### UNITED STATES ENV IRONMENTAL PROTECTION AGEN CY WASHINGTON

, D

. C

. 20460



### MEMORANDUM

DATE:

SUBJECT:



### TO:

AN D:

FROM:

APPROVED BY: Apri l 23, 2015 OFFICE OF CHEM I CAL SAFETY AND POLLUTION PREVENTION



### Estimated Drinking Waters Concentrations for the Registration Review of Hexaz i none 

### (PC Code 107201 ; DP Barcode 0424532)

Dana Friedman, Chemical Review Manager Tom Myers, Team Leader Kevin Costello, Branch Chief Risk Manag e ment and Impl ementation Branch II Pesticide Re-evaluation Division (7508P)

Shei l a Pip er, Chemist Donna Davi s, Acting Branch Ch i ef Risk Assessment Branch VI Health Effects Division (7509P)

Jose Melendez

, Chemist 

## Qt4.e"'

# ~;,.J- 

# /J"kb;;,4

_ Environmenta l Risk Branch V 

# t/' 

# 25

Environmenta l Fate and Effects Division (7507P)

# ~ Mah 

### T. Shamim, Ph.D., Branch Ch i ef Environmental Risk Branch V Env ir onmenta l Fate and Effects Division (7507P)

This memorandum presents the Ti e r II Estimated Drinking Water Concentrations (EDWCs)

, calcu l ated using the Tier II surface waters model SWCC, the Tier I/TI groundwater model PRZM-GW (in the Tier I mode), and the Tier J 

### groundwater model SCI-GROW fo r use in the human health risk assessment. for the Registration Review of hexazinone (CAS No. 51235

- 04- 

### 2)

.

For the hexazinone total toxic residues 

### (i. e., hexazinone plus its transformation products)

, the

re s ults of this Drinking Waters Assessment (DWA) show that for surface water, the maximum

acute EDWC i s 502 ppb of hexazinone

, wh i ch is associated with the use on sugarcane in HI ; the chronic value is 206 ppb; and the cancer/chronic value is 77.3 ppb. The maximum groundwater screening E DW C for acute exposure is 3090 ppb ; and the chron i c value is 2260 ppb, associated with the use on rights-of-way 

### (Ta ble la ).

### Additionally, EFED calculated upperbound estimates of the EDWCs associated to hexazinone total toxic residues , including the unextracted residues (UERs) observed in the aerobic soil metabolism study . T he results show that for surface water , the maximum acute EDWC is 5 02 ppb of hexazinone TTRs + UERs , which is associated with the use on sugarcane in HI ; the chronic value is 207 ppb ; and the cancer/chronic value is 77.6 ppb . The maximum groundwater screening EDWC for acute exposure is 3710 ppb ; and the chronic value is 260 0 ppb , associated with the use on rights

- of

- ways ( Table 1 b ).

Finally, as a refinement, EFED calculated groundwater EDWCs associated to hexazinone total toxic residues, applied on past ures/rangeland . As explained in more detail below, the results presented in Table 1c represent applications on sandy loam or sandy soils ( which are the soils in the six standard PRZM scenarios in PRZM

- GW) , for which the lab eled application rate is smaller than for other types of soils . The maximum groundwater screening EDWC for acute exposure is 773 ppb; and the chronic value is 564 ppb, assoc iated with the use on pastures/ rangeland.

A more definitive assessment may be performed, using the Tier II aquatic model SWCC with regional PCAs, using additional refine ment strategies with PRZM

- GW (groundwater) , or using typical application rates

. There are no major data gaps for hexazinone ; h owever, certain uncertainties have been identified in the database as shown and detailed below

. Sho uld any questions arise, plea se contact José Meléndez at melendez.jose@epa.gov

.

EXECUTIVE SUMMARY

Hexazinone [ CAS Name: 3

- cyclohexyl

- 6

- (dimethylamino)

- 1

- methyl

- 1,3,5

- triazine

- 2,4(1 H ,3 H )

- dione, IUPAC Name: 3

- cyclohexyl

- 6

- dimethylamino

- 1

- methyl

- 1,3,5

- triazine

- 2,4(1 H ,3 H )

- dione, CAS Number of 51235

- 04

- 2 and a PC Code of 107201 ], is a triazinone herbicide. According to the sample label for Velpar L, hexazinone is a n “herbicide...applied as a spray for weed contro l in certain crops, Christmas trees, forestry site preparation and release areas, and industrial areas. It may also be applied undiluted as a basal soil treatment for brush control in reforestation areas, rangeland, pastures and noncrop areas, or by stem i njection for brush control.” There are also agricultural uses such like sugarcane, alfalfa, pineapple and blueberries. Hexazinone “is an effective general herbicide providing both contact and residual control of many annual, biennial and perennial weeds and woody plants.” It appears that hexazinone is systemic since it “can absorb...through roots extending into treated areas.” According to the Herbicide Resistance Action Committee (HRAC), hexazinone belongs to the HRAC Group C1 with a site of action inhib ition of photosynthesis at photosystem II. The h erbicide belong s to the triazinone chemical family 1



### .

1 http://www.hracglobal.com/Education/ ClassificationofHerbicideSiteofAction.aspx (accessed 12/04/2014).



### 2O

N C H 3

N

C H 3 C H 3 O N

N



### Figure 1. Structure of Hexazinone

Nationally, hexazinone is an herbicide used to control a broad spectrum of weeds including undesirable woody plants in alfalfa, rangeland and pasture, woodland, pineapples, sugarcane and blueberries. It is also used on ornamental plants, forest trees and other non

- crop areas. Exposure to surface water is possible through surface water runoff, soil erosion and/or off

- target spray drift. Hexazinone has a high solubility, has a low propensity to volatilize, and will remain in the aqueous phase based on the low Henry's Law Consta nt. In laboratory tests, hexazinone was resistant to hydrolysis at all pHs tested and to photolysis in water and on soil. Hexazinone also appears to be relatively resistant to aerobic and anaerobic degradation in soils and aquatic environments with half

- lives greater than 200 days in soils and in water.

The Health Effects Division ’s (HED) Metabolism Assessment Review Committee (MARC) met

on 01/29/ 20 02 and then again on 03/ 12 / 2002 to consider residues of hexazinone and metabolites in/on plant and animal com m odities and in water. The committee decided that hexazinone, the degradate G3170, and all metabolites with conjoined cyclohexyl and triazine rings should be included in the expression of the total toxic residues (TTRs) (memorandum from Sherrie Kinard to Christine Olinger dated April 25, 2002, DP Barcode D282111).

Table 8 lists chemical names and provides structures for the degradates, as they were observed in the submitted environmental fate studies (further information about the degradates is also provided in Appendix B ) . The table shows the chemical structures of hexazinone ’s transformation products : IN

- G3170 (Met. G), IN

- JS472 (Met. 1), IN

- B2838 (Met. D), IN

- G3453 (Met. A

- 1), IN

- A3928 (Met. B), I N

- JT677 (Met. 2), and IN

- T3937 (Met. A)

. T hese transformation products are structurally similar to the parent compound (except for G3170 or Met. G, which contains only one ring) . T hey have essentially the same backbone structure with slight variations in the ring moieties . All the degradation products are considered stressors and the total residue (TR) approach was used to model the total toxic residues (TTR s ). This modeling strategy requires an assumption that all residues of concern have similar physi cal, chemical, and partitioning characteristics. Application rates for the parent pesticide are used to represent the total mass loading of pesticide and its degradation product. This modeling approach does not consider temporal occurr ence of degradation products

. This DWA is mainly based on modeling results

. In this DWA, EDWCs were calculated for the

use s with the maximum application rate s: for SWCC , the use on sugarcane resulted in the highest EDWCs ; further, f or groundwater, the use of PRZM

- GW was implemented and EDWCs are reported relative to the use on rights

- of

- ways

. Results obtained from the models that yielded the highest EDWCs are summarized in Table s 1 a through 1 c ; furthermore, results from all

3

### models are provided later in this review. A m ore definitive assessment could be explored , for example, using Tier II aquatic models SWCC with regional PCAs, performing additional refinements with PRZM

- GW (groundwater) , or using typical application rates

.

Table 1a . Maximum Estimated Drinking Water Concentrations for the Use of Hexazinone Total Toxic Residues ( TTRs, excluding the unextracted residue s)

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year ) MAXIMUM ESTIMATED DRINKING WATER CONCENT RATION (EDWC) ( ppb )
Groundwater ( PRZM

- GW ) NC coast 1 (rights

- of

- way) (8 lb a.i.) Acute 3090 WI sand 1 (rights

- of

- way) (8 lb a.i.) Chronic 2260

Surface water (SWCC ) LA sugarcane with HI meteorological file 2 (sugarcane in HI) (3.6 lb a.i.) Acute 502 Chronic 206 Cancer/Chronic 77.3 1 Scenario was used as a surrogate and run with the maximum application rate for rights

- of

- ways

. 2 Represents applications of hexazinone on sugarcane in Hawaii.



### Table 1b . Maximum Estimated Drinking Water Concentrations for the Use of Hexazinone Total Toxic Residues (TTRs) , including the unextracted residues (UERs) (these E DWCs provide an upperbound estimate of the TTRs )

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year ) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) ( ppb )
Groundwater ( PRZM

- GW ) NC coast 1 (rights

- of

- way) (8 lb a.i.) Acute 3,710 Chronic 2,600

Surface water (SWCC ) LA sugarcane with HI meteorological file 2 (sugarcane in HI) (3.6 lb a.i.) Acute 502 Chronic 207 Cancer/Chronic 77.6 1 Scenario was used as a surrogate and run with the maximum application rate for rights

- of

- ways

. 2 Represents applications of hexazinone on sugarcane in Hawaii.



### Table 1c. Refined Estimated Groundwater Drinking Water Concentrations for the Use of Hexazinone, for the TTRs

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) ( ppb )
Groundwater (PRZM

- GW) NC coast 1 (pastures/rangeland) (2 lb a.i.) Acute 773 WI sand 1 (pastures/rangeland) (2 lb a.i.) Chronic 564 1 Scenario was used as a surrogate and run with the prescribed application rate for sandy loam and loamy sand soils

on pasture/rangeland.



### Uncertainties

Even though the database for hexazinone is substantially complete, one major limitation of the aerobic soil metabolism studies is that they showed high levels of unextracted radioactivity. However, f or the aquatic metabolism studies, the levels of unextracted radioactivity were very low

. Upperbound estimates of the EDWCs were calculated using the half

- lives derived for the TTRs and the UERs. Furthermore, for some of the studies, the duration was too short compared to the derived representative half

- lives. Uncertainty arises in these half

- life estimates. Other

4

### uncertainties of the aquatic models used in this DWA ( i.e

. , SWCC v.1.106 and PRZM

- GW v.1.07 ), are described in the characterization section.

PROBLEM FORMULATION

T he purpose of this DWA is to assess the existing uses for hexazinone and update EDWCs accordingly. Previous assessments have been conducted for this chemical and this DWA builds upon their results. EDWCs w ere obtained based on mode ling, as opposed to monitoring . Even though there is a prospective groundwater monitoring study, it represented the use of alfalfa at 0.75 lb a.i./A (maximum application rate for hexazinone on alfalfa is up to 1.5 lb a.i./A). For hexazinone , the maximum rate for the chemical is 8 lb a.i./A on rights

- of

- ways . Monitoring data was used qualitatively

. Hexazinone may reach surface drinking waters via runoff or drift. It may also reach groundwater through leaching

. Background

A p revious DWA h a s been conducted for hexazinone (DP Barcode D215026 , dated 04/16 /200 2 )

. The surface water concentrations, for hexazinone residues were as follows: acute (peak) value, 130 ppb , and the chronic annual average value, 47 ppb , based on the application of hexazinone on alfalfa, which is the major food crop for the chemical. The groundwater screening
concent ration for hexazinone residues was 41.8 ppb , which were based on monitoring

. Since the latest DWA the model SWCC has replaced PRZM/EXAMS and the ground water PRZM

- GW ha s been approved for use in EFED , in addition to SCI

- GROW . This DWA reflect s those changes. Furthermore, t here is a fair amount of new environmental fate data included in this
assessment.

Use Characterization

Use Information

Nationally, hexazinone is an herbicide used to control a broad spectrum of weeds in alfalfa, rangeland and pasture, woodland, pineapples, sugarcane and blueberries. It is also used on ornamental plants, forest trees and other non

- crop areas. Hexazinone i s registered for pre

emergent, post

- emergence, layby , directed spray and basal soil applications. It is used as a non

selective herbicide in non

- cropland areas and as a selective herbicide in reforestation practices. Hexazinone products are formulated as pellets/tablets, emulsifiable concentrates, soluble concentrates/solids and a technical grade active ingredient. Products are applied using aerial or ground equipment

, by hand, or using a hand

- held, boom, knapsack or power sprayer. There are no indoor us es.

National (Section 3) uses for hexazinone are presented in Table 2 with label maximum application rates. Although the maximum number of applications from the label for some of the

uses is one (1 application per season or year)

, for certain uses the maximum number of applications per year is not specified

. For this assessment, one application per year for those other uses is based on additional information from the label. For example, b lueberry uses may be modeled at a maximum of one application per year due to no application within 450 days of

5

### harvest. Pineapple is modeled as one application per year due to the growing season, which is nearly a year long . Non

- crop uses and forest site preparation and rangeland, are modeled as one application per year due to the requirement for rain to activate hexazinone and because maximum effects are achieved after 12

- 24 months. Hexazinone is usually applied in the spring after ground thaws, or in the fall before snowfall (see Table 2 )

.

Table 2

. Summary of Hex azinone Uses and Application Information

Available SWCC Scenario Crop Methods of Application Max Appl ication Rate (lb a.i./A) Timing of Application 

### Non

- granular applications
NC alfalfa Alfalfa (grown for hay or seed production),

Alfalfa (MT, ND, SD, WY)

Seed alfalfa (CA, ID, MT, NV, OR, UT, WA)

,

Seed alfalfa (Walla Walla, WA) Ground, aerial, chemigation , or impregnated on dry bulk fertilizer

(except CA & AZ) 1.5 (PHI = 30 d),

1,

1 .5

,

1.5 Most w estern states winter ;

e astern states spring

LA sugarcane, (using a HI meteorological file to represent sugarcane in HI ) Sugarcane (except in FL) Ground; or aerial (for pre

emergence only) HI 3.6 (PHI= 180 d); LA 0.9 and 1.5/yr (PHI=

234 d); PR 0.5 and 1/yr (PHI=

288 d); TX 1.75 and 1.75/yr (PHI= 234 d) P re and post

emergence; Spring and fall;

Pre

- and post

emergence;

Pre

- emergence &

layby (60

- day

interval) No available scenario, not modeled Pineapple

Field edges and roadsides Ground ; or aerial 1.75/A/app

, 3.6/A/year (PHI=181 d);

3.6 Intercrop period, post

- mulch pre

plant, post

- plant, post

- emergence (3

- 10 months after planting)

CA wine grape Blueberry (low bush) ;

Blueberry (high bush) Ground (avoid contact with leaves ) , or impregnated on dry bulk fertilizer 3 (PHI 450 d);

2 (PHI 90 d) Spring



### 6Available SWCC Scenario Crop Methods of Application Max Appl ication Rate (lb a.i./A) Timing of Application CA rights

- of

- way Non

- crop sites (weed and brush control) : U ncultivated nonagricultural areas (such as, airports, highway, railroad and utility right

- o f way, sewage disposal areas); U ncultivated agricultural areas (non

- crop producing, which includes: farmyards, fuel storage areas, fence rows, barrier strips); industrial sites (outdoor, such as, lumberyards, pipeline and tank farms) ;

Non

- crop brush control.

Basal (soil) single stem treatment Ground or aerial (helicopter only) ;

Ground or aerial (helicopter only) ;

Handgun applicator 8 ground and 6 for aerial
apps;

8 ground and 6 for aerial
apps;

2

- 4 mL 3 per ea. stem in diameter, do not exceed 8 lb a.i./A/yr Pre

- emergence or post

- emergence when weeds are actively growing

Late winter through summer

CA forestry (see below) Forestry site preparation Eastern and L akes states;

Western US

Grid application (applied directly to the soil surface)

Basal (soil) single stem treatment

Injection Ground or aerial (helicopter only)

Handgun applicator

Handgun applicator

Tree injector 5 ;

4;

5 ;

2

- 4 mL 3 per ea. stem in diameter;

1 mL 3 through

the bark of undesirable
trees Early spring to early summer; Rain belt late winter or spring and snow belt fall ;

From hardwood bud break to early

summer ;

NS;

Summer

CA forestry ( using a MI meteoro

logical scenario to represent eastern forests) Conifer release Eastern and L akes states;

Western US

Grid application (applied directly to the soil surface)

Basal (soil) single stem treatment

Injection Ground

, aerial (helicopter only)

, or impregnated on dry bulk fertilizer

Handgun applicator

Handgun applicator

Tree injector 4 ;

3 ;

4;

2

- 4 mL 3 per ea. stem in diameter; 1 mL 3 through

the bark of undesirable
trees Early spring to early summer; Rain belt late winter or spring and snow belt fall ;

From hardwood bud break to early

summer ;

NS;

Summer

OR Christmas
trees Christmas tree plantations (except in 22 states listed in label) Ground or aerial First year plantings 1.5; Established

trees 2 lb

a.i./A East spring; West >20 in rainfall spring;

West <20 in rainfall fall



### 7Available SWCC Scenario Crop Methods of Application Max Appl ication Rate (lb a.i./A) Timing of Application No available scenario, not modeled Yellow poplar plantations Ground or aeri al 2 Spring

CA rangeland hay ( using a NY meteorological file to represent eastern pastures) Pastures /Rangeland Brush control: Eastern and lakes states,

Western US ;
Basal (soil) single stem treatment Ground or aerial (helicopter only) ;

Handgun applicator 4

,

3 ;

2

- 4 mL 3 per ea. stem in diameter, do not exceed 0.8 lb a.i./yr Late winter through summer

PA turf Bermudagrass /Bahiagrass; Industrial turfgrass Ground 1.125 When weeds are actively growing 

### Granular applications CA rangeland hay Rangeland (pellets) By hand or in a grid pattern for

area control 600 pellets/A= 0.63 lb a.i./A 2 Late Winter to early Summer

CA forestry Conifer release (granular)

Conifer release (pellets) NS (assumed ground) By hand or in a grid pattern for

area control 3;

3800 pellets/A= 4.0 lb a.i./A 2 Late Winter to early Summer

CA forestry Forestry site preparation (granular)

Forestry site preparation (pellets) NS (assumed ground)

By hand or in a grid pattern for

area control 4.7 (Eastern), 4 (Western);

5800 pellets/A= 6.1 lb a.i./A 2 Spring Spring or Fall

CA rights

- of

- way Non

- crop sites (granular) Uncultivated, nonfood producing agricultural areas: farmyards, fuel storage areas, fence rows, rights

- of

- way, fallow land, barrier strips; Uncultivated, outdoor nonagricultural areas: airports, highway rights

- of

- way, railroad rights

- of

- way, utility rights

of

- way (pipelines), sewage disposal areas; Industrial sites (lumberyards, tank farms), etc.

Non

- crop sites (p ellets) Noncropland areas such as utility, highway, pipeline and railroad rights

- of

- way, petroleum tank farms, lumberyards, storage areas, industrial plant sites, the berm of drainage ditches (do not apply to the inside of ditch banks or to the inside of banks along waterways) and other similar are as. Ground, except for military installations (aerial allowed)

By hand or in a grid pattern for

area control 8

7000 pellets/A= 7.4

lb a.i./A 2 Late Winter to Summer

NS

1 Uses assessed based on LUIS report Table 1, EFED label data report, and inspection of labels. 2 Based on the n umber of pellets in a 5.5 lb container ~3900 , and 75% A.I. in formulation (source of number of pellets is Pro

- Serve Inc. ’s website (registrant’s website), at http://www.pro

- serveinc.com/powerpellet.html

, accessed 11/21/14). 3 Application rates in mL are representative of Velpar L labels. They vary for other products , but the rate is the

same

.



### Environm ental Hazard Statements

The following statements appear in the example label for Velpar L Herbicide:

8

### “ Do not apply directly to water, or to areas where surface water is present or to intertidal areas below the mean high water mark. Do not contaminate wa ter when disposing of equipment wash waters.

The active ingredient, hexazinone, in this product is known to leach through soil into ground water under certain conditions as a result of agricultural use. Use of this chemical in areas where soils are perme able, particularly where the water table is shallow, may result in groundwater contamination. ”

Usage

A summary from the Screening Level Usage Analysis (SLUA , provided by BEAD ) for hexazinone is provided in Table 3 . According to the SLUA, the major use for hexazinone by far is alfalfa, followed by sugarcane and pastureland. For all crops, ≤10% of the crop is treated. It should be pointed out that t he SLUA does not provide information about non

- agricultural use
pa tterns of hexazinone

.

Table 3 . Summary of Screening

- Level Estimates of Agricultural Uses of Hexazinone (SLUA, dated 06/16/ 20 09)

Crop (alphabetical) lb a.i. Percent (%) Crop Treated Average Maximum Alfalfa 300,000 <2.5 5 Cotton + 1,000 <1 <2.5 Fallow, Summer <500 <1 <2.5 Hay, Other (NPUD ‘02)+ 4,000 N/C <1 Pasture 20,000 <1 <2.5 Pastureland 8,000 <1 <2.5 Sugarcane 20,000 5 10 All numbers rounded. ‘<500’ indicates less than 500 pounds of active ingredient. ‘<2.5’ indicates less than 2.5 percent of crop is treated. ‘<1’ indicates less than 1 percent of crop is treated. SLUA data sources include: USDA

- NASS (United States Department of Agriculture’s National Agricultural Statistics Service); 2001

- 2007; Private Pesticide Market Researc h, 2001

- 2007; NPUD 2002 (National Pesticide Use Database) of the CropLife America Foundation and California DPR data. These results reflect amalgamated data developed by the Agency and are releasable to the public. N/C = Not Calculated + These crops were not known to be listed on active end use product or emergency exemption (Section 18) registrations when this report was run.



### The U.S. Geological Survey (USGS) pesticide use map ( Fig ure 2 ) show s regional scale patterns in use intensity within the United States

. In comparison to the SLUA, the major use of hexazinone in 20 09

- 11 is pastures and hay (~9 0 % of the use), followed by other (~10%)

. It is noted that the USGS website provides additional u sage maps for 2010 and 2011; however, it is indicated that they are preliminary at this time (and thus, not provided here) . It is apparent from the map, that hexazinone wa s more frequently used in the w est ern half of the continental U.S. in 2009. Additio nally, it wa s used frequently in FL, areas of the MS Delta, and the PA/ NJ region.

9

### Figure 2 . Hexazinone Estimated Agricultural Use (20 09 ) and Use by Year and Crop

Conceptual Model

The conceptual model is a written description and visual representation of potential routes of off

site movement of the pesticide or degradates of concern into surface or ground water that may be a source of drinking water. This is a drinking water assessment that uses modeling d ata to estimate the ground water and surface water concentrations of pesticides in drinking water

10

### source water (pre

- treatment) resulting from pesticide use on sites that are highly vulnerable. This initial tier DWA, using Tier II tools, screens out chemic als with low potential risk and provides estimated exposure concentrations for the human health dietary risk assessment. For hexazinone , the following drinking water hypothesis is being employed for this assessment:

Hexazinone use in accordance with the label, results in potential contamination of, both, surface and ground water resources by the parent compound and its metabolites of concern

. 

### The conceptual site model is depicted in Figure 3 . Through a preliminary iterative process of examining available data, the conceptual model ( i.e. , the drinking water hypothesis) was refined to reflect the likely exposure pathways that are most relevant and applicable to this assessment.

Figure 3

. General Conceptual Model for Pesticide Transport for Hexaz inone

Hexazinone is applied to the fi eld (on the surface of the soil, foliarly

, or as pellets ); a erial and ground applications are allowed on several of the use sites, such as rights

- of

- ways . Crop absorption (crop uptake) is likely when there is foliage since this chemical is systemic

. S pray drift is possible due to the methods of application, except for pellet applications , resulting in possible contamination of nearby bodies of water. As the field may be kept irrigated, large

ru noff events may be a factor in horizontal movement due to the high tendency of the chemical to dissolve and low potential to partition with the soils. Since hexazinone and its residues are
p ersistent , they may be available for very long periods of time in the field (on the order of many months to years, depending on the environmental conditions). F urther, they can also be applied at very high rates of up to 8 lb a.i./A . Vertical movement to subsurfaces ( i.e. , leaching) is expected to be a n important comp onent for hexazinone in vulnerable sites , d ue to its high mobility, combined with its persistence of the chemical and its residues in most environments, and its high application rates. Volatilization is not expected to be an important route of dissipation for the active ingredient due to its relatively low Henry’s Law Constant

. Several degradates were observed in the laboratory environmental fate studies (refer to Table 8 )

. Per the MARC recommendations, i n this assessment they were considered stressors.

11

### The ground water conceptual model (PRZM

- GW), is based on a rural drinking water well beneath an agricultural field (a high pesticide use area) drawing from an unconfined, high water

table aquifer. The depth of the well is site specific ( i.e. , scenario sp ecific). The well extends into a shallow unconfined aquifer and has a well

- screen that starts at the top and extends down into the aquifer 2



### . The length of the well

- screen represents the region of the aquifer where drinking water is collected. The well

- s creen length is well

- specific and can be adjusted. Processes included in the conceptual model that influence pesticide transport through the soil profile include water flow, chemical specific dissipation and transportation parameters ( i.e. , degradation an d sorption), and crop specific factors, including transpiration, pesticide interception and management practices.



### Analysis Plan

Evaluation of submitted labels for the new uses indicates that the highest seasonal rate is for rights

- of

- ways, at 8 lb a.i ./A (for ground applications) . Therefore, primar y focus on this use will be placed in SWCC (v.1.106) , SCI

- GROW (v.2.3) , and PRZM

- GW (v.1.0 7 )

. Additionally, other uses of hexazinone will also be modeled in the SWCC. In all models, the maximum application rate indicated in the label will be used. The timing of application will be the one typical for the crop modeled (a ccording to the label directions )

. Even though the database for hexazinone is essentially complete, one uncertainty arises related to the levels of unextracted radioactivity in the aero bic soil metabolism studies. In order to clear this uncertainty, for the crops yielding the highest EDWCs, special run s will be performed using the half

- lives for the total residues, including the unextracted radioactivity. For more details, see the Characterization section.

Exposure output of interest to HED will be primarily point estimates and

, if necessary in future modeling, distributions will be provided. Acute and chronic EDWCs will be provided.

ANA LYSIS

Fate and Transport Characterization

The chemical profile of hexazinone is provided in Table 4

. Environmental fate characteristics of the parent compound hexazinone are listed in Tables 5 and 6 and are discussed in greater detail in the following sections.

Hexazinone has a moderately high molecular weight of 252.3 g/mol. With a very high solubility (29800 ppm) and a low octanol/water partition coefficient (K OW 

### = 15) . Based on these properties, i t appears that hexazinone has a very low potential to bioaccumulate/bioconcentrate. With a very high solubility , a relatively low vapor pressure (1.9 x 10

- 7 

### mmHg), and a very low Henry’s Law Constant (2 x 10

- 12 

### atm

- m 3 

### /mol), hexazinone does not appear to volatilize substantially from wet / moist surfaces.

2 A well screen is a filtering device that allows groundwater from unconsolidated and semi

- consolidated aquifers to enter the well while at the same time keeping the majority of sand and gra vel out of the well.



### 12

### Table 4 . Chemical Profile of Hexazinone
Property Value Reference and Comments

Chemical Structure O

N C H 3

N

C H 3 C H 3 O N

N Product Chemistry

Pesticide type Herbicide

Product Chemistry Chemical class Triazinone Molecular Formula C 12 H 20 N 4 O 2 Molecular Weight 252.3 g/mol CAS No. 51235

- 04

- 2

CAS name 3

- Cyclohexyl

- 6

- (dimethylamino)

- 1

- methyl

- 1,3,5

- triazine

2,4(1 H ,3 H )

- dione

IUPAC name 3

- Cyclohexyl

- 6

- dimethylamino

- 1

- methyl

- 1,3,5

- triazine

2,4(1 H ,3 H )

- dione Water solubility 29800 ppm at 25°C MRID 41203201 ( reported in DP Barcode D279324 ) Vapor pressure 1.9 x 10

- 7 torr at 25 ° C [‘ Non

- volatile under field conditions’ from dry non

adsorbing surfaces (1) ] Henry’s Law Constant 2 x 10

- 12 atm

- m 3 /mol; at 25 ° C Calculated from WS and VP

Octanol /Water Partition 15 at pH 7.0 (temperature unspecified) MRID 41203201 ( reported in DP Barcode D279324 ) (1) For classification scheme, see USEPA, 2008. See also “ Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem Formulations,” available at http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/endangered_species_reregistration_work group/esa_reporting_fate.htm#guidance (accessed 12/04/2014).



### Based on the available information, hexazinone residues (hexazinone and various metabolites) appear to be persistent and mobile in soil and aquatic environments and considered as the
stressor ( s ) in this assessment ( note that the half

- lives for the total toxic residues or TTRs of hexazinone a re presented in the next to the last column in Table 5 , before the study classification ). The mobility of hexazinone was demonstrated in batch equilibrium as well as terrestrial field, forestry dissipation , and a prospective groundwater monitoring studies ( Table 6 )

. Hexazinone is stable to hydrolysis and photolysis and degrades at moderate ly slow rates under aerobic soil metabolism conditions . Aerobic and anaerobic aquatic metabolism and anaerobic soil metabolism studies show slow degradation for hexazin one

. Consistent with this persistence, f ield di ssipation half

- lives were 123 to 154 days for the parent compound in bare ground silt loam, silty clay loam and sandy loam soils. Laboratory adsorption data show low water/soil partitioning for hexazinone (K OC 

### = 38

- 77 mL/g OC 

### , mobile according to FAO 2000 mobility classification). These data indicate that hexazinone is mobile, thus, combined with its persistence, having stro ng potential to leach to ground water systems, especially in soil systems such as loam y and sand y soils that are poor in organic matter. Based on laboratory

13

### bioaccumulation in rainbow trout, hexazinone is not expected to bioaccumulate substantially in fish tissue , which is consistent with the low K OW 

### value of 15 ( i.e.
, l og K OW 

### = 1.1).

Tab le 5 . Summary of Environmental Fate Properties of Hexazinone Related to Degradation and Metabolism

Study System Name/ Characteristics Value for Hexazinone 1 (Kinetic Model if Applicable) Half

- life Value Used to Derive

Model Input Parameters TTRs 2 Reference, ( Study Classification* ) DT 50 (days) DT 90 (days)

Abiotic Hydrolysis pH 5, 25 0 C Stable Stable 41587301 (A) pH 7, 25 0 C Stable Stable Stable (0) pH 9, 25 0 C Stable Atmospheric Degradation 3 Hydroxyl radical 3 0.119 (estimated) EPI Suite v.4.11
Aqueous Photolysis pH 7, 25 0 C Stable Stable Stable (0) 41300801 (A)

Soil Photolysis Sandy loam from CA, pH 6.5, 0.6 % OM, 2 0 0 C 82 (light exposed); stable (dark

control) 41300802 (A)

Aerobic Soil Metabolism Sandy loam (CA), pH 6.5, 0.6 % OM, 2 5 0 C 216 604 days (SFO) 41807401/ 42635001 (A) Audrain clay loam soil (M O ) , pH 6.6, 4.1% OM, 20 ° C 45.2 ( IORE ) 180 ( IORE ) 208 days (SFO)

48898001 (S) Sassafras sandy loam ( MD ) , pH 5.4, 2.0% OM, 20 ° C DFOP slow
t 1/2 = 143 days 416 days (SFO)

Porterville loam ( CA ) , pH 7.7, 1.11% OM, 20 ° C 115 (SFO) 381 (SFO) 534 days (SFO)

Input value for modeling with the SWCC , at 25 0 C. from the four above mentioned systems 90 th percentile confidence bound on the mean half

- life value : four values are available: 208, 416 and 534 (at 20°C)

, and 604 (at 25°C) days; the corrected half

- lives at 25°C, are 147, 294, 378, and 604 days; mean = 355.75 days; std. dev. = 191.06 days , n = 4,
t 90,n

- 1 = 1.638. n s t t t 1

- n 90, 1/2 input + =



### = 512.2 days

Anaerobic Soil Metabolism Raymondville sandy clay loam (TX), pH 8.0, 0.83% OM, 20oC 389 ( SFO ) 1292 (SFO)

48898002 (S) Mexico clay loam (MO), pH 6.6, 4.1% OM, 20 ° C 997 ( SFO ) 3311 (SFO)
Sassafras sandy loam (MD), pH 5.4, 2.0% OM, 20 ° C 309 ( SFO ) 1026 (SFO)

Porterville loam (CA), pH 7.7, 1.11% OM, 20 ° C 1,165 ( SFO ) 3872 (SFO)



### 14Study System Name/ Characteristics Value for Hexazinone 1 (Kinetic Model if Applicable) Half

- life Value Used to Derive

Model Input Parameters TTRs 2 Reference, ( Study Classification* ) DT 50 (days) DT 90 (days)

Aerobic Aquatic Water:sandy loam sediment (CA), water pH 7.9

- 8.0 4

, sediment pH not reported, 0.7% OM, 2 5 ° C >2 months 1046 days (SFO) 41811801 (A)

Wabasha Water:sandy loam sediment (MN), water pH 7.2, sediment pH 6.0, 7.1% OM, 20 ° C 528 (SFO) 1755 (SFO) 1274 days (SFO)

49109901 (S) Tift Water:sandy loam sediment GA, water pH 7.7, sediment pH 7.5, 1.2% OM, 20 ° C 719 (SFO) 2389 (SFO) 1900 days (SFO)

Input value for modeling with the SWCC , at 25 0 C. from the three above mentioned systems 90 th percentile confidence bound on the mean half

- life value: three values are available: 1274 and 1900 days ( at 20°C), and 1046 days (25°C); the corrected half

- lives at 25°C, are 901, 1344, and 1046 days; mean = 1097 days; std. dev. = 225.86 days , n = 3,
t 90,n

- 1 = 1.886. n s t t t 1

- n 90, 1/2 input + =



### = 1343 days

Anaerobic Aquatic Water:loam sediment (CA), water pH 7.83, sediment pH 8.5 , 1.24% OC

, 2 5 ° C 230 1837 days (SFO) 41807402 (A)

Wabasha Water: sandy loam sediment (MN), water pH 7.2, sediment pH 6.0, 7.1% OM 20 ° C 482 (SFO) 1602 (SFO) 1395 days (SFO)

49109902 (S) Tift Water:sandy loam sediment (GA), water pH 7.7, sediment pH 7.5, 1.2% OM, 20 ° C 961 (SFO) 3192 (SFO) 1343 days (SFO)

Input value for modeling with the SWCC , at 25 0 C. from the three above mentioned systems 90 th percentile confidence bound on the mean half

- life value: three values are available: 1 395 and 1 383 days ( at 20°C) , and 1837 days (25°C); the corrected half

- lives at 25°C, are 986, 978, and 1837 days; mean = 1267 days; std. dev. = 493.65 days , n = 3, t 90,n

- 1 = 1.886. n s t t t 1

- n 90, 1/2 input + =



### = 1805 days

* (A) = Acceptable; (S) = Supplemental Bolded values represent input values in the aquatic modeling in SWCC and/or PRZM

- GW

. 1 DT 50 and DT 90 values were calculated using nonlinear regression and single first

- order (SFO), double first

- order

in parallel (DFOP), or indeterminate

- order equation (IORE). For DFOP, the overall DT 50 and DT 90 are reported when available. Otherwise, a first and secon d DT 50 are reported. The equations can be found in the document, Standard Operating Procedure for Using the NAFTA Guidance to Calculate Representative Half

- life Values and



### 15Characterize Pesticide Degradation, U.S. Environmental Protection Agency dated Nove mber 30, 2012 and approved December 17, 2012. 2 The value used to estimate a model input value is the calculated SFO DT 50 , t R I ORE , or the 2 nd DT 50 from the DFOP

equation. The model chosen is consistent with that recommended using the, Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media , Health Canada, U.S. Environmental Protectio n Agency, December 21, 2012. 3 Estimated value. In order to make this estimate, there are certain assumptions made by the module of EPISUITE

,

which represent a typical hydroxyl reaction in the atmosphere (refer to AOPWIN module at http://www.epa.gov/opptintr/exposure/pubs/episuite.htm accessed 12/09/14 ). There is no ozone reaction calculation available in EPI Suite v.4.1 for this chemical. 4 Measured in the first test interval.



### Hexazinone was stable to hydrolysis in buffered solutions at pH 5, 7 and 9 at 25oC. The chemical comprised from 99

- 100% of the total radioactivity in all samples. When exposed to an artificial light source, hexazinone did not appear to degrade significantly in pH 7 buffered solutions. Similar hexazinone recoveries were observed for the light irradiated and dark control samples. No major degradates were identified in these samples. In a soil photodegradation study, using a sandy loam soil from Modesto, CA (pH 6.5 ), hexazinone’s half

- life was 82 days, equivalent to an environmental half

- life of 228 days at latitude 30 to 50oN, assuming a 12

- hour photoperiod. The major transformation product was Met

. B, which was 9.5

- 10.1% of the applied at 30 days (last test inter val).

Hexazinone’s half

- lives were 216 and 1440 days, when applied to viable and sterile (autoclave d ) sandy loam soil (pH 6.5) from Modesto, CA, and maintained under aerobic conditions in the dark at 25oC. The viable and sterile soil data indicate that d egradation was mainly a result of microbial activity. Carbon dioxide accounted for 2.2 and 0.03% of the applied after 365 days for the viable and sterile soils, respectively. The aerobic transformation of hexazinone was also studied in three U.S. soils i n a separate study : a sandy loam from MD (Sassafras, pH 5.4), a clay loam soil from Missouri (Audrain, pH 6.6), and a loam soil from CA (Porterville, pH 7.7) for up to 150 days at 20°C

. Representative IORE half

- life ( t R IORE 

### ) was 54.3 days in the clay loam soil; slow t 1/2 

### DFOP was 143 days in the sandy loam soil; the SFO half

- life was 115 days in the loam soil . Evolved 14 

### CO 2 

### totalled a maximum of 2.8

- 9.7% of the applied at study termination. Unextracted radioactivity was sig nificant and increased to a maximum of 25.6% of the applied at 150 days (for the Audrain clay loam soil)

. A transformation pathway was provided by the study author ( Figure 4 )

.

16

### Figure 4

. Transformation Pat hway Proposed by the Registrant (source : MRID 48898001)

The anaerobic soil metabolism of hexazinone was studied in four U.S. soils: a sandy clay loam soil from T X (Raymondville, pH 8.0), a clay loam soil from M O ( Mexico, referred to as Audrain ; pH 6.6), a sandy loam soil from M D (Sassafras, pH 5.4), and a loam soil from CA (Porterville, pH 7.7) for 31 days under aerobic conditions

, followed by 149 days under anaerobic conditions in darkness at 20 ° C. Half

- lives were 389 days in the Raymondville sandy clay loam soil, 997 days in the Audrain clay loam soil, 3 09 days in the Sassafras sandy loam soil, and 1 ,165 days in the Porterville loam soil (SFO in all instances)

. Unextracted radioactivity increased to a maximum of 28.2% of the applied at 31 days posttreatment (0 day po st

- flood), and was 12.6% at 180 days (149 days post

- flood) in the clay loam soil

. Total evolved 14 

### CO 2 

### was ≤1.3% of the applied in all four soils.

The half

- life for hexazinone in an aerobic aquatic metabolism study, consisting of a sandy loam sediment (pH 7.8, %OM = 0.7) and water (pH 8.2) from Madera, CA was >60 days, both in viable and sterile (autoclave) systems. Hexazinone accounted for ~80

- 84% and ~86

- 87% of the applied radioactivity at the end of the study (56 days) in the viable and sterile samples

, respectively. The majority of the applied radioactivity was related to the water (as opposed to

17

### the sediment). At the beginning and end of the study, 88.3% and 76.4% of the applied radioactivity were related to the water, respectively. T he aerobic aqu atic metabolism of hexazinone was also studied in a MN water:sandy loam sediment system (Wabasha; water pH 7.2, sediment pH 6.0 and OC 4.1%) and a GA water:sandy loam sediment system (Tift; water pH 7.7, sediment pH 7.5, and OC 0.70%) in closed systems at 20 ° C. Hexazinone dissipated with half

- lives of 528 days in the Wabasha water:sandy loam sediment system and 719 days in the Tift water:sandy loam system. Unextracted radioactivity was ≤4.9%. 14 

### CO 2 

### was a maximum of 0.1% of the applied at 100 days posttrea tment.

In an anaerobic aquatic metabolism study, tha t consisted of a loam (pH 8.5, OC = 1.24 % ) and pond water (pH 7.83), the half

- lives were 230 and >1,500 days for the viable and sterile (autoclave d ) systems. Hexazinone was an average of 95.6% and decreased to 29.0%, at times 0 and 365 days, respectively. In another study, t he anaerobic aquatic transformation of hexazinone was studied in a MN water:sandy loam sediment system (Wabasha; water pH 7.2, sediment pH 6.0 and O C 4.1 % ) and a GA water:sandy loam sediment system (Tift; water pH 7.7, sediment pH 7.5, and OC 0.70%) in closed systems at 20 ° C. Hexazinone dissipated with half

- lives of 4 82 days in the Wabasha water:sandy loam sediment system and 9 61 days in the Tift wat er:sandy loam system. Unex tracted radioactivity was ≤ 4.8 % of the applied and 14 

### CO 2 

### was not detected during the study

.

Table 6 . Summary of Other Environmental Fate Properties of Hexazinone ( Mobility , Field Dissipation and Fish BCF )

Study System Name/ Characteristics Value (units if applicable) Reference, ( Study Classification* ); Comments

Mobility for Hexazinone Soil \ Property K F (mL/g) K FOC (mL/g OC ) MRID 43621501 (A);

K OC model describes the mobility better than the K d model. For K OC the coefficient of variation is smaller than for K d
. Sassafras sandy loam 0.21 40 Trevino sandy loam 0.59 77 Chino loam 0.84 75 Tama silt loam 0.53 38 Mean Value 57.5 Mobile 1

Additional notes 1/n range 0.86

- 0.93 for the adsorption isotherms

. Desorption step done at a single conc entration

.

Terrestrial Field Dissipation Bareground s ilt loam in Newark, DE 123 days; >95% confined to the upper 30 cm of soil 42377901 (A); Met s A, A

- 1, B, C, and 1 were identified in

one or mor e sites at max. of 0.04, 0.21, 0.31, 1.23, and 0.71 ppm, respect

. Bareground s ilty clay loam in Greenville, MS 154 days; hexazinone did move to a depth of 60

- 75 cm

Bareground sandy loam soil in Madera, CA 140 days; hexazinone leached to the 90 cm depth level of soil

. 4237920 (S) ; Met s A, A

- 1, B, C, and 1 were identified in soils at max

. of 0.05, 0.04, 0.29, 0.62, and 0.20 ppm, respect.



### 18Study System Name/ Characteristics Value (units if applicable) Reference, ( Study Classification* ); Comments

Forestry Field Dissipation Forest

- land watersheds (loams) in Coosa county, AL Hexazinone

, at 6.72 lb a.i./A , dissipated with h alf

- lives of 26 to 59 days and 19 to 36 days in plants, for the Velpar ULW site and the Velpar L site, respectively. Half

- lives of 55 to 77 days were reported for litter and soil. For litter covered soil, a half

- life of 265 days was reported. Hexazinone was observed in soil at depths >30 cm (0.01 to 0.04 ppm). H exazinone was detected in runoff water up to 6 months post

- application (80 to 140 ppb). Hexazinone was also detected in stream samples ( both sites )

. 42336401 (A) ; Met s A, B, C, D, E, G, and B were discernible in various matrices (soil, water, litt er and/or vegetation) samples. Hexazinone and metabolites were consistently disce rnible in soil samples taken to a depth of 15 to 30 cm from both sites.

Prospective groundwater monitoring Velpar L was applied at 0.75 lb a.i./A in Merced County, CA sand planted with alfalfa The leaching potential of hexazinone and IN

T3937 (Met. A), IN

- A3928 (Met. B), IN

- T3935 (Met. C), IN

- G3453 (Met. A

- 1), IN

- JS472 (Met. 1), and IN

- G3170 (Met. G3170) was studied in a

vu lnerable site for up to 35 months. Soil, groundwater, and soil pore

- water samples we re analyzed for hexazino ne and m etabolites

. Hexazinone dissipated from the upper 2 feet of soil with a ca lculated half

- life of 25 days

. Results indicated that hexazinone and its degradates are very mobile and persistent. They leach ed through the soil profile and into the
groun dwater. Hexazinone concentrations above background (~0.05 ppb) were first detected in pore water at the 3

- foot depth at 60 days posttreatment and in the 6

- and 9

- foot depths at 95 days. The breakthrough of hexazinone and degradate B into the shallow grou ndwater

occu rred at 152 days posttreatment. 45132801 (S) ; Hexazinone and all metabolites except Met. G m oved at the same rate through the unsaturated zone and into groundwater as the bromide tracer, while Met. G movement was somewhat retarded. Met. G

was the predominant degradate in the soil, soil pore water, and groundwater; its breakthrough into the shallow groundwater occurred at 336 days.

Fish BCF Rainbow trout The studies showed that hexazinone did not have the tendency to bioaccumulate in fish. Based on its low octanol/ water partition coefficient (15 at pH 7.0, temperature unspecified ), hexazinone is not be expected to substantially accumulate in fish. 00064265 (00078032) ; 41203201 ( reported in DP Barcode D279324 ) (W)

* (A) = Acceptable; (S) = Supplemental ; (W) = Waived

Bolded values represent input values in the aquatic modeling in SWCC and/or PRZM

- GW

. 1. Mobility classification per FAO 2000.



### Mobility

In a Madera loam, Hanford sandy loam, Cecil sandy loam and Flanagan silty loam, the adso rption K d 

### values were 10.8, 0.24, 0.45 and 1.03 mL/g, respectively. Meanwhile, in a Tama silty loam, Chino L, Trevino sandy loam and Sassafras sandy loam, the Freundlich K F 

### values were 0.53, 0.84, 0.59 and 0.21, respectively. For the latter soils, the Freundlich K FOC 

### values were 38, 75, 77 and 40, respectively. The 1/N values were relatively close to unity (0.93, 0.91, 0.91 and 0.86, respectively). Additional s upplemental data provided by the second study, indicate that the metabolites A, B, D, H, 1, 2 and A

- 1 have similar mobility than the parent compound ( Table 7 ).

19

### Table 7 . Mobility of Hexazinone Metabolites Adsorption (Mobility) Studies K d K OC Source (MRID) Metabolite 1 0.20 122

43621501 (s upplemental portion of the study) Metabolite 2 0.15 45 Metabolite A 0.69 176 Metabolite A

- 1 0.03 27

Metabolite B 0.44 90 Metabolite D 0.34 59 Metabolite H 0.31 51



### Field Studies

One terrestrial field dissipation study was conducted at two sites, on a silt loam in Newark, DE and on a silty clay loam in Greenville, MS. The respective half

- lives were 123 and 134 days in bare ground plots. The metabolites A, A

- 1, B, C and 1 were identified in soils at maximum concentrations of 0.04, 0.21, 0.31, 1.23 and 0.71 ppm, respectively. The reported data indicate that hexazinone, at 12 lb a.i./A, did not move substantially beyond the top 30 cm of soil (>95% confined to the upper 30 cm of soil) at the Newark site. However, hexazinone did move to a depth of 60

- 75 cm at the Greenville site. In addition , the hexazinone metabolites (particularly C in Newark) leached to a depth of 75 cm of soil during the testing period.

Hexazinone, at 12 lb a.i./A, had a dissipation half

- life of 140 days in a bareground sandy loam in Madera, CA. Metabolites A, A

- 1, B, C and 1 were identified in soils at maximum concentrations of 0.05, 0.04, 0.29, 0.62 and 0.20 ppm, respectively. The reported data indicate that hexazinone leached through the 90 cm soil depth. The hexazinone metabolites were not reported below a depth of 30 cm of soil during the testing period. The study was considered supplemental because the concentrations at time zero were too low, compared to the theoretical (or expected) value; however, the day 7 thru 60 post

- treatment samples had concentrations of 40

- 51% of the theoretical maximum rate.

Forestry Field Study

Hexazinone dissipated with reported half

- lives of 26 to 59 days and 19 to 36 days in plants for the Velpar ULW site and the Velpar L site, respectively, in a forestry field dissipation study. Hexazinone was applied to typical piedmont pine forestland; an application rate of 6.72 lb a.i./A was used on separate forestland watersheds in Coosa County, AL. Similar half

- lives of 55 to 77 days were reported for litter and soil for the two sites (exce pt litter covered soil). For litter

covered soil, a half

- life of 265 days was reported. By day 365 post

- treatment, hexazinone was discernible only in sediment samples. Hexazinone moved off

- site through leaching and runoff. Hexazinone (0.01 to 0.04 ppm) was observed in soil at depths >30 cm. In addition, it was detected (80 to 140 ppb) in runoff water up to 6 months post

- application. In the study, hexazinone was detected from stream samples from both sites (maximum concentration 473 ppb at 1150 hours po st

- treatment at the Velpar L site).

In addition, metabolites A, B, C, D, E, G, and H were discernible in various matrices (soil, water, litter and/or vegetation) samples. M etabolite G was not confirmed by MS. Metabolites A, B

20

### and H were detectable in the peripheral drainages (1

- 3 ppb, <25 of 293 samples). Metabolites A, B, C, D and E were discernible in fern, dogwood, grass and blueberry plant tissues (both sites). B and D were the most frequently detected metabolites (Velpar L site). I n the soil sa mples, hexazinone and its metabolites were consistently observed thru 30 cm depth, with detections thru 75

- 90 cm soil depth. The metabolites A

- 1 and 1 were not analyzed for in the study. A prescripted burn of all three watersheds (Velpar ULW, Velpar L an d control plots) took place 6 months post

- treatment.

Small Scale Prospective Groundwater Monitoring Study

Hexazinone [Velpar L, 2 lb a.i/gallon water

- dispersible liquid] was broadcast applied once at 0.75 lb a.i./A in January 1996 onto a field of alfalfa underlain with sandy soil in Merced County, C A . The site is located within the recharge area for a shallow unconfined aquifer. The treated area consisted of five 100 x 300 foot strips separated by irrigation berms, and the control area was 100 f eet distant and upgradient from the treated area. The organic matter content of the soil

was ≤ 0.7%, the pH was 7.5

- 8.9 in the upper 1.5 feet, and there were no continuous impeding layers.

The first rainfall was received at 7 days and the first irrigation event was at 75 days. T he site r an a slight water deficit through January 29, 1996 (18 days posttreatment). The cumulative water budget was ca. 1.5 inches by 1 month and 2 inches by 2 and 3 months posttreatment. During the length of the study, the tota l rainfall received was 41.62 inches and the total irrigation received was 133.7 inches for a combined water input of ca. 175 inches, which was reported as 111% of the normal water input. The cumulative water budget through the study was positive, as the sum of precipitation plus irrigation remained greater than evapotranspiration. However, the cumulative water budget decreased in the summer when evapotranspiration was high, despite the irrigation , while the water budget increased in the winter when evapo transpiration was low. No substantial runoff events were reported.

Bromide concentrations in soil pore

- water and groundwater showed that the total water input was sufficient to facilitate leaching to groundwater during the study period. The depth of the water table ranged from 8 to 15 feet below ground surface (bgs) during the study. Potassium bromide was used as a tracer; breakthrough into the shallow groundwater occurred at about 152 days post

- treatment. Soil (measured to 2 feet), soil pore water (ly simeters at 3, 6, 9, and 12 feet), and groundwater (wells screened at ~14

- 19 and ~20

- 25 feet bgs) samples were collected at up to 1063 days (~35 months) post

- treatment and analyzed using HPLC for hexazinone and six metabolites: G3170, A, B, C, A1, and 1.

Hexazinone dissipated from the upper 2 feet of soil with a calculated half

- life of 25 days (r 2 

### = 0.9997; first order kinetics). Hexazinone and its ’ degradates exhibited a pattern of leaching through the soil profile and into the groundwater. Hexazinone c oncentrations above background (~0.05 ppb) were first detected in pore water at the 3

- foot depth at 60 days post

- treatment and in the 6

- and 9

- foot depths at 95 days. The breakthrough of hexazinone and degradate B into the shallow groundwater occurred at 152 days post

- treatment. G3170 (or Met. G) was the predominant degradate in the soil, soil pore water, and groundwater; G3170 breakthrough into the shallow groundwater occurred at 336 days. Hexazinone and Mets

. G3170 (or G) , B, and A

- 1

21

### were the major ana lytes detected when the residues reached groundwater at 336 days posttreatment. Following 824 days and at the end of the study period, Met. G3170 was the dominant analyte.

A verage background hexazinone concentrations in shallow monitoring wells were 0. 05

- 0.18 ppb from pre

- application to 214 days, increasing to 0.43 ppb at 271 days, 0.71 ppb at 336 days, and 2.02 ppb at 363 days. The first detections in groundwater were observed between 125 and 152 days in Clusters 1 and 4, with higher detections observ ed beginning at 271 days. Met. G3170 first increased above background levels to an average of 1.27 ppb at 363 days, and was a maximum average concentration of 2.95 ppb in shallow wells at 424 days. Met. B first increased above background levels at 363 da ys, and was an average maximum concentration of 1.31 ppb at 424 days. Met. A

- 1 first increased above background levels at 363 days, and was an average maximum concentration of 0.71 ppb at 424 days. Met. 1 first increased above background levels at 363 da ys, and was an average maximum concentration of 0.42 ppb at 424 days. Metabolite C was first observed consistently above background levels at 641 days, and was an average maximum concentration of 0.54 ppb at 851 days. Met

. A was not observed above backgro und levels.

H exazinone was first detected in deep monitoring wells above background levels in Cluster 1 at 214 days (0.258 ppb), in Cluster 4 at 487 days (0.113 ppb), in Cluster 6 at 522 days (0.212 ppb), in Cluster 2 at 578 days (0.408 ppb), in Cluster 3 at 673 days (0.142 ppb), in Cluster 7 at 673 days (0.115 ppb), and was not observed in deep wells at Clusters 5 and 8, which were located in the eastern portion of the test plot (refer to next paragraph)

. There was a distinct difference in the movement of hexazinone through soil in the western and eastern portions of the site. Hexazinone residues were detected infrequently and at later intervals in groundwater in the eastern portion of the site, where soil s were less sandy with thicker soil lens. Results indicated that hexazinone and its’ degradates are very mobile and persistent. The Mets. D and 2 were not monitored in the small

- scale prospective groundwater monitoring study.

Bioconcentration in Fish

B ased on laboratory bioaccumulation in rainbow trout, hexazinone is not expected to bioaccumulate in fish substantially , which is consistent with the low octanol/water partition coefficient, K OW 

### value of 15 (log K OW 

### = 1.12). Hexazinone has been shown to ac cumulate in rotational crops.

Transformation Products

Transformation products of hexazinone are generally formed slowly and are also mobile and persistent ( Table 8 )

. The major photodegradation product on soil, was Met. B (10.1% of applied). Under aerobic soil and aquatic conditions, major metabolites included G, 1, and A

- 1, with various other minor metabolites observed. In anaerobic soil and aquatic conditions, Mets. G, 1, D, and 2 were among the major degradates. Mets. A, A

- 1, B, C and 1 w ere identified in soils in terrestrial field. M et s

. A, B, C, D, E, G, and H were discernible in various matrices (soil, water, litter and/or vegetation) samples in forestry field samples. Mets. D and 2 were major

22

### degradates found in anaerobic conditions; however, the field dissipation and the small

- scale prospective groundwater monitoring studies did not monitor these two metabolites. The fate of Mets. D and 2 could not be assessed under natural environment; the registrant believed that both field studie s were mostly aerobic and the metabolites were unlikely to be observed. The field dissipation studies did not monitor the fate of Met. G3170 (G) ; however, it was found to be at the highest concentrations in the small

- scale prospective groundwater monitori ng study. This metabolite was found to increase with time in three aerobic soils in a 150

- day long aerobic soil metabolism study

. 

### Further information about the degradates of hexazinone can be found in Appendix B

.

Unextracted Residues

It was observed that in the aerobic soil and anaerobic soil metabolism studies high levels of unextracted radioactivity were formed, by using only simple extraction techniques. In this assessment, to clear the uncertainty relative to the unextracted resid ues (UERs), EDWCs were calculated using both the total toxic residues and the total toxic residues plus the UERs, to provide an upperbound level for the EDWCs.

Table 8 . Transformation Products of Hexazinone

Common Name Chemical Name Structure IN

- G3170; Met. G or G3170 IUPAC: 1

- Methyl

- 6

- (methylamino)

- 1,3,5

- triazine

2,4

- dione

Formula: C 5 H 8 N 4 O 2 MW: 156.14 g/mol SMILES: [H]n1c(=O)nc(n(c1=O)C)N([H])C H

N

O N

C H 3 N C H 3

H N O

IN

- JS472; Met. 1 IUPAC: 6

- (Dimethylamino)

- 1

- methyl

- 3

- (4

- oxocyclohexyl)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 18 N 4 O 3 MW: 266.3 g/mol SMILES: Cn1c(nc(=O)n( c1=O)C2CCC(=O)CC2)N(C)C O

N N

N

C H 3 C H

N

C H 3 O O



### 23Common Name Chemical Name Structure IN

- B2838; Met. D IUPAC: 1

- Cyclohexyl

- 3

- methyl

- 1,3,5

- triazinane

2,4,6

- trione

Formula: C 10 H 15 N 3 O 3 MW: 225.2 g/mol SMILES: Cn1c(=O)[nH]c(=O)n(c1=O)C2CCCCC2 N

O N

C H 3 O N O

IN

- G3453; Met. A

- 1 IUPAC: 6

- (Dimethylamino)

- 3

- (2

- hydroxycyclohexyl)

- 1

- methyl

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 20 N 4 O 3 MW: 268.3 g/mol SMILES: Cn1c(nc(=O)n(c1=O)C2CCCCC2O)N(C)C

O H

O N

N

C H 3 N C H

C H 3 N O

IN

- A3928; Met. B IUPAC: 3

- Cyclohexyl

- 1

- methyl

- 6

- ( methylamino)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 11 H 18 N 4 O 2 MW: 238.28 g/mol SMILES: [H]N(C)c1nc(=O)n(c(=O)n1C)C2CCCCC2 N

O N

C H 3 N H

C H 3 N O



### 24Common Name Chemical Name Structure IN

- JT677; Met. 2 IUPAC: 6

- (Dimethylamino)

- 1

- methyl

- 3

- (2

- oxocyclohexyl)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 18 N 4 O 3 MW: 266.3 g/mol SMILES: Cn1c(nc(=O)n(c1=O)C2CCCCC2=O)N(C)C

O N

O N

C H 3 N

C H 3 C H 3 N O

IN

- T3937; Met. A IUPAC: 6

- (Dimethylamino)

- 3

- (4

- hydroxycyclohexyl)

- 1

- methyl

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 20 N 4 O 3 MW: 268.3 g/mol SMILES: Cn1c(nc(=O)n(c1=O)C2CCC(CC2)O)N(C)C O

N N

N

C H 3 C H 3 N

C H 3 O O H

Carbon dioxide IUPAC: Carbon dioxide

Formula: CO 2 MW: 44 g/mol SMILES: C(=O)=O C O O



### Drinking Water Exposure Modeling

Surface Water Models

SWCC For agricultural and certain non

- agricultural uses, exposure concentrations for surface drinking waters assessments are estimated based on EFED’s Tier II aquatic model PRZM/VVWM. A graphical user interface Surface Water Concentration Calculator (SWCC v.1. 106, May 6, 2014), developed by the EPA, was used to facilitate inputting chemical and use specific parameters into the appropriate input files and chemical files, replacing the older PE5 shell (November 2006), which used PRZM3 and EXAMS. The SWCC estimat es pesticide concentrations in water bodies that result from pesticide applications to land. The calculator was designed for regulatory applications as applied in the Office of Pesticide Programs, USEPA, as well as PMRA, Health Canada. The calculator us es the Pesticide Root Zone Model (PRZM v5.0+, May 6, 2014) and the Varying Volume Water Body Model (VVWM, May 6, 2014, a replacement for the older EXAMS model). The PRZM field or orchard crop scenario is the basic file which describes the local or regiona l climatological information, soil hydrology, soil characteristics, crop characteristics, and the pesticide properties necessary to determine pesticide loadings to surface water. This basic file constitutes the first part of the “exposure scenario.” It s imulates the processes in the agricultural field, such as runoff and erosion, on a daily time step. The runoff and erosion flux output data from PRZM are used as chemical loadings to the VVWM, which simulates surface water, in order to



### 25predict the EDWCs. The VVWM is conceptually similar to the current EXAMS

- based model in that both are 2

- compartment models driven by first

- order processes. It simulates the USEPA standard water bodies (i.e., farm pond and/or index reservoir) but with greater efficiency and flexibility for incorporation into a user interface. The VVWM also allows for variations in water body volume on a daily basis due to runoff, precipitation, and evaporation. Temperature, wind speeds, and pesticide dissipation processes are also allowed to vary daily. EDWCs were determined using the Index Reservoir scenario which describes a vulnerable surface drinking waters scenario for the VVWM component of the modeling exercise. For further information see http://www.epa.gov/oppefed1/models/water/index.htm#swcc (accessed 12/15/ 20 14).



### Ground Water Models

PRZM

- GW Tier 1 groundwater estimated drinking water concentrations (EDWCs) for a chemical, were derived with PRZM

- GW (Pesticide Root Zone Model for Groundwater, version 1.0 7

, March 6, 2014 ), using the GW

- GUI (Graphical User Interface, version 1.0 7

, March 6, 2014 ). PRZM

- GW is a one

- dimensional, finite

- difference model that estimates the concentrations of pesticides in gr oundwater. It accounts for pesticide fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field. PRZM

- GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site. Six standard scenarios, each representing a different region known to be vulnerable to groundwater contaminations, are available for use with PRZM

- GW for risk assessment purposes. In PRZM

- GW simulations, e ach of these standard scenarios was used. PRZM

- GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agricultural field. See http://www.epa.gov/oppefed1/models/water/index.htm#przm_gw (accessed 12/15/ 20 14 ).



### SCI

- GROW SCI

- GROW (Screening Concentration I n G R ound Water version 2.3 ) is a regression model used as a screening tool to estimate pesticide concentrations found in ground water used as drinking water. SCI

- GROW was a model developed by fitting a linear model to groundwater concentrations with the Relative Index of Leaching Potential (RILP) as the independent variable. Groundwater concentrations were taken from 90

- day average high concentrations from Prospective Ground Water studies; the RILP is a function of aerobic soil metabolism and the soil

- water partition coefficient. The output of SCI

- GROW represents the concentrations that might be expected in shallow unconfined aquifers under sandy soils, which is representative of the ground water most vulnerable to pesticide contamination likely to serve as a drinking water source

. More information at http://www.epa.gov/oppefed1/models/water/#scigrow (accessed 12/15/ 20 14 )

.



### Scenario Selection

Three agricultural crops were modeled: alfalfa, sugarcane and blueberries. For alfalfa, the NC alfalfa scenario was selected. For sugarcane, it was noted that the highest application rate applies only to sugarcane in Hawaii. Since there is no available scenario for HI sugarcane, the LA sugarcane was used as a surrogate, with a HI weather scenario. For blueberries, the CA wine grape scenario was used as a surrogate for the crop

.

26

### For the non

- agricultural crops, the CA rights

- of

- way scenario was used to m odel both aerial and ground applications (the rights

- of

- way has the maximum allowed application rate among all

uses ) . Additionally, other crops were run as shown in Table 9

. To the extent possible, crops from diverse regions from across the U.S. were sel ected.

Model Inputs

Table s 9 and 10 show the input values used in SWCC

. It should also be noted that three non

agricultural uses may be applied aerially, but only by means of helicopter. T he agricultural module of AgDRIFT was used, using the Wasp Helic opter as the aircraft, to estimate the spray drift. At this time, EFED does not recommend to use the forestry module of AgDRIFT; thus the agricultural module was to estimate forestry spray drift

.

Table 9

. Hexazinone Uses, Scenarios, and Application Information Used for Aquat ic Exposure Inputs in Drinking Water Exposure Assessment

Run NO, Scenario (bold font) / Uses Represented M ethod of App. Drift/ App Eff iciency Single A pp R ate kg a.i./A (lb a.i./A) Max No

. of Apps at Max

Rate Min. Interval Between

Apps (days) Day of A pp (day

month) CAM IPSCND

Agricultural Use Pa tterns 01 NC alfalfa /Alfalfa Aerial 0.135/0.95 1 .68 (1.5) 1 N/A 01

- 04 Foliar Surface applied 02 LA sugarcane ( HI meteoro

logical file 22521 )/ Sugarcane in HI Aerial 0.135/0.95 4 .0 3 (3.6) 1 N/A 10

- 01 Foliar Surface applied

03 CA wine grape /Blueberries Ground 0.066 /0.99 2.24 (2) 1 N/A 01

- 04 Ground Sur face applied Non

- Agricultural Use Patterns 04 CA rights

- of

- way/CA impervious / Non

- crop sites (weed and brush control) Aerial helicopter 0.124/0.95 6.72 (6) 1 N/A 01

- 04 Foliar Surface applied

05 CA rights

- of

- way/CA impervious / Non

- crop sites (weed and brush control) Ground 0.066 /0. 99 8.97 (8) 1 N/A 01

- 04 Foliar Surface applied

06 CA forestry ( MI meteorological file 14850 )/Conifer release in Eastern and Lakes states Aerial helicopter 0.124/0.95 4.48 (4) 1 N/A 01

- 05 Foliar Surface applied

07 OR Christmas trees / Christmas trees plantations (except in 22 states listed in label) Aerial 0.135/0.95 2.24 (2) 1 N/A 01

- 04 Foliar Surface applied

08 CA rangeland hay ( NY meteorological file 14860 ) / Pastures/ Rangeland in Eastern U

. S

. Aerial helicopter 0.124/0.95 4.48 (4) 1 N/A 01

- 03 Foliar Surface applied

09 PA turf / Bermudagrass/ Bahiagrass ; Industrial turfgrass Ground 0. 066 /0.99 1.26 (1.125) 1 N/A 01

- 03 Foliar Surface applied



### 27

### The chemical input parameters are summarized in Table 10

. Note that two aerobic soil metabolism half

- lives are included in the table . One is for the total toxic residues (TTRs), which are hexazinone plus its metabolites of concern. The other one includes the TTRs plus the unextracted residues (UERs) . For the aerobic and anaerobic aquatic metabolism studies, only one half

- life for the TTRs is rep orted since the levels of unextracted radioactivity were very low in the se studies.

Table 10 . Environmental fate data used for aquatic exposure inputs in Hexazinone aquatic risk assessment in the SWCC 1

Parameter (units) Value(s) Sources Comments Chemical Name Hexazinone Label s Label Application Rate ( Kg a.i./ha) Refer to Table 9 Highest single application rates according to the label s ---

Number of Applications Allowed Refer to Table 9 Label s Maximum allowed by the label, at the maximum rate.

Interval between Applications (days) Refer to Table 9 Label s Minimum allowed by the label.

Crop Names and Days of Application (day

- month) Refer to Table 9 Label s

K OC (ml/g OC ) 57.5 43621501 Sorption is better correlated with organic carbon content. Represents the mean of the following four values: 38 mL/g OC Tama silt loam 75 mL/g OC Chino loam 77 mL/g OC Trevino sandy loam 40 mL/g OC Sassafras sandy loam Aerobic Soil Metabolism (days) 25°C = 512.2 for the TTRs 41807401/ 42635001; 48898001 90 th percentile confidence bound on the mean half

- life value : four values are available: 208, 416 and 534 (at 20°C)

, and 604 (at 25°C) days; the corrected half

- lives at 25°C, are 147, 294, 378, and 604 days; mean = 355.75 days; std. dev. = 191.06 days , n = 4, t 90,n

- 1 = 1.638.

= 1093 for the TTRs + UERs 41807401/ 42635001; 48898001 90 th percentile confidence bound on the mean half

- life value: four values are available: 611, 1078 and 1604 (at 20°C)

, and 1023 (at 25°C) days; the corrected half

- lives at 25°C, are 432, 762, 1134, and 1023 days; mean = 837.75 days; std. dev. = 312.22 days , n = 4, t 90,n

- 1 = 1.638. Method of Application Refer to Table 9 Label s Label s

Buffer zone (ft) 0 Label s No buffer r estrictions

. Application Efficiency (fraction) Refer to Table 9 Label s

---
Spray Drift (fraction) Refer to Table 9 Label s

--- Solubility in Water (ppm) (25°C) 29800 41203201 DP Barcode D279324. t t t s

n input n
= + − 1 2 90 1
/ , ( )

t t t s

n input n
= + − 1 2 90 1
/ , ( )



### 28Parameter (units) Value(s) Sources Comments Aerobic Aquatic Metabolism (days) 25°C = 1343 for the TTRs 2 41811801; 49109901 90 th percentile confidence bound on the mean half

- life value: three values are available: 1274 and 1900 days ( at 20°C), and 1046 days (25°C); the corrected half

lives at 25°C, are 901, 1344, and 1046 days; mean = 1097 days; std. dev. = 225.86 days , n = 3, t 9 0,n

- 1 = 1.886. Anaerobic Aquatic Metabolism (days) 25°C = 1805 for the TTRs 2 41807402; 49109902 90 th percentile confidence bound on the mean half

- life value: three values are available: 1 395 and 1 383 days ( at 20°C)

, and 1837 days (25°C); the corrected half

lives at 25°C, are 986, 978, and 1837 days; mean = 1267 days; std. dev. = 493.65 days , n = 3, t 90,n

- 1 = 1.886. Hydrolysis at pH 7 0 41587301 Stable at pH 5

- 9

. Aqueous Photolysis (days) 0 41300801 Stable under the testing conditions. For the modeling, a ssume 40° latitude. Mol ecular Weight (g/mol ) 252.32 EPI Suite v.4.11 ---
Vapor Pressure (25°C) (torr) 1.9 x 10

- 7 41203201 DP Barcode D279324.

Henry’s Law Constant (25°C) (atm

- m 3 /mol) ~2 x 10

- 12 VP/WS This value is calculated by the SWCC.

EXAMS Environment EPA Reservoir and EPA Standard Pond --- Default for index reservoir and standard pond. In this instance, the applicable results are for the Index Reservoir. Field Size In dex Reservoir and EPA Pond ---

PRZM Scenario and Metfile As suggested by the shell SWCC, with exceptions noted in Table 9

. SWCC shell Exceptions include LA sugarcane (run with a HI met file), and CA forestry (run with a MI met file). See Table 9 for selected met file. Incorporation Depth (cm) 0.0 Label s Proposed label

CAM, Chemical Application Method Refer to Table 9 Label s

---

IPSCND, Condition for disposition of pesticide remaining on foliage after harvest) Surface applied Label s

---

FEXTRC, Foliar extraction 0.5 Default value

---
PLDKRT, Decay
rate on foliage 0 Default value

---

PLVKRT, Volatilization rate from foliage 0 Default value

---

UPTKF, Uptake factor 0 Default value

---
1 Data were selected according to EFED Guidance on Input Parameters v.2.1, dated 10/22/2009 and approved 11/10/2009 (US EPA 2009). 2 In the aerobic and anaerobic aquatic metabolism studies the levels of UERs were very low at all test intervals. t t t s

n input n
= + − 1 2 90 1
/ , ( )

t t t s

n input n
= + − 1 2 90 1
/ , ( )



### 29

### The input parameter values in PRZM

- GW are as shown in Table 11

. For PRZM

- GW, only rights

- of

- way were modeled, since they involve the maximum application rate. Again, two half

lives for the TTRs and TTRs + UERs were modeled (see above)

.

Table 11

. Hexazinone PRZM

- GW Input Parameters for Modeling A pplications of the C hemical on R ights

- of

- W ays

PARAMETER (units) VALUE 1 SOURCE COMMENT

Application date (day/month) 15

- 03

A ccording to the label, applications

occur late winter to

summer

. Delmarva emergence 10

- 04, crop maturation 30

- 05, harvest 15

- 06

15

- 03 FL citrus crop emergence 01

- 01, crop maturation 01

- 02, harvest 31

- 12

15

- 03 FL potatoes emergence 15

- 02, crop maturation 01

- 05, harvest 01

- 06

15

- 03 GA coast emergence 01

- 05, crop maturation 01

- 08, harvest 01

- 10

15

- 03 NC coast emergence 15

- 05, crop maturation 01

- 08, harvest 01

- 11

15

- 03 WI sand emergence 01

- 05, crop maturation 21

- 07, harvest 20

- 10 Maximum Application Rate (kg a.i./ha) 8.97

Label Maximum application rate is 8 lb a.i./A. Number of Applications per Year 1
Retreatment Intervals (days) N/A Chemical Application Method (CAM) 2 Label Foliar
Incorporation Depth (cm) 0 .0

--- Air diffusion coefficient (cm 2 /day) 0 .0 N/A Assum e no volatilization.
Vaporization enthalpy (kcal/mol) 0 .0 N/A Assum e no volatilization.
Henry’s Law Constant ( atm

m 3 / mol) 0 .0 N/A Assum e no volatilization.

Partition Coefficient (K OC ; mL/g OC ) 57.5 43621501 Sorption is better correlated with organic carbon content. Represents the mean of the following four values: 38 mL/g OC Tama silt loam 75 mL/g OC Chino loam 77 mL/g OC Trevino sandy loam 40 mL/g OC Sassafras sandy loam

Aerobic So il Metabolism Half

- life (days) 512.2 (TTRs) 41807401/ 42635001; 48898001 90 th percentile confidence bound on the mean half

- life value : four values are available: 208, 416 and 534 (at 20°C)

, and 604 (at 25°C) days; the corrected half

- lives at 25°C, are 147, 294, 378, and 604 days; mean = 355.75 days; std. dev. = 191.06 days , n = 4, t 90,n

- 1 = 1.638. t t t s

n input n
= + − 1 2 90 1
/ , ( )



### 30PARAMETER (units) VALUE 1 SOURCE COMMENT

1093 (TTRs + UERs) 41807401/ 42635001; 48898001 90 th percentile confidence bound on the mean h alf

- life value: four values are available: 611, 1078 , and 1604 (at 20°C)

, and 1023 (at 25°C) days; the corrected half

- lives at 25°C, are 432, 762, 1134, and 1023 days; mean = 837.75 days; std. dev. = 312.22 days , n = 4,
t 90,n

- 1 = 1.638. Hydrolysis Half

- life (days) 0 41587301 Stable at pH 5

- 9

. 1 Parameters are selected as per “Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model” v.1.0, dated October 15, 2012.



### The input parameter values in SCI

- GROW are as shown in Table 12

. In SCI

- GROW, like for the PRZM

- GW and SWCC, two half

- lives for the TTRs and TTRs + UERs were modeled.

Table 12 . SCI

- GROW (v 2.3) Input Parameter V a lues for Hexazinone TTRs on Rights

- of

W ay s 1



### .

PARAMETER (units) VALUE(S) SOURCE COMMENT

Output File Name HexazinonePRA2.txt Hexazinone_PRA.txt N/A Output file names for the runs for the TTRs and TTRs + UERs, respectively Maximum Application Rate (lb a.i./A) 8 Label Represents most

- conservative scenario in which the total maximum rate per year is applied in a single application. Number of Applications per Year 1 Label

Organic Carbon Partition Coefficient (K OC ; mL/g OC ) 57.5 43621501 Represents the median of the following four values: 38 mL/g OC Tama silt loam ; 40 mL/g OC Sassafras sandy loam ; 75 mL/g OC Chino loam ; 77 mL/g OC Trevino sandy loam

. There is les s than a three

- fold variation.

Aerobic Soil Metabolism Half

- life (days) 475 ( TTRs ) 41807401/ 42635001; 48898001 There are four or more half

- lives available, therefore, use the median of the following values : 208, 416, 534

, and 604 days

. There is less than a five

- fold difference.

1051 ( for the TT Rs + UERs ) 41807401/ 42635001; 48898001 There are four or more half

- lives available, therefore, use the median of the following values : 611, 1023, 1078, and 1604 days. There is less than a five

- fold difference. 1 Data were selected according to the Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides ( Version 2.1 , dated October 22, 2009).



### Model Results / EDWCs for the Use of Hexazinone

Tabl es 13 and 14 show summaries of the EDWCs obtained in SWCC

. For the TTRs + UERs, only the results of the crop that yielded the highest and lowest EDWCs were reported. It was noted that when the UERs were included, the peak EDWCs were the same than for the TTRs without the UERs.

31

### Table 13 . Tier II Estimated Dr inking Wa ter Concentrations (EDWCs) for S urface Water Based on A pplication of H exazinone P roduct s Modeled in the SWCC, for the TTRs ( E xcluding the UERs )

Scenario App. Method App. Rate (lb a.i./A) Date of First Application

(dd

- mm) No. of Apps App. Interval (days) National PCA 1 (fraction) Surface Waters EDWCs ( μg/L )

Acute (1

- in

- 10

-

year) Chronic (1

- in

- 10

-

year) Cancer 30

- year

Daily Average NC alfalfa /A lfalfa Aerial 1.5 01

- 04 1 N/A 1.00 2 35.5 11.2 5.81 LA sugarcane ( HI met file)/Sugarcane in HI Aerial 3.6 10

- 01 1 N/A 1.00 2 502 206 77.3

CA wine grape / Blueberries Ground 2 01

- 04 1 N/A 1.00 2 20.9 12.7 8.58

CA rights

- of

- way/CA impervious / Non

- crop sites (weed and brush control) Aerial helicopter 6 01

- 04 1 N/A 1.00 3 2 04 88.0 45.2

CA rights

- of

- way/CA impervious / Non

- crop sites (weed and brush control) Ground 8 01

- 04 1 N/A 1.00 3 260 112 52.5

CA forestry (MI met file)/ Conifer release in Eastern and Lakes states Aerial helicopter 4 01

- 05 1 N/A 1.00 3 103 84.9 64.6

OR Christmas trees / Christmas trees Aerial 2 01

- 04 1 N/A 1.00 3 28.9 21.8 18.8

CA rangeland hay (NY met file)/ Pastures/ Rangeland in Eastern US Aerial helicopter 4 01

- 03 1 N/A 1.00 3 159 71.9 36.5

PA turf / Bermudagrass/ Bahiagrass; Industrial turfgrass Ground 1.125 01

- 03 1 N/A 1.00 2 10.4 8.24 6.05

Bolded values represent the highest EDWCs in surface waters. 1 Guidance on Development and Use of Community Water System Drinking Water Intake Percent Cropped Area Adjustment Factors for use in Drinking Water Exposure Assessments: 2014 Update, dated 09/09/2014 and approved 09/12/2014. 2 PCA for Turf

- All Agriculture. 3 No PCAs have been issued for these non

- agricultural uses.



### Table 14 . Tier II Estimated Drinking Wa ter Concentrations (EDWCs) for S urface Water Based on A pplication of Hexazinone P roduct s Modeled in the SWCC, for TTRs + UERs 1

Scenario App. Method App. Rate (lb a.i./A) Date of First Application

(dd

- mm) No. of Apps App. Interval (days) National PCA 2 (fraction) Surface Waters EDWCs ( μg/L )

Acute (1

- in

- 10

-

year) Chronic (1

- in

- 10

-

year) Cancer 30

- year

Daily Average LA sugarcane ( HI met file)/Sugarcane in HI Aerial 3.6 10

- 01 1 N/A 1.00 3 502 207 77.6

PA turf / Bermudagrass/ Bahiagrass; Industrial turfgrass Ground 1.125 01

- 03 1 N/A 1.00 3 10.4 8.25 6.06

Bolded values represent the highest EDWCs in surface waters. 1 Only the crops that yielded the highest and lowest EDWCs were presented, calculating the TTRs + UERs. 2 Guidance on Development and Use of Community Water System Drinking Water Intake Percent Cropped Area Adjustment Factors for use in Drinking Water Exposure Assessments: 2014 Update, dated 09/09/2014 and approved 09/12/2014. 3 PCA for Turf

- All Agriculture.



### 32

### The PRZM

- GW results obtained for each scenario for the use of hexazinone on rights

- of

- ways are summarized in Table s 1 5 and 16

. It should be noted that each of the PRZM

- GW scenarios were used as surrogates for rights

- of

- ways.

Table 15

. Hexazinone G roundwater Estimated Drinking Water Concentrations (EDWCs) R esulting from the U se of the C hemical on Rights

- of

- W ay s, for the TTRs ( E xcluding the UERs )

Crop/Scenario Highest Daily Value (μg/L) Post Breakthrough Average

(μg/L) Average Simulation Breakthrough Time (days) Rights

- of

- way /Tier I Delmarva 2470 1920 1752 Rights

- of

- way /Tier I FL citrus 2210 1840 1294 Rights

- of

- way /Tier I FL potatoes 1080 951 1800 Rights

- of

- way /Tier I GA coast 944 765 2166 Rights

- of

- way /Tier I NC coast 

### 3090 2210 2485 Rights

- of

- way /Tier I WI sand 2530 

### 2260 3141 Bolded values represent the highest groundwater EDWCs.



### Table 16

. Hexazinone G roundwater Estimated Drinking Water Concentrations (EDWCs) R esulting from the U se of the Chemical on Rights

- of

- Ways, for the TTRs + UERs

Crop/Scenario Highest Daily Value (μg/L) Post Breakthrough Average

(μg/L) Average Simulation Breakthrough Time (days) Rights

- of

- way /Tier I Delmarva 2760 2110 1752 Rights

- of

- way /Tier I FL citrus 2390 1990 1294 Rights

- of

- way /Tier I FL potatoes 1530 1250 1800 Rights

- of

- way /Tier I GA coast 1060 852 2166 Rights

- of

- way /Tier I NC coast 

### 3710 2600 2485 Rights

- of

- way /Tier I WI sand 2680 2390 3141 Bolded values represent the highest groundwater EDWCs.



### Table 1 7 gives EDWCs for the same use (rights

- of

- ways), using SCI

- GROW.

Table 17 . Tier I EDWCs for S urface Water B ased on A pplication of H exazinone on Rights

- of

- W ays
Drinking Water Source (Model Used) Use Scenario (rate modeled) Estimate d Drinking Water Concentrations (EDWCs) (ppb) Acute and Chronic

Groundwater (SCI

- GROW) Rights

- of

- ways (8 lb a.i./A) TTRs 180
Rights

- of

- ways (8 lb a.i./A) TTRs + UERs 527



### 33

### Additional Refinements of Groundwater EDWCs

EFED shared with HED preliminary EDWCs (as shown in Tables 15 to 17 ). HED indicated that for chronic exposure, the EDWCs exceeded the maximum recommended level for the rights

- of

way scenarios using the results of PRZM

- GW. Therefore, EFED pursued additional refinements in the PRZM

- GW modeling results.

I nspection of the labels for hexazinone indicate s that the application rate range for the chemical on right s

- of

- way is wide ( range is 2

– 8 lb a.i./A) ; furthermore, it depends on the soil texture and pest to be treated. For example, the recommended range is 2

– 5 lb a.i./A for certain pests

, and 6

– 8 lb a.i./A for others. Further, the maximum rate is higher for the ground (8 lb a.i./A) than aerial (6 lb a.i./A) applications. The label further instructs the applicator to

... “ U se lower rate on coarse textured soils (sand to sandy l oam). Use the higher rate on fine textured soils (clay loam to clay) and on soils high in organic matter.”

EFED conducted in 2006 an analysis of the percentage of land that is covered by rights

- of

- ways in the Chesapeake Bay area. The analysis can be fou nd in Section 3.2.1.2 of the atrazine endangered species assessment located at: http://www.epa.gov/oppfead1/endanger/litstatus/effects/atrazine/20 07/determination

- cheasp.pdf (accessed 03/05/2015) (excerpts are reproduced in Appendix C ). According to this analysis, approximately 10% of the surface area (in the evaluated area) is rights

- of

- way (refer to the appendix). Therefore, if such a factor is applied to the rights

- of

- way uses, the equivalent application rate range is reduced from 2

– 8 lb a.i./A to 0.2

– 0.8 lb a.i./A.

Given this reduced equivalent application rate for rights

- of

- ways , other uses of hexazinone would have higher application rates than rights

- of

- way ( i.e. , higher than 0.2

– 0.8 lb a.i./A) ; therefore

, EFED explored the uses with the next highest application rate for hexazinone , which are pasture/rangeland and forestry. For the pasture/rangeland use (which among the conventional agricultural uses is second in pounds active ingredient applied, refer to the Usage section) , the maximum application rate is 4 lb a.i./A, but for loamy sand and sandy soils the applica tion rate range is 1

– 2 lb a.i./A. An application rate range for different soil textures is

c ommon for other crops as well for hexazinone as explained above

.

EFED verified the soil textures of the six standard PRZM scenarios in PRZM

- GW

. Table 18 shows the percent sand, clay and organic carbon, and soil textures for the top soils (0

– 0.4 m depth) in the standard PRZM

- GW scenarios. Lower soil layers (below 0.4 m depth), were excluded from this analysis. Inspection of the table reveals that all the PRZM

- GW scenarios have sandy

, sandy loam or loamy sand textures in the top layers (0

- 0.4 m depth ), with the exception of the lower ( 0.2

- 0.4 m ) layer of the NC coast scenario. In addition, the majority of the scenarios have a low level of organic carbon ( <1%). The exceptions are the top layer (0

- 0.1

m depth ) of the FL potato scenario (4.19%), and the lower ( 0.2

- 0. 4 m ) layer of the FL citrus scenario.

Table 18 . Percent Organic Carbon, Sand , and Clay, and Soil Textures for the Top Soils in the Standard PRZ M

- GW Scenarios Scenario/depth (m) Organic Carbon (%) Sand (%) Clay (%) Soil texture

Delmarva (0

- 0.1) 0.52 92.3 2.4 Sand



### 34Scenario/depth (m) Organic Carbon (%) Sand (%) Clay (%) Soil texture Delmarva (0.1

- 0.2) 0.52 92.3 2.4 Sand Delmarva (0.2

- 0.4) 0.20 91.5 2.7 Sand

FL citrus (0

- 0.1) 0.144 96 2.4 Sand FL citrus (0.1

- 0.2) 0.144 95 2.8 Sand FL citrus (0.2

- 0.4) 1.44 95 2.8 Sand FL potato (0

- 0.1) 4.19 93 0.001 Sand FL potato (0.1

- 0.2) 0.78 95 0.2 Sand FL potato (0.2

- 0.4) 0.18 92 0.6 Sand

GA coast (0

- 0.1) 0.75 66 3.7 Sandy loam GA coast (0.1

- 0.2) 0.75 66 3.7 Sandy loam GA coast (0.2

- 0.4) 0.25 67 12.2 Sandy loam NC coast (0

- 0.1) 0.61 76 2.4 Loamy sand NC coast (0.1

- 0.2) 0.61 75 2.4 Loamy sand NC coast (0.2

- 0.4) 0.19 55 20 Sandy clay loam

WI sand (0

- 0.1) 0.46 95 2.3 Sand WI sand (0.1

- 0.2) 0.46 95 2.3 Sand WI sand (0.2

- 0.4) 0.14 96 2.5 Sand



### As an alternative to the rights

- of

- ways use , runs with a lowe r value in the application rate were conducted for the pasture/rangeland use, at 2 lb a.i./A. This is the application rate recommended for sandy soils for pasture/rangeland

. All other parameters were the same than the ones previously described. Results are summarized in Table 19

. As expected, s ince the application rate for this use is 1⁄4 the one modeled previously for rights

- of

- way, the EDWCs were approxi m ately 4

- fold lower

.

Table 19

. Hexazinone Groundwater Estimated Drinking Water Concentrations (EDWCs) Resulting from the Use of the Chemical on Pasture/Rangeland , for the TTRs (Excluding the UERs), Applied at 2 lb a.i./A

Crop/Scenario Highest Daily Value ( μg/L) Post Breakthrough Average

(μg/L) Average Simulation Breakthrough Time (days) Rangeland /Tier I Delmarva 616 480 1752 Rangeland /Tier I FL citrus 551 460 1294 Rangeland /Tier I FL potatoes 270 238 1800

Rangeland /Tier I GA coast 236 191 2166 Rangeland /Tier I NC coast 

### 773 552 2485 R angeland /Tier I WI sand 632 

### 564 3141 Bolded values represent the highest groundwater EDWCs.



### Monitoring Data

There is available monitoring data for this chemical. H exazinone in groundwater was previously considered by the California Department of Pesticide Regulation (CDPR), as shown in the following site : http://www.cdpr.ca.gov/docs/emon/grndwtr/hexazino ne.htm (accessed 01/12/2015). Their findings were as follows: “The Director concurs with the subcommittee that based on the detected concentrations of hexazin one (ranging from 0.05 to 0.27 μ g/L) and the health

- protecti ve drinking water level of 170 μ g/L e stablished by the Office of Environmental

35

### Health Hazard Assessment (OEHHA), hexazinone cannot be found to have polluted ground water.”

Hexazinone and a number of its degradates were found to be monitored in the USGS National Water Quality Assessment Data Warehouse (NAWQA), when verified by constituent finder (at http://cida.usgs.gov/nawqa_public/apex/f?p=136:1:0

, accessed 01/12/2015 )

. Table 20 summarizes the findings for hexazinone

. Across the U.S. (excluding territories), a total of 3872 samples were analyzed for hexazinone, of which 1265 (33%) were positive detections. Of the detections, 157 (4.1%) were positive groundwater detections. Additionally, certain degradates of hexazin one were tested for in the NAWQA database.

Table 20

. Summary of Hexazinone Monitoring Data from the NAWQA Database State Number of Detections Number of Samples Number of Groundwater Detections Alabama 39 189 0 Alaska 0 2 0 Arizona 13 103 1 Arkansas 4 19 0 California 427 >511 20 Connecticut 39 123 0 Delaware 0 33 0 District of Columbia 0 0 0

Florida 99 337 49 Georgia 80 270 20 Hawaii 4 15 4 Idaho 9 148 4 Illinois 3 188 0 Indiana 4 13 3 0 Iowa 7 220 0 Kansas 0 31 0 Kentucky 1 4 0 Louisiana 61 274 0 Maine 0 37 0 Maryland 3 128 0 Massachusetts 2 86 2 Michigan 0 113 0 Minnesota 4 172 3 Mississippi 28 97 0 Missouri 1 43 0 Montana 0 43 0 Nebraska 2 105 0 Nevada 2 55 0 New Hampshire 0 35 0
New Jersey 36 264 0 New Mexico 3 157 3 New York 7 131 4 North Carolina 25 126 0

North Dakota 0 0 0 Ohio 8 78 1 Oklahoma 0 12 0



### 36State Number of Detections Number of Samples Number of Groundwater Detections Oregon 181 252 0 Pennsylvania 0 40 0 Rhode Island 1 5 1 South Carolina 42 211 3

South Dakota 0 0 0 Tennessee 6 113 6 Texas 43 414 13 Utah 4 124 3 Vermont 0 3 0 Virginia 36 110 0 Washington 41 275 10 West Virginia 0 5 0 Wisconsin 0 123 0 Wyoming 0 6 0 Total 1265 3872 157



### It is noted that sampling and testing for hexazinone in the NAWQA database does not represent necessarily source (reservoir) or finished (treated) drinking waters. Despite the relatively high level of detections, EFED believes that modeling reflects concentrations in surface and ground waters, which are re alistically conservative for each site represented. The NAWQA monitoring program analyzed for this drinking water assessment do es not specifically target hexazinone

. Consequently, detections cannot be directly associated with a particular use pattern or site, nor are the detections expected to represent the potential peak hexazinone exposure

. This result is attributed to the fact that water monitoring sampling programs do not specifically target hexazinone use areas, may not represent high hexazinone use areas , and may not correspond with applications of hexazinone ; therefore, peak concentrations of hexazinone may not be detected.

S ampling frequencies are not designed to capture peak concentrations. Model generated times series data suggest that mon itoring programs need to sample daily in order to capture peak concentrations of hexazinone in surface water. There are also limited sampling data available for the U .S. In order to use monitoring data as an exposure endpoint for a chemical with an acute exposure concern, sampling needs to be intensive (likely daily) in order to capture the peak exposure concentrations.

Because currently available monito ring data likely underestimate hexazinone concentrations, monitoring results are not an appropriate pr ediction of the potential exposure resulting from hexazinone use. For these reasons, EFED does not recommend that hexazinone water monitoring data be used by HED in the human health risk assessment.

Drinking Water Treatment

There is no readily available data on impacts of water treatment on the dissipation and/or the formation of transformation products that may occur. Hexazinone is persistent under hydrolysis and aqueous photolysis condition. Further, its half

- li ves under aquatic metabolism condition also indicate high persistence. Its mean K OC 

### of ~58 mL/g OC 

### shows that the chemical is mobile (FAO 2000). It appears unlikely that primary treatment may reduce the levels of hexazinone due to its low tendency to bind.

37

### EXPOSURE CHARACTERIZATION

Table s 21 and 2 2 provide a summary of the maximum EDWCs obtained from each of the models used in this DWA.

Table 2 1 . Maximum Estimated Drinking Water Concentrations for the Use of Hexazinone , for the TTRs ( excluding the UERs)

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year ) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) ( ppb )
Groundwater ( PRZM

- GW ) NC coast 1 (rights

- of

- way) (8 lb a.i.) Acute 3090 WI sand 1 (rights

- of

- way) (8 lb a.i.) Chronic 2260

Surface water (SWCC ) LA sugarcane with HI meteorological file 2 (sugarcane in HI) (3.6 lb a.i.) Acute 502 Chronic 206 Cancer/Chronic 77.3 1 Scenario was used as a surrogate and run with the maximum application rate for rights

- of

- ways

. 2 Represents applications of hexazinone on sugarcane in Hawaii.



### Table 2 2 . Maximum Estimated Drinking Water Concentrations for the Use of Hexazinone , for the TTRs + UERs

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year ) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) ( ppb )
Groundwater ( PRZM

- GW ) NC coast 1 (rights

- of

- way) (8 lb a.i.) Acute 3 710 Chronic 2 600

Surface water (SWCC ) LA sugarcane with HI meteorological file 2 (sugarcane in HI) (3.6 lb a.i.) Acute 502 Chronic 207 Cancer/Chronic 77.6 1 Scenario was used as a surrogate and run with the maximum application rate for rights

- of

- ways

. 2 Represents applications of hexazinone on sugarcane in Hawaii.



### Results presented in Table 23 represent EDWCs for refined groundwater estimates for the use of hexazinone on pastures/rangeland, assuming that the soils are sands or sandy loams.

Table 23. Refined Estimated Groundwater Drinking Water Concentrations for the Use of Hexazinone, for the TTRs

DRINKING WATER SOURCE (MODEL USED) SCENARIO (USE) (rate modeled per year) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) ( ppb )
Groundwater (PRZM

- GW) NC coast 1 (pastures/rangeland) (2 lb a.i.) Acute 773 WI sand 1 (pastures/rangeland) (2 lb a.i.) Chronic 564 1 Scenario was used as a surrogate and run with the prescribed application rate for sandy loam and loamy sand soils on pasture/rangeland.



### Input Parameters It appears that the main route of dissipation of hexazinone is aerobic soil metabolism (even though it occurs slowly ). T he aq uatic metabolism is very slow (both aerobic and anaerobic)

. There are four aerobic soil half

- lives available. Three of them were obtained at 20 0 C;

38

### temperature adjustment was required for PRZM

- GW and the SWCC, resulting in shorter half

lives.

As indicated earlier, the environmental fate database for hexazinone is essentially complete. It was noted that for the aquatic metabolism studies, the study duration was short compared to the half

- l ives obtained. T he aerobic soil metabolism study (MRID 48898001 ) was conducted for a period of only 150 days ( in a study where three soils were tested) , with half

- lives of 54

- 143 days (note that these half

- lives do not include the total residues or the un extracted residues , they only include the parent compound ). T he aerobic aquatic metabolism study (MRID 49109901 ) was conducted for a period of only 100 days , compared to half

- li ves of 5 28

- 719 days (for the parent )

. Meanwhile, the anaerobic aquatic metab o lism study (MRID 49109902 ) was conducted for 10 1 days, compared to a half

- life of 482

- 961 days (for the parent )

. In this assessment two aerobic and two anaerobic aquatic systems were available. Further four aerobic soils were available. There is also an anaerobic soil metabolism study (four soils

, MRID 48898002 ) , but the results of this study wi ll not affect this DWA since they are not used in hexazinone drinking water models. The fact that multiple soils and sediments were available tends t o reduce t he uncertainty; however, the short duration of the studies bring s uncertainty in the half

- life estimates.

Application Rates In this DWA, a number of uses were assessed ; rights

- of

- ways (for groundwater) and sugarcane (for surface water) were found to yield the highest EDWCs

. T he range of application rates on rights

- of

- ways is

~ 2 to 8 lb a.i./A (depending on the weeds controlled and the soil texture)

, and on HI sugarcane it is

~ 0.45 to 3.6 lb a.i./A (depending on the soil texture)

. In both cases the maximum application rate was assumed to be applied in a single application per year. It is uncertain the degree to which this is true under actual use conditions.

Additional refinements were conducted for the pastures/rangeland use, and using the ap plication rate for coarse textured soils since the six PRZM scenarios in PRZM

- GW have coarse textured soils. This modeling was performed only to obtain groundwater EDWCs since according to HED there was no acute concern with results obtained from the righ ts

- of

- way and other modeling runs

. In this assessment, applications were assumed to occur at once and every year for 30 consecutive years. Due to possible pest resistance (as indicated in the labels), consecutive applications for such an extended period of time appear to be unlikely

.
Percent Crop Area It is noted that for the model that yielded the highest EDWCs (PRZM

- GW for groundwater), a PCA is not applicable

. A percent cropped area (PCA) adjustment factor should not be applied to PRZM

- GW model outpu t data to generate EDWCs. The conceptual model for groundwater exposure, as implemented using PRZM

- GW, represents pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a single, rural agricultural field and assumes
t he entire field (zone of influence) is treated. The zone of influence does not represent an entire watershed.

39

### For surface waters, the PCA for turf

- all agriculture was used (1.00) and for the non

- agricultural uses, no PCA adjustment was used since no valu es have been established for such uses (in other words, a PCA of 1.00 was assumed)

.

Residues of Concern As indicated earlier, the MARC committee had decided that for hexazinone the residues of concern were comprised by the parent compound and all its identified metabolites

. Citation is as follows : “For water, the Committee concluded that for risk assessment purposes, hexazinone, G3170, and all metabolites with conjoined cyclohexyl and triazine rings should be included.” ( Source: Memorandum from Sherr ie Kinard, DP Barcode D282111, April 25, 2002).

SWCC In general, the linked SWCC model produces EDWCs that are expected to be exceeded once within a ten

- year period. The Pesticide Root Zone Model is a process or “simulation” model that calculates what ha ppens to a pesticide in an agricultural field on a day

- to

- day basis. It considers factors such as rainfall and plant transpiration of water, as well as how and when the pesticide is applied. It has two major components: hydrology and chemical transport. Water movement is simulated by the use of generalized soil parameters, including field capacity, wilting point, and saturation water content. The chemical transport component can simulate pesticide application on the soil or on the plant foliage. Disso lved, adsorbed, and vapor

- phase concentrations in the soil are estimated by simultaneously considering the processes of pesticide uptake by plants, surface runoff, erosion, decay, volatilization, foliar wash

- off, advection, dispersion, and retardation.

Un certainties associated with each of these individual components add to the overall uncertainty of the modeled concentrations. Additionally, model inputs from the environmental fate degradation studies are chosen to represent the upper confidence bound on the mean values that are not expected to be exceeded in the environment approximately 90 percent of the time. Mobility input values are chosen to be representative of conditions in the environment. The natural variation in soils adds to the uncertainty o f modeled values. Factors such as application date, crop emergence date, and canopy cover can also affect estimated concentrations, adding to the uncertainty of modeled values. Factors within the ambient environment such as soil temperatures, sunlight in tensity, antecedent soil moisture, and surface water temperatures can cause actual aquatic concentrations to differ for the modeled values.

PRZM

- GW PRZM

- GW has been determined to be an effective tool for establishing upper bound pesticide concentrations i n groundwater for national as well as site

- specific assessments. As such, it could be used as a screening model for Tier I drinking water assessments. Since hydrolysis is generally the only transformation pathway considered at soil depths greater than on e meter, it can have a large impact on the PRZM

- GW EDWCs. Hexazinone is stable to hydrolysis in a pH range of 5 to 9. For Tier I assessments, all six scenarios should be run for national scale pesticide assessments. However, if the use is restricted by geography, the user should identify the best representative surrogate scenario(s). Since the use on rights

- of

- ways can occur nationwide, in a first tier try, a ll the scenarios were modeled.

40

### In cases where the “throug hputs” value for a model run are less than one, modeling is repeated with the appropriate extended weather file. An extended weather file contains the same weather as the standard 30

- year weather file and allows the user to run the simulation for up to 10 0 years in order to observe breakthrough. This was not needed for hexazinone

. Even though six scenarios modeled are not strictly rights

- of

- way scenarios, they were regarded as if they were rights

- of

- way , in the first tier screening

- level exposure assessm ent. Additionally, the maximum application rate was used, despite the fact that a wide range of application rates is prescribed in the labels, including that for coarse textured soils, the rate is lower than the maximum. Note that all the PRZM scenarios in PRZM

- GW have coarse textured top soils.

Furthermore, available evidence suggests that the application rate on rights

- of

- way are usually around 10% the value indicated in the labels. As an additional refinement, EFED conducted modeling of the pastures/ rangeland use, with the application rate prescribed in the labels for coarse textured soils (2 lb a.i./A)

.

I t appears that both the rights

- of

- way and pasture/rangeland uses are less likely to be in the vicinity of groundwater wells. Agricultural uses like sugarcane

, blueberries or alfalfa , all of which have lower application rates than rights

- of

- way and pastures/rangeland, appear more likely to be present in the proximity of drinking water wells. Furthermore, t hree of the si x standard scenarios (FL citrus, WI sand and Delmarva) represent rare

, but r ealistic for the specific sites, vulnerability conditions that are unlikely to be associated with many of the hexazinone use sites

.

The results of the above stated uncertainties suggest the highly conservative nature of the groundwater EDWCs noted in this DWA

.

SCI

- GROW Pesticide concentrations estimated by SCI

- GROW represent conservative or high

- end exposure values because the model is based on groundwater monitoring studies whic h were conducted by applying pesticides at maximum allowed rates and frequency to vulnerable sites ( i.e. , shallow aquifers, sandy, permeable soils, and substantial rainfall and/or irrigation to maximize leaching). In most cases, a large majority of the use areas will have ground water that is less vulnerable to contamination than the areas used to derive the SCI

- GROW estimate. The SCI

- GROW estimate is based on environmental fate properties of the pesticide, the application rate, and the aerobic soil metabo lism of the chemical. Experience shows that if a pesticide is substantially subject to abiotic hydrolysis ( i.e. , not stable over the 30

- day period used in most hydrolysis studies ), this generally mitigates its long

- term groundwater contamination potential

. If the hydrolysis data demonstrate that the pesticide in question is subject to hydrolysis, then this should be noted because it means that the SCI

- GROW value may be an overestimate ev en for highly vulnerable ground water. For hexazinone , this is not th e case . Hexazinone is stable to hydrolysis at pH 7. The SCI

- GROW concentration has usefulness as a screening or upper

- bound value because the regression is based solely upon scenarios in which the vulnerability of groundwater contamination was much highe r than the vast majority of agricultural use scenarios.

All Models

41

### This assessment is national in character and EDWCs should be regarded as upper bound estimates. National PCAs were used in SWCC , while PCAs are not applicable for the PRZM

GW or SCI

- GROW. For the non

- agricultural uses of hexazinone, no PCA adjustment factor was applied (assumed to be 1.00).

A more definitive assessment could be performed, for example, using regional PCAs in the SWCC should they be applicable , or performing additional ref inements with PRZM

- GW (groundwater). For PRZM

- GW a number of refinement strategies have been ident ified and they can be used in definitive assessment s

. Additionally, typical application rates may be modeled for characterization purposes.

REF E RENCES

Fo od and Agriculture Organization of the United Nations 2000

. FAO PESTICIDE DISPOSAL SERIES 8. Assessing Soil Contamination: A Reference Manual. Appendix 2. Parameters of pesticides that influence processes in the soil. Editorial Group, FAO Information D ivision: Rome, 2000. Accessed at the following URL 08/15/2013: http://www.fao.org/DOCREP/003/X2570E/X2570E00.htm

.

U.S. Environm ental Protection Agency (USEPA) 2002. Hexazinone . The Outcome of the HED Metabolism Assessment Review Committee for Water. OCSPP/OPP/ Health Effects Division. DP Barcode: D282111. Dated 04/25/2002.

USEPA 2006. Tier I Drinking Water Assessment Guidance and 

### Guidance for Developing a Tier I Drinking Water Exposure Assessment

. 

### OCSPP/OPP/Environmental Fate and Effects Division. Dated 01/27/2006.

USEPA 2007 a

. Tier II Drinking Water Exposure Assessment Guidance

. OCSPP/OPP/ Environmental Fate and Effects Division. Dated 05/28/ 20 07.

USEPA 2007 b . Characteri zation of Drinking Water Exposure for Dietary Risk Assessment. OCSPP/OPP/Environmental Fate and Effects Division. Dated 12/13/2007.

USEPA 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides Version 2.1. OCSPP/OPP/Environmental Fate and Effects Division. Dated 10/22/2009

.

USEPA 2010 a . Development and Use of the Index Reservoir in Drinking Water Exposure Assessments. OCSPP/OPP/Environmental Fate and Effects Division. Dated 04/15/2010 and app roved 09/14/2010.

USEPA 2010 b . Guidance for Making Temperature Adjustments to Metabolism Inputs to EXAMS and PE5 and WQTT Advisory Note Number 9: Temperature Adjustments for Aquatic Metabolism Inputs to EXAMS and PE5. OCSPP/OPP/Environmental Fate and Effe cts Division. Dated 09/21/2010 and approved 10/18/2010

.

42

### USEPA 2011. Finalization of Guidance on Incorporation of Water Treatment Effects on Pesticide Removal and Transformations in Drinking Water Exposure Assessments and The Incorporation of Water Treatm ent Effects on Pesticide Removal and Transformations in Food Quality Protection Act (FQPA) Drinking Water Assessments

. OCSPP/OPP/ Environmental Fate and Effe cts Division. Dated 12/05/2011.

USEPA 2012 a

. Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model. OCSPP/OPP/Environmental Fate and Effects Division. Dated 10/15/2012

.

U SEPA 2012 b

. Guidance for Using PRZM

- GW in Drinking Water Exposure Assessments

. OCSPP/OPP/Environmental Fa te and Effects Division. Dated 10/15/2012

.

USEPA 2012c. Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media, Health Canada, U.S. Environmental Protection Agency, OCSPP/OPP/ Environmental Fate and Effects Division. Dated D ecember 21, 2012.

USEPA 2012d

. Standard Operating Procedure for Using the NAFTA Guidance to Calculate Representative Half

- life Values and Cha racterize Pesticide Degradation. OCSPP/OPP/ Environmental Fate and Effects Division. D ated November 30, 2012 and approved December 17, 2012.

USEPA 2014 a

. Guidance on Development and Use of Community Water System Drinking Water Intake Percent Cropped Area Adjustment Factors for use in Drinking Water Exposure Assessments: 2014 Update

. OCSPP/OPP/ Environmental Fate and Effects Division. D ated September 9, 2014 and approved September 12, 2014

.

USEPA 2014b

. Guidance for Addressing Unextracted Residues in Laboratory Studies

. OCSPP/OPP/ Environmental Fate and Effects Division. A pproved Se ptember 12, 2014

.

43

## APPENDIX A

Example Model Input and Output Files

SWCC

Run for LA Sugarcane, for the Total Toxic Residues, Excluding the Unextracted Residues


# Summary of Water Modeling of Hexazinone and the USEPA Standard Reservoir

Estimated Environmental Concentrations for Hexazinone are presented in Table 1 for the USEPA standard reservoir with the LAsugarcaneSTD field scenario. A graphical presentation of the year

- to

- year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are summarized in Tables 2 and 3.

This model estimates that about 3.6% of Hexazinone applied to the field eventually reaches the water body. The mai n mechanism of transport from the field to the water body is by runoff ( 88% of the total transport), followed by spray drift (11.5%) and erosion (0.53%). In the water body, pesticide dissipates with an effective water column half

- life of 114.0 days. (This value does not include dissipation by transport to the benthic region; it includes only processes that result in removal of pesticide from the complete system.) The main source of dissipation in the water column is washout (effective average half

- life = 1 24.4 days) followed by metabolism (1363.8 days) and volatilization (1.085964E+08 days).

In the benthic region, pesticide dissipation is negligible (1833.0 days). The main source of dissipation in the benthic region is metabolism (effective average half

- li fe = 1833 days). Most of the pesticide in the benthic region (86%) is sorbed to sediment rather than in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Hexazinone.

Peak (1

- in

- 10 yr) 502.

4

- day Avg (1

- in

- 10 yr) 495.

21

- day Avg (1

- in

- 10 yr) 469.

60

- day Avg (1

- in

- 10 yr) 422.

365

- day Avg (1

- in

- 10 yr) 206.

Entire Simulation Mean 77.3

44

### Table 2. Summary of Model Inputs for Hexazinone.

Scenario LAsugarcaneSTD
Cropped Area Fraction 1.0 Koc (ml/g) 57.5

Water Half

- Life (days) @ 25 °C 1343

Benthic Half

- Life (days) @ 25 °C 1805
Photolysis Half

- Life (days) @ 40 °Lat 0

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 512.2

Foliar Half

- Life (days) 0

Molecular Wt 252.32 Vapor Pressure (torr) 1.9E

- 7 Solubility (mg/l) 29800

Table 3. Application Schedule for Hexazinone.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift 01/10 Foliar 4.03 0.95 0.135

45

### Figure 1. Yearly Peak Concentrations

SCI

- GROW

Total Toxic Residues, Excluding the Unextracted Radioactivity

SCIGROW VERSION 2.3 ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY SCREENING M ODEL FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3 chemical:Hexazinone time is 12/11/2014 12: 2:45

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

Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 8.000 1.0 8.000 5.75E+01 475.0

-------------------------- ---------------------------------------------- groundwater screening cond (ppb) = 1.80E+02

************************************************************************



### 46

### Total Toxic Residues, Including the Unextracted Radioactivity

SCIGROW VERSION 2.3 ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY SCREENING MODEL FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3 chemical:Hexazinone time is 12/ 4/2014 8:23:10

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

Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 8.000 1.0 8.000 5.75E+01 1051.0

------------------------------- ----------------------------------------- groundwater screening cond (ppb) = 5.27E+02

************************************************************************



### PRZM

- GW

Run of the Total Toxic Residues, Excluding the Unextracted Residues , NC Coast



# G roundwater Analysis for Hexazinone and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario Estimated groundwater concentrations and breakthrough times for Hexazinone 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 values for the model are summarized in Tables 2 an d 3.

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

- Norfolk loamy sand

- Cotton Scenario.

Peak Concentration (ppb) 3.09E+03

Post

- Breakthrough Mean Concentration (ppb) 2.21E+03

Entire Simulation Mean Concentration (ppb) 1.68E+03

Average Breakthrough Time (days) 2484.538

Throughputs 4.411282

47

### Table 2. Chemical Properties for Groundwater Modeling of Hexazinone. Koc (ml/g) 57.5 Surface Soil Half Life (days) 512.2 Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0
Henry's Constant 0.0 Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Hexazinone. This application scheme was applied every year of the simulation.

Application Date (Month/Day) Application Method Application Rate (kg/ha) 03/15 Above canopy application 8.97

Figure 1. Aquifer Breakthrough Curve for Hexazinone and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario

48

## APPENDIX B

Hexazinone and Its Environmental Transformation Products

. A



### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

PARENT Hexaxinone (DPX

- A3674) IUPAC: 3

- Cyclohexyl

- 6

- dimethylamino

- 1

- methyl

- 1,3,5

- triazine

- 2,4(1 H ,3 H )

- dione

CAS: 3

- Cyclohexyl

- 6

- (dimethylamino)

- 1

- methyl

- 1,3,5

- triazine

- 2,4(1 H ,3 H )

- dione

CAS No.: 51235

- 04

- 2

Formula: C 12 H 20 N 4 O 2 MW: 252.3 g/mol SMILES: O=C(N=C(N(C1=O)C)N(C)C)N1C (CCCC2)C2 O

N C H 3

N

C H 3 C H 3 O N

N Hydrolysis 41587301 pH 5 99.5 (0 d) 99.6 (30 d) Hydrolysis 41587301 pH 7 99.3 (0 d) 99.4 (30 d) Hydrolysis 41587301 pH 9 99.6 (0 d) 99.5 (30 d) Aq Photol 41300801 Irradiated 92.8 (0 d) 86.6 (30 d) B Aq Photol 41300801 Dark (pH 7) 94.3 (0 d) 93.6 (30 d) Soil Photol 41300802 Sandy loam 88.1 (0 d) 67.5 (30 d) C
Soil Photol 41300802 SL dark ctrl 88.9 (0 d) 86.7 (30 d)

835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 92.6 (0 d) 34.3 (365 d)

Sterile 91.5 (0 d) 82.3 (365 d)

48898001 Clay loam 101.2% (0 d) 15.5% (150 d) Sandy loam 103.1% (0 d) 52.8% (150 d)
Loam 100.0% (0 d) 38.6% (150 d)

835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 100.7% (0 d) 60.7% (180 d)
Clay loam 101.2% (0 d) 36.1% (180 d) Sandy loam 100.7% (0 d) 61.4% (180 d)
Loam 100.4% (0 d) 69.6% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 99.7 (3) 80.3 (56)

Sterile 99.9 (7) 86.8 (56)

49109901 Wabasha water:sandy loam 101.3% (0 d) 87.4% (100 d)

Tift water:sandy loam 100.5% (0 d) 91.6% (100 d)

835.4400 41807402 Non

- sterile loam 96.7 (7 d) 39.7 (365 d)

Sterile 96.0 (0 d) 81.3 (365 d)



### 49

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

Anaerobic

aquatic metabolism 49109902 Wabasha water:sandy loam 101.6% (0 d) 86.5% (101 d)

Tift water:sandy loam 100.5% (0 d) 92.1% (101 d)

MAJOR (>10%) TRANSFORMATION PRODUCTS
IN

- G3170; Met. G IUPAC: 1

- Methyl

- 6

- (methylamino)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 5 H 8 N 4 O 2 MW: 156.14 g/mol SMILES: [H]n1c(=O)nc(n(c1=O)C)N([H])C
H

N

O N

C H 3 N C H 3

H N O 835.4100 Aerobic

soil metabolism 48898001 Clay loam 42.2% (150 d) 42.2% (150 d) Sandy loam 16.4% (150 d) 16.4% (150 d)

Loam 26.8% (150 d) 26.8% (150 d)

835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 4.8% (46 d) 4.7% (180 d)
Clay loam 25.7% (122 d) 20.4% (180 d) Sandy loam 8.9% (180 d) 8.9% (180 d)
Loam 11.1% (122 d) 10.4% (180 d)

835.4300 Aerobic aquatic metabolism 49109901 Wabasha water:sandy loam 0.2% (15 d) ND (100 d)

Tift water:sandy loam 0.2% (15 d) ND (100 d)

835.4400 Anaerobic

aquatic metabolism 49109902 Wabasha water:sandy loam 1.3% (70 d) ND (101 d)

IN

- JS472; Met. 1 IUPAC: 6

- (Dimethylamino)

- 1

- methyl

- 3

- (4

- oxocyclohexyl)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 18 N 4 O 3 MW: 266.3 g/mol SMILES: Cn1c(nc(=O)n( c1=O)C2CCC(=O)C C2)N(C)C 835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 13.9 (180 d) 10.8 (365 d)

Sterile 4.0 (120 d) ND (365 d)

48898001 Clay loam 9.4% (10 d) 4.7% (150 d) Sandy loam 8.3% (60 d) 7.5% (150 d)
Loam 13.3% (150 d) 13.3% (150 d)
835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 6.6% (31 d) 5.5% (180 d)

Clay loam Aerobic 14.8% (14 d) ND (180 d)



### 50

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

O

N N

N

C H 3 C H 3 N

C H 3 O O Anaerobi c 14.7% (33 d) Sandy loam 8.5% (33 d) 5.0% (180 d)
Loam 8.1% (33 d) 6.7% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 6.5 (28 d) 3.7 (56 d)

Sterile 2.0 (56 d) 2.0 (56 d)

49109901 Wabasha water:sandy loam 5.8% (100 d) 5.8% (100 d)

Tift water:sandy loam 4.4% (100 d) 4.4% (100 d)

835.4200 Anaerobic soil metabolism 49109902 Wabasha water:sandy loam 6.5% (101 d) 6.5% (101 d)

IN

- B2838; Met. D IUPAC: 1

- Cyclohexyl

- 3

- methyl

1,3,5

- triazinane

- 2,4,6

- trione

Formula: C 10 H 15 N 3 O 3 MW: 225.2 g/mol SMILES: Cn1c(=O)[nH]c(=O)n(c1=O)C2CC CCC2

N

O N

C H 3 O N O 835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 5.1 (365 d) 5.1 (365 d)

Sterile 4.1 (365 d) 4.1 (365 d)

48898001 Clay loam 1.1% (150 d) 1.1% (150 d) Sandy loam 4.2% (150 d) 4.2% (150 d)
Loam 1.3% (150 d) 1.3% (150 d)

835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 32.0% (180 d) 32.0% (180 d)
Clay loam 2.2% (180 d) 2.2% (180 d) Sandy loam 2.9% (180 d) 2.9% (180 d)

Loam 2.9% (150 d) 2.8% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 1.3 (56 d) 1.3 (56 d)

Sterile 0.1 (56 d) 0.1 (56 d)

49109901 Wabasha water:sandy loam 0.8% (15, 70 d) 0.4% (100 d)



### 51

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

Tift water:sandy loam 1.8% (100 d) 1.8% (100 d)

835.4400 Anaerobic

aquatic metabolism 41807402 Non

- sterile loam 24.2 (365 d) 24.2 (365 d)

Sterile 12.5 (90 d) 1.9 (365 d)

49109902 Wabasha water:sandy loam 0.4% (70 d) 0.3% (101 d)

Tift water:sandy loam 1.6% (70, 101 d) 1.6% (101 d)

IN

- G3453; Met. A

- 1 IUPAC: 6

- (Dimethylamino)

- 3

- (2

- hydroxycyclohexyl)

- 1

- methyl

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 20 N 4 O 3 MW: 268.3 g/mol SMILES: Cn1c(nc(=O)n(c1=O)C2CCCCC2O )N(C)C O H

O N

N

C H 3 N C H 3

C H 3 N O 835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 19.5 (365 d) 19.5 (365 d)

Sterile 2.0 (120 d) ND (365 d)

835.4200 Anaerobic soil metabolism 48898002 Clay loam 9.5% (180 d) 9.5% (180 d) Sandy loam 4.0% (150 d) 2.6% (180 d)

Loam 0.7% (122 d) 0.6% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 5.1 (14 d) 5.0 (56 d)

Sterile 6.8 (56 d) 6.8 (56 d)

IN

- A3928; Met. B IUPAC: 3

- Cyclohexyl

- 1

- methyl

- 6

- (methylamino)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 11 H 18 N 4 O 2 MW: 238.28 g/mol SMILES: [H]N(C)c1nc(=O)n(c(=O)n1C)C2C CCCC2 Soil Photol 41300802 Sandy loam 10.1 (30 d) C 10.1 (30 d) C
SL dark ctrl 1.4 (30 d) 1.4 (30 d)

835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 2.4 (60 d) 2.3 (365 d)

Sterile 2.3 (120 d) 1.8 (365 d)

48898001 Clay loam 3.7% (122 d) 3.2% (150 d) Sandy loam 5.3% (150 d) 5.3% (150 d)
Loam 3.5% (150 d) 3.5% (150 d)
835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 1.1% (33, 180 d) 1.1% (180 d)
Clay loam 2.6% (180 d) 2.6% (180 d) Sandy loam 6.2% (180 d) 6.2% (180 d)



### 52

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

N

O N

C H 3 N H

C H 3 N O Loam 3.2% (46 d) 2.8% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 5.3 (28 d) 0.7 (56 d)

Sterile 6.3 (56 d) 6.3 (56 d)

49109901 Wabasha water:sandy loam 2.2% (100 d) 2.2% (100 d)

Tift water:sandy loam 0.2% (70 d) ND (100 d)

835.4400 Anaerobic

aquatic metabolism 41807402 Non

- sterile loam 3.5 (365 d) 3.5 (365 d)

Sterile 7.1 (270 d) 5.3 (365 d)

49109902 Wabasha water:sandy loam 1.6% (70 d) ND (101 d)

Tift water:sandy loam 0.2% (70 d) ND (101 d)

IN

- JT677; Met. 2 IUPAC: 6

- (Dimethylamino)

- 1

- methyl

- 3

- (2

- oxocyclohexyl)

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 18 N 4 O 3 MW: 266.3 g/mol SMILES: Cn1c(nc(=O)n(c1=O)C2CCCCC2= O)N(C)C

O N

O N

C H 3 N

C H 3 C H 3 N O 835.4100 Aerobic

soil metabolism 48898001 Clay loam 1.4% (122 d) ND (150 d) Sandy loam 0.8% (122 d) ND (150 d)

Loam 1.1% (122 d) ND (150 d)

835.4200 Anaerobic soil metabolism 48898002 Clay loam 1.9% (150 d) 1.8% (180 d) Sandy loam 1.2% (150 d) ND (180 d)

Loam 1.0% (180 d) 1.0% (180 d)

835.4300 Aerobic aquatic metabolism 49109901 Wabasha water:sandy loam 1.3% (15 d) ND (100 d)

835.4400 Anaerobic

aquatic metabolism 41807402 Non

- sterile loam 27.5 (365 d) 27.5 (365 d)

Sterile 2.7 (90 d) ND (365 d)

49109902 Wabasha water:sandy loam 1.3% (70 d) ND (101 d)

IUPAC: Carbon dioxide Soil Photol 41300802 Sandy loam 0.23 (30 d) C 0.23 (30 d) C



### 53

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

Carbon dioxide Formula: CO 2 MW: 44 g/mol SMILES: C(=O)=O

C O O SL dark ctrl 0.02 (30 d) 0.02 (30 d)

835.4100 Aerobic

soil metabolism 41807401 / 42635001 Non

- sterile sandy loam 2.0 (365 d) 2.0 (365 d)

Sterile <0.1 (365 d) <0.1 (365 d)

48898001 Clay loam 9.7% (150 d) 9.7% (150 d) Sandy loam 2.8% (150 d) 2.8% (150 d)
Loam 2.8% (150 d) 2.8% (150 d)

835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 0.5% (180 d) 0.5% (180 d)
Clay loam 1.3% (90

- 180 d) 1.3% (180 d) Sandy loam 0.4% (180 d) 0.4% (180 d)
Loam 0.7% (180 d) 0.7% (180 d)

835.4300 Aerobic aquatic metabolism 41811801 Non

- sterile sandy loam 0.5 (56 d) 0.5 (56 d)

Sterile 0.1 (56 d) 0.1 (56 d)

49109901 Wabasha water:sandy loam 0.1% (100 d) 0.1% (100 d)

Tift water:sandy loam 0.1% (100 d) 0.1% (100 d)

Unextract ed residues

NA NA 835.4100 Aerobic

soil metabolism 48898001 Clay loam 25.6% (150 d) 25.6% (150 d) Sandy loam 14.3% (150 d) 14.3% (150 d)

Loam 14.3% (150 d) 14.3% (150 d)

835.4200 Anaerobic soil metabolism 48898002 Sandy clay loam 11.0% (33 d) 5.1% (180 d)
Clay loam 28.2% (31 d) 12.6% (180 d) Sandy loam 10.6% (180 d) 10.6% (180 d) MINOR (<10%) TRANSFORMATION PRODUCTS

IN

- T3937; Met. A IUPAC: 6

- (Dimethylamino)

- 3

- (4

- hydroxycyclohexyl)

- 1

- methyl

- 1,3,5

- triazine

- 2,4

- dione

Formula: C 12 H 20 N 4 O 3 MW: 268.3 g/mol 835.4100 Aerobic

soil metabolism 48898001 Clay loam 0.5% (150 d) 0.5% (150 d) Sandy loam 0.5% (150 d) 0.5% (150 d)

Loam 2.6% (150 d) 2.6% (150 d)

835.4200 48898002 Sandy clay loam 1.0% (60 d) ND (180 d)



### 54

### Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR (study length)

SMILES: Cn1c(nc(=O)n(c1=O)C2CCC(CC2) O)N(C)C O

N N

N

C H 3 C H 3 N

C H 3 O O H Anaerobic soil metabolism Clay loam 5.8% (180 d) 5.8% (180 d) Sandy loam 3.4% (180 d) 3.4% (180 d)

Loam 2.5% (90 d) 1.3% (180 d)

A AR means “applied radioactivity”. MW means “molecular weight”. ND means “not detected”. NA means “not applicable”. B Equivalent to 69.0 days of natural sunlight. C Equivalent to 84.0 days of natural sunlight.



### 55

## APPENDIX C . Excerpts from th e Atrazine Endangered Species Assessment

EFED conducted in 2006 an analysis of the percentage of land that is covered by rights

- of

- ways in the Chesapeake Bay area. The analysis can be found in Section 3.2.1.2 of the atrazine endangered species assessment located at: http://www.epa.gov/oppfead1/endanger/litstatus/effects/atrazine/2007/determination

- cheasp.pdf (accessed 03/05/2015) (excerpts are rep roduced below).

Right

- of

- way

- Surrogate scenario for all rights of way uses including roads, fence line, power lines, and railroads

. Unlike most of EFED existing scenarios, the scenario is conceptually different in that it represents a linear surface that drains into an adjacent water body (drainage ditch). However, for this exercise, EFED assumes that while conceptually different, the scenario is for practicality purposes developed in a similar manner as a standard scenario that assumes a 10 hectare field draining into a 1 hectare static pond. For purposes of this assessment, EFED will assume equivalency between the concept of the adj acent drainage ditch (assumed to be perennial) and EFED’s standard pond. This conceptual model also assumes that the receiving drainage ditch is adjacent and connected to the standard pond. Development of this scenario should focus on curve numbers ident ified in Table 2

- 2a from the USDA Publication Urban Hydrology for Small Watersheds, Technical Release 55 (TR

- 55) dated June 1986 for impervious areas

- paved open ditches (including right

- of

- way). EFED geospatial analysis indicates that the Barton Springs Segment in Hays and Travis counties (see figure 1 in Attachment B) is dominated by Hydrologic Group C and D soil types and emphasis should be placed on identifying a representative soil series which will yield high end runoff and sediment loads. This sce nario will need research into the appropriateness of this cover type and the percentage of impervious surface typically present in rights

- of

- ways where pesticides would be applied.

Conceptually, this scenario assumes that the entire 10 hectare treated a rea will drain directly into either an adjacent waterbody or into a drainage ditch/channel which in turn flows directly into a receiving waterbody.

For the rights

- of

- way scenario, it was assumed that rights

- of

- way consist of 50% impervious and 50% pervi ous cover. In addition, it was assumed that no single watershed will be completely covered by a rights

- of

- way use. This assumption seems reasonable given that rights

- of

- way (roads, rail and utility lines) are typically long linear features that traverse a watershed. For the screening level assessment, it was assumed that no more than 10% of the watershed is covered in rights

- of

- way.

An analysis was completed for the Chesapeake Bay endangered species assessment for atrazine to assess the amount of righ ts

- of

- way likely to be present in the action area. In this analysis, spatial data specific to the Chesapeake Bay watershed compiled by the Chesapeake Bay Program (CBP) for roads and railways and obtained on July 12, 2006 that may be found at;

( http://www.chesapeakebay.net/data/data_desc.cfm?DB=CBP_GIS )

56

### and internal Agency data for pipelines was obtained (spatial data for utility easements was unavailable). The road, rail, and pip eline land cover data were added to a GIS map of the action area (Figure 3

- 2) and a comparison of the density of the total network of potential use sites was made. Each land cover feature in the GIS map is presented as a line with no width associated. EF ED applied a buffer using the Arc Toolbox within Arc Map in order to account for the potential width of the each linear feature. This assignment of area to each feature was done in order to compare the total area of each feature type (e.g. railways) with the total area of the action area.

For each feature, an assumption was made about the typical width of the feature (e.g. width of the road surface plus shoulders) plus the right of way area adjacent to the feature that could potentially be treated. In ea ch case, a conservative assumption for the width of the feature zone plus the potentially treated area surrounding each was made. These assumed widths were based on professional judgment but skewed the total feature estimate to the largest feature in the class. For example, it was assumed that a national highway would yield that largest width which was then applied to all primary and secondary highways within the action area. This approach is also assumed to be conservative because it is unlikely that al l features within the available data will be treated with atrazine because many of the areas are likely to be maintained using mechanical methods (e.g. mowing) or not treated at all. Using the CBP data different road types were able to be distinguished us ing the USGS’ classification scheme for digital line graph (DLG) data. In these data set distinguishing between highways (primary and secondary roads), state and county highways, state and local streets, unimproved trails, as well as minor features such a s interchanges and traffic circles was possible. Different buffer widths were applied to each category of roadway depending upon the general use of the feature. For example, it is generally assumed that primary and secondary roads are wider than state/co unty roads, which in turn are generally wider than local streets. Based on this approach the following assumptions were made for the width of each feature.

• Primary/Secondary Roads

– 200 feet

• Class 3 Roads (State/County)

– 100 feet

• Class 4 Roads (Streets in built up areas)

– 50 feet

• Unimproved Trails

– 25 feet

• Rail

– 200 feet

• Pipeline

– 100 feet

• Utility Line

– 200 feet

Given these assumptions the percentage of rights

- of

- way land cover types plus associated buffers for roads, railways, and pipelines within the action are a for the Chesapeake Bay is 0.2 % of the total area for rail, 3.6 % for all primary and secondary roads (interstates, national and state highways), and 0.5% for pipelines. Including all classes of roads in the data set yields a road density o f 9.5%. This is believed to be an over estimation because it includes a high number of roads in urban and suburban areas unlikely to be treated with pesticides for right of way control. Locally, it appears that higher percentages occur near more urbanize d areas, however, it was assumed that less right of way application of pesticides occur in urbanized areas. Additional roads may be present in the action area not captured by the available spatial data and the analysis above does not include utilities for which no spatial data are available. Therefore, the10%

57

### assumption of rights

- of

- way in the action area used in this assessment is an over

- estimation but given the uncertainties is reasonable while still being conservative and protective.

Figure 3

- 2 De nsity of Road, Railways, and Pipelines as Surrogate for Right of Way Density in Chesapeake Bay Watershed (Action Area)

58