UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

PC Code: 125601 

DP Barcode: D427 l 5 l 

Date: May 6, 2015 

MEMORANDUM 

SUBJECT: Amended Terrestrial Plant Risk Quotients for the Paclobutrazol Registration 

Review Ecological Risk Assessment 

TO: 

FROM: 

Khue Nguyen, Chemical Review Manager 

Tom Moriarty, T earn Leader 

Neil Anderson, Branch Chief 

Risk Management and Implementation Branch I 

Pesticide Re-Evaluation Division 

::::::f:a:,:::d:::o~:i::~:: 08P) i Sujatha Sankula, Ph.D., Branch Chie \J..;- :::>===="'" 

Environmental Risk Branch I 

Enviromnental Fate and Effects Division (7507P) 

Office of Pesticide Programs 

In the October 9, 2014, response to comments document for paclobutrazol (USEPA 2014, 

D417019), the Environmental Fate and Effects Division presented new risk quotients (RQs) for 

terrestrial plants, based on endpoints from the newly submitted seedling emergence study (MRID 

49300408). The text of the document correctly asserted that the RQs for terrestrial plants were 

now higher than those presented in the original registration review risk assessment (USEPA 

2013, D393895). However, the terrestrial plant values presented in the appendix were actually 

lower, and thus incorrect, for all uses but the seed treatments. 

Table l presents the endpoints used in the original registration review risk assessment (based on 

5 th percentile estimates from other structurally similar conazoles) and the empirical values from 

the paclobutrazol seedling emergence study. 
T a e bl 1 C ompanson o f di' d . t see mg emergence en pom s 

5th Percentile (based on data Empirical Data 

from other conazoles) 

Monocot EC2s > 0.098 lb ail A EC2s = 0.0824 lb ai/A 

NOAEL = 0.071 lb ai/A NOAEL = 0.0098 lb ail A 

Di cot EC2s = 0.009 lb ai/A EC2s = 0.0063 1 lb ai/ A 

NOAEL = 0.002 lb ail A ECos = 0.000567 lb ail A* 

*The ECos was used because the NOAEL was calculated to be greater than the EC2s. 

Table 2 presents the corrected RQs, based on the seedling emergence empirical data. General 

input parameters for Terr Plant include the solubility of paclobutrazol (27 ppm), application rates, 

incorporation depth ( 1 to 3 inches, depending on use), and drift fraction (0.0 1 for spray 

applications and 0 for drench, inj ection, and seed treatments). The seed treatment RQs remai ned 

the same (RQs < 0. 1 ); however, some of the other RQs increased by a maximum of I Ox. 

Although the RQs increased in magnitude, no new risk concerns were identified. There r emain 

potential risk concerns for non-listed/listed dicots and listed monocots for the turf, potted 

ornamental spray, soil injection/basal drench, and potted ornamental drench uses. There 

are risk concerns for non-listed monocots for turf, soil injection/basal drench, and the 

potted ornamental drench. 

Table 2. Revised terrestrial plant RQs, based on new seedling emergence data (MRlD 

49300408) 

Plant Type Listed Status Dry Semi-Aqua tic Spray Drift 

Turf (1 avo at 0. 75 lb ail A) 

Monocot Non-listed 0.27 1.91 *** <0.1 

Monocot Listed 2.30*** 16.07*** 0.77 

Di cot Non-listed 3.57*** 24.96*** 1.19*** 

Di cot Listed 39.68*** 277.78*** 13.23*** 

Potted ornamental spray (1 app at 0.26 lb ai/A) 

Monocot Non-listed <0. 1 0.66 <0. 1 

Monocot Listed 0.80 5.57*** 0.27 

Di cot Non-listed 1.24*** 8.65*** 0.4 1 

Di cot Listed 13.76*** 96.30*** 4.59*** 

Soil injectio11/basal drench (1 app at 3 inches deep at 1.9 lb ai/A) 

Monocot Non-listed 0.15 1.54*** NIA 

Monocot Listed 1.29*** 12.93*** NIA 

Di cot Non-listed 2.01 *** 20.07*** NIA 

Di cot Listed 22.34*** 223.40*** NIA 

Potted ornamental drench (1 arJD at 6. I lb ail A) 

Monocot Non-listed 1.48*** 14.81 *** NIA 

Monocot Listed 12.45*** 124.49*** NIA 

Di cot Non-listed 19.33*** 193.34*** NIA 

Di cot Listed 215.17*** 2151.68*** NIA 

Tomato seed treatment (1 avo at 3 inches deep at 0.0004 lb ai/A) 

2 
Plant Type Listed Status Dry Semi-Aquatic Spray Drift 

Monocot Non-listed <0. 1 <0.1 NIA 

Monocot Listed <0. 1 <0.1 NIA 

Di cot Non-listed <0.1 <0.1 NIA 

Di cot Listed <0.1 <0.1 NIA 

Pepper seed treatment (1 aoo at 3 inches deep at 0.00079 lb ai/A) 

Monocot Non-listed <0.1 <0.1 NIA 

Monocot Listed <0.1 <0.1 NIA 

Di cot Non-listed <0.1 <0.1 NIA 

Di cot Listed <0.1 <0.1 NIA 

Cucurbit seed treatment (J app at 3 inches deep at 0.00029 lb ai/A) 

Monocot Non-listed <0. 1 <0. 1 NIA 

Monocot Listed <0. 1 <0.1 NIA 

Di cot Non-listed <0.1 <0.1 NIA 

Di cot Listed <0.1 <0.1 NIA 

Broccoli seed treatment (J app at 3 incites deep at 0.000096 lb ail) 

Monocot Non-listed <0. 1 <0.1 NIA 

Monocot Listed <0.1 <0.1 NIA 

Di cot Non-listed <0.1 <0.1 NIA 

Di cot Listed <0.1 <0.1 NIA 

Cauliflower seed treatment (1 app at 3 incites deep at 0.000064 lb ai/A) 

Monocot Non-listed <0.1 <0. 1 NIA 

Monocot Listed <0.1 <0.1 NIA 

Di cot Non-listed <0.1 <0.1 NIA 

Di cot Listed <0. 1 <0. 1 NIA 

Cabbage seed treatment (1 app at 3 incites deep at 0.00012 lb ai/A) 

Monocot Non-listed <0. 1 <0.1 NIA 

Monocot Listed <0. 1 <0. 1 NIA 

Di cot Non-listed <0. 1 <0. 1 NIA 

Di cot Listed <0. 1 <0.1 NIA 

NI A - not applicable because spray drift does not occur with seed treatment/drench/soil injection 

uses 

*** - exceeds the LOC of I 

References 

US EPA. 20 13. Registration review - ecological risk assessment and effects determination of 

paclobutrazol. Environmental Fate and Effects Division, Office of Pesticide Programs, 

United States Environmental Protection Agency. 

USEPA. 2014. Response to Public Comments on the Paclobutrazol Registration Review 

Ecological Risk Assessment. Environmental Fate and Effects Division, Office of 

Pesticide Programs, United States Environmental Protection Agency. 

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