEPA). 2012. Problem Formulation for the Environmental 

Fate and Ecological Risk Assessment for Atrazine. White Paper for the FIFRA Scientific Advisory 

Panel, June 12 - 14, 2012. 

U.S. Environmental Protection Agency (USEPA). 2013. Addendum to the Problem Formulation for 

the Ecological Risk Assessment to be Conducted for the Registration Review of Atrazine.