UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFIO : OF I~ £1\I CAL SAFETY 

Al\0 POLLliTIO;\ PREVE' liON 

PC Code: 128810 

DP Barcodes: 422726 

MEMORANDUM September 11, 20 14 

SUBJECT: 

TO: 

FROM: 

THRU: 

Drinking Water Exposure Assessment for new use of Azoxystrobin on 

Ornamental Plants and Vegetable Transplants. 

Christine Olinger, Branch Chief 

Kristin Rury, Risk Assessor 

Risk Assessment Branch III 

Health Effects Division (7509P) 

Ibrahim Abdel-Saheb, Ph.D, Environmental Scientist~~ Cf - \l - \ '-\ 

Environmental Risk Branch VI 

Environmental Fate and Effects Division (7507P) 

Mark Corbin, Branch Chief 

William P. Eckel, Ph.D., Senior Science Advisor 

Environmental Risk Branch VI 

Environmental Fate and Effects Division (7507P) 

Office of Pesticide Programs 

Office of Chemical Safety & Pollution Prevention 

The Environmental Fate and Effects Division (EFED) estimates drinking water concentrations of 

a chemical based on the highest rate of application of the chemical on all registered and proposed 

use sites. The proposed new product that contains azoxystrobin and difenoconazole (100-RLNA 

Alibi Flora) is proposed to control fungal diseases on ornamental plants and vegetable 

transplants grown in both indoor and outdoor production facilities (the vegetable transplants 

grown for retail sale to residential consumers only). The proposed maximum single application 

rate is 0.55 lb a.i./A, with a maximum annual application rate of0.80 lb a.i./A, and an application 

interval of7-21 days. 

In the case of azoxystrobin, turf, a previously registered use, has the highest application rate of 

all currently registered use sites: 0.55 lb a.i./ A with up to 9 applications per year and a 1 0-day 

interval between applications. (D278783, D279444, and D279561 ; Feb. 4, 2002). The model 

Page 1 of6 
FIRST was used in the 2002 drinking water assessment (DW A) cited above and resulted in 

estimated drinking water concentrations (EOWCs) for peak (acute) of 173 ppb, and for annual 

mean (chronic) of 0.33 ppb. For groundwater, the model SCI-GROW gave EDWCs for - acute 

and chronic of 3. 1 ppb. 

Since 2002, EFED has introduced new surface water and groundwater models (i.e Surface Water 

Concentration Calculator (SWCC), and PRZM-GW, respectively]. A comparison was made 

between output from current EFED models for azoxystrobin for the proposed use on ornamentals 

and vegetable transplants with the output from the currently registered use on turf (0.55 lb ai/A, 

9x, 10 d). Results are shown in Table 1 (see model input and output in Appendix I). 

The resulting surface water EDWCs for ornamental plants and vegetable transplants are 24.8 ppb 

for peak, 7.30 ppb for chronic, and 4.04 ppb for cancer while the maximum surface water 

EDWCs for turf are 70.2 ppb for peak, 48.5 ppb for chronic, and 38.5 ppb for cancer; and 

groundwater of 3.1 ppb (Acute and chronic). 

EDWCs calculated with PRZM-GW for ornamental plants and vegetable transplants range from 

0.008 ppb (peak) to 0.001 ppb (post breakthrough average); and for turf range from 0.044 ppb 

(peak) to 0.007 ppb (post breakthrough average). 

Thus, EFED recommends that the Health Effects Division use the following surface water and 

groundwater EDWCs resulting from turf modeling. Please note that the surface water EDWCs 

are reduced from the previous 2002 DW A due to the use of the tier 2 model, SWCC. The 

groundwater EDWC presented below is from the SCI-GROW model, since it provides the more 

conservative estimate of exposure. 

Surface water (turf, SWCC): 

Peak (acute)= 

Chronic= 

Cancer= 

70.2 ppb, 

48.5 ppb, and 

38.5 ppb. 

Groundwater (turf, SCI-GROW): 

Acute and chronic = 3.1 ppb 

Page 2 of 6 
Table 1. Estimated Drinking Water Concentrations (EDWCs) for drinking water risk assessment 

use on Ornamental Plants and Vegetable Transplants and Turf. 

Surface Water (ppb) Groundwater (ppb) 

2014 Modeling 2014 Modeling 2014 

(SWCC)* (SWCC)* 2014 Modeling** Modeling** 

(0.55 lb a.i./A, 9x, 10 d) (Max single appl. 0.55 lb PRZM-GW PRZM-GW 

a. i./A on Ornamental 

on Turf Max annual appl. 0.8 lb a.i./A on Turf Plants and 

@7 d) Vrgetable 

Transplants 

on O rna mental Plants and 

Vegetable Transplants 

Peak-ppb 0.044 0.008 

Peak ( 1-in-1 0 yr) 24.8 A verage-ppb 0.007 0.001 

70.2 Post 

breakthrough 

Avg.-ppb Incomplete Incomplete¥ 

Average Incomplete Incomplete 

365-day Avg(l-in-10 48.5 7.30 Breakthrough 

yr) Time-day 

Throughputs 0.283 0.283 

Entire Simulation Mean 38.5 4.04 

*:For the SWCC model 

The following available NURSERY scenarios were used to represent ornamentals in nurseries: 

CA, FL. MI, NJ, OR, and TN. 

The TN scenario gave the highest EDWCs. 

The following available TURF scenarios were used: 

FL, and PA 

The PA scenario gave the highest EDWCs. 

**: For the PRZM-GW model; the following available scenarios were used to represent ornamentals and turf: 

FLpotato, GAcoastal, NCcoastal, and Wlsand. 

The FL scenario gave the highest EDWCs for both uses. 

¥:The chemical did not reach groundwater even after running the model with an extended 100-year weather file 

Page 3 of6 
,Appendix I 

SWCCModel 

Summary of Model Inputs for Azoxystrobin on Ornamental Plants and Vegetable 

Transplants. 

Scenario TNnurserySTD _ V2 

Cropped Area Fraction 1.0 

Koc (ml/g) 8.87 

Water Half-Life (days) @ 25 °C 322.2 

Benthic Half-Life (days) @ 25 °C 0 

Photolysis Half-Life (days) @ 40 23.23 0 Lat 

Hydrolysis Half-Life (days) 0 

Soil Half-Life (days)@ 22 °C 161.2 

Foliar Half-Life (days) 35 

Molecular Wt 403.3 

Vapor Pressure (torr) 8.2E-13 

Solubility (mg/1) 6.7 

Page 4 of6 
Models Output 

Ornamental Plants and Vegetable Transplants 

SWCC Model Estimated Drinking Water Concentrations (ppb) for azoxystrobin 

Output Scenario 

(ppb) CA FL MI NJ OR TN 

Peak ( 1-in-1 0 yr) 12.9 17.4 12.2 17.5 19.9 24.8 

4-day Avg (1-in-10 12.9 16.9 12.0 17.1 19.6 24.1 

yr) 

21-day Avg (1-in-10 12.7 14.9 11.3 15.9 18.9 22.5 

yr) 

60-day Avg (1 -in-1 0 12.2 12.5 10.3 14.5 17.3 20.0 

yr) 

365-day A vg ( 1-in- 8.63 3.72 5.67 7.85 10.1 7.30 

10 yr) 

Entire Simulation 6.14 2.13 4.25 4.83 6.70 4.04 

Mean 

Turf 

SWCC Model Estimated Drinking Water Concentrations (ppb) for azoxystrobin 

Output Scenario 

(ppb) 

FL PA 

Peak (l-in-1 0 yr) 51.2 70.2 

4-day Avg ( 1-in-10 yr) 50.7 69.6 

21-day Avg (1-in-10 yr) 49.6 68.6 

60-day Avg (1-in-10 yr) 47.1 66.5 

365-day Avg ( 1-in-1 0 yr) 32.0 48.5 

Entire Simulation Mean 26.6 38.5 

Page 5 of6 
PRZM-GW Model 

Ornamental Plants and Vegetable Transplants 

PRZM-GW Model Estimated Drinking Water Concentrations (ppb) for azoxystrobin 

Scenario ID 

DELMARVA STD.SCN 

FLCITRUS_STD.SCN 

FLPOTATO_STD.SCN 

GACOASTAL STD.SCN 

NCCOASTAL-STO.SCN 

WISANDS_STO.SCN 

Peak(ppb) 

9.72E-08 

0.00766 

0.000818 

2.48£-09 

4.98£-10 

1.93E-16 

PBT Avg(ppb) 

Incomplete 

Incomplete 

Incomplete 

Incomplete 

Incomplete 

Incomplete 

Turf 

SimAvg BT(d) Throughputs 

7.49E-09 Incomplete 0.1543425 

0.00128 Incomplete 0.2835361 

0.000146 Incomplete 0.3307775 

1.97E-10 Incomplete 0.1934483 

4.06E-ll Incomplete 0.1078497 

1.08E-17 Incomplete 0.07385527 

90-day Avg 

9.15£-08 

0.00765 

0.000817 

2.43E-09 

4.9£-10 

1.93E-16 

PRZM-GW Model Estimated Drinking Water Concentrations (ppb) for azoxystrobin 

Groundwater Results for Azoxystrobin and the Florida Citrus - FL Central Ridge 

Scenario. 

Peak Concentration (ppb) 

Post-Breakthrough Mean 

Concentration (ppb) 

Entire Simulation Mean 

Concentration (ppb) 

Average Breakthrough 

Time (days) 

Throughputs 

0.0441 

Incomplete 

0.00735 

Incomplete 

0.2835361 

Page 6 of6