Document ID: EPA-HQ-OPP-2010-0865-0007
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-12-30T05:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

	WASHINGTON, D.C.  20460

						Chemical: 	Tepraloxydim

PC Code:	121005

DP Barcode: 	D338939

						Date:  	5/1/2007

MEMORANDUM

Subject:	Tier I Drinking Water Assessment for Tepraloxydim

To: 		Jim Tompkins, RM 25, Vickie Walters, CRM

Registration Division (7501P)

From: 		James Breithaupt, Agronomist

Environmental Risk Branch II

Environmental Fate and Effects Division (7507P)

Thru:		Dana Spatz, Team Leader

Environmental Risk Branch II

		Tom Bailey, Chief

Environmental Risk Branch II

Environmental Fate and Effects Division (7507P)

This memorandum contains the Tier I drinking water assessment for the
uses on the tepraloxydim label dated 8/8/01.  These uses are canola,
cotton, fallow/non-cropland, and soybeans. The half-lives used in
modeling were based on parent compound and the DP-1, DP-2, and DP-8
metabolites when they were present in the studies. Tepraloxydim can be
applied using either aerial or ground equipment.  

The following drinking water EEC’s are recommended for use in the
human health risk assessment.  For tepraloxydim, the acute and chronic
surface water values are 1.4 ppb and 0.7 ppb, respectively, based on the
FIRST model.  The acute and chronic ground water EEC is 0.002 ppb, using
SCIGROW.  The scenarios chosen for modeling were cotton, soybeans, and
fallow ground which have the highest annual application rate of 0.025 lb
ai/A. 



Environmental Fate and Transport

Based on fate properties and application methods, it is expected that
tepraloxydim will persist long enough to be available for transport in
runoff events to non-target environments.  Based on the persistence in
hydrolysis, aerobic soil metabolism, and aerobic aquatic metabolism
studies, tepraloxydim can be reasonably assumed to reach and persist in
surface water.  If any residues of tepraloxydim were to reach ground
water, they would be expected to persist based on the stability to
hydrolysis.  Tepraloxydim is degraded to a number of different
compounds, but the major ones include DP-1, DP-2, and DP-6. 
Tepraloxydim is relatively mobile in soils, increasing the plausibility
of runoff to non-target environments. However, no mobility data have
been submitted for the metabolites.  

EFED calculated half-lives in the fate studies for the total residue of
parent, DP-1 (Imine), DP-2 (oxazole), and DP-8 (dechlorinated,
de-ethylated parent) in accordance with the HED MARC memo (D272004). 
Total residues are stable to hydrolysis at pH values from 4 to 8.8 (MRID
44467231) but degrade by photolysis in water with linear half-lives of
9-13 days (MRID 44467232).  In studies conducted with DP-1 and DP-2 as
individual parent compounds, the linear half-lives in irradiated water
were 24 and 6 days, respectively (MRID 44467233).  No photodegradation
studies were conducted using DP-8 as the parent compound. 
Photodegradation on soil is also a significant route of dissipation with
a linear half-life of 7 days (MRID 44467234). In aerobic soil, the
linear and non-linear half-lives were 38 (poor fit) and 3.5 days,
respectively.  Under anaerobic aquatic conditions (MRID 44467236), the
linear half-life was 147 days while the aerobic aquatic metabolism
half-lives were 65 and 198 days (MRID 44467237).  Tepraloxydim is mobile
in the environment, based on Freundlich Kads values ranging from 0.01 to
1.5 ml/g and Koc values ranging from 3.7 to 77 ml/g (MRID 44467243).  

Modeling Assessment – Tepraloxydim

Surface Water Modeling of Terrestrial Uses  for Tepraloxydim

Proposed drinking water concentrations are based on modeling estimates. 
The uses on soybeans, cotton, and fallow ground were chosen for modeling
since they contain the highest application rate of 0.0125 lb ai/A and
two applications 14 days apart.  Modeling was conducted using this rate
and interval.  The estimates of tepraloxydim concentrations in surface
water were based on the FIRST model, and include two significant
degradates, DP-1 and DP-2, because these two residues were present in
some of the environmental fate studies and are residues of concern based
on the MARC memo.  DP-8 was not observed in any of the fate studies.

The FIRST modeling was performed with Index Reservoir (IR) scenarios and
a percent cropped area (PCA) adjustment factor of 0.87 as a default
value, according to the IR/PCA guidance from R.D. Jones et al (March 21,
2000).   The PCA adjusted model results are presented in Table 1.  

Table 2 presents the input parameters used in the Tier I FIRST modeling
for drinking water from a surface water source.  The FIRST modeling was
based on EFED guidance (“Guidance for Chemistry and Management
Practice Input Parameters for Use in Modeling the Environmental Fate and
Transport of Pesticides” dated February 28, 2002).

Table 1. Drinking Water EECs for Tepraloxydim from Surface Water using
the FIRST Model.

Scenario and crop

	Peak	Chronic Value

Soybean	1.4 ppb	0.7 ppb

Table 2.  Surface Water Exposure Inputs for Drinking Water Exposure from
Existing Terrestrial Uses of Tepraloxydim using the FIRST Model.

MODEL INPUT VARIABLE1	INPUT VALUE	SOURCE/COMMENTS

Application Rate

Nursery crops	0.0125	lb ai/A from 8/8/01 label

No. applications	2	Per 8/8/01 label

Interval between applications (days)	14	Per 8/8/01 label

Percent Cropped Area Adjustment

	0.87	All uses

Koc (ml/g)	8.4	Lowest non-sand  Koc from 5 soils (MRID 44467239

Aerobic Soil Metabolic Half-life (days) 	10.5	Non-linear half-life (3.5
days) * 3 because only one half-life was available (MRID 44467235)

Linear fit was poor

Parent + DP-1 + DP-2

DP-8 not formed

Is pesticide wetted-in	No	Per 8/8/01 label

Method of application	Aerial	Per 8/8/01 label

Depth of Incorporation (inch)	0	Per 8/8/01 label

Solubility (mg/L)	1,400	140 ppm * 10

pH 7

6/8/00 drinking water memorandum, D262823

Aerobic Aquatic Metabolic Half-life (days) = Kbacw in EXAMS	336	Upper
10th confidence bound of mean

65 and 198 day half-lives for Parent + DP-1 (DP-2 and DP-8 not formed)

MRID 44467237

Aqueous photolysis Half-life (days)	9	MRID 44467232

pH 7

Parent + DP-1 + DP-2 ( no DP-8 formed)

1 Input parameters based on Input Parameter Guidance (2/28/02) unless
stated otherwise

Ground Water Assessment – Tepraloxydim

Ground water EECs were modeled using SCI-GROW, a screening ground water
regression model developed using data from prospective groundwater
studies submitted to the OPP in support of registration.  SCI-GROW
provides a high-end estimate of ground water concentrations of
pesticides on soils that are known to be vulnerable to pesticide
leaching (i.e. high sand content with shallow depth to groundwater).

μg/L.  According to the label, up to two applications are allowed with
a maximum annual rate of 0.025 lb ai/A.  Modeling was conducted using
the one-time rate and the 14-day interval.  The estimated concentration
of 0.002 ug/L could not be compared to monitoring because EFED is
unaware of any monitoring. 

Table 3.  SCI-GROW Inputs for Tepraloxydim using the SCI-GROW2 Model.

MODEL INPUT VARIABLE2	INPUT VALUE	SOURCE/COMMENTS

Application Rate (kg ai/ha)3

Nursery crops

	

0.0125	lb ai/A maximum one-rate from 8/8/01 label

Maximum No. of Applications

Nursery crops	

2	Per 8/8/01 label

Koc (ml/g)	20.2	Median Koc from 5 soils (MRID 44467239), range of
3.7-77.2 ml/g

Aerobic Soil Metabolic half-life (days) – parent	10.5	Half-life from
MRID (44467235) * 3

EEC from model

0.002 ug/l

Comparison of Modeling and Monitoring.  

Comparison of monitoring and modeling is not possible for tepraloxydim
because EFED is not aware of any monitoring data.

FIRST and SCIGROW  Model Outputs

RUN No.   1 FOR tepraloxydim     ON   soybean       * INPUT VALUES * 

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

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

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

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

   .013(   .017)   2  14       8.4 1400.0   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.) 

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

     10.50        2          N/A      9.00- 1116.00   336.00    258.25

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

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

        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      

          CONCENTRATION             CONCENTRATION            

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

              1.444                       .656

 

                         

SCIGROW

                                                     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:tepraloxydim

 time is  4/24/2007  11:54:16

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

  Application      Number of       Total Use    Koc      Soil Aerobic

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

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

      0.013           2.0           0.025      2.02E+01       10.5

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

 groundwater screening cond (ppb) =   2.14E-03 

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

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