UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM

Date: 9 July 2010 

SUBJECT: Imazosulfuron. Dissipation of Dislodgeable Foliar Residues on Tomato Leaves. 

 

PC Code: 118602 DP Barcode: D380799 

Decision No.: NA Registration No.: NA 

Petition No.: NA Regulatory Action: NA 

Risk Assessment Type: NA Case No.: NA 

TXR No.: NA CAS No.: 122548-33-8 

MRID No.: 47679129 40 CFR: NA

FROM: Nancy J. Tsaur, Chemist 

 Risk Assessment Branch 3 (RAB3) 

 Health Effects Division (7509P)

 

THROUGH: Barry O’Keefe, Biologist, ORE Team Leader

Risk Assessment Branch 3 (RAB3) 

Health Effects Division (7509P) 

 

TO: Sheila Healy, Toxicologist, Risk Assessor 

Risk Assessment Branch 3 (RAB3) 

Health Effects Division (7509P) 

Attached is a review of the study “Dissipation of Dislodgeable Foliar Residues of Imazosulfuron 

on Tomato Leaves” submitted by Valent U.S.A. Corporation (Valent). The primary review was 

conducted by Versar and the secondary review was conducted by the Health Effects Division 

(HED). This document was reviewed by the HED Exposure Science Advisory Council 

(ExpoSAC) on 07/08/2010. 

Page 1 of 22 
Dislodgeable Foliar Residue (2008)/Page 2 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Executive Summary 

This study was designed to determine the dissipation of dislodgeable foliar residues (DFRs) of 

imazosulfuron applied to tomato plants at a test site located in Madera, CA. One application of 

V-10142 75 WDG, a water dispersible granular formulation containing 75% imazosulfuron as 

the active ingredient, was made at a target application rate of 0.5 lb ai/A. Applications were 

made as a foliar broadcast spray at a spray volume of approximately 29.9 gallons per acre 

(GPA). Samples were collected before the application, within 1.5 hours of application and 1, 2, 

3, 4, 5, 7, 10, 14, 21, 28, and 35 days after treatment (DAT). At each sampling interval, single 

samples were collected from the control plot and triplicate samples were collected from the 

treated plot. Field-fortified samples prepared using leaf samples from the control plot were 

prepared on days 1, 7, and 14 after the application to evaluate the stability of the field samples 

during shipment and storage and to determine extraction efficiency in the analytical laboratory. 

The Registrant provided dislodgeable foliar residues in μg/cm2

. The overall average low and 

high level field fortification recoveries were >90%, therefore, HED did not correct the data for 

field fortification recoveries. For calculation purposes, DFR values reported as between the limit 

of quantitation (LOQ) and the limit of detection (LOD) were assigned a value of 1⁄2 LOQ and 

DFR values less than the LOD were assigned a value of 1⁄2 LOD. 

The highest average DFR value occurred immediately after the application (0.761 μg/cm2

). The 

residues declined rapidly to an average of 0.163 μg/cm2

 by Day 1, and then declined gradually to 

less than the LOD by Day 35. 

HED assumed first-order dissipation kinetics to generate a dissipation curve for imazosulfuron. 

HED used individual residue data collected immediately after the application through the first 

day where all of the residue values were below the LOQ (0.00625 μg/cm2). Based on linear 

regression of the natural log transformed data, HED’s calculated half-life for imazosulfuron was 

4.11 days (R2 = 0.838). The actual DFR residue level on Day 0 (0.761 μg/cm2) is significantly 

greater than the predicted DFR (0.178 μg/cm2

), based on linear regression analysis of logtransformed data. Additionally, the analytical method was validated using samples fortified at 

levels less than the highest initial measurement of 0.808 μg/cm2

. Since the concurrent laboratory 

recovery for the highest fortified sample was only 85.8%, it is more appropriate and protective to 

use the actual residue data for Day 0 while also correcting for an 85.8% laboratory recovery 

when assessing risks to postapplication workers (resulting in a residue value of 0.887 μg/cm2

). 

The field recoveries were much higher than the lab recoveries, and therefore indicate a greater 

range of viability. 

The Registrant attempted to more clearly characterize the biphasic dissipation pattern of the 

regression by calculating two half life estimates. A half-life of 10 hours was determined for the 

samples collected in the time period immediately after the application to Day 1 and a half-life of 

5.2 days was determined for the samples collected from Day 2 to Day 28 after application. 

This study met the majority of the Series 875.2100 Guidelines. The following issues of concern 

are noted: 
Dislodgeable Foliar Residue (2008)/Page 3 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

• The production of metabolites, breakdown products, or the presence of contaminants of 

concern were not discussed in the Study Report. However, the imazosulfuron parent 

compound has been selected as an adequate marker for tolerance enforcement. 

• DFR data should be collected from at least three geographically distinct locations but only 

one geographical location was used in this study. 

• Although few samples exceeded the field fortification levels used in the study (0.0500 and 

0.250 μg/cm2

), HED does not believe this to be of significant concern given the relative 

performance. 

• Field fortifications were performed on only three of the study days -- days 1, 7, and 14. 

• Information verifying that the application equipment was properly calibrated was not 

included in the Study Report. 

• It is uncertain if this site is representative of reasonable worst-case climatic conditions 

expected in intended use areas. Meteorological conditions including temperature, wind 

speed, daily rainfall, and humidity were not provided for the duration of the study. Only 

precipitation/irrigation data were provided for the duration of the study.

• Results from a separate storage stability study were not provided with the study. Field 

fortification samples were intended to assess the stability of imazosulfuron during storage. 

The longest storage interval for a field sample was 55 days, and the longest storage interval 

for a set of field fortification samples was 55 days (demonstrating an overall recovery 

>90%). 

• The Registrant validated the analytical method using samples fortified at 0.0063 and 0.031 

μg/cm2

. One concurrent laboratory fortified sample was analyzed with a concentration 

approximating the highest concentration found in the field samples (0.808 μg/cm2

). The 

concurrent recovery for this laboratory fortified sample was corrected based on the percent 

recovery (85.8%). 

• According to the product label, the maximum application rate is 0.3 lb ai/A. In this study, the 

target application rate was 0.5 lb ai/A. 
Dislodgeable Foliar Residue (2008)/Page 4 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

EPA Reviewer: Nancy J. Tsaur Date: 25 June 2010 

Risk Assessment Branch 3 (RAB3) 

Health Effects Division (7509P) Template version 02/06

DATA EVALUATION RECORD

STUDY TYPE: Determination of Dislodgeable Foliar Imazosulfuron Residues from 

Tomato Leaves Treated with V-10142 75 WDG: OPPTS 875.2100 

PC CODE: 118602 

TEST MATERIAL V-10142 75 WDG is formulated as a water dispersible granular 

formulation containing 75% active ingredient, imazosulfuron. 

SYNONYMS: Imazosulfuron; CAS No. 122548-33-8. 

CITATION: Authors: C.A. Green 

 Title: Dissipation of Dislodgeable Foliar Residues of 

Imazosulfuron on Tomato Leaves (122 pages). 

Report Date: June 5, 2008 

 Analytical Laboratory: Valent U.S.A. Corporation 

Valent Technical Center 

6560 Trinity Court 

Dublin, CA 94568 

Identifying Codes: Valent Project No. 30582; MRID 47679129; 

Unpublished 

SPONSOR: Valent U.S.A. Corporation 

P.O. Box 8025 

Walnut Creek, CA 94596-8025 

COMPLIANCE: 

Signed and dated GLP, Quality Assurance, and Data Confidentiality statements were provided. 

The study sponsor waived claims of confidentiality within the scope of FIFRA Section 10 

(d)1(A), (B), or (C). The Study Report indicated that the study was conducted under EPA Good 

Laboratory Practice Standards (40 CFR Part 160), with the following exceptions: Weather data, 

pesticide history, cultural practices, application of maintenance chemicals, irrigation data, crop 

history and the pH measurement of the carrier water were not documented in compliance with 

GLP Standards. In addition, the dilution of a fortification standard (which had degraded) was 

not documented in compliance with GLP Standards. 

CONCURRENT EXPOSURE STUDY: No 
Dislodgeable Foliar Residue (2008)/Page 5 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

GUIDELINE OR PROTOCOL FOLLOWED: Series 875, Part B: Dislodgeable Foliar 

Residue Dissipation: Agricultural, Guideline 875.2100. 

I. MATERIALS AND METHODS

A. MATERIALS:

1. Test Material: 

Formulation: V-10142 75 WDG is formulated as a water dispersible granular 

formulation containing 75% active ingredient, imazosulfuron. 

Batch/Lot #: V06C-102DG-3 (formulated product) 

AS 2146a (reference standard) 

Formulation Guarantee: The Study Report stated that the test product contained 76.1% 

imazosulfuron (assayed on March 8, 2006). Expiration date: 

March 8, 2007. 

Purity: The imazosulfuron reference standard was analyzed and found to 

have a purity of 99.7% (assayed on January 12, 2004). Expiration 

date: January 5, 2007. 

CAS #: 122548-33-8 

Other Relevant Information: EPA Registration Number 59639-RLL. 

2. Relevance of Test Material to Proposed Formulation(s):

The test product used in this study was V-10142 75 WDG, containing 75% imazosulfuron. A 

label for V-10142 AG Herbicide (EPA Reg. No. 59639-RLL) was provided with the Study 

Report. This label appears to be the same or similar to the test product. 

B. STUDY DESIGN:

The study protocol was provided in the Study Report. There was one amendment to the study 

protocol: the lot number for the test substance was changed and the VC# listed was changed to 

the correct number. The Study Report did not provide any information detailing protocol 

deviations. 
Dislodgeable Foliar Residue (2008)/Page 6 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

1. Site Description:

Test Locations: The DFR portion of the study was conducted at a test site in Madera, 

CA. The test site was said to be representative of climate and crop 

growing conditions expected in the intended-use areas. One control plot 

and one treated plot were established at the test site. According to the 

study protocol, the control plot was to be located upwind and upslope 

from the treated plot at a minimum distance of 50 feet.

Areas Sprayed and 

Sampled: 

The treated plot measured 120 ft by 21.6 ft (2,592 ft2

 or 0.0595 acre). 

The untreated plot measured 50 ft by 20 ft (1,000 ft2

 or 0.0230 acre).

Meteorological Data: Precipitation data were reported for the months of the trial along with 

comparative 10-year historical data. Total monthly rainfall for the 

months of the trial was within the historical 10-year average. No rainfall 

occurred during the sampling period; furrow irrigation was applied four 

hours after the first postapplication sampling interval. 

Air temperature and wind speed and direction recordings were provided 

for the day of application. Air temperature was recorded as 81°F during 

the application; wind speed was reported as ranging from 0 to 1 mph 

(NW direction) during the application. No other meteorological data 

were provided; however, the protocol required daily air temperature and 

relative humidity to be recorded, which could be in the form of reports 

from the nearest NOAA or other governmental recording station.

2. Crop Characteristics: 

Crop, Variety: Tomato, Sun Bright; planted April 29, 2006. 

Row Width, Plant Spacing: 8 rows spaced 5 ft apart. 

Stage of Growth: Green and ripe tomato fruit. 

Other Products Used on Crop: No maintenance or fertilizer compounds were applied 

immediately before the application or during the study. 

3. Application Rates and Regimes: 

Application Rate(s): The target application rate was 0.5 lb ai/A; the actual application rate 

was 0.4996 lb ai/A (99.8% of target rate). According to the label for 

V-10142 AG Herbicide (EPA Reg. No. 59639-RLL), the maximum 

recommended application rate for tomatoes is 0.3 lb ai/A.

Application Regime: One application was made at the test site on July 24, 2006.
Application Equipment: A 60-gal power sprayer was used for the test substance application. 

The power sprayer was equipped with Tee Jet 8002 VS flat fan 

nozzles.

Spray Volume: The product label for V-10142 AG Herbicide (EPA Reg. No. 59639-

RLL) indicates that the product should be applied in 20 to 40 gallons 

of water carrier per acre (GPA). The actual spray volume used was 

29.9 GPA. No additives or adjuvants were used.

Equipment Calibration 

Procedures: 

The Study Report did not mention calibrating the application 

equipment.

4. Dislodgeable Foliar Residue Sampling Procedures: 

Method and 

Equipment: 

DFR samples replicates consisted of 40 leaf discs which were 

collected with a leaf puncher (1-inch diameter). The punch samples 

were collected directly into pre-labelled glass jars on July 24, 2006.

Sampling Procedure: At each sampling interval, three samples were collected from the 

treated plot; a single sample was collected from the control plot. Leaf 

discs were collected when the foliage was dry. The untreated plot was 

sampled prior to the treated plot. A specific randomization procedure 

was used for sampling throughout the plot.

Total Surface Area per 

Replicate: 

The double sided surface area per leaf punch was approximately 10 

cm2 and 40 leaf discs were collected for each replicate (400 cm2

).

Replicates per Activity: - Replicates per sampling time: At each sampling interval, triplicate 

DFR samples were collected from the treated plot and one sample 

was collected from the control plot. 

- Number of sampling times: There were a total of 13 sampling 

events, including one pre-application sampling event.

Times of Sampling: Samples were collected before the application, within 1.5 hours of 

application and 1, 2, 3, 4, 5, 7, 10, 14, 21, 28, and 35 days after the 

application.

Part(s) of Foliage 

Sampled: 

The Study Report stated that all areas of the plants were sampled.

5. Sample Handling:

Samples were transported in coolers with substitute ice to the field laboratory for dislodging. 

According to the Study Report, dislodging was performed within 2 hours of sample collection. 

The dislodged samples were maintained frozen at the testing facility until they were shipped. 

Sample bottles were shipped in dry ice overnight to Valent Technical Center. Samples were 

Page 7 of 22 
Dislodgeable Foliar Residue (2008)/Page 8 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

received at the analytical facility from July 27, 2006 through August 31, 2006 and stored at about 

-20oC until extraction and analysis. The analytical portion of the study was carried out from 

September 6, 2006 through September 25, 2006. The maximum length of frozen storage was 55 

days for the field samples and field fortification samples. 

6. Analytical Methodology: 

Dislodging Solution: Imazosulfuron residues were dislodged with 0.01% Aerosol® OT 

solution to dislodge surface residue.

Dislodging Procedure: Samples were dislodged within the sampling jars twice. Each 

dislodging used 100 mL of the 0.01% Aerosol OT solution. 

Dislodging was conducted by shaking the sample on a mechanical 

shaker for 10 minutes. The resulting solutions were combined and the 

foliage was discarded.

Time Interval (Sample 

Collection to Dislodging): 

All samples were dislodged within 2 hours of collection.

Extraction Method: The DFR solution samples were extracted with methylene chloride. 

After rotary evaporation to remove the methylene chloride, residues 

were re-dissolved in acetonitrile, partitioned with hexane and rotary 

evaporated to remove the acetonitrile. Residues were then dissolved 

in ammonium acetate solution (in methanol/water) and analyzed by 

high-pressure liquid chromatography with mass selective detection 

(LC/MS-MS).

Detection Methods: All samples were analyzed using high-pressure liquid 

chromatography with mass selective detection (LC/MS-MS). A 

summary of the conditions are shown in Table 1.

Table 1. Summary of Typical LC/MS-MS Conditions 

HPLC Conditions 

Column: Luna (C18), 3 μm, 50 mm x 3.0 mm 

Mobile Phases: A = Methanol, 0.05% formic acid and B = Water, 0.05% formic acid 

Flow Rate: 300 μL/minute 

Injection Volume: 10 μL 

Gradient Program: Time (min) %A %B

0 50 50 

0.5 50 50 

7.0 90 10 

10.5 90 10 

12 50 50 

14 50 50 

Retention Time: 14 minutes 
Dislodgeable Foliar Residue (2008)/Page 9 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Table 1. Summary of Typical LC/MS-MS Conditions 

LC/MS Interface Conditions 

Interface: Electrospray Ionization 

Source CID Collision Energy: 16 

Polarity: Positive 

Q2 Collision Gas Pressure: 0.9 mTorr 

Scan Type: SRM 

Parent Ion Mass: m/z 413 

Quantitation Ion Mass: m/z 156.1 

Collision Energy: 34 

Method 

Validation: 

Samples of dislodging solution were analyzed for residues of imazosulfuron 

using analytical method RM-42D-1. The method was validated prior to 

analysis of the field samples collected for this study. Recoveries from samples 

fortified with 2.5 μg (0.00625 μg/cm2

) ranged from 81.9 to 90.4%, and 

recoveries from samples fortified with 12.5 μg (0.03125 μg/cm2) ranged from 

94.5 to 102%. The validated limit of quantitation (LOQ) was 0.00625 μg/cm2

. 

The limit of detection (LOD) was 0.0031 μg/cm2.

Instrument 

Performance: 

The linearity of the LC system was verified within each analytical sequence 

with five linearity standards. The calibration was performed using a linear fit 

with a non-zero intercept. The slope and the intercept were calculated using a 

linear regression weighed by 1/concentration. The r-squared value was also 

calculated from this data set, and this value was required to be greater than 

0.99 for the instrument response to be considered linear for the range of 

standard concentrations. In addition, the concentration calculated from the 

peak area of each of the standards, using the slope and intercept form the linear 

fit, was required to be within 15% of the actual concentration. All of the 

sample sets met this requirement. 

The reproducibility of the LC system was verified by comparison of the 

detector responses obtained from the repeated analysis of a reference standard 

analyzed with the study samples. The coefficient of variation of these 

responses was required to be 10% or less for an analytical sequence to be 

acceptable. All of the samples sets met this requirement.

Quantification: The analyte concentration in the sample extracts was determined using the 

slope and intercept of the linear fit equation, the peak area of the sample, and 

the dilution factor, if any. The resulting concentration in μg/mL was converted 

to μg/ cm2 using the total volume of the detergent solution used to dislodge the 

residues and the surface area of the leaf punches.
Dislodgeable Foliar Residue (2008)/Page 10 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

7. Quality Control: 

Lab Recovery: Concurrent laboratory fortified samples were analyzed with each set of field 

samples. Control 0.01% AOT samples were fortified with imazosulfuron at 

concentrations ranging from 0.00625 μg/cm2

 to 0.750 μg/cm2. Individual 

concurrent laboratory recoveries ranged from 84.5% to 97.5% with an overall 

mean recovery of 89.9% ± 4.4% (n= 14).

Field Blanks: One control sample was collected at each sampling interval from the untreated 

plot. There were no imazosulfuron residues detected above the LOQ in any of 

the untreated control samples.

Field Recovery: Field fortification samples were prepared at two concentrations using control 

dislodging solution fortified with imazosulfuron. The samples were prepared 

on days 1, 7, and 14 after application. The fortification levels were 0.05 and 

0.250 μg/cm2

. The field fortified samples were shipped and stored in the 

freezer for up to 55 days under the same conditions as the field samples.

Field Blanks: One control sample was collected at each sampling interval from the untreated 

plot. There were no imazosulfuron residues detected above the LOQ in any of 

the untreated control samples. 

The field fortification recoveries were reported as corrected for the concurrent 

recovery of the high level lab fortification sample from the analytical set that 

the fortified samples were analyzed with. Because the residue levels were not 

corrected for concurrent laboratory recovery, HED found it more appropriate 

to present field fortification values which were also not corrected for 

concurrent laboratory recovery. Table 2 provides a summary of the 

uncorrected field fortification recoveries. The overall mean field fortification 

recovery was 93.1% ± 5.97%. 

The fortification levels did not bracket the residue levels found in the field 

samples. The first sampling interval field samples had residues greater than 

the high field fortification level of 0.250 μg/cm2

.

Table 2. Summary of Field Fortification Recoveries

Sampling 

Event 

Fortification 

Level 

(μg/cm2) 

Imazosulfuron 

Residue 

(μg/ cm2) 

Percent 

Recovery 

(%) 

Average 

Percent 

Recovery 

per Level 

(%) 

Overall 

Low Level 

Percent 

Recovery 

(%) 

Overall 

High Level 

Percent 

Recovery 

(%) 

Overall 

Percent 

Recovery 

(%) 

Std. Dev.

0.0500 0.0473 94.7 

0.0500 0.0461 92.2 

0.0500 0.0459 91.7 

92.9 

0.250 0.240 95.8 

0.250 0.245 98.2 

1 DAT 

0.250 0.235 93.8 

95.9 

94.1 92.0 93.1 5.97 
Dislodgeable Foliar Residue (2008)/Page 11 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Table 2. Summary of Field Fortification Recoveries

Sampling 

Event 

Fortification 

Level 

(μg/cm2) 

Imazosulfuron 

Residue 

(μg/ cm2) 

Percent 

Recovery 

(%) 

Average 

Percent 

Recovery 

per Level 

(%) 

Overall 

Low Level 

Percent 

Recovery 

(%) 

Overall 

High Level 

Percent 

Recovery 

(%) 

Overall 

Percent 

Recovery 

(%) 

Std. Dev.

0.0500 0.0481 96.2 

0.0500 0.0478 95.7 

0.0500 0.0471 94.2 

95.3 

0.250 0.176 70.2 

0.250 0.232 92.8 

7 DAT 

0.250 0.243 97.2 

86.7 

0.0500 0.0466 93.2 

0.0500 0.0476 95.2 

0.0500 0.0470 94.0 

94.1 

0.250 0.233 93.1 

0.250 0.238 95.0 

14 DAT 

0.250 0.230 91.9 

93.3 

Formulation: V-10142 75 WDG is formulated as a water dispersible granular formulation 

containing 75% active ingredient, imazosulfuron.

Tank Mix: Tank mix samples were not collected for this study.

Travel Recovery: Travel recovery samples were not used in this study.

Storage Stability: A separate storage stability study was not conducted. However, the fieldfortified samples were stored and shipped under the same conditions as the 

field samples and were used to provide storage stability data for the treated 

samples. The resulting field fortification recovery data indicate that 

imazosulfuron was stable under the freezer storage and shipping conditions 

used in the study for up to 55 days. The field samples were stored in the 

freezer for up to 55 days.

II. RESULTS AND CALCULATIONS

The Registrant provided dislodgeable foliar residues in μg/cm2. The overall average low and 

high level field fortification recoveries were >90%, therefore, HED did not correct the data for 

field fortification recoveries. For calculation purposes, DFR values reported as between the limit 

of quantitation (LOQ) and the limit of detection (LOD) were assigned a value of 1⁄2 LOQ and 

DFR values less than the LOD were assigned a value of 1⁄2 LOD. 

A summary of the DFR values calculated by HED is provided in Table 3. Additionally, a 

graphical presentation of the DFR values is shown in Figure 1. The highest average DFR value 

occurred immediately after the application (0.761 μg/cm2

). The residues declined rapidly to an 

average of 0.163 μg/cm2

 by Day 1, and then declined gradually to less than the LOD by Day 35. 
Dislodgeable Foliar Residue (2008)/Page 12 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Additionally, the analytical method was validated using samples fortified at levels less than the 

highest initial measurement of 0.808 μg/cm2

. Since the concurrent laboratory recovery for the 

highest fortified sample was only 85.8%, it is more appropriate and protective to use the actual 

residue data for Day 0 while also correcting for an 85.8% laboratory recovery when assessing 

risks to postapplication workers (resulting in a residue value of 0.887 μg/cm2

). 

Both HED and the Registrant assumed first order decline of the residues in determining the halflife of dislodgeable imazosulfuron residues for tomato leaves and performed a linear regression 

analysis. The Registrant stated that the decline in dislodgeable residues was biphasic and 

therefore, estimated half-life values for the time period between Day 0 and Day 1 after the 

application and the time period from Day 2 to Day 28 after the application. The Registrant’s 

half-life for the time period between Day 0 and Day 1 was 10 hours (R2

= 0.9582) and the halflife for the time period from Day 2 to Day 28 was 5.2 days (R2

 = 0.8934). 

HED assumed first-order dissipation kinetics to generate a dissipation curve for imazosulfuron. 

HED used individual residue data collected immediately after the application through the first 

day where all of the residue values were below the LOQ (0.00625 μg/cm2

). HED used a value of 

1⁄2 the LOD for residue values which dropped below the LOD and 1⁄2 the LOQ when values 

dropped below the LOQ but were greater than the LOD. As shown in Appendix B, HED's 

estimated half-life value was 4.11 days (R2 = 0.838). 

III DISCUSSION:

A. LIMITATIONS OF THE STUDY:

This study met the majority of the Series 875.2100 Guidelines. The following issues of concern 

are noted: 

• The production of metabolites, breakdown products, or the presence of contaminants of 

concern were not discussed in the Study Report. However, the imazosulfuron parent 

compound has been selected as an adequate marker for tolerance enforcement. 

• DFR data should be collected from at least three geographically distinct locations but only 

one geographical location was used in this study. 

• The field fortification levels used in the study (0.0500 and 0.250 μg/cm2

). 

• Field fortifications were performed on only three of the study days -- days 1, 7, and 14. 

• Information verifying that the application equipment was properly calibrated was not 

included in the Study Report. 

• It is uncertain if this site is representative of reasonable worst-case climatic conditions 

expected in intended use areas. Meteorological conditions including temperature, wind 

speed, daily rainfall, and humidity were not provided for the duration of the study. Only 

precipitation/irrigation data were provided for the duration of the study.
Dislodgeable Foliar Residue (2008)/Page 13 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

• Results from a separate storage stability study were not provided with the study. Field 

fortification samples were intended to assess the stability of imazosulfuron during storage. 

The longest storage interval for a field sample was 55 days, and the longest storage interval 

for a set of field fortification samples was 55 days (demonstrating an overall recovery >90%). 

• The Registrant validated the analytical method using samples fortified at 0.0063 and 0.031 

μg/cm2. One concurrent laboratory fortified sample was analyzed with a concentration 

approximating the highest concentration found in the field samples (0.808 μg/cm2). The 

concurrent recovery for this laboratory fortified sample was corrected based on the percent 

recovery (85.8%). 

• According to the product label, the maximum application rate is 0.3 lb ai/A. In this study, the 

target application rate was 0.5 lb ai/A. 

B. CONCLUSIONS: 

Immediately following application of imazosulfuron, 15.8% of the original application rate was 

dislodged from the tomato leaves. Average DFR values dissipated rapidly from 0.761 μg/cm2

collected at approximately 1 hr after the application to 0.163 μg/cm2

 by Day 1; average DFR 

residues then declined gradually to less than the LOD by Day 35. 
Dislodgeable Foliar Residue (2008)/Page 14 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Table 3. Imazosulfuron DFR Residues from Tomato Leaves Treated with V-10142 75 WDG 

Sample Interval 

Measured 

Residue 

(μg/cm2) 

Arithmetic 

Mean 

(μg/cm2) 

Standard 

Deviation 

(μg/cm2) 

Coefficient of 

Variance 

(%) 

Natural Log of 

Mean 

(μg/cm2) 

Percent of 

Application 

Rate 

Dislodgeable

0.942 

0.042DAT 0.902 a 

0.818 

0.887 0.063 7.11 -0.121 15.8 

0.218 

1 DAT 0.140 

0.130 

0.163 0.048 29.6 -1.816 -- 

0.135 

2 DAT 0.118 

0.0770 

0.110 0.030 27.11 -2.207 -- 

0.0980 

3 DAT 0.0923 

0.0929 

0.094 0.003 3.3 -2.360 -- 

0.0800 

4 DAT 0.0636 

0.0602 

0.068 0.011 15.6 -2.689 -- 

0.0423 

5 DAT 0.0492 

0.0713 

0.054 0.015 27.9 -2.914 -- 

0.0505 

7 DAT 0.0417 

0.0455 

0.046 0.004 9.6 -3.081 -- 

0.0321 

10 DAT 0.0254 

0.0216 

0.026 0.005 20.2 -3.636 -- 

0.0101 

14 DAT 0.0116 

<LOQ 

0.008 0.005 54.65 -4.795 

0.0063 

21 DAT 0.0080 

0.0109 

0.008 0.002 27.7 -4.780 -- 

<LOQ 

28 DAT <LOD 

<LOQ 

0.003 0.001 35.0 -5.952 -- 

<LOD

35 DAT <LOD

<LOD

0.002 0.000 0.0 -6.470 -- 

a Measured residues for Day 0 were corrected based on concurrent laboratory recovery of highest fortified sample 

(85.8%). Actual measurements were: 0.808, 0.774, and 0.702 μg/cm2

. 

DAT = Day after Treatment 

LOQ = 0.00625 μg/cm2 
Dislodgeable Foliar Residue (2008)/Page 15 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 
Dislodgeable Foliar Residue (2008)/Page 16 of 22 

Imazosulfuron/PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

APPENDIX A 

Compliance Checklist for 

“Dissipation of Dislodgeable Foliar Residues of Imazosulfuron on Tomato Leaves”
Dislodgeable Foliar Residue (2008)/Page 17 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Compliance Checklist for 

"Dissipation of Dislodgeable Foliar Residues of Imazosulfuron on Tomato Leaves" 

Compliance with OPPTS Series 875, Occupational and Residential Exposure Test Guidelines, 

Group B: Postapplication Exposure Monitoring Test Guidelines, Dislodgeable Foliar Residue 

Dissipation: Agricultural, 875.2100 is critical. The itemized checklist below describes 

compliance with the major technical aspects of OPPTS 875.2100. 

• The test substance must be the typical end use product of the active ingredient. This criterion was 

met. 

• The production of metabolites, breakdown products, or the presence of contaminants of concern, 

should be considered in the study design on a case-by-case basis. It is not certain if this criterion was 

met. Metabolites or breakdown products for imazosulfuron were not discussed in the Study Report. 

However, the imazosulfuron parent compound has been selected as an adequate marker for tolerance 

enforcement. 

• Applications should occur at the time of season that the end-use product is normally applied to 

achieve intended pest control. This criterion was met. 

• Initiating testing immediately before a precipitation event should be avoided. This criterion was met. 

• The end use product should be applied by the application method recommended for the crop. 

Information that verifies that the application equipment (e.g., sprayer) was properly calibrated 

should be included. These criteria were partially met. The Study Report stated that the application 

equipment at each test site was calibrated before use. However, the procedures used for calibrating 

the equipment were not provided in the Study Report 

 

• The application rate used in the study should be provided and should be the maximum rate specified 

on the label. However, monitoring following application at a typical application rate is more 

appropriate in certain cases. This criterion was mostly met. According to the product label, the 

maximum application rate is 0.3 lb ai/A. In this study, the target application rate was 0.5 lb ai/A. 

• If multiple applications are made, the minimum allowable interval between applications should be 

used. Not applicable. Only one application was made. 

• Dislodgeable foliar residue (DFR) data should be collected from at least three geographically 

distinct locations for each formulation and crop type. The sites should be representative of the 

regions (and crops) where the chemical is used. Technically, this criterion was not met. Only one 

geographical location was used in this study. However, persistence of residues in California is 

expected to be higher due to minimal rainfall, and the DFR data are well representative of the 

anticipated geographical high use areas of tomatoes and peppers. 

• The site(s) treated should be representative of reasonable worst-case climatic conditions expected in 

intended use areas. Meteorological conditions including temperature, wind speed, daily rainfall, and 

humidity should be provided for the duration of the study. These criteria were partially met. Air 

temperature, wind speed, wind direction, and rainfall were recorded for each application event. Only 

precipitation/irrigation data were provided for the duration of the study.
Dislodgeable Foliar Residue (2008)/Page 18 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

• Sampling should be sufficient to characterize the dissipation mechanisms of the compound (e.g., three 

half-lives or 35 days after the final application, unless the compound has been found to fully dissipate 

in less time; for more persistent pesticides, longer sampling periods may be necessary). Sampling 

intervals may be relatively short in the beginning and lengthen as the study progresses. Background 

samples should be collected before application of the test substance occurs. These criteria were met. 

Samples were collected out to 35 days after the application. 

• Triplicate, randomly collected samples should be collected at each sampling interval. This criterion 

was met. 

• A leaf punch apparatus should be used unless the nature of the crop precludes its use. Samples 

should represent at least an area of 400 cm2

. These criteria were met. 

• Control plots should be established from which sufficient control samples can be collected. Control 

sites should be upwind and a reasonable distance from the treatment site. These criteria were mostly 

met. However, it is uncertain if the control plots were located upwind and at a reasonable distance 

from the treated plots. 

• Residues should be dislodged from leaf surfaces using an aqueous surfactant solution within a 

reasonable time period (i.e., EPA recommends that dislodging occur within 4 hours). Dislodging 

should be repeated at least once and the resultant solutions pooled for analysis. This criterion was 

met. 

• Samples should be stored in a manner that will minimize deterioration and loss of analytes between 

collection and analysis. Information on storage stability should be provided. These criteria were met. 

A storage stability study was not performed. However, storage stability of imazosulfuron during the 

study period was demonstrated by analysis of fortified field samples stored and shipped under the 

same conditions as the field samples. 

• Validated analytical methods of sufficient sensitivity are needed. Information on method efficiency 

(residue recovery), and limit of quantitation (LOQ) should be provided. These criteria were met. The 

limit of quantitation (LOQ) was 0.00625 μg /cm2

. The method was validated prior to sample analysis 

using samples fortified at 0.0063 and 0.031 μg/cm2

. Field samples with high concentration were 

diluted up to 16 times for quantitation purposes. 

• Information on recovery samples must be included in the study report. A complete set of field 

recoveries should consist of at least one blank control sample and three or more each of a low-level 

and high-level fortification. These fortifications should be in the range of anticipated residue levels 

in the field study. This criterion was partially met. The field fortification samples were prepared at 

two levels: 0.0500 and 0.250 μg/cm2

. Many of the first field samples collected demonstrated residue 

levels higher than the highest field fortification value. 

• Raw residue data must be corrected if appropriate recovery values are less than 90 percent. This 

criterion did not apply. Average low and high level field fortification recoveries were >90%, therefore 

the raw residue data did not require correction. 

• Dislodgeable foliar residues should be reported as mg or μg per m2

 or cm

2

 of leaf sampled. 

Distributional data should be reported, to the extent possible. This criterion was met. 
Dislodgeable Foliar Residue (2008)/Page 19 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

APPENDIX B 

Regression Analysis Results 
Dislodgeable Foliar Residue (2008)/Page 20 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Regression Analysis: Summary Output for Imazosulfuron - CA 

Regression Statistics 

Multiple R 0.908947 

R Square 0.826185 

Adjusted R2 0.820578 

Standard Error 0.68183 

Observations 33 

ANOVA 

 df SS MS F Signif. F 

Regression 1 68.50204 68.50204 147.35053 2.5873E-13 

Residual 31 14.41164 0.464892

Total 32 82.91368 

 Coeff. Std. Error t Stat P-value Lower 95% Upper 95% 

Intercept -1.69607 0.168759 -10.0502 2.843E-11 

-

2.04025067 

-

1.35187967 

Slope -0.16854 0.013885 -12.1388 2.587E-13 

-

0.19686118 

-

0.14022526 

Half Life = 4.112578 Days 

Predicted DFR Levels 

Time (Days) 

Residue 

(ug/cm2

) 

Time 

(Days) 

Residue 

(ug/cm2) 

0 0.183404 21 0.0053243 

1 0.154957 22 0.0044985 

2 0.130922 23 0.0038007 

3 0.110616 24 0.0032112 

4 0.093458 25 0.0027131 

5 0.078963 26 0.0022923 

6 0.066715 27 0.0019368 

7 0.056367 28 0.0016364 

8 0.047624 29 0.0013826 

9 0.040238 30 0.0011681 

10 0.033997 31 0.0009869 

11 0.028723 32 0.0008339 

12 0.024268 33 0.0007045 

13 0.020504 34 0.0005952 

14 0.017324 35 0.0005029 

15 0.014637 

16 0.012367 

17 0.010448 

18 0.008828 

19 0.007459 

Page 20 of 22 
Dislodgeable Foliar Residue (2008)/Page 21 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

20 0.006302 

Regression Analysis: Means and CVs for Imazosulfuron - CA 

Days after Last 

Treatment 

Residues 

(ug/cm2

) 

Mean 

(ug/cm2) 

Standard 

Deviation 

(ug/cm2) 

Coefficient 

of 

Variation 

(%) 

0.042 0.941725 0.887 0.0631 7.11 

0.902098 

0.818182 

1 0.218000 0.163 0.0482 29.6 

0.140000 

0.130000 

2 0.135000 0.11 0.0298 27.1 

0.118000 

0.077000 

3 0.098000 0.0944 0.00313 3.32 

0.092300 

0.092900 

4 0.080000 0.0679 0.0106 15.6 

0.063600 

0.060200 

5 0.042300 0.0543 0.0151 27.9 

0.049200 

0.071300 

7 0.050500 0.0459 0.00441 9.62 

0.041700 

0.045500 

10 0.032100 0.0264 0.00532 20.1 

0.025400 

0.021600 

14 0.010100 0.00828 0.00452 54.6 

0.011600 

0.003125 

21 0.006300 0.0084 0.00233 27.7 

0.008000 

0.010900 

28 0.003125 0.0026 0.000909 35 

0.001550 

0.003125 

Page 21 of 22 
Dislodgeable Foliar Residue (2008)/Page 22 of 22 

Imazosulfuron//PC Code 118602 OPPTS 875.2100 / DACO 5.9a 

Page 22 of 22