1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF

CHEMICAL SAFETY AND POLLUTION PREVENTION

DP Barcode : 432215

PC Code: 288008

March 1 5 , 2016

MEMORANDUM

SUBJECT: A minocyclopyrachlor ac id

– Addendum to the Drinkin g W ater A ssessment for

Non

- Crop Uses

TO: Mindy Ondish, Risk Manager Reviewer

Reuben Baris

, Product Manager Team 25

Herbicide Branch

Registration Division

FROM: William P. Eckel, Ph.D. , Senior Science Advi sor

Environm ental Ri sk Branch V I

Environmental Fate and Effects Division

THRU: Mark Corbin , Branch Chief

Monica Wait, RAPL

Environmental Risk Branch V I

Environmental Fate and Effects Division

CONCLUSIONS

A revised drinking water assessment (DWA) for aminoc yclopyrachlor acid (ACP) and its

degradate IN

- V0977 was completed on January 8, 2010 (DP 368238) . This memorandum

updates the previous DWA by reviewing the T ier I surface water analysis (FIRST model) and by

updating the ground water analysis using the PRZ M

- GW model.

Surface Water

. The previous FIRST surface water modeling was found to be appropriately

conservative by testing in the Tier II model SWCC, including both the experimental Tier I

scenario and the PA turf scenario. The acute and chronic estimat ed drinking water

concentrations ( EDWCs ) for surface water were reported in the 2010 DWA to be 25.6 and 15.9

ug/L (ppb), respectively for a single ground or aerial application at 0.284 lb/A. However, a

percent cropped area (PCA) of 0.87 was applied to the se results, which is not appropriate for this2 use pattern. The corrected results, with a PCA value of 1.0, are 29.4 ppb (acute) and 18.3

ppb (chronic). The results for the degradate IN

- V0977 are 1.7 ppb (acute) and 1.2 ppb (chronic)

after correcting the PCA factor. These results apply to both aerial and ground application. Pease

refer to the 2010 DWA for details of the environmental fate profile and properties of ACP

.

Ground Water. For ground water, the six PRZM

- GW scenarios were run, and the highest result

was for the NC Coastal scenario. The acute EDWC is 116 ug/L (ppb)

, and the chronic EDWC is

78 ppb.

Recommended EDWCs

. EFED therefore recommends the following EDWCs for the non

- crop

areas use

.

Surface water (parent) , acute: 29.4 ppb; chronic, 18.3 ppb.

Surface water (IN

- V0977), acute, 1.7 ppb; chronic 1.2 ppb.

Ground water, acute (parent only) : 116 ppb; chronic 78 ppb.

Ground Water Modeling

Due to the stability and mobility of the parent aminocyclopyrachlor acid, the compound may

move from t he treated field t o ground water through lea ching. Since the parent is not susceptible

to soil photolysis (t 1/2 = 129 days; MRID 47560213), the degradate is not an issue for ground

water contamination; therefore, no PRZM

- GW modeling was performed on the degradate.

Table 1 details the input parameters for the Tier I/II l evel groundwater model, PRZM

- GW , for

the pare n t aminocyclopyrachlor acid only. Model outputs are included in the Appendix.

Table 1 : PRZM

- GW Input Parameters for Aminocyclopyrachl or Aci d for Non

- Crop

Use

Parameter: Input

Value: Data Source/Rationale

Application Rate (lbs a.i./acre)

(kg/hectare) 0.284

0.32 EPA Reg. No. 352

- TII (non

- crop

– parent)

Maximum Number of

Applications/ Year 1 EPA Reg. No. 352

- TII (non

- crop

– paren t)

Aerobic Soil Metabolism Half

- l ife

(days)

Parent 373 Value represents the upper 90% confidence

limit on the mean value

(MRID 47560214 and 47560221).

Hydrolysis Half

- life stable MRID 47835701

K

oc

Parent 12 L/kg oc Average Koc value: MRID 475602193 

### Appendix

Groundwater Analysis for aminocyclopyrachlor and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario

Estimated groundwater concentrations and breakthrough times for aminocyclopyrachlor are

presented in Table 1 for the NC Eastern Coastal Plain

- Norfolk loamy sand

- Cotton

groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is

presented in Figure 1. These values were generated with the PRZM

- GW (Version 1.07). Critical

input valu es for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for aminocyclopyrachlor and the NC Eastern Coastal Plain

- Norfolk loamy sand

- Cotton Scenario.

Peak Concentration (ppb) 116

Post

- Breakthrough Mean

Concentration (ppb) 78.1

Entire Simulation Mean

Concentration (ppb) 63.3

Average Breakthrough

Time (days) 2063.52

Throughputs 5.311313

Table 2. Chemical Properties for Groundwater Modeling of aminocyclopyrachlor.

Koc (ml/g) 12

Surface Soil Half Life (days) 373

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for aminocyclopyrachlor. This application

scheme was applied every year of the simulation.

Appl ication Days

Relative to

Emergence Date

(05/15) Application Method Application Rate

(kg/ha)

7 Ground application with mass

distribution increasing 0.324 proportionally with depth to 4 cm

Figure 1. Aquifer Breakthrough Curve for aminocyclopyrachlor and th e NC Eastern

Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario