Executive Summary 

The Health Effects Division (HED) Hexazinone Registration Review Team has evaluated the 

status of the human health assessments for the triazine-dione herbicide to determine the scope of 

work necessary to support Registration Review. Hexazinone is an herbicide registered for use on 

alfalfa, blueberries, pasture and range grasses, pineapples and sugarcane. It was first registered 

on November 1975 for general weed control in non-cropland areas. The Tolerance 

Reassessment Eligibility Decision (TRED) for hexazinone was revised on August 22, 2002. 

Exposures can be expected to occur via the dietary, drinking water, and occupational (handler 

and post-application) routes for hexazinone. 

Hexazinone is a triazine herbicide, which is structurally and toxicologically dissimilar to the 

other triazines herbicides, such as atrazine. The selectivity of triazine herbicides depends on the 

plant’s ability to degrade or metabolize the parent compound. Sensitive plants have limited 

ability to metabolize hexazinone. Hexazinone acts through inhibition of photosynthesis. 

The toxicology database for hexazinone has been determined to be nearly complete. The newly 

established data requirements for registration of a pesticide (food and non-food uses) under 40 

CFR Part 158 will be requested for hexazinone. A 28 day inhalation study was previously 

requested due to concern for the use pattern (a 90 day inhalation study was submitted; however, 

it does not meet the present guideline or GLP requirements). An immunotoxicity study will be 

required under a data call-in (DCI) in the near future. Following the data evaluation, HED will 

determine if these studies will impact the toxicity endpoints for hexazinone. 

Tolerances for residues of hexazinone in/on plant, livestock, and processed commodities are 

currently expressed in terms of the combined residues of hexazinone and its metabolites 

(calculated as hexazinone). The tolerance expression should be modified to include the specific 

metabolites (A, B, C, C-1, C-2, D, E and F) by the appropriate chemical name (See Table 1). 

Reassessed tolerances range from 0.1 ppm to 250 ppm. Tolerances are reassessed for alfalfa 

(hay and forage), blueberry, pineapple, sugarcane and pasture grass forage and hay as well as for 

secondary residues in cattle, goat, horse, sheep and milk. The registrant submitted field trial data 

for hexazinone and five of its metabolites (A-E) in/on warm-season pasture grass forage and hay 

and a reasonably balanced dietary burden (RBDB) was recalculated. 

Also, the data requirements for field accumulation in rotational crops are only partially satisfied. 

The data from the limited field trials indicate that quantifiable residues occur in field corn stover 

and wheat straw, extended field rotational crop trials for corn stover, sorghum stover, and wheat 

straw to support a 12-month rotational interval and a tolerance for inadvertent hexazinone 

residues are required. 

The Environmental Fate and Effects Division (EFED) has determined that a new drinking water 

assessment should be conducted which considers the potential for hexazinone formation during 

water treatment. Upon receipt of the revised drinking water assessment, new acute and chronic 

dietary exposure and risk assessments will be required which incorporate current consumption 

information, updated residue values and percent crop treated information while directly 

incorporating drinking water values into the assessment. 

Page 2 of 23 
There are currently no registered residential uses for hexazinone; however, it is registered for use 

on industrial turf grass with ground spray application. Given that no language exists on the label 

restricting the use of this herbicide on turf grass to be used in residential settings, the turf grass 

application could result in potential postapplication residential exposure. A residential exposure 

and risk assessment may be necessary for this scenario based on use on turf grass once new 

toxicological endpoints are determined. 

No occupational handler and post-application exposure or risk estimates were quantitatively 

assessed as part of the 2002 TRED. No toxicological endpoints were identified at that time; 

therefore, an exposure and risk assessment was not performed. 

An updated occupational handler exposure assessment is necessary. The mixer/loader and 

applicator scenarios must be assessed in accordance with current guidelines and standard 

operating procedures for all scenarios and use sites that are currently registered. For postapplication exposure, there are many cultural practices which require hand labor that may lead to 

the exposure of fieldworkers engaged in task such as harvesting, irrigation, scouting or weeding. 

Exposure and risk estimates will need to be updated with the most current transfer coefficient 

values anticipated to be developed based on data from the Agricultural Reentry Task Force and 

as discussed at the 2008 meeting of the FIFRA Scientific Advisory Panel meeting on this issue. 

Once the hazard endpoints are updated, a new occupational handler risk assessment and postapplication exposure and risk assessment will be needed for registration review. The existing 

Restricted Entry Interval (REI) of 48 hours appears to be adequate. 

New acute, short-term, and chronic aggregate risk assessments will be required to support 

registration review. These assessments should incorporate any new PoDs and/or uncertainty 

factors identified. 

Prior to a final registration review decision for hexazinone, the Agency will determine if there is 

any new information, such as new hazard or exposure data or changes to the use pattern, which 

would affect the cumulative risk assessment. Should the Agency determine that new information 

on hexazinone is available that could potentially impact the cumulative risk assessment and 

result in a risk of concern, the Agency will revisit the cumulative risk assessment. 

Introduction 

Hexazinone is a triazine-dione herbicide registered for use on alfalfa, blueberries, pasture and 

range grasses, pineapple, and sugarcane. It is also registered for use on ornamental plants, forest 

trees, and non-crop areas. Hexazinone is used to control a variety of weed species including 

geratum, alder, and alexander grass and works through inhibition of photosynthesis. Hexazinone 

is a proprietary chemical of E.I. du Pont de Nemours Inc. which is the sole producer and primary 

registrant of this broad spectrum herbicide. HED has evaluated the most recent human health 

exposure and risk assessments for hexazinone to determine if sufficient data are available and if 

updates are needed to support registration review. HED has considered the most recent exposure 

and risk assessments for this chemical, updates to its toxicity, exposure and usage databases, and 

the latest Agency science policy and risk assessment methodologies. 

Page 3 of 23 
Chemical Identity 

Tolerances for residues of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine2,4-(1H, 3H)-dione] in/on plant, animal, and processed commodities are currently expressed in 

terms of the combined residues of hexazinone and its metabolites (calculated as hexazinone). 

Permanent tolerances are established for plant and animal commodities under 40 CFR 

§180.396(a). Hexazinone tolerances with regional (Florida sugarcane) registrations are 

established under 40 CFR §180.396(c). Current tolerances range from 0.2 to 5.0 ppm on raw 

agricultural commodities, 8.0-10.0 ppm on agricultural feed items, and are 0.1 ppm for 

secondary residues in meats and milk. The Agency has determined that tolerances for 

hexazinone residues in eggs and poultry tissue are not required based on the results of the 

respective poultry metabolism and feeding studies (CFR §180.6(a)(3)). The chemical structure 

and nomenclature of hexazinone and its metabolites and the physicochemical properties of 

technical grade hexazinone are presented in Tables 1 and 2. 

Hazard Identification/Toxicology 

Hexazinone is a triazine herbicide, which is structurally and toxicologically dissimilar to the 

other triazines herbicides, such as atrazine. The selectivity of triazine herbicides depends on the 

plant’s ability to degrade or metabolize the parent compound. Sensitive plants have limited 

ability to metabolize hexazinone. Hexazinone acts through inhibition of photosynthesis. 

The toxicology database for hexazinone has been determined to be nearly complete. The newly 

established data requirements for registration of a pesticide (food and non-food uses) under 40 

CFR Part 158 will be requested for hexazinone. A 28 day inhalation study was previously 

requested due to concern for the use pattern (a 90 day inhalation study was submitted in 1976, 

EPA MRID# 00063972; however, it does not meet the present guideline or GLP requirements), 

also an immunotoxicity study will be required under a DCI in the near future. Following the data 

evaluation, HED will determine if these studies will impact the toxicity endpoints for 

hexazinone. 

Hexazinone has low acute toxicity by the oral (Category III), dermal (Category IV) and 

inhalation routes (Category III) of exposure. Primary eye irritation was severe, causing corneal 

opacity and moderate irritation in unwashed eyes (Category I). Hexazinone also causes mild 

skin irritation and is classified Category IV for skin irritation (see Table 4). Hexazinone is not a 

skin sensitizer in the guinea pig. Hexazinone is classified as “not likely” to be a human 

carcinogen based on carcinogenicity studies in rats and mice. 

Hexazinone is not known to be an endocrine disruptor. However, EPA is required under the 

FFDCA, as amended by FQPA, to develop a screening program to determine whether certain 

substances (including all pesticide active and other ingredients) “may have an effect in humans 

that is similar to an effect produced by a naturally occurring estrogen, or other such endocrine 

effects as the Administrator may designate.” Following the recommendations of its Endocrine 

Disruptor Screening and Testing Advisory Committee (EDSTAC), EPA determined that there 

were scientific bases for including, as part of the program, androgen and thyroid hormone 

systems, in addition to the estrogen hormone system. EPA also adopted EDSTAC’s 

recommendation that the Program include evaluations of potential effects in wildlife. When the 

Page 4 of 23 
appropriate screening and/or testing protocols being considered under the Agency’s Endocrine 

Disrupter Screening Program (EDSP) have been developed and vetted, hexazinone may be 

subjected to additional screening and/or testing to better characterize effects related to endocrine 

disruption. 

There is no evidence of qualitative or quantitative susceptibility in prenatal developmental or 

post-natal reproduction studies; hexazinone is not a developmental or reproductive toxicant in 

the rat. A rabbit developmental study showed possible skeletal anomalies and delayed 

ossification at the highest dose tested; however, this study is classified as unacceptable, but 

potentially upgradable, due to technical deficiencies. The registrant conducted a second prenatal 

developmental toxicity study in rabbits for which a NOAEL for developmental effects could be 

adequately determined and there was no increase in susceptibility noted (both the fetal and 

maternal endpoints were based on decreased body weights). 

An acute dietary endpoint was identified for females 13-50 years of age. The endpoints of 

decreased male and female fetal weight, increased incidence of kidneys with no papilla and an 

increased incidence of misaligned sternebrae in the fetuses were identified from a developmental 

toxicity study in rats. Because the toxic endpoint for acute dietary exposure concerns in utero

exposure, the risk assessment is performed for females of childbearing age (females 13-50), 

since only members of this group are at risk for being pregnant at the time of exposure. The dose 

selected for establishing the acute reference dose (RfD) is the developmental No Observed 

Adverse Effect Level (NOAEL) of 400 mg/kg/day. The chronic dietary endpoint was identified 

in an oral toxicity study in the dog and is based upon severe body weight decrement, clinical 

chemistry changes in the liver and microscopic lesions in the liver [NOAEL=5.0 mg/kg-bw/day]. 

Toxicological endpoints were established for acute and chronic dietary exposure scenarios as 

well as dermal (intermediate- and long-term) and inhalation (short-, intermediate-, and longterm) exposure scenarios. Incidental oral endpoints are now selected because of a potential postapplication exposure from the indicated label use on industrial turf. See Table 5. 

Conclusions 

As specified in the new 40 CFR Part 158 data requirements, an immunotoxicity study on 

hexazinone will be required, as is a neurotoxicity battery. The Agency also requires a 28-day 

inhalation study. Once all data have been received and reviewed, the Agency will determine if 

there is any new information, such as the points of departure and safety factors used for risk 

assessment purposes for hexazinone which would affect the cumulative risk assessment. 

Residue Chemistry 

The existing residue chemistry database for hexazinone is adequate for risk assessment purposes. 

The qualitative nature of the residue(s) of hexazinone in plants and animals has been adequately 

identified/characterized and is understood. 

The HED Metabolism Assessment Review Committee (MARC) has reviewed the hexazinone 

toxicology and metabolism data (meeting dates 01/29/02 and 03/12/02) and recommends that the 

tolerance expression for plant material should include hexazinone (parent) and metabolites A, B, 

C, D, and E. The tolerance expression for milk should include hexazinone (parent) and 

metabolites B, C, C-2, and F, and the tolerance expression for ruminant tissue should include 

Page 5 of 23 
hexazinone (parent) and metabolites B and F. The tolerance expression should be modified to 

include the specific metabolites (A, B, C, C-2, D, E and F) by the appropriate chemical name 

(See Table 1). The MARC also recommended that for the purposes of risk assessment estimates 

of dietary exposure and risk should be based on residue estimates of hexazinone and metabolites 

B, C, C-1, C-2, and F for ruminant commodities and metabolites A, B, C, D, and E for plant 

commodities. The Agency has determined that tolerances for hexazinone residues in eggs and 

poultry tissue are not required based on the results of the respective poultry metabolism and 

feeding studies (CFR §180.6(a)(3)). Adequate analytical methods exist for data collection and 

tolerance enforcement. Adequate storage stability, processed food, and magnitude of the residue 

in plants and animals data exist. 

Residue data are not adequate to reassess tolerances for pasture and rangeland grass (forage and 

hay) and a recommendation has been made to revoke those tolerances and to withdraw this use 

from the product labels. The Hexazinone Residue Chemistry Chapter (TRED, 05/20/02) required 

data depicting magnitude of the residues of hexazinone and metabolites A, B, C, D, and E in/on 

grass forage and hay harvested 0 day following a single broadcast application of representative 

formulations at 1.125 lb ai/A. A tolerance of 10 ppm for grass forage (listed as “grasses, 

pasture” and “grasses, range” under 40 CFR §180.396) was established based on residue data 

reflecting basal soil application only. The registrant submitted field trial data for hexazinone and 

its five metabolites (A-E) in/on warm-season pasture grass forage and hay; the HED has 

reviewed these data and found them to be adequate; therefore, this requirement is fulfilled. See 

Table 7 for recommended tolerances. Since grasses are major feed items, the established 

hexazinone tolerances for milk and the fat, meat, and meat byproducts of livestock will need to 

be reassessed and a reasonably balanced dietary burden (RBDB) will need to be recalculated. 

The RBDB of hexazinone to beef cattle are based on using the average residues for dairy cattle 

(108 ppm) and the HAFT for beef cattle (19.3 ppm). 

Additionally, the data requirements for field accumulation in rotational crops are only partially 

satisfied based on a recent review of a limited field crop rotation study (MRID 45084101). 

Because the data from the limited field trials indicate that quantifiable residues occur in field 

corn stover and wheat straw, extended field rotational crop trials for corn stover, sorghum stover, 

and wheat straw to support a 12-month rotational interval and a tolerance for inadvertent 

hexazinone residues are required. 

Conclusions 

The database for hexazinone is considered adequate for risk assessment; however, data 

deficiencies have been identified including a field rotational crop study for corn and wheat. The 

Agency is recommending new tolerances on all commodities listed under 40 CFR §180.396 (see 

Table 7).

Dietary Exposure and Risks 

An unrefined (tolerances and 100% crop treated) dietary risk assessment was completed in 2002 

using DEEM (J.Punzi, D279898, 07/30/02). 

Acute

An acute dietary endpoint was only identified for females 13-50 years of age. Estimated acute 

dietary (food only) risk for females age 13-50 associated with the use of hexazinone and its 

Page 6 of 23 
metabolites do not exceed the Agency’s level of concern. The acute dietary risk estimate for 

females 13-50 years of age is approximately 1% of the acute population adjusted dose (aPAD) at 

the 95th percentile. 

Chronic

Chronic dietary (food) risk estimates associated with the use of hexazinone do not exceed the 

Agency’s level of concern for any population subgroup, including the most highly exposed 

subgroup children 1-6. The chronic dietary risk for children ages 1-6 years is approximately 15% 

of the chronic population adjusted dose (cPAD) and approximately 4% for the U.S. population. 

Drinking Water

At the time of the most recent assessment, drinking water residues were not incorporated directly 

into the DEEM program. In the 2002 hexazinone risk assessment, the Agency performed surface 

and groundwater modeling to estimate drinking water concentrations which were then compared 

to the Drinking Water Level of Comparison (DWLOC). The GENEEC and PRZM-EXAMS 

models were used to estimate surface water concentrations and Screening Concentration in 

Ground Water (SCI-GROW) was used to estimate groundwater concentrations. This model 

simulated hexazinone and its metabolites in drinking water concentrations (for the alfalfa use) of 

130 μg/L for the surface water peak untreated water concentration. The results of the SmallScale Prospective Groundwater Monitoring Study were used to estimate concentrations of 

hexazinone and its degradates in groundwater (42 μg/L). The DWLOC calculated for acute 

aggregate risk for females 13-50 years old was 12,000 μg/L. HED concluded with reasonable 

certainty that residues of hexazinone and its metabolites in drinking water will not contribute 

significantly to the acute human health risk and that the acute aggregate exposure from residues 

of hexazinone and its metabolites in food and drinking water will not exceed the Agency’s level 

of concern for acute aggregate exposure for females 13-50 years old. 

The DWLOC calculated for chronic aggregate risk for all populations range from 427-1680 

μg/L. Because the estimated environmental concentrations (EECs) are less than the calculated 

DWLOC, HED concluded with reasonable certainty that residues of hexazinone and its 

metabolites in drinking water will not contribute significantly to the chronic human health risk 

and that the chronic aggregate exposure from residues of hexazinone and its metabolites in food 

and drinking water will not exceed the Agency’s level of concern for chronic aggregate exposure 

for any sub-population. 

Conclusions 

It will be necessary for HED to conduct a new dietary exposure assessment for hexazinone 

including new and updated information and policies. Further, HED’s policy with respect to 

drinking water risk assessment has been revised since the most recent human health risk 

assessment based on concerns that the DWLOC approach may underestimate risk for some 

subpopulations. Once the Environmental Fate and Effects Division (EFED) has updated the 

drinking water assessment, HED will need to revisit potential risks from drinking water by 

directly incorporating drinking water estimates into the acute and chronic aggregate dietary risk 

assessment. A drinking water assessment will be conducted to support future human health risk.

Page 7 of 23 
Residential Exposure and Risks 

There are no residential uses of hexazinone; however, it is registered for use on industrial turf 

grass with ground spray application. Given that no language exists on the label restricting the use 

of this herbicide on turf grass to be used in residential settings, the turf grass application could 

result in potential postapplication residential exposure. A residential exposure and risk 

assessment may be necessary for this scenario based on use on turf grass once new toxicological 

endpoints are determined. If information becomes available or label language is amended 

restricting the use of industrial turf grass on residences, places of recreation, schools, and other 

comparable areas, a residential exposure and risk assessment may not be warranted. 

Aggregate Risk Assessment 

The aggregate risk assessment evaluates the combined risk from dietary exposure (food and 

drinking water) and any non-occupational (residential) uses. The hexazinone aggregate risk 

assessment will include only dietary exposure (food and drinking water). As stated above under 

dietary risk, new acute and chronic dietary risk assessments are required to support the 

registration review of hexazinone and residential exposure to hexazinone from the use on 

industrial turf grass has not been assessed for the potential for residential exposure. Once the 

new toxicity data have been reviewed and new toxicity endpoints have been selected, a new 

aggregate risk assessment will be needed to support the registration review of hexazinone.

Conclusions 

Revised acute, short-term, and chronic aggregate risk assessments will be required to support 

registration review of hexazinone. 

Occupational Exposure and Risks 

Hexazinone is marketed as a liquid, soluble granules, water dispersible granules, and pellets. 

Hexazinone can also be used to impregnate dry bulk fertilizers and for stem injection 

applications. Hexazinone is used to control a variety of pests in crops including alfalfa, high and 

low brush blueberry, pineapple, and sugarcane. It can also be used to control pests in noncropland sites, Christmas trees, forestry site preparation, industrial areas, as brush control in 

reforestation areas, rangeland, pastures, yellow poplar plantings, and on industrial turf grass. 

Foliar and soil applications may be made by chemigation, injection, ground, or aerial equipment 

which may include fixed-boom sprayer, tank-type sprayer, backpack, handgun, tubular injection 

equipment, aerial (helicopter only), and by hand (hand dispersed pellets). 

Occupational Handlers

No occupational handler and post-application exposure or risk estimates were quantitatively 

assessed as part of the 2002 TRED. No toxicological endpoints were identified at that time; 

therefore, an exposure and risk assessment was not performed. 

An updated occupational handler exposure assessment is necessary. The mixer/loader and 

applicator scenarios must be assessed in accordance with current guidelines and standard 

operating procedures for all scenarios and use sites that are currently registered. Once the hazard 

Page 8 of 23 
endpoints are updated, a new occupational handler risk assessment will be needed for registration 

review. 

Occupational Post-application Workers

No occupational handler and post-application exposure or risk estimates were quantitatively 

assessed as part of the 2002 TRED. No toxicological endpoints were identified at that time 

therefore an exposure and risk assessment was not performed. 

There are many cultural practices which require hand labor that may lead to the exposure of 

fieldworkers such as harvesting, irrigation, scouting or weeding. Exposure and risk estimates will 

need to be updated with the most current transfer coefficient values that will be developed based 

on data from the Agricultural Reentry Task Force and as discussed at the 2008 meeting of the 

FIFRA Scientific Advisory Panel meeting on this issue. Once the hazard endpoints are updated, 

a new occupational post-application exposure and risk assessment will be needed for registration 

review. The existing Restricted Entry Interval (REI) of 48 hours appears to be adequate. For 

those use sites that are not covered within the Worker Protection Standard, the Agency had 

previously established an entry restriction for hexazinone end products stated as follows: “Do not 

enter or allow others to enter the treated area until sprays have dried” to apply to all applications 

other than the pellet formulation. 

Public Health and Pesticide Epidemiology Data 

The EPA is supplying the following incident report to fulfill our requirement to docket 

summaries of incident data that were reported to the Agency, as well as to ensure human incident 

data are part of the problem formulation phase of registration review. For this evaluation, both 

the OPP Incident Data System (IDS) and the Centers for Disease Control and 

Prevention/National Institute for Occupational Safety and Health (CDC/NIOSH) Sentinel Event 

Notification System for Occupational Risk (SENSOR) database were consulted for poisoning 

incident data on the active ingredient hexazinone. For IDS, we identified 0 incidents occurring in 

the United States from 2002 to the present for the single chemical only. 

For the NIOSH SENSOR database, there are eight cases reported that involve the active 

ingredient hexazinone (from 1998-2005). Of these eight cases, those that involve only 

hexazinone and where exposure was determined to be definite, probable or possible were 

reviewed in detail, as these cases provide more certain information about the potential effects of 

hexazinone exposure. These criteria eliminated six cases. One of the remaining cases was a 57 

year old male who was exposed through spray drift. He reported dermal symptoms. The other 

case was a 40 year old male who reported ocular and upper respiratory symptoms. No other 

details were reported about this case. There were no fatalities and both cases were ranked low 

severity. 

Based on the low severity and low number of incident cases, there does not appear to be a risk 

concern at this time that would warrant further investigation. The Agency will continue to 

monitor the incident information and if a concern is triggered, additional analysis will be 

included in the risk assessment. (M. Hawkins, Updated Review of Hexazinone Incident Reports, 

11/24/2009) 

Page 9 of 23 
Tolerance Assessment and International Harmonization 

Tolerances for hexazinone on raw agricultural commodities are currently established under 40 

CFR §180.396 and are expressed in terms of the combined residues of the herbicide hexazinone 

(3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione) and its metabolites, 

calculated as hexazinone. The tolerance expression must be revised in accordance with the most 

current guidance as follows: Tolerances for hexazinone on raw agricultural commodities are 

currently established under 40 CFR §180.396 and are expressed in terms of the combined 

residues of the herbicide hexazinone (parent) and metabolites A, B, C, D, and E. The tolerance 

expression for milk should include hexazinone (parent) and metabolites B, C, C-2, and F, and the 

tolerance expression for ruminant tissue should include hexazinone (parent) and metabolites B 

and F. The tolerance expression should be modified to include the specific metabolites (A, B, C, 

C-2, D, E and F). The Agency has determined that tolerances for hexazinone residues in eggs 

and poultry tissue are not required based on the results of the respective poultry metabolism and 

feeding studies (CFR §180.6(a)(3)). The chemical structure and nomenclatures are summarized 

in Table 1. There are no Codex Alimentarius Commission and Mexico maximum residue limits 

(MRLs) for hexazinone. 

Environmental Justice 

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations," 

http://www.epa.gov/compliance/resources/policies/ej/exec_order_12898.pdf. The Office of 

Pesticide Programs (OPP) typically considers the highest potential exposures from the legal use 

of a pesticide when conducting human health risk assessments, including, but not limited to, 

people who obtain drinking water from sources near agricultural areas, the variability of diets 

within the U.S., and people who may be exposed when harvesting crops. Should these high 

exposures indicate potential risks of concern, OPP will further refine the risk assessments to 

ensure that the risk estimates are based on the best available information. 

Cumulative Risk Assessment 

The Food Quality Protection Act (FQPA) requires the Agency to consider the cumulative risks of 

chemicals sharing a common mechanism of toxicity. The preliminary evaluation of common 

mechanisms of toxicity indicated that hexazinone would not have a common mechanism of 

toxicity sufficient to be grouped with the triazines. 

Prior to a final registration review decision for hexazinone, the Agency will determine if there is 

any new information, such as new hazard or exposure data or information on changes to the use 

pattern, which would affect the cumulative risk assessment. Should the Agency determine that 

new information on hexazinone is available that could potentially impact the cumulative risk 

assessment and result in a risk of concern, the Agency will revisit the cumulative risk 

assessment. 

Page 10 of 23 
Human Studies 

Future exposure and risk assessments will rely in part on the use of the Pesticide Handlers Exposure 

Database (PHED), the Agricultural Handlers Exposure Task Force (AHETF), and the Agricultural 

Reentry Task Force (ARTF). All data from PHED have been reviewed and found to be compliant 

with requirements for the ethical conduct of such studies. Studies conducted as part of the AHETF 

prior to 2006 have gone through appropriate ethics review. Protocols and subsequent reviews for 

studies conducted after 2006 will be addressed by the Human Subjects Review Board. In addition, 

data from the ARTF would be used to calculate current worker postapplication risks. These data have 

been reviewed and found acceptable from an ethical perspective. As the studies in PHED, AHETF, 

and ARTF are considered appropriate (or ethically conducted) they will be used for 

incorporation into future risk assessments. 

. 

Data Requirements 

HED does not anticipate that additional residue chemistry, toxicology or occupational/residential 

exposure data will be required for the hexazinone registration review process, with the exception 

of the following studies listed below: 

• Immunotoxicity Study (OPPTS 870.7800). 

• Neurotoxicity Battery 

• A 28-day inhalation study 

• A field rotational crop study for corn and wheat 

References 

Author Barcode Date Title 

John Punzi D279899 May 20, 2002 Residue Chemistry Chapter for the Tolerance 

Reassessment Eligibility Decision (TRED) 

John Punzi D279898 July 30, 2002 Acute and Chronic Dietary Exposure Assessments for 

the TRED 

TXR#0051049 August 8, 2002 Second Report of the FQPA Safety Factor Committee 

TXR#0051033 August 12, 2002 Third Report of the Hazard Identification Assessment 

Review Committee 

TXR#0051040 August 20, 2002 The Revised Toxicology Chapter for the TRED for 

Hexazinone 

Carol Christensen D275621 August 22, 2002 Revised HED Chapter for the Hexazinone Tolerance 

Reassessment Eligibility Decision 

P.Yvonne Barnes D328433 May 18, 2006 Protocol Review for the Magnitude of Residues of 

Hexazinone in Pasture Grass Forage and Hay 

Sheila Piper D339967 October 16, 2009 Magnitude of the Residue for Hexazinone in WarmSeason Pasture Grass Forage and Hay Following 

Application of Velpar DF Herbicide 

Monica Hawkins -- November 24, 

2009 

Updated Review of Hexazinone Incident Reports 

Page 11 of 23 
Tables 

Table 1: Chemical Structures of Hexazinone and its Regulated Metabolites (Metabolites A 

through F) 

Table 2: Physicochemical Properties - Hexazinone 

Table 3: Toxicology Data Requirements 

Table 4: Acute Toxicity Profile - Hexazinone 

Table 5: Summary of Toxicological Doses and Endpoints for Hexazinone for Use in Dietary and 

Non-Occupational Human Health Risk Assessments 

Table 6: Rationale for Requiring the Toxicological Data 

Table 7: Tolerance Summary for Hexazinone 

Table 1: Chemical Structures of Hexazinone and its Regulated Metabolites (Metabolites 

A through F) 

Common Name/Code

Chemical name Structure 

Hexazinone

3-cyclohexyl-6-(dimethylamino)-1-

methyl-1,3,5-triazine-2,4-(1H,3H)-

dione 

N

N

N

O

O

CH3

N

CH3

CH3

IUPAC 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4-

dione 

PC Code 107201 

Chemical Abstracts Number 51235-04-2 

Registration Review Case Number. 0266 

Metabolite A

3-(4-hydroxycyclohexyl)-6-

(dimethylamino)-1-methyl-1,3,5-

triazine-2,4-(1H,3H)-dione 

Metabolite A-1 is hydroxylated at the 

2- position of the cyclohexyl ring; 

Metabolite A-2 is hydroxylated at the 

3-position of the cyclohexyl ring. 

N

N

N

O

O

CH3

N

CH3

CH3

OH

Metabolite B

3-cyclohexyl-6-(methylamino)-1-

methyl-1,3,5-triazine-2,4-(1H,3H)-

dione 

Page 12 of 23 
Page 13 of 23 

Table 1: Chemical Structures of Hexazinone and its Regulated Metabolites (Metabolites 

A through F) 

Common Name/Code

Chemical name Structure 

N

N

N

O

O

CH3

N

H

CH3

Metabolite C

3-(4-hydroxycyclohexyl)-6-

(methylamino)- 

1-methyl-1,3,5-triazine-2,4-(1H,3H)-

dione 

Metabolite C-1 is hydroxylated at the 

2- position of the cyclohexyl ring; 

Metabolite C-2 is hydroxylated at the 

3- position of the cyclohexyl ring. 

N

N

N

O

O

CH3

N

H

CH3

OH

Metabolite D

3-cyclohexyl-1-methyl-1,3,5-triazine2,4,6-(1H,3H,5H)-trione N

N

NH

O

O

CH3

O

Metabolite E

3-(4-hydroxycyclohexyl)-1-methyl1,3,5-triazine-2,4,6-(1H,3H,5H)-trione N

N

NH

O

O

CH3

O

OH

Metabolite F
Table 1: Chemical Structures of Hexazinone and its Regulated Metabolites (Metabolites 

A through F) 

Common Name/Code

Chemical name Structure 

3-cyclohexyl-6-amino-1-methyl1,3,5-triazine-2,4-(1H,3H)-dione 

N

N

N

O

O

CH3

NH2

Table 2. Physicochemical Properties - Hexazinone 

Parameter Value Reference 

Melting point/range 113.5 oC 

pH Not Applicable, a solid 

Water solubility 25 oC is 2.98g/100g. 

Solvent solubility (g/100mL) Methanol 265, Acetone79, and Hexane 0.3 g/100 g. 

Vapor pressure 1.9 x 10-7 mm Hg at 25 oC 

Chemical class/use triazinones

Page 14 of 23 
Table 3. Toxicology Data Requirements

Test Technical

Required Satisfied

870.1100/§81-1 Acute Oral Toxicity............................................... 

870.1200/§81-2 Acute Dermal Toxicity.......................................... 

870.1300/§81-3 Acute Inhalation Toxicity...................................... 

870.2400/§81-4 Primary Eye Irritation ........................................... 

870.2500/§81-5 Primary Dermal Irritation...................................... 

870.2600/§81-6 Dermal Sensitization ............................................. 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

870.3100/§82-1 Oral Subchronic Toxicity (rodent) ........................ 

870.3150/§82-1 Oral Subchronic Toxicity (nonrodent) .................. 

870.3200/§82-2 21/28-Day Dermal Toxicity .................................. 

870.3250/§82-3 90-Day Dermal Toxicity ....................................... 

870.3465 §82-4 90-Day Inhalation Toxicity ................................... 

Yes 

Yes 

Yes 

No1 

No2

Yes 

Yes 

Yes 

Yes 

No 

870.3700/§83-3 Prenatal Developmental Toxicity (rodent) ............ 

870.3700/§83-3 Prenatal Developmental Toxicity (nonrodent) ...... 

870.3800§83-4 Multigeneration Reproductive Toxicity ................ 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

870.4100/§83-1 Chronic Toxicity (rodent)...................................... 

870.4100/§83-1 Chronic Toxicity (nonrodent)................................ 

870.4200/§83-2 Carcinogenicity (rat) ............................................. 

870.4200/§83-2 Carcinogenicity (mouse) ....................................... 

870.4300/§83-5 Chronic/Carcinogenicity ....................................... 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

870.5100/§84-2 Mutagenicity—Gene Mutation - bacterial............. 

870.5300/§84-2 Mutagenicity—Gene Mutation - mammalian ....... 

870.5375/§84-2 Mutagenicity—Struct. Chromosomal Aberrations 

870.5395/§84-2 Mutagenicity—Struct. Chromosomal Aberrations 

870.5550/§84-2 Mutagenicity—Other Genotoxic Effects............... 

Yes 

Yes 

Yes 

Yes 

Yes 

No3 

Yes 

Yes 

Yes 

Yes 

870.6100/§81-7 Acute Delayed Neurotoxicity (hen) ...................... 

870.6100/§82-5 90-Day Neurotoxicity (hen) .................................. 

870.6200/§81-8 Acute Neurotoxicity Screening Battery (rat).......... 

870.6200/§82-7 90-Day Neurotoxicity Screening Battery (rat) ....... 

870.6300/§83-6 Developmental Neurotoxicity......................... 

No4

No4 

Yes 

Yes 

- 

- 

No5 

No5 

- 

870.7485/§85-1 General Metabolism............................................... 

870.7600/§85-2 Dermal Penetration................................................. 

Yes 

No6

Yes 

No 

Special Studies for Ocular Effects7

Acute Oral (rat)........................................................... 

Subchronic Oral (rat) .................................................. 

Six-month Oral (dog).................................................. 

- 

- 

- 

- 

- 

- 

1

 Study not required for exposure pattern. 2 A 28-day inhalation study is required. 3 Another study is not required. 4

Required for organophosphates only. 5

 No required by exposure pattern Studies are required. 6 Study is optional. 7

Not required for this class of pesticides. 

Page 15 of 23 
Table 4. Acute Toxicity Profile - Hexazinone 

Guideline No. 

Study Type MRID(s) Results Toxicity 

Category 

870.1100 

§81-1 

Acute oral toxicity - rat 41235004 

(1989) 

LD50 = 1200 

mg/kg 

III 

870.1200 

§81-2 

Acute dermal toxicity - rabbit 00104974 

(1973) 

LD50 > 5278 

mg/kg 

IV 

870.1300 

§81-3 

Acute inhalation toxicity - rat 41756701 

(1990) 

LC50 > 3.94 mg/L 

(4 hour) 

III 

870.2400 

§81-4 

Acute eye irritation - rabbit 00106003 

(1982) 

Severe, 

irreversible 

corneal opacity 

I 

870.2500 

§81-5 

Acute dermal irritation - rabbit 00106004 

(1982) 

Mild IV 

870.2600 

§81-6 

Skin sensitization – guinea pig 

Buehler Method 

4123005 

(1989) 

Not a skin 

sensitizer 

NA 

Table 5. Summary of Toxicological Doses and Endpoints for Hexazinone for Use in 

Dietary and Occupational Human Health Risk Assessments 

Exposure/ 

Scenario 

Point of 

Departure 

Uncertainty/FQPA 

Safety Factors 

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment 

Study and Toxicological Effects 

Acute Dietary 

females 13-50 

years of age 

NOAEL 

400 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Acute RID = 

4.0 

mg/kg/day 

Developmental Toxicity – Rat LOAEL is 

900 mg/kg/day based on decreased male 

and female fetal weight, kidneys with no 

papilla (malformation) and misaligned 

sternebrae (variation). 

Acute Dietary 

general 

population 

including infants 

and children 

An appropriate endpoint attributable to a 

single dose was not identified in the oral 

studies (including rat and rabbit 

developmental studies) for all populations 

Chronic Dietary 

(All 

Populations) 

NOAEL= 

5.0 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Chronic RfD 

= 0.05 

mg/kg/day 

cPAD = 0.05 

mg/kg/day 

Chronic Feeding - Dog 

LOAEL = 41.24/37.57 (m/f) mg/kg/day 

based on severe body weight decrements 

and clinical chemistry changes. 

Incidental Oral 

Short-Term (1-

30 days) and 

Intermediate 

Term (1-6 

months) 

NOAEL= 

25.9/31.6 

(m/f) 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Residential 

LOC for 

MOE = 100 

Subchronic Feeding - Dog 

LOAEL = 440/451 (m/f) mg/kg/day based 

on decreased body weight gains, increased 

liver weights with clinical chemistry 

changes (both sexes). 

Page 16 of 23 
Table 5. Summary of Toxicological Doses and Endpoints for Hexazinone for Use in 

Dietary and Occupational Human Health Risk Assessments 

Exposure/ 

Scenario 

Point of 

Departure 

RfD, PAD, 

Uncertainty/FQPA 

Safety Factors 

Level of Study and Toxicological Effects 

Concern for 

Risk 

Assessment 

Dermal ShortTerm (1-30 

days) 

No hazard was identified in the dermal 

toxicity study in the rabbit submitted to 

fulfill the guideline recommendation. No 

systemic toxicity was seen up to the limit 

dose following repeat dermal application. 

Dermal 

IntermediateTerm (1-6 

months)1

NOAEL= 

5.0 (oral) 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Residential 

LOC for 

MOE = 100 

Chronic Feeding - Dog 

LOAEL = 41.24/37.57 (m/f) mg/kg/day 

based on severe body weight decrements 

and clinical chemistry changes. 

Inhalation ShortTerm (1-30 

days)2

NOAEL= 

50 (oral) 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Residential 

LOC for 

MOE = 100 

Developmental Toxicity - Rabbit 

LOAEL = 125 mg/kg/day based on 

decreases in maternal food consumption, 

dose related decease in body weight and 

fetal body weights. 

Inhalation 

IntermediateTerm (1-6 

months)2

NOAEL= 

5.0 (oral) 

mg/kg/day 

UFA= 10x 

UFH=10x 

FQPA SF= 1x 

Residential 

LOC for 

MOE = 100 

Chronic Feeding - Dog 

LOAEL = 41.24/37.57 (m/f) mg/kg/day 

based on severe body weight decrements 

and clinical chemistry changes. 

Dermal ShortTerm (1-30 

days) 

No hazard was identified in the dermal 

toxicity study in the rabbit submitted to 

fulfill the guideline recommendation. No 

systemic toxicity was seen at the limit 

dose following repeat dermal application. 

Dermal 

IntermediateTerm (1-6 

months)1

NOAEL= 

5.0 (oral) 

mg/kg/day 

UFA=10x 

UFH=10x 

Occupational 

LOC for 

MOE = 100 

Chronic Feeding - Dog 

LOAEL = 41.24/37.57 (m/f) mg/kg/day 

based on severe body weight decrements 

and clinical chemistry changes. 

Inhalation ShortTerm (1-30 

days)2

NOAEL= 

50 (oral) 

mg/kg/day 

UFA=10x 

UFH=10x 

Occupational 

LOC for 

MOE = 100 

Developmental Toxicity - Rabbit 

LOAEL = 125 mg/kg/day based on 

decreases in maternal food consumption, 

dose related decease in body weight and 

fetal body weights. 

Inhalation 

Intermediateterm (1-6 

months)2

NOAEL= 

5.0 (oral) 

mg/kg/day 

UFA=10x 

UFH=10x 

Occupational 

LOC for 

MOE = 100 

Chronic Feeding - Dog 

LOAEL = 41.24/37.57 (m/f) mg/kg/day 

based on severe body weight decrements 

and clinical chemistry changes. 

Cancer (oral, 

dermal, 

inhalation) 

Classification: “D” – Not Classifiable as to human carcinogenicity potential. 

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response 

data and used to mark the beginning of extrapolation to determine risk associated with lower 

environmentally relevant human exposures. NOAEL = no observed adverse effect level. LOAEL = lowest 

observed adverse effect level. UF = uncertainty factor. UFA = extrapolation from animal to human 

(interspecies). UFH = potential variation in sensitivity among members of the human population 

(intraspecies). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). 

RfD = reference dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable. Limit 

Dose = in oral and dermal systemic toxicity studies, 1000 mg/kg/day. 

1

 Since an oral NOAEL was selected, a 12.5% dermal absorption factor should be used for route to route 

exposures. 2

 Absorption via the inhalation route is assumed to be equivalent to oral absorption. 

Page 17 of 23 
Table 6a. Guideline Number: 870.3465 

Study Title: 28-Day Inhalation Toxicity 

Rationale for Requiring the Data 

A 28 day repeat inhalation study was recommended instead of a full 90 day study based on use 

patterns. The 28-day inhalation toxicity study evaluates the potential hazard of a pesticide 

chemical following repeated inhalation exposures. This study is critical for pesticides with use 

pattern in which there is potential for repeated human exposures (e.g., professional applicators, 

green house use etc) exposure. The study design simulates the route of human exposure 

(inhalation). In this study animals are exposed (nose/whole body) to aerosol concentrations of 

the test material for 6 hours/day, 5 day/week for 28 days. A detailed toxicological 

examination including the histopathology of the respiratory system is conducted. This is 

route-specific study would provide data for hazard characterization, dose response assessment, 

and a dose and endpoint for assessing potential risks via the inhalation route. 

Practical Utility of the Data 

How did the Agency make its re-registration decision without these data? 

A subchronic inhalation study provides critical scientific information needed to characterize 

potential hazard to human population on the respiratory system from pesticide exposure. A 

28-day repeated exposure study that follows the Test Guidelines (870.3465) will characterize 

hazard and provide data for a much accurate inhalation risk assessment. 

How will the data be used? 

This study will identify hazard (i.e., provide a dose and endpoint) following longer repeated 

exposures, this data will be used in risk assessments. If the Agency does not have this data, a 

10X database uncertainty factor may be applied for conducting a risk assessment from the 

available studies. 

Page 18 of 23 
Page 19 of 23 

Table 6b. Guideline Number: 870.7800 

Study Title: Immunotoxicity

Rationale for Requiring the Data 

This is a new data requirement under 40 CFR Part 158 as a part of the data requirements for 

registration of a pesticide (food and non-food uses). 

The Immunotoxicity Test Guideline (OPPTS 870.7800) prescribes functional immunotoxicity 

testing and is designed to evaluate the potential of a repeated chemical exposure to produce 

adverse effects (i.e., suppression) on the immune system. Immunosuppression is a deficit in 

the ability of the immune system to respond to a challenge of bacterial or viral infections such 

as tuberculosis (TB), Severe Acquired Respiratory Syndrome (SARS), or neoplasia. Because 

the immune system is highly complex, studies not specifically conducted to assess 

immunotoxic endpoints are inadequate to characterize a pesticide’s potential immunotoxicity. 

While data from hematology, lymphoid organ weights, and histopathology in routine chronic 

or subchronic toxicity studies may offer useful information on potential immunotoxic effects, 

these endpoints alone are insufficient to predict immunotoxicity. 

Practical Utility of the Data 

How will the data be used? 

Immunotoxicity studies provide critical scientific information needed to characterize potential 

hazard to the human population on the immune system from pesticide exposure. Since 

epidemiologic data on the effects of chemical exposures on immune parameters are limited 

and are inadequate to characterize a pesticide’s potential immunotoxicity in humans, animal 

studies are used as the most sensitive endpoint for risk assessment. These animal studies can 

be used to select endpoints and doses for use in risk assessment of all exposure scenarios and 

are considered a primary data source for reliable reference dose calculation. For example, 

animal studies have demonstrated that immunotoxicity in rodents is one of the more sensitive 

manifestations of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) among developmental, 

reproductive, and endocrinologic toxicities. Additionally, the EPA has established an oral 

reference dose (RfD) for tributyltin oxide (TBTO) based on observed immunotoxicity in 

animal studies (IRIS, 1997). 

How could the data impact the Agency's future decision-making? 

If the immunotoxicity study shows that the test material poses either a greater or a diminished 

risk than that given in the interim decision’s conclusion, the risk assessments for the test 

material may need to be revised to reflect the magnitude of potential risk derived from the new 

data. 

 

If the Agency does not have this data, a 10X database uncertainty factor may be applied for 

conducting a risk assessment from the available studies.
Table 6c. Guideline Number: 870.6200 

Study Title: Neurotoxicity Battery (Acute and Subchronic Studies)

Table 6c. Guideline Number: 870.6200 Study Title: Neurotoxicity Screening Battery 

Rationale for Requiring the Data Rat

This is a new data requirement under 40 CFR Part 158 as a part of the data requirements for registration of a pesticide (food and nonfood uses). The Neurotoxicity Screening Battery (OPPTS 870.6200) is designed to evaluate the potential adverse effects on the nervous system from exposure to pesticide chemicals. The Agency believes that the guideline studies are inadequate in their assessment of behavioral effects and do not use optimal methods to evaluate the potential toxicity to the nervous tissue structure and function. To detect and characterize these potential effects more fully, a battery of more sensitive testing is required. The objective of this neurotoxicity battery testing is to evaluate the incidence and severity of the functional and/or behavioral effects, the level of motor activity, and the histopathology of the nervous system. The acute neurotoxicitystudy is required to detect possible effects resulting from a single exposure. The subchronic neurotoxicity study is intended to detect possible effects resulting from repeated or long-term exposures. 

An acute neurotoxicity study with hexazinone wsigns of neurotoxicity from a single dose. Howstudy with hexazinone were not conducted, hexof being a neurotoxicant in the provided long te evidence of neurotoxicity in open literature sea studies did no examine neurotoxicity endpointsunder the revised CFR 158.340. 

Practical Utility of the Data P

How will the data be used? The acute and subchronic neurotoxicity studies provide critical scientific information needed to characterize potential hazard to the human population on the nervous system from pesticide exposure. These studies can provide data on a wide range of functional tests for evaluating neurotoxicity including sensory effects, neuromuscular effects, learning and memory and histopathology of 

How did the Agency make its re-registration deciFor many chemicals, the amount of toxicity data would be considered to be a complete toxicity d

able to select doses and endpoints for conductinavailable studies. However, the toxicity databasany long term neurotoxicity studies and there is 

 potential of hexazinone as none of the submitte

Page 20 of 23 
Page 21 of 23 

the nervous system For example, animal studies with organophosphorous chemicals have shown neurotoxicity to be the primary toxic endpoints (e.g., cholinesterase inhibition) of concernsin rodents and non-rodents. These animal studies can be used to select endpoints and doses for use in risk assessment of all exposure scenarios and are considered a primary data source for reliable reference dose calculation. The Agency has established an oral reference dose (RfD) for assessing dietary risks for a number of chemicals (e.g., organophoshates and carbamates) where neurotoxicity was the most sensitive endpoint of concern. 

How could the data impact the Agency's future decision-making?If the acute or subchronic neurotoxicity studies show that hexazinone poses either a greater or a diminished risk than that given in the interim decision’s conclusion, the risk assessments for 

hexazinone may need to be revised to reflect the magnitude of potential risk derived from the new data. 

If the Agency does not have this data, a 10X database uncertainty factor may be applied when conducting a risk assessment using the 

currently available studies.

measured neurotoxicity endpoints. How will the data be used? After the review and evaluation of the subchron

possible that Agency could choose a dose and en

neurotoxicity study for the deriving the acute RfHow could the data impact the Agency’s future dIf the acute RfD changes, then the hexazinone awould need to be conducted. At present there wtoxicity studies including developmental toxicitcould be attributable to a single dose (exposure)for the acute RfD. 
Table 7. Tolerance Summary for Hexazinone 

Commodity Proposed 

Tolerance 

(ppm) 

Established 

Tolerance 

(ppm) 

Recommended 

Tolerance (ppm) 

Comments; 

Correct 

Commodity 

Definition

Tolerances for combined residues of hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-

triazine-2,4(1H,3H)-dione) and its metabolites, calculated as hexazinone 

 [40 CFR 180.396] 

Alfalfa green forage -- 2.0 2.0 

Alfalfa, hay -- 8.0 4.0 

Alfalfa, seed -- -- 2.0 HED is requesting the 

registrant to propose a 

tolerance for hexazinone 

residues of concern in/on 

alfalfa seed of 2.0 ppm 

based upon a residue 

field trial study at 1.5x 

the maximum registered 

rate on alfalfa grown for 

seed. 

Blueberry -- 0.2 0.6 Tolerance should be 

increased based on the 

combined LOQ (0.55 

ppm) of the enforcement 

method.

Cattle, fat -- 0.1 0.1 

Cattle, meat -- 0.1 0.5 

Cattle, meat byproducts -- 0.1 4.0 

Goat, fat -- 0.1 0.1 

Goat, meat -- 0.1 0.5 

Goat, meat byproducts -- 0.1 4.0 

Grass, forage -- 10 250 

Grass, hay -- -- 230 

Hog, fat -- 0.1 0.1 

Hog, meat -- 0.1 0.5 

Hog, meat byproduct -- 0.1 4.0 

Horse, fat -- 0.1 0.1 

Horse, meat -- 0.1 0.5 

Horse, meat byproduct -- 0.1 4.0 

Milk -- 0.1 11 

Pineapple -- 0.5 0.6 Tolerance should be 

increased based on the 

combined LOQ (0.55 

ppm) of the enforcement 

method. 

Sheep, fat -- 0.1 0.1 

Page 22 of 23 
Page 23 of 23 

Table 7. Tolerance Summary for Hexazinone 

Commodity Proposed 

Tolerance 

(ppm) 

Established 

Tolerance 

(ppm) 

Recommended 

Tolerance (ppm) 

Comments; 

Correct 

Commodity 

Definition

Sheep, meat byproduct -- 0.1 4.0 

Sugarcane, cane -- 0.2 0.6 Tolerance should be 

increased based on the 

combined LOQ (0.55 

ppm) of the enforcement 

method.

Sugarcane, molasses -- 5.0 4.0