Carbophenothion was reviewed at the Joint Meeting in 1972 (FAO/WHO,
    1973), when further studies to substantiate the marked species
    difference in sensitivity to plasma cholinesterase depression and an
    adequate reproduction study were required. At the Joint Meeting of
    1976 (FAO/WHO, 1977) the temporary ADI was withdrawn since the
    additional data required by the Joint Meeting of 1972 had not been
    made available.

    Part of the additional studies required by the 1972 Meeting have been
    received and are reviewed in this monograph addendum. In addition
    short-term and lone-term rat and dog studies, in which cholinesterase
    activity was determined are re-evaluated.



    Absorption, distribution and excretion

    Excretion via faeces, urine and expired air was studies after oral
    administration (2.5 mg/kg) of phenyl-14C carbophenothion to 2 male
    and 2 female Simonsen albino rats. Twelve similarly treated rats were
    placed in plastic metabolism cages and allowed food and water
    ad libitum. Four animals of each group were killed 1, 2, 4 and 8
    days after administration of the radiolabelled dose and blood, brain,
    adipose tissues, gonad, skin, kidney, liver, lung, muscle, stomach,
    intestine and remaining carcass were collected for determination of
    14C content.

    Within 96 hours after receiving a single oral dose of phenyl-14C
    carbophenothion an average of 97.8% of the administered radiocarbon
    was excreted in the urine (78.5%) and faeces (19.3%). No radiocarbon
    was found in the expired air trap. In all tissues only small amounts
    of 14C (<0.1% of the administered dose) were detected 96 hours after
    dosing (Hoffman et al., 1976).

    Male Simonsen albino rats (200g) were dosed orally by stomach
    intubation with 3 mg/kg b.w. of phenyl-14C carbophenothion dissolved
    in propylene glycol. The animals were housed in metabolism cages
    designed for the separate collection of urine and faeces. Urine was
    collected 24 and 48 hours after dosing.

    The animals remained healthy and active during the 48-hour collection
    period during which time an average of 66% of the administered 14C
    was excreted in urine; 14% was present in the ethyl acetate extract,
    while virtually all of the 14C in the extracted aqueous phase was
    soluble in methanol after lyophilization.

    The metabolic study resulted in the following identified urinary
    metabolites: 4-chloro-benzenesulphinic acid (46.8%), 4-chlorobenzene
    sulphonic acid (5.3%), 4-chlorobenzenethio-sulphuric acid (3.0%),
    4-chlorothio-phenyl-S-glucuronide (2 8%), 4-chlorophenyl methyl
    sulphone (1.7%), 4-chloro-3-chydroxyphenyl methyl sulphone (23.9%,
    both free and conjugated), 4-chlorophenylsulphinylmethyl methyl
    sulphone (0.7%), and 4-chlorophenylsulphonylmethyl methyl sulphone
    (1.9%). None of the oxygen analogues of carbophenothion were detected
    in urine. Of the 13.5% of the metabolites which could not be
    completely identified 6.3% was extractable in ethylacetate.

    Figure 1, shows the proposed metabolism of carbophenothion in the rat
    based on the present results. The metabolism in the rat is similar to
    that observed in the goat (De Baun et al., 1976a). The major
    degradative route appears to involve sulfoxidation and subsequent
    conversion to 4-chlorobenzene sulphinic and 4-chlorobenzene sulphonic
    acid. Another significant metabolic pathway involves methylation,
    sulfoxidation, and ring-hydroxylation of liberated 4-chlorothiophenol.
    The resultant 4-chloro-3-chydroxyphenyl methyl sulphone is converted
    in nearly equal proportions to the sulfate and glucuronide conjugates.
    Other metabolites including 4-chlorophenylsulphinylmethyl
    methylsulphone and 4-chlorophenylsulphonylmethyl methylsulphone
    presumably arise from cleavage of the carbophenothion P-S bond,
    followed by methylation and sulphoxidation. The results show that
    carbophenothion is readily degraded in the rat, primarily to water
    soluble products which are excreted in the urine (DeBaun et al.,
    1976b, Menn et al., 1976, DeBaun and Menn, 1976).

    In an experiment with 4-chlorothiophenol, one of the metabolites of
    carbophenothion, 4 male rats were dosed by stomach intubation of 1 ml
    of aqueous ring 14C-4-chlorothiophenol. The animals remained active
    and healthy throughout the 144-hours study. Complete urine and faecal
    excretion of the administered 14C was not achieved until
    approximately 6 Days after dosing. No 14C was detected in the expired
    air at any interval. The metabolites are shown in figure 1 (DeBaun et
    al., 1974).

    Carbophenothion sulphoxide, an oxidative metabolite of carbophenothion
    is also reduced to carbophenothion by an in vitro system containing
    rat liver enzymes, reduced nicotinamide adenine dinucleotide
    phosphate, and flavin adenine dinucleotide phosphate. After incubation
    for 2 hours 78% unmetabolized carbophenothion and sulphoxide, 1%
    carbophenothion sulphone acid and 12% carbophenothion were found
    (DeBaun and Menn, 1976).

    FIGURE 2

    Two lactating miniature Mexican goats were used to study the uptake,
    distribution, excretion, and metabolic fate of phenyl-14C
    carbophenothion in a polygastric animal, after oral application. The
    goats were preconditioned with 10 mg unlabelled carbophenothion, twice
    daily. After the preconditioning procedure of seven days, the animals
    were dosed once with approximately 22 mg carbophenothion/kg b.w. The
    goats were sacrificed 1 and 8 days after administration. With the
    exception of the digestive system and the central nervous system, no
    overt clinical changes were observed after treatment with
    carbophenothion. Some diarrhoea and behavioural changes were observed
    after carbophenothion administration. At necropsy no detectable
    macroscopic lesions due to carbophenothion exposure were noticed.

    Eight days after dosing, 82.6% of the administered radiocarbon was
    recovered in urine, 15.6% in faeces, 1.4% in cage washes and 1.0% in
    milk. The excretion was rapid; 90% of the dose was recovered within 72
    hours. There was no evidence of selective storage of 14C in tissues.
    Eight days after dosing less than 0.04 mg/kg carbophenothion
    equivalents was recovered in tissues and organs. The maximum
    concentration of 14C in milk, which occurred in the first 24 hours
    after dosing, was 0.7-0.8 mg/kg carbophenothion equivalents. Of this,
    0.014 mg/kg was characterized as carbophenothion and no oxidized
    carbophenothion metabolites were detected. The remaining 14C in milk
    was characterized as detoxication products resulting from cleavage of
    the leaving group (e.g. from carbophenothion sulphoxide and
    carbophenothion oxon sulphone). In this experiment the urine was also
    examined for metabolites of carbophenothion. The proposed metabolism
    in the goat based on these results as is shown in Figure 1. In general
    the fate of carbophenothion is similar to that observed in rats:
    methylation, sulphoxidation and ring-hydroxylation of liberated
    4-cholorothiophenol, formation of 4-chlorobenzenesulphinic and
    4-chlorobenzenesulphonic acids and the metabolites arising from
    cleavage of the carbophenothion P-S bond, followed by methylation and
    sulphoxidation of the resultant thiol intermediate. The goat
    desalkylates carbophenothion to yield the desethyl derivative (Menn et
    al., 1976, DeBaun et al., 1976b).

    Eighty-seven percent of the urinary 14C and 88% of the milk 14C was
    identified (DeBaun et al., 1976a). After an oral dose of 25 mg/kg body
    weight, Greylag and Pink-footed geese died with brain and plasma
    cholinesterase inhibition of 90%. The Canada goose showed symptoms
    after 2-3 hours, but appeared normal after 8 hours, with less
    cholinesterase inhibition than the other two species.

    The highest residue levels were found in fat and were considerably
    higher than in the other tissues. A range of tissues was also examined
    for the presence of carbophenothion metabolites. Oxidative metabolites
    were detected in muscle, brain# kidney and liver. Three of these were
    tentatively identified as the oxygen analogue and its sulphone and
    sulphoxide. The sulphone and sulphoxide of the parent compound
    appeared to be present in liver (Stanley at al., 1976).

    Effects on enzymes and other biochemical parameters

    Eighteen organophosphorus insecticides were fed to 30-day-old female
    rats for 1 week at various dietary levels. For each compound the
    dietary levels was calculated to produce a 50% inhibition of liver and
    serum aliesterases as well as brain, liver and serum cholinesterase.
    Inhibition of liver aliesterases was generally found at a much lower
    dose level than cholinesterase inhibition. Carbophenothion inhibited
    aliesterases in liver by 50% at a dose level of 0.5-2.7 ppm and in
    serum at 6.0-9.3 ppm in the diet. For brain, liver and serum
    cholinesterase these levels were 17.0, 60.0 and 21.0 ppm respectively
    (Su et al., 1971).


    Special studies on reproduction

    A three generation (1 litter) reproduction study with 120 rats (10
    males and 20 females/group) per generation was carried out.


    The dietary administered doses were 0, 3, 10 and 30 ppm
    carbophenothion (95%, technical). Only the second generation was mated
    twice. The foetuses of these litters (F2b) were examined for possible
    teratological or embryo-toxicological effects.

    The parameters studied were: individual body weight, food consumption
    behaviour and observation of physical appearance of the parental
    generation, fertility index, the total number of live and still-born
    pups, the total weight of live pups per sex at day 1, 7 and 21, the
    lactation index, viability index and the individual grossly observable
    findings. In the F2b the number of corpora lutea of pregnancy per
    ovary, the number and placement of implantation sites, resorption
    sites and live and dead foetuses were recorded. The foetus was
    examined individually and the weight, crown-rump distance and sex were
    determined. Necropsies were performed in 10 males and 10 females of
    the F3a generation at an age of 3 weeks. Approximately one-third of
    the F2b fetuses from each litter were examined internally,
    eviscerated, macerated and stained. The stained skeletons were
    examined for degree of ossification and anomalies.

    Mean body weights of the 10 and 30 ppm F1a females were significantly
    lower during the first half of the prebreeding growth phase.
    Significant decreases in the F2a growth period body weight data were
    limited to the males of the 10 ppm dose group and to the females of
    the 30 ppm dose group (during the first weeks after birth). The
    incidence of a hunched appearance was somewhat higher among the
    high-dose animals in all generations. No other signs of
    compound-induced toxicity were observed during the growth, gestation
    or lactation periods. In the F3a live birth, lactation and survival
    indices in the 30 ppm group were lower. In addition the lactation
    index (0-21) of the F2a generation was also lower than those of the
    control group. In all three generations significantly lower mean body
    weight of the pups was noted in the 30 ppm dose group, while in the
    F1a this effect was found even in the 3 and 10 ppm dose groups.
    Except for a higher incidence of treated pups appearing small in size,
    generally corresponding to the compound-related weight suppression,
    and a not-dose-related dilated pelvis of the kidney and enlarged lymph
    nodes found in some animals of the treatment groups, no clinical or
    gross pathological signs of toxicity were observed.

    The incidences of resorption were somewhat higher and the
    corresponding incidences of foetal viability were lower in the 10 and
    30 ppm carbophenothion dose groups. A relationship between these
    findings and the decreased neonate viability is likely. No significant
    teratological effects due to the treatment were noted (Trutter J.A.,

    Special studies on potentiation

    In a study in which potentiation of sixteen organophosphorus compounds
    with triamiphos was studied no potentiation in LD50 was found for
    carbophenothion. (Speyers et al., 1976)

    Acute toxicity
        TABLE 1. Acute toxicity of carbophenothion
    Species        Sex       Route     (mg/kg)   References
    Rat            M         Oral      37        Speyers et al., 1976
                   F         Oral      12        Speyers et al., 1976
    Pigeon                   Oral      35        Jennings et al., 1975
    Quail                    Oral      57        Jennings et al.  1975
    Canada goose             Oral      29-35     Jennings et al., 1975
    Starling                 Oral      5.6       Shafer, 1972
    Redwing                  Oral      7.5       Shafer, 1972
    In addition to the acute toxicity data, the acute toxicity of certain
    of the metabolites of carbophenothion to the rat are summarized in
    Table 2.

        Table 2. Acute toxicity of proposed metabolites and intermediates
    of carbophenothion in the rat. (Hoffman et al., 1976)

              Compound                                oral LD50
                                                      mg/kg b.w.
    desethyl-carbophenothion (sodium salt)            >1000

    4-chlorobenzenesulphinic acid (sodium salt)       > 500

    4-chlorobenzenesulphonic acid (sodium salt)       > 500

    4-chlorobenzene thiosulphate (sodium salt)        > 500

    4-chlorothiophenol1/                              316

    4-chlorophenyl methyl sulphoxide                  > 500

    4-chlorophenyl methyl sulphone                    > 500

    4-chloro-3-hydroxyphenyl methyl sulphone          > 500

    4-chlorophenylsulphenylmethyl methyl sulphone     > 500

    1/ The values for 4-chlorothiophenol represents the actual oral LD50.

    One calf was given carbophenothion 1 mg/kg body weight by oral
    capsule. The animal developed diarrhoea and showed ChE inhibition of
    77%. In addition the plasma tocopherol and carotene contents were
    lower (Hunt and McCarty, 1972).


    Seven members of a family became ill after eating tortillas made from
    flour contaminated with 0.3% carbophenothion. They all showed
    inhibition of serum cholinesterase. The level of cholinesterase
    inhibition corresponded to the number of tortillas eaten and the
    severity of the illness. The main symptoms were gastro-intestinal
    upset (vomiting, diarrhoea), salivation and lacrimation. Four of the
    affected people became comatose, but all recovered (Older and Hatcher,

    Values for potential dermal and respiratory exposure and for total
    exposure in terms of fraction of toxic doses were determined for 11
    different pesticides during orchard spraying. The highest total
    exposure was found for carbophenothion and was calculated to be 1.12%
    (range 0.26-2.38) of a toxic dose-hour. Dermal exposure was much
    greater than respiratory exposure (Wolfe et al., 1972).


    Carbophenothion was previously reviewed and further studies to
    substantiate the marked species difference in sensitivity to plasma
    cholinesterase depression and an adequate reproduction study were

    In 1976 the temporary ADI for humans was withdrawn because the
    information previously requested had not been provided. Part of this
    information has now been received and has been considered together
    with re-evaluation of short-term and long-term rat and dog studies in
    which cholinesterase activity was determined.

    Present carbophenothion metabolism studies confirm and extend the
    studies previously reported. Results show that carbophenothion is
    readily degraded both in the rat and the goat, primarily to water
    soluble products, which are excreted in the urine.

    None of the oxygen analogues of carbophenothion or its sulphoxide and
    sulphone were detected. The acute toxicity of the major metabolites of
    carbophenothion was considerably lower than that of carbophenothion.

    From both the data previously reported and the present data it is
    clear that plasma cholinesterase inhibition is the most sensitive
    criterion in both short- and long-term studies in rats and dogs. In a
    two-year study in dogs 5 ppm or 0.125 mg/kg bw-day was not a no-effect
    level with respect to plasma cholinesterase inhibition. In a 90 day
    experiment in dogs an effect was found even at 0.04 mg/kg bw/day,
    while 0.02 mg/kg bw was a marginal no-effect level in this respect. In
    a two-year experiment with rats 5 ppm in the diet (0.25 mg/kg bw/day)
    caused an inhibition of RCB-cholinesterase after 13 and 26 weeks.

    A three generation reproduction study including a teratological study
    revealed a no-effect level of 3 ppm equivalent to 0.15 mg/kg bw. With
    respect to the lowest no-effect level this study has no consequence
    for the calculation of the acceptable daily intake for humans, the
    most sensitive criterion still remaining is the plasma cholinesterase
    depression in dogs. An extreme difference in sensitivity between
    humans and dog is noticed in the reported cholinesterase depression
    studies. There seems to be an indication that 018 mg/kg/ day for 30
    days did not result in cholinesterase inhibition in humans. However, 1
    mg/kg bw in a calf caused symptoms and severe cholinesterase
    inhibition. The Meeting decided to allocate a temporary ADI for humans
    at a lower value owing to the marked species difference in sensitivity
    to plasma cholinesterase depression.


    Level causing no toxicological effect

    Rat: 3 mg/kg in the diet, equivalent to 0.15 mg/kg bw

    Dog: 0.02 mg/kg bw/day


    0-0.0002 mg/kg bw


    No new data were evaluated. Since the Meeting allocated a temporary
    ADI, the previously recorded guideline levels were converted to
    recommended temporary maximum residue limits.


    Required (before July 1979)

    1. Further studies to substantiate the marked species difference in
    sensitivity to plasma cholinesterase depression.


    1. Further elucidation of the nature of the terminal residues on
    crops, particularly as regards the reported possibility of the
    presence under field conditions of photolysis products.


    FAO/WHO (1973) 1972 evaluations of some pesticide residues in food.
    AGP:1972/M/9/1; WHO Pesticide Residues Series, No. 2.

    FAO/WHO (1977) 1976 evaluations of some pesticide residues in food.
    FAO/APG: 1977/M/5.

    De Baun, J.R. and Menn, J.J. (1976) Sulfoxide reduction in relation to
    organophosphorus insecticide detoxification. Science, 191, 187-188.

    De Baun, J.R., Finley, K.A., Gruwell, L.A. and Menn, JJ. (1976a)
    Metabolism of (Phyenyl-14C) carbophenothion in the lactating goat.
    Stauffer Chemical Company, Report MRC-B-54, Mountain View, California,
    USA. (Unpublished report)

    De Baun, J.R., Hoffman, L.J., Rose, J.H. and Menn, J.J. (1976b)
    Metabolism of (Phenyl-14C) carbophenothion in the rat: Urinary
    metabolite identification. Stauffer Chemical Company, Report MRC-B-61,
    Mountain View, California, USA. (Unpublished report)

    De Baun, J.R., Rose, J.H. and Menn, J.J. (1974) Metabolism of
    4-chloro-(U-14C) thiophenol in the rat. Stauffer Chemical Company,
    Report MRC-B-50, Mountain View, California, USA. (Unpublished report)

    Hoffman, L.J., Ross, J.H. and Menn J.J. (1976) Metabolism of
    (Phenyl-14C carbophenothion in the rat: Blance and tissue residue
    study. Stauffer Chemical Company, Report MRC-B-62, Mountain View,
    California, USA. (Unpublished report)

    Hunt, L.M. and McCarthy, R.T. (1972) Effects of some organophosphorus
    insecticides on vitamin E and other blood constituents and on the
    apparent inducement of diarrhoea in neonatal calves.
    Bull. Environ. Contam. Toxicol. 8: 297-305

    Jennings, D.M., Bunyan, P.J., Brown, P.M., Stanley, P.I. and Jones,
    F.J.S. (1975) Organophosphorus poisoning: a comparative study of the
    toxicity of carbophenothion to the Canada goose, the pigeon and the
    Japanese quail. Pestic. Sci. 6: 245-257

    Older J.J. and Hatcher, R.L. (1969) Food poisoning caused by
    carbophenothion JAMA 209: 1328-1330.

    Shafer E.W. (1972) The acute oral toxicity of 369 pesticidal,
    pharmaceutical and other chemicals to wild birds.
    Toxicol. Appl. Pharmacol., 21: 315-330

    Speijers, G.J.A., Verschuuren, H.G., Van Logten, MJ. an Van Esch, G.J.
    (1976) Onderzoek naar de potentiŽrende werking van 16 organische
    fosfor verbindingen en carbaryl. Intern Report N.I.P.H. 36-76 Tox.
    (Unpublished report)

    Stanley, P.I., Brown, P.M., Martin, A.D., Steed, L.C., Westlake, G.E.,
    Howells, L.C. and Machin, A.J. The avian toxicology of carbophenothin.
    Pest Infestation Control Laboratory and the Central Veterinary
    Laboratory, Ministry of Agriculture, Fisheries and Food. (Unpublished

    Su, M.Q., Kinoshita, F.K., Frawley, J.P. and DuBois, K.P. (1971)
    Comparative inhibition of aliesterases and cholinesterase in rats fed
    eighteen organophosphorus insecticides. Toxicol. Appl. Pharmacol.
    20: 241-249

    Trutter, J.A. (1976) A three-generation reproduction study in rats
    with trithion (technical C). Hazleton Laboratories America, Report
    submitted to the World Health Organization, by Stauffer Chemical
    Company, Mountain View, California, USA. (Unpublished report)

    Wolfe, H.R., Armstron, J.F., Staiff, D.A. and Corner, S.W. (1972)
    Exposure of spraymen to pesticides. Arch. Environ. Health 25: 29-31

    See Also:
       Toxicological Abbreviations
       Carbophenothion (ICSC)
       Carbophenothion (WHO Pesticide Residues Series 2)
       Carbophenothion (Pesticide residues in food: 1976 evaluations)
       Carbophenothion (Pesticide residues in food: 1979 evaluations)
       Carbophenothion (Pesticide residues in food: 1980 evaluations)
       Carbophenothion (Pesticide residues in food: 1983 evaluations)