IPCS INCHEM Home



    PESTICIDE RESIDUES IN FOOD - 1979


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1979





    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Expert Group on Pesticide Residues
    Geneva, 3-12 December 1979



    CARBON TETRACHLORIDE

    Explanation

    This fumigant pesticide was evaluated at the Joint Meeting in 1965,
    was further considered in 1967 and 1968, and was re-evaluated in 1971.
    The report of the 1978 Meeting made reference to problems caused in
    member countries of FAO and WHO by the use of certain fumigants and
    recommended of carbon tetrachloride.

    RESIDUES IN FOOD AND THEIR EVALUATION

    The report of the 1971 Meeting contained a statement of general
    principles relating to residues of fumigants.

    USE PATTERN

    Post harvest use

    Carbon tetrachloride (CTC) has been used widely as a grain fumigant in
    postharvest storage either alone or mixed with other fumigants which
    are generally more toxic to insects.  In mixtures, in addition to its
    moderately insecticidal properties, carbon tetrachloride in useful as
    an aid to distribution and fire suppressant for other fumigants.
    Compounds with which it has been used include 1,2-dichloroethane
    (EDC), 1,2-dibromoethane (EDB), trichloroethylene, acrylonitrile and
    carbon disulphide.  The liquid fumigant in generally sprayed on to the
    surface of the grain and the vapour is distributed by gravity.  As
    well as its use in bulk grain fumigation in silo and floor storage,
    carbon tetrachloride has been used on a small scale in developing
    countries for disinfestation of single bags of grain by application of
    a small quantity, typically 20 ml, from a gelatin capsule.  There is
    also a continuing use in small-scale farm bin storage practice where
    the handling of more acutely toxic compounds is undesirable.

    Concern amongst some authorities about the continued use of certain
    chlorinated hydrocarbons because of the possibility of exposure to the
    vapour of people engaged in, or working adjacent to fumigation
    operations, coupled with the availability of alternative fumigants,
    has led to a reduction in the use of liquid grain fumigants containing
    carbon tetrachloride over the past few years.  In some instances their
    use has been abandoned or restricted (e.g. to application by
    professional pest control operators).  However, for deep grain silo
    insect disinfestation, where the installation does not have a fumigant
    circulatory facility and the grain cannot be turned to allow mixing in
    of pesticide, the liquid fumigants still hold a unique place with
    their ability to disinfest the whole bulk.  Recent research (Heunser,
    1979) has shown that the carbon tetrachloride content of liquid grain
    fumigants might be replaced by 1,1,1-trichloroethane, a compound
    having similar physical and pesticidal properties but which has shown
    a more favourable toxicological pattern in chronic mammalian
    exposures.

    RESIDUES ARISING FROM SUPERVISED TRIALS

    Carbon tetrachloride is usually applied to stored cereals as a liquid
    ether alone or in admixture at rates equivalent to 160-1400 mg/kg
    calculated on the whole bulk treated.   However, the fumigant is
    usually not distributed evenly throughout the commodity when applied
    to the surface; after a few days the lower parts of the bulk generally
    contain the higher residue levels.  After the larger physical
    movements of vapour within the grain bulk have stabilized, there is a
    steady loss of adsorbed vapour during storage, the rate of loss
    depending on the temperature, moisture content of grain and conditions
    of storage e.g. the air-tightness of the enclosure.

    Results from earlier trials on the rate of loss of such residues were
    evaluated at the 1971 Meeting.  Scudamore and Heuser (1973)
    established rates of loss of residual carbon tetrachloride from maize
    and wheat fumigated at normal insect control dosage levels, over
    periods of up to a year, under constant temperature and air moisture
    conditions.  They found that maize contained about 50 mg/kg after 6
    months free aeration at 10C but less than 10 mg/kg when aired at
    25C.  Wheat fumigated at the same dosage level contained 7 mg/kg
    residual carbon tetrachloride after six months aeration at 20C and 2
    mg/kg when held at 25C.  The reduction in residue levels in 7 days
    immediately after fumigation varied from 34-55% in maize and from
    14-52% in wheat, the greater reduction in each case being recorded at
    high aeration temperatures.  However, Beilorai and Alumot (1975) in
    confirmation of results reported earlier (Alumot and Beilorai, 1969)
    gave results of aeration experiments with several liquid fumigants,
    including carbon tetrachloride, which indicated a higher rate of loss
    of residue at 14C than at 32C.  The reasons for the differing
    findings of these two groups of workers remains unresolved.  It is
    possible that under the atmospheric conditions prevailing in the
    Israeli work, the moisture content of the fumigated cereals changed
    during aeration and that this had a greater effect than that of
    temperature alone.  Since this could be the case under practical
    conditions, the temperature during aeration may not be the most
    critical factor.

    Berck (1974) found carbon tetrachloride residues in wheat stored in a
    farm bin after fumigation with a CTC/EDC/EDB mixture at 4 gal/1000 bu
    ranging from 7-73 mg/kg one week after fumigation and from 2-30 mg/kg
    six weeks later.

    In experiments carried out in a model silo, Jagielski et al. (1978)
    fumigated wheat and maize at insect control dosage levels and
    determined residual carbon tetrachloride levels up to three months
    after treatment.  These ranged from over 1000 mg/kg at the time of
    application, falling to between 250 and 990 mg/kg in maize at 7 days
    after fumigation and from 12-62 mg/kg at three months.  For wheat the
    corresponding figures were 7 days: 140-300 mg/kg and three months:
    20-49 mg/kg.

    Jagielski et al. (1978) found that a substantial proportion of
    residual carbon tetrachloride present in wheat appeared in the milled
    fractions, especially in the bran, with about 10% found in white flour
    and 20% in wholemeal flour.  A maximum of 0.03 mg/kg was found in
    bread (white and wholemeal).  Berck (1974) reported more substantial
    reductions in initial residue content of fumigated wheat on milling;
    about 1% remaining in white flour and 5% in bran.  Residues in bread
    baked from the flour however ranged from 0.01 to 0.13 mg/kg in Berck's
    work.

    FATE OF RESIDUES

    General - Plant Materials

    The major route of residue reduction in stored fumigated produce is by
    volatilisation.  No reaction products of carbon tetrachloride
    occurring in plant materials under normal storage conditions have been
    substantiated an far as is known, though Larmour and Bergsteinesson
    (1938) suggested that deterioration of fumigated stored wheat of 24%
    moisture content could be due to hydrolysis of the fumigant with
    formation of hydrochlorid acid.  However, during steam distillation of
    residual carbon tetrachloride from wheat or maize, Malone (1969) and
    Scudamore and Heuser (1973) found traces of chloroform in the
    distillate which they postulated must have been formed in situ in
    the boiling water, since cold organic solvent extraction methods gave
    a higher recovery of carbon tetrachloride and no chloroform residue.

    In Animals

    There is an abundance of published material on changes in liver cells
    induced by carbon tetrachloride exposure.  Recknagel (1977) has 
    reviewed probable chemical mechanisms of carbon tetrachloride
    toxicity.  It is generally postulated that CCl3 free radicals are
    formed and ESR studies have been claimed to identify the transient
    existence of the trichloromethyl radical in exposed rat livers
    (Calligaro et al., 1975; Sancier, 1976).

    In Storage and Processing

    The persistence of residual carbon tetrachloride in cereal grains
    after application under commercial or farm storage conditions depends
    on method of storage, air movement, grain moisture content and
    temperature during storage.  About 5-20% of the applied dose is
    initially absorbed and may air off only slowly under cool storage
    conditions with little air movement.  This residual fumigant desorbs
    considerably during milling processes and virtually disappears in the
    baking process (see under Supervised trials).

    EVIDENCE OF RESIDUES IN FOOD IN COMMERCE

    Selective monitoring of cargoes of wheat and other grains imported
    into the United Kingdom during 1978-79 showed the large majority of
    wheat samples (out of 233) to contain less than 0.1 mg/kg of residual
    carbon tetrachloride.  18 samples contained between 0.1 and 0.99
    mg/kg, 8 between 1.0 and 9.9 mg/kg, 7 contained between 10 and 49
    mg/kg and 1 sample exceeded 50 mg/kg.  Residues of a similar order and
    frequency distribution were also found in rice, maize and sorghum
    (Fishwick and Rutter, 1979).  Thus the great majority of samples
    contained less than the 1971 JMPR guideline level for raw cereals.  Of
    66 samples of imported grain analysed in the Netherlands, only 3
    contained residues exceeding 1 mg/kg and none exceeded 13 mg/kg
    (Admiral et al., 1979).

    METHODS OF RESIDUE ANALYSIS

    Residual carbon tetrachloride in cereal grains, milled products and
    other stored products, can be determined by gas chromatography after
    cold extraction (Heuser and Scudamore, 1969).  This method has been
    collaboratively tested on wheat and maize (Panel on Fumigant Residues
    in Grain, 1974) and has a limit of determination of better than 0.001
    mg/kg.  Grave and Hogendoorn (1979) claim a sensitivity of 0.001 mg/kg
    for residual carbon tetrachloride in grain using a head-space
    analytical method.

    NATIONAL RESIDUE LIMITS REPORTED TO THE MEETING

    A number of countries including Australia, Canada and the United
    States have hitherto taken the view that no residue will be present in
    foods ready for consumption when carbon tetrachloride is applied to
    raw commodities and require that residues must not be present
    (Australia), or exempt foods from a tolerance (eg USA).  An EEC draft
    directive in 1976 proposed a limit of 0.1 mg/kg in cereals put into
    circulation for human consumption.  Dutch tolerances were reported to
    the meeting as: cereals, 50 mg/kg, flour 10 mg/kg fruit and
    vegetables, nil.

    APPRAISAL

    Although carbon tetrachloride has been widely used for many years as a
    grain and animal feedstuff fumigant on its own or mixed with other
    liquid fumigants, it is considered that this use is declining and in
    some countries such use is prohibited.  In the United Kingdom tests
    have shown that 1,1,1-trichloroethane is a satisfactory substitute for
    carbon tetrachloride in fumigation practice (Pest Infestation Control
    Laboratory, 1978) and has a much more satisfactory toxicological
    record, especially in relation to the effects of carbon tetrachloride
    on mammalian liver.

    Although very little carbon tetrachloride residue from grain
    fumigation persists through to prepared food such as bread or
    fermented products highly sensitive analytical methods now available

    can detect the presence of minute amounts.  If bran or wholemeal
    products subjected to little or no processing are consumed there is a
    possibility of ingestion of larger residues.

    In view of the difficulty of assessing the toxicological significance
    of even small residues of carbon tetrachloride in the diet, the
    Meeting concluded that guideline levels for residues in food as
    offered for consumption should be set at lower levels than hitherto
    recommended.  They recommended a new category of cereal foods not to
    be subjected to cooking or baking for which a low guideline residue
    level should be set. The meeting further expressed the view that
    because the hazards of ingestion of even small amounts of residual
    carbon tetrachloride could not be adequately evaluated its use as a
    food fumigant should be phased out as and when practicable.

    From available information on residue levels occurring in raw
    commodities in storage and transit practice, it is recommended that
    the levels given below be used as guidelines only.

    The following residue levels may occur after currently recognized
    fumigation practice.

              Cereal grains                           50a
              Milled cereal products
              (to be subjected to baking
              or cooking)                             10
              Milled cereal products intended
              for consumption without cooking         0.01b*
              Bread and other cooked cereal
              products                                0.01c*

    The meeting concluded that these levels are suitable for use as
    guideline levels and should not be exceeded if good fumigation
    practice, including adequate aeration, is followed.

                   

    a)  At point of entry into a country, and in the case of cereal for
    milling, if product has been freely exposed to air for a period of at
    least 24 hours.

    b)  To comply with the guideline level proposed for milled cereal
    products intended for consumption without cooking, the cereal grain
    must be selected from lots which have not been treated with carbon
    tetrachloride.

    c)  To apply to commodity at point of retail sale or when offered for
    consumption.

    *   At or about the limit of determination

    FURTHER WORK OR INFORMATION

    Desirable

    Development of alternative fumigants for cereal grain disinfestation
    for use in circumstances where carbon tetrachloride is presently
    employed.

    REFERENCES

    Admiral, P., de Bruin, A., Cats, H., Dornseiffen, J., Greve, P.A.,
    Hogendoorn, E.A. and Mulders, E.J. - Rept. No. 95/79 (1979), Rijts
    Instituut voor de Volksgezondheid Bilthoven Netherlands.

    Alumot, E. and Beilorai, R. - Residues of fumigant mixture in cereals
    fumigated at two different temperatures. J. Agric. Fd. Chem. 17, 869.

    Beilorai, R. and Alumot, E. - The temperature effect on fumigant
    desorption from cereal grain. J. Agric. Fd. Chem. 23, 426.

    Berck, B. - Fumigant residues of carbon tetrachloride, ethylene
    dichloride and ethylene dibromide in wheat, flour, bran, middlings and
    bread. J. Agric. Fd. Chem. 22, 977.

    Calligaro A. et al. - Electron spin resonance study of homolytic
    cleavage of carbon tetrachloride in rat liver. Trichloromethyl free
    radicals. Chem. Abstr. 83 (15), 12130.

    Fishwick, F.B. and Rutter, I.R. - U.K. Survey of pesticide residues in
    cereals, 1979. Unpublished report Ministry of Agriculture, Slough Lab.
    U.K.

    Jagielski, J., Scudamore, K.A. and Heuser, S.G. - Residues of carbon
    tetrachloride and  ethylene dibromide in cereals and processed foods
    after liquid fumigant grain treatment for pest control. Pestic.
    Science 9, 117.

    Heuser, S.G. - New fumigation standards for the eighties. Proc. 5th
    British Pest Control Assn. Conf. (1979), Paper No. 15, 2

    Heuser, S.G. and Scudamore, K.A. - Determination of fumigant residues
    in cereals and other foodstuffs: a multi-detection scheme for gas
    chromatography of solvent extracts. J. Sci. Fd. Agric. 20, 566.

    Larmour, R.K. and Bergsteineson, H.N. - Effect on wheat quality of
    long exposures to carbon tetrachloride.  Can J. Res. 16c, 241.

    Malone, B. - Analysis of grains for multiple residues of organic
    fumigants.  J. Ass. Off. Agric. Chem. 52, 800.

    Panel on Fumigant Residues in Grain.  The determination of residues of
    volatile fumigants in grain. Analyst 99, 570.

    Pest Infestation Control Laboratory. Development of
    1,1,1-trichloroethane as a grain fumigant.  Pest Infestation Control
    Lab. Report 1974-76, pp.77, HMSO, London.

    Recknagal, R.O. et al. - Chemical mecshisms in carbon tetrachloride
    toxicity.  Free Radicals Biol. 3, 97.

    Sancier, K.M. - Electron-spin resonance study of homolytic cleavage of
    carbon tetrachloride in rat liver. Pharmacol. Res. Commun. 8, 429.

    Scudamore. K.A. and Heuser, S.G. - Determination of carbon
    tetrachloride in fumigated cereal grains during storage. Pestic. Sci.
    4, 1.
    


    See Also:
       Toxicological Abbreviations
       Carbon Tetrachloride (EHC 208, 1999)
       Carbon Tetrachloride (HSG 108, 1998)
       Carbon tetrachloride (ICSC)
       Carbon tetrachloride (FAO Meeting Report PL/1965/10/2)
       Carbon tetrachloride (FAO/PL:1967/M/11/1)
       Carbon tetrachloride (FAO/PL:1968/M/9/1)
       Carbon tetrachloride (WHO Pesticide Residues Series 1)
       Carbon Tetrachloride (IARC Summary & Evaluation, Volume 71, 1999)