CHLORMEQUAT                      JMPR 1972


    The data relative to identity and residues in food and their
    evaluation were reviewed at the 1970 Joint FAO/WHO Meeting on
    Pesticide Residues (FAO/WHO, 1971). At that time the original reports
    of most of the biochemical and toxicological studies conducted with
    chlormequat were not available. Many of these data are now reviewed.



    Absorption, distribution and excretion

    An oral dose of chlormequat (chlorocholine chloride) labelled with
    14C was administered to male rats. The bulk (60.6%) was excreted in
    the urine in four hours and 96% was eliminated within 46.5 hours.
    Faecal excretion accounted for 2.3% and <1% was expired as 14CO2.
    The remaining 0.5% was found in the tissues, the largest amount being
    in the carcass (0.25%), intestines (0.11%) and liver (0.08%).
    Chromatography indicated that the radioactivity was all in the form of
    chlormequat (Blinn, 1967).

    In an earlier study 330 mg were administered to male and female rats.
    The compound was detected in the urine after 30 min. and reached a
    peak at 1-8 hours. It could no longer be detected after 56 hours
    (Shaffer, 1970).

    In an analysis of the urine of rats that had received 200 mg/kg of
    chlormequat orally, only chlormequat and two other compounds, which
    may have been other salts of chlorocholine, were found. Choline itself
    was not identified (Bronisz und Romanowski, 1968).

    Rats were administered orally a single (60 mg) dose of 15N-labelled
    chlormequat or they received 2 mg of the labelled compound daily for
    100 days. After the single dose the amount of compound in the brain
    decreased rather quickly, but there was considerable accumulation in
    the kidneys over the 20 days of the investigation. After the
    continuous administration, chlormequat was noted particularly in
    active muscles such as the heart and diaphragm (Bier and Ackermann,

    When a lactating cow received a single oral dose of 1 000 mg of
    15N-labelled chlormequat, the compound was demonstrated in the milk
    and urine three hours after administration. The main excretion of
    chlormequat was 15-39 hours after administration, the total during
    that time being 489 mg. Only 22 mg was excreted in the milk and the
    concentration in the milk never exceeded 1 ppm, the peak
    concentrations being 12-60 hours after administration (Lampeter and
    Bier, 1970).

    Effect on enzymes and other biochemical parameters

    Suggestions that chlormequat may inhibit acetylcholinesterase and
    microsomal oxidation are not based on substantial evidence. A study in
    which rats were fed diets containing 500 - 3 000 ppm chlorocholine
    and/or chlormequat, with or without cysteine, produced no evidence to
    suggest that chlormequat has a lipotropic effect on the formation of
    fatty liver produced by choline deficiency (Proll et al., 1970).

    Groups of 4 male and 4 female rats were fed a diet containing 0 or 2
    000 ppm of chlormequat for 21 days. The animals were then sacrificed
    for cholinesterase determinations. There was no difference between
    test animals and controls with respect to plasma, RBC or brain
    cholinesterase (Levinskas, 1965).


    Special studies on reproduction

    Groups of 20 male and 20 female rats received diets containing 0, 100,
    300 or 900 ppm of chlormequat in a standard three-generation study.
    Chlormequat produced no abnormalities in the appearance, behaviour,
    food intake, weight gain, fertility, gestation, lactation or viability
    of offspring. No foetal malformations or macro- or
    micro-histopathological abnormalities could be attributed to
    chlormequat (Leuschner et al., 1967).

    In a long-term feeding study in which rats received a diet containing
    10 to 1 000 ppm chlormequat, there was no evidence of effect on
    fertility, development of young or of teratogenicity (Ackermann
    et al., 1970).

    Special studies on teratogenicity

    Groups of pregnant mice received an i.p. injection (30 mg/kg) of
    chlormequat either on days 14 and 15 or on days 11 to 15 inclusive, of
    gestation. Another group of mice received 200 mg/kg by gavage daily on
    days 11 to 15. On day 19 all mice were sacrificed. The mean number of
    foetuses per mother, foetal size, frequency of resorption and
    incidence of malformation did not vary between test and control
    animals (Shaffer, 1970).

    Pregnant mice were fed dietary levels of 0, 1 000 or 10 000 ppm of
    chlormequat from days 1 to 15 of gestation or 25 000 ppm from days 11
    to 15 inclusive. All animals were sacrificed on day 19. The average
    number of foetuses per mother, size of foetuses and number of
    resorption sites did not vary between test and control groups. The
    number of malformations among foetuses of mothers fed 1.0% or 2.5% of
    chlormequat was slightly higher than that of the controls (Shaffer,

    Groups of mature male and female mice were fed dietary levels of 0,
    1 000 or 5 000 ppm of chlormequat for ten weeks. Matings were
    conducted after 1, 3, 4 and 10 weeks between the controls and animals
    on the various dose levels. Upon sacrifice on day 19 of gestation, the
    feeding of chlormequat was found to have no effect on the fertility of
    the mice and produced no terata among the offspring (Shaffer, 1970).

    Groups of rats were fed dietary levels of 0, 1 000 and 5 000 ppm of
    chlormequat from days 1 to 21 of gestation. The animals were
    sacrificed the day before parturition and no teratogenic effect was
    observed (Shaffer, 1970).

    Groups of pregnant golden hamsters (treatment groups of 8 animals and
    15 controls) were given chlormequat by gavage at levels of 0, 25, 50,
    100, 200, 300 or 400 mg/kg body-weight once on day 8 of gestation.
    Another group received 100 mg/kg daily on days 7, 8 and 9 of
    gestation. Signs of toxicity were evident in the higher dosed groups.
    All surviving animals were sacrificed on day 14 of gestation. The
    number of foetuses produced was less than in the controls and an
    increase in foetal resorption was observed at 100 mg/kg and above.
    Foetal size and weight was significantly reduced at 200 mg/kg and
    above. No abnormalities were encountered in the foetuses from the
    groups given 0, 25 or 50 mg/kg nor in the group given one dose of 100
    mg/kg. Malformed or underdeveloped foetuses occurred in the groups
    given three doses of 100 mg/kg and above. Malformations consisted of
    anophthalamus, microphthalamus, encephaloceles, head deformation,
    harelip, polydactylism, subcutaneous effusion of blood and body oedema
    (Juszkiewicz et al., 1970).

    Pregnant rabbits were fed 1 000 ppm chlormequat from day 1 to 28 of
    pregnancy. Two days before parturition the animals were sacrificed. No
    evidence of teratogenicity was observed (Shaffer, 1970).

    Acute toxicity

    Acute toxicity to chlormequat has been studied in several animal
    species, and findings are summarized in Table 1.

    Short-term studies


    Rats exposed to chlormequat at doses equal to or greater than 18 mg/kg
    showed slight traces of damage to the internal organs. At high doses
    (162 mg/kg) changes in the liver and lungs appeared in the form of
    diffuse fatty degeneration and hemorrhagic inflammation, respectively.
    Necrotic changes in the testicles were observed in one animal being
    treated with a dose of 18 mg/kg body-weight. No effects were noted at
    6 mg/kg or below in this study, the results of which have not been
    confirmed (Niepolomski et al., 1970).

    TABLE 1  Acute toxicity of chlormequat in different animal species


    Species     Route       mg/kg             Reference

    Mouse       oral        215 - 1 020       Oettel, 1965; Levinskas
                                              and Shaffer, 1966,
                                              Ignatiev, 1967.

    Mouse       ip          60                Shaffer, 1970

    Hamster     oral        1 070             Levinskas and Shaffer,

    Rat         oral        330-750           Oettel, 1965; Levinskas
                                              and Shaffer, 1966; Ignatiev,
                                              1967; Anonymous, 1969;
                                              Stefaniak, 1969

    Guinea      oral        215               Oettel, 1965

    Guinea      oral        620               Levinskas and Shaffer,
    pig                                       1966

    Rabbit      oral        60-81             Oettel, 1965; Levinskas
                                              and Shaffer, 1966;
                                              Anonymous, 1969

    Cat         oral        7-50              Oettel, 1965; Levinskas
                                              and Shaffer, 1966;
                                              Anonymous, 1969

    Dog         oral        100               Anonymous, 1969

    Dog         oral        <50               Levinskas and Shaffer, 1966

    Monkey      oral        >800              Costs et al., 1967

    Sheep       oral        >150-<200         Schulz et al., 1970

    Groups of ten male rats were fed dietary levels of chlormequat of 0,
    500, 1 000 or 2 000 ppm for 29 days. There were no deaths nor were
    there any signs of abnormal behaviour. Mean body-weight gain and mean
    food intake did not differ between test animals and controls. At
    sacrifice, after completion of the study, no gross pathological
    abnormalities were observed (Levinskas and Shaffer, 1962).

    Rats fed the equivalent of 600 mg/kg body-weight of chlormequat in
    their diet for three months showed no adverse effect other than
    reduced weight gain. When the daily dietary dosage was increased to
    1 200 mg/kg the only abnormality was a more pronounced reduction in
    growth rate. No gross or histopathological abnormalities were observed
    (Shaffer, 1970).

    Groups each containing 20 male and 20 female rats were fed dietary
    levels of 0, 200, 600 or 1 800 ppm of chlormequat for 90 days. There
    were no deaths and there was no difference in behaviour, blood
    chemistry or appearance between test and control. The mean weight gain
    in the males (but not the females) was significantly less in the group
    fed 1 800 ppm compared to the controls and other test groups. A trend
    was observed toward increased kidney to body-weight ratios in females,
    and liver to body-weight ratios in males with increasing doses. These
    increases appeared to be significant only at the 1 800 ppm level.
    Histological examination of all major organs from animals fed 1 800
    ppm were normal (Levinskas, 1965).

    Addition of 10 or 1 000 ppm of chlormequat to a suboptimal,
    protein-deficient, diet in rats resulted in significant reduction in
    relative liver weights (Ackermann et al., 1970).


    Two castrated male and two female cats received 1 mg/kg body-weight
    per day of chlormequat five days a week for six months without any
    harmful effects as evidenced by behaviour, weight gain and absence of
    toxic signs and abnormal results of blood analyses (Shaffer, 1970).


    Groups of dogs (2 males and 2 females/group) received dietary levels
    of 0, 20, 60 or 180 ppm of chlormequat for 106-108 days. Food intake,
    weight gain, behaviour, appearance, clinical and chemical tests were
    unaffected by chlormequat. At the end of the test period, gross
    histopathological examination of all main organs revealed no lesions
    that could be related to feeding chlormequat. Organ to body-weight
    ratios showed no marked changes (Levinskas, 1965).

    Groups of dogs (10 males and 10 females in the control and 3 males and
    3 females in the test groups) were fed dietary levels of 0, 100, 300
    or 1 000 ppm chlormequat for two years. Some animals on 1000 ppm
    exhibited excessive salivation and weakness of the hindquarters. This
    problem was reduced or overcome by feeding the dogs a daily ration in
    two stages rather than all at once. One male and one female on 1 000
    ppm died at 22 and 38 days. At 300 ppm and below there were no overt
    signs of toxicity. Food intake was unaffected at all levels. Extensive
    blood and urine analysis revealed no abnormalities except the presence
    of chlormequat in the urine of the test animals. At sacrifice, organ
    to body-weight ratios were not significantly different between test
    and control groups. Extensive gross and histopathological examination
    of all major organs revealed no changes attributable to feeding
    chlormequat (BASF, 1967b).


    One of four rhesus monkeys receiving an oral dose of 500 mg/kg
    body-weight of chlormequat died. At this high dose level heavy
    salivation and emesis were noted, but the survivors appeared normal
    after administration and remained so during the 7 day follow-up
    period. Gross pathology revealed little change that could be related
    to chlormequat (Costa et al., 1967).


    Sheep administered a single dose of 200 mg/kg body-weight of
    chlormequat died in 5-20 hours. Serum cholinesterase, total bilirubin
    and direct bilirubin were decreased. Acute liver damage was found in
    three and massive excretion of protein in the proximal segment of the
    renal tubules was described (Schulz et al., 1970).

    Signs of intoxication after a single dose in all species studied
    appear characteristic of cholinergic agents and most deaths occur
    between 6 and 24 hours after administration of the dose. The variation
    in species susceptibility is reported to be typical of ganglionic
    blocking agents of the decamethonium type (Shaffer, 1970).

    Daily administration of 1, 2, 5 or 10 mg/kg body-weight of chlormequat
    to sheep was not lethal. There were no important changes in the
    clinical status or in the results of laboratory tests and there was no
    evidence of injury to the parenchyma of internal organs. The feeding
    of meat from these sheep to cats and dogs had no adverse effect
    (Schulz et al., 1970).

    Long-term studies


    Groups of 52 male and 52 female CFLP mice were fed dietary levels of 0
    or 1 000 ppm of chlormequat for up to 78 weeks. Survival was not
    adversely affected. The rate of gain in body-weight began to be
    reduced in the test group after 24 weeks and was about 6% lower in the
    surviving animals during the final weeks of the study. No overt signs
    due to treatment were seen. The incidence of benign lung tumours was
    higher (20 out of 52) in the males fed 1 000 ppm of chlormequat than
    in the controls (10 out of 51). It was considered that this incidence
    in the treated mice fell within the normal range under the conditions
    studied. Incidence of lung tumours in the males and incidence of
    tumours in all other organs examined in both species was not
    significantly higher in the test group than in the controls (Weldon
    et al., 1971).

    Two hybrid strains of mice (18 males and 18 females of each
    strain/group) were given chlormequat by gavage at a dose of 21.5 mg/kg
    from 7 to 28 days and then fed a diet containing 65 ppm for 18 months.
    Based upon the number of hepatomas encountered in test and control
    groups the authors considered that the evidence was inconclusive to
    categorize chlormequat as being tumorigenic and stated that further
    studies were required (Innes et al., 1969). Hepatomas were found in
    five males of each strain (5 out of 18) compared to the control values
    of 6 out of 257 for one strain and 7 out of 240 for the other strain
    (Shaffer, 1970).


    Groups each of 50 male and 50 female rats were fed diets containing 0,
    500 or 1 000 ppm of chlormequat for two years. There were no signs of
    abnormal behaviour or appearance or other signs of toxicity. Food
    intake and body-weight gain were comparable in test and control
    groups. Haematological and blood chemical determinations were normal,
    as were urinalysis and microscopic examination of urine sediment.
    Gross and histopathological examination of organs revealed no
    abnormalities attributable to chlormequat (BASF, 1967a).


    Chlormequat is a stable quaternary compound that appears to act by
    depolarizing the post-junctional membrane, and although the signs of
    toxicity from high dosages in mammals resemble those of
    anticholinesterase agents, it does not inhibit cholinesterase.
    Chlormequat is rapidly absorbed and excreted mainly unchanged in the
    urine of mammals.

    A three-generation study in rats did not reveal adverse effects on
    reproduction. Teratogenic studies in several species indicate effects
    only at dose levels exceeding 50 mg/kg/day.

    Long-term studies in mice and rats indicate no effects at 1 000 ppm.
    However, in the rat, reproduction study levels of 300 ppm may have
    caused delayed maturation of stages of spermatogenesis in 9-week-old
    offspring whilst 100 ppm caused no effect. A two-year study in dogs
    demonstrated a no-effect level at 300 ppm; at 1 000 ppm some signs of
    cholinergic effect were noted.


    Level causing no toxicological effect

         Mouse:    1 000 ppm in the diet equivalent to 150 mg/kg

         Rat:      100 ppm in the diet equivalent to 5.0 mg/kg

         Dog:      300 ppm in the diet equivalent to 7.5 mg/kg


         0 - 0.05 mg/kg body-weight


    In addition to those uses referred to in the 1970 evaluations
    (FAO/WHO, 1971) information was received on the use of chlormequat on
    pears for promoting fruit bud formation and reducing excessive
    vegetative growth. The major use, however, remains on cereal crops,
    especially wheat, to reduce straw length, strengthen straw and prevent

    Pears are treated about 14 days after full flowering with chlormequat
    solutions at 0.1 - 0.2%. Treatment may be repeated once 14 days later.
    Split applications at low concentrations are more effective than a
    single treatment at higher concentrations.



    One application with 4.5 kg a.i./ha when wheat was 10-20 cm in height
    and one spraying with 3 kg a.i./ha at a height of 30-35 cm gave
    residues of 0.5-1 ppm in wheat grain (Jung and Henjes, 1964a).

    In experiments on winter wheat with applications of from 1.2 - 6 kg
    a.i./ha, the residues summarized in Table 2 were found in wheat grain
    and straw.

    Winter wheat treated with 1.25 to 10 kg a.i./ha 3-4 months before
    harvest was found to have residues in grain ranging from 0.02 - 2.36
    ppm. Spring varieties treated with 1.2 - 10 kg a.i./ha 2-3 months
    before harvest had residues ranging from 0 - 2.5 ppm in the grain at
    harvest. In a variety of soft wheat grown in Italy and treated at
    various stages of growth with 2 and 4 kg a.i./ha the following
    residues were detected in the grain: 1.36 - 2.18 ppm when treated 2
    weeks after initiation of stem elongation; 2.24 - 6.78 ppm, when
    treated at the boot stage (Cyanamid International 1966).

    TABLE 2  Chlormequat residues in wheat


                                   Residues (ppm)
    Chlormequat           Grain                      Straw
    (kg a.i./ha)    Average    Range           Average     Range

    1.2             0.5

    2.4             0.8        N.D.1 - 2.0     15.8        N.D. - 40

    3.0             -          N.D. - 0.5      20          10 - 40

    6.0             0.5

    1  N.D. = not detectable (<0.5 ppm).

    In dry years when the dose is high or the application is made late,
    higher chlormequat residues can be found in the grain of treated wheat
    plants. It seems that high rainfall can reduce or eliminate
    chlormequat residues resulting from high or late application of the
    growth regulator. After the wet summer of 1965 analysis of wheat grain
    from a crop which had been treated with 12 kg a.i. chlormequat/ha,
    showed no trace of any chlormequat (Jung and El-Fouly, 1966). It is
    interesting to observe that residues decrease with increasing storage
    time. This is obviously connected with the enzymatic transformation of
    chlormequat in the plant. Jung and El-Fouly (1966) found only 0.5 ppm
    or less in 12 samples of wheat grain, which originally contained
    1.0 - 2.5 ppm chlormequat, after they had been stored for 12 months.


    For short-straw winter ryes, chlormequat is applied at the rate of
    1.5 kg a.i./ha at a growth height of 20-30 cm. Analysis of rye grain
    from the 1966 harvest after 1.8 kg a.i./ha had been applied, showed
    1.0-1.3 ppm chlormequat in the dry grain, average of four locations
    (Jung, 1968a).


    The question of chlormequat residues in oats is of special interest,
    as the most effective time of chlormequat application is when growth
    height is 40-50 cm. Harvest samples from field trials in various parts
    of West Germany in 1967 showed a definite dependency on the time of
    treatment (Jung, 1968b).

    Early sprayed plants, when treated at a height of 20-30 cm with
    1.5 - 3 kg a.i./ha, generally showed not more than 1.0 to 1.4 ppm
    chlormequat in the dry grain. The values for late treated (at a growth
    height of 40-50 cm) were 3.8 and 6.1 ppm, respectively. Straw residues
    averaged 1.2 - 1.7 ppm (early) and 9.5 - 14.1 ppm (late) from the two
    different times of application. Analysis of oat grain and straw of the
    1968 harvest, based on an average of 11 field trials in all parts of
    West Germany (Jung, 1969), are given in Table 3.

    TABLE 3  Chlormequat residues in grain and straw of oats from
             field trials1


    Treatment2                  Chlormequat in the dry grain
    (l/ha Cycocel)                        (ppm)
                             Grain                     Straw

    Untreated                0.4                       0.7

    2                        1.7                       5.9

    4                        2.3                       9.9

    6                        3.5                       16.2

    1  Average of 11 field trials at each treatment rate.
    2  At growth height of 40-50 cm.

    Analysis of samples harvested from trials at the same location near
    Cologne showed an average residue in grain of 0.9 - 1.5 ppm
    chlormequat (dry basis), after treatment with 1 and 1.5 kg a.i./ha at
    a growth height of 20 cm, and of 2.3 - 3.5 ppm chlormequat after
    treatment with the same quantity at a growth height of 40 cm. The
    straw of early treated plants was found to have an average of
    0.7 - 1.1 and later treated plants 4.2 - 11.4 ppm (Jung, 1969a).
    Results are shown in Table 4.

    Apples and pears

    In 1967 after treatment of eight varieties of apples with 0.3%
    chlormequat solution, residue levels were found to range between 0.95
    and 1.6 ppm in the fresh fruit. Repeated treatments led to residue
    levels up to 3 ppm. The method used was capable of determining 0.2 ppm
    chlormequat in apples (Jung, 1969b).

    In 1968, five apple varieties were sprayed with 0.2% chlormequat
    solution. The residue in the fresh fruit was between 0.2 and 1.4 ppm.
    In the year following a single treatment with 0.2% chlormequat, no

    residue was traceable in the apples. After two sprays, about 0.4 ppm
    could be traced in the fruit the following year. Apples from trees
    which had been treated with chlormequat in both 1967 and 1968
    contained residues of 0.4 - 1.4 ppm when harvested in 1969.

    The analyses of treated pears showed a distinct dependence on the date
    of treatment. After a normal treatment with 0.2% solution, the average
    of four varieties was 0.2 to 1 ppm chlormequat in the fresh fruit. An
    extreme four-time spraying with 0.25% chlormequat solution led to
    residue of 6 ppm. Fruit from the succeeding year did not contain any
    residue (Jung, 1969b).


    Analysis of several types of vegetables in 1967 and 1968 (Jung, 1969b)
    led to the following results: cucumbers in the pot, which had been
    treated with 0.25% solution, contained 1.6 ppm chlormequat. After
    treating the soil with 0.15% and 0.5% solution and comparative spray
    treatment with 0.25% solution, the residue fluctuated between 0.2 and
    1.1 ppm chlormequat. Capsicum, after spraying with 0.15 - 1.0%
    solution, contained 5.8 - 8.9 ppm chlormequat. In tomatoes which were
    cultivated under greenhouse conditions no residue was found after soil
    treatment with 10 and 30 mg chlormequat per pot, and 0.5 - 1.4 ppm
    chlormequat was found after spraying with 0.1 - 0.25% solution.
    Tomatoes raised in the field showed 0.6 ppm chlormequat in the fruit
    after soil treatment with 50 cc 0.5% solution. No residue could be
    traced in radish after soil and spray treatment with 0.15 - 0.25%

    TABLE 4  Chlormequat residues in grain and straw of oats


    Treatment        Nitrogen       Growth       Chlormequat, dry basis
    (kg a.i./ha)     fertilizer     stage                (ppm)
                     (kg/ha)                     Grain            Straw

    Untreated        60                          0.37             0.34
    Untreated        80                          0.41             0.24

    1.0              60                          0.89             0.93
    1.5                                          1.25             0.72

    1.0              80             at 20 cm     1.16             1.11
    1.5                                          1.47             0.77

    1.0              60                          2.42             4.16
    1.5                                          3.23             6.61

    1.0              80             at 40 cm     2.18             5.23
    1.5                                          3.52             11.45


    In animals

    Orloski (1970) reported experiments designed to determine chlormequat
    residues in the milk of dairy cows receiving 10 ppm chlormequat in the
    ration for 14 consecutive days. Each animal received 128 mg
    chlormequat daily via oral dose syringe. The results show trace
    residues of chlormequat ranging from 0.024 to 0.034 ppm at each of
    milk samplings 1, 4, 7 and 14 days during feeding. When the
    chlormequat was removed from the ration no residues above the limit of
    detection (0.01 ppm) were found in the milk.

    In plants

    The chlormequat level in vegetative parts of plants declines quickly
    after treatment. Residue analyses based on the half-quantitative
    method, in 1963 showed 2200 and 3600 ppm for winter wheat ("Werla")
    and 1200 and 2400 ppm for summer wheat ("Koga") after treatment with 2
    and 4 kg chlormequat/ha. After five weeks the residue in the complete
    plant was reduced to 7 and 25 ppm, respectively, in winter wheat and
    17 and 47 ppm, respectively, in summer wheat. No chlormequat could be
    traced in the ears. The ripe wheat grains were also free of traceable
    residue; 5 and 7 ppm chlormequat were found in the ripe straw of
    winter wheat and 6 and 11 ppm chlormequat in the straw of summer wheat
    (Jung and Henjes, 1964a).

    Analysis of summer wheat in the year 1965, after treatment with up to
    12 kg chlormequat/ha, showed the same tendency (Jung and El-Fouly,
    1966). A similar rapid reduction of residues was also found by Mooney
    and Pasarela (1967) in wheat plants of the "Redcoat" type. The residue
    level was reduced from 218 ppm on the day of the treatment to 125 ppm
    after 21 days, 20 ppm after 42 days and 5 ppm (straw) after 64 days.
    After 91 days, the average residue content in six samples was 1.4 ppm
    and in the straw 2.8 ppm. The untreated grain sample contained 0.15
    ppm chlormequat. The plants had been treated with 4.5 kg a.i/ha at a
    growth height of 20 cm, the precipitation during the vegetation period
    being 344.5 mm. The biological half-life for chlormequat determined by
    this study was 13 days.

    High chlormequat applications frequently increase the content of
    choline chloride (CC) shortly after treatment, and it therefore is
    possible that chlormequat is transformed into CC and possibly betain.
    Consequently, Jung and El-Fouly (1966) carried out tests in vivo and
    in vitro to determine whether chlormequat is transformed into betain
    and/or choline chloride. Their results are shown in Table 5.

    It is not fully understood whether chlormequat, which is closely
    related to the choline and betain contained in plants, is already
    acting in the plant as a "natural" growth regulator. On the other
    hand, the quarternary ammonium combinations choline and betain,
    chemically closely related to chlormequat, can be traced in the plant
    in relatively large quantities (Jung and El-Fouly, 1966; Jung and
    Henjes, 1964b; Paxton and Mayr, 1962).

    In the process of decomposition in vitro, transformation evidently
    starts a few minutes after chlormequat solution has been added to the
    plant extract. In each case, choline chloride could be traced as the
    decomposition product.

    It is noticeable that chlormequat decomposes differently in leaf
    extracts of different plants. Plants sensitive to chlormequat seem to
    decompose the growth regulator more slowly than plants which are less
    sensitive. Perhaps the explanation for the different effect of
    chlormequat on different plants and/or plant types can be found here.
    If the speed of decomposition of chlormequat in wheat is 100, the
    relative values in maize and rice would be 180, in beetroot and apples
    130, in rapeseed 120, in poinsettia and cotton 100, in tomatoes 70, in
    beans 40 and in grapes and chrysanthemums 20 (Jung and El-Fouly,

        TABLE 5  Choline chloride and betain content in wheat plants after
             treatment with high rates of chlormequat


    Treatment         3 days after treatment           24 days after treatment
    (kg a.i./
     ha)         Chlormequat   CC        betain      Chlormequat   CC       betain
                 (ppm)         (ppm)     (ppm)       (ppm)         (ppm)    (ppm)

    Untreated    -             3 100     3 500       -             900      1 000

    6            1 400         3 900     4 300       100           900      1 200

    12           2 800         3 800     4 200       200           1 000    1 300

    These authors have established the following scheme (figure 1) for the
    decomposition of chlorine choline chloride.

    FIGURE 1

    (chlorine choline chloride)-> (choline chloride)-> (betain)

    Figure 1 - Decomposition of chlorine choline chloride

    As choline occupies a central position in plant metabolism and can be
    oxidized to betain, the increase of betain content after chlormequat
    treatment could thus be explained. Paxton and Mayr (1962) have shown
    the transformation of choline and betain in a further scheme.

    According to the latest research, the enzymatic system controlling the
    decomposition of chlormequat into CC, is pH-dependent and thermostable
    (Jung and El-Fouly 1969). On the whole, the decomposition of
    chlormequat increases with the increasing pH value of the plant
    extract and reached a maximum at pH6. Above this value the rate of
    decomposition decreases since chlormequat is decomposed in alkaline
    medium. Heading (40-90°C) the plant extracts and subsequent cooling to
    room temperature did not affect the rate of decomposition of
    chlormequat which was added later. Only by cooking the extracts for
    several hours could inactivation be obtained. Temperatures which
    increase from 10-40°C, however, accelerate the decomposition of
    chlormequat into CC, if the chlormequat is already present in the
    extract. The enzymatic system only becomes active in the presence of
    at least two components (one precipitated with ZnCl2 and one
    dialysable). Schneider (1967) demonstrated chromatographically that
    radio-labelled chlormequat was transformed into a substance identical
    to choline in barley and chrysanthemum sprouts. He was able to isolate
    radioactive choline or radioactive choline metabolites from plant
    tissue, which had been standing in chlormequat-containing solutions
    for some time. During decomposition the carbohydrate skeleton of
    chlormequat seems, therefore to remain intact. The unknown metabolites
    were identical to the metabolites isolated from plants after a choline
    or choline plus chlormequat treatment. An additional combination,
    which only appeared after chlormequat treatment, is taken as an
    intermediate of the decomposition processes. On the whole, 50-80% of
    the added radioactivity was found unchanged in the chlormequat
    solution, 15-40% in the residue solutions and 35-40% in the methanol
    extracts. At least 10-15% of the added radioactivity had been
    transformed in metabolic products of chlormequat.

    Schneider (1967) sees a contradiction in the relatively fast
    decomposition of chlormequat and its long lasting effect on plant
    growth. Since choline also, though at ten times higher concentrations
    than chlormequat, delayed the growth of barley roots and sprouts in
    such tests, this author believes that the effect normally assigned to
    chlormequat alone could result from chlormequat choline and further
    unknown metabolites of these combinations. The contradiction between
    chlormequat decomposition and lasting effect could be explained if the
    metabolism of chlormequat only takes place in one part of the plant
    tissue, whilst other parts store unchanged chlormequat. This
    explanation would comply with observations of Sachs and Kofranek
    (1963), who have noted that chlormequat activities mainly take place
    in the subapical meristem.

    In soil

    Chlormequat decomposition in soil takes place relatively fast. Cathey
    and Stuart (1961) assess the persistency of choline chloride in soil
    as only three weeks. The opinion that the soil does not provide the
    plant with a continuous subsequent supply of chlormequat is also
    shared by Schneider (1967). Trials were carried out by Jung (1965) in
    which four different soils were treated with 5 mg chlormequat 0-6
    weeks before sowing wheat seeds in all pots. After 4-6 weeks there was
    almost complete inactivation. In further tests it was established that
    chlormequat in quantities of 3, 30 and 300 kg/ha did not exert a
    definable influence on the microbic activity of five different soils.
    CO2 production and nitrification were taken as the basis for these
    observations (Jung, 1964).

    In storage and processing

    Jung and El-Fouly (1966) found that chlormequat residues in wheat
    decline significantly in storage. Twelve samples of wheat which
    originally contained 1.0 - 2.5 ppm chlormequat were found to have less
    than 0.5 ppm after being stored for 12 months.

    Cyanamid International (1971) reports trials to determine the level of
    chlormequat residues in milling products processed from wheat treated
    with chlormequat at the rate of 1.2 kg per ha by aircraft and
    harvested 95 days later. The wheat was milled five months after
    harvest and the bran and flour collected. The flour was made into
    bread. The treated grain was found to contain 0.26 ppm chlormequat.
    The bran contained 0.8 ppm, the flour 0.32 ppm and the bread 0.06 ppm
    chlormequat. It is apparent that milling does not substantially reduce
    the level of chlormequat residues in wheat but that baking of the
    flour in the production of bread largely eliminates the residue. The
    analytical method used had a limit of determination of 0.05 ppm.

    The work of Tafuri et al. (1970) indicates that wine made from
    grapes grown under chlormequat treatment will contain residues
    substantially similar to those in the fresh grapes (up to 1 ppm).


    Chlormequat is used as a growth regulator in cereals, grapes and

    Residues in wheat grain which mostly lie below 1 ppm, may range up to
    2 ppm. When such wheat is milled, the flour will contain substantially
    similar levels but these are largely destroyed in the baking of bread.

    Cows fed on the straw of chlormequat-treated cereals excrete small
    traces of chlormequat in milk during the period of feeding, but
    residues disappear as soon as the treated feed is withdrawn.

    The treatment of pear trees at flowering in order to prevent
    vegetative growth and encourage fruit bud formation for the next
    season gives rise to residues ranging up to 2.6 ppm in fruit at
    harvest. Residues are not found in the succeeding crop.

    The gas chromatographic method of Tafuri et al. (1970) is
    recommended as suitable for regulatory purposes. It is suitable for
    use with the commodities included in the list of recommended
    tolerances having a limit of determination of 0.05 ppm.



    The following tolerances are for residues likely to be found at
    harvest. Due to the stability of chlormequat residues, it is not
    anticipated that residue levels will change significantly in storage,
    although they will be largely destroyed by cooking.


         Oats and rye                                 5
         Wheat                                        3
         Pears                                        3
         Grapes, raisins and other dried
         vine fruits                                  1
         Milk and milk products                       0.1*

         * at or about the limit of determination



    1.   Information on other registered uses for chlormequat.

    2.   Further information on residues of chlormequat in raw
         agricultural commodities from a number of different countries.

    3.   Information on chlormequat residues in commodities moving in
         international trade.


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    See Also:
       Toxicological Abbreviations
       Chlormequat (AGP:1970/M/12/1)
       Chlormequat (Pesticide residues in food: 1976 evaluations)
       Chlormequat (Pesticide residues in food: 1994 evaluations Part II Toxicology)
       Chlormequat (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)
       Chlormequat (JMPR Evaluations 1999 Part II Toxicological)