1

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 122019

DP Barcode: 428641

August 17, 2015

MEMORANDUM 

SUBJECT: Response to Comments on the Preliminary Environmental Fate and Ecological 

Risk Assessment for the Registration Review of Propoxycarbazone-sodium

FROM: Elyssa Arnold, Biologist, Risk Assessment Process Leader

James Lin, Environmental Engineer

Environmental Risk Branch 2

Environmental Fate and Effects Division (7507P)

THROUGH: Brian Anderson, Branch Chief

Environmental Risk Branch 2

Environmental Fate and Effects Division (7507P)

TO: Marianne Mannix, Chemical Review Manager

Avivah Jakob, Team Leader

Neil Anderson, Acting Branch Chief

Risk Management and Implementation Branch 3

Pesticide Re-evaluation Division (7508P)

Attached please find the Environmental Fate and Effects Division’s Response to Comments on 

the Preliminary Environmental Fate and Ecological Risk Assessment for the Registration Review 

of propoxycarbazone-sodium. Comments addressed in this document were submitted by Bayer 

Crop Science in Docket No. EPA-HQ-OPP-2015-0095.
2

EFED Response to Comments from Bayer CropScience on the Preliminary Risk 

Assessment for the Registration Review of Propoxycarbazone-sodium

Comment 1: Table 3.6, page 24/66: the emergence date, maturation date and harvest date for 

North Dakota Wheat and Texas Wheat is not correct. This information is swapped.

EFED Response: EFED re-ran the Surface Water Concentration Calculator (SWCC) for the 

North Dakota and Texas Wheat scenarios based on the registrant’s comments. The adjusted 

inputs, estimated environmental concentrations (EECs), and resulting risk quotients (RQs) 

are presented below in Tables 1, 2, and 3, respectively. The error in emergence, maturation, 

and harvest date inputs had only a minor impact on the EECs and no impact on the risk 

conclusions for the assessment. RQs are presented only for aquatic plants as no acute RQs 

were calculated for other aquatic taxa due to a lack of toxic effects, and chronic RQs were all 

<0.0001.

Table 1. SWCC Modeling Scenarios for Propoxycarbazone-sodium 

Modeling Scenario Met. File

(.dvf) Emergence Date Maturation Date

Harvest 

Date

North Dakota Wheat 14914 May. 16 July 25 August 5

Texas Wheat 13958 Oct. 16 April 30 June 17

Table 2. Propoxycarbazone-sodium Screening-level EECs 

PRZM Scenario Type of 

Application

1-in-10-year Peak 

Exposure (μg/L)

1-in-10-year 

21-day Average 

Exposure (μg/L)

1-in-10-year 

60-day Average 

Exposure (μg/L)

ND Wheat

(2 @ same rate)

Aerial 0.928 0.882 0.899

Ground 0.757 0.726 0.747

ND Wheat

(different rates)

Aerial 1.97 1.83 1.68

Ground 0.960 0.911 0.826

TX Wheat

(2 @ same rate)

Aerial 1.03 0.982 0.886

Ground 0.898 0.852 0.790

TX Wheat

(different rates)

Aerial 1.14 1.09 0.986

Ground 0.982 0.936 0.850

Bolded values are the maximum EECs for use in risk estimation (i.e., RQ calculations).

Table 3. RQ Values for Aquatic Plants from Exposure to Propoxycarbazone-sodium TGAI

Taxonomic 

Group

Listed 

Status

Toxicity Endpoint 

(mg a.i./L)

Original RQ Values1

Triticale, Wheat

(EEC = 2.29 μg/L)

Recalculated RQ Values1

Triticale, Wheat

(EEC = 1.97 μg/L)

Vascular 

aquatic plants

Non-listed EC50 = 0.0064 0.36 0.31

Listed NOAEC = 0.0031 0.74 0.64

Non-vascular 

aquatic plants

Non-listed EC50 = 1.57 0.0015 0.0013

Listed NOAEC = 0.53 0.0043 0.0037 1 RQ=EEC/toxicity endpoint. 
3

Comment 2: BCS used the same information presented in Tables 3.4 and 3.5 to parameterize the

SWCC and found variations in the results, from <2% for the Texas Wheat scenario to >25% for 

Florida Cabbage. The other scenarios varied in between.

EFED Response: EFED cannot speculate as to why the registrant obtained different 

modeling results without reviewing the model input and output files.

Comment 3: The propoxycarbazone labels require a medium to coarse drop size. The analysis of 

the drift buffers using AgDrift should not include fine drop sizes.

EFED Response: EFED’s Tier 1 AgDrift analysis reflects the propoxycarbazone labels and 

the drop size distribution categories available for modeling in the program. Four of the 

propoxycarbazone end-use product labels specify medium drop size and one specifies coarse 

drop size. Both medium and coarse droplet sizes were included in the categories modeled, as 

indicated by the underlined categories in the lists below.

For aerial applications, the droplet size categories are: 

1. Very fine to fine

2. Fine to medium

3. Medium to coarse

4. Coarse to very coarse

For ground applications, the droplet categories are: 

1. Very fine to fine 

2. Fine to medium/coarse