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 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   REF
_Ref255384952 \h  \* MERGEFORMAT  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   SEQ Table \* ARABIC  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   REF _Ref255384905 \h
\* MERGEFORMAT  Table 2 .

Table   SEQ Table \* ARABIC  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

˚ 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   REF _Ref239065349 \h  \*
MERGEFORMAT  Table 3 .  Properties and fate data for the major
degradates are presented in   REF _Ref255387192 \h  \* MERGEFORMAT
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   SEQ Table \* ARABIC  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.

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)

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 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 (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   SEQ Table \* ARABIC  4 . Physical/chemical properties and
environmental fate data for isoxaben and degradates.

Isoxaben / Degradate	Solubility (mg/L)	Log KOW	KOC1

(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 (  HYPERLINK "http://water.usgs.gov/nawqa"
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.

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   REF
_Ref238874419 \h  \* MERGEFORMAT  Table 5  and   REF _Ref238874433 \h
\* MERGEFORMAT  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   SEQ Table \* ARABIC  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

	Percent Crop Area	1.0

0.87	---

---	Assumption for non-ag uses (ornamental).

Default for agricultural uses.

Solubility in Water at 20oC (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
half-life.1

1  EFED input parameter guidance is located at:
http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

Table   SEQ Table \* ARABIC  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:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm"
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
  REF _Ref255384858 \h  \* MERGEFORMAT  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 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   SEQ Table \* ARABIC  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.

	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 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:   HYPERLINK "http://www.epa.gov/scipoly/sap/1999/index.htm"
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:
HYPERLINK "http://www.epa.gov/scipoly/sap/1998/index.htm"
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.  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:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm"
http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

USEPA. 2002. SCIGROW: Users Manual. Online at:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/#scigrow"
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.

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.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

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

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

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

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

 PAGE

Page   PAGE  1  of   NUMPAGES  13

Page   PAGE  13  of   NUMPAGES  13


RESPONSE TO SIGNIFICANT PUBLIC COMMENTS ON THE PROPOSED CLEAN AIR MERCURY RULE Received in response to:

Proposed National Emission Standards for Hazardous Air Pollutants; and, in the Alternative, Proposed Standards of Performance for New and Existing Stationary Sources: Electric Utility Steam Generating Units ( 69 FR 4652; January 30, 2004)

Supplemental Notice for the Proposed National Emission Standards for Hazardous Air Pollutants; and, in the Alternative, Proposed Standards of Performance for New and Existing Stationary Sources: Electric Utility Steam Generating Units ( 69 FR 12398; March 16, 2004)

Proposed National Emission Standards for Hazardous Air Pollutants; and, in the Alternative, Proposed Standards of Performance for New and Existing Stationary Sources, Electric Utility Steam Generating Units: Notice of Data Availability ( 69 FR 69864; December 1, 2004)

Docket Number OAR 2002 0056 4.0 PERFORMANCE STANDARDS FOR OIL FIRED ELECTRIC UTILITY STEAM GENERATING UNITS US Environmental Protection Agency Emissions Standards Division Office of Air Quality Planning and Standards Research Triangle Park, North Carolina 27711 15 March 2005 i General Outline 1.0 INTRODUCTION AND BACKGROUND 2.0 APPLICABILITY AND SUBCATEGORIZATION 3.0 PERFORMANCE STANDARDS FOR COAL FIRED ELECTRIC UTILITY STEAM GENERATING UNITS 4.0 PERFORMANCE STANDARDS FOR OIL FIRED ELECTRIC UTILITY STEAM GENERATING UNITS 5.0 MERCURY CAP AND TRADE PROGRAM 6.0 MERCURY EMISSIONS MONITORING 7.0 IMPACT ESTIMATES 8.0 COMPLIANCE WITH EXECUTIVE ORDERS AND STATUTES 9.0 NODA 10.0 OTHER Appendix A LIST OF COMMENTERS 4 1 4.0 PERFORMANCE STANDARDS FOR OIL FIRED ELECTRIC UTILITY STEAM GENERATING UNITS 4.1 NEED FOR REGULATION Comment:

One commenter ( OAR 2002 0056 2046) questioned the threshold decision to regulate nickel ( Ni) emissions from oil fired units at all. According to the commenter, based on what it termed conservative assumptions ( i. e., assumptions that overstate the risk), EPA concluded in its 1998 Report to Congress on the emission of hazardous air pollutants ( HAP) from oil fired units that Ni emissions from these units were responsible for one excess cancer case every 5 years. According to the commenter, the Agency concluded in the same report that only 11 units in the country contributed to an excess maximum individual risk of cancer of one in a million, but only barely so. The commenter provided updated information indicating that many of these units have changed their operations so as to drastically limit their oil use, or have shut down entirely. Moreover, the commenter added that there is information to suggest that EPA's assumptions regarding the toxicity of Ni emissions from oil fired units were overly conservative. The commenter recommended that EPA re evaluate its conclusion that these emissions warrant regulation at all.

One commenter ( OAR 2002 0056 2828) stated that EPA should not set a MACT standard for Ni emissions from electric utility steam generating units because the cost/ benefit ratio of the proposed MACT is exorbitant and EPA's risk assessment is extremely over conservative and greatly overstates risks which are not significant. The commenter stated that EPA assumed that Ni emissions from electric generating units are 50 percent Ni subsulfide although a more realistic estimate based on data that became available to EPA after the Report To Congress was issued indicates that the level of Ni subsulfide in electric utility emissions is far lower than even 10 percent, and may actually be 0 percent.

The commenter noted that in the proposed rulemaking, EPA asked for comment on the finding in the Utility RTC that only 11 of 137 oil fired utility units considered in the Utility RTC posed an inhalation risk to human health of greater than one in one million. The commenter noted that this estimate is for the year 1990, for which it is estimated that a population of 110,000 would be exposed to a risk greater than one in one million. The commenter further noted that in 2010, after imposition of the requirements of the Clean Air Act ( CAA), EPA estimates that the population at risk decreases to 11,000 because several of the 11 units have already been converted to natural gas, are burning more gas or are shut down. According to the commenter, EPA did not specify which of the 11 units these are although it seems reasonable that the number of power plants would be substantially less than 11.

Regarding the cost benefit calculation, the commenter stated that a cost benefit calculation using EPA's numbers shows a cost benefit ratio of $ 2.08 billion dollars per avoided cancer case, clearly exorbitant and unjustifiable. According to the commenter, using more reasonable numbers 4 2 for the percent of emissions that are Ni subsulfide would result in even higher cost per avoided cancer.

One commenter ( OAR 2002 0056 2504) stated that the scientific risk data does not support the need for regulating Ni.

One commenter ( OAR 2002 0056 2891) stated that risks posed by Ni emissions from oil fired generators are negligible and do not justify a finding that the regulation of such units is appropriate and necessary.

One commenter ( OAR 2002 0056 3402) submitted that there is a serious question as to whether Ni emissions from oil fired units should initially have been or should now be regulated at all, in light of evidence relating to the decreasing use of oil generation and the toxicity of Ni emissions. The commenter recommended that EPA re evaluate its conclusion that these emissions warrant regulation at all.

One commenter ( OAR 2002 0056 2850) supported exempting Ni emissions from oil fired plants as there is no public health justification for developing regulations. According to the commenter, any actions taken by their industry that could raise the cost of electricity to consumers should bring commensurate health and environmental benefits.

One commenter ( OAR 2002 0056 2452) noted that the power generation industry has changed significantly since EPA's 1998 Report to Congress. The commenter stated that updated data on the nation's oil fired units and their operating characteristics are important to developing a sound final rule.

Response:

Based on the comments received, EPA has reexamined the available information relating to both the number of oil fired units and the combinations of fuels fired in such units. Based on that reexamination, EPA believes that Ni emissions from oil fired Utility Units have been substantially reduced since the 1998 Utility Report to Congress through a combination of unit closures and fuel switching. In addition to the information provided by the commenters, EPA analyzed the latest information provided by the U. S. Department of Energy, Energy Information Administration ( DOE/ EIA), particularly with regard to the 11 plants identified as causing the greatest risk. The 11 oil fired plants identified in the Utility Study as having a cancer maximum individual risk of greater than 10 6 based on Ni emissions were comprised of 42 individual units. Of those 42 units, 12 units have permanently ceased operation or are out of service. ( OAR 2002 0056 2046 at pp. 12  13; OAR 2002 0056 5998). In addition, 6 of the original 42 units have reported to the U. S. Department of Energy ( DOE) that their fuel mix now includes natural gas. Earlier reports did not show these units as using natural gas as a fuel. ( OAR 2002 0056 5998). The use of natural gas as a part of their fuel mix would decrease the Ni emissions from these 6 units. Similarly, another 5 units report using a mix of natural gas and distillate oil ( rather than residual oil) in 2003. ( OAR 2002 0056 5998). Since distillate oil contains less Ni than the residual oil previously burned by these units, it is reasonable to assume that these units 4 3 currently emit less Ni than was previously the case. Another 2 units now fire a residual oil/ natural gas mixture and have limited their residual oil use through permit restrictions to no greater than 10 percent of the fuel consumption between April 1 and November 15, with natural gas being used for at least 90 percent of total fuel consumption. ( OAR 2002 0056 2046 at p. 13). Finally, five units have effectively eliminated their mercury emissions since the Utility Study by switching to burning natural gas exclusively. ( OAR 2002 0056 2046 at pp. 12  13; OAR 2002 0056 5998). Taken as a whole, these changes mean that 30 of the original 42 units identified in the Utility Study have taken steps to effectively reduce or actually eliminate their Ni emissions. Of the original 11 plants identified in the Utility Study, only 2, both in Hawaii, have units for which actions that will result in reduced Ni emissions do not appear to have been taken. (" Analysis of operating oil fired electric utility steam generating units," OAR 2002 0056 6178). In addition to the closure of the 12 units identified as being of potential concern in the Utility Study, there has been a steady decrease in the number of oil fired Utility Units generally over the past decade and this trend is likely to continue. In fact, the latest DOE/ EIA projections ( OAR 2002 0056 5999) estimate no new utility oil fired generating capacity and decreasing existing oil fired generating capacity through 2025, with an additional 29.2 gigawatts of combined oil and natural gas fired existing capacity being retired by 2025. Based on the foregoing, EPA concludes that it is not appropriate to regulate oil fired Utility Units under section 112 because we do not anticipate that the remaining level of utility Ni emissions will result in hazards to public health.

4.2 OTHER Because EPA, in the final rule, is not taking final action on the proposal to regulate Ni emissions from oil fired units, we are not providing responses to the remaining comments received on the proposal to regulate such emissions.