FAO, PL:CP/15
    WHO/Food Add./67.32


    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party and the WHO Expert Committee on
    Pesticide Residues, which met in Geneva, 14-21 November 1966.1

    1 Report of a Joint Meeting of the FAO Working Party and the WHO
    Expert Committee on Pesticide Residues, FAO Agricultural Studies, in
    press; Wld Hlth Org. techn. Rep. Ser., 1967, in press







    Explanatory Note

    Phenylmercury acetate is an important example of twenty or more
    organomercury compounds used as fungicides in agriculture. They have
    the general structure R-Hg-X where R is an alkyl, alkoxyalkyl or aryl
    organic radical and where the bond with the X group has the character
    of a salt with a substance (acid, amide, phenol, etc.) having a
    dissociating hydrogen ion.

    Some other important compounds, listed in accordance with their
    organic radicals, are as follows:-

    a)   methylmercury compounds               Synonym

         methylmercury dicyandiamide           MMD Panogen(R)
         methylmercury iodide                  MMI

    b)   ethylmercury compounds

         ethylmercury chloride                 EMC
         ethylmercury urea                     EMU
         ethylmercury phosphate                EMP
         ethylmercury p-toluene sulphonamide   EMTS
         ethylmercury sulphate                 EMS

    c)   alkoxyethylmercury compounds

         ethoxyethylmercury chloride
         methoxyethylmercury chloride          MMC
         methoxyethylmercury acetate

    d)   arylmercury compounds

         phenylmercury chloride                PMC
         phenylmercury iodide                  PMI
         phenylmercury urea                    PMU
         methanodinaphtho-disulphonate         Murfixtan,(R) PMF
         phenylmercury salicylate
         NN-dimethyldithiocarbamate            Phelam(R)
         tolylmercury chloride                 TMC
         p-toluenesulfonanilide                TMTS

    Physical properties

    The alkyl compounds are generally the more volatile and the aryl the
    least volatile. The solubility in water of the aryl compounds also is
    lower than the corresponding alkyl ones. The stability and
    particularly the sensitivity to reducing agents with the eventual
    production of metallic mercury, varies from one compound to another.

    (R) = proprietary name.


    Biochemical aspects

    In rats, phenylmercuric acetate is readily absorbed from the
    gastrointestinal tract (Fitzhugh et al., 1950, Prickett et al., 1950).
    The major route of elimination of mercury after oral, intramuscular or
    intravenous administration of PMA is by way of the bile and excretion
    into the alimentary tract (Berlin & Ullberg, 1963; Prickett et al.,

    PMA given orally and intramuscularly to 87 chicks, intramuscularly to
    12 rats, and intravenously to 4 dogs, was absorbed apparently
    unchanged.  After about 96 hours no PMA could be detected in the
    tissues, but inorganic mercury accumulated in the liver and kidney
    (Miller et al., 1960). These findings were confirmed by studies with
    radioactive PMA (Berlin & Ullberg, 1963). Excretion by the kidneys was
    in the form of inorganic mercury and not as PMA (Berlin, 1963; Miller
    et al., 1960).

    The influence of 2,3-dimercaprol (BAL), 0.4 mg/kg, on the body
    distribution of mercury was studied in mice. When
    phenyl-203Hg-acetate was given as a single intravenous dose (0.5
    mg/kg as Hg) or as daily injections (1 and 3 mg/kg as Hg for 16 days),
    it was shown that BAL effected a redistribution of the body mercury
    load. A persistent increase in the concentration of mercury was noted
    in the brain, liver and muscle, while a decrease was found in the
    kidney (Berlin & Rylander, 1964).

    In comparison with methylmercurydicyanamide (MMD), a steady state of
    excretion was reached much faster when rats were given PMA;
    furthermore, a much lower accumulation of Hg was found in the brain of
    rats after the administration of PMA than after MMD (Gage, 1964).

    Acute toxicity

    Animal      Route             LD50                          References
                                  mg/kg body-weight

    Rat         Intraperitoneal       10                         Swensson, 1952
                                  (approx. lethal dose)

    Mouse       Oral                  70                         Goldberg et al.,1950
    Chick       Oral                  60                         Miller et al., 1960
                                  (approx. lethal dose)
    Short-term studies

    Rat. Rats were given intraperitoneal injections of PMA at dosages of
    1-2.5 mg/kg body-weight every other day for 4 weeks. The animals
    showed gradually increasing apathy, loss of weight, and finally
    neurological signs - (ataxia and paresis), especially at the higher
    dosages. Histopathological examination revealed damage to the granular
    layer and the Purkinje cells of the cerebellum, and to the spinal cord
    (Swensson, 1952).

    Rabbit. A rabbit was fed with a diet containing PMA for 130 days,
    the total amount of mercury consumed during the experimental period
    being 770 mg. The animal showed marked growth depression and died
    after 130 days. Chemical analysis revealed large amounts of mercury in
    the organs - 29 mg/kg organ-weight in the kidney, 0.52 mg/kg in the
    liver and 5.18 mg/kg in the gastro-intestinal tract - whereas a
    control rabbit showed only 0.06 mg/kg in the kidney and traces in the
    liver. Another rabbit fed a diet containing PMA for 100 days received
    a total amount of 6.9 mg of mercury. There was no abnormality in
    appearance or growth. The contents of mercury in the organs were 0.455
    mg/kg in the kidney and 0.042 mg/kg in the liver (Kluge et al., 1938).

    Guinea-pig. A guinea-pig was fed a diet containing PMA for 670 days
    and consumed a total of 20.4 mg during the whole experimental period.
    No ill-effects were observed in general appearance or growth. The
    mercury content of the kidney was 4.76 mg/kg organ-weight, whereas
    that of a control animal was 0.3 mg/kg (Kluge et al., 1938).

    Long-term studies

    Rat. Groups, each of 10-12 male and 10-12 female rats, were fed
    diets containing 0.1, 0.5, 2.5, 10, 40 and 160 ppm of PMA for 2 years.
    The growth was significantly retarded at 40 ppm and upward, and also
    retarded in males at 10 ppm. The average survival period was reduced
    at 160 ppm, while other dosage levels did not affect the mortality
    rates. Gross pathological examination revealed enlargement and
    granularity of the kidney, and moderate paleness of the viscera
    suggestive of anaemia at 0.5 ppm and upward. Microscopic studies
    demonstrated severe damage of the tubules of the kidney at 10 ppm in
    females at one year, and there was detectable kidney damage at 0.5 ppm
    in both sexes at 2 years. In males, marked changes in the renal
    tubules were observed at 160 ppm at one year, and moderate to slight
    at 40 ppm in both sexes. There were also some changes in the bone
    marrow and caeca at high dosage levels. Accumulation of mercury
    occurred in the organs and the storage of mercury in the kidney and
    liver in the group at 0.1 ppm PMA was higher than that in the control
    group (Fitzhugh et al., 1950).


    It is clear from the biochemical studies that PMA may give rise to
    mercury accumulation in the tissues and the long-term study in the rat
    failed to demonstrate a no-effect level.


    Level causing no toxicological effect in rat

    A no-effect level has not been demonstrated.

    Estimate of acceptable daily intake for man

    The level of 0.1 ppm, equivalent to 0.005 mg/kg body-weight per day,
    produced a slight effect in the rat. Even if this figure were to be
    adopted as a maximum no-effect level and the customary safety factor
    applied this would give an acceptable daily intake for man of 0.00005
    mg/kg body-weight. This is tantamount to zero. It is undesirable that
    for the general population there should be any increase in the natural
    intake of mercury.


    Use pattern

    (a) General properties

    The suitability of a particular organomercury compound for a
    particular purpose is partly dependent upon its physical properties.
    Phenyl mercury acetate and other aryl compounds, which have a low
    volatility, are more suitable where persistence is required. Under

    certain conditions however (e.g. in enclosed seed dressing machinery)
    their higher volatility enables the alkyl compounds to be applied more
    effectively. Phillips, Dixon & Lidzey (1959) list the vapour pressures
    of many of these compounds and compare their volatilities under
    different conditions.

    (b) Pre-harvest treatments

    Organomercury compounds are used in seed dressings, orchard sprays,
    foliar dusts and as glass house aerosols for the control of fungal
    diseases. Since analysis seldom distinguishes between organically
    bound and inorganic mercury, it is worth noting also that inorganic
    mercury compounds are used for soil and root treatment. Powdered and
    liquid preparations containing both alkyl and aryl mercury compounds
    are used as cereal seed dressing. Ethylmercury phosphate is fairly
    specifically used on beet seed and this and other seed dressings are
    likely to lead to residue problems. Phenylmercury foliar dusts are
    used to control rice blast disease.

    (c) Post-harvest treatments

    Organomercurials are not used post-harvest other than as bulb, tuber
    and cereal seed dressings. It is possible that small residues may be
    picked up e.g. by fruits, from paper wrappings or other containers
    which have been treated with organomercurial fungicides.

    (d) Other uses

    Organomercury compounds, particularly phenylmercury salts, are used
    widely as fungicides in industry, e.g. on wood pulp, paper and various
    building materials.


    Existing tolerances all refer to residues found and expressed as
    mercury (Hg) without distinction between the forms in which the metal
    may actually be present in food. Uses of organomercurials which could
    lead to a detectable residue in food produce are not allowed in the
    United States.

    Residues resulting from supervised trials

    (a) Pre-harvest treatments

    A number of workers have measured residues in apples (summarized by
    Miller, 1957) and tomatoes, (e.g. Beidas & Higgins 1957, 1959; Ross
    & Stewart, 1960; Stone, 1962). Foliar applications of organomercurials
    in general lead to translocation of the mercury. Pickard & Martin
    (1963) studied the uptake of mercury by roots, leaves and fruits after
    applications at commercial rates. The roots of lettuce and dwarf
    bean plants accumulate mercury from nutrient solution containing
    phenylmercuric acetate, but little translocation to the foliage

    occurs. Root treatment of cauliflower seedlings with calomel or
    mercuric chloride before planting lead to absorption by the roots but
    the curds are uncontaminated. Carrots grown in soil treated with
    mercuric chloride contained up to 0.05 ppm and roots from
    calomel-treated soil showed 0.02 ppm Hg when seed was sown immediately
    after soil treatment; delay in seeding eliminated contamination.
    Lettuces, dwarf beans, carrots, potatoes and turnips from field
    experiments using calomel and mercuric oxide soil treatments showed
    mercury residues not exceeding 0.03 ppm. Apple leaves absorbed
    mercury deposited as phenylmercuric acetate, within a few days.
    Mercury was found in young coffee and citrus lime leaves that
    emerged after spraying with phenylmercuric acetate, indicating
    translocation. Broad bean plants sprayed with phenylmercuric
    acetate at early flowering later showed 0.02 ppm in the pods, 0.04 ppm
    in the seeds and 0.07 ppm Hg in the roots. Application of
    phenylmercuric acetate to the leaves of potato plants led to
    residues in the tubers (0.1 ppm in peel, 0.18 ppm Hg in flesh) and
    roots (1.2 ppm Hg). Apples from commercially sprayed orchards
    contained 0.05 ppm Hg distributed between the peel, flesh and core.
    Five applications of phenylmercuric acetate under experimental
    conditions, gave 0.24 ppm on whole fruits; one third of the mercury
    was located in the flesh. Mercury deposited on the surface of the
    fruits was largely held in the cuticle; much of the mercury in the
    flesh arose from translocation from the leaves. Mercury was detected
    in the fruitlets (0.4 ppm) and young leaves (0.07 ppm) of trees
    sprayed the previous year. The bark of trees treated for six
    consecutive years contained 4 ppm Hg. Naturally-occurring mercury in
    soils varied between 0.05 and 0.12 ppm. Soil from beneath sprayed
    apple trees contained 0.2 ppm Hg. Soils treated with inorganic
    mercurials showed up to 2 ppm Hg (untreated 0.05 ppm).

    In Japan the stage of plant growth affected the amount of residual Hg
    in rice. Unpolished rice harvested from the rice plant sprayed with
    PMA before the plant comes to ear contained 0.12 ppm of Hg, whereas,
    the grain harvested from the plant treated with PMA after the plant
    comes to ear contained 0.23 ppm of Hg. Epps (1966) examined rice and
    various milling by-products, from rice treated in field tests with
    phenylmercury acetate; residues ranged from 1.3 ppm Hg in straw and
    0.8 ppm in bran to 0.1 - 0.2 ppm in the endosperm.

    Smart (1963, 1964) measured residues in the eggs, flesh, etc., of hens
    fed wheat treated with methylmercury dicyandiamide and in potatoes
    following foliar spray application with phenylmercury chloride. Only
    about 10 per cent of an organomercury compound on dressed grain was
    removed by washing. Translocation of residues from potato foliage to
    tubers has been demonstrated by Ross & Stewart (1964). Egan & Lidzey
    (1960) and Bland & Egan (1963) showed that successive treatments of
    tomatoes with phenylmercury salicylate under commercial greenhouse
    conditions resulted in residues of the order of 0.01 (n + 1) ppm where
    "n" is the number of treatments up to the eighth; and falls thereafter
    by about 0.01 ppm for each subsequent treatment.

    Mercury residues measured in Japan (direct communications, 1965) were
    found to be 0.098 + 0.008 ppm Hg in peel and 0.025 + 0.008 ppm
    in flesh of mandarin orange. Untreated fruit contained 0.03 - 0.05 ppm
    Hg in peel and 0.01 - 0.02 ppm Hg in flesh. The residues in mandarin
    oranges sprayed with water-soluble mercurial fungicides (PMA or PMF)
    were generally greater than those in fruit sprayed with less
    water-soluble fungicides (PMI or PMO). After five foliar applications
    of MMC (12.5 ppm as Hg) to peach trees, amounts of Hg were in the
    range of 0.21 - 0.25 ppm in peel and 0.02 - 0.04 ppm in flesh. Similar
    treatments of a mixture of PMPS, EMP, and EMU (12.5 ppm as Hg)
    resulted in an Hg residue in the range of 0.27 - 0.28 ppm in peel and
    0.06 - 0.07 ppm in flesh.

    Residues in food moving in commerce

    Since 1961 surveys have been undertaken in Sweden on the occurrence of
    mercury in eggs, game, fish and various other foodstuffs. This has
    been associated with enquiries into possible effects on wildlife from
    the use of mercury fungicides in industry and agriculture. The
    residues found in human food have ranged from a mean of 29 parts per
    thousand million in eggs marketed in Sweden, to over 20 ppm in the
    livers of some 10 per cent of the game birds examined. Wheat, thought
    to be untreated, from various parts of the United States of America,
    examined by atomic absorption spectroscopy by Pappas and Rosenberg
    (1966) showed 0.013 to 0.13 ppm Hg and 1.5 ppm Hg in commercially
    treated samples. The same authors found an average of 0.02 ppm in
    haddock fillets while eggs were virtually mercury-free (less than
    0.005 ppm). In the examination of various foods in Japan (direct
    communication) residues found were: polished rice 0.04 - 0.07;
    unpolished rice 0.07 - 0.14; wheat flour 0.05; fruits and vegetables
    0.02 - 0.06; meats 0.03 - 0.16; fish 0.00 - 0.10, (tuna 0.3 - 0.55);
    milk 0.01 and hen eggs 0.08. Small amounts of mercury are very
    widespread in nature. The extent of general environmental
    contamination has been reviewed by Goldwater (1964) who quotes results
    of residue analysis of food including bananas (0.31 ppm) canned
    chicken (0.15 ppm) butter (0.14 ppm) Cheddar Cheese (0.082 ppm)
    white bread (0.08 ppm) beer (0.04 ppm) and rice (0.02 ppm).

    In each of these instances the figures are quoted as ppm Hg. Figures
    for "organic" and "inorganic" mercury have rarely been obtained, there
    appear to be none for residues as specified organomercury compounds.

    Residues at the time or consumption

    The meeting had no data on the effects of storage, cooking and other
    processing. Reductions no doubt occur from volatilisation during
    storage and from washing of crops and trimming (e.g. of outside parts
    of fruits and vegetables) prior to cooking. Some losses during
    cooking, also are likely due to the volatility of these compounds, but
    figures for such losses were not available.

    Methods of residue analysis

    There is an extensive literature on mercury residue analysis, the
    greater part of which is concerned only with total mercury and not
    with intact organomercury residues as such. There is a wide 
    divergence between the toxicities of the various mercury compounds and
    often a lack of information concerning the chemical nature of the 
    residues (e.g. in edible animal material) after the use of a given

    (a) Total mercury (inorganic and organic)

    Relatively simple methods, such as the Reinsch test, have long been
    used to detect traces of metals including mercury and, with
    supplementary confirmatory tests, can be used to distinguish mercury
    from other residues and approximately to measure them. Very many of
    the modern total mercury methods are based on extraction of the metal
    by organic complexing agents, principally diphenyl thiocarbazone
    (dithizone) into chloroform solution (e.g. Kanazawa & Sato, 1959).
    Examples are the IUPAC method of Ljunggren and Westermark (1960) for
    the determination of mercury foodstuffs and the method of the
    Association of Official Analytical Chemists (1965), both based on the
    method of Klein (1952). Conditions can be adjusted so that mercury is
    selectively extracted. There are a number of variations of the method
    of measuring the extracted mercury complex. These are normally based
    on the intensity of colour of the complex solution, or of the
    uncomplexed dithizone remaining when a measured excess is used;
    alternatively a combined titrimetric-colorimetric procedure is used in
    which small measured amounts of standardized dithizone are added
    successively to the prepared sample extract until no reagent colour
    change occurs. Such methods, which are sensitive to 0.01 ppm of Hg or
    less in favourable cases, have been applied to a wide range of
    biological tissue including many foods.

    A source of difficulty, which arises also in the more modern
    radioactivation method of analysis (q.v.), lies in the relatively high
    volatility of mercury and its compounds. Biological tissue is normally
    first oxidized, e.g. by warming with nitric acid. If too much heat is
    applied or is allowed to generate, some of the mercury may be lost
    from the sample as in some of the earlier work of Klein, in which the
    condensate was trapped in a closed (reflux) oxidation system the main
    digest thus becoming more concentrated with respect to acid with a
    consequent elevation in boiling point. Gorsuch (1950) has made a
    thorough study of losses in wet ashing, using radiochemical methods;
    he has in this way shown the need to condense digestion vapours and
    return them to the main digest. Gutenmann & Lisk (1960) and Gouverneur
    & Hoedman (1964) used a modified Schoniger combustion method in place
    of wet digestion. Conditions which emphasize cool oxidation were
    described by Abbott and Johnson (1957), and examined collaboratively
    for apples and tomatoes in Britain by the Joint Mercury Residues Panel
    (1961). A further collaborative study of a method for amounts of

    mercury down to 0.5 micrograms in organic matter has been described by
    the Society in Analytical Chemistry (1965). Truhaut and Boudene (1963)
    have used a simple flask in which oxidation, complex extraction and
    colorimetric measurement can be completed without transfer.

    Radioactivation methods of residue analysis are sensitive to at least
    0.01 ppm Hg and avoid the need for oxidation and extraction steps.
    However, preliminary removal of water from biological tissue may be
    necessary and this again poses the problem of volatility of mercury
    and its compound. Erwall & Westermark (1964) described the application
    of this technique to foods. An atomic pile is necessary for the
    activation stage and where this is available the technique can be
    widely applied provided the dehydration stage is satisfactory with a
    chemical separation the sensitivity level is 0.005 ppm on a 0.2 gram
    sample. This sensitivity could also be obtained with a gamma counter
    without spectrometry. If the irradiated sample is counted direct
    without chemical separation, a gamma spectrometer would have to be
    used. The sensitivity would then depend on the other short-lived
    activities produced (e.g. sodium-24) and 0.5 ppm on a 0.2 gram sample
    appears to be reasonable. A typical conventional dithizone method has
    a sensitivity of 0.02 ppm on a 10 gram sample. Neutron activation
    analysis using Hg-203 (half-life 47 days) would be less sensitive than
    using Hg-197 by a factor of 20 and a longer irradiation time would be
    needed. In the method of Ljunggren & Westermark (1960) biological
    material is sealed into quartz tubes, activated and 77-keV gamma
    radiation emission from Hg-197 measured after a cooling period of two
    days. This method is sensitive to five nanograms of Hg.

    Schachter (1966) has described the use of atomic absorption
    spectroscopy to mercury vapour in the cold state. High sensitivity is
    achieved using the whole of the ultraviolet spectrum of a quartz
    mercury vapour lamp. Thus one gram of ground wheat is combusted in a
    Schoniger flask and the mercury vapour collected in dil. HCl,
    converted to sulfide, pyrolysed in a train of nitrogen in a small
    furnace at 650°C and the mercury vapour cooled and measured. Hamilton
    & Ruthven (1966) have described a field apparatus for the detection
    and estimation of organomercury dusts and vapours in the atmosphere; a
    similar official method is published in Britain.

    (b) Organically bound mercury

    Limited work has been done on the separation and measurement of
    unchanged organomercury compounds. Miller, Lissis & Csonka (1958)
    extract phenylmercury compounds from animal's tissue with chloroform
    and determine the phenylmercury adsorptiometrically as the dithizone
    complex. Kimura & Miller (1964) use different extraction solvents for
    (a) phenyl and alkyl mercurials and (b) diphenyl dialkyl mercurials
    and (c) ionic mercury. The reaction of dithizone with organomercury
    compounds has been reviewed by Irving & Cox (1961). It should be
    possible to devise extraction procedures in which intact radicals such
    as phenyl-mercury can be isolated (e.g. as the chloride) and then
    separated by paper. Electrophoretic separations have also been studied
    or thin layer chromatographic procedures and identified and measured.


    Since no acceptable daily intake level can be given for mercury it is
    not possible to recommend a tolerance or a temporary tolerance. Small
    natural concentrations of mercury appear to be widespread but the
    levels vary from area to area; it is also difficult therefore, to
    suggest a practical residue limit for mercury. By way of guidance,
    however, practical residue limits of from 0.02 ppm of mercury to 0.05
    ppm, according to local conditions, are suggested.

    Further work or information

    Sensitive methods of analysis specifically for alkyl, alkoxy and aryl
    mercurials should be developed and used to study the occurrence of
    these forms of mercury in foodstuffs from different sources: these
    should include food stuffs known to have been treated with specified
    compounds. Such analytical methods should also be used to study the
    possible conversion of aryl mercury compounds to more toxic ones.


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    Movement and accumulation of mercury in apple trees and soil, (1962),
    Can. J. Plant Sci., 42: 280-285. Note on mercury residues in
    potatoes, (1962), Can. J. Plant Sci., 42; 370 and Mercury residues
    in potatoes in relation to foliar sprays of phenyl mercury chloride,
    (1964) Can. J. Plant Sci., 44: 123-125)

    Schachter, M. M. (1966) Apparatus for cold vapour atomic absorption of
    mercury. J. Assoc. Off. Anal. Chemists, 49 (4): 778-782

    Smart, N. A., and Lloyd, M. K. (1963) Mercury residues on eggs, Flesh
    and livers of hens fed on wheat treated with methylmercury
    dicyandiamide. J. Sci. Food Agric., 14: 734-740

    Smart, N. A. (1963) Retention of organomercury compounds in dressed
    grain after washing. Nature, 199: 1206-1207

    Smart, N. A. (1964) Mercury residues in potatoes following application
    of foliar spray containing phenylmercury chloride. J. Sci. Food
    Agric., 15: 102-107

    Society or Analytical Chemistry, Analytical Methods Committee. (1965)
    The determination of small amounts of mercury in organic matter.
    Analyst, 90: 515-530

    Stone, H. M. (1964) Mercury content of apples treated with
    phenylmercury dimethyl-dithiocarbamate. New Zealand J. Agr. Res.,
    7: 439

    Swensson, H., and Ulfarson, U. (1963) Toxicology of organic mercury
    compounds used as fungicides. Occup. Hlth Rev., 15 (3): 5

    Truhaut, R. and Boudene, C. (1963) Microdosage du mercure dans les
    dendtrees alimentaires. Ann. Falsif. Expert. Chim., 56: 225-242

    See Also:
       Toxicological Abbreviations