FAO Nutrition Meetings
    Report Series No. 40A,B,C
    WHO/Food Add./67.29


    The content of this document is the result of the deliberations of the
    Joint FAO/WHO Expert Committee on Food Additives which met at Rome,
    13-20 December, 19651 Geneva, 11-18 October, 19662


    1 Ninth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, FAO Nutrition Meetings Report Series, 1966 No. 40; 
    Wld Hlth Org. techn. Rep. Ser., 1966, 339

    2 Tenth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, FAO Nutrition Meetings Report Series, 1967, in press; 

    Food and Agriculture Organization of the United Nations
    World Health Organization



    Chemical name                 Sulfur dioxide; Sulfurous acid anhydride

    Chemical formula              SO2

    Molecular weight              64.07

    Definition                    Sulfur dioxide contains not less than 95
                                  per cent. SO2.

    Description                   Sulfur dioxide is a colourless,
                                  nonflammable gas, with a strong,
                                  pungent, suffocating odour.

    Biological Data

    (See Sodium Sulfite)


    Chemical names                Potassium metabisulfite; Potassium
                                  pyrosulfite; Potassium disulfite

    Empirical formula             K2S2O5

    Molecular weight              222.33

    Definition                    Potassium metabisulfite contains not
                                  less than 90 per cent. of K2S2O5.

    Description                   Potassium metabisulfite occurs as
                                  colourless free-flowing crystals,
                                  crystalline powder, or granules, usually
                                  having an odour of sulfur dioxide

    Biological Data

    (See Sodium Sulfite)


    Synonyms                      Sodium bisulfite; Sodium acid sulfite

    Chemical name                 Sodium hydrogen sulfite

    Chemical formula              NaHSO3

    Molecular weight              104.06

    Definition                    Sodium hydrogen sulfite contains not
                                  less than 95 per cent. of NaHSO3 and
                                  not less than 60 per cent. SO2.

    Description                   Sodium hydrogen sulfite is a white
                                  crystalline or granular solid with an
                                  odour of sulfur dioxide.

    Biological Data

    (See Sodium Sulfite)


    Chemical name                 Sodium pyrosulfite

    Chemical formula              Na2S2O5

    Molecular weight              190.11

    Definition                    Sodium metabisulfite contains not less
                                  than 95 per cent. of Na2S2O5 and not
                                  less than 64 per cent. SO2.

    Description                   Sodium metabisulfite is a white
                                  crystalline solid with an odour of
                                  sulfur dioxide.

    Biological Data

    (See Sodium Sulfite)


    Chemical name                 Sodium sulfite

    Chemical formula              (a) Na2SO3 (anhydrous)

                                  (b) Na2SO3.7H2O

    Definition                    (a) Sodium sulfite (anhydrous) contains
                                  not less than 95 per cent. Na2SO3 and
                                  not less than 48 per cent. SO2.

                                  (b) Sodium sulfite heptahydrate contains
                                  not less than 48 per cent. Na2SO3 and
                                  not less than 24 per cent. SO2.

    Description                   a) Sodium sulfite (anhydrous) is a white
                                  powder with not more than a faint odour
                                  of sulfur dioxide.

                                  (b) Sodium sulfite heptahydrate is a
                                  transparent or white crystalline solid
                                  with not more than a faint odour of
                                  sulfur dioxide.

    Biological Data

         The biological data as they were available at the end of 1964
    have been summarized in the document entitled "Specifications for
    Identity and Purity and Toxicological Evaluation of Some
    Antimicrobials and Antioxidants" (FAO/WHO, 1965). Since its
    publication some new experimental work has been carried out on this
    substance. This and other work not included in the above document are
    summarized in this monograph.

    Biochemical aspects

         Four rats given oral doses of sodium metabisulfite as a 0.2 per
    cent. solution eliminated 55 per cent. of the sulfur as sulfate in the
    urine within the first 4 hours (Bhagat & Lockett, 1960). A rapid and
    quantitative elimination of sulfites as sulfate was also observed in
    man and dog (Rost, 1933).

         Sulfite is a strong inhibitor of some dehydrogenases, e.g.
    lactate dehydrogenase (heart) and malate dehydrogenase; 50 per cent.
    inhibition by about 10-5 M sulfite (Pfleiderer et al., 1956).

         Small amounts of sulfite are regularly formed in the intermediary
    metabolism of the body in the catabolism of cystine by the
    non-enzymatic decomposition of 8-sulfinyl pyruvic acid to pyruvic acid
    and SO2. The stationary concentration of sulfite in the cells is too
    small to be measured. However, 0.10-0.12 meq./100 ml was found in bull
    seminal fluid (Larson & Salisbury, 1953).

         Exposure of cells in tissue culture to various concentrations of
    SO2 in the medium showed that strain L cells could tolerate 5 ppm
    SO2 for periods of 8 hours provided a recovery period followed each
    exposure. At higher concentrations (500-2000 ppm) of SO2 there was
    inhibition of growth; at the 500 ppm level the growth was comparable
    to control cultures. The addition of salts of SO2 caused stimulation
    of growth at lower levels and complete inhibition at 2000 ppm NaHSO3
    (Thompson & Pace, 1962).

    Effect on thiamine

         Treatment of foods with sulfites reduced their thiamine content
    (Morgan et al., 1935; Williams et al,, 1935), It has been suggested
    that the ingestion of SO2 in a beverage may effectively reduce the
    level of thiamine in the rest of the diet (Hötzel, 1962).

         Six rats ware given a diet providing 40 mg thiamine daily. At
    weekly intervals an additional 160 mg thiamine was given and the
    urinary excretion of thiamine measured on the following 2 days. When
    the response, in terms of urinary output of thiamine, appeared to be
    constant, 160 mg thiamine was given together with 120 mg potassium
    metabisulfite. It was found that the addition of SO2 greatly reduced
    the urinary output of thiamine, especially on the day when both were
    given together (Causeret et al,, 1965).

         In wine containing 400 ppm SO2, 50 per cent. of the thiamine was
    destroyed in one week. However, no loss of thiamine was observed in 48
    hours. The small amounts of SO2, resulting from the recommended
    levels of usage in wine are therefore not likely to inactivate the
    thiamine in the diet during the relatively short period of digestion
    (Jaulmes, 1965).

    Calcium balance

         Interest in this aspect arises from the possibility that sulfate
    formed metabolically from sulfite may serve to increase loss of
    calcium in urine and faeces of man.

         Levels of 0.5-0.7 per cent. calcium carbonate in the diet caused
    increased faecal excretion and diminished urinary levels of Ca. Levels
    up to 0.2 per cent. had no effect on the excretion of Ca. (Causeret &
    Hugot, 1960). In a further experiment, diets containing 0.5 and 1 per
    cent. calcium carbonate and 0.5 and 1 per cent. potassium
    metabisulfite (2885 and 5770 ppm SO2 ) were administered to young
    rats and the faecal and urinary excretion of Ca measured for 10 days.
    At the lower level of dietary Ca (0.5 per cent.) both levels of the
    metabisulfite caused a significant increase in the urinary excretion
    of Ca but had no effect on the faecal excretion. At the higher dietary
    Ca level (1 per cent.) the reverse was found. There was no difference
    between the effects of the two levels of metabisulfite. This was
    interpreted as being due to saturation of the body's capacity to
    convert sulfite to sulfate (Hugot et al., 1965).

         The levels of hepatic vitamin  A were determined on both control
    and test rats receiving 1.2 g/l potassium metabisulfite in the
    drinking water (700 ppm as SO2). There was an insignificant decrease
    in the vitamin A level in the liver of test animals after 10 days.  In
    another experiment, two groups of 40 rats each were kept for 4 months
    on a diet containing only traces of vitamin A. The drinking water of
    one group contained 1.2 g/l potassium metabisulfite. Hepatic vitamin A
    levels were determined at the end or each month. A gradual reduction
    in liver vitamin A levels was observed in both groups. The addition of
    SO2 to the drinking water did not accentuate this reduction (Causeret
    et al., 1965).

    Short-term studies

         Rat. Groups of 20 Wistar rats (10 of each sex) were fed diets
    containing 0.125, 0.25, 0.5, 1.0 and 2.0 per cent. of sodium hydrogen
    sulfite (770-12 300 ppm as SO2) for 17 weeks. A group of 20 rats on
    untreated diet served as controls. Immediately after preparation, all
    diets ware stored at -18°C in closed glazed earthenware containers,
    for not longer than 2 weeks. Measurements of loss of SO2 on keeping
    each diet in air for 24 hours at room temperature revealed losses
    amounting to 12.5, 10.0, 14.3, 8.2 and 2.5 per cent. of the sulfite
    present in the diets as listed above, i.e. with Increasing SO2
    content a decreasing proportion was lost.

         After 124 days there was no effect on the growth of male rats. In
    females, the 2.0 per cent. group grew as well as the controls; both
    these female groups ware used for fertility studies, had given birth
    to litters during the course of the test, and had raised their young.
    The other female groups on lower levels of dietary sulfite were not
    mated and showed significant depression of growth (as compared with
    controls that had been mated). Haematological measurements at 7-8
    weeks (all groups) and at 13 weeks (2 per cent. and controls) revealed
    no effect of sulfite.

         In the diet containing 2 per cent. sulfite, thiamine could not be
    measured after 14 days at -18°C; at 1.0 per cent. and 0.25 per cent.
    sulfite there was some loss of thiamine but this cannot be assessed
    precisely since the initial values are not quoted. Measurements of
    urinary thiamine excretion revealed substantial reduction at 1 week
    and particularly at 13 weeks in all groups receiving more than 0.125
    per cent, sulfite in the diet. Urine concentration tests were not
    carried out on a sufficient number of animals to permit any firm
    conclusion to be drawn.

         Males and females of the control and 2 per cent. groups were
    mated with rats drawn from the main colony. The only untoward
    findings, with females of the 2 per cent. group, were lower weight of
    the offspring at 7 and 21 days of life and 44.3 per cent. mortality as
    compared with mortalities of 0, 2.8 and 3.8 per cent. in the other
    groups of young rats. It is claimed that no changes were found in
    relative organ weight (liver, heart, spleen, kidneys, adrenals,
    testes) nor in microscopical appearance (above organs, stomach,
    intestine, uterus, teeth and eyes). Since no measure of dispersion is
    quoted, it is impossible to say weather the apparent severe reduction
    in relative liver weight at the 0.125, 0.25, 0.5 and 1.0 per cent.
    levels is significant (Centraal Instituut voor Voedingsonderzoek
    T.N.O., 1965).

    Long-term studies

         Rat. A solution containing 1.2 g of potassium metabisulfite per
    litre of water (700 ppm SO2) was administered to 80 weanling rats (40
    of each sex) over a period of 20 months. A group of 80 rats given
    distilled water served as controls. It was shown that the intake of
    fluid by the test group was the same as that of the controls (but no
    study appears to have been made of SO2 loss from the metabisulfite
    solution). The intake of SO2 calculated from the consumption of water
    was 30-60 mg/kg body-weight/day for males and 40-80 mg/kg
    body-weight/day for females. The, following criteria provided no
    evidence of toxic effect: growth rate, food intake, clinical
    condition, haematological indices of blood and bone marrow (except
    peripheral leucocyte count, which was increased in males), organ
    weights (except spleen weight, which was heavier in females),
    micropathological examination of a large number of tissues and
    mortality rate. Fatty change in the liver was mostly slight or absent,
    with a similar incidence and severity in test and control groups.
    Reproduction studies over two generations revealed no effect except
    for a slightly smaller number of young in each litter from test
    animals and smaller proportion of males in each of these litters.
    Growth of the offspring up to 3 months was almost identical in test
    and control groups (Cluzan et al., 1965).

         Four groups of 20 rats (10 of each sex on standard diet) were
    given daily doses (30 ml/kg body-weight) of red wine containing 100
    and 450 ppm SO2 an aqueous solution of potassium metabisulfite (450
    ppm SO2) and pure water by oral intubation on 6 days each week for
    four successive generations. The females ware treated for 4 and the
    males for 6 months; the second generation was treated for 1 year. The
    only effect seen was a slight reduction in hepatic cellular
    respiration. All other parameters examined: weight gain, weight and
    macroscopic or histological appearance of various organs, appearance
    and behaviour, proportion of parturient females, litter size and
    weight, biological value of a protein sample, showed no changes
    attributable to SO2 (Lanteaume et al, 1965).


         The long-term studies involving the administration of
    metabisulfite in drinking water (700 ppm SO2) equivalent to 35 ml/kg
    body-weight/day SO2 shows that this level apparently causes no toxic
    effects in the rat.

         From the long-term studies on metabisulfite in wine and water it
    appears that the daily administration of fluid (30 ml/kg body-weight)
    containing an equivalent of 450 ppm 50 SO2 (14 mg/kg body-weight/day)
    produces no adverse effects in the rat.

         Sulfite administered in food appears to be more toxic in animal
    experiments than when administered in drinking water or wine. Further
    studies are desirable [Note: text missing]

    See Also:
       Toxicological Abbreviations
       Sulfur dioxide (FAO Nutrition Meetings Report Series 38a)
       SULFUR DIOXIDE (JECFA Evaluation)