Document ID: EPA-HQ-OPP-2009-0814-0007
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-09-17T04:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

	WASHINGTON D.C., 20460

	OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

									DP Barcode: 368735

									PC Code: 108800

										April 22, 2010

MEMORANDUM 

SUBJECT: 	Drinking Water Assessment for S-Metolachlor and its Degradates
Ethanesulfonic Acid (ESA) and Oxanilic Acid (OA) for Various Crop Uses

TO:		Sidney Jackson, Risk Manager Reviewer

		Barbara Madden, Risk Manager	

		Registration Division	

FROM:	Christopher M. Koper, Chemist

		Environmental Risk Branch I

		Environmental Fate and Effects Division

THRU:	Anita Pease, Acting Branch Chief 

		Brian Anderson, Risk Assessment Process Leader

		James Lin, Secondary Reviewer

		Environmental Risk Branch I

		Environmental Fate and Effects Division

1.	Executive Summary:

1.1.	Assessed Chemicals and Commodities:

This drinking water assessment was conducted for a petition submitted by
the Interregional Research Project Number 4 (IR-4) to establish
s-metolachlor tolerances for sesame, melon subgroup 9A, bushberry
subgroup 13-07B, lowbush blueberry, caneberry subgroup 13-07A, sweet
sorghum, leafy brassica greens subgroup 5B, turnip greens, carrot,
cucumber, okra, bulb onion subgroup 3-07A and green onion subgroup
3-07B.  S-Metolachlor is a broad spectrum herbicide that acts to inhibit
seedling development.  It can be applied to crops as a pre-emergent or
post-emergent broadcast ground application as well as a surface band
application.  This assessment was based on information contained in the
Dual Magnum( (EPA Reg. No. 100-816) label.  

This drinking water assessment was conducted on the parent s-metolachlor
and its major degradates ethanesulfonic acid (ESA) and oxanilic acid
(OA).  It is important to note that the environmental fate data has been
bridged from the racemic mixture (50:50) of metolachlor to the newer
isomer (88:12) s-metolachlor, based on similarities in environmental
fate behavior.  

1.2.	Application Rates:

The Estimated Drinking Water Concentrations (EDWCs) for use in the human
dietary health risk assessment are based on the maximum new proposed
application rate specified in the Dual Magnum( label, which is a single
yearly application of 3.81 lbs a.i./acre for use on caneberry.  

The application rate for the degradate ESA was calculated by multiplying
the application rate of the parent active ingredient by the fraction of
the maximum detected degradate from the submitted fate studies (0.12;
MRID 43928936) and then multiplying by the ratio of the molecular
weights of the degradate to parent (329.1 g/mol /283.8 g/mol). 
Following this equation, the maximum single application rate for the ESA
degradate is 0.53 lbs a.i./acre for caneberry use.  The application rate
for the OA degradate was calculated by multiplying the application rate
of the parent active ingredient by the fraction of the maximum detected
degradate from the submitted fate studies (0.28; MRID 41309801) and then
multiplying by the ratio of the molecular weights of the degradate to
parent (279.1 g/mol /283.8 g/mol).  Following this equation, the maximum
single application rate for the OA degradate is 1.05 lbs a.i./acre for
caneberry use.  

S-Metolachlor and its degradates ESA and OA have been detected
extensively in surface water and groundwater as reported in the
Tolerance Reassessment Document (US EPA, 2002).  Based on the proposed
application rates and the environmental fate properties of
s-metolachlor, surface water and groundwater contamination may occur
from s-metolachlor as well as its degradates ESA and OA. 

	

Modeling Approach:

Tier I and Tier II screening models were employed for this assessment. 
For surface water, PRZM/EXAMS (PE5) and FIRST (FQPA Index Reservoir
Screening Tool) Version1.1.1 models were used to estimate drinking water
concentrations for the parent s-metolachlor and the ESA and OA
degradates, respectively.  The SCI-GROW model (Screening Concentration
in Ground Water Program Version 2.3) was used to predict the maximum
acute and chronic concentrations present in shallow groundwater.  

1.4.	Monitoring Data:

Since the previous EDWCs for surface water for the parent s-metolachlor
were based on NAWQA monitoring data, a search of the available
monitoring data was performed on March 30, 2010 to ensure that the most
current monitoring data were considered in this assessment.  The data
set captured the timeframe of October 1991 to October 2009 and included
the parent s-metolachlor and its degradates ESA and OA.  Based on a
review of the current monitoring data, concentrations of parent
s-metolachlor and its degradates were less than values reported from the
previous monitoring data (US EPA, 2002).  Therefore, EDWCs based on
previous monitoring are still valid.

1.5.	Results and EDWC Recommendations:

A summary of recommended surface and groundwater EDWCs for the human
dietary risk assessment for the parent s-metolachlor and its degradates
ESA and OA are presented in Table 1.   Table 1 contains EDWCs based on
this current assessment as well as values reported in the previous
drinking water assessment (D324967) dated 20 March 2006.  Values derived
from the current modeling exercise are bolded in Table 1.  

Table 1. Recommended Drinking Water Concentrations (EDWCs) for Surface
Water and Groundwater for Human Dietary Health Risk Assessment

Chemical Identity – Drinking Water Source	Acute

 (µg/L)	Chronic 

(µg/L)	Cancer Chronic 

(µg/L)

Surface Water

S-Metolachlor (parent) – Surface Water

Crop Use or Monitoring Data	77.60

monitoring data	18.15

CA cole crop	9.15

KS sorghum

Ethanesulfonic Acid (ESA) – Surface Water

Crop Use or Monitoring Data	47.61

caneberry	34.04

caneberry	34.04

caneberry

Oxanilic Acid (OA) – Surface Water

Crop Use or Monitoring Data	93.57

caneberry	66.62

caneberry	66.62

caneberry

Groundwater

S-Metolachlor (parent) – Groundwater

Crop Use or Monitoring Data	32.8

monitoring data	32.8

monitoring data	32.8

monitoring data

Ethanesulfonic Acid (ESA) – Groundwater

Crop Use or Monitoring Data	63.7

monitoring data	63.7

monitoring data	63.7

monitoring data

Oxanilic Acid (OA) – Groundwater

Crop Use or Monitoring Data	29.7

caneberry 	29.7

caneberry	29.7

caneberry

Bold values denote the maximum EDWCs modeled in this assessment that
exceed the EDWCs based on monitoring and modeling data reported in the
previous drinking water assessment (D324967) dated 20 March 2006. 

For surface water, the single chronic value from FIRST is used as the
chronic and cancer chronic values.

For groundwater, the single output value from SCI-GROW is used as the
acute, chronic and cancer chronic values.

2.	Environmental Fate and Transport Summary:

The information from all acceptable and upgradable environmental fate
data indicate that parent metolachlor/s-metolachlor appears to be
moderately persistent to persistent.  It is mobile to highly mobile in
different soils and has been detected extensively in surface water and
groundwater.  Metolachlor/s-metolachlor degradation appears to be
dependent on microbially mediated (aerobic soil metabolism t1/2 = 66
days, 37.8 days, 37.8 days, 14.9 days, 13.9 days, and 50.3 days,
anaerobic soil metabolism t1/2 =81 days) and abiotic processes
(photodegradation in water t1/2  = 70 days under natural sunlight and
photodegradation on soil t1/2 = 8 days under natural sunlight).

The major degradates were identified as CGA-51202 (metolachlor OA),
CGA-50720, CGA-41638, CGA-37735, and CGA-13656.  Subsequent studies
identified CGA-354743 (metolachlor ESA) as a major degradate (of these
major degradates, metolachlor ESA and metolachlor OA have been
identified in both groundwater and surface water).  Depending on the
soil (i.e. organic matter content), metolachlor/s-metolachlor has the
potential to range from a moderately mobile to a highly mobile material
with Kd values ranging from 0.11 to 44.8 mL g/oc, and Koc values ranging
from 21.6 to 367 L/kg oc.  

EFED concluded there is no difference in soil sorption affinity between
metolachlor and s-metolachlor.  There was no statistical difference
between Koc values in non-paired batch equilibrium studies; similar Koc
coefficients for metolachlor (mean Koc=249.250) and s-metolachlor (mean
Koc=265.875) were observed in paired batch equilibrium studies.  These
data suggest that metolachlor and s-metolachlor are expected to be
highly mobile to mobile in soil and water environments.  A more detailed
summary of the fate data are presented in Appendix A.

Field dissipation studies indicate that metolachlor/s-metolachlor is
persistent in surface soil with half lives ranging from 7 to 292 days in
the upper six inch soil layer depending on geographic location. 
Metolachlor/s-metolachlor was reportedly detected as deep as the 36 to
48 inch soil layer in some of the studies.  Metolachlor OA (CGA-51202),
was detected (0.11 ppm) as deep as the 30-36 inch soil depth (MRID No.
41335701); CGA-40172 was detected as deep as the 36-48 inch depth (MRID
No. 41309802); CGA-40919 was detected in the 36-48 inch depth (0.21 ppm
in MRID No. 41309802); and CGA-50720 was not detected (LOD = 0.07 ppm)
in any soil segment at any interval.

3.	Water Resources Summary:

3.1.	Monitoring:  

S-Metolachlor and its degradates ESA and OA have been detected
extensively in surface water and groundwater.  A more detailed summary
of the monitoring data can be found in the Tolerance Reassessment
Document (US EPA, 2002).  Since the previous EDWCs for surface water for
the parent s-metolachlor were based on NAWQA monitoring data, a search
of the available monitoring data was performed on March 30, 2010 to
ensure that the most current monitoring data were considered in this
assessment.  The data set captured the timeframe of October 1991 to
October 2009 and included the parent s-metolachlor and its degradates
ESA and OA.  Based on a review of the current monitoring data,
concentrations of parent s-metolachlor and its degradates were less than
values reported from the previous monitoring data (US EPA, 2002). 
Therefore, EDWCs based on previous monitoring are still valid.  However,
some of the previously reported EDWCs, which were based on monitoring
data, were exceeded based on modeled concentrations derived from the
proposed uses in this assessment.

3.2.	Drinking Water Exposure Modeling:

EDWCs were generated using EFED’s standard suite of models.  The
proposed uses from the provided label were assessed.  Two specialty
scenarios, OR Berry OP and CA Cole Crop RLF were used to characterize
caneberry and leafy Brassica and turnip greens, respectively.  

The Pesticide Root Zone Model (PRZM v3.12.2, May 12, 2005) and Exposure
Analysis Modeling System (EXAMS v2.98.04.06, April 25, 2005) are
simulation models coupled with the input PE5.pl shell (PE5, PE Version
5.0, November 15, 2006) was used to generate EDWCs of the parent
s-metolachlor that may occur in surface water used as drinking water. 
The PRZM model simulates pesticide movement and transformation on and
across the agricultural field resulting from crop applications.  The
EXAMS model simulates pesticide loading via runoff, erosion, and spray
drift assuming a standard watershed of 172.8 ha that drains into an
adjacent standard drinking water index reservoir of 5.26 ha, an average
depth of 2.74 m.  A more detailed description of the index reservoir
watershed can be found in Jones et al., 1998.  The coupled PRZM/EXAMS
model and users manuals may be downloaded from the U.S. Environmental
Protection Agency (EPA) Water Models web-page (USEPA, 2006).  Percent
Crop 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.

In addition, the standard FL carrot scenario is based on a sandy soil,
although carrots in FL are oftentimes grown in muck soils.  In order to
characterize the potential impact on EDWCs based on FL carrots grown in
muck soils, the organic carbon and bulk density parameters from the
first soil horizon were modified from the standard carrot scenario.  The
percent organic carbon content of 1.16% was changed to 12.00% (Brady,
1990) and the bulk density was changed from 1.65 g/m3 to 1.50 g/m3 to
reflect muck characteristics of the soil.  The acute, chronic and cancer
chronic EDWCs were 52.57 µg/L, 7.75 µg/L, and 4.99 µg/L,
respectively.  In general, EDWCs values generated using the muck soil
scenario are lower than those derived based on the standard sandy soil
FL carrot scenario.  These values are used to characterize EDWCs
associated with carrots grown in muck soils and are further discussed as
uncertainty in this assessment.

The FIRST (FQPA Index Reservoir Screening Tool) model is a Tier I model
used to estimate both acute and chronic pesticide concentrations in
untreated drinking water.  The FIRST model was employed to derive EDWCs
for the ESA and OA degradates only. 

The SCI-GROW model (v2.3, Jul. 29, 2003) is a regression-based screening
tool used 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.  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 of residues that might be
expected in shallow unconfined aquifers under sandy soils, which are
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   HYPERLINK
"http://epa.gov/oppefed1/models/water/" 
http://epa.gov/oppefed1/models/water/  (USEPA, 2006).  

3.3.	Surface Water Model Inputs:

Due to the stability and mobility of the parent s-metolachlor, the
compound may move from the treated field to surface water through
run-off which occurs shortly after application (i.e. rainfall events). 
Because limited data are available on the fate characteristics of the
degradates ESA and OA, the aerobic soil metabolism rate constant was
conservatively estimated using the Comparative Aerobic Soil Metabolism
Study (MRID 43928936) submitted to support bridging of fate data from
the racemic to the s-isomer of metolachlor.  Aerobic soil metabolism
half-lives were estimated using only the decline portion of the data for
each degradate.  Half-lives for other parameters (i.e. aerobic aquatic
metabolism, hydrolysis, photolysis) where no data were available were
conservatively assumed to be stable as per EFED guidance.  An
adsorption/desorption study (MRID 40494605) was previously submitted for
metolachlor OA.  The lowest non-sand Kd value (0.079 mL g/oc for
Maryland clay) was selected for surface water degradate modeling, and
the lowest Koc measured for all available soil types (2.82 L/kg oc for
the Maryland clay) was used for groundwater modeling.   An
adsorption/desorption study (MRID 44931722) was previously submitted for
metolachlor ESA and is currently under review.  The lowest non-sand Kd
value (0.041 mL g/oc for Maryland clay) was selected for surface water
degradate modeling, and the lowest Koc (2.01 L/kg oc for the Maryland
sandy loam) was used for groundwater modeling.

The drinking water concentrations derived from surface water for the
parent s-metolachlor and its degradates (ESA and OA) were estimated
using PRZM/EXAMS and FIRST models, respectivley.  Input paremeters for
s-metalachlor, ESA, and OA are reported in Tables 2, 3, and 4,
respectively.  Model outputs are included in Appendix B.

Table 2.  PRZM/EXAMS Input Parameters for S-Metolachlor (Parent).  

Input Parameter:	Value:	Comment:	Source:

Scenario(s):	Sesame:  KS Sorghum

Melon:  MI, MO, NJ Melons  

Bushberry:  OR Berries

Caneberry:  OR Berries

Sorghum:  KS Sorghum

Leafy (Brassica), Turnip Greens: CA Cole Crop

Carrot:  FL Carrot

Cucumber:  FL Cucumber

Okra:  CA, FL, PA Tomato

Dry Bulb Onions:  CA, GA Onions

Green Onions:  CA, GA Onions	representative scenarios for each use	N/A 

Maximum Single 

Application Rate

lbs a.i./A (kg a.i./ha)	Sesame:  1.90  (2.13)

Melon:  1.21  (1.36)

Bushberry: 1.27  (1.43)

Caneberry:  3.81  (4.28)

Sorghum:  1.67  (1.88)

Leafy (Brassica), Turnip Greens:  1.27  (1.43)

Carrot (mineral soil):  1.27  (1.43)

Carrot (muck soil):  1.90  (2.13)

Cucumber:  1.27  (1.43)

Okra:  1.90  (2.13)

Dry Bulb Onions:  1.27  (1.43)

Green Onions:  1.27  (1.43)	proposed rates	proposed  label

Applications per Year	Sesame:  1

Melon:  1

Bushberry: 1

Caneberry:  1

Sorghum:  1

Leafy (Brassica), Turnip Greens:  1

Carrot:  1

Cucumber:  1

Okra:  1

Dry Bulb Onions:  2

Green Onions:  1	label directions.  Label specifies rates per season. 
If crops are rotated with those on which s-metolachlor is used, yearly
rates may be higher.	proposed label

Application Interval (days)	Sesame:  N/A

Melon:  N/A

Bushberry: N/A

Caneberry:  N/A

Sorghum:  N/A

Leafy (Brassica), Turnip Greens:  N/A

Carrot:  N/A

Cucumber:  N/A

Okra:  N/A

Dry Bulb Onions:  21

Green Onions:  N/A	intervals were selected to reflect labeled
application patterns.	proposed label

Date of Initial Application

(scenario/day/month)	Sesame: 

KS Sorghum:  13-05

Melon:  

MI Melon:  23-04

MO Melon:  03-04

NJ Melon:  24-04

Bushberry:

OR Berry:  Highbush:  25-03

OR Berry:  Lowbush:  08-04

Caneberry: 

OR Berry:  25-03

Sorghum: 

KS Sorghum:  13-05

Leafy (Brassica), Turnip Greens: 

CA Cole Crop:  25-12

Carrot:

FL Carrot:  09-10

Cucumber: 

FL Cucumber:  09-10

Okra: 

CA Tomato:  08-03

FL Tomato:  08-02

PA Tomato:  23-04

Dry Bulb Onions: 

CA Onion:  23-01

GA Onion:  22-09

Green Onions:  

CA Onion:  23-01

GA Onion:  22-09	7 days before crop emergence was selected for
pre-emergent applications.  

7 days after crop emergence was selected for post-emergent applications.
 

Label directions were followed for ground surface band applications.

	Crop Scenarios

Application Method	Foliar Ground: for pre- and post-emergent
applications

Ground: for Surface Band Applications	label directions	proposed label

CAM Input	2

1	foliar – ground

ground - surface band	proposed label

IPSCND Input	3

N/A	remaining pesticide on foliage is retained as surface residue and
continues to undergo decay.

ground – surface band	US EPA, 2005

Spray Drift Fraction	0.064

0	foliar - ground

ground – surface band	Input parameter guidance (USEPA, 2009) 

Application Efficiency	0.99

1.00	foliar - ground

ground – surface band	Input parameter guidance 

(USEPA, 2009)

Molecular Mass (g/mol)	283.8	product chemistry data	US EPA, 2002 TRED

Vapor Pressure at 25°C (torr)	2.8 x 10-5	product chemistry data	US EPA,
2002 TRED

Henry’s Law Constant

(atm-m3/mol)	2.2 x 10-8	calculated from volatility and solubility data
registrant submitted data

Solubility in Water at 25oC (mg/L)	480	product chemistry data	US EPA,
2002 TRED

Organic Carbon Partition Coefficient (Koc) (L/kg oc)	181	represents the
average KOC	represents the average value from all non-paired adsorption
data

Aerobic Soil Metabolism Half-life (days)	48.9	represents the upper 90th
percentile based on linear regression of all aerobic soil metabolism
data for racemic and s-metolachlor	US EPA, 2002 TRED

Aerobic Aquatic Metabolism Half-life (days)	141	based on three times the
single aerobic aquatic metabolism linear first order half-life	MRID
41185701

Anaerobic Aquatic Metabolism Half-life (days)	234	based on three times
the single anaerobic aquatic metabolism linear first order half-life
MRID 41185701

Hydrolysis Half-lives (days)	0  (stable)	no data available; assume
stable as conservative assumption	US EPA, 2002 TRED

Aqueous Photolysis

Half-life (days)	70

US EPA, 2002 TRED

-N/A = Not Applicable    



Table 3:  FIRST Input Parameters for the S-Metolachlor Degradate
Ethanesulfonic Acid (ESA) for Caneberry Use 

Parameter: 	

Input Value:	

Data Source/Rationale: 1

Application Rate (lbs a.i./acre)	

0.53 2

	

EPA Reg. No. 100-816

Maximum Number of Applications/Year	

1	

EPA Reg. No. 100-816

Application Interval (days)	

NA	

EPA Reg. No. 100-816

Percent Crop Area (as decimal) 

	

0.87	

National Default Value

Kd (mL/g oc)

	

0.041	

MRID 44931722  (lowest non-sand value)

Aerobic Soil Metabolism Half-life (days)

	

162.5

	

MRID 43928936 (upper 90th percentile of linear first order half-lives
derived from decline portion of racemic (150.6 days) and s-isomer (156.4
days) from paired aerobic soil metabolism data.

Is the pesticide wetted-in?

	

No	

Chemical not known to be activated by water

Method of Application

	

D

	

Granular Application 3

Incorporation Depth (inches)

	

0	

Broadcast Application

Water Solubility (ppm)

	

480	

Product Chemistry Data (assumed to be equivalent to parent)

Aerobic Aquatic Metabolism Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

Hydrolysis (pH 7) Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

Photolysis Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

1  Input Parameters were selected in accordance with the Guidance for
Selecting Input Parameters  Version 2.1  

   dated October 22, 2009

2  Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.12) x (329.1/283.8) = 0.53
lbs. a.i./acre

3  Granular method of application was selected for the degradate (Drift
= 0.0% and App. Efficiency = 100%).  

NA = Not Applicable



Table 4:  FIRST Input Parameters for the S-Metolachlor Degradate
Oxanilic Acid (OA) for Caneberry Use 

Parameter: 	

Input Value:	

Data Source/Rationale: 1

Application Rate (lbs a.i./acre)	

1.05 2

	

EPA Reg. No. 100-816

Maximum Number of Applications/Year	

1	

EPA Reg. No. 100-816

Application Interval (days)	

NA	

EPA Reg. No. 100-816

Percent Crop Area (as decimal) 

	

0.87	

National Default Value

Kd (mL/g oc)

	

0.079	

MRID 40494605  (lowest non-sand value)

Aerobic Soil Metabolism Half-life (days)

	

127.5

	

MRID 43928936 (upper 90th percentile of linear first order half-lives
derived from decline portion of racemic (82.9 days) and s-isomer (104.8
days) from paired aerobic soil metabolism data.

Is the pesticide wetted-in?

	

No	

Chemical not known to be activated by water

Method of Application

	

D

	

Granular Application 3

Incorporation Depth (inches)

	

0	

Broadcast Application

Water Solubility (ppm)

	

480	

Product Chemistry Data (assumed to be equivalent to parent)

Aerobic Aquatic Metabolism Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

Hydrolysis (pH 7) Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

Photolysis Half-life (days)

	

0 (stable)	

No data is available; entered zero for conservative assumption as
suggested by FIRST users manual

1  Input Parameters were selected in accordance with the Guidance for
Selecting Input Parameters  Version 2.1  

   dated October 22, 2009

2  Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.28) x (279.1/283.8) = 1.05
lbs. a.i./acre

3  Granular method of application was selected for the degradate (Drift
= 0.0% and App. Efficiency = 100%).  

NA = Not Applicable

3.4.	Groundwater Modeling Inputs:

Due to the stability and mobility of the parent s-metolachlor, the
compound may move from the treated field to groundwater through
leaching.  

The drinking water concentrations derived from groundwater for the
parent s-metolachlor and its degradates ESA and OA were estimated using
the SCI-GROW model.  Input paremeters for s-metalachlor, ESA, and OA are
reported in Tables 5, 6, and 7, respectively.  Model outputs are
included in Appendix B.

Table 5.  SCI-GROW Input Parameters for S-Metolachlor for Caneberry Use 

Input Parameter	Value	Comment	Source

Maximum Application Rate per growing season (lbs a.i./A)	3.81	maximum
application rate representing caneberry	proposed label

Applications per Year	1	label directions	proposed label

 Organic Carbon Partition Coefficient (Koc) (L/kg oc)	21.6	lowest Koc
value since there was a greater than three-fold difference within data
set from non-paired adsorption data	US EPA, 2002 TRED

Aerobic Soil Metabolism

Half-life (days)	37.8	represents the median half-life value of all
aerobic soil metabolism data for racemic and s-metolachlor since more
than 4 half-lives are available.  	US EPA, 2002 TRED

Table 6.  SCI-GROW Input Parameters for the S-Metolachlor Degradate
Ethanesulfonic Acid (ESA) for Caneberry Use

Input Parameter	Value	Comment	Source

Maximum Application Rate per growing season (lbs a.i./A)	0.53 1  
assumes 12% conversion of parent to degradate from the aerobic soil
metabolism (MRID 43928936) study; application rate adjusted to parent
equivalents using molecular weight	proposed label

Applications per Year	1	label directions	proposed label

 Organic Carbon Partition Coefficient (Koc) (L/kg oc)	2.01	lowest Koc
value since there was a greater than three-fold difference within data
set from non-paired adsorption data (MRID 44931722)	US EPA, 2002 TRED

Aerobic Soil Metabolism

Half-life (days)	153.5	represents the median half-life value of all
aerobic soil metabolism data (MRID 43928936) for racemic and
s-metolachlor since more than 4 half-lives are available.  	US EPA, 2002
TRED

1  Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.12) x (329.1/283.8) = 0.53
lbs. a.i./acre

Table 7.  SCI-GROW Input Parameters for the S-Metolachlor Degradate
Oxanilic Acid (OA) for Caneberry Use

Input Parameter	Value	Comment	Source

Maximum Application Rate per growing season (lbs a.i./A)	1.05 1  
assumes 28% conversion of parent to degradate from the aerobic soil
metabolism (MRID 41309801) study; application rate adjusted to parent
equivalents using molecular weight	proposed label

Applications per Year	1	label directions	proposed label

 Organic Carbon Partition Coefficient (Koc) (L/kg oc)	2.82	lowest Koc
value since there was a greater than three-fold difference within data
set from non-paired adsorption data (MRID 40494605)	US EPA, 2002 TRED

Aerobic Soil Metabolism

Half-life (days)	93.8	represents the median half-life value of all
aerobic soil metabolism data (MRID 43928936) for racemic and
s-metolachlor since more than 4 half-lives are available.  	US EPA, 2002
TRED

1  Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.28) x (279.1/283.8) = 1.05
lbs. a.i./acre

3.5.	Modeling Results:

For this assessment, the surface and groundwater EDWCs for the parent
s-metolachlor and its degradates ESA and OA are presented in Tables 8,
9, and 10, respectively.  For drinking water derived from surface water
for the parent s-metolachlor, the maximum reported acute concentration
of 71.33 µg/L for the Florida carrot (mineral soil) scenario does not
exceed the previous EDWC of 77.6 µg/L from the monitoring data reported
in the previous drinking water assessment (D324967) dated 20 March 2006.
 However, the maximum annual mean (chronic) concentration of 18.15 µg/L
from the California Cole Crop scenario and the maximum 30 year annual
average concentration of 9.15 µg/L from the Kansas Sorghum scenario
exceed the previous reported EDWC of 4.3 µg/L from the monitoring data
reported in the previous drinking water assessment.  For the degradate
ESA, the FIRST model’s acute and chronic (annual average)
concentrations of 47.61 µg/L and 34.04 µg/L, respectively, exceed the
previously reported EDWCs of 31.9 µg/L and 22.8 µg/L from the modeling
data reported in the previous drinking water assessment.  For the
degradate OA, the FIRST model’s acute and chronic (annual average)
concentrations of 93.57 µg/L and 66.62 µg/L, respectively, exceed the
previously reported EDWCs of 91.4 µg/L and 65.1 µg/L from the modeling
data reported in the previous drinking water assessment.  

For drinking water derived from groundwater for the parent
s-metolachlor, the SCI-GROW model’s acute and chronic concentration of
5.26 µg/L does not exceed the previously reported EDWC of 32.8µg/L
from the monitoring data reported in the previous drinking water
assessment.  For the degradate ESA, the SCI-GROW model’s acute and
chronic concentration of 45.9 µg/L does not exceed the previously
reported EDWC of 63.7µg/L from the monitoring data reported in the
previous drinking water assessment.  However, for the degradate OA, the
SCI-GROW model’s acute and chronic concentration of 29.7 µg/L does
exceed the previously reported EDWC of 13.4µg/L from the monitoring
data reported in the previous drinking water assessment.

Table 8. Estimated Drinking Water Concentrations (EDWCs) resulting from
applications of S-Metolachlor.

Drinking Water Source (model)	Use Scenario 

(modeled rate)	1-in-10 year acute (µg/L)	1-in-10 year chronic (µg/L)
30- year average (µg/L)

Surface Water (PRZM/EXAMS)	(Previous EDWCs for Surface Water)	(77.6)
(4.3)	(4.3)

	Sesame:

KS Sorghum – pre-emergence

KS Sorghum – ground surface band

(1 app. @ 1.90 lbs ai/acre)	

57.77

54.23

	

16.08

15.07	

9.15

8.07

	Melon:

MI Melon - pre-emergence

MI Melon – ground surface band

MO Melon - pre-emergence

MO Melon – ground surface band

NJ Melon - pre-emergence

NJ Melon – ground surface band

(1 app. @ 1.21 lbs ai/acre)	

20.71

18.14

49.59

47.28

25.02

22.41

	

7.29

6.37

9.39

8.95

7.33

6.53	

3.73

2.38

3.59

3.11

3.38

2.53

	Bushberry:

OR Berries – post-emergence

OR Berries – ground surface band

(1 app. @ 1.27 lbs ai/acre)	

7.72

12.07	

3.02

6.04	

1.98

2.00

	Caneberry:

OR Berries – ground surface band

(1 app. @ 3.81 lbs ai/acre)	

51.10	

18.07	

6.00

	Sorghum:

KS Sorghum - pre-emergence

(1 app. @ 1.67 lbs ai/acre)	

50.98	

14.19	

8.08

	Leafy (Brassica), Turnip Greens:

CA Cole Crop - pre-emergence

(1 app. @ 1.27 lbs ai/acre)	

41.46	

18.15	

8.63

	Carrot:

FL Carrot (mineral soil) - pre-emergence

(1 app. @ 1.27 lbs ai/acre)	

71.33

	

9.96

	

5.59

	Cucumber:

FL Cucumber - pre-emergence

(1 app. @ 1.27 lbs ai/acre)	

73.64	

9.71	

5.57

	Okra:

CA Tomato - post-emergence

CA Tomato – ground surface band

FL Tomato - post-emergence

FL Tomato – ground surface band

PA Tomato - post-emergence

PA Tomato – ground surface band

 (1 app. @ 1.90 lbs ai/acre)	

16.83

11.05

52.51

48.35

28.56

24.13	

7.61

4.85

7.13

6.38

9.26

7.62	

4.80

2.28

3.52

2.92

4.69

3.22

	Dry Bulb Onions:

CA Onion - post-emergence

CA Onion – ground surface band

GA Onion - post-emergence

GA Onion – ground surface band

(2 app. @ 1.27 lbs ai/acre

Application Interval = 21 days)	

21.90

14.80

70.41

67.10	

10.45

6.75

13.03

11.81	

5.32

1.82

5.81

4.69

	Green Onions:

CA Onion - post-emergence

CA Onion – ground surface band

GA Onion - post-emergence

GA Onion – ground surface band

 (1 app. @ 1.27 lbs ai/acre	

10.27

6.59

42.17

39.76	

5.16

3.18

6.12

5.61	

2.90

1.11

3.25

2.73

Groundwater 

(SCI-GROW)	(Previous EDWCs for Groundwater)

Caneberry:

(1 app. @ 3.81 lbs a.i./acre)

	(32.8)

5.26	(32.8)

5.26	(32.8)

5.26

Bold text denotes maximum estimated EDWC values from the proposed uses. 

PRZM/EXAMS values adjusted with PCA factor of 0.87.

Table 9. Estimated Drinking Water Concentrations (EDWCs) resulting from
applications of S-Metolachlor Degradate Ethanesulfonic Acid (ESA) for
Caneberry Use.

Drinking Water Source (model)	Use Scenario 

(modeled rate)	Peak Day

Acute (µg/L)	Annual Average

Chronic (µg/L)

Surface Water (FIRST)	(Previous EDWCs for Surface Water)

Caneberry:

 (1 app. @ 0.531 lbs ai/acre)	(31.9)

47.61	(22.8)

34.04

Groundwater 

(SCI-GROW)	(Previous EDWCs for Groundwater)

Caneberry:

(1 app. @ 0.53 lbs a.i./acre)	(63.7)

45.9	(63.7)

45.9

1 = Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.12) x (329.1/283.8) = 0.53
lbs. a.i./acre

Note:  FIRST program automatically adjusts EDWC value with PCA factor of
0.87.

Table 10. Estimated Drinking Water Concentrations (EDWCs) resulting from
applications of S-Metolachlor Degradate Oxanillic Acid (OA) for
Caneberry Use.

Drinking Water Source (model)	Use Scenario 

(modeled rate)	Peak Day

Acute (µg/L)	Annual Average

Chronic (µg/L)

Surface Water (FIRST)	(Previous EDWCs for Surface Water)

Caneberry:

 (1 app. @ 1.051 lbs ai/acre)	(91.4)

93.57	(65.1)

66.62

Groundwater 

(SCI-GROW)	(Previous EDWCs for Groundwater)

Caneberry:

(1 app. @ 1.05 lbs a.i./acre)

	(13.4)

29.7	(13.4)

29.7

1 = Application Rate of Degradate = (max. application rate of parent) x
(fraction of maximum detected degradate) x 

  (molecular weight of degradate/ molecular weight of parent)

    Caneberry = (3.81 lbs. a.i./acre) x (0.28) x (279.1/283.8) = 1.05
lbs. a.i./acre

Note:  FIRST program automatically adjusts EDWC value with PCA factor of
0.87.

Uncertainties:

In order to characterize EDWCs for carrots grown in muck soils, the
organic carbon and bulk density parameters from the first soil horizon
were modified from the standard carrot scenario.  Based on these
modifications, the predicted acute, chronic, and cancer chronic EDWCs
for FL carrots grown in muck soils are 52.57 µg/L, 7.75 µg/L, and 4.99
µg/L, respectively.  Predicted EDWCs for FL carrots grown in muck soils
are generally lower that EDWCs based on the standard sandy soil
scenario.  EDWCs are presented for comparative purposes only and are not
included in Table 8 of the risk assessment.  Therefore, it is possible
that FL carrot EDWCs presented in Table 8 may overestimate exposure for
carrots grown in muck scenarios.

References:

Brady N.C. 1990. The Nature and Properties of Soils. 10th Edition. 

MacMillan Publishing Company, NY.

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 

US EPA.  2002.  Revised Metolachlor/S-Metolachlor Tolerance Reassessment
Document 

	(TRED), D248805, D228814, D258817, D258824, D258822, D258812, D259119, 

	D259037, D259034).

US EPA.  2005.  PRZM-3, A Model for Predicting Pesticide and Nitrogen
Fate in the Crop Root and Unsaturated Soil Zones:  Users Manual for
Release 3.0.  May 2005.

US EPA.  2009.  Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides, Version 2.1.  U.S.
Environmental Protection Agency, Office of Prevention, Pesticides and
Toxic Substances, Office of Pesticide Programs, Environmental Fate and
Effects Division, October 22, 2009. 

US EPA.  2010.  Water Models.  U.S. Environmental Protection Agency,
Pesticides: Science and Policy.  Last updated: November 25, 2009. 
Online at:   HYPERLINK "http://www.epa.gov/oppefed1/models/water/" 
http://www.epa.gov/oppefed1/models/water/ 

Appendix A:  Environmental Fate Assessment (from the 1994 RED)

Metolachlor appears to be stable to hydrolysis at pH’s of 5, 7, and 9
without significant degradation of parent material after 30 days.

The aqueous photolysis half-life was 70 days when exposed to natural
sunlight and 0.17 day when exposed to artificial sunlight (450 watt
mercury arc lamp with light intensity of 4500-4800 uW/cm2).  After 30
days exposure to natural sunlight the degradation products were
CGA-41638 (3.63% of applied radiocarbon), CGA-51202 (3.54%), CGA-46129
(3.42%), CGA-50720 (3.20%), and parent metolachlor remaining was 62.92%.

The soil photolysis half-life of metolachlor when exposed to natural
sunlight was 8 days, and when exposed to artificial  light conditions
(mercury arc lamp with intensity of 1600-2400 uW/cm2) the half-life was
37 days.  The major degradates reported after 21 days exposure to
natural sunlight were CGA-51202 (maximum of 3.4% of applied
radiocarbon), CGA-37735 (9.0%), CGA-41638 (5.7%), and CGA-37913 (7.3%).

Under aerobic soil conditions metolachlor degraded with a half-life of
67 days in a sandy loam soil.  The major metabolite was CGA-51202
(maximum of 28.09% of applied radioactivity at 90 days posttreatment). 
Other identified metabolites were CGA-37735 (maximum of 14.85% at 272
days), CGA-41638 (maximum of 2.06% at 90 days), and CGA-13656 (maximum
of 1.02% immediately posttreatment).  Other metabolites were detected
but not quantified were CGA-40172, CGA-41507, CGA-40919, and CGA-37913.

The aerobic aquatic metabolism half-life of metolachlor was 47 days. 
The major metabolites in the sediment were CGA-41507 (3.34% of applied
radiocarbon at 29 days), CGA-50720 (1.17%), CGA-40172 (1.13%), CGA-46127
(1.54%), and parent metolachlor was 34.56%.  In the water fraction after
29 days incubation parent metolachlor was 30.90% and the metabolite
CGA-41507 was 1.21% and CGA-51202 was 1.9(%.

Under anaerobic soil conditions metolachlor degraded with a half-life of
81 days in a sandy loam soil that was incubated under anaerobic
conditions for 60 days at 25oC following 30 days of aerobic incubation. 
The major degradate in both the soil and flood water was CGA-51202
(maximum of 23.33% of applied radiocarbon at 29 days after anaerobic
conditions were established); and other reported degradates were
CGA-37735 (1.25% at 29 days), CGA-41638 (8.3% at 60 days), CGA-13656
(1.46% at 29 days), and CGA-50720 (maximum of 7.34% at 60 days).

The anaerobic aquatic metabolism half-life for metolachlor was 78 days. 
In the anaerobic waters the major degradates were CGA-40172 (maximum of
5.64% at 12 months), CGA-37913 (maximum of 4.28% at 6 months), CGA-46127
(maximum of 4.69% at 12 months) and CGA-41507 (maximum of 4.85% at 6
months).  The major degradates in sediment were CGA-41507 (maximum of
15.88% of applied radiocarbon at 12 months), CGA-40172 (maximum of 3.18%
at 12 months), CGA-46127 (maximum of 13.02% at 12 months), CGA-50720
(maximum of 1.67% at 29 days), and CGA-37913 (maximum of 2.33% at 6
months), and after 12 months the sediment contained 1.47% parent
metolachlor.

In the unaged portion of the leaching and adsorption and desorption
study metolachlor was shown to range from being highly mobile in a sand
soil (kd value of 0.08) to being moderately mobile (Kd value of 4.81 in
a sandy loam) from column leaching studies using four soils.  The
leachate contained from 15.03% to 82.91% (comprised of 75.5% parent
metolachlor, 1.14% of CGA-51202, 3.69% of CGA-37735, and 2.26%
CGA-41638) of the applied radioactivity.  In batch equilibrium studies
employing the same four soils, the Freundlich adsorption (Kad) values
ranged from 0.108 to 2.157.  These data indicate that metolachlor has
the potential to range from being moderately mobile material (clay soil
and sandy loam soil) to being a highly mobile material (loam soil and
sand soil).

In the aged leaching portion of the leaching and adsorption and
desorption study the reported cumulated Kd for aged metolachlor and its
degradates in columns of an Iowa sandy loam soil was 2.01.  This
indicates that metolachlor and its identified degradates (CGA-51202,
CGA-37735, and CGA-41638) have the potential to be mobile since in other
studies it was shown that metolachlor and its CGA-51202 degradate
leached the slowest in the Iowa sandy loam soil compared to their
leaching rate in the other three soils tested.  Batch equilibrium
studies showed that CGA-51202 has the potential to be extremely mobile
with reported Freundlich adsorption (Kad) values ranging from 0.04 in
the Maryland sand to 0.171 in the Iowa sandy loam soil.

Laboratory volatility studies indicated that volatility is not a
significant mode of dissipation for metolachlor from soil.  The maximum
dissipation was 0.05% of the metolachlor dose volatilizing per day.

In numerous terrestrial field dissipation studies using metolachlor
(Dual 8E and Dual 25G) both applied at 4 and 6 lb ai/A the half life of
metolachlor in the 6-12 inch soil layer ranged from 7 days (Iowa) to 292
days (California) with a range of the total water applied ranging from
16.97 inches to > 40 inches during the study period.  Detections of
metolachlor were made as far as the 36-48 inch soil layer in some of the
tests.  The degradate CGA-40172 (0.07 ppm) and CGA-40919 (0.21 ppm) were
detected in the 36-48 inch soil layers in one Iowa site.  CGA-50720 was
not detected (0.07 ppm) in any soil sampled at any interval.

Metolachlor appears to have a low potential to bioaccumulate in fish
with a reported whole body bioconcentration factor of 69X and a whole
body elimination of 93% after 14 days depuration.Appendix B: Modeling
Outputs

PRZM/EXAMS Outputs:

SCI-GROW Output:  S-Metolachlor Parent

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:S-Metolachlor

 time is  4/ 8/2010  19:41:46

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

  Application      Number of       Total Use    Koc      Soil Aerobic

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

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

      3.810           1.0           3.810      2.16E+01       37.8

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

 groundwater screening cond (ppb) =   5.26E+00 

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

FIRST Output:  S-Metolachlor Degradate Ethanesulfonic Acid (ESA)

   RUN No.   1 FOR S-Metolachlor ESA ON   Caneberry     * INPUT VALUES *

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

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

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

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

  0.530(  0.530)   1   1       0.0  480.0   GRANUL( 0.0)  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.) 

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

    162.50        2          N/A      0.00-    0.00     0.00      0.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1  MAR 26, 2008

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

             47.611                     34.040

SCI-GROW Output:  S-Metolachlor Degradate Ethanesulfonic Acid (ESA)

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:S-Metolachlor ESA

time is  4/11/2010  10:39:35

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

Application      Number of       Total Use    Koc      Soil Aerobic

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

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

0.530           1.0           0.530      2.01E+00      153.5

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

groundwater screening cond (ppb) =   4.59E+01

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

FIRST Output:  S-Metolachlor Degradate Oxanillic Acid (OA)

RUN No.   1 FOR S-Metolachlor OA ON   Caneberry     * INPUT VALUES * 

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

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

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

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

  1.050(  1.050)   1   1       0.1  480.0   GRANUL( 0.0)  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.) 

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

    127.50        2          N/A      0.00-    0.00     0.00      0.00

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.1  MAR 26, 2008

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

66.617

SCI-GROW Output:  S-Metolachlor Degradate Oxanillic Acid (OA)

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL

FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:S-Metolachlor OA

time is  4/11/2010  11: 1:15

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

Application      Number of       Total Use    Koc      Soil Aerobic

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

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

1.050           1.0           1.050      2.82E+00       93.8

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

groundwater screening cond (ppb) =   2.97E+01

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

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