FAO, PL:CP/15
    WHO/Food Add./67.32


    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party and the WHO Expert Committee on
    Pesticide Residues, which met in Geneva, 14-21 November 1966.1

    1 Report of a Joint Meeting of the FAO Working Party and the WHO
    Expert Committee on Pesticide Residues, FAO Agricultural Studies, in
    press; Wld Hlth Org. techn. Rep. Ser., 1967, in press



    Chemical name



    3,4-methylenedioxy-6-propylbenzyl n-butyl diethyleneglycol ether




    The piperonyl butoxide used in commerce and in the work here reviewed
    consists of a technical product containing not less than 80 per cent
    of the above chemical together with related compounds which result
    from the process of synthesis via the chloromethyl derivative of
    dehydrosafrole and the sodium salt of the mono-n-butyl ether of
    diethylene glycol.


    Biochemical aspects

    High oral doses produce haemorrhage into the intestinal tract with
    loss of appetite and prostration (Sarles et al., 1949). It may be that
    these are the effects of local irritation and that the
    hyperexcitability and convulsions produced by large dermal doses
    (Lehman, 1952) are more indicative of the action of the absorbed drug.
    The compound produces liver injury (Sarles et al., 1949, Sarles &
    Vandergrift, 1952), and at least in dogs, and in rats at high dosage
    levels, liver injury was recognized as the cause of death (Sarles &
    Vandergrift, 1952).

    In rats, large subcutaenous doses produce an increased bleeding
    tendency and "rusty" (bloody) urine (Sarles et al., 1949). Massive
    bleeding was found in some animals at autopsy (Sarles & Vandergrift,

    Chamberlain (1950) explored the hypothesis that, in insects, piperonyl
    butoxide synergizes pyrethrins by inhibiting lipase (esterase), but
    his results were inconclusive.

    In an experiment in which 87.6 per cent of a large dose given to a dog
    was recovered (chiefly from the faeces), only 0.09 per cent was found
    in the urine (Sarles & Vandergrift, 1952).

    In vitro experiments using purified bovine erythrocyte acetyl
    cholinesterase showed that malathion had decreased anti-cholinesterase
    activity in the presence of piperonyl butoxide (Rai & Roan, 1956).

    Piperonyl butoxide at dose levels of 0.1-1.0 ml per rat given by the
    oral, intraperitoneal or intravenous routes retarded the elimination
    of intravenously administered 3,4-benzpyrene. Detoxification and
    biliary excretion of this carcinogen were also decreased. It was
    suggested that the induced hepatic damage may have increased the
    retention of the carcinogen (Falk et al., 1965).

    Acute toxicity

    Animal     Route     LD50                  References
                         mg/kg body-weight

    Mouse      Oral      4030                  U.S.F.D.A., 1946

    Rat        Oral      7960-10600            Sarles et al., 1949

    Rat        Oral      13500                 Lehman, 1948

    Rat        Oral      11500                 Lehman, 1951

    Rat        s.c.      >15900                Sarles et al., 1949

    Rabbit     Oral      2650-5300             Sarles et al., 1949

    Cat        Oral      >10600                Sarles et al., 1949

    Dog        Oral      >7950                 Sarles et al., 1949

    Simultaneous administration of piperonyl butoxide potentiates the
    toxicity of coumaphos and its phosphate by a factor of 4 to 6. There
    is some evidence that piperonyl butoxide interferes with
    detoxification of the organo-phosphorus insecticides (Robbins et al.,
    1959). Apparently no additional toxicity was produced in rats when
    one-sixth as much pyrethrin was added to their diet containing
    piperonyl butoxide at a concentration of 1000 ppm (Sarles &
    Vandergrift, 1952).

    Short-term studies

    Mouse. Four groups of Swiss mice were given subcutaneous injections
    of tricaprylin solutions containing one of the following compounds:
    fluoromethane, tetrachlorodifluoroethane and trichlorotrifluoroethane
    in concentrations of 10 per cent.; and piperonyl butoxide in a
    concentration of 5 per cent. Two groups of mice were given the
    following combinations by subcutaneous injection:
    tetrachlorodifluoroethane (10 per cent) plus piperonyl butoxide (5 per
    cent); and trichlorodifluoroethane (10 per cent) plus piperonyl
    butoxide (5 per cent). The mice received the injections at the ages of
    1, 7, 14 and 21 days. In those groups which received piperonyl
    butoxide, either alone or in combination, the total dose of piperonyl
    butoxide was about 5-10 g/kg body-weight. After 50-52 weeks, the
    incidence of hepatomas in the groups which received the individual
    compounds was 5 of 126 (about 4 per cent), and the total incidence in
    the two groups which received piperonyl butoxide in combination with a
    "Freon(R)" was 8 of 33 (about 24 per cent). No influence on the
    incidence of malignant lymphomas was seen (Epstein et al., 1966).

    Rat. In a 17-week study, a dietary level of 5000 ppm piperonyl
    butoxide caused gross and tissue damage to liver (enlargement and
    periportal hepatic cell hypertrophy with slight fatty change) and
    kidney (renal tubular pigmentation of a "wear and tear" type) (Lehman,
    1952 b and c).

    Single weekly doses of between 530 and 4240 mg/kg body-weight
    administered six times to rats, and of 1060-4240 mg/kg body-weight
    administered three times to rabbits showed no effects at autopsy three
    weeks after the final dose (Sarles et al., 1949).

    A 31-day test in rats showed terminal anorexia. Early deaths were
    largely due to damage of ganglionic cells of the brain stem. (Sarles &
    Vandergrift, 1952).

    Dog. Body-weight gain was reduced compared with controls in dogs
    dosed with 32 mg/kg/day for 1 year; dogs dosed with 106 mg/kg/day or
    higher lost weight. At 3 mg/kg/day there was a slight increase in
    liver weight without gross or microscopic pathology. The kidneys and
    adrenals were progressively enlarged at dosages of about 100 mg/kg/day
    and above. Microscopic pathology was evident in the liver at dosage
    rates of 32 mg/kg/day and over. Hepatoma and carcinoma were not seen
    (Sarles & Vandergrift, 1952).

    Monkey. At comparable dosage, symptomatology was somewhat less than
    in dogs. Microscopical pathology of the liver in monkeys at 100
    mg/kg/day was comparable to that in dogs receiving 30 mg/kg/day (a
    dosage that produced no observed effect in the monkey). The apparent
    difference in the sensitivity of the two species may be explained by
    the shorter exposure of the monkey (1 month) compared with the dogs (1
    year) (Sarles & Vandergrift, 1952).

    Long-term studies

    Rat. In two-year studies, concentrations of piperonyl butoxide at
    high as 1000 ppm caused no decrease in the growth rate of female rats;
    concentrations as low as 100 ppm produced some reduction in the growth
    rate of males, but the difference was not considered significant. A
    concentration of 10 000 ppm caused a significant reduction in the
    growth rate of both sexes that was accounted for, at least in part, by
    decreased food consumption (78 per cent of control). A concentration
    of 25 000 ppm, reduced food consumption to 37 per cent of control and
    stunted the animals. However, in subacute experiments, anorexia was
    terminal and therefore not the simple effect of unpalatability of the
    food. A concentration of 10 000 ppm caused a distinct increase in
    mortality rate in both sexes evident in 2 years and a concentration of
    25 000 killed about half the animals in half a year. Only
    concentrations of 10 000 ppm or higher produced significant increase
    in the relative weight of the liver and kidney. Liver changes were
    found at levels of 10 000 ppm and more. Less marked changes occurred
    in the kidney and adrenal. Benign or malignant tumours occurred in 30
    per cent of the test animals but the authors claimed that their
    occurrence was not related to piperonyl butoxide. Reproduction was 
    decreased by a dietary level of 10 000 ppm and stopped by a
    concentration or 25 000 ppm (Sarles & Vandergrift, 1952).


    So far as is known, the colorimetric tests used responded to piperonyl
    butoxide only. Thus, the 12 per cent of the single dose administered
    to the dog that was unaccounted for (see Biochemical aspects) may
    have been the most important from a toxicological standpoint.

    From the long-term studies in the rat a level of 100 ppm was without
    toxicological effect when compared to the controls.

    From the one-year study in the dog the dose of 3 mg/kg body-weight/day
    was without toxicological effect.

    For future toxicological studies, specifications of the test material
    should be stated.


    Level causing no toxicological effect

    Rat. 100 ppm in the diet, equivalent to 5 mg/kg body-weight per day.

    Dog. 3 mg/kg body-weight per day.

    Estimate of temporary acceptable daily intake for man

    0-0.03 mg/kg body-weight

    Further work required

    Biochemical studies on the qualitative and quantitative aspects of
    metabolism of the compound.

    Studies on the effect of piperonyl butoxide on the liver of dogs. (For
    details see Report of Scientific Group on Procedures for Investigating
    Intentional and Unintentional Food Additives - July 1966).

    The effects of this compound on reproduction in at leant one more

    Long-term feeding studies in another species, with careful observation
    to detect any possible tumours. These studies should be done using
    piperonyl butoxide alone and in combination with other agents, such as
    pyrethrins and freons, with which it might be combined in practice.

    Results of the above work should be made available not later than five
    years after the publication of this report, when a re-evaluation of
    this compound will be made.


    Use Pattern

    Piperonyl butoxide has little or no insecticidal activity. Its primary
    use is as a synergist for pyrethrins. Piperonyl butoxide may act as a
    true synergist, as an antioxidant, as an extender, or as a combination
    of any two or all three. In those countries where tolerances have been
    established for piperonyl butoxide and pyrethrins, the two materials
    are usually formulated, in a ratio of about 10:1 (w/w), respectively.

    (a) Pre-harvest treatments

    Formulations containing piperonyl butoxide are employed for
    controlling insects on growing plants just before harvest and on dairy
    and meat animals. They have been used in many countries on growing
    bush and vine fruits, deciduous fruits and nuts, forage crops, and on
    dairy and meat animals. Malathion and other insecticides have replaced
    synergized pyrethrins for some of the above uses and, therefore,
    piperonyl butoxide is not used on food prior to harvesting as
    extensively now as it was 10 or more years ago.

    (b) Post-harvest treatments

    Piperonyl butoxide, in combination with pyrethrins, has been used in a
    spray or dust formulation on freshly picked fruits and vegetables
    after harvest while in the field, in storage, or in processing plants
    for the control of drosophila and other insects. It is also used
    directly on dried fruits, treenuts, grains and oil seeds as a
    protective treatment against insect infestation during storage.

    Piperonyl butoxide is usually formulated in a 10:1 ratio with
    pyrethrins for application as a spray or dust directly on the food
    commodities as they are placed in containers or as they move on a
    conveyor into storage. It is used with pyrethrins in water emulsion or
    wettable powder formulations as surface sprays on stacked bagged
    peanuts and other oil seeds, and on animal feeds. Piperonyl butoxide
    is very commonly used in aerosols as space treatments in food
    handling, processing and storage facilities.

    As with pre-harvest treatments, piperonyl butoxide is not being used
    as extensively as it was a number of years ago. Malathion has replaced
    synergized pyrethrins in many of the above uses.

    (c) Other uses

    Piperonyl butoxide (50 mg/sq. ft) in combination with pyrethrins has
    been found to be effective in protecting cereal products against
    insect attack, when applied to the outside surface of the outer ply of
    multiwall paper bags. This treatment is becoming widely used,
    particularly in the United States, for cereal products destined for
    storage or shipment overseas.

    Perhaps the greatest use of piperonyl butoxide is in formulations to
    treat farm buildings and food processing, handling, shipping, storage
    and marketing facilities. The treatment consists of spraying the
    floors, walls, working areas and machinery, applying it in an aerosol
    form to the insect infested area, or both. Again, malathion has
    replaced synergized pyrethrins for some of these uses.

    Piperonyl butoxide is present in most of the pyrethrins formulations
    used for household insect control but the ratio of the two compounds
    in such formulations varies considerably.

    Tolerances (established or considered)

    Country             Product                         Parts per million

    Brazil              cereals                         10

    Canada              grain sorghum                   8
                        barley, buckwheat, corn         20
                        pop-corn, rice, rye, wheat

    Czechoslovakia      grain                           -

    Germany             grain                           15

    Italy               cereals                         20

    Netherlands         cereal                          10

    Tolerances (cont'd)

    Country             Product                         Parts per million

    USA                 bush and vine fruits            exempt
                        (post-harvest)                  8
                        deciduous fruits and
                        nuts                            exempt
                        flax                            8
                        forage crops                    exempt
                        fruits and nuts                 8
                        grain (post-harvest)            20
                        mushrooms                       exempt
                        (post-harvest                   8
                        vegetables                      exempt
                        (post-harvest)                  8

    Residues resulting from supervised trials

    No data were available on the fate of piperonyl butoxide residues on
    growing crops, and on fruits and vegetables which had received
    post-harvest treatments. The bulk of the information available on the
    fate of piperonyl butoxide residues has been obtained from
    post-harvest application to cereals, cereal products, dried fruits and
    dried citrus pulp animal feed. The evaluation of the use of the
    insecticide mixture for protecting stored wheat is described by
    Walkden and Nelson (1959): an unpublished document from the US
    Department of Agriculture also was reviewed by the meeting and
    provided the following information:

    In order to protect grain from insect attack, piperonyl butoxide, in
    combination with pyrethrins, is applied to various grains at rates
    equivalent to 14.2 ppm on wheat, 15.2 ppm on shelled corn, 26.7 ppm on
    oats, 17.8 ppm on barley, 15.2 ppm on rye and 19.0 ppm on rough rice.
    Some 30 per cent or more of the insecticide is normally lost during
    application; furthermore, the deterioration is rather rapid during the
    first few months after storage.

    Two space treatments applied respectively at rates of two and four
    ounces of 0.5 per cent piperonyl butoxide in combination with 0.4 per
    cent pyrethrins per 1000 cubic feet produced a maximum of piperonyl
    butoxide residue of 1.5 ppm on the top 1-1/2 inches of exposed flour.

    When dried fruit (apricots, peaches, pears) were exposed to 10
    treatments, at two and three day intervals over a period of one month,
    with a formulation containing 0.5 per cent of pyrethrins, 1.0 per cent
    of piperonyl butoxide, 1.67 per cent of MGK 264(R) and 96.83 per
    cent of light petroleum distillate applied at the rate of one gallon
    per 50 000 cubic feet of space, the maximum residues obtained were 1.9
    ppm of pyrethrins, 7.7 ppm of piperonyl butoxide and 7.2 ppm of MGK

    Bagged dried citrus animal feed was exposed to weekly treatments over
    a three month period to aerosol formulations containing 0.2 per cent
    of pyrethrins and two per cent of piperonyl butoxide applied at the
    rate of 2.5 pints/1000 cu. ft of total warehouse space. The maximum
    piperonyl butoxide residue obtained in the feed during the entire
    period was 5.5 ppm. A similar result was obtained with a wettable
    powder formulation (Laudani et al. 1959).

    Multiwall paper bags with special insect-tight closures and pyrethrins
    with piperonyl butoxide (540 mg/m2) applied to the outer surface
    have provided effective protection to cereal products against outside
    insect infestation during long-term storage period, and the maximum
    piperonyl butoxide residues from composite samples were:

    Rice - 5.5 ppm, non-fat dried milk 2.5 ppm; dry beans - 0.5 ppm,
    flour - 6.0 ppm.

    A similar test involving cornmeal stored for six months in bags
    treated with pyrethrins and piperonyl butoxide (540 mg/m2) showed a
    maximum of piperonyl butoxide in the cornmeal to be 10.7 in 50 lb.
    bags and 3.3 ppm in 100 lb. bags.

    Residues in food moving in commerce

    In 99 samples taken from cargoes shipped from all over the world to
    Rotterdam and Amsterdam, piperonyl butoxide was found in 11 samples.
    The residues ranged from 0.1 to 1.0 ppm. The limit of the sensitivity
    of the method used was 0.5 ppm.

    Residues at time of consumption

    At the time of preparation of this report no data were available on
    the fate of piperonyl butoxide residues on or in fresh fruit,
    dried-fruit, tree nuts, fresh and dried vegetables. Information is
    available on the fate of piperonyl butoxide on cereals but this is not
    as complete as it should be.

    In controlled studies the deposit on wheat, from an application dosage
    of 13.2 ppm, was shown to be 5.6 ppm in two months and 3.6 ppm in four
    months after treatment. On another occasion a theoretical 17.4 ppm was
    down to 3 ppm after two months of storage. Since the treatment is used
    only on grain going into storage for three months, or longer, it can

    be assumed that there would be at least a 50 percent loss of residue.
    Other studies have also shown that when treated wheat is milled most
    of the remaining residue goes into the screenings and scourings. A
    very small percentage of the piperonyl butoxide ends up in the flour
    traction. These same studies showed milled fractions of treated corn
    had either none or a very small percentage of the piperonyl butoxide
    originally present. Cooking reduced the residue from 4.7 to 0.6 ppm.

    Methods of residue analysis

    The method of Jones, Ackerman and Webster (1952) as modified by
    Williams and Sweeney (1956), in which the colour produced on treatment
    with tannic acid in phosphoric-acetic acid is measured, is suitable
    for the determination of residues of piperonyl butoxide. The clean-up
    techniques as appropriate to various foodstuffs are indicated. The
    method is in general sensitive to 0.1 ppm piperonyl butoxide. Beroza
    (1963) has described a thin-layer chromatographic method which should
    be capable of development into a satisfactory technique for many


    The primary use of piperonyl butoxide has been as a synergist for
    pyrethrins which have been used rather extensively in the past to
    protect a variety of foods, raw and processed, against insect
    infestation. Malathion and certain other insecticides have proved to
    be successful for similar purposes during recent years. Therefore
    piperonyl butoxide is probably used less than previously for purposes
    that may lead to residues in foods.

    Information is lacking on the identity, persistence and effects of the
    breakdown products of piperonyl butoxide and the other related
    compounds present in piperonyl butoxide concentrates.

    Although some information is available on the residues and their fate
    on or in cereal and cereal products, there are insufficient data on
    residues obtained from good agricultural practices on fresh and dried
    fruits, tree nuts, fresh and dried vegetables and peanuts and other
    oil seeds. Similarly there are very few data on the actual occurrence
    of residues in food in commerce. The above information should be
    obtained and considered before tolerances are established. Therefore,
    tolerances for piperonyl butoxide at this time should be temporary
    and reviewed in three years.

    The proposed temporary tolerances are:

    Cereal and cereal products        20 ppm
    Fresh fruits for canning only      8 ppm
    Dried fruits                       8 ppm
    Tree nuts                          8 ppm
    Dried vegetables                   8 ppm
    Peanuts and oil seeds              8 ppm

    At these levels, which are considered to be those which might possibly
    result from adequately supervised use on the crops in question the
    intake would not reach the acceptable daily figure, using the ninth
    decile food consumption figures for the United States of America and
    disregarding other safeguarding as outlined in Part I of the report on
    this meeting.

    The need for treatment, with insecticides containing piperonyl
    butoxide, of fresh fruits for canning is questionable. If such a need
    exists, the countries interested should provide information on the
    extent of its use and on the resulting residues.

    Further work or information

    (a) Further information is desirable on the levels of piperonyl
    butoxide obtained on the various foods and the effect of handling,
    cleaning, processing and storing.

    (b) Research should be conducted to determine the identity,
    persistency and toxicological effects of the breakdown products of
    piperonyl butoxide and the related compounds present with piperonyl

    (c) The analytical methods for piperonyl butoxide should be reviewed.
    A faster, more sensitive method is desirable.


    Chamberlain, R. W. (1950) Amer. J. Hyg., 52, 153

    Epstein, S. S., Joshi, S., Andrea, J., Clapp, P., Falk, H. & Mantel,
    N. (1966) Unpublished report

    Falk, H. L., Thompson, S. J. & Kotin, P. (1965) Arch. Environ.
    Health, 10, 847

    Lehman, A. J. (1948) Quart. Bull. Assoc. Food and Drug Officials
    U.S., 12, 82

    Lehman, A. J. (1951) Quart. Bull. Assoc. Food and Drug Officials
    U.S., 15, 122

    Lehman, A. J. (1952 a) Quart. Bull. Assoc. Food and Drug Officials
    U.S., 16, 3

    Lehman, A. J. (1952 b) Quart. Bull. Assoc. Food and Drug Officials
    U.S., 16, 47

    Lehman, A. J. (1952 c) Quart. Bull. Assoc. Food and Drug Officials
    U.S., 16, 126

    Rai, L. & Roan, C. C. (1956) J. econ. Entomol., 49, 591

    Robbins, W. E., Hopkins, T. L. & Darrow, D. I. (1959) J. econ.
    Entomol., 52, 660

    Sarles, M. P., Dove, W. E. & Moore, D. H. (1949) Amer. J. trop.
    Med., 29, 151

    Sarles, M. P. & Vandergrift, W. B. (1952) Amer. J. trop. Med. Hyg.,
    1, 862

    U.S. Food and Drug Admin., (1946) Unpublished data


    Beroza, M. (1963) Identification of 3,4-Methylenedioxyphenyl
    Synergists by Thin-layer Chromatography. Agric. Food Chem., 11 (1):

    Jones, H. A., Kerby, G. F. & E. J. Incho. (1952) Insect proofing of
    paper. Chemical Specialities Manufacturers Association 38th Mid-Year
    Meeting, Boston, Mass., USA

    Jones, H. A., Akerman, H. J. & M. E. Webster. (1952) The colorimetric
    determination of piperonyl butoxide. J. Assoc. Offic. Agric. Chem.,
    35: 771-780

    Laudani, H., Gillenwater, H. B., Kantack, B. H. & M. F. Phillips.
    (1959) The protection of citrus pulp against insect infestation with
    surface applications of pyrethrum - piperonyl butoxide wettable
    powder. J. Econ. Ent., 52 (2): 224-7

    Walkden, H. H. & H. D. Nelson. (1959) Evaluation of synergized
    pyrethrum for the protection of stored wheat and shelled corn from
    insect attack. U.S. Dept. Agriculture, Marketing Research Report No.

    Williams, H. L. & Sweeney, J. P. (1956) Isolation of piperonyl
    butoxide from oils, fats and waxes. J. Assoc. Offic. Agric. Food
    Chem., 11: 51-54

    See Also:
       Toxicological Abbreviations
       Piperonyl butoxide (ICSC)
       Piperonyl Butoxide (FAO Meeting Report PL/1965/10/1)
       Piperonyl butoxide (FAO/PL:1967/M/11/1)
       Piperonyl Butoxide (FAO/PL:1969/M/17/1)
       Piperonyl butoxide (WHO Pesticide Residues Series 2)
       Piperonyl butoxide (Pesticide residues in food: 1992 evaluations Part II Toxicology)
       Piperonyl butoxide (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)
       Piperonyl Butoxide (IARC Summary & Evaluation, Volume 30, 1983)