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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

 POLLUTION PREVENTION

MEMORANDUM

Date: 14-August-2013

Subject: Linuron. Petition for the Establishment of Permanent Tolerances and Registration 

for Use on Coriander, Dill, Parsley, Pea (Dry), and Horseradish; and Submission of 

Residue Analytical Methods of Plants and Animal Matrices. Summary of Analytical 

Chemistry and Residue Data. 

PC Code: 035506 DP Barcodes: D404359, D411652

Decision No.: 469722 Registration No.: 61842-23

Petition No.: 2E8083 Regulatory Action: Section 3

Risk Assessment Type: NA Case No.: NA

TXR No.: NA CAS No.: 330-55-2

MRID No.: See Appendix A 40 CFR:§180.184

From: Nancy Tsaur, Chemist

Risk Assessment Branch 3 (RAB3)

Health Effects Division (7509P)

Through: Steve Funk, Senior Chemist

Risk Assessment Branch 3 (RAB3)

Health Effects Division (7509P)

To: Kristin Rury, Biologist, Risk Assessor

Risk Assessment Branch 3 (RAB3)

Health Effects Division (7509P)
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Table of Contents

1.0 Executive Summary............................................................................................................ 3

2.0 Regulatory Recommendations............................................................................................ 3

2.1 Tolerance Considerations................................................................................................. 3

2.1.1 Enforcement Analytical Method............................................................................... 3

2.1.2 Recommended Tolerances........................................................................................ 4

2.2.3 Revisions to Petitioned-For Tolerances.................................................................... 5

2.2.4 International Harmonization ..................................................................................... 5

3.0 Introduction......................................................................................................................... 5

3.1 Chemical Identity ............................................................................................................. 6

3.2 Physical/Chemical Characteristics................................................................................... 6

3.3 Pesticide Use Pattern/Directions for Use (860.1200)....................................................... 7

4.0 Metabolite/Degradate Residue Profile................................................................................ 8

4.1 Nature of the Residue....................................................................................................... 8

4.2 Comparison of Metabolic Pathways ................................................................................ 9

4.3 Residues of Concern Summary and Rationale................................................................. 9

5.0 Residue Profile.................................................................................................................. 10

5.1 Residue Analytical Methods (860.1340)........................................................................ 10

5.2 Submittal of Analytical Reference Standards (860.1650).............................................. 11

5.3 Storage Stability (860.1380) .......................................................................................... 11

5.4 Residue Data .................................................................................................................. 12

5.4.1 Crop Field Trials (860.1500) .................................................................................. 12

5.4.2 Meat, Milk, Poultry and Eggs (860.1480) .............................................................. 13

5.5 Food Residue Profile...................................................................................................... 13

6.0 Tolerance Derivation ........................................................................................................ 13

Appendix A. Summary of Submitted Residue Chemistry Studies.............................................. 15

Appendix B. International Residue Limits Table for Linuron..................................................... 16

Appendix C. OECD MRL Calculation Procedure Inputs/Outputs.............................................. 17
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1.0 Executive Summary

Interregional Research Project No. 4 (IR-4) has submitted a petition (PP#2E8083) for tolerances 

on coriander, dill, parsley, pea (dry), and horseradish; and has proposed to add these uses to the 

Tessenderlo Kerley label for Lorox® DF (EPA Reg. No. 61842-23). IR-4 has submitted crop 

field trials utilizing comparable formulations, all of which consist of 50% active ingredient (ai) 

in a dry flowable formulation. The residue chemistry database is adequate for tolerance 

assessment of the proposed uses.

Based on residues found in forage/foliage from three plant metabolism studies where the active 

ingredient was applied in a soil-directed fashion early in the growing season, linuron is 

understood to have systemic activity in plants. The field trials indicate that finite residues are 

found in food commodities and that the residues concentrate upon drying herbs and/or 

processing dill for oil. It has been shown that linuron and its metabolites, including unknown 

metabolites characterized as polar, can be converted quantitatively to 3,-4-dichloroaniline (3,4-

DCA). Therefore, linuron can be regulated by using the enforcement analytical method in which

identified metabolites, unidentified polar components, and bound residues in plant and animal 

commodities are hydrolyzed to 3,4-DCA. The total residue convertible to 3,4-DCA will be 

compared to the reference dose for parent linuron for purposes of dietary risk assessment.

Concomitant with this IR-4 petition, additional analytical method data have been submitted by 

Tessenderlo Kerley to support the newly proposed uses. A new enforcement method for plant 

and livestock commodities was previously required as conditional data (K. Rury, DP375451, 

04/01/2010). A high performance liquid chromatography/tandem mass spectrometry

(HPLC/MS/MS) method based on extraction of residues and identification of parent and specific 

metabolites has been submitted. Also submitted was a method that hydrolyzes commodities 

with base to transform the total linuron residue to 3,4-DCA. Gas chromatography with mass 

spectrometry detection (GC/MS) is used to quantitate the 3,4-DCA. Independent laboratory

validation of the latter method has been provided. In reviewing these data, HED has determined 

that the continued use of a common moiety definition (1,3-dichloraniline) is appropriate, and that 

the validated GC/MS method for 3,4-DCA will be adequate for tolerance enforcement purposes. 

Thus, the requirement for additional enforcement analytical methods is fulfilled.

2.0 Regulatory Recommendations

HED has examined the residue chemistry database for linuron and concluded that, provided a 

revised label and a revised Section F, there are no residue chemistry deficiencies that would 

preclude granting Section 3 registration for the requested crop commodity uses of linuron, or 

establishment of tolerances for residues of linuron. The specific tolerance recommendations are 

discussed in Section 2.1.2.

2.1 Tolerance Considerations

2.1.1 Enforcement Analytical Method

Various acceptable enforcement methods are available.
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For linuron residues of concern in plant commodities, Method ABC-68406-M, is available and 

suitable for the enforcement of tolerances. This method involves reflux of crop samples in 

strong base to hydrolyze residues of linuron and its metabolites to 3,4-DCA. Then, 3,4-DCA is 

analyzed by gas chromatography with mass spectrometry detection (GC/MS). Based on the 

lowest level of method validation (LLMV) from the independent laboratory validation (ILV) 

study, the validated limit of quantitation (LOQ) is 0.01 ppm for linuron and its metabolites 

hydrolyzable to 3,4-DCA in/on oily (soybean seed), watery (celery), and starch (potato) crop 

matrices.

In addition, Method ABC-65790 is a confirmatory method that is also available that may be used 

to confirm results from the use of Method ABC-68406-M. In this method, extractions are 

conducted with methanol and each analyte is analyzed by liquid chromatography/tandem mass 

spectrometry (LC/MS/MS). This method separately determines residues of linuron and 

metabolites 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), N-(3,4-dichlorophenyl)urea 

(DCPU), and desmethyl linuron in crop commodities. Based on the LLMV, the validated LOQ 

is 0.01 ppm each for linuron, DCPMU, DCPU, and desmethyl linuron.

For linuron residues of concern in livestock commodities Method ABC-67638-M is available 

and suitable for the enforcement of tolerances. This method involves reflux of livestock 

commodity samples in strong base to hydrolyze residues of linuron and its metabolites to 3,4-

dichloroaniline (3,4-DCA). Then, 3,4-DCA is analyzed by gas chromatography with mass 

spectrometry detection (GC/MS). Based on the LLMV, the validated LOQ is 0.01 ppm for 

linuron and its metabolites hydrolyzable to 3,4-DCA in milk, muscle, and liver.

2.1.2 Recommended Tolerances

In addition to the recommended tolerances listed below in Table 2.2.2, the tolerance with 

regional registration under 40 CFR §180.184(c) for parsley, leaves (0.25 ppm) should be deleted.

Table 2.2.2. Tolerance Summary for Linuron.

Commodity Established/Proposed 

Tolerance (ppm)

HED-Recommended 

Tolerance (ppm)

Comments

(correct commodity definition)

Cilantro, fresh leaves 3.0 1.5 coriander, leaves

Cilantro, dried leaves 27 10 coriander, dried leaves

Coriander, seed 0.01 0.05

Dillweed, fresh leaves 1.5 0.6

Dillweed, dried leaves 7.1 3.0

Dill, seed 0.3 0.5

Dill, oil 4.8 2.0

Horseradish 0.05 0.05

Parsley, leaves 3.0 4.0

Parsley, dried leaves 8.3 3.0

Pea, dry, seed 0.08 0.06
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2.2.3 Revisions to Petitioned-For Tolerances

All of the petitioned-for tolerance levels(except for horseradish) must be revised to reflect the 

tolerance levels recommended by HED for linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-

methylurea) and its metabolites convertible to 3,4-dichloroaniline, calculated as linuron, in or on 

the commodities.

The Organization for Economic Cooperation and Development (OECD) calculation procedures

were used to calculate the tolerance levels for the following three commodities: cilantro, fresh 

leaves; dillweed, fresh leaves; and pea, dry, seed. Based on the OECD calculations, all three 

tolerance levels should be decreased.

Instead of using the OECD calculator due to a limited number of field trials, the formula of 5X 

the mean was used to establish tolerance levels for the following three commodities: coriander, 

seed; dill, seed; and parsley, leaves. Based on this calculation method, all three tolerance levels 

should be increased.

For the dried herbs (cilantro, dillweed, and parsley) and the dill oil, the formula of the highest 

average field trial (HAFT) multiplied by the concentration factor was used to calculate the 

recommended tolerance levels (the concentration factors were derived from dividing the average 

dried/oil commodity residue by the average fresh commodity residue). Based on this calculation 

method, all four tolerance levels should be decreased.

2.2.4 International Harmonization

There are no established maximum residue limits (MRLs) for linuron in Codex for any

agricultural commodity. Furthermore, no Canadian or Mexican MRLs have been established for 

linuron. Therefore, there are no harmonization issues that exist with respect to U.S. tolerances.

2.3 Label Recommendations

Since there are livestock feed items associated with field pea, the following restriction should be 

added to the label: “Do not apply to field pea used for livestock feed.”

3.0 Introduction

Linuron is a selective phenylurea herbicide used to control broadleaf weeds and annual grasses

by systemically inhibiting photosynthesis. It may be applied pre-plant, pre-emergence, postemergence or post-transplant to various field crops and noncrop areas.
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3.1 Chemical Identity

Table 3.1. Linuron Nomenclature.

Compound

Common name Linuron

Company experimental name DPX-Z0326

IUPAC name 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea

CAS name N‘-(3,4-dichlorophenyl)-N-methoxy-N-methylurea

CAS # 330-55-2

End-use product/EP

Metabolite

Common name DCPMU

Chemical name 3-(3,4-dichlorophenyl)-1-methylurea

Metabolite

Common name DCPU

Chemical name N-(3,4-dichlorophenyl)urea

Metabolite

Common name Desmethyl linuron

Chemical name N-(3,4-dichlorophenyl)-N‘-methoxyurea

3.2 Physical/Chemical Characteristics

Linuron is an off-white powder with a molecular weight of 249.1 g/mol, which indicates that the 

potential to cross biological barriers, such as the skin, is somewhat limited. Furthermore, the low 

log of the octanol/water partition coefficient (log Pow = 2.76 at 25C) suggests low potential for 

dermal absorption; the relatively low water solubility and low lipophilic potential, indicate that 

linuron is not likely to bioaccumulate. The vapor pressure for linuron is low (3.011×10-7 mm Hg 

at 25C), and linuron is considered relatively insoluble in water. The Henry’s Law constant was 

calculated to be 1.97×10-9atm·m

3

/mol. Thus, linuron is unlikely to volatilize significantly, and 

N

H

Cl

Cl

O

N

O

CH3

CH3

N

H

Cl

Cl

O

N

H

CH3

N

H

Cl

Cl

O

NH2

N

H

Cl

Cl

O

N

H

O

CH3
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inhalation via chemical vaporization is unlikely. 

Linuron is moderately persistent with an aerobic soil metabolism half-life ranging from 57 to 100 

days. Because parent linuron is sufficiently persistent and may be mobile under certain 

environmental conditions, it has the potential to impact ground water quality. More detailed 

physicochemical properties of the technical grade of linuron are summarized in Table 3.2.

Table 3.2. Physicochemical Properties of the Technical Grade Test Compound Linuron.

Parameter Value Reference

Molecular weight (g/mole) 249.1 42213301

Melting point/range 91-94±1°C 42213301

pH 6.98, 7.09 for a 0.2% solution and 9.38, 

9.41, for a 2.5% solution at 22.5±0.5C

42213301

Density 1.4963 g/mL at 22.3±0.5C 

(air comparison pycnometer)

42213301

Water solubility (20.5 ± 0.5 C) 5.88×10-3

g/100 mL 42213301

Solvent solubility (20 C)

dichloromethane 44.1 g/100 mL

toluene 7.91 g/100 mL

methanol 12.6 g/100 mL

hexane 0.220 g/100 mL

42213301

Vapor pressure at 25°C 4.015×10-5

Pa

3.011×10-7 mm Hg 42213303

Henry’s Law Constant at 25°C 1.97×10-9atm·m3/mol http://toxnet.nlm.nih.gov

Dissociation constant (pKa)

dissociation constant could not be 

determined; physical and chemical 

properties deemed all methods in OECD 

guidelines inappropriate

42213302

Octanol/water partition coefficient 

Log(KOW)

8.2×102at 23±1C (GC method)

log Pow = 2.76 42213301

3.3 Pesticide Use Pattern/Directions for Use (860.1200)

IR-4 is proposing new uses for the 50% DF formulation Lorox® DF (EPA Reg. No. 61842-23). 

The use directions are summarized below in Table 3.3.

Table 3.3. Summary of Proposed Directions for Use of Linuron (Lorox® DF, EPA Reg. No. 61842-23).

Application, 

Type, and 

Equipment

App Rate

(lb ai/A)

Timing

Max No. 

App per 

Season

Max. 

Seasonal 

App Rate

(lb ai/A)

PHI

(days) Product Use Directions and Limitations

Coriander

Broadcast

Ground, 

Chemigation

0.5 - 1.0

preemergence

1

2.0

East of 

Rocky Mtns

1.5

West of 

Rocky Mtns

21

Do not apply by air. Do not apply to sand or loamy 

sand soil types to avoid crop injury. Do not use on 

soils with less than 1% organic matter to avoid crop 

injury. Do not exceed 4 lbs. LOROX® DF per acre 

per year East of Rocky Mountains. Do not exceed 3 

lbs. LOROX® DF per acre per year West of Rocky 

Mountains. Additional applications allowed, but do 

not exceed maximum rate. Do not apply within 155 

days of harvest for seed.

0.5 - 1.0

postemergence

2
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Dill

Broadcast

Ground, 

Chemigation

1.0

preemergence

1

2.0

East of 

Rocky Mtns

1.5

West of 

Rocky Mtns

21

Do not apply by air. Do not apply to sand or loamy 

sand soil types to avoid crop injury. Do not use on 

soils with less than 1% organic matter to avoid crop 

injury. Do not exceed 4 lbs. LOROX® DF per acre 

per year East of Rocky Mountains. Do not exceed 3 

lbs. LOROX® DF per acre per year West of Rocky 

Mountains. Additional applications allowed, but do 

not exceed maximum rate.

0.5 - 1.0

postemergence

2

Parsley

Broadcast

Ground, 

Chemigation

0.5 - 1.5

preemergence

1 1.5

30

Do not apply by air. Apply after planting, but before 

the crop emerges. Do not exceed a total of 3 lbs. of 

LOROX® DF per acre per season. Use lower rates 

on coarse soils and higher rates on heavier soils. 0.5

postemergence

1 0.5

Parsley Grown for Seed (Oregon and Washington Only)

Broadcast

Ground, 

Chemigation

0.5 - 1.0

preemergence

2 2.0 NA

Do not apply by air. For best results apply 

preemergence to weeds or early postemergence 

while weeds are small. Wait at least 21 days 

between applications. Do not make more than two 

applications in the first growing season and do not 

make more than two applications in the second

growing season.

Pea (Dry)

Broadcast

Ground, 

Chemigation

1.0

preemergence

1 1.0 NA

Do not apply by air. Do not apply to sand or loamy 

sand soil types. Do not use on soils with less than 

1% organic matter. Apply post planting but 

preemergence to the crop. Use lower rates on coarse 

soils and higher rates on heavier soils.

Horseradish

Broadcast

Ground, 

Chemigation

1.5

preemergence

1 1.5 NA

Do not apply by air. Apply after planting or during 

dormancy, but before the leaves emerge in spring. 

Use lower rates on lighter soils and higher rates on 

heavier soils.

Conclusions: The submitted use directions are adequate to allow evaluation of the residue data 

relative to the proposed use pattern for coriander, dill, parsley, pea (dry), and horseradish.

4.0 Metabolite/Degradate Residue Profile

4.1 Nature of the Residue

New metabolism data were not submitted to support this registration request. The qualitative 

nature of the residue in plants and animals is adequately understood. The chemical structures of 

the metabolites of concern are listed in Table 3.1.

Plant metabolism studies show the major plant metabolites to be DCPMU and DCPU. There 

was a significant amount of unidentified polar components in corn, potato, and soybean plant 

metabolism studies; however, it was concluded that the components in plants are hydrolyzable to 

3,4-dichloroaniline (3,4-DCA). There was almost quantitative conversion (via base hydrolysis) 
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of the total radioactive residue (TRR) to 3,4-DCA in the metabolism studies.

In animals, linuron is metabolized to DCPU and hydroxy-norlinuron (through DCPMU and 

desmethyl-linuron intermediates). Small amounts of 3,4-DCA were detected in both the corn 

and poultry studies. 

Water degradates identified in linuron aerobic soil metabolism are the same as the identified 

plant metabolites. 

4.2 Comparison of Metabolic Pathways

The metabolic pathways in plants and livestock are similar. Linuron is converted to DCPMU, 

DCPU, hydroxy-norlinuron, and unidentified polar metabolites, all of which may be converted to 

3,4-DCA via base hydrolysis..

Metabolism studies also illustrate the distribution of residues of linuron within plant and animals. 

Radiolabeled 14C-linuron equivalents were found at the highest levels in the forage or foliage of 

corn, potato, and soybean following early season soil-directed application of linuron. Detectable 

residues (0.01 – 0.03 ppm) were also found in the potato tuber and corn grain, and quantifiable 

residues were found in soybean seed. Linuron and/or its metabolites are systemic.

In animals, the highest levels of 14C-linuron equivalents were found in the liver of both goat and 

poultry. No intact linuron (<0.001 ppm) was detected in the milk, tissues, or urine of the test 

animals, except egg yolk. Approximately 95% of the radioactivity in milk was characterized as 

polar metabolites.

For both livestock and plant commodities, the residues listed in the tolerance expression are the 

same as those that will be included in the dietary risk assessment, linuron and metabolites 

convertible to 3,4-DCA. This essentially encompasses the entire total radioactive residues from 

plant and livestock metabolism studies.

In rats, the major metabolites identified in the urine were hydroxy-norlinuron, DCPU, and 

DCPMU; and those in feces were hydroxy-norlinuron and DCPU. The major metabolites DCPU 

and DCPMU were identified in the rat metabolism study, in both plant and animal metabolism 

studies, and as water metabolites in the aerobic soil metabolism study. These metabolites, in 

addition to desmethyl-linuron, are the metabolites of toxicological concern referenced in the 

tolerance expression and considered in this risk assessment. Neither hydroxy-3,4-

dichloroanaline, 3,4-dichloroanaline nor 3,3',4,4'-tetrachloroazobenzene (TCAB) were present in 

any of the samples in the rat metabolism study. 

4.3 Residues of Concern Summary and Rationale

D. McNeilly. 11/17/1993. Linuron Plant and Animal Metabolism: Results of the HED Metabolism Committee 

Meetings held October 21, and October 29, 1993. MARC Decision Memo.

The residue definitions for enforcement of tolerance and for risk assessment are identical, 

namely, linuron and metabolites convertible to 3,4-DCA.
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The terminal residues of concern in plants and animals are linuron (parent) and metabolites 

convertible to 3,4-DCA including DCPMU, DCPU, desmethyl linuron, and hydroxy-norlinuron. 

3,4-DCA is not of regulatory concern in connection with the registered use of linuron due to the 

very low levels at which the chemical is detected in plants and animals (<0.01ppm). Metabolites 

convertible to 3,4-DCA are not likely to be more toxic than the parent compound. Linuron can 

therefore be regulated by using the enforcement analytical method in which known metabolites 

and unidentified polar components in plants and bound residues in animal tissues are hydrolyzed 

to 3,4-DCA. The total residue convertible to 3,4-DCA will be compared to the reference dose 

for parent linuron for purposes of dietary risk assessment. 

The linuron drinking water exposure assessment is based upon review of environmental fate 

studies for parent linuron, modeling and monitoring results for parent linuron, and modeling 

results for the degradates of linuron based upon parent linuron model input parameters. Parent 

linuron appears to be moderately persistent and relatively immobile. Water degradates identified 

in the linuron aerobic soil metabolism study are desmethyl linuron, DCPMU, and DCPU. The 

degradate 3,4-DCA was not included in the water assessment as it was not detected in the 

aerobic soil metabolism study (0.01 ppm detection limit). According to acceptable fate studies, 

3,4-DCA is formed under anaerobic aquatic conditions rarely found in the environment and is 

not relevant to drinking water assessment. The environmental fate assessment for linuron is 

incomplete and tentative because information on the persistence, mobility and dissipation 

pathways of several degradates of linuron is not available. However, none of the linuron water 

degradates are present at levels greater than 10% of the applied parent, and therefore not 

considered major water metabolites.

Table 4.3. Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance 

Expression

Matrix Residues included in Risk Assessment Residues included in Tolerance 

Expression

Plants Primary Crop

linuron and 

metabolites convertible to 3,4-DCA

linuron and metabolites convertible to 

3,4-DCA

Rotational Crop

Livestock Ruminant

Poultry

Drinking Water Not Applicable

5.0 Residue Profile

5.1 Residue Analytical Methods (860.1340)

Various adequately validated analytical methods are now available for linuron.

For linuron residues of concern in plant commodities, Method ABC-68406-M is available and 

suitable for residue collection as well as enforcement of tolerances. This method has been used 

previously for data collection and is used with the current field trial submissions. This method 

involves reflux of crop samples in strong base to hydrolyze residues of linuron and its 

metabolites to 3,4-DCA. Then, 3,4-DCA GC/MS. Based on the LLMV from the ILV study, the 

validated LOQ is 0.01 ppm for linuron and its metabolites hydrolyzable to 3,4-DCA in/on oily

(soybean seed), watery (celery), and starch (potato) crop matrices.
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In addition, Method ABC-65790 was presented. It is a multi-residue method that is suitable for

screening for enforcement of tolerances for linuron residues in plant commodities. It may also 

be used as a confirmatory method for Method ABC-68406. In this method, extractions are 

conducted with methanol and each analyte is analyzed by LC/MS/MS. This method separately 

determines residues of linuron and metabolites DCPMU, DCPU, and desmethyl linuron in crop 

commodities. Based on the LLMV, the validated LOQ is 0.01 ppm each for linuron, DCPMU, 

DCPU, and desmethyl linuron. Transition ions monitored were: m/z 249→160 for linuron, m/z 

219→127 for DCPMU, m/z 205→127 for DCPU, and m/z 235→160 for desmethyl linuron. 

HED notes that this method is not acceptable as the primary enforcement method because of the 

following reasons: (1) the residue definition contains components in addition to those 

determined; and (2) the method does not include a secondary ion transition for each analyte, 

which is required for enforcement methods.

For linuron residues of concern in livestock commodities Method, ABC-67638-M, is available 

and suitable for residue collection as well as enforcement of tolerances. This method involves 

reflux of livestock commodity samples in strong base to hydrolyze residues of linuron and its 

metabolites to 3,4-DCA. Then, 3,4-DCA is analyzed by GC/MS. Based on the LLMV, the 

validated LOQ is 0.01 ppm for linuron and its metabolites hydrolyzable to 3,4-DCA in milk, 

muscle, and liver.

Conclusions. The analytical methods, ABC-68406-M and ABC-67638-M, are adequate for 

enforcement of the tolerance expression and they been validated.

5.2 Submittal of Analytical Reference Standards (860.1650)

The analytical reference standard of linuron at the EPA National Pesticide Standards Repository, 

expired as of April 18, 2013. The registrant must send an updated COA, or five grams of new 

material to the Repository as soon as possible. The reference standard can be sent to the 

Analytical Chemistry Branch, to the attention of either Theresa Cole or Thuy Nguyen, at the 

address listed below:

USEPA

National Pesticide Standards Repository/Analytical Chemistry Branch/OPP

701 Mapes Road

Fort George G. Meade, MD 20755-5350

The full 9 digit zip code is mandatory or the mail will be returned to the sender.

5.3 Storage Stability (860.1380)

The storage durations and conditions of samples from the submitted crop field trials are 

presented in Table 5.3. Freezer storage stability data were generated concurrently with the crop 

field trials. Data showed that linuron residues were stable in all matrices under frozen storage 

for the duration of the storage period.
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Table 5.3 Stability of Linuron Residues in Following Storage.

Matrix Storage 

Temperature

Actual Storage Duration

(days)

Interval of Demonstrated 

Storage Stability (days)

Coriander Fresh Leaves and Stems

-21±7°C

378 - 514 530

Coriander Dried Leaves and Stems 468 427

Coriander Seed 271 288

Dill Fresh Leaves and Stems 64 - 165 212

Dill Dried Leaves and Stems 164 160

Dill Seed 31 - 128 193

Dill Oil 147 139

Parsley Fresh Leaves and Stems 264 264

Parsley Dried Leaves and Stems 220 220

Pea (Dry) 125 - 138 145 - 147

Horseradish 62 - 70 62 - 70

Conclusions: The storage stability data are adequate to support the storage intervals and 

conditions for the residue samples of coriander, dill, parsley, pea (dry), and horseradish from the 

field trials. 

5.4 Residue Data

5.4.1 Crop Field Trials (860.1500)

DER References: MRIDs 48928501, 48928502, 48928503, 48928504, 45633501, 45633502

All of the field trials were conducted according to the proposed label use directions in the 

appropriate representative geographical regions. Adjuvants were not used in any of the field 

trials. Residue decline studies were not conducted. 

Table 5.4.1. Summary of Residues from Field Trials with Linuron.

Crop Matrix Analyteb Applic. Rate

(lb ai/acre)

PHI 

(days) n

Residuesa,b (ppm)

Min. Max. HAFT Mean SD

Coriander: Proposed Use = 2.0 lb ai/acre total application rate, 21-day PHI.

Fresh Leaves and Stems

Linuron 1.997 - 2.118

19-21 8 0.08 1.14 1.055 0.65 0.4

Dried Leaves and Stems 19 1 8.5 NA NA NA

Seed 155 2 <0.01 NA NA NA

Dill: Proposed Use = 2.0 lb ai/acre total application rate, 21-day PHI.

Fresh Leaves and Stems

Linuron 2.005 - 2.026

20 - 22 7 0.3 0.67 0.56 0.48 0.1

Dried Leaves and Stems 22 2 1.8 3.5 2.65 2.65 1.2

Seed 59 - 85 4 0.06 0.12 0.12 0.09 0.03

Oil 48 1 1.8 NA NA NA

Parsley: Proposed Use = 1.5 lb ai/acre total application rate, 30-day PHI.

Fresh Leaves and Stems Linuron 1.510 29 - 32 4 0.43 1.3 1.02 0.75 0.387

Dried Leaves and Stems 1.511 29 1 2.8 2.8 2.8 NA

Pea (Dry): Proposed Use = 1.0 lb ai/acre total application rate, unspecified PHI.

Pea (Dry) 0.972 - 1.015 65 - 92 12 <0.01 0.052 0.051 0.014 0.018

Horseradish: Proposed Use = 1.5 lb ai/acre total application rate, unspecified PHI.

Roots Linuron 1.43 – 1.55 77 - 100 <0.05 NA NA NA

a HAFT = highest average field trial. SD = Standard Deviation. For samples with no detectable residues (< 0.01 ppm) 

the LOQ value (0.01 ppm) was used to calculate the Mean and Standard Deviation.

b Residues were converted to and measured as 3,4-DCA. Values were converted to linuron equivalents.
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Conclusions: The available residue data are acceptable and reflect the proposed use patterns 

provided in Section B. The number and geographical locations of the field trials are in 

accordance with the test guidelines. Furthermore, an acceptable method was used for residue 

quantitation and the data are supported by adequate storage stability data.

5.4.2 Meat, Milk, Poultry and Eggs (860.1480)

There are no feed items associated with this current petition. Cowpea commodities would affect 

the dietary burden of cattle but since they are a bean rather than a pea, they are not included in 

the petition for dry peas. Dry peas only includes the following commodities listed under 40 

CFR§180.1(g): Cajanus cajan (includes pigeon pea); Cicerspp. (includes chickpea and garbanzo 

bean); Lens culinaris (lentil);Pisumspp. (includes dwarf pea, garden pea, green pea, English 

pea, field pea, and edible pod pea). Therefore, the previous livestock dietary intake calculations 

and resulting tolerance recommendations are not changed. However, since there are livestock 

feed items associated with field pea, the following restriction should be added to the label: “ Do 

not apply to field pea used for livestock feed.”

5.5 Food Residue Profile

The residue data on coriander, dill, parsley, pea (dry), and horseradish are adequate for tolerance 

assessment and for use in dietary risk assessment. Based on detectable residues found in 

forage/foliage of a few metabolism studies, linuron is assumed to have systemic activity in 

plants. Finite residues of linuron and/or its metabolites are anticipated on food and feed 

commodities, even from early season soil-directed applications. Transfer to livestock 

commodities has been demonstrated, although the residue is primarily metabolites and 

unidentified polar components. The analytical methods account for the total residue by 

conversion of parent, metabolites, and polar, and bound (non-releasable) components to 3,4-

DCA.

6.0 Tolerance Derivation

As shown in Appendix C, the statistical goal of the OECD calculation procedures is to produce 

an MRL proposal in the region of the 95th percentile of the underlying residues distribution. 

Coriander (MRID 48928501)

The dataset used to establish a tolerance for linuron consisted of field trial data on coriander 

representing two applications within -5% to +10% of 1 lb ai/A per application for a total of 2 lb 

ai/A per crop, and 19- to 21-day PHIs. The average residue values used to calculate the 

tolerance are provided below. Combined residues of linuron and its metabolites hydrolyzed to 

2,4-DCA were quantifiable (LOQ = 0.01 ppm) in/on samples. Data from four field trials were 

used in the OECD tolerance calculation procedures for fresh coriander, resulting in a 

recommended tolerance of 1.5 ppm. For dried coriander, a 9X concentration factor was derived 

from a single residue field trial where the coriander was dried, resulting in a recommended 

tolerance of 10 ppm (calculated by: HAFT of fresh coriander residue 1.055 ppm × concentration 

factor 9). For coriander seed, no detectable residues were found, resulting in a recommended 

tolerance of 0.05 ppm (calculated by: 5 × LOQ 0.01 ppm).
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Dill (MRID 48928502)

The dataset used to establish a tolerance for linuron consisted of field trial data on dill 

representing two applications within -5% to +10% of 1 lb ai/A per application for a total of 2 lb 

ai/A per crop, and 20- to 22- day PHIs. The average residue values used to calculate the 

tolerance are provided below. Combined residues of linuron and its metabolites hydrolyzed 

to3,4-DCA were quantifiable (LOQ = 0.01 ppm) in/on all samples. Data from three field trials 

were used in the OECD tolerance calculation procedures for fresh dill, resulting in a

recommended tolerance of 0.6 ppm. For dried dill, a 4.73X concentration factor was derived 

from a single residue field trial where the dill was dried, resulting in a recommended tolerance of 

3.0 ppm (calculated by: HAFT of fresh dill 0.56 ppm × concentration factor 4.73). For dill seed, 

the OECD calculation procedures could not be used because there were only two field trials, thus 

resulting in a recommended tolerance of 0.5 ppm (calculated by: 5 × mean dill oil residue 0.9 

ppm). For dill oil, a 3.21X concentration factor was derived from a single residue field trial, 

resulting in a recommended tolerance of 2.0 ppm (calculated by: HAFT of fresh dill 0.56 ppm × 

concentration factor 3.21).

Parsley (MRID 48928503)

The dataset used to establish a tolerance for linuron consisted of field trial data on parsley

representing one application of 1.51 lb ai/A and 29- to 32-day PHIs. The average residue values 

used to calculate the tolerance are provided below. Although the LOQ were not statistically

calculated in this study, all combined residues of linuron and its metabolites hydrolyzed to 2,4-

DCA were quantifiable in/on samples above the LLMV (0.05 ppm). For fresh parsley, the 

OECD calculation procedures could not be used because there were only two field trials, thus 

resulting in a recommended tolerance of 4.0 ppm (calculated by: 5 × mean fresh parsley residue 

0.75 ppm). For fresh parsley, the recommended tolerance is 4.0 ppm. For dried parsley, a 2.76X 

concentration factor was derived from a single residue field trial where parsley was dried, 

resulting in a recommended tolerance of 3.0 ppm (calculated by: HAFT of fresh parsley 1.015 

ppm × concentration factor 2.76).

Pea (Dry) (MRID 48928504)

The dataset used to establish a tolerance for linuron consisted of field trial data on peas (dry)

representing one application within -5% to +10% of 1 lb ai/A, and 65- to 92-day PHIs. The 

average residue values used to calculate the tolerance are provided below. Combined residues of 

linuron and its metabolites hydrolyzed to 2,4-DCA were quantifiable in/on two of six trials. 

Data from all six field trials were used in the OECD calculation procedures, resulting in a 

recommended tolerance of 0.06 ppm.

Horseradish (MRIDs 45633501 and 45633502)

The dataset used to establish a tolerance for linuron consisted of field trial data on horseradish

representing one application within -5% to +10% of 1.5 lb ai/A per application, and 76- to 100-

day PHIs. The average residue values used to calculate the tolerance are provided below. An 

LOQ was not statistically calculated in this study, but the LLMV was determined to be 0.05 

ppm. Data from three field trials indicated that detectable residues were not found. Thus, data 

consisting of <LOQ values from three field trials were used in the OECD tolerance calculation 

procedures, resulting in a recommended tolerance equivalent to the LOQ of 0.05 ppm.
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Appendix A. Summary of Submitted Residue Chemistry Studies

Table A1. Summary of Submitted Residue Chemistry Studies

OCSPP 

Guideline MRID Title

860.1340

Residue 

Analytical 

Method

48832101 Determination of the Substituted Urea Herbicide Linuron and its Metabolites in Oily, 

Watery, and Starch Crop Matrices

48832102

Independent Laboratory Validation of “Determination of the Substituted Urea Herbicide 

Linuron and its Metabolites in Soil and Agricultural Products” for Oily, Watery, and Starch 

Crop Matrices

48832103 Determination of the Substituted Urea Herbicide Linuron and its Metabolites in Animal 

Tissue

48832104 Independent Laboratory Validation of the Draft Method “Determination of the Substituted 

Urea Herbicide Linuron and its Metabolites in Animal Tissues”

48832105 Method Transfer and Validation of “Determination of the Substituted Urea Herbicide 

Linuron and its Metabolites in Soil and Agricultural Products” for Animal Matrices

48832106 Analytical Method for the Determination of Linuron and Metabolites in Crops using 

LC/MS/MS

48832107

Independent Laboratory Validation of “Determination of the Substituted Urea Herbicide 

Linuron and its Metabolites in Soil and Agricultural Products” for Oily, Watery, and Starch 

Crop Matrices

48832108

Independent Laboratory Validation of Residue Analytical Method 20001407/01-RVP, 

“Residue Analysis of Diuron and Metabolites in Plants Method Validation” for the 

Determination of Residues of Linuron and Metabolites in Grapes, Olives, and Wheat Grain

48832109 Analytical Method for the Determination of Linuron and Metabolites in Animal Tissue 

using LC/MS/MS

48832110

Independent Laboratory Validation of “Analytical Method for the Determination of Linuron 

and Metabolites in Animal Tissue using LC/MS/MS” and “Analytical Method for the 

Determination of Diuron and Metabolites in Animal Tissue using LC/MS/MS”

860.1500

Crop 

Field 

Trial

48928501 Linuron: Magnitude of the Residue on Coriander

48928502 Linuron: Magnitude of the Residue on Dill

48928503 Linuron: Magnitude of the Residue on Parsley

48928504 Linuron: Magnitude of the Residue on Pea (Dry)

45633501

45633502 Linuron: Magnitude of the Residue on Horseradish
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Appendix B. International Residue Limits Table for Linuron

Table B1. Summary of US and International Tolerances and Maximum Residue Limits of Linuron

Residue Definition

US Canada Mexicob Codex

40 CFR 180.184:

Plant and Livestock:

(3-(3,4-dichlorophenyl)-1-methoxy-1-

methylurea) and its metabolites convertible to 

3,4-dichloroaniline

None None

Commoditya Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexicob Codex

Cilantro, fresh leaves 1.5

Cilantro, dried leaves 10

Coriander, seed 0.05

Dillweed, fresh leaves 0.6

Dillweed, dried leaves 3.0

Dill, seed 0.5

Dill, oil 2.0

Horseradish 0.05

Parsley, leaves 4.0

Parsley, dried leaves 3.0

Pea, dry, seed 0.06

Completed: M. Negussie; 07/30/2013

a Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and 

not those proposed by the applicant.

b Mexico adopts US tolerances and/or Codex MRLs for its export purposes.
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Appendix C. OECD MRL Calculation Procedure Inputs/Outputs

Coriander (MRID 48928501)

2.0 lb ai/A; 19-21 day PHIs

Residues (mg/kg)

0.940 4.000

0.086 4.000

0.525 4.000

1.055 4.000

Compound Linuron

Crop Fresh Coriander

Region / Country CA/OR/TN/TX

GAP

Total number of data (n) 4

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.086

Highest residue 1.055

Median residue 0.733

Mean 0.651

Standard deviation (SD) 0.441

Correction factor for censoring 

(CF) 0.333

Proposed MRL estimate

- Highest residue 1.055

- Mean + 4 SD 2.414

- CF x 3 Mean 0.651

Unrounded MRL 1.055

Rounded MRL 1.5

High uncertainty of MRL estimate due to small dataset and 

high level of censoring.
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Dill (MRID 48928502)

2.0 lb ai/A; 20-22 day PHIs

Residues (mg/kg)

0.335 3.000

0.490 3.000

0.560 3.000

Compound Linuron

Crop Fresh Dill

Region / Country CA/FL/WA

GAP

Total number of data (n) 3

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.335

Highest residue 0.560

Median residue 0.490

Mean 0.462

Standard deviation (SD) 0.115

Correction factor for censoring 

(CF) 0.333

Proposed MRL estimate

- Highest residue 0.560

- Mean + 4 SD 0.922

- CF x 3 Mean 0.462

Unrounded MRL 0.560

Rounded MRL 0.6

High uncertainty of MRL estimate due to small dataset and 

high level of censoring.
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Pea (Dry) (MRID 48928504)

1.0 lb ai/A; 65-92 day PHIs

Residues (mg/kg)

0.015 6.000

0.010 *

0.010 *

0.010 *

0.051 6.000

0.010 *

Compound Linuron

Crop Pea (Dry)

Region / Country ID/ND/WA

GAP

Total number of data (n) 6

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.010

Highest residue 0.051

Median residue 0.010

Mean 0.018

Standard deviation (SD) 0.016

Correction factor for censoring 

(CF) 0.333

Proposed MRL estimate

- Highest residue 0.051

- Mean + 4 SD 0.083

- CF x 3 Mean 0.018

Unrounded MRL 0.051

Rounded MRL 0.06

High uncertainty of MRL estimate due to small dataset and 

high level of censoring.
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Horeseradish (MRIDs 45633501 and 45633502)

1.5 lb ai/A; 76-100 day PHIs

Residues (mg/kg)

<0.05

<0.05

<0.05

Compound Linuron

Crop Horseradish

Region / Country MD/WI/NJ

GAP

Total number of data (n) 3

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.050

Highest residue 0.050

Median residue 0.050

Mean 0.050

Standard deviation (SD) 0.000

Correction factor for censoring 

(CF) 0.333

Proposed MRL estimate

- Highest residue 0.050

- Mean + 4 SD 0.050

- CF x 3 Mean 0.050

Unrounded MRL 0.05

Rounded MRL 0.05

High uncertainty of MRL estimate due to small dataset and 

high level of censoring.