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    WORLD HEALTH ORGANIZATION             FOOD AND AGRICULTURE
                                          ORGANIZATION
    ORGANISATION MONDIALE DE LA SANTE     ORGANISATION POUR L'ALIMENTATION
                                          ET L'AGRICULTURE

  
                                          VBC/DS/75.4 (Rev.1)
                                          ORIGINAL : ENGLISH



    DATA SHEETS ON PESTICIDES No. 4 Rev.1


    PARAQUAT


                                     CLASSIFICATION:
		                     Primary use:  Herbicide
		                     Secondary use:  None
		                     Chemical group:  Bipyridyl
		                     Data sheet No. 4, Rev.1 (8/78)


         It must be noted that the issue of a Data Sheet for a
    particular pesticide does not imply endorsement of the pesticide by
    WHO or FAO for any particular use, or exclude its use for other
    purposes not stated. While the information provided is believed to
    be accurate according to data available at the time when the sheet
    was compiled, neither WHO nor FAO are responsible for any errors or
    omissions, or any consequences therefrom.

    The issue of this document does    Ce document ne constitue pas une
    not constitute formal              publication. Il ne doit faire
    publication. It should not be      l'objet d'aucun compte rendu ou
    reviewed, abstracted or quoted     résumé ni d'aucune citation sans
    without the agreement of the       l'autorisation de l'Organisation
    Food and Agriculture               des Nations Unies pour
    Organization of the United         l'Alimentation et l'Agriculture
    Nations or of the World Health     ou de l'Organisation Mondiale de
    Organization.                      la Santé.

    1.    GENERAL INFORMATION

    1.1   COMMON NAME: Paraquat (ISO)

    1.1.1 Identity: 1,1'-dimethyl-4.4'-bipyridilium ion.  It should be 
          stated which anion is resent (e.g. paraquat dichloride). 
                                                         
    Figure 1


     
          Synonyms:                                 Local synonyms:

    1.2   SYNOPSIS - Paraquat is a bipyridyl herbicide, highly toxic to man 
          on oral ingestion; its toxic effect in mammals is due largely to 
          damage to lung alveoli.  It is a severe eye and moderate skin 
          irritant, but is not significantly absorbed through intact skin.  
          Absorption of spray mist can occur but does not appear to be of 
          practical significance. 

    1.3   SELECTED PROPERTIES 

    1.3.1 Physical characteristics - Available as the dimethyl sulfate or 
          the dichloride.  White crystalline solids; the dimethyl sulfate 
          is deliquescent.  Both have m.p. ca 300°C with decomposition.  
          Concentrated solutions corrode steel, tinplate, galvanized iron 
          and aluminium. 

    It must be noted that the issue of a Data Sheet for a particular 
    pesticide does not imply endorsement of the pesticide by WHO or FAO for 
    any particular use, or exclude its use for other purposes not stated. 
    While the information provided is believed to be accurate according to 
    data available at the time when the sheet was compiled, neither WHO nor 
    FAO are responsible for any errors or omissions, or any consequences 
    therefrom. 

    The issue of this document does not constitute formal publication.  
    lt should not be reviewed, abstracted or quoted without the  
    agreement of the Food and Agriculture Organization of the  
    United Nations or of the World Health Organization.            

    Ce document ne constitue pas une publication.  If ne doit faire l'objet
    d'aucun compte rendu ou résumé ni d'aucune citation sans I'autorisation 
    de l'Organisation des Nations Unies pour l'Alimentation et 
    l'Agriculture ou de l'Organisation Mondiale de la Santé. 

    R 683                             


    1.3.2 Solubility - Water at 20°C about 700 g/l; slightly soluble in 
          alcohol, insoluble in most other organic solvents.

    1.3.3 Stability - Stable in acid and neutral solutions, unstable in 
          alkaline solutions.  Decomposes in ultra-violet light.  
          Inactivated by anionic surface-active agents and by inert clays.  
          Rapidly inactivated on contact with soil. 

    1.3.4 Vapour pressure (volatility) - Not measurable:  nonvolatile.

            
    1.4 AGRICULTURE, HORTICULTURE AND FORESTRY

    1.4.1 Common formulations - Aqueous solutions of the dichloride 
          containing 200 g/l of the cation, together with anticorrosive and 
          surface-active agents.  A formulation without surface active 
          agents is used as an aquatic herbicide. 

          Mixtures containing 100-200 g/l paraquat with diquat (80-90 g/l) 
          or a residual herbicide are available. 

          Also formulated as water-soluble granules containing 25 g/kg 
          paraquat + 25 g/kg diquat. 

          There is an FAO specification for the aqueous salt solution.

    1.4.2 Susceptible pests - Green plant tissue generally, on contact and 
          in the presence of light.  Used particularly to control broad-
          leaved weeds and grasses.

    1.4.3 Use pattern - As contact herbicide before and after crop 
          emergence on plantation and vegetable crops, in orchards, for 
          aquatic weed control, stubble clearing and pasture renovation.  
          Main uses are for weed control around trees in orchards and 
          plantations and, by directed application, between rows of growing 
          crops, and as cotton defoliant and dessicant on various crops, 
          particularly potato haulm and sugar cane.  Application rates 
          usually range from 250 to 1500 g/ha.  Up to 2200 g/ha is used for 
          grass and stubble clearing. 

    1.4.4 Unintended effects - Damage can occur to bulbs in very sandy 
          soil.  Not harmful to wildlife or soil processes when used 
          correctly. 

            
    1.5   PUBLIC HEALTH PROGRAMME - Not used.

            
    1.6    HOUSEHOLD USE - The granule formulation (25 g/kg paraquat + 25 
          g/kg diquat) is used for weed control in home gardens.  Liquid 
          formulations for dilution before use are sometimes marketed. 

            
    2.    TOXICOLOGY AND RISKS

    2.1   TOXICOLOGY - MAMMALS

    2.1.1 Absorption route - May be absorbed through the gastrointestinal 
          tract.  Paraquat is not absorbed to any great extent by intact 
          skin and there is no evidence of significant absorption from 
          spray mist. 

    2.1.2 Mode of action - After a latent period, produces marked 
          congestion of the lungs with oedematous fluid in many of the 
          alveoli and excess macrophages in others.  Paraquat may also 
          produce severe kidney damage giving rise to renal failure. 

    2.1.3 Excretion products - Oral administration of paraquat dichloride 
          to rats resulted in 94% excretion in the faeces and 6% in the 
          urine within 48 hours. 

    2.1.4 Toxicity, single dose

          Oral: LD50 rat (M): 100 mg/kg
                  LD50 rat (F): 110 mg/kg

          Dermal: LD50 rat (M):  80 mg/kg
                    LD50 rat (F):  90 mg/kg

          Inhalation: LC50 (four hours) rabbit, dichloride, 6.4 mg/m3

          Most susceptible species - Guinea-pig, oral LD50 30 mg/kg.  
          Man appears to be a highly susceptible species. 

    2.1.5 Toxicity, repeated dose

          Oral: Daily oral doses of 20 (mg/kg)/day to sheep for five days 
          resulted in the death of all animals within two weeks.  At 10 
          (mg/kg)/day for five days, one out of six sheep died while 5 
          (mg/kg)/day for 14 days resulted only in listless animals.  
          Similar effects were observed in cattle. 

          Dermal: Rabbits were given daily percutaneous doses of paraquat.
          At 14.5 (mg/kg)/day, two out of three animals died within 20 
          days.  At 7.3 (mg/kg)/day there were no deaths but there was some 
          consolidation in lung alveoli.  The no-effect level was 2.8 
          (mg/kg)/ day.  In another study, one out of five rabbits died 
          when a daily percutaneous dose of 1.5 (mg/kg)/day was 
          administered under an impervious layer for 20 days. 

          Inhalation: Repeated daily six-hour exposure of rats to 
          paraquat aerosols over a three week period produced signs of lung 
          irritation but no deaths at 0.4 µg/m3.

          Cumulation of compound: Does not appear to accumulate in
          mammalian tissues. 

    2.1.6 Dietary studies

          Short-term: No information.

          Long-term: In a 26-27 month feeding study of paraquat 
          dichloride to dogs there was increased mortality and lung changes
          at 125 mg/kg diet (3.125 (mg/kg)/day) but no effect at 50 mg/kg 
          (1.25 (mg/kg)/day).  No adverse effects were observed at a 
          dietary level of 250 mg//kg (12.5 (mg/kg)/day) of paraquat
          dichloride (the maximum level) fed to rats over a two-year 
          period. 

    2.1.7 Supplementer studies of toxicity

          Carcinogenicity

          Rat: No increase in tumour incidence at a maximum dietary level 
          of 250 mg/kg diet (12.5 (mg/kg)/day) for two years. 

          Reproduction studies: A multi-generation study in rats has
          shown that 100 mg/kg paraquat in the diet did not interfere with
          the reproduction of three successive generations. 

          Teratogenicity

          Rat: A single intraperitoneal injection of 6.5 mg/kg of 
          paraquat on day 6 of gestation produced a high incidence of 
          costal cartilage malformation in the embryos.  This defect was 
          not noted when injections were given on days 7 to 14 of 
          gestation. 

          Grazing studies: Paraquat, when ingested as a residue in 
          herbage, has been reported to present no toxicological hazard to 
          farm animals. 
                
    2.1.8 Modifications of toxicity: No special features reported.

            
    2.2   TOXICOLOGY - MAN

    2.2.1 Absorption - See 2.1.1

          Ingestion has proved to be the main cause of poisoning with this 
          compound.  One fatal case of percutaneous absorption has been 
          described. 

    2.2.2 Dangerous doses

          Single: The fatal dose in adults is estimated to be 10-15 ml of 
          the 20 g/l concentrate (i.e., 30-50 mg/kg).  However, it has been 
          suggested that the ingestion of 3 g is the maximum compatible 
          with survival. 

          Repeated: No information.

    2.2.3 Observations of occupationally exposed workers - No reported 
          incidence of serious systemic toxic effects from plant workers 
          engaged in the manufacture of paraquat.  Irritation of skin and 
          mucous membranes, severe irritation of the eye and effects on 
          finger-nails have resulted from careless use. 

    2.2.4 Observations on exposure of the general population - No 
          information available. 

    2.2.5 Observations of volunteers - No information available.

    2.2.6 Reported mishaps - There are no known outbreaks of poisoning by 
          paraquat.  There have, however, been numerous cases, mostly with 
          a fatal outcome.  About half of these have been accidents, the 
          others suicides.  It has been suggested that the incidence of 
          mortality from accidental ingestion of paraquat is 50%.  In 40% 
          of all fatal cases the interval between ingestion and death has 
          been more than a week. 

            
    2.3   TOXICITY TO NON-MAMMALIAN SPECIES

    2.3.1 Fish - Not hazardous: rapidly absorbed by aquatic plants and 
          inactivated in mud.

    2.3.2 Birds - Not highly toxic.  No hazard under normal conditions of
          use. 

    2.3.3 Other species - Toxic to bees, but method of use avoids risk.

            
     3.    FOR REGULATORY AUTHORITIES - RECOMMENDATIONS ON REGULATION OF 
          COMPOUND

    3.1   RECOMMENDED RESTRICTIONS ON AVAILABILITY

          (For definition of categories, see introduction).

          Liquid formulations 10% or more, category 4.

          Solids over 25% category 4, all other formulations, category 5.

            
    3.2   TRANSPORTATION AND STORAGE

          All formulations in categories 3 and 4 - Should be transported 
          or stored in clearly labelled rigid and leak-proof containers. 
          No food or drink should be transported or stored in the same 
          compartment.  Storage should be under lock and key, and secure 
          from access by unauthorized persons and children. 

          Formulations in category 5 - Should be transported or stored in 
          clearly labelled leakproof containers away from food.

                
    3.3   HANDLING

          All formulations in categories 3 and 4 - Protective clothing 
          should be provided for those handling concentrates.  Adequate 
          washing facilities should be available close at hand.  Eating, 
          drinking and smoking should be prohibited during handling and 
          before washing after handling. 

          Formulations in category 5 - No facilities other than those
          needed for the handling of any chemical are required. 


            
    3.4   DISPOSAL AND/OR DECONTAMINATION OF CONTAINERS - Containers must 
          either be burned or crushed and buried below topsoil. Containers 
          may be decontaminated (for method see paragraph 4.3 or sheet 4).  
          Decontaminated containers should not be used for food and drink. 

            
    3.5   SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS

          All formulations in categories 3 and 4 - Training of workers in 
          techniques to minimize contact essential.

          Formulations in category 5 - Warning of workers to avoid contact 
          essential. 

            
    3.6   ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT 

          All formulations - Pilots and loaders should receive special
          training in application methods.  Use of flagmen not recommended.  
          Flagmen, if used, should wear overalls and be located well away 
          from the dropping zone. 

            
    3.7   LABELLING

          All formulations in categories 3 and 4 - Minimum cautionary
          statement - Paraquat is a toxic substance.  It is poisonous if 
          swallowed and highly irritating to the eyes if splashed into 
          them.  Avoid skin contact; wear protective gloves while mixing 
          and wear protective clothing while mixing and using the material.  
          Wash thoroughly with soap and water after using. Keep the 
          material out of reach of children and well away from foodstuffs, 
          animal feed and their containers. 

          Formulations in category 5 - Minimum cautionary statement - 
          This formulation contains paraquat which is a toxic substance.
          It is poisonous if swallowed and highly irritating to the eyes if 
          splashed into them.  Keep the material out of reach of children 
          and well away from foodstuffs, animal feed and their containers. 

            
    3.8   RESIDUES IN FOOD

    3.8.1 Maximum residue levels (tolerances) - The Joint FAO/WHO Meeting
          on Pesticide Residues has recommended maximum residue levels. 

            
    3.9   SPECIAL NOTE ON PARAQUAT - While poisoning is frequently fatal, 
          it usually only results from misuse of paraquat, i.e. by 
          accidental or deliberate ingestion.  The hazard can be diminished 
          by limiting the maximum concentrations of the chemical as 
          marketed. 


            
    4.    PREVENTION OF POISONING IN MAN AND EMERGENCY AID

    4.1   PRECAUTIONS IN USE

    4.1.1 General - Paraquat is a bipyridyl herbicide, highly toxic to man 
          by oral ingestion, its toxic effect in mammals is due largely to 
          the damage that it produces to lung alveoli.  It is a severe eye
          and moderate skin irritant but is not absorbed to any great 
          extent by intact skin; there is no evidence of significant 
          absorption from spray mist. 
                
    4.1.2 Manufacture and formulations

          T.L.V.

          ACGIH - 0.5 mg/m3.

          Closed systems and forced ventilation may be required to reduce 
          as much as possible the exposure of workers to the chemical. 

    4.1.3 Mixers and applicators - When opening the container and when 
          mixing, protective impermeable boots, clean overalls, gloves and 
          a face mask should be worn. Mixing, if not mechanical, should 
          always be carried out with a paddle of appropriate length.  When 
          spraying tall weeds or during aerial application a face visor 
          should be worn as well as an impermeable hood, clothing, boots 
          and gloves.  The applicator should avoid working in spray mist 
          and avoid contact with the mouth.  Particular care is needed when 
          equipment is being washed after use.  All protective clothing 
          should be washed immediately after use, including the insides of 
          gloves. Splashes must be washed immediately from the skin or eyes 
          with large quantities of water.  Before eating, drinking or 
          smoking, hands and other exposed skin should be washed. 

    4.1.4 Other associated workers (including flagmen in aerial operations)
          - Persons exposed to paraquat and associated with its application 
          should wear protective clothing and observe the precautions 
          described in 4.1.3 under "mixers and applicators". 

    4.1.5 Other populations likely to be affected - With good agricultural 
          practice subject to 4.2 below, other populations should not be 
          exposed to hazardous amounts of paraquat. 

            
    4.2   ENTRY OF PERSON INTO TREATED AREAS - No restrictions.


            
    4.3   SAFE DISPOSAL OF CONTAINERS AND SPILLAGE - Containers should be 
          emptied in a diluted form into a deep pit.  The empty container 
          may be decontaminated by rinsing two or three times with water 
          and scrubbing the sides.  An additional rinse should be carried 
          out with 5% sodium hydroxide solution which should remain in the 
          container overnight.  Impermeable gauntlets should be worn during 
          this work and a soakage pit should be provided for the rinsings.  
          Decontaminated containers should not be used for food and drink. 

          Spillage of paraquat and its formulations should be removed by 
          covering the area with soil and rinsing with large quantities of 
          water. 

            
    4.4   EMERGENCY AID

    4.4.1 Early symptoms of poisoning - Early symptoms of poisoning may 
          include epigastric discomfort and vomiting as well as general 
          malaise and weakness.  There may be irritation of the mouth, 
          pharynx and oesophagus with local burning.  With very large doses 
          there may be excitement and convulsions. 

    4.4.2 Treatment before person is seen by a physician if these symptoms 
          appear following exposure - If swallowed, vomiting should be 
          induced.  A high fluid intake should be maintained, the patient 
          kept at rest and sent to hospital immediately.  In cases of 
          contamination of skin or clothing, wash the affected skin with 
          soap and water, if available, and flush the area with large 
          quantities of water. 

            
    5.    FOR MEDICAL AND LABORATORY PERSONNEL

    5.1   MEDICAL DIAGNOSIS AND TREATMENT OF CASES OF POISONING

    5.1.1 General information - A bipyridyl herbicide of moderately high
          acute toxicity which may be absorbed through the intact skin as 
          well as by inhalation.  The main hazard, however, is absorption 
          by oral intake.  Paraquat owes its toxic effect largely to the 
          delayed damage that it produces on the lung alveoli.  In rats it 
          is excreted largely in the faeces but after absorption can be 
          readily detected in the urine.  The extent to which it persists 
          in the tissues is still unclear. 

    5.1.2 Symptoms and signs - Initial symptoms of poisoning may be 
          epigastric discomfort, diarrhoea and vomiting along with general 
          malaise and weakness.  There may be irritation of the mouth, 
          pharynx and oesophagus with local burning.  After one or two days 
          signs of tissue and possibly liver damage will appear, if 
          appreciable quantities have been swallowed.  After one to two 
          weeks there may be dyspnoea with pulmonary oedema leading to 
          massive pulmonary fibrosis and death due to respiratory 
          insufficiency.  With very large doses there may be excitement and 
          convulsions. 

    5.1.3 Laboratory - The presence of paraquat in the urine is indicative 
          of absorption of the compound.  Urinary levels should be measured 
          at frequent intervals.  Blood levels are very low and do not 
          provide a satisfactory method for determining the extent of 
          absorption. 

    5.1.4 Treatment - If the pesticide has been ingested it is imperative 
          that a prompt effort be made to remove as much paraquat as 
          possible before absorption takes place so as to supplement its
          elimination via the kidneys.  Gastric lavage should be carried 
          out with care because of the possible oesophageal injury.  At 
          least 500 ml of a 7% bentonite (colloidal aluminium silicate)
          suspension should be introduced into the stomach within one to
          two hours after the paraquat has been ingested.  The suspension
          is prepared by triturating bentonite with glycerine and adding
          water to a final concentration of 7% bentonite and 10% glycerine.
          Fuller's earth 30% can be used in place of bentonite.  As 
          paraquat is freely excreted by the renal glomeruli but is 
          reabsorbed in the tubules, forced diuresis is of benefit in
          hastening excretion. Haemodialysis and peritoneal dialysis may be
          indicated if there is evidence of renal failure.  Additional
          treatment may include immunosuppressive therapy and prednisone 60
          mg and cyclophosphomide 3 mg/kg per day have been recommended to
          try to prevent the lung lesions.  Oxygen may be necessary if
          cyanosis or dypsnoea occurs but there is some evidence that its
          effect may be harmful. 

    5.1.5 Prognosis - The prognosis in cases of paraquat poisoning is very 
          poor.  In 40% of cases death has occurred more than a week after 
          ingestion. Progressive respiratory embarrassment may occur five 
          to 10 days after taking the paraquat,  sometimes after a period 
          of apparent recovery.  Once the lung changes become evident 
          chances of recovery are practically nil. 

    5.1.6 References of previously reported cases - The following 
          references give methods of treatment used in cases of poisoning: 

          Kerr, F., Patel, A. R., Scott, P. D. R. & Thompsett, S. L. (1968) 
              Brit. med. J., 3, 290-291

          McDonagh, B. J. & Martin, J. (1970) Arch. Dis. Childh., 45, 
              425-427

          Clinicopathological Conference (1971) Scot. med. J., 16, 407

          Malone, J. D. G., Carmody, M., Keogh, B. & O'Dwyer, W. F. (1971)
              J. Irish med. Ass., 64, 69


       
    5.2   SURVEILLANCE - Levels of paraquat in the urine provide the most 
          readily available method for indicating absorption of paraquat. 
          However, actual levels cannot be correlated with the severity of 
          intoxication because recovery is probably also dependent on the 
          volume of urine excreted and therefore the total amount of 
          paraquat eliminated from the body.  By way of guidance the 
          highest concentration of paraquat found in the urine of spray 
          workers was 0.32 mg/l and the average was well below 0.1 mg/l.  
          In poisoning cases it has been found that recovery may occur if 
          the peak level is below 200 mg/l. 

      
    5.3   LABORATORY METHODS

          References only are given.

    5.3.1 Detection and assay of compounds - Detection of paraquat depends
          upon reduction to the free radical with sodium dithionite.  In 
          alkaline solution a stable blue colour is then formed which may 
          be measured spectrophotometrically.  For determination in urine 
          see Thompsett (1970) and Berry & Grove (1971). (Thompsett also 
          describes determination in other body fluids and tissues.) 
          Residues in food crops can be determined by the method of 
          Calderband & Yuen (1965) (see also Pack, 1967); later 
          modifications are suitable for determinations in meat, milk and 
          animal tissues (Plant Protection Ltd., 1972). 

    5.3.2 Other tests in cases of poisoning - None.


                                     REFERENCES

    Thompsett, S. L. (1970) Paraquat poisoning, Acta. Pharmacol. Toxicol.,
          28, 346 

    Berry, D. J. & Grove, J. (1971) The determination of paraquat (1,1'-
          dimethyl-4.4'-bipyridilium cation) in urine, Clin. chim. Acta,
          34, 5 

    Calderband, A. & Yuen, S. H. (1965) An ion-exchange method for 
          determining paraquat residues in food crops, Analyst, 90, 99 

    Pack, D. E. (1967) In:  Zweig, G., ed., Analytical Methods for 
          Pesticides, Plant Growth Regulators and Food Additives, 
          Academic Press, New York and London, vol. V, p. 473

    Plant Protection Limited (1972) Details of the methods are available 
          from Plant Protection Limited, Fernhurst, Hazlemere, Surrey, 
          England (Personal communication) 





    See Also:
       Toxicological Abbreviations
       Paraquat (HSG 51, 1991)
       Paraquat (PIM 399)
       Paraquat (JMPR Evaluations 2003 Part II Toxicological)
       Paraquat (AGP:1970/M/12/1)
       Paraquat (WHO Pesticide Residues Series 2)
       Paraquat (Pesticide residues in food: 1976 evaluations)
       Paraquat (Pesticide residues in food: 1978 evaluations)
       Paraquat (Pesticide residues in food: 1981 evaluations)
       Paraquat (Pesticide residues in food: 1982 evaluations)
       Paraquat (Pesticide residues in food: 1986 evaluations Part II Toxicology)