UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460



	

	

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

MEMORANDUM

										PC Code: 128901

										DP Barcode:  341850

SUBJECT:	Tier 1 Drinking Water Assessment for Chlorimuron-ethyl Use on
Cranberry and Low-growing Berry Subgroup 13H, Except Strawberry

FROM:	Wm. J. Shaughnessy, Ph.D.

			Environmental Risk Branch II

			Environmental Fate and Effects Division

TO:		Daniel Rosenblatt, Chief

			RIMUERB

			Registration Division

THROUGH:	Dana Spatz, Chief (Acting)

			Environmental Risk Branch II

			Environmental Fate and Effects Division

DATE:	July 24, 2007

	The attachment to this memorandum presents the results of a Tier 1
(screening level) drinking water assessment on the use of the herbicide
chlorimuron-ethyl (PC# 128901), and its E.I. du Pont de Nemours and
Company end-product Classic®, on cranberries and  other low-growing
berries in subgroup 13H (except strawberries).  Subgroup 13H berries
include: bearberry, bilberry, low-bush blueberry, cloudberry,
lingonberry, muntries, and partridgeberry.  Chlorimuron-ethyl (EPA Reg.
No. 352-528 and Classic® (EPA Reg. No. 352-436 have previously been
approved for use on soybeans, peanuts, and non-crop lands.

	Questions related to this assessment can be directed to Mr. Dana Spatz,
(703) 305-6063 (  HYPERLINK "mailto:spatz.dana@epa.gov" 
spatz.dana@epa.gov ) or Dr. Wm. Shaughnessy, (703) 305-6155   HYPERLINK
"(shaughnessy.william@epa.gov)"  (shaughnessy.william@epa.gov) .

Attachment: As stated

Chlorimuron-ethyl Use on Cranberries and Subgroup 13H Berries

Tier 1 Drinking Water Assessment

July 24, 2007

EXECUTIVE SUMMARY

	Chlorimuron-ethyl [ethyl
2-(4-chloro-6-methoxypyrimidin-2-ylcarbamoylsulfamoyl) benzoate] is a
sulfonylurea class herbicide with a herbicidal mode of action of
inhibiting acetolactate synthase.  Chlorimuron-ethyl is used for the
postemergent control of certain weeds, such as buttercup and yellow
nutsedge and for the suppression of weeds such as purple aster and
silverleaf. 

The proposed application rate for chlorimuron-ethyl on cranberries and
subgroup 13H berries is 1 oz. (0.063 lb.) per acre applied in an aqueous
solution of water and surfactant using ground spraying techniques.  It
appears that use on cranberries is before flooding, so use of the FIRST
model is appropriate.  Soil metabolism, surface runoff and spray drift
appear to be the major fate and transport mechanisms.  

The FIRST and SciGrow models were used to conduct the Tier 1 surface and
ground drinking water assessments.  For the proposed label use rates,
the FIRST model predicted raw surface drinking water acute and chronic
exposure concentrations of 5.7 ppb and 2.4 ppb, respectively.  The
SciGrow model predicted an acute and chronic groundwater exposure
concentration of 1.76 ppb.  These expected environmental concentrations
(EECs) are comparable to those calculated in the April 16, 2004 Tier I
drinking water assessment for use on soybeans, peanuts and non-crop
land.  In that assessment, drinking water concentrations were 5.4 ppb
(acute) and 2.3 ppb (chronic) for surface water.  The acute and chronic
groundwater concentration was 2.2 ppb.

PROBLEM FORMULATION

	This is a Tier I drinking water assessment that uses modeling and
available monitoring data to estimate the ground water and surface water
concentrations of the herbicide chlorimuron-ethyl in drinking water
source water (pre-treatment) resulting from the use of the herbicide on
sites that are highly vulnerable.  This initial tier screens out
chemicals with low potential risk and provides estimated exposure
concentrations for the human health dietary risk assessment.

ANALYSIS

Use Characterization

	Chlorimuron-ethyl is a dispersible granule formulation to be mixed with
water and sprayed for selective post emergence weed control of many
broadleaf weeds and yellow nutsedge.  According to the proposed
supplemental labeling prepared by DuPont, the maximum amount of active
ingredient that can be applied is 1 oz. or 0.063 lbs. per acre which can
be applied once during the growing season.  A late spring application is
recommended but not later than 60 days before harvest.  Applications of
the herbicide may include a crop oil concentrate or nonionic surfactant
as specified in the label at the rate of 0.25% (1 quart/100 gallons of
spray solution).

Fate and Transport Characterization

	Details regarding the environmental fate of chlorimuron-ethyl have been
previously reported.  The expected major route of degradation is by
metabolism in soil, with disappearance half-lives (for parent plus
demethylated parent) of 75 to 112 days measured in sandy loam
(Woodstown) and silt loam (Flanagan) soils.  Terrestrial field
dissipation studies in Delaware and North Caroline yielded soil
half-lives of 6.4 to 27 days for the disappearance of the parent. 
Abiotic hydrolysis is as fast as soil metabolism at pH 5 (half-lives 17
to 27 days) but is slow at pH 7 and 9.  Aqueous and soil photolysis were
found not to be significant processes.  Aerobic aquatic metabolism was
not tested; anaerobic aquatic metabolism yielded half-lives of 2-3 weeks
in a Florida sediment-water system, and 5-6 weeks in a Pennsylvania
sediment-water system.

	Chlorimuron-ethyl has 6 major degradates, and no minor degradates.  The
major degradates include demethylated parent, a “sulfonamide,” and
“pyrimidine-amine,” saccharin, dechlorinated pyrimidine-amine, and
demethylated pyrimidine-amine.  The demethylated parent, saccharin,
sulfonamide and pyrimidine-amine each remained at greater than 10% of
applied radioactivity at the end of some of the aerobic soil metabolism
studies (one year), and were major degradates in the field dissipation
studies.

In the environment, parent chlorimuron-ethyl is very mobile in soil,
with Kd values of <0.03 (sandy loam), 0.28 (silt loam), and >1.6 (silt
loam).  The parent is not expected to be volatile, with a reported vapor
pressure of 4E-12 atm.  In soil column leaching studies using
phenyl-ring labeled parent, saccharin and the sulfonamide were observed
at up to 28% and 4.3%, respectively, of the applied radiation in the
leachate.  Saccharin has Koc values of 4.6 to 15.5, indicating that it
is mobile (MRID 45012638).  Overall, chlorimuron-ethyl is expected to
dissipate by metabolism in soil and transport in water by run-off, or
leaching.

A summary of the physical/chemical and environmental fate/transport
properties of chlorimuron-ethyl, including measured parameters, values,
and data sources is presented in Table 1.

Table 1.  Summary of physical/chemical and environmental fate and
transport properties of chlorimuron-ethyl

Input Parameter	Value	Reference

Application Rate	0.063 lb/acre, once per year for cranberries	IR-4
Petition Proposing a Tolerance for Chlorimuron-ethyl 12/08/06

Application Type	Ground application	IR-4 Petition Proposing a Tolerance
for Chlorimuron-ethyl 12/08/06

Laboratory Soil Metabolism Half-life (parent plus demethylated parent)
106 days 90th percentile upper confidence limit on 4 values) 

91 days (average of 4 values)	MRID 131580, 145402

Laboratory Aerobic Aquatic Metabolism Half-life	212 days (2x soil input
value, as per Input Parameter Guidance)	Guidance for Selecting Input
Parameters in Modeling the Environment Fate and Transport of Pesticides,
Version II, February 28, 2002

Laboratory Hydrolysis half-life (pH 7)	Stable at pH 7	MRID 131580

Laboratory Aqueous Photolysis Half-life	Stable	MRID 145779, 154438

Soil-Water Partitioning Coefficient (Koc)	2.5 ml/g for Cecil sandy loam
MRID 145778, 143120, 154436, 154440

Solubility (ppm)	1200 (parent at pH 7) solubility is a strong function
of pH above pKa of 4.2	One-liner database

Vapor Pressure	4E-12 atm.	MRID 43896401

Percent Cropped Area	87%	Model default for ‘Other’ cropland category

Wet-in?	No	Label



Drinking Water Exposure Modeling 

	The FIRST and SciGrow models were used to conduct the Tier 1 surface
and ground drinking water assessments.  FIRST concentrations (ppb)
represent untreated surface water concentrations.  The one-in-10-year
peak day concentration is used for acute endpoints and the
one-in-10-year annual average concentration is used for chronic
endpoints.

SciGrow concentration (ppb) represents the groundwater concentration
that might be expected in shallow unconfined aquifers under sandy soils.
 Output is used for both acute and chronic endpoints.

The modeled acute and chronic surface drinking water concentrations were
estimated to be 5.7 and 2.4 ppb, respectively.  The modeled ground water
concentration was estimated to be 1.76 ppb.  Modeling results are
presented in Table 2.  Model outputs are included in the Appendix.

Table 2.  Maximum Tier I Estimated Drinking Water Concentrations (EDWCs)
for drinking water assessment based on ground application of
chlorimuron-ethyl.

DRINKING WATER SOURCE (MODEL USED)	USE (rate modeled)	MAXIMUM ESTIMATED
DRINKING WATER CONCENTRATION (EDWC) (ppb)

Surface Water (FIRST)	Other (cranberries) 0.063 lbs. a.i./acre	Acute	5.7

	Other (cranberries) 0.063 lbs. a.i./acre	Chronic	2.4

Groundwater (SciGrow)	Other (cranberries) 0.063 lbs. a.i./acre	Acute and
Chronic	1.76



Monitoring Data 

The US Geological Survey (USGS) reports that chlorimuron-ethyl has been
detected in the drinking water facilities presented in Table 3.  The
data show the percent of the total number of samples in which the
herbicide was detected and the maximum concentration observed at that
location.  The reported concentrations are less than those predicted by
the FIRST model.

Table 3.  Detection Frequency and Maximum Concentration at Four Drinking
Water Facilities 

Reservoir Location	Concentration at Water-supply Intake	Concentration at
Reservoir Outflow Site	Concentration of Treated Effluent

	Detection %	Max Conc. (ppb)	Detection %	Max Conc. (ppb)	Detection %	Max
Conc. (ppb)

Indianapolis Water Co., IN	-	-	-	-	5	0.04

Higginsville Reservoir, MO	11	0.018	10	0.026	-	-

East Fork Lake, OH	47	0.05	36	0.021	-	-

Lake Mitchell, SD	5	0.021	11	0.023	9	0.026

Source: USGS Open file report 01-456 (Pesticides in Selected
Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: Summary
of results from a Pilot Monitoring Program)

EFED has no information on the effect of drinking water treatment on
chlorimuron-ethyl.  From the laboratory fate studies, it can be
concluded that alkaline hydrolysis is slow (as during water softening). 
Low Kd values indicate that precipitation of the parent (as during
flocculation and coagulation) may be difficult.

CONCLUSIONS

Modeling Results

Surface raw drinking water concentrations estimated by the FIRST model
are 5.7 ppb and 2.4 ppb for acute and chronic exposures, respectively. 
These modeled concentrations are between 48 and 285 times greater than
concentrations measured in the drinking water facilities surveyed by the
USGS.

The SciGrow model yielded an estimated groundwater concentration for an
acute and chronic drinking water exposure of 1.76 ppb.

Uncertainties

The organic carbon partitioning coefficient (Koc) used (2.5 ml/g) was
the minimum value of those measured, from a soil with pH 6.5.  Use of a
small Koc value tends to increase partitioning to, and therefore
concentration in water.  Koc is a strong function of soil pH for
chlorimuron-ethyl, and the lowest measured values were for soils with pH
above the chemical’s pKa of 4.2, where it exists as a charged species.

The solubility value used (1200 ppm) was for pH 7, where
chlorimuron-ethyl exists as a charged ion.  Below the pKa of 4.2, the
solubility is 1.5 ppm.

No study of degradation in aerobic water-sediment systems (aerobic
aquatic metabolism) was submitted by the registrant.  A half-life of 212
days, or twice the calculated soil half-life value, was used, in
accordance with the Input Parameter Guidance for EFED models.

Appendix

FIRST Model Results  

RUN No. 1 for Chlorimuron-ethyl on Cranberries    * INPUT VALUES *

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

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

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

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

  .063(   .063)               1   1           2.5       1200.0   GROUND(
6.4)      87.0            .0

  FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

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

  METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED

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

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

   106.00        		2          	N/A       	00-     .00               
212.00           212.00

  UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007

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

       PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)

         CONCENTRATION             CONCENTRATION

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

             5.7                      			2.4

SciGrow Model Results

SciGrow Version 2.3

Chemical: Chlorimuron-ethyl

Date: 07/06/07

Application Rate (lbs./acre)	Number of applications	Total Use
(lbs./acre/yr)	Koc (ml/g)	Soil Aerobic Metabolism (days)

0.063	1	0.063	2.5	91.0

Groundwater Concentration (ppb):   1.76



  Memorandum from William P. Eckel, Ph.D. Environmental risk Branch II
to Eric Olson, Special Review and Reregistration Division, Subj:
Preliminary Tier 1 Drinking Water Assessment for Chlorimuron-ethyl Use
on Soybeans, Peanuts and Non-crop Land.  April 16, 2004.  DP Barcode:
D301318

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