-Page 2 of 74- 

### anticipated from exposure to isoxaben. Acute risk to mammals is not antic ipated, but there is the potential for chronic risk to ma mmals on a chronic dose-basis (RQs ≤ 3.84). Risk to listed and non-listed species of te rrestrial plants (RQs ≤ 80.1) and aquatic vascular plants (RQs ≤ 14.7) may

occur.

Table 1 summarizes the representative uses assessed a nd the taxa that may potentially be directly at risk from exposure to isoxaben.

Table 1. Risk Resulting from Isoxa ben Exposure Presented by Taxon

Use Pattern Category Aquatic

Invertebrates Fish (surrogatefor aquaticphase amphibians) Birds, (surrogate

for

terrestrialphase amphibians

and reptiles) Mammals Plants Terrestrial

Invertebrates

Turfgrass /

Groundcover/ perennials / Non-cropland /

Christmas

tree/conifer plantations, hardwood nursery /

Ornamentals/ Non-bearing fruit &

nut trees & vineyards / Bearing fruit and

nut trees and vineyards / Eucalyptus Acute risk: Not expected; acute toxicity is limited by solubility

Chronic risk: Not expected Acute risk:

Not expected; acute toxicity is limited by solubility

Chronic risk: Not expected Acute risk:

Not expected

Chronic

risk:

Not expected Acute risk:

Not expected

Chronic

risk:

Potential risk; RQs(dosebased)

exceed

LOC for

all uses

based on

foliar application (RQs

≤ 3.84) Terrestrial:

Potential

risk to

listed and

non-listed plants; RQs

exceed LOC (RQs

≤ 80.1)

Aquatic

Vascular:

Potential

risk to

listed and

non-listed plants; RQs

exceed LOC (RQs

≤ 14.7)

Aquatic

nonvascular:

Not expected Non-listed

and Listed: Not expected-Page 3 of 74- 

## Environmental Fate and Ecological Risk Assessment for the Regist ration Review of Isoxaben

Isoxaben N- [3-(methylpent-3-yl)isoxazol-5-yl]-2,6-dimethoxy-benzamide

CAS Registry Number 

### 82558-50-7

PC Code 125851

Prepared by: Andrew Shelby, Physical Scientist Amy Blankinship, Chemist
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: Brian Kiernan, Biologist, ERB VI Ibrahim Abdel-Saheb, Physical Scientist, ERB VI
Mark Corbin, Branch Chief, ERB VI



### September 3, 2014

### Page 4 of 74 

## Table of Contents

1. Executive Summary

.............................................................................................................................. ............. 5

2. Problem Formulation

.............................................................................................................................. .......... 8

2.1. Nature of Regulatory Action ......................................................................................................................... 8

2.2. Nature of the Chemical Stressor ................................................................................................................... 9

2.3. Use Characterization

.............................................................................................................................. ........ 9

2.4. Conceptual Model

.............................................................................................................................. ........... 12 Analysis Plan ................................................................................................................. .............................................. 14



### Residues of Concern ..................................................................................................................14 Measures of Exposure .......................................................................................................... ....15

Measures of Effect ............................................................................................................ ........16

3. Analysis

.............................................................................................................................. ............................... 16

3.1. Exposure Characterization .......................................................................................................................... 16

3.2. Ecological Effects Characterization ............................................................................................................ 32

4. Risk Characterization

.............................................................................................................................. ........ 37

4.1. Risk Estimation

.............................................................................................................................. ............... 37

4.2. Risk Description

............................................................................................................................... ............. 43

4.2.1. R isks to Aquatic Organisms ................................................................................................................... 44

4.2.2. Risks to Terrestrial Organisms ............................................................................................................. 46

5. Federally Threatened and Endanger ed (Listed) Speci es Concerns ................................................................. ... 52



### 6. Endocrine Disruptor Screening Program .......................................................................54

7. Literature Cited

.............................................................................................................................. .................. 55

### Page 5 of 74 1. Executive Summary

The Environmental Fate and Effects Division (E FED) has completed the registration review preliminary ecological risk assessment for is oxaben (N- [3-(methylpent-3-yl)isoxazol-5-yl]-2,6- dimethoxy-benzamide; CAS No. 82558-50-7; PC Code 125851) and its end-use products. Isoxaben is a pre-emergent benzamide herbicide us ed for the control of broadleaf (dicotyledonous) weeds. Isoxaben is formulated as a dry flowable , granule, and suspension concentrate. Isoxaben is registered for use on a va riety of non-agricultural uses in cluding: turfgrass, ornamentals (landscape, container and field) , groundcovers/perennials, conife r plantations/har dwood nurseries, non-bearing fruit and nut trees, non-be aring vineyards, and other non-cropl and. It is also registered for agricultural use on bearing fruit and nut trees, vineyards, and eucalyptus. The majority of uses have a maximum application rate of 1.0 lb a.i./A/applic ation (pounds of active ingredient per acre per application), with three applications per year and a 60-day reapplication interval (i.e., yearly application of 3.0 lb a.i./A). However, ther e is at least one label (EPA reg. no. 62719-658 ) 

### where the maximum yearly application rate is 4.0 lb a.i. /A. Isoxaben products are ge nerally registered for

both non-residential and residential use. Recent isoxaben ecologica l risk assessments include the Section 3 new use assessment for bearing nut trees and vineyards (USEPA, 2010; D341496).

Isoxaben is moderately persiste nt and mobile. Isoxaben does not hydrolyze and does not appear to readily degrade in terrestrial environments. Pr imary routes of degradation appear to be biodegradation in aerobic and an aerobic water bodies and photolys is in shallow, clear water

bodies.

Isoxaben is not acutely toxic to freshwater and es tuarine/marine fish and invertebrates at its limit of solubility. On a ch ronic exposure basis, is oxaben resulted in decr eased reproduction (number of young/female) and growth of freshwater inve rtebrates and decreased reproduction (number of young/female) of estuarine/marine invertebrates at te st concentration levels greater than estimated

environmental concentrations. Chroni c toxicity data for freshwater fish indicate it is not toxic near the limit of solubility. Chronic data for estuarin e/marine fish are not available, however, the freshwater fish chronic toxicity data was consid ered sufficient to evaluate potential risk to estuarine/marine fish. Isoxaben is practically nont oxic to birds, mammals, and beneficial insects ( i.e. , honey bees) on an acute exposure basis as no effects were record ed in the available studies ( i.e. , the no effect level was greater than the highest concentration tested). Chronic toxicity testing with birds did not identify an adverse respons e threshold (i.e., no eff ects observed at highest concentration tested). In the chronic mammalian reproduction study, significant treatment-related reductions in parental bodyweight and decrease s in viable pups were observed. Based on the available plant toxicity data, is oxaben exhibited low toxicity to aquatic non-vascular plants, but exhibited toxicity to terrestria l and aquatic vascular plants.

Potential effects to federally-lis ted endangered and threatened sp ecies (listed species) based on level of concern (LOC) exceedances require an in-d epth listed species evaluation determining the potential co-occurrence of listed species and use pa tterns of isoxaben. Identified potential risks to listed species are summarized in Table 1.

### Page 6 of 74 Table 1. Potential Effects to Federally Listed Taxa Associated with Direct Effects from the Registered Uses of Isoxaben.

Listed Plant Taxon Potential Direct Effects Terrestrial and semi-aquatic plants – monocots and dicots Yes 1

Aquatic nonvascular plants No 2
Aquatic vascular plants Yes 1

Listed Animal Taxon Potential Direct Effects

Acute Chronic

Terrestrial invertebrates No 3 No

Mammals No 3 Yes 4

Birds No 3 No 3
Reptiles No 3 No 3
Amphibians No 3 No 3

Freshwater fish No 3 No 3

Freshwater invertebrates No 3 No 3

Estuarine/marine fish No 3 No 3

Estuarine/marine invertebrates No 3 No 3

1 RQs exceed the listed LOC based on toxicity data for bo th terrestrial plants and aquatic vascular plants.

2 Risk of direct effects from isoxaben exposure expected to be below the LOC

3 Risk of direct effects from acute and chronic exposure to terres trial and aquatic animals is exp ected to be below the LOC, exce pt for chronic

risk to mammals.

4 Chronic risk to mammalian species may occu r as the LOC was exceeded for all register ed uses from exposure to isoxaben on a chro nic dosebasis, but not on a dietary basis.



### Based on this screening-level assessment, acute risk resulting from direct effects is not expected for listed birds (surrogates for terrestrial-phase amphibians and reptiles), mammals, freshwater and estuarine/marine fish (surrogates for aquatic-pha se amphibians), freshwater and estuarine/marine

invertebrates and terrestri al invertebrates (using honeybees as a surrogate) from the use of isoxaben on all of its registered use sites. Chronic risk resu lting from direct effects to listed birds, freshwater and estuarine/marine fish, freshwater and estuarine/marine invertebrates is not expected from the use of isoxaben on all of its registered use sites. Direct effects to aquati c non-vascular plants are not anticipated. Potential direct effects on liste d terrestrial and aquatic vascular plants and mammals (chronic exposure) from the use of isoxa ben 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 th e Registration Review process, it is premature to

make effects determinations until further refine ments are conducted. In order to make speciesspecific effects determinations, useful refinement s include more detailed 1) species-specific ecological and biological da ta; 2) information on use patterns fo r isoxaben; and 3) sub-county level spatial proximity analyses for the co-occurrence of potential areas of effects and listed species/designated critical habitats of concern. Examples of such refinements are described below.

EFED is currently developing to ols that are expected to furt her refine the species-specific assessment and designed to aid in making effects determinations for individual listed species and/or their designated critical habi tats (if applicable). Information obtained from the U.S. Fish & Wildlife Service (USFWS), the National Marine Fisheries Service (NMFS) , and other reliable sources is being collated by EFED to address all currently listed sp ecies. The information will be stored in an Office of Pesticide Programs Pe sticide Registration Information System (PRISM) knowledgebase, which consists of an information repository for biological and behavioral data

### Page 7 of 74 relevant to specific species and/or their habitats and a document re pository that contains supporting documents (e.g., USFWS recovery plan s) and electronic information ( e.g ., GIS data files). These data will be relied upon to provide information on habitat, diet, life history variables, and temporal and spatial data. For terrestrial taxa specifica lly, the biological informa tion relevant to Risk Quotient (RQ) calculations ( e.g ., diet and body weight) will be used to parameterize exposure estimates to derive species-specif ic RQs consistent with currently used methods in the T-REX and

T-HERPS models.

Refinements may also include more detailed analyses of the registered uses and their use patterns that result in level of concern (LOC) exceedan ces for listed species in the screening-level assessment. The analyses may include more information on where, when, and how isoxaben is used on turfgrass, groundcover, perennials, no n-cropland, Christmas tr ee/conifer plantations, hardwood nursery, ornamentals, non-bearing fruit & nut trees & vineyards, bearing fruit and nut trees and vineyards, and eucalyptus. Actual us age data (when available) and national land-cover datasets that indicate potential use sites ( e.g ., national land cover dataset (NLCD), crop data layer (CDL)) may be used to s upport a more refined anal ysis of where isoxaben is reasonably expected to be used. Similarly, refinements for the timi ng of applications and how isoxaben is used may involve an analysis of reported usage data (if available) and a more in-depth exploration of agronomic practices.

The U.S. Environmental Protection Agency (EPA), along with the U.S. Department of Agriculture (USDA), the U.S. Fish and Wildlife Service (FWS ), and the National Mari ne Fisheries Service (NMFS), have announced the availability of a report developed by the National Academy of Sciences’ (NAS) National Research Council (NRC) outlining recommendations on specific

scientific and technical issues related to the development of endangered and threatened species risk assessments for pesticides that are complia nt with the Endangered Species Act (ESA) and the Federal Insecticide, Fungicide, and Rodenticid e Act (FIFRA). The EPA, USDA, FWS and NMFS asked the NRC to consider a range of sc ientific and technical issues including: • identifying best available scientific data and information; • considering sub-lethal, indire ct and cumulative effects; • assessing the effects of chemical mixtures and inert ingredients; • analyzing the effects of pesticid e use through the us e of models; • incorporating uncertainties into the evaluations; and • using geospatial information and datasets th at can be employed by the agencies in the

course of these assessments.

After reviewing the NRC’s recommendations on th ese scientific and technical issues, the EPA and its federal partners will determine how th ese recommendations can be implemented and incorporated into the scientific approaches for developing listed species ri sk assessments. It is anticipated that any draft guida nce and/or science policies de veloped by EPA and its federal partners as a result of the NAS recommendations would be released for public comment prior to implementation.

The refinements based on species-specific data a nd detailed usage information, when available, are expected to help to more accurately identify pote ntial areas of effect and to better inform effects

### Page 8 of 74 and habitat determinations for listed species and a ny designated critical habitats. For example, if isoxaben is used when a particular species of concern is not present (e.g., it is migrat ory) or is not co-located in space, then risk to the species may often be precluded. If LOCs are still exceeded for mammals, and terrestrial and aquatic vascular plants after conducting the refined analyses, then further analyses of the potential spatial/temporal co-occurrence of listed species of concern (and any designated critical ha bitat) may be conducte d. The extent of possi ble refinement in the analyses of spatial/temporal co-occurrence will largely depend on the scale and quality of the available sub-county level use site (e .g., NLCD, CDL) and species location data

.

2. Problem Formulation

The purpose of problem formulation is to provide the foundation for the environmental fate and ecological risk assessment in suppor t of the registration review of the herbicide isoxaben (N- [3- (methylpent-3-yl)isoxazol-5-yl]-2,6-dimethoxy- benzamide; CAS No. 82558-50-7; PC Code 125851). The problem formulation sets the objectives for the risk assessment, establishes a risk hypothesis and conceptual model depicting potentia l risk, and provides a plan for analyzing the data and characterizing the risk associated with the uses of isoxaben (USEPA, 1998).

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 threaten ed species (hereafter referred to as “listed”) and th eir designated critical habitat are also considered under the Endangered Species Act (ESA) in order to ensure th at the continued registra tion of isoxaben is not likely to jeopardize the continued existence of listed species or adversel y 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).

1 http://www.epa.gov/oppsrrd1/registration_review/

### Page 9 of 74 Recent isoxaben ecological risk assessments include the Section 3 new use assessment for bearing nut trees and vineyard s (USEPA, 2010; D341496).

2.2. Nature of the Chemical Stressor

Isoxaben is a pre-emergent benzamide herbicide us ed for the control of broadleaf (dicotyledonous)

weeds. Isoxaben has been shown to inhibit th e conversion of glucose to cellulose in cell wall synthesis in sensitive species, with grasses (Fam ily: Poaceae) tending to be more tolerant than other plant groups (Salihue et al. 1998). Isoxaben is not thought to be highly mobile in adult plant tissues, apparently limiting its toxicity to older plants, but allowing increased efficacy in emerging seedlings. The vegetative vigor of early growth pl ants, particularly ryeg rass, is affected by isoxaben, as discussed in the Ec ological Effects Characterization. Chemical properties of isoxaben are presented in Table 2

.

Table 2. Nature of the Chemical Stressor

Common name Isoxaben (EL-107)

Chemical Name N- [3-(methylpent-3-yl)isoxazol-5-yl]-2,6- dimethoxy-benzamide

Chemical Structure

Pesticide type Herbicide

Chemical class Benzamide

CAS number 82558-50-7 Empirical formula C 18 

### H 24 

### N 2 

### O 4 

### Molecular Mass (g/mol) 332.39 g

· mol -1


### Vapor pressure (torr) <3.9 X 10 -7


### Henry’s Law Constant at 20 o 

### C (atm-m 3 

### /mole) 8.5x10 -10



### Solubility in water (ppm) 1.42 Log K ow 

### 2.64 pK a 

### at 25 o 

### C 9.78

2.3. Use Characterization

Isoxaben is formulated as a dr y flowable, granule, and suspen sion concentrate. Isoxaben is registered for use on a variety of non-agricultu ral uses including: tu rfgrass, ornamentals (landscape, container and field) , groundcovers/perennials, conife r plantations/har dwood nurseries, non-bearing fruit and nut trees, non-be aring vineyards, and other non-cropl and. It is also registered for agricultural use on bearing fruit and nut trees and vineyards. The majority of uses have an

### Page 10 of 74 application rate of 1.0 lb ai/A/a pplication, three applica tions per year with a 60-day reapplication interval. However, there is at l east one label where the maximum y early application rate is 4.0 lb a.i./A (EPA reg. no. 62719-658 ) 

### . Isoxaben products are genera lly registered for both nonresidential and residential use. Current labels allow for broadcast and spot treatment applications with spot treatments potentially resulting in less exposure; howeve r, in this assessment exposure modeling was based on a per acre basis. Based on label instructions for the registered isoxaben product labels, most prohibit aeria l application; it is not clear whether all of the current product labels prohibit aeri al application ( e.g. usage on conifer seed orchar ds). While there are reported geographical (U.S.state) restrictions for some registered uses on so me of the labels, other labels for the same registered uses do not indicate any geographical restrictions. As such, where there was not a consistent geographica l restriction, potential environmental exposures were estimated assuming no geographic restrictions . There appears to be consiste nt label prohibitions on direct applications to water. Warnings regarding th e potential toxicity to aquatic organisms and avoidance of spray drift are on the labels. Labeled use patt erns for isoxaben are summarized in

Table 3 , below.

Table 3 Summary of the Maximum Isoxaben Application Rates by Use Site

Use Application

method Residential

or Agricultural Max. Single
app rate (lb a.i./A) Max #

apps per

year Max App rate

per year (lb a.i/A) Min. App

interval (days) Comment

Turfgrass (Established) Ground (spray) Both 1.02 NS/4 4.03 56-60 AZ and NY

use restriction

inconsistent among labels,

as well as for chemigation Granule Reside ntial 1.08 2 2.16 56-84

Lawns (turfgrass) Ground (spray) Agricultural 1.0 NS 1.0 60 No use in NY,

AZ

Granule Both 1.0 NS/4 3.2 60/NS

Ornamentals (landscape, container, field) Ground (spray) Both 1.02 NS/4 4.03 NS/56-60 AZ

restrictions for

commercial

use Granule Both 1.0 3 3.0 60

Groundcovers/perennials Ground (Spray) Both 1.02 NS/4 4.03 60 AZ use

restriction

inconsistent among labels.

Not for

commercial

use. Granule Both 1.0 NS/3 3.0 60

Non-cropland Ground (spray) Both 1.02 NS/4 4.03 60 AZ restriction

inconsistent among labels.

Not for

commercial

use. Granule 1.0 NS/3 3.0 60

Non-bearing fruit & nut trees & non-bearing vineyards Ground (spray) Both 1.0 NS/3 3.0 60/NS Restrictions in

AZ Granule Agricultural 1.0 NS/3 3.0 60

Christmas tree/conifer plantations, hardwood

nursery Ground (spray) Both 1.02 NS/4 4.03 60 Not for

commercial

use in AZ Granule NS 1.0 NS/3 3.0 60

### Page 11 of 74 Fruit and nut trees and vineyards Ground (spray) NS 1.02 2 1.0 30/NS Not for use in

NY Eucalyptus Ground (spray) NS 0.75 2 1.0 30 62719-612:

Not for use in NY; do not apply w/in

200ft of susceptible
non-target plants NS= the number of application was not specif ically reported on label but rather calcul ated using the single maximum application rate and yearly rate. NS/# - the number of applications was not specified on some labels while others pr ovided a discrete numbe r of applications



### A screening level estimate of curren t usage of isoxaben is presented in Table 4 . This screening level usage assessment from the Biological and Economic Analysis Division (BEAD) presents usage data on an annual basis from USDA’s National Agricultural Statistics Service, the California Department of Pesticide Regulation, and private pe sticide market research, with data updated to 2012. This analysis indicates that on an annual basis, grapes a nd pistachios (based on pounds a.i. used) along with caneberries are the dominant agricultural use patt erns. Non-agricultural uses, which comprise the majority of registered uses for isoxaben, are not repr esented in this table.

Table 4. Isoxaben Screening Level Us age Analysis (SLUA) for 2004-2012 Average Percent Crop Treated
Crop Lbs. A.I. Average Maximum

Almonds <500 <1 <2.5

Apples <500 <1 <2.5
Apricots <500 <1 <2.5

Caneberries <500 5 5
Grapes 8,000 <2.5 5

Hazelnuts <500 <1 <2.5

Nectarines * <500 NC NC

Olives * <500 NC NC

Peaches <500 <1 <2.5

Pecans <500 <1 <2.5

Pistachios 3,000 <2.5 <2.5

Plums/Prunes <500 <1 <2.5

Walnuts <500 <1 <2.5

All numbers are rounded. <500: less than 500 pounds of active ingredient. <2.5: less than 2.5 percent of crop is treated. <1: less than 1 percent of crop is treated. * Based on CA DPR data only (80% or more of U.S. acres grown are in California) NC: not calculated, only pounds a.i. available.

### Page 12 of 74 In addition to the screening level use inform ation from BEAD, the U.S. Geological Survey (USGS) also provides use data with geographical mapping. As shown in Figure 1, based on USGS National Water Quality Assessment Progr am (NAWQA) from 2011, isoxaben agricultural uses appear to be used predominately on orch ards and grapes in California and Oregon. NAWQA does not consider non-ag ricultural uses in its data.

Figure 1 . Reported Isoxaben Use from USGS NAWQA database
http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2011&map=ISOXABEN&hilo=L&disp=

Isoxaben (accessed June 26, 2014).



### 2.4. Conceptual Model

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

isoxaben are shown in Figure 2 . The conceptual model used to de pict the potential ecological risk associated with the registered uses of isoxaben as sumes that, as an herbicide, isoxaben is capable of adversely affecting terrestri al and aquatic animals and plan ts, provided that environmental concentrations are sufficiently elevated as a re sult of the labeled uses. Solid arrows in Figure 2 depict the most likely routes of exposure and effects; dashed lines depict potential routes of exposure that are not consid ered likely for isoxaben.Page 13 of 74Foliage applied Isoxaben and its resulting degradatesSTRESSORVolatilization/Wind SuspensionSpray DriftRunoff/ ErosionLeaching (Infiltration)/PercolationDirect DepositionSOURCE/TRANSPORTPATHWAYSTerrestrial FoodResidues (foliage, fruit,seeds, insects,granules)UplandFoliage/ SoilRiparian/WetlandFoliage/ SoilReceivingWater Body/SedimentGroundwaterTerrestrialUplandPlantsRiparian/WetlandPlantsTerrestrial Vertebrates(Birds, Mammals,Reptiles, Terrestrial PhaseAmphibians)AquaticPlantsAquaticInvert. &VertebratesPlantPopulation:ReducedPopulationGrowth,BiomassIndividual Animals: ReducedSurvival, Growth,Reproduction,IndividualInvertebrates,Vertebrates:ReducedSurvival, Growth,ReproductionIndividual Plants:Reduced SeedlingEmergence,Vegetative VigorIngestionDirect ContactRoot UptakeUptake/AdsorptionGill/IntegumentUptakeDirect ContactRoot UptakeSOURCE/ EXPOSUREMEDIAEXPOSURE ROUTERECEPTORSATTRIBUTECHANGEIngestion Upthe FoodChainPiscivorousVertebratesIndividual Animals:Reduced Survival,Growth,ReproductionEpibenthic,and BenthicInvertebratesEpibenthic andBenthic Animals:Reduced Survival,Growth,ReproductionIngestion/Gill/IntegumentUptakeFigure 2.Conceptual Model of the Transport and Effects ofIsoxaben in Terrestrial and Aquatic Environments*Dotted lines indicate that, although this exposure route/mediawas considered, its contribution to the fate and transport of isoxabenis expected to be negligible

### Page 14 of 74 The hypothesis for the risks of isoxaben 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. Volatility is not considered a significan t route of transport considering isoxaben’s vapor pressure. For terrestrial organisms, the major route of exposure is via diet, such as through consumption of plant leaves or insects, which c ontain isoxaben residues as a result of direct application and/or spray drift, or from consumpt ion of isoxaben granules directly. For aquatic animal species, the major routes of exposure are dire ct contact via the respir atory surface (gills) or the integument. Aquatic vascular and non-vascular plants may also be exposed via direct uptake and adsorption. Risk to terr estrial plants is also considered in this screening-level assessment. Estimated exposure concentrations for all orga nisms are obtained through 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 is oxaben have the potential to reduce survival, reproduction, and/or growth in listed and non-listed terrestrial and aquatic organisms.

Analysis Plan

Residues of Concern

The stressors of ecological concern for aquati c and terrestrial organisms are isoxaben and degradates of similar chemical structure to the parent (other residues of concern). Therefore, these degradates can be available to runoff a nd translocated to water bodies based on their observed formation due to the biodegradation of isoxaben in aerobic and anaerobic soil metabolism studies. Major degradates, those o ccurring at more than 10% of applied isoxaben, detected during aerobic and anaerobic soil metabolism studies and aerobic and anaerobic aqueous metabolism studies include: hydroxyisoxaben; dimethoxybenzamide; methoxyphenylpyrimidinol and amino ethyl methyl (AEM) hexenoylisoxaben. Mobility studies (MRIDs 41106303 and 48533302) indicate that several of these isoxaben degradates are more mobile than the parent. Add itionally, four major photolytic de gradates (Unk 3, Unk 3i, Unk 5a, and Unk 5b) were detected but not c onclusively identified (MRID 47140003).

The Health Effects Division (HED ) evaluated the isoxaben residues of concern for human health.

Because the formation of the unidentified de gradates was considered inconsequential ( i.e.

, formed only during aqueous photolysis) and a stru ctural activity relati onship (SAR) analysis performed by HED concluded that none of these de gradates were expected to be more toxic than the parent compound, these photodegradates were not of exposure concern and were excluded as

residues of concern for human health. HED concl uded that the major degradates detected during

the aerobic and anaerobic soil a nd aqueous metabolism studies were not expected to be more toxic to humans than the parent compound, but da ta were not available to exclude them as residues of concern. As such, the degr adates hydroxy isoxaben, dimethoxybenzamide, methoxyphenylpyrimidinol, and AEM hexenoyl isoxabe n were included as residues of concern for human health (USEPA, 2010a).

### Page 15 of 74 For this ecological risk assessment, in the absence of ecotoxicity da ta, these degradates were also included as residues of concern for aquatic organi sms using a total toxic residue (TTR) analysis. Additionally, Unk 3, Unk 3i, Unk 5a, and Unk 5b from the aqueous photolysis study are also included in the TTR approach as HED’s method of exclusion using SAR does not necessarily reflect ecological endpoints.

Mixtures

Evaluation of pesticide environmental mixtures is beyond the scope of this assessment because of myriad factors that cannot be quantified based on the available data. Those factors include identification of other possible co-contaminants and their concentrations, differences in the pattern and duration of exposure among contaminan ts, and the differential effects of other physical/chemical characteristic s of the receiving waters ( e.g. organic matter present in sediment and suspended water). Evaluation of factors that could influence additivity/synergism is beyond the scope of this assessment and the capabilities of the available data to allow for an evaluation. However, it is acknowledged that not consideri ng mixtures could over- or under-estimate risks depending on the type of interact ion and factors discussed above.



## Measures of Exposure

EFED uses standard available models to evaluate potential exposures to aquatic and terrestrial organisms as described at http://www.epa.gov/pesticid es/science/models_db.htm

.

Since the previous exposure assessments were completed, four main changes in standard procedures have occurred:

1) Transformation rates for environmental fate studi es were recalculated according to the North American Free Trade Agreement (NAFTA) Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media (Bohaty et al. , 2012; NAFTA, 2012). These updated results will be used in estimating m odel inputs for estimating aquatic exposure. 2) A new model for estimating concentrations in groundwater was developed called the

Pesticide Root Zone Model – Groundwater (PRZM-GW) (Baris et al. , 2013). This model will be used along with SCI-GROW to es timate concentrations in ground water. 3) Surface Water Concentration Calculator (SWCC) replaces PE5 (linked PRZM and EXAMS) with the primary difference being an improved user interface. However, PRZM5 replaces PRZM 3.12 and daily average concentrations are being used to produce EECs and EDWCs whereas PE5 used daily peak concentrations . This results in small differences in concentration but not substantially and should not change risk conclusions. 4) Revised spray drift values (USEPA, 2013b) for aquatic expos ure in ecological risk assessment are increased from previous values and accurately reflect edge-of-field spray drift

exposure.

### Page 16 of 74 The most up to date procedures and models are used in the registration review exposure

assessments.



## Measures of Effect

Selected toxicity data are used to calculate ri sk estimates. Any additional information submitted by the registrant or found in the open literature are also considered. The open literature studies are identified using EPA’ s ECOTOXicity (ECOTOX) 2 

### database, which employs a literature search engine for locating chemical toxici ty data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide insight into the direct and indirect effects of pesticides on biotic communities from loss of speci es that are sensitive to the chemicals and from changes in structure and functional charac teristics of the affected communities.

During the registration review pr ocess for isoxaben (USEPA, 2007), additional ecological toxicity data were submitted by the registrants and subseque ntly reviewed by EFED. These data include:

1) OCSPP 850.1350 - Mysid shrimp life-cy cle toxicity study (MRID 49090201); 2) OCSPP 850.2100 - Acute avian oral toxicity study (MRID 48952601); 3) OCSPP 850.2300 - Avian reproduction toxicity study (MRID 49091601); 4) OCSPP 850.4250 – Vegetative Vigor toxicity study (MRID 47428405); 5) OCSPP 850.4400 – Aquatic vascular plant toxicity study (MRID 47428401,47428402, 4748406); and 6) OCSPP 850.5400 - Non-vascular aquatic pl ant toxicity studies (MRIDs 48533202, 48533203, 48534801, 4853802, and 48952602).

The toxicity studies above were classified as either acceptable or supplemental, and no additional studies are requested for these taxa.

3. Analysis

3.1. Exposure Characterization

3.1.1.Environmental Fate and Transport Characterization

The environmental fate data from submitted studies for isoxaben are summarized in Table 5

. Environmental fate and transport properties of isoxaben and its de gradates are characterized in further detail in the following sections.

Table 5. Environmental fate data for parent isoxaben

Property Value Source Comments and Study Status

Chemical Name N- [3-(methylpent-3-yl)isoxazol-5- yl]-2,6-dimethoxy-benzamide -

2 http://cfpub.epa.gov/ecotox/

### Page 17 of 74 Property Value Source Comments and Study Status Hydrolysis Half-life (pH 5, 7, and 9; 25°C) Stable MRID

00250449 Acceptable

Aqueous Photolysis Half-life (days) 6 MRID

47140003 Acceptable

Soil Photolysis Half-life (days) 49 MRID

47428403 Acceptable

Aerobic Soil Metabolism Half-life (days) 161 (sandy loam) 210 (silt loam) 277 (silt loam) 866 (sand) MRID

47140004 Supplemental

Anaerobic Soil Metabolism Half-life (days) 224 (loam) MRID

41106302 Acceptable

Aerobic Aquatic Metabolism Half-life (days) 21 (2 systems; sand and sandy loam) MRID

46393202 Acceptable

Anaerobic Aquatic Metabolism Half-life (days) 18 (sandy clay loam) MRID

46393201 Acceptable

Soil-Water Partition Coefficients (mL/g) (K d ) 0.81 (sand) 2.18 (loamy sand) 2.48 (sandy loam) 4.41 (loam) 6.63 (clay loam) MRID

41106303 Acceptable

Henry’s Law Constant (atmm 3 /mol) 8.5x10 -10

– Calculated from

vapor pressure, molecular weight, and solubility.

Log K
ow 2.64 Product Chemistry

Bioaccumulation At 0.25 ppm: 14x for edible, 134x for non-edible,

70x for whole fish tissues

92-99% of 14 C residues eliminated by 14 days MRID

40059509 Supplemental

Terrestrial field dissipation half-life (soil texture) in top

6 inches of soil 34-55 days in spring treated sand soil (Florida) and loam soil (Indiana)

78-174 days in autumn treated sand soil (Florida) and sandy loam soil (Texas)

72 days in clay loam soil (Illinois)

122-134 days in silt loam soil (Indiana) MRID

40059508

MRID

40059508

MRIDs

40532102 &

40532103

MRID

00250449 &

00153107 Supplemental

--- Supplemental

--- Acceptable & Acceptable

--- Supplemental & Supplemental



### Transport and Mobility

Isoxaben is not volatile, with a va por pressure of less than 3.9 x 10 -7 

### torr at 26oC (MRID 40059506). The compound exhibits weak acid behavior (pK a 

### = 9.8), at neutral environmental

### Page 18 of 74 pHs, and is moderately soluble in wa ter (1 mg/L; MRID 40059506). The reported K ow 

### for isoxaben is 434 (MRID 40059506).

Isoxaben is considered mobile, with repor ted soil-water partition coefficients (K d 

### ) from five soils ranging from 0.81 to 6.63 mL/g (MRID 41106303). A regression analysis of the adsorption coefficients versus the organic carbon content yielded a p-value >0.1; as such, the Koc model was deemed inappropriate and K d 

### values were used in the modeling.

Leaching and adsorption/desorption studies were conducted on three of the identified major degradates: hydroxy isoxaben, AEM hexenoyl is oxaben, and 2,6-dimethoxybenzamide. With reported K d 

### s ranging from 0.06 to 0.84, 4.8 to 10.9, and 0.09 to 0.24 mL/g, respectively, hydroxy isoxaben and AEM hexenoyl isoxaben are mo re mobile than parent isoxaben while 2,6- dimethoxybenzamide is less mobile (MRID 41106303, 48533301, 48533302).

Compounds with K d 

### values <5 mL/g present a potentia l concern for ground water (USEPA, 2008a). Therefore, isoxaben and its major degr adates, based on study data , present a potential ground water concern in some soils, especially th ose that are sandy and have low organic carbon content (all K d 

### values for both compounds, except for clay loam soil, were less than 5; MRID 41106303).

Degradation

Isoxaben is stable to hydrolysis at pH 5, 7 a nd 9 (MRID 00250449). It is rapidly photolyzed in shallow, clear water, with a corrected envir onmental half-life of 6 days at pH 7 (MRID 47140003). Major photodegradates include dimethoxybe nzamide and four degradates that were detected but not conclusively identified; a uracil (Unk 3), an oxime (Unk 3i), a pyrazolone (Unk 5a), and an isoquinolone (Unk 5b). Study authors i ndicated that ex tensive efforts were made to identify the compounds, but in the end the best that could be done was to identify structural and functional group changes that occurred during phot odegradation. The names and structures of these unknowns that were proposed by the study aut hors based on this analysis are provided in Table 7. Isoxaben photodegrades comparatively sl owly in soil, with a corrected environmental photodegredation half-life in soil of 49 days in sandy loam soil at pH 7.0 and 0.99% organic carbon (MRID 47428403).

Isoxaben does not readily biodegrade in soil und er aerobic or anaerobic conditions, with half lives of greater than 150 days. In four forei gn soils held under aerobic conditions, isoxaben degraded with half-lives of 161 days (sandy lo am), 210 days (silt loam), 277 days (silt loam), and 866 days (sand) (MRID 47140004). Overall recoveries were greater than 90%. The only major degradate identified in the study was hydroxy isoxaben. Th e study was classified as supplemental, as all of the soils were foreign a nd it was unclear if the soil microbial communities were comparable to those in the United States.

Loam soil was incubated anaerobically for 60 da ys after 60 days of aerobic incubation (MRID 41106302). Isoxaben degraded with a half-life of 224 days. Over all recoveries were greater

### Page 19 of 74 than 90%. The only major degradate identifi ed in the study was hydroxy isoxaben. The study was classified as acceptable.

Primary routes of biodegradati on are in aerobic and anaerobic water bodies. In two aerobic aquatic systems (brook water-sand sediment a nd brook water-sandy loam sediment), isoxaben degraded with a half-life of 21 days (MRID 46393202). Major degradates include dimethoxybenzamide and AEM hexenoyl-isoxaben. The study was classified as acceptable. In an anaerobic aquatic system (water and sandy clay loam soil), isoxaben degr aded with a half-life of 18 days (MRID 46393201). Overall recoveries were above 90%. Major degradates include dimethoxybenzamide, methoxyphenylpyrimidinol, and AEM hexenoyl-isoxaben. The study was classified as acceptable.

Field Studies

Three terrestrial field dissipati on studies were conducted for is oxaben using five sites in the

United States. Two of the studies were conducted on turf plots (MRIDs 40059508 and 40532102); the spring and autumn treated turf plots in Florida (sand) were level grade while the plot in Illinois (clay loam) had a slope of 5-10% . The remaining plots were bare ground (MRID 40059508); the plot in Indiana (loam sand) had a sl ope of 2% and the Texas (sandy loam) plot was level grade. Of the five sites, only the I ndiana site reported subs urface drainage. Turf applications were made using a backpack sprayer while bare soil applications were made using a tractor-drawn boom. Isoxaben, as a 75% dry flowable concentrate, was applied to all plots at a rate of 1.0 lbs ai/A. Florida sites were irrigated with 0.2 inches (spring) and 0.5 inches (fall) of water following treatment, with additional irri gation applied during the May to September

timeframe if less than 0.1 inches per day occurred. A total of 74 in ches of rain (plus irrigation) were received in Florida over 313 days, 28 inches in Illinois over 211 days, 13 inches in Indiana over 127 days, and 21 inches in Texas over 182 da ys. Samples were collected to a maximum depth of 24 inches in Florida and 12 inches in Indiana and Texas. Samples were analyzed for isoxaben and the degradate hydroxy isoxaben. In th e majority of terrestrial field dissipation studies, isoxaben was equal to or less than 1% in soil samples collected at depths greater than 6 inches. However, one sample in Florida (M RID 40531202) had an isoxaben level of 2% at a depth of 6-12 inches at 129 days after application. The study noted that the water table at the site

was within 10 inches of the surface and that potential groundwater contamination could have

occurred. In all but one of the terrestrial field dissip ation studies, hydroxy isoxaben was ≤ 1% of the applied in all soil samples collected below 6 inches. Howe ver, in a supplemental Florida study (MRID 40532101), hydroxy isoxaben was detected in four soil samples at depths of 15-30

cm at levels ≤ 2% of the applied. The lim it of detection (LOD) in the studies was 0.01 lbs ai/A (MRID 40059508) and 0.02 lbs ai/A (MRID 40532102). Half-lives for isoxaben ranged from 34 to 147 days. These half-lives compare well to aerobic soil metabolism half-lives ranging from 161 days to 866 days as metabolism is the primar y route of dissipation with run-off and leaching also contributing substantially consideri ng the precipitation in the field studies.

A third field dissipation study (MRID 00250449/00153107) was c onducted using two outdoor lysimeter-enclosed bareground plots (0.656 m 2 

### ) of silt loam soil in Indiana. In the first test, isoxaben ( 14 

### C isoxaben labeled on the carbonyl carbon) was applied at a target rate of 250 g ai/ha

### Page 20 of 74 (0.22 lbs ai/A) to two plots seeded with winter barley in October, 1980. In a second test, isoxaben was applied at a target ra te of 150 g ai/ha (0.13 lbs ai/A) to two plots (one plot received

14 

### C isoxaben labeled on the carbonyl car bon while the second plot received 14 

### C isoxaben labeled in the 5-position on the isoxazole ring) which we re maintained free of vegetation in November, 1981. Soil samples were collected to a depth of 15 cm in the first test and 37.5 cm in the second

test. In the second test radiolabeled isoxabe n was not detected below 15 cm until week 50 and was always below 4%. The half -life for isoxaben ranged from 122 to 134 days. In the second test, two degradates were identified in samp les collected to a depth of 15 cm: hydroxy isoxaben and hydroxy ethyl isoxaben. The maximum amo unt of hydroxyisoxaben occurred on Day 32 at 8.6% of the applied amount and declined to 4.6% at Day 100. The maximum amount of hydroxyisoxaben occurred on Day 86 at 3.9% of the applied amount and dec lined to 3.8% at Day 100. This study was classified as supplemental, as the use of lysimeter plots were not truly representative of field plot s due to their limited size.

Monitoring and Clean Water Act

Isoxaben is not included as an analyte in the National Water Quality Assessment (NAWQA) and monitoring data has not been submitted to EP A; therefore, surface water and groundwater monitoring data is not readily available. Additionally, isoxa ben is not responsible for any impaired waterbodies under 303( d) of the Clean Water Act.

Bioconcentration

Isoxaben residues accumulated in bluegill sunfish with maximu m bioconcentration factors of 14x in edible tissue, 134x in non-edible tissue, a nd 70x in whole fish tissue during 28 days of exposure (MRID 40059509). Residues accumula ted by exposure day 28 were depurated quickly; at day 14 of depuration, isoxaben residue s had been reduced by 92-99% in the edible, non-edible, and whole fish tissues . The study was classified as supplemental because isoxaben residues were incompletely characterized and residues in the whole fish tissue were not determined experimentally. Due to the relatively low K OW 

### and bioconcentration factors in fish, isoxaben is not expected to accumulate in aquatic or terrestrial food chains.

Degradates

Major biodegradates of isoxaben incl ude hydroxyisoxaben, dimethoxybenzamide, methoxyphenylpyrimidinol, and AEM hexenoyl-isoxa ben. Additionally, f our major photolytic degradates (Unk 3, Unk 3i, Unk 5a, and Unk 5b) we re detected but not conclusively identified (MRID 47140003). Chemical names, structures, and fa te data for these de gradates are provided

in Table 6 . Based on recently submitted data, three of the biode gradates (hydroxy isoxaben, dimethoxy benzamide, and 2,6-dimethoxybenzamide) are incrementally more mobile than isoxaben, with methoxyphenylpyrimidinol appearing to be very immobile. As mentioned above, hydroxy isoxaben was detected in all of the terres trial field studies. In two of the studies (MRIDs 40059508 and 40532102), hydroxy isoxaben was ≤ 1% of the applied in all soil samples collected below 6 inches. However, in th e Florida study (MRID 40532101), it was detected in four soil samples at depths of 15-30 cm at levels ≤ 2% of the applied. In a third study (MRID

### Page 21 of 74 00250449/00153107), the degradate hydroxy isoxaben was detected in samples collected to a depth of 15 cm. Hydroxy isoxaben was ≤ 9% of the applied in all soil samples collected below 15 cm. Degradates vary in mobility with dimethoxy benzamide and hydroxy isoxaben being more mobile than parent isoxaben and Met hoxyphenolpyrimidinol and AEM hexenoyl isoxaben being less mobile than parent isoxaben.

Residues of Concern

For this assessment, in the absence of eco toxicity data, the de gradates hydroxy isoxaben, dimethoxybenzamide, methoxyphenylpyrimidinol, AEM hexenoylisoxaben, and the unidentified degradates from the aqueous photolysis study were included as residues of concern for aquatic organisms using a total toxic resi due (TTR) analysis. Parent on ly EECs are also provided for

characterization.Page 22 of 74Table 6. Environmental Degradates of Isoxaben.Name(s) Structure Occurrence Fate PropertiesDimethoxy benzamide2,6-DimethoxybenzamideAqueous photolysis (major)Aerobic Aquatic Metabolism (major)Anaerobic Aquatic Metabolism (major)Soil Photolysis (minor)VP = 1.6x10-5torrSol = 8.4x104mg/LLog KOW= -0.22KOC= 4.9 – 10 mL/gKd= 0.09-0.24(MRID 48533302;Supplemental)Hydroxy isoxabenPseudonyms- AA-045N-[3-(1-hydroxyl-1-methylpropyl)-5-isoxazoyl]-2,6-dimethoxy-benzamideAerobic Soil Metabolism (major)Anaerobic Soil Metabolism (major)Aerobic Aquatic Metabolism (minor)Terrestrial Field DissipationVP = 9.8x10-12torrSol = 462 mg/LLog KOW= 1.53KOC= 17 – 31 mL/gKOC= 21 – 73(MRID 41106303;Acceptable)Methoxyphenolpyrimidinol6-(1-ethyl-1-methylpropyl)-2-(2-hydroxy-6-methoxyphenyl)-4-pyrimidinolAnaerobic Aquatic Metabolism (major)Aerobic Aquatic Metabolism (minor)VP = 4x10-10torrSol = 41.2 mg/LLog KOW= 3.56KOC= 4800 – 38,000 mL/g(MRID 48533302;Supplemental)AEM hexenoyl isoxabenN-[3-amino-4-ethyl-4-methyl-2-hexenoyl]-2,6-dimethoxybenzamideAnaerobic Aquatic Metabolism (major)Aerobic Aquatic Metabolism (minor)VP = 3.1x10-13torrSol = 265 mg/LLog KOW= 1.71KOC= 21 - 102 mL/gKd= 4.2-10.1 mL/g(MRID 48533301;Supplemental)Page 23 of 74Name(s) Structure Occurrence Fate PropertiesUnk326-(1-ethyl-1-methylpropyl)pyrimidine2,4(1H,3H)-dioneAqueous Photolysis (major) VP = 5.6x10-8torrSol = 853 mg/LLog KOW= 2.0KOC= 80 – 113 mL/gUnk3i4-ethyl-3-(hydroxyimino)-4-methylhexanoic acidAqueous Photolysis (major) VP = 3.8x10-6torrSol = 698 mg/LLog KOW= 2.8KOC= 51 – 126 mL/gUnk5a2-(2,6-dimethoxybenzoyl)-5-(1-ethyl-1-methylpropyl)1,2-dihydro-3H-pyrazol-3-oneAqueous Photolysis (major) VP = 2.0x10-10torrSol = 29 mg/LLog KOW= 2.85KOC= 222 – 228 mL/gUnk5b4,6-diethyl-4a,8-dimethoxy-4-methyl4a,8a-dihydropyrazolo[1,5-b]isoquinoline-2,9(1H,4H)-dioneAqueous Photolysis (major) VP = 1.3x10-10torrSol = 2221 mg/LLog KOW= 0.65KOC= 12 – 331 mL/g

### Page 24 of 74 3.1.2. Measures of Aquatic Exposure

Aquatic exposures are quantitatively estimated fo r all of the assessed uses using scenarios that represent high exposure sites for is oxaben use. Each of these site s represents a 10-hectare field that drains into a 1-hectare pond that is 2 me ters deep and has no ou tlet. Exposure estimates generated using the standard pond are intended to represent a wide variety of vulnerable water bodies that occur at the top of watersheds including prairie po t holes, playa lakes, wetlands, vernal pools, man-made and natural ponds, and in termittent and first-order streams. 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 es timated environmental concentrati ons (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 st orage capacity, and thus, tend to overflow and carry pesticide in the discharge whereas the st andard pond has no discharge. As watershed size increases beyond 10 hectares, at some point it be comes unlikely that the entire watershed is planted to a single crop, which is all treated with the pe sticide. Headwater streams can also have peak concentrations higher than the standard pon d, but they tend to persist for only short periods

of time and are then carried downstream.

Isoxaben environmental fate data used for gene rating model parameters for the Pesticide Root Zone Model (PRZM) and the Exposure Analysis Model System (EXAMS) and use specific input parameters are in Table 7. Chemical property input values we re chosen in accordance with current input parameter guidance (USEPA, 2009 3 

### ). SWCC with the variable volume pound is used. Initial application was set for pre-emerge nce in the PRZM scenario as isoxaben is a preemergence herbicide. However, given the maximum number of applications (4) and reapplication interval (56 to 60 days) subsequent applications are assumed to be made substantially after emergen ce. All uses are modeled assuming ground application ( i.e. , 99% application efficiency a nd 6.2% spray drift).

Table 7. Summary of SWCC Environmental Fate Data Used for Aquatic Exposure Inputs for Isoxaben and Isoxaben Total Toxic Residues (TTR).

PARAMETER (units) VALUE(S) SOURCE COMMENT

Application Rate (kg a.i./ha) 1.12 Product

labels 1.02 lbs a.i./A; Maximum application rate forturfgrass, ornamentals, groundcover/perennials, noncropland, Christmas tree/conifer plantations, hardwood nursery, fruit and nut trees and vineyards.

Number of Applications 4 Product

labels Maximum number of applications for turfgrass, ornamentals, groundcover/perennials, non-cropland,

Christmas tree/conifer plantations, and hardwood

nursery

3 http://www.epa.gov/oppefed1/models/w ater/input_parameter_guidance.htm

### Page 25 of 74 PARAMETER (units) VALUE(S) SOURCE COMMENT

Interval between Applications (days) 56 Product

labels Minimum application interval for use patterns with 4 applications per year (turfgrass and ornamentals). Most labels specify a 60 day interval but some allow for a 56 day interval

Molecular weight (g/mol) 332.39

Henry’s Law Constant (atmm 3 /mol) 1.26*10 -9 Calculated (VAPR/760)/ (SOL/MWT),

where VAPR is vapor pressure in torrs, MWT is the molecular weight in g mol -1

, and SOL is the solubility in water in mg L -1

. Vapor Pressure (torr) 4.1*10 -9 IUPAC Footprint MRID 153106 reports a value of <3.9*10 -7 torr

Solubility in Water @ 20 O C, (mg/L or ppm) 1.42 MRID

47140001

Soil Partition Coefficient (K OC ) (mL/g) 38 MRID

41106303 The most mobile degradate is hydroxy isoxaben. Average of 21, 26, 27, 42, and 73 mL/g o.c. 1

Chemical Application Method Ground Broadcast, applied to bareground and unincorporated.

Application efficiency (decimal) 0.99 Ground Application

Spray drift fraction (decimal) 0.0616 Ground Application with high boom and ASAE very fine to fine droplet spectrum (default) (EPA, 2013b)

Application date (day/month)

March 1

April 26

June 23

August 20 Product

Labels 4 applications with 56 day retreatment intervals. Initial application is in early season to allow for allow applications to be within growing season.

Hydrolysis Half-life (days) Stable MRID

250449

Aqueous Photolysis Half-life @ pH 7 (days) Parent 6.0

TTR 93.5 MRID

47140003

Aerobic Aquatic Metabolism Half-life (days) Parent 22.0

TTR 282 MRID

46393202 63 (TTR) and21.5 (parent) days in Water-sand; SFO

171 (TTR) and 21 (parent)Stable in Water-sandy loam; N/A

90 th percentile mean of values used as input 1

### Page 26 of 74 PARAMETER (units) VALUE(S) SOURCE COMMENT

Anaerobic Aquatic Metabolism Half-life (days) Parent 17.4

TTR 1608 Anaerobic soil input = single t 1/2 x 3 1

Anaerobic aquatic input = anaerobic soil input x 2 1

Aerobic Soil Metabolism Half-life (days) Parent 443

TTR 723 MRID

47140004

MRID

49090101 274 (TTR) and 150 (parent)days in Sandy Loam; DFOP; isoxazole label

264 (TTR) and 199(parent) days in Sandy Loam; SFO; phenyl label

340 (TTR) and 207 (parent)days in Silt Loam; SFO; phenyl label

360(TTR) and 280 (parent)days in Silt Loam; SFO; phenyl label

1123(TTR) and 891(parent) days in Sand; SFO; phenyl label

185 days in Sandy clay loam; DFOP; combined label

90 th percentile mean of values used as input 1

Anaerobic Soil Metabolism Half-life (days) Parent 2.9

TTR 268 MRID

46393201 Sandy clay loam; SFO; total system

1 “Input Parameter Guidance” refers to Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; Version 2.1, October 22, 2009. DFOP – Double first order in parallel degradation kinetics SFO – Single first order degradation kinetics



### Aquatic exposure modeling, using SWCC, was performed to estimate exposures for registered uses of isoxaben. Many isoxaben us es can be represented by various aquatic modeling scenarios. To organize which scenarios are representative of which uses, the modeling scenarios for each registered use category are presented in Table 8 and the results from th e highest PRZM scenario for each use pattern are presented in Table 9. Output that generates peak EECs are reported in Appendix 1

.

### Page 27 of 74 Table 8

. EECs for Use Pattern Categories. Scenario from which EECs used in the assessment for RQs are in bold (scenario with highest EECs)

Modeling Scenarios

used to Represent

Registered Uses Registered Uses of Isoxaben

FL turf

PA turf Turfgrass / Groundcover/ perennials / Non-cropland

CA Almond

CA Citrus

CA Fruit CA Grapes CA Nursery

FL Citrus FL Nursery MI Nursery NC Apple NJ Nursery NY Grape OR Apple OR Nursery

OR Xmas Tree PA Apple TN Nursery Ornamental / Christmas tree/ conifer plantations, hardwood nursery / Non-bearing fruit & nut trees & vineyards

Bearing fruit and nut trees and vineyards / Eucalyptus

### Page 28 of 74 Table 9. Tier II Concentrations of Isoxaben (usi ng Total Toxic Residues and Parent Only)

in Surface Water modeled with SWCC.

Registered

Use EECs (TTR) EECs (Parent)

App Rate (lb a.i./A) x No. of Apps (modeling

scenario used
to represent registered use) Peak (μg/L) 21-day

average (μg/L) 60-day

average (μg/L) Peak (μg/L) 21-day

average (μg/L) 60-day

average (μg/L)

Turfgrass

1.0 x 4 (PA turf) 43.6 42.7 41.6 10.2 7.9 5.48 Groundcover/ perennials Non-cropland

Christmas

tree/conifer plantations,

hardwood

nursery 1.0 x 4 (FL citrus) 88.4 86.0 81.5 36.5 27.6 15.8

Ornamentals Non-bearing

fruit & nut

trees & vineyards 1.0 x 3 (FL citrus) 76.0 73.9 69.7 32.4 23.4 15.6

Bearing fruit

and nut trees and vineyards 1.0 x 1 (FL citrus (TTR) / MI

Nursery (Parent)) 32.8 32.6 32.2 19.8 14.3 11.2

Eucalyptus 0.75 x1, 0.25 x

1 (FL citrus/ MI Nursery) 30.6 26.2 17.9 16.2 13.6 9.28



### Data in Table 9 indicate that the maximum surface water EECs for total toxic residues of isoxaben were generated with the Florida (FL) Citrus scenario and are as follows:

88.4 μg/L for the 1 in 10 year a nnual peak concentration; 86.0 μg/L for the 21-day average concentration; and 81.5 μg/L for the 60-day average concentration

3.1.3.Measures of Terrestrial Exposure

3.1.3.1. Terrestrial Animals

Ingestion of Food Items Ba sed on Foliar Application

### Page 29 of 74 Exposure estimates for terrestrial animals assumed to be in the target area or in an area exposed to spray drift are derived using the T-REX 4 

### model (version 1.5.1., 10/12/2012). 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 residu e value observed in th e data set (Hoerger and Kenaga 1972). Consideration is given to differe nt types of feeding strategies for mammals and birds, including herbivores, insectivores and granivores. For dose- based exposures, three weight classes of birds (20, 100, and 1000 g) and mammals (15, 35, a nd 1000 g) are considered. The dose-based

calculation takes into account that different-sized animals have to consume different amounts of food. The dose-based risk quotient s do account for the fact that small animals need to consume more food relative to their body weight than large animals or th at differential amounts of food are consumed depending on the water conten t and nutritive value of the food.

Given that no acceptable data for evaluating di ssipation from foliar surfaces are available for isoxaben, a default foliar dissipation half-life of 35 days is used based on the work of Willis and McDowell (1987). The EECs modeled in this asse ssment are based on parent isoxaben. For isoxaben, there are two main use s cenarios, a ground spray and a gr anule applicati on. The isoxaben application rates are similar betw een the non-agricultural registered uses in that for ground spray application, the maximum single applic ation rate is 1 lb a.i./A with a yearly maximum rate of 3 or 4 lb a.i./A at a minimum of 56-60 days between a pplications. For register ed uses with granular application, the maximum single app lication rate is 1 lb a.i./A with a yearly maximum rate of 3 lb a.i./A. Finally, for the bearing fruit and nut tr ees and vineyards the single maximum application is the same as the yearly maximum rate at 1 lb a.i./A, and while the yearly maximum for the eucalyptus use is 1 lb a.i./A, the single maximu m rate is 0.75 lb a.i./A. The dietary-based EECs on a variety of food items from the use of isoxaben applied at the maximum label rates are provided

in Table 10 ; dose-based EECs are provided in Table 11

.

Table 10

. T-REX Calculated Dietary-Based EECs of Isoxaben on Terrestrial Food

Residues for the Maximum Use Scen ario (Ground Spray Application).

Registered Use Application

Scenario (registered use) Food Type Maximum Dietary-based EECs (mg/kg)

1.02 lb a.i./A w/4 applications @ 56-d

retreatment interval(Turfgrass/Ornamentals/ Noncropland/ conifers plantations& hardwood nursery) Short Grass 354

Tall Grass 162
Broadleaf plants 199
Fruits/pods/seeds 22.1
Arthropods 139

1.0 lb a.i./A w/3 apps @ 60-d interval Short Grass 335

Tall Grass 154

4 USEPA. 2013. Pesticides: Science and Poli cy. Terrestrial Models, T-REX Version 1.5/1. http://www.epa.gov/oppefed1/models/terrestrial/

### Page 30 of 74 (non-bearing fruit & nut trees and vineyards) Broadleaf plants 189
Fruits/pods/seeds 21.0
Arthropods 131

1.0 lb a.i/A w/1 app (bearing fruit & nut trees and vineyards) Short Grass 240

Tall Grass 110
Broadleaf plants 135
Fruits/pods/seeds 15.0
Arthropods 94.0

0.75 lb a.i/A then 0.25 lb a.i/A @ 30-d

interval (eucalyptus) Short Grass 180

Tall Grass 82.5
Broadleaf plants 101
Fruits/pods/seeds 11.3
Arthropods 70.5



### Table 11

. T-REX Calculated Dose-Based EECs of Isoxaben Uses on Terrestrial Food

Residues for the Maximum Use Scen ario (Ground Spray Application).

Registered Use Application Scenario (registered use) Food Type Dose-based EECs (mg/kg-bw) (birds) Dose-based EECs (mg/kg-bw) (mammals)

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

1.02 lb a.i./A w/4 applications @ 56-d

retreatment interval (Turfgrass/Ornamentals/ Non-cropland/ conifers plantations& hardwood nursery) Short grass 403 230 103 337 233 54.1 Tall grass 185 105 47.2 155 107 24.8

Broadleaf

plants 227 129 57.9 190 131 30.4 Fruits/pods 25.2 14.4 6.43 21.1 14.6 3.38 Arthropods 158 90.0 40.3 132 91.3 21.2

Seeds (granivore) 5.60 3.19 1.43 4.69 3.24 0.75

1.0 lb a.i./A w/3 apps @

60-d interval (non-bearing fruit & nut trees and vineyards) Short grass 382 218 97.5 320 221 51.2 Tall grass 175 99.9 44.7 147 101 23.5

Broadleaf

plants 215 123 54.9 180 124 28.8

Fruits/pods 23.9 13.6 6.10 20.0 13.8 3.20 Arthropods 150 85.3 38.2 125 86.6 20.1

Seeds (granivore) 5.31 3.03 1.35 4.40 3.10 0.70

1.0 lb a.i/A w/1 app (bearing fruit & nut trees and vineyards) Short grass 273 156 69.8 229 158 36.7 Tall grass 125 71.4 32.0 105 72.5 16.8

Broadleaf

plants 154 87.7 39.3 129 89.0 20.6

Fruits/pods 17.1 9.74 4.36 14.3 9.88 2.29 Arthropods 107 61.1 27.3 89.6 61.9 14.4

Seeds (granivore) 3.80 2.16 0.97 3.18 2.2 0.51

### Page 31 of 74 0.75 lb a.i/A then 0.25 lb a.i/A @ 30-d interval (eucalyptus) Short grass 205 117 52.3 172 119 27.5 Tall grass 94.0 53.6 24.0 78.7 54.4 12.6

Broadleaf

plants 115 65.8 29.4 96.5 66.7 15.5

Fruits/pods 12.8 7.31 3.27 10.7 7.41 1.72 Arthropods 80.3 45.8 20.5 67.2 46.5 10.8

Seeds (granivore) 2.85 1.62 0.73 2.38 1.65 0.38



### Ingestion of Food Items Ba sed on Granular Application

As mentioned, isoxaben is register ed for several uses that empl oy a granular application. The EEC for acute exposure for this application method was calculated using T-REX and the LD 50 

### /ft 2 

### methodology. Conceptually, an LD 50 

### /ft 2 

### is the amount of a pesticide estimated to kill 50% of exposed animals in each square foot of applie d area. Although a square foot does not have defined ecological relevance, and any unit area coul d be used, risk presumably increases as the

LD 50 

### /ft 2 

### value increases. The LD 50 

### /ft 2 

### value is calculat ed using a toxicity value (adjusted LD 50 

### ) and the EEC (mg a.i./ft 2 

### ) and is directly compared with th e Agency’s levels-of-concern (LOCs). For isoxaben, a broadcast application with no incorporation was modeled using a single maximum application rate of 1.0 lb a.i./A. The EEC for this use scenario is 10.41 mg a.i./ft 2



### .

3.1.4. Terrestrial Plants

Isoxaben exposure to terrestrial and semi-aqua tic plants is estimated using the TerrPlant 5 

### (version 1.2.2) model and AgDrift (v2.1.1). The TerrPlant mode l generates EECs for plants residing near a use area that may be exposed via runoff and/or sp ray drift. The EECs are generated from one application at the maximum rate for a particular use and compound-specific solubility information. Only a single application is consid ered because it is assumed that fo r plants, toxic effects are likely to manifest shortly after the ini tial exposure and that subsequent exposures do not contribute to the response. Hence, the model estimates EECs based on application rate, the solubility factor, and default assumptions of drift. The EECs for te rrestrial and semi-aquatic plants for a single application of isoxaben at the maximum label rate are presented in Table 12. AgDrift provides point estimates of mass deposition at distances from the application site.

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

### Page 32 of 74 Table 12

. EECs for Terrestrial and Semi-Aquatic Plants near Isoxaben Use Areas (TerrPlant and AgDrift model).

Single Max. Application

Rate (lbs a.i./A) TerrPlant Model

EECs (lb a.i./A)

Total Loading to Adjacent Dry Areas (sheet runoff + drift) Total Loading to SemiAquatic Areas (channelized runoff + drift) Drift

Ground spray

1.02 0.02 0.11 0.01 Granular application

0.01 0.10 0.0 AgDrift Model (ground spray) Distance in feet from edge of field Drift EEC (lb/A)

0 1.02

50 0.051

100 0.025

200 0.0122

500 0.004

995 0.0014



### 3.2. Ecological Effects Characterization

The ecological effects characterization for isoxa ben is based on data generated from guideline studies submitted by the registrant and from open literature studies in the ECOTOX database (http:/www/epa.gov/ecotox).

A brief description of available aquatic and terrestrial toxicity data used to calculate RQs is provided below in Sections 3.2.1 and 3.2.2 . Additional details on the available toxicity data for isoxaben are provided in Appendix 2

.

3.2.1.Aquatic Effects Characterization

Toxicity data for aquatic animals and plants are summarized in Table 13 . For freshwater and estuarine/marine fish and invertebrates, the acute toxicity of the compound (in terms of an

LC/EC 50 

### ) is limited by its solubility, i.e ., 1.0 mg/L, as none of the studi es established a definitive

LC/EC 50 

### . In the acute toxicity te st with Quahog clam larvae ( Mercenaria mercenaria ; MRID 40531302) there was a 40% reduction in normally developed larv ae after 48-h at the limit concentration of 0.96 mg a.i./L. On a chronic exposure basis, isoxaben resulted in decreased growth and reproduction for water fleas ( Daphnia magna ) and decreased reproduction for estuarine/marine shrimp ( Americamysis bahia ), with NOAEC values for freshwater and

estuarine/marine invertebrates at 0.69 and 0.24 mg a.i./L, respectivel y. Chronic toxicity data are available for two species of freshwater fish with no effects on survival or growth up to approximately 0.4 mg a.i./L, which appears to be lower than the reported wa ter solubility (i.e., 1 mg/L). Chronic toxicity data are not available fo r estuarine/marine fish, but data from freshwater fish will be used to evaluate exposure of isoxaben to estuarine/marine fish.

### Page 33 of 74 The 7-day IC 50 

### for the vascular aquatic plant duckweed ( Lemna gibba) was 0.010 mg a.i./L, based on a reduction in biomass. Similar to the aquatic animals, for aquatic non-vascular plants,

definitive IC 50 

### values were not established up to the isoxaben’s limit of solubility ( i.e ., IC 50 

### values greater than 1.0 mg a.i./L). Toxi city data were available for green algae, freshwat er and saltwater diatoms, and cyanobacteria. The available aquatic non-vascular plant data were classified as supplemental, and given the lack of a definitive IC 50 

### value or classified for only qualitative use, they were not used quantitatively in the assess ment. Four of the six available studies were

conducted at test concentrations well above the reported water so lubility of isoxaben (isoxaben formulations used in three studies), and in all studies, the IC 50 

### values are greater than the reported limit of solubility of isoxaben. Two studies using green algae tested an isoxaben formulation and

derived 72-h EC 50 

### values of 17 and 43 mg a.i./L based on measured concentrations. While isoxaben may be more soluble when testing a formul ation, in these studies, the test solutions were not centrifuged/filtered prior to analysis; therefor e, there is uncertainty in the actual dissolved

concentration of isoxaben. While these studies were clas sified as supplemental, collectively they provided sufficient information to adequately assess potential direct effects to aquatic non-vascular plants, and this evaluation is discu ssed in the risk description section.

Degradate toxicity data for aquatic organisms were not available.

Table 13

. Summary of Most Sensitive Acute and Chronic Toxicity Data for Aquatic Animals and Plants Exposed to Isoxaben

.

Species Acute Toxicity Chronic Toxicity

96-hr

LC 50 /EC 50 (mg a.i./L) 48-hr EC 50 (mg a.i./L) Toxicity

Classification /Study

Classification (MRID) NOAEC/

LOAEC (mg a.i./L) Endpoints / Study

Classification (MRID)

Rainbow trout ( Oncorhynchus mykiss) > 1.0 -- NA 1 / Supplemental (00132146) 0.42/ >0.42 None affected / Supplemental (00137847)

Fathead minnow ( Pimphales promelas ) NA -- -- 0.40 / >0.40 None affected / Supplemental (00137848)

Waterflea ( Daphnia magna ) -- > 1.3 NA 1 / Supplemental (00132144) 0.69/1.01 Growth, reproduction / Supplemental (00137845) Sheepshead minnow ( Cyprinodon variegatus ) > 0.86 -- NA 1 / Supplemental (40531304) NA

--

Quahog clam (Mercenaria

mercenaria -- >0.96 NA 1 / Supplemental (40531302) 2 NA --

Mysid shrimp (Americamysis bahia ) NA -- -- 0.238 /

0.460 Reproduction / Acceptable (49090201)

### Page 34 of 74 Species Acute Toxicity Chronic Toxicity

96-hr

LC 50 /EC 50 (mg a.i./L) 48-hr EC 50 (mg a.i./L) Toxicity

Classification /Study

Classification (MRID) NOAEC/

LOAEC (mg a.i./L) Endpoints / Study

Classification (MRID)

Duckweed ( Lemna gibba ) -- 7-day IC 50 = 0.010 /

NOAEC =

0.006 Supplemental /

47428402 -- --

Saltwater diatom toxicity ( Skeletonema costatum ) 96-hr IC 50 = 0.922;

NOAEC =

0.922 -- Supplemental /

48952602 -- --

1 No mortality was observed up to the practical solubility limit of the compound in water; therefore, the toxicity of the compoun d appears to be limited by its solubility.

2 A 40% decrease in normal larvae was reported at the limit concentration (0.96 mg a.i./L).

NA = Not available



### 3.2.2.Terrestrial Effects Characterization

Toxicity values for terrestrial animals and plants are summarized in Table 14 . Isoxaben is practically non-toxic to mammals, birds (used as surrogates for re ptiles and terr estrial-phase amphibians), and honey bees ( Apis mellifera ) (surrogates for terrestrial invertebrates) on an acute exposure basis. No sublethal e ffects were observed in either th e acute bird or mammalian studies up to the limit doses/concentrations. In chronic avian studies, no treatment-related effects were observed in the northern bobwhite ( Colinus virginianus ) & mallard duck ( Anas platyrhynchos ) studies up to dietary concentra tions of 1073 and 1035 mg a.i./kg-di et, respectively. There is an additional avian reproduction study with the mallard duck in which there was a reported decrease in the percent hatch of offspring (relative to 3-wk live embryos) at 946 mg a.i./L (MRID 00153109). However, there were concerns with th is study regarding cont rol performance (high variability, high % of cracked e ggs) and possible husbandry condi tions. Therefore this study is classified as supplemental for qualitative use. In the chronic mammalian study using the rat ( Rattus norvegicus ), there were decreases in parental bodyweight at 2500 mg /kg-diet (200 mg/kg-bw) and

decreases in number of viable pups and bodyweight at 12,500 mg /kg-diet (1000 mg/kg-bw); the overall NOAEL for the study was 500 mg/kg-diet (40 mg/kg-bw). On an acute exposure basis, isoxaben is classified as ‘pract ically nontoxic’ to non-target te rrestrial invertebrates including young adult honey bees (honeybee acute contact LD 50 

### >101.7 μg a.i./bee).

Seedling emergence testing (MRID 47428404) indicat e monocot grass species (Family: Poaceae)

tested were unaffected at treatm ent rates equivalent to an application rate of 0.888 lbs ai/A, the highest rate tested. However, only three monocot species were tested. Among broadleaf plants (dicots), lettuce ( Lactuca sativa ) was the most sensitive (EC 25 

### = 0.0095 lbs ai/A). A NOAEC was not established in this study, thus the lettuce EC 05 

### (0.0014 lbs ai/A) is used in lieu of a NOAEC.

For vegetative vigor testing (MRID 47428405), among the tested monocots (only three species tested), ryegrass ( Lolium perenne ) was the most sensitive species tested (EC 25 

### = 0.014 lbs ai/A;

### Page 35 of 74 NOAEC 0.0034 lbs ai/A). For the dicots, cucumber ( Cucumis sativus ) was the most sensitive species, with an EC 25 

### of 0.089 lbs ai/A, and the NOAEC was 0.028 lbs ai/A.

Degradate toxicity data were not av ailable for terrestrial organisms.

Table 14. Isoxaben Terrestrial Animal and Plant Toxicity Summary

Taxa Study Type Species Exposure

Duration Toxicity

Value Reference (Study Classification)

Birds (surrogates for terrestrial-phase amphibians and reptiles) Acute (Dosebased) Northern Bobwhite ( Colinus virginianus) Single oral

dose >2000 mg/kg bw (LD 50 ) 00132146 (acceptable)

Zebra finch ( Taeniopygia

guttata ) >2000 mg/kg bw (LD 50 ) 48952601 (acceptable)

Acute(Dietarybased) Northern Bobwhite ( Colinus virginianus ) &

Mallard duck ( Anas platyrhynchos ) 8-Day dietary >4500 (bobwhite) &

>4800 (mallard) mg/kg diet

(LC 50 ) 00132142;

00132143 (acceptable)

Chronic(Dietarybased) Northern Bobwhite ( Colinus virginianus ) &

Mallard duck ( Anas platyrhynchos ) Avian reproduction study 1073 (bobwhite) &

1035 (mallard) mg/kg diet (NOAEC) 00153110 (bobwhite; supplemental);

49091601 (mallard; acceptable)

Mammals Acute Rat ( Rattus norvegicus ) Single oral

dose >10,000 mg/kg bw

(LD 50 ) 00132126 (acceptable)

Chronic Rat ( Rattus norvegicus ) 2-Generation reproduction study 500 mg/kgdiet (40 mg/kg-bw) (NOAEL);2500 mg/kgdiet (200 mg/kg-bw )

(LOAEL) 00153529 (acceptable)

Terrestrial

invertebrates Acute Contact Honey Bee ( Apis mellifera ) 48 hours > 101.7 μg/bee 0015311 (acceptable)

Terrestrial

Plants Seedling Emergence Monocot: Oat, ryegrass, wheat

21-days IC 25 : >0.888 lb ai/A;

NOAEC:

0.888 lb ai/A 47428404 (supplemental)

Dicot: Lettuce IC 25 : 0.0095 lb ai/A;

NOAEC:

0.0014 lb ai/A

Vegetative Vigor Monocot: ryegrass 22-days IC 25 : 0.014 lb ai/A;

NOAEC:

0.0034 lb ai/A 4748405 (supplemental)

### Page 36 of 74 Taxa Study Type Species Exposure

Duration Toxicity

Value Reference (Study Classification)

Dicot: cucumber IC 25 : 0.089 lb ai/A;

NOAEC:

0.028 lb ai/A



### 3.2.3.Review of Incident Data

A review of the Environmental Incident Inform ation System (EIIS, version 2.1) database, which is maintained by the Agency’s Office of Pesticide Programs, and the Avian Monitoring Information System (AIMS), which is maintained by the American Bird Conservancy, for ecological incidents involving isoxaben was co mpleted on June 30, 2014. In addition to the incidents recorded in EIIS and AIMS, a search of the Agency’s incident data system (aggregated reports) was conducted on July 1, 20 14 with no reported incidents.

Six incidents involving plants are reported for isoxaben in EIIS ( Table 15 ). For the incidents reported as registered uses or undetermined, five of the incidents have a certainty index of ‘Possible’ and one as ‘Unlikely’ to involve the use of isoxaben. The ‘Possible’ incidents span

1994 to 2003 and involved ornamental and tree farm applications . The reported numbers of affected plants range from 298,346 to 676,000, and included woody plants. All incidents report the application rate as 1.0 lbs a i/A. There was one incident repor ted in 2010 as a misuse for use on roses for which the applica tion rate was not reported.

Incident reports for isoxaben have not been received by the Agency since 2010 and only 6 incidents total have been reported to the Agency; however, the absence of reported incidents should not be

construed as the absence of incidents. Incident reports for non-target organisms typically provide information only on mortality events and plant da mage. Sublethal effects in organisms such as abnormal behavior, reduced growth and/or impair ed reproduction are rare ly reported, except for phytotoxic effects in terrestrial pl ants. EPA’s changes in the regist rant reporting requirements for incidents in 1998 may account for a reduced number of reported incidents. Registrants are now only required to submit detailed information on ‘maj or’ fish, wildlife, and plant incidents. Minor fish, wildlife, and plant incidents, as well as all other non-target incidents, are generally reported aggregately and are not included in EIIS. In addition, there have b een changes in state monitoring

efforts due to a lack of reso urces. However, the incident da ta that are available suggest that exposure pathways for isoxaben are complete and that exposure levels are su fficient to result in field-observable effects for terrestrial plants.

### Page 37 of 74 Table 15. Summary of incident informatio n reported to the Agency as of 6/30/2014.

Incident ID Use Site Legality Certainty State County Year Total

No. Total

Area

I014702-017 Ornamental, woody Registered

use Possible CA Santa Cruz 2003 35000 NR*

I013636-027 Ornamental Registered

use Possible OR Washington 2002 NR 6 acres

I001485-001 Tree farm/plantation Undetermi

ned Possible NR NR 1994 676000 NR

I010414-002 Ornamental Registered

Use Possible CA Santa Cruz 2000 627405 6.5

acres

I006865-001 Nursery Registered

Use Unlikely OR Multnomah NR 298346 NR

I023787-532 Roses Misuse Possible IL Clinton 2010 100% of

all plants NR



### *NR=not reported

4. Risk Characterization

4.1. Risk Estimation

4.1.1.Aquatic Organisms

The peak EECs in surface water generated fr om the PRZM/EXAMS model represents acute exposure to fish, aquatic inverteb rates, and aquatic plants, and the highest 21-day and 60-day average EECs represents chronic exposure to aquatic invertebrates and fis h, respectively. Acute and chronic RQs for freshwater and estuar ine/marine animals are summarized in Table 16 . RQs for aquatic vascular plants are presented in Table 17.

4.1.1.1. Aquatic Animals

Fish (surrogates for aquatic-phase amphibians)

Acute RQs were not calculated for freshwater or estuarine/ma rine fish because the LC/EC50 values for the acute studies were great er than the limit of solubility ( Table 16 ).

For chronic exposure, the RQs for freshwater fish were below the LO C. No effects to freshwater fish from chronic exposure to is oxaben were reported up to the ma ximum concentration tested for fathead minnows and rainbow trout, i.e., NOAECs of 400 and 420 μg ai/L, respectively. While these test concentrations are below the reported solubility of isoxaben (approximately 1 mg/L), the maximum 60-day EEC (using TTR approach) is 81.5 μg ai/L (FL citrus scenario) and the resulting RQ is 0.20. The highest chronic RQ for freshwater fish is 5X below the chronic risk LOC of 1.0,

### Page 38 of 74 and, therefore, chronic risk to freshwater fish is anticipated to be low. While there are no chronic toxicity data available for estuarine/marine fish, based on the availa ble acute and chronic freshwater fish data along with th e lack of effects from acute exposure, up to the limit of solubility, for estuarine/marine fish, effects to estuarin e/marine fish from chronic exposure are not anticipated.

Aquatic invertebrates

As with the fish, acute RQs could not be calculate d for freshwater invertebrates because no effects were reported to the limit of solubility. For estuarine/marine invertebrates, the acute EC 50 

### value was also greater than the limit of solubility. However, for the estuarine/marine clam, a 40%

reduction in normal larvae wa s reported at the solubility limit. In the estuarine/marine grass shrimp ( Palaemonetes pugio ) toxicity test, no effects were reported up to the limit of solubility, 1.0 mg/L.

Chronic RQs for freshwater inve rtebrates are below the LOC and therefore, chronic risk to

freshwater invertebrates is anticipated to be low (RQs ≤ 0.12). Similarly, the RQs for estuarine/marine invertebrates are below the LOC (RQs ≤ 0.36), and chronic risk is anticipated to

be low.Page 39 of 74Table 16. Summary of Acute and Chronic RQs for Freshwater and Estuarine/Marine Fish and Invertebrates Exposed toIsoxaben (Maximum EECs by use pattern, assuming TTR)Toxicity Value (μg a.i./L)>860(LC50)400(NOAEC)-->1300(EC50)>960(EC50)690(NOAEC)238(NOAEC)RegisteredUsesApp Rate(lb a.i./A)x No. ofAppsPeakEEC(μga.i./L)21-dayEEC (μga.i./L)60-dayEEC (μga.i./L)Acute FWand E/MFishChronicFW FishChronicE/MFishAcuteFWInvertAcuteE/MInvertRQChronicFWInvertRQChronicE/MInvertRQTurfgrass1.0 x 443.642.7 41.6 NO EFFECS UP TO SOLUBILITY LIMIT0.10 NO TOXICITY DATA AVAILABLE NO EFFECS UP TO SOLUBILITY LIMIT EC50 > LIMIT of SOLUBILITY0.06 0.18Groundcover/perennialsNon-croplandChristmastree/coniferplantations,hardwoodnursery1.0 x 488.486.081.5 0.200.120.36OrnamentalsNon-bearingfruit & nut trees& vineyards1.0 x 376.073.969.7 0.170.110.31Bearing fruitand nut treesand vineyards1.0 x 132.832.6 32.20.080.05 0.14Eucalyptus0.75 x1,0.25 x 130.626.2 17.90.040.04 0.11All exposure scenarios modeled ground applicationLOCs: Non-listed acute 0.5; listed acute 0.05;chronic 1.0, for non-listed and listed species.Acute RQs use peak EEC; Chronic invertebrate RQs use 21-day EEC; Chronic vertebrate RQs use 60-day EEC

### Page 40 of 74 4.1.1.2. Aquatic Plants

As shown in Table 17 , RQs for vascular plants exceed the listed and non-listed species LOC (1.0) for all of the currently registered uses of is oxaben. The RQs exceed the LOC using EEC values using the TTR approach as well as EECs from parent isoxaben only (RQ=1.02-14.7).

For aquatic non-vascular plants, th e available toxicity data were classified as supplemental for qualitative use only and/or di d not provide definitive IC 50 

### values, and were not used quantitatively in the assessment. Therefore, RQs were not calcul ated. An evaluation of potential risk to aquatic non-vascular plants is discussed in the risk desc ription section.

Table 17. RQs for Aquatic Vascular Plants Exposed to Isoxaben

Registered

Use App

rate
lbs ai/A / #app TTR EECs Parent Only EECs

Peak

EECs (ppb) Vascular Aquatic Plant RQs

EC 50 = 10 μg a.i./L NOAEC = 6 μg a.i./L Peak

EECs (ppb) Vascular Aquatic Plant RQs

EC 50 = 10 μg a.i./L NOAEC = 6 μg a.i./L

Non-listed

Species Listed Species Non-listed Species Listed Species
Turfgrass

1.0 x 4 43.6 4.36 7.27 10.2 1.02 1.7 Groundcover / perennials

Noncropland

Christmas

tree/conifer plantations,

hardwood

nursery 1.0 x 4 88.4 8.84 14.7 36.5 3.65 6.08

Ornamentals Non-bearing

fruit & nut

trees & vineyards 1.0 x 3 76.0 7.60 12.7 32.4 3.24 5.40

Bearing fruit

and nut trees

and vineyards 1.0 x 1 32.8 3.28 5.47 19.8 1.98 3.3

Eucalyptus 0.75 x1,

0.25 x 1 30.6 3.06 5.1 16.2 1.62 2.7

Bolded values ex ceed the non-listed or listed LOC of 1



### 4.1.2.Terrestrial Organisms

4.1.2.1. Birds and Mammals

Ingestion of Food Items Base d on Ground Spray Application

Based on the available toxicity data, no acute mort ality and/or sublethal effects were observed in any of the avian or mammalian studies at the high est levels tested. Only non-definitive acute and

### Page 41 of 74 sub-acute toxicity endpoints are available for birds and mammals; therefore, acute RQs were not

calculated. Further discu ssion of the predicted exposure values relative to the leve ls at which no mortality occurred is provided as part of the risk description in Section 4.2.2

.

In the acceptable chronic avian reproduction studies, there were no effects reported at the highest concentration tested, resulting in a NOAEC of 1035 or 1073 mg ai/ kg-diet. Chronic RQ values did not exceed the LOC for birds for any registered use ( Table 18 ).

For the chronic mammalian toxicity data, eff ects on parental bodyweight were reported at 200 mg/kg-bw for a NOAEL of 40 mg/kg-bw. There were no LOC exceedances for chronic exposure on a dietary basis for mammals; however, there were exceedances on a dose basis for all registered uses for all size classes ( Table 19 ).

Table 18. Chronic Dietary-Based RQs Derive d Using T-REX for Birds (Surrogates for Reptiles and Terrestrial-Phase Amphibians) and Mammals Exposed to Ground Spray Applications of Isoxaben*

Uses (represents the highest

EECs from ground application) Application Rate (lb a.i./A) x No. of Apps RQs for Birds RQs for Mammals

Chronic Dietary Based 1 Chronic Dietary Based 2

Turfgrass / ornamentals / Groundcover/ perennials / Non-cropland / Christmas tree/conifer plantations, hardwood nursery 1.0 x 4 (56-d

retreatment

interval) ≤ 0.34 ≤ 0.71

*No LOC exceedances (chronic RQ ≤ 1.0). RQs calculated using default folia r dissipation half-life of 35 days using

T-REX version 1.5.1.

1 Based on dietary-based EEC and mallard duck NOAEC = 1035 mg/kg diet, highest concentration tested (MRID 49091601).

2 Based on dietary-based EEC and Norway rat NOAEC = 500 mg/kg diet (MRID 00153529).



### Table 19. Chronic Dose-Based RQs Derive d Using T-REX for Mammals Exposed to Ground Spray Applications of Isoxaben*

Application Rate (Crop) Functional Feeding Group Dietary Item 15 g mammals 35 g mammals 1000 g mammals

Chronic 1 Chronic 1 Chronic 1

0.75 lb a.i./A then

0.25 lb a.i./A/30-d

interval (eucalyptus) Herbivores/Insectivores

Short Grass 1.95 1.67 0.89

Tall Grass 0.89 0.76 0.41

Broadleaf plants 1.10 0.94 0.50

Fruits/pods 0.12 0.10 0.06

Arthropods 0.76 0.65 0.35

Granivore

Seeds 0.03 0.02 0.01

### Page 42 of 74 Application Rate (Crop) Functional Feeding Group Dietary Item 15 g mammals 35 g mammals 1000 g mammals

Chronic 1 Chronic 1 Chronic 1

1 lb a.i./A @ 1 app (bearing fruit & nut trees and vineyards) Herbivores/Insectivores

Short Grass 2.60 2.22 1.19

Tall Grass 1.19 1.02 0.55

Broadleaf plants 1.46 1.25 0.67

Fruits/pods 0.16 0.14 0.07

Arthropods 1.02 0.87 0.47

Granivore

Seeds 0.04 0.03 0.02

1 lb a.i./A @3 apps/60-d interval (non-bearing fruit &

nut trees and vineyards) Herbivores/Insectivores

Short Grass 3.64 3.11 1.67

Tall Grass 1.67 1.42 0.76

Broadleaf plants 2.05 1.75 0.94

Fruits/pods 0.23 0.19 0.10

Arthropods 1.42 1.22 0.65

Granivore

Seeds 0.05 0.04 0.02

1 lb a.i./A @ 4 apps

/ 56-d interval (Turfgrass /

ornamentals /

Groundcover/perennials / Noncropland / Christmas

tree/conifer plantations, hardwood nursery) Herbivores/Insectivores

Short Grass 3.84 3.28 1.76

Tall Grass 1.76 1.50 0.81

Broadleaf plants 2.16 1.84 0.99

Fruits/pods 0.24 0.20 0.11

Arthropods 1.50 1.28 0.69

Granivore

Seeds 0.05 0.05 0.02 * LOC exceedances in bold (chronic RQ > 1.0). RQs calculated using default fo liar dissipation half-life of 35 days using T-REX version 1.5.1.

1 Chronic RQ = (upper bound dose-based EEC, mg/kg-bw) / (NOAEL; mg/kg-bw).



### 4.1.2.2. Terrestrial Invertebrates

On an acute exposure basis, isoxab en is classified as ‘practically nontoxic’ to non-target terrestrial invertebrates including honey b ees (honeybee acute contact LD 50 

### >101.7 μg ai/bee). Therefore, RQs were not calculated but eval uation of potential risk is disc ussed in the Risk Description

section.

4.1.2.3. Terrestrial Plants

At the maximum single application rate, RQs fo r both listed and non-listed dicots exceed the terrestrial plant LOC for species exposed to runo ff plus drift in adjacent upland and wetlands as well as drift alone for foliar applications and from runoff alone for granular applications ( Table

### Page 43 of 74 20 ). The LOC for nonlisted dicot plants is exceede d by more than 11-fold and exceeded for listed dicot species by 80-fold. The RQ for lis ted monocots exceeds the LOC by 3-fold.

Table 20. Risk quotients (RQs) for non-listed and listed terrestrial plants for ground spray and granular application of isoxaben at the maximum single application rate (1.02 lbs ai/A). 1

Terrestrial Plant Group Ground Spray

Adjacent uplands Adjacent wetlands Drift Only

Monocots 2 <0.1 0.13 0.73

Dicots 2 2.15 1 11.8 1.07

Listed Monocots <0.1 0.13 3.0

Listed Dicots 14.6 80.1 7.29

Terrestrial Plant Group Granular Application

Adjacent uplands Adjacent wetlands Drift Only

Monocots 2 <0.1 0.11 NA

Dicots 2 1.07 10.7 NA

Listed Monocots <0.1 0.11 NA

Listed Dicots 7.29 72.9 NA

1 Bold values denote an exceedance of the LOC (RQ ≥ 1.0).

2 In the seedling emergence study, no monocots were affected (EC 25 >0.888 lb ai/A); most sensitive dicot was lettuce (EC 25 = 0.0095 lbs ai/A; NOAEC = 0.0014 lb ai/A). Rye grass is the most sensitive monocot in the vegetative vigor study (EC 25 = 0.014 lbs ai/A; NOAEC = 0.0034 lb ai/A); cucumber is the most sensitive dicot, with an EC 25 0.089 lbs ai/A (NOAEC = 0.028 lbs ai/A)



### 4.2.Risk Description

Isoxaben is characterized as a moderately pe rsistent and mobile compound. Although primary routes of degradation include aqueous photol ysis, aerobic aqueous metabolism and anaerobic aqueous metabolism, uncertainty regarding the potential toxicity of its residues increases aquatic

estimated environmental concentrations.

Additionally, the compound is characterized as pr actically nontoxic to terrestrial animals on an acute exposure basis. For aquatic animals, the acu te toxicity of isoxaben appears to be limited by its solubility, with the exception of estuarine/marine invertebrate s. Although chronic effects on survival, growth, and/or reproduction were obs erved for freshwater and estuarine/marine invertebrates, chronic toxicity data for freshwater fish suggest that no effects on survival or growth

### Page 44 of 74 may occur near the limit of solubility. As expected, isoxaben is toxic to terrestrial plants and to aquatic vascular plants, but fo r aquatic non-vascular plants, toxicity appears to be limited by solubility.

4.2.1. R isks to Aquatic Organisms

Animals

For freshwater and estuarine/marine fish and invert ebrates, the acute toxicity of isoxaben (in terms

of an LC/EC 50 

### ) is limited by its solubility (1.0 mg/L (1000 μg/L)) as none of the studies were able

to establish a definitive LC/EC 50 

### . Except for the estuarine/marine invertebrate (clam larvae), no mortality or sublethal effects were observed at the limit of solubility. The highest peak EEC (FL citrus using TTR) is 88.4 μg a.i./L which is 9.7X lo wer than the lowest non-d efinitive acute toxicity value reported (LC 50 

### > 860 μg a.i./L for sheepshead minnow). A 40% decrease in normal larvae was reported in the estuarine/marine clam study at a limit test concentration of 960 μg a.i./L which is 11X greater than the highest peak EEC. Theref ore, given the general lack of acute effects to fish and aquatic invertebrates up to the limit of solubility and the differe nce between the EECs and isoxaben’s solubility, acute risk to aqua tic animals is cons idered unlikely.

The chronic LOC for freshwater fi sh and freshwater and estuarin e/marine invertebrates was not exceeded for any registered use. While chronic toxicity data were not available for

estuarine/marine fish and the freshwater fish st udies were conducted below the reported solubility limit, given the difference between the highe st EECs (81.5 μg a.i./L) and the no effect concentration (400 μg a.i./L), chronic risk to fish is not anticipated.

Given that isoxaben has a log Kow of < 3 and is charac terized as mobile in soils, it is not anticipated to partition to sediment. Theref ore, while there are no data for se diment-dwelling organisms, given the potential lack of exposure, risk to these animals is not anticipated.

Plants

While RQs were not calculated for aquatic non-vasc ular plants, based on the available data, the toxicity of isoxaben appears to be limited by its so lubility. In the studies using technical grade isoxaben, the IC 50 

### values are greater than the solubility limit. The highest peak EEC (using TTR) is 88.4 μg a.i./L, which is 10X lowe r than the lowest non-definitive IC 50 

### value (IC 50 

### > 922 μg a.i./L for saltwater diatom). For the two studies that tested an isoxaben formulation and derived 72-h

IC 50 

### values (17 and 43 mg a.i./L), a comparison of potential exposures from spray drift of an

isoxaben formulation to the IC 50 

### values was conducted using AgDr ift (v2.1.1). The concentration of isoxaben in a receiving water body (standard EPA farm pond) immediately adjacent to the field from the maximum single application rate of 1.0 lb a.i./A is 3.45 μg a.i./L 6 

### . This drift EEC is over

4900X lower than the lowest definitive IC 50 

### value. Based on these co mparisons, potential risk to aquatic non-vascular plants from isoxaben exposure from runoff and spray drif t is not anticipated.

6 Initial average water concentration mode led using ground application using high boom, very fine to fine droplet size, and 90 th percentile

### Page 45 of 74 For aquatic vascular plants, the RQs exceeded both the listed and non-listed LOC for all registered uses for isoxaben, (RQ=1.02-15.2). As discussed above, the water concentration in an adjacent water body exposed to spray drift is 3.45 μg a.i. /L, which is 1.7X lower than the NOAEC from the most sensitive aquatic vascular plant study (NOAEC = 6 μg a.i./L). Therefore, potential exposure from runoff is likely the main exposure route of concern. While the RQs were calculated using the maximum EECs (derived using either FL citrus or PA turf scenario), EECs were calculated using other scenario types ( i.e ., other geographic lo cations and/or applic ation sites including nurseries and fruit/nut trees). EECs were grouped by use type ( i.e ., nut and fruit trees, nurseries, turf, etc .) and broad U.S. geographic regions ( i.e ., west, south, etc .). EECs based on one application at the maximum single app lication rate of 1.0 lb a.i./A as well as 3 applic ations at 1 lb a.i./A and the resulting non-listed and listed RQs are presented in Table 21 . It is noted that the maximum yearly application rate is 4 lb a.i./A for some uses, but several registered labels state that the maximum yearly rate is only 3 lb a. i./A for many uses. Therefore, EECs using 3 applications were used for characterization. Overall, the results in the table indicate that there are

both non-listed and listed LOC exceedances when evaluating both on a use type basis as well as across several geographic areas. Therefore, this evaluation supports the conclusion of potential risk to aquatic vascular plants.

Aquatic EECs were calculated based on a total toxi c residue approach as well as based on parent only. Degradate toxicity data were not available for aquatic vascular plants. Toxicity values for aquatic vascular plants were not calculated using Quantitative Structure Activity Relationship (QSAR) methodology as the current tools do not calc ulate toxicity values for aquatic vascular plants. EECs using the TTR approach included de gradates resulting from the aqueous photolysis study. While there are no aquatic plant toxicity data available on these de gradates, inclusion of these degradates may be more relevant for sha llow or clearer water bodies that contain isoxaben as they may be more susceptible to photolysis. However, the RQs based on parent alone exceed the listed LOC for all registered uses and exceed the non-listed LOC for all. Hence, based on the lines of evidence, there is a potential for risk to aquatic vascular plan ts from exposure via runoff from both isoxaben parent as well as a combina tion of isoxaben and its de gradates of concern.

### Page 46 of 74 Table 21. Aquatic Vascular Plant RQs when Using EECs Grouped by Use Type or U.S. Geographic Area.

App Rate (lb a.i./A) x

No. of Apps Use Type or Geographic

Area 

### Aquatic Vascular Plant RQs 1


### TTR Approach Parent Only

Peak

EECs (TTR) (μg/L) Nonlisted RQs Listed RQs Peak EECs (Parent)

(μg/L) Non-listed RQs Listed RQs

Specific Registered Use

1.0 x 3 Nut, fruit trees 20-76 2.0

- 7.9 3.4

- 13 4.8-32 0.48- 3.2 0.8- 5.4
Grapes 24-60 2.4-6.0 4-10 6.6-15 0.7- 1.5 1.1-2.4 Nursery 29-82 2.9

- 8.2 4.8-14 8-24 0.8- 2.4 1.3-3.9

X-mas trees 31.3 3.1 5.2 6.6 0.7 1.1

Turf 23-30 2.3

- 3.0 3.8-5 6.7-7.7 0.7-0.8 1.1-1.3

1.0 x 1 Nut, fruit trees 7.3-31 0.7- 3.0 1.2

- 5.1 3.7-20 0.4- 2 0.6- 3.3 Grapes 11-24 1.1-2.4 1.8-2.8 5.4-7.6 0.5-0.8 0.9- 1.3
Nursery 14-33 1.4-3.3 2.4-5.5 5.4-16 0.5- 1.6 0.9- 2.7

X-mas trees 11.3 1.1 1.9 5.0 0.5 0.8

Turf 7.6-10.7 0.76- 1.1 1.3-1.8 3.5-4.4 0.4-0.4 0.6-0.7 Specific Geographical Region

1.0 x 3 West Coast (CA, OR) 20-45 2.0-4.5 3.4-7.5 4.8-9.5 0.5-0.95 0.8- 1.6

East Coast (PA, NY, NJ) 30-60 3.0-6.0 5-10 13-21 1.3-2.1 2.2-3.5

Mid-West (MI, TN) 57-82 5.7-8.2 9.5-14 13-24 1.3-2.4 2.1-3.9

Southeast (FL, NC) 23-52 2.3-5.2 3.8-8.7 6.7-32 0.7- 3.2 1.1-5.4

1.0 x 1 CA, OR 7.3-19 0.7- 1.9 1.2-3.2 3.7-9.4 0.4-0.9 0.6- 1.6
PA, NY, NJ 11-27 1.1-2.7 1.8-4.5 4.4-14 0.4- 1.4 0.7- 2.3

MI, TN 26-33 2.6-3.3 4.3-5.5 7-16 0.7- 1.6 1.2-2.7
FL, NC 7.6-31 0.8- 3.1 1.3-5.1 3.5-20 0.4- 2.0 0.6- 3.3

1 RQs based on the most sensitive aquatic vascular plants toxicity values (EC50 = 10 μg/L; NOAEC = 6 μg/L); Bold

values exceed the LOC



### 4.2.2.Risks to Terrestrial Organisms

Animals

Based on the results of the screening-level assessment , the registered uses of isoxaben result in no

direct acute effects to birds and mammals. Furt hermore, for two avian reproduction studies, there were no effects at the highest dietary concentrations tested.

In an effort to evaluate potential risk from acute exposure for birds and mammals, the maximum EECs were compared to the acute toxicity data cu rrently available. T-REX was used to compare EECs to the highest value in the avian acute oral study ( i.e., adjusted acute LD 50 

### = 1,441 mg a.i./kgbw for a 20-g bird) and the highest valu e in the avian sub-acute dietary study ( i.e., acute LC 50 

### = 4,500 mg a.i./kg-diet). If RQs were calculated assuming the LD 50 

### to be 2,000 mg/kg-bw, the

### Page 47 of 74 resulting RQs would be ≤ 0.28, which is less than the acute no n-listed LOC of 0.5, but exceeds the acute listed LOC of 0.1. However, there were no effects observed at 2,000 mg/kg-bw in either the bobwhite quail or zebra finch acu te oral study. The highest dose-based EEC is 403 mg/kg-bw and is 3.6X lower than the adjusted LD 50 

### (20-g bird). For the avian dietary-based acute comparison, RQs, based on the highe st EEC and assumption of an LC 50 

### value of 4,500 mg/kg-diet, were <0.08, all of which are less than the listed species LOC of 0.1. A similar comparison was conducted for mammals assuming an acute LD 50 

### value of 10,000 mg/kg-bw (highest dose tested which resulted in no effects), and the resulting RQs were ≤ 0.02. Overall, potential risk from acute exposure to birds and mammals is not anticipated.

The RQs for birds did not exceed the chronic LOC based on no effects re ported at the highest

concentration tested in bot h a bobwhite quail (NOAEC = 1073 mg/kg-diet) and mallard duck reproduction (NOAEC = 1035 mg/kg-diet) study. Ther e is an additional reproduction study with mallard duck that was not adequate for quantit ative use (MRID 00153109). This study was deemed insufficient to provide a definitiv e endpoint as there were concerns with control performance (high percentage of cracked eggs, hi gh variability in egg production). In this study there was also a significant decrease in the percent of eggs hatc hed relative to live 3-we ek old embryos at 946 mg/kg-diet with an apparent eff ect on hatchling survival per egg set and the number of hatchlings per pen. However, these effect s were not observed in the mallard study conducted at a later date at a concentration of 1035 mg/kg-diet (MRID 49091601), where control performance was deemed adequate. Therefore, the results from the later study were used to evalua te potential effects to

mallard ducks.

While risk of mortality from acu te exposure to isoxaben is expect ed to be low for mammals from the registered uses of isoxaben, there is a poten tial for chronic risk. Although dietary-based RQs do not exceed the chronic risk LOC of 1.0 (RQs ≤ 0.71), dose-based RQs exceed the LOC for all registered uses (RQs ≤ 3.84). The dose-based calculation take s into account that different-sized

animals have to consume different amounts of food. The dose-based risk quotients do account for

the fact that small anim als need to consume more food rela tive to their body we ight than large

animals or that differential amounts of food ar e consumed depending on the water content and

nutritive value of the food. Overa ll, small- and medium-sized mamma ls foraging on short grass, tall grass, broadleaf plants a nd arthropods exceed the LOC for all uses except eucalyptus and medium mammals consuming arthropods for the us e on bearing fruit and nut trees. Large-sized mammals consuming short grass exceed the LOC fo r all uses, except eucalyptus. For eucalyptus,

chronic LOCs were exceeded for small and me dium mammals consuming short grass and small mammals consuming broadleaf plants.

In the modeling scenario for ground spray appli cation for birds and mammals, the default foliar dissipation rate (i.e., 35 days) was used due to lack of adequate dissipation data. However, there are still LOC exceedances for all mammal size classes when a single application at the maximum single application rate is modeled (i .e., bearing fruit and nut trees; RQs ≤ 2.60). Also, given the large retreatment interval of 56-60 days for most uses, the default dissipation rate had limited impact on increasing the EECs and resultant RQs. While the maxi mum single application rate (1.0 lb a.i./A) was used to calculate RQs, based on information in the available incident reports, this was the application rate generally reported, suggesting that users may be applying at the maximum

### Page 48 of 74 single application rate. The minimum single applic ation rate reported on several labels is 0.5 lb a.i./A, and the LOC is exceeded slightly for small and medium mammals (RQs ≤ 1.30) when a single application at this minimum application rate is used. Furthermore, while RQs were calculated based on upper bound Kenaga EECs, the LO C is still exceeded for small and medium mammals using the mean Kenaga EECs when using an annual rate of 3 or 4 lb a.i./A (RQs ≤ 1.36), and are just below the LOC for a single a pplication rate of 1.0 lb a.i./A (RQs ≤ 0.92).While the RQs were calculated using the NOAEL value (40 mg/kg-bw; based on reductions in parental body weight), if the LOAEL was used (200 mg/kg- bw), there were no LOC exceedances for any mammalian size class. Additionally, in prenatal de velopmental studies in the rat and rabbit, no effects on development or maternal toxicity we re observed at doses up to 1000 mg/kg/day (dosed by oral gavage for 10-12 days; MRID 00153119 and 00153118). However, overall, based on the application rate and resultant EECs and RQs, there may be a potential for chronic risk to mammals.

In addition to the evaluation of potential risk to birds and ma mmals from ground spray, isoxaben is also applied as a granule, therefore potential ac ute risk to birds and mammals from this exposure route was also examined. Using the maximum single application rate (1.0 lb a.i./A), the EEC is 10.41 mg a.i./ft 2 

### . Similar to the evaluation for acute e xposure from ground spray, if RQs were calculated assuming the LD 50 

### to be 2,000 mg/kg-bw for bird s, the resulting RQs would be ≤ 0.36,

which is less than the acute non-listed LOC of 0.5, but exceeds the acu te listed LOC of 0.1. For mammals assuming an acute LD 50 

### value of 10,000 mg/kg-bw (highest dose tested which resulted in no effects), and the resulting RQs were ≤ 0.03. However, these RQs would be lower than the

estimated values because no effects were identif ied at 2,000 mg a.i./kg-bw or 10,000 mg/kg-bw in the acute oral studies. Therefore, potential for acute risk from inge stion of granular isoxaben is

considered low.

Acute risk from inhalation was also evaluated for birds and mammals using the STIR model (v1.0). Isoxaben is not anticipated to be volatile and the results of the STIR model indicate that potential

risk to birds and mammals via this exposure route is not anticipated ( APPENDIX 3 ).

There are no reported incident re ports for terrestrial animals for isoxaben. However, the lack of reported incidents does not necessarily imply an absence of adverse effects in the field.

Overall, potential risk from acute exposure for birds (and their surrogates) and mammals is not anticipated. Additiona lly, chronic risk to birds is not anticipated. However, based on the lines of evidence, there appears to be a poten tial for chronic risk to mammals.

For terrestrial invertebrates, only non-definitive acute contact toxicity data were submitted for terrestrial arthropods (honeybees). If an RQ were calculated for terrestrial invertebrates 7



### , conservatively assuming the LD 50 

### to be 101.7 μg ai/bee and the e xposure equal to the application rate multiplied by 2.7 μg ai/bee per 1 lb ai/A, th e resultant acute contact RQ would be 0.11 (using an annual maximum rate of 4 lb a.i/A). This RQ va lue is more than four times below the terrestrial invertebrate LOC (0.4). In an acute oral toxicity st udy with adult honeybees (unreviewed; EFSA

7 The employed methodology for calculating a honey bee acute contactRQ was proposed in the 2012 Pollinator Risk Assessment Framework SAP White Paper. The White Pape r is accessible online at regulations.gov, under docket EPA-HQ-OPP-2012-0543

### Page 49 of 74 2010), there was no mortality or behavioral abno rmalities reported at an oral dose of 100 μg a.i./bee, suggesting low toxicity from oral exposur e. Therefore, risk to non-target terrestrial

invertebrates is c onsidered unlikely.

Plants

Although the seedling emergence RQs which are de rived from runoff plus drift are much higher than those for drift alone (deriv ed using the vegetative vigor endpoint), RQs for listed and nonlisted

dicots and listed monocots also exceed the LOC for terrestrial plants from drift alone as well as

from a combination of runoff and drift. While grasses do not appear to be affected by isoxaben based on seedling emergence, some grasses appear to be susceptible to inju ry by isoxaben at later growth stages as evidenced by observed effects in the vegetative vigo r toxicity studies.

Runoff is a major factor in nontarge t terrestrial plant exce edances based on TerrPlant. It is difficult to estimate how far from the application site ad verse effects may occur. While RQs cannot be directly used to estimate the magnitude or likeli hood of effects, it is true that lower application rates result in lower EECs. However, given that the LOC for listed dicots would be exceeded 80- fold at a single application of 1.0 lbs ai/A, the potential for nontarget pl ant effects would remain even with a reduction in application rate. RQ s were based on the most sensitive monocot and dicot, and it is noted that there is a range of sensitivities to isox aben among the dicots tested in the seedling emergence study. In the available data, isoxaben did not a ppear to be toxic to cucumber in the seedling emergence test at the highest concentration tested ( 0.88 lb a.i./A, whic h is slightly lower than the maximum single application rate of 1.0 lb a.i./A), but cucumber was the most sensitive dicot tested in the vegetative vigor stud y. If RQs are calculated in TerrPlant using the second most sensitive dicot in the seedling emer gence study (i.e., pea), the LOC is exceeded for listed dicots under semi-aquatic conditions (RQ=2).

It is also important to consider that modeled runoff is only compared to endpoints from the seedling emergence study. The method of pes ticide application in the guideline studies allows for analysis of effects to seedlings from both spray drift and runoff, but the guideline vegetative vigor studies are only analyzed for effects from spray drift (p esticide applied by overspray in toxicity studies and exposure from runoff is not co nsidered). The potential for e ffects on older plants, such as those in the vegetative vigor st udy, from runoff through stem contact or root uptake remains an uncertainty and plant risk may be unde restimated in this assessment.

For isoxaben, the only monocots te sted in the submitted toxicity studies were grass species (Family: Poaceae), which did not app ear to be particularly sensitiv e to isoxaben at the application rates tested (most IC 25 

### s greater than highest concentration tested), especially in the seedling emergence study. Typically, onion (Family: Liliaceae) is the tested species representing the other monocot families ( e.g. Orchidaceae, Smilacaceae). The lack of a second monocot family tested results in considerable uncertainty about the poten tial risk to non-grass species. While not at the maximum single application rate, an applicati on of isoxaben at 0.25 lb ai/A prior to bulb emergence reported minimal visual injury 5-7 mont hs after application to Golden Apeldoorn tulips (0-5% reported injury) and 0% injury to Ice Fo llies daffodils and Ideal irises (Al-Khatib et al

. 1996). In this study, the total bul b dry weight after isoxaben expos ure for tulips, daffodils, and irises were 96, 104, and 110% of the control.

### Page 50 of 74 Effects to sensitive trees and other perennial sp ecies may occur that cannot be accounted for by current modeling and phytotoxicity studies. Howeve r, the reported incidents included effects to woody plants. Changes in plant community compos ition may occur due to differences in species sensitivity. Such changes could lead to local reductions in biodiversity and influence animal species through changes in available habitat and preferred food sources.

The AgDRIFT model was used to refine the potential effect of isoxaben drift to nontarget plants. Ground applications at the single application rate, 1.0 lbs ai/A, were modeled for all of the species tested in the seedling emergen ce and vegetative vigor studies ( Table 22 ). This table indicates the distance from the edge of the appl ication area where the RQ for that endpoint falls below the risk to terrestrial plant LOCs. For lettuce, the mo st sensitive species tested, effects on seedling emergence may be seen at out to 249 ft from the application area, and beyond 997 ft for listed species. For vegetative vigor, effect s may be seen out to 174 ft fr om the application area, and out to 554 ft for listed species.

Table 22 Distance (feet) from the edge of fi eld where the RQ falls below the risk to terrestrial plant LOC for seed ling emergence endpoints for ground application, based on Tier 1 AgDRIFT EECs.

Plant Species Seedling Emergence Vegetative vigor

Listed Nonlisted Listed Nonlisted

Monocots

Oat 3.3 <3.3 325 <3.3

Ryegrass 3.3 <3.3 554 174

Wheat 3.3 <3.3 3.3 <3.3

Dicots

Oilseed rape 125 92 6.6 >3.3

Pea 46 10 46 <46

Cucumber 3.3 <3.3 92 30

Carrot 177 59 554 <3.3

Lettuce >997 249 46 <3.3

Tomato 331 154 3.3 <3.3

Sugarbeet 46 36 6.6 3.3

### Page 51 of 74 The distance estimates are derived using EFED’s AgDRIFT default values, which include the use of a high-boom (50 in height) ground application and ASABE dropl et size spectrum ‘very fine to fine.’ However, if isoxaben wa s applied using larger droplets si zes and/or a lower boom height, then the distances off-field would presumably be lower. AgDRIFT modeling was also conducted using low boom (20 in height) and ASAE droplet size spectrum ‘fine to medium/coarse’. Using these parameters, the longest distance to an e xposure value equal to the vegetative vigor NOAEC is 144 ft and to the seedling emergence NOAEC is 430 ft . While this is still a considerable distance from the edge of the application area, it is appreciably less than the undefined >997 ft distance predicted using the de fault parameters.

Current labels do not have specific droplet size dist ributions or boom heights. Larger droplet sizes or lower boom heights may reduce the drift dist ance off-field for isoxaben, however, it is noted that potential risk may still occur from runoff alone based on LOC exceedances.

Because isoxaben is moderately persistent and moderately mobile, contamination of ground water used as irrigation was considered as a possible route of exposure to terrestrial plants. The highest peak estimated groundwater concentration valu e from PRZM-GW (1010 ppb; WI sands scenario) applied in one inch of water on an acre of land corresponds to an application rate of 0.22 lbs ai/A, roughly 24 times the most sensitive terrestrial pl ant endpoint, lettuce seedling emergence (0.0095 lb a.i./A; Appendix 4 ). The peak EEC represents the groundwater concentration after 30 years assuming 4 applications per year at 1 lb a.i./A for 30 years; the time to breakthrough to the water table for isoxaben was calculated as approximately 19 years. If a single app lication at 1 lb a.i./A is applied, the 30 year estimated peak concen tration is 20 ppb, with a breakthrough time of 19 years. This single application EEC corresponds to an application rate of 0.0045 lb a.i./A (based on 1-in of irrigation water over an acre), which is roughly one-half the most sensitive plant toxicity value suggesting that a limited numb er of applications over that time until breakthrough (19 years) may pose a potential risk to nontarget terrestrial pl ants. Additionally, should this estimated ground

water concentration result in e xposure to aquatic plants via gr ound water recharge, the aquatic plants may be affected.

The incident data discussed earlier suggest that, at least for plants, exposure pathways for isoxaben are complete and that exposure levels are sufficient to result in field-observable effects. Therefore, based on the lines of evidence, there is a potenti al for adverse effects to terrestrial plants.

4.3. Overall conclusions

The results of this screening-level risk assessment indicate that the registered uses of isoxaben are unlikely to cause potential direct adverse acu te or chronic effects to freshwater and

estuarine/marine fish and invertebrates nor effects to aquatic non-vascular pl ants. Isoxaben is not acutely toxic to avian, mammalian, or honeybee speci es, nor do data indicat e likelihood of chronic

effects to birds. Chronic eff ects to mammals were identified on a dose-based exposure but not on a dietary-based exposure basi s. There is also potential risk to terrestrial and a quatic vascular plants. Therefore, this analysis ( i.e. , the preliminary registration review risk assessment) failed to reject the risk hypothesis for terrestri al and aquatic vascular plants and mammals (chronic risk).

### Page 52 of 74 5. Federally Threatened and Endang ered (Listed) Species Concerns

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the National Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department of Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks to listed species from pesticides. The Interim Appro aches were developed join tly by the agencies in response to the National Academy of Sciences ’ (NAS) recommendations and reflect a common approach to risk assessment shared by the agencies as a way of addressing scientific differences

between the EPA and the Services. The NAS report outlines recommendations on specific

scientific and technical issues related to the de velopment of pesticide risk assessments that EPA

and the Services must conduct in connection with their obligations under the Endangered Species Act (ESA) and FIFRA.

The joint Interim Approaches were released prior to a stakeholder workshop held on November 15, 2013. In addition, the EPA presented the join t Interim Approaches at the December 2013 Pesticide Program Dialogue Commit tee (PPDC) and State-FIFRA Issues Research and Evaluation Group (SFIREG) meetings, and held a stakeholde r workshop in April 2014, allowing additional opportunities for stakeholders to comment on the Interim Approaches. As part of a phased, iterative process for developing the Interim Appr oaches, the agencies will also consider public comments on the Interim Approaches in conn ection with the development of upcoming Registration Review decisi ons. The details of the joint Interi m Approaches are contained in the white paper “Interim Approaches for National-Le vel Pesticide Endangered Species Act

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 Report,” dated November 1, 2013.

Given that the agencies are continuing to develo p and work toward implementation of the Interim Approaches to assess the potential risks of pesticid es to listed species and their designated critical habitat, this preliminary risk assessment for is oxaben does not contain a complete ESA analysis that includes effects determinations for specific listed species or designated critical habitat. Although EPA has not yet completed effects determin ations for specific species or habitats, for this preliminary assessment EPA co nducted a screening-le vel assessment for all taxa of non-target wildlife and plants that assumes for the sake of the assessment that listed species and designated critical habitats may be present in the vicinity of the application of isoxaben. This screening level

assessment will allow EPA to focus its future evaluations on the types of species where the potential for effects exists once the scientific me thods being developed by th e agencies have been fully vetted. This screening-level risk assessment for isoxaben indicates pot ential risks of direct effects to listed mammals, terrestrial and aquatic va scular plants from regist ered use sites. Listed species of birds (surrogates for aquatic-phase am phibians and reptiles) a nd aquatic animal taxa may also be affected through indirect effects becau se of the potential for direct effects on listed and non-listed species upon which such species ma y rely. Potential direct effects on listed mammals, terrestrial and aquatic va scular plants from the use of is oxaben may be associated with modification of Primary Constituent Elements (PCEs) of designated critical habitats, where such designations have been made. Once the agenci es have fully developed and implemented the

### Page 53 of 74 scientific methods necessa ry to complete risk assessments fo r endangered and thre atened (listed) species and their designated critical habitats, these methods will be applied to subsequent analyses for isoxaben as part of completi ng this registration review ( Table 23 ).54 

### Table 23. Potential Effects to Federally Listed Taxa Associated with Direct Effects from the Registered Uses of Isoxaben.

Listed Plant Taxon Potential Direct Effects Terrestrial and semi-aquatic plants – monocots and dicots Yes 1

Aquatic nonvascular plants No 2
Aquatic vascular plants Yes 1

Listed Animal Taxon Potential Direct Effects

Acute Chronic

Terrestrial invertebrates No 3 No

Mammals No 3 Yes 4

Birds No 3 No 3
Reptiles No 3 No 3
Amphibians No 3 No 3

Freshwater fish No 3 No 3

Freshwater invertebrates No 3 No 3

Estuarine/marine fish No 3 No 3

Estuarine/marine invertebrates No 3 No 3

1 RQs exceed the listed LOC based on toxicity data for bo th terrestrial plants and aquatic vascular plants.

2 Risk of direct effects from isoxaben exposure expected to be below the LOC

3 Risk of direct effects from acute and chronic exposure to terres trial and aquatic animals is exp ected to be below the LOC, exce pt for chronic

risk to mammals.

4 Chronic risk to mammalian species may occu r as the LOC was exceeded for all register ed uses from exposure to isoxaben on a chro nic dosebasis, but not on a dietary basis.



### 6. Endocrine Disruptor Screening Program

As required by FIFRA and the Federal Food Dr ug and Cosmetic Act (FFDCA), EPA reviews numerous studies to assess potenti al adverse outcomes from exposur e to chemicals. Collectively, these studies include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxic ity, developmental, reproductive, a nd general or systemic toxicity. These studies include endpoints whic h may be susceptible to endocrine influence, including effects on endocrine target organ histopa thology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reprodu ctive loss, and sex ratios in o ffspring. For ecological hazard assessments, EPA evaluates acute tests and chroni c studies that assess growth, developmental and reproductive effects in different taxonomic groups. As part of its registration review decision,

EPA reviewed these data and selected the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. However, as required by FFDCA section 408(p), isoxaben is subject to the endocri ne screening part of the Endocr ine Disruptor Screening Program (EDSP).

EPA has developed the EDSP to determine whether certain substances (inc luding pesticide active and other ingredients) may have an effect in humans or wildlife si milar to an effect produced by a “naturally occurring estrogen, or ot her such endocrine effects as the Administrator may designate.” The EDSP employs a two-tiered approach to maki ng the statutorily required determinations. Tier 1 consists of a battery of 11 scr eening assays to identify the potenti al of a chemical substance to interact with the estrogen, androge n, or thyroid (E, A, or T) horm onal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of55 

### the Tier 2 tests are necessary based on the availabl e data. Tier 2 testing is designed to identify any adverse endocrine-related effects caused by th e substance, and esta blish a dose-response relationship between the dose a nd the E, A, or T effect.

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, which contains 58 pest icide active ingredient s and 9 inert ingredients. A second list

of chemicals identified for EDSP sc reening was published on June 14, 2013 8 

### and includes some pesticides scheduled for registration review and chemicals found in water

. Neither of these lists

should be construed as a list of know n or likely endocrine disruptors.

Isoxaben is on List 2. List 2 repr esents the next set of chemicals for which EPA intends to issue

test orders/data call-ins in the near future. For further informati on on the status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test gui delines and the Tier 1 screening battery, plea se visit our website. 9



### 7. Literature Cited

Al-Khatib, K. 1996. Tulip (Tulipa sp p), daffodil (Narcissus spp.) and iris (Iris spp.) response to preemergence herbicides. Weed Tech . 10:710-715.

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the EPA food-chain (Kenaga) nomogram, an instru ment for estimating pesticide residues on plants. Environ. Tox. Chem. 13:1383-1391.

Hoerger, F. and E. E. Kenaga. 1972. Pe sticide Residues on Plants: Correlation of Representative Data as a Basis for Estimation of their Magnitude in the Environment. In F. Coulston and F. Korte, eds., Environmental Quality and Safety: Chemistry, Toxicology, and Technology, Georg Thieme Publ., Stuttgart, West Germany, pp. 9-28.

Salihue, S., Hatzios, K.K., Derr, J.F. 1998. Comp arative Uptake, Translocation, and Metabolism of Root-Applied Isoxaben in Ajuga (Ajuga reptans) and Two Ornamental Euonymus Species. Pesticide Bidchemistry and Physiology, 60:2 pp. 1 19-1 3 1

United States Environmental Protection Agen cy. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, Office of Research and Development, Washington, D.C. EPA/ 630/R-95/002F. April 1998. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759

8 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of

chemicals.

9 http://www.epa.gov/endo/56 

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

USEPA, 2007. Problem Formulation for Is oxaben in Isoxaben Summary Document: Registration Review. Office of Pesticide Programs, January, 2007.

USEPA, 2009. Input Parameter Guidance. Ve rsion 2.1. Environmental Fate and Effects Division. October 22, 2009 http://www.epa.gov/oppefed1/models/w ater/input_parameter_guidance.htm

USEPA, 2010. Environmental Fate and Ecological Risk Assessment for the Section 3 New Uses of Isoxaben on Bearing Nut Trees and Vineya rds. Environmental Fate and Effects

Division. Office of Pesticides. June 7, 2010. DP Barcode D341496.

USEPA, 2010a. The Drinking Water Degradat es Identification Memorandum for Isoxaben. Memo to Dennis McNeilly. DP Barcode 374529.

USEPA 2012. Ecological Stru cture Activity Relationshi ps (ECOSAR) version 1.11. http://www.epa.gov/oppt/newchems/tools/21ecosar.htm

USEPA. 2013. Pesticides: Science and Po licy. Terrestrial Models , T-REX Version 1.5/1. 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/

USEPA. 2013b. Guidance on Modeling Offsite Depos ition of Pesticides via Spray Drift for Ecological and Drinking Water Assessments. Environmental Fate a nd Effects Division. Decemeber 20, 2013.

Willis G.H. and L.L. McDowell (1987) Pesticide persistence on foliage. Rev Environ Contam

Tox: 100:23-62.57 

### Appendix 1 – PRZM/EXAMS output from scenario with highest EECs

Variable Volume Water Model, SWCC Compatible Version

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

Performed on: 8/15/2014 at 16:19

Peak 1

‐ in

‐ 10 = 88.4 ppb

Chronic 1

‐ in

‐ 10 = 64.0 ppb

Simulation Avg = 49.8 ppb

4

‐ day avg 1

‐ in

‐ 10 = 87.8 ppb

21

‐ day avg 1

‐ in

‐ 10 = 86.0 ppb

60

‐ day avg 1

‐ in

‐ 10 = 81.5 ppb

90

‐ day avg 1

‐ in

‐ 10 = 78.3 ppb

Benthic Pore Water Peak 1

‐ in

‐ 10 = 71.0 ppb

Benthic Pore Water 21

‐ day avg 1

‐ in

‐ 10 = 70.9 ppb

Benthic Conversion Factor = 1.89 ‐ Pore water (ug/L) to (total mass, ug)/(dry sed mass,kg)

Benthic Mass Fraction in Pore Water = 0.196

YEAR Peak 4

‐ day 21

‐ day 60

‐ day 90

‐ day Yearly Avg Benthic Pk Benthic 21

‐ day

1 1.94E+01 1.92E+01 1.87E+01 1.78E+01 1.71E+01 1.08E+01 1.51E+01 1.51E+01

2 4.63E+01 4.60E+01 4.48E+01 4.27E+01 4.21E+01 2.95E+01 3.71E+01 3.70E+01

3 7.06E+01 7.03E+01 6.88E+01 6.57E+01 6.39E+01 4.71E+01 5.48E+01 5.48E+01

4 8.58E+01 8.52E+01 8.30E+01 7.83E+01 7.52E+01 6.02E+01 7.04E+01 7.03E+01

5 6.20E+01 6.22E+01 6.32E+01 6.59E+01 6.83E+01 5.02E+01 6.61E+01 6.70E+01

6 5.59E+01 5.55E+01 5.45E+01 5.17E+01 4.97E+01 4.33E+01 4.73E+01 4.73E+01

7 5.18E+01 5.16E+01 5.10E+01 4.86E+01 4.78E+01 4.24E+01 4.52E+01 4.52E+01

8 4.65E+01 4.62E+01 4.51E+01 4.34E+01 4.36E+01 3.83E+01 4.12E+01 4.11E+01

9 5.80E+01 5.77E+01 5.65E+01 5.42E+01 5.44E+01 4.54E+01 5.03E+01 5.03E+01

10 6.58E+01 6.55E+01 6.43E+01 6.30E+01 6.16E+01 5.42E+01 5.88E+01 5.87E+01

11 6.97E+01 6.94E+01 6.78E+01 6.41E+01 6.31E+01 5.18E+01 5.75E+01 5.74E+01

12 7.31E+01 7.27E+01 7.10E+01 6.90E+01 6.77E+01 5.60E+01 6.34E+01 6.33E+01

13 5.16E+01 5.14E+01 5.03E+01 5.11E+01 5.32E+01 4.43E+01 5.30E+01 5.40E+01

14 5.72E+01 5.69E+01 5.57E+01 5.29E+01 5.22E+01 4.43E+01 4.87E+01 4.87E+01

15 4.71E+01 4.68E+01 4.58E+01 4.36E+01 4.30E+01 3.75E+01 4.22E+01 4.29E+01

16 5.16E+01 5.13E+01 5.04E+01 4.79E+01 4.74E+01 4.04E+01 4.42E+01 4.41E+01

17 8.56E+01 8.51E+01 8.35E+01 7.99E+01 7.78E+01 5.68E+01 6.71E+01 6.70E+01

18 8.40E+01 8.35E+01 8.13E+01 7.67E+01 7.48E+01 6.00E+01 6.72E+01 6.72E+01

19 5.97E+01 5.94E+01 5.83E+01 5.77E+01 5.98E+01 5.19E+01 5.91E+01 6.01E+01

20 8.87E+01 8.81E+01 8.63E+01 8.16E+01 7.84E+01 6.27E+01 7.10E+01 7.10E+01

21 7.87E+01 7.82E+01 7.66E+01 7.27E+01 7.04E+01 6.42E+01 6.77E+01 6.85E+0158

22 7.29E+01 7.24E+01 7.09E+01 6.88E+01 6.86E+01 6.04E+01 6.55E+01 6.54E+01

23 4.82E+01 4.79E+01 4.72E+01 4.90E+01 5.09E+01 4.24E+01 5.10E+01 5.21E+01

24 5.96E+01 5.94E+01 5.84E+01 5.54E+01 5.33E+01 4.38E+01 5.04E+01 5.04E+01

25 6.45E+01 6.42E+01 6.29E+01 6.08E+01 6.10E+01 5.27E+01 5.75E+01 5.75E+01

26 5.11E+01 5.09E+01 5.03E+01 4.92E+01 4.87E+01 4.36E+01 4.75E+01 4.84E+01

27 5.67E+01 5.65E+01 5.52E+01 5.23E+01 5.14E+01 4.29E+01 4.77E+01 4.77E+01

28 1.45E+02 1.44E+02 1.39E+02 1.30E+02 1.25E+02 7.89E+01 1.07E+02 1.07E+02

29 9.95E+01 9.97E+01 1.01E+02 1.06E+02 1.10E+02 8.31E+01 1.04E+02 1.05E+02

30 6.30E+01 6.31E+01 6.39E+01 6.64E+01 6.88E+01 5.37E+01 6.91E+01 7.03E+01

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

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

Effective compartment halflives averaged over simulation duration:

zero washout 0

water col metab halflife (days) = 303.336213300958

zero hydrolysis 0
photolysis halflife (days) = 7952.62695872797

volatile halflife (days) = 169345.374914618

total water col halflife (days) = 291.687912334577

zero burial 0

benthic metab halflife (days) = 1729.66181201397

zero benthic hydrolysis 0

total benthic halflife (days) = 1729.66181201397

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

Fractional Contribution of Transport Processes to Waterbody & Total Mass (kg):

Due to Runoff = 0.7005 19.42

Due to Erosion = 0.0008 0.2236E

‐ 01

Due to Drift = 0.2987 8.279

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

Flow in/out Characteristics of Waterbody:

Average Daily Runoff Into Waterbody (m3/s) = 1.294828998867743E

‐ 003

Baseflow Into Waterbody (m3/s) = 0.000000000000000E+000

Average Daily Flow Out of Waterbody (m3/s) = 1.294828998867728E

‐ 003

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

Inputs:

38.00 = oc partitioning coefficient

282.0 = water column half Life

25.00 = reference temp for water column degradation

1608. = benthic Half Life59

25.00 = Reference temp for benthic degradation

2.000 = Q ten value

93.50 = photolysis half life

40.00 = reference latitude for photolysis study

0.000 = hydrolysis half life

332.4 = molecular wt

0.4100E

‐ 08 = vapor pressure

1.420 = solubility

0.1000E+06 = field area

0.1000E+05 = water body area

2.000 = initial depth

2.000 = maximum depth

2 1=vvwm, 2=usepa pond, 3 = usepa reservoir, 4 = const vol no flow, 5 = const vol w/flow

F T = burial, else no burial

0.1000E

‐ 07 = mass transfer coefficient

0.5000 = PRBEN

0.5000E

‐ 01 = benthic compartment depth

0.5000 = benthic porosity

1.350 = benthic bulk density

0.4000E

‐ 01 = OC frcation in benthic sediment

5.000 = DOC in benthic compartment

0.6000E

‐ 02 = benthic biomass

1.190 = DFAC

30.00 = SS

0.5000E

‐ 02 = chlorophyll

0.4000E

‐ 01 = OC frcation in water column SS

5.000 = DOC in water column

0.4000 = biomass in water column

FRACTION AREA CROPPED = 1.0000000000000060 

### Appendix 2. Isoxaben Ecological Effects Summaries

Many of the following study summaries were presen ted in previous risk assessment on bearing fruit and nut trees (D341496).

1. Aquatic Effects Characterization

The registrant has submitted a suite of studies, as required by CFR 40 Part 158 10 

### , which examine the toxicity of isoxaben to representative aquatic organisms that serve as surrogates for organisms that may be exposed. Both acute and chronic effects were determined for freshwater

fish and invertebrates. Acute effects on marine/estuarine fish and invertebrates and aquatic vascular and nonvascular plants were also examined.

a. Aquatic Animals

i. Effects from Acute Exposure

Most of the available aquatic effects studies were conducted at nominal concentrations of 0 (control) and 100 mg ai/L. Very few were conducted with a co-solvent, and the water solubility of isoxaben is 1 mg/L. There was no reported effort to cen trifuge or filter the solute.

If the solutions were ac tually prepared with a nominal c oncentration of 100 mg ai/L and the measured concentration is roughly 1 mg ai/L in th e acute studies, a precipitate should have been reported. However, no precipitate is repor ted for any of the available studies.

Freshwater Fish

In 96-h acute toxicity studies, rainbow trout ( Oncorhynchus mykiss ; MRID 00132146), bluegill sunfish ( Lepomis macrochirus ; MRID 00132145) and common carp ( Cyprinus carpio ; MRID 00137844) were exposed to isoxaben at mean -measured concentrations of 0 (negative control) and 1.0 mg ai/L. No sub-lethal effects were observed in any study. The LC 50 

### and NOAEC values ( Table 1 ), based on a lack of mortal ity and sub-lethal effects, were >1.0 and 1.0 mg ai/L.

Table 1. Freshwater fish and amphibian ac ute toxicity for tec hnical grade isoxaben.

Species 96-hour

LC 50 mg ai/L Toxicity Category MRID No. Study Classification

Rainbow trout ( Oncorhynchus mykiss ) >1.0 NA (no effects up to solubility limit) 00132146 Supplementa

Bluegill sunfish (Lepomis macrochirus) >1.0 NA (no effects up to solubility limit) 00132145 Supplemental

10 Code of Federal Regulations 40, Part 158.subpart 630. Terr estrial and aquatic nontarget or ganism data requirements.http://ecfr.gpoaccess.gov/cgi/t/text/textidx?c=ecfr;sid=fe712efed37d095118c7637457e011 b3;rgn=div5;view=text;node= 40%3A23.0.1.1.9;idno=40;cc=ecfr#40:23.0.1.1.9.7.1.161

Species 96-hour

LC 50 mg ai/L Toxicity Category MRID No. Study Classification

Common carp ( Cyprinus carpio ) >1.0 NA (no effects up to solubility limit) 00137844 Supplemental



### Estuarine/marine Fish

In a 96-h acute toxicity study, sheepshead minnows ( Cyprinodon variegatus ; MRID 40531304) were exposed to isoxaben at time-wei ghted average (TWA) concentrations were <0.02 (<LOQ; controls) and 0.86 mg ai/L. The 96-h LC 50 

### was >0.86 mg ai/L. The LC 50 

### and NOAEC values ( Table 2 ), based on a lack of mortality and sub-lethal effects, were 0.86 and >0.86 mg ai/L, respectively.

Table 2. Estuarine/marine fish acute toxicity to technical grade isoxaben.

Species 96-hour

LC 50 mg

ai/L Toxicity Category MRID

No. Study

Classification

Sheepshead minnow (Cyprinodon variegatus) >0.86 NA (no effects up to solubility limit) 40531304 Supplemental



### Freshwater Invertebrates

Water fleas, Daphnia maga (MRID 00132444), were exposed to isoxaben at meanmeausured concentrations of 0 (control) and 1.3 mg ai/L. No effects were seen in either the control or treatment groups . Therefore the 48-h EC 50 

### and NOAEC were >1.3 mg ai/L and 1.3 mg ai/L, respectively ( Table 3 ).

Table 3. Freshwater invertebrate acute toxicity for techni cal grade isoxaben.

Species 96-hour

LC 50 mg ai/L Toxicity Category MRID

No. Study Classification

Waterflea (Daphnia magna) >1.3 NA (no effects up to solubility limit) 00132444 Supplemental

*at the limit of solubility



### Estuarine/marine

Quahog clam larvae ( Mercenaria mercenaria ; MRID 40531302) were exposed to isoxaben at for 48-h under static conditions. Larvae were exposed to mean-measured concentrations of <0.02 (<LOQ; negative control) and 0.96 mg ai/L. The 48-hr EC 50 

### was >0.96 mg ai/L ( Table 4 ). The NOAEC was <0.96 mg ai/L, ba sed on a 40% reduction in normally developed larvae. The only observed toxic effect was an inhibition of normal larval development. It is not clear from the study how ‘normal larvae’ is differentiated from ‘abnormal

larvae’.62



### Grass shrimp ( Palaemonetes pugio ; MRID 40531303) demonstrated no effect from exposure to a measured concentratio n of 1 mg ai/L of isoxoaben.

Table 4. Estuarine/marine invertebrate ac ute toxicity for tec hnical grade isoxaben.

Species 96-hour

LC 50 mg ai/L Toxicity Category MRID

No. Study

Classification
Quahog clam (Mercenaria mercenaria) >0.96 NA (EC50 > solubility limit) 40531302 Supplemental

Grass shrimp (Palaemonetes pugio) >1.0 NA (no effects up to solubility limit) 40531303 Supplemental



### ii. Effects from Chronic Exposure

Aquatic vertebrates

A 66-day early-life stage study of the effect of chronic exposur e of isoxaben to rainbow trout (MRID 00137847) was conducted under flow-through c onditions. Fertilized eggs/embryos (100/level, early-eyed stage) of rainbow trout we re exposed to mean-measured concentrations of<0.002 (<LOD, controls), 0.024, 0.048, 0.093, 0.19, and 0.42 mg ai/L, respectively. No treatmentrelated effects were observed on any measured parameter during the study. The 66-day NOAEC and LOAEC were 0.42 and >0.42 mg ai./L, respectively ( Table 5 ).

A 33-day early-life stage study of isoxaben with fathead minnows ( Pimephales promelas ; MRID 00137848) was conducted under flow-through conditions. Fe rtilized eggs/embryos (100/level, <48 hours old) of fathead minnow were exposed to mean-measured concentrations of<0.002 (<LOD, controls), 0.025, 0.048, 0.095, 0.18, and 0.40 mg ai/L, respectively. No treatmentrelated effects were observed on any measured parameter during the study. The 33-day NOAEC and LOAEC values were 0.40 and >0.40 mg ai/L, respectively.

Table 5. Early life-stage toxicity of t echnical grade isoxaben to freshwater fish.

Species NOAEC mg ai/L LOAEC mg ai/L Endpoints Affected MRID

No. Study

Classification

Rainbow trout ( Oncorhynchus mykiss ) 0.42 >0.42 None 00137847 Supplemental

Fathead minnow (Pimphales promelas) 0.40 >0.40 None 00137848 Supplemental



### No chronic toxicity data were submitted for estuarine/marine fish.

Aquatic Invertebrates63



### In a 21-day static renewal life-cycle study, first instar daphnids (MRID 00137845) were exposed to isoxaben at mean-measured concen trations of 0 (contro l), 0.13, 0.69 and 1.01 mg

ai/L. No effects were observed in the c ontrol, 0.13 or 0.69 mg ai/L treatment groups ( Table 6 ), but 13% of the daphnids were immobilized in the highest treatment group. Additionally, statistically significant effects were reported for growth and reproduction (brood size) at the highest treatment concentra tion. The NOAEC and LOAEC for the study are 0.69 mg ai/L and 1.01 mg ai/L, respectively, based on impaired growth and reproduction.

Table 6. Freshwater invertebrate full life-c ycle toxicity for t echnical grade isoxaben.

Species NOAEC mg ai/L LOAEC mg ai/L Endpoints Affected MRID

No. Study

Classification

Waterflea (Daphnia magna) 0.69 1.01 Growth and Reproduction 00137845 Supplemental



### In a 28-day flow-through life-cycle st udy, <24-hr old mysid shrimp (MRID 49090201) were exposed to isoxaben at mean-measured con centrations of 0 (contro l), 0 (solvent control DMF 0.01%), 0.0581, 0.121, 0.238, 0.460 and 0.841 mg ai/L. Statistically significant effects were reported for reproduction (# of young pe r female) at the two highest treatment

concentration. The NOAEC and LOAEC for the study are 0.238 mg ai/L and 0.841 mg ai/L, respectively, based on impair ed reproduction (Table 7).

Table 7. Estuarine/marine invertebrate full li fe-cycle toxicity for technical grade isoxaben.

Species NOAEC mg ai/L LOAEC mg ai/L Endpoints

Affected MRID

No. Study

Classification Mysid Shrimp (Americamysis bahia) 0.238 0.841 Reproduction 49090201 Acceptable

b. Aquatic Plants

Three studies assessing the effect of is oxaben on the aquatic vascular plant duckweed, Lemna gibba , are available ( Table 8 ). In a 14-day toxicity study, the freshwater floating aquatic vascular plant duckweed (MRID 47428401) was e xposed to isoxaben (technical grade active ingredient;TGAI) at mean-measured concentratio ns of<0. 5 (<LOQ, control), 5.8, 13, 24, 46, and 93 μg ai/L. A NOAEC was not defined in the study. The EC 05 

### and EC 50 

### values for decreased biomass, the most sensitive endpoint, were 2.9 and 13  g ai/L, respectively. Inhibition in biomass in the treatment groups ranged from 13 to 96%.

In a 7-day acute toxicity study, duckw eed (MRID 47428402) was exposed to isoxaben

TGAI at mean-measured concentrations of <0.50 (<LOQ, control), 3.1, 6.0, 12.3, 23.6, and 45.964



###  g ai/L. The 7-day NOAEC and EC 50 

### values for biomass inhibition, the most sensitive endpoint,

were 6.0 and 10  g ai/L, respectively. The inhibition in biomass in the treatment groups ranged

from -1 to 95%.

In a 14-day acute toxicity study (MRI D 47428406), duckweed was exposed to Isoxaben ® 

### 500 SC (formulation) at mean-measured concen trations of <0.5 (<LOD, control), 5.1, 10.1, 20.3,
38.5, 84.2 and 172.1  g ai/L. The 14-day NOAEC and EC 50 

### values for biomass inhibition, the most sensitive endpoint, were 10.1 and 15  g ai/L, respectively. A hormetic (low-dose stimulatory) effect of 18% increased biomass was s een at the lowest test concentration. In the remaining treatment groups, percent inhibiti on in biomass ranged from 6 to 95%.

Studies of nonvascular plants are also required and typically involve microalgae. In a supplemental (quantitative use) 96-hour acute toxicity study, culture s of marine diatom,

Skeletonema costatum , were exposed to technical grad e isoxaben at in itial measured concentrations (test material unstable during e xposure) of <0.03 (<LOD, negative and solvent controls), 0.640, 0.127, 0.256, 0.492, and 0.922 mg ai/L. The NOAEC and EC 50 

### /IC 50 

### values based on all endpoints (yield, growth ra te, and AUC) were 0.922 and >0.922 mg ai/L, respectively.

In a supplemental (qualitative use) 72-hour acute toxicity study (MRID 48534802), cultures of the freshwater diatom ( Navicula pelliculosa ) were exposed to isoxaben technical at meanmeasured concentrations of <0.035 (<LOD; c ontrols), 3.2, 5.1, 11, 20, 47, and 86 mg ai/L. The

IC 50 

### values for cell density, biomass, and grow th rate were >86 mg ai/L, while the NOAEC values were 47, 20, and 20 mg ai/L, respectively.

A supplemental (qualitiative us e) 14-day static study reports a NOAEC of 1.4 mg ai/L for the green algae Pseudokirchneriella subcapitata (formerly Selenastrum capricornutum ) (MRID 00153111). The study is from 1984, before microalgae studies were routinely submitted to the Agency; raw data were not included and the study is not consistent with Agency guidelines.

In a supplemental (qualitative use) 72 hour acute toxicity study (MRID 48533202), cultures of the unicellular green alga ( Chlorella vulgaris ) were exposed to Isoxaben 500 SC (Flexidor 50 SC) at mean-measured concentrations of <0.002 (<LOQ; control), 2.30, 4.99, 9.56, 20.1, and 43.4 mg ai/L. The NOAEC was 9.56 mg ai/L for ce ll density, growth rate, and biomass and the most sensitive endpoints were cell density and biomass, both with IC 50 

### values of 43 mg ai/L.

A supplemental (qualitiativ e use) 96-hour acute toxicity study (MIRD 48533203), cultures of blue-green algae ( Anabaena sp .,) were exposed to Isoxaben 500 SC (Flexidor 50 SC) at meanmeasured concentrations of <0.002 (<LOQ, control) and 36.6 mg ai/L. The NOAEC and IC 50 

### values based on cell density, biomass (area under the growth curve), and the specific growth rates were 36.6 and >36.6 mg ai/L, respectively.

In a supplemental (qualitative use) 72-hour acute toxicity study (MRID 48534801), cultures of the unicellular algae ( Scendesmus subspicatus ) were exposed to Flexidor at nominal65 

### concentrations of 0 (negative contro l), 0.430, 1.376, 4.30, 13.76, 43.0, and 137.6 mg ai/L under

static conditions. The 72-hr mean-measured concentrations were <0.11 (<LOD; control), 0.46, 1.51, 4.60, 14.4, 43.7, and 142.7 mg ai/L. Cell density was the most sensitive endpoint, with a NOAEC of 4.6 mg ai/L and an IC 50 

### value of 17 mg ai/L.

Table 8. Toxicity of technical grade isoxaben to aquatic plant species.

Species/ (duration) % ai IC 50

 g ai/L NOAEC

 g ai/L MRID Study

Classification

Duckweed ( Lemna gibba ) (14 days) Technical 13 2.9 47428401 Supplemental

Duckweed ( Lemna gibba ) (7 days) Technical 10 6 47428402 Supplemental

Duckweed ( Lemna gibba ) (14 days) Formulation 15 10.1 47428406 Supplemental

Marine diatom ( Skeletonema

costatum ) (96-hrs) Technical >922 922 48952602 Supplemental

Freshwater diatom ( Navicula pelliculosa ) (72-hr) Technical >86000 20,000 48534802 Supplemental

Green algae ( Pseudokirchneriella subcapitata ) (14-d) Technical >1400 1400 00153111 Supplemental

Green algae ( Chlorella vulgaris ) (72-hr) Formulation 43,000 9,560 48533202 Supplemental

Green algae (Scendesmus subspicatus ) (72-hr) Formulation 17,000 4,600 48534801 Supplemental

Blue-gree algae ( Anabaena

sp. ) (96-hr) Formulation >36,600 36,600 48533203 Supplemental

### Page 66 of 74 2. Terrestrial Effects Characterization

The registrant has submitted a battery of studies that examine the toxicity of isoxaben to representative terrestrial organisms that stand as surrogates for animals a nd plants at risk of exposure. Effects of acute and chronic exposur e were evaluated for mammals; data are also available for birds which serve as a surrogate for terrestrial-phase amphibians and reptiles. Data

on the effects of isoxaben on terres trial invertebrates are availabl e with studies of the honeybee ( Apis mellifera ). The toxicity of isoxaben to terrestria l plants was evaluated using representative monocotyledonous (monocots) and di cotyledonous (docots) plants.

a. Terrestrial Animals

i. Effects from Acute Exposure

Birds

The acute oral toxicity of is oxaben to 20-wk-old bobwhite quail ( Colinus virginianus ; MRID 00132146) was assessed over 14 days. Isoxa ben was administered by oral gavage at nominal doses of 0 (vehicle control), 125, 250, 500, 1000 and 2000 mg/kg. The 14-day acute oral

LD 50 

### was >2000 mg/kg-bw ( Table 9 ). Since no effects were obs erved in any of the treatment levels, the 14-day NOAEL, based on a lack of treatment-related effects, was 2000 mg/kg-bw. Isoxaben is classified as practica lly non-toxic to bobwhite quail ( Colinus virginianus ) on an acute oral exposure basis.

The acute oral toxicity of Isoxaben to 8- to 10-month old Zebra finches ( Taeniopygia

guttata ) (MRID 48952601) was assessed over 14 days in a limit-dose study. Isoxaben was administered to the birds via gavage (5 mL/kg) at nominal concentrations of 0 (control) and 2000 mg ai/kg bw. No mortality, c linical signs of toxicity, or effects on body weight or food consumption were observed in the 2000 mg ai/kg bw group. The acute oral LD 50 

### was >2000 mg ai/kg bw. Isoxaben is classified as pr actically non-toxic to Zebra finches ( Taeniopygia guttata ) on an acute oral exposure basis

Table 9. Avian acute oral toxici ty for technical grade isoxaben.

Species LD 50 (mg ai/kg bw) Toxicity Category MRID Study

Classification

Northern bobwhite quail (Colinus virginianus) >2000 Practically

non-toxic 00132146 Acceptable

Zebra finches ( Taeniopygia guttata ) >2000 Practically

non-toxic 48952601 Acceptable



### The subacute dietary toxicity of is oxaben to 12-d old bobwhite quails ( Colinus virginianus ; MRID 00132142) was assessed over 8 days (5 days with treated feed and 3 days with basal diet).

Isoxaben was administered to the birds in their di et at measured concentrations of 0 (negative67 

### control), 56, 180, 480, 1500, and 4500 mg ai/ kg diet. The 8-day subcute dietary LC 50 

### was >4500 mg ai/kg diet ( Table 10 ). The NOAEC, based on a lack of tr eatment-related effects, was 4500 mg ai/kg-diet. Isoxaben is considered to be prac tically nontoxic to bobwhite quail on an subacute dietary exposure basis.

The subacute dietary toxicity of is oxaben to 10-d-old mallard ducks ( Anas platyrhynchos ; MRID 00132143) was assessed over 8 days. Measured concentrations were 0 (negative control), 63, 190, 540, 1600, and 4800 mg ai/kg diet. The 8-day subacute dietary LC 50 

### was >4800 mg ai/kg diet. The NOAEC, based on a lack of trea tment-related effects, was 4800 mg ai/kg diet. Isoxaben is considered to be practically nontox ic to mallard ducks on an subacute dietary exposure basis

Table 10. Avian subacute dietary t oxicity for technical grade isoxaben.

Species LC 50 (mg ai/kg diet) Toxicity Category MRID Study

Classification

Northern bobwhite quail (Colinus virginianus) >4500 Practically

non-toxic 00132142 Acceptable

Mallard duck (Anas platyrhynchos) >4800 Practically

non-toxic 00132143 Acceptable



### Mammals

The aucte LD 50 

### used in this assessment is >10,000 mg ai/kg-bw ( Table 11 ) and is classified as practically nontoxic to mammals on an acu te oral exposure basis.

Table 11. Acute oral mammalian toxicity for isoxaben.

Species LD 50 Toxicity Category Affected Endpoints MRID No. Classification

Wistar rat

Rattus rattus >10000 mg ai/kg-bw practically nontoxic none 00132126 Acceptable68



### Terrestrial Invertebrates

Honeybees ( Apis mellifera ) were exposed via contact to dos es of isoxaben technical at 0 (control), 33.9, 67.4 and 101.7 μg ai/bee (MRID 0015311). No mortality or ot her subeffects were reported at any of the doses tested. The LD 50 

### for isoxaben is >101.7 μ g ai/bee and isoxaben is classified as practically nont oxic to honeybees on an acute contact exposure basis.

ii. Chronic Effects

Birds

The one-generation reproductive toxicity st udy of isoxaben to 20 pairs per level of 17- week old northern bobwhite quail ( Colinus virginianus ; MRID 00153110) -was assessed over 24

weeks. Isoxaben was administered to the birds in the diet at mean-measured concentrations of <LOD (control), 105, 313, and 1073 mg ai/kg-diet, re spectively. No treatment-related effects were observed on any adult or offspring paramete r at any treatment level. Therefore the NOAEC and LOAEC for the study are 1073 and >1073 mg ai/kg-diet, respectively ( Table 12 ).

The one-generation chronic toxicity of is oxaben to 12 pairs per level of 20-week old mallard duck ( Anas platyrhynchos ; MRID 00153109) was assessed over 23 weeks. Isoxaben

was administered to the birds in their diet at mean-measured c oncentrations of <LOD (control), 100, 298, and 946 mg ai/kg-diet, resp ectively. The study is classifi ed as ‘Supplemental’, because it provides insight into the potenti al for effects of chronic exposur e of isoxaben to avian species, but the study is insufficient to provide a definiti ve endpoint. There was a significant reduction in the proportion of eggs hatched to live 3-wk old embryos, indicati ng reproductive effects at least as low as 298 mg ai/kg diet. There was a high pe rcentage of cracked eggs in the control (11%), nearly double the high-end nor mal value (6%) as stated in the OPPTS 850.2300 harmonized guideline 11 

### ; the elevated number of cracked eggs in the control raises uncertainty regarding the conditions under which the study was conducted. Fu rthermore, the number of eggs laid per hen was higher than expected (59 vs 38), and the mean percentage of viable embryos per eggs set was very low in the control (71% vs 85-98%). There was also an apparent effect on hatchling survival per egg set and the number of hatchli ngs per pen, but high cont rol variability did not

allow for statistical detection. Additionally, data for two import ant growth endpoints, hatchling weight and 14-d survivor weight were not provided. While these problems are not enough to invalidate the study, a definitive e ndpoint could not be determined.

The one-generation reproductive to xicity of Isoxaben to 16 pa irs per level of 24-week old mallard duck ( Anas platyrhynchos ) was assessed over 20 weeks (MRID 49091601). Isoxaben

was administered to the birds in the diet at nominal concentra tions of 0 (negative control), 100, 300, and 1000 mg ai/kg diet. Mean-measured con centrations were <25 (LOD, control), 103  3.41, 313  16.5, and 1035  37.8 mg ai/kg diet.

11 USEPA 1996. Ecological Effects Test Guideline 850.2300 Avian Reproduction Test. http://www.epa.gov/opptsfrs/publications/OPPTS_Harmoni zed/850_Ecological_Effects_Test_Guidelines/Drafts/85 0-2300.pdf69



### There were no treatment-related mortalities, overt signs of toxicity, or treatment-related effects upon body weight or feed consumption in the control and treatment groups. No significant treatment-related effects upon a ny of the reproductive parameters were observed. No treatmentrelated differences upon egg shell thickness were observed at any trea tment level. The NOEC was 1035 mg ai/kg diet (mean -measured concentration).

Table 12. Avian reproduction chronic to xicity for technical grade isoxaben.

Species % a.i. NOAEC (mg ai/kg diet) LOAEC (mg ai/kg-diet) MRID Study Classification

Northern bobwhite quail ( Colinus virginianus ) 94.5

Technical 1073 >1073 00153110 Supplemental

Mallard duck ( Anas platyrhynchos ) 94.5

Technical Not established 100 00153109 Supplemental

Mallard duck

( Anas platyrhynchos ) 93.5

Technical 1035 >1035 49091601 Acceptable



### Mammals

In a three-generation reproduction study (MRID 00153529) ( Table 13 ), 25 Wistar rats/sex/dose group were administered EL-107 (Isoxaben tech nical; 93.7-94.5% a.i.; Lot Nos. H02-2G6-118 and Z10025) continuously in the diet at doses of 0, 0.05, 0.25 or 1.25% (equivalent to 0, 40, 200 or 1000 mg/kg/day). Each generation was maintain ed on the test diets for a growth period of approximately 10 weeks prior to mating (1 male : 1 female). Rats from the P, F1 and F2 generations were continued on the test diets for 2, 3 and 1 breeding trial(s), respectively. From the F1a and F2b weanlings, 25 rats /sex/dose were selected to be parents of the F2 and F3 generations, respectively. Selected weanlings were fed the same test diet concentrations as their parents. At sacrifice, livers and reproductive organs were co llected for histological examination. In addition, eyes from F2 parental animal s were saved and examined histologically.

Additionally from the F2b litters, high-dose progeny with microphtha lmia (8 rats/sex), 10 control weanlings with linear retinal dysplasia (dia gnosed during ophthalmic examinations), and 10 normal control weanlings from each sex were retain ed as F2 parental animals. These additional

animals were also maintained on the test diet s for approximately 10 weeks prior to mating. The study also contained a developmenta l assessment: F2c and F3a litters were subjected to complete teratological evaluation. Females were grossly ex amined and livers and reproductive organs were collected for histological examination. The uter us was removed via cesarean section, and its contents examined. Fetuses were weighed, sexe d, and examined for ex ternal, visceral, and

skeletal malformations and variations.

The LOAEL for parental toxicity is 0.25% (200 mg/kg bw/day), based on decreased body weights, body weight gains and food effici ency. The NOAEL is 0.05% (40 mg/kg bw/day).

The LOAEL for offspring toxicity is 1.25% (1000 mg/kg bw/day), based on decreased pup70 

### body weights, decreased live pups/litter and gest ation survival in F 2b litters and possibly

increased incidence of malformations in cluding microphthalmia, coloboma and/or exencephaly, and hydroureter, in some li tters beginning in th e F2b generation. The NOAEL is 0.25% (200 mg/kg bw/day).

The LOAEL for reproductive toxicity is 1.25% (equivalent to 1000 mg/kg bw/day), based

on decreased mean number of live pups/litter, gestation survival, corpora lutea, implantations, and reduced milk production seen in some nursing dams. The NOAEL is 0.25% (equivalent to 200 mg/kg bw/day in males/females).

Table 13. Chronic toxicity of isoxaben to mammals.

Species % a.i. NOAEL (mg ai/kg-bw) LOAEL (mg ai/kg-bw) MRID Study Classification

Wistar rat ( Rattus norvegicus ) 93.7-94.5

Technical 40 200 00153529 Acceptable



### b. Terrestrial Plants

Seedling emergence testing (MRID 47428404) indicate moncot gra ss species (Family: Poaceae) tested were unaffected at treatment rates equivalent to an application rate of 0.888 lbs ai/A, the highest rate tested. However, only three monocot species were tested. Corn ( Zea

mays ), a required test species, was not included in the study. Onion ( Allium cepa ), which typically represents non-graminoi d monocot species such as lilie s and orchids, was also not included. Among broadleaf plan ts (dicots), cucumber ( Cucumis sativus ) was unaffected at the highest rate tested, while fresh weight was affected in pea ( Pisum sativum ) and sugarbeet ( Beta vulgaris ). Emergence was the most sensitive endpoint for carrot ( Daucus carota ), lettuce ( Lactuca sativa ), oil seed rape ( Brassica napus ), and tomato ( Solanum lycopersicum ). Lettuce was the most sensitive dicot (EC 25 

### = 0.0095 lbs ai/A); a NOAEC wa s not established in the study, but the lettuce EC 05 

### (0.0014 lbs ai/A) is used in lieu of a NOAEC.

Vegetative vigor testing (MRI D 4748405) indicated that all sp ecies tested except wheat ( Triticum aestivum ) and tomato were at least somewhat sensitive to isoxaben. Among monocots, ryegrass ( Lolium perenne ) was particularly sensitive to isoxaben and was the most sensitive species tested (EC 25 

### = 0.014 lbs ai/A; NOAEC 0.0034 lbs ai/A. As with the seedling emergence study, only three monocot species were tested. Corn, a required test species, was not included in the study. Onion, which typically represents non- graminoid monocot species such as lilies and orchids, was also not included. Among broadl eaf plants, cucumber was the most sensitive species, with an EC 25 

### of 0.089 lbs ai/A, and the NOAEC was 0.028 lbs ai/A. Table 14 provides the most sensitive endpoints from all plant species tested.

Table 14. The most sensitive terres trial plant endpoints (lbs a i/A) in the studies submitted

for isoxaben.

Species Seedling emergernce Vegetative vigor71

Endpoint NOAEC EC 25 Endpoint NOEC EC 25

Oat None 0.888 >0.888 Fresh weight 0.0069 >0.888 Ryegrass None 0.888 >0.888 Fresh weight 0.0034 0.014

Wheat None 0.888 >0.888 None 0.888 >0.888 Oilseed rape Emergence 0.020* 0.028 Survival 0.444 <0.888 Pea Fresh weight 0.056 0.29 Fresh weight 0.056 >0.056

Cucumber None 0.888 >0.888 Fresh weight 0.028 0.089 Carrot Emergence 0.0138 0.043 Fresh weight 0.0034 0.888 Lettuce Emergence 0.0014* 0.0095 Fresh weight 0.056 >0.888 Tomato Emergence 0.0067 0.016 Fresh weight 0.888 >0.888 Sugarbeet Fresh weight 0.056 0.073 None 0.444 0.73

* -EC 05 is used when calculated EC 25 is less than derived NOAEC.72 

### Appendix 3. STIR results



# 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 isoxaben Enter Chemical Use non-ag Is the Application a Spray? (enter y or n) y If Spray What Type (enter ground or air) ground Enter Chemical Molecular Weight (g/mole) 332.39 Enter Chemical Vapor Pressure (mmHg) 3.90E-07 Enter Application Rate (lb a.i./acre) 1

Toxicity Properties

Bird

Enter Lowest Bird Oral LD 50 (mg/kg bw) 2000
Enter Mineau Scaling Factor 1.15 Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD 50 (mg/kg bw) 10000

Enter Lowest Rat Inhalation LC 50 (mg/L) 1.99
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 ) 6.98E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 8.77E-04

Adjusted Inhalation LD 50 2.22E+00

Ratio of Vapor Dose to Adjusted Inhalation LD 50 3.95E-04 Exposure not Likely Significant
Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.06E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 4.76E-02 Exposure not Likely Significant



### Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 6.98E-03 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.10E-03

Adjusted Inhalation LD 50 1.18E+02

Ratio of Vapor Dose to Adjusted Inhalation LD 50 9.30E-06 Exposure not Likely Significant
Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.33E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 1.12E-03 Exposure not Likely Significant **NOTE**: When entering values, press the "Enter" key in order to update linked cells.7374 

### Appendix 4. Calculations for Irrigation Exposure

To estimate exposure to plants when ground water contaminated by isoxaben is applied to crops, the following method was used.

Assume a field is irrigated w ith one inch of water containi ng 1010 μg/L isoxaben (concentration estimate from PRZM-GW).

This results in 6,272,640 cubic inches of water on each acre of the field (one acre = 6,272,640

in 2 

### ), or 1.0 × 10 5 

### L/acre of water (6,272,640 in 3 

### ÷ 61 in 3 

### /L = 1.0 × 10 5 

### L). Therefore, 1.01 × 10 8 

### μg isoxaben are applied to each acre of the field (1010 μg/L × 1.0 × 10 5 

### L = 1.01 × 10 8 

### μg), which is equivalent to an applicati on rate of 0.22 lbs isoxaben/acre (1.01 × 10 8 

### μg = 0.22 lbs)