UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE  OF 

PREVENTION, PESTICIDES AND 

TOXIC SUBSTANCES

Chemical: Myclobutanil

PC Code: 128857

DP Barcode:  D329419, D323804

July 21, 2006

WATER ASSESSMENT

SUBJECT:	Water Assessment for proposed new myclobutanil uses on hops
(Section 3 under 			IR-4, D329419) and soybeans (Tolerance Petition, Dow
Agrosciences, D323804).

 TO:		Mary Waller, RM21

		Fungicide Branch

		Registration Division (7505P)

FROM:	James K. Wolf, Environmental Scientist

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P)

THRU:	Stephanie Syslo, RAPL

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P) 

		Daniel Rieder, Branch Chief

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P) 

	The Environmental Fate and Effects Division (EFED) has prepared a water
assessment for myclobutanil used on hops (Section 3) and soybeans
(Tolerance Petition).  A Tier 2 drinking water assessment was conducted
to provide HED (Health Effects Division) estimates of exposure
concentrations for human risk assessments and aquatic exposure
ecological risk assessments for EFED biologists.  A Tier 1 water
assessment was also conducted for ground water.  Myclobutanil
(alpha-butyl-alpha (4-chlorophenyl)-1H-1,2-triazole-1-propane-nitrile)
is a fungicide proposed for use to control powdery mildew on hops (Rally
40W EPA Reg. No. 62719-411) and rust in soybeans (Laredo EW EPA Reg. No.
62719-493).  

	The proposed rates and numbers of applications, and repeat intervals on
the proposed labels are shown in Table 1.  Myclobutanil is to be applied
to foliage by either ground or aerial spray.

Table 1.  Proposed new myclobutanil use rates for hops and soybeans.  

Hops (DP Barcode D329419)

Section 3	Rally (40 W) EPA Reg. No. 62719-411

Growth Stage	Application Rate

(lbs ai/acre1:total2	Spray Interval

(days:number3)	Use Precautions.

Emergence to training	0.125 to 0.250:1.0	7 to 10:4	Do not apply less
than 2 oz of Rally 40 W or adequate efficacy may not be achieved.

Training to wire 	0.250 to 0.375:1.0	5 to 10:4	Do not apply less than 4
oz of Rally 40 W or adequate efficacy may not be achieved

Wire to 14 days to preharvest	0.375 to 0.625:1.0	7 to 10:4	Do not apply
less than 6 oz of Rally 40 W or adequate efficacy may not be achieved

Soybeans (DP Barcode D323804)

Laredo EW EPA Reg. No. 62719-493

Tolerance Petition	Application Rate

(lbs ai/acre4:total2	Spray Interval

(days:number3)	Use Precautions.

Not Specified	0.0625 to 0.125:0.25	14 to 21:2 

	1 1 oz = 0.0625 lbs

2  Total seasonal rate (lbs ai/acre/season)

3  Maximum number of applications

4  1 oz = 0.01302 lbs.

	The proposed hops use rates (Table 1) are different from rates
previously considered (Table 2), the environmental fate data used as
inputs to the models may have changed due to differences in EFED
guidance for preparing modeling inputs, and different or updated
versions of the models were used (D329420).  The soybean rust assessment
(D317281) was completed more recently and thus followed current Division
policy and guideline; the fate data (Tables 5 and 6), the use rates, and
models for soybeans were the same as proposed in the new label.

Table 2.  Comparison of myclobutanil application rates, models used and
modeling input parameters   considered in previous assessments compared
to the proposed new uses.

Soybeans

  	

The proposed myclobutanil application rate; 2 applications, 7 days apart
at 0.125 lbs ai/acre per application is the same rate as considered in
the previous assessments  (D296319, D317281, D317279).

The assessment for actions D317281 and D317279 used the current
PRZM/EXAMS and SCI-GROW models.  The input parameters for both were the
same (prepared following EFED Guidelines, 02/28/02). 

 Hops  

 

D329419

(current)

D243037

(1998)

D289700, 290167

(06/11/03)

	

The new rates proposed in the Section 3 allow for a lower seasonal total
(from 15 to 1 lb ai/acre), fewer applications (from 15 to 4
applications), and shorter reapplication intervals (5 to 10 days
compared to 10 to 14 days) compared to the previous Section 18 rates. 
Although the seasonal total is less, the proposed new label is proposing
variable individual application rates that vary from 0.25 lb ai/acre up
to 0.625 lb ai/acre. Thus, the maximum individual rate between current
and previous assessment are essentially the same (0.625 lb ai/acre
versus 0.65 lb ai/acre). In the previous assessment for hops the
myclobutanil was applied as a ground spray, the new label proposes both
ground and aerial spray. The PRZM/EXAMS and SCI-GROW models were used in
this assessment. 

In a previous (oldest) assessment (Section 18, D243037, 1998)
myclobutanil was applied to hops in eight 0.25 lb ai/acre and a 10 day
minimum reapplication intervals. The GENEEC and SCI-GROW models were
used in this assessment.  

A revised drinking water assessment (most recent) was conducted on June
11, 2003 (D289700, 290167) for peppers in CA and NM using FIRST,
GENEEC2, and SCI-GROW models.  The revised assessment (06/11/03)
included hops, since hops represented the highest concentration for any
crops and used the same modeling input values as used in the current
assessment (Tables 5 and 6). The myclobutanil application rate on hops
however was higher than called for in the current assessment.  The
application rate used in the “revised” assessment call for 15
applications per year with a maximum individual rate of 0.65 lb ai/acre
and a 14 day reapplication interval. 





Models and Scenarios

	The estimated drinking water concentrations (EDWCs) and estimated
environmental concentrations (EECs) for myclobutanil were generated with
standard crop [Oregon hop and Mississippi soybean] scenarios using PRZM3
(version 3.12 beta compiled (05/24/01, Carsel, 1997) and EXAMS (version
2.98.04 compiled 07/18/04, Burns, 2002).  PRZM simulates pesticide fate
and transport as a result of leaching, direct spray drift, runoff and
erosion from an agricultural field and EXAMS estimates environmental
fate and transport of pesticides in surface water body. The EDWCs and
EECs assessment for surface water uses a single or multiple sites which
typically represent a high-end exposure scenario from pesticide use on a
particular crop or non-crop use site.  PRZM and EXAMS were linked by the
program (PE4-PL, version 01).  Ground water concentrations were
estimated using the Tier I screening model SCI-GROW

(version 2.3, compile 08/08/03). Detailed description, documentation,
and direct links for running these models can be found in:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/index.htm" 
http://www.epa.gov/oppefed1/models/water/index.htm .

	The standard farm pond scenario is used to estimate EECs for ecological
exposure.  The farm pond scenario, represents a 10-ha corn (all cropped)
field that is adjacent to a 1-ha pond that is 2 meters deep standard
pond (10,000-m2 pond, that has neither hydraulic inlets nor outlets
(i.e., pesticide cannot leave by outflow).  The Index Reservoir (IR) is
intended as a drop-in replacement for the standard pond for use in
drinking water exposure assessment.  It is used in a manner similar to
the standard pond, except that flow rates have been modified to reflect
local weather conditions.  The index reservoir (IR) is approximately 82
m wide and 640 m long, with an area of 5.3 ha.  The area of the entire
watershed is 172.8 ha.  Weather and agricultural practices are simulated
for 30 years so that the 10-year exceedance probability at the site can
be estimated. The simulation was generated using 30 years of
meteorological data, encompassing the years from 1961 to 1990. Guidance
for using the standard farm pond and IR is located at:   HYPERLINK
"http://www.epa.gov/pesticides/trac/science/.%20%20" 
http://www.epa.gov/pesticides/trac/science/.    

	The Percent Crop Area (PCA) is a generic watershed-based adjustment
factor that is applied to pesticide concentrations estimated for the
surface water component of the drinking water exposure assessment using
PRZM/EXAMS with the index reservoir (IR).  The output generated by the
linked PRZM/EXAMS models is multiplied by the maximum percent of crop
area (PCA) in any watershed (expressed as a decimal) generated for the
crop or crops of interest. Currently, OPP will apply PCA adjustments for
four major crops, one of which is soybeans.  Guidance for using PCAs and
a thorough discussion of this method and comparisons of monitoring and
modeling results for selected pesticide/crop/site combinations is
located at:   HYPERLINK "http://www.epa.gov/pesticides/trac/science/" 
http://www.epa.gov/pesticides/trac/science/ .  The PCA for soybeans was
0.41; the PCA for hops was 0.87 (default value).   The PCA for the hops
scenario is likely to be overly conservative (too high), but data
currently are not available to get a better estimate. No PCA adjustment
is required for the standard pond scenario and SCI-GROW.  

	Previously developed reviews, risk and water assessments by EFED
(D289700, D290167, D296319, D317279, D243037, D244639, D274305, and
D244639) were also considered in this assessment. This includes Section
18s previously prepared for myclobutanil use on hops (D243037) and for
use on soybeans to control soybean rust (D289700, D290167, D317281, and
D317279).

	The modeling outputs are attached in Appendix 1.

Modeled Myclobutanil Concentrations In Drinking Water

μg/L for soybeans and hops, respectively.  The 0.35 μg/L value is
recommended for use for both acute and chronic exposures.  

 

	The major reason for difference between the myclobutanil concentrations
(EDWCs and EECs) in this assessment compared to earlier assessments is
due to changes in application rates to hops.  The previous hops
assessment (D289700, D290167) was based upon 15 applications @ 0.65 lb
ai/acre with 14 day intervals (total 9.75 lb ai/acre/year), the rate in
the proposed label calls for a maximum of 1.0 lbs ai/acre/year. 

Table 3.  Estimated Drinking Water Concentrations (EDWC), PCA Corrected,
from PRZM/EXAMS Concentration Values for Myclobutanil with the Proposed
New Uses.



Standard Crop Scenario (Percent Cropped Area, PCA)	

Acute Exposure from  One in Ten Year Peak Values (μg/L)	

Non-Cancer Chronic Exposure  from One in Ten Year Annual Mean (μg/L )	

Average of Yearly Average for Cancer Exposure (μg/L)

	Not  Corrected	PCA Corrected	Not  Corrected	PCA Corrected	Not 
Corrected	PCA Corrected

Hops (0.87)	17.57	15.29	9.74	8.47	5.96	5.19

Soybeans (0.41)	8.56	3.51	2.03	0.83	1.24	0.51



Monitoring

The reviewer was unable to locate any monitoring data which included
myclobutanil as an analyte

Myclobutanil Concentrations For Aquatic Exposure

 .  

	The estimated environmental concentrations (EECs) for the aquatic
exposure assessment were estimated using the linked PRZM and EXAMS
models (Table 4).  The previous EECs for the hops risk assessment used
the GENEEC2 model, and assumed myclobutanil was applied as ground spray,
and used model inputs (fate data) that differ from current EFED
guidance.  The EECs are less than or similar to the previously
determined use rates, thus, the risk from exposure to myclobutanil would
be the same as previously determined.  The peak surface water EECs
represents the upper 1-in-10-year peak event concentration, and other
EECs represent the upper 1-in-10-year mean concentrations for 96-hr,
21-day, and 60-day exposure periods. 

Table 4.  Estimated environmental concentrations (EECs) of myclobutanil
in standard pond applied to a soybeans and hops for the proposed new
ratesa,c and the previous ratesb,d. 

	1- in 10-year Myclobutanil Concentration (μg/L)

Soybeans	Rate	Peak	96-hr (4-day)	21-day	60-day

2 @ 0.125 lb ai/ac	Proposeda	5.3	5.2 	5.0 	4.7 

2 @ 0.125 lb ai/ac	Previousb	5.1	5.0	4.8	4.5

Hops





	4 @  0.25 lb ai/ac	Proposedc	13.1	13.0	12.9	12.7

1 @ 0.625 lb ai/ac	Proposedc	8.1	8.0	7.9	7.8

8 @ 0.25 lb ai/ac	Previousd	34.6	34.1	31.4	27.6

a DP Barcode D323804 PRZM-EXAMS [PLDKRT = 0]

b DP Barcode D317281 PRZM-EXAMS [PLDKRT = 0.0198/day]

c DP Barcode D329419 PRZM-EXAMS

d DP Barcode D243037 GENEEC2

	In a previous Section 18 (D243037, 1998), myclobutanil concentrations
were estimated for hops using the GENEEC model.  For that assessment the
median Koc of 581 mL/g and the metabolic (field) degradation of 129 days
were used for model input which do not agree with current EFED guidance
for modeling input.  More recently a Section 18 was submitted to control
soybean rust on soybeans (D317281); fate properties used in this
assessment were obtained from these assessments (D317281).  The
difference in EECs for soybeans (Table 4) is that in the PRZM variable
PLDKRT (Record 18: pesticide decay rate on plant foliage (days-1) was
set to 0.0198/days (T1/2 - 35 days).  Typically, it would be EFED’s
policy to not include this dissipation pathway because there was no
specific data support its use.  However, the EECs were essentially the
same with or without the PLDKRT value selected. 

Environmental Fate Data Summary   

 

	The environmental fate data for myclobutanil and modeling input
parameters used in this assessment are summarized in Table 5.

	

	Myclobutanil is stable to hydrolysis (Subdivision N guidelines 161-1)
at pH 5, 7 and 9, and to photolysis in water (161-2).  However, it
photo-degrades with a half-life of approximately 143 days in soil
(161-3).  The aerobic metabolism half-life values are 61 to 71 days
(162-1), and the terrestrial field dissipation values are 92 to 292 days
(164-1).  Myclobutanil is mobile to moderately mobile as indicated by
the Koc values (163-1) (from 224 for clay loam to 919 for silty clay). 
Its major degradate (1,2,4-triaziole) has lower Koc values (average of
112), suggesting it would be more mobile than the parent compound. 
However, a lower adsorption (average Kads of 0.651) than desorption
coefficient (average Kdes of 1.15) indicates that this degradate may be
partially irreversibly bound to soils and may not be as mobile as one
would predict from the adsorption results alone.

	

Input parameters were selected from existing assessments either
previously conducted, or currently being completed for each pesticide
which were selected in accordance with EFED’s Guidance for Selecting
Input Parameters in Modeling the Environmental Fate and Transport of
Pesticides, Version II, dated February 28, 2002,    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 .  No
new environmental fate data was reviewed as part of this assessment. 
Application rates and intervals were determined from a review of the
specific request and in several instances are different from previous
assessments.  Application timing was estimated by evaluation crop
profiles relative to the agronomic practices documented in the PRZM
scenarios (crop emergence, maturity and harvest dates).  The application
date was assumed to be July 1 and July 15 for soybeans and hops,
respectively.  

Table 5 PRZM and EXAMS Inputs for Myclobutanil



Parameter	

Input Value and Unit	



	

Maximum Application Rate	

0.14 kg/ha	

Label



Maximum No. of Applications	

2	

Label

 Application  Efficiency (APPEFF)	0.95	EFED Guidance



Drift  (DRFT) 

Aerial Spray	

Aerial (0.05 Drift) eco

Aerial (0.16 Drift) drinking water	

Label



Minimum Interval	

7 days	

Label



Partition Coefficient, Kd	

 2.39 mg/L	

DP Barcode D289700 (6/25/03)



Partition Coefficient, Koc	

 224 mg/L	

DP Barcode D289700 (6/25/03)



Henry’s Law Constant	

	





Hydrolysis	

0 days (Stable)	

DP Barcode D289700 (6/25/03)



Aerobic Soil Metabolism (t1/2)	

81 days	

DP Barcode D289700 (6/25/03)



Aerobic Aquatic Metabolism (t1/2)	

162 days   [2 * 81= 162]	

DP Barcode D289700 (6/25/03)



Anaerobic Aquatic Metabolism (t1/2)	

0 days (Stable)	

DP Barcode D289700 (6/25/03)



Aquatic Photolysis (t1/2)	

0 days (Stable)	

DP Barcode D289700 (6/25/03)



Vapor Pressure	

	





Solubility in water (pH 7, 20oC)	

1420 mg/L (142 mg/L * 10)	

DP Barcode D289700 (6/25/03)



Molecular Weight	

288.8 g/ mol	

Product Chemistry

Decay on foliage (PLDKRT)	0.0198/day (half-life = 35 days)

Only used in (D317281, D317279)	

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	The myclobutanil concentration in ground water was estimated using the
Tier 1 model SCI-GROW (Screening Concentration in Ground Water).  This
is a regression model that uses a candidate chemical's soil/water
partition coefficient and degradation half-life values to estimate
groundwater concentrations arising from labeled uses at a highly
vulnerable agricultural site. The program assumes pesticide application
at the maximum label rate to a field that is highly vulnerable due to a
rapidly permeable soil overlying shallow groundwater. The input
parameters for SCI-GROW are listed in Table 6.

Table 6. SCI-GROW Inputs for Myclobutanil

Parameter	Input Value and Unit	Source

Maximum Application Rate	Soybean 0.125 lb ai/acre

Hops        0.25 lb ai/acre 	Labels

Maximum No. of Applications	Soybeans 2

Hops  4	Label

Partition Coefficient, Koc	224 mg/L	DP 289700, 6/9/2003

Aerobic Soil Metabolism (T1/2)	66 days	DP 289700, 6/9/2003



cc:/ George Kramer, HED/RAB1 (7509P)

       Jennifer R. Tyler, HED/RAB1 (7509P)

       Barbara Madden, RD/MUIERB (7509P)

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