Sponsored jointly by FAO and WHO


    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Expert Group on Pesticide Residues
    Geneva, 3-12 December 1979



    Edifenphos was evaluated by the 1976 Joint Meeting (FAO/WHO 1977) and
    a temporary ADI and temporary MRLs were allocated.

    Further studies were required on the hepatic involvement observed in
    several animal species.  Information was also desired with respect to
    observations in man, the residues of edifenphos and its main
    metabolites on rice in husk at harvest and a method of residue
    analysis suitable for edifenphos together with its main metabolites.

    Although all of these needs had not been met, additional data on acute
    and short-term toxicity and on the residue aspects had become
    available and they are evaluated in this monograph addendum.



    Absorption, Distribution and Excretion

    Edifenphos is rapidly absorbed, metabolized and eliminated from mice
    and rats following oral administration within six hours after
    administration.  At dosage levels of 10 mg/kg in female rats and 20
    mg/kg in mice and male rats, only 15-30% of the administered
    radioactivity was detected in digestive organs.  After 72 hours, only
    trace amounts of radioactivity were found in the whole body.  The
    major quantity of radioactivity was excreted in the urine (75-90%) and
    faeces (5-20%).  Accumulation of edifenphos in essential organs can be
    excluded as observed with data from single and multiple dose
    administration (Ueyama, et al, 1978).


    The main metabolite of the rat is ethyl hydrogen S-phenyl
    phosphorothiolate (54-57%) and that of mice is dihydrogen S-phenyl
    phosphorothiolate (31-42%).  Diphenyl disulfide was found in faeces of
    both species.  No qualitative differences were found in the metabolic
    pattern of edifenphos between males and females (Ueyama, et al.,

    Effects on Enzymes and Other Biochemical Parameters

    The cholinesterase inhibiting ability of malathion, fenitrothion, and
    edifenphos was compared using both plasma (pseudo-cholinesterase) and
    erythrocytes (acetylcholinesterase) from buffalo calves.  Malathion
    caused the greatest inhibition of erythrocyte cholinesterase, followed
    by edifenphos and fenitrothion.  For plasma cholinesterase, malathion
    was again the strongest inhibitor followed by fenitrothion and
    edifenphos (Malik, et al, 1978a).


    Special Studies on Potentiation

    Oral administration of single equitoxic doses (LD50) of edifenphos
    with fenthion and "Bassa-Wirkstoff" to male rats did not result in
    potentiation of the acute toxicity of the combination (Thyssen,

    Simultaneous oral administration of edifenphos and azinphos-ethyl to
    male rats revealed a greater than additive toxicity, suggesting a
    potentiating effect with these two organophosphorus compounds
    (Thyssen, 1977b).

    Short Term Studies

    Water Buffalo (Babalus bubalis)

    The effect of edifenphos on serum transaminase and alkaline
    phosphatase activity was studied after repeated oral dosing of 4 or 8
    mg/kg/day for 28 days.  Doses of 4 mg/kg/day brought on anorexia,
    depression, increased salivation, lacrimation and diarrhea, being
    initiated between days 11 and 14.  SGOT activity was elevated
    significantly, and this increased activity was both dose- and
    time-dependent.  No significant changes were observed for SGPT and
    alkaline phosphatase (Malik, et al, 1978b).


    Additional information confirming the rapid absorption, metabolism and
    elimination following oral administration have been evaluated.
    However, the required information about the liver involvement
    requested by a previous meeting has not been provided.

    The meeting was informed that a carcinogenicity study with mice was
    underway.  While the data reviewed did not increase the concern
    relating to edifenphos, the absence of the previously requested
    information precluded the allocation of an ADI.  However, the data
    permitted extension of the existing temporary ADI.


    Level Causing No Toxicological Effect.

    Mouse:  10 ppm in the diet, equivalent to 1.53 mg/kg body weight
    Dog:    20 ppm in the diet, equivalent to 0.58 mg/kg body weight
    Rat:     5 ppm in the diet, equivalent to 0.25 mg/kg body weight


    0 - 0.003 mg/kg body weight



    Edifenphos was applied either as emulsifiable concentrate (EC) or dust
    (DP) to rice plants cultivated in five geographically different paddy
    fields in Japan (Kamochi, 1979).  The harvest rice grains were
    separated into hulled rice, polished rice, bran, and chaff for
    analysis.  The residues of edifenphos in each part were determined by
    gas chromatography utilizing a flame photometric detector.  The
    minimum detectable limits for this method were 0.005 mg/kg for hulled
    and polished and 0.01 mg/kg for chaff and bran. Recoveries averaged
    80-93% for the various rice parts analysed.

    Application methods and cultivation conditions for the tests are shown
    in Table 1.  Table 2 shows the analytical results for concentration
    and distribution of edifenphos in rice grains.  Some edifenphos was
    found in control samples, presumably due to spray drift.  Residues
    resulting from dust applications were about 40% of those resulting
    from emulsifiable concentrate applications.

    There was no confirmative relation between residue concentration and
    the application frequency or waiting period after last application. 
    Most of the residue in rough rice was found in the chaff (98.4%) with
    average values of 2.8 mg/kg for DP and 6.2 mg/kg for EC.  Only 1.6% of
    the total residue was found in the hulled rice with average values of
    0.015 mg/kg for DP and 0.047 mg/kg for EC.  The distribution of the
    residue in hulled rice was 88.5% in the bran and 11.5% in the polished
    rice.  Average residue levels in the bran were 0.14 mg/kg for DP and
    0.43 mg/kg for EC whereas in polished rice the levels were 0.005 mg/kg
    for DP and 0.010 mg/kg for EC.  In the case of EC application, the
    range of edifenphos residues in polished rice was from <0.005 to
    0.016 mg/kg.  For DP application, the residue in polished rice was
    scarcely detectable, <0.005 to 0.005 mg/kg.


    In animals

    In a study involving rats and mice, 35S-edifenphos was fed orally at
    1/10th of the LD50 level (Ueyama, 1978).  It was rapidly metabolized
    and excreted, and only trace amounts of labelled materials were
    detectable in whole body after 72 hours.  The metabolites isolated
    were similar to those found in the goat.

        Table 1.  Site, cultivation conditions and application methods for edifenphos trials on rice
    (Kamochi, 1979)

        Site          Rice               Applications                 Harvest      Days from last appl.
    (Prefecture)    Variety        Test Plot1    Dates (day/mo.)       Date             to harvest

    Miyagi          Sasanishiki       DP         (7/8, 14/8)           18/9                 21
    Monoo                             EC         (21/8, 28/8           18/9                 21

    Miyagi          Sasanishiki       DP         (8/7, 2/8, 9/8,)      15/9                 21
    Furukowa                          EC           (18/8, 25/8)        15/9                 21

    Fukai           Nihonbare         DP         28/7, 21/8, 29/8      25/9                 27
    Sakai                             EC         31/7, 23/8, 31/8      26/9                 26

    Kochi           Jukkoku           DP         29/8, 5/9             9/10                 21
    Agawa                             EC         11/9, 18/9            9/10                 21

    Saga            Reiho             DP         (4 applications)
    Miyaki                            EC

    1  DP: 2.5% dust, 40 kg/ha (a.i. 1 kg/ha)
       EC: 30% Emulsifiable Concentrate, 1000 times dilution, 1.5 kg/ha (a.i. 0.45 kg/ha).

    Table 2.  Residual Concentration and Distribution of Edifenphos in Rice Grains (Kamochi, 1979)

                                           Residual Concentration (ppm) and Distribution (%) of edifenphos
    Site1         Test plot1       rough rice1       chaff          hulled rice         bran          polished rice
                                       ppm        ppm     %3        ppm      %3      ppm     %4

    Miyagi            DP              0.463       2.00  (97.2)      0.017  (2.8)     0.15  (100)       <0.005  (0)
    Monoo             EC              1.67        7.10  (96.6)      0.074  (3.4)     0.56  (89.2)       0.010  (10.8)

    Miyagi            DP              0.070       0.38  (100)       0.005  ( 0 )     <0.01 (-)         <0.005  (-)
    Furukawa          EC              0.068       0.37  (100)       0.005  ( 0 )     <0.01 (-)         <0.005  (-)

    Fukui             DP              0.561       2.97  (98.4)      0.011  (1.6)     0.09  (67.2)      0.005   (32.8)
                      EC              0.839       4.00  (98.1)      0.020  (1.9)     0.22  (100)       <0.005  (0)

    Fochi             DP              0.395       2.03  (96.5)      0.017 (3.5)      0.14  (100)       <0.005   (0)
                      EC              1.54        7.74  (96.1)      0.074 (3.9)      0.42  (81.6)      0.016   (18.4)

    Saga              DP              1.30        6.44  (98.6)      0.023 (1.4)      0.32 (84.7)       0.005   (15.3)
                      EC              2.80        12.0  (98.3)      0.062 (1.7)      0.94 (84.9)       0.014   (15.1)
    Average residue   DP              0.558       2.76              0.015            0.14              <0.005
         (ppm)        EC              1.38        6.24              0.047            0.43               0.010
    Average                           100                   98.43              1.63             1.33             0.23
    distribution                                                                               88.54            11.54

    1  As Table 1;
    2  This item was calculated by summing up the other four items;
    3  Percentage distribution of edifenphos against rough rice;
    4  Percentage distribution of edifenphos against hulled rice.

    Table 3.  Residual concentrations (mg/kg) and distribution of three
    metabolites of edifenphos in rice grain1
    (Kamochi, 1979) (All samples of hulled rice contained <0.01 mg/kg or
    any of the three metabolites)


    Test plot2                     Chaff                  Rice Grain3
                  diphenyl       m-hydroxy     p-hydroxy    p-hydroxy

    DP            <0.02          <0.02         0.07         <0.02
    EC            <0.02          <0.02         0.24          0.05

    DP            <0.02          <0.02         <0.02       <0.02
    EC            <0.02          <0.02         <0.02       <0.02

    DP            <0.02          <0.02         0.10          0.02
    EC            <0.02          <0.02         0.13          0.03

    DP            <0.02          <0.02         0.14          0.03
    EC            <0.02          <0.02         0.40          0.08

    DP            <0.02          0.02          0.15          0.03
    EC            <0.02          0.04          0.44          0.09

    Average  DP   <0.02          0.02          0.10*         0.02
             EC   <0.02          0.02          0.25*         0.05

    1  Average of duplication;
    2  Sites as Tables 1 and 2;
    3  Rice grain = rough rice; weight ratios of hulled rice and chaff
         are 80% and 20%, respectively
    *  Significance = 5%

    In plants (rice)

    In an experiment to determine the distribution and residue levels (if
    any) of three presumed metabolites of edifenphos: (I) diphenyl
    disulfide, (II) ethyl S-p-hydroxyphenyl S-phenyl phosphorodithiolate
    (p-hydroxy edifenphos), and (III) ethyl S-m-hydroxy phenyl S-phenyl
    phosphorodithiolate (m-hydroxy edifenphos) in the various parts of
    rice grain (rough rice) from the five regions in Japan and treatment
    programs shown in Table 1, samples were analysed using a
    newly-developed method to be described later (Ueyama, 1979a).  The
    results of these analyses are shown in Table 3 and can be summarized
    as follows: 1) the amounts if diphenyl disulfide and m-hydroxy

    edifenphos in rough rice were less than the detectable limit, 2)
    p-hydroxy edifenphos was found only in the chaff and was not found in
    hulled rice.  By comparing the residue levels of edifenphos (Table 2)
    and p-hydroxy edifenphos in chaff it was found that a linear
    relationship was obtained giving the formula Y = 0.037 × 0.007 (Y =
    p-hydroxy, mg/kg and X = edifenphos, mg/kg) with a correlation co-
    efficient r of 0.93.  This result could have significance for the
    regulatory analysis of rough rice, since 98% of the edifenphos residue
    is also found in the chaff and therefore it would be possible to
    calculate the total residue, edifenphos plus m-hydroxy edifenphos,
    based on a determination of edifenphos alone in a multi-residue

    Behaviour in soil

    Absorption and translocation

    The movement of 35S-labelled edifenphos was studied in three types of
    soil.  The vertical movement in the soil column differed with soil
    type and the order of mobility was: sandy loam > alluvial clay loam
    > volcanic ash loam. (Timme, 1977; Tomizawa, et al., 1976).


    The degradation of edifenphos in alluvial soil was more rapid under
    flooded than under non-flooded conditions (Rajaram and Sethunathan,

    In studies with 35S-edifenphos it was found that the main degradation
    products at the initial stage of soil metabolism were S,S,S-triphenyl
    phosphorotrithioate, O,O-diethyl S-phenyl phosphorothioate, S-phenyl
    phosphorothioate and diphenyl disulfide. The sulphur atom of
    edifenphos was converted to sulfuric acid through diphenyldisulfide
    and benezenesulfonic acid (Timme, 1977; Tomizawa et al, 1976).


    Edifenphos was degraded by UV light in hexane, water and as a film,
    cleavage of the P-S bond being the main reaction (Murai, 1977).  The
    products isolated were O-ethyl, S-phenyl phosphorothioic acid,
    S-phenyl hydrogen phosphorothioic acid, ethyl and hydrogen phosphoric
    acid.  The phenylthio radicals were oxidized to sulfuric acid except
    in hexane where diphenyl di- and mono-sulfide and benzene sulfinate
    and sulfonate were isolated.  No transesterification occurred.


    An analytical method was developed for determining the three
    organosoluble metabolites of edifenphos (1) diphenyl disulfide, (2)
    p-hydroxy edifenphos, and (3) m-hydroxy edifenphos in rough rice
    (Ueyama, 1979b).  These metabolites were extracted overnight by 80%
    acetone in water from hulled rice or chaff and the extracts

    partitioned with dichloromethane.  A second partition between
    acetonitrile/hexane was needed for hydroxy edifenphos in hulled rice. 
    After a suitable cleanup procedure for all metabolites employing
    Florisil column chromatography, the hydroxy metabolites were
    derivatized with diazomethane and all compounds determined by gas
    chromatography employing a flame photometric detector.  The limit of
    detection by this method was 0.01 mg/kg for hulled rice and 0.02 mg/kg
    for chaff.  Recoveries ranged from 64 to 86%.  The method appears to
    be quite suitable for regulatory analysis.

    A very sophisticated method of analysis for the major aqueous
    metabolite des-3-phenyl edifenphos in rice grains was developed
    (Kurogochi, 1979).  The procedure involves the use of stable isotope
    dilution analysis by fortifying the sample with d5-des-S-phenyl
    edifenphos at the initial blending step, methylation with
    diazomethane, and measuring the residue by GC-MS with selected ion
    current monitoring.  The minimum detectable amount was 0.1 ng and
    detection limits in hulled rice and chaff were 0.01 mg/kg and 0.05
    mg/kg, respectively.  Although the method would certainly seem
    reliable and useful in the hands of a research chemist with proper
    experience and equipment, its utility for routine regulatory analysis
    is questionable.


    The following information was received for edifenphos on rice (Bayer,
    AG, 1979)

    Country         MRL, mg/kg       Pre-harvest interval in days

    Brazil                                       15
    Italy               0.05                     60
    Japan               0.1                      21
    Mexico                                       20


    In response to requests from the 1976 Meeting, information was
    received on the residues of edifenphos and its main metabolites on
    rice in husk at harvest and on a method of residue analysis suitable
    for edifenphos together with its main metabolites.

    Emulsifiable concentrate (diluted) and dust of edifenphos were applied
    in accordance with good local practice to rice plants in paddy fields
    at five geographic locations in Japan.  After harvest the rice grains
    were separated into hulled rice, chaff, polished rice, and bran for
    analysis by gas chromatography using a flame photometric detector. 
    Residues of edifenphos in rough rice ranged from 0.068 to 2.80 mg/kg
    with 98.4% of the residue distributed into the chaff.  In hulled rice
    the residues ranged from <0.005 to 0.074 mg/kg, while in polished

    rice the residues ranged from <0.005 to 0.016 mg/kg.  Further
    analysis for the three main metabolites of edifenphos revealed that
    only the p-hydroxy edifenphos could be detected in rough rice, ranging
    from <0.02 to 0.09 mg/kg and concentrated almost entirely in the
    chaff.  These results indicate a need to increase the maximum residue
    limit for rice (in husk) from 0.2 to 5 mg/kg for rice (hulled) from
    0.05 to 0.1 mg/kg, and for rice (polished) from 0.01 to 0.02 mg/kg.

    Data from analytical experiments on rice grains from the five
    geographic locations in Japan, mentioned above, showed that field
    incurred residues of the metabolites diphenyl disulfide and m-hydroxy
    edifenphos were below the detectable limit (<0.02 mg/kg) in rough
    rice whereas p-hydroxy edifenphos could be found mainly in the chaff
    at levels ranging from <0.02 to 0.44 mg/kg (<0.02 to 0.09 mg/kg in
    rough rice).  A linear relationship obeying the equation Y= 0.037 ×
    0.007, r = 0.93 was found between residue levels of edifenphos and
    p-hydroxy edifenphos in chaff.

    Additional information on the fate of 35S-edifenphos fed orally to
    mice and rats at 1/10th of the LD50 showed that the compound was
    rapidly metabolized and excreted within 72 hours.

    A gas chromatographic method of residue analysis suitable for
    edifenphos and its main metabolites diphenyldisulfide, m-hydroxy
    edifenphos, and p-hydroxy edifenphos in rice grains was developed. The
    method is acceptable for regulatory purposes and probably could be
    adopted or modified for use on other cereal and vegetable food crops
    if the need arises.

    A method of analysis for the major aqueous metabolite des-S-phenyl
    edifenphos was also developed, but is primarily of research or
    academic interest since it requires the use of stable isotope dilution
    techniques and GC-selected ion current monitoring mass spectroscopy.


    The temporary residue limits on rice (in husk), rice (hulled) and rice
    (polished) recommended by the 1976 Meeting are increased as follows. 
    The limits refer to the parent compound.

                                       Preharvest interval on which
    Commodity         Limit (mg/kg)    recommendation is based (days)

    Rice (in husk)        5                         21
    Rice (hulled)         0.1                       21
    Rice (polished)       0.02                      21


    Required by June 1981:

    1.  Further studies to examine the hepatic involvement observed in
        several animal species;
    2.  Results of the carcinogenicity study currently in progress.


    1.  Observations on man relative to occupational exposure;
    2.  Information on residues of edifenphos and its p-hydroxy metabolite
        in food animals arising from the use of rice straw and bran in
        animal feeds.


    Kamochi, Sachiko, Ueyama, Isao and Talsase, Iwao.  Determination of
    residues of edifenphos (HINOSAN(R)) in rice grains. (1979) Report No.
    1096 (RA), Nihon Tokushu Noyaku Seizo K.K., Japan

    Kurogochi, Shin, Ueyama, Isao, Kamochi, Sachiko and Takase, Iwao.
    Determination of ethyl-S-phenyl hydrogen phosphorothiolate by gas
    chromatography selected ion current monitoring (GC-SICM) coupled with
    stable isotope dilution analysis.  (1979) Report No. 1107(R), Nihon
    Tokushu Noyaku Seizo K.K., Japan.

    Malik, J.K., Gupta, R.C. and Paul, B.A. - In Vitro study on the
    Comparative Inhibitory Effect of Malathion, Sumithion, and Hinosan on
    Blood Cholinesterase on Bubalus bubalis. (Reviewed in summary
    only). Indian J. Exp. Biol. 16: 496-497.

    Malik, J.K., Garg, B.D., Verma, S.P. and Ahmad, A. - Serum
    Transaminases and Alkaline Phosphatase Activities During Subacute
    Toxicity of Hinosan in Bubalus Bubalis. (Reviewed in summary
    only). Indian J. Exp. Biol., 16: 497-499.

    Murai, T.  Agr. Biol. Chem. 41: 71 - 1977, abstracted in report of
    IUPAC Commission on Pest. Chemistry, 1979.

    Thyssen, J. Untersuchungen zur Kombinationstoxizatät von difenphos,
    enthion und Bassa-Wirkstoff. (1977a) Unpublished report from Instituut
    für Toxikologie, submitted by Bayer, AG.

      Untersuchungen zur Kombinationstoxizatät von Azinphos-Athyl und
    edifenphos. (1977b) Unpublished report from Instituut für Toxikologie,
    submitted by Bayer, AG.

    Timme, G. - Hinosan metabolic fate behaviour in the environment.
    (1977) Unpublished report Pflanzenschutz Anwendungstechnik Biologische
    Forschung, submitted to the WHO by Bayer, AG.

    Tomizawa, C., Uesugi, Y., Ueyama, I., Yamamoto, H. - Movement and
    metabolism of S-benzyl O,O-diisopropyl phosphorothiolate (Kitazin P)
    and O-ethyl S,S-diphenyl phosphorodithiolate (edifenphos) in various
    types of soil. J. Environ. Sci. Health, 11: 231-251. (Cited by Timme,

    Ueyama, I., Takase, I., Tomizawa, C. - Metabolism of Edifenphos
    (O-ethyl Diphenyl Phosphorodithiolate) in Mouse and Rat. Agric. Biol.
    Chem., 42: 885-887.

    Ueyama, Isao, Kamochi, Sachiko and Takase, Iwao.  Results of the
    residual determination in hulled rice and chaff. (1979a) Report No.
    1108(RA), Nihon Tokushu Noyaku Sezio K.K., Japan.

      Determination of diphenyl disulfide and p- and m-hydroxy edifephos
    by gas chromatography (FPD). (1979b) Report No. 1106 (RA), Nihon
    Tokushu Noyaku Seizo K.K., Japan.

    See Also:
       Toxicological Abbreviations
       Edifenphos (Pesticide residues in food: 1976 evaluations)
       Edifenphos (Pesticide residues in food: 1981 evaluations)