Page 3 of 22

Introduction

HED has evaluated the existing human health risk assessments for paraquat to determine 

whether sufficient data are available and whether a new human health risk assessment is needed 

to support Registration Review. HED has considered the most recent risk assessments for 

paraquat, updates to its toxicity, exposure and usage databases, and current Agency science 

policies and risk assessment methods. 

Use Profile 

Paraquat is a non-selective herbicide currently registered for the control of weeds and 

grasses in agricultural and non-agricultural areas. It is a contact herbicide that desiccates and 

destroys plant cell membranes within hours of application. Paraquat is used in/on a variety of 

food, feed and non-food crops with tolerances currently established for crop and livestock food 

commodities (40 CFR 180.205). It is applied to agricultural and non-agricultural areas with 

aerial, ground, and handheld spray equipment. There are no paraquat products registered for 

homeowner use and no products registered for application to residential areas. 

Hazard Identification/Toxicology

Subchronic and chronic toxicity studies in mice, rats and dogs indicate that the lung is the 

principal target organ for repeated exposure to paraquat. Based on a subchronic inhalation study 

in rats, paraquat is severely toxic when inhaled as indicated by observations of increasingly 

severe lung effects at increased doses and an 80% mortality rate from respiratory failure in high 

dose animals (1.3 μg/L) within two weeks of a single administered dose. Prolonged oral 

ingestion of paraquat in chronic studies in rats, mice and dogs also led to mortality with effects 

seen in the lung, kidney, and eyes. The results of a two-generation reproduction study and 

developmental toxicity studies in rats indicate that paraquat is not a developmental or 

reproductive toxicant. Required neurotoxicity studies were not available and were expressly not 

required for the 2006 paraquat risk assessment (D328653, 7/31/2006). At that time, HED 

determined that there was limited concern for neurotoxicity resulting from exposure to paraquat

based on the following considerations: paraquat does not inhibit cholinesterase activity, produce 

cholinergic-like toxic signs, or affect morphology of the central or peripheral nervous systems; 

the molecular structure is not similar to compound classes known to have effects on the nervous 

system; there is no evidence of neurotoxicity based on the available toxicity data for paraquat. 

HED classified paraquat as a "Group E" chemical for carcinogenicity, no evidence for 

carcinogenicity to humans, based on the absence of evidence of carcinogenicity in chronic and 

carcinogenicity studies performed in rats and mice. The Group E classification corresponds to a 

designation of “Not Likely to be Carcinogenic to Humans” based on the 2005 EPA Guidelines 

for Carcinogenic Risk Assessment. Paraquat is highly acutely toxic via inhalation, dermal and 

oral routes of exposure. The toxicology database for paraquat was deemed incomplete due to 

lack of an acceptable developmental study in rabbits, but was considered adequate for hazard 

characterization and FQPA assessment given the availability of four acceptable developmental 

studies in rats and mice. 
Page 4 of 22

For the 2006 paraquat risk assessment, toxicity endpoints or points of departure (PODs)

were selected for oral (food and drinking water), dermal, and inhalation exposure routes. An 

acute dietary population adjusted dose (aPAD) was selected for the general population, including 

females 13-49 years old, from the rat reproduction study based on lung effects. A chronic

dietary population adjusted dose (cPAD) was selected from a chronic dog toxicity study based on 

lung effects. A POD for short- and intermediate-term dermal exposure was selected from the rat 

reproduction study. A POD for long term dermal exposure was selected from the chronic dog 

study. A dermal absorption factor of 0.3% derived from a dermal absorption study in humans 

was used to convert the oral doses to equivalent dermal doses for the risk assessment. A POD 

for inhalation exposure for all durations was selected based on the 21-day inhalation study in 

rats. The FQPA safety factor was reduced to1x for the following reasons: (1) there is no 

evidence of neurotoxicity in the registrant submitted studies; (2) there is no indication of 

quantitative or qualitative increased susceptibility of rats or mice to in utero and/or pre-/postnatal 

exposure to rats; (3) the dietary (food and drinking water) exposure assessments will not 

underestimate the potential exposures for infants and children; and (4) there are no registered 

residential uses of paraquat. However, a database uncertainty factor (UFDB) of 3x was applied

to the subpopulation of females 13-49 years old due to lack of an acceptable developmental 

study in a non-rodent species. An uncertainty factor of 100x (10x for interspecies extrapolation 

and 10x for intraspecies variation) was applied for all for dietary exposure to the general 

population and all subpopulations except females 13-49 years old. A typical uncertainty factor 

of 100x was applied for dermal and inhalation exposure. No toxicity data were required for the 

2006 assessment.

Data Requirements

An evaluation of open literature studies on paraquat conducted by HED in 2009 indicates 

that there is potential for paraquat to cause neurotoxicity in adults (D375436, 5/11/10). Based on 

that finding and new 40 CFR Part 158 requirements data requirements, HED concluded that 

acute and subchronic neurotoxicity studies would be required for paraquat for Registration 

Review. In response, the registrant conducted acute and subchronic neurotoxicity studies. These 

studies have been submitted to the Agency and reviewed by HED. Based on HED’s evaluation, 

the submitted studies satisfy guideline requirements for neurotoxicity data. A developmental 

toxicity study in the rabbit is required for food and non-food use pesticides under 40 CFR Part 

158. Immunotoxicity studies are also required under 40 CFR Part 158 as a part of the new data 

requirements for registration of a pesticide for food and non-food uses. The registrant submitted 

a protocol for the immunotoxicity study for HED’s review in November, 2010. HED determined 

that an immunotoxicity study conducted in accordance with the submitted protocol would satisfy 

the guideline data requirement for an immunotoxicity study in rats. 

Conclusions

Based on HED’s re-evaluation of the toxicity analysis conducted for the 2006 paraquat

risk assessment a developmental toxicity study in rabbits, and an immunotoxicity study in rats 

are required for Registration Review: PODs for oral, dermal and inhalation exposure are 

adequate but endpoints may need to be reevaluated for Registration Review based submission of 
Page 5 of 22

required toxicity data. The FQPA safety factor determination should be reevaluated for 

Registration Review based on newly required toxicity data.

Dietary and Drinking Water Exposure

The residue of concern for dietary exposure in plants and livestock is paraquat per se. 

Acute and chronic dietary and drinking water exposure assessments were conducted in 2006

using the Dietary Exposure Evaluation Model DEEM-FCIDTM (D327805, 7/31/06). The acute 

dietary assessment used tolerance level residues and maximum estimates of percent crop 

treated. The chronic assessment assumed tolerance level residues and 100% crop treated. 

Based on an evaluation of available groundwater monitoring studies, the Environmental Fate 

and Effects Division (EFED) recommended use of monitoring data reported in Virginia (1.52 

μg/L) for the drinking water exposure assessment, as a high-end, but not worst-case value for 

the acute and chronic analyses. The groundwater monitoring value was incorporated directly 

into the dietary assessments. Acute and chronic dietary and drinking water assessments

indicated that estimated risks were not of concern for the general U.S. population and all 

population subgroups. The acute food and water risk estimate was 33% of the aPAD for the 

U.S. population and 66% of the aPAD for the most highly-exposed population subgroup 

(children 1-2 years old). The chronic food and water risk estimate was 8% of the cPAD for the 

U.S. population and 26% of the cPAD for the most highly-exposed population subgroup 

(children 1-2 years old). 

Residue chemistry data requirements included in the 2006 assessment included crop 

field trial data for okra and corn aspirated grain fractions. 

 

Data Requirements

The data base for the dietary assessment is incomplete. Crop field trial data for okra has 

not been submitted but is no longer required because, under newly established crop groupings, 

okra is included in Crop Group 8-10 (Fruiting Vegetable Group) for which adequate data are 

available. However, the data requirement for aspirated grain fractions remains outstanding. 

In order to bring the drinking water assessment up to date with current data, simulation 

models and guidance, a new drinking water exposure assessment will be conducted to support 

future human health dietary risk assessments of paraquat. The drinking water assessment will 

incorporate model estimates of paraquat in surface water and ground water. Concentrations of 

paraquat in surface waters will be estimated using PRZM/EXAMS (see description above) with 

Index Reservoir as the receiving water body. With paraquat’s high adsorptive properties, the 

regular water treatment process is expected to remove almost all paraqat in the water. EFED is 

requesting the treatability study form the registrant to confirm this property. An Estimated 

Drinking Water Concentration (EDWC) of paraquat in groundwater will be estimated using the 

Tier I aquatic model SCIGROW (Screening Concentration in Ground Water, version 2.3; 

8/8/2003). SCIGROW is a regression model used as a screening tool to estimate pesticide 

concentrations found in ground water used as drinking water. The output of SCIGROW 

represents the concentrations that might be expected in shallow unconfined aquifers under sandy 

soils, which is representative of the ground water most vulnerable to pesticide contamination 
Page 6 of 22

likely to serve as a drinking water source. The drinking water assessment will also include 

available surface and ground water monitoring data with consideration of changes in use patterns 

that may have occurred. States are encouraged to submit monitoring data for review.

Conclusions

An updated dietary risk assessment will likely be required during the registration review

process to include changes to the drinking water assessment as well as any revised points of 

departure (PODs) or uncertainty factors. The revised assessments should be conducted using the 

newest version of DEEM-FCID which includes updated consumption information. 

Tolerances and International Harmonization

U.S. tolerances and International maximum residue levels (MRLs) for paraquat are not 

compatible for a significant number of commodities for which tolerances have been established

by both entities. U.S. and Canadian tolerances are compatible for all jointly registered 

commodities. A summary of US and international tolerances and maximum residue limits 

including Commodities for which U.S. tolerances differ from Codex MRLs is attached. The 

tolerance expression for paraquat needs to be reviewed and updated as necessary based on 

HED’s Interim Guidance on Tolerance Expressions (S. Knizner, 5/27/09). 

Residential Exposure

There are no paraquat products registered for homeowner use and there are no products 

registered for application to residential areas. However, residential bystander inhalation 

exposures resulting from off-site transport (e.g., spray drift) may occur as a result of applications 

of paraquat dichloride. The Agency is in the process of examining its policies and refining the 

methods used to complete residential exposure assessments. Therefore, the potential need for a 

bystander inhalation risk assessment will be examined during registration review.

Aggregate Exposure

Since there are no residential uses of paraquat, acute and chronic aggregate risks are 

equivalent to estimated acute and chronic dietary (food and water) risks respectively. Estimated 

chronic dietary risks for paraquat are not of concern based on the 2006 risk assessment

Conclusions

The aggregate exposure assessment is adequate. However, as previously indicated, the 

dietary exposure and risk assessments may need to be revised if new PODs are selected based 

on required toxicity data submissions. 
Page 7 of 22

Occupational Exposure 

Risk assessments were conducted for occupational handler and post-application exposure 

scenarios based on registered uses. Occupational handler exposures to paraquat are expected to 

be short- and intermediate-term based on use patterns. Chemical-specific applicator 

biomonitoring exposure data submitted to the Agency for the 1997 RED were used to estimate 

dermal and inhalation exposure and risk for aerial, ground and hand spray applications of 

paraquat for the 2006 risk assessment. Standard HED unit exposure data were use to estimate 

risk to handlers from spot treatment and flagging scenarios. Estimated MOEs were not of 

concern for any of the handler and post-application exposure scenarios assessed for the 2006

paraquat risk assessment. 

Conclusions

The occupational exposure assessment is adequate but needs to be updated to reflect 

current standard operating procedures. Recommended unit exposures for occupational handler 

assessments have generally been derived only from PHED. However, recently both the ORETF 

and AHETF have produced pesticide handler exposure monitoring data that the Agency is using 

in place of PHED (http://www.epa.gov/pesticides/science/handler-exposure-data.html). As more 

reliable data become available (such as that from the AHETF and ORETF), the Agency will 

continue to replace existing data. Reviewers should incorporate new exposure monitoring data, 

as necessary, during Registration Review. In addition, the use of chemical specific 

biomonitoring data to estimate exposures should be reevaluated. Based on the findings of a 

FIFRA Science Advisory Panel meeting held in January 2007, pooled passive dosimetry data 

may be as representative as biomonitoring data but more robust. Consequently, use of passive 

dosimetry data from HED’s generic pesticide exposure databases for the occupational exposure 

assessment may be preferable to chemical specific data. 

Incident Report

An updated incident report was conducted for paraquat for Registration Review (K Oo, 

D392273, 10/18/11). In general, a moderately large number of incidents have been reported 

involving paraquat dichloride. There were 46 cases reported for products containing paraquat 

dichloride present as a single chemical only; 73 cases reported for products containing paraquat 

dichloride as non-single active chemical, and 78 cases reported in the Aggregate Icident Data 

System. In addition, epidemiologic findings from the Agricultural Health Study (AHS) 

investigated a possible link of paraquat exposure in the etiology of Parkinson’s disease. The 

Agency will consider these AHS findings and any other literature pertinent to paraquat exposure 

and toxicity as part of the Registration Review evaluation for paraquat. 

Endocrine Disruption

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential 

adverse outcomes from exposure to chemicals. Collectively, these studies include acute, 

subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, 

developmental, reproductive, and general or systemic toxicity. These studies include endpoints 
Page 8 of 22

which may be susceptible to endocrine influence, including effects on endocrine target organ 

histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, 

reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates 

acute tests and chronic studies that assess growth, developmental and reproductive effects in 

different taxonomic groups. As part of its reregistration decision, EPA reviewed these data and 

selected the most sensitive endpoints for relevant risk assessment scenarios from the existing 

hazard database. However, as required by FFDCA section 408(p), paraquat is subject to the 

endocrine screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to an 

effect produced by a “naturally occurring estrogen, or other such endocrine effects as the

Administrator may designate.” The EDSP employs a two-tiered approach to making the 

statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify 

the potential of a chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or 

T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the 

potential to interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP 

where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available 

data. Tier 2 testing is designed to identify any adverse endocrine-related effects caused by the 

substance, and establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. Paraquat was 

included on that list and has been issued an order to conduct the Tier 1 testing. Once all required 

Tier 1 and Tier 2 data have been received and reviewed, the endpoints and safety factors used for 

risk assessment purposes will be examined and a new risk assessment performed if necessary. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/.

Cumulative

EPA does not have, at this time, available data to determine whether paraquat has a 

common mechanism of toxicity with other substances. EPA has not made a common mechanism 

of toxicity finding for paraquat and any other substances and, paraquat does not appear to 

produce a toxic metabolite produced by other substances which have tolerances in the U. S. 

Therefore, EPA has not assumed that paraquat has a common mechanism of toxicity with other 

substances.

Human Studies

Past paraquat risk assessments have relied in part on human studies which have involved 

intentional exposure to paraquat (MRIDs 00126096-00126099 (1982). In the course of 

registration review EPA will reconsider these studies, as well as any other research involving 

intentional exposure of human subjects to paraquat or related chemicals brought to its attention. 
Page 9 of 22

If EPA decides to rely on any of these studies, EPA will ensure that all applicable regulatory 

requirements are met, including but not limited to the requirements for EPA ethics review and 

Human Studies Review Board review of certain research involving intentional exposure of 

human subjects.

 

Future occupational assessments conducted for registration review of paraquat will use 

data contained in HED’s generic pesticide exposure databases such as Pesticide Handlers 

Exposure Database (PHED), the Agricultural Reentry Task Force (ARTF) Database and the 

Outdoor Residential Exposure Task Force (ORETF) Database). Recommended unit exposures 

for occupational handler assessments have generally been derived only from PHED. However, 

recently both the ORETF and AHETF have produced pesticide handler exposure monitoring data 

that the Agency is using in place of PHED (http://www.epa.gov/pesticides/science/handlerexposure-data.html). As more reliable data become available, the Agency will continue to 

replace existing data and new exposure monitoring data will be incorporated into HED’s 

Registration Review assessments as necessary. EPA has reviewed all the studies supporting 

these multi-pesticide generic exposure databases, and has found no clear and convincing 

evidence that the conduct of any of them was either fundamentally unethical or significantly 

deficient relative to the ethical standards prevailing at the time the research was conducted. All 

applicable requirements of EPA’s Rule for the Protection of Human Subjects of Research (40 

CFR Part 26) have been satisfied, and there is no regulatory barrier to continued reliance on 

these studies.

Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered 

in the human-health risk assessment, in accordance with U.S. Executive Order 12898, “Federal 

Actions to Address Environmental Justice in Minority Populations and Low-Income 

Populations,” (http://www.hss.energy.gov/nuclearsafety/env/guidance/justice/eo12898.pdf). The 

OPP typically considers the highest potential exposures from the legal use of a pesticide when 

conducting human-health risk assessments, including, but not limited to, people who obtain 

drinking water from sources near agricultural areas, the variability of diets within the U.S., and 

people who might be exposed when harvesting crops. Should these highest exposures indicate 

potential risks of concern, OPP further refines the risk assessments to ensure that the risk 

estimates are based on the best available information.
Page 10 of 22

Conclusions/Future Actions Needed

The actions needed in the future Registration Review for paraquat are listed below.

Hazard Identification and Endpoint Selection

Rabbit developmental toxicity and immunotoxicity studies are required for Registration Review. 

PODs for oral, dermal and inhalation exposure are adequate but endpoints may need to be 

reevaluated for Registration Review based submission of required toxicity data. 

Dietary and Drinking Water Exposure and Risk

The dietary and drinking water exposure assessments will likely need to be revised to include 

updated drinking water values and any revised points of departure (PODs) or uncertainty factors. 

The revised assessments should be conducted using the newest version of DEEM-FCID which 

includes updated consumption information.

Residential Exposure and Risk

A residential exposure assessment is not required based on currently registered uses. However, 

residential bystander inhalation exposures resulting from off-site transport (e.g., spray drift) may 

occur as a result of applications of paraquat dichloride. The Agency is in the process of 

examining its policies and refining the methods used to complete residential exposure 

assessments. Therefore, the potential need for a bystander inhalation risk assessment will be 

examined during Registration Review.

Aggregate Exposure and Risk

The aggregate exposure assessment is adequate. However, the dietary exposure and risk 

assessments may need to be revised if new PODs are selected based on required toxicity data 

submissions. 

Occupational Exposure and Risk

The occupational exposure assessment is adequate but needs to be updated to reflect current 

standard operating procedures. In addition, the use of chemical specific biomonitoring data to 

estimate exposures should be reevaluated. 

Incident Report

In general, a moderately large number of incidents have been reported involving paraquat 

dichloride. Human incident data may warrant further analysis for the risk assessment and/or risk 

management of paraquat dichloride. In addition, the Agency will consider AHS and other 

literature findings regarding a potential link between paraquat exposure and Parkinson’s disease 

as part of Registration Review. 
Page 11 of 22

Data Requirements

Toxicity Data Requirements

- Developmental Toxicity Study – nonrodent (GLN 870.3700b)

- Immunotoxicity study (GLN 870.7800) 

Residue Chemistry Data Requirements

- Crop Field Trials for Corn Aspirated Grain Fractions (GLN 860.1500)
Page 12 of 22

References

Paraquat Dichloride: Human Health Risk Assessment for Proposed Uses on Ginger and Okra 

and Amended Uses on Soybeans, Wheat, Cotton, Cucurbits, Onions, and Tanier. D. Dotson, 

D328653, 7/31/2006.

Paraquat Dichloride. Request to Amend Uses on Cotton, Cucurbits, Onion, Soybean, Tanier, 

and Wheat, and Add Uses on Ginger and Okra. Summary of Analytical Chemistry and Residue 

Data. D. Dotson, D343438, 7/31/2006

Paraquat Dichloride: Acute and Chronic Dietary Exposure Assessments for the Section 3 

Registration Action on Wheat, Soybeans, Cucurbits, Cotton, Onions, Tanier, Okra, and Ginger

D. Dotson, D327805, 7/31/2006.

Tier 2 Drinking Water Assessment for Paraquat Dichloride, J. Angier, D311410, 3/3/06

Paraquat Dichloride: Occupational and Residential Exposure/Risk Assessment for the New Uses 

of Paraquat Dichloride on Onion (dry bulb), Ginger, Wheat, Soybean, Cotton, Cucurbits, Okra, 

and Tanier, S. Wang, D327807, 4/20/2006

Paraquat - Report of the Hazard Identification Assessment Review Committee, S. Williams-Foy, 

TXR 0014110, 4/19/00

Paraquat - Report of the FQPA Safety Factor Committee, J. Rowland, TXR 0014137, 5/4/00

Evaluation of Acute Paraquat Toxicokinetic Studies, J. Ryman, TXR 0055274, 6/30/10

Evaluation of Acute and Subchronic Neurotoxicity Studies for Paraquat, J. Ryman, A. Assaad, 

TXR 0055342, 5/11/10

Evaluation Of Paraquat Brain Accumulation Data In Open Scientific Literature: Implications For 

Future Risk Assessments, J. Ryman, R. Kent, TXR 0055101, 3/11/09

Paraquat dichloride: Review of Human Incidents, K. Oo, D392273, 10/18/2011. 

Paraquat: Report of the Dose Adequacy Review Team (DART) – Concurrence with the Protocol 

and Dose Selection for the Immunotoxicity Study, J. Kidwell, TXR 0055562, 12/8/10
Page 13 of 22

Attachments

Chemical Identity

Table 1. Paraquat Nomenclature

Chemical structure

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)

Commodities for which US and International Limits Differ

Table 2. Commodities for which US and International Tolerances and Maximum Residue Limits Differ

Residue Definition:

US Canada Mexico Codex

40 CFR 180.205:

Plants/Livestock: paraquat (1,1′-dimethyl4,4′-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'-dimethylPlants/Livestock: paraquat cation.

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

US Canada Mexico1 Codex2

Almond, hulls 0.5 0.01 (*)

Asparagus 0.5

Avocado 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Banana 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Beet, sugar, roots 0.5 0.05 Root and tuber vegetables

Beet, sugar, tops 0.05

Berry group 13 0.05 0.05 0.01 (*) Berries and other 

small fruits

Carrot, roots 0.05 0.05 0.05 Root and tuber vegetables

Cattle, fat 0.05

Cattle, kidney 0.5 0.05 Edible offal (mammalian)

Cattle, meat 0.05 0.005 (*) Meat from mammals 

other than marine mammals)

Cattle, meat byproducts, except 

kidney

0.05 0.05 Edible offal (mammalian)

Corn, field, grain 0.1 0.1 0.03 Maize; 0.05 maize flour

Corn, field, stover 10.0 10 Maize fodder (dry)

N

+

N

+

H C3

CH3

Cl

2
Page 14 of 22

Table 2. Commodities for which US and International Tolerances and Maximum Residue Limits Differ

Residue Definition:

US Canada Mexico Codex

Cotton, undelinted seed 3.5 2 Cotton seed

Cranberry 0.05 0.01 (*) Berries and other 

small fruits

Egg 0.01 0.005 (*)

Endive 0.05 0.07 Leafy vegetables

Fruit, citrus, group 10 0.05 0.02 Citrus fruits

Fruit, pome, group 11 0.05 0.05 0.01 (*) Pome fruits

Fruit, stone, group 12 0.05 0.05 0.01 (*) Stone fruits

Ginger 0.1 0.05 Root and tuber vegetables

Goat, kidney 0.5 0.05 Edible offal (mammalian)

Goat, meat 0.05 0.005 (*) Meat from mammals 

other than marine mammals)

Goat, meat byproducts, except 

kidney

0.05 0.05 Edible offal (mammalian)

Guar, seed 0.5 0.5 Pulses

Guava 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Hog, kidney 0.5 0.05 Edible offal (mammalian)

Hog, meat 0.05 0.005 (*) Meat from mammals 

other than marine mammals)

Hog, meat byproducts, except 

kidney

0.05 0.05 Edible offal (mammalian)

Hop, dried cones 0.5 0.1 Hops, dry

Horse, kidney 0.5 0.05 Edible offal (mammalian)

Horse, meat 0.05 0.005 (*) Meat from mammals 

other than marine mammals)

Horse, meat byproducts, except 

kidney

0.05 0.05 Edible offal (mammalian)

Kiwifruit 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Lentil, seed 0.3 0.5 Pulses

Lettuce 0.05 0.07 Leafy vegetables

Milk 0.01 0.005 (*) 

Nut, tree, group 14 0.05 0.05 Filberts 0.05 Tree nuts

Okra 0.05 0.05 Fruiting vegetables, other 

than cucurbits

Olive 0.05 0.1

Papaya 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Passionfruit 0.2 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Pea and bean, dried shelled, except 

soybean, subgroup 6C, except guar 

bean

0.3 0.5 Pulses

Persimmon 0.05 0.01 (*) Assorted tropical and 

subtropical fruits-inedible peel

Pistachio 0.05 0.05 Tree nuts

Potato 0.5 0.05 Root and tuber vegetables

Rice, grain 0.05 0.05

Rice, straw 0.06 0.05 Rice straw and fodder, 

dry
Page 15 of 22

Table 2. Commodities for which US and International Tolerances and Maximum Residue Limits Differ

Residue Definition:

US Canada Mexico Codex

Sheep, kidney 0.5 0.05 Edible offal (mammalian)

Sheep, meat 0.05 0.005 (*) Meat from mammals 

other than marine mammals)

Sheep, meat byproducts, except 

kidney

0.05 0.05 Edible offal (mammalian)

Sorghum, forage, forage 0.1 0.3 Sorghum straw and fodder, 

dry

Sorghum, grain, grain 0.05 0.03

Soybean, hay 10.0 0.5 Soya bean fodder dry

Soybean, seed 0.7 0.5 Pulses

Turnip, greens 0.05 0.05 0.07 Leafy vegetables

Turnip, roots 0.05 0.05 0.05 Root and tuber vegetables

Vegetable, brassica, leafy, group 5 0.05 0.05 0.07 Leafy vegetables

Vegetable, cucurbit, group 9 0.05 0.05 cucumber 0.02 Fruiting vegetables, 

Cucurbits

Vegetable, fruiting, group 8 0.05 0.05 Fruiting vegetables, other 

than cucurbits

MRLs with NO US equivalent

Poultry meat 0.005 (*)

Poultry, Edible offal of 0.005 (*)

Sunflower seed 2

Tea, Green, Black (black fermented 

and dried)

0.2

Summary of Points of Departure

Summary of Toxicological Doses and Endpoints for Paraquat for Use in Human Health Risk Assessments

Exposure

Scenario

Dose Used in Risk 

Assessment, UF 

Special FQPA SF and 

Level of Concern for 

Risk Assessment

Study and Toxicological Effects

Acute Dietary

(females 13-49)

NOAEL = 1.25 

mg/kg/day

UF = 300

Acute RfD = 0.0125 

mg/kg/day

FQPA SF = 1x

aPAD = 0.0042 

mg/kg/day

Multi-generation rat study

LOAEL = 3.75 mg/kg/day, based on 

increased incidences of alveolar histiocytes 

in both sexes

Acute Dietary

(general population)

NOAEL = 1.25

mg/kg/day

UF = 100

Acute RfD = 0.0125 

mg/kg/day

FQPA SF = 1x

aPAD = 0.0125 

mg/kg/day

Multi-generation rat study

LOAEL = 3.75 mg/kg/day, based on 

increased incidences of alveolar histiocytes 

in both sexes

Chronic Dietary

(all populations)

NOAEL = 0.45

mg/kg/day

UF = 100

Chronic RfD = 

0.0045 mg/kg/day

FQPA SF = 1x

cPAD = 0.0045 

mg/kg/day

Chronic toxicity in dogs

LOAEL = 0.93 mg/kg/day, based on 

increased severity of chronic pneumonitis 

and gross lung lesions in both sexes, and 

focal pulmonary granulomas in males

Dermal 

Short- -

Intermediate - Term

NOAEL = 1.25 

mg/kg/day

LOC = MOE = 100

Dermal absorption 

Multi-generation rat study

LOAEL = 3.75 mg/kg/day, based on 

increased incidences of alveolar histiocytes 
Page 16 of 22

Summary of Toxicological Doses and Endpoints for Paraquat for Use in Human Health Risk Assessments

Exposure

Scenario

Dose Used in Risk 

Assessment, UF 

Special FQPA SF and 

Level of Concern for 

Risk Assessment

Study and Toxicological Effects

(1day – 6 months) factor = 0.3% in both sexes

Dermal 

Long-Term

(> 6 months)

NOAEL = 0.45 

mg/kg/day

LOC = MOE = 100

Dermal absorption 

factor = 0.3%

Chronic toxicity in dogs

LOAEL = 0.93 mg/kg/day, based on 

increased severity of chronic pneumonitis 

and gross lung lesions in both sexes, and 

focal pulmonary granulomas in males

Inhalation 

Short - through 

Long - Term

(1 day - > 6 months)

NOAEL = 0.01 

μg/L for respirable 

particles

NOAEL = 1.25 

mg/kg/day for nonrespirable particles

LOC = MOE = 100

Inhalation absorption 

factor = 100%

21-Day inhalation toxicity study in rats 

(respirable particles)

LOAEL = 0.10 μg/L, based on squamous 

keratinizing metaplasia and hyperplasia of 

the epithelium of the larynx

3-generation reproduction study (nonrespirable particles) 

Cancer (oral, 

dermal, inhalation)

Classification: Category E (evidence of non-carcinogenicity to humans)

UF = uncertainty factor, FQPA SF = Special FQPA safety factor, NOAEL = no observed adverse effect level, 

LOAEL = lowest observed adverse effect level, PAD = population adjusted dose (a = acute, c = chronic) RfD = 

reference dose, MOE = margin of exposure, LOC = level of concern, NA = Not Applicable

International Residue Limits 

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

40 CFR 180.205:

Plants/Livestock: paraquat (1,1′-dimethyl4,4′-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'-dimethylPlants/Livestock: paraquat cation.

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

US Canada Mexico1 Codex2

Acerola 0.05

Almond, hulls 0.5 0.01 (*)

Animal feed, nongrass, group 18, 

forage

75.0

Animal feed, nongrass, group 18, 

hay

210.0

Artichoke, globe 0.05

Asparagus 0.5

Avocado 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel
Page 17 of 22

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Banana 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Barley, grain 0.05 0.05

Barley, hay 3.5

Barley, straw 1.0

Beet, sugar, roots 0.5 0.05 Root and tuber 

vegetables

Beet, sugar, tops 0.05

Berry group 13 0.05 0.05 aronia berries, 

blackberries, 

buffalo currants, 

Chilean guavas, 

currant, elderberries, 

European barberry, 

gooseberries, 

highbush 

blueberries, 

highbush 

cranberries,honeysu

ckle, huckleberries, 

jostaberries, 

lingonberries, 

loganberries, 

raspberries, lowbush 

blueberries, native 

currants, raspberries, 

salal berries, 

saskatoon berries 

(juneberries), sea 

buckthorn, wild 

raspberries

0.01 (*) Berries and 

other small fruits

Cacao bean, bean 0.05

Carrot, roots 0.05 0.05 0.05 Root and tuber 

vegetables

Cattle, fat 0.05

Cattle, kidney 0.5 0.05 Edible offal 

(mammalian)

Cattle, meat 0.05 0.005 (*) Meat from 

mammals other than 

marine mammals)

Cattle, meat byproducts, except 

kidney

0.05 0.05 Edible offal 

(mammalian)

Coffee, bean, green 0.05

Corn, field, forage 3.0

Corn, field, grain 0.1 0.1 0.03 Maize; 0.05 

maize flour

Corn, field, stover 10.0 10 Maize fodder 

(dry)

Corn, pop, grain 0.1 0.1

Corn, pop, stover 10.0
Page 18 of 22

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Corn, sweet, kernel plus cob with 

husks removed

0.05 0.05

Cotton, gin byproducts 110.0

Cotton, undelinted seed 3.5 2 Cotton seed

Cowpea, forage 0.1

Cowpea, hay 0.4

Cranberry 0.05 0.01 (*) Berries and 

other small fruits

Egg 0.01 0.005 (*)

Endive 0.05 0.07 Leafy 

vegetables

Fig 0.05

Fruit, citrus, group 10 0.05 0.02 Citrus fruits

Fruit, pome, group 11 0.05 0.05 apples, asian 

pears, crabapples, 

loquats, mayhaws, 

pears, quinces

0.01 (*) Pome fruits

Fruit, stone, group 12 0.05 0.05 apricots, 

nectarines, peaches, 

plumcots, plums, 

prune plums, sweet 

cherries, tart 

cherries

0.01 (*) Stone fruits

Ginger 0.1 0.05 Root and tuber 

vegetables

Goat, fat 0.05

Goat, kidney 0.5 0.05 Edible offal

(mammalian)

Goat, meat 0.05 0.005 (*) Meat from 

mammals other than 

marine mammals)

Goat, meat byproducts, except 

kidney

0.05 0.05 Edible offal 

(mammalian)

Grain, aspirated fractions 65.0

Grape 0.05 0.05

Grass, forage 90.0

Grass, hay 40.0

Guar, seed 0.5 0.5 Pulses

Guava 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Hog, fat 0.05

Hog, kidney 0.5 0.05 Edible offal 

(mammalian)

Hog, meat 0.05 0.005 (*) Meat from 

mammals other than 

marine mammals)

Hog, meat byproducts, except 

kidney

0.05 0.05 Edible offal 

(mammalian)

Hop, dried cones 0.5 0.1 Hops, dry
Page 19 of 22

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Horse, fat 0.05

Horse, kidney 0.5 0.05 Edible offal 

(mammalian)

Horse, meat 0.05 0.005 (*) Meat from 

mammals other than 

marine mammals)

Horse, meat byproducts, except 

kidney

0.05 0.05 Edible offal 

(mammalian)

Kiwifruit 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Lentil, seed 0.3 0.5 Pulses

Lettuce 0.05 0.07 Leafy 

vegetables

Milk 0.01 0.005 (*) 

Nut, tree, group 14 0.05 0.05 Filberts 0.05 Tree nuts

Okra 0.05 0.05 Fruiting 

vegetables, other 

than cucurbits

Olive 0.05 0.1

Onion, bulb 0.1 0.1 Dry bulb onions

Onion, green 0.05 0.05

Papaya 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Passionfruit 0.2 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Pea and bean, dried shelled, except 

soybean, subgroup 6C, except guar 

bean

0.3 0.5 Pulses

Pea and bean, succulent shelled, 

subgroup 6B

0.05 0.05 succulent 

shelled (blackeyed 

peas, broad beans, 

cowpeas, english 

peas, 

garden peas, green 

peas, lima beans, 

peas, pigeon peas, 

southern peas)

Pea, field, hay 0.8

Pea, field, vines 0.2

Peanut 0.05

Peanut, hay 0.5

Peppermint, tops 0.5
Page 20 of 22

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Persimmon 0.05 0.01 (*) Assorted 

tropical and 

subtropical fruitsinedible peel

Pineapple 0.05

Pineapple, process residue 0.25

Pistachio 0.05 0.05 Tree nuts

Potato 0.5 0.05 Root and tuber 

vegetables

Rhubarb 0.05

Rice, grain 0.05 0.05

Rice, straw 0.06 0.05 Rice straw and 

fodder, dry

Safflower, seed 0.05

Sheep, fat 0.05

Sheep, kidney 0.5 0.05 Edible offal 

(mammalian)

Sheep, meat 0.05 0.005 (*) Meat from 

mammals other than 

marine mammals)

Sheep, meat byproducts, except 

kidney

0.05 0.05 Edible offal 

(mammalian)

Sorghum, forage, forage 0.1 0.3 Sorghum straw 

and fodder, dry

Sorghum, grain, forage 0.1

Sorghum, grain, grain 0.05 0.03

Soybean, forage 0.4

Soybean, hay 10.0 0.5 Soya bean 

fodder dry

Soybean, hulls 4.5

Soybean, seed 0.7 0.5 Pulses

Spearmint, tops 0.5

Strawberry 0.25

Sugarcane, cane 0.5

Sugarcane, molasses 3.0

Sunflower, seed 2.0

Turnip, greens 0.05 0.05 0.07 Leafy 

vegetables

Turnip, roots 0.05 0.05 0.05 Root and tuber 

vegetables
Page 21 of 22

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Vegetable, brassica, leafy, group 5 0.05 0.05 bok choy 

Chinese cabbages, 

broccoli, broccoli 

raab, Brussels 

sprouts, cabbages, 

cauliflower, Chinese 

broccoli, chinese 

mustard cabbages, 

collards, kale, 

kohlrabi, mustard 

greens, mustard 

spinach, napa 

Chinese cabbages, 

rape greens

0.07 Leafy 

vegetables

Vegetable, cucurbit, group 9 0.05 0.05 cucumber 0.02 Fruiting 

vegetables, 

Cucurbits

Vegetable, fruiting, group 8 0.05 0.05 Fruiting 

vegetables, other 

than cucurbits

Vegetable, legume, edible podded, 

subgroup 6A

0.05 0.05 Ediblepodded ( dwarf 

peas, jackbeans, 

moth beans, peas, 

pigeon peas, runner 

beans, snap beans, 

snow peas, 

soybeans, sugar 

snap peas, sword 

beans, wax beans, 

yardlong beans)

Wheat, forage 0.5

Wheat, grain 1.1

Wheat, hay 3.5

Wheat, straw 50.0

MRLs with NO US equivalent

Poultry meat 0.005 (*)

Poultry, Edible offal of 0.005 (*)

Sunflower seed 2

Tea, Green, Black (black fermented 

and dried)

0.2

Completed by: M.Negussie; 06/10/2011

c) Tolerances with regional registrations. Tolerances with regional registration as defined in §180.1(m), are 

established for residues of the pesticide 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) in or on the following food 

commodities:
Page 22 of 22

Commodity Parts per million Canada Codex2

Cassava 0.05 0.05 Root and tuber vegetables

Pea, pigeon, seed 0.05 0.5 Pulses

Tanier 0.05 0.05 Root and tuber vegetables

Taro, corm 0.1 0.05 Root and tuber vegetables

Tyfon 0.05

Yam, true, tuber 0.05 0.05 Root and tuber vegetables

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

2

* = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = 

processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the 

fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.