Toxicological evaluation of some food
additives including anticaking agents,
antimicrobials, antioxidants, emulsifiers
and thickening agents
WHO FOOD ADDITIVES SERIES NO. 5
The evaluations contained in this publication
were prepared by the Joint FAO/WHO Expert
Committee on Food Additives which met in Geneva,
25 June - 4 July 19731
World Health Organization
Geneva
1974
1 Seventeenth Report of the Joint FAO/WHO Expert Committee on
Food Additives, Wld Hlth Org. techn. Rep. Ser., 1974, No. 539;
FAO Nutrition Meetings Report Series, 1974, No. 53.
NITRATE, POTASSIUM AND SODIUM SALTS
Explanation
These compounds have been evaluated for acceptable daily intake
by the Joint FAO/WHO Expert Committee (see Annex 1, Refs No. 6 and
No. 9) in 1961 and 1964.
Since the previous evaluation, 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.
BIOLOGICAL DATA
BIOCHEMICAL ASPECTS
Nitrates are readily absorbed and their excretion is similar to
that of halogen ions. Practically the whole quantity administered
orally is excreted unchanged in the urine but a small amount may be
reduced to nitrite. Normal urine contains 0.1-0.4% nitrate, the excess
over intake from food probably arising as end-product of metabolism
(Sollmann, 1957).
In certain circumstances reduction of nitrate to nitrite can take
place in the digestive tract by the activity of the intestinal flora.
If appreciable reduction occurs before the normal rapid elimination of
the nitrate, poisoning can result. This appears to have occurred in
cattle (Bradley et al., 1940), and in babies less than six months old,
especially in dyspeptic infants (Kübler, 1958).
In experiments with rabbits about one-half of the ingested amount
of nitrate was excreted in the urine, and only 0.5% was recovered as
nitrite in the urine (Kübler, 1958).
Several monovalent anions, including nitrate, when injected into
animals interfere with the uptake of iodine by the thyroid (Wyngaarden
& Wright, 1952). Dietary levels of 0.5, 1.0 and 2.5% also reduce the
rate of iodine uptake by the thyroid. This is significant for animal
nutrition (Bloomfield et al., 1961). High nitrate content of the diet
is also responsible for vitamin A deficiency in livestock and for low
liver stores in other species. Rats given a vitamin A deficient diet
for two to three weeks to deplete liver stores and then given for six
days 3% sodium nitrate in their diet as well as vitamin A or carotene
orally or s.c. on the third and fourth day, had livers assayed on the
sixth day for vitamin A levels. Animals receiving vitamin A showed no
reduction but those given carotene had low liver stores. This effect
was considered due to the toxic action of nitrate on the thyroid since
conversion of carotene to vitamin A in the body depends on thyroid
activity (Emerick & Olson, 1962). Calves receiving 54 ppm (0.0054%)
nitrate in their drinking-water alone or with E. coli or with a
thyroid depressant showed increased methaemoglobin and interference
with vitamin A formation without intoxication (McIlwain & Schipper,
1963).
TOXICOLOGICAL STUDIES
Special studies on reproduction
Guinea-pig
Several groups were given drinking-water with 300 (0.03%) to
3000 ppm (0.3%) nitrate for 100-240 days. Male fertility was
unimpaired as all groups conceived. Reproductive performance was poor
at 3000 ppm (0.3%). Food and water consumption and weight gain were
normal at all levels. No significant gross and microscopic lesions
were seen in the reproductive organs. No significant alteration was
seen in serum nitrite, blood urea or serum potassium (Sleight &
Atallah, 1968).
Cattle
Nitrate given in the diet to two-months pregnant cows until they
calved or aborted at levels inducing 40-50% methaemoglobinaemia ended
in the majority in normal pregnancies. Two abortions occurred but
probably not related to nitrate dosing. No gross pathology was seen
(Winter & Hokanson, 1964).
Acute toxicity
Route Minimum lethal dose LD50
Animal (mg/kg bw) (mg/kg bw) Reference
Rat - male oral 190-2 000 - Spector,
1956
Rat - female oral 460-1 200 - Spector,
1956
Rat oral - 3 236 USFDA
Short-term studies
Dog
Two dogs were fed 2% of sodium nitrate in their diets for 105
days and for 125 days without any adverse effects (Lehman, 1958).
Cattle
Most data have been obtained from livestock fed various forage
crops with a high nitrate content. Poisoning depends upon the
conversion of the nitrate to nitrite by the intestinal flora. The
lowest level that may result in fatal poisoning in cattle has been
reported to be 1.5% of potassium nitrate in the forage (Bradley et
al., 1940).
Long-term studies
Rat
Sodium nitrate was fed to four groups of 20 rats each at dosages
of 0.1%, 1%, 5% and 10% of the diet for two years. Slight growth
depression occurred at the 5% level, and additional morphological
changes due to inanition occurred at the 10% level (Rosenfield &
Huston, 1950).
OBSERVATIONS IN MAN
Poisoning in man may result from a total oral daily dose in
excess of 4 g or from a single dose of more than 1 g. 8 g may be fatal
and 13-15 g are generally fatal (Sollmann, 1957).
Numerous cases have been reported of poisoning in small children
and infants from the use of well water containing nitrates. Among
these, there were 26 cases in which the nitrate nitrogen content
of the well water was 21-50 ppm (0.0021-0.005%) (93-221 ppm
(0.0093-0.0221%) as NO3); 54 cases in which it was 51-100 ppm
(0.0051-0.01%) (221-443 ppm (0.0221-0.0443%) as NO3, and 52 cases in
which it was over 100 ppm (0.01%) (443 ppm (0.0443%) as NO3)
(Rosenfield & Huston, 1950).
On the other hand 30-60 g/day of sodium nitrate have been taken
for two months as acidifying diuretic without marked disturbance
(Sollmann, 1957). A 13-year-old boy took 0.12 g/kg daily for a year
without injury (Harper, 1949).
In one instance, a level as low as 50 ppm (0.005%) (as NO3) in
tap water produced 72% methaemoglobinaemia in a dyspeptic child (Thal
et al., 1961).
Healthy babies, however, have tolerated quantities up to
21 mg/kg bw (as NO3) for one week without any disturbance (Kübler,
1958).
The safe upper limit for nitrate in the drinking-water of babies
is probably 10-20 ppm (0.001-0.002%). Hypersensitivity to sodium
nitrate, taking the form of recurrent arthritic attacks has been
reported in man (Epstein, 1969).
Comments:
In the toxicological evaluation of nitrates, it is important to
take into account the amount of nitrate already present in the food as
well as in potable water (WHO, 1971).
Babies less than six months are especially sensitive to nitrate.
There are no data on which to arrive at an ADI for them. Nitrate
should on no account be added to baby foods. Water with high nitrate
content is unsuitable for the preparation of baby foods (WHO, 1971).
EVALUATION
Level causing no toxicological effect
From consideration of the long-term study in rats, the level
of sodium nitrate causing no demonstrable effect over a period
approximating to the life span is assessed at 1% of the diet, or
500 mg/kg bw daily. In the short-term study with dogs fed 2% sodium
nitrate in the diet for 105 days, the level producing no demonstrable
effect likewise corresponds to 500 mg/kg bw per day.
Estimate of acceptable daily intake for man
0-5 mg/kg bw.*
REFERENCES
Bloomfield, R. A. et al. (1961) Bibra Bull., 1, 32
Bradley, W. B., Eppson, H. F. & Beath, O. A. (1940) Wyom. Univ. agr.
exp. Stat. Bull., 241, 20
Emerick, R. J. & Olson, O. E. (1962) J. Nutr., 79, 171
Epstein, S. (1969) Ann. Allergy, 27, 343
Harper, E. (1949) Virginia Med. Monthly, 76, 32
Kübler, W. (1958) Z. Kinderheilk., 81, 405
Lehman, A. J. (1958) Quart. Bull. Ass. Food Drug Off., 22, 136
McIlwain, P. K. & Schipper, I. A. (1963) J. Amer. Vet. Med. Ass., 142,
502
* Calculated as sodium nitrate.
Rosenfield, A. B. & Huston, R. (1950) Minn. Med., 33, 787
Sleight, S. D. & Atallah, O. A. (1968) Toxic. appl. Pharmac., 12, 170
Sollmann, T. (1957) A manual of pharmacology, Saunders, Philadelphia &
London
Spector, W. S. ed. (1956) Handbook of toxicology, Saunders,
Philadelphia & London, vol. 1
Thal, W. Lachhein, L. & Martinek, M. (1961) Arch. Toxikol., 19, 25
United States Food and Drug Administration (Unpublished data)
World Health Organization (1971) International standards for drinking
water, 3rd ed.
Winter, A. J. & Kokanson, J. F. (1964) Am. J. Vet. Res., 35, 353
Wyngaarden & Wright (1952) Endocrinol., 50, 537
See Also:
Toxicological Abbreviations