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


    Chemical name

    7-methyleneindene, or 1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-
    tetrahydro-4, 7-methanoindene.

    Empirical formula


    Structural formula



    Biochemical aspects

           In plants and soil heptachlor is converted to its epoxide which
    is more persistent on plants than the parent heptachlor (Gannon &
    Bigger, 1958; Gannon & Decker, 1958).

           Heptachlor is also readily transformed in the animal body into
    heptachlor epoxide, which is stored in the fat of dogs and rats. Some
    storage occurs in the liver, kidney and muscle, but none in the brain.
    In dogs, after feeding heptachlor in a concentration of 1-3 mg/kg
    body-weight the metabolite was found (Davidow & Radomski, 1953). When
    heptachlor was fed at high dosage levels to dogs, small amounts of
    unmetabolized heptachlor were also found in the fat of dogs but this
    was not the case in the rat regardless of the level fed.

           In the rat the maximum amount of the metabolite appeared after
    feeding 1, 5, 15 and 30 ppm heptachlor for two weeks. At 0.3 ppm
    storage occurred in females but not in males and 0.1 ppm no storage
    occurred in either sex. Female rats accumulate about 6 times as much
    epoxide as males. Twelve weeks were required for complete
    disappearance of the metabolite from the fat after discontinuing
    heptachlor feeding (Radomski & Davidow, 1953).

           When cows were fed 3 mg/kg body-weight (in corn oil) daily for 14
    days the epoxide level in the milk rose to a maximum of 1.8 ppm
    equivalent to 44 ppm in butter fat. Residues could be detected in milk
    51 days after feeding ceased (Davidow et al., 1953). Mixtures of
    heptachlor and heptachlor epoxide were fed daily to 4 dairy cows for
    20 days (2 at a 5 ppm and 2 at a 10 ppm dally intake). Three days
    after feeding commenced, the minimum levels of heptachlor epoxide in
    the milk were 0.26 and 0.34 ppm in the 2 cows fed 5 ppm and 0.23, and
    0.65 ppm in the 2 cows fed 10 ppm; the maximum levels after 15 days'
    feeding were 0.63 and 0.80 ppm, and 1.51 and 1.66 ppm respectively
    (Storherr et al., 1960).

           Disturbance of the acid-base balance seem to be of great
    significance in the mechanism of action of heptachlor (Spynu &
    Osetrov, 1960).

    Acute toxicity

    Animal             Route      LD50 mg/kg      References

    Rat, male          Oral         60-169*       Negherbon, 1959; Velsicol, 1959

    Mouse              Oral            68         Negherbon, 1959

    Guinea-pig         Oral           116         Negherbon, 1959

    Chick              Oral            63         Sherman & Ross, 1961

    Heptachlor epoxide

    Animal             Route      LD50 mg/kg      References

    Rat                Oral         34-88*        Velsicol Corporation, 1959

    Mouse, male        Oral          32-48        Velsicol Corporation, 1959

    * Sex differences.
           Intravenous lethal doses for heptachlor and heptachlor epoxide 
    in the mouse are given as 40 and 100 mg/kg body-weight respectively
    (Negherbon, 1959). In the rabbit the lethal dose of epoxide is 5-10
    mg/kg body-weight (Velsicol, 1959).

           The acute effects are neurotoxic disturbances like those 
    observed with other chlorinated hydrocarbons.

    Short-term studies

           Rat. The addition of heptachlor (up to 45 ppm) or its epoxide
    (up to 60 ppm) or both to diet of rats for 140 days produced liver
    microscopical changes, i.e. enlarged centrolobular cells showing big
    nuclei with prominent nucleolim cytoplasm fat accumulation and
    occasional aggregation of granules (Stemmer & Jolley, 1963). In an
    experiment involving 269 rats it was demonstrated that these changes
    regress after withdrawal of the pesticide. It has also been suggested
    that these changes are produced indirectly, through the autonomic
    nervous system and the adrenal medulla (Stemmler & Hamdi, 1963).
    Electron microscopic studies demonstrated an increase of rough and
    smooth endoplasmic reticulum (Stemmler & Hamdi, 1963).

           Dog. Three dogs given heptachlor epoxide orally in dosages of
    2, 4 and 8 mg/kg a day for 5 days a week died after 22, 10 and 3 weeks

           One mg/kg given in the same way to 2 dogs resulted in the death
    of one animal after 42 weeks, but the other survived for 52 weeks.
    This animal showed only a slight growth inhibition. Doses of 0.25 and
    0.5 mg/kg body-weight did not produce any sign of illness during 52
    weeks (Velsicol, 1959).

           When heptachlor was fed orally, dissolved in corn oil, to 
    groups of 2 and 4 dogs at levels of 5 mg/kg and 1 mg/kg body-weight
    respectively, all the animals at the higher dose level died within 21
    days. At the lower dose level 3 out of 4 dogs died within 424 days but
    one was living at 455 days. No pathological data are available from
    this experiment (Lehman, 1952).

           Diets containing 0.5, 2.5, 5.0 and 7.5 ppm of heptachlor 
    epoxide were given to groups of 5 dogs (2 males and 3 females ranging 
    from 23 to 27 weeks of age) for 60 weeks. No deaths attributable to 
    heptachlor epoxide occurred. The weights of the male dogs tended to 
    be inversely proportional to the concentration of the compound in the 
    diet. The female dogs had normal weights. The liver weights of all 
    the animals were increased in proportion to the concentration of 
    heptachlor epoxide in the diet, and degenerative liver changes were 
    seen at 2.5 ppm and above (Velsicol, 1959).

    Long-term studies

           Rat. Groups of rats (usually 10 males or 10 females) were fed
    diets containing 5, 10, 20, 40, 80, 160, and 300 ppm of heptachlor
    epoxide for 2 years. Concentrations of 80 ppm or higher resulted in
    100% mortality in 2-20 weeks. All the female animals given 40 ppm died
    within a period of 54 weeks. This concentration had no effect on the
    mortality of the male animals up to 104 weeks. Diets containing 20 ppm
    or less produced no signs of illness in male or female rats during a

    2-year period but an increase in liver-weight was observed in diets
    containing more than 10 ppm (males) and 5 ppm (females)(Velsicol,

           Groups of 20 rats of strain CFW fed heptachlor epoxide at 10, 
    20 and 40 ppm for 2 years showed significant increases in mortality 
    only in females at 40 ppm. Liver-weights in the females were slightly
    increased. Tumour incidence was lower in the experimental groups than
    in the controls and was independent of the content of heptachlor
    epoxide in the diet (Velsicol, 1959).

           In another experiment which has already been considered1 CFN
    rats were fed heptachlor epoxide in concentrations of 0.5, 2.5, 5, 7.5
    and 10 ppm. More details are now available about the tumour incidence
    in untreated controls as well as the distribution or tumours among the
    different groups. No differences have been observed among the five
    experimental groups and their results can be considered together. The
    incidence of tumour-bearing animals was 8/23 (34%) and 13/24 (54%) in
    the control males and females respectively; it was 65/111 (58%) and
    92/114 (80%) in the experimental males and females respectively.
    Again, many tumours were located in endocrine organs. Liver tumours
    were observed in 7 males and 12 females in the experimental groups
    only (over-all incidence 19/225 (8.4%), but only two of them were
    malignant (Kettering Laboratory, 1959).

           Finally, in another experiment heptachlor dissolved in ethanol
    was added to the diet of CF rats as 1.5, 3, 5, 7 and 10 ppm for 110
    weeks. Each group, as well as an untreated control, included 40
    animals (20 of each sex). Mortality was comparable in all groups. The
    number of tumour-bearing animals was 16/40 at 0 ppm, 9/40 at 1.5 ppm,
    13/40 at 3 ppm, 12/40 at 5 ppm, 15/40 at 7 ppm and 12/40 at 10 ppm.
    Most tumours were found in the pituitary and other endocrine organs.
    No liver tumours were recorded. No preferential tumour site in any
    particular group was observed but all the 4 thyroid tumours observed
    were in the 7 and 10 ppm groups (Witherup et al., 1955).

           In some other experiments, the continuous exposure of rats to
    doses of over 7 ppm of either heptachlor or its epoxide increased the
    mortality during the suckling period. In others, 10 ppm fed to 3
    generations of rats showed no adverse effects on reproductive
    capacity, probability of survival or growth (Witherup et al., 1955;
    Kettering Laboratory, 1959).

    Comments on experimental studies reported

           It is well established that heptachlor and its epoxide accumulate
    in body fat and persist them for long periods. The formation of
    epoxide is relatively rapid in the animal, plants and in the soil.

    1 Report of a joint meeting of the FAO Committee on Pesticides in
    Agriculture and the WHO Expert Committee on Pesticide Residues. FAO
    Meeting Report No. PL/1963/13 and WHO/Food Add./23 (1964).

           The epoxide is more persistent than the parent compound and
    calculations of toxicity should perhaps be based on the data obtained
    with the epoxide rather than heptachlor, particularly since most
    reports indicate that the epoxide is the more toxic of the 2

           A sex difference in toxicity has been observed, particularly in
    the rat, females accumulating heptachlor and its epoxide more than
    males. The toxic dose for female rats is lower than that for males.

           The changes observed in the liver cells are difficult to 
    explain. A possible relation with tumour formation has not been 
    demonstrated, while evidence has been presented that the change is 

           Some suspicion of carcinogenicity can arise from one of the
    long-term experiments with heptachlor epoxide, since in both males and
    females the total number of tumour-bearing animals was higher than in
    the controls and liver tumours were only found in the experimental
    group. However, the interpretation of this finding is debatable: in
    the first place it concerns only one experiment among several
    long-term studies. In addition to this, the over-all incidence of
    liver tumours was low, most of them were histologically benign and no
    dose-response relationship was observed among the different
    experimental groups. For these reasons the carcinogenicity of
    heptachlor epoxide appears doubtful. Nevertheless, until new data are
    available from other long-term experiments involving other strains of
    rats or other species a definite statement is not possible.


           From the data presented an acceptable daily intake for man 
    cannot be estimated. Until further evidence is forthcoming every 
    effort should be made to see that the intake of heptachlor for man is 
    kept at the lowest possible level.

    Further work required

           As the residue in the crop may contain the epoxide, the
    experiments should be done with this compound also. A maximum
    no-effect level should be determined in more than one species.
    Additional long-term toxicity studies in rats and other species are


    Davidow, B. & Radomski, J. L. (1953) J. Pharmacol. exp. Ther.,
    107, 259

    Davidow, B., Radomski, J. L. & Ely. R. (1953) Science, 118, 383

    Gannon, N. & Bigger, J. H. (1958) J. econ. Ent., 51, 1

    Gannon, N. & Decker, G. C. (1958) J. econ. Ent., 51, 3

    The Kettering Laboratory (1959) University of Cincinnati

    Lehman, A. J. (1952) Quart. Bull. Assoc. Food and Drug Officials
    U.S.,15, 47

    Negherbon, W. O. (1959) Handbook of Toxicology, Philadelphia and
    London, Saunders, vol. III

    Radomski, J. L. & Davidow B. (1953) J. Pharmacol. exp. Ther., 107,

    Sherman, M. & Ross, E. (1961) Toxicol. Appl. Pharmacol., 3, 521

    Spynu, E. I. & Osetrov, V. I. (1960) Chem. Abstr. 54, 13435

    Stemmler, K. L. & Hamdi, E. (1963) Data submitted by the Kettering
    Laboratory, University of Cincinnati

    Stemmler, K. L. & Jolley, W. P. (1963) Data submitted by the Kettering
    Laboratory, University of Cincinnati

    Storherr, R. W., Tighe, J. F. & Sykes, J. F. (1960) J. Assoc. Offic.
    Agr. Chemists, 43, 731

    Velsicol Corporation (1959) Unpublished report

    Witherup, S. et al. (1955) Data submitted by the Kettering Laboratory,
    University of Cincinnati

    See Also:
       Toxicological Abbreviations
       Heptachlor (EHC 38, 1984)
       Heptachlor (HSG 14, 1988)
       Heptachlor (ICSC)
       Heptachlor (PIM 578)
       Heptachlor (FAO/PL:CP/15)
       Heptachlor (FAO/PL:1967/M/11/1)
       Heptachlor (FAO/PL:1968/M/9/1)
       Heptachlor (FAO/PL:1969/M/17/1)
       Heptachlor (AGP:1970/M/12/1)
       Heptachlor (WHO Pesticide Residues Series 4)
       Heptachlor (WHO Pesticide Residues Series 5)
       Heptachlor (Pesticide residues in food: 1991 evaluations Part II Toxicology)
       Heptachlor (CICADS 70, 2006)