UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

PC Code: 125601 

DP Barcode: D425024 

Date: January 15, 2015 

MEMORANDUM 

SUBJECT: 

TO: 

FROM: 

Revised Chronic Mammalian Risk Conclusions for the Paclobutrazol Registration 

Review Ecological Risk Assessment 

Khue Nguyen, Chemical Review Manager 

Neil Anderson, Branch Chief 

Risk Management and Implementation Branch I 

Pesticide Re-Evaluation Division 

Office of Pesticide Pro~rams (7508P) 

Meghan Radtke, Ph.D., Biologist Al~ I I I TO /IS ct r 

Sujatha Sankula, Ph.D., Branch Chief ~ ~~}-..~~ \'-\to:> '., 

Environmental Risk Branch I ,......-r 

Environmental Fate and Effects Division (7507P) 

Office of Pesticide Programs 

As part of a general data review in support of Registration Review, the Health Effects Division 

recently revised the endpoints in the two generation rat study (MRID 40734303) that are used to 

characterize chronic risks for mammals. The ToxStat committee determined that the effects at 

23.3 mg aifkg.:bw (increased incidenc¢ of chromodacryorrhea and thickened eyelids observed in 

both generations) were generally within the provided historical control ranges, and, thus, not 

considered a treatment-related effect. Consequently, the NOAEC changed from 2.5 to 23.2 mg 

ai/kg-bw (250 mg ailkg-diet). 

In the original Registration Review risk assessment (USEPA 2013, D393895), the 

Environmental Fate and Effects Division (EFED) identified potential chronic risk concerns for 

all uses of paclobutrazol, except the seed treatments. EFED has now re-evaluated chronic risk, 

based on the revised chronic rat endpoint. Using the new chronic endpoint, all risk quotients 

(RQs) were lowered, but all uses still exceeded the level of concern. However, chronic risk 

concerns for mammals were still identified for the following uses: 

• Turf (all size classes of mammals on several food items) 

• Potted ornamental spray (small and medium sized mammals on short grass) 

• Tree injection (hardwoods only, all size classes of mammals) 

• Soil injection/drench (hardwoods and softwoods, all size classes of mammals) 
• Potted woody ornamental drench (hardwoods only, small sized mammals) 

• Potted non-woody ornamental drench (small and mJctium sized mammals) 

See Tables I and 2 for th.e RQs based on the new chronic Jarnmalia'n endpoint, which replace 

those in the original risk assessment. Appendix A contains risk quotient calculations for the 

drench and injection application methods. 

Table 1 T . -REX upper bound chronic risk quotients for mammals for paclobutrazol turf 

and spray applications to potted ornamentals 

Chronic Dose-Based RQs 

Risk Quotients Chronic 

Based Dietaryon Kenaga 15 g 35 g 1000 g Based RQs Upper Bound EEC 

Profile 2SC on Turf- 3 applications at 0. 75 lb ail A (28 day interval)1 

Short grass 6.41 *** 5.47*** I 2.93*** 1.37*** 

Tall grass 2.94*** 2.51 *** 1.35*** 0.63 

Broadleaf 

plants/small insects 3.61 *** 3.08*** 1.65*** 0.77 

Fruits/pods/seeds/lg 

insects 0.40 0.34 0.18 0.09 

Granivores 0.09 0.08 0.04 0.09 

Bonzi II Spra_vfor Potted Ornamentals -1 application at 0.26 lb ai/A 

Short grass 1.17*** 1.00*** 0.53 0.25 

Tall grass 0.53 0.46 I 0.24 0.11 

Broadleaf 

plants/small insects 0.66 0.56 0.30 0.14 

Fruits/pods/ seeds/l g 

insects 0.07 0.06 0.03 0.02 

Granivores 0.02 0.01 0.01 0.02 

1

3 applications at 0.75 lb ai/A exceeds the maximum seasonal rate of2lb ai/A by 0.25 lb ai/A. A 

T-REX scenario was run wit}}. 3 applications at 0.66 lb ai/ A. Jitisk quotients were -12% lower, 

but none of the exceeding risk quotients were reduced below the level of concern. Thus the 

higher application rate was used for this assessment to ensure that it was maximally protective. 

***Exceeds the chronic LOC of 1 

2 
Table 2. Chronic risk quotients for mammals for paclobutrazol tree injection, soil 

injection/drench, potted ornamentals drench, and seed treatment applications (see 

Appendix A for RQ calculations) 

Chronic Mammal Dose-Based RQs 

I 

15 g 3Sg_ 1000 g 

Tree injection at 0.36lh ai!A 

Hardwoods 3.9*** 3.4*** 1.8*** 

Softwoods 0.18 0.10 0.08 

Soil injection/drench at J.9lh ai!A 

Hardwoods 20*** 17*** 9*** 

S0ftwoods 9*** I 8*** 4*** 

Woody potted ornamental drench at 6.1lh ai!A 

Hardwoods 1.2*** 0.95 0.50 

Softwoods 0.45 0.39 0.20 

Non-woody potted ornamental drench at 6.1 lh ai!A 

Non-woody plants 2.1 *** 1.8*** 0.95 

***Exceeds chronic LOC of 1 

References 

USEP A. 2013. Registration review- ecological risk assessment and effects determination of 

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

States Environmental Protection Agency. 

3 
Appendix A- Risk Quotient Calculations for Drenches and Injections 

The EECs reported in this appendix are taken from the paclobutrazol registration review risk 

assessment (USEPA 2013, D393895). Please refer to that document for details on the EEC 

calculations. 

Clipper 20 UL Ornamental Tree Injection - 1 application at 0.36 lb ail A 

Risk Quotient= EEC I Toxicological Value 

Mammals 

The following definitive data are available for mammals: 

NOEL = 23.2 mg/kg-bw 

Adjusted toxicity values were calculated for mammal size classes by T-REX 

15 g mammal NOEL = 50.99 mg/kg-bw 

35 g mammal NOEL = 41.26 mglkg-bw 

1000 g mammal NOEL = 17.84 mg/kg-bw 

Chronic Dose-Based Risk Quotients= EEC/NOEL 

Hardwoods 

15 g mammal= (201 mg ailkg-bw) I (50.99 mg ai!kg-bw) = 3.9 

35 g mammal = (140 mg ailkg-bw) I ( 41.26 mg ai/kg-bw) = 3.4 

1000 g mammal = (32 mg ai/kg-bw) I (17.84 mg ai/kg-bw) = 1.8 

Softwoods 

15 g mammal = (9 mg ailkg-bw) I (50.99 mg ai/kg-bw) = 0.18 

35 g mammal= (4.2 mg ai/kg-bw) I (41.26 mg ai/kg-bw) = 0.10 

1 OOOg mammal = ( 1.4 mg ailkg-bw) I ( 17.84 mg ailkg-bw) = 0.08 

4 
Paclobutrazol 2SC Soil Injection/Basal Drench for Ornamental Trees- 1 

application at 1.9 lb ail A 

Risk Quotient= EEC I Toxicological iValue 

Mammals 

The following definitive data are available for mammals: 

NOEL = 23 .2 mg/kg-bw I 

Adjusted toxicity values were calculated for mammal size classes by T -REX 

15 g mammal NOEL = 50.99 mglkg-?w 

35 g mammal NOEL= 41.26 mg/kg-bw 

1000 g mamm·al NOEL = 17.84 mg/kg-bw 

Chronic Dose-Based Risk Quotients = EEC/NOEL 

Hardwoods ) 

15 g mammal = (1005 mg ailkg-bw) J (50.99 mg ailkg-bw) = 20 

35 g mammal= (698 mg ai/kg-bw) I ~4 1.26 mg ai/kg-bw) = 17 

1000 g mammal = ( 159 mg ailkg-bw) I ( 17.84 mg ai/kg-bw) = 9 

Softwoods 

15 g mammal= (459 mg ailkg-bw) I ~50 .99 mg ailkg-bw) = 9 

35 g mammal = (319 mg ailkg-bw) I (41 .26 mg ailkg-bw) = 8 

1 OOOg mammal= (72 mg ai/kg-bw) I (17.84 mg ai/kg-bw) = 4 

Bonzi II Drench for Potted Otinamentals -1 application at 6.llb ail A 

Woody Potted Ornamentals 

Risk Quotient= EEC I Toxicological.Value 

Mammals 

The following definitive data are available for mammals: 

NOEL= 23.2 mg/kg-bw 

5 
Adjusted toxicity values were calculated for mammal size classes by T-REX 

15 g mammal NOEL= 50.99 mg/kg-bw 

35 g mammal NOEL = 41.26 mglkg-bw 

1000 g mammal NOEL = 17.84 mg/kg-bw 

Chronic Dose-Based Risk Quotients = EEC/NOEL 

Hardwoods 

15 g mammal = (59 mg ai/kg-bw) I (50.99 mg ai/kg-bw) = 1.2 

35 g mammal= (39 mg ailkg-bw) I (41.26 mg ai/kg-bw) = 0.95 

1000 g mammal = (9 mg ailkg-bw) I (17.84 mg ailkg-bw) = 0.50 

Softwoods 

15 g mammal= (23 mg ai!kg-bw) I (50.99 mg ailkg-bw) = OA5 

35 g mammal = (16 mg ailkg-bw) I (41.26 mg ailkg-bw) = 0.39 

1 OOOg mammal = (3 .6 mg ai/kg-bw) I (17 .84 mg ai/kg-bw) = 0.20 

Non-Woody Potted Ornamentals 

Mammals 

The following definitive data are available for mammals: 

NOEL= 23.2 mg/kg-bw 

Adjusted toxicity values were calculated for mammal size classes by T -REX 

15 g mammal NOEL = 50.99 mg/kg-bw 

35 g mammal NOEL = 41.26 mg/kg-bw 

1000 g mammal NOEL = 17.84 mg/kg-bw 

Chronic Dose-Based Risk Quotients= EEC/NOEL 

15 g mammal = (106 mg ailkg-bw) I (50.99 mg ailkg-bw) = 2.1 

35 g mammal = (74 mg ailkg-bw) I (41.26 mg ai/kg-bw) = 1.8 

1 OOOg mammal = (17 mg ailkg-bw) I (17.84 mg ailkg-bw) = 0.95 

6