1

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF PREVENTION, 

PESTICIDES AND TOXIC 

SUBSTANCES

PC Code: 035506

DP Barcode: 405829

MEMORANDUM 

DATE: June 19, 2013

SUBJECT: Revised Linuron Drinking Water Assessment for an IR-4 New Use on Coriander, Dill, 

Celeriac, Horseradish, Parsley, Dry Peas and Rhubarb

TO: Laura Nollen, Risk Manager

Barbara Madden, Risk Manager Reviewer

Registration Division (7505P)

Christine Olinger, Branch Chief

Risk Assessment Branch III, 

Health Effects Division (7509P)

FROM: He Zhong, Ph.D., Biologist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

THROUGH: Sujatha Sankula, Ph.D., Acting Branch Chief

Environmental Risk Branch I

Environmental Fate and Effects Division (EFED) (7507P)

This revised linuron Drinking water assessment includes PRZM-GW model results. The document 

provides estimated drinking water concentrations (EDWCs) for linuron (3-(3,4-dichlorophenyl)-

1-methoxy-1-methylurea; (CAS 330-55-2) in support of human health risk assessment for a new 

use on Coriander, Dill, Celeriac, Horseradish, Parsley, Dry Peas and Rhubarb. The EDWCs for 

Horseradish, Parsley and Dry Peas were previously assessed based on the percentage crop area 

(PCA) value of 0.87 (USEPA 2010). These are updated to PCA =1 based on EFED guidance 

(USEPA 2012) for non-agricultural weed control (Proposed Label, page 13) in this document. 

According to the proposed supplemental label, Lorox® 50% DF Herbicide can be applied 

annually in a single application as pre-emergence or up to two applications as post-emergence by 

ground spray, fertilizer spray mixture, and chemigation to control certain broadleaf weeds and 

grasses. The application directions also specified to not apply by air, to the sand or loamy sand 

soil or use on soils with less that 1% organic matter. Table 1 is a summary of the proposed 

supplemental label. 
2

The chemical and environmental fate properties of linuron are listed in Appendix I. Same as the 

previous DWA (USEPA2010), a total toxic residue approach is applied in this assessment to 

include the parent linuron and three degradates, desmethoxy linuron, desmethoxy monolinuron, 

and norlinuron observed in environmental fate studies. This assessment did not include the 

common urea herbicide degradate 3,4-DCA, which was concluded as not a residue of concern for 

human health for linuron (USEPA 1993). The calculated EDWCs from Tier-II PRZM/EXAMs

(see input values in Appendix II) for surface water are listed in Table 2. The maximum surface 

water EDWCs in this assessment (see Appendix III) supersede the previous upper bound 

EDWC values of 77.4 μg/L, 42.4 μg/L and 26.8 μg/L (PCA = 0.87) for peak (acute), annual 

average (non-cancer chronic), and 30-year annual average (cancer chronic) respectively (USEPA 

2010, DP371421, 371396, 371471, 371472, 371473). Therefore, EFED recommends the new

maximum EDWC values of 89.05 μg/L, 48.69 μg/L and 30.81 μg/L (PCA=1) for surface water 

peak (acute), annual average (non-cancer chronic), and 30-year annual average (cancer chronic) 

respectively. 

Ground water EDWC from SCI-GROW model is 0. 23 μg/L (see input and output values in 

Appendix IV), which does not supersede the previous recommended value of 0.61 ppb. Ground 

water EDWC is also calculated by PRZM-GW model (Table 3 and Appendix V PRZM-GW 

Modeling Input and Output). The highest daily value is 54.5 μg/L and post breakthrough 

average is 48.8 μg/L with average simulation breakthrough time over 20,101 days for Wisconsin 

corn scenario. Ground water EDWC from PRZM-GW model supersedes the previous postmitigation monitoring concentration of 0.61 ppb and therefore, EFED recommends the PRZMGW highest acute value of 54.5 μg/L and chronic value of 48.69 for groundwater.

Table 1. Summary of Application Information Used in PRZM/EXAMS for Surface Water EECs

Crop PRZM/EXAMS 

Scenarios1

Application 

Rate 

(lb a.i./A)

2

Application 

Rate 

(kg a.i./ha)2

Maximum 

Number of 

Applications3

Application 

Date

(DayMonth)4

Coriander

Dill (East of 

Rocky Mtns)

FL Peppers 1.0 1.12 2 24-4

FLCarrot 1.0 1.12 2 9-10

PA Vegetable 1.0 1.12 2 15-5

Coriander

Dill (West of 

Rocky Mtns)

CARowCrop 0.75 0.84 2 10-12

CALettuce 0.75 0.84 2 9-2

ORmint 0.75 0.84 2 8-4

Celeriac

Rhubarb

Horseradish

Parsley

FL Peppers 1.5 1.68 1 24-4

FLCarrot 1.5 1.68 1 9-10

PA Vegetable 1.5 1.68 1 15-5

CARowCrop 1.5 1.68 1 10-12

CALettuce 1.5 1.68 1 9-2

ORmint 1.5 1.68 1 8-4

Dry Peas IL Beans NMC 1.0 1.12 1 9-6

MI BeansSTD 1.0 1.12 1 25-5

Abbreviations: A=acre; ha=hectare; a.i.=active ingredient

1 There are no crop scenarios in PRZM/EXAMS for the crops listed in this table. Alternative surrogate scenarios 

based on similarities in plant structure and growth characteristics were used in the modeling.

2 Calculated by the equation: kg a.i./A = (lbs a.i./A) x (1 kg/2.205 lbs) x (2.47 A/hectare). 

3A 15-days application intervals for all two applications

4Application date is estimated for the region one week before crop emergence date per proposed label.
3

Table 2. Surface Water EECs for Linuron by PRZM/EXAMS for IR-4 New Use on Coriander, Dill, Celeriac 

Horseradish, Parsley, Dry Peas and Rhubarb

Crop PRZM/EXAMS 

Scenarios1

Application 

Rate 

(kg a.i./ha)2

Maximum 

Number of 

Applications

Peak 

(ppb)

Annual 

Mean 

(ppb)

Long-term

Mean 

(ppb)

Coriander

Dill (East of 

Rocky Mtns)

FL Peppers 1.12 2 81.79 17.76 12.97

FLCarrot 1.12 2 88.91 14.81 12.08

PA Vegetable 1.12 2 49.07 25.03 19.57

Coriander

Dill (West of 

Rocky Mtns)

CARowCrop 0.84 2 40.35 26.19 16.81

CALettuce 0.84 2 66.74 36.03 27.00

ORmint 0.84 2 11.58 6.91 5.73

Celeriac

Rhubarb

Horseradish

Parsley

FL Peppers 1.68 1 72.21 12.11 9.45

FLCarrot 1.68 1 84.91 15.34 8.65

PA Vegetable 1.68 1 37.81 19.08 15.25

CARowCrop 1.68 1 45.16 27.01 17.62

CALettuce 1.68 1 89.05 48.69 30.81

ORmint 1.68 1 13.20 7.09 5.74

Dry Peas IL Beans NMC 1.12 1 30.74 14.22 10.93

MI BeansSTD 1.12 1 23.76 11.99 9.36

Table 3. Ground Water EECs for Linuron by PRZM-GW in Six Vulnerable Sites for IR-4 New Use on 

Coriander, Dill, Celeriac Horseradish, Parsley, Dry Peas and Rhubarb

Crop/Scenario Highest Daily Value 

μg/L

Post Breakthrough 

Average 

μg/L

Average Simulation 

Breakthrough Time 

Days

DELMARVA sweet corn -

Evesboro loamy sand

Met File (13781.dvf)

16.9 15.1 10,082.8

Florida Citrus - FL Central 

Ridge, Polk County 

Astatula sand, hrgb A 

Met File (12842.dvf) 

37.6 37.5 10,009.13

Florida - potato 

Jacksonville

Met File (13889.dvf) 

0.0246 0.0203 25,376.8

GA - Southern Coastal 

Plain, Tifton loamy sand –

PEANUTS

Met File 

(w93805Extended.dvf)

7.13 6.51 20,395.9

NC Eastern Coastal Plain -

Norfolk loamy sand –

Cotton

Met File (13722.dvf)

19.4 18.2 10,755.64

Wisconsin Corn - WI 

Central Sands

Met File 

(14920Extended.dvf)

54.5 48.8 20,101.2
4

References

USEPA. 1993. Linuron Plant and Animal Metabolism: Results of the HED Metabolism 

Committee Meetings held October 21, and October 29, 1993. MARC’s Memo. Pp3

USEPA. 2010. Drinking Water Assessment for the Section 3 Registration of Linuron for New 

Use on Parsley, Dry Pea and Horseradish. DP Barcodes: 371421, 371396, 371471, 371472, 

371473. pp10

USEPA. 2012. Guidance on Development and Use of Percent Cropped Area and Percent Turf 

Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update. pp50
5

Appendix I

Chemical and Environmental Fate Properties of Linuron

Chemical/Fate Parameter Value(s) Source (MRID)

Common Name Linuron Product Chemistry

Empirical formula C9H10Cl2N2O2 EPI V4.10

SMILES O=C(N(OC)C)Nc(ccc(c1Cl)Cl)c1 EPI V4.10

Chemical Name (CAS) N'-(3,4-dichlorophenyl)-Nmethoxy-N-methylurea

http://sitem.herts.ac.

uk/aeru/iupac/419.ht

m (Accessed 

3/20/2013)

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

methoxy-1-methylurea

http://sitem.herts.ac.

uk/aeru/iupac/419.ht

m (Accessed 

3/20/2013)

CAS No 330-55-2 Product Chemistry

Structural formula

Molecular weight (MW) (g/mol) 249.1 Product Chemistry

Vapor pressure (VP) (torr; at 24C) 1.5 × 10-5

Product Chemistry

Water solubility (mg/L; at 20C) 81 Product Chemistry

Henry’s Law Constant (atm-m

3

/mol; at 25C) 6.1 x 10-8 Calculated1

Hydrolysis half-lives (25C) (days), pH 5, 7 and 9 Stable 40916201

Water photolysis half-life 49 days 40103601

Soil photolysis half-life >15 days (assumed stable) 40171711

(supplemental)

Aerobic soil metabolism half-life (days) 49 days2, 71 days3and 113 days3 41625401 (valid)4

Organic carbon normalized partition coefficients 

(KOC) (L/kgOC)

1200 (Sandy loam)

2200 (Sandy loam)

830 (Silt loam)

550 (Clay loam)

43995301 

(supplemental)

Octanol-water partition coefficient (KOW) 1010 Product Chemistry

Fish bioconcentration

34x (muscle)

39× (carcass)

240× (viscera)

49× (whole fish)

00142933 

1 Calculated according to USEPA 2002 by: (VP*MW) ÷ (760*solubility).

2 Calculation from original data evaluation review.

3 Calculated using total toxic residue method.

4 This study was found to be valid under old review standards. 
6

Appendix II

PRZM/EXAMS1 modeling input values for linuron use 

on Coriander, Dill, Celeriac Horseradish, Parsley, Dry Peas and Rhubarb

Model Input Parameter Input Value and Unit Source/Comments

Molecular Weight. 249.1 Product Chemistry

Henry’s Law Constant (atmm

3

/mole)

6.1 x 10-8 Calculated according to Input Parameter 

Guidance: (VP*MW) / (760*solubility) 

Vapor pressure (torr @ 24°C) 1.5 x 10-5 Product Chemistry

Solubility (mg/L @ 20oC) 81

Koc (ml/g) 1195 MRID 43995301; average of 4 values per Input 

Parameter Guidance (1200, 2200, 830 and 550)

Kd 6.3 MRID 43995301; average of 4 values per Input 

Parameter Guidance (5.5,17,12 and 13)

Type of Application CAM 1 The proposed label recommends pre-emergent 

crop application.

Incorporation Depth 0 Proposed label

Application Efficiency 0.99 (ground spray) Input parameter guidance

Spray Drift Fraction 0.064 (ground) Input parameter guidance

IPSCND 1 (surface applied) Input parameter guidance

Hydrolysis half-lives (25°C) 

(days). pH5, pH7 and pH9

Stable MRID 40916201 

Aqueous Photolysis Half-life 

(days) 

49 MRID 40916201

Aerobic Aquatic Metabolism 

Half-life (days)

426 Calculated: 71 (aerobic soil metabolism) x3 x2 

per input parameter guidance. 

Anaerobic Aquatic 

Metabolism Half-life (days)

Stable In the absence of an acceptable study this 

metabolic half-life is considered to be stable

Aerobic Soil Metabolism 

Half-life (days)

213 MRID 41625401; calculated using total toxic 

residue method. 71 x 3 per input guidance 

when only one valid study is available.

 

1 Model input values for ‘Application rate and data’, and ‘Number of applications’, are presented in Table 1.
7

Appendix III

Examples of PRZM/EXAMS Modeling Output

stored as CALettuce-1app.out

Chemical: Linuron

PRZM environment: CAlettuceSTD.txt modified Tuesday, 21 February 2006 at 15:38:22

EXAMS environment: ir298.exv modified Tuesday, 26 August 2008 at 06:14:07

Metfile: w23273.dvf modified Tuesday, 26 August 2008 at 06:15:39

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 14.52 14.14 12.86 8.053 5.709 2.497

1962 118 116 112 93.68 83.77 49.8

1963 78.12 76.7 72.42 69.24 67.12 49.06

1964 39.95 39.64 38.66 37.21 37.1 32.51

1965 38.96 38.45 36.64 33.48 31.75 27.17

1966 28.99 28.55 26.97 25.27 24.89 20.91

1967 31.48 31.05 29.45 28.54 27.89 22.2

1968 23.99 23.69 22.64 21.09 20.53 17.13

1969 54.57 53.36 50.21 43.92 40.58 27.69

1970 57.76 56.57 52.95 46.22 42.55 30.09

1971 29.56 29.3 28.32 27.67 27.1 22.93

1972 28.46 27.95 26.18 22.67 19.65 17.26

1973 89.66 87.97 81.14 71.29 65.38 43.22

1974 63.77 62.77 60.01 55.23 51.92 39.32

1975 45.52 44.98 43.06 40.41 39.25 31.6

1976 51.52 50.58 47.28 42.98 40.43 31.48

1977 38.26 37.89 36.23 33.27 32.76 27.67

1978 121 119 110 104 95.66 62.88

1979 58.42 57.92 56 53.79 52.2 42.19

1980 83.6 82.57 78.58 69.59 64.53 45.4

1981 70.44 69.2 65.76 59.45 55.6 41.01

1982 44.59 44.08 42.57 40.48 39.4 32.24

1983 56.38 55.4 52.23 47.42 44.87 32.78

1984 26.8 26.6 25.87 24.64 24.35 20.34

1985 23.31 23.05 22.09 20.79 20.63 16.95

1986 76.93 75.02 68.13 65.3 61.14 39.88

1987 58.73 57.85 54.18 48.16 44.95 34.02

1988 45.15 44.46 41.89 38.68 37.85 29.85

1989 27.56 27.33 26.44 25.35 25.01 19.85

1990 21.59 21.33 20.45 19.07 18.21 14.39

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.032258064516129 121 119 112 104 95.66 62.88

0.0645161290322581 118 116 110 93.68 83.77 49.8

0.0967741935483871 89.66 87.97 81.14 71.29 67.12 49.06

0.129032258064516 83.6 82.57 78.58 69.59 65.38 45.4

0.161290322580645 78.12 76.7 72.42 69.24 64.53 43.22

0.193548387096774 76.93 75.02 68.13 65.3 61.14 42.19

0.225806451612903 70.44 69.2 65.76 59.45 55.6 41.01

0.258064516129032 63.77 62.77 60.01 55.23 52.2 39.88

0.290322580645161 58.73 57.92 56 53.79 51.92 39.32

0.32258064516129 58.42 57.85 54.18 48.16 44.95 34.02

0.354838709677419 57.76 56.57 52.95 47.42 44.87 32.78

0.387096774193548 56.38 55.4 52.23 46.22 42.55 32.51
8

0.419354838709677 54.57 53.36 50.21 43.92 40.58 32.24

0.451612903225806 51.52 50.58 47.28 42.98 40.43 31.6

0.483870967741936 45.52 44.98 43.06 40.48 39.4 31.48

0.516129032258065 45.15 44.46 42.57 40.41 39.25 30.09

0.548387096774194 44.59 44.08 41.89 38.68 37.85 29.85

0.580645161290323 39.95 39.64 38.66 37.21 37.1 27.69

0.612903225806452 38.96 38.45 36.64 33.48 32.76 27.67

0.645161290322581 38.26 37.89 36.23 33.27 31.75 27.17

0.67741935483871 31.48 31.05 29.45 28.54 27.89 22.93

0.709677419354839 29.56 29.3 28.32 27.67 27.1 22.2

0.741935483870968 28.99 28.55 26.97 25.35 25.01 20.91

0.774193548387097 28.46 27.95 26.44 25.27 24.89 20.34

0.806451612903226 27.56 27.33 26.18 24.64 24.35 19.85

0.838709677419355 26.8 26.6 25.87 22.67 20.63 17.26

0.870967741935484 23.99 23.69 22.64 21.09 20.53 17.13

0.903225806451613 23.31 23.05 22.09 20.79 19.65 16.95

0.935483870967742 21.59 21.33 20.45 19.07 18.21 14.39

0.967741935483871 14.52 14.14 12.86 8.053 5.709 2.497

0.1 89.054 87.43 80.884 71.12 66.946 48.694

Average of yearly averages: 30.8105666666667

Inputs generated by pe5.pl - November 2006

Data used for this run:

Output File: CALettuce-1app

Metfile: w23273.dvf

PRZM scenario: CAlettuceSTD.txt

EXAMS environment file: ir298.exv

Chemical Name: Linuron

Description Variable Name Value Units Comments

Molecular weightmwt 249.1 g/mol

Henry's Law Const. henry 6.1e-8 atm-m^3/mol

Vapor Pressure vapr 1.5e-5 torr

Solubility sol 81 mg/L

Kd Kd mg/L

Koc Koc 1195 mg/L

Photolysis half-life kdp 49 days Half-life

Aerobic Aquatic Metabolism kbacw 426 days Halfife

Anaerobic Aquatic Metabolism kbacs 0 days Halfife

Aerobic Soil Metabolism asm 213 days Halfife

Hydrolysis: pH 7 0 days Half-life

Method: CAM 1 integer See PRZM manual

Incorporation Depth: DEPI 0 cm

Application Rate:TAPP 1.68 kg/ha

Application Efficiency: APPEFF0.99 fraction

Spray Drift DRFT 0.064 fraction of application rate applied to pond

Application Date Date 9-2 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND1

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR Reservoir

Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run)
9

Appendix IV

SCI-GROW2 Input:

Input values used for modeling groundwater concentrations of linuron using SCI-GROW2

Model Input Parameter Input Value and Unit Source/Comments

Aerobic Soil Metabolism Halflife (days)213 days MRID 41625401; calculated using total toxic 

residue method; 71 x 3 per input guidance 

when only one valid study is available

Organic-Carbon Normalized 

Partition Coefficient Koc

1195 (mL/g) MRID 43995301; average of 4 values per 

Input Parameter Guidance 

Application Rate 1.0 lbs ai/A Proposed label

Maximum No. of 

Applications/Year

2 Proposed label

SCI-GROW2 Output:

 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:Linuron

time is 4/ 4/2013 14:32:47

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

 Application Number of Total Use Koc Soil Aerobic

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

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

1.0 2.0 2.000 1.20E+03 213.0

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

groundwater screening cond (ppb) = 2.30E-01 

************************************************************************
10

Appendix V PRZM-GW Modeling Input and Output

PRZM-GW Modeling Input
11

PRZM-GW Modeling Output
12