UnH«i Sttt« Office of Pesticides end Toxic Sut»tanee>
EiiKliuniiuitil Protection Office of Pesticide Programs (TS-766C)
Agency Washington. DC 20460
&EPA Pesticide
Fact Sheet
Name of Chemical: Paraquat
Reason for Issuance: Registration Standard
Date Issued: Jfe It W
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Fact Sheet Number: 131
1. Description of Chemical
Generic Name: 1 ,1'-dimethyl-4-41-bipyridinium ion
Common Name: Paraquat
Trade Names: Actor Cekuquat, Crisquat, Dextrone, Dexuron,
Esgrara, Gramanol, Gramoxone, Gramuron, Hebaxon, Herboxone,
Goldquat 276, Paracol Paraquat CL, Pillarquat, Pillarxone,
Sweep, PP148 (dichloride) and Dextrone X.
EPA Shaughnessy Code: 061601 (dichloride)
Chemical Abstracts Service (CAS) Number: 1910-42-5 (dichloride)
Year of Initial Registration: 1964
Pesticide Type: Herbicide, defoliant, desiccant, and plant
growth regulator
Chemical Family: Bipyridylnium or dipyridylnium
U.S. and Foreign Producers: ICI Americas, Inc.; Taiwan by
Comlets Chemical Industrial Company, Ltd., and Shinung
Corp., Italy by VisplantChriraiasero S.p.I.; Spain by
Hightex S.A.; Great Britain by ICI Plant Protection
Division.
2. Use Patterns and Formulations
Application Sites: Terrestrial food crops; terrestrial
nonfood crops; terrestrial noncrop, forestry and domestic
outdoor sites.
Major Crops Treated: Field crops (corn and soybeans), and
fruit and nut crops.
Types and Method of Application: Foliarly applied by
broadcast, band, or directed spray by ground equipment
or broadcast by aircraft. It may be applied preplant,
preemergence, or preharvest in relation to the crop.
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Application Rates: 0.25 lb active ingredient/A to 1.0 lb
active ingredient/A (0.28 to 1.12 kg active ingredient/ha).
Types of Formulation: Aqueous solution containing 2 lbs
(0.24 kg) paraquat cation per gal (L).
Usual Carrier: Water.
3. Science Findings
Summary Science Statement: Paraquat is extremely toxic
(Category I) via oral, dermal, and inhalation exposure
routes to mammals. It is not teratogenic to mice or
rats. Paraquat is not oncogenic to mice but is oncogenic
to rats. Paraquat is weakly genotoxic - it was negative
for mutagenicity in eight studies, weakly positive in
four studies and positive in four studies.
Paraquat is moderately toxic to birds, slightly toxic to
freshwater fish, moderately toxic to aquatic invertebrates,
and relatively nontoxic to honeybees. Paraquat is not
believed to cause problems 1th stable wildlife populations
but may be hazardous to unstable or endangered populations
of plants and animals.
Paraquat dichioride was stable to hydrolysis and photo-
lysis in soil, preliminary data indicate that paraquat
has a half-life of greater than 2 weeks in water plus
soil, is immobile in silt loam and silty clay loam, and
slightly mobile in sandy loam and potentially mobile in
sandy soils extremely low in organic matter. The half-
life of paraquat in water is approximately 23 weeks.
Paraquat is not readily desorbed from the soil and is not
likely to contaminate ground water in agricultural soils.
Preliminary data indicate that the paraquat degradate
14 C-carboxy-1-methyl pyridiniuni (QINA) chloride is loosely
absorbed in the soil and is potentially mobile and has a
leaching potential.
Chemical Characteristics: Analytical grade of paraquat
dichioride is a colorless odorless hygroscopic powder,
whereas the technical product is yellow. Paraquat is
very soluble in water, slightly soluble in alcohols and
insoluble in hydrocarbons. It is nonvolatile, corrosive
to metals, stable at room temperature (either as a solid
or an aqueous solution at neutral or acidic pH), but is
hydrolyzed by alkali, decomposes photocheTnically , and
melts (with decomposition) at 300 °C.
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Toxicology Characteristics:
Acute Toxicology
Acute Oral Toxicity = 100 and 126 mg paraquat cation/kg
(rat) for males; 112-150 mg paraquat
cation/kg for females
Toxicity Category II
Acute Oral Toxicity = 22 mg paraquat cation/kg for
(guinea pig) males and females
Toxicity Category I
Acute Dermal Toxicity = 59.9 mg paraquat cation/kg
(rabbit) Toxicity Category I
Acute Inhalation = 0.6 to 1.4 ug paraquat ion/L
(rat) Toxicity Category I
Eye Irritation = Severe Eye Irritant
(rabbit) Toxicity Category I
Primary Derraal Irritation = Primary irritation score of
(rabbit) 2.1 - Toxicity Category III
Skin Sensitization = Not a sensitizer
(guinea pig)
Major Routes of Exposure:
Acute Inhalation: Two inhalation studies were submitted.
One study had an inhalation toxicity of about 1.0 ugfL
(Toxicity Category I) with 90 percent of the particle
diameters below 0.3 urn. A second study was performed
with particles of median diameter of 21.5 to 23 urn.
The inhalation toxicity for this study was 3.5 ugiL
(Toxicity Category 1). These studies show that inhala-
tion toxicity is highly dependent on particle size.
Information received on particle size of paraquat
droplets formed during aerial application and during
knapsack spraying indicate that virtually no droplets
smaller than 15 urn were formed during either method
of application.
Subchronic Dermal Exposure: A 21-day dermal toxicity study
in rabbits was submitted with a NOEL of 1.15 mg paraquat
cation/kg body weight (bwt) for local skin effects and a
NOEL for systemic toxicity of 6 mg paraquat cation/kg bwt.
Data are available indicating that a dermal absorption
rate for humans is about 0.5 percent. These data are
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preferable to dermal data from other species, therefore,
the dermal data in rabbits are not of cond ern.
Combination of Acute Inhalation and Dermal Exposure: Mar-
gins of safety were calculated for combined inhalation
and dermal exposure of workers repeatedly exposed to
paraquat. Combined inhalation and dermal exposures
of several groups of workers were then compared to a
NOEL of 0.5 mg paraquat cation/kg/day derived from a
90-day dog-feeding study. The lowest effect level
(LEL) for this study was 1.5 mg paraquat cation/kg/day,
at which dosage level toxic effects in the lung were
observed. All but two of the margins of safety are
greater than 100.
Chronic Toxicology:
Teratology and Reproduction
Paraquat was not teratogenic to mice. The fetotoxic
NOEL is 5 ing paraquat cation/kg bwt and the maternal
NOEL is 1.0 mg paraquat cation/kg bwt.
Paraquat was not teratogenic to rats. Both the feto-
toxic and maternal NOEL are 1.0 mg paraquat cation/kg
bwt.
Paraquat had no effect on reproduction in rats. The
systemic NOEL for reproduction is 25 parts per million
(ppm).
The teratology and reproduction studies are acceptable
and show no reason to place paraquat in Special Review.
Chronic Feeding - Oncogenic Studies
In the rat chronic feeding study, the systemic NOEL is
25 ppm of paraquat cation per kilogram of body weight
and the systemic LEL is 75 ppm.
In the 1-year dog study the systemic NOEL Is 15 ppm
paraquat cation per kilogram of body weight. The
systemic LEL is 30 ppm.
Paraquat was not oncogenic to mice. The systemic NOEL
is 12.5 ppm of paraquat cation per kilogram of body
weight. This study is acceptable.
Paraquat was oncogenic to rats. Squamous cell carci-
noma occurred in 51.6 percent of all rats having tumors
of the skin and suhcutis in the head region. In high
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dose males, the incidence was significantly increased
over concurrent controls.
Mutagenicity: Paraquat was negative in eight studies
(mostly in gene mutation and chromosomal aberration
assays); weakly positive in two gene mutations, one
chromosomal aberration and one DNA damage/repair
assays; and positive in four DNA damage/repair
assays.
Physiological and Biochemical Behavior Characteristics:
Foliar Absorption: Very rapidly absorbed by the foliage.
Translocation: Can occur via the xylem under certain
conditions.
Mechanism of Pesticidal Action: Lipid peroxidation result-
ing in disruption of cell membrane.
Metabolism and Persistence in Plants: In sunlight, limit-
ed photochemical breakdown occurs for paraquat which
remains on the outside of treated plants. Since
plants are killed rapidly in bright sunlight, signifi-
cant quantities of the breakdown products are formed
only on surfaces of dead tissues and there is no
movement of these substances from the dead tissues to
other parts of the plant.
Environmental Characteristics:
Absorption and Leaching in Basic Soil Types: Langmuir
adsorption maxima values (m) ranged from 17 to 46.8
mg/100 grams on seven clay soils and one silty clay
loam soil. Adsorption is positively correlated with
soil cation exchange capacity (CEC). Paraquat is not
readily desorbed from the soil and is not likely to
contaminate ground water in agricultural soils. Data
are required to determine the potential for the QINA
degradate to leach in soils.
Microbial Breakdown: Bound paraquat is degraded with
difficulty or not at all.
Loss from Photodecomposition and/or Volatilization: Does
not volatilize; limited photodecomposition may occur
on sprayed leaf surfaces and dead vegetation.
Contamination of Ground and Surface Water: Paraquat binds
tightly to the soil and does not leach in agricultural
soils.
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Exposure of Humans and Nontarget Organisms to Chemical or
Degradates: Margins of safety for humans appear ade-
quate when product is used according to label direc-
tions. Use of paraquat nay have an effect on a few
mammals or ground nesting birds under unusual circum-
stances. Wildlife populations should not be adversely
affected when paraquat is used according to label
directions.
Exposure During Reentry: Current precautionary labeling
and worker safety rules adequately protect worker,
mixer, loader, applicator.
Ecological Characteristics: Paraquat is moderately toxic
to birds and aquatic invertebrates and slightly toxic
to freshwater fish.
Avian Acute Oral Toxicity with Bobwhite quail: 176 mg/kg
Aviari Dietary Toxicity with Bobwhite quail: 981 ppm
Ring-neck pheasant: 1468 ppm
Mallard duck: 4048 ppm
Avian Reproduction Studies: Bobwhite quail: 100 ppm
Mallard duck: 30 ppm
Acute Toxicology: Freshwater Fish:
Rainbow trout: 15-38.7 ppm
Bluegill sunfish: 13-156 ppm
Acute Toxicity to Invertebrates (Daphnia): 1.2 to 4.0 mg/L
Endangered Species: Although paraquat is not believed to
cause problems with stable wildlife populations, its
acute and subacute toxicity may be hazardous to
unstable or endangered populations (primarily plant
species).
Tolerance Reassessment: Tolerances are established for
residues of the plant regulator, desiccant, defoliant,
and herbicide paraquat (1 ,1-dimethyl-4,4’-bipyridinium
ion) derived from application of either the his(methyl-
sulfate) or dichioride salt (both calculated as the
cation) in or on the following raw agricultural
commodities (40 CFR 180.205):
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Commodities Parts Per Million
Acerola 0.05
Alfalfa 5.0
Almond hulls 0.5
Apples 0.05
Apricots 0.05
Asparagus 0.5
Avocados 0.05
Bananas 0.05
Barley, grain 0.05
Beans, forage 0.1
Beans, hay 0.4
Beans, lima (succulent) 0.05
Beans, snap (succulent) 0.05
Beets, sugar 0.5
Beets, sugar (tops) 0.5
Birdsfoot trefoil 5.0
Broccoli 0.05
Cabbage 0.05
Carrots 0.05
Cattle, fat - 0.01
Cattle, meat 0.01
Cattle, meat byproducts 0.01
Cauliflower 0.05
Cherries 0.05
Chinese Cabbage 0.05
Citrus fruit 0.05
Clover 5.0
Coffee beans 0.05
Collards 0.05
Corn, fresh, inc. sweet corn
(K + CWHR) 0.05
Corn, fodder 0.05
Corn forage 0.05
Corn grain 0.05
Cottonseed 0.5
Cucurbits 0.05
Eggs 0.01
Figs 0.05
Goats, fat 0.01
Goats, meat 0.01
Goats, meat byproducts 0.01
Grass, pasture 5.0
Grass, range 5.0
Guar beans 0.5
Guava 0.05
Hogs, fat 0.01
Hogs, meat 0.01
Hogs, meat byproducts 0.01
Hops, fresh 0.1
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Commodities Parts Per Million
Hops vines 0.5
Horses, fat 0.01
Horses, meat 0.01
Horses, meat byproducts 0.01
Kiwifruit 0.05
Lettuce 0.05
Milk 0.01
Mint, hay 0.5
Nectarines 0.05
Nuts 0.05
Oat grain 0.05
Olives 0.05
Onions, dry bulb 0.05
Onions, green 0.05
Papayas 0.05
Passion fruit 0.2
Peaches 0.05
Pears 0.05
Peas, succulent 0.05
Peas, hay 0.8
Pineapples 0.05
Pistachio nuts 0.05
Plums (fresh prunes) 0.05
Potatoes 0.5
Poultry, fat 0.01
Poultry, meat 0.01
Poultry, meat byproducts 0.01
Rhubarb 0.05
Rye grain 0.05
Safflower seed 0.05
Sheep, fat 0.01
Sheep, meat 0.01
Sheep, meat byproducts 0.01
Small fruit 0.05
Sorghum forage 0.05
Sorghum grain 0.05
Soybeans 0.05
Soybean forage 0.05
Strawberries 0.25
Sugarcane 0.5
Sunflower seeds 2.0
Turnips (roots) 0.05
Turnips (tops) 0.05
Vegetables, fruiting 0.05
Wheat grain 0.05
A food additive tolerance of 0.2 ppm is established
for residues of the defoliant, desiccant, and herbicide
paraquat (1,1’_dimethyl-4,4’-bipyridifliUm ion) derived
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from the application of either the bis(methylsulfate)
or dichioride salt (both calculated as the cation) in
or on dried hops resulting from application of the
pesticide to growing hops (21 CFR 193.331).
Feed additive tolerances are established for residues
of the defoliant, desiccant, and herbicide paraquat
(1,l’dimethyl4-4’-bipyridifliUlfl ion) derived from the
application of either the bis(methylsulfate) or
dichioride salt (both calculated as the cation) in
the following processed feeds when present therein as
a result of application of paraquat to growing crops
(21 CFR 561.289):
Feeds Parts Per Million
Mint, hay, spent 3.0
Sunflower, seed, hulls 6.0
The acceptable daily intake (ADI) based on the 1-year dog
study (NOEL of 0.45 mg/kg/day) and using a safety
factor of 100 is calculated to be 0.0045 mg/kg/day.
The maximum permitted intake (MPI) for a 60-kg human
is calculated to be 0.27 mg/day. The theoretical
maximum residue contribution (TMRC) for paraquat,
based on published tolerances is 0.1134 mg/day. The
TMRC constitutes 42 percent of the MPI.
Reported Pesticide Incidents: The Agency’s Pesticide
Incident Monitoring System (PIMS) indicated that the
majority of the poisoning incidents involving paraquat
resulted from the purposeful ingestion of the chemical
in apparent suicide attempts.
4. Summary of Regulatory Position and Rationale
The Agency has classified paraquat as a Group C oncogen
(Possible Human Carcinogen). However, after considering
applicator exposure to paraquat, the Agency has concluded
that the risks posed by paraquat are not of concern in
terms of the magnitude of risk to the individual appli-
cators.
The Agency is continuing to require that an emetic
cleared under 40 CFR 180.1001 be incorporated into all
manufacturing-use products (MUP’s) and end-use products
containing paraquat. The emetic is needed in the formu-
lations to induce rapid vomiting thereby reducing absorp-
tion of paraquat if swallowed.
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The Agency is requiring those agricultural products contain-
ing paraquat already classified as “Restricted Use” maintain
this classification. Based on submitted acute toxicity and
subchronic toxicity data the “Restricted Use” classification
and current precautionary statements are necessary to protect
mixer-loaders and applicators from effects of derrnal toxicity.
The Agency has determined that the homeowner product contain-
ing 0.276 percent paraquat presently unrestricted will remain
unrestricted. The Agency believes that this relatively dilute
formulation, when used according to label directions, is not
likely to present a significant health hazard to humans.
The Agency is requiring additional residue data on several
crops and processed commodities as well as some changes
in the tolerance listings. The Agency is requiring certain
label revisions pertaining to application and grazing restric-
tions, as determined by review of available residue data.
The Agency is requiring labeling to protect endangered
species. This labeling is addressed in Pesticide Regis-
tration (PR) Notices 87-4 and 87-5.
The Agency will issue registrations for substantially similar
products while data gaps are being filled. Significant new
uses for paraquat will be considered on a case-by-case basis.
5. Summary of Major Data Gaps Date due (from issuance
of Standard )
Environmental fate data 9-50 months
Subchronic inhalation toxicity 15 months
Residue chemistry data 24 months
Product chemistry 6 months
6. Contact Person at EPA : Robert J. Taylor
Office of Pesticide Programs, EPA
Registration Division (TS-767C)
401 M Street SW.
Washington, DC 20460
Phone: (703) 557-1800
Disclaimer : The information presented in this Pesticide Fact
Sheet is for informational purposes only and may not be used
to fulfill data requirements for pesticide registration and
reregistration.
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