OFFICE OF

CHEMICAL SAFETY AND

POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

PC Code: 129701

 DP Barcode: 425426

Date: 10/19/2015

MEMORANDUM

Subject: Hymexazol: Ecological Risk Assessment for Registration Review

To: Caitlin Newcamp, Chemical Review Manager

Ricardo Jones, Chemical Review Manager

Risk Management and Implementation Branch 1

Pesticide Re-evaluation Division

Through: Dana Spatz, Branch Chief

Environmental Risk Branch 3

Environmental Fate and Effects Division

From: Tanja Crk, Biologist 

James K. Wolf, PhD. Environmental Scientist 

Environmental Risk Branch 3

Environmental Fate and Effects Division

Peer Review: Melissa Panger, Ph.D., Senior Scientist

Rosanna Louie-Juzwiak, RAPL

Environmental Risk Branch 3

Environmental Fate and Effects Division

This memorandum transmits the Environmental Fate and Effects Division’s (EFED) ecological risk 

assessment for hymexazol. The results of this risk assessment indicate: 

For seed treatment on sugar beets: 

• Growth effects to non-target plants are not expected.

• Effects of mortality, growth, and reproduction of fish, aquatic-phase amphibians, and 

aquatic invertebrates are not expected.
• Risk of mortality and reproductive effects have been identified for mammals and birds.

Although this chemical is slightly toxic to mammals and birds on an acute oral basis and 

practically non-toxic to birds on an acute dietary basis, the LOC exceedances identified in 

this assessment can be attributed to potentially high application rates (i.e., 0.15- 1.25 lb 

a.i./A), which are based on the seed treatment application and seeding rate. For details, 

see Risk Characterization Section and Appendix E. 

• Despite risk identified for birds (i.e., considered surrogates for terrestrial-phase 

amphibians and reptiles), the effects of mortality, growth, and reproduction of terrestrialphase amphibians and reptiles are not expected on the basis of low likelihood of seed 

consumption.

• Risk to terrestrial invertebrates is not expected based on toxicological data from the 

European Food Safety Authority (EFSA). The data was submitted by the registrant upon 

request for this risk assessment and has been reviewed for this risk assessment.

The EPA reviewed honey bee studies and the EFSA (2010) report cite acute oral and contact 

honey bee endpoints as LD50>100 mg/bee and LC50>100 mg/bee, respectively. Hymexazol is 

registered for use as a fungicide and is applied via seed treatment on sugar beets. The compound 

is systemic1 but the mode and extent of systemic transport as well as persistence specifically in 

sugar beet plants is expected to be minimal -- for details, see the general explanation of 

anticipated systemic transport of hymexazol in plants in Section I.A. below.

The biennial crop needs the first year to produce sugar and second year to use the sugar for 

flower production. Therefore, sugar beets grown for their roots (for sugar) do not have flowers 

for pollination. However, sugar beets can also be grown for seed production and given that the 

sugar beet is both wind and insect pollinated, data to assess the effect on pollinators is 

recommended. Furthermore, sugar beets are attractive via nectar to honeybees and other bees.

However, given the rapid metabolization of the parent to CO2 and incorporation into sugars in 

the plant (MRID 42826314) and flowering time a year after planting, only the following studies

on the adult honey bee would be needed in order to conduct a risk assessment for honey bees

taking into account the seed treatment use:

1. Acute oral2 toxicity to adult honey bees (Non-guideline, OECD TG 213)

2. Acute contact2 toxicity to adult honey bee (OCSPP Guideline 850.3020)

At this time, data from these studies has been incorporated in this assessment on the basis of 

EFSA2 and EPA reviews.

 1 http://sitem.herts.ac.uk/aeru/iupac/Reports/388.htm

“Systemic, inhibits fungal growth by inhibiting nucleic acid synthesis (DNA / RNA synthesis).”

2 Report available online: http://www.efsa.europa.eu/en/scdocs/doc/1653.pdf
I. EXECUTIVE SUMMARY

A. Nature of the Stressor

Systemic properties of hymexazol

Hymexazol is a systemic fungicide, or more specifically, a partially (locally) systemic fungicide. It 

is rapidly translocated and has locally systemic distribution properties (Ypema, 2003). The 

chemical has upward properties (Mueller and Bradley, 2015) and is taken up by roots and rapidly 

transformed into glucosides for fungitoxic activity or stimulation of lateral root hair development 

in seedlings (Ypema, 2003).

Hymexazol is registered as a seed treatment to control soilborne pathogens on sugar beet such 

as Aphanomyces spp root rot and Pythium spp root rot. The fungicide is active for a few weeks 

after planting, plays an important role for early season control, does not protect against chronic 

root rot, and does not result in detectable residues in mature sugar beet roots (Harveson et al., 

2007). Though the two pathogens listed on the label cause root rot, implying that hymexazol 

ought to be present in the plant after germination for protection against the disease, a 

metabolism in sugar beets study (MRID 42826314) on the determination of food/non-food use, 

finds substantial evidence that hymexazol rapidly metabolizes (degrades) to CO2 in the plant and 

subsequently gets incorporated into sugars. In the study plants were treated with 45 g Tachigaren 

70WP/kg raw seed; total radioactive residues were 0.006-0.007ppm in aerial samples and 0.015-

0.022 ppm in roots. The study evaluation suggests that greater than 85% of the radioactivity in 

the sugar beets grown from hymexazol treated seeds was present due to incorporation of 14CCO2 into the natural sugars of the beet. As a result of this study, the Chemistry Branch Tolerance 

Support (CBTS, extant at the time within the Health Effects Division) determined that the sugar 

beet use of hymexazol is a non-food use.

II. PROBLEM FORMULATION

a. Pesticide Type, Class, and Mode of Action 

Hymexazol (5-methyl-3(2H)-isoxazolone; CAS No. 10004-44-1) is a fungicide belonging to the 

isoxazole chemical family. Hymexazol affects nucleic acid synthesis, possibly inhibiting 

DNA/RNA. FRAC3 has classified this MOA as a nucleic acid synthesis inhibitor. Hymexazol is

registered as a fungicide, but it may also function as a growth rate regulator4,5. The parent 

hymexazol is assumed to be the only stressor as the degradation products were shorted lived.

 3 Fungicide Resistance Action Committee – www.frac.info

4 http://www.alanwood.net/pesticides/hymexazol.html

5 Payne and Williams, 1990.
b. Overview of Pesticide Use and Usage

Hymexazol is used as a seed treatment for sugar beet (Beta vulgaris) seeds to protect against 

seed and seedling diseases such as Aphanomyces spp. and Pythium spp. 

Hymexazol Usage 

Based on the Screening Level Usage Analysis memorandum produced by the Biological and 

Economical Analysis Division (EPA, June 11, 2014), an average of 3,000 pounds of hymexazol for 

seed treatment was used annually, with an average of 15 percent crop treated and a maximum 

of 25 percent crop treated (reporting years 2004 – 2012).

Sugar beet cultivation is found in many parts of the US but appear to be most prominent in 

California, Colorado, Michigan, Montana, Minnesota, Nebraska, North Dakota, Oregon, and 

Washington. Because sugar beets are grown nationwide, it is believed that hymexazol could be 

applied anywhere in the country. The acres of sugar beets planted and harvested for several 

years from the USDA National Agricultural Statistics Service (USDA, NASS, 20156) are 

summarized in Table 1. 

Table 1. Acres of sugar beets harvested in 2007, 2012, 2014, and 2015 and sugar beets 

 planted in 2014 and 2015.

State Acres

Harvesteda

2012

Harvesteda

2007

Planted

2014b

Harvested

2014b

Planted

2015b

Harvested

2015b,c

California 27,193 42,984 24,300 25,000 22,600 25,000

Colorado 30,553 29,235 29,600 27,000 29,300 26,700

Idaho 184,510 163,598 171,000 168,000 169,000 167,000

Michigan 156,447 150,054 151,000 154,000 150,000 153,000

Minnesota 480,847 485,650 440,000 430,000 434,000 416,000

Montana 45,807 47,533 45,100 44,700 44,400 44,400

Nebraska 51,671 44,938 49,000 48,000 45,900 46,500

North Dakota 227,771 245,735 216,000 224,000 215,000 218,000

Oregon 11,731 11,232 67,000 12,700 6,500 12,600

Vermont 6 - - - - -

Washington - 2,076

Wyoming 31,302 30,782 30,700 31,000 30,000 30,800

Total for sugard 1,249,481 1,253,817 1,163,400 1,644,000 1,146,700 1,140,000

Pennsylvania 2,344 2,510

Washington 1,351 -

Total for seedd 4,588 3,199 a http://www.agcensus.usda.gov/Publications/2012/Full_Report/Volume_1,_Chapter_2_US_State_Level/st99_2_025_025.pdf

b http://usda.mannlib.cornell.edu/usda/current/Acre/Acre-06-30-2015.pdf

c Relates to year of intended harvest for fall planted sugar beets in central California and to the year of planting for 

overwintered sugar beets in central and southern California.

d Totals may not add up because some states information was withheld to avoid disclosing data for individual operations

 6 http://www.nass.usda.gov/Data_and_Statistics/index.asp
The US Geological Survey as part of the NAWQA program7 reported national-level pesticide 

usage data for hymexazol available for a three year period (2009-2011). Figure 1 shows the use

areas for 2010. 

Figure 1. Hymexazol usage map for 2010 and by use year for 2009 to 2011 (USGS, 2014).

Hymexazol is not applied to the soil before sowing nor are seeds treated in the field. Sugar beet 

seeds are treated and pelletized in commercial operations and then sown through broadcast 

spreader or seed drill.

Application information for hymexazol is summarized in Table 2. Hymexazol is formulated as a 

wettable powder (70% active ingredient) in the fungicide seed treatment – Tachigaren 70 WP 

(EPA Reg. No. 48210-1). The application rate for hymexazol according to the label is 45 to 90 

 7http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2011&map=HYMEXAZOL&hilo=L&disp=Hy

mexazol
grams of Tachigaren 70 WP (hymexazol 70% active ingredient, a.i.) to 100,000 pelleted sugar beet 

seeds, or 31.5 to 63.0 gram a.i. to 100,000 seeds [0.315 to 0.63 mg a.i./seed]. The mass of the 

100,000 sugar beet seeds is about 1 kg (45,359 seeds per pound). Single application rates for 

hymexazol in lb a.i./A (needed for EFED exposure models) for seed treatment were not provided 

on the labels; however, EFED was able to convert the rates from lbs a.i./kg seed to lb a.i./A and 

the range is 0.126 to 1.25 pounds active ingredient/acre (lb a.i./A), depending upon sugar beet 

seeding rates (Table 3).

Table 2. Maximum Hymexazol Use Rates on Sugar beets (EPA Reg. No. 48210-1)

Seeding 

Ratea

(lb seed/A)

Max. Rate

per App

(lb a.i./kg seed)b

Max. App

Rate 

(lb a.i./A)

NON-FOOD/NON-FEED USES

2.0 0.139 0.126

3.6 0.139 0.23

4 0.139 0.25

4.8 0.139 0.30

5 0.139 0.32

5.5 0.139 0.35

8 0.139 0.50

10.0 0.139 0.63

15.0 0.139 0.95

19.8 0.139 1.25

a Based upon seeding rates given in Table 3.

b(0.139 lb a.i./kg seed or 0.063 lb a.i./lb seed)

The seeding rate (lb seed/A or # of seeds/A) varies from region or state and has changed over 

time (Table 3). Seed planting depth also varies from location to location on the basis of the 

moisture content in the soil needed for seed germination. Tables 2 and 3 capture the range of 

seeding rates found in the literature. However, the standard seeding rates used for terrestrial 

exposure calculations are found in T-REX and based on input from BEAD. These include seeding 

rates at 4.8 lb seed/A for sugar beets and 19.8 lb seed/A for sugar beet seed production.
Table 3. Sugar beet seed source, depth of seeding, seeding rate, and application methods.

Sugar beet seed 

Source

Seeding Depth 

(inch)

Seeding Rate

(lb seed/A or #seed/A)

Khana 1 to 1.25 13,068 – 53,894 #/A

Bucklunchb 0.5 to 1.5 10 – 15c lb seed/A 

5 - 10 lb seed/A 

8 – 10 lb seed/A b,c,d

CO Crop Profiled 0.75 to 1.25 55,000 #/A

Sugar beet 

productione

0.75 6 - 10 lb seed/A

Seedlandf 0.25 to 0.5 8 -10 lb seed/A 

3 - 4 lb seed/A 

Handcock seed 

companyg

0.25 to 0.50 10 - 15 lb seed/A

OR sugar Beet 

productionh

0.75 4-10 lb seed/A

2015 Sugar beet 

Productioni

(ND and MN)

1.0 to 1.25 81,463 #seed/A; 22”row

3.5 inches between seed

Sugar beetj 1.5 1 – 2 lb seed/A

Holly Seedk 100,000 seeds/pellet

USEPA, 2011l 34,848 to 435,600 seeds/A

1.25 to 4.0 lb seed/A

a Khan 2013: http://www.sbreb.org/production/2013/2013SBProductionGuide.pdf

b http://www.bucklunch.com/docs/bucklunch_brochure.pdf; c http://www.bucklunch.com/docs/bucklunch_plantinstruct.pdf'

d http://www.ipmcenters.org/cropprofiles/docs/cosugarbeets.pdf

e http://cropandsoil.oregonstate.edu/system/files/classes/css460-560/Chapter_9.pdf f http://www.seedland.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=Seedland&Category_Code=WG-BEETS

g https://hancockseed.com/seed-varieties-241/sugar-beets-seed-668/

h Chastain T.G. http://cropandsoil.oregonstate.edu/system/files/u528/Sugar%20Beet%20Seed%20Production.pdf I http://www.smbsc.com/pdf/2015SBGuide.pdf

j http://corn.agronomy.wisc.edu/Crops/Sugarbeet.aspx

k http://www.hollyseed.com/seed/seed-packaging-sizing l USEPA, 2011. Becker, J. and S Ratnayake. 2011. Acres planted per day and seeding rates of crops grown in the United 

States. OCSPP/BEAD March 24, 2011.

c. Previous Ecological Risk Assessments and Evaluations

Hymexazol was registered in 1995 as a seed treatment for sugar beet (USEPA 1995a, DP 209885; 

USEPA 1995b, DP 209851, 205149). The concentrations of hymexazol (peak to 54-days) were < 6 

μg/L (ppb). The estimates were based on 0.126 lb a.i./A, assuming a typical planting (or seeding)

rate of 1.5 to 2.0 lbs of seed per acre. The environmental exposure concentrations (EECs) in 
aquatic systems were estimated with the Tier 1 GENEEC model, Version 1. A seed treatment 

assessment using the analysis currently available in T-REX was not conducted, nor was the Seed 

Consumption Approach (SCA) available at the time of this earlier assessment. Toxicity data used 

for this PRA on the passerine (acute oral), the chronic avian, and chronic mammalian studies were 

not available for this earlier assessment. Hymexazol did not reach the acute Levels of Concern 

(LOCs) for birds, mammals, freshwater fish and freshwater invertebrates. No study was available 

to evaluate the risk to estuarine and marine animals, but it was noted that the exposure was

limited by the use pattern, together with the low aquatic toxicity of hymexazol. Although the risk 

could not be quantitatively evaluated, it was concluded that no estuarine data were required. In 

addition, the label cautions phytotoxicity could occur when use rates are >45 g of product per 

seed. The risk to non-target plants could not be evaluated due to a lack of data. At that time, it 

was concluded that all RQs were well below the LOCs for endangered species for which data had 

been submitted on birds, mammals, fish and invertebrates. 

A registration review preliminary problem formulation was completed in 2010 (USEPA 2010a). 

III. Risk Hypothesis and Conceptual Model

a. Measures to Evaluate Risk Hypotheses

Measures of exposure are based on terrestrial and aquatic exposure models 8 that estimated

environmental concentrations (EEC) of hymexazol (parent) using maximum labeled application 

rates. The T-REX model (version 1.5.2) is used to produce terrestrial EECs on wildlife food items.

The TerrPlant model is used to estimate exposure to non-target plants. Because the use is a seed 

treatment, spray drift is assumed to be zero for both broadcast with incorporation or drilled

seeding. The Surface Water Concentration Calculator (SWCC9; version 1.106) is used to produce 

EECsfor aquatic exposure. Though the STIR model can be used to account for potential inhalation 

exposure, the model was not used in this assessment because inhalation is not anticipated to be 

a significant route of exposure from the seed treatment use; the seeds are expected to be coated 

and inhibit volatilization of the active ingredient leading to ingestion as the primary route of 

exposure.

Measures of effect are obtained from a suite of studies conducted with a limited number of 

surrogate species. The lowest toxicity endpoints for the most sensitive surrogate test species are 

used to estimate treatment-related effects on growth, reproduction and/or survival.

 8http://www.epa.gov/pesticides/science/models_pg.htm

9 http://www.epa.gov/oppefed1/models/water/index.htm#swcc
b. Environmental Fate and Modeling Input Parameters

Physical/Chemical and Environmental Fate Properties 

The physical/chemical properties are in Table 4 and the environmental fate properties of 

hymexazol are listed in Table 5.

Table 4. Select Identifiers and Physical and Chemical Properties of Hymexazol a

Parameter Value

Common name Hymexazol

Chemical name IUPAC: 5-methylisoxazol-3-ol 

 5-methyl-1,2-oxazol-3-ol

CAS:5-methyl-3(2H)-isoxazolone

Pesticide type Fungicide

Chemical class Isoxazoles chemical group

CAS number 10004-44-1, assigned to the enol tautomer

Trade name Tachigaren®

Empirical formula C4H5NO2

Chemical Structure

Molecular mass (g/mole) 99.09

Vapor pressure, at 25 ̊C 1.37 E-3 torr (mm Hg)

Henry’s Law Constant 6.5 E-9 atm-m3/mole*

2.74E-9 atm-m3/mole (calculated @ pH7)

Solubility in water (g/L) , 20 ̊C @ pH7 5.82 g/mLb (pH 3) 58.2 g/L

6.51 g/mLb (pH 7) 65.1 g/L (bold value used to 

calculate Henry’s constant

6.78 g/mLb (pH 9) 67.8 g/L

There appears to be a conversion error in one of the 

sources of solubility data as (e.g., 6.51 g/mL does not 

equal 65.1 g/L).

Log Kow 0.48

pKa 5.92

* Estimated via EPISuite

a MRIDs 428263-01/-02/-03. Reviewed 03/29/1995.

b Solubility in the Problem Formulation (02/16/2010) solubility was reported in g/mL however in other sources report 

solubility in g/L. 
Environmental Fate/Exposure Summary

Four Guideline studies were required when hymexazol (Tachigaren® 70 WP) was initially 

registered, in 1995, as a fungicidal seed treatment, pelletized for field-planted sugar beet seeds. 

The guideline studies were hydrolysis (161-1), aerobic soil metabolism (162-1), anaerobic soil 

metabolism (162-2), and adsorption/desorption (mobility, 163-1) (Table 5). These studies were 

discussed in detail for the new chemical registration action (D209851; 04/28/95). Since then, no 

additional information has been submitted. The environmental fate of hymexazol is summarized 

in Table 5 based on submitted fate and transport studies.

Table 5. Select Environmental Fate Data for Hymexazol.

Environmental Fate Property Value Comments MRID

Hydrolysis (t1⁄2) Stable @pH 5,7, 9 and 25 to 70°C 42826311

Aerobic Soil Metabolism (t1⁄2) 7.7 days SFOa (Single First Order) 42826312

Anaerobic Soil Metabolism (t1⁄2) 1.72 days SFOa (Single First Order) 43253801

Adsorption (mL/g or mL/goc) Kd Koc

<0.10 9.1

<0.10 11.8

0.25 193

0.423 18

0.526 66

AZ (SiCLm); Koc assume Kd = 

0.1

CA (SLm); Koc assume Kd = 0.1

Plainfield (Sand)

Kewaunee (Clay)

Mississippi (SiLm)

42826313

Octanol/water Partition 

Coefficient(Kow)

3.0 (Log Kow = 0.48) D209851b

a USEPA, 2014. Standard Operating Procedure for Using the NAFTA Guidance to Calculate Representative Half-life Values and 

Characterizing Pesticide Degradation (Nov. 26, 2014) OPP/EFED Arlington, VA.

b Clem, A. 1995. New Chemical Registration of the Fungicide Hymexazol. (D209851 04/28/95)

Biotransformation in aerobic and anaerobic soils is the major route of dissipation of hymexazol. 

Hymexazol is stable to abiotic hydrolysis. Biodegradation is a relatively rapid process with halflife of less than 12 days under aerobic conditions and less than 2-days under anaerobic 

conditions. The chemical biodegrades through ring-cleavage producing degradates that are 

mostly of lower molecular weight and are associated to naturally occurring products (e.g., 

acetoacetamide, crotonic acid, acetoacetic acid). These chemical species are short lived and 

transient. The end products are carbon dioxide under aerobic conditions and methane under 

anaerobic conditions. The metabolite 5-methyl-2(3H)-oxazolone was proposed as a possible, 

intermediate product in the degradation of hymexazol to CO2, where about 1 to 2% of applied 

was detected, but was not identified in the aerobic soil metabolism study (MRID 42826312).

Batch-equilibrium sorption studies indicate that hymexazol is very mobile. Mobility increases 

with pH, as expected from a weak acid with a pKa of 5.92. The Kd values ranged from < 0.1 to 

0.526 mL/g and calculated Koc values of 18 to 193 mL/goc indicating it is high to very high 

mobility10.

 10 Bradbury, S. 2006. Standardized Soil Mobility Classification Guidance. 
Possible volatilization of parent from dry soil is also suggested by the vapor pressure (1.37 X 10-3

torr) and Henry’s Law Constant value (2.74 x 10-9 atm-m3/mol). 

Hymexazol does not appear to have a potential to bioaccumulate in fish. Its n-octanol partition 

coefficient is very low (Kow = 3.0).

Monitoring Data Detections in Environmental Media 

The Agency was unable to locate or identify any monitoring data for hymexazol in the USGS 

NAWQA11 database, USDA Pesticide Data Program (PDP)12 database, and the California 

Department of Pesticide Regulation Surface Water Data Base13. 

Ecological Effects Characterization

Effects to Aquatic Organisms

A summary of the most sensitive aquatic toxicity data for hymexazol is provided in Table 6. Data 

indicate that hymexazol is practically non-toxic to freshwater fish and slightly toxic to 

invertebrates on an acute exposure basis. There are no available chronic toxicity data for fish 

and invertebrates, or toxicity data for estuarine/marine animals or marine non-vascular plants. 

The toxicity to these species exposed to hymexazol is uncertain.

Table 6. Aquatic Toxicity Profile for Hymexazol.

Taxon Exposure 

Duration

Most Sensitive 

Species Tested

Toxicity Value Toxicity 

Category

MRID /

Classification 

Freshwater 

Fish

Acute Rainbow trout

Oncorhynchus mykiss

LC50 >100 mg a.i./L

No Effects

Practically nontoxic

42960005

(acceptable; 

limit test)

Chronic EFSA Data Available Only. See risk characterization section.

Estuarine/ 

Marine Fish

Acute / 

Chronic No data available

Freshwater 

Invertebrates

Acute

Water Flea

Daphnia magna EC50 = 30.8 mg a.i./L Slightly toxic 42960007

(acceptable)

Chronic EFSA Data Available Only. See risk characterization section.

Estuarine/ 

Marine 

Invertebrates

Acute / 

Chronic No data available

 

11 USGS National Water Quality Assessment Data Warehouse (07/20/15)

NAWQA http://cida.usgs.gov/nawqa_public/apex/f?p=136:23:0:QUERY:NO 12 USDA, PDP 

http://www.ams.usda.gov/AMSv1.0/ams.fetchTemplateData.do?template=TemplateO&navID=PDPOviewBox2Link6&rightNav1

=PDPOviewBox2Link6&topNav=&leftNav=ScienceandLaboratories&page=PDPTestingHistory&resultType=&acct=pestcddataprg

13 CDPR, Surface Water Database (SURF) http://www.cdpr.ca.gov/docs/emon/surfwtr/surfdata.htm
Taxon Exposure 

Duration

Most Sensitive 

Species Tested

Toxicity Value Toxicity 

Category

MRID /

Classification 

Vascular 

plant Acute

Duckweed

Lemna gibba

EC50 = 7.9 mg a.i./L

NOAEC < 3.1 mg a.i./L

EC05 = 1.1 mg a.i./L

Not applicable 43926302

(supplemental1)

Non-vascular 

plant Acute Cyanobacteria

Anabaena flos-aquae2

EC50 = 23.39 mg a.i./L

NOAEC = 5.79 mg a.i./L

Reduced yield (for pHadjusted samples)

Not applicable 49021702

(acceptable)

1 Data on biomass was not available

2 Data on A. flos-aquae, P. subcapitata (formerly known as S. capricornutum), and N. pelliculosa were submitted. However, 

data on the marine diatom S. costatum are not available. 

Effects to Terrestrial Animals and Plants

A summary of the most sensitive terrestrial toxicity data for hymexazol is provided in Table 7. 

The data indicate that hymexazol is slightly toxic to mammals and is slightly toxic to practically 

nontoxic to birds on an acute exposure basis. A second avian reproduction study was reviewed 

for this assessment (MRID 49268101) and is reported below the avian reproduction study that 

was used in risk estimation (i.e., MRID 48716602). The EPA reviewed honey bee studies and the 

European Food Safety Authority (EFSA) risk assessment indicate acute oral and contact honey 

bee toxicity as LD50> 100 μg/bee and LC50 >100μg/bee, respectively, for the hymexazol technical.

Table 7. Terrestrial Toxicity Profile for Hymexazol.

Taxon Exposure 

Duration

Most Sensitive 

Species Tested Toxicity Value Toxicity 

Category

MRID

Reference

Mammals1

Acute

Rat

Rattus norvegicus

♂ LD50 = 1600 mg a.i./kg bw

Mortality

Slightly 

toxic

42960008

(acceptable)

[TGAI: 99.1% a.i. 

via gavage]

Chronic

NOAEL = 100 mg/kg-bw/day

LOAEL = 500 mg/kg-bw/day

Reduced fetal weight, 

evidence of other 

developmental abnormalities 

N/A

42826307

[teratogenicity 

studyw/TGAI: 

92.7% a.i. via 

gavage]

Acute Oral

Zebra Finch 

Taeniopygia guttata

(body weight: 12.7 g)2

LD50 = 827 mg a.i./kg bw

Mortality

Slightly 

toxic

49018701

(supplemental, for 

quantitative use)

Acute 

Dietary

Bobwhite quail

Colinus virginianus LC50 >5200 mg a.i./kg diet Practically nontoxic

42960004

(acceptable)

Chronic

Bobwhite quail

Colinus virginianus

NOAEC = 385 mg a.i./kg-diet

LOAEC = 962 mg a.i./kg-diet

Egg shell thickness

N/A 48716602 

(acceptable)

Mallard duck

Anas platyrhynchos

NOAEC = 902 mg a.i./kg-diet

LOAEC = 4467 mg a.i./kg-diet

Eggshell thickness

N/A 49268101 

(supplemental3)

Terrestrial 

Insects Acute Honey bee

Apis mellifera

LD50 >100 μg/bee

LC50 >100 μg/bee

Practically 

nontoxic

49718601

(supplemental, 

quantitative4)
Taxon Exposure 

Duration

Most Sensitive 

Species Tested Toxicity Value Toxicity 

Category

MRID

Reference

Terrestrial 

Plants -

Seedling 

Emergence

Survival 

and 

growth

Onion (monocot)

Allium cepa

IC25 = 174 lb a.i./A

NOAEC = 152 lb a.i./A

Reduced fresh weight 

(biomass) N/A

44071301 to 

44071310

(acceptable5) Cabbage (dicot)

Brassica oleracea

IC25 = 35 lb a.i./A

NOAEC = 16 lb a.i./A

Reduced fresh weight 

(biomass)

Terrestrial 

Plants –

Vegetative 

Vigor

Survival 

and 

growth

Ryegrass (monocot)

Lolium perenne

IC25 = 437 lb a.i./A

NOAEC = 166 lb a.i./A

Reduced fresh weight 

(biomass)

44071311 to 

44071320 

(acceptable);

44071319

(supplemental6)

Tomato (dicot)

Lycopersicon 

esculentum

IC25 = 63.5 lb a.i./A

NOAEC < 16.2 lb a.i./A

(IC05 = 32.1 lb a.i./A)

Reduced dry weight

48677801

(supplemental, for 

quantitative use)

1 An acute oral (gavage) toxicity study in rats using the TEP (70% a.i.; MRID42956301) is also available, where the male LD50: 

2700 mg a.i./kg-bw. Furthermore, a rat 2-generation reproduction study (MRID 42826309) suggests effects to postimplantation survival rate and litter size at the high dose (LOAEL: 159 mg a.i./kg-bw); the NOAEL in the study is 31 mg a.i./kgbw. However, the developmental NOAEL (100 mg/kg/day) is protective of the reproductive effects at 159 mg/kg/day in the 

2-generation study.

2 The body weight cited here was used in T-REX. It is based on the mean of mean body weights taken in the control from day 

0, day 7, and day 14 for both males and females. The means for the 5 control males at those respective time steps are: 12.8g,

13.4g, 13.6g; the means for the 5 control females are: 11.9g, 12.3g, 12.2 grams. The average of these values is 12.7 grams.

3 Quantitative for eggshell thickness only.

4 The honeybee study did not include a negative control. Treatment data were compared to a solvent control.

5 Upgraded from supplemental per US EPA 2010b memo. 6 Tomato plant only because the plants were not cultivated under optimal growing conditions.

IV. ANALYSIS

a. Exposure Modeling

Model inputs include values for certain physical-chemical properties of the pesticide, application 

practices, and crop agronomic information.

The input parameters used in this aquatic and terrestrial modeling assessment are selected from 

the environmental fate data submitted by the registrant or available in open literature or 

estimated (following EFED Model Input Guidance). Input parameters were prepared in 

accordance with US EPA-OPP EFED water model parameter selection guidelines, Guidance for 

Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides14.

Detailed information about the water models, selection of input parameters and scenarios can 

be obtained from http://www.epa.gov/oppefed1/models/water/index.htm.

 14 Parameters are selected as per Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of 

Pesticides; Version 2.1, October 22, 2009. 
Aquatic Modeling

Potential aquatic exposure (estimated environmental concentration, EECs) were estimated using 

the Surface Water Concentration Calculator (SWCC; Version 1.106, 05/22/2014) for surface 

water. The SWCC simulates the fate and transport of pesticides on the agricultural field and the 

fate and resulting daily concentrations of pesticides that reach an adjacent water body through 

runoff and erosion. Spray drift is assumed to be zero for treated seeds.

Surface water simulations are based on crop-specific scenarios developed to represent 

environmental conditions at sites with a generally high runoff vulnerability. For this assessment 

the standard Minnesota sugar beet scenario was used. Aquatic ecological exposure is estimated 

using the “standard pond” scenario based on a 10-ha field bordering a 1-ha water body, 2-m deep 

(20,000 m3) with no outlet. Weather and agricultural practices are simulated for 30 years so that 

the 10-year exceedance probability at the site can be estimated. The simulation was generated 

using 30 years of meteorological data, encompassing the years from 1961 to 1990.

Aquatic Model Inputs

The hymexazol is applied to the seed and the seed is broadcast with incorporation or drilled in 

by ground equipment. The date of application is assumed to be 7 days before crop emergence 

which is defined in each scenario. Spray drift is assumed to be zero, since the pesticide is applied 

to the seed. Because the label only specifies a maximum rate per 100 kg of treated seed, a range 

of seeding rates were considered, because of the range of sugar beet seeding rates (Table 3). The 

seeding rate (lb seed/A) therefore will influence the “hymexazol” application rate. There is also 

variability in the “pelleting of seed” which can also influence application rates (i.e., seeding rates).

The aerobic soil metabolism and anaerobic soil metabolism half-lives for modeling were obtained

using R Foundation for Statistical Computing (version 3.1.2 and xxDeg_08.13) following NAFTA15

guidance. The R statistics following the NAFTA guidance recommended using the SFO (single first 

order degradation model). The selection and procedure for selecting model input parameters 

followed EFED guidance16. Since no seed leaching study has been submitted, EFED assumed that

100 percent of the hymexazol applied to the seed was available for leaching and runoff17. Model 

inputs for the SWCC are summarized in Table 8.

 15 http://www.epa.gov/oppefed1/ecorisk_ders/degradation_kinetics/ftt_sop_using_nafta_guidance.pdf

16 http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm 17 USEPA, 2000. Standard Methods of Determining the Leachability of Pesticides from Treated Seed. (Keehner, D. 07/06/00).
Table 8. SWCC Input Parameters for Hymexazol. 

Input Parameter Value Reference/Discussion

Molecular Weight (g/mole)a 99.09 USEPA, 2010 (D371500)b

Henry’s Law Constanta

(atm-m3/mol)

2.74E-9 Estimated from solubility of 65.1 g/L

(@pH7, 20°C) 

Vapor Pressure @ 25oC (torr)a 1.37 x 10-3 USEPA, 2010 (D371500)

Solubility (mg/L) @ 25°Ca 65,100 (65.1 g/L)

Aqueous Photolysis Half-life [t1⁄2](days)a 0 No data

Hydrolysis [t1⁄2] @ pH 7 (days)a,c 0 Stable

Aerobic Soil Half-life [t1⁄2] (days)a,c 23.1 7.7 x 3 (single value x 3) EFED Guidance

Aerobic Aquatic Half-life [t1⁄2] (days)a 46.2 ASM x 2 (23.1 x 2) EFED Guidance

Anaerobic Aquatic Half-life [t1⁄2] (days) 0 No Data

Organic Carbon Partitiona,c

Coefficient (Koc) (mL/goc)

59.6 Average of 5 values (9.1, 11.8, 193, 18, 

66)

Pesticide Application 

Chemical Application Method 

 

Incorporated 2 cm. Estimated from Table 3 where 2 cm ≈ 

0.75 inch d.

Application Datea,c -7 days (7days before) Days before emergence (scenario 

specific)

Application Efficiencya 1 EFED Guidance

Spray Drift (fraction)a 0 EFED Guidance

Application Rate (lb a.i/A) Range 0.126 to 1.25 See Table 2; depends upon seed 

treatment rate and seeding rate.

a Input for SWCC

bUSEPA, 2010. Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered 

Species, and Drinking Water Exposure Assessments for Hymexazol (03/04/10; D371500).

c Input for PRZM-GW

d Depth estimate also supported by https://www.hort.purdue.edu/newcrop/afcm/sugarbeet.html

Modeling Results

Surface water EECs estimated by the SWCC for the MN sugar beet scenario are summarized in 

Table 9, assuming a 2-cm seed incorporation depth. Other incorporation depths were evaluated

and found to have no effect on the risk conclusion concerning the aquatic exposure. For 

example, the peak EECs for the maximum rate with and a 1-cm seed incorporation depth was 

23.4 μg/L. Example outputs are given in Appendix C.
Table 9. Surface Water EECs for Aquatic Exposure: SWCC estimated Peak, 96-hour, 21-day and 

60-day average concentrations in standard farm pond for 6 rates and 2-cm seed incorporation 

depth (estimated from Table 3).

Scenario

MN Sugar beets

(lb seed/A)*

Application

Rate

(lb a.i./A)

Peak 96-hr 21-day 60-day

μg/L 

2.0 0.126 1.39 1.37 1.33 1.15

3.6 0.23 2.54 2.51 2.42 2.11

4.8 0.30 3.31 3.27 3.16 2.75

5.0 0.32 3.53 3.48 3.36 2.93

5.5 0.35 3.86 3.81 3.68 3.21

8.0 0.50 5.52 5.45 5.26 4.58

10.0 0.63 6.99 6.91 6.67 5.81

19.8 1.25 13.8 13.6 13.2 11.5

*The seeding rate at 2 lb seed/A was used in a previous risk assessment. A current potential conservative estimate 

from J. Becker, BEAD (email 03-12-15) is 3.6 lb seed/A. An ExpoSAC SOP (#15, 2004) cites a range between 2-8 lb 

seed/A. Estimates reported in T-REX include 4.8 lb seed/A and 19.8 lb seed/A.

Ecological Exposure

Terrestrial Exposure Modeling-Animals 

Terrestrial exposure estimates (EECs) for avian and mammalian risk assessments were derived 

using the T-REX model (version 1.5.2). Table 10 presents five scenarios analyzed in T-REX for 

mammals and birds. Table 11 presents only the highest application rate analyzed in TerrPlant. 

The foliar half-life value has no effect on modeling EECs for seed treatment uses; thus, no value 

was entered for this parameter in T-REX. The highest seeding rate used was based on sugar beet 

seeds planted for seed production (i.e., 19.8 lb seed/acre); the lowest seeding rate used was 

based on sugar beets presumably for root harvest (i.e., 4.8 lb seed/acre). The T-REX equations 

for estimating residues on seeds assumes that the product is a liquid formulation (e.g., accounts 

for a default product density of 8.33 lb/gallon). The application rate units that are prompted for 

in T-REX are fluid ounces/100 pound weight, or fl. oz/cwt. In order to achieve the correct 

estimates, the application rate from the label (for example, the highest rate: 90 grams of product 

per kg of seed) was used to derive an input of 138.8 fl. oz./cwt (based on 1 g = 0.034 fl oz and 1 

cwt sugar beet seeds = 45.36 kg). A complete description of the input parameters and output is 

contained in APPENDIX B. For reference, the values used are below:

Standard pellet

• High application (treatment) rate = 90 g TEP / kg-seed (138.8 fl oz TEP/cwt)

• Low application (treatment) rate = 45 g TEP/kg-seed (69.4 fl oz TEP/cwt)

Build-up Pellet

• High application (treatment) rate = 30 g TEP/kg-seed (46.27 fl oz TEP/cwt)

 Seeding rates

• High seeding rate = 19.8 lb seed/A
• Low seeding rate = 4.8 lb seed/A

Table 10. Intermediate Calculationsfor Seed Treatment Applications of Hymexazol Using the 

T-REX Model.

Animal 

Size

Scenario1

(treatment 

rate/seeding 

rate)

Maximum 

Application 

Rate

Maximum Seed 

Application 

Rate

Avian Nagy 

Dose

Mammalian 

Nagy Dose Available AI

(lbs a.i./A)

(mg a.i./kg 

seed)

(mg a.i./kgbw/day)(mg a.i./kgbw/day) (mg a.i. ft-2)

Small

High app rate/ 

High seed rate 1.25 63,230

16,003 13,397

Medium 9,126 9,259 13.06

Large 4,086 2,147

Small

High app rate/ 

Low seed rate 0.30 63,230

16,003 13,397

Medium 9,126 9,259 3.14

Large 4,086 2,147

Small

Low app rate/ 

High seed rate 0.63 31,615

8,001 6,698

Medium 4,563 4,629 6.53

Large 2,043 1,073

Small

Low app rate/ 

Low seed rate 0.15 31,615

8,001 6,698

Medium 4,563 4,629 1.57

Large 2,043 1,073

Small High app rate 

(build up) / Low 

seed rate

0.10 21,078

5,335 4,466

Medium 3,042 3,087 1.05

Large 1,362 716

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

Plants

The model used to derive EECs relevant to terrestrial and wetland/semi-aquatic plants for the 

registered uses of hymexazol for seed treatment is TerrPlant (version 1.2.2.). This model uses 

estimates of pesticides in surface water runoff based upon solubility (i.e., 65.1 g/L = 6.51 x 104

mg/L at 20oC and pH 7), highest single application rate (i.e., 1.25 lb a.i./A), and minimum 

incorporation depth18 (i.e., 0.5 inch) to calculate EECs. 

TerrPlant estimates potential exposure from a single application using default assumptions for 

runoff (fraction of 0.05 given the solubility is >100 ppm) (Table 11). Because effects due to 

spray drift are not expected with seed treatment uses, the spray drift fraction was defined to 

equal zero (i.e., also the default for granular applications) in the model; in addition, the 

 18 Mayberry, K.S. 2000. U.C. Cooperative Extension Sample Cost to Establish and Produce Sugar Beets. 

http://coststudies.ucdavis.edu/files/sugarbeets.pdf
vegetative vigor study is not used for RQ calculation. Instead, this analysis only uses the 

seedling emergence study to assess exposure via runoff19. See APPENDIX B for more 

information.

Table 11. EECs on Plants Following Label-Specified Seed Treatment Applications of Hymexazol 

Using the TerrPlant Model (lb a.i./A).

USE RATE

(lb a.i./A)

EEC from runoff to 

dry areas

EEC from runoff to 

semi-aquatic areas

Tachigaren ® 70 WP 1.25 0.125 1.25

V. Risk Characterization

a. Risk Estimation - Integration of Exposure and Effects Data

Toxicity data and exposure estimates are used to evaluate the potential for adverse ecological 

effects on non-target species. For this assessment of hymexazol the deterministic risk quotient 

method is used to provide a metric of potential risks. The RQ is a comparison of exposure 

estimates to toxicity endpoints; estimated exposure concentrations are divided by acute and 

chronic toxicity values. The resulting unitless RQs are compared to the Agency’s levels of concern 

(LOCs) (see Table 12), which are the Agency’s interpretive policy such that when LOCs are 

exceeded, the need for regulatory action may be considered. These criteria are used to indicate 

when the use of a pesticide, as directed on the label, has the potential to cause adverse effects 

on non-target organisms.

Table 12. Agency Levels of Concern (LOC).

Risk Description RQ Taxa

Acute Potential for acute risk to non-target organisms 

which may warrant regulatory action in 

addition to restricted use classification

acute RQ > 0.5 aquatic animals, 

mammals, birds

Acute Listed 

Species

Listed species may be potentially affected by 

use

acute RQ > 0.05 aquatic animals

acute RQ > 0.1 mammals and 

birds

Chronic Potential for chronic risk may warrant 

regulatory action, listed species may potentially 

be affected through chronic exposure

chronic RQ > 1 all animals

 19 “For defining RQ values for plants exposed to runoff, measures of effect to seedling emergence are used; 

however, vegetative vigor could be affected by runoff (i.e. effects to plant roots). Due to limitations of testing 

methods, these effects are not measured and cannot be incorporated into RQ development.” (TerrPlant v.1.2.2 User 

Guide, 2006)
Risk Description RQ Taxa

Non-Listed and 

Listed Plant 

Potential for effects in non-listed and listed 

plants

RQ > 1 all plants

1. Non-target Aquatic Animals and Plants

On an acute exposure basis, hymexazol is classified as “practically non-toxic” to freshwater fish 

and “slightly toxic” to aquatic invertebrates. With a peak surface water EEC of 13.8 μg a.i./L, the 

resulting RQ values were below the LOC thresholds (acute and ES) at <0.01 for fish and 

invertebrates, respectively (Table 13). However, this is based on a limited toxicity set with only 

one species of freshwater fish tested and no data for estuarine/marine (E/M) species (fish or 

invertebrates). In the absence of data, the freshwater species will serve as a surrogate for E/M 

species, however, there is uncertainty with using freshwater values as a proxy for E/M species, 

especially given that only one species of freshwater fish was tested. When comparing the toxicity 

endpoint for freshwater fish (>100,000 μg/L) to the peak EEC of 13.8 μg a.i./L, hymexazol would 

need to be at least over 7,200 times more toxic on an acute basis to reach the level of concern 

for fish (freshwater and estuarine/marine). Considering the labeled application rates and the 

available acute toxicity data for freshwater fish, acute risk is expected to be low for 

estuarine/marine fish.

Chronic toxicity data is available for freshwater fish and invertebrates through the EFSA (2010) 

risk assessment; the NOAEC for a 28-day rainbow trout study is >100 mg/L and the NOAEC (based 

on the number of live juveniles) for a 21-day Daphnia magna is 0.8 mg/L. At these levels, the

LOC would not be exceeded (Table 13). Considering the predicted EECs (for the maximum labeled 

rate) and the EFSA chronic toxicity data, risk is expected to be low for exposures to fish and 

invertebrates on a chronic basis.

There are no LOC exceedances for vascular and non-vascular aquatic plants. 

Table 13. Aquatic Exposure Surface Water RQ Values for Hymexazol

Taxonomic 

Group 

Exposure 

Type Toxicity (μg/L) EEC ( μg/L ) RQ 

Exceeds 

LOC 

(Y/N) 

Freshwater Fish

Acute LC50 >100,000 13.8 <0.01 N

Chronic* NOAEC > 100,000 11.5 <0.01 N

Freshwater 

Invertebrate

Acute LC50 = 30,800 13.8 <0.01 N

Chronic* NOAEC= 800 13.2 0.02 N

Aquatic 

Vascular plants 

Non-listed EC50 = 7,900 13.8 <0.01 N

Listed EC05 =1,100 13.8 0.01 N

Non-listed EC50 = 23,390 13.8 <0.01 N
Taxonomic 

Group 

Exposure 

Type Toxicity (μg/L) EEC ( μg/L ) RQ 

Exceeds 

LOC 

(Y/N) 

Aquatic NonVascular Listed NOAEC = 5,790 13.8 <0.01 N

*Based on EFSA (2010) risk assessment: 

http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/1653.pdf

2. Non-Target Terrestrial Animals

For reference, the values used in the calculations for the tables below:

Standard pellet

• High application (treatment) rate = 90 g TEP / kg-seed (138.8 fl oz TEP/cwt)

• Low application (treatment) rate = 45 g TEP/kg-seed (69.4 fl oz TEP/cwt)

Build-up Pellet

• High application (treatment) rate = 30 g TEP/kg-seed (46.27 fl oz TEP/cwt)

Seeding rates

• High seeding rate = 19.8 lb seed/A

• Low seeding rate = 4.8 lb seed/A 

The acute RQs are calculated using two different equations. Equation for RQ #1 (as well as the 

chronic RQ calculation) does not take into account the seeding rate parameter. Instead, the 

Nagy dose is calculated on the basis of the daily food intake, maximum seed application rate, 

and animal body weight. As a result, these values demonstrably do not change across the low 

and high seed rate scenarios for a given application rate. On the other hand, the equation for 

RQ#2, which is analogous to the LD50 per ft2 method, does take into account seeding rates and 

tends to be a lower RQ estimate than RQ#1. In determining risk concern both equations should 

be considered.

Mammals

Acute

The shaded cells indicate the acute LOC (0.5) exceedances and the bold indicate the additional 

ES LOC (0.1) exceedances.

For the Tachigaren ® 70 WP standard pellet uses at the highest application rate (i.e., 1.25 lb

a.i./A), there were acute listed and non-listed species exceedances for allmammalian size classes 

(Table 14). The non-listed species RQs (i.e., LOC ≥0.5) range from 1.74-3.81 and the listed species 

RQs (i.e., LOC ≥0.1) from 0.13-3.81 for the highest application rate. LOC exceedances are 

observed down to the low end scenario as well -- at the lowest application rate (i.e., 0.15 lb 

a.i./A). The Tachigaren ® 70 WP build-up pellet scenario at the lowest application rate (i.e., 0.10 

lb a.i./A) and low seeding rate is similar to the low end scenario for the standard pellet use.
Chronic

The chronic RQ was calculated using the NOAEL and LOAEL to demonstrate that LOC 

exceedances occur at the frank effects levels (i.e., LOAEL), noting that the LOAEL (the lowest 

observed adverse effect level) stands for the lowest tested concentration where effects are 

observed. The RQ is based on either the NOAEL or LOAEL as marked in Table 14. The NOAEL = 

100 mg/kg-bw/day and LOAEL = 500 mg/kg-bw/day based on the teratogenicity study (MRID 

42826307). The frank effect is reduced fetal weight (9.3% relative to the control at the highest 

tested dose, 500 mg/kg-bw/day). Additional developmental delays were also observed in the 

study. In terms of chronic exposure, there were LOC exceedances (i.e., LOC ≥ 1.0) for all 

mammalian size classes for all scenarios and at both effect levels.

Table 14. Mammalian Seed Treatment RQs -- for Tachigaren ® 70 WP as a single seed 

treatment application on sugar beets.

Scenario1

Mammalian (15 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 3.81 0.25 60.95 12.19 1.25

High app rate / Low seed rate 3.81 0.06 60.95 12.19 0.30

Low app rate / High seed rate 1.90 0.12 30.48 6.10 0.63

Low app rate / Low seed rate 1.90 0.03 30.48 6.10 0.15

High app rate (build up) / Low seed rate 1.27 0.02 20.32 4.06 0.10

Mammalian (35 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 3.25 0.13 52.07 10.41 1.25

High app rate / Low seed rate 3.25 0.03 52.07 10.41 0.30

Low app rate / High seed rate 1.63 0.07 26.03 5.21 0.63

Low app rate / Low seed rate 1.63 0.02 26.03 5.21 0.15

High app rate (build up) / Low seed rate 1.08 0.01 17.36 3.47 0.10

Mammalian (1000 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 1.74 0.01 27.91 5.58 1.25

High app rate / Low seed rate 1.74 <0.01 27.91 5.58 0.30

Low app rate / High seed rate 0.87 0.01 13.95 2.79 0.63

Low app rate / Low seed rate 0.87 <0.01 13.95 2.79 0.15

High app rate (build up) / Low seed rate 0.58 <0.01 9.30 1.86 0.10

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

*Bold values exceed acute listed and chronic listed and non-listed species LOCs; highlighted cells signify values that also 

exceed acute non-listed LOCs

Acute RQ #1 = (mg a.i. /kg-bw/day) / LD50

Acute RQ #2 = mg a.i. ft-2 /(LD50*bw)

 Mammalian Chronic RQ = mg a.i./kg-bw/day / adjusted NOAEL
Birds

Acute

The shaded cells indicate the acute LOC (0.5) exceedances and the bold indicate the additional 

ES LOC (0.1) exceedances. For the Tachigaren ® 70 WP standard pellet uses at the highest 

application rate (i.e., 1.25 lb a.i./A), there were acute listed and non-listed species LOC 

exceedances for all avian size classes (Table 15). The acute non-listed species LOC exceedances 

(i.e., LOC ≥0.5) range from 0.74-18.08 and the listed species exceedances (i.e., LOC ≥0.1) from 

0.12-18.08. LOC exceedances are observed down to the low end scenario as well -- at the lowest 

application rate (i.e., 0.15 lb a.i./A).

Chronic

The chronic RQ was calculated using the NOAEC and LOAEC to demonstrate that LOC 

exceedances occur at the frank effects levels (i.e., LOAEC), noting that the LOAEC (the lowest 

observed adverse effect concentration) stands for the lowest tested concentration where 

effects are observed. The RQ is based on either the NOAEC or LOAEC as marked in Table 15. 

The NOAEC = 385 mg a.i./kg-diet and LOAEC = 962 mg a.i./kg-diet are based on the quail study 

(MRID 48716602). The frank effect is reduced eggshell thickness (5% reduction in thickness 

relative to the control at the highest dose level tested 962 mg a.i./kg-diet). No other treatment 

related effects were observed in this study. However, in a reproduction study for the mallard 

(MRID 49268101), eggshell thickness was also significantly different (8.35% effect) relative to 

the control in the highest dose level tested (4467 mg a.i./kg-diet), which led to a NOAEC of 902 

mg a.i./kg-diet.

In terms of chronic exposure, there were LOC exceedances (i.e., LOC ≥ 1.0) for all avian size 

classes for all scenarios and at both effect levels. 

Table 15. Avian Seed Treatment RQs -- for Tachigaren ® 70 WP as a single seed treatment 

application on sugar beets.

Scenario1

Avian (20 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 18.08 0.74 164.23 65.73 1.25

High app rate / Low seed rate 18.08 0.18 164.23 65.73 0.30

Low app rate / High seed rate 9.04 0.37 82.12 32.86 0.63

Low app rate / Low seed rate 9.04 0.09 82.12 32.86 0.15

High app rate (build up) / Low seed rate 6.03 0.06 54.75 21.91 0.10

Avian (100 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 8.10 0.12 164.23 65.73 1.25

High app rate / Low seed rate 8.10 0.03 164.23 65.73 0.30
Low app rate / High seed rate 4.05 0.06 82.12 32.86 0.63

Low app rate / Low seed rate 4.05 0.01 82.12 32.86 0.15

High app rate (build up) / Low seed rate 2.70 0.01 54.75 21.91 0.10

Avian (1000 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 2.57 0.01 164.23 65.73 1.25

High app rate / Low seed rate 2.57 <0.01 164.23 65.73 0.30

Low app rate / High seed rate 1.28 <0.01 82.12 32.86 0.63

Low app rate / Low seed rate 1.28 <0.01 82.12 32.86 0.15

High app rate (build up) / Low seed rate 0.86 <0.01 54.75 21.91 0.10

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

*Bold values exceed acute listed and chronic listed and non-listed species LOCs; highlighted cells signify values that 

also exceed acute non-listed LOCs

Acute RQ #1 = (mg a.i. /kg-bw/day) / LD50

Acute RQ #2 = mg a.i. ft-2 /(LD50*bw)

Avian Chronic RQ = mg kg-1 seed / NOAEL

3. Terrestrial Invertebrates

EPA reviewed data and EFSA (2010) risk assessment report acute oral and contact honey bee 

toxicity as LD50>100 μg/bee and LC50>100 μg/bee, respectively, for the hymexazol technical. 

4. Non-target Terrestrial Plants 

The risk to plants was assessed using TerrPlant v. 1.2.2 (Appendix B) using calculations of runoff 

only EECs as described previously and seedling emergence data: onion (monocot) IC25 = 174 lb 

a.i./A and NOAEC = 152 lb a.i./A; and, cabbage (dicot) IC25 = 35 lb a.i./A and NOAEC = 16 lb a.i./A. 

From the TerrPlant analysis, there were no LOC exceedances for applications at the 1.25 lb a.i./A 

rate (Table 16).

Table 16. Screening Level Analysis-TerrPlant RQsfor runoff only in dry and semi-aquatic areas

Plant Type

Rate lb

a.i./A 

1.25

Monocot <0.1

Monocot (listed) <0.1

Dicot <0.1

Dicot (listed) <0.1
b. Risk Description and Characterization

Risks to Aquatic Organisms

Animals

On an acute and chronic exposure bases, the risk to freshwater fish and invertebrates is 

considered low. Data are not available for estuarine/marine (E/M) species (fish or invertebrates).

In the absence of data, the freshwater species may serve as a surrogate for E/M species, thus, 

the acute risk is anticipated to be low. Chronic toxicity data for freshwater fish and invertebrates 

is available through the EFSA (2010) risk assessment. 

Plants

All of the RQs for aquatic vascular and non-vascular plants are below the LOCs for risk to listed 

and non-listed species. Therefore, likelihood of direct risk to aquatic plants from the use of 

hymexazol is considered low. 

Risks to Terrestrial Organisms

Terrestrial invertebrates

Hymexazol is a registered systemic fungicide applied to sugar beets, a pollinator attractive crop. 

The EPA study review and EFSA (2010) risk assessment reporting acute oral and contact honey 

bee toxicity as LD50 > 100μg/bee and LC50 >100μg/bee, respectively, for the hymexazol technical, 

suggests that the risk to honey bees on an acute oral and contact basis is expected to be low. In 

addition, the metabolism in sugar beets study (MRID 42826314) finds substantial evidence that 

hymexazol rapidly metabolizes (degrades) to CO2 in the plant and subsequently gets incorporated 

into sugars. This suggests that by the time this biennial crop blooms – i.e., in the second year of 

growth -- it is expected that the degradation pathway of hymexazol inside the plant is not likely 

to lead to exposure to adults or younger life stages in the hive.

Terrestrial Plants 

In the screening level analysis with TerrPlant, there were no LOC exceedances for applications at 

the 1.25 lb a.i./A rate. Only the seedling emergence data were used for RQ calculations because 

these data are more representative of effects resulting from runoff. Vegetative vigor data are 

representative of effects resulting from spray drift. Given that spray drift is not an expected 

exposure route, vegetative vigor results and the spray drift analysis were not included. These 

results are consistent with a lack of incidents reported for terrestrial plants. As a result, effects 

are not expected to terrestrial plants. 

Terrestrial Vertebrates

Modifications to application rate (in terms of lb a.i./A) may substantially reduce risk to mammals 

and birds. Critical information on the label and usage reports that contribute to changing the 

application rate includes seed treatment application rate (i.e. gram of TEP/kg seed) and seeding 

rate (i.e., lb seed/A). 
With respect to the outputs in T-REX, if seeding rates are changed, the risk quotients change for

the acute RQ (#2) for birds and mammals. This is on account of the types of equations used in 

the T-REX model; RQ (#2) equations account for risk on the basis of the amount of pesticide 

present per square foot and needed to reach the LD50. However, when the application rates are 

reduced, the risk quotients decrease for all risk categories: acute (#1 and #2) as well as the chronic 

(NOAEL-based and LOAEL-based). 

Given this limitation on the seeding rates parameter in T-REX additional calculations were 

developed – i.e., the seed consumption approach (SCA)-- that confirm the T-REX based risk 

conclusions but highlight the importance of accurate seeding rate assumptions. Appendix D

provides a logical outline of the calculations used for the development of the SCA using the lowest 

and highest application rates (40 and 90 g TEP/kg-seed) for the standard pellet, the highest 

application rate (30 g TEP/kg-seed) for the build-up pellet, and the lowest and highest seeding 

rates (4.8 and 19.8 lb seed/Acre) from those listed in T-REX. For clarity, the SCA approach is 

presented in the risk characterization section for the highest rates scenario. However, Appendix 

E outlines all refinements of the RQ estimates including those calculated in T-REX and the SCA for 

combinations (or ‘scenarios’) of application rates (standard pellet high: 90 g TEP/kg-seed and low: 

45 g TEP/kg-seed; build up pellet high: 30 g TEP/kg-seed) and seeding rates (high: 19.8 lb seed/A; 

and low: 4.8 lb seed/A). Conclusions of the T-REX modeling only are presented throughout the 

body of this document. For details on the SCA refinements and real-world case study examples 

with the wood mouse and zebra finch, see Appendix E.

Mammals

Hymexazol is classified as “slightly toxic” to mammals on an acute oral basis, however, because 

of the high seed treatment application rate (1.25 lb a.i./A), the expected residues on the treated 

seeds, should direct consumption occur, are high (maximum seed application rate: 63,230 mg 

a.i./kg-seed; amount of available a.i.: 13.1 mg a.i./ft2) as are the calculated doses received by the 

three size classes (a range of 2,147-13,397 mg a.i./kg-bw/day), thus leading to acute and chronic 

LOC exceedances for all mammalian size classes. 

If the seeding rate from above (19.8 lbs a.i./A) is changed to 4.8 lbs a.i./A, if the seeding rate 

remains 19.8 lbs a.i./A but the application (treatment) rate is halved (from 138.8 fl oz/cwt to 69.4 

fl oz/cwt), or if a seeding rate of 4.8 lbs a.i./A and application (treatment) rate of 69.4 fl oz/cwt is 

used, the risk quotients decrease but risk conclusions do not change for mammals. 

Thus, a combination of seeding rate and application (treatment) rate reduction may substantially 

reduce risk, as suggested by results of the build-up pellet scenario. Given that the label does not 

specify a maximum application rate per acre – i.e., it only indicates the weight of end use product 

per weight of seed – means that there is uncertainty in the above estimates. 

In an effort to refine the T-REX output, EFED calculated the amount of seeds a mammal would 

need to consume to reach the acute risk, acute endangered species risk, and chronic risk LOC

levels. Table 17 through Table 19 provide the following refinements: the number of sugar beet 
seed pellets that a 15, 35, and 1000g mammal would need to consume at the highest application 

rate, the percentage of the daily dietary intake of that size class, and the area the organism would 

need to forage in order to attain the LOC. Consuming more seeds than reported in the tables 

would yield an LOC exceedance for that risk category. The following assumptions were made: the 

highest seeding rate available in T-REX was used (i.e., 19.8 lb seeds/acre), that the mammals 

assessed are granivores, and, as a result, the mass fraction of water in the food items is 0.1 (TREX User Guide) – i.e. relevant for determination of the daily mass food intake. A detailed 

description of the calculations -- including the low application (treatment) rate and low seeding 

rate -- can be found in Appendix D. The multiple scenario outputs and real-world case study 

example with the wood mouse are presented in Appendix E.

Based on the acute exposure below, the foraging areas covered to result in consuming sufficient 

seed to reach a level of concern by all size classes seem reasonable and very likely. Specifically,

the small and middle size class mammals cover less ground and need to consume a smaller 

percentage of their daily mass intake to reach the acute LOC and much less so to reach the acute 

endangered mammal LOC than do the larger size class mammals. The number of seeds consumed 

required to reach the chronic LOC is lower than that required for reaching either acute level of 

concern. The risk to larger mammals increases with respect to chronic exposure as they would

need to cover less ground and consume less than they would for acute exposure to show effects. 

Chronic exposure is based on a teratogenicity study (MRID 42826307) that showed reduced mean 

fetal weight (9.3% below control) at the highest tested concentration (also LOAEL: 500 mg a.i./kgbw), a dose which was not maternally toxic. As a result, the developmental NOAEL for the study 

is 100 mg a.i./kg-bw. Additional developmental delays were also observed in the study. Though 

a 2-generation reproduction study (MRID 42826309) suggests no treatment related effects on 

the general physical condition, body weight, or developmental landmarks of the F1 and F2 pups, 

post-implantation survival rate and litter size were significantly reduced in the high dose (also 

LOAEL: 159 mg a.i./kg-bw) F1 (↓17%) and F2 (↓20%) offspring compared to controls. Lower 

survival rates led to reduced litter size at birth/on postnatal day (PND) 1 in both the F1 (↓26-

27%) and F2 (↓17%) generations. This reduction continued until PND 4 (pre-cull), with 16% fewer 

F1 pups and 19% fewer F2 pups per litter compared to controls. It was impossible to determine if 

this was a maternal or in utero effect without more data; therefore, it was attributed to both. 

The paternal and offspring NOAEL in the 2-generation study is 31 mg a.i./kg-bw and further 

supports the risk conclusions based on the development/teratogenicity study. Furthermore, the 

developmental NOAEL (100 mg/kg/day) is protective of the reproductive effects at 159 

mg/kg/day in the 2-generation study. If this laboratory-observed effect occurs in the 

environment, it could, in return, have effects on reproduction, survival, and growth of individuals 

and subsequent effects on a given mammalian population.

The refinements presented below (high application rate for the standard pellet use and high 

seeding rate) further support the acute and chronic risk conclusions calculated from T-REX; that 

is, there is potential risk of mortality and reproductive effects to mammals resulting from acute 

and chronic exposures. In other words, the fraction of pellets consumed and required to reach 

the LOC is in many cases much lower than 100% and the area required to collect as many pellets 
is not unreasonable. However, these refinements further emphasize the importance of accurate 

seeding rate assumptions in risk calculations for seed applications; see Appendix E for a 

comprehensive analysis of alternative application scenarios. High seeding rates, for example, 

imply a reduced foraging area required to consume the amount of seed needed to reach a given 

LOC. The greatest risk concern is evidenced by high application and seeding rates; in particular, 

in the standard pellet case. The build-up pellet application rate is lower and presents a possibility 

of concern on a chronic basis particularly for small and mid-size mammals (Appendix E). 

Table 17. Acute Risk to Mammals: Comparisons to non-listed species LOC for mammals 

foraging on hymexazol treated seed. 

Size 

(g) 

0.5 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.5 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.5 

adj. LD50

(mgpellet)

# Pellets 

consumed to 

reach 0.5

adj. LD50

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach 0.5 adj. 

LD50 (%)*

Area covered 

(ft2)**

15 1,758 26 1,256 42 3,178 39.5 2.02

35 1,423 50 2,371 79 5,125 46.3 3.82

1000 615 615 29,301 977 33,951 86.3 47.2

The LD50 = 1600 mg a.i./kg-bw for a 350g rat. The adjusted LD50 = 3,517 mg a.i./kg-bw for a 15g mammal, 2,845 mg 

a.i./kg-bw for a 35g mammal, and 1231 mg a.i./kg-bw for a 1000g mammal

*(Mass of pellet to reach 0.5 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.5 adjusted LD50 / 20.7 seed pellets ft-2 (See Appendix D for details)

Table 18. Acute Endangered Mammal Species Risk: Comparisons to listed species LOC for 

threatened and endangered mammals consuming hymexazol treated seed.

Size 

(g) 

0.1 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.1 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.1 

adj. LD50

(mgpellet)

# Pellets 

consumed to 

reach 0.1 

adj. LD50

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach 0.1 adj. 

LD50 (%)*

Area covered 

(ft2)**

15 352 5.3 251 8 3,178 7.9 0.40

35 285 10 474 16 5,125 9.3 0.76

1000 123 123 5,860 195 33,951 17.3 9.44

The LD50 = 1600 mg a.i./kg-bw for a 350g rat. The adjusted LD50 = 3,517 mg a.i./kg-bw for a 15g mammal, 2,845 mg 

a.i./kg-bw for a 35g mammal, and 1231 mg a.i./kg-bw for a 1000g mammal

*(Mass of pellet to reach 0.1 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.1 adjusted LD50 / 20.7 seed pellets ft-2 (See Appendix D for details)
Table 19. Chronic Risk to Mammals: Comparisons to chronic LOC for mammals consuming 

hymexazol treated seed.

Size 

(g) 

Adjusted 

NOAEL

(mg 

a.i./kgbw)

Mass of 

a.i. to 

reach adj 

NOAEL

(mg a.i.)

Mass of 

pellet to 

reach 

adj. 

NOAEL 

(mgpellet)

# Pellets 

consumed to 

reach adj. 

NOAEL

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach adj. 

NOAEL (%)*†

Area covered 

(ft2)**

15 220 3.3 157 5 3,178 4.9 0.25

35 178 6.2 296 10 5,125 5.8 0.48

1000 77 76.9 3,662 122 33,951 10.8 5.90

The NOAEL = 100 mg a.i./kg-bw for a 350g rat (based on teratogenicity study, MRID 42826307)

*(Mass of pellet to reach adjusted NOAEL / Daily mass intake) x 100

**Number of pellets consumed to reach the adjusted NOAEL / 20.7 seed pellets ft-2 (See Appendix D for details)

†See Appendix E for calculations based on the LOAEL.

Birds

Hymexazol is classified as “slightly toxic” to birds on an acute oral basis and “practically nontoxic” to birds on an acute dietary basis, however, because of the high seed treatment application 

rate (1.25 lb a.i./A), the expected residues on the treated seeds, should direct consumption occur, 

are high (maximum seed application rate: 63,230 mg a.i./kg-seed; amount of available a.i.: 13.1 

mg a.i./ft2) as are the calculated doses received by the three size classes (a range of 4,086-16,003 

mg a.i./kg-bw/day), thus leading to acute and chronic LOC exceedances for all avian size classes. 

As for the mammals, if the seeding rate from above (19.8 lbs a.i./A) is changed to 4.8 lbs a.i./A, if 

the seeding rate remains 19.8 lbs a.i./A but the application (treatment) rate is halved (from 138.8 

fl oz/cwt to 69.4 fl oz/cwt), or if a seeding rate of 4.8 lbs a.i./A and application (treatment) rate 

of 69.4 fl oz/cwt is used, the risk quotients decrease but risk conclusions do not change for the 

birds. 

Thus, a combination of seeding rate and application (treatment) rate reduction may substantially 

reduce risk. Given that the label does not specify a maximum application rate per acre – i.e., it 

only indicates the weight of end use product per weight of seed – means that there is uncertainty 

in the above estimates.

Once again in an effort to refine the T-REX output, EFED calculated the amount of seeds a bird 

would need to consume to reach the acute risk, acute endangered species risk, and chronic risk 

LOC levels. Table 20 through Table 22 provide the following refinements: the number of sugar 

beet seed pellets that a 20, 100, and 1000g bird would need to consume at the highest application 

rate, the percentage of the daily dietary intake of that size class, and the area the organism would 

need to forage in order to attain the LOC. Consuming more seeds than reported in the tables 

would yield an LOC exceedance for that risk category. The following assumptions were made: the 

highest seeding rate available in T-REX was used (i.e., 19.8 lb seeds/acre), that the birds assessed 

are granivores, and, as a result, the mass fraction of water in the food items is 0.1 – i.e. relevant 
for determination of the daily mass food intake. A detailed description of the calculations --

including the low application (treatment) rate and low seeding rate -- can be found in Appendix 

D. The multiple scenario outputs and real-world case study example with the zebra finch are 

presented in Appendix E.

Based on the acute exposure below, the foraging areas covered to result in consuming sufficient 

seed to reach a level of concern by all size classes seem reasonable and very likely. Specifically, 

the small and middle size class birds cover less ground and need to consume a smaller percentage 

of their daily mass intake to reach the acute LOC and much less so to reach the acute endangered 

bird LOC than do the larger size class birds. Generally, the number of seeds consumed and

required to reach the chronic LOC is lower than that required for reaching either acute level of 

concern. The risk to larger birds increases with respect to chronic exposure as they would need 

to cover less ground and consume less than they would for acute exposure to show effects.

The chronic endpoint used in this assessment from the avian reproduction study for the quail

(MRID 48716602) is based on egg shell thickness (5% reduction relative to the control at the 

highest dose level tested, 962 mg a.i./kg-diet, which led to a NOAEC of 385 mg a.i./kg-diet). 

Though statistical difference in egg shell thickness was detected it is possible that this difference 

is not biologically significant given that the mean egg shell difference at the highest level tested 

(1000 mg/kg-diet) is 0.219 ± 0.014 mm, comparable to (according to the study author’s) the 

historical control value of 0.219 ± 0.010 mm. The control mean for egg shell thickness for the 

study, however, is 0.231 ± 0.015 mm. No other treatment related effects were observed in this 

study. However, in a reproduction study for the mallard (MRID 49268101), eggshell thickness was 

also significantly different (8.35% effect) relative to the control in the highest dose level tested 

(4467 mg a.i./kg-diet), which led to a NOAEC of 902 mg a.i./kg-diet.

The refinements presented below (high application rate for the standard pellet use and high 

seeding rate) further support the acute and chronic risk conclusions calculated from T-REX; that 

is, there is potential risk of mortality and reproductive effects to birds resulting from acute and 

chronic exposures. In other words, the fraction of pellets consumed and required to reach the 

LOC is in many cases much lower than 100% and the area required to collect as many pellets is 

not unreasonable. However, these refinements further emphasize the importance of accurate 

seeding rate assumptions in risk calculations for seed applications, see Appendix E for a 

comprehensive analysis of alternative application scenarios. High seeding rates, for example, 

imply a reduced foraging area required to consume the amount of seed needed to reach a given 

LOC. The greatest risk concern is evidenced by high application and seeding rates; in particular, 

in the standard pellet case. The build-up pellet application rate is lower but presents a possibility 

of concern on a chronic basis for all size classes (Appendix E). 
Table 20. Acute Risk to Birds: Comparisons to 0.5 Adj. LD50

Size 

(g) 

0.5 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.5 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.5 

adj. LD50

(mg-pellet)

# Pellets 

consumed 

to reach 0.5 

adj. LD50

Daily mass 

of food 

intake (mg)

Fraction of 

Daily mass 

intake to 

reach 0.5 

adj. LD50 (%)*

Area covered 

(ft2)**

20 443 8.9 422 14 5,062 8.3 0.68

100 564 56 2,683 89 14,432 19 4.32

1000 796 796 37,904 1,263 64,615 59 61.04

The LD50 = 827 mg a.i./kg-bw for a 12.7 g passerine. The adjusted LD50 = 885 mg a.i./kg-bw for a 20g bird, 1,127 mg 

a.i./kg-bw for a 100g bird, and 1,592 mg a.i./kg-bw for a 1000g bird

*(Mass of pellet to reach 0.5 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.5 adjusted LD50 / 20.7 seed pellets ft-2 (See Appendix D for details)

Table 21. Acute Endangered Bird Species Risk: Comparisons to 0.1 Adj. LD50

Size 

(g) 

0.1 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.1 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.1 

adj. LD50

(mgpellet)

# Pellets 

consumed to 

reach 0.1 

adj. LD50

Daily mass 

of food 

intake 

(mg)

Fraction of 

Daily mass 

intake to 

reach 0.1 adj. 

LD50 (%)*

Area covered 

(ft2)**

20 88.5 1.8 84 3 5,062 1.7 0.14

100 113 11 537 18 14,432 3.7 0.86

1000 159 159 7,581 253 64,615 12 12.21

The LD50 = 827 mg a.i./kg-bw for a 12.7 g passerine. The adjusted LD50 = 885 mg a.i./kg-bw for a 20g bird, 1,127 mg 

a.i./kg-bw for a 100g bird, and 1,592 mg a.i./kg-bw for a 1000g bird

*(Mass of pellet to reach 0.1 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.1 adjusted LD50 / 20.7 seed pellets ft-2 (See Appendix D for details)

Table 22. Chronic Risk to Birds: Comparisons to chronic LOC for birds consuming hymexazol 

treated seed.

Size 

(g) 

Adjusted 

NOAEC 

(mg 

a.i./kgdiet)

Mass of 

a.i. to 

reach adj 

NOAEC

(mg a.i.)

Mass of 

pellet to 

reach 

adj. 

NOAEC

(mgpellet)

# Pellets 

consumed to 

reach adj. 

NOAEC

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to

reach adj. 

NOAEC (%)*†

Area covered 

(ft2)**

20 385 1.95 92.8 3 5,062 1.8 0.15

100 5.56 265 9 14,432 1.8 0.43

1000 24.9 1,185 39 64,615 1.8 1.91

The NOAEC = 385 mg a.i./kg-diet (based on bobwhite quail study MRID 48716602)

*(Mass of pellet to reach NOAEC / Daily mass intake) x 100

**Number of pellets consumed to reach NOAEC / (20.7 or 5.01)seed pellets ft-2 (See Appendix D for details)

†See Appendix E for calculations based on the LOAEC.
Review of Incident Data

Reviews of the Ecological Incident Information System (EIIS) v.2.1.1, OPPs Incident Data System 

(IDS), and the Avian Incident Monitoring System (AIMS)20 were conducted on 2/11/15. There are 

no reported incidents for hymexazol in the EIIS, IDS or AIMS databases.

Federally Threatened and Endangered (Listed) Species Concerns

Before completing this Registration Review, the Agency will conduct an ecological risk 

assessment to address the Agency’s obligations under both the Endangered Species Act (ESA) 

and FIFRA. While the risk assessment supporting this proposed interim Registration Review 

decision evaluates risks to species that are not subject to the ESA, EPA is still in the process of 

conducting a risk assessment for endangered and threatened (listed) species and their 

designated critical habitats for hymexazol. Therefore, EPA has not completed effects 

determinations for listed species associated with the registered uses of hymexazol.

At this time, EPA has not fully developed its risk assessment process for listed 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 

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, available at 

http://www.nap.edu/catalog.php?record_id=18344, 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 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, 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 NationalLevel Pesticide Endangered Species Act Assessments Based on the Recommendations of the 

National Academy of Sciences April 2013 Report,” dated November 1, 2013, available at 

http://www.epa.gov/espp/2013/nas.html. 

 20 http://www.abcbirds.org/abcprograms/policy/pesticides/aims/aims/index.cfm
Clean Water Act 

Hymexazol is not identified as a cause of impairment for any water bodies listed as impaired 

under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885.

In addition, no Total Maximum Daily Loads (TMDL) have been developed for hymexazol, based 

on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_polluta

nt_group_name=PESTICIDES. More information on impaired water bodies and TMDLs can be found 

at http://www.epa.gov/owow/tmdl/.

Endocrine Disruptor Screening Program 

Hymexazol was not included in the first group of 67 chemicals issued an order to conduct Tier 1 

EDSP testing. For additional information on the EDSP, visit http://www.epa.gov/endo/.

References

Doran PM. 1997. Hairy Roots: Culture and Applications. Harwood Academic Publishers, 

Amsterdam, The Netherlands.

European Food Safety Authority. 2010. Conclusion of Pesticide Peer Review: Conclusion on the 

peer review of the pesticide risk assessment of the active substance hymexazol. Parma, 

Italy. November 4, 2010. http://www.efsa.europa.eu/en/scdocs/doc/1653.pdf

Harvesion RM, Windels CE, Smith JA, Brantner JR, Cattanach AW, Giles JF, Hubbell L, Cattanach 

NR. 2007. Fungicide registration and a small niche market: A case history of hymexazol 

seed treatment and the U.S. sugar beet industry. Plant Disease 91:780-790.

Mueller DS, Bradley CA. 2015. Field Crop Fungicides for the North Central United States. Iowa 

State University. University of Illinois. Accessed March 2015 at 

https://www.ncipmc.org/resources/Fungicide%20Manual4.pdf.

Payne, PA, Williams, GE. 1990. Hymexazol treatment of sugar-beet seed to control seedling 

disease caused by Pythium spp. and Aphanomyces cochlioides. Crop Protection. 9:371-

377.

U.S. EPA. 1995a. Request to Review the New Chemical Tachigaren Technical (Hymexazol) for 

Use as a Seed Treatment (Chemical No. 129107). Office of Prevention, Pesticides, and 

Toxic Substances. Office of Pesticide Programs. Washington, DC. April 4, 1995. DP 

Barcode: 209885.
U.S. EPA. 1995b. New chemical registration of the fungicide hymexazol: Transmittal of 

Administrative Conclusions, Environmental Fate Assessment and Results of Study 

Reviews. Office of Prevention, Pesticides, and Toxic Substances. Office of Pesticide 

Programs. Washington, DC. April 28, 1995. DP Barcodes: 209851, 205149.

U.S. EPA. 2010a. Registration Review: Preliminary Problem Formulation for Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for 

Hymexazol. Office of Prevention, Pesticides, and Toxic Substances. Office of Pesticide 

Programs. Washington, DC. March 4, 2010. DP Barcode: 371500.

U.S. EPA. 2010b. EFED Response: Rebuttal to EPA’s Classification of Ecotoxicity Studies for 

Hymexazol (MRIDs 43926302, 43926301, 44071301-44071310, 44071311-44071320). 

Office of Chemical Safety and Pollution Prevention. Office of Pesticide Programs. 

Washington, DC. December 7, 2010. DP Barcode: 384399.

Ypema H. 2003. Fungicides, Hymexazol. Encyclopedia of Agrochemicals. Accessed March 2015 

at http://onlinelibrary.wiley.com/doi/10.1002/047126363X.agr110/abstract.
Appendix A. TREX Model Sample Input (Note: Outputs are available in the body of the document) 

 

 

INPUT 

Table 1. Input- Sugar Beet Seed Treatment (1.25 lb a.i./A) 

Chemical Name: Hymexazol Application Rate (lb ai/acre)

Seed Treatment? 

(Check if yes)

TRUE Seeding Rate 

(lbs/acre)

 Use: 135 19.8

Product name and 

form: Tachigaren 70 WP

% A.I. (leading zero 

must be entered for 

formulations <1% 

a.i.): 70.00%

Application rate (fl 

oz/cwt) 138.8

Half-life (days): 35

Application Interval 

(days):

Number of 

Applications: 1

Are you assessing 

applications with 

variable rates or 

intervals? no 

Avian

Endpoint Toxicity value

Indicate test 

species below

Optional 

Test 

Organism 

Body 

weight (g)

Optional 

Test Species 

Name

LD50 (mg/kg-bw)

827.00 3 12.70

Zebra 

finch

LC50 (mg/kgdiet) 5200.00 1

NOAEL (mg/kgbw) 1

NOAEC (mg/kgdiet) 385.00 1

Enter the Mineau et al. Scaling Factor 1.15
Mammalian

Acute Study Chronic Study

Size (g) of mammal used in toxicity study

Default rat body weight is 350 grams 350 350

Endpoint Toxicity value

Reference 

(MRID)

LD50 (mg/kg-bw) 1600.00

LC50 (mg/kgdiet)

Reported 

Chronic 

Endpoint

100.00

1

Is dietary 

concentration 

(mg/kg-diet) 

reported from the 

available chronic 

mammal study? 

(yes or no)

no

Enter dietary 

concentration 

(mg/kg-diet)

Estimated Chronic 

Diet Concentration 

Equivalent to 

Reported Chronic 

Daily Dose

2000 mg/kg-diet based 

on standard FDA 

lab rat conversion

Anima

l Size Crop

Maxim

um 

Applic

ation 

Rate

Maximu

m Seed 

Applicati

on Rate

Avian 

Nagy 

Dose

Mammalia

n Nagy 

Dose

Availa

ble AI

(lbs 

ai/A)

(mg 

ai/kg 

seed)

(mg ai/kgbw/day)(mg ai/kgbw/day)(mg ai 

ft-2)

Small

sugar beet for 

seed production 1.25 63229.91

16002.78 13396.64

13.06 Mediu

m 9125.47 9258.87

Large 4085.59 2146.70
Appendix B. Terr Plant Model Input/output

 

Table 1. Chemical Identity.

Chemical Name Hymexazol

PC code 129701

Use sugar beets

Application Method seed treatment

Application Form wettable powder

Solubility in Water 

(ppm) 65,100

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value Units

Application Rate A 1.25 lb a.i./A

Incorporation I 0.5 none

Runoff Fraction R 0.05 none

Drift Fraction D 0 none

Table 3. EECs for Hymexazol. Units in lb a.i./A.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.125

Runoff to semi-aquatic areas (A/I)*R*10 1.25

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.125

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 1.25

Table 4. Plant survival and growth data used for RQ derivation. Units are in lb a.i./A.

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 174 152 x x

Dicot 35 16 x x

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Hymexazol through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed <0.1 <0.1 <0.1

Monocot listed <0.1 <0.1 <0.1

Dicot non-listed <0.1 <0.1 <0.1

Dicot listed <0.1 <0.1 <0.1

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

 

 
Appendix C. Example of SWCC Aquatic Exposure 

 

Summary of Water Modeling of Hymexazol and the USEPA Standard Pond

Estimated Environmental Concentrations for Hymexazol are presented in Table 1 for the USEPA 

standard pond with the MNsugarbeetSTD field scenario. A graphical presentation of the year-toyear 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 0.65% of Hymexazol applied to the field eventually reaches the 

water body. The main mechanism of transport from the field to the water body is by runoff 

(99.1% of the total transport) followed by erosion (0.87%).

In the water body, pesticide dissipates with an effective water column half-life of 128.5 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 = 128.8 days) followed 

by volatilization (59224 days).

In the benthic region, pesticide dissipates relatively quickly (2.5 days). The main source of 

dissipation in the benthic region is metabolism (effective average half-life = 2.5 days). Most of 

the pesticide in the benthic region (87%) is sorbed to sediment rather than in the pore water.

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

Peak (1-in-10 yr) 6.99

4-day Avg (1-in-10 yr) 6.91

21-day Avg (1-in-10 yr) 6.67

60-day Avg (1-in-10 yr) 5.81

365-day Avg (1-in-10 yr) 1.90

Entire Simulation Mean 0.711

Table 2. Summary of Model Inputs for Hymexazol.

Scenario MNsugarbeetSTD

Cropped Area Fraction 1

Koc (ml/g) 59.6

Water Half-Life (days) @ 25 °C 46.2

Benthic Half-Life (days) @ 0 °C 5.16

Photolysis Half-Life (days) @ 40 °Lat 0

Hydrolysis Half-Life (days) 0
Soil Half-Life (days) @ 25 °C 23.1

Foliar Half-Life (days) 0

Molecular Wt 99.09

Vapor Pressure (torr) 1.37e-3

Solubility (mg/l) 65100

Table 3. Application Schedule for Hymexazol.

Date (Days Since 

Emergence)

Type Amount (kg/ha) Eff. Drift

-7 Incorporated to 2 

cm

0.71 1.0 0.0

Figure 1. Yearly Peak Concentrations

 

 

 
Appendix D. Characterization Calculations for Avian and Mammalian Exposure to Treated Sugar Beet 

Seeds

Calculations applicable for acute exposure to a 20g bird. The values marked in italics would need to change 

for other size classes; the values in bold stay constant for each size class – however, these values can 

change if assumptions change (e.g. seeding rate) or the label specifications change (e.g. application rate). 

Similar calculations apply for chronic risk to birds and for acute/chronic risk to mammals. Note that the 

‘adjustment’ to the endpoints refers to the body weight adjustment to the three size classes of birds and

mammals; this adjustment is not conducted for chronic bird endpoints because no data exist to 

incorporate scaling factors (see T-REX User Guide).

Assuming birds eat seed pellets, how many seed pellets would it need to eat to reach LD50, how does 

this compare to its daily feeding rate, and how much ground area (on field) would the bird need to 

forage to consume that many seeds?

I. Baseline Calculations

1. What is the weight of raw seed and seed pellet?

Given (from label): 

• 100,000 seeds = 1 kg of raw sugar beet seed

o 1 seed weight = 1 kg /100,000 seed x 1,000,000 mg/1 kg = 10 mg

Standard pellet

• 2:1 weight ratio of pelleting mixture to raw seed

o 1 seed pellet weight = 10 mg x 3 = 30 mg

Build-up pellet

• 3:10 weight ratio of pelleting mixture to raw seed 

o 1 seed pellet weight = 10 mg x 13 = 130 mg

2. How much pesticide is in a seed pellet?

Given (from label):

Standard pellet

• 45-90 grams of TEP (70% a.i.) per unit of 100,000 seeds 

• 45,000-90,000 mg of TEP (70% a.i.) per 1 kg of raw seed

High application rate

o 90,000 mg (0.70) / kg = 63,000 mg a.i./kg-seed

o 63,000 mg a.i./kg-seed x 1 kg-seed/3kg-pellet = 21,000 mg a.i./kg-pellet

Low application rate

o 45,000 mg (0.70)/kg = 31,500 mg a.i./kg-seed

o 31,500 mg a.i./kg-seed x 1 kg-seed/3kg-pellet = 10,500 mg a.i./kg-pellet

Build-up pellet

• 20-30 grams of TEP (70% a.i.) per unit of 100,000 seeds

• 20,000-30,000 mg of TEP (70% a.i.) per 1 kg of raw seed
High application rate

o 30,000 mg (0.70) / kg = 21,000 mg a.i./kg-seed

o 21,000 mg a.i./kg-seed x 1 kg-seed/13kg-pellet = 1,615 mg a.i./kg-pellet

Low application rate

o 20,000 mg (0.70) / kg = 14,000 mg a.i./kg-seed

o 14,000 mg a.i./kg-seed x 1 kg-seed/13 kg-pellet = 1,077 mg a.i./kg-pellet

3. How much pesticide mass is needed to reach the adjusted LD50 of a 20 g bird? *See Section III 

below for specific case of chronic avian characterization equations. 

Given (from T-REX): Adjusted LD50 = 885.30 mg a.i./kg-bw

• 885.30 mg a.i./kg-bw x 0.02 kg/bird = 17.7 mg a.i.

4. How much pellet mass is in the above pesticide mass (i.e. needed to reach the adjusted LD50 of a 

20g bird)? 

Standard Pellet (max rate)

• 17.7 mg a.i. / (21,000 mg a.i./kg-pellet) = 8.43 x 10-4 kg-pellet 

• 8.43 x 10-4 kg-pellet x 1,000,000 mg/1 kg = 843 mg-pellet

Build-up Pellet (max rate)

• 17.7 mg a.i. / (1,615 mg a.i./kg-pellet) = 0.011 kg-pellet 

• 0.011 kg-pellet x 1,000,000 mg/1 kg = 10,963 mg-pellet

II. Characterization Component:

1. How many pellets constitute the above mass? 

Standard Pellet (max rate; recall 30 mg is weight of one pellet) 

• 843 mg-pellet / 30 mg-pellet= 28.1 or 28 seed pellets

Build-up Pellet (max rate; recall 130 mg is weight of one pellet)

• 10,963 mg-pellet /130 mg-pellet= 84.3 or 84 seed pellets

2. Based on the daily mass intake of a 20g granivore bird (i.e. 5.1 grams), what is the percent of its 

daily diet it would have to consume to reach the adjusted LD50?

• 5.1 g x 1,000 mg / 1g = 5,100 mg of food consumed in a day

Standard pellet (max rate)

• 843 mg-pellet / 5,100 mg = 0.165 or 16.5% of a 20g birds diet would have to be 

consumed to reach the adjusted LD50

Build-up Pellet (max rate)

• 10,960 mg-pellet / 5,100 mg = 2.15 or 215% of a 20g birds diet would have to be 

consumed to reach the adjusted LD50
3. How many seed pellets are in a square foot?[this value stays constant with seeding rate]

High seeding rate:

Given max seeding rate for sugar beets (from T-REX): 19.8 lb seeds/acre

Knowing that 1kg = 2.2 lb, the seeding rate becomes 9 kg seeds/acre

Recall: 100,000 seeds = 1 kg of raw sugar beet seed

o 100,000 seeds/ 1kg seeds x 9 kg seeds/acre = 900,000 seeds/acre

Assuming that the seeding rate applies to both raw seeds and seed pellets:

o 900,000 seeds pellets/acre x 1 acre/43,560 ft2 = 20.7 seed pellets/ft2

Low seeding rate:

Given min seeding rate for sugar beets (from T-REX): 4.8 lb seed/acre

The seeding rate becomes 2.18 kg-seeds/acre

o 100,000 seeds/kg seeds x 2.18 kg seeds/acre = 218,182 seeds/acre

o 218,182 seed pellets/acre x 1 acre/ 43,560 ft2 = 5.01 seed pellets/ft2

a. How much square footage would a 20g bird need to cover to consume enough pellets to 

reach the adjusted LD50?

o Standard pellet (max rate), High seeding rate: 28 seed pellets / (20.7 seed 

pellets/ft2) = 1.35 ft2

o Build-up pellet (max rate), High seeding rate: 84 seed pellets / (20.7 seed 

pellets/ft2) = 4.06 ft2

o Standard pellet (max rate), Low seeding rate: 28 seed pellets / (5.01 seed 

pellets/ft2) = 5.6 ft2

o Build-up pellet (max rate, Low seeding rate: 84 seed pellets / (5.01 seed 

pellets/ft2) = 16.8 ft2

III. Particular case of chronic avian characterization equations(Standard pellet at the maximum 

rate and high seeding rate). The equations are valid for LOAEC calculations as well.

Assumption: 20g bird; also a granivore

Known: daily food intake = 5,062 mg 

Convert to kg with: 5,062 mg x (1kg/1,000,000 mg) = 5.062 x 10-3 kgor 0.0051 kg

Given: NOAEC = 385 mg a.i./kg-diet (MRID 48716602); 

From above sections: max pesticide in seed pellet = 21,000 mg a.i./kg-pellet; weight of pellet 

= 30 mg; max seed pellets in square foot = 20.7

Note: Unlike the mammalian chronic endpoint, the avian chronic endpoint is not adjusted as 

no data exist for incorporating scaling factors for birds (T-REX User Guide).

1. How much pesticide mass is needed to reach the NOAEC for a 20g bird? 

• 385 mg a.i./kg-diet x (0.0051 kg diet / 20g bird )= 1.95 mg a.i. / 20g bird

2. How much pellet mass is in the above pesticide mass (i.e. needed to reach the NOAEC for a 20g 

bird)? 

Standard Pellet (max rate)

• (1.95 mg a.i./20g bird) / (21,000 mg a.i./kg-pellet) = 9.28 x 10-5 kg-pellet / 20g bird

• (9.28 x 10-5 kg-pellet /20g bird) x 1,000,000 mg/1 kg = 92.8 mg-pellet / 20g bird
3. How many pellets constitute the above mass? (i.e., the number of pellets at the 20 g bird dose)

• (92.8 mg-pellet /20g bird) / 30 mg-pellet = 3.09 pellets at the 20g bird dose

4. Based on the daily mass intake of a 20g granivore bird (i.e. 5.1 grams), what is the percent of its 

daily diet it would have to consume to reach the NOAEC? (i.e., the percent daily diet that is the 

number of pellets calculated above?)

• 5.1 g x 1,000 mg / 1g = 5,100 mg of food consumed in a day

Standard pellet (max rate)

• (92.8 mg-pellet/ 20g bird)/ 5,100 mg = 0.0183 or 1.83% of a 20g birds diet would have 

to be consumed to reach the NOAEC

5. How much square footage would a 20g bird need to cover to consume enough pellets to reach 

the NOAEC?

• Standard pellet (max rate), High seeding rate: 3.09 pellets / (20.7 pellets/ft2) = 0.15 ft2
Appendix E. Comparison of T-REX and Seed Consumption Approach (SCA) Refinements 

The calculations below represent a set of refinements from the maximum application rate and 

maximum seeding rate. Two tools were used, the T-REX seed treatment function as well as a 

novel approach to calculation of seed consumption rates (for clarity called the ‘seed 

consumption approach’ or SCA). In each tool four different analyses were performed to account 

for the high end and low end options of the two variables of interest: application rate and 

seeding rate. The application rate for the standard pellet is a range provided in the label (EPA 

Reg. No. 48210-1): 45-90 g TEP/kg-seed (recall: 2:1 pelleting mixture to raw seed). The seeding 

rate is also a range used in standard practice in T-REX: 4.8 and 19.8 lb seed/A. To better 

characterize risk, a fifth analysis was also conducted on using the build-up pellet high end rate, 

30 g TEP/kg-seed (recall: 3:10 pelleting mixture to raw seed), and the low end seeding rate in TREX, 4.8 lb seed/A. This combination was selected on account of the instance where acute RQs 

in T-REX (for the area based RQ#2) did not exceed LOCs (Tables E1 and E2). 

For reference, the values used in the calculations for the tables are outlined below. Values 

before the semicolon were used in T-REX; values after the semi-colon were used in SCA. For 

detailed derivation of the values see Appendix D.

Standard pellet

• High application (treatment) rate = 90 g TEP / kg-seed (138.8 fl oz TEP/cwt); 21,000 mg a.i./kg-pellet

• Low application (treatment) rate = 45 g TEP/kg-seed (69.4 fl oz TEP/cwt); 10,500 mg a.i./kg-pellet

Build-up Pellet

• High application (treatment) rate = 30 g TEP/kg-seed (46.27 fl oz TEP/cwt); 1,615 mg a.i./kg-pellet

Seeding rates

• High seeding rate = 19.8 lb seed/A; 20.7 seed pellets/ft2

• Low seeding rate = 4.8 lb seed/A ; 5.01 seed pellets/ft2

T-REX Calculations

The shaded cells indicate the acute LOC (0.5) exceedances and the bold indicate the additional 

acute ES LOC (0.1) and chronic LOC (1.0) exceedances. 

The acute RQs are calculated using two different equations. Equation for RQ #1 (as well as the 

chronic RQ calculation) does not take into account the seeding rate parameter. Instead, the 

Nagy dose is calculated on the basis of the daily food intake, maximum seed application rate, 

and animal body weight. As a result, these values demonstrably do not change across the low 

and high seed rate scenarios for a given application rate. On the other hand, the equation for 

RQ#2, which is analogous to the LD50 per ft2 method, does take into account seeding rates and 

tends to be a lower RQ estimate than RQ#1. In determining risk concern both equations should 

be considered.

The chronic endpoint was calculated using the NOAEL/C and LOAEL/C to demonstrate that LOC 

exceedances occur at the frank effects levels (i.e., LOAEL/C), noting that the LOAEL (the lowest 

observed adverse effect level) stands for the lowest tested concentration where effects are 

observed.
The application rates in lbs a.i./A are calculated for reference using a combination of application 

rates reported in the label (in g TEP/kg-seed) and seeding rates from T-REX (in lb seed/A). A 

sample calculation for the high label reported application rate and high seeding rate is below:

Maximum rate (from label21) = 90 g TEP/kg-seed *(0.70) * = 63 g a.i./kg-seed

Conversions: 1 g = 0.001 kg; 1 kg = 2.2 lb

Assumptions: 19.8 lb-seed/A [i.e. seeding rate]

Maximum rate (calculated) = 63 g a.i./kg-seed *(0.001 kg/1g)*(2.2 lb/ 1kg)*(1 kgseed/2.2 lb-seed)*(19.8 lb-seed/A) = 1.25 lb a.i./A 

Mammals

Hymexazol is classified as “slightly toxic” to mammals on an acute oral basis, however, the 

range of seed treatment application rates (0.10 to 1.25 lb a.i./A) implies high residue 

concentrations on the treated seeds leading to LOC exceedances on both the acute and chronic 

levels. The high application rate (standard pellet) + high seeding rate scenario consistently 

leads to LOC exceedances for small and medium size mammals when seeding rate is taken into 

account (i.e., RQ#2); however, in all scenarios and in particular on a dose basis, low end to high 

end, risk concern for mammals is high.

Table E1. Mammalian Seed Treatment RQs -- for Tachigaren ® 70 WP as a single seed 

treatment application on sugar beets

Scenario1

Mammalian (15 g) App rate 

(lbs a.i./A)

Acute (# 1) Acute (# 2)

Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 3.81 0.25 60.95 12.19 1.25

High app rate / Low seed rate 3.81 0.06 60.95 12.19 0.30

Low app rate / High seed rate 1.90 0.12 30.48 6.10 0.63

Low app rate / Low seed rate 1.90 0.03 30.48 6.10 0.15

High app rate (build up) / Low seed rate 1.27 0.02 20.32 4.06 0.10

Mammalian (35 g) App rate 

(lbs a.i./A)

Acute (# 1) Acute (# 2)

Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 3.25 0.13 52.07 10.41 1.25

High app rate / Low seed rate 3.25 0.03 52.07 10.41 0.30

Low app rate / High seed rate 1.63 0.07 26.03 5.21 0.63

Low app rate / Low seed rate 1.63 0.02 26.03 5.21 0.15

High app rate (build up) / Low seed rate 1.08 0.01 17.36 3.47 0.10

 21 Note 0.70 is the fraction of hymexazol active ingredient in the formulation (i.e., 70 % a.i. in Tachigaren® 70 WP 

EPA Reg. No. 48210-1)
Mammalian (1000 g) App rate 

(lbs a.i./A)

Acute (# 1) Acute (# 2)

Chronic

(NOAEL*)

Chronic

(LOAEL*)

High app rate / High seed rate 1.74 0.01 27.91 5.58 1.25

High app rate / Low seed rate 1.74 <0.01 27.91 5.58 0.30

Low app rate / High seed rate 0.87 0.01 13.95 2.79 0.63

Low app rate / Low seed rate 0.87 <0.01 13.95 2.79 0.15

High app rate (build up) / Low seed rate 0.58 <0.01 9.30 1.86 0.10

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

*Bold values exceed acute listed and chronic listed and non-listed species LOCs; highlighted cells signify values 

that also exceed acute non-listed LOCs

Acute RQ #1 = (mg a.i. /kg-bw/day) / LD50

Acute RQ #2 = mg a.i. ft-2 /(LD50*bw)

 Mammalian Chronic RQ = mg a.i./kg-bw/day / adjusted NOAEL

*The RQ is based on either the NOAEL or LOAEL as marked. The NOAEL = 100 mg/kg-bw/day and 

LOAEL = 500 mg/kg-bw/day based on the teratogenicity study (MRID 42826307). The LOAEL (the 

lowest observed adverse effect level) stands for the lowest tested concentration where effects 

are observed. In this study, the frank effect is reduced fetal weight. The teratogenicity study 

showed reduced mean fetal weight (9.3% below control) at the highest tested concentration 

(also LOAEL: 500 mg a.i./kg-bw), a dose which was not maternally toxic. As a result, the 

developmental NOAEL for the study is 100 mg a.i./kg-bw. Additional developmental delays were 

also observed in the study. Though a 2-generation reproduction study (MRID 42826309) suggests 

no treatment related effects on the general physical condition, body weight, or developmental 

landmarks of the F1 and F2 pups, post-implantation survival rate and litter size were significantly 

reduced in the high dose (also LOAEL: 159 mg a.i./kg-bw) F1 (↓17%) and F2 (↓20%) offspring 

compared to controls. Lower survival rates led to reduced litter size at birth/on postnatal day 

(PND) 1 in both the F1 (↓26-27%) and F2 (↓17%) generations. This reduction continued until PND 

4 (pre-cull), with 16% fewer F1 pups and 19% fewer F2 pups per litter compared to controls. It 

was impossible to determine if this was a maternal or in utero effect without more data; 

therefore, it was attributed to both. The paternal and offspring NOAEL in the 2-generation study 

is 31 mg a.i./kg-bw and further supports the risk conclusions based on the 

development/teratogenicity study. Furthermore, the developmental NOAEL (100 mg/kg/day) is

protective of the reproductive effects at 159 mg/kg/day in the 2-generation study. If this 

laboratory-observed effect occurs in the environment, it could, in return, have effects on 

reproduction, survival, and growth of individuals and subsequent effects on a given mammalian 

population.

Birds

Hymexazol is classified as “slightly toxic” to birds on an acute oral basis and “practically nontoxic” to birds on an acute dietary basis, however, the range of seed treatment application 

rates (0.10 to 1.25 lb a.i./A) implies high residue concentrations on the treated seeds leading to 

LOC exceedances on both the acute and chronic levels. The high application rate (standard 
pellet) + high seeding rate scenario consistently leads to LOC exceedances for small and 

medium size birds when seeding rate is taken into account (i.e., RQ#2); however, in all 

scenarios and in particular on a dose basis, low end to high end, risk concern for birds is high.

Table E2. Avian Seed Treatment RQs -- for Tachigaren ® 70 WP as a single seed treatment 

application on sugar beets

Scenario1

Avian (20 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 18.08 0.74 164.23 65.73 1.25

High app rate / Low seed rate 18.08 0.18 164.23 65.73 0.30

Low app rate / High seed rate 9.04 0.37 82.12 32.86 0.63

Low app rate / Low seed rate 9.04 0.09 82.12 32.86 0.15

High app rate (build up) / Low seed rate 6.03 0.06 54.75 21.91 0.10

Avian (100 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 8.10 0.12 164.23 65.73 1.25

High app rate / Low seed rate 8.10 0.03 164.23 65.73 0.30

Low app rate / High seed rate 4.05 0.06 82.12 32.86 0.63

Low app rate / Low seed rate 4.05 0.01 82.12 32.86 0.15

High app rate (build up) / Low seed rate 2.70 0.01 54.75 21.91 0.10

Avian (1000 g) App rate 

Acute (# 1) Acute (# 2) (lbs a.i./A) Chronic

(NOAEC*)

Chronic

(LOAEC*)

High app rate / High seed rate 2.57 0.01 164.23 65.73 1.25

High app rate / Low seed rate 2.57 <0.01 164.23 65.73 0.30

Low app rate / High seed rate 1.28 <0.01 82.12 32.86 0.63

Low app rate / Low seed rate 1.28 <0.01 82.12 32.86 0.15

High app rate (build up) / Low seed rate 0.86 <0.01 54.75 21.91 0.10

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

*Bold values exceed acute listed and chronic listed and non-listed species LOCs; highlighted cells signify values that 

also exceed acute non-listed LOCs

Acute RQ #1 = (mg a.i. /kg-bw/day) / LD50

Acute RQ #2 = mg a.i. ft-2 /(LD50*bw)

Avian Chronic RQ = mg kg-1 seed / NOAEL

* The RQ is based on either the NOAEC or LOAEC as marked. The NOAEC = 385 mg a.i./kg-diet 

and LOAEC = 962 mg a.i./kg-diet based on the quail study (MRID 48716602). The LOAEC (the 

lowest observed adverse effect concentration) stands for the lowest tested concentration 

where effects are observed. In this study, the frank effect is reduced eggshell thickness (5% 
reduction in thickness relative to the control at the highest dose level tested, 962 mg a.i./kgdiet). No other treatment related effects were observed in this study. However, in a 

reproduction study for the mallard (MRID 49268101), eggshell thickness was also significantly 

different (8.35% effect) relative to the control in the highest dose level tested (4467 mg a.i./kgdiet), which led to a NOAEC of 902 mg a.i./kg-diet.

Seed Consumption Approach Calculations

In an effort to refine the T-REX outputs above, EFED calculated the amount of seeds mammals 

and birds would need to consume to reach the acute risk (0.5 of the adjusted acute endpoint), 

acute endangered species risk (0.1 of the adjusted acute endpoint), and chronic risk LOC levels. 

Table E3 through Table E10 provide the following refinements: the number of sugar beet seed 

pellets (i.e., a raw seed with a pelleting mixture coating) that a 15, 35, and 1000g mammal and a 

20, 100, and 1000g bird would need to consume, the percentage of the daily dietary intake of a 

given size class, and the area the organism would need to forage in order to attain the LOC. 

Consuming more seeds than reported in the tables would yield an LOC exceedance for that risk 

category. The following assumptions were made: the lowest and highest seeding rates available 

in T-REX were used (i.e., 4.8 and 19.8 lb seeds/acre, respectively), that the mammals and birds 

assessed are granivores, and, as a result, the mass fraction of water in the food items is 0.1 – i.e. 

relevant for determination of the daily mass food intake. A detailed description of sample

calculations can be found in Appendix D. 

Mammals

The values in Table E3 through Table E6 provide estimates of seed consumption (i.e., #pellets 

consumed) and forage area (i.e., area covered) for mammals under the same five scenarios 

presented in the above T-REX calculations. The seed consumption to reach the given threshold 

changes with application rate (i.e., recall that application rate determines the amount of a.i. on 

a seed pellet), while forage area covered to consume enough seeds to reach a given risk level 

changes with both the application rate and seeding rate. A lower seeding rate always leads to a 

higher foraging area, which would effectively minimize the exposure of the organism on a per 

area basis.

Table E3 and Table E4 focus on seed consumption and forage area to reach the acute and acute 

listed LOC, respectively. Table E5 and Table E6 present seed consumption and forage area to 

reach the chronic LOC using the weight adjusted NOAEL and LOAEL (or frank effects endpoint), 

respectively. The ‘adjustment’ to the endpoints refers to the body weight adjustment to the 

three size classes of mammals (see T-REX User Guide).

Using the nocturnal wood (or field) mouse22 or Apodemus sylvaticus (belonging to the small to 

medium mammalian size class; i.e., 13-27g) as a case example we show that the calculated 

 22 Putman, R.J. Ed. 1989. Mammals as Pests. Chapter 3: The Mammal Society. New York, New York. ISBN: 0 412 

32590X. Available online: 

https://books.google.com/books?hl=en&lr=&id=hOEM7IC8XhUC&oi=fnd&pg=PA34&dq=predators+beet+seed&

ots=1A5O3k9AOe&sig=YYtp2NCmrexgDhVGJ24x2F0QloI&safe=on#v=onepage&q=predators%20beet%20seed

&f=false
consumption rates are plausible. The wood mouse is an abundant granivore that feeds on sugar 

beet seeds. It can easily locate them by smell and excavate them from the soil. It removes the 

seed coat orally and consumes the plant embryo. A single wood mouse can, on average, 

consume 800 seeds in one night; the highest consumption by a single individual is reported to 

be 1400 seeds in one night23. That is, assuming the wood mouse only feeds on sugar beets. The 

forage area is 10-20 m along a row followed by movement to an adjacent row. The mouse can 

detect ungerminated sugar beet seeds at depths of at least 3 cm; rabbits (Oryctolagus 

cuniculus) and hares (Lepus capensis) also feed on cotyledons, leaves, petioles, and crowns of 

sugar beet plants 24. 

Assuming the average consumption rate of 800 seeds/night, the wood mouse could easily 

consume enough pelleted seeds to reach and exceed LOCs for the acute (84 seeds/day), listed 

(17 seeds/day), chronic (10 seeds/day), and frank effects chronic (52 seeds/day) risk categories 

at the low end scenario (i.e., low application rate and low seeding rate) for the standard pellet. 

With respect to the high application rate for the build-up pellet and the low seeding rate, the 

most compelling result is for the chronic values whereby the wood mouse could conceivably 

consume over 16 pellets/day (or 64% of its daily mass intake) to exceed the adjusted NOAEC.

Taking the less conservative approach and assuming a typical 25 sugar beet row spacing of 22 

inches (or 0.5588 m), the minimum row forage distance (10m) of the wood mouse22, and that 

the wood mouse only reaches two consecutive rows to forage, the forage area covered is 

5.588m2 (or 60 ft2). Therefore, the wood mouse can cover 60 ft2 and in that area encounter 

enough pelleted seeds to reach and exceed LOCs for the acute (17 ft2), listed (3 ft2), chronic (2 

ft2), and frank effects chronic (10 ft2) risk categories at the low end scenario (i.e., low 

application rate and low seeding rate). With respect to the high application rate for the build-up 

pellet and the low seeding rate, the wood mouse would cover only 3.13 ft2 to obtain enough 

seeds (i.e., 16 pellets/day) to reach the adjusted NOAEC.

Though larger size mammals require consumption of a greater number of pellets and a larger 

foraging area to reach the given risk categories, the potential of reaching or exceeding the LOC 

levels is high, especially for the high application rate (standard pellet) + high seeding rate 

scenarios and even more so in the cases of acute exposure to listed species and chronic 

exposure in general.

 23 Putman, R.J. 1989 citing Pelz 1979.

24 Draycott, A.P. Ed. 2006. Sugar Beet. Chapter 13: Pests. Blackwell Publishing. ISBN-10: 1-4051-1911-X. ISBN13: 978-1-4051-1911-5. Available online:

https://books.google.com/books?id=h1hMUuA59QC&pg=PA341&lpg=PA341&dq=birds+feeding+on+sugar+beet+seeds&source=bl&ots=xxfn0cjEe5&sig=_r

vKXnq77KSfc9jJ0DhurvsvEKg&hl=en&sa=X&ved=0CDAQ6AEwBWoVChMIvtS6sLTbxgIVBXsCh3rywuh#v=onepage&q=birds%20feeding%20on%20sugar%20beet%20seeds&f=false

25 Minimum row spacing is 15 inches (or 0.381m). (EPA draft guidance)
Table E3. Acute Risk to Mammals: Comparisons to 0.5 Adj. LD50

Scenario1

(app 

rate/seed 

rate)

0.5 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of a.i. 

to reach 

0.5 adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.5 

adj. LD50

(mgpellet)

# Pellets 

consumed 

to reach 

0.5 adj. 

LD50

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach 0.5 adj. 

LD50 (%)*

Area 

covered 

(ft2)**

15 g size class

High/High 1,758 26 1,256 42 3,178 39.5 2.02

High/Low 8.36

Low/High 2,512 84 79 4.04

Low/Low 16.71

High (build 

up)/Low

16,330 126 514 25.1

35 g size class

High/High 1,423 50 2,371 79 5,125 46.3 3.82

High/Low 15.78

Low/High 4,742 158 92.5 7.64

Low/Low 31.55

High (build 

up)/Low

30,830 237 602 47.34

1000 g size class

High/High 615 615 29,301 977 33,951 86.3 47.2

High/Low 194.95

Low/High 58,603 1,953 172.6 94.4

Low/Low 389.9

High (build 

up)/Low

381,008 2,931 1,122 585

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LD50 = 1600 mg a.i./kg-bw for a 350g rat. The adjusted LD50 = 3,517 mg a.i./kg-bw for a 15g mammal, 2,845 mg 

a.i./kg-bw for a 35g mammal, and 1231 mg a.i./kg-bw for a 1000g mammal

*(Mass of pellet to reach 0.5 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.5 adjusted LD50 / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)

Table E4. Acute Endangered Mammal Species Risk: Comparisons to 0.1 Adj. LD50

Scenario1

(app 

rate/seed 

rate)

0.1 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.1 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.1 

adj. LD50

(mgpellet)

# Pellets 

consumed 

to reach 

0.1 adj. 

LD50

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach 0.1 adj. 

LD50 (%)*

Area 

covered 

(ft2)**

15 g size class

High/High 352 5.3 251 8 3,178 7.9 0.40

High/Low 1.67

Low/High 502 17 15.8 0.81

Low/Low 3.34

High (build 

up)/Low

3,266 25 103 5.01
35 g size class

High/High 285 10 474 16 5,125 9.3 0.76

High/Low 3.16

Low/High 948 32 18.5 1.53

Low/Low 6.31

High (build 

up)/Low

6,166 47 120 9.47

1000 g size class

High/High 123 123 5,860 195 33,951 17.3 9.44

High/Low 38.99

Low/High 11,721 391 34.5 18.87

Low/Low 77.98

High (build 

up)/Low

76,202 586 224 117

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LD50 = 1600 mg a.i./kg-bw for a 350g rat. The adjusted LD50 = 3,517 mg a.i./kg-bw for a 15g mammal, 2,845 mg 

a.i./kg-bw for a 35g mammal, and 1231 mg a.i./kg-bw for a 1000g mammal

*(Mass of pellet to reach 0.1 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.1 adjusted LD50 / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)

Table E5. Chronic Risk to Mammals: Comparisons to Adj. NOAEL 

Scenario1

(app 

rate/seed 

rate)

Adjusted 

NOAEL

(mg 

a.i./kgbw)

Mass of 

a.i. to 

reach adj 

NOAEL

(mg a.i.)

Mass of 

pellet to 

reach adj. 

NOAEL 

(mgpellet)

# Pellets 

consumed 

to reach 

adj. NOAEL

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach adj. NOAEL 

(%)*

Area 

covered 

(ft2)**

15 g size class

High/High 220 3.3 157 5 3,178 4.9 0.25

High/Low 1.04

Low/High 314 10 9.9 0.51

Low/Low 2.09

High (build 

up)/Low

2,041 16 64.2 3.13

35 g size class

High/High 178 6.2 296 10 5,125 5.8 0.48

High/Low 1.97

Low/High 593 20 11.6 0.95

Low/Low 3.94

High (build 

up)/Low

3,854 30 75.2 5.92

1000 g size class

High/High 77 76.9 3,662 122 33,951 10.8 5.90

High/Low 24.37

Low/High 7,325 244 21.6 11.8

Low/Low 48.74

High (build 

up)/Low

47,626 366 140.3 73.12

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)
The NOAEL = 100 mg a.i./kg-bw for a 350g rat (based on teratogenicity study, MRID 42826307)

*(Mass of pellet to reach adjusted NOAEL / Daily mass intake) x 100

**Number of pellets consumed to reach the adjusted NOAEL / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)

Table E6. Chronic Risk to Mammals: Comparisons to Adj. LOAEL 

Scenario1

(app 

rate/seed 

rate)

Adjusted 

LOAEL

(mg 

a.i./kgbw)

Mass of 

a.i. to 

reach adj 

LOAEL

(mg a.i.)

Mass of 

pellet to 

reach adj. 

LOAEL 

(mgpellet)

# Pellets 

consumed 

to reach 

adj. LOAEL

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach adj. LOAEL 

(%)*

Area 

covered 

(ft2)**

15 g size class

High/High 1,099 16.5 785 26 3,178 24.7 1.26

High/Low 5.22

Low/High 1,570 52 49.4 2.53

Low/Low 10.4

High (build 

up)/Low

10,207 79 321 15.7

35 g size class

High/High 889 31.1 1,482 49 5,125 28.9 2.39

High/Low 9.86

Low/High 2,964 99 57.8 4.77

Low/Low 19.7

High (build 

up)/Low

19,269 148 376 29.6

1000 g size class

High/High 385 385 18,313 610 33,951 53.9 29.5

High/Low 121.8

Low/High 36,627 1,221 108 58.98

Low/Low 243.7

High (build 

up)/Low

238,130 1,832 701 365.6

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LOAEL = 500 mg a.i./kg-bw for a 350g rat (based on teratogenicity study, MRID 42826307)

*(Mass of pellet to reach adjusted LOAEL / Daily mass intake) x 100

**Number of pellets consumed to reach the adjusted LOAEL / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)

Birds

The values in Table E7 through Table E10 provide estimates of seed consumption (i.e., #pellets 

consumed) and forage area (i.e., area covered) for birds under the same five scenarios 

presented in the above T-REX and SCA mammalian calculations. As for the mammals, the seed 

consumption to reach the given threshold changes with application rate (i.e., recall that 

application rate determines the amount of a.i. on a seed pellet), while forage area covered to 

consume enough seeds to reach a given risk level changes with both the application rate and 

seeding rate. A lower seeding rate always leads to a higher foraging area, which would 

effectively minimize the exposure of the organism on a per area basis.
Table E7 and Table E8 focus on seed consumption and forage area to reach the acute and acute 

listed LOC, respectively. Table E9 and Table E10 present seed consumption and forage area to 

reach the chronic LOC using the avian NOAEL and LOAEL (or frank effects endpoint), 

respectively. The weight adjustment is not calculated for birds as no data exist for incorporating 

scaling factors for birds.

Using the zebra finch26 or Taeniopygia guttata (belonging to the small avian size class; i.e., 

12.7g) as a case example we show that the calculated consumption rates are plausible. The 

zebra finch is a passerine granivore but may also feed on fruits and vegetables 27. Though little 

information is available on the finch’s sugar beet seed consumption, one open literature study 

(Lemon & Barth 1992) notes that when fed a diet of mixed grass seeds without seed hulls or 

chaff, a single zebra finch adult could consume approximately 2.3g of seeds per day.

Furthermore, birds like skylarks (Alauda arvensis), house sparrows (Passer domesticus L.), 

partridges (Perdix perdix L.), woodpigeons (Columba palumbus L.), and pheasants (Phasianus 

colchicus) feed on sugar beet seedlings and foliage; rooks (Corvus frugilegus) can uproot them 

in search of soil invertebrates; and, skylarks can also feed on sugar beet cotyledons24. 

Assuming the grass seeds approximate a standard pelleted sugar beet seed in weight (30 mg, or 

0.03 g, see Appendix D), the consumption rate of sugar beet seeds for comparison with 

calculations becomes 77 seeds/day; for build-up pellets (130 mg is 0.13g) becomes 18 

seeds/day. With this in mind, the zebra finch could easily consume enough pelleted seeds to 

reach and exceed LOCs for the acute (28 seeds/day), listed (6 seeds/day), chronic (6 seeds/day), 

and frank effects chronic (15 seeds/day) risk categories at the low end scenario (i.e., low 

application rate and low seeding rate) for the standard pellet. The fraction of the daily mass 

intake is less than 20% for acute exposure meaning that the zebra finch would not have to 

consume a lot of sugar beet seed to reach the acute risk categories.

With respect to the high application rate for the build-up pellet and the low seeding rate, the 

most compelling results are for the acute listed, chronic, and frank effects chronic risk 

categories whereby the zebra finch could conceivably consume over 8 pellets/day (or 22% of its 

daily mass intake), 40 pellets/day (23.8%), and 101 pellets/day (59.6%), respectively, to exceed 

the LOCs.

Taking the less conservative approach, as was calculated for the wood mouse, and assuming a 

typical 28 sugar beet row spacing of 22 inches (or 0.5588 m), the minimum row forage distance 

(10m) of the wood mouse22 (since data on the zebra finch is not available), and that the zebra 

 26 Lemon, W.C. and R.H. Barth, Jr. 1992. The effects of feeding rate on reproductive success in the zebra finch, 

Taeniopygia guttata. Animal Behavior (44): 851-857. 

Available online: http://ac.els-cdn.com/S0003347205805810/1-s2.0-S0003347205805810-

main.pdf?_tid=cebfcac2-2587-11e5-b1ee00000aacb35f&acdnat=1436370272_c91241597d91c91a2f01627aa3c043a0

27 http://www.finchinfo.com/diet/safe_toxic_and_unsafe_foods.php 28 Minimum row spacing is 15 inches (or 0.381m). (EPA draft guidance)
finch only reaches two consecutive rows to forage, the forage area covered is 5.588m2 (or 60 

ft2). Therefore, the zebra finch can cover 60 ft2 and in that area encounter enough pelleted 

seeds to reach and exceed LOCs for the acute (6 ft2), listed (1 ft2), chronic (1 ft2), and frank 

effects chronic (3 ft2) risk categories at the low end scenario (i.e., low application rate and low 

seeding rate) for the standard pellet. With respect to the high application rate for the build-up 

pellet and the low seeding rate, the zebra finch would cover only 2, 8 and 20 ft2 to obtain 

enough seeds (i.e., 8, 40, 101 pellets/day) to reach the adjusted LD50, non-adjusted NOAEL and 

LOAEL for the acute listed, chronic, and frank effects chronic risk categories, respectively. 

Though larger size birds require consumption of a greater number of pellets and a larger 

foraging area to reach the given risk categories, the potential of reaching or exceeding the LOC 

levels is high, especially for the high application rate (standard pellet) + high seeding rate 

scenarios and even more so in the cases of acute exposure to listed species and chronic 

exposure in general.

Table E7. Acute Risk to Birds: Comparisons to 0.5 Adj. LD50

Scenario1

(app 

rate/seed 

rate)

0.5 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.5 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.5 adj. 

LD50 (mgpellet)

# Pellets 

consumed 

to reach 0.5 

adj. LD50

Daily mass 

of food 

intake (mg)

Fraction of 

Daily mass 

intake to 

reach 0.5 

adj. LD50 (%)*

Area 

covered 

(ft2)**

20 g size class

High/High 443 8.9 422 14 5,062 8.3 0.68

High/Low 2.8

Low/High 843 28 16.7 1.36

Low/Low 5.61

High (build 

up)/Low

5,482 42 108 8.42

100 g size class

High/High 564 56 2,683 89 14,432 19 4.32

High/Low 17.85

Low/High 5,367 179 37.2 8.64

Low/Low 35.71

High (build 

up)/Low

34,893 268 242 53.6

1000 g size class

High/High 796 796 37,904 1,263 64,615 59 61.04

High/Low 252.2

Low/High 75,808 2,527 117.3 122.1

Low/Low 504.4

High (build 

up)/Low

492,870 3,791 763 756.8

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LD50 = 827 mg a.i./kg-bw for a 12.7 g passerine. The adjusted LD50 = 885 mg a.i./kg-bw for a 20g bird, 1,127 mg 

a.i./kg-bw for a 100g bird, and 1,592 mg a.i./kg-bw for a 1000g bird

*(Mass of pellet to reach 0.5 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.5 adjusted LD50 / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)
Table E8. Acute Endangered Bird Species Risk: Comparisons to 0.1 Adj. LD50

Scenario1

(app 

rate/seed 

rate)

0.1 

Adjusted 

LD50 (mg 

a.i./kgbw)

Mass of 

a.i. to 

reach 0.1 

adj LD50 

(mg a.i.)

Mass of 

pellet to 

reach 0.1 

adj. LD50 (mgpellet)

# Pellets 

consumed 

to reach 0.1 

adj. LD50

Daily mass 

of food 

intake (mg)

Fraction of 

Daily mass 

intake to 

reach 0.1 

adj. LD50 (%)*

Area 

covered 

(ft2)**

20 g size class

High/High 88.5 1.8 84 3 5,062 1.7 0.14

High/Low 0.56

Low/High 169 6 3.3 0.27

Low/Low 1.12

High (build 

up)/Low

1,096 8 22 1.68

100 g size class

High/High 113 11 537 18 14,432 3.7 0.86

High/Low 3.57

Low/High 1,073 36 7.4 1.73

Low/Low 7.14

High (build 

up)/Low

6,979 54 48 10.7

1000 g size class

High/High 159 159 7,581 253 64,615 12 12.21

High/Low 50.44

Low/High 15,162 505 23.5 24.4

Low/Low 100.9

High (build 

up)/Low

98,574 758 153 151.4

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LD50 = 827 mg a.i./kg-bw for a 12.7 g passerine. The adjusted LD50 = 885 mg a.i./kg-bw for a 20g bird, 1,127 mg 

a.i./kg-bw for a 100g bird, and 1,592 mg a.i./kg-bw for a 1000g bird

*(Mass of pellet to reach 0.1 adjusted LD50 / Daily mass intake) x 100

**Number of pellets consumed to reach the 0.1 adjusted LD50 / (20.7 or 5.01) seed pellets ft-2 (See Appendix D for 

details)

Table E9. Chronic Risk to Birds: Comparisons to NOAEC

Scenario1

(app 

rate/seed 

rate)

NOAEC

(mg 

a.i./kgdiet)

Mass of 

a.i. to 

reach 

NOAEC

(mg a.i.)

Mass of 

pellet to 

reach 

NOAEC 

(mgpellet)

# Pellets 

consumed 

to reach 

NOAEC

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach NOAEC 

(%)*

Area 

covered 

(ft2)**

20 g size class

High/High 385 1.95 92.8 3 5,062 1.8 0.15

High/Low 0.62

Low/High 186 6 3.7 0.30

Low/Low 1.23

High (build 

up)/Low

1,207 40 23.8 8.03

100 g size class
High/High 385 5.56 265 9 14,432 1.8 0.43

High/Low 1.76

Low/High 529 18 3.7 0.85

Low/Low 3.52

High (build 

up)/Low

3,441 115 23.8 22.89

1000 g size class

High/High 385 24.9 1,185 39 64,615 1.8 1.91

High/Low 7.88

Low/High 2,369 79 3.7 3.82

Low/Low 15.76

High (build 

up)/Low

15,404 513 23.8 102.5

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The NOAEL = 385 mg a.i./kg-diet (based on bobwhite quail study MRID 48716602)

*(Mass of pellet to reach NOAEC / Daily mass intake) x 100

**Number of pellets consumed to reach NOAEC / (20.7 or 5.01)seed pellets ft-2 (See Appendix D for details)

Table E10. Chronic Risk to Birds: Comparisons to LOAEC

Scenario1

(app 

rate/seed 

rate)

LOAEC 

(mg 

a.i./kgdiet)

Mass of 

a.i. to 

reach 

LOAEC

(mg a.i.)

Mass of 

pellet to 

reach 

LOAEC

(mgpellet)

# Pellets 

consumed 

to reach 

LOAEC

Daily 

mass of 

food 

intake 

(mg)

Fraction of Daily 

mass intake to 

reach LOAEC (%)*

Area 

covered 

(ft2)**

20 g size class

High/High 962 4.9 232 8 5,062 4.6 0.37

High/Low 1.54

Low/High 464 15 9.2 0.75

Low/Low 3.09

High (build 

up)/Low

3,015 101 59.6 20.1

100 g size class

High/High 962 13.9 661 22 14,432 4.6 1.06

High/Low 4.40

Low/High 1,322 44 9.2 2.13

Low/Low 8.80

High (build 

up)/Low

8,597 287 59.6 57.2

1000 g size class

High/High 962 62.2 2,960 99 64,615 4.6 4.77

High/Low 19.7

Low/High 5,920 197 9.2 9.53

Low/Low 39.4

High (build 

up)/Low

38,489 1,283 59.6 256.1

1 High and low app rates are for the standard pellet use unless otherwise specified (i.e., the fifth scenario)

The LOAEC = 962 mg a.i./kg-diet (based on bobwhite quail study MRID 48716602)

*(Mass of pellet to reach LOAEC / Daily mass intake) x 100

**Number of pellets consumed to reach LOAEC / (20.7 or 5.01)seed pellets ft-2 (See Appendix D for details)