. . 

~~) 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

Office of Chemical Safety and Pollution Prevention 

Date: Septembet·2s, 2014 

Subject:Paraquat Dichloride. Request For Expansion of the Potato Tolerance to Crop Subgroup 

1C. -

PC Code: 061601 

Decision No.: 483239 

Petition No.: 3E8201 

Risk Assessment Type: NA 

TXRNo.: NA 

DP Barcode: D419828 

Registration No.: None 

Regulatory Action: Section 3 Registration 

Case No.: 0262 

CAS No.: 1910-42-5 

MRID No.: None 40 CFR: 180.205 /d--

From: Thurston G. Morton, Chemist ~ ~.....r Risk Assessment Branch IV 

Health Effects Division (7509P) 

Through: Elissa Reaves, PhD, Branch Chief 

Risk Assessment Branch IV 

Health Effects Division (7509P) 

To: Andrew Ertman 

Barbara Madden 

Risk Integration, Minor Use & Emergency Response Branch 

Registration Division (RD) (7505P) 

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Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828 

Executive Summary 

Paraquat dichloride (hereafter in this document referred to solely as paraquat) is a non-selective 

herbicide currently registered for the control of weeds and grasses in agricultural and nonagricultural areas, and for use as a defoliant, desiccant, and plant growth regulator. The Paraquat 

Reregistration Eligibility Decision (RED) Document (EPA 738-F-96-018) was issued in August 

1997. The Product and Residue Chemistry Chapters of the RED were completed in July of 1995 

(D217262, D. Miller). Currently all registered end-use products are formulated as paraquat 

dichloride, and the active ingredient is expressed in terms of the paraquat cation. 

The Interregional Research Project No.4 (IR-4), in PP#3E8201, has proposed the expansion of 

the potato tolerance for residues of the herbicide paraquat (1,1 '-dimethyl-4,4'-bibyridinium ion) 

derived from the application of the dichloride salt (calculated as the cation) to Tuberous and 

Corm Vegetables Subgroup 1 C. 

Tolerances for residues of paraquat have been established under 40CFR§180.205. The 

tolerances are expressed in terms of residues of paraquat derived from application of either the 

bis(methyl sulfate) or the dichloride salt (both calculated as the cation). Because there are 

currently no registered products containing paraquat dimethyl sulfate, the tolerance expression 

listed under 40CFR§180.205(a) and §180.205(c) should be revised to remove reference to the 

bis(methyl sulfate) salt of paraq~t. This was previously recommended by HED in 2006. In 

2009 HED issued guidance on tolerance expressions (S. Knizner, 2009). We now conclude the 

tolerance expression should be as follows: Tolerances are established for residues of paraquat, 

including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only 

paraquat dichloride and calculated as the paraquat cation. 

General tolerances have been established under 40CFR§180.205(a), and range from 0.01 ppm for 

egg and milk to 210 ppm for Animal feed, nongrass, group 18, hay. Tolerances with regional 

registration have been established under 40CFR§ 180.205( c) at 0.05 ppm for cassava, pigeon pea 

seed, tanier, tyfon, and true yam, and at 0.1 ppm for taro corm. 

The qualitative nature of paraquat residues in plant commodities is understood based upon 

studies depicting the metabolism of paraquat in carrots and.lettuce folloWing preemergence 

treatment and in potatoes and soybeans following desiccant treatment. The residue of concern in 

plants is the parent, paraquat. The qualitative nature of residues in livestock is adequately 

understood based on the combined results of studies conducted with ruminants (goats and cows), 

swine, and poultry. The residue of concern in eggs, milk, and poultry and livestock tissues is 

also parent paraquat. 

An adequate spectrophotometric method, Method I of the Pesticide Analytical Manual (PAM) 

Vol. II, is available for enforcing tolerances for residues of paraquat in/on plant commodities. 

For the method, samples are heated at reflux with 0.5 M sulfuric acid and then applied to a cation 

exchange column. Paraquat residues are eluted with saturated ammonium chloride solution. 

Cotton seed samples are first subjected to Soxhlet extraction in hexane, and the hexane extract is 

refluxed with sulfuric acid and then applied to the cation exchange column. An aliquot of the 

column eluate is mixed with 0.2% (w/v) sodium hydrosulftte in 0.3 M sodium hydroxide, which 

reduces paraquat to a free radical. Residues are determined using a variable wavelength 

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Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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spectrophotometer, measuring the light absorption of the paraquat free radical. The validated 

limits of quantitation (LOQ) vary from 0.01 ppm up to 0.5 ppm.

PAM Vol. II lists a spectrophotometric method, designated as Method Ia (LOD = 0.005 ppm), as 

available for the enforcement of tolerances for paraquat residues in animal commodities. In 

addition, an adequate HPLC/UV method is available for the enforcement of tolerances for 

paraquat residues in livestock tissues and eggs (RAM 004/04, MRID 43226902; this method has 

not yet been published in PAM Vol. II); the reported LOQ is 0.005 ppm for livestock tissues and 

eggs. 

Adequate storage stability data are available indicating that residues of paraquat are stable under 

frozen storage conditions in/on representative examples of the following crop groups for at least 

18 months: non-oily grains, including corn grain; leafy vegetables, including corn forage, fodder, 

and silage; root crops; and fruits or fruiting vegetables. In addition, residues of paraquat have 

been found to be stable in/on cantaloupe stored frozen for up to 3.7 months, cucumber stored 

frozen for up to 4.0 months, summer squash stored frozen for up to 2.6 months, ginger root 

stored frozen for up to 2.4 months, and okra pod stored frozen for up to 7.3 months. It was

previously concluded that storage stability data for corn grain may be translated to oilseeds. 

The available ruminant and poultry feeding study data indicate that the tolerance 

recommendations of the RED Document (8/97) are appropriate, and that increased tolerances for 

livestock commodities are not needed to support the requested expansion to crop group 1C. 

Regulatory Recommendations and Residue Chemistry Deficiencies

Pending the submission of a revised Section F, there are no residue chemistry issues that would 

preclude granting a registration for paraquat on the Crop Subgroup 1C, as follows:

In 2009 HED issued guidance on tolerance expressions (S. Knizner, 2009). We now conclude 

the tolerance expression should be as follows: Tolerances are established for residues of 

paraquat, including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only 

paraquat dichloride and calculated as the paraquat cation.
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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Table 1. Tolerance Summary for Paraquat Dichloride

Commodity Tolerance (ppm) Comments (correct commodity 

definition) Established Proposed Recommended

Tolerances to be established under 40 CFR '180.205(a):

Tuberous and corm 

vegetables subgroup 1C

-- 0.5 0.50

Potato 0.5 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Tolerances to be revoked under 40 CFR '180.205(c):

Cassava 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Tanier 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Yam, true, tuber 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Background

IR-4 has submitted a petition (PP#3E8201) requesting for the expansion to tuberous and corm 

vegetables subgroup 1C using the current potato tolerance. Potato is the representative crop for 

subgroup 1C. The PC Code, nomenclature, and chemical structure of paraquat are listed below 

in Table 1. The physicochemical properties of paraquat are listed in Table 2. 

Table 1. Nomenclature of Paraquat Dichloride.

Compound

N

+

N

+

H C3

CH3

Cl

2

Common name Paraquat dichloride

IUPAC name 1,1’-dimethyl-4,4’-bypyridinium dichloride

CAS name 1,1’-dimethyl-4,4’-bypyridinium dichloride

CAS registry number 1910-42-5

(4685-14-7 for the cation)

End-use product (EP) 2.0 lb paraquat cation/gal SC (Gramoxone Inteon; EPA Reg. No. 100-1217)
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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Table 2. Physicochemical Properties of Technical Grade Paraquat Dichloride.

Parameter Value Reference

Melting point/range decomposes at ca. 340 °C Product Chemistry Chapter 

of the Paraquat Dichloride 

Update, 10/10/91

pH 6.4 at 20 °C

Density 1.5 g/cm3at 25 °C

Water solubility (20 °C) freely soluble in water:

618-620 g/L at pH 5.2, 7.2, and 9.2 

Solvent solubility (20 °C) <0.1 g/L in acetone, dichloromethane, 

toluene, ethyl acetate, and hexane;

143 g/L in methanol

Vapor pressure <<10-8 kPa at 25 °C

Octanol/water partition coefficient, 

Log(KOW)

log KOW = -4.5 at 20 °C

Dissociation constant, pKa 0.95 (pure active ingredient) Product Chemistry Chapter 

of the Paraquat 

Reregistration Standard, 

11/25/85

UV/visible absorption spectrum Not available
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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860.1200 Directions for Use

IR-4 has submitted a petition (PP#3E8201) for expansion of the use on potato to Crop Subgroup 

1C. The product to be used is Gramoxone SL 2.0 (EPA Reg. No. 100-1431), an emulsifiable 

concentrate (EC) formulation which contains 2 lb paraquat cation/gal. Gramoxone SL 2.0 is 

proposed for pre plant or preemergence directed spray to tuberous and corm vegetables subgroup 

1C. Maximum application rate is 0.5 lb a.i./A. A maximum of three applications is proposed. 

No pre-harvest interval (PHI) is specified. 

Table 3. Summary of Proposed End-Use Product.

Trade Name Reg. 

No.

ai (% of 

formulation)

Formulation TypeTarget Crops Target Pests Label Date

Gramoxone 

SL 2.0 

100-

1431

2 lb 

paraquat 

cation/gal

EC Tuberous and 

Corm Vegetables 

Subgroup 1C

A variety of small 

annual weeds 

(broadleaves and 

grasses), and 

perennial weeds; also 

used as a harvest aid 

and desiccant.

Proposed 

supplemental label 

+ registered label

Table 4. Summary of Proposed Directions for Use of Gramoxone Inteon (100-1217).

Application Timing Application 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per 

Season

RTI1

(days)

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Use Directions and other 

Limitations

Tuberous and Corm Vegetables Subgroup 1C

Preplant or 

Preemergent Broadcast 

spray 

0.25-0.5 3 28 NS NS Apply up to ground 

cracking before crop has 

emerged using ground 

equipment in a minimum 

of 10 gal/A or aerial in 5 

gal/A. 

1 RTI = Retreatment interval
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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The supplemental label specifies that preplant and preemergence applications must be made prior 

to crop emergence. Intentional or accidental contact (including drift) with the crop may result in 

severe damage or loss of the crop.

The current product label prohibits application through any type of irrigation system. All 

rotational crops may be planted immediately after the last application. 

Conclusions. The proposed use directions are adequate to allow evaluation of the available 

residue data relative to the proposed use. 

860.1300 Nature of the Residue - Plants

The residue chemistry chapter of the RED (D217262, D. Miller, 7/28/95) concluded that, for the 

purposes of reregistration and risk assessment, the qualitative nature of the residue in plants is 

adequately understood based on studies depicting the metabolism of paraquat in carrots and 

lettuce following preemergence treatment and in potatoes and soybeans following desiccant 

treatment. The residue of concern in plants is parent paraquat.

860.1300 Nature of the Residue - Livestock

The residue chemistry chapter of the RED (D217262, D. Miller, 7/28/95) concluded that for 

purposes of reregistration and risk assessment, the qualitative nature of the residue in animals is 

adequately understood based on the combined results of studies conducted with ruminants (goats 

and cows), swine, and poultry. The residue of concern in eggs, milk, and poultry and livestock 

tissues is parent paraquat.

860.1340 Residue Analytical Methods

Plant commodity method

PAM Vol. II lists a spectrophotometric method, designated as Method I (LOD = 0.01-0.06 ppm), 

as available for the enforcement of tolerances in plant commodities. Several modifications of 

Method I have been developed for analysis of specific crops, and these modified methods have 

been used for data collection. 

The RED Document (EPA 738-F-96-018, 8/97) reported that radiovalidation data had been 

provided for Method 1B of the enforcement method using radiolabeled samples. The Agency 

tentatively concluded that Method 1B adequately recovers paraquat cation residues from samples 

of potatoes and soybeans treated with [14C]paraquat. At the time of the RED document, the 

registrant had recently submitted representative spectra and other supporting raw data from the 

radiovalidation study (MRID 43954002). It was concluded that, upon the Agency’s review of 

this additional information, the requirements for residue analytical methods for plant 

commodities would be considered fulfilled for reregistration purposes. HED has not conducted a 

formal review of the data. A preliminary review has been conducted, however, and the data are 

considered to be adequate for the purposes of these tolerance petitions.
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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Conclusions. The existing spectrophotometric method (Method I of PAM Vol. II) is adequate for 

collecting data on residues of paraquat in/on plant commodities. The method is adequate for 

tolerance enforcement purposes for these commodities.

Animal commodity method

PAM Vol. II lists a spectrophotometric method, designated as Method Ia (LOD = 0.005 ppm), as 

being available for the enforcement of tolerances in animal commodities. The registrant has 

submitted descriptions and adequate independent laboratory validation data for a highperformance liquid chromatography method (HPLC; designated as Method 4B) to determine 

paraquat residues in animal tissues and eggs. The method has been validated by the Analytical 

Chemistry Branch (ACB). The registrant was requested to make minor changes in the method 

write-up. A revised version of the method has been submitted (RAM 004/04; MRID 43226902)

and is now available for enforcement purposes. The reported LOQ is 0.005 ppm for livestock 

tissues and eggs.

860.1360 Multiresidue Methods

The FDA PESTDATA database (dated 11/01) does not have an entry for paraquat. The residue 

chemistry chapter of the RED (D217262, D. Miller, 7/28/95) concluded that the existing FDA 

multiresidue methods are not likely to recover residues of paraquat because of its ionic nature.

860.1380 Storage Stability

This guideline is not relevant to the current petition.

860.1400 Water, Fish, and Irrigated Crops

This guideline is not relevant to the current petition.

860.1460 Food Handling

This guideline is not relevant to the current petition.

860.1480 Meat, Milk, Poultry, and Eggs

This guideline is not relevant to the current petition.

860.1500 Crop Field Trials

No residue field trial data have been submitted for this petition.

The registrant is requesting for the expansion to tuberous and corm vegetables subgroup 1C 

using the current potato tolerance. Potato is the representative crop for subgroup 1C.
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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860.1520 Processed Food and Feed

This guideline is not relevant to the current petition.

860.1650 Submittal of Analytical Reference Standards

paraquat dichloride, Syngenta, expiration date 

10/31/2016 

paraquat impurity 2,2.6,2" terpyridine, Syngenta, expiration date 

10/1/2009 

paraquat impurity 2,3,diphenylquinoxaline, Syngenta, expiration date 

4/1/2002 

 

The registrant must submit paraquat dichloride analytical reference standards when required to:

Theresa M. Cole

US EPA National Pesticide Standard Repository

Environmental Science Center

701 Mapes Road

Fort Meade, MD 20755-5350

Cole.Theresa@epa.gov

(410) 305-2907

860.1850/1900 Confined/Field Accumulation in Rotational Crops

This guideline is not relevant to the current petition.

860.1550 Proposed Tolerances

HED previously determined that the residue of concern for paraquat in/on plant and animal 

commodities is paraquat per se (D217262, D. Miller, 7/28/95). Because there are currently no 

registered products containing paraquat dimethyl sulfate, the tolerance expression listed under 40 

CFR§180.205(a) and §180.205(c) should be revised to remove reference to the bis(methyl 

sulfate) salt of paraquat. 

In 2009 HED issued guidance on tolerance expressions (S. Knizner, 2009). We now conclude 

the tolerance expression should be as follows: Tolerances are established for residues of 

paraquat, including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only 

paraquat dichloride and calculated as the paraquat cation.

A summary of the recommended tolerances for the current petition is given in Table 6. 
Paraquat Dichloride Summary of Analytical Chemistry and Residue Data Barcode: D419828

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Table 6. Tolerance Summary for Paraquat Dichloride

Commodity Tolerance (ppm) Comments (correct commodity 

definition) Established Proposed Recommended

Tolerances to be established under 40 CFR '180.205(a):

Tuberous and corm 

vegetables subgroup 1C

-- 0.5 0.50

Potato 0.5 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Tolerances to be revoked under 40 CFR '180.205(c):

Cassava 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Tanier 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Yam, true, tuber 0.05 Revoke Covered by Tuberous and corm 

vegetables subgroup 1C

Codex/International MRL Harmonization

The Codex Alimentarius Commission has established a maximum residue limit (MRLs) for 

paraquat residues in root and tuber vegetables. The Codex and U.S. tolerances are in harmony 

with respect to MRL/tolerance expression; both regulate the parent paraquat cation only. The 

Agency cannot harmonize with the Codex MRL of 0.05 ppm since residues of paraquat 

dichloride in potatoes occurred above the Codex MRL of 0.05 ppm. A comparison of the Codex 

MRLs and the proposed U.S. tolerances is presented in the following table. 

No Canadian or Mexican MRLs have been established for paraquat. Registered food/feed uses 

of paraquat exist in Canada. These uses presumably fall under the PMRA General MRL of 0.1 

mg/kg. Regulation B.15.002(1) of the Canadian Food and Drugs Regulations (FDR) establishes 

0.1 ppm as the General Maximum Residue Limit. This regulation states that a food is adulterated

if it contains residues of a pesticide at a level greater than 0.1 ppm unless a specific MRL has 

been established in Table II, Division 15 of the FDR.
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International Residue Limits 

Paraquat Dichloride (060601; 04/30/2014)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico2 Codex3

40 CFR 180.205:

Plant: paraquat (1,1′-dimethyl-4,4′-

bipyridinium-ion) derived from application 

of either the bis(methyl sulfate) or the 

dichloride salt (both calculated as the 

cation) 

4,4'-

bipyridinium, 

1,1'-dimethylParaquat cation

Commodity1 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex

Tuberous and corm vegetables 

subgroup 1C

0.50 0.05 root and tuber 

vegetables

Completed: M. Negussie; 04/30/14 

1

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

not those proposed by the applicant.

2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.

References

Paraquat Dichloride. (061601) Product Chemistry Chapter and Residue Chemistry Chapter for

the Reregistration Eligibility Document: CBRS No. 15906; Rereg. Case No. 0262, D217262,

D. Miller, 7/28/95