UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF PREVENTION, PESTICIDES ANO
TOXIC SUBSTANCES

PC Code : 09870 I

DP Barcode: D425910



### MEMORANDUM

DATE: March 10, 2015



### SUBJECT: Tier I Drinking Water Assessment for the Registration Review of Phenrnedipham

and its De gradate, MHP C, for use in Human Health Risk Assessment.



### TO: Miguel Zavala

, C h emical Review Manager

Neil Ande r son, Acting B ranch Chief

Risk Management and Implementation Branch 3

Pesticide Re-evaluation Division (7508P)

AND



### FROM: Sum i tra Biswas, Risk Assessor

Donna Davis, Branch Chief

Risk Assessment Branch 6

Health Effects D i vision (7509P)

William P. Eckel

, Ph.D.

___.

# ~,;.._y**~** 3 

# /I "/

Senior Science Advisor

Environmental Risk Branch 6

Environmental Fate and Effects Division (7507 P )



### THROUGH: Mark Corbin

, Chief

## ·~**l()/~s**

Monica Wait, RA PL

### ~ \,J**~** Environmental Risk Branch 6 

## 3 /\Q 

## /\5

Env ironm ental Fate and Effects Divi sion (7507 P)

The purpose of this memorandum is to provide the Estimate d Dri nking Water Concentrations (EDWCs) of phenmedipham (PC code 098701; CAS number 1 3684-63 -4 ), and it s transformation product MHPC (methyl-3-hydroxyphenylcarbamate), for use in H ED's registrati on review

human health risk assessment.

### The surface water EDWCs are based on the assessment of August 4, 2004, as cited in the new

use risk assessment of October 30, 2006 (DP Barcode 327030) . The results from the FIRST

model as stated in the October 2006 document have been updated in this drinking water assessment ( DWA ) to use the corrected molecular weight of the degradate, MHP C (167.16 amu).

The ground water EDWCs are based on the new PRZM

- GW model. In the previous drinking

water assessment

, EDWCs from the SCI

- GROW model were reported. The new results show basically no exposure to parent phenmedipham, but up to 11 ppb peak e xposure to MHPC in the

Wisconsin sands scenario.

The values in Table 1 generally represent upper

- bound estimates of the concentrations that might be found in surface water and groundwater due to the use of phenmedipham by aerial spraying. EFED emphasize s that this is a Tier 1 screening level analysi s, and should there be a need by HED, additional refinements to this estimate could be attempted. The monitoring data search provided only limited detections in one site in Denmark; therefore, the modeling est imates are considered to be more appropriate and suitable for national estimation of drinking water values.

EXECUTIVE SUMMARY

Table 1 provides a summary of the Tier I modeled drinking water concentrations (EDWC) for

surface water sources , a dapted from the October 30, 2006 DWA (DP Barcode 327030) and corrected for MHPC molecular weight.

The highest ground water EDWCs were obtained for the degradate MHPC in the Wisconsin sands scenario. Parent phenmedipham concentrations were essentially zero in all si x PRZM

- GW

scenarios.

Table 1. Tier I Estimated Drinking Water Concentrations

– FIRST Model

Chemical Acute (peak) Surface

Water Concentration (ppb) Annual Average Surface

Water Concentration (ppb) 30

- year mean (ppb)

Phenmedipham 29.1 10.8 Not calculated for Tier I

MHPC 5.6 1.8 Not calculated for Tier I

Total Residues 3 4.7 12.6

-- Tier I Estimated Drinking Water Concentrations

– PRZM

- GW Model (Wisconsin sands scenario)

Chemical Peak Concentration (ppb) Post

- Breakthrough mean (ppb) Entire Simulation Mea n (ppb) Phenmedipham < 1 < 1 < 1

MHPC 10.9 9.8 6.3



### Phenmedipham [ CAS name 3

- [(methoxycarbonyl)amino]phenyl (3

- methylphenyl)carbamate ; IUPAC name methyl 3

- (3

- methylcarbaniloyloxy)carbanilate ], is a carbanilate herbicide . Its PC

code is 098701 and its C AS number is 13684

- 63

- 4

. Phenmedipham is a n herbicide of the phenyl carbamate family with a mode of action that interferes with the Hill Reaction during

### photosynthesis by decreasing the rate of carbon dioxide assimilation, at photosystem II.

Of the curr ently registered uses on table beets and spinach, p henmedipham ’s maximum application rate is 0.975 lb a.i./A. The application rate for MHPC (0.076 lb/A) was calculated as its maximum production in the aerobic soil metabolism study (MRID 00142744) (14%) ti mes the application rate of phenmedipham (0.975 lb/A), adjusted for the difference in molecular weight (167.16/300.34).

This is a Tier I screening

- level DWA. For surface water

, the tier 1 aquatic model FIRST was used, and for ground water, the tier 1 a quatic model PRZM

- GW was utilized. For the

assessment, the maximum application rate and one application per year were used in the input
parameters

.

The Metabolism Assessment Review Committee’s (MARC) decision document (July 26, 1994)

, concluded that th e transformation product MHPC (methyl

- 3

- hydroxyphenylcarbamate) of phenmedipham is of potential concern for drinking water sources. Therefore, EDWCs of th is compound w ere also simulated using FIRST and PRZM

- GW models. The approach used to

calculate the t ransformation products was the separate degradate calculation, as opposed to the

total residues a pproach

.

The aquatic models FIRST and PRZM

- GW were utilized to obtain EDWCs in surface water and groundwater, respectively. The major data gaps are related to the transformation product MHPC

. M odeling was used to obtain some of the parameters needed for the estimation of the drinking water concentrations of the above mentioned degradate, using EPI Suite (EPIWIN)

.

Structure of Phenmedipham

### Struct ure of MHPC

Background Information About Phenmedipham and its Degradate, MHPC : 

### Phenmedipham is a post

- emergence herbicide of the chemical class bis

- carbamate (non

cholinesterase inhibitor). It is a strong inhibitor of photosynthesis. The major routes of dissipation in the environment for phenmedipham are hydrolysis, and biodegradation. The hydrolysis rate increases with the pH. The rate of biodegradation in aerobic soils and in the field appears to depend on the pH of the soil as well. It appears to be relatively immobile in various soils and remains in the top layers of aged and unaged soil columns. The major degradates were MHPC, and m

- toluidine. Phenmedipham was stable to photolysis in pH 4 buffered solution (irradiated with a xenon arc lamp). Th e aerobic metabolism of phenmedipham in soils appears to depend on the soil pH and its organic matter. In a pH 5 soil with 0.85% organic matter , it degraded with a half

- life of 120 days while in a pH 6.8 soil with 1.85% organic matter it degraded with a h alf

- life of 20 days. The degradate MHPC formed at a maximum of 14.0% at 14 days in the aerobic soil metabolism study . Several minor degradates were also formed. Phenmedipham does not photolyze in aqueous solutions, but appears to photoly z e rapidly on

s oils, and it does not bioaccumulate substantially in fish due to rapid depuration.

Approach for Phenmedipham According to the label

, the maximum seasonal application rate for phenmedipham for all agricultural uses is 0.975 lb a.i./A. The worst

- case scena rio involving single application at the maximum seasonal rate was chosen for the conducting the modeling runs. Amongst the methods of application, the aerial spray is considered to yield the highest concentration in surface

water modeling due to the pote ntial for spray drift causing direct deposition in the water bodies.

S ince this chemical has been in use for several years, available surface and ground water monitoring data were searched as described later.

Table 2 summarizes the input values used in the model runs for FIRST1.0 and PRZM

- GW 1.07

, respectively. The K
oc 

### value (1860 ml/g) was used in FIRST. The same K
oc 

### value was used in the ground water modeling using PRZM

- GW . According to the modeling guidelines

, the 90 th

### percentile upper confidence bound value from two available aerobic soil metabolism half

- life values for phenmedipham was used in FIRST and PRZM

- GW . Some of the physical and chemical properties of p henmedipham and its degradate, MHPC have been obtained from the TOXNET (peer reviewed) database and estimated by EPI suite modeling ( see Appendix A of

10/30/06 DWA ). The modeling results obtained by using the upper bound scenario s are presented in Table 1. Output from the models (FIRST and PRZM

- GW ) are also attached (Appendix A).

Table 2. Environmental Fate and Other Input Parameters for Phenmedipham and MHPC (degra date) used in FIRST and PRZM

- GW

Parameter Phenmedipham MHPC Source

Water Solubility (25 ° C) 4.7 ppm

46,960 ppm Phenmedipham

- product chemistry and [Worthing, C.R. and S.B. Walker (eds 1987). ]

MHPC

- EPI suite.

Hydrolysis Half

- Life (pH 7) 14.5 hrs. N/A MRID 40502708

Aerobic Soil Metabolism Half

- Life (upper confidence bound value, 90 th percentile,

from 2 values

- 20 and 120 days). 224 days

104 days P henmedipham

- MRID #00142744, Supplemental;

MHPC half

- life derived by EFED (same study): 2.3 Hatzenbuhl 72.2 days; 2.2 Neuhofen 41.5 days; 90 th percentile upperbound value 104 days. Aerobic Soil Metabolism Half

- Life (average median/mean for SCIGROW) 70 days 57 days

Aerobic Aquatic Metabolism Half

- life (2X aerobic soil metabolism input value) 448 days 208 days Used EFED modeling guidance to estimate.

Aqueous Photolysis Half

- Life 0 (stable) N/A MRID# 42429901 default input value is 0

for stabl e products (modeling guidance)

Adsorption/Desorption Coefficient (Modeled K OC ) 1860 ml/g

138 ml/g Phenmedipham

- Lyman, Reehl, and Rosenblatt (1990)

MHPC

- MRID# 46286303, Supplemental

Application Date (PRZM

- GW) 7 days after

emergence 7 days after

emergence postemergence application

PCA (worst case scenario) 0.87 0.87 Default value for other

crops

Application Method (for max. application rate) Aerial Spray Aerial Spray LabelTable 2. Environmental Fate and Other Input Parameters for Phenmedipham and MHPC (degra date) used in FIRST and PRZM

- GW

Parameter Phenmedipham MHPC Source

Application Rate (lb a.i./A) 0.975 0.07 6 (1) Label

Applications Permitted per Year 1 1 Label

Application Interval (minimum days) NA NA Label

Depth of Incorporation NA NA Label

N/A

- Not available; NA

- Not applicable (1). Maximum concentration observed in the aerobic soil metabolism study x application rate x mole ratio =
(0.14)(0.975)(167.16 /300.34) =0.07 6



### Monitoring Data

Surface Water : The US GS National Water Quality Assessment (NAWQA) database was

searched for p henmedipham and MHPC separately. No detection s of either of these compounds were reported in this monitoring database. Also, the state of California (Cal EPA) database was

searched

, and no detections were reported there. Amongst all of the pesticides used, including phenmedipham, the database listed the pesticides which were detected during the monitoring

effort.

Ground Water : Based upon the US Geological Survey National Wa ter Quality Assessment (NAWQA) data search

, no specific detection s of phenmedipham ha ve been reported. However, results from a Danish (Denmark) Pesticide Leaching Assessment Program reported detection of

p henmedipham (0. 01

- 0.02 μg/l) and MHPC (0.03

- 0.19 μg/l) in two samples at the Faardrup site containing predominantly clay till soil ( Pesticide leaching at Faardrup , Chapter 6, PLAP monitoring results, May 1999

- June 2002, Denmark EPA)

. This information is available on th e internet at: http://pesticidvarsling.dk/monitor_uk/2002_uk/vap

- results

- 99

- 02

- 6

- uk.html These concentrations are substantially lower than those calculated by the PRZM

- GW model for MHPC (up to 11 ug/L). Parent phenmedipham detections in the Danish monito ring data are less than 1 ug/L as would be expected based on the PRZM

- GW modeling

.

### Appendix A

Results from FIRST modeling for parent phenmedipham

- Phenmedipham Aerial Spray

1. Aerial Spray One Application **( upper bound**  **scenario** ) July 20, 2004

RUN No. 1 FOR Phenmedipham ON Sugar Beet * INPUT VALUES *

--------------------------------------------------------------------

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .975( .975) 1 1 1860.0 4.7 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

---------------------------------- ---------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/RUNOFF (RESERVOIR) (RES.

- EFF) (RESER.) (RESER.)

--------------------------------------------------------------------

224.00 2 N/A .00

- .00 448.00 448.00

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAG E (CHRONIC)

CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- **29.090 10.820**



### Results from FIRST modeling for MHPC July 21, 2004
Reported results are corrected for actual molecular weight (167) versus previous value used (159)

1. One Application of Parent

RUN No. 1 FOR MHPC ON Sugarbeet * INPUT VALUES *

---------------------------------------------------- ----------------

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .07 2 ( .07 2 ) 1 1 138.046960.0 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

--------------------------------------------------------------------
METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/ RUNOFF (RESERVOIR) (RES.

- EFF) (RESER.) (RESER.)

--------------------------------------------------------------------

104.00 2 N/A .00

- .00 208.00 208.00

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

--------------------------------------------------------------------PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONCENTRATION

----------------------------------------- --------------------------- 5.340 1.726



### Modeling Results (PRZM

- GW) :

Groundwater Analysis for MHPC and the Wisconsin Corn

- WI Central Sands Scenario Estimated groundwater concentrations and breakthrough times for MHPC are presented in Table

1 for the Wisconsin Corn

- WI Central Sands 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 in put values for the model are summarized in Tables 2

and 3.

Table 1. Groundwater Results for MHPC and the Wisconsin Corn

- WI Central Sands

Scenario.

Peak Concentration (ppb) 10.9

Post

- Breakthrough Mean Concentration (ppb) 9.82

Entire Simulation Mean Concentration (ppb) 6.34

Average Breakthrough Time (days) 4219.351

Throughputs 2.597556

Table 2. Chemical Properties for Groundwater Modeling of MHPC.

Koc (ml/g) 138

Surface Soil Half Life (days) 104

Hydrolysis Half Life (days) 0

Diffusion Coeffici e nt Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for MHPC. This application scheme was

### applied every year of the simulation.

Application Days

Relative to Emergence Date (05/01) Appl ication Method Application Rate

(kg/ha)

7 Ground application with mass distribution increasing proportionally with depth to 4 cm 0.076

Figure 1. Aquifer Breakthrough Curve for MHPC and the Wisconsin Corn

- WI Central

Sands Scenario