WHO/FOOD ADD./69.35



    Issued jointly by FAO and WHO

    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party of Experts and the WHO Expert
    Committee on Pesticide Residues, which met in Geneva, 9-16 December,



    Geneva, 1969


    This pesticide was evaluated for acceptable daily intake under the
    heading "Methyl parathion" by the Joint Meeting of the FAO Committee
    on Pesticides in Agriculture and the WHO Expert Committee on Pesticide
    Residues (FAO/WHO, 1965).

    Since that time additional toxicological data have become available as
    well as data on its residues in food and their evaluation. The earlier
    monograph is now rendered obsolete and a completely revised monograph
    is presented in its entirety below.


    Chemical name

    OO-dimethyl O-(4-nitrophenyl) phosphorothioate (IUPAC)


    Metaphos, Folidol M, E 605, Nitrox, Wofatox



    Other information on identity and properties

    Typical analyses of technical parathion-methyl are not available. In
    1966 the world production of parathion-methyl was 31 700 metric tons
    (United States of America production, 14 800 metric tons).


    Biochemical aspects

    When 32P-labelled parathion-methyl was administered orally to
    guinea-pigs, the phosphorus was found to enter the organs almost
    immediately, and the maximum tissue level was attained in one to two
    hours. A high degree of absorption was found in the liver (Gar et al.,

    Parathion-methyl is biologically similar to parathion and is
    metabolized to its oxygen analogue, paraoxon-methyl (Augustinsson and
    Jonsson, 1957).

    Parathion-methyl is an in vivo cholinesterase inhibitor (Williams et
    al., 1959). It also inhibits this enzyme in vitro, however it is
    weaker in this respect than its ethyl analogue, parathion (DuBois and
    Coon, 1952). The same is true of the respective oxygen metabolites;
    paraoxon-methyl being a weaker cholinesterase inhibitor than paraoxon.

    The in vitro molar I50 value for paraoxon-methyl, using rat brain
    cholinesterase, is 4 × 10-8 (Davison, 1955).

    Acute toxicity

    Animal        Route      LD50 (mg/kg     References


    Mouse         oral       32.1          Ikeda, 1962

    Mouse         oral       150           Wills, 1968

    Rat (M)       oral       14            Wills, 1968

    Rat (F)       oral       24            Wills, 1968

    Rat           oral       17.2          Hagan, 1958

    Rat (F)       oral       9.7-14.8      Deichmann et al., 1952

    Rat           i.p.       3.5           DuBois and Coon, 1952

    Rabbit        oral       420           Wills, 1968
               (in oil)

    Rabbit        oral       1 270         Wills, 1968

    Short-term studies

    Dog. Pairs of dogs, comprising one male and one female, were fed
    parathion-methyl for 12 weeks at dietary levels of 5, 20, and 50 ppm
    along with four dogs used as controls. In the 20 and 50 ppm group,
    erythrocyte cholinesterase began to be significantly depressed soon
    after commencement of the test-diet. The same was true of plasma
    cholinesterase in the 50 ppm group. Maximum extent of depression was
    attained at the end of the 12-week period but recovery was complete
    within four to eight weeks after withdrawal of parathion-methyl.
    Depression of plasma cholinesterase was questionable at the 20 ppm
    level and no significant anti-cholinesterase activity was found in the
    5 pm group.

    Long-term studies

    No information available.

    Special studies

    (a)  Reproduction

    A three-generation reproduction study using 10 male and 20 female rats
    per dose level for each generation, at 0, 10 and 30 ppm
    parathion-methyl, and comprising two litters per generation, revealed
    no consistent effect on the number of live or stillbirths, birth
    weights, physical structure of newborn, litter size, weanling weights
    or percentage survival to weaning.

    Sporadic effects included lower weanling survival rate in F1a, F1b
    and F2a generations at 30 ppm, and in F3a generation at 10 ppm,
    increased stillbirth rate in F1b and F3a generations at 30 ppm,
    and F3a at 10 ppm; reduced mean weanling rate in F2a generation at
    30 ppm, and F1b generation at 10 ppm. Reduced reproductive
    performance in F1a, F1b, F2aand F3b generations at 30 ppm, was
    the only parameter consistently affected. No such activity was evident
    at the 10 ppm level (Woodard Research Corp., 1966).

    (b) Teratogenicity

    Some cases of foetal deaths and malformations have been reported in
    Japan and may possibly be related to the use of organo-phosphorus
    insecticides in the field (Ogi and Hamada, 1965). Parathion was
    identified in a human term foetus whose mother had used it to commit
    suicide (Le Breton et al., 1963). No significant developmental defects
    in rats whose mothers had been injected intraperitoneally with methyl
    parathion was observed (Fish, 1966).

    Because of these reports, the effect on organogenesis in the rat and
    mouse was studied by injecting intraperitoneally parathion-methyl
    suspended in a 0.5 per cent aqueous solution of sodium carboxymethyl
    cellulose once on day 12 of gestation in rats and once on day 10 in
    mice. The dosage was 5 to 15 mg/kg of body-weight in rats and 20 to 60
    mg/kg in mice. The animals were killed near term on day 21 in rats and
    on day 18 in mice. The foetuses were examined for intrauterine death,
    external malformations, internal abnormalities and skeletal
    abnormalities. All animals of both species showed signs of toxicity
    about 30 minutes after administration of parathion-methyl. Ataxia and
    paralysis of voluntary muscles were followed by hypersecretion of
    saliva and tears, urinary incontinence, tremor and general
    convulsions. Some died and the others recovered by the next day. Food
    and water intake in rats was noted to be lower for three or four days
    and there was a weight loss. No external or internal malformations
    were found. In mice lethality, teratogenicity and suppression of
    growth were noted in the group treated with the higher dosage. The
    only malformation was cleft palate, the incidence of which was 0.71
    per cent when used as control groups in other experiments.
    Retardation of ossification of the caudal vertebrae and increased
    incidence of cervical rib occurred in the group treated with the
    higher dose (Tanimura et al., 1967).

    Observations in man

    Normal levels of red blood cell and plasma cholinesterase were
    established in 12 human subjects, five of these subjects were given
    parathion-methyl in dose levels of 3 mg/day for 28 days, 3.5 mg/day
    for 28 days and 4.0 mg/day for 43 days. No anti-cholinesterase
    activity in plasma on red blood cells, and no side effects, were
    observed (Moeller and Rider, 1961)

    In a second study, three groups of five subjects were given
    parathion-methyl, The first group received 4.5 mg/day for 30 days
    followed by 5.0 mg/day for 29 days; the second group, 5.5 mg/day for
    28 days, then 6.0 mg/day for 29 days; and the third group, 6.5 mg/day
    for 35 days, then 7.0 mg/day for 24 days. The maximum depression of
    cholinesterase occurred in plasma and was approximately 15 per cent
    of the control values established beforehand (Moeller and Rider,

    In a continuing experiment, groups of five subjects were given
    parathion-methyl for 30 days at daily doses of 7 mg, 7.5 mg, 8 mg and
    9 mg. Plasma and red blood cell cholinesterase activities were within
    20 per cent of the pre-established control values (Moeller and Rider,


    Teratogenic effects were observed in mice only after parenteral
    administration, on the other hand the reproduction studies in rats
    showed some disturbance of the physiology of the reproductive process.
    It was therefore found necessary to re-evaluate this compound by using
    a higher safety factor and to change the acceptable daily intake to a
    temporary acceptable daily intake.


    Estimate of temporary acceptable intake

    0-0.001 mg/kg body-weight


    Use pattern

    Pre-harvest treatments

    Parathion-methyl is a broad spectrum insecticide and is mainly used on
    cotton, but is also used on food crops including fruits and

    For plant protection one, two or more applications are usually made,
    the pre-harvest interval varying from 14 to 21 days and is usually
    twice as long under greenhouse conditions.

    Reported application rates are given in the following table:

                             Application rate*
         Crop                (g/ha)
         Fruit               240-720
         Vegetables          240-720
         Grain crops (rice)  240-720
         Hay, forage crops,
         and cotton          100-1 000
         * USDA, 1967.

    Prescribed pre-harvest intervals in various countries are given below:

                Country                        interval (days)
                Austria                        21
                Belgium                        14
                Denmark                        14
                Finland                        21
                France                         15
                Germany (B.R.D.)               14
                Germany (D.D.R.)               14/21
                Italy                          14
                Netherlands, field conditions  21
                Netherlands, greenhouses       28
                Norway                         14
                Portugal                       21
                Switzerland                    21
                United States of America       5/21

    Post-harvest treatments

    Parathion-methyl is not used on stored food.

    Other uses

    Parathion-methyl has a very limited use for public health purposes.

    Residues resulting from supervised trials

    Many residue studies based on chemical methods, gas-liquid
    chromatography and cholinesterase inhibition, are available. Residue
    data include the oxon derivative. Parathion-methyl penetrates through
    the cuticula but is usually not translocated within plants (Shipp,
    1963; Stobwasser, 1967). Only in the case of carrots was it found that
    parathion-methyl penetrates into the oil-cells and undergoes very slow
    degradation (Engst, 1966). On the surfaces of plants parathion-methyl
    residues decrease very rapidly as shown by Shipp (1963) on cotton. The
    half-life is usually one to two days:

                                 Pre-harvest       Residue (ppm)
    Crop             Country      interval                                 Author      Half-life
                                   (days)       range          average                 (days)

    Cabbage-         Germany          3         0.1-0.7        0.3         III         1-1.5
    lettuce                           7        <0.15          <0.15

    Cabbage-         Germany          4                        0.76        II          2-3
    lettuce                           7                        0.65
    (greenhouse)                     14                        0.06

    Tomatoes         Germany          3                        0.06        I
    (field)                           7                        n.d.

    Tomatoes         Germany          3         n.d.-0.15      0.08        I           1.5
    (greenhouse)                      7         n.d.          <0.03
                                      3                        0.07        II
                                      7                        0.04

    Apples           Italy           10                        0.05        I

    Apples           Germany          3         0.38-0.54                  II          2.5-5
                                      7         0.11-0.12
                                     14         0.05-0.15

    Cabbage          United          14        <1             <1           Hoelscher
                     States of                                             1968

    Peas             United           5         1.1                        Hoelscher
                     States of                                             1968

    Sorghum          United           3         0.36                       Dorough     1-1.5
    grain            States of        6         n.d.                       1966

                                 Pre-harvest       Residue (ppm)
    Crop             Country      interval                                 Author      Half-life
                                   (days)       range          average                 (days)

    Cotton           United           3         2.5-18.0       8.7         Shipp       1
                     States of        7         1.0-11.8       5.3         1963
                     America         12         0.8-9.9        4.2

    References:   I  Institut für Pflanzenschutz, Hohenheim, Germany
                 II  Professor Maier-Bode, Bonn, Germany
                III  Biologisches Institut der Farbenfabriken Bayer, A.G. Leverkusen, Germany

    Disappearance of residues is dependent on climatic factors, rain appreciably reducing
    the residues (Hightower, 1958).


    Fate of residues

    General comments

    Under ultra-violet irradiation parathion-methyl is isomerized to the
    S-methyl compound (I) (Metcalf, 1953). Ultra-violet degradation under
    field conditions has not been reported. Upon heating to 140-160°C,
    parathion-methyl is transformed to the S-methyl compound (I)
    (McPherson, 1956; Metcalf, 1953). Thermal decomposition under field
    conditions is not reported.


    Parathion-methyl is quickly hydrolyzed by 1 N NaOH (K/min = 0.69), but
    no information of hydrolysis under field conditions is available
    (Metcalf, 1953).

    No data on metabolism in humans has been reported. Dietary intake for
    all organo-phosphates in the United States of America in 1966/1967 was
    0.00025 mg/kg body-weight/day, the three-year average being 0.00013
    mg/kg body-weight/day (Duggan, 1968).

    In soils

    Parathion-methyl is quickly broken down in soil. In silty loam, 30
    days after application of 0.1 ppm active ingredient, only three per
    cent was recovered. Disappearance of residues is accelerated by
    moisture and micro-organisms (Lichtenstein and Schulz, 1964). Trials
    on leaching in soil showed that in soil-water, parathion-methyl has a
    persistence of two weeks and in lake-water of three months, but no
    conclusions can be drawn concerning leaching of parathion-methyl from
    soil to rivers (Lichtenstein et al., 1966).

    In plants

    Three metabolites of parathion-methyl were found in cottonleaves, one
    of which was identified as paraoxon-methyl (II) (Shipp, 1963; Coffin,
    1964). After application of parathion-methyl to lettuce only small
    amounts of residues of paraoxon-methyl were found (one to four per
    cent of the total active residue) (Möllhoff, 1968). Under normal
    field conditions, paraoxon-methyl constitutes only a small fraction (a
    few per cent) of the residue of the parent compound (Möllhoff, 1968).
    Under elevated temperatures (72-112°F) and high humidity (40-62 per
    cent) the total residue on cotton after an interval of 72 hours
    consisted of 14.5 per cent parathion-methyl and 38.5 per cent
    paraoxon-methyl (Shipp, 1963). However, the oxon, when formed, is
    subject to rapid hydrolysis in and on the plant (Möllhoff, 1968). The
    classical colorimetric method by Averell et al. (1948) is able to

    determine the parent compound plus the oxon. When applying GLC methods
    the parent compound and the oxon can be determined separately.
    Probably, breakdown of parathion-methyl in higher plants is the same
    as the breakdown of parathion, but more rapid. The products of
    hydrolysis - phosphorothioate and 4-nitro-phenol - are only present in
    small amounts and seem to have no toxicological importance.


    In animals

    In warm-blooded animals parathion-methyl is transformed enzymatically
    to paraoxon-methyl (II) (Augustinsson and Jonsson, 1957).

    In storage and processing

    Although residues of parathion-methyl in vegetables and fruit are
    found near the peel, washing does not markedly reduce residues
    (Stobwasser, 1967). During ensilage of pea plants the active
    ingredient is quickly broken down because of the weak acids present.
    One month after ensilage, residues up to 0.2 ppm were found; after
    another month no residues could be detected (Heinisch, 1966).

    Evidence of residues in food in commerce or at consumption

    Samples of beef, butter and rice were examined for the presence of
    organo-phosphorus compounds by the non-specific cholinesterase
    inhibition method. Calculated as diasinon or parathion-methyl,
    residues in all samples were 0.1 ppm or less (data from Woodstock
    Agricultural Research Centre, Sittingbourne, 1967).

    Methods of residue analysis

    The residue analysis of parathion-methyl is usually carried out
    colorimetrically, the results including metabolites and all other
    substances with the nitrophenyl-group (Averell, 1948). Specific
    detection of parathion-methyl is possible by paper and thin-layer
    chromatography (Abbott, 1965; Getz, 1963). Gas-liquid chromatographic
    analysis is carried out with microcoulometric (Nelson, 1966), electron
    capture (Giuffrida, 1966; Egan, 1964; Möllhoff, 1967) and phosphorus
    detectors (Möllhoff, 1967), The sensitivity of the colorimetric method
    is 0.05 ppm, and of the gas-liquid chromatography methods, 0.01-0.02
    ppm. The latter can be used as a referee method.


    National tolerances

    Country             Crop                  Tolerance*
    Germany (Fed. Rep.) Fruit, vegetables       0.5
    Netherlands         General                 0.5
    Switzerland         Fruit                   0.75
    United States of
    America             Fruit, vegetables       1.0
    * Total of parathion and parathion-methyl.


    Parathion-methyl is a broad spectrum insecticide which is widely and
    heavily used in many countries for many purposes. It is especially
    valuable in the control of cotton insects and is frequently used in
    combination with DDT, endrin, toxaphene, and parathion. Although its
    use involves an acute toxic hazard, the residues are relatively
    non-persistent and rapidly disappear from treated crops. Residues
    actually found after reasonable waiting periods rarely exceed 1 ppm
    and are composed of the parent compound and paraoxon-methyl plus three
    metabolites which have been identified and can be detected by
    currently available analytical methods. However, additional
    information on the occurrence of paraoxon-methyl and the three
    metabolites is required. Further, the residue data which is available
    comes mostly from experimental trials in the Federal Republic of
    Germany with some data originating in the United States of America.
    Residue data from other countries are required. Sensitive methods of
    residue analysis are available for the parent compound and the oxygen
    analogue. The meeting considered the possibility of combining
    tolerances for parathion and parathion-methyl but rejected this
    concept since modern analytical techniques allow for the
    differentiation of the two compounds and their metabolites,
    Accordingly, recommendations for tolerances of parathion-methyl
    include paraoxon-methyl. If a tolerance is required for rice, residue
    data should be furnished.


    Temporary tolerances

    The following temporary tolerances, to be in effect until 1972, are to
    apply to raw agricultural products moving in commerce unless otherwise
    indicated. In the case of fruit and vegetables the tolerances should
    be applied as soon as practicable after harvest and in any event prior
    to actual retail to the public. In the case of commodities entering
    international trade, the tolerances should be applied by the importing
    country at the point of entry or as soon as practicable thereafter.

        Vegetables                            1     ppm
        Cole crops, cucurbits, fruit          0.2   ppm
        Cotton-seed oil (as processed)        0.05  ppm

    The above figures are for parathion-methyl and its oxygen analogue.

    Further work or information

    Required before 30 June 1972

    1.  Quantitative data on the occurrence of paraoxon-methyl and the
        other metabolites in plants and animal products.

    2.  Data from countries other than the Federal Republic of Germany and
        the United States of America on the required rates and frequencies
        of application, pre-harvest intervals, and the resultant residues.

    3.  If a tolerance is required on rice, data on the required rates and
        frequencies of application, pre-harvest intervals, and the
        resultant residues.

    4.  Further data on residue levels in raw agricultural products moving
        in commerce.

    5.  Data on residue levels in total diet studies.

    6.  Comparative evaluation of available methods for regulatory

    7.  Oral studies on teratogenicity and reproduction in species other
        than rats and mice, preferably in subhuman primates.


    Collaborative studies to establish a referee method.


    Abbott, D. C., Crosby, N. T. and Thomson, J. (1965) Use of thin-layer
    and semipreparative gas-liquid chromatography in the detection,
    determination and identification of organophosphorous pesticide
    residues. Proc. Soc. Anal. Chem. Conf., pp. 121-133

    Augustinsson, K.-B. and Jonsson, G. (1957) Acta chem. scand.,
    11:275. See Schrader: Die Entwicklung neuer insektizider
    Phosphorsäureester, 444 pp. (1962). Verlag Chemie, Weinheim

    Averell, P. R. and Norris, M. V. (1948) Estimation of small amounts of
    O,O-di-ethyl O-(p-nitrophenyl) thiophosphate. Anal. Chem.,
    20: 753-756

    Coffin, D. E. (1964) Residues of parathion, methylparathion, EPN, and
    their oxons in Canadian fruits and vegetables. Res. Rev., 7: 61-73

    Davison, A. N. (1955) Return of cholinesterase activity in the rat
    after inhibition by organophosphorus compounds. 2. A comparative study
    of true and pseudo cholinesterase. Biochem. J., 60: 339-346

    Deichmann, W. B., Pugliese, W. and Cassidy, J. (1952) Effects of
    dimethyl and diethyl paranitrophenyl thiophosphate on experimental
    animals. A.M.A. Arch. industr. Hyg., 5: 44-51

    Dorough, H. W., Randolph, N. M. and Wimbish, G. H. (1966) Residual
    nature of certain organophosphorus insecticides in grain sorghum and
    coastal Bermuda grass. Bull. environm. Contam. Toxicol., 1: 46-58

    DuBois, K. P. and Coon, J. M. (1952) Toxicology of
    organicphosphorus-containing insecticides to mammals. A.M.A. Arch
    industr. Hyg., 6: 9-13

    Duggan, R. E. (1968) Residues in food and feed. Pesticides Monitoring
    J., 2: 2-12

    Egan, H., Hammond, E. W. and Thomson, J. (1964) The analysis of
    organo-phosphorous pesticide residues by gas chromatography. Analyst,
    89: 175-178

    Engst, R., Seidler, H. and Härtig, M. (1966) Nahrung, 10: 413-425

    FAO/WHO. (1965) Evaluation of the toxicity of pesticide residues in
    food, FAO Mtg. Rept. PL/1965/10/1; WHO/Food Add/27.65

    Fish, S. A. (1966) Organophosphorus cholinesterase inhibitors and
    fetal development. Amer. J. Obstet. Gynec., 96: 1148-1154

    Gar, K. A., Sazonova, N. A., Fadeev, Y. N., Vladimirova, I. L. and
    Golubeva, Z. Z. (1958) Incorporation and excretion of dimethyl
    4-nitrophenyl thiophosphate in guinea pigs. Org. Insektofungitsidy
    i Gerbitsidy, pp. 93-105 [Chem. Abstr., 54: 15688e (1960)]

    Getz, M. E. (1963) The determination of organophosphate pesticides and
    their residues by paper chromatography. Res. Rev., 2: 9-25

    Giuffrida, L., Ives, N. F. and Bostwick, D. C. (1966) J. Assoc. Off.
    Anal. Chemists, 49: 8-21

    Hagan, E. C. (1958) Personal communication cited in Williams at al.,
    1959, q.v.

    Heinisch, E. (1966) Nachrichtenblatt dt. Pflanzenschutzdienst,
    20: 57-64

    Hightower, B. G. and Martin, D. F. (1958) Effects of certain climatic
    factors on the toxicities of several organic phosphorus insecticides.
    J. Econ, Entomol., 51: 669-671

    Hoelscher, C. E., Wolfenbarger, D. A. and Foster, N. E. (1968)
    Parathion and methyl parathion residues on cabbage and southern peas.
    J. Econ. Entomol., 61: 56-58

    Ikeda, Y. (1962) "Report to the Japan Academy of Sciences"

    Le Breton, R., Leyrie, J. and Garat, J. (1963) Intoxication
    materno-foetale aigüe par dérivé organo-phosphoré. Ann. Méd. lég.,
    43: 258-261

    Lichtenstein, E. P. et al. (1966) Toxicity and fate of insecticide
    residues in water. Insecticide residues in water after direct
    applications or by leaching of agricultural soil. Arch. environm.
    Hlth, 12: 199-212

    Lichtenstein, E. P. and Schulz, K. R. (1964) Effect of moisture and
    micro-organisms on the persistence of some organophosphorus
    insecticides in soil, with special emphasis on parathion. J. Econ,
    Entomol., 57: 618-627

    McPherson, J. B. and Johnson, G. A. (1956) Thermal decomposition of
    some phosphorothioate insecticides. J. Agr. Food Chem., 4: 42-49

    Metcalf, R. L. and March, R. B. (1953) The isomerization of organic
    thionophosphate insecticides. J. Econ. Entomol., 46: 228-294

    Moeller, H. C. and Rider, J. A. (1961) Studies on the
    anti-cholinesterase effect of parathion and methyl parathion in
    humans. Fed. Proc., 20: 434

    Moeller, H. C. and Rider, J. A. (1962) Threshold of incipient toxicity
    to Systox and methyl parathion. Fed. Proc., 21: 451

    Moeller, H. C. and Rider, J. A. (1963) Further studies on the toxicity
    of Systox and methyl parathion. Fed. Proc., 22: 189

    Möllhoff, E. (1968) Beitrag zur Frage der Rückstände und ihrer
    Bestimmung in Pflanzen nach Anwendung von Präparaten der E 605- und
    Agritox-Reihe. Pflanzenschutz-Nachrichten "Bayer", 21: 331-358

    Möllhoff, E. (1967) Gas chromatographic determination of residues of
    E 605 products and Agritox in plants and soil samples.
    Pflanzenschutz-Nachrichten "Bayer", 20: 557-574

    Nelson, R. C. (1966) Screening procedure for organothiophosphate
    pesticide residues on fruits and vegetables by microcoulometric gas
    chromatography. J. Assoc. Off. Anal. Chemists, 49: 763-766

    Ogi, D. and Hamada, A. (1965) Case reports on fetal deaths and
    malformations of extremities probably related to the insecticide
    poisoning. Cited in Tanimura et al., 1967, q.v.

    Shipp, O. E., Lindquist, D. A. and Brazzel, J. R. (1963)
    Characteristics of residues of methyl parathion applied to field
    cotton. J. Econ. Entomol., 56: 793-798

    Stobwasser, H., Rademacher, B. and Lange, E. (1967) Effect of post
    harvest factors on occurrence of pesticide residues in fruit,
    vegetables, etc. Res. Rev., 22: 45-112

    Tanimura, T., Katsuya, T. and Nishimura, H. (1967) Embryotoxicity of
    acute exposure to methyl parathion in rats and mice. Arch. environm.
    Hlth., 15: 609-613

    USDA. (1967) Summary of Registered Agricultural Pesticide Chemical

    Williams, M. W., Fuyat, H. N. and Fitzhugh, O. G. (1959) The subacute
    toxicity of four organic phosphates to dogs. Toxicol. appl.
    Pharmacol., 1: 1-7

    Wills, H. (1968) To Coulston, F., Division of Pharmacology, Albany
    Medical College, Albany, N.Y. Unpublished report

    Woodard Research Corp. (1966) Methyl parathion. Three-generation
    reproduction study in the rat. Unpublished report

    See Also:
       Toxicological Abbreviations
       Parathion-methyl (WHO Pesticide Residues Series 2)
       Parathion-methyl (WHO Pesticide Residues Series 5)
       Parathion-methyl (Pesticide residues in food: 1978 evaluations)
       Parathion-methyl (Pesticide residues in food: 1979 evaluations)
       Parathion-methyl (Pesticide residues in food: 1980 evaluations)
       Parathion-methyl (Pesticide residues in food: 1984 evaluations)
       Parathion-methyl (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)