Sponsored jointly by FAO and WHO


    Data and recommendations of the joint meeting
    of the FAO Panel of Experts on Pesticide Residues
    in Food and the Environment and the
    WHO Expert Group on Pesticide Residues
    Rome, 23 November - 2 December 1982

    Food and Agriculture Organization of the United Nations
    Rome 1983




         Isofenphos was evaluated by the Joint Meeting in 1981 (FAO/WHO
    1982)1, and a temporary ADI was allocated. The absence of an
    appropriate neurotoxicity study in hens was the basis for the
    temporary nature of the ADI. Such a study was required for a full
    evaluation of the insecticide.

         The required study has not been provided, although another acute
    delayed neurotoxicity study in hens, a teratology study in rats and a
    mutagenicity study have been made available. These new studies are
    summarized in this monograph addendum.



    Special Studies in Teratogenicity


         Groups of 25 mated rats (Wistar KFM-HAN outbred strain) were
    intubated with isofenphos (91.8% pure) as a suspension in
    carboxymethylcellulose at 0, 0.3, 1.0 or 3 mg/kg bw/day from day 6
    through day 15 of pregnancy (day 0 = day positive vaginal smear or
    vaginal plug observed). The dams were sacrificed on day 21 of
    pregnancy and foetuses were removed by caesarean section for external,
    skeletal and visceral examination. There were no mortalities or signs
    of toxicity. Maternal body weight and food consumption from day 0 to
    day 21 of pregnancy, the number of embryonal deaths, foetal deaths,
    dead foetuses and live foetuses as well as foetal weight were not


    1  See Annex 2 for WHO and FAO documentation.

    significantly different between control and treated groups. A
    significant difference from the concurrent control group in the sex
    ratio of foetuses was noted at 3 mg/kg bw/day. This was unlikely to be
    related to treatment, since a similar sex ratio (approximately 44%
    males) reportedly occurred in historical untreated controls. No foetal
    external malformations and no treatment-related increase in incidence
    of skeletal anomalies were evident. Visceral examination revealed
    bilateral hydrocephalus internus in one control foetus, medial
    dystopia of an undescended testis and bilateral hydrocephalus
    internus, respectively, in 2 foetuses (from 2 litters) at 0.3 mg/kg
    bw/day, ventral dystopia of the kidney and unilateral hydrocephalus
    internus respectively in 2 foetuses (from 2 litters) at 1 mg/kg bw/day
    and dilated aqueductus cerebre silvii and anasarca respectively in 2
    foetuses (from 2 litters) at 3 mg/kg body weight/day. The author of
    the report stated that such malformations occurred spontaneously in
    untreated rats of this strain. Indeed, in view of their low and
    isolated incidences, it would appear unlikely that the observed
    malformations were induced by isofenphos (Becker 1981).

    Special Studies on Mutagenicity


         In a micronucleus test, three groups of 5 male and 5 female mice
    (Bor: NMRI (SPF Han)) strain were treated orally with a 0, 15 or
    30 mg/kg bw dose of isofenphos (91.8% pure) on two occasions,
    separated by 24 hours. Six hours after the second dose, the animals
    were sacrificed and femoral bone marrow smears were prepared. There
    were no mortalities or clinical signs of toxicity. The incidence of
    micronucleated polychromatic erythrocytes or of micronucleated cells
    in normochromatic erythrocytes was not significantly different between
    controls and treated groups. Under the conditions of the test,
    isofenphos was not mutagenic (Herbold 1981).

    Special Studies on Neurotoxicity


         Thirty White Leghorn laying hens, approximately 12 1/2 months
    old, were intubated with a single dose of 32 mg isofenphos (91.9%
    pure)/kg bw. (The oral LD50 of the compound was not determined in the
    study. It was found to be 21 mg/kg body weight in an earlier study by
    another laboratory, see FAO/WHO 1982). These birds were also treated
    with 50 mg/kg bw of atropine i.p. at the time isofenphos was given.
    Seventeen of the treated hens died within 24 hours of dosing.
    Locomotor ataxia and paralysis were observed in all treated hens
    beginning on day 1 or 2 but these signs were not seen beyond day 6.
    Histopathological examination of the brain, spinal cord and sciatic

    nerve from the 13 surviving hens sacrificed at the end of a 21-day
    observation period revealed minimal changes that were similar in
    incidence and severity to those noted in concurrent controls (5 hens
    given water by gavage as dosing controls, and 5 hens as untreated
    controls). Positive controls, treated orally with tri-o-tolyl
    phosphate (TOTP) at 500 mg/kg bw, displayed clinical signs and
    histopathological lesions of the nervous tissue typical of delayed
    neurotoxicity (Hixson 1982).


         The available teratogenicity study in rats and micronucleus test
    in mice were both negative. The single-dose delayed neurotoxicity
    study in hens, while indicating no delayed neurotoxic potential of the
    insecticide, could be considered to be only a screen, as was a similar
    study previously evaluated (FAO/WHO 1982). Similarly, the suitability
    of a single litter per generation study in the multigeneration study
    was questioned by the Meeting. Because of the absence of an
    appropriate delayed neurotoxicity study and the deliberations
    regarding the multigeneration studies, the Meeting recommended an
    extension of the temporary ADI estimated in 1981.


    Level Causing no Toxicological Effect

    Mouse : 1 ppm in the diet, equivalent to 0.15 mg/kg bw

    Rat   : 1 ppm in the diet, equivalent to 0.05 mg/kg bw

    Dog   : 2 ppm in the diet, equivalent to 0.05 mg/kg bw

    Estimate of a Temporary Acceptable Daily Intake for Man

    0 - 0.0005 mg/kg bw.


    Required (by 1986)

    1.  An appropriate delayed neurotoxicity study.

    2.  Two-generation (two litters/generation) reproduction study.


    1.    In vitro biochemical studies on purified isofenphos with
         respect to anticholinesterase activity.

    2.   Further observations in humans,


    Becker, H. Embryotoxicity and teratogenicity study in rats, Report
    1981      from RCC Research and Consulting Company Ltd., Switzerland,
              submitted to the World Health Organization by Bayer AG.

    Herbold, B. Micronucleus test on mouse to evaluate SRA 12869
    1981      (isofenphos: active ingredient of Oftanol) for mutagenic
              potential. Report from Bayer AG Institut Fur Toxikologie
              submitted to the World Health Organization by Bayer AG.

    Hixson, E.J. Acute delayed neurotoxicity of technical isofenphos in
    1982      hens. Report from Mobay Chemical Corporation, U.S.A.
              submitted to the World Health Organization by Bayer AG.




         Isofenphos was evaluated by the 1981 Joint Meeting. 1 A
    temporary acceptable daily intake for man and maximum residue levels
    for several commodities were recommended. Additional data from
    supervised trials on potatoes and onions were considered desirable.
    New information on use pattern, residues resulting from supervised
    trials and on the fate of residues were made available for evaluation
    and they are discussed in this addendum.



         In addition to the use pattern included in the 1981 Monograph,
    the following new recommendations were submitted.


    Crop             Application rate    Formulation   No. of treatments

    Citrus fruit     0.05%               EC, WP               2
    Bananas          2 g/plant           GR                   3
    Pears            0.05-0.075%         EC                   3


         Supervised trials were carried out on various crops in Finland,
    France, Germany, Italy and South Africa. Analyses were done for
    isofenphos and isofenphos oxygen analogue (IOA).


    1  See Annex 2 for FAO and WHO documentation.


         Five supervised trials were carried out in various countries.
    Oftanol GR was applied at rates of 1.2-4 g a.i./plant two or three
    times, three to five months apart. Samples were taken at intervals
    from 3 to 154 days after last application. Isofenphos and isofenphos
    oxon were analysed in the peel and whole fruit. The residue was below
    the limit of determination (0.01 mg/kg) in every case.

    Citrus Fruit

         Navel orange and lemon trees were treated with Oftanol 50 EC at
    the normal (0.05% a.i.) and at double (0.1% a.i.) application rate in
    South Africa. Samples taken at various intervals were analysed for
    isofenphos and its oxygen analogue applying a method having a
    0.05 mg/kg limit of determination for both compounds. The results are
    summarized in Table 1 (South Africa, 1981).


         In supervised trials, Oftanol 500 EC was applied one to four
    times in a solution containing 0.05-0.075% a.i. for the treatment of
    'Alexander' and 'Williams' pear trees in Italy and once in France.
    Details and results of experiments are summarized in Table 2. The
    residue declined moderately during the first 4 weeks after treatment;
    there was little difference in the residue range and in the average
    residue level thereafter.

    Brassica Leafy Vegetables

         Narrow-stem kale seed was treated at the recommended rate
    (16 g a.i./kg seed) with Oftanol C. The plants were sampled 133-169
    days after sowing. No residue could be detected over the limit of
    determination (0.01 mg/kg).

         Supervised trials were carried out in Norway applying OftanolR
    at the approved rates and time. Residues (the parent compound and its
    oxon) in broccoli, Chinese cabbage and kohlrabi were generally below
    0.02 mg/kg and did not exceed 0.1 mg/kg.

    Oilseed Rape

         Seed dressing was carried out at a rate of 16 g a.i./kg seed with
    Oftanol C or Oftanol T in four experiments. Samples of mature seed
    taken 125-305 days after sowing contained only non-detectable

        Table 1.  Residues resulting from supervised trials in citrus fruit, 1980

               Application                   Residues 1 (mg/kg) at intervals (days) after application
    Crop       No.   Rate       Compound
                     (% a.i.)                1         7         14       21         28        35       42

    Lemon      1     0.05       I            1.3       1.1       0.8      0.53       0.75      0.82     0.56
                                IOA          0.13      0.26      0.23     0.15       0.22      0.19     0.17

    Lemon      1     0.1        I            2.9       1.8       1.1      1          0.8       0.63     0.54
                                IOA          0.25      0.42      0.36     0.31       0.28      0.29     0.23

    Orange     1     0.05       I            2.7       1.7       1.1      1          0.87      0.76     0.67
                                IOA          0.11      0.17      0.12     0.12       0.12      0.1      0.1

    Orange     1     0.1        I            3.4       2         1.6      1.4        1.3       0.85     0.78
                                IOA          0.13      0.2       0.18     0.15       0.19      0.14     0.12

    1  Results are the average of two replicates

    Table 2.  Residues resulting from supervised trials in pears 1

                                     Application                Residues (mg/kg) at intervals (days)
    Variety     Country  Year  No.   Rate                       after application
                                     (kg a.i./ha     Interval                                                       
                                     and %)          (weeks)    0      14       21      28      35      40-43   60

    Alexander   France   1977  2     0.6(0.06)       2                                                  0.12
    Alexander   Italy    1974  1     1.5(0.075)                 2.24   0.71     0.71    0.41
    Alexander   Italy    1976  4     1.5(0.05)       4                                                  0.27    0.16
    Alexander   Italy    1976  4     1.5(0.05)       4                                                  0.47    0.11
    Alexander   Italy    1976  3     1.5(0.05)       4                                                  0.2     0.29
    Alexander   Italy    1976  3     1.5(0.05)       4                                                  0.17    0.39

    Williams    Italy    1976  1     1.75(0.05)                 0.97   0.62     0.47    0.47    0.27    0.12

    Alexander   Italy    1975  1     1.75(0.05)                 2.54   0.84             0.32    0.23    0.22
    Alexander   Italy    1975  1     1.75(0.05)                 5.21   0.86             0.35    0.32    0.25

    Williams    Italy    1975  1     1.75(0.05)                 1.12   0.46             0.38    0.44    0.44

    Alexander   Italy    1976  1     2.25(0.075)                                                        0.42    0.34
    Alexander   Italy    1976  4     2.25(0.075)     4                                                  0.63    0.33
    Alexander   Italy    1976  3     2.25(0.075)     4                                                  0.32    0.42
    Alexander   Italy    1976  3     2.25(0.075)     4                                                  0.44    0.75

    Williams    Italy    1975  1     63 (0.0075)                1.06   0.84             0.69    0.64    0.34

    Alexander   Italy    1975  1     2.63(0.075)                0.86   0.88             0.53    0.4     0.28
    Alexander   Italy    1975  1     2.63(0.075)                5.35   0.75             0.39    0.3     0.27

    Williams    Italy    1975  1     2.63(0.075)                0.99   0.61             0.67    0.72    0.34

    1  Bayer AG 1982.

         Swedes were treated at a rate of 16 g a.i,/kg seed with Oftanol C
    in the Federal Republic of Germany (FRG). No residue was detected
    either in the leaves or in the roots 140-169 days after treatment. In
    supervised trials carried out in Finland, no residue was detectable in
    washed plants grown after seed dressing, while 0.008-0.07 mg/kg
    isofenphos and 0.015-0.01 mg/kg IOA were detected following soil
    treatment at planting at a rate of 0.25 g a.i./m2.


         Oftanol 500 EC was used at a rate of 0.075 g a.i./m for the
    treatment of the plots in 10 cm band at planting. Residues detected in
    the leaves and roots are summarized in Table 3.

    Table 3.  Residues in turnips after soil treatment with isofenphos

    Residues (mg/kg)at intervals (days) after application

         42               60               80
    root   leaf      root   leaf      root    leaf

    0.05   0.03      0.04   0.01     <0.01   <0.01
    0.15   0.08      0.02   0.01      0.05    0.01
    0.2    0.05      0.02  <0.01      0.01    0.01

         Turnip plants grown from seeds treated with isofenphos at a
    dosage rate of 16 g a.i./kg seed did not contain detectable residues
    in trials carried out in FRG and Finland.

    Other Crops

         Supervised trials were carried out in Finland in various
    vegetables. Carrot and radish were treated with 0.5 g a.i./m2 and
    onion seeds were dipped in a solution containing 0.025% a.i. The crops
    were washed before analysis. The sum of isofenphos and IOA found in
    different crops at various intervals after treatment was the
    following: carrot-2 mg/kg (22 days), 0.4 mg/kg (84 days), radish:
    1.2 mg/kg (6 days), 1.25 mg/kg (13 days), onion 0.024 mg/kg (62 days)
    (Finland undated).


    In Plants

         Ethoxy-1-3H, ring UL-14C isofenphos, formulated as 6E, was
    applied to cabbage seeds in furrow at planting at a rate of
    0.13 g a.i./m. At transplanting, 28 days after planting, some of the
    cabbage plants were transferred to untreated soil. The remaining
    cabbage plants received a second application of labelled isofenphos as
    a direct spray at the base of the plants at a rate of 1.68 kg a.i./ha
    (Strankowski and Murphy 1980). At various sampling intervals the
    radioactivity was released from the cabbage tissues by methanol-water
    extraction, enzyme, acid and basic hydrolyses. In plants receiving one
    and two treatments, 80-98% and 89-96% of the radioactivity were
    identified respectively.

         The major degradation pathway for isofenphos in cabbage involved
    oxidation to its oxon analogue (IOA) and subsequent hydrolysis to
    isopropyl salicylate (IPS) and salicylic acid (SA). Further breakdown
    then produced 2,3-dihydroxy benzoic acid (2,3-DHBA) and benzoic acid
    (BA). Des-N-isopropyl isofenphos oxygen analogue (des IOA) was also
    identified. The IPS, 2,3-DHBA and BA were found in free and conjugated
    form while 2,3-DHBA appeared only in conjugated form.

         In Norway the results of supervised trials indicated that the
    residues were below 0.05 mg/kg in celeriac potted out in soil
    containing 225 g isofenphos/m3. Residues were not detectable in
    carrots, onion and winter radish following seed dressing.

         The radioactive residues (0.001-0.006 mg/kg) identified in mature
    samples were characterized as being very polar hydrolysis products.
    The amount of organosoluble residue and the metabolites identified in
    maize and onion [FAO/WHO 1981) and in cabbage were very similar. The
    main difference between the metabolism of isofenphos in cabbage and
    maize or onion was that no IPS was found in the latter two crops.

         The uptake of radioactivity in cabbage seedlings appeared to be
    continuous. Each successive new leaf contained radioactivity, but in
    decreasing concentration. The concentration of total radioactivity in
    cabbage plants decreased with time, and 189 days after planting the
    total residue was equivalent to <0.012 mg/kg and 0.057 mg/kg
    isofenphos in mature cabbage heads receiving one or two treatments
    respectively. The overall distribution of radioactivity at various
    intervals after applications is summarized in Table 4.

        Table 4.  Distribution of isofenphos and its metabolites in cabbage

                                 Total radioactivity (%) at intervals (days) after
                                                 one and two applications

    Days/                7       14      28         42               56             189
    No. of applications  1       1       1       1       2       1       2       1       2

    Total residue 1      14.2     5.28    2.36    0.17    0.61    0.06    0.3    <0.012   0.057
    Isofenphos           79      53      37      15      33       5      29      <1       0

    IOA                  14      34      43      24      28      19      32       4      13

    Des IOA              <1       1       2       2       1      <1       1       1       1

    IPS                   1       3       4      24      16      30      13      12      29

    SA                    1       2       2      12      10      21      12      31      19

    BA                   <1       1       3       1      <1       2      <1       3       2

    2,3 DHBA             <1       1       1       2       2       3       1       3       6

    1  Expressed in mg/kg isofenphos equivalent.
    In Soil

         The mobility of isofenphos was studied in German standard soils
    2.1, 2.2 and 2.3. Equivalents of 2-4 kg a.i./ha of two formulations
    were applied to the soil and leached for two days. Neither isofenphos
    nor its oxon derivative was detectable in the leachates (limit of
    determination 0.0001 mg/kg) (Bayer AG 1982).


         Available information on national MRLs reported to the Meeting is
    given in Table 5.

    Table 5.  National Maximum Residue Limits and preharvest intervals

    Country             Crop                    interval      MRL
                                                (days)        (mg/kg)

    Federal Republic
    of Germany          Leafy and other
                        sprouting vegetables                  0.1

                        Root vegetables,
                        rape seed                             0.05

    Italy               Artichokes                            0.1
                        Brassicas                             0.1
                        Eggplant                              0.1
                        Fruit                                 0.1
                        Garlic                                0.1
                        Onion                                 0.1
                        Pear                    42            0.1
                        Pepper                                0.1
                        Sugarbeet               42            0.1
                        Tomato                                0.1

    Netherlands         Cabbage                 56            0.1
                        Brussels sprouts        56            0.05
                        Cauliflower             56            0.05
                        Colerisc                              0.05
                        Celery                                0.05
                        Leek                                  0.1
                        Onion                                 0.1

    Norway              Root vegetables         90
                        Stem vegetables         90

    South Africa        Citrus                  42            0.2

    Spain               Garlic                  21
                        Onion                   21

    Table 5.  (con't)

    Country             Crop                    interval      MRL
                                                (days)        (mg/kg)

    U.S.                Maize (fodder)          75            1.0
                        Maize (forage)          75            1.0
                        Maize (fresh, incl.
                        sweet corn)             75            0.1
                        Maize (grain)           75            0.1
                        Eggs                                  0.02
                        Meat, fat, meat by-
                        products of cattle,
                        goats, pigs, horses,
                        sheep and poultry                     0.1
                        Milk                                  0.02


         Since isofenphos was last evaluated by the 1981 JMPR, additional
    data have been made available for further consideration.

         The use of isofenphos is recommended in banana, citrus fruit and
    pear. It is applied as a spray containing 0.05% and 0.05-0.075% a.i. 2
    and 3 times in citrus fruit and pear respectively. Banana trees can be
    treated with 2 g a.i./plant up to 3 times annually.

         Supervised trials were carried out on various crops and the
    residues of isofenphos (I) and its oxygen analogue (IOA) were
    analysed. The limit of determination was 0.01-0.05 mg/kg for both
    compounds. Bananas did not contain detectable residues after three
    treatments at the recommended rate. Residue levels in lemons and
    oranges are approximately similar 42 days after treatment, and
    isofenphos amounts to 70-87% of the total residues. In pear, the
    initial residues declined moderately in the first month after
    application while there was little difference in range and average
    level of residue in samples taken in the second month.

         The treatment of soil at planting or sowing resulted in residues
    in carrots, onions, swedes and turnips; however, no measurable
    residues were found in subsequent crops after seed dressing.

         Isofenphos residues are readily taken up by cabbage plants from
    soil. The major degradation pathway for isofenphos in cabbage involved
    oxidation (IOA) and subsequent hydrolysis to isopropyl salicylate
    (IPS) and salicylic acid (SA). The parent compound and its three
    metabolites formed the major part of the total residue in the plant.
    The proportion of these compounds varied with time. At maturity IOA,
    IPS and SA were the only residues present while intact isofenphos was
    not detectable. The total radioactivity, expressed in isofenphos
    equivalents, was 0.057 mg/kg in mature cabbage treated at planting and
    one month later. There was no difference in the degradation pathway
    for isofenphos in cabbage receiving one or two treatments. The amounts
    of organosoluble residues in cabbage were similar to those found in
    maize and onions in previous experiments (FAO/WHO 1981). The
    degradation products were also similar with the exception of IPS,
    which was found only in cabbage.

         Further leaching experiments confirmed the low mobility of
    isofenphos in different soils, indicating that the contamination of
    underground water with isofenphos residues used for soil treatment is


         The Meeting examined residue data from new supervised trials and
    was able to estimate maximum residue levels for the following
    commodities in addition to those previously recommended. Results of
    other experiments supported the recommendations of the 1981 meeting,
    and no amendments were necessary. The levels refer to the sum of
    isofenphos and isofenphos oxygen analogue.


                      Temporary Maximum  Preharvest
                      Residue Level      Interval
                      (mg/kg)            (weeks)

    Citrus fruit      1                  6
    Pears             0.5                6
    Bananas           0.02 1             8

    1  Level at or about the limit of determination.



    1.   Further information on the residue in different varieties of
         citrus treated at the recommended rate with isofenphos and
         on the distribution of residues in the peel and pulp of
         citrus fruits.

    2.   Additional data from supervised trials on potatoes and
         onions, including information on soil residues and soil
         moisture content.


    Bayer AG. Pflanzenschutzmittle-Rückstände: Bananas: Report Nos. 4042-
    1982      4043/78, 4000/80, 4001/I/80, 4001/II/80, Narrow-stem kale:
              Report Nos. 4010-4012/78; Pears: Report Nos. 4019/77,
              4055/74, 4019/B/76, 4019/A/76, 4017/B/76, 4017/A/76,
              4009/75, 4049/75, 4043/75, 4011/75, 4020/B/76, 4020/A/76,
              4018/B/76, 4018/A/76, 4010/75, 4046/75, 4044/75, 4041/75;
              Oilseed Rape; Report Nos, 4007-4009/78, 4019/78; 
              Swedes:Report Nos. 4016/78, 4018/78; Turnips: Report Nos
              4014-4015/78, 4006-4008/77; Water: Report Nos, 4046-4048/74,
              4008-4010/81, (Unpublished)

    Finland. Information on pesticides included in the priority list.

    South Africa, Determination of isofenphos residues in citrus fruit,
    1981      Bureau of Standards, Report No. 311/88005/U9. (Unpublished)

    Strankowsky, K.J. and Murphy, J.J. Metabolism of AMAZE in cabbage,
    1980      Mobay Report No. 69 174. (Unpublished)

    See Also:
       Toxicological Abbreviations
       Isofenphos (Pesticide residues in food: 1981 evaluations)
       Isofenphos (Pesticide residues in food: 1984 evaluations)
       Isofenphos (Pesticide residues in food: 1986 evaluations Part II Toxicology)