WHO Food Additives Series 1972, No. 1


    The evaluations contained in this publication were prepared by the
    Joint FAO/WHO Expert Committee on Food Additives which met in Rome,
    16-24 June 19711

    World Health Organization




    1 Fifteenth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, Wld Hlth Org. techn. Rep. Ser., 1972, No. 488; FAO
    Nutrition Meetings Report Series, 1972, No. 50.

    The monographs contained in the present volume are also issued by the
    Food and Agriculture Organization of the United Nations, Rome, as FAO
    Nutrition Meetings Report Series, No. 50A

    (c) FAO and WHO 1972


    Biological data

    Biochemical aspects

    Under acid conditions, or in the presence of proteins,
    hexamethylenetetramine (HMT) decomposes gradually yielding ammonia mid
    formaldehyde (Hutschenreuter, 1956).

    Because of these chemical and biochemical properties it is pertinent
    to consider biochemical information on formaldehyde and its metabolite
    formic acid in relation to the toxicological evaluation of HMT.

    Formaldehyde and formic acid occur in fresh unpreserved codfish muscle
    (Amano & Yamada, 1964), also in honey, roasted foods and some fruits
    (Malorny, 1969a).

    Formaldehyde and formic acid are excreted in the urine of dogs and
    cats fed a meal of fish not treated with preservatives, the source of
    the substances being trimethylamine oxide occurring naturally in fish
    muscle (Malorny & Rieforock. 1962; Malorny et al., 1963; Schassan,
    1963). The concentration of free formaldehyde in the urine of these
    dogs and cats given unpreserved fish was 1 to 5 times higher than that
    found in human subjects who had consumed fish preserved with
    hexamethylenetetramine. Humans fed almost exclusively on unpreserved
    fish did not show an increase in the excretion of formaldehyde or
    formic acid (Malorny & Rieforock, 1962). Formic acid present in the
    diet is mostly metabolized by man, only 25 mg is excreted daily in the
    urine (Malorny, 1969b).

    Hexamethylenetetramine liberated free formaldehyde in the stomach
    (Malorny & Rieforock, 1963).

    Intravenous infusion in dogs of formaldehyde, 35 mg/kg as a 0.6 per
    cent. solution during 8 to 10 minutes, was carried out.  Two minutes
    after completion of the infusion there was no increase in formaldehyde
    but a high increase in the formic acid level in the blood.  The formic
    acid level decreased by 50 per cent. in 1 hour, by 75 per cent. after
    2 hours, and was back to normal after 4 hours.  In vitro human blood
    oxidizes 30 per cent. formaldehyde (0.7 mg to 1 ml blood) to formic
    acid within 4 hours.  Addition of methylene blue (0.05 per cent. to
    0,2 per cent.) results in a complete oxidation of the formaldehyde
    (Malorny et al., 1964).

    Similar maximal plasma concentrations of formic acid were found after
    intravenous injection of equimolar solutions of formaldehyde, formic
    acid, or sodium formate, and the elimination constants and biological
    half-lives of formic acid in these different cases were also similar
    (Malorny et al., 1965).  In another study, it was found that
    elimination of formic acid from the body is much more rapid in rats

    than in dogs, the biological half-lives being about 12 min and 77 min
    respectively, while those of the guinea-pig are 12 min, rabbit 32 min
    and for the cat the value is 67 min.  The rate of oxidation of
    formaldehyde to formic acid is comparable in all these species, with a
    half-life of only 1 min (Rieforock, 1965).

    The kinetics of the absorption of formaldehyde by erythrocytes and its
    conversion to formic acid were studied in rabbits, guinea pigs, rats
    and cats.  The elimination of formic acid was proportional to the
    concentration present but formaldehyde had the same biological
    half-life of 1 min irrespective of species.  Using 3 different i.v.
    infusion rates (8, 2 or 0.5 mi/min) for formaldehyde showed that only
    at 0.5 ml/min there was no free formaldehyde present in the blood but
    only formic acid.  Formic acid was eliminated from erythrocytes,
    plasma, liver. kidney, testes, muscle and brain in an exponential
    manner.  The half-life varied with species but was always shortest in
    the liver.  No relation to catalase activity of the blood was
    established.  Pre-treatment of the cat with folic acid reduces the
    half-life for formic acid. Treatment with methotrexate, a folic acid
    inhibitor, prolongs the half-life in the dog from 61 to 480 min
    Malorny, 1966).

    Formaldehyde, administered orally to dogs, was rapidly absorbed and
    converted to formic acid.  No formaldehyde was detected in the plasma
    and only traces occurred transiently in the erythrocytes.  In cats the
    production of formic acid and influx of lactic acid into the blood
    caused a temporary acidosis.  When formaldehyde was added to human
    blood in vitro it was rapidly absorbed on to the erythrocytes and
    then oxidized to formate.  Both NAD and NADP-independent formaldehyde
    dehydrogenase and catalase appeared to be involved in this oxidation,
    so that both erythrocytes and the liver played an important role in
    the rapid detoxication of orally and parenterally-administered
    formaldehyde (Malorny et al., 1965).

    The elimination of formate is folic acid dependent, since in the cat
    daily injections of folic acid for several days before giving formate
    have been shown to reduce the biological half-life of formate
    considerably, from 67 min without folic acid pretreatment to 46 min
    after 4 days' treatment and 17 min after 10 days' treatment
    (Rieforock, 1965).  Interference with liver function prolongs the
    biological half-life of formic acid in rabbits from 35 to 130 min
    (Malorny, 1969a).  In vitro experiments with liver homogenate showed
    that after 30 min 31.6 per cent., 3.9 per cent. and 8.0 per cent. of
    formaldehyde was found in the case of rat, guinea-pig and rat liver
    respectively (Neugebauer, 1967).

    Experiments with 14C-labelled formaldehyde given by stomach tube to
    rats and mice showed that 5 min after application the radioactivity
    was distributed over the total body.  After 12 hours, approximately 40
    per cent. had been expired as 14CO2, 10 per cent. had been excreted
    in the urine and 1 per cent. in the faeces.  The homogenized whole
    animals contained 20 per cent. of the radioactivity after 24 hours and
    10 per cent. after 96 hours (Buss of al., 1964).

    When female rats were given 70 mg/kg of 14C-labelled formaldehyde
    intraperitoneally, 82 per cent. was detected as 14CO2 and the urine
    contained 13-14 per cent. of the isotope in the form of methionine,
    serine and a formaldehyde-cysteine adduct (Neely, 1964).

    The yellow discoloration observed in rats treated with oral or i.m.
    HMT was shown to be due to a reaction between formaldehyde in the
    urine and kynurenine in the rat hair (Kewitz & Welsch, 1966).

    Twelve human volunteers received orally 1.48-2.96 g sodium formate.
    They excreted on average 13 mg formic acid/24 hours from control diet
    and only 23 per cent./24 hours of the additional formic acid.  Most of
    the additional load was excreted within 6 hours and all had been
    eliminated after 12 hours.  No cumulation was observed.  Excretion of
    formate is accompanied by alkaline urinary pH and mild diuresis.  The
    biological half-life of orally administered sodium formate was found
    to be 46 min as determined by plasma levels in 3 volunteers.  Four to
    7 per cent. of the administered dose was excreted in 24 hours.  No
    metabolic acidosis was found in man because of rapid metabolism of the
    formate anion but the excess of bicarbonate is excreted as alkaline
    urine.  Formic acid is absorbed rapidly from the stomach in
    undissociated form (Malorny, 1969b).

    Special studies

    Both HMT (Auerbach, 1951) and formaldehyde (Rapoport, 1946) have been
    shown to act as mutagens in Drosophilia.  Stumm-Tegethoff (1964) has
    demonstrated that formic acid, present as an impurity in formaldehyde,
    is the causative agent in producing the mutagenic effect in
    Drosophilia melanogaster.  Nafei & Auerbach (1964) have shown that
    mutations only occur in the larval spermatocytes and that the
    conditions necessary for the change only exist for a short time.

    Acute toxicity

    Animal   Route              LD50 (mg/kg    Reference
    Mouse    Oral
             (formic acid)       1 100           Malorny, 1968a
             (Sod. formate)     11 200             "
             (Pot. formate)      5 500             "
             (Amm. formate)      2 250             "
             (Calc. formate)     1 920             "
             (formic acid)         145             "
             (Sod. formate)        807             "
             (Pot. formate)         95             "
             (Amm. formate)        410             "
             (Calc. formate)       154             "
    Rat      i.v. (HMT)          9 200             Malorny et al., 1965

    One group of 14 6-week old male and female rats were given a single
    intravenous injection of 10 g HMT/kg body-weight as an 80 per cent.
    aqueous solution.  All animals survived without evidence of toxic
    effect.  Two groups of 5 adult rats were given 10 or 20 g HMT/kg
    body-weight as an 80 per cent. aqueous solution by oral intubation.
    All animals survived (Della Ports, 1966).

    Short-term studies


    Groups of 13 mice were treated daily by cutaneous application 10 per
    cent. HMT in chloroform, 1.5 per cent. aqueous formaldehyde, and
    chloroform alone, for 300 days.  No malignant tumours were found in
    any group (Kewitz, 1966).

    One group of 5 male and 5 female rats was given by gavage 400 mg HMT
    daily for 90 days.  A second group of 5 male and 5 female rats was
    given daily intramuscular injections of 200 mg HMT for 90 days.  A
    third group of 15 male and 15 female rats was given repeated oral
    doses of 400 mg HMT by gavage over 333 days.  No adverse effects were
    noted in any group except for a citrus-yellowish discoloration of the
    fur (Brendel. 1964).


    One male and 3 female cats were fed approximately 15 000 ppm of
    formaldehyde (375 mg/kg/day) and two males and three females were fed
    approximately 50 000 ppm of HMT (1250 mg/kg/day) for 2 years.  The
    control group consisted of 3 males and 3 females.  One female in the
    formaldehyde group died in the seventh month of pleuritis and a female
    of the HMT group died in the twenty-third month of a pyogenic
    infection of the nasal cavity and paranasal sinuses.  No effect of
    formaldehyde or MT was found on food consumption, weight gain or
    appearance.  Preliminary microscopic examination of tissues from test
    and control animals show no changes attributable to formaldehyde or
    HMT (Kewitz, 1966).

    Long-term studies

    1. Oral administration


    Sixteen groups of 30, 50 or 100 males and an equal number of females
    of CTM, SWR or C3Hf strain mice received in their drinking-water
    either 0, 0.5, 1 or 5 per cent. hexamethylenetetramine over 60 weeks. 
    The group receiving 5 per cent. was treated for 30 weeks only.  After
    the end of treatment animals were observed for the remainder of their
    lifetimes.  The coats of treated mice showed no discoloration.  The
    group on 5 per cent. HMT showed slightly reduced growth rate and
    survival and the SWR group on 1 per cent. showed also slight growth
    retardation.  Gross and histopathology did not show any pathological

    lesions related to treatment.  As regards tumour incidence there was
    no significant difference between treated and control groups (Della
    Porta et al.p 1968).

    Groups of 30 male and 30 female NMRI/Han albino mice were fed 0 per
    cent. and 1 per cent. of HMT and 0.15 per cent. formaldehyde for 2
    years.  Benign and malignant tumours were found in a total of 43
    animals: 20 in the HMT group, 12 in the formaldehyde group and 11 in
    the control group.  Except for 1 control male and 2 males receiving
    HMT all tumours occurred in females.  Twenty-nine of 36 malignant
    tumours were subcutaneous carcinomas and adeno carcinomas.  The author
    concluded from the data that the possibility of an increased tumour
    incidence effect by HMT could not be ruled out.  A further study was
    instituted using groups of 50 female mice at levels of 0 per cent.,
    0.1 per cent., 0.5 per cent. and 1 per cent. hexamethylenetetramine,
    which, after 31 weeks, showed no difference in tumour incidence
    between the groups (Kewitz, 1966).


    Four groups of 48 male and 48 female rats received for 104 weeks
    either 0 or 1 per cent. HMT in their drinking-water while another 2
    groups of 12 male and 12 female rats received 5 per cent. in their
    drinking-water for only 2 weeks.  The coat of treated rats showed a
    yellowish discoloration due to a reaction between formaldehyde present
    in the urine and kynurenine in the rat hair.  Fifty per cent. of the
    rats given the high dose level died within the 2 weeks of
    administration, the remainder survived for 104 weeks.  Growth,
    mortality experience, gross and histopathology of the treated animals
    showed no specific changes due to administration of HMT.  Tumour
    incidence was essentially similar in controls and treated animals at 1
    per cent. level and lower than in controls at the 5 per cent. level
    (Della Porta et al., 1968).

    Two groups of 16 male and 16 female rats were given either 0 or 0.16
    per cent. HMT in their diet and were observed over 28-30 months.
    General health and behaviour as tested by activity in the revolving
    drum at 1, 3, 7 and 14 months showed no significant differences
    between controls and test groups.  Body-weights of male rats were
    slightly lower in the treated animals.  Mortality experience was
    similar for all groups.  The addition of HMT had no effect on
    palatability of the diet.  Organ weights showed no gross differences
    and tumour incidence was not different between controls and test
    animals, although not all rats were examined by autopsy.  Separate
    mating of the test and control groups revealed no differences in
    fertility as measured by numbers of pups produced.  The young showed
    no difference in activity as measured by the revolving drum, nor did
    they show any abnormalities or differences in body-weight.  Organ
    weights and gross and histopathology were unremarkable.  Some test
    rats showed yellowish staining of hair (Natvig et al., 1971).

    2. Subcutaneous administration


    Two groups of 39 male and 44 female CTM mice received 5 subcutaneous
    injections on 5 alternate days of 5 g/kg HMT, a 30 per cent. aqueous
    solution, beginning on day 10 of age.  They were observed for 100
    weeks.  No pathological findings related to treatment were noted nor
    was there any difference from controls regarding tumour incidence
    (Della Porta et al,, 1968).


    Twenty rats were given subcutaneous doses of 1 ml of a 0.4 per cent.
    aqueous solution of formaldehyde, in the dorsal region, weekly for 15
    months.  Half the animals died during the experiment without
    developing tumours; of the remaining 10, 4 showed sarcomas 3-5 months
    after cessation of treatment.  Two of these tumours developed at the
    site of injection and were diagnosed as spindlecell sarcomas.  One
    tumour developed in the liver (male, 21 months) with metastases to the
    colon; the other was in the colon (female, 21 months) (Watanabe of
    al., 1953; Watanabe et al., 1954).

    Twenty rats were injected subcutaneously on the left dorsal side once
    or twice weekly with 1-2 ml solution of hexamethylene-tetramine, using
    at first a concentration of 9.23 per cent. but, after the middle of
    the experiment, a concentration of 35-40 per cent.  In addition,
    shortly before each injection of hexamethylenetetramine, an injection
    of 0.5 ml 0.1 per cent. formic acid was given on the right dorsum.  Of
    14 survivors, 8 showed tumours at the sites of injection of
    hexamethylenetetramine.  At the sites of formic acid injection small
    ulcers sometimes formed but no subcutaneous thickening or nodules.  Of
    the 8 tumours 7 were sarcomas and 1 syringadenoma (Watanabe &
    Sugimotop 1955).

    Groups of 15 male and 15 female albino rats were injected
    subcutaneously with 1 ml of 40 per cent. HMT solution and 1 ml of 0.1
    per cent. formaldehyde solution weekly for 1-1/2 years.  Control
    groups of 7 males and 7 females and 8 males and 8 females were
    similarly injected with doses of sodium chloride or sucrose
    (equiosmotic with 40 per cent. hexamethylenetetramine) for 1-1/2
    years, by which time the last animal had died.  In the HMT group, 1
    injection-site spindle-cell sarcoma, 1 distal spindle-cell sarcoma, 1
    alveolar mammary carcinoma and 1 fibrosarcoma, in addition to 2 benign
    tumours were seen.  In the formaldehyde group, 2 malignant tumours and
    3 benign fibro-adenomas were seen.  In the control group, 1 blastoma
    (in a sodium chloride-injected animal) was found (Kewitz, 1966).

    Two groups of 20 male and 20 female rats received 5 subcutaneous
    injections of 5 g/kg HMT as 30 per cent. aqueous solution on alternate
    days starting at day 10 of age and were observed for 104 weeks.  No
    treatment-related abnormalities were seen regarding growth, mortality,
    gross or histopathology or tumour incidence.  The test animals had a
    lower tumour incidence than the controls (Della Porta et al., 1968).

    Reproduction studies


    In a 5-generation study lasting 3-1/2 years, a total of 80, 80 and 245
    rats were fed 0, 5 and 50 mg/kg daily of HMT in the drinking-water.
    Animals, including pregnant dams, were selected from each group at
    half-yearly intervals, starting at 1-1/2 years, for pathological
    study.  No changes attributable to HMT were found in test animals or
    foetuses and placentas at either level.  Tumours were observed on 3 of
    48 animals at the high dose level (Malorny, 1966b).

    Groups of 10 male and 10 female rats were fed 0 ppm, 400 ppm, 800 ppm
    and 1600 ppm of hexamethylenetetramine in a normal basic diet for 2
    years.  The 10 pairs were mated at the age of 20 weeks, 28 weeks and
    35 weeks.  No effect was found at all levels on growth, 2-year
    survival, reproduction and viability of offspring.  Post-sacrifice
    examination of survivors (organs examined and type of examination not
    stated) disclosed no specific pathological changes (Berglund, 1966).

    Twelve female and 6 male Wistar rats were given 1 per cent. HMT in the
    drinking-water starting 2 weeks before mating.  The females were kept
    under treatment during pregnancy and lactation.  A similar untreated
    group of 12 females and 6 males served as control.  Twelve treated
    females and 11 controls became pregnant and gave birth to 124 and 118
    babies respectively; no malformations were noted.  From these animals,
    24 for each sex were continued on the 1 per cent. HMT up to the
    twentieth week of age or were kept untreated.  The body-weight of
    treated animals was significantly lower than that of the controls,
    only up to the ninth week of age for the males and up to the
    thirteenth week for the females.  At the end of the treatment both
    groups were sacrificed; the weight of organs was identical in the
    treated and control animals; there was no gross or histological
    pathology.  In a second experiment, rats were given 1 per cent. HMT in
    the drinking-water for 3 successive generations, up to the age of 40
    weeks in the F1 and F2 groups and of 20 weeks for F3.  The 3
    groups were composed of 13 male and 7 female, 15 male and 11 female,
    12 male and 12 female, respectively.  In addition, a group of 16 male
    and 16 female descendants of 2 per cent. HMT-treated parents were
    given 2 per cent. HMT for 59 weeks.  A group of 48 males and 48
    females served as untreated controls.  All groups were kept under
    observation for over 2 years.  No evidence of carcinogenicity was
    found in any of the HMT-treated groups (Della Porta et al., 1970).

    A 5-generation study using 8 male and 24 female rats as P generation
    is in progress using 8 controls.  Test animals received 0.2 per cent.
    calcium formate in their drinking-water.  No abnormalities were
    detected regarding growth and fertility.  No disturbances of organ
    function or retinal or fundal abnormalities were noted.  Gross and
    histopathology of 250 rats from 3 generations revealed no abnormal
    findings related to the administration of calcium formate.  Tumour
    incidence was no different from controls.  Pregnancy and foetuses as
    well as numbers of pups per litter were similar to controls.  No
    malformations or placental changes were detected.  Similar groups were
    given 0.4 per cent. calcium formate in their drinking-water for 2
    generations and will be continued.  No abnormalities, including
    histopathology, related to the test substances have been seen.


    A group of 2 male and 4 female mongrel dogs was fed from 1250 to 1875
    ppm of HMT and a group of 4 males and 4 females was fed from 125 to
    375 ppm of formaldehyde for 32 months.  The control group consisted of
    2 males and 1 female.  Groups formed from litters of these animals
    were also fed test diets; 3 males and 2 females were fed 1250 ppm of
    HMT, 3 males and 2 females were fed 375 ppm of formaldehyde and 2
    animals of each sex served as a control group for 22 months.  At the
    end of the test period, the test animals were placed on a normal diet
    and the controls on 1250 ppm of HMT for 1 year.  No effect of
    formaldehyde or HMT was found on food consumption, growth,
    reproduction or litter numbers and weights or in monthly observations
    on blood chemistry and cell total and differential counts, and
    periodic urine examinations.

    However, of 30 litters in the HMT group, 66.7 per cent. were noted as
    unusual in that there were stillborn and eaten animals as well as 5
    cases of defective animals born; in the formaldehyde group, 60 per
    cent. of 34 litters were noted as unusual, with 10 cases of defective
    animals.  Of 16 litters in the control group, 7.7 per cent. were noted
    as unusual, with no malformations (Kewitz, 1966).

    According to a preliminary report, groups of 8 pregnant female beagle
    dogs received from the fourth to fifty-sixth day after mating either
    0, 0.0125 per cent. and 0.0375 per cent. of formalin or 0.06 per cent.
    and 0.125 per cent. of HMT in their food.  Many litters are still in
    the pre-weaned stage at present.  So far no adverse effects have been
    reported with regard to rate of pregnancy and duration, behaviour and
    weight of the mothers or litter size, pup weight, incidence of
    congenital defects or survival to weaning of the pups (Tierfarm,

    Chick embryo

    Two hundred fertilized chicken eggs were injected with 5 mg HMT after
    96 hours incubation.  The distribution of GMT and formaldehyde was
    determined between the sixth and nineteenth day of incubation in the
    various components of the egg.  HMT is continuously metabolized.  No
    toxic effect was noted in the chick embryos examined (Pilz, 1967).

    Formaldehyde was injected in another experiment into fertilized eggs.
    There was rapid oxidation to formic acid.  After 48 hours some 90 per
    cent. had been converted to formic acid.  The remaining formaldehyde
    was probably bound to the albumin and the shell proteins.  Injected
    sodium formate is metabolized at a much slower rate but had
    disappeared by the twelfth day of incubation.  Practically no
    formaldehyde metabolism occurs in the extra-embryonal components but
    embryonic liver and erythrocytes rapidly oxidize formaldehyde to
    formic acid (Lange. 1968).

    Sodium formate did not show any toxic or teratogenic effect when
    submitted to the chick embryo test (Malorny, 1969a),


    As the toxicological effects of hexamethylenetetramine (HMT) appear to
    be due to the liberation of formaldehyde and its oxidation product,
    formic acid, much work has been done on formaldehyde and formates as
    well as on hexamethylenetetramine (HMT).  The metabolic studies point
    to rapid conversion of formaldehyde to formate and then to water and
    carbon dioxide particularly by the liver and the erythrocytes.  Very
    little formate is excreted by man in his urine after its oral
    ingestion.  Only one of many long-term studies in mice conflicts with
    other studies in this species as well as in the rat.  These long-term
    studies point to a dietary level of 1 per cent. hexamethylenetetramine
    (HMT) as causing no effect in rodents.  The initial observations from
    a teratogenicity study in dogs revealed no adverse effects on the
    foetuses and the neonates.  Other reproduction studies in rats using
    dietary levels from 0.1-1 per cent. hexamethylenetetramine (HMT)
    revealed no adverse effects.  The probability of carcinogenic
    potential suggested by the production of local sarcomata in rats at
    the site of repeated injections appears to be excluded as a result of
    the findings in adequate studies using oral administration.  In
    addition, the experiments on pregnant and lactating rats indicate the
    absence of carcinogenic effects in the offspring.


    Level causing no toxicological effect in rats

    1 per cent. (10 000 ppm) in the diet equivalent to 500 mg/kg

    Estimate of acceptable daily intake for man     mg/kg body-weight
             Temporary acceptance                             0-5

    Further work required by 1972

    Report on the completed teratogenicity study in dogs.


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    Malorny, G. & Rietbrock, N. (1964) Phamakologisch-toxikologische
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    See Also:
       Toxicological Abbreviations
       Hexamethylenetetramine (ICSC)
       Hexamethylenetetramine (FAO Nutrition Meetings Report Series 38a)
       Hexamethylenetetramine (WHO Food Additives Series 5)