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U. S. ENVIRONMENTAL PROTECTION AGENCY

Washington, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

PC Code: 125851

DP Barcode: 341497

Date: March 18, 2010

MEMORANDUM

SUBJECT: Tier I Drinking Water Assessment for the Isoxaben Proposed New Use on Bearing Nut 

Trees and Vineyards

TO: Joanne Miller, Risk Manager 

Kathyrn Montague, Risk Manager Reviewer

Herbicide Branch

Registration Division (7505P) 

Dennis McNeilly, Risk Assessor

Christina Swartz, Branch Chief

RAB2

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 assessment was conducted for isoxaben for the proposed 

new use on bearing nut trees and vineyards (62719-00LIN). Isoxaben (CAS 82558-50-7), an herbicide, 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 proposed 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 on 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 lbs

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 major 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 from the degradate study. 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.

Table 1. Tier I Estimated Drinking Water Concentrations (EDWCs) resulting from applications of 

isoxaben and its degradates on ornamentals and bearing nut trees.

Drinking water source 

(model)

Use 

(modeled rate)

Acute

(μg/L)

Chronic 

(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. 1998). Isoxaben 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 ornamentals.

Use

Max. Single 

Application

Rate 

(lbs. a.i./A)

No. of 

Application

Annual 

Application

Rate 

(lbs. a.i./A/yr)

Interval 

Between 

Application

(days)

Application

Method

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 isoxaben degrades by hydrolysis. Isoxaben does not readily 

undergo aerobic and anaerobic degradation in soil with half lives of greater than 150 days. Isoxaben 

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. Isoxaben is not expected to volatize (vapor pressure less than 3.9x10-7torr at 26 ̊ 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. Based on structural analysis of these 

degradates in EPISuite, three of the degradates (hydroxyisoxaben, dimethoxybenzamide, and AEM 

hexenoylisoxaben) have the potential to be more mobile than isoxaben (Koc values ranging from 4.6 to 

102 ml/goc), with methoxyphenylpyrimidinol appearing to be very immobile (Koc values from 4,800 to 

38,000 ml/goc). The isoxaben physical and chemical properties and the environmental fate source data 

from submitted studies are presented in Table 3. Properties and fate data for the major degradates are

presented in Table 4.

There is a potential for isoxaben and its degradates to reach surface water through spray drift, as 

products may be applied via ground spray. Because isoxaben and its degradates are persistent in surface 

soils, there 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 its 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 @ 26 °C) <3.9x10-7

torr

MRID 

40059506

Octanol-water partition 

coefficient (K ow)

437

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 (TTR1)

MRID

47140003

Two replicates were 

conducted.
Page 4 of 13

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

Property Value Source Comments

Soil Photolysis Half-life (days) 49 (isoxaben)

63 (TTR)

MRID 

47428403

Aerobic Soil Metabolism Halflife (days)161 (isoxaben, sandy loam, UK)

210 (isoxaben, silt loam, France)

277 (isoxaben, silt loam, Greece)

866 (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 Halflife (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 (isoxaben, 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)

8.5x10-10 – 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/gOC)

Source

Isoxaben 1 2.64 434 See Table 3

Hydroxyisoxaben 462 1.53 17-31

57

EPISuite 4.0

MRID 41106303

2,6-Dimethoxybenzamide 8.4x104-0.22 4.9 – 10 EPISuite 4.0

Methoxyphenylpyrimidinol 41.2 3.56 4,800 – 38,000 EPISuite 4.0

AEM hexenoylisoxaben 265 1.71 21 - 102 EPISuite 4.0

1. Koc estimated in EPISuite using two methods: one using the Molecular Connectivity Index and one using the Kow. 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 six surface water and sediment samples collected and analyzed for isoxaben 

by California Department of Pesticide Regulation (CDPR) in 2006 in Stanislaus County.
Page 5 of 13

Drinking Water Exposure Modeling

EDWCs 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. EDWCs from FIRST represent concentrations which 

might 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 model 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 mimic 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). Percent 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 tool to estimate pesticide concentrations found in ground water used as drinking 

water. SCI-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 SCI-GROW models are listed in Table 5 and Table 6, 

respectively. For adsorption to soil, 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 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 

20

oC (mg/L) 1.0 MRID 40059506

Freundlich Adsorption 

Coefficient (mL/g) (Kd)

3.3 (isoxaben)

0.36 (hydroxyisoxaben)

MRID 41106303 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 90th 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 46393202

Represents the 90th percentile of the 

upper confidence bound on the mean 

(114) of 2 TTR half-life values.1

Aqueous Photolysis

Half-life (days) 15 MRID 47140003 Maximum dark control corrected halflife.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 41106303 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 major degradates with similar toxicity as isoxaben, a total 

toxic residue (TTR) approach was used in the modeling. However, 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 from the degradate study.

Exposure Modeling Results

Tier I surface water and groundwater modeling results for isoxaben 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 are 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 for 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 vineyards.

Table 7. Tier I Estimated Drinking Water Concentrations (EDWCs) resulting from applications of 

isoxaben and its degradates on ornamentals and bearing nut trees.

Drinking water source 

(model)

Use 

(modeled rate)

Acute

(μg/L)

Chronic 

(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. For 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. However, isoxaben does degrade due 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 relied on maximum use patterns and national default 

PCAs to reflect potential surface and groundwater concentrations. To 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.
Page 8 of 13

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 Manual 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 Watershedderived 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 RootApplied Isoxaben in Ajuga (Ajuga reptans) and Two Ornamental Euonymus Species. Pesticide 

Biochemistry and Physiology, 60:2 pp. 119-131

USEPA. 2009. Guidance for Selecting Input Parameters 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 conducted 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.
Page 9 of 13

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 22, 1986.

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 isoxaben in aquatic sediment systems. Unpublished study 

performed by ABC Laboratories, Inc., Columbia, MO and Dow AgroSciences LLC, Indianapolis, IN; 

sponsored and submitted by Dow AgroSciences LLC, Indianapolis, IN. ABC Study No.: 4688 1, Dow 

AgroSciences Study No.: 010044 and Dow AgroSciences PTR No.: 30258020-5037-1. Final report issued 

May 23, 2003.

MRID 41106302

Rainey, D.P. 1989. 14C Isoxaben anaerobic soil 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. Soil 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. Aerobic soil degradation of isoxaben. Unpublished study performed b 

ABC Laboratories, Inc., Columbia, Missouri; sponsored and submitted by Dow AgroSciences 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. Isoxaben photodegradation on soil. Unpublished study 

performed, sponsored, and submitted by DowElanco, Indianapolis, Laboratory Study ID No.: ENV95011. 

Final report issued March 20, 1996.
Page 10 of 13

Appendix 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 Contains 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)

62719-280 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% 

benefin

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
Page 11 of 13

Appendix B. Model output files

SURFACE WATER MODELING OUTPUT FILES - FIRST Results

 RUN No. 1 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 3.3 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.-EFF) (RESER.) (RESER.) 

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

 710.00 2 0.00 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 

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

 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/LITER (PPB)) Ver 1.1.1 MAR 26, 2008

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

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

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

 61.491 16.869

 
Page 12 of 13

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.-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 

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

 284.441 120.023

 RUN No. 4 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 0.4 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/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 Aerobic

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) = 1.45E+01

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