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.


    SODIUM NITRATE

    CHEMICAL NAME         Sodium nitrate

    SYNONYMS              Chile saltpetre; cubic or soda nitre

    EMPIRICAL FORMULA     NaNO3

    MOLECULAR WEIGHT      85.00

    DEFINITION            Sodium nitrate after drying contains not less
                          than 99.0% of NaNO3 and conforms to the
                          following specifications.

    DESCRIPTION           Clear, colourless, odourless, transparent
                          crystals, or white granules or powder.
                          Deliquescent in moist air.

    USE                   As an antimicrobial preservative and colour
                          fixative in meat, fish and cheese products.
                          Often need In combination with nitrites.

    IDENTIFICATION TESTS

    A.   Solubility:  Water:      1 g is soluble in 1.1 ml
                      Ethanol:    1 g is soluble in 125 ml 
                      Glycerol:   Slightly soluble

    B.   Sodium nitrate yields with uranyl zinc acetate TS a golden-yellow
         precipitate, which forms after several minutes' agitation.

    C.   Brownish red fumes are evolved when sodium nitrate is heated with
         sulfuric acid and metallic copper.

    PURITY TESTS

    Loss on drying:  Not more than 2% after drying at 105°C for 4 hours.

    pH of a 5% solution:  Dissolve 10 g in 200 ml of carbon dioxide- and
    ammonia-water, the pH of this solution is between 5.5 and 8.3.

    Arsenic:  Not more than 3 mg/kg.

    Lead:  Not more than 10 mg/kg.

    Nitrite:  Not more than 1000 mg/kg.

    Dissolve 1 g in 50 ml of carbon dioxide- and ammonia-free water, add 2
    drops of dilute ammonia TS, and filter if necessary through paper into
    a 100-ml volumetric fleck.  Add 10 ml of dilute acetic acid TS, shake
    the mixture, and allow to stand for 5 minutes.  Any colour produced is

    not darker than that of a complete blank to which 1 ml of nitrite
    standard TS is added.

    Heavy metals:  Not more than 20 mg/kg.

    Dissolve 3 g in water and dilute to 30 ml.  Adjust 20 ml of this
    solution to a pH between 3.0 and 4.0 and dilute with water to 40 ml.
    To the remaining 10 ml of sample solution add water to make 35 ml, add
    a volume of standard lead TS equivalent to 0.02 mg of lead and adjust
    to a pH between 3.0 and 4.0 and dilute to 40 ml.  To each solution add
    10 ml of hydrogen sulfide TS, mix, transfer to 50-ml Nessler tubes and
    observe after 10 minutes.  The colour of the test solution should be
    no darker than that of the solution containing the standard lead
    solution.

    ASSAY

    Weigh 1.000 g of sodium nitrate previously dried at 105°C for 4 hours
    into the flask of an ammonia distillation apparatus.  Add 10 g of
    Devarda's Alloya and 25 ml of N sulfuric acid and allow the flask
    to stand, protected from ammonia in the atmosphere, for 1 hour.  Add
    100 ml of a solution of sodium hydroxide (15 in 100), connect the
    flask to the remainder of the apparatus and distil 100 ml, collecting
    the distillate under the surface of 25.0 ml of N hydrochloric acid. 
    Rinse the condenser into the receiving flask, add methyl red-methylene
    blue TS and titrate the excess acid with N sodium hydroxide.

               (25-x) 
    %NaNO3 =            ? 8.5
                 w

    POTASSIUM NITRATE

    CHEMICAL NAME         Potassium nitrate

    SYNONYMS              Saltpetre, nitre

    EMPIRICAL FORMULA     KNO3

    MOLECULAR WEIGHT      101.11

    DEFINITION            Potassium nitrate after drying contains not
                          less than 99% of KNO3 and conforms to the
                          following specifications.

    DESCRIPTION           Colourless, odourless, transparent prisms, or
                          white granular or crystalline powder, having a
                          cooling, saline, pungent taste.

                   

    a Devarda's Alloy (Devarda's Metal) is a grey powder composed of 50
    parts of copper, 45 parts of aluminium and 5 parts of zinc.

    USE                   As an antimicrobial preservative and colour
                          fixative in meat, fish and cheese products;
                          often used in combination with nitrites.

    IDENTIFICATION TESTS

    A.   Solubility:  Water:     1 g is soluble in 3 ml
                      Ethanol:   1 g is soluble In 620 ml
                      Glycerol:  Soluble

    B.   In neutral, concentrated or moderately concentrated solutions of
         potassium salts, sodium bitartrate TS slowly produces a white,
         crystalline precipitate which is soluble in ammonia TS and in
         solutions of alkali hydroxides or carbonates.

    C.   Brownish red fumes are evolved when potassium nitrate is heated
         with sulfuric acid and metallic copper.

    PURITY TESTS

    Loss on drying:  Dry at 105°C for 4 hours: it loses not more than 1%
    of its weight.

    pH of a 5% solution:  Dissolve 10 g in 200 ml of carbon dioxide- and
    ammonia-free water: the pH of this solution is between 4.5 and 8.5.

    Arsenic:  Not more than 3 mg/kg.

    Lead:  Not more than 5 mg/kg.

    Heavy metals:  Not more than 20 mg/kg.

    Dissolve 3 g in water and dilute to 30 ml.  Adjust 20 ml of this
    solution to a pH between 3.0 and 4.0 and dilute with water to 40 ml.
    To the remaining 10 ml of sample solution add water to make 35 ml, add
    a volume of standard lead TS equivalent to 0.02 mg of lead, and adjust
    to a pH between 3.0 and 4.0, and dilute to 40 ml.  To each solution
    add 10 ml of hydrogen sulfide TS,  mix, transfer to 50-ml Nessler
    tubes and observe after 10 minutes.  The colour of the test solution
    should be no darker than that of the solution containing the standard
    lead solution.

    Nitrite:  Not more than 1000 mg/kg.

    Dissolve 1 g in 50 ml of carbon dioxide- and ammonia-free water, add 2
    drops of diluted ammonia TS, and filter if necessary through paper
    into a 100-ml volumetric flask.  Add 10 ml of potassium iodide TS, 
    2 ml of starch TS, and 10 ml of diluted acetic acid TS, shake the
    mixture and allow to stand for 5 minutes.  Any colour produced is not
    darker than that of a complete blank to which 1 ml of nitrite standard
    TS is added.

    ASSAY

    Weigh 1.000 g of potassium nitrate previously dried at 105°C for 4
    hours into the flask of an ammonia distillation apparatus.  Add 10 g
    of Devarda's Alloy and 25 ml of 1 N sulfuric acid and allow the
    flask to stand, protected from ammonia in the atmosphere, for 1 hour. 
    Add 100 ml of a solution of sodium hydroxide (15 in 100), connect the
    flask to the reminder of the apparatus and distil 100 ml, collecting
    the distillate under the surface of 25.0 ml of 1 N hydrochloric
    acid. Rinse the condenser into the receiving flask, add methyl
    red-methylene blue TS and titrate the excess acid with 1 N sodium
    hydroxide.

                (25-x) 
    %KNO3  =             ?10.11
                   w

    Biological Data

    Biochemical aspects

    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,1 and in babies less than 6 months old, especially in
    dyspeptic infants.2

    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.3

    Acute toxicity

                                                                                   

    Animal        Route    Minimum lethal dose        LD50          Reference
                           (mg/kg body-weight)       (mg/kg 
                                                   body-weight)
                                                                               

    Rat-male      oral         190-2000               -                4
    Rat-female    oral         460-1200               -                4
    Rat           oral         -                      3236             5

                                                                               
    
    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.6

    Short-term studies

    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.1

    Dog.  Two dogs were fed 2% of sodium nitrate in their diets for 105
    days and for 125 days without any adverse effects.7

    Man.  Numerous cases have been reported of poisoning in small
    children and infants from the use of well-water containing nitrates. 
    Among these, them were 26 cases in which the nitrate nitrogen content
    of the well-water was 21-50 ppm (93-221 ppm as NO3), 54 cases in
    which it was 51-100 ppm (221-443 ppm as NO3), and 52 cases in which
    it was over 100 ppm (443 ppm as NO3).

    In one instance, a level as low as 50 ppm (as NO3) in tap water
    produced 72% methaemoglobinaemia in a dyspeptic child.2  Healthy
    babies, however, have tolerated quantities up to 21 mg/kg body-weight
    (as NO3) for one week without any disturbance.9

    Long-term studies

    Rat.  Sodium nitrate was fed to 4 groups of 20 rats each at dosages of
    0.1%, 1%, 5% and 10% of the diet for 2 years.  Slight growth
    depression occurred at the 5% level, and additional morphological
    changes due to inanition occurred at the 10% level.7

    Evaluation

    Levels causing no significant toxicological effect in animals

    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 body-weight
    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 body-weight per day.

    Estimate of acceptable daily intakes for man

                                               mg/kg body-weight
                                              (as sodium nitrate)

             Unconditional acceptance                 0-5

             Conditional acceptance                   5-10

    Comment

    In establishing tolerances for added nitrate it is important to take
    into account the amount of nitrate already present in other foods.

    The sensitivity of normal babies and the apparent sensitivity of
    dyspeptic babies makes it impossible to make an estimate of an
    acceptable dose for babies of 6 months of age or less on the basis of
    animal experimentation or clinical experience.  Nitrate should on no
    account be added to baby-foods.  Water with high nitrate content is
    unsuitable for the preparation of baby-foods.

    It is recommended that, if possible, sodium nitrate should be used as
    a 2.5% mixture with common salt.

    References

    1.  Bradley, W. B., Eppson, H. F. & Beath, O. A. (1940) Wyom. Univ.
    agr. exp. Stat. Bull., 24l, 20

    2.  Thal, W., Lachhein, L. & Martinek, M. (1961) Arch. Toxikol., 19,
    25

    3.  Kilgore, L., Almon, L. & Geiger, M. (1959) J. Nutr., 69, 39

    4.  Spector, W. S. ed. (1956) Handbook of toxicology, Saunders,
    Philadelphia & London, vol. 1

    5.  United States Food and Drug Administration (Unpublished data)

    6.  Sollmann, T. (1957) A manual of pharmacology, Saunders,
    Philadelphia & London

    7.  Lehman, A. J. (1958) Quart.  Bull. Ass. Food Drug Off., 22, 136

    8.  Rosenfield, A. B. & Huston, R. (1950) Minn. Med., 33, 787

    9.  Kübler, W. (1958) Z. Kinderheilk., 81, 405
    

    See Also:
       Toxicological Abbreviations
       Sodium nitrate (ICSC)
       SODIUM NITRATE (JECFA Evaluation)