WHO/Food Add./68.30



    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party of Experts and the WHO Expert
    Committee on Pesticide Residues, which met in Rome, 4 - 11 December,
    1967. (FAO/WHO, 1968)

    Rome, 1968

    This document contains summaries of data considered by the Joint
    Meeting of the FAO Working Party of Experts and the WHO Expert
    Committee on Pesticide Residues in arriving at recommendations for
    acceptable daily intakes, tolerances and methods of analysis.

    A summary Report of the Joint Meeting (FAO/WHO, 1968) has also been
    published which contains general considerations, including the
    principles adopted for the evaluations and a summary of the results of
    evaluations of a number of pesticide residues.



    Note to the reader

    The Monographs



         Carbon disulfide

         Carbon tetrachloride




         Demeton-S-methyl sulfoxide - see oxydemeton-methyl







         Ethylene dibromide

         Ethylene dichloride



         Hydrogen phosphide





         Methyl bromide

         MGK 264


         Organomercury compounds



         Piperonyl butoxide





         Appendix I - Glossary


    A Joint Meeting of the FAO Working Party of Experts on Pesticide
    Residues and the WHO Expert Committee on Pesticide Residues was held
    in Rome in December 1967. The general considerations, including the
    principles adopted for the evaluations and a summary of the results of
    evaluations on a number of pesticide residues will appear in a
    publication entitled "Report of the 1967 Joint Meeting of the FAO
    Working Party of Experts on Pesticide Residues and the WHO Expert
    Committee on Pesticide Residues" (FAO/WHO, 1968). Additional
    information, including previously unpublished summaries of data
    considered by the Joint Meeting in arriving at recommendations for
    acceptable daily intakes, tolerances and methods of analysis, is to be
    found in this document.

    Many of the compounds considered at this meeting have been previously
    evaluated in earlier publications. If only a limited amount of
    additional data on these compounds has become available in the
    intervening years, only this latter data is summarized in the
    pertinent monograph and reference is made to the previously published
    evaluation which should also be consulted by the reader who wishes to
    obtain a complete evaluation of the compound. If a large amount of
    data has become available since the previously published evaluation,
    or if the compound was first considered by the Joint Meeting in 1967,
    the pertinent monograph is reproduced in its entirety.

    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. Early and complete publication of the results of research in
    this field is very important, particularly of that part which could
    form the basis for estimation of acceptable daily intakes and
    appropriate tolerances.

    Publication allows the research to be scrutinized and criticised by
    scientists from disciplines not necessarily represented at the
    meeting. Data contained in unpublished reports, because they may
    include more detail than published work, are often acceptable.
    However, such reports must be complete and non-confidential and
    indicate authorship.

    As indicated in the Report of the 1967 Joint Meeting, the terms used
    in previous reports were reviewed. Those employed in the current
    Report and these monographs were carefully studied and, where
    necessary, redefined and explained in the accompanying glossary
    (Appendix 1). The Joint Meeting wished to emphasize, however, that the
    agreed definitions are solely for convenience in clarifying the
    present monographs which are specifically concerned with the hazards
    to consumers arising from the use of pesticides in the production and
    protection of food.


    Organochlorine insecticides

    The organochlorine insecticides have been proved to be very effective
    and they have been used extensively with very beneficial effects.
    Their acute toxicities are much lower than many other pesticides.
    However, many of them have been shown to be persistent in the animal
    and human body. In addition, even at relatively low doses they have
    effects on the liver. The toxicological significance of the induction
    of liver enzymes and of the associated morphological changes are
    difficult to evaluate. It was therefore recommended that further
    studies on this matter be undertaken.

    Organophosphorus insecticides

    On the other hand, some of the organophosphorus insecticides have
    relatively high acute toxicities and their improper transportation and
    use has resulted in numerous cases of intoxication and death. Although
    these matters are outside the terms of reference of the WHO Expert
    Committee on Pesticide Residues, the FAO Working Party of Experts on
    Pesticide Residues wished to emphasize that both acute and chronic
    toxicity hazards should be taken into consideration when selecting
    pesticides for agricultural use.


    Much work has been done during recent years on the mechanisms by which
    fumigants are retained by foodstuffs and the chemical and physical
    reactions which occur during and after sorption. This is valuable in
    both assessing the toxicological importance of any residues in food
    and in devising methods for their measurement. However, the Joint
    Meeting of the FAO Committee on Pesticides in Agriculture and the WHO
    Expert Committee on Pesticide Residues (FAO/WHO, 1965) pointed out
    that relatively little information is available on residues of parent
    fumigant substances in individual commodities and that the possible
    chemical reactions between fumigants and, for example, amino acids or
    vitamins, have not been fully investigated.


    1. General Remarks

    The meeting has considered the analytical methods available for the
    determination of residues of the various pesticides studied. By way of
    guidance only, a single method of analysis (which may be a
    multidetection procedure) has, where possible, been suggested for each
    pesticide in each monograph. This is not to say that methods which are
    not suggested for these compounds are unsuitable. In the following
    paragraphs guiding suggestions on the limitations and means of

    achieving adequate sensitivity for the tolerances and practical
    residue limits in this compendium of monographs are given. Special
    review articles on residue analysis are published from time to time in
    Residue Reviews (Gunther, 1962 to date).

    2. Multidetection Systems of Analysis

    Many modern chromatographic methods of residue analysis are highly
    sensitive and specific. When properly conducted the system permits the
    analyst in a single analytical operation to detect and measure any of
    a large number of different residues in a sample. It is particularly
    emphasized that to do this successfully, it is very necessary for the
    extraction and cleanup processes to be properly designed and for the
    operational techniques of layer and gas chromatography to be well
    understood and controlled.

    The multidetection systems of analysis comprise paper chromatography,
    layer chromatography and gas-liquid chromatography. Thin-layer and
    loose-layer chromatography are themselves essentially simple
    techniques useful for the cleanup of extracts in residue analysis.
    They can also be used in some cases to separate, identify and measure
    individual residues. Gas-liquid chromatography in an excellent method
    for the separation and measurement of individual residues, by using
    suitable detectors, it is capable of a very high degree of
    sensitivity. These features can be further developed when gas-liquid
    and thin-layer chromatography are suitably combined in a single system
    of analysis, so providing confirmation of the identity of the
    residues. Paper chromatography also is a simple and useful
    confirmatory method. Other confirmatory methods include the use of two
    or more different gas-liquid chromatographic columns, two independent
    detector systems, micro-infrared spectrophotometry and

    When using highly sensitive electron capture gas-liquid
    chromatographic techniques, the detector system must function and be
    controlled correctly. It must not give erroneous responses arising
    from poor geometric design or incorrectly applied voltage, or from the
    use of unsuitable operating conditions such as the wrong choice of
    carrier gas, flow-rate or column materials. Column temperature also is
    very important since pyrolytic changes can occur and, if not properly
    recognized, can lead to erroneous conclusions. Even when such methods
    are properly used, some pesticides such as toxaphene, if present in
    extracts, may cause difficulty. Toxaphene is a complex mixture of a
    large number of similar substances and gives a general and perhaps
    variable 'background' response which is not readily amenable to
    precise measurement.

    Provided all of the above considerations are thoroughly understood, it
    is possible for the residue analyst to use sensitive gas-liquid
    chromatographic detectors which are virtually specific for phosphorus,
    halogen, or sulphur compounds. In some cases the sensitivity may be
    adjusted to extend to, or to exclude, other types of residue such as

    the triazine or pyrethroid compounds. However, while in skilled hands
    the multidetection methods are capable of giving highly accurate
    results, they are less easy to specify in operational detail than are
    most chemical analytical methods. With gas-liquid chromatography, this
    is due in part to various factors which affect the behaviour of a
    set-up of apparatus. These factors include the column length and
    support material, the amount and nature of the liquid phase, the
    column and injection temperatures, the detector design and the voltage
    applied to it, the nature and flow rate of the gas phase and the
    previous use history of the column system as a whole. Some of these
    factors are affected by the design and model of the gas chromatograph.
    For this reason the monographs do not contain detailed specifications
    of such methods; although in appropriate cases general statements of
    the nature and capabilities of the methods are given. For general
    guidance to these methods and their capability and limitations, see
    Cook and Williams (1965) and Williams and Cook (1967); and for thin
    layer chromatography, Abbott and Thomson (1965).

    Bioassay methods are recognized as being useful for research purposes
    and an screening tests for the presence of pesticide residues and in
    conjunction with other confirmatory procedures. As they are
    non-specific, however, their uses are limited.

    3. Methods for Residues of Organochlorine Pesticides

    Methods of organochlorine residue analysis have been reviewed by
    Beynon and Elgar (1966); thin layer chromatographic methods have been
    reviewed by Abbott et al (1964 and 1965). Until a few years ago, the
    only methods available for the detection and determination of
    organochlorine pesticide residues were insensitive and lacked
    specificity. With the development of modern quantitative
    chromatographic methods it has become possible to isolate and detect
    the principal organochlorine pesticides, together with a number of
    their decomposition products, in sub-microgram quantities. Indeed the
    most sensitive gas chromatographic methods now enable the skilled
    residue analyst to measure down to a picogram (one million millionth
    of a gram) of pesticide in favourable cases. An efficient cleanup
    stage is essential in all quantitative chromatographic methods;
    layer chromatography itself is a valuable cleanup technique. Some of
    the important considerations when using these methods are indicated in
    section (2) on 'Multidetection Systems'. For the most effective use of
    a gas chromatograph for the organochlorine compounds the samples
    should be cleaned up well enough so that the pen of the chart recorder
    returns to very near the baseline within one minute of the sample
    injection. In the absence of residues of toxaphene the pen should
    return to the baseline between many of the individual eluting
    compounds, such as lindane, aldrin, heptachlor, etc. The injection of
    only one uncleaned extract may cause conversion of p,p'-DDT to a
    series of compounds which elute earlier than p,p'-DDT and may even
    appear to be heptachlor. If an essentially straight baseline to the
    chart record is not obtained, sensitivities may be one-half or less of
    the values indicated in the individual monographs for organochlorine

    compounds. An extended account of the application of gas-liquid
    chromatographic methods of residue analysis to organochlorine
    pesticides has been compiled for the U.S. Food and Drug Administration
    by Berry, et al (1967).

    4. Methods of Analysis for Organophosphorus Compounds

    Methods of organophosphorus pesticide residue analysis have been
    reviewed by Abbott and Egan (1967). Generally, the wet chemical
    methods for the organophosphorus pesticide chemicals are limited to
    residues of about 0.1-0.2 ppm or above, and some are not useful in
    determining oxygen analogs or other metabolic products.

    The procedure outlined by Barry, et al (1967) for the organochlorines
    will detect and measure a number of the parent organophosphorus
    compounds such as parathion, methyl parathion, diazinon, malathion and
    ethion. The development of multidetection schemes for residues of the
    organophosphorus pesticides (which include the significant metabolic
    products) for use for monitoring food products of unknown spray
    history is very important. However, the development of such schemes
    for the organophosphorus pesticides has proved to be considerably more
    difficult than for the organochlorine pesticides. The organophosphorus
    compounds have a much wider spectrum of polarities and have a much
    greater propensity to convert to more polar yet toxic residues. Thin
    layer and paper chromatography have been utilized for some time in
    studying methods of analysis. Since the development of detectors for
    gas chromatography which are highly sensitive and selective for
    phosphorus compounds (Giuffrida (1964); Hartmann (1966); Brody and
    Chaney (1966)), there has been considerable work in gas chromatography
    on these compounds. (For a review of both subjects see Williams and
    Cook (1967)).

    Even though much work has been done, no single procedure of
    extraction, cleanup and determinative step has emerged which has been
    proved to yield both quantitative recovery and qualitative separation
    of a number of the parent compounds in food, especially total diets.
    However, some schemes appear very promising and it is expected that
    the supporting data will become available in the near future. One of
    the schemes is the extraction of Watts and Storherr (1965) and the
    column cleanup of Storherr et al (1964). The column, consists of 14 g
    of an absorbent mix containing 1 part Norit S G Extra (acid washed in
    lab), 2 parts hydrated MgO (Mills), and 4 Parts celite. The column is
    eluted with 300 mls of 25 per cent ethylacetate in benzene. This is
    concentrated to a small volume and aliquots are chromatographed either
    by gas or thin layer. The KCI thermionic detector to utilized
    following chromatography on (1) 10 per cent DC 200 on Gas Chrom Q-ABS
    or (2) 2 per cent diethylene glycol succinate on the same support. A
    number of organophosphorus pesticide chemicals and some of their
    oxygen analogs have been added to blank kale samples and analyzed by
    the above procedure. Demeton-S-sulfoxide, demeton-S-sulfone and
    phorate-S-sulfone have been shown to be extracted, etc., by the same
    procedure, but the purity of the sample was not high enough to judge
    efficiency of the process.

    For guthion, oxygen analog of guthion, and Ruelene (R), the succinate
    column must be used and dimethoate and its oxygen analog are much
    better chromatographed on the succinate column.

    5. Methods of Fumigant Residue Analysis

    Earlier methods of analysis for residues of unchanged fumigants mainly
    involved classical chemical techniques; they are time-consuming to
    perform and are neither very specific nor very sensitive.

    The possibility of using gas-liquid chromatography for the detection
    and determination of unchanged fumigants has been investigated in
    recent years. Such analytical methods are in general far more
    sensitive than the earlier classical methods, as well as being more
    specific. Of the fumigants, carbon tetrachloride has the greatest
    electron capture affinity, a sensitivity some 200 times greater than
    that for ethylene dichloride. For this reason, small amounts of carbon
    tetrachloride will tend to mask moderate amounts of other halogenated
    fumigants when these methods are used. It should, however, be quite
    possible to perfect rapid multidetection systems for unchanged
    fumigant residues by such methods and it is important to do this. In
    the meantime, recommendations for alternative methods are made.

    Note to the reader

    Any comments on evaluations for tolerances should be addressed to :

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

    Any comments on evaluations for acceptable daily intakes should be
    addressed to :

         Food Additives Unit
         World Health Organization
         Geneva, Switzerland


    Abbott, D.C., Egan, E., and Thomson, J. (1964) Thin layer
    chromatography of organochlorine pesticides. J. Chromatography 16,

    Abbott, D.C. and Thomson, J. (1965) The application of thin layer
    chromatographic techniques to the analysis of pesticide residues.
    Residue Reviews 11, 1-59.

    Abbott, D.C. and Egan, H. (1967) Organophosphorus pesticides residue
    analysis: a review.  Analyst 92, 475-492.

    Barry, H.C., Hundley, J. and Johnson, L.V. (1967) Pesticide Analytical
    Manual, Vol. 1., (Revised 1967) U.S. Food and Drug Adm., Washington,

    Beynon, I. and Elgar, K.E. (1966) Organochlorine pesticide residue
    analysis: a review. Analyst 91, 143-175.

    Brody, S.S. and Chaney, J.E. (1966) The application of a specific
    detector for phosphorus and sulfur compounds - Sensitive to
    subnanogram quantities. J. Gas Chromatography 4, 42-46.

    Cook, J.W. and Williams, S. (1965) Pesticide Residues. Anal. Chem.
    37, 131R-142R 

    FAO/WHO. (1965) Evaluation of the toxicity of pesticide residues in
    food. FAO Mtg. Rept. PL/1965/10; WHO/Food Add./26.65.

    FAO/WHO. (1968) Report of the 1967 Joint Meeting of the FAO Working
    Party and WHO Expert Committee on Pesticide Residues. FAO Mtg. Rept.
    No. PL:1967/M/11; WHO Technical Report Series No. 391.

    Giuffrida, L. (1964) A flame ionization detector highly selective and
    sensitive to phosphorus - A sodium thermionic detector. J. Assoc. Off.
    Agr. Chem. 47, 293-300.

    Gunther, F.A. (1962-present) Residue Reviews. Springer Verlag,
    Berlin-Heidelberg-New York 

    Hartmann, C.H. (1966) Phosphorus detector for pesticide analysis.
    Bull.Envir. Contam. Toxicol. 1, 159-168.

    Storherr, R.W., Getz, M.E., Watts, R.R., Friedman, S.J., Erwin, F.,
    Giuffrida, L., and Ives, R. (1964) Identification and analysis of five
    organophosphorus pesticides: Recoveries from crops fortified at
    different levels. J. Assoc. Off. Agr. Chem. 47, 1087-1093.

    Watts, R.R. and Storherr, R.W. (1965) Rapid extraction method for
    crops. J. Assoc. Off. Agr. Chem. 48, 1158-1160.

    Williams, S and Cook, J.W. (1967) Pesticide Residues. Anal. Chem.
    39, 142R-157R.

    See Also:
       Toxicological Abbreviations