OFFICE OF CHEMICAL 

SAFETY AND 

POLLUTION 

PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

 

PC Code: 114401, 114402

DP Barcode: 431361

Date: March 01, 2016

MEMORANDUM

SUBJECT: Addendum to: Registration Review: Preliminary Environmental Fate and 

Ecological Risk Assessment Endangered Species Effects Determination for 

Acifluorfen

TO: Nathan Sell, Chemical Review Manager

Tracy Perry, Team Leader

Kelly Sherman, Branch Chief

Risk Management and Implementation Branch III

Pesticide Re-evaluation Division (7508P)

FROM: Brian D. Kiernan, Biologist 

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507P)

REVIEWED

BY: Monica Wait, Risk Assessment Process Leader

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507P)

APPROVED

BY: Mark Corbin, Branch Chief

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507P)

The Environmental Fate and Effects Division (EFED) has completed an addendum to the

preliminary risk assessment for the herbicidal active ingredient acifluorfen (PC Codes 114401, 

114402). This addendum corrects the rates used in the TerrPlant modeling, somewhat altering 

the resultant risk quotients (RQs). Also presented is additional modeling with AgDRIFT.

Additionally, a correction has been made to the labeling text in the table of chronic RQs for 

mammals. 

In the preliminary risk assessment (PRA; D426394), TerrPlant modeling was conducted using 

the maximum annual label rate for each use site. However, as the risk assessment was nearing 
completion, a minimum retreatment interval of 15 days was specified. As a result, TerrPlant 

modeling should have been conducted on the maximum single application rate for each use site 

in accordance with current protocol. Below are Tables 4.9 and 4.10 (from the assessment) 

displaying results for the maximum single application rates. Change in the RQs are most 

noticeable for the strawberry use, where the modeled use rate is half that presented in the PRA; 

note that no changes are made to the rice use pattern.

Table 4.9. Terrestrial Plant RQs for Ground Spray Applications of Acifluorfen. (Bold 

values indicate an LOC exceedance.)

Application 

Rate

lbs a.i./A Plant Type

Listed 

Status Dry Semi-Aquatic Spray Drift

0.375

Soybean/Peanut/

Strawberry

Grass non-listed ND* ND <0.1

Grass listed ND ND 0.11

Non-grass non-listed 1.07 9.11 0.99

Non-grass listed 1.50 12.75 4.17

0.25

Rice

Grass non-listed ND ND <0.1

Grass listed ND ND <0.1

Non-grass non-listed 0.71 6.07 0.66

Non-grass listed 1.00 8.50 2.78

* Not determined

Table 4.10. Terrestrial Plant RQs for Aerial Spray Applications of Acifluorfen. (Bold 

values indicate an LOC exceedance.

Application 

Rate

lbs a.i./A Plant Type

Listed 

Status Dry Semi-Aquatic Spray Drift

0.375.

Soybean/Peanut/

Strawberry

Grass non-listed ND* ND 0.22

Grass listed ND ND 0.27

Non-grass non-listed 1.79 9.82 4.93

Non-grass listed 2.50 13.75 20.83

0.25

Rice

Grass non-listed ND ND 0.15

Grass listed ND ND 0.18

Non-grass non-listed 1.19 6.55 3.29

Non-grass listed 1.67 9.17 13.89

* Not determined

PRD requested additional AgDRIFT modeling to account for the current droplet size spectrum 

on the labels (medium-coarse) and to illustrate the impact of increasing the droplet size spectrum 

on the distance to the level of concern (i.e. RQ=1.0). Table A presents selected results for aerial 

application. It should be noted that this modeling holds all parameters but droplet size as Tier 1 

terrestrial model defaults. These defaults are assumed to be on the label.

For aerial, standard label spray drift mitigation is:

• 3-10 mph wind speed

• 10 ft release height above canopy

• 1/2 swath offset upwind at the edge of the field
• no sprays made during temperature inversions (the 3 mph low wind speed restriction is 

essentially equivalent

• spray length 75% of the wing or rotor length or less

Table A. Distance (in feet) to the LOC for selected plant sensitivity and application rate of 0.375 

lbs ai/A, representative of soybean, peanut and strawberry maximum single application rate. Note 

these distances are for aerial applications.

Crop Endpoint IC25

Mediumcoarse

Coarsevery 

coarse

Corn Dry Weight 0.085 20 16

Onion Dry Weight 0.12 10 3.3

Cabbage Plant Height 0.028 79 49

Radish Dry Weight 0.0038 420 269

Soybean Dry Weight 0.087 16 13

Tomato Dry Weight 0.046 43 30

Additionally, in Table 4.5 of the assessment, the label for the soybean and peanut use patterns 

indicates a single seasonal application of 0.5 lbs ai/A. This label is incorrect, although the results 

presented are correct for the use patterns. The single maximum application rate is 0.375 lbs ai/A 

with a seasonal maximum application rate of 0.5 lbs ai/A. Thus, the modeling was actually 

conducted for a first application at 0.375 lbs ai/A on day zero and a follow-up application of 

0.125 lbs ai/A on day 15. The RQs in the table are correct for this application scenario.