SULFUR DIOXIDE AND SULFITES
These compounds were evaluated for acceptable daily intake at the
sixth, eighth, ninth, and seventeenth meetings of the Joint FAO/WHO
Expert Committee on Food Additives (Annex 1, references 6, 8, 11, and
32). The ADI allocated to sulfur dioxide at the seventeenth meeting
encompassed the sulfur dioxide equivalents arising from sodium
metabisulfite, potassium metabisulfite, sodium sulfite, and sodium
hydrogen sulfite. Subsequently, calcium hydrogen sulfite, sodium
thiosulfate, and potassium hydrogen sulfite have been included in the
group ADI (Annex 1, references 41, 47, and 62). Toxicological
monographs were published after the sixth, eighth, ninth, seventeenth,
and twenty-seventh meetings (Annex 1, references 6, 9, 12, 33, and
Since the last review, additional data have become available and
are summarized and discussed in the following monograph. The
previously-published monographs have been expanded and are reproduced
in their entirety below.
Sulfur dioxide and sulfur (IV) oxoanions in solution undergo
pH-dependent equilibration reactions between sulfur dioxide, sulfurous
acid, bisulfite ion, and sulfite ion. At normal physiological pH
values and concentrations of greater than 1 M, the equilibrium is
between approximately equal proportions of sulfite and bisulfite while
at the lower pH of the stomach of fasting humans, the equilibrium is
essentially between bisulfite ion and free sulfur dioxide
Sulfur dioxide reacts with a wide range of food components. It
forms adducts by reversible action with aldehydes and ketones
(including reducing sugars, acetaldehyde, quinones, and ketoacids),
with anthocyanins, and with cysteine residues in proteins. In most
foods and beverages, the adducts with carbonyl compounds, the
hydroxysulfonates, comprise most of the bound sulfite, and this
equilibrium reaction has been studied in detail. In the range pH 1 to
pH 8 the hydroxysulfonates predominate, while at higher pH values
dissociation occurs (Burroughs & Sparks, 1973a,b,c; Adachi et al.,
Stable adducts with alpha, ß-unsaturated carbonyl intermediates
of the Maillard reaction have also been described (McWeeny et al.,
1974; Wedzicha & McWeeny, 1974a), and irreversible reactions with
other intermediates of the non-enzymic browning reactions lead to the
formation of stable 3-deoxy-4-sulpho-osuloses. These stable products
may account for much of the sulfite originally added to stored
dehydrated vegetables (Wedzicha & McWeeny, 1974b, 1975) and may be the
major end-product of sulfite in jams made from sulfited fruit
(McWeeny et al., 1980).
Sulfur dioxide reacts irreversibly with thiamine to yield
pyrimidine sulfonic acid and 4-methylhydroxyethyl thiazole (Dwivedi &
Arnold, 1973) and, at high concentrations, may destroy cobalamins via
the formation of photolabile complexes (Gunnison et al., 1981a;
Gunnison & Jacobsen, 1983).
Sulfite forms adducts with nicotinamide adenine dinucleotide
(NAD), flavins, and with cytosine and uracil, their nucleosides, and
nucleotides (Gunnison, 1981, Shapiro, 1983).
A comprehensive monograph on the chemistry of sulfur dioxide in
foods has been published (Wedzicha, 1984).
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).
Sulfite is oxidized in vivo to sulfate, catalysed by the enzyme
sulfite oxidase (sulfite;ferricytochrome C oxidoreductase, EC 188.8.131.52)
located in the mitochondrial intramembranous space. This enzyme has
been well-characterized as a dimer with subunits containing a
molybdenum atom, a cytochrome b5 type of haemoprotein, and a pterin
cofactor. The enzyme is inhibited by tungstate both in vitro and
in vivo (Cohen & Fridovich, 1971; Johnson et al., 1980).
Sulfite oxidase is widely distributed in mammalian tissues, with
most activity being found in liver, heart, and kidney (Gunnison,
1981). Comparative studies on sulfite oxidase activity nave been
carried out in the livers of several species, including rats, rabbits,
dogs, cattle, monkeys, and man (MacLeod et al., 1961; Johnson &
Rajagopalan, 1976a,b). In general, sulfite oxidase activity in the
human is slightly less than in the rhesus monkey and rabbit, and
substantially less than in the other mammals studied; human liver has
only 5-10% of the specific sulfite oxidase activity of rat liver. It
has been estimated that sulfite oxidase in the rat is capable of
oxidizing 750 mmoles sulfite/kg b.w./day, equivalent to 48 g SO2/kg
b.w./day (Cohen et al., 1975).
In assays on normal human liver biopsy samples, 3 subjects had
sulfite oxidase activity of 1.78 mmoles cytochrome c reduced/ min./g
protein and a fourth had approximately twice this activity
(Johnson et al., 1980). Sulfite oxidase activity in cultured
fibroblasts from normal human subjects was found to be 1.07 nmoles
cytochrome c reduced/min./mg protein (range 0.75-1.76) (Shih et al.,
1977) and 2.10 nmoles cytochrome c reduced/min./mg protein (range
0.75-3.03) (Johnson et al., 1980).
Sulfite oxidase deficiency can be induced in the rat by inclusion
of sodium tungstate in drinking water, and sulfite oxidase activity
can be reduced to any required extent by modifying the dose of
tungstate (Johnson et al., 1974). Using this model, sulfite
oxidase-deficient rats were shown to have substantially-increased
levels of urinary and tissue thiosulfate and S-sulfonates (Gunnison
et al., 1981a,b,c). Administration of 0.5 mmole sulfite/kg b.w. to
sulfite oxidase-deficient rats produced levels of S-sulfonates in the
plasma similar to those produced in normal rats by a dose of 10 mmole
sulfite/kg b.w.; higher levels of plasma sulfite were observed.
Intubation of 10 to 20 times as much sulfite to normal rats was
required to produce a systemic sulfite level equivalent to that of
sulfite oxidase-deficient rats, although the normal animals had 100
times the sulfite oxidase activity of the deficient animals
(Gunnison et al., 1981a). It has been suggested that sulfite
oxidation is limited by the rate of diffusion into the mitochondria
(Oshino & Chance, 1975).
Exogenous sulfite arising from inhalation or ingestion of sulfur
dioxide is oxidized to a significant extent in the lung and intestine
before entering systemic circulation. About 50% of a dose of
radiolabelled sulfite was oxidized by empty rat intestines and a
larger proportion was oxidized in filled intestines. Oxidation may
occur in the intestinal wall and/or by the gut microflora
(Pfleiderer et al., 1968).
Four rats given oral doses of sodium metabisulfite as a 0.2%
solution eliminated 55% of the sulfur as sulfate in the urine within
the first four hours (Bhagat & Lockett, 1960). A rapid and
quantitative elimination of sulfites as sulfate was also observed in
man and dog (Rost, 1933).
Following oral administraton of 10 or 50 mg SO2/kg (as NaHSO3
mixed with Na235SO3), 70 to 95% of the 35S was absorbed from
the intestine and voided in the urine of mice, rats, and monkeys
within 24 hours. The majority of the remaining 35S was eliminated in
the faeces, the rate being species-dependent. Only 2% or less of the
35S remained in the carcass after one week. Free sulfite was not
detected in rat urine even after a single oral dose of 400 mg
SO2/kg. Induction of liver sulfite oxidase was not demonstrated
either after single or 30 daily doses of 200 mg SO2/kg/day (Gibson &
Sulfite administered i.v. was cleared rapidly in the rhesus
monkey with a half-life of 10 minutes for doses of 0.3 to 0.6 mmole/kg
b.w. The half-life in man was estimated to be about 15 minutes
(Gunnison & Jacobsen, 1983).
As a result of rapid metabolism by sulfite oxidase, sulfite does
not accumulate in the tissues on chronic administration, but is
eliminated in the urine mainly as sulfate. In several species, less
than 10% of the dose administered appeared in the urine as sulfite
(Gunnison & Palmes, 1978).
A proportion of the sulfite absorbed is converted to thiosulfate
following (a) reaction with mercaptopyrnvate (Sörbo, 1957), (b)
metabolism of cysteine-S-sulfonate (Sörbo, 1958), and (c) reaction
with thiocystine (Szczepkowski & Wood, 1967). Elevated levels of
thiosulfate in body fluids are observed in sulfite oxidase deficiency
(vide supra). The mean daily urinary excretion of thiosulfate in
normal humans was found to be 31.7 ± 12.8 mmole/day (Sörbo & Ohman,
1978), but this does not represent the extent of formation of
thiosulfate, since thiosulfate is further metabolized to sulfate
(Gunnison et al., 1981c; Skarzynski et al., 1959).
Non-enzymatic reactions of sulfite with tissue components include
lysis of disulfide bonds, with the formation of S-sulfonates and
thiols (Cecil, 1963). Under conditions of sulfite loading, appreciable
amounts of S-sulfonates may be formed, and cysteine-S-sulfonate has
been found in urine (Gunnison & Palmes, 1974), while glutathione-
S-sulfonate has been detected in bovine ocular lenses (Waley, 1959).
Only interchain disulfide bridges of native proteins undergo
sulfitolysis (Cecil & Wake, 1962), and the protein S-sulfonates formed
slowly released sulfite ions in the presence of sulfhydryl compounds
(Swan, 1959). Sulfites are strongly bound in the form of S-sulfonates
by plasma proteins and are gradually cleared from the blood by
mechanisms which are not totally clear (Gunnison, 1981; Gunnison &
Sodium sulfite solutions were administered to Sprague-Dawley rats
in which the portal vein and vena cava were cannulated for blood
sampling. Examination of plasma showed the presence of S-sulfonates in
both pre- and post-hepatic blood, whereas free sulfite was detected
only in portal blood. The author concluded that the sulfite was
absorbed and rapidly metabolized by oxidation or the formation of
S-sulfonates (Wever, 1985).
The formation of protein S-sulfonates is concentration dependent
in vitro and in vivo. At a dose level of 2 mmole sulfite/kg
b.w./day, the plasma of rabbits and rhesus monkeys contained
measurable concentrations of S-sulfonates, while the plasma of rats
did not. Parenteral administration of 3.2 mmole sulfite/kg b.w./day
to rats for 5 consecutive days increased plasma S-sulfonate
concentrations up to 19-30 nmoles/ml. Plasma S-sulfonate fractions had
half-lives of 4 and 8 days in the rat and rhesus monkey, respectively
(Gunnison & Palmes, 1978). Levels of plasma S-sulfonates in human
subjects exposed to atmospheric sulfur dioxide concentrations of
0.3, 1.0, 3.0, 4.2, and 6.0 ppm for 120 hours increased by
1.1 ± 0.16 nmoles/ml for each increment of 1 ppm in exposure level
(Gunnison & Palmes, 1974).
Lungs and aortas of rabbits exposed to arterial sulfite
concentrations of 545-560 µM for 0.6 to 6 hours were analysed for
S-sulfonates. Formation was first order, with asymptotic
concentrations of S-sulfonates of approximately 900 and 9000 nmole/g
dry tissue in lung and aorta, respectively. Clearance from both
tissues was first order, with a half-life of 2-3 days. Appreciable
amounts of S-sulfonates were not found in liver, kidneys, testes,
heart, brain, skeletal muscle, stomach, ovaries, duodenum, spleen, or
eyes (Gunnison & Farrugella, 1979).
Levels of S-sulfonates in the tracheas of rabbits exposed to
3 ppm sulfur dioxide in air for 3 and 24 hours were constant at
approximately 53 nmoles/g dry weight. Plasma concentrations of
S-sulfonates in rabbits exposed to 10 ppm sulfur dioxide were found to
be 9 and 30 nmoles/ml after 3 and 24 hours, respectively. No exogenous
S-sulfonates were detected in aortas and only traces were detected in
the distal region of posterior lung lobes, indicating that sulfur
dioxide was partially metabolized in pulmonary tissues. Tracheal
concentrations of S-sulfonates of 107 nmoles/g dry weight were
attained after 3 hours exposure to 10 ppm sulfur dioxide, increasing
to 163 nmoles/g dry weight after 72 hours, the increase being
attributed to increased mucus production. During exposure for 72 hours
plasma concentrations of S-sulfonates rose to 70 nmoles/ml, but no
free sulfite was detected in plasma. It was concluded that, with the
possible exception of heart and lungs, there was no transport of
inhaled sulfur dioxide to organs distant from the absorption site
(Gunnison et al., 1981c).
Sulfur dioxide can promote cross-linking of protein molecules,
and electrophoresis of nasal mucus glycoproteins from rats exposed to
5 or 20 ppm SO2 in air for 7 days showed the appearance of 3 to 5
new bands in the acidic fraction which were attributed to increased
cross-linking; the effect was first noticeable after 2 hours exposure.
The polymerization of glycoprotein molecules may account for the
decrease in the nasal mucus flow rate and increased viscosity commonly
associated with inhalation of sulfur dioxide (Gause & Barker, 1978).
It was found that sulfitolysis of seven disulfide bonds in bovine
serum albumin caused topographical changes resulting in an 80%
reduction in its ability to bind to antiserum (Habeeb, 1971).
Effects on thiamine
It has been known for many years that treatment of foods with
sulfites reduces 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 were given a diet providing 40 mg thiamine daily. At
weekly intervals an additional 160 mg thiamine was given and the
urinary excretion of thiamine was measured on the following two 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. 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% of the thiamine was
destroyed in one week. However, no loss of thiamine was observed in 48
hours. The small amount 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,
A group of subjects on a thiamine-deficient diet were given
400 mg sulfite/person/day. The diet produced signs of vitamin
deficiency in 50 days. In another experiment, sulfite dissolved in
wine or grape juice was given between days 15-40. No effect on
thiamine status was detected by measurement of blood thiamine levels,
urinary thiamine excretion, or by determination of thiamine-dependent
enzyme activity. Clinical, neurophysiological, and biochemical
investigations produced no indication of adverse effects from sulfite
(Hötzel et al., 1969).
Other work supports the view that SO2 in beverages does not
reduce the level of thiamine in the rest of the diet (Sharratt, 1970).
It has not been demonstrated that destruction of thiamine by
sulfite in vivo is sufficient to deplete reserves of thiamine nor
that the symptoms of bisulfite toxicity are coincident with thiamin
deficiency (Gunnison et al., 1981a).
Effects on cyanocobalamin
Rats fed a diet containing 6% sodium metabisulfite for 21 days
became severely anaemic; destruction of cyanocobalamin by high
concentrations of sulfite in the diet or gut was considered a possible
mechanism in the production of anaemia (Gunnison et al., 1981a).
Cyanocobalamin has been claimed to be an effective blocking agent
for sulfite-induced bronchoconstriction in asthmatics, but the
mechanism is unexplained (Jacobsen et al., 1984).
Effects on enzymes
Sulfite is a strong inhibitor of some dehydrogenases, e.g.
lactate dehydrogenase (heart) and malate dehydrogenase; 50% inhibition
was caused by about 10-5 M sulfite (Pfleiderer et al., 1956).
Flavins in the flavoproteins form chemical adducts with sulfites
leading to sulfonation at the N5 atom of flay in, the active site
that accepts hydrogen. This is the probable mechanism of inhibition of
dehydrogenases. Several flavoprotein oxidases (e.g. D-and L-amino
oxidases, oxynitrilase, lactate oxidase, and glycolate oxidase) form
stable adducts, with dissociation constants from 10-3 to 10-7 M.
The flavoprotein dehydrogenases did not form adducts with sulfite at
concentrations of 20 mM (Muller & Massey, 1971).
Cytochrome oxidase was inhibited 37% by 0.5 mM sulfite at pH 7
(Cooperstein, 1963), and alpha-glucan phosphorylase was inhibited by
10 to 30 mM sulfite (Kamogawa & Fukui, 1973). Sulfite was a
competitive inhibitor of phosphate in glycogen synthesis and
degradation, and alkaline phosphatase was inhibited in vivo.
Conversely, the activity of 2,3-diphosphoglyceric acid phosphatase was
enhanced 15-fold by 2.5 mM sulfite (Harkness & Roth, 1969). Sulfite
has been found to be a potent inhibitor of many sulfatases
Effects on calcium balance
Interest in this aspect arises from the possibility that sulfate
formed metabolically from sulfite may serve to increase the loss of
calcium in urine and faeces of man.
Levels of 0.5 to 0.7% calcium carbonate in the diet caused
increased faecal excretion and diminished urinary levels of calcium.
Levels up to 0.2% had no effect on the excretion of calcium (Causeret
& Hugot, 1960).
Diets containing 0.5 and 1% calcium carbonate and 0.5 and 1%
potassium metabisulfite (0.29 and 0.58% as SO2 respectively) were
administered to young rats, and the faecal and urinary excretion of
calcium were measured for 10 days. At the lower level of dietary
calcium, both levels of the metabisulfite caused a significant
increase in the urinary excretion of calcium but had no effect on the
faecal excretion of calcium. At the higher dietary calcium level, 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).
Effects on vitamin A
The levels of hepatic vitamin A were determined in both control
and test rats receiving 1.2 g/l potassium metabisulfite in the
drinking water (700 mg/l as SO2). There was a slight decrease in the
vitamin A level in the liver of test animals after 10 days. In another
experiment, two groups of 40 rats were kept for four 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 of each month. A gradual reduction in the
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).
Effects on lipids
Low concentrations of bisulfite (0.5 mM) induced oxidation of
corn oil emulsified in 1.5% polysorbate solution (Kaplan et al.,
1975), and similar effects were reported in liver homogenates
(Inouye et al., 1978).
Incubation of unsaturated membrane lipids with a large excess of
bisulfite caused changes in the chromatographic behaviour indicative
of addition of bisulfite across double bonds. Such changes in membrane
lipids could account for the irritant effect of sulfur dioxide
(Akogyeram & Southerland, 1980).
In brains of guinea-pigs exposed to 10 ppm sulfur dioxide in air
for 1 hour daily for 21 days, total lipids and free fatty acids were
decreased in all regions of the brain, but changes in other fractions
varied with the region. The rates of peroxidation and the activity of
lipase were increased significantly in all regions of the brain
(Haider et al., 1981).
Special studies on carcinogenicity
(see also Long-term studies)
Groups of 50 male and 50 female ICR/JCL mice received potassium
metabisulfite in drinking water at concentrations of 0.1 or 2% for 24
months. At termination detailed pathological examination did not
reveal any increase in tumour incidence in treated animals relative to
controls (Tanaka et al., 1979).
In a study not designed as an orthodox carcinogenicity bioassay,
4 out of 149 female rats with low sulfite oxidase activity induced by
low molybdenum diets in association with tungstate treatment displayed
mammary adenocarcinomas after 9 weeks of treatment. The animals were
not exposed to exogenous sulfite and no tumours were seen in control
animals with normal levels of sulfite oxidase (Gunnison et al.,
Special studies on mutagenicity
Using E. coli as an indicator, the frequency of mutation of the
C gene of phage-lambda was shown to be increased by a factor of 10,
when compared with controls, by treatment with 3 M sodium hydrogen
sulfite at pH 5.6 at 37°C for 1.5 hours (Hayatsu & Miura, 1970).
Sodium hydrogen sulfite induces mutations in only those mutants which
have cytosine-guanine at the mutant site (Mukai et al., 1970).
The possibility that SO2 might cause point mutations was put
forward by Shapiro et al. (1970), who showed that sulfite can
convert the nucleic acid base cytosine (which occurs in DNA and RNA)
into uracil (which is found in RNA only). Hayatsu & Miura (1970)
confirmed this finding and showed that bisulfite binds to certain
nucleotides. However, 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. In another study at higher
concentrations of SO2, growth was comparable to that in control
cultures at 500 ppm SO2, while there was inhibition of growth at
2000 ppm SO2. The addition of salts of SO2 caused stimulation of
growth at lower levels, and complete inhibition at 2000 ppm sodium
hydrogen sulfite (Thompson & Pace, 1962).
Bisulfite at a concentration of 10 mM (pH not specified) induced
mutations in Staphylococcus aureus; 5 mM bisulfite induced mutations
in Saccharomyces cerevisiae at pH 3.6, but not at pH 5.5 (Shapiro,
1983). Bisulfite at a concentration of 0.1 M was non-mutagenic to
E. coli (Mallon & Rossman, 1981). At concentrations similar to those
found in wine (150 ppm, pH 3.0-6.5), bisulfite was not mutagenic to
Bacillus subtilis (Khoudokormoff, 1978). Higher concentrations of a
sodium sulfite-bisulfite mixture showed mutagenic effects in a
B. subtilis test system at concentrations of 0.1 to 0.5 M, pH 7, but
not at 0.05 M. Cells treated with adductS of sodium hydrogen sulfite
and cytidine monophosphate or uridine monophosphate exhibited
mutagenic effects at concentrations of 0.25 and 0.5 M (Chang et al.,
Sulfite forms reversible adducts with the 5,6-double bond of
cytosine and uracil and their nucleosides and nucleotides. The
reaction is pH- and concentration-dependent (Gunnison, 1981; Shapiro,
1983). Deamination of cytosine to uracil nucleotides in single-
stranded DNA occurs in bisulfite solutions of 1 M or higher at pH 5-6
(Bayatsu, 1976; Shapiro, 1983). The cytosine adduct can be
transaminated with primary and secondary amines, including lysine,
with the formation of N4-substituted cytosines. Cross-linking of
heat-denatured calf thymus DNA occurred after 6 days in 0.15 M sodium
hydrogen sulfite, but double-stranded DNA did not cross-link (Shapiro
& Gazit, 1977).
In cultures of mouse hepatocytes, HeLa cells, human embryonic
lung cells, lymphocytes, and oocytes, inhibition of DNA synthesis was
observed at bisulfite concentrations from 0.1 to 10 mM (Shapiro,
1983). Intranucleotide bonds of DNA were cleaved by 1 to 10 mM sodium
hydrogen sulfite solutions by a mechanism believed to involve free
radical formation (Hayatsu & Miller, 1972).
Transformation of Syrian hamster embryo cells occurred in a
dose-dependent manner on treatment with 1, 5, or 10 mM bisulfite for
24 hours, but the authors suggested that this might not occur by a
mutagenic mechanism (DiPaolo et al., 1981). Further work in this
system indicated that bisulfite caused no detectable DNA damage and
may have decreased the rate of DNA replication by blocking the
operation of part of the functioning replicons (Doniger et al.,
Dose- and time-dependent induction of sister chromatid exchange
was demonstrated in Chinese hamster ovary cells following exposure to
0.03 to 7.3 mM bisulfite for 2-24 hours (MacRae & Stich, 1979). In
contrast, Chinese hamster V-79 cells exhibited no mutations to ouabain
resistance after exposure to 10 and 20 mM bisulfite for 15 minutes.
Similarly, exposure to 10 mM bisulfite produced no mutations to
6-thioguanine resistance. Long-term exposure of V-79 cells (recultured
for 8 weeks in a medium containing 5 mM bisulfite) failed to induce
ouabain-resistant mutations (Mallon & Rossman, 1981).
Cultures of human lymphocytes exhibited chromosomal abnormalities
(clumping), decreased DNA synthesis, cell growth, and mitotic indices
after exposure to 100 ml of 5.7 ppm sulfur dioxide in air on days 0 or
1 of incubation but not on days 2 or 3 (Schneider & Calkins, 1970).
Mutagenic effects have not been reported in whole animals exposed
to sulfur dioxide or sulfites. Dominant lethal mutations were not
observed in female C3Hx101 mice given a single i.p. injection of
550 mg sodium hydrogen sulfite/kg b.w. and mated with untreated males.
In the same study, neither heritable translocations nor dominant
lethal mutations occurred when male mice were mated after receiving
i.p. injections of 400 mg sodium hydrogen sulfite/kg b.w. 20 times
over a 26-day period or 300 mg/kg b.w. 38 times over a 54-day period
(Generoso et al., 1978).
Chromosomal aberrations were not found in oocytes of female Camm
mice given i.v. doses of 1.0, 2.5, or 5.0 mg sodium sulfite, although
structural abnormalities were reported when cultures of Camm mouse
oocytes were treated with sodium sulfite in vitro (Jagiello et al.,
The influence of low levels of sulfite oxidase activity on
cytogenetic effects was studied in Chinese hamsters and NMRI mice made
sulfite oxidase-deficient by treatment with tungstate in association
with low molybdenum diets. No effects on sister chromatid exchange,
chromosomal aberrations, or micronucleus tests were seen in either
species after oral, s.c., or i.p. administration of sodium
metabisulfite, although control animals tolerated higher doses of
metabisulfite than those made sulfite oxidase-deficient (Renner &
Synergistic effects of sulfur dioxide and sulfites with other
treatments have been studied for possible co-mutagenic effects.
Mutation frequency was approximately doubled in UV-irradiated Chinese
hamster V-79 cells exposed to 10 mM bisulfite either during or after
irradiation. Tryptophan revertants were increased more than eight-fold
in U.V.-irradiated E. coli cells exposed to 75 mM bisulfite
(Mallon & Rossman, 1981). Treatment of phage-lambda with bisulfite and
several amines (1 M bisulfite plus 1 M semicarbazide, hydrazine,
methoxyamine, or hydroxylamine) caused an increase in mutation
frequency (plaque-forming activity) compared with treatment with
bisulfite alone (Hayatsu & Kitajo, 1977). Combinations of bisulfite
(150 ppm) with nitrite (100, 200, or 400 ppm) were reported to be
weakly mutagenic in B. subtilis (Khoudokormoff, 1978). Mutagenic
effects of coffee on S. typhimurium strains TA98 and TA100 without
S-9 preparations were completely inhibited by the addition of 300 ppm
sulfite, bisulfite, or metabisulfite, and the activity of coffee in
the prophage-lambda induction test was also suppressed (Suwa et al.,
1982). Sodium sulfite was a weak inhibitor of benz(a)pyrene
mutagenicity in S. typhimurium TA98 (Calle & Sullivan, 1982).
Bisulfite concentrations of 0.5, 2.5, and 5.0 µg/ml and the much
higher concentration of 100 mg/ml inhibited transformation of C3H 1OT
1/2 cells by X-rays or benz(a)pyrene; pre-treatment of hamster embryo
cells with 100 ppm bisulfite inhibited transformation by X-rays
(personal communication with attachments from C. Borek, Columbia
University, New York, NY, USA, to S.A. Anderson, Federation of
American Societies for Experimental Biology (FASEB), Bethesda, MD,
USA, 1984, submitted to WHO by FASEB).
Special study on reproduction
Six groups of 20 male and female rats were mated after 21 weeks
on diets containing 0, 0.125, 0.25, 0.5, 1.0, or 2.0% sodium
metabisulfite; 10 males and 10 females were remated at 34 weeks. Ten
male and 10 female F1a rats were mated at 12 and 30 weeks of age to
give F2a and F2b offspring. Ten males and 15 females of the F2a
generation were then mated at 14 and 22 weeks to give F3a and F3b
offspring. F1a parents and F2a parents were kept on the diet for
104 and 30 weeks, respectively.
Pregnancy incidence, birth weight, and postnatal survival were
all normal. In the F0 first mating, the body-weight gain of
offspring was decreased at 2% sodium metabisulfite and in the F1
mating it was decreased at 1 and 2% sodium metabisulfate. The F2
first mating showed decreased weight gain of offspring in all test
groups at weaning, but little effect was seen in offspring of the
second F2 mating. Litter size was significantly decreased at 0.5%
sodium metabisulfate and above in the first F2 mating. The body
weights of F0 adults were unaffected, while high-dose F1 females
and high-dose F2 males and females both showed slightly decreased
body-weight gains (Til et al., 1972a).
Special study on teratogenicity
Reproductive performance was studied in normal female
Wistar-derived rats and in similar rats treated with tungstate to
induce sulfite oxidase deficiency. The rats received 25 or 50 mM
sodium metabisulfite in drinking water from 3 weeks prior to mating
until day 20 of gestation. No treatment-related effects on
reproductive performance or incidence of malformations were observed
(Dulak et al., 1984).
LD50 (mg/kg b.w.)
Species Route Hydrogen sulfite Sodium sulfite Reference
Mouse i.p. 675 - Wilkins et al., 1968
i.v. 130 175 Boppe & Goble, 1951
Rat i.p. 500-740 - Wilkins et al., 1968
i.v. 115 - Hoppe & Goble, 1951
Hamster i.v. 95 - Hoppe & Goble, 1951
Rabbit oral - 600-700 Rost & Franz, 1913
i.p. 300 - Wilkins et al., 1968
i.v. 65 - Hoppe & Goble, 1951
Dog i.p. 244 - Wilkins et al., 1965
In thiamine-deficient rats, daily oral administration of fruit
syrup containing 350 ppm sulfur dioxide at 0.5 ml/150 g b.w. for 8
weeks failed to influence growth (Lockett, 1957).
Groups of weanling rats numbering 5 per group were fed 0.6%
sodium metabisulfite (not less than 0.34% as SO2) for 6 weeks. The
diets were either freshly sulfited or stored at room temperature
before use. A reduction in growth occurred in rats receiving the fresh
diet, which was attributed to lack of thiamine. Rats fed the diet
which had been stored for 75 days developed signs of thiamine
deficiency and additional toxic effects including diarrhoea and
stunting of growth, which could not be reversed by the administration
of thiamine (Bhagat & Lockett, 1964).
Three groups of 20 to 30 rats containing equal numbers of males
and females received daily doses of sulfite dissolved in water or
added to wine; a control group received the same volume of water. The
levels of sulfite in the two groups receiving wine were equivalent to
105 or 450 mg SO2 per litre, and the aqueous solution contained
potassium metabisulfite equivalent to 450 mg SO2 per litre. The
effect of this treatment was studied in 4 successive generations, the
duration being 4 months in females and 6 months in males. Groups of
animals from the second generation were treated for 1 year. No effects
were observed on weight gain, efficiency of utilization of protein,
biological value of the same protein, or reproduction. There was no
effect on the macroscopic or microscopic appearance of organs or organ
weights. The only effect observed was a slight diminution in the rate
of tissue respiration by liver slices in vitro (Personal
communication of work in progress from P. Jaulmes, 1964).
Rats were fed sulfite as sodium metabisulfite in stock or
purified diet at levels from 0.125 to 6% for up to 8 weeks. In a
preliminary study, increasing levels of sulfite (0.125 to 2.0%
in the diet) resulted in decreased urinary thiamine excretion.
Supplementation of the diet with 50 mg thiamine/kg diet prevented the
thiamine deficiency as evidenced by reduction of offspring mortality
and weight loss to weaning at the 2% level of sulfite feeding. Toxic
manifestations were noted at 1% and above, comprising occult blood in
the faeces (1% and over), reduced growth rate (2% purified diet and 6%
purified and stock diet), blood in the stomach and anaemia (2% and
above), spleen enlargement, increased haematopoiesis, and diarrhoea
(4% and above), and increased white blood cells (6%). Histopatho-
logical changes in the stomach occurred at 1% metabisulfite and above
Groups of 10 male and 10 female rats were fed diets containing 0
to 8% sodium metabisulfite for 10-56 days. Vitamin deficiency was
prevented by adding thiamine to the diet. Diets containing 6% and
above metabisulfite depressed food intake and growth; glandular
hyperplasia, haemorrhage, ulceration, necrosis, and inflammation of
the stomach occurred. Anaemia occurred in all animals receiving 2%
metabisulfite and above and a leucocytosis occurred in those receiving
6% metabisulfite. At 4% and above, splenic haematopoiesis was found.
The effects were reversible when metabisulfite was removed from the
diet (Til, 1970).
About 120 rats containing equal numbers of each sex were divided
into two groups, one receiving potassium metabisulfite equivalent to
0.6% SO2 in the drinking water, the other group serving as a
control. No effects were observed after treatment for 3 months on
reproduction, mortality, or blood count. The second and third
generations were treated in the same way for 3 months, the only effect
observed being a significant reduction in the size of the litters of
treated mothers. No effect of sulfite on digestive enzymes in vitro
was observed at a level equivalent to 360 mg SO2 per gram of
protein. No effect on the incidence of dental caries in the rat was
produced by 0.5% potassium metabisulfite in the dietary regime
(personal communication from J. Causeret to WHO, 1964).
Groups of 20 Wistar rats (10 of each sex) were fed diets
containing 0.125, 0.25, 0.5, 1.0, or 2.0% sodium hydrogen sulfite
(0.077-1.23% as SO2) for 17 weeks. A group of 20 rats on untreated
diet served as controls. Immediately after preparation, all diets were
stored at -18°C in closed glazed earthenware containers for not longer
than two 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% of the sulfite present in the
respective 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% group grew as well as the controls; the control and
2.0% female groups, which were used for fertility studies, gave birth
to litters during the course of the test and 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% group and controls) revealed no effect of
Thiamine could not be measured in the diet containing 2% sulfite
after being stored for 14 days at -18°C; at 1.0% and 0.25% sulfite
there was some loss of thiamine, but this cannot be assessed precisely
since the initial values were not quoted. Measurements of urinary
thiamine excretion revealed substantial reduction at one week and
particularly at 13 weeks in all groups receiving more than 0.125%
sulfite in the diet. Urine concentration tests were not carried out on
a sufficient number of animals to permit firm conclusions to be drawn.
Males and females of the control and 2% groups were mated with
rats drawn from the main colony. The only adverse findings observed in
females of the 2% group were lower weight of the offspring at 7 and 21
days of life and 44.3% mortality as compared with mortalities of 0,
2.8, and 3.8% in the other groups of young rats. It was claimed that
no changes were found in relative organ weight (liver, heart, spleen,
kidneys, adrenalin, and testes) nor in microscopic appearance (above
organs, and the stomach, intestine, uterus, teeth, and eyes)
In a study of the gastric lesions produced in short-term studies
at high dose levels of metabisulfite, Cpb:Wu Wistar rats were fed
thiamine-supplemented diets containing 0, 4, or 6% sodium
metabisulfite for 8 or 12 weeks and 0 or 6% sodium metabiaulfite for
4, 7, 14, 21, or 28 days in a related time-course study. In the
subchronic study, the fundic mucosa of the treated rats contained
scattered hyperplastic glands lined with enlarged gastric chief cells
containing large numbers of pepsinogen granules that were devoid of
fat, glycogen, or mucus. The time course study suggested that
pre-existing chief cells were transformed to hyperactive chief cells
having proliferative capability. The pathogenesis of these lesions
remains to be clarified (Beems et al., 1982).
One rabbit given 3 g of sodium sulfite by stomach tube each day
for 185 days lost weight, but all organs were normal on post mortem
examination. Two rabbits given 1.08 g daily for 127 days gained
weight. Autopsy showed haemorrhages in the stomach. Three rabbits
given 1.8 g daily for between 46 and 171 days lost weight, and autopsy
showed stomach haemorrhages (Rost & Franz, 1913).
A daily dose of 3 g sodium sulfite was given by stomach tube to a
dog weighing 17 kg for 23 days. Another dog weighing 34 kg was given
6-16 g sodium sulfite daily for 20 days (total dose 235 g). No
abnormalities were observed on autopsy in the first dog, but the
second dog had haemorrhages in several organs. Sodium sulfite was
given by stomach tube to 16 growing dogs in daily doses of 0.2-4.8 g
for 43-419 days; no damage was observed in any of the dogs. Sodium
hydrogen sulfite was given to two dogs by the same method and for the
same length of time as in the preceding experiment in daily doses of
1.082.51 g. Examination of heart, lungs, liver, kidneys, and intestine
showed no damage. A total of 91-265 g of sodium sulfite fed to five
pregnant dogs over a period of 60 days had no effect on the weight of
the mothers or on the weight gain of the litters (Rost & Franz, 1913).
Groups of 20 castrated male and 20 female weanling Dutch landrace
pigs were placed on diets supplemented with 50 mg/kg thiamine
containing 0, 0.06, 0.16, 0.35, 0.83, or 1.72% sodium metabisulfite.
Fourteen males and 14 females/group were sacrificed at 15-19 weeks and
the remainder were killed at 48-51 weeks. In addition, a paired-
feeding study on 15 male and 15 female weanling pigs/group was
performed for 18 weeks at 0 and 1.72% sodium metabisulfite. Food
intake and weight gain were reduced at the 1.72% level; however, in
the paired-feeding study, growth and food conversion were not
affected. Mortality was not related to metabisulfite ingestion.
Urinary and liver thiamine levels decreased with increasing dose, but
they were reduced below the levels found in pigs on basal diet alone
only at 1.72%. Haematology and faecal occult blood determinations were
comparable in all groups. Organ/body-weight ratios were elevated at
0.83 and 1.72% for the heart, kidneys, and spleen, and at 1.72% for
the liver. The paired-feeding study showed liver- and kidney-weight
ratios to be increased at 1.72% metabisulfite. Mucosal folds in the
stomach and black colouration of the caecal mucosa at the top 2 dose
levels were observed on gross pathological examination. At 0.83 and
1.72% metabisulfite, histopathological examination showed hyperplasia
of mucosal glands and surface epithelium in the pyloric and cardiac
regions. Intra-epithelial micro-abscesses, epithelial hyperplasia, and
accumulations of neutrophilic leucocytes in papillae tips were
observed in the pars oesophagea. In the caecal mucosa, macrophages
laden with pigment granules (PAS-positive containing Cu and Fe) were
observed at all dose levels, including controls. Incidence was
markedly increased at 0.83% and above. At 1.72% metabisulfite,
fat-containing Kupffer cells were present in unusually high numbers in
the liver (Til et al., 1972b).
Groups of rats numbering from 18 to 24 per group were fed sodium
hydrogen sulfite at dosages of 125, 250, 500, 1000, 2500, 5000,
10,000, or 20,000 ppm of the diet for periods ranging from 1 to 2
years. The rats fed 500 ppm sodium hydrogen sulfite (307 ppm as SO2)
for 2 years showed no toxic symptoms. Sulfite at concentrations of
1000 ppm (615 ppm as SO2) or more in the diet inhibited the growth
of the rats, probably through destruction of thiamine in the diet
(Fitzhugh et al., 1946).
Three groups of weanling rats containing 18, 13, and 19 animals
received drinking-water containing sodium metabisulfite at levels of
0, 350, or 750 ppm SO2, respectively. Prior interaction of the
sulfite with dietary constituents was thus prevented. The experiment
lasted 2.5 years and extended over 3 generations of rats. No effects
were observed on food consumption, fluid intake, faecal output,
reproduction, lactation, or the incidence of tumours (Lockett &
A solution containing 1.2 g of potassium metabisulfite per litre
of water (700 ppm as 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. The intake of fluid by the test
group was the same as that of the controls (but no measurements of
SO2 loss from the metabisulfite solution appear to have been made).
The intake of SO2 calculated from the consumption of water was
3060 mg/kg b.w./day for males and 40-80 mg/kg b.w./day for females.
The following observations provided no evidence of toxic effects;
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
higher 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
effects of treatment except for a slightly smaller number of young in
each litter from test animals and a smaller proportion of males in
each of these litters. Growth of the offspring up to three months was
almost identical in test and control groups (Cluzan et al., 1965).
Four groups of 20 rats (10 of each sex on a standard diet) were
given daily doses (30 ml/kg b.w.) of red wine containing 100 or
450 ppm SO2, an aqueous solution of potassium metabisulfite (450 ppm
SO2), or pure water by oral intubation on 6 days each week for 4
successive generations. The females were 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, which comprised weight gain, weight and
macroscopic or histological appearance of various organs, appearance
and behaviour, proportion of parturient females, litter size and
weight, and biological value of a protein sample, showed no changes
attributable to SO2 (Lanteaume et al., 1965).
Groups of 20 male and 20 female rats were fed 0, 0.125, 0.25,
0.5, 1.0, or 2.0% sodium metabisulfite in a diet enriched with 50 ppm
thiamine for 2 years. Animals were stressed by breeding at 21 weeks,
and again by breeding of half of each group at 34 weeks (see Special
study on reproduction). Percentage loss of sulfite from the diet
decreased with increasing dietary concentration, but increased with
increasing time. Thiamine loss increased with increasing sulfite
concentration. Body weight, food consumption, kidney function, and
organ weights were all unaffected by treatment. Thiamine content of
the urine and liver showed a dose-related decrease commencing at 0.125
and 0.25% metabisulfite, respectively. However, thiamine levels at 2%
metabisulfite were comparable to thiamine levels in control rats.
Marginally-reduced haemoglobin levels were noted on 3 occasions in
females in the 2%-dose group, and occult blood was noted in faeces at
1% metabisuliite and above. In 10% of the females at 0.25%
metabisulfite, and in 10% of the males at 0.5% metabisulfite, slight
indications of intestinal blood loss were noted at week 32 only.
Pathological changes were limited to the stomach (either hyperplasia
or inflammation) and occurred at 1% metabisulfite and above. The
incidence of neoplasms was not increased above normal levels at any
site at any dose. The NOEL in this study was 0.25% sodium
metabisulfite (Til et al., 1972a).
Observations in man
In man, a single oral dose of 4 g of sodium sulfite caused toxic
symptoms in 6 of 7 persons. In another subject, 5.8 g caused severe
irritation of the stomach and intestine (Rost & Franz, 1913).
The vomiting reflex in man appeared regularly with doses of
sulfite equivalent to less than 250 mg SO2, i.e. 3.5 mg SO2 per kg
b.w. (Lafontaine & Goblet, 1955).
Idiosyncratic sensitivity to sulfites
The most commonly-reported adverse reaction to sulfur dioxide or
sulfiting agents in man is bronchoconstriction and bronchospasm,
particularly among a sensitive sub-group of asthmatics. Less commonly,
symptoms similar to anaphylaxis, flushing, hypotension, and tingling
sensations have been reported (NIH, 1984).
A mildly-asthmatic child was reported to suffer acute, transient
asthmatic episodes following ingestion of sulfited foods, but no
controlled challenge test was performed (Kochen, 1973).
Of 272 asthmatic patients, 30 were reported to experience
bronchoconstriction after ingesting orange drinks containing sodium
hydrogen sulfite. Challenge tests on 14 of the 30 sensitive ptients
using a single dose of 25 mg sodium metabisulfite (100 ppm in an
acidic solution) resulted in a fall of at least 12% in FEV1 (forced
excretory volume in one second) in 8 subjects within 2 to 25 minutes.
No placebo test was performed (Freedman, 1977).
An asthmatic patient who experienced bronchospasm after ingestion
of canned crabmeat salad with vinegar dressing developed severe
bronchospasm within 30 minutes of receiving an oral challenge (dose
not stated) of sodium metabisulfite; no reaction occurred after
ingestion of crabmeat alone. A second patient, whose asthma was
provoked by wine, was given a single-blind oral challenge with a
capsule containing 500 mg sodium metabisulfite. Peak respiratory flow
rate fell from 440 1/min. before challenge to 100 1/min. afterward. No
effect was observed with a lactose placebo (Baker et al., 1981).
Four patients with histories of severe bronchoconstriction and
anaphylaxis associated with restaurant meals were subjected to a
single-blind challenge test. Placebo capsules (lactose) were
administered at 30 min. intervals to the fasting subjects on the first
day and capsules containing 1, 5, 10, 25, and 50 mg potassium hydrogen
sulfite were given sequentially on the following day. All 4 patients
developed asthmatic symptoms after challenge doses of 10, 25, and
50 mg. FEV fell 34-49% at 30 to 90 minutes after challenge. Subjective
symptoms (flushing, tingling, and/or faintness) were also reported. No
adverse reactions to an oral challenge with bisulfite were reported in
5 steroid-dependent asthmatics without histories of adverse reactions
to restaurant meals (Stevenson & Simon, 1981).
Fifteen asthmatics with histories of asthmatic reactions to food
and beverages were challenged sequentially with oral capsules
containing 5, 10, 25, and 50 mg sodium metabisulfite. Only one subject
reacted significantly to the challenge, with a fall of 28% in FEV
within 2 minutes of receding a dose of 5 mg sodium metabisulfite
(Koepke & Selner, 1982).
Oral challenge of 6 sulfite-sensitive asthmatics with solutions
of sulfite produced reactions at doses approximately half those
required to produce similar reactions when given in capsule form
(Goldfarb & Simon, 1984).
Administration of atropine, cromolyn, doxepin, or vitamin B12
prior to sulfite challenge ameliorated the asthmatic reaction of 6
sulfite-sensitive subjects (Simon et al., 1984).
Twelve patients with idiopathic anaphylaxis, 9 of whom had a
history of adverse reactions to restaurant meals, and 10 control
subjects received sequential challenges with increasing oral doses
(1, 5, 10, 25, 50, 100, and 200 mg) sodium metabisulfite in lemonade.
A similar degree of non-specific irritant and subjective symptoms were
reported in both groups and no anaphylactic reactions were observed.
Pulmonary function was abnormal in 3 subjects, but no bronchospasm was
induced (Sonin & Patterson, 1985).
Sequential capsule challenge tests with similar doses of sodium
bisulfite in 32 patients (14 with recurrent idiopathic anaphylaxis, 8
with systemic mastocytosis, and 10 with reported allergic reactions to
meals) resulted in anaphylactic reactions in 2 of the idiopathic
anaphylaxis patients, but these 2 patients responded similarly to the
placebo challenge (Metcalfe, 1984).
Of 61 asthmatic patients with no history of sulfite sensitivity,
5 patients (8.2%) had a fall in FEV1 of more than 25% following a
single-blind oral challenge with increasing capsule doses (10, 25, 50,
and 100 mg) of bisulfite at 30-minute intervals. Patients who did not
react to this challenge were further challenged with acidic solutions
of 1 or 10 mg of sodium metabisulfite. The symptoms reported in the 5
patients who reacted to the challenge were milder and required larger
challenge doses than in sulfite-sensitive asthmatic patients with a
history of reactions to restaurant meals (Simon et al., 1982).
Pulmonary function was assessed in 25 asthmatic and 25
non-asthmatic subjects before and after consuming 112 ml wine
containing 140 mg sulfur dioxide per litre. A decrease of more than
12% in FEV1 occurred in 1 non-asthmatic and 5 asthmatic subjects.
Two of the asthmatic responders were challenged with 2 solutions, one
a model solution containing all the wine ingredients except sulfur
dioxide and the other a metabisulfite solution alone. Both subjects
displayed a fall in FEV1 after receiving metabisulfite alone and one
also reacted to the model wine solution without metabisulfite
(Seyal et al., 1984).
Five sulfite-sensitive asthmatic patients with a history of
adverse reactions to sulfited foods were challenged with lettuce
treated with a commercial vegetable freshener containing sodium
hydrogen sulfite; a control experiment was performed using lettuce
treated with a commercial freshener not containing sulfite.
Approximately 10 ml of the freshener solution (80-90 mg sodium
hydrogen sulfite) adhered to the 3-ounce portions of lettuce used. All
the patients displayed a reduced FEV1 (mean decrease 44%, range
31-64%) after the challenge with sulfited lettuce but not after
receiving the control lettuce. Four of the patients were described as
having moderate asthmatic reactions, while the fifth reacted severely
and required extensive emergency treatment (Howland & Simon, 1985;
Two patients who showed symptoms (dizziness, weakness, nausea,
chest tightness, tachycardia, and dyspnea) associated with restaurant
meals reported vague, general symptoms after an oral challenge with
sodium metabisulfite, but pulmonary function showed no changes after
challenge (Schwartz, 1953).
Estimates of the frequency of sulfite sensitivity among
asthmatics have been made, based on experimental studies, but they are
complicated by the fact that different end-points have been used to
define an adverse reaction and by bias in the sample population
(e.g. in referral practices where a disproportionate number of
severely affected, steroid-dependent asthmatic patients are seen).
Capsules containing 1.4, 14, 144, and 288 mg potassium
metabisulfite were given sequentially to 134 asthmatic patients
selected from a clinic population of 1073 patients with asthma and
related symptoms. Decreases in FEV1 of more than 15% were reported
in 50 of the subjects challenged. Based on this study, it was
estimated that 4.6% of asthmatic patients respond to sulfite challenge
(Buckley et al., 1985). Oral challenge studies with potassium
metabisulfite on 100 non-steroid-dependent asthmatic subjects resulted
in no cases of sulfite sensitivity that could be confirmed in
double-blind trials. Single-blind challenge studies on 69 steroid-
dependent asthmatics resulted in a greater than 20% decrease
in FEV1 in 14 subjects. Double-blind challenges of 5 of these
patients resulted in a significantly-decreased FEV1 in 2 cases.
Based on these studies, it was estimated that 5-10% of steroid-
dependent asthmatics and 1-2% of all asthmatics may be sulfite
sensitive (Taylor, 1984). Other workers have suggested that 5-10% of
asthmatics may be sulfite sensitive (Simon et al., 1982; Simon,
1984). However, Patterson (personal communication with attachments
from R. Patterson, Northwestern University, Evanston, IL, USA, to S.A.
Anderson, Federation of American Societies for Experimental Biology
(FASEB), Bethesda, MD, USA, 1984, submitted to WHO by FASEB) failed to
identify sulfite sensitivity among idiopathic anaphylactic patients
from an extensive population of asthmatics, from which he concludes
that sulfite sensitivity may be a minor problem.
Bronchoconstriction and bronchospasm occur with greater frequency
after inhalation of sulfur dioxide than after oral ingestion of
sulfites in both asthmatic and non-asthmatic individuals (Koenig
et al., 1982; Nadel et al., 1965; Schachter et al., 1984;
Sheppard et al., 1980). Inhalation of bronchodilators containing
sulfites has also been associated with bronchospasm and anaphylaxis
(Koepke et al., 1984; Twarog & Leung, 1982). Inhalation of sulfur
dioxide by 6 known sulfite-sensitive asthmatics induced falls in FEV1
of more than 25% at doses of 1 to 10% of that required by ingestion
(Goldfarb & Simon, 1984).
It is possible that inhalation of sulfur dioxide after eructation
may have occurred in some oral challenge studies. Concentrations of
4-50 ppm sulfur dioxide were reported in the stomach contents of 5
subjects challenged with 25 or 50 mg metabisulfite under unspecified
conditions (Allen & Delohery, 1985). Inhalation of air containing
sulfur dioxide in the headspace gases of sulfited foods may also be a
contributory factor. A patient who had a wheezing episode after
inhalation of headspace gas from sulfited dried apricots did not react
to an oral challenge of 50 mg sodium metabisulfite (Werth, 1982). It
was estimated that the airspace above an aqueous solution of 70 ppm
sulfur dioxide contained 1 ppm sulfur dioxide at room temperature
(Freedman, 1977), a concentration causing bronchoconstriction in some
asthmatics (Sheppard et al., 1980). Administration of a mouthwash
containing up to 100 mg sodium metabisulfite in 30 ml citric acid
solution resulted in a fall of more than 20% in FEV1 in 9 of 15
asthmatics, but the 9 who reacted did not respond when they held their
breath during the challenge (Allen & Delohery, 1985).
I.v. infusion of sulfite-containing medication (theophylline and
dexamethaone) seriously worsened an asthmatic attack in a patient who
had previously shown a large decrease in peak flow rate following an
oral capsule challenge of 500 mg sodium metabisulfite. I.v. injection
of metaclopromide, which contained metabisulfite, also caused
bronchospasm in this patient (Baker et al., 1981). Injection of a
dose of lidocaine hydrochloride containing metabisulfite was followed
by plantar pruritis in an individual who had complained of similar
symptoms after eating chili soups, sandwiches, salads, jalapenos,
pizza, Chinese pickled green turnips, or dried shrimp (Huang & Fraser,
Conversely, patients receiving total parenteral nutrition (TPN)
solutions preserved with bisulfites may receive up to 950 mg bisulfite
per day, but no sensitivity reactions have been associated with this
practice (Metcalfe, 1984). One report of excretion of abnormal sulfur
metabolites in a patient receiving TPN for 18 months (Abumrad et al.,
1981) led to the suggestion that tachypnoea in this patient might have
been associated with abnormal metabolism of sulfite (Gunnison &
As indicated above, there is normally a considerable reserve of
activity of sulfite oxidase in man, but a few cases of sulfite oxidase
deficiency have been identified (Irreverre et al., 1967; Shih et al.,
1977; Duran et al., 1979; Ogier et al., 1982). In these extreme
cases, the symptoms included severe neurological injury, dislocated
ocular lenses, and premature death. Sulfite oxidase activity in
hepatic tissue and/or skin fibroblasts from these individuals was
below detectable levels (Johnson & Rajagopalan, 1976a,b; Shih et al.,
1977; Johnson et al., 1980; Ogier et al., 1982). Sulfite oxidase
activities in skin fibroblasts of both parents of one of these
patients were below the lowest normal control level (Shih et al.,
1977), while in another case both parents and a brother had activities
below average but within the control range; all these relatives were
asymptomatic. There is currently insufficient information to
associate sulfite oxidase deficiency with adverse reactions to
Life-threatening reactions and deaths of 4 asthmatic individuals
have been reported following ingestion of restaurant meals, including
foods treated with sulfiting agents (Food Chemical News, 1984).
Following 2 of the deaths, samples of the foods ordered by the
deceased were analysed for sulfite. Two samples of lettuce contained
78 and 409 ppm sulfite, and guacamole contained 272 ppm sulfite
(Riddle, 1983). In one of these cases, analysis in U.S. FDA
laboratories of shredded potatoes (cottage fries) indicated a sulfite
concentration of 96 ppm; the results of re-analysis of the same
product before and after cooking were 615 and 582 ppm sulfite,
respectively (Spears, 1984).
In another case, a sulfite-sensitive asthmatic patient lapsed
into a coma after consuming a meal including cottage-fried potatoes.
Analysis revealed that samples of the potatoes used for cottage fries
contained 2240 ppm sulfite before cooking and 2210 ppm after cooking
(Whetstone, 1984). The patient remained comatose for 3 weeks, and 6
months after the incident still displayed several motor and
neurological deficits (Simon, 1984).
Adverse reactions in non-asthmatic individuals appear to be rare,
but a case has been reported of anaphylaxis in a non-asthmatic male
who consumed a meal including salad sprayed with bisulfite. Oral
challenge with 10 mg sodium hydrogen sulfite produced erythema,
itching, nausea, warmness, coughing, and bronchoconstriction for about
1 hour (Prenner & Stevens, 1976). Contact dermatitis in response to
sulfite has also been reported (Fisher, 1975), as has hypotension
without respiratory distress (Schwartz, 1983).
Earlier data were considered by the Committee in light of the
results of new studies performed since the last review; these include
studies on the chemistry of sulfur dioxide in foods and reactions
with nutrients, metabolism, teratogenicity, mutagenicity, and
carcinogenicity studies, effects on the gastric mucosa, and, in
particular, adverse reactions (bronchoconstriction and anaphylactic-
type reactions) in man.
In reviewing case studies, and challenge tests relating to
idiosyncratic sensitivity to sulfiting agents, the Committee noted the
serious, life-threatening nature of the adverse effects in some cases
and that a number of fatalities associated with sulfite-treated foods
have been reported. Such adverse reactions appear to occur principally,
but not exclusively, in a sub-population of sulfite-sensitive
asthmatics and are associated with consumption of salads treated with
sulfite preparations; other vegetable products with high residual free
sulfite levels or sulfite-treated acidic beverages have less-commonly
been implicated. Many sulfite-treated processed foods contain a
substantial proportion of the residual sulfur dioxide equivalents in
bound form, but it is not known whether bound sulfur dioxide
contributes to adverse reactions.
While sulfiting agents can interact with DNA and may induce
mutations in bacteria, in vivo mutagenicity studies in mammals were
negative, as were long-term carcinogenicity studies on potassium and
sodium metabisulfite in mice and rats, respectively. Long-term anti
3-generation studies in rats receiving metabisulfite in the diet with
added thiamine showed a no-effect level of 0.125% sodium metabisulfite
(equivalent to 70 mg SO2/kg.b.w./day).
Sulfur (IV) oxo anions are normal intermediates in the metabolism
of endogenous sulfur compounds in mammals and are oxidized enzymically
to sulfate prior to urinary excretion. In general, there is a large
reserve capacity of sulfite oxidase and the systemic toxicity of
sulfites is low. This conclusion is supported by clinical experience
with total parenteral nutrition solutions preserved with sulfiting
While recognizing the utility and versatility of sulfiting agents
as food additives, the Committee recommended that the use of suitable
alternative technology, where it exists, should be encouraged,
particularly in those applications (e.g. control of enzymic browning
in fresh salad vegetables) where the use of sulfites may lead to high
levels of acute exposure and which have most commonly been associated
with life-threatening adverse reactions. There is concern about uses
of sulfiting agents in situations where such use may be unexpected by
the consumer and no indication of their presence is given. The
Committee reiterated the view of the twenty-seventh meeting (Annex 1,
reference 62, section 2.4) in respect of intolerance to food additives
that appropriate labelling was the only feasible means of offering
protection to susceptible individuals.
The ADI was retained. However, the Committee recommended that the
frequency of idiosyncratic adverse reactions and the relative toxic
effects of free and bound sulfur dioxide should be kept under review.
Information on the chemical forms of sulfur dioxide in food is also
Level causing no toxicological effect
Rat: 0.25% sodium metabisulfite in the diet, equivalent to
70 mg/kg b.w./day calculated as SO2.
Estimate of acceptable daily intake for man
0-0.7 mg/kg b.w. for sulfur dioxide and sulfur dioxide
Further work or information
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