Document ID: EPA-HQ-OPP-2008-0362-0007
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2009-04-01T04:00Z

SEQ CHAPTER \h \r 1 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

OFFICE OF

PREVENTION, PESTICIDES, AND

TOXIC SUBSTANCES

	PC Code: 055459

	DP Barcode:  351023

MEMORANDUM	October 20, 2008	

		

SUBJECT:	Quinoxyfen (New Uses)

Tier I Drinking Water Exposure Assessment in Support of the Proposed New
Uses of Quinoxyfen on stone fruits group 12 (excluding cherry),
artichokes, winter squash, pumpkin and edible gourds

TO:	Sidney Jackson/Barbara Madden

	Registration Division (7505P)

	

	John Redden

	Health Effects Division (7509P)

FROM:	Amy McKinnon, Environmental Scientist

	Environmental Fate and Effects Division (7507P)

THROUGH:	Cheryl Sutton, Ph.D.,  Environmental Scientist

	Environmental Fate and Effects Division (7507P)

	Marietta Echeverria, RAPL

	Environmental Fate and Effects Division (7507P)

	Elizabeth Behl, Branch Chief

	Environmental Fate and Effects Division (7507P)

EXECUTIVE SUMMARY

This assessment provides estimated drinking water concentrations (EDWCs)
of quinoxyfen in surface water and in ground water in support of the
IR-4 tolerance petition for the proposed use of quinoxyfen (Quintec®
22.58% active ingredient; 2.08 lb ai/gal.; PC Code 055459) as a
fungicide on stone fruits group 12 (excluding cherry), artichokes,
winter squash, pumpkins and edible gourds. Quinoxyfen is proposed for
use as an aerial spray/foliar application with up to four applications
of 0.13 lbs a.i./A (8 oz. Quintec) with a six-day minimum re-application
interval, for a maximum total application rate of 0.52 lbs a.i./A/crop
(32 oz. Quintec).  Tier I EDWCs (Table 1) of quinoxyfen were generated
with the models FIRST for surface water and SCI-GROW for ground water. 
Modeled application rates represent the maximum use pattern for use on
stone fruits group 12 (excluding cherry), artichokes, edible gourds,
winter squash and pumpkins and the previously assessed highest use rate
on cherries (EPA Registration 124495-18-7).  Remaining model input
parameters were chosen according to current guidance (USEPA, 2002). 
EDWCs reflect exposure to quinoxyfen and the degradate of concern 3-OH
quinoxyfen (USEPA, 2007).  

The EFED Risk Assessment for the Section 3 Registration of quinoxyfen
(DP Barcodes: D278515, D285770, D286376) was completed in August 2003;
uses assessed included grapes, hops and cherries.  In that assessment,
EDWCs for use in the human health risk assessment were determined using
a maximum annual application rate for cherries of 0.57 lb a.i./A (five
applications of 0.114 lb a.i./A/application).  Because the label did not
specify a minimum application interval at the time the assessment was
conducted, a default of one day was assumed.  However, an updated label
for application to cherries dated June 21, 2004 with a minimum
re-application interval of seven days has since been identified.  

The maximum application rates for the proposed uses on stone fruits
group 12 (excluding cherry), artichokes, winter squash, pumpkins and
edible gourds do not exceed the previous maximum application rate for
any crop and the previous human health dietary risk assessment indicated
that the previously estimated drinking water levels were not a concern. 
Modeling using current methodologies and models was done for the highest
existing use (cherries) as well as the proposed new uses.  The EDWCs
presented below are recommended for use in HED’s risk assessment
(Table 1).  All input parameter values used for modeling are presented
below in Tables 2 and 3.  If the screening EDWCs listed in this memo
result in dietary risk exceedences, please contact Amy McKinnon
(703-347-8010) of Environmental Risk Branch IV (7507P) to request a
refined drinking water exposure assessment.

Table 1.  Maximum Tier 1 EDWCs for quinoxyfen in ground water and
surface water based on proposed new uses and current highest rate on
cherries 

Use Pattern	Use/Rate Modeled (lbs. a.i./A)	Surface Water Acute EDWC
(ppb)	Surface Water Chronic EDWC (ppb)	Ground water EDWC (ppb)

Proposed New Uses*	Aerial spray/0.13x 4 applications; annual total of
0.52	9.3	0.66	3.1 x 10-03

Cherries	orchard air blast spray/0.114x 5 applications; annual total of
0.57	9.9	0.62	3.4 x 10-03

*Proposed new uses include stone fruits group 12 (excluding cherry),
artichokes, edible gourds, winter squash and pumpkins.

Quinoxyfen (PC Code 055459) is a fungicide belonging to the
phenoxyquinoline class of chemicals.  Dow AgroSciences first developed
the active ingredient quinoxyfen for use on grape, hops and cherry crops
in the United States and elsewhere.  The end use product in the U.S. is
Quintec®, a suspension concentrate containing quinoxyfen as the single
active ingredient.   tc \l2 "Mode of Action The chemical’s main mode
of action occurs at the cellular level and is specific to powdery
mildews (e.g., Erysiphe, Uncinula).  

Based on the submitted fate data, its chemical properties and the
proposed use patterns, quinoxyfen is, in general, expected to be a
slowly biodegradable compound that is hardly mobile in soil. Quinoxyfen
is a relatively high molecular weight compound with low water
solubility.  The primary degradation pathway is aqueous photodegradation
when the compound is present in an unsorbed state in clear and shallow
surface water under favorable light conditions. Quinoxyfen degrades
moderately quickly via soil photolysis and is not expected to persist in
aerobic or anaerobic aquatic environments.  Quinoxyfen is hydrolytically
stable at most environmentally relevant pHs and temperatures, but
hydrolyzes slowly at more acidic pHs.  Quinoxyfen is expected to degrade
slowly under aerobic and anaerobic soil conditions. 

Five major degradates of quinoxyfen were identified in the submitted
environmental fate studies which include: 5,7-dichloroquinoline-4-ol
(DCHQ); 5,7-dichloro-4-(4-fluorophenoxy)quinolin-3-ol (3-OH quinoxyfen);
2-chloro-10-fluoro[1]benzopyrano[2,3,4-de]quinoline (CFBPQ);
5,7-dichloro-4-methoxyquinoline (DCMQ; methylated DCHQ) and CO2.   In
accordance to a decision made by the MARC committee (dated 3/26/03; DP
Barcode D287939), the drinking water assessment considers the parent
compound plus 3-OH quinoxyfen, a degradate considered to be a residue of
concern (due to its structural similarity to the parent) for drinking
water.  EDWCs reflect exposure to quinoxyfen and 3-OH quinoxyfen.

PROBLEM FORMULATION

This drinking water assessment uses environmental modeling to provide
estimates of surface water and ground water concentrations in drinking
water source water (pre-treatment) resulting from quinoxyfen use on
vulnerable sites.  Estimates reflect drinking water exposure to residues
of concern for quinoxyfen, which include the parent compound and the
degradate of concern, 3-OH quinoxyfen (USEPA, 2007).  Primary routes of
transport to source water include runoff/erosion and spray drift.  The
screening model FQPA Index Reservoir Screening Tool (FIRST) was used to
assess exposure in surface water due to runoff, erosion, and spray drift
from the proposed quinoxyfen uses.  Exposure in ground water due to
leaching was assessed with the screening model Screening Concentration
in Ground Water (SCI-GROW).

ANALYSIS

Use Characterization

Quinoxyfen is currently registered for use on cherries, grapes, hops,
lettuce, melons, peppers (bell and non-bell), eggplant and strawberries
plants in the United States.  The fungicide is a protectant fungicide
that is used as a foliar application.  Based on the proposed label (for
stone fruits group 12 (excluding cherry), artichokes, winter squash,
edible gourds and pumpkins), quinoxyfen will likely be applied as an
orchard airblast spray (a form of ground spray) or aerial spray (which
is not recommended according to the proposed label).  The label
prohibits use of the product for applications made using irrigation
systems (chemigation) and aerial is only allowed on the proposed label. 
The maximum application rates (per application), maximum number of
applications per year, maximum annual rates, minimum application
intervals, and methods of application are listed by proposed crop type
in Table 2. 

Table 2.  Summary of the Proposed Maximum Application Rate, Number of
Applications, Application Interval and Maximum Yearly Application Rate
for the Proposed New Uses of Quinoxyfen and current highest rate on
cherries

Use	Formulation	Maximum application rate	Maximum applications per year
Maximum Annual Rate	Minimum application interval	Application Method

Proposed New Uses*	Quintec	0.13 lb a.i./A	4	0.52 lb a.i./A	6	aerial

Cherry	Quintec	0.114 lb a.i./A	5	0.57 lb a.i./A	7	orchard air blast

*Proposed new uses include stone fruits group 12 (excluding cherry),
artichokes, edible gourds, winter squash and pumpkins.

Fate and Transport Characterization

Based on the submitted fate data, its chemical properties and the
proposed use patterns, quinoxyfen is, in general, expected to be a
slowly biodegradable compound that is hardly mobile in soil.  Table 3
summarizes the chemical properties of quinoxyfen, a relatively high
molecular weight compound with low water solubility.  The primary
degradation pathway is aqueous photodegradation when the compound is
present in an unsorbed state in clear and shallow surface water under
favorable light conditions.  

Table 3. General Chemical Properties and Environmental Fate Parameters
of quinoxyfen.

Chemical Fate / Parameter	Value	Source

Chemical Name	quinoxyfen

	Molecular Mass	308.14 g/mol	Physical/

chemical property data.

Vapor Pressure (Pa @ 20 ºC, extrapolated)	1.2 x 10-5 Pa (20(C)

2.0 x 10-5 Pa (25(C)	Physical/

chemical property data.

Solubility (20°C)	0.116 mg/L, distilled water(20(C)

0.128 mg/L, pH 5 buffer (20(C)

0.047 mg/L, pH 7 buffer (20(C)

0.036 mg/L, pH 9 buffer (20(C)	Physical/

chemical property data.

Log Octanol-water partition coefficient (K ow)	4.66	MRID 45360712

Mean adsorption coefficient (K d) 	366, 385, 433, 252, 146, 73, 1803,
311 mL/g (parent only)	MRIDs 45360701, 45360703

Mean organic carbon partioning coefficient (K oc)	21550 (sandy clay
loam), 18339(sandy loam), 28897(loamy sand), 53401(loam), 61523 (sandy
loam), 45287(sand), 75178(loam), 75930 (clay)(parent only)	MRID s
45360701, 45360703

Hydrolysis half-life (pH 4, 50(C)

Hydrolysis half-life (pH 7, 50(C)

Hydrolysis half-life (pH 9, 50(C)	6 days

stable

stable	MRID 45360620

Aqueous photolysis half-life 	<1 day  (parent only)	MRIDs 45360623
,45360624

Soil photolysis half-life	74 days  (parent only)	MRIDs 45360625

Aerobic soil metabolism half-life (soil texture)	102(sandy loam),
110(sandy loam), 210(loamy sand), 257(loam), 315(loam), 433(clay loam),
495 (sandy clay loam), 577 days(sandy loam) (parent only);

210(sandy loam), 415(sandy loam), 433(loamy sand), 436(loam), 495(loam),
577(clay loam), 642(sandy clay loam, 648  (sandy loam)days (parent plus 
3-OH quinoxyfen)1	MRIDs 45360626 & 45360627  

Anaerobic soil metabolism half-life (soil texture)	108 days (sandy loam
soil)	MRIDs 45360711

Aerobic aqueous metabolism half-life (sandy loam)	50 days (parent only);

165 days (parent plus  3-OH quinoxyfen)1	MRID 45360630

Anaerobic aqueous metabolism half-life (sandy loam)	18 days  (parent
only)

2013 days  ( parent plus  3-OH quinoxyfen)	MRID 45360629

Bioconcentration Factor (BCF) in fish	5040X	MRID 45360425

Terrestrial field dissipation half-life (soil texture)	94 days (sandy
loam; California)

65 days (loam; Ontario Canada)

Half life not determined(sandy clay loam, Ile de France)

Half life not determined (loamy silt, Oberbayern Germany)

Half life not determined(sandy clay loam, Oxfordshire England)	MRIDs
45360704, 45360705, 45360708, 45360709, 45360710

1Half-lives were re-calculated using combined concentration data for the
parent compound plus 3-OH quinoxyfen when the latter compound was
present.  Data are listed in ascending order and do not correspond
pairwise to the values listed for parent only.

Transport and Mobility

Based on a reported vapor pressure of 1.2 x 10-5 Pa (@20(C) quinoxyfen
is not expected to volatilize.  Quinoxyfen is a relatively high
molecular weight compound with low water solubility.  Quinoxyfen is
hardly mobile (FAO) in soil, and its adsorption correlates well with
organic carbon content.  Data from batch equilibrium studies, when
considered along with results from Tier I screening models and guideline
terrestrial field dissipation studies, indicate a low potential for
leaching to groundwater.  Because adsorption of the compound is related
to soil organic carbon content, a slightly higher, though still low,
potential for leaching to groundwater might exist for quinoxyfen in
soils which are relatively low in organic matter, as is often the case
with coarse-textured soils.  There is a potential for quinoxyfen to
reach surface water through spray drift when applied using ground spray
and aerial spray.  The potential for overland surface runoff of the
compound in the water phase is low given the low aqueous solubility of
the compound.  However, because quinoxyfen is generally persistent under
field conditions, over time the compound may be present in field runoff
as a sorbed residue.  The slow biodegradation of quinoxyfen in most
soils will increase the potential for both groundwater and surface water
contamination.  While quinoxyfen is likely to adsorb to aquatic
sediments, the potential for the compound to accumulate in such is
mediated by the degradation of the compound in aquatic environments. 
However, although quinoxyfen is degraded in the environment, its major
degradate in most soil and aquatic systems is the transformation product
3-OH quinoxyfen, which is essentially stable to biodegradation in both
aerobic and anaerobic aquatic systems.   Based on the submitted
laboratory and field studies, it is likely that 3-OH quinoxyfen has
mobility characteristics similar to those of the parent compound.  In
addition, based on the results of a guideline study, quinoxyfen has a
very high potential to bioaccumulate in fish and is not metabolized in
such, but will be depurated rapidly when the fish are no longer exposed
to the compound.

Degradation

Photodegradation of quinoxyfen in clear, shallow surface water is rapid
(<1 day) and results in the formation of a degradate which is also
rapidly degraded. However, direct photolytic degradation of either the
parent or the degradate in turbid and/or deeper waters may be limited by
the attenuation of sunlight due to unfavorable conditions with regard to
light penetration.  Also, adsorption of the compound to suspended
particles in the water column will decrease the amount of compound
available for photolytic degradation.  In aerobic soil and in aerobic
and anaerobic aquatic systems the primary degradation pathway is
biodegradation, with more rapid degradation in the aquatic environments,
particularly where anaerobic conditions exist.  Quinoxyfen only slowly
biodegrades in aerobic soil, but is moderately rapidly degraded in the
sediment phase of aquatic environments.  While the photodegradation on
soil half-life (74 days) is shorter than the aerobic soil metabolism
half-lives (102-577 days), the former was determined under ideal
laboratory conditions where the compound remained on the soil surface
and was irradiated consistently; this is not likely to occur in the
natural environment.  Additionally, the soil photodegradation half-life
was extrapolated beyond the scope of the data and, thus, is of
questionable value in terms of representing an actual degradation rate
expected in the environment.  For these reasons, photodegradation on
soil is not likely to be as significant a fate process in the
environment as biodegradation will be.  Although quinoxyfen is degraded
in the environment, its major degradate in most soil and aquatic systems
is the transformation product 3-OH quinoxyfen, which is structurally
similar to the parent compound, the only difference being the addition
of an hydroxyl group on the quinoline ring of the degradate.  Based on
the submitted laboratory data, 3-OH quinoxyfen is essentially stable to
biodegradation in both aerobic and anaerobic aquatic systems. 
Quinoxyfen is hydrolytically stable at most environmentally relevant pHs
and temperatures, but hydrolyzes slowly at more acidic pHs.  Quinoxyfen
is stable to photodegradation on soil.  Degradates of quinoxyfen include
5,7-dichloroquinoline-4-ol (DCHQ);
5,7-dichloro-4-(4-fluorophenoxy)quinolin-3-ol (3-OH quinoxyfen);
2-chloro-10-fluoro[1]benzopyrano[2,3,4-de]quinoline (CFBPQ); and
5,7-dichloro-4-methoxyquinoline (DCMQ; methylated DCHQ).   

Field Studies

In the terrestrial field dissipation studies (conducted in California
and Ontario, Canada), quinoxyfen dissipated with half-lives ranging from
65 to 94 days.  Soil samples were analyzed for quinoxyfen and the major
degradate 3-OH quinoxyfen.  No major degradates were identified in the
studies conducted in California or Ontario, Canada.  Based on the
results of nonguideline field studies conducted during a 5-year period
in France, Germany and the UK to determine the residues of the parent
and 3-OH quinoxyfen, and potential for accumulation of such over time
following five annual applications of the pesticide, the accumulation of
both the parent compound and 3-OH quinoxyfen in the field is found to be
likely over time.  

Degradates

Five major degradates of quinoxyfen were identified in the submitted
environmental fate studies: 5,7-dichloroquinoline-4-ol (DCHQ);
5,7-dichloro-4-(4-fluorophenoxy)quinolin-3-ol (3-OH quinoxyfen);
2-chloro-10-fluoro[1]benzopyrano[2,3,4-de]quinoline (CFBPQ);
5,7-dichloro-4-methoxyquinoline (DCMQ; methylated DCHQ) and  carbon
dioxide (IUPAC names in Table 4).  The major degradates were identified
in the hydrolysis, aqueous photolysis, aerobic soil metabolism,
anaerobic soil metabolism, aerobic aquatic metabolism and anaerobic
aquatic metabolism studies.  

Table 4. Chemical Names for the Transformation Products of quinoxyfen.

Synonym	IUPAC Chemical Name

 DCHQ 	5,7-dichloroquinoline-4-ol

3-OH quinoxyfen	5,7-dichloro-4-(4-fluorophenoxy)quinolin-3-ol

 CFBPQ	2-chloro-10-fluoro[1]benzopyrano[2,3,4-de]quinoline

DCMQ; methylated DCHQ	5,7-dichloro-4-methoxyquinoline

CO2	Carbon dioxide

Drinking Water Exposure Modeling

	Models

An EDWC in surface water was estimated using EFED’s Tier I aquatic
model FIRST (v1.1.1; 3/25/08).  FIRST (FQPA Index Reservoir Screening
Tool) is a metamodel of PRZM and EXAMS used as a screening tool to
estimate pesticide concentrations found in surface water used as
drinking water.  FIRST was developed by making multiple runs of PRZM
using varying sorption coefficients and determining the concentration in
the EXAMS index reservoir scenario after a two-inch single storm event. 
(The Index Reservoir is a standard water body used by the Office of
Pesticide Programs to assess drinking water exposure (Office of
Pesticide Programs, 2002).  It is based on a real reservoir (albeit not
currently in active use as a drinking water supply), Shipman City Lake
in Illinois, that is known to be vulnerable to pesticide contamination. 
The single runoff event moves a maximum of 8% of the applied pesticide
into the reservoir.  This amount can be reduced by degradation or
effects of binding to soil in the field.  Additionally, FIRST can
account for spray drift and adjusts for the area within a watershed that
is planted with the modeled crop (Percent Cropped Area).  Spray drift
(modeled as direct deposition of the pesticide into the reservoir) is
assumed to be 16% of the applied active ingredient for aerial
application, 6.3% for orchard air blast application, and 6.4% for other
ground spray application. Despite being a single event model, FIRST can
account for spray drift from multiple applications.  The default
agricultural Percent Cropped Area (PCA) is 87%.  The PRZM scenario used
for FIRST development was among the most vulnerable, and thus resulting
surface water concentrations represent the upper bound values on the
concentrations that might be found in drinking water from the use of a
pesticide.

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.  Ground water concentrations were taken from 90-day average
high concentrations from Prospective Ground Water studies.  The RILP is
a function of aerobic soil metabolism and the soil-water partition
coefficient.  The output of SCI-GROW represents the concentrations of
quinoxyfen 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 and FIRST models and user’s manual may
also be downloaded from the EPA Water Models web-page (USEPA, 2007a).  

Modeling Approach and Input Parameters

The approach was to model Total Toxic Residues which includes the parent
compound (quinoxyfen) and the degradate 3-OH quinoxyfen.  In this
approach, the aerobic soil metabolism and the aerobic and anaerobic
aquatic metabolism half-lives determined for the parent compound in the
guideline studies were recalculated using concentration data for the
parent compound plus 3-OH quinoxyfen when the latter compound was
present in the study samples.  Because separate aqueous photolysis data
were not available for 3-OH quinoxyfen, and the compound was not
detected in the irradiated test solutions treated with the parent
compound, the photolysis half-life used in the modeling was calculated
using parent compound concentration data only.  The lack of information
on the photolysis rate of 3-OH quinoxyfen comprises an uncertainty
surrounding the surface water EDWCs.  However, the results of additional
modeling conducted with the conservative assumption that the compounds
(i.e., the parent and degradate combination) are stable to aqueous
photodegradation indicated that changes in the value of the input
parameter did not have a significant effect on the EDWCs.  Additionally,
there are only soil adsorption data for the parent compound; however, a
preliminary study conducted as part of the acceptable guideline studies
indicates that 3-OH quinoxyfen approaches the mobility of the parent
compound.  Regardless, because the parent is hardly mobile and parent
data were used in lieu of definitive adsorption coefficient data for the
degradate, this increases the uncertainty surrounding the surface water
EDWCs as well as the groundwater EDWC.  

The highest concentrations in this assessment for acute surface water
acute and groundwater EDWCs are based on the cherry use, using a maximum
annual application rate of 0.57 lb a.i./A (five applications of 0.114 lb
a.i./A/application).  The highest concentrations in this assessment for
surface water chronic EDWCs are based on the proposed new uses (stone
fruits group 12 (excluding cherry), artichokes, pumpkins, winter squash
and edible gourds), using a maximum annual application rate of 0.52 lb
a.i./A (four applications of 0.13 lb a.i./A/application). Because the
label did not provide a minimum application interval at the time the
first assessment (2003) was conducted, a default of one day was
utilized.  However, a label for application to cherries dated June 21,
2004 with a minimum re-application interval of seven days has since been
identified and is used in this modeling.  The application method modeled
for cherries in this assessment was orchard air blast and as aerial for
the proposed new uses since it is allowed on the label.    SEQ CHAPTER
\h \r 1 Input parameters for the FIRST model follow in Table 5; data
source and justification descriptors accompany values for each
parameter. 

Table 5 Input values used for quinoxyfen Tier I surface water modeling
with FIRST.

Parameter (units)	Value(s)	Source	Comment

Application Rate 

(lb a.i./A)	0.13 (new uses*)

0.114 (cherries)	Label	Maximum application rate allowed for proposed new
uses.

Maximum application rate allowed for cherries.

Number of Applications	4 (new uses*)

5 (cherries)	Label	Four per season for proposed new uses.

Five per season for cherries.

Interval between Applications (days)	6 (new uses*)

7 (cherries)	Label	Proposed Label for new uses

Label dated 6/21/04 for cherries

Percent Cropped Area (decimal)	0.87(new uses* and cherries)	EFED PCA
guidance.	Default PCA factor for crops other than corn, soybean and
wheat.

Mean Organic Carbon Partitioning Coefficient (Koc)	18339	MRIDs 45360701,
45360703	Represents the lowest non-sand value among eight values ranging
from 18339 to 75930. 

Aerobic Soil Metabolism Half-life 	554 days	MRIDs 45360626 & 45360627  
Value calculated from data for parent plus 3-OH quinoxyfen.  Represents
the 90th percentile of the upper confidence bound on the mean of 8
half-life values. 

Wetted in?	No	Label	

Depth of Incorporation (inches)	0	Label	Aerial and orchard airblast
application 

Method of Application	aerial (new uses*)

orchard airblast (cherries)	Label	

Solubility in Water (mg/L or ppm) distilled water at 20ºC.	0.116
Physical/

chemical property data.	

Aerobic Aquatic Metabolism Half-life 	495 days	MRID 45360630	Value
calculated from data for parent plus 3-OH quinoxyfen.  Input value was
determined by multiplying the calculated half-life by 3 to account for
the uncertainty associated with using a single value, per EFED model
input parameter guidance.  

Hydrolysis Half-life (pH 7)	stable	MRID 45360620	

Aquatic Photolysis Half-life  @ pH 7 	1 day	MRIDs 45360623, 45360624
Input value is based only on parent data.  Separate data were not
available for 3-OH quinoxyfen, and the degradate was not detected in the
irradiated test solutions.  

*Proposed new uses include stone fruits group 12 (excluding cherry),
artichokes, edible gourds, winter squash and pumpkins.

Input parameters for the SCI-GROW model appear in Table 6; data source
and justification descriptors accompany values for each parameter.  

Table 6. SCI-GROW input parameters for quinoxyfen.

Input Parameter	Value	Justification	Source

Application Rate

(lbs a.i./A)	0.13 (new uses*)

0.114 (cherries)	Label	Maximum application rate allowed per season for
proposed new uses and for cherries.

Applications per season	4 (new uses*)

5 (cherries)	Label directions	Proposed label

Organic Carbon Partition Coefficient (KOC) (mL/gOC)	18339	Represents the
lowest value of eight values ranging from 18339 to 75930 for the parent
compound only.  	MRID 45360703

Aerobic Soil Metabolism Half-life (days)	465.5	Represents the median
value of eight values ranging from 210 to 648, based on concentration
data for the parent plus 3-OH quinoxyfen. 	MRIDs 45360626 & 45360627

*Proposed new uses include stone fruits group 12 (excluding cherry),
artichokes, edible gourds, winter squash and pumpkins.

Modeling Results

Screening estimates generated for drinking water exposure assessment are
listed in Table 7.  The use pattern on cherries is the maximum use
pattern modeled for surface water and ground water exposure estimates,
as described above.  Modeled input/output data for these estimates are
attached in Appendix A.  

Table 7 Maximum Tier 1 EDWCs for quinoxyfen in ground water and surface
water based on proposed new uses and current highest rate on cherries

Use Pattern	Use/Rate Modeled (lbs. a.i./A)	Surface Water Acute EDWC
(ppb)	Surface Water Chronic EDWC (ppb)	Ground water EDWC (ppb)

Proposed New Uses*	Aerial spray/0.13x 4 applications; annual total of
0.52	9.3	0.66	3.1 x 10-03

Cherries	orchard air blast spray/0.114x 5 applications; annual total of
0.57	9.9	0.62	3.4 x 10-03

*Proposed new uses include stone fruits group 12 (excluding cherry),
artichokes, edible gourds, winter squash and pumpkins.

SCIGROW concentration (ppb) represents the ground water concentration
that might be expected in shallow unconfined aquifers under sandy soils.
Output is used for both acute and chronic endpoints.  FIRST
concentrations (ppb) represent untreated surface water concentrations. 
The one-in-10-year peak day concentration is used for acute endpoints
and the one-in-10-year annual average concentration is used for chronic
endpoints.  The estimated concentrations provided in this assessment are
conservative estimates of concentrations in drinking water.  If dietary
risks require refinement, higher tiered crop-specific and
location-specific models and modeling scenarios can be used.

Drinking Water Treatment

OPP does not have direct data on the effects of drinking water treatment
on quinoxyfen.  Flocculation and sedimentation removal may be effective
at reducing quinoxyfen concentrations.  Carbon filtering may also reduce
quinoxyfen concentrations due to the compound’s moderate affinity to
organic carbon.  Because of the absence of data on quinoxyfen, the
effects of drinking water treatment were not quantitatively considered
in this assessment.

Uncertainties tc \l2 "Uncertainties 

Uncertainties associated with the determination of EDWCs stemmed from
the use of the aqueous photolysis half-life and the soil adsorption
coefficient determined for the parent only, while the aerobic soil
metabolism and the aerobic and anaerobic aquatic metabolism half-lives
used in modeling were calculated using concentration data for the parent
compound plus 3-OH quinoxyfen when the latter compound was present in
the study samples. Definitive data were not available on the photolysis
rate or the mobility of 3-OH quinoxyfen, which is structurally similar
to the parent compound, having only the addition of a hydroxyl group on
the quinoline ring.  However, the results of additional modeling
conducted with the conservative assumption that the compounds (i.e., the
parent and degradate combination) are stable to aqueous photodegradation
(vs. the rapid photodegradation which occurs for the parent compound)
indicated that changes in the value of the input parameter did not have
a significant effect on the EDWCs.  Additionally, there are only soil
adsorption data for the parent compound; however, a preliminary study
conducted as part of the acceptable guideline studies indicates that
3-OH quinoxyfen approaches the mobility of the parent compound.    

LITERATURE CITATIONS

USEPA.  2002.  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, Feb. 28, 2002.  Online at:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/input_guidance2_28_02.htm/" 
http://www.epa.gov/oppefed1/models/water/input_guidance2_28_02.htm/ 

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a.  Water Models.  U.S. Environmental Protection Agency, Pesticides:
Science and Policy, Models and Databases.  Last updated Aug. 23, 2007. 
Online at:   HYPERLINK "http://www.epa.gov/oppefed1/models/water/" 
http://www.epa.gov/oppefed1/models/water/ .

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