Page 1 of 121 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D.C., 20460

OFFICE OF
CHEMICAL SAFETY AND
POLLUTION PREVENTION

PC Code: 105501

DP Barcode: D414217

MEMORANDUM

DATE: May 20, 2014

SUBJECT: Transmittal of the Draft Environmental Fa te and Ecological Risk Assessment in Support of the Registration Review of Tebuthiuron

TO: Joel Wolf, Chemical Review Manager Risk Management and Implementation Branch IV

Pesticide Re-evalu ation Division

7508P

FROM: Ibrahim Abdel-Saheb, Ph.D., Environmental Scientist Steve Carey, Biologist

Environmental Risk Bran ch 6

Environmental Fate and Effects Division

7507P

THROUGH: Mark Corbin, Branch Chief

Environmental Risk Branch 6

Environmental Fate and Effects Division

7507P

The Environmental Fate and Effects Division (EFED) has completed the preliminary ecological risk, environmental fate, endangered species, and drin king water assessments c onducted in support of the Registration Review of the herbicide Tebuthiuron (PC Code 105501).-Page 2 of 121- Risk Conclusions

The results of this screening-level risk assessmen t indicate that the curren t uses of tebuthiuron may potentially cause direct adverse effects to Federally-listed thre atened and endangered (hereafter referred to as “listed”) and non-lis ted mammals, terrestrial-phase am phibians, reptiles, small-sized birds on an acute exposure basis. Chronic risk to listed and non-listed bi rds, terrestrial-phase amphibians, reptiles, and mammals may also occu r. Risk to listed a nd non-listed species of terrestrial plants and aquatic vascular and nonvasc ular plants may occur. Whereas for terrestrial invertebrates, available lines of ev idence indicate that the potential for risk is low. Tebuthiuron is not expected to adversely affect aqua tic vertebrates and invertebrates. The risks may extend to indirect effects upon listed species that depend upon that taxonomic group as a resource.

At this current stage of the regist ration review process, it is premat ure to make dir ect or indirect

effects determinations until further refinements ar e conducted. An in-depth listed species evaluation determining the potential co-occurrence of listed speci es and use patterns of tebuthiuron is needed; however, additional information on the biology of liste d species, the locations of these species, and

the locations of use sites are needed to determ ine the extent to which screening assumptions regarding an action area apply to a particular listed organism.

Tables 1 and 2 summarize the maximum uses assessed and the taxa that may potentially be directly at risk from exposure to tebuthi uron as a result of broadcast sp ray and granular applications, respectively. Table 3 summarizes the area percentage of spot treatment uses needed to exceed the listed species LOC from spraying or with granules /pellets/tablets using ground-based equipments.Page 3 of 121Table 1. Risk to Taxon Resulting from Tebuthiuron Use Patterns Sprayed at Maximum Single Application Rate of 6 lb a.i./AUsePatternCategoryAquatic Organisms(surrogate foraquatic-phaseamphibians)Birds, (surrogate for terrestrialphase amphibians and reptiles)MammalsPlants1TerrestrialInvertebratesRangelandandPasturesAcute risk:Not expected.Highest RQ = 0.02Chronic risk:Not expectedHighest RQ = 0.2Acute risk: Expected for small-sizedbirds consuming tebuthiuron directly.Highest RQ=0.98, up to 10x the listedLOC of 0.1; however, extremely lowfood consumption of the test materialwas observed in passerines. No effectfor medium- and large-sized birds.Days of exceedance for acute risk tobirds using maximum scenario = 115days. Application rate needed to notexceed the listed species LOC = 0.25lb a.i./A.Chronic risk: Expected for birds.Highest RQ = 14, exceeds 14x thelisted LOC of 1. Days of exceedancefor chronic risk to birds usingmaximum scenario = 140 days.Application rate needed to not exceedthe listed species LOC = 0.4 lb a.i./A.Distance of risk to non-target birdsdownwind (drift only) from edge offield:Up to 139 feet with aerialapplications; up to 38 feet withground applications.Acute risk:Expected for all sizes ofmammals. Highest RQ=1.6,exceeds 16x the listed LOCof 0.1. Days of exceedancefor acute risk to mammalsusing maximum scenario =60 days. Application rateneeded to not exceed thelisted species LOC = 0.15 lba.i./A.Chronic risk:Expected for mammals.Highest RQ=45, exceeds 45xthe listed LOC of 1. Days ofexceedance for chronic risk tomammals using maximumscenario = 100 days.Application rate needed tonot exceed the listed speciesLOC = 0.15 lb a.i./A.Distance of risk to non-targetmammals downwind (driftonly) from edge of field: upto 479 feet (aerial app.); up to125 feet (ground app.).Terrestrial and Aquatic:Risk to plants is expected.Highest RQ for listed terrestrialplants = 188 (dry area), 1031(semi-aquatic area), and 94(drift). Highest RQ for listedaquatic plants = 22 (vascular) and55 (alga/diatoms).Application rate needed to notexceed listed LOC from runoffand/or drift:Terrestrial = 0.03 lb a.i./A (dryarea), 0.005 lb a.i./A (semiaquatic area), and 0.06 lb a.i./A(drift only). Aquatic = 0.27 lba.i./A (vascular) and 0.11 lb a.i./A(alga/diatoms)Distance of risk to listed plantspecies downwind (drift only)from edge of field usingmaximum scenario: Terrestrial,up to and extends more than 997feet; Aquatic nonvascular, up to10 feet; and Aquatic vascular,None, runoff is main route ofexposure to aquatic plants.Non-listed andListed:Uncertain; lowlikelihood ofrisk.1Results are from aerial-based applicationsat which exposure is at its highest.-Page 4 of 121-Table 2. Risk to Taxon Resulting from Tebuthiuron Use Patterns Applied as Granules atMaximum Single Application Rate of 6 lba.i./AUsePatternCategoryAquatic Organisms(surrogate foraquatic-phaseamphibians)Birds, (surrogate forterrestrial-phase amphibiansand reptiles)MammalsPlants1TerrestrialInvertebratesRangelandandPasturesAcute risk:Not expected.Highest RQ = 0.02Acute risk: Expected for smallsized birds that consumetebuthiuron-treated granules astheir only source of food;however, low food consumptionand regurgitation of the activeingredient were observed in thepasserine bird studies. GranularRQs not available, assumed to beequivalent to spray RQs;however, some uncertainty existssince granular and pelletedformulations do not contain100% of the active ingredient.No effect for medium- and largesized birds.Acute risk:Expected for small- andmedium-sized mammals thatconsumes tebuthiuron-treatedgranules directly. HighestRQ=1.96, exceeds up to 20xthe listed LOC of 0.1. Notexpected for large-sizedmammals; highest RQ = 0.08Application rate needed tonot exceed the listed speciesLOC for pelleted (40% a.i.)formulations = 0.3 lb a.i./A.Application rate needed tonot exceed the listed speciesLOC for granular (5% a.i.)formulations = 2.5 lb a.i./ATerrestrial and Aquatic:Expected for plants inhabitingareas adjacent to a site treatedwith granules containing 100%tebuthiuron. Highest RQ forlisted terrestrial plants = 94 (dryarea) and 938 (semi-aquaticarea). Highest RQ for listedaquatic plants = 20 (vascular)and 26 (alga/diatoms).Application rate needed to notexceed listed LOC from runoff:Terrestrial = 0.06 lb a.i./A (dryarea) and 0.006 lb a.i./A (semiaquatic area). Aquatic = 0.3 lba.i./A (vascular) and 0.23 lba.i./A (alga/diatoms)Non-listed andListed:Uncertain; lowlikelihood ofrisk.1Results are from the maximum application rate of6 lb a.i./A at which exposure is at its highestPage 5 of 121 Table 3. Area Percentage of Spot Treatment Needed to Exceed the Listed Species LOC
Taxa Application

rates (lb a.i./A) RQs assuming

100% area

treated (highest to lowest)* Listed Species LOC Area Percentage of application

needed to exceed

LOC 1

Birds (acute effects, liquid spray, broadcast) 6 0.98

Acute = 0.1 10%

4 0.66 15%

Mammals (acute effects, liquid spray, broadcast) 6 1.6 6%

4 1.1 9%

Mammals (acute effects, pellets, broadcast) 6 1.96 5%

4 1.31 8%

Mammals (acute effects, granules, broadcast) 6 0.24 42%

4 0.16 63%

Birds (chronic effects,broadcast, dietarybased) 6 14

Chronic = 1.0 7%

4 10 10%

Mammals (chronic effects, liquid spray,broadcast, dietarybased) 6 7 14%

4 5

20%

Mammals (chronic effects, broadcast, liquid spray, dose-based) 6 45 2%

4 30 3%

Terrestrial Plants (listed effects, liquid spray, ground, broadcast) 6 956

Listed plants = 1.0 0.1%

4 638 0.2%

Terrestrial Plants (listed effects, granules, ground, broadcast) 6 938 0.1%

4 625 0.2%

Aquatic vascular plants (listed effects, liquid spray, ground, broadcast) 6 20 5%

4 14 7%

6 26 4%-Page 6 of 121- Table 3. Area Percentage of Spot Treatment Needed to Exceed the Listed Species LOC
Taxa Application

rates (lb a.i./A) RQs assuming

100% area

treated (highest to lowest)* Listed Species LOC Area Percentage of application

needed to exceed

LOC 1

Aquatic nonvascular plants (listed effects, liquid spray, ground, broadcast) 4 18 6%

Aquatic vascular plants (listed effects, granules, ground, broadcast) 6 20 5%

4 13 8%

Aquatic nonvascular plants (listed effects, granules, ground, broadcast) 6 26 4%

4 17 6%

*Bold values indicate LOC exceedance

1 The threshold percentage is assessed to determine how much percent of exposure that RQ needs to exceed the LOC. For example, the highest acute RQ for birds inhabiting a field treated at 6 lb a.i./A is 0.98, which is up to 10x the listed species LOC of 0.1; to assess the % of exposure needed at which the LOC exceedance occurred, results indicate 10% is needed for the RQ to exceed the LOC. A “no effect” or “may affect” determination was not made

since it is unknown what % of an actual area is typical spot treatment.

Basic Uncertainties

Application dates were chosen in accordance with the product label: “For optimum results, applications should be made prior to the resump tion of active seasonal growth in the spring or before expected seasonal rainfall.” This can oc cur through a broad portion of a crop year and applications can therefore occur over a broad range of time. This creates uncertainty as to when to assign the application date for aquatic expos ure modeling. Additional information regarding tebuthiuron usage, specifically concerning th e timing of applications and geographical limitations of use, is of high value to EFED.-Page 7 of 121- 

## Environmental Fate and Ecological Risk Assessment for the Registration of Tebuthiuron

Tebuthiuron 1-( 5-tert-butyl-1 ,3,4-thiadiazol-2-yl)-1,3-dimethylurea

CAS Registry Number 34014-18-1

PC Code 105501

Prepared by:
Ibrahim Abdel-Saheb, Ph.D., Environmental Scientist Steve Carey, Biologist

U. S. Environmental Protection Agency Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch VI

1200 Pennsylvania Ave., NW

Mail Code 7507P Washington DC 20460 Reviewed by: Amy Blankinship, Senior Scientist, ERB VI
William P. Eckel, Ph.D, Senior Science Advisor, ERB VI
Mark Corbin, Branch Chief, ERB VI

May 20, 2014Page 8 of 121 

## Table of Contents

1. Executive Summary ............................................................................................................. .... 9

2. Problem Formulation ........................................................................................................... ... 13 3. Analysis................................................................................................................. ................. 19

4. Risk Characterization ......................................................................................................... .... 46

4.1. Risk Estimation................................................................................................................ 46

4.1.1 Risk Quotient Calculations for Aquatic Organisms ................................................ 47

4.1.2 Risk Quotient Calculations for Aquatic Plants ........................................................ 51

4.1.3. Risk Quotient Calculations for Terrestrial Animals ............................................... 54

4.1.4. Risk Quotient Calculations for Terrestria l Plants in Terrestrial and Semi-aquatic

Environments .................................................................................................................. ...... 62

4.2. Risk Description .............................................................................................................. .63

4.2.1. Risks to Aquatic Animals and Plants ...........................................................................64

4.2.2. Risks to Terrestrial Animals and Plants ........................................................................66 5. Federally Threatened and Endangered (Listed) Species Concerns ........................................ 78Page 9 of 121 1. Executive Summary

EFED has completed the Registratio n Review draft ecological risk assessment for Tebuthiuron (1- ( 5-tert-butyl-1 , 3,4-thiadiazol-2-yl)-1 ,3-dimethylurea; CAS#: 34014-18-1; PC Code: 105501) and its end-use products. Tebuthiuron is a systemic, relatively nons elective herbicide, which is absorbed into the plant roots and is then transl ocated into other plant tissues. Once absorbed by the roots and translocated into the plan t, it acts by inhibiting photosynthesis.

Tebuthiuron is used to contro l broadleaf and woody weeds, gra sses and brush on feed crop sites (pasture and rangeland) and a variety of non-food crop sites including air ports/landing fields, outdoor industrial areas, non-agri cultural rights-of-way, fencer ows, hedgerows, uncultivated areas/soils, and under paved road s and sidewalks in areas wh ere no future landscaping is planned. Primary uses include rangeland and near ra ilroads and other indust rial facilities. Single active ingredient formulations include granul ar, pelleted/tableted, wettable powder, water dispersible granules, and technical grade/so lid products. Four multip le active ingredient formulations (granules) also are registered. All formulations may be applied as broadcast, banded or spot treatments using ground equipment. The pelleted/tableted formulations also may be applied using aerial equipment.

The currently registered yearly si ngle application rate of tebuthiur on is 6 lb a.i./A for the use on rangeland.

Tebuthiuron is persistent, mobile and can leach to ground water. It is resi stant to biological and chemical degradation, and its principal route of dissipation in the envi ronment appears to be leaching and/or runoff. Transport to ground wate r through leaching and to surface water through runoff are likely as a result of tebuthiuron's envi ronmental persistence and low sorption to soil. Tebuthiuron has been detected in ground water in Texas and California. Considering its low Henry's Law constant (7.58 x 10 -11 atm-m3/mol; at 25°C), the potential for vapor phase and longrange transport is not important.

With the exception of the pink shrimp, an estuar ine/marine invertebrate, a small number of

available data indicates tebuthiuron is practically non-toxic to freshwater and estuarine/marine fish and invertebrates on an acute exposure ba sis. On a chronic exposure basis, tebuthiuron

resulted in decreased survival , reproduction (number of young/fema le), and growth (length) in these aquatic organisms.

On an acute exposure basis, tebu thiuron is slightly toxic to pa sserines, practically nontoxic to upland game birds and waterfowls and modera tely toxic to mammals. Significant treatmentrelated reductions in eggs laid per pen, 14- day hatchling per number hatched, hatchling body weight, 14-day survivor weight, female and male weight gains, and eggshell thickness were determined from the chronic avian reproducti on studies, while signifi cant reductions in body weight and body weight gains were determined from the chronic mammalian reproduction study.

Available studies with beneficial insects ( i.e. , honey bees) recorded no effects ( i.e. , the no-effect level was greater than the highest concentration tested). As expected for an herbicide, thePage 10 of 121 available plant toxicity data show ed tebuthiuron to be toxic to aqua tic and terrestrial plants based on reduced growth.

Risks are anticipated for terrestr ial vertebrates that directly consume vegetation and granules treated with tebuthiuron on a daily basis. Exceed ances of the listed species LOC were up to 10x for birds and up to 20x for mammals. The highest chronic RQs were approximately 14x and 45x the chronic LOC for birds and mammals, respectiv ely. For spot treatment uses using sprayers, T-REX modeling indicates a fiel d applied at the maximum app lication rate and with an assumption that 100% of the field is treated; an area percentage (threshold) of less than 10% and 5% of the field treated is needed to not exceed the listed species LOC for birds and mammals, respectively, consuming tebuthiur on-treated vegetation. Of the sa me scenario above, an area percentage of less than 7% and 2% is needed to not exceed the chronic LOC for birds and mammals, respectively. For granule uses, applying less than 42% of the field at the maximum rate would not exceed the listed species LOC for mammals.

Tebuthiuron is an herbicide; listed plant LOC exceedances for broadcast spraying and granular uses were expected. RQs were as high as 1031 for terrestrial plants and 55 for aquatic plants; and as high as 938 and 26 for terrestrial and aquatic plants, respectively, when granules are used.

No risks are expected for fish and aquatic invertebrates. Risks to terrestrial invertebrates are unlikely.

Identified potential risks to li sted species are summarized in Table 1.1 and detailed in Table 5.1.

Table 1.1. Potential Effects to Federally-Liste d Taxa Associated with Direct Effects from the Registered Uses of Tebuthiuron.

Listed Plant Taxon Potential Direct Effects Terrestrial and semi-aquatic plants – monocots and dicots Yes*

Aquatic nonvascular plants Yes* Aquatic vascular plants Yes*

Listed Animal Taxon Potential Direct Effects

Acute Chronic

Terrestrial invertebrates Uncertain 1 N/A 2

Mammals Yes* Yes*

Birds Yes* for small-sized classes;No effect for mid- and largesized classes Yes* (all size classes)

Reptiles 3 Yes* Yes* Terrestrial-phase amphibians 3 Yes* Yes*

Freshwater fish No Effect No Effect Aquatic-phase amphibians 4 No Effect No Effect

Freshwater invertebrates No Effect No Effect

Estuarine/marine fish No Effect No Effect

Estuarine/marine invertebra tes No Effect No EffectPage 11 of 121 * At this current stage of the Registration Review process, it is premature to make effect s determinations until further

refinements ar e conducted.

1 Although no effects were seen in the acute contact toxicity test with honey bees at the max dose (100 μg a.i./bee), public dat a suggest individual terrestrial invertebra te taxonomic groups increased or decreased in population when exposed to tebuthiuron. Further, given that no endpoints were availabl e, EFED cannot preclude effects to this taxon.

2 No methodology available to measure chroni c effects to terrestrial invertebrates.

3 Birds are surrogates for reptiles and terrestrial-phase amphibians

4 Fish are surrogates for aquatic phase amphibians.

Potential effects to federally-listed endangered and depth threatened sp ecies (listed species) based on LOC exceedances require an in-depth listed species evaluation determining the potential co-occurrence of listed spec ies and use patterns of tebuthiuron.

Based on this screening-level assessment, acute a nd chronic risk resulting from direct effects is not expected for listed freshwater and estuarin e/marine fish (surrogates for aquatic-phase amphibians), and freshwater and es tuarine/marine invertebrates.

Precautionary labeling for benefici al insects is not required ba sed on acute toxicity data for honeybees. Risk resulting from direct effects to listed terrestrial i nvertebrates is uncertain from the

use of tebuthiuron on its re gistered use sites.

Potential direct effects on liste d birds (surrogates for terrestria l-phase amphibians and reptiles), mammals, and terrestrial and aquati c plants from the use of tebuth iuron may be associated with modification of primary constituent elements (PCEs) of designated critical habitat, where such designations have been made. However, at this current stage of the Registration Review process, it is premature to make effects determinations fo r listed species until furt her scientific analysis and refinements are conducted, based on recomme ndations received from the National Academy of Sciences’ (NAS) National Research Council (NRC) April 2013 report, available at http://www.nap.edu/cata log.php?record_id=18344 . The NAS report outlines recommendations on specific scientific and technical issues re lated to the development of pesticide risk assessments that are compliant with the Endangered Species Act (ESA) and the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).

The EPA along with the U.S. Fish & Wildlife Se rvice (USFWS), the National Marine Fisheries Service (NMFS) (collectively, the Services), a nd the U.S. Department of Agriculture (USDA), released a summary of their implem entation plan for assessing risks of pesticides to listed species ahead of the stakeholder workshop held on N ovember 15, 2013. This plan was developed in response to the NAS’ recommendations, including a common approach to ri sk assessment as a way of addressing scientific differences betw een EPA and the Services. During the workshop, the agencies received feedback from the public on the interim scientific approaches that were developed as part of the initial implementati on of the NAS recommendations. These approaches will be jointly implemented and vetted as part of a phased iterative process. Once fully vetted, EPA will further refine the listed species effects de termination portion of this risk assessment.

To make effects determinations for individual listed species, us eful refinements may include, but are not limited to, analyses of: 1) more detaile d, species-specific ecological and biological data; 2) more detailed and accurate in formation on tebuthiuron use patte rns; and 3) sub-county levelPage 12 of 121 spatial proximity data for the co -occurrence of potential effects areas and listed species and any designated critical habitat. Examples of such refinements are described below.

EFED is currently developing tools that are expe cted to further refine the assessment and are designed to support effects determinations for individual federally list ed species and their designated critical habitats (w here applicable). Scientific information obtained from the Services, and other reliable s ources is being collated by EFED to address all currently listed species. This information is being stored in an Office of Pesticide Programs (OPP) Pesticide Registration Information SysteM (PRISM) listed species knowledgebase. The listed species knowledgebase consists of an information repos itory that houses biological and behavioral

information relevant to individual species ( e.g. , habitat, diet, and life history, including specific temporal and spatial associations) and a documen t repository that contains supporting documents ( e.g ., USFWS recovery plans) a nd electronic information ( e.g ., GIS data files). For terrestrial taxa, biological information re levant to the assessment ( e.g ., diet and body weight) will be used to parameterize exposure estimates using a method c onsistent with currently used methods in the

T-REX and T-HERPS models.

Refinements will also include more detailed analyses of the registered uses and specific use patterns that result in either “Likely to Advers ely Affect” (LAA) or “Not Likely to Adversely Affect” (NLAA) determinations for federally li sted species. The analyses may include more information on where, when, and how tebuthiuron is used on all use sites. Actual usage data (when available) and national land-cover datasets that indi cate potential use sites [ e.g ., National Land Cover Dataset (NLCD), Cropland Data Laye r (CDL)] may be used to support a more refined analysis of where tebuthiuron is reasonabl y expected to be used. Similarly, refinements on the timing of applications and a more in-d epth exploration of ag ronomic practices for tebuthiuron may be included as part of the refinement.

The refinements based on individu al species data; additional, de tailed usage information, when available; and recommendations from the NRC re port are expected to help to more accurately identify potential areas of effect and to better inform effects and habitat determinations for listed species and any designate d critical habitats.

Uncertainties

The conclusions of this risk assessment are li mited by uncertainties concerning both exposure and toxicity.

Degradate 104 (N-[5-(1,14-dimethylethyl)-1,3,4-thia diazol-2-yl]-N-methylurea) has the highest

concentrations detected. Additi onally, degradate 104 was detected in a retrospective ground water monitoring study and was a major degradate in a terrestrial field dissipa tion study, accounting for up to 23% of the mass applied. The degradate 1 04 was also found in an aerobic soil metabolism and soil photolysis studies comprising close to l7% of the mass applied. Degradate 104 was identified by the Health Effects Division (HED ) as the only environmental fate degradate of tebuthiuron of toxicological conc ern to human health. The lack of data regarding maximum occurrence, mobility, and toxicity of degradate 1 04 are further uncertainties which are addressed through a total toxic residues approach.Page 13 of 121 2. Problem Formulation

2.1. Nature of Regulatory Action

Under the Federal Insecticide, Fungicide, and Rode nticide Act (FIFRA), all pesticides distributed or sold in the United States must be register ed by the United States Environmental Protection Agency (EPA or the Agency). To determine whether a pesticide can be registered, the EPA evaluates the product’s safety to non-target species based on a wi de range of environmental and health effects studies. In 1996, FIFRA was amen ded by the Food Quality Protection Act (FQPA), and EPA was mandated to implement a new program for the periodic review of pesticides, i.e

., Registration Review 1 . The registration review program is inte nded to ensure that as the ability to assess risk evolves and as policies and practices change, all registered pesticides continue to meet the statutory standard of no unreasonable adverse effects to human health and the environment. Changes in science, public polic y, and pesticide use practices w ill occur over time. Through the registration review program, the Ag ency periodically reevaluates pesticides to make sure that as changes occur, products in the marketplace can be used safely.

Additionally, potential effects to Federally liste d endangered and threatened species (hereafter referred to as “listed”) and th eir designated critical habitat are also considered under the Endangered Species Act (ESA) in or der to ensure that the continue d registration of tebuthiuron is not likely to jeopardize the contin ued existence of listed species or adversely modify their critical habitat. In order to meet the requirements of FIFRA and the ESA, this assessment follows EPA guidance on conducting ecologica l risk assessments (USEPA, 1998) and Office of Pesticide Program’s Overview Document, which contains guidance for assessing pesticide risks to nonlisted and listed species (USEPA, 2004).

Recent tebuthiuron ecological risk assessment- related documents performed by EFED include Tier II Aquatic Exposure Assessment for Selected Tebut hiuron Uses on Rangel and, Pastureland, and Other Non-Crop Lands in the Pacific Northwest: Endangered Species (ES) Consultation Package. Dated: July 12, 2004. DP Barcode D304225, and an in itial Problem Formulation for Registration Review (2009, DP Barcode D363982).

2.2. Mode of Action

Tebuthiuron is a systemic, relatively nonselective herbicide which is absorbed into plant roots and is then translocated throughout the pl ant. It acts by inhibiting photosynthesis.

2.3. Use Characterization

1 http://www.epa.gov/oppsrrd1/registration_review/Page 14 of 121 Single active ingredient formula tions include granular, pelleted /tableted, wettable powder, water dispersible granules, and technical grade/so lid products. Four multip le active ingredient formulations (granules) also are registered. All formulations may be applied as broadcast, banded or spot treatments using ground equipment. The pelleted/tableted formulations also may be applied using aerial equipment.

Labeled use patterns for tebuthiuron are summarized in Table 2.1 , below.

Table 2.1. Tebuthiuron Uses by Label

Reg.No. Formul

ation % a.i. Uses # of apps/yr Method of App.

013283-

00018 Granular 2 6 (Diuron) COMMERCIAL/INSTITU

TIONAL/INDUSTRIAL PREMISES/EQUIPMENT (OUTDOOR) 2 Broadcast, No aerial app allowed

013283-

00021 Granular 1 3 (Diuron) COMMERCIAL/INSTITU

TIONAL/INDUSTRIAL PREMISES/EQUIPMENT (OUTDOOR) 2 Broadcast, Application via

shaker can

034913-

00010 Granular 5 DRAINAGE SYSTEMS 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A, no more than 6 lbs a.i./A per 2

consecutive treatments in any 6 year period Broadcast, Band treatment, Spot

treatment, , no aerial applications

034913-

00015 Granular 1 3 (Diuron) INDUSTRIAL AREAS (OUTDOOR),

NONAGRICULTURAL

RIGHTS-OFWAY/FENCEROWS/HED GEROWS,

NONAGRICULTURAL

UNCULTIVATED AREAS/SOILS, PAVED AREAS (PRIVATE ROADS/SIDEWALKS) 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A, no more than 6 lbs a.i./A per 2

consecutive treatments in any 6 year period Soil band treatment, Spot soil treatment, Soil

broadcast

treatment

034913-

00016 Granular 2 6 (Diuron) TERRESTRIAL NONFOOD+OUTDOOR

RESIDENTIAL 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A,

no more than 6 lbs a.i./A per 2 consecutive treatments in any 6 year period Soil band treatment, Spot soil treatment, Soil

broadcast

treatment

062719-

00107 Wettable powder 80 TERRESTRIAL NONFOOD CROP;

TERRESTRIAL FEED

CROP Max rate is 1-2 lb a.i./A, every 3 years for vulnerable sites; 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A, no more than 6 lbs ai/A per 2

consecutive treatments in Soil band treatment, Spot soil treatment, Soil

broadcast

treatmentPage 15 of 121 any 6 year period; spot treatment is allowed up

to 6 lb a.i./A when

needed

062719-

00121 Pelleted/

Tableted 20 TERRESTRIAL NONFOOD CROP,

TERRESTRIAL FEED

CROP Max rate is 1-2 lb a.i./A, every 3 years for vulnerable sites; 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A, no more than 6 lbs a.i./A per 2

consecutive treatments in any 6 year period; spot treatment is allowed up

to 6 lb a.i./A when

needed Soil band treatment, Spot soil treatment, Soil

broadcast

treatment

062719-

00122 Pelleted/

Tableted 40 AQUATIC NON-FOOD INDUSTRIAL,

TERRESTRIAL NONFOOD CROP,

TERRESTRIAL FEED

CROP Max rate is 1-2 lb a.i./A, every 3 years for vulnerable sites; 1/3 yr, 1 time in 3 yr period up to 4 lbs a.i./A, no more than 6 lbs a.i./A per 2

consecutive treatments in any 6 year period; spot treatment is allowed up

to 6 lb a.i./A when

needed Soil band treatment, Spot soil treatment, Soil

broadcast

treatment

81927-37 Pelleted 80 TOTAL VEGETATION

CONTROL IN NONCROPLAND AND FOR

WOODY PLANT

CONTROL IN NONCROPLAND,

RANGELAND AND

PERMANENT

PASTURES. Max rate is 1-2 lb a.i./A, every 3 years for vulnerable sites; 1/3 yr, 1 time in 3 yr period up to 4 lb a.i./A; spot treatment is allowed up

to 6 lb a.i./A when

needed Surface applied,

broadcast

treatment, as a banded treatment,

and aerial Application on rights-of-way is

limited to helicopter only
81927-41 Pelleted 20 Max rate is 1-2 lb a.i./A, every 3 years for vulnerable sites; For all other areas, the

maximum use rate and frequency of application is up to 4 lb a.i/acre once every three years,

and no more than two treatments totaling 6 lb a.i./acre in any 6 year period, spot treatment is allowed up to 6 lb a.i./A

when needed

A screening level estimate of current usage of tebuthiuron is presented in Table 2.2 . This screening level usage assessment presents usage data on an annual basis and is derived fromPage 16 of 121 USDA’s National Agricultural Statistics Service w ith data updated to 2013. This analysis amounts to 8,000 pounds of active ingredient used na tionally on an annual basis with use on Pastureland being the dominant use pattern.

Table 2.2. Tebuthiuron Screening Level Usage Analysis (SLUA) for 2013 Average Percent Crop Treated
Crop Lbs. a.i. Average Maximum

1 Pastureland 8,000 <1 <2.5

2.4. Conceptual Model

The potential terrestrial and aquatic exposure path ways and effects of the registered uses of

tebuthiuron are shown in Figures 1 and 2 . The conceptual model used to depict the potential ecological risk associated with the registered us es of tebuthiuron assumes that, as an herbicide, tebuthiuron is capable of adversely affecting terrestrial animals and plants including aquatic plants, provided that environmental concentrations are suffici ently elevated as a result of the labeled uses.

Solid arrows in Figures 1 and 2 depict the most likely routes of exposure and effects; dashed lines depict potential routes of exposure that are not consid ered likely for tebuthiuron.Page 17 of 121 Figure 1. Conceptual Model of the Transport and Effects of Tebuthiuron fo r Aquatic Environments.
*Dotted lines indicate that, although this e xposure route/media was considered, its contribution to the fate and transport of tebuthiuron is expected to be negligiblePage 18 of 121 Figure 2. Conceptual Model of the Transpor t and Effects of Tebuthiuron for Terrestrial

Environments.
*Dotted lines indicate that, although this exposure route/ media was considered, its contribution to the fate and transport of tebuthiuron is expected to be negligiblePage 19 of 121 The hypothesis for the risks of tebuthiuron to non-target animals focuses on both aquatic and terrestrial environments via poten tial exposure to the parent from direct spray, spray drift, and runoff. Leaching is considered a significant rout e of transport considering tebuthiuron is mobile in water. Dotted exposure routes are not likel y (not anticipated to vol atize). For terrestrial organisms, the major route of exposure is via diet , such as through consump tion of plant leaves or insects, which contain tebut hiuron residues as a result of direct application and/or spray drift. For aquatic animal species, the major routes of exposu re are direct contact vi a the respiratory surface (gills) or the integument. Aquatic vascular and no n-vascular plants may also be exposed via direct uptake and adsorption. Risk to terrestrial plants is also considered in this screening-level assessment. In addition, tebuthiuron has a low potential for sorption to sediment; therefore, exposure to organisms that reside primarily in the benthos is not lik ely. Estimated exposure concentrations for all organisms are obtained th rough the use of several Agency exposure models.

The following risk hypothesis is presumed for this screening level assessment:

Based on the application methods, mode of acti on, direct toxicity to non-target aquatic and terrestrial species, the registered uses of te buthiuron have the potential to reduce survival, reproduction, and/or growth in listed and non-li sted terrestrial and aqua tic animals and plants.

3. Analysis

3.1. Exposure Characterization

3.1.1. Environmental Fate and Transport Characterization

Tebuthiuron is persistent, mobile and can leach to ground water, as indicated by a small-scale retrospective ground water study (MRID 42390901). It is resistant to biological and chemical degradation, and its principle route of dissipation in the environment appears to be leaching and/or runoff. Transport to ground water through leaching and to surface water through runoff are likely

as a result of tebuthiuron's envi ronmental persistence and low sorption to soil. Because tebuthiuron has the potential to leach through the ground and because of the detections in Texas and California, the Agency is concerned about the potential fo r ground water contamination. Considering its low Henry's Law constant, (7.58 x 10 -11 atm-m3/mol; at 25°C), the pot ential of vapor phase and long range transport is considered insignificant. The environmental fate study summaries are presented as Appendix A.

Based on available environmental fate laboratory studies, several minor de gradates (< 10%) were identified (Table 3.1; Appendix B). Among th ese degradates, degradate 104 (N-[5-(1,14- dimethylethyl)-1,3,4-thiadiazol- 2-yl]-N-methylurea) has the hi ghest concentration detected. Additionally, degradate 104 was detected in a retrospective ground wate r monitoring study and was a major degradate in a terrestrial field diss ipation study accounting for up to 23% of the mass applied. The degradate 104 was also found in an aerobic soil metabolism (t 1/2 = 0.8 d) and soil photolysis (t 1/2 = 18 d) studies (MRID # 41050201) comprisi ng close to 7% of the mass applied. Degradate 104 was identified by the Health Effect s Division (HED) as the only environmental fate degradate of tebuthiuron of toxico logical concern to human healt h. A cumulative residue approachPage 20 of 121 to model total tebuthiuron residues was applied fo r drinking water assessmen t purposes as well as in this ecological risk assessment.

In regards to the bioconcentrati on potential of tebuthiuron, a 28 -day flow-through study in which bluegill sunfish were exposed to a nominal te buthiuron concentration of 5.0 ppm resulted in bioconcentration factors of 1.98, 3.40, and 2.63 for edible tissue, non-edib le tissue, and whole fish, respectively. Residues in the tissues consisted primarily of tebuthiuron and two metabolites (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2- yl]-N-methyl-N’ hydroxymethyl-urea [compound 109] and compound 103(OH) (hydroxylated form of parent tebuthiuron). Accumulated residues depurated rapidly from fish tissue with depurat ion half-lives of 0.33 and 0.51 days reported for edible and non-edible tissue, respectivel y (MRID 40819501). Due to the rapid depuration,

bioaccumulation is not a concern.

Table 3.1. Tebuthiuron and It s Environmental Degradates.

Parent / Degradate Name and

Structure Percent of Applied

MRID # Study Type Maximum Day

104 : N-[5-(1,1-dimethylethyl)-1,3,4- thiadiazol-2-yl]-N-methylurea ND * N/A ** N/A hydrolysis

ND N/A 41305101 aqueous photolysis

6.8 14 41050201 soil photolysis

6.9 270 41328001 aerobic soil metabolism

2.9 60 41328002 anaerobic soil metabolism

1.5 21 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

22.9 408 43318101 terrestrial field dissipation

2.2 (edible) 21 40819501 bioaccumulation in fish

105 : N-[5-(1,1-dimethylethyl)-1,3,4- thiadiazol-2-yl]-N = -methylurea ND N/A N/A hydrolysis

ND N/A 41305101 aqueous photolysis

3.5 19 41050201 soil photolysis

0.4 90 41328001 aerobic soil metabolism

0.2 60 41328002 anaerobic soil metabolism

0.4 28 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium N

H

2

O N C H

3

N N S H

H

3 C H

3 C C H

3

MolWt: 214.29 C8 H14 N4 O1 S1

C H

3

N

H O

N

H

N N S H

H

3 C H

3 C C H

3

MolWt: 214.29 C8 H14 N4 O1 S1Page 21 of 121 Parent / Degradate Name and

Structure Percent of Applied

MRID # Study Type Maximum Day

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

ND N/A 43318101 terrestrial field dissipation

4.7 (edible) 21 40819501 bioaccumulation in fish

106 : N-[5-(1,1-dimethylethyl)-1,3,4- thiadiazol-2-yl] urea ND N/A N/A hydrolysis

ND N/A 41305101 aqueous photolysis

2.7 5 41050201 soil photolysis

ND N/A 41328001 aerobic soil metabolism

ND N/A 41328002 anaerobic soil metabolism

ND N/A 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

ND N/A 43318101 terrestrial field dissipation

ND N/A 40819501 bioaccumulation in fish

107 : 5-(1,1-Dimethylethyl)-2- methylamino-1,3,4-thiadiazole ND N/A N/A hydrolysis

ND N/A 41305101 aqueous photolysis

ND N/A 41050201 soil photolysis

1.1 270 41328001 aerobic soil metabolism

ND N/A 41328002 anaerobic soil metabolism

0.3 21 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

ND N/A 43318101 terrestrial field dissipation

ND N/A 40819501 bioaccumulation in fish

108 : 2-dimethylethyl-5-amino-1,3,4-

thiadiazole ND N/A N/A hydrolysis

ND N/A 41305101 aqueous photolysis H

2 N

O

N

H

N N S H

H

3 C H

3 C C H

3

MolWt: 200.26 C7 H12 N4 O1 S1

N H C

H

3

N N S H

H

3 C H

3 C C H

3

MolWt: 171.26 C7 H13 N3 S1Page 22 of 121 Parent / Degradate Name and

Structure Percent of Applied

MRID # Study Type Maximum Day

ND N/A 41050201 soil photolysis

0.6 270 41328001 aerobic soil metabolism

ND N/A 41328002 anaerobic soil metabolism

0.1 7 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

ND N/A 43318101 terrestrial field dissipation

ND N/A 40819501 bioaccumulation in fish

109 : N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N'-hydroxymethylN-methylurea ND N/A N/A hydrolysis

ND N/A 41305101 aqueous photolysis

ND N/A 41050201 soil photolysis

ND N/A 41328001 aerobic soil metabolism

0.2 60 41328002 anaerobic soil metabolism

0.3 7 41372501 aerobic aquatic metabolism

ND N/A 41913101 anaerobic aquatic metabolism

ND N/A 40768401 batch equilibrium

N/A N/A N/A laboratory volatility

N/A N/A N/A field volatility

ND N/A 43318101 terrestrial field dissipation

40.1 (edible) 21 40819501 bioaccumulation in fish

*: Not determined. **: Not applicable. N H

2

N N S H

H

3 C H

3 C C H

3

MolWt: 157.23 C6 H11 N3 S1

O H N H O N C

H 3

N N S H

H 3 C H 3 C C H 3

MolWt: 258.34 C10 H18 N4 O2 S1Page 23 of 121 Table 3.2 lists the environmental fate properties of tebuthiuron in the submitted environmental fate and transport studies

.

Table 3.2. Summary of tebuthiuron Environmental Fate Properties

Study/Parameter Value (units) MRID #

Or

Source Study Status

and Comments

Hydrolysis Stable Acc. No 000207 79 Acceptable Solubility 2500 (mg/L @ 25 o C) Tomlin CDS, ed (2004-05) N/A Vapor Pressure 3.0 x 10 -7 (torr) Tomlin CDS, ed (2004-05) N/A log Kow 1.79 (estimation) BioByte. 1995. ClogP for Windows Program (v1.0). BioByte Corp., Claremont, CA. N/A

Direct Aqueous Photolysis Stable 4130510 1 Acceptable

Aerobic Soil

Metabolism t 1/2 = 1062 days 4 1328001 Acceptable

Anaerobic Soil

Metabolism Stable 4132800 2 Acceptable

Aerobic Aquatic

Metabolism 683 41372501 Acceptable

Anaerobic Aquatic

Metabolism > 1 year 41913101 Acceptable

Kd-ads 0.11, 0.62, 0.82, and 1.82 mL/g 40768401 Acceptable

Terrestrial Field Dissipation t 1/2 = 1-2 years 4331 8101 Acceptable

Fish

Bioaccumulation Bioconcentration factor BCF= 1.98, 3 .40, and 2.63 for edible tissue, non-edible tissue, and whole fish, respectively. 40819501 Acceptable

3.1.2. Measures of Aquatic Exposure

Aquatic exposures are quantitatively estimated for a ll assessed uses using scenarios that represent high exposure sites for tebuthiuron use. Each of thes e sites represents a 10-hectare field that drains into a 1-hectare pond that is 2 meters deep and has no outlet. Exposure es timates generated using the standard pond are intended to represent a wide variety of vulnerable wate r bodies that occur at the top of watersheds including prairie pot holes , playa lakes, wetlands, vernal pools, man-made and natural ponds, and intermittent and first-order st reams. As a group, there are factors that make

these water bodies more or less vulnerable than the standard surrogate pond. Static water bodies that have larger ratios of drainage area to water body volume would be expected to have higher peak EECs than the standard pond. These water bodies will be either shallower or have large drainage areas (or both). Shallow water bodies tend to have limited additional storage capacity, and thus, tend to overflow and carry pesticide in the discharge whereas the standard pond has no discharge. As watershed size incr eases beyond 10 hectares, at some point, it becomes unlikely that the entire watershed is planted to a single crop, which is all treate d with the pesticide. Headwater streams can also have peak concentrations highe r than the standard pond, bu t they tend to persist for only short periods of time and are then carrie d downstream.Page 24 of 121 Tebuthiuron environmental fate data used fo r generating model parameters are listed in Table 3.3

. Chemical property input values were chosen in accordance with current input parameter guidance (USEPA, 2009 1 ). Using meteorological files informati on associated with each PRZM scenario, application dates were chosen in according wi th the product label: “For optimum results, applications should be made prior to the resump tion of active seasonal growth in the spring or before expected seasonal rainfall”.

The maximum labeled single and annual applicati on rate for tebuthiuron is at 6 lb a.i./A for broadcast applications via spray or granules. Only one application pe r year or every three years is assumed. However, a maximum applica tion rate of 4 lb a.i./A is al so expected for several of the same uses that is applied at 6 lb a.i./A. Thus, th e application rate of 4 lb a.i./A was included in the assessment to evaluate whether the risk pict ure would improve significantly when the 6 lb a.i./A application rate is reduced to 4 lb a.i. /A. The application methods assumed are as follows: aerial, ground, shaker can, spreader, hand held sp ray gun, backpack sprayer, and band sprayer. For this assessment, aerial and ground broadcast applications i nvolve the highest application rates and are used to assess the pot ential risk to wildlife exposed to tebuthiuron. EECs for spot treatment applications are not available; however, exposure from spot treatment using backpack sprayers or granules will be s ubsequently discussed for any poten tial risks to non-target wildlife and plants after the assessment on broadcast appl ications as a liquid sp ray or with granules.

Table 3.3. Summary of PRZM/EXAMS Environm ental Fate Data Used for Aquatic Exposure Inputs for Tebuthiuron

Fate Property Value (unit) MRID (or source) Comment

Molecular Weight 228.3 Tomlin CDS, ed (2004-05)

Henry’s constant 1.2E-10 (atm-m 3 /mol) Tomlin CDS, ed (2004-05)

Vapor Pressure 3.0E-7 (torr) Tomlin CDS, ed (2004-05)

Solubility in Water 2500 (mg/L) Tomlin CDS, ed (2004-05)

Application Rate 6.72 (kg a.i./ha)

4.48 (kg/ha) EPA Reg No. 62719-122

Number of Applications 1 EPA Reg No. 62719-122

Interval between Applications (days) Not applicable EPA Reg No. 62719-122

Photolysis in Water Stable MRID 41305101

Aerobic Soil

Metabolism Half-life 270.6 (day) MRID 41328001 3X aerobic soil metabolism half-life for total residues ( a single aerobic soil metabolism half-life value is available) ; input parameter per Input Parameter Guidance (1)Page 25 of 121 Fate Property Value (unit) MRID (or source) Comment

Hydrolysis Stable Acc. No 00020779

Aerobic Aquatic Metabolism (water column) 2050 (day) MRID 41372501 3X aerobic aquatic metabolism half-life for total residues ( a single aerobic aquatic

metabolism half-life value is

available ); input parameter per Input Parameter Guidance (1)
Anaerobic Aquatic Metabolism (benthic) Stable MRID 41913101

K
oc 85.2 (mg/L) MRID 40768401 Binding is correlated to organic

carbon content. Mean Koc ; input parameter per Input Parameter Guidance (1) Chemical Application Method (CAM) 2 pre-plant or pre-emergence, unincorporated

1 Guidance for Selecting Input Parameters in Modeling th e Environmental Fate and Transport of Pesticides; Version 2.1, October 22, 2009.

Results from each PRZM scenario are presented in Table 3.4. Output that generates peak EECs are reported in Appendix C . A typical available grass PRZM scenario used as pasture is alfalfa.

Table 3.4. Tier II Concentrations of Tebuthiuron in Surface Water

Tier II

PRZM/EXAMS Scenario Application rate

6 lbs a.i./A 4 lbs a.i./A (ppb)

TXalfalfaOP Aerial 1109 736.3

Ground 1018 679

Granular 997.3 664.9

MNalfalfaOP Aerial 558.6 372.7

Ground 376 251

Granular 330.8 220.8

NCalfalfaOP Aerial 604 403

Ground 453.1 301.5

Granular 414.7 276.8

PAalfalfaOP Aerial 693.9 462.9

Ground 534.8 355.9

Granular 494.8 329.9

CAalfalfa_WirrigOP Aerial 498.9 332

Ground 367.9 245

Granular 335 223

Because of the persistence of this com pound, the 1 in 10 year PRZM/EXAMS EECs are expected to represent 30 years of residue accu mulation in the pond. This fact was presented by plotting time against the EECs from the following scenarios modeled: TX alfalfaOP (aerial), andPage 26 of 121 PAalfalfaOP (aerial) (ones with highest EECs) show a continuous accumulation of tebuthiuron in pond ( Appendix D ). Such residue accumulation is driv en mostly by the persistence of the compound as well as by the lack of flow out of the pond. In cases where a flowing water exists, the EEC over the long run would not be as high.

3.1.3. Measures of Terrestrial Exposure

3.1.3.1. Terrestrial Animals

Exposure estimates for terrestrial an imals assumed to be in the target area or in an area exposed to spray drift or granules are derived using the T-REX 2 model (version 1.5.2.). This model incorporates the Kenaga nomogr aph, as modified by Fletcher et al. (1994), which is based on a large set of actual field residue data. The upper limit values from the nomograph represent an approximation of the highest residue value observe d in the data set (Hoerger and Kenaga 1972). Consideration is given to different types of feeding strategi es for mammals and birds, including herbivores, insectivores and granivores. For dose- based exposures, three we ight classes of birds (20, 100, and 1000 g) and mammals (15, 35, and 1000 g) are considered. A default foliar dissipation half-life of 35 days is used based on the work of Willis and McDowell (1987).

Ingestion of Food Items Ba sed on Foliar Application

The same tebuthiuron application and seasonal rate limitations as evaluated in previous assessments ( i.e ., maximum broadcast application rates of 6.0 and 4.0 lb a.i. and one application per year) are taken from active la bels and are used to estimate terrestrial exposure for this assessment. The dietary-based EECs on a variety of food items from the use of wettable powder and water dispersible granule formulations of te buthiuron applied at the maximum label rate are provided in Table 3.5 ; dose-based EECs are provided in Table 3.6

.

Table 3.5. T-REX Calculated Dietary-Based EECs of Tebuthiuron on Food Residues.

Application Rate (lb a.i./A) Food Type Maximum Dietary-based EECs (mg/kg-diet)

6.0 Short Grass 1440

Tall Grass 660

Broadleaf plants 810

Fruits/pods/seeds 90

Arthropods 564

4.0 Short Grass 960

Tall Grass 440

Broadleaf plants 540

Fruits/pods/seeds 60

Arthropods 376

2 USEPA. 2013. Pesticides: Science and Poli cy. Terrestrial Models, T-REX Version 1.5.2. http://www.epa.gov/oppefed1/models/terrestrial/Page 27 of 121 Table 3.6. T-REX Calculated Dose-Based EECs of Tebuthiuron on Food Residues.

Application Rate (lb a.i./A) Food Type Dose-based EECs for

Birds (mg/kg-bw) Dose-based EECs for Mammals (mg/kg-bw)

Small (20 g) Medium (100 g) Large (1000 g) Small (15 g) Medium (35 g) Large (1000 g)

6.0 Short grass 1640 935 419 1373 949 220
Tall grass 752 429 192 629 435 101
Broadleaf plants 922 526 236 772 534 124
Fruits/pods 103 58 26 86 59 14
Arthropods 642 366 164 538 372 86

Seeds (granivore) 23 13 6 19 13 3

4.0 Short grass 1093 623 279 915 633 147
Tall grass 501 286 128 420 290 67
Broadleaf plants 615 351 157 515 356 83
Fruits/pods 68 39 17 57 40 9
Arthropods 428 244 109 358 248 57

Seeds (granivore) 15 9 4 13 9 2

Ingestion of granules base d on broadcast applications

T-REX includes the capability to calculate the LD 50 /ft 2 risk index values for granular applications. Conceptually, an LD 50 /ft 2 is the amount of a pesticide estima ted to kill 50% of exposed animals in each square foot of applied area. Although a square foot does not have defined ecological relevance, and any unit area could be use d, risk presumably increases as the LD 50 /ft 2 value

increases. For additional information on the LD 50 /ft 2 risk index, please refer to USEPA (1992).

The LD 50/ ft 2 value is calculated using a toxicity value (adjusted LD 50 ) and the EEC (mg a.i./ft 2 ) and is directly compared with the Agency’s levels-of-concern (LOCs). In addition, pellets and granules are considered equivalent.

Assuming a maximum of 40% active ingredient in pelleted/tableted formulations, the EEC for tebuthiuron-treated pelleted/tableted formulations applied at the maximum label rate of 6 and 4 lb a.i./A is 25 and 16.7 mg a.i./ft 2 , respectively. For granular fo rmulations which contains a maximum of 5% tebuthiuron, the EEC at 6 a nd 4 lb a.i./A is 3.12 and 2.08 mg a.i./ ft 2

, respectively.

3.1.3.2. Terrestrial Plants

Tebuthiuron exposure to terrestrial and semi-a quatic plants is estimated using the TerrPlant 3
(version 1.2.2) model. The model generates EECs for plants residing near a use area that may be exposed via runoff and/or spray drift from fo liar and granular applications. The EECs are generated from one application at the maximum ra te for a particular use and compound-specific

3 USEPA. 2013a. Pesticides: Science and Policy. Terrestrial Models, TerrPlant Version 1.2.2. http://www.epa.gov/oppefed1/models/terrestrial/Page 28 of 121 solubility information. Only a single application is considered because it is assumed that for plants, toxic effects are likely to manifest shortly after the initial exposure and that subsequent exposures do not contribute to the response. Hence, the mo del estimates EECs based on application rate, the solubility limit, and default assumptions of drift. The EECs for terrestrial and semi-aquatic plants for a single application of tebuthiuron at 6 and 4 lb a.i./A are presented in Table 3.7

.

To characterize potential non-targ et plant exposure from spray drift alone, Tier 1 modules in AgDRIFT (v. 2.1.1) were used to estimate EECs for off-site spray drift exposure in dry and semiaquatic areas and water bodies ( i.e. , standard farm pond) ( Table 3.8 ) for wettable powder and water dispersible granule formulations. For aeria l applications, EFED used the American Society of Agricultural and Biological E ngineers (ASABE, formerly ASAE) Fine-to-Medium droplet size category in its modeling. This drop size category is EFED’s default distribution when labels do not specify application paramete rs. For ground applications, EFED used the ASABE Very Fineto-Fine droplet size category with a high boom hei ght. Again, this droplet size category is EFED’s

default distribution when labels do not specify the app lication parameters for ground applications. Negligible amount of drift is likely from granul ar applications; thus, drift EECs for granular

formulations are not include d in the AgDRIFT modeling.

Table 3.7. TerrPlant EECs for Terrestrial Plants Located Adjacent to Tebuthiuron Treated Sites.

Broadcast Application Rate (lb a.i./A) Application

Method TerrPlant EECs (lbs a.i./A) Total Loading to Dry Areas Adjacent

to Treated Areas 1 Total Loading to SemiAquatic Areas Adjacent

to Treated Areas 2 Drift to Adjacent Areas 3

6 Aerial Unincorp. Spray 0.6 3.3 0.3

4 0.4 2.2 0.2

6 Ground Unincorp. Spray 0.36 3.06 0.06

4 0.24 2.04 0.04

6 Granular 0.3 3 0.0

4 0.2 2 0.0

1 EEC = Sheet Runoff + Drift (1% for ground)

2 EEC = Channelized Runoff + Drift (1% for ground)

3 EEC for ground (appl. rate x 1% drift)

Table 3.8. Maximum Drift Loadin gs at Specific Distances for Terres trial and Semi-Aquatic Areas and

Ponds Near Tebuthiuron Use Areas.

Broadcast Application

Rate (lb a.i./A) Application

Method Distance from Edge of

Field

(ft) Drift EEC

Dry Areas (lb a.i./A) Wetland (lb a.i./A) Pond (mg/L)

6.0 Ground 0 6.0 0.4 0.02

10 1.6 0.2 0.01

50 0.3 0.1 0.007

100 0.1 0.08 0.004

500 0.02 0.02 0.001

997 0.009 0.007 0.0004

6.0 Aerial 0 3 0.8 0.04

10 2 0.6 0.036

50 1 0.4 0.025

100 0.6 0.3 0.017Page 29 of 121 The Screening Tool for Inhalation Risk (STI R v.1.0, November 19, 2010) was used to calculate an upper-bound estimate of wildlife inhalation e xposure using tebuthiuron’s vapor pressure and molecular weight for vapor phase exposure as we ll as the maximum application rate and method of application for spray drift. STIR incorporates results from several to xicity studies including

acute oral and inhalation rat toxic ity endpoints obtained from the “s ix-pack” of core studies, which is a series of six guidelin e studies that are submitted to the Re gistration Division of the Office of Pesticide Programs for technical and form ulated products of a pesticide (rat LD 50 = 388 mg/kgbw; rat inhalation LC 50 = 3.696 mg/L) as well as the most se nsitive acute oral avian toxicity endpoint (mallard LD 50 >2000 mg/kg-bw). Based on the results of the STIR model ( Appendix

E ), exposure through inhalation of sp ray drift or the vapor phase of tebuthiuron is not determined to be a potential pathway of concern for either avian or mammalian species on an acute exposure

basis.

The analysis of the inhalation rout e in STIR does not consider that aggregation with other exposure pathways such as dietary, dermal, or drinking wa ter may contribute to a to tal exposure that has a potential for effects to non-target animals. However, the Agency does consider the relative importance of other routes of exposure in situatio ns where data indicate that pesticide exposures through other routes may be potentially significan t contributors to wild life risk (USEPA 2004). The risk characterization section ( Section 4.2 ), discusses the impact of consideration of other routes of exposure that have been identified as potentially important and the degree of certainty associated with screening-level risk assessment conclusions. Detailed information about STIR v.1.0, as well as the tool, can be found on EPA’s website ( http://www.epa.gov/pesticides/s cience/models_pg.htm#terrestrial ).

The Screening Imbibition Program (SIP v.1.0, releas ed June 15, 2010) was used to calculate an upper-bound estimate of wildlife drinking water exposure using tebuthiuron’s solubility ( i.e ., 2500 mg/L at 20 o C), and compared to the most sensitive acute and chronic avian and mammalian toxicity endpoints. U pon results of the screening model SIP, drinking water exposure alone is a concern for birds and mammals ( Appendix F ). Tebuthiuron has a very high solubility, which is the only parameter used in estimating potential e xposure, and birds and mammals are particularly

sensitive to tebuthiuron on either an acute and/or chronic basis. This pathway will be explored further with the development of SIP v.2.0 in a fu ture Ecological Risk Assessment for tebuthiuron. For a sample of the output generated by SIP v.1.0, please see Appendix F . Detailed information 500 0.1 0.1 0.005

997 0.07 0.07 0.004

4.0 Ground 0 4.0 0.25 0.013

10 1.0 0.15 0.008

50 0.2 0.08 0.004

100 0.1 0.05 0.003

500 0.02 0.01 0.0007

997 0.006 0.005 0.0003

4.0 Aerial 0 2 0.5 0.028

10 1.3 0.4 0.024

50 0.7 0.3 0.02

100 0.4 0.2 0.01

500 0.07 0.06 0.004

997 0.05 0.04 0.003Page 30 of 121 about the SIP v.1.0, as well as the tool, can be found on the EPA’s website at http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial

.

3.3.2. Ecological Effects Characterization

In screening-level ecological risk assessments, effects characterization describes the types of effects a pesticide can have on aquatic and terrestr ial organisms. This char acterization is based on the registrant-submitted toxicity data for birds, mammals, fish, invertebrates, and plants for the active ingredient selected for this ecological risk assessment phase of Registration Review.

This assessment evaluates the potential for tebuthiur on to directly or indire ctly affect Federallylisted species or modify designate d critical habitat. As discussed, assessment endpoints include direct toxic effects on the survival, reproduction, and growth of listed entities, as well as indirect effects, such as reduction of the prey base or modification of habitat. In addition, potential

modification of critical habita t is assessed by evaluating effects to the principle constituent elements (PCEs), which are components of the critical habitat areas that provide essential life cycle

needs of listed entities.

As described in the Agency’s Overview Docu ment (USEPA 2004), the most sensitive endpoint

for each taxon is used for risk estimation. For this assessment, evaluated taxa include freshwater and estuarine/marine fish (freshwater fish al so a surrogate for aquatic phase amphibians),

freshwater and estuarine/marine i nvertebrates, aquatic pl ants, birds (also surrogate for terrestrialphase amphibians and reptiles), mammals, honeybees, and terrestrial plants.

Toxicity endpoints are established based on data generated from guideline studies submitted by the registrant, and from open literature studies th at meet the criteria for inclusion into the ECOTOX database maintained by EPA/Office of Research and Development (ORD) (U.S. EPA, 2004). In general, effects data in the open literature that indicate effects at lower concentrations than the registrant-submitted data are considered. The degree to which open literature data are quantitatively or qualitatively charac terized is dependent on whether the information is relevant to the assessment endpoints (surviva l, reproduction, and growth). Fo r example, endpoints such as behavior modifications are likely to be qualitatively evaluated, because quantitative relationships between modifications and reduction in species survival, reproduction, and/or growth are not available. On December 24, 2013, none of the open literature that passed the ECOTOX screen

obtained effects at lower concentrations than the submitted studies and thus are not used in this

risk assessment.

In addition to registrant-submitted and open litera ture toxicity information, other sources of information, including use of the acute prob it dose-response relations hip to establish the probability of an individual eff ect and reviews of the Ecological Incident Information System (EIIS), are conducted to further refi ne the characterization of potenti al ecological effects associated with exposure to tebuthiuron. A summary of the available aquati c and terrestrial ecotoxicity information and use of the probi t dose-response relationship fo r tebuthiuron are provided in

Section 4 , respectively.Page 31 of 121 A review of the Ecological Incident Information System (EIIS) maintained by the Agency’s Office of Pesticide Programs (OPP) indicates a total of 4 reported ecological incidents associated with the use of tebuthiuron. The reported incidents involve d damage to terrestrial plants. Two incidents were associated with misuse use of tebuthiuron, one to a registered use, and the legality of the used in another was not determined. In addition, there is one aggregate minor fish and wildlife incident reported for tebuthiuron in 2003 that was reported by the pesticide registrant.

Summary of Ecological Incidents Associated with Tebuthiuron Uses, By Certainty.

Incident

type Incident

ID Use Type Legality Certainty

All (excluding unlikely) Unlikely Possible Probable Highly

Probable

Damage

to
terrestrial plants 1003503-

001 Power line Misuse (accidental) X

1015921-

002 Agricultural

area Undetermined X

1-13603-

002 Rangeland Registered

use X

100512-

001 Right-ofway, road Misuse (accidental) X

Similarly, a search of the Avian Incident Monitoring System (AIMS; http://www.abcbirds.org/abcprograms /policy/toxins/aims/aims/index.cfm ) was conducted on December 24, 2013. AIMS is a database administ ered by the American Bird Conservancy that contains publicly available data on reported avia n incidents involving pest icides. No incidents involving tebuthiuron were found.

A major degradate of tebuthiuron, identified as co mpound 104, was measured in a terrestrial field dissipation study accounting for up to 23% of the ma ss applied and was concluded to be the only degradate of toxicological concern due to the stru ctural similarity to tebuthiuron. While similar to the parent chemical, it lacks an N-methyl group; however, it may still have the same herbicidal toxic mode of action. As of an uncertainty si nce the toxicity of co mpound 104 to plants is unknown, EFED presumes that the degradate has the equivalent toxicity of its parent compound to terrestrial plants. Previous risk assessmen ts indicate the parent compound resulted in LOC exceedances for terrestrial plants; thus, under this presumption, LOC exceedances would be expected with degradate compound 104. Additiona l data testing with th e degradate compound 104 ( e.g. , OCSPP 850.4100 and/or 850.4150 Tier II terrestrial plant toxicity test) would be needed to reduce the uncertainty associat ed with this presumption.

3.3.2.1. Aquatic Effects Characterization

The most sensitive acute and chronic effects meas urement endpoints associated with tebuthiuron exposure to freshwater and estuarin e/marine species are summarized in Table 3.9. Selected effects endpoints for the risk assessment are from accepta ble and supplemental studies for tebuthiuron and are briefly described below.

Based on the available toxicity da ta, tebuthiuron is clas sified as practically non-toxic to aquatic organisms with the exception of the slightly toxic toxicity classification to estuarine/marinePage 32 of 121 invertebrates. In addition, freshwater fish ar e surrogates for aquatic-phase amphibians in the absence of amphibian-specific data; therefore, usi ng the acute toxicity data with freshwater fish,

tebuthiuron would be classified as practically non-t oxic to aquatic-phase amphibians. Chronic toxicity data were only available for freshwater fish and invertebrates, for which effects on reproduction and growth were observed in the inve rtebrate study and growth in the fish study.

Acute-to-Chronic Ratio calculati ons were used to estimate the NOAEC for chronic effects to estuarine/marine fish using rainbow trout data and to invertebrates using data from the daphnid

studies.

Summaries of the ecological toxi city studies are provided in Appendix G

.Page 33 of 121 Table 3.9. Most Sensitive Acute and Chroni c Toxicity Data fo r Aquatic Organisms Exposed to Tebuthiuron.
Exposure

Scenario Species Affected Endpoint Toxicity Measurement MRID (Classification)

Freshwater Fish

Acute Bluegill sunfish ( Lepomis

macrochirus ) Mortality 96-hr LC 50 = 106 mg a.i./L 40098001 (acceptable)

Chronic Fathead minnow ( Pimephales promelas ) Sub-lethal 33-day NOAEC = 9.3 mg a.i./L (length) 00090084 (acceptable)

Freshwater Invertebrates

Acute Water flea ( Daphnia spp.) Immobility 48-hr EC 50 = 297 mg a.i./L 00041694 (acceptable)

Chronic Sub-lethal 21-day NOAEC = 21.8 mg a.i./L (growth, fecundity, time of first brood release, young per adult) 00138700 (acceptable)

Estuarine/Marine Fish

Acute Sheepshead

minnow ( Cyprinodon variegates) Mortality 96-hr LC 50 >98 mg a.i./L 48722702 (acceptable)

Chronic No data

available Estimated NOAEC >18 mg

a.i./L ACR 1

Estuarine/Marine Invertebrates

Acute Pink shrimp ( Penaeus duorarum) Mortality 96-hr LC 50 = 62 mg a.i./L 00041684 (acceptable)

Chronic No data

available Estimated NOAEC = 4.56 mg

a.i./L ACR 1

Aquatic Plants 7-day

exposure Duckweed ( Lemna gibba ) Frond count 7-day EC 50 = 0.13 mg a.i./L NOAEC = 0.05 mg a.i./L 41080404 (supplemental)

96-hour

exposure Marine diatom ( Skeletonema

costatum ) Cell density 96-hr EC 50 = 0.05 mg a.i./L NOAEC = 0.038 mg a.i./L 41080402 (supplemental)

1 Estimated value based on Acute to Chronic Ratio (ACR) method using rainbow trout data; ACR = 5.5. Sheepshead minnow NOAEC = (LC 50 of >98 mg/L ÷ 5.5) = >18 mg/L

2 Estimated value based on Acute to Chronic Ratio (ACR) method using daphnid data; ACR = 13.6. Shrimp NOAEC = (LC 50 of 62 mg/L ÷ 13.6) = 4.56 mg/L



### Freshwater Fish, Acute Effects

Fish toxicity studies using the technical grade ac tive ingredient (TGAI) were submitted to establish the acute toxicity of tebuthiuron to fish. The preferred test species are the rainbow trout and bluegill

sunfish. Results of the acute studies with freshwater fish indicate the LC 50 value of 106 mg a.i./L

for the sunfish is the most sensitive endpoint for fish ( Table 3.10 ). As a result, tebuthiuron isPage 34 of 121 categorized as practically nont oxic to fish. The sunfish LC 50 will be used to evaluate potential

acute effects of tebuthiur on to freshwater fish.



### Freshwater Fish, Chronic Effects

Laboratory toxicity studies using the TGAI were submitted to establish the chronic toxicity of

tebuthiuron to freshwater fi sh. The preferred test species is the mo st sensitive fish of the freshwater fish acute toxicity tests; when a 96-hour LC 50 is not available, rainbow trout or fathead minnow is preferred. Results of the chronic studies with th e TGAI to freshwater fish indicate the lowest NOAEC value to be 9.3 mg a.i./L ( Table 3.11 ). Thus, the NOAEC of 9.3 mg a.i./L will be used to evaluate potential chronic effects of tebuthiuron to freshwater fish.

Table 3.11. Freshwater Fish Chronic T oxicity Profile for Tebuthiuron.
Species %

a.i. LOAEC /

NOAEC (mg a.i./L) Endpoint

Affected MRID No.

Author/Year Study

Classification

Rainbow trout

( Oncorhynchus mykiss ) 98 52/26 Adult survival and length 00090083
Sauter, Meyerhoff,

Todd et al . (1981) Acceptable

Fathead minnow

(Pimephales promelas) 98 18/9.3 Length 00090084
Sauter, Meyerhoff,

Todd et al . (1981) Acceptable Table 3.10. Freshwater Fish Acute Toxicity Profile for Tebuthiuron. Species % a.i. LC 50 (mg a.i./L) Toxicity Category MRID No.

Author/Year Study

Classification

Rainbow trout ( Oncorhynchus mykiss ) 98 143 A Practically

nontoxic 00020661 Anon. (1972) Acceptable

Bluegill sunfish ( Lepomis macrochirus ) 98 106 B Practically

nontoxic 00020661 Anon. (1972) Acceptable

Goldfish ( Carassius auratus ) 98 >160 Practically

nontoxic 00020661 Anon. (1972) Supplemental 1

Fathead minnow ( Pimephales promelas ) 98

>180 Practically

nontoxic 00041685

Hamelink and

Kehr (1976) Supplemental 2 80

20 (pellet)

A Trout 95% Confidence Interval (C.I.) = 118 -224 mg a.i./L; slope = N/A (binominal)

B Sunfish 95% C.I. = 87-120 mg a.i./L; slope = N/A (binomial)

1 Dilution water, pH and dissolved oxygen were not measured; goldfish is not a recommended species.

2 Inadequate reporting of test conditions and aeration during the test.Page 35 of 121 

### Freshwater Invertebrates, Acute Effects

A toxicity study using the TGAI was submitted to establish the acute toxicity of tebuthiuron to freshwater invertebrates. Daphnids are the preferre d test species. Results of the acute study with

freshwater invertebra tes indicate an EC 50 value of 297 mg a.i./L ( Table 3.12 ), which categorizes tebuthiuron as practically nontoxic to freshwater invertebrates. Thus, the EC 50 will be used to evaluate potential acute eff ects of tebuthiuron to fres hwater invertebrates.



### Freshwater Invertebrates, Chronic Effects

A laboratory toxicity study using the TGAI was s ubmitted to establish the chronic toxicity of

tebuthiuron to freshwater invertebra tes. The preferred test species is the water flea. Results of the reproduction study with freshwater invertebrate s indicate a NOAEC value of 21.8 mg a.i./L ( Table

3.13 ). The NOAEC will be used to ev aluate potential chroni c effects of tebuthiuron to freshwater

invertebrates.

Table 3.13. Freshwater Invertebrate Chroni c Toxicity Profile for Tebuthiuron. Species %

a.i. LOEAC /

NOAEC (mg a.i./L) Endpoint

Affected MRID No.

Author/Year Study

Classification

Water flea
(Daphnia magna) 97.4 44.2/21.8 Time to first brood release, offspring per adult and length 000138700

Grothe and Meyerhoff. (1983) Acceptable



### Estuarine/Marine Fish, Acute Effects

An estuarine/marine fish toxicity study using the TGAI was submitted to establish the acute toxicity of tebuthiuron to estuarine/marine fish. The preferred test species is the Atlantic silversides; however, the registrant submitte d an acceptable species, the Sheepshead minnow. Results of the acute study indicate an LC 50 value of >98 mg a.i./L ( Table 3.14 ). With no mortality at and up to 98 mg a.i./L, tebuthi uron is categorized as practically nontoxic to estuarine/marine

fish. The LC 50 value of >98 mg a.i./L will be used to ev aluate potential acute effects of tebuthiuron

to estuarine/marine fish. Table 3.12. Freshwater Invertebrate Acut e Toxicity Profile for Tebuthiuron. Species % a.i. EC 50 (mg a.i./L) Toxicity Category MRID No.

Author/Year Study

Classification

Water flea

( Daphnid magna ) 99.2 297 A Practically

nontoxic 00041694

Hamelink, Todd,

Brannon et al

. (1978) Acceptable

A D. magna 95% Confidence Interval = 279-316 mg a.i./L; Probit slope = 13.3 (9.06-17.6)Page 36 of 121 

### Estuarine/Marine Fish, Chronic Effects

No chronic ecological effects studies of tebuthiur on using estuarine/marine fish were submitted. The Acute-to-Chronic Ratio (ACR) approach was used to estimate the chronic toxicity to

estuarine/marine fish in absence of data. The A CR using rainbow trout acute and chronic data is 5.5. Employing the ACR of 5.5 to the sheepshead LC 50 of >98 mg a.i./L calculates a chronic toxicity value of >18 mg a.i./L for estuarine/marine fish. The NOAEC of >18 mg a.i./L will be used to evaluate potential chronic effects of tebuthiuron to estuar ine/marine fish.



### Estuarine/Marine Invertebrates, Acute Effects

Toxicity studies using the TGAI were submitted to establish the acute toxicity of tebuthiuron to estuarine/marine invertebrates. The preferred test species are the mysid shrimp and Eastern oyster (shell deposition). Results of the acute studies indicate the lowest LC 50 value for estuarine/marine invertebrates to be 62.3 mg a.i./L ( Table 3.15 ). As of a result, tebuthiuron is categorized as slightly

toxic to estuarine/marine invertebrates. The LC 50 of 62.3 mg a.i./L will be used to evaluate potential acute effects of tebuthiuron to estuarine/marine invertebrates.

Table 3.15. Estuarine/Marine Invertebrate Ac ute Toxicity Profile for Tebuthiuron. Species % a.i. LC 50 /EC 50 (mg a.i./L) Toxicity Category MRID No.

Author/Year Study

Classification

Pink shrimp

(Penaeus duorarum)

98 62.3 A Slightly

toxic

00041684

Heitmuller and Parrish (1976) Acceptable

Fiddler crab

( Uca pugilator ) >100 Practically

nontoxic Supplemental 1

Eastern oyster

[embryos]

( Crassostrea

virginica ) >100 B Practically

nontoxic Acceptable 2

Eastern oyster
[shell deposition]

( Crassostrea

virginica ) 99.8 >95 Practically

nontoxic 48722701
York (2011) Acceptable

A Shrimp 95% Confidence Interval = 38.7-90.1 mg a.i./L; slope = 4.5 (2.1-6.9) Table 3.14. Estuarine/Marine Fish Acut e Toxicity Profile for Tebuthiuron. Species % a.i. LC 50 (mg a.i./L) Toxicity Category MRID No.

Author/Year Study

Classification

Sheepshead minnow
(Cyprinodon variegates) 99.8 >98 Practically

nontoxic 48722702
Fournier (2011) AcceptablePage 37 of 121 Table 3.15. Estuarine/Marine Invertebrate Ac ute Toxicity Profile for Tebuthiuron. Species % a.i. LC 50 /EC 50 (mg a.i./L) Toxicity Category MRID No.

Author/Year Study

Classification

B The 48-hour LC 50 is actually between 180 and 320 mg a.i./L due to 100% mortality at 320 mg a.i./L and 0% mortality at 180 mg a.i./L. Because a definite LC 50 could not be calculated, the EPA reviewer determined a LC 50 of >100 mg a.i./L which still classifies tebuthiuron as practically nontoxic to oyster embryos.

1 Not a recommended species

2 Bivalve acute toxicity study (OCSPP 850.1055; embryo-larval)



### Estuarine/Marine Invertebrates, Chronic Effects

No chronic ecological effects st udies of tebuthiuron using estuar ine/marine invertebrates were submitted. The Acute-to-Chronic Ratio (ACR) approach was used to estimate the chronic toxicity to estuarine/marine i nvertebrates in absen ce of data. The ACR using Daphnia acute and chronic data is 13.6. Employing the ACR of 13.6 to the shrimp LC 50 of 62.3 mg a.i./L calculates a chronic toxicity value of 4.56 mg a.i./L for estuarine/marine invertebrates. The NOAEC of 4.56 mg a.i./L will be used to evaluate potential ch ronic effects of tebuthiuron to estuarine/marine

invertebrates.



### Effects to Aquatic Vascular and Non-vascular Plants

Tebuthiuron studies were submitted for a freshwater vascular plant (duckweed, Lemna gibba ) and four phytoplanktonic nonvascular plants: green algae ( Selenastrum capricornutum ), cyanobacteria ( Anabaena flos-aquae ), freshwater diatom ( Navicula pelliculosa ) and marine alga ( Skeletonema

costatum ) ( Table 3.16 ).

Aquatic plant toxicity studies using the TGAI were submitted to establish the toxicity of

tebuthiuron to vascular and non- vascular species. The aquatic vascular plant duckweed EC 50 and NOAEC of 0.13 and 0.05 mg a.i./L, respectively, and the most sensitive EC 50 of aquatic nonvascular plants studies us ing the marine diatom EC 50 and NOAEC of 0.05 and 0.038 mg a.i./L, respectively, will be used to evaluate potential e ffect of tebuthiuron to aquatic plants. While the green algae and marine di atom, when based on the EC 50 , were the most sensitive nonvascular plants; the No Effect level for the freshwater gr een algae may be more sensitive than the marine diatom; however, the results of the algae study could not be verifie d, the NOAEC for marine

diatom was determined to be more re liable than the algae’s NOAEC.

EC 50 values of 0.13 and 0.05 mg a.i./L ( Table 3.16 ) will be used to evaluate potential effects of tebuthiuron to non-listed aquatic vascular and non-vascular plants, respectively. Corresponding NOAEC values of 0.05 and 0.038 mg a.i./L will be used to evaluate potential effects of tebuthiuron to listed aquatic vascular and nonva scular plants, respectively.Page 38 of 121 Table 3.16. Aquatic Plant Toxici ty Profile for Tebuthiuron. Species % a.i. EC 50 (mg a.i./L) NOAEC (mg a.i./L) MRID No.

Author/Year Study

Classification

Vascular Plants

Duckweed

( Lemna gibba ) 99.08 0.13 A 0.05 41080404
Negilski and Cocke (1989) Supplemental 1

Non-Vascular Plants

Marine diatom ( Skeletonema

costatum ) 99.08 0.05 B 0.038 41080402
Negilski and Cocke (1989) Supplemental 1

Freshwater blue-green algae ( Anabaena flos-aquae ) 99.08 0.81 C <0.31

(EC 05 =

0.03) 41080401
Negilski, Grothe and Cocke (1989) Supplemental 1

Freshwater diatom ( Navicula pelliculosa ) 99.08 0.09 D 0.056 41080403
Negilski and Cocke (1989) Supplemental 1

Freshwater green algae ( Selenastrum capricornutum ) 98 0.05 0.013 00138697
Todd, Meyerhoff, Grothe, et al. (1983) Supplemental 1,2

A Duckweed 95% Confidence Interval (C.I.) = 0.06-0.26 mg a.i./L

B Marine diatom 95% C.I. = 0.04-0.06 mg a.i./L

C Blue-green algae 95% C.I. = 0.59-1.12 mg a.i./L

D Freshwater diatom 95% C.I. = 0.08-0.14 mg a.i./L

1 Three replicates per treatment level were used . EPA requires four replicates per level.

2 Results could not be verified since raw data were not provided. Results are based on a 5-day exposure.

3.3.2.2. Terrestrial Effects Characterization

The most sensitive acute and chronic effects meas urement endpoints associated with tebuthiuron exposure to terrestrial species are summarized in Table 3.17. Selected effects endpoints for the risk assessment are from acceptable and supplemen tal studies for tebuthiuron and are described

below.

Overall, tebuthiuron is practically nontoxic to mallard ducks on an acute basis. Tebuthiuron caused no mortality or sub-lethal effect s up to and including 2,000 mg a.i./kg bw and 5093 mg a.i./kg diet

to waterfowl via oral and dietar y routes, respectively; and up to 500 mg a.i./kg bw and 5113 mg a.i./kg diet for upland game birds. On the other hand, tebuthiuron is sligh tly toxic to small birds ( i.e. , passerines) on a dietary basis. In addition, birds also act as surrogates for reptiles and terrestrial-phase amphibians in the absence of taxa specific data; therefore, using the acute toxicityPage 39 of 121 data with passerines, tebuthiuron would be classified as slightly toxic to reptiles and terrestrialphase amphibians of similar body weight. Observati ons of reproductive eff ects in birds were as low as 500 mg a.i./kg diet; the resulting NOAECs for two avian species were both 100 mg a.i./kg

diet.

Tebuthiuron is moderately toxic to mamma ls on an acute oral basis (female LD 50 = 387.5 mg a.i/kg-bw; male LD 50 = 477.5 mg a.i/kg-bw). In the chroni c 2-generation studies, reproductive effects are as low as 30 mg a. i./kg/day (NOAEL = 14 mg a.i./ kg/day), based on decreased body weight and decreased body wei ght gains for female rats.

Results of the honeybee acute contact test with tebuthiuron indicate the TGAI is practically nontoxic to honeybees (LD 50 = >100 μg a.i./bee)

.

As may be anticipated with an herbicide, terrestr ial plants were affected at the seedling and the 3- leaf plant stages with the lowest EC 25 ’s at 0.018 and 0.16 lb a.i./A, respectively.

Table 3.17. Most Sensitive Acute and Chroni c Toxicity Data for Terrestrial Animals and Plants Exposed to Tebuthiuron. Exposure

Scenario Species Exposure

Duration Toxicity Reference

Value MRID (Classification)

Mammals

Acute (Dose-based) Laboratory rat ( Rattus norvegicus ) Single oral

dose Female LD 50 = 387.5 mg a.i./kg-bw 40583901 (acceptable)

Chronic(Dietarybased) Onegeneration LOAEL = 400 ppm NOAEL = 200 ppm (14 mg/kg/day) 00090108 (acceptable)

Birds

Acute (Dose-based) Mallard duck ( Anas platyrhynchus ) 14-day single oral

dose LD 50 >2000 mg a.i./kg bw 00041692 (acceptable)

Acute(Dietarybased) Zebra finch ( Taeniopygia

guttata ) 8-day dietary LC 50 = 1465 mg a.i./kgdiet 48928201 (acceptable)

Chronic(Dietarybased) Mallard duck ( Anas platyrhynchus ) Onegeneration NOAEC = 100 mg a.i./kgdiet 000104243 (acceptable)

Terrestrial Plants Seedling

emergence Ryegrass (monocot)

14 days EC 25 = 0.27 lbs a.i./A

NOAEC = 0.25 lbs a.i./A 48722703 (supplemental)

Carrot (dicot) EC 25 = 0.018 lbs a.i./A

EC 05 = 0.0032 lbs a.i./A* Vegetative Vigor Ryegrass (monocot) EC 25 = 0.30 lbs a.i./A

NOAEC = 0.12 lbs a.i./A 48722704 (supplemental) Sugarbeet (dicot) EC 25 = 0.16 lbs a.i./A

NOAEC = 0.062 lbs a.i./APage 40 of 121 Table 3.17. Most Sensitive Acute and Chroni c Toxicity Data for Terrestrial Animals and Plants Exposed to Tebuthiuron. Exposure

Scenario Species Exposure

Duration Toxicity Reference

Value MRID (Classification)

Beneficial Insects

Contact Honey bee 48 hours LD 50 >100 μg a.i./bee 40840401 (acceptable)

* The NOAEC was above the EC 25 ; thus, the EC 05 was used instead.



### Birds, Acute Oral

An acute oral toxicity study using the TGAI is requ ired to establish the acute toxicity of tebuthiuron to birds. The preferred guideline bird test species is either mallar d duck (a waterfowl) or Northern bobwhite quail (an upland game bird), and a pass erine bird. The submitted acute data indicate that the TGAI is categorized as practi cally nontoxic to waterfowls (LD 50 >2000 mg a.i./kg bw, the maximum dose tested), and no effects to domestic chickens and upland game birds were observed at and up to 500 mg a.i./kg bw ( Table 3.18 ).

However, for passerines, regurgita tion occurred at all test doses of an acute oral range-finding study, preventing the estimation of an oral LD 50 ; therefore the registrant op ted to conduct a dietarybased study using OCSPP 850.2200 with food consum ption closely monitored. The study design

switch was intended to estimate an oral LD 50 value for passerines using the LC 50 data from the passerine dietar y study (MRID 48928201; Table 3.19 ). An oral LD 50 could not be estimated due to variability in the study results; thus, the dose-ba sed oral toxicity of tebut hiuron to passerines is unknown. The toxicity of the active ingredient to passe rines is discussed in more detail in the avian acute dietary toxicity profile following this section.

Thus, with no mortality at doses as high as 2,000 mg a.i./kg-bw, the LD 50 of >2000 mg a.i./kg-bw will be used to evaluate potential acute effects of the TGAI to birds via the oral route. The available avian acute oral toxicity data are summarized in Table 3.18.

Table 3.18. Avian Acute Oral Toxi city Profile for Tebuthiuron. Species % a.i. LD 50 (mg a.i./kg bw) Toxicity Category MRID No.

Author/Year Study

Classification

Domestic

chicken ( Gallus sp. ) 98 >500 No effects up to 500

ppm 00020661

Todd, Kehr, West and et
al . (1972) Supplemental 1

Mallard duck

( Anas platyrhynchos ) 98 >2000 Practically

nontoxic 00041692

Kehr, Hamelink, Todd

and et al . (1978) Acceptable

98 >500 No effects up to 500

ppm 00020661

Todd, Kehr, West and et
al . (1972) Supplemental 1Page 41 of 121 Table 3.18. Avian Acute Oral Toxi city Profile for Tebuthiuron. Species % a.i. LD 50 (mg a.i./kg bw) Toxicity Category MRID No.

Author/Year Study

Classification

Northern bobwhite quail
(Colinus virginianus) 98 >500 No effects up to 500

ppm 00020661

Todd, Kehr, West and et
al . (1972) Supplemental 1

1 The highest concentration was below the re commended limit dose of 2000 mg a.i./kg bw.



### Birds, Subacute Dietary

Dietary studies using the TGAI ar e required to establish the subacu te toxicity of tebuthiuron to birds. The preferred test species are mallard duck (waterfowl) and bobwhite quail (upland game bird). The submitted data indicate no mortality occurred and that the 8-day acute dietary LC 50 for duck and quail were >5093 and >5113 mg a.i./kg di et, respectively, the maximum concentrations tested. The TGAI is categorized as practically non-toxic to upland game birds and waterfowl on a subacute dietary basis ( Table 3.19 ).

While results indicate the duck and quail were equally insensitive to the TGAI; passerines were slightly sensitive to tebuthiuron as mortality a nd extremely low food consumption were observed in the three highest concentrations (1590, 2870, and 5380 mg a.i./kg-diet). At the 1590 mg a.i./kgdiet treatment level, 8 birds died (80%). At the 2870 mg a.i./kg-diet treatment level, two birds were

taken off of treated feed before the full five da y exposure was complete due to extremely reduced feed consumption and were counted as mortalities. Of the 8 birds that stayed on the treated diet, 7 birds died (87.5%). At the highest treatment level, two birds died on Day 2 of the test and the other eight birds were switched to untre ated feed due to overall extreme reduction in feed consumption. One bird died on Day 4. All other surviving bird s on untreated food were normal in appearance and behavior from Day 4 to test termination but were considered to have died (100%) due to

insufficient caloric intake to sust ain life had the birds remained on treated food. Clinical signs of toxicity were observed as follows: at 497 mg a.i. /kg-diet, up to 50% of birds displayed slightly ruffled appearance and wing droop between Days 2 a nd 6; at 895 mg a.i./kg-diet, up to 60% of birds displayed ruffled appearance and wing droop between Days 2 and 7; at 1590 mg a.i./kg-diet, all birds displayed at least one clinical sign of toxicity (ruffled appearance, lethargy, and wing droop) by Day 4; at 2870 mg a.i./kg-diet, all birds were noted with at least one clinical sign of toxicity (ruffled appearance, lethargy, wing droop, loss of coordina tion, prostrate posture, and loss of righting reflex) or died by Day 3; and at 5380 mg a.i./kg-diet, al l birds were noted with ruffled appearance by the afternoon of Day 1. Due to the mo rtality pattern that o ccurred, there was not a dose-response effect. Not all mortal ities were related to the toxicity of tebuthiuron but were a result of avoidance of the treated feed. Assuming all bird s removed from treated diets because of reduced feed consumption would ha ve died, the resulting LC 50 is 1465 mg a.i./kg diet for passerines.

Therefore, the LC 50 value of 1465 mg a.i./kg-diet will be us ed to evaluate potential acute effects of the TGAI to birds via the dietary route. Th e available avian subacu te dietary studies are

summarized in Table 3.19

.Page 42 of 121 Table 3.19. Avian Acute Dietary Toxi city Profile for Tebuthiuron Species % a.i. Nominal

LC 50 (mg a.i./kg diet) Toxicity Category MRID No.

Author/Year Study

Classification

Zebra finch

( Taeniopygia guttata) 99.8 1465 A Slightly toxic 48928201

Hubbard, Martin and Beavers (2012) Acceptable

Mallard duck

( Anas platyrhynchos ) 98 >2500 No effects up to 2500 mg a.i./kg diet 00041680/ (00041693; addendum)

West and Hamelink (1976) /

Kehr, Brannon,

Todd and et al. (1978) Supplemental 1

99.1 >5093 Practically

nontoxic 40601001
Negilski, Grothe &

Meyeroff (1988) Acceptable

Northern bobwhite quail (Colinus

virginianus) 98 >2500 No effects up to 2500 mg a.i./kg diet 00041681/ (00041693; addendum)

West and Hamelink. (1976) /

Kehr, Brannon,

Todd and et al. (1978) Supplemental 1

99.1 >5113 Practically

nontoxic 40601002
Negilski, Grothe &

Meyeroff (1988) Acceptable

A Finch 95% Confidence Interval = 1145 to 1883 mg a.i./L; slope = 6.5 (2.997-10.03)

1 The concentrations used (when adjusted for active ingredient) did not produce a precise LD 50 and the highest concentration was below 5000 mg a.i./kg bw.



### Birds, Reproduction

Avian reproduction studies using the TGAI are re quired to establish th e chronic toxicity of tebuthiuron to birds ( Table 3.20 ). The preferred test species ar e mallard duck and bobwhite quail. The lowest reproduction NOAEC of 100 mg a.i./kg diet will be used to evaluate potential chronic

effects of the TGAI to birds. The available avian reproduction studies are summarized in Table

3.20

.

Bobwhite quail showed dose-dependent effects for offspring survival. At 903 and 1550 mg a.i./kg diet, the offspring survival ( 14-day hatchlings per number hatched) was slightly (4-7%), but significantly reduced, compar ed to the control (p<0.05; Jonckheer e-Terpstra test). Also, at the 1550 mg a.i./kg diet level, egg production was redu ced 23%, from an average of 44.8 eggs laid perPage 43 of 121 pen in the control group to 34.7 eggs laid per pen in the treated gr oup (p<0.05; Jonckheere-Terpstra test); both the study author and reviewer conclude d that this effect was treatment-related, despite the non-monotonicity of the data. No statistica lly significant differenc es in eggshell thickness were observed between the control group and any of the treatment groups. Adult male body weight gain was significantly reduced in a dose-depende nt manner 53-121% at all treated levels, relative to the negative control (p<0.05, William’s test ). Adult female body weight was significantly reduced at the 1550 mg a.i./kg diet level, relative to the control (p <0.01; Jonckheere-Terpstra test). No statistically significant di fferences were observed between the control group and any of the treated groups for food consumption. Offspri ng body weights were significantly reduced in a dose-dependent manner, with reductions from cont rol detected at the 903 and 1550 mg a.i./kg diet levels for hatchling body weights (p<0.01; Jonckh eere-Terpstra test) and at the 1550 mg a.i./kg diet level for 14-day old survivor weight (p<0.05; William’s test).

In the mallard study, a statistic ally significant (p<0.05) dose-de pendent reduction in hatchling body weight and eggshell thickness was observed at 1550 mg a.i./kg diet compared to the controls. There were statistically significant (p<0.05; Williams test, 26-41%) reductions from control in egg production (eggs laid per pen) in the 500, 903 and 1550 mg a.i./kg diet groups. A slight (<1%) reduction from control in eggs not cracked per e ggs laid was detected at the lowest treatment level (p = 0.04), but was not considered to be treatment-related.

Table 3.20. Avian Reproduction Toxi city Profile for Tebuthiuron.
Species %

a.i. NOAEC / LOAEC (mg a.i./kg-diet) Affected endpoints MRID no.

Author/Year Study

classification

Northern bobwhite quail
(Colinus virginianus) 96.4 100/>100 None 00104243

Fink, Beavers

& Brown

(1978) Acceptable

99.8 <500/500 Eggs laid per pen, 14- day hatchlings per number hatched, hatchling body weight, 14 day survivor weight, female weight gain and male weight gain. 48928203
Frey et al

.

(2012) Supplemental 1

Mallard duck

( Anas platyrhynchos ) 96.4 100/>100 None 00093690

Fink, Beavers

& Brown

(1978) Acceptable

99.8 <500/500 Eggs laid per pen, hatchling weight, and

eggshell thickness 48928202
Frey et al

.

(2012) Supplemental 1

1 An NOAEC was not available.Page 44 of 121 

### Mammals, Acute Oral

Wild mammal testing is require d on a case-by-case basis, depending on the results of lower Tier laboratory mammalian studies, in tended use pattern and pertinent environmental fate characteristics. In most cases, rat or mouse t oxicity values obtained from the Agency's Health Effects Division (HED) subs titute for wild mammal testing. These toxicity values are reported

below in Table 3.21

.

The results indicate tebuthiuron is cate gorized as moderate ly toxic (female LD 50 = 387.5 mg a.i/kgbw; male LD 50 = 477.5 mg a.i/kg-bw) to small mammals on an acute oral basis. The LD 50 value of 387.5 mg a.i./kg-bw will be used to eval uate potential acute effects to mammals.

Table 3.21. Mammalian Acute Oral T oxicity Profile for Tebuthiuron.

Species %

a.i. Test Type LD 50 (mg a.i./kg bw) Affected Endpoints MRID No. Author, Year Toxicity Category

Rat (Fischer

344) 99.1 acute oral Females = 387.5

Males = 477.5 Mortality 40583901

Negilski and Hawkins (1988) Moderately toxic



### Mammals, Reproduction

In the 2-generation reproduction study ( Table 3.22) , rats exposed to the TGAI showed no reproductive or offspring effects; however, redu ced body weight and decreased body weight gains

were observed. Parental female rats in the 200 and 400 ppm groups had mean weekly body weights 7-9% (not biologically significan t) and 8-13% (p<0.01 or <0.05), re spectively, less th an the control group throughout the premating period starting w ith day 21 for the 200 ppm group and day 7 for the 400 ppm group. Weight gain ove r the entire premating period was 7% (not significant) less than control for 200 ppm group and 14% (p<0.05) less for the 400 ppm group. The lowest NOAEC value of 200 ppm (14 mg a.i./kg-bw/day) will be used to evaluate potential chronic effects of the

TGAI to mammals. The available mammalia n reproduction studies are summarized in Table 3.22

.

Table 3.22. Mammalian Reproductive Toxicity Profile for Tebuthiuron.

Species %

a.i. Test Type Toxicity

ppm (mg a.i./kg bw/day) Affected Endpoints MRID No.

Rat (Wistar) 98 2-generation Parental Female NOAEL = 200 (14)

Male NOAEL = 400 (30)

Female LOAEL = 400 (30)

Male LOAEL = >400 (>30) Decreased body weight and body weight gains for

female rats
00090108

Reproductive NOAEL = 400 (30)

LOAEL = >400 (>30) None

Offspring NOAEL = 400 (30)

LOAEL = >400 (>30) NonePage 45 of 121 

### Beneficial Insects, Acute

A honeybee acute contact study using te buthiuron is required to estab lish the toxicity of the TGAI

to beneficial insects because of outdoor uses that will result in honeybee exposure ( Table 3.23 ).

The acute contact LD 50 , using the honey bee, Apis mellifera , is derived from a laboratory study designed to estimate the quantity of toxicant required to cause 50% mortality in a test population

of bees. Results of the acute co ntact study with honeyb ees indicate tebuthiur on is practically nontoxic to bees on a contact exposure basis. The available honeybee acute contact study is

summarized in Table 3.23

.

Table 3.23. Honeybee Acute Contact T oxicity Profile for Tebuthiuron.

Species %

a.i. LD 50 (μg a.i./bee) Toxicity Category MRID No. Study

Classification

Honey bee ( Apis mellifera ) 99.1 >100 Practically

nontoxic 40840401

Hoxter and Jaber (1988) Acceptable



### Terrestrial Plants, Seedling Em ergence and Vegetative Vigor

Terrestrial plant studies are required for all terrestri al outdoor pesticides. Tier II terrestrial plant toxicity studies were con ducted to establish the toxicity of tebuthiuron ( Table 3.24 ) to non-target terrestrial plants tested at 4 lb a.i./A. The recommendations for seedling emergence and vegetative vigor studies are for testing of (1) six species of at least four dicotyledonous families, one species of which is soybean ( Glycine max ), and the second of which is a ro ot crop, and (2) four species of at least two monocotyledonous fam ilies, one of which is corn ( Zea mays ). The tests indicate seedlings and young plants for each species were generally equally sensitive when exposed to tebuthiuron, except for dicots in which seedlings were more sensitive. EC 50 values were used to evaluate potential effects of tebuthiuron to non-listed terrestrial pl ant species. Corresponding NOAEC values were used to evaluate potential e ffects of tebuthiuron to listed terrestrial plant species.

Results of the seedling emergence test indicate the most sensitiv e monocot species, based on fresh weight, was ryegrass with an EC 25 of 0.27 lb a.i./A and a NOAEC of 0.25 lb a.i./A. The most sensitive dicot species, based on fresh weight, was carrot with an EC 25 of 0.018 lb a.i./A and a

NOAEC of 0.031 lb a.i./A.

In the vegetative vigor test, the most sensi tive monocot species, based on fresh weight, was ryegrass with an EC 25 of 0.30 lb a.i./A and a NOAEC of 0.1 2 lb a.i./A. The most sensitive dicot species, based on fresh weight, was sugarbeet with an EC 25 of 0.16 lb a.i./A and a NOAEC of

0.062 lb a.i./APage 46 of 121 Both studies are scientifica lly sound but do no t fulfill the guideli nes (OCSPP 850.4100 and 850.4150) and are classified as supplemental becau se fresh weight instead of dry weight was measured, and only the three highest test levels instead of all test levels were verified.

EC 25 values will be used to evaluate potential effects of tebuthiuron to non-listed plants, respectively. Corresponding NOAEC values will be used to evaluate potential effects of tebuthiuron to listed pl ants, respectively.

The description and classification of the availabl e terrestrial plants studies are summarized in

Table 3.24

.

Table 3.24. Summary of Tier II Seedling Emer gence and Vegetative Vigor Toxicity

Profile for Tebuthiuron. A
Seedling Emergence * Vegetative Vigor **
Species Endpoint NOAE

C EC 05 EC 25 Endpoint NOAEC EC 05 EC 25

Onion Fresh weight 0.25 0.23 0.46 Fresh weight 0.25 0.25 0.57 Corn Shoot length 2.0 1.8 3.1 Fresh weight 2.0 1.8 2.6 Oat Fresh weight 0.50 0.27 0.52 Shoot length 0.5 0.16 0.93 Ryegrass Fresh weight 0.25 0.12 0.27 Fresh weight 0.12 0.065 0.30 Carrot Fresh weight 0.031 0.0032 0.018 Fresh weight 0.50 0.30 0.52 Cucumber Fresh weight 0.12 0.13 0.33 Fresh weight 0.12 0.097 0.28 Cabbage Fresh weight 0.12 0.14 0.23 Fresh weight 0.12 0.18 0.32 Soybean Fresh weight 1.0 0.79 1.2 None 0.12/0.50

/2.0 B NC NC

Sugarbeet Fresh weight 0.12 0.11 0.20 Fresh weight 0.062 0.053 0.16 Tomato Fresh weight 0.062 0.13 0.26 Fresh weight 0.25 0.25 0.43 * 22.1% a.i; MRID 48722703, Bergfield 2012. ** 22.1% a.i; MRID 48722704, Bergfield 2012.

NC – Not calculated or converged.

A Measured concentrations for sugarbeet, tomato, and ca bbage were 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, and 1.0 lb a.i./A. For soybean, measured concentrations were 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, 1.0, and 2.0 lb a.i./A. For onion, ryegrass, oat, carrot, and cucumber, measured concentrations were 0.0078, 0.016, 0. 031, 0.062, 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb a.i./A. The measured concentrations for corn were 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb ai/A.

B NOAEC values for fresh weight, shoot length, and survival, respectively.



### 4. Risk Characterization

4.1. Risk Estimation

Toxicity data and exposure estimates are used to evaluate the potential for adverse ecological effects on non-target species. This assessment for tebuthiuron relies on the deterministic RQ method to provide a metric of potential risks. The RQ provides a comparison of exposure estimates to toxicity endpoints ( i.e. , the estimated exposure concentratio ns are divided by acute and chronic toxicity values). The resulting RQs are compared to the Agency’s LOCs. LOCs are used by the Agency to indicate when the use of a pesticide, as directed by th e label, has the potential to cause

adverse effects to non -target organisms.Page 47 of 121 4.1.1 Risk Quotient Calculat ions for Aquatic Organisms

There is a potential for exposure of the active ingredient to aquatic organisms (fish and invertebrates); toxicity information is used to esti mate the risks to aquatic organisms as a result of surface runoff and spray drift from tebuthiuron uses. The LD 50 and EC 50 are used to estimate acute

risk for adverse effects on survival to fish and invertebrates, respectivel y, and the NOAEC is used

to estimate chronic risk for advers e effects to both fish and inverteb rates. A single application at 4 and 6 lb a.i./A was modeled. Applications from aerial, ground and granular uses were modeled.

Tables 4.1 and 4.2 list acute and chronic RQs calculated fo r aquatic organisms (freshwater fish also surrogates for aquatic-phase amphibians) ex posed to tebuthiuron based on the EECs generated from PRZM-EXAMS modeling.

Results of the assessment on aquatic organisms indicate no acute or chronic LOC exceedances for fish and invertebrates exposed to tebuthiuron ( Table 4.1 – freshwater fish; Table 4.2 – freshwater invertebrates; and Table 4.3 – estuarine/marine invertebrate s); acute and chronic RQs were generally <0.01 and <0.1, respec tively. Maximum acute and ch ronic RQs were 0.02 and 0.2, respectively, using the surrogate scenario of aeri al applications in Texas, which exposure from aerial applications is expected to be the highe st. Because RQs did not exceeded the LOCs for the Texas scenario with aerial applica tions, at which exposure is the hi ghest; it is anti cipated RQs for ground and granular applications al ong with the remaining aerial ap plication scenarios modeled to

be below the LOCs as well. Acut e and chronic RQs for estuarine/ma rine fish were not calculated since mortality and sub-lethal e ffects were not established (LC 50 >98 mg a.i./L; ACR-derived NOAEC >18 mg a.i./L).

For listed species, LOC exceedances require an additio nal in-depth listed sp ecies evaluation of the potential co-occurrence of listed species in te buthiuron-treated areas to characterize risks. Likewise, the probability of an acute effect ( i.e. , mortality) to an endange red species based on the acute RQ value was calculated. Based on results, th e probability of an acute effect to aquatic animals was minimal (ranges from 1 in 9x10 18 to 1 in >3x10 155 ).

The potential risks to fish and inve rtebrates are discussed further in Section 4.2

.Page 48 of 121Table 4.1. Risk Quotients for Freshwater FishCropScenarioApp Ratein lbs a.i./A(Method ofApplication)1-in-10-yearPeak EEC(mg/L)Freshwater FishLC50= 106 mg a.i./L (slope = NA)1-in-10-year60-day EEC(mg/L)FreshwaterFishNOAEC =9.3 mg a.i./LAcute RQsProbability of AcuteEffect1(1 in ...)ChronicRQsRangeland/PasturesCAalfalfa_WirrigOP6.0(Aerial)0.5 <0.01 >9x10180.5 <0.1MNalfalfaOP 0.56 <0.01 >9x10180.55 <0.1NCalfalfaOP 0.60 <0.01 >9x10180.60 <0.1PAalfalfaOP 0.69 <0.01 >9x10180.69 <0.1TXalfalfaOP 1.1 0.01 9x10181.1 0.12CAalfalfa_WirrigOP4.0(Aerial)0.33 <0.01 >9x10180.33 <0.1MNalfalfaOP 0.37 <0.01 >9x10180.37 <0.1NCalfalfaOP 0.40 <0.01 >9x10180.40 <0.1PAalfalfaOP 0.46 <0.01 >9x10180.46 <0.1TXalfalfaOP 0.74 <0.01 >9x10180.73 <0.1Abbreviations:App.Application;NANot availableAboldcell indicates that the RQ meets or exceedsthe aquatic LOC for acute risk to listed species (LOC = 0.05), restricted use (LOC= 0.1), or non-listedspecies (LOC = 0.5) or chronic risk tolisted and non-listed species (LOC=1).1Probability of individual mortality based on actual screening level RQ value for tebuthiuron.A default concentration-response slope value of 4.5 is used togenerate the probability value when slope values were not available from the available test data (USEPA 2004).Page 49 of 121Table 4.2. Risk Quotients for Freshwater InvertebratesCropScenarioApp Ratein lbs a.i./A /(Method ofApplication)1-in-10-yearPeak EEC(mg/L)Freshwater InvertebratesLC50= 297 mg a.i./L (slope = 13.3)1-in-10-year21-day EEC(mg/L)FreshwaterInvertebratesNOAEC =21.8 mg a.i./LAcute RQsProbability of AcuteEffect1(1 in ...)Chronic RQsRangeland/PasturesCAalfalfa_WirrigOP6.0(Aerial)0.5 <0.01 >3x101550.5 <0.1MNalfalfaOP 0.56 <0.01 >3x101550.56 <0.1NCalfalfaOP 0.60 <0.01 >3x101550.60 <0.1PAalfalfaOP 0.69 <0.01 >3x101550.69 <0.1TXalfalfaOP 1.1 <0.01 >3x101551.1 <0.1CAalfalfa_WirrigOP4.0(Aerial)0.33 <0.01>3x101550.33 <0.1MNalfalfaOP 0.37 <0.01>3x101550.37 <0.1NCalfalfaOP 0.40 <0.01>3x101550.40 <0.1PAalfalfaOP 0.46 <0.01>3x101550.46 <0.1TXalfalfaOP 0.74 <0.01>3x101550.74 <0.1Abbreviations:App.Application.Aboldcell indicates that the RQ meets or exceeds the aquatic LOCs.1Probability of individual mortality based on actual screening level RQ value for tebuthiuron. A concentration-response slopevalue of 13.3 is used to generatethe probability value (USEPA 2004).Page 50 of 121Table 4.3. Risk Quotients for Estuarine/marine InvertebratesCropScenarioApp Ratein lbs a.i./A /(Method ofApplication)1-in-10-yearPeak EEC(mg/L)Estuarine/marine InvertebratesLC50= 62 mg a.i./L (slope = N/A)1-in-10-year21-day EEC(mg/L)Estuarine/marineInvertebratesNOAEC =4.56 mg a.i./LAcute RQsProbability of AcuteEffect1(1 in ...)Chronic RQsRangeland/PasturesCAalfalfa_WirrigOP6.0(Aerial)0.5 <0.01 >9x10180.5 0.1MNalfalfaOP 0.56 <0.01 >9x10180.56 0.1NCalfalfaOP 0.60 <0.01 >9x10180.60 0.1PAalfalfaOP 0.69 0.01 9x10180.69 0.2TXalfalfaOP 1.1 0.02 10x10131.1 0.2CAalfalfa_WirrigOP4.0(Aerial)0.33 <0.01 >9x10180.33 <0.1MNalfalfaOP 0.37 <0.01 >9x10180.37 <0.1NCalfalfaOP 0.40 <0.01 >9x10180.40 <0.1PAalfalfaOP 0.46 <0.01 >9x10180.46 0.1TXalfalfaOP 0.74 0.01 9x10180.74 0.2Abbreviations:App.Application.Aboldcell indicates that the RQ meetsor exceeds the aquatic LOCs.1Probability of individual mortality based on actual screening level RQ value for tebuthiuron. A default concentration-response slope value of 4.5 is used togenerate the probability value when slope values were not available from the available test data (USEPA 2004).Page 51 of 121 4.1.2 Risk Quotient Calculat ions for Aquatic Plants

There is a potential for exposure of the active ingredient to aqua tic vascular and nonvascular plant species. Toxicity information are used to estimate the risks to aquatic plants as a result of surface runoff and spray drift from broadcast ground a pplications via spray or granules. The IC 50 is used to estimate risk for adverse effects on growth to non-listed aquatic plants and the NOAEC (or EC 05 when a NOAEC is not available) is used to estimate risk for adverse effects on growth to listed aquatic plants.

According to peak PRZM/EXAMS EECs and the range of application rates for tebuthiuron uses every year and toxicity to aqua tic plants, the non-listed and liste d RQs for aquatic plants (both vascular and nonvascular species) are above Agen cy’s plant LOC of 1. The RQs were 2-29 for aquatic plants exposed to tebuthiuron uses ( Table 4.4 ).

The potential risks to aquatic pl ants are discussed further in Section 4.2

.Page 52 of 121Table 4.4. Risk Quotients for Aquatic PlantsCropScenarioApp Rate(lbs/A)1-in-10year PeakEEC4(mg/L)Aquatic Vascular PlantsIC50= 0.13 mg a.i./LNOAEC = 0.05 mg a.i./LAquatic Nonvascular PlantsIC50= 0.05 mg a.i./LNOAEC = 0.038 mg a.i./LNon-listedRQsListed RQsNon-listedRQsListed RQsRangeland /PasturesCAalfalfa_WirrigOP6.0(Aerial)0.5410 10 13MNalfalfaOP0.56411 11 15NCalfalfaOP0.60512 12 16PAalfalfaOP0.69514 14 18TXalfalfaOP1.1822 22 29CAalfalfa_WirrigOP4.0(Aerial)0.3337 7 9MNalfalfaOP0.3737 7 10NCalfalfaOP0.4038 8 11PAalfalfaOP0.4649 9 12TXalfalfaOP0.74615 15 19CAalfalfa_WirrigOP6.0(Ground)0.3737 7 10MNalfalfaOP0.3838 8 10NCalfalfaOP0.4539 9 12PAalfalfaOP0.53411 11 14TXalfalfaOP1.0820 20 26CAalfalfa_WirrigOP4.0(Ground)0.2525 5 7MNalfalfaOP0.2525 5 7NCalfalfaOP0.3036 6 8PAalfalfaOP0.3637 7 9TXalfalfaOP0.68514 14 18CAalfalfa_WirrigOP6.0(Granules)0.3437 7 9MNalfalfaOP0.3337 7 9NCalfalfaOP0.4138 8 11Page 53 of 121Table 4.4. Risk Quotients for Aquatic PlantsCropScenarioApp Rate(lbs/A)1-in-10year PeakEEC4(mg/L)Aquatic Vascular PlantsIC50= 0.13 mg a.i./LNOAEC = 0.05 mg a.i./LAquatic Nonvascular PlantsIC50= 0.05 mg a.i./LNOAEC = 0.038 mg a.i./LNon-listedRQsListed RQsNon-listedRQsListed RQsPAalfalfaOP0.49410 10 13TXalfalfaOP1.0820 20 26CAalfalfa_WirrigOP4.0(Granules)0.2224 4 6MNalfalfaOP0.2224 4 6NCalfalfaOP0.2826 6 7PAalfalfaOP0.3337 7 9TXalfalfaOP0.66513 13 17Abbreviations:App.ApplicationAboldcell indicates that the RQ meets or exceeds theLOC for non-listed or listed plants (LOC = 1).Page 54 of 121 4.1.3. Risk Quotient Calculatio ns for Terrestrial Animals

For this screening-level risk assessment with birds and mammals, acute and chronic RQs are derived based on ecological toxic ity data for tebuthiuron, and then directly compared to the dietary-based EECs generated from T-REX. For dose-based RQs, the EECs and toxicity values are first adjusted based on food intake and body weight differences of the terrestrial animals prior to the assessment. Size classes are not used in dietary-based RQs. The LD 50 and LC 50 are used to estimate acute risk for adverse effects on survival to both birds and mammals; the

NOAEC/NOAEL is used to estimate chronic risk for adverse effects on reproduction and growth to birds and mammals. Dietary-based exposure modeling for granular consumption was not available. Therefore, dietary-based RQs for granul ar uses could not be calc ulated; it is presumed the dietary-based RQs for granular uses are equi valent to the RQs for spray uses. Dose-based exposure modeling for granular consumption is avai lable; however, all of the dose-based toxicity values for birds were non-definitive; thus, th e dose-based RQs for granular uses were not calculated for birds. On the other hand, the mammal dose-based toxicity value was definitive, and RQs for mammals consuming granules were calcula ted. The potential risk for granular exposure

to birds and mammals is discussed in the Risk Description section.

Similar to aquatic organisms, the probability of an acute effect to terrestrial organisms was estimated for the additional endangered species assessment and is included in the RQ tables below, where applicable. As of a result, the probability of an acute effect to terrestrial animals ranges from negligible (1 in 2x10 19 ) to absolute certainty (1 in 1).

Birds

There is a potential for acute exposure to birds vi a the oral route, but ac ute dose-based RQs were not calculated because definitive toxicity endpoint s for upland game bird and waterfowl were not established (mallard an d northern quail oral LD 50s >2000 mg a.i./kg-bw), and there were difficulties in obtaining a dose-based value for the passerine ( e.g. , severe regurgitation).

At the maximum application rate of 6 lb a.i./A ap plied broadcast as a liqui d spray, the acute dietarybased RQs of 0.38 – 0.98 for birds based on a LC 50 of 1465 mg a.i./kg-diet for the zebra finch were 3-10x above the listed species LOC of 0.1, for birds that cons ume vegetation and insects in

tebuthiuron-treated sites (Table 4.5) . Only birds consuming fruits/pods/seeds did not exceeded the LOC (Highest RQ = 0.06). There is an uncertainty with the RQs calculated for the bobwhite quail

and mallard that exceeded the LOC when the zebra LC 50 of 1465 mg a.i./kg-diet was used in the calculations. If the toxicity of the upland game bird (LC 50 >5113 mg a.i./kg diet) or mallard (LC 50 >5093 mg a.i./kg-diet) was used instead, the acute RQs would be <0.01 or 10x greater than the highest EECs for the mallard and quail species , suggesting the effects to upland game and

waterfowl birds would be minimal.

At 4 lb a.i./A applied broadcast as a liquid sp ray, the acute dietary-ba sed RQs of 0.26-0.66 were 2-7x above the listed species LOC of 0.1 for birds that cons ume vegetation an d insects in

tebuthiuron-treated sites (Table 4.5)

.Page 55 of 121 As stated above, the dietary-based acute RQs could not be calculated for granular or pellet uses, it is presumed the acute RQs would be the same for liq uid sprays if sprayed at 6 or 4 lb a.i./A. Thus, granule uses would be 3-10x above the LOC at 6 lb a.i./A and 2-7x above the LOC at 4 lb a.i./A. This is an uncertainty since the modeling for li quid spraying assumes 100% of the active ingredient when the pelleted and granular formulations actually has only 40% a nd 5% of tebuthiuron, respectively.

For liquid sprays at 6 lb a.i./A, chronic RQs of 6-14 for birds based upon an NOAEC of 100 mg a.i./kg-diet were 6-14x above the LOC of 1 fo r potential risk to non- listed and listed birds consuming vegetation and insect s with tebuthiuron residues ( Table 4.6 ). Only birds consuming fruits/pods/seeds did not exceed the chronic LOC (Highest RQ = 0.9).

For liquid sprays at 4 lb a.i./A, chronic RQs were 4-10 for birds; which is 4 to 10x above the LOC

of 1.

No methodology is available to model chronic exposur e to birds from granular or pellet uses. Thus it is presumed the chronic RQs for granular uses would be the same of the RQs for liquid sprays

which is 6-14x and 4-10x above the chronic LOC for 6 and 4 lb a.i./A, respectively.

The potential for risk to birds is disc ussed in the Risk Description section.Page 56 of 121Table 4.5. Acute Avian Dietary-Based Risk QuotientsSiteLC50(mga.i./kgdiet)EECs and RQsShort GrassTall GrassBroadleaf PlantsFruits/Pods/SeedsArthropodsEECRQIEC3EECRQIECEECRQIECEECRQIECEECRQIECRangeland11465 14400.982.1 6600.4583 8100.5522 90 0.06 1x10155640.38317Rangeland21465 9600.668.3 4400.302950 5400.37400 60 0.04 2x10193760.261x1004Size class not used for dietary risk quotientsBoldvalues indicate terrestrial LOC exceedances for acute risk to listed species (LOC = 0.1), restricted use (LOC = 0.2), or non-listedspecies (LOC = 0.5) or chronic risk tolisted and non-listed species (LOC=1).1Exposure scenario based on 1 broadcast spray at 6 lb a.i./A2Exposure scenario based on 1 broadcast spray at 4 lb a.i./A3Probability of individual mortality based on actual screening level RQ value for tebuthiuron (1 in ....). A concentration-response slopevalue of 6.5 is used to generate the probability value (USEPA 2004).Table 4.6. Chronic Avian Dietary-Based Risk QuotientsSiteNOAEC(mga.i./kgdiet)EECs and RQsShort GrassTall GrassBroadleaf PlantsFruits/Pods/SeedsArthropodsEECRQEECRQEECRQEECRQEECRQRangeland1100 1440146607810890 0.9 5646Rangeland2100 960104404540560 0.6 3764Size class not used for dietary risk quotientsBoldvalues indicate LOC exceedances (exceeds the LOC of 1 for chronic risk)1Exposure scenario based on 1 broadcast spray at 6 lb a.i./A2Exposure scenario based on 1 broadcast spray at 4 lb a.i./APage 57 of 121 Terrestrial-phase Amphibians and Reptiles

EFED currently uses surrogate data (birds) for te rrestrial-phase amphibians and reptiles when data

are not available. There were LOC exceedances fo r birds; these exceedances apply to terrestrialphase amphibian and reptiles. Risks are disc ussed in the Risk De scription section.

Mammals

Acute dose-based RQ values of 0.19-1.6 for mammals based on toxicity data for the laboratory rat (female LD 50 = 385 mg a.i./kg-bw) were above the LO C for mammals that eat vegetation and insects exposed to tebuthiuron from ground or ae rial applications at 4 and 6 lb a.i./A ( Table 4.7 ). These RQs were 2-16x higher than the listed species LOC of 0.1 a nd 3x higher than the non-listed species LOC of 0.5. The RQ of 0.1 was at the LOC for 15-g mammals that consume fruits/pods/seeds for the 6 lb a. i./A application scenario. RQs for 35-g and 1000-g mammals that consume fruits/pods/seeds for the 6 lb a.i./A application and for 15-g mammals that eat fruits/pods/seeds for the 4 lb a.i./A application we re not above the acute listed LOC (Highest RQ = 0.09). RQs for granivorous mammals that eat grai n and seeds were not a bove the LOC (Highest RQ = 0.02).

For granular and pellet consumption, RQs for 15-g and 35-g mammals exceeded the acute LOCs, while the RQs for 1000-g mammals do not exceeded th e LOCs. However, for gr anular uses at 4 lb a.i./A, the RQ of 0.09 for 35-g mammals does not exceed the acute listed species LOC of 0.1. The RQs that exceeded the listed species LOC of 0.1 ranged from 0.13 to 1.96, which were 1 to 19x higher than the listed species LOC.

The probability for an acute e ffect to 15-g mammals that consume tebuthiuron-exposed short grass, using the highest a pplication scenario, at 6 lb a.i./A w ith broadcast liquid sprays is 1 in 1.22; for 35-g mammals, it is 1 in 1.34; and for 1000-g mammal it is 1 in 4. Table 4.7 provides more details on the probability of an acute effect to 15-g, 35-g, 1000-g mammals that consume

these selected feed items treated with tebuthiuron. For pellet uses at 6 lb a.i./A with 40% of tebuthiuron in the formulation, the probability for an acute effect to 15-g mammals is 1 in 1.1; for 35-g mammals, it is 1 in 1.88; and for 1000-g mammals it is 1 in 3x10 6 . For granular applications at 6 and 4 lb a.i./A with 5% of tebuthiuron in its form ulation, the probability to 15-g mammals is 1 in 378 and 1 in 5850, respectively.Page 58 of 121Table 4.7. Acute Mammalian Dose-Based Risk QuotientsSiteSize Class(grams)Adjusted7LD50EECs and RQs for Spray UsesShort GrassTall GrassBroadleaf PlantsEEC7RQIEC (1 in ..)9EECRQIEC (1 in ..)EECRQIEC (1 in ..)Rangeland(6 lb/A broadcast spray)115 851.6613731.61.22 6290.744 7720.91235 689.089491.41.34 4350.645 5340.7831000 298.05 2200.74 1010.3457 1240.4222Rangeland(4 lb/A broadcast spray)215 851.669151.11.74 4200.5011 5150.61635 689.086330.92 2900.4222 3560.52101000 298.05 1470.511 670.23491 830.28156SiteSize Class(grams)Adjusted7LD50EECs and RQs for Spray UsesFruits/Pods/ SeedsArthropodsGranivoreEECRQIEC (1 in ..)EECRQIEC (1 in ..)EECRQIEC (1 in ..)Rangeland(6 lb/A broadcast spray)115 851.66860.103x1055380.64519 0.0210x101335 689.0859 0.098x1053720.54913 0.0210x10131000 298.05 14 0.05 4x108860.29129 3 0.01 9x1018Rangeland(4 lb/A broadcast spray)215 851.6657 0.0710x1063580.422213 0.0210x101335 689.0840 0.065x1072480.36448.8 0.019x10181000 298.05 9 0.03 3x1011570.191710 2.1 <0.01 >9x1018SiteSize Class(grams)Adjusted7LD50EECs and RQs for Granular UsesEEC8RQIEC (1 in ..)Rangeland(6 lb/A pellet broadcast)315 851.66251.961.135 689.08251.041.881000 298.05250.083x106Rangeland(4 lb/A pellet broadcast)415 851.6616.71.311.4335 689.0816.70.694.271000 298.0516.70.065x107Rangeland(6 lb/A granular broadcast)515 851.663.120.2437835 689.083.120.133x1041000 298.053.120.019x1018Rangeland(4 lb/A granular broadcast)615 851.662.080.16585035 689.082.080.098x1051000 298.052.080.016x1021Boldvalues indicate terrestrial LOC exceedancesPage 59 of 1211Exposure scenario based on 1 broadcast spray at 6 lb a.i./A2Exposure scenario based on 1 broadcast spray at 4 lb a.i./A3Exposure scenario based on 1 broadcast pellet application at 6 lb a.i./A with 40% of tebuthiuron4Exposure scenario based on 1 broadcast pellet application at 4 lb a.i./A with 40% of tebuthiuron5Exposure scenario based on 1 broadcast granular application at 6 lb a.i./A with 5% of tebuthiuron6Exposure scenario based on 1 broadcast granular application at 4 lb a.i./A with 5% of tebuthiuron7mg a.i./kg-bw8mg a.i./ft29Probability of individual mortality based on actual screening level RQ value for tebuthiuron. A default concentration-response slope value of 4.5 is used togenerate the probability value when slope values were not available from the available test data (IEC model V.1.1 USEPA 2004).Page 60 of 121 Chronic RQ values for mammals are presented in Tables 4.8 and 4.9. Based on the rat chronic NOAEL of 14 mg a.i./kg-bw/day (200 mg/kg-diet) for exposure to tebuthiuron, both dietary and dose-based RQ values exceed the chronic risk LOC (L OC = 1) for all size classes of mammals that consume short grass, tall grass, broadleaf plants, fruits and pods (dose-based only), and arthropods (RQs ranged 1.9-45). These chronic RQs were 2- 45x higher than the chronic LOC of 1.0. Chronic dietary-based RQs for applications of 4 and 6 lb a.i/A tebuthiuron do not exceed the chronic risk LOC for mammals consuming fruits/pods/seeds (H ighest RQ = 0.45). Chronic dose-based RQs do

not exceed the chronic risk LOC for all size classe s of mammals that consume seeds (Highest RQ = 0.62) and 1000 g mammals that consume fr uits/pods/seeds (Highest RQ = 0.85).

Chronic RQs for granular and pelleted formulations are not calculated.

The potential for risk to mammals is furthe r discussed in the Risk Description section.

Table 4.8. Chronic Mammalian Dietary-Based Risk Quotients

Site NOAEL (mga.i./kgdiet) EECs and RQs

Short Grass Tall Grass Broadleaf

Plants Fruits/Pods/

Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ Rangeland 1 200 1440 7.2 660 3.3 810 4.1 90 0.45 564 2.8

Rangeland 2 200 960 4.8 440 2.2 540 2.7 60 0.30 376 1.9
Size class not used for dietary risk quotients

Bold values indicate LOC exceedances (exc eeds the LOC of 1 for chronic risk)

1 Exposure scenario based on 1 broadcast spray at 6 lb a.i./A

2 Exposure scenario based on 1 broadcast spray at 4 lb a.i./APage 61 of 121Table 4.9. Chronic MammalianDose-Based Risk QuotientsSiteSizeClass(grams)AdjustedNOAELEECs and RQsShort GrassTall GrassBroadleafPlantsFruits/Pods/SeedsArthropodsGranivoreEECRQEECRQEECRQEECRQEECRQEECRQRangeland115 30.7713734562920773258635381719 0.635 24.909493843517534215923721513 0.51000 10.77220201019124111418683 0.3Rangeland215 30.779153042014515175723581213 0.435 24.90633252901235614402248109 0.41000 10.77147146768389 0.9 5752 0.2Boldvalues indicate LOC exceedances (exceeds the LOC of 1 for chronic risk)1Exposure scenario based on 1 broadcast spray at 6 lb a.i./A2Exposure scenario based on 1 broadcast spray at 4 lb a.i./APage 62 of 121 Beneficial Insects

Tebuthiuron is classified as “p ractically nontoxic” to non-target beneficial insects including honeybees (honeybee acute contact LD 50 >100 μg a.i./bee) on an acute exposure basis. The need for precautionary label language for beneficial insects is not required and is discussed further in the Risk Description section.

Terrestrial Invertebrates

EFED currently uses surrogate data (bees) for terres trial invertebrates when data are not available. There is a potential for acute exposure to terr estrial invertebrates, but acute RQs were not calculated because tebuthiuron toxicity info rmation for the honeybee was not established (honeybee acute contact LD 50s >100 μg a.i./bee). Risks to terrestrial inverteb rates are discussed in the Risk Description section.

4.1.4. Risk Quotient Calculations for Terrestrial Plants in Terrestrial and Semi-aquatic Environments

For this risk assessment with te rrestrial monocots and dicots, non- listed and listed plant species RQs are derived based on ecologica l toxicity data for the active i ngredient and then compared to TerrPlant EECs for plants in non-target area recei ving surface runoff combined with spray drift adjacent to the target area. Details of th e TerrPlant model and EECs are presented in Table 2.11

.

There is a potential for exposure of tebuthiuron to terrestrial plan ts. Toxicity information on the TEP (Typical End-use Product) are used to estima te the risks to non-target terrestrial plants inhabiting dry or semi-aquatic area s adjacent to a treated field as a result of surface runoff and/or spray drift. The EC 25 was used to estimate risk fo r adverse effects on growth to non-listed plant species while the NOAEC (or EC 05 when a NOAEC is not available) was used to estimate risk for adverse effects on growth to listed plant species. Note: TerrPlant doe s not consider exposures to plants from multiple pesticide applications; thus, results are based on single pesticide applications

.

Table 4.10 presents RQs for exposure of terrestrial pl ants to tebuthiuron via ground and aerial spray applications as well as granular applications.

RQs (1.11-1031) for non-listed and listed monocots and dicots inhabiting dry and semi-aquatic areas adjacent to a treated site exposed to te buthiuron through a combin ation of surface water runoff and spray drift exceed the plant LOC of 1.0 for broadcast applications by aerial, ground, and granular at 4 and 6 lb a.i./A. However, when reduced to 4 lb a.i./A from 6 lb a.i./A, non-listed

and listed monocots inhabiting dry areas adjacent to a treated site exposed to tebuthiuron through runoff and drift via ground or gr anular applications were no longer above the LOC of 1.0; the highest RQ was 0.96.

There is no LOC exceedance for non-listed and listed monocots exposed to drift alone from aerial uses at 4 lb a.i./A tebuthiuron or from ground or granular applications at 4 and 6 lb a.i./A tebuthiuron; the highest RQ is 0.74.Page 63 of 121 For granular uses, no drift is produc ed; thus, there are no exceedances for non-listed and listed plants exposed to sp ray drift alone.

The potential risks to terrestrial plants are discussed further in the Risk Description section.

Table 4.10. Terrestrial Plant Risk Quotient 1, 2, 3, 4

Scenario Non-listed RQs Listed RQs

Terrestrial Adjacent area Semi-aquatic Adjacent

Area Drift Terrestrial Adjacent area Semi-aquatic Adjacent

Area Drift

One Aerial Spray at 6 lb a.i./A

Monocot 2.22 12.2 1.11 2.4 13.2 1.2

Dicot 33.3 183 16.7 188 1031 94 One Aerial Spray at 4 lb a.i./A

Monocot 1.48 8.15 0.74 1.6 8.8 0.8

Dicot 22.2 122 11.1 125 688 62.5

One Ground Spray at 6 lb a.i./A

Monocot 1.3 11.3 0.22 1.4 12.2 0.24

Dicot 20 170 3.3 113 956 18.8 One Ground Spray at 4 lb a.i./A

Monocot 0.89 7.56 0.15 0.96 8.16 0.16

Dicot 13.3 113 2.22 75 638 12.5
One Granular Application at 6 lb a.i./A

Monocot 1.11 11.1 N/A 1.2 12 N/A

Dicot 16.67 167 N/A 94 938 N/A One Granular Application at 4 lb a.i./A

Monocot 0.74 7.41 N/A 0.8 8 N/A

Dicot 11.1 111 N/A 62.5 625 N/A

1 RQs for aerial and ground spray and granular applicati ons in this table were calculated using the maximum application rates for tebuthiuron uses.

2 Non-listed toxicity thresholds (EC 25 ) were 0.27, 0.018, 0.3, and 0.16 lb a.i./A for seedling emergence monocot, seedling emergence dicot, vegetative vigor monocot, and vegetative vigor dicot.

3 Corresponding listed toxicity thresholds (NOAEC) were 0.25, 0.0032, 0.12, and 0.62 lb a.i./A for seedling emergence monocot, seedling emergence dicot, vegetative vigor monocot, and vegetative vigor dicot.

4 Values in bold are LOC exceedances (Exceeds the LOC of 1 for potential risk to non-listed and listed plant species).

4.2. Risk Description

The risk hypothesis states that th e use of tebuthiuron as an herbic ide for terrestrial crop sites has the potential to adversely affect survival, repro duction, and/or growth of non-target aquatic and terrestrial animals and plants, including Federally- listed endangered and threatened species. Based on the available ecotoxicity da ta and predicted environmenta l exposures, the hypothesis is confirmed for potential adverse eff ects to birds, terrestrial-phase amphibians, reptiles, mammals, terrestrial plants, terrestrial invertebrates and aqua tic plants (vascular and algae/diatoms) based on the registered uses for tebuthiuron. Results of the risk estimation indicate aquatic animals are notPage 64 of 121 expected to be affected. Label protections for beneficial insects are not required. The following sections discuss the potential risks of tebuthiuron to these taxonomic groups.

4.2.1. Risks to Aquatic Animals and Plants

In the conceptual model, spray drift and surface runoff/leaching to adjacent bodies of water were predicted as the most likely sources of exposur e of tebuthiuron to non-target aquatic organisms and plants. Risks to aquatic species ( i.e. , fish, invertebrates, and plan ts) were assessed based on modeled estimated environmental concentrations ( EECs) and available toxicity data. The aquatic EECs for the ecological exposure to the TGAI we re estimated using the PRZM/EXAMS model to evaluate whether the potential for exposure is nationwide or limited to certain locations ( Table

3.8 ).

Risk to Aquatic Organisms

Available acute toxicity data indi cates that tebuthiuron is practical ly non-toxic to fi sh and generally practically non-toxi c to invertebrates on an acute basis. The pink shrimp was the only aquatic animal to show slight sensitivity to tebuthiur on. The other invertebrates exposed to tebuthiuron were the daphnid, fiddler crab, and oyster bivalve; none of them we re affected up to the highest concentration tested. The acute endpoint for pink shrimp, the most sensitive aquatic animal from the available studies, was compared to PR ZM/EXAMS peak EECs for non-target fish and invertebrates inhabiting waterbodies adjacent to fields applied with tebuthiuron. The highest acute RQ was 0.02, which did not exceed the Agency’s endangered species LOC of 0.05. With a maximum RQ of 0.02 for acute effect s to aquatic animals, the probabi lity for acute effect is 1 in

9x10 18 or lower.

The lowest test level of no observed adverse reproduction ef fects for aquatic animals ( i.e. , 9.3 mg a.i./L based on reduced length in fathead mi nnow) was compared to PRZM/EXAMS 60-day EECs for non-target organism exposed to tebuthiuron as a result of surface water runoff and spray drift. The highest chronic RQ was 0.2, which is be low the chronic LOC of 1.0. Aquatic animals, including aquatic-phase amphibians for which fres hwater fish served as a surrogate, are not anticipated to be at risk for a dverse effects on survival, reproduc tion, and growth when exposed to

tebuthiuron.

Bluegills exposed to tebuthiuron concentrations of 5.0 ppm demonstrated bioconcentration factors of 1.98, 3.40, and 2.63 for edible tissue, nonedible tissue, a nd whole fish, respectively. Accumulated residues depurated ra pidly from fish tissue with de puration half-liv es of 0.33 and 0.51 days reported for edible and non edible tissue, respectively, whic h indicates tebuthiuron is not expected to bioaccumulate in fish. An asse ssment using the Agency’s KABAM (KOW (based) Aquatic BioAccumulation Model) v1.0 model was not conducted si nce both the environmental properties of tebuthiuron and results of bioconcen tration studies indicated bioaccumulation in fish and biomagnification through th e food chain is unlikely.Page 65 of 121 Risk to Aquatic Vascular and Non-Vascular Plants

The most sensitive EC 50 ’s derived from the duckweed ( Lemna gibba ) study for aquatic vascular plants and from available studies for aquatic non-v ascular plants (marine diatom) were compared to EECs from several PRZM/EXAMs exposure scenarios for non-targ et, non-listed plants inhabiting bodies of water adjacen t to fields treated with tebu thiuron. Non-listed plant RQs for aquatic vascular and non-vascular plants exceeded the non-listed plant species LOC of 1 following one broadcast application of tebuthiuron at 4 and 6 lb a.i./A (RQs = 2-22).

The corresponding NOAECs derived from the duckw eed study for aquatic vascular plants and from the marine diatom study for aquatic non- vascular plants were compared to several PRZM/EXAMs exposure scenarios fo r non-target Federally-listed pl ants inhabiting bodies of water adjacent to fields treated with tebuthiur on. Listed plant RQs for aquatic vascular and nonvascular plants all exceeded the listed plant sp ecies LOC of 1 for tebuthiuron uses (RQs = 4-29).

To assess the range of sensi tivity in aquatic non-vascular pl ant species when exposed to tebuthiuron, a comparison of the least sensitive species (blue-green algae EC 50 of 0.81 mg a.i./L) and the most conservative PRZM/EXAMS EEC using the TX alfalfa scenario (1.1 mg a.i./L) yields an RQ of 1.4 which does exceed the plant LOC of 1.0. Thus it is anticipated that all algae would be adversely affected when exposed to tebuthiuron. Aquatic vascular plant data were limited to the duckweed study; therefore, the range of sensitivity in aquatic vascular plants adversely affected by tebuthiuron applications could not be assessed.

In addition, the labels state that tebuthiuron is a th iadiazolylurea herbicide th at is readily absorbed through the roots and translocated. Once it enters th e plant, it acts by inhibiting photosynthesis in the plant. Thus, some herbicidal effect s to aquatic plants are anticipated.

The AgDRIFT spray drift model was used to assess the distance from the edge of a site at which RQs for spray drift fall below the aquatic plant LOC of 1 ( Table 4.11 ). The RQs were calculated by comparing the amount of deposition at a spec ific distance (EEC) and the toxicity endpoints for duckweed and marine diatom (EC 50 ). As the distance increases, the chance for exposure to non-target species outside a treated site increases. This spray dr ift exposure analysis indicates that when aerial-based applica tion methods are used (which produc es the highest exposures) at the maximum label rate, exposure falls below th e LOC for the most sensitive aquatic vascular and non-vascular plants at 0 and 10 feet, respectively, off-site. At 4 lb a.i./A, there were no LOC exceedances from spray drift exposures via aer ial or ground application for aquatic plants inhabiting waterbodies (e.g. pond) adjacent to the e dge of a site. Therefor e, adverse effects to non-target aquatic plants in waterbodies adjacent to treated site exposed to spray drift alone at or greater than 10 feet are not likely. This suggest aquatic plants inhabiting water bodies adjacent to treated sites subjected to surf ace water runoff with tebuthiuron residues would more likely be adversely affected than when exposed to off-site spray drift alone.Page 66 of 121 Table 4.11. Spray Drift (Aquatic) Assessment for Non-Target Listed and Non-Listed Aquatic Vascular and Non- Vascular Plant Species

No. of Applications and Application Rate (lb a.i./A) Distance from Edge of Field % of Application

Rate EEC (mg a.i./L) Non-listed

Plant

RQ (EEC/EC 50 ) Listed

Plant RQ (EEC/ NOAEC) Spray

Method

Aquatic vascular plants inhabiting pond a
1 @ 6 0 feet 13 0.04 0.3 0.8 Aerial

A quatic non-vascular plants inhabiting pond b

1 @ 6 0 feet 13 0.04 0.8 1 Aerial 1 @ 6 10 feet 11 0.036 0.7 0.95 1 @ 6 0 feet 2.7 0.009 0.2 0.2 Ground 1 @ 6 10 feet 1.4 0.005 0.1 0.1 1 @ 4 0 feet 13 0.03 0.6 0.8 Aerial 1 @ 4 10 feet 11 0.024 0.5 0.6 1 @ 4 0 feet 2.7 0.006 0.1 0.2 Ground 1 @ 4 10 feet 1.4 0.003 0.06 0.08

a Based on duckweed EC 50 of 0.13 mg a.i./L and NOAEC of 0.05 mg a.i./L. (MRID #41080404)

b Based on marine diatom EC 50 and NOAEC of 0.05 and 0.038 mg a.i./L, respectively. (MRID #41080402) *Value in bold indicates the LOC (=1) is exceeded.

4.2.2. Risks to Terrestrial Animals and Plants

In the conceptual model, dietary ingestion of tebuthiuron residues on ve getative matter, insects and granules on treated areas are predicted as the most likely sour ces of tebuthiuron exposure to terrestrial animals. Spray drift, runoff and wind er osion of soil particles wi th resulting residues on upland and/or wetland foliage and soil are the most likely sources of tebuthiuron exposure to nontarget terrestrial plants, including Federally-lis ted endangered and threat ened species. Risks to terrestrial species ( i.e. , birds, mammals and plants) are assessed based on modeled estimated environmental concentrations (EECs) and available toxicity data. Terrestrial EECs for ecological exposure to the TGAI are estimated using T-REX ( Tables 3.9, 3.10, and 3.11 ) and TerrPlant ( Table 3.12 ).

Risk to Terrestrial Animals

Available avian acute toxicity data indicate that te buthiuron is practically non-toxic to upland game

birds and waterfowl on an acute basis for both oral and dietary routes ( e.g. , >2000 mg a.i./kg bw and >5113 mg a.i./kg diet). However, the TGAI is slightly toxic to passeri ne birds via the dietary route; the dietary-based LC 50 for passerines is 1465 mg a.i./kg di et as a result of counting extremely low food consumption as mortal ities since the birds would not survive througho ut the test, including those birds th at died. Dietary-based risk quotient calculations focusing on the most conservative T-REX scenario using the short gr ass EEC of 1440 mg a.i./kg diet was 10 times higher than EPA’s LOC of 0.1 for potential risk to Federally-li sted endangered and threatened birds and 2 times higher than EPA’s LOC of 0.5 for potential risk to non- listed birds. Using the maximum RQ of 0.98 for short grass based upon a br oadcast application of 6 lb a.i./A and 20 g birds, this indicates 1 in 2 small-sized birds that consume tebuthiuron-treat ed short grass would bePage 67 of 121 affected. At 4 lb a.i./A of the same scenario with highest RQ at 0.66, 1 in 8.3 small-sized birds

would be affected.

Meanwhile, since dietary concentrations that caus ed no mortality or acute sub-lethal effects in bobwhite quail and mallard are 3.5x environmentally re levant concentrations, acute risk to upland and waterfowl birds is anticipated to be low.

Chronic avian RQs for ground spray of tebuthiuron were above the ch ronic risk LOC of 1, with a calculated maximum RQ of 14.4.

Acute and chronic RQs for granular and pellet applications were not available. All acute dosebased endpoints were non-definitive and tools to model chronic EEC s were not available in this screening-level assessment; thus , the RQs for granul ar/pellet and spray uses were assumed equivalent. However, an uncertainty is introduced since this assumption is that all formulations are 100% tebuthiuron. With granular and pelleted formulations containing up to 5% and 40% of tebuthiuron, respectively, it is uncertain the RQs fo r granular and pellet uses are as high as the

spray uses.

No mortalities were observed in the acute studie s with the upland game bird and waterfowl, yet significant sub-lethal effects were observed in the re production studies at 500 mg a.i./kg diet and higher. These same large birds demonstrated no regur gitation or food avoidance of the test material

in the acute oral studies. On th e other hand, smaller birds such as passerines were more acutely sensitive to tebuthiuron due to severe regurgi tation and extreme food avoidance, which these

observations were counted as mort alities in the dietary study. This suggests the acute effects of tebuthiuron may be observed more often in smaller birds compared to larg er birds when exposed to tebuthiuron. While chronic reproduction eff ects were not evaluated for small birds ( i.e.

, passerines), as growth and repr oduction (chronic) effects were obs erved in other avian species, chronic effects could be anticipated in several bird class sizes.

Available mammalian acute toxicity data indicate that tebuthiuron is moderately toxic to mammals on an acute oral basis. Dose-based RQ calcula tions focusing on the most conservative T-REX scenario indicate that the short grass EEC of 144 0 mg a.i./kg diet is 16 times higher than EPA’s LOC of 0.1 for potential risk to Federally-listed endangered and threatened mammals and 3 times higher than EPA’s LOC of 0.5 for po tential risk to non-listed mamm als. In addition, rabbits are slightly more acutely sensitive to tebuthiuron than rats; RQs calculated using the rabbit toxicity endpoint would be more than 16 times higher than the LOC. These acute LOC exceedances indicate mammals may be at risk for adverse effects on survival from exposure to tebuthiuron. Using the maximum RQ of 1.6 for short grass an d 15 g mammals, 1 in 1.22 small-sized mammals

that consume tebuthiuron-trea ted short grass would be aff ected. A maximum RQ of 4.9 for granules and 15 g mammals indicates that 1 in 1 small-sized mammals that consume granules

would be affected.

Based on the most sensitive mammalian 2- generation NOAEL and upper bound T-REX EECs, the dose-based RQs of 13-45 exceed the chronic LO C for 15 g, 35 g and 1000 g mammals foraging on short grass, tall grass, broadleaves and arthro pods following one tebuthiuron application at 4 orPage 68 of 121 6 lb a.i./A. For the dietary-based risk estimations , the results were similar; however, there were no LOC exceedances for mammals foraging on fruits/s eeds/pods (highest RQ = 0.45). Thus, these exceedances indicate mammals may be at potential risk for adverse effects on reproduction and growth from exposure to tebuthiuron as a resu lt of the labeled uses of the herbicide.

Those adverse effects discussed above would be observed for those terrestrial vertebrates that

remain in a tebuthiuron-treated site all the time. The less amount of time a bird or mammal remains in the treated site, the less the risk to terrestrial vertebrates. Also, the smaller the application site ( i.e. driveway vs. agricultural field) is, the less chance for terrestria l vertebrates to be at risk.

Considering the maximum single tebuthiuron app lication at 6.0 lbs a.i./A, the potential for adversely affecting the reproduction and growth of terrestrial animals in treated sites is likely. Reducing the application rate would mitigate risks to birds and mammals residing inside the treated site. A reduced application rate that would not result in an acute LOC ex ceedance for birds would be 0.35 lb a.i./A. For mammals, it would be 0.14 lb a.i./A. At 6.0 lbs a.i./A, the mitigated applications for birds and mammals need to be reduced 17x and 40x, respectively, of the maximum application rate. Using the maximum application rate as an example, Graphs 4-1 and 4-2 illustrate the days needed to exceed the chronic LOC for adve rse effects to birds and mammals, respectively, foraging on food resources in fields /sites treated with tebuthiuron.

Graph 4-1 below illustrates one tebuthiuron application at the maximum applic ation rate of 6.0 lb a.i./A applied as a broadcast applic ation to selected feed items that terrestrial vertebrates rely as a food resource.. Pictured are the EECs for short grass, tall grass, broadleaf pl ants, fruits/pods/seeds, and arthropods following one application of tebuthiuron. Based on the graph, the upper-bound Kenaga dietary-based EECs exceed the LOC of 1 (NOAEC = 100 mg a.i./kg diet) for birds foraging in tebuthiuron-treated si tes following application. Likewise, the number of days in exceedance of the LOC for reproduction and growth effects to birds that forage on vegetation in tebuthiuron-treated sites lasts approximately 80-140 days, the longest when foraging on short grass. Arthropods covered with tebuthiuron resi dues may be toxic to birds for 55 days. T-REX provides graphs for dietary-based assessments onl y; graphs for dose-based assessments are not

available.Page 69 of 121 Graph 4-1. Number of a pplications and days needed to exceed the LO C of 1 for adverse effects of growth and reproduction to birds following tebuth iuron application at 6 lb/A on rangeland and pastures as per label

directions.

In Graph 4-2 , the upper-bound Kenaga dietary-based EECs exceed the LOC of 1 (NOAEC = 200 mg a.i./kg diet) for mammals fora ging in tebuthiuron-trea ted sites following application. Likewise, the number of days in exceedance of the LOC fo r reproduction and growth effects to mammals that forage on short grass, broadleaves, tall gra ss, and arthropods in tebuthiuron-treated sites lasts approximately 100, 75, 60, and 50 days, respectively.Page 70 of 121 Graph 4-2. Number of a pplications and days needed to exceed the LO C of 1 for adverse effects of growth and reproduction to mammals following tebuthiuron applicatio n at 6 lb/A on rangeland and pastures as per label

directions.

AgDRIFT was used to assess whether the LOC ex ceedances should apply to non-target birds and

mammals that inhabits areas outside tebuthiuron-treated sites. Table 4.12 shows the spray drift distances estimated using LOCs di vided by risk quotients (calculate d based on a single application) as the “Fraction of Applied” in AgDRIFT to estima te the spray drift distance for terrestrial animals. The spray drift exposure analysis indicates that for aer ial-based applications, the RQ falls below

the LOC for the non-listed bird and mammal at 138 and 479 feet, respectively, off-site. For groundbased applications, the RQ falls below the LOC for bird and mammal at 39 and 125 feet, respectively. This suggests that effects to non-targ et terrestrial vertebrate s could occur outside the site of application.Page 71 of 121 Risk to Terrestrial Monocots and Dicots

Based on the available data, monocots are less sens itive to tebuthiuron than dicots. The RQs for runoff to semi-aquatic areas result in the highest RQs compared to dry areas. This scenario represents a 10 acre area running off into a one acre area. The highest RQ for a combination of runoff and spray drift to semi-aquatic areas is 1031, which exceeds the Agency’s LOC of 1 for potential risk to plants. Sinc e the herbicide is absorbed th rough the roots and translocated throughout, the plant the LOC exceedance for potentia l risk to non-listed and listed plants inhabiting semi-aquatic ar eas cannot be discounted.

AgDRIFT was used to assess whether the LOC ex ceedances should apply to non-target terrestrial plants in dry ( Table 4.13 ) and semi-aquatic ( Table 4.14 ) areas adjacent to tebuthiuron-treated sites. The spray drift exposure analysis indicates that for aerial-based applications, exposure falls

below the LOC for non-listed and lis ted terrestrial plant e xposed to tebuthiuron as a result of spray drift at and greater than 997 feet off-site. Howe ver, for ground-based applications, exposure falls below the LOC at approximately 500 and >997 feet for non-listed and listed plants, respectively. This suggests that effects to non-target terrestrial plants could occur outside the site of application. Table 4.12. Spray Drift (Terrestrial) Assessment for Non-Listed Terrestrial Vertebrate Species Exposed to 6 lb a.i./A Tebuthiuron

Taxa Type of Endpoint Highest Risk Quotient LOC* Fraction of Applied (LOC/RQ) Distance from Edge of Field

Where RQ

Falls below

LOC

Aerial Applications

Birds Acute 0.98 0.5 0.51 0 feet

Chronic 14 1 0.07 138 feet

Mammals Acute 1.6 0.5 0.3 16 feet

Chronic 45 1 0.02 479 feet

Ground applications

Birds Acute 0.98 0.5 0.51 7 feet

Chronic 14 1 0.07 39 feet

Mammals Acute 1.6 0.5 0.3 10 feet

Chronic 45 1 0.02 125 feet

* The LOCs shown are for non-listed species.Page 72 of 121 In addition to the AgDRIFT assessment using the mo st sensitive plant species, an assessment was conducted on the least sensitive plant species and th e highest exposure scenario to observe whether all or some terrestrial plants would be affected when exposed. Corn was used as the least sensitive species with seedling emergence EC 25 and NOAEC values of 3.1 and 2.0 lb a.i./A, respectively. For plants inhabiting dry area ad jacent a treated site, AgDRIFT i ndicates exposure to drift from aerial and ground broadcast appl ications using the corn EC 25 and NOAEC values does not exceed

the LOC for both non-listed and list ed plant species beyond a distance of 50 feet from the edge of a site ( Table 4.15 ), suggesting exposure is limited to the treated site. Neverthe less, with the least sensitive NOAEC (corn) of the 10 test species no t exceeding the LOC for listed species inhabiting semi-aquatic areas beyond the edge of a treated site as well ( Table 4.16 ), it is anticipated that potential risk to not all but some listed terrestr ial plants exposed to o ff-site drift is likely.

Overall, there is a potential of risk for adverse effects on survival and growth to terrestrial monocots and dicots, including Fede rally-listed endangered and threat ened species, that inhabit dry and semi-aquatic areas adjacen t to tebuthiuron-treated fields through a combination of runoff and spray drift or by drift alone. Sp ray drift from granular/pelleted/ta bleted uses is expected to be negligible; however, risk to plants from ru noff-borne residues alon e cannot be discounted ( Discussed in Table 4.10 ).

Table 4.13. Spray Drift (Terrestrial) Assessme nt for Non-target Listed and Non-listed Terrestrial Plant Species a

No. of Applications and Application Rate (lb a.i/.A) Distance from Edge of Field % of Application

Rate Dry Area

EEC (lb a.i./A) Non-listed

Plant RQ Listed

Plant RQ Spray

Method

Terrestrial plants inhabiting dry areas
1 @ 6 0 feet 0.5 3 167 938

Aerial 1 @ 6 50 feet 0.17 1 56 313
1 @ 6 500 feet 0.02 0.1 6 31
1 @ 6 997 feet 0.01 0.07 4 22
1 @ 6 0 feet 1 6.0 352 1978

Ground 1 @ 6 50 feet 0.05 0.3 17 94
1 @ 6 500 feet 0.004 0.02 1 6
1 @ 6 997 feet 0.001 0.0085 0.7 3

a Based on carrot EC 25 of 0.018 lb a.i./A and EC 05 of 0.0032 lb a.i./A.

*Value in bold indicates the LOC is exceeded.Page 73 of 121 Table 4.14. Spray Drift (Aquatic) Assessment for Listed and Non-Listed Terrestrial Plant Species a

No. of Applications and Application Rate (lb a.i./A) Distance from Edge of Field % of Application

Rate Semi-Aquatic

EEC (lb a.i./A) Non-listed

Plant RQ Listed

Plant RQ Spray

Method

Terrestrial plants inhabiting semi-aquatic areas 1 @ 6 0 feet 0.1 0.8 44 250

Aerial 1 @ 6 50 feet 0.07 0.4 22 125 1 @ 6 500 feet 0.02 0.1 6 31 1 @ 6 997 feet 0.01 0.07 4 22
1 @ 6 0 feet 0.06 0.37 21 116

Ground 1 @ 6 50 feet 0.02 0.1 6 31 1 @ 6 500 feet 0.003 0.02 1 6 1 @ 6 997 feet 0.001 0.007 0.4 2

a Based on carrot EC 25 of 0.018 lb a.i./A and EC 05 of 0.0032 lb a.i./A

*Value in bold indicates the LOC is exceeded.

Table 4.15. Spray Drift (Terrestrial) Assessme nt for Least Sensit ive Terrestrial Plant Species a

No. of Applications and Application Rate (lb a.i/.A) Distance from Edge of Field % of Application

Rate Dry Area

EEC (lb a.i./A) Non-listed

Plant RQ Listed

Plant RQ Spray

Method

Terrestrial plants inhabiting dry areas
1 @ 6 0 feet 50 3 0.97 1.5 Aerial 1 @ 6 50 feet 17 1 <0.1 0.5
1 @ 6 0 feet 100 6 1.9 3 Ground 1 @ 6 50 feet 1.7 0.1 0.03 0.05
1 @ 4 0 feet 50 2 0.6 1 Aerial 1 @ 4 50 feet 17 0.7 0.2 0.4
1 @ 4 0 feet 100 4 1.3 2 Ground 1 @ 4 50 feet 1.7 0.07 0.02 0.04

a Based on corn EC 25 of 3.1 lb a.i./A and NOAEC of 2.0 lb a.i./A.

*Value in bold indicates the LOC is exceeded.Page 74 of 121 Table 4.16. Spray Drift (Aquatic) Assessment fo r Least Sensitive Terrestrial Plant Species a

No. of Applications and Application Rate (lb a.i/.A) Distance from Edge of Field % of Application

Rate Semi-aquatic

Area EEC (lb a.i./A) Non-listed

Plant RQ Listed

Plant RQ Spray

Method

Terrestrial plants inhabiting semi-aquatic areas
1 @ 6 0 feet 13 0.75 0.2 0.4 Aerial 1 @ 6 50 feet 7.3 0.44 0.1 0.2
1 @ 6 0 feet 6.2 0.37 0.1 0.2 Ground 1 @ 6 50 feet 1.9 0.11 0.04 0.06
1 @ 4 0 feet 13 0.5 0.2 0.3 Aerial 1 @ 4 50 feet 7.3 0.29 0.09 0.1
1 @ 4 0 feet 6.2 0.25 0.08 0.1 Ground 1 @ 4 50 feet 1.9 0.08 0.03 0.04

a Based on corn EC 25 of 3.1 lb a.i./A and NOAEC of 2.0 lb a.i./A.

*Value in bold indicates the LOC is exceeded.

Risk to Beneficial Insects and Terrestrial Invertebrates

The available beneficial insect toxicity data, based on tests with honeybees, suggest that the TGAI is practically non-toxic to bees on an acute contact basis. The LD 50 value is >100 μg a.i./bee. Risk

to beneficial insects in the direct treatment area e xposed to tebuthiuron is expected to be minimal; consequently, precautionary labeling for honeybee protection is not required at this time.

For the assessment on terrestrial invertebrates, no mortality occurred in the honeybee study at concentrations as high as 100 μg a.i./bee. Howe ver, two studies (Doerr, T.B. 1980 and Zavaleta, J. 2012) suggest tebuthiuron does not affect terres trial invertebrates, but increases the abundance and number of families in treated areas compared to untreated areas. However, Zavaleta reported

that selected individual invert ebrate taxonomic groups reacted diffe rently to treatment with a 200% increase in grasshoppers and a 92% decrease in ca terpillar larvae; treehoppers were not affected. No toxicity endpoints were provided; thus, it was not possible to assess whether the reduction in the larvae of caterpillars was a re sult of tebuthiuron treatment or a reduction in forb cover. Hagen et al. (2005) and Jamison (2002) s uggest invertebrate abundance is dependent on herbaceous cover and structure, with invertebrates increasing in trea ted areas with more forb than in untreated areas.

Regardless of the effects, the adverse effects of the use patterns outside the target area would

extend no farther than 100 feet off site. Accordi ng to AgDRIFT and bee toxicity as a surrogate value, the potential for risk to non-target terrestrial invertebrates adjacent to treated sites exposed

to tebuthiuron falls below the interim LOC of 0 .05 for terrestrial inverteb rates at approximately 100 feet off-site from the edge of the fi eld as a result of aerial application. ( Table 4.17 ). Until definitive endpoints are available for listed terrestr ial invertebrates, it is uncertain whether all, some, or none of the listed terrestrial inverteb rates would be adversely affected when exposed directly to tebuthiuron.Page 75 of 121 In addition, there is an uncertainty of the LOC exceedances for terrestrial invertebrates. While the RQ of 0.36 may exceed the LOC of 0.05, it is uncerta in whether there are actually any adverse

effects for terrestrial invertebrate s since no effects occurred at the highest dose tested. The highest RQ could be much lower than 0.36.

Table 4.17. Spray Drift (Terrestrial) Assessment for Listed Terrestrial Invertebrate Species a

No. of Applications and Application rate (lb a.i/.A) Distance from Edge of Field % of Application

Rate Dry Area

EEC (lb a.i./A) Listed

Terrestrial Invertebrate RQ Spray Method

Terrestrial invertebrate s inhabiting dry areas
1 @ 6 0 feet 0.5 3 0.36

Aerial 1 @ 6 50 feet 0.17 1 0.12 1 @ 6 100 feet 0.1 0.6 0.07 1 @ 6 500 feet 0.02 0.1 <0.01

a Based on honeybee LD 50 of >100 μg a.i./bee where 0% mortality was ob served. This is equivalent to an exposure of 780 mg/kg body weight or 8.3 lb T-REX/A assuming 1.0 lb/A = 94 mg T-REX arthropod/kg for terrestrial

invertebrates.

*Value in bold indicates the LOC of 0.05 is exceeded.

Taxa Exposed to Tebuthiuron As a Resu lt of Spot Treatment Applications

There is uncertainty with the risk assessment fo r spot treatment uses. EFED has modified the risk assessment for spot treatment uses using an assumption that the rates are broadcast ( Table

4.18 ). While aerial applications is permitted in some labels; however, to characterize the risks from spot treatment uses, only ground and gran ular application scenarios were used. EFED believes that exposure estimates for resources are overly conservative for spot treatments because the underlying assumption in the models is that 100% of the field is treated with the pesticide. In order to better characterize the importance of th e 100% area treated assumption on the overall risk conclusions; an estimate of th e area threshold of spot treatment for each taxon where the LOC would no longe r be exceeded is given.

As an example, it is estimated that for the highe st application rate (i.e. 6 lbs a.i./acre) the area

treated would need to exceed 10% for the LOC to be exceeded for birds. However, EFED does not have information on typical spot treatment area percentages. Also, the labels that do specify spot treatment and the total ar ea the container can cover (squar e feet) can be compared with

Table 4.18 to determine whether effects are possible from these uses.Page 76 of 121 Table 4.18 Area Percentage of Spot Treatment Us es (Spray or Granules) Needed to Exceed

the LOC
Taxa Application

rates (lb a.i./A) RQs assuming

100% area

treated (highest to lowest)* LOC Area Percentage of application

needed to exceed

LOC 1

Birds (acute effects, liquid spray, broadcast) 6 0.98

Acute = 0.1 10%

4 0.66 15%

Mammals (acute effects, liquid spray, broadcast) 6 1.6 6%

4 1.1 9%

Birds (acute effects, granules and pellets, broadcast) 6 No granule or pellets RQs

were calculated;

assumed equivalent to liquid spray RQs --
4

--

Mammals (acute effects, pellets, broadcast) 6 1.96 5%

4 1.31 8%

Mammals (acute effects, granules, broadcast) 6 0.24 42%

4 0.16 63%

Birds (chronic effects,broadcast, dietarybased) 6 14

Chronic = 1.0 7%

4 10 10%

Mammals (chronic effects, liquid spray,broadcast, dietarybased) 6 7 14%

4 5

20%

Mammals (chronic effects, broadcast, liquid spray, dose-based) 6 45 2%

4 30 3%

Terrestrial Plants (non-listed effects, liquid spray, ground, broadcast) 6 170

Non-listed and listed plants = 1.0 0.6%

4 113 0.9%

Terrestrial Plants 6 956 0.1%Page 77 of 121 Table 4.18 Area Percentage of Spot Treatment Us es (Spray or Granules) Needed to Exceed

the LOC
Taxa Application

rates (lb a.i./A) RQs assuming

100% area

treated (highest to lowest)* LOC Area Percentage of application

needed to exceed

LOC 1

(listed effects, liquid spray, ground, broadcast) 4 638

0.2%

Terrestrial Plants (non-listed effects, granules, ground, broadcast) 6 167 0.6%

4 111 0.9%

Terrestrial Plants (listed effects, granules, ground, broadcast) 6 938 0.1%

4 625 0.2%

Aquatic vascular plants (non-listed effects, liquid spray, ground, broadcast) 6 8 13%

4 5 20%

Aquatic vascular plants (listed effects, liquid spray, ground, broadcast) 6 20 5%

4 14 7%

Aquatic nonvascular plants (non-listed effects, liquid spray, ground, broadcast) 6 20 5%

4 14 7%

Aquatic nonvascular plants (listed effects, liquid spray, ground, broadcast) 6 26 4%

4 18 6%

Aquatic vascular plants (non-listed effects, granules, ground, broadcast) 6 8 13%

4 5 20%

Aquatic vascular plants 6 20 5%

4 13 8%Page 78 of 121 Table 4.18 Area Percentage of Spot Treatment Us es (Spray or Granules) Needed to Exceed

the LOC
Taxa Application

rates (lb a.i./A) RQs assuming

100% area

treated (highest to lowest)* LOC Area Percentage of application

needed to exceed

LOC 1

(listed effects, granules, ground, broadcast)
Aquatic nonvascular plants (non-listed effects, granules, ground, broadcast) 6 20 5%

4 13 8%

Aquatic nonvascular plants (listed effects, granules, ground, broadcast) 6 26 4%

4 17 6%

*Bold values indicate LOC exceedance

1 The threshold percentage is assessed to determine how much percent of exposure that RQ needs to exceed the LOC. For example, the highest acute RQ for birds inhabiting a field treated at 6 lb a.i./A is 0.98, which is up to 10x the listed species LOC of 0.1; to assess the % of exposure needed at which the LOC exceedance occurred, results indicate 10% is needed for the RQ to exceed the LOC. A “no effect” or “may affect” determination was not made

since it is unknown what % of an actual area is typical spot treatment.



### 5. Federally Threatened and Endang ered (Listed) Species Concerns

Section 7 of the Endangered Species Act, 16 U.S.C. Section 1536(a)(2), requires all federal agencies to consult with the National Marine Fisheries Service (NMFS) for marine and anadromous listed species, and/or the United Stat es Fish and Wildlife Serv ice (USFWS) for listed wildlife and freshwater organisms, if they are proposing an "action" that may affect listed species or their designated critical habita t. Each federal agency is requi red under the Act to ensure that any action they authorize, fund, or carry out is not likely to jeopa rdize the continued existence of a listed species or result in the destruction or adve rse modification of designated critical habitat. To jeopardize the continued exis tence of a listed species means "to engage in an action that reasonably would be expected, dire ctly or indirectly, to reduce appreciably the likelihood of both the survival and recovery of a listed species in the wild by reduc ing the reproduction, numbers, or distribution of the species" (50 C.F.R. § 402.02).

To facilitate compliance with the requirements of the Endangered Species Act (subsection (a)(2)), the Office of Pesticide Programs has establishe d procedures to evaluate whether a proposed registration action may directly or indirectly appreciabl y reduce the likelihood of both the survival and recovery of a listed species in the wild by reduci ng the reproduction, numbers, or distributionPage 79 of 121 of any listed species (U SEPA, 2004). After the Agency’s sc reening level risk assessment is conducted, if any of the Agency’s listed species’ LOCs are exceeded fo r either direct or indirect effects, an analysis is conducted to determine if any listed or candidate species may co-occur in the area of the proposed pesticide use or ar eas downstream or downwind that could be

contaminated from drift or runoff/erosion. If lis ted or candidate species may be present in the proposed action area, further biological assessmen t is undertaken. The extent to which listed species may be at risk is considered, which then determines the need for the development of a more comprehensive consultation package, as required by the Enda ngered Species Act.

The federal action addressed herein is the pr oposed renewed registration of tebuthiuron on agricultural use sites. It is expected that its use could occur nationwide.

5.1. Action Area

For listed species assessment purposes, the action area is considered to be the area affected directly or indirectly by tebuthiuron use and not merely th e immediate area where tebuthiuron is applied. At the initial baseline, the risk assessment considers broadly described taxonomic groups and conservatively assumes that listed species with in those broad groups are co-located with the pesticide treatment area. This means that listed terrestrial plants and wildlife are assumed to be located on or adjacent to the treated site and listed aquatic organisms are assumed to be located in a surface water body adjacent to the treated site. The assessment also assumes that the listed species are located within an assumed area, whic h has the relatively highest potential exposure to the pesticide, and that exposures are likely to decrease with distance from the treatment area.

5.2. Taxonomic Groups Po tentially at Risk

If the assumptions associated with the baseline action area result in RQs that are below the listed species LOCs, a "no effect" determin ation conclusion is made with respect to listed species in that taxa, and no further refinement of the action area is necessary. Furthermore, RQs below the listed species LOCs for a given taxonomic group indicate no concern for indirect e ffects on listed species that depend upon the taxonomic group for which the RQ was calculated. However, in situations where the screening assumptions lead to RQs in excess of the listed species LOCs for a given taxonomic group, a potential for a "may affect" conclusi on exists and may be associated with direct effects on listed species belongi ng to that taxonomic group or ma y extend to indirect effects upon listed species that depend upon that taxonomic gr oup as a resource. In such cases, additional information on the biology of listed species, the loca tions of these species, and the locations of use sites are considered to determine the extent to which screening assumptions regarding an action area apply to a particular listed organism. Thes e subsequent refinement steps will consider how this information would impact the action area fo r a particular listed organism and potentially include areas of exposure that are downwind and downstream of the pesticide use site.

Assessment endpoints, exposure pathways, and th e conceptual models addressing tebuthiuron uses, and the associated exposure and effects analyses conducted fo r the tebuthiuron baseline risk

assessment are in Sections 2 to 3 . The assessment endpoints used in the baseline risk assessment include those defined operationa lly as reduced survival and reproductive impairment for bothPage 80 of 121 aquatic and terrestrial animal species and surv ival, reproduction, and gr owth of aquatic and terrestrial plant species from bot h direct acute and chronic exposur es. These assessment endpoints

are intended to address the sta ndard set forth in th e Endangered Species Act requiring federal agencies to ensure that any action they authorize does not appreciably reduce the likelihood of both the survival and recovery of a listed speci es in the wild by re ducing the reproduction, numbers, or distribution of the species. Risk estimates (RQs) which, integrating exposure and effects, are calculated for broad based taxonomic groups in the screening-level risk assessment presented in Section 4.

Both acute endangered species and chronic risk LOCs are considered in the baseline risk assessment to identify direct and indi rect effects to taxa of listed species. This section identifies direct effect concerns, by taxa that are triggered by exceeding endangered LOCs in the baseline risk assessment, with an evaluation of the potenti al probability of indivi dual effects for exposures that may occur at the established endangered spec ies LOC. Data on exposure and effects collected under field and laboratory conditions are evaluated to make determinations on the predictive utility of the direct effect screening assessment findings to listed species. Potentia l for direct effects to

listed taxa are described in Table 5.1

.

Table 5.1. Potential Effects to Federally-Listed Taxa Associated with Direct Effects from the Registered Uses of Tebuthiuron.

Listed Plant Taxon Potential Direct Effects Terrestrial and semi-aquatic plants –

monocots and dicots Yes*

Aquatic nonvascular plants Yes* Aquatic vascular plants Yes*

Listed Animal Taxon Potential Direct Effects

Acute Chronic

Terrestrial invertebrates Uncertain 1 N/A 2

Mammals Yes* Yes*

Birds Yes* for small-sized classes;No effect for mid- and largesized classes Yes* (all size classes)

Reptiles 3 Yes* Yes* Terrestrial-phase amphibians 3 Yes* Yes*

Freshwater fish No Effect No Effect Aquatic-phase amphibians 4 No Effect No Effect

Freshwater invertebrates No Effect No Effect

Estuarine/marine fish No Effect No Effect

Estuarine/marine invertebra tes No Effect No EffectPage 81 of 121 

### 6. Literature Cited

Tomlin CDS, ed. Tebuthiuron ( 34014-18-1). In: The e-Pesticide Manual, 13th Edition Version 3.1 (2004-05). Surrey UK, British Crop Protection Council.

USEPA, 2009. Registration Review -Preliminary Problem Form ulation for Ecological Risk and Environmental Fate, Endangered speci es and Drinking Water Assessments for Tebuthiuron (PC Code 105501; DP Barcode D363982).

USEPA, 2004. Tier II Aquatic Exposure Asse ssment for Selected Tebuthiuron Uses on Rangeland, Pastureland, and Other Non- Crop Lands in the Pacific Northwest: Endangered Species (ES) Consultation Package.

USEPA, 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. Office of Prevention, Pesticides, an d Toxic Substances. Office of Pesticide Programs. Washington, D.C. January 23, 2004.

USEPA. 2013. Pesticides: Science and Po licy. Terrestrial Mode ls, T-REX Version 1.5.2. http://www.epa.gov/oppefed1/models/terrestrial/

USEPA. 2013a. Pesticides: Science and Polic y. Terrestrial Models , TerrPlant Version 1.2.2. http://www.epa.gov/oppefed1/models/terrestrial/

Zavaleta, J. 2012. Community Response to use of Prescribed Grazing and Tebuthiuron Herbicide

for Restoration of Sand Shinne ry Oak Communities. M.S. Thesis. Texas Tech University.

Doerr, T. (1980). Effects of tebuthiuron on lesser prairie chicken habita t and food supplies. M.S. Thesis, Texas Tech University, Lubbock.

Doerr, T., & Guthery, F. (1980). Effects of shinnery oak control on lesser pr airie chicken habitat. pp. 59-63. In: P. A. Vohs and F. L. Knopf, editors, Proceedings of the Prairie Grouse Symposium . Stillwater: Oklahoma State University. 89 pp.

Doerr, T., & Guthery, F. (1983). Effects of te buthiuron on lesser prairi e chicken habitat and

foods. Journal of Wildlife Management 47: 1138-1142

Hagen, C. A, G. C. Salter, J. C. Pitman, R. J. Robel, and R. D. Applegate. 2005. Lesser prairiechicken brood habitat in sand sagebrush: invertebrate biomass and vegetation. Wildlife Society Bulletin 33(3): 1080-1091.

Jamison, B. E., R. J. Robel, J. S. Pontius, and R. D. Applegate. 2002. Invertebrate biomass: associations with lesser prairie-chicken habitat use and sand sagebrush density in southwestern Kansas. Wildlife Society Bulletin 30: 517-526Page 82 of 121 

### Submitted Ecological Effects Studies

MRID 00041679 Todd, G.C.; Kehr, C.C.; West, H.C.; et al. (1972) The Acute Toxicity of EL-103 in Mice, Rats, Rabbits, Cats, Dogs, Quail, Ducks, Chickens, and Fish. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00020661 Todd, G.C.; Kehr, C.C.; West, H.C.; et al. (1972) The Acute Toxicity of EL-103 in Mice, Rats, Rabbits, Cats, Dogs, Quail, Ducks, Chickens, and Fish. Unpublished study prepared by Lilly Research Laboratories in cooperation with Biono mics, Inc. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041692 Kehr, C.C.; Hamelink, J.L.; Todd, G.C.; et al. (1978) The Acute Oral Toxicity of Compound 75503 (EL-103) in Mallard Ducks: Study 7021- 77. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041680 West, H.C.; Hamelink, J.L. (1976) The Acut e Toxicity of Compound 75503 (EL-103) in Mallards (Anas platyrhynchos): Eight Day Dietary Study 9007-6. Unpublished study prepared by Lilly Research Laboratories. Submitted by El anco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041681 West, H.C.; Hamelink, J.L. (1976) The Acut e Toxicity of Compound 75503 (EL-103) in Bobwhites (Colinus virginianus ): Eight Day Dietary Study 9012- 6. Unpublished study prepared by Lilly Research Laboratories. Submitted by El anco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041693 Kehr, C.C.; Brannon, D.R.; Todd, G.C.; et al. (19 78) Addendum to Section J: Fish and Wildlife Safety: EPA Submission (EL-103): Pasture and Rangeland. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 40601001 Negilski, D.; Grothe, D.; Meyerhoff, R. (1988) The Toxicity of Tebuthiuron to Juvenile Bobwhite in a Five-day Dietary Study. Laboratory Project ID A00188. Unpublished study prepared by Lilly Research Laboratories. Subm itted by Elanco Products Company, Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 40601002Page 83 of 121 Negilski, D.; Grothe, D.; Meyerhoff, R. (1988) Th e Toxicity of Tebuthiur on to Juvenile Mallards in a Five-day Dietary Study. Laboratory Pr oject ID A00288. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elan co Products Company, Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 48928201 Hubbard, P.M, K.H. Martin, and J.B. Beavers. 2012. Tebuthiuron: An LD50/LC50 Study Using Dietary Exposure with the Zebra Finch ( Taeniopygia guttata ). Unpublished study performed by Wildlife International, Ltd., Easton, MD. La boratory Project No. 379-264. Study sponsored by Dow Chemical Company, Midland, MI for Dow Agro Sciences, Indianapolis, IN. Study initiated July 27, 2012 and completed August 31, 2012.

MRID 00093690 Fink, R.; Beavers, J.B.; Brown, R. (1978) Fina l Report: One-generation Reproduction Study with Mallard Duck: Compound 75503, Tebuthiuron. Labor atory Project No. 151-105. Unpublished study prepared by Wildlife International, Lt d., Easton, MD. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00104243 Fink, R.; Beavers, J.B.; Brown, R. (1978) Fina l Report: One-generation Reproduction Study with Bobwhite Quail: Compound 75503, Tebuthiuron . Laboratory Project No. 151-104. Unpublished study prepared by Wildlife International, Lt d., Easton, MD. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041685 Hamelink, J.L.; Kehr, C.C. (1976) The Acute Sta tic Toxicity of Two Formulations of Compound 75503, EL-103, to Fathead Minnows (Studies no. 1012-6, 1013-6, 1014-6). Unpublished study prepared by Lilly Research Laboratories. Subm itted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041683 Hamelink, J.L.; Froman, R.O. (1976) An Acute Study of EL-103 to Daphnia magna Expressed as Tolerance Limit (TL50). Unpublished study prepar ed by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041694 Hamelink, J.L.; Todd, G.C.; Brannon, D.R.; et al. (1978) Acute Toxi city of Compound 75503 (EL-103) to Daphnia magna. Study No. 5058-77. Unpub lished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Di v. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041684 Heitmuller, T.; Parrish, R. (1976) Acute Toxici ty of EL-103 to Embryos of Eastern Oysters (Crassostrea virginica), to Pink Shrimp (Pen aeus duorarum), and to Fiddler Crabs (Uca pugilator). Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.Page 84 of 121 MRID 48722701 York, D. (2011) Tebuthiuron TGAI - Ac ute Toxicity to Eastern Oyster ( Crassostrea virginica ) under Flow-Through Conditions, Following OPPTS Guideline (Draft) 850.1025. Project Number: 12550/6630, 110205. Unpublished study prepared by Smithers Viscient Laboratories, Wareham, MA. Study sponsored by Dow Ch emical Company, Midland, MI for Dow AgroSciences, Indianapolis, IN.

MRID 48722702 Fournier, A.E. 2011. Tebuthi uron - Acute Toxicity to Sheepshead Minnow ( Cyprinodon variegatus ) Under Static-Renewal Conditions, Fo llowing OPPTS Draft Guideline 850.1075. An unpublished study performed by Smithers Viscient, Wareham, MA. Laboratory report number: 12550.6629. Study sponsored by Dow Chemical Compa ny, Midland, MI for Dow AgroSciences, Indianapolis, IN. Sponsor report numb er: 110204. Study initiated March 18, 2011 and completed on November 28, 2011.

MRID 00020735 Hamelink, J.L.; Jordan, W.H.; Kitchen, D.N.; etal. (1978) Final Data Report: Aquatic MiniEcosystem Evaluation of EL-103 (Compound 75503, Tebuthiuron). Unpublished study prepared by Lilly Research Laboratories. Submitted by El anco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00041682 Hamelink, J.L.; Kehr, C.C. (1976) The Acute Toxicity of Compound 75503 (EL-103), Lot B30- 23-149, to Rainbow Trout ( Salmo gairdneri ) and Bluegills ( Lepomis macrochirus ). Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00090083 Sauter, S.; Meyerhoff, R.D.; Todd, G.C.; et al. (1981) The Toxicity of Tebuthiuron (EL-103, Compound 75503) in Water to Rainbow Trout (Sal mo gairdneri) in a 45-day Embryo-larvae Study. Study No. F14580. Unpublished study prepar ed by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00090084 Sauter, S.; Meyerhoff, R.D.; Todd, G.C.; et al. (1981) The Toxicity of Tebuthiuron (EL-103, Compound 75503) in Water to Fathead Minnows (P imephales promelas) in a 33-day Embryolarvae Study. Study No. F08381. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00138700 Grothe, D.; Meyerhoff, R.; T odd, G.; et al. (1983) The Toxi city of Tebuthiuron (EL-103, Compound 75503) to Daphnia magna in a 21-day St atic Renewal Full Life-Cycle Study. Study No. C02882. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, IN.Page 85 of 121 MRID 00041686 Hamelink, J.L.; Mohr, R.M.; Todd, G.C.; et al. (1977) Progress Report for EL-103 (Tebuthiuron) Mini-Ecosystem Study. Study No. 7001-6. Unpublishe d study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Di v. of Eli Lilly and Co., Indianapolis, Ind,

MRID 00041695 Hamelink, J.L.; Todd, G.C.; Brannon, D.R.; et al. (1978) Progress Report Nu mber Two: Aquatic Mini-Ecosystem Evaluation of EL-103. Study No. 7001-6. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 41066901 Waldrep, T. (1988) Influence of Tebuthiuron on Seedling Emergence and Vegetative Vigor of Ten Crop Plants. Laboratory Project ID 61988008. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, IN.

MRID 41066902 Waldrep, T. (1988) Influence of Tebuthiuron on th e Germination of Seeds of Ten Crop Plants. Laboratory Project ID 61988007. Unpublished study pr epared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, IN.

MRID 48722703 Bergfield, A. 2012. Spike 20P (Tebuthiuron 200 g a.s./kg WG): Effects on the Seedling Emergence and Growth of Non-Target Terrestria l Plants (Tier II). Unpublished study performed by ABC Laboratories, Inc., Columbia, Missour i. ABC Study Number : 67305. Study sponsored by The Dow Chemical Company, Midland, Michigan, for Dow AgroSciences, LLC, Indianapolis, Indiana. Study initiated Oc tober 10, 2011 and completed January 16, 2012.

MRID 48722704 Bergfield, A. 2012. Spike 20P (Tebuthiuron 200 g a. s./kg WG): Effects on the Vegetative Vigor of Non-Target Terrestrial Plan ts (Tier II). Unpublished study performed by ABC Laboratories, Inc., Columbia, Missouri. ABC Study Numb er: 67306. Study sponsored by The Dow Chemical Company, Midland, Michigan, for Dow AgroScie nces, LLC, Indianapolis, Indiana. Study initiated October 10, 2011 and completed January 16, 2012.

MRID 41080401 Negilski D.S., Grothe D.W., and Cocke P.J. 1989. Toxicity of Tebuthiuron to the Blue-Green Alga (Anabaena flos-aquae) in a Static Test System. Unpublished study performed by Lilly Research Laboratories, Greenfield, IN. Labor atory Report No. J00489. Sponsored by Elanco Products Company. Study initiated on January 5, 1989 and completed on March 31, 1989.

MRID 41080402Page 86 of 121 Negilski, D.S. and P.J. Cocke. 1989. Toxic ity of Tebuthiuron to Marine Diatom ( Skeletonema

costatum ) in a Static Test System. Conducted by Lilly Research laboratories, Greenfield, Indiana. Laboratory Project No. J00389. S ponsored by Elanco Products Company. Study initiated on January 6, 1989 a nd completed on April 6, 1989.

MRID 41080403 Negilski D.S. and Cocke P.J. 1989. Toxicity of Tebuthiuron to a Freshwater Diatom (Navicula pelliculosa) in a Static Test System. Unpublished study performed by Lilly Research Laboratories, Greenfield, IN . Laboratory Report No. J00888. Sponsored by Elanco Products Company. Study initiated on November 23, 1988 and completed on April 7, 1989.

MRID 41080404 Negilski, D.S. and P.J. Cocke. 1989. Toxi city of Tebuthiuron to Duckweed ( Lemna gibba ) in a Static Renewal Test System. Conducted by Lilly Research laboratories, Greenfield, Indiana. Laboratory Project No. J00588. Sponsored by Elan co Products Company. Study initiated on October 26, 1988 and completed on April 20, 1989.

MRID 00138697 Todd, G.; Meyerhoff, R.; Grothe, D.; et al . (1983) The toxicity of Tebuthiuron (EL-103, Compound 75503) to Algae (Selenas trum capricornutum) in a 14-Day Study. Laboratory Project No. J00383. Unpublished study prepared by Lilly Re search Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, IN.

MRID 40840401 Hoxter, K.; Jaber, M. (1988) Th e Acute Contact Toxicity of Te buthiuron to the Honey Bee: Wildlife International Ltd. Project No.: 151-108. Unpublished study prepared by Wildlife International Ltd. Submitted by Elanco Products C o., Div. of Eli Lilly and Co., Indianapolis, IN.

MRID 00090099 Kline, R.M.; Preston, D.A.; Turner, J.R. (1977) The Effect of Tebuthiur on on Microorganisms. Unpublished study prepared by Lilly Research La boratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00090100 Kline, R.M.; Peloso, J.S. (1978) Effect of Tebuthiuron on Microorganisms: Nitrogen Fixation. Unpublished study prepared by Lilly Research La boratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00138699 Grothe, D.; Todd, G.; Kehr, C.; et al. (1982) The Toxicity of So il Incorporated Tebuthiuron (EL103, Compound 75503) to Earthworms in a 14-Day Study. Study No. W00682. Unpublished study prepared by Lilly Research Laboratories. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, IN.

MRID 43329501Page 87 of 121 Crosswhite, F.; Feldman, W.; Minch, E. (1993) Impact of Pesticides on Cacti: Lab Project Number: E-009572-01-0. Unpublished study prepared by University of Arizona and Arizona Dept. of Agriculture.

MRID 47736301 Havens, P. (2009) Tebuthiuron - Use of Bureau of Land Management Assessments to Fulfill ESA Consultation Requirements. Project Nu mber: 091092. Unpublished study prepared by Dow AgroSciences LLC.

MRID 00034756 Davis, E.A., A. Loh, W.L. Sullivan (1980) April 17, 1980. Tebuthiuron Residues in Stream Water Following the Spot Treatment of Chaparral Watershed in Arizona. Prepared by Lilly Research Laboratories, Greenfield, Indiana 46140. Submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Ind.

MRID 00049579 Elanco Products Company (1980) Proposed Fiel d Monitoring Study with Graslan for Rangeland Brush Control. (Unpublished Study Recei ved Nov. 6, 1980 under 1471-109; CDL: 243738-A).

MRID 00090105 Loh, A., G.R. Stephenson, M.D. Hammond, B.J. Eaton (1981) September 1981. Sagebrush to

Grass Conversion in Southwest Idaho Wateshed Study with Tebuthiuron (Experiment MDH80- 0). Prepared by Lilly Research Labs., Greensf ield, IN. Submitted by Elanco Products Co., Div. of Eli Lilly and co., Indianapolis, IN.Page 88 of 121 

# Appendix A

Environmental Fate Studies Summary

Hydrolysis (MRID 00020779)

14 C tebuthiuron (radiochemical purit y~ 99.5%), at 10 and 100 ppm, did not degradf during 64 days of incubation in sterile aqueous solutio ns at pH 3, 6, and 9 in the dark at 25 °C.

Photodegradatoin in water (MRID 41328001) Tebuthiuron did not photodegrade in sterile aqueous buffered (p H 5) solutions that were Continuously irradiated for 33 days With a xenon light source at approximately 25 °C. Tebuthiuron was the only compound identified in the irradiated and dark control solutions at all sampling intervals. At 33 days pos ttreatment, tebuthiuron comprised 96.3-97. % and 99.7-100% of the recovered radioactivity in th e irradiated and dark control solutions, respectively. The major products of photodegrad ation were soil bound residues and five minor products (each less than 7% of applied radioactivity ).

Photodegradatoin in soil (MRID 41050201)

Asieved (2mm) sandy loam soil (60% sand, 22 % silt , 12 % clay , 1.4% orga nic matter , 11.86% field moisture capacity at 0.33 bar , 5.7 pH , 4.9 meq/100g CEC and 1.28 g/ml bulk density) was used in this study . Thin laye rs of soil in petri dishes were fortified with 28.0 ppm of thiadiazol ring - labeled 14 C-tebuthiuron ( specificac tivity , 17.1 uCi/mg and 97.2% radio purity) and non radio labele d tebuthiuron at a rate o f 58 8.5 ppm. tebuthiuron photolyzed on soil with a half-life of 39.7 days.

I Aerobic soil metabolism (MRID 41328001) In a 9-month study, thiadiazole-labeled 14C te buthiuron, at a concen tration of 6 ppm in sandy

loam soil incubated in darkness at 24 °C and 75% field moisture capacity, degraded with ! a half-life (calculated by the re gistrant) of 35.4 months. Th e degradates identified by twodimensional TLC were N-[5-(1,1- dimethylethyl)-1,3,4-thiadiazol-2-yl ]-N-methylurea (degradate 104), N-[5-(1,1-dimethylethyl )-1,3,4-thiadiazol-2-yl]-N'-m ethylurea (compound 105), 5-(1,1- dimethylethyl)-2 methylamino-1,3,4-thiadiazol (compound 107), and 5-(1,1- dimethylethyl)-2 amino-1,3,4-thiadiazol (compound 108). The concentration of degrad ate 104, which accounted for 6.9% of the applied radioactivity af ter 9 months of incubation, appear ed to be increasing at the end of the experiment

.

Anaerobic soil metabolism (MRID41328002)

Following 30 days of aerobic incubation at 24 ± 1 °C and 75% of 0.33 bar moisture capacityPage 89 of 121 and 60 days under flooded conditions in a sandy loam soil, thiadiazo le-labeled 14C tebuthiuron (nominal concentration 6 ppm) exhibited very li ttle metabolism. After 60 days of anaerobic incubation, the concentration of parent tebuthiur on had decreased 4.7% from the concentration at initiation of flooding. Degradates identified were N-[5-:(1,1-dimethylet hyl)- 1,3,4-thiadiazol-2- yl]-N-methylurea (compound·104), N-[5-(1,1-dime thylethyl)-1,3,4-th iadiazol-2-yl]-N'- methylurea (compound 105), and N-[5-(1,1-di methylethyl)-1,3,4-thiadiazol-2-yl]-N'- (hydroxymethyl)-N-methyl urea (compound 109).

Anaerobic aquatic metabolism (MRID 41913101)

Tebuthiuron degrad~d with a half-life (calcula ted by the registrant) of > 1 year in anaerobic system containing pond water and sediment inc ubated for 365 days in darkness at 25.5 ± 0.8 °C. During the study there was very little degradation oftebuthi uron, with 93.7% the applied radiocarbon remaining as parent material at day 365. Degradates were repqrted to comprise approximately 1.4% of the applied radioa ctivity at the termination of the study.

Aerobic aquatic metabolism (MRID 41372501) Tebuthiuron did not degrade appr eciably in pond water and sedi ment that was incubated in

darkness at 24 ± 1 °C fro 4 weeks under aerobic conditions. After 4 weeks of incubation, 95.2% of the applied radioactivity was present in pa rent tebuthiuron. Degradat es identified by twodimensional TLC were N-[5-(1,1-dimethylet hyl)-1,3,4-thiadiazol-2-yl]-N-methylurea (compound 1 04), N-[5-(1, 1-dimethylethyl)-1 ,3,4-th iadiazol-2-yl]-N' -methyl urea (compound 105), 5-(1,1-dimethylethyl)-2 methylami no-1,3,4-thiadiazol (compound 107), 5-(1,;1- Dimethylethyl)-2-amino-1,3,4-thiadiazol (com pound 108), and N-[5-(1- 1, dimethylethyl)-1,3,4- thiadiazol-2-yl]-N’-(hydroxymethyl )-N-methylurea (compound 109).

Leaching, Adsorption/Desorption (MRID 40768401)

Tebuthiuron is mobile in all 4 soils and has a Kads for sand, sandy loam, loam, boe!dmbz loam of 0.11, 0.62, 0.82, and 1.82, respectively. The co rresponding Koc values are 38, 716! 75, and 152, respectively.

Bioaccumulation in fish (MRID 40819501)

In a 28-day flow-through study in which bluegill sunfish were exposed to a nominal tebuthiuron concentratio11 of 5.0 ppm, bioconcentration factors of 1.98, 3.40, and 2.63 were reported for edible tissue, nonedible tissue, and whole fish, respectively. Residues in the tissues consisted primarily of tebu thiuron and two metabolites N- [5-(1,1-dimethylethyl)-1, 3,4-thiadiazol-2-yl]-N'- (hydroxymethyl)-N-methylurea (c ompound 109) and compound 103(OH) (hydroxylated form of parent tebuthiuron). Accumulated re sidues depurated rapidly from fi sh tissue with depuration halflives of0.33 and 0.51 days reported for edible a nd lqnedible tissue, respectively. Based on thePage 90 of 121 reported octanollwater coefficient (log Kow=1.79) , there is slight po tential for tebuthiuron

residues to accumulate in fish.

Terrestrial Field Dissipation (MRID 43318101)

Tebuthiuron was broadcast applied once 'as a spray at nominal application rates of 6.6 lb ai/ A on bareground plots of Lakeland fine sand (Flori da), Watsonville sandy loam (California), and Sharpsburg silty clay loam (Nebraska). EFED cal culated soil dissipation half-lives for Florida Of 385 days(r2 = 0.66) for the total parent (su mmed across 0 to 72 inches) and 123 days (r2 = 0.92) for the surface layer (0 to 6 inches), for Ca lifornia of 770 days (r2 = 0.89) for the total parent (summed across 0 to 72 inches) and 462 days (r 2 = 0.97) for the surface layer (0 to 6 inches), and for Nebraska of 575 days (r2 = 0.89) for the total parent (summed across 0 to 72 inches) and 433 days (r2 = 0.91) for the surface laye r (0 to 6 inches). The registrant calculated halflives (total parent profile) of383 days for Florida, 806 days for California, and 575 days

for Nebraska.

Tebuthiurori was detected in the deepest soil sample (60 to 72 inches) at the Florida site indicating that migration to gr ound water is a concern. · Tebuth iuron was not detected below

24 to 30 inches at the California site or below 30 to 36 inches at the Nebraska site, although these depths indicate that tebuthiuron is leaching. Th e metabolite (Compound 109383) was

detected at all three sites but was not observed to have migr ated below 6 to 12 inches in Florida, 12 to 18 inches in California, and 0 to 6 inches in Nebraska. The registrant did not

calculate the half life for the metabolite. EFED estimated the half life for the metabolite from each study by performing linear regression on th e decline pattern (as determined by peak concentration of metabolite). EFED calculated ha lf lives for the total profile for Florida, California, and Nebraska, respectively were 81 days (r2 = 0.92), 495 days (r2 =0.96), and 385 days (r2 = 0.57).

Finally, it should be noted that evaporation exceeded water input at the Califonia and

Nebraska sites and therefore the vertical move ment (leaching potential) of tebuthiuron and its degradate may be underestimated at these two sites. The reported data indicate that tebuthiuron is mobile and persistent. Based on the data provided, leaching to ground water is likely to be a significant route of dissipation.

Small Scale Retrospective Gr ound Water Monitoring Study (MRID 42390901) A small-scale retrospective ground water mon itoring study was performed on a ran ch near Sarita, Texas, that has last been treated w ith tebuthiuron on March 24, 1986. The results of the study indicated that tebuthiur on was mobile enough to leach at least 15 feet to the water table, then still be present above minimum detection levels more th an 4 years after the application. Soil sampling at and near the study site showed convincingl y that tebuthiuron can persist at relatively high c oncentrations in soil and soil wate r if restrictive layer blocks leaching to the ground water.Page 91 of 121 

# Appendix B

Chemical structures for the parent (tebuthiuron) and degradates 104, 106, 108, and 109

Tebuthiuron N-[5-(1,1-dimethyleth yl)-1,3,4-thiadiazol-z-yl]- N,N-dimethylureaPage 92 of 121Page 93 of 121 

# Appendix C

PRZM-EXAMS output files

Eco modeling outputs.zipPage 94 of 121 

# Appendix D

Tebuthiuron pond accumulation with time

TXalfalfaOP (aerial)

SUMMARY OUTPUT

Regression Statistics

Multiple R 0.933674633

R Square 0.871748319

Adjusted R Square 0.867167902

Standard Error 123.7752708

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 2915774 2915774 190.32073 5.189E

‐ 14

Residual 28 428968.89 15320.318

Total 29 3344742.9

Coefficients Standard

Error t Stat P

‐ value Lower 95% Upper 95% Lower

95.0% Upper

95.0%

Intercept 210.068046 46.350473 4.5321661 9.954E

‐ 05 115.12341 305.01269 115.12341 305.01269

X Variable 1 36.01862069 2.6108627 13.795678 5.189E

‐ 14 30.670511 41.36673 30.670511 41.36673Page 95 of 121 SUMMARY OUTPUT

Regression Statistics

Multiple R 0.9337579

R Square 0.8719039 Adjusted R
Square 0.867329

Standard Error 123.20537

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 2893009.8 2893009.8 190.5858 5.101E

‐ 14

Residual 28 425027.79 15179.564

Total 29 3318037.6

Coefficients Standard

Error t Stat P

‐ value Lower 95% Upper 95% Lower

95.0% Upper

95.0%

Intercept 209.06 46.137062 4.5312811 9.98E

‐ 05 114.55251 303.56749 114.55251 303.56749

X Variable 1 35.877742 2.5988415 13.805283 5.1E

‐ 14 30.554256 41.201227 30.554256 41.201227Page 96 of 121 SUMMARY OUTPUT

Regression Statistics

Multiple R 0.9342

R Square 0.8727

Adjusted R Square 0.8681

Standard Error 122.3

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 2869847 2869847 191.8721 4.7E

‐ 14

Residual 28 418798.3 14957.08

Total 29 3288645

Coefficients Standard Error t Stat P

‐ value Lower 95% Upper

95% Lower

95.0% Upper

95.0%

Intercept 205.85 45.79771 4.494775 0.00011 112.038 299.6627 112.038 299.6627

X Variable 1 35.734 2.579726 13.85179 4.7E

‐ 14 30.44949 41.01815 30.44949 41.01815Page 97 of 121 PAalfalfaOP (aerial)

SUMMARY OUTPUT

Regression Statistics

Multiple R 0.9745036

R Square 0.9496573 Adjusted R
Square 0.9478594

Standard Error 48.564216

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 1245722.9 1245722.9 528.1882 1.028E

‐ 19

Residual 28 66037.525 2358.483

Total 29 1311760.5

Coefficients Standard

Error t Stat P

‐ value Lower 95% Upper 95% Lower

95.0% Upper

95.0%

Intercept 80.422943 18.185978 4.42225 0.000134 43.170655 117.67523 43.170655 117.67523

X Variable 1 23.54295 1.0243928 22.982346 1.03E

‐ 19 21.444576 25.641323 21.444576 25.641323Page 98 of 121 SUMMARY OUTPUT

Regression Statistics

Multiple R 0.9748338

R Square 0.9503009 Adjusted R
Square 0.9485259

Standard Error 1.997309

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 2135.8012 2135.8012 535.3901 8.584E

‐ 20

Residual 28 111.69881 3.9892432

Total 29 2247.5

Coefficients Standard

Error t Stat P

‐ value Lower 95% Upper 95% Lower

95.0% Upper

95.0%

Intercept 1957.5453 0.8573801 2283.1707 2.49E

‐ 75 1955.789 1959.3015 1955.789 1959.3015

X Variable 1 0.0403955 0.0017458 23.138498 8.58E

‐ 20 0.0368194 0.0439716 0.0368194 0.0439716Page 99 of 121 SUMMARY OUTPUT

Regression Statistics

Multiple R 0.9751028

R Square 0.9508254 Adjusted R
Square 0.9490692

Standard Error 1.9867413

Observations 30

ANOVA

df SS MS F Significance

F

Regression 1 2136.9801 2136.9801 541.3995 7.397E

‐ 20

Residual 28 110.51994 3.9471408

Total 29 2247.5

Coefficients Standard

Error t Stat P

‐ value Lower 95% Upper 95% Lower

95.0% Upper

95.0%

Intercept 1957.5685 0.8517472 2298.2975 2.07E

‐ 75 1955.8238 1959.3132 1955.8238 1959.3132

X Variable 1 0.040447 0.001738 23.26799 7.4E

‐ 20 0.036886 0.044008 0.036886 0.044008Page 100 of 121 

# Appendix E

STIR Results for Tebuthiuron



## Welcome to the EFED Screening Tool for Inhalation Risk

This tool is designed to provide the risk assessor with a rapid method for determining the potential significance of the inhalation exposure route to birds and mammals in a risk assessment.



### Input

Application and Chemical Information

Enter Chemical Name Teb Enter Chemical Use Rangeland Is the Application a Spray? (enter y or n) y If Spray What Type (enter ground or air) air Enter Chemical Molecular Weight (g/mole) 228.3 Enter Chemical Vapor Pressure (mmHg) 3.00E-07 Enter Application Rate (lb a.i./acre) 6

Toxicity Properties

Bird

Enter Lowest Bird Oral LD 50 (mg/kg bw) 2000
Enter Mineau Scaling Factor 1.15 Enter Tested Bird Weight (kg) 1.58

Mammal
Enter Lowest Rat Oral LD 50 (mg/kg bw) 388

Enter Lowest Rat Inhalation LC 50 (mg/L) 3.696
Duration of Rat Inhalation Study (hrs) 4 Enter Rat Weight (kg) 0.35



### Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 3.69E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 4.63E-04
Adjusted Inhalation LD 50 7.66E+01

Ratio of Vapor Dose to Adjusted Inhalation LD 50 6.05E-06 Exposure not Likely Significant
Maximum Post-treatment Spray Inhalation Dose (mg/kg) 5.76E-01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 7.53E-03 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 3.69E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 5.82E-04
Adjusted Inhalation LD 50 2.20E+02

Ratio of Vapor Dose to Adjusted Inhalation LD 50 2.65E-06 Exposure not Likely Significant
Maximum Post-treatment Spray Inhalation Dose (mg/kg) 7.25E-01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 3.29E-03 Exposure not Likely Significant **NOTE**: When entering values, pres s order to update linked cells.Page 101 of 121 

# Appendix F

SIP Results for TebuthiuronPage 102 of 121 Table 1. Inputs

Parameter V alue

Chemical name Teb
Solubility (in water at 25 o C; mg/L) 2500

Mammalian LD 50 (mg/kg-bw) 388
Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 20 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg-bw) >2000
Avian test species mallard duck Body weight (g) of "other" avian species Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 100 Bobwhite quail NOAEC (mg/kg-diet) 100 NOAEC (mg/kg-diet) for other bird species Body weight (g) of other avian species NOAEC (mg/kg-diet) for 2nd other bird species Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter A cute Chronic Upper bound exposure (mg/kg-bw) 430.0000 430.0000 Adjusted toxicity value (mg/kg-bw) 298.4343 15.3832 Ratio of exposure to toxicity 1.4409 27.9526

Conclusion* Exposure through drinking water alone is a potential

concern for mammals Exposure through drinking water alone is a potential

concern for mammals

Table 3. Avian Results

Parameter A cute Chronic Upper bound exposure (mg/kg-bw) 2025.0000 2025.0000 Adjusted toxicity value (mg/kg-bw) #VALUE! 4.9613 Ratio of exposure to acute toxicity #VALUE! 408.1627

Conclusion* #VALUE! Exposure through drinking water alone is a potential

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated with other routes ( i.e ., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure tPage 103 of 121 

# Appendix G

Tebuthiuron Ecological Effects Summaries

OCSPP 850.1010 – Daphnia Acute Toxicity Test

MRID 00041694 The acute toxicity of tebuthiu ron to 10 hours old first instar daphnia was assessed for 48 hours.

Nominal concentrations of the test material we re set at 0 (control), 225, 300, and 400 mg a.i./L with 9, 10, 11 daphnia placed in each test vesse l. All treatment and control groups were triplicated. There were 6, 50, and 97% mortalit y in the 225, 300, and 400 mg a.i./L treatment groups, respectively. Affected daphnia were re ported light colored and lethargic swimming behavior followed by prostration, i mmobilization and death. The 48-hour EC 50 (95% C.I.) was 297 (279-316) mg a.i./L, which would classify te buthiuron to be practical ly nontoxic to trout, in accordance with the toxicity classification of USEPA.

The study is classified as scientifically sound and satisfies the guideline requirement for a

freshwater invertebrate acute toxicity test with daphnia magna . The study is classified as acceptable.



### OCSPP 850.1025 – Estuarine/marin e Mollusk Shell Deposition

MRID 48722701 The 96-hour acute toxicity of te buthiuron to the Eastern oyster, Crassostrea virginica , was studied under flow-through conditi ons. Oysters were exposed to the test material at nominal concentrations of 0 (nega tive control), 6.3, 13, 25, 50, and 100 mg a.i./L. Mean-measured concentrations were <LOD, 6.5, 14, 26, 50, and 95 mg a.i./L. Mortality and shell deposition were observed daily. No mortality was observed in th e dilution water control or treatment groups. After 96 hours, the reviewer-calculated mean per cent inhibition in shell growth compared to negative control was 26, 16, 7, 21, and 23% in the 6.5, 14, 26, 50, and 95 mg a.i./L test concentrations, resp ectively. The 96-hour EC 50 based on shell deposition and mean measured concentrations was >95 mg a.i./L, categorizi ng tebuthiuron as practic ally non-toxic to the Eastern oyster.

The study is scientifically sound and satisfies the guideline requirements for an acute

estuarine/marine invertebrate toxic ity study with the Eastern oyster ( Crassostrea virginica ). This study is classified as acceptable.



### OCSPP 850.1035 – Mysid Acute Toxicity Test

MRID 00041684Page 104 of 121 In a 96-hr acute toxici ty study, Fiddler crab ( Uca pugilator ) a crustacean similar to the mysid shrimp were exposed to tebuthiuron at nominal concentrations of 0 (control), 10, 32, 100, 180, and 320 mg a.i./L. Mortality was 0, 0, 10, 0, 0, 20% in the 0 (control), 10, 32, 100, 180, and 320 mg a.i./L treatment groups, respectivel y, at test termination. The 96-hour LC 50 was >320 mg a.i./L, which would classify tebuthiuron to be practically nontoxic to the Fiddler crabs, in accordance with the toxicity classification of USEPA.

This study is scientifically sound but does not satisfy the gui deline requirement for a mysid shrimp acute toxicity study with Fiddler crab. Th is study is classified as supplemental since the

fiddler crab is not a r ecommended test species.



### OCSPP 850.1045 – Penaei d Acute Toxicity Test

MRID 00041684

In a 96-hr acute toxici ty study, pink shrimp (P enaeus duorarum ) were exposed to tebuthiuron at nominal concentrations of 0 (control), 10, 32, 100, 180, and 320 mg a.i./L. Mortality in the highest concentration was 100% at 24 hours, 100% in the 2 nd highest concentr ation at 48 hours, and 11% and 77% in the 32 and 100 mg a.i./L trea tment groups, respectively, at test termination.

The 96-hour LC 50 with 95% confidence intervals was 62 (39- 90) mg a.i./L, which would classify tebuthiuron to be slightly toxic to pink shrimp, in accordance with the toxicity classification of

USEPA.

This study is scientifically s ound and satisfies the guideline re quirement for a penaeid acute toxicity study with pink shrimp. This study is classified as acceptable.



### OCSPP 850.1055 – Bivalve Acute Toxicity Test (embryo larval)

MRID 00041684 The acute toxicity of tebuthiuron to normal Eastern oyster ( Crassostrea virginica ) embryos was

assessed for 48 hours. Nominal concentrations of tebuthiuron were 0 (seawater control), 32, 56, 100, 180, and 320 mg a.i./L. Three replicates per level. Each test replicate wa s inoculated with an estimated 27,000 ± 1350 embryos. The highest test concentration at 320 mg a.i./L nominal was the only level to experience mortality with 100% embryos dead. All other treatment groups embryos were normal at test termination. Since th ere were no concentration at which the percent reduction was between 100 and 0%, a definite LC 50 could not be calculated. The 48-hour LC 50 for eastern oyster embryos is estimated to be >180 and < 320 mg a.i./L. With an LC 50 greater than 100 mg a.i./L, tebuthiuron is classified as practically nontoxic to Ea stern oyster embryos, in accordance with the toxicity classification of USEPA.

This study is classified as scientifically sound a nd fulfills the guideline requirement for a bivalve (embryo larval) acute toxicity test with Eastern oyster. This study is classified as acceptable.



### OCSPP 850.1075 – Freshwater and Estua rine/marine Fish Acute Toxicity

MRID 00020661 (Goldfish)Page 105 of 121 In a 96-hr acute toxi city study, goldfish ( Carassius auratus ) were exposed to tebuthiuron at nominal concentrations of 0 (control), 5, 10, 20, 40, 80, and 160 mg a.i./L without a solvent in

the first test and at nominal concentrations of 0 (control), 6.25, 12.5, 25, 50, and 100 mg a.i./L

with the solvent added in the second test. Goldfi sh were also exposed to the solvent alone at nominal concentrations of 0.33, 0.67, and 1.33 ml/L. Ten goldfish pe r replicate with two, three, four, or 6 replicates, depending on which test was performed. One fish died throughout the tests.

The 96-hour LC 50 was >160 mg a.i./L, which would cla ssify tebuthiuron to be practically nontoxic to goldfish, in accordance with th e toxicity classifi cation of USEPA.

This study is scientifically sound however does not satisfy the guideline requirement for a freshwater fish acute toxicity study with Carassius auratus , due to several departures from guideline protocols. This study is classified as supplemental.

MRID 00020661 (Rainbow trout)

In a 96-hr acute toxici ty study, rainbow trout ( Oncorhynchus mykiss ) were exposed to

tebuthiuron at nominal concentrations of 0 (control), 1, 10, 50, 87, 120, and 160 mg a.i./L. Ten fish per test level. 10% mortal ity was observed in the highest le vel at 24 hours, which increased to 70% at 96 hours. Mortality was 20% in the 120 mg a.i./L test level at te st termination. No fish died in the 87 mg a.i./L test level but dark co loration and lethargy in th e fish were observed. The author reported the behavior of fish succumbing to the test material was generally similar to a syndrome characteristic of chemically poisoned fish. The gills of the trout at 160 mg a.i./L became irritated and inflamed exhibiting a red color although hemorrhaging was not prevalent.

Moribund fish were then observed to become dar k, lose equilibrium and then drop to the bottom of the test vessel where they eventually expired. The 96-hour LC 50 (95% C.I.) was 143 (118-224) mg a.i./L, which would classify tebuthiuron to be practically nontoxic to trout, in accordance with the toxicity clas sification of USEPA.

This study is scientifically sound and satisfies the guideline requi rement for a freshwater fish acute toxicity study with Rainbow trout, a warmwater fish. This study is classi fied as acceptable.

MRID 00020661 (Bluegill sunfish) In a 96-hr acute toxicity study, bluegill sunfish ( Lepomis macrochirus ) were exposed to

tebuthiuron at nominal concentrations of 0 (control), 1, 10, 50, 87, 120, and 160 mg a.i./L. Ten fish per test level. At 24 hours, mortality wa s 0, 0, 0, 0, 0, 10, and 10% in the 0 (control), 1, 10, 50, 87, 120, and 160 mg a.i./L test levels. At 96 hours, 90 and 100% were observed in the 120 and 160 mg a.i./L test group, respectively. Dark co loration and lethargy were observed in fish of the 87 mg a.i./L test level. The author reporte d the behavior of fish succumbing to the test material was generally similar to a syndrome characteristic of chem ically poisoned fish.

Moribund fish were then observed to become dar k, lose equilibrium and then drop to the bottom of the test vessel where they eventually expired. The 96-hour LC 50 (95% C.I.) was 106 (87-120) mg a.i./L, which would classify tebuthiuron to be practically nontoxic to bluegill sunfish, in accordance with the toxicity classification of USEPA.Page 106 of 121 This study is scientifically sound and satisfies the guideline requi rement for a freshwater fish acute toxicity study with Lepomis macrochirus , a coldwater fish. This study is classified as acceptable.

MRID 00041685 In a 7-day acute toxicity study, fathead minnow ( pimephales promelas ) were exposed to a 98% technical formulation, an 80% wettable powder, and a 20% pelleted formulation of tebuthiuron at nominal concentrations equivalent to 0 (c ontrol), 70, 90, 110, 140, and 180 mg a.i./L. Ten fish per test level. Mortality was mini mal in the tests however there were signs of sub-lethal effects.

Sub-lethal effects observed were exploratory behavior and hypoactiv ity in concentrations at and greater than 140 mg a.i./L. Fish treated with 70, 90, 110 mg a.i./L of tebuthiuron appeared normal; however, periods of less aggressive feed ing activity were observed compared to the control group throughout the test. The 96-hour LC 50 was >180 mg a.i./L, which would classify tebuthiuron to be practically nontoxic to fath ead minnow, in accordan ce with the toxicity

classification of USEPA.

This study is scientifically s ound but does not satisfy the guidelin e requirement for a freshwater fish acute toxicity study with Pimephales promelas , a warmwater fish. This study is classified as supplemental since study deviates from recomme nded protocol and inadequate reporting of the

data.

MRID 48722702 In a 96-hr acute toxicity study, sheepshead minnows ( Cyprinodon variegates ), an estuarine/marine fish, were expos ed to tebuthiuron at nominal concentrations of 0 (negative control), 6.3, 13, 25, 50, and 100 mg a.i./L under static-renewal conditions. Mean measured concentrations were <0.42 (<LOQ, negative co ntrol), 6.5, 13, 25, 50, and 98 mg a.i./L. There was no mortality observed in this study. The 96-hr LC 50 was >98 mg a.i./L. Based on sub-lethal effects (loss of equilibrium) observed at 98 mg a.i./L, the NOAEC was determined to be 50 mg a.i./L, based on mean-measured concentrations. Based on the results of this study, tebuthiuron

would be classified as practically non-toxic to Cyprinodon variegatus up to the exposure levels tested, in accordance with the classifi cation system of the U.S. EPA.

This study is scientifically sound and satisfies the guideline require ment for an estuarine/marine fish acute toxicity study with Cyprinodon variegatus . This study is classified as acceptable.



### OCSPP 850.1300 – Freshwater Invertebrate Life Cycle

MRID 00138700 In a 21-day static renewal full life cycl e study, <24-hours first instar water fleas ( daphnia

magna ) were exposed to tebuthiuron at nominal concentration of 0 (control), 5.63, 11.25, 22.5, 45, and 90 mg a.i./L. The mean-measured co ncentrations were 0 (control), 5.47, 11, 21.8, 44.2, and 90.2 mg a.i/L. Ten replicates per treatment le vel. Seven replicates with one daphnia each were used for fecundity and thr ee replicates of five daphnia each were used for survival data. Two sets of replicates were used for control. No significant levels of mortality occurred at any of the levels tested. Daphnia from the 44.2 and 90.2 mg a.i./L treatment groups were significantlyPage 107 of 121 shorter than control daphnia. Daphnia from the 44.2 and 90.2 mg a.i./L treatment groups had significant reductions in number of broods per reproducing adult and number of offspring per adult when compared to control daphnia. Daphnia from the 90.2 mg a.i./L treatment group required a significantly longer time to release th eir first brood. As of a result of significant differences in growth and fecundity at the 44.2 and 90.2 mg a.i./L trea tment levels, the NOAEC is 21.8 mg a.i/L. The LOAEC is 44.2 mg a.i./L.

This study is scientifically s ound and satisfies the guideline requirement for a freshwater invertebrate life cycle study with Daphnia magna. This study is classified as acceptable.



### OCSPP 850.1500 – Fish Full Life Cycle Toxicity Test

MRID 00090083 In a 45-day flow-through fish em bryo-larval study, a total of 50 eyed embryos of Rainbow trout, Oncorhynchus mykiss , in each of two replicates per treatment were exposed to tebuthiuron at nominal concentrations of 0 (control), 3.1, 6.2, 12.5, 25, and 50 mg a.i./L. Mean-measured concentrations were 0 (control), 3.1, 6.3, 12.5, 25, a nd 52 mg a.i./L. On Day 2 when the hatching of all embryos was complete, a total of 25 normal larvae were transferred from the two egg cups in each replicate aquarium. These larvae were continuously exposed to the same treatment level for 43 days.

Hatching was 100% successful in all replicate aquaria. Su rvival was 100, 100, 98, 94, 92, and 80% in the control, 3.1, 6.3, 12.5, 26, and 52 mg a.i./L groups. Only exposure to the highest test

concentration resulted in a statis tically and biologically significan t reduction of larvae survival at days 30 and 45. The behavior and feeding respon se of larvae in the treatment groups were considered normal when compared to control larv ae. When compared to control larvae, the total length of the larvae in the highest test concen tration was significantly reduced by test days 30 and 45. This reduction in mean lengt h correlated well with an averag e weight of control larvae.

Statistically significant differen ces in total length of <6% were found on Day 30 between control larvae exposed in the 6.3, 12.5, and 25 mg a.i./L treatment groups. No weights were recorded on day 30 to substantiate this size differen ce and by day 45 statistic ally significant length

differences at these concentrations did not exist. The differences noted on day 30 were therefore considered to be biolog ically insignificant.

Based on significant reduction in the survival and size of rainbow trout larv ae at 52 mg a.i./L, the highest test concentration; th e NOAEC is 26 mg a.i./L. This fish embryo-larval study was request in exchange of a fish fu ll life cycle test. This study is sc ientifically sound and shows that a chronic exposure to tebuthiuron as low as 52 mg a.i./L can resu lt in impaired reproduction and reduced growth in rainbow trout. This study is classified as acceptable.

MRID 00090084 In a 33-day flow-through fish embryo-larval study, a total of 50 embryos of fathead minnow, Pimephales promelas , in each of two replicates per treat ment were exposed to tebuthiruon at nominal concentrations of 0 (control), 5, 10, 20, 40, and 80 mg a.i./L. Mean-measuredPage 108 of 121 concentrations were 0 (control), 4.7, 9.3, 18, 38, and 76 mg a.i./L. Four replicates were used for

the water control. After hatch at day 5, larvae were transfer red to the aquaria and were continuously exposed to tebuthiuron for 28 days.

Hatching was 93, 90, 88, 86, 90, and 95% in the control, 4.7, 9.3, 18, 38, and 76 mg a.i./L groups. Survival was 88, 90, 88, 85, 92, and 89% in these same groups. No significant reduction in hatching or survival of mi nnows was observed as high as 76 mg a.i./L. When compared to

control larvae and the three hi ghest concentrations, the larvae in the 18, 38 and 76 mg a.i./L groups were statistically significantly shorter. The NOAEC was 9.3 mg a.i./L.

This fish embryo-larval study with the fathead mi nnow was request in exchange of a fish full life cycle test. This study is scientif ically sound and shows that a chr onic exposure to tebuthiuron as low as 18 mg a.i./L can result in reduced gr owth but not reproductive effects in fathead

minnows.



### OCSPP 850.2100 – Avian Acute Oral

MRID 00041692 The acute oral toxicity of Tebuthiur on to 9-month-old mallard ducks ( Anas platyrhynchos ) was assessed over 14 days. Tebuthiuron was administ ered to the birds by gavage at nominal concentrations of 0 (contro l), 1000, and 2000 mg a.i./kg bw. No mortality was observed throughout the test in the treatment groups or control group. The 14-day acute oral LD 50 was >2000 mg a.i/kg bw. According to the US EPA t oxicity classification, tebuthiuron would be classified as practically nontoxic to mallard ducks on an acute oral basis.

Body weight was taken on days 3, 7 and 14; however, results were not reported. Food consumption was not observed or measured, th e results are unknown. Signs of toxicity of anorectic, low appetite in fema les, hypoactivity, and lethargy were reported; however, by day two, birds were no longer hypoactivity or lethargy.

This toxicity study is classified as scie ntifically sound and sa tisfies the OCSPP 850.2100 guideline requirement for acute oral toxicity st udy for the mallard duck. Th is study is classified as acceptable.

MRID 00020661 (Bobwhite quail) The acute oral toxicity of tebuthi uron to Northern bobwhite quail ( Colinus virginianus ) was assessed for 14 days. Tebuthiuron was administered to the birds by gavage at the limit dose of 500 mg a.i./kg bw nominal. No evidence of toxi city was observed during the test period and all birds survived. The behavior, appearance and appe tite of the birds remained normal during the test period and each of the birds gain ed weight. The 14-day acute oral LD 50 was >500 mg a.i/kg bw. No mortality occurred up to and at 500 mg a.i./kg bw, the limit dose; however, because the test concentration was not tested as high as 2,000 mg a.i./kg bw, a firm toxicity classification could not be made this time. As of a result, the study is classified as supplemental as the test did not comply with protocols recommended by the guideline for the following reasons: 1. The age of the birds was not reported, 2. Individual body weight and mean food consumption were notPage 109 of 121 reported, and the test did not established a definite LD 50 , neither does it show that the LD 50 is greater than 2000 mg a.i./kg bw.

MRID 00020661 (Mallard duck) The acute oral toxicity of tebuthi uron to one-year old mallard duck ( Anas platyrhynchos ) was assessed for 14 days. Tebuthiuron was administered to the birds by gavage at the limit dose of 500 mg a.i./kg bw nominal. No evidence of toxi city was observed during the test period and all birds survived. The behavior, appearance, and a ppetite of the birds re mained normal during the test period and each of the birds gain ed weight. The 14-day acute oral LD 50 was >500 mg a.i/kg bw. No mortality occurred up to and at 500 mg a.i./kg bw, the limit dose; however, because the test concentration was not tested as high as 2,000 mg a.i./kg bw, a firm toxicity classification could not be made this time. As of a result, the study is classified as supplemental as the test did not comply with protocols recommended by the guideline for the following reasons: Individual body weight and mean food consumption were no t reported; the test did not established a

definite LD 50 , neither does it show that the LD 50 is greater than 2000 mg a.i./kg bw.

MRID 00020661 (Domestic chicken) The acute oral toxicity of te buthiuron to adult chickens ( White Rock Cross ) was assessed for 14 days. Tebuthiuron was administered to the birds by gavage at the limit dose of 200 mg a.i./kg and in a second study at 500 mg a.i./kg bw nomina l. In the 200 mg a.i. /kg bw limit dose study, a slight hypoactivity and mild anorexia were noted 24 hours post-treatme nt; however, appeared normal thereafter. All birds survived and gained weight during the test period. In the 500 mg a.i./kg bw limit dose study, all chickens appeared normal, survived, and gained weight during the test period. The 14-day acute oral LD 50 was >500 mg a.i/kg bw. No mortality occurred up to and at 500 mg a.i./kg bw, the limit dose; however, becau se the test concentration was not tested as high as 2,000 mg a.i./kg bw, a firm toxicity clas sification could not be made this time. As of a result, the study is classified as supplemental as the test did not comply with protocols recommended by the guideline for the following reasons: Individual body weight and mean food consumption were not reported; the te st did not established a definite LD 50 , neither does it show

that the LD 50 is greater than 2000 mg a.i./kg bw.



### OCSPP 850.2200 – Avian Acute Dietary

MRID 00041680 The acute dietary toxicity of Tebuthi uron to 7 days old mallard ducks ( Anas platyrhynchos ) was assessed for 8 days. Tebuthiuron was administer ed to the ducks in the diet at nominal concentrations of 0 (control), 400, 1000, and 2500 mg a.i./kg diet. The 8-day acute dietary LC 50 was >2500 mg a.i./kg diet, the highest concentrati on tested. No mortality occurred up to and at 2500 mg a.i./kg diet; however, because the test concentration was not tested as high as 5,000 mg a.i./kg diet, a firm toxicity classi fication could not be made this time.

Ten birds per test levels. The au thor reported there were no diffe rence in behavior, appearance, and posture in the treated ducks when compared to the control group ducks. None of the groups appeared reluctant to eat the compound containing diets. With additional data submitted (MRID 41693) on food consumption and body weight gai n, a significant reduction in food consumptionPage 110 of 121 in all treatment groups compared to the contro l was noted from day 0 to 5. With no significant reduction in body weight gain between treated an d control groups and the small difference in food consumption, the apparent reduction in f ood consumption has probably not affected the outcome of the test significantly.

This toxicity study is classified as scien tifically sound but does not satisfy the OCSPP 850.2200 guideline requirement for acute dietary toxici ty study with the mallard duck. This study is classified as supplemental. Test concentrations were not tested as high as 5,000 mg a.i/kg diet.

MRID 00041681 The acute dietary toxicity of Tebuthi uron to 7 days old bobwhite quails ( Anas platyrhynchos ) was assessed for 8 days. Tebuthiuron was administ ered to the chicks in the diet at nominal concentrations of 0 (control), 400, 1000, and 2500 mg a.i./kg diet. The 8-day acute dietary LC 50 was >2500 mg a.i./kg diet, the highest concentrati on tested. No mortality occurred up to and at 2500 mg a.i./kg diet; however, because the test concentration was not tested as high as 5,000 mg a.i./kg diet, a firm toxicity classi fication could not be made this time.

Ten chicks per test level were used. The author reported there were no difference in behavior, appearance, and posture in the tr eated quails when compared to th e control group quails. None of the groups appeared reluctant to eat the compound containing diets. With additional data submitted (MRID 41693) on food consumption and body weight gain, a significant reduction in food consumption in all treatment groups compared to the control was noted from day 0 to 5. With no significant reduction in body weight gain between treat ed and control groups and the small difference was not pronounced in food c onsumption, the apparent reduction in food consumption has probably show that the test mate rial is not toxic or ha s repellent effects.

This toxicity study is classified as scien tifically sound but does not satisfy the OCSPP 850.2200 guideline requirement for acute dietary toxici ty study with the bobwhite quail. This study is classified as supplemental. Test concentrations were not tested as high as 5,000 mg a.i/kg diet.

MRID 40601001 The acute dietary toxicity of Tebuthiuron to 11-day-old Northern bobwhite quail ( Colinus virginianus ) was assessed over 8 days. Tebuthiuron was ad ministered to the bi rds in the diet at nominal concentrations of 0 (control), 600, 1200, 2500, and 5000 mg a.i./kg diet. Meanmeasured concentrations were 0 (<LOQ, control), 636, 1210, 2573, and 5113 mg a.i./kg diet, respectively. No significant mort ality or behavioral signs of t oxicity were noted throughout the test. The 8-day acute dietary LC 50 was determined to be >5113 mg a.i./kg diet. According to the US EPA classification, Tebuthiur on would be classified as practically non-toxic to bobwhite quails on an acute dietary basis.

One bird in the 1210 mg a.i./kg di et test group and one bird in th e 5113 mg a.i./kg diet test group died during the three-day period that the birds were fed untreat ed diet. Both birds were the smallest in their pens and one was the smallest in the study. Both birds gained weight while feeding on the treated diet and no signs of toxicity were noted. It is possible that the stress of handling these small birds, for weighing on da y 5 contributed to their deaths. No otherPage 111 of 121 mortalities or signs of toxici ty were recorded during the st udy. Birds in the 2573 and 5113 mg a.i./kg diet test groups gained significantly less weight as co mpared with the control group during the 5-day treatment phase. However, there were no significant differences between mean body weight gain values of cont rol and treatment birds during th e 3-day basal diet phase. There were no significant differences between the mean food consumption of c ontrol birds and any of the treatment group birds duri ng any phase of the study.

This toxicity study is classified as scie ntifically sound and sa tisfies the OCSPP 850.2200 guideline requirement for acute dietary toxici ty study with the bobwhite quail. This study is classified as acceptable.

MRID 40601002 The acute dietary toxicity of Tebut hiuron to 4-day-old mallard ducks ( Anas platyrhynchos ) was assessed over 8 days. Tebuthiuron was administ ered to the ducks in the diet at nominal concentrations of 0 (control), 600, 1200, 2500, and 5000 mg a.i./kg diet. Mean-measured concentrations were 0 (<LOQ, control), 583, 1176, 2578, and 5093 mg a.i./kg diet, respectively. No mortality or behavioral signs of toxicity were noted thro ughout the test. The 8-day acute dietary LC 50 was determined to be >5093 mg a.i./kg diet. According to the US EPA classification, Tebuthiuron w ould be classified as practically non-toxic to mallard ducks on an acute dietary basis.

During the five-day treatment phase, there was no significant differen ce between the mean body weight gain values of control birds and birds at the 583 mg a.i./kg diet level. However, ducks exposed to diets containing te buthiuron concentrations of >1 176 mg a.i./kg diet gained significantly less weight as compared with the control group. During the 3-day basal diet phase, there were no significant differen ces in mean body weight gain va lues of control and treat ducks. Ducks in the 2578 and 5093 mg a.i./kg diet mean-meas ured treatment levels ate significantly less food than control ducks. Ducks at the 1176 mg a. i./kg diet treatment level also consumed less food than control ducks, although this difference was not significantly significant. During the 3- day basal diet phase, ducks at the 2578 and 5093 mg a.i./kg diet test le vels consumed less food than control ducks; however, these differen ces were not statistically significant.

This toxicity study is classified as scie ntifically sound and sa tisfies the OCSPP 850.2200 guideline requirement for acute dietary toxici ty study with the mallard duck. This study is classified as acceptable.

MRID 48928201 The acute dietary toxicity of Tebuthi uron to 5-7 month-ol d Zebra Finches ( Taeniopygia guttata ) was assessed over 8 days. Tebuthiuron was administ ered to the birds in the diet at nominal concentrations of 0 (control), 562, 1000, 1780, 3160, and 5620 mg a.i./kg diet. Mean-measured concentrations were <50 (<LOQ, cont rol), 497, 895, 1590, 2870, and 5380 mg a.i./kg diet, respectively. The 8-day acute dietary LC 50 (with 95% C.I.) was 1465 (1145 to 1883) mg a.i./kg diet. According to the US EPA classifica tion, Tebuthiuron would be classified as slightly toxic

to Zebra Finches on an acute dietary basis.Page 112 of 121 Mortality was 80, 90, and 100% in the mean-measured 1590, 2870, and 5380 mg a.i./kg diet levels, respectively. During the exposure period, some birds were taken off of treated feed before the full 5-day exposure period was complete due to extremely reduced food consumption values.

These birds were counted as mortalities.

Treatment-related decreases in body weight gains were observed at 895, 1590, and 2870 mg a.i./kg diet during the exposure period (Days 0- 5). Body weight gains at these doses were comparable or greater than cont rols during the post-dosing peri od (Days 6-8). However, overall mean body weights were still reduced compared to controls in the 1590 and 2870 mg a.i./kg diet survivors. A direct comparis on of body weights and body weight gains could not be made in the 5380 mg a.i./kg diet group as all birds were ta ken off of treated feed after only 2 days of

exposure.

There was a slight reduction in food consumpti on noted in the 497 mg a.i./kg diet group.

Treatment-related reductions in f ood consumption were observed at ≥ 895 mg a.i./kg diet during the exposure period (Days 0-5). Post-exposure food consumption was comparable to controls at all doses. Mean daily dietary doses were 115.6, 170.5, 211.3, 250.2, and 175.8 mg a.i./kg bw/day in the mean-measured 497, 895, 1590, 2870, and 5380 mg a.i./kg diet levels, respectively. Clinical signs of toxicity were observed as follows: at 497 mg a.i./kg, up to 50% of birds displayed slightly ruffled appearance and wing droop between Days 2 and 6; at 895 mg a.i./kg, up to 60% of birds displayed ruffled appearance and wing droop between Days 2 and 7; at 1590 mg a.i./kg, all birds displa yed at least one clinical sign of toxicity (ruffled appearance, lethargy, and wing droop) by Day 4; at 2870 mg a.i. /kg, all birds were noted with at least one clinical sign of toxicity (ru ffled appearance, lethargy, wing dr oop, loss of coordination, prostrate posture, and loss of righting reflex) or died by Day 3; and at 5380 mg a.i./kg, all birds were noted with ruffled appearance by the afternoon of Day 1.

This toxicity study is classified as scie ntifically sound and sa tisfies the OCSPP 850.2200 guideline requirement for acute dietary toxici ty study with the Zebra Finch. This study is classified as acceptable.



### OCSPP 850.2300 – Avian Reproduction

MRID 00093690 The one-generation reproductive toxicity of tebuthiuron to 5-month-old mallard ducks ( Anas platyrhynchos ) was assessed over 22 weeks. Tebuthiuron was administered to the ducks in the diet at nominal concentrations of 0 (cont rol), 20 and 100 mg a.i./kg diet. Measured

concentrations in the diet we re not significan tly different.

There was no treatment-related mortality, signs of toxicity, or effect s on body weight or food consumption at any dietary level. No significant reduction in the reproductive parameters of egg laid, eggs cracked, viable embryos, live thr ee-week embryos, normal hatchlings, 14 day-old survivors, and eggshell thickness were observed. A statistically significan t but non-dose –related reduction in 14-day old survivors was observed at the 20 mg a.i. /kg-diet. With no tebuthiuron-Page 113 of 121 related effects observed in mallard ducks up to and at 100 mg a.i./kg diet, the NOAEC is 100 mg a.i./kg-diet, the highest concentration tested.

This study is scientifically sound and fulfills the guideline requirement for a mallard duck ( Anas platyrhynchos ) reproductive toxicity study. This study is classified as acceptable.

MRID 00104243 The one-generation reproductive to xicity of tebuthiuron to 6- month-old bobwhite quails ( Colinus virginianus ) was assessed over 22 weeks. Tebuthiuron was ad ministered to the chicks in the diet at nominal concentrations of 0 (control), 20 and 1 00 mg a.i./kg diet. Measur ed concentrations in the diet were not sign ificantly different.

There was no treatment-related mortality, signs of toxicity, or effect s on body weight or food consumption at any dietary level. No significant reduction in the reproductive parameters of egg laid, eggs cracked, viable embryos, live thr ee-week embryos, normal hatchlings, 14 day-old survivors, and eggshell thickness were observed in the treatment groups compared to control group. With no tebuthiuron-related effects observe d in bobwhite quails up to and at 100 mg a.i./kg diet, the NOAEC is 100 mg a.i./kg-di et, the highest con centration tested.

This study is scientifically sound and fulfills the guideline requirement for a bobwhite quail ( Anas platyrhynchos ) reproductive toxicity study. This st udy is classified as acceptable.

MRID 48928202 The one-generation reproductive to xicity of Tebuthiuron to 16 pa irs per level of 22-week old mallards ( Anas platyrhynchos ) was assessed over 20 weeks. Te buthiuron was administered to

the birds in the diet at nomi nal concentrations of 0 (negat ive control), 500, 900, and 1500 mg a.i./kg diet. Mean-measured concentrations were <50 (<LOQ, control), 500, 903, and 1550 mg a.i./kg diet.

There were no treatment-related mo rtalities, signs of toxicity, or effects on body weight or food consumption at any dietary level. A statisti cally significant (p<0.05) dose-dependent reduction in hatchling body weight and eggshell thickness was observed at 1550 mg a.i./kg diet compared to the controls. There were statistically si gnificant (p<0.05; Williams test, 26-41%) reductions from control in egg production (eggs laid pe r pen) in the 500, 903 and 1550 mg a.i./kg diet groups. A slight (<1%) reduction fr om control in eggs not cracked per eggs laid was detected at the lowest treatment level (p = 0.04), but was not considered to be treatment-related. No statistically significant differen ces in the other endpoints were observed between the control group and any of the treatment groups. Based on th e dose-dependent reductions in eggs laid, the NOAEC could not be determined in this study (i.e., <500 mg a.i./kg diet).

This study is scientifically s ound but does not satisfy the guide line requirement for a mallard ( Anas platyrhynchos ) reproductive toxicity study. The study is classified as supplemental due to significant effects in eggs laid at all test levels that a NOAEC coul d not be determined; while this deviation impacted the acceptabil ity of the study, the reviewer felt this study provides useful information that it should not be rejected. Th is study was conducted with progressively higherPage 114 of 121 concentrations of what was used in the orig inal study (MRID 00093690) at which no effects in birds were observed at and up to 100 mg a.i./kg di et. Combining the studies with test levels at 20, 100, 500, 903, and 1550 mg a.i./kg diet, the resu lting LOAEL and NOAEL would be 500 and 100 mg a.i./kg diet , respectively.

MRID 48928203 The one-generation reproductive to xicity of Tebuthiuron to 16 pa irs per level of 36-week old Northern bobwhite quail ( Colinus virginianus ) was assessed over 20 weeks. Tebuthiuron was

administered to the birds in the diet at nomin al concentrations of 0 (negative control), 500, 900, and 1500 mg a.i./kg diet. Mean-measured con centrations were <50 (<LOQ, control), 500, 903, and 1550 mg a.i./kg diet.

No treatment-related mortalities we re observed at any treatment leve l. Three control birds were found dead during Weeks 6, 13, and 14. One ma le bird in the 1550 mg a.i./kg group was euthanized on Day 4 of Week 16 due to fractur ed right leg. Adult male body weight gain was significantly reduced in a dose-de pendent manner 53-121% at all tr eated levels, relative to the negative control (p<0.05, William’s test). Adult female body weight was significantly reduced at the 1550 mg a.i./kg diet level, relative to the control (p<0.01; Jonckheer e-Terpstra test). No statistically-significant differences were obser ved between the control group and any of the treated groups for food consumption. Offspri ng body weights were significantly reduced in a dose-dependent manner, with reductions from c ontrol detected at the 903 and 1550 mg a.i./kg diet levels for hatchling body we ights (p<0.01; Jonckheere-Terpst ra test) and at the 1550 mg a.i./kg diet level for 14-day old survivor weight (p<0.05; William’s test).

No treatment-related effects on reproductive perfo rmance parameters were observed in the 500 mg a.i./kg diet group, but dose-dependent effects were detected for offspring survival. At 903 and 1550 mg a.i./kg diet, the offspring survival (14-day hatchlings per number hatched) was slightly (4-7%), but sign ificantly reduced, compared to the co ntrol (p<0.05; Jonckheere-Terpstra test). Also, at the 1550 mg a.i./kg diet level, egg production was reduced 23%, from an average of 44.8 eggs laid per pen in the control group to 34.7 eggs laid per pen in the treated group (p<0.05; Jonckheere-Terpstra test); both the study author and review er concluded that this effect was treatment-related, despite th e non-monotonicity of the data. No statistically significant differences in egg shell thickness were observe d between the control group and any of the treatment groups. The reviewer concluded that the NOAEC could not be determined in this study due to dose-dependent reductions in a dult male body weight ga in (i.e., NOAEC<500 mg a.i./kg diet).

This study is scientifically s ound but does not satisfy the guidelin e requirement for a Northern bobwhite quail ( Colinus virginianus ) reproductive toxicity study. Th e study is classified as supplemental due to significant effects in male we ight gain at all test levels that a NOAEC could not be determined; while this deviation impacted the acceptability of th e study, the reviewer felt this study provides useful information that it sh ould not be rejected. This study was conducted with progressively higher con centrations of what was used in the original study (MRID 00104243) at which no effects in birds were observe d at and up to 100 mg a.i./kg diet. If thePage 115 of 121 studies were combined with test concentrations at 20, 100, 500, 903, and 1550 mg a.i./kg diet, the resulting LOAEL and NOAEL would be 500 and 100 mg a.i./kg diet, respectively.



### OCSPP 850.3020 – Honeybee Ac ute Contact Toxicity Test

MRID 40840401

The acute contact toxicity of tec hnical tebuthiuron to honey bees ( Apis mellifera ) was tested in the laboratory. In the 48-hour acu te contact test, bees were ex posed to technical tebuthiuron administered topically to the thorax, at an app lication rate of 0 (negat ive control), 0 (solvent control), 13, 22, 36, 60, and 100 μg a.i./bee. No tr eatment-related effects were noted throughout the study period. Mortality rates did not exceed 11% in any of the treatment groups; mortality in the negative and solvent contro ls was 5% and 7%, respectivel y. The 48-hour acute contact LD 50 was >100 μg a.i./bee, the highest dose test ed. According to the US EPA classification,

Tebuthiuron would be classified as practically non-toxic to honeybees on an acute contact basis.

The study is scientifically sound and satisfies the guideline requirements for a honeybee acute contact toxicity test. This study is classified as Acceptable.



### OCSPP 850.4100 – Seedling Emergence and Seedling Growth Toxicity Test

MRID 41066901 The effect of the technical grade of tebuthiur on on the seedling emergence of monocot (corn, Zea

mays ; wheat, Triticum aestivum ; sorghum, Sorghum bicolor ; and rice, Oryza sativa ) crops at 0.04, 0.08, 0.16, 0.32, 0.64, and 1.28 lb a.i./A and dicot (cabbage, Brassicacea oleracea ; cotton, Gossypium hirsutum; cucumber, Cucumis sativus ; radish, Raphanus sativus ; soybean, Glycine

max ; and sunflower, Helianthus annuus ) crops at 0.02, 0.04, 0.08, 0.16, 0.32, 0.64 lb a.i./A was studied for 21 days.

Tebuthiuron did not interf ere with seed emergence of any of the species tested. One week after emergence, radish was determined to be extrem ely sensitive to tebuthiuron at 0.08 lb a.i./A. After three weeks, radish, cucumb er, cabbage, and wheat were seve rely injured. At the high rate tested, seedlings of these species were killed. Co rn, rice, cotton, and sunflower were intermediate in susceptibility and were injured 50% or more at the highest test level tested. The study author

determined a NOAEC of 0.02 lb a.i./A for dicots and 0.04 lb a.i./A fo r monocots three weeks after treatment. Early injury symptoms were ch lorosis and stunting of plants followed by burning of leaves and eventual plant death of some speci es at the highest test level. All species were reduced in height as the app lication rate was increased. Cucu mber, radish, cabbage, and wheat

were reduced the most.

The most sensitive monocot species was wheat based on fresh weight, with NOAEC and EC 25 values of 0.04 and 0.07 lb a.i./A, respectively. The most sensitive dicot species was cabbage based on fresh weight, with NOAEC and EC 25 values of 0.02 and 0.03 lb a.i./A, respectively.Page 116 of 121 This toxicity study is scientific ally sound and satisfies the guide line requirement for a Tier II seedling emergence toxicity study. This study is classified as Acceptable.

MRID 41066902 The effect of the technical grade of tebuthiur on on the seed germination of monocot (corn, Zea

mays ; wheat, Triticum aestivum ; sorghum, Sorghum bicolor ; and rice, Oryza sativa ) crops and dicot (cabbage, Brassicacea oleracea ; cotton, Gossypium hirsutum; cucumber, Cucumis sativus ; radish, Raphanus sativus ; soybean, Glycine max ; and sunflower, Helianthus annuus ) crops at the maximum application rate of 6.0 lb a.i./A was studied for 5 days.

Analysis of the data was by visual observati on. No significant differen ces were noted between treated and control groups. Corn, sorghum, wh eat, rice, soybean, cucumber, sunflower, and radish seeds were not affected, while cotton and cabbage germinati on was 2.8% and 3.8% less than the controls. The germination percenta ge for corn, sorghum, wheat, rice, soybean, cucumber, sunflower, cabbage, cotton, and radish was 100%, 95%, 99%, 76%, 88%, 99%, 96%, 73%, 97%, and 100%, respectively.

This study is no longer required by EPA; however, provides useful information on tebuthiuron to terrestrial plants.

MRID 48722703

The effect of Spike 20P (AI: Tebuthiuron) on the seedling emergence of monocot (onion, Allium cepa ; corn, Zea mays ; oat, Avena sativa ; and ryegrass, Lolium perenne ) and dicot (carrot,

Daucus carota ; cucumber, Cucumis sativus ; cabbage, Brassicacea oleracea ; soybean, Glycine

max ; sugarbeet, Beta vulgaris ; and tomato, Lycopersicon esculentum ) crops was studied at the following nominal concentrations:

Sugarbeet, tomato, and cabbage:
0 (negative control), 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, and 1.0 lb

a.i./A
Soybean:
0 (negative control), 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, 1.0, and 2.0 lb

a.i./A
Onion, ryegrass, oat, carrot, and cucumber:
0 (negative control), 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb a.i./A

Corn:
0 (negative control), 0.062, 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb a.i./A.

The growth medium used in the seedling emergen ce test was natural soil mixed with silica sand (loam, pH 6.5, organic ca rbon 1.0%). On day 21 the surviving plants per pot were recorded and cut at soil level for measuring the plant height and fresh weight.

Fresh weight and height were significantly affected in every species tested. Survival (% survived of planted) was signi ficantly affected in all species except soybean. Emergence wasPage 117 of 121 only significantly affected in cabbage and tomat o. The % inhibition in seedling emergence in the treated species as compared to the control range d from 3 to 52%. The most sensitive monocot species, based on fresh weight, in the seedli ng emergence test was ryegrass with an EC 25 of 0.27

lb a.i./A and a NOAEC of 0.25 lb a.i./A. The most sensitive dicot species, based on fresh weight,

was carrot with an EC 25 of 0.018 lb a.i./A and a NOAEC of 0.031 lb a.i./A.

However, the study author reported analytical recoveries of the test material from nominal 1.0, 2.0, and 4.0 lb a.i./A test levels yielded pre-appli cation recoveries ranging from 37 to 76% of the

nominal concentrations. At the first post-application, recoveries ranged from 63 to 66% of the

nominal concentrations. At the second post-application, recoveries ranged from 39 to 50% of the

nominal concentrations. The lower test concen trations were not veri fied. The study author averaged all of the application data and averaged all the percen t recoveries to obtain a single recovery value of 56% of nominal. If the revi ewer’s results are adjusted for the 56% average recoveries, the most sensitive monocot specie s was ryegrass based on fresh weight, with

NOAEC and EC 25 values of 0.14 and 0.15 lb a.i./A, respectively. The most sensitive dicot species was carrot based on fr esh weight, with NOAEC and EC 25 values of 0.017 and 0.010 lb a.i./A, respectively.

There were compound related phytot oxic effects observed in every species tested, with a doseresponse relationship expressed in the upper 4-5 test levels. Based on the phytotoxicity rating system used by the study author (0 = no injury, 100 = complete mortality), soybean and corn had maximum effects of 63 and 70. All other spec ies tested ex cept carrot and cucumber had maximum ratings ranging from 85 to 97. Carrot and cucumber experienced complete mortality, with a rating of 100.

This toxicity study is scientifically sound but does not satisfy the guideline requirement for a Tier II seedling emergence toxicity study. Th is study is classified as Supplemental.



### OCSPP 850.4150 – Vegetati ve Vigor Toxicity Test

MRID 48722704

The effect of Spike 20P (AI: Tebuthiuron) on the vegetative vigor of monocot (onion, Allium

cepa ; corn, Zea mays ; oat, Avena sativa ; and ryegrass, Lolium perenne ) and dicot (carrot, Daucus

carota ; cucumber, Cucumis sativus ; cabbage, Brassicacea oleracea ; soybean, Glycine max ; sugarbeet, Beta vulgaris ; and tomato, Lycopersicon esculentum ) crops was studied at the following nominal concentrations up to 4.0 lb a.i./A:

Sugarbeet, tomato, and cabbage: 0 (negative control), 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, and 1.0 lb

a.i./A Soybean: 0 (negative control), 0.0020, 0.0039, 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, 1.0, and 2.0 lb

a.i./A Onion, ryegrass, oat, carrot, and cucumber: 0 (negative control), 0.0078, 0.016, 0.031, 0.062, 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb a.i./APage 118 of 121 Corn: 0 (negative control), 0.12, 0.25, 0.50, 1.0, 2.0, and 4.0 lb a.i./A.

The growth medium used in the vegetative vi gor test was natural soil mixed with silica sand (loam, pH 6.5, organic ca rbon 1.0%). On day 21 the surviving plants per pot were recorded and cut at soil level for measuring the plant height and fresh weight.

In the vegetative vigor test, the plant fresh weight a nd shoot length were si gnificantly affected by the test material. Survival was significantly affected in onion, oat, carrot, cucumber, and sugarbeet.

The most sensitive monocot species, based on fresh weight, in the vegetative vigor test was ryegrass with an EC 25 of 0.30 lb a.i./A and a NOAEC of 0.12 lb a.i./A. The most sensitive dicot species, based on fresh weight, was sugarbeet with an EC 25 of 0.16 lb a.i./A and a NOAEC of

0.062 lb a.i./A.

However, the study author reported analytical recoveries of the te st material in the nominal 1.0, 2.0, and 4.0 lb a.i./A test levels yielded pre-appli cation recoveries ranging from 50 to 84% of the nominal concentrations for all sp ecies except cucumber, and 38 to 71% of nominal for cucumber. At post-application, recoveries ranged from 55 to 84% (all speci es except cucumber), and from 44 to 88% (cucumber) of the nominal concentrati ons. The lower test co ncentrations were not verified. The study author averag ed all of the application data and averaged all the percent recoveries to obtain a single rec overy value of 61% of nominal. If the reviewer’s results are adjusted for the 61% average recoveries, the mo st sensitive monocot species was ryegrass based on fresh weight, with NOAEC and EC 25 values of 0.07 and 0.18 lb a.i. /A, respectively. The most sensitive dicot species was sugarbeet based on fresh weight, with NOAEC and EC 25 values of 0.04 and 0.10 lb a.i./A, respectively.

There were compound related phytot oxic effects observed in every species tested, with a doseresponse relationship expressed in the upper 3-5 test levels. Based on the phytotoxicity rating system used by the study author (0 = no injury, 100 = complete mortality), corn and soybean had maximum effects of 36 and 46, respectively. Ryegrass, tomato, sugarbeet, and cabbage had maximum ratings ranging from 54 to 76. Onion, oa t, carrot, and cucumber had maximum ratings ranging from 86 to 98.

This toxicity study is scientifically sound but does not satisfy the guideline requirement for a Tier II vegetative vigor toxi city study. This study is classified as Supplemental.



### OCSPP 850.4400 – Aquatic Plant Toxicity Test Using Lemna spp.

MRID 41080404 In a 14-day acute toxicity study, freshwater aquatic vasc ular plants, duckweed ( Lemna gibba ), were exposed to tebuthiuron mean-measured concentrations of <0.005 (<LOD), 0.005, 0.0096, 0.049, 0.091, 0.19, 0.38, and 0.78 mg a.i./L.Page 119 of 121 The percent inhibition of frond density after 7 and 14 days ranged from 15% to 86% and -6% (stimulation) to 98%, respectively. The percent i nhibition of yield at 7 and 14 days, calculated from frond density, ranged from 16% to 90% a nd -6% to 100%, respectively. The percent inhibition of growth rate at 7 and 14 days, calculated from frond density, ranged from 6% to 61% and -1% to 99%, respectively. The percent inhibiti on of frond dry weight (biomass) after 14 days ranged from -21% to 98%. The percent inhibiti on of yield after 14 da ys, calculated from frond dry weight, ranged from -22% to 100%. The percent inhibition of growth rate after 14 days, calculated from frond dry weight, range d from -5% to 100%. The 7-day EC 50 reviewercalculated for yield and growth rate of frond density was 0.192 a nd 0.495 mg a.i./L, respectively. The 14-day EC 50 reviewer-calculated for yield and gr owth rate of frond dry weight was 0.126 and 0.205 mg a.i./L, respectively. Yield in frond dr y weight was the most sensitive endpoint, its corresponding NOAEC was 0.091 mg a.i./L due to significant differences between the negative control and the three highest test concentrations.

This toxicity study is scientifically sound and doe s not fulfill the guideline requirement for a Tier II aquatic vascular plant t oxicity study with duckweed, Lemna gibba . This study is classified as supplemental.



### OCSPP 850.4500 – Algal Toxicity Test

MRID 00138697 In a 14-day toxicity stud y, freshwater green alga, Selenastrum capricornutum , were exposed to tebuthiuron nominal concentrations of 0 (n egative control), 5, 10, 15, 20, 40, 80, 160, and 320 μg/L under static conditions. Th e mean-measured test concentra tions were 0 (control; LOD <0.5 μg/L), 5, 10, 13, 16, 33, 79, 168, and 338 μg a.i./L. After 5 days, the percent inhibition in

biomass relative to the control ra nged from 0% to 83%. The 5-day EC 50 and NOAEC was 50 and 13 μg a.i./L, respectively.

This toxicity study is scientifically sound and doe s not fulfill the guideline requirement for a Tier II algal toxicity study with freshwater green algae, Selenastrum capricornutum . This study is classified as supplemental.

MRID 41080402 In a 7-day toxicity study, cu ltures of the marine diatom, Skeletonema costatum , were exposed to

tebuthiuron nominal concentrations of 0 (negative control), 0.002, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 mg a.i./L under static conditions. Mean-measured concentrations were 0.0018, 0.0092, 0.018, 0.038, 0.076, 0.16, and 0.3 mg a.i./L.

After 96-hr and 168-hr, the percent inhibition in yield, calculated from cell density, relative to the control ranged from 38% to 105% and -36% to >100%, respectively. The percent inhibition in AUC (area under the curve), calculated from cell density, relative to the control ranged from -

4% to 82% and -21% to 98% at these respectively times. The percent inhibition in growth rate, calculated from cell density, relativ e to the control at 96-hr an d 168-hr ranged from 15% to >100% and -9% to >100%, respectively. The 96-hr EC 50 for yield, AUC and growth rate was 0.05 mg a.i./L, 0.06 mg a.i./L, and not calculable, re spectively. With yield as the most sensitivePage 120 of 121 endpoint, its corresponding NOAEC was 0.038 mg a. i./L based upon significant reductions in yield detected between the contro l and the three highest test concentrations of the seven test

concentrations tested.

This toxicity study is scientifically sound but does not satisfy EPA guideline requirements for a Tier II aquatic nonvascular plant toxi city study with the marine diatom, Skeletonema costatum

. This toxicity study is classified as supplemental.

MRID 41080403 In a 7-day toxicity study, cultu res of the freshwater diatom, Navicula pelliculosa , were exposed

to tebuthiuron nominal con centrations of 0 (negative control), 0.005, 0.01, 0.05, 0.1, 0.2, 0.4, and 0.8 mg a.i./L. Mean-measured concentrations were <0.005 (<LOD), 0.0012, 0.011, 0.056, 0.11, 0.22, 0.46, and 0.89 mg a.i./L, 82-107% of nominal concentrations.

After 96-hr and 168-hr, the review er-calculated percent inhibition in yield based on cell density

relative to the cont rol ranged from 11% to 100% and - 17% to 100%, respec tively. The percent inhibition in area under the growth curve, calculated from cell density, relative to the control ranged from -5% to 109% at 96 hours and -19% to 98% at 168 hours. The percent inhibition in growth rate relative to the control at 96 and 168 hours ranged from 4% to 100% and -3% to 112%, respectively. The review er-calculated 96-hour EC 50 for yield, area under the growth curve, and growth rate was 0.09, 0.1, and 0.18 mg a.i./L . Significant reductions in yield, the most sensitive endpoint, were detected between the control and the four highest test concentrations; as of a result, the corresponding NOAEC was 0.056 mg a.i./L.

This toxicity study is scientifically sound but does not fulfill EPA guideline requirements for a Tier II aquatic nonvascular plant toxic ity study with the freshwater diatom, Navicula pelliculosa

. This toxicity study is classified as supplemental.



### OCSPP 850.4550 – Cyanobacteria (Anabaena flos-aquae) Toxicity Test

MRID 41080401 In a 7-day toxicity study, cultures of the freshwat er blue-green algae, Anabaena flos-aquae , were exposed to tebuthiuron nomina l concentrations of 0 (neg ative control), 0.31, 0.62, 1.25, 2.5, 5, and 10 mg a.i./L. Mean-measured concentrations were <0.012 (<LOD), 0.31, 0.62, 1.32, 2.62, 5.49, and 11.05 mg a.i./L, 98-105% of nominal concentrations.

At 96-hr and 168-hr, the reviewe r-calculated percent inhibition in yield based on cell density relative to the control ranged from 13% to 88% and -2% (growth) to 88%, respectively. The percent inhibition in area under the growth curve based on cell de nsity relative to the control ranged from 10% to 87% and 7% to 87% at these respectively times. The percent inhibition in growth rate based on cell density relative to th e control at 96-hr and 168-hr ranged from 3% to 43% and -0.2% (growth) to 39%, respectively. Th e study author based it conclusions upon test

termination that lasted 168 hours; however, OSCPP guidelin e 850.4500 prefers 96 hours toxicity endpoints. The reviewer-calculated 96-hour EC 50 for yield, area under the growth curve, and growth rate was 0.81, 1.09, and >11.05 mg a.i./L, respectively. Significant reductions in yield,Page 121 of 121 AUC, and growth rate were detected between th e control and all test concentrations, its NOAEC

could not be established. W ith yield as the most sensit ive endpoint, its corresponding EC 05 was 0.03 mg a.i./L.

This toxicity study is scientifically sound howev er does not fulfill EPA guideline requirements for a Tier II aquatic nonvascular plant toxicity study with the freshwater blue-green algae, Anabeana flos-aquae . This toxicity study is classified as Supplemental.