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                                          VBC/DS/75.6 (Rev.1)
                                          ORIGINAL: ENGLISH




    Primary use: Insecticide
    Secondary use: Acaricide, avicide
    Chemical Group: Organophosphorus compound
    Data sheet No. 6 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.


    1.1   COMMON NAME: Parathion (ISO)

    1.1.1 Identity: O,O-diethyl O-(4-nitrophenyl) phosphorothioate

    FIGURE 1

    1.1.2 Synonyms: OMS  19
                    E 605    - Belgium
                    Thiophos - USSR
                    SNP      - France
          Local synonyms:

    1.2   SYNOPSIS - An organophosphorus pesticide of very high mammalian 
          toxicity.  It may be absorbed through the skin, by inhalation and 
          via the gastrointestinal tract.  It is active upon metabolism. 

    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 

    R 683

    The issue of this document does not constitute formal publication.  
    It 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. Il ne doit faire l'objet
    d'aucun compte rendu ou résumé ni d'aucune citation sans l'autorisation
    de l'Organisation des Nations Unies pour l'Alimentation et 
    l'Agriculture ou de l'Organisation Mondiale de la Santé.                               


    1.3.1 Physical characteristics - When pure a colourless almost 
          odourless liquid m.p. 6.1°C, b.p. 157-162°C at 0.6 torr. The 
          technical material is a yellow to dark brown liquid with a 
          pungent garlic-like odour. 

    1.3.2 Solubility - Water at 25°C, very slightly soluble (24 mg/l).  
          Miscible with most organic solvents, slightly soluble in 
          petroleum oils. 

    1.3.3 Stability - Fairly stable at neutral or slightly acid pH.  At pH
          5-6, 1% is hydrolyzed in 62 days at 25°C.  Rapidly hydrolyzed in
          alkali.  Isomerizes on heating to the O,S-diethyl isomer.  
          Darkens on exposure to sunlight. 

    1.3.4 Vapour pressure (volatility) 3.78 x 10-5 torr at 20°C.

    1.4.1 Common formulations - Dispersible powders, 150 and 250 g/kg; 
          dusts, 5, 10, 20, 50 and 100 g/kg; granules 100 g/kg, 
          emulsifiable concentrates and solutions; aerosols 100 g/l.  There 
          are FAO specifications for the technical product, powders, dusts, 
          oncentrates and solutions. 

    1.4.2 Susceptible pests - Effective against most insects and mites as 
          contact and stomach poison.  Some fumigant action.  Has been used 
          for the control of nuisance birds. 

    1.4.3 Use pattern - Used as pre-harvest soil and foliage treatment on a 
          wide variety of crops, outdoor and in glasshouses. The pre-
          harvest interval, depending on crop is usually 7-15 days after 
          last application, but twice as long in glasshouses.  Uses include 
          tree and berry fruits, nuts, cotton, maize, small grains except 
          rye, root and leafy vegetables, legumes, tomatoes, grasses, 
          tobacco, ornamentals.  Used as mosquito larvicide on rice fields, 
          non-crop areas, pastures, and range lands.  Usual application 
          rates are 0.2-1 kg/ha. 

          Not used on stored crops.

    1.4.4 Unintended effects - Not generally phytotoxic, but can, at high 
          concentrations, injure cucumbers, tomatoes and some ornamentals, 
          and under certain weather conditions, pears and McIntosh and 
          related apples. 

    1.5   PUBLIC HEALTH PROGRAMMES - Use limited to larvicide against 
          mosquitos in developed countries. 

    1.6    HOUSEHOLD USE - Parathion is too toxic for household use. 



    2.1.1 Absorption route - Absorbed by the intact skin as well as by 
          inhalation and from the gastrointestinal tract.

    2.1.2 Mode of action - Cholinesterase inhibition after conversion to
          the oxygen analogue paraoxon. 

    2.1.3 Excretion products - In mammals parathion is converted into its 
          oxygen analogue, paraoxon which is the active form.  Parathion 
          and paraoxon are broken down and excreted as p-nitrophenol and 
          ethyl and diethyl esters of phosphoric and/or thiophosphoric 

    2.1.4 Toxicity, single dose

          Oral: LD50 rat (M): 13 mg/kg
                     rat (F): 3.6 mg/kg

          Dermal: LD50 rat (M):  21 mg/kg
                       rat (F):  6.8 mg/kg

          Most susceptible species:  Dog - lethal dose 3-5 mg/kg.  
          (An oral dose of 3-5 mg/kg is reported to be usually fatal to

    2.1.5 Toxicity, repeated doses 

          Oral: See dietary studies.
          Dermal: No information.  

          Inhalation: No information.

          Cumulation of compound: Parathion does not accumulate in body 

          Cumulation of effect: Repeated exposure to sub-lethal amounts may 
          reduce cholinesterase activity to hazard levels. 

    2.1.6 Dietary studies

          Short-term: In rats which were fed 0.05, 0.5 or 5.0 mg/kg diet
          (0.0025, 0.025 or 0.25 (mg/kg)/day) of parathion for 12 weeks the 
          no-effect level with respect to inhibition of blood 
          cholinesterases was 0.5 mg/kg (0.025 (mg/kg)/day). 

          Long-term: In a two-year study groups of rats were maintained 
          on diets containing 10.25 and 100 mg/kg (0.5, 1.25, 5 
          (mg/kg)/day) of parathion.  No morbid anatomical effects were
          seen at any level.  There is no information on cholinesterase 
          activity levels in this study. 

    2.1.7 Supplementary studies of toxicity

          Mutagenicity: Parathion in the diet of mice at three dosage 
          levels for seven weeks did not induce any dominant lethal 
          effects.  No mutagenic tendency was demonstrated in four 
          microbial assay systems.  In a three generation reproduction 
          study on rats, the no-effect level was 10 mg/kg diet (0.5 
          (mg/kg)/day).  Information on cholinesterase levels is, however, 
          not available. 

    2.1.8 Modifications of toxicity: The acute toxicity of parathion was 
          increased by a factor of 7.6 when rats were fed a low protein 

    2.2   TOXICOLOGY - MAN

    2.2.1 Absorption - See 2.1.1. Both the oral and dermal routes have been 
          responsible for many instances of poisoning. 

          Dangerous doses

          Single: In a number of fatal cases of human poisoning the dosage 
          which the victims received orally was exactly 900 mg. In another 
          case death resulted from 120 mg.  Children five to six years old 
          have been killed by ingestion of 2 mg of parathion (about 0.1 

          Repeated: See "observations on volunteers".
    2.2.3 Observations on occupational exposed workers - Several operators 
          have died after rather extensive skin contact with diluted 
          agricultural sprays or dusts. 

    2.2.4 Observations on exposure of the general population - Total diet 
          studies in one country have demonstrated a daily intake of 0.001 
          mg Of parathion per person (0.00002 mg/kg) which is well below 
          the no-effect level in animal studies. 

    2.2.5 Observations on volunteers - A daily oral dose of 7.2 mg produced 
          a 33% reduction in whole blood cholinesterase activity in adult 
          volunteers in 42 days. 

          Parathion, given to groups of five subjects in doses of 6
          mg/day for 43 days produced 10-15% reduction in plasma and 
          erythrocyte cholinesterase activity.  The inhibition of plasma 
          cholinesterase persisted for two weeks after discontinuation of 
          feeding parathion whereas erythrocyte cholinesterase was 
          inhibited for 43 days.  There was no effect from 3 mg and 4.5 
          mg/day doses given for 28 days. 

          In another study subjects were fed 0.003, 0.010, 0.025 and 0.050 
          mg/kg of parathion for successive periods, each of three weeks.  
          A significant increase in the plasma cholinesterase activity 
          occurred early in the feeding programme but the level declined to 
          control values when doses of 0.05 mg/kg were reached.  No change 
          in the erythrocyte cholinesterase activity occurred. 

    2.2.6 Reported mishaps - There are probably more reported cases of 
          poisoning with parathion than with any pesticide currently in 
          frequent use.  There have been a number of cases where 
          intoxication and death have resulted from ingestion of foodstuffs 
          that have been grossly contaminated with parathion. The list of 
          outbreaks below is not complete. 

          In one Asian country there were 828 cases of poisoning with 106 
          deaths due to flour, sugar and other foodstuffs becoming 
          contaminated because parathion was transported in the same ship's 
          hold as the foodstuff.  In another Asian country barley became 
          contaminated with parathion.  There were 38 cases of poisoning 
          with nine deaths. 

          In a country in the Americas there were 559 cases of poisoning 
          and 16 deaths when sacks of sugar and possibly flour absorbed 
          parathion from the floor of a truck.  In another country in the 
          Americas there were 165 known and 445 more suspected cases of 
          poisoning with 63 deaths when parathion from broken containers 
          contaminated sacks of flour during transportation in a truck.  In 
          a Caribbean country there were 27 known and 8-13 more suspected 
          cases of poisoning with 21 deaths when foodstuffs were 
          contaminated when placed in paper sacks which had previously been 
          used to package insecticides.  Parathion was the predominant 
          pesticide but malathion and a chlorinated hydrocarbon were also 
          involved.  In a European country there were 26 cases of poisoning 
          but no deaths when flour became contaminated because of 
          transportation in a wagon which was previously used for the 
          transportation of parathion.  In a Caribbean country an outbreak 
          of poisoning - 79 cases including 17 deaths - occurred due to 
          contamination of cotton sacks containing flour.  The 
          contamination was believed to have occurred in a European 


          The entries in these sections are intended to draw attention to 
          special risks and to give warnings of any needs for special 

    2.3.1 Fish - Toxic to fish.  Toxicity varies fairly widely in different 
          species (LC50 0.05 ppm for bluegills, 2 ppm for trout).

    2.3.2 Birds - Very toxic to birds and has been used, applied to seed 
          bait, for the control of nuisance birds. 

    2.3.3 Other species - Toxic to bees.  Toxic to wildlife and domestic 
          animals generally.



          (for definition of categories, see introduction)

          All formulations Category 3, 4


          All formulations - UN classification 6.1 No. 1668

          Should be transported or stored in clearly labelled rigid and 
          leakproof containers and away from containers of food and drink. 
          Storage should be under lock and key and secure from access by 
          unauthorized persons and children. 

    3.3   HANDLING

          All formulations - Full protective clothing (see part 4) should
          be used for all handling of the compound.  Adequate washing 
          facilities should be available at all times during handling and 
          should be close to the site of handling.  Eating, drinking and 
          smoking should be prohibited during handling and before washing 
          after handling. 


          All formulations - Containers must either be burned or crushed 
          and buried below topsoil.  Care must be taken to avoid subsequent 
          contamination of water sources.  Decontamination of containers in 
          order to use them for other purposes should not be permitted. 


          All formulations - Pre-employment medical examination of workers 
          necessary.  Workers suffering from active hepatic or renal 
          disease should be excluded from contact.  Pre-employment and 
          periodic cholinesterase test for workers desirable.  A urinary p-
          nitrophenol test periodically may be used as an alternative. 
          Special account should be taken of the workers' mental ability to 
          comprehend and follow instructions.  Training of workers in 
          techniques to avoid contact is essential. 


          All formulations - Pilots and loaders should have special 
          training in application methods and early symptoms of poisoning, 
          and must wear a suitable respirator.  Use of flagmen not 
          recommended. Flagmen, if used, should wear protective clothing 
          and be located well away from the dropping zone. 

    3.7   LABELLING

          All formulations - "POISON" (skull-and-cross-bones insignia)

          "Parathion is an organophosphorus compound which inhibits 
          cholinesterase.  It is a very toxic substance.  Contact with the 
          skin, inhalation of dust or spray, or swallowing may be fatal. 
          Wear protective gloves, clean protective clothing, and a 
          respirator of the organic-vapour type when handling this 
          material.  Bathe immediately after work.  Ensure that containers 
          are stored under lock and key.  Empty containers must be disposed 
          of in such a way as to prevent all possibility of accidental 
          contact with them. Keep the material out of reach of children and 
          well away from foodstuffs, animal feed and their containers.  In 
          case of contact, immediately remove contaminated clothing and 
          wash the skin thoroughly with soap and water; for eyes, flush 
          with water for 15 minutes. 

          If poisoning occurs, call a physician.  Atropine and pralidoxime 
          are specific antidotes and repeated doses may be necessary. 
          Artificial respiration may be needed." 

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



    4.1.1 General - Parathion is a highly toxic organophosphorus pesticide.
          It penetrates the intact skin and is also absorbed by inhalation 
          and via the gastrointestinal tract.  Most formulations should be 
          handled by trained personnel wearing protective clothing. 

    4.1.2 Manufacture and formulation

          T.L.V.: 0.1 mg/m3 (ACGIH); 0.05 mg/m3 (USSR).  Closed systems
          and forced ventilation may be required to reduce as much as 
          possible the exposure of workers to the chemical. Formulation
          should not be attempted without advice from the manufacturer. 

    4.1.3 Mixers and applicators - When opening the container and when 
          mixing, protective impermeable boots, clean overalls, gloves and 
          respirator should be worn.  Beware of possible positive pressure 
          build-up especially with liquid formulations in metal containers 
          with inverted pour spout.  Mixing, if not mechanical, should 
          always be carried out with a paddle of appropriate length.  When 
          spraying tall crops or during aerial application a respirator 
          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 the 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 parathion and associated with its 
          application should wear protective clothing and observe the 
          precautions described above in 4.1.3 under "mixers and 

    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 parathion. 

    4.2   ENTRY OF PERSON INTO TREATED AREAS - There have been reports of 
          workers having been poisoned because they entered fields too soon 
          after they had been treated with parathion. Unprotected persons 
          should be kept out of treated areas for considerable periods: a 
          minimum of 14 days has been suggested and 21 days after the 
          spraying of peaches, nectarines and grapes. 

    4.3   SAFE DISPOSAL OF CONTAINERS AND SPILLAGE - Residues in containers 
          should be emptied in a diluted form into a deep pit taking care 
          to avoid contamination of ground waters. Decontamination of 
          containers in order to use them for other purposes must not be 
          permitted.  Spillage of parathion and its formulations should be 
          removed by washing with 5% sodium hydroxide solution and then 
          rinsing with large quantities of water. 


    4.4.1 Early symptoms of poisoning - Early symptoms of poisoning may 
          include excessive sweating, headache, weakness, giddiness, 
          nausea, vomiting, stomach pains, blurred vision, slurred speech, 
          and muscle twitching.  Later there may be convulsions, coma, loss 
          of reflexes and loss of sphincter control. 
    4.4.2 Treatment before person is seen by a physician, if these symptoms 
          appear following exposure - The person should stop work 
          immediately, remove contaminated clothing and wash the affected 
          skin with water and soap, if available, and flush the area with 
          large quantities of water.  If swallowed, vomiting should be 
          induced if the person is conscious.  In the event of collapse, 
          artificial respiration should be given, bearing in mind that if 
          mouth-to-mouth resuscitation is used vomit may contain toxic 
          amounts of parathion. 



    5.1.1 General information - An organophosphorus pesticide of very high 
          acute toxicity which is easily absorbed through the intact skin 
          as well as by inhalation and via the gastrointestinal tract.  It 
          is converted in vivo to the oxygen analogue paraoxon which then 
          inhibits acetyl cholinesterase. Continued exposure to low amounts 
          may inhibit blood cholinesterase to dangerous levels. 

    5.1.2 Symptoms and signs - Initial symptoms of poisoning may include 
          excessive sweating, headache, weakness, giddiness, nausea, 
          vomiting, stomach pains, blurred vision, slurred speech and 
          muscle twitching.  More advanced symptoms of poisoning may be 
          convulsions, coma, loss of reflexes and loss of sphincter 

    5.1.3 Laboratory - The most important laboratory finding is reduction 
          in activity of blood cholinesterases.  Other findings are raised 
          urinary levels of 2-nitrophenol. 

    5.1.4 Treatment - If the pesticide has been ingested, unless the 
          patient is vomiting, rapid gastric lavage should be performed 
          using 5% sodium bicarbonate, if available.  For skin contact, the 
          skin should be washed with soap and water.  If the compound has 
          entered the eyes, they should be washed with isotonic saline. 

          Persons without signs of respiratory inefficiency but with 
          manifest peripheral symptoms should be treated with 2-4 mg of 
          atropine sulfate and additionally with 1000-2000 mg of 
          pralidoxime chloride or 250 mg of toxogonin (adult dose) by slow 
          intravenous injection.  More atropine may be given as needed.  
          Persons with severe intoxication with respiratory difficulties, 
          convulsions and unconsciousness should immediately be given 
          atropine and a reactivator.  In such severe cases 4-8 mg of 
          atropine sulfate should be given initially followed by repeated 
          doses of 2 mg at 5-10 minute intervals.  The patient's condition, 
          including respiration, blood pressure, pulse frequency, 
          salivation and convulsions should be carefully observed as a 
          guide to further adminis-tration of atropine.  If the patient is 
          cyanotic, artificial respiration should be given at the same time 
          as atropine. 

          The airways should be kept free and artificial respiration should 
          be applied, if required, preferably by mechanical means. If 
          necessary intubation should be performed. 

          Contraindications are morphine, barbiturates, phenothiazine 
          tranquillizers and central stimulants of all kinds. 

    5.1.5 Prognosis - If the acute toxic effect is survived and adequate 
          artificial respiration has been given if needed the chances of 
          complete recovery are good.  However, in very severe cases, 
          particularly if artificial respiration has been inadequate, 
          prolonged hypoxia may give rise to permanent brain damage. 

    5.1.6 References of previously reported cases - Case histories and 
          general methods for treatment are given in: Hayes, W. J., jr, 
          Clinical handbook on economic poisons, United States Public
          Health Service, No. 476, revised 1963. 

          See also "Safe use of pesticides in public health" (1967) Wld 
          Hlth Org. techn. Ser., No. 356, pp. 58-59. 

          For reports of individual cases of poisoning see: Namba, T. & 
          Hiraki, K. (1968) J. Amer. med. Ass., 166, 1834 and 
          Kanagartnam, K., Boon, W. H. & Hoh, J. K. (1960) Lancet,
          1, 538-542.  A recent outbreak of poisoning is described by 
          Diggory, H. J. P. et al., Amer. J. Epidemiol., 106(2), 
          145-153 (1977). 


    Test                     Normal     Action     Symptomatic
                               level     level      level

    Plasma cholinesterase        100%*     50%         variable
    Erythrocyte cholinesterase   100%        70%         usually  < 40%.

          It has been reported that absorption of parathion is tolerated 
          without illness and with little or no reduction in cholinesterase 
          activity so long as the concentration of the metabolite p-
          nitrophenol in the urine does not rise much above 2.0 mg/l.  Both 
          determination of the activities of blood cholinesterase and.2-
          nitrophenol in the urine (see 5.3.2 below) should be used in 
          cases of suspected poisoning. 


          References are given only.

    5.3.1 Detection and assay of compound - lt is unlikely that unchanged 
          parathion will be detectable in human tissue after exposure.  
          Determination of levels of blood cholinesterase and urinary p-
          nitrophenol (see 5.3.2 below) should be used in cases of 
          suspected poisoning. 

          Parathion and other p-nitrophenyl esters such as 
          parathion-methyl and EPN can be determined in foodstuffs by the
          colorimetric method of Averell & Norris (1948) or a later 
          modification (Sutherland & Miskus, 1964). 

          Parathion can be determined separately by gas chromatography, e.g. 
          Abbott et al. (1970) and Storherr et al. (1971).  Identity can be 
          confirmed by thin-layer chromatography (Abbott et al., 1965 and 
          Gardner, 1971). 

    5.3.2 Other tests in cases of poisoning

          Levels of cholinesterase in the blood, particularly plasma 
          provide the most useful diagnosis of poisoning, see: Michel, N. 
          0. (1949) J. Lab. Clin. Med., 34, 1564-1568 and Ellman, G. 
          L., Courtney, K. D., Andres, V., jr & Featherstone, R. M. (1961) 
          Biochem. Pharmacol., 7, 88-95. 

          Urinary levels of p-nitrophenol or diethyl phosphate and 
          phosphorothioate are also indexes of poisoning: p-nitrophenol
          may be determined colorimetrically (Elliott et al., 1960) or gas-
          chromatographically (Crammer, 1970), and diethyl phosphate by the 
          method of Shafik & Enos (1969) as modified by Shafik et al. 

        * Percentage of pre-exposure activity by any test.


    Abbott, D. C., Crisp, S., Tarrant, K. R. & Tatton, J. O'G. (1970) 
          Pesticide residues in the total diet in England and Wales, 1966-
          1967.  III.  Organophosphorus pesticide residues in the total 
          diet, Pestic. Sci., 1, 10 

    Abbott, D. C., Crosby, N. T. & Thompson, J. (1965) Use of thin-layer 
          and semi-preparative gas liquid chromatography in the detection, 
          determination and identification of organophosphorus pesticide 
          residues, Proc. Soc. anal. Chem. Conf., Nottingham, p. 121 

    Averell, P. R. & Norris, M. V. (1948) Estimation of small amounts of 
          O,O-diethyl O,p-nitrophenyl thiophosphate, Anal. Chem., 
         20, 753

    Crammer, M. (1970) Determination of p-nitrophenol in human urine, 
          Bull. environm. Contamin. Toxicol., 5, 329

    Elliott, J. W., Walker, K. C., Penick, A. E. & Durham, W. F. (1960) A 
          sensitive procedure for urinary.E-nitrophenol determination as a 
          measure of exposure to parathion, J. Agric. Fd. Chem., 8, 111 

    Gardner, A. M. (1971) Confirmation of organophosphorus pesticide 
          residues at nanogram levels by two-dimensional thin-layer 
          chromatography, J. Assoc. Offic. Anal. Chem., 54, 517 

    Shafik, M. T., Bradway, D., Biros, F. J. & Enos, H. F. (1970) 
          Characterization of alkylation products of diethyl 
          phosphorothioate, J. Agric. Fd. Chem., 18, 1174 

    Shafik, M. T. & Enos, H. F. (1969) Determination of metabolic and 
          hydrolytic products of organophosphorus pesticide chemicals in 
          human blood and urine, J. Agric. Fd. Chem., 17, 1186 

    Storherr, R. W., Ott, P. & Watts, R. R. (1971) A general method for
          organophosphorus pesticide residues in non-fatty foods,
          J. Assoc.  Offic. Anal. Chem., 54, 513 

    Sutherland, G. L. & Miskus, R. (1964) In: Zweig, G. (ed.) Analytical 
          methods for pesticides, plant growth regulators and food 
          additives.  Vol.  II.  Academic Press, New York and London, p. 

See Also:
        Parathion (IARC Summary & Evaluation, Volume 30, 1983)
        Parathion (ICSC)
        Parathion (PIM 400)