UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

Chemical: Myclobutanil

PC Code: 128857

DP Barcode: D336254

September 26, 2007

DRINKING WATER EXPOSURE CONCENTRATIONS

SUBJECT:	Drinking Water Exposure Concentrations for proposed new
myclobutanil uses on fruiting vegetables (Crop Group 8), leafy
vegetables (Crop Subgroup 4), and tropical fruits. (Tolerance Petitions
6E7138 and 3E6562).  

 TO:		Daniel Rosenblatt, RIMUERB  

		William Cutchin, RIMUERB

		John Redden, RIMUERB

		Registration Division (7505P)	 

FROM:	James K. Wolf, Ph.D. Environmental Scientist

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P)

THRU:	James Hetrick, Ph.D. Senior Scientist

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P) 

		Karen Whitby, Branch Chief

		Environmental Risk Branch 3

		Environmental Fate and Effects Branch (7507P) 

Executive Summary

The Environmental Fate and Effects Division (EFED) has prepared a
drinking water assessment for several proposed new uses on fruiting
vegetables (Crop Group 8), leafy vegetables (Crop Subgroup 4), and
tropical fruits for the fungicide myclobutanil (Rally® (No. 62719-410) 
and Nova® (EPA Reg. 62719-411). 

, β-4-chlorophenyl-β-cyano-γ-(1H-1,2,4-triazole)-butyric acid,
unknown, or non-extractable residues.  Myclobutanil is stable to
hydrolysis and to photolysis in water. 

The screening level surface and ground water estimated drinking water
concentrations (EDWCs) for myclobutanil in drinking water are calculated
using Tier I models of FIRST (version 1.1.0) and SCI-GROW (version 2.3)
(Table 1).   

Table 1. Maximum Tier I myclobutanil EDWCs for drinking water assessment
based on aerial application of myclobutanil for the proposed new
tropical fruit use (in bold) compared to the previously assessed hop
use.

Use	Maximum Surface water EDWC (µg/L)	Maximum Ground water

Acute/Chronic EDWC (µg/L)

	Acute Value	Chronic/Cancer Value

	Tropical Fruit	120.1 	46.3	2.83

Hop Use (D289700, D290167)	333	86	3.2

. 

The EDWC values for myclobutanil represent upper-bound estimates of
concentrations that might be found in surface water and ground water due
to the proposed new use of the chemical on tropical fruits.  This use
represents the highest proposed new use rate (8 applications at 0.25 lb
a.i./A; total 2.0 lb a.i./A/year) and therefore should result in the
highest exposure concentrations.  EFED emphasizes that this is a Tier I
screening-level analysis, and should there be a need, by HED, additional
refinements can be made.  The EDWC values are less than previously
assessed for the hop use which had higher application rates (0.65 lb
a.i./A, 15 applications per year, and 9.75 lb a.i./A/year) (D289700,
D290167).

Myclobutanil has been detected in ambient surface water and ground water
in samples collected for the USGS’s National Water Quality Assessment
Program (NAWQA, 2007).  Twenty percent (20.4%) of 2647 surface water
samples had detectable levels of myclobutanil.  The maximum peak
concentration was 0.51µg/L and the maximum average concentration is
0.35µg/L.  The minimum reporting limit (MRL) varied from 0.00022 to
0.25 µg/L.  In NAWQA, less than 1% (3 wells) of 2061 wells had
detectable levels of myclobutanil with MRLs ranging from 0.0022 to 0.033
µg/L.  These monitoring studies were not specifically conducted for
myclobutanil.  Additionally, it is generally not included in many
monitoring studies.   Myclobutanil was detected in a limited number of
samples collected at different at drinking water source facilities. 
When detections occurred, 1- to 2 percent of the samples contained low
levels of myclobutanil.  The maximum concentration was of 0.019 µg/L.  

The Office of Pesticide Program’s Health Effects Division (HED) has
conducted aggregate human health risk assessments for 1,2,4-triazole and
triazole conjugates (triazole alanine and triazole acetic acid) derived
from conazole fungicides (D322215, D334221).  1,2,4-Triazole and its
conjugates are common metabolites to the class of compounds know as the
triazoles (a.k.a. triazole-derivative fungicides, T-D fungicides,
conazoles).  These compounds all have a triazole ring with nitrogen
atoms at the 1, 2, and 4 positions.  The drinking water portion of the
triazole residues assessment (D320682) considered application rates that
were higher than those proposed for the new uses of myclobutanil.  The
maximum use rate was for turf (6 applications at 1.73 lb a.i/A; total
10.38 lb a.i./A/year).  The exposure from triazole and its metabolites
for the proposed new myclobutanil uses would be less than previously
considered (D320682, D322215).  

II. PROBLEM FORMULATION

This Tier I drinking water assessment uses modeling and available
monitoring data to provide estimates of surface water and ground water
concentrations of myclobutanil residues in drinking water source water
(pre-treatment) resulting from the proposed new uses of myclobutanil on
vulnerable use sites.  Primary routes of transport to source water
include runoff, leaching, and spray drift.  The screening level
estimates of the drinking water concentrations (EDWCs) for myclobutanil
were obtained with the Tier I surface (FIRST) and ground water
(SCI-GROW) models.  The assessment was conducted as a national
assessment using the high-end exposure conditions represented by the
FIRST and SCI-GROW models and the maximum application rates.

III. ANALYSIS

Use Characterization

The myclobutanil labels considered in this assessment include RALLY® 40
WSP (EPA Reg. No. 62719-410) and NOVA® 40 W and RALLY® 40 W (EPA Reg.
No. 62719-411).  Myclobutanil will be used to control powdery mildew on
Fruiting Vegetables (Crop Group 8), leafy vegetables (Crop Subgroup 4A),
artichokes, and disease in tropical fruits.  The proposed methods of
myclobutanil application are through ground and aerial spray as well as
sprinkler irrigation (chemigation).  

The rates proposed for each crop (crop group) are given in Table 2.  The
individual application rates range from 0.10 to 0.25 lb a.i./A.  The
number of applications range from 4 to 8; the minimum reapplication
interval ranges from 10 to 14 days.   The maximum proposed rate is for
tropical fruit is 0.25 lb a.i./A per application with a maximum seasonal
application rate of 2.0 lb a.i./A with a minimum reapplication interval
of 14 days.  The maximum application rate and number of applications is
proposed for the tropical fruit use.  

Table 2. Proposed new uses and use patterns of myclobutanil (PC 128857
D336254, D336613)  

Supplemental Product Label	Reg. No.	Use Restriction	New Use – Crop
Groups, crops	Max # Appl. /Interval	Rate/Season1 Rate

Petition 6E7138

Rally 40 WSP	62719-410	None	Tropical fruits2	 8/14	0.25/2.0

Rally 40 WSP	62719-410	None	Okra	4/10 to 14	0.125/0.50

Rally 40 WSP	62719-410	None	Crop Group 83; Pepper, Eggplant	4/10 to 14
0.125/0.50

Rally 40 WSP	62719-410	None	Artichoke	6/14	0.10/0.60

Rally 40 WSP	62719-410	None	Crop subgroup 4A4 Head & Leaf lettuce; FL, -
3 crops/year1	4/14

31 x 4/14	0.125/0.50

0.125/1.50

Nova 40 W	62719-411	Not for use in5	Okra	4/10 to 14	0.125/0.50

Nova 40 W	62719-411	Not for use in5	Crop Group 83; Pepper, Eggplant	4/10
to 14	0.125/0.50

	Petition 3E6562

Rally 40 W

[Product label]	62719-411	For use only in6	 Tropical fruits2	 8/14
0.25/2.0

1  Number of seasons per year is not defined; as many as 3 crops from
the same ground in Florida (communication B. Madden, 08-24-07).

2 Tropical fruits; Black Sapote, Canistel, Mamey Sapote, Mango, Papaya
Sapodilla, and Star Apple

3  Crop group 8 Fruiting vegetables  – Peppers and Egg Plant 
[6E7138], except tomatoes; leafy vegetables

4  Crop subgroup 4A, Leafy vegetables. except tropical fruits, spinach;
artichoke, cilantro, and okra. (Amaranch, Arugula, chervil, garland,
chrysanthemum, corn salad, garden cress, upland crass, dandelion, dock,
endive, lettuce, orach, parsley, garden purslane, and winter purslane,
radicchio, and Cilantro).

5 Not for use in AK, AZ, CA, HI, ID, MT, NV, OR, UT, WA, WY

6  For use only in AK, ID, MT, NV, OR, UT, WA, WY. 	

Label Uncertainty

The labels do not define whether “per season” means that only one
crop may be grown from a given field in a year (or more than 1 crop
cycle per year is possible which infers multiple seasons or crops per
year).  According to IR-4 sources, as many as three crops of lettuce may
be grown from the same ground per year in Florida (communication from B.
Madden, 08-24-08).  The remaining uses assume only 1 application per
year. 

The geographic restrictions on the NOVA® 40 W and RALLY® 40 W labels
does not appear to agree with the proposed new uses.  The master Rally
40 W label restricts its use to AK, ID, MT, NV,OR, UT, WA, and WY and
the master Nova 40 W label precludes its use in 11 states, including AZ,
CA, and HI (D336254).     

The draft Rally 40 WSP labels restricts its use to AZ, CA, and HI and
the Nova 40 W label precludes its use in 11 states, including AZ, CA,
and HI, yet the proposed new use is tropical fruit (D336613).  The
confusion in the labs should be addressed.    

Mode of Action

Myclobutanil is a triazole fungicide in the conazole class of fungicides
which is a systemic fungicide used to control powdery mildew on a number
of crops.  Myclobutanil appears to be a specific inhibitor of sterol
14-demethylase, which disrupts the ergosterol biosynthesis pathway which
is vital to fungal cell wall formation.  It is classified as a
demethylation inhibitor (DMI) fungicide.    

Fate and Transport Characterization

Our understanding of the environmental fate and transport properties of
myclobutanil is based on a sparse data set.  Available environmental
fate parameters, including the chemical structure of myclobutanil, are
listed in Table 3.  These data are based on studies that may not be
acceptable under current classification standards as they were conducted
prior to 1986 before Good Laboratory Practice (GLP) standards (40 CFR
160) and data requirements for registration (40 CFR 158) were
promulgated in the Code of Federal Regulations.  Additionally, the
aerobic and anaerobic aquatic metabolism study requirements have not
been met by the registrant.  Therefore, the Agency assumes that the
residues of concern are persistent for the exposure assessment.  The
previously submitted studies have not been re-reviewed, although rate of
degradation (decline) of myclobutanil in the aerobic soil metabolism
study was re-estimated.

Due to its persistence and mobility, the primary routes of dissipation
are through leaching, runoff, and spray drift.  Myclobutanil is stable
to hydrolysis and to photolysis.  

Myclobutanil dissipation is controlled by microbial-mediated
transformations.  The major degradation products observed in the aerobic
soil metabolism (ASM) studies were 1,2,4-triazole (maximum 18%), CO2, a
polar degradate
(β-4-chlorophenyl-β-cyano-γ-(1H-1,2,4-triazole)-butyric acid; maximum
9 %), and unextractable residues.  At the conclusion of the 367 day ASM
study, 29 to 33 percent of the applied radioactivity remained as parent
myclobutanil and 13 percent was identified as 1,2,4-triazole. 

Myclobutanil was moderately persistent to persistent (DT50 > 70 days) in
aerobic soils and persistent in anaerobic soils.  Myclobutanil
degradation does not appear to follow a first order  kinetics based upon
visual inspection, but tended to follow a “hockey stick” degradation
pattern (a rapid initial decline followed by a slower decline), thus the
first-order half-life was does not accurately describe the decline of
myclobutanil residues.  The observed (visible inspection) aerobic
metabolism DT50 for myclobutanil value ranged between 75 and 90.   The
DT90 for myclobutanil was not reached during the course of the study
(367 days).  Terrestrial field dissipation half-life values ranged from
92 to 292 days.  Myclobutanil photo-degrades with a half-life of
approximately 143 days on soil.  Thus, myclobutanil residues are
persistent.  The potential for accumulation in soil is possible due to
the persistence, especially when there are multiple applications. 
Further discussion is provided in Appendix 1.   

Myclobutanil is mobile as indicated by the Freundlich Kads values (from
1.46 to 9.77 mL/g) (Appendix 1, Table 3).  The lowest non-sand value is
2.39 mL/g.  Desorption coefficients were generally less than the
sorption coefficients.  The sorption is not strongly correlated to soil
organic carbon (matter), thus Koc is not a good measure of mobility for
modeling. 

Because log Kows for parent and degradation products are low (log Kow=
2.94), myclobutanil residues are not expected to bioaccumulate (Acc #
264484).

Table 3. Selected Fate and Transport data for Myclobutanil.  

Parameter	Input Value and Unit	Source

Chemical Formula

Myclobutanil:  alpha-butyl-alpha
(4-chlorophenyl)-1H-1,2-triazole-1-propane-nitrile

 

Chemical Structure:



	Myclobutanil

Molecular Weight	

288.8 g/ mol	 DP Barcode D289700 (6/25/03)

Solubility in water (pH 7, 20oC)	 142 mg/L 	DP Barcode D289700 (6/25/03)

161-1 Hydrolysis at pH 5,7, and 9	Stable	MRID 001416-79

161-2 Aqueous photolysis (t1/2)	Stable	MRID # 406415-01, 403198-01,
405288-01

161-3 Soil Photolysis	143 days	Acc# 266121, 214084 (D197478)

Myclobutanil 

163-1 Partition Coefficient, Kads a	1.46, 2.39, 4.44, 7.08, 9.77 mL/g
MRID#  141602

162-1 Aerobic Soil Metabolism (T½)b                                    
                            	198, 224 days	MRID# 164561

162-3 Anaerobic Soil Metabolism	Assume Stable, No appreciable
degradation in 62 days	DP Barcode D289700 (6/25/03)

162-3 Anaerobic Aquatic Metabolism 	No Data Submitted

	162-4 Aerobic Aquatic Metabolism	No Data Submitted

	164-1 Terrestrial field dissipation	92 to 292 days	MRID # 164563

a  Kocs are presented in Appendix 1, Tables 3. 

b  (T½) – Myclobutanil decline does not follow first-order kinetics,
therefore the decay rate is not a half-life.  Estimate of DT50 dependant
upon method used to determine value.

Drinking Water Exposure 

Modeling 

EFED Tier I models were used to estimate the drinking water exposure for
use in the dietary risk assessment of myclobutanil.  The following is a
description of the models used, the selection of the model input
parameters, and a characterization of the output from these simulations.

Surface Water:  The FIRST (FQPA Index Reservoir Screening Tool, Version
1.1.0) model by the Environmental Fate and Effects Division (EFED) of
the USEPA Office of Pesticide Programs (OPP) was used to assess
potential for contamination of surface drinking water sources from the
proposed myclobutanil use.  

FIRST is a single-event model (one runoff event), but can account for
spray drift from multiple applications.  FIRST is hardwired to represent
the Index Reservoir, 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, Shipman
City Lake in Illinois, which 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 due to
degradation on the field and the effects of binding to soil in the
field.  FIRST also uses a Percent Cropped Area (PCA) factor to adjust
for the area within the watershed that is planted to the modeled crop. 
The national default PCA of 0.87 was applied in this assessment.

Ground Water:  Myclobutanil concentrations in ground water were
estimated by the Screening Concentration in Ground Water (SCI-GROW v2.3,
Jul. 29, 2003) model.  SCI-GROW is a regression model used as a
screening tool to estimate pesticide concentrations found in groundwater
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.  Groundwater
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 myclobutanil residues that might
be expected in shallow unconfined aquifers under sandy soils. 

Further information on these models can be found at the EFED water model
website at http://   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/html" 
www.epa.gov/oppefed1/models/water/html .

Input Parameters

Model input parameters were estimated from the fate and transport
properties given Table 3 and the other default values are prepared or
selected as recommended by EFED Input Guidance document (USEPA, 2002). 
Pesticide usage information was obtained from the draft labels.  The
inputs values used in FIRST and SCI-GROW models are summarized in Table
4.

The models currently used by EFED, assume that the degradation follow
first order kinetics, and therefore require an estimate of the
half-life.  Myclobutanil degradation, however, is best described using a
hockey stick degradation pattern.  This type of degradation pattern
cannot be modeled using first-order kinetics.

The previously reported half-lives for myclobutanil cite a range of
between 61 and 71 days (D289700), which described the decline reasonably
well for the first 90 days of the study, but grossly overestimates the
remaining decline.  The method used to estimate these half-lives was not
stated, but it appears that only the first 90 (or less) days of a 367
day study were used.   EFED reevaluated the data and re-estimated the
decline rate constants utilizing all the data for myclobutanil (see
discussion in Appendix 1 and Appendix 1, Tables 1 and 2).  

The linear regression of the log-normal transformed myclobutanil
radioactivity provided the best estimate of the measured residues (as
percent of applied radioactivity) versus time (e.g., 29 to 33%
myclobutanil) remaining at 367 days.  The study was not conducted long
enough to observe a DT75 or DT90.  The 90-percent upper bound of the
mean (n=2) aerobic soil metabolism half-life for myclobutanil was
estimated to be 251 days.  Additionally, the models currently used by
EFED were not developed for a persistent chemical where accumulation
might occur.

Analysis of the sorption data (Appendix 1, Tables 3) indicate sorption
is not significantly correlated with organic matter (carbon) (EAB# 6087.
03/05/86).  Therefore, lowest non-sand Freundlich Kads was used to
estimate the EDWCs for myclobutanil (USEPA, 2002). 

The aerobic aquatic metabolism half-life was assumed to be twice that of
the aerobic soil metabolism half-life estimated as a model input (USEPA,
2002).



Table 4.  Input parameters for the Tier I FIRST and SCI-GROW models used
in  Myclobutanil Drinking Water Assessment

Input 	Value	Rationale

Application rate/number/interval	0.25 lb a.i.A-1 /8/14 days	Maximum
proposed label use

Incorporation depth	0	USEPA, 2002

Hydrolysis	0 (stable)	USEPA, 2002 

Aquatic Photodegradation	0 (stable)	USEPA, 2002 

Solubility	142.0 mg/L	 USEPA, 2002

Aerobic Soil Metabolism

               Myclobutanil	

251 days

	= Upper 90th bound on mean

Aerobic Aquatic Metabolism 

              Myclobutanil  	

Estimated as 502 days	

= 2 x ASM per USEPA, 2002



Anaerobic Aquatic Metabolism 	0 Stable	= Assumed stable to be
conservative

Mobility (Freundlich Kads) 

Myclobutanil	

2.39 mL/g	For FIRST

= Lowest non-sand value

Mobility (Koc) Myclobutanil		224 	For SCI-GROW1

= Lowest Koc 

Aerial Spray Drift	0.16 (fraction)	USEPA, 2002

Wetted In	No	Label

PCA (Percent Crop Area)	0.87 (fraction)	USEPA, 2002

1 SCI-GROW input specifies a Koc rather than Kads as an input value.

Modeling Results

EFED estimated the drinking water exposure concentrations for
myclobutanil. 

As expected, the maximum use rate (8 applications at 0.25 lb a.i/A, 14
day reapplication interval) produced the highest EDWCs (Table 5).  It is
recommend that the EDWCs (surface water peak = 120 µg/L, chronic = 46
µg/L, and acute and chronic for ground water =2.8 µg/L) for the
proposed tropical fruit use of myclobutanil be used for the human health
exposure assessment.  Model input/outputs for these estimates are
attached in Appendix 2.

Table 5.  Tier I EDWCs for myclobutanil from use on tropical fruits.  

Chemical	Application	Peak Day (Acute)	Annual Average (Chronic)

Surface Water	 Rate 	   Number  	Interval 	Concentration (µg/L)

Myclobutanil	0.25 (lb a.i./A)	8	14 days	120.1	46.3

Ground Water





	Myclobutanil	0.25 (lb a.i./A)	8	Not Used	2.83	2.83



Monitoring

Three monitoring studies were found which included myclobutanil.  Two
studies were located at drinking water sources (treatment facilities),
finished (and raw water) samples were analyzed.  The monitoring studies
were not targeted to myclobutanil use areas.  Myclobutanil has also been
included in the USGS National Water-Quality Assessment Program (NAWQA)
Program.  Myclobutanil monitoring data are summarized in Tables 6
through 9.  

USDA, Pesticide Data Program (PDP).  

The PDP is a program implemented by the USDA in 1991 to test commodities
in the U.S. food supply for pesticide residues (2001).  Sampling of
finished drinking water was added until 2001. The PDP is a partner ship
with cooperation State Agencies responsible for sample collection and
analysis of fresh and processed fruit and vegetables, grain, grain
products, milk and dairy products, beef, pork, drinking water, and
bottle water.  Ten to twelve states participate in PDP program.  In
2005, the twelve states were CA, CO, FL, MD, MI, MN, MT, NY, OH, TX, WA,
and WI

Paired samples of raw (untreated) intake and disinfected finished
(treated) water were collected for analysis by the PDP in 2004 and 2005.
 Treated water samples were collected after the untreated samples at a
time interval with the hydraulic residence time.  The frequency of  
myclobutanil detections was 2 percent for the treated water and 1
percent for the untreated water (Table 6) in the 2005 samples.  There
were no detections in any of the other years.  Triazoles and it
conjugates were detected in several food commodities, but not in water
samples in the PDP study.

Table 6.  Distribution of myclobutanil and 1,2,4-triazole residues in
drinking water in the USDA Pesticide Data Program (PDP) (USDA, 2001 -
2006).

Myclobutanil	No. of Samples	No. of Detects

(year)	% samples with detection	Range of Detections1 (µg/L)	Range of
LODs (µg/L) 

Finished (treated)	288	0 (2001)	0	0	0.0113-0.10

Finished (treated)	582	0 (2002)	0	0	0.005-0.020

Finished (treated)	782	0 (2003)	0	0	0.005-0.020

Finished (treated)	380	0 (2004)	0	0	0.0013 – 0.0113

Unfinished (untreated)	381	0 (2004)	0	0	0.0013 – 0.0113

Finished (treated)	230	4 (2005)	1.7	0.019	0.0050 – 0.0113

Unfinished (untreated)	232	2 (2005)	0.9	0.019	0.0050 – 0.0113

1 Only one distinct detected concentration or LOD value was reported for
the pair. 

Reservoir Pilot Monitoring Program (USGS, 2001).  Myclobutanil was
included in a study that monitored a number of water supply reservoirs
and finished water (USGS, 2001).  Residues were detected, at low
concentrations, about 1 percent of 317 samples, in raw water with no
detections in the finished water (Table 7). The degradation products
were not included.

Table 7.  Myclobutanil results from the summary of analysis of
moderate-use pesticides and degradates in water samples from water
supply intakes and finished-supply taps in Reservoir Pilot Monitoring
Program. (USGS, 2001).

	No. of Samples	No. of Detections

(Quantifiable No. of Detections)	Frequency of Detection

(%)	Maximum Detection

(µg/L)	Method Reporting Level

(µg/L)

Raw Water	317	3 (2)	0.9	0.015	0.008

Finished Water	221	0	0	0	0.008

	

National Water Quality Analysis Program (NAQWA)(USGS, 2007)

Surface Water Analysis:  Myclobutanil is detected in ambient surface
water (Table 8) (Appendix 3).  The detection frequency is 20.4 %
(541/2647).  The maximum daily myclobutanil concentration 0.507 μg/L is
for a sampling site (USGS Sampling Station # 2335870) in Cobb County,
GA.   Land use in the Cobb County, GA watershed is designated as urban. 
The maximum average myclobutanil concentration 0.347 μg/L is for a
sampling site (USGS Sampling Station # 3730112120393401) in Merced
County, CA.  The minimum reporting limit (MRL) varies from 0.0022 to
0.25 μg/L with a median MRL of 0.008 μg/L.

Table 8.  Distribution of Myclobutanil Concentrations in USGS NAWQA
Surface Water Monitoring Data  Monitoring Data

Exposure Value

	Detects

(%)	Percentile



Max	99.9	99	95	90	80	70	60	50

Peak	20.4	0.507	0.486	0.344	0.074	0.033	0.033	0.033	0.010	0.008

Average

0.347	0.320	0.149	0.033	0.020	0.014	0.011	0.008	0.008



μg/L is for a well (USGS Sampling Station # 295358095374101) in Harris
County, TX.   Land use in the Harris County recharge zone is designated
as urban.  The minimum reporting limit (MRL) varies from 0.0022 to 0.033
μg/L with a median MRL of 0.008 μg/L.

Table 9: Distribution of Myclobutanil Concentrations in USGS NAWQA
Ground Water Monitoring Data  Monitoring Data

Station ID	Concentration

(μg/L)	Well Description

295358095374101	0.0338	Harris County, TX; Well Depth 33.5 ft: Urban Land
Use

322237086112101	0.0208	Montgomery County, AL; Well Depth  31.5 ft; Urban
Land Use

465509119371501	0.0079	Grant County, Washington; Well Depth 15 ft; Ag
Land Use



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Division, Office of Pesticide Programs, U.S. Environmental Protection
Agency, Arlington, VA

USDA.  2001 to 2006.  Pesticide Data Program (PDP). Annual Summary
Calendar, Year 2005. USDA-AMS-S&T-Monitoring Programs Office.  Manassas,
VA.   HYPERLINK "http://www.ams.usda.gov/science/pdp/Index.htm" 
http://www.ams.usda.gov/science/pdp/Index.htm 

USEPA, 2002.  Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides. Version II 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 .  
U.S. Environmental Protection Agency, Office of Pesticide Programs,
Environmental Fate and Effects Division.  Arlington, VA.

USGS. 2001.  J. Bloomquist, J. Denis, J. Cowles, J. Hetrick, R. Jones,
and N. Birchfield. Pesticides in Selected Water-Supply Reservoirs and
Finished Drinking Water, 1999-2000: Summary of Results from a Pilot
Monitoring Program. Open File Report 01-456

USGS. 2007. National Water-Quality Assessment (NAWQA) Program. 
Data-warehouse      HYPERLINK "http://water.usgs.gov/nawqa/data.html" 
http://water.usgs.gov/nawqa/data.html 

 Appendix 1. Additional Environmental Fate Discussion   

 

The method used to determine the aerobic soil metabolism (MRID 164561)
half-lives reported in earlier DERs could not be replicated.  The
pattern of decline appears to fit the common degradation pattern termed
the “hockey stick”.  An analysis of degradation kinetics was
conducted to derive the best description of the measured decline curves
in aerobic soil metabolism studies.   The entire data set (0 to 367
days) and a portion of the data (0 to 90 days) were analyzed using
linear regression of the ln-transformed data and non-linear regression
of the untransformed data.  

The following equations and assumptions were made (based
upon搠慲瑦朠極慤据⁥敢湩⁧敤敶潬数⁤祢琠敨䘠瑡⁥
敔档吠慥Ɑ䔠正汥‬⼱〲㜰മ䔍ⁱ⸱†搠⽃瑤㴠ⴠ䍫൮
††उ晩渠ㄽ‬桴湥氠⡮ぃ䌯 ‽欭⁴昨物瑳漠摲牥攠
畱瑡潩⥮

    		if n ≠ 1 then

      Eq. 2.  (1/(n-1))*((1/Cn-1) – (1/C0n-1)) = -kt

	C =((n-1)*k*t + (1/co^(n-1)))^(-1/(n-1)); co = Co/100

The rings of myclobutanil, triazole and chlorophenyl rings were labeled
[14C), thus, the decline (of radioactivity) of myclobutanil was measured
by each ring.  The formation and decline of 1,2,4-triazole could also be
tracked with the triazole ring.     

Assuming first-order kinetics (eq. 1) a half-life (T½) was calculated
using linear regression on the ln-transformed concentration versus time
(time = 0 to 90 days or time = 0 to 367) and a DT50 was calculated using
non-liner regression (the Levenberg-Marquardt least squares method for
curve fitting) of concentration versus time (time = 0 to 90 days or time
= 0 to 367).  The decay rate (k, or slope) and R2 are summarized in
Appendix 2, Table 1.    

The second equation (Eq 2.) result using all the data (0 to 367 days)
fit the data points (Levenberg-Marquardt least squares), but was not a
first order.  

	 

Appendix 1, Table 1.  Summary of regression method, time, decay rate,
coefficient of determination (R2), intercept, and reaction order.

Parent (myclobutanil)

Regression

Time (days)	k	R2	n

Linear 	lnc = lnCo exp (-kt)	90	0.0096a

0.0077b	0.99

0.97	1

1

Linear

367	0.0035

0.0031	0.81

0.82	1

1

Nonlinear	C=CoExp(-kt)	90	0.10

0.0091	0.99

0.95	1

1



367

	0.0067

0.0058	0.83

0.77	1

1

Nonlinear-Nst order	Cc	367	0.01676	0.98	n = 2.929

co = 1.012

Myclobutanil + 1,2,4-triazole

 Regression	lnc = lnCo exp (-kt) 	Time (days)



	Linear

90	0.0058a	0.96	1

Linear

367	0.0022	0.85	1

Nonlinear	C=CoExp(-kt)	90	0.0069	0.92	1

Nonlinear

367	0.0037	0.68	1

Nonlinear-Nst order	Cc	367	0.01434	0.978	n = 4.789

co = 0.978

a Triazole ring labeled  will include 1,2,4-triazole.

b Chlorophenyl ring label.(1,2,4-triazole not label)

cC =((n-1)*k*t + (1/co^(n-1)))^(-1/(n-1)); co = Co/100

Appendix 1, Table 2 summarizes the distribution of measured
radioactivity, and the estimated half-life or DT50, DT75, and 367 days
(end of study).  The rate constant (k /day) and coefficient of
determination (R2) is also shown.  From a statistical stand point (the
linear and nonlinear methods) were significant (slopes) and the R2 were
fair to good, and therefore, acceptable.  But in reality the linear or
nonlinear methods did not fit the data very well.  Either the method it
fit the data well at times less than 90 days, but not at day 367 or
more, or it fit at both ends, but not in the middle.

The non-linear, n-order curve fitting equation (eq. 2) fit the data also
exactly.  Unfortunately, it is not a first-order equation.

In summary, neither the first-order linear regression nor nonlinear
regression (curve fitting) gives totally satisfactory results.  When
only part of the data is used the initial decline can be fit quite well,
but the later data is underestimated.  Using all the data, over
estimated the half-life (or DT50), but under estimated the DT70 or DT90.
 The first-order linear regression (transform data), using all the data,
was the only method that gave a reasonable estimate of the residue
remaining at the end of the study (367).  Neither DT75 or DT90 were
reached in the study, the residues remaining at day 367 was used to
evaluate the results.  This was selected because it was the most
conservative as it fit the data best at both the beginning and end of
the study.  This would result in a conservative estimate of myclobutanil
concentrations in water.

Appendix 1, Table 2.  Summary of half-lives, DT50, DT75, DT90, and decay
rate of myclobutanil and myclobutanil + 1,2,4 triazole estimated by
linear and non-linear regression.

	Half-life or DT50	DT75	DT90	% Radioactivity

  at 367 days	Rate constant	Coefficient of Determination

PARENT ONLY	50% decline	 75% decline	90% decline



	Triazole Label Position	Time (days)

Days-1	 R2 

Observed Mycobutanil 	75	>365	>365	29



Liner Regression 

(t <100 days)	72.2	144	239	3.0	0.0096	0.99

Linear Regression (all)	198.0	396	657	27.9	0.0035	0.81

Nonlinear 1st order 

(t <100 days)	69.3	138	230	2.6	0.010	0.99

Nonlinear 1st order	103.5	206	343	8.7	0.0067	0.83

Nonlinear nst order	87.6	400	2600	26.7	0.0167	0.98

Observed

Chlorophenyl Label 	90	>365	>365	33



Liner Regression 

(t <100 days)	90	180	299	6.0	0.0077	0.97

Linear Regression (all)	224	447	742	32.3	0.0031	0.82

Nonlinear 1st order 

(t<100 days)	76	152	253	3.6	0.0091	0.95

Nonlinear 1st order	113	237	354	11.6	0.0059	0.77

Nonlinear nst order	103	630	>1000	31.2	0.0164	0.98

PARENT + DEGRADATE







Observed Myclobutanil + 1,2,4 triazole	220	>365	>365	42



Liner Regression 

(t <100 days)	119.5	239	397	12.0	0.0058	0.96

Linear Regression (all)	315.1	630	1047	44.8	0.0022	0.85

Nonlinear 1st order 

(t<100 days)	100.5	201	334	8.1	0.0069	0.92

Nonlinear 1st order	186.3	372	619	25.9	0.0037	0.68

Nonlinear nst order	235.2	 

44.85	0.0144	0.98



Adsorption/Desorption Data Summary

The sorption and desorption data for myclobutanil are summarized in
Appendix 1, Table 3.  

Appendix 1, Table 3 Textural class, Organic Matter, Freundlich Kads,
Koc, and Desorption (MRID # 141682).

Myclobutanil





	 	MRID  141602	Texture Class	OM%	Kads mL/g 	Koc1 ml/gsoil carbon	Kdes

	Clay	0.44	2.39	936	0.588

	Sand	0.95	1.46	265	0.468

	Silty loam	2.05	7.08	595	4.178

	Sandy loam	2.9	9.77	581	4.082

	Clay loam	3.42	4.44	224	1.186

1Koc = (Kd/(%OM/1.724)) * 100 where Kads is assumed to equal to Kd and
OC% = OM%/1.724



APPENDIX 2.  FIRST and SCI-GROW OUTPUTS

Tropical Fruit

   RUN No.   1 FOR myclobutanil     ON   tropical fruit  * INPUT VALUES
* 

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

   RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE  %CROPPED INCORP

    ONE(MULT)    INTERVAL     Kd   (PPM )    (%DRIFT)     AREA    (IN)

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

   .250(  1.754)   8  14       2.4  142.0   AERIAL(16.0)  87.0      .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED

    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 

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

    251.00        2          N/A       .00-     .00   502.00    502.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 DEC 12, 2005

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

            120.095                     46.301

	OKRA

   RUN No.   1 FOR myclobutanil     ON   okra          * INPUT VALUES * 

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

   RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE  %CROPPED INCORP

    ONE(MULT)    INTERVAL     Kd   (PPM )    (%DRIFT)     AREA    (IN)

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

   .125(   .480)   4  10       2.4  142.0   AERIAL(16.0)  87.0      .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED

    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 

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

    251.00        2          N/A       .00-     .00   502.00    502.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 DEC 12, 2005

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

             32.711                     12.585

LETTUCE

   RUN No.   1 FOR myclobutanil     ON   lettuce       * INPUT VALUES * 

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

   RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE  %CROPPED INCORP

    ONE(MULT)    INTERVAL     Kd   (PPM )    (%DRIFT)     AREA    (IN)

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

   .125(  1.224)  12  14       2.4  142.0   AERIAL(16.0)  87.0      .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED

    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 

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

    251.00        2          N/A       .00-     .00   502.00    502.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 DEC 12, 2005

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

             83.948                     32.344

ARTICHOKE

   RUN No.   2 FOR myclobutanil     ON   artichoke     * INPUT VALUES * 

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

   RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE  %CROPPED INCORP

    ONE(MULT)    INTERVAL     Kd   (PPM )    (%DRIFT)     AREA    (IN)

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

   .100(   .546)   6  14       2.4  142.0   AERIAL(16.0)  87.0      .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED

    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 

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

    251.00        2          N/A       .00-     .00   502.00    502.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 DEC 12, 2005

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

             37.288                     14.352

     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:myclobutanil

 time is  9/13/2007  14:16:33

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

  Application      Number of       Total Use    Koc      Soil Aerobic

  rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism
(days)

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

      0.250           8.0           2.000      2.24E+02      251.0

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

 groundwater screening cond (ppb) =   2.83E+00 

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



Appendix 3: Analysis Summary of Myclobutanil Concentrations in USGS
NAWQA Surface Water Monitoring Data  

USGS Station ID	Count	Maximum	Average

01104615	11	0.033	

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280248082220200	1	0.008	0.008

320132084004303	1	0.008	0.008

372323120481700	5	0.0981	0.08188

372829120420801	7	0.152	0.084271429

372839120413901	19	0.166	0.078010526

373012120393401	4	0.423	0.34675

373020120385201	1	0.0298	0.0298

373112120382901	23	0.507	0.241226087

373115120382801	26	0.079	0.033961538

374111121000301	1	0.124	0.124

374115120591601	1	0.176	0.176

393557105033101	2	0.008	0.0074

393613104511401	2	0.015	0.0115

393944084120700	18	0.131	0.016311111

393948105053501	6	0.008	0.008

394107105021001	2	0.008	0.008

394340085524601	75	0.033	0.008845333

394409105020501	6	0.008	0.008

394553105075101	2	0.008	0.008

394629105063101	2	0.01	0.009

394919105074601	6	0.008	0.007566667

394921105015701	6	0.008	0.008

395324105035001	2	0.008	0.008

395554105085601	2	0.13	0.0725

395707105100401	2	0.008	0.008

395743086030501	29	0.008	0.008

395958105113501	2	0.008	0.008

400000105125400	2	0.008	0.008

400023105142301	2	0.008	0.008

400217105123701	6	0.008	0.008

400607105094401	2	0.008	0.008

400810105071301	2	0.008	0.008

400855105090501	6	0.008	0.008

400925105023201	2	0.0099	0.00895

402549105043101	2	0.008	0.008

403035105035301	2	0.008	0.008

403048105042701	6	0.008	0.008

403308105001601	6	0.008	0.008

403356105024001	2	0.008	0.008

404200105145600	17	0.008	0.008

434745123040200	2	0.008	0.008

435212122483300	2	0.008	0.008

440257123103200	2	0.008	0.008

443326123165200	2	0.008	0.008

445029122592600	2	0.008	0.008

445551123015800	6	0.008	0.008

450022123012400	6	0.008	0.008

451734122585400	2	0.008	0.008

452149123194900	2	0.008	0.008

452231122200000	6	0.008	0.008

452337122243500	6	0.045	0.02305

452414122213200	6	0.06	0.023683333

452526122364400	7	0.008	0.008

452912122291200	2	0.008	0.008

453506123125700	2	0.008	0.008

454321122352300	2	0.008	0.00605

454510122424900	6	0.008	0.008

454543122524900	2	0.008	0.008

454549122295800	6	0.008	0.008

455122122310600	6	0.008	0.008

462023120075200	65	0.0296	0.008101538

462023120075240	9	0.0194	0.008722222



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