FAO Meeting Report No. PL/1965/10/2
    WHO/Food Add/28.65


    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Committee on Pesticides in Agriculture and
    the WHO Expert Committee on Pesticide Residues, which met 15-22 March

    Food and Agriculture Organization of the United Nations
    World Health Organization

    1 Report of the second joint meeting of the FAO Committee on
    Pesticides in Agriculture and the WHO Expert Committee on Pesticide
    Residues, FAO Meeting Report No. PL/1965/10; WHO/Food Add./26.65.

    (As derived from aluminium phosphide)



    Chemical name

         Hydrogen phosphide



    Empirical formula


    Structural formula


    Relevant physical and chemical properties

    Physical state (atmospheric pressure, 20°C): gas

    Boiling-point: -87.7°C

    Odour: like carbide

    Flammability limits in air: 1.79% and above, by volume


    Water: slightly soluble

    Specific gravity (liquid): 0.746

    Specific gravity (gas): 1.53


         Phosphine is not applied directly but is evolved from aluminium
    phosphide powders or tablets by the action of atmospheric moisture.
    The tablets contain fire-suppressing materials such as ammonium
    carbamate which gives off both ammonia gas and carbon dioxide to
    prevent combustion as the phosphine is generated at the beginning of
    fumigation. Phosphine is used principally as a grain fumigant. A usual
    rate of application is 6 to 10 tablets, each yielding 1 g of phosphine

    per ton of grain which is kept under fumigation for 72 hours at
    temperatures at or above 20°C. Under very favourable conditions doses
    as low as 3 tablets per ton have been used.


         As far as is known at present there are three different residues
    left in fumigated grains:

    (a) Phosphine itself.

    (b) Traces of unreacted aluminium phosphide.

    (c) A fine grey powder of aluminium hydroxide as the product of the
        reaction of water with aluminium phosphide.

         A detailed study (Bruce et al., 1962) of residues of phosphine in
    wheat fumigated under field conditions revealed a maximum residue of
    0.046 ppm of phosphine in grain which had been turned. In this sample
    the residue dropped to 0.006 ppm after aeration. The range of residues
    in fumigated wheat was from 0.001 ppm to 0.046 ppm. These residues
    were found in wheat fumigated at doses from 3 to 10 tablets per ton
    with the analyses made from 1 to 14 days after fumigation following
    various grain handling procedures, singly or in combination, such as
    turning, aerating, cleaning or washing. No significant residue of
    phosphine could be found in bread made from fumigated flour.

         Most of the unreacted aluminium phosphide decomposes rapidly as
    soon as the grain is moved.

         Aluminium phosphide is reported as being removed during the
    cleaning and washing of grain (Horak and Strosova, 1963).

    Effect of fumigant on treated crop

         As far as is known at present, with normal fumigation procedures,
    phosphine does not react chemically with the treated materials. In
    moist foodstuffs a slight increase of the total, phosphorus content
    may appear (Laue, 1954).

    Toxicological studies

         Phosphine is a very toxic gas with a cumulative effect. There are
    no data available on the acute LD50 of aluminium phosphide. The LD50
    for rats of the related compound zinc phosphide is 40.5 + 2.9 mg/kg
    (Johnson and Voss, 1952).

    Man:    2.8 mg phosphine/l are lethal for man in a short time (Flury
            and Zernik, 1931).

    The threshold limit for phosphine is set at 0.4 mg/m3 (Anon, 1964).

    Acute toxicity (Phosphine)

    Animal       Route    Concentration   Death occurred after the     References
                                          following time of exposure

    Rat          inhal.     0.68 mg/l     65-75 min.                   Neubert &
                                                                       Hoffmeister, 1960

    Rat            "        1.47 mg/l     35-50 min.

    Rat, rabbit    "         0.2-1%       30 min.                      Laue, 1954

    Rabbit         "         10 ppm       120 min. daily, during 2     Harger &
                                          days                         Spolyar, 1958

    Guinea-pig     "         25 ppm       4 hr daily, during 2 days          "

    Mouse          "         50 ppm       2 hr daily, during 1 day           "

    Cat            "         25 ppm       2, 3 to 4 hr daily, during
                                          3 days
    Short-term and long-term studies

         It is reported that rats, fed with grain which had been fumigated
    at excessive dosages, showed no ill effects, even when the grain was
    not cleaned before consumption (Schulemann, 1953).


         Materials treated with aluminium phosphide must be properly
    cleaned and washed before being processed for food, so that no residue
    of powder derived from the fumigant material reaches the consumer.

         An acceptable daily intake of phosphine or aluminium phosphide
    cannot be estimated until long-term toxicity data and metabolic
    studies are available.

    Further work required

         Long-term studies on two species of animals and research on the
    fate of the compound in food and its biochemical mechanism of action
    in animals.


    Anon. (1964) Threshold limit values for 1964, Arch. environm.
    Hlth., 9, 545

    Bruce, R. B, Robbins, A. J. & Tuft, T. O. (1962) J. Agric. Food
    Chem., 10, 18

    Flury, F. & Zernik, F. (1931) Schädliche Gase, Berlin, Springer

    Harger, R. N. & Spolyar, L. W. (1958) Arch. industr. Hlth, 18, 497

    Horak, E. & Strosova, J. (1963) Nlynsko Pekarensky Prumysl Tech.
    Skladovani Obili, 9, 486 (Chem. Abstr., 60, 16445c)

    Johnson, H. D. & Voss, E. (1952) J. Amer. pharm. Ass., 41, 468

    Laue, V. G. (1954) Nachrichtenblatt fur den deutschen
    Pflanzenschutzdienst., 8, 13

    Neubert, D. & Hoffmeister, I. (1960) Arch. exp. Path. u. Pharmak.,
    239, 219

    Schulemann (1953) Unpublished report from Degesch, Frankfurt-am-Main

    See Also:
       Toxicological Abbreviations