WHO/Food Add./24.65
FAO Nutrition Meetings
Report Series No. 38A
SPECIFICATIONS FOR IDENTITY AND
PURITY AND TOXICOLOGICAL EVALUATION
OF SOME ANTIMICROBIALS AND
ANTIOXIDANTS
The content of this document is the result of the deliberations of the
Joint FAO/WHO Expert Committee on Food Additives which met 8-17
December 1964a
a Eighth Report of the Joint FAO/WHO Expert Committee on Food
Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO
Nutrition Meetings Report Series 1965, 38.
SULFUR DIOXIDE
CHEMICAL NAMES Sulfur dioxide; sulfurous acid anhydride
EMPIRICAL FORMULA SO2
MOLECULAR WEIGHT 64.1
DEFINITION Sulfur dioxide contains not less than 95% SO2
DESCRIPTION A colourless, non-inflammable gas with a
strong, pungent, suffocating odour. Soluble in
water and ethanol.
USE As an antimicrobial preservative and as an
anti-browning agent.
SODIUM SULFITE
CHEMICAL NAME Sodium sulfite
EMPIRICAL FORMULA Anhydrous: Na2SO3
Heptahydrate: Na2SO3.7H2O
MOLECULAR WEIGHT Anhydrous: 126.05
Heptahydrate: 252.16
DEFINITION Anhydrous sodium sulfite contains not less than
95.0% Na2SO3. Sodium sulfite heptahydrate
contains not less than 48.0% Na2SO3.
DESCRIPTION Anhydrous sodium sulfite is a white powder,
with not more than a faint odour of sulfur
dioxide; 1 g is soluble in 4 ml of water.
Sodium sulfite heptahydrate is a transparent or
white crystalline solid, with not more than a
faint odour of sulfur dioxide; 1 g is soluble
in 2 ml of water.
USE As an antimicrobial preservative and as an
anti-browning agent.
SODIUM METABISULFITE
CHEMICAL NAME Sodium pyrosulfite
EMPIRICAL FORMULA Na2S2O5
MOLECULAR WEIGHT 190.1
DEFINITION Sodium pyrosulfite contains not less then 95.0%
of Na2S2O5.
DESCRIPTION A white crystalline solid, with an odour of
sulfur dioxide. 1 g is soluble in 2 ml of
water.
USE As an antimicrobial preservative and as an
anti-browning agent.
SODIUM HYDROGEN SULFITE
CHEMICAL NAMES Sodium hydrogen sulfite; sodium bisulfite;
sodium acid sulfite
EMPIRICAL FORMULA NaHSO3
MOLECULAR WEIGHT 104.06
DEFINITION Sodium hydrogen sulfite contains not less than
95% of NaHSO3.
DESCRIPTION A white crystalline or granular solid, with an
odour of sulfur dioxide. 1 g is soluble in 2.5
ml of water.
Biological Data
Biochemical aspects
Sulfite is oxidized in the body to sulfate. Bisulfite reacts with
aldehydes and ketones, including aldehydic sugars. This is a
reversible reaction; the equilibrium concentrations depend on
temperature. The acute effects of sulfite in foods are related to the
amount and concentration of free sulfur dioxide and to the speed at
which the additive compounds liberate the bound sulfur dioxide.
Sulfite may also react reversibly with disulfide linkages in proteins.
The disulfide is split into one part containing a thiol group and
another part with an S-sulfonic acid group.1 Sulfite reacts with
dried yeast to form a component with anti-thiamine activity.2
Acute toxicity
In rabbits, the oral LD50 of sulfite, measured as SO2, was found to
be between 600 and 700 mg/kg body-weight.3
Animal Route LD50 (mg/kg body-weight) Reference
Sodium bisulfite Sodium sulfite
Mouse Intravenous 130 175 4
Rat Intravenous 115 - 4
Hamster intravenous 95 - 4
Rabbit Intravenous 65 - 4
In man, a single oral dose of 4 g of sodium sulfite caused toxic
symptom in 6 of 7 persons. In another subject, 5.8 g caused severe
irritation of the stomach and intestine.3
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
body-weight.5
Short-term studies
Rat. In thiamine-deficient rats, daily oral administration of fruit
syrup containing 350 ppm of sulfur dioxide in a dose of 0.5 ml/150 g
rat for 8 weeks failed to influence growth.6
Groups of weanling rats numbering 5 per group were fed 0.6% sodium
metabisulfite (not less than 3400 ppm 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.2
(Work in progress) 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, and a control group received the same
volume of water. The levels of sulfite in the 2 groups receiving wine
were equivalent to 105 mg and 450 mg SO2 per litre respectively 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 effect was observed on weight gain, efficiency
of utilization of protein, biological value of the same protein or
reproduction. There was also 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.7
(Work in progress) About 120 rats containing equal numbers of each
sex were divided into 2 groups, one receiving potassium metabisulfite
equivalent to 0.6% SO2 in the drinking-water, the other group serving
as controls. No effect was 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. Work is in
progress on the effects of sulfite on the metabolism of thiamine,
vitamin A and calcium.8
Rabbit. One rabbit given 3 g of sodium sulfite by stomach tube each
day for 185 days lost weight, but all organs were normal post mortem.
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.3
Dog. A dose of 3 g of sodium sulfite daily was given by stomach
tube to a dog weighing 17 kg for 23 days. Another weighing 34 kg was
given 6-16 g of 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
bisulfite was given to 2 dogs by the same method and for the same
length of time as in the preceding experiment in daily doses of
1.08-2.51 g. Examination of heart, lungs, liver, kidney and intestine
showed no damage. A total of 91-265 g of sodium sulfite fed to 5
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.3
Long-term studies
Rat. Groups of rats numbering from 18 to 24 per group were fed
sodium bisulfite in dosages of 0.0125%, 0.025%, 0.05%, 0.1%, 0.25%,
0.5%, 1% or 2% of the diet for periods ranging from 1 to 2 years. The
rats fed 0.05% sodium bisulfite (307 ppm as SO2) for 2 years showed
no toxic symptoms. Sulfite in concentrations of 0.1% (615 ppm as
SO2), or more, in the diet inhibited the growth of the rats, probably
through destruction of thiamine in the diet.9
Three groups of weanling rats containing 18, 13 and 19 animals
received drinking-water containing sodium metabisulfite at levels of 0
ppm SO2, 350 ppm SO2 and 750 ppm SO2. Prior interaction of the
sulfite with dietary constituents was thus prevented. The experiment
lasted 2´ 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.10
Comment on experimental studies reported
Sufficient data are not available to indicate the lowest dosage
causing acute effects in man or the highest dosage that will normally
be tolerated without producing harmful effects. The position of the
lowest level at which sulfite produced a significant effect in the
long-term feeding experiments in rats may have been determined by the
destruction of thiamine and possibly other essential dietary
components rather than by a direct action of sulfite on the animals.
The absence of toxic effect on long-term ingestion of sulfite in the
drinking-water (750 ppm as SO2) is consistent with this. Although
the toxicity of sulfite in the drinking-water was lower than that in
the food, this was not considered sufficient evidence for alteration
of the evaluation given previously in the Sixth Report of the Joint
FAO/WHO Expert Committee on Food Additives.
Evaluation
Level causing no significant toxicological effect in the rat
0.05% of sodium bisulfite (= 307 ppm as SO2) in the diet, equivalent
to 15 mg/kg body-weight per day, calculated as SO2.
0.1% of sodium metabisulfite (= 750 ppm as SO2) in the
drinking-water, equivalent to 37 mg/kg body-weight per day, calculated
as SO2.
Estimate of acceptable daily intakes for man (calculated as SO2)
mg/kg body-weight
Unconditional acceptance 0-0.35
Conditional acceptance 0.35-1.5
References
1. Swan. J. M. (1957) Nature (Lond.), 180, 643
2. Bhagat, B. & Locket, M. F. (1964) Food Cosmet. Toxicol., 2, 1
3. Rost, E. & Franz, F. (1913) Arb. Gesundh.-Amte (Berl.), 43, 187
4. Hoppe, J. O. & Goble, F. C. (1951) J. Pharmacol. exp. Ther., 101,
101
5. Lafontaine, A. & Goblet, J. (1955) Arch. belges Méd. soc., 13, 281
6. Locket, M. F. (1957) J. Pharm. (Lond.), 9, 605
7. Jaulmes, P. (Unpublished report of work in progress submitted to
WHO in 1964)
8. Causeret, J. (Unpublished report of work in progress submitted to
WHO in 1964)
9. Fitzhugh. O. G., Knudsen, L. F. & Nelson, A. A. (1946) J.
Pharmacol. exp. Ther., 86, 37
10. Locket, M. F. & Natoff, I. L. (1960) J. Pharm. Pharmacol., 12, 488
See Also:
Toxicological Abbreviations
Sulfur dioxide (FAO Nutrition Meetings Report Series 40abc)
SULFUR DIOXIDE (JECFA Evaluation)