FAO Meeting Report No. PL/1965/10/1
    WHO/Food Add./27.65


    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Committee on Pesticides in Agriculture and
    the WHO Expert Committee on Pesticide Residues, which met in Rome,
    15-22 March 19651

    Food and Agriculture Organization of the United Nations
    World Health Organization

    1 Report of the second joint meeting of the FAO Committee on
    Pesticides in Agriculture and the WHO Expert Committee on Pesticide
    Residues, FAO Meeting Report No. PL/1965/10; WHO/Food Add./26.65


    General considerations

    The concept of acceptable daily intakes as applied to pesticides

    Re-evaluation of consumer hazards of pesticides

    Additional pesticides

    Biological data presented in the monographs

    Note to the reader
















    Demeton-S-Methyl Sulfoxide











    Lead arsenate








    Methyl Parathion

    Phenylmercuric Acetate

    Piperonyl Butoxide





    Triphenyltin compounds




         At the present time, to feed the people of the world, recourse
    must be had to pesticides to protect the crops both during growth and
    during their subsequent storage and transport. While some of the
    chemicals used for this purpose will not contaminate the final crop,
    others, even when used in accordance with good agricultural or food
    storage practice, will leave residues which will be present in the
    food at the time of consumption. This meeting was concerned, as were
    the previous ones, with the protection of the consumer against the
    hazards that might result from the presence of these residues, and its
    aim was to give guidance to authorities responsible for the health,
    nutrition and welfare of people from this point of view. In carrying
    out this task, the participants were mainly guided by the principles
    governing consumer safety in relation to pesticide residues enunciated
    at the 1961 joint meeting of the WHO Expert Committee on Pesticide
    Residues and the FAO Panel of Experts on the Use of Pesticides in

         The following definitions of the terms used in work on pesticide
    residues are reproduced from that report.

    Residue: A pesticide chemical, its derivatives and adjuvants in or
    on plant or animal. Residues are expressed as parts per million (ppm)
    based on the fresh weight of the sample.

    Food factor: The average fraction of the total diet made up by the
    food or class of foods under discussion. Details of the diet of a
    country may be obtained from the FAO Food Balance Sheets or other
    similar data.

    Acceptable daily intake: The daily dosage of a chemical which,
    during an entire lifetime, appears to be without appreciable risk on
    the basis of all the facts known at the time. "Without appreciable
    risk" is taken to mean the practical certainty that injury will not
    result even after a lifetime of exposure. The acceptable daily
    intake is expressed in milligrams of the chemical, as it appears in
    the food, per kilogram of body-weight (mg/kg/day).

    Permissible level: The permissible concentration of a residue in or
    on a food when first offered for consumption, calculated from the
    acceptable daily intake, the food factor, and the average weight
    of the consumer. The permissible level is expressed in ppm of the
    fresh weight of the food.

    1 FAO Plant Production and Protection Division Report No.
    PL/1961/11; Wld Hlth Org. techn. Rep. Ser., 1962, 240.

    Tolerance: The permitted concentration of a residue in or on a food,
    derived by taking into account both the range of residue actually
    remaining when the food is first offered for consumption (following
    good agricultural practice) and the permissible level. The tolerance
    is also expressed in ppm. It is never greater than the permissible
    level for the food in question and is usually smaller.

         The meeting was not concerned with tolerances and it wished to
    re-emphasize the fundamental difference between a tolerance and an
    acceptable daily intake. Only acceptable daily intakes are based
    entirely on toxicological evidence.

         A tolerance is then the smallest residue consistent with control
    of the pest, but to be toxicologically acceptable it must not exceed
    the permissible level. In the report on principles governing consumer
    safety in relation to pesticide residues,1 the method outlined for
    calculating a permissible level is most useful for a pesticide which
    is used on a single article or class of articles of the diet, if these
    form the only source of that substance for the consumer. In many
    cases, a pesticide is used on a number of different types of foodstuff
    and may also have non-agricultural uses, as in public health
    programmes. DDT is a good example of this type of pesticide. Account
    must be taken of such multiple uses of pesticides and in these cases
    it may be preferable to adopt an alternative method of calculation
    based on that advocated for food additives.2 The possible consumer
    hazards arising from the intake of a pesticide could then be assessed
    by adopting the follow procedure:

    (1) Determine the residue in each type of food and drink liable to
    contain the pesticide in question.

    (2) Calculate the daily intake level of the pesticide that might occur
    if it had been used on all the foodstuffs for which it might be used,
    working on the basis of the average daily diet.

    (3) Knowing the average body-weight, calculate the daily intake of the
    pesticide, expressed as mg per kg per day.

    (4) Check this figure against the acceptable daily intake for that

    (5) If the figure does not exceed the acceptable daily intake, the
    proposed was of the pesticide are acceptable. If the figure exceeds
    the acceptable daily intake, one or more of the proposed uses will
    have to be reconsidered with a view to reducing the residues resulting
    from such use (or uses) or abandoning one or more uses entirely.
    1 FAO Plant Production and Protection Division Report No.
    PL/1961/11; Wld Hlth Org. techn. Rep. Ser., 1962, 240.

    2 See the Sixth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, FAO Nutrition Meetings Report Series, 1962, 31; Wld
    Hlth Org. techn. Rep. Ser., 1962, 228.

    (6) When there is a margin between the figure and the acceptable daily
    intake, proposals for further uses of that pesticide on foodstuffs can
    be considered.


         Since pesticides are, from their very nature, poisonous to some
    forms of life, any intake by man in the food may be considered
    undesirable. For this reason the rate of application of the pesticide
    to the crop should be as low as possible, and the interval between its
    last application and the consumption of the crop should be as long as
    possible so that the residue is reduced to a minimum. Nevertheless, if
    pesticides are to be used, as they must be, some ingestion will occur.
    It would help in the assessment of any possible hazards arising from
    the consumption of these tiny amounts of pesticides if it were known
    how much could be consumed daily without risk.

         In order to determine an acceptable daily intake the following
    information should be available.

    (a) The chemical nature of the residue in food as presented for
    consumption. Pesticides may undergo chemical changes and are
    frequently metabolized by the tissues of the plants and animals that
    have been treated with them. Even when a single substance has been
    applied, the residue may consist of a number of substances with
    distinct properties, the exact nature of which may differ in animals
    and plants and in different crops and products.

    (b) The toxicities of the substances forming the residue, as judged by
    acute, short-term and long-term studies in animals. In addition,
    knowledge is required of the metabolism, mechanism of action, and the
    possible carcinogenicity of pesticide residues when consumed.

    (c) A sufficient knowledge of the effects of these residues on man.

         Information on this scale is not often available at the present
    time, but if it is, a daily level of intake having no observable
    effect on a sensitive species of animal can be determined. In some
    cases, this level has been determined for man himself. From this
    starting point an acceptable daily intake for man can be proposed by
    employing a suitable factor.

         When an acceptable human daily intake of a residue has been
    proposed, the nature of the food bearing the residue is probably

         The amount of data available varies considerably for the
    different pesticides. Nevertheless, even when the information about a
    particular pesticide appears very complete and an acceptable intake is
    proposed, it must be realized that, however carefully the data are
    evaluated, the statement that x mg/kg body-weight can be eaten every
    day for a lifetime without appreciable risk remains an expression of

    opinion which carries no guarantee of "absolute" safety. Such a
    guarantee would be impossible.1

         On the other hand, the desire to use the most sensitive criteria
    for the determination of the threshold effect levels, coupled with the
    natural conservatism of an international body, inevitably leads to
    great caution in the proposals for acceptable daily intakes. This
    should be taken into account when these values are used. At the
    meeting, a single set of acceptable daily intake figures was proposed.
    It was recognized, however, that exceptional situations might arise
    when the possibility of exceeding these figures would have to be
    considered, e.g., in the event of serious food shortage. The meeting
    was not in a position to offer guidance to cover all such
    circumstances; each case will have to be decided on its merits by the
    national authorities responsible, who should take expert advice on the
    risks to health from excess intake of pesticides and the medical
    consequences arising from the loss of the crop. There are obviously
    conditions in which it would be unrealistic to adhere to these levels.
    The only advice which can be given to those faced with making this
    type of decision is to consider the nature of the criterion used to
    determine the level. Obviously, when the criterion used is a minimal
    change in cholinesterase activity of the blood, the level can be more
    safely exceeded than when the criterion is some more serious
    functional change.

         Only a limited number of the many pesticides now available have
    been considered. The omission of a pesticide from the monographs does
    not imply criticism of that pesticide, nor does it suggest that it can
    be used without restraint.

         The meeting strongly emphasized that new data or new knowledge
    could always lead to a re-evaluation of an acceptable daily intake.
    Values of this nature are always provisional. It is the duty of all
    who use the material contained in the monographs to ensure that they
    possess the latest information.


         The 37 pesticides evaluated in 1963 were reconsidered by the
    meeting, not only on the basis of the information contained in the
    previous report,2 but also in the light of further data that have
    since become available.

         For 21 substances the monographs remain unchanged.

         For 11 substances (aldrin, dieldrin, endrin, heptachlor,
    dimethoate, malathion, parathion, carbaryl, captan, triphenyltin
    compounds and lead arsenate) new information was added to the
    monographs without affecting the evaluation of the hazard to man.
    1 Stoner, H. B. (1964) J. Food Cosmet. Toxicol., 2, 457.
    2 FAO Meeting Report No. PL/1963/13 (mimeographed); WHO/Food
    Add./23/1964 (mimeographed).

         A re-evaluation was made for chlordane, propham and chlorpropham.
    For chlordane, new data have demonstrated a maximum no-effect level in
    the rat, and the meeting was informed that the suggestion that propham
    and chlorpropham possessed co-carcinogenic activity had not been
    substantiated. Nevertheless, the information about these compounds was
    still insufficient to allow an acceptable daily intake for man to be

         In the case of DDT, the meeting considered that in view of the
    vast amount of information on the metabolism, fate and toxic effects
    of this compound in man obtained from observations on large numbers of
    people in many countries, a wider range could be accepted for the
    "acceptable daily intake" for man. This has now been set at 0-0.01

         Finally, in the case of diazinon it was considered on
    re-evaluation of new data that an "acceptable daily intake" for man
    could be estimated to be 0.0002 mg/kg/day. This was based on the
    threshold level for the dog which is very sensitive to this pesticide.
    The meeting re-emphasized the lack of information on the toxicity of
    diazinon to man.

         The meeting found that there was still insufficient knowledge for
    complete assessment of the possible consumer hazards from these
    pesticides. An attempt has been made in the monographs to indicate in
    a little more detail than in the previous monographs what information
    is still missing. The heading "Further work required" indicates a
    higher priority than "Further work considered desirable". In some
    cases it has been possible, under the heading "Comments on
    experimental studies reported", to draw attention to the absence of a
    specific piece of information which would materially assist in setting
    an "acceptable daily intake" value. It is hoped that such work will be
    forthcoming for consideration at future meetings.

         The meeting still felt concern about some results indicating that
    certain organo-chlorine compounds could evoke the formation of tumours
    in susceptible strains of laboratory animals. Since it was realized
    that a precipitate withdrawal of these pesticides would create
    difficulties in agriculture and public health in some countries, the
    meeting urged that serious attempts should be made to remove the
    doubts concerning the significance of these findings.


         The meeting also considered five additional pesticides
    - dichlorvos, pyrethrins, allethrin, dimethrin and piperonyl butoxide
    - using the same criteria for their evaluation as were used in the
    previous report.1

    1 FAO Meeting Report No. PL/1963/13 (mimeographed); WHO/Food
    Add./23/1964 (mimeographed).

         No acceptable daily intake was determined for any of these
    pesticides. It would have been possible to set a figure for dichlorvos
    based on inhalation experiments in man. The value would have been an
    extremely low one. However, it is known, from animal experiments, that
    dichlorvos is more toxic when inhaled than when taken by mouth, and no
    data are available on the effects of oral administration in man.
    Although the available data for the pyrethrins and the related
    allethrin and dimethrin were insufficient to establish acceptable
    daily intakes for those substances, there was no reason to question
    the customary uses of pyrethrins. Piperonyl butoxide was considered
    because it is often present, as a synergist, in pyrethrin
    formulations. Although there is no evidence that the uses of piperonyl
    butoxide as at present approved involve any danger, there is not
    enough information on the compound to allow the setting of an
    acceptable daily intake figure for man.


         In using the concept of acceptable daily intakes in the control
    of consumer hazard from pesticides it is not sufficient merely to
    consult a list of figures. Account must also be taken of the evidence
    on which the figures are based.

         As much relevant information as possible has been included in the
    monographs. Wherever possible this has been obtained from the
    published literature but other sources of information have also been
    used. The members of the meeting thanked all those who had made
    information available to them and offered their apologies to any
    authors whose work may not have been taken into consideration. They
    emphasized the need for the early and complete publication of the
    results of research in this field, particularly of that part which
    could form the basis of the determination of an acceptable daily
    intake for man. This is necessary so that the work reported can be the
    subject of scrutiny and informed criticism by a wider group of
    scientists covering disciplines not necessarily represented at the
    Committee meeting.

         Unpublished data, because they may include more detail than
    published work, may often be required for the determination of
    acceptable daily intakes. These data most be complete non-confidential
    and with an indication of the authorship of the report. The
    information will not be considered unless it is received by FAO/WHO at
    least six months before the announced date of the Committee meeting in
    sufficient copies (at least two) to be distributed to suitable

         For many substances the amount of information fell short of that
    required for the setting of an acceptable daily intake for man but not
    all the substances for which no figure was proposed seem to offer the
    same hazard. An attempt has been made to indicate the degree of hazard
    in each case and an indication has also been given of further work
    needed. When the additional information is forthcoming, the substances

    in this category will be reconsidered. The figures already set will be
    reviewed in the light of further knowledge.

         The biological data are presented under various headings, as in
    previous reports of this type.

    Biochemical studies

         These are important because they reveal the metabolism of the
    pesticide in the crop during the formation of the residue and
    subsequently in the animal which consumes it. It is important to know
    whether a substance is absorbed, its distribution in the body after
    absorption, its mechanism of action including its influence on enzyme
    systems, how it is metabolized, and the routes of final elimination.
    The toxicity of a pesticide may be altered at all these stages. In the
    crop or - in the case of veterinary pesticides - in the animal, a
    number of metabolites may be produced, some of which may be the active
    forms of the pesticides, as in the formation of paraoxon from
    parathion. After ingestion, these active products may be further
    broken down to compounds that are excreted. Storage of these or of the
    parent chemical may occur. The fact that a substance appears to be
    rapidly broken down and excreted does not necessarily mean that it is
    more desirable as a residue than one which is stored, say, in the
    adipose tissue. Short-lived compounds formed during the breakdown
    might be very poisonous, whereas persistent compounds might be stored
    in an inactive form.

         Broadly speaking, the more that is known of the fate and
    mechanism of action of a pesticide the better should be the
    understanding of its toxicity and consequently the easier it will be
    to set an acceptable daily intake for man.

    Acute toxicity

         The value of data on acute toxicity is that they give an idea of
    the inherent toxicity of the material. Where there is information of
    the acute sensitivity of man to pesticides it has been included under
    this heading.

    Short-term studies

         Investigations covering less than half the animal's life-span,
    are included under this heading.

         In the case of some of the pesticides considered, studies have
    been made in which they have been fed to man. These data are clearly
    of great value and have also been taken into consideration. In a few
    instances studies on workers exposed to pesticides have contributed
    some information or help in arriving at figures for acceptable daily
    intakes. It is desirable that further careful studies on workers be
    made because of their prolonged intensive exposure.

    Long-term studies

         These studies include tests covering the greater part of the
    animal's life-span and research on the possible carcinogenicity of the
    residues. The requirements of the latter tests have been discussed in
    previous reports.1,2,3

         Long-term studies are important for the determination of the
    dietary level of the compound which produces no effect, particularly
    when dealing with compounds that do not produce any measurable
    biochemical changes. Obviously such tests must be carried out on a
    species that has been shown by acute and/or short-term studies to be
    sensitive to the compound. The sensitivity should be as similar as
    possible to that of man and the metabolism of the compound in the
    animal should also be similar to that in man.

    Special studies

         The Committee again considered the significance of the inhibition
    of the liver esterases by many organo-phosphorus pesticides at
    concentrations below those required for the inhibition of
    cholinesterase. Again, the Committee did not think that it was
    possible to utilize these effects in the assessment of consumer hazard
    since the functional importance of these enzymes are not known, no
    symptoms appear to be attributable to their inhibition and the
    symptoms of poisoning by organo-phosphorus pesticides can be related 
    to their effect on cholinesterase activity.

         At the end of the introduction to the last report, the Committee
    mentioned those additional factors which should be borne in mind when
    using the acceptable daily intake figures, namely, addition
    (summation), potentiation and the possibility of genetic differences
    in the populations at risk. The Committee did not consider that it
    could amplify its previous remarks on "addition" or "genetic
    differences". Those remarks are now repeated.

    (a) Addition. The values given in the monographs have been
    calculated on the assumption that the diet is contaminated by a single
    chemical residue. In practice, foodstuffs frequently contain residues
    of more than one compound, and an additive effect may then occur. The
    meeting did not feel able to make any specific recommendations under
    this heading, but emphasized as a general safeguard against these
    additive effects the importance of always keeping the residues to a

    1 Wld Hlth Org. techn. Rep. Ser., 1958, 144; FAO Nutrition
    Meetings Report Series, 1958, 17.
    2 Wld Hlth Org. techn. Rep. Ser., 1961, 220; FAO Nutrition
    Meetings Report Series, 1961, 29.
    3 Wld Hlth Org. techn. Rep. Ser., 1962, 240; FAO Plant
    Production and Protection Division Report No. PL/1961/11

    (b) Genetic differences. The increasing appreciation that
    genetically determined differences in the enzymic pattern of man can
    affect his reaction to toxic agents is a further indication that
    acceptable daily intakes should not be applied too rigidly.

         Regarding the possibility of the potentiation of the effect of
    one pesticide residue by the residue of another pesticide, the
    Committee considered that the evidence which was available indicated
    that potentiation was unlikely to occur at the concentrations for
    pesticide residues found in food.

         Since the last report more information1,2,3,4,5 has come to hand 
    on the results of the use of behavioural tests in the investigation of
    the toxicity of pesticides. These tests offer additional ways of
    investigating the actions of pesticides on mammals and the results
    have been taken into account in the evaluation of the toxicity of the
    pesticides considered in these monographs. At the present time it
    would appear that for some substances behavioural tests are not more
    sensitive than other tests (biochemical, etc.) used to detect toxicity
    and the information obtained must be considered together with all the
    other available information.

    Comments on experimental studies reported

         Under this heading is given a short commentary summarizing the
    available evidence and leading to its evaluation from the point of
    view of the determination of a maximum acceptable daily intake for


         In evaluating the toxicological information, the meeting was
    mainly concerned to establish the maximum dose of the compound that
    could be given over a long period without producing ill effects. In
    most cases this was a dose level for some animal species. For some
    compounds this level had been determined in man, and such human data,
    although often covering a relatively short period, naturally took
    precedence. When human data of this type were not available and in the
    absence of evidence to the contrary, human sensitivity in principle
    was equated with that of the most sensitive animal species.

    1 Medved, L. I., Spyn, E. I. & Kagan, I. S. (1964) Residue Reviews,
    6, 42.
    2 Goldberg, M. E. & Johnson, H. E. (1964) J. Pharm. (Lond.), 16,
    3 Goldberg, M. E. & Johnson, H. E. (1964) J. Pharmacol. exp. Ther.,
    145, 367.
    4 Goldberg, M. E., Johnson, H. E. & Knaak, J. B., Psychopharma (In
    5 Goldberg, M. E., Johnson, H. E. & Knaak, J. B., Biochem.
    Phamacol. (In press).

         It is unfortunate that only crude criteria exist for estimating
    the mammalian toxicity of many pesticides. It was felt that a cautious
    attitude should be adopted towards compounds whose mechanism of action
    was unknown. The meeting wished to draw the attention of research
    workers to the need for more sensitive criteria for use in this type
    of work. Increasing sensitivity is not valuable of itself unless it is
    significant from the point of view of toxicity. The sensitivity of
    those tests used to measure the toxicity of the pesticide at high
    dosage levels should be increased so that proper dose-response curves
    can be determined.

    Extrapolation to man

         Where a maximum no-effect level of dietary intake has been
    established in a sensitive animal species and where there are no
    comparable data for man, the animal dose rate must be taken as a basis
    for calculating an acceptable daily intake for man. This can be done
    in several ways.1,2 Unfortunately the more scientific methods of
    making this adjustment require an amount of information that is seldom
    available, and was certainly lacking for the compounds studied in the
    present report. Accordingly the meeting adopted the commonly used
    empirical method: the maximum no-effect dietary level obtained by
    animal experiment, expressed in mg/kg bodyweight per day, was divided
    by a "factor", generally 100.

         Where the maximum no-effect level for oral intake in man was
    known, a smaller factor was used - in certain cases as low as 10.

         The acceptable daily intake figures in the monographs that follow
    are intended to be of value as a check to ensure that tolerances are
    toxicologically acceptable.

    Note to the reader

         Any comments on chemical and physical information and
    agricultural data should be addressed to:

         Crop Protection Branch
         Plant Production and Protection Division
         Food and Agriculture Organization
         Rome, Italy

    Any comments on biological data and their evaluation should be
    addressed to:

         Nutrition Unit
         World Health Organization
         Geneva, Switzerland

    1 Gaddum, J. H. (1956) Brit. J. Pharmacol., 11, 156.
    2 Mantel, N. & Bryan, W. R. (1961) J. nat. Cancer Inst., 27, 455

    See Also:
       Toxicological Abbreviations