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Preliminary Ecological Risk Assessment in

Support of the Registration Review of Hexazinone

Hexazinone (CAS 51235-04-2)

Prepared by:

Hannah Yingling, Biologist

José Meléndez, Chemist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Geoffrey Sinclair, Ph.D., Biologist

Mohammed Ruhman, Ph.D., Senior Agronomist

Mah Shamim, Ph.D., Branch Chief

Office of Chemical Safety 

and Pollution Prevention
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Table of Contents

Executive Summary........................................................................................................................ 4

1.0 Problem Formulation......................................................................................................... 6

1.1 Nature of Regulatory Action ............................................................................................. 6

1.2. Mechanism of Action ........................................................................................................ 6

1.3 Use Characterization ......................................................................................................... 7

1.4 Stressors of Concern.......................................................................................................... 7

1.5 Risk Hypothesis................................................................................................................. 8

1.6 Analysis............................................................................................................................. 9

2.0 Exposure Characterization ................................................................................................ 9

2.1 Use Information................................................................................................................. 9

2.2 Environmental Fate and Transport.................................................................................. 16

2.3 Aquatic Modeling Approach ........................................................................................... 30

2.4 Terrestrial Exposure Modeling........................................................................................ 37

3.0 Ecological Toxicity ......................................................................................................... 44

3.1 Aquatic Organisms.......................................................................................................... 45

3.2 Terrestrial Organisms...................................................................................................... 48

3.3 Incident data .................................................................................................................... 50

4.0 Risk Characterization ...................................................................................................... 51

4.1 Risk Estimation for Aquatic Organisms for Spray and Granular Uses........................... 54

4.2 Risk Estimation for Terrestrial Organisms Non-Granular Uses ..................................... 60

4.3 Risk Estimation to Terrestrial Organisms for Granular and Pelleted Uses..................... 70

4.4 Risk Description.............................................................................................................. 72

4.5 Endangered species ......................................................................................................... 79

4.6 Uncertainties and Limitations ......................................................................................... 81

References....................................................................................................................... 87

Appendix A.Environmental Fate / Chemistry Bibliography........................................................ 89

Appendix B.Ecological Effects Bibliography.............................................................................. 96

Appendix C. Hexazinone and its transformation products......................................................... 101

Appendix D. Sample SWCC Output File ................................................................................... 109

Appendix E. T-REX non-granular example output .................................................................... 111

Appendix F. LD50 per ft2 T-REX example output....................................................................... 115

Appendix G. Granular Characterization T-REX example output............................................... 117

Appendix H. Terrplant example output ...................................................................................... 119

Appendix I. Classifications of Environmental Fate Studies....................................................... 120

Appendix J. Hexazinone Refresh Acceptable Bibliographies November 2014 ......................... 125

Appendix L. STIR Output........................................................................................................... 132
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Executive Summary

Hexazinone is a systemic herbicide for weed control in certain crops like pineapples, sugarcane 

and blueberries, Christmas trees, forestry site preparation and release areas, industrial areas, 

reforestation areas, rangeland, pastures and noncrop areas. The herbicide belongs to the triazinone 

chemical family. Hexazinone is usually applied once per year, in the winter or early spring.

Based on the available information, hexazinone residues (sum of hexazinone and Metabolites A1

(or A-1), B, D, G, 1, 2, and minor Metabolite A) are persistent and mobile in soil and aquatic 

environments and considered as the stressors in this ecological risk assessment. The mobility of 

hexazinone was demonstrated in batch equilibrium as well as terrestrial field, forestry dissipation, 

and a prospective groundwater monitoring studies. Hexazinone is stable to hydrolysis and 

photolysis and degrades at relatively slow rates under aerobic soil metabolism conditions. Aerobic 

and anaerobic aquatic metabolism and anaerobic soil metabolism studies show slow degradation 

for hexazinone. Consistent with this persistence and mobility, field dissipation 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 (KOC = 38-77 mL/gOC, 

mobile according to FAO 2000). Given this mobility and persistence, hexazinone has a strong 

potential to leach to ground water systems, especially in soil systems such as loamy and sandy 

soils that are poor in organic matter. Hexazinone is not expected to bioconcentrate substantially 

in fish tissue, with its low KOW value of 15 (i.e., log KOW = 1.1).

Table 1 provides a summary of the environmental risk conclusions for hexazinone, for aquatic and 

terrestrial organisms, based on primarily on risk quotient (RQ) values and whether they exceed 

levels of concern (LOCs) for Federally-listed threatened and endangered species (hereafter refers 

to as listed species) and non-listed species.

Table 1. Summary of Ecological Risk Conclusions for Hexazinone Uses

Taxonomic Group Summarized Risk Characterization and Major Uncertainties

Fish and Aquatic 

Invertebrates 

(freshwater and 

estuarine/marine)

The potential for acute or chronic risk to freshwater fish, freshwater 

invertebrates and estuarine/marine invertebrates is considered low for 

flowable and granular uses, as acute and chronic RQ values do not 

exceed the risk to listed or nonlisted species LOC.

Aquatic and 

Terrestrial Plants

There is a potential for risk to aquatic and nontarget terrestrial plants, 

aquatic vascular plants, and aquatic nonvascular plants for all uses. 

This risk is consistent with the mode of action of the chemical. 

Birds There is a potential for acute and chronic risk to birds for flowable 

and granular uses; only one flowable use resulted in a chronic LOC 

exceedance. RQ values that exceed the risk to listed species at the 

LOC were observed with higher application rates, smaller bird sizes, 

and birds consuming short grass, tall grass and broadleaf plants. 

LD50 per ft2 analysis for granular and pelleted uses showed concern 

for small and medium birds. Pelleted uses were further characterized 

based on the size of the pellet; despite toxic risk to all bird sizes, only 

the largest birds are expected to consume the pellets (640 mg). There 
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is some uncertainty due to the lack of available data for smaller birds

(passerine species). 

Mammals There is the potential for acute and chronic risk to mammals for 

flowable and granular uses. Acute dose based RQs and dietary based

RQ values that exceed the risk to listed species LOC trend toward to 

higher application rates, smaller mammal size, and mammals

consuming short grass, tall grass and broadleaf plants. Chronic dosebased RQ values exceeded the LOC across the top 6 application rates 

for small and medium mammals across all feeding strategies. LD50

per ft2 analysis for granular and pelleted uses showed concern for 

small and medium mammals. Pelleted uses were further 

characterized based on the size of the pellet; despite toxic risk to all 

mammal sizes, only the largest mammals are expected to consume 

the pellets (640 mg).

Bees The potential for risk to terrestrial invertebrates is considered low 

because the LC50>100 μg/bee. However, there is uncertainty 

concerning the lack of toxicity data from chronic exposure to adults 

and acute and chronic exposure for larva. The chemical is persistent 

but is applied in winter or early spring.
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1. 0 Problem Formulation

The purpose of problem formulation is to provide the foundation for the environmental fate and 

ecological risk assessment being conducted for hexazinone. The problem formulation sets the 

objectives for the risk assessment and provides a plan for analyzing the data and characterizing the 

risk (USEPA 1998). As part of the Registration Review process, a detailed Problem Formulation 

(DP Barcode D369269) for this risk assessment was published to the docket [Docket ID: EPAHQ-OPP-2009-0755] in March 31, 2010. The following sections summarize the key points of that 

document and discusses any differences between the analysis outlined previously and the analysis 

conducted in this risk assessment.

1.1 Nature of Regulatory Action

This risk assessment is conducted as part of the Agency’s Registration Review process for 

pesticide active ingredients. The Registration Review process was established under the Food 

Quality Protection Act (FQPA 1996).

1.2. Mechanism of Action

Hexazinone (Figure 1), CAS Name: 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine2,4(1H,3H)-dione, and IUPAC Name: 3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine2,4(1H,3H)-dione, has a CAS Number of 51235-04-2 and a PC Code of 107201. It is a triazinone 

herbicide. According to the sample label for Velpar L, hexazinone is an “herbicide...applied as a 

spray for weed control 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 injection for brush control.” 

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 (HRAC1

), hexazinone belongs to the HRAC Group C1 with a site 

of action inhibition of photosynthesis at photosystem II. The herbicide belongs to the triazinone 

chemical family (other members of the trizinone family include ametridione, amibuzin, ethiozin, 

isomethiozin, metamitron, metribuzin and trifludimoxazin; however, only a few of these chemicals 

are currently approved for use in the U.S.).

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

N

C H 3

N

C H 3

C H 3

O

N

N

Figure 1. Structure of Hexazinone

1.3 Use Characterization

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 (right-ofway). Hexazinone is 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 uses. Refer to Section 2.1 for further detail about 

the use information.

1.4 Stressors of Concern

According to the available environmental fate data for hexazinone, it undergoes a number of 

transformations, which result in transformation products with essentially the same backbone 

structure of the parent compound (with the exception of G), with slight differences in substituent 

moieties. Hexazinone degradates include Metabolites A-1, B, D, G (or G3170), 1, 2 and minor 

metabolite A. Structures of these degradates are presented in Table 8. Information about 

maximum formation in the individual studies is presented in the Appendix C. Inspection of Table 

8 shows that all the metabolites except for metabolite G have two rings from the parent structure. 

Metabolite G contains only the triazine ring. Based on the available information, hexazinone 

residues (hexazinone plus all its metabolites) appear to be persistent and mobile in soil and aquatic 

environments and they are all considered as the stressors of concern. Exposures in aquatic habitats 

will be quantified considering hexazinone plus all these metabolites, considered of concern (total 

toxic residues or TTRs). More information about the degradates is available in Section 3.1.1 and 

the table in the Appendix K.

Since there were high levels of unextracted residues (UERs) in the aerobic soil metabolism studies

and it appeared that the extraction methods may not have been exhaustive, additionally, aquatic 

exposure will be quantified using estimated exposure concentrations (EECs) for TTRs(hexazinone
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plus its metabolites) and the UERs for selected representative scenarios. It should be noted that in 

the aerobic and anaerobic aquatic metabolism studies the levels of UERs were very low. As will 

be discussed later, including the UERs in the expression of the TTRs did not change the overall 

risk picture, since the hexazinone plus its’ degradates (TTRs excluding the UERs) and the TTRs 

plus the UERs are very persistent in the environment. [The soil was only extracted three times by 

shaking for 30 minutes with methanol:water (80:20, v:v).]

Exposures in terrestrial habitats will be calculated using hexazinone parent only.

1.5 Risk Hypothesis

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure.

The risk hypothesis for hexazinone provides a written description of the predicted relationships 

between hexazinone, potential routes of exposure, and the predicted effects for the assessment 

endpoint. The previous assessments highlighted in the preliminary problem formulation and more 

recent data serve as a basis for the risk hypothesis and conceptual model developed for current 

registered uses of hexazinone. 

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For hexazinone, the 

following ecological risk hypothesis is being employed for this national-level ecological risk 

assessment:

Hexazinone, when used in accordance with current labels, can result in offsite movement of the compound and its transformation products via runoff, 

spray-drift, and atmospheric transport leading to exposure of nontarget plants 

and animals. Monitoring data indicate frequent detections of hexazinone and 

its residues in surface waters. Applications of hexazinone may result in 

exposure to non-target aquatic and terrestrial organisms at concentrations 

high enough to result in adverse effects upon the survival, growth, and 

reproduction. These nontarget organisms include Federally-listed threatened 

and endangered species.
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The ecosystems potentially at risk are often extensive in scope; therefore, it may not be possible 

to identify specific ecosystems during the development of a nationwide ecological risk assessment. 

However, in general terms, terrestrial ecosystems potentially at risk could include the treated field 

and immediately adjacent areas that may receive drift or runoff. Areas adjacent to the treated field 

could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, 

woodlands, riparian habitats, and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to, or downstream from, the 

treated field and might include impounded bodies such as ponds, lakes and reservoirs, or flowing 

waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also includes marine 

ecosystems, including estuaries. 

1.6 Analysis

The analysis plan will follow the approach described in the Preliminary Problem Formulation (DP 

barcode D369269). Modifications or updates to the approach described in the preliminary problem 

formulation are described below. 

2.0 Exposure Characterization

2.1 Use Information

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, among others. It is also used on ornamental plants, forest trees and other non-crop 

areas (e.g., rights-of-way). Hexazinone is 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 handheld, boom, knapsack or power sprayer. There are no indoor uses.

Currently there is only one technical registration and there are 14 Section 3 registrations and 2 

Special Local Needs (SLNs). Of the Section 3 registrations, seven are multi-active ingredient (coformulations) that include hexazinone with either sulfometuron (EPA Reg. Nos. 352-603, 352-

626) or diuron (EPA Reg. Nos. 352-618, 352-634, 352-663, 352-665, 352-666). The active SLNs 

are in the state of Louisiana. National (Section 3) uses for hexazinone are presented in Table 2

with label maximum application rates. For some uses the maximum number of applications per 

year at the maximum rate is one (i.e., 1 application/year), while for some uses assumptions were 

made based on additional information found on the label or what is known about the crop and the 

chemical. For this assessment, 1 (one) application/year for those other uses was assumed. For 

example, blueberry uses may be modeled at a maximum of one application per year due to no 

application 450 days before harvest (note that it would mean fewer than one application per year). 

Pineapple may be modeled as one application per year due to the growing season, which is nearly 
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a year long. Non-crop uses and forest site preparation and rangeland, are modeled as one 

application per year since rainfall is required to activate hexazinone and because maximum effects 

are achieved after 12-24 months (thus, it is unlikely that repeated applications are made, 

considering that a waiting period is required to observe the effects). Hexazinone is usually applied 

in the spring after ground thaws, or in the fall before snowfall (see Timing of Application in Table 

2). Note that the table also presents available Surface Water Concentration Calculator (SWCC) 

PRZM crop scenarios, which will be discussed later in this document (Section 2.3.1).

There are two granular products and one pelleted product containing hexazinone as the sole active 

ingredient as follows: DuPontTM Velpar® ULW (352-450) and Alligare Hexazinone 75 ULW 

(81927-31) herbicides are formulated as soluble granules, while Pronone® Power Pellet (33560-

41) is formulated as pellets. All three products contain 75% hexazinone and 25% other ingredients. 

For Velpar®, according to the label, “Rainfall dissolves the VELPAR® ULW granules, releasing 

the active ingredient (hexazinone) into the root zone, where it is absorbed during periods of 

vigorous plant growth.” For Alligare, the instructions say that, “Alligare Hexazinone 75 ULW 

granules are activated by rainfall. The active ingredient in Alligare Hexazinone 75 ULW, 

hexazinone, dissolves in the water and is moved into the soil.” Finally, for the pelleted product, 

Pronone, according to the label, “Moisture is required to activate PRONONE POWER PELLETS 

in the soil. Best results are obtained when the soil is moist at time of application and 1⁄4 to 1⁄2 inch 

of rainfall occurs within 2 weeks after application.”

Table 2. Summary of Hexazinone Uses and Application Information

Available 

SWCC Scenario Crop Methods of Application

Max 

Application 

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 western 

states winter;

eastern states 

spring

LA sugarcane, 

(using a HI 

meteorological file 

to represent 

sugarcane in HI)

Sugarcane (except in FL) Ground;

or aerial (for preemergence 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)

Pre and postemergence;

Spring and fall;

Pre- and postemergence;

Pre-emergence & 

layby (60-day 

interval)
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Table 2. Summary of Hexazinone Uses and Application Information

Available 

SWCC Scenario Crop Methods of Application

Max 

Application 

Rate

(lb a.i./A)

Timing of 

Application

No available 

scenario, not 

modeled, but note 

that sugarcane in 

HI represents the 

same application 

rate than 

pineapple.

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 preplant, 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

CA rights-of-way Non-crop sites (weed and brush control):

Uncultivated nonagricultural areas (such as, airports, 

highway, railroad and utility right-of way, sewage disposal 

areas);

Uncultivated 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);

Handgun 

applicator

8 ground and

6 for aerial 

apps;

2-4 mL3 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 (using 

a MI meteorological station or 

file to represent 

eastern and lakes 

states)

Forestry site preparation

Eastern and Lakes 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 mL3 per 

ea. stem in 

diameter;

1 mL3 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
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Table 2. Summary of Hexazinone Uses and Application Information

Available 

SWCC Scenario Crop Methods of Application

Max 

Application 

Rate

(lb a.i./A)

Timing of 

Application

CA forestry (using 

a MI meteorological station or 

file to represent 

eastern and lakes 

states)

Conifer release

Eastern and Lakes 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 mL3 per 

ea. stem in 

diameter;

1 mL3 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 the following 22 states 

listed in label: Alabama, Louisiana, New Jersey, Texas, 

Arkansas, Maine, New York, Vermont, Connecticut, 

Maryland, North Carolina, Virginia, Delaware, 

Massachusetts, Pennsylvania, West Virginia, Georgia, 

Mississippi, Rhode Island, Florida, New Hampshire, and 

South Carolina)

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

Not modeled, but 

may be represented 

by OR Christmas 

trees or CA 

forestry, which are 

modeled 

separately.

Yellow poplar plantations Ground or aerial 2 Spring

CA rangeland hay 

(using a NY 

meteorological file 

to represent eastern 

and lakes states)

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 mL3 per 

ea. stem in 

diameter,

do not exceed 

0.8 lb a.i./yr

Late winter 

through summer

PA turf Bermudagrass/Bahiagrass;

Industrial turf grass

Ground 1.125 When weeds are 

actively growing

Granular and pelleted applications

CA rangeland hay Rangeland (pellets) By hand or in a 

grid pattern for 

area control

600 pellets/A= 

0.63 lb a.i./A2

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./A2

Late Winter to 

early Summer
Page 13 of 133

Table 2. Summary of Hexazinone Uses and Application Information

Available 

SWCC Scenario Crop Methods of Application

Max 

Application 

Rate

(lb a.i./A)

Timing of 

Application

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./A2

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 rightsof-way (pipelines), sewage disposal areas; Industrial sites 

(lumberyards, tank farms), etc.

Non-crop sites (pellets)

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 areas.

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./A2

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 number 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 06/05/2015).

3 Application rates in mL/stem are representative of Velpar L labels. The rate in mL/stem vary for other products

with different percent hexazinone, but the rate in lb a.i. is the same.

Inspection of the labels for hexazinone indicates that the application rate range for the chemical 

may vary according to soil texture and organic matter content and/or pest to be treated. For 

example, in the sample label for Velpar L, on rights-of-way the range in application rates is wide 

(range is 2–8 lb a.i./A). For rights-of-way, 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 instructs the applicator to...“Use lower rate on 

coarse textured soils (sand to sandy loam). Use the higher rate on fine textured soils (clay loam to 

clay) and on soils high in organic matter.” Similar instructions regarding the soil types are 

expressed in the majority of the labels and uses.

Environmental Hazard Statements:

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

appear in other labels. It should be noted that a groundwater advisory is stated:

“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 water when disposing of 

equipment wash waters.
Page 14 of 133

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 permeable, particularly where the water table is shallow, may 

result in groundwater contamination.”

2.2.1 Usage Information

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 the SLUA does not provide information about non-agricultural use patterns of 

hexazinone. Hexazinone has uses such as non-cropland (represented by rights-of-way) and 

forestry, which are not represented in the SLUA. SLUA data sources include: USDA-NASS 

(United States Department of Agriculture’s National Agricultural Statistics Service); 2001-2007; 

Private Pesticide Market Research, 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.

Table 3. Summary of Screening-Level Estimates of Agricultural Uses of Hexazinone (SLUA, 

dated 06/16/2009)

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. N/C = Not Calculated.

‘<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.

+ 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 (Figure 2) shows regional scale patterns 

in use intensity within the United States. In comparison to the SLUA, the major use of hexazinone 

in 2008-12 is alfalfa (>90% of the use), followed by pastures and hay (<10%). It is noted that the 

USGS website2 provides additional usage maps for other years. It is apparent from the map, that 

hexazinone was more intensively used in the western half of the continental U.S. in 2012. 

Additionally, it was used intensively in FL, areas of the MS Delta, and sections of the Midwest.

 2 At http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2012&map=HEXAZINONE&hilo=L

(accessed 06/29/2015).
Page 15 of 133

Figure 2. Hexazinone Estimated Agricultural Use (2012) and Use by Year and Crop
Page 16 of 133

2.2 Environmental Fate and Transport

The chemical profile of hexazinone is provided in Table 4. Environmental fate characteristics of 

the parent compound hexazinone are listed in Tables 5a, 5b, 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 

(29,800 ppm), and a low octanol/water partition coefficient (KOW = 15). Based on these properties, 

it 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-m3/mol), hexazinone is not expected to volatilize substantially from 

wet/moist surfaces.

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 C12H20N4O2

Molecular Weight 252.3 g/mol

CAS No. 51235-04-2

CAS name 3-Cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine2,4(1H,3H)-dione

IUPAC name 3-Cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine2,4(1H,3H)-dione

Water solubility 29800 ppm at 25°C

MRID 41203201 (reported 

Vapor pressure in DP Barcode D279324)

1.9 x 10-7 torr at 25°C

[‘Non-volatile under field conditions’ from dry nonadsorbing surfaces(1)]

Henry’s Law Constant 2 x 10-12 atm-m3/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 “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).
Page 17 of 133

Synopsis of Environmental Fate

Based on the available information, hexazinone residues (sum of hexazinone and Metabolites A1, 

B, D, G, 1, 2 and minor Metabolite A) appear to be persistent and mobile in soil and aquatic 

environments and considered as the stressors in this assessment. The half-lives for parent 

hexazinone are summarized in Table 5, while the representative half-lives for the total toxic 

residues or TTRs of hexazinone are presented in the Table 6 (total toxic residues (TTRs) include 

hexazinone and its transformation products, which were found to be of concern: Metabolites A-1, 

B, D, G, 1, 2 and minor Metabolite A). The mobility of hexazinone was demonstrated in batch 

equilibrium as well as terrestrial field, forestry dissipation, and a prospective groundwater 

monitoring studies (Table 7). Hexazinone is stable to hydrolysis and photolysis and degrades at 

relatively slow rates under aerobic soil metabolism conditions. Aerobic and anaerobic aquatic 

metabolism and anaerobic soil metabolism studies show slow degradation for hexazinone. 

Consistent with this persistence and mobility, field dissipation 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 (KOC = 38-77 mL/gOC, mobile 

according to FAO 2000 mobility classification). These data indicate that hexazinone is mobile, 

thus, combined with its persistence, having strong potential to leach to ground water systems, 

especially in soil systems such as loamy and sandy soils that are poor in organic matter. Based on 

laboratory bioconcentration in rainbow trout, hexazinone is not expected to bioconcentrate

substantially in fish tissue, which is consistent with the low KOW value of 15 (i.e., log KOW = 1.1).

Table 5. Summary of Degradation and Metabolism Fate Properties of Parent Hexazinone

Study System Name/ Characteristics

Value for Parent Hexazinone1

(Kinetic Model if Applicable)

Reference, 

Study 

DT50 (days) DT90 (days) Classification*

Abiotic Hydrolysis

pH 5, 250C Stable Stable

pH 7, 250C Stable Stable 41587301 (A)

pH 9, 250C Stable Stable

Atmospheric 

Degradation Hydroxyl radical2 0.119 (estimated) EPI Suite v.4.11

Aqueous 

Photolysis pH 7, 250C Stable Stable 41300801 (A)

Soil Photolysis Sandy loam from CA, pH 6.5, 

0.6% OM, 200C

82 (light 

exposed);

stable (dark 

control)

41300802 (A)

Aerobic Soil 

Metabolism

Sandy loam (CA), pH 6.5, 0.6% 

OM, 250C 216 41807401/ 

42635001 (A)

Audrain clay loam soil (MO), pH 

6.6, 4.1% OM, 20°C 45.2 (IORE) 180 (IORE)

48898001 (S) Sassafras sandy loam (MD), pH 

5.4, 2.0% OM, 20°C

DFOP slow 

t1/2 = 143 days

Porterville loam (CA), pH 7.7, 

1.11% OM, 20°C 115 (SFO) 381 (SFO)

Anaerobic Soil 

Metabolism

Raymondville sandy clay loam 

(TX), pH 8.0, 0.83% OM, 20oC 389 (SFO) 1,292 (SFO)

48898002 (S) Mexico clay loam (MO), pH 6.6, 

4.1% OM, 20°C 997 (SFO) 3,311 (SFO)
Page 18 of 133

Table 5. Summary of Degradation and Metabolism Fate Properties of Parent Hexazinone

Study System Name/ Characteristics

Value for Parent Hexazinone1

(Kinetic Model if Applicable)

Reference, 

Study 

DT50 (days) DT90 (days) Classification*

Sassafras sandy loam (MD), pH 

5.4, 2.0% OM, 20°C 309 (SFO) 1,026 (SFO)

Porterville loam (CA), pH 7.7, 

1.11% OM, 20°C 1,165 (SFO) 3,872 (SFO)

Aerobic Aquatic

Water:sandy loam sediment (CA), 

water pH 7.9-8.03, sediment pH not 

reported, 0.7% OM, 25°C

>2 months 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) 49109901 (S)

Tift Water:sandy loam sediment 

GA, water pH 7.7, sediment pH 

7.5, 1.2% OM, 20°C

719 (SFO) 2,389 (SFO)

Anaerobic Aquatic

Water:loam sediment (CA), water 

pH 7.83, sediment pH 8.5, 1.24% 

OC, 25°C

230 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)

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)

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

1 DT50 and DT90 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 DT50 and DT90 are reported when 

available. Otherwise, a first and second DT50 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 Characterize 

Pesticide Degradation, U.S. Environmental Protection Agency dated November 30, 2012 and approved December 

17, 2012.

2 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.

3 Measured in the first test interval.

Table 6. Summary of Information Used to Derive Input Parameters for the Total Toxic Residues

of Hexazinone*

Study

System Name/ 

Characteristics Description

Half-life Value 

Used to Derive 

Model Input 

Parameters TTRs1,2

Reference, 

Study 

Classification**

Abiotic 

Hydrolysis pH 7, 250C Stable (0) 41587301 (A)

Aqueous 

Photolysis pH 7, 250C Stable (0) 41300801 (A)

Aerobic Soil 

Metabolism

Sandy loam (CA), pH 

6.5, 0.6% OM, 250C 604 days (SFO) 41807401/ 

42635001 (A)
Page 19 of 133

Table 6. Summary of Information Used to Derive Input Parameters for the Total Toxic Residues

of Hexazinone*

Study

System Name/ 

Characteristics Description

Half-life Value 

Used to Derive 

Model Input 

Parameters TTRs1,2

Reference, 

Study 

Classification**

Audrain clay loam soil 

(MO), pH 6.6, 4.1% OM, 

20°C

208 days (SFO)

48898001 (S) Sassafras sandy loam 

(MD), pH 5.4, 2.0% OM, 

20°C

416 days (SFO)

Porterville loam (CA), pH 

7.7, 1.11% OM, 20°C 534 days (SFO)

Input value for modeling 

with the SWCC, at 250C. 

from the four above 

mentioned systems (for 

the TTRs)

90% percent upper confidence 

limits 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, 

t90,n-1 = 1.638.

n

t s

t t 90,n-1

input = 1/2 +

= 512.2 days

Aerobic 

Aquatic

Water:sandy loam 

sediment (CA), water pH 

7.9-8.03

, sediment pH not 

reported, 0.7% OM, 25°C

1,046 days (SFO) 41811801 (A)

Wabasha Water:sandy 

loam sediment (MN), 

water pH 7.2, sediment 

pH 6.0, 7.1% OM, 20°C

1,274 days (SFO)

49109901 (S) Tift Water:sandy loam 

sediment GA, water pH 

7.7, sediment pH 7.5, 

1.2% OM, 20°C

1,900 days (SFO)

Input value for modeling 

with the SWCC, at 250C. 

from the three above 

mentioned systems (for

the TTRs)

90% percent upper confidence 

limits 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, 

t90,n-1 = 1.886.

n

t s

t t 90,n-1

input = 1/2 +

= 1,343 days

Anaerobic 

Aquatic

Water:loam sediment 

(CA), water pH 7.83, 

sediment pH 8.5, 1.24% 

OC, 25°C

1,837 days (SFO) 41807402 (A)

Wabasha Water: sandy 

loam sediment (MN), 

water pH 7.2, sediment

pH 6.0, 7.1% OM 20°C

1,395 days (SFO) 49109902 (S)
Page 20 of 133

Table 6. Summary of Information Used to Derive Input Parameters for the Total Toxic Residues

of Hexazinone*

Study

System Name/ 

Characteristics Description

Half-life Value 

Used to Derive 

Model Input 

Parameters TTRs1,2

Reference, 

Study 

Classification**

Tift Water:sandy loam 

sediment (GA), water pH 

7.7, sediment pH 7.5, 

1.2% OM, 20°C

1,343 days (SFO)

Input value for modeling 

with the SWCC, at 250C. 

from the three above 

mentioned systems (for 

the TTRs)

90% percent upper confidence 

limits on the mean half-life 

value: three values are 

available: 1395 and 1383 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, t90,n-1

= 1.886.

n

t s

t t 90,n-1

input = 1/2 +

= 1805 days

* Total toxic residues (TTRs) include hexazinone and its transformation products, which were found to be of concern 

(Metabolites A-1, B, D, G, 1, 2 and minor Metabolite A).

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

Bolded values represent input values in the aquatic modeling in SWCC (and/or PRZM-GW). A discussion of the 

SWCC and additional details about the modeling approach are provided below.

1 DT50 and DT90 values were calculated using nonlinear regression and single first-order (SFO), double first- order in 

parallel (DFOP), or indeterminate-order equation (IORE). The equations can be found in the document, Standard 

Operating Procedure for Using the NAFTA Guidance to Calculate Representative Half-life Values and Characterize 

Pesticide Degradation, U.S. Environmental Protection Agency dated November 30, 2012 and approved December 

17, 2012.

2 The value used to estimate a model input value is the calculated SFO DT50, tR IORE, or the 2nd DT50 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 Protection Agency, 

December 21, 2012.

3 Measured in the first test interval.

Degradation and Metabolism

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 Metabolite B, which was 9.5-10.1% of the applied at 30 days 

(last test interval).

Hexazinone’s half-lives were 216 and 1,440 days, when applied to viable and sterile (autoclaved) 

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 degradation 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 
Page 21 of 133

and sterile soils, respectively. The aerobic transformation of hexazinone was also studied in three 

U.S. soils in 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. IORE tR IORE half-life was 54.3 days in the clay loam soil; slow t1/2 DFOP was 143 days in 

the sandy loam soil; the SFO half-life was 115 days in the loam soil. Evolved 14CO2 totalled a 

maximum of 2.8-9.7% of the applied at study termination. Unextracted radioactivity was 

significant 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 3). In general, 

EFED agrees with the proposed pathway, except that the possible presence of metabolites of 

concern in the “non-extractable residues” in the figure is uncertain. EFED regards those residues 

as unextracted radioactivity instead.3 (The soils were extracted three times by shaking for 30 

minutes with methanol:water (80:20, v:v).)

Figure 3. Transformation Pathway Proposed by the Registrant (source: MRID 48898001)

The anaerobic soil metabolism of hexazinone was studied in four U.S. soils: a sandy clay loam 

 3 It should be noted that in the aerobic and anaerobic aquatic metabolism studies the levels of unextracted radioactivity 

were very low, and not considered.
Page 22 of 133

soil from TX (Raymondville, pH 8.0), a clay loam soil from MO (Mexico, referred to as Audrain; 

pH 6.6), a sandy loam soil from MD (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, 309 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 post-flood), and was 12.6% at 180 days (149 

days post-flood) in the clay loam soil. Total evolved 14CO2 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 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. The aerobic aquatic 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%. 14CO2 was a maximum of 0.1% of the applied at 100 days posttreatment.

In an anaerobic aquatic metabolism study, that 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 (autoclaved) 

systems. Hexazinone was an average of 95.6% of the applied radioactivity (AR) and decreased to 

29.0% AR, at times 0 and 365 days, respectively. In another study, the 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 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 482 days in the Wabasha water:sandy loam sediment system and 961 days in the 

Tift water:sandy loam system. Unextracted radioactivity was ≤4.8% AR and 14CO2 was not 

detected during the study.

Table 7. Summary of Mobility, Field Dissipation, and Fish BCF Fate Properties of Hexazinone*

Study

System Name/ 

Characteristics Value (units if applicable)

Reference, 

Study Classification**

and Comments

Mobility for 

Hexazinone

Soil\Property KF (mL/g) KFOC (mL/gOC) MRID 43621501 (A);

KOC model describes the 

mobility better than the Kd

model. For KOC the 

coefficient of variation is 

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 Mobile1
Page 23 of 133

Table 7. Summary of Mobility, Field Dissipation, and Fish BCF Fate Properties of Hexazinone*

Study

System Name/ 

Characteristics Value (units if applicable)

Reference, 

Study Classification**

and Comments

Additional notes 1/n range 0.86-0.93 for the adsorption isotherms. 

Desorption step done at a single concentration.

smaller than for Kd.

Terrestrial 

Field 

Dissipation

Bareground silt loam 

in Newark, DE

123 days; >95% confined to the upper 30 cm of 

soil

42377901 (A); Metabolites 

A, A-1, B, C, and 1 were 

identified in one or more 

sites at max. of 0.04, 0.21, 

0.31, 1.23, and 0.71 ppm, 

respectively.

Bareground silty 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.

42379201 (S); Metabolites 

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, respectively.

Forestry 

Field 

Dissipation

Forest-land 

watersheds (loams) 

in Coosa county, AL; 

hexazinone was 

applied at 6.72 lb 

a.i./A

Hexazinone dissipated with 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. 

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). Hexazinone was detected in runoff water 

up to 6 months post-application (80 to 140 ppb). 

Hexazinone was detected in stream samples at 

both sites.

42336401 (A); Metabolites

A, B, C, D, E, G, and B were 

discernible in various 

matrices (soil, water, litter 

and/or vegetation) samples. 

Hexazinone and metabolites 

were consistently discernible 

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 

Metabolites A, B, C, A-1, 1, and G3170 (or G) 

was studied in a vulnerable site for up to 35 

months. Soil, groundwater, and soil pore-water 

samples were analyzed for hexazinone and 

metabolites. Hexazinone dissipated from the 

upper 2 feet of soil with a calculated half-life of 

25 days. Results indicated that hexazinone and 

its degradates are very mobile and persistent. 

They leached through the soil profile and into the 

groundwater. 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 

Metabolite B into the shallow groundwater 

occurred at 152 days posttreatment.

45132801 (S); Hexazinone 

and all metabolites except 

Metabolite G moved at the 

same rate through the 

unsaturated zone and into 

groundwater as the bromide 

tracer, while Metabolite G 

movement was somewhat 

retarded. Metabolite 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 bioconcentrate in fish. Further, 

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)
Page 24 of 133

Table 7. Summary of Mobility, Field Dissipation, and Fish BCF Fate Properties of Hexazinone*

Study

System Name/ 

Characteristics Value (units if applicable)

Reference, 

Study Classification**

and Comments

*Monitored and detected metabolites in the field.

**(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.

2.2.1 Mobility

In a Madera loam, Hanford sandy loam, Cecil sandy loam and Flanagan silty loam, the adsorption 

Kd values were 10.8, 0.24, 0.45 and 1.03 mL/g, respectively. Meanwhile, in a Tama silty loam, 

Chino loam, Trevino sandy loam and Sassafras sandy loam, the Freundlich KF values were 0.53, 

0.84, 0.59 and 0.21, respectively. For the latter soils, the Freundlich KFOC 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 supplemental 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 8).

Table 8. Mobility of Hexazinone Metabolites

Adsorption (Mobility) Studies Kd KOC Source (MRID)

Metabolite 1 0.20 122

43621501 (supplemental 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

2.2.2 Terrestrial Field Dissipation Studies

One terrestrial field dissipation study was conducted on a silt loam in Newark, DE and another on 

a silty clay loam in Greenville, MS. The respective half-lives were 123 and 134 days in bare 

ground plots. The maximum hexazinone residue level in the 0-15 cm segments were 3.93 and 3.74 

ppm, at 0 and 7 days posttreatment, respectively for the DE and MS sites. The metabolites A, A1, B, C and 1 were identified in soils at maximum concentrations of 0.04, 0.21, 0.31, 1.23 and 0.71 

ppm in the soil, 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.

In another study, hexazinone at 12 lb a.i./A, had a dissipation half-life of 140 days in a bareground 

sandy loam in Madera, CA. The maximum hexazinone residue level in the 0-15 cm segment was 

3.08 ppm, at 60 days posttreatment. Metabolites A, A-1, B, C and 1 were identified at maximum 

concentrations of 0.05, 0.04, 0.29, 0.62 and 0.20 ppm in the soil, respectively. The reported data 

indicate that hexazinone leached through the 90 cm soil depth. The hexazinone metabolites were 
Page 25 of 133

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.

2.2.3 Forestry Field Study

In a forestry 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 [note that the sites are 

identified by the end-use products containing hexazinone used: Velpar ULW and Velpar L]. 

Hexazinone was aerially (helicopter) 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 (except 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 post-treatment at the Velpar L site).

Metabolites A, B, C, D, E, G, and H were discernible in various matrices (soil, water, litter and/or 

vegetation) samples. Metabolite G was not confirmed by MS. Metabolites A, B and H were 

detectable in drainages sampled and located in the periphery of the site (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). 

In the soil samples, 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 and control plots) took 

place 6 months post-treatment.

2.2.4 Small Scale Prospective Groundwater Monitoring Study

Hexazinone [end-use product 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, CA. 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 feet 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. The site ran 

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 total 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 
Page 26 of 133

water budget decreased in the summer when evapotranspiration was high, despite the irrigation, 

while the water budget increased in the winter when evapotranspiration 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 posttreatment. Soil (measured to 2 feet), soil pore water (lysimeters 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 (or G), A, B, C, A1, and 1.

Hexazinone dissipated from the upper 2 feet of soil with a calculated half-life of 25 days. 

Hexazinone and its degradates exhibited a pattern of leaching through the soil profile and into the 

groundwater. Hexazinone concentrations 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 Metabolites G3170, B, and A-1 were the major analytes 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. 

Average 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 observed beginning at 271 days. Metabolite 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. Metabolite B first increased above 

background levels at 363 days, and was an average maximum concentration of 1.31 ppb at 424 

days. Metabolite A-1 first increased above background levels at 363 days, and was an average 

maximum concentration of 0.71 ppb at 424 days. Metabolite 1 first increased above background 

levels at 363 days, 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. Metabolite A was not observed above 

background levels. 

Hexazinone 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 
Page 27 of 133

in groundwater in the eastern portion of the site, where soils were less sandy with thicker soil lens

(thicker regions of heavier soils). Results indicated that hexazinone and its degradates are very 

mobile and persistent. The Metabolites D and 2 were not monitored in the small-scale prospective 

groundwater monitoring study.

2.2.5 Bioconcentration in Fish

Based on laboratory bioaccumulation in rainbow trout, hexazinone is not expected to 

bioconcentrate in fish substantially, which is consistent with the low octanol/water partition 

coefficient, KOW value of 15 (log KOW = 1.12).

2.2.6 Transformation Products

Transformation products of hexazinone are generally formed slowly and are also mobile and 

persistent (Table 9). 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 were identified in soils in terrestrial 

field. Mets. 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 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 studies were mostly 

aerobic and the metabolites were unlikely to be observed. The field dissipation studies did not 

monitor the fate of Met. G3170; however, it was found to be at the highest concentrations in the 

small-scale prospective groundwater monitoring 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, including maximum formation and levels at study 

termination, can be found in Appendix C.

Table 9. Transformation Products of Hexazinone

Common Name Chemical Name Structure

IN-G3170; Met. G 

or G3170

IUPAC: 1-Methyl-6-(methylamino)-1,3,5-triazine2,4-dione

Formula: C5H8N4O2

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
Page 28 of 133

Table 9. Transformation Products of Hexazinone

Common Name Chemical Name Structure

IN-JS472; Met. 1 IUPAC: 6-(Dimethylamino)-1-methyl-3-(4-

oxocyclohexyl)-1,3,5-triazine-2,4-dione

Formula: C12H18N4O3

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

IN-B2838; Met. D IUPAC: 1-Cyclohexyl-3-methyl-1,3,5-triazinane2,4,6-trione

Formula: C10H15N3O3

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: C12H20N4O3

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

IN-A3928; Met. B IUPAC: 3-Cyclohexyl-1-methyl-6-(methylamino)-

1,3,5-triazine-2,4-dione

Formula: C11H18N4O2

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
Page 29 of 133

Table 9. Transformation Products of Hexazinone

Common Name Chemical Name Structure

IN-JT677; Met. 2 IUPAC: 6-(Dimethylamino)-1-methyl-3-(2-

oxocyclohexyl)-1,3,5-triazine-2,4-dione

Formula: C12H18N4O3

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: C12H20N4O3

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

H O

Carbon dioxide IUPAC: Carbon dioxide

Formula: CO2

MW: 44 g/mol

SMILES: C(=O)=O

O C O

2.2.7 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. The soils were

only extracted three times by shaking for 30 minutes with methanol:water (80:20, v:v), with no 

attempt to use other extraction solvents of different polarity. It was not clear whether the 

unextracted residues (UERs) contained in fact any degradate of ecological concern. In this 

assessment, to clear the uncertainty relative to the UERs, EECs were calculated using both the 

total toxic residues (TTRs), and the TTRs plus the UERs, to provide an upperbound level for the 

EECs. In the aquatic metabolism studies, the levels of unextracted residues were low. As will be 

shown later, the aquatic EECs obtained from the TTRs plus the UERs were similar to the EECs 

obtained with the TTRs alone.

2.2.8 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 

(UERs). However, for the aquatic metabolism studies, the levels of unextracted radioactivity were 
Page 30 of 133

very low. As per EFED UER Guidance (USEPA 2014), upper bound estimates of the EECs were 

calculated using the half-lives derived for the total toxic residues (TTRs) and the UERs for a 

selected number of SWCC runs. This was done due to the lack of evidence that a reasonable effort 

was executed to extract/identify these significant residues in the aerobic soil systems. As will be 

shown later, the aquatic EECs obtained from the TTRs plus the UERs were similar to the EECs 

obtained with the TTRs alone.

Furthermore, for some of the studies, the duration was too short compared to the derived 

representative half-lives (i.e., estimated half-lives were beyond the study duration). Uncertainty 

arises in these half-life estimates.

2.3 Aquatic Modeling Approach

A brief description of the aquatic models used in this risk assessment follows. Additional 

information about these models is provided in the Agency’s website at 

http://www.epa.gov/pesticides/science/models_pg.htm#aquatic. For agricultural and certain nonagricultural uses, exposure concentrations for surface 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 estimates 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 uses 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 regional 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 simulates 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 predict the EECs. 

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. EECs were determined using the 

standard pond scenario which describes a vulnerable surface waters scenario for the VVWM 

component of the modeling exercise.

2.3.1 Scenario Selection

Three representative agricultural crops were modeled: alfalfa, sugarcane and blueberries. For 

alfalfa, the NC alfalfa scenario was selected (note that there are other alfalfa scenarios; however, 

to the extent possible, crops from diverse regions from across the U.S. were selected; Table 10). 
Page 31 of 133

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.

For the non-agricultural crops, the CA rights-of-way scenario was used to model both aerial and 

ground applications (the rights-of-way has the maximum allowed application rate among all uses 

and the application rate for ground applications is higher than for aerial applications). 

Additionally, other crops were run as shown in Table 10.

2.3.2 Model Inputs

Tables 10 and 11 show the input values used in SWCC. It should be noted that three nonagricultural uses may be applied aerially, but only by means of helicopter. At this time, EFED 

does not recommend to use the forestry module of AgDRIFT; thus the agricultural module of 

AgDRIFT was used as a surrogate, to estimate forestry spray drift, using the Wasp Helicopter as 

the aircraft. For aerial applications, the following assumptions were made: Tier II Aerial 

application using ASABE Fine to Fine to Medium DSD, 5 gallons diluted product per acre, wind 

speed 10 mph, aircraft Wasp Helicopter, boom height 10 feet.

Two representative runs were performed, one for granular and the other for pelleted applications, 

where the value of spray drift was assumed to be 0 (zero) and the application efficiency 1.00, using 

other similar assumptions, compared to spray applications. It was found that the EECs for the 

forestry applications decreased substantially while for the rights-of-way the EECs were around 

two thirds those for the ground spray applications at the same active ingredient application rate.

Table 10. Hexazinone Uses, Scenarios, and Application Information Used for Aquatic Exposure 

Inputs in Ecological Exposure Assessment (all applications are into the surface)

Run Number, Scenario (bold 

font)/ Uses Represented 

(meteorological file if not the 

default one)

App. 

Equipment

Drift/

App 

Efficiency

Single 

App 

Rate

kg a.i./A

(lb a.i./A)

Max 

No. of 

Apps 

at Max 

Rate

Min. 

Interval 

Between 

Apps 

(days)

Day of 

App 

(daymonth)

App. Method

Agricultural Use Patterns

NC alfalfa/Alfalfa Aerial 0.125/0.95 1.68 

(1.5)

1 N/A 01-04 Foliar

LA sugarcane (HI meteorological file 22521)/Sugarcane 

in HI

Aerial 0.125/0.95 4.03 

(3.6)

1 N/A 10-01 Foliar

CA wine grape/Blueberries Ground 0.062/0.99 2.24 (2) 1 N/A 01-04 Ground

Non-Agricultural Use Patterns

CA rights-of-way/ Non-crop 

sites (weed and brush control)

Aerial 

helicopter

0.113/0.95 6.72 (6) 1 N/A 01-04 Foliar

CA rights-of-way/ Non-crop 

sites (weed and brush control)

Ground 0.062/0.99 8.97 (8) 1 N/A 01-04 Foliar
Page 32 of 133

Table 10. Hexazinone Uses, Scenarios, and Application Information Used for Aquatic Exposure 

Inputs in Ecological Exposure Assessment (all applications are into the surface)

Run Number, Scenario (bold 

font)/ Uses Represented 

(meteorological file if not the 

default one)

App. 

Equipment

Drift/

App 

Efficiency

Single 

App 

Rate

kg a.i./A

(lb a.i./A)

Max 

No. of 

Apps 

at Max 

Rate

Min. 

Interval 

Between 

Apps 

(days)

Day of 

App 

(daymonth)

App. Method

CA forestry (MI 

meteorological file 14850)/

Conifer release in Eastern and 

Lakes states

Aerial 

helicopter

0.113/0.95 4.48 (4) 1 N/A 01-05 Foliar

OR Christmas trees/ 

Christmas trees plantations 

(except in 22 states listed in 

label)

Aerial 0.125/0.95 2.24 (2) 1 N/A 01-04 Foliar

CA rangeland hay (NY 

meteorological file 14860)/ 

Pastures/Rangeland in Eastern 

U.S.

Aerial 

helicopter

0.113/0.95 4.48 (4) 1 N/A 01-03 Foliar

PA turf/ Bermudagrass/ 

Bahiagrass; Industrial turfgrass

Ground 0.062/0.99 1.26 

(1.125)

1 N/A 01-03 Foliar

Pellet and Granule Applications

CA forestry (MI 

meteorological file 

14850)/Conifer release

Ground 

(Pellets)

0.00/1.00 4.48 (4) 1 N/A 01-05 Ground

CA rights-of-way/ Non-crop 

sites (weed and brush control)

Ground 

(Granules)

0.00/1.00 8.97 (8) 1 N/A 01-04 Ground

The chemical input parameters are summarized in Table 11. Note that two aerobic soil metabolism 

input half-lives are included in the table (see bold and underlined font). One is for the total toxic 

residues (TTRs), which are hexazinone plus its metabolites of concern. The other one includes 

the TTRs (as defined above), plus the unextracted residues (UERs). For the aerobic and anaerobic 

aquatic metabolism studies, only one half-life for the TTRs is reported since the levels of 

unextracted radioactivity were very low in these studies and the UERs were not considered.

Table 11. Environmental fate data used for aquatic exposure inputs in Hexazinone 

aquatic risk assessment in the SWCC1

Parameter (units) Value(s) Sources Comments

Chemical Name Hexazinone Labels Label

Application Rate

(Kg a.i./ha)

Refer to Table 10 Labels Highest single application rates 

according to the labels.

Number of 

Applications Allowed

Refer to Table 10 Labels Maximum allowed by the label, at the 

maximum rate.

Interval between 

Applications (days)

Refer to Table 10 Labels Minimum allowed by the label.

Crop Names and 

Days of Application 

(day-month)

Refer to Table 10 Labels ---
Page 33 of 133

Table 11. Environmental fate data used for aquatic exposure inputs in Hexazinone 

aquatic risk assessment in the SWCC1

Parameter (units) Value(s) Sources Comments

KOC (ml/gOC) 57.5 43621501 Sorption is better correlated with 

organic carbon content. Represents the 

mean of four values.

Aerobic Soil 

Metabolism (days)

25°C = 512.2 for the TTRs

41807401/ 

42635001;

48898001

90% percent upper confidence limits on 

the mean for the following corrected 

half-life values at 25°C: 147, 294, 378, 

and 604 days.

= 1,093 for the TTRs +

UERs

41807401/ 

42635001;

48898001

90% percent upper confidence limits on 

the mean for the following corrected 

half-life values at 25°C: 432, 762, 

1134, and 1023 days.

Solubility in Water 

(ppm) (25°C)

29,800 41203201 DP Barcode D279324.

Aerobic Aquatic 

Metabolism (days)

25°C = 1343 for the TTRs2

41811801;

49109901

90% percent upper confidence limits on 

the mean for the following corrected 

half-life values at 25°C: 901, 1344, and 

1046 days; mean = 1097 days.

Anaerobic Aquatic 

Metabolism (days)

25°C = 1805 for the TTRs2

41807402;

49109902

90% percent upper confidence limits on 

the mean for the following corrected 

half-life values at 25°C: 986, 978, and 

1837 days; mean = 1267 days.

Hydrolysis at pH 7 0 41587301 Stable at pH 5-9.

Aqueous Photolysis 

(days)

0 41300801 Stable under the testing conditions. For 

the modeling, assume 40° latitude.

Molecular 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 

Dimensionless

(25°C)

8.65 x 10-11 VP/WS This value is calculated by the SWCC.

PRZM Scenario and 

Metfile

As suggested by the shell 

SWCC, with exceptions noted 

in Table 10.

SWCC shell Exceptions include LA sugarcane (run 

with a HI met file), and CA forestry 

(run with a MI met file). See Table 10

for selected met file.

Foliar Half-life 0 Default 

value

Assume no degradation.

Post-harvest Foliage Surface applied Default 

value

---

FEXTRC, Foliar 

extraction

0.5 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 

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )
Page 34 of 133

11/10/2009 (USEPA 2009).

2 In the aerobic and anaerobic aquatic metabolism studies the levels of UERs were very low at all test intervals. Thus, 

the UERs were not considered.

Table 12. Tier II Estimated Environmental Concentrations (EECs) for surface water 

based on application of hexazinone products modeled in the SWCC, including the TTRs 

(but excluding the UERs)

Scenario App. 

Method

App. 

Rate

(lb a.i./A)

Date of 

First 

Application

(dd-mm)

No. of 

Apps

App. 

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average 

EEC

(μg/L)

60-day 

average 

EEC

(μg/L)

NC alfalfa/Alfalfa Aerial 1.5 01-04 1 N/A 139 138 137

LA sugarcane (HI 

met file)/Sugarcane 

in HI Aerial 3.6 10-01 1 N/A 600 596 593

CA wine grape/ 

Blueberries Ground 2 01-04 1 N/A 78.8 78.6 78.1

CA rights-of-way/

Non-crop sites (weed 

and brush control)

Aerial 

helicopter 6 01-04 1 N/A 645 644 640

CA rights-of-way/

Non-crop sites (weed 

and brush control) Ground 8 01-04 1 N/A 653 651 648

CA forestry (MI met 

file)/Conifer release 

in Eastern and Lakes 

states

Aerial 

helicopter 4 01-05 1 N/A 369 368 366

OR Christmas 

trees/Christmas trees Aerial 2 01-04 1 N/A 161 160 160

CA rangeland hay 

(NY met file)/ 

Pastures/Rangeland 

in Eastern US

Aerial 

helicopter 4 01-03 1 N/A 493 492 490

PA turf/ 

Bermudagrass/ 

Bahiagrass; 

Industrial turfgrass Ground 1.125 01-03 1 N/A 41.7 41.6 41.4

CA forestry (MI 

meteorological file 

14850)/Conifer 

release

Ground 

(Pellets) 4 01-05 1 N/A 24.1 24.0 23.8

CA rights-of-way/ 

Non-crop sites (weed 

and brush control)

Ground 

(Granules) 8 01-04 1 N/A 408 407 405

EECs were calculated using the half-lives for the TTRs + UERs for the agricultural and nonagricultural crops that yielded the highest EECs (from Table 12). The EECs for the TTRs plus 

the UERs provide an upper bound estimate of the TTRs should the UER contain any residue of 

ecological concern. It was noted that the EECs with and without the UERs for the selected 

scenarios were very similar; therefore, the overall risk picture for hexazinone is not expected to 

vary substantially.
Page 35 of 133

Table 13. Tier II Estimated Environmental Concentrations (EECs) for surface water 

based on application of hexazinone products modeled in the SWCC, including the TTRs 

and UERs

Scenario App. 

Method

App. 

Rate

(lb a.i./A)

Date of 

First 

Application

(dd-mm)

No. of 

Apps

App. 

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average 

EEC

(μg/L)

60-day 

average 

EEC

(μg/L)

LA sugarcane (HI 

met file)/Sugarcane 

in HI Aerial 3.6 10-01 1 N/A 601 597 594

CA rights-of-way/

Non-crop sites (weed 

and brush control) Ground 8 01-04 1 N/A 656 654 651

2.3.3 Monitoring

There is available monitoring data for this chemical. Hexazinone in groundwater was previously 

considered and evaluated by the California Department of Pesticide Regulation (CDPR), as shown 

in the following site http://www.cdpr.ca.gov/docs/emon/grndwtr/hexazinone.htm (accessed 

01/12/2015). Their findings were summarized as follows: “The Director concurs with the 

subcommittee that based on the detected concentrations of hexazinone (ranging from 0.05 to 0.27 

μg/L) and the health-protective drinking water level of 170 μg/L established by the Office of 

Environmental Health Hazard Assessment (OEHHA), hexazinone cannot be found to have 

polluted ground water.” (It should be noted that the safety of hexazinone to humans is not within 

the scope of this ecological risk assessment or the Environmental Fate and Effects Division, and 

the citation is provided only to state the range of detected concentrations in the California 

groundwater database.)

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 14

summarizes the findings for hexazinone. Across the U.S. (excluding territories), a total of 6,185

samples were analyzed for hexazinone, of which 1,286 (21%) were positive detections. Of the 

detections, 1,134 (18%) were positive surface water detections and 152 (2.5%) were positive 

groundwater detections. The maximum surface water concentration was 0.545 μg/L (detected in 

Riverside, CA), and the maximum groundwater detection was 0.265 μg/L (detected in Mitchell, 

GA).

Table 14. Summary of Hexazinone Monitoring Data from the NAWQA Database

State Total No.

Samples

Total No.

Detects (%)

No. SW 

Detects

Max. Conc. in 

SW (μg/L)

No. GW 

Detects

Max. Conc. in 

GW (μg/L)

Alabama 189 39 39 0.0948 0 N/A

Alaska 2 0 0 N/A 0 N/A

Arizona 103 13 12 0.0937 1 0.0058

Arkansas 19 4 4 0.0102 0 N/A

California >500 416 396 0.545 20 0.0635

Colorado 240 32 27 0.0228 5 0.0237
Page 36 of 133

Table 14. Summary of Hexazinone Monitoring Data from the NAWQA Database

State Total No.

Samples

Total No.

Detects (%)

No. SW 

Detects

Max. Conc. in 

SW (μg/L)

No. GW 

Detects

Max. Conc. in 

GW (μg/L)

Connecticut 123 39 39 0.0368 0 N/A

Delaware 33 0 0 N/A 0 N/A

District of 

Columbia 0 0 0 N/A 0 N/A

Florida 337 99 50 0.0303 49 0.0867

Georgia 268 80 59 0.132 21 0.265

Hawaii 15 4 0 N/A 4 0.0869

Idaho 148 9 5 0.0281 4 0.0173

Illinois 188 3 3 0.0315 0 N/A

Indiana 131 4 4 0.0258 0 N/A

Iowa 218 7 7 0.0195 0 N/A

Kansas 31 0 0 N/A 0 N/A

Kentucky 4 1 1 0.0521 0 N/A

Louisiana 274 61 61 0.0669 0 N/A

Maine 37 0 0 N/A 0 N/A

Maryland 128 3 3 0.0101 0 N/A

Massachusetts 86 2 0 N/A 2 0.0079

Michigan 113 0 0 N/A 0 N/A

Minnesota 172 4 1 0.0097 3 0.156

Mississippi 97 28 28 0.0213 0 N/A

Missouri 43 1 1 0.0022 0 N/A

Montana 43 0 0 N/A 0 N/A

Nebraska 105 2 2 0.0096 0 N/A

Nevada 55 2 2 0.0168 0 N/A

New 

Hampshire 35 0 0 N/A 0 N/A

New Jersey 264 36 36 0.264 0 N/A

New Mexico 157 3 0 N/A 3 0.0411

New York 131 7 3 0.0143 4 0.0565

North 

Carolina 126 25 25 0.0738 0 N/A

North Dakota 0 0 0 N/A 0 N/A

Ohio 78 8 8 0.0602 0 N/A

Oklahoma 12 0 0 N/A 0 N/A

Oregon 252 181 181 0.339 0 N/A

Pennsylvania 40 0 0 N/A 0 N/A

Rhode Island 5 1 0 N/A 1 0.0097

South 

Carolina 211 42 39 0.0214 3 0.0343

South Dakota 1 0 0 N/A 0 N/A

Tennessee 113 6 0 N/A 6 0.153

Texas 414 43 30 0.0495 13 0.126

Utah 124 4 1 0.0084 3 0.0109

Vermont 3 0 0 N/A 0 N/A

Virginia 110 36 36 0.167 0 N/A

Washington 275 41 31 0.0483 10 0.177

West Virginia 5 0 0 N/A 0 N/A

Wisconsin 121 0 0 N/A 0 N/A

Wyoming 6 0 0 N/A 0 N/A

Totals 6,185 1,286 1,134 0.545 152 0.265
Page 37 of 133

It is noted that sampling and testing for hexazinone in the NAWQA database does not represent 

necessarily vulnerable bodies of surface waters or vulnerable aquifers. Despite the relatively high 

level of detections, EFED believes that modeling reflects concentrations in surface waters, which 

are realistically conservative for each site represented. The NAWQA monitoring program 

analyzed for this assessment does 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. Therefore, currently available monitoring 

data may underestimate hexazinone concentrations, and monitoring results are not an appropriate 

prediction of the potential exposure resulting from hexazinone use. For these reasons, EFED does 

not recommend that hexazinone water monitoring data be used by EFED in ecological effects risk 

assessment quantitatively and only a qualitative discussion was provided.

Seven metabolites of hexazinone were monitored on a few occasions only in the state of Texas; 

however, no detections were reported. Sampling occurred once or twice per metabolite. The 

following metabolites were included: D, G, E, 4-hydroxyhexazinone (A), didemethyl hexazinone 

(F), demethyl hexazinone (B), and C.

2.4 Terrestrial Exposure Modeling

2.4.1 Exposure to Birds and Mammals 

For spray applications, the T-REX model (Terrestrial Residue EXposure model; v. 1.5.2; June 6, 

2013) is used to predict dietary exposure to hexazinone residues on foliar surfaces and insects 

using the Kenaga nomogram as modified by Fletcher (Hoerger and Kenaga 1972, Fletcher et al. 

1994). Estimated exposures of terrestrial insects to hexazinone are evaluated in terms of the 

insects’ potential relevance as dietary items for terrestrial vertebrates and for use in risk 

characterization for listed terrestrial invertebrates. 

T-REX (v. 1.5.2) is used to calculate dietary and dose-based EECs of hexazinone residues on food 

items for mammals and birds generated by spray applications for the labeled uses. Input values for 

the use scenarios used to derive EECs using T-REX and TerrPlant are located in Table 15 for 

foliar spray uses that represent a range of single as well as seasonal application rates and in Table 

16 for pelleted and granular applications. Upper-bound Kenaga nomogram values are used to 

derive EECs for hexazinone exposures to terrestrial mammals and birds based on a 1-year time 

period. Consideration is given to different types of feeding strategies for mammals, including 

herbivores, insectivores and granivores. Dose-based exposures are estimated for three weight 

classes of birds (20 g, 100 g, and 1000 g) and three weight classes of mammals (15 g, 35 g, and 

1000 g). Terrestrial EECs for foliar spray uses and seed treatment uses of hexazinone are provided 

in Tables 17, 18, and 19.
Page 38 of 133

Table 15. Input Parameters for Deriving Terrestrial EECs for Labeled Spray Uses of 

Hexazinone Related to Terrestrial Plants and Animals. A foliar dissipation half-life of 35 

days was used.

Use

Maximum Single 

App Rate (lb. 

a.i./A)

Number of 

Apps. at Max 

Rate

Maximum 

Seasonal App. 

Rate (lb. a.i./A)

Minimum 

Interval Between 

Apps. (days)1

Application 

Method Used in 

Modeling

PreHarvest 

Interval

Agricultural Uses

Alfalfa 1.5 1 1.5 NA Aerial NA

Sugarcane HI 3.6 1 3.6 NA Aerial NA

Blueberries 2.0 1 2.0 NA Ground NA

Non-Agricultural Uses

Non-crop sites 6.0 1 6.0 NA Aerial NA

Non-crop sites 8.0 1 8.0 NA Ground NA

Christmas Tree 

Plantation 2.0 1 2.0 NA Aerial NA

Rangeland 4.0 1 4.0 NA Aerial NA

Industrial 

Turfgrass 1.125 1 1.125 NA Ground NA

N/A=does not apply; G=ground; A=aerial, S=spray (low or high volume), AB=airblast

Differences in exposures between ground and aerial applications cannot be assessed with the 

current T-REX model; exposure and risk estimates from the T-REX model are considered relevant 

to both application scenarios. A further uncertainty with the model is the inability to model 

systemic chemicals like hexazinone as T-REX only simulates residues directly on food items. 

T-REX (v. 1.5.2) and Terr Plant are also used to calculate dietary and dose-based EECs of 

hexazinone residues on food items for mammals and birds generated by granular and pelleted 

applications for the labeled uses. Input values for the use scenarios used to derive EECs using TREX and TerrPlant are located in Table 16. The LD50/ft2 tab is used estimate risk for granular and 

pelleted formulations. It is designed to estimate the amount of pesticide estimated to kill 50% of 

exposed animals in each square foot of applied area. Although a square foot does not have defined 

ecological relevance, risk presumable increases as the LD50/ft2 increases. The LD50/ft2 is 

calculated using a toxicity value (adjusted LD50) and the EEC and is directly compares with the 

Agency’s LOC. 

Table 16. Input Parameters for Deriving Terrestrial EECs for Labeled Granular and 

Pelleted Uses of Hexazinone Related to Terrestrial Plants and Animals. 

Use

Maximum 

Single App 

Rate (lb. a.i./A)

Number of 

Apps. at Max 

Rate

Maximum 

Seasonal App. 

Rate (lb. a.i./A)

Minimum 

Interval 

Between Apps. 

(days)1

Application 

Method Used in 

Modeling

Pre-Harvest 

Interval

Rangeland 0.63 1 0.63 NA Ground/ Granular NA

Conifer Release 3 1 3 NA Ground/ Granular NA

Conifer Release 4 1 4 NA Ground/ Pellet NA

Forestry Site Prep: 

Eastern 4.7 1 4.7 NA Ground/ Granular NA

Forestry Site Prep: 

Western 4 1 4 NA Ground/ Granular NA

Forestry Site Prep 6.1 1 6.1 NA Ground/ Pellet NA

Non Crop Sites 8 1 8 NA Ground/ Granular NA

Non Crop Sites 7.4 1 7.4 NA Ground/ Pelleted NA

N/A=does not apply; G=ground; A=aerial, S=spray (low or high volume), AB=airblast
Page 39 of 133

Terrestrial wildlife exposure estimates are typically calculated for birds and mammals by 

emphasizing the dietary exposure route of uptake of pesticide active ingredients. These exposures 

are considered to be surrogates for exposures to terrestrial-phase amphibians and reptiles. For 

exposures to terrestrial organisms, such as birds and mammals, pesticide residues on food items 

are estimated based on the assumption that the pesticide residues on the organism’s food are 

dependent on the use pattern of the pesticide. 
Page 40 of 133

Table 17. Dose-based EECs (mg/kg bw) as Food Residues for Birds, Reptiles, and Terrestrial-phase Amphibians from Labeled Non-Granular Uses of 

Hexazinone (T-Rex v. 1.5.2). Toxicity to birds is based on data for hexazinone. 

Primary Feeding 

Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size*  Small Med Large Small Med Large Small Med Large

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s)1 

Non-Agricultural Uses

Alfalfa 410 187 230 25.6 233 107 131 14.6 104 47.9 58.8 6.54 160 91.5 41 5.69 3.25 1.45

Sugarcane in HI 984 451 553 61.5 561 257 315 35.0 251 115 141 15.7 385 219 98.4 13.6 7.79 3.49

Blueberries 546 250 307 34.1 311 142 175 19.4 139 63.9 78.5 8.72 214 122 54.6 7.59 4.33 1.94

Agricultural Uses

Non-Crop sites 

(Aerial) 1640 751 922 102 935 428 526 58.4 418 191 235 26.1 642 366 163 22.7 12.9 5.82

Non-Crop sites

(Ground) 2180 1002 1230 136 1240 571 701 77.9 558 255 314 34.9 856 4888 218 30.3 17.3 7.75

Christmas Tree 

Plantations 546 250 307 34.1 311 142 175 19.4 139 63.9 78.5 8.72 214 122 54.6 7.59 4.33 1.94

Rangeland 1093 501 615 68.3 623 285 350 38.9 279 127 157 17.4 428 244 109 15.1 8.66 3.88

Industrial Turfgrass 307 140 172 19.2 175 80.3 98.6 10.9 78.5 35.9 44.1 4.91 19.22 68.8 30.75 4.27 2.44 1.09

Avian adjusted LD50 (mg/kg bw): 1626 (20g bird); 2070 (100g bird); 2925 (1000g bird)
Page 41 of 133

0

Table 18. Dose-based EECs (mg/kg bw) as Food Residues for Mammals from Labeled Non-Granular Uses of Hexazinone (T-Rex v. 1.5.2). 

Primary Feeding Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size*  Small Med Large Small Med Large Small Med Large

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s)1 

Non-Agricultural Uses

Alfalfa 343 157 193 21.4 237 108 133 14.8 55 25.2 30.9 3.44 134 92.9 21.5 4.76 3.29 0.763

Sugarcane in HI 823 377 463 51.4 569 260.9 320 35.5 132 60.5 74.2 8.25 322 222 51.7 11.4 7.90 1.83

Blueberries 457 209 257 28.6 316 144 177 19.7 73.3 33.6 41.2 4.58 179 123 28.7 6.35 4.39 1.01

Agricultural Uses

Non-Crop sites (Aerial) 1372 629 772 85.8 948 434 533 59.3 220 100 123 13.7 537 371 86.1 19.0 13.1 3.05

Non-Crop sites

(Ground) 1830 839 1029 114 1265 579 711 79.0 293 134 165 18.3 716 495 114 25.4 17.5 4.07

Christmas Tree Plantations 457 209 257 28.6 316 144 177 19.7 73.3 33.6 41.2 4.58 179 123 28.7 6.35 4.39 1.01

Rangeland 915 419 514 57.2 632 289 355 39.5 146 67.2 82.5 9.17 358 247 57.4 12.7 8.78 2.03

ndustrial Turf grass 257 117 144 16.0 177 81.5 100 11.1 41.2 18.9 23.2 2.58 100 69.6 16.1 3.57 2.47 0.572

*Mammalian adjusted LD50 (mg/kg bw): 1164 (15g mammal); 942 (35g mammal); 407 (1000g mammal)

1
Page 42 of 133

Table 19. Dietary-based EECs (mg/kg bw) as Food Residues for Mammals, Birds, 

Reptiles, and Terrestrial-phase Amphibians from Labeled Non-Granular Uses of 

Hexazinone (T-Rex v. 1.5.2).

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods

Use(s) 

Non-Agricultural Uses

Alfalfa 360 165 202 22.5 141

Sugarcane in HI 864 396 486 54.0 338

Blueberries 480 220 270 30 188

Agricultural Uses

Non-Crop sites (Aerial) 1440 660 810 90.0 564

Non-Crop sites

(Ground) 1920 880 1080 120 752

Christmas Tree Plantations 480 220 270 30 188

Rangeland 960 440 540 60.0 376

Industrial Turfgrass 270 123 151 16.8 105

Another route of exposure to pesticides for mammalians and avian wildlife is through inhalation. 

STIR (Screening Tool for Inhalation Risk v. 1.0) is a screening to used to assess the potential for 

risk to brid and mammals from inhalation exposure; STIR is intended to be run at the Problem 

Formulation stage, however the model was not finalized at the time of publication for Hexazinone. 

STIR uses the avian oral toxicity data with the mammalian oral and inhalation toxicity data to 

derive an estimate of avian inhalation toxicity. STIR relied on the application rate, application 

method, defined droplet spectra, molecular weight, and vapor pressure to obtain an estimate of the 

droplet and vapor concentration in the air. These concentrations are compared with an estimated 

inhalation LD50 of a specific chemical as a ratio that is then compared with a threshold of 0..1 If 

the ration of the exposure to the toxicity exceed 0.1, then the screening tool indicates that the 

results should be refined. For this assessment, an application of 8.0 lb ai/A (association with noncrop sites) was used for modeling. Based on this application rate, and an LD50 >2258 mg/kg/day 

exposure is not likely significant for vapor dose or inhalation dose for avian species. For mammals, 

an LD50 = 530 mg/kg/day, and an inhalation LC50 = 3.94 mg/L determined that exposure was not 

likely significant for vapor dose or inhalation dose. An example output table can be found in 

Appendix L. 

2.4.2 Exposure to Terrestrial and Semi-Aquatic Plants

The TerrPlant Model (v. 1.2.2; December 26, 2006) is used to derive EECs relevant to terrestrial 

and wetland plants for hexazinone. The model employs the assumption that default fractions of 

the intended application are transported to an adjacent field through runoff and spray drift. 

Measures of exposure to terrestrial plants are expressed as a fraction of the mass of hexazinone 
Page 43 of 133

applied to the treated field. Total for Dry areas is representative of the sum of spray drift and 

runoff to dry areas; total for semi-aquatic areas is representative of the sum of spray drift and 

runoff to semi-aquatic areas.

Loading via spray drift to dry, nontarget, adjacent areas is assumed to occur from one acre of 

treated land to one acre of an adjacent non-target area. Runoff is also expected to be a source of 

pesticide loading to non-target areas. TerrPlant calculated EECs as a function of application rate, 

solubility, and default assumptions regarding spray drift. The default spray drift assumptions are 

1% of the application rate for ground spray applications and 5% for aerial applications (USEPA 

2006b). The EECs for terrestrial and semi-aquatic plants for a single application of hexazinone at 

the maximum labeled rates for representative uses are presented in Table 20. See example output 

in Appendix H. 

Table 20. Screening-level based EECs (ppm) for Terrestrial Plants from Labeled Uses of 

Hexazinone (TerrPlant v. 1.2.2)

Use (s) App. Method

App 

Rate

(lb 

ai/A)

Runoff 

to Dry 

Areas

Runoff 

to 

SemiAquatic 

Areas

Spray 

Drift

Total 

for Dry 

Areas

Total 

for 

SemiAquatic 

Areas

Agricultural Sites

Alfalfa Flowable/Aerial 1.5 0.075 0.75 0.075 0.15 0.825

Sugarcane in HI Flowable/Aerial 3.6 0.18 1.8 0.18 0.36 1.98

Blueberries Flowable/Ground 2.0 0.1 1.0 0.02 0.12 1.02

Non-Agricultural Sites

Non-crop sites (weed 

and brush control)

Flowable/Aerial 

helicopter 6.0 0.3 3.0 0.3 0.6 3.3

Non-crop sites (weed 

and brush control) Flowable/Ground 8.0 0.4 4.0 0.08 0.48 4.08

Conifer release in 

Eastern and Lakes states

Flowable/Aerial 

helicopter 4.0 0.2 2.0 0.2 0.4 2.2

Christmas trees Flowable/Aerial 2.0 0.1 1.0 0.1 0.2 1.1

Rangeland in Eastern US Flowable/Aerial 

helicopter 4.0 0.2 2.0 0.2 0.4 2.2

Industrial turfgrass Flowable/Ground 1.125 0.56 0.56 0.011 0.0675 0.573

Rangeland Pellets/Ground 0.63 0.0315 0.315 0 0.0315 0.315

Conifer Release Granular/Ground 3.0 0.15 1.5 0 0.15 1.5

Conifer Release Pellet/Ground 4.0 0.2 2.0 0 0.2 2.0

Forestry Site Prep 

Eastern US Granular/Ground 4.7 0.235 2.35 0 0.235 2.35

Forestry Site Prep 

Western US Granular/Ground 4.0 0.2 2.0 0 0.2 2.0

Forestry Site Prep Pellet/Ground 6.1 0.305 3.05 0 0.305 3.05

Non-Crop sites Pellet/Ground 7.4 0.37 3.7 0 0.37 3.7
Page 44 of 133

Table 20. Screening-level based EECs (ppm) for Terrestrial Plants from Labeled Uses of 

Hexazinone (TerrPlant v. 1.2.2)

Use (s) App. Method

App 

Rate

(lb 

ai/A)

Runoff 

to Dry 

Areas

Runoff 

to 

SemiAquatic 

Areas

Spray 

Drift

Total 

for Dry 

Areas

Total 

for 

SemiAquatic 

Areas

Non-crop sites Granular/Ground 8.0 0.4 4.0 0 0.4 4.0

3.0 Ecological Toxicity

Ecological effect data are used as measures of direct and indirect effects to biological receptors. 

Data were obtained from registrant-submitted studies or from literature studies identified by 

ECOTOX. The ECOTOXicology database (ECOTOX) was searched in order to provide more 

ecological effects data to bridge existing data gaps. ECOTOX is a source for locating single 

chemical toxicity data and potential chemical mixture toxicity data for aquatic life, terrestrial 

plants, and wildlife. ECOTOX was created and is maintained by the USEPA, Office of Research 

and Development, and the National Health and Environmental Effects Research Laboratory's MidContinent Ecology Division (USEPA 2007b). A search of the ECOTOXicology database in 2015, 

yielded additional data from suitable studies to complement those data submitted by the registrant. 

Those studies that have been considered as acceptable have been tabulate in Appendix J. There 

were no studies that were considered acceptable for quantitative use that yielded endpoints more 

sensitive than the registrant submitted studies.

Information on the potential effects of hexazinone on non-target animals is also collected from the 

Ecological Incident Information System (EIIS; USEPA 2007c). The EIIS is a database containing 

adverse effect (typically mortality) reports on non-target organisms where such effects have been 

associated with the use of pesticides. Other Ecological Incident databases used are IDS, 

Aggregated Incident Database and Avian Information System, AIMS. 

Where available, sublethal effects observed in both registrant-submitted and open literature studies 

will be evaluated qualitatively. Such effects have included behavioral changes. Quantitative 

assessments of risks, though, are limited to those endpoints that can be directly linked to the 

Agency’s assessment endpoints of impaired survival, growth and reproduction.

The assessment of risk for direct effects to non-target organisms makes the assumption that toxicity 

of hexazinone to birds is similar to terrestrial-phase amphibians and reptiles. The same assumption 

is made for fish and aquatic-phase amphibians. 

The acute measures of effect used for animals in this assessment are the LD50, LC50 and EC50. LD 

stands for "Lethal Dose", and LD50 is the amount of a material, given all at once, that is estimated 

to cause the death of 50% of the test organisms. LC stands for “Lethal Concentration” and LC50

is the concentration of a chemical that is estimated to kill 50% of the test organisms. EC stands 
Page 45 of 133

for “Effective Concentration” and the EC50 is the concentration of a chemical that is estimated to 

produce a specific effect in 50% of the test organisms. Endpoints for chronic measures of exposure 

for listed and non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for “No 

Observed-Adverse-Effect-Level” and refers to the highest tested dose of a substance that has been 

reported to have no harmful (adverse) effects on test organisms. The NOAEC (i.e., “No-ObservedAdverse-Effect-Concentration”) is the highest test concentration at which none of the observed 

effects were statistically different from the control. The NOEC is the No-Observed-EffectsConcentration. For non-listed plants, only acute exposures are assessed (i.e., EC25 for terrestrial 

plants and EC50 for aquatic plants); for listed plants, either the NOAEC or EC05 is used. 

The following section presents a summary of the data that have been submitted since the 

preliminary problem formulation, their classification, and their impact upon the risk assessment 

(i.e., whether they represent more sensitive endpoints that could alter the risk conclusion). Table 

21 and 22 provide a summary of the taxonomic groups and the surrogate species tested to further 

characterize the potential acute and chronic ecological effects of hexazinone following the 

preliminary problem formulation. 

3.1 Aquatic Organisms

Technical grade hexazinone is classified as practically nontoxic to freshwater fish and freshwater

invertebrates on an acute exposure basis. Hexazinone is classified as slightly toxic to 

estuarine/marine invertebrates. The most sensitive endpoints used quantitatively in this 

assessment have been summarized in Table 21. 

There are four fish acute exposure mortality studies available for hexazinone. For technical grade 

hexazinone, the reported 96 hour LC50 values were >320 mg/L for rainbow trout (MRID 

00104980), and 274 mg/L for Fathead minnow (MRID 00104980). Two studies were available 

for bluegill sunfish, 96 hour LC50 > 370mg/L and 96 hour LC50 = 505 mg/L (MRID 00104980 and 

00076959). The results of these tests indicate that hexazinone is practically nontoxic to fish. The 

fathead minnow LC50 of 274 mg/L will be used to assess the acute effects to freshwater fish for 

hexazinone. There are no studies available for estuarine/marine fish; the data was waived in 

previous assessments due to the low toxicity to freshwater fish.

In MRID 00104980, for rainbow trout, there was no morality in the controls of in the three lowest 

dosage levels. At 24 hours, mortality was 100% in the highest treatment level (490 ppm). Within 

96 hours, mortality was 100% at the second highest treatment level (420 ppm). Sublethal effects 

were reported in the 320 ppm dosage group; the fish began to darken, the number of fish exhibiting 

these effects were not reported. In MRID 00104980, for the fathead minnow, there was no 

mortality seen in the controls. At 24 hours, there was 100% mortality in the highest treatment 

level (560 ppm). The second highest level showed 100% mortality at 48 hours, and the third and 

fourth levels showed 60% mortality by 96 hours. In MRID 00104980 for bluegill sunfish, there 

was 100% mortality shown at 24 hours in the highest treatment group (490 ppm), and showed one 

partial mortality in the second highest concentration; there were no other mortalities seen in the 

lower three doses. 
Page 46 of 133

A fish full life cycle test with a fathead minnow was submitted for hexazinone (MRID 41406001). 

No abnormal behavior for juvenile fish was noted at any test concentration. A chronic NOAEC = 

17 mg/L was reported for juvenile survival (day 39), length and weight; the MATC was reported 

to be 24 mg/L. The NOAEC will be used in the assessment.

There are four invertebrate acute exposure studies available for hexazinone. For freshwater 

invertebrates, there is one study available using the preferred test species, Daphnia magna. The 

study found a 48 hour EC50 = 151.6 mg/L (MRID 00116269), indicating that hexazinone is 

practically nontoxic to aquatic invertebrates. This value will be used in the risk assessment to 

represent freshwater invertebrates. There is data available for three estuarine/marine species to 

determine the effects of hexazinone (MRID 00047164). A 48-h EC50 > 320 mg/L for the Eastern 

Oyster (Crassostrea virginica) was estimated, as well as the grass shrimp (Palaemonetes pugio) 

with a 96 hour LC50 = 78 mg/L and the fiddler crab (Uca pugila) with a 96 hour LC50 > 1,000 

mg/L. These studies demonstrate that hexazinone ranges from slightly to practically nontoxic to 

mollusks and slightly toxic to practically nontoxic to crustaceans. The value for the grass shrimp 

will be used in this assessment. 

Chronic toxicity values are available for the Daphnia magna. Two supplemental studies for 

daphnia resulted in NOAECs of 20 mg/L for survival and reproduction (MRID 00078041) and 29 

mg/L for daphnid survival (MRID 41406002). MRID 00078041 was classified as supplemental 

because the dilution water, volume of water and source of water were not provided; these are 

deficiencies do not affect the endpoints from the study. MRID 41406002 was classified as 

supplemental because the dry weight for the first generation of daphnids wasn not taken. The 

reproductive NOAEC will be used in this assessment as the most sensitive endpoint.

Due to the lack of estuarine/marine toxicity data, an acute to chronic ratio was calculated using the 

acute and chronic values for the daphnid, LC50 = 151.6 and NOAEC = 20 mg/L, and the acute 

value for the grass shrimp, LC50 = 78 mg/L. The resulting NOAEC for grass shrimp was 10.3 

mg/L. This value will be used in the assessment.

Aquatic plant toxicity studies are used to estimate the potential non-target effects to plants. An 

acceptable study is available for vascular aquatic plants using Lemna gibba with frond count as an 

endpoint. The EC50 = 0.0374 mg/L (MRID 43225101) will be used in the assessment to estimate 

risk to nonlisted species and the NOAEC = 0.026 mg/L will be used in the assessment to estimate 

risk to listed species. 

Four studies for nonvascular aquatic plants were available. The acceptable nonvascular aquatic 

plant study with Anabaena flos-aquae resulted in an EC50 = 0.210 mg/L and NOAEC of 0.15 mg/L 

based on growth inhibition (MRID 43302701). The acceptable study with freshwater diatom 

Navicula pelliculosa resulted in an EC50 = 0.012 mg/L with a NOAEC = 0.035 mg/L based on 

growth inhibition (MRID 43302701). The acceptable study with the estuarine/marine diatom 

Skeletonema costatum resulted in an EC50 = 0.012 mg/L and a NOAEC of 0.041 mg/L based on 

growth inhibition (MRID 43225102). An acceptable study is available for Selenastrum 

capricornutum. The EC50 = 0.007 mg/L with a NOAEC = 0.004 mg/L based on cell density 

(MRID 41287001) were based on nominal concentrations. The most sensitive value for

Selenastrum capricornutum will be used to calculate RQs. 
Page 47 of 133

3.1.1. Estimating Aquatic Toxicity to Metabolites using ECOSAR

ECOSAR v. 1.11was used to determine the potential toxicity of Hexazinone and its metabolites to 

aquatic organisms. ECOSAR is able to estimate based on the structure of the chemical, input into 

the database as a SMILES code. ECOSAR will return toxicity estimates for the parents, degradates 

for one or more of the QSAR classes; the neutral organic model is always included. Several other 

QSAR chemical classes are usually included, each with a somewhat different estimate of toxicity. 

A table of comparisons between the degradate, parents and different chemical classes is compiled 

for each taxon; these results have been tabulated in Appendix K. The QSAR estimates are 

compared to available laboratory data to judge the ability of the program to estimate the toxicity 

for that particular structure; for hexazinone, there was significant variability between the known 

parent values and predicted parent values. It was determined that ECOSAR would not be a reliable 

resource to predict the toxicity of the individual metabolites for any specific chemical class. 

Table 21. Most sensitive aquatic species evaluated for assessing potential ecological 

effects of Hexazinone

Study Type Tested Species Toxicity Endpoint

Study MRID and 

Toxicity 

Classification

850.1075 Acute Freshwater Fish Fathead minnow

(Pimephales promelas) LC501 = 274 mg/L

00104980

Practically nontoxic

850.1400 Chronic Freshwater 

Fish

Fathead minnow

(Pimephales promelas) NOAEC = 17 mg/L 41406001NA

850.1010 Acute Freshwater 

Invertebrate

Daphnid

(Daphnia magna) EC50 = 151.6 mg/L

00116269

Practically nontoxic

850.1300 Chronic Freshwater 

Invertebrate

Daphnid

(Daphnia magna) NOAEC= 20 mg/L 00078041NA

850.1075 Acute Estuarine/marine 

Fish Waived on the basis of low Freshwater Fish Toxicity

850.1400 Chronic 

Estuarine/marine fish

850.1350 Acute Estuarine/marine 

Invertebrate Grass Shrimp LC50 = 78 mg/L 00047164Slightly toxic

NA

Chronic 

Estuarine/marine 

Invertebrate

Grass Shrimp NOAEC2 = 10.3 mg/L NA

850.4400 Vascular Plant Duckweed

(Lemna gibba)

EC50 = 0.0374 mg/L

NOAEC = 0.026 mg/L

43225101

NA

850.4550 Nonvascular Plant

Cyanobacteria

Skeletonema 

costatum

EC50 = 0.007 mg/L

NOAEC = 0.004 mg/L

41287001

NA

1 Freshwater fish are considered surrogates for aquatic-phase amphibians. 2

NOAEC based on ACR ratio calculated using acute and chronic daphnid data, and acute grass shrimp data from 

table
Page 48 of 133

3.2 Terrestrial Organisms

Technical grade hexazinone is practically nontoxic to avian species, mammals and terrestrial 

invertebrates on an acute exposure basis. The available toxicity studies have been summarized 

below; the most sensitive endpoints used in this assessment have been tabulated in Table 22.

There is one avian acute oral toxicity study available for hexazinone. The study was conducted 

using a bobwhite (Colinus virginianus) and resulted in an LD50 = 2,258 mg/kg-bw (MRID 

00073988). These results indicate that hexazinone is practically nontoxic to birds. This value will 

be used for risk assessment purposes. There is not acute oral data available for a passerine species.

There are two dietary acute toxicity studies available using the bobwhite (MRID 0010787, MRID 

0010498) and mallard (Anas platyrhynchos) (MRID 0010498) both resulting in LC50>5,000 

mg/kg-diet. For the bobwhite study, there were no treatment related mortalities. There was no 

abnormal behavior observed; gross pathological examination did not reveal any tissue alterations. 

Food consumption and body weight increased over the course of the study. For the mallard study, 

there was no mortality in the control or test groups. Food consumption and body weight both 

increased. These values indicate that hexazinone is practically nontoxic to birds. 

Chronic reproductive toxicity data is available for the bobwhite resulting in a reproductive 

NOAEC = 1,000 mg/kg-bw. This was the highest concentration tested. There was no overt signs 

of toxicity observed at any concentration; clinical signs such as lethargy, wing droop, depression, 

reduced reaction to external stimuli, ruffled appearance, and lower limb weakness were observed 

but were not reported as treatment related. There were no significantly significant differences in 

adult body weights between the groups. There was no apparent treatment related effects upon food 

consumption among birds at test concentrations of 100 and 300 ppm. There was a slight but 

statistically significant reduction in food consumption at 100 ppm during week 3. There was also 

a slight reduction in food consumption during weeks 6 and 12 at all test concentrations. In all 

cases, these reductions were not considered to be treatment related. At 1,000 ppm there was a 

treatment related increase in feed consumption from week 14 through termination that was 

statistically confirmed. There were no apparent treatment related effects upon reproductive 

parameters or eggshell thickness at any of the concentrations tested; there were no apparent 

treatment related effects upon hatchling body weight of 14-day old survivor body weight at any 

tested concentration. The NOAEC for reproductive parameters was 1,000 ppm; based upon the 

effects upon feed consumption at 1,000 ppm, the NOAEC was 300 ppm. The reproductive 

NOAEC will be used in the assessment as increased food consumption is not considered an adverse 

effect. Another additional avian chronic study is available conducted using the mallard, resulting 

in a NOAEC = 1,000 ppm (MRID 41764902).

A registrant submitted rat acute oral study, LD50 = 1,200 mg/kg, indicated that hexazinone is 

practically nontoxic to mammals (MRID 41235004). 

An acceptable two-generation rat study (MRID 42066501) is available. The systemic toxicity 

LOAEC is 2000 ppm (117-154 mg/kg/day for males and 143-180 mg/kg/day for females) based 

on reduced body weight and body weight gains by F1 males and F0 and F1 females. Decreased 

mean weight gains of 11 to 18% were observed in the 5000 ppm in F1 males. In P1 and F1 female 
Page 49 of 133

rats, there were significant decreases in body weight and weight gain at 5000 ppm and at 2000 

ppm for P1 females. The systemic toxicity NOAEC is 200 ppm (11.8-153 mg/kg/day for males 

and 14.3-17.7 mg/kg/day for females). No reproductive effects were seen in the study aside from 

the weight effects on the offspring. The offspring LOAEC is also 2000 ppm (117-154 mg/kg/day 

for males and 143-180 mg/kg/day for females) based on reduced female pup body weights at birth 

and during lactation. The reproductive NOAEC was 200 ppm (11.8-15.3 mg/kg/day for males and 

14.3-17.7 mg/kg/day for females). The systemic toxicity NOAEC and reproductive toxicity 

NOAEC = 200 ppm will be used in this assessment. 

Terrestrial invertebrate toxicity data are used to assess the potential direct and indirect effects of 

hexazinone to non-target species, as well as to endangered species. An acceptable honeybee acute 

contact study resulted in LD50>100 μg/bee (MRID 41216502). At test termination the negative 

control and solvent control mortalities were 2% and 0%. Morality at the 13, 22, 36, 60 and 100 

μg ai/bee doses were 4%, 8%, 2%, 4% and 8% respectively. No sublethal effects were reported. 

Based on the LC50<100 μg/bee, the study indicates that hexazinone is practically nontoxic to 

terrestrial invertebrates; this value will be used qualitatively in the risk description.

Plant toxicity data was available for seedling emergence and vegetative vigor registrant submitted 

studies (MRID 43162501). Sublethal endpoints such as plant growth, dry weight and biomass are 

evaluated for both monocots and dicots in the seedling emergence and vegetative life stages. The 

results of the studies are used to evaluate the effects on non-target plants and are used to evaluate 

direct and indirect effects for endangered species. 

For the vegetative vigor study, the cucumber data is considered to be invalid because the seeds 

were treated with a different pesticide. The percent germination was not reported; in addition, a 

description of the phytotoxicity rating system was not included in the report. The weight parameter 

was mostly affected. The most sensitive monocot species were wheat and corn. The most sensitive 

dicot species was oilseed rape. In this study, cucumber was treated with thiram and hexazinone—

this is unacceptable since it is difficult to evaluate the effects of hexazinone on cucumber. A 

baseline for the cucumber is needed with and without the treatment. It is important to understand 

if there are antagonistic or synergistic interactions between or among the three pesticides used. 

This part of the study was classified as invalid and a new study is thus required. The study results 

suggest that cucumber has the potential to be the most sensitive species tested, however this cannot 

be determined with the available data.

For the seedling emergence data, the cucumber data is also considered to be invalid because the 

seeds were treated with a different pesticides. The onion and pea data is also considered to be 

invalid due to damage to the plants observed. Sorghum, soybean, pea and tomato showed growth 

retardation. The other species did not show growth retardation. The percent germination of oilseed 

rape was low for controls (54%); the study report suggests that a better stock of seed should have 

been used. The seeds of cucumber were treated with multiple pesticides; a control for the two 

pesticides should have been included in the study design. This would have been helpful in 

evaluating the effects of hexazinone on the cucumber seeds. This part of the study in invalid. 
Page 50 of 133

3.3 Incident data

The Ecological Incident Information System (EIIS, v. 2.1.1), which is maintained by the Agency’s 

Office of Pesticide Programs, was searched to determine if ecological incidents have been reported 

for hexazinone. Based on a search of EIIS conducted in May 2015, there were 13 reported 

incidents with the use of hexazinone, all of which involved terrestrial plants only. There were no 

incidents reported involving terrestrial or aquatic animals. 

A summary of the incidents found in EIIS can be found in Table 23. Each incident is accompanied 

by whether the incident occurred due to a misuse, registered use, or whether it is undetermined. 

Of the 13 incidents, 2 were considered a misuse, 4 were undetermined, and 7 of them were due to 

a registered use. 6 of the incidents occurred in the last 10 years. Each incident is additionally 

classified with a certainty to indicate whether hexazinone was responsible for the incident; these 

classifications are as follows: “highly probable,” “probable,” “possible,” and “unlikely.” Of the 7 

incidents that occurred due to a registered use, 1 of them was listed as “highly probable,” 2 were 

listed as “probable,” 3 were listed as “possible,” and 1 was listed as unlikely. 

Table 22. Most sensitive terrestrial species evaluated for assessing potential ecological 

effects of Hexazinone.

Study Type Tested Species Toxicity Endpoint

Study MRID 

and Toxicity 

Classification

850.2100 Avian Acute Oral Northern Bobwhite Quail

(Colinus virginianu) LD50= 2,258 mg/kg

00073988

Practically 

nontoxic

850.2200 Avian Dietary Northern Bobwhite Quail

(Colinus virginianus) LC50 > 5,000 mg/kg diet

00107878

Practically 

nontoxic

850.2300 Avian Reproduction Northern Bobwhite Quail

(Colinus virginianus) NOAEC = 300 mg/kg diet 41764901NA

- Mammalian Acute 

Oral

Norway Rat

(Rattus novegicus) LD50 = 530 mg/kg bw

Kennedy, 1984

Practically 

nontoxic

- Mammalian 

Reproduction

Norway Rat

(Rattus novegicus) NOAEL = 200 mg/kg diet 42066501NA

850.3020 Honeybee Acute 

Contact Toxicity

Honeybee

(Apis mellifera)

LD50 > 100 μg/bee 41216502

Practically 

nontoxic

850. 4100 Seedling Emergence

Wheat

EC25 = 0.0259 lb a.i./A

NOAEC = 0.0781 lb 

a.i./A 4316250

NA

Tomato

EC25 = 0.0063 lb a.i./A

NOAEC =0.00695 lb 

a.i./A

850.4150 Vegetative Vigor

Wheat EC25 = 0.020 lb a.i./A

NOAEC = 0.010 lb a.i./A

43162501

NA Oilseed Rape

EC25 = 0.011lb a.i./A

NOAEC = 0.0071 lb 

a.i./A
Page 51 of 133

Table 23. Summary of Incidents from EIIS v. 2.1.1

Incident ID Use Site State Appl. 

Method Air/Gnd Year Magnitude Legality Certainty

I000548-001 Forest FL Broadcast Air NR NR Registered Use Highly 

Probable

I000611-001 N/R GA Broadcast Air 1993 NR Undetermined Possible

I005822-001 Residential LA NR NR 1997 NR Misuse 

(intentional)

Highly 

Probable

I007984-008 Tree TX Spray Gnd NR NR Misuse 

(intentional) Probable

I012233-001 Home/Lawn KS Spray Gnd NR NR Registered Use Unlikely

I014407-036 Alfalfa WA NR NR 1994 NR Registered use Possible

I015265-001 Seedling TX Unknown Gnd 2004 NR Registered use Possible

I016312-001 Forest OR Spray Both 2005 300 acres Undetermined Possible

I016680-001 Right-ofwayOR Spray Gnd 2005 13 acres Undetermined Possible

I020000-001 Ornamental MO Broadcast Gnd 2008 NA Registered Use Probable

I020592-001 Agricultural 

area

WI Broadcast Gnd 2008 80 acres Registered Use Possible

I020744-001 Pasture FL NR Gnd 2008 135 acres Registered Use Probable

I025246-001 Potato ME Broadcast Gnd 2013 30 acres Undetermined Unlikely

“NR” indicates that the information was Not Reported in the Incident report.

The American Bird Conservancy (ABC) Avian Incident Monitoring System (AIMS) was searched 

in May 2015 and returned zero records of incidents associated with hexazinone.

A search in May 2015 of the Incident Database System (IDS) maintained by OPP’s Information 

Technology and Resource Management Division (ITRMD) yielded 23 aggregate ecological 

incidents (18 involving plants and 5 involving wildlife). It is not possible to discern from the 

available information if the aggregated wildlife incidents involve fish, birds, and/or mammals. 

Because only limited data are currently available for the aggregate incidents, they are assumed to 

be from registered uses of hexazinone.

4.0 Risk Characterization

As discussed in the problem formulation, risk characterization integrates EECs and toxicity 

estimates and evaluated the likelihood of adverse ecological effects to non-target species. For 
Page 52 of 133

hexazinone, a deterministic approach is used to evaluate the likelihood of adverse ecological 

effects to non-target species. In this approach, RQs are calculated by dividing EECs by acute and 

chronic ecotoxicity values for non-target species. 

Risk Quotient (RQ) = Exposure Estimate/Toxicity Estimate

RQs are then compared to LOCs. These LOCs are criteria used to indicate potential risk to nontarget organisms and the need to consider regulatory action. LOC exceedance is interpreted to 

mean that the labeled use (or proposed use) of the pesticide has the potential to cause adverse 

effects on non-target organisms. LOCs currently address the following risk presumption 

categories:

Animals:

• Acute risk—potential for acute risk to non-target organisms which may warrant 

regulatory action in addition to restricted classification

• Acute risk, restricted use—potential for acute risk to non-target organisms, but may be 

mitigated through restricted use classification

• Acute risk, listed species—listed species may be potentially affected by use

• Chronic risk—potential for chronic risk may warrant regulatory action, listed species 

may potentially be affected through chronic exposure

Plants:

• Non-listed plant risk—potential for effects in non-target (non-endangered) plants

• Listed plant risk—potential for effects in endangered plants
Page 53 of 133

Table 24. Agency Risk Quotient (RQ) Metrics and Levels of Concern (LOC) Per Risk 

Class.

Risk Class Risk Description RQ LOC

Aquatic Animals (fish and invertebrates)

Acute Potential for effects to non-listed animals from acute 

exposures

Peak EEC/LC501 0.5

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification Peak EEC/LC501 0.1

Acute Listed 

Species

Listed species may be potentially affected by acute 

exposures

Peak EEC/LC501 0.05

Chronic Potential for effects to non-listed and listed animals from 

chronic exposures

60-day EEC/NOAEC 

(fish) 1

21-day EEC/NOAEC 

(invertebrates)

Aquatic Plants

Non-Listed Potential for effects to non-listed plants from exposures Peak EEC/LC501 1

Listed Potential for effects to listed plants from exposures Peak EEC/NOAEC 1

Terrestrial Animals (mammals and birds)2

Acute Potential for effects to non-listed animals from acute 

exposures

EEC/LC50 (Dietary) 0.5

EEC/LD50 (Dose)

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification

EEC/LC50 (Dietary) 0.2

EEC/LD50 (Dose)

Acute Listed 

Species

Listed species may be potentially affected by acute 

exposures

EEC/LC50 (Dietary) 0.1

EEC/LD50 (Dose)

Chronic Potential for effects to non-listed and listed animals from 

chronic exposures EEC/NOAEC 1

Terrestrial and Semi-Aquatic Plants

Non-Listed Potential for effects to non-target, non-listed plants from 

exposures

EEC/ EC25 1

Listed Plant Potential for effects to non-target, listed plants from 

exposures

EEC/ NOAEC

1

EEC/ EC05

The resulting unitless RQ values are compared to the Agency’s LOCs, as shown in Tables 22. 

The LOCs are used by the Agency to indicate when the use of a pesticide, as directed through the 

label, has the potential to cause adverse effects to non-target organisms. In this assessment, RQs 

that exceed the non-listed species LOC also exceed the listed species LOC.

Tables 23-36 prove the resulting, screening level RQ values, for taxa with sufficient data. Note 

that with plants, unlike with animals, RQ values are not presented for acute versus chronic risk; 

instead, RQ values are presented for listed and nonlisted species based on a comparison of a given 

EEC to NOAEL and EC25/EC50 values respectively. A discussion of the RQ values for hexazinone 

and of other information that provides context for the interpretation of potential risk to various 

taxa is presented in the Risk Description.
Page 54 of 133

4.1 Risk Estimation for Aquatic Organisms for Spray and Granular 

Uses

4.1.1 Freshwater and Estuarine/Marine Fish

For hexazinone there is only acute and chronic data available for freshwater fish; RQ calculations 

can be found in Table 25. Maximum acute RQ values are an order of magnitude below the acute 

risk to listed species LOC, thus there were no LOC exceedances for listed or nonlisted species. 

The RQs for freshwater fish ranged were <0.01 across all scenarios. Additionally, there were no 

LOC exceedances for freshwater fish on a chronic basis; the chronic RQs ranges from <0.01 to 

0.03. 

Table 25. Acute and Chronic RQs for Direct Effects to Freshwater Fish from Hexazinone 

TGAI.1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Acute RQ 

calculated 

using

Freshwater

EC50 = 274 

mg/L

60-

day 

EECs

(μg 

ai/L)

Chronic RQ 

calculated using

Freshwater

NOAEC =0.43 

mg/L

Alfalfa NC alfalfa Aerial 139 <0.01 137 <0.01

Sugarcane in HI

LA sugarcane (HI 

meteorological file 

22521)

Aerial 600 <0.01 593 0.03

Blueberries CA wine grape Ground 78.8 <0.01 78.1 <0.01

Non-crop sites 

(weed and brush 

control)

CA rights-of-way

Aerial 

helicopter 645 <0.01 640 0.03

Non-crop sites 

(weed and brush 

control)

CA rights-of-way Ground 653 <0.01 648 0.03

Conifer release in 

Eastern and Lakes 

states

CA forestry (MI 

meteorological file 

14850)

Aerial 

helicopter 369 <0.01 366 0.02

Christmas trees 

plantations (except 

in 22 states listed 

in label)

OR Christmas trees Aerial 161 <0.01 160 <0.01

Pastures/Rangeland 

in Eastern U.S.

CA rangeland hay 

(NY meteorological 

file 14860)

Aerial 

helicopter 493 <0.01 490 0.02

Bermudagrass/ 

Bahiagrass; 

Industrial turfgrass

PA turf Ground 41.7 <0.01 41.4 <0.01

Conifer release

CA forestry (MI

meterological file 

14850)

Ground

Pellets 24.1 <0.01 23.8 <0.01

Non-crop sites CA rights-of-way Ground 408 <0.01 405 0.02
Page 55 of 133

Table 25. Acute and Chronic RQs for Direct Effects to Freshwater Fish from Hexazinone 

TGAI.1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Acute RQ 

calculated 

using

Freshwater

EC50 = 274 

mg/L

60-

day 

EECs

(μg 

ai/L)

Chronic RQ 

calculated using

Freshwater

NOAEC =0.43 

mg/L

(weed and brush 

control)

Granules

App. = Application

Bolded and shaded values indicate an exceedance of an LOC 1

Acute listed species LOC = 0.05; acute restricted use LOC = 0.1, acute high risk LOC = 0.5; chronic risk LOC = 1.0

RQs were additionally calculated using the EECs generated from inclusion of TTRs and UERs for 

two of the scenarios and the data for freshwater fish. The scenarios selected to run the TTRs and 

UERs were the ones that yielded the highest EECs among the conventional agricultural and nonagricultural crops, following the current Unextracted Residue Guidance. The resulting RQ 

calculations can be found in Table 26. There were no LOC exceedances on an acute or chronic 

basis. Acute RQs were 0.002 and were similar to those calculated for parent plus degradates only. 

Chronic RQs ranged from 0.034 and 0.038 and were also similar to those calculated for the parent 

only.

Table 26. Acute and Chronic RQs for Direct Effects to Freshwater Fish with Hexazinone, including 

TTRs and UERs

Use(s) Scenario App. Method

Peak 

EECs

(μg 

ai/L)

Acute RQ 

calculated using

Freshwater

EC50 = 274 

mg/L

60-

day 

EECs

(μg 

ai/L)

Chronic RQ 

calculated 

using

Freshwater

NOAEC =0.43 

mg/L

Sugarcane in HI

LA sugarcane (HI 

meteorological file 

22521)

Aerial 601 <0.01 594 0.03

Non-crop sites (weed and brush 

control) CA rights-of-way Ground 656 <0.01 651 0.03

App. = Application

Bolded and shaded values indicate an exceedance of an LOC

1

Acute listed species LOC = 0.05; acute restricted use LOC = 0.1, acute high risk LOC = 0.5; chronic risk LOC = 1.0

4.1.2 Freshwater and Estuarine/Marine Invertebrates

For aquatic invertebrates there is data available for freshwater and estuarine/marine species on an 

acute and chronic basis; the data has been tabulated in Table 27. Maximum acute RQ values are 
Page 56 of 133

an order of magnitude below the acute risk to listed species LOC, there were no LOC exceedances 

for listed or non-listed species. The acute RQs for freshwater invertebrates were all <0.01; acute 

RQs for estuarine/marine invertebrates were all<0.01. Maximum chronic RQ values are also an 

order or magnitude below the chronic risk LOC. For freshwater invertebrates the chronic RQs 

ranged from <0.01 to 0.03; for estuarine/marine invertebrates the chronic RQs ranged from <0.01 

to 0.06.

Maximum acute RQ values are two orders of magnitude below the acute risk to listed species LOC, 

thus there were no LOC exceedances. The RQs for freshwater invertebrates were all <0.01. 

Additionally, there were no LOC exceedances for freshwater invertebrates on a chronic basis; the 

chronic RQs ranges from <0.01 to 0.03.

Table 27. Acute and Chronic RQs for Direct Effects to Freshwater and Estuarine/Marine 

Invertebrates from Hexazinone TGAI.1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 

151.6 mg/L

Estuarine/

Marine

EC50 = 78

mg/L

21-day 

EECs

(μg ai/L)

Freshwater

NOAEC =

20.0 mg/L

Estuarine/ 

marine 

NOAEC = 

10.3 mg/L

Acute RQ Chronic RQ

Alfalfa NC alfalfa Aerial 139 <0.01 <0.01 138 <0.01 0.013

Sugarcane in HI

LA sugarcane 

(HI 

meteorological 

file 22521)

Aerial 600 <0.01 <0.01 596 0.02 0.05

Blueberries

CA wine 

grape

Ground 78.8 <0.01 <0.01 78.6 <0.01 <0.01

Non-crop sites 

(weed and brush 

control)

CA rights-ofwayAerial 

helicopter 645 <0.01 <0.01 644 0.03 0.06

Non-crop sites 

(weed and brush 

control)

CA rights-ofway

Ground 653 <0.01 <0.01 651 0.03 0.06

Conifer release in 

Eastern and Lakes 

states

CA forestry

(MI meteorological file 

14850)

Aerial 

helicopter 369 <0.01 <0.01 368 0.01 0.03

Christmas trees 

plantations (except 

in 22 states listed 

in label)

OR Christmas 

trees Aerial 161 <0.01 <0.01 160 <0.01 0.01

Pastures/Rangeland 

in Eastern U.S.

CA rangeland 

hay (NY 

meteorological 

file 14860)

Aerial 

helicopter 493 <0.01 <0.01 492 0.02 0.04

Bermudagrass/ 

Bahiagrass; PA turf Ground 41.7 <0.01 <0.01 41.6 <0.01 <0.01
Page 57 of 133

Table 27. Acute and Chronic RQs for Direct Effects to Freshwater and Estuarine/Marine 

Invertebrates from Hexazinone TGAI.1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 

151.6 mg/L

Estuarine/

Marine

EC50 = 78

mg/L

21-day 

EECs

(μg ai/L)

Freshwater

NOAEC =

20.0 mg/L

Estuarine/ 

marine 

NOAEC = 

10.3 mg/L

Acute RQ Chronic RQ

Industrial turfgrass

Conifer release

CA forestry 

(MI meterological file 

14850)

Ground

Pellets 24.1 <0.01 <0.01 24 <0.01 <0.01

Non-crop sites 

(weed and brush 

control)

CA rights-ofway

Ground

Granules 408 <0.01 <0.01 407 0.02 0.04

App. = Application

Bolded and shaded values indicate an exceedance of an LOC 1

Acute listed species LOC = 0.05; acute restricted use LOC = 0.1, acute high risk LOC = 0.5; chronic risk LOC = 1

RQs were additionally calculated using the EECs generated from inclusion of TTRs and UERs for 

two of the scenarios and the data for freshwater and estuarine/marine invertebrates. The resulting 

RQ calculations can be found in Table 28. There were no LOC exceedances on an acute or chronic 

basis. Acute RQs for freshwater invertebrates were <0.01; acute RQs for estuarine/marine 

invertebrates were <0.01. Chronic RQs for freshwater invertebrates were 0.02 and 0.03; chronic 

RQs for estuarine/marine invertebrates were 0.05 and 0.06. Both acute and chronic RQs for 

freshwater and estuarine/marine invertebrates were similar to those calculated for the parent plus 

degradates only.

Table 28. Acute and Chronic RQs for Direct Effects to Freshwater and Estuarine/Marine 

Invertebrates with Hexazinone, including TTRs and UERs

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 

151.6 mg/L

Estuarine/

Marine

EC50 = 78 

mg/L

21-day 

EECs

(μg ai/L)

Freshwater

NOAEC = 

20.0 mg/L

Estuarine/ 

marine 

NOAEC = 

10.3 mg/L

Acute RQ Chronic RQ

Sugarcane in HI

LA sugarcane 

(HI meteorological file 

22521)

Aerial 601 <0.01 <0.01 597 0.02 0.05

Non-crop sites 

(weed and brush 

control)

CA rights-ofway

Ground 656 <0.01 <0.01 654 0.03 0.06
Page 58 of 133

Table 28. Acute and Chronic RQs for Direct Effects to Freshwater and Estuarine/Marine 

Invertebrates with Hexazinone, including TTRs and UERs

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 

151.6 mg/L

Estuarine/

Marine

EC50 = 78 

mg/L

21-day 

EECs

(μg ai/L)

Freshwater

NOAEC = 

20.0 mg/L

Estuarine/ 

marine 

NOAEC = 

10.3 mg/L

Acute RQ Chronic RQ

App. = Application

Bolded and shaded values indicate an exceedance of an LOC 1

Acute listed species LOC = 0.05; acute restricted use LOC = 0.1, acute high risk LOC = 0.5; chronic risk LOC = 1

4.1.3 Aquatic Plants

All scenarios for aquatic vascular plants and aquatic nonvascular plants result in LOC exceedances 

for listed and nonlisted RQs; the results have been tabulated in Table 29. For aquatic vascular

plants, the RQs range from 1.60 to 25.1 for listed species and from 1.11 to 17.4 for nonlisted 

species. Aquatic nonvascular plants, the RQs range from 10.4 to 163 for listed species and 5.95 

to 93.2 for nonlisted species. The maximum RQs were associated with the CA rights-of-way 

scenario (ground application, at 8 lb a.i./A) across both taxa. 

Table 29. RQ Values for Direct Effects to Aquatic Vascular and Nonvascular Plants from 

Hexazinone TGAI.1,2

Use(s) Scenario

Applicat

ion 

Method

Peak 

EECs 

(μg ai/L)

Aquatic Vascular Plants

EC50 = 0.0374 mg/L

NOAEL = 0.026 mg/L

Aquatic Nonvascular

Plants

EC50 0.007 mg/L

NOAEL = 0.004 mg/L

Listed RQs3 Nonlisted

RQs4

Listed 

RQs3

Nonlisted

RQs4

Alfalfa NC alfalfa Aerial 139 5.34 3.71 34.7 19.8

Sugarcane in HI

LA sugarcane 

(HI meteorological file 22521)Aerial 600 23.0 16.0 150 85.7

Blueberries CA wine grape Ground 78.8 3.03 2.10 19.7 11.2

Non-crop sites 

(weed and brush 

control)

CA rights-of-way

Aerial 

helicopter 645 24.8 17.2 161 92.1

Non-crop sites 

(weed and brush 

control)

CA rights-of-way Ground 653 25.1 17.4 163 93.2

Conifer release 

in Eastern and 

Lakes states

CA forestry (MI 

meteoro-logical 

file 14850)

Aerial 

helicopter 369 14.1 9.86 92.2 52.7

Christmas trees 

plantations 

(except in 22 

states listed in 

label)

OR Christmas 

trees Aerial 161 6.19 4.30 40.2 23.0
Page 59 of 133

Table 29. RQ Values for Direct Effects to Aquatic Vascular and Nonvascular Plants from 

Hexazinone TGAI.1,2

Use(s) Scenario

Applicat

ion 

Method

Peak 

EECs 

(μg ai/L)

Aquatic Vascular Plants

EC50 = 0.0374 mg/L

NOAEL = 0.026 mg/L

Aquatic Nonvascular

Plants

EC50 0.007 mg/L

NOAEL = 0.004 mg/L

Listed RQs3 Nonlisted

RQs4

Listed 

RQs3

Nonlisted

RQs4

Pastures/Rangela

nd in Eastern 

U.S.

CA rangeland 

hay (NY 

meteorological 

file 14860)

Aerial 

helicopter 493 18.9 13.7 123 70.4

Bermudagrass/ 

Bahiagrass; 

Industrial 

turfgrass

PA turf Ground 41.7 1.60 1.11 10.4 5.95

Conifer release

CA forestry (MI

meterological file 

14850)

Ground

Pellets 24.1 0.92 0.64 6.02 3.44

Non-crop sites 

(weed and brush 

control)

CA rights-of-way

Ground

Granules 408 15.6 10.9 102 58.2

1

Bolded and shaded values indicate an exceedance of an LOC. 2

Listed aquatic plant LOC = 1; Non-listed aquatic plant LOC = 1 3

Estimated by dividing the peak EEC by the most sensitive NOAEC

4

Estimated by dividing the peak EEC by the most sensitive EC50

RQs were additionally calculated using the EECs generated from inclusion of TTRs and UERs for 

two of the scenarios and the data for aquatic vascular and nonvascular plants. The resulting RQ 

calculations can be found in Table 30. There were LOC exceedances for both listed and nonlisted 

species for both species. RQs for aquatic vascular plants were 23.1 and 25.2 for listed species and 

16.0 and 17.5 for nonlisted species. RQs for aquatic nonvascular plants were 150 for 164 for listed 

species and 85.8 and 93.7 for nonlisted species. 

Table 30. Listed and Non-listed RQs for Direct Effects to Vascular and Nonvascular Aquatic 

Plants with Hexazinone, including TTRs and UERs

Use(s) Scenario

Applica

tion 

Method

Peak 

EECs 

(μg ai/L)

Aquatic Vascular Plants

EC50 = 0.0374 mg/L

NOAEL = 0.026 mg/L

Aquatic Nonvascular 

Plants

EC50 0.007 mg/L

NOAEL = 0.004 mg/L

Listed RQs3 Nonlisted

RQs4

Listed 

RQs3

Nonlisted

RQs4

Sugarcane in HI

LA sugarcane 

(HI meteorological file 22521)Aerial 601 25.2 17.5 164 93.7

Non-crop sites 

(weed and brush 

control)

CA rights-of-way Ground 656 23.1 16.0 150 85.8

1

Bolded values indicate an exceedance of an LOC. 2

Listed aquatic plant LOC = 1; Non-listed aquatic plant LOC = 1 3

Estimated by dividing the peak EEC by the most sensitive NOAEC
Page 60 of 133

Table 30. Listed and Non-listed RQs for Direct Effects to Vascular and Nonvascular Aquatic 

Plants with Hexazinone, including TTRs and UERs

Use(s) Scenario

Applica

tion 

Method

Peak 

EECs 

(μg ai/L)

Aquatic Vascular Plants

EC50 = 0.0374 mg/L

NOAEL = 0.026 mg/L

Aquatic Nonvascular 

Plants

EC50 0.007 mg/L

NOAEL = 0.004 mg/L

Listed RQs3 Nonlisted

RQs4

Listed 

RQs3

Nonlisted

RQs4

4

Estimated by dividing the peak EEC by the most sensitive EC50

4.2 Risk Estimation for Terrestrial Organisms Non-Granular Uses

4.2.1 Acute Dose-based Risk to Birds

Acute dose based RQs for birds exceed the LOCs for listed and non-listed species for some uses. 

Exceedances trend toward smaller bird sizes and uses associated with higher application rates. 

Results have been summarized in Table 31.

For a small bird, there were a number of scenarios resulting in RQs exceeding the listed and 

nonlisted species LOCs. For a small bird consuming short grass, the RQs ranged from 0.19 to 1.34 

with four of the uses exceeding the nonlisted species LOC and four of the uses exceeding the listed 

species LOC. For a small bird consuming tall grass, RQs ranged from 0.09 to 0.62 with only one 

of the uses exceeding the nonlisted species LOC, six of the uses exceeding the listed species LOC 

and one of the uses that does not exceed any LOC. For a small bird consuming broad-leaf plants 

RQs ranged from 0.11 to 0.76 with two of the uses exceeding the nonlisted species LOC and 6 of 

the uses resulting in RQs which exceed the listed species RQ. For small birds consuming 

arthropods RQs ranged from 0.07 to 0.53 with only one use exceeding the nonlisted species LOC, 

five uses exceeding the listed species LOC and one use with an RQ below both LOC levels. 

For a medium bird, there were fewer uses resulting in RQs exceeding the listed and nonlisted 

species LOCs as compared to a small bird; only one of the uses across all feeding strategies 

resulting in an RQ above the nonlisted species LOC. For a medium bird consuming short grass, 

the RQs ranged from 0.08 to 0.60 with only one of the uses above the LOC for nonlisted species, 

six of the uses above the LOC for listed species. For medium birds consuming tall grass, broadleaf 

plants, and arthropods, four of the uses resulted in RQs above the LOC for listed species, and four 

of the uses did not exceed any LOCs. The RQs for tall grass ranged from 0.04 to 0.28, 0.05 to 0.3 

for broadleaf plants and 0.03 to 0.24 for birds consuming arthropods.

For a large bird, there were even fewer uses resulting in RQs exceeding the listed species LOCS 

and no uses resulting in RQs above the nonlisted species LOC. For a large bird consuming short 

grass, there were three uses resulting in RQs above the LOC for listed species. The RQs ranged 

from 0.03 to 0.19. For a large bird consuming broadleaf plants, only one of the uses resulting in 

an RQ above the LOC with the remaining seven uses below the LOC; the RQs ranged from 0.02 

to 0.11. For large birds consuming tall grass and arthropods, there were no uses resulting in RQs 

above the LOC for listed species. RQs ranged from 0.01 to 0.09 for large birds consuming tal 

grass and 0.01 to 0.07 for large birds consuming arthropods.
Page 61 of 133

For small, medium and large birds consuming fruits, pods, seeds etc. and seeds, grains etc. there 

were no uses that resulted in RQs above the LOC for listed species or nonlisted species. For birds 

consuming fruits, pods, seeds etc. RQs ranged from <0.01 to 0.08. For granivores consuming

seeds, grains etc. RQs ranged from <0.01 to 0.02 across all birds sizes.
Page 62 of 133

Table 31. Acute Dose-based RQ values for Birds Exposed to Hexazinone (T-REX v. 1.5.2)1,2 for Non-Granular Uses

Primary 

Feeding 

Strategy 

Herbivores and Omnivores Insectivores Granivores

Animal Size 

 Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 



Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s) 

Agricultural Uses

Alfalfa 0.25* 0.12* 0.14* 0.02 0.11* 0.05 0.06 0.01 0.04 0.02 0.02 <0.01 0.10* 0.04 0.01 <0.01 <0.01 <0.01

Sugarcane in HI 0.60 0.28* 0.34* 0.04 0.27* 0.12* 0.15* 0.02 0.09 0.04 0.05 0.01 0.24* 0.11* 0.03 0.01 <0.01 <0.01

Blueberries 0.34* 0.15* 0.19* 0.02 0.15* 0.07 0.08 0.01 0.05 0.02 0.03 <0.01 0.13* 0.06 0.02 <0.01 <0.01 <0.01

Non-Agricultural Uses

Non-Crop sites 

(Aerial) 1.01 0.46* 0.57 0.06 0.45* 0.21* 0.25* 0.03 0.14* 0.07 0.08 0.01 0.39* 0.18* 0.06 0.01 0.01 <0.01

Non-Crop sites

(Ground) 1.34 0.62 0.76 0.08 0.60 0.28* 0.34* 0.04 0.19* 0.09 0.11* 0.01 0.53 0.24* 0.07 0.02 0.01 <0.01

Christmas Tree 

Plantations 0.34* 0.15* 0.19* 0.02 0.15* 0.07 0.08 0.01 0.05 0.02 0.03 <0.01 0.13* 0.06 0.02 <0.01 <0.01 <0.01

Rangeland 0.67 0.31* 0.38* 0.04 0.30* 0.14* 0.17* 0.02 0.10* 0.04 0.05 0.01 0.26* 0.12 0.04 0.01 <0.01 <0.01

Industrial 

Turfgrass 0.19* 0.09 0.11* 0.01 0.08 0.04 0.05 0.01 0.03 0.01 0.02 <0.01 0.07 0.03 0.01 <0.01 <0.01 <0.01

1 RQ values in bold exceed the non-listed species LOC of 0.5. Values in red indicate that the RQ exceeds the LOC for acute risk to listed birds. 2

Acute endangered species LOC = 0.1; acute restricted use LOC = 0.2; acute high risk LOC = 0.5
Page 63 of 133

4.2.2 Acute Dietary-based Risk to Birds

RQs for acute dietary based risk to birds cannot be calculated based on the non-definitive endpoints 

found in the studies (both reported LC50 >5000 ppm). When making a conservative assumption 

comparing the highest test concentration, 5,000 ppm, to the EECs reported in Table 19, there are 

no LOC exceedances for nonlisted species, but some uses associated with the highest application 

rates exceed the LOC for listed species consuming short grass, tall grass and broadleaf plants. 

4.2.3 Chronic Dose-based Risk to Birds

Chronic dietary based RQs for birds have been tabulated in Table 32. These RQs are based on a 

NOAEC from a non-adverse effect at the highest dose. For birds consuming short grass, two uses 

resulted in RQs which exceeded the chronic LOC; short grass RQs ranged from 0.27 to 1.92. There 

were no RQs above the LOC for birds consuming tall grass; the RQs ranged from 0.12 to 0.88. 

Birds consuming broadleaf plants showed one use that resulted in an RQ that narrowly exceeded 

the LOC; the RQs ranged from 0.15 to 1.08. For birds consuming fruits, pods, seeds etc. the RQs 

ranged from 0.02 to 0.12 and had no uses that resulted in LOC exceedances. For birds consuming 

arthropods there were no RQs that exceeded the LOC; the RQs ranged from 0.11 to 0.75.

Table 32. Chronic Dose-Based RQs for Birds, Reptiles, and Terrestrial-phase 

Amphibians of Different Feeding Classes (T-REX v. 1.5.2)* for Non-Granular Uses

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short 

Grass

Tall 

Grass

Broadleaf 

Plants

Fruits, 

pods, 

seeds, 

etc.

Arthropods

Use(s) 

Agricultural Uses

Alfalfa 0.36 0.17 0.20 0.02 0.14

Sugarcane in HI 0.86 0.40 0.49 0.05 0.34

Blueberries 0.48 0.22 0.27 0.03 0.19

Non-Agricultural Uses

Non-Crop sites (Aerial) 1.44 0.66 0.81 0.09 0.56

Non-Crop sites

(Ground) 1.92 0.88 1.08 0.12 0.75

Christmas Tree Plantations 0.96 0.44 0.54 0.06 0.38

Rangeland 0.48 0.22 0.27 0.03 0.19

Industrial Turfgrass 0.27 0.12 0.15 0.02 0.11

*RQ values in bold exceed the chronic LOC of 1 for both listed and non-listed species.
Page 64 of 133

4.2.4 Acute Dose-based Risk to Mammals

Acute dose based RQs for mammals exceed the LOCs for listed and nonlisted species for some 

uses. Exceedances trend toward smaller mammal sizes and uses associated with higher application 

rates. Results have been summarized in Table 33.

For a small mammal, there were five uses resulting in RQs exceeding the non-listed species LOCs. 

For a small mammal consuming short grass, the RQs ranged from 0.10 to 0.79 with three of the 

uses exceeding the nonlisted species LOC and five of the uses exceeding the listed species LOC. 

For a small mammal consuming tall grass, RQs ranged from 0.04 to 0.36 with four of the uses 

exceeding the listed species LOC; none of the uses exceeded the non-listed species LOC. For a 

small mammal consuming broadleaf plants, RQs ranged from 0.05 to 0.44 with six of the uses 

exceeding the listed species LOC; none of the uses exceeded the nonlisted species LOC. For a 

small mammal consuming arthropods, RQs ranged from 0.04 to 0.31 with four of the uses 

exceeding the listed species LOC; none of the uses exceeded the nonlisted species LOC. For small 

mammals consuming fruits, pods, seeds etc. or seeds, grains etc., RQs ranged from 0.01 to 0.05 

and <0.01 to 0.01 respectively; there were no LOC exceedances for listed or nonlisted species.

For medium sized mammals, there were fewer uses resulting in RQs exceeding the listed and nonlisted species LOCs as compared to small mammals. For a medium mammals consuming short 

grass, the RQs ranged from0.08 to 0.67, with two of the uses resulting in RQs above the nonlisted 

species LOC and five of the uses exceeding the listed species LOC. For a medium mammals 

consuming tall grass, RQs ranged from 0.04 to 0.31 with four of the uses exceeding the listed 

species LOC; there were no exceedances for non-listed species. For a medium mammals 

consuming broadleaf plants, RQs ranged from 0.05 to 0.38 with four of the uses exceeding the 

listed species LOC and none of the uses exceeding the nonlisted species LOC. For a medium 

mammals consuming arthropods, there were four uses which exceeded the listed species LOC and 

RQs ranged from 0.03 to 0.26. For medium mammals consuming fruits, pods, seeds etc. or seeds, 

grains etc. RQs ranged from 0.01 to 0.04 and <0.01 to 0.01 respectively; there were no LOC 

exceedances for listed or nonlisted species.

For large mammals, there were no LOC exceedances for any nonlisted species. For large mammals 

consuming short grass there were five uses resulting in RQs above the listed species LOC; RQs 

ranged from 0.04 to 0.36. For large mammals consuming tall grass there were three uses resulting 

in RQs above the listed species LOC with RQs ranging from 0.02 to 0.16. For large mammals 

consuming broadleaf plants there were three uses with RQs exceeding the listed species LOC; RQs 

ranged from 0.03 to 0.20. For large mammals consuming arthropods there were two uses with 

RQs exceeding the listed species LOC, ranging from 0.02 to 0.14. For large mammals consuming 

fruits, pods, seeds etc. and seeds, grains etc. there were no exceedances for listed species; RQs 

ranged from <0.01 to 0.02 and <0.01 to 0.01 respectively.
Page 65 of 133

Table 33. Acute Dose-based RQ values for Mammals Exposed to Hexazinone (T-REX v. 1.5.2)1,2 for Non-Granular Uses

Primary Feeding 

Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size  Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s) 

Agricultural Uses

Alfalfa 0.13* 0.06 0.07 0.01 0.11* 0.05 0.06 0.01 0.06 0.03 0.03 <0.01 0.05 0.04 0.02 <0.01 <0.01 <0.01

Sugarcane in HI 0.31* 0.14* 0.17* 0.02 0.27* 0.12* 0.15* 0.02 0.14* 0.07 0.08 0.01 0.12* 0.10* 0.06 <0.01 <0.01 <0.01

Blueberries 0.17* 0.08 0.10* 0.01 0.15* 0.07 0.08 0.01 0.08 0.04 0.04 <0.01 0.07 0.06 0.03 <0.01 <0.01 <0.01

Non-Agricultural Uses

Non-Crop sites (Aerial) 0.52 0.24* 0.29* 0.03 0.44* 0.20* 0.25* 0.03 0.24* 0.11* 0.13* 0.01 0.20* 0.17* 0.09 0.01 0.01 <0.01

Non-Crop sites

(Ground) 0.69 0.32* 0.39* 0.04 0.59 0.27* 0.33* 0.04 0.32* 0.15* 0.18* 0.02 0.27* 0.23* 0.12* 0.01 0.01 <0.01

Christmas Tree Plantations 0.17* 0.08 0.10* 0.01 0.15* 0.07 0.08 0.01 0.08 0.04 0.04 <0.01 0.07 0.06 0.03 <0.01 <0.01 <0.01

Rangeland 0.79 0.36* 0.44* 0.05 0.67 0.31* 0.38* 0.04 0.36* 0.16* 0.20* 0.02 0.31* 0.26* 0.14 0.01 0.01 <0.01

Industrial Turfgrass 0.10* 0.04 0.05 0.01 0.08 0.04 0.05 0.01 0.04 0.02 0.03 <0.01 0.04 0.03 0.02 <0.01 <0.01 <0.01

1 RQ values in bold exceed the non-listed species LOC of 0.5. Starred values indicate that the RQ exceeds the LOC for acute risk to listed mammals. 
Page 66 of 133

4.2.5 Chronic Dose and Dietary-based Risk to Mammals

Chronic dose based RQ values for mammals exposed to hexazinone resulted in a significant 

number of LOC exceedances across all uses, mammal sizes and feeding strategies; results have 

been tabulated in Table 34.

For small mammals, chronic RQs exceeded the LOC for all use for mammals consuming short 

grass, tall grass, broadleaf plants and arthropods. The RQs ranged as follows: 11.7 to 83.2 for 

short grass, 5.37 to 38.1 for tall grass, 6.59 to 46.8 for broadleaf plants, and 4.59 to 32.6 for 

arthropods. For small mammals consuming fruits, pods, seeds etc. there were two uses that did 

not exceed the chronic LOC; RQs ranged from 0.73 to 5.21. For small mammals consuming seeds, 

grains etc. there were six uses that resulted in RQs below the chronic LOC.

For medium mammals, chronic RQs exceeded the LOC for all uses for mammals consuming short 

grass, tall grass, broadleaf plants and arthropods. The RQs ranged as follows: 10.0 to 71.1 for 

short grass, 4.59 to 32.6 for tall grass, 5.63 to 40.0 for broadleaf plants, and 3.92 to 27.8 for 

arthropods. For medium mammals consuming fruits, pods, seeds etc. there were two uses that did 

not exceed the chronic LOC; RQs ranged from 0.63 to 4.45. For medium mammals consuming 

seeds, grains etc. there were no uses that resulted in RQs exceeding the chronic LOC.

For large mammals, chronic RQs exceeded the LOC for all uses for mammals consuming short 

grass, tall grass, broadleaf plants and arthropods. The RQs ranged as follows: 5.36 to 38.1 for 

short grass, 2.46 to 17.4 for tall grass, 3.02 to 21.4 for broadleaf plants and 2.10 to 14.9 for 

arthropods. For medium mammals consuming fruits, pods, seeds etc. there were four uses that did 

not exceed the chronic LOC with RQs ranging from 0.34 to 2.38. For large mammals consuming 

seeds, grains etc. there were no uses that resulted in RQs exceeding the chronic LOC.
Page 67 of 133

Table 34. Chronic Dose-based RQ Values for Mammals Exposed to Hexazinone (T-REX v.1.5.2)1,2 for Non-Granular Uses

Primary Feeding Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size  Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s) 

Agricultural Uses

Alfalfa 15.9 7.16 8.78 0.98 13.3 6.11 7.50 0.83 7.15 3.28 4.02 0.45 6.12 5.22 2.80 4.77 0.19 0.10

Sugarcane in HI 37.4 17.1 21.0 2.34 32.0 14.6 18.0 2.00 17.1 7.87 9.65 1.07 14.6 12.4 6.72 0.52 0.44 0.24

Blueberries 20.8 9.84 11.7 1.30 17.7 8.15 10.0 1.11 9.53 4.37 5.36 0.60 8.16 6.97 3.73 0.29 0.25 0.13

Non-Agricultural Uses

Non-Crop sites (Aerial) 62.4 28.6 35.1 3.90 53.3 24.4 30.0 3.33 28.6 13.1 16.0 1.79 24.4 20.9 11.2 0.87 0.74 0.40

Non-Crop sites

(Ground) 83.2 38.1 46.8 5.21 71.1 32.6 40.0 4.45 38.1 17.4 21.4 2.38 32.6 27.8 14.9 1.16 0.99 0.53

Christmas Tree Plantations 20.8 9.54 11.7 1.30 17.7 8.15 10.0 1.11 9.53 4.37 5.36 0.60 8.16 6.97 3.73 0.29 0.25 0.13

Rangeland 41.6 19.0 23.4 2.60 35.5 16.3 20.0 2.22 19.0 8.74 10.7 1.19 16.3 13.9 7.47 0.58 0.49 0.26

Industrial Turfgrass 11.7 5.37 6.59 0.73 10.0 4.59 5.63 0.63 5.36 2.46 3.02 0.34 4.59 3.92 2.10 0.16 0.14 0.07

1

RQ values in bold exceed the chronic LOC of 1 for both listed and non-listed species.2Using adjusted NOAEL values of 21.98, 17.78, and 7.69 for small,

medium, and large mammals, respectively.

2

Chronic risk LOC = 1.
Page 68 of 133

Chronic dietary based RQs for mammals exceed the LOC for some uses across mammals 

consuming short grass, tall grass and broadleaf plants; the results have been tabulated in Table 35. 

For mammals consuming short grass, the chronic LOC is exceeded for all uses and the RQs ranged 

from 1.35 to 9.60. For mammals consuming tall grass, the chronic LOC is exceeded for six of the 

eight uses with RQs ranging from 0.62 to 4.40. For mammals consuming broadleaf plants, the 

chronic LOC is exceeded for seven of the eight uses with RQs ranging from 0.76 to 5.40. For 

mammals consuming arthropods, the chronic LOC is exceeded for 4 uses, with four of the uses 

resulting in RQs below the LOC; the RQs range from 0.53 to 3.76. Lastly, for mammals 

consuming fruits, pods, seeds etc. there are no uses that result in RQs exceeding the chronic LOC.

Table 35. Chronic Dietary-Based RQs for Mammals of Exposed to Hexazinone (T-REX 

v.1.5.2) 1,2 for Non-Granular Uses

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short 

Grass

Tall 

Grass

Broadleaf 

Plants

Fruits, 

pods, 

seeds, 

etc.

Arthropods

Use(s) 

Agricultural Uses

Alfalfa 1.80 0.83 1.01 0.11 0.71

Sugarcane in HI 4.32 1.98 2.43 0.27 1.69

Blueberries 2.40 1.10 1.35 0.15 0.94

Non-Agricultural Uses

Non-Crop sites (Aerial) 7.20 3.30 4.05 0.45 2.82

Non-Crop sites

(Ground) 9.60 4.40 5.40 0.60 3.76

Christmas Tree Plantations 2.40 1.10 1.35 0.15 0.94

Rangeland 4.80 2.20 2.70 0.30 1.88

Industrial Turfgrass 1.35 0.62 0.76 0.08 0.53

1

Chronic risk LOC = 1.

4.2.6 Risk to Terrestrial Plants

The LOC for non-target monocots adjacent to hexazinone use areas for non-granular uses was 

exceeded across uses for spray drift only, runoff and spray drift in dry areas and runoff and spray 

drift in semi aquatic areas with a single exception. For nonlisted species considering spray drift 

only, the lowest use rate resulted in an RQ below the LOC for nontarget monocots. The RQs 

ranged from 0.56 to 15.0. The highest RQs can be found for nontarget monocots in semi-aquatic 

areas, with RQs ranging from 22.1 to 157 for nonlisted monocots, and 73.4 to 522 for listed species. 

The results have been summarized in Table 36.
Page 69 of 133

Table 36. RQs for Nontarget Monocots Adjacent to Hexazinone Use Areas1 for NonGranular Uses

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Monocot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic 

Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Alfalfa Aerial: 1.5 3.75 7.50 5.79 19.2 31.8 105

Sugarcane in HI Aerial: 3.6 9.00 18.0 13.9 46.0 76.4 253

Blueberries Ground: 2.0 1.00 2.00 4.63 15.3 39.3 130

Noncrop sites

Aerial: 6.0 15.0 30.0 23.1 76.8 127 422

Ground: 8.0 4.0 8.0 18.5 61.4 157 522

Forestry Aerial: 4.0 10.0 20.0 15.4 51.2 84.9 281

Christmas trees Aerial 2.0 5.0 10.0 7.72 25.6 42.4 140

Eastern Rangeland Aerial 4.0 10.0 20.0 15.4 51.2 84.9 281

Industrial turfgrass Ground: 1.125 0.56 1.13 2.61 8.64 22.1 73.4

1

LOCfor listed and non-listed species = 1; values in bold exceed the LOC

The LOC for non-target dicots adjacent to hexazinone use areas for non-granular uses was 

exceeded across uses for spray drift only, runoff and spray drift in dry areas and runoff and spray 

drift in semi aquatic areas. The lowest RQs can be found for nontarget dicots when considering 

spray drift only with RQs ranging from 1.79 to 47.6 for nonlisted species and 1.62 to 43.1 for listed 

species. The highest RQs can be found for nontarget dicots in semi-aquatic areas, with RQs 

ranging from 91.0 to 647 for nonlisted species, and 82.5 to 587 for listed species. The results have 

been summarized in Table 37.

Table 37. RQs for Nontarget Dicots Adjacent to Hexazinone Use Areas1 for NonGranular Uses

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Monocot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic 

Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Alfalfa Aerial: 1.5 11.9 10.7 23.8 21.5 130 118

Sugarcane in HI Aerial: 3.6 28.5 25.9 57.1 51.8 314 284

Blueberries Ground: 2.0 3.17 2.88 19.0 17.2 161 146

Noncrop sites

Aerial: 6.0 47.6 43.1 95.2 86.3 523 474

Ground: 8.0 12.7 11.5 76.1 69.0 647 587

Forestry Aerial: 4.0 31.7 28.7 63.4 57.5 349 316

Christmas trees Aerial 2.0 15.8 14.3 31.7 28.7 174 158

Eastern Rangeland Aerial 4.0 31.7 28.7 63.4 57.5 349 316

Industrial turfgrass Ground: 1.125 1.79 1.62 10.7 9.71 91.0 82.5

1

LOCfor listed and non-listed species = 1; values in bold exceed the LOC
Page 70 of 133

4.3 Risk Estimation to Terrestrial Organisms for Granular and 

Pelleted Uses

4.3.1 Risk to Birds and Mammals

Granular and pelleted applications have been summarized in Table 2. Summary of Hexazinone 

Uses and Application Information under the Granular Applications tab. There are four crops that 

have a pelleted and/or granular application. 

For the granular and pelleted applications the LD50 per ft2 tab within T-REX (v.1.5.2) have been 

used to quantify the risk to terrestrial organisms. Although a bird’s or mammal’s habitat is not 

limited to a square foot, there is presumably a direct correlation between the concentrations of a 

pesticide in the environment (mg/ft2) and the chance than an animal will be exposed to a 

concentration that could adversely affect its survival. Typically for granular applications, 

terrestrial EECs are calculated based on an estimated loading of pesticides per unit area. This 

approach compares the available mass of pesticide per square foot to the acute oral dose for toxicity 

(LD50); the resulting value can be compared directly the Agency’s LOC. Results have been 

tabulated in Table 38 for birds and Table 39 for mammals. A sample output can be found in 

Appendix F. Because the mass of the pellets is known, the pelleted formulations will later be 

characterized using T-REX; there will be no further characterization of the granular formulations.

A comparison of the LC50 / ft2 show that consumption of the granules and pellets affect the smallest 

weight class more than the largest weight class. The highest values are associated with the smallest 

bird and highest application rates. 

Table 38. Analysis LD50 per ft2 for Birds for Granular and Pelleted Uses

Application Weight Class

Use Application 

Rate mg a.i./ft2 20 g 100 g 1000 g

Rangeland 

(pellets) 0.63 lb ai/A 4.92 0.15 0.02 0.00

Conifer Release

(granular) 3 lb ai/A 23.43 0.72 0.11 0.01

Conifer Release

(pellets) 4.0 lb ai/A 31.24 0.96 0.15 0.01

Forestry Site 

Preparation

Eastern

(granular)

4.7 lb ai/A 36.71 1.13 0.18 0.01

Forestry Site 

Preparation

Western

(granular)

4.0 lb ai/A 31.24 0.96 0.15 0.01

Forestry Site 

Preparation 6.1 lb ai/A 47.64 1.46 0.23 0.02
Page 71 of 133

(pellets)

Non-Crop Site

(pellets) 8.0 lb ai/A 62.48 1.92 0.30 0.02

Non-Crop Site 

(granular) 7.4 lb ai/A 57.79 1.78 0.28 0.02

Table 39. Analysis LD50 per ft2 for Mammals for Granular and Pelleted Uses

Application Weight Class

Use Application 

Rate mg a.i./ft2 15 g 35 g 1000 g

Rangeland 

(pellets) 0.63 lb ai/A 4.92 0.12 0.07 0.01

Conifer Release

(granular) 3 lb ai/A 23.43 0.59 0.31 0.03

Conifer Release

(pellets) 4.0 lb ai/A 31.24 0.79 0.42 0.03

Forestry Site 

Preparation 

Eastern

(granular)

4.7 lb ai/A 36.71 0.93 0.49 0.04

Forestry Site 

Preparation 

Western

(granular)

4.0 lb ai/A 31.24 1.58 0.84 0.07

Forestry Site 

Preparation

(pellets)

6.1 lb ai/A 47.64 1.20 0.64 0.05

Non-Crop Site

(pellets) 8.0 lb ai/A 62.48 1.58 0.84 0.07

Non-Crop Site

(granular) 7.4 lb ai/A 57.79 1.46 0.77 0.06

4.3.2 Risk to Terrestrial Plants

The LOC for non-target monocots adjacent to hexazinone use areas for granular and pelleted uses 

was exceeded across all uses for dry areas and semi-aquatic areas. Because it is a granular or 

pelleted formulation, there is negligible spray drift. For non-listed species, the lowest application 

rate resulted in an RQ minimally above the LOC for nontarget monocots. For dry areas, the RQs 

ranged from 1.22 to 15.4 for non-listed species and 4.03 to 51.2 for listed species. For semi-aquatic 

areas, the RQs ranged from 12.1to 154 for nonlisted species and 40.3 to 512 for listed species. 

Results have been tabulated in Table 40. 
Page 72 of 133

Table 40. RQs for Nontarget Monocots Adjacent to Hexazinone Use Areas1 for Granular 

and Pelleted Uses

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Monocot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic 

Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Rangeland Ground: 0.63 <0.1 <0.1 1.22 4.03 12.1 40.3

Conifer Release

Ground: 3.0 <0.1 <0.1 5.79 19.2 57.9 192.

Ground: 4.0 <0.1 <0.1 7.72 25.6 77.2 256

Forestry Site Prep

Ground: 4.7 <0.1 <0.1 9.07 30.0 90.7 300

Ground: 4.0 <0.1 <0.1 7.72 25.6 77.2 256

Ground: 6.1 <0.1 <0.1 11.7 39.0 117 390

Non-Crop sites

Ground: 7.4 <0.1 <0.1 14.2 47.3 142 473

Ground: 8.0 <0.1 <0.1 15.4 51.2 154 512

1

LOCfor listed and non-listed species = 1; values in bold exceed the LOC

The LOC for non-target dicots adjacent to hexazinone use areas for granular and pelleted uses 

was exceeded across all uses for dry areas and semi-aquatic areas. The lowest RQs are found in 

dry areas. For nonlisted species in dry areas, the RQs range from 5.00 to 63.4 and 4.53 to 57.5 

for listed species. For nonlisted species in semi-aquatic areas, RQs range from 50.0 to 634 and 

45.3 to 575 for listed species. 

Table 41. RQs for Nontarget Dicots Adjacent to Hexazinone Use Areas1 for Granular 

and Pelleted Uses

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Monocot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic 

Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Rangeland Ground: 0.63 <0.1 <0.1 5.00 4.53 50.0 45.3

Conifer Release

Ground: 3.0 <0.1 <0.1 23.8 21.5 238 215

Ground: 4.0 <0.1 <0.1 31.7 28.7 317 287

Forestry Site Prep

Ground: 4.7 <0.1 <0.1 37.3 33.8 373 338

Ground: 4.0 <0.1 <0.1 31.7 28.7 317 287

Ground: 6.1 <0.1 <0.1 48.4 43.8 484 438

Non-Crop sites

Ground: 7.4 <0.1 <0.1 58.7 53.2 587 532

Ground: 8.0 <0.1 <0.1 63.4 57.5 634 575

1

LOCfor listed and non-listed species = 1; values in bold exceed the LOC

4.4 Risk Description
Page 73 of 133

In risk description, the results from the risk estimation are interpreted and synthesized into overall 

risk conclusions. This description considers other lines of evidence (e.g., monitoring data, field 

data, refined exposure and effects modeling) for characterizing ecological risk. In addition, the 

risk description also contains a discussion of relevant sources of uncertainty in the risk assessment 

and sensitivity of the risk assessment findings to important methodological assumptions. The risk 

description also addresses other concerns including risks to threatened and endangered species, a 

discussion of uncertainty, and the sensitivity of risk conclusions to assumptions made in the 

assessment. 

4.4.1 Risk to Aquatic Organisms

A summary of the maximum hexazinone acute and chronic RQ values derived for aquatic animals 

is shown in Table 42. The RQ values for freshwater fish, freshwater invertebrates and 

estuarine/marine invertebrates do not exceed the acute or chronic LOC for listed or nonlisted 

species for flowable or granular uses. Specifically, the chronic values are multiple orders of 

magnitude below the chronic LOC of 1.0. There is no data available for estuarine/marine fish, 

however based on the toxicity of hexazinone to freshwater fish, there is no risk expected to 

estuarine/marine fish. 

Table 42. Summary of aquatic animal risk profile for Hexazinone

Exposure FW Fish RQ FW Invert. RQ SW Invert. RQ

Acute 0.002 0.004 0.032

Chronic 0.038 0.008 0.063

RQ values based on the maximum aquatic EECs derived from the 05_ CA rights of way scenario; see 

Risk Estimation Section 5.1 for derivation of these RQ values 

Characterization of UER and TTR data

RQs for freshwater fish, freshwater invertebrates and estuarine/marine invertebrates were 

calculated using the EECs for Hexazinone including the TTRs and UERs. A comparison of the 

TTR and UER EECs to the parent and degradates EECs show that the TTR and UER EECs are 

vary no more than 5 μg/L from parent only EECs. Thus the resulting RQs of the TTS and UER 

are not significantly different from the parent and degradates and do not change the risk picture 

for any aquatic organisms. The reason for the similarity between the EECs for the parent plus 

degradates (TTRs) and parent plus degradates plus UERs is that the levels of UERs were high only 

in the aerobic soil metabolism study. In both the aerobic and anaerobic aquatic metabolism studies 

the levels of UERs were very low.

Risk Characterization Fish:

Based on the results of risk estimation, EFED does not perceive the potential for risk to freshwater 

fish. None of the RQ values for freshwater fish exceed the applicable acute or chronic risk LOC. 

Additionally there were no incidents reported in EIIS; there is some uncertainty concerning IDS, 

as it is unknown if fish were involved in the reported wildlife incidents, however considering the 
Page 74 of 133

toxicity profile for fish, this is unlikely.

There is some uncertainty regarding the lack of toxicity data for estuarine/marine fish. However, 

based on the lack of toxicity as is illustrated in freshwater fish, it can be assumed that 

estuarine/marine fish will exhibit a similar response. Additionally, based on the mode of action of 

the chemical, risk to aquatic animals is assumed to be low.

Risk Characterization Aquatic Invertebrates:

Based on the results of risk estimation, EFED does not perceive the potential for risk to freshwater 

and estuarine/marine invertebrates. None of the acute or chronic RQ values resulted in 

exceedances for the listed or nonlisted species. Additionally, there were no incidents reported in 

EIIS, AIMS, or IDS.

Risk Characterization Aquatic Plants:

A summary of the maximum hexazinone RQ values derived for aquatic plants is shown in Table

43. The RQ values for aquatic vascular and nonvascular plants for both listed species and nonlisted 

species exceed the LOC. These toxicity values are consistent with the mode of action of the 

chemical in that it is an herbicide acting through photosynthesis inhibition. The primary exposure 

is through run off leaching rather than spray drift. There were no incidents reported for aquatic 

plants in EIIS or IDs. 

Table 43. Summary of Aquatic Plant Risk Profile for Hexazinone

Exposure Aquatic Vascular Aquatic Nonvascular

Listed 25.1 163

Nonlisted 17.4 93.2

RQ values based on the terrestrial EECs derived from 05 CA Rights of way; see Risk Estimation 

for derivation of these RQ values

Bolded values exceed LOC risk

4.4.2 Risk to Terrestrial Organisms

A summary of the maximum hexazinone acute and chronic RQ values derived for terrestrial 

animals is shown in Table 44. The dose based and dietary based RQ values for both birds and 

mammals exceed and acute and chronic LOC. Avian acute dose based risk exceeds Nonlisted 

species LOC. The avian dietary RQ is the only value that exceeds the LOC for listed species but 

not for nonlisted species; all other RQs for avian dose based, and mammalian dose and dietary 

based exceed the LOC for listed and nonlisted species.

Table 44. Summary of the Avian and Mammalian Risk Profile for 

Hexazinone for Non Granular Uses

Exposure Avian Dose 

RQ

Avian Dietary 

RQ

Mammalian 

Dose RQ

Mammalian 

Dietary RQ
Page 75 of 133

Acute 1.34 0.38 1.57 NA

Chronic NA 1.92 83.2 9.60

RQ values based on the terrestrial EECs derived from 05 CA Rights of way; see Risk Estimation 

for derivation of these RQ values

Bolded values exceed LOC risk

Risk Characterization Birds for Non-Granular Uses:

Based on the results of risk estimation, there is a potential risk to avian species. The maximum 

dose based RQ was 1.34 and exceeds the LOC for listed and nonlisted species. An examination 

of the entire Acute dose-based RQ values for birds exposed to hexazinone, Table 31, shows that 

the LOC exceedances for nonlisted species are concentrated in small birds consuming short grass. 

Of the eight uses resulting in LOC exceedances for birds, four of them occurred for nonlisted 

species. For other bird sizes, the LOC exceedances for listed species tended to concentrate around 

the short grass feed items, followed by tall grass and then broadleaf plants. The dietary and chronic 

based RQs exhibited a similar pattern of RQs increased with the food items as previously listed.

There is uncertainty in the acute toxicity data for birds due to the absence of passerine data. A 

passerine study was requested as part of the DCI released with the 2010 Problem Formulation for 

Hexazinone (D369269). The submitted study (MRID 48718401) was deemed invalid and did not 

fill the guideline requirement for 850.2100; the submitted document consisted of a simulation of 

existing data and was not an actual passerine study that was conducted in a lab. 

Due to the lack of available passerine data, the avian RQs were based on toxicity values for a 

mallard. In the absence of passerine data, there is significant uncertainty as to whether or not the 

RQs predict a sensitivity representative of smaller birds on the field which tend to exhibit higher 

sensitivities than larger birds.

Risk Characterization Mammals for Non-Granular Uses:

Based on the results of risk estimation, there is a potential risk to small mammalian species. The 

maximum dose based RQ was 0.79 and exceeds the LOC for listed and nonlisted species. An 

examination of the entire Acute Dose-Based RQ values for Mammals Exposed to Hexazinone, 

Table 33, shows that the LOC exceedances for nonlisted species are concentrated in small 

mammals consuming short grass, however there are still LOC exceedances for nonlisted species

for medium mammals. 

Chronic dietary based RQs show a maximum of 9.60; exceedances are found across all uses and 

dietary items, with the exception of fruits, pods, seeds etc. For tall grass and broadleaf plants, 

there was no LOC exceedance for the lowest application rate, industrial turfgrass and for 

arthropods there were only four uses resulting in LOC exceedances. Chronic dose-based RQs, 

found in Table 34, show a maximum of 83.2 and are found across all uses, mammalian sizes, and 

feeding strategies with the exception of granivores. For the alfalfa and turfgrass, the two lowest 

application rates, there is no LOC exceedance for small medium or large mammals consuming 
Page 76 of 133

fruits, pods, seeds etc. 

 

Risk Characterization for Birds and Mammals for Granular Uses:

There are eight uses of hexazinone that are granular or pelleted and are not assessed via T-REX 

spray drift calculations. The LD50 per ft2 analysis can be found in the risk estimation for all eight 

uses. Because there was no data available on the mass of the granule, no further characterization 

can be made to the granular uses. Information available stated that the granular formulations 

were “Ultra Low Weight” and were intended to have smaller granules than the pelleted 

formulations. The model assumes that 100% of the granules are available for consumption; 

some of the labels instruct the granular formulated products to be watered into the soil, this there 

is some uncertainty as to what percent of the granules would be available for the organisms to 

consume. The size of the granules used in the formulations are needed to properly characterize 

the risk to small birds and mammals; until this information is submitted risk to birds and 

mammals due to granular uses will be considered an uncertainty. There is additional uncertainty 

as to the likelihood that the birds and mammals would purposefully consume the granules. 

Risk Characterization for Birds and Mammals for Pelleted Uses:

This characterization will seek to refine the pelleted formulations of hexazinone. There are eight 

uses of hexazinone that are granular or pelleted and are not assessed via T-REX spray drift 

calculations. The LD50 per ft2 analysis can be found in the risk estimation for all eight uses. This 

characterization will seek to refine the pelleted formulations; because there was no data available 

on the mass of the granule, no further characterization can be made to the granular uses. The 

characterization was run for the highest application rate, Non-Crop Site. The pellets for hexazinone 

formulated product are 640 mg4

—due to the size of the pellet, it is assumed that it will only be 

potentially consumed by the largest weight class of birds and mammals. The output from T-REX 

can be found in Appendix G. 

Table 45. shows the estimated of the number of granules, and area foraged needed for a 1000 g 

bird to achieve the EEC equivalent dose that would trigger an exceedance of the acute risk (0.1) 

and acute endangered species (0.5) LOC for the Non-Crop Site pelleted formulation used at an 

application rate of 8.0 lb ai/A; this use scenario is representative of the highest application rate. 

This analysis shows that a 1,000 gram bird would have to consume less than one pellet to exceed 

the LOC for listed species and would consume a little over three pellets to exceed the LOC for 

nonlisted species. 

Table 45. Estimates of the number of granules, area foraged, and process time needed for 

a 1000 g bird to achieve the EEC equivalent dose that would trigger an exceedance of the 

acute risk (0.1), and acute endangered species (0.5) level of concern for the Non-Crop Site 

Pelleted formulated at 8 lb ai/A

 4 Based on the number 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 

06/05/2015).
Page 77 of 133

EPA Level of Concern

0.1 0.5

EEC Equivalent Dose requires to reach the specified LOC (mg 

ai/kg-bw) 292 1,460

Number of Consumer Granules required to reach the specified 

LOC 0.61 3.05

Area of field to be 

foraged (ft 2)

Assuming 100% feeding efficiency 4.68 ft2 23.3 ft2

Assuming 50% feeding efficiency 9.36 ft2 46.7 ft2

Assuming 10% feeding efficiency 46.8 ft2 233 ft2

Table 46. shows the estimated of the number of granules, area foraged needed for a 1000 g 

mammal to achieve the EEC equivalent dose that would trigger an exceedance of the acute risk 

(0.1) and acute endangered species (0.5) LOC for the Non-Crop Site pelleted formulation used at 

an application rate of 8.0 lb ai/A; this use scenario is representative of the highest application rate. 

This analysis shows that the acute LOC would be exceeded for both listed and non listed species 

should they consume one granule or more.

Table 46. Estimates of the number of granules, area foraged, and process time needed for 

a 1000 g mammal to achieve the EEC equivalent dose that would trigger an exceedance of 

the acute risk (0.1), and acute endangered species (0.5) level of concern for the Non-Crop 

Site Pelleted formulated at 8 lb ai/A

EPA Level of Concern

0.1 0.5

EEC Equivalent Dose requires to reach the specified LOC (mg 

ai/kg-bw) 92.3 462

Number of Consumer Granules required to reach the specified 

LOC 0.19 0.95

Area of field to be 

foraged (ft 2

)

Assuming 100% feeding efficiency 1.48 ft2 7.40 ft2

Assuming 50% feeding efficiency 2.95 ft2 14.8 ft2

Assuming 10% feeding efficiency 14.8 ft2 74.0 ft2

Risk Characterization Pollinators:

A 48-hour acute contact study was conducted with the honeybee (Apis mellifera), MRID 

41216502. The study concluded that hexazinone was relatively nontoxic to bees based on an LD50

> 100 μg/bee with a NOAEC of 100 μg/L. The toxicity of hexazinone to larval bees on an acute 

and chronic basis, and the chronic toxicity of hexazinone to adult bees is unknown and will be 

considered an uncertainty at this time.

To characterize risk to pollinators, a back calculation was used to understand the EEC required to 

exceed the Agency’s acute risk LOC of 0.4. With an endpoint of >100 μg/bee, the EEC which 

could result in an LOC exceedance is 400μg. 
Page 78 of 133

Risk Characterization Terrestrial Plants:

Based on the results of risk estimation there is potential risk to nontarget terrestrial plants. A 

summary of the maximum hexazinone RQ values derived for terrestrial plants is shown in Table

47. The RQ values for monocots and dicots for both listed and nonlisted species exceed the LOC. 

These toxicity values are consistent with the mode of that action in that it is an herbicide acting 

through photosynthesis inhibitions. There were a number of incidents reported for terrestrial plants 

in EIIS and IDS. These incidents have been summarized in Table 23.

Table 47. Summary of Terrestrial Plant Risk Profile for Hexazinone

Exposure Monocot Dicot

Listed 522 587

Nonlisted 157 647

RQ values based on the terrestrial EECs derived from 05 CA Rights of way; see Risk Estimation 

for derivation of these RQ values

Bolded values exceed LOC risk

Spray Drift Analysis

A spray drift analysis was conducted for the ground and aerial applications of hexazinone. In order 

to conduct this analysis, the most sensitive species (terrestrial plants) was selected. The tomato 

seedling emergence endpoint was found to be the most sensitive of all terrestrial plant species 

(EC25 = 0.00695 lb a.i./A). In short, a buffer zone needed to approach the LOC was calculated 

(LOC for terrestrial plants is 1.0). The example label used for this analysis was Velpar L. For this 

product, there are no special spray drift restrictions, other than the spray volume, which is specified 

in specific instances.

For ground applications, the following assumptions were made: high boom height, ASABE Very 

Fine to Fine drop size distribution (DSD), 90th percentile data percentile (USEPA 2013). For aerial 

applications, the following assumptions were made: Tier II Aerial application using ASABE Fine 

to Fine to Medium DSD, 5 gallons diluted product per acre, wind speed 10 mph, aircraft Wasp 

Helicopter, boom height 10 feet.

The Terrestrial Point module calculates the buffer zone required. It was found that for the ground 

applications, the buffer needed ranged from 384 feet for turfgrass to >1000 feet (out of range) for 

non-crop sites. For all the aerial applications, the buffer zone was >1000 feet (out of range).

Table 38. Needed Buffer Distances to Approach or Exceed the Non-Listed LOC for 

Terrestrial Plant Exposure for Hexazinone, Using EFED’s Default Assumptions

Scenario App. Rate

(lb a.i./A) App. Method Need Buffer Distance (ft) App. Method Need Buffer Distance (ft)

Alfalfa 1.5 Ground 476 Aerial >1000

Sugarcane in HI 3.6 Ground 869 Aerial >1000

Blueberries (low bush) 3 Ground 771
Page 79 of 133

Table 38. Needed Buffer Distances to Approach or Exceed the Non-Listed LOC for 

Terrestrial Plant Exposure for Hexazinone, Using EFED’s Default Assumptions

Scenario App. Rate

(lb a.i./A) App. Method Need Buffer Distance (ft) App. Method Need Buffer Distance (ft)

Non-crop sites (weed and brush 

control)

6 for aerial;

8 for ground Ground >1000

Aerial 

(helicopter) >1000

Conifer release in Eastern and 

Lakes states 4 Ground 932

Aerial 

(helicopter) >1000

Christmas trees 2 Ground 584 Aerial >1000

Pastures/Rangeland in Eastern US 4 Ground 932

Bermudagrass/Bahiagrass; 

Industrial turfgrass 1.125 Ground 384

Out of range is >1000 feet for aerial and ground applications.

For additional characterization, runs were performed using different less conservative 

assumptions. For ground applications, the following assumptions were made: low boom height, 

ASABE Fine to Medium/Coarse drop size distribution (DSD), 90th percentile data percentile. For 

aerial applications, the following assumptions were made: Tier II Aerial application using ASABE 

Medium to Coarse DSD, 5 gallons diluted product per acre, wind speed 10 mph, aircraft Wasp 

Helicopter, boom height 10 feet.

As expected, the buffer distances were lower with the less conservative assumptions. It was found 

that for the ground applications, the buffer needed ranged from 66 feet for turfgrass to 709 feet for 

non-crop sites. For all the aerial applications, the buffer zone was 932 feet for alfalfa and >1000 

feet (out of range) for all the other crops.

Table 49. Needed Buffer Distances to Approach or Exceed the Non-Listed LOC for 

Terrestrial Plant Exposure for Hexazinone, Using Less Conservative Assumptions

Scenario App. Rate

(lb a.i./A) App. Method Need Buffer Distance (ft) App. Method Need Buffer Distance (ft)

Alfalfa 1.5 Ground 95 Aerial 932

Sugarcane in HI 3.6 Ground 292 Aerial >1000

Blueberries (low bush) 3 Ground 236

Non-crop sites (weed and brush 

control)

6 for aerial;

8 for ground Ground 709

Aerial 

(helicopter) >1000

Conifer release in Eastern and 

Lakes states 4 Ground 331

Aerial 

(helicopter) >1000

Christmas trees 2 Ground 141 Aerial >1000

Pastures/Rangeland in Eastern US 4 Ground 331

Bermudagrass/Bahiagrass; 

Industrial turfgrass 1.125 Ground 66

Out of range is >1000 feet for aerial applications.

4.5 Endangered species

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the National 

Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department of 

Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks to 
Page 80 of 133

listed species from pesticides. The Interim Approaches were developed jointly by the agencies in 

response to the National Academy of Sciences’ (NAS) recommendations and reflect a common 

approach to risk assessment shared by the agencies as a way of addressing scientific differences 

between the EPA and the Services. The NAS report outlines recommendations on specific 

scientific and technical issues related to the development of pesticide risk assessments that EPA 

and the Services must conduct in connection with their obligations under the Endangered Species 

Act (ESA) and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on November 

15, 2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 

Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and Evaluation 

Group (SFIREG) meetings, and held a stakeholder workshop in April 2014, allowing additional 

opportunities for stakeholders to comment on the Interim Approaches. As part of a phased, 

iterative process for developing the Interim Approaches, the agencies will also consider public 

comments on the Interim Approaches in connection with the development of upcoming 

Registration Review decisions. The details of the joint Interim Approaches are contained in the 

white paper “Interim Approaches for National-Level Pesticide Endangered Species Act 

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 

Report,” dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the Interim 

Approaches to assess the potential risks of pesticides to listed species and their designated critical 

habitat, this preliminary risk assessment for hexazinone does not contain a complete ESA analysis 

that includes effects determinations for specific listed species or designated critical habitat. 

Although EPA has not yet completed effects determinations for specific species or habitats, for 

this preliminary assessment EPA conducted an assessment for all taxa of non-target wildlife and 

plants that assumes for the sake of the assessment that listed species and designated critical habitats 

may be present in the vicinity of the application of hexazinone. This screening level assessment 

will allow EPA to focus its future evaluations on the types of species where the potential for effects 

exists once the scientific methods being developed by the agencies have been fully vetted. This 

risk assessment for hexazinone indicates potential risks of direct effects to listed aquatic plants, 

terrestrial plants, birds and mammals on some of its registered use sites. Listed species of birds, 

mammals and terrestrial invertebrate taxa may also be affected through indirect effects because of 

the potential for direct effects on listed and non-listed species upon which such species may rely. 

Potential direct effects on listed birds, mammals and terrestrial invertebrates from the use of 

hexazinone may be associated with modification of Primary Constituent Elements (PCEs) of 

designated critical habitats, where such designations have been made. Once the agencies have 

fully developed and implemented the scientific methods necessary to complete risk assessments 

for endangered and threatened (listed) species and their designated critical habitats, these methods 

will be applied to subsequent analyses for hexazinone as part of completing this registration 

review. 
Page 81 of 133

4.6 Uncertainties and Limitations

4.6.1 Input Parameters

It appears that the main route of dissipation of hexazinone is aerobic soil metabolism (even though 

it occurs at moderately slow rates). There are four half-lives available (refer to Tables 5 for the 

half-lives of the parent only). Three of them were obtained at 200C; temperature adjustment was 

required for the SWCC, resulting in shorter half-lives at 250C (refer to Table 6 for the half-lives 

for the TTRs).

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-lives obtained. For example, the 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 unextracted 

residues, they include only the parent compound). The aerobic aquatic metabolism study (MRID 

49109901) was conducted for a period of only 100 days, compared to half-lives of 528-719 days 

(for the parent only). Meanwhile, the anaerobic aquatic metabolism study (MRID 49109902) was 

conducted for 101 days, compared to a half-life of 482-961 days (for the parent only). 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 were not used in modeling in the SWCC, since the 

anaerobic soil metabolism is not used as an input value in the model when anaerobic aquatic 

metabolism studies are available. The fact that multiple soils and sediments were available tends 

to reduce the uncertainty; however, the short duration of the studies increases the uncertainty in 

the half-life estimates.

4.6.2 Application Rates

In this assessment, a number of uses were assessed; rights-of-ways (non-agricultural crop) and 

sugarcane (conventional agricultural crop) were found to yield the highest EECs. The 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.

4.6.3 Environmental Fate Database

Regarding the input values used in this risk assessment, the environmental fate database for 

hexazinone was considered to be complete and no estimated values, or uncertainty factors were 

used. See also Input Parameters above.

4.6.4 Application Information

Meteorological data and crop profiles, as well as best professional judgment, and label 

information, were used to establish an application date for modeling; however, the selected date 
Page 82 of 133

may not represent the intended or actual application dates. The application date used for model 

runs can significantly alter the EECs; thus, EECs reported could over or under predict the potential 

exposure. The dates of application used in this risk assessment were generally selected based on 

the crop cycle and label information. It is unclear how much the application dates differ from the 

typical timing of application, which is based on pest pressure, and in some instances, the weather 

forecast.

4.6.5 Number of Seasons per Year

Although the maximum number of applications from the label for some of the uses is one, for 

certain uses the maximum number of applications per year is not specified. For this assessment, 

one application per year for those other uses was assumed, based on additional information from 

the label. For example, blueberry uses may be modeled at a maximum of one application per year 

due to no application within 450 days of harvest (therefore, on average, fewer than one application 

per year would be used). Pineapple may be modeled as one application per year due to the growing 

season, which is nearly a year long (note that pineapple was not modeled in this assessment). Noncrop 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; therefore, it is likely that a waiting period would occur prior to the next application. 

Hexazinone is usually applied in the spring after ground thaws, or in the fall before snowfall (see 

Timing of Application in Table 3).

4.6.6 Use of Maximum Labeled Rates

According to the labels, hexazinone is an herbicide to which plants can develop resistance if 

applied repeatedly in the same field in consecutive years. “Naturally-occurring resistant biotypes 

may survive a correctly applied herbicide treatment, propagate, and become dominant in that 

field.” For that reason, it is recommended to avoid its consecutive use and to base its use on a 

comprehensive Integrated Pest Management (IPM) program “that can include biological, cultural, 

and genetic practices aimed at preventing economic pest damage.” Thus, even though the initial 

EECs were based on maximum application rates and annual applications, it appears unlikely that 

users will apply this chemical under these circumstances on a yearly basis for 30 consecutive years, 

like the modeling performed in this ecological risk assessment. The frequency at which actual 

uses approach this maximum use application may be dependent on pest resistance, timing of 

applications, cultural practices, and market forces.

4.6.7 Unextracted Radioactivity

Regarding the aerobic soil metabolism studies, there were observed high levels of unextracted 

radioactivity. (The soils were extracted three times by shaking for 30 minutes with methanol:water 

(80:20, v:v).) In this assessment, besides the EECs calculated using the half-lives for the total 

toxic residues (TTRs, these are hexazinone and its degradates of concern, corrected half-life values 

at 25°C: 147, 294, 378, and 604 days, 90% upper confidence limit 512.2 days), EECs were also 

calculated using half-lives for the TTRs plus the unextracted residues (UERs, corrected half-life 

values at 25°C: 432, 762, 1134, and 1023 days, 90% upper confidence limit 1,093 days). These 

EECs provide upperbound estimates of what could be the EECs should the unextracted 
Page 83 of 133

radioactivity be residues of ecotoxicological concern. Nonetheless, it was observed that the EECs 

derived for the TTRs and for the TTRs plus the UERs were similar and that the UERs were not 

the risk drivers.

4.6.8 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 happens 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. Dissolved, 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. Note 

that the latter three processes are not actually simulated by PRZM when calculating runoff (they 

only come into play in simulating infiltration).

Uncertainties 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 (i.e., half-life inputs) 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

(an average value is used). The natural variation in soils adds to the uncertainty of 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 intensity, antecedent soil moisture, and surface 

water temperatures can cause actual aquatic concentrations to differ for the modeled values.

4.6.9 Aquatic Modeling with the SWCC

The standard ecological water body scenario (VVWM standard pond) used to calculate potential 

aquatic exposure to pesticides such as hexazinone is intended to represent conservative estimates, 

and to avoid underestimating the actual exposure. The standard scenario consists of application to 

a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3

) pond with no outlet. Exposure 

estimates generated using the VVWM pond is intended to represent a wide variety of vulnerable 

water bodies that occur at the top of watersheds including prairie pot holes, playa lakes, wetlands, 

vernal pools, man-made and natural ponds, and intermittent and lower order streams. As a group, 

there are factors that make these water bodies more or less vulnerable than the VVWM pond. 

Static water bodies that have larger ratios of pesticide-treated drainage area to water body volume 

would be expected to have higher peak EECs than the VVWM pond. These water bodies will be 

either smaller in size or have larger drainage areas. Smaller water bodies have limited storage 

capacity and thus may overflow and carry pesticide in the discharge, whereas the VVWM pond 

has no discharge. As watershed size increases beyond 10-hectares, it becomes increasingly 

unlikely that the entire watershed is planted with a single crop that is all treated simultaneously 
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with the pesticide. Headwater streams can also have peak concentrations higher than the VVWM 

pond, but they likely persist for only short periods of time and are then carried and dissipated 

downstream.

The Agency acknowledges that there are some unique aquatic habitats that are not accurately 

captured by this modeling scenario and modeling results may, therefore, under- or over-estimate 

exposure, depending on a number of variables. For example, some organisms may inhabit water 

bodies of different size and depth and/or are located adjacent to larger or smaller drainage areas 

than the VVWM pond. However, the existing VVWM pond represents the best currently available 

approach for estimating aquatic exposure to pesticides.

In general, the linked PRZM/VVWM model (through the SWCC GUI) produces EECs 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 happens 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. Dissolved, adsorbed, and vaporphase 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.

Uncertainties 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 conservative estimates of the mean half-life, given the 

observed variability in the limited sample size of data. Mobility input values are chosen to be 

representative of conditions in the environment (an average value). The natural variation in soils 

adds to the uncertainty of 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 intensity, 

antecedent soil moisture, and surface water temperatures can cause actual aquatic concentrations 

to differ for the modeled values.

4.6.10Uncertainties Regarding Dilution and Chemical Transformations in 

Estuaries

SWCC modeled EECs are intended to represent exposure of aquatic organisms in relatively small 

ponds and low-order streams. Therefore it is likely that EECs generated from the SWCC model 

will over-estimate potential concentrations in larger receiving water bodies such as estuaries, 

embayments, and coastal marine areas because chemicals in runoff water (or spray drift, etc.) 

should be diluted by a much larger volume of water than would be found in the ‘typical’ VVWM 

pond. However, as chemical constituents in water draining from freshwater streams encounter 

brackish or other near-marine-associated conditions, there is potential for important chemical 

transformations to occur. Many chemical compounds can undergo changes in mobility, toxicity, 

or persistence when changes in pH, Eh (redox potential), salinity, dissolved oxygen (DO) content, 
Page 85 of 133

or temperature are encountered. For example, desorption and re-mobilization of some chemicals 

from sediments can occur with changes in salinity (Jordan et al., 2008; Means, 1995; Swarzenski

et al., 2003), changes in pH (e.g., Wood and Baptista 1993), Eh changes (Velde and Church, 1999; 

Wood and Baptista, 1993), and other factors. Thus, although chemicals in discharging rivers may 

be diluted by large volumes of water within receiving estuaries and embayments, the 

hydrochemistry of the marine-influenced water may negate some of the attenuating impact of the 

greater water volume; for example, the effect of dilution may be confounded by changes in 

chemical mobility (and/or bioavailability) in brackish water. In addition, freshwater contributions 

from discharging streams and rivers do not instantaneously mix with more saline water bodies. In 

these settings, water will commonly remain highly stratified, with fresh water lying atop denser, 

heavier saline water – meaning that exposure to concentrations found in discharging stream water 

may propagate some distance beyond the outflow point of the stream (especially near the water 

surface). Therefore, it is not assumed that discharging water will be rapidly diluted by the entire 

water volume within an estuary, embayment, or other coastal aquatic environment. SWCC model 

results should be considered consistent with concentrations that might be found near the head of 

an estuary unless there is specific information – such as monitoring data – to indicate otherwise. 

Conditions nearer to the mouth of a bay or estuary, however, may be closer to a marine-type 

system, and thus more subject to the notable buffering, mixing, and diluting capacities of an open 

marine environment. Conversely, tidal effects (pressure waves) can propagate much further 

upstream than the actual estuarine water, so discharging river water may become temporarily 

partially impounded near the mouth (discharge point) of a channel, and resistant to mixing until 

tidal forces are reversed.

The Agency does not currently have sufficient information regarding the hydrology and 

hydrochemistry of estuarine aquatic habitats to develop alternate scenarios for assessed species 

that inhabit these types of ecosystems. The Agency acknowledges that there are unique brackish 

and estuarine habitats that may not be accurately captured by SWCC modeling results, and may, 

therefore, under- or over-estimate exposure, depending on the aforementioned variables.

4.6.11 Terrestrial Exposure Modeling

There is some uncertainty regarding the extent to which the chronic dose based RQs exceed the 

LOC. For the model inputs, the default value of 35 days was used for the foliar dissipation halflife. Due to the magnitude of the half-life, there is uncertainty surrounding the T-REX generated

chronic RQs; these EECs compared to those exhibited on the field may be different because TREX is unable to model the dissipation of the pesticide in the environment. These RQs may be 

refined in the future with the submittal of a foliar dissipation half-life study. There is additional 

uncertainty in that T-REX assumes that organisms diet consists 100% of one feed item; thus when 

the LOC is triggered for a bird consuming short grass, there is a chance that bird does not derive 

100% of their diet via a single feeding strategy. 

Another terrestrial model, TERRPlant, was used to derive the EECs and RQs for terrestrial plants. 

There are a number of uncertainties concerning this model and its ability to predict the EECs on 

the field. Modeled pesticide concentrations in runoff are dependent solely upon the solubility of 

the pesticide; the amount of pesticide in the runoff does not consider other relevant transport 

properties of the pesticide. 
Page 86 of 133

4.6.12 Formulation Toxicity

There are seven multi-active ingredient co-formulations that include hexazinone with 

sulfometuron or diuron. There are no toxicity studies available with multi a.i. products, thus 

there is uncertainty as to whether the formulation products exhibit additive or synergistic toxicity 

to organisms on the field. 

4.6.13 Size of Granules

There is uncertainty in characterizing risk to birds and mammals because the size of the granules 

in the granular formulations is unknown. This information would enable further characterization 

and an understanding of the number of granules the organism could consume without exceeding

the LOC. Without this information, this characterization is incomplete and considered an 

uncertainty. There is additional uncertainty in the attractiveness of the pellets and granules to the 

organisms and whether they would be attractive enough for an organism to consume to the extent 

that it would trigger risk.

4.7 Identification of Data Gaps

4.7.1 Environmental Fate

Even though the environmental fate data base for hexazinone is essentially complete, there are two 

environmental chemistry methods (soil and water; MRIDs 45132802 and 45132803), that were 

classified as unacceptable, but upgradable. Portions of the studies appeared to meet guideline 

criteria and may be upgraded with the submission of additional information. For further details, 

refer to the Appendix I.

4.7.2 Environmental Effects

The toxicological database for hexazinone is essentially complete with the exception of 850.2100 

passerine study, and a tier II vegetative vigor and seedling emergence study. Portions of the 

vegetative vigor and seedling emergence study may be upgradeable with the submission of 

additional information. There is additional plant uncertainty with regards to effects on non-target 

woody plants. There is no data available for toxicity of hexazinone to woody plants, as they are 

not part of the standard suite of species submitted in the registrant studies; based on the mode of 

action, risk would be expected. Without toxicity studies, risk to woody plants remains an 

uncertainty. In accordance with the pollinator guidance, there are a number of data gaps 

concerning pollinators; these include larval acute toxicity, larval chronic toxicity, residue on 

foliage, adult chronic toxicity and semi-field test. There is currently one acute contact honeybee 

study available; the study found an LD50>100 μg/bee. However, there is uncertainty concerning 

the systemic toxicity of hexazinone and the potential affects this may have on pollinators. 
Page 87 of 133

References

Food and Agriculture Organization of the United Nations. 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 Division: 

Rome, 2000. 

http://www.fao.org/DOCREP/003/X2570E/X2570E00.htm (accessed January 29, 2015).

Jordan, T. E., Cornwell, J. C., Walter, R. B., & Anderson, J. T. 2008. Changes in phosphorus 

biogeochemistry along an estuarine salinity gradient. Limnology and Oceanography 53(1), 

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Means, J. C. 1995. Influence of salinity upon sediment-water partitioning of aromatic 

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Swarzenski, P. W., Porcelli, D., Andersson, P. S., & Smoak, J. M. 2003. The behavior of U- and 

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Effects Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of 

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http://www.epa.gov/oppfead1/endanger/consultation/ecorisk-overview.pdf (accessed 

January 27, 2015).

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Transport of Pesticides, Version 2.1. Office of Chemical Safety and Pollution Prevention, 

Office of Pesticide Programs, Environmental Fate and Effects Division, dated October 22, 

2009 and issued November 10, 2009. Available online at: 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm (accessed 

January 27, 2015).

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of Concern in Problem Formulations for Registration Review, Registration Review Risk 

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from Donald Brady dated and approved December 20, 2013. Office of Pesticide Programs. 
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Pesticide Programs. Environmental Fate and Effects Division. URL: 

http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/environmental

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Geochemistry, 14(5), 559-568.

Wood, T. M., & Baptista, A. M. 1993. A model for diagnostic analysis of estuarine geochemistry. 

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Appendix A. Environmental Fate / Chemistry Bibliography

161-1 Hydrolysis

MRID Citation Reference

64260 Rhodes, R.C. (1974) Studies with Velpar Weed Killer in Water. (Unpublished study 

received May 7, 1975 under 352-378; submit- ted by E.I. du Pont de Nemours & Co., 

Wilmington, Del.; CDL: 110699-E) 

104982 Rhodes, R. (1973) Biodegradation Studies on 14C-DPX-3674. Interim progress rept., 

Oct 15, 1973. (Unpublished study received Dec 5, 1973 under 352-EX-85; submitted 

by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:223386-O)

41587301 Chrzanowski, R. (1990) Hydrolysis of ?carbon 14| Hexazinone in pH 5, 7 and 9 Buffer 

Solutions: Lab Project Number: AMR 1643-90. Unpublished study prepared by E. I. 

Du Pont de Nemours and Co., Ag Products Dept. 51 p. 

161-2 Photodegradation-water

MRID Citation Reference

64260 Rhodes, R.C. (1974) Studies with Velpar Weed Killer in Water. (Unpublished study 

received May 7, 1975 under 352-378; submit- ted by E.I. du Pont de Nemours & 

Co., Wilmington, Del.; CDL: 110699-E)

104982 Rhodes, R. (1973) Biodegradation Studies on 14C-DPX-3674. Interim progress rept., 

Oct 15, 1973. (Unpublished study received Dec 5, 1973 under 352-EX-85; submitted 

by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:223386-O) 

41587301 Chrzanowski, R. (1990) Hydrolysis of ?carbon 14| Hexazinone in pH 5, 7 and 9 Buffer 

Solutions: Lab Project Number: AMR 1643-90. Unpublished study prepared by E. I. 

Du Pont de Nemours and Co., Ag Products Dept. 51 p. 

161-3 Photodegradation-soil

MRID Citation Reference

64261 Rhodes, R.C. (1974?) Decomposition of Velpar Weed Killer in Soil. (Unpublished 

study received May 7, 1975 under 352-378; submit- ted by E.I. du Pont de Nemours & 

Co., Wilmington, Del.; CDL: 110699-F) 
Page 90 of 133

41300802 Hawkins, D.; Elsom, L.; Gray, S. (1989) The Photodegradation of ?Carbon-14|-

hexazinone on Soil: HRC Report No. HRC/DPT 197/ 891455; Du Pont Document No. 

AMR-1413-89. Unpublished study prepared by Huntingdon Research Centre Ltd., 

Dept. of Chemical Metabolism and Radiosynthesis. 63 p. 

162-1 Aerobic soil metabolism

MRID Citation Reference

64261 Rhodes, R.C. (1974?) Decomposition of Velpar Weed Killer in Soil. (Unpublished 

study received May 7, 1975 under 352-378; submit- ted by E.I. du Pont de Nemours & 

Co., Wilmington, Del.; CDL: 110699-F) 

104982 Rhodes, R. (1973) Biodegradation Studies on 14C-DPX-3674. Interim progress rept., 

Oct 15, 1973. (Unpublished study received Dec 5, 1973 under 352-EX-85; submitted 

by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:223386-O) 

41807401 Hawkins, D.; Elsom, L.; Kane, T.; et al. (1990) The Metabolism of ?carbon 14|-

Hexazinone in a California Type Soil Under Aerobic Conditions: Lab Project Number: 

HRC/DPT 194/901364: AMR-1329-88. Unpublished study prepared by Huntingdon 

Research Centre Ltd. 68 p. 

42635001 Hawkins, D.; Elsom, L.; Kane, T.; et al. (1993) The Metabolism of (carbon 14)-

Hexazinone in a California Type Soil under Aerobic Conditions: Supplement 1: Lab 

Project Number: HRC/DPT 194/901364. Unpublished study prepared by Huntingdon 

Research Centre Ltd. 17 p. 

48898001 Clark, B. 2012. Aerobic Soil Metabolism of 14C-Hexazinone. Unpublished study 

performed by ABC Laboratories, Inc., Columbia, Missouri; sponsored and submitted 

by E.I. du Pont de Nemours and Company, Wilmington, Delaware. DuPont Study No.: 

32436; ABC Study No.: 66928. Experimental work conducted between June 15, 2011, 

and February 22, 2012 (p. 6). Final report issued July 25, 2012.

162-2 Anaerobic soil metabolism

MRID Citation Reference

48898002 Clark, B. 2012. Anaerobic Soil Metabolism of 14C-Hexazinone. Unpublished study 

performed by ABC Laboratories, Inc., Columbia, Missouri; sponsored and submitted 

by E.I. du Pont de Nemours and Company, Wilmington, Delaware. DuPont Study No.: 

32400; ABC Study No.: 66929. Experimental work conducted between June 22, 2011 

and February 22, 2012 (p. 6). Final report issued July 25, 2012.

162-4 Aerobic aquatic metabolism

MRID Citation Reference
Page 91 of 133

41811801 Chrzanowski, R. (1991) Aerobic Aquatic Metabolism of ?Carbonyl- ?carbon 14|| 

Hexazinone in Madera, California Field Water and Sediment: Lab Project Number: 

AMR 1690-90. Unpublished study prepared by E.I. du Pont de Nemours and Co. 64 p. 

44196301 Chrzanowski, R. (1996) The Degradation of (Carbonyl-(carbon 14))Hexazinone in 

Aerobic Aquatic Sediment Systems Under Natural Sunlight: Lab Project Number: 

AMR 2102-91. Unpublished study prepared by DuPont Agricultural Products. 157 p. 

49109901 Clark, B. 2013. Aerobic Aquatic Metabolism of [14C]DPX-A3674 (Hexazinone) in Two 

Water-Sediment Systems. Unpublished study performed by ABC Laboratories, Inc., 

Columbia, Missouri; sponsored and submitted by E.I. du Pont de Nemours and 

Company, Wilmington, Delaware. DuPont Study No.: 32435; ABC Study No.: 66974. 

Experimental work conducted between April 17, 2012 and October 25, 2012 (p. 6). 

Final report issued January 11, 2013.

162-3 Anaerobic aquatic metabolism

MRID Citation Reference

41807402 Hawkins, D.; Elson, L.; Kane, T.; et al. (1990) The Anaerobic Aqua- tic Metabolism of 

?carbon 14|-Hexazinone: Lab Project Number: AMR-1328-88: HRC/DPT 193/901475. 

Unpublished study prepared by Huntingdon Research Centre Ltd. 80 p. 

42657301 Hawkins, D.; Elsom, L.; Kane, T.; et al. (1993) The Anaerobic Aquatic Metabolism of 

(carbon 14)-Hexazinone: Supplement 1: Analysis of 2 Additional Non-Sterile 

Anaerobic Water-Sediment Systems after 365 Days Incubation and Structural 

Assignment of Metabolite 2: Lab Project Number: HRC/DPT 193/901475: AMR-1328-

88. Unpublished study prepared by Huntingdon Research Centre Ltd. 20 p. 

49109902 Clark, B. 2013. Anaerobic Aquatic Metabolism of [14C]DPX-A3674 (Hexazinone) in 

Two Water-Sediment Systems. Unpublished study performed by ABC Laboratories, 

Inc., Columbia, Missouri; sponsored and submitted by E.I. du Pont de Nemours and 

Company, Wilmington, Delaware. DuPont Study No.: 32437; ABC Study No.: 66975. 

Experimental work conducted between April 17, 2012 and October 29, 2012 (p. 6). 

Final report issued January 11, 2013.

163-1 Leach/adsorption/desorption

MRID Citation Reference

64262 Rhodes, R.C. (1974?) Mobility and Adsorption Studies with Velpar Weed Killer on 

Soils. (Unpublished study received May 7, 1975 under 352-378; submitted by E.I. du 

Pont de Nemours & Co., Wilmington, Del.; CDL:110699-G) 

104982 Rhodes, R. (1973) Biodegradation Studies on 14C-DPX-3674. Interim progress 

rept., Oct 15, 1973. (Unpublished study received Dec 5, 1973 under 352-EX-85; 

submitted by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:223386-O) 

41528101 Priester, T.; Sheftic, G. (1990) Batch Equilibrium (Adsorption/Des- orption)of ?Carbon 

14|Hexazinone and Soil Thin-Layer Chromato- graphy Studies of ?Carbon 

14|Hexazinone and Its Major Soil De- grades: Lab Project Number: AMR-1421-89. 

Unpublished study pre- pared by E. I. du Pont de Nemours and Co. 85 p. 
Page 92 of 133

43621501 Sheftic, G. (1995) Batch Equilibrium (Adsorption/Desorption) of (Carbonyl-(carbon 

14)) Hexazinone and its Major Soil Degradates: Lab Project Number: AMR 3019-94. 

Unpublished study prepared by Dupont Agricultural Products and Harris Labs, Inc. 90 

p. 

164-1 Terrestrial field dissipation

MRID Citation Reference

64267 Holt, R.F. (19??) Residues Resulting from Application of DPX-3674 to Soil. 

(Unpublished study received May 7, 1975 under 352- 378; submitted by E.I. du Pont 

de Nemours & Co., Wilmington, Del.; CDL:110699-L) 

42377901 Bollin, E. (1992) Field Soil Dissipation of Hexazinone Herbicide: Lab Project Number: 

AMR 1474-89: 9045258: 9140414. Unpublished study prepared by E. I. du Pont de 

Nemours and Comp., Harris Environmental Tech., Inc. and Enviro Test Laboratories. 

419 p. 

42379201 Bollin, E. (1992) Dissipation of Hexazinone in California Soil Following Application of 

Velpar L Herbicide: Lab Project Number: AMR 1923-91: 9100226: 91-P1368. 

Unpublished study prepared by E. I. du Pont de Nemours and Comp., Harris 

Environmental Technologies, Inc., Enviro-Test Laboratories. 272 p. 

164-3 Forest field dissipation

MRID Citation Reference

72664 Neary, D.G.; Douglass, J.E.; Bush, P.B.; et al. (1980) Movement of Hexazinone in 

Forest Watersheds after a Hand Application of Velpar^(R)I Gridball^(TM)I Pellets for 

Site Preparation. Progress rept., Nov 1980. By U.S. Forest Service, Southeastern 

Experiment Station, Coweeta Hydrologic Laboratory and Univ. of Georgia, Extension 

Poultry Science Dept. and Institute of Ecology. ?: USFS, SE. (FS-SE-1651-26(1); 

available from: U.S. Government Printing Office; published study; CDL:244106-B) 

42336401 Michael, J. (1992) Fate of Hexazinone After Application for Pine Planting Site 

Preparation: Lab Project Number: 1786-90. Unpublished study prepared by Auburn 

University. 700 p. 

165-1 Confined rotational crop

MRID Citation Reference

41008401 Rapisarda, C. (1980) Rotational Crop Studies with ?Carbon 14|-Lab- eledhexazinone: Proj. ID AMR-26-80. Unpublished study prepared by E.I. du Pont de 

Nemours and Co., Inc. 25 p. 

42824001 Rapisarda, C. (1993) Rotational Crop Studies with (carbon 14)-Labeled Hexazinone: 

Supplement No. 1: Lab Project Number: AMR 26-80. Unpublished study prepared by 

E. I. du Pont de Nemours and Co. 11 p. 
Page 93 of 133

43892401 Djanegara, T.; Reardon-Green, L. (1996) Confined Accumulation Study of (4-

Carbonyl-(carbon 14))-Hexazinone (DPX-A3674) in Rotational Crops: Lab Project 

Number: AMR 2800-93. Unpublished study prepared by DuPont Agricultural Products. 

115 p. Relates to letter L0000071. 

165-2 Field rotational crop

MRID Citation Reference

45084101 Brill, F. (2000) Magnitude of Residues of Hexazinone in Rotational Crops Following 

Application of Velpar Herbicide at Maximum Label Rates to Alfalfa: Lab Project 

Number: AMR 4336-97. Unpublished study prepared by E.I. du Pont de Nemours and 

Co. 253 p. {OPPTS 860.1900} 

166-1 Ground water-small prospective

MRID Citation Reference

44060101 DeAndrea, P.; Kelley, J.; Murrow, D.; et al. (1996) A Small-Scale Prospective 

Groundwater Monitoring Study for Hexazinone: Interim Report #2: Site 

Instrumentation: Lab Project Number: AMR 3202-94: 94210. Unpublished study 

prepared by Stone Environmental, Inc.; ABC Labs, Inc.; and DuPont Agricultural 

Products. 142 p. 

44082801 Farajalla, N.; Kelley, J.; Klein, T.; et al. (1996) A Small-Scale Prospective 

Groundwater Monitoring Study for Hexazinone: Interim Report #3: Application and 

First Quarterly Report: Lab Project Number: AMR 3202-94: 94210. Unpublished study 

prepared by Stone Environmental, Inc. and ABC Labs., Inc. 116 p. 

44106601 Kelley, J.; Klein, T.; McElwain, D.; et al. (1996) A Small-Scale Prospective 

Groundwater Monitoring Study for Hexazinone: Interim Report #4: Second Quarterly 

Report, April-June, 1996: Lab Project Number: AMR 3202-94: 94210. Unpublished 

study prepared by DuPont Agricultural Products; Stone Environmental, Inc.; and ABC 

Labs, Inc. 82 p. 

44194001 Kelley, J.; Klein, T.; McElwain, D.; et al. (1996) A Small-Scale Prospective 

Groundwater Monitoring Study for Hexazinone: Interim Report #5, Third Quarterly 

Report: Lab Project Number: 94210: AMR 3202-94. Unpublished study prepared by 

E.I. du Pont de Nemours and Co., Stone Environmental, Inc.; and ABC Laboratories, 

Inc. 97 p. 

44310901 Kelley, J.; Klein, T.; Stone, C.; et al. (1997) A Small-Scale Prospective Groundwater 

Monitoring Study for Hexazinone: Interim Report #6: Fourth Quarterly Report OctoberDecember, 1996: Lab Project Number: AMR 3202-94: 94210. Unpublished study

prepared by Stone Environmental, Inc.; ABC Laboratories, Inc.; and Morse Lab., Inc. 

113 p. 

44389001 Kelley, J.; Klein, T.; Stone, C. et al. (1997) A Small-Scale Prospective Groundwater 

Monitoring Study for Hexazinone: Interim Report #7: Fifth Quarterly Report: JanuaryMarch, 1997: Lab Project Number: AMR 3202-94: 94210:. Unpublished study 

prepared by Stone Environmental, Inc., ABC Labs., Inc. and Morse Labs., Inc. 96 p. 
Page 94 of 133

44442801 Kelley, J.; Klein, T.; Stone, C. et al. (1997) A Small-Scale Prospective Groundwater 

Monitoring Study for Hexazinone: Interim Report #8: Sixth and Seventh Quarter 

Report April-September, 1997: Lab Project Number: 94210: AMR 3202-94. 

Unpublished study prepared by Stone Environmental, Inc., ABC Labs., Inc. and Morse 

Labs., Inc. 80 p. 

45132801 Hanson, C.; Collins, M.; Warren, R. et al. (2000) A Small-Scale Prospective 

Groundwater Monitoring Study for Hexazinone: Lab Project Number: AMR 3202-94: 

94210. Unpublished study prepared by E.I. du Pont de Nemours and Company. 499 

p. 

201-1 Droplet size spectrum

MRID Citation Reference

41322701 Dawson, J. (1989) Velpar L Droplet Size Spectrum Study of Nozzle Systems Used in 

Aerial Application: Lab Project Number: 1707: AMR/1475/89. Unpublished study 

prepared by Agrisearch Inc. 43 p. 

202-1 Drift field evaluation

MRID Citation Reference

41309003 Merricks, L. (1989) Velpar L Aerial Application Spray Drift Study: Lab Project Number: 

1706 : AMR/1478/9. Unpublished study prepared by Agrisearch, Inc. 87 p. 

41309004 Collum, W. (1989) Spray Drift Evaluation of Velpar ULW Herbicide: Lab Project 

Number: AMR/1538/89. Unpublished study prepared by du Pont de Nemours and Co. 

46 p. 

94681 Akesson, N.B.; Yates, W.E. (1980) Report on Field Application and Drift Loss Tests 

with Dupont Herbicides. (Unpublished study received Feb 4, 1982 under 352-378; 

prepared by Univ. of Cali- fornia--Davis, submitted by E.I. du Pont de Nemours & Co., 

Inc., Wilmington, Del.; CDL:246737-A) 

850.6100 Environmental Chemistry Method/Independent Laboratory 

Validation

45132802 Zheng, S. (1999) Independent Laboratory Validation of a Proposed Environmental 

Chemistry Analytical Method for the Determination of Hexazinone and Metabolites in 

Soil By GC/NPD Analysis and Confirmation by LC/MS/MS: Lab Project Number: 008-

036: DUPONT-2547. Unpublished study prepared by E.I. du Pont de Nemours and 

Company. 145 p. 

45132803 Zheng, S. (1999) Independent Laboratory Validation of a Proposed Environmental 

Chemistry Analytical Method for the Determination of Hexazinone and Metabolites in 

Water By GC/NPD Analysis and Confirmation by LC/MS/MS: Lab Project Number: 008-

035: DUPONT-2548. Unpublished study prepared by E.I. du Pont de Nemours and 

Company. 193 p. 
Page 95 of 133

Non-Guideline Selections

41713 Mattson, A.M.; Kahrs, R.A.; Murphy, R.T. (1970) Quantitative deter- mination of 

Triazine herbicides in soils by chemical analysis. Pages 371-390, ~In~ Residue 

Reviews: Volume 32. Edited by Fran- cis A. Gunther. New York, N.Y.: SpringerVerlac. (GAC 903811; also~In~unpublished submission received Jul 30, 1971 under 

2F1284; CDL:092076-F) 

64263 Krause, R.L. (19??) Evaluation of Possible Effects of DPX-3674 on Soil Microorganism 

Populations. (Unpublished study received May 7, 1975 under 352-378; submitted by 

E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL:110699-H) 

64264 Williams, M.H. (19??) Evaluation of Possible Effects of Velpar Weed Killer on Nitrifying 

Bacteria in Two Different Soils. (Unpublished study received May 7, 1975 under 352-

378; submit- ted by E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL: 110699-I) 

46575001 Mulderig, L. (1996) Magnitude of Residues of Hexazinone in Forest Grasses Following 

Application of Velpar Herbicides at Maximum Label Rates. Project Number: 

AMR/2896/94, ML94/0483/DUP, 008/04. Unpublished study prepared by E.I. du Pont 

de Nemours and Co., Inc., Morse Laboratories, Inc. and Centre Analytical Laboratories, 

Inc. 444 p.
Page 96 of 133

Appendix B. Ecological Effects Bibliography

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

73988 Fink, R.; Beavers, J.B.; Brown, R. (1978) Final Report: Acute Oral LD50--Bobwhite 

Quail: Project No. 112-121. (Unpublished study received May 23, 1978 under 352-

387; prepared by Wildlife Inter- national, Ltd., and Washington College, submitted by 

E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL:233989-A) 

44112701 Palmer, S.; Grimes, J.; Beavers, J. (1996) DPX-KG333-5: An Acute Oral Toxicity 

Study with the Northern Bobwhite: (Final Report): Lab Project Number: 112-433: AMR 

3907-96: 3907-96. Unpublished study prepared by Wildlife International Ltd. 45 p. 

Possibly a Mixture

71-2 Avian Dietary Toxicity

MRID Citation Reference

72663 Dudeck, S.H.; Bristol, K.L. (1980) Avian Dietary Toxicity (LC50) Study in Bobwhite 

Quail: Project No. 201-547. Final rept. (Un- published study received Jan 23, 1981 

under 352-387; prepared by Hazleton Laboratories America, Inc., submitted by E.I. du 

Pont de Nemours & Co., Wilmington, Del.; CDL:244106-A) 

104970 E.I. du Pont de Nemours & Co., Inc. (1973) Toxicity Summary: DPX- 3674. 

Summary of studies 223386-C through 223386-N. (Unpub- lished study received Dec 

5, 1973 under 352-EX-85; CDL:223386-B) 

104981 Fletcher, D. (1973) Report to...: 8-day Dietary LC50 Study with H-7759; MR-581 in 

Mallard Ducklings: IBT No. 651-03194. (Unpub- lished study received Dec 5, 1973 

under 352-EX-85; prepared by Industrial Bio-Test Laboratories, Inc., submitted by E.I. 

du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:223386-N) 

107878 Fletcher, D. (1973) Report to E.I. du Pont de Nemours & Company: 8- day Dietary 

LC50 Study with H-7759; MR-581 in Bobwhite Quail: IBT No. 651-03199. 

(Unpublished study received Dec 5, 1973 under 352-EX-85; prepared by Industrial 

Bio-Test Laboratories, Inc., submitted by E.I. du Pont de Nemours & Co., Inc., 

Wilming- ton, DE; CDL:223386-M) 

71-4 Avian Reproduction

MRID Citation Reference

41764901 Beavers, J.; Campbell, S.; Smith, G. (1991) H 17,705: A One Generation 

Reproduction Study With the Northern Bobwhite (Colinus virginianus): Lab Project 

Number: 112-225: 772-90. Unpublished study prepared by Wildlife International Ltd. 

168 p. 
Page 97 of 133

41764902 Beavers, J.; Campbell, S.; Smith, G. (1991) H 17,705: A One Generation 

Reproduction Study With the Mallard (Anus platyrhynchos) Lab Project Number: 112-

226: 773-90. Unpublished study prepared by Wildlife International Ltd. 167 p. 

41938001 Beavers, J.; Campbell, S.; Smith, G.; et al. (1991) Supplement to H 17,705: A OneGeneration Reproduction Study with the Mallard (Anas platyrhynchos): Lab Project 

Number: 112-226: HLO-773-90. Unpublished study prepared by Wildlife International 

Ltd. 9 p. 

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

76959 Schneider, P.W., Jr. (1976) 96-hour LC50 to Bluegill Sunfish: Haskell Laboratory No.

408-76. (Unpublished study received May 20, 1981 under 352-378; submitted by E.I. 

du Pont de Nemours & Co., Wilmington, Del.; CDL:245117-D) 

76960 Okolimna (1980) Fish Toxicity: ?~Leuciscus idus melanotus~|. (Translation; 

unpublished study received May 20, 1981 under 352- 378; submitted by E.I. du Pont 

de Nemours & Co., Wilmington, Del.; CDL:245117-E) 

76961 Okolimna (1980) Fish Toxicity: ?~Salmo gairdneri~|. (Transla- tion; unpublished study 

received May 20, 1981 under 352-378; submitted by E.I. du Pont de Nemours & Co., 

Wilmington, Del.; CDL:245117-F) 

104970 E.I. du Pont de Nemours & Co., Inc. (1973) Toxicity Summary: DPX- 3674. Summary 

of studies 223386-C through 223386-N. (Unpub- lished study received Dec 5, 1973 

under 352-EX-85; CDL:223386-B) 

104980 Sleight, B. (1973) Acute Toxicity of H-7759, MR-581 to Bluegill (Lepomis 

macrochirus), Rainbow Trout (Salmo gairdneri) and Fathead Minnow (Pimephales 

promelas). (Unpublished study re- ceived Dec 5, 1973 under 352-EX-85; prepared by 

Bionomics, Inc., submitted by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; 

CDL:223386-L) 

41235001 Hutton, D. (1989) Static Acute 96-Hour LC50 of IN A3674-208 to Bluegill Sunfish 

(Lepomis macrochirus): Project ID 462-89. Un- published study prepared by E. I. du 

Pont de Nemours and Co., Inc. 17 p. 

41235002 Hutton, D. (1989) Static Acute 96-Hour LC50 of IN A3674-208 to Rainbow Trout 

(Salmo gairdneri): Project ID 463-89. Unpublished study prepared by E. I. du Pont de 

Nemours and Co. 18 p. 

47178 E.I. du Pont de Nemours & Company (1976) 96-Hour LC50 to Bluegill Sunfish: 

Haskell Laboratory Report No. 409-76. (Unpublished study received Aug 29, 1978 

under 352-378; CDL:099674-E) 

40098001 Mayer and Ellersieck 1986 USFWS- multiple species tested

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference
Page 98 of 133

116269 Schneider, P. (1976) 48-hour LC50 to Daphnia magna: Haskell Labo- ratory Report 

No. 262-76. (Unpublished study received Dec 30, 1977; under 352-387; submitted by 

E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:232556-A; 235401) 

41235003 Hutton, D. (1989) Static Acute 48-Hour EC50 of IN A3674-208 to Daphnia magna: 

Project ID 452-89. Unpublished study prepared by E. I. du Pont de Nemours and Co. 

17 p. 

72-3 Acute Toxicity to Estuarine Organisms

47164 or 

78018 

Heitmuller, T. (1976) Acute Toxicity of H-9877 to Embryos of East- ern Oysters 

(~Crassostrea virginica~), to Grass Shrimp (~Palaemonetes pugio~), and to Fiddler 

Crabs (~Uca pugila~- ~tor~). (Unpublished study received Jul 25, 1979 under 352-

378; prepared by EG&G Bionomics, submitted by E.I. du Pont de Nemours & Co., 

Wilmington, Del.; CDL:099674-B) 

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

MRID Citation Reference

41406001 Pierson, K. (1990) Effects of IN A3674-207 on the Embryos and Lar- vae of Fathead 

Minnows (Pimephales promelas): Lab Project Number HLR 656-89: MR-8705-001. 

Unpublished study prepared by E. I. du Pont de Nemours and Co., Inc. 221 p. 

41406002 Pierson, K. (1990) Chronic Toxicity of IN A3674-207 to Daphnia mag- na: Lab Project 

Number: HLR 68-90: MR-8705-001. Unpublished study prepared by E. I. du Pont de 

Nemours and Co., Inc. 198 p. 

114038 Schneider, P. (1977) Chronic Toxicity of ... (INA-3674) to Daphnia magna: Haskell 

Laboratory Report No. 544-77. (Unpublished study received Aug 29, 1978 under 352-

378; submitted by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:097321-

D) 

122-1 Seed Germination/Seedline Emergence and Vegetable Vigor

MRID Citation Reference

41216501 Leavitt, J. (1988) Hazard Evaluation of Hexazione on Non-Target Plants Grown under 

Greenhouse and field Conditions - Tiers I, II, III: Project ID JRCL 89-1. Unpublished 

study prepared by E. I. Du Pont de Nemours and C0., Inc. 51 p. 

43162501 McKelvey, R.; Heldreth, K. (1994) Influence of Hexazinone on Seed Germination, 

Seedling Emergence, and Vegetative Vigor of Several Terrestrial Plants: Lab Project 

Number: AMR 2678-93: AMR 2736-93. Unpublished study prepared by DuPont 

Agricultural Products. 351 p. 

43605001 McKelvey, R. (1995) Influence of Hexazinone on Seed Germination, Seedling 

Emergence, and Vegetative Vigor of Several Terrestrial Plants: Supplement No. 1: 

Lab Project Number: AMR 2678-93. Unpublished study prepared by DuPont 

Agricultural Products. 112 p. 
Page 99 of 133

122-2 Aquatic plant growth

MRID Citation Reference

41287001 Forbis, A. (1989) Acute Toxicity of Hexazinone to Selenastrum capricornutum Printz: 

Lab Project Number 38069; AMR-1446-89. Unpublished study prepared by Analytical 

Bio-Chemistry Laboratories, Inc. 31 p. 

41287002 Schuster, L. (1989) Method Validation for the Analysis of Hexazinone in Algae Test 

Media: Dupont Study No. AMR-1503-89; ABC Final Report No. 38068. Unpublished 

study prepared by Analytical Bio-Chemistry Laboratories, Inc. 20 p. 

123-1 Seed germination/seedling emergence and vegetative vigor

MRID Citation Reference

41216501 Leavitt, J. (1988) Hazard Evaluation of Hexazione on Non-Target Plants Grown under 

Greenhouse and field Conditions - Tiers I, II, III: Project ID JRCL 89-1. Unpublished 

study prepared by E. I. Du Pont de Nemours and C0., Inc. 51 p. 

43162501 McKelvey, R.; Heldreth, K. (1994) Influence of Hexazinone on Seed Germination, 

Seedling Emergence, and Vegetative Vigor of Several Terrestrial Plants: Lab Project 

Number: AMR 2678-93: AMR 2736-93. Unpublished study prepared by DuPont 

Agricultural Products. 351 p. 

43183901 Vaught, R. (1994) Letter Sent to Office of Pesticide Programs Dated Mar. 29, 1994 

(Hexazinone: influence on seed germination seedling emergence and vegetative vigor 

of several terrestrial plants). Prepared by DuPont Agric. Products. 2 p. 

43605001 McKelvey, R. (1995) Influence of Hexazinone on Seed Germination, Seedling 

Emergence, and Vegetative Vigor of Several Terrestrial Plants: Supplement No. 1: 

Lab Project Number: AMR 2678-93. Unpublished study prepared by DuPont 

Agricultural Products. 112 p. 

123-2 Aquatic plant growth

MRID Citation Reference

41287001 Forbis, A. (1989) Acute Toxicity of Hexazinone to Selenastrum capricornutum Printz: 

Lab Project Number 38069; AMR-1446-89. Unpublished study prepared by Analytical 

Bio-Chemistry Laboratories, Inc. 31 p. 

43225101 Kannuck, R.; Sloman, T. (1994) Hexazinone (DPX-A3674): Influence on Growth and 

Reproduction of Lemna gibba G3: Lab Project Number: AMR 2874-93: MR 9785-001. 

Unpublished study prepared by Stine-Haskell Research Center, DuPont Agricultural 

Products. 41 p. 

43225102 Baer, K. (1994) Hexazinone (DPX-A3674): Influence on Growth and Reproduction of 

Skeletonema costatum: Lab Project Number: 241-94: AMR 2884-93: MR 8785. 

Unpublished study prepared by Stine-Haskell Research Center, DuPont Agricultural 
Page 100 of 133

Products. 38 p. 

43241101 Vaught, R. (1994) Letter Sent to Office of Pesticide Programs dated May 18, 1994: 

Report of studies with hexazinone: Plant protection studies. Prepared by Du Pont Ag. 

Products. 2 p. 

43302701 Thompson, S. (1994) Hexazinone (DPX-A3674): Influence on Growth and 

Reproduction of Two Select Algal Species: Lab Project Number: AMR 3011-94: 335-

94: 9785. Unpublished study prepared by Wildlife International Ltd. and E.I. du Pont 

de Nemours & Co. 75 p. 

43340001 Vaught, R. (1994) Letter Sent to Office of Pesticide Programs dated August 10, 1994 

concerning a plant protection study with hexazinone. Prepared by DuPont Ag 

Products. 1 p. 

43400401 Baer, K. (1994) Hexazinone (DPX-A3674): Influence on Growth and Reproduction of 

Skeletonema costatum: Revision No. 2: Lab Project Number: AMR 2884-93: MR 

9785: HLR 241-94. Unpublished study prepared by DuPont Haskell Lab for 

Toxicology and Industrial Medicine. 40 p. 

141-1 Honey bee acute contact

MRID Citation Reference

41216502 Hoxter, K.; Thompson, M.; Jaber, M. (1989) An Acute Contact Toxici- ty with the 

Honey Bee: Project ID 112-217. Unpublished study prepared by Wildlife International 

Ltd. 15 p. 

Non-Guideline Selections

43149701 Vaught, R. (1994) Letter Sent to Office of Pesticide Programs dated March 1, 1994 

containing follow-up report of leaf spotting and hexazinone detection on vegetation 

adjacent to a site treated with DuPont Velpar ULW Herbicide. Prepared by DuPont 

Agricultural Products. 2 p. 

43329501 Crosswhite, F.; Feldman, W.; Minch, E. (1993) Impact of Pesticides on Cacti: Lab 

Project Number: E-009572-01-0. Unpublished study prepared by University of Arizona 

and Arizona Dept. of Agriculture. 33 p. 

47164601 Moore, D.; Breton, R.; Rodney, S.; et al. (2007) Generic Problem Formulation for 

California Red-Legged Frog. Project Number: 89320, 05232007. Unpublished study 

prepared by Cantox Environmental Inc. 87 p.

47164602 Holmes, C.; Vamshi, R. (2007) Data and Methodology Used for Spatial Analysis of 

California Red Legged Frog Observations and Proximate Land Cover Characteristics. 

Project Number: 3152007, WEI/252/03. Unpublished study prepared by Waterborne 

Environmental, Inc. (WEI). 19 p.
Page 101 of 133

Appendix C. Hexazinone and its transformation products

Hexazinone and Its Environmental Transformation Products. A
Page 102 of 133

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(1H,3H)-dione

CAS: 3-Cyclohexyl-6-

(dimethylamino)-1-methyl-1,3,5-

triazine-2,4(1H,3H)-dione

CAS No.: 51235-04-2

Formula: C12H20N4O2

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

Anaerobic 

aquatic 

metabolism

41807402

Non-sterile 

loam 96.7 (7 d) 39.7 (365 d)

Sterile 96.0 (0 d) 81.3 (365 d)

49109902

Wabasha 

water:sandy 

loam

101.6% (0 d) 86.5% (101 d)

Tift 

water:sandy 100.5% (0 d) 92.1% (101 d)
Page 103 of 133

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR 

(study 

length)

loam

MAJOR (>10%) TRANSFORMATION PRODUCTS

IN-G3170; Met. G IUPAC: 1-Methyl-6-

(methylamino)-1,3,5-triazine-2,4-

dione

Formula: C5H8N4O2

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: C12H18N4O3

MW: 266.3 g/mol

SMILES: 

Cn1c(nc(=O)n(c1=O)C2CCC(=O)C

C2)N(C)C

O

N N

N

C H 3

C H 3

N

C H 3

O

O

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)

Anaerobic 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 41811801 Non-sterile 6.5 (28 d) 3.7 (56 d)
Page 104 of 133

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR 

(study 

length)

Aerobic 

aquatic 

metabolism

sandy loam

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-methyl1,3,5-triazinane-2,4,6-trione

Formula: C10H15N3O3

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)

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 0.4% (70 d) 0.3% (101 d)
Page 105 of 133

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR 

(study 

length)

water:sandy 

loam

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: C12H20N4O3

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: C11H18N4O2

MW: 238.28 g/mol

SMILES: 

[H]N(C)c1nc(=O)n(c(=O)n1C)C2C

CCCC2

N

O N

C H 3

N

H

C H 3

N

O

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)

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)
Page 106 of 133

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR 

(study 

length)

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: C12H18N4O3

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)

Carbon dioxide IUPAC: Carbon dioxide

Formula: CO2

MW: 44 g/mol

SMILES: C(=O)=O

O C O

Soil Photol 41300802 Sandy loam 0.23 (30 d)C 0.23 (30 d)C

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)
Page 107 of 133

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day)

Final %AR 

(study 

length)

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)

Unextractable 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: C12H20N4O3

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

H O 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

Anaerobic 

soil 

metabolism

48898002

Sandy clay 

loam 1.0% (60 d) ND (180 d)

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)
Page 108 of 133

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.
Page 109 of 133

Appendix D. Sample SWCC Output File

Summary of Water Modeling of Hexazinone and the USEPA 

Standard Pond

Estimated Environmental Concentrations for Hexazinone are presented in Table 1 for the 

USEPA standard pond 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 4.4% of Hexazinone applied to the field eventually reaches the 

water body. The main mechanism of transport from the field to the water body is by runoff 

(71.2% of the total transport), followed by spray drift (28.3%) and erosion (0.43%).

In the water body, pesticide dissipates with an effective water column half-life of 1363.8 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 metabolism (effective average half-life = 1363.8 days) 

followed by volatilization (7.926746E+07 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-life = 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) 600.

4-day Avg (1-in-10 yr) 599.

21-day Avg (1-in-10 yr) 596.

60-day Avg (1-in-10 yr) 593.

365-day Avg (1-in-10 yr) 546.

Entire Simulation Mean 391.

Table 2. Summary of Model Inputs for Hexazinone.

Scenario LAsugarcaneSTD

Cropped Area Fraction 1

Koc (ml/g) 57.5

Water Half-Life (days) @ 25 °C 1343

Benthic Half-Life (days) @ 25 °C 1805
Page 110 of 133

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 0.125

Figure 1. Yearly Peak Concentrations
Page 111 of 133

Appendix E. T-REX non-granular example output
Page 112 of 133

Summary of Risk Quotient Calculations Based on Upper Bound Kenaga EECs

Table X. Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 1626.73 2186.69 1.34 1002.23 0.62 1230.01 0.76 136.67 0.08 856.45 0.53 30.37 0.02

100 2070.91 1246.94 0.60 571.52 0.28 701.40 0.34 77.93 0.04 488.39 0.24 17.32 0.01

1000 2925.24 558.27 0.19 255.87 0.09 314.03 0.11 34.89 0.01 218.66 0.07 7.75 0.00

Table X. Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

5000 1920.00 0.38 880.00 0.18 1080.00 0.22 120.00 0.02 752.00 0.15

Size class not used for dietary risk quotients 
Page 113 of 133

Table X. Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

300 1920.00 6.40 880.00 2.93 1080.00 3.60 120.00 0.40 752.00 2.51

Size class not used for dietary risk quotients

Table X. Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 1164.85 1830.57 1.57 839.01 0.72 1029.70 0.88 114.41 0.10 716.9744 0.6155 25.425 0.0218

35 942.49 1265.17 1.34 579.87 0.62 711.66 0.76 79.07 0.08 495.5252 0.5258 17.572 0.0186

1000 407.66 293.33 0.72 134.44 0.33 165.00 0.40 18.33 0.04 114.8893 0.2818 4.0741 0.01

Table X. Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0 1920.00 #DIV/0! 880.00 #DIV/0! 1080.00 #DIV/0! 120.00 #DIV/0! 752.00 #DIV/0!

Size class not used for dietary risk quotients
Page 114 of 133

Table X. Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds/

Large Insects Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

200 1920.00 9.60 880.00 4.40 1080.00 5.40 120.00 0.60 752.00 3.76

Size class not used for dietary risk quotients 

Table X. Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 21.98 1830.57 83.29 839.01 38.17 1029.70 46.85 114.41 5.21 716.97 32.62 25.42 1.16

35 17.78 1265.17 71.15 579.87 32.61 711.66 40.02 79.07 4.45 495.53 27.87 17.57 0.99

1000 7.69 293.33 38.14 134.44 17.48 165.00 21.45 18.33 2.38 114.89 14.94 4.07 0.53
Page 115 of 133

Appendix F. LD50 per ft2 T-REX example output

Chemical: Hexazinone

LD50 ft-2

INPUTS Do not overwrite these numbers. Changes to the inputs must be 

Application Rate: 8

lbs / 

acre made in the "INPUTS" worksheet.

% A.I.: 75.00%

Avian LD50 (20g): 1626.73 mg/kg bw

(100g) 2070.91

(1000g) 2925.24

Mammalian LD50 (15g): 1164.85 mg/kg bw

(35g) 942.49

(1000g) 407.66

Row Spacing: 0 inches

Bandwidth: 0 inches

Unincorporation: 100%

Row/Band/In-furrow applications

Granular N/A

Intermediate Calculations Intermediate Calculations

# rows acre-1: N/A mg a.i./1000 ft row: N/A

row length (ft): N/A bandwidth: N/A

lb ai/1000 ft row: N/A mg a.i./ft2: N/A

bandwidth (ft): N/A exposed mg a.i./ft2: N/A

mg ai/ft2: N/A

exposed mg ai/ft2: N/A

LD50 ft-2 N/A

wgt class 

(grams)

wgt class 

(grams)

Avian 20 N/A Avian 20 N/A

100 N/A 100 N/A

1000 N/A 1000 N/A

Mammal 15 N/A Mammal 15 N/A

35 N/A 35 N/A

1000 N/A 1000 N/A

Broadcast applications

Granular
Page 116 of 133

Intermediate Calculations

mg ai/ft2: 62.48

LD50 ft-2

wgt class 

(grams)

Avian 20 1.92

100 0.30

1000 0.02

Mammal 15 3.58

35 1.89

1000 0.15

Formulas used in the calculations are in the User's Guide
Page 117 of 133

Appendix G. Granular Characterization T-REX example output

Estimation of the number of granules needed to achieve toxicity thresholds

Step 1. Estimate mass of a.i. consumed for the assessed species weight to achieve the desired toxicity threshold

Parameter

Value 

Bird Mammal Comment

Weight of assessed animal (kg)

1.00 1.000 INPUT (0.02 kg and 0.015 kg are typically used for general assessments for 

birds and mammals, respectively).

LD50, mg/kg-bw 2925.24 407.66 Calculated from the body weight entered in B13 and C13 and the LD50 entered 

in the "Inputs" sheet.

Mg a.i. needed to achieve the LD50 for 

animal of assessed weight

2925.24 407.66

mg a.i./kg-bw * kg-bw = mg a.i. Mg a.i. needed to achieve the LOC of 0.5 

(1/2 LD50) for animal of assessed weight

1462.62 203.83

Mg a.i. needed to achieve the LOC of 0.1 

(1/10th LD50) for animal of assessed 

weight

292.52 40.77

Step 2. Determine the mass of a.i. per granule

Percent of a.i. in formulated product 75.00% 75.00% Must enter percent a.i. specified on the label

Weight of 1 granule (mg, obtained from 

registrant)

640.00 640.00 INPUT (Note: Be sure to enter units in mg!)

mg a.i./granule 480.0000 480.0000 weight of granule (mg) x fraction of a.i. = mg a.i./granule 

Step 3. Calculate number of granules with mass of a.i. equivalent to adjusted LD50 for bird of assessed weight

The analysis below calculates the number of granules needed to be consumed by a bird and mammal to achieve a dose that would exceed the LD50 and trigger 

the LOC of 0.1 and 0.5. In addition, the minimum foraging area with sufficient number of granules to achieve a dose that exceeds the LD50, 1/2 the LD50, or 

1/10th the LD50 is estimated by assuming that a bird consumes 100%, 50%, and 10% of the available granules. This analysis may be used to characterize the 

LD50/square foot calculation presented in the "LD50 ft-2" worksheet.
Page 118 of 133

No. of granules needed to achieve LD50 6.09 0.85 mg a.i. needed to achieve adjusted LD50 (B/C14) / mg a.i. per granule (B/C20)

No. of granules needed to achieve the 

LOC of 0.5 (1/2 LD50) 

3.05 0.42 mg a.i. needed to achieve 1/2 adjusted LD50 (B/C15) / mg a.i. per granule 

(B/C20)

No. of granules needed to achieve the 

LOC of 0.1 (1/10 LD50) 

0.61 0.08 mg a.i. needed to achieve 1/10 adjusted LD50 (B/C16) / mg a.i. per granule 

(B/C20)

Minimum Foraging Area Needed to Allow for Ingestion of Sufficient Mass of a.i. to Achieve LOC Exceedance 

EEC (mg a.i./square foot) 62.48 62.48 From LD50 ft-2 page

Foraging area (square feet) needed to 

achieve LOC of 0.1 exceedance 

assuming 100% feeding efficiency 4.68 0.65

mg a.i. needed to achieve LD50 in 20-gram bird (B/C16) / mg a.i.per sq. ft 

(B/C27)

Foraging area (square feet) needed to 

achieve LOC of 0.1 exceedance 

assuming 50% feeding efficiency 9.36 1.30

Foraging area needed to achieve LOC Exceedance assuming 100% feeding 

efficiency (B/C28) * 2 (i.e., twice the foraging area is needed for 50% feeding 

efficiency)

Foraging area (square feet) needed to 

achieve LOC of 0.1 exceedance 

assuming 10% feeding efficiency 46.82 6.52

Foraging area needed to achieve LOC Exceedance assuming 100% feeding 

efficiency (B/C28) * 10 (i.e., 10 times the foraging area is needed for 10% 

feeding efficiency)
Page 119 of 133

Appendix H. Terrplant example output

TerrPlant v. 1.2.2

Green values signify user inputs (Tables 1, 2 and 4). 

Input and output guidance is in popups indicated by red arrows.

Chemical Name

PC code

Use

Application Method

Application Form 

Solubility in Water (ppm)

Input Parameter Symbol Value Units

Application Rate A 4.5 lb. a.i/A

Incorporation I 1 none

Runoff Fraction R 0.05 none

Drift Fraction D 0.05 none

Equation EEC

(A/I)*R 0.225

(A/I)*R*10 2.25

A*D 0.225

((A/I)*R)+(A*D) 0.45

((A/I)*R*10)+(A*D) 2.475

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 1.48 0.745 1.46 0.48

Dicot 0.84 0.23 1.51 0.5

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed 0.30 1.67 0.15

Monocot listed 0.60 3.32 0.47

Dicot non-listed 0.54 2.95 0.27

Dicot listed 1.96 10.76 0.98

Total for semi-aquatic areas

Table 1. Chemical Identity.

Dimethoate 

Douglas fir (seed orchards) (only in OR and WA)

Table 2. Input parameters used to derive EECs.

Aerial

Airblast

39800

128975

Table 3. EECs for Dimethoate . Units in lb. a.i/A.

Runoff to dry areas

Runoff to semi-aquatic areas

Spray drift

Total for dry areas

Description

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Seedling Emergence Vegetative Vigor

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Dimethoate through runoff 

and/or spray drift.*

Table 4. Plant survival and growth data used for RQ derivation. Units are in lb. a.i/A.
Page 120 of 133

Appendix I. Classifications of Environmental Fate Studies

Table I-1. Classification of Environmental Fate Studies Conducted on Hexazinone

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

835.2120 Hydrolysis 41587301 Acceptable ---

835.2240 Photolysis in 

Water 41300801 Acceptable ---

835.2410 Photodegradation 

on Soil 41300802 Acceptable ---

835.2370 Photodegradation 

in Air

Not 

available Not applicable ---

835.4100 Aerobic Soil 

Metabolism

41807401/ 

42635001

Acceptable 

(Partial) ---

48898001 Supplemental 

(Partial)

The soil extraction procedures may not have been adequate to extract all 

identifiable [14C]residues in the soils; unextracted residues totaled 

maximums of 14.3-25.6% of the applied for the three test soils. In the 

absence of details about the suitability of the extractions, the total toxic 

residue approach will be taken (i.e., hexazinone residues + unextracted 

residues). Insufficient data were provided regarding the soils used in this 

study, including collection and storage procedures, and whether they were 

free of pesticide residues prior to use.

835.4200 Anaerobic Soil 

Metabolism 48898002 Supplemental

Measured rather than standard redox potentials were provided by the study 

author, so it was uncertain whether study conditions were oxic or suboxic. 

The viability of the test soils at the initiation and finalization of the study 

was not reported. The soil extraction procedures may not have been 

adequate to extract all identifiable [14C]residues in the soils; in the clay 

loam soil, unextracted [14C]residues totaled a maximum of 28.2% of the 

applied. Soil collection and storage procedures prior to use were not 

described. It was not confirmed that the soils were free of pesticide 

residues prior to use. Tests were conducted for a period of only 149 days 

of anaerobic incubation; all observed DT50s were reported as >149 days. 

The pattern of decline of the degradate IN G3170 could not be established 

in the Audrain soil. Also, the degradate IN B2838 was a maximum at 149 

days of anaerobic incubation in the Raymondville soil.

835.4300 Aerobic Aquatic 

Metabolism

41811801 Acceptable 

(Partial) ---

49109901 Supplemental 

(Partial)

Measured rather than standard redox potentials were provided by the study 

author, so it was uncertain whether study conditions were oxic or suboxic. 

Insufficient data were provided regarding the soils and water used in this 

study, including source of the water, collection and storage procedures, 

and whether they were free of pesticide residues prior to use. The study 

lasted only 100 days, at which time 87.4-91.6% AR was still undegraded 

hexazinone, and the calculated half-lives were considerably beyond the 

study duration. Data on certain individual replicate concentrations was 

not provided. The LOQ for the HPLC analysis of the aqueous phase 

appeared to be extraordinarily high (30.5% AR) and is not in line with all 

the other LOQs.

835.4400 41807402 Acceptable

(Partial) ---
Page 121 of 133

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

Anaerobic 

Aquatic 

Metabolism

49109902 Supplemental

(Partial)

Measured rather than standard redox potentials were provided by the study 

author, so it was uncertain whether study conditions were oxic or suboxic. 

Given the presence of dissolved oxygen in the waters of both test systems, 

they may not have been anaerobic. Storage stability data for the water 

samples and soil extracts were not provided. Insufficient data were 

provided regarding the soils and water used in this study, including source 

of the water, collection and storage procedures, and whether the soils were 

free of pesticide residues prior to use. HPLC data for the replicate 

samples were not reported. The study lasted only 101 days, at which time 

86.5-92.1% AR was still undegraded hexazinone, and the calculated halflives were considerably beyond the study duration. Data on certain 

individual replicate concentrations was not provided. For HPLC of the 

aqueous phase, the LOQ was 29.40%. This value appeared to be 

extraordinarily high, compared to all the other LOQs.

835.1230

LeachingAdsorption/ 

Desorption

43621501 Acceptable ---

835.1410 Laboratory 

Volatility

No data 

submitted Not applicable ---

835.6100 Terrestrial Field 

Dissipation

42377901 Acceptable ---

42379201 Supplemental

The application rate was not confirmed by the Day 0 posttreatment 

sample. The Day 0 posttreatment sample was <30% of the theoretical 

application rate. However, the Day 7 thru Day 60 posttreatment samples 

had a higher concentration (40 to 51% of the theoretical application rate) 

of hexazinone than the Day 0 posttreatment.

835.6100 Long-term Soil 

Dissipation

No data 

submitted Not applicable ---

835.6200 Aquatic 

Dissipation

No data 

submitted Not applicable ---

835.6300 Forestry 42336401 Acceptable ---

835.6400 Combination and 

Tank Mixes

No data 

submitted Not applicable ---

860.1400 Accumulation in 

Irrigated Crops

No data 

submitted Not applicable ---

850.1730 Accumulation in 

Fish

00064265, 

00078032; 

41203201

Waived Reported in DP Barcode D279324.

850.1950 Aquatic Nontarget Organism

No data 

submitted Not applicable ---

835.7100 Ground Water 

Monitoring 45132801 Supplemental

Storage stability of the analytes could not be adequately determined in soil 

or water samples. No rainfall or irrigation was received within the first 

week of the test application.

835.8100 Field Volatility No data 

submitted Not applicable ---
Page 122 of 133

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

850.6100

ECM/ILV in Soil 45132802 Unacceptable 

(Upgradable)

This analytical method is considered unacceptable, for the following 

reasons.

• No originating ECM performance data were reported for either 

method. For both methods, complete, finalized ECM reports 

with implemented ILV major modifications were not provided. 

Two sets of performance data should be submitted, one for the 

initial or other internal validation (ECM), and one for the ILV. 

Furthermore, these reports should be provided separate from 

each other.

• For ILV analysis of IN-T3935 by GC-NPD, no performance 

data at 10xLOQ were provided.

• For the LC/MS/MS method, ILV performance data for 2.0 

μg/kg (LOQ) fortified IN-JS472 and 20 μg/kg (10x LOQ) 

fortified IN-G3170 in soil did not meet OCSPP Guideline 

850.6100 criteria.

• The determination of LOQ and LOD were not based on 

scientifically acceptable procedures (for guidance, refer to the 

references section of this DER).

• Linearity (r2

) of the calibration standards was not always 

≥0.995.

Portions of the study appeared to meet guideline criteria and may be 

upgradable with the submission of additional information.

ECM/ILV in 

Water 45132803 Unacceptable (Upgradable)

This analytical method is considered unacceptable, for the following 

reasons.

• For both methods, complete, finalized ECM reports with 

implemented ILV major modifications were not provided. No 

originating ECM performance data were reported for either 

method. Two sets of performance data should be submitted, 

one for the initial or other internal validation (ECM), and one 

for the ILV. These reports should be provided separate from 

each other.

• For ILV analysis of all analytes in lysimeter water, insufficient 

performance data were provided to validate either method at 

the LOQ or 10x LOQ (minimum of 5 samples required).

• For ILV ground water analysis of IN-T3935 and IN-G3170 by 

GC-NPD and all analytes by LC/MS/MS, no performance data 

at 10x LOQ were provided.

• ILV performance data for 2.0 μg/L (LOQ) fortified hexazinone 

in ground water using GC-NPD did not meet OCSPP Guideline 

850.6100 criteria.

• The determination of LOQ and LOD were not based on 

scientifically acceptable procedures (see reference at the end of 

this DER for guidance).

• ILV reported recoveries were corrected if residues were 

present in the matrix controls.

• Water matrices used in the ILV were not characterized.

• Linearity (r2

) of the calibration standards was not always 

≥0.995.

Portions of the study appeared to meet guideline criteria and may be 

upgradable with the submission of additional information.

ECM=Environmental Chemistry Method; ILV=Independent Laboratory Validation
Page 123 of 133

Table I-2. Classification of Environmental Effects Studies Conducted on Hexazinone

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

850.2100 Avian Acute Oral 00073988 Acceptable ---

850.2100 Avian Acute Oral 

(passerine) 48718401 Invalid

A passerine study was requested as part of the DCI released with the 2010 

Problem Formulation for Hexazinone (D369269). The submitted study 

(MRID 48718401) was deemed invalid and did not fill the guideline 

requirement for 850.2100; the submitted document consisted of a 

simulation of existing data and was not an actual passerine study that was 

conducted in a lab.

850.2200 Avian Dietary

00107878

00072663

00010498

Acceptable ---

850.2300 Avian 

Reproduction

41764901

41764902 Acceptable ---

850.2400 Wild Mammal 

Toxicity

No data 

submitted Not applicable ---

850.2500 Terrestrial Field 

Testing

No data 

submitted Not applicable ---

850.1075 Acute Freshwater 

Fish

00076959

00104980 Acceptable ---

850.1075 Acute Freshwater 

Fish (TEP)

No data 

submitted Not applicable ---

850.1010 Acute Freshwater 

Invertebrate 00116269 Acceptable ---

850.1010

Acute Freshwater 

Invertebrate 

(TEP)

41235003 Acceptable ---

850.1075

Acute 

Estuarine/marine 

Fish

Waived Not applicable ---

850.1075

Acute 

Estuarine/marine 

Fish (TEP)

No data 

submitted Not applicable ---

850.1350

Acute 

Estuarine/Marine 

Invertebrate

00047164 Acceptable ---

850.1350

Acute 

Estuarine/marine 

Invertebrate 

(TEP)

No data 

submitted Not applicable ---

850.1400 Early Life Stage 

Fish 41406001 Acceptable ---

850.1300

Life Cycle 

Aquatic 

Invertebrate

00078041

41406002

45822101

Acceptable ---

850.1500 Life Cycle Fish No data 

submitted Not applicable ---

850.1950 Aquatic Field 

Study

No data 

submitted Not applicable ---
Page 124 of 133

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

850.4100 Seedling 

Emergence 43162501 Partial

There were a number of deviations that resulted in the invalidation of 

some of the species included in the seedling emergence study:

• Cucumber seeds were treated with Thiram resulting in 

invalidation of cucumber results; a control for the two 

pesticides should have been included in the design in order to 

isolate the effects of hexazinone

• Onion and Pea data were invalidated based on significant 

damage to the plants

• Sorghum, soybean, pea and tomato showed growth retardation

• Percent germination of oilseed rape was low in the controls 

(54%)

850.4150 Vegetative Vigor 43162501 Partial

There were a number of deviations that resulted in the invalidation of 

some of the species included in the vegetative vigor:

• Cucumber seeds were treated with Thiram resulting in 

invalidation of cucumber results; a control for the two 

pesticides should have been included in the design in order to 

isolate the effects of hexazinone

• The percent germination was not reported and the phytoxicity 

rating was not included

850.4400 Aquatic Vascular 

Plant Growth 43225101 Acceptable ---

850.4550

Aquatic 

Nonvascular Plant 

Growth

41287001

43302701

43225102

Acceptable ---

850.3020 Honeybee Acute 

Contact

No data 

submitted Not applicable

Pollinator data will be requested as part of the newly implemented plan to 

assess risk to Pollinators.

850.3030

Honeybee toxicity 

on residues on 

foliage

No data 

submitted Not applicable

850.3040 Field Testing for 

Pollinators

No data 

submitted Not applicable

NG Honeybee Acute 

Adult Oral

No data 

submitted Not applicable

NG Honeybee larvae 

Acute Oral

No data 

submitted Not applicable

NG

Honeybee Adult 

Chronic Oral 

Toxicity

No data 

submitted Not applicable

NG Honeybee Larvae 

Chronic Oral 

No data 

submitted Not applicable

NG

Semi-field 

testing for 

pollinators 

(tunnel or 

colony 

feeding 

studies)

No data 

submitted Not applicable

NG

Field trial of 

residues in 

pollen and 

nectar

No data 

submitted Not applicable
Page 125 of 133

Appendix J. Hexazinone Refresh Acceptable Bibliographies 

November 2014

1. Cai, Z.; Brauen, S. E.; Gealy, D. R.; Johnston, W. J., and Lumpkin, T. A. Tolerance of Chinese Milkvetch 

(Astragalus sinicus) to Herbicides. GRO,MOR,PHYSOIL,ENV; 1992; 6, (1): 104-107. 

Rec #: 10

Call Number: LITE EVAL CODED (ACF,BT,HXZ,PZM), OK 

(ACR,CPP,DCPA,DU,EPTC,LCF,MTL,PMT,QZFE,SXD,TFN)

Notes: EcoReference No.: 161547

Chemical of Concern: 

24DB,ACF,ACR,BMN,BT,CPP,DCPA,DFPM,DU,EPTC,FZFB,HXZ,IMQ,IZT,LCF,MBZ,MCPA,

MTL,PMT,PZM,QZFE,SXD,TFN,TRB,TRL

2. Cain, M. D. Japanese Honeysuckle and Associated Ground Cover Inhibit Establishment and Growth of Pine 

Seedlings in All-Aged Stands. GRO,MOR,POPSOIL,ENV; 1985; 54, 300-304. 

Rec #: 20

Call Number: LITE EVAL CODED (HXZ)

Notes: EcoReference No.: 161024

Chemical of Concern: HXZ

3. Chenault, E. W. and Wiese, A. F. Annual Grass Control in Irrigated Alfalfa. 

PHY,POPSOIL,ENV,MIXTURE; 1977; 30, 147-151. 

Rec #: 30

Call Number: LITE EVAL CODED (HXZ,SZ), OK (CPP,DU,PDM,PRM,PZM,TFN)

Notes: EcoReference No.: 163875

Chemical of Concern: CPP,DU,HXZ,MBZ,PDM,PRM,PZM,SZ,TFN,TRB

4. Diaz, G.; Carrillo, C., and Honrubia, M. Differential Responses of Ectomycorrhizal Fungi to Pesticides in 

Pure Culture. POPENV; 2003; 24, (3): 199-211. 

Rec #: 180

Call Number: LITE EVAL CODED (HXZ,HYX), OK (GYP,SZ), TARGET2012 

(BMY,Captan,IPD,THM)

Notes: EcoReference No.: 167816

Chemical of Concern: BMY,Captan,GYP,HXZ,HYX,IPD,SZ,THM

5. Elskus, A. A. Pilot Study of Sublethal Effects on Fish of Pesticides Currently Used and Proposed for Use on 

Maine Blueberries. BEH,GRO,MOR,PHYAQUA,MIXTURE; 2007: 14 p. (NTIS #PB2008-

108606). 

Rec #: 130

Call Number: LITE EVAL CODED (HXZ,PSM)

Notes: EcoReference No.: 104953

Chemical of Concern: HXZ,PSM,SS

6. Figueroa, P. F. First-Year Results of a Herbicide Screening Trial in a Newly Established Red Alder Plantation 

with 1 + 0 Bare-Root and Plug Seedling Stock. GRO,MOR,POPSOIL,ENV,MIXTURE; 1988; 41, 

108-124. 

Rec #: 40

Call Number: LITE EVAL CODED (HXZ), NO MIXTURE 

(24D,24DXY,ATZ,OYZ,SXD,SZ,TPR), OK (GYP,IZP,MTSM,PZM,SMU)

Notes: EcoReference No.: 161862

Chemical of Concern: 

24D,24DXY,ATZ,CPR,GYP,HXZ,IZP,MTSM,NPP,OYZ,PZM,SMU,SXD,SZ,TPR
Page 126 of 133

7. Flores, F.; Collier, C. J.; Mercurio, P., and Negri, A. P. Phytotoxicity of Four Photosystem II Herbicides to 

Tropical Seagrasses. PHY. a.negri@aims.gov.au//: AQUA; 2013; 8, (9): 12 p. (e75798). 

Rec #: 200

Call Number: LITE EVAL CODED (ATZ,DU,HXZ,TET)

Notes: EcoReference No.: 167314

Chemical of Concern: ATZ,DU,HXZ,TET

8. Frans, R. E.; Richardson, J. T., and Gordon, E. C. Herbicide Field Evaluation Trials on Field Crops, 1976. 

GRO,PHY,POPSOIL,ENV,MIXTURE; 1977; 249, 33 p. 

Rec #: 120

Call Number: LITE EVAL CODED (ATZ,HXZ), NO MIXTURE (BT), OK 

(ACR,DU,FDE,LNR,MFD,MTL,PDM,PMT,PRM,TFN)

Notes: EcoReference No.: 78899

Chemical of Concern: 

ACR,ATZ,BFL,BT,BTL,CZE,DEE,DFPM,DU,EFL,FDE,FMU,HXZ,LNR,MBZ,MFD,MSMA,MT

L,MTZ,PDM,PMT,PRM,TFN,VNT

9. Haywood, J. D. Effects of Herbaceous and Woody Plant Control on Longleaf Pine Growth and Understory 

Plant Cover. GRO,POPSOIL,ENV,MIXTURE; 2013; 37, 108-112. 

Rec #: 210

Call Number: LITE EVAL CODED (HXZ), NO MIXTURE (SXD), OK (TPR)

Notes: EcoReference No.: 167326

Chemical of Concern: HXZ,SXD,TPR

10. Holt, H. A.; Wickham, S. H., and Wichman, J. R. Forest Nursery Weed Control Results. GRO,POP. Dep. 

For. Nat. Resour., Purdue Univ., West Lafayette, IN//: SOIL,ENV; 1975; 30, 175-177. 

Rec #: 110

Call Number: LITE EVAL CODED (HXZ,SZ), OK (DCPA)

Notes: EcoReference No.: 71304

Chemical of Concern: DCPA,HXZ,NPP,ODZ,SZ

11. James, T. K. and Atkinson, G. C. Control of Browntop in Lucerne on Pumice Soils. 

POPSOIL,ENV,MIXTURE; 1979; 32, 58-61. 

Rec #: 50

Call Number: LITE EVAL CODED (GYP,HXZ,PZM), NO MIXTURE (SZ), OK (PAQT)

Notes: EcoReference No.: 161678

Chemical of Concern: CZE,GYP,HXZ,PAQT,PZM,SZ,TRB

12. Kalmbacher, R. S.; Colvin, D. L.; Martin, F. G., and Kretschmer, A. E. Jr. Reaction of Suerte Paspalum 

atratum to Herbicides. MOR,PHY,POPSOIL,ENV; 1996; 55, 110-115. 

Rec #: 60

Call Number: LITE EVAL CODED (HXZ), OK 

(CMZ,DMB,DMDP,DU,GYPI,MTSM,NFZ,SMM,TFN,TPR)

Notes: EcoReference No.: 162657

Chemical of Concern: 

CMZ,DMB,DMDP,DU,FMU,FZFB,GYPI,HXZ,IZT,MBZ,MTSM,NFZ,NSF,SMM,TFN,TPR

13. Liu, M. Y.; Hulting, A. G., and Mallory-Smith, C. A. Characterization of Multiple-Herbicide-Resistant Italian 

Ryegrass (Lolium perenne spp. multiflorum). CEL,GRO,PHYSOIL,ENV,MIXTURE; 2014; 70, 

1145-1150. 

Rec #: 220

Call Number: LITE EVAL CODED (HXZ), OK (ATZ,CLT,DU,GFSNH,GYPMK,IZPI,SMM,SXD)

Notes: EcoReference No.: 167327

Chemical of Concern: ATZ,CLT,DU,FFC,FZFB,GFSNH,GYPMK,HXZ,IZPI,PXSF,SMM,SXD

14. Meyers, S. L.; Jennings, K. M.; Monks, D. W.; Ballington, J. R., and Jordan, D. L. POST Control of Carolina 
Page 127 of 133

Redroot (Lachnanthes caroliniana). POPSOIL,ENV; 2013; 27, 534-537. 

Rec #: 230

Call Number: LITE EVAL CODED (HXZ), OK (DU,FMX,FSF,GFSNH,GYPMK,PQT,SXD)

Notes: EcoReference No.: 167324

Chemical of Concern: CPR,DU,FMX,FSF,GFSNH,GYPMK,HXZ,PQT,SXD

15. Meyers, S. L.; Jennings, K. M.; Monks, D. W.; Jordan, D. L., and Ballington, J. R. Effect of PRE and POST 

Herbicides on Carolina Redroot (Lachnanthes caroliniana) Growth. POPSOIL,ENV; 2013; 27, 747-

751. 

Rec #: 240

Call Number: LITE EVAL CODED (HXZ), OK (FMX,GFSNH,GYPMK,MTC,PQT)

Notes: EcoReference No.: 167323

Chemical of Concern: FMX,GFSNH,GYPMK,HXZ,MTC,PQT,TRB

16. Miller, J. H. and Andrews, G. W. Banded Herbicides can be as Effective as Windrowing. 

GRO,POPSOIL,ENV; 1985; 38, 216-225. 

Rec #: 160

Call Number: LITE EVAL CODED (HXZ,TET), OK (DMB)

Notes: EcoReference No.: 162948

Chemical of Concern: DMB,HXZ,PCLK,TET

17. Moyer, J. R.; Hironaka, R.; Kozub, G. C., and Bergen, P. Effect of Herbicide Treatments on Dandelion, 

Alfalfa and Sainfoin Yields and Quality. POPSOIL,ENV; 1990; 70, (4): 1105-1113. 

Rec #: 90

Call Number: LITE EVAL CODED (HXZ,SZ), NO EFFECT (EPTC,TFN)

Notes: EcoReference No.: 70404

Chemical of Concern: CSF,EPTC,HXZ,MBZ,SZ,TFN,TRB

18. Peng, S. Y. Isouron and Velpar in a New Criterion for Field Evaluation of Herbicides. 

GRO,POPSOIL,ENV,MIXTURE; 1980; 27, (3): 94-99. 

Rec #: 70

Call Number: LITE EVAL CODED (HXZ), NO MIXTURE (ATZ,NaDPA), OK (DU)

Notes: EcoReference No.: 163466

Chemical of Concern: ASM,ATZ,CZE,DU,HXZ,NaDPA

19. Peters, E. J.; McKelvey, R. A., and Mattas, R. Controlling Weeds in Dormant and Nondormant Alfalfa 

(Medicago sativa). POPSOIL,ENV; 1984; 32, (2): 154-157.

Rec #: 80

Call Number: LITE EVAL CODED (HXZ,SZ), OK (BT,DU,PAQT,PZM)

Notes: EcoReference No.: 161968

Chemical of Concern: BT,DU,HXZ,MBZ,PAQT,PZM,SZ,TRB

20. Samples, T. J.; Cargill, L. M., and Brede, A. D. Silver Beardgrass (Andropogon saccharoides) Control on 

Highway Rights-of-Way. POPSOIL,ENV,MIXTURE; 1987; 35, (1): 123-126. 

Rec #: 140

Call Number: LITE EVAL CODED (ATZ,HXZ,SZ), NO MIXTURE (MTL), OK 

(DU,GYP,PZM,SMU)

Notes: EcoReference No.: 31143

Chemical of Concern: ATZ,DU,GYP,HXZ,MTL,PZM,SMU,SZ

21. Schoenholts, S. H. and Barber, B. L. The Impact of Hericides on Loblolly Pine Plantation Establishment in 

East Texas. GRO,MOR,PHY,POPSOIL,ENV,MIXTURE; 1989; 74, 341-348. 

Rec #: 150

Call Number: LITE EVAL CODED (HXZ), NO MIXTURE (24D,24DXY,GYPI,SMM), OK 

(DMB,TPRT)

Notes: EcoReference No.: 44193
Page 128 of 133

Chemical of Concern: 24D,24DXY,DMB,GYPI,HXZ,PCL,SMM,TPRT

22. Sellers, B. A.; Ferrell, J. A., and MacDonald, G. E. Influence of Hexazinone on Pensacola Bahiagrass Growth 

and Crude Protein Content. BCM,POPSOIL,ENV; 2008; 100, (3): 808-812. 

Rec #: 170

Call Number: LITE EVAL CODED (HXZ)

Notes: EcoReference No.: 163441

Chemical of Concern: HXZ

23. Shipman, R. D. and Prunty, T. J. Effects of Herbicide Residues on Germination and Early Survival of Red 

Oak Acorns. GRO,REP. Pennsylvania State Univ., University Park, PA, 16802//: 

SOIL,ENV,MIXTURE; 1988; 42, 86-91. 

Rec #: 100

Call Number: LITE EVAL CODED (HXZ,SZ), OK (24D,24DXY,DMB,GYP,SMM,TPR)

Notes: EcoReference No.: 71308

Chemical of Concern: 24D,24DXY,DMB,GYP,HXZ,PCL,SMM,SZ,TPR

24. Sutton, R. F. and Weldon, T. P. White Spruce Establishment in Boreal Ontario Mixedwood: 5-Year Results. 

GRO,MORSOIL,ENV; 1995; 71, (5): 633-638. 

Rec #: 190

Call Number: LITE EVAL CODED (HXZ), OK (GYPI)

Notes: EcoReference No.: 163440

Chemical of Concern: GYPI,HXZ

25. Velisek, J.; Kouba, A., and Stara, A. Acute Toxicity of Triazine Pesticides to Juvenile Signal Crayfish 

(Pacifastacus leniusculus). MORAQUA; 2013; 34, (2): 31-36. 

Rec #: 250

Call Number: LITE EVAL CODED (ATZ,HXZ,PMT,SZ)

Notes: EcoReference No.: 167249

Chemical of Concern: ATZ,HXZ,MBZ,PMT,SZ
Page 129 of 133

Appendix K. Summary Hexazinone ECOSAR Runs

96-hr Fish LC50 (ppm)

Chemical

Aliphatic Amines Imides

Substituted Ureas

Triazines Amides

Neutral Organics

Hexazinone 

Measured

Fathead Minnow LC50 = 274 ppm

Hexazinone 

Estimated

38.465 6.138 49.424 45.150 54.251 151.119

IN-G3170; Met. G 1293.132 130.602 na 3752.027 8680.794 24467.182*

IN-JS472; Met. 1 850.211* 95.771 1930.158* 1987.807* 3933.477* 11055.558*

IN-B2838; Met. D Na 0.207 0.547 0.432 0.283 0.780

IN-G3453; Met. A-1 401.056 49.278 789.944 789.565 1379.543 3868.724

IN-A3928; Met. B 49.699 7.65 67.716 62.629 79.222 220.881

IN-JT677; Met. 2 274.584 35.204 504.537 496.969 817.016 2288.694

IN-T3937; Met. A 401.056 49.278 789.944 789.565 1379.543 3868.724

Values marked w/ yellow are lower than the measured fathead minnow endpoint.
Page 130 of 133

48-hr Daphnid LC50 (ppm)

Chemical

Aliphatic Amines Imides

Substituted Ureas

Triazines Amides

Neutral Organics

Hexazinone 

Measured

Daphnia magna acute EC50 = 151.6 ppm

Hexazinone 

Estimated

4.667 2.669 8.963 30.009 47.912 82.302

IN-G3170; Met. G 123.980 4.495 Na 593.454 1184.400 7995.650

IN-JS472; Met. 1 86.227 6.037 2654.802* 442.845 837.993 4081.089*

IN-B2838; Met. D Na 0.943 0.008 1.085 1.409 0.682

IN-G3453; Met. A-1 42.536 5.029 655.377 231.050 419.068 1573.630

IN-A3928; Met. B 5.920 2.727 15.131 37.192 60.430 115.570

IN-JT677; Met. 2 29.767 4.548 326.871 166.186 295.233 976.200

IN-T3937; Met. A 42.536 5.029 655.377 231.050 419.068 1573.630

Values marked w/ yellow are lower than the measured Daphnia magna endpoint.
Page 131 of 133

Welcome to the EFED 

Screening Tool for Inhalation Risk

This tool is designed to provide the risk assessor with a rapid method for determining the potential

significance of the inhalation exposure route to birds and mammals in a risk assessment.

Input

Application and Chemical Information

Enter Chemical Name Hexazinone

Enter Chemical Use Pastures

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 252.3

Enter Chemical Vapor Pressure (mmHg) 1.90E-07

Enter Application Rate (lb a.i./acre) 8

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 2258

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 530

Enter Lowest Rat Inhalation LC50 (mg/L) 3.94

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.58E-03

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.24E-04

Adjusted Inhalation LD50 9.36E+01

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.46E-06 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 8.45E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 9.03E-03 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.58E-03
Page 132 of 133

ppendix L. STIR Output

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 4.08E-04

Adjusted Inhalation LD50 2.35E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.74E-06 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.06E+00

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 4.53E-03 Exposure not Likely Significant
Page 133 of 133