INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
WORLD HEALTH ORGANIZATION
SAFETY EVALUATION OF CERTAIN
FOOD ADDITIVES
WHO FOOD ADDITIVES SERIES: 42
Prepared by the Fifty-first meeting of the Joint FAO/WHO
Expert Committee on Food Additives (JECFA)
World Health Organization, Geneva, 1999
IPCS - International Programme on Chemical Safety
SULFUR DIOXIDE AND SULFITES (addendum)
First draft prepared by
E.J. Vavasour
Chemical Hazard Assessment Division, Bureau of Chemical Safety, Food
Directorate, Health Protection Branch, Health Canada, Ottawa, Ontario,
Canada
Explanation
Biological data
Biochemical aspects
Biotransformation
Effects on enzymes and other biochemical
parameters
Toxicological studies
Short-term studies of toxicity
Genotoxicity
Developmental toxicity
Special studies
Nephrotoxicity
Promotion of carcinogenesis
Observations in humans
Case studies
Food challenges
Prevalence studies
Adults
Children
Comments and evaluation
References
1. EXPLANATION
Sulfur dioxide and sulfites were evaluated at the sixth, eighth,
ninth, and seventeenth meetings of the Committee (Annex 1, references
6, 8, 11, and 32). An ADI of 0-0.7 mg/kg bw was allocated at the
seventeenth meeting to sulfur dioxide and to sulfur dioxide
equivalents arising from sodium and potassium metabisulfite, sodium
sulfite, and sodium hydrogen sulfite. At subsequent meetings (Annex 1,
references 41, 47, and 62), potassium and calcium hydrogen sulfite and
sodium thiosulfate were included in the group ADI.
At its thirtieth meeting, the Committee retained the ADI of 0-0.7
mg/kg bw allocated to this group of compounds (Annex 1, reference 73).
The ADI was based on long-term studies in rats, including a
three-generation study of reproductive toxicity, with a NOEL of 0.25%
sodium metabisulfite in the diet (supplemented with thiamine, as
treatment of foods with sulfites reduces their thiamine content),
equivalent to 70 mg/kg bw per day of sulfur dioxide equivalents. At
higher doses (> 1%), local irritation of the stomach was observed,
with inflammatory changes and hyperplasia, and occult blood was
detected in the faeces at even higher doses. The histopathological
changes were limited to the stomach; the incidence of neoplasms was
not increased at any site or at any dose. A safety factor of 100 was
used. Similar local changes in the stomach were observed in pigs fed
thiamine-supplemented diets to which sodium metabisulfite was added.
The Committee also reviewed case studies and challenge tests for
idiosyncratic sensitivity to sulfiting agents and noted the
life-threatening nature of the adverse effects in some cases. It
recommended that, where a suitable alternative method of preservation
exists, its use should be encouraged, particularly in those
applications in which the use of sulfites may lead to high acute
intake. The Committee also reiterated the view expressed at the
twenty-seventh meeting (Annex 1, reference 62, section 2.4) that
appropriate labelling is the only feasible means of protecting
individuals who cannot tolerate certain food additives. The Committee
recommended that the situation with regard to the prevalence of
idiosyncratic adverse reactions and the relative toxicity of free and
bound sulfur dioxide be kept under review. It also requested
information on the chemical forms of sulfur dioxide in food.
2. BIOLOGICAL DATA
2.1 Biochemical aspects
2.1.1 Biotransformation
The metabolic disposition of sulfite was studied in isolated,
perfused rat liver and in isolated rat hepatocytes. In particular, the
kinetics of metabolism of sulfite ion to inorganic sulfate ion and the
effect of sulfite ion on the concentrations of the endogenous,
low-molecular-mass thiol-containing molecules glutathione and cysteine
were considered to be of interest. Sulfite was rapidly converted to
sulfate by isolated hepatocytes at concentrations ranging from 200
µmol/L to 2 mmol/L. The rate of conversion was linear and quantitative
over this range. These results confirm the presence of substantial
concentrations of sulfite oxidase in liver. Cytotoxicity was not seen,
even at the highest concentration of sulfite. Perfusion of isolated
rat liver with 1 mmol/L sulfite resulted in nearly 98% extraction of
sulfite from the perfusate during the first 3 min of single-pass
perfusion. At the same time, sulfate ion was shown to accumulate
rapidly in the perfusate, reaching 830 µmol/L by 5 min and nearly 100%
conversion within 30 min. Perfusion of the liver also resulted in
release of glutathione into the perfusate in a rapid phase in which 11
µmol/L glutathione accumulated over 5 min and a slow phase in which 17
µmol/L glutathione accumulated over 60 min. Free cysteine was not
dected in the perfusate at any time. Incubation of isolated
hepatocytes with 0.5, 1, or 2 mmol/L sulfite resulted in a
time-dependent increase in the amount of free glutathione, but not
cysteine, associated with the cells. The authors speculated that
glutathione was released from mixed disulfides of protein and
low-molecular-mass thiols and from oxidized glutathione in hepatocytes
and perfused liver, and was not synthesized de novo. Sulfitolysis of
disulfides by sulfite ion at physiological pH was demonstrated by
incubation of sulfite with oxidized glutathione, resulting in a time-
and concentration-dependent release of glutathione from the disulfide
(Sun et al., 1989).
2.1.2 Effects on enzymes and other biochemical parameters
In studies of glutathione S-sulfonate, a well-documented
reaction product of sulfite with oxidized glutathione, and the enzyme
glutathione S-transferase from rat liver and lung and human
tumour-derived lung cells, glutathione S-sulfonate was a strong
competitive inhibitor of both cytosolic and microsomal glutathione
S-transferase in all cell lines. Glutathione S-sulfonate
subsequently underwent reduction to oxidized glutathione or
glutathione. These results indicate that the glutathione pathway may
be vulnerable to the effects of sulfur dioxide through its reaction
with oxidized glutathione, which depletes the glutathione supply
(Leung et al., 1985).
The activities of some intestinal enzymes were measured in female
rats exposed to sodium metabisulfite in the diet. Groups of 10 female
Wistar rats weighing 70-100 g received diets containing 0, 0.5, or
2.5% sodium metabi-sulfite ad libitum for five weeks. After
sacrifice, the entire small intestine was removed and homogenized. The
activities of maltase, sucrase, lactase, and alkaline phosphatase were
assayed in crude intestinal homogenates and in brush-border membrane
fractions. Feeding with 2.5% metabisulfite resulted in small increases
in the activities of maltase and lactase in the homogenates, which did
not reach statistical significance. The activities of all three
disaccharidases in the brush-border fractions were statistically
significantly increased at the high dose. Alkaline phosphatase
activity was significantly increased in both the crude homogenates and
the brush-border fractions from rats receiving the high dose. The
authors considered the possibility that the increased activity of the
enzymes involved in carbohydrate digestion was due to a decrease in
their degradation; however, since the increase in alkaline phosphatase
activity was probably due to an increase in enzyme concentrations,
this could also be a factor in the increased activity of the
disaccharides (Rodriguez-Vieytes et al., 1994).
The possibility that the adverse effects attributed to ingestion
of sulfites, including bronchoconstriction, are mediated through
effects on nitric oxide as part of the parasympathetic pathway was
tested in a series of experiments in vitro. Sulfites were shown to
react in solution with nitric oxide and with biological carriers of
nitric oxide (S-nitrosylated bovine serum albumin and
S-nitrosoglutathione) and to interfere with the effects of nitric
oxide in biological processes such as inhibition of platelet
aggregation. The results suggest that sulfites interfere with the
biological effects of nitric oxide at physiologically realistic
concentrations (Harvey & Nelsestuen, 1995).
2.2 Toxicological studies
2.2.1 Short-term studies of toxicity
Rats
The subchronic toxicity of free inorganic sulfite (as sodium
metabisulfite) and acetaldehyde hydroxysulfonate, a major bound form
of sulfite in beer and wine, was evaluated after their addition to the
drinking-water of normal and sulfite oxidase-deficient rats. Groups of
eight female Wistar rats weighing 175-199 g were assigned to one of 14
groups receiving sodium metabisulfite or acetaldehyde hydroxysulfonate
in the drinking-water for eight weeks at doses of 0, 7, 70, or 350
(three weeks)/175 (five weeks) mg/kg bw per day of sulfur dioxide
equivalents. The study included both normal rats and rats that had
been made sulfite oxidase-deficient by the addition of 200 ppm
tungsten to their drinking-water in the form of sodium tungstate. The
animals were observed daily throughout the experiment; body weights
were measured weekly, food consumption twice per week, and water
consumption three times per week throughout the study. Blood and urine
samples were collected before and every two weeks during the
experiment for determination of haemoglobin and plasma protein,
S-sulfonates and sulfite, and urinary sulfite and thiosulfate. At
the end of the study, the rats were killed and autopsied. Liver
samples were collected for determination of thiamine content and
sulfite oxidase activity, the latter as an indication of the
effectiveness of tungsten treatment. Histopathological examination was
conducted on the aortic arch, heart, representative portions of the
liver, left kidney, left lung, ovaries with fallopian tubes,
oesophageal-forestomach junction, forestomach, fundic area of the
stomach, pylorus-duodenal junction, mid- and distal duodenum, jejunum,
ileum, caecum, and mid-colon.
Tungstate treatment effectively obliterated hepatic sulfite
oxidase activity; untreated animals had an average value of 350
units/g liver. The overall health of the animals was not affected by
treatment, except that sulfite oxidase-deficient rats receiving either
of the sulfite treatments had dried blood around their noses four to
five weeks after the beginning of treatment, whereas sulfite
oxidase-deficient controls did not. This effect was attributed to
respiratory distress related to the lung oedema noted at necropsy. The
rats were not deficient in thiamine. After eight weeks of treatment,
the body weights of the sulfite oxidase-deficient rats receiving the
highest dose of metabisulfite were significantly lower than those of
controls. All groups of rats receiving metabisulfite consumed more
feed, when calculated as grams per kilogram bodyweight per day, than
either the respective control groups or those receiving acetaldehyde
hydroxysulfonate, although no dose-response relationship was apparent.
A dose-related decrease in water consumption was noted in the sulfite
oxidase-deficient rats, which reached statistical significance in
those receiving metabisulfite but not in those receiving acetaldehyde
hydroxysulfonate. Haemoglobin and plasma protein concentrations were
not affected by treatment.
Urinary sulfite was found at low concentrations or was
undetectable in rats with normal sulfite oxidase activity, even when
they were treated with sulfite in the drinking-water, indicating
rapid, efficient metabolism of sulfite by this enzyme. Sulfite was
detected in the urine of sulfite oxidase-deficient rats even before
sulfite treatment was initiated. The urinary sulfite concentrations
increased in the enzyme-deficient rats after initiation of treatment
with either the free or the bound forms of sulfite; however, the
sulfite concentrations were variable, and no correlation with dose or
length of treatment was apparent, although rats treated with
acetaldehyde hydroxysulfonate tended to excrete more free sulfite than
did metabisulfite-treated rats. The authors suggested that the lower
water intake of the latter groups may have contributed to this
phenomenon. By contrast, the plasma sulfite concentrations were low
and variable in all groups. This effect was attributed to the ability
of the sulfite ion to react with many biological compounds to form
S-sulfonates, possibly by sulfitolysis of disulfide bonds in
proteins and free cysteine. Plasma S-sulfonate concentrations were
generally lower in rats with normal sulfite oxidase activity, but even
the enzyme-deficient control rats had elevated plasma S-sulfonate
concentrations, indicating that these substances are formed
endogenously. There was no dose-response relationship between plasma
S-sulfonate concentration and administered sulfite; however, these
substances were present at higher concentrations in enzyme-deficient
rats treated with free sulfite than in those treated with acetaldehyde
hydroxysulfonate or in controls. The urinary thiosulfate
concentrations were higher in sulfite oxidase-deficient than in normal
rats given either sulfite treatment or in controls. As for urinary
sulfite and plasma S-sulfonates, no general increase in urinary
thiosulfate was observed with increasing dose of administered sulfite.
The urinary thiosulfonate concentrations were low and variable in the
enzyme-deficient rats, although they were still higher than in normal
rats, suggesting that this is a minor pathway for excretion of excess
sulfite.
The only finding at gross necropsy was white patches in the lungs
of the sulfite oxidase-deficient rats receiving sulfite treatment.
Histopathological examination revealed lesions in the fore- and
glandular stomachs of both normal and sulfite oxidase-deficient rats
receiving the highest dose (350/175 mg/kg bw per day) of bound or free
sulfite. The enzyme-deficient rats had the most severe lesions. These
included moderate hyperkeratosis of the forestomach and alterations of
the fundic portion of the stomach, including a thinner fundic mucosa,
distention of the basal portion of the fundic glands, chief-cell
hypertrophy along the fundic glands with varying amounts of apical
acidophilic granules and fewer parietal and mucous cells (less evident
in acetaldehyde hydroxysulfonate-treated rats), clusters of aberrant
fundic glands with hyperplastic chief cells (metabisulfite-treated
rats only), and damage to the surface epithelium and gastric pits,
with oedema and sloughing, resulting in bleeding (acetaldehyde
hydroxysulfonate-treated rats only). In addition, pathological changes
in the liver were seen in the acetaldehyde hydroxy-sulfonate-treated
rats, affecting sulfite oxidase-deficient animals receiving the
intermediate and high doses and normal animals receiving the high
dose. The changes were described as cytoplasmic vacuoles within
hepatic parenchymal cells. It could not be determined whether the
vacuoles contained lipid or glycogen. In enzyme-deficient rats
receiving the high dose, the death of about 0.5% of the parenchymal
cells was seen, which was more prevalent in extensively vacuolated
cells. The authors speculated that the liver lesions were due to the
effects of free acetaldehyde. They concluded that the toxicity of
acetaldehyde hydroxysulfonate is equivalent to that of free sulfite
and that although sulfite oxidase-deficient rats were more sensitive
to the effects of sulfite the no-effect levels were identical. The
NOEL was 70 mg/kg bw per day of sulfur dioxide equivalents (Hui et
al., 1989).
2.2.2 Genotoxicity
Sodium bisulfite, as a 1:3 mixture of NaHSO3 and Na2SO3, was
tested at concentrations of 0.05-1 mmol/L in human peripheral
lymphocytes in vitro. Positive results were obtained in assays for
chromosomal aberrations, micronucleus formation, and sister chromatid
exchange (Meng & Zhang, 1992).
2.2.3 Developmental toxicity
Rats
Groups of 12 or 13 pregnant Wistar rats (body weights not
specified) received potassium metabisulfite in the diet on days 7-14
of gestation at concentrations of 0, 0.1, 1, or 10%. Two-thirds of the
rats receiving 0, 0.1, and 10% and all those given 1% were killed on
day 20 of gestation for examination of the fetuses; the remaining rats
were allowed to deliver their litters and to rear their offspring for
15 weeks.
The body-weight gain of dams receiving 10% potassium
metabisulfite was markedly depressed during the treatment period: the
animals lost weight during this period but by day 20 had nearly
compensated by faster body-weight gain. The body-weight gain of the
other treated animals was similar to that of controls. The actual
intakes of metabisulfite were 0, 130, 1300, and 2900 mg/kg bw per day,
respectively, corresponding to 0, 75, 760, and 1700 mg/kg bw per day
of sulfur dioxide equivalents. There were more resorptions and fetal
deaths in the treated groups than in controls, but the difference was
not statistically significant and was not dose-related. There was no
difference in the number of live fetuses per dam or in the sex ratio
of the fetuses. The fetal body weights in dams given 10% were
significantly lower than in controls. No skeletal or external
anomalies were detected in any group; delayed ossification and some
skeletal variations were noted in all of the groups but the incidence
was not related to dose. Several fetuses with visceral anomalies were
found in all groups, both control and treated, with no relationship to
dose. The number of liveborn pups, the live birth index (number of
liveborn pups divided by number of implantation sites), and the
survival rate of offspring on day 4 after birth were decreased and the
number of stillborn pups increased in dams receiving the 10% dose that
were allowed to bring their litters to term in comparison with
controls. None of these differences was statistically significant. The
total litter loss between day 0 and day 4 in one dam at 10% had a
large effect on the survival index for the whole group. Survival and
body-weight gain were similar in all groups during the remainder of
the preweaning period and after weaning. The adverse effects on pup
birth weights observed with the 10% dietary dose were probably due to
the drastic maternal body-weight loss during the treatment period. No
teratogenic effects were observed, and there were no persistent
effects on pup survival or body-weight gain. The NOEL was 760 mg/kg bw
per day of sulfur dioxide equivalents (Ema et al., 1985).
Groups of 10-12 pregnant Wistar rats (mean body weight, 240 g)
were fed diets containing 0, 0.32, 0.63, 1.25, 2.5, or 5% sodium
sulfite heptahydrate in the diet ad libitum on days 8-20 of
gestation. Satellite groups of four pregnant rats received 0, 0.32, or
5% in the diet on the same days. Body weights, food consumption, and
clinical signs of toxicity were recorded daily. On day 20 of
gestation, rats in the main group were sacrificed and the uteri opened
and examined for the presence and position of resorptions, viable and
non-viable fetuses, and implantation sites. Live fetuses were weighed,
sexed, and examined for external abnormalities. Half of the fetuses
were subjected to visceral examination, and the other half were
prepared for skeletal examination. Dams in the satellite group were
allowed to deliver and rear their litters to weaning. The average
daily intake of sodium sulfite heptahydrate, in order of ascending
dose, was 0, 300, 1100, 2100, and 3300 mg/kg bw per day (0, 80, 280,
530, and 840 mg/kg bw per day of sulfur dioxide equivalents).
Both food intake and body-weight gain during treatment were
reduced in the animals receiving the 5% diet. Food intake was also
reduced in the groups receiving the two lowest doses, with no apparent
dose-response relationship. The total number of implantations was
higher in dams at the three highest doses than in the controls or rats
at the two lower doses, although the difference was not statistically
significant. The percentage of intrauterine deaths (resorptions and
dead fetuses) was also increased over that in controls in dams at the
two highest doses. As a result, the litter sizes in all groups were
comparable. The fetal body weights were statistically significantly
lower in all treated groups than in controls, with the exception of
dams at 2.5%. No external, skeletal, or visceral anomalies were
observed in fetuses in any group, although the incidences of several
fetal skeletal variations, such as lumbar rib, hypoplastic 13th rib,
and delayed ossification of the skull and sternum, were slightly
increased in some of the sodium sulfite-treated groups in a weakly
dose-related manner. Dilatation of the renal pelvis and of the lateral
ventricle were also observed, with no significant dose-response
relationship. None of these effects was statistically significant.
Dams that brought their litters to term had normal weight gain over
the lactation period. Treatment had no effect on litter parameters
(number of liveborn pups, live birth index, survival rate at days 7
and 28 post partum, or pup body weight on day 21). The authors noted
that maternal toxicity occurred only at the highest dose (5% of the
diet); however, since mild growth retardation was seen at all doses
and may have caused the slight increase in developmental variations,
the LOEL for the study was 80 mg/kg bw per day of sulfur dioxide
equivalents (Itami et al., 1989).
2.2.4 Special studies
2.2.4.1 Nephrotoxicity
The effect of continuous consumption of metabisulfite on rat
kidney cells was studied by assaying the activities of selected
enzymes before and during its administration. Groups of 18 male albino
rats (strain not indicated) received distilled water or sodium
metabisulfite solution orally by syringe to deliver a dose of 5 mg/kg
bw daily (equivalent to 3.4 mg/kg bw of sodium dioxide equivalents)
for 1, 3, 7, 9, 11, 13, or 15 days. A subset of the rats were
sacrificed 24 h after each dose, and blood and kidneys were collected.
An additional 18 rats were held in metabolism cages for daily
collection of urine; 12 of these rats were fed sodium metabisulfite
solution every 24 h for 15 days, with daily urine collection, and the
remaining six rats served as controls and received 1 ml distilled
water. The activities of alkaline phosphatase, acid phosphatase,
lactic dehydrogenase, and glutamate dehydrogenase were measured in
serum, renal tissue, and urine. Protein excretion was also measured.
The activity of alkaline phosphatase in renal tissue was reduced
immediately after the first dose of metabisulfite, reaching a level
that was one-third that of the controls and persisting over the two-
week treatment period; there were concomitant increases in the
activity of this enzyme in serum and urine. Lactate dehydrogenase
activity was also reduced in renal tissue, starting after five days of
treatment and reaching a value about one-half that of controls by the
end of the experiment; concomitant increases were seen in the activity
of this enzyme in urine but not in serum. The activity of neither acid
phosphatase nor glutamate dehydrogenase was affected by treatment.
Urinary excretion of total protein was increased by nearly 10-fold by
the end of the experiment. The authors concluded that chronically
ingested sulfite can damage renal-cell membranes but is quickly
inactivated after entering the cell, as indicated by the leakage of
two enzymes found in the cell membrane or the cytosol, and does not
affect enzymes located in other cell organelles (Akanji et al., 1993).
2.2.4.2 Promotion of carcinogenesis
N-Methyl- N'-nitro- N-nitrosoguanidine (MNNG) was
administered at a concentration of 100 mg/L in the drinking-water of
male Wistar rats given a diet supplemented with 10% sodium chloride,
for eight weeks. After this treatment, the animals received standard
diet and drinking-water to which potassium metabisulfite had been
added at a concentration of 1% for 32 weeks. Rats initiated with MNNG
and then treated with metabisulfite had a higher incidence of
adenocarcinomas of the glandular stomach, located in the pyloric
region, than initiated controls. Lesions of the gastric mucosa were
found in sulfite-treated animals, regardless of whether they had
received prior treatment with MNNG. The lesions were described as
diffuse, deep gastric pits with clearly increased numbers of mucous
neck cells in the fundic mucosa (Takahashi et al., 1986).
2.3 Observations in humans
2.3.1 Case studies
In a double-blind, placebo-controlled trial, a 49-year-old woman
with a history of allergic rhinitis and who was a steroid-dependent
asthmatic received a sulfite challenge of 5 mg by capsule, solution,
or subcutaneously, which resulted in a drop in forced expiratory
volume in one second (FEV1). Skin-prick tests with sulfite produced
inconsistent reactivity, but reproducible reactions were elicited by
the intradermal technique. The skin reactivity could be transferred
via a heat-sensitive principle in the serum. Tests for histamine
release from leukocytes with sulfite gave inconsistent results. The
authors suggested that skin-sensitizing antibodies mediate
sulfite-sensitive asthma through involvement of immunoglobulin (Ig) E
(Simon & Wasserman, 1986).
Three patients from a larger group suspected of being sensitive
to ingested sulfites were shown to have allergic reactions. These
subjects ranged in age from 22-55 and all were female. Two had
steroid-dependent asthma, and all three had experienced extreme
reactions in response to foods eaten in restaurants and to wine. One
subject had experienced similar reactions after inhalation of
potassium metabisulfite during wine-making. Their serum IgE
concentrations were elevated, and skin tests (prick or intradermal)
for reaction to potassium metabisulfite were positive. Similar
responses to those to ingestion of food were provoked by oral
challenge with potassium metabisulfite at doses of 1-50 mg. The
responses consisted of urticaria or angio-oedema, asthma, headache,
rhinoconjunctivitis, abdominal pain, and anaphylaxis. A passive
transfer test (heat-sensitive principles in serum) was positive in
both subjects in whom it was conducted, confirming that an
IgE-mediated mechanism was involved in these two individuals (Yang et
al., 1986).
Six girls and two boys aged two to six were enrolled in a study
for sensitivity to food additives and found to be sensitive to sulfite
in an oral provocation test. The primary manifestation was urticaria
with or without accompanying angio-oedema (Botey et al., 1987).
A 31-year-old steroid-dependent woman with asthma who had begun
to experience severe episodes of bronchospasm of sudden onset five
years previously, sometimes to restaurant meals, was tested for
sensitivity to sulfites. She had a significant reduction in pulmonary
function (> 20% drop in FEV1) in response to a single-blind, oral
challenge with 25 mg sodium metabisulfite in acidic solution, tidal
inhalation of non-nebulized sodium metabisulfite solution (10 mg/ml),
and a double-blind, oral challenge with 10 mg potassium metabisulfite
in capsules. Skin prick and intradermal challenge with potassium
metabisulfite also produced positive responses, as did intradermal
challenge with acetaldehyde hydroxysulfonate. The patient also had a
significant drop in FEV1 in response to a double-blind oral challenge
with sulfited lettuce and mushrooms but not with sulfited shrimp.
Sulfited potatoes produced an inconsistent response (Selner et al.,
1987).
A fatal anaphylactic reaction was reported in a 33-year-old man
with chronic steroid-dependent asthma. He had been treated previously
for an acute asthma attack after consumption of dried apricots; in a
subsequent incident, he had developed dizziness, nausea, and dyspnoea
shortly after eating a salad in a restaurant. The man had then began
to avoid foods known to contain sulfite. The anaphylactic reaction was
precipitated by only a few sips of white wine, which was found to
contain sulfites at a concentration of 92 ppm (Tsevat et al., 1987).
An analysis of reports of adverse reactions to sulfites to the
Adverse Reaction Monitoring System at the Center for Food Safety and
Applied Nutrition of the US Food and Drug Administration showed that
the food items most frequently associated with adverse effects were
salad-bar items, non-salad-bar fresh fruit and vegetables, wine, and
seafood. The most frequently reported symptoms were those associated
with asthmatic or allergic reactions (difficulty in breathing,
wheezing, difficulty in swallowing, hives, itching, local swelling)
and with gastrointestinal distress (diarrhoea, vomiting and nausea,
abdominal pain, and cramps). Most (74%) of the reporting consumers
were female. Of those reporting severe reactions, 25% reported
difficulty in breathing. A small percentage of the reports were of
death after exposure to sulfites. In August 1986, the US Food and Drug
Administration banned the use of sulfiting agents on fresh fruits and
vegetables, other than potatoes and grapes, as a result of the
accumulating evidence that sulfiting agents are a hazard to public
health (Tollefson, 1988).
A 38-year old female patient with a family history of allergy and
elevated serum total IgE, who suffered severe bronchospasm in response
to a number of stimuli, including pharmaceutical preparations, foods,
and beverages containing sulfite, was subjected to a double-blind oral
challenge procedure with sodium metabisulfite. The oral challenge
clearly resulted in moderate obstruction of the central airways and
lesser obstruction of the peripheral airways, which correlated well
with the increased plasma concentrations of sulfites. The authors
suggested that the rapid onset of symptoms and the lack of atopy
markers to sulfites, as established by negative results in tests for
skin hypersensitivity, are consistent with mediation of effects
through the parasympathetic system (Acosta et al., 1989).
A group of patients with chronic asthma and histories suggestive
of sulfite sensitivity was studied in order to determine whether the
ingestion of aqueous potassium metabisulfite was associated with
degranulation of mast cells, as measured by the release of the
neutrophil chemotactic factor of anaphylaxis. Single-blind, oral
aqueous challenges of up to a maximum of 200 mg potassium
metabisulfite were given to 13 patients. Serum samples were obtained
from all the patients before the challenge and for 180 min afterwards.
The samples were tested for the presence of neutrophil chemotactic
factor by both a 51Cr microchamber chemotaxis assay and a leukocyte
polarization technique. Six of the patients gave positive responses,
as indicated by a fall in FEV1 > 20% of prechallenge values. No
significant increase in the amount of neutrophil chemotactic factor
was detected in post-challenge serum samples from any patient. Skin
testing with potassium metabisulfite in 10 of the patients yielded
uniformly negative reactions. The authors concluded that sensitivity
to aqueous metabisulfite is not associated with mast-cell
degranulation in patients in whom the result of a skin test is
negative (Sprenger et al., 1989).
Evidence for an IgE-mediated reaction to oral challenge with
metabisulfite was reported in a 34-year-old woman with a long-standing
history of allergic rhinitis, nasal polyposis, and recurrent
sinusitis, who had reported reactions to restaurant meals on several
occasions. Various allergies had been confirmed by skin-prick testing
and did not include foods eaten at restaurants. Her serum IgE
concentrations were within the normal range. Repeated oral challenges
with sodium metabisulfite resulted in a consistent spectrum of
reactions with doses of 50 mg by gelatin capsule or 1 mg in lemonade,
which consisted of nasal congestion, profuse rhinorrhoea, swelling of
the face and lips, and urticarial reactions on the hands, antecubital
fossae, soles of the feet, and midriff. Close inspection revealed
swelling of the nasal polyps. These symptoms were resolved after
administration of epinephrine. Pulmonary function was unaffected in
this patient after the metabisulfite challenge. Subsequent oral
challenges with 10 mg metabisulfite at six months produced similar
results. Skin-prick testing induced a positive reaction to
metabisulfite, as did a basophil histamine release test. This case of
adverse reaction to metabisulfite is one of the few in which
convincing evidence was found for an IgE-mediated mechanism. The
authors indicate that the case is somewhat unusual in that the patient
was not asthmatic and asthma was not part of the clinical reaction;
while it is probably quite rare, IgE-mediated sulfite sensitivity
obviously exists (Sokol & Hydick, 1990).
A two-year old boy in whom asthma had been diagnosed at the age
of two months experienced attacks of wheezing in association with
ingestion of foods containing sulfites. He also had a history of
adverse food reactions (hives) to peanuts and milk and showed
immediate skin test hypersensitivity to inhaled allergens. In order to
confirm that sulfites were the precipitating agent in the attacks of
wheezing, a double-blind oral challenge test was conducted with
graduated doses of powdered potassium metabisulfite mixed with apple
sauce. Reaction to the challenge was assessed by measuring pulse,
respiratory rate, and blood pressure. A reaction to a dose of 25 mg
was observed after 2 min, consisting of an increase in all the
measured parameters and accompanied by cough, profuse perspiration,
and wheezing. No reaction was observed to challenges with placebo. On
a separate occasion, intradermal testing with metabisulfite resulted
in a wheal-and-flare reaction comparable to that with histamine,
although the result of previous skin-prick tests had been negative.
The significance of this result was considered equivocal in light of
the fact that an identical response had been obtained in a control
without asthma who did not have a history of wheezing after ingestion
of foods containing sulfites (Frick & Lemanske, 1991).
A series of oral challenges was carried out with metabisulfite in
a 22-year-old woman with a history of seasonal rhinoconjunctivitis due
to sensitivity to grass pollen, who had experienced episodes of
urticaria and angio-oedema affecting the face, neck, and upper chest
and difficulty in speaking (dysphonia), without respiratory
difficulties or gastrointestinal symptoms, after ingestion of a number
of grape-based beverages, salad-bar items, and shellfish. The subject
had a normal blood count, including eosinophils, total serum IgE at
the high end of the normal range, and negative results in skin-prick
tests for several foods and positive results for grass pollen.
Skin-prick and intradermal tests showed no sensitivity to potassium
metabisulfite. Pulmonary function was normal. A positive response was
induced with a 25-mg challenge, with urticaria on the face and upper
thorax, nasal itching, rhinorrhoea, and dysphonia. The symptoms were
resolved by the administration of epinephrine. A challenge one week
later with 25 mg potassium metabisulfite 30 min after administration
of chromolyn sodium induced a similar positive response. Two months
later, the same challenge given 90 min after administration of 5000 µg
cyanocobolamin (vitamin B12) induced the same symptoms as seen
previously, but they were less intense. Consequently, the patient's
urticaria was considered to have been sulfite-mediated. The authors
indicated that the clinical manifestations in the subject suggested an
IgE-mediated mechanism, but the results of skin tests were negative
and the oral challenge with metabisulfite was not inhibited by prior
administration of cromolyn sodium. The authors were unable to identify
a pathogenic mechanism (Belchi-Hernandez et al., 1993).
Three further cases of adverse reactions to ingested sulfites
were reported. The first was in a 45-year-old woman who had had
bronchial asthma and rhinitis during the previous year and who
developed anaphylactoid syndrome during a restaurant meal, with flush,
generalized urticaria, severe wheezing, and dyspnoea, leading to
shock. The blood eosinophil count was elevated, but the serum IgE was
within the normal range. A scratch test with sodium metabisulfite
solution resulted in a strongly positive reaction, and the diagnosis
was an IgE-mediated allergy to sulfites in an asthma patient.
The second case involved a 36-year-old woman with a history of
intrinsic asthma and rhinitis, who experienced generalized itching,
feelings of heat, tachycardia, angio-oedema of the face and lips, and
chest tightness while eating a cafeteria meal. A prick test for sodium
bisulfite gave negative results. An oral challenge test with sodium
metabisulfite in capsules resulted in a decreased FEV1 when a dose of
25 mg was reached. This was accompanied by nasal congestion, a
sensation of heat in the head, redness of the fingers, and shortness
of breath. The diagnosis was an anaphylactoid reaction due to sulfite
sensitivity.
In the third case, the patient was a 37-year-old man who had
experienced recurrent, severe episodes of acute urticaria,
angio-oedema, and dyspnoea, mainly during the night, at least once
every three months for the previous year. The IgE level was somewhat
elevated (180 kU/L). Single-blind challenge tests were performed
during a symptom-free period. One hour after a single dose of 50 mg
sodium metabisulfite, urticaria appeared on the hands, with
progression and generalization, despite treatment with antihistamines
and cortisone. A biopsy taken 5 h after the appearance of urticaria
indicated a leukocytoclastic vasculitis with eosinophilia, confirming
the diagnosis of sulfite-induced urticarial vasculitis (Wüthrich 1993;
Wüthrich et al., 1993).
A 25-year-old man experienced numerous episodes of itchy
erythematous rash and swelling in the face within minutes of consuming
various brands of wine and a particular brand of beer. When an oral
challenge test was performed with the beer, 100 ml were found to
provoke the same reaction, accompanied by a statistically significant
increase in serum histamine, as detected by radioimmunoassay.
Identical symptoms were observed after a dose of 10 mg sodium
metabisulfite. No specific IgE or IgG antibodies were detected in the
patient's serum by a radioimmunosorbent test. The beer was found to
contain 3-4 mg/L of sulfite. As the metabisulfite challenge provoked
the same symptoms as those encountered by the patient when he ingested
the particular brand of beer, sulfite was considered to be the most
likely causative agent. The authors suggested that the dose-dependence
and the release of histamine in the absence of specific antibodies
indicate a diagnosis of intolerance rather than allergy (Gall et al.,
1996).
A 53-year old woman was given a single-blind oral challenge test
with 200 mg sodium bisulfite after having experienced several episodes
of periorbital oedema in response to eye drops. Intramuscular
treatment of the oedema with dexamethasone containing metabisulfite
exacerbated the periorbital oedema and erythema, which was relieved by
administration of antihistamine medications. The patient had no
history of rhinoconjunctivitis or lower respiratory symptoms, and
negative responses were elicited to 80 common inhaled allergens in
skin-prick tests. Twelve hours after ingestion of sodium bisulfite,
periorbital erythemous oedema developed in her left eye, which
disappeared with antihistamine medication. Avoidance of
sulfite-containing foods and medications was found to prevent
recurrences (Park & Nahm, 1996).
2.3.2 Food challenges
Three men and five women aged 25-55, with asthma, who had been
identified as sulfite-sensitive on the basis of double-blind capsule
or beverage challenges, were challenged with various sulfited foods.
Positive responses were measured by reductions in the FEV1. The first
challenge was conducted double-blind with sulfited lettuce; subsequent
challenges comprised fresh mushrooms, dried apricots, white grape
juice, dehydrated potatoes, and shrimp. Four subjects reacted to the
lettuce challenge, and three of these reacted to one or more of the
other sulfited foods. Several of these individuals had positive
responses to skin-prick and intradermal tests with the bound and free
forms of sulfite, suggesting an immunological basis for their
hypersensitivity to sulfites. One subject had a history of reacting to
acidic solutions of sulfite and not to capsules. This patient reacted
only to sulfited lettuce, which, because of its composition, contains
no bound sulfites. The remaining four subjects failed to react to any
of the food challenges. The authors noted the variation in the
responses to sulfited foods other than lettuce. In addition, the
likelihood of a reaction to a particular sulfited food was not
correlated with the amount of sulfite ingested from that food (Taylor
et al., 1988).
A double-blind placebo-controlled study with sulfited lettuce was
performed with four women and one man, aged 25-71 with asthma, who had
previously given positive responses to sulfite capsule challenges.
Four of the subjects had a history of atopy to various aeroallergens.
All of the patients reacted positively to sulfite-treated lettuce, as
indicated by a reduction in pulmonary function. Two of these
experienced severe reactions. Other symptoms experienced were flushing
and itching around the mouth, throat, and skin. None of the patients
responded to placebo-treated lettuce (Howland & Simon, 1989).
A study was conducted to determine whether asthma attacks
precipitated in 10 males and eight females aged 12-23 years
immediately after consumption of pickled onions were due to the
presence of sulfite. All had a history of allergy to airborne
allergens, but only two were steroid-dependent. Most of them did not
react to other potential sulfite-containing foods such as salads,
vinegar, fruit juices, beer, cider, grape juice, shellfish, and
several pickled vegetables, nor did they react to raw or cooked onion.
A single-blind challenge test was conducted with solutions of
metabisulfite in lemon juice, the pH being adjusted to 4.2 and 3.3 to
deliver doses up to 150 mg in stepwise increments. A result was
considered positive when the drop in FEV1 was > 20% A positive
response to metabisulfite at pH 4.2 was observed in six of the
patients and at pH 3.3 in four others. Skin-prick tests with
metabisulfite, pickled onions, the preserving liquid, and raw onions
gave negative results in all patients. Seven of the patients
subsequently consented to undergo a challenge with pickled onions:
three gave a positive response. All of these patients had reacted to
one of the metabisulfite challenges. The sulfite concentration in the
pickled onions in question was determined to be 800-1200 ppm, much
higher than in other varieties of pickled onion (< 200 ppm) and
exceeding the permitted concentration (100 ppm). Decreasing the pH of
the metabisulfite solution resulted in a 2.5-fold increase in the
amount of sulfur dioxide released. The authors suspected that
inhalation of sulfur dioxide was the mechanism for precipitation of
the asthma attacks (Gastaminza et al., 1995).
2.3.3 Prevalence studies
2.3.3.1 Adults
In a prospective single-blind screening study, 120
non-steroid-dependent and 83 steroid-dependent patients with asthma
were challenged orally with capsules of potassium metabisulfite. On
the basis of a > 20% reduction in FEV1 within 30 min of the oral
challenge, five of the non-steroid-dependent and 16 of the
steroid-dependent patients were judged to have had a positive
response. The non-steroid-dependent and seven of the steroid-dependent
responders were re-challenged with increasing doses of potassium
metabisulfite capsules in a double-blind study. In this protocol, a
considerable number of the patients who gave positive reactions in the
single-blind study did not react: positive responses were seen in one
of the five non-steroid-dependent patients and three of seven
steroid-dependent patients. The authors therefore estimated the
prevalence of sulfite sensitivity in their overall study population to
be 3.7%. They considered this figure to be an overestimate, since
there was a larger percentage of steroid-dependent patients in their
study population than in the general population of asthma patients.
Less than 1% of the non-steroid-dependent asthmatics were affected,
while the figure was closer to 8% in the steroid-dependent group,
indicating that the latter are at greater risk for sulfite sensitivity
(Bush et al., 1986).
Oral challenge tests were given to 44 non-atopic patients with
steroid-dependent bronchial asthma (14 males, 30 females; aged 14-74),
with incre-mental doses of sodium metabisulfite in solution and in
capsules for the higher doses. The participants had no clinical
history of sulfite sensitivity. A single-blind challenge protocol was
used for 22 of the patients and a double-blind protocol for the
remaining 22 patients; those who reacted in the single-blind challenge
were re-tested in a double-blind protocol. A positive response was
considered to be a reduction of > 20% in the FEV1. Of six
initially positive responses, only two were confirmed by double-blind
testing. These results suggest that the prevalence of sulfite
sensitivity is 4.5% in steroid-dependent asthma patients (Prieto et
al., 1988).
A study was undertaken among adult Melanesians with recurrent
asthma in Papua-New Guinea to determine whether common food additives
had precipitated asthma in this population. Two female and five male
patients, including three who were steroid-dependent, with a mean age
of 34 years (range, 22-50), received sodium metabisulfite dissolved in
freshly squeezed, pure orange juice, or placebo, in a double-blind
procedure. The solution was swilled around the mouth for 5 s before
being swallowed. Graduated doses of 5-200 mg metabisulfite were used
for the challenge. A positive response was considered to be a decrease
of > 20% in FEV1. Positive responses were demonstrated in three of
the patients, including one who was steroid-dependent, all after the
200-mg dose (Timberlake et al., 1992).
False-positive results may be generated in asthma patients by
oral challenge owing to the fact that hyperactive airways and
bronchial hypersensitivity may be exacerbated by the common practice
in trials of withholding all bronchodilators on the day of challenge.
The author was unable to establish cross-sensitivity to sulfites in 70
patients with documented sensitivity to aspirin, and none of 33
sulfite-sensitive patients were found to be sensitive to aspirin. It
was suggested that accounts of cross-sensitivity of sulfite-sensitive
patients to aspirin and to other food additives had not been confirmed
by oral challenges (Simon, 1994).
The incidence of delayed hypersensitivity reactions to sulfites
was investigated in a series of 2894 patients with eczematous
dermatitis. The patients were subjected to a series of patch tests,
starting with sodium metabisulfite, and positive reactions to sodium
metabisulfite were elicited in 1.7% (50 patients). Patients with a
positive reaction were subsequently tested with sodium sulfite, sodium
bisulfite, and potassium metabisulfite. Those who reacted to sodium
metabisulfite also reacted to potassium metabisulfite and sodium
bisulfite, while only two had positive reactions to sodium sulfite.
Prick tests and intradermal tests with a sodium metabisulfite solution
were carried out on 20 patients, and an oral challenge with doses of
30 and 50 mg sodium metabisulfite was administered to five patients.
None of the subjects who reacted to the patch test reacted to either
the prick or intradermal tests, and no flare-ups of dermititis or
patch site were precipitated by the oral challenge (Vena et al.,
1994).
2.3.3.2 Children
Sodium metabisulfite was administered to 29 children with chronic
asthma in a single-blind challenge. The children ranged in age from
5.5 to 14 years and were essentially evenly divided by sex; 28 of the
29 were atopic for airborne allergens. A positive response was judged
by a reduction in pulmonary function. The patients were challenged
both with capsules at doses up to 100 mg and citric acid solution
containing sodium metabisulfite at doses up to 50 mg. Metabisulfite
hypersensitivity was detected in 19 children; all reacted to
metabisulfite in solution, and none responded when it was administered
in capsule form. Most of the responders experienced immediate
reactions, which consisted initially of a burning sensation in the
throat, tight cough, wheezing, and signs of respiratory distress.
Seven of the 19 had a history which suggested sensitivity to
metabisulfite in foods. The authors considered that the lack of
response to metabisulfite in capsules and the rapid onset of bronchial
symptoms suggested that inhalation of sulfur dioxide was the trigger
(Towns & Mellis, 1984).
The prevalence of sulfite sensitivity was determined in a group
of 51 children with chronic asthma, who were recruited from an allergy
clinic. They ranged in age from five to 16 years, with a mean age of
10.3 years. Nearly 90% of the children were atopic, and 18% were
steroid-dependent. Potassium metabisulfite was administered in
lemonade in an open challenge, in graduated doses of 0.5-100 mg.
Eighteen of the 51 reacted with a decrease > 20% in FEV1 after
drinking the metabisulfite solution. Placebo challenges given to 14 of
the 18 subjects resulted in one positive reaction. There was no
difference in the prevalence of sulfite sensitivity between
steroid-dependent and non-steroid-dependent subjects. All of the
patients who reacted to metabisulfite solution but only two-thirds of
those who did not react were reported to be sensitive to smog
(Friedman & Easton, 1987).
Six children aged five months to 14 years with a history of
severe atopic dermatitis were tested for their reactions to sodium
metabisulfite in a double-blind, placebo-controlled challenge, as part
of a larger study of foods and food additives. The test compound was
administered by nasogastric tube. Two of the children reacted
positively to the challenge, the reactions consisting of exacerbation
of isolated pruritis and redness of the skin. No respiratory symptoms
were seen (Van Bever et al., 1989).
Bronchorestrictive airway responses were evaluated in a group of
35 boys and 21 girls aged 6-14 years with chronic asthma, by open
challenge after ingestion of incremental doses of potassium
metabisulfite solution or capsules. All but two of the children had a
history of allergy to various agents, but none showed allergy to
metabisulfite in a skin-prick test. When the challenge was given with
capsules, positive responses (reduction in pulmonary function) were
noted in four of the children, only at the maximum challenge of 200
mg. Two children who had not reacted to the challenge with
encapsulated metabisulfite responded positively to metabisulfite
solution. None had systemic symptoms (flushing, tingling, and/or
faintness) or hypotensive symptoms after metabisulfite challenge. All
the patients who reacted positively to either challenge had severe to
moderate bronchial reactivity to methacholine, while those who did not
react had only mild reactivity to methacholine (Boner et al., 1990).
The prevalence of sensitivity to sulfite was determined in a
group of 15 boys and five girls with steroid-dependent asthma. Only
one child was suspected of intolerance to this agent. A single-blind
oral challenge test was performed with increasing doses of sodium
metabisulfite solution. The solution was held in the mouth for 10 s
before being swallowed, and FEV1 was evaluated 10 min later. Children
who did not react were re-tested for up to 90 min to evaluate possible
late reactions. A double-blind challenge was performed on those who
reacted. The single-blind challenge resulted in positive responses in
six of the children; four of these cases were confirmed in the double-
blind study. The authors postulated a prevalence of 20% among children
with steroid-dependent asthma (Sanz et al., 1992).
The prevalence of sensitivity to sulfite was determined in 14
girls and 23 boys, aged 5-13 years, with chronic asthma. Five of the
children were steroid-dependent. A double-blind challenge was
conducted, in which the children received a dose of 66 mg sodium
metabisulfite (equivalent to 41 mg sulfur dioxide) dissolved in apple
juice; a control group of 22 children received pure apple juice.
Response to the challenge was determined on the basis of a 10% or
> 20% drop in FEV1. Eight of the 37 children experienced a drop of
> 20%, consistent with the rates in boys only, in girls only, and
in steroid-dependent asthma patients only (Steinman et al., 1993).
4. COMMENTS AND EVALUATION
The Committee identified two main issues in the toxicological
evaluation of sulfites: general toxicity and idiosyncratic
intolerance. The latter does not appear to be related to sulfite
oxidase deficiency in humans. Since general toxicity and idiosyncratic
intolerance appeared to be unrelated, they were considered separately.
General toxicity
Studies performed since the thirtieth meeting have demonstrated
the quantitative conversion of sulfite ion to sulfate ion. Release of
reduced glutathione by both isolated hepatocytes and perfused liver is
probably due to sulfitolysis of oxidized glutathione by sulfite ion.
The other product of sulfitolysis, glutathione S-sulfonate, was
found to be a strong competitive inhibitor of both microsomal and
cytosolic glutathione S-transferase in rat lung and liver cells and
human lung tumour cells. These results suggest that sulfite ion could
interfere with the glutathione pathway through its reaction with
oxidized glutathione. Dietary administration of 2.5% metabisulfite to
rats for five weeks increased the content of three disaccharidases
involved in carbohydrate metabolism and of alkaline phosphatase in the
brush-border membrane of small-intestinal cells.
The short-term toxicity of bound and free forms of sulfite
(acetaldehyde hydroxysulfonate and sodium metabisulfite, respectively)
administered in drinking-water was assessed in normal rats and rats
made sulfite oxidase-deficient by administration of tungstate ion,
also in drinking-water, for eight weeks. The sulfite oxidase-deficient
rats were considered to be a better model for humans than conventional
rats, which have an estimated 10-20 times higher concentration of this
enzyme in the liver. Acetaldehyde hydroxysulfonate is a major bound
form of sulfite in wines and other fermented foods and beverages and
is considered to be a very stable form of bound sulfite. The doses of
bound and free sulfite chosen were calculated to deliver the same dose
in terms of sulfur dioxide equivalents (7, 70, or 350 mg/kg bw per
day, the highest dose being reduced to 175 mg/kg bw per day after
three weeks). The effects on body weight, food consumption, and water
intake were strongest in rats receiving free rather than bound sulfite
and in enzyme-deficient as compared with normal rats. The
concentrations of sulfite and thiosulfate in urine and of
S-sulfonates in plasma were elevated in untreated, sulfite
oxidase-deficient rats. Administration of bound sulfite to these rats
resulted in increased excretion of sulfite in the urine, while
administration of free sulfite was associated with increases in the
concentrations of urinary thiosulfate and plasma S-sulfonates. The
measured concentrations were variable and were not clearly related to
dose. Histopathological lesions of the forestomach and glandular
stomach were detected in all groups of rats treated at the high dose.
The severity and frequency of the gastric lesions were greater in the
sulfite oxidase-deficient rats. Hepatic lesions were observed in
animals receiving acetaldehyde hydroxysulfonate, and the NOEL was
lower in the sulfite oxidase-deficient rats than in normal rats (7 and
70 mg/kg bw per day of sulfur dioxide equivalents, respectively). The
effect may have been due to acetaldehyde formed after dissociation.
The results showed that the gastric toxicity of bound sulfites, in the
form of acetaldehyde hydroxysulfonate, is equivalent to that of free
sulfite: while the enzyme-deficient rats were more sensitive at doses
above the NOEL, the NOEL was the same as that in normal rats.
The results of three assays for genotoxicity in vitro were
reviewed, which confirmed the previously noted observation that
sulfites are genotoxic in vitro but not in vivo. This conclusion
is consistent with the high reactivity of sulfite and its rapid
inactivation in mammals. Two studies of teratogenicity involving
dietary administration of sulfite were available: neither was
completely satisfactory, as treatment did not cover the entire period
of organogenesis. Maternal toxicity was demonstrated in both studies
at doses equivalent to 840 mg/kg bw per day of sulfur dioxide
equivalent or higher. No teratogenic effects were noted at intakes up
to this concentration.
The results of a study of the effects of ingested sulfite on the
rat kidney demonstrated that administration of sodium metabisulfite by
gavage at a dose of 5 mg/kg bw per day (3.4 mg/kg bw per day of sulfur
dioxide equivalent) for up to two weeks reduced alkaline phosphatase
activity in renal tissue and concomitantly increased the serum and
urinary concentrations of the enzyme; the effects occurred after the
first dose. The activity of lactate dehydrogenase was likewise
decreased in renal tissue and was increased in urine but not in serum.
Urinary excretion of protein was increased 10-fold by the end of two
weeks. These effects would appear not to be related to treatment, as
sulfite is quickly and quantitatively metabolized to sulfate and no
sulfite was detected in urine, nor were lesions of the kidney detected
after eight weeks in normal rats receiving 20-50 times higher doses of
sulfite in drinking-water.
The previous NOEL in studies of animals that ingested sulfite was
confirmed in an eight-week study in which the NOEL for gastric lesions
was 70 mg/kg bw per day of sulfur dioxide equivalents in both normal
and sulfite oxidase-deficient rats, whether they were fed free sulfite
or a stable and prevalent form of bound sulfite, acetaldehyde
hydroxysulfonate. The gastric effects of sulfite reported in rats and
pigs arise from local irritation. These effects would therefore be
dependent on concentration rather than dose, and a numerical ADI might
not be appropriate. The Committee considered that the role of
acetaldehyde in the reported hepatic effects of acetaldehyde
hydroxysulfonate should be resolved before a re-evaluation of the
safety could be completed. In view of these reservations, the
previously established ADI of 0-0.7 mg/kg bw was maintained.
Idiosyncratic reactions in humans
A number of human case studies were available in which suspected
hypersensitivity to sulfites based on adverse reactions to foods was
confirmed by administration of single- or double-blind oral challenges
with sulfites in solution or capsule form. While many of the cases
involved individuals with chronic asthma whose response was primarily
respiratory, a number of reports described adverse allergic-type
responses in people without asthma, which did not involve respiratory
symptoms. Some of these individuals had chronic allergic conditions.
The responses were consistent with self-reported reactions documented
by the United States Food and Drug Administration's Adverse Reaction
Monitoring System. Evidence for an allergic basis for the adverse
reactions to free and bound sulfites was provided in a number of the
case reports; in studies in which only skin-prick testing had been
attempted, allergy could not be ruled out, as further testing had not
been done. Challenges with various sulfited food commodities also
resulted in positive responses. In a double-blind study, sulfited
lettuce elicited the most consistent responses; sulfite in
sulfite-treated lettuce is considered to be present mostly as free
sulfite. While the mechanism by which sulfite ingestion precipitates
idiosyncratic adverse reactions has not been established, some
evidence was available that the adverse effects of ingested sulfites
are mediated through effects of nitric oxide on parasympathetic
receptors.
The prevalence of sulfite sensitivity was determined in groups of
steroid-dependent and non-steroid-dependent adults and children with
asthma. In adults, the prevalence was 4-8% among steroid-dependent
asthmatic patients and appeared to be less than 1% among non-steroid
dependent patients. The prevalence in the total adult asthmatic
population has been estimated to be 4%, but the prevalence in
asthmatic children was higher, approximately 20-30%, after
double-blind challenges to both steroid-dependent and
non-steroid-dependent asthmatic children.
The Committee reiterated the recommendation made at its thirtieth
meeting (Annex 1, reference 73) that, when a suitable alternative
method of preservation exists, its use should be encouraged,
particularly in those applications (e.g. control of enzymic browning
in fresh salad vegetables) in which the use of sulfites may lead to
high levels of acute intake and which have most commonly been
associated with life-threatening adverse reactions. The Committee
considered that appropriate labelling would help in alerting
individuals who cannot tolerate sulfites.
The intake of sulfites is assessed in "Evaluation of National
Assessments of Intake of Sulfites".
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