paraquat; Herbicide Profile 2/85
CHEMICAL NAME: 1,1'-dimethyl-4,4'-bipyridinium ion; present as the
dichloride salt (ICI/Chevron) or dimethyl sulfate
TRADE NAME(S): Ortho Paraquat, Gramoxone (58).
FORMULATION(S): Only available as an aqueous solution containing
0.24 kg (2 lb) paraquat cation per L (gal) as the
dichloride salt (58).
TYPE: Dipyridyl herbicide
BASIC PRODUCER(S): Chevron Chemical Co.
575 Market St.
San Francisco, CA 94105
STATUS: Restricted use. RPAR: criteria possibly met or
exceeded: emergency treatment, chronic effects. Decision document
returning paraquat to the Registration Process was signed on 6/29/82.
Decision Document outlines data gaps and voluntary cancellation of
certain noncrop use sites (22).
PRINCIPAL USES: For desiccation of seed crops, for noncrop and
industrial weed control in bearing and nonbearing fruit orchards, shade
trees and ornamentals, for defoliation and desiccation of cotton, for
harvest aid in soybeans, sugarcane, guar and sunflowers, for pasture
renovation, for use in "No-Til' or before planting or crop emergence,
dormant alfalfa and clover, directed spray and for killing potato
vines. Paraquat is also effective for eradication of weeds in rubber
plantations, coffee plantations, and paddy bund (56).
APPLICATION METHOD(S): Ground or air foliar spray - contact activity
Important Weeds Controlled: Most annual weeds and grasses (8b).
Regrowth may occur in perennials with large underground root
systems. Rainfall after application has little bearing on effectiveness
II. PHYSICAL PROPERTIES
MOLECULAR FORMULA: C12 H14 N2 (cation only) (62); C12 H14 N2 Cl2
(dichloride salt) (58).
MOLECULAR WEIGHT: 186.2 (cation only); 257.2 (dichloride salt) (58).
PHYSICAL STATE: White crystalline solid (pure salt); dark red
solution (technical product) (58).
Technical product > 95% pure (62).
ODOR: Faint ammoniacal odor (pure compound) (58).
DECOMPOSITION TEMPERATURE: approximately 300c (pure compound) (58).
BOILING POINT: Salts decompose at high temperatures, charring
rather than melting or boiling (58).
VAPOR PRESSURE: Nonvolatile. Vapor pressure of salts is very low,
below 1 x 10-7 mmHg (pure compound) (58).
SOLUBILITY: Completely soluble in water (pure compound) (58).
III. HEALTH HAZARD INFORMATION
OSHA STANDARD: 0.5 mg/m3 averaged over an eight-hour work shift (14).
NIOSH RECOMMENDED LIMIT: NA
ACGIH RECOMMENDED LIMIT: TWA (Time Weighted Average) = 0.1 mg/m3
(respirable sizes) (15c).
A. ACUTE TOXICITY
DERMAL: LD50 = >480 mg paraquat ion (rabbit). The
concentrate is irritant to skin. Absorption through
intact skin is minimal, but may be facilitated if the
skin is damaged (58).
LD50 = c. 236 mg/kg (rabbit) (62).
ORAL: LD50 = 120 mg parathion ion /kg (58).
LD50 = 150 mg paraquat ion/kg (rat); 104 mg/kg (mouse);
25-50 mg/kg (dog); 262 mg/kg (Rhode Island hen); 70
mg/kg (sheep) (62).
INHALATION: As paraquat has no appreciable vapor pressure,
there is no hazard from inhalation. Prolonged,
direct contact with the spray mist may cause oral
and nasal irritation, and should be avoided (58).
EYES: The concentrate is irritating to the eye (58).
B. SUBACUTE AND CHRONIC TOXICITY:
Subacute percutaneous LD50 (20 applications), greater than 24 mg
paraquat ion/kg (rabbit).
Rats: 2-year feeding studies did not reveal significant
abnormalities at dietary levels up to 170 ppm paraquat ion.
Dogs: No significant abnormalities were seen after feeding a diet
containing 34 ppm paraquat ion for 27 months. Effects were apparent at
dietary levels of 85 and 170 ppm (58).
IV. ENVIRONMENTAL CONSIDERATIONS
Paraquat has a wide margin of safety between recommended dosages
and rates necessary to cause toxic symptoms to fish and wildlife
Toxicity to fish depends on the formulation and wetter used, LC50
(96-hr) is: for rainbow trout 32 mg/l; for brown trout 2.5-13 mg/l
Behavior In Or On Soils
1. Adsorption and leaching characteristics in basic soil types: An
important and unique property of paraquat is its very rapid
and complete inactivation by soil. This results from
reaction between the double positively charged paraquat
cation and clay minerals present in soils to form complexes
with the negatively charged sites on the clay minerals (and
even insertion into the layer planes of such minerals as
Paraquat cannot be removed from such sites by washing, even
with saturated solutions of salts, and can only be
regenerated by breaking down the clay mineral with 18 N
sulfuric acid. Most soils have sufficient capacity in the
top inch of soil alone to bind many hundred times the normal
field rates of application of paraquat in this form. There
are also other forms of binding of paraquat in soils -- e.g.,
by reaction with humic acids and by normal Langmuir type
adsorption onto organic matter and soil particles. In the
case of this rather weaker binding there is a true
equilibrium between the quantity adsorbed and free paraquat
in an aqueous phase in contact with the soil. However, even
in this case, fairly high concentrtions in the soil are
required to give phytotoxic concentrations of paraquat in the
2. Microbial breakdown: Experiments with micoorganisms in culture
media have shown that certain of these are capable of
decomposing paraquat in the absence of soil. However, they
degrade bound paraquat with difficulty or not at all.
3. Loss from photodecomposition and/or volatilization: Loss of
paraquat can occur by photochemical decomposition on sprayed
leaf surfaces and on dead and decaying vegetation.
Photochemical decomposition of paraquat has also been shown
in the laboratory by irradiating thin layers of soil, but
such decomposition on the soil has not been unequivocally
demonstrated under field conditions.
4. Resultant average persistence at recommended rates: When bound to
soil is very persistent but biologically unavailable (58).
V. EMERGENCY AND FIRST AID PROCEDURES
The chemical information provided below has been condensed
from original source documents, primarily from "Recognition and
Management of Pesticide Poisonings", 3rd ed. by Donald P. Morgan,
which have been footnoted. This information has been provided in
this form for your convenience and general guidance only. In
specific cases, further consultation and reference may be required
and is recommended. This information is not intended as a sub-
stitute for a more exhaustive review of the literature nor for the
judgement of a physician or other trained professional.
If poisoning is suspected, do not wait for symptoms to develop.
Contact a physician, the nearest hospital, or the nearest Poison
FREQUENT SYMPTOMS AND SIGNS OF POISONING: Exposure to paraquat
may cause irritation of the eyes, nose, throat, and skin. It may also
cause nose bleeding and abnormalities or loss of fingernails. Exposure
to mixtures of paraquat and a related compound, diquat, may cause
serious and permanent injury to the eyes (14).
The earliest (1-4 days) symptoms of injury and signs following
ingestion of a toxic dose of PARAQUAT are burning PAIN (oral,
substernal, abdominal), NAUSEA, VOMITING, DIARRHEA, and sometimes
melena. Early symptoms are sometimes so mild that vigorous treatment
is improperly delayed.
From 24-74 hours, indications of renal and hepatic insult appear.
Albuminuria, hematuria, pyuria, and ELEVATED BUN and CREATININE may
occur. OLIGURIA may develop, and this signals severe poisoning.
JAUNDICE and elevations of serum GOT, GPT, LDH, and alkaline
phosphatase reflect hepatocellular injury. These injuries are usually
reversible, although severe renal tubular damage may require
A progressive decline in arterial oxygen tension and CO diffusion
capacity commonly precedes the appearance of pulmonary symptomatology.
COUGH, DYSPNEA, and TACHYPNEA usually appear 72-96 hours after paraquat
ingestion, but may be delayed as long as 14 days. Progressive CYANOSIS
reflects deteriorating gas exchange caused by the fibrogenic reaction
in the alveolar sacs. In a few cases, the production of COPIOUS WATERY
SPUTUM (pulmonary edema) has followed ingestions of large amounts (200
ml) of paraquat or diquat concentrate (25).
SKIN CONTACT: If paraquat or solutions containing paraquat get on
the skin, immediately flush the contaminated skin with water. If
paraquat or solutions containing paraquat soak through the clothing,
remove the clothing immediately and flush the skin with water. If
irritation persists after washing, get medical attention (14).
INGESTION: Induce vomiting and send to a hospital as quickly as
INHALATION: If a person breathes in large amounts of paraquat,
move the exposed person to fresh air at once. If breathing has
stopped, perform artificial respiration. Keep the affected person warm
and at rest. Get medical attention as soon as possible (14).
EYE CONTACT: If paraquat or solutions containing paraquat get
into the eyes, wash eyes immediately with large amounts of water,
lifting the lower and upper lids occasionally. Get medical attention
immediately. Contact lenses should not be worn when working with this
NOTES TO PHYSICIAN:
1. After a DIPYRIDYL compound has been INGESTED, EVACUATE the
STOMACH, then LOAD the gastrointestinal tract with an effective
ADSORBENT, to minimize toxicant absorption. These measures must
be undertaken immediately, even though the patient is free of
signs of systemic toxicity, and even when, by all accounts, the
ingested dose was probably small and was taken as long as several
days prior to treatment.
INTUBATE the STOMACH, ASPIRATE content, then LAVAGE with at least
two liters of a slurry of ADSORBENT in normal saline. Then,
slowly instill several hundred additional ml of adsorbent slurry,
allowing the stomach and intestine to accommodate this volume
without overdistension and vomiting.
A. The ideal adsorbent is BENTONITE, administered as a 7 gm per
100 ml suspension. If not immediately available, use
ACTIVATED CHARCOAL, 30-50 gm in 300-400 ml of water, or any
concentration that will flow through the tube. As soon as
bentonite has been obtained, administer it as rapidly as the
patient will tolerate it. If patient cannot swallow
bentonite, administer it by stomach tube at the highest
concentration that will flow through the tube.
B. Initiate SALINE CATHARSIS. Give SODIUM SULFATE, 0.25 gm/kg,
and repeat in two hours if no bowel movement has occurred.
Magnesium salts are probably contraindicated, because of the
risk of magnesium retention in the presence of impaired renal
C. Continue administering bentonite suspension and sodium
sulfate until the gut has been thoroughly flushed. This may
require several days.
2. Secure samples of blood and urine for dipyridyl analysis. (See
Confirmation of Diagnosis.)
3. Commence INTRAVENOUS INFUSIONS of glucose and electrolyte to
minimize toxicant concentrations in the tissues, and expedite
excretion of the dipyridyl. Attempt to establish a diuresis of
10-15 liters per day.
CAUTION: Monitor fluid balance and electrolytes continuously to
insure against fluid overload if acute tubular necrosis
4. Although cases of paraquat poisoning have been successfully
managed by forced diuresis regimens alone, it is more effective to
use extracorporeal HEMODIALYSIS and/or HEMOPERFUSION over
specially coated charcoal. This procedure for toxicant removal is
best executed in tertiary care centers where blood levels of
paraquat can be monitored regularly, and various complications of
hemoperfusion can be detected and forestalled. The prognosis is
generally good when blood levels do not exceed 0.05 to 0.10 ppm by
24-48 hours after paraquat ingestion.
5. DO NOT ADMINISTER SUPPLEMENTAL OXYGEN in paraquat poisoning.
Increased levels of alveolar oxygen accelerate the pathologic
process in the lung caused by paraquat. Some clinicians recommend
maintaining the patient in an atmosphere of 15-16% oxygen as soon
as possible, to retard the fibrogenic process.
6. The topical injuries to mucous membranes produced by ingested
dipyridyls are painful and may require topical local anesthetic.
7. The effectiveness of various medicines and procedures in paraquat
poisoning remains uncertain. The free-radical scavenger
superoxide dismutase is theoretically appropriate as an antidote,
but is unproved. Corticosteroids are often given, and may be
helpful. There is limited laboratory evidence supporting the use
of propranolol and expectorants: glyceryl guaicolate, anise oil,
terpin hydrate, ammonium chloride and potassium iodide. One
victim is thought to have benefited from a combination of
azathioprine and potassium aminobenzoate. Lung transplant in one
case of paraquat poisoning was not successful (25).
VI. FIRE AND EXPLOSION INFORMATION
Commercial formulation is an aqueous salt solution, nonflammable
Not compatible with some alkyl sulfonate or alkyl aryl sulfonate
wetting agents or alkali-metal salts of hormone weed killers. Liable
to hydrolysis in the presence of alkaline materials including alkaline
waters. At all dilutions generally used, paraquat is virtually
noncorrosive to materials commonly used in spraying equipment. It is
generally not advisable to store undiluted paraquat in contact with
metals; the undiluted material is best kept in the original container
VIII. PROTECTIVE MEASURES
STORAGE AND HANDLING: Under normal storage conditions, in original
containers, shelf life is indefinitely long. The dry chemical is
somewhat sensitive to ultraviolet light. The product is stable to heat
beyond the range of ordinary ambient temperatures (58). Paraquat can
kill if swallowed. Do not put in food or drink containers. Keep out
of reach of children (56).
PROTECTIVE CLOTHING: Personnel must wear full protective equipment at
all times. This includes: Neoprene-coated or rubber glvoes, workshoes
or overshoes, latex rubber apron, goggles to protect eyes, overalls or
rubber suit (56).
RESPIRATORY PROTECTION FOR PARAQUAT
Minimum Respiratory Protection*
Condition Required Above 0.5 mg/m3
1.5 mg/m3 or less Any chemical cartridge respirator with an
organic vapor cartridge(s) and dust and
mist filter(s), including pesticide
respirators which meet the requirements of
Any supplied-air respirator.
Any self-contained breathing apparatus.
Greater than 1.5 mg/m3** or Self-contained breathing apparatus with a
entry and escape from full facepiece operated in pressure-demand
unknown concentrations or other positive pressure mode.
A combination respirator which includes a
Type C supplied-air respirator with a full
facepiece operated in pressure-demand or
other positive pressure or continuous-flow
mode and an auxiliary self-contained
breathing apparatus operated in
pressure demand or other positive pressure
Fire Fighting Self-contained breathing apparatus with a
full facepiece operated in pressure-demand
or other positive pressure mode.
Escape Any gas mask providing protection against
organic vapors and particulates, including
pesticide respirators which meet the
requirements of this class.
Any escape self-contained breathing
* Only NIOSH-approved or MSHA-approved equipment should be used.
** Use of supplied-air suits may be necessary to prevent skin contact
while providing respiratory protection from airborne concentrations
of paraquat; however, this equipment should be selected, used, and
maintained under the immediate supervision of trained personnel.
Where supplied-air suits are used above a concentration of 1.5
mg/m3, an auxiliary self-contained breathing apparatus operated in
positive pressure mode should also be worn (14).
IX. PROCEDURES FOR SPILLS AND LEAKS
IN CASE OF EMERGENCY, CALL, DAY OR NIGHT
PESTICIDE TEAM SAFETY NETWORK/CHEMTREC
Persons not wearing protective equipment and clothing should be
restricted from areas of spills until cleanup has been completed.
If paraquat is spilled, the following steps should be taken:
1. Ventilate area of spill.
2. Collect spilled material in the most convenient and safe manner and
deposit in sealed containers for reclamation or for disposal in a
secured sanitary landfill. Liquid containing paraquat should be
absorbed in vermiculite, dry sand, earth or a similar material.
Waste disposal method:
Paraquat may be disposed of in sealed containers in a secured
sanitary landfill (14).
X. LITERATURE CITED
8b. Thomson, W.T. 1981. Agricultural chemicals - book 2:
herbicides. Revised ed. Thomson Publications, Fresno, CA.
14. U. S. Department of Health and Human Services, National Institute
for Occuptational Safety and Health. 1981. Occupational
health guidelines for chemical hazards. F. W. Mackinson, R.
S. Stricoff, L. J. Partridge, Jr., and A. D. Little, Inc.,
eds. DHHS (NIOSH) Publ. No. 81-123. Washington, DC.
15c. American Conference of Governmental Industrial Hygienists. 1984.
TLVs: threshold limit values for chemical substances and
physical agents in the work environment and biological exposure
indices with intended changes for 1984-85. Cincinnati, OH.
22. U.S. Environmental Protection Agency, Office of Pesticide
Programs. 1983. June 1983 status report on rebuttable
presumption against registration (RPAR) or special review
process, registration standards and the data call in
programs. Washington, DC. 45 pp.
25. Morgan, D.P. 1982. Recognition and management of pesticide
poisonings, 3rd ed. U.S. Environmental Protection Agency,
Washington, DC. 120 pp.
56. Farm Chemicals Handbook, 70th ed. 1984. R. T. Meister, G. L.
Berg, C. Sine, S. Meister, and J. Poplyk, eds. Meister
Publishing Co., Willoughby, OH.
58. Weed Science Society of America, Herbicide Handbook Committee.
1983. Herbicide handbook of the weed science society of
America, 5th ed. Weed Science Society of America, Champaign,
IL. 515 pp.
62. The Pesticide Manual: A World Compendium, 7th ed. 1983. C.R.
Worthing, ed. The British Crop Protection Council, Croydon,
England. 695 pp.