### Page 1 of 13 U. S. ENVIRONMENTAL PROTECTION AGENCY

Washington, D.C. 20460

OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES PC Code: 125851 DP Barcode: 3 41497 Date: March 18 , 2010 MEMORANDUM SUBJECT: Tier I Drinking Water Assessment for the Isoxaben Proposed New Use on Bearing Nut

Trees and Vineyards TO: Jo anne Miller , Risk Manager

Kathyrn Montague , Risk Manager Reviewer Herb icide Branch Registration Division (7505P) Dennis McNeilly , Risk Assessor Christina Swartz , Branch Chief RAB 2 Health Effects Division FROM: Chuck Peck, Environmental Engineer

Environmental Risk Branch IV Environmental Fate and Effects Division (7507P ) REVIEWED BY: R. David Jones, Ph.D., Senior Agronomist

Environmental Risk Branch IV Environmental Fate and Effects Division (7507P ) APPROVED BY: Elizabeth Behl, Branch Chief

Environmental Risk Branch IV Environmental Fate and Effects Division (7507P ) A Tier I screening
- level drinking water ass essment was conducted for isoxaben for the proposed new use on bearing nut trees and vineyards (62719
- 00LIN)
. Isoxaben (CAS 82558 - 50 - 7 ), an herb icide, is an active ingredient in the pesticide FN - 3133 (EPA Reg. No. 62719 - 00LIN ) and a number of other products (see Appendix A for complete list of labels )
. This drinking water assessment is limited to the exposure associated with isoxaben alone and does not include exposure associated with other active ingredients that may be combined with isoxaben
. The maximum proposed application rate for the propos ed new use on bearing nut trees and vineyards considered for this assessment is 1.0 lbs ai/acre/application, applied 1 time per year, for a

### Page 2 of 13

maximum total annual application rate of 1.0 lb ai/A/yr. Isoxaben is formulated as a dry flowable or granular product, or is incorporated into soil fertilizer. All applications are made by ground spray (dry flowable) or drop or rotary spreaders (granular)
. Because the maximum annual application rate for the new use assessed here is less than the application rate for ornamentals o n the label for Isoxaben 75DF (EPA Reg. No. 34704 - 917 ) , the values for ornamentals are recommended for use in the human health risk assessment. The annual application rate for ornamentals, which is used in this current assessment, is 3 lb s ai/A /year with a 60 day re
-treatment interval
. The estimated drinking water concentrations ( EDWCs ) are based on the maximum proposed application rates specified in the product labels. The EDWCs for the human health risk assessment are presented in Table 1 . Because isoxaben has a number of maj or degradates with similar toxicity as isoxaben, a total toxic residue (TTR) approach was used in the modeling. In the TTR approach, half
- lives are calculated for the combined isoxaben and degradate residue and modeling runs are conducted using these half
- lives. Additionally , a mobility study (MRID 41106303 ) and EPISuite analysis indicated that several of the isoxaben degradates were more mobile than the parent. As such, two sets of modeling runs were completed: one set using the mobility estimates of the parent and one set using mobility estimates derived f rom the degradate s tudy
. The maximum 1 - in
- 10 -year peak and annual mean EDWCs in surface water were 28 4 and 1 20 μg/L, respectively , for ornamental use . The maximum estimated acute concentration in groundwater was 43.6 μg/L for ornamental use . The maximum 1 - in
- 10 -year peak and annual mean EDWCs in surface water were 87.6 and 37 μg/L, respectively, for bearing nut trees and vineyards. The maximum estimated acute concentration in groundwater was 14.5 μg/L for bearing nut trees and vineyards. Table 1 . Tier I Estimated Drinking Water Concentrations (EDWCs) resulting fromapplications of isoxaben and its degradates on ornamentals and bearing nut trees. Drinking water source (model) Use (modeled rate) Acute ( μg/L ) C hronic

( μg/L ) Parent Kd Data Surface water (FIRST) Ornamental 200 54.7 Groundwater (SCIGROW) Ornamental 2.13 2.13 Surface water (FIRST ) Bearing nut trees and vineyards 61.5 16.9 Groundwater (SCIGROW) Bearing nut trees and vineyards 0.71 0.71 Degradate Kd Data Surface water (FIRST) Ornamental 284 120 Groundwater (SCIGROW) Ornamental 43.6 43.6 Surface water (FIRST) Bearing nut trees and vineyards 87.6 37.0 Groundwater (SCIGROW) Bearing nut trees and vineyards 14.5 14.5 Use Characterization Isoxaben is a pre - emergent benzamide herbicide used for control of broadleaf ( dicotyledonous ) weeds. The specific mode of action for isoxaben is not well understood, but it has been shown to inhibit the conversion of glucose to cellulose in the cell wall synthesis for sensitive species, with grasses (Family: Poaceae) tending to be more tolerant than other plant groups (Salihue et al. 199 8 ). I so xaben is not thought to be highly mobile in adult plants, limiting its toxicity to older plants, but allowing efficacy in emerging seedlings. Maximum use pattern information is presented in Table 2 .

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Table 2 . Summary use information for isoxaben proposed new use and ornam entals.

Use Max. Single

Applic ation Rate (lbs. a.i./A) No. of

Applic ation Annual

Applic ation Rate (lbs. a.i./A/yr) Interval

Between Applic ation (days) Applic ation

Meth od Ornamental 1.0 3 3.0 60 Ground spray Bearing nut trees and vineyards 1.0 1 1.0 Not Applicable Ground spray Environmental Fate and Transport Characterization There is no significant evidence that i soxaben degrades by hydrolysis
. Isoxaben does not readily undergo aerobic and anaerobic degradation in soil with half lives of greater than 150 days. I soxaben degrades via soil photolysis with a half life of 49 days. Primary routes of degradation are aqueous photolysis, aerobic aqueous metabolism and anaerobic aqueous metabolism with half lives ranging from 6 to 18 days. I soxaben is not expected to volatize (vapor pressure less than 3 .9x10 - 7 torr at 2 6  ̊ C). Isoxaben is classified as moderately mobile based on adsorption Kd values in five soils ranging from 0.81 to 6.63 ml/g. Major degradates of isoxaben include hydroxyisoxaben, dimethoxybenzamide, methoxyphenylpyrimidinol, and AEM hexenoylisoxaben
. B ased on structural analysis of these degradates in EPISuite, three of the degradates (hydroxyisoxaben, dimethoxybenzamide, and AEM hexenoylisoxaben) have the potential to be more mo bile than isoxaben (Koc values ranging from 4.6 to 102 ml/g oc ) , with methoxyphenylpyrimidinol appearing to be very immobile (Koc values from 4,800 to 38,000 ml/g oc )
. The isoxaben physical and chemical properties and the environmental fate source data from submitted studies are presented in Table 3 . Properties and f ate data for the major degradates are presented in Table 4 . There is a potential for isox aben and its degradates to reach surface water through spray drift, as products may be applied via ground spray. B ecause isoxaben and its degradates are persistent in surface soils, th ere is also the potential for them to reach surface water through surface runoff either in solution or adsorbed to the soil. Isoxaben and its degradates have the potential to leach to ground water when applied to certain soils , where high water tables are present , and high rainfall/ irrigation occurs.
Table 3 . Physical/chemical properties and environmental fate source data for isoxaben and it s degradates.

Property Value Source Comments Chemical Name N - [3 - (methylpent
- 3 - yl)isoxazol
- 5 - yl]
- 2,6 - dimethoxy
-benzamide Molecular Weight (g/mol) 332.39 Solubility in Water ( mg/L @ 20 °C , pH 7 ) 1 MRID 40059506 Vapor Pressure (torr @ 2 6 °C) <3. 9x 10 - 7 torr MRID 40059506 Octanol
- water partition coefficient (K ow) 43 7 MRID 40059506 Hydrolysis Half

- life (pH 7; 25C; in days) no significant degradation MRID 00250449 Aqueous Photolysis Half
- life (@ pH 7; in days) 6 (isoxaben) 6 - 15 (TTR 1 ) MRID 47140003 Two replicates were

conducted.

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Table 3 . Physical/chemical properties and environmental fate source data for isoxaben and it s degradates.

Property Value Source Comments Soil Photolysis Half

- life (days) 49 (isoxaben) 63 (TTR) MRID 47428403 Aerobic Soil Metabolism Half
life (days) 161 (isoxaben, sandy loam, UK) 210 (isoxaben, silt loam, France) 277 (isoxaben, silt loam, Greece) 86 6 (isoxaben, sand, UK) 206 (TTR, sandy loam, UK) 342 (TTR, silt loam, France) 358 (TTR, silt loam, Greece) 1,116 (TTR, sand, UK) MRID 47140004

Anaerobic Soil Metabolism Half
life (days) 224 (isoxaben) 446 (TTR) MRID 41106302 Aerobic Aquatic Metabolism Half
- life (days) 21 (isoxaben) 62 - 166 (TTR) MRID 46393202 Two replicates were

conducted. Anaerobic Aquatic Metabolism Half
- life (days) 18 (isoxaben) 265 (TTR) MRID 46393201 Freundlich Adsorption Coefficient (mL/g) (Kd) 0.81 (isoxaben, sand) 2.48 (isoxab en, sandy loam) 4.41 (isoxaben, loam) 6.63 (isoxaben, clay loam) 2.18 (isoxaben, loamy sand) 0.06 (hydroxyisoxaben, sand) 0.22 (hydroxyisoxaben, sandy loam) 0.37 (hydroxyisoxaben, loam) 0.84 (hydroxyisoxaben, clay loam) 0.3 (hydroxyisoxaben, loamy sand) MRID 41106303

Henry’s Law Constant (atm
- m3/mol) 8.5x 10 - 10

– Estimated from vapor pressure, molecular weight, and solubility
. 1. TTR

– total toxic residue. Isoxaben plus its degradates. Table 4 . Physical/chemical properties and environmental fate data for isoxaben and degradates. Isoxaben / Degradate Solubility (mg/L) Log KOW KOC 1 ( mL/g OC ) Source Isoxaben 1 2.64 434 See Table 3 Hydroxyisoxaben 462 1.53 17 - 31 57 EPISuite 4.0

MRID 41106303 2,6 - Dimethoxybenzamide 8.4x10 4

- 0.22 4.9

– 10 EPISuite 4.0 Methoxyphenylpy

rimidinol 41.2 3.56 4,800

– 38,000 EPISuite 4.0 AEM hexenoylisoxaben 265 1.71 21 - 102 EPISuite 4.0 1. K oc estimated in EPISuite using two methods: one using the Molecular Connectivity Index and one using the K ow . The range depicts the two estimates. Monitoring Data Isoxaben is not included as one of the analytes monitored in U.S. surface and groundwater under the USGS’s National Water Quality Assessment (NAWQA) program (http://water.usgs.gov/nawqa). There were no detections in s ix surface water and sediment samples collected and analyzed for isoxaben by California Department of Pesticide Regulation (CDPR) in 2006 in Stanislaus County
.

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Drinking Water Exposure Modeling EDWC s were generated using EFED’s standard suite of models. The FQPA Index Reservoir Screening Tool ( FIRST ) is a surface water model that is used to estimate both acute and chronic potential pesticide concentrations in untreated drinking water. EDWC s from FIR ST represent concentrations which mi ght occur from a single 1
- in
- 10 -year storm event following the last application of pesticide at a location more vulnerable than most locations in the United States to runoff, regardless of the crop being produced. The mo del considers reductions in dissolved concentration due to the percentage of the watershed which is cropped (percent cropped area - PCA), due to adsorption of pesticide to field soil and to reservoir bottom sediment, due to incorporation of the pesticide at the time of application, due to degradation in soil before washoff to the reservoir, and due to degradation of the pesticide within the water body. Reservoir water concentrations may be increased due to deposition of spray drift into the feeding stream or directly into the reservoir itself. FIRST is designed to mi mic a more complex simulation using the linked PRZM3 (Carsel et. al ., 1997) and EXAMS 2.97.7 (Burns et. al ., 2000) models , but requires less time and effort to complete. A more detailed description of the index reservoir watershed can be found in Jones et al. , 1998. The FIRST model and users manuals may be downloaded from the U.S. Environmental Protection Agency (EPA) Water Models web
-page (USEPA, 2006). P ercent Cropped Areas (PCA) that account for the maximum area within a watershed that may be planted with the modeled crop are applied to concentrations predicted by PRZM/EXAMS
. Screening Concentration in Ground Water (SCI
- GROW v2.3, Jul. 29, 2003) is a regression model used as a screening to ol to estimate pesticide concentrations found in ground water used as drinking water. S CI - GROW was developed by fitting a linear model to ground water concentrations with the Relative Index of Leaching Potential (RILP) as the independent variable. The RILP is a function of aerobic soil metabolism and the soil
-water partition coefficient. The output of SCI
- GROW represents the concentrations of isoxaben residue that might be expected in shallow unconfined aquifers under sandy soils, which is representative of the ground water most vulnerable to pesticide contamination and likely to serve as a drinking water source. The SCI - GROW model and user’s manual may also be downloaded from the EPA Water Models web
-page (USEPA, 2006). Input Parameters Input parameters for the FIRST and SC I - GROW model s are listed in Table 5 and Table 6 , respectively
. For adsorption to soil, a regression analysis of the adsorption coefficients versu s the organic carbon content yielded a p - value>0.1; as such, the Koc model wa s deemed inappropriate and Kd values were used in the modeling
. Per EFED’s Input Parameter Guidance, the mean value of the Kd values was used in FIRST . SCI - GROW, however, requires the use of the Koc value; as such, the Koc value estimated from the regression analysis was used. Table 5 . FIRST input parameters for isoxaben and its degradates Input Parameter Value Source Comment Application Rate (lbs a.i. /A) 1 .0 Isoxaben 75DF and FN - 3133 labels Applications per Year 3 / 1 Isoxaben 75DF and FN - 3133 labels 3 for ornamentals, 1 for bearing nut trees

and vineyards Application Intervals (days) 60 Isoxaben 75DF label Ornamentals only Application Method Ground Isoxaben 75DF and FN - 3133 labels

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Table 5 . FIRST input parameters for isoxaben and its degradates Input Parameter Value Source Comment Percent Crop Area 1.0 0.87 ---

--- Assumption for non
- ag uses

(ornamental)
. Default for agricultural uses. Solubility in Water at 2 0 o C (mg/L) 1 .0 MRID 40059506 Freundlich Adsorption Coefficient (mL/g) (Kd) 3 . 3 ( isoxaben) 0. 36 (hydroxyisoxaben) MRID 411 06303 Mean Kd value
. 1 Application Method Ground Isoxaben 75DF and FN - 3133 labels Aerobic Soil Metabolism Half

- life (days) 710 (TTR) MRID 47140004 Represents the 90 th percentile of the upper confidence bound on the mean ( 450 ) of 5 TTR half

- life values. 1 Aerobic Aquatic Metabolism Half

- life (days) 274 (TTR) MRID 4 6393202 Represents the 90 th percentile of the upper confidence bound on the mean ( 114 ) of 2 TTR half

- life values. 1 Aqueous Photolysis Half
- life (days) 15 MRID 4 7140003 Maximum dark control corrected half
life. 1 1 EFED input parameter guidance is located at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm Table 6 . SCI - GROW2 input parameter values for isoxaben and its degradates on ornamentals. Input Parameter Value Source Comment Aerobic Soil Metabolism Half
- life (days) 342 ( TTR) MRID 47140004 Median value per input parameter guidance. 1 Organic Carbon Normalized Partition Coefficient Koc 434 ( isoxaben) 57 (hydroxyisoxaben) MRID 411 06303 Values derived from regression analysis. Application Rate (lb ai/A) 1 Isoxaben 75DF and FN - 3133 labels – Maximum No. of Applications/Year 3 (ornamental) 1 (bearing nut tree and vineyard) Isoxaben 75DF and FN - 3133 labels – 1 EFED input parameter guidance is located at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm Because isoxaben has a number of maj or degradates with similar toxicity as isoxaben, a total toxic residue (TTR) approach was used in the modeling. H owever, a mobility study (MRID 41106303) and EPISuite analysis indicated that several of the isoxaben degradates were more mobile than the parent. As such, two sets of modeling runs were completed: one set using the mobility estimates of the parent and one set using mobility estimate s derived f ro m the degradate s tudy
. Exposure Modeling Results Tier I surface water and groundwater modeling results for isoxab en for ground spray application to container
- grown ornamentals are presented in Table 7 . These values are recommended for use in the human health risk assessment. Output values for surface water for ornamentals a re not modified using the percentage crop area (PCA) adjustment factor since the value used is 1.0
. Output surface water values for bearing nut trees and vineyards are modified using the default agricultural PCA adjustment factor of 0.87
. Output values f

or groundwater are not adjusted for a PCA. The maximum 1 - in
- 10 -year peak and annual mean EDWCs in surface water were 284 and 120 μg/L, respectively, for ornamental use. The maximum

### Page 7 of 13

estimated acute concentration in groundwater was 43.6 μg/L for ornamental use. The maximum 1 - in
- 10 - year peak and annual mean EDWCs in surface water were 87.6 and 37 μg/L, respectively, for bearing nut trees and vineyards. The maximum estimated acute concentration in groundwater was 14.5 μg/L for bearing nut trees and vineyard s. Table 7 . Tier I Estimated Drinking Water Concentrations (EDWCs) resulting fromapplications of isoxaben and its degradates on ornamentals and bearing nut trees. Drinking water source (model) Use (modeled rate) Acute ( μg/L ) C hr onic

( μg/L ) Parent Kd Data Surface water (FIRST) Ornamental 200 54.7 Groundwater (SCIGROW) Ornamental 2.13 2.13 Surface water (FIRST) Bearing nut trees and vineyards 61.5 16.9 Groundwater (SCIGROW) Bearing nut trees and vineyards 0.71 0.71 Degradate Kd Data Surface water (FIRST) Ornamental 284 120 Groundwater (SCIGROW) Ornamental 43.6 43.6 Surface water (FIRST) Bearing nut trees and vineyards 87.6 37.0 Groundwater (SCIGROW) Bearing nut trees and vineyards 14.5 14.5 DRINKING WATER TREATMENT The EDWCs in this assessment are representative of concentrations in drinking water source water (pre
-treatment) and are derived from daily instantaneous peak concentrations. F or surface water, the conceptual model assumes that a pesticide reaches surface water via spray drift or surface runoff, where it is instantaneously mixed and concentrations are observed in the water body. Isoxaben is relatively stable to hydrolysis
. Therefore, isoxaben will not degrade by hydrolysis during the time that elapses from drinking water intake through distribution to the first tap. Because of its low Kd values, treatment methods such as sedimentation, flocculation, and activated carbon, are not expected to be effective at removing isoxaben. H owever, isoxaben does degrade d ue to photolysis and aerobic aquatic metabolism. If ultraviolet light were used as a means of disinfection, some degradation of isoxaben could also be expected. Additionally, while unlikely, if an aerobic digester were used in the drinking water treatment train, some degradation may potentially occur, depending on the retention time. CONCLUSIONS AND RISK CHARACTERIZATION Tier I drinking water exposure estimates are based on isoxaben maximum use rates currently on the label for ornamentals and bearing nut trees and vineyards
. The maximum 1 - in
- 10 -year peak and annual mean EDWCs in surface water were 284 and 120 μg/L, respectively, for ornamental use. The maximum estimated acute concentration in groundwater was 43.6 μg/L for ornamental use. The maximum 1 - in
- 10 -year peak and annual mean EDWCs in surface water were 87.6 and 37 μg/L, respectively, for bearing nut trees and vineyards. The maximum estimated acute concentration in groundwater was 14.5 μg/L for bearing nut trees and vineyards. The Tier I drinking water assessment was a screening
- level assessment based on simplified models and assumptions. The modeling assessment relie d on maximum use patterns and national default PCA s to reflect potential surface and groundwater concentrations
. T o the extent that actual use patterns are less than the labeled maximums and the location
- specific PCAs are less than assumed in this assessment, actual environmental exposures could be lower. As such, if EDWCs exceed levels of concern, refinements can be made to this assessment to account for regional use patterns.

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Isoxaben was not detected in surface or ground water monitoring. However, monitoring data that is not targeted specifically in isoxaben use areas or during times of known isoxaben use may not reflect potential peak isoxaben concentrations that may occur in surface waters when runoff events occur shortly after application. REFERENCES Burns, L.A. 2000. Exposure Analysis Modeling System (EXAMS), Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA. R.F. Carsel, J.C. Imhoff, P.R. Hummel, J.M. Cheplick and J.S. Donigian, Jr. 1997. PRZM
- 3, A Model for Predicting Pesticide and Nitrogen Fate in Crop Root and Unsaturated Soil Zones: Users M anual for Release 3.0; Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA. Effland, W. R., N. C. Thurman, I. Kennedy. 1999. Proposed Methods for Determining Watershed
derived Percent Crop Areas and Considerations for Applying Crop Area Adjustments to Surface Water Screening Models. Presentation to the FIFRA Science Advisory Panel, May 27, 1999. Online at: http://www.epa.gov

/scipoly/sap/1999/index.htm Jones, R. D., S. Abel, W. R. Effland, R. Matzner, R. Parker. 1998. An Index Reservoir for Use in Assessing Drinking Water Exposure. Proposed Methods for Basin
- scale Estimation of Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment. Presentation to FIFRA Science Advisory Panel, June 29
- 30, 1998. Online at: http://www.epa.gov/scipoly/sap/1998/index.htm Salihue, S. , Hatzios, K.K. , Derr, J.F. 1998. Comparative Uptake, Translocation, and Metabolism of Root
Applied Isoxaben in Ajuga ( Ajuga reptans ) and Two Ornamental Euonymus Species. Pesticide Biochemistry and Physiology , 60:2 pp. 119 - 131 USEPA. 200 9 . Guidance for Selecting Input P arameters in Modeling the Environmental Fate and Transport of Pesticides. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009 . Online at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm USEPA. 2002. SCIGROW: Users Manual . Online at: http://www.epa.gov/oppefed1/models/water/#scigrow MRIDs MRID 00250449 Mosier, J.W. and Saunders, D.G. 1983. Hydrolysis of EL
- 107 in buffer solution. A Chapter within: EL
- 1 07. Application for 2
-year EUP. Unpublished study cond ucted by Lilly Research Laboratories, Greenfield, Indiana. Sponsored and submitted by Elanco Products Company, A Division of Eli Lilly and Company, Indianapolis, Indiana. Report No.: I - EWD - 82 - 05. Final report issued June 9, 1983.

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MRID 40059506 Rutherford, B. 1986. Physical and Chemical Characteristics of Technical Isoxaben. Laboratory Project ID BSR8506 . Unpublished study performed and submitted by Lilly Research Laboratories, Greenfield , IN. Final report issued October 2 2 , 19 8 6. MRID 46393201 Sarff, P. and L.G. Heim. Anaerobic soil degradation of isoxaben. 2003. Unpublished study performed by ABC Laboratories, Inc., Columbia, MO; sponsored and submitted by Dow AgroSciences LLC, Indianapolis, IN. ABC Study No.: 46880, Dow study No.: 010045 and Dow PTRNo.: 30258020 - 5562 - 1. Final report issued May 23, 2003. MRID 46393202 Sarff, P. 2003. Aerobic transformation of isoxab en in aquatic sediment systems. Unpublished study performed by ABC Laboratories, Inc., Columbia, MO and Dow AgroSciences LLC, Indianapolis, I N; sponsored and submitted by Dow AgroSciences LLC, Indianapolis, IN. ABC Study No.: 4688 1 , Dow AgroSciences Study No.: 0 10044 and Dow AgroSciences PTR No.: 30258020
- 5037 - 1. Final report issued May 23, 2003. MRID 41106302 Rainey, D.P. 1989. 14 C Isoxaben anaerobic so il metabolism study. Laboratory Project ID ABC
- 0224. Unpublished study performed and submitted by Lilly Research Laboratories, Greenfield, IN. Final report issued May 4 , 1989 . MRID 41106303 Saunders, D.G. and F.L. Powers. 1989. So il adsorption and desorption of isoxaben and soil metabolite 201469. Laboratory Project ID AAC8851. Unpublished study performed and submitted by Lilly Research Laboratories, Greenfield, IN. Final report issued March 21 , 1989 . MRID 47140003 Cook, W.L., F.R. Batzer and J.L. Balcer. Photodegradation of isoxaben in aqueous buffer. Unpublished study performed, sponsored and submitted by DowEIanco, Indianapolis, Indiana. Study ID No.: ENV93 144. Final report issued March 25, 1996. MRID 47140004 Huhtanen, K. and L. Heim. 2003. Aerobi c soil degradation of isoxaben. Unpublished study performed b ABC Laboratories, Inc., Columbia, Missouri; sponsored and submitted by Dow AgroScienc e s LLC, Indianapolis, Indiana. Lab Study ID.: 46879, Dow Study No. 010043. Final report issued May 12, 2003. MRID 47428403 Saunders, D.G., and F.L. Powers. 1996. Iso xaben photodegradation on soil. Unpublished study performed, sponsored, and submitted by DowElanco, Indianapolis, Laboratory Study ID No.: ENV95011. Final report issued March 20, 1996
.

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Ap pendix A. Current Isoxaben Labels Trade Name EPA Reg. No. %

Isoxaben Maximum Single

Application Rate (lbs ai/A) Maximum Annual

Application Rate (lbs ai/A) Retreatment

Interval (days) Comments FN - 133 75.0 1.0 1.0 NA Propreen 961 - 370 0.375 1.0 3.0 60 Co ntains 1.5% trifluralin Preen Landscape Mulch 961 - 408 0.0008 1.02 Contains 0.0032% trifluralin Isoxaben 75DF 34704 - 917 75 .0 1.0 3.0 60 Weed
- Free 111 52287 - 13 0.05 1.0 3.0 60 Contains 0.2% trifluralin Gallery 75 Dry Flowable 62719 - 145 75.0 1.0 3.0 60 Snapshot 2.5TG 62719 - 175 0.5 1.0 3.0 60 Contains 2% trifluralin Gallery Turf Fertilizer 62719 - 178 0.38 1.0 3.2 Turf Fertilizer (Gallery + Team) 62719 - 192 0.29 1.1 2.2 70 Contains 0.27% trifluralin and 0.53% benefin T&O Fertilizer (Gallery + Team) 6 2719 - 280 0.38 1.0 2.0 70 Contains 0.39% trifluralin and 0.76% benefin Showcase 62719 - 516 0.25 0.5 1.5 60 Contains 2% trifluralin and 0.25% oxyfluorfen Turf Fertilizer (Gallery + Team) Pro 62719 - 565 0.38 1.0 2.0 70 Contains 0.5% trifluralin and 0.5% benef in Snapshot 80 70506 - 53 20 1.0 3.0 120 Contains 60% oryzalin Turf Fertilizer (Gallery + Surflam) 70506 - 55 0.29 0.7 2.0 90 Contains 0.86% oryzalin Lawn 3iP Ready
- to - Spray 72155 - 87 2.63 0.49 1.0 14 Contains 4.73% 2,4
- D, 0.52% dicamba, and 1.1% mecoprop
-p Lawn 3iP Ready
- to -Use 72155 - 88 0.069 Contains 0.31% 2,4
- D, 0.033% dicamba, and 0.072% mecoprop
-p

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Appendix B. Model output files SURFACE WATER MODELING OUTPUT FILES - FIRST Results RUN No. 1 FOR isoxaben ON ornamental * INPUT VALU ES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

-------------------------------- ------------------------------------ 1.000( 2.833) 3 60 3.3 1.0 GROUND( 6.4) 100.0 0.0 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL H YDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.
- EFF) (RESER.) (RESER.)

-------------------------------------------------------------------- 710.00 2 0.00 15.00 - 1860.00 274.00 23 8.82 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCEN TRATION

--------------------------------------------------------------------

199.498 54.677

RUN No. 2 FOR isoxaben ON nut tree * INPUT VALUES *

-------------------------------------- ------------------------------ RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- 1.000( 1.000) 1 1 3.3 1.0 GROUND( 6.4) 87.0 0.0 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.
- EFF) (RESER.) (RESER.)

-------------------------------------------------------------------- 710.00 2 N/A 15.00
- 1860.00 274.00 238.82 UNTREATED WATER CONC (MICROGRAMS/LITE R (PPB)) Ver 1.1.1 MAR 26, 2008

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

------------------------ --------------------------------------------

61.491 16.869

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RUN No. 3 FOR isoxaben ON ornamental * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- 1.000( 2.833) 3 60 0.4 1.0 GROUND( 6.4 ) 100.0 0.0 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.
- EF F) (RESER.) (RESER.)

-------------------------------------------------------------------- 710.00 2 N/A 15.00
- 1860.00 274.00 238.82 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

--------- ----------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

--------------------------------------------------------------------

284.441 120.023

RUN No. 4 FOR isoxaben ON nut tree * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROP PED INCORP ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- 1.000( 1.000) 1 1 0.4 1.0 GROUND( 6.4) 87.0 0.0
FIELD AND RESERVOIR HALFLI FE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.
- EFF) (RESER.) (RESER.)

------------------ -------------------------------------------------- 710.00 2 N/A 15.00
- 1860.00 274.00 238.82 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

-------------------------------------------------------- ------------ PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

--------------------------------------------------------------------

87.587 36.961

### Page 13 of 13

GROUND WATER MODELING OUTPUT FILES SCIGROW VERSION 2.3 ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL FOR AQUATIC PESTICIDE EXPOSURE SciGrow version 2.3 chemical:Isoxaben time is 3/15/2010 9:40:54

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

--------------------- --------------------------------------------------- 1.000 3.0 3.000 4.34E+02 342.0

------------------------------------------------------------------------

groundwater screening cond (ppb) = 2.13E+00 ************************ ************************************************ SciGrow version 2.3 chemical:Isoxaben time is 3/15/2010 9:41:24

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobi c rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 1.000 1.0 1.000 4.34E+02 342.0

------------------------------------------------ ------------------------

groundwater screening cond (ppb) = 7.11E - 01 ************************************************************************ SciGrow version 2.3 chemical:Isoxaben time is 3/15/2010 9:41:11

-------------------------------------------- ---------------------------- Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 1.000 3.0 3.000 5.70E+01 342.0

------------------------------------------------------------------------

groundwater screening cond (ppb) = 4.36E+01 ************************************************************************ SciGrow version 2.3 chemical:Isoxaben time is 3/15/2010 9:41:29

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 1.000 1.0 1.000 5.70E+01 342.0

------------------------------------------------------------------------

groundwater screening cond (ppb) = 1.45 E+01 ************************************************************************